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A    SYSTEM 


OF 


INORGANIC  CHEMISTRY 


BY 


WILLIAM     EAMSAY,    PH.D.,    F.E.S. 


PROFESSOR   OF   CHEMISTRY   IN    UNIVERSITY   COLLEGE.    LONDON. 


LONDON 
J.     &    A.     CHURCHILL 

11,  NEW  EUELINGTON  STEEET 
1891 


f 


7EKSIT7 


PREFACE 


FOR  more  than  twenty  years,  the  compounds  of  carbon  have 
been  classified  in  a  rational  manner  ;  and  the  relations 
between  the  different  groups  of  compounds  and  between  the 
individual  members  of  the  same  groups  have  been  placed  in 
a  clear  light.  It  is,  doubtless,  owing  to  the  brilliant  origin- 
ators of  this  method  of  classification — Kekule,  Hofmann, 
Wurtz,  Frankland,  and  others  too  numerous  to  mention,  but 
whose  names  occupy  a  prominent  place  in  the  history  of  our 
science — that  the  domain  of  organic  chemistry  has  been  so 
systematically  and  successfully  enlarged,  and  that  it  presents 
an  aspect  of  orderly  arrangement  which  can  scarcely  be 
surpassed. 

This  has  unfortunately  not  been  the  fate  of  the  chemistry 
of  the  other  elements.  Nearly  twenty-five  years  have 
elapsed  since  the  discovery  by  Newlands,  Mendeleeff,  and 
Meyer  of  the  periodic  arrangement  of  the  elements ;  and,  in 
spite  of  the  obvious  guide  to  a  similar  classification  which  it 
furnishes,  no  systematic  text-book  has  been  written  in  English 
with  the  periodic  arrangement  of  the  elements  as  a  basis. 

The  reasons  for  this  neglect  have  probably  been  that  the 
ancient  and  arbitrary  line  of  demarcation  between  the  non- 
metals  and  the  metals  has  been  adhered  to ;  that  too  great 
importance  (from  the  standpoint  of  pure  chemistiy)  has  been 
assigned  to  the  distinction  between  acid  hydroxides  and 
basic  hydroxides  (acids  and  bases),  which  has  tended  to 
obscure  the  fact  that  they  belong  essentially  to  the  same 
class  of  compounds,  viz.,  the  hydroxides  ;  and  that  the 
chemistry  of  text-books  has  almost  always  been  influenced 
by  commercial  considerations.  The  first  of  these  reasons 


vi  PREFACE. 

has  often  led,  among  other  anomalies,  to  the  separation  of  such 
closely  allied  elements  as  boron  and  aluminium,  antimony 
and  bismuth,  silicon  and  tin ;  the  second  reason  has  often  led 
to  the  ignoring  of  the  double  halides,  except  in  a  few  special 
instances,  and  to  the  neglect  of  compounds  such  as  double 
oxides  of  the  sesquioxides  of  the  iron  group,  in  which  these 
oxides  play  an  acidic  part ;  while,  for  the  third  reason,  those 
methods  of  preparing  compounds  which  are  of  commercial 
importance  are  usually  given,  while  other  methods,  as  im- 
portant from  a  scientific  point  of  view,  are  often  ignored ;  the 
borides,  nitrides,  &c.r  have  been  almost  completely  neglected 
since  the  time  of  JBerzelius ;  and  the  less  easily  obtained 
elements  and  compounds  have  been  dismissed  with  scant 
notice  because  of  their  rarity ;  whereas  they  should  obviously 
be  considered  as  important  as  the  commoner  ones  in  any 
treatise  on  scientific  chemistry. 

The  methods  of  classification  adopted  in  this  book  are,  as 
nearly  as  the  difference  of  subject' will  permit,  those  which 
have  led  to  the  systematic  arrangement  of  the  carbon  com- 
pounds. After  a  short  historical  preface,  the  elements  are 
considered  in  their  order;  next  their  compounds  with  the 
halogens,  including  the  double  halides ;  the  oxides,  sulphides, 
selenides,  and  tellurides  follow  next,  double  oxides,  such  as 
sulphates,  for  example,  being  considered  among  the  com- 
pounds of  the  simple  oxides  with  the  oxides  of  other  ele- 
ments ;  a  few  chapters  are  then  occupied  with  the  borides, 
carbides,  and  silicides,  and  the  nitrides,  phosphides,  arsen- 
ides, and  antimonides  ;  and  in  these  the  organo-metallic  com- 
pounds, the  double  compounds  of  ammonia,  and  the  cyanides 
are  considered;  while  a  short  account  is  given  of  alloys  and 
amalgams.  The  chemistry  of  the  rare  earths,  which  must  at 
present  be  relegated  to  a  suspense  account,  is  treated  along 
with  spectrum  analysis  in  a  special  chapter  ;  and  the 
systematic  portion  of  the  book  concludes  with  an  account 
of  the  periodic  table. 

The  periodic  arrangement  has  been  departed  from  in  two 
instances :  the  elements  chromium,  iron,  manganese,  cobalt, 
and  nickel  have  been  taken  after  those  of  the  aluminium 


PREFACE.  Vll 

group ;  and  the  elements  copper,  silver,  gold,  and  mercury 
have  been  grouped  together  and  considered  after  the  other 
elements.  It  appeared  to  me  that  the  analogies  of  these 
elements  would  have  been  obscured,  had  the  periodic  arrange- 
ment been  strictly  adhered  to. 

'  It  has  bee^n  thought  desirable,  instead  of  treating  of 
processes  of  manufacture  under  the  heading  of  the  re- 
spective elements  or  compounds,  to  defer  a  description  of 
them  to  the  end  of  the  book,  and  to  group  them  under 
special  headings,  those  compounds  beipg,  considered  together 
which  are  generally  manufactured  under  one  roof.  In 
describing  manufactures,  chemical  principles  have  been  con- 
sidered, rather  than  the  apparatus  by  means  of  which  the 
manufactures  are  carried  on.  The  student,,  having  acquired 
the  requisite  acquaintance  with  facts,  is  now  better  able  to 
appreciate  these  principles. 

The  physical  aspects  of  chemistry  have  generally  been 
kept  in  the  background,  and  introduced  only  when  necessary 
to  explain  modern  theories.  I  hold  that  a  student  should 
have  a  fair  knowledge  of  a  wide  range  of  facts  before  he 
proceeds  to  the  study  of  physical  chemistry,  which,  indeed, 
is  a  science  in  itself.  But  short  tables  of  the  more  important 
physical  properties  of  elements,  and  of  the  simpler  com- 
pounds, have  been  introduced  for  purposes  of  reference. 

It  may  be  asked  if  such  a  system  is  easily  grasped  by  the 
student,  and  if  it  is  convenient  for  the  teacher.  To  this 
question  I  can  reply  that,  having  used  it  for  four  years,  I  am 
perfectly  satisfied  with  the  results.  For  the  student,  memory 
work  is  lightened ;  for  the  teacher,  the  long  tedious  descrip- 
tion of  metals  and  their  salts  is  avoided ;  and  I  have  found 
that  the  student's  interest  is  retained,  owing  to  the  fact  that 
all  the  "  fire-works "  are  not  displayed  at  the  beginning  of 
the  course,  but  are  distributed  pretty  evenly  throughout. 

It  need  hardly  be  mentioned  that  the  teacher  is  not 
required  to  teach,  nor  the  student  to  remember,  all  the  facts 
as  they  are  here  set  forth.  It  is  necessary  to  make  a 
judicious  selection.  But  it  is  of  advantage  to  have  the  list 
fairly  complete  for  purposes  of  reference.  It  should  be  stated 


Vlll  PREFACE. 

that,  in  the  case  of  compounds  of  questionable  existence, 
they  have  received  the  benefit  of  the  doubt.  It  is  at  least 
well  that  they  should  be  known,  in  order  that  their  existence 
may  be  brought  to  the  test  of  renewed  experiment. 

References  to  original  memoirs  have  been  given  where 
important  theoretical  points  are  involved;  or  where  doubt 
exists ;  and  an  attempt  has  been  made  to  guide  the  reading 
of  students.  As  a  rule,  references  to  recent  papers  are 
given ;  the  older  references  may  be  found  in  one  of  the 
chemical  dictionaries. 

WILLIAM  RAMSAY. 

UNIVEESITT  COLLEGE,  LONDON, 
January,  1891. 


CONTENTS. 


PART  I. 

PAGE 

CHAPTER  I.     Introductory  and  Historical 1 

CHAPTER  II.    Historical         14 

PART  II. 
THE  ELEMENTS. 

CHAPTER  III.     Group    1.       Hydrogen,     lithium,     sodium,     potassium, 

rubidium,  and  caesium        . .          . .          . .          . .          . .          . .  25 

Group  2.     Beryllium,  or  glucinum,  calcium,  strontium,  barium    . .  31 

Group  3.     Magnesium,  zinc,  cadmium           . .          . .          . .       -   . .  33 

Group  4.     Boron,  scandium,  (yttrium),  lanthanum,  (ytterbium)  ..  35 

Group  5.     Aluminium,  gallium,  indium,  thallium  . .          . .          . .  37 

CHAPTER  IV.     Group  6.     Chromium,  iron,  manganese,  cobalt,  nickel     ..  40 

Group  7.     Carbon,  titanium,  zirconium,  cerium,  thorium  . .          . .  43 

GroupS.     Silicon,  germanium,  tin,  (terbium),  lead. .          ..          ..  49 

CHAPTER  V.     Group  9.      Nitrogen,    vanadium,    niobium,   (didymium), 

tantalum      . .          . .          . .          . .          . .          . .          . .          . .  53 

Group  10.     Phosphorus,  arsenic,  antimony,  (erbium),  bismuth     . .  56 
Group  11.     (Oxygen,  chromium). — Molybdenum,  tungsten,  uran- 
ium           ..  60 

Group  12.     Oxygen,  sulphur,  selenium,  tellurium  . .          . .          . .  61 

Appendix.     Air  . .          . .          . .          . .          . .          . .          . .          . .  70 

CHAPTER  YI.     Group  13.     Fluorine,  chlorine,  bromine,  iodine  . .          . .  72 

Groups  14  and  15.     Ruthenium,   rhodium,    palladium,    osmium. 

iridium,  platinum   . .          . .          . .          . .          . .          . .          . .  77 

Groupie.     Copper,  silver,  gold,  mercury     "V         ..          ..          ..  79 

General  remarks  on  the  elements         . .          «V^V     . .          . .          . .  83 

PART  III. 
THE  HALIDES. 

CHAPTER  VII.     Compounds  and  mixtures ;  nomenclature           . .         . .  88 
The  states  of  matter ;  Boyle's  law ;  Gay-Lussac's  law ;  Avogadro's 

law " 91 

Methods  of  determining  the  densities  of  gases          . .          . .          . .  97 


X  CONTENTS. 

PAGE 

CHAPTER  VIII.     Hydrogen  fluoride,  chloride,  bromide,  and  iodide         . .  104 
Halides  of  lithium,    sodium,   potassium,   rubidium,    caesium,   and 

ammonium  . .          . .          . .          . .          . .          . .          . .          . .  115 

CHAPTEE  IX.     Halides  of  beryllium,  calcium,  strontium,  and  barium    ..  120 

Halides  of  magnesium,  zinc,  and  cadmium    . .          . .          . .          . .  123 

Molecular  formulae ;  specific  heats  of  elements         . .          . .          . .  126 

CHAPTEE  X.     Halides   of   boron,  scandium,  (yttrium),   and  lanthanum, 

(ytterbium) 131 

Halides  of  aluminium,  gallium,  indium,  and  thallium        . .          . .  133 

Halides  of  chromium,  iron,  manganese,  cobalt,  and  nickel. .          . .  137 

CHAPTEE  XI.     Halides   of    carbon,    titanium,   zirconium,    cerium,    and 

thorium        . .          . .          . .          . .          , .          . .          . .          . .  144 

Halides  of  silicon,  germanium,  tin,  (terbium),  and  lead     ..          ..  148 

CHAPTEE  XII.     Halides  of  nitrogen,  vanadium,  niobium,  tantalum        . .  157 

Halides  of  phosphorus,  arsenic,  antimony,  -(erbium),  and  bismuth. .  160 

Halides  of  molybdenum,  tungsten,  and  uranium      . .          . .          . .  164 

Halides  of  sulphur,  selenium,  and  tellurium. .          . .          . .          . .  166 

CHAPTEE  XIII.     Compounds  of  the  halogens  with  each  other     . .          . .  169 

Halides  of  ruthenium,  rhodium,  and  palladium       . .          . .          . .  170 

Halides  of  osmium,  iridium,  and  platinum    . .          . .          . .  172 

Halides  of  copper,  silver,  gold,  and  mercury. .          . .          . .          . .  174 

CHAPTEE  XIY.     Review  of  the  halides ;  their  sources,  preparation,  and 
properties ;  their  combinations  and  their  reactions  ;  also  their 

molecular  formulae . .  181 


PART  IV. 

THE  OXIDES,  SULPHIDES,  SELENIDES,  AND 
TELLURIDES. 

CHAPTEE  XV.     Compounds  of  oxygen,  sulphur,  selenium,  and  tellurium 

with  hydrogen         . .          . .          . .          . .          . ,          . .          . .  191 

Physical  properties  of  water     . .          . .          . .          . .          . .          . .  199 

Compounds  of  water  with  halides        203 

CHAPTEE  XVI.     Classification  of  oxides      . .          . .         205 

The  dualistic  theory . .      207 

Constitutional  and  rational  formulae    . .          . .          . .          . .          . .      208 

Oxides,  sulphides,  &c.,  of  lithium,    sodium,  potassium,  rubidium, 

caesium,  and  ammonium    ..          ..          ..          ..          ..          ..211 

Hydroxides  and  hydrosulphides  . .          . .          . .          '. .          . .      214 

CHAPTEE  XVII.     Oxides,  sulphides,  and  selenides  of  beryllium,  calcium, 

strontium,  and  barium       . .          . .          . .          . .          . .          . .      218 

Hydroxides  and  hydrosulphides  . .          . .          . .          . .          . .      222 

Oxides,   sulphides,  selenides,    and  tellurides  of  magnesium,    zinc, 

and  cadmium  225 


CONTENTS.  Xi 

PAGB 

Hydroxides  and  hydrosulphides          229 

Double  oxides  (zincates)  ;  oxyhalides . .          ..          ..          ..         ...  229 

CHAPTER  XVIII.     Oxides  and  sulphides  of  boron,  scandium,  (yttrium), 

lanthanum,  (and  ytterbium)         . .          232 

Double  oxides  (boracic  acid  and  borates)        . .          . .          . .          . .  233 

Oxyhalides 236 

Oxides,  sulphides,  and  selenides  of  aluminium,  gallium,  indium, 

and  thallium           ..          237 

Hydroxides  and  double  oxides  (aluminates,  &c.)       . .          . .          . .  239 

Double  sulphides  and  oxyhalides         . .          . .          . .          . .          . .  242 

CHAPTEB  XIX.     Monoxides,  monosulphides,  monoselenides,  and   mono- 

tellurides  of  chromium,  iron,  manganese,  cobalt,  and  nickel   . .  243 

Dihydroxides ;  double  sulphides          246 

Sesquioxides,  sesquisulphides,  and  sesquiselenides     . .          . .          . .  248 

Trihydroxides 251 

Double  oxides  (spinels) ..          ..          ...          ..          ..          ..          ..  253 

Double  sulphides  and  oxyhalides         . .          . .          . .          . .          . .  256 

Dioxides  and  disulphides           . .          . .          *.          . .          . .          . .  258 

Hydrated  dioxides  and  double  oxides  (manganites)  . .          . .          . .  260 

Trioxides  . .          . . 261 

Double  oxides  (chromates,  ferrates,  and  manganates)          . .          . .  262 

Perchromates  and  permanganates        . .          . .          . .          . .          . .  266 

Oxyhalides           268 

CHAPTER  XX.     Monoxides    and    monosulphides    of    carbon,    titanium, 

zirconium,  cerium,  and  thorium  ..          ..          ..          ..          ..  270 

Sesquioxides  and  sesquisulphides         273 

Dioxides  and  disulphides          . .          . .          . .          . .          . .          . .  274 

Compounds  with  water  and  with  hydrogen  sulphide            . .          . .  283 

Carbonates,   titanates,    zirconates,    thorates;  carbon  oxysulphide; 

oxysulphocarbonates  and  sulphocarbonates         . .          . .          . .  284 

Oxyhalides          ..          ....          ....         .292 

CHAPTER  XXI.     Monoxides,  monosulphides,  monoselenides,  and  mono- 

tellurides  of  silicon,  germanium,  tin,  and  lead 294 

Hydroxides ;  compounds  with  oxides  and  with  halides        . .          . .  297 

Sesquioxides  and  sesquisulphides         . .          . .          . .          . .          . .  299 

Dioxides,  disulphides,  diseknides,  and  ditelluride 300 

Compounds   with    water    and    oxides:     silicates,    stannates,    and 

plumbates    . .          . .          . .          . .          . .          . .          . .          . .  303 

Sulphostannates  ..          ..          316 

Oxyhalides           317 

CHAPTER  XXII.  Oxides  and  sulphides  of  nitrogen,  vanadium,  niobium, 

and  tantalum  319 

Compounds  of  pentoxides  with  water  and  oxides  ;  nitric,  Tanadic, 
niobic,  and  tantalic  acids :  nitrates,  vanadates,  niobates,  and 

tantalates 322 

Oxyhalides           331 


Xll  CONTENTS. 

PAGE 

Tetroxides  or  dioxides  :  tetrasulphide  or  disulphide             . .          . .  333 

Compounds  with  oxides  and  sulphides ;  hyporanadates  and  hypo- 

sulphovanadates      . .          . .          . .          . .          . .          . .          . .  335 

Compounds  with  halides.     Trioxides  . .          . .        •  . .          . .          . .  336 

Nitrites  and  vanadites   . .          . .          . .          . .          . .          . .          . .  337 

Compounds  with  halides            ..          ..          ..          ..          ..       •._;•,  340 

Nitric  oxide ;  yanadium  monoxide       . .          . .          . .          . .          . .  341 

Nitrogen  sulphide  and  selenide.     Nitrosulphides      . .          . .          . .  343 

Nitrous  oxide  ;  hyponitrites     . .          . .          . .          . .          . .          , .  343 

CHAPTEE  XXIII.     Oxides,  sulphides,  selenides,  and  tellurides  of  phos- 
phorus, arsenic,  antimony,  and  bismuth. .          . .          . .          it  346 

Compounds   of   the   pentoxides    and    pentasulphides ;    orthophos- 

phates,  orthoarsenates,  and  orthoantimonates,  &c.        . .          . .  352 

Pyrophosphates,  pyrarsenates,  and  pyrantimonates  . .          . .          . .  363 

Metaphosphates,  metarsenates,  and  metantimonates             . .          . .  369 

CHAPTER  XXIY.     Hypophosphoric  acid      . .         373 

Compounds  of  trioxides  and  trisulphides  ;    phosphites,   arsenites, 

and  antimonites ;  their  sulphur  analogues          .  >          . .          . .  374 

Hypophosphites  . .          . .          . .          . .          . .          . .          . .          . .  380 

Compounds  of  oxides  and  sulphides  with  halides     . .          . .          . .  332 

CHAPTER  XXV.     Ozone  (oxide  of  oxygen)  . .          . .          . .          . .          . .  387 

Oxides  and  sulphides  of  molybdenum,  tungsten,  and  uranium       , .  392 
Hydroxides  ;     molybdates,    tungstates,     and    uranates ;     sulphur 

analogues     . .          . .          . .          . .          . .          . .          . .          . .  396 

Peruranates,  persulphomolybdates      . .          . .          . .          . .          . .  405 

Compounds  with  halides           . .          . .          . .          . .          . .          . .  406 

CHAPTER  XXVI.     Oxides  of  sulphur,  selenium,  and  tellurium     . .          . .  409 

Sulphuric,  selenic,  and  telluric  acids  . .          . .          . .          . .          . ,  414 

Sulphates,  selenates,  and  tellurates 419 

Anhydrosulphuric  acid  and  anhydrosulphates          . .          . .          . .  432 

CHAPTER  XXVII.     Sulphurous,  selenious,  and  tellurous  acids     . .          . .  435 

Sulphites,  selenites,  and  tellurites       . .          . .          . .          . .          . ,  436 

Compounds  of  oxides  with  halides  j  sulphuryl  chloride ;  chloro- 

sulphonic  acid         . .          . .          . .          . .          . .          . .          . .  440 

Other  acids  of  sulphur  and  selenium  . .  . .  . .  . .  . .  443 

Thiosulphates 444 

Seleniosulphates 447 

Hyposulphurous  acid  and  hyposulphites 447 

Dithionic  acid  and  dithionates , .          . .          . .          . .          . .          . .  448 

Trithionic  acid  and  trithionates           . .          . .          . .          . .          . .  449 

Seleniotrithionic  acid ;  tetrathionic  acid  . .  . .  . .  . .  450 

Pentathionic  acid  451 

Hexathionic  acid.  Constitution  of  the  acids  of  sulphur  and 

selenium  . .  . .  . .  . .  . .  . .  . .  . .  452 

Nitrososulphates 455 

Compounds  of  sulphur,  selenium,  and  tellurium  with  each  other  . .  455 


'ERSITY 

CONTENTS.  o  _  x 


PAGB 

CHAPTEE  XXVIII.     Oxides  of  chlorine,  bromine,  and  iodine       . .          . .  459 

Hypochlo rites,  hypobromites,  aiid  hypoiodites          . .          . .          . .  461 

Chlorous  acid  and  chlo rites       ..          ..          ..     '  "...         ••          ••  464 

Chlorates,  bromates,  and  iodates         . .    ,      . ,  464 

Perchlorates  and  periodates      . .          . .          . »          . .          . .          . .  469 

CHAPTER  XXIX.     Oxides,  sulphides,  and  selenides  of  rhodium,  ruthen- 
ium, and  palladium            . .          . .          . .          . .          . .          . .  476 

Hydroxides         478 

Sulphopalladites  ;  ruthenates  and  perruthenates      . .          . .          . .  479 

Oxides,  sulphides,  and  selenides  of  osmium,  iridium,  and  platinum.  480 

Hydroxides          ..          ..  482 

Osmites  and  platinates  . .          . .          . .          . .          . .          . .          . .  483 

Platinonitrites ;      platinochlorosulphites ;      platinicarbonyl      com- 
pounds ;  dichloroplatiniphosphonic  acid. .          . .          .  .          . .  485 

Oxides,  sulphides,  selenides,  and  tellurides  of  copper,  silver,  gold, 

and  mercury            . .          . ,          . .          . .          . .          . .          . .  487 

Hydroxides          ..  491 

Aurates.     Double  sulphides.     Oxy-  and  sulpho-halides       . .          . .  492 
Concluding  remarks  on  the  oxides,  sulphides,  &c. ;  classification  of 

oxides 494 

Constitutional  formulae  ;  oxyhalides  and  double  halides     . .          . .  495 


PART  V. 
THE  BOBIDES.     THE  CARBIDES  AND  SILICIDES. 

CHAPTER  XXX.     The  borides ;  hydrogen  boride    . .          497 

Magnesium,  aluminium,  manganese,  silver,  and  iron  borides          . .  498 

The  carbides  and  silicides  ;  methane,  or  marsh-gas  . .          . .          . .  498 

Hydrogen  silicide           . .          . .          . .          . .          . .          . .          . .  500 

Ethane ;  silicoethane     . .          . .          . .          . .          . .          . .          . .  501 

Double  compounds  of  ethyl  and  methyl ;  "  organo-metallic  "  com- 
pounds        . .          . .          . .          . .          . .          . .          . .   '      . .  502 

Ethylene..          ..  '        ..          ..          ..       <  ..       ;.'.'*'      ..          ..  507 

Acetylene ..      '    ..f      WJR     ••  508 

Carbides  and  silicides  of  iron,  &c.        . .          . .          . .          . .  510 


PART  VF. 

THE  NITRIDES,  PHOSPHIDES,  ARSENIDES,  AND 
ANTIMONIDES. 

CHAPTER  XXXI.     Hydrogen   nitrides,  phosphides,  arsenide,   and   anti- 

monide ;  ammonia,  hydrazine,  hydrazoic  acid,  &c.      . .          . .  512 

Salts  of  phosphonium     . .          . .          .  •          . .          . .          . .          . .  517 

Hydroxylamine  . .          523 


XIV  CONTENTS. 

PAGE 

Amido-compouads  or  amines    . .          . .          . .          . .          . .  524 

Salts  of  the  amines         525 

Chromamine  salts           . .          . .          . .          . .          . .          . .          . .  526 

Cobaltamiiie  salts           . .          . .          . .        ...          . .          . .          . .  528 

Methylamine,  &c. ;  the  phosphines  and  arsines         ..          ..          ..  532 

Carbamide           . .          . .          . .          . .          . .          . .          . .          . .  532 

Silicamines,  titanamine,  and  zirconamine  salts          . .          . .          . .  533 

Amides  of  phosphorus  ;  phosphamic  acids     . .          . .          . .          . .  534 

Sulphamines  (sulphamic  acids)            . .          . .          . .          . .          . .  536 

Amines  of  rhodium,  ruthenium,  and  palladium        . .          . .          . .  537 

Osmamines,  iridamines,  and  platinamines      . .          . .          . .          . .  539 

Cupramines,  argentamines,  auramines,  arid  mercuramines  . .          . .  545 

CHAPTER  XXXII.     The  nitrides,  phosphides,  arsenides,  and  antimonides.  550 

Cyanogen  (carbon  nitride)  and  its  compounds         ..          ..          ..  558 

Ferrocyanides  and  ferricyanides,  and  analogous  compounds          . .  562 

Platino-  and  platini-cyanides,  and  similar  compounds        . .          . .  570 

Constitution  of  cyanides           . .          . .          . .          . .          . .          . .  572 


PART  VII. 

CHAPTEE  XXXIII.     Alloys.— Hydrides 575 

Alloys  of  lithium,  sodium,  potassium,  &c.      ..  ..          ..          ..  577 

„         calcium,  barium,  magnesium,  zinc,  &c.  ..          ..          ..  578 

„         aluminium,  chromium,  iron,  &c.     . .  , .          . .          . .  581 

„         tin  and  lead  . .          . .          . .          . .  . .          . .          . .  585 

„         antimony  and  bismuth         . .          . .  . .          . .          . .  587 

„         the  palladium  and  platinum  metals          588 

„         copper,  silver,  gold,  and  mercury  . .  . .          . .          . .  589 


PAET  VIII. 

CHAPTEE  XXXIV.     Spectrum  analysis        591 

Spectroscopy  applied  to  the  determination  of  atomic  weights        . .  598 
The  rare  earths;  the  didymium   group;  the   erbium   group;  the 

yttrium  group         ..          ..602 

Solar  and  stellar  spectra           . .          . .          . .          . .          . .          . .  606 

CHAPTEE  XXXV.     The  atomic  and  molecular  weights  of  elements,  and 

the  molecular  weights  of  compounds      . .          . .          . .          . .  611 

The  specific  heats  of  elements  and  compounds          617 

The  law  of  replacement. .          . .          . .          . .          . .          . .          . .  619 

Isomorphism       . .          . .          . .          . .          . .          . .          . .          tt  620 

The  complexity  of  molecules    ..          ..          ..          ..          ..          ,.  621 

The  monatomic  nature  of  mercury  gas         . .          . .          . .          . .  624 

CHAPTER  XXXVI.     The  periodic  arrangement  of  the  elements  . .          . .  627 

Numerical  relations  between  atomic  weights. .          . .  629 


CONTENTS.  XV 

PAGE 

Relations  between   atomic   weights   and  physical    properties    of 

elements       . .          . .          . .          .  •          •  •          •  •          •  •          •  •  633 

Comparison  of  the  elements  and  their  compounds 634 

Prediction  of  undiscovered  elements 639 


PART  IX. 

CHAPTEB  XXXVII.    Processes  of  manufacture 642 

Combustion;  fuels         642 

CHAPTEB  XXXVIII.     Commercial  preparation  of  the  elements  . .          . .  651 

Manufacture  of  sodium. .          . .          . .          . .          . .          . .          • .  651 

„  magnesium,  zinc,  and  aluminium    . .          . .          . .  652 

„  iron  and  steel. .          . .          . .          •  •          •  •          •  •  653 

„  nickel  . .          . .          . .          . .          •  •          •  •          •  •  658 

„  tin  and  lead 659 

„  antimony         . .          . .          . .          . .          . .          •  •  660 

„  'bismuth  and  copper  . .          . .          •  •          •  •          •  •  661 

„  silver    . .          •  •          •  •          •  •          •  •          •  •          •  •  662 

gold 663 

„  mercury  . .          •  •          •  •          •  •          •  •          •  •  664 

„  phosphorus ••  665 

CHAPTER  XXXIX.    Utilisation  of  sulphur  dioxide  . .  . .  667 

Manufacture  of  sulphuric  acid. .          . .          .  •          •  •          •  •          •  •  667 

alkali 670 

Preparation  of  sodium  sulphate  . .          .  •          •  •          •  •          •  •  672 

The  Leblanc  soda-process          673 

Manufacture  of  caustic  soda     . .          . .          •  •          •  •          » •          •  •  675 

Utilisation  of  tank-waste  . .          . .          •  •          •  •          •  •          •  •  676 

Manufacture  of  chlorine  . .          . .          •  •          •  •          •  •          •  •  678 

„  bleaching  powder       . .          . .          .  •          •  •          •  •  681 

„  potassium  chlorate     . .          . .          •  •          •  •          •  •  682 

The  ammonia- soda  process       . .          . .          •  •          •  •          •  •          •  •  683 


^S^A^f 

PART  I. 


CHAPTER  I. 
INTRODUCTORY  AND  HISTORICAL. 

THE  first  object  of  the  Science  of  Chemistry  is  to  ascertain  the 
composition  of  the  various  things  which  we  see  around  us.  Thus, 
among  familiar  objects  are  air,  water,  rocks  and  stones,  earth,  the 
baric,  wood,  and  leaves  of  plants,  the  flesh,  fat,  and  bones  of  animals, 
and  so  on.  Of  what  do  these  things  consist  ? 

The  second  is  to  ask,  Can  such  things  be  made  artificially,  and, 
if  so,  by  what  methods  ?  Attempts  to  answer  these  questions 
have  led  to  the  discovery  of  many  different  kinds  of  matter,  some 
of  which  have  as  yet  resisted  all  efforts  to  split  them  up  into  still 
simpler  forms.  Such  ultimate  kinds  of  matter  are  termed  elements. 
But  other  kinds  of  matter  can  often  be  produced  when  two  or 
more  of  the  simpler  forms  or  elements  are  brought  together ;  the 
elements  are  then  said  to  combine,  and  the  new  substances  resulting 
from  their  combination  are  called  compounds. 

The  third  object  of  the  Science  of  Chemistry  is  the  correct 
classification  of  the  elements  and  of  their  compounds ;  those  sub- 
stances which  are  produced  in  a  similar  manner,  or  which  act  in  a 
similar  manner  when  treated  similarly,  being  placed  in  the  same 
class. 

The  fourth  inquiry  relates  to  the  changes  which  different  forms 
of  matter  undergo  when  they  unite  with  each  other,  or  when  they 
split  into  simpler  forms. 

Fifthly,  the  conditions  of  change  are  themselves  compared 
with  each  other  and  classified ;  and  thus  general  laws  are  being 
deduced,  applicable  to  all  such  changes. 

Lastly,  the  Science  of  Chemistry  and  the  sister  Science  of 
Physics  join  in  speculations  regarding  the  nature  and  structure  of 
matter,  in  the  hope  that  it  may  ultimately  be  possible  to  account 
for  its  various  forms,  the  changes  which  they  undergo,  and  the 
relations  existing  between  them. 


2  INTRODUCTORY  AND   HISTORICAL. 

To  answer  questions  such  as  these,  it  is  obvious  that  experi- 
ments must  be  made.  Each  form  of  matter  must  be  separately 
exposed  to  different  conditions  ;  heated,  for  example ;  or  placed 
under  the  influence  of  an  electric  current;  or  brought  together 
with  other  kinds  of  matter ;  before  it  is  possible  to  know  what  it  will 
do.  Now,  the  ancient  philosophers  did  not  perceive  this  necessity  ; 
nor  indeed  were  they  much  concerned  in  making  the  inquiry. 
Those  nations  which  have  left  behind  them  a  record  of  their 
thoughts,  the  ancient  inhabitants  of  India,  Egypt,  Greece,  and 
Rome,  devoted  their  attention,  if  they  aspired  to  be  learned,  to 
oratory,  to  history,  or  to  poetry.  Their  only  scientific  pursuits 
were  politics,  ethics,  and  mathematics.  Distinction  was  to  be 
gained  in  the  forum,  in  the  temple,  or  in  the  battlefield  ;  not  in 
wresting  secrets  from  Nature.  The  practice  of  such  of  the  arts  as 
were  then  known  was  in  the  hands  of  slaves  and  the  lower  classes 
of  the  people,  who  were  content  to  transmit  their  methods  from 
father  to  son,  and  whose  achievements  were  unchronicled.  The 
citizens  of  the  State,  the  wealthy  and  the  leisured,  despised  these 
low-class  arts ;  and,  indeed,  it  was  taught  by  Socrates  and  his  fol- 
lowers that  it  was  foolish  to  abandon  the  study  of  those  things 
which  more  nearly  concern  man,  for  that  of  things  external 
to  him.  It  was  generally  believed  that  by  the  exercise  of  pure 
thought,  without  careful  observation  and  experiment,  a  man 
could  know  best  the  true  nature  of  the  objects  external  to  him. 
Thus  Plato  says  in  the  7th  Book  of  the  "  Republic,"  "  We  shall 
pursue  Astronomy  with  the  help  of  problems,  just  as  we  pursue 
Geometry;  but,  if  it  is  our  design  to  become  really  acquainted  with 
Astronomy,  we  shall  let  the  heavenly  bodies  alone."  Elsewhere 
he  states  that,  even  if  we  were  to  ascertain  these  things,  we  could 
neither  alter  the  course  of  the  stars,  nor  apply  our  knowledge  so  as 
to  benefit  mankind.  And  in  "Timseus,"  Plato  remarks,  "  God  only 
has  the  knowledge  and  the  power  which  are  able  to  combine  many 
things  into  one,  and  to  dissolve  the  one  into  the  many.  But  no  man 
either  is  or  ever  will  be  able  to  accomplish  either  the  one  or  the 
other  operation." 

It  was  impossible,  with  such  a  mental  attitude  towards  science, 
for  any  accurate  knowledge  to  exist,  or  for  any  probable  theories 
to  be  devised.  Yet,  as  it  is  interesting  to  know  something  of  the 
old  ideas  concerning  matter  and  its  nature,  a  short  sketch  will  be 
given  here. 

The  origin  of  the  world  was  for  the  ancient  philosophers  of 
Egypt,  India,  and  Greece,  as  it  is  for  ourselves,  a  subject  of  the 
greatest  interest ;  and  in  attempting  to  frame  some  theory  to  explain 


INTRODUCTORY   AND    HISTORICAL.  £ 

the  Creation  it  was  necessary  to  speculate  on  the  nature  of  matter. 
The  various  aspects  of  matter  which  we  see  around  us  were  sup- 
posed by  Empedocles  (492  B.C.),  and  later  by  Aristotle  (384  B.C.), 
to  be  modi 6 cations  of  one  fundamental  original  material,  occurring 
in  various  forms,  the  difference  between  which  was  caused  by  the 
assumption  of  certain  "  elements,"  or  as  we  should  now  name  them 
"  properties."  This  original  material  was  imagined  by  Empedocles 
to  consist  of  small  particles,  which  he  termed  atoms,  or  "  indi- 
visibles," because  they  were  in  his  view  the  ultimate  particles  into 
which  matter  could  be  divided.  Plato  imagined  such  atoms  to 
have  the  form  of  triangles  of  different  sizes,  equilateral,  isosceles, 
or  scalene  ;  and  ascribed  the  "  perfection  "  or  "  imperfection  "  of 
matter  to  be  due  to  the  form  of  its  ultimate  particles.  But  such 
particles  were  modified  by  the  "elements"  earth,  water,  air,  and 
fire;  that  is,  they  assumed  a  solid,  liquid,  aeriform,  or  naming 
nature,  according  to  the  element  which  predominated  in  them. 
Along  with  this  view,  a  certain  confusion  of  thought  arose  which 
led  to  the  conception  that  earth,  water,  air,  and  fire  were  actually 
present  in,  and  constituents  of,  matter,  and  that  all  the  elements 
originated  in  one,  supposed  by  Thales  (600  B.C.)  to  be  water,  and 
by  Anaximenes  (about  550  B.C.)  to  be  air  or  fire.  The  well- 
known  poem  of  Lucretius,  De  rerum  naturd,  is  a  transcript  of 
these  views  of  the  atomic  constitution  of  the  universe.  But  such 
speculations  were  wholly  without  a  basis  of  fact,  and  led  to  no 
new  knowledge.  These  ideas,  in  all  probability,  were  originally 
derived  from  India,  where  the  four  elements  already  men- 
tioned were  associated  with  a  fifth  and  sixth,  ether  and 
consciousness,  as  appears  from  the  teaching  of  Buddha.  The 
notion  that  matter  was  one  in  kind,  modified  by  certain  attributes, 
developed  the  belief  that  by  changing  the  attributes,  the  matter 
itself  would  be  transmuted.  Thus  Tima3us  is  made  to  say  by 
Plato  : — "  In  the  first  place,  that  which  we  are  now  calling  water, 
when  congealed,  becomes  stone  and  earth,  as  our  sight  seems  to 
show  us  [here  he  refers  probably  to  rock-crystal,  a  transparent, 
hard  material,  which  was  supposed  to  be  petrified  ice]  ;  and  this 
same  element,  when  melted  and  dispersed,  passes  into  vapour  and 
fire.  Air  again,  when  burnt  up,  becomes  fire,  and  again  fire,  when 
condensed  and  extinguished,  passes  once  more  into  the  form  of  air  ; 
and  once  more  air,  when  collected  and  condensed,  produces  cloud 
and  vapour ;  and  from  these,  when  still  more  compressed,  comes 
flowing  water ;  and  from  water  come  earth  and  stones  once  more  ; 
and  thus  generation  seems  to  be  transmitted  from  one  to  the  other 
in  a  circle."  Here  the  elements  are  evidently  conceived  in  their 

B  2 


4  INTRODUCTORY  AND  HISTORICAL. 

concrete  sense  ;  but  lie  goes  on  to  say  that  certain  matter  in  a  state 
of  change  partakes  of  the  nature  of  fire  to  some  extent,  and  to  some 
extent  of  the  nature  of  the  other  elements. 

Guided  by  such  considerations,  Aristotle  gave  precision  to  these 
speculations  by  his  system  of  "  contraries."  The  properties  shared 
by  all  matter  in  varying  proportions  were  "  hotness,"  "  coldness," 
"moistness,"  and  "  dryness."  Thus  air  was  hot  and  moist;  fire, 
hot  and  dry ;  water,  cold  and  moist ;  and  earth,  cold  and  dry.  By 
imparting  heat  to  water  it  becomes  steam,  that  is,  air,  hot  and 
moist ;  by  taking  away  its  moisture  it  becomes  earth,  that  is,  ice, 
cold  and  dry. 

The  "  Timaeus"  of  Plato,  which  has  been  quoted  several  times 
here,  was  held  in  high  esteem  by  the  great  school  of  learning  which 
existed  at  Alexandria  during  the  first  centuries  of  our  era.  It  was 
here,  in  all  likelihood,  that  the  second  great  era  of  chemical  theory 
began.  Based  on  such  ideas  regarding  the  constitution  of  matter, 
attempts  were  made  to  change  one  substance  into  another,  and 
above  all  to  transmute  the  baser  metals  into  gold.  The  attempt 
was  called  Alchemy  (the  Arabic  prefix  al  signifying  "  the  "),  and 
from  that  word,  which  probably  means  the  dark  or  secret  art,  is 
derived  our  modern  name  Chemistry. 

In  order  to  realise  the  attitute  of  mind  which  led  to  the  belief 
in  the  possibility  of  the  transmutation  of  metals,  as  the  change  of 
one  metal  into  another  is  called,  we  must  note  that  it  was  supposed 
that  the  apparent  change  of  one  form  of  matter  into  another  in- 
volved the  destruction  of  the  first  form,  and  the  creation  of  the 
second  ;  the  properties  of  the  matter  were  changed,  and  hence  the 
matter  itself  was  supposed  to  be  changed  ;  no  attempt  was  made, 
so  far  as  we  know,  to  compare  the  weights  (or  masses)  of  the 
matter  before  and  after  the  change  had  taken  place.  Pure  sub- 
stances, moreover,  were  almost  unknown,  and  the  separation  of  an 
impurity  from  a  compound  in  many  cases  entirely  altered  its  pro- 
perties. Now,  the  Arabs,  who  conquered  Egypt  in  the  7th  century, 
and  transmitted  their  knowledge  to  posterity,  possessed  a  theory 
of  which  we  learn  in  the  writings  of  Geber,  an  Arabian  alchemist 
of  the  8th  century,  and  in  which  we  can  trace  a  germ  of  the 
modern  views  concerning  matter,  inasmuch  as  we  find  here  the 
first  dawn  of  a  conception  of  a  chemical  compound,  in  the  modern 
sense  of  the  word. 

Geber,  and  probably  his  predecessors  the  Alexandrians,  re- 
garded the  metals  as  alloys  of  mercury  and  sulphur  in  varying 
proportions.  Now-a-days,  mercury  is  the  name  of  a  metal  which 
possesses  definite  unalterable  properties  ;  nor  does  sulphur  vary, 


INTRODUCTORY   AND   HISTORICAL.  0 

but  is  always  a  distinct  substance  capable  of  certain  changes, 
though  radically  the  same  throughout  these  changes.  But  Geber 
held  that  the  mercury  and  the  sulphur  each  varied  in  kind  and  in 
properties,  and  were  not  what  we  should  now  term  definite 
chemical  individuals.  His  views  may  best  be  learned  from  his 
own  words: — "  It  is  folly  to  attempt  to  extract  one  substanc.e  from 
another  which  does  not  contain  it.  But,  as  all  metals  consist  of  mer- 
cury and  sulphur,  it  is  possible  to  add  to  one  what  is  wanting,  or 
to  take  from  another  what  is  in  excess."  Yet  he  did  not  discard 
the  older  elements,  earth,  water,  air,  and  fire,  but  appears  to  have 
regarded  them  as  more  remote  constituents  of  matter,  while  mer- 
cury and  sulphur  were  the  proximate  constituents.  The  mercury 
was  supposed  to  impart  to  metals  their  brilliancy,  their  malleability, 
and  their  fusibility ;  while  the  sulphur  which  they  contained  ren- 
dered them  alterable  by  fire,  which  changes  many  metals  to  earthy 
powders.  In  his  writings  also  we  find  the  first  allusion  to  a  con- 
nection between  the  curing  of  disease  and  the  transmutation  of 
metals,  in  his  illustration,  "  Bring  me  the  six  lepers,  and  I  will 
heal  them,"  referring  to  the  conversion  of  six  of  the  metals  then 
known  into  gold,  the  seventh. 

It  is  not  wonderful  that  the  alchemists  should  have  been  led 
into  error  by  attempts  to  transmute  the  metals  into  gold;  for 
their  properties  are  radically  changed  by  the  presence  of  mere 
traces  of  foreign  bodies. 

Thus  the  presence  of  a  minute  trace  of  lead  or  arsenic,  for 
example,  renders  gold  exceedingly  brittle,  and  alters  its  colour; 
the  presence  of  a  very  small  quantity  of  carbon  in  iron  renders  it 
elastic,  or  if  more  be  present,  hard  and  brittle ;  a  small  amount  of 
arsenic  in  copper  colours  it  white  and  lowers  enormously  its  power 
of  conducting  electricity.  These  changes,  which  are  still  un- 
explained, received  much  more  attention  in  the  early  days  of 
chemistry  than  of  recent  years  ;  but  it  is  to  be  hoped  that  they 
will  again  be  exhaustively  studied. 

For  many  centuries  after  Geber's  time,  although  numerous 
compounds  were  discovered  in  the  search  for  gold,  no  new 
development  of  theory  can  be  noticed.  The  attitude  of  •  the 
Roman  Church  was  hostile  to  the  progress  of  any  knowlege  of 
nature.  All  learning  was  in  the  hands  of  the  priests,  and  the 
study  of  the  ancient  writers  was  discouraged  or  forbidden,  as  not 
only  useless  in  itself,  but  as  tending  to  distract  the  mind  from  the 
higher  studies  of  Divine  things.  When  permitted  on  sufferance  it 
was  with  the  avowed  object  of  combatting  disbelief  with  its  own 
weapons.  Roger  Bacon  (1214 — 1294)  even,  who  published 


(>  INTRODUCTORY  AND   HISTORICAL. 

several  works  on  alchemy,  wrote  that  that  science  which  is  not 
prosecuted  with  a  view  of  defending  the  Christian  faith  leads  "  to 
the  darkness  of  hell."  Yet  after  the  conquest  of  Spain  by  the 
Arabs,  in  the  beginning  of  the  8th  century,  the  study  of  medicine, 
of  mathematics,  and  of  optics  slowly  grew  in  the  west  of  Europe. 
The  works  of  many  of  the  Greek  philosophers  were  known  only 
through  Arabic  translations.  It  was  not  in  the  nature  of  the 
Arabs  to  originate  new  theories;  they  merely  preserved  those 
which  they  had. 

In  the  15th  century,  Basil  Valentine,  a  Benedictine  friar, 
added  one  to  the  two  supposed  constituents  of  metals.  This 
was  a  principle  of  fixity;  something  which  resisted  the  action 
of  heat  without  volatilising  into  gas.  Valentine  termed  this 
principle  "  salt."  Again,  it  is  not  to  be  understood  that  any 
particular  salt  is  referred  to  ;  yet,  in  the  minds  of  many  of  Basil 
Valentine's  disciples,  the  earthy  residue  obtained  by  calcining 
metals  such  as  lead  in  the  air  was  regarded  as  the  same  in  essence, 
fr6m  whatever  source  it  had  been  derived.  And  this  theory  was 
extended  to  include  all  matter ;  it  is  well  described  in  the  words  of 
Paracelsus  (born  1493,  died  1541).  "  In  all  things  four  elements 
are  mingled  with  each  other ;  among  those  four,  only  one  is  fixed 
and  perfect ;  in  that  element  lies  the  true  *  quintessence.'  The 
other  elements  are  imperfect;  yet  any  one  of  them  is  able  to 
tinge  and  qualify  the  others,  according  to  its  nature.  Thus  in 
some  the  element  water  predominates ;  in  some  fire ;  in  some 
earth;  in  others  air.  In  order  to  separate  the  predominating 
element  as  salt,  sulphur,  and  mercury,  each  must  be  broken  and 
destroyed  by  solution,  and  calcination,  or  by  such  means." 
"  There  are  various  minerals  in  which  the  elements  are  not  FO 
firmly  locked  up  as  in  the  metals,  and  which  can  be  split  into  their 
three  principles  :  salt,  the  fixed  element ;  sulphur,  tiery  and  oily  ; 
and  mercury,  aeriform  and  watery."  (  Wunsch  Hiittlein,  Erfurt, 
1738,  p.  27.) 

The  language  of  the  mediaeval  alchemists  is  most  obscure. 
Not  only  did  they  confuse  substances  now  known  to  be  perfectly 
distinct;  not  only  was  their  nomenclature  ambiguous;  but  a 
spirit  of  mysticism  pervaded  their  writings  which  led  them  to 
believe  that  it  would  have  been  impious  to  reveal  to  the  common 
people  the  processes  with  which  they  were  acquainted.  Chemical 
elements  and  com  pounds,  form  in  the  pages  of  their  books  proces- 
sions of  kings  and  queens,  bridegrooms  and  brides,  lions  and 
dragons,  eagles  and  swans ;  gold  is  the  Sun  ;  silver  the  Moon ;  this 
king  and  queen,  Apollo  and  Diana,  are  devoured,  on  their  bridal 


INTRODUCTORY  AND   HISTORICAL.  7 

eve,  by  Saturn,  (lead),  a  dragon  and  serpent  which  has  for  ages 
slept  in  his  rocky  cavern.  Pluto  enters  with  exceeding  heat, 
expelling  the  dragon  as  an  eagle  with  scorched  wings,  and  leaving 
the  royal  pair  reposing  on  a  bed,  white  as  the  mountain  snows. 
Such  is  Basil  Valentine's  account  of  the  refining  of  gold  in  the 
second  of  his  "  Twelve  keys  to  unlock  the  door  leading  to  the 
ancient  stone  ";  among  innumerable  descriptions  of  the  kind  it  is 
one  of  the  few  in  which  the  actual  processes  can  be  followed  under 
their  mystical  disguise.  We  meet  with  fanciful  analogies  between 
the  Divine  Trinity  ;  the  human  body,  soul,  and  spirit ;  and  the 
trio  of  salt,  sulphur,  and  mercury,  in  which  religion,  medicine,  and 
chemistry  are  mingled  in  inextricable  entanglement.  Yet  such 
analogies  served  a  good  purpose ;  they  led  to  the  combatting  of 
disease,  not  as  before  with  charms  and  incantations,  and  remedies 
of  a  disgusting  and  fantastic  nature,  but  by  the  administration  of 
chemical  substances  as  drugs.  In  spite  of  all  their  false  theories, 
connecting  certain  of  the  organisms  of  the  bodies  with  the  stars, 
and  these  again  with  the  metals,  the  compounds  of  which  were 
supposed  to  act  on  those  organisms  with  which  they  were  so 
fancifully  related,  true  progress  was  made  by  the  only  way  in 
which  progress  is  possible — by  experiment  and  deduction  ;  and  the 
virtues  of  antimony,  of  mercury,  and  of  other  remedies  were 
gradually  discovered.  This  change  in  the  ultimate  goal  of  chemical 
research  was  begun  by  Basil  Valentine ;  its  chief  advocate,  how- 
ever, was  Paracelsus,  who  boldly  announced  that  "  The  true  scope 
of  chemistry  is  not  to  make  gold,  but  to  prepare  medicines."  Yet 
in  his  writings  there  are  numerous  receipts  for  the  preparation  of 
the  alcahest,  or  universal  solvent ;  and  of  that  magic  elixir,  capable 
not  only  of  converting  baser  metals  into  gold,  but  of  conferring  on 
its  fortunate  possessor  long  life  and  eternal  youth. 

Although  no  advance  in  chemical  theory  was  made  by  the 
school  of  alchemists  represented  by  Valentine  and  Paracelsus,  yet 
the  indefatigable  labours  of  these  men  and  of  their  disciples 
enriched  chemistry  by  the  discovery  of  many  new  compounds, 
and  laid  a  foundation  of  facts  for  chemists  of  a  later  age. 

The  era  of  modern  chemistry  opens  with  Robert  Boyle 
(1626 — 1691).  In  his  works,  which  are  very  voluminous,  we  meet 
with  no  traces  of  the  spirit  of  mysticism  which  prevailed  up  to  his 
time,  but  he  manifests  that  aspect  of  rational  inquiry  which  is 
typical  of  modern  science.  His  most  important  work  on  chemistry 
is  named  "  The  Sceptical  Chymist,  or  considerations  upon  the 
experiments  usually  produced  in  favour  of  the  four  elements,  and 
of  the  three  chymical  principles  of  the  mixed  bodies."  In  it  he 


INTEODUCTOKY  AND   HISTOIUCAL. 

defines  the  word  element :  "  The  words  element  and  principle  are 
here  used  as  equivalent  terms :  and  signify  those  primitive  and 
simple  bodies  of  which  the  mixed  ones  are  said  to  bo  composed, 
and  into  which  they  are  ultimately  resolved.  'Tis  said  that  a 
piece  of  green  wood,  by  burning,  discovers  the  four  elements  of 
which  mixed  bodies  are  composed,  the  fire  appearing  in  the  flame 
by  its  own  light;  the  smoke  ascending  and  readily  turning  into  air, 
as  a  river  mixes  with  the  sea  ;  the  water,  in  its  own  form,  boiling 
out  at  the  end  of  the  stick,  and  the  ashes  remaining  for  the  element 

of  earth But  there  are  many  bodies  from  whence 

it  seems  impossible  to  extract  four  elements  by  fire,  and  which  of 
these  can  be  obtained  from  gold  by  any  degree  of  fire  whatsoever  ?" 
He  then  proceeds  to  consider  in  detail  the  supposed  evidence  for 
the  existence  of  the  Aristotelian  elements,  and  of  the  principles, 
salt,  sulphur,  and  mercury ;  and  he  finally  shows  that  they  cannot 
be  considered  as  elements,  using  the  word  in  the  modern  sense  of 
the  constituents  of  bodies ;  and  he  incidentally  points  out  that 
compounds,  as  a  rule,  do  not  resemble  the  elements  of  which  they 
are  composed. 

Boyle  thus  successfully  combatted  the  ancient  doctrines  of  the 
alchemists ;  and  although  a  belief  in  alchemy  lingered  on  into  the 
last  century,  and  has  even  had  a  few  disciples  in  our  own  day,  yet 
the  formation  of  the  learned  societies  of  Florence  (1657),  London 
(1662),  Paris  (1666),  and  Vienna,  and  the  open  interchange  of 
ideas  among  men  who  submitted  every  doubtful  point  to  the  test  of 
experiment,  did  much  to  destroy  the  veil  of  mysticism  which  had 
surrounded  the  labours  of  the  ancient  alchemists,  and  has  ulti- 
mately proved  the  correctness  of  Boyle's  views. 

The  phenomena  of  burning  and  combustion  played  a  great  part 
in  the  theories  of  the  mediaeval  alchemists,  and  were  held  to  sub- 
stantiate their  views.  For  when  a  candle  burns,  it  disappears  ;  the 
solid  is  changed  into  air  and  flame  ;  a  transmutation  has  taken 
place,  proving  the  identity  of  the  elements.  Many  metals,  when 
heated  in  air,  are  converted  into  earthy  powders,  differing  entirely 
from  their  originals  in  properties.  Paracelsus  seems  to  have 
imagined  that  in  certain  similar  cases,  for  example  when  iron 
pyrites  lies  exposed  to  air,  "the  old  demogorgon,"  as  he  calls  this 
compound  of  iron  and  sulphur,  "  absorbs  the  universal  salt, 
whereby  it  is  converted  into  a  greyish  crystalline  powder."  But 
no  consistent  theory  had  been  advanced  to  account  for  the  pheno- 
mena of  combustion.  John  Mayow  (1645 — 1679),  indeed,  a  con- 
temporary of  Boyle's,  a  medical  graduate  of  Oxford,  who  practised 
at  Bath,  had  he  lived,  would  in  all  probability  have  advanced  the 


INTRODUCTORY  AND   HISTORICAL.  9 

knowledge  of'  chemical  theory  to  the  stage  which  it  reached  more 
than  a  century  after  his  death.  During  his  short  life,  he  antici- 
pated most  of  the  deductions  of  Lavoisier,  who,  as  we  shall  shortly 
see,  effected  a  revolution  in  the  science.  Guided  by  Boyle's 
researches,  and  with  a  rare  faculty  of  devising  experiments  admi- 
rably adapted  to  decide  the  points  at  issue,  Mayow  pointed  out 
that  atmospheric  air  consists  of  two  kinds,  one  capable  of  sup- 
porting combustion  and  life,  which  he  named  "  spiriius  igno-aerit-.s," 
and  another,  devoid  of  these  properties.  He  concluded  from 
his  experiments  that  this  "  spiritus  igno-aerius,"  or  to  give 
ib  Lavoisier's  name,  oxygen,  was  a  constituent  of  nitre  or  salt- 
petre, and  was  also  contained  in  nitric  acid  ;  that  when  oxygen 
combines  with  other  bodies,  such  as  metals,  it  increases  their 
weight ;  that  it  is  the  common  constituent  of  acids,  sulphuric  acid 
being  its  compound  with  sulphur,  and  nitric  acid  its  compound 
with  the  inactive  constituent  of  air,  now  known  as  nitrogen ;  and 
he  also  devised  a  method  of  estimating  oxygen  by  mixing  with  it 
one  of  the  compounds  of  nitrogen  and  oxygen,  nitric  oxide,  a  process 
which  was  afterwards  largely  employed,  and  which  has  been  re- 
cently revived.  Lastly,  he  showed  the  function  of  oxygen  in  acid 
fermentation,  and,  in  his  "  Tractatus  quinque  medico-physici"  in 
which  his  investigations  and  conclusions  are  recorded,  he  showed 
very  clearly  the  part  played  by  oxygen  in  restoring  venous  blood 
to  the  arterial  state,  and  in  maintaining  animal  heat. 

But  Mayow  was  alone  in  his  work ;  his  early  death  cut  short 
his  researches  ;  and  his  contemporaries  and  successors  did  not  recog- 
nise their  merit.  Stephen  Hales,  for  example,  though  he  pre- 
pared in  an  impure  state  carbonic  acid,  nitrogen,  hydrogen,  and 
oxygen  gases,  and  also  marsh-gas,  regarded  them  all  as  modifica- 
tions of  air,  not  as  distinct  gaseous  substances.  He  ascribed  to 
atmospheric  air  "  a  chaotic  nature,"  inasmuch  as  it  was  found  to 
be  endowed  with  so  many  different  properties. 

But  in  spite  of  Mayow's  correct  surmises  regarding  the  nature 
of  combustion,  the  opinion  which  chemists  generally  held  was  that 
when  a  body  was  burnt  something  escaped  from  it,  viz.,  fire  or 
heat.  For  although  it  was  well  known  that  combustible  sub- 
stances do  not  continue  to  burn  in  a  confined  space,  this  was 
attributed  not  to  the  exclusion  of  air,  but  to  the  prevention  of  the 
escape  of  flame.  And  in  spite  of  its  having  been  noticed  by  Boyle 
and  others  that  metals  gain  in  weight  by  being  calcined,  yet  no 
special  attention  was  paid  to  the  fact.  So  long  indeed  as  what  we 
now  know  to  be  different  kinds  of  gases  were  assumed  to  be  only 
common  air  containing  impurities,  it  was  impossible  to  account 


10  INTRODUCTORY   AND   HISTORICAL. 

for  the  apparent  loss  of  weight  which  many  combustible  substances 
suffer  when  burnt. 

A  consistent  though  erroneous  theory  of  combustion,  which 
served  to  unite  in  one  group  such  apparently  different  processes  as 
the  burning  of  a  candle  and  the  conversion  of  a  metal  into  a 
"  calx  "  or  earthy  powder  when  it  was  heated  in  air,  was  first  pro- 
pounded by  Stahl  (1660—1734).  Stahl  taught  that  when  a 
substance  burns,  it  loses  something  ;  this  he  called  "  phlogiston  " 
(from  0Xo7t<7To'$,  inflammable),  which  signified  the  common  con- 
stituent of  all  combustible  bodies.  This  theory,  however,  dates 
from  before  Stahl's  time  ;  phlogiston  is  identical  with  the  "terra- 
pinguis"  of  Becher  (1635 — 1682),  and  the  idea  that  combustible 
bodies  lost  a  fiery  matter,  a  "  sulphur,"  is  even  older  than  Becher. 
The  more  readily  a  substance  burns,  according  to  Stahl,  the  more 
phlogiston  it  contains.  A  substance  containing  much  phlogiston 
was  carbon,  or  charcoal.  And  when  a  metal  had  lost  its  phlogiston 
and  had  become  a  "  calx,"  it  was  possible  to  restore  the  lost 
phlogiston  by  heating  it  with  charcoal,  which  would  yield  up  to 
the  calx  its  phlogiston,  again  converting  it  into  the  metallic  state. 

But  in  the  meantime  the  progress  of  chemistry  was  furthered 
by  the  discovery  of  many  new  gases,  and  the  conviction  spread 
not  only  that  gases  were  not  impure  atmospheric  air,  but  that 
matter  was  capable  of  existence  in  three  forms,  solid,  liquid,  and 
gaseous.  Black  (1728 — 1799)  was  the  first  clearly  to  show 
(probably  about  1755)  that  carbonic  acid  gas  (carbon  dioxide)  or 
';  fixed  air  "  was  radically  distinct  from  ordinary  air,  inasmuch 
as  it  could  combine  with  or  be  "  fixed  "  by  lime,  magnesia,  and 
the  caustic  alkalies,  potash  and  soda.  As  acids  have  this  pro- 
perty, Keir  suggested  that  it  belonged  to  the  class  of  acids,  and 
Bergmann  (1735—1784),  following  Priestley's  suggestion  that  it 
was  a  constituent  of  air,  named  it  "aerial  acid."  It  is  the  first 
substance  which  was  named  "  gas  "  (from  geist,  equivalent  to  gust) ; 
the  name  is  due  to  Van  Helmont  (1577 — 1644),  who  had  noticed 
that  it  could  be  obtained  by  heating  limestone. 

The  merit  of  Black's  work  consists  in  his  having  shown  that, 
whereas  limestone  lost  a  definite  weight  by  being  calcined,  its 
weight  is  exactly  restored  if  the  lime  resulting  from  its  calcination 
is  reunited  with  carbonic  acid  gas.  This  was  the  first  success- 
ful chemical  experiment  dealing  with  quantities.  A  complete 
investigation  of  "  inflammable  air,"  or,  as  it  is  now  named, 
hydrogen  gas,  is  due  to  Henry  Cavendish  (1731 — 1810).  It  is 
the  gaseous  substance  produced  when  metals  such  as  iron,  tin,  or 
zinc  are  treated  with  acids.  Cavendish,  in  1766,  proved  the 


INTRODUCTORY  AND   HISTORICAL.  11 

identity  of  the  substance  from  whichever  source  it  was  prepared, 
and  examined  its  properties.  He  found  it  to  be  exceedingly  light, 
and  to  burn  very  readily ;  and  it  was  supposed  by  some  to  be  the 
long  sought  "  phlogiston  "  of  Stahl.  Cavendish  also  discovered 
that  its  product  of  combustion  was  water. 

But  the  chemistry  of  gases,  or  as  it  was  then  termed  "  pneu- 
matic chemistry,"  was  most  advanced  by  the  researches  of  Joseph 
Priestley  (1733—1804).  He  was  the  first  to  devise  a  convenient 
method  of  collecting  gases  over  water  or  mercury,  and  his  plan  is 
still  used  in  our  own  day.  To  him  is  due  the  discovery  of  most 
of  the  gaseous  substances  now  known,  especially  of  oxygen  gas,  on 
August  1st,  1774,  which  he  named  "  vital  air,"  owing  to  its 
property  of  supporting  life,  or  "  dephlogisticated  air,"  because  it 
was  the  most  ardent  supporter  of  combustion,  though  not  itself 
combustible.  The  discovery  of  oxygen  was  made  independently 
and  almost  simultaneously  by  Scheele,  a  Swede  (1742—1786),  to 
whom  we  also  owe  the  discovery  of  chlorine. 

These  discoveries  prepared  the  way  for  the  grand  generalisation 
of  Lavoisier.  Black,  Cavendish,  Priestley,  and  Scheele  were  all 
adherents  of  Stahl's  phlogistic  theory.  But  Lavoisier  (1743 — 
1794),  having  been  shown  the  method  of  preparing  oxygen  by 
Priestley,  who  paid  him  a  visit  in  the  autumn  of  1774,  saw  the 
grand  importance  of  the  discovery,  and  made  the  great  generalisa- 
tion that,  when  bodies  burn,  they  combine  with  this  constituent  of 
air,  to  which  he  gave  the  name  oxygen.  This  discovery  laid  the 
foundation  of  the  present  science  of  chemistry  ;  the  time  was  now 
ripe ;  and  in  a  very  complete  series  of  researches  Lavoisier  showed 
first : — that  water  cannot  be  converted  into  earth  by  boiling,  but 
that  it  merely  dissolves  some  of  the  constituents  of  the  glass  vessel 
in  which  it  is  boiled,  leaving  the  dissolved  matter  as  a  residue 
after  it  has  evaporated ;  second,  that  when  tin  is  heated  with  air 
in  a  closed  vessel,  although  it  is  changed  into  a  whitish-grey  calx, 
yet  the  combined  weight  of  the  vessel  and  the  tin  remains 
unchanged ;  thus  showing  that  nothing  has  escaped  from  the  tin 
or  been  lost  from  the  vessel ;  and  that  on  opening  the  vessel  air 
entered,  so  that  the  whole  apparatus  increased  in  weight ;  and 
that  this  increase  in  weight  was  practically  equal  to  the  increase 
in  weight  of  the  tin  due  to  its  conversion  into  "  calx."  From  this 
experiment  he  drew  the  correct  conclusion  that  the  gain  in  weight 
of  the  tin  was  due  to  its  absorption  of  one  of  the  constituents  of 
air.  Thirdly,  he  repeated  this  experiment,  substituting  the  metal 
mercury  for  tin  ;  the  red  powder  produced,  when  heated  strongly, 
yielded  up  the  absorbed  gas,  identical  with  the  "vital"  or 


12  INTRODUCTORY  AND   HISTORICAL. 

"  dephlogisticated  "  air  of  Priestley,  to  which.  Lavoisier  gave  the 
name  oxygen.  Fourthly,  he  showed  that  organic  matters  yield, 
when  burnt,  carbonic  acid  and  water;  and  that  carbonic  acid, 
identical  with  Black's  "  fixed  "  air,  is  produced  by  the  combustion 
of  carbon  or  charcoal.  His  views  are  stated  by  himself  as 
follows : — 

1.  Bodies  burn  only  in  pure  air. 

2.  This   air  is  used  up  during  combustion,  and  the   gain  in 
weight  of  the  body  burned  is  equal  to  the  loss  of  weight  of  the  air. 

3.  The  combustible  body  is  generally  converted  into  an  acid  by 
its   union   with    pure   air;    but   the   metals    are    converted   into 
calces  or  earthy  matters. 

To  this  last  statement  is  due  the  name  "  oxygen,"  or  "  pro- 
ducer of  acids."  Up  to  that  date,  acid  (from,  acetum,  vinegar)  was 
the  name  applied  to  substances  with  a  sour  taste,  which  acted 
on  calces,  producing  crystalline  substances,  termed  salts.  Many 
attempts  have  since  been  made  to  give  precision  to  the  conception 
of  the  word  acid ;  but,  however  convenient  the  colloquial  use  of  the 
word,  it  has  ceased  to  have  a  definite  chemical  signification.  It 
was  soon  after  shown  that  bodies  may  possess  the  defined  pro- 
perties of  an  acid  and  yet  contain  no  oxygen. 

The  discoveries  of  Lavoisier  were  owing  in  great  degree  to  two 
fundamental  conceptions,  with  regard  to  which  he  held  the  firmest 
convictions  :  first,  that  heat  was  not  a  substance  capable  of  entering 
and  escaping  from  bodies  like  a  chemical  element,  but  a  condition 
of  matter ;  and  that  its  gain  or  loss  implied  no  gain  or  loss  of 
weight ;  and  second,  that  matter  was  indestructible  and  uncreat- 
able ;  and  that  the  true  measure  of  its  quantity  was  its  mass,  or 
weight ;  hence  the  weight  of  a  compound  body  must  equal  the 
sum  of  the  weights  of  its  constituents. 

It  was  many  years  before  Lavoisier's  views  gained  complete 
acceptance  amongst  chemists ;  but  the  discovery  of  Cavendish  in 
1784 — 85,  that  the  only  product  of  the  combustion  of  hydrogen 
was  water,  showed  the  true  relations  of  that  important  substance 
to  oxygen,  and  explained  many  difficulties. 

To  Lavoisier,  too,  belongs  the  merit  of  having  invented  a 
systematic  nomenclature,  which  is  still  retained  in  its  main 
features;  its  convenience  and  general  applicability  did  much  to 
promote  the  acceptance  of  the  theory  on  which  it  was  based. 

We  have  traced  the  gradual  evolution  of  the  science  of 
chemistry  from  the  earliest  speculations  of  the  Greek  philosophers 
to  the  end  of  last  century.  With  this  century  opens  a  new  era, 
which  will  form  the  subject  of  the  next  chapter. 


INTRODUCTORY  AND   HISTORICAL.  13 

Note. — The  chief  worts  on  the  history  of  chemistry  are  Kopp's  Geschichte 
der  Chemie,  1843-47  ;  EntwicJcelung  der  Chemie  in  der  neueren  Zeit,  1873  ; 
Thomson's  History  of  Chemistry,  1830;  Meyer's  Geschichte  der  Chemie, 
Leipzig,  1889  :  the  last  is  specially  to  be  recommended.  For  short  sketches  of 
the  subject,  see  also  Muir's  Heroes  of  Chemistry,  and  Picton's  The  Story  of 
Chemistry. 


14 


CHAPTEK  II. 
HISTOKICAL  (CONTINUED). 

As  most  of  the  common  substances  which  we  see  around  us  contain 
oxygen,  their  composition  could  not  be  determined  before  it  had 
been  shown  by  Lavoisier  that  the  phlogistic  theory  was  untenable, 
and  before  the  phenomena  of  oxidation  had  received  their  true 
explanation.  Lavoisier  himself  showed  the  true  nature  of  sulphuric 
acid,*  viz.,  that  it  was  a  compound  of  sulphur  and  oxygen,  and  not 
a  constituent  of  sulphur,  deprived  of  phlogiston ;  and  also  of 
carbonic  acid,t  that  it  was  an  oxide  of  carbon,  and  not  carbon 
deprived  of  phlogiston.  These  and  similar  discoveries  of  Lavoi- 
sier's pointed  the  way  to  others,  and  numerous  attempts  were 
made  to  discover  the  composition  of  substances,  or  to  analyse 
them  (ai/aXv<rt<?).  And  from  the  time  of  Lavoisier's  enunciation 
of  the  true  nature  of  combustion,  to  the  beginning  of  the  19th 
century,  many  analyses  were  made,  and  confirmed  in  many  cases 
also  by  synthesis,  that  is  placing  together  (avvOeai^)  the  con- 
stituents of  the  compounds,  so  as  to  reproduce  the  compound 
which  had  been  analysed. 

At  that  time  very  few  accurate  methods  of  analysis  were 
known.  The  qualitative  composition  of  compounds  was  as  a  rule 
not  difficult  to  ascertain  ;  but  the  proportions  in  which  the  con- 
stituents were  contained  in  the  compounds  analysed,  or  their 
quantitative  composition,  were  not  accurately  determined,  and  the 
results  of  the  same  experimenter  often  varied  among  themselves. 
It  is  therefore  not  to  be  wondered  at  that  two  views  were  held 
regarding  the  composition  of  compounds  :  one,  of  which  Berthollet 
(1748 — 1822)  was  the  author,  and  which  is  set  forth  in  his  Essai 
de  Statique  Chimique  (1803)  ;  he  regarded  every  compound  as 
variable  in  composition,  or,  if  in  some  cases  its  composition  was 
found  to  be  constant,  attributed  such  constancy  to  the  fact  that  it 
had  been  submitted  to  precisely  similar  conditions  during  its 

*  The  name  "  sulphuric  acid "  used  to  be,  but  is  not  now,  applied  to  the 
compound  of  sulphur  and  oxygen  referred  to.  According  to  present  nomencla- 
ture, the  acid  contains  in  addition  the  elements  of  water. 

f  See  former  note. 


HISTOEICAL.  15 

preparation  at  successive  times.  Berthollet  held  that  the  propor- 
tion in  which  elements  existed  in  a  compound  depended  on  the 
relative  amounts  of  the  elements  present  during  the  change  which 
led  to  their  combination,  and  on  other  conditions  such  as  tempe- 
rature. The  other  and  contrary  view,  that  the  same  substance  had 
always  the  same  composition,  was  defended  by  Proust  (1755 — 
1826),  and  the  dispute,  which  was  eagerly  watched  by  all  chemists, 
lasted  from  1799  to  1808. 

Bat  the  question  had  already  been  decided  by  Richter 
(1762 — 1807).  The  law  of  "constant  proportions,"  as  it  is 
termed,  was  announced  by  Richter  in  the  involved  language 
of  the  phlogistic  theory  in  papers  which  appeared  between 
1792  and  1794.  Stated  in  ordinary  language,  his  discovery 
is  as  follows  : — If  two  acids,  A:  and  A2,  combine  with  two 
bases,  Bt  and  B2,  to  form  compounds,  A^j,  A2Bj,  AiB2,  and 
A2B2,  the  proportion  by  weight  between  A]  and  Aa  in  the  first 
two  compounds  is  the  same  as  that  between  Al  and  A2  in  the 
second  pair  if  the  weight  of  Bj  and  also  of  B2  is  the  same  in  both 
cases.  Or,  to  take  a  particular  case  : — If  80  grams  of  sulphuric 
acid*  combine  with  62  grams  of  soda,*  or  with  94  grams  of 
potash  ;*  and  if  108  grains  of  nitric  acid*  likewise  combine  with 
62  grams  of  soda ;  then  108  grams  of  nitric  acid  will  combine 
with  94  grams  of  potash.  Therefore  94  grams  of  potash  are  said 
to  be  equivalent  (or  of  equal  value)  to  62  grams  of  soda  in  their 
power  of  combining  with  acid  ;  and  80  grams  of  sulphuric  acid 
are  equivalent  to  108  grams  of  nitric  acid  in  their  power  of  com- 
bining with  base.  Richter  determined  and  tabulated  a  number  of 
such  "  equivalent  weights."  And  Proust  went  still  further.  In 
1799 — 1801,  he  showed  that  tin  forms  two  compounds  with  oxygen. 
in  which  the  proportion  of  oxygen  varies  not  gradually  but 
suddenly;  and  that  iron  forms  two  similar  compounds  with 
sulphur;  but  here  he  stopped.  The  discovery  of  the  reason  of 
definite  proportions  is  due  to  Dalton ;  it  gave  a  new  impetus  to  the 
study  of  chemistry,  and  has  been,  in  its  results,  perhaps  the  most 
fruitful  speculation  of  any  known  to  science. 

John  Dalton  was  born  in  1766,  at  Eaglesfield,  in  Cumberland. 
In  his  younger  days  he  was  a  schoolmaster  at  Kendal ;  he  went  to 
Manchester  in  1793  as  Lecturer  on  Mathematics  and  Natural  Philo- 
sophy in  the  New  College,  and  afterwards  acted  as  a  private 
mathematical  and  chemical  tutor  in  Manchester,  giving  occasional 

*  These  names  are  used  in  their  old  sense  of  the  combinations  of  the  ele- 
ments sulphur,  nitrogen,  sodium,  and  potassium  with  oxygen.  See  previous 

note. 


10  HISTORICAL. 

lectures  in  the  larger  towns  of  England  and  Scotland.  He  inves- 
tigated the  relations  between  the  temperature  and  pressure  of 
liquids,  the  expansion  of  gases  by  heat,  the  solubility  of  gases  in 
liquids,  and  other  similar  subjects ;  but  his  discoveries  in  chemical 
theory  were  those  which  conferred  on  him  a  world- wide  fame,  and 
have  exercised  a  lasting  influence  on  the  science. 

It  was  the  habit  of  the  analysts  of  that  time,  as  it  is  now,  to 
state  their  results  in  parts  per  100.  Thus  Proust  gives  the 
following  analyses  of  the  compounds  of  copper  and  tin  with 
oxygen : — 

"  Suboxide        "  Protoxide      "  Suboxide       "  Protoxide 
of  Copper."       of  Copper."       of  Tin."  of  Tin." 

Metal 86-2  80  87  78 '4 

Oxygen 13  '8  20  13  21  "6 

100-0  100  100  100-0 

It  is  obvious  that,  from  inspection  of  the  above  numbers,  no 
simple  relation  between  the  amounts  of  oxygen  in  the  lower  and 
higher  oxides  of  copper,  and  in  the  lower  and  higher  oxides  of  tin, 
is  evident ;  yet,  if  Proust  had  calculated  the  ratios,  he  might  have 
guessed  that  the  proportion  of  oxygen  to  copper  in  the  second 
oxide  is  nearly  double  that  in  the  first,  viz.,  13'8  :  21'5 ;  and 
similarly  with  tin,  13  :  24.  But  still  the  analyses  are  not  accurate 
enough  to  render  this  proportion  self-evident,  even  if  thus  stated. 

It  was  during  an  investigation  of  two  compounds  of  carbon 
with  hydrogen,  viz.,  marsh  gas  and  olefiant  gas,  or,  as  they  are 
now  named,  methane  and  ethylene,  and  two  compounds  of  carbon 
with  oxygen,  carbonic  oxide  and  carbonic  acid,  or,  as  the  latter 
gas  is  now  called,  carbonic  anhydride,  that  Dalton  was  led  to 
investigate  the  subject.  He  found  that,  if  he  reckoned  the  carbon 
in  each  the  same,  then  marsh  gas  contains  just  twice  as  much 
hydrogen  as  olefiant  gas ;  and  carbonic  acid  just  twice  as  much 
oxygen  as  carbonic  oxide.  He  then  considered  the  proportions  of 
hydrogen  and  oxygen  in  water,  and  of  hydrogen  and  nitrogen  in 
ammonia,  and  having  found,  first,  that  when  two  elements  combine 
with  each  other,  they  do  so  in  constant  proportions  ly  weight,  and 
second,  that  when  two  elements,  A  and  J3,  form  more  than  one  com- 
pound  with  each  other,  they  combine  in  simple  multiple  proportions, 
he  deduced  the  following  laws  to  account  for  these  facts  : — 

1.  Each  element  consists  of  precisely  similar  atoms  of  constant 
weight. 

2.  Chemical  compounds  consist  of  complex  "  atoms,"*  which  are 

*  As  the  expression  "  complex  atom  "  is  a  contradictory  one,  it  was  after- 
wards replaced  by  the  word  "  molecule,"  or  "  little  mass"  of  atoms. 


HISTORICAL.  17 

produced  by  the  union  of  the  atoms  of  the  constituent  elements  in 
simple  numerical  ratios.* 

An  example  will  render  these  statements  clear.  Olefiant  gas 
consists  of  six  parts  of  carbon  by  weight  united  with  one  part  of 
hydrogen ;  marsh  gas  of  six  parts  of  carbon  united  with  two  parts 
of  hydrogen.  Similarly,  carbonic  oxide  contains  six  parts  of 
carbon  and  eight  parts  of  oxygen;  and  "  carbonic  acid,"  six  parts 
of  carbon  and  16  of  oxygen.  The  following  table  shows  the 
relations  : — 


Carbon  .   .  .  . 

Olefiant  Gas. 
85  '71  per  cent. 

Ratio. 
6 

Marsh  Gas.      '. 
75  '0  per  cent. 

Ratio. 
6 

Hydrogen.  .  . 

14-28       „ 

1 

25-0      „ 

2 

Carbon  

Carbonic  Oxide. 
42  '86  per  cent. 

Ratio. 
6 

"  Carbonic  Acid." 
27  '27  per  cent. 

Ratio. 
6 

Oxveren.  . 

57-14 

8 

72-72 

16 

It  is  again  evident  here  that  no  obvious  relation  exists  between 
the  amounts  of  hydrogen  in  marsh  gas  and  defiant  gas,  unless 
they  are  compared  with  a  uniform  weight  of  carbon.  From  these 
results  Dalton  concluded  that  olefiant  gas  consists  of  one  atom  of 
carbon  united  to  one  atom  of  hydrogen,  and  marsh  gas  of  one 
atom  of  carbon  united  to  two  atoms  of  hydrogen ;  and,  similarly, 
that  carbonic  oxide  is  composed  of  one  atom  of  carbon  and  one  of 
oxygen,  and  carbonic  acid  of  one  atom  of  carbon  and  two  of 
oxygen. 

It  necessarily  follows  from  this  conception  that  the  atom  of 
carbon  is  six  times  as  heavy  as  the  atom  of  hydrogen,  and  that  the 
relative  weights  of  the  atoms  of  carbon  and  oxygen  are  as  6  to  8. 

Extending  these  observations  to  water,  the  only  compound  of 
hydrogen  and  oxygen  then  known,  the  following  relation  was 
determined  :— 

Water.  Ratio. 

Hydrogen 11 '  11  per  cent.  1 

Oxygen 88  '88       „  8 

Hence  Dalton  concluded  that  water  is  a  compound  of  one  atom 
of  hydrogen  with  one  atom  of  oxygen,  and  that  the  atom  of  oxygen 
is  eight  times  as  heavy  as  the  atom  of  hydrogen,  thus  bearing  out 
the  conclusions  of  his  former  analyses. 

Dalton  then  proceeded  to  determine  the  relative  weights  of  the 
atoms  of  other  elements  by  similar  methods.  His  numbers  are  far 

*  Dalton' s  New  System  of  Chemical  Philosophy,  1808;  Thomson's  Chemlstey 
1807  ;  also  edition  1810,  Vol.  Ill,  p.  441. 


18  HISTORICAL. 

from  accurate,  and  indeed,  in  the  above  tables,  the  actual  numbers 
found  by  him  have  not  been  stated,  in  order  to  avoid  confusion. 
He  next  arranged  a  number  of  compounds  of  the  elements  in 
classes,  according  to  the  number  of  atoms  contained  in  each  class. 
Thus  if  only  one  compound  of  two  elements  was  known,  Dalton 
assumed  it  to  contain  one  atom  of  each  element,  and  named  it  a 
binary  compound,  "  unless  some  cause  appear  to  the  contrary." 
If  two  compounds  were  known,  they  were  represented  as  A  +  B, 
and  as  A  +  2B ;  the  latter  was  named  a  ternary  compound, 
because  it  contained  three  atoms  ;  and  so  on  with  quaternary,  &c. 
Thus  he  regarded  water  as  a  binary  compound,  in  which  one  atom 
of  hydrogen  weighing  1,  and  one  atom  of  oxygen  weighing  8  rela- 
tively to  the  hydrogen  were  united.  Ammonia,  a  compound  of 
nitrogen  and  hydrogen,  was  regarded  as  also  composed  of  one  atom 
of  hydrogen  weighing  1  and  one  atom  of  nitrogen  weighing  4|. 
Thus  he  constructed  a  table  of  atomic  weights ;  and  to  render  his 
theory  more  tangible,  he  assigned  to  each  element  a  symbol ;  thus 
oxygen  was  O>  hydrogen  0,  nitrogen  ®,  sulphur  0,  and  so  on; 
and  the  symbols  of  the  metals  consisted  of  circles  circumscribed 
round  the  initial  letter  of  the  name  of  the  metal ;  thus  (?)  stood 
for  iron,  (z)  for  zinc,  and  so  on.  These  symbols  also  stood  for  the 
relative  weights  of  the  atoms  ;  hence  O0  denoted  water,  Q®  am- 
monia,  ^0  olefiant  gas,  OSO  marsh  gas,  and  so  with  others. 

Now  it  is  evident  that  Dalton  here  made  a  great  assumption,  in- 
asmuch as  he  had  no  sure  basis  to  guide  him  in  assigning  such 
atomic  weights.  Let  us  consider  his  results  from  another  point  of 
view,  and  we  shall  see  that  another  set  of  atomic  weights  might 
with  equal  justice  have  been  adopted. 

Turning  back  to  the  table  on  p.  17,  it  is  seen  that  Dalton 
assumed  that  the  four  substances,  marsh  gas,  olefiant  gas,  carbonic 
oxide,  and  "  carbonic  acid  "  each  contained  one  atom  of  carbon.  But 
it  is  equally  justifiable  to  assume  that  each  of  the  first  pair  contains 
one  atom  of  hydrogen,  and  each  of  the  second  pair  one  atom  of 
oxygen.  We  should  then  have  the  ratio : — 

Olefiant  Gas.       Ratio.  Marsh  Gas.      Eatio. 

Carbon    8571  per  cent.         6  75'0  per  cent.         3 

Hydrogen. .  .       14'28        „  1  25 "0  1 

Carbonic  Oxide.     Ratio.       "  Carbonic  Acid."    Ratio. 

Carbon    42'86  per  cent.  6  27'27  per  cent.          3 

Oxygen 57'14         „  8  72'72         „  8 

The  smallest  amount  of  carbon  in  combination  is  now  found 


HISTORICAL.  19 

to  weigh  three  times  as  much  as  the  hydrogen ;  i.e.  the  atomic 
weight  of  carbon  is  8.  And  the  first  body  would  then  consist  of 
2  atoms  of  carbon  and  1  of  hydrogen ;  while  the  second,  marsh 
gas,  would  contain  1  atom  of  carbon  and  1  of  hydrogen.  Similarly, 
carbonic  oxide  might  be  composed  of  2  atoms  of  carbon  and  1  of 
oxygen,  while  "  carbonic  acid  "  might  consist  of  1  atom  of  carbon 
and  1  of  oxygen. 

Dalton  himself  was  quite  aware  of  this  difficulty,  as  is  seen  by 
his  remarks  in  the  appendix  to  his  second  volume,  published  in 
1827.  He  therefore  contented  himself  by  assuming  those  numbers 
to  be  the  correct  atomic  weights  which  give  the  simplest  propor- 
tions between  the  numbers  of  atoms  contained  in  all  the  known 
compounds  of  the  elements.  But  Dalton  did  not  possess  the 
analytical  skill  necessary  to  determine  the  composition  of  the 
compounds  from  which  such  deductions  were  to  be  made.  In  1808, 
Wollaston  published  an  account  of  accurate  experiments  on  the 
carbonates  and  oxalates  of  sodium  and  potassium,  in  which  he 
showed  that  the  ratio  of  carbonic  acid  or  oxalic  acid  in  one  (the 
"  subcarbonate  "  or  "  suboxalate  ")  to  the  sodium  or  potassium  was 
half  that  which  it  bore  in  the  other  (the  "  supercarbonate "  or 
"  superoxalate  ") .  The  work  of  determining  the  composition  of 
compounds  was,  however,  chiefly  undertaken  by  Berzelius,  pro- 
fessor of  chemistry,  medicine,  and  pharmacy  in  Stockholm 
(1779 — 1848).  The  aim  of  this  great  chemist  was  to  forward  the 
work  which  had  been  suggested  by  Dalton,  and,  by  preparing 
numerous  compounds  and  analysing  them,  to  determine  the  ratios 
of  the  weights  of  their  atoms.  His  industry  was  untiring,  and  the 
number  of  new  compounds  prepared  and  analysed  by  him  almost 
incredible.  But  it  is  obvious  that  for  the  reasons  stated  it  is  impos- 
sible, even  by  comparing  all  the  compounds  which  one  element  forms 
with  others,  to  determine  which  compound  contains  only  1  atom  of 
that  element.  What  Dalton  and  Berzelius  really  determined  was 
the  equivalents  of  the  elements,  that  is,  the  proportion  by  weight 
in  which  they  are  capable  of  combining  with  or  replacing  1 
part  by  weight  of  hydrogen  ;  they  had  no  data  sufficient  to  enable 
them  to  determine  what  multiple  of  the  equivalent  is  the  true 
atomic  weight.  In  subsequent  chapters  the  various  reasons  in 
favour  of  the  atomic  weights  at  present  assigned  to  the  elements 
will  be  discussed.  We  must  leave  the  historical  part  of  the 
subject  at  this  point,  and  proceed  to  discuss  the  facts  of  the  science, 
and  to  arrange  the  various  compounds  in  an  orderly  manner. 

Assuming,  then,  that,  for  reasons  to  be  given  hereafter,  the 
relative  weights  of  the  atoms  are  represented  by  the  numbers  used 

c  2 


20  HISTORICAL. 

in  this  book,  the  question  arises,  what  element  should  be  made 
the  standard  of  comparison  ?  Dalton  having  found  that,  of  all  the 
elements  investigated  by  him,  a  smaller  weight  of  hydrogen 
entered  into  combination  than  of  any  other  element,  assigned  the 
weight  1  to  the  atom  of  that  element,  and  arranged  the  other 
atomic  weights  accordingly.  Thus,  according  to  him,  the  weight 
of  an  atom  of  oxygen  was  8  times  that  of  an  atom  of  hydrogen, 
because  water,  which  he  supposed  to  consist  of  1  atom  of  each, 
was  found  on  analysis  to  contain  1  part  by  weight  of  hydrogen 
combined  with  8  parts  by  weight  of  oxygen.  And  so  with  the 
other  elements.  There  are  reasons  which  will  follow  in  their  place 
(p.  202)  for  believing  that  a  number  between  15'87  and  16*00  (or 
double  the  number  assigned  by  Dalton)  represents  the  relative 
weight  of  an  atom  of  oxygen  referred  to  hydrogen  as  unity.  But 
it  happens  that  the  equivalents  of  most  of  the  elements  have 
been  determined  by  synthesising  or  analysing  their  compounds 
with  oxygen,  or  with  oxygen  and  some  other  element.  Hence  it 
appears  advisable  to  accept  the  atomic  weight  of  oxygen  as  16, 
and  to  refer  the  weights  of  the  other  elements  to  that  scale. 
Until  the  ratio  between  the  atomic  weights  of  hydrogen  and 
oxygen  is  satisfactorily  determined,  this  appears  the  best  course  to 
pursue ;  for  then  the  accepted  atomic  weights  of  the  majority  of 
the  elements  need  not  be  altered  to  suit  any  proposed  alteration  in 
the  ratio  of  the  accepted  atomic  weights  of  hydrogen  and  oxygen. 
Moreover  this  plan  has  the  great  advantage  that  many  of  the 
atomic  weights  are  whole  numbers,  and  are  therefore  more  easily 
remembered.  It  should  here  be  noticed  that  if  the  ratio  between  the 
atomic  weights  of  hydrogen  and  oxygen  is  really  1  to  15'96,  then 
by  placing  the  atomic  weight  of  oxygen  equal  to  16,  that  of 
hydrogen  is  no  longer  1,  but  1'0025,  for  15'96  :  16  ::  1  :  V0025. 
A  very  remarkable  relation  between  the  atomic  weights  of  the 
elements  and  their  chemical  and  physical  properties  was  pointed 
out  by  Mr.  J.  A.  R.  Newlands  in  18&4,*  and  this  relation  has  been 
further  studied  by  Professors  Mendeleefff  and  Lothar  MeyerJ 
It  is  briefly  this.  If  the  elements  be  arranged  in  the  order  of  their 
atomic  weights  in  seven  double  columns,  those  elements  which 
resemble  each  other  fall  in  the  same  column.  It  is  on  this  principle 
that  the  elements  and  their  compounds  are  classified  in  this  text- 
book. Such  an  arrangement  is  termed  a  periodic  arrangement, 

*   Chem.  News,  July  30th,  1864 ;  August,  1865 ;  March,  1866  j  also  On  the 
Discovery  of  the  Periodic  Law,  Spon,  1884. 
t  Annalen,  SuppL,  8,  133  (1869). 
J  Annalen,  SuppL,  7,  354. 


HISTORICAL.  21 

and  the  following  table  is  named  the  periodic  table.  The  letters, 
such  as  H,  Li,  <fec.,  are  abbreviations  for  the  names  of  bhe  elements  ; 
they  are  termed  symbols ;  and  they  also  represent  the  numbers 
which  precede  or  follow  them.  Thus  0  represents  not  merely 
oxygen,  but  16  parts  by  weight  of  oxygen  ;  CaO  represents  not 
merely  a  compound  of  calcium  and  oxygen,  but  of  4O08  parts  by 
weight  of  calcium,  and  16  parts  by  weight  of  oxygen ;  CaCl2 
represents  a  compound  of  40  parts  by  weight  of  calcium  with 
2  x  35*46  parts  by  weight  of  chlorine.  Such  a  representation  of 
compounds  by  the  symbols  of  the  elements  which  they  contain  is 
termed  a  formula. 

While  most  of  the  elements  are  represented  by  the  initial  letters 
of  their  English  names,  some  of  the  symbols  require  explanation. 
The  following  is  a  list: — 

Na,  Natrium  (connected  with  the  word  nitre) Sodium. 

K,  Kalium  (from  alkali,  an  Arabic  name) Potassium. 

Cu,  Cuprum  (Latin) Copper. 

Ag,  Argentum  (Latin) Silver. 

Au,  Atirum  (Latin) Gold. 

Hg,  Hydrargyrum  (Greek  =  water-silver)     Mercury. 

Sn,  Stannum  (Latin) Tin. 

Pb,  Plumbum  (Latin) Lead. 

Sb,  Stibium  (Latin) Antimony. 

W,  Wolfram,  a  mineral  containing  Tungsten Tungsten. 

Fe,  Ferrum  (Latin)    Iron. 

Note. — For  this  portion  of  chemical  history,  Wurtz's  History  of  the  Atomic 
Theory,  London,  1880,  may  be  consulted ;  also  Cook's  The  New  Chemistry ; 
and  the  works  previously  referred  to. 


22 


HISTORICAL 


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Table  of  Atomic  Weights  of  Elements  (0  =  16. 


Aluminium  

Al 

27-01 

Nickel  

Ni 

Antimony  

Sb 

120-30 

Niobium  

Nb 

As 

75-09 

Nitrogen  

is 

Barium  

Ba 

137-00 

Osmium  

Os 

Be 

9-1 

Oxygen  

o 

Bismuth  

Bi 

208  -10 

Pd 

B 

11-0 

Phosphorus  

P 

Bromine  

Br 

79-95 

Platinum  

Pt 

Cadmium  

Cd 

112-1 

K 

Caesium  

Cs 

132-9 

Praseodimium  .  .  . 

Prd 

Ca 

40-08 

Rhodium  

Bh 

Carbon  

C 

12-00 

Kb 

Ce 

140-3 

Bu 

Chlorine  

Cl 

35-46 

Sc 

Chromium  

Cr 

52'3 

Selenium  

Se 

Cobalt  

Co 

58-7 

Silicon  

Si 

Copper  

Cu 

63-40 

Silver  

Ag 

Er 

166 

Na 

Fluorine  

F 

19-0 

Strontium  

Sr 

Grallium  

Ga 

69-9 

Sulphur  

S 

Germanium  

Ge 

72-3 

Ta 

Gold  

Au 

197  -22 

Tellurium  

Te 

Hydrogen  

H 

1  to  1  -0082      Terbium  

Tb 

Indium  

In 

113-7 

Thallium  

Tl 

Iodine  

I 

126-85 

Thorium  

Tb. 

Iridium  

Ir 

193-0 

Tin  

Sn 

Iron  

Fe 

56-02 

Titanium  

Ti 

Lanthanum  

La 

142-3 

Tungsten  

W 

Lead  

Pb 

206-93 

TT 

Lithium  

Li 

7-02 

Vanadium  

V 

Magnesium  

Mg 

24-30 

Ytterbium  

Yb 

Manganese  

Mn 

55-0 

Yttrium  

Y 

Mercury  

H& 

200-2 

Zinc  

Zn 

Molybdenum  

Mo 

95-7 

Zr 

Neodymium  

Ndi 

140-8 

Solid, 

Liquid,  Gas. 

58-6 
94 

14-03 
191'3 
16*00 

106  -35 
31  -03 

194-3 
39-14 

143-6 

103-0 
85-5 

101  -65 
44-1 
79-0 
28-33 

107  -930 
23-043 
87-5 
32-06 

182-5 
125  ? 
162  ? 
204-2 
232-4 
119-1 

48-13 
184-0 
240-0 

51-4 
173 

89 

65^3 

90 


Note. — In  this  table  recent  determinations  have  been  incorporated  with  the 
mean  results  given  by  Clarke  ("  Constants  of  Nature,"  Part  V,  1882).  It  is  to 
be  understood  that  the  last  digit  of  the  figures  given  may  vary  within  one  or 
two  units.  Thus  zirconium  =  90  means  that  the  atomic  weight  is  not  certain, 
and  may  be  89'5  or  90'5  ;  thallium  =  204'2  leaves  it  uncertain  whether  the 
true  weight  is  204'1  or  204'3 ;  and  so  on.  Where  a  query  (?)  is  appended,  it 
is  to  be  understood  that  the  weight  given  may  be  one  or  more  units  wrong. 
The  standard  works  on  the  subject  are  by  Clarke,  mentioned  above  ;  by  Lothar 
Meyer  and  Seubert,  Die  Atomgewichte  der  Elemente ;  and,  as  a  model  of 
research,  by  Stas,  Eecherches  sur  les  Rapports  reciproyues  des  Poids  alvmiques, 
Brussels,  1860. 


Table  of  Metric  Weights  and  Measures 


Measures  of  Length. 

1  metre  =  10  decimetres  =  100  centimetres  =  1000  millimetres. 

1  metre  =  1  '09363  yard  ==  3  '28090  feet  =  39 '37079  inches. 

Log  n  metres  +  0*0388704  =  log  yards;  +  0 '5159930  =  log  feet;  +  1 '5951743 
=  log  inches. 

Logw  yards  +  0' 9611296  =  log  metres ;  log  n  feet  +  0' 4840071  =  log  deci- 
metre ;  log  n  inches  +  0  '4048257  =  log  centimetres. 

Measures  of  Capacity. 

1  cubic  metre  =  1000  litres  =  1,000,000  cubic  centimetres  =  1,000,000,000  cubit- 
millimetres. 

1  litre  =  61  '02705  cubic  inches  =  0  '035317  cubic  foot  =  1  '76077  pints  = 
0  '22097  gallon. 

Log  n  litres  +  1 '  7855223  =  log  cubic  inches  ;  +  2  '5479838  =  log  cubic  feet ; 
+  0-2457026  =  log  pints  ;  +  1 '3443333  =  log  gallons. 

Log  n  cubic  inches  +  1  '2144774  =  log  cubic  centimetres. 

Log  n  cubic  feet  +  1' 4520162  =  log  litres. 

Log  n  gallons  -t-  0  '6556667  =  log  litres. 

Measures  of  Weight. 
1  gram  =  weig-ht  of  1  cubic  centimetre  of  water  at  4°. 

1  kilogram  =  1000  grams  =  100,000  centigrams  =  1,000,000  milligrams. 

1  kilogram  =  2  '2046213  Ibs. ;   =  35*273941  oz.  =  15432  '35  grains. 

Log  n  kilos.  +  0 '3433340  =  log  Ibs.;    log  n  grams  +  1' 5474540  =  log  oz. ; 

+  1  '1884323  =  log  grains. 
Log  n  Ibs.  +  T6566660  =  log  kilograms;  log  n  grains  +  2  '8115677  log  grams. 


25 


PART  II.— THE  ELEMENTS. 


CHAPTER  III. 

HYDROGEN  ;  LITHIUM,  SODIUM,  POTASSIUM,  RUBIDIUM,  CZESIUM  ; 
BERYLLIUM,  CALCIUM.  STRONTIUM,  BARIUM  ;  MAGNESIUM,  ZINC, 
CADMIUM  ;  BORON,  SCANDIUM,  YTTRIUM,  LANTHANUM,  YTTERBIUM  ; 
ALUMINIUM,  GALLIUM,  INDIUM,  THALLIUM. 

THE  elements,  it  has  been  seen,  when  arranged  in  the  order  of 
their  atomic  weights,  fall  into  certain  groups.  The  various 
members  of  these  groups  resemble  each  other  in  their  physical  and 
chemical  properties,  and  it  is  therefore  advisable  to  consider  the 
members  of  each  group  in  connection  with  each  other.  They 
possess  certain  properties  in  common,  while  exhibiting  individual 
peculiarities.  In  the  following  chapters,  an  account  will  be  given 
of  the  sources  of  the  elements,  whether  they  occur  "free,"  or 
**  native,"  that  is,  as  elements,  or  whether  combined  with  other 
elements  in  the  form  of  compounds  ;  of  their  properties  \  and  of 
the  methods  of  their  preparation ;  but  fuller  details  will  in  some 
cases  be  given  under  the  heading  of  the  compounds  from  which 
they  are  prepared. 

In  the  main,  the  order  of  the  periodic  table  will  be  followed  ; 
but,  as  it  is  still  under  investigation,  and  the  position  of  all  the 
elements  cannot  be  regarded  as  finally  settled,  certain  elements 
will  be  grouped  together  which  do  not  occur  near  each  other  in  the 
table. 


GROUP  I.— Hydrogen,  Lithium,  Sodium,  Potassium, 
Rubidium,  Caesium. 

Sources. — Hydrogen  occurs  free  in  the  neighbourhood  of 
volcanoes,  owing  probably  to  the  decomposition  of  its  compound 
with  sulphur,  hydrogen  sulphide,  by  the  hot  lava  through  which 
it  issues.  It  has  also  been  proved  by  the  evidence  of  the  spectro- 


28  THE  ELEMENTS. 

scope  (see  chap.  XXXV),  to  exist  as  element  in  the  atmosphere  of 
the  sun,  in  certain  fixed  stars;  in  nebulae,  and  in  comets.  It  has 
been  found  associated  with  iron  and  nickel  in  many  meteorites.  In 
combination  with  [oxygen  it  occurs  in  water  (hence  its  name 
from  vSwp,  water,  ryevvaw,  I  produce}  in  the  sea,  lakes,  rivers,  in 
the  atmosphere,  in  many  minerals;  in  all  organised  matter,  animal 
and  vegetable.  It  is  thus  one  of  the  most  widely  distributed  and 
abundant  of  elements. 

Preparation. — 1.  By  heating  its  compounds  with  boron, 
carbon,  silicon,  nitrogen,  phosphorus,  arsenic,  antimony,  sulphur, 
selenium,  tellurium,  iodine,  or  palladium  to  a  red  heat ;  or  with 
oxygen,  chlorine,  or  bromine  to  a  white  heat  (see  these  com- 
pounds). 

2.  By  the  decomposition  of  its  compounds  dissolved  in  water 
by  an  electric  current  (see  p.  62). 

3.  By  displacing  it  from  these  compounds  by  means  of  certain 
metals.     The  most  usual  methods  of  preparation  are  by  the  action 
(a)  of  sodium  on  water  (oxide  of  hydrogen,  see  p.  192)  ;   (6)  of 
iron  on  gaseous  water  at  a  red  heat  (see  p.  255)  ;  or  (c)  of  zinc  on 
dilute  sulphuric  or  hydrochloric  acid  (see  pp.  415,  112). 

Method  (a).  Ajar  is  filled  with  water,  covered  with  a  glass  plate,  and  in- 
verted in  a  trough  of  water  as  shown  in  figure  1.  A  piece  of  the  metal  sodium 


FIG.  1. 

not  larger  than  a  pea  is  placed  in  a  spoon  made  of  wire  gauze,  which  is  passed 
quickly  under  the  water  beneath  the  jar,  when  the  hydrogen  evolved  passes  in 
bubbles  into  the  jar.  The  sodium  melts,  moves  about,  and  displaces  hydrogen 
from  the  water.  Other  small  fragments  are  successively  introduced  into  the 
spoon  until  the  jar  is  full.  (Note. — Large  pieces  must  not  be  used,  else  an  ex- 
plosion may  ensue.) 

Method  (1).  A  piece  of  iron  gas-pipe,  of  £-inch  bore,  is  filled  loosely  with 
iron  turnings,  and  closed  by  stoppers  made  of   asbestos  cardboard  moistened 


HYDROGEN.  27 

with  water,  and  moulded  round  glass  tubes,  placed  as  shown  in  figure  2.  The 
iron  tube  is  then  heated  in  a  gas  furnace,,  and  the  water  in  the  flask  is  boiled. 
The  iron  combines  with  the  oxygen  of  the  steam,  setting  free  the  hydrogen, 
which  may  be  collected  in  a  jar  as  shown  in  the  figure. 


Fm.  2. 

Method  (c).  A  flask  or  bottle,  as  shown  in  figure  3,  is  provided  with  a  cork 
and  delivery  tube.  Some  granulated  zinc,  prepared  by  pouring  melted  zinc  into 
water,  is  placed  in  the  flask  A  ;  and  a  mixture  of  one  volume  of  hydrochloric  acid 
and  four  volumes  of  water,  or  of  one  volume  of  oil  of  vitriol  (sulphuric  acid),* 
and  eight  volumes  of  water,  is  poured  through  the  funnel  B.  Bubbles  begin  to 
appear  on  the  surface  of  the  zinc,  and  the  liquid  effervesces.  A  few  minutes 
must  be  allowed,  so  that  the  hydrogen  may  displace  the  air  from  the  bottle.  It 
can  then  be  collected  in  jars.  The  zinc  displaces  the  hydrogen  from  its  com- 


Fm.  3. 

pound  with  chlorine  in  hydrochloric  acid,  or  from  its  compound  with 
sulphur  and  oxygen  in  sulphuric  acid.  The  substances  produced  are  named  zinc 
chloride,  or  zinc  sulphate,  according  as  one  or  other  acid  has  been  used. 


*  If  sulphuric  acid  be  used,  sulphur  dioxide  and  hydrogen  sulphide  are 
produced  if  the  proportion  of  water  be  not  a  large  one. — Chem.  Soc.,  53,  54. 


28  THE   ELEMENTS. 

Properties. — A  colourless,  odourless  gas ;  the  lightest  of  all 
known  bodies.  As  it  is  nearly  fourteen  and  a  half  times  as  light 
as  air,  it  may  be  poured  upwards  from  one  jar  into  another  ;  or  if 
a  light  jar  or  beaker  be  suspended  mouth  downwards  from  the 
arm  of  a  balance,  and  counterpoised,  and  hydrogen  be  poured  into 
it  from  below,  that  arm  of  the  balance  rises,  the  heavier  air  being 
replaced  by  the  lighter  hydrogen.  Balloons  used  to  be  filled  with 
it ;  but  coal  gas  is  now  employed.  It  burns  in  air,  combining 
with  oxygen  to  form  water,  and  when  mixed  wibh  air  (about 
2^  times  its  volume)  the  resulting  mixture  is  explosive  (see  p. 
192).  It  is  sparingly  soluble  in  water;  100  volumes  of  water 
absorb  1'93  volumes  of  hydrogen  gas.  It  is  not  poisonous,  but 
cannot  be  respired  for  any  long  time,  as  the  oxygen  of  the  air, 
which  is  necessary  for  the  support  of  life,  is  thereby  excluded. 
Owing  to  the  rate  at  which  it  conveys  sound,  speaking  with 
hydrogen  gives  a  curious  shrill  tone  to  the  voice.  It  has  never 
been  condensed  to  the  liquid  or  solid  states.  Cailletet,  and  also 
Pictet,  who  claim  to  have  condensed  it  by  cooling  it  to  a  very  low 
temperature,*  and  at  the  same  time  strongly  compressing  it,  had 
in  their  hands  impure  gas.  Its  critical  temperature,  above  which 
it  cannot  appear  as  liquid,  is  probably  not  above  — 230°. 

It  unites  directly  with  the  halogens  ;  with  oxygen  and  with 
sulphur  ;  also  with  carbon  at  a  very  high  temperature  ;  and  with 
potassium  and  sodium.  It  is  absorbed  by  certain  metals,  notably 
by  palladium,  which  can  be  made  to  take  up  900  times  its  own 
volume  (see  p.  576).  From  this  its  density  and  its  specific  heat  in 
the  solid  state  have  been  calculated.f 

Lithium,  sodium,  potassium,  rubidium,  and  caesium  are 
always  found  in  combination  with  chlorine,  or  with  oxygen  and 
the  oxides  of  other  elements  such  as  silicon,  carbon,  boron,  sulphur, 
phosphorus,  &c.  ;  they  never  occur  free.  They  are  named  "  metals 
of  the  alkalies." 

Sources. — Lithium  occurs  as  silicate  in  lepidolite  and petallite; 
as  phosphate  in  triphylline ;  as  chloride  in  many  mineral  waters, 
especially  in  the  Wheal- Clifford  Spring,  near  Eedruth,  in  Cornwall ; 
in  sea- water ;  and  in  many  soils,  whence  it  is  absorbed  by  plants, 
tobacco-ash,  for  example,  containing  about  0*4  per  cent.  Its  com- 
pounds are  usually  prepared  from  lepidolite. 

Sodium  forms,  in  combination  with  chlorine,  common  salt,  or 
sodium  chloride ;  it  occurs  in  deposits  in  Chili  and  Peru  as  nitrate 
and  iodate,  in  which  its  oxide  is  combined  with  the  oxides  of  nitrogen 
*   Comptes  rend.,  98,  304. 
f  Ibid.,  78,  968;  also  Phil.  Mag.  (4),  47,  324.     See  Palladium. 


POTASSIUM,   RUBIDIUM   AND   (LESIUM.  29 

and  iodine  respectively ;  as  sulphate  in  mineral  springs  (Glauber's 
salts)  ;  as  silicate  in  soda-felspar  or  albite ;  and  as  fluoride  along 
with  aluminium  flnoride  in  cryolite;  as  borate  in  certain  American 
lakes.  It  is  obtained  as  carbonate  by  incinerating  sea-plants. 

Potassium  is  found  as  chloride  in  mineral  deposits  at  Stass- 
furth,  in  N.  Germany;  the  mineral  is  termed  sylvin ;  as  nitrate 
(saltpetre,  nitre),  forming  an  incrustation  on  the  soil  in  countries 
where  rain  seldom  falls ;  and  as  silicate  in  many  rocks,  chiefly  in 
potash  felspar  and  mica.  It  is  abundant  and  very  widely  dis- 
tributed, being  a  constituent  of  every  soil.  It  remains  as  car- 
bonate on  burning  to  ash  all  kinds  of  wood,  hence  its  name, 
from  "  pot-ash." 

Rubidium  and  Caesium  are  widely  distributed,  but  occur  in 
small  amount.  They  are  contained  in  lepidolite,  along  with  lithium 
and  potassium,  as  silicates ;  also  in  castor  and  pollux,  two  rare 
minerals,  found  in  the  Isle  of  Elba.  They  also  occur  in  some 
mineral  waters,  particularly  in  a  spring  at  Diirkheim,  in  the 
Bavarian  Palatinate,  from  which  they  were  first  extracted  by 
Bunsen,  their  discoverer,  in  1860.  They  are  widely  distributed  in 
the  soil,  and  are  absorbed  by  some  plants  to  a  considerable  extent. 
Thus  the  ash  of  beetroot  contains  1'75  per  mille  of  rubidium. 

Preparation. — These  metals  are  prepared  :  1.  By  passing  a 
current  of  electricity  through  their  fused  hydroxides,  chlorides, 
or  cyanides.  It  was  in  this  way  that  Davy,*  in  1807,  obtained 
potassium  and  sodium  from  their  hydroxides,  which  up  to  that 
date  had  not  been  decomposed  ;  the  electrolysis  of  lithium  chloride 
is  still  the  only  method  of  preparing  lithium ;  and  Setterberg,f  in 
1881,  prepared  considerable  quantities  of  rubidium  and  caBsinm  by 
electrolysing  a  fused  mixture  of  their  cyanides  with  cyanide  of 
barium,  using  as  poles  strips  of  aluminium. 

To  prepare  lithium,  which  may  serve  as  a  type  of  this  kind  of  operation, 
about  30  grams  of  lithium  chloride  are  melted  over  a  Bunsen  flame  in  a  nickel 
crucible  ;  when  the  chloride  is  quite  fused,  a  piece  of  gas  carbon  (the  sticks  of 
a  Jablochkoff  candle  answer  well),  is  connected  with  the  positive  pole  of  four  or 
six  Bunsen  or  Grove  cells  ;  and  a  knitting-needle,  passing  through  the  hole  in  the 
stem  of  a  tobacco  pipe,  made  into  a  shallow  cup  at  its  broken  end,  is  connected 
with  the  negative  pole  ;  these  are  dipped  in  the  fused  chloride  ;  and  when  a  bead 
of  lithium  as  large  as  a  small  pea  has  collected  on  the  negative  electrode,  the  fused 
chloride  is  allowed  to  cool,  and  the  bead  plunged  into  rock  oil.  The  bead  of 
lithium  is  then  scraped  off  with  a  knife,  and  the  process  repeated,  until  a  suffi- 
cient quantity  has  been  collected. 


*  Phil.  Trans.,  1808,  1 ;  1809,  39  ;  1810,  16. 
t  Annalen,  211,  100. 


30 


THE   ELEMENTS. 


2.  Sodium,  potassium,  and  rubidium  may  be  prepared  by  dis- 
tilling the  hydroxides  with  carbon.*  The  carbon  unites  with  the 
oxygen  of  the  hydroxide,  while  the  hydrogen  is  liberated  and 
comes  off  as  gas.  (A  hydroxide,  it  should  be  here  explained,  is  a 
compound  of  oxygen  with  hydrogen  and  with  a  metal.)  The 
industrial  preparation  of  sodium  is  thus  carried  out  (see  Chapter 
XXXVIII,  p.  651). 

Properties. — These  elements  are  all  white  metals,  so  soft  at 
the  ordinary  temperature  that  they  can  be  cut  with  a  knife,  but 
brittle  at  low  temperatures;  they  are  malleable,  and  may  be 
squeezed  into  wire  by  forcing  them  through  a  small  hole  by  means 
of  a  screw-press ;  they  may  be  welded  by  pressing  clean  surfaces 
together ;  they  melt  at  moderate  temperatures,  and  are  all  com- 
paratively volatile;  hence,  lithium  excepted,  they  may  be  distilled  at 
a  bright  red  heat  from  a  malleable  iron  tube  or  retort.  They  are 
all  lighter  than  water;  lithium,  indeed,  is  the  lightest  solid  known. 
Each  imparts  its  special  colour  to  a  Bunsen  or  spirit  flame ;  thus 
compounds  of  lithium  give  a  splendid  crimson  light ;  of  sodium 
a  yellow  light;  potassium  compounds  colour  the  flame  violet; 
rubidium  red,  hence  the  name  of  the  metal  (from  rubidus)  •  and 
caesium  blue  (ccesius).  (See  Spectrum  Analysis,  Chapter  XXXV.) 
Potassium  vapour  is  green,  and  sodium  vapour,  violet.  These  ele- 
ments crystallise,  when  melted  and  cooled,  in  the  dimetric  system. 

They  all  combine  readily  with  the  elements  chlorine,  bromine, 
iodine  (these  elements  are  termed  the  "halogens"),  oxygen, 
sulphur,  phosphorus,  &c.,  with  evolution  of  light  and  heat;  and 
they  all  decompose  water  at  the  ordinary  temperature,  liberating 
hydrogen  (see  p.  26). 

Physical  Properties. 
Mass  of  1  cub.  cent. 


Solid. 

Liquid. 

—  \ 
Gaa. 

Density, 
H  =  1. 

melting- 
point. 

Hydrogen    .  . 

0-62—  0-63f 

0  -025  J 

0  '0000896 

1 

Below  -230° 

Lithium   .... 

0-59 

? 

— 

p 

180° 

Sodium  

0-985 

p 



12-75 

95  -6° 

Potassium    .  . 

0-865 

p 

— 

18-85 

62-5° 

Rubidium     .  . 

1-50 

p 

— 

p 

38-5 

Caesium  

1-88 

p 

; 

? 

26—27° 

*  Castner,  Chem.  News,  54,  218. 

f  Deduced  from  the  mass  of  1  c.c.  of  its  alloy  with  palladium. 
%  At  0°,  under  a  pressure  of  275  atmospheres  ;  deduced  from  the  density  of 
a  mixture  of  1  volume  of  hydrogen  with  8  yols.  of  carbonic  anhydride. 


BERYLLIUM,   CALCIUM,   STRONTIUM,   BAKIUM.  31 

Boiling-  Specific  Atomic         Molecular 

point.  Heat.  Weight.          Weight. 

Hydrogen Below  -230°  (Gas)  2  "411          1  '0025  ?          2  '0 

(SolitN  5  -88 

Lithium ?  0-941               7  "02 

Sodium 742°  0'293  23'04               23 '04 

Potassium 667°  0'166  39-14              39 -14 

Eubidium ?  ?  85  '5 

Cffisiuni ?  ?  132-9 

GROUP  II.— Beryllium  or  GLucinum,  Calcium, 
Strontium,  Barium. 

These  metals,  like  those  of  the  previous  group,  always  occur  in 
nature  in  combination,  never  in  the  metallic  state.  They  are 
found  combined  with  silicon  and  oxygen,  as  silicates  ;  with  carbon 
and  oxygen,  as  carbonates ;  with  sulphur  and  oxygen,  as  sul- 
phates ;  and  with  phosphorus  and  oxygen,  as  phosphates.  Calcium 
i8  also  associated  with  fluorine  and  with  chlorine.  They  are  named 
"  metals  of  the  alkaline  earths." 

Sources. — Beryllium  is  a  somewhat  rare  element.  Its  most 
common  sources  are  :  beryl,  a  silicate  of  beryllium  and  aluminium, 
a  pale  greenish-white  mineral,  which,  when  transparent,  and  of  a 
pale  sea-green  colour,  is  named  aquamarine ;  and  when  bright 
green,  emerald  (the  green  colour  is  due  to  the  element  chromium)  ; 
phenacite,  also  a  silicate  of  beryllium ;  and  chrysoberyl,  a  compound 
of  the  oxides  of  beryllium  and  aluminium. 

Calcium  is  one  of  the  most  abundant  elements.  Its  carbonate 
when  pure  and  crystalline  is  named  Iceland-spar  or  calc-spar ; 
earthy  and  less  pure  varieties  are  limestone,  chalk,  and  marble.  When 
associated  with  magnesium  carbonate,  the  mineral  is  named  dolo- 
mite. Calcium  sulphate  is  named  gypsum,  selenite,  and  anhydrite, 
according  to  its  state  of  aggregation.  Its  phosphate,  in  which  it 
is  combined  with  phosphorus  and  oxygen,  is  named  phosphorite  or 
apatite.  The  fluoride  is  named  Jluor-  or  Derby  shire- spar  •  and  its 
chloride  is  a  constituent  of  sea-water  and  many  mineral  waters. 
Most  natural  water  contains  hydrogen  calcium  carbonate  (bi- 
carbonate) in  solution. 

Strontium,  like  calcium,  occurs  as  carbonate,  in  strontianite, 
and  as  sulphate  in  celestine.  Its  name  recalls  the  source  in 
which  it  was  first  found — Strontian,  a  village  of  Argyllshire,  in 
Scotland. 

Barium  also  occurs  as  carbonate,  witherite;  and  as  sulphate, 
barytes  or  heavy-spar,  so  named  from  its  high  specific  gravity. 
Hence  the  name  of  the  metal,  from  /3a/>t/s,  heavy. 


32  THE  ELEMENTS. 

Preparation. — Beryllium,  the  chloride  of  which  volatilises 
at  a  red  heat,  may  for  that  reason  be  prepared  from  that  compound 
by  passing  its  vapour  over  fused  sodium  contained  in  an  iron  boat.* 
The  sodium  combines  with  the  chlorine,  which  leaves  the  metal  as 
such.  Sodium  reacts  with  cold  water,  while  beryllium  does  not ; 
hence  the  sodium  may  be  removed  by  treatment  with  water. 

Barium,  strontium,  and  calciumf  are  best  prepared  by  passing 
a  current  of  electricity  through  their  respective  chlorides,  fused  in 
a  porcelain  crucible  over  a  blowpipe,  using  a  carbon  rod  (see 
lithium)  as  one  electrode,  and  an  iron  wire  as  the  other.  Solutions 
of  the  metals  in  mercury  are  easily  made  by  electrolysing  strong 
solutions  of  the  chlorides  of  the  metals,  using  mercury  as  the 
negative  electrode.  Barium  amalgam  crystallises  out  of  the 
mercury;  it  may  be  collected,  and  after  washing  it  with  cold 
water  and  drying  it,  the  mercury  can  be  distilled  off  in  a  vacuum, 
leaving  the  barium  as  a  yellowish-white  metallic  powder,  still, 
however,  containing  mercury.  Another  method  of  preparing  an 
amalgam  of  mercury  and  barium  (alloys  of  mercury  are  termed 
"amalgams")  is  to  shake  up  sodium  amalgam  with  a  strong 
solution  of  barium  chloride.  The  sodium  combines  with  the 
chlorine,  leaving  the  barium  in  the  mercury.  Amalgams  of 
strontium  and  calcium  cannot  be  made  in  this  manner. 

Properties. — Beryllium  and  calcium  are  white  metals;  the 
other  two  have  a  yellow  tinge.  They  melt  at  a  bright  red  heat, 
oxidising  in  presence  of  air.  Calcium  and  beryllium  are  brittle  ; 
strontium  and  barium  malleable.  They  are  all  heavier  than  water. 
The  compounds  of  the  last  three  impart  characteristic  colours  to  a 
Bunsen  flame,  and  have  well-marked  spectra  (see  Chapter  XXXV). 
The  chloride  of  calcium  tinges  the  flame  brick-red ;  of  strontium, 
bright  crimson-red  like  lithium  ;  and  of  barium,  pale-green.  The 
metals  have  not  been  volatilised.  They  unite  readily  with  the 
halogens,  with  oxygen  and  sulphur,  and  with  phosphorus. 
Beryllium  does  not  decompose  water  unless  boiled  with  it ;  the 
others  act  on  it  at  the  ordinary  temperature,  with  evolution  of 
hydrogen. 

Physical  Properties. 

Mass  of  1  cub.       Melting-  Specific  Atomic 

cent,  solid.  point.  Heat.  Weight. 

Beryllium 1  '85  at  20°       Ked  heat  Variable  9  '1 

(above  1230°).  (See  Appendix) . 


Calcium  

1'58 

Bright  red 

0'167             40  08 

Strontium  .... 
Barium 

2-54 
4-0 

Bright  red 
White 

?                87-5 
?              137  '00 

Chem.  News,  42,  297.  f  Annalen,  183,  367. 


MAGNESIUM.  33 

Appendix. — The  specific  heat  of  beryllium  varies  greatly  with  the  tempera- 
ture. The  following  results  were  found  by  Humpidge.* 

Temperature    ..          0Q  100°  200°  300°  400°  500° 

Specific  Heat  ..      0*3756      Q'4702      0*5420      0 '5910      0-6172      0-6206 

GROUP  III. — Magnesium,  Zinc,  Cadmium. 

Sources. — These  three  metals  are  never  found  native.  All 
three  occur  as  carbonate  and  as  silicate;  and  the  two  latter  as 
sulphide.  Magnesium  sulphide  is  decomposed  by  water ;  hence 
its  non-occurrence  in  nature.  Magnesium  occurs  also  in  consider- 
able quantity  as  sulphate  (Epsom  salts},  in  sea- water,  and  in  many 
mineral  springs.  Its  native  compounds  are  named  as  follows : — 
Magnesium  carbonate,  magnesite ;  double  carbonate  of  magnesium 
and  calcium,  dolomite ;  it  occurs  in  great  rock  masses  in  the  range 
of  hills  in  the  Italian  Tyrol  named  the  Dolomites.  There  are 
many  silicates  of  magnesium  and  other  metals.  Among  the  more 
important  are  talc,  steatite  or  soap-stone  (French  chalk),  serpentine, 
and  meerschaum.  Augite,  hornblende,  asbestos,  olivine,  and  biotite 
(a  variety  of  mica}  are  also  rich  in  magnesium  (see  Silicates,  p.  313). 
Garnallite,  a  chloride  of  magnesium  and  potassium,  is  found  at 
Stassfurth.  The  commercial  sources  of  metals  are  named  "  ores." 
The  ores  of  zinc  are  : — Calamine,  zinc  carbonate  ;  silicious  cala- 
mine,  the  silicate ;  and  blende,  or  "  Black  Jack,"  the  sulphide. 
Cadmium  always  accompanies  zinc ;  the  only  pure  mineral  con- 
taining it  is  greenockite,  cadmium  sulphide.  The  name  magnesium 
is  derived  from  the  town  of  Magnesia,  in  Asia  Minor.  Its  oxide 
is  sometimes  called  magnesia  alba,  from  its  white  colour.  The 
word  zinc  is  perhaps  connected  with  the  German  equivalent 
for  tin,  Zinn.  "  Cadmium  "  is  adopted  from  the  name  given  by 
Pliny  to  the  sublimate  found  in  brass-founders'  furnaces  (cadmia 
fornacum) . 

Preparation. — Magnesium  is  prepared  like  beryllium ;  dried 
carnallite,  a  double  chloride  of  magnesium  and  potassium  com- 
bined with  water,  is  heated  with  sodium.  The  sodium  unites 
with  the  chlorine,  removing  it  from  the  magnesium,  which  is  set 
free. 

The  mixture  is  heated  in  large  iron  crucibles  to  a  high  temperature.  When 
the  reaction  is  over,  the  crucible  is  allowed  to  cool,  and  the  contents  chiselled 
out.  Small  globules  of  magnesium  are  disseminated  throughout  the  fused 
mass,  and  at  the  bottom  of  the  crucible  is  a  mass  of  magnesium  embedded  in 

*  Proc.  Roy.  Soc.,  39,  1. 


34 


THE  ELEMENTS. 


flux,  as  the  fused  chlorides  are  termed.  The  salt  with  the  globules  of  mag- 
nesium is  transferred  to  a  crucible,  A,  the  bottom  of  which  is  perforated,  as  shown 
in  the  figure,  and  a  tube,  B,  passes  through  the  bottom,  reaching  up  to  near  the 
top  of  the  crucible.  -The  lid  is  then  luted  on  (i.e.,  fastened  on  by  clay),  the 


FIG.  4. 

top  of  the  tube  having  been  closed  by  a  wooden  plug.  When  the  temperature 
rises  to  bright  redness,  the  magnesium  rises  in  vapour,  and  distils  down  the 
centre  tube,  condensing  on  the  lower  portion,  whence  it  drops  into  heavy  oil. 
Hence  the  old  term  for  this  process — "  distillatio  per  descensum." 

Zinc  is  produced  by  distilling  its  oxide  with  coke  (carbon)  in 
clay  cylinders.  The  carbon  unites  with  the  oxygen,  setting  free 
the  zinc,  which  distils  over. 

The  old  English  method  of  extracting  zinc  from  its  oxide  used  to  be  carried 
out  in  apparatus  like  that  employed  in  making  magnesium.  The  roasted  zinc 
ore,  consisting  of  oxide  of  zinc,  was  mixed  with  coke  or  anthracite  coal  (carbon), 
and  placed  in  clay  crucibles,  similar  in  construction  to  the  iron  one  shown  in 
Fig.  4.  On  raising  the  temperature  to  bright  redness,  the  zinc  distils  over,  and 
drops  through  the  tube  which  passes  through  the  bottom  of  the  furnace. 

The  Belgian  process,  which  is  now  all  but  universally  adopted,  consists  in 
distilling  the  zinc  ore  with  coke  from  clay  cylinders,  arranged  in  tiers.  The 
zinc  condenses  in  conical  tubes  of  cast  iron  or  iron  plate,  which  fit  the  mouths 
of  the  cylinders,  and  are  made  tight  at  the  joint  by  a  luting  of  clay.  When 
the  operation  is  over,  these  tubes  are  removed,  and  the  zinc,  which  forms  a 
crust  adhering  to  their  interiors,  is  chiselled  off. 

Cadmium  accompanies  zinc,  and  as  it  boils  at  a  lower  tempe- 
rature, the  first  portions  wLich  distil  over  contain  it. 

Properties. — These  three  metals  are  all  white.  Zinc,  however, 
has  a  bluish  tinge,  and  cadmium  a  yellow  tinge.  Of  the  three, 


BORON. 


35 


magnesium  is  the  hardest,  and  cadmium  the  softest ;  it  may  be  cut 
with  a  knife,  but  with  difficulty.  Magnesium  and  zinc  are  malle- 
able and  ductile  at  a  moderately  high  temperature  (zinc  at  120°), 
but  are  brittle  at  the  ordinary  temperature.  Zinc  is  also  brittle  at 
200°,  and  may  be  easily  powdered  in  a  hot  iron  mortar.  These 
metals  may  all  be  distilled,  cadmium  most  easily,  and  magnesium 
at  the  highest  temperature.  They  are  all  heavier  than  water. 
They  combine  directly  with  the  halogens ;  they  burn  when  heated 
in  air,  combining  with  its  oxygen.  Magnesium  gives  out  a  brilliant 
white  light,  and  it  is  prepared  in  the  form  of  ribbon,  wire,  or  dust 
for  signalling,  pyrotechnic,  and  photographical  purposes.  Zinc 
burns  with  a  light  blue -green  flame,  and  cadmium  with  a  dull 
flame ;  they  tarnish  very  slowly  in  air.  They  also  unite  directly 
with  sulphur,  phosphorus,  &c.  When  boiled  with  water,  mag- 
nesium and  zinc  slowly  decompose  it,  hydrogen  being  evolved. 
•Cadmium  is  without  action  on  water  except  at  a  red  heat. 


AlaTiesium  

Physical  Properties. 

Mass  of  1  c.c.                Density, 
Solid.                      H  =  1. 
.      1-743                              p 

7-15 

34-5 
52-15 

Specific 
Heat. 
0-250 
0-095 
0-056 

Atomic 
Weight. 
24-30 
65-43 
112-1 

Cadmium  

,.     8-6 

Boiling-point 
at  760  mm. 
About  1000° 
930°  to  942° 
About  770° 

Zinc    

Cadmium  . 

Melting- 
point. 
700—800° 

412° 

315° 

Molecular 

Weight. 

24-30 

65-43 

112-1 


GROUP  IV.— Boron,  Scandium,  Yttrium,*  Lantha- 
num,* Ytterbium.* 

These  elements  are  never  found  in  the  free  state.  They  all 
exist  in  nature  in  combination  with  oxygen,  and  other  oxides. 

Sources. — Boron  issues  from  the  earth  as  hydroxide,  or 
boracic  acid,  along  with  steam  in  the  neighbourhood  of  vol- 
canoes. The  hydroxide  also  occurs  as  sassolite ;  its  other  sources 
are  tincal  or  native  borax,  in  which  its  oxide  is  combined  with 
oxide  of  sodium  and  with  water  (the  beds  of  certain  dried  up 
American  lakes  contain  enormous  quantities  of  borax) ;  boracite, 
boron  oxide  with  magnesium  oxide  and  chloride ;  boronatrocalcite, 


*  It  is  doubtful  if  these  metals  belong  to  this  group. 


36  THE   ELEMENTS. 

boron  oxide,  calcium  oxide,  and  sodium  oxide ;  and  datolite,  boron 
and  silicon  oxides  with  calcium  oxide. 

The  remaining  elements  of  this  group  are  usually  associated 
with  cerium,  didymium,  erbium,  terbium,  samarium,  &c.,  as 
oxides,  in  combination  with  oxides  of  silicon,  niobium,  tantalum, 
titanium,  and  other  elements.  The  minerals  containing  them 
are  named  euxenite,  orthite,  columbite,  gadolinite,  yttrotantalite^ 
samarskite,  and  cerite.  They  have  been  found  chiefly  at  Arendal 
and  Hittero,  in  Norway,  and  in  Connecticut,  U.S. 

Preparation. — Boron  is  obtained  by  heating  with  metallic 
sodium  the  compound  which  its  fluoride  forms  with  potassium 
fluoride ;  or  by  heating  its  oxide  with  potassium,  or  better,  with 
magnesium  dust.  The  fluorine  or  oxygen  combines  with  the  potas- 
sium or  magnesium,  leaving  the  boron  in  the  free  state.  It  was 
by  the  latter  method  that  it  was  first  prepared  in  1808  by  Gay- 
Lussac  and  Thenard,  and  later  by  Deville  and  Wohler.* 

Metallic  scandium  has  not  been  prepared. 

Yttrium  was  prepared  in  an  impure  state,  mixed  with  erbium, 
by  Berzelius,  by  the  action  of  potassium  on  the  impure  chloride. 
It  was  a  greyish-black  lustrous  powder. 

Lanthanum  has  been  prepared  by  passing  a  current  of 
electricity  through  its  fused  chloride  (see  Lithium). 

Metallic  ytterbium  has  not  been  obtained. 

Properties. — Boron  is  a  brown  amorphous  (i.e.,  non-crystalline) 
powder,  which  has  not  been  melted  even  at  a  white  heat.  It  is 
insoluble  in  all  solvents  which  do  not  act  on  it  chemically.  It  was 
for  long  supposed  possible  to  crystallise  it  from  molten  aluminium ; 
the  resulting  black  crystals,  however,  are  not  pure  boron,  but  a 
compound  of  boron  and  aluminium.  Yellow  crystals,  obtained  by 
Wohler  and  Deville,  and  also  supposed  by  them  to  be  pure  boron, 
consist  of  a  compound  of  boron,  carbon,  and  aluminium.  The  mass 
of  1  c.c.  of  pure  boron  has  not  been  determined.  Boron  combines 
with  the  oxygen  and  nitrogen  of  air,  burning  to  oxide  and  nitride. 
It  is  one  of  the  few  elements  which  combine  directly  with  nitrogen. 
It  is  also  attacked  by  chlorine  and  by  bromine.  Lanthanum  is 
the  only  one  of  these  elements  which  has  been  prepared  in  a 
compact  state.  It  resembles  iron  in  colour ;  is  hard,  malleable, 
and  ductile.  It  melts  at  a  lower  temperature  than  silver  (below 
1000°),  and  burns  with  great  brilliancy  when  heated  in  air;  its 
specific  gravity  is  6'05  at  the  ordinary  temperature. 

The  specific  heat  of  boronf  undergoes  a  remarkable  change  as  the  tempera- 
ture is  raised.  The  following  results  were  obtained  by  Weber : — 

*  Annales  (3),  52,  63.  f  Phil.  Mag.  (4),  49,  161,  276. 


ALUMINIUM,   GALLIUM,  INDIUM.  37 

Temperature  ..       -  40°          +27°  77°  126°  177°  233° 

Specific  Heat  ..      0-1915       0'2382       0'2737       0'3069      0'3378      0'366;j 

In  this  it  resembles  beryllium,  carbon,  and  silicon. 

GEOUP  V.— Aluminium,  Gallium,  Indium,  Thallium. 

These  elements  are  found  only  in  combination.  The  sources  of 
aluminium  are  its  oxide,  corundum;  when  coloured  blue,  probably 
by  cobalt,  it  forms  the  precious  stone  the  sapphire,  and  when  red, 
coloured  by  chromium,  the  ruby.  Associated  with  iron  oxide,  it  is 
named  emery.  Silicate  of  aluminium  is  a  constituent  of  many 
rocks ;  it  exists  in  felspar,  hornblende,  mica,  and  numerous  other 
minerals.  China  clay  or  kaolin  is  a  slightly  impure  silicate  of 
aluminium  (see  Silicates).  The  mineral  cryolite,  found  in  Green- 
land, is  a  fluoride  of  aluminium  and  sodium.  The  sulphide  of 
aluminium  is  decomposed  by  water ;  hence  its  non-occurrence  in 
nature. 

The  other  three  elements  of  this  group  occur  as  sulphides. 
Gallium  and  indium  are  found  in  extremely  minute  amount  in 
some  zinc  ores ;  thallium  is  contained  in  some  specimens  of  iron 
pyrites  (disulphide  of  iron)  and  copper  pyrites.  Zinc  sulphide,  or 
blende,  from  the  Pyrenees,  contains  about  0'002  per  cent,  of 
gallium ;  the  zinc  ores  from  Freiberg,  in  Saxony,  about  0'05  to  O'l 
per  cent,  of  indium. 

Preparation.     Aluminium  is  prepared : — 

1.  By  passing  the  vapour  of  its  chloride  over  heated  sodium  ;* 
the  sodium  unites  with  the  chlorine,  while  the  aluminium  remains 
in  the  metallic  state. 

2.  By  heating  its  oxide  mixed  with  carbon  to  an  enormously 
high  temperature  in  the  electric  arc.f     The  oxide  is  thus  decom- 
posed, and  the  carbon  unites  with  the  oxygen,  while  the  metal  is 
left.     This  process  is  better  adapted  for  preparing  the  alloys  of 
aluminium  than  the  metal  itself. 

3.  By   heating    with    metallic    sodium    cryolite,    the   double 
fluoride  of  aluminium  and  sodium,  previously  fused  with  salt.J 

Gallium§  is  prepared  by  passing  a  current  of  electricity 
through  a  solution  of  its  oxide  in  caustic  potash. 

Indium  1 1   may  be  obtained  by  passing  a  stream  of  hydrogen 

*  Wohler,  Annalen,  37,  66  ;  Deyille,  Annales  (3),  43,  5,  and  46,  415.     The 
literature  on  this  subject  is  now  very  large, 
f  Chem.  News,  1889,  211,  225,  241. 
4;  Brit.  Asscn.,  1889. 
§   Comptes  rend.,  82,  1098 ;  83,  636. 
||  J.  praTct.  Chem.,  1863,  89,  441 ;  92,  480;  94,  1;  95,  414;  102,  273. 

f^*  •^VNV 

OFTHt  X 


38  THE  ELEMENTS. 

gas  over  its  oxide  heated  to  a  high  temperature ;  the  hydrogen 
combines  with  the  oxygen,  producing  water,  and  the  indium  is 
left;  or  by  heating  its  oxide  with  sodium;  or  by  removing  chlorine 
from  indium  chloride  by  placing  metallic  zinc  in  a  solution  of 
that  substance. 

Thallium*  is  most  easily  obtained  by  heating  its  chloride  to  a 
red  heat  with  potassium  cyanide,  a  compound  of  carbon,  nitrogen, 
and  potassium.  The  potassium  removes  the  chlorine,  forming 
potassium  chloride ;  cyanogen,  a  compound  of  carbon  and  nitrogen, 
escapes  as  gas ;  and  thallium  remains  behind  as  fused  metal. 

Properties. — Aluminium,  gallium,  and  indium  are  tin-white 
metals,  while  thallium  has  a  duller  lustre,  resembling  that  of  lead. 
These  metals  are  moderately  malleable  and  ductile.  Indium  and 
thallium  are  soft,  and  may  be  cut  with  a  knife ;  aluminium  and 
gallium  are  hard.  Thallium  and  its  salts  impart  a  magnificent 
green  colour  to  the  flame  of  a  Bunsen's  burner  ;  indium  burns  with 
a  violet  light ;  aluminium  and  gallium  do  not  volatilise  sufficiently 
easily  to  colour  the  flame. 

All  these  elements  unite  readily  with  oxygen  at  a  red  heat; 
aluminium  and  thallium  become  tarnished  in  air  at  the  ordinary 
temperature.  They  also  combine  directly  with  the  halogens  and 
with  sulphur.  They  are  not  acted  on  by  water  at  the  ordinary 
temperature,  but  decompose  it  at  higher  temperatures,  combining 
with  its  oxygen. 

Aluminium  is  contained  in  alum,  hence  its  name ;  gallium  was 
discovered  in  1875  by  the  French  chemist,  Lecoq  de  Boisbaudran, 
and  patriotically  named  after  Gaul ;  indium  derives  its  name  from 
the  blue  line  in  its  spectrum  (from  "indigo  ")  ;  and  thallium  was 
named  by  its  discoverer  Crookes,  from  0aAXo'v,  a  green  twig,  in 
allusion  to  the  green  colour  it  imparts  to  the  flame. 

Of  these  elements  aluminium  is  the  only  one  which  has  found 
a  commercial  use;  the  barrels  of  opera  glasses,  telescopes,  and 
optical  instruments  are  made  of  it ;  and,  alloyed  with  copper,  it  is 
employed  for  cheap  jewellery,  under  the  name  of  "  aluminium 
bronze."  Of  recent  years  its  manufacture  has  been  greatly  in- 
creased, and  in  the  near  future  it  will  rank  as  one  of  the  commoner 
metals. 

The  metals  beryllium,  magnesium,  zinc,  cadmium,  lanthanum,  didymium, 
cerium,  and  aluminium  used  to  be  classified  together  as  "  metals  of  the  earths;  " 
the  so-called  earths  being  their  oxides,  which  are  insoluble  in  water,  and  hence 
have  not  an  alkaline  reaction  like  those  of  calcium,  strontium,  and  barium. 

*   Chem.  News,  3,  193,  303  ;  Proc.  Eoy.  Soc.,  12,  150. 


THALLIUM. 


39 


Physical  Properties. 


Aluminium. 


Gallium 


Indium    . 
Thallium. 


Mass  of  1  c.c.      Melting-              Specific             Atomic  Molecular 
Solid.                point.                  Heat.              Weight.   Weight. 
2  -583  at  4°     About  700°  0  "2253  from  0°  to      27  '01       27  '01 
100° 

5  -94  at  23° 

29-5° 

Solid  0  -079  from 
12°  to  23° 

69-9        69-9 

Liquid  0  "080  from 
106°  to  119° 

7  '42  at  16-8° 
11-9.. 

176° 
290° 

0-0565  to  0-0574 
0  -0336.  . 

113-7        — 
204-2     204  "2  to 

APPENDIX. 

The  equations  expressing  the  preparation  of  the  foregoing  elements  are  as 

follows  : 

Hydrogen.— (1)  2H2O  =  2H2  +  O2. 

(2)  2H2O  +  2Na  =  2NaOH  +  H2 

(3)  4H2O  +  3Fe  =  Fe3O4  +  4H2. 

(4)  H2SO4  +  Zn  =  ZnSO4  +  H2. 
Lithium,  $c—  2LiCl  =  2Li  +  C12- 

Sodium  and  Potassium.— 2NaOH  +  20  =  2Na  +  2CO  +  H2. 

2KOH  +  2C  =  2K  -i-  2CO  +  H2. 
Beryllium.— BeCl2  +  2Na  =  Be  +  2NaCl. 
Calcium,  Strontium,  and  Barium. — BaCl2  =  Ba  +  CJ2. 
Magnesium.— MgCl2.KCl  +  2Na  =  Mg  +  2NaCl  +  KC1. 
Zinc,  Cadmium. — ZnO  +  C  =  Zn  +  CO. 
CdO  1-  C  =  Cd  +  CO. 
Boron.—  (1)  BC13  +  3Na  =  B  +  3NaCl. 

(2)  KF.BF3  +  3Na  =  B  +  KF  +  3NaF ; 

(3)  B2O3  +  3Mg  =  2B  +  3MgO. 
Aluminium.— (\)  A1C13  +  3Na  =  Ai  +  3NaCl. 

(2)  A12O3  +  3C  =  2A1  +  3CO. 

(3)  AlF3.3NaF  +  3Na  =  Al  +  6NaF. 
Gallium.— 2Ga2O3  =  2Ga  -I-  3O2. 

Indium.— (1)  In2O3  +  3H2  =  2In  +  3H2O. 

(2)  2InCl3  +  3  Zn  =  2In  +  3ZnCl2. 
Thallium.— 2T1C13  +  6KCN  =  2T1  +  6KC1  +  3(CN)2. 


40 


CHAPTER  IV. 
THE  ELEMENTS  (CONTINUED). 

GROUP    VI,     THE     CHROMIUM     GROUP  ;     GROUP    VII,    THE     CARBON    GROUP ; 
GROUP  VIII,  THE  SILICON  GROUP. 

GROUP  VI.— Chromium,  Iron,  Manganese,   Cobalt, 

Nickel. 

The  elements  of  this  group  are  not,  generally  speaking,  asso- 
ciated in  the  periodic  table,  yet  they  closely  resemble  each  other ; 
and  it  is  convenient  to  consider  them  together. 

Sources. — They  invariably  occur  in  combination  with  oxygen, 
when,  of  terrestrial  origin.  Certain  meteorites,  however,  consist 
largely  of  metallic  iron  and  nickel  with  a  little  cobalt  and  a  trace  of 
hydrogen.  Common  proportions  are  90  per  cent,  of  iron,  9  per 
cent,  of  nickel,  and  1  per  cent,  or  less  of  cobalt. 

The  chief  ore  of  chromium  is  chrome  iron  ore,  or  chromite ;  it 
is  a  compound  of  oxygen  with  chromium  and  iron  (see  Chromium, 
oxides,  p.  254).  It  is  found  in  Silesia,  Asia  Minor,  Hungary, 
Norway,  and  JST.  America.  The  green  colour  of  the  emerald  and 
serpentine  is  due  to  traces  of  chromium. 

Compounds  of  iron  are  very  numerous  in  nature.  Its  oxides, 
when  found  native,  are  named: — Hcematile,  of  which  varieties 
are  termed  specular  iron  ore,  kidney  ore,  and  titaniferous  ore 
(these  occur  largely  in  Cumberland,  also  in  the  south  of  Spain) ; 
combined  with  water,  gothite,  brown  iron  ore,  bog  iron  ore,  and 
ake  ore,  the  latter  of  which  are  named  from  their  sources  : 
they  are  found  in  Northamptonshire,  the  Forest  of  Dean,  and 
Glamorganshire ;  magnetic  iron  ore,  magnetite  or  loadstone,  an 
oxide  of  a  different  composition  (see  p.  255)  :  it  does  not 
occur  largely  in  England,  but  is  worked  in  Sweden ;  the  largest 
deposit  of  iron  ore  in  the  world  consists  of  magnetite  :  it  occurs  in 
Southern  Lapland,  but  is  as  yet  inaccessible.  Spathic  ore,  or  car- 
bonate of  iron,  is  a  white  crystalline  substance  when  pure,  but  is 
usually  inters tratified  and  mixed  with  clay  or  shale,  when  it  is 


CHROMIUM.  41 

termed  " clay-band "  or  "black-band."  Spathic  ores  occur  in 
Durham,  Cornwall,  Devon,  and  Somerset ;  clay  iron-stone  in  the 
coal-measures  in  Staffordshire,  Shropshire,  Yorkshire,  Derbyshire, 
Denbigh,  and  South  Wales ;  while  black-band  is  mined  largely  in 
the  Clyde  basin,  in  Scotland. 

Iron  occurs  in  combination  with  sulphur  as  pyrites ;  it  is  very 
widely  distributed ;  perhaps  the  largest  sources  are  in  the  south 
of  Spain.  At  Bio  Tinto  this  ore  is  worked,  not  for  the  iron 
which  it  contains,  but  for  its  copper  (about  3  per  cent.)  and  its 
sulphur.  Iron  is  also  a  constituent  of  most  rocks  and  soils  :  it  is 
one  of  the  most  abundant  as  well  as  one  of  the  most  widely  dis- 
tributed of  elements. 

Manganese  is  nearly  always  found  associated  with  iron,  in 
combination  with  oxygen.  Its  most  important  source  is  pyrolusite 
or  black  oxide.  Other  manganese  minerals  are  braunite  and  haus- 
inannite,  also  oxides ;  manganite,  psilomelane,  and  wad,  compounds 
of  oxides  and  water ;  manganese-spar,  the  carbonate ;  it  also  occurs 
in  combination  with  silicon  and  oxygen  as  silicate,  and  with  sulphur 
as  sulphide. 

Cobalt  and  nickel  are  almost  invariably  associated.  As 
already  mentioned,  they  accompany  iron  in  some  meteorites  in  the 
state  of  metals.  Cobalt  occurs  as  smaltite  or  tin-white-cobalt,  in 
combination  with  arsenic;  and  as  glance-cobalt,  in  combination 
with  arsenic  and  sulphur. 

The  chief  ore  of  nickel  is  the  oxide  and  the  double  silicate 
of  nickel  and  magnesium,  large  quantities  of  which  are  now  im- 
ported from  New  Caledonia,  a  French  convict  settlement  north-east 
of  Australia.  It  is  found  on  the  continent  of  Europe  chiefly  as 
the  arsenide,  a  compound  of  nickel  and  arsenic  named  Kupfer- 
nickel  or  copper-nickel,  from  its  red  colour  resembling  copper  ;  it  is 
also  called  niccolite.  The  sulphide,  or  capillary  pyrites,  also  occurs 
native. 

Preparation. — These  metals  in  an  impure  state  may  all  be 
prepared  by  reducing  (i.e.,  removing  oxygen  from)  their  oxides  by 
means  of  carbon.  Iron  and  nickel  are  prepared  for  commercial 
purposes  ;  alloys  of  iron  and  manganese,  and  iron  and  chromium 
are  also  produced ;  and  nickel  is  often  deposited  by  means  of  an 
electric  current  on  the  surface  of  other  metals,  which  are  then  said 
to  be  nickel-plated. 

Chromium,  in  the  pure  state,  has  been  prepared  by  removing 
chlorine  from  its  chloride,  by  means  of  metallic  zinc  or  magnesium.* 
The  chloride  is  mixed  with  potassium  and  sodium  chlorides,  and 
*  Annalen,  111,  117. 


42  THE  ELEMENTS. 

heated  with  metallic  zinc  to  the  boiling-point  of  the  latter  metal 
(about  940°).  An  alloy  of  zinc  and  chromium  remains,  from  which 
the  zinc  may  be  removed  by  treatment  with  nitric  acid;  the 
chromium  remains  as  a  pale-grey  crystalline  powder.  It  has  also 
been  prepared  by  decomposing  by  electricity  its  chloride  in  con- 
centrated solution.  It  then  deposits  in  brittle  scales  with  the 
lustre  of  metallic  iron. 

Iron,  in  a  state  of  purity,  is  hardly  known.  It  has  been 
prepared  by  reducing  its  oxide  by  means  of  hydrogen  at  a  red  heat, 
and  heating  the  resulting  greyish-black  powder,  which  consists  of 
pure  iron  in  a  state  of  fine  division,  to  whiteness  in  a  porcelain 
crucible  under  a  layer  of  fused  calcium  fluoride  in  the  oxyhydrogen 
flame.*  It  does  not  fuse,  but  agglomerates  to  a  sintered  mass.  It 
may  also  be  deposited  electrically  from  solution.  Ordinary  iron 
contains  small  quantities  of  several  elements,  notably  carbon  and 
silicon,  which  completely  alter  its  properties,  and  it  must,  there- 
fore, be  considered  as  a  compound.  A  description  of  the  metallurgy 
of  iron  is  therefore  deferred  to  Chapter  XXXVI. 

Manganese,  like  iron,  is  almost  unknown  in  a  pure  state; 
when  produced  by  the  aid  of  carbon,  it  combines  with  that  element 
and  acquires  peculiar  properties.  Its  metallurgy  will  be  considered 
along  with  that  of  iron.  It  has  recently,  however,  been  prepared 
in  a  pure  coherent  state  by  heating  to  redness  with  magnesium 
dust  a  mixture  of  manganese  dichloride  with  potassium  chloride. f 

Nickel  is  prepared  in  a  manner  exactly  similar  to  that  by  which 
iron  is  made.  Impure  nickel  can  be  prepared  by  heating  its  oxide 
with  charcoal ;  the  pure  metal  is  obtained  by  electrolysis.  The 
same  remarks  apply  to  cobalt. 

Properties. — These  elements  are  all  greyish-white,  with  metallic 
lustre,  like  iron.  Manganese  and  cobalt  have  a  reddish- tinge; 
nickel  is  whiter  than  iron,  but  not  so  white  as  silver.  They  all 
melt  at  a  very  high  temperature,  so  high,  indeed,  that  it  is  reached 
only  by  means  of  the  oxyhydrogen  blowpipe.  The  addition  of  a 
small  amount  of  carbon,  as  has  been  remarked,  profoundly  modifies 
their  properties ;  and,  indeed,  the  pure  elements  are  almost  un- 
known in  a  compact  state,  owing  to  the  difficulty  of  melting  them 
into  a  compact  mass  in  any  vessel  capable  of  withstanding  the 
requisite  temperature,  and  not  attacked  by  the  metal.  The  figures 
in  the  following  table  refer,  for  the  most  part,  to  such  impure 
specimens. 

They  all  combine  with  oxygen,  on  exposure  to  moist  air,  but  are 
*  Troost,  Sull.  Soc.  Chim.  (2),  9,  250. 
t  Glatzel,  £er.  Deutsch.  Chew.  Ges..  22,  2857. 


CARBON.  43- 

permanent  in  dry  air ;  they  unite  directly  with  the  halogens ;  with 
sulphur,  selenium,  and  tellurium;  with  phosphorus,  arsenic,  and 
antimony;  with  carbon,  silicon,  and  titanium;  and  they  form 
alloys  with  each  other  and  with  many  other  metals.  Iron  and 
nickel  also  absorb  hydrogen  gas  to  a  small  extent. 

Physical  Properties. 

Specific  Atomic  Molecular 

Mass  of  1  c.c.     Solid.                Heat.  Weight.  Weight. 

Chromium..      7  '3 ;  6  ;81  (at  25°) Not  determined  52 -3  ? 

Iron 8  -00  (at  10°)  pure 0  "112  (impure)  56  '02  ? 

8  -14  (at  15  -5°)  electro- 
lytic) 

Manganese. .      7  -39  at  22° 0  '122     55  -0  55  '0 

Nickel About  9-0 0'109     58'6  ? 

Cobalt..,           About  9-0..  0'107     587  ? 


GEOUP  VII. — Carbon,  Titanium,  Zirconium, 
Cerium,*  Thorium. 

Of  these  elements,  carbon  is  the  only  one  found  in  the  free 
state.  The  others  are  always  found  combined  with  oxygen,  and 
usually  with  silicon  and  oxygen  as  silicates. 

The  native  forms  of  carbon  are  the  diamond,  carbonado,  and 
graphite,  black-lead,  or  plumbago.  Diamonds  are  found  in  situ, 
in  pegmatite,  or  graphic  granite,  near  Bellary,  in  the  Nizam* 
India,  and  also  in  an  aqueous  magnesian  breccia  in  S.  Africa.  It- 
is  probable  that  they  have  been  formed  simultaneously  with  these 
rocks;  the  conditions  of  their  formation  are  unknown.  Diamond- 
fields,  or  districts  which  yield  diamonds,  occur  in  Brazil,  India,  the- 
Cape,  California,  Borneo,  and  the  Ural  Mountains. 

Carbonado,  a  variety  of  carbon  found  in  the  Soap  Mountains  of 
Bahia,  is  a  reddish-grey,  porous  substance ;  it  is  evidently  closely 
allied  with  diamond. 

Graphite  occurs  in  nests  of  trap  in  the  clay  slate  at  Borrowdale, 
Cumberland,  and  is  also  found  in  certain  coal-measures,  e.g.,  at 
Xew  Brunswick. 

Such  different  forms  of  an  element  are  said  to  be  allotropic,  a- 
word  which  signifies  "  different  forms." 

Carbon  also  occurs  in  combination  with  oxygen  (tha  atmo- 
sphere contains  about  0'04  per  cent,  by  weight  of  carbon  dioxide)  ; 
and  its  dioxide,  with  the  oxides  of  various  metals ;  the  most 

*  It  is  doubtful  if  cerium  belongs  to  this  group  of  elements. 


44  THE  ELEMENTS. 

important  of  the  carbonates  are  those  of  calcium,  of  magnesium, 
and  of  irou  (q.v.). 

Along  with,  hydrogen,  oxygen,  and  nitrogen,  it  is  a  constituent 
of  all  organised  matter  ;  coal,  which  consists  of  ancient  vegetable 
matter,  agglomerated  by  pressure  and  decomposed  by  heat,  contains 
a  large  percentage  of  carbon,  anthracite,  for  instance,  containing 
over  90  per  cent. 

Titanium,  occurs  only  in  combination  with  oxygen,  as  rutile, 
anatase,  and  brookite ;  and  associated  with  oxides  of  iron,  as  titani- 
ferous  iron ;  with  oxide  of  calcium  in  perowskite  ;  and  with  the 
oxides  of  silicon  and  calcium  in  sphene. 

Zirconium  is  found  as  oxide,  in  combination  with  oxide  of 
silicon  in  zircon,  and  in  other  rare  minerals. 

The  chief  source  of  cerium  is  cerite,  a  compound  of  oxide  of 
cerium  with  oxide  of  silicon  and  with  water  ;  and  it  occurs  asso- 
ciated with  oxides  of  niobium,  tantalum,  lanthanum,  didymium,  &c., 
in  orthite,  euxenite,  and  gadolinite,  and  other  very  rare  minerals. 

Thorium  occurs  in  thorite  as  oxide,  in  combination  with  oxide 
of  silicon  and  with  water ;  it  also  occurs  in  euxenite,  &c.,  along 
with  cerium. 

Preparation. — Carbon  is  produced  by  the  decomposition  by 
heat  of  its  compounds  with  hydrogen,  sulphur,  and  nitrogen ;  at  a 
very  high  temperature  its  oxide  is  also  decomposed.  It  may  also 
be  produced  by  withdrawing  chlorine  from  any  of  its  chlorides  by 
means  of  metallic  sodium,  or  oxygen  from  its  oxides  by  metallic 
potassium.  Chlorine  also  removes  hydrogen  at  a  red  heat  from 
its  compounds  with  that  element,  setting  free  carbon  in  the  form 
of  soot.  It  is  best  prepared  in  a  pure  state  by  the  first  of  these 
processes.  Sugar  and  starch  consist  of  carbon  in  union  with  hydro- 
gen and  oxygen.  On  heating  these  bodies  out  of  contact  with  air,  a 
large  portion  of  the  carbon  which  they  contain  remains  in  the  state 
of  element.  It  is  advisable,  in  order  to  remove  hydrogen  com- 
pletely, to  heat  to  redness  in  a  current  of  chlorine.  The  deposit  on 
the  upper  surface  of  the  interior  of  retorts  during  the  manufacture 
of  coal-gas  by  the  distillation  of  coal  is  named  gas- carbon,  and  is 
nearly  pure.  It  is  thus  produced  by  the  decomposition  of  hydro- 
carbons (compounds  of  hydrogen  with  carbon)  by  heat.  Various 
impure  forms  of  carbon  are  prepared  for  industrial  purposes.  Wood 
charcoal  is  obtained  by  heating  wood  to  redness  in  absence  of  air. 
This  used  to  be  the  work  of  "  charcoal  burners,"  and  the  manufac- 
ture still  survives  in  Epping  Forest.  Faggots  of  wood  are  piled 
into  a  tightly  packed  heap,  covered  over  with  turf,  and  set  on  fire, 
a  limited  quantity  of  air  being  admitted  to  support  combustion. 


TITANIUM,  ZIRCONIUM.  45 

Most  of  the  wood  is  thus  charred  ;  and  when  smoke  ceases  to  be 
emitted  more  turf  is  heaped  on,  so  as  to  extinguish  the  fire. 
The  mass  of  charcoal  is  then  allowed  to  cool,  and  when  cold,  the 
covering  of  turf  is  removed,  and  the  billets  of  charcoal  unpiled. 
The  wood  yields  about  34  per  cent,  of  its  -weight  of  charcoal.  In 
the  present  day,  oak  or  beech  wood  is  distilled  from  iron  retorts, 
for  the  production  of  acetic  acid,  or  vinegar ;  the  retorts  are  heated 
with  coal,  and  the  charcoal  remains  in  the  same  form  as  the  logs 
which  are  put  into  the  retort.  The  charcoal  made  in  this  way  is 
used  chiefly  by  iron -founders  to  mix  with  sand  in  making  moulds 
for  castings.  Charcoal  for  gunpowder  is  made  from  willow,  dog- 
wood, or  alder. 

Coke,  the  residue  on  distilling  coal,  is  also  impure  carbon.  The 
coke  forms  from  40  to  75  per  cent,  of  the  weight  of  the  coal. 
Coke  is  largely  used  as  a  fnel,  especially  in  iron  smelting. 

Bone  or  animal  charcoal,  or  bone-Mack,  produced  by  distilling 
bones,-  contains  about  10  per  cent,  of  carbon,  the  remainder  chiefly 
consisting  of  the  mineral  constituents  of  bones,  calcium  phosphate 
and  carbonate.  It  is  used  for  decolorising  solutions  of  impure 
sugar,  which  are  filtered  through  the  bone-black,  ground  to  a 
coarse  powder.  Its  decolorising  properties  are  much  increased  by 
dissolving  out  the  calcium  compounds  by  washing  it  with  hydro- 
chloric acid. 

Lamp-black,  chiefly  used  for  printers'  ink,  is  prepared  by  burning 
certain  compounds  of  carbon  and  hydrogen,  especially  one  con- 
stituent of  coal-tar  oil,  named  naphthalene.  The  hydrogen  and  a 
portion  of  the  carbon  burn,  while  the  greater  portion  of  the  carbon 
is  carried  away  as  smoke,  and  condensed  in  long  flues. 

Titanium,*  like  carbon,  may  be  produced  by  passing  the 
vapour  of  its  chloride  over  heated  sodium, .  when  the  sodium 
removes  the  chlorine  as  sodium  chloride,  leaving  the  element,  with 
which  sodium  does  not  appear  to  form  a  stable  compound.  It  may 
also  be  produced  by  projecting  into  a  red  hot  crucible  potassium, 
cut  into  small  pieces,  along  with  potassium  titanifluoride  (a  com- 
pound of  titanium,  potassium,  and  fluorine)  ;  the  fluorine  is  removed 
by  the  potassium  as  potassium  fluoride,  which  is  soluble  in  water, 
and  may  be  separated  from  the  titanium  by  treatment  with  water, 
in  which  titanium  is  insoluble,  and  with  which  it  does  not  react  in 
the  cold. 

Zirconium,t  like  titanium,  may  be  produced  by  heating  potas- 

*  Wohler,  Annales  (3),  29,  181. 

t  Berselius,   Fogg.  Ann.,  4,  124,  and  8,  186.     Troost,  Comptes  rend.,  61, 
109. 


46  THE   ELEMENTS. 

slum  zirconifluoride  with  potassium,  or  magnesium.  The  metal 
aluminium  also  withdraws  fluorine  from  this  compound  and  the 
zirconium  dissolves  in  the  metal,  crystallising  from  it  when  it 
cools.  The  aluminium  is  removed  by  treatment  with  dilute  hydro- 
chloric acid,  in  which  zirconium  is  insoluble. 

Cerium*  has  been  prepared  by  electrolysing  cerium  chloride, 
covered  with  a  layer  of  ammonium  chloride,  contained  in  a  porous 
earthenware  cell,  placed  inside  a  non-porous  crucible,  filled  with  a 
mixture  of  sodium  and  potassium  chlorides.  The  whole  arrange- 
ment is  heated  to  redness,  so  as  to  melt  the  compounds.  On 
passing  an  electric  current,  the  cerium  deposits  on  the  negative 
electrode,  which  is  made  of  iron,  inserted  through  the  stem  of  a 
clay  pipe  to  prevent  its  oxidation  by  the  hot  air. 

Thormmf  has  also,  like  carbon  and  titanium,  been  prepared 
by  heating  with  sodium  in  an  iron  crucible  potassium  thorifluoride, 
covered  with  a  layer  of  common  salt. 

Properties. — Carbon,  as  already  mentioned,  exists  in  several 
different  forms,  each  of  which  has  distinct  properties.  It  is  there- 
fore said  to  display  allotropy. 

The  diamond  is  transparent,  crystalline,  the  hardest  of  all 
known  substances  ;  it  is  nearly  pure  carbon.  It  is  usually  colour- 
less, but  is  occasionally  coloured  green,  brown,  or  black  by  mineral 
matter.  It  was  found  to  be  combustible  by  the  Florentine 
Academicians,  in  the  17th  century,  who  succeeded  in  burning  it 
by  concentrating  the  sun's  rays  on  it  by  means  of  a  large  lens. 
Lavoisier  discovered  its  identity  with  carbon.  It  can  be  converted 
into  a  coke-like  substance  when  exposed  to  the  intense  heat  of  the 
electric  arc.  It  is  used  as  a  gem,  also  for  rock  boring,  and  for  cut- 
ting glass.  Its  dust  is  employed  in  cutting  and  polishing  precious 
stones,  and  in  cutting  other  diamonds. 

The  weight  of  diamonds  is  measured  in  carats^  (1  carat 
=  0'205  gram,  or  3'165  grains).  The  value,  however,  is  not  pro- 
portional to  the  weight,  but  to  approximately  the  square  of  the 
weight.  Among  the  most  remarkable  diamonds  one  of  the  largest 
belongs  to  the  Nizam  of  Hyderabad,  and  weighs  277  carats  ;  the 
Crown  of  Russia  possesses  another,  of  a  somewhat  yellow  colour, 
weighing  194  carats;  the  Koh-i-Noor,  or  "mountain  of  light," 
belonging  to  the  British  Crown,  weighs  106  carats.  It  was 

*  Hillebrand  and  Norton,  Pogg.  Ann.,  155,  633  ;  156,  466. 
f  Nilson,  Serickte,  1882,  2519  and  2537 ;  1883,  153. 

£  Kerat  (Arab.),  supposed  to  be  derived  from  rati,  the  Indian  name  for  the 
seeds  of  Abrus  precatorius. 


CARBON.  47 

originally  much  larger,  but  was  reduced  in  weight  by  cutting. 
The  cutting  of  diamonds  is  intended  to  display  their  great  power 
of  refracting  light.  The  two  forms  in  which  diamonds  are  cut  are 
that  of  the  brilliant,  which  fig.  5  represents,  and  the  table  or 
rosette  form,  shown  in  fig.  6.  The  former  is  the  most  valuable. 


FIG.  5.  FIG.  6. 

Carbonado  is  a  very  hard  substance,  which  is  also  used  for  rock 
boring.  It  has  been  noticed  as  a  constituent  of  some  meteorites. 

Graphite  is  a  blackish-grey,  lustrous,  soft  substance,  chiefly 
used  for  making  very  refractory  crucibles,  when  mixed  with  clay  ; 
also  for  fine  iron-castings,  and  for  lead  pencils. 

No  attempt  to  produce  diamonds  artificially  has  succeeded, 
except  perhaps  one  in  which  carbon  was  kept  in  contact  with  a 
large  quantity  of  melted  silver  ;  the  carbon  appears  to  be  slightly 
soluble  in  the  fused  metal,  and  microscopic  crystals  which  sepa- 
rated out  on  cooling  were  said  to  possess  the  properties  of  the 
diamond. 

Graphite  may  be  made  artificially  by  dissolving  carbon  in 
molten  iron,  which  dissolves  1  or  2  per  cent.  When  the  metal  is 
slowly  cooled,  part  of  the  carbon  separates  in  this  form.  It  has 
also  been  prepared  by  heating  amorphous  carbon  to  an  extremely 
high  temperature  by  passing  an  electric  current  of  high  potential 
through  a  rod  of  carbon,  and  thus  heating  it  to  brilliant  incan- 
descence. The  temperature  at  which  the  change  is  produced  is 
unknown,  but  is  enormously  high. 

Carbon  is  infusible  at  the  ordinary  pressure.  It  is  volatile  in 
the  electric  arc,  which  when  formed,  as  is  usually  the  case,  by 
passing  an  electric  current  between  two  rods  of  gas-carbon,  always 
possesses  the  temperature  at  which  carbon  volatilises.  What  that 
temperature  is  has  not  yet  been  ascertained. 

The  diamond  is  a  non-conductor  of  electricity,  like  indeed  all 
transparent  bodies ;  but  the  other  forms  of  carbon  conduct,  though 
not  so  well  as  metals. 

Carbon  in  one  form  or  another,  especially  as  coal,  is  the  source 
of  all  the  heat  and  energy  practically  utilised  by  mankind.  To 
utilise  this  energy  stored  in  carbon  it  is  burned  in  air,  uniting  with 
its  oxygen.  Charcoal  unites  very  slowly  with  oxygen  at  the 


48  THE   ELEMENTS. 

ordinary  temperature,  but  rapidly  at  a  red  heat.  The  other  forms 
of  carbon  also  burn,  but  slowly,  when  heated  to  redness  in  oxygen. 
At  a  red  heat  carbon  deprives  most  other  oxides  of  their  oxygen, 
and  is  therefore  used  in  extracting  metals  from  their  oxides.  It 
unites  directly  with  sulphur  when  heated  to  redness  in  sulphur 
vapour ;  and  with  hydrogen  at  the  temperature  of  the  electric  arc, 
to  form  acetylene.  It  does  not  appear  to  combine  directly  with  the 
other  elements,  although  many  compounds  have  been  prepared  by 
indirect  methods. 

Animal  charcoal  and,  to  a  less  degree,  wood  charcoal,  owing 
probably  to  their  cellular  nature  and  to  the  great  amount  of 
surface  which  they  possess,  have  the  power  of  condensing  and 
absorbing  gases.  The  amount  of  absorption  is  in  the  same  order 
to  the  condensibilities  of  the  gases,  those  gases  which  are  condensed 
to  liquids  by  the  smallest  lowering  of  temperature  being  absorbed 
in  greatest  amount.  Thus  1  volume  of  boxwood  charcoal  absorbs 
90  volumes  of  ammonia-gas,  which  condenses  to  a  liquid  at  —36°, 
whereas  it  absorbs  only  1*75  vols.  of  hydrogen,  which  is  probably 
not  liquid  at  a  temperature  of  —230°. 

Titanium  is  a  dark  grey  powder,  like  iron  which  has  been 
reduced  from  its  oxide  by  hydrogen.  It  has  not  been  fused.  It 
unites  directly  with  oxygen  and  with  chlorine,  burning  when 
heated  in  these  gases.  It  has  also  the  rare  property  of  uniting 
directly  with  nitrogen  when  heated  in  that  gas.  It  decomposes 
water  at  100°,  combining  with  its  oxygen,  and  liberating 
hydrogen. 

Zirconium  forms  brittle  lustrous  scales.  It  fuses  at  a  very 
high  temperature,  and  does  not  combine  with  oxygen  at  a  red 
heat ;  but  at  a  white  heat  it  burns  to  oxide.  It  unites  directly 
with  chlorine. 

Thorium  is  an  iron-grey  powder,  which  burns  brilliantly 
when  heated  in  air,  forming  oxide.  Like  titanium  and  zirconium, 
it  is  attacked  by  chlorine,  burning  brilliantly  in  the  gas  ;  also  by 
bromine  and  iodine.  It  unites  directly  with  sulphur. 

Physical  Properties. 


Carbon  (Diamond)  .  . 
(Graphite)  .  . 
(Charcoal)  .. 

Mass  of  1  c.c. 
Solid. 
3-514  at  18°  .  . 
2:25    at     ?  .  . 
About  1-8  at  ? 
TJndetermined 

Specific 
Heat, 
(see  below)  .  . 
(see  below)  .  . 

"LJnclGtBrniiiiGcl. 

Atomic   Molecular 
Weight.    Weight. 
12  -00            ? 

? 

48-13            ? 

4  '15  at     ?.. 

0  '0660 

90  '0              ? 

Thorium    . 

11-1    at  17° 

0  -0279 

232  -4                ? 

SILICON.  49 

Note. — The  specific  heat  of  carbon  increases  very  rapidly  with  rise  of  tem- 
perature (cf.  beryllium  and  boron).* 

Temperature   ..  -50°          -10°  +10°  +33°          +58°           +86° 

Sp.  heat — 

Diamond..  0-0635  0'0955  0 '1128  0"1318       0'1532       0'1765 

Graphite  . .  0  "1138  0  "1437  0  '1604  0  '1990 

Temperature   ..  +140°  +206°  +247°        +600°  +800°  -1-1000° 

Sp.  heat — 

Diamond..  02218  0*2733  0'3026       0'4408  0'4489  0*4589 

Graphite..  0'2542  0 '2966  0-4431  0-4529  04670 

It  is  noticeable  that,  although  at  low  temperatures  the  specific  heat  of  the 
diamond  differs  considerably  from  that  of  graphite,  yet  at  high  temperatures 
they  nearly  coincide. 

GROUP  VIII.— Silicon,  Germanium,  Tin,  Terbium  (?), 

Lead. 

The  first  of  these  elements,  silicon,  closely  resembles  titanium ; 
it  is  a  blackish,  lustrous  substance.  Germanium  and  tin  are  white 
metals,  with  bright  lustre ;  lead  is  of  a  greyer  hue.  Terbium,  as 
element,  has  not  been  prepared  in  a  pure  state. 

Sources. — The  element  silicon,  next  to  oxygen  is  the  most 
widely  distributed  and  abundant  of  the  elements  on  the  surface  of 
the  globe,  forming  about  25  per  cent,  of  its  total  weight.  It 
never  occurs  in  the  free  state,  being  attacked  by  oxygen ;  hence 
it  exists  only  as  oxide  (silica),  alone  ;  or  in  combination  with  other 
oxides,  as  silicates.  As  such,  it  is  contained  in  a  vast  number 
of  minerals.  Some  of  the  most  typical  of  these  are  described 
under  the  heading  silica  (p.  300).  The  more  commonly  occurring 
forms  of  silica  are  quartz,  sandstone,  and  flint ;  pure  crystallised 
silica  is  named  rocJc-crystal,  bog  diamond,  or  Irish  diamond ;  agate, 
chalcedony,  opal,  &c.,  are  other  forms.  Granite,  trap,  basalt, 
porphyry,  schist,  and  clay  are  rocks  entirely  composed  of  silicates. 
The  name  is  derived  from  silex,  flint.  Germanium,t  an  element 
patriotically  named,  has  been  recently  discovered  by  Winkler  in 
a  mineral  termed  argyrudite  found  in  the  Himmelsfiirst  mine,  near 
Freiberg.  It  contains  6  or  7  per  cent.  (?)  of  sulphide  of  ger- 
manium. Euxenite  is  also  said  to  contain  a  trace  of  germanium, 
— about  O'l  per  cent. 

Tin  is  a  moderately  abundant  element,  although  not  widely  dis- 
tributed. The  chief  mines  are  in  Cornwall;  it  also  occurs  in  the 
Erzgebirge,  in  Saxony  and  Bohemia,  in  the  Malay  Peninsula,  and 

*  Weber,  Fogg.  Ann.,  154,  367. 

t  Winkler,  Serichte,  19,  210;  J.praU.  Chem.  (2),  34,  177. 


50  THE   ELEMENTS. 

in  Peru.  Large  deposits  of  tin-ore  have  recently  been  discovered 
in  Australia  and  in  Borneo.  It  occurs  as  oxide,  in  tin-stone  or 
cassiterite,  and  as  sulphide,  a  comparatively  rare  mineral.  It  is 
never  found  as  n,  metal,  owing  to  its  tendency  to  oxidise. 

Terbium,  the  connection  of  which  with  this  group  of  elements 
is  open  to  question,  is  associated  with  yttrium  (q.v.),  and  is  con- 
tained in  the  same  minerals  as  yttrium. 

Lead,  like  tin,  is  always  found  in  combination,  chiefly  with 
sulphur  in  galena,  a  very  widely  distributed  ore,  found  in  the  Isle 
of  Man,  in  Cornwall,  in  Derbyshire,  in  the  south  of  Lanarkshire, 
and  in  many  foreign  countries.  Other  ores  of  smaller  impor- 
tance are  the  carbonate  or  cerussite,  the  sulphate,  phosphate,  and 
arsenate. 

Preparation. — Silicon,*  like  titanium,  is  produced  by  with- 
drawing chlorine  from  its  chloride  by  passing  the  vapour  of  the 
latter  over  red  hot  sodium  ;  or  by  removing  fluorine  from  its  double 
compound  with  fluorine  and  sodium,  sodium  silicifluoride,  by 
means  of  metallic  sodium ;  the  metal  zinc  may  also  be  used 
alorg  with  sodium  to  withdraw  the  fluorine,  when  the  silicon 
crystallises  from  the  zinc,  which  may  be  removed  by  dissolving 
it  in  weak  hydrochloric  acid.  Germanium,  tin,  and  lead  are 
reduced  from  their  oxides  by  heating  in  hydrogen  or  with  carbon. 
Terbium  has  not  been  prepared.  For  the  preparation  of  tin  and 
lead  on  the  large  scale,  the  chapter  on  the  oxides  and  sulphides  of 
these  metals  mast  be  consulted  (p.  296,  and  also  Chap.  XXXVIII) ; 
for  their  metallurgy  involves  somewhat  intricate  operations. 

Properties. — Silicon  lacks  metallic  lustre,  and  is  therefore 
usually  classed  with  the  non-metals.  It  is  a  blackish  brown 
powder,  which,  when  crystallised  from  zinc  or  aluminium, 
separates  either  in  black  lustrous  tablets  resembling  graphite,  or  in 
brilliant  hard  iron-grey  prisms.  It  fuses  at  a  high  temperature, 
and  may  be  cast  into  rods.  It  is  contained  in  cast  iron,  probably 
however  in  combination  with  the  iron.  The  crystalline  variety 
conducts  electricity.  When  heated  in  oxygen,  chlorine,  bromine, 
or  sulphur  gas,  silicon  combines  with  these  elements.  «  The  crystal- 
line variety  can  be  dissolved  only  by  fusion  with  caustic  potash 
(see  Silicates,  p.  310). 

Germanium  is  a  white  metal,  somewhat  resembling  antimony. 
It  is  very  brittle  and  can  be  readily  powdered.  It  may  bo  melted 
under  a  layer  of  borax,  which  prevents  oxidation  ;  it  is,  however,  not 
very  easily  oxidised.  It  melts  at  a  bright  red  heat.  It  combines 

*  Deville  and  Caron,  Annales  (3),  67,  435. 


TIN,   LEAD. 


51 


Directly  with  oxygen,  sulphur,  and  the  halogens  when  heated  in 
the  vapour  of  these  elements. 

Tin  is  a  lustrous  white  metal  resembling  silver.  It  is  very 
soft  and  malleable,  and  may  be  hammered  into  foil  (tin  foil),  but 
its  wire  has  little  tenacity.  Up  to  100°  its  malleability  increases  ; 
but,  like  zinc,  it  becomes  brittle  at  higher  temperatures,  and  may 
be  powdered  at  200°.  Its  fracture  is  crystalline.  It  melts  at  a 
low  temperature. 

Although  not  oxidised  at  the  ordinary  temperature,  it  burns  in 
air  with  a  white  flame  when  strongly  heated  ;  it  also  unites  directly 
with  the  halogens  and  with  sulphur.  It  forms  alloys  with  many 
other  metals  which  find  commercial  use.  It  is  also  largely  used 
in  tinning  iron  (see  Alloys,  p.  583).  An  allotropic  form  of  tin  is 
produced  when  tin  is  cooled  to  a  low  temperature,  or  when  it  is  kept 
for  a  long  time  ;  it  is  greyish-red,  and  exceedingly  brittle.  When 
heated  to  50°  for  some  hours  it  is  reconverted  into  ordinary  tin.* 

Lead  has  a  greyer  shade  than  tin.  It  is  soft,  and  may  be  cut 
with  a  knife.  It  may  be  hammered  into  foil,  and  drawn  into  wire, 
which  however  has  little  tenacity.  It  is  easily  fused,  and  volati- 
lises at  a  white  heat. 

Lead  combines  directly  with  oxygen  at  a  high  temperature, 
forming  "  dross "  ;  although  not  affected  by  dry  oxygen,  moist 
atmospheric  air  soon  tarnishes  it.  When  heated  with  the  halogens 
or  with  sulphur,  it  combines  directly  with  them.  It  is  used 
largely  for  pipes,  for  covering  roofs,  for  bullets,  shot,  &c.  ;  and 
its  various  alloys  find  a  very  wide  application. 


Physical  Properties. 


Mass  of  1  c.c. 

Solid. 
Silicon — 

Grraplritoidal     2  •  2  at  ? 


Adamantine 
Germanium    . . 

Tin  (solid) .... 
»         »      .... 

„    (liquid)     . . 

,,     (allotropic) 

Lead  (solid)    . . 


2  -48  at  ? 

5  -47  at  20  -4° 

7  '29  at  13°. . 
7  '18  at  226° 
6 -99  at  226° 
5'8to6-0.. 

11-35  at  14°. . 

11  -0  at  325°. . 

10-65     . 


Melting- 
point. 


Specific 
Heat. 


Atomic     Molecular 
Weight.      Weight. 


(see  below)     28  "33 
About  1100° 

About  900°        0-0758        72  '3 
(100°  to  440°) 


226° 


325° 


0 '0562       119  -1 


0-0637 
0 -0545 
0-0314 


206-93 


? 

119-1 
206  -93 


,     (liquid)., 
The  speci6c  heat  of  silicon,  like  that  of  beryllium,  boron,  and  carbon,  varies 


*  Fritsehe,  Phil.  Mag.  (4),  38,  207. 


52  THE   ELEMENTS. 

greatly  with  the  temperature,  and  attains  approximate  constancy  only  at  high 
temperatures.     The  following  determinations  were  made  by  Weber.* 

Temp -40°        +22°        +57°       +86°       +129°      +184°      +232° 

Sp.  heat...      0-1360    0'1697     0'1833    0'1901    0'1964    0-2011    0'2029 


APPENDIX. 

Equations  expressing  the  preparation  of  elements  of  Groups  VI,  VII,  and 
VIII. 

Chromium. — 2CrCl3  +  3Zn  =  2Cr  +  3ZnCl2. 
Iron.— FeO  +  H2  =  Fe  -f  H2O. 
Manganese.— MnO  +  C  =  Mn  +  CO. 
Carbon.— CC14  +  4Na  =  C  +  4NaCl. 
Titanium—  2KF.TiF4  +  4K  =  Ti  +  6KF. 
Cerium. — 2CeCl3  =  2Ce  +  3C12. 
Silicon.— 2NaF.SiF4  +  4Na  =  Si  +  6NaF. 
Germanium.— GeO  %  +  2H2  =  Ge  +  2H2O. 
Tin.— SnO2  +  20  =  Sn  +  2CO. 
Lead.— PbO  +  C  =  Pb  +  CO. 


*  Fogg.  Ann.,  154,  367. 


CHAPTEE  V. 
THE  ELEMENTS  (CONTINUED). 

GROUP  IX,  THE  NITROGEN  GROUP  ;  GROUP  X,  THE  PHOSPHORUS  GROUP  ; 
GROUP  XI,  THE  MOLYBDENUM  GROUP  ;  GROUP  XII,  THE  OXYGEN  AND 
SULPHUR  GROUP. 

GROUP  IX.— Nitrogen,  Vanadium,  Niobium  (or 
Columbium),  Didymium*  (?),  Tantalum. 

THE  first  element  of  this  group,  like  the  first  of  the  seventh  gronp, 
does  not  outwardly  resemble  the  remaining  ones.  .  It  is  a  colourless 
gas,  whereas  the  others  are  solids  with  metallic  lustre.  It  exists 
free,  like  carbon,  while  the  others  occur  only  as  oxides,  because 
they  readily  combine  with  oxygen. 

Sources. — Nitrogen  forms  nearly  four-fifths  of  the  volume 
as  well  as  of  the  weight  of  air.  It  occurs  also  in  small  amount  in 
air  as  ammonia,  in  which  it  is  combined  with  hydrogen.  Am- 
monia also  exists  in  the  soil,  being  carried  down  by  the  rain,  and 
yields  its  nitrogen  to  plants,  which  use  it  as  food,  assimilating  it 
by  means  of  their  roots.  Nitrogen  is  essential  to  the  life  of  plants 
and  animals,  and  is  a  constituent  of  the  albuminous  matters  of 
which  they  largely  consist.  Coal,  the  relic  of  a  former  vegetation, 
also  contains  nitrogen  in  combination  with  carbon,  hydrogen,  and 
oxygen.  Lastly,  it  occurs  in  combination  with  oxygen  and  sodium, 
and  with  oxygen  and  potassium,  in  sodium  and  potassium  nitrates, 
which  encrust  the  surface  of  the  soil  of  dry  countries.  They  are 
exported  from  India,  and  from  S.  America.  Nitrogen  has  no 
great  tendency  to  combine  with  other  elements ;  hence  it  chiefly 
occurs  in  the  free  state.  The  spectroscope  has  also  revealed  its 
presence  in  some  nebulae. 

Vanadium  is  a  comparatively  rare  element.     It  is  found  in 

*  It  is  doubtful  whether  didymiuin  belongs  to  this  group  of  elements.  It 
appears  to  be  a  mixture,  not  a  simple  substance.  See  p.  602. 


54:  THE   ELEMENTS. 

combination  with  oxygen,  along  with  lead,  copper,  and  zinc  oxides, 
as  vanadates  of  these  metals.  A  crystalline  incrustation  on  the 
Keuper  Sandstone,  at  Alderley  Edge,  in  Cheshire,  in  which  vana- 
dium is  associated  with  phosphorus  and  copper,  named  mottra- 
mite,  is  one  of  its  chief  sources. 

Niobium,  tantalum,  and  didymium  are  associated  with  rare 
metals,  such  as  yttrium,  cerium,  lanthanum,  &c.,  in  euxenite  and 
similar  minerals.  The  two  former  are  also  found  in  combination 
with  iron  and  manganese  in  niobite  and  tantalite,  minerals  found 
in  the  United  States  and  in  Greenland. 

Preparation. — Nitrogen  is  usually  prepared  by  removing 
oxygen  from  air,  which  consists  mainly  of  these  two  gases.  By 
heating  ammonia,  its  compound  with  hydrogen,  to  a  red  heat,  it  is 
decomposed  into  its  constituents ;  but  the  hydrogen  is  not  easily 
separated  from  the  nitrogen  ;  hence  the  plan  usually  adopted  is  to 
decompose  ammonia  by  the  action  of  chlorine,  or  by  oxygen  at  a 
red  heat,  both  of  which  unite  with  the  hydrogen,  liberating 
nitrogen.  Perhaps  the  best  method  is  one  in  which  the  oxygen  of 
the  air  is  made  to  combine  with  the  hydrogen  of  the  ammonia  ; 
the  nitrogen  of  both  air  and  ammonia  is  thus  collected.  The  appa- 
ratus is  shown  in  the  accompanying  figure. 

A  gas-holder,  A,  is  connected  with  a  L)-tube,  B,  filled  with  weak 
sulphuric  acid,  which  in  its  turn  communicates  by  means  of 
indiarubber  tubing  with  a  tube  of  hard  glass,  c,  containing  bright 
copper  turnings.  The  other  end  of  the  hard-glass  tube  is  joined 


FIG.  7. 


to  a  wash-bottle,  half  full  of  strong  ammonia  solution.  The  copper 
is  heated  to  bright  redness,  and  the  water  in  the  gas-holder  is 
allowed  to  escape,  a  current  of  air  being  thus  drawn  through  the 


NITROGEN,   VANADIUM.  55 

ammonia-solution.  The  gaseous  ammonia  is  carried  along  with 
the  air  over  the  red-hot  copper.  The  oxygen  of  the  air  unites  in 
presence  of  the  red-hot  copper  with  the  hydrogen  of  the  am- 
monia, forming  water,  and  the  nitrogen  of  the  air  along  with 
the  nitrogen  from  the  ammonia  both  pass  on.  The  sulphuric 
acid  in  the  {J-tube  serves  to  retain  excess  of  ammonia,  and  pure 
nitrogen  is  the  product. 

Nitrogen  may  also  be  prepared  by  leaving  air  in  contact  with 
any  absorbent  for  oxygen;  for  example,  phosphorus  ;  or  a  solution 
of  cuprous  chloride  in  ammonia;  or  potassium  pyrogallate. 

Vanadium*  has  been  prepared  by  withdrawing  chlorine  from 
one  of  its  compounds  with  that  element  by  the  action  of  hydrogen. 
a  red  heat.  The  utmost  precautions  must  be  taken  to  exclude 
oxygen  and  moisture,  as  vanadium  is  at  once  oxidised  at  a  red  heat 
by  these  substances.  As  it  attacks  porcelain,  it  must  be  heated  in 
a  platinum  boat  placed  in  a  porcelain  tube,  during  the  passage  of 
the  hydrogen.  The  method  of  preparation  of  niobiumf  is  similar 
to  that  of  vanadium. 

Tantalum  is  said  to  have  been  prepared  by  a  method  similar 
to  that  which  yields  silicon,  viz.,  by  heating  with  metallic  sodium 
its  compound  with  potassium  and  fluorine. 

Didymium  has  been  made  in  the  same  manner  as  cerium 
{q.v.}.  The  substance  thus  called  is  certainly  a  mixture  of  at 
least  two  metals  (see  p.  605). 

Properties. — Nitrogen  is  a  coJourless,  odourless,  tasteless  gas, 
somewhat  lighter  than  air.  It  condenses  to  a  colourless  liquid  at 
the  very  low  temperature  — 193' 1,J  and  solidifies  to  white  flakes 
at  —214°,  when  cooled  by  boiling  oxygen.  The  liquid  is  lighter 
than  water. 

The  only  elements  with  which  it  combines  easily  and  directly 
at  a  red  heat  are  magnesium,  boron,  titanium,  and  vanadium.  At 
a  higher  temperature,  that  of  the  electric  spark,  it  combines  with 
hydrogen  and  with  oxygen  ;  indeed  combination  between  oxygen 
and  nitrogen  may  be  caused  by  burning  magnesium  in  air,  when 
the  constituents  of  air  unite  to  form  peroxide  of  nitrogen ;  and 
this  gas  is  suddenly  cooled  by  escaping  away  from  the  source  of 
heat,  and  therefore  remains  undecomposed. 

Vanadium  is  a  white  substance  with  metallic  lustre.  It  does 
not  combine  with  oxygen  at  the  ordinary  temperature,  nor  even 

*  Roscoe,  Proc.  Roy.  Soc.,  18,  37  and  316. 
t  Roscoe,  Cham,  yews,  37,  25. 
X   Comptes  rend.,  100,  350. 


OO  THE   ELEMENTS. 

at  100°,  but  it  takes  fire  spontaneously  and  burns  in  chlorine.  It 
is  unaltered  by  water,  except  at  high  temperatures. 

Niobium  forms  an  irridescent  steel-grey  powder. 

Didymium  is  a  white  metal  with  a  faint  yellow  tinge. 

Tantalum  is  said  to  be  a  black  powder,  but  it  is  doubtful 
whether  it  has  been  isolated. 

Physical  Properties. 
Mass  of  1  c.c. 


Nitrogen  .  .  . 

Solid. 
0 

Liquid. 
•89  at  —194-4° 

Gas. 
0  -001258 

H  =  1. 

14-08 

Vanadium  . 
Niobium  .  . 
Didymium  . 
Tantalum  .  . 

.    .  .  .      5  87  at  15° 
.    .  .  .      7  '06  at  15  -5° 
6-54  
.    10  -5  ?    . 

Nitrogen  . . 
Vanadium 

Niobium   . . 
Didymium 
Tantalum. . 


Melting-      Boiling- 
point,  point. 
-214°        -194-4° 
Not  at  bright      — 

red  heat 
Very  high 


Specific 

Atomic 

Molecular 

Heat. 

Weight. 

Weight. 

0-2438 

14-03 

28-06 

? 

51-4 

? 

? 

94-0 

? 

0-0456 

/Ndi*140-8 
\Prdil43-6 

}    ^ 

p 

182-5 

p 

The  critical  temperature  of  nitrogen  is  — 146°,  and  the  critical  pressure  35 
atmospheres. f     Its  vapour-pressures  are  as  follows  : — 

Pressure  in  atmospheres  35  31  17  1         Very  low 

Temperature    - 146°     - 148  '2°     - 160  "5°     - 194  '4°     -  213° 

Under  a  pressure  of  about  4000  atmospheres,  nitrogen  has  the  density  0*8293, 
at  ordinary  temperature,  compared  with  -water. 


GROUP  X. — Phosphorus,  Arsenic,  Antimony, 
Erbium^  Bismuth. 

Owing  to  the  great  tendency  of  phosphorus  to  unite  with 
oxygen,  t  is  always  found  in  combination  with  it.  Arsenic,  too, 
is  seldom  found  native;  it  also  is  easily  oxidised.  Antimony 
and  bismuth  are  both  found  native.  P]rbium  is  always  asso- 

*  Neodymium  and  praseodymium,  two  bodies  into  which  didymium  has  been 
resolved. 

+   Comptes  rend.,  99,  133,  184 ,-  100,  350. 

£  It  is  doubtful  whether  erbium  belongs  to  this  group. 


PHOSPHORUS,   ARSENIC,   ANTIMONY.  57 

ciated  with  cerium,  lanthanum,  yttrium,  &c.  Phosphorus,  arsenic, 
and  antimony  display  allotropy. 

Sources. — Phosphorus  occurs  chiefly  in  combination  with 
oxygen  and  calcium,  as  calcium  phosphate,  in  minerals  named  apatite, 
in  which  it  is  associated  with  fluorine  ;  phosphorite,  an  earthy 
variety ;  and  in  coprolites.  It  is  also  found  as  phosphate  of  alu- 
minium, or  wavellite  in  large  deposits ;  lead  and  copper  phosphates 
also  occur  native.  It  is  a  constituent  of  ail  soils,  though  in 
minute  amonnt.  From  them  it  is  absorbed  by  plants,  and  is 
hence  a  constituent  of  all  vegetable  matter,  especially  seeds. 
Through  plants  it  is  assimilated  by  animals,  and  forms  a  con- 
stituent of  the  bones  (about  58  per  cent.)  and  the  nerves.  Ignited 
bones  consist  mainly  of  calcium  phosphate. 

Arsenic  occurs  most  abundantly  in  combination  with  iron  as 
arsenical  iron,  and  with  nickel  and  cobalt  as  kupfer-nickel  and 
smaltite ;  also  with  iron  and  sulphur  in  arsenical  pyrites  and 
mispickel.  With  sulphur  it  forms  realgar  and  orpiment ;  and  it  is 
also  found  combined  with  oxygen  and  metals  as  arsenates.  It  is 
sometimes  found  native. 

Antimony  is  rarely  found  native ;  its  most  abundant  ore  is 
stibnite,  or  antimony  sulphide ;  it  also  occurs  as  antimony  ochre  or 
oxide ;  and  it  is  associated  in  various  minerals  with  sulphur  and 
lead,  mercury,  copper,  silver,  &c. 

Bismuth  is  a  comparatively  rare  metal,  and  nearly  always 
occurs  native.  It  is  sometimes  associated  with  tellurium. 

Erbium  accompanies  yttrium,  cerium,  &c.  (q.v.).  It  is 
extremely  rare. 

Preparation.  —  Phosphorus  was  originally  obtained  by 
Brandt  by  distilling  dried  and  charred  urine  at  a  white  heat. 
The  carbon  resulting  from  the  decomposition  of  the  animal 
matter  deprived  the  sodium  phosphate  of  its  oxygen,  and  phos- 
phorus distilled  over.  It  is  still  made  by  a  somewhat  similar 
process.  Metaphosphoric  acid,  a  compound  of  phosphorus  with 
oxygen  and  hydrogen,  is  distilled  with  powdered  coke  or  charcoal 
from  clay  retorts.  The  carbon  deprives  this  substance  of  its 
oxygen,  and  phosphorus,  hydrogen,  and  oxide  of  carbon  pass  over  in 
the  gaseous  state.  The  hydrogen  and  carbonic  oxide  gases  escape, 
while  the  phosphorus  is  condensed  and  falls  into  warm  water.  For 
a  detailed  description  of  the  process  see  Chap.  XXXVIII. 

Arsenic  is  produced  by  distilling  mispickel,  when  the  arsenic, 
which  is  very  volatile,  distils  over,  leaving  the  sulphur  and  iron 
behind  as  ferrous  sulphide. 

Antimony  is  prepared  by  heating  its  sulphide  (stibnite)  with 


58  THE   ELEMENTS. 

scrap  iron.  The  iron  withdraws  the  sulphur,  and  the  antimony 
separates  in  the  metallic  stare.  It  is  not  sufficiently  volatile  to  be 
conveniently  distilled,  but  it  flows  down,  forming  a  layer  below 
the  sulphide  of  iron.  These  operations  must  all  be  conducted  in 
absence  of  air,  for  phosphorus,  arsenic,  and  antimony  readily  com- 
bine with  oxygen. 

Bismuth  is  freed  from  earthy  impurities  by  melting  it  in  a 
crucible,  when  it  sinks  to  the  bottom.  Arsenic,  antimony,  and 
bismuth  may  also  be  obtained  by  heating  their  oxides  in  a  current 
of  hydrogen.  Erbium  has  not  been  prepared. 

Properties.— Phosphorus  exists  in  two  ailotropic  forms. 
The  variety  longest  known,  called  yellow  or  ordinary  phosphorus, 
is  a  yellowish-white,  waxy  substance,  possessing  a  strong  disagree- 
able smell.  It  has  a  great  tendency  to  combine  with  oxygen  even 
at  ordinary  temperatures,  and  shines  in  the  dark  owing  to  slow 
oxidation  ;  hence  the  name  phosphorus  (from  0<I's,  light,  and 
06/jeti/,  to  bear).  It  must,  therefore,  be  kept  under  water.  It  is 
easily  fusible,  but  when  melted  in  air  it  takes  fire  and  burns.  It 
also  catches  fire  when  rubbed  on  a  rough  surface,  owing  to  the 
heat  produced  by  friction.  Hence  its  use  for  lucifer  matches.  It 
is  soluble  in  carbon  disnlphide,  a  liquid  compound  of  carbon  and 
sulphur,  and  may  be  obtained  in  crystals  by  the  slow  evaporation 
of  the  disulphide  ;  this  solution  is  named  "  Greek  fire."  When 
the  solvent  evaporates,  the  phosphorus  is  left  in  a  finely  divided 
state,  and  is  spontaneously  inflammable.  It  is  also  soluble  in 
alcohol,  ether,  olive  oil,  turpentine,  benzene,  and  in  certain  of  its 
own  compounds,  such  as  chloride  and  oxychloride  of  phosphorus. 
It  is  easily  distilled  at  a  moderate  temperature  (290°).  Its  vapour 
is  yellow. 

When  heated  to  240°  for  some  time  in  a  closed  vessel  in 
absence  of  oxygen,  it  changes  to  a  red  variety,  named  red,  or 
amorphous,  phosphorus.  The  change  may  be  brought  about  more 
quickly  by  a  higher  temperature,  or  by  addition  of  a  trace  of  iodine 
to  the  phosphorus.  It  is  also  produced  under  water  on  exposure 
of  the  yellow  variety  to  light.  But  red  phosphorus,  when  heated, 
also  changes  back  to  yellow  phosphorus.  Such  a  change,  which 
can  take  place  in  two  directions,  is  termed  a  limited  reaction.  Red 
phosphorus  is  insoluble  in  all  ordinary  solvents  ;  hence  it  may  be 
purified  from  yellow  phosphorus  by  digestion  with  carbon  disul- 
phide. It  does  not  combine  with  oxygen  at  the  ordinary  tempera- 
ture, nor  perhaps  at  any  temperature,  for  it  burns  in  air  only  when 
made  so  hot  that  the  change  into  the  yellow  variety  begins.  The 
colour  of  ailotropic  phosphorus  varies,  according  to  the  tempera- 


ARSENIC,   ANTIMONY,   BISMUTH.  59 

ture  at  which  it  is  formed.  If  prepared  at  260°  it  is  deep  red,  and 
has  a  glassy  fracture ;  at  440U  it  is  orange,  and  has  a  granular 
fracture;  at  550°  it  is  violet-grey;  it  fuses  at  580°,  and  solidifies 
to  red  crystals,  which  have  a  ruby-red  fracture.*  It  is  necessary 
to  exclude  air  and  to  heat  the  phosphorus  under  pressure  to  pro- 
duce these  changes.  It  dissolves  in  melted  lead,  and  separates  on 
cooling  in  nearly  black  crystals. 

Yellow  phosphorus  combines  directly  and  very  readily  with 
oxygen  and  the  halogens.  It  also  unites  with  sulphur,  selenium, 
and  tellurium,  and  with  most  metals.  Red  phosphorus  combines 
directly  with  the  halogens.  Neither  variety  unites  directly  with 
nitrogen  or  with  hydrogen.  Yellow  phosphorus  is  poisonous,  doses 
of  1  grain  and  upwards  producing  fatal  effects,  but  in  small  doses 
it  is  a  powerful  remedy  for  nervous  disorders.  Yellow  phosphorus 
is  a  non-conductor  of  electricity,  but  red  phosphorus  conducts. 

Arsenic  is  a  very  brittle  steel-grey  substance  with  metallic 
lustre  on  freshly  broken  surfaces.  When  heated,  it  sublimes  with- 
out melting,  and  condenses  partly  in  crystals,  partly  in  a  black 
amorphous  (i.e.,  non-crystalline)  state.  It  may,  however,  be 
melted  under  great  pressure.  The  amorphous  variety  is  rendered 
crystalline  by  heating  it  to  360°. f  It  readily  combines  with 
oxygen,  and  hence  loses  its  lustre  on  exposure  to  moist  air.  It 
burns  when  heated  in  air,  spreading  a  garlic-like  smell.  It  unites 
directly  with  oxygen,  with  the  halogens,  and  with  most  other  ele- 
ments. 

Antimony,  like  phosphorus  and  arsenic,  also  exists  in  two 
forms.  Ordinary  a.ntimony  is  a  bluish-white  metal,  very  brittle 
and  crystalline.  It  is  not  oxidised  by  air  at  ordinary  tempera- 
tures, and  does  not  tarnish  on  exposure.  Allotropic  antimony J  is 
obtained  by  electrolysing  a  strong  solution  of  antimony  chloride. 
A  greyish  deposit  is  formed  on  the  negative  pole,  which  has  the 
remarkable  property  of  exploding  when  struck.  Its  specific 
gravity  is  considerably  less  than  that  of  the  ordinary  variety.  It 
is  said,  however,  to  contain  hydrogen.  Antimony  unites  directly 
with  all  elements,  except  nitrogen  and  carbon. 

Bismuth  is  a  greyish- white  metal  with  a  red  tinge,  also  very 
brittle  and  crystalline.  The  conductivity  for  electricity  of  the 
three  elements  arsenic,  antimony,  and  bismuth  rises  in  the  order 
given.  Bismuth  is  the  most  diamagnetic  of  the  elements. 

Erbium  has  not  been  isolated. 

*   Complex  rend.,  78,  748. 

t  Ibid.,  96,  497  and  1314. 

J  Gore,  Chem.  Soc.  J.,  16,  365 ;  Bottger,  J.  pralct.  Chem.,  73,  484 ;  107,  43. 


60 


THE    ELEMENTS. 


Physical  Properties. 
Mass  of  1  c.c. 


A                                Dcn^itv        ]Vfcltin£r 

Solid.             Liquid.                H  =  1.            point. 

Phosphorus,  yellow  .  . 

1  '83  at  10°     1  75  at  40°       65  -0  at  1040°       44  "4° 

1  -49  at  278° 

„              red    

2  -15  to  2  -3             —            45  -4  at  1700°         580° 

(at  0°) 

Arsenic,  amorphous  .  . 

4-7  at  14°                —        r  147  "2  at  8fiO° 

,,         crystalline   .  . 

5-73  at  14°              —        L   77-5  at  1736° 

Antimony,  ordinary  .  . 

6  -67  at  155°          6  -5  ?      f  155  "1  at  1572°         425° 

„           explosive  .  . 

5  -7  to  5'8               —        1  141  -2  at  1640° 

Bismuth            . 

9  "8  at  13  '5°          10  "0         246  '2  at  1700°     268  "3° 

Boiling-      Specific          Atomic             Molecular 

point.          Heat.           Weight.               Weight. 

Phosphorus,  yellow   .  . 

278  -3°    |  0  .'oi  895  1      31  °3         62  °6  to  124  12 

„            red    .... 

0  -0170 

Arsenic,  amorphous  .  . 

0  •  0758           75  -09       150  -18  to  300  "36 

,,         crystalline    .  . 

0  -0830 

Antimony,  ordinary  .  . 

1300°      0  -0508          120  '30       120  '3  to  ? 

„          explosive  .  . 

0  -0541 

Bismuth  

1640°      0-0308          208-1         208-1  to? 

GROUP  XI.— (Oxygen,  Chromium).— Molybdenum, , 
Tungsten,  Uranium. 

The  resemblance  between  oxygen  and  the  other  four  members 
of  this  group  is  a  slight  one.  It  is  advisable  to  consider  oxygen 
along  with  the  three  elements  sulphur,  selenium,  and  tellurium, 
with  which  it  displays  much  greater  analogy. 

The  elements  molybdenum,  tungsten,  and  uranium  present 
some  analogy  with  chromium,  both  in  their  properties  as  well  as 
in  the  compounds  which  they  form.  But  chromium  is  best  con- 
sidered along  with  aluminium,  iron,  and  manganese. 

Sources. — The  chief  source  of  molybdenum  is  the  sulphide, 
molybdenum  glance,  or  molybdenite,  and  wulfenite,  a  compound  of 
molybdenum,  oxygen,  and  lead.  These  are  rare  minerals ;  an 
allo^y  of  lead  and  molybdenum  has  also  been  found  native  in  the 
State  of  Utah. 

Tungsten  occurs  in  wolfram,  combined  with  oxygen,  iron,  and 
manganese ;  and  in  scheelite,  with  oxygen  and  calcium. 

Uranium  is  chiefly  found  as  pitchblende,  in  combination  with 
oxygen. 


OXYGEN.  61 

Preparation. — Molybdenum*  is  prepared  by  heating  its 
chloride  to  bright  redness  in  a  tube  through  which  a  stream  of 
hydrogen  gas  is  passed.  The  hydrogen  unites  with  the  chlorine, 
forming  gaseous  hydrogen  chloride,  leaving  the  non- volatile 
molybdenum.  It  may  also  be  obtained  by  heating  its  oxide  with 
charcoal. 

Tungstenj  can  be  prepared  in  a  similar  manner,  or  from  its 
oxide  by  the  action  of  hydrogen  ;  the  hydrogen  removes  the 
oxygen  as  water,  which  passes  off  as  gas,  while  the  metal  remains. 

Uranium J  is  best  got  from  its  chloride  by  heating  it  with 
metallic  sodium  in  an  iron  crucible.  The  sodium  and  chlorine 
unite,  forming  common  salt,  while -the  uranium,  which  does  not 
unite  with  sodium,  sinks  to  the  bottom  of  the  crucible,  being 
heavier  than  the  fused  salt. 

Properties.  —  These  elements  all  possess  metallic  lustre. 
Molybdenum  is  a  brittle  silver-white  substance,  exceedingly 
hard.  It  fuses  at  a  high  temperature.  Tungsten  is  a  steel-grey 
crystalline  powder,  which  fuses  at  a  white  heat.  Uranium  is  a 
black  powder  which  is  fusible  to  a  grey  metallic  button  of  great 
hardness. 

These  metals  do  not  combine  with  oxygen  at  the  ordinary  tem- 
perature, bnt  are  converted  into  chlorides  when  thrown  into  chlorine 
gas  in  the  state  of  powder.  At  a  high  temperature  they  burn  in 
air,  forming  oxides.  They  also  unite  with  sulphur  at  a  red  heat. 
They  are  unchanged  by  water  at  the  ordinary  temperature. 


Atomic  Molecular 

Weight.  Weight. 

95  '7  Unknown. 
184 

240 


GROUP  XII— Oxygen,  Sulphur,  Selenium,  Tellurium. 

These  elements  all  occur  native,  as  well  as  in  combination. 
The  first  is  a  gas ;  the  other  three  are  solids  at  the  ordinary 
temperature,  and  are  often  associated  with  each  other. 

*  Debray,  Comptes  rend.,  46,  1098. 

t  Eoscoe,  Chem.  Soc.  J.,  10,  286. 

J  Peligot,  Annales  (3),  5,  53;  12,  549. 


Physical  Properties. 

Mass  of  1  c.c, 
Solid. 

Melting- 
point. 

Specific 
Heat. 

Molybdenum  .  . 

8'G 

White  heat.  . 

0-0722 

Tungsten  

19-2 

White  heat.  . 

0  -0334 

(at  12°). 

Uranium  

18-7 

Eed  heat  .  .  . 

0  -0277 

(at  4°). 

G2  THE   ELEMENTS. 

Sources. — Oxygen  is  the  most  abundant  and  widely  distri- 
buted of  the  elements,  forming,  as  has  been  estimated,  50  per  cent, 
of  the  earth's  crust.  About  one-fifth  of  the  weight  as  well  as  of  the 
volume  of  air  consists  of  oxygen,  the  remaining  four-fifths  being 
nitrogen,  with  which  the  oxygen  is  mixed.  It  constitutes  eight- 
ninths  of  the  weight  of  water,  and  is  found  in  union  with  every 
element  in  nature,  except  fluorine,  chlorine,  bromine,  platinum 
and  its  analogues,  and  gold,  silver,  and  mercury.  Many  compounds 
into  which  it  enters  have  been  already  mentioned  as  sources  of  the 

/lements. 
Sulphur  occurs  native  in  the  neighbourhood  of  volcanoes,  and 
coats  the  surface  of  the  soil  in  districts  of  volcanic  activity.  It  is 
chiefly  mined  in  Italy  and  Sicily.  It  also  occurs  in  combination 
with  iron  as  iron  pyrites,  and  with  iron  and  copper  as  copper 
pyrites ;  with  lead  as  galena,  with  zinc  as  blende,  with  mercury  as 
cinnabar.  It  also  occurs  in  union  with  oxygen  and  a  metal,  e.g., 
in  the  sulphates  of  calcium,  magnesium,  sodium,  &c.  Its  principal 
sources  are  native  sulphur;  and  copper  pyrites,  of  which  large 
mines  exist  in  the  South  of  Spain..  It  exists  also  in  certain 
volatile  oils,  such  as  oil  of  mustard,  oil  of  garlic,  &c. 

Selenium  in  small  quantities  almost  invariably  accompanies 
sulphur  ;  both  native  and  in  its  compounds.  It  is  also,  but  rarely, 
found  in  combination  with  lead  and  copper ;  and  with  nickel, 
silver,  molybdenum,  &c. 

Tellurium  is  found  in  the  free  state,  and  also  in  combination 
with  bismuth,  silver,  lead,  and  gold.  It  is  a  very  rare  element. 

Preparation. — There  is  no  convenient  method  of  separating 
nitrogen  from  air ;  hence  pure  oxygen,  unlike  pure  nitrogen,  cannot 
be  directly  prepared  from  that  source.  Owing  to  its  tendency  to 
unite  with  almost  all  elements,  it  cannot  well  be  prepared  by  dis- 
placing it  from  any  one  of  its  compounds.  The  only  elements 
capable  of  displacing  it  appear  to  be  fluorine  and  chlorine,  for 
almost  all  other  elements  combine  directly  with  it.  It  must 
therefore  be  prepared  by  heating  certain  of  its  compounds  with 
other  elements — certain  oxides  and  double  oxides  or  salts  ;  or  by 
the  electrolysis  of  certain  of  its  compounds,  e.g.,  water.  The 
methods  of  preparing  it  may  be  grouped  under  three  heads  : — 

1.  The  electrolysis  of  water,  or  of  fused  oxides  or  hydroxides,  i.e., 
oxides  of  hydrogen  and  another  element.  Water,  however,  is  a 
non-conductor  of  electricity  when  pure,  and  it  is  necessary,  in 
order  to  make  it  conduct,  to  dissolve  in  it  some  substances  with 
which  it  reacts.  In  practice,  the  operation  is  conducted  as  follows  : — 
A  LMuke>  ^°»  *s  filled  with  dilute  sulphuric  acid.  Through  the 


OXYGEN. 


G3 


lower  end  of  each  of  these  tubes  is  sealed  a  piece  of  platinum 
wire,  connected  each  with  a  slip  of  platinum  foil,  and  the  pieces 
of  wire  projecting  outside  are  connected  by  copper  wires  to  the 
poles  of  a  battery  of  four  Bunsen's  or  Groves'  or  bichronie  elements 
(two  are  sufficient,  but  the  operation  is  more  rapid  with  four  cells). 
The  oxygen  is  evolved  from  the  electrode  connected  with  the  car- 


hon  or  platinum  plate  ;  the  gns  issuing  from  the  other  electrode  is 
hydrogen.  After  the  current  has  passed  for  some  time,  the  tube  o 
is  partly  filled  with  oxygen  gas,  and  the  hydrogen  in  the  tube  h 
occupies  about  twice  the  volume  of  the  oxygen.  On  opening  the 
stopcock  o  carefully,  the  characteristic  property  possessed  by 
oxygen  of  rekindling  a  glowing  piece  of  wood  may  be  shown  by 
allowing  the  escaping  gas  to  play  on  it ;  and  the  hydrogen  may  be 
set  on  fire  as  it  escapes  from  the  tube  h. 

2.  The  heating  of  certain  oxides. — All  compounds  with  oxygen 
of  the  metals  of  the  platinum  group  ;  of  gold,  silver,  or  mercury ;  of 
the  chlorine  group  of  elements;  of  the  higher  oxides  of  nitrogen;  the 
higher  oxides  of  the  chromium  group  of  elements  (£.<?.,  chromium 
trioxide,  chromates,  potassium  ferrate,  manganate  or  permanga- 
nate, manganese  dioxide,  nickel  and  cobalt  sesquioxides)  ;  of  the 
calcium  group  of  elements,  and  of  lead  ;  all  these  part  with  oxygen 


64  THE   ELEMENTS. 

at  a  bright  red  heat,  and  in  many  cases  at  a  lower  temperature. 
The  action  of  sulphuric  acid  on  the  higher  oxides  also  yields  oxygen 
(see  Manganese  Dioxide,  and  Chromate  of  Potassium) . 

Three  typical  examples  are  chosen  : — 

(«•).  The  action  of  heat  on  mercuric  oxide. — The  apparatus  is 
shown  in  fig.  9.  A  is  a  tube  of  combustion  glass,  which  is  more 
difficult  of  fusion  than  ordinary  glass,  sealed  at  one  end,  and  closed 
at  the  other  end  with  a  perforated  indiarubber  cork  through  which 
a  bent  glass  tube  is  inserted.  This  tube  dips  below  the  surface 
of  the  water  in  a  glass  trough,  B,  and  its  open  end  bends  upwards, 


so  as  to  deliver  gas  into  an  inverted  jar,  D,  full  of  water.  The 
hard  glass  tube  contains  some  mercuric  oxide.  Heat  is  applied 
with  a  Bunsen's  burner,  B,  care  being  taken  to  wave  about  the 
flame  at  first,  so  as  to  heat  the  glass  tube  gradually;  else  it  is  apt 
to  crack.  After  allowing  some  bubbles  to  escape,  so  as  to  ensure 
the  expulsion  of  a^r  from  the  tube,  the  glass  jar  is  placed  above 
the  exit  tube,  and  the  gas  is  collected.  The  mercury  collects  in 
the  depression  c.  It  was  by  this  means  that  Priestley,  one  of  the 
discoverers  of  oxygen,  first  prepared  it  in  1774.  He  named  it 
dephlogisticated  air  (see  p.  11). 

(6).  The  action  of  heat  on  potassium  chlorate. — This  body  is  a 
compound  of  potassium,  chlorine,  and  oxygen.  The  oxygen  is 
wholly  expelled,  potassium  chloride,  a  compound  of  chlorine  and 
potassium,  remaining  behind.  The  chlorate  is  heated  in  a  hard 
glass  flask,  by  aid  of  a  Bunsen  burner  (see  Potassium  Cldurate, 
p.  466).  The  salt  melts  and  begins  to  froth,  owing  to  the  evolution 
of  oxygen.  If  some  manganese  dioxide  be  mixed  with  the  chlorate, 
the  gas  is  evolved  at  a  lower  temperature,  but  is  not  so  pure 
(see  Perchlorates  ;  also  Oxides  of  Manganese).* 

(c).  The  action  of  heat  on  barium  dioxide. — Barium  forms  two 
oxides,  one,  the  monoxide,  containing  less  oxygen  than  the  second, 

*   Chem.  Soc.  J.,  51,  274. 


SULPHUR. 


65 


the  dioxide.  When  the  monoxide,  a  grey  porous  solid,  is  heated  to 
dull  redness  in  contact  with  dry  air,  it  absorbs  oxygen  from  the 
air,  producing  the  dioxide;  the  absorption  is  increased  by  pressure. 
On  decreasing  the  pressure,  the  dioxide  formed  is  decomposed; 
the  oxygen  may  be  pumped  off  by  means  of  an  air-pump  and 


FIG.  10. 

forced  into  iron  or  steel  bottles.  This  process  is  now  carried  out  on 
a  large  scale,  and  indeed  is  the  only  method  by  which  oxygen  is 
made  commercially.  The  barium  dioxide  is  contained  in  vertical 
iron  tubes,  which  are  heated  with  gas  from  a  Siemens's  "  pro- 
ducer," the  temperature  being  carefully  regulated. 

3.  By  displacement. — The  gaseous  element  fluorine,  which 
has  only  recently  been  prepared,  at  once  acts  on  water,  combining 
with  its  hydrogen,  and  liberating  its  oxygen  (see  Ozone,  p.  387). 
Chlorine  and  steam  at  a  red  heat  react  in  a  similar  manner, 
hydrogen  chloride  and  oxygen  being  produced.  Chlorine  gas 
also  slowly  acts  on  water  exposed  to  sunlight,  liberating  oxygen. 
The  halogens  expel  oxygen  from  certain  oxides  at  a  red  heat; 
e.g.,  from  the  oxides  of  lead,  bismuth,  zinc,  &c.  None  of  these  are 
practical  methods  of  preparing  the  gas  (see  Oxides  of  Manganese, 
Chlorine,  Silver,  and  Lead;  also  Hypochlorites). 

Sulphur. — Sulphur  may  be  prepared  (1)  by  heating  certain 
sulphides,  e.g.,  those  of  gold  and  platinum,  which  part  with  their 
sulphur,  leaving  the  metal;  or  by  heating  hydrogen  sulphide,  which 
splits  into  sulphur  and  hydrogen  ;  and  (2)  by  heating  certain  per- 
sulphides  (compounds  of  metals  with  sulphur  which  form  more 
than  one  sulphide),  the  most  important  of  which  is  iron  pyrites.  As 
sulphur  combines  directly  with  most  other  elements,  there  are  few 
methods  of  preparing  it  by  displacing  it  from  its  compounds;  yet 
chlorine,  bromine,  or  iodine  dissolved  in  water  combines  with  the 


66  THE  ELEMENTS. 

hydrogen  of  hydrogen  sulphide  in  preference  to  the  sulphur,  so  that 
the  element  is  liberated  (see  also  Poly  sulphides  of  Sodium). 

The  elements  selenium  and  tellurium  are  most  readily  pre- 
pared by  displacement.  The  compounds  which  they  form  with 
oxygen  are  decomposed  by  sulphur  dioxide,  which  absorbs  their 
oxygen,  itself  changing  to  sulphur  trioxide,  and  liberating  the 
selenium  or  tellurium  (see  Selenium  and  Tellurium  Dioxides). 
Their  compounds  with  hydrogen,  dissolved  in  water,  are  decom- 
posed by  atmospheric  oxygen,  the  element  falling  to  the  bottom  of 
the  solution. 

An  important  source  of  sulphur  is  native  sulphur,  of  which  the 
chief  impurity  is  earthy  matter.  The  modern  method  of  extraction 
is  to  melt  it  under  water  in  a  boiler  by  forcing  in  steam  until  the 
pressure  rises  to  25  Ibs.  on  the  square  inch.  The  temperature  of 
the  water  is  thus  raised  to  over  115°,  the  melting  point  of  sulphur. 
The  melted  sulphur  is  run  off  through  a  stop-cock  in  the  side  of 
the  boiler,  and  when  cold  a  fresh  charge  of  impure  sulphur  is 
introduced,  and  the  operation  repeated.  Sulphur  is  usually  brought 
into  commerce  in  the  form  of  sticks  cast  in  wooden  moulds,  and  is 
in  this  form  named  roll  sulphur. 

Sulphur  is  a  by-product  in  the  manufacture  of  alkali,  being 
obtained  from  iron  or  copper  pyrites  (see  Chapter  XXXIX). 

Selenium  is  best  obtained  from  certain  residues  in  the  manu- 
facture of  sulphuric  acid,  by  treating  them  with  nitric  acid,  and 
then  precipitating  the  selenium  with  sulphur  dioxide. 

Tellurium  may  be  purified  by  distilling  native  tellurium  at  a 
red  heat  in  a  current  of  hydrogen  gas.  It  is  precipitated  from  its 
solutions  by  metallic  zinc. 

Properties. — Oxygen  is  a  colourless,  odourless,  tasteless  gas, 
somewhat  heavier  than  atmospheric  air.  It  is  very  sparingly 
soluble  in  water;  100  volumes  of  water  at  4°  dissolve  3'7  volumes 
of  oxygen.  It  has  been  condensed  to  a  colourless  transparent 
liquid  by  application  of  great  pressure  at  a  very  low  temperature, 
and  when  still  further  cooled,  it  freezes  to  a  white  crystalline  solid. 
It  was  discovered  independently  by  Priestley  and  by  Scheele  (see 
p.  11)  in  1774  and  1775;  it  had  previously,  however,  been  recog- 
nised as  a  distinct  "air"  or  gas  by  Mayow,  about  1675  (see  p.  9). 
Its  true  nature  was  made  public  by  Lavoisier,  as  has  already  been 
noticed,  although  Mayow  anticipated  him  in  most  of  his  con- 
clusions. Its  name,  "acid-producer"  (o£vs  ryevvaia),  was  invented 
by  Lavoisier. 

Oxygen  combines  directly  with  all  elements  except  the  halogens, 
gold,  and  some  metals  of  the  platinum  group.  Silver  and  mercury, 


SULPHUR,   SELENIUM,   TELLURIUM.  67 

although  they  do  not  readily  combine  directly  with  oxygen,  can  be 
made  to  unite  under  pressure.  Many  elements,  such  as  carbon, 
sulphur,  and  certain  metals,  do  not  unite  with  oxygen  except  when 
heated  ;  others,  such  as  sodium,  phosphorus,  &c.,  combine  at  the 
ordinary  temperature.  The  word  "  combustion  "  usually  signifies 
union  with  oxygen,  with  evolution  of  light.  All  substances  which 
burn  in  air  burn  with  increased  brilliancy  in  oxygen  gas.  It  is 
respirable ;  in  its  usual  dilute  state  in  air,  it  is  when  breathed 
absorbed  by  the  blood,  and  serves  to  oxidise  the  carbon  and 
hydrogen  in  the  body,  thereby  generating  animal  heat ;  if  breathed 
in  a  pure  state,  however,  oxidation  takes  place  with  too  great 
rapidity,  and  acute  febrile  symptoms  are  produced  after  a  short 
time,  followed  by  death  unless  the  animal  is  allowed  to  respire  air. 
The  respiration  of  fishes  is  sustained  by  the  small  amount  of  oxygen 
dissolved  in  the  water  in  which  they  exist. 

When  an  electric  discharge  is  passed  through  oxygen,  or  when 
the  element  is  liberated  by  the  action  of  fluorine  on  water,  a  portion 
of  it  is  changed  to  an  allotropic  form,  which  from  its  strong  smell 
has  been  named  ozone  (»£e«>,  to  smell).  This  substance  will  be 
considered  as  an  oxide  of  oxygen,  and  is  described  on  p.  387. 

The  remaining  three  elements  of  this  group,  sulphur,  sele- 
nium, and  tellurium,  form  a  well-marked  series.  They  show 
progression  in  their  atomic  weights :  thus  S  =•  32,  Se  =  79, 
Te  =  125.  The  atomic  weight  of  selenium  is  nearly  the  mean  of 
those  of  sulphur  and  tellurium.  They  show  a  gradation  of  colour  ; 
sulphur  is  yellow,  selenium  red,  and  tellurium  metallic.  Sulphur 
is  practically  a  non-conductor  of  electricity,  selenium  conducts 
when  exposed  to  light,  and  tellurium  is  a  conductor.  N"o  allo- 
tropic form  of  tellurium  is  known.  Selenium  is  known  to  exist  in 
three  forms  :  amorphous,  which  changes  to  crystalline  when  fused 
and  kept  for  some  time  at  210°;  this  crystalline  variety  is  insoluble 
in  carbon  disulphide ;  the  amorphous  variety,  produced  by  precipi- 
tating selenium  with  sulphur  dioxide,  is  a  bright-red  powder,  soluble 
in  carbon  disulphide,  from  which  it  deposits  on  evaporation  in  dark 
red  crystals.  Sulphur  crystallises  in  two  distinct  forms  :  rhombic 
crystals  (fig.  11),  which  are  found  native,  and  which  may  be  arti- 


FIG.  11.  FIG.  12. 

F  2 


68  THE   ELEMENTS. 

ficially  produced  by  crystallising  sulphur  from  carbon  disulphide ; 
and  monoclinic  needles  (fig.  12),  which  may  be  prepared  by  melting 
sulphur,  allowing  it  to  cool  till  the  surface  has  solidified,  breaking 
the  solid  surface  layer,  and  pouring  out  the  liquid.  The  interior  of 
the  mass  is  filled  with  crystals.  The  monoclinic  form  also  deposits 
from  a  solution  of  sulphur  in  ether  or  in  benzene.  The  monoclinic 
form  is  less  stable  than  the  rhombic ;  and  the  crystals,  which  are 
clear,  transparent,  and  brownish-yellow,  soon  become  opaque  on 
standing,  changing  spontaneously  into  a  mass  of  minute  rhombic 
octohedra.  This  change  is  accompanied  with  evolution  of  heat. 
Other  crystalline  forms  have  recently  been  obtained. 

Selenium  or  sulphur,  when  distilled  into  a  large  chamber, 
condenses  in  part  as  a  fine  powder,  named  flowers  of  sulphur,  or  of 
selenium.  This  is  really  a  mixture  of  two  varieties,  one  of  which 
is  insoluble  in  carbon  disulphide,  the  other  soluble. 

Again,  in  the  state  of  liquid,  sulphur  exhibits  allotropy.  It 
melts  at  115°  to  a  clear,  pale  yellow,  mobile  liquid.  At  200°  it 
turns  brown  and  viscous.  When  the  first  variety  is  poured  into 
water,  it  at  once  solidifies  to  -ordinary  brittle  crystalline  sulphur, 
soluble  in  tcarbon  disulphide.  The  viscous  variety,  however,  if 
poured  into  water,  changes  to  a  curious  elastic,  indiarubber-like 
substance,  insoluble  in  carbon  disalphide,  which  only  slowly  regains 
its  former  condition.  Between  40v/  and  446°,  its  boiling  point, 
sulphur  again  becomes  mobile,  still  remaining  brown.  A  variety 
of  sulphur  soluble  in  water  has  recently  been  discovered.*  Sulphur 
produced  by  precipitation  has  a  white  colour,  and  its  mixture  with 
water  is  known  as  milk  of  sulphur. 

In  the  gaseous  state  also,  sulphur  displays  allotropy.  Its 
density  at  low  temperatures  implies  a  high  molecular  weight,  but 
at  high  temperatures  the  molecule  is  simpler  and  weighs  less 
(see  p.  614). 

These  elements  unite  directly  with  oxygen,  burning  in  the  air 
when  heated;  they  also  combine  with  each  other,  with  the  halogens 
(the  compounds  with  bromine  and  with  iodine  are  ill-defined),  and 
with  all  other  elements  except  nitrogen,  when  heated  in  contact 
with  them.  They,  are  without  action  on  water  at  the  ordinary 
temperature. 


*  Chem.  Sue.  ,7.,  53,  283. 


OXYGEN,  SULPHUR,  SELENIUM,  TELLURIUM. 


C9 


Physical  Properties. 

Mass  of  1  c.c. 

f * N        Density, 

Solid.  Liquid.  Gas.         H  =  1. 

Oxygen    .  ?  1 -24  at -200°    0-001429      15 '96 

(at  0°  and 
760  mm.) 
Sulphur  (rhombic)    ..      2  -07  at  0°  1 '8  32 '27 

(at  1040°) 

„        (monoclinic)        1 "  98 
„        (plastic)  ....      l'95atO° 

Selenium,  crystallised      4' 4 4  "3  82 "2 

from  fusion  .    :  (at  1040°) 

Selenium,  crystallised      4  '8  at  15° 
from  solution 

Selenium,    amorphous      4*3 — 

Tellurium 6'23atO°  —  —  131'4 

(at  1440°) 

Melting-      Boiling-  Specific    Atomic     Molecular 

point.          point.  Heat.     Weight.      Weight. 

Oxygen Below  -  212°  - 186°  0  '2175        16  '0             32 

Sulphur  (rhombic)  ..           115°            446°  0'1776       32-06        64-02 

„         (monoclinic)             120°  to 

(plastic)....  —          252-16? 

Selenium,  crystallised            217°            665°  0'0746        79'0           158-0 

from  fusion  to  ? 
Selenium,  crystallised 

from  solution 

Selenium,  amorphous     About  100°  —               — 

Tellurium Below      Bright  red  0  '0483       125  "0           250 

redness          heat      (crystalline)  to 

0-0518                               ? 

(amorphous) 

Vapour  Pressures  of  Oxygen  at  different  Temperatures* 

Temperature..,.      -118-8°  (crit.)       -121-6°      -125  "6°      -129'0° 
Pressure,  atmos. ..  50 '8   (crit.)  46 '7  40 '4  34 '4 

Temperature -146 '8°       -155 -6°       -166 '1°       -175 '4 

Pressure,  atmos.     ..  13  "7  8 '23  4'25  2 '16 


Temperature — 

-181-5°     -190°     -192-71°     -196-2° 
Pressure,  mm. — 

740  160  71  50 


198  -7°    -200-4°    -211-5° 
20  20  9 


These  low  temperatures  were  produced  by  the  evaporation  of  liquid  ethylenc 
under  reduced  pressure.  The  mass  of  1  c.c.  of  oxygen  at  its  boiling  point, 
— 181-4°,  under  a  pressure  of  742'1  mm.  was  found  to  be  1'124  grams. 


*  Comptes  rend.,  93,  982  ;  100,  350,  979 ;  102,  1010. 


70  THE  ELEMENTS. 

Vapour  Densities  of  Sulphur,   Selenium,  and  Tellurium. — These  are  dis- 
cussed on  p.  614. 

Appendix. — Air. — Air  is  not  a  chemical  compound,  but  a 
mere  mixture  of  nitrogen  and  oxygen  gases.  That  this  is  the  case 
is  shown  by  the  following  considerations  : — (1.)  There  is  no  heat 
change  on  mixing  oxygen  and  nitrogen  gases ;  when  a  compound 
is  formed,  heat  is  usually  evolved.  (2.)  The  density  of  air  is  the 
mean  of  the  densities  of  the  constituent  gases  ;  its  refractive  index 
for  light  is  also  the  mean  of  those  of  oxygen  and  nitrogen  taken  in 
the  proportions  in  which  they  occur  in  air  ;  and  so  with  other 
physical  properties.  Such  properties,  possessed  by  a  compound, 
are  not  the  mean  of  those  of  its  constituents.  (3.)  Oxygen  is 
more  soluble  in  water  than  nitrogen.  On  saturating  water  with 
air,  oxygen  dissolves  in  greater  amount  than  nitrogen ;  and  the 
gas  evolved  from  the  water  when  it  is  heated  contains  a  larger 
proportion  of  oxygen  than  does  air.  (4.)  There  is  no  simple  rela- 
tion between  the  atomic  proportions  of  the  nitrogen  and  oxygen  in 
the  air.  Such  a  relation  would  be  characteristic  of  a  compound. 
The  actual  composition  by  weight  is,  approximately,  nitrogen 
=  77  per  cent. ;  oxygen  =  23  per  cent.  Dividing  these  numbers 
by  the  atomic  weights  of  nitrogen  and  oxygen  respectively,  14  and 
16,  we  obtain  the  quotients  5'55  and  1*44,  representing  the  relative 
number  of  atoms  of  nitrogen  and  oxygen  in  air.  The  simplest 
proportion  between  these  numbers  is  3'85  to  1 ;  although  the  ratio 
approximates  to  the  ratio  4:1,  yet  it  is  far  from  being  a  simple 
one,  as  it  would  be,  were  air  a  compound.  A  substance  of  the 
formula  N40  would  contain  77'8  per  cent,  of  nitrogen  and  22'2  per 
cent,  of  oxygen. 

Air  contains,  in  addition  to  nitrogen  and  oxygen,  water-vapour 
(about  O84  per  cent,  by  weight,  or  1*4  per  cent,  by  volume,  on  the 
average),  carbon  dioxide,  from  0*049  to  0*033  per  cent,  by  volume, 
and  a  few  parts  of  ammonia  per  million.  Subtracting  these  from 
air,  tLe  ratio  of  oxygen  to  nitrogen  by  volume  approximates  to 
79'04  volumes  of  nitrogen,  and  20'96  volumes  of  oxygen.  But 
its  composition  varies  slightly  in  different  places  and  at  different 
times,  although  the  action  of  air  currents  and  winds  tends  to 
keep  it  nearly  constant. 

Air  has  been  liquefied  by  cooling  to  —192°  ;  but,  as  oxygen  and 
nitrogen  have  not  the  same  boiling  points,  the  less  volatile  oxygen 
doubtless  liquefies  first. 

Air  is  analysed  (1)  by  mixing  a  known  volume  with  a  known 
volume  of  hydrogen,  and  exploding  the  mixture.  The  oxygen  is 
withdrawn  as  water,  and  the  residual  nitrogen  is  measured. 


AIR.  71 

2.  By  passing  air  deprived  of  carbon  dioxide  and  moisture  over 
ignited  copper.  The  oxygen  unites  with  the  copper,  forming 
oxide;  and  its  amount  is  ascertained  by  the  gain  in  weight  of  the 
copper;  the  nitrogen  passes  on  into  an  empty  globe,  previously 
weighed.  The  gain  in  weight  of  the  globe  gives  the  weight  of 
nitrogen. 


APPENDIX. 

Equations  expressing  the  preparation  of  elements  of  Groups  IX,  X,  XI,  and 
XII. 

Nitroffe*.—2'N1I9  =  N2  +  3F2. 

2NH3  +  3C12  =  N2  +  3HCL 
4NH3  +  3O2  =  2N2  +  6H2O. 
Vanadium.— 2VC1,  +  3H2  =  2V  +  6HC1. 
Phosphorus.— 4HPO3  +  12C  =  P4  +  2H2  +  12CO. 
Arsenic.— FeSAs  =  As  +  FeS. 
Antimony.— Sb2S3  +  3Fe  =  2Sb  -f  3FeS. 
Molybdenum.— MoCl4  +  2H2  =  Mo  +  4HC1. 
Tungsten.— WO3  +  3H2  =  W  +  3H2O. 
Uranium.— UC14  +  4Na  =  U  +  4NaCl. 
Oxygen.— ^2H2O  =  O2  +  2H2. 

2HgO  =  O2  +  2Hg. 

2KC103  =  3O2  +  2KCL 

2BaO2  =  O2  +  2BaO. 

H2O  +  C12  =  O  +  2HC1. 
Sulphur.— 2AuaS3  =  3S2  +  4Au. 

2FeS2  =  S2  +  2FeS. 

2H2S  +  O2  =  S2  +  2H2O. 
Selenium.— SeO2  +  2SO2  +  2H3O  =  Se  +  2H2S04. 


72 


CHAPTEE  VI. 
THE  ELEMENTS  (CONTINUED). 

GROUP   XIII,    THE     HALOGEN    GROUP;     GROUPS    XIV  AND    XV,    THE    PALLA- 
DIUM  AND    PLATINUM    GROUPS  ;    GROUP   XVI,    THE    COPPER   GROUP. 

GROUP  XII L— Fluorine,  Chlorine,  Bromine,  Iodine. 

The  elements  fluorine  and  manganese  present  little,  if  any, 
analogy.  Hence,  just  as  oxygen  is  best  classified  along  with 
sulphur,  selenium,  and  tellurium,  presenting  little,  if  any,  analogy 
with  chromium,  so  with  the  elements  of  this  group,  manganese  and 
fluorine  having  little  or  nothing  in  common.  Both  chromium  and 
manganese,  it  will  be  remembered,  are  most  conveniently  cla.ssed 
with  iron,  nickel,  and  cobalt. 

The  halogens,  as  these  elements  are  called,  are  strikingly  like 
each  other.  They  have  all  low  boiling  and  melting  points ;  and 
they  all  combine  readily  with  other  elements,  oxygen  and  nitrogen 
excepted.  They  all  are  found  in  combination ;  free  iodine  has 
been  found  in  the  water  from  Woodhall  Spa,  near  Lincoln.* 

Sources. — Fluorine  occurs  in  nature,  combined  with  calcium, 
influor  spar  or  Derbyshire  spar  ;  in  cryolite,  combined  with  sodium 
and  aluminium  ;  and  sometimes  in  apatite,  a  compound  of  phos- 
phorus, oxygen,  and  calcium — calcium  phosphate,  combined  with 
calciam  fluoride.  It  occurs  in  small  quantity  also  in  the  enamel 
of  the  teeth  and  in  the  bones :  it  is  very  widely  distributed  in 
nature,  although  not  very  abundant. 

Chlorine,  bromine,  and  iodine  are  all  contained  in  sea- 
water,  in  combination  with  sodium,  potassium,  and  magnesium. 
Chlorine  also  occurs  in  rock  salt,  of  which  large  mines  exist  in 
Cheshire,  and  in  the  neighbourhood  of  the  Tyne,  in  Northumber- 
land. Certain  rare  ores  of  silver  and  mercury  contain  these  metals 
in  combination  with  chlorine,  bromine,  and  especially  with  iodine. 
The  chief  source  of  bromine  and  iodine  is  sea-weed,  which 
absorbs  the  compounds  of  these  elements  from  sea-water.f  Iodine 
is  also  largely  obtained  from  Chili  saltpetre,  or  sodium  nitrate, 

*  Chem  News,  54,  300.  f  Dingl.  polyt.  J.,  126,  85. 


FLUORINE.  73 

which  contains  it  in  small  amount  in  combination  with  oxygen  and 
sodium  as  sodium  iodate.* 

Preparation. —  1.  By  electrolysis. — This  is  the  only  method  of 
preparing  fluorine  ;  liquid  compounds,  or  solutions  of  compounds 
in  water,  of  the  other  halogens  also  yield  the  elements  by  this 
process.  The  preparation  of  lithium  by  the  electrolysis  of  its  fused 
chloride  (see  p.  29)  affords  an  example  of  the  application  of  elec- 
trolysis to  a  fused  compound  of  chlorine.  The  gas  is  evolved  at  the 
positive  or  carbon  polerthe  metal  being  deposited  on  the  negative  or 
zinc  pole.  Concentrated  solutions  in  water  of  chlorides,  bromides, 
or  iodides  yield  these  elements  on  electrolysis,  for  such  solutions 
conduct  electricity,  and  the  halogens,  with  exception  of  fluorine, 
are  not  readily  acted  on  by  water.  Thus  hydrogen  chloride  dis- 
solved in  water  (hydrochloric  acid)  splits  into  chlorine  and  hydro- 
gen gases  when  electrolysed.  The  poles  should  consist  of  gas 
carbon,  or  platinumr  all  other  substances  being  attacked,  more  or 


FIG.  13. 

less,  by  the  chlorine  produced.  Fluorine,  however,  cannot  be 
liberated  in  presence  of  water,  for  it  immediately  acts  on  it,  liberat- 
ing oxygen  as  ozone.  Hence,  it  is  prepared  by  electrolysing  in  a 

*  Dingl.  polyt.  J.,  253,  48. 


74  THE  ELEMENTS. 

(J-tube  made  of  an  alloy  of  platinum  and  iridium,  which  is  bnt 
slightly  attacked,  a  solution  of  potassium  fluoride  in  dry  hydro- 
fluoric acid  cooled  to  a  low  temperature.  It  is  necessary  to  use 
such  a  solution,  inasmuch  as  pure  hydrogen  fluoride  does  not  conduct 
electricity,  and  unless  the  liquid  conduct,  electricity  cannot  pass,  and 
electrolysis  cannot  take  place.  The  apparatus  used  by  M.  Moissan,* 
who  has  recently  isolated  this  element,  is  shown  in  fig.  13. 

2.  By  displacement. — ~No  element  appears  capable  of  displacing 
fluorine    from   its  compounds  without  combining  with    it.       But 
chlorine,  bromine,  and  iodine  are  usually  prepared  by  displacing 
them   from   their    compounds    with   potassium,    sodium,    magne- 
sium,  &G.J  by  means  of  oxygen.      The  oxygen,  however,    is  not 
employed  in  the  gaseous   state.      At  a  red  heat,  indeed,  such  dis- 
placement is  possible.     The  action  of  oxygen,  for  instance,  on  red- 
hot  magnesium  chloride  yields  chlorine,  while  a  double  compound 
of  chlorine,  oxygen,  and  magnesium  (oxychloride)  remains  behind  : 
again,  Deacon's  process  for  producing  chlorine,  which  depends  on 
the  interaction  of  the  oxygen  of  the  air  and  hydrogen  chloride  at 
330°  in  presence  of  bricks  coated  with  dry  copper  chloride,  yields 
chlorine  and  water  as  products.    The  usual  method,  however,  of  pre- 
paring halogens  consists  in  acting  on  hydrogen  chloride  dissolved 
in   water    (hydrochloric   acid)  with   a   peroxide.       The    peroxide 
yields  a  portion  of  its  oxygen  to  the  hydrogen  chloride,  forming 
water    and    chlorine.       The   remaining   hydrogen   chloride    sub- 
sequently reacts  with  the  oxide.       The  peroxide    generally  used 
is  manganese  dioxide ;    but  peroxides  of  lead,  barium,  &c.,  potas- 
sium permanganate,  bichromate,  and  other  peroxides  may  also  be 
employed.     When  a  mixture  of  chloride,  bromide,  and  iodide  of 
potassium   or   sodium   is  treated  so   as  to  liberate  the  halogens, 
the   iodine   is    liberated  first,  then  the    bromine,  and   lastly  the 
chlorine. 

3.  By  beating  compounds  of  the  elements. — Most  of  the  com- 
pounds of  the  halogens  are  remarkably  stable,  and  although  some, 
such  as  hydrogen  chloride,  may  be  decomposed  by  exposure  to  an 
exceedingly  high  temperature,  yet  re-combination  takes  place  on 
cooling,  so  that  the  halogen  cannot  be  isolated.     Fluorine,  how- 
ever, is  said  to  have  been  prepared  by  heating  cerium  or  lead  tetra- 
fluoride.f      The  chloride,  bromide,  and  iodide  of  nitrogen  are  ex- 
tremely explosive  bodies,  at  once  decomposing  into  their  elements 
when  warmed  or  when  exposed  to  shock;    the  higher  chlorides 
and  bromides  of  phosphorus  and  arsenic,  when  heated,  yield  lower 

*  Comptes  rendus,  102,  1543  j  103,  202  and  256. 
f  Serichte,  14,  1944. 


CHLORINE. 


75 


compounds  and  the  halogens;  compounds  of  halogens  with 
oxygen  are  also  unstable,  and  are  resolved  with  explosion  into 
their  elements  when  heated ;  compounds  of  the  halogens  with 
each  other  are  also  easily  decomposed  by  heat.  The  halogen 
compounds  of  gold,  platinum,  &c.,  are  decomposed  into  their 
elements  by  heat.  This  type  of  reaction,  however,  does  not  afford 
a  practical  method  of  preparation. 

Preparation  of  chlorine. — About  30  grams  of  powdered  man- 
ganese dioxide  are  placed  in  a  flask  closed  with  a  double  bored 
cork ;  through  one  hole  passes  a  tube  communicating  with  a  wash- 
bottle  full  of  water;  through  the  other  a  thistle  funnel  passes. 
Strong  hydrochloric  acid  (solution  of  hydrogen  chloride  in  water) 


FIG.  14. 

is  added,  and  gentle  heat  is  applied.  The  gas  issues  from  the  exit 
tube  of  the  wa^h-bottle,  and  may  be  collected  over  warm  water,  in 
which  it  is  less  soluble  than  in  cold ;  or,  better,  by  downward  dis- 
placement, for  it  is  heavier  than  air.  The  latter  arrangement  is 
shown  in  the  figure.  To  show  the  tendency  of  chlorine  to  com- 
bine with  other  elements,  powdered  antimony  may  be  thrown  into 
a  jar  containing  it ;  the  metal  will  burn.  A  candle  will  be  found 
to  burn  in  chlorine  with  a  sooty  flame ;  the  hydrogen  combines, 
but  the  carbon  is  liberated  as  soot.  A  solution  of  chlorine  in 
water  acts  as  a  bleaching  agent :  a  coloured  rag  dipped  in  such  a 
solution  is  soon  bleached ;  the  chlorine  combines  with  the  hydro- 
gen of  the  water,  liberating  oxygen,  which  oxidises  the  coloured 


76  THE   ELEMENTS. 

substances  to  colourless  ones.  Lastly,  some  chlorine-water,  as  a 
solution  of  chlorine  in  water  is  termed,  added  to  a  solution  of  a 
bromide  or  iodide,  e.g.,  potassium  bromide  or  iodide,  liberates  these 
elements.  Similarly,  bromine-water,  added  to  an  iodide,  liberates 
iodine. 

Properties. — In  the  gaseous  state  these  elements  have  all  a 
strong  disagreeable  smell ;  that  of  fluorine,  however,  is  the  smell 
of  ozone,  for  it  acts  on  the  moisture  in  the  nose,  liberating  ozone. 
Fluorine  appears  to  be  colourless,  chlorine  is  greenish-yellow, 
bromine  deep  red,  and  iodine  violet.  The  names  %Xw/>o's, 
yellowish-green,  /3/Jw/uo9,  a  stench,  and  roet&/<?,  violet,  refer  to  these 
properties.  As  it  is  impossible  to  confine  fluorine  in  any  vessel 
which  it  does  not  attack,  no  attempt  to  liquefy  it  has  been  made. 
Chlorine  may  be  condensed  to  a  greenish-yellow  liquid,  boiling  at 
a  very  low  temperature;  it  solidifies  to  a  solid  of  the  same  colour.* 
Bromine  is  at  ordinary  temperatures  a  deep  brownish-red  liquid, 
freezing  to  a  blackish-red  solid  ;  and  iodine  at  ordinary  tempera- 
tures is  a  bluish-black  lustrous  solid,  melting  to  a  brownish-black 
liquid.  It  sublimes  readily. 

Chlorine,  bromine,  and  iodine  dissolve  in  carbon  disulphide  and 
tetrachloride,  in  alcohol  and  ether,  and  also,  in  water.  One  volume 
of  water  at  0°  absorbs  2'58  volumes  of  chlorine;  and  at  15°, 
2'36  volumes.  Bromine  is  soluble  in  30  times  its  weight  of  water 
at  10° ;  iodine  is  very  sparingly  soluble  in  pure  water.  The 
presence  of  chlorides,  bromides,  and  iodides  in  the  water  greatly 
increases  the  solubility  of  the  halogens :  it  is  possible  that  the 
solubility  of  chlorine  and  bromine  in  water  depends  on  their 
interaction  with  the  water.  Chlorine  and  bromine  combine  with 
water  to  form  crystalline  hydrates.  Bromine  and  iodine  form 
compounds  with  starch;  the  former  has  an  orange  colour,  the 
latter  is  deep  blue.  The  compound  of  iodine  with  starch  is  used 
as  a  delicate  test  both  for  iodine  and  for  starch. 

These  elements  combine  directly  with  each  other,  and  at  a 
high  temperature,  or  when  moist,  with  all  others  except  carbon, 
nitrogen,  and  oxygen. f  The  only  solid  elements  which  withstand 
their  action  even  partially  are  carbon,  and  iridium,  or  better,  its 
alloy  with  platinum.  Fluorine  attacks  glass  and  porcelain,  but  the 
other  halogens  are  without  action  on  these  substances,  and  may  be 
exposed  in  glass  or  porcelain  vessels  to  a  high  temperature. 

All  these  elements  tend  to  combine  with  hydrogen,  whether 
free  or  in  combination,  hence  their  irritating  action  on  the 

*  Monat.sk.  Chem.,  5,  127.  f  Chem.  Soc.  J.,  43,  153. 


GROUPS  XIV  AND   XV.  77 

organism,  which  chiefly  consists  of  compounds  of  carbon,  hydrogen, 
and  oxygen.  They  produce  catarrh  of  the  mucous  membranes 
when  breathed. 

No  allotropic  modifications  of  these  elements  are  known. 

Physical  Properties. 

Mass  of  1  c.c. 

f * ^  Density,  Melting- 
Solid.          Liquid.  H  =  1.  point. 

Fluorine    ?                   ?  18 "3  at  15°..  ? 

Chlorine     ?         1  "33  at  15  '5°  35  '4  at  200°  Below  - 102° 

Bromine     ?          3 '18  at  0°..  80 '0  at  228°  -7  "05° 

Iodine     4-95    4 '00  at  m.  p.  128 '85  at  445°  114 -15C 


Fluorine 
Chlorine 
Bromine 
Iodine 


Boiling- 
point, 
p 

Specific 
Heat. 

p 

Atomic          Molecular 
Weight.            Weight. 
19-0               38-0 

-102° 

? 

35  -46      35  '46—  70  -92 

58  -75° 

0-0843  solid 

79-95      79-95—159-9 

184  -35° 

0-0541    .... 

126-85     126-85—253-7 

Vapour-densities  of  Chlorine,  Bromine,  and  Iodine.  —  These  are  considered 
on  p.  616. 


GROUPS  XIV  AND  XV. — Ruthenium,  Rhodium,  Pal- 
ladium; Osmium,  Iridium,  Platinum. 

These  metals  are  always  associated.  They  fall  into  two  groups 
of  three,  members  of  the  first  of  which  have  atomic  weights  of 
about  105,  and  of  the  second,  about  193.  They  are  always  found 
native,  or  in  combination  with  each  other.  They  are  very  difficult 
of  attack  by  any  process :  even  chlorine  or  oxygen  at  a  red  heat 
produces  little  effect;  hence  their  occurrence  in  the  free  state. 

Sources. — (a).  Metallic  particles,  consisting  chiefly  of  plati- 
num and  palladium,  but  containing  small  quantities  of  the  other 
metals,  occur  as  flattened  grains  in  the  sand  of  certain  rivers  in 
Brazil,  Mexico,  California,  and  on  the  west  side  of  the  Ural 
Mountains. 

(b).  Metallic  particles,  chiefly  consisting  of  osmium  and 
iridium,  and  named  osmiridium,  occur  along  with  the  grains  of 
platinum.  The  complete  separation  of  these  metals  is  a  matter  of 
great  difficulty  (see  p.  475).*  3,000  kilos,  of  platinum  ore  were 
exported  from  the  Ural  Mountains  in  1881. 

*  Consult  Annales  (3),  56,  1  and  385;  also  Chem.  News,  39,  175. 


78 


THE  ELEMENTS. 


Properties. — These  elements  are  all  white,  with  a  greyish 
tinge,  and  possess  strong  metallic  lustre.  They  melt  only  at  a 
very  high  temperature ;  in  practice  they  are  fused  by  means  of  a 
blowpipe  flame  of  oxygen  and  hydrogen  in  crucibles  of  lime,  on 
which  they  are  without  action  (see  fig.  31,  p.  194).  Owing  to 
their  ability  to  resist  oxidation,  an  alloy  of  90  per  cent,  of  plati- 
num and  .10  per  cent,  of  iridinm  is  used  for  crucibles,  retorts 
for  evaporating  oil  of  vitriol,  &c.,  and  for  standards  of  length  (e.g., 
the  French  standard  metre).  The  alloy  of  osmium  and  iridium, 
owing  to  its  extreme  hardness,  is  employed  in  tipping  gold  pens, 
and  as  bearings  for  very  delicate  wheel  work.  These  alloys  are 
very  costly,  which  somewhat  limits  their  use.  The  metals  can  be 
welded. 

Platinum  and  palladium  form  compounds  with,  hydrogen,  in 
which  the  last  element  appears  to  play  the  part  of  a  metal  in  an 
alloy  (see  Alloys,  p.  576). 

The  name  platinum,  signifying  "little  silver,"  was  given  to  the 
metal  by  the  Spaniards.  The  name  rhodium  refers  to  the  red 
colour  of  its  salts.  The  other  names  are  fanciful,  except  osmium, 
so  called  from  Off/ay,  a  smell,  in  allusion  to  the  strong  odour  of  its 
volatile  oxide. 

Allotropic  forms  of  iridium,  ruthenium,  and  rhodium  have  been 
prepared  by  fusing  the  metals  with  zinc  or  lead,  and  subsequently 
dissolving  out  the  zinc  or  lead  with  an  acid.*  The  iridium, 
ruthenium,  or  rhodium  is  left  as  a  black  powder  which  explodes 
on  gently  warming,  being  converted  into  the  ordinary  form  of  the 
metal.  Osmium,  iridium,  and  platinum  are  the  heaviest  substances 
known,  being  more  than  21  times  as  heavy  as  water. 

Physical  Properties. 

Mass  of  1  c.c. 
Solid. 

Buthenium    12  '26  at  0°. . 

Khodium   12 '1  at  ?    .. 

Palladium 1 1  •  4  at  225° 

10  -8  (liquid) 

Osmium 22'48at?.. 

Iridium 22  -42  at  17  '5° 

Platinum 21'50  at  17  '6° 

18-91  (liquid) 


Melting- 
point. 

Specific 
Heat. 
0-0611 

Atomic   Molecular 
Weight.    Weight. 
101  -65 

— 

0  -0580 

103-0 

p 

— 

0  -0593 

106-35 

? 



0-0311 

191  -3 

p 

- 

0  -0326 

193-0 

? 

1700? 

0-0324 

194-3 

p 

*  Debray,  Comptes  rend.,  90,  1195. 


COPPER,   SILVER,   GOLD,   MERCURY.  79 


GROUP  XVI.— Copper,  Silver,  Gold,  Mercury. 

Of  these  elements  copper,  silver,  and  gold  probably  belong  to 
the  same  group:  owing  to  considerable  resemblance  which  mer- 
cury bears  to  them  in  its  compounds,  it  is  convenient  to  include  it 
in  the  group. 

Sources. — All  these  metals  are  found  native,  for  all  can  resist 
the  action  of  oxygen  at  the  ordinary  temperature.  All  occur, 
besides,  in  combination  with  sulphur  and  with  arsenic.  The  chief 
ore  of  copper  is  copper  pyrites,  in  which  it  is  combined  with  iron 
sulphide  and  sulphur ;  and  other  important  ores  are  the  oxide, 
cuprite,  or  red  copper  ore,  and  the  sulphide,  copper-glance;  besides 
these,  it  is  found  in  two  forms  in  combination  with  carbon  and 
oxygen  as  carbonate,  viz.,  malachite  and  azurite. 

Silver  is  mostly  found  native.  But  silver-glance  or  sulphide, 
pyrargyrite,  proustite,  and  silver-copper-glance,  in  which  it  is  associ- 
ated with  sulphur,  antimony,  arsenic,  and  copper,  are  also  impor- 
tant, and  it  also  occurs  in  combination  with  the  halogens.  The 
chloride  is  named  horn-silver. 

Gold  chiefly  occurs  native,  forming  veins  and  nuggets  in 
quartz-rock;  but  it  also  accompanies  copper  and  silver  as  arsenide 
and  sulphide ;  and  is  sometimes  associated  with  tellurium  and 
bismuth.  The  chief  mines  are  in  California,  Australia,  and  the 
Cape;  but  it  is  now  mined  in  Wales,  and  it  is  found  in  upper 
Lanarkshire,  in  the  Leadhills. 

Mercury  sometimes  occurs  free,  but  its  most  important  ore  is* 
cinnabar,  the  sulphide,  of  which  large  mines  are  worked  in  Austria, 
Spain,  China,  and  California. 

Preparation. — The  preparation  of  copper  from  ores  in  which 
it  is  not  associated  with  sulphur  is  simple.  The  ore  is  powdered 
and  heated  with  some  form  of  carbon.  The  carbon  unites  with  the 
oxygen,  forming  gaseous  carbon  monoxide,  and  the  copper  fuses, 
and  owing  to  its  greater  specific  gravity  settles  at  the  bottom  of 
the  furnace.  Copper  oxide  does  not  decompose  by  heat  alone  ; 
but  when  heated  in  an  atmosphere  of  hydrogen  it  is  "  reduced," 
the  hydrogen  uniting  with  the  oxygen  to  form  water. 

If  in  union  with  sulphur,  one  of  two  methods  may  be  adopted : 
(1.)  The  sulphide  of  copper  is  roasted  in  air,  whereby  it  absorbs 
oxygen,  and  is  converted  into  sulphate  of  copper.  This  is  some- 
times brought  about  by  leaving  the  copper  ore  lying  exposed  to  air 
for  years.  The  sulphate  of  copper  is  treated  with  water,  which 
dissolves  it;  and  on  addition  of  scrap-iron,  the  iron  replaces  the 


80 


THE  ELEMENTS. 


.copper  in  its  compound  with  sulphur  and  oxygen,  forming  sulphate 
of  iron,  and  the  copper  is  precipitated  as  a  metallic  sponge.  It  is 
then  collected,  dried,  and  smelted.  This  is  called  the  "wet" 
process  of  extraction.  The  latter  part  of  this  process  may  be  shown 
on  a  small  scale  by  dipping  into  a  solution  of  copper  sulphate  a 
piece  of  bright  iron,  such  as  the  blade  of  a  knife ;  it  will  soon 
become  covered  with  a  deposit  of  metallic  copper.  (2.)  The  dry 
process  consists  in  roasting  the  ore  :  the  iron  contained  in  it  com- 
bines with  oxygen,  the  copper  remaining  as  sulphide.  The  oxide 
of  iron  is  made  to  unite  with  sand,  or  silica,  forming  a  "  slag,"  and 
by  repeating  this  process  several  times  the  copper  is  finally 
obtained  as  sulphide.  The  sulphide  is  roasted  ;  both  copper  and 
sulphur  are  oxidised,  and  a  reaction  occurs  whereby  copper  sepa- 
rates in  the  metallic  state ;  the  oxygen  of  the  copper  oxide  unites 
with  the  sulphur  of  the  copper  sulphide,  forming  sulphur  dioxide, 
a  gas,  which  escapes,  while  metallic  copper  remains.  It  is  melted 
and  brought  to  market  (see  Chapter  XXXVIII). 

Copper  chloride  loses  its  chlorine  when  heated  in  hydrogen ; 
hydrogen  chloride  is  formed,  and  the  metal  remains. 

Mercury  is  easily  separated  from  the  sulphur  with  which  it  is 
combined  in  cinnabar,  by  roasting  in  specially  constructed  fur- 
naces ;  the  oxygen  of  the  air  unites  with  the  sulphur,  forming 
gaseous  sulphur  dioxide,  and  the  mercury  passes  in  the  form  of 
gas  through  a  series  of  cold  chambers  or  earthenware  pots,  in 
which  it  condenses  to  the  metallic  state,  while  the  sulphur  dioxide 
escapes.  This  process  may  be  illustrated  by  heating  in  a  hard 
glass  tube  some  powdered  cinnabar  and  aspirating  over  it  a 


.  15. 


SILVER.  81 

current  of  air.  The  metallic  mercury  will  condense  in  the  cold 
part  of  the  tube  in  small  globules,  while  the  sulphur  dioxide  gas 
will  be  carried  on  into  the  aspirator  (see  fig.  15). 

Mercury  can  also  be  prepared  bj  heating  its  oxide  (see  p.  491) 
although  its  compounds  with  the  halogens  also  split  into  mercury 
and  halogen  when  heated,  yet  they  recombine  on  cooling ;  hence 
the  metal  cannot  be  prepared  by  this  method  unless  hydrogen,  or 
some  other  metal,  e.0.,  iron,  is  present  to  combine  with  the  halogen. 

Mercury  may  be  purified  from  iron,  zinc,  lead,  and  other  metals 
accompanying  it  by  distillation,  preferably  at  a  low  pressure ;  and 
by  drawing  a  slow  stream  of  air  for  several  days  through  an 
inclined  tube  containing  the  impure  metal. 

Silver  is  extracted  from  its  ores,  in  which  it  exists  chiefly  as 
sulphide,  by  roasting  the  ore  with  common  salt,  which  is  a  com- 
pound of  sodium  and  chlorine.  The  change  is  represented  as 
follows : — 

«  -i.  /  Sodium ,  Sodium  sulphide. 

Salt (Chlorine 


f  Silver  .  .  -  ^"-  -  •    '    a  Silver  chloride. 
Silver  sulphide  | 


The  silver  and  chlorine  combine,  and  the  sulphur  and  sodium. 
Such  a  reaction  is  termed  a  "  double  decomposition."  The  next 
stage  in  the  process  is  to  mix  the  mass  with  water,  and  to  add 
scrap-iron,  rotating  the  mixture  in  wooden  barrels.  The  chlorine 
and  iron  combine,  the  silver  separating  as  a  spongy  mass. 
Mercury  is  added  to  dissolve  the  silver  ;  and  after  renewed  rota- 
tion of  the  barrels,  the  mercury  is  drawn  off,  dried,  and  distilled. 
The  volatile  mercury  distils  away,  leaving  the  much  less  volatile 
silver  behind. 

Silver  is  also  largely  extracted  from  lead  ores  and  from  copper 
ores  (see  Chapter  XXXVIII).* 

The  process  of  extracting  gold  from  gold  quartz  is  a  mechani- 
cal one,  for  the  most  part.  The  ore  is  stamped  to  fine  powder  in 
mills  for  the  purpose,  and  washed  with  water.  The  fine  powder 
is  made  to  run  over  a  runnel  of  copper,  coated  with  mercury  ;  the 
sand  is  carried  on,  but  the  grains  of  gold  unite  with  the  mercury, 
and  are  retained.  The  mercury  is  then  squeezed  through  chamois- 
leather  :  the  alloy  (or  amalgam)  of  gold  and  mercury  is  very 
sparingly  soluble  in  mercury;  hence  it  remains  almost  entirely 
behind.  The  mercury  is  then  distilled  off,  and,  along  with  that 

*  Eor  the  preparation  of  pure  silver,  see  Stas,  Annalen,  Suppl.  4,  168. 

G 


82  THE  ELEMENTS. 

portion  which  had  passed  through  the  chamois-leather,  used  for 
re-coating  the  copper  plates. 

When  the  gold  exists  mixed  with  sulphides,  these  are  roasted 
to  remove  sulphur  and  arsenic,  which  unite  with  the  oxygen  of 
the  air  and  volatilise  away.  The  residue  containing  the  gold  is 
heated  under  pressure  with  chlorine-water,  when  the  gold  unites 
with  the  chlorine,  going  into  solution  as  chloride  of  gold.  The 
gold  is  then  precipitated  on  metallic  copper. 

The  preparation  of  mercury,  silver,  and  gold  from  the  chlorides 
may  be  shown,  (a)  by  placing  a  piece  of  bright  copper  in  a  solution 
of  mercuric  chloride ;  (6)  by  laying  on  the  top  of  a  bead  of  fused 
silver  chloride  a  piece  of  zinc  and  adding  a  little  hydrochloric 
acid  ;  (c)  by  placing  a  slip  of  clean  copper  foil  in  a  solution  of 
chloride  of  gold. 

Properties. — Copper  is  a  red  metal ;  silver,  brilliant  white ; 
gold,  yellow  ;  and  mercury,  white  with  a  faint  grey  tinge.  Mercury 
is  liquid  at  the  ordinary  temperature,  but  freezes  at  —40°  to  a 
malleable  solid.  Silver  is  the  most  ductile  of  the  remaining  three 
metals ;  gold  is  the  softest,  and  the  most  malleable.  Gold  and 
silver  leaf,  used  for  gilding  and  silvering,  are  made  by  beating  the 
metals  into  leaves  with  wooden  mallets  :  when  thin  they  are  pro- 
tected from  the  direct  blow  of  the  mallet  by  layers  of  gold-beaters' 
skin.  Copper  may  also  be  beaten  or  rolled  into  foil  and  leaf. 
Gold  leaf  transmits  green  light ;  silver  leaf,  blue  light ;  and  copper 
leaf,  bluish  or  pink  light.  All  of  those  metals  conduct  electricity 
well.  Placing  silver  equal  to  100  at  0°,  copper  has  a  conductivity 
of  77-43  at  18° '8,  and  gold  of  55'19  at  22'7°;  mercury  follows  with 
a  conductivity  of  1*63  at  22*8°. 

Silver  can  be  distilled  at  a  white  heat.  Its  vapour  is  bluish- 
purple.  It  has  the  peculiarity  of  dissolving  oxygen  (about 
22  times  its  volume)  when  liquid  and  discharging  it  during  solidi- 
fication ("spitting"). 

Mercury  distils  about  358°.     Its  vapour  is  colourless. 

Copper  is  rendered  brittle  by  slow  cooling,  and  is  softened  by 
rapid  cooling.  The  properties  of  all  these  elements  are  very 
singularly  modified  by  the  presence  of  traces  of  others.  Thus  the 
smallest  trace  of  arsenic  renders  gold  exceedingly  brittle  ;  a  trace 
of  phosphorus  in  copper  greatly  increases  its  tensile  strength  ;  a 
minute  trace  of  zinc  in  mercury  completely  modifies  its  surface 
tension. 

For  the  composition  .of  coins,  jewellers'  metal,  &c.,  see  Alloys 
(p.  587). 

Of  these  elements,  none  is  oxidised  on   exposure  to  air,  but 


GENERAL   REMARKS. 


83 


copper  at  a  red  heat,  mercury  at  the  temperature  of  ebullition, 
and  silver  heated  in  air  under  a  pressure  of  several  atmospheres 
unite  with  oxygen.  Gold  does  not  combine  directly  with  oxygen. 
The  oxides  of  the  last  three  are  easily  decomposed  by  heat.  These 
metals  all  unite  directly  with  sulphur,  selenium,  and  tellurium,  and 
with  arsenic  ;  with  chlorine,  bromine,  and  iodine,  and  with  most 
metals.  They  do  not  unite  directly  with  nitrogen. 

Physical  Properties. 

Mass  of  1  c.c. 

f ' ^  Density.  Melting- 
Solid.                 Liquid.  H  =  1.  point. 

Copper 8-90                  8  '2  ?  1330° 

(atO0) 

Silver 10'57                  9'5  ?  1040° 

Oold 19-29                17-1  ?  1240° 

Mercury.. 14-19                 13 '596  100 '1  -40° 

(-40°)  (atO°) 

Boiling-  Specific  Atomic  Molecular 

point.  Heat.  Weight.  Weight. 

Copper ?  0  -0935  63  "40  ? 

Silver White  heat  0'0570  107*93  107'93 

Gold ?  0-0324  197-22  197'22 

Mercury 358'2°  0  '03 1 9  2OO  '2  200'2 

(solid) 


General  Remarks  on  the  Elements. 

(1.)  Classification. — It  has  been  customary  to  divide  the 
elements  into  two  classes :  the  metals,  those  which  are  opaque  and 
which  exhibit  metallic  lustre ;  such  elements  are  more  or  less  good 
conductors  of  electricity  and  heat ;  and  the  non-metals,  comprising 
the  remaining  elements.  Such  a  division  tends  to  obscure  the  rela- 
tions between  them  ;  it  is,  so  far  as  we  know,  an  arbitrary  division, 
and  is  sanctioned  only  by  long  custom.  Other  objections  which 
might  be  taken  to  this  division  are  that  a  number  of  elements,  such 
as  titanium,  arsenic,  and  tellurium,  are  difficult  to  classify,  being 
sometimes  considered  as  metals,  sometimes  as  non-metals :  and  a 
still  more  important  objection  is  that  certain  elements  can  exist  in 
both  forms.  Thus  silicon,  phosphorus,  and  carbon  exist  in  com- 
pact crystalline  forms,  with  dull  metallic  lustre,  and  are  then 
conductors  of  electricity ;  while  they  also  exist  in  forms  incapable 
of  conducting,  and  without  metallic  lustre.  Such  reasons  have 
led  to  the  abandonment  of  this  classification  here.  Still  the  name 
metal  has  generally  been  applied  in  this  book  to  those  elements 

G  2 


84  THE   ELEMENTS. 

which  are  usually  ranked  as  such  ;  though  it  is  to  be  understood  in 
a  loose,  colloquial  sense. 

It  will,  however,  be  convenient  to  give  a  list  of  non-metals,  so 
that  the  old  classification  may  be  understood. 

List  of  non-metals. — Hydrogen  (?),  boron,  carbon,  silicon, 
titanium  (?),  zirconium  (?),  nitrogen,  phosphorus,  vanadium  (?), 
arsenic  (?),  antimony  (?),  oxygen,  sulphur,  selenium,  tellurium  (?), 
fluorine,  chlorine,  bromine,  iodine. 

The  sign  (?)  denotes  that  these  elements  are  sometimes  in- 
cluded in,  sometimes  excluded  from,  the  class  of  non-metals.  The 
remaining  elements  are  classed  as  metals. 

(2.)  Sources. — As  a  general  rule,'  those  elements  are  found 
native  which  are  unaffected  by  oxygen  and  moisture  in  air  at  the 
ordinary  temperature.  Thus  carbon,  nitrogen,  sulphur,  selenium, 
tellurium,  the  platinum  group  of  metals,  and  copper,  silver, 
mercury,  and  gold  are  among  these.  It  is  curious  that  hydrogen 
is  not  found  native  to  any  great  extent,  for  it  fulfils  these  condi- 
tions. There  appears  no  reason  why  air  should  not  contain  small 
traces  of  hydrogen,  unless,  indeed,  its  molecular  motion  may  carry 
it  out  of  the  sphere  of  the  earth's  attraction.* 

Those  compounds  of  elements  with  the  halogens  which  are  not 
decomposed  by  water  as  a  rule  exist  native.  Among  these  are 
chlorides,  bromides,  and  iodides  of  sodium,  and  potassium ;  of 
silver,  lead,  and  mercury.  From  the  abundance  of  oxygen,  and 
the  tendency  which  most  elements  have  to  combine  with  it,  the 
oxides  and  double  oxides  are  the  most  widely  spread  compounds  : 
for  example,  the  silicates,  carbonates,  phosphates,  nitrates,  &c. 
The  sulphides  rank  next  in  order  of  distribution ;  only  those 
stable  in  presence  of  air  arid  water,  however,  occur  abundantly. 
It  is  indeed  probable  that  the  mass  of  the  earth  consists  largely 
of  sulphides;  for  the  specific  gravity  of  our  globe  has  been  found 
by  astronomical  measurements  to  be  5-J  times  that  of  water,  while 
the  average  specific  gravity  of  the  crust  cannot  well  exceed  3. 
It  appears  not  unlikely  that  the  greater  density  is  caused  by 
the  presence  of  the  denser  sulphides  in  the  interior;  and  the 
prevalence  of  sulphur  in  volcanic  districts,  where  the  interior  of 
the  earth  is  in  a  state  of  disturbance,  would  support  this  supposi- 
tion. Some  few  elements  occur  in  combination  with  arsenic  alone, 
or  with  arsenic  and  sulphur. 

3.  Preparation. — -It   will  have   been  noticed   that   there  are 

*  A  similar  theory  would  account  for  the  absence  of  an  atmosphere  on  the 
moon. 


GENERAL  REMARKS.  85 

three  general  methods  of  preparing  elements  from  their  com- 
pounds. These  are — 

(a.)  Electrolysis  of  a  liquid  compound  of  the  element  or 
of  a  solution  of  a  solid  compound  in  water. — It  is  question- 
able whether  solids  or  gases  can  be  electrolysed ;  at  all  events,  the 
constituents  cannot  be  conveniently  collected  ;  hence  the  limitation 
to  the  liquid  state.  It  appears  probable  that  no  perfectly  pure 
compound  is  capable  of  conducting  electricity ;  those  at  least,  such 
as  pure  water,  hydrogen  chloride,  &c.,  which  can  be  obtained 
nearly  pure  do  not  appear  to  do  so.  A  liquid  mixture,  however,  is 
almost  always  an  electrolyte,  i.e.,  capable  of  yielding  its  elements 
under  the  influence  of  a  current  of  electricity.  In  many  cases  no 
easily  fusible  compound  of  the  element  required  is  known,  or  it 
is  difficult  of  preparation,  or  it  does  not  conduct ;  in  other  cases 
the  liberated  element  acts  upon  water,  forming  an  oxide  and 
liberating  hydrogen  ;  hence  the  method  is  somewhat  limited. 

(b.)  Heating  a  compound  of  the  element  required. — It  is 
almost  certain  that  all  compounds,  if  heated  to  a  sufficiently  high 
temperature,  would  decompose  into  their  elements.  Bnt,  unless 
one  of  the  elements  possesses  a  much  lower  boiling-point  than  the 
others  with  which  it  is  combined,  separation  cannot  be  effected,  as 
a  rule,  for  in  most  instances  recombination  occurs  on  cooling.  It 
is  owing  to  the  great  difference  in  volatility  of  mercury  and 
oxygen  that  the  latter  can  be  prepared  by  heating  mercuric  oxide ; 
on  similar  grounds,  chlorine  can  be  prepared  from  gold  chloride ; 
or  sulphur,  by  heating  platinum  sulphide  or  hydrogen  sulphide. 
In  many  cases  only  a  portion  of  one  of  the  combined  elements  is 
evolved  as  gas,  as,  for  instance,  oxygen  from  manganese,  barium,  or 
lead  dioxides,  or  from  chromium  trioxide. 

(c.)  By  displacing  one  element  from  a  compound  by 
the  action  of  another. — This  method  is  very  largely  used. 
The  agents  of  displacement,  however,  are  limited  in  number.  It 
is  obviously  essential  to  the  success  of  the  process  that  the  element 
used  as  a  displacer  shall  not  combine  with  the  one  to  be  displaced ; 
or,  if  it  do  so  combine,  that  it  shall  be  easily  expelled  from  its  com- 
bination by  heat;  or  that  it  shall  combine  much  moro  readily 
with  one  of  the  elements  in  the  compound  acted  on  than  with  the 
other. 

Thus  no  metal  will  displace  phosphorus  or  oxyen  from  their 
compound,  phosphorus  pentoxide,  because  all  metals  combine  with 
phosphorus  and  oxygen.  Again,  aluminium  may  be  prepared  by 
removing  chlorine  from  its  chloride  by  the  action  of  sodium  ;  for 
the  compound  or  alloy  of  aluminium  and  sodium  which  is  doubt- 


86  .     THE  ELEMENTS. 

Jess  produced  is  easily  decomposed  by  heat  into  sodium,  which 
volatilises  away,  and  aluminium,  which  remains  non-volatile  at 
the  temperature  employed.  And  lastly,  sulphur  may  be  produced 
by  the  action  of  an  insufficient  quantity  of  oxygen  on  its  com- 
pound with  hydrogen;  for  hydrogen  combines  so  much  more 
readily  with  oxygen  than  sulphur  does  that  water  is  formed, 
little  of  the  sulphur  combining  with  the  oxygen;  and,  as  another 
instance,  carbon  is  liberated  from  its  compounds  with  hydrogen 
when  they  burn  in  chlorine  gas,  because  at  the  temperature  of 
reaction  the  chlorides  of  carbon  are  decomposed. 
In  practice  the  following  methods  are  used  : — 

1.  The  action  of  carbon  (coal,  charcoal)  on  the  oxide  of  the 
element,  or  on  its   compound  with  oxygen  and  hydrogen  (hydr- 
oxide), at  a  red  heat.    The  most  important  elements  thus  prepared 
are  I—- 
Hydrogen,   potassium,    rubidium ;    zinc,     cadmium ;    impure 

chromium,  iron,  manganese,  nickel  and  cobalt  (these  elements 
combine  with  a  small  quantity  of  the  carbon  employed  in  their 
liberation)  ;  germanium,  tin,  lead ;  phosphorus,  arsenic,  antimony, 
bismuth  ;  molybdenum,  tungsten  ;  copper.  In  many  cases  this  is 
in  reality  the  action  of  carbon  monoxide  on  the  oxide  of  the  ele- 
ment :  the  carbon  monoxide  unites  with  the  oxygen  combined  with 
the  element,  forming  carbon  dioxide,  and  the  element  is  liberated. 

2.  The  action  of   hydrogen  on  the   oxide  of  the   element 
required  at  a  red  heat.     Elements  which  may  be  thus   prepared 
are  : — Indium,   thallium,  tin,  lead  ;    nitrogen,    arsenic,    antimony, 
bismuth,  tungsten  ;  iron,  nickel,  cobalt,  and  copper. 

3.  The  action  of  hydrogen  on  the  chloride  of  the  element 
at  a  red  heat.  Examples  : — Vanadium,  niobium,  arsenic,  antimony, 
bismuth,  and  others. 

4.  The   action    of   sodium   or   potassium,   or    of    zinc,   on 
the  fused  chloride,   double  chloride,   or  double  fluoride   of   the 
element  required.      Examples  : — Magnesium,    boron,   aluminium, 
yttrium,    carbon,  titanium,  zirconium,  thorium,  tantalum,  chrom- 
ium, uranium. 

5.  The  action   of  another  element  on   the   solution  of  a 
compound  of  the  element  required.     Examples  : — Iodine  may  be 
prepared  by  the  action  of  chlorine  or  bromine  on  iodide  of  potas- 
sium ;  bromine,  by  the  action  of  chlorine  on  potassium  bromide  ; 
sulphur,  selenium,  or  tellurium,  by  the  action  of  atmospheric  oxygen 
on   a  solution  of  their  compounds  with  hydrogen;  copper,  by  the 
action  of  iron  on  a  solution  of  copper  chloride  or  sulphate  ;  mer- 
cury or  silver,  by  the  action  of  copper  on  a  solution  of  mercuric  or 


GENERAL  REMARKS.  87 

silver  nitrates ;  gallium,  by  the  action  of  zinc  on  a  solution  of 
gallium  chloride,  and  many  others. 

Properties. — The  elements,  like  other  forms  of  matter,  exist  in 
the  three  states  of  gas,  liquid,  and  solid.  Those  gaseous  at  the 
ordinary  temperature  are  hydrogen,  nitrogen,  oxygen,  fluorine, 
and  chlorine.  Two  are  liquid,  viz.,  bromine  and  mercury;  the 
remainder  are  solid. 

The  mass  of  one  cubic  centimetre  varies  from  0*0000896  gram 
in  the  case  of  hydrogen  gas  to  22*48  grams  in  the  case  of  osmium. 
The  variation  of  this  constant  with  atomic  weight  will  be  considered 
in  Chapter  XXXVI. 

The  atomic  weights  of  the  elements  vary  from  1  (hydrogen)  to 
240,  (uranium)  ;  and  their  specific  heats  from  5*4  (hydrogen  alloyed 
with  palladium)  to  0*0277  (uranium).  It  will  subsequently  be 
shown  that  the  product  of  the  two  is  usually  a  constant  number. 

It  cannot  be  doubted  that  many  elements  remain  to  be  dis- 
covered. On  referring  to  the  periodic  table  on  p.  '23,  it  will  be 
seen  that  many  atomic  weights  are  accompanied  by  queries  (?). 
Within  the  last  few  years  several  such  gaps  have  been  filled; 
notably  thallium  (Crookes),  gallium  (Lecoq  de  Boisbaudran), 
scandium  (Cleve),  and  germanium  (Winckler).  But  this  subject 
will  be  fully  considered  in  a  later  chapter. 


APPENDIX. 
Equations  expressing  the  preparation  of  elements  of  Groups  XIII  and  XVJ. 

Fluorine.— 2HF  =  H2  +  F2. 

Chlorine.— MnO2  +  4HC1  =  C12  +  MnCl2  + 
Bromine—  2KBr  +  C12  =  Br2  +  2KC1. 
Iodine.— 2KI  +  Br2  =  I2  +  2KBr. 
Copper.— CuO  +  C  =  Cu  +  CO. 

f  CuS  +  2O2  =  CuSO4. 

I  CuSO4  +  Fe  =  Cu  +•  FeSO4. 
CuS  +  2CuO  =  3Cu  +  SO2. 
Mercury.— HgS  +  O2  =  Hg  +  SO2. 
„.,  fAgoS  +  2XaCl  =  2AgCl  +  Na<S. 

Sllver--\2llc\  +  Fe  =  2Ag  ?  FeCL,   * 


88 


PART  III.— THE  HALIDES. 


CHAPTEK  VII. 

COMPOUNDS  : — NOMENCLATURE  AND  CLASSIFICATION  ; — THE  STATES  OF 
MATTER. — RELATION  OF  THE  VOLUME  OF  GASES  TO  PRESSURE  AND  TO 
TEMPERATURE. METHODS  OF  DETERMINING  DENSITY. 

Compounds  and  Mixtures. 

Elements  are  said  to  combine  when  on  bringing  them  together  a 
new  substance  is  produced,  differing  from  its  constituents  and  pos- 
sessing properties  which,  as  a  rule,  are  not  the  mean  of  their  pro- 
perties. Such  combination  is  always  attended  with  a  rise  or  fall  of 
temperature,  or  "  heat  change ;  "  and,  as  heat  is  a  form  of  energy, 
or  power  of  doing  work,  elements  either  gain  or  lose  energy  by 
combination  with  each  other.  It  appears  that  direct  combination 
is  always  attended  with  loss  of  energy,  heat  being  evolved.  This 
is  illustrated  by  the  combustion  of  carbon  in  oxygen,  of  antimony 
in  chlorine,  and  by  many  other  instances  ;  and  the  evolution  of 
heat  in  many  such  cases  is  so  great  as  to  raise  the  substance  to  the 
temperature  of  incandescence,  so  that  it  emits  light. 

Two  or  more  elements  may,  however,  be  mingled  without 
sensible  evolution  of  heat.  They  are  then  said  to  constitute  a 
mixture.  Atmospheric  air  is  an  instance  in  point.  On  mixing  its 
constituent  gases,  oxygen  and  nitrogen,  no  heat  change  takes  place. 
But  if  electric  sparks  be  passed  through  the  air,  its  constituents 
are  raised  to  a  high  temperature  and  combine ;  the  product  is  an 
oxide  of  nitrogen,  possessing  a  brown-red  colour  and  a  strong  smell. 
Certain  mixtures  are  thus  definitely  distinguished  from  compounds. 
But  in  many  cases  it  is  difficult  to  affirm  positively  that  an  element 
is  or  is  not  combined.  Some  metals  mix  freely  with  others,  as,  for 
example,  tin  and  lead ;  but  there  is  no  way  of  absolutely  testing 
whether  or  not  they  are  combined.  Another  instance  is  that  of  a 
solution  of  chlorine  in  bromine.  In  such  cases,  however,  the  pro- 


NOMENCLATURE.  89 

pcrties  of  the  mixture  are  apparently  the  mean  of  those  of  its 
constituents. 

The  best  criterion  of  a  compound  is  its  definite  composition. 
With  this  are  associated  definite  physical  properties,  such  as  con- 
stancy of  melting  point,  of  boiling  point,  and  of  crystalline  form. 
An  amorphous  condition,  i.e.,  lack  of  crystalline  form,  almost 
always  accompanies  indefinite  composition;  but,  on  the  other  hand, 
a  substance  may  possess  a  definite  crystalline  form  (as,  for  example, 
many  silicates),  and  yet  have  an  indefinite  composition.  Such 
bodies  are,  however,  usually  mixtures  of  compounds  with  each 
other. 

Nomenclature. — Chemical  nomenclature  in  its  present  form 
was  mainly  devised  by  Lavoisier,  and,  although  extended,  its  prin- 
ciple has  not  been  materially  modified  since  his  time,  •  But  even  he 
was  constrained  to  adopt  certain  expressions  which  had  been  in  use 
from  a  very  early  date,  such  as  "  base,"  "  acid,"  and  "  salt."  These 
terms  are  incapable  of  accurate  definition,  and  must  therefore  be 
used  loosely.  It  may  be  said  generally  that  the  word  base  is  applied 
to  the  oxides  of  certain  elements,  either  alone  or  in  combination  with 
hydrogen  oxide  (water)  ;  the  word  acid,  the  oxide  of  hydrogen  and 
certain  other  elements,  not  usually  those  of  which  the  oxides  are 
called  bases  ;  and  the  word  salt,  a  body  produced  by  the  interaction 
of  a  basic  oxide  with  an  acid  oxide.  The  words  salt  and  acid,  however, 
are  frequently  applied  to  substances  containing  no  oxygen,  such  as 
sodium  chloride,  or  hydrochloric  acid.  In  fact,  no  rule  can  be 
given,  and  the  words  must  be  employed  in  a  vague  sense,  custom 
alone  determining  their  use. 

A  compound  formed  by  the  union  of  two  elements  retains  the 
names  of  both,  one  of  them,  however,  acquiring  the  termination 
"  ide."  It  is  a  matter  of  indifference  which  receives  that  ending ;  but, 
as  most  compounds  which  have  been  investigated  contain  one  of 
ten  or  twelve  elements,  the  names  of  these  are  commonly  modified. 
Thus  we  speak  of  oxides,  sulphides,  selenides,  tellurides,  fluorides, 
chlorides,  bromides,  iodides,  nitrides,  phosphides,  arsenides,  borides, 
carbides,  and  silicides  ;  also  of  hydrides.  The  Greek  numeral  pre- 
fixes mono-,  di-,  tri-,  tetra-,  penta-,  and  the  Latin  one  sesqui-,  signi- 
fying respectively,  one,  two,  three,  four,  five,  and  one-and-a-half, 
are  employed,  when  required,  to  denote  the  relative  numbers  of 
atoms  in  the  compound. 

Many  compounds  of  fluorides,  chlorides,  bromides,  and  iodides 
with  each  other,  and  of  oxides  and  sulphides  with  chlorides,  &c., 
arejknown.  These  have  generally  been  named  double  chlorides, 
oxychlorides,  or  basic  chlorides,  sulphochlorides,  &c.  Another 


90  THE   HALIDES. 

nomenclature  is  sometimes  used.  It  is  as  follows ;  an  example 
will  render  it  plain.  Platinum  forms  two  compounds  with  chlorine, 
one  containing  twice  as  much  chlorine  as  the  other,  proportionately 
to  the  metal.  The  one  containing  least  chlorine  is  named  platinows 
chloride;  that  containing  most,  platimc  chloride.  Each  of  these 
forms  a  compound  with  potassium  chloride;  the  first  is  named 
potassium  platinochloride,  platino-  being  contracted  from  platinoids ; 
the  second  potassium  platinochloride,  the  word  platim- standing  for 
platim'c.  So  with  ferrous  and  ferric,  phosphorous  and  phos- 
phor^, &c. 

The  double  oxides  have  names  which  do  not  show  that  they 
contain  oxygen.  Thus  compounds  of  oxides  of  chlorine  and  of  a 
metal  are  named  hypochlorites  (hypo  =  below),  chlor^es,  chlorates 
or  perchlorat es  (per  =  over,  from  hyper^,  according  to  the  amount 
of  oxygen  in  combination  with  the  chlorine  ;  so  also  with  com- 
pounds of  nitrogen,  phosphorus,  sulphur,  gold,  &c.,  &c. 

In  the  case  of  a  few  common  substances,  such  as  water  (hydrogen 
monoxide),  ammonia  (hydrogen  nitride),  vitriol  (sulphuric  acid  or 
hydrogen  sulphate),  old  and  familiar  names  have  been  retained. 
These  are  fortunately  in  many  cases  becoming  obsolete. 

The  Elements 

Will  be  considered  in  the  following  order : — 

1.  Compounds  of  the  halogens — fluorine,  chlorine,  brom- 

ine, and  iodine — with  the  elements,  arranged  in 
groups  according  to  the  periodic  table,  including 
double  compounds. 

2.  Compounds  of  oxygen,  sulphur,  selenium,  and  tellur- 

ium with  the  elements;  including  oxychlorides, 
sulphoehlorides,  &c.,  and  double  oxides  and  sul- 
phides, usually  called  hydroxides,  hydrosulphides, 
acids,  and  salts. 

3.  Borides,  carbides,  silicides. 

4.  Nitrides,    phosphides,    arsenides,    and    antimonides. 

Double  compounds. 

5.  Alloys  and  amalgams. 

Before  proceeding  with  the  consideration  of  the  halogen  com- 
pounds it  is  necessary,  in  order  to  understand  the  relations  between 
thnse  substances,  to  study  the  methods  of  expressing  chemical  change, 
and  some  of  the  reasons  for  assigning  definite  atomic  weights  to 
the  elements.  This  involves  a  knowledge  of  the  nature  of  gases, 
and  their  behaviour  as  regards  temperature  and  pressure. 


THE   STATES   OP   MATTER.  91 

The  States  of  Matter. 

Matter  is  known  in  three  states  :  the  solid,  the  liquid,  and  the 
gaseous. 

Solids. — Solids  are  peculiar  in  possessing  form;  they  have 
rigidity,  enabling  them  to  keep  their  shape.  It  is  believed  that 
minute  particles  of  which  all  matter  consists,  which  are  named 
molecules,  are  so  closely  packed  together  in  solids  as  to  attract 
each  other  powerfully,  and  to  possess  very  little  freedom  of  motion. 
Such  particles  possess  symmetrical  arrangement  in  crystals;  but 
are  heaped  together  at  random  in  amorphous  solids.  Solids 
generally  expand  when  their  temperature  is  raised,  but  only  to  a 
small  degree.  At  a  sufficiently  high  temperature,  they  either 
melt,  volatilise  without  melting,  or  decompose.  They  are  very 
slightly  compressible. 

Liquids. — Liquids  differ  from  solids  in  not  possessing  form, 
and  from  gases  by  possessing  a  surface.  The  condition  of  the 
liquid  matter  at  the  surface  differs  from  that  in  the  interior,  and 
the  surface  is  under  a  lateral  strain,  named  surface-tension.  A 
drop,  for  example,  behaves  as  if  it  were  covered  with  a  stretched 
skin  or  film.  The  molecules  of  which  liquids  consist  possess 
greater  freedom  of  motion  than  do  those  of  solids ;  so  that  they 
move  about,  continually  gliding  past  each  other,  and  hence  a  liquid 
has  no  fixity  of  form.  On  raising  the  temperature  of  a  liquid,  this 
motion  increases.  The  motion  of  the  molecules  of  a  liquid  is  termed 
diffusion  or  osmosis.  When  liquids  are  cooled  they  generally  con- 
tract, and  at  a  sufficiently  low  temperature  they  freeze,  or  turn  to 
s«  >lids ;  on  raising  their  temperature  they  expand,  and  at  a  suffi- 
ciently high  temperature  they  volatilise,  changing  into  gas. 
Vapour  is  continually  being  evolved  from  the  surface  of  a  liquid, 
and  if  the  liquid  be  in  a  closed  vessel  the  pressure  which  its 
vapour  exerts  can  be  measured.  This  pressure  is  termed  its 
vapour-pressure.  The  vapour-pressure  increases  with  rise  of  tem- 
perature ;  and  when  it  exceeds  the  pressure  of  the  atmosphere  the 
liquid  boils  and  changes  wholly  into  gas,  if  heat  be  supplied  in 
sufficient  amount. 

Gases. — Gases  or  vapours  have  neither  form  nor  surface.  A 
solid  or  a  liquid  in  changing  into  vapour  acquires  a  greatly  increased 
volume  ;  thus  the  gas  of  water  occupies  about  1700  times  the  space 
occupied  by  its  own  weight  of  liquid  water  at  the  same  tempera- 
ture and  at  the  same  pressure,  viz.,  100°  and  760  mm.  pressure. 
While  solids  and  liquids  are  but  slightly  altered  in  volume  by 
alteration  of  pressure  and  temperature,  the  volumes  of  gases  are 


92  THE   HALTDES. 

greatly  changed.  The  molecules  of  gases  are  evidently  much 
more  distant  from  one  another  than  those  of  solids  or  liquids,  and 
therefore  possess  much  greater  freedom  for  motion,  or  free  path. 
They  occupy  but  a  small  portion  of  the  space  which  they  inhabit. 
And  while  the  molecules  of  solids  and  of  liquids  are  so  near  each 
other  as  to  exercise  great  attraction  on  one  another,  those  of  gases 
are  so  far  apart  that  the  attraction  is  barely  sensible.  Hence 
gases  exhibit  simple  relations  to  temperature  and  pressure. 

Relation  between  the  volume  of  a  gas  and  the  pressure 
to  which  it  is  exposed. — Boyle's  law.  The  temperature  of 
a  gas  being  kept  constant,  its  volume  varies  inversely  as 
the  pressure  to  which  it  is  exposed.  This  law  was  discovered 
by  Robert  Boyle  in  1660. 

The  barometer. — It  has  been  remarked  in  Chapter  II  that  gases 
have  weight;  the  weight  of  a  given  quantity  of  matter  is  not 
changed  by  change  of  state :  thus  a  pound  of  water  weighs  a 
pound,  whether  it  be  ice,  water,  or  steam.  Air,  which  is  a  mixture 
of  nitrogen  and  oxygen  gases,  therefore  possesses  weight ;  and,  the 
longer  or  higher  a  column  of  air,  the  greater  its  weight.  A  column 
of  air  reaching  to  the  upper  confines  of  the  atmosphere  and  rest- 
ing on  the  earth  at  the  level  of  the  sea,  of  1  square  centimetre 
in  section,  weighs  on  the  average  1033  grams  ;  or,  if  1  square 
inch  in  section,  about  16  Ibs.  ;  but  1033  grams  is  the  weight  of 
a  column  of  mercury  at  0°  of  1  square  centimetre  in  sectional 
area  and  760  millimetres  in  length ;  and  16  Ibs.  is  the  approxi- 
mate weight  of  a  mercury  column  1  square  inch  in  sectional  area 
and  approximately  30  inches  long ;  or  of  a  column  of  water  about 
33  feet  in  length,  also  1  square  inch  in  sectional  area.  Hence,  if  it 
were  possible  to  support  the  end  of  such  a  column  of  air  on  one 
pan  of  a  balance,  and  to  place  on  the  other  pan  a  column  of 
mercury  760  millimetres  in  length,  removing  the  pressure  of  the 
air  from  its  upper  surface  (else  the  weight  of  both  air  and  mer- 
cury would  press  on  the  other  pan),  the  two  columns  would 
balance.  Such  an  operation  is  actually  performed  in  construct- 
ing a  barometer.  The  air  is  removed  from  the  upper  portion 
of  a  glass  tube,  the  lower  end  of  which  is  open  and  dips  in  mer- 
cury ;  and  the  mercury  rises  in  the  tube  until  it  balances  a  column 
of  air  of  equal  sectional  area  to  the  tube,  rising,  in  order  that  it 
may  do  so,  to  a  height  of  760  millimetres.  If  the  weight  of  the 
atmosphere  increases,  owing  to  its  cooling,  or  to  its  compression, 
the  column  of  mercury  rises  proportionately,  so  as  to  balance  it; 
and,  conversely,  when  the  weight  of  the  atmosphere  decreases,  the 


BOYLE  S   LAW. 


93 


balancing  column  is  shorter.  The  pressure  of  the  atmosphere 
might  be  expressed  in  units  of  weight  for  a  given  sectional  area, 
say,  1  square  centimetre;  it  might  be,  and  indeed  sometimes  is, 
measured  in  fractions  or  multiples  of  1033  grams,  just  as  it  is 
the  custom  for  engineers  to  express  the  steam  pressure  in  a  boiler, 
which  is  closely  analogous,  in  pounds  on  the  square  inch  of 
boiler  surface ;  but  it  is  commonly  expressed  as  equal  to  the  pres- 
sure of  760  millimetres  of  mercury,  or  of  a  column  of  greater  or 
less  length,  according  as  the  weight  of  the  atmosphere  varies. 

All  gases  contained  in  vessels  communicating  with  the  atmo- 
sphere are  therefore  under  this  pressure ;  hence  it  must  be  allowed 
for  in  ascertaining  the  relation  between  the  volume  of  a  gas  and 
the  pressure.  That  Boyle's  law  is  approximately  true  can  be 
proved  by  the  following  experiment: — A  U'ttl^e»  as  shown  in 
no-.  16,  about  50  centimetres  in  length,  contains  air  in  its  closed 


FIG.  16. 

limb.  The  amount  of  air  is  adjusted  so  that  when  the  mercury 
is  level  in  both  limbs  it  occupies  a  volume  represented  by 
273  millimetres  -f-  a  number  of  millimetres  equal  to  the  tem- 
perature of  the  day.  Thus,  for  example,  if  the  temperature  of 
the  surrounding  atmosphere  is  15°  C.,  the  length  of  the  column 
of  air  enclosed  should  be  288  millimetres.  The  reason  of  this 
adjustment  will  appear  later.  Now  mercury  is  poured  into  the 


94  THE   HALIDES. 


open  limb  of  the  U'^u^e  so  as  nearly  to  fill  it;  the  difference  in 
level  of  the  mercury  in  the  open  and  in  the  closed  limb  is  read 
off.  The  air  in  the  closed  limb  will  be  compressed  by  the  weight 
of  the  mercury  in  the  open  limb,  the  column  being  equal  in  length 
to  the  difference  in  level  of  the  mercury  in  the  open  and  in  the 
closed  limb.  For  example  :  — 

Distance  from  top  of  tube  to  surface  of  mercury, 

that  in  both  limbs  being  at  the  same  level.  .  288  mm, 

Level  of  mercury  in  open  limb,  after  filling  it.  .          0      „ 

Level  of  mercury  in  closed  limb,  after  filling 

open  limb  ............................  223  „ 

Difference  in  level  between  mercury  in  closed 

and  open  limbs  ........................  223  „ 

The  initial  volume  of  the  gas  was  288  X  x  cubic  centimetres. 

After  compression  the  volume  decreased  to  223  X  x  cubic 
centimetres. 

The  initial  pressure  was  that  of  the  atmosphere,  say,  760  milli- 
metres.* 

The  final  pressure  on  the  gas  was  that  of  the  atmosphere. 
760  millimetres  +  223  millimetres  =  983  millimetres  of  mercury. 

But     983  :   760   ::  288a?   :   223#,  nearly. 

Hence  the  volume  of  the  gas  decreases  proportionately  to  the  in- 
crease of  pressure  at  a  temperature  of  15°. 

If  plt  p2,  v},  and  v2  represent  the  pressures  and  volumes  respec- 
tively before  and  after  alteration,  then 

p&i  =  p-2,v^  provided  temperature  be  kept  constant. 
Similar  experiments  may  be  performed,  decreasing  the  amount 
of  mercury  in  the  U^^e,  by  running  out  mercury  through  the 
stopcock,  and  so  reducing  the  pressure  on  the  gas  ;  and  Boyle's 
law  may  thus  be  proved  true  for  such  small  alterations  of  pres- 
sure. When  the  pressure  is  very  great,  it  ceases  to  hold  :  gases 
become  more  compressible  up  to  a  certain  point,  and  then  less 
compressible  with  greater  rise  of  pressure. 

Gay-Lussac's  law.  —  The  volume  of  a  gas  increases  one 
two  hundred  and  seventy-third  of  its  volume  at  0°  (0-00367) 
for  each  rise  of  1°  C.,  provided  pressure  remain  constant. 
Thus  1  cubic  centimetre  of  air  or  other  gas  measured  at  0°  becomes, 
when  heated  to  1°,  1-^  or  1'00367  c.c.  ;  at  2°,  l-^fg-,  or  1  +  (0*00367 

*  The  barometer  should  be  read  at  the  time,  and  its  height  substituted  here. 
In  the  above  instance  it  is  supposed  to  be  at  its  normal  height. 


GAY-LUSSAC'S   LAW. 


95 


X  2)  ;  at  100°,  Hf§,  or  1  +  (O00367  x  100).  This  can  be  illus- 
trated by  means  of  the  apparatus  used  for  demonstrating  Boyle's 
law,  with  a  slight  addition  to  allow  of  an  alteration  in  the  tem- 
perature of  the  gas.  The  closed  limb  of  the  U'^u^e  ig  sur- 
rounded  by  a  jacket  or  mantle  of  glass,  the  lower  part  of  which 
is  closed  by  an  indiarubber  cork,  perforated  to  allow  the  limb 
of  the  U'tuke  to  Pasa  through.  The  liquid  in  the  bulb  is 
water.  It  is  boiled  by  a  flame,  and  the  steam  jackets  the 


FIG.  17. 

U-tu.be,  raising  its  temperature  to  100°,  provided  the  atmo- 
spheric pressure  is  760  millimetres.  If  the  pressure  does  not 
differ  much  from  the  normal  one,  the  difference  in  temperature 
may  be  neglected.  At  15°,  supposed  to  be  the  atmospheric  tem- 
perature of  the  day,  the  air  in  the  closed  limb  of  the  U-tu^e 
is  adjusted  so  as  to  occupy  288  millimetres  of  the  tube's 
length,  measured  from  the  top  downwards,  the  mercury  in  both 
limbs  being  level.  On  boiling  the  water  so  as  to  raise  the  tem- 
perature of  the  gas  to  100°,  the  gas  will  expand,  pushing  down 


I 

96  THE   HALIDES. 

the  mercury  in.  its  own  limb,  and  raising  it  in  the  other.  When 
the  level  is  stationary,  mercury  is  run  out  of  the  \J  -tube,  so  as 
to  restore  equal  level  in  both  limbs.  The  gas  will  then  occupy 
373  millimetres  of  the  length  of  the  U-tube.  Thus  : 

Initial  volume  of  gas  at  15°,  at  atmospheric  pressure,  2SSx  c.c. 
Final  volume  of  gas  at  100°,  and  at         „  „          373#    „ 

Expansion,  373#  —  28&c  =  85*  c.c. 
Rise  of  temperature,  100°  —  15°  =  85°. 

The  expansion  is  thus  seen  to  be  proportional  to  the  rise  of 
temperature. 

It  is  obvious  that  by  cooling  the  gas  to  0°,  by  surrounding  the 
tube  with  melting  ice,  the  volume  would  contract  from  288x  c.c.  to 
273.K  c.c.  This  may  also  be  proved  experimentally.  It  may  also 
be  -shown  that  Boyle's  law  holds  equally  well  at  the  temperature 
100°  as  at  15°  by  means  of  this  apparatus. 

Such  an  instrument  might  be,  and  indeed  with  altered  con- 
struction is,  used  as  a  thermometer.  It  would-  be  convenient  to 
place  the  number  273°  at  the  level  of  the  mercury  when  ice  sur- 
rounds the  tube ;  then  the  expansion  of  the  gas  and  the  tempera- 
ture will  march  pari  passu.  The  zero  of  such  a  scale  will  mani- 
festly be  at  the  top  of  the  tube ;  the  degrees  are  ordinary 
Centigrade  degrees,  the  interval  of  temperature  between  the 
melting-point  of  ice  and  the  boiling-point  of  water  under  normal 
pressure  being  100°;  but  on  this  scale  the  former  is  marked  273° 
and  the  latter  373°.  Such  a  scale  is  termed  the  absolute  scale; 
and  the  temperature  —273°  C.  is  equal  to  0°  absolute. 

As  this  behaviour  with  respect  to  pressure  and  temperature  is 
common,  speaking  approximately,  to  all  gases,  it  may  be  con- 
jectured that  they  possess  some  property  in  common,  as  the  cause 
of  their  similar  changes.  This  property  was  discovered  in  1811 
by  Avogadro,  and  is  known  as — 

Avogadro's  law. — Equal  volumes  of  gases,  under  the 
same  pressure,  and  at  the  same  temperature,  contain  equal 
numbers  of  molecules.  It  must  be  noted  that  this  state- 
ment postulates  nothing  as  regards  the  actual  size  of  the  gaseous 
molecules ;  it  merely  asserts  that,  temperature  and  pressure  being 
constant,  a  definite  number  of  molecules  of  one  gas,  say,  hydrogen, 
inhabit  the  same  space  as  the'  same  number  of  molecules  of  any 
other  gas,  say,  oxygen  or  chlorine.  The  actual  number  of  mole- 
cules is,  of  course,  unknown  ;  and,  although  attempts  to  estimate  it 
have  been  made,  they  do  not  concern  us  here.  From  the  known 


METHODS    OF   DETERMINING   THE   DENSITY   OF   GASES.          97 

laws  of  expansion  of  gases,  and  their  relation  towards  pressure,  it 
is  possible  to  compare  the  weights  of  equal  volumes  of  different 
gases,  and  so  to  compare  the  relative  weights  of  the  molecules  of 
which  they  are  composed  ;  for  it  is  obvious  that  if  the  weight  of 
n  molecules  of,  say,  oxygen  is  16  times  that  of  n  molecules  of 
hydrogen  at  some  temperature  and  pressure  the  same  for  both,  the 
weight  of  1  molecule  of  oxygen  is  16  times  that  of  1  molecule  of 
hydrogen. 

It  is,  therefore,  exceedingly  important  to  be  able  to  compare 
the  relative  weights  of  gases,  inasmuch  as  it  affords  a  simple 
means  of  comparing  the  relative  weights  of  their  molecules. 
The  term  density  is  applied  to  the  weight  of  a  gas  relative  to 
hydrogen,  the  density  of  which  is  arbitrarily  placed  =  1.  Some- 
times air  is  chosen  as  the  unit  of  comparison.  The  absurdity  of 
this  is  evident ;  for  it  has  been  repeatedly  shown  that  the  composi- 
tion, and  hence  the  density,  of  air,  which  is  a  chance  mixture  of  the 
gases  oxygen  and  nitrogen,  is  not  uniform,  but  varies  within  small 
limits.  The  variation,  however,  is  so  small  as  to  be  within  the 
usual  errors  of  experiment  in  determining  the  density  of  gases ; 
hence,  for  practical  purposes,  as  air  is  about  14*47  times  as  heavy  as 
hydrogen,  densities  compared  with  air  may  be  converted  to  the 
hydrogen  standard  by  multiplying  the  number  expressing  them  by 
14'47.  The  density  of  a  gas  which  exists  as  a  liquid  at  ordinary 
atmospheric  temperature  is  termed  a  vapour-density ;  there  is  no 
real  distinction  between  the  words  gas  and  vapour. 


Methods  of  determining  the  Density  of  Gases. 

1.  When  the  substance  is  a  gas  at  the  temperature  of  the 
atmosphere. — Two  globes  of  nearly  equal  capacity  (half  a  litre  to 
five  litres,  and  which  should  have  as  nearly  as  possible  the  same 
weight),  provided  with  tight-fitting  stop-cocks,  are  pumped  empty, 
first  by  means  of  a  water-pump,  and  finally  with  a  Sprengel's  or 
other  mercury-pump ;  the  stop-cocks  are  then  closed,  and  they 
are  suspended  one  from  each  arm  of  a  balance,  as  shown  in  fig.  18, 
and  if  not  quite  equal  in  weight,  counterpoised  by  addition  of 
weights  to  one  or  other  pan.  The  gas  to  be  weighed,  is  then 
admitted  from  a  gas-holder  into  one  of  the  globes,  care  being  taken 
to  dry  it,  by  passing  it  slowly  through  \J  -tubes  filled  with  strong 
sulphuric  acid  or  phosphorus  pentoxide,  which  has  a  great  ten- 
dency to  combine  with  water,  and  so  removes  it  from  the  gas.  If 
the  gas  be  soluble  in  water,  it  may  be  passed  straight  from  the 


98 


THE   HALIDES. 


generating  flask  through  the  drying  tubes  "into  the  empty  globe, 
the  stop-cock  of  the  latter  being  opened  slowly  so  as  to  ensure  the 
gas  being  thoroughly  dried.  It  is  again  suspended  from  the  hook  of 
the  balance  pan,  and  after  some  hours,  the  amount  of  gas  which  has 
entered  is  weighed.  The  volume  of  the  globe  is  then  ascertained 


Fia.  18. 

by  filling  it  completely  with  water  and  weighing  it.  The  difference 
between  the  weight  of  the  vacuous  globe  and  the  globe  full  of 
water  gives  the  weight  of  water  tilling  the  globe.  It  is  sufficient 
for  the  present  purpose  to  consider  that  1  gram  of  water  occupies 
1  cubic  centimetre,  though  for  accurate  determinations  the  true 
volume  of  the  water  at  4°  must  be  calculated.  Here,  also,  the 
expansion  of  the  globe  between  0°  and  atmospheric  temperature, 
and  also  its  diminution  of  volume  when  empty  of  air,  due  to  the 
presence  of  the  atmosphere,  have  been  neglected. 
We  have  accordingly  the  data. 

Weight  of  globe  full  of  gas  at  T°  temp.,  and 

P  mm.  pressure W2  grams. 

Weight  of  empty  globe Wl       „ 

Weight  of  V  cub.  centimetres  of  gas  ......      W  grams. 

From,  this  the  volume  of  1  litre  of  the  gas  at  0°  and  760  milli- 
metres pressure  can  be  calculated  thus  : 

(a.)   To  ascertain  the  volume  of  the    gas  at  760  millimetres 
pressure, 


DUMAS'  METHOD.  99 

Law. — The  volume  is  inversely  as  the  pressure.     Hence, 
Y760  =  VP  x  P/760. 

(6.)   To  ascertain  the  volume,  corrected  for  pressure,  at  0°C. 
Law. — The  volume  of  a  gas  increases  by  0*00367  of  its  volume  at 
0°  for  each  rise  of  1°.     Hence, 

v  VP  x  P/760 

"  1  +  (0-00367  x  T). 

(c.)  This  volume  of  gas  weighed  W  grams.  To  find  the  weight 
of  1  litre  :  WIOOo  c.c.  =  1000  W/V0o  and  760  mra. 

(d.)  From  Regnault's  very  accurate  experiments  we  learn  that 
1000  cubic  centimetres  of  hydrogen  weigh  0'0896  gram.  Hence, 
the  density  of  the  gas  =  W100o  c.c.  /0'0896. 

The  relative  weight  of  a  molecule  of  hydrogen  is  taken  as  2, 
for  reasons  which  will  afterwards  be  considered  (p.  109).  Hence, 
the  relative  weight  of  a  molecule,  or  the  molecular  weight  of  the 
gas  =  2Wmoo  c.c./0"0896,  or  is  equal  to  twice  its  density. 

2.  When  the  substance  becomes  gaseous  at  a  tempera- 
ture higher  than  that  of  the  atmosphere. — One  of  the  follow- 
ing methods  may  be  employed. 

(a.)  Dumas'  Method.— This  method  differs  from  the  method 
already  described  only  in  one  particular,  viz.,  in  the  manner  of 
filling  the  globe.  The  globe  usually  has  a  capacity  of  250  to 
500  cubic  centimetres.  About  10  cubic  centimetres  of  the  liquid 
or  solid,  of  which  the  density  in  the  gaseous  state  is  required,  is 
introduced  into  the  globe  by  warming  it  gently  so  as  to  expel  air, 
and  dipping  the  thin  neck  of  the  globe  into  the  liquid ;  or  by 
introducing  the  solid  into  the  globe  before  its  neck  is  drawn  out. 
It  is  then  placed  in  a  bath  of  some  liquid  or  vapour,  depending  on 
the  temperature  required.  If  the  boiling-point  is  below  100°, 
water  may  be  used  ;  if  between  100°  a,nd  250°,  olive  or  castor-oil ; 
and  vapour-baths,  such  as  that  of  boiling  mercury  (358°),  or 
sulphur  (444°),  or  phosphorus  pentasulphide,  or  stannous  chloride, 
or  even  the  vapours  of  boiling  cadmium  or  zinc,  may  be  used  for 
higher  temperatures,  but  with  the  last  two  the  globe  must  be  a 
porcelain  one,  for  glass  softens  at  about  700°.  The  liquid  or  solid 
begins  to  evaporate,  and  its  vapour  displaces  the  air  from  the 
globe.  As  soon  as  vapour  ceases  to  escape,  the  drawn-out  end  of 
the  neck  of  the  globe  is  sealed  by  means  of  a  hand- blowpipe,  or  of 
an  oxy hydrogen  blowpipe,  if  a  porcelain  globe  is  used  (see  fig.  1 9) . 
The  globe  is  then  removed,  allowed  to  cool,  cleaned,  and  weighed, 
balancing  it,  as  before,  by  a  similar  globe  hung  from  the  other  pan 

H  2 


100 


THE    HALIDES. 


of  the  balance.  The  calculations  are  performed  exactly  as  before, 
but  the  expansion  of  the  globe  must  here  be  allowed  for ;  if  of 
glass,  it  may  be  calculated  as  V  +  (0'000025tf)  ;  it  is  assumed  that 
the  gas  will  remain  a  gas  when  cooled  to  0°.  It  would  be  more 


FIG.  19. 

rational  to  compare  the  weight  of  the  gas  with  that  of  an  equal 
volume  of  hydrogen  at  the  same  temperature  and  pressure  as 
those  of  the  vapour  at  the  time  of  sealing  the  globe,  but  the  end 
result  is  the  same  whichever  method  of  calculation  be  used. 

(6.)  Hofmaim's  Method,  modified. — The  principle  of  this 
method  is  to  ascertain  the  volume  of  a  known  weight  of  the  gas.  The 
apparatus  consists  of  a  graduated  tube  of  the  form  shown  in  fig.  20. 
The  tube  is  filled  with  mercury  and  inverted  into  a  glass  basin 
containing  mercury,  and  after  the  jacketing  tube  has  been  put  on, 
the  apparatus  is  clamped  in  a  vertical  position.  The  graduated 
tube  passes  through  a  wide  hole  in  an  indiarubber  cork  fitting  the 
jacket ;  but  as  this  cork  is  apt  to  be  attacked  by  the  boiling 
liquid,  a  little  mercury  is  poured  in,  so  as  to  cover  and  protect) 
it.  The  substance  is  weighed  out  in  a  small  bulb,  and  pushed 
under  the  open  end  of  the  tube,  so  that  it  floats  up  to  the  surface  of 
the  mercury  in  the  closed  end.  The  temperature  is  then  raised  by 
boiling  the  liquid,  which  must  be  pure,  in  the  bulb  of  the  jacket. 


HOFMANN'S  METHOD,  MODIFIED. 


101 


FIG.  20. 

The  following  is  a  list  of  convenient  substances,  -with  their  respe  - 
tive  boiling  points  under  a  pressure  of  760  millimetres  :•*— 

T.  A. 

Carbon  disulphide.      46'2°  25 

Alcohol 78-3°  30 

Chlorobenzene 132'1°  25 

Bromobeuzene. .        156'1°  20 


T. 

Aniline 184'5° 

Chinoline 237'5° 

Bromonaphthalene     280'4° 


A 

20 
17 
16 


The  column,  A,  represents  the  average  difference  in  pressure  in 
millimetres  per  degree  at  about  the  pressure  760  millimetres. 
Thus,  if  the  height  of  the  barometer  is  740  millimetres,  i.e., 
20  millimetres  less  than  760,  the  temperature  of  the  carbon  di- 
sulphide vapour  will  be  not  46'2°,  but  46'2°  —  f£ths  of  1°  =  45'4°. 
The  mercury  in  the  tube  will  be  displaced  by  the  vapour,  and 
will  enter  the  glass  basin  in  which  the  tube  stands.  The  volume 


102  THE   HALIDES. 

of  the  vapour  is  then  read  off,  if  the  tube  is  a  graduated  one ;  if 
not,  the  level  of  the  mercury  in  the  tube  is  read  on  the  graduated 
scale,  and  also  the  level  of  the  top  of  the  tube.  The  volume  may 
be  afterwards  determined,  by  inverting  the  tube,  and  filling  it  to 
the  required  height  with  water  from  a  burette.  The  pressure  is 
that  of  the  atmosphere,  diminished  by  the  length  of  the  column  of 
mercury  in  the  tube.  But  mercury  itself,  when  heated,  expands, 
and  a  correction  must  be  introduced,  because  at  0°  the  length  of 
the  mercury  column  would  be  less.  Again,  the  gas  in  the  tube 
consists  partly  of  mercury  vapour ;  its  pressure  must  be  calculated 
and  subtracted.*  But  neglecting  these  corrections,  the  plan  of  cal- 
culation is  as  follows  : — 

A  certain  volume  of  gas,  V,  has  been  produced  from  a  known 
weight  of  liquid  or  solid,  W.  This  gas  is  at  the  temperature  of 
the  jacketing  vapour,  and  under  atmospheric  pressure  diminished 
by  the  length  of  the  column  of  mercury,  equal  to  the  distance 
between  the  level  of  mercury  in  the  glass  basin  and  that  in  the 
tube.  The  weight  of  an  equal  volume  of  hydrogen  at  the  same 
temperature  and  pressure  is  calculated,  and  the  weight  of  the 
vapour  is  divided  by  the  weight  of  the  hydrogen.  The  quotient  is 
the  density. 

(c.)  Victor  Meyer's  Method.— In  this  case  not  mercury  but 
air  (or  some  other  gas)  is  displaced ;  and  the  volume  of  a  known 
weight  of  the  vapour  is  deduced  from  that  of  the  displaced  gas,  or 
air.  A  cylindrical  bulb,  c  (fig.  21),  with  a  long  stem,  6,  closed  by 
a  cork  at  its  upper  extremity,  as  shown  in  the  figure,  is  heated  to 
some  constant  temperature  by  an  oil-  or  vapour-bath,  as  already 
described.  The  air  expands  while  the  temperature  is  rising,  and 
issues  through  the  side  tube,  d,  escaping  in  bubbles  through  the 
water  in  the  trough.  When  bubbles  cease  to  rise  the  temperature 
is  assumed  to  be  constant.  The  tube  is  quickly  uncorked,  a  small 
tube,  full  of  the  liquid  or  solid  whose  vapour- density  is  sought,  is 
dropped  in,  falling  on  sand,  placed  at  the  bottom  of  the  cylinder, 
so  as  to  avoid  breaking  it.  The  cork  is  then  rapidly  replaced. 
The  substance  turns  to  gas,  and  expels  air  from  the  cylindrical 
bulb.  This  air  is  cooled  in  passing  up  the  stem  and  through 

*  The  following  data  are  available  for  this  calculation : — 

Temperature 46°         78°        132°       156°       184°       237°      280° 

Expansion  of  1  c.c.  of 

mercury  between  0° 

and  t° 1  -0083  1  '0141  1  '0240  1  '0285  1  '0338  1  '0438  1  '0521 

Vapour  -  pressure     of 

mercury,  in  mm.  ..  0 '1         1 '0         3 '0       10 '0       52  "5      157'0 


VICTOR  MEYER'S  METHOD. 


103 


the  water;  it  is  collected  in  a  graduated  tube.  Its  volume  is 
equal  to  that  of  the  vapour,  supposing  the  latter  to  have  been 
cooled  to  the  atmospheric  temperature,  and  to  have  withstood  the 
process  without  condensing.  We  have  then  a  given  volume  of 
air  at  atmospheric  temperature  and  pressure  corresponding  to  that 
of  the  vapour ;  and  also  the  weight  of  substance  which  has  pro- 
duced the  vapour  by  which  the  air  has  been  expelled.  From  these 
data  it  will  be  seen  the  density  of  the  vapour  may  be  calculated. 

Such  are  the  available  means  of  ascertaining  the  weights  of 
one  litre  of  various  gases  and  their  densities.  The  processes  have 
been  described  in  some  detail,  because  such  determinations  have 
the  utmost  chemical  importance.  The  deductions  to  be  drawn 
from  them  will  appear  in  the  next  chapter. 


FIG.  21. 


104 


CHAPTEE  VIII. 

COMPOUNDS  OF  THE  HALOGENS  WITH  HYDROGEN,  LITHIUM,  SODIUM, 
POTASSIUM,  RUBIDIUM,  CESIUM,  AND  AMMONIUM.  ATOMS  AND 
MOLECULES  :  FORMULA  AND  EQUATIONS. 

Hydrogen  Fluoride,  Chloride,  Bromide,  and 
Iodide. 

Only  one  compound  of  each  of  these  elements  with  hydrogen 
is  known. 

Sources. — Hydrogen  chloride  is  present  in  the  atmosphere  in 
the  neighbourhood  of  volcanoes ;  it  has  been  doubtless  formed  by 
the  action  of  steam  on  certain  chlorides,  easily  decomposed  by 
water  into  oxide  of  the  element  and  hydrogen  chloride.  The 
others  do  not  exist  free. 

Preparation. — 1.  By  direct  union,  («.)  Hydrogen  Fluo- 
ride.— During  the  preparation  of  fluorine  by  Moissan,  by  the 
electrolysis  of  hydrogen  potassium  fluoride,  hydrogen  was  liberated 
from  the  negative,  and  fluorine  from  the  positive  pole  (see  p.  73). 
When  a  bubble  of  hydrogen  escaped  round  the  bend  of  the 
U-tube,  and  mixed  with  the  fluorine,  an  explosion  was  heard, 
showing  that  these  two  elements  unite  at  the  ordinary  tempera- 
ture, and  in  the  dark. 

(6.)  Hydrogen  Chloride. — Equal  volumes  of  hydrogen  and 
chlorine  gas  unite  directly  on  exposure  to  violet  light,  or  on 
application  of  heat.  This  may  be  shown  as  follows  : — 

A  tube  of  the  form  shown  in  fig.  22  is  employed.  The  stop- 
cock in  the  middle  divides  it  equally  into  two  halves.  The  stop- 
cock in  the  middle  being  shut,  one  side  is  filled  with  dry  chlorine 
by  downward  displacement,  a  capillary  tube  serving  to  conduct 
the  chlorine  gas  to  the  lower  closed  end,  as  shown  in  the  figure. 
The  stop-cock  is  then  closed.  The  other  half  of  the  tube  is  then 
filled  with  dry  hydrogen  by  upward  displacement,  for  hydrogen  is 
lighter,  though  chlorine  is  heavier,  than  air.  The  tube  is  then 
placed  in  a  dark  place,  for  example,  a  close  fitting  drawer,  for 
some  hours,  the  stop-cock  in  the  middle  being  opened.  The  two 
gases  will  mix,  but  will  not  combine.  It  is  then  placed  for  an 
instant  in  direct  sunlight,  or,  if  that  is  not  available,  illumined  by 


HYDROGEN   CHLORIDE.  105 

burning  a  piece  of  magnesium  ribbon  within  a  few  inches  of  it.    A 
flash  will  be  seen  inside  the  tube,  showing  that  combination  has 


FIG.  22. 

taken  place,  and  the  green  colour  of  the  chlorine  will  disappear. 
It  is  safer,  however,  to  expose  the  tnbe  for  some  hours  to  diffuse 
daylight.  One  end  of  the  tube  is  now  dipped  in  mercury,  and  the 
lower  stop-cock  is  opened.  The  mercury  does  not  enter  the  tube, 
showing  that  the  hydrogen  chloride  retains  the  same  volume  as  its 
constituents;  it  does  not  act  on  mercury.  The  stop-cock  is  again 
closed,  and  the  lower  end  of  the  tube  is  now  dipped  in  water,  and 
the  stop-cock  again  opened.  The  water  rushes  in,  and  completely 
fills  the  tube,  provided  both  compartments  were  exactly  equal,  and 
that  all  air  was  displaced  on  filling  it  with  chlorine  and  hydrogen. 
Chlorine  is  sparingly  soluble  in  water,  hydrogen  nearly  insoluble. 
Hence  a  gas  has  been  produced  by  the  combination  of  equal 
volumes  of  hydrogen  and  chlorine,  which  occupies  the  same 
volume  as  its  two  constituents,  but  which  differs  from  them  in 
properties. 

A  jet  of  hydrogen  gas  may  be  burned  in  a  jar  of  chlorine.  The 
hydrogen  is  lit,  and,  while  burning  in  the  air,  a  jar  of  chlorine  is 
brought  under  it,  and  raised  so  that  the  jet  dips  into  the  chlorine. 


106  THE    HALIDES. 

The  hydrogen  continues  to  burn,  but  with  a  greenish-white  flame. 
Fumes  are  produced. 

(c.)  Hydrogen  Bromide. — Hydrogen  and  bromine  do  not 
combine  so  readily  as  hydrogen  and  fluorine  or  as  hydrogen  and 
chlorine.  Their  direct  combination  may  be  shown  as  follows  : — A 
bulb  tube  is  connected  with  an  apparatus  for  generating  hydrogen. 
A  few  cubic  centimetres  of  bromine  are  placed  in  the  bulb  ;  the 
hydrogen  passes  over  the  bromine,  and  carries  some  with  it  as  gas. 


,  23. 


The  hydrogen  is  lit,  and  burns,  combining  partly  with  the  oxygen 
of  the  air,  partly  with  the  bromine.  The  hydrogen  bromide 
formed  unites  with  the  water-vapour  forming  a  white  cloud  of 
small  liquid  particles.  It  is  owing  to  the  formation  of  a  similar 
compound  with  water  that  fumes  are  produced  when  hydrogen 
burns  in  chlorine. 

A  practical  plan  of  preparing  hydrogen  bromide  is  to  pass  the 
mixture  of  hydrogen  and  bromine,  prepared  as  described,  through 
a  glass  tube  containing  a  spiral  coil  of  platinum  wire,  heated  to 
redness  by  an  electric  current.  The  uncombined  bromine  is 
absorbed  by  passing  the  resulting  gas  through  a  tube  filled  with 
powdered  antimony. 

(d.)  Hydrogen  and  Iodine  may  be  made  to  combine  directly  by 
heating  them  together  in  a  sealed  tube  to  440°  for  many  days.  Com- 
plete combination  does  not  take  place,  however  long  the  mixture 
is  heated,  and  about  one  quarter  of  the  hydrogen  and  one  quarter 
of  the  iodine  remain  uncombined. 

2.  By  the  Action  of  the  Halogen  on  most  Compounds  of 
Hydrogen.  Instances.  —  (a.)  On  water.  —  A  solution  of  chlorine 


HYDROGEN   CHLORIDE,   BROMIDE,   AND   IODIDE.  107 

gas  in  water  exposed  to  sunlight  yields  oxygen  and  hydrogen 
chloride  ;  if  chlorine  and  water-gas  be  led  through  a  red-hot  tube, 
some  of  the  water-gas  reacts  with  the  chlorine,  yielding  hydrogen 
chloride  and  oxygen.  (6.)  On  hydrogen  sulphide,  dissolved  in 
wrater.  The  products  are  sulphur  and  the  hydrogen  compound  of 
the  halogen.  This  is  a  convenient  method  of  preparing  hydrogen 
iodide.  Sulphuretted  hydrogen  gas  (see  p.  196)  is  passed  through 
water  in  which  iodine  is  suspended.  The  liquid  becomes  milky, 
owing  to  separation  of  sulphur,  and  the  colour  gradually  dis- 
appears, owing  to  the  union  of  the  iodine  with  the  hydrogen  of 
the  hydrogen  sulphide.  When  the  reaction  is  over,  the  sulphur  is 
separated  by  nitration,  and  the  liquid  distilled.  It  is,  however, 
impossible  to  separate  hydrogen  iodide  from  its  solution  in  water 
by  distillation.  The  aqueous  solution  is  termed  hydriodic  acid, 
(c.)  Chlorine,  bromine,  and  iodine  act  on  ammonia,  yielding  nitro- 
gen and  the  compound  of  the  halogen  with  hydrogen.  Nitrogen 
combines  with  the  halogen,  if  the  latter  is  in  excess,  yielding  very 
explosive  bodies  (see  p.  158).  (d.)  Chlorine  and  bromine  act  on 
hydrocarbons  (carbides  of  hydrogen)  giving  compounds  of  carbon 
with  both  chlorine  (or  bromine)  and  hydrogen,  and  the  haloid 
acid.  Generally  it  may  be  stated  that  almost  all  compounds  of 
hydrogen  are  decomposed  by  the  halogens,  yielding  a  haloid  com- 
pound of  the  element,  and  hydrogen  chloride,  bromide,  or  iodide. 

3.  By  the  Action  of  Water,  or  of  Double  Oxides  of 
Hydrogen  and  some  other  Element  on  Compounds  of  the 
Halogens,  a.  Action  of  Water. — The  halogen  compounds  of 
boron,  silicon,  titanium,  phosphorus,  sulphur,  selenium,  and 
tellurium,  are  at  once  decomposed  by  cold  water.  Hence  the 
halogen  added  to  water  in  which  one  of  these  elements  is  sus- 
pended, combines  with  part  of  the  hydrogen  of  the  water,  the 
remaining  hydrogen  and  oxygen  combining  with  the  element  (see 
these  haloid  compounds,  p.  188).  Instances; — (a.)  This  is  a 
practical  method  of  preparing  hydrogen  bromide.  The  bromine  is 
added  very  gradually  to  phosphorus,  lying  in  water  in  a  retort. 
Phosphorus  bromide  is  produced,  and  decomposed  by  the  water, 
forming  phosphorous  and  phosphoric  acids,  and  hydrogen  bromide. 
After  all  the  phosphorus  has  disappeared,  the  liquid  is  distilled. 
The  solution  of  hydrogen  bromide  in  water  is  named  hydrobromic 
acid. 

There  is  little  doubt  that  all  soluble  chlorides,  bromides,  and 
iodides  are  decomposed  by  excess  of  water,  forming  the  hydroxide 
of  the  metal  and  hydrogen  chloride,  bromide,  or  iodide.  But  in 
most  cases  there  is  no  available  method  of  separating  the  hydr- 


108  THE   HALIDES. 

oxide  from  the  hydrogen  halide,  for,  on  evaporation,  the  reverse 
reaction  takes  place,  and  water  alone  escapes.  Yet,  at  a  high 
temperature,  magnesium  chloride  and  some  other  chlorides  react 
with  water-gas,  giving  an  oxy-chloride  and  hydrogen  chloride. 

(6.)  This  is  a  recently  patented  method  of  manufacturing 
hydrogen  chloride,  and  promises  to  be  successful.  Steam  is  led  over 
magnesium  chloride,  heated  in  tubes  ;  hydrogen  chloride  is  evolved, 
and  a  compound  of  magnesium  oxide  and  chloride  remains.* 

6.  Action  of  Hydroxides. — The  hydroxides  which  react  in 
this  manner  are  termed  acids.  Generally  stated,  the  hydrogen 
halides  can  be  prepared  by  the  action  of  any  hydroxide  which  does 
not  react  with  them.  Phosphoric,  sulphuric,  and  selenic  acids  are 
such. 

c.  This    is    the     common    method    of     preparing    hydrogen 
fluoride.     The  fluoride  generally  employed  is  calcium  fluoride,  or 

fluor-spar,  which  occurs  native ;  it  is  treated  with  sulphuric  acid 
in  leaden  vessels,  and  the  gas  evolved  is  condensed  in  a  worm  of 
lead  and  stored  in  leaden  or  gutta-percha  bottles.  It  acts  on 
silica,  which  is  a  large  constituent  of  glass  and  porcelain ;  hence 
the  use  of  lead,  which  is  but  slightly  attacked.  On  a  small  scale, 
platinum  vessels  and  potassium  fluoride  answer  better. 

d.  This    is    also    the    best    method    of    preparing    hydrogen 
chloride.     On  a  small  scale,  about  50  grams  of  sodium  chloride 
(common  salt)  are  placed  in  a  retort,  and  covered  with  a  mixture 
of  equal  volumes  of    sulphuric  acid  and  water.     On  applying  a 
gentle  heat  the  hydrogen  chloride  comes  over  in  the  gaseous  state. 
It  may  be  led  into  water;  the  solution  is  called  hydrochloric  acid. 

On  a  large  scale,  the  operation  is  conducted  in  circular  furnaces 
with  a  revolving  bed.  The  salt  and  sulphuric  acid  are  introduced 
from  above,  and  fall  on  to  the  middle  of  a  revolving  plate  of  iron 
covered  with  fire-clay,  which  forms  the  bed  of  the  furnace.  The 
product,  sodium  sulphate,  or  "salt-cake,"  is  raked  by  mechanical 
means  towards  the  circumference  of  the  plate,  and  drops  through 
traps  for  the  purpose.  The  hydrogen  chloride  is  led  up  brick  towers 
filled  with  small  lumps  of  coke,  kept  moist  with  water  from  above. 
The  water  dissolves  the  hydrogen  chloride,  which  is  sent  to  market 
in  carboys. 

e.  As   both   hydrogen   bromide    and    iodide    react  with   and 
decompose  sulphuric  acid  (see  p.  Ill),  bromine   or  iodine  being 
liberated,   phosphoric  acid  must  be   used   for  their  preparation. 
The  method  of  operation  is  similar  to  that  of  preparing  hydrogen 
chloride. 

*  Soc.  Chem.  Industry,  1887,  775. 


ATOMS   AND   MOLECULES.  109 

4.  Heating  Compounds  of  the' Hydrogen  Halide  with  the 
Haloid  Compounds  of  other  Elements. — Such  compounds 
always  decompose  when  heated.  In  practice,  this  method  is 
employed  for  the  preparation  of  pure  hydrogen  fluoride.  Its 
compound  wilh  potassium  fluoride,  after  being  dried,  is  heated  to 
redness  in  a  platinum  retort,  and  the  hydrogen  fluoride  which 
distils  over  is  condensed  by  passing  through  a  platinum  tube 
surrounded  with  a  freezing  mixture,  and  collected  in  a  platinum 
bottle.  The  preparation  of  pure  hydrogen  fluoride  is  exceedingly 
dangerous,  owing  to  its  great  corrosive  action. 

Before  considering  the  properties  of  these  bodies,  the  nature 
of  the  changes  which  have  been  described,  and  the  method  of 
representing  these  changes,  must  be  discussed. 


Atoms  and  Molecules. 

It  was  stated  in  last  chapter  that  equal  volumes  of  gases  contain 
equal  numbers  of  molecules.  Now,  it  has  been  shown  that  equal 
volumes  of  hydrogen  and  chlorine  unite  to  form  hydrogen  chloride. 
It  might  be  concluded  that  such  a  compound  consists  of  1  molecule 
of  chlorine  in  union  with  1  molecule  of  hydrogen ;  but  the  follow- 
ing considerations  will  show  that  such  a  supposition  is  inconsistent 
with  Avogadro's  law.  The  actual  facts  are  that  1*0025  gram 
of  hydrogen,  occupying  at  standard  temperature  and  pressure 
1T16  litres,  combines  with  35*46  grams  of  chlorine,  also  occupying 
11 '16  litres,  and  that  the  volume  of  the  product  is  11' 16  X  2,  or 
22*32  litres.  We  de  not  know  the  actual  number  of  molecules  of 
hydrogen,  or  of  chlorine,  in  11 '16  litres  of  these  gases ;  let  us  call 
it  n.  Then  n  molecules  of  hydrogen,  on  this  supposition,  unite 
with  n  molecules  of  chlorine,  and  as  chemical  combination  has 
occurred,  n  molecules  of  hydrogen  chloride  are  formed.  But  the 
volume  of  the  hydrogen  chloride  is  22*32  litres  ;  hence  n  molecules 
of  hydrogen  chloride  would  thus  occupy  (11*16  X  2)  litres,  instead 
of  11*16;  or  the  requirements  of  Avogadro's  law  would  not  be 
complied  with,  inasmuch  as  there  would  be  only  half  as  many 
molecules  in  a  given  volume  of  hydrogen  chloride  as  in  the  same 
volume  of  hydrogen  or  of  chlorine.  But  there  is  no  reason  to 
suppose  that  hydrogen  chloride  does  not  fulfil  Avogadro's  law  ; 
its  expansion  by  rise  of  temperature  and  behaviour  as  regards 
pressure  are  practically  the  same  as  those  of  hydrogen  and 
chlorine,  hence  the  conclusion  is  evidently  false.  The  accepted 
explanation  is  as  follows  : — 


110  THE   HALIDES. 

A  molecule  of  hydrogen,  or  a  molecule  of  chlorine,  is  not  a 
simple  thing;  it  consists  of  two  portions  in  combination  with 
each  other  ;  these  portions  are  named  atoms.  When  chlorine  and 
hydrogen  combine  to  form  hydrogen  chloride,  their  double  atoms 
or  molecules  split,  each  atom  of  hydrogen  leaving  its  neighbour 
atom,  and  uniting  to  an  atom  of  chlorine,  which  has  also  parted 
with  its  neighbour  atom.  The  original  arrangement  may  be 
represented  thus  :  — 


and  the  final  arrangement,  thus  :  — 


In  11*16  litres  of  hydrogen  chloride  there  is,  therefore,  the 
same  number  of  molecules  as  in  an  equal  volume  of  hydrogen  or 
of  chlorine;  but  whereas  the  hydrogen  chloride  molecules  contain 
an  atom  of  each  element,  those  of  hydrogen  contain  two  atoms  of 
hydrogen,  and  those  of  chlorine  contain  two  atoms  of  chlorine. 

Symbols  are  employed  to  express  such  changes.  The  expression 
of  the  change  is  termed  an  equation ;  and  the  above  change  is 
written  thus : — 

H,  +  Clz  =  2HCL 

Where  the  small  numeral  follows  the  letter,  it  signifies  the 
number  of  atoms  in  the  molecule,  as  JBT2,  Clz ;  where  a  large 
numeral  precedes  the  formula,  it  signifies  the  number  of  molecules; 
thus,  2HCI.  2H  would  mean  two  uncombined  atoms  of  hydrogen  ; 
H2  signifies  two  atoms  combined  into  a  molecule.  Atoms  of 
hydrogen  have  not  been  obtained  uncombined  with  each  other ; 
atoms  of  chlorine,  however,  exist  uncombined,  or  in  the  free  state, 
at  a  sufficiently  high  temperature. 

Such  an  equation  expresses  the  following  facts  : — 

1.  That  22-32  litres  of    hydrogen  react  with   22*32    litres  of 
chlorine,  producing  44*64  litres  of  hydrogen  chloride ;  and 

2.  That  2*005  grams  of  hydrogen  react  with   70*92  grams  of 
chlorine,  forming  72*925  grams  of  hydrogen  chloride. 

It  is  obvious  that  22'32  litres  of  hydrogen  chloride  weigh 
72*925/2  grams ;  and  as  22*32  litres  of  hydrogen  weigh  2*005  grams, 
hydrogen  chloride  is  18*231  times  as  heavy  as  hydrogen.  This 
has  been  found  to  be  the  case  by  direct  experiment.  Hence  the 
molecular  weight  of  hydrogen  chloride  =  36 '4625  is  twice  its 
density  compared  with  hydrogen. 

Such  formulae  as  HCl,  JET2,  (7Z2,  apply  only  to  gases.  In  this 
book  the  symbols  for  gaseous  elements  and  compounds  are  printed 


ATOMS   AND   MOLECULES.  Ill 

in  italics  ;  those  for  liquids  in  ordinary  type  ;  and  those  for  solids 
in  bold  type.  It  is  still  doubtfnl  whether  liquids  and  solids  possess 
such  simple  formulas  ;  it  is  the  author's  opinion  that  in  many 
cases  they  do;  but  there  are  certainly  many  cases  in  which  they 
possess  more  complex  formulae.  There  is,  however,  as  yet  no 
method  of  determining  with  certainty  the  degree  of  complexity  ; 
hence,  the  simplest  formulae  are  employed.  Liquid  hydrogen 
chloride  may  have  the  formula  HC1  ;  or  it  may  have  the  formula 
(HCl)w  ;  but  what  the  value  of  n  is,  there  is  no  means  of  deter- 
mining. 

The  reactions,  whereby  the  halides  of  hydrogen  are  prepared, 
are  represented  thus  :  — 

la.  H^  +  .Fo  =  2HF  at  high  temperatures  (see  p.  115). 

b.  HZ  +  CL  =  2HCL 

c.  HI  +  1-2    =  2HL 

2a.  2H2O  +  2^2  =  4HCI  +  O2,  or  2H2O  +  2C72  =  4HCI  +  02. 
Water. 

b.  H2S    +    I2  +  Aq  =  2HI.Aq   +    S.     (Aq  =  aqua,  water). 
Hydrogen  sulphide.    Hydriodic  acid. 


c.  2H3KAq  +  3C72  =  6HCl.Aq  +  N2. 
Ammonia. 

d.  CH4  +  a2  =  CH3ci  +  sci. 

Methane.  Chloro- 

methane. 

3a.  2P  +  SBr.^.Aq  +  8H2O  -  2H3PO4.Aq  +  lOHBr.Aq. 
Phosphoric  acid. 

J.  2M&C12  +   H»O  =  Mg-Cls.MgO   +   2HCL 
Magnesium  Magnesium 

chloride.  oxychloride. 

c.  CaF2     +     H2SO4     +     CaS04     -f     2HF. 
Calcium        Sulphuric         Calcium 
fluoride.  acid.  sulphate. 

d.  NaCl     -f-     H2SO4     =  NaHS04      +      HCl. 
Sodium         Sulphuric  Sodium  hydrogen 

chloride.  acid.  sulphate. 

NaCl     +     NaHSO4       =       Na2SO4     +     HCL 

Sodium    Sodium  hydrogen  Sodium  sulphate. 
chloride.  sulphate. 

e.  NaBr      +      H3PO4     =     NaH2PO4      +      HBr. 

Sodium        Phosphoric  Dihydrogen  sodium 
bromide.  acid.  phosphate. 

The  action  of  hydrogen  bromide  or  iodide  on  hot  sulphuric  acid  is  repre- 
sented thus  :  — 

H2SO4  +  2HBr  (or  2HI)  =  S0.2  +  2H2O  +  Sr.2  (or  72). 


112  THE   HALIDES. 

4.  KF.HF  KF  +  HF. 

Hydrogen  potassium  Potassium 

fluoride.  fluoride. 

Properties. — Hydrogen  fluoride  is  a  colourless  very  volatile 
liquid,  boiling  at  about  19°  under  atmospheric  pressure  ;  hydrogen 
chloride,  bromide,  and  iodide  are  all  colourless  gases.  Hydrogen 
fluoride  is  fearfully  corrosive  ;  a  drop  on  the  skin  produces  a 
painful  sore,  and  several  deaths  have  occurred  through  inhaling 
its  vapour.  The  other  three  gases  are  suffocating,  but  do  not 
produce  permanent  injury  when  breathed  diluted  with  air.  They 
condense  to  liquids  at  low  temperatures.  They  are  exceedingly 
soluble  in  water,  in  all  probability  forming  compounds  which  mix 
with  excess  of  water  or  of  the  halide.  One  volume  of  water  at  0° 
dissolves  about  500  times  its  volume  of  hydrogen  chloride  ;  the 
solution  is  about  1*21  times  heavier  than  water,  and  contains 
42  per  cent,  of  its  weight  of  the  gas.  On  cooling  a  strong  solution 
of  hydrogen  chloride  in  water  to  —18°,  and  passing  into  the  cold 
liquid  more  hydrogen  chloride,  crystals  of  the  formula  HC1.2H20* 
separate  out.  It  is  probable  that,  at  the  ordinary  temperature,  this 
compound  exists  in  an  aqueous  solution  of  hydrogen  chloride,  and 
is  decomposed  into  its  constituents  to  an  increasing  extent  with 
rise  of  temperature.  Hydrogen  fluoride,  bromide,  and  iodide  are 
also  exceedingly  soluble  in  water,  and  their  solutions  probably 
contain  similar  hydrates.  The  corresponding  compound  of 
hydrogen  bromide,  HBr.2H20,  has  been  prepared;  it  melts  at 
— 11°.  The  solutions  of  these  compounds  are  termed  hydrofluoric, 
hydrochloric,  hydrobromic,  and  hydriodic  acids.  When  saturated, 
they  are  colourless  fuming  liquids;  they  possess  an  exceedingly 
sour  taste,  and  are  very  corrosive ;  they  change  the  blue  colour  of 
litmus  (a  substance  prepared  from  a  lichen  named  lecanora  tinctoria, 
and  itself  the  calcium  salt  of  a  very  weak  acid)  to  red,  owing  to 
the  liberation  of  the  red-coloured  acid.  This  is  the  usual  test  for 
an  acid. 

The  great  solubility  of  hydrogen  chloride  may  be  illustrated  by  help  of  the 
apparatus  shown  in  the  figure.  (Fig.  24.) 

The  lower  flask  is  filled  with  water  coloured  blue  with  litmus  ;  the  upper  flask 
is  filled  with  hydrogen  chloride  by  downward  displacement,  and  inverted  over 
the  lower  flask.  The  stopcock  is  then  opened,  establishing  communication 
between  the  two  flasks.  By  blowing  through  the  tube,  a  little  water  is  forced 
up  into  the  hydrogen  chloride.  It  immediately  dissolves,  producing  a  partial 
vacuum  in  the  upper  flask ;  and  the  pressure  of  the  atmosphere  causes  a 
fountain  of  water  to  enter  it.  The  blue  colour  of  the  litmus  is  at  the  same  time 
changed  to  red. 

*   Comptes  rendus,  86,  279. 


HYDROFLUORIC  ACID. 


113 


All  elements  are  attacked  and  dissolved  by  these  acids, 
hydrogen  being  liberated,  while  the  halogen  combines  with  the 
element,  with  the  exception  of: — Silver,  gold,  mercury;  boron 
(attacked  by  hydrofluoric  acid),  carbon;  silicon,  zirconium  (both 
attacked  by  hydrofluoric  acid),  lead;  nitrogen,  vanadium,  phos- 


FIG.  24. 

phorus,  arsenic,  antimony,  bismuth;  molybdenum;  oxygen, 
sulphur,  selenium,  tellurium,  and  the  elements  of  the  platinum 
group.  Mercury  and  lead  are  attacked  by  strong  hydriodic  acid ; 
moist  hydrogen  chloride,  bromide,  and  iodide  are  decomposed  by 
light  in  presence  of  oxygen.*  The  first  two  are  not  decomposed 
when  dry ;  dry  hydriodic  acid,  however,  yields  water  and  iodine. 

Uses. — Hydrofluoric  acid  is  employed  for  etching  on  glass. 
The  glass  is  protected  by  a  coating  of  beeswax,  and  a  pattern  is 
drawn  on  the  wax.  The  article  is  then  dipped  in  the  strong  acid, 
and  the  pattern  remains  after  removing  the  wax,  the  glass 
appearing  frosted  where  the  acid  has  attacked  it.  Hydrochloric 
acid  is  used  for  many  purposes,  one  of  the  chief  of  which  is  the 
manufacture  of  chlorine  and  the  chlorides  of  metals. 

*  Chem.  Soc.,  51,  800. 


114  THE   HALIDES. 

Proofs  of  the  Volume-Composition  of  the  Halides 
of  Hydrogen. 

It  has  already  been  shown  that  hydrogen  chloride  con- 
sists of  equal  volumes  of  hydrogen  and  chlorine  united  with- 
out contraction ;  it  may  be  shown  to  contain  its  own  volume  of 
hydrogen  by  the  following  experiment : — A  \J  -tube,  as  shown  in 
fig.  25,  is  filled  with  mercury,  which  is  then  displaced  in  the 


FIG.  25. 

closed  limb  by  gaseous  hydrogen  chloride.  The  level  of  the 
mercury  is  made  equal  in  the  two  limbs,  and  the  position  marked. 
The  open  limb  is  then  filled  with  liquid  sodium  amalgam  (an  alloy 
of  mercury  and  sodium  containing  about  2  per  cent,  of  sodium) 
and  closed  with  the  thumb.  The  tube  is  then  inverted,  so  as  to 
bring  the  gas  into  contact  with  the  sodinm  amalgam.  The  sodium 
reacts  with  the  hydrogen  chloride,  liberating  hydrogen,  thus : — 

2HCI  +  2Na  =  2NaCl  +  #2. 

The  hydrogen  is  then  again  transferred  into  the  closed  limb  by 
inclining  the  tube,  and  the  levels  again  equalised ;  it  will  be  seen  to 
occupy  half  the  volume  originally  occupied  by  the  hydrogen  chloride. 

That  hydrogen  bromide  and  iodide  yield  half  their  volume  of 
hydrogen  when  similarly  treated  has  also  been  proved.  Hydrogen 
fluoride  has  been  synthesised  by  heating  silver  fluoride  with 
hydrogen  gas.  The  product  occupied  at  100°  twice  the  volume  of 
the  hydrogen  employed  for  its  formation.  The  equation  is  2AgF  + 
Hy,  =  2HF  +  2Ag,  silver  being  set  free  as  metal. 

It  is  argued  that  hydrogen  fluoride,  bromide,  and  iodide  possess 
respectively  the  formula  HF,  HBr,  and  HI,  from  these  experiments, 


SODIUM   FLUORIDE. 


115 


from  their  densities,  and  from  their  similarity  to  hydrogen 
chloride.  Recent  experiments  have,  however,  shown  that  at  low 
temperatures  gaseous  hydrogen  fluoride  has  a  greater  molecular 
weight  than  that  expressed  by  the  formula  HF;  bat  the  actual 
degree  of  complexity  is  not  yet  certain  (see  below). 

Physical  Properties. 
Mass  of  1  e.c. 


Solid. 

Liquid. 

Gas.              H  =  1. 

Hydrogen  fluoride  .  . 

?        0 

•988  at  12 

•7°         See  below         See  below 

Hydrogen  chloride  .  . 

? 

? 

0  -001633*          18  -23* 

Hydrogen  bromide  .  . 

9 

? 

0-003626*          40-47* 

Hydrogen  iodide  

p 

p 

0  -005727*          63  '92* 

Melting- 

Boiling- 

Specific             Molecular 

point. 

point. 

Heat.                Weight. 

Hydrogen  fluoride.  . 

-92  -3° 

19-4° 

?              20  (see  below) 

Hydrogen  chloride  . 

-112-5° 

-102° 

0-1304  (gas)           36-46 

Hydrogen  bromide  . 

.  -73° 

-8T 

?                     80-95 

Hydrogen  iodide.  .  . 

-55° 

? 

?                   127  -85 

Heat  of  formation.  —  H*> 


=  2HCI  + 
=  2HSr  + 
=  2HI  + 


440K. 
242K. 
OK  at  about  184°. 


Note. — Molecular  weight  of  hydrogen  fluoride.^  The  vapour- density  of 
hydrogen  fluoride  increases  with  fall  of  temperature,  implying  the  association  of 
molecules  of  HF  to  form  (HFjn.  (The  value  of  n  appears  to  be  4.)  The- 
highest  density  was  found  at  atmospheric  pressure,  and  at  26'4°,  to  be  25'59r 
implying  the  molecular  weight  of  51'18.  This  corresponds  to  a  mixture  of 
81-24  per  cent,  molecules  of  S4F4  and  18'76  per  cent,  of  molecules  of  HF.  At 
100°  and  above,  the  density  is  normal,  and  corresponds  to  the  formula  HF. 


Compounds  of  the  Halogens  with  Lithium, 
Sodium,  Potassium,  Rubidium,  and  Caesium 
(Ammonium). 

Sources. — Sodinm  fluoride  occurs  native  in  Greenland  in  com- 
bination with  aluminium  fluoride,  as  cryolite,  3NaF.AlF3.  Lithium, 
sodium,  and  potassium  chlorides,  bromides,  and  iodides  occur  in  sea- 
water;  sodium  chloride  in  by  far  the  greatest  amount — about  3' 5 
per  cent. ;  and  also  in  many  mineral  springs.  That  at  Durkheim, 
in  the  Bavarian  Palatinate,  is  comparatively  rich  in  caesium  and 
rubidium  chlorides,  and  was  the  source  from  which  Bunsen  and 


*  These  numbers  are  calculated. 

t  Thorpe,  Chem.  Soc.,  53,  765 ;  55,  163. 


i  2 


116  THE   HALIDES. 

Kirehhoff  extracted  these  elements  for  the  first  time.*  The  Wheal 
Clifford  spring,  in  Cornwall,  is  specially  rich  in  lithium  chloride. 
Sodium  chloride  also  occurs  as  rock-salt  in  mines,  in  various  parts 
of  the  world  ;  the  largest  in  Britain  are  in  Cheshire,  but  recently 
other  deposits  have  been  discovered  near  the  Tyne.  Very  large 
deposits  of  potassium  chloride  occur  at  Stassfurth,  near  Magdeburg, 
in  N.  Germany.  It  also  occurs  in  kelp,  the  ash  of  fucus  palmatus, 
species  of  seaweed.  The  ash  of  the  beetroot  contains  about 
0'17  per  cent,  of  rubidium  chloride. 

Preparation.— 1.  By  direct  union  of  the  elements.— This 
takes  place  with  great  loss  of  energy  (i.e.,  evolution  of  heat)  ;  the 
elements  take  fire  and  burn  in  chlorine  gas.  Perfectly  dry  chlorine, 
bromine,  or  iodine,  however,  does  not  act  on  sodium  in  the  cold.f 
A  subchloride  of  a  purple  colour  is  said  to  be  produced  by  the 
action  of  chlorine  on  metallic  potassium. 

2.  By  double  decomposition,  (a.)  Action  of  the  halogen 
acids  on  the  oxides,  hydroxides,  or  carbonates  of  the  metals ; 
in  the  first  two  cases,  the  hydrogen  of  the  halogen  acid  unites  with 
the  oxygen  of  the  oxide,  or  the  hydroxyl  (a  name  applied  to  the 
group  OH)  of  the  hydroxides;  in  the  third  case,  carbon  dioxide 
and  water  are  liberated.  Examples  of  this  action  are  given  in 
the  following  equations  : — 

KOH  +  HF  =  KF  4-  H-OH. 
Na2O  +  2HCI  =  2NaCl  +  H80. 
Li3CO3  +  2.HT  =  2LiI  +  H20  +  CO,. 

These  reactions  also  occur  in  solution. 

On  adding  to  a  solution  of  a  hydroxide,  containing  an  unknown 
quantity  of  the  hydroxide,  a  solution  of  a  hydrogen  halide,  the 
completion  of  the  reaction,  or  the  "point  of  neutralisation,"  may 
be  ascertained  by  the  addition  of  litmus,  or  of  phenol-phthaleiin, 
to  the  hydroxide ;  the  former  gives  a  blue,  the  latter  a  cherry- 
red  colour  with  these  hydroxides ;  when  the  colour  is  on  the  point 
of  changing  to  brick-red,  with  litmus,  or  being  discharged  entirely, 
with  phenol-phthalein,  the  reaction  is  complete,  and  there  is  no 
excess  either  of  acid,  or  of  alkali,  as  such  hydroxides  are  named. 

If  carbonates  be  used,  the  solution  must  be  boiled  during  the 
addition  of  acid,  so  as  to  expel  carbon  dioxide  gas,  else  it  will 
produce  a  colour  change. 

(6.)  By  certain  other  "double  decompositions;"  thus 
sodium  chloride  is  obtained  as  a  by-product  in  the  manufacture 

•*  Poffff.  Ann.,  110,  161 ;  113,  337  ;   119,  1 ;  Annales  (3),  64,  290. 
f  Berichte,  6,  1518  ;   Chem.  Soc.,  43,  155. 


AMMONIUM.  -117 

of   potassium   nitrate  from  sodium  nitrate   and  potassium  chlor- 
ide :— 

KCl.Aq  +  NaN03.Aq  =  KN03.Aq  +  NaCl. 

The  sodium  chloride,  being  much  less  soluble  in  water  than 
potassium  nitrate,  separates  in  crystals  on  evaporation.  The 
sulphides  and  hydrosulphides  of  these  metals  also  yield  halides 
on  treatment  with  halogen  acids. 

3.  By  heating  compounds  of  these  metals  with  oxygen 
and  with  the  halogens,  e.g.,  chlorates,  iodates,  &c.  (see  p.  466). 

4.  Compounds  of  ammonium  with  the  halogens  are  pre- 
pared by  addition  of  the  halogen  acid  to  a  solution  of  ammonia  in 
water.     Direct  combination  ensues,  thus  : — 

NH3.Aq  +  HCl.Aq  =  NH4Cl.Aq. 


Ammonium,  NH4. 

The  group  of  elements  to  which  the  name  ammonium  has  been 
given  exhibits  the  greatest  similarity  to  metals  of  the  sodium  group, 
and  is  usually  classed  along  with  them.  It  has  never  been  isolated 
(see,  however,  pp.  577,  578).  But  ammonia,  consisting  of  one  atom 
of  nitrogen  and  three  atoms  of  hydrogen,  NH3  (see  p.  512),  has 
the  power  of  union  with  acids  (as  well  as  with  oxides  and  double 
oxides);  compounds  of  ammonium  with  the  halogens  differ  from 
those  of  sodium  and  the  other  metals  by  splitting  up  when 
heated  into  ammonia  and  the  hydrogen  halide. 

The  union  of  ammonia  with  a  halide  of  hydrogen  may  be 
illustrated  by  placing  a  jar  filled  with  ammonia  gas  (see  p.  512) 
mouth  to  mouth  over  a  jar  of  hydrogen  chloride,  both  being 
covered  with  glass  plates ;  when  the  plates  are  withdrawn,  dense 
white  fumes  of  ammonium  chloride  are  seen ;  they  gradually  settle 
in  the  lower  jar  as  a  white  powder. 

The  decomposition  of  this  compound  by  heat  may  be  shown  by 
applying  heat  to  a  fragment  in  a  platinum  basin ;  it  will  volatilize 
completely,  being  decomposed  into  its  constituents — ammonia,  NHZ, 
and  hydrogen  chloride,  HCl ;  they  unite  when  cooled  by  the  air, 
forming  dense  white  fumes. 

Special  methods  of  extraction  and  preparation. — Owing  to  their  im- 
portance, the  following  compounds  require  consideration : — Common  salt,  or 
sodium  chloride,  is  produced  by  the  evaporation  of  sea- water  in  "  salt  pans," 
shallow  ponds  exposed  to  the  air.  To  promote  evaporation,  the  salt  Water  is 
sometimes  allowed  to  trickle  over  ledges,  running  into  gutters  which  lead  it  to 


118  .  THE  HALIDES. 

the  ponds.  Wlien  a  portion.  of  the  water  has  been  thus  removed,  it  is  boiled 
down  in  shallow  iron  pans.  Eapid  evaporation  produces  fine-grained  salt,  such 
as  is  used  for  the  table  ;  slow  evaporation  causes  the  salt  to  separate  in  larger 
crystals  ;  it  is  used  for  curing  fish,  &c. 

In  Cheshire,  water  is  run  into  the  mines,  and  the  brine  is  pumped  up  and 
evaporated.  In  cold  climates,  the  salt  is  sometimes  extracted  from  sea-water  by 
freezing  ;  the  ice  which  separates  is  nearly  pure,  while  the  salt  remains  dissolved 
in  the  last  portions  of  water. 

Potassium  bromide  and  iodide  are  prepared  (a)  by  the  action  of  bromine 
or  iodine  on  a  solution  of  potassium  carbonate  ;  the  water  is  removed  by  evapora- 
tion,, and  the  residue  is  heated  to  redness  (see  p.  467)  ;  or  (6)  by  treating  iron 
filings  with  bromine  or  iodine,  producing  ferrous  bromide  or  iodide,  to  which  a 
solution  of  potassium  carbonate  is  then  added.  The  resulting  ferrous  carbonate  is 
in-soluble  in  water  ;  it  is  removed  by  filtration,  and  the  filtrate  is  evaporated  to 
dryness.  The  equations  are  :  — 


Fe  +  Br2  +  Aq  = 

FeBr2.Aq  +  K2C03.Aq  =  2KBr.Aq  +  FeCO3. 

The  equation  for  the  preparation  of  potassium  iodide  is  similar. 

Properties.  —  These  substances  are  all  white  solids,  crystallis- 
ing in  the  cubical  system,  with  the  exception  of  caesium  chloride, 
which  crystallises  in  rhombohedra.  They  are  all  soluble  in  water  ; 
lithium  chloride,  sodium  bromide,  and  sodium  and  potassium 
iodides  are  also  soluble  in  alcohol. 

100  grams  of  water  dissolve  at  the  ordinary  temperature  (about  15°)  — 

Fluoride.  Chloride.  Bromide.     Iodide. 
Lithium   ............      trace 

Sodium  .............         4  36  88  373 

Potassium  ...........  33  65  143 

Ammonium  ........  .  .        —  37  72 

grams  of  these  salts. 

They  all  form  double  compounds  with  water,  e.g.,  NaC1.2H2O, 
crystallising  at  a  low  temperature.  They  melt  at  a  red  heat  and 
volatilise  at  a  bright  red  heat  ;  ammonium  chloride  dissociates  at 
339°,  under  ordinary  atmospheric  pressure,  into  hydrogen  chloride 
and  ammonia  ;  the  other  compounds  of  ammonium  behave  similarly. 

Melting-points.  Mass  of  1  c.c. 


F.  Cl.  Br.  I.               F.  Cl.  Br.        I. 

Lithium  801°  598°  547°  446°  2 '29  2  "00  3 '10  3 -48 

Sodium 902°  772°  708°  628°  2 '56  2  '16  308  3 '65 

Potassium....  789°  734°  699°  634°  2 '10  1 '98  2 '60  3 '01 

Rubidium 753°  710°  683°  642°  3  "20  2 '80  3 '36  3  "57 

Cesium ?  4-00  4 -46  4 '54 

Ammonium   . .  —  —  —  —                ?  1  '52  2  '46  2  '44 


DOUBLE  COMPOUNDS.  119 

The  vapour  densities  of  the  following  compounds  have  recently 
been  determined  at  about  1200°  by  Y.  Meyer's  method : — 

Found. KI  =  184-1 ;  RbCl  =  139'4 ;  Rbl  =  221-6 

Calculated ....      KI  =  166'0  ;  RbCl  =  121-0  ;  Rbl  =  212'3  • 

Found CsCl  =  179-2;  Csl  =  267; 

Calculated CsCl  =  168'4 ;  Csl  =  259'8* 

These  numbers  represent  molecular  weights,  i.e.,  vapour- 
densities  multiplied  by  two. 

It  may  be  concluded  from  analogy  that  the  other  halides,  in 
the  gaseous  state,  have  also  simple  formulae,  such  as  NaCl ;  at 
present  we  know  nothing  about  the  molecular  weights  of  these 
bodies  in  the  liquid  or  solid  state. 

Double  compounds. — 1.  With,  halogens. — Iodine  unites  directly  with, 
potassium  iodide  in  aqueous  or  alcoholic  solution,  and  forms  dark  lustrous  prisms, 
possessing  the  formula  KI3.f  The  mass  of  1  c.c.  is  3 '50  grams  at  15°.  It  melts 
at  45°.  Chlorine  and  bromine  are  more  soluble  in  solutions  of  chlorides  and 
bromides  than  in  pure  water,  owing  probably  to  the  formation  of  similar 
compounds,  which  are  partially  dissociated  at  the  ordinary  temperature. 
Ammonium  tri-iodide  and  tribromide,  (NH4)I3  and  (NH4)Br3,  have  been 
prepared  by  a  similar  method,  and  are  closely  analogous. 

2.  With,  hydrogen  halides. — Potassium  fluoride  unites  with  hydrogen 
fluoride  in  three  proportions,  forming  (a)  KF.HF,  (5)  KF.2HF,  and  (c) 
KF.3HF.J  They  are  all  stable  in  dry  air,  but  decompose  when  heated  into 
potassium  and  hydrogen  fluorides.  No  doubt,  similar  compounds  of  the  other 
halogen  salts  would  prove  stable  at  low  temperatures. 

For  compounds  of  the  formula  4NH3.HC1,  and  7NH3.HC1,  see  p.  525. 

Heats  of  formation — 

Li  +  Cl  =  LiCl   -r  938K  +  Aq  =  +84K.§ 

Na  +  Cl  =  NaCl  -I-  976K  +  Aq  =  -ll'SK. 

.  Na  +  Br  =  NaBr  +  858K  +  Aq  =  - 1  '9K. 

Na+  I    =  Nal    +  691Z  +  Aq  =  -12K. 

K .  +  Cl  =  KC1    -i-  1056K  +  Aq  =  -44  'IK. 

K   +  Br  =  KBr   +  951K  +  Aq  =  -  50  -8K. 

X  +  I     =  KI      +  801K  +  Aq  =  -51 '1Z. 

*  Scott,  Brit.  Assn.,  1887,  668 ;  Proc.  Roy.  Soc.  Edin.,  14. 
f  Chem.  Soc.,  31,  249 ;  33,  397 ;  Eerichte,  14,  2398. 

*  Comptes  rendus,  106,  547. 

§  For  an  explanation  of  "  K,"  see  p.  127. 


120 


CHAPTEE  IX. 

COMPOUNDS  OF  THE  HALOGENS  WITH  BERYLLIUM,  CALCIUM,  STRONTIUM, 
AND  BARIUM;  WITH  MAGNESIUM,  ZINC,  AND  CADMIUM.  DOUBLE 
HALIDES.  SPECIFIC  AND  ATOMIC  HEATS.  REASONS  FOR  MOLECULAR 
FORMULA.  VALENCY. 

Beryllium,  Calcium,  Strontium,  and  Barium 
Halides. 

Sources.— Calcium  fluoride,  or  fluor-spar,  CaF2. — This 
beautiful  mineral,  crystallising  in  cubes,  sometimes  showing  octa- 
hedral modifications,  occurs  in  granite  and  porphyry  rocks, 
especially  where  the  veins  border  other  strata.  It  forms  the 
gangue  of  the  lead- veins  which  intersect  the  coal-formations  of 
Northumberland,  Cumberland,  Durham,  and  Yorkshire;  it  is 
abundant  in  Derbyshire  and  also  in  Cornwall,  where  the  veins 
intersect  much  older  rocks.  A  large  vein  occurs  in  Jefferson  Co., 
New  York  State,  in  granular  limestone.  It  often  possesses  a  pink, 
amethyst,  or  green  colour,  from  the  presence  of  certain  metallic 
fluorides. 

Calcium  chloride  is  a  constituent  of  all  natural  waters,  and 
exists  in  small  amount  in  sea-water.  Traces  of  the  chlorides  of 
strontium  and  barium  are  also  found  in  some  mineral  waters. 

Preparation. — The  methods  of  preparation  are  similar  to  those 
of  the  halides  of  the  alkali-metals. 

1.  By  direct  union  of  tne  elements. — The  metals  of  this 
group  are  so  difficult  to  prepare  that  the   method  is  impractic- 
able. 

2.  By  double  decomposition. — (a.)  The  action  of  the  haloid 
acid  on  the  oxides,  hydroxides,  sulphides,  or  hydrosulphides,  or  on 
double  oxides,  such   as   carbonates,  silicates,   &c.      This   method 
serves  for  the  production  of  the  chlorides,  bromides,  and  iodides  ; 
not  well  for  the  fluorides,  for  the  fluorides  of  calcium,  strontium, 
and  barium,  are  insoluble  in  water,  and  the  hydroxide  or  carbonate 
becomes  coated  over  with  the  insoluble  fluoride,  and  action  ceases. 
The  reactions  may  be  typified  by  the  following  equations  : — 


HALIDES   OF  BERYLLIUM,   STRONTIUM,  AND  BARIUM.        121 

BeO  +  2HCI  =  BeCl2  +  H2O. 
Ca(OH)a  +  2HCI  =  CaCl2  +  2H30. 
SrCO3  +  2HCI  =  SrCl2  +  H20  +  C02. 
BaS  +  2HCI  =  BaCl2  +  U.S. 

These  reactions  occur  both,  in  solution  and  with  the  dry 
materials. 

This  process  is  practically  made  use  of  in  preparing  strontium 
and  barium  chlorides,  from  their  carbonates  and  sulphides. 

(6.)  The  fluorides  of  calcium,  strontium,  and  barium,  being 
insoluble  in  water,  may  be  precipitated  by  adding  a  soluble  fluoride, 
such  as  potassium  fluoride,  to  a  soluble  salt  of  one  of  these  metals, 
such  as  calcium  chloride,  barium  iodide,  &c.  The  reaction  is,  for 
example : — 

CaCl2.Aq  +  2KF.Aq  =  CaP2  +  2KCLAq. 

Potassium  chloride  is  soluble  in  water,  and  may  be  separated 
from  the  insoluble  calcium  fluoride  by  filtration. 

Doubtless  similar  reactions  occur  on  mixing  soluble  compounds 
of  the  other  halogens  with  soluble  compounds  of  these  metals ;  thus 
it  may  be  supposed  that 

2KI.Aq  +  BaCl2.Aq  =  2KCl.Aq  +  BaI2.Aq. 

But  as  all  the  compounds  concerned  in  the  change  are  soluble 
in  water,  they  cannot  be  separated.  It  is  probable  that  such 
changes  are  only  partial;  i.e.,  not  all  the  potassium  iodide  is  con- 
verted into  chloride,  nor  all  the  barium  chloride  converted  into 
iodide,  but  that  after  mixture  the  solution  contains  all  four  com- 
pounds. 

This  method  of  "  double  decomposition,"  i.e.,  reciprocal  ex- 
change, is  also  practically  applied  in  the  preparation  of  strontium 
and  barium  chlorides  on  a  large  scale.  The  chief  sources  of  these 
metals  are  the  sulphates  of  strontium  and  barium  (see  p.  422). 
These  substances  are  heated  to  redness  with  calcium  chloride, 
when  the  calcium  transfers  its  chlorine-  to  the  strontium  or  barium, 
itself  being  converted  into  sulphate,  thus  : — 

BaSO4  +  CaCl2  =  BaCl2  +  CaSO4. 

On  treatment  with  water  the  insoluble  calcium  sulphate  re- 
mains, while  the  soluble  strontium  or  barium  chloride  dissolves, 
and  may  be  purified  by  crystallisation  from  water. 

Properties. — Beryllium  fluoride  has  not  been  prepared  free 
from  water ;  on  attempting  to  dry  the  gummy  mass  obtained  by 
its  evaporation  it  reacts  with  the  water  (see  below). 


122  THE   HALIDES. 

The  fluorides  of  calcium,  strontium,  and  barium  are  white  crys- 
talline powders,  insoluble  in  water. 

The  remaining  halides  of  this  group  are  all  white  solids,  soluble 
in  water.  They  unite  with  water,  forming  crystalline  compounds. 
Among  these  are  BeCl2.2HoO  ;  CaCl2,6H2O;  SrCl2.3H2O  ; 
BaBr2.2H2O;  and  BaI2.7H2O.  The  only  one  of  the  halides 
which  has  been  volatilised  is  beryllium  chloride,  which  becomes 
vapour  somewhat  below  520°  under  ordinary  pressure.  At  higher 
temperatures  (812°)  it  has  the  vapour-  density  4O42,  implying  the 
molecular  weight  80'02.*  The  compounds  of  beryllium  have  a 
sweet,  disagreeable  taste  ;  the  soluble  compounds  of  the  other 
elements  are  saline  and  burning. 

Uses.  —  Calcium  fluoride  is  employed  as  a  flux,  or  material  to 
be  added  to  metals  to  make  them  flow  (fluo)  when  they  are  being 
fused.  It  probably  acts  by  dissolving  a  film  of  oxide  encrusting 
the  globules,  and  thereby  causes  the  metallic  surfaces  to  come 
in  contact  and  unite.  It  is  also  a  source  of  hydrogen  fluoride 
(see  p.  106).  Calcium  chloride  is  employed  on  a  small  scale  for 
drying  gases,  and  liquid  compounds  of  carbon  ;  it  has  a  great 
tendency  to  unite  with  water,  hence  it  deliquesces  on  exposure  to 
moist  air,  attracting  so  much  moisture  as  to  dissolve. 

Some  of  these  substances  react  with  water  ;  hence  beryllium 
halides,  calcium  chloride,  bromide,  and  iodide,  and  strontium  and 
barium  bromides  and  iodides,  cannot  be  prepared  pure  in  .  an  an- 
hydrous state  by  evaporating  their  solutions*  The  reaction  is  a 
partial  one.  With  calcium  bromide,  for  instance,  it  is  :  — 

CaBr2  +  H20  =  CaO 


But  the  calcium  bromide  and  oxide  unite,  forming  various 
oxybromides,  which  remain,  while  a  portion  of  the  hydrogen 
bromide  escapes. 

Physical  Properties. 


Melting-points. 

Mass  of  1  c.c. 

Beryllium  .... 
Calcium  .  .... 

.  F.        Cl.      Br.         L 

?        600°     600°        ? 
902°    719°    676°    631° 

F.         Cl.       Br.         L 
3-14     2-20     3'32        ? 

Strontium  .... 
Barium  

902°     825°     630°     507° 
908°     860°     812°        ? 

4'21     3-05     3-98    4  '41 
4-83     3-82     4-23    4  '92 

*  Nilson  and  Petterssen,  Comptes  rendvs,  98,  988. 


HALIDES   OF  MAGNESIUM,  ZINC,  AND   CADMIUM.  123 

Heats  of  formation  : — 

Ca  +  CT2  =  CaCl2  +  1698K  +  .Aq  =  +174K. 
Ca  +  Br2  =  CaBr2  1-  14-OUK  +  Aq  =  +  256K. 
Ca  +  I2  =  CaI2  +  1073K  +  Aq  =  +  277K. 
Sr  +  Civ  =  SrCl2  +  1846  K  +  Aq  =  +  111K. 
Sr  +  Br2  =  SrBr2  +  1577K  +  Aq  =  +  161K. 
Ba  +  C72  =  BaClg  +  1947K  +  Aq  =  +  21K. 
Ba  +  Br2  =  BaBr  +  1700K  +  Aq  =  +  50K. 

Double  compounds. — The  scare  all  prepared  by  direct  addition.  Among 
them  may  be  mentioned : — BeFo.2KF,  BeCL>.2KCl,  and  similar  compounds 
with  sodium  and  ammonium  chlorides,  and  BaF.2.BaCl2.  The  solubility  of 
barium  and  strontium  fluorides  in  hydrofluoric  acid  is  probably  due  to  the 
formation  of  double  compounds  with  hydrogen  fluoride. 


Magnesium,  Zinc,  and  Cadmium  Halides. 

Sources. — Magnesium  chloride,  bromide,  and  iodide  are  con- 
tained in  sea-water,  and  in  many  mineral  springs.  Carnallite, 
Mgdft.KCl.6HsQ,  occurs  in  large  quantities  at  Stassfurth,  and  is  a 
valuable  source  of  magnesium  and  potassium  compounds. 

Preparation. — 1.  By  direct  union. — The  halogens  unite 
•with  these  metals  directly,  even  in  the  cold,  to  produce  halides. 
In  presence  of  water,  solutions  are  obtained. 

2.  By  the  action  of  the  halogen  acid  on  the  metal  hy- 
drogen is  evolved,  and  the  halide  of  the  metal  is  formed. 

3.  By    double    decomposition. — (a.)  By  the  action  of  the 
halogen   acid  on  the   oxides,  hydroxides,  sulphides,  and  on  some 
double  oxides,  such  as  carbonates,  borates,  &c.    This  process  yields 
solutions  of  the  halides  (except  in  the  case  of  magnesium  fluoride, 
which  is  insoluble  in  water).     But  the  water  cannot  be  removed 
completely  by  heat,  for  it  reacts  with  the  chlorides,  forming  oxy- 
chlorides.     The  double  chlorides  with  ammonium  chloride,  how- 
ever, are  unacted  on  when  evaporated  with  water,  hence  anhydrous 
magnesium  chloride  may  be  produced  by  heating  the  compound, 
MgCl2.2NH4Cl,  to  redness  ;  the  ammonium  chloride  sublimes  (see 
p.  117),  leaving  the  anhydrous  magnesium  chloride.     It  can  also 
be  prepared  by  heating  the  aqueous  chloride  in  a  current  of  hydro- 
gen chloride.     Similar  methods  would  probably  succeed  with  the 
bromides  and  iodides. 

(&.)  Other  methods  of  double  decomposition  may  be  sometimes 
employed;  e.g.,  MgS04.Aq  -f  BaCl2.Aq  =  MgCl2.Aq  +  BaSO4. 
Barium  sulphate  is  insoluble,  and  may  be  removed  by  filtration. 
Another  method,  which  succeeds  on  a  large  scale,  is  to  heat,  under 


124  THE   HALIDES. 

pressure,  magnesium  carbonate  with  a  solution  of  calcium  chloride  ; 
the  equation — 

MgC03  +  CaCl2.Aq  =  MgCl2.Aq  +  CaCO3 

represents  the   reaction,  the   insoluble   calcium   carbonate   being 
removed  by  filtration. 

Typical  Equations — 

1.  Zn  +  C72  =  ZnCL, 

2..  Cd  +  2HI.Aq  =  CdI2.Aq  +  Ht. 

3.  MgO  +  2HBr.Aq  =  MgBr2.Aq  -f  H20. 

ZnS  +  2HCLAq  =  ZnCl2.Aq  +  H28. 

CdCO3  +  2HF.Aq  =  CdF2,Aq  +  H20  +  00a. 

Properties. — "With  the  exception  of  magnesium  fluoride,  the 
halides  of  these  metals  are  soluble  in  water..  They  are  white  and 
crystalline.  The  fluorides  excepted,  they  are  all  volatile  and  are 
decomposed  at  a  red  heat  by  atmospheric  oxygen,  yielding  the 
halogens  and  oxyhalides.  This  has  been  proposed  as  an  effec- 
tive method  of  manufacturing  chlorine.  They  also  react  with 
water  at  a  red  heat ;  the  products  are  oxyhalide  and  hydrogen 
halide.  This  method  is  in  operation  for  the  preparation  of 
hydrogen  chloride  ;  the  equation  has  been  given  on  p.  111.  They 
all  unite  with  water,  forming  crystalline  compounds  ;  for  example, 
MgCl2.6H2O  ;  MgBr2.3H2O ;  ZnF2.4H2O ;  ZnCl2.H2O ; 
CdCl2.2H2O  ;  CdBr2.H2O  ;  CdI2  crystallises  as  such  from  water. 
Zinc  chloride  has  such  a  strong  tendency  to  combine  with  water 
as  to  be  able  to  withdraw  the  elements,  hydrogen  and  oxygen, 
from  compounds  in  which  they  do  not  exist  as  water ;  thus  it 
chars  wood  and  destroys  the  skin  ;  it  is  therefore  used  in  surgery 
as  a  caustic.  They  all,  except  magnesium  fluoride,  attract  mois- 
ture from  moist  air,  and  deliquesce. 

Uses. — Magnesium  chloride  is  employed  as  a  disinfectant,  and 
is  also  used  fraudulently  for  "  weighting  "  flannel  and  cotton  goods. 
Zinc  chloride  is  also  employed  as  a  disinfectant  under  the  name 
of  "  Burnett's  Disinfecting  Fluid."  Cadmium  bromide  and  iodide 
are  used  in  photography. 

Physical  Properties. 
Mass  of  1  c.c.  solid.  Melting-point.  Boiling-point. 

F.      CL-  Br.      ~I.     .F!      Cl.     Br.  ~I.       F.    Cl.     Br.      T. 

Magnesium.  2 '86  2 -18    ?         ?          ?      708°  695°      ?       ?       ?         ?          ? 


Zinc 4-60  2-75  3-64  4-7    734°  262°   394°  446°    ?    680°|g^0    624° 

Cadmium..    6-00  3-62  4-8    5 '7    520°  541°  570°  404°    ?  {  954°  {  gi?  {  719° 


HALTDES   OF  MAGNESIUM,  ZINC,  AND   CADMfOT  125 


Another  variety  of  cadmium  iodide  is  known,  -with,  the  specific  gravity 
4'6  or  4'7  ;  it  has  a  brownish  colour,  whereas  the  usual  variety  is  white.  It  is 
converted  at  50°  into  the  usual  modification.* 

Heats  of  formation.  —  Mfe  +   Cl.2  =  M&CL,  +  1510K  +  Aq  =   +  359K. 

Zn    +  C12  =  ZnCl2  +  972K  +  Aq  *=   +  156K. 

Zn   +  Br2  =•  ZnBr  +  760K  +  Aq  =   +  150K. 

Zn    +  I2    =  ZnI2  +  492  K  +  Aq  =   +113K. 

Cd  +  Civ  =  CdCl2  +  932K  +  Aq  =  +   30K. 

Cd   +  Br2  =  CdBr2  +  952K  +  Aq  =   +  4  "4K.    '.  ' 

Cd  +  I2    =  CdI2  +  488K  -f  Aq  =  -  9  '6K. 

Molecular  weig-hts.  —  The  vapour-densities  of  zinc  chloride  and  of  cad- 
mium chloride,  bromide,  and  iodide  nearly  correspond  to  the  formula  ZnCl%  and 
CdCl*  ;f  there  is  slight  dissociation  at  the  temperatures  employed  (898°  and 
1200°)  ;  cadmium  iodide  undergoes  considerable  dissociation  at  the  higher 
temperature. 

Double  compounds.  —  1.  "With  hydrogen  lialides.  — 

2ZnClo.HC1.2H.,O  and  ZnCl2.HC1.2H2O 

are  produced  in  crystals  by  saturating  a  concentrated  aqueous  solution  of  zinc 
chloride  with  hydrogen  chloride.     They  decompose  on  rise  of  temperature.^ 

2.  With  halides  of  the  alkali  metals.— 

(a.)  Fluorides.—  MgF2.NaF  ;  ZnP2.2KF. 

(5.)  Chlorides.—  MgCl2.NaCl.H.20  ;  MgCL2.KC1.6H2O. 

ZnCli.NH4Cl;  ZnCL2  2NH4C1;  ZnCl^NH^l  ;  ZnCl2.2KCl; 
ZnCl2.2NaC1.3H2O  ;  2CdCl2.2B:Cl.H2O  ;  CdCl2.2NaCl. 
3H2o';  CdCl2.2NH4Cl.H20  ;  CdCl^NH^l  ;  CdCl2. 
4KC1. 

(c.)  Bromides—  CdBr2.KBr.H2O  ;   2CdBr2.2NaBr.5H2O  ;   2CdBr2.2NH4Br. 
HsO;  CdBr2.4KBr;  CdBr2.4NH4Br. 

(d.)  Iodides.—  ZnI2.KI  ;  ZnI2.2NH4I. 

CdL2.KI.H2O;      CdI2.2NaI.6H2O  ;     CdI2.2KI.2H2O  ;     CdI2. 
2NH4I.2H2O. 

3.  With  calcium,  strontium,  and  barium  halides  — 

2CdCl2.CaCl2.7HoO  ;  CdCl2.SrCl2.7H2O  ; 
CdCL,.BaCl2.4H2O  ;  CdCL,.2CaCl2.2H2O. 
2ZnBr2.BaBr2  ;  CdBr2.BaBr2  2H2O 
2ZnI2.BaI2;  2CdI2.ZnI2.8H2O  ;  2CdI2.BaI2. 

4.  With  each  other—  MgrCl2.ZnCl2.6H2O  ;  Mg-Cl2.2CdCl2.12H2O. 

Thase  are  some  of  the  numerous  compounds  which  have  been  prepared. 
The  ratios  between  the  numbers  of  atoms  of  chlorine  in  the  constituents  ap- 
pear to  be  :—  2  :  1  ;  2  :  2  ;  2  :  3  ;  2  :  4  ;  and  4  :  1. 


*  Amer.  Chem.  Jour.,  5,  235. 

f  Srit.  Assn.,  1887,  668;  Eerichte,  12,  1195. 

J  Compt.  rend.,  102,  1068. 


126  THE   HALIDES. 

As  examples  we  may  select : — 2  :  1 ;  MgCl^NaCl ;  2CdCL,.CaCl.>; 
2  :  2— CdCL,.2NaCl;  CdBr^BaBr, ;  2  :  3— ZnCl2.3NH4Cl; 
2  :  4— CdCl2.4KCl ;  CdCl2.2CaCL ;  4  :  1— 2ZnCl2.HCl. 

These  bodies  are  all  prepared  by  direct  addition,  concentrated  aqueous  solu- 
tions of  their  constituents  being  added  to  one  another. 

Concluding  remarks  on  these  groups. — Molecular  for- 
mulae.— Jt  has  been  seen  that  whereas  the  metals  of  the  alkalies 
combine  with  the  halogens  in  the  ratio  1:1,  as  a  rule,  e.g., 
NaCl,  those  of  the  beryllium  and  magnesium  groups  display  the 
ratio  2  :  1,  as  for  example,  CaCl2,  BeCl2.  The  inquiry  may  here 
be  made  :  How  is  this  known  to  be  the  case?  To  take  a  specific 
instance  : — We  know,  from  the  densities  of  gaseous  HCl,  HBr, 
KBr,  -E6J,  &c.,  that  these  compounds  contain  an  atom  of  each 
element ;  the  vapour-density  of  zinc  chloride  has  been  found  to 
correspond  to  the  molecular  weight  136 '37 ;  now  subtracting 
35'46  x  2,  corresponding  to  the  weight  of  two  atoms  of  chlorine, 
the  remainder,  65 '45,  is  the  relative  weight  of  an  atom  of  zinc, 
provided  the  compound  contains  only  one  atom  of  zinc.  But  how  is 
this  known  ?  Might  not  its  formula  be  Zn2Clz  ?  In  which  case 
65'45  would  represent  the  relative  weight  of  two  atoms  of  zinc, 
and  32' 72  that  of  one.  And  if  such  a  question  may  be  asked  in 
the  case  of  zinc,  where  we  know  the  molecular  weight  of  one  of 
its  compounds  in  the  gaseous  state,  the  uncertainty  in  the  case  of 
barium  would  appear  to  be  much  greater,  for  in  this  instance  no 
compound  has  ever  been  gasified. 

The  answer  to  this  question  is  to  be  found  (1)  in  a  study  of 
the  specific  heats  of  these  elements,  and  (2)  in  their  position  in 
the  periodic  table.  These  will  now  be  considered  in  their  order. 

1.  Specific  Heats  of  Elements. 

The  data  for  these  have  been  given  in  the  tables  of  physical 
properties  appended  to  the  description  of  the  groups  of  elements. 

The  specific  heat  of  a  body  is  defined  as  the  amount  of 
heat  required  to  raise  the  temperature  through  1°,  compared 
with  the  amount  of  heat  required  to  raise  the  temperature 
of  an  equal  weight  of  water  through  1°.  Or,  as  water  is 
chosen  as  unit  of  weight  as  well  as  of  specific  heat,  specific  heat 
may  be  defined  as  the  amount  of  heat  required  to  raise  the  tem- 
perature of  1  gram  of  a  body  through  1°.  But  the  specific  heat 
of  water  is  not  -constant;  more  heat  is  required  to  raise  a  gram  of 
water  from  99°  to  100°,  than  from  0°  to  1°.  Hence  the  unit  is  now 
generally  accepted  to  be  the  hundredth  part  of  the  heat  required 
to  raise  the  temperature  of  1  gram  of  water  from  0°  to  100°.  This 


SPECIFIC   HEATS   OF   ELEMENTS.  127 

happens  nearly  to  coincide  with  the  value  of  1  heat  unit  at  the 
temperature  18°.  Such  a  heat  unit  is  termed  a  calory,  and  its 
abbreviated  symbol  is  c.  Where  large  amounts  of  heat  are  in 
question  a  unit  of  100  calories  is  often  used,  and  is  represented  by 
the  letter  K.  This  unit  is  convenient  in  expressing  heat  changes 
which  take  place  during  chemical  action. 

In  1819,  a  simple  relation  was  discovered  by  Dulong  and  Petit 
to  exist  between  the  amount  of  heat  required  to  raise  the  tempera- 
ture of  1  gram  of  each  of  the  following  thirteen  elements  through 
1°  : — copper,  gold,  iron,  lead,  nickel,  platinum,  sulphur,  tin,  zinc, 
bismuth,  cobalt,  silver,  and  tellurium, 

Dulong  and  Petit's  law. — The  specific  heats  of  the  ele- 
ments are  inversely  proportional  to  their  atomic  weights, 
approximately,  or 

(Sp.  Ht.)A  x  (At.  Wt.)A  =  (Sp.  Ht.)B  x  (At.  Wt.)B- 

Now  the  product  of  the  specific  heat  of  an  element,  or  heat  re- 
quired to  raise  the  temperature  of  1  gram  of  the  element  through  1° 
into  its  atomic  weight,  is  termed  its  atomic  heat.  For  instance,  the 
atomic  weight  of  sodium  is  23,  and  its  specific  heat  0'293 ;  and 
the  atomic  weight  of  lithium  is  7,  and  its  specific  heat  0'941.  The 
product  of  the  first  pair,  23  x  0'293  =  6' 74  calories,  represents 
the  amount  of  heat  necessary  to  raise  the  temperature  of  23  grams 
of  sodium  through  1° ;  and  the  product  of  the  second  pair, 
7  X  0'941  =  6'59  calories,  is  similarly  the  amount  of  heat  re- 
quired to  raise  the  temperature  of  7  grams  of  lithium  through  1°. 
But  23  and  7  are  the  relative  weights  of  the  atoms  of  sodium 
and  lithium ;  and  to  raise  these  relative  weights  expressed  in 
grams  through  1°  requires  6'74  and  6*59  calories  respectively  ; 
these  numbers  are  approximately  equal.  Hence  the  conclusion 
from  this  and  similar  instances,  that  the  atomic  heats  of  the 
elements  are  approximately  equal. 

This  law  is  not  without  apparent  exceptions,  as,  for  example, 
in  the  cases  of  beryllium,  boron,  carbon,  and  silicon,  but  it  holds 
closely  enough  to  be  a  valuable  guide  in  selecting  the  true 
atomic  weights.  It  appears  also  to  apply  only  to  solids.  As 
regards  the  real  meaning  of  this  law,  we  have  at  present  no 
knowledge.  We  can  form  no  probable  conception  of  the  change 
in  the  motion  or  position  of  the  atoms  in  a  molecule  due  to  their 
rise  of  temperature ;  but  it  is  a  valuable  empirical  adjunct  for  the 
purpose  mentioned. 

The  product  of  atomic  weight  and  specific  heat,  in  the  instances 
given,  is  approximately  6*5 ;  in  other  cases  it  falls  as  low  as  5'5. 


128  THE   HALIDES. 

It  may  be  stated  then,  that  this  product  is  approximately  a  con- 
stant, not  differing  much  from  the  number  6.  Hence  6/specific 
heat  of  any  element  should  approximately  equal  its  atomic  weight ; 
and  conversely  6/atomic  weight,  should  give  an  approximation  to 
its  specific  heat. 

As  the  atomic  weight  of  hydrogen  is  1,  its  atomic  heat  should 
be  6,  and  should  be  identical  with  its  specific  heat.  Solid  hydro- 
gen, however,  has  never  been  prepared.  But  it  forms  a  solid 
alloy  with  palladium ;  and  as  the  specific  heat  of  an  alloy  is  the 
mean  of  those  of  its  constituents,  that  of  solid  hydrogen  has  been 
indirectly  determined.  It  has  been  found  equal  to  5*88,  a  suffi- 
ciently close  approximation  to  6. 

To  return  now  to  the  atomic  weights  of  members  of  the  beryl- 
lium and  magnesium  groups  ;  the  following  table  gives  their 
atomic  heats : — 

Atomic 
Name.  Weight       Specific  Heat.  Atomic  Heat. 

Beryllium ....  9'1  x  0'6206  (at  500°)*  =  5'65 

Calcium 40-08  x  0-167  =  6'69 

Strontium 87'5  X          ?  =     ? 

Barium  ......  137'00  x          ?  =      ? 

Magnesium  . . .  24-30  x  0'250  =  6'07 

Zinc 65-43  x  0'095  =  6'22 

Cadmium 112'1  x  0'056  =  6'28 

At  100°  the  specific  heat  of  beryllium  is  0*4702 ;  its  atomic 
heat  is  therefore  4'28.  It  was  for  long  doubtful  whether  beryllium 

9*1 

had  not  the  atomic  weight  13'65,  i.e.,  3   X  — ;  the  formula  of  its 

chloride  would  then  have  been  BeCl3,  and  its  atomic  heat 
0'4702  X  13'65  =  6"42,  agreeing  with  those  of  many  other 
elements ;  but  its  vapour-density  decided  the  question.  A  sub- 
stance of  the  formula  BeCl3  should  have  had  the  vapour-density 
{13-65  +  (3  X  35-46)}2  =  60'01.  Actual  experiment  gave  40-42 
(see  p.  122),  hence  its  molecular  weight  is  80'84  (9'1  +  (2  x  35*46) 
=  80-02). t 

The  atomic  weights  of  calcium,  magnesium,  zinc,  and  cadmium 
given  in  the  table,  correspond,  it  will  be  seen,  with  the  usual 
atomic  heat. 

2.  The  similarity  of  the  metals  calcium,  strontium,  and  barium, 
and  of  their  compounds,  lead  to  the  inference  that  they  belong  to 
the  same  group  of  elements,  hence  they  find  their  position  in  the 

*  See  p.  33.  t   Comptes  rend.,  98,  988. 


SPECIFIC   HEATS. 


129 


periodic  table.      The  atomic  weights  are  deduced  from  this  simi- 
larity, and  from  their  position  in  the  table  (see  p.  22). 

For  these  reasons  it  is  concluded  that  the  general  formula  of 
the  halides  of  this  group  of  elements  is  MX2,  where  M  stands  for 
metal  and  X  for  halogen ;  that  of  the  members  of  the  lithium 
group  is  MX.  Lithium  and  its  congeners  are  termed  monad  or 
monovalent  elements  in  these  compounds ;  beryllium,  magnesium, 
and  elements  of  their  groups,  are  termed  dyad  or  divalent  in  their 
compounds.  But  it  has  been  amply  shown  that  valency,  as  the 
property  of  acting  as  a  monad,  a  dyad,  a  triad  element  is  termed,  is 
not  a  constant  quality  of  any  element ;  nor  in  such  compounds  as 
:KI3,  or  in  the  double  halides  mentioned,  can  we  tell  how  the 
atoms  are  held  together,  whether  the  metal  attracts  halogen,  or 
halogen  attracts  halogen,  or  both  attracts  both.  We  are  at  present 
without  any  satisfactory  theory  to  account  for  such  compounds,  and 
must,  in  the  meantime,  simply  accept  the  fact  of  their  existence. 

The  specific  heats  of  some  elements  may  be  simply  determined  with  fair 
approximation  by  the  "  method  of  mixture,"  and  Dulong  and  Petit' s  law  may 
be  easily  illustrated.  A  cylindrical  can  of  thin  sheet  brass  serves  as  a  calori- 
meter (fig.  26).  It  should  hare  a  capacity  of  about  300  cubic  centimetres. 
Having  placed  in  it  200  cubic  centimetres  of  water,  the  temperature  of  the 
water  is  accurately  ascertained  by  a  delicate  thermometer,  graduated  in  tenths 
of  a  degree.  Three  small  hemispheres  of  zinc,  tin,  and  lead,  each  weighing  100 
grams,  are  suspended  in  a  bath  of  boiling  water  by  thin  wires.  The  zinc  is 


FIG. 


quickly  lifted  out  and  dropped  into  the  calorimeter  ;  the  water  is  stirred  with 
the  thermometer  or  with  a  special  stirrer,  as  shown  in  the  figure,  and  its  tem- 
perature ascertained.  Similarly,  the  amount  of  heat  given  up  to  fresh  supplies 
of  cold  water  by  tlie  other  two  metals,  tin  and  lead,  is  found.  Their  specific 
heats  may  be  calculated  as  follows  :  — 


130  THE  HALIDES. 

Rise  of  temperature  of  the  water  x  200  =  heat  given  up  to  the  water  by 
100  grains  of  metal  in  cooling  from  100°  to  the  final  temperature  of  the  water. 
Hence,  if  t  —  t'  rise  of  temperature,  then  (t  —  t')  200  =  (100  —  t)x,  where  x  = 
capacity  for  heat  of  the  metal ;  and  x/100  =  specific  heat  of  the  metal. 

This  experimental  illustration,  rough  as  it  is,  yields  fairly  good  results, 
prohably  because  the  errors  neutralise  each  other  in  part.  The  sources  of  error 
are — (1)  Hot  water  is  carried  over  by  the  metal  into  the  calorimeter  ;  (2)  heat 
is  lost  by  the  metal  during  its  transit ;  (3)  no  allowance  is  made  for  the  capacity 
for  heat  of  the  metal  of  the  calorimeter  ;  and  (4)  no  correction  is  made  for  the 
loss  of  heat  of  the  calorimeter  by  radiation. 


131 


CHAPTEE  X. 

COMPOUNDS  OF  THE  HALOGENS  WITH  BORON,  SCANDIUM,  YTTRIUM, 
LANTHANUM,  AND  YTTERBIUM  ;  WITH  ALUMINIUM,  GALLIUM,  INDIUM, 
AND  THALLIUM  ;  WITH  CHROMIUM,  IRON,  MANGANESE,  COBALT,  AND 
NICKEL.  —  DOUBLE  HALIDES  OP  ELEMENTS  OF  THESE  GROUPS. 

Boron,  Scandium,  Yttrium,  Lanthanum,  and 
Ytterbium  Halides. 

Of  these  elements  boron  is  the  only  one  the  halides  of  which 
are  well  known. 

Sources.  —  None  of  the  haloid  compounds  of  these  elements 
exist  in  nature. 

Preparation.  —  1.  By  direct  union.  —  Boron  burns  when 
heated  in  chlorine  gas,  producing  the  chloride  BClz  ;  the  bromide 
may  also  be  prepared  by  passing  bromine  vapour  through  a  tube 
in  which  amorphous  boron  is  heated  to  redness.  The  iodide  is 
unknown. 

2.  By  the  simultaneous  action  of  chlorine  or  bromine 
and  carbon  (charcoal)  on  the  oxide  at  a  bright  red  heat.  — 
The  carbon  withdraws  the  oxygen,  producing  carbon  monoxide, 
while  the  halogen  unites  with  the  boron  ;  thus  :  — 

B203  +  30  +  3CZ.  =  2BCk  +  SCO. 


An  intimate  mixture  of  sugar-charcoal,  oil,  and  boron  oxide  is 
made  into  balls,  and  ignited  to  carbonise  the  oil  out  of  contact  with 
the  air.  They  are  then  heated  to  bright  redness  in  an  atmosphere 
of  halogen. 

Carbon  monoxide  is  a  gas,  very  difficult  to  condense;  boron 
chloride  and  bromide  are  liquids  at  the  ordinary  temperature  ; 
hence  by  leading  the  products  through  a  freezing-mixture,  the 
halide  condenses.  The  halides  of  the  other  elements  may  be  simi- 
larly prepared  ;  but  as  they  are  solids,  difficult  to  volatilise,  they 
remain  mixed  with  the  surplus  carbon. 

3.  By  double  decomposition.  —  (a.)  The  action  of  the  halo- 
gen acid  on  the  oxides  or  hydroxides.  —  This  is  the  usual  method  of 

K  2 


132  THE  HALIDES. 

preparing  boron  fluoride.  The  hydrogen  fluoride  is  prepared  from 
calcium  fluoride  and  sulphuric  acid  (see  p.  108),  and  while  being 
formed  acts  on  boron  oxide  contained  in  the  mixture. 

The  first  action  is  3CaP2  +  3H2S04  =  3CaSO4  +  6HF;  and 
the  second  B,O3  +  QHF  =  2BF3  +  3H20.  The  water  produced 
would  decompose  the  boron  fluoride,  were  it  not  that  it  combines 
with  the  sulphuric  acid  (see  p.  415),  and  it  is  thus  withdrawn 
from  the  action.  The  other  hydrogen  halides  have  no  action  on 
boron  trioxide.  With  other  oxides  of  the  group,  and  with  the 
hydroxides,  aqueous  solutions  of  the  halogen  acids  yield  halides. 

(6.)  Boron  chloride  may  be  produced  by  heating  together 
phosphorus  pentachloride,  PC15,  and  boron  trioxide  in  sealed  tubes 
to  150°.  The  equation  6PC15  +  5B2O3  =  3P2O5  +  10J3C7,  ex- 
presses  the  change. 

Properties. — Boron  fluoride  is  a  colourless  gas  very  soluble  in 
water  (1059  volumes  at  0°).  Boron  chloride  and  bromide  are 
volatile  colourless  liquids,  the  former  boiling  at  18'23°,  the  latter 
at  90*5°  ;  they  react  at  once  with  water,  forming  the  hydroxide  and 
hydrogen  halide,  -thus  :— BCla  -f  3H20  =  B(OH)3  4-  3HCL  Boron 
fluoride  has  such  a  tendency  to  combine  with  water  that  it  with- 
draws hydrogen  and  oxygen  from  carbon  compounds  containing 
them,  liberating  carbon,  and  in  this  respect  resembling  zinc 
chloride.  It  also  reacts  with  water  ;  the  first  stage  of  the  reaction 
is  2BF3  +  3H20  =  B2O3.6HF.*  On  heating  the  solution,  BF3  and 
H%0  are  evolved,  and  the  compound  HB02.3HF  named  fluoboric 
acid  remains  (see  p.  236).  On  dilution  with  water,  boron  hydroxide 
deposits  and  hydroborofluoric  acid  is  formed,  thus  : — 

4(HB02.3HF)  =  B(OH)3  +  3HF.BF3  +  5H20.f 

The  halides  of  the  other  elements  of  this  group  are  white  crys- 
talline substances  soluble  in  water,  and  decomposed  on  evaporation 
with  water.  They  are  not  easily  volatile,  hence  they  may  be  pro- 
duced anhydrous  l)y  evaporation  with  ammonium  chloride,  as 
anhydrous  magnesium  chloride  is  prepared  (see  p.  123).  Yttrium 
iodide  is  unstable  in  moist  air. 

Heat  of  formation.— B  +  CZ3  =  SC13  +  1040K. 

Double  halides. — The  double  halides  of  boron  fluoride  only  have  been 
studied.  It  was  mentioned  above  that  on  heating  a  solution  of  boron  fluoride, 
some  fluoride  escapes,  but  some  reacts  with  the  water,  giving  HF.BF3,  named 
hydroborqftuoric  acid.  It  is  also  produced  by  dissolving  boron  oxide,  B2O3,  in 
hydrofluoric  acid.  It  is  known  only  in  aqueous  solution,  for  on  concentration 

*  Basarois,  Comptes  rend.,  78,  1598. 

f  Considerable  doubt  exists  regarding  these  changes  (see  p.  236). 


ALUMINIUM,   GALLIUM,  INDIUM,  AND  THALLIUM.  133 

hydrogen  fluoride  is  evolved,  while  boron  hydroxide,  B(OH)3,  remains  in  solu- 
tion, thus:— HF.BF3  +  3H2O  =  B(OH)3  +  4HF.  Compounds  with  other 
luorides  can  also  be  produced  by  direct  union  of  boron  fluoride  with  the 
fluorides  of  these  elements  ;  but  such  compounds  are  also  formed  by  the  action 
of  hydro borofluoric  acid  on  the  oxides,  hydroxides,  or  carbonates  of  the  metals. 
They  are  almost  all  soluble  in  water  and  crystalline.  The  potassium  compound 
has  the  formula  KF.BF3  ;  the  barium  compound  BaF2.2BF3.H.2O.  The  zinc 
compound  may  be  prepared  by  the  action  of  the  hydrogen  compound  on  metallic 
zinc,  when  hydrogen  is  evolved,  thus : — 2HF.BF3.Aq  -hZn  =  ZnF2.2BF3  +  H^. 
These  bodies  are  commonly  termed  salts  of  hydroborofluoric  acid  or  bora- 
fluorides. 


Aluminium,  Gallium,  Indium,  and  Thallium 
Halides. 

Sources. — The  only  important  compound  found  native  is  alu- 
ninmm  fluoride,  which,  in  combination  with  sodium  fluoride, 
orms  the  white  crystalline  mineral  cryolite,  3NaF.AlF3. 

Formation. — These  elements  combine  with  the  halogens  in 
several  proportions,  as  seen  in  the  following  table: — 

Fluorine.  Chlorine.  Bromine.  Iodine. 

Aluminium.     A1F2*;A1F3  A1C13  —    AlBr3  —  AU3. 

Gallium  ...          ?         GaF3     GaCL, ;  GaCl3t        ?      GaBr3  ?  GaI3. 

Indium ?         InF3      InCl;     InC^;  ?      InBr3  ?  InI3. 

InCl3 

Thallium..      T1F;     T1F3      T1C1 ;     TICLj ;    TlBr;TlBr2;  TIT;  T1I3. 

T1C13  TlBrs 

Preparation. — 1.  By  direct  union. — The  compounds  of  the 
general  formula  MX3  are  formed  in  this  way. 

2.  By  replacement. — A1X3,  GaX3,  and   InX3,  are  produced 
by  dissolving  the  respective  metals  in  the  haloid  acid;  hydrogen 
is  evolved ;  thallium  dissolves  very  slowly,  being  protected  by  a 
layer  of  sparingly  soluble  halide,  forming  a  thallous  salt,  TLX. 
By  heating  indium  in  dry  hydrogen  chloride,  however,  InCl2  is 
produced. 

3.  The  lower  chlorides,  GaCl2,  InCl2,  and  InCl,  have  been 
produced  by  heating   the   higher   chlorides  with   the   respective 
metals. 

4.  By  double  decomposition. — (a.)  Solution  of  the  respective 
oxides,  hydroxides,  or  sulphides  in  the  haloid  acid. 

*  Only  known  in  the  compound  2NaF.AlF2. 
f  Comptes  rend.,  93,  294  and  329. 


134  THE   HALIDES. 

Thus:—  A1203  +  GHCl.Aq  =  2AlCl3.Aq  +  3H20  ; 
T12O  +  2HCl.Aq  =  2TlCLAq  +  H20  ; 
T1203  -f  6HCl.Aq  =  2TlCl3.Aq  +  3H20  ; 
In2S3  +  CHCl.Aq  =  2InCl3.Aq  +  3JB2S. 

Thallous  carbonate  dissolves  in  haloid  acids,  giving  thallous  salts. 
(&.)  By  precipitation.  —  The  chloride,  bromide,  and  iodide  of  thal- 
lium being  nearly  insoluble  in  water,  may  be  prepared  by  treating 
a  soluble  compound,  e.g.,  the  nitrate,  TUST03,  with  a  soluble  halide  ; 
thus  — 

TlN03.Aq  +  KI.Aq  =!  Til  +  KN03.Aq. 

(c.)  Aluminium  chloride  and  bromide,  like  the  corresponding 
halides  of  boron,  may  be  produced  by  passing  chlorine  over  a  mix- 
ture of  the  oxide  and  charcoal  heated  to  redness  ;  or  by  passing  the 
vapour  of  carbon  tetrachloride,  CCU,  over  red-hot  alumina.  The 
equations  are  :  — 

A12O3  +  3C  +  30Zs  =  ZAIClz  +  3(70;  and 
2A12O3  +  3CCk  =  4>AW13  +  3(702. 


Properties.  —  MX3.  —  These  compounds,  with  the  exception  of 
InI3,  which  is  yellow,  T1P3,  green  (?),  TlBr3,  yellow,  and  T1I3, 
red,  are  colourless  crystals  ;  they  are  all  soluble  in  water.  They 
melt  and  sublime  at  comparatively  low  temperatures.  They 
crystallise  from  water  with  water  of  crystallisation.  Their  solu- 
tions, when  evaporated,  decompose,  halogen  acid  being  liberated, 
and  an  oxyhalide  being  left.  The  anhydrous  halides  all  attract 
atmospheric  moisture. 

MX2.—  Gallium  and  indium  dichlorides  are  white  ;  that  of 
thallium  pale  yellow,  as  also  its  dibromide.  They  are  attacked  by 
water,  indium  and  gallium  dichlorides  apparently  decomposing 
into  mono-  and  trichlorides,  thus  :  — 

2InCl2  +  Aq  =  InCl  +  InCl3.Aq. 

The   monochloride  in   contact   with   water    deposits   the   metal, 
trichloride  remaining  in  solution,  thus  :  — 

3InCl  +  Aq  =  InCl3.Aq  +  2In. 

MX.  —  InCl*  is  reddish-yellow,  and  is  decomposed  by  water 
(see  above).  TIP,  T1C1,  and  TIBr,  are  white  crystalline  bodies  ; 
Til  is  yellow.  The  fluoride  is  the  most  soluble,  the  iodide  almost 
insoluble  in  cold  water.  They  all  crystallise  from  solution  in  hoi 
water,  and  do  not  react  with  it  on  evaporation. 

*  Chcm.  Soc.,  53,  820. 


ALUMINIUM,  GALLIUM,  INDIUM,  AND  THALLIUM.  135 

Molecular  weights.* — The  chloride  of  aluminium  at  tempera- 
tures between  218°  and  440°,  and  at  pressures  varying  from  300 
to  760  mms.  has  the  formula  J.Z2C76,  and  similarly  the  bromide  and 
iodide  possess  the  respective  formulae  Al^Er*  and  -AZ2J6,  as  shown 
by  their  respective  vapour-densities.  As  the  temperature  rises 
above  440°  these  molecules  dissociate :  thus  Al2Ck  =  SAW!*.  The 
vapour-density  therefore  falls  with  rise  of  temperature,  an  ever- 
increasing  number  of  simpler  molecules  being  produced  by  the 
splitting  up  of  the  more  complex  ones ;  till  at  800-900°  the  density 
reveals  the  fact  that  the  gas  consists  wholly  of  molecules  of  the 
formula  A1C13.  At  still  higher  temperatures  chlorine  gas  is 
liberated,  possibly  owing  to  the  formation  of  a  lower  chloride,  pos- 
sibly owing  to  the  separation  of  aluminium.  Gallium  trichloridef 
at  temperatures  below  270°,  and  at  atmospheric  pressure,  appears 
also  to  possess  the  formula  Ga^Gl^ ;  its  density  likewise  decreases 
with  rise  of  temperature  and  with  fall  of  pressure,  and  at  440° 
and  higher  temperatures  its  density  corresponds  to  the  formula 
GaCl3.  On  the  other  hand,  indium  trichloride  does  not  gasify  till 
it  has  nearly  reached  its  temperature  of  complete  dissociation ;  at 
850°  and  upwards  its  formula  is  InCl*.  It  is  not  known  whether 
the  other  chlorides  possess  the  formulae  M2Cl4,  M2C12,  or  not ;  for 
at  the  temperature  at  which  they  gasify,  they  are  already  resolved 
into  the  simpler  molecules,  MCl^  and  MGl.  It  appears  then  that 
just  as  these  halides  form  double  compounds  with  the  halides  of 
other  metals,  so  they  form  double  compounds  with  themselves, 
acquiring  thereby  a  double  molecular  formula.  Thallous  chloride 
has  a  vapour-density  corresponding  to  the  formula  TICl. 

The  atomic  heats  of  these  elements  is  normal.  The  results 
are: — 

Aluminium.  Gallium.  Indium.  Thallium. 

6-08  5-52  6-42  6'86 

Hence  the  molecular  formula  of  these  compounds. 

That  of  boron,  it  will  be  seen  on  reference  to  p.  37,  increases 
rapidly  with  rise  of  temperature ;  at  233°  it  is  4'03  ;  but  at  still 
higher  temperatures  it  would  doubtless  become  normal. 

*  Annales  (3),  58,  257. 

f  ZeHschr.  PJiys.  Chem.,  1,  460 ;  and  2,  659 ;  Comptes.  rend.,  106,  1764, 
and  107,  306 ;  Chem.  Soc.,  53,  814. 


136 


THE   HAUDES. 


Physical  Properties. 
Mass  of  1  e.c.  solid.  Melting-point. 


Boiling-point. 


F3.     C13.  Br3.  I3.        F.     01.     Br.      1.      F.     Cl.     Br.      I. 

Boron   (liquid    ?      1-35  2'69  ?        ?         ?       —      ?  18'2°  90'5°   — 

compounds) 

Aluminium..    31      ?  2'54  2'63     ? 

G-allium   ....     ?     2'36       ?  ?         ? 

at  80° 

Indium  . .           ?        ?          ?  ?         ? 


?*      93°    125°     ?      *      264°  350° 
75-5°      ?        ?        ?   220°      ?         ? 


Thallium,TlX    ?      7'0     7*54     7'8       ?      427  J  458°  439°  719°  ?         ? 
GaCl2:  m.-p.,  164°;  b.-p.,  c.  535°. 


? 
800° 


Heats  of  formation  :  — 

1.  Al  +  SCI  =  A1C13  +  1610K  +  Aq  =  768K. 
Al  +  3Br  =  AlBr3  +  1197K  +  Aq  =  853K. 
Al  +  31    =  A1I3    +     704  K  +  Aq  =  890K. 

2.  Tl   +  Br    =  TIBr   +     413K. 
Tl   +  I       =  Til      +     302K. 

Double  halides.  —  Of  these,  only  the  compounds  of  aluminium  and  thallium 
seem  to  have  been  prepared.  They  are  all  obtained  by  direct  addition,  some- 
times, however,  being  prepared  in  presence  of  water,  sometimes  by  fusion. 


Derivatives  of  MX3. 
AlF3.3NaP.         A1F3.2KF. 
A1F3.3KF.  AlF3.2NaF. 

T1C13.3NH4C1.    T1C13.2KC1. 
T1C13.3T1C1. 
TlBr3.3TlBr.  — 


AlCl:3.NaCl  J  Similar  iodides  are 

AlBr3.KBr  \     said  to  exist. 

TlBr3.NH4Br. 

T1C13.T1C1. 

TlBr3.TlBr. 

T1I3.KI. 


Besides  these  are  known: — T1I|V5T1I;  2TlBr3.3KBr;  and  its  analogue, 
2T1I3.3KI;  also  4AlF3.MgrF2.NaF,  a  mineral  named  ralstonite.  The  most 
important  of  these  is  the  mineral  cryolite,  AlF3.3NaF,  which  is  mined  at 
Evigtok,  in  West  Greenland,  where  it  forms  a  deposit  80  x  300  feet  in  depth 
and  length.  It  is  used  as  a  source  of  fluorine,  of  pure  alumina,  and  of  caustic 
soda. 

2.  Derivatives  of  MX,. — The  compound  AlF2.2NaF,  belonging  to  this 
group,  is  an  interesting  one,  inasmuch  as  it  is  the  only  one  in  which  aluminium 
is  combined  with  two  atoms  of  a  halogen,  or,  more  comprehensively,  the  only 
one  in  which  aluminium  functions  as  a  dyad  (see  p.  129).  It  has  recently  been 
prepared  by  heating  cryolite  with  metallic  aluminium  to  redness,  in  an  iron 


Sublimes  without  fusing. 


CHKOMIUM,  IRON,  MANGANESE,   COBALT,   AND   NICKEL.       137 

crucible  in  a  current  of  hydrogen.  It  is  a  white  insoluble  substance,  evolving 
hydrogen  on  treatment  with  hydrochloric  acid.* 

3.  Derivatives  of  MX. — The  only  representative  known  is  T1F.HF,  which 
is  produced  by  direct  addition.  It  resembles  its  potassium  analogue,  KF.HF 
(see  p.  119),  in  being  decomposed  by  heat. 

It  has  been  shown  that  the  compound  T1I3KI  may  equally  well  be  produced 
from  Til  and  KI3.f  We  cannot  therefore  regard  it  as  necessarily  composed  of 
thalltc  iodide  and  potassium  iodide  ;  it  may  equally  well  be  viewed  as  a  compound 
of  potassium  triiodide,  KI3,  and  Shallow*  iodide,  Til.  In  fact  we  have  to  confess 
our  complete  ignorance  of  the  manner  of  combination  of  the  atoms  in  the  mole- 
cule. It  might  therefore  be  better  to  write  the  formula  KT1I4,  thus  committing 
ourselves  to  neither  view ;  but  simplicity  of  arrangement  is  certainly  aided  by 
the  method  adopted. 


Chromium,  Iron,  Manganese,  Cobalt,  and  Nickel 

Halides. 

Sources. — None  of  these  compounds  is  found  native  except 
ferric  chloride,  Fe2Cl6,  which  sometimes  occurs  in  the  waters  of 
volcanic  districts. 

These  elements,  generally  speaking,  combine  with  the  halogens 
in  two  proportions,  as  shown  in  the  following  table : — 

Fluorine.  Chlorine.  Bromine.  Iodine. 

Chromium ...          —      CrF3.  CrCl2 ;  CrCl3.  CrBr2 ;   CrBr3.       —     CrI3. 

Iron FeF2  ;  FeF3.  FeCl2 ;  FeCl3.  FeBr2  ;  FeBr3.  FeI2  ;  FeI3. 

Manganese...      MnF2;  MnF3.  MnCl2 ;  MnCl3t  MnBr2;    —  MnI2; — 
MnF4. 

Cobalt CoF2 ;       —  CoCL2 ;  CoCl3t  CoBr2 ;  CoI2 ;    — 

Nickel NiF2 ;       —  NiCl2 ;      —  NiBr2 ;      —  NiI2 ;    - 

Manganese  forms  a  tetrachloride,  stable  in  ethereal  solution ;  chromium  a 
hexafluoride,  CrF6. 

Preparation. — 1.  By  direct  union. — Chromium  and  iron 
form  dihalides,  if  the  halogen  be  not  in  excess  ;  and  trihalides 
with  excess  of  halogen;  manganese,  nickel,  and  cobalt,  form 
only  dihalides. 

2.  By  the  action  of  the  halogen  acid  on  the  metals  with 
or  without   presence  of  water. — In  all  cases  the  dihalide  is 
formed,  thus  : — 

Fe  +  2HC1  =  FeCl3  -f  H2. 

3.  By  double  decomposition. — The  action  of  the  halogen 

*  Chem.  News,  59,  75. 

t  Johnson,  Chem.  Soc.,  33,  183. 

£  Known  only  in  solution. 


138  THE   HAL1DES. 

acid  on  the  oxide,  hydroxide,  sulphide,  carbonate,  sulphite, 
&c.  —  With  oxides,  sulphides,  &c.,  in  which  the  metal  acts  as  a 
dyad,  the  dihalides  are  formed,  thus  :  — 

FeO  +  2HCl.Aq  =  FeCl2.Aq  +  H20. 
Mn(OH)2  +  2HCl.Aq  =  MnCl2.Aq  +  H20. 
NiS  +  2HCl.Aq  =  NiCl2.Aq  +  H2S. 
CoCO3  +  2HCl.Aq  =  CoCL.Aq  +  CO,  +  H20. 

If  the  sesquioxide,  dry  or  hydrated  (hydroxide),  be  employed, 
the  trihalides  are  produced  when  capable  of  existence  ;  if  not,  the 
halogen  is  evolved,  thus  :  — 

Fe2O3  +  GHCl.Aq  =  2FeCl3.Aq  +  3H20. 
Cr(OH)3.Aq  +  SHCl.Aq  =£  CrCl3.Aq  +  3H20. 
Ni2O3  +  6HCl.Aq  =  2MCl2.Aq  +  3H20  +  C7a. 
Mn2O3  +  OHBr.Aq  =  2MnBr2.Aq  +  3H20  +  Br2. 

With  a  higher  oxide  of  the  metal,  or  a  double  oxide  containing 
such  a  higher  oxide,  the  highest  halide  capable  of  existence  at  the 
temperature  of  action  is  produced,  and  the  halogen  is  liberated  : 
thus,  if  the  solution  be  cold, 

2MnO2  +  4HCLAq  =  2MnCl3.Aq  +  4H20  +  Cl,  ;  but  if  hot, 
MnO2  +  4HCl.Aq  =  MnCl2.Aq  +  2H20  +  Ch. 
Similarly,  2Cr03.Aq  +  12HLAq  =  2CrI3.Aq  +  6H20  +  3I2;  and 
K2O207.Aq(=  K20.2Cr03)  +  14HCl.Aq  =  2KCl.Aq  + 

2CrCl3.Aq  +  7H20  +  30Z8. 

Also,  2KMn04.Aq(  =  K2O.Mn207)  +  IGHCl.Aq  =  2KCl.Aq  + 
2MnCl2.Aq  +  8H20 


These  last  methods,  involving  the  use  of  higher  oxides,  are  the 
practical  methods  of  preparing  the  elements  —  chlorine,  bromine, 
and  iodine  (see  p.  75).  Fluorine  cannot  be  thus  liberated.  Hydro- 
gen fluoride  either  is  without  action,  or  it  liberates  oxygen  as  ozone, 
or  (in  the  case  of  manganese  dioxide  or  of  chromium  trioxide), 
higher  fluorides  are  produced  (see  p.  142). 

4.  With  chromium  alone,  the  action  of  hydrogen  at  a  low 
red  heat  on  the  trihalide  produces  the  dihalide,  thus  :  — 

2CrCl3  +  H2  =  2CrCl2  +  2HCL 

This  is  best  carried  out  practically  by  heating  a  mixture  of 
chromic  chloride  and  ammonium  chloride  to  bright  redness  in  a 
porcelain  retort. 

On  treatment  with  hydrogen  at  a  red  heat,  the  other  chlorides 


CHROMIUM,   IRON,  MANGANESE,   COBALT,  AND   NICKEL.        Iu9 

are  reduced  to  metal ;  as  is  that  of  chromium  at  a  high  tem- 
perature. 

5.  By  the  action  of  the  halogen  on  a  red-hot  mixture  of 
the  oxide  and  carbon. — This  method  is  specially  used  for  pre- 
paring the  trihalides  of  chromium,  for  the  metal  is  difficult  to 
prepare.  The  halide  volatilises,  and  is  thus  separated  from  the 
excess  of  carbon. 

Properties. — Dihalides. — These  compounds,  if  anhydrous, 
crystallise  in  lustrous  scales.  Their  colours  are : — 

Chromium.     Iron.      Manganese.       Nickel.  Cobalt. 

Fluoride..  ?         White  ?  ?  ? 

Chloride..     White    White         Rose  Yellow  Blue. 

Bromide  .     White    Yellowish   Pale-red    Yellow  Green. 

Iodide...          ?         Grey  White?     Dark,  metallic  Black,  lustrous. 

They  are  all  deliquescent,  and  dissolve  in  water,  heat  being 
evolved  by  the  union.  They  also  dissolve  in  alcohol.  They 
crystallise  from  such  solutions,  with  more  or  less  water  of 
crystallisation.  They  cannot  be  dried,  for  they  react  with  water, 
giving  oxyhalides.  The  colours  of  these  compounds  with  water 
are: — 

Chromium.        Iron.        Manganese.  Nickel.  Cobalt. 

Fluoride ?  Colourless       Amethyst  Green  Eose. 

Chloride Blue  Blue-green     Eose  Green  Pink. 

Bromide. .      Blue  Green             Bed  Green  Red. 

Iodide .        ?  Green             White  Green  Green. 

Manganous  fluoride  is  insoluble  in  water,  but  dissolves  in 
aqueous  hydrofluoric  acid,  doubtless  forming  a  double  fluoride. 
Almost  all  these  compouDds  are  soluble  in  alcohol;  manganous 
chloride  dissolves  with  a  green  colour.  The  halides  of  nickel  and 
of  cobalt  undergo  a  curious  change  on  concent  ration,  or  on  addition 
of  halogen  acid ;  those  of  nickel  turn  yellow  ;  those  of  cobalt  blue, 
or  green.  This  is  probably  due  to  the  formation  of  the  anhydrous 
chloride.  The  solutions  are  used  as  "  sympathetic  inks." 

When  the  paper  on  which  they  are  traced  as  ink  is  warmed,  a  change  of 
colour  takes  place.  A  very  curious  effect  may  be  produced  by  combination  of 
ordinary  water-colours  with  such  sympathetic  inks ;  a  landscape,  cleyerly 
painted,  may  be  made  to  show  a  transition  from  a  winter  to  a  summer  scene 
when  held  before  the  fire. 

The  chromous  and  ferrous  halides,  on  exposure  to  air,  combine 
with  its  oxygen,  forming  chromic  or  ferric  oxyhalides  (see  p.  257). 
Their  solutions,  especially  those  of  the  chromium  halides,  rapidly 
absorb  oxygen ;  the  oxidation  being  accompanied  by  a  change  of 


140  THE   HALIDES. 

colour — to  green,  in  the  case  of  chromium,  and  to  brown-yellow,  in 
the  case  of  iron.  Such  substances  are  said  to  have  power  of 
"  reduction,"  meaning  that  they  tend  to  absorb  oxygen  from 
bodies  capable  of  parting  with  it,  they  themselves  being 
"oxidised."  In  presence  of  halogen  acid,  such  a  reaction  as  this 
occurs :— 2FeCl2  +  2HC1  +  0  =  2FeCl3  +  H2O  ;  the  oxygen  being 
derived  from  the  air,  or  from  any  substance  capable  of  yielding  it. 
Hence,  chromous  and  ferrous  halides  are  converted  into  chromic 
or  ferric  halides,  by  the  action  of  the  halogen  in  presence  of 
water. 

Physical  Properties. 

Mass  of  1  c.c.  Melting-points.  Boiling-points. 


Chromium  .  . 
Iron  

F.  Cl.  Br.  I. 

?  275  ?  ?^| 
?  2*53  ?  ?  1 

Manganese.  . 
Cobalt  

?  2-48  ?  ?  j, 
?  2-94  ?  ?  | 

Unknown.  Unknown. 

?   ?i 

Nickel 2-86    2'56      ?       ?  j 

Hydrated :— NiCl2.4H2O,  2'01 ;  FeCL,.4H2O,  1'93  j  CoCl2.6H2O,  1'84. 


Heats  of  formation  : — 

Cr    +  <?Z2  =  CrCl2     +       ?  +  Aq  =  ? 

Fe    +   C12  =  FeCl2    +  821K  +  Aq  =  179K. 

Mn  +  C12  =  MnCl2  +  1120K  +  Aq  =  160K. 

Ni    +  Clz  =  NiCl2    -1-  745K  +  Aq  =  192K. 

Co    +  C12  =  CoCl2     +  765K  +  Aq  -  183K. 

Double  compounds  of  the  dihalides. — One  hydrochloride  is  known,  viz., 
2HC1.3CrCl2.13H2O  ;  and  crystals,  too  unstable  to  be  collected,  have  also  been 
obtained  by  passing  hydrogen  chloride  into  a  cold  solution  of  cobaltous  chloride. 
The  other  double  salts  may  be  divided  into  two  groups,  of  which  instances  are 
FeF2.2KF,  FeCl2.2KC1.2H2O,  MnCI2.2NH4Cl;  also  NiCl2.NH4Cl,  and 
MnCl2.NH4Cl. 

Not  many  such  compounds  have  been  prepared. 

Trihalides.—  The  anhydrous  trihalides  also  form  lustrous 
scales.  Their  colours  are — 

Chromium.  Iron. 

Fluoride Park  green  Pale  yellow. 

Chloride Pale  violet  Black. 

Bromide Dark  olive  green  Black.  ? 

Iodide ?  Black. 

Chromic  chloride,  after  sublimation,  is  insoluble  in  cold  water, 
but  dissolves  after  long  boiling.  If  prepared  by  drying  the 
hydrated  chloride  in  a  current  of  hydrogen  chloride,  it  is  soluble  ; 
as  soon  as  it  has  been  sublimed,  it  is  insoluble.  The  presence  of  a 


CHROMIUM,  IRON,  MANGANESE,   COBALT,  AND   NICKEL.       141 

trace  of  chromous  chloride  causes  the  insoluble  variety  to  dissolve 
at  once.  The  other  halides  are  deliquescent,  and  readily  soluble 
in  water.  They  also,  like  the  dihalides,  react  with  water,  forming 
oxyhalides  (see  p.  257). 

The  trihalides  of  manganese  and  cobalt -are  unknown  in  the 
anhydrous  state. 

The   aqueous   solutions  have    different   colours,   owing,    no  doubt,  to   the 
presence  in  solution  of  a  compound  with  water.     They  are — 

Chromium.            Iron.  Manganese.  Cobalt. 

Fluoride   ....      Green  Colourless  Ruby  ? 

Chloride   ....      Green  Yellow  Brown-yellow  Brown 

Bromide  ....      Green  Brown- red                    ?  ? 

Iodide Green  Brown                         ?  ? 

Chromic  chloride  exists  in  two  modifications,  green  and  violet. 
The  green  solution  has  possibly  a  more  complex  molecule  than 
the  violet  one.  The  violet  modification  is  produced  from  the 
violet  sulphate  (see  p.  426)  by  double  decomposition  with  barium 
chloride,  thus,  Cr23S04.Aq  +  3BaCl2.Aq  =  2CrCl3.Aq  +  3BaSO4 ; 
or  by  dissolving  the  grey  modification  of  the  hydroxide  (see  p.  252) 
in  hydrochloric  acid.  These  chlorides  probably  all  react  with 
water,  giving  oxychlorides.  That  of  manganese,  indeed,  if  much 
water  be  added,  gives  a  precipitate  of  sesquioxide,  thus : — 

2MnCl3.Aq  +  3H20  =  Mn2O3.Aq  +  6HCl.Aq. 

Manganic  fluoride,  when  heated  with  water,  gives  off  oxygen, 
and  hydrogen  fluoride,  thus :  2MnF3.Aq  +  H2O  =  2MnF2.Aq  +  2#F 
+  02.  Manganese  and  cobalt  trichlorides  are  very  unstable, 
evolving  chlorine  at  the  ordinary  temperature,  thus :  2MnCl3.Aq 
=  2MnCl2.Aq  +  (7?2.  Ferric  chloride  is  more  stable,  but  it  may  be 
reduced  or  deprived  of  chlorine  by  means  of  nascent  hydrogen, 
i.e.,  hydrogen  in  process  of  formation.  Hydrogen  gas  may  be 
passed  through  a  solution  of  ferric  chloride  without  action;  but  if 
the  hydrogen  be  prepared  in  a  solution  of  ferric  chloride  by  the 
action  of  zinc  and  hydrochloric  acid  for  example  (see  p.  27), 
the  ferric  chloride  is  changed  to  ferrous  chloride,  thus : — 
FeCl3.Aq  +  H  =  FeCl2.Aq  +  HCl.Aq.  It  is  supposed,  with  great 
probability,  that  the  hydrogen  is  liberated  in  the  atomic  condition. 
In  presence  of  ferric  chloride  it  unites  with  chlorine ;  but  if  no 
reducible  substance  is  present,  it  combines  with  itself  to  form 
molecular  hydrogen,  H2,  which  is  then  without  action.  Chromic 
chloride  cannot  be  easily  reduced  in  aqueous  solution. 


142  THE   HALIDES. 


Physical  Properties. 
Mass  of  1  c.c.  solid.        Melting-point.  Boiling-point. 

F.       01.      Br.   I.        F.    01.   Br.     I.         F.     01.   Br.     I. 
Chromium....        ?       2'76       ?       PI  Unknown.  Unknown. 

Iron  ..........        ?       2-80       ?       ff 

Heat  of  formation  :  — 

Fe  +  C13  =  FeCl3  +  961K  ;  +  Aq  =  FeCl3.Aq  4  633K. 

Double  compounds  of  the  trihalides.  —  These  are  made  by  direct  addition 
and  belong  to  the  following  four  types  :  — 

;  CrBr3.KBr  ;  CrI3.KI  ;  FeF3.KF. 


These  are  stable  in  presence  of  excess  of  the  hydrogen  -halide,  but  decom- 
pose with  water. 

2.  CrF3.2KF;    FeF3.2KF;    FeCl3.2KCl  ;    FeCl3.2NH4Cl;    FeCl3.MgrCl2  ; 

MnF3.2KF;  MnF3.2NH4F;  MnF3.2NaF;  MnF3.2AgF. 

3.  CrF3.3KF. 

4.  2FeI3.FeI2;  2MnF3.M:nF2. 

The  green  modifications  of  chromic  halides  do  not  form  double  compounds. 
They  are  possibly  combinations  of  molecules  of  the  chromium  halides  with 
each  other. 

Higher  halides.  —  Manganese  tetrafluoride,  MnF4,  is  produced 
by  treating  manganese  dioxide  with  aqueous  hydrogen  fluoride, 
thus  :  — 

MnO2  +  4HF.Aq  =  MnF4.Aq  +  2H20. 

It  is  soluble  in  alcohol  and  in  ether.  Its  aqueous  solution,  when 
warmed,  decomposes,  depositing  the  dioxide,  MnO2.Aq.  On  ad- 
dition of  a  solution  of  potassium  fluoride  it  forms  the  double 
compound,  2KF.MnF4,  as  a  rose-coloured  precipitate. 

Manganese  dioxide,  suspended  in  ether,  and  saturated  with 
hydrogen  chloride,  gives  a  green  solution  of  MnCl4. 

Chromium  hexafluoride,  CrF6,  is  produced  by  the  action  of 
hydrogen  fluoride  on  chromium  trioxide,  Cr03,  in  presence  of 
anhydro-sulphuric  acid  to  absorb  the  resulting  water,  thus  :  — 

O03  +  6HF  +  3H2S207  =  CrF6  +  6H2S04. 

It  is  a  fuming  volatile  liquid,  of  a  blood-red   colour,   which 
attacks  silicon  oxide,  and  hence  cannot  be  kept  in  glass  vessels.* 
General  remarks.  —  The  elements  of  this  group  combine  with 

*  This  substance  is  also  said  to  be  an  oxyfluoride  of  the  formula  Cr02F2 
(Gazzetta  chimica  italiana,  16,  218). 


CHROMIUM,   IRON,   MANGANESE,   COBALT,  AND   NICKEL.       143 

halogens  in  four  different  proportions,  thus  :  MX2,  MX3,  MX^  and 
MXe.  The  higher  members  are  most  stable  with  chromium, 
and  the  lower  ones  most  stable  with  nickel.  The  molecular 
formulae  of  these  bodies  have  given  rise  to  much  dispute. 
Chromium  dichloride  appears  to  exist  partly  as  OC?2,  partly 
as  CrzCl4,  in  the  gaseous  state  at  1600° ;  at  1400-1500°,  ferrous 
chloride  possesses  the  simpler  formulae,  Fed*.  Chromic  chloride, 
above  its  volatilising-point,  about  1060°,  has  the  formula,  OC73 ; 
ferric  chloride,  at  temperatures  below  620°,  is  FezCl6  ;*  but  as  tem- 
perature rises,  these  complex  molecules  dissociate,  and  at  750°  and 
upwards,  its  density  shows  it  to  have  the  formula,  FeCl^  The 
molecular  weights  of  the  double  compounds  of  these  halides  are 
unknown,  but  it  appears  probable  that  they  possess  the  simpler 
formulae  given  them. 

The  formulae  of  these  compounds  are  deduced — 

1.  From  the  simplicity  of  the  ratios  of  metal  and  halogen : — 
viz.,  1 :  2  ;   1  :  3  ;   1  :  4  ;  and  1  :  6. 

2.  From  the  vapour- densities. 

3.  From  the  atomic  heat  of  the  metals.     These  are  : — 

Or.  Fe.  Mn.  Ni.  Co. 

?         6-27  6-69  6-43  6'31 

*  Comptes  rend.,  107,  301. 

f  Zeitschr.  Phys.  Chem.,  2,  659 ;   Chem.  Soc.,  53,  814. 


144 


CHAPTER  XI. 

COMPOUNDS  OF  THE  HALOGENS  WITH  CARBON,  TITANIUM,  ZIRCONIUM, 
CERIUM,  AND  THORIUM  ;  WITH  SILICON,  GERMANIUM  (TERBIUM), 
TIN,  AND  LEAD. — DOUBLE  HALIDES  OF  ELEMENTS  OF  THESE  GROUPS. 
— PROOF  OF  THEIR  MOLECULAR  FORMULA. 

Carbon,  Titanium,  Zirconium,  Cerium,  and 
Thorium  Halides. 

The  halides  of  carbon  differ  from  those  of  the  remaining  elements 
of  this  group,  in  being  more  numerous,  and  in  being  insoluble  in 
water.  It  appears  advisable,  in  the  present  state  of  our  know- 
ledge, to  include  cerium  in  this  group,  although  its  halides  do  not 
closely  resemble  those  of  the  other  elements  of  the  group. 

Sources. — None  of  these  halides  occur  native,  except  Jluocerite, 
to  which  Berzelius  gave  the  formula  CeF3,  and  tysonite,  4CeF3, 
3LaF3. 

These  elements  form  the  following  compounds  with  the 
halogens: — 

Fluorine.  Chlorine.  Bromine.  Iodine. 

Carbon CF4  CC14.C2C16;  C2Cl4,&c.  CBr4;  C2Br6;  C2Br4.   CI4. 

Titanium..    TiF3;  TiF4     T1C12;  Ti2Cl6;  TiCl4  TiBr4  TiI4. 

Zirconium .    ZrF4  ZrCl4  ZrBr4*  ? 

Cerium....    CeF3;*CeF4*CeCl3  CeBr3*  CeI3* 

Thorium  ..    ThF4  ThCl4  ThBr4*  ThI4*. 

Preparation.— 1.  By  direct  union.— Carbon  does  not  com- 
bine directly  with  halogens,  except  with  fluorine.  The  other 
elements  are  converted  into  those  compounds  which  contain  the 
largest  amount  of  halogen. 

2.  By  the  action  of  the  halogen  on  a  red-hot  mixture  of  the 
oxide  with  charcoal.— By  this  means,  TiCl4,  TiBr4,  ZrCl4,  and 
ThCl4  have  been  prepared.  The  preparation  of  chloride  of 
titanium  may  serve  as  a  type  of  the  rest : — 

TiO2  +  20  +  2012  =  TiOh  +  2<70.f 

*  These  have  been  obtained  only  in  combination  with  water, 
f   Chem.  Soc.,  47,  119  ;   Comptes  rend.,  104,  111;  106,  1074.     Carbon  tetra- 
chloride  may  be  substituted  for  free  carbon  and  free  chlorine. 


CARBON,   TITANIUM,  ZIRCONIUM,   CERIUM,   THORIUM.          145 

CeCLj  has  also  been  prepared  by  passing  a  mixture  of  carbon 
monoxide,  CO,  and  chlorine  over  the  ignited  oxide  ;  and  TiCl4,  by 
the  action  of  CC14  on  ignited  TiO,. 

3.  By  the  action  of  the  halogen  on  the  hydride  or 
sulphide  of  the  element.  —  This  is  the  method  by  which 
carbon  tetrachloride,  CC14,  is  commercially  prepared.  The 
disulphide  (see  p.  282),  mixed  with  chlorine,  is  passed  through 
a  tube  filled  with  pumice-stone  and  heated  to  redness.  The 
chlorine  combines  with  both  carbon  and  sulphur,  thus  :  — 

C8t+  3Ck  =  GCl,  +  SZCI*. 

The  chloride  of  sulphur  is  afterwards  decomposed  by  the  action 
of  lime-water  (see  p.  167),  and  the  carbon  tetrachloride  purified 
by  distillation. 

Methane  or  marsh  gas  (hydrogen  carbide),  CH^  (see  p.  560), 
is  also  converted  by  the  prolonged  action  of  chlorine  into  the  tetra- 
chloride, thus  :  — 

+  4CZ,  = 


There  are,  however,  three  intermediate  stages,  CH3Cl,  CH,C12, 
andCHCL,. 

Similarly,  CZH6  can  be  converted  into  C2C16,  through  the 
following  stages  :  — 

CZH6CI;  C2H4C12;  C2H3C13;  C2H2C14;  C2HCI5,  and  C2CV 

4.  By  the  action  of  the  hydrogen  halide  on  the  element. 
—By  this  method  TiCl3,  ZrF4,  CeF3r  CeCl3,  CeBr3,  Cels,  and  ThCl4, 
have  been  produced  in  solution.     Hydrogen  is  evolved.  . 

5.  By  the  aetipn  of  heat  on  C'C14  other  chlorides  are  pro- 
duced,  thus  :—l2CCk  =  dCk  +  Cl*\  2CUZ4  =  C2Cl,  +  2(7k;  6CCk 
=  C6C16  +  12C72.     Special  names  are  given  to  these  bodies,  viz., 
CC14,  tetrachloromethane  ;    C2C16,  hexachlorethane  ;    C^CU,  tetra- 
chlorethylene  ;  C6C16,  hexachlorobenzene. 

6.  By  the  action  of  hydrogen  at  a  red  heat  on  titanium 
tetrachloride   or   tetrafluoride   they   yield   the   trifluoride   or  tri- 
chloride.     The  dichloride  is  produced  by  the  further  action  of 
hydrogen  on  the  trichloride. 

7.  Double    decomposition.  —  (a.)     The    action    of    the 
hydrogen  halide  on  the  oxide  or  hydroxide  of  the  element. 
—  All  the  fluorides,  except  that  of  carbon,  have  been  thus  prepared 
in   solution;    also    solutions  of  ZrCl4,  ZrBr4,  CeCl3,  CeBr3,   CeI3, 
ThCl4,  ThBr4,  and  ThI4.     These  substances,  in  solution,  react  with 
water  on  evaporation.    Cerium  chloride  has  been  dried  in  the  same 
manner  as  magnesium  chloride,  viz.,  by  preparing  the  double  salt 

L 


146  THE   HALIDES. 

with  ammonium  chloride,  and,  after  drying  it,  igniting  it  to  remove 
ammonium  chloride;  also  by  passing  a  mixture  of  chlorine  and 
carbon  monoxide  over  the  sesquioxide  at  a  red  heat.  It  is  probable 
that  the  others  could  be  obtained  anhydrous  in  a  similar  manner. 

(&.)  This  process  is  applied  to  the  preparation  of  carbon 
bromide  and  iodide  from  tbe  tetrachloride.  A  mixture  of  alu- 
minium bromide  or  iodide  and  carbon  tetrachloride,  all  diluted 
with  carbon  disulphide,  yields  carbon  tetrabromide  or  iodide  on 
heating ;  carbon  tetrafluoride,  CF4,  is  produced  by  heating  silver 
fluoride,  AgF,  in  a  sealed  tube  with  carbon  tetrachloride.  Cerous 
fluoride,  CeF3,  which  is  an  insoluble  white  substance,  is  also  pre- 
pared by  this  general  method  by  the  interaction  between  solutions 
of  sodium  fluoride  and  cerium  chloride,  thus  :  CeCl3.  Aq  -f  SNaF.Aq 
=  2CeP3.H2O  +  SNaCl.Aq. 

Properties. — The  tetrahalides  are  all  volatile  at  compara- 
tively low  temperatures.  Carbon  tetrafluoride  is  a  gas  ;  carbon 
tetrachloride,  bromide,  and  iodide,  titanium  tetrachloride,  and 
tetrachlorethylene  are  colourless  liquids;  hexachlorethane,  zir- 
conium chloride,  cerium  trichloride,  and  thorium  chloride  are 
colourless  solids,  which  can  be  sublimed.  Titanium  dichloride  is 
a  black  powder,*  which  rapidly  decomposes  water,  with  evolution 
of  hydrogen,  combining  with  the  oxygen  to  form  an  oxy chloride. 
Titanium  trifluoride  and  trichloride  consist  of  violet  scales, 
soluble  in  water  with  a  violet  colour.  Titanium  tetrabromide 
is  a  red  liquid ;  and  the  -tetriodide  forms  brown  needle-shaped 
crystals.  Ceric  fluoride  is  not  known  in  the  anhydrous  state. 
Combined  with  water  as  CeF4.H2O,  it  is  a  brown  insoluble 
powder,  produced  by  treating  the  hydrated  -dioxide  with  aqueous 
hydrofluoric  acid.  It  is  doubtful  whether  the  substance  described 
as  thorium  fluoride  is  not  in  reality  an  oxyfluoride,  Th.OF2. 

Carbon  tetriodide  decomposes  when  heated,  or  when  exposed  to 
air.  With  the  exception  of  the  carbon  compounds,  cerium  tetra- 
fluoride, and  possibly  thorium  fluoride,  these  substances  are  deli- 
quescent, and  soluble  in  water,  probably  reacting  with  it  to  form 
oxyhalides  ;  this  change  certainly  takes  place  on  evaporation,  in 
some  cases  an  oxyhalide,  in  others  the  oxide,  being  produced. 
Carbon  tetrabromide  occurs  as  an  impurity  in  commercial  bromine. 

*  Friedel  and  G-uerin,  Annales  (5),  7,  24. 


CARBON,  TITANIUM,  ZIRCONIUM,   CERIUM,  THORIUM.         147 
Physical  Properties  of  Bodies  of  the  Formula  MX*. 


Mass  of  1  c.c.  solid 
or  liquid. 

f.      Cl.     Br.       I. 
Carbon  ...      —  1  '632  3  '42  4  '34 
atO°  at  14°  at  20° 
Titanium  .      ?     1-761.2 '6       ? 

atO° 
Zirconium.      ?         ?         ?          ? 

Cerium  ?       —       —       — 

Thorium  .       ?         ?         ?          ? 

Of  the  other  halides :— 


Melting-points. 


Boiling-points. 


P.    Cl.     Br.         I.       F.     Cl.      Br.         I. 

?     ?       91°    100°*    ?    76-73  189-5°    — 

?      ?       39°    150°      ?    136-4°  230°  360C* 

?      ?         ?        —  white     ?         ?          ? 
heat 


C2C16       .  , 

Mass  of  1  c.e.         '. 
.      1-62 

Melting-point. 
187° 

Boiling-point. 
187* 

CoBr*  . 

9 

170° 

C2CL  

....     1  -65  at  0° 

-18° 

121° 

CoBr,. 

P 

50° 

decomposed 

TiF3  

? 

9 

Ti,CL  . 

9 

9 



CeCl3. 


not  at  bright  redness 


Heats  of  formation. — The  following  only  have  been  determined : — 

C  +  2CL  =  CC14  +  210K. 
2C  +  2CT2  =  C2CZ4-  12K. 

The  vapour-densities  of  many  of  these  compounds  have  been 
determined,  and  it  may  be  safely  concluded  that,  in  the  gaseous 
state,  most  of  them  possess  the  molecular  formulas  given  above. 

Double  halides. — These  are  for  the  most  part  produced  by  mixing  solutions 
of  the  two  halides  and  crystallisation.  Those  of  carbon  are  produced  by  sub- 
stitution of  chlorine  for  bromine,  or  by  addition  of  bromine  to  a  chloride  (e.g., 
C2C14  -I-  Br.2  =  C2Cl4Br2) ,  or  of  chlorine  to  a  bromide. 

Carbon  compounds.  CCl3Br ;  a  liquid  boiling  at  104'3°.  CCl2Br2  boils  at 
a  higher  temperature.  C2Cl4Br2  exists  in  two  forms,  isomeric  with  each  other, 
one  produced  by  direct  addition  of  bromine  to  C2C14 ;  the  other  by  the  action  of 
bromine  on  C2HC15.  There  are  also  known  :— C2Br4Clo ;  C2Br3Cl ;  and  C2Br2Cl2. 
These  bodies  have  vapour-densities  corresponding  with  the  formulae  given. 

The  other  halides  combine  in  varying  amount  with  halides  of  other  elements. 
As  instances,  the  following  compounds  may  be  given : — 


8  :  1.—  2ThCl4.KC1.18H2O. 
6  :  1.—  3TiCl4.2PH4Cl.  " 
4  :  1.—  ZrF4.KF  ;   ThF4.KF. 
4  :  2.—  TiF4.2HF  ;     TiF4.2KF  ; 
TiF4.NiF.,  ;  ZrF4.2KF; 


TiF4.2NH4F;    TiF4.CaF2;    TiF4.CaFi; 
ZrF4.M&F2;    ZrF4.MnF2;  ZrCl4.2NaCl; 


8  :  3.—  2CeF4.3KF. 


Melts  with  decomposition. 


148  THE   HALIDES. 

4:3.— TiCl4.3NH4Cl;  ZrF4.3KF;  2ZrF4.3CuF2. 

4:4.— ZrF4.2ZnF2;    ZrF4.2CdF2;    ZrF4.2MnF2;    ZrF4.2NiF2 ; 

2ZrF4.2KF.NiF2. 

4:6.— TiF4.2FeF3;  TiCl4.6NH4Cl. 
4  :  8.— ThCl4.8NH4Cl. 
3  :  3.— TiF3.3NH4F. 

These  halides  are  able  to  combine  with  others  in  many  proportions.  The 
products  are  crystalline  substances  often  combined  with  water,  sometimes  anhy- 
drous. As  regards  their  molecular  weights,  nothing  is  known  ;  hence  the 
simplest  possible  formula  hare  been  assigned  to  them. 

Halides  of  Silicon,  Germanium,  Tin,  Terbium, 
and  Lead. 

It  has  been  already  remarked  as  doubtful  whether  terbium 
belongs  to  this  group  of  elements.  These  bodies,  like  those  of  the 
last  group,  show  a  decrease  of  volatility  with,  increase  of  the 
atomic  weight  of  the  metallic  element. 

Sources. — The  only  native  halide  is  lead  chloride,  PbCl2, 
which  was  found  in  the  crater  of  Vesuvius,  after  the  eruption  of 
1822.  A  chloride  and  carbonate  of  lead  also  occurs  native,  though 
rarely,  as  corneous  lead ;  its  formula  is  PbCO3.PbCl2. 

The  following  compounds  are  known  : — 

Fluorine.  Chlorine.  Bromine.  Iodine. 

Silicon Si2F6;  8iF4.  Si2Cl4 ;  Si2Cl6;  SiCl4.  Si2Br6;  SiBr4.  SiI2 ;  Si2I6 ;  SiI4. 

Germanium.     ?       G-eF4.  QeCl2?  G-eCl4.  ?  GeI4. 

Tin SnF2;  SnF4.*  SnCl2 ;  SnCl4.  SnBr2 ;  SnBr4.  SnI2 ;  SnI4. 

Terbium. . . .  TbClJ?* 

Lead PbF«j.  PbCl2 ;  PbCl4  ?*        PbBr2.  PbI2. 

Preparation. — 1.  By  direct  union. — These  elements  readily 
combine  with  the  halogens,  when  they  are  heated  together,  forming 
the  compounds  containing  the  greatest  amount  of  halogen. 

Silicon  takes  fire  in  fluorine  gas,  burning  to  silicon  fluoride. 

This  is  the  only  method  of  preparing  silicon  tetriodide,  SiI4. 

2.  By  the  action  of  the  halogen  on  a  red-hot  mixture  of 
the  oxide  with  charcoal  (see  p.  131). — This  is  the  most  con- 
venient method  of  preparing  silicon  tetrachloride  and  tetrabromide. 
It  is  necessary  to  take  the  utmost  precaution  to  exclude  moisture 
by  scrupulously  drying  the  halogen  ;  for  the  chloride  and  bromide 
are  instantly  decomposed  by  water.  The  silicon  chloride  or 

*  Not  known  in  the  anhydrous  state. 


SILICON,  GERMANIUM,  TIN,  LEAD.  149 


bromide  is  condensed  in  a  U'^11^6?  cooled  by  a  freezing  mixture. 
The  equation  is:—  SiO2  +  20  +  2C7,  =  SiCl*  +  200. 

3.  By  the  action  of  the  hydrogen  halide  on  the  element. 
—  By  this  means  germanium  fluoride  and  tin  dichloride,  bromide, 
and  iodide  may  be  conveniently  prepared.  Silicon  fluoride  may  also 
be  formed  thus.  Hydrogen  gas  is  in  every  case  evolved.  It  is 
believed  that  hydrogen  chloride,  at  a  red  heat,  converts  germanium 
into  the  dichloride,  GeCl2. 

The  usual  method  of  preparing  stannic  chloride,  which  bears  a 
close  analogy  to  the  action  of  a  haloid  acid  on  the  element,  is  by 
distilling  a  mixture  of  granulated  tin  with  mercuric  chloride.  The 
stannic  chloride  distils  over,  leaving  the  mercury  in  combination 
with  the  excess  of  tin,  thus  :  — 


2HgCl2  +  Sn  =  2Hg  + 

4.  By  double  decomposition.  —  (a.)  This  is  the  usual  and 
easiest  method  of  preparing  the  halides  of  lead,  a  solution  of  the 
nitrate  or  the  acetate  of  lead  being  treated  with  a  solution  of  any 
soluble  halide,  for  example,  with  the  nitrate,  Pb(N03)2.Aq  +  2KF.Aq 
=  PbP2  +  2KN03.Aq;  and  with  the  acetate,  Pb(C2H302)2.Aq  + 
2HCl.Aq  =  PbClj  +  2C2H402.Aq. 

(6.)  The  action  of  the  hydrogen  halide  on  the  oxide  or 
hydroxide  of  the  element.  —  Silicon  tetrafluoride,  the  halides  of 
tin,  and  terbium  chloride  have  been  thus  produced.  The  oxides  of 
lead  are  attacked  superficially  by  the  halogen  acids  ;  but,  the  halides 
of  lead  being  sparingly  soluble,  a  coating  of  halide  is  formed,  which 
renders  the  action  slow.  By  alternately  boiling  lead  oxide  with 
the  halogen  acid,  and  with  water,  in  order  to  dissolve  this  coating, 
complete  conversion  into  halide  may  be  accomplished. 

Lead  dioxide,  thus  treated  with  solutions  of  hydrogen  chloride, 
bromide,  or  iodide,  undergoes  the  following  reactions,  half  the 
halogen  being  liberated  :  — 

PbO2  +  4HCl.Aq  =  PbCl2  +  2H20  +  OZ2  +  Aq. 

Hydrogen  fluoride  is  without  action  on  lead  dioxide. 

5.  By  the  action  of  the  element  at  a  red  heat  on  the 
tetrahalide  the  disilicon  hexahalide  has  been  prepared,  thus  :  — 

6SiCU  +  2Si  =  4Si2Cl«5. 

As  examples  of  these  methods  of  preparation,  the  following  instances  may  be 
chosen  :  — 

1.  Tin,  melted  in  a  deflagrating  spoon,  and  plunged  into  ajar  of  chlorine 
gas,  burns  to  the  tetrachlojide. 


150 


THE   HALIDES. 


2.  A  mixture  of  silica  and  carbon,  made  into  a  paste -with  starch,  and 
moulded  into  balls,  and  then  strongly  ignited,  is  heated  in  a  porcelain  tube 
by  means  of  a  Fletcher's  tube-furnace,  provided  with  a  blast,  in  a  current 
of  chlorine,  perfectly  dried  by  passing  through  tubes  filled  with  phosphorus 
pentoxide. 


FIG.  27. 


The  silicon  chloride  produced  must  be  condensed  in  a  U^'u^e  dipping 
in  a  freezing-mixture.  The  preparation  is  not  easy,  and  is  not  well  adapted  for 
a  lecture  experiment. 

3.  Tin,  granulated  by  pouring  the  melted  metal  into  water,  is  boiled  in  a 
flask  with  strong  hydrochloric  acid,  a  few  pieces  of  platinum-foil  being  added  to 
form   a   galvanic   couple    and   assist   solution.      It   slowly   dissolves,    forming 
stannous  chloride. 

4.  Silicon  tetrafluoride  may  be  prepared  by  heating  in  a  glass  flask  a 
mixture  of  equal  parts  of  fine  sand  and  powdered  fluorspar  with  excess  of  sul- 
phuric acid.     The  hydrogen  fluoride  liberated  attacks  the  sand,  forming  water, 
which  unites  with  the  sulphuric  acid,  and  hence  does  not  exercise  a  decomposing 
action  on  the  silicon  fluoride.      The  latter  escapes  as  a  colourless  gas.     It  may 
be   made  to  react   with   water,  by  causing  the  exit-tube  to  dip  into  a  little 
mercury  in  a  beaker,  the  beaker  being  filled  up  with  water.     The  mercury  is 
required,   else  the  exit-tube  would  be  soon  blocked  by   deposition   of   silicon 
hydroxide  (or  silicic  acid),  resulting  from  the  decomposition  of  the  fluoride  (see 
p.  153). 

The  action  of  lead  dioxide  on  the  halides  of  hydrogen  may  be  easily  shown 
by  warming  in  a  test-tube  a  few  grams  with  some  hydriodic  acid.  Yiolet  fumes 
of  iodine  escape,  and  the  dioxide  is  converted  into  yellow  iodide. 

5.  The  formation  of  the  halides  of  lead  may  be  shown,  as  in  4a. 

Properties.— Tetrahalides.— These  compounds  boil  at  com-* 
paratively  low  temperatures.  Silicon  tetrafluoride  is  a  colourless 
gas  at  ordinary  temperatures,  the  chloride  and  bromide  are  volatile 
liquids ;  and  the  iodide  a  white  solid.  Germanium  chloride*  is  a 
colourless  volatile  liquid ;  and  tin  tetrachloride  is  also  mobile  and 
colourless,  boiling  at  a  somewhat  higher  temperature.  Germanium 

*  J.  praJct.  Chem.  (2),  34,  177. 


SILICON,   GERMANIUM,  TIN,  LEAD.  lol 

bromide  and  fluoride  do  not  appear  to  have  been  prepared ;  the 
iodide  is  a  yellow  solid,  giving  a  yellow  vapour.  It  dissociates 
somewhat  below  658°.  Tin  tetrafluoride  has  not  been  obtained  in 
the  anhydrous  condition  ;  the  bromide  forms  volatile  white  crystals, 
and  the  iodide  is  yellowish-red,  and  also  volatile.  All  these  sub- 
stances react  with  water,  forming  oxides,  or  oxyhalides;  hence, 
being  volatile,  they  all  fume  in  the  air.  The  vapour- den  si  ties  of 
most  of  them  have  been  determined,  and  correspond  to  the  simple 
formulas  MX^ 

Bodies  of  the  formula  M2X6.— These  are  only  known  to  exist 
as  compounds  of  silicon.  The  fluoride,  Si2F6  (?),  is  a  white  powder 
(probably  an  oxyfluoride).  The  iodide,  Si2I6,  produced  by  the 
action  of  finely-divided  silver  on  the  tetriodide,  is  separated  from 
the  excess  of  silver  by  solution  in  carbon  disulphide,  from  which 
it  deposits  in  colourless  prisms.  By  warming  it  with  mercuric 
chloride  it  is  converted  into  the  corresponding  chloride,  Si2Cl6, 
which  is  a  colourless  mobile  liquid.  The  corresponding  bromide 
is  produced  by  shaking  a  solution  of  the  iodide  with  bromine  dis- 
solved in  carbon  disulphide,  and  removing  the  iodine  by  agitation 
with  mercury.  It  forms  white  crystals.  A  determination  of  the 
vapour-density  of  the  chloride,  Si^Cl^  showed  it  to  possess  the 
molecular  weight  corresponding  to  that  formula.* 

Dihalides. — Silicon  dichloride  is  a  liquid,  which  has  not  yet 
been  obtained  pure ;  the  di-iodide  remains  as  an  orange-coloured 
residue  on  distillation  of  the  compound  Si2I6,  which  splits  into  the 
tetriodide  and  di-iodide,  thus  :— Si2I6  =  SiI4  +  SiI2.  It  is  in- 
soluble in  all  known  solvents,  and  is  decomposed  by  water. 

Germanium  dichloride  is  a  colourless  liquid.  Its  formula  is 
as  yet  uncertain,  and  it  may  possibly  be  GeHCl3,  for  it  has  not. 
been  analysed. 

Tin  difluoride  has  not  been  obtained  anhydrous.  It  crystallises 
from  water  in  small  opaque  prisms.  The  dichloride  crystallised 
from  water  is  known  as  "  tin-salt."  On  evaporation  of  its  solution, 
a  portion  reacts  with  water,  forming  oxychloride  and  hydrogen 
chloride.  The  excess  of  water  evaporates  along  with  the  hydrogen 
chloride.  On  raising  the  temperature  the  undecomposed  stannous 
chloride  distils  over,  leaving  the  oxychloride.  It  forms  a  white 
lustrous  crystalline  mass.  With  a  large  quantity  of  water  it  gives 
a  precipitate  of  oxychloride,  SnCL.SnO.2H2O.  Its  solution  is  a 
powerful  reducing  agent,  for  it  tends  to  take  chlorine  from 
hydrogen  chloride  or  oxygen  from  water,  liberating  hydrogen, 

*  Annales  (4),  9,  5;  19,  334;  23,  430;  27,  416;   (5),  19,  390. 


152  THE   HALIDES. 

when  there  is  any  substance  present  with  which  the  hydrogen  can 
combine.  The  dibromide  is  similar  to  the  dichloride.  The  di-iodide 
is  a  dark-red  mass  ;  its  iodine  is  replaced  by  oxygen  when  it  is 
heated  in  air. 

Lead  difluoride,  dichloride,  and  dibromide  are  white  solids, 
sparingly  soluble  in  boiling  water  and  crystallising  therefrom  in 
long  needles..  The  iodide  is  yellow  and  crystallises  in  golden- 
yellow  spangles. 

From  the  vapour-  density  of  stannous  chloride  it  would  appear 
that  these  bodies  in  the  state  of  gas  have,  at  temperatures  not  far 
removed  above  their  boiling-points,  the  double  formula,  e.gr., 
Sn2Cl4*  ;  but  that,  as  the  temperature  rises,  the  complex  molecule 
dissociates  into  two  simpler  ones,  viz.,  SnCl2  (see  ^Oi,  p.  333). 
Lead  chloride  appears  to  dissociate  before  its  volatilises,  for  its 
density  corresponds  to  the  simple  formula  PbCl2.t 


Tetra- 

halides. 
Silicon  .  . 

Physical  Properties. 
Mass  of  1  c.c.  liquid.              Melting-point. 

Boiling-point. 

F.     01.     Br.    ~I. 
?    57-6°  153°    ? 

F. 

? 

.   01. 
1  -524  1 

Br. 

2-823 

1. 

p 

F.     01. 
-102°t  ? 

Br. 

-12° 

—  -i 
? 

atO°    atO° 
Germanium.    ?    1  '887       ?         ?  ?         ?         ?      144°     ?      86°     ?     350- 

at  18°  400° 

Tin  ........     ?   2-379       ?    4  -696       ?         ?       30°   146°     ?     114°  201°  295° 

atO°  at  11° 

Hexahalides  :—  Si2Cl6,   sp.    gr.    T58   at  0°  j    m.-p.    -1°;    b.-p.    146—148°. 
Si2Br6,  b.-p.  about  240°.     Si2I6,  m.-p.  about  250°,  with  decomposition. 
Dihalides  :—  Sp.  gr.  :  SnCl2      ?.         SnBr2,  5'117  at  17°.     SnI2        ?. 
M.-p.:        „       249-3°.         „      215'5°  „         316°. 

B.-p.:         „      601°.  „      620°  „  ? 

Sp.  gr.  :  PbF2)~8'24  at  2°  j  PbCl2,  5'80  at  15°  ;  PbBr2,  6'60  at  7*5°  j  PbI2,  6"06 

at?. 

M.-p.  :  PbUJ2,  498°;  PbBr2,  499°;   PbT2,  383°. 
B.-p.  :    PbCl2,  900°  ;  PbBr2,  above  861°  ;  PbI2,  861—954°. 

*  Zeitschr.  phys.  CJiem.,  2,  184.  The  author  differs  entirely  from  the  con- 
cluding words  of  this  memoir  regarding  the  non-existence  of  Sn2Cl4  in  the  state 
of  gas. 

f  Brit.  Assn.,  1887,  668. 

%  Volatilises  without  melting.  This  behaviour  is  explained  as  follows  :  —  The 
boiling-point  of  a  liquid  is  dependent  on  the  pressure.  By  lowering  the  pressure, 
the  boiling-point  is  lowered,  whereas  the  melting-point  is  almost  unaffected  by 
small  alteration  of  pressure.  It  is  evident  that  by  a  sufficient  reduction  of 
pressure  the  boiling-point  may  be  lowered  till  it  occurs  at  a  temperature  below 
the  melting-point.  Such  bodies  as  silicon  fluoride,  hexachlorethane,  C2C16,  and 
many  others  are  in  this  condition  under  ordinary  atmospheric  pressure.  By  in- 
creasing the  pressure,  so  as  to  raise  their  boiling-points,  they  can  be  melted. 


SILICON,   GERMANIUM,  TIN,  LEAD.  153 

Heats  of  formation  :  — 

Sn  +  Cl.3  -  SnCLj  +  808K  ;    +  Aq  =  811K. 
Sn  +  2C12=  SnCl4  +  1273K;  +  Aq  =  299K. 

The  last  number  implies  decomposition  when  solution  takes  place  :  — 

Pb  +  CZ2  -»  PbCL,  +  828K;   +  Aq  =  -68K. 
Pb  +  Br2=  PbBr2  +  645K;   +  Aq  =  —  100K(?). 
Pb  +  I2    =  PbI2     +  398K;    +  Aq  =  -160K(?). 

Double  halides.  —  Silicon,  like  carbon,  forms  double  halides, 
of  which  the  molecular  weights  have  been  determined  in  many 
cases.  For  example,  by  the  action  of  bromine  on  the  compound 
SiHCl3,  named  silicon  chloroform  (see  p.  501),  three  chloro- 
bromides  have  been  obtained  :  one  has  the  formula  SiCl3Br,  the 
second,  SiCl2Br2,  and  the  third,  Si01Br3.*  They  are  all  liquids  : 
the  first  boiling  at  80°,  the  second  at  about  100°,  and  the  third  at 
140  —  141°.  There  appear  to  be  similar  chlorobromides  of  tin, 
which,  however,  are  not  stable  in  the  gaseous  state. 

The  tetrahalides  form  numerous  double  salts.  Those  of  silicon  tetrafluoride 
have  been  most  carefully  studied  ;  they  are  named  silicifluorides.  G-ermani- 
fluorides  and  stannifluorides  have  also  been  prepared.  The  following  is  a  list 
the  more  important  ones  :  — 

SiF4.2HF.Aq;  SiF4.2KF;  SiF4.BaF2;  &c. 

GeF4.2KF. 

SnF4.2KF;  SnF4.BaF2. 
SnCl4.2HCl;  SnCl4.2KCl;  SnCl^CaCL,;  SnCij.BaCLj.    SnCl4.2NH4Cl. 

SnBr4.2HBr;  SnBr4.2NaBr;  SnBr4.MgBr.,,  and  others. 
PbCl4.2HCl.Aq  (?)  ;  PbCl4.9NaCl; 


The  compound  SnCl4.2NH4Cl  is  known  as  "  pink  salt,"  being  used  as  a 
means  of  fixing  pink  dyes. 

These  compounds  are  mostly  prepared  by  direct  addition  ;  but'  those  of 
silicon  may  also  be  produced  by  the  action  of  SiF4.2HF.Aq  on  the  oxides, 
hydroxides,  or  carbonates  of  the  metals.  When  silicon  fluoride  is  passed  into 
water  the  following  reaction  takes  place  (see  Borpfluorides,  p.  132)  — 
3SiF4  +  3H2O  +  Aq  =  H2SiO3  +  2HiSiF6.Aq.  The  gelatinous  precipitate 
formed  when  silicon  tetrafluoride  is  passed  through  water  consists  of  silicic 
acid,  H.2SiO3  ;  the  aqueous  solution  contains  the  body  H2SiF6,  hydrosilicifluoric 
acid  ;  its  formula  is  deduced  from  that  of  its  salts,  as  it  decomposes  on  evapora- 
tion into  hydrofluoric  acid  and  silicon  fluoride,  a  portion  of  which  reacts  with 
the  water  to  form  more  silicic  acid. 

The  more  important  compounds  of  this  acid  are  potassium  silicifluoride, 
K2SiF6,  which  is  one  of  the  few  sparingly  soluble  salts  of  potassium  ;  it  is  used 
as  a  source  of  silicon  (see  p.  50)  ;  and  the  barium  salt,  which  is  insoluble  in 
water,  the  corresponding  salts  of  strontium  and  calcium  being  soluble.  This  is 
utilised  as  a  method  of  separating  barium  from  these  metals. 

*  Chem.  Soc.,  51,  590. 


154  THE   HALIDES. 

Caesium  stannichloride,  SnCl42CsCl,  being  nearly  insoluble  in  water,  may 
be  separated  as  such  from  the  corresponding  compounds  of  sodium,  potassium, 
and  rubidium. 

All  these  double  salts  crystallise  in  the  same  form,  and  are  therefore  termed 
isomorphous. 

Many  double  halides  are  known  of  the  dihalides  of  tin  and  lead.  None  have 
been  gasified;  hence  their  molecular  weights  are  unknown  ;  the  simpler  formulae 
are  therefore  given  as  a  rule. 

Compounds  containing-  two  different  halog-ens  : — 

SnClI;  PbFCl;  PbClBr;  PbBrl. 
2FbClo.PbI2;  3PbBr2.PbI2;  6PbBr2.PbI2. 

Compounds  with  the  halides  of  other  elements  : — 

2  :  1.— SnCLj.HCl ;    SnCloKCl ;   SnBr2.KBr ;    SnBr2.NH4Br;    SnI2.KI ; 

SnIi.NH.jI;  PbI2.KI. 
2  :2.-SnCl2.2KCl;  SnCl2.BaCl2;  SnBr2.2NH4Br ;  SnI2.2KI; 

PbI2.2HI;  PbI2.2KI;  PbI2.2NH4Cl. 

Many  more  complex  ratios  have  also  been  noticed  among  the  lead 
halides,  e.g.  :— 2  :  3,  PbI2.3NH4Cl ;  2  :  4,  PbI2.4KI ;  2  :  6,  PbBr2.6NH^Br ; 
2:7,  PbBr2.7NH4Br ;  2:9,  PbCl2.9NH4Cl ;  2:10,  PbCl2.10NH4Cl,  and 
others  still  more  complex.  These  last  bodies  possess  the  qualifications  usually 
attributed  to  definite  chemical  compounds,  viz.,  definite  crystalline  form, 
coupled  with. constant  composition. 

The  formulae  of  these  halides  of  the  carbon  and  silicon  groups 
have  been  determined  : — 

.  1.  From  the  vapour-densities  of  many  of  the  compounds, 
and  from  the  analogy  of  those  of  which  the  vapour-densities  have 
not  been  determined  with  those  in  which  that  constant  is  known. 

2.  By  the  method  of  replacement. — It  is  argued,  for  instance, 
that  the  formula  of  the  compound  CCl3Br  implies  the  existence  of 
four  atoms  of  chlorine  in  the  compound  CC14,  inasmuch  as  one- 
fourth  of  the  total  amount  of  chlorine  it  contains  has  been  replaced 
by  bromine.     In  this  case,  and  in  that  of  the  similar  silicon  com- 
pounds, SiCl3Br,  SiCl2Br2,  and  SiClBr3,  this  view  is  confirmed  by 
the    vapour-densities  of   the  bodies.     But  there  is  no  means  of 
ascertaining  whether  such  a  body  as  SnClI  possesses  that  formula 
or  the  formula  SnCl2.SnI2,  for  it  has  never  been  gasified.     Indeed, 
judging  from  the  vapour-density  of  Sn2Cl4,   the   latter   formula, 
would  appear  the  more  probable  ;  and  no   simpler  formula  than 
2PbCl2PbI2  is  possible  in  the  case  of  the  tetrachlorodiiodide  of 
lead. 

3.  The  atomic  heats  of  carbon  and  silicon  present  special 
anomalies.     It  has  been  shown  by  Weber,*  however,    that,  like 

*  Pogg.  Ann.,  154,  367. 


SILICON,   GERMANIUM,  TIN,  LEAD. 


155 


those  of  beryllium  and   boron,  they  approach  constancy  at  high 

temperatures,  and   become  approximately  normal.     They  are  as 
follows  :  — 

T.     -50°.      -10°.       +10°.        33°.           58°.  86°. 

C.  Diamond.  Sp.  ht.    0-0635    0-0955    0-1128    0'1318  0'1532  0-1765 

Graphite.       „          0-1138    0'1437    0'1604        —  0-1990  — 

T.     140°.        206°.        247°.        600°.        800°.  1000°. 

C.  Diamond.  Sp.  ht.     0-2218    0'2733    0'3026    0  -4408  0-4489  0*4589 

Graphite.       „         0-2542    0-2966        —        0-4431  0'4529  0'4670 

T.      -40°.       +22°.        57°.          86°.         129°.        184°. 

Si.     Sp.  ht.    0-1360    0-1697    0'1833    0'1901     0-1964  0-2011 


232°. 
0  -2029 


The  atomic  weights  of  carbon  and  silicon  have  been  deduced 
from  their  atomic  heats  at  1000°  and  232°  respectively,  which  are, 
for  carbon,  5'608,  and  for  silicon,  5'671. 

A  few  words  must  be  added  as  to  the  views  which  are  held  re- 
garding the  nature  of  the  atomic  combination  in  the  compounds 
C2C16,  Si2Cl6,  C2C14,  Sn2Cl4,  and  analogous  bodies.  These  views  are 
based  on  the  behaviour  of  the  compound  of  carbon  and  hydrogen 
named  ethane,  C2Ht,  which  is  analogous  to  C2Cl6,  and  which, 
indeed,  can  be  converted  into  the  latter  by  the  continuous  action 
of  chlorine,  whereby  all  the  hydrogen  atoms  are  successively  re- 
placed by  an  equal  number  of  atoms  of  the  halogen.  The  compound 
CH3I,  named  iodomethane,  when  acted  on  by  sodium,  loses"  its 
iodine,  sodium  iodide  being  produced.  But  the  vapour-density  of 
the  resulting  gas  shows  it  to  possess  not  the  formula  CH3,  but  the 
double  formula  CH3  —  CH3,  or  CZH6.  This  is  also  borne  out  by  the 
fact  that  the  hydrogen  in  ethane,  C2H6,  may  be  replaced  by 
chlorine  in  sixths,  giving  CzH6Gl,  monochlorethane,  C2H4C12, 
dichlorethane,  &c. 

It  is  argued  that  the  group  CH3  may  be  regarded  as  replacing 
an  atom  of  chlorine  in  CH^Cl,  or  of  iodine  in  CH3I,  and  that  the 
compounds  CH3C1  and  CH3  —  CH3  are  in  that  sense  analogous. 
Hence  the  formula  of  C2C16  may  be  written  CC13  —  CC13;  and  of 
Si2Cl6,  SiCl3  —  SiCl3.  And  by  similar  reasoning  it  is  argued  that 
the  compound  C2C14  may  be  regarded  as  composed  of  two  separate 
portions,  viz.,  CC12ZZCC12,  the  two  horizontal  lines  expressing  the 
hypothesis  that  the  group  CC12  replaces  two  atoms  of.  chlorine  in 
the  compound  CC14.  And  the  vapour-  density  of  these  compounds 
C2C16  and  C2C14,  and  of  their  hydrogen  analogues,  C2S6  and  C2H4, 
even  at  the  highest  temperatures  to  which  they  can  be  submitted 
without  decomposition,  shows  that  they  still  possess  the  formulae 
given.  On  the  other  hand,  there  can  be  no  doubt  that  stannous 


156  THE  HALIDES. 

chloride,  $ra3C74,  at  a  sufficiently  high  temperature,  has  a  vapour- 
density  corresponding  to  the  simpler  formula  SnCl2.  The  conclu- 
sion appears,  therefore,  to  follow,  that,  if  it  were  possible  to  subject 
(72C74  to  a  sufficiently  high  temperature  without  inducing  decom- 
position, it,  too,  would  possess  the  formula  CC12.  SizCle,  when 
heated,  splits  into  SiCl±  and  SiClZ',  it  is,  therefore,  extremely 
improbable  that  any  member  of  this  group,  at  any  temperature, 
will  be  found  to  have  the  formula  MX3,  for  more  stable  forms  of 
union  exist.  But,  in  the  chromium  group,  chlorides  of  both 
the  general  formula?  MC12  and  MCl3are  known-;  and  these  appear 
capable  of  existence  in  the  two  molecular  states,  MC12  and  MC13,  and 
M2Cl&  and  JLf9(%,  respectively  ;  it  will  be  remembered  that,  in  the 
chromium  group,  chlorides  of  the  general  formula  MC14  are  ex- 
ceedingly unstable,  the  only  representative  definitely  known  being 
MnF4,  and  that  only  in  aqueous  solution.  Hence  the  stability  of 
compounds  with  the  simpler  molecular  form 


157 


CHAPTEE  XII. 

HALIDES  OP  NITROGEN,  VANADIUM,  NIOBIUM,  AND  TANTALUM  ;  OF  PHOS-r 
PHORUS,  ARSENIC,  ANTIMONY,  AND  BISMUTH;  OF  MOLYBDENUM, 
TUNGSTEN,  AND  URANIUM;  OF  SULPHUR,  SELENIUM,  AND  TELLU- 
RIUM.— DOUBLE  HALIDES  OF  THESE  ELEMENTS, — PROOFS  OF  THEIR, 
MOLECULAR  FORMULA. 

Halides  of  Nitrogen,  Vanadium,  Niobium,  Tan- 
talum (Neodymium,  see  p.  605). 

Again  it  is  to  be  noticed  that  the  compounds  of  nitrogen,  th^r 
first  element  of  this  group,  differ  considerably  from  those  of  the> 
other  members.  While  the  halogen  compounds  of  nitrogen  are 
exceedingly  explosive,  those  of  the  other  elements  are  stable, 
though  decomposed  by  water.  For  these  reasons  none  of  them  are 
found  in  nature.  The  following  table  shows  the  compounds 
known : — 

Fluorine.  Chlorine.  Bromine.  Iodine. 

Nitrogen...       —  NC13.                      NBr3?  NI3. 

Vanadium..      VF4?*  VC12;  VC13;  YC^.          VBr3.  VI4?* 

Niobium....      NbF5.*  NbCl3;  NbClg.             NbBr5.         — 

Tantalum  ..     TaF5.*  TaCl5.                  TaBr5. 

The  iodides  of  niobium  and  tantalum,  though  probably  capable  of  existence, 
have  not  been  prepared. 

Preparation.— 1.  By  direct  union.— -Nitrogen  will  not  com- 
bine directly  with  the  halogens.  Vanadium  tetrachloride  and  tri- 
bromide  are  prepared  by  passing  the  vapour  of  the  halogen  over 
the  heated  element ;  and  tantalum  pentachloride  has  also  been  thus 
obtained. 

2.  By  the  action  of  the  halogen  on  a  red-hot  mixture  of 
the  oxide  with  charcoal. — This  is  the  method  of  preparation  of 
niobium  and  of  tantalum  pentachloride  and  pentabromide.  Vana- 
dium oxytrichloride,  VOC13  (see  p.  332),  when  passed  over  red-hot 
charcoal  along  with  chlorine,  also  yields  the  trichloride. 

*  Known  ctaly  in  solution. 


158  THE   HALIDES. 

3.  By  heating   a  higher  halide.— Vanadium  tetrachloride 
by  distillation  alone  splits  up  into  chlorine  and  the  trichloride ;  along 
with  hydrogen,  the  dichloride  is  formed ;  and  niobium  pentachlo- 
ride,  passed   through  a  red-hot  tube,  yields  the    trichloride  and 
chlorine. 

4.  By  the  action  of  the  halogen  on  a  compound  of  the 
element. — Ammonia  (hydrogen  nitride,  N"H3)  on  treatment  with 
excess  of  chlorine,  bromine,  orjiodine,  yields  exceedingly  explosive 
bodies.     The  method  of  preparation  is  as  follows  : — 

A  flat  leaden  dish,  in  which  a  smaller  thick  dish  is  placed,  is  filled  with  a 
strong  solution  of  ammonium  chloride.  A  small  jar,  of  about  200  cubic  centi- 
metres capacity,  provided  with  a  neck,  is  placed  in  the  solution,  standing  on 
the  smaller  leaden  dish.  The  neck  is  closed  with  a  cork,  through  which  a 
tube  passes,  which  is  connected  with  an  apparatus  for  generating  chlorine  by 
means  of  a  short  piece  of  india-rubber  tubing,  on  which  a  clip  is  placed.  The 
solution  of  ammonium  chloride  is  drawn  up  into  the  jar  by  suction,  and  when 
the  jar  is  full  the  clip  is  closed.  The  chlorine  apparatus  is  then  connected, 
and  by  opening  the  clip  the  jar  is  quickly  filled  with  chlorine.  The  chlorine  is 
absorbed  by  the  solution,  while  oily  drops  collect  on  the  surface,  and  sink,  col- 
lecting in  the  leaden  dish.  Air  is  then  admitted  by  disconnecting  the  chlorine 
apparatus  arid  opening  the  clip,  and  the  jar  is  removed.  These  drops,  when 
touched  with  an  oiled  feather  tied  to  the  end  of  a  long  stick,  explode  with  the 
greatest  violence,  shooting  a  column  of  water  into  the  air  and  flattening  the 
leaden  vessel. 

Recent  analysis*  has  shown  that  the  hydrogen  of  the  ammonia 
is  replaced  by  stages,  exactly  as  in  the  case  of  the  hydrogen  of 
methane,  CH^  (see  p.  145).  By  passing  chlorine  for  half  an  hour 
into  water  in  which  these  drops  are  suspended,  the  trichloride  is 
finally  formed.  The  equations  are  these  : — 

ffH4Cl.Aq  +  CZ2  =  2HCl.Aq  +  NH2C1. 
.     NH4Cl.Aq'  +  2Clz  =  SHCl.Aq  +  NHC12. 
NHC12 .+  Aq  +  Gk  =  HCl.Aq  +  NC13. 

The  corresponding  bromine  compounds  have  been  little  investi- 
gated, but  are  made  by  treating  ammonia  with  excess  of  bromine. 
Aqueous  ammonia  reacts  with  iodine  dissolved  in  alcohol  giving 
NI3 ;  but  with  a  weaker  solution  of  ammonia  NHI2  is  produced. 
The  action  of  chlorine  or  bromine  on  vanadium  nitride,  VN, 
at  a  red  heat  gives  the  trichloride  or  di bromide,  and  nitrogen. 

The  oxygen  in  niobium  oxytrichloride,  NbOCl3,  is  replaced  by 
chlorine  when  its  vapour  mixed  with  chlorine  is  passed  through  a 
red-hot  tube. 

5.  By  double  decomposition.     Action  of  the  hydrogen 
halide  on  the  oxide  of  the  element. — Vanadium  tetroxide  dis- 

*  Serickte,  21,  751. 


NITROGEN,   VANADIUM,   NIOBIUM,   TANTALUM. 


159 


solves  in  hydrofluoric  acid,  yielding  a  blue  solution,  which  on  evapora- 
tion deposits  green  crystals.  This  oxide  is  also  soluble  in  the  other 
haloid  acids,  giving  similar  solutions.  The  pentoxide,  when  boiled 
with  hydrochloric  acid,  yields  chlorine.  Tantalum  pentoxide,  if 
hydrated,  likewise  dissolves  in  hydrofluoric  acid,  and  the  solution 
on  evaporation  is  said  to  evolve  the  fluoride,  leaving  a  residue  of 
oxyfluoride.  Niobium  pentoxide  is  also  soluble  in  hydrofluoric 
acid. 

Properties. — The  halides  of  nitrogen  are  exceedingly  explo- 
sive, and  the  preparation  of  more  than  a  drop  or  two  of  the  chloride 
and  bromide  is  attended  by  great  danger.  They  are  oily  yellow 
liquids,  insoluble  in  water,  which  slowly  decompose  when  left  in 
contact  with  water  or  solution  of  ammonia.  The  iodide  is  a  brown- 
ish black  powder,  of  which  it  is  also  advisable  to  prepare  only  a 
few  decigrams  at  a  time.  They  explode  on  contact  with  an  oiled 
feather,  or  indeed  by  the  slightest  impact,  and  often  without  any 
apparent  cause.  The  pure  chloride  has  been  heated  to  90°  without 
decomposition,  but  at  95°  a  violent  explosion  occurred. 

Vanadium  dichloride  forms  apple-green  crystalline  plates.  The 
element  may  be  obtained  from  it  by  heating  it  to  redness  in  a 
current  of  very  carefully  dried  hydrogen.  Vanadium  trichloride 
closely  resembles  chromium  trichloride  in  appearance.  When 
heated  in  air,  its  chlorine  is  replaced  by  oxygen,  and  the  pentoxide 
is  formed  by  further  absorption  of  oxygen.  The  tribromide  is  a 
greyish-black  amorphous  mass  ;  it  is  very  unstable.  The  tetra- 
^hloride  is  a  reddish-brown  volatile  liquid,  soluble  in  water  with  a 
jlue  colour. 

Niobium  and  tantalum  pentafluorides  form  colourless  solutions. 
Niobium  trichloride  closely  resembles  iodine  in  appearance ;  it  is 
unaffected  by  water.  Niobium  and  tantalum  pentachlorides  form 
yellow  volatile  crystals ;  the  bromides  are  similar  in  appearance, 
but  of  a  darker  colour. 


Physical  Properties. 


Mass  of  1  c.c. 

Melting-point. 

Boiling-point. 

Dichloride. 

Vanadium  .  . 

3-23  c.c.  at  18° 

9 

? 

Trichlorides. 

Nitrogen  ... 

1-65    „       „ 

? 

Above  90°. 

Vanadium  .  . 

3-00    „       „ 

Decomposes. 

Decomposes. 

Niobium.  .  .  . 

? 

? 

? 

Tetrachloride. 

Vanadium  .  . 

1-858  at  0°. 

Below  -18°. 

154°. 

Pentachlorides. 

Niobium  .  .  . 

? 

194° 

240-5°. 

Tantalum  .. 

? 

211° 

242°. 

The  properties  of  the  other  halides  have  not  been  determined. 


160 


THE  HALIDES. 


Double  halides. — Although  double  halidesof  the  oxyfluorides  of  vanadium, 
niobium,  and  tantalum  have  been  studied  (see  p.  336) ,  the  tantalifl  uorides  are 
the  only  compounds  of  any  of  the  halides  of  this  group  with  the  halides  of  other 
elements.  They  have  all  the  general  formula  TaF5.2MF.  They  are  produced 
by  direct  union  of  the  respective  fluorides  in  aqueous  solution,  and  crystallise 
well.  They  are  soluble  in  water.  The  following  have  been  prepared  : — 

TaF5.2NH4F ;  TaF5.2KF;  TaF5.2NaF;  TaF5.CuF2;  and  TaF5.ZnF2. 


Chlorine. 

Bromine.             Iodine. 

PC13;  PC15. 

PBr3;  PBr6.     P2I4;  : 

PI3. 

AsCl3. 

AsBr  {.                As2I4  ; 

AsI3. 

SbCl3;  SbCls. 

SbBr3. 

SbI3. 

ErCl3.* 

ErBr3.* 

Bi2Cl4;  BiCl3. 

BioBro  ;  BiBr3. 

BiI3. 

Halides  of  Phosphorus,  Arsenic,  Antimony, 
(Erbium),  and  Bismuth. 

Sources. — None  of  these  compounds  are  found  in  nature. 
The  halogen  compounds  known  are  given   in  the   following 
table  :— 

Fluorine. 
Phosphorus..     PJ?3;  PF5. 

Arsenic AsF3. 

Antimony. . . .      SbF3 ;  SbF5. 
(Erbium)  ....      ErF3.* 
Bismuth   ....      BiF3. 

Preparation. — 1.  By  direct  union. — All  these  bodies  are 
best  prepared  thus,  except  the  fluorine  compounds ;  phosphorus, 
arsenic,  and  antimony  take  fire  spontaneously  in  fluorine  and  chlo- 
rine gases,  and  all  combine  with  the  halogens  with  great  evolution 
of  heat.  With  excess  of  halogen,  the  higher  halide  is  formed 
where  they  exist;  with  excess  of  the  other  element,  the  lower 
halides.  l 

As  examples  of  this  method  of  formation,  the  following  types  may  be 
chosen  : — 

(a.)  A  retort  is  half  filled  with  dry  sand,  and  on  it  are  placed  a  few  pieces  of 
phosphorus.  Dry  chlorine  is  led  into  the  retort,  so  as  to  impinge  on  the  phos- 


Fio.  28. 
*  Known  only  in  aqueous  solution. 


PHOSPHORUS,   ARSENIC,   ANTIMONY,   AND   BISMUTH.          161 

phorus  from  the  generating  flask.  The  phosphorus  burns  with  a  greenish  flame, 
and  the  liquid  chloride  distils  over,  and  may  be  condensed  in  the  receiver.  It  is 
purified  by  distillation. 

(5.)  A  little  powdered  antimony  is  thrown  into  a  jar  of  dry  chlorine.  It 
burns  with  scintillation,  and  on  standing,  the  fumes  condense  to  crystals  of  the 
pentachloride. 

(c.)  A  mixture  is  made  of  1  volume  of  bromine  and  3  volumes  of  carbon  disul- 
pliide  and  placed  in  a  flask.  Powdered  antimony  is  added  in  small  quantities 
at  a  time,  and  the  flask  is  warmed  gently  with  continuous  shaking  over  a  water- 
bath,  taking  care  to  have  no  flame  near,  for  fear  the  disulphide  vapour  should 
inflame.  It  is  then  allowed  to  cool,  when  the  tribromide  separates  in  crystals. 

2.  By  heating  a  higher  halide. — Phosphorus  and  antimony 
pentachlorid.es   yield    the    trichloride   when   heated ;    phosphorus 
pentabromide   behaves    similarly.     Phosphorus  pentafluoride,   on 
the  other  hand,  is  stable,  showing  no  decomposition,  even  at  the 
high  temperature  of  the  electric  spark.    The  decomposition  of  phos- 
phorus pentachloride  may  be  well  seen  by  heating  it  in  a  flask ; 
its  vapour  has  a  greenish-yellow  colour,  due  to  the  presence  of  free 
chlorine.     Phosphorus  tri-iodide  gives  off  iodine  when  heated. 

3.  By   heating  a  lower    halide. — Bismuth    dichloride    at 
330°,  and  the  dibromide  at  a  temperature  not  much  above  that  of 
the  atmosphere  decompose  into  bismuth  and  the  trihalide. 

4.  By  the  action  of  the  halogen  on  a  compound  of  the 
element. — This  method  is  not  generally  employed ;  yet  hydrogen 
phosphide,  arsenide,   and   antimonide   are   at   once   acted   on   by 
chlorine  or  bromine,  yielding  hydrogen  halide,  and  the  halide  of 
the  element.     It  is  certain  that  all  other  compounds,  except  per- 
haps the  oxides,  would  behave  similarly. 

5.  By  double   decomposition.— (a.)   The   action  of   the 
hydrogen  halide  on  the  oxide  or  sulphide  of  the  element. 
—The  oxides  of  phosphorus  are  not  attacked.    But  the  oxides  and 
sulphides  of  the  other  elements  yield  the  respective  halides,  either 
when  heated  in  a  current  of  the  hydrogen  halide,  or  when  treated 
with  a  halogen  acid.      In  presence  of    a  great  excess  of  wafer, 
the  halides  are  decomposed;  hence   the  acids   must  not   be   too 
dilute. 

Arsenious  fluoride  is  prepared  by  heating  together  arsenious 
oxide,  As4O6,  fluorspar,  CaF2,  and  sulphuric  acid,  H2S04.*  The 
hydrogen  fluoride  liberated  by  the  action  of  the  sulphuric  acid  on 
the  calcium  fluoride  (see  p.  108)  attacks  the  arsenious  oxide,  pro- 
ducing arsenious  fluoride  and  water,  which  combines  with  the 
excess  of  sulphuric  acid,  thus : — 

As,03  -f  6HF  +  3H2S04  =  3(H2S04.H20)  +  2AsF9. 
*  Comptes  rend.,  99,  874. 

M 


162  THE   HALIDES. 

The  chloride  may  be  similarly  prepared  from  sulphuric  acid, 
sodium  chloride,  and  arsenious  oxide.     Ifc  may  also  be  obtained  by 
distilling  arsenic  with  mercuric  chloride,  thus  : — 
2As  +  3HgCl2  =  2AsCl3  +  3Hg. 

(6.)  Phosphorus  trichloride  or  peiitachloride  reacts  with  arsenic 
trifluoride,  yielding  the  trifluoride*  or  pentafluoridef  of  phos- 
phorus, thus : — 

PCI3  +  AsF3  =  PF3  +  AsCl3 ; 
and  3PC15  +  5AsF3  =  3PF5  +  5AsCl3. 

Properties. — The  pentafluorides  of  phosphorus  and  arsenic  are 
gases  at  the  ordinary  temperature  ;  the  trichloride  and  tribromide 
of  phosphorus,  the  trifluoride  and  trichloride  of  arsenic,  and  the 
pentachloride  of  antimony  are  colourless  liquids,  fuming  in  air, 
owing  to  their  reacting  with  the  water-vapour  which  it  contains  ; 
the  remaining  trifluorides,  chlorides,  and  bromides  are  colourless 
crystalline  solids.  Phosphorus  di-iodide  forms  orange-coloured, 
and  tri-iodide,  red,  crystals.  Arsenic  di-iodide,  produced  by 
melting  arsenic  with  iodine  in  theoretical  proportion,  forms  a  dark 
cherry-red  mass,  which  crystallises  from  carbon  disulphide  in 
prisms,  and  which  decomposes  into  arsenic  and  the  tri-iodide  on 
addition  of  water.  The  tri-iodide  forms  red  tablets.  Antimony 
tri-iodide  exists  in  three  forms  :  when  crystallised  from  carbon  di- 
sulphide, it  forms  red  hexagonal  crystals ;  when  sublimed  below 
114°,  yellow  trimetric  crystals;  and  from  its  solution  in  carbon 
disulphide  exposed  to  sunlight,  in  monoclinic  crystals.  The  last 
variety  is  converted  into  the  hexagonal  modification  at  125°. 
Bismuth  tri-iodide  forms  a  greyish  mass  with  metallic  lustre. 

Phosphorus  pentachloride  and  pentabromide  are  yellowish 
crystalline  solids  ;  antimony  pentachloride  is  a.  colourless  fuming 
liquid.  These  three  substances  dissociate  when  heated  into  the 
trihalides  and  two  atoms  of  the  halide;  hence,  their  vapour- 
densities  do  not  correspond  to  their  formulae.  In  excess  of  tri- 
chloride, however,  the  decomposition  of  phosphorus  pentachloride  is 
prevented,  and  it  volatilises  as  PC7ft.J  Bismuth  dichloride,  on  the 
other  hand,  decomposes  into  bismuth  and  the  trichloride  when 
heated,  thus : — 

3Bi2Cl4  =  4BiCl3  +  2Bi. 

These  substances  are  all,  with  the  exception  of  bismuth  tri- 
fluoride, deliquescent,  attracting  water,  and  reacting  with  it  to 

*   Comptes  rend.,  99,  655;  100,  272. 

f  Proc.  Roy.  Soc.,  25,  122 ;   Comptes  rend.,  101,  1496. 

%  Comptes  rend.,  76,  601. 


PHOSPHOKUS,  AESENIC,  ANTIMONY,  AND   BISMUTH.          163 


form  oxyhalides  or  hydroxides  (acids).  They  are  all  soluble  in 
carbon  disulphide,  benzene,  &c.  The  erbium  halides  form  colour- 
less solutions. 


Physical  Properties. 

Mass  of  1  c.c.  solid 
or  liquid. 


Trihalides. 


Melting-point. 


I. 


F.  Cl.       Br. 

Phosphorus.        ?        1 '613  2 '923      ? 

at  0°    at  0° 

Arsenic....     2 '66    2'2053'66    4'39 
at  0°    at  0°    at  15°  at  13° 
Antimony  . .         ?        3  '064  4  '148  4  '85* 
at  26°   at  23°  at  24= 

Bismuth...     5 '32     4 -56     5 -4      5 '64 
at  20°  at  11°  at  20°   at  20° 


F. 


292 


Cl. 


Br. 

P 


I. 
55° 


-18°      20-25°       146° 


73-2° 


90° 


167 


227°        200° 


Boiling-point. 


Phosphorus   . . 

Arsenic 

Antimony  .... 
Bismuth  . 


F. 


60 


Cl. 

76-0° 
130-2° 
223-5° 


Br. 
172  -9° 

220° 
275  -4° 


I. 

p 

394-414° 
401° 


427-439°       454-498° 


SbCl5 :  mass  of  1  c.c.  2 '346  at  20° ;  rn.-p.  -6°.      PC15:  m.-p.  148°,  under 
increased  pressure  ;  volatilises  at  148°. 

Bi.2Cl4  :  m.-p.  176°.     Bi2Br4  :   m.-p.  202°  (uncorr.). 


Heat  of  formation  : — 

P     +  3CI  =  PC13    +  755K. 

p    +  5C7  =  PC15    +  1050K. 

P    +  21    =  PI2     +  99K. 

As  +  3CT  =  AsCl3  +  715K. 

As  +  31     =  AsI3  +  127K. 

Sb  +  3  CZ  =  SbCl3+  914K. 

Bi  +  3CI  =  Bid,  -r  906K. 


P    +  3Br  =  PBr3   +  448K. 

P    +  5Br  =  PBr5    +  591K. 

P    +  31     =  PI3      +  109K. 

As  +  3Br  =  AsBr3  +  449K. 


Sb  + 


=  SbCl5  +  1049K. 


The  vapour-densities  of  phosphorus  tri-  and  penta-fluorides,  tri- 
and  penta- chlorides,  tribromide,  and  tri-iodide  have  been  deter- 
mined; also  those  of  the  trihalides  of  arsenic  and  of  antimony 
and  bismuth  trichlorides  ;  their  molecular  weights  are  represented 
by  the  formulae  given.  Diphosphorns  tetriodide  has  a  vapour- 
density  corresponding  to  the  formula  P2l4 ;  moreover,  the 
analogous  compounds  of  bismuth  easily  decompose  into  the  tri- 
halide  and  metal ;  hence,  the  more  complex  formulae  have  been 
chosen,  although  the  choice  is  not  justified  by  any  absolute  proof 
in  the  case  of  bismuth. 


*  Hexagonal ;  monoclinic  :  4  '77  at  22°. 
f  Decomposed. 


M    2 


164 


THE   HALIDES. 


Double  halides. — 1.  Compounds  containing-  two  halogens.— These  are 
known  only  in  the  case  of  phosphorus.     They  are,  for  the  most  part,  made  by 
adding  the  halogen  to  the  halide  dissolved  in  carbon  disulphide,  and  crystal- 
lising from  that  solvent.     Their  molecular  weights  are  unknown. 
They  are  as  follows  : — * 

PF3Br2.  PC15IC1.  PCloBr-.  PCl3Br8. 

PCl3Br.2.  PCl3Br4. 

PCl4Br.  PCl2Br5. 

The    following    compounds   with  the   halides   of    other  elements  are 
known  : — 

|-PCl5.FeCl3. 

Phosphorus     J  PC15.A1C13. 
pentahalides  1  PCl5.CrCl3. 
lPCl5.AsCl3. 
Arsenic  pentahalides  . . 
SbF5.NaF. 
SbF5.KF. 
SbF5NH4F. 
Trihalides.  Phosphorus.  P013.AuCl. 

Antimony.  SbF3.KF.     SbF3.2KF.  SbF:i.3NaF.    2SbI3.3KI. 

2SbCl3.HC1.2H2O.     SfcI3.KI.       SbCl3.2NH4Cl.    SbCl3.3KCl. 
SbI3.NH4I.  SbCl3.BaCl2-         SbCl3.3KBr.f 


AiJtimony 
pentahalides 


PCl5.SnCl4. 

PCl5.SbCl5. 

PCl5.3HgCl2. 

PCl5.SeCl4. 

PC15.UC15. 

PC15.WC14. 

PCl5.MoCl4. 

,.      AsF5.KF. 

AsF5.2KF. 

SbF5.2KF. 

SbCl5.SCl4. 

SbCl5.5HC1.10H20. 

SbF5.2NH4F. 

SbCl5.SeCl4. 

Sblo.Bal.,. 


SbBr,.3KCl.t 


BiCl3.3NH4Cl. 

BiCl3.4NH4Cl. 
BiF3.3HF. 


Bismuth....    2BiCl3.NH4Cl.     BiI3.HI.     BiCl3.2NaCl. 

2BiI3.3NaI.         BiF3.HF.  BiI3.BaI2. 
2BiCl3.HC1.3H20.    BiI3.KI.     BiCl3.2KBr. 

These  are  some  of  the  compounds  known.  It  will  be  noticed  that  the  ratios 
of  the  number  of  atoms  of  halogen  in  the  two  components  vary  between  6  :  1 
and  3  : 4.  All  these  substances  react  with  water,  producing  oxyhalides 
(seep.  385). 


Halides  of  Molybdenum,  Tungsten,  and  Uranium. 

These  bodies  present  some  analogy  with  the  halides  of  chro- 
mium, which,  indeed,  in  the  periodic  table,  falls  in  this  group. 
Sources. — None  of  these  halides  occurs  native. 
The  following  is  a  list  of  the  known  compounds : — 


Fluorine. 


Chlorine. 


Molybdenum  MoF3;J  MoF4 ; I  MoF6.  MoCl2;  MoCl3 ;  MoCl4 ;  MoCl5 
Tungsten      . .  WF2J  WF6.     WC12;  WC14      WC15;    WC1C. 

Uranium....  UF4  —       TTC13 ;     UC14 ;     TJC13 

*  Chem.  Soc.,  49,  815. 

t  These  bodies  are  identical,  although  prepared  by  direct  addition. 

£  Known  only  in  solution. 


MOLYBDENUM,  TUNGSTEN,   AND   URANIUM.  165 

Bromine.  Iodine. 


Molybdenum...      MoBr2;  MoBr3;  MoBr4         — ~^  MoI2;* 

Tungsten WBr2  WBr4 ;     WBr5.  WI2. 

Uranium —  —         UBr4  TTI2. 

Preparation. — 1.  By  direct  union. — It  is  important  to  avoid 
the  presence  of  air  and  water- vapour,  else  oxyhalides  are 
obtained.  This  process  yields  molybdenum  and  uranium  penta- 
chlorides,  tungsten  hexachloride,  molybdenum  tetrabromide,  and 
tungsten  pentabromide,  all  of  which  are  volatile. 

2.  By  the  action  of  the  halogen  on  a  mixture  of  the 
oxide  and  charcoal. — By  this  means,  molybdenum  tribromide 
and   uranium  pentachloride   have   been  prepared ;  it  is  doubtless 
adapted  for  the  production  of  any  of  the  higher  halides. 

3.  By  heating  the  higher  halides.— Molybdenum  tri-  and 
tetra-bromides,  when  distilled,  undergo  decomposition  into  bromine 
and  the  dibromide,  MoBr2.      Tungsten  hexachloride,  between  360° 
and   440°,   dissociates  into   pentachloride  and  free  chlorine.     In 
other  cases,  the  distillation  of  a  halide  yields  a  mixture  of  two 
halides ;    for  example,  molybdenum  trichloride,  sublimed  in  dry 
carbon  dioxide,   splits  into   the  di-  and   tetra-chlorides,  thus: — 
23/0(7/3  =  MoCl2  +  HoCl±.  '  And  the  tetrachloride  is  also  unstable 
when  distilled,  giving  tri-  and  penta-chlorides,  2JtfoC/4  =  MoCl^  + 
HoCl* 

4.  By  the  action  of  hydrogen  on  the  heated  halide.— 
Molybdenum  pentachloride  yields  hydrogen  chloride  and  the  tri- 
choride   at    250°.      Tungsten   hexachloride   and   uranium   penta- 
chloride   also   yield   a   mixture   of    lower    chlorides    when    thus 
treated. 

5.  By  double  desomposition. — The  action  of  a  halide  on 
the  oxide. — (a.)  The  fluorides  are  all  thus  prepared  from  the  cor- 
responding oxides    by  the  action  of  aqueous   hydrofluoric  acid. 
Solutions  of  many  of  the  other  halides  may  also  be  prepared  thus. 

(fe.)  Tungsten  hexachloride  is  produced  by  heating  in  a  sealed 
tube  to  200°  a  mixture  of  tungsten  trioxide  and  phosphoric 
chloride. 

Properties.  — 1.  Dihalides. — Molybd3num  dihalides  when  pre- 
pared in  the  dry  way  are  insoluble  in  water ;  but  when  obtained 
from  the  oxides  they  form  brown  or  purple  solutions.  The  di- 
chloride  is  a  sulphur-yellow  powder.  Tungsten  dichloride  is  a 
loose  grey  powder ;  the  fluoride  forms  a  yellow  solution. 

2.  Trihalides. — Molybdenum  trichloride  is  a  red  powder  like 

*  Known  only  in  solution. 


166  THE  HALIDES. 

amorphous  phosphorus ;  the  tribromide  forms  dark  needles ;  both 
are  insoluble  in  water.     Uranium  trichloride  is  dark  brown. 

3.  Tetrahalides. — Molybdenum  tetrafluoride  forms  a  red  solu- 
tion ;    and    uranium    tetrafluoride    an   insoluble    green    powder. 
Molybdenum  tetrachloride  is  a  volatile  brown  substance ;  that  of 
tungsten    a    greyish-brown    crystalline    powder;    while    uranium 
tetrachloride  forms  magnificent  dark  green  octohedra,  and  yields 
a  red  vapour.     The  tef.rabromides  form  brown  or  black  crystals. 
These  compounds  are  deliquescent,  and  soluble  in  water. 

4.  Pentah.alid.es. — Molybdenum  pentachloride  is  a  black  sub- 
stance   yielding   a   brown-red    vapour;    those   of    tungsten    and 
uranium  consist  of  black  needles. 

5.  Hexahalide. — Tungsten  hexachloride  volatilises  in  bluish- 
black  needles,  resembling  iodine. 

Many  of  these  compounds  require  further  investigation.  As 
has  been  seen,  they  are  very  numerous,  and  their  reactions  have 
by  no  means  been  exhaustively  studied. 

Physical  Properties. 

The  mass  of  1  cubic  centimetre  has  not  been  determined  for  any  one  of  these 
halides.  The  following  melting-  and  boiling-points  and  vapour-densities  have 
been  determined  : — 

MoCl5.     M.-p.,  194° ;  b.-p.,  268° ;  vap.-dens.  at  350°,  136'0  to  137'9.    Calc.  136'5. 

WC15.     M.-p.,  248° ;  b.-p.,  275-6°  ;  vap.-dens.  at  360°,  182'8.     Calc.  180  65. 

WC16.     M.-p.,  275°    b.p,,  ?  ;  vap.-dens.  at  360°,  190'9.     Calc.  208'65. 
TJC15  dissociates    when    its    vapour,   mixed    with  carbon  dioxide,    is    heated. 
Dissociation  begins  at  120°  and  is  complete  at  235°. 

The  heats  of  combination  are  undetermined. 

Double  Halides. — These  again  have  been  very  little  studied.  Some  com- 
pounds of  molybdenum  containing  two  halogens  are  known,  e.g.,  2MoCL.MoBr2, 
2MoBr2  MoI2,  &c.,  and  one  compound  of  the  formula  2MoClo.MoBr2.KBr ;  a 
compound  of  the  tetrachloride- has  also  been  prepared,  viz.,  3MoC1^.2KCl.  No 
similar  compounds  of  tungsten  have  been  prepared,  and  only  one  of  uranium, 
viz.,  UF4.KF.  These  bodies  much  require  investigation. 

The  atomic  weights  of  these  elements  have  been  determined 
from  the  equivalents,  and  by  the  vapour-densities  given  above. 

Halides  of  Oxygen,  Sulphur,  Selenium,  and 
Tellurium. 

The  halides  of  oxygen  are  best  considered  as  oxides  of  the 
halogens,  q.  v.  (p.  459).  Those  of  the  three  other  elements  form  a 
well-marked  group.  None  of  them  occurs  in  nature.  They  are  as 
follows : — 


SULPHUR,  SELENIUM,   AND  TELLURIUM.  167 

Fluorine.              Chlorine.  Bromine.  Iodine. 

Sulphur.....          ?  S2C12;  SC12;  SC14.  ?  S2I,? 

Selenium.'..          ?  Se2Cl2;  SeCl4.  Se2Br2;  SeBr4.  ? 

Tellurium..          ?  TeCl2 ;  TeCl4.  TeBro ;  TeBr4.  TeI2;  TeI4? 

Preparation.— 1.  By  direct  union.— This  is  the  general 
method  of  preparing  these  bodies.  Sulphur  is  said  to  burn  in 
fluorine.  When  chlorine  is  led  over  sulphur  contained  in  a  retort 
it  grows  warm,  and  disnlphur  dichloride  is  formed ;  by  keeping 
sulphur  in  excess  it  is  the  only  product.  Diselenium  dichloride  is 
similarly  produced,  and  may  be  obtained  fairly  pure  by  distillation 
in  presence  of  selenium.  But  it  dissociates  to  some  extent  daring 
distillation,  with  formation  of  tetrachloride  and  free  selenium. 
Sulphur  dichloride,  produced  by  saturating  S2C12  with  chlorine,  is 
stable  up  to  nearly  20°,  but  above  that  temperature  dissociation 
proceeds  rapidly,  so  that  at  120°  it  has  nearly  all  decomposed  into 
the  compound  S2C12  and  chlorine.  The  tetrachloride  is  still 
more  unstable;  at  —22°  it  can  exist,  but  at  4-6°  it  has  wholly 
split  up  into  dichloride  and  chlorine.  It  will  be  remembered  that 
it  forms  a  double  chloride  with  antimony  trichloride,  which 
crystallises  and  has  a  definite  composition,  2SbCl3.3SCl4. 

Selenium  tetrachloride  is  freed  from  accompanying  dichloride 
by  washing  it  with  carbon  disulphide,  in  which  it  is  sparingly 
soluble.  It  may  be  volatilised  without  decomposition. 

Sulphur  and  bromine  mix  in  all  proportions  with  evolution  of 
heat,  but  no  definite  compound  has  been  isolated.  It  is  not  im- 
probable that  the  resulting  liquid  is  a  mixture  of  the  compounds 
S2Br2  and  SBr4  with  excess  of  uncombined  sulphur  and  bromine. 

Sulphur  and  iodine,  and  selenium  and  iodine,  mix  in  all  propor- 
tions when  melted  together,  but  no  products  of  definite  composition 
have  been  isolated.  Tellurium  di-iodide  is  similarly  prepared  ;  the 
excess  of  iodine  is  volatilised  away  by  gentle  heat. 

2.  By  double  decomposition. — Sulphur  and  selenium 
fluorides  are  said  to  have  been  prepared  by  distilling  a  mixture  of 
dry  lead  fluoride  and  sulphur  or  selenium.  They  have  not  been 
analysed.  Tellurium  dioxide  dissolves  in  hydrofluoric  acid,  but  no 
definite  compound  has  been  isolated.  With  hydriodic  acid  tellu- 
rium yields  the  tetriodide  as  a  soft  black  powder. 

Properties. — The  chlorides  of  sulphur  are  yellow-brown  oily 
liquids  decomposed  by  water  with  separation  of  sulphur,  thus  : — 

2S2C12  +  2H,O  +  Aq  =  H2SO3.Aq  +  4HCl.Aq  +  3S. 
2SC12  +  2H2O  +  Aq  =  H2SO3.Aq  +  4HCl.Aq  +  S. 
SC14     +  2H,0  +  Aq  =  H2S03.Aq  +  4HCl.Aq. 


168  THE   HALIDES. 

Diselenium  dichlorlde  and  dibromide  are  dark-brown  liquids, 
which,  when  vaporised,  dissociate  partially  into  free  selenium  and 
tetrahalide.  The  tetrachloride  and  tetrabromide  form  yellow 
crystals.  Tellurium  dichloride  is  a  black  amorphous  solid,  melt- 
ing to  a  black  liquid,  and  giving  a  yellow  vapour.  The  di- 
bromide forms  black  needles,  and  the  diiodide  black  flocks. 
The  tetrachloride  is  a  yellow  crystalline  mass,  melting  to  a 
yellow  liquid  ;  it  is  volatile  without  decomposition.  The  tetra- 
bromide sublimes  in  pale-yellow  needles,  which  melt  to  a  red 
liquid.  The  tetraiodide  is  a  black  powder.  All  these  bodies  are 
decomposed  by  water. 

Physical  Properties. 

The  following  determinations  have  bean  made  of  the  mass  of  1  c.ck  of 
these  compounds :  — 

S2C12  :    1709  grams  at  0°.     Se2Cl2 :    2'906  grams  at  17'5° 
S2Br2:   2628      „      at  4°.     Se2Br2;   3604      „      at  15°. 

The  other  known  constants  are  as  follows  : — 

Melting  and  boiling  points  :— S2C12 :  b.-p.  138°  ;  TeCl2  :  m.-p.  175°,  b.-p.  324°  ; 
TeI2 :  m.-p.  160°  ;  TeCl4  :  m.-p.  209°,  b.-p.  380°.  The  vapour-densities  of  S2C12, 
SeCl4,  SeCl3Br,  TeCl2,  and  TeCl4  have  been  determined,  and  are  normal,  cor- 
responding to  the  formulae  given. 

Heats  of  combination : — 

2S    +  2CI  =  S2C12    +  143K. 

2Se  +  2CI  =  Se2Cl2  +  222K  ;  Se  +  4CT  =  SeCl4  +  351K. 

Te     +  4CI  =  TeCl4  +  774K. 

It  is  thus  seen  that  the  more  stable  compounds  are  formed  with  greatest 
evolution  of  heat. 

Double  halides. — 1.  SeClBr3,  SeCl2Br2,  and  SeCl3Br,  have  been  prepared 
by  addition.  They  are  yellowish  powders.* 

2.  By  acting  with  chlorine  on  sulphides,  the  following  bodies  have  been 
obtained : — 

SC14.2A1C13  ;  3SCl4.2SbCl3  ;  2SCl4.SnCl4  ;  and  2SCl4.TiCl4. 

3.  By  mixing  aqueous  solutions  of  the  constituent  halides,  tellurium 
halides  combine  thus  : — 

TeF4.KF;  2TeF4.BaF2.     TeCl4.2KCl ;  TeCl4.2AlCl3.     TeBr4.2KBr;  TeI4.2KI. 

These  compounds  form  reddish  crystals.    Few  attempts  hare  been  made  to  pre- 
pare double  halides. 


*  Chem.  Soc.,  45,  70. 


169 


CHAPTEE  XIII. 

COMPOUNDS  OF  THE  HALOGENS  WITH  EACH  OTHER  ;  WITH  RHODIUM, 
RUTHENIUM,  AND  PALLADIUM  ;  WITH  OSMIUM,  IR1DIUM,  AND  PLATINUM  ; 
AND  WITH  COPPER,  SILVER,  GOLD,  AND  MERCURY. 

Compounds  of  the  Halogen  Elements  with  each 

other. 

These  compounds  have  no  great  stability.  Fluorides  of  chlorine 
and  bromine  are  unknown.  Iodine  is  said  by  Moissan  to  unite 
with  fluorine  when  exposed  to  it,  and  to  be  a  colourless  fuming 
liquid.  Chlorine  and  bromine  mix,  but  yield  no  definite  com- 
pound; similarly,  iodine  dissolves  in  bromine,  but  separates  on 
distillation.  No  attempts  are  recorded  of  cooling  mixtures  of  these 
elements,  but  it  is  highly  probable  that  evidence  of  combination 
would  be  obtained  if  the  experiment  were  made.  The  only  com- 
pounds investigated  are  the  chlorides  of  iodine.  They  do  not 
occur  in  nature.  They  are  two  in  number,  IC1,  of  which  two 
modifications  exist,  aad  IC13. 

Preparation. — 1.  By  direct  union. — Iodine  heated  in  chlo- 
rine yields  the  monochloride  with  iodine  in  excess ;  with  excess  of 
chlorine,  the  trichloride. 

2.  By  displacement  and  subsequent  combination. — This 
is   accomplished  by  heating  a  mixture  of   iodine  and  potassium 
chlorate,  KC1O3.    This  body  decomposes  thus  :  K2O.C12O5  +  I2  = 
K2O  +  50    +   2ICL      Subsidiary   reactions    take   place,    thus  : — 
K,O.C1205  =  2KC1  +  60;   KC1  +  40  =  KC1O4;  KI  +  30  = 
KIO3,  perchlorate  and  iodate   of  potassium  being  simultaneously 
formed.    The  reaction  is  a  violent  one,  and  the  iodine  monochloride 
distils  over  very  rapidly ;  hence  the  arrangements  for  condensing  it 
must  be  complete. 

3.  By    double    decomposition. — The    trichloride    is    thus 
formed  by  treating  iodine  pentoxide  with  dry  hydrogen  chloride, 
thus:— I2O6    +    IOHCI   =   5H2O    +   2Ck   +   2I<7Z3.     The  higher 
chloride,  2I2C15,  presumably  formed  for  an  instant,  is  unstable,  and 
decomposes,  liberating  chlorine. 


170  THE   HALIDES. 

Properties. — Monochloride,  IC1.  The  liquid  product,  if 
cooled  to  —25°,  solidifies  in  long  dark-red  needles,  melting  at 
27*2°.  This  is  the  a-modification.  The  /3-rnodification  is  sometimes 
obtained  as  dark-red  plates,  melting  at  13'9°,  on  crystallising  the 
liquid  between  +5°  and  —10°.  On  cooling  it  below  —12°  it 
changes  into  the  a  form.* 

The  trichloride  forms  yellow  needles,  melting  under  pressure 
a.t  101°.  The  monochloride  is  only  slightly  decomposed  at  80°, 
boiling  with  partial  dissociation  between  102°  and  106° ;  whereas 
the  trichloride  dissociates  when  gasified. 

Seats  of  combination. — 

I  +  Cl  =  ICl    +     58K. 
I  +  C/3  =  ICL,  +  215Z. 

Both  of  these  bodies  react  with  water,  forming  iodic  acid,  HI03, 
hydrogen  chloride,  and  free  iodine.  Among  the  products  a  yellow 
body  of  the  formula  ICl.HClf  is  said  to  exist,  soluble  in  ether. 


Halides  of  Ruthenium,  Rhodium,  and  Palladium. 

Sources. — These  substances  do  not  occur  native. 
The  following  compounds  are  known  : — 

Fluorine.  Chlorine.  Bromine.         Iodine. 

Ruthenium. .  RuCl2  ;  RuCl3  (RuCl4)  J 
Rhodium  .. .  BhCl3 

Palladium...        PdF2.  PdCl2  PdCl4.         PdBr4.  PdI2. 

Preparation.— 1.  By  direct  union. — The  respective  metals, 
heated  in  chlorine,  yield  RuCL,  RuCl;j,  and  RhCl3. 

2.  By  the  action  of  hydrogen  chloride  on  the  metal. — 
The  presence  of  nitric  acid,  HN03,  is  necessary  to  furnish  oxygen, 
with  which  the  hydrogen  of  the  hydrogen  chloride  may  combine. 
By  this  means,  PdCl2  is  formed;   with  excess  of  nitric  acid  the 
product  is  PdCl4. 

3.  By  heating    a    higher    halide. — PdCl4  loses    chlorine, 
yielding  PdCl2. 

4.  By  removing    chlorine    from    a    higher    chloride. — 
A  solution  of  RhCl3,  on  treatment  with  hydrogen  sulphide,  yields 
EhCl2. 

5.  By  double  decomposition. — (a.)  The  action  of  the  hydro- 

*  Eec.  trav.  chim.,  7,  152. 
f  Compt.  Rend.,  84,  389. 
£  Known  only  in  combination  with  KC1. 


RUTHENIUM,   RHODIUM,   AND   PALLADIUM.  171 

gen  halide  on  the  hydrated  oxide,  in  presence  of  water.  This  is 
the  method  of  preparing  PdF2  (from  PdO),  RuCl3  (from 
Ru203.wH2O),  and  RuCl4.2KCl  (from  Ru02.nH,0),  in  presence  of 
KC1 ;  also  RhCl3  (from  Rh203,nH,0)  ;  and  PdBr4. 

(6.)  By  double  decomposition. — On  adding  a  solution  of 
an  iodide  to  that  of  a  soluble  compound  of  palladium,  e.gr.,  the 
nitrate,  Pd(N03)2,  palladous  iodide,  PdI2,  is  precipitated  in  a 
gelatinous  form. 

Properties. — Ruthenium  dichloride  remains  as  a  black  crys- 
talline powder  when  chlorine  is  passed  over  ruthenium,  while  the 
trichloride  volatilises.  The  trichloride,  prepared  in  the  wet 
way,  is  a  yellow- brown  crystalline  substance.  On  passing  hydro- 
gen sulphide  through  its  solution  it  is  converted  into  ruthenious 
chloride,  thus  :— 2RuCl3.Aq  +  H^S  =  2RuCl2.Aq  +  2HC1  +  S. 
The  dichloride  forms  a  blue  solution. 

Rhodium  trichloride,  prepared  in  the  dry  way,  is  a  reddish- 
brown  insoluble  body.  Prepared  from  the  hydrated  oxide,  it  forms 
a  red  solution. 

Palladium  difluoridc,  obtained  by  evaporating  palladous 
nitrate,  Pd(N03)2,  with  hydrogen  fluoride,  forms  colourless 
soluble  crystals.  The  dichloride  fuses  to  a  black  mass.  The 
tetrachloride  and  tetrabromide  are  said  to  form  dark-brown 
solutions.  It  is  probable  that  they  are  really  compounds  with 
hydrogen  chloride  and  bromide,  PdCl4.2HCl  and  PdBr4.2HBr. 
The  di-iodide  is  a  black  gelatinous  precipitate,  drying  to  a  black 
powder,  and  decomposing  into  its  elements  at  300 — 360°.  The 
only  one  of  these  compounds  which  finds  practical  application  is 
palladium  di-iodide,  which  is  insoluble,  the  corresponding  chlorides 
and  bromide  being  soluble.  It  is  therefore  used  as  a  means  of  sepa- 
rating iodine  from  the  other  halogens.  The  physical  constants  and 
molecular  weights  of  these  bodies  are  unknown. 

Double  halides. — Palladium  fluoride  is  said  to  form  double  compounds 
with  fluorides  of  potassium,  sodium,  and  ammonium.  The  following  compounds 
of  the  other  halides  have  been  prepared  : — 

PdCL2.2KCl.  BuCl3.2KCl.  BuCl4.2KCl. 

BhCl3.2KCl.  PdCl4.2KCl. 

BhCl3.3KCl.  PdBr4.2KBr. 

These  bodies  are  generally  prepared  by  addition.  The  ruthenic  chloride, 
BuCl4.2KCl,  is  obtained  by  dissolving  the  hydrated  dioxide  in  hydrogen  chlo- 
ride in  presence  of  potassium  chloride,  and  evaporating  the  solution.  Com- 
pounds with  some  other  chlorides  have  also  been  prepared.  The  corresponding 
palladium  salt  is  very  unstable,  decomposing  even  when  its  solution  is  warmed, 
with  evolution  of  chlorine. 


172  THE   HALIDES. 


Halides  of  Osmium,  Iridium,  and  Platinum. 

None  of  these  compounds  is  found  in  nature. 

The  following  is  a  list  of  the  known  compounds  : — 

Fluorine.  Chlorine.  Bromine.  Iodine. 

Osmium. . .          —         OsCl2 ;   OsCl3 ;  OsCl4. 

Iridium...  IrCl2?;    IrCl3  ;  IrCl4.    IrBr3  :  IrBr4.  IrI2  ;  IrI3 ;  IrI4. 

Platinum..        PtF4      PtCl2 ;      —       PtCl4.   PtBr2;  PtBr4.  PtI2;    —    PtI4. 

Preparation.— 1.  By  direct  action  of  the  halogen  on  the 

metal  at  a  red  heat,  osmium  dichloride,  trichloride,  and  tetra- 
chloride,  iridium  trichloride,  and  platinum  tetrafluoride  and  tetra- 
chloride  have  been  prepared.  The  double  chlorides  are  in  many 
cases  produced  by  the  action  of  chlorine,  at  a  red  heat,  on  a  mixture 
of  chloride  of  potassium,  &c.,  with  the  metal.  Platinum  tetra- 
bromide  is  formed  by  the  action  of  bromine  and  hydrobromic  acid 
on  spongy  platinum  at  180°  in  a  sealed  tube. 

2.  By  the  action  of  nitro-hydrochloric  acid  on  the  metal. 
—The  action  between  nitric  and  hydrochloric  acids  generates  free 

chlorine,  thus  : — 

HN03  +  SHCl.Aq  =  2H8O.Aq  +  NOCl  +  Ck. 

Metallic  iridium  and  platinum  dissolve  in  aqua  regia,  as  the 
mixture  is  called,  with  formation  of  the  double  compounds  of 
hydrogen  chloride  \\ith  tetrachlorides.  Platinum  tetrachloride, 
PtCl4.4H2O,  is  produced  by  dissolving  the  calculated  amount  of 
platinic  oxide  in  this  solution.  Similarly,  a  mixture  of  nitric  and 
hydrobromic  acids  yields  the  tetrabromides  in  solution. 

3.  By  heating  higher  halides. — Iridium  trichloride  and  tri- 
bromide  have  been  obtained  from  the  tetrachloride  and  tetrabrom- 
ide  by  heat.     Platinic  chloride  (i.e.,  the  tetrachloride)  yields  the 
dichloride  at  440°.     There  is   little  doubt  that  in  every  case  the 
application  of  heat  to  a  tetrahalide  would  be  followed  by  the  forma- 
tion of  a  lower  halide  ;  but  in  many  cases  it  appears  to  be  difficult 
to  avoid  complete  loss  of  halogen  and  reduction  to  metal. 

4.  Double  decomposition. — (a.)  The  action  of  a  halogen 
acid  on  the  corresponding  oxide  or  hydroxide  of  the  metal. 
— Osmium  dichloride  in   solution  has  been  thus  prepared  from 
osmium   monoxide,    OsO ;    similarly,    iridium   trichloride  is  pro- 
duced from  Ir2O3. 

(6.)  Iridium  tetriodide  is  produced  by  mixing  solutions  of  the 
tetrachloride  and  potassium  iodide.     On  mixing  it  with  ammonium 


OSMIUM,  IKIDIUM,  AND   PLATINUM.  173 

iodide,  the  tetraiodide  is  probably  formed  at  first,  but  it  loses 
iodine,  yielding  the  tri-iodide.  Platinum  tetrafluoride  is  produced 
by  adding  silver  fluoride  to  platinum  tetrachloride,  filtering  from 
the  precipitated  silver  chloride,  and  evaporating  the  solution. 
Platinum  di-  and  tetra-iodides  are  formed  on  addition  of  potas- 
sium iodide  to  the  di-  and  tetra-chlorides.  Iridium  tetrabromide 
may  be  similarly  produced  by  the  action  of  potassium  bromide  on 
the  tetrachloride. 

5.  By  reduction  of  a  higher  halide. — Various  reducing 
agents  may  be  used  to  prepare  a  lower  from  a  h'gher  halide.  The 
one  commonly  used  is  sulphurous  acid,  which  absorbs  oxygen  from 
water,  liberating  hydrogen,  which  combines  with  a  portion  of  the 
halogen.  By  this  means  osmium  di-  and  tri-chlorides  and  iridium 
di-iodide  are  produced.  The  last  reaction  is  as  follows  : — 

IrI4.Aq  +  H20  +  H2S03.Aq  =  IrI2.Aq  +  H2SO4.Aq  +  2HI.Aq. 

Properties. — Most  of  these  bodies  are  non-crystalline  powders. 
Iridium  trichloride,  tetrachloride,  tri-iodide,  and  tetra-iodide  are 
black  powders.  Osmium  dichloride  is  blue-black.  It  is  very 
unstable,  but  its  compound  with  chloride  of  potassium  is  more 
permanent.  The  trichloride  is  known  only  in  solution.  The 
tetrachloride  is  a  red  mass.  Iridium  dichloride  is  an  olive-green, 
and  the  di-iodide  a  brown,  powder.  The  tribromide  forms  olive- 
green  crystals.  Platinum  tetrafluoride  is  a  buff-yellow  crystalline 
deliquescent  mass.  The  tetrachloride  forms  orange-brown  crystals 
containing  water.  The  tetrabromide  is  a  non-deliquescent  black 
mass,  soluble  with  brown  colour.  The  dichloride  and  dibromide 
are  greenish-brown  masses.  These  substances  are  all  easily  decom- 
posed by  heat.  The  following  are  soluble  in  water: — OsCl2, 
dark-violet;  OsCl3,  green;  OsCl4,  red.  IrCl3  and  IrCl4  are  de- 
liquescent ;  PtF4,  yellow  ;  PtCl2,  oransre :  PtCl4,  orange-brown  ; 
IrBr.3,  olive-green  ;  IrBr4,  red.  Osmium  tetrachloride  decomposes 
on  addition  of  much  water. 

Double  halides. — These  bodies  are,  as  a  rule,  crystalline  in  this  group,  and 
are  more  stable  than  the  simple  halides.  The  following  is  a  list : — 

Fluorides.  Chlorides. 

Pt.I>KF.        OsCUwKP.        IrCL>.wKCl.       PtCL-.KCl.  PtCl4.2KCl. 

OsCl3.3KCl.       IrCU.SKCl.       PtCL,.2HCl.  PtCl4.2NH4Cl. 

OsCl4.2KCl.      IrCl3.3Ag-Cl.     PtCl2.2KCl.  PtCl4.BaCL. 

OsCl4.2NaCl.    IrCl4.2KCl.       SPtCL^AlClg.      PtCl4.AlCl3. 
OsCl4.2AgCl.  2PtCL>.SnCl4.        PtCl4.FeCl3. 

PtCl4.SnCl4. 
PtCl4.SeCl4. 


174  THE   HALIDES. 

Bromides  and  Iodides. 

PtBr2.2KBr.  IrBr3.3HBr.  IrBr4.2KBr.  IrCl4.NH4I. 
PtBr2.CuBr2.  IrBr3.3KBr.  PtBr4.2HBr.  IrI4.2NH4I. 
IrI2.2NH4I.  IrI3.3KI.  PtBr4.2KBr.  PtI4.2KI. 

IrI3.3AgI.       PtBr4.BaBr2. 
Also,  PtCl4.PtI4,  or  PtCl2I2  is  known. 

A  compound  of  platinum  dichloride  with  phosphorus  trichloride  is  formed 
by  heating  to  250°  spongy  platinum  with  phosphorus  pentachloride  ;  its  formula 
is  PtCl2.PCl3.  The  resulting  crystals  melt  at  170°,  and  are  soluble  in  carbon 
tetrachioride  and  in  chloroform.  It  combines  with  chlorine  to  form  the  double 
compound  PtCl3.PCl4. 

The  most  important  of  these  compounds  are  PtCl^HCl,  pro- 
duced by  direct  addition,  and  the  corresponding  potassium  and 
ammonium  compounds,  produced  by  double  decomposition,  thus  : — 

Pt014.2HCl.Aq  +  2KCl.Aq  =  PtCl4.2KCl  +  2HCl.Aq. 

These  compounds  are  yellow  crystalline  powders,  sparingly  soluble 
in  water,  and  nearly  insoluble  in  a  mixture  of  alcohol  and  ether. 
As  the  similar  sodium  platinichloride  dissolves  in  these  solvents, 
potassium  and  ammonium  are  usually  separated  from  sodium  by 
precipitation  as  platinichlorides,  and  weighed  as  such.  The 
ammonium  salt  at  a  red  heat  yields  spongy  platinum  as  a  porous 
grey  metallic  mass.  All  these  compounds,  indeed,  lose  halogen 
when  heated,  leaving  a  mixture  of  the  metal  of  the  platinum 
group  with  the  halide  of  the  conjoined  metal. 

The  mass  of  1  c.c.  of  platinum  dichloride  is  0'87  gram  at  11°.  The  mass  of 
1  c.c.  of  many  of  the  platinichlorides  has  also  been  determined,  but  with  these 
exceptions  the  physical  constants  are  unknown. 


Halides  of  Copper,  Silver,  Gold,  and  Mercury. 

These  elements  resemble  each  other  in  their  monohalides.  The 
monochlorides,  bromides,  and  iodides  are  all  insoluble  in  water. 
They  have  a  certain  analogy  with  the  compounds  of  the  palladium 
and  platinum  groups,  and  in  their  formulae  correspond  with  those  of 
the  elements  of  the  potassium  group,  in  which  the  first  three 
members  are  classed.  Mercury,  in  the  periodic  table,  is  the  last 
element  in  the  magnesium  group,  which  it  resembles  in  the  formulae 
of  its  dihalide  compounds. 

Sources. — Silver  chloride,  AgCl,  occurs  native  as  horn  silver, 
or  kerargyrite,  in  waxy  translucent  masses.  Bromargyrite  is  the 


COPPER,   SILVER,  GOLD,  AND   MERCURY.  175 

name  of  native  silver  bromide,  a  lustrous  yellow  or  greenish 
mineral.  Chlorobromides  of  silver  of  the  formulae  SAgCl.AgBr, 
3AgC1.2AgBr,  SAgBr.AgCl,  5AgC1.4AgBr,  and  3AgCl.AgBr 
also  occur  native.  Native  iodide  or  iodargyrite  is  also  found  in 
yellow-green  masses.  AgCl.AgBr.AgI  has  also  been  found 
native. 

Mercurous  chloride,  HgCl,  or  horn  quicksilver,  accompanies 
cinnabar,  HgS,  occurring  in  dirty-white  crystals. 

The  following  halides  are  known  :  — 

Fluorine.               Chlorine.                   Bromine.  Iodine. 

Copper..      Cu^Fo;  CuF2.     Cu2CL2;  CuCl2  Cu2Br2;  CuBr2.  Cu2I2;  CuI2. 

Silver  ..      AgF.                    AgCl.  AffBr.  Agl. 

Mercury.     H&F;  H?F2.      Hg-Cl;  HgrCL,.  H&Br;  Hg-Br.,.  Hgl;  HgrI2. 

Gold...                                   AuCl;AuCL2;  AuBr  Aul 
AuCl3.                          AuBr3. 


Preparation.—  1.  By  direct  union.—  Fluorine,  chlorine,  bro- 
mine, and  iodine  attack  these  elements  when  finely  divided  in  the 
cold,  but  the  action  is  promoted  by  heat.  In  this  way  cuprous 
and  cupric  chlorides  and  bromides,  and  cuprous  iodide  have  been 
prepared,  the  monohalide  being  formed  in  presence  of  a  small 
amount  of  halogen  ;  but  the  dihalide  with  excess  of  halogen.  Silver 
chloride,  bromide,  and  iodide,  mercurous  and  mercuric  chloride 
and  iodide  and  mercurous  bromide,  and  gold  dichloride,  AuCL 
or  AUoCli,  and  the  corresponding  bromide,  AuBr2  or  Au2Br4,  have 
also  been  thus  obtained. 

The  higher  halides  are  often  prepared  by  the  action  of  a 
mixture  of  nitric  and  hydrochloric,  or  nitric  and  hydrobromic, 
acids  on  the  elements  (see  p.  172).  The  free  halogen  attacks  the 
metal,  forming  the  halide.  Thus  mercuric  chloride,  HgCL,  cupric 
chloride,  CuCL,  and  auric  chloride  and  bromide,  AuCl3  and  AuBr3, 
are  produced  in  solution  by  this  means:  3Hg  +  GHCl.Aq  + 
2HNO3.Aq  =  3HgCl2.Aq  +  4H.O  +  2NO;  Au  +  3HBr.Aq  + 
HN03.Aq  =  AuBr3.Aq  4-  2H20  +  AT0. 

2.  By  the  action  of  the  halide  of  hydrogen  on  the  metal. 
—  A  solution  of    hydrogen  iodide   dissolves    silver,    forming   the 
double  halide,  Agl.HI.      Hydrochloric  aoid   dissolves   copper  in 
presence  of  air  :  Cu  +  0  +  2HC1.  Aq  =  CuCl2.Aq  +  HZ0. 

3.  By    heating    a    higher    halide.  —  Cupric    chloride    and 
bromide,  CuCL  and   CuBr2,  when  heated,  yield  cuprous  halide, 
Cu2CL  and  Cu.,Br2;  and  cupric  iodide  decomposes  spontaneously 
into  cuprous  iodide,   Cu2I2,  and  iodine.      Aurous  chloride  is  pro- 
duced   at    185°  from   auric    chloride,    and    auric   bromide   yields 


176  THE   HA.LIDES. 

aurons  bromide  at  115°.      Auric  iodide  decomposes  spontaneously 
into  aiirous  iodide  and  iodine. 

4.  By  the  action  of  the  metal  on  the  higher  halide. — A 
solution  of  cupric  chloride  in  hydrochloric  acid,  when  shaken  with 
scraps  of  metallic  copper,  is  converted  into  the  dichloride,  thus  : — 
Cu  +  CuCl2.wHCl.Aq  =  Cu2Cl2.wHCl.Aq.      Mercuric  chloride  or 
bromide   triturated   with  mercury   yields  mercurous  chloride  or 
bromide. 

5.  By  double  decomposition. — (a.)  By  the  action  of  the 
halogen  acid  on  the  oxide   or  carbonate  of  the  metal.— 
All  these  compounds  may  be  thus  prepared.     It  is,  however,  not 
convenient   for   the    preparation    of    insoluble    compounds,    inas- 
much as  the  oxides,  being  insoluble,  become   coated  over  with  a 
film  of  the  insoluble  halide  and  protected  from  the  further  action 
of  the  halogen  acid.     The  following  compounds  have  been  pre- 
pared thus:— Cu2F2,  CuF2,  Cu2012,  CuCl2,  CnBr2,  AgF,  HgF  (by 
the   action  of  HF  on  Hg20)  ;    HgF2,  HgCl2,  HgBr2,  Aul  (from 
Au203  and  HI,  thus:— Au2O3   +   6HI  =   2AuI  +  3H20  +  I2; 
the  auric  iodide,  AuI3,  decomposing  at  the  moment  of  its  forma- 
tion). 

(&.)  Other  cases  of  preparation  by  double  decomposition : — 

Cu2Cl2.  This  is  the  best  method  of  preparation.  A  strong 
solution  of  copper  sulphate,  CuS04,  and  sodium  chloride, 
NaCl,  in  equivalent  proportions,  is  saturated  with  sulphur 
dioxide.  The  sulphur  dioxide  liberates  hydrogen  from 
water,  itself  forming  sulphuric  acid  ;  and  the  nascent 
hydrogen  removes  chlorine  from  cupric  chloride,  produced 
by  the  interaction  of  copper  sulphate  and  sodium  chloride, 
precipitating  cuprous  chloride,  thus  : — 

CuS04.Aq  +  2NaCl.Aq  =  CuCl2.Aq  +  NaaS04.Aq;  and 

2CuCl2.Aq  +  2H,0  +  SOa.Aq  =  Cu2Cl2  +  H2S04.Aq  + 

2HCl.Aq 

HgoCl2  may  be  similarly  prepared  from  mercuric  chloride, 
HgCl2,  and  sulphur  dioxide. 

Cu2I2.  Copper  sulphate,  or  any  other  soluble  salt  of  copper, 
reacts  with  potassium  iodide,  giving  in  very  dilute  solution 
a  blue  solution  of  cupric  iodide ;  in  strong  solution  the 
cupric  iodide  decomposes  into  cuprous  iodide  and  free 
iodine.  The  reactions  are  as  follows  :  — 

CuS04.Aq  +  2KI.Aq  =  CuI2.Aq  +  K2S04.Aq;  and 
2CuI2.Aq  =  Cu2I2  +  I2  +  Aq. 


COPPER,   SILVER,   GOLD,  AND   MERCURY.  177 

AgCl,  AgBr,  and  Agl.  These  are  prepared  by  adding  a  soluble 
salt  of  silver,  e.g.,  the  nitrate,  to  the  required  halide  of 
hydrogen,  or  to  any  other  soluble  halide,  thus  :  — 


q  +  KI.Aq  =  Agl  +  KlTO3.Aq. 

AuF3?  An  attempt  to  prepare  auric  fluoride  by  adding  silver 
fluoride  to  auric  chloride  resulted  in  the  precipitation  of 
auric  oxide,  Au2O3,  through  the  action  of  water  on  the 
fluoride,  thus:  — 

2AuF3  +  3H3O  =  An2O3  +  6HF. 

AuI3.  Auric  iodide  is  formed  by  the  addition  of  auric  chloride 
to  potassium  iodide,  thus  :  — 

AuCl3.Aq  -I-  4KI.Aq  =  AuI^KI.Aq  +  SKCLAq. 

The  double  iodide  is  decomposed  on  addition  of  more  auric 
chloride,  with  precipitation  of  auric  iodide  :  — 

3KI.AnIa.Aq  +  AuCl3.Aq  =  4AuI3  +  SKCl.Aq. 

HgP.  Mercurous  chloride,  digested  with  silver  fluoride,  yields 
mercurous  fluoride  and  silver  chloride,  thus  :  — 

AgF.Aq  +  HgCl  =  AgCl  +  HgF.Aq. 

HgCl,  HgBr,  and  Hgl.  By  precipitation.—  Mercurous 
nitrate,  Hg(N03),  and  a  soluble  halide  yield  mercurous 
halide  and  a  soluble  nitrate,  e.g.,  HgN03.Aq  +  NaCl.Aq 
=  HgCl  +  NaNO3.Aq.  Another  method  of  preparing 
HgCl  is  to  sublime  mercurous  sulphate,  Hg2SO4,  with  salt, 
NaCl  :— 

Hg2SO4  +  2NaCl  =  2HgCl  +  Na2SO4. 

HgCl2.  Mercuric  sulphate,  HgSO4,  and  salt  yield  mercuric 
chloride  on  sublimation  ;  hence  its  name  corrosive  sublimate. 

HgI2.  Mercuric  iodide,  being  insoluble,  is  precipitated  by 
addition  of  mercuric  chloride  to  potassium  iodide.  The 
sesquiiodide,  HgI2.HgI,  is  similarly  precipitated  from  a 
mixture  of  mercurous  and  mercuric  nitrates  by  potassium 
iodide. 

Properties.  —  These  substances  are  all  solid.  The  cuprous  and 
mercurous,  and  the  silver  and  aurous  compounds  are  all  insoluble 
in  water,  but  dissolve  in  concentrated  halogen  acids  ;  mercurous 
and  aurous  halides  are  decomposed  when  boiled  with  acids. 
Cuprous  fluoride  is  a  red  powder,  fusing  to  a  black  mass  ;  when 


178  THE   HALIDES. 

prepared  by  precipitation  it  is  white.  The  chloride  is  also  white, 
but  is  affected  by  light,  which  turns  it  dirty  violet;  it  appears  to  lose 
chlorine.  The  bromide  is  greenish -brown,  and  the  iodide  brownish- 
white.  Silver  fluoride  is  a  white  soluble  mass  ;  the  chloride  is  white, 
but  turns  purple  on  exposure  to  light.  This  is  said  to  be  owing  to 
the  formation  of  asubchloride,  Ag2Cl,  inasmuch  as  the  purple  sub- 
stance is  not  dissolved  by  nitric  acid,  in  which  silver  itself  is  soluble. 
The  bromide  is  pale-yellow,  and  the  iodide  darker  yellow.  These 
substances  are  used  to  detect  and  estimate  the  halogens,  for  they 
are  almost  absolutely  insoluble  in  water.  They  melt  to  horny 
masses.  Mercurous  fluoride  is  a  light-yellow  crystalline  powder, 
partly  decomposed  on  boiling  with  wat^r,  and  decomposed  by 
heat.  The  chloride,  the  common  name  for  which  is  calomel,  is 
dirty  white  in  colour,  and  also  partially  decomposes  when  volati- 
lised, but  its  constituents  recombine  on  cooling ;  hence  it  can 
be  sublimed.  It  condenses  as  a  fibrous,  translucent,  very  heavy 
solid.  It  is  quite  insoluble  in  water.  The  bromide  is 'also  a 
fibrous  yellow  mass.  The  iodide  is  a  greenish-yellow  powder, 
sparingly  soluble  in  water. 

Aurous  chloride,  AuCl,  is  white,  insoluble  in  water,  but  decom- 
posed on  boiling  with  water  into  gold,  and  auric  chloride,  AuCl^. 
The  bromide  is  also  insoluble  in  water,  and  yellowish-grey  in  colour. 
It  is  decomposed  by  hydrobromic  acid,  thus : — 

3AnBr  +  HBr.Aq  =  AuBr3.HBr.Aq  +  2Au. 

Aurous  iodide  is  an  insoluble  yellow  powder,  soluble  in  hydriodic 
acid. 

The  higher  halides  are  all  soluble  in  water.  Those  of  mercury 
and  cupric  chloride  are  also  soluble  in  alcohol  and  in  ether. 

Cupric  fluoride  forms  sparingly  soluble  blue  crystals  ;  mercuric 
fluoride  is  a  white  crystalline  mass. 

Cupric  chloride  is  a  brownish-yellow  deliquescent  powder;  it 
dissolves  in  water  with  a  blue  colour,  and  deposits  blue  crystals 
of  CuCl2.2H2O.  The  bromide  consists  of  iron-black  crystals, 
soluble  in  water  with  a  brown  colour. 

Gold  dichloride,*  Au^Cl^,  is  regarded  as  a  compound  of  AuCl;} 
with  AuCl.  Its  molecular  weight,  however,  is  unknown.  It  is  a 
hard  dark-red  substance,  decomposed  by  water  into  AuCl3  and 
AuCl.  The  trichloride,  AnCl3,  forms  dark-red  crystals,  and  is 
soluble  in  water,  alcohol,  and  ether.  The  dibromide  is  a  black 
substance,  which  reacts  with  water  like  the  corresponding 
chloride,  yielding  monobromide  and  tribromide.  The  latter  is 
*  J.  prakt.  Chem.  (2),  37,  105. 


COPPER,   SILVER,   GOLD,   AND   MERCURY. 


179 


dark- brown  and  dissolves  in  water,  alcohol,  and  ether.  Anric 
iodide,  AuI3,  is  a  dark-green  precipitate,  decomposing  spontane- 
ously into  aarous  iodide  and  iodine. 

Mercuric  chloride,  or  corrosive  sublimate,  is  a  white  crystalline 
substance  ;  100  parts  of  water  dissolve  7*4  parts  at  20°  ;  100  parts 
of  alcohol  dissolve  40  parts  at  the  ordinary  temperature.  The 
bromide  crystallises  in  soft  white  lamin®.  The  iodide  is  a 
scarlet  powder,  sparingly  soluble  in  water,  more  soluble  in  alcohol 
and  ether.  It  crystallises  from  aqueous  potassium  iodide  in  red 
octahedra.  When  sublimed,  it  condenses  in  yellow  prisms,  which, 
when  rubbed,  suddenly  change  into  red  octahedra. 


Physical  Properties. 
Mass  of  1  c.c.  Melting-point.  Boiling-point. 


Cl. 
434° 
451 


F.       Cl.  Br.       I.      F. 

Copper.   —        ?  (ous)  4'72     5'70  908° 
Silver..    —    5-505         6'215  5'67     ? 

at  0°        at  17° 

Gold...   —        ?  ?  ?        ? 

Mercury  _  {  6'56  (ous)  7'31     7'64 
7        L5-45(ic)     5-73     6'30 

Double  balides. — Cupric  fluoride  is  said  to  combine  with  the  fluorides  of 
the  alkaline  metals  to  form  black  compounds.  The  following  compounds  of  the 
other  halides  have  been  prepared : — 


Br.       I.   F.   Cl.      Br.       I. 
504°  601°  ?  954t  861°    759° 
427°  527°  ?      ?        ?     White 
heat. 

?        250°*  115°*   *     *     *       *  * 

?  J       405°  290°  ?  400°    J?      310° 

130°*  288°     244°  238°  ?  303°  319°    339° 


Cu3CU4HCl. 

HgClo.KCl. 

CuCl,.2HCl. 

AuCl3.KCl. 

OusXt.Hffl* 

2Hj?Cl2.CaCl2. 

CuCl2.2KCl. 

AuCl3.NaCl. 

Ag-F.HF. 

HgBr2.E:Br. 

CuCL2.2NH4Cl. 

2AuCl3.CaCL2. 

A*C1.NH4C1. 

2Hg-Br2.SrBr2. 

H&C12.2NH4C1. 

2AuCl3.ZnCl2. 

AgCl.KCl. 

Hg-Io.KI. 

HgI2.2NH4I. 

AuBr3.HBr. 

Agl.HI. 

HgCL2.NH4Cl. 

HgCL2.2KCl. 

AuBr3.KBr. 

AgrLKI. 

HgrI2.HsI. 

HgI2.2KI. 

AuI3.KI. 

AgI.2KI. 

2H&I2.BaI2. 

HgI2.HgrCl2. 

2Hg:Cl.SrCl2. 

2HgCl2.HgI2. 

2HgCl.SClz. 

Besides  these,  2HgCl2.K:Cl,  3HgCl2.MgCl2,  and  5HgCl2.CaCl2  are  known,  in 
which  the  mercuric  chloride  bears  a  larger  ratio  to  the  other  chloride  than  in 
the  tabulated  examples.  The  name  aurichlorides  (sometimes,  but  incorrectly, 
"chloraurates")  has  been  applied  to  the  compounds  of  auric  chloride.  The 
compound  Cu2I2.HgI2  is  a  red  body,  and  has  the  curious  property  of  turning 
black  when  heated.  It  has  been  used  as  a  means  of  indicating  whether  the 
axles  of  engines  become  superheated.  The  compound  HgCl2.2NH4Cl  has  been 

*  Decomposes. 

t  Between  954°  and  1032° ;  CuCl2,  498°  ;  Cu2Br2,  861-954°. 

J  Sublimes  between  400°  and  500°  without  melting. 

N    2 


180  THE  HALIDES. 

known  since  the  times  of  the  alchemist,  and  was  termed  by  them  sal  alembroth. 
All  these  bodies  are  prepared  by  direct  addition.  Those  of  silver  are  decom- 
posed on  dilution,  giving  precipitates  of  halides.  The  compound  HgCl2.SnCl2 
is  produced  by  subliming  an  alloy  of  tin  and  mercury  with  mercurous  chloride. 

The  molecular  weights  of  some  of  these  compounds  have  been 
determined.  The  density  of  cuprous  chloride,  Cu2Cl2,  was  found  to 
be  102-0,  while  the  calculated  number  for  tha.t  formula  is  106-86.* 
Silver  chloride  gave  a  density  corresponding  to  the  molecular 
weight  160-8,  instead  of  the  theoretical  one,  143*39,  for  the 
formula  AgCl.f  As  regards  mercurous  chloride,  it  is  most  pro- 
bable that  the  molecular  weight  is  that  equivalent  to  the  formula 
HgCl.  It  is  not  difficult  to  vaporise  mercurous  chloride ;  the 
difficulty  has  been  to  ascertain  whether  it  decomposes,  in  the  state 
of  gas,  into  mercuric  chloride,  HgCl2,  and  mercury,  or  is  stable. 
In  each  case  the  density  found  corresponded  to  the  formula 
HgCl,  not  to  the  formula  Hg2Cl2.  The  actual  number  was 
231'8 ;  the  calculated  molecular  weight,  235'4.  The  density  was 
determined  in  presence  of  an  atmosphere  of  mercuric  chloride,  and 
under  these  circumstances  little  or  no  dissociation  takes  place.  J 

The  molecular  weights  of  the  remaining  halides  are  unknown, 
but  the  formulae  have  been  made  to  accord  with  those  of  which  the 
value  has  been  ascertained. 

*  Berichte,  2,  1116. 

f  Proc.  Soy.  Soc.  Edin.,  vol.  14. 

%  Gazzetta,  1881,  341 ;  CJiem.  Soc.  Abs.,  42,  466. 


181 


CHAPTEE  XIV. 


TIES,     PHYSICAL     AND     CHEMICAL. — THEIR     COMBINATIONS. THEIR 

REACTIONS     WITH     WATER     AND     HYDROXIDES. — CONSIDERATION     OF 
THEIR   MOLECULAR   FORMULA. 

Having  concluded  the  description  of  the  compounds  of  the 
halogens  with  other  elements,  and  with  each  other,  it  may  be  here 
advisable  to  give  a  summary  of  their  leading  features.  This  will 
be  done  in  the  same  order  as  that  observed  in  the  special  descrip- 
tion of  each  class  of  compounds,  viz.,  their  sources,  their  prepara- 
tion, and  their  properties. 

1.  Sources. — If  a  compound  occur  free  in  nature,  it  must 
either  be  unacted  on  by  substances  around  it  at  the  temperature 
at  which  it  exists,  or  must  have  only  an  ephemeral  existence. 
The  two  most  important  and  widely  spread  agents  are  the  oxygen 
of  the  air  and  water.  It  must,  therefore,  be  able  to  resist  the 
combined  action  of  both  of  these  substances. 

As  an  instance  of  a  compound  produced  under  certain  unusual 
circumstances,  hydrogen  chloride  may  be  named.  It  is  found  in 
the  air  and  water  in  the  neighbourhood  of  volcanoes ;  but,  although 
not  altered  by  air  or  water,  it  soon  is  dissolved  by  the  rain,  and 
reacts  with  the  constituents  of  the  soil,  forming  chlorides  of  cal- 
cium, sodium,  potassium,  &c.,  which  ultimately  find  their  way  into 
the  sea,  being  carried  down  by  rivers.  It  is,  therefore,  only  found 
in  the  locality  where  it  is  formed  before  it  has  been  exposed  to 
those  influences.  Ferric  chloride,  Pe2Cl6,  occurs  under  similar 
conditions. 

The  chlorides,  bromides,  and  iodides  of  lithium,  sodium,  potas- 
sium, calcium,  and  magnesium  are  all  soluble  in  water.  It  is  net 
improbable  that  they  are  partially  decomposed  by  solution ;  thus, 
for  example,  NaCl  +  H30  =  NaHO  +  HC1.  But  when  such  a 
solution  is  evaporated,  the  reaction,  if  there  is  one,  occurs  in  the 
inverse  sensej  and  the  water  evaporates,  leaving  the  chloride.  By 
the  evaporation  of  inland  lakes,  such  as  the  Dead  Sea,  these  salts 
are  deposited.  Such  has  doubtless  been  the  case  where  mines  of 


182  THE   HALIDES. 

rock  salt  exist ;  and  at  Stassfurth,  in  N.  Germany,  the  layers  of 
salt  are  found  in  the  order  of  their  solubility,  the  least  soluble 
forming  the  lowest  layers. 

Insoluble  salts,  such  as  fluorspar  (calcium  fluoride),  cryolite 
(aluminium  sodium  fluoride,  AlF3.3NaF),  silver  chloride,  bromide, 
and  iodide,  lead  chloride,  &c.,  which  are  not  attacked  by  water  or 
oxygen,  are  also  found  in  nature. 

Preparation. — The  general  methods  of  preparation  may  be 
summed  up  as  follows  : — 

1.  Direct  union. — The  halides  may,  as  a  rule,  be  thus  pre- 
pared.     Fluorine    appears  to    act   on  all   elements,    oxygen   and 
nitrogen   excepted,    at   the   ordinary   temperature.       The   metals 
iridium  and  platinum  are,  perhaps,  the  least  affected  of  any  in 
the  cold ;  hence  the  use  of  an  alloy  of  these  metals  in  forming  the 
vessel  in  which  fluorine  was  isolated  by  electrolysis.     Chlorine, 
when  dry  and  cold,  appears   not  to  attack  some  metals,  such  as 
sodium  and  zinc,  which  are  readily  acted  on  when  hot ;  but,  as  a 
rule,  the  elements   combine   with  chlorine,  bromine,  and   iodine 
when  heated  in  contact  with  them.     Those  which  do  not  combine, 
even  at  a  red  heat,  are  carbon,  nitrogen,  and  oxygen. 

2.  Replacement. — Action  of  a  compound  of  the  halogen  on  the 
element ;  or  action  of  the  halogen  on  a  compound  of  the  element. 
The  most  common  instance  of  the  first  method  is  the  action  of  the 
halide  of  hydrogen  on  a  metal.     A  list  of  the  elements  not  thus 
attacked  is  given  on  p.  112.     But  there  are  many  other  processes 
involving  similar  reactions,   where  the  method  is  not  used  as  a 
means  of  preparing  a  halide,  but  of  liberating  the  element  with 
which  the  halogen  was  in  combination.     The  elements  magnesium, 
boron,  aluminium,  silicon,  and  others  are  prepared  by  the  action 
of  sodium  or  potassium  on  their  halides,  which,  of  course,  results  in 
the  formation  of  sodium  or  potassium  halides.     The  action  of  the 
halogen  on  a  compound  of  the  element,  of  which  the  halide  is 
required,  is  also  a  method  not  frequently  employed ;  for,  owing  to 
the  fact  that  there  are  few  elements  which  do  not  combine  with 
the  halogen,  a  mixture  of  two  halides  is  thus  obtained,  which  are 
often  not  easily  separated.     An  instance  of  its  application,  how- 
ever, is  found  in  the  preparation  of  hydrogen  iodide,  by  the  action 
of  iodine  and  water  on  hydrogen  sulphide ;  and  of  carbon  tetra- 
chloride,  by  the  action  of   chlorine   on  carbon  disulphide.      The 
preparation  of  nitrogen,  too,  by  the  action  of  chlorine  on  ammonia 
would  also  come  under  this  head,  yielding  hydrogen  chloride. 

3.  Double  decomposition. — Mutual  action  of  two  com- 
pounds on  each  other,  one  containing  halogen. — This  is, 


REVIEW   OF   METHODS   OF   PREPARING   HALIDES*  183 

perhaps,  the  most  usual  method  of  preparing  compounds  of  the 
halogens.  As  a  rule,  the  resulting  halide  must  be  gaseous  or  solid, 
or  water  or  hydrogen  sulphide  must  be  the  product  of  the  action. 
Instances  of  such  action  are  very  numerous.  Among  them  may- 
be mentioned  the  action  of  sulphuric  or  phosphoric  acid  on  halides 
of  the  metals,  whereby  the  hydrogen  halide  is  formed ;  the 
action  of  the  halides  of  boron,  silicon,  phosphorus,  &c.,  on  water; 
the  action  of  a  halide  of  hydrogen  on  oxides,  hydroxides,  sulphides, 
or  carbonates  of  the  metals  ;  the  action  of  calcium  chloride  on 
barium  sulphate  at  a  red  heat;  the  precipitation  of  calcium 
fluoride ;  the  preparation  of  magnesium  chloride  ;  of  boron  fluoride  : 
boron  chloride ;  and  many  other  cases.  The  method  is  almost 
universally  applicable ;  but  it  does  not  yield  halides  of  nitrogen  or 
of  oxygen. 

A  special  method,  applicable  to  the  preparation  of  aluminium 
chloride,  is  the  action  of  the  vapour  of  carbon  tetrachloride  on  the 
red-hot  oxide.  The  simultaneous  action  of  carbon  and  chlorine  on 
the  oxides  of  silicon,  boron,  &c.,  at  a  red  heat  can  hardly  be 
considered  double  decomposition,  inasmuch  as  the  chlorine  and 
carbon  are  not  combined,  but  it  is  difficult  to  classify  such  actions 
elsewhere,  unless  they  be  regarded  as  cases  of  direct  union. 

To  distinguish  the  halogens  when  all  three  may  be  present,  the 
mixture  is  distilled  with  strong  sulphuric  acid  and  potassium  di- 
chromate.  If  chlorine  be  present,  the  volatile  chromyl  chloride, 
CrOCl2,  is  produced,  and  distils  over.  If  the  distillate  contains 
chlorine,  chromium  will  be  found  therein.  To  detect  bromine  and 
iodine  in  presence  of  each  other,  chlorine- water  is  gradually  added 
to  the  solution  of  their  sodium  or  potassium  salts,  and  the  liquid 
is  shaken  with  carbon  disulphide  or  chloroform,  which  do  not  mix 
with  water.  If  iodine  be  present,  a  violet  solution  is  obtained;  if 
bromine  be  also  present,  further  addition  of  chlorine-water  will 
destroy  the  violet  colour  of  the  chloroform  or  carbon  disulphide, 
and  it  will  be  replaced  by  an  orange-red  colour. 

4.  If  two  or  more  halides  exist,  the  compound  containing  most 
halogen  may  almost  always  be  prepared  by  heating  the  one  con- 
taining less  with  the  required  halogen.     Thus,  iron  dichloride 
yields  the  trichloride  when  heated  in  chlorine ;  mercurous  is  con- 
verted into  mercuric  chloride ;  stannous  into  stannic,  &c. 

5.  By  heating   the    higher    halide,   in   certain   cases,   the 
halogen  is   evolved,   and  the  lower  halide  is  left.     Thus,   thallic 
chloride,  T1C13,  yields  thallous   chloride,  T1C1,  when  heated ;  and 
auric  chloride  similarly  gives  aurous  chloride,  two  atoms  of  chlorine 
being  lost. 


184  THE  HALIDES. 

Sometimes,  but  rarely,  the  lower  halide  decomposes  into  the 
element  and  the  higher  halide.  This  is  the  case  with  bismuth 
dichloride,  BiCl2.  It  is  sometimes  necessary  to  heat  in  contact 
with  some  element  capable  of  combining  with  the  halogen.  For 
example,  aluminous  sodium  fluoride,  AlF2.2NaF,  is  prepared 
by  heating  cryolite  with  metallic  aluminium;  the  compounds 
GaCl2,  InCl2,  and  InCl,  by  heating  Ga013  and  InCl3,  with 
gallium  and  indium  respectively ;  disilicon  hexachloride  is  similarly 
prepared  from  the  tetrachloride  ;  and  chromous  chloride,  CrCl2, 
results  from  the  action  of  hydrogen  at  a  red  heat  on  CrCl3 ; 
the  lower  chlorides  of  titanium,  molybdenum,  and  tungsten  are 
also  prepared  thus. 

Sometimes  the  removal  of  halogen  from  the  higher  halide  may 
be  accomplished  in  solution.  Thus,  the  familiar  operation  of 
"reducing"  ferric  chloride  in  solution  by  means  of  the  hydrogen 
generated  from  zinc  and  hydrochloric  acid,  or  by  sulphur  dioxide, 
or  by  stannous  chloride,  falls  under  this  head  ;  also  the  formation  of 
mercurous  from  mercuric  chloride,  and  that  of  osmium  di-  and  tri- 
chlorides, and  iridium  di-iodide.  Hydrogen  sulphide  is  also  used  as 
a  reducing  agent  for  ferric  halides,  for  rhodium  trichloride,  &c. 

Properties. — (a.)  Physical  properties : — Colour. — The  colour 
of  objects  is  due  to  their  absorbing  light  rays  of  certain  wave- 
lengths in  the  visible  part  of  the  spectrum.  It  is  to  be  noticed 
that  the  iodides  of  those  metals  which  form  white  fluorides, 
chlorides,  and  bromides  often  are  yellow  or  red ;  as  examples,  the 
cases  of  thallium,  silver,  mercury,  &c.,  may  be  noticed.  In  general, 
those  halides  with  higher  molecular  weights  towards  the  end  of 
the  periodic  table  display  colour.  But  substances  which  appear 
colourless  to  our  eyes  have  the  power  of  absorbing  vibrations  of 
wave-lengths  which  do  not  affect  our  sight,  and  to  eyes  sensitive 
to  other  scales  of  vibration  than  ours  such  bodies  would  appear 
coloured.  It  may  also  be  generally  stated  that  halides  containing 
a  large  proportion  of  halogen  display  colour  when  those  containing 
less  are  colourless. 

Form. — The  halides  are  almost  without  exception  crystalline, 
but  up  to  the  present  their  crystalline  form  has  not  yet  been 
connected  with  their  chemical  nature  (see  Isomorphism, 
Chap.  XXXV). 

State  of  aggregation. — Compared  with  the  oxides  and  sulphides, 
the  halides  may  generally  be  said  to  be  easily  fusible  and  volatile. 
This  is  probably  due  to  their  simplicity  of  structure  and  low 
molecular  weight.  The  fluorides,  however,  have,  as  a  rule,  greater 
complexity  than  the  chlorides,  bromides,  and  iodides.  For  example, 


PHYSICAL   AND   CHEMICAL   PROPERTIES   OF   HALIDES.        185 

hydrogen  fluoride  is  known  to  have  a  more  complex  molecule  than 
hydrogen  chloride,  even  in  the  gaseous  state  (see  p.  115)  ;  and  the 
non-volatility  of  many  fluorides,  compared  with  the  volatility  of 
the  corresponding  chlorides,  would  lead  to  the  inference  that  their 
molecules  are  complex.  Some  fluorides,  however,  such  as  those 
of  boron  and  silicon,  have  undoubtedly  simple  formulae ;  and  it  is 
to  be  remarked  that  these  bodies  are  very  stable.  The  comparative 
insolubility  of  many  fluorides,  e.g.,  those  of  calcium,  strontium, 
barium,  magnesium,  tin,  &c.,  may  also  point  to  complex  molecular 
structure ;  and  further  evidence  may  be  derived  from  the  fact  that 
the  fluorides  form  double  compounds  more  easily  than  the  other 
halides. 

The  solubility  of  a  compound,  however,  may  perhaps  partly 
depend  on  its  chemical  action  on  the  solvent,  though  probably  not 
invariably.  It  certainly  appears  to  be  connected  with  simplicity 
of  molecular  structure,  implying  low  molecular  weight. 

The  mass  of  one  cubic  centimetre  of  the  halides  also  shows  regu- 
larity. The  iodides  are,  as  a  rule,  specifically  heavier  than  the 
bromides ;  the  bromides  than  the  chlorides ;  the  chlorides,  how- 
ever, are  not  always  heavier  than  the  fluorides ;  but,  again,  this 
may  depend  on  molecular  complexity,  contraction  always  occurring 
when  chemical  union  occurs,  even  between  molecules  of  the  same 
kind.  It  is  also  to  be  noticed  that,  in  each  group  of  elements,  the 
halides  of  those  which  possess  the  highest  atomic  weights  are 
specifically  heavier  than  the  earlier  members  of  each  series. 

(b.)  Chemical  properties. — Some  halides,  when  heated, 
decompose  into  their  elements,  or  into  lower  halides  and  halogen. 
It  is  probable,  indeed,  that  at  a  sufficiently  high  temperature  all 
chemical  compounds  would  decompose  thus.  In  certain  cases,  for 
example,  the  halides  of  nitrogen,  oxygen,  and  carbon,  when  the 
elements  are  once  apart,  they  do  not  again  combine.  The  halides  of 
oxygen  and  nitrogen  are  formed,  not,  as  usual,  with  evolution  of 
heat,  but  with  absorption,  and  such  compounds  are  always  readily 
decomposed.  Those  of  nitrogen  and  of  oxygen  are  exceedingly 
explosive,  and  cannot  be  produced  by  direct  union.  Other  halides, 
such  as  those  of  gold,  platinum,  &c.,  decompose  into  their  elements 
when  heated,  but  if  kept  in  contact  the  elements  would  again 
recombine.  But,  as  the  metallic  element  is  volatile  only  at  a  very 
high  temperature,  the  halogen,  which  is  easily  volatile,  distils 
away,  leaving  the  metal.  Other  halides,  such  as  the  higher  ones 
of  selenium,  phosphorus,  and  antimony,  are  also  decomposed,  out 
the  lower  halide  is  not  so  different  in  volatility  from  the  halogen 
itself ;  hence,  the  two  are  difficult  to  separate.  When  a  compound 


186  THE   HALIDES. 

decomposes  into  constituents  which  reunite  on  cooling,  it  is  said 
to  dissociate.  The  term  decomposition  includes  dissociation,  but 
may  be  employed  in  the  stricter  sense  of  splitting  up  without 
recombination.  There  is  a  temperature  of  decomposition  peculiar 
to  each  compound,  at  which,  if  recombination  does  not  occur,  after 
sufficient  time,  all  the  compound  would  be  decomposed;  whereas, 
if  recombination  is  possible,  a  state  of  balance  is  maintained,  the 
relative  proportions  of  the  constituents  depending  on  the  tempera- 
ture, on  the  pressure,  and  on  the  relative  amounts  of  the  con- 
stituents. Excess  of  one  constituent  prevents  decomposition. 
Thus,  phosphorus  pentachloride  is  stable  in  the  gaseous  form  in 
presence  of  excess  of  chlorine  or  of  phosphorus  trichloride,  and 
mercurous  chloride  can  exist  as  gas  in  presence  of  mercuric 
chloride.  These  statements  probably  also  apply  to  bodies  in  solution. 

The  halogens  are  capable  of  replacing  each  other.  Here, 
again,  the  relative  amounts  have  a  great  influence  on  the  result. 
Bromine  replaces  iodine  from  its  compounds  with  elements  of  the 
potassium,  calcium,  and  magnesium  groups  dissolved  in  water; 
and  chlorine  replaces  bromine  and  iodine.  But  a  current  of 
bromine  vapour  led  over  hot  potassium  chloride  results  in  the 
formation  of  potassium  bromide.  Again,  on  digesting  precipitated 
silver  chloride  with  bromine-water,  silver  bromide  is  formed ;  and 
iodine,  under  similar  circumstances,  replaces  both  chlorine  and 
bromine.  Yet,  on  heating  silver  iodide  in  a  current  of  chlorine  or 
bromine,  the  iodine  is  expelled,  and  replaced  by  chlorine  or 
bromine.  In  these  cases,  the  mass  of  the  halogen  acting  on  the 
halide  has  the  effect  of  reversing  the  process  which  takes  place 
in  presence  of  water. 

Combinations. — The  halides  of  the  elements  in  most  cases  com- 
bine with  water  to  form  crystalline  compounds  containing  water 
of  crystallisation.  It  is  sometimes,  but  not  always,  possible  to 
expel  such  water  by  heat ;  in  many  cases,  the  water  reacts  with 
the  halide,  forming  hydroxide,  oxide,  or  oxyhalide.  The  crystalline 
form  is  altered  by  the  presence  of  the  water,  and  when  several 
hydrates  exist,  they  have  usually  different  crystalline  forms.  The 
lower  the  temperature,  the  greater  the  amount  of  water  with 
which  the  substance  will  combine.  A  halide  crystallising  without 
water  at  the  ordinary  temperature  sometimes  forms  a  hydrate  at 
low  temperatures,  as  is  the  case  with  sodium  chloride.  The 
remarkable  change  of  colour  of  some  halides,  e.g.,  those  of  nickel, 
cobalt,  iron,  &c.,  when  hydrated  appears  to  point  to  some  profound 
modification  in  molecular  structure  by  hydration  ;  and  the  per- 
sistence of  this  colour  in  dilute  solution  leads  to  the  inference 


GENERAL  REMARKS   ON  DOUBLE  HALIDES.  187 

that  the  hydrate  exists  dissolved  in  the  water.  It  has  been 
pointed  ont  that  compounds  of  halides  with  hydrogen  halides 
invariably  contain  two  molecules  of  water  of  crystallisation  for 
every  molecule  of  hydrogen  halide  present. 

Double  halides. — The  halides  in  almost  all  cases,  as  has  been 
seen,  combine  with  each  other,  forming  double  compounds.  These 
are  usually  prepared  by  mixing  solutions  of  the  two  halides  of 
which  it  is  desired  to  form  a  compound,  and  evaporating  the  mix- 
ture, best  at  the  ordinary  temperature,  for  a  low  temperature  is 
favourable  to  combination.  The  compounds  with  halides  of  hydro- 
gen are  generally,  but  not  always,  called  acids.  In  many  cases 
they  are  exceedingly  unstable,  and  mere  removal  from  the  presence 
of  a  strong  solution  of  the  halogen  acid  is  sufficient  to  decompose' 
them,  the  hydrogen  halide  escaping  as  gas.  They  usually  crystallise 
with  water,  if,  indeed,  thev  can  be  obtained  crystalline  ;  the  anhy- 
drous compounds  are  rare.  Of  the  four  halogens  fluorine  is  most 
prone  to  form  double  compounds.  This  is  probably  connected  with 
the  tendency  of  its  compounds  to  polymerise,  i.e.,  the  tendency  for 
several  molecules  to  enter  into  combination  with  each  other.  It  is 
probable,  indeed,  that  there  is  no  difference  in  kind  between  com- 
pounds of  two  molecules  of  the  same  halide,  such  as  Pe2Cl6  (which 
may  be  regarded  as  a  compound  with  each  other  of  two  molecules 
of  FeCl3),  and  compounds  produced  by  the  union  of  the  halides  of 
two  different  elements,  such  as  PtCl4.2KCl,  SbCl5.SCl4,  &c. ;  such 
bodies,  however,  exhibit  very  different  degrees  of  stability,  certain 
of  them  withstanding  a  fairly  high  temperature  without  decompo- 
sition, so  far  as  can  be  ascertained,  while  others  exist  only  at  a  low 
temperature.  If  one  of  the  halide  constituente  of  a  double  halide 
is  easily  decomposed  by  heat,  it  is  usually  rendered  more  stable  by 
combination  ;  although  on  heating  such  a  double  halide,  the  more 
easily  decomposable  halide  is  decomposed,  while  the  more  stable 
one  resists  decomposition.  An  instance  is  given  above ;  SbCls.SCl* 
is  stable  at  the  ordinary  temperature,  while  SC14  can  exist  only 
below  —  22°  ;  but  on  heating  the  double  halide  chlorine  is  evolved, 
while  the  stable  chloride  of  sulphur,  S2C12,  is  formed,  the  anti- 
mony pentachloride  remaining  unaffected.  Similarly  the  other 
double  halide  mentioned  above,  PtCl4.2KCl,  when  heated,  decom- 
poses, a  mixture  of  metallic  platinum  and  potassium  chloride  being 
left,  while  chlorine  is  evolved.  Here,  again,  the  comparatively 
unstable  platinum  tetrachloride  is  decomposed,  the  stable  potassium 
chloride  resisting  decomposition.  It  is  said  that  solution  in  watei 
decomposes  such  double  halides  into  their  constituent  halides. 
But  it  appears  more  likely  that  the  degree  of  decomposition 


188  THE  HAL1DES. 

depends  on  the  relative  proportion  of  water  and  doable  halide, 
and  on  the  temperature  of  the  solutions ;  and  that  such  a  solution 
really  contains  in  many  cases  both  the  double  halide  and  the  two 
simple  halides.  With  increase  of  solvent,  or  with  rise  of  tem- 
perature, it  is  probable  that  the  relative  amount  of  the  double 
halide  decreases,  while  that  of  the  single  halides  increases.  These 
are  matters,  however,  still  involved  in  considerably  obscurity. 

Action  of  water. — The  action  of  water  on  many  of  the  halides  is 
to  decompose  them,  hydrogen  halide  and  the  oxyhalide  or  hydrox- 
ide of  the  element  being  produced.  The  following  halides  are 
known  to  be  thus  decomposed  by  water  : — (a.)  At  the  ordinary  tem- 
perature : — Halides  of  boron,  silicon,  zirconium,  germanium ;  tetra- 
halides  of  tin ;  halides  of  phosphorus,  arsenic,  antimony,  bismuth, 
vanadium,  niobium,  tantalum,  molybdenum,  tungsten,  uranium, 
sulphur,  selenium,  and  tellurium.  In  certain  cases  the  halide  is 
not  decomposed  in  presence  of  great  excess  of  hydrogen  halide, 
even  although  water  be  present,  possibly  owing  to  the  formation  of 
a  double  halide  of  the  element  and  hydrogen.  This  is  known  to  be 
the  case  with  the  fluorides  of  boron  and  of  silicon,  which  form  the 
compounds  BF3.HF,  and  SiF4.*2HF,  which  are  stable  even  in  pre- 
sence of  a  large  amount  of  water.  Arsenic,  antimony,  and  bismuth 
trihalides  dissolve  in  excess  of  halogen  acid,  probably  forming 
similar  stable  compounds.  (6.)  At  a  red  heat,  most  of  the  halides 
react  with  water-gas  to  form  the  oxides,  those  of  lithium,  sodium, 
potassium,  rubidium,  and  caesium  excepted. 

It  is,  however,  not  improbable  that,  as  has  been  already  stated, 
solutions  of  all  halides  in  water  are  partially  decomposed  by  the 
water,  sodium,  chloride,  for  example,  reacting  to  form  sodium 
hydroxide  and  hydrogen  chloride,  thus  : — NaCl  +  H20  =  NaOH 
+  HC1 ;  and  so  with  other  chlorides.  The  degree  of  this  decom- 
position depends,  no  doubt,  largely  on  the  relative  amounts  of 
water  and  halide,  and  on  the  temperature,  and  varies  for  each  salt. 
The  presence  of  a  second  halide  appears  in  many  cases  to  retard  or 
diminish  such  decomposition,  and  to  render  salts  stable  in  solution 
which  would  decompose  or  react  with  water  in  their  absence. 

Action  of  hydroxides. — Halides  which  are  not  decomposed  by 
water,  so  that  their  constituents  can  be  separated,  and  which  are  not 
re-formed  on  alteration  of  temperature,  dilution,  &c.,  can  in  most 
cases  be  decomposed  by  a  soluble  hydroxide.  Thus  sodium  or 
potassium  hydroxides  react  with  almost  all  halides  producing 
hydroxides,  that  is,  oxides  in  combination  with  water.  Ammonia 
dissolved  in  water  has  in  most  cases  a  similar  action,  the  solution 
acting  as  if  it  were  hydroxide  of  ammonium,  NH4OH.  In 


ACTION   OF   HYDROXIDES   OF   SODIUM,  ETC.,   ON   HALIDES.      189 

many  instances,  particularly  if  the  element  belongs  to  the  class 
generally  termed  "non-metals,"  the  hydroxide  produced  com- 
bines with  the  reacting  hydroxide,  forming-  a  donble  oxide,  or 
salt,  and  water.  Oxides  such  as  these  are  termed  "  acid-forming 
oxides,"  or  "chlorous"  oxides;  those  which  have  less  tendency 
to  such  combination  being  named  "  basic  "  or  "  basylous  " 
oxides.  The  following  instances  will  exemplify  what  has  been 
stated : — 

The  action  of  potassium  hydroxide  on  cupric  chloride  is  to 
form  potassium  chloride  and  cupric  hydroxide,  thus  : — 

CuCl2.Aq  +  2KOH.Aq  =  Cu(OH)2  +  2KCl.Aq. 

Cupric  hydroxide  may  be  viewed  as  a  distinct  individual, 
or  as  a  compound  of  cupric  oxide,  CuO,  with  water.  This 
point  will  be  discussed  later.  A  great  excess  of  caustic  potash, 
KHO,  develops  the  slight  power  of  combination  of  copper  oxide, 
which  dissolves  with  a  blue  colour,  forming,  no  doubt,  some  com- 
pound such  as  CuO.K20,  or  Cu(OK)2.  Such  a  compound  is 
certainly  formed  by  the  action  of  zinc  chloride,  ZnCl2,  on  caustic 
potash,  KOH,  the  body  Zn(OK)2  being  produced.  But  this  kind 
of  change  is  the  usual  and  normal  one  of  the  chlorides  of  those 
elements  whose  halides  are  decomposed  by  water  ;  thus  phosphorous 
chloride  at  once  gives  with  water  phosphorous  acid,  H3P03,  or 
P(OH)3  (?),  and  with  caustic  potash,  KOH,  potassium  phosphite, 
the  caustic  potash  reacting  thus  with  the  phosphorous  acid  : — 

2KOH.Aq  +  H3P03.Aq  =  HK2P03.Aq  +  2H20. 

As  the  hydroxides  when  heated  are  as  a  rule  transformed  into 
oxides  with  loss  of  water,  this  forms  one  of  the  most  convenient 
methods  of  preparing  hydroxides  and  oxides,  as  will  soon  appear. 

The  formulae  of  the  halides  are,  as  a  rule,  undoubtedly  simple. 
It  has  already  been  remarked  that  we  do  not  know  with  certainty 
the  formulas  of  liquids  and  of  solids,  inasmuch  as  their  molecular 
complexity  is  unknown.  But  it  is  probable  that  mere  change  of 
physical  state  from  gas  to  liquid,  or  from  liquid  \<o  solid,  is  not 
necessarily  accompanied  by  chemical  aggregation.  Thus,  if  the 
formula  of  hydrogen  chloride  as  gas  is  HCl,  and  if  no  sign  of 
aggregation  is  seen  on  its  approaching  its  temperature  of  lique- 
faction ;  that  is,  if  its  contraction  on  cooling  runs  pari  passu  with 
that  of  hydrogen,  there  would  appear  to  be  no  good  reason  to 
suppose  that  merely  because  it  has  liquefied  its  formula  is  thereby 
rendered  more  complex ;  but  where,  as  in  the  case  of  hydrogen 
fluoride,  distinct  signs  of  molecular  aggregation  are  to  be  noticed 


190  THE   HALIDES. 

as  the  temperature  falls,  no  doubt  can  be  entertained  as  regards 
the  fact  that  the  molecular  structure  is  complex  in  liquid  hydrogen 
fluoride;  but  that  it  begins  to  occur  before  the  liquid  state  is 
reached  would  appear  to  negative  the  supposition  that  it  is  directly 
connected  with  change  of  state.  In  the  present  state  of  our  know- 
ledge, therefore,  it  may  be  concluded  that  the  formula  possessed 
by  a  halide  in  the  gaseous  state  also  represents  its  molecular 
weight  in  the  liquid  condition,  although  there  may  well  be  examples 
of  aggregation  beginning  in  the  liquid  or  solid  states  with  fall  of 
temperature,  which  are  not  to  be  detected  by  determination  of  the 
density  of  the  gas.  A  full  discussion  of  this  point  is  better  reserved 
until  the  oxides  and  sulphides  have  been  studied  ;  for  there  is 
strong  ground  for  the  belief  that  their  molecular  structure  is 
complex. 

In  every  case,  however,  where  the  molecular  complexity  of  a 
compound  is  unknown,  the  simplest  formulae  have  been  adopted. 

These  formulae  are  deducible : — 

1.  From  the  results  of  analysis,  which  yields  the  equi- 

valents of  the  elements,  but  gives  no  information 
as  regards  their  atomic  weights. 

2.  By  the  law  of  simplicity,  as  applied  by  Dalton  and 

Berzelius. 

3.  By  use  of  Avogadro's  law,  that  equal  volumes  of  gases 

contain  equal  numbers  of  molecules :  the  chief 
method  of  investigation  being  the  method  de- 
pending on  the  vapour-densities  of  compounds. 

4.  From  the  atomic  heats  of  the  elements  (Dulong  and 

Petit's  law). 

Other  methods  will  be  considered  in  a  subsequent  chapter. 

Detection  and  Estimation  of  the  Halogens. — Fluorine  is  detected  by 
heating  the  suspected  fluoride  with  strong  sulphuric  acid,  and  trying  if  the  gas 
evolved  will  etch  glass,  i.e.,  will  produce  silicon  fluoride.  Chlorine,  bromine, 
and  iodine,  when  in  combination,  are  detected  by  adding  to  a  solution  of  the 
suspected  compound  in  nitric  acid  a  solution  of  silver  nitrate.  A  chloride  gives 
a  white  precipitate  ;  a  bromide,  a  yellowish  precipitate ;  an  iodide,  a  yellow 
precipitate.  These  may  be  further  distinguished  by  addition  of  excess  of 
aqueous  ammonia.  Silver  chloride  easily  dissolves ;  the  bromide  is  sparingly 
soluble ;  and  the  iodide  insoluble. 


191 


PART  IV.— THE   OXIDES,   SULPHIDES, 
SELENIDES,  AND   TELLURIDES. 


CHAPTER  XV. 

OXIDES,     SULPHIDES,      SELENIDE,     AND      TELLURIDE       OF      HTDROGEN. 

VOLUME-COMPOSITION. PHYSICAL     PROPERTIES.  —  ATTEMPTS     TO 

ASCERTAIN    THE    QUANTITATIVE    COMPOSITION    OP   WATER. — DOUBLE 
COMPOUNDS. 

The  elements  oxygen,  sulphur,  selenium,  and  tellurium,  like 
the  elements  fluorine,  chlorine,  bromine,  and  iodine,  combine 
readily  with  other  elements,  and  many  of  their  compounds  have 
been  carefully  studied.  Like  the  halogens,  these  four  elements 
bear  a  marked  resemblance  to  each  other,  oxygen  being  the 
analogue  of  fluorine,  while  the  other  three  elements  correspond 
more  or  less  closely  to  chlorine,  bromine,  and  iodine.  The  pre- 
vious arrangement  of  matter  will  be  adhered  to  ;  but  additional 
paragraphs  must  be  added,  describing  the  double  compounds  of 
the  elements  of  this  group  with  those  of  the  halogens  and  with 
each  other. 

Compounds  of  Oxygen,  Sulphur,  Selenium,  and 
Tellurium  with  Hydrogen. 

Hydrogen  oxides,  sulphides,  selenide,  and  telluride ;  H20  ; 
H202;  #28;  H2S3;  HzSe-,  H.Te. 

Sources. — Water,  H20,is  the  most  widely  distributed  of  com- 
pounds, and  occurs  in  larger  proportion  in  nature  than  any  other. 
It  forms  the  sea,  lakes,  and  rivers  ;  as  ice  it  caps  the  tops  of  high 
mountains,  and  covers  the  land  in  the  neighbourhood  of  the  North 
and  South  Poles  ;  in  the  form  of  small  liquid  particles  it  forms 
clouds,  fogs,  and  mist ;  its  vapour  is  always  present  in  the  atmo- 
sphere in  greater  or  less  amount,  and  is  known  as  "  humidity."  It 
is  a  constituent  of  many  minerals,  and  of  all  organised  beings, 
vegetable  and  animal,  forming  from  70  to  95  per  cent,  of  their 
weight.  It  is  conjectured,  from  the  appearance  of  the  planets 


192      THE  OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

Mars  and  Venus,  that  their  atmospheres  contain  water-vapour, 
and  that  their  land  is  intersected  by  seas.  It  has  not  been  proved 
to  exist  in  the  Moon,  and  it  probably  does  not  exist  as  such  in  the 
Sun. 

Hydrogen  dioxide,  H202,  is  present  in  minute  amount  in  rain 
and  snow,  and  in  all  natural  waters,*  and,  being  a  body  prone  to 
give  up  oxygen,  probably  plays  an  important  part  in  oxidising 
dead  vegetable  and  animal  matter.  It  appears  to  be  produced 
by  the  evaporation  or  exposure  to  light  of  water  in  which  oxygen 
gas  is  dissolved. 

Hydrogen  sulphide,  H2S,  escapes  from  fissures  in  the  earth 
in  volcanic  districts,  and  is  a  constituent  of  many  mineral  springs ; 
such  waters  are  termed  "  hepatic,"  and  are  used  as  a  cure  for 
diseases  of  the  skin.  The  wells  at  Harrogate  are  much  fre- 
quented on  this  account.  It  is  not  widely  spread,  being  slowly 
oxidised  on  exposure  to  air.  Hydrogen  selenide  and  telluride  do 
not  occur  in  nature. 

Preparation. — 1.  By  direct  union. — (a.)  Water. — A  mix- 
ture of  hydrogen  and  oxygen  gases  in  the  proportion  of  two 
volumes  of  the  former  to  one  volume  of  the  latter  explodes 
violently  when  heated  to  its  igniting  point  at  the  ordinary  pres- 
sure, forming  water.  The  fact  that  by  the  union  of  hydrogen 
with  oxygen  water  is  the  sole  product  was  first  proved  by 
Cavendish,  though  its  true  nature  was  first  determined  by 
Lavoisier. 

The  combination  may  be  easily  shown  by  filling  a  strong  soda-water  bottle 
two-thirds  full  of  hydrogen  and  one-third  witli  oxygen,  and  after  wrapping  it 
in  a  cloth,  for  fear  of  the  glass  being  shattered  to  fragments  by  the  explosion, 
applying  a  lighted  taper  to  the  mouth.  A  violent  explosion  will  occur,  owing  to 
the  sudden  expansion  of  the  water-gas  caused  by  the  heat  evolved  by  the  union 
of  its  constituents. 

The  quantitative  relations  between  the  volumes  of  the  gases  and  their  pro- 
duct, water-gas,  may  be  shown  in  a  more  instructive  manner  as  follows: — 

A  is  a  strong  U^ube,  of  about  15  mm.  in  internal  diameter,  with  platinum 
wires  sealed  through  its  upper  end,  surrounded  by  a  jacketing  tube,  B,  in  the 
bulb  of  which  water  is  boiled.  A  is  filled  with  dry  mercury,  and  placed  in 
position  in  a  mercury  trough.  A  mixture,  obtained  by  electrolysing  water  (see 
below) ,  of  oxygen  and  hydrogen  in  the  approximate  proportions  of  two  volumes 
of  hydrogen  to  one  volume  of  oxygen  is  introduced  into  the  tube  A,  so  as  to  fill 
it  about  one-third.  The  water  is  then  boiled  so  as  to  jacket  the  inner  tube,  A, 
with  steam.  The  mixed  gases  expand,  and  when  the  temperature  has  become  con- 
stant the  mercury  is  run  out  by  opening  the  stop-cock  C  until  it  is  level  in  both 
limbs  of  the  U'tube.  The  level  of  the  gases  in  then  marked  by  an  india-rubber 

*  Schone,  Berichte,  7,  1693. 


THE   COMPOSITION   OF   WATER, 


193 


ring,  and  mercury  is  again  allowed  to  flow  out  so  as  to  reduce  the  pressure  on  the 
gas.  A  spark  from  an  induction  coil  is  then  caused  to  pass  between  the 
platinum  wires  sealed  through  the  glass.  The  gases  are  heated  to  their 
temperature  of  ignition ;  the  portions  thus  heated  unite,  and  the  heat  evolved 
by  the  union  raises  the  neighbouring  portions  to  their  ignition-point.  An 
explosion  takes  place,  but  owing  to  the  increased  volume  of  the  gas,  it  is  not 
so  violent  as  it  would  be  at  atmospheric  pressure  and  ordinary  temperature. 


FIG.  29. 


The  gases  after  combination  contract,  and,  to  bring  them  back  to  atmospheric 
pressure,  mercury  is  poured  into  the  open  limb  of  the  y-tube  until  it  stands  at 
equal  height  in  both  limbs.  The  volume  of  the  water-gas  is  seen  to  be  about 
two-thirds  of  that  of  the  mixed  gases  before  combination  ;  three  volumes  have 
become  two.  This  experiment  is  adapted  only  as  an  illustration  ;  it  is  inaccu- 
rate owing  to  the  non- introduction  of  various  corrections;  for  example,  a 
mixture  of  oxygen  and  hydrogen,  prepared  by  electrolysis,  contains  ozone 
(see  p.  387),  and  hence  occupies  too  small  a  volume;  and  some  water- vapour 
condenses  on  the  glass,  and  hence  possesses  a  smaller  volume  than  it  ought  to 
occupy. 

Oxyhydrogen   blowpipe. — By   forcing   mixed   hydrogen  and   oxygen   gases 
through  a  narrow  tube  and  setting  them  on  fire,  a  pointed  name  is  produced 

0 


194      THE    OXIDES,   SULPHIDES,    SELENIDES,  AND   TELLURIDES. 

of  a  very  high  temperature.  But  the  rate  of  explosion  of  a  mixture  of  these  gases 
is  very  rapid,  and  there  is  great  danger  of  the  explosion  travelling:  back  through 
the  narrow  tube  and  inflaming  the  mixture.  Hence  a  special  form  of  blowpipe 
must  be  employed.  The  temperature  of  ignition  of  the  mixed  gases  is  a  high  one ; 
probably  600°  to  700°  at  the  ordinary  pressure.  By  cooling  the  gases  below  this 
temperature  they  will  not  ignite.  The  cooling  is  effected  by  passing  the  mixed 
gases  through  a  tube  filled  with  copper  gauze,  or  packed  with  fragments  of 
copper  wire.  The  explosion  cannot  travel  back  through  such  a  tube,  for  the 
flame  is  extinguished  owing  to  its  giving  up  its  heat  to  the  copper,  which  is  a 
good  conductor  of  heat.  The  danger  of  explosion  can  be  thus  avoided.  An 
almost  equally  hot  flame,  however,  may  be  produced  without  danger  by  urging 
oxygen  under  pressure  through  a  flame  of  hydrogen  gas  by  a  blowpipe  of 
the  form  shown  in  fig.  30.  The  temperature  of  such  a  flame  is  estimated  at 


FIG.  31. 


2200°  to  2400°.  The  very  infusible  metal,  platinum,  can  be  melted,  and  even 
boiled  when  thus  heated;  silica  can  be  melted  and  drawn  into  threads  like 
glass  ;  and  the  stem  of  a  pipe,  which  is  composed  of  aluminium  silicate,  can  be 
softened  and  bent.  With  such  a  flame  the  hardest  glass  (combustion  glass)  can 
be  worked  as  easily  as  ordinary  glass ;  and  when  directed  on  a  piece  of  lime  or 
of  zirconium  oxide,  a  dazzling  light  is  emitted,  the  solid  being  raised  to  the  tem- 
perature of  brilliant  incandescence.  Coal-gas,  which  contains  about  50  per 
cent,  of  hydrogen,  is  usually  substituted  for  hydrogen  in  such  experiments  : 
the  temperature,  though  not  quite  so  high,  is  still  high  enough  for  practical 
purposes.  The  applications  of  such  a  blowpipe  are  the  fusion  of  platinum  and 
iridium,  and  the  production  of  the  lime-light,  or,  as  it  is  named  from  its  dis- 
coverer, Captain  Drummond,  the  "  Drummond"  light  (Fig.  30).  The  crucible 
shown  in  Fig.  31  is  made  of  lime,  which  is  almost  the  only  material  capable  of 
withstanding  such  a  high  temperature  without  softening.  In  it  such  metals  as 
platinum,  iridium,  &c.,  can  be  melted. 

Hydrogen  dioxide,  H202,  is  also  formed  in  small  amount 
when  water  is  evaporated ;  it  exists  in  very  minute  quantity  in 
all  natural  waters,  and  is  apparently  produced  by  the  action  of 
heat  and  light  on  water  containing  oxygen  in  solution. 

Hydrogen    sulphide. — Hydrogen   burns   in  sulphur  vapour, 


OXIDES,   SULPHIDES,   SELEXIDE,  ETC.,   OF   HYDROGEN.        195 

with  formation  of  monosulphide,  H2S.  This  may  be  shown  by 
boiling  sulphur  in  a  flask,  and  introducing  a  jet  of  burning  hydro- 
gen into  the  vapour;  the  hydrogen  continues  to  burn  feebly  in  the 
sulphur  gas.  Selenium  and  tellurium  also  unite  directly  with 
hydrogen  at  about  500°. 

2.  By  replacement. — (a.)  Action  of  hydrogen  on  an  oxide. 
—This  process  has  already  been  alluded  to  as  a  means  of  obtaining 
the  elements  indium,  iron,  germanium,  tin,    and  lead,  nitrogen, 
arsenic,  antimony,  and  bismuth,  tungsten,  the  metals  of  the  plati- 
num group,  and  copper,  silver,  mercury,  and  gold.     The  method 
consists  in  heating  the  solid  oxide  to  redness  in  a  tube  through 
which  a  current  of  hydrogen  is  passing,  when  the  hydrogen  unites 
with  the  oxygen  of  the  oxide,  forming   water,  and  the  reduced 
element  is  left.     In  some  cases  higher  oxides,  such  as  manganese 
dioxide,  chromium  trioxide,  &c.,   are  reduced  not  to  the  state  of 
element,  but  only  to  lower  oxides.     Similar  experiments  on  sulph- 
ides, selenides,  and  tellurides  have  not  been  thus  carried  out,  but 
would  doubtless  prove  efficient  in  many  cases. 

(6.)  Action  of  oxygen,  sulphur,  &c.,  on  a  compound  of 
hydrogen. — All  compounds  of  hydrogen,  excepting  hydrogen 
fluoride,  are  thus  decomposed  by  oxygen.  This  is  the  principle  of 
Deacon's  chlorine  process  (p.  74),  and  of  the  manufacture  of 
lampblack  (p.  45)  ;  while  a  useful  method  of  preparing  hydrogen 
sulphide  consists  in  heating  a  mixture  of  paraffin  wax  (a  mixture 
of  compounds  of  carbon  and  hydrogen)  with  sulphur.  The  sul- 
phur replaces  some  of  the  hydrogen,  which  combines  with  excess 
of  sulphur  to  form  hydrogen  sulphide.  Similarly,  by  heating 
selenium  with  colophene,  hydrogen  selenide  is  continuously 
evolved. 

3.  By  double   decomposition.— Water  is  produced  by  in- 
numerable interactions  of  this  kind.     For  example,  when  many 
oxides,   hydroxides,    carbonates,   silicates,   &o.,    are    treated   with 
halogen   acids,   halides  are  formed  together  with  water.     This  is 
also  the  usual  and  only  available  method  of  manufacturing  hydro- 
gen dioxide.*     For  this  purpose  barium  dioxide  is  dissolved  in 
dilute    hydrochloric    acid    until    the    acid    is    nearly   neutralised. 
Dilute   baryta-water   is   then   added   to    the   filtered   and   cooled 
solution  in  order  to  precipitate  foreign  oxides  and  silica,  which  are 
often  present  as  impurities  in  commercial  barium  dioxide.     The 
solution,  again  filtered,  is  again  treated  with  a  strong  solution  of 
barium  hydroxide,  which  throws  down  a  precipitate  of  hydrated 

*  Thenard,  Annales  (2),  9,  441;  10,  114,  and  335;  11,  208.  BericUe,  7, 
73 ;  Annalen,  192,  257. 

0  2 


196      THE   OXIDES,   SULPHIDES,   SELEN1DES,  AND   TELLURIDES. 

barium  peroxide.  This  precipitate  is  filtered  and  washed  until  free 
from  hydrogen  chloride.  It  is  then  added  to  dilute  sulphuric  acid 
(1  part  H2S04to  5  parts  H20)  with  constant  stirring,  until  the  acid 
is  nearly  neutralised.  The  precipitated  barium  sulphate,  which  is 
practically  insoluble  in  water,  is  then  removed  by  filtration,  and 
the  small  trace  of  sulphuric  acid  remaining  is  precipitated  by 
careful  addition  of  dilute  baryta-water.  The  slight  precipitate  is 
allowed  to  settle,  and  the  clear  liquid  decanted  and  evaporated  in 
a  vacuum  over  strong  sulphuric  acid.  The  equations  are  as  fol- 
lows : — 

BaO2  +  2HCl.Aq  =  BaCl2.Aq  +  H202.Aq ; 
Ba(OH)2.Aq  +  H202.Aq  =  BaO2.8H2O  +  Aq  ; 
BaO2.8H2O  +  H2S04.Aq  =  BaSO4  +  H202.Aq. 

Hydrogen  sulphide,  selenide,  and  telluride  are  also  usually 
prepared  by  double  decomposition.  Sulphide  of  iron,  PeS,  is 
treated  with  dilute  sulphuric  acid ;  or  sulphide  of  antimony,  Sb2S3, 
or  selenide  of  zinc  or  telluride  of  magnesium,  ZnSe  or  MgTe, 
are  treated  with  hydrochloric  acid,  thus  : — 

PeS  +  H2S04.Aq  =  FeS04.Aq  +  HZS ; 
Sb2S3  4-  6HCl.Aq  =  2SbCl3.Aq  +  3#2S; 
ZnSe  +  H2S04.Aq  =  ZnS04.Aq  +  H2Se. 

Hydrogen  sulphide,  prepared  from  crude  ferrous  sulphide  con- 
taining metallic  iron,  obtained  by  heating  together  iron  and 
sulphur,  always  contains  hydrogen.  The  pure  gas  may  be  pro- 
duced from  antimony  sulphide.  Many  other  sulphides  are  simi- 
larly attacked;  among  those  which  resist  the  action  of  acids 
(dilute  sulphuric  or  hydrochloric)  are  the  sulphides  of  tin,  lead, 
arsenic,  bismuth,  platinum,  &c.,  copper,  silver,  mercury,  and 
gold.  Certain  sulphides  and  hydrosulphides  are  decomposed  by 
water  alone  ;  among  these  are  sulphides  of  magnesium,  alumi- 
nium, boron,  silicon,  phosphorus,  chlorine,  &c.  The  heating  of  a 
solution  of  magnesium  hydrosulphide  to  100°  causes  such  a  reac- 
tion :— Mg(SH)2.Aq  =  Mg(OH)2  4-  HZ8  +  Aq.  This  method 
yields  pure  hydrogen  sulphide.  The  selenide  and  telluride  could 
nioubtless  be  similarly  prepared.  The  gases  are  best  collected  by 
downward  displacement. 

Hydrogen  trisulphide  is  prepared  in  an  impure  state  by 
pouring  into  cold  hydrochloric  acid  a  solution  of  sodium  poly- 
sulphide.  The  resulting  yellow  oil  does  not  correspond  to  the 
formula  H2S3,  for  it  contains  sulphur  in  solution.  An  orange- 


OXIDES,   SULPHIDES,   SELENIDE,   ETC.,   OF   HYDROGEN.         197 

coloured  compound  with  the  alkaloid  strychnine  is,  however, 
known,  which  on  treatment  with  strong  sulphuric  acid  yields 
colourless  drops  of  the  trisulphide,  H2S3.  No  persulphides  of 
selenium  or  tellurium  are  known. 

Properties. — Water  is  a  liquid  at  ordinary  temperatures, 
colourless  in  thin  layers,  but  blue  when  a  white  light  is  passed 
through  a  stratum  6  feet  long  contained  in  a  blackened  tube.  Ice, 
when  seen  in  thick  masses,  has  also  a  bluish-green  colour.  The 
vapour  of  water  also  appears  to  be  blue.  Hydrogen  sulphide, 
selenide,  and  telluride  are  colourless  gases ;  the  first  has  been 
condensed  to  a  clear  liquid,  and  frozen  to  a  colourless  solid. 
Water,  when  pure,  possesses  no  smell  or  taste;  hydrogen  sulphide 
has  the  smell  of  rotten  eggs,  being  produced  by  the  decomposition 
of  the  albumen  of  eggs,  which  contains  sulphur;  the  odour  of 
hydrogen  selenide  and  telluride  is  not  so  offensive  as  that  of  the 
sulphide,  but  they  produce  exceedingly  disagreeable  nervous  effects. 
The  sulphide,  selenide,  and  telluride  are  exceedingly  poisonous ; 
when  breathed  undiluted  with  air,  instant  insensibility  is  produced. 
Hydrogen  dioxide  is  a  colourless  viscid  liquid,  miscible  in  all  pro- 
portions with  water.  It  has  a  faint  pungent  smell,  and  a  sharp 
metallic  taste.  Hydrogen  trisulphide  has  a  pungent  smell,  and  is 
insoluble  in  water. 

These  compounds  are  of  very  different  degrees  of  stability. 
While  water  decomposes  only  at  a  very  high  temperature — that  of 
melted  platinum,  for  example — into  its  elements,  hydrogen  sulphide 
is  resolved  into  hydrogen  and  sulphur  at  a  low  red  heat,  and 
hydrogen  selenide  and  telluride  slowly  decompose  at  the  ordinary 
temperature. 

The  dissociation  of  water  may  be  shown  by  passing  steam  through  a  tube 
containing  a  spiral  of  platinum  wire  heated  to  whiteness  by  an  electric  current. 
The  hydrogen  and  oxygen  produced  by  the  dissociation  mix  with  the  steam, 
and  are  cooled  below  the  temperature  of  ignition ;  and  a  test-tube  full  of  explo- 
sive gas  may  thus  easily  be  collected.  The  dissociation  of  sulphuretted  hy- 
drogen may  be  shown  by  passing  the  gas  through  a  red-hot  glass  tube,  when 
sulphur  deposits  on  the  cool  part  of  the  tube. 

Hydrogen  dioxide  and  hydrogen  trisulphide  are  very  unstable 
bodies.  The  former,  even  at  18°  or  20°,  begins  to  decompose 
into  water  and  oxygen.  It  thus  dilutes  itself,  and  in  dilute 
solution  it  is  more  stable.  On  warming  even  a  very  dilute  solu- 
tion, however,  it  decomposes,  bubbles  of  oxygen  being  evolved. 
Many  substances  of  a  porous  consistency  cause  this  decomposition 
to  take  place  at  the  ordinary  temperature  ;  and  it  reacts  with 
certain  oxides  and  peroxides,  depriving  them  of  oxygen,  while  it 


198      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

also  loses  oxygen.  Silver  oxide,  manganese  dioxide,  and  potas- 
sium permanganate  have  an  action  of  this  nature.  With 
silver  oxide,  for  example,  the  action  is  shown  by  the  equation 
Ag.,O  +  H202.Aq  =  2Ag  +  H2O.Aq  +  02.  The  tendency  of  the 
oxygen  of  the  silver  oxide  to  combine  with  one  atom  of  the  oxygen 
of  the  dioxide  so  as  to  form  a  molecule  of  oxygen,  02,  causes  the 
change  to  take  place.  Hydrogen  dioxide  cannot  be  vaporised 
appreciably  without  decomposition,  but  the  fact  of  its  possessing 
a  smell  points  to  its  being  able  to  exist  for  some  time  as  gas.* 

Hydrogen  trisulphide-j*  when  heated,  at  once  splits  up  into 
snlphur  and  hydrogen  sulphide.  This  decomposition  occurs  spon- 
taneously when  hydrogen  trisulphide  is  kept  in  a  sealed  tube,  and 
pressure  rises  until  the  resulting  hydrogen  sulphide  is  liquefied, 
solid  sulphur  separating  out. 

Many  instances  have  already  been  given  of  the  decomposition 
of  water  by  elements.  Some,  such  as  sodium  and  calcium,  decom- 
pose it  at  the  ordinary  temperature ;  others,  such  as  magne- 
sium, iron,  copper,  carbon,  phosphorus,  &c.,  act  on  it  at  a  high 
temperature.  In  all  such  cases  hydrogen  is  evolved,  while  the 
element  combines  with  the  oxygen  ;  the  resulting  oxide  often  itself 
combines  with  the  excess  of  water,  forming  a  hydroxide  or  an  acid. 
Sulphuretted,  seleniuretted,  and  telluretted  hydrogen  are  similarly 
decomposed,  yielding  sulphides,  selenides,  and  tellurides  of  the 
elements,  with  evolution  of  hydrogen.  But  when  fluorine  or  chlo- 
rine acts  on  water,  oxygen  is  evolved. 

Hydrogen  sulphide,  selenide,  and  telluride  are  soluble  in  water, 
but  their  solutions  soon  decompose  on  exposure  to  air.  A  solution 
of  the  first  is  largely  employed  as  a  reagent  in  qualitative  and 
quantitative  analysis. 

The  presence  of  water  can  be  detected  and  estimated  by  heat- 
ing the  substance  containing  it  in  a  current  of  dry  air,  and  leading 
che  current  through  a  weighed  tube  containing  dry  calcium  chlor- 
ide, phosphorus  pentoxide,  or  strong  sulphuric  acid,  all  of  which 
bodies  are  hygroscopic.  The  amount  of  water  presei-t  is  deter- 
mined by  weighing  the  absorbing  tube  a  second  time.  Hydrogen 
dioxide  may  be  detected J  by  adding  to  the  liquid  containing  it  a 
little  ether,  and  one  drop  of  a  solution  of  potassium  bichromate  ; 
on  shaking,  the  ether  is  tinged  blue,  if  dioxide  be  present,  by  a 
compound  of  chromium  of  the  formula  Cr03.H202,  produced  by 
the  union  of  the  hydrogen  dioxide  with  the  chromium  trioxide, 

*   Comptes  rend.,  100,  57. 

f  Comptes  rendus,  66,  1095 ;  Chem.  Soc.,  27,  857. 

I  Annales  (3),  20,  364. 


PHYSICAL   PROPERTIES   OF  WATER.  199 

Cr03,  of  the  bichromate.  Another  very  delicate  test  is  freshly  pre- 
pared titanium  hydroxide,  with  which  the  peroxide  gives  a  yellow 
colour.  Hydrogen  sulphide  is  recognised  by  its  smell  and  its 
blackening  a  piece  of  paper  soaked  in  a  solution  of  lead  acetate  ; 
black  sulphide  of  lead  is  formed. 

Physical  properties  of  water.— As  water,  owing  to  its  abun- 
dance, and  the  ease  with  which  it  can  be  purified,  serves  as  the 
standard  substance  for  many  physical  constants,  a  somewhat  detailed 
description  of  its  .physical  properties  is  necessary. 

(a.)  Mass  of  1  cubic  centimetre. — The  mass  of  1  cubic 
centimetre  of  water  at  4°  is  accepted  as  the  unit  of  weight,  1  gram. 
Ice  is  specifically  lighter  than  water.  1  cubic  centimetre  of  ice  at 
0°  weighs  0'917  gram ;  hence  ice  floats  in  water  with  about  9/10ths 
of  its  bulk  submerged. 

(fc.)  Expansion. — Water,  unlike  other  liquids,  has  a  point  of 
maximum  density  at  4°;  when  cooled  below  that  temperature,  or 
warmed  above  it,  it  expands.  It  is  possible  to  cool  water  a  few 
degrees  below  0°  without  its  freezing ;  it  continues  to  expand  on 
fall  of  temperature,  instead  of  contracting  as  all  other  known  sub- 
stances do. 

(c.)  Vapour-pressures. — At  100°  Centigrade,  80°  Reaumur,  or 
212°  Fahrenheit,  water-vapour  exerts  a  pressure  equal  to  that  of 
760  millimetres  of  mercury ;  it  is  then  at  its  boiling-point  under 
normal  atmospheric  pressure.  With  decrease  of  temperature  its 
vapour-pressure  decreases,  and  at  0°  its  vapour-pressure  is  equal  to 
that  of  4'6  millimetres  of  mercury.  When  pressure  is  reduced  by 
pumping  out  air,  its  temperature  falls,  that  portion  of  water 
which  evaporates  withdrawing  heat  from  the  remainder,  until  at 
a  pressure  of  4*6  millimetres  its  temperature  is  0°-.  On  still 
further  reducing  pressure,  its  temperature  falls  still  lower,  but  it 
is  difficult  to  prevent  freezing.  It  is,  however,  possible  to  lower 
temperature  to  —  5Q  or  — 7°  without  freezing.  Ice  has  also  a 
vapour-pressure.  At  0°  it  is  equal  to  that  of  water  at  the  same 
temperature,  viz.,  4*6  millimetres ;  on  reducing  the  pressure  still 
further,  the  temperature  of  the  ice  falls  by  evaporation,  exactly  as 
with  water,  owing  to  its  cooling  itself  by  evolving  vapour ;  if  heat 
be  communicated  to  the  ice,  it  does  not  raise  the  temperature 
of  the  ice,  provided  the  pressure  does  not  rise,  but  is  entirely 
expended  in  evaporating  the  ice,  which  passes  directly  from  the 
state  of  solid  to  that  of  vapour.  The  vapour-pressures  of  water 
are  as  follows  : — 

T.        0°.       10°.       20°.        30°.       4Sf .        50°.        60°.          70°. 
P.  mm.  .        4-60    9'16     17 '40    31'55  ,54'91     91'98    148'79    23309 


200      THE   OXIDES,   SULPHIDES,   SELENIDES,  A1S7D   TELLURIDES. 


T. 

P.  mm.  .  . 

80°.    90°.    100°.   110°.   120°.  130°.  140°.  150°. 
354-64  525-45  760  '0  1075  '4  1484  2019  2694  3568 

T. 

P.  mm.  .  . 

160°.   170°.   180°.   190°.   200°.   210°.    220°. 
....  4652   5937   7478   9403   11625   14240   17365 

T. 

230°.     240°.     250°.     260°.     270°. 
20936    25019    29734    35059    41101 

(d.)  Specific  heat. — The  amount  of  heat  required  to  raise  the 
temperature  of  1  gram  of  water  through  1°  is  termed  a  calory. 
But  the  specific  heat  of  water,  like  that  of  other  substances,  is  not 
a  constant ;  hence  the  hundredth  part  of  the  heat  required  to  raise 
the  temperature  of  a  gram  of  water  from  0°  to  100°  is  generally 
accepted  as  the  value  of  a  calory.  This  amount  is  practically 
coincident  with  the  amount  required  to  raise  the  temperature  of 
1  gram  from  18°  to  19°.  A  unit  of  100  calories  is  employed  in 
this  book  under  the  symbol  K.  It  is  better  adapted  to  express 
large  amounts  of  heat,  such  as  are  evolved  or  absorbed  during 
chemical  reactions.  The  specific  heat  of  ice  between  —78°  and  0° 
is  0'474  calory  per  degree ;  that  of  water-gas  at  constant  volume  is 
0-4805  calory. 

(e.)  Heat  of  fusion  of  ice.— To  melt  1  gram  of  ice,  80  calories 
are  absorbed  ;  hence  to  melt  18  grams  (or  1  gram-molecule)  of  ice 
requires  14"4  K  at  atmospheric  pressure. 

(/.)  Heat  of  evaporation  of  water. — To  evaporate  1  gram  of 
water  at  100°  into  steam  of  that  temperature  requires  an  absorp- 
tion of  537  calories;  hence  to  evaporate  18  grams,  or  1  gram- 
molecule  requires  (537  X  18)/100  =  96'66  K.  To  convert  1  gram 
of  water  at  0°  into  steam  at  t°  requires  an  absorption  of  heat  of 
(606-5  -|-  0-3050  calories. 

(g.)  Volumes  of  saturated  steam. — From  direct  measure- 
ments the  following  numbers  have  been  obtained : — 

Temperature 140°.      150°.       160°.      170°.      180°.      190°. 

Vol.  of  1  gram;  c.c...      506 '0    392 -4    307 '9    246 "4    197 '1     160 '9 

Temperature 200°.      210°.        220°.      230°.     240°.       250°. 

Yol.  of  1  gram;  c.c...      129'8     108 '7      89  "2      73'8      62-1       52-1 

Physical  properties  of  water ',  hydrogen  sulphide,  hydrogen  selenide, 

and  hydrogen  telluride. 

Mass  of  1  c.c.  Melting-point. 

H2O.      H2S.      H2Se.  H2Te.             H2O.       H2S.     H2Se.     HoTe. 

Solid....     0-917         ?            ?  ?                 '    0°         -85°        ?             ? 

at  0°  at  760  mm. 

Liquid..      TOO        1-19          ?  ?                    _____ 
at  4°        at  ? 


PROOFS   OF   COMPOSITION   OF   H20,   ETC.  201 

Boiling-point. 

H2O.       H2S.        H2Se.      H2Te. 
Liquid 100°  ?  ?  ? 

Heats  of  combination : — 

2H  +  0  =  H20  +  684K;   +  0  +  Aq  =  H202.Aq  -231K. 
2H  +  S  =  HZS  +  47K;  H2S  +  Aq  =  H2S.Aq  +  46K. 
2R  +  Se  =  H2Se  -  111K. 

Proofs  of  the  composition  of  the  oxide,  sulphide,  selen- 
ide,  and  telluride  of  hydrogen. — We  have  seen  that  two 
volumes  of  hydrogen  and  one  volume  of  oxygen  unite  to  form  two 
volumes  of  water-gas.  An  experiment  has  also  been  described  on 
p.  62,  whereby  it  is  shown  that  when  water  is  electrolysed,  it 
decomposes  into  two  volumes  of  hydrogen  and  one  volume  of 
oxygen  approximately.  From  Avogadro's  law  it  may  therefore  be 
concluded  that  the  reaction  occurs  between  2  molecules  of  hydro- 
gen and  1  molecule  of  oxygen,  2  molecules  of  water-gas  being 
formed,  thus : — 


or  in  gram-molecules,  4  grams  of  hydrogen,  occupying  11*16  X  4 
=  44*64  litres,  unite  with  32  grams  of  oxygen,  occupying 
11*16  x  2  =  22*32  litres,  to  form  44*64  litres  of. water-gas  weigh- 
ing 36  grams.  Hence,  as  the  weight  of  11*16  litres  of  hydrogen  is 
1  gram,  water-gas  under  similar  conditions  of  pressure  and  tem- 
perature weighs  36/4  =  9  times  as  much  as  hydrogen.  Its 
molecular  weight  is  therefore  18 ;  that  is,  a  molecule  of  water-gas 
weighs  18  times  as  much  as  an  atom  of  hydrogen. 

Similarly  the  weight  of  22*32  litres  of  hydrogen  sulphide  is 
34  grams,  and  its  specific  gravity  17  ;  and  the  specific  gravities  of 
hydrogen  selenide  and  telluride  have  been  found  equal  to  40*5  and 
64-3  respectively,  giving  molecular  weights  of  81  and  128*6. 

The  fact  that  hydrogen  sulphide  contains  approximately  its  own  volume  of 
hydrogen  may  be  shown  by  heating  in  a  tube,  by  means  of  a  spiral  of  platinum 
wire  traversed  by  a  current,  a  known  volume  of  hydrogen  sulphide.  The  gas  is 
decomposed  into  hydrogen  and  sulphur,  and  on  opening  the  tube  under  water 
no  contraction  takes  place. 

The  exact  quantitative  composition  of  water  has  been  the 
subject  of  numerous  researches,  and  is  even  now  by  no  means  certain. 
The  processes  for  ascertaining  the  composition  may  be  grouped  in 
two  divisions  :  (1)  Determination  of  the  relative  weights  of 
oxygen  and  hydrogen  gases,  and  of  the  exact  proportions 

<$*  TH*^s£\ 


202      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

by  volume  in  which  they  combine;  and  (2),  Synthesis  of 
water  by  passing  a  known  weight  of  hydrogen  over  a 
weighed  quantity  of  red-hot  copper  oxide,  CuO,  and  esti- 
mating its  loss  of  weight,  the  weight  of  the  water  produced 
being  also  determined. 

1.  By  the  second  method,  Erdmann  and  Marchand,*  in  1842, 
established  the  ratio  between  the  weights  of  hydrogen  arid  oxygen 
in  water  as  2  :  16. 

2.  In  the  same  year,  Dumas  also  obtained    the   ratio  2  :  16, 
and  therefore  the  ratio  between  the  atomic  weights  of  hydrogen 
and  oxygen  of  1  :  16.f 

3.  Stas,  in  1867,  determined   the    ratio   between    the  atomic 
weight  of  silver,  and  the  molecular  weights  of  ammonium  chloride 
and  bromide,  by  precipitating  the  chlorine  and  bromine  contained 
in  weighed  quantities  of  these  compounds  by  silver  nitrate  pro- 
duced from  pure  silver.      As  he  had  previously  determined  the 
ratios  of   the    atomic    weights    of    silver,    chlorine,    bromine,    and 
nitrogen   to    oxygen    (these  numbers    are    given    on    p.    23),    the 
ratio    of   hydrogen   to    oxygen    could   be    calculated.      He  found 
H  :  0  :  :  1  :  IS'8854 

4.  Begnault,  in  1847,  found  the  relative  densities  of  hydrogen 
and  oxygen  1  :  15'964.§     Applying  a  correction  overlooked  by  him, 
but  necessary  on  account  of  the  decrease  of  the  volume  of  the 
vacuous  globe,  owing  to  the  external  pressure  of  the  atmosphere, 
the  ratio  is  reduced  to  15 '939. 

5.  Scott,  in    1887-8,||    redetermined   the   ratios    between   the 
volumes  of  hydrogen  and  oxygen  combining  with  one  another,  and 
found  it  to  be   0  =  1,  H  =  1'994;    applying  this  correction  to 
Begnaulfc's  results,  the  ratio  1  :  16'01  is  obtained. 

6.  Van  der  Plaats,  in  1886,  found  the  ratio  1  :  15*95  by  oxi- 
dising a  known  volume  of  hydrogen. 

7.  Lord  Bayleigh,  in  1888  and  1889,^"  found  the  ratio  1  :  15'89, 
from  the  relative  weights  of  the  gases. 

8.  Cooke    and    Bichards,  in  1888,**  by  weighing   the  water 

*  J.  pr.  Chem.,  20,  461. 

f  Annales  (3),  8,  189. 

£  Recherches  sur  les  Rapports  reciproques  des  Poids  atomiques,  Brussels, 
1860. 

§  Relations  des  Experiences,  Paris,  1847,  151, 

j|  Proc.  Roy.  Soc.,  42,  396 ;  JBrit.  Assn.  Rep.,  1888,  631.  Scott  has  since 
found  the  ratio  to  exceed  1  :  2. 

1  Proc.  Roy.  Soc.,  43,  356. 

**  Amer.  Chem.  Jour.,  10,  81. 


COMPOUNDS   OF    WATER   WITH   HALIDES.  203 

produced  by  the  combustion  of  known  weights  of  hydrogen,  ob- 
tained the  number  15'869.  Lastly, 

9.  Keiser,  in  1888,*  weighed  hydrogen  in  combination  with 
palladium,  and  after  combining  it  with  oxygen,  found  the  ratio 
1  :  15-949. 

These  numbers  vary  between  15'869  and  16*01 ;  their  difference 
amounts  to  nearly  1  per  cent.,  and  the  question  cannot  be  regarded 
as  settled.  Hence,  as  remarked  on  p.  20,  seeing  that  most  atomic 
weights  have  been  determined  by  the  analysis  of  oxides,  it  is 
advisable  to  assume  as  the  basis  of  atomic  weight,  0  =  16,  leaving 
the  exact  ratio  between  hydrogen  and  oxygen  to  the  test  of  further 
experiment. 

Compounds  of  water  with  halides. — The  compounds  of 
water  with  halides  are  very  numerous.  The  water  thus  com- 
bined is  generally  termed  "  water  of  crystallisation,"  and  com- 
pounds containing  water  are  said  to  be  "hydrated."  To  give  a 
complete  list  of  such  compounds  would  occupy  too  much  space. 
In  some  instances,  the  amount  of  water  has  been  stated  in  the 
formulae  given.  The  same  salt  may  crystallise  with  several  different 
amounts  of  water;  thus,  ferric  chloride,  Fe2Cl6,  forms  the  hydrates, 
Fe,Cl6.10H2O  and  Fe2Cl6.5H2O ;  calcium  chloride  combines  with 
water  in  the  proportions  CaCla^H^O,  and  2H2O ;  and  so  with 
other  halides.  It  may  generally  be  stated  that  the  lower  the 
temperature,  the  larger  the  amount  of  water  of  crystallisation 
with  which  the  halide  will  combine.  The  halides  of  hydrogen 
also  form  compounds  with  water  (see  p.  112),  which  are  partially 
decomposed  at  the  ordinary  temperature  ;  but  when  distilled,  an 
acid  of  a  definite  strength  always  comes  over;  the  relative 
amounts  of  halide  and  water  depend,  however,  on  the  pressure. 

Some  double  halides  are  unstable,  and  are  not  known  in  a  solid 
state  unless  combined  with  water.  This  is  particularly  the  case 
with  .the  double  halides  of  hydrogen  with  those  of  other  elements. 
The  compounds  SiF^HF,  PtCl4.2HCl,  and  many  others,  are 
unknown  except  in  combination  with  water.  Their  formulae  are 
deduced  from  those  of  their  salts,  i.e.,  from  compounds  such  as 
SiF4/2KF,  PtCl^KCl,  &c.,  which  can  be  dried.  Such  hydro- 
chlorides  appear  to  be  unstable  unless  for  every  molecule  of 
hydrogen  chloride  two  molecules  of  water  are  present. 

This  water  tends  to  leave  the  substance  with  which  it  is  com- 
bined, evaporating  into  the  air.  Its  vapour,  therefore,  exerts  a 
definite  pressure.  If  the  pressure  of  the  water- vapour  in  the  air 

*  Berichte,  20,  2323. 


204      THE   OXIDES,   SULPHIDES,  SELENIDES,  AND   TELLURIDES. 

be  equal  to  or  but  little  greater  than  that  of  the  water  of  crystal- 
lisation, evaporation  is  balanced  by  assimilation  of  water,  and  no 
change  occurs.  If,  however,  it  be  greater,  the  compound  turns  wet, 
and  is  said  to  "  deliquesce ;  "  such  substances  are  termed  "  hygro- 
scopic ; "  if  less,  the  compound  loses  water,  turns  opaque  and 
lustreless,  and  is  said  to  "  effloresce."  Water  of  crystallisation  is 
usually  expelled  by  heating  to  100°,  but  a  much  higher  tem- 
perature is  often  required. 

Compounds  of  hydrogen  sulphide,  selenide,  and  telluride  with 
the  halides  are  unknown. 

Compound  of  hydrogen  sulphide  with  water.— Crystals 
of  the  compound  H3S.7H2O  are  deposited  when  a  saturated  solu- 
tion of  hydrogen  sulphide  in  water,  under  a  pressure  slightly 
higher  than  that  of  the  atmosphere,  is  cooled  to  0°. 


205 


CHAPTER  XVI. 

THE    OXIDES. CLASSIFICATION. — THE     DUALISTIC     THEORY. HYDROXTL  ; 

THE      THEORY      OF      SUBSTITUTION. CONSTITUTIONAL      FORMULA. — 

MOLECULAR   AND   ATOMIC    COMPOUNDS. OXIDES,    SULPHIDES,    SELEN- 

IDES,  AND    TELLURIDES    OF   LITHIUM,  SODIUM,    POTASSIUM,    RUBIDIUM, 

CESIUM,     AND     AMMONIUM. HYDROXIDES     AND     HYDROSULPH1DES. — 

PREPARATION    OF    SODIUM. 

The  Oxides,  Sulphides,  Selenides,  and  Tellurides. 

Like  the  halogens,  oxygen,  sulphur,  selenium,  and  tellurium  form 
many  double  compounds.  But  (and  this  is  especially  true  of  the 
double  oxides)  such  compounds  have  been  usually  placed  in  a  differ- 
ent class,  and  viewed  in  a  different  manner  from  the  double 
halides.  Many  of  the  double  halides  are  decomposed  into  their 
constituent  single  halides  on  treatment  with  water ;  but  there  is 
no  obvious  sign  of  decomposition  with  most  of  the  double  oxides. 
Water,  also,  is  an  oxide,  and  enters  into  combination  with  other 
oxides,  as,  indeed,  it  does  with  halides ;  but  it  is  often  expelled 
only  at  a  high  temperature,  and,  in  one  or  two  cases,  cannot 
apparently  be  expelled  at  any  temperature  short  of  that  of  the 
electric  arc,  in  which  the  constituent  oxide  is  itself  decomposed 
into  oxygen  and  element.  But,  besides  such  firmly  bound  water, 
some  oxides  crystallise  with  water,  and  such  "  water  of  crystal- 
lisation "  is  expelled  with  more  or  less  readiness  at  a  moderate  tem- 
perature, as  it  is  from  the  double  halides  also  united  with  water 
of  crystallisation.  Some  double  sulphides,  selenides,  and  tellurides 
are  also  known,  but  they,  unlike  the  double  oxides,  are  often 
unstable  in  presence  of  water,  tending,  indeed,  to  react  with  the 
water  in  which  they  are  dissolved,  forming  hydrogen  sulphide  and 
an  oxide.  The  sulphides,  moreover,  do  not,  as  a  rule,  form  stable 
compounds  with  hydrogen  sulphide,  and  the  few  compounds  which 
exist  have  been  little  investigated. 

Classification  of  oxides. — The  oxides  of  the  commoner 
elements  have  long  been  divided  into  two  classes  ;  those  of  the  one 
class  chiefly  consist  of  the  oxides  of  elements  of  low  atomic  weight, 


206      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

with  some  marked  exceptions,  and  have  been  termed  acids  or  acid- 
forming  oxides ;  elements  forming  such  oxides  are  generally  termed 
non-metals  ;  while  those  of  the  other  class  which  yield  compounds 
with  acid  oxides  have  been  termed  bases,  or  basic  oxides.  Examples 
of  the  first  class  are :  B2O3,  boron  oxide ;  SiO2,  silica,  or  silicon 
dioxide;  002,  carbon  dioxide;  $02  and  SO3,  sulphur  di-  and  tri- 
oxides ;  and  of  the  second,  Na.O,  sodium  oxide ;  CaO,  calcium 
oxide ;  A12O3,  aluminium  oxide ;  Fe2O3,  iron  sesquioxide,  &c.  In 
certain  cases,  an  oxide  may  belong  to  both  of  these  classes,  as,  for 
example,  A12O3,  which  combines  with  basic  oxides,  on  the  one 
hand,  to  form  compounds  such  as  A12O3.K2O,  or  KA1O2 ;  and,  on 
the  other,  with  acid  oxides,  such  as  SO3,  to  form  such  compounds  as 
A12O3.3SO3,  or  A123SO4.  And  with  some  elements,  which  combine 
with  oxygen  in  several  proportions,  basic  properties  are  displayed 
by  those  oxides  containing  least  oxygen,  as,  for  example,  Cr2O3 ; 
while  the  higher  oxides  show  acid  properties,  for  instance,  CrO3. 

The  Dualistic  Theory.— Such  properties  led  Lavoisier  to 
assign  the  nomenclature  to  bodies  which  he  did,  and  suggested  to 
Davy*  the  theory  of  "  dualism,"  as  it  was  subsequently  termed  by 
Berzelius,  its  great  expositor.f  Inasmuch  as  an  oxide,  decomposed 
by  the  electric  current,  yields  up  its  oxygen  at  the  positive  pole,  and 
the  other  constituent  element  at  the  negative  pole  of  the  battery, 
Berzelius  supposed  that  the  atoms  of  oxygen  were  negatively,  and 
the  atoms  of  the  element  with  which  it  is  in  combination,  positively 
electrified.  When  combinations  of  such  oxides  are  electrolysed,  it 
was  supposed  by  Berzelius  that  they  also  decompose  in  like  manner, 
the  electro-negative  constituent  of  the  double  oxide  being  attracted 
to  the  positive  pole,  and  the  electro-positive  constituent  to  the 
negative  pole  of  the  battery.  Thus,  as  examples,  the  oxides 

FeO,       BaO,       S03,       C02, 

were  supposed  to  be  constituted  of  electro-positive  and  electro- 
negative atoms  respectively,  while  the  compounds 

+         —  +         — 

BaO.S03,  and  FeO.C02, 

were  likewise  imagined  to  consist  of  groups  of  atoms,  which, 
taken  as  a  whole,  themselves  displayed  positive  or  negative  electri- 
fication. On  these  grounds,  he  explained  the  dualistic  theory, 
namely,  that  every  chemical  compound  is  composed  of  two  con- 

*  Phil.  Trans.,  1807,  1. 

f  Schwaigger's  Jour.,  6,  119. 


THE  DUALISTIC  THEORY.  207 

stituents,  one  electro-negative  and  one  electro-positive,  in  combin- 
ation with  each  other. 

But  among  the  reasons  which  led  to  the  abandonment  of  this 
view,  two  are  of  special  importance.  First,  many  compounds 
exist,  especially  of  the  element  carbon,  which  cannot  be  repre- 
sented on  the  dualistic  system.*  Such  compounds  are,  for  example, 
CCl3Br,  C2H5C1,  and  numerous  others,  the  molecular  weights  of 
which  are  established  by  their  vapour- densities ;  hence  they  have 
not  such  formulae  as  3CCl4.CBr4,  5C2H6.C2C16,  &c.  Second,  on 
electrolysis  of  solutions  of  compounds,  such  as  Na2S04,  or 
Na^O.SOa,  the  basic  oxide  does  not  accumulate  at  the  negative, 
and  the  acid  oxide  at  the  positive  pole,  but  the  compound  splits 
into  the  element  sodium  and  the  group  S04,  neither  of  which  are 
stable  in  the  presence  of  water,  but  react  with  it,  sodium  com- 
bining with  its  oxygen  and  half  its  hydrogen,  liberating  the 
other  half;  while  the  group,  S04,  parts  with  a  fourth  of  its 
oxygen,  remaining  as  SO3.  It  cannot,  therefore,  be  supposed 
that  compounds  such  as  sodium  sulphate,  Na^O.SOs,  really  consist 
of  two  distinct  portions  Na20  and  S03 ;  but  its  molecule  exists  as 
a  complete  individual,  Na^SO^  In  further  support  of  the  second 
argument,  it  has  also,  been  adduced  that  a  similar  compound, 
PbS04,  lead  sulphate,  may  be  produced  by  the  following  methods  : 
union  of  PbO  and  S03 ;  union  of  Pb02  and  S02 ;  and  union  of 
PbS  with  4O. 

The  first  argument  is  termed  the  argument  from  substitu- 
tion; it  was  suggested  by  the  French  chemist,  Dumas,  and  by  the 
Swiss  chemists,  Laurent  and  Gerhardt,  and  its  development  has 
led  to  the  classification  of  the  compounds  of  carbon,  and  to  the 
discovery  of  an  enormous  number  of  new  bodies. t 

This  view  of  the  constitution  of  chemical  compounds  has  also 
been  extended  to  include  compounds  other  than  those  of  carbon, 
and  compounds  of  which  the  molecular  weight  is  absolutely  un- 
known. Thus,  sodium  monoxide  has  a  composition  most  simply 
expressible  by  the  formula  Na2O.  This  oxide  unites  with  water 
with  great  readiness,  producing  the  compound  Na2O.HoO.  But 
the  same  compound  may  be  produced  by  the  action  of  the  metal 
sodium  on  water  ;  the  equation  is — 

2Na  +  2H20  =  2NaHO  4-  32. 

An  atom  of  sodium  expels  and  replaces  an  atom  of  hydrogen 
from  water.  The  secondary  action  of  the  union  of  two  atoms  of 

*  Dumas,  Annales  (2),  56,  113  and  14Q. 

f  References  are  not  introduced,  as  they  refer  almost  exclusively  to  the 
compounds  of  carbon.  See  E.  v.  Meyer's  Geschichte  der  Chemie,  Leipsig,  1889. 


208      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

hydrogen  to  form  a  molecule  afc  once  occurs,  and  ordinary,  hydrogen 
is  evolved.  The  formula  NaHO  is  identical  with  the  formula 
Na^O.HjjO,  so  far  as  concerns  the  expression  of  the  composition  of 
the  body,  for  Na2O.H20  =  2NaHO ;  but,  as  the  further  action  of 
sodium  on  fused  NaHO  is  to  yield  Na^O  and  hydrogen,  thus : — 

2NaHO  +  2Na  =  Na2O  +  £T2, 

the  reactions  are  adduced  as  a  proof  that  water  contains  two  atoms 
of  hydrogen,  inasmuch  as  the  hydrogen  can  be  replaced  by  sodium 
in  two  stages,  the  series  of  compounds  being 
H20,  NaHO,  Na20. 

Again,  many  chlorides  on  treatment  with  water  exchange  their 
chlorine  for  oxygen.  Thus,  PC15  with  a  small  quantity  of  water 
forms  PC130,  thus  :— 

PC15  +  H20  =  PC130  +  2HOI, 

one  atom  of  oxygen  taking  the  place  of  two  atoms  of  chlorine ; 
and  that  PC130  is  really  the  formula  of  the  compound  is  proved 
by  its  vapour- density ;  it  is  not  3PC15.P205,  which  would  express 
the  same  percentage  composition.  And  so  with  many  other 
instances. 

Constitutional  or  rational  formulae. — The  analogy  between 
the  halides  and  the  hydroxides,  as  bodies  such  as  NaOH  are 
termed  (the  word  being  a  contraction  for  "  hydrogen-oxides"),  is 
also  a  close  one.  Thus  we  have  NaCl,  NaOH ;  CaCl2,  Ca(OH)2 ; 
SiCl4,  Si(OH)4,  and  so  on;  and  although  no  hydroxide  is  volatile 
enough  at  high  temperatures,  or  indeed,  as  a  rule,  stable  enough  to 
make  it  possible  to  determine  its  molecular  weight  by  means  of  its 
vapour-density,  the  analogy  is  an  instructive  one.  The  molecule 
of  chlorine,  moreover,  Clz,  finds  its  analogue  in  hydrogen  peroxide, 
or  dihydroxyl,  (OH)2. 

The  action  of  halides  of  hydrogen  on  the  hydroxides  can  also 
be  well  represented  on  the  scheme  of  replacement.  Thus  we  have 
NaOH  -f  HCl  =  NaCl  +  H.OH ;  sodium  hydroxide  being  con- 
verted into  sodium  chloride,  while  hydrogen  chloride  is  changed 
to  hydrogen  hydroxide  or  water;  and  so  with  Ca(OH)2  -f  2HCI 
=  CaCl2  -f  2H.OH. 

An  example  of  the  reverse  action,  viz.,  replacement  of  chlorine 
by  hydroxyl,  is  given  in  the  action  of  water  on  phosphorus  trichlo- 
ride, PC13,  thus : — 

Cl        H.OH  fOH        JBT.CZ 

Cl  +  HOH   =  P<  OH  +  H.Cl. 
Cl         H.OH  [OH        H.Cl 


\ 


CONSTITUTIONAL   OR  RATIONAL  FORMULA.  209 

(See,  however,  p.  375).     Certain  oxy chlorides  of  known  molecular 
weight  undergo  similar  changes,  for  instance  : — 


S0,{ 


Cl        H.OH          ~n  /OH        HOI 
Cl  "  H.OH    :       bU2OH  ""  HCl; 


and  so  with  many  other  examples.  Such  formulae  as  those  given 
above  are  termed  constitutional  or  rational  formulas,  in  contradis- 
tinction to  empirical  formulae,  such  as  H3P03,  H2S04,  by  which  the 
percentage  composition  of  the  body  only  is  expressed,  and  not  the 
possible  functions  which  it  may  exhibit. 

The  action  of  such  compounds  on  hydroxides  may  also  be 
similarly  represented.  Thus,  the  formation  of  sodium  sulphate  by 
the  action  of  sulphuric  acid  on  sodium  hydroxide  is  represented 
empirically  :  — 


H3S04  +  2NaHO  =  Na^SO*  +  2H20. 
Its  rational  representation  is  :  — 


«n  ^  NaOH  _    ~n  /OlSTa         H.OH 

>02<OH  '-  NaOH-     >°2<ONa  "  H.OH' 


In  both  instances,  however,  the  exchange  of  hydrogen  for  sodium 
and  of  sodium  for  hydrogen  is  obvious.  The  name  "  sodoxyl  "  may 
be  given  to  the  group  (ONa),  and  it  may  be  supposed  to  exist  in 
combination  with  itself  in  sodium  peroxide  (ONa)2,  or  N^Oo. 

PI 
Intermediate  compounds  are  also  known,  such  as   S02 


chlorosnlphonic  acid,  half  chloride,  half  hydroxide;  and  S02 

sodium  hydrogen  sulphate,  only  half  of  the  hydrogen  being  ex- 
pelled by  sodium  (see  p.  421). 

This  method  of  representation  has  evidently  great  advantages  ; 
it  permits  an  insight,  if  only  a  limited  one,  into  the  constitution 
of  such  double  oxides  and  chlorides;  and  it  has  been  almost 
universally  adopted,  save  among  certain  French  chemists.  It  has 
been  founded  largely  on  the  behaviour  of  compounds  of  carbon, 
the  constitution  of  which  is  elucidated  in  a  similar  manner  and 
in  a  much  more  extended  degree. 

Molecular  Compounds.  —  The  universal  acceptance  of  this 
system,  however,  has  not  been  wholly  good.  There  are  many  com- 
pounds which  cannot  be  thus  classified,  and  which  have  conse- 
quently been  relegated  to  the  position  of  so-called  "  molecular  " 
compounds.  Such  is  the  case  with  the  double  halides  described 
in  previous  chapters.  The  name  "  molecular  "  has  been  applied  to 

p 


210      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLUEIDES. 

all  double  compounds  the  formation  of  which  cannot  be  represented 
by  the  device  of  replacement,  and  it  has  been  attempted  to  draw  a 
distinction  between  "  atomic  "  compounds,  such  as  the  simple 
halides,  and  compounds  such  as  those  represented  above,  and 
"molecular"  compounds.  Thus,  NaCl,  CaCl2,  FeCl3,  CC14,  PF5, 
are  regarded  as  atomic  compounds,  the  halogen  being  in  direct  com- 
bination with  its  neighbour  element;  and  such  elements  are 
termed  monad,  dyad,  triad,  tetrad,  or  pentad,  according  as  they 
combine  with  one,  two,  three,  four,  or  five  atoms  of  halogen.  And 
compounds  such  as  S02Cla,  SO,(OH)2,  S02(ONa)2,  POC13,  PO(OH)3, 
&c.,  are  also  regarded  as  atomic  compounds,  inasmuch  as  they 
fulfil  the  required  condition  of  replacement.  But  compounds  like 
BF3.HF,  AlF3.3NaF,  FeCl3.2KCl,  and  of  double  oxides  with  each 
other,  such  as  MgS04.K2S04  (although  the  latter  compounds  may 
often  be  represented  as  formed  by  replacement)  have  been  regarded 
as  molecular  or  addition  compounds.  The  water  which  often 
accompanies  crystalline  salts,  commonly  called  water  of  crystalli- 
sation, has  also  been  regarded  as  molecularly  combined. 

Now  it  is  questionable  whether  it  is  permissible  to  arbitrarily 
divide  compounds  into  two  classes  without  sufficient  reason.  And 
there  is  justice  in  the  view  that  a  uniform  system  of  representation 
should  be  adopted.  Yet,  as  we  know  nothing  of  the  true  internal 
arrangement  of  atoms  in  a  molecule,  any  systems  which  contribute 
towards  classification  of  like  compounds,  and  representation  of 
like  changes  which  they  undergo,  may  be  made  use  of  in  arrang- 
ing compound  bodies.  The  method  of  representing  compounds 
constitutionally  often  serves  a  useful  purpose,  and  likewise  the 
method  of  representation  of  compounds  as  addition-products.  There 

is  advantage  to   be  gained  by  representing  sodium  sulphate  as 

i 
S02(OH)2,  inasmuch  as  its  analogy  with  S02C12  and   S02 


is  thereby  brought  out  :  and  there  is  also  advantage  in  repre- 
senting it  as  S03.H20,  inasmuch  as  reactions  occur  in  which  the 
group  S03  remains  unaltered,  while  the  group  H20  is  affected. 
For  example,  on  distillation  with  phosphorus  pentoxide,  the  com- 
pound S03  is  liberated  as  such,  while  the  water  combines  with  the 
phosphoric  oxide.  Both  systems  of  representation  will  therefore 
be  employed  as  occasion  offers. 

With  these  preliminary  remarks,  which  apply  mutatis  mutandis 
to  the  sulphides,  selenides,  and  tellurides,  we  proceed  to  the  con- 
sideration of  the  compounds  of  elements  of  the  sodium  group. 


211 


Compounds  of  Oxygen,  Sulphur,  Selenium,  and 
Tellurium,  with  Lithium,  Sodium,  Potassium, 
Rubidium,  Caesium,  and  Ammonium. 

The  following  table  gives  a  list  of  these  compounds  :— 

Oxygen.  Sulphur.  Selenium.  Tellurium. 

Lithium  ____      LLO;  Ia2O2?      Li2S  ?  ?  ? 

Sodium....      Na,0;  Na,O2*  Na,2S;  Na2S2;  Na.2S3.  Na.Se.  ? 

Na,S4;  Na,S5.f 
Potassium..      K2O;  K2O2.         K^S;  K.2S2;  K2S3.          K2Se.          K.2Te? 

K,03;  K.264.*     K,S4;  K2S5.t 

Kubidium..      Rb2O?  Bb2S?  Bb2Se?       Bb2Te? 

Csesium    ...      Cs.>O?  Cs.2S?  Cs2Se?        Cs.2Te? 

Ammonium.         —  (NH4)2S;  S2;  S3;  S4;        "? 

S5;  andS7.t 

It  will  be  seen  that  the  compounds  of  potassium,  sodium,  and 
ammonium  alone  have  been  investigated  with  any  degree  of  com- 
pleteness. 

Sources.  —  None  of  these  compounds  occurs  free  in  nature; 
the  monoxides  of  the  type  M20  occur  in  combination  with  other 
oxides,  especially  with  CO2,  Si02,  N205,  and  S03,  as  carbonates, 
silicates,  nitrates,  and  sulphates. 

Preparation.  —  1.  By  direct  union.  —  The  monoxides  are  pro- 
duced when  thin  slices  of  the  metals  are  exposed  to  dry  oxygen. 
At  higher  temperatures  higher  oxides  are  formed  when  the  metals 
are  heated  in  oxygen  or  nitrous  oxide,  NZ0  ;  this  process  yields 
K,O2,  Na^O;,  and  higher  oxides.  The  formula  of  lithium  monoxide 
is  conjectural  ;  the  monoxides  of  potassium  and  sodium  have  been 
analysed. 

A  mixture  of  sulphides  is  produced  on  heating  the  metals 
with  sulphur,  unless  excess  of  sulphur  is  used,  when  the  penta- 
sulphides  are  formed. 

Ammonium  monosulphide  is  produced  by  the  union  of  am- 
monia and  hydrogen  sulphide  at  a  temperature  not  higher  than 
-18°,  thus:— 

2NH3  +  H28  = 


2.  By  expelling  or  withdrawing  an  element  from  a  com- 
pound. —  Sodium  and  potassium  monoxides   have  been  produced 

*  Chem.  Soc.,  14,  267;  30,  565. 
f  Pogg.  Ann.,  131,  380, 
J  J.  prakt.  Chem.,  24,  460. 


212      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES 

by  heating  the  hydroxides    NaOH    and   KOH  with  the  metal, 

thus  :  — 

-f  2Na  =  2Na,O  +  H2. 


The  higher  oxides  of  potassium  are  formed  on  exposing  the 
dioxide  to  moist  air  ;  a  portion  of  the  potassium  is  converted  into 
hydroxide,  and  the  remainder  stays  in  combination  with  oxygen 
as  trioxide  and  tetroxide,  thus  :  — 

3K2O2  +  2H20  =  2KOH  -f  jffa  +  2K,O8; 
2K2O2  +  2H20  =  2KOH  +  H9  +  K2O4. 

The  hydrosulphides  on  exposure  to  air  yield  the  polysulphides, 
the  hydrogen  uniting  with  atmospheric  oxygen,  thus  :  — 

2KSH  +  0  =  K2S2  +  HaO. 

The  sulphates,  selenates,  and  tellurates,  when  heated,  do  not 
lose  oxygen  as  the  chlorates,  hromates,  and  iodates  do,  leaving 
sulphide,  selenide,  or  telluride  as  the  halogen-  compounds  leave 
halide  ;  but  if  hydrogen  or  carbon  is  present,  oxygen  is  lost  at  a 
red  heat,  thus  :  — 


4#2  =  4H20  +  Na2S; 
or  NaoSO*  +  40  =  400  +  Na^S. 


The  action  of  heat  on  ammonium  pentasulphide,  (NH4)2S5, 
yields  ammonium  mono-  and  heptasulphides,  thus  :  —  3(NH4)2S5  = 
2(NH4)2S7  +  (NH^S.  The  sulphide  being  unstable  at  tempera- 
tures above  —  18°,  decomposes  into  hydrosulphide  and  ammonia, 
thus  :  — 

8  = 


3.  By  double  decomposition.  —  Hydrogen  sulphide  passed 
over  fused  sodium  chloride  produces  monosulphide,  H*S  +  2NaCl 
=  Na2S  +  2HCI.  The  sulphides  of  potassium  have  also  been 
produced  by  double  decomposition  ;  the  trisulphide  by  exposing 
red  hot  potassium  carbonate  to  the  vapour  of  carbon  disulphide, 
thus  :  — 

2K2CO3  +  3C82  =  2K2S3  +  400  +  002. 


And  the  tetrasulphide  by  similar  treatment  of  the  sulphate  :  — 
K,SO4  +  20S2  =  K2S4  +  200  +  S02  (?). 


The  existence  of  this  compound  is  doubtful. 

By  distillation  of  ammonium  chloride  with  a  sulphide  of  potas- 
sium,   the   corresponding  ammonium  sulphide  is    produced,   e.g., 


OF  LITHIUM,   SODIUM,  POTASSIUM,  ETC.  213 

K2S2  +  2NH4C1  =  2KC1  4-  (NH&S*     In  this  manner  (NH4)2S2, 
(NH4),S3,  (NH4)>S4,  and  (NH4)2S5  have  been  prepared. 

"  Liver  of  sulphur  "  or  "  hepar  sulpfwms,"  a  substance  which 
has  been  long  known,  is  produced  by  fusing  4  gram  molecules  of 
potassium  carbonate  with  10  gram  atoms  of  sulphur,  thus  : — 

4K2C03  +  10S  =  K2S04  +  SKaSg  +  4(702. 

It  is  a  mixture  of  sulphate  and  trisulphide.. 

Properties.. — The  monoxides,  so  far  as  they  have  been  pro- 
pared,  are  white  or  grey  solids.  Lithium  monoxide  is  said  to  be 
non-volatile  at  a  white  heat ;  the  others  melt  with  difficultly  and 
volatilise  at  a  very  high  temperature.  Ammonium  monoxide  is 
incapable  of  existence,  decomposing  at  once  into  ammonia  and 
water. 

Sodium  dioxide  is  a  white,  and  potassium  dioxide  a  brownish- 
yellow  solid.  Potassium  trioxide  is  lemon-yellow,  and  the  tetroxide 
sulphur-yellow  ;  both  fuse  to  orange-red  liquids,  turning  black  with 
rise  of  temperature,  but  returning  to  yellow  on  solidification. 

The  sulphides  of  potassium,  sodium,  and  ammonium  are  all 
yellow  or  brownish-yellow  solids  which  have  a  peculiar  "  hepatic  " 
smell.  Ammonium  heptasulphide  is  a  deep-red  substance,  vola- 
tilising without  dissociation  at  300°.  With  acids,,  the  polysulphides 
give  off  hydrogen  sulphide,  while  sulphur  separates  as  a  white 
emulsion  (milk  of  sulphur). 

Potassium  selenide  is  a  greyish  or  brownish  mass  ;.  the  telluride 
is  a  brittle  substance  with  metallic  lustre.  Both  are  soluble  in 
water  and  deposit  selenium  or  tellurium  on  exposure  to  air. 

All  these  substances  are  soluble  in  water,  in  all  probability 
combining  with  it.  The  union  of  the  monoxides  with  water  takes 
place  with  great  evolution,  of  heat,  and  the  water  cannot  be  ex- 
pelled on  ignition  (see  Hydroxides,  below).  But  water  may  be 
expelled  from  solutions  of  sodium  dioxide,  and  of  sodium  and  potas- 
sium monoselenides  and  disulphides,  the  anhydrous  salts  being 
left  on  evaporation.  Hy drated  sulphides  are  known  of  the  formulae 
ILS.2H2O,  K2S.5H2O,  2Na2S.9H2O,  Na2S.5H2O,  and  sulphide, 
selenide,  and  telluride  of  sodium  with  9H20. 

Little  is  known  of  the  physical  properties  of  these  substances.  The 
following  data,.  howeverr  are  approximate  : — 

Mass  of  1  c.c.—'Li^O,  2 '102  at  15°;   Na2O,  2. '805;   B^O,  2 '656;  Na2S, 
2  -471 ;  K2S,  2  '130. 

Volatility. — Li2O  has  not  been  volatilised ;  K2O  volatilises  at  a  red  heat ; 
Xa-jO  melts  at  a  red  heat  and  volatilises  with  difficultly.  The  sulphides  appear 
to  be  difficultly  volatile  -T  potassium  pentasulphide  melta  at  a  red  heat. 


214      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLU RIDES 

Heats  of  formation  : — 

2Na  +   O  =  Na2O  +  804K;    +  H2O  =  2NaOH  +  352E!;    +  Aq  =  198K. 

2Na  +  S  =  Na2S  +  870K ;    +  Aq  =  Na2S.Aq  +  150K. 

K2O  lias  not  been  investigated. 

2K  +  S  =  K2S  +  1012K;    +  Aq  =  K2S.Aq  +  100K. 

None  of  these  substances  has  been  gasified ;  their  molecular 
weights  are  therefore  unknown. 

Double  Compounds. — Double  oxides  of  potassium  are  known  of  the 
formula  K2O2.KoO  ;  KoO^K^O  ;  and  K2O2.3K2O.  These  are  bluish  solids 
produced  by  heating  potassium  in  oxygen  or  nitrous  oxide.  They  melt  to  deep 
red  liquids. 


Hydroxides,  Hydrosulphides,  Hydroselenides, 
and  Hydrotellurides. 

These  names  are  given  to  compounds  of  the  oxides  with  water, 
or  of  the  sulphides,  &c.,  with  hydrogen  sulphide,  selenide,  or 
telluride.  None  of  these  compounds  occurs  free  in  nature.  The 
double  selenides  and  tellurides  have  not  been  investigated. 

Monoxides  and  MonosulpJiides ;  Monohydrates  and  Mon3sulphydrates. 

H2O.  Li2O.H2O  j  Na2O.H2O ;  KoO.H2O;  Rb2O.H2O;  Cs2O.H2O. 

H2S.  Na2S.H2S.  K2S.H2S.  (NH4)2S.H2S 

Poli/hydrates  and  Polysulphydrates. 

Li2O.3H3O;  Na2O.5H2O.  K2O.5H2O. 
Na20.8H20. 

Na2S.5H2O.  K2S.2H2O. 

Na2S.9H2O.  K2S.5H2O. 

Na2S.H2S.12H20.  K2S.H2S.H2O. 

Sydrated  Polyoxides  and  Poly  sulphides. 

Na2O2.2H2O.     Na2S2.5H2O.     Na2S3.3H2O.     Na2S4.8H2O.     Na2S58H2O, 
Na202.8H20.  K2S4.2H20. 

Preparation. — 1.  By  direct  addition. — All  of  these  substances 
may  be  thus  prepared.  As  has  been  remarked,  it  is  still  an  open 
question  whether  the  formula  of  sodium  hydroxide  is  NaOH,  one 
atom  of  sodium  replacing  one  atom  of  hydrogen  in  water ;  or 
Na2O.H2O,  which  may  be  viewed  as  an  additive  product.  If  the 
second  view  be  chosen,  the  analogy  with  the  halides  is  concealed, 
and  the  substances  should  be  named  hydrates:  if  the  first,  the 
compounds  with  more  molecules  of  water  are  difficult  to  classify ; 


OF   LITHIUM,   SODIUM,   POTASSIUM,   ETC.  215 

and  there  appears  no  good  reason  for  preferring  one  method  of 
representation  to  another.  These  remarks  apply  also  to  the 
sulphides.  Similar  compounds  of  the  selenides  and  tellurides  hare 
not  been  investigated. 

The  compound  NaX).5H2O  is  prepared  by  crystallising  a  solu- 
tion of  NaoO.HoO  from  alcohol  containing  2  per  cent,  of  water ; 
the  similar  compound  of  potassium  separates  from  water;  this 
compound,  when  treated  with  metallic  sodium,  gives  a  liquid  alloy 
of  potassium  and  sodium. 

The  hydrate,  Na.,O.8H2O,  crystallises  from  water. 

The  compound,  Na>O2.8H>O,  crystallises  from  water,  and  when 
dried  over  sulphuric  acid  it  loses  water,  and  has  then  the  formula 
Na2022H20. 

The  hydrates  of  the  mono-  and  polysulphides  are  all  obtained 
by  crystallising  them  from  water.  In  most  cases  the  water  may 
be  evaporated  by  heat,  leaving  the  anhydrous  sulphides. 

Ammonium  hydrosulphide,  NH4HS,  is  produced  by  direct 
addition  of  ammonia  to  hydrogen  sulphide  above  — 18°. 

2.  By  double  decomposition. — The  hydrates  are  prepared 
by  (a)  the  action  of  barium  hydroxide  on  the  sulphate,  thus  : — 

Li2S04.Aq  +  Ba(OH)2.Aq  =  2LiOH.Aq  +  BaSO,; 
the  barium  sulphate  being  insoluble,  it  may  be  separated  by  filtra- 
tion ;  (/)),  the  action  of  calcium  hydroxide  on  the  carbonate — 

Na2C03.Aq  +  Ca(OH>..Aq  =  2tfaOH.Aq  +  CaCO3; 

or  (c)  by  the  action  of  silver  hydroxide  on  the  chloride,  bromide, 
or  iodide — 

KCl.Aq  +  AgOH  =  KOH.Aq  +  AgCl. 

The  second  method  (6)  has  been  long  made  nse  of  in  cauticising 
soda  or  potash,  i.e.,  in  converting  the  carbonate  into  the  hydroxide, 
named  caustic  soda  or  caustic  potash  •  a  solution  of  the  carbonate 
is  boiled  with  milk  of  lime  (i.e.,  calcium  hydroxide  stirred  up 
with  water)  in  an  iron,  nickel,  or  silver  vessel,  for  vessels  of  other 
metals  or  of  glass  or  china  are  attacked  by  the  soluble  hydroxide. 

Potassium  hydrosulphide  has  been  prepared  by  passing  a 
stream  of  hydrogen  sulphide  over  red-hot  potassium  hydroxide  or 
carbonate,  thus : — 

KOH  +  H2S  =  KSH  +  H20 ; 
K2O.CO2  +  2H,S  =  2K2S.H2S  +  002  +  H,0, 
Various  other  methods  of  preparing  caustic  soda  and  caustic 
potash  (NaOH  and  KOH)  have  been  employed  on  a  manufacturing 
scale.     The  most  important  of  these,  which  yields  a  mixture  of 


216      THE   OXIDES,   SULPHIDES,  SELENIDES,  AND   TELLUKIDES. 

hydroxide  and  carbonate,  is  the  Leblanc  process.  The  principle  of 
this  process  is  the  simultaneous  action  of  calcium  oxide  and  carbon 
on  sodium  sulphate.  The  reaction  may  be  conceived  to  take  place 
in  two  stages,  which,  however,  are  not  separated  in  practice : — 

Na2SO4  +  20  =  Na2S  +  2(702;  and 
Na2S  +  CaO  =  Na2O  +  CaS. 

The  product  is  termed  "  black-ash."  On  treatment  with  lukewarm 
water  in  tanks,  the  hydroxide  dissolves  and  the  calcium  sulphide 
remains  insoluble. 

If  the  mixture  were  boiled,  the  hydroxide  of  sodium  would 
react  with  the  calcium  sulphide,  reversing  the  second  of  these 
equations,  thus  :— 2NaOH.Aq  +  CaS  =  2NaSH.Aq  f  Ca(OH)2.Aq. 
But  the  solution  is  separated  from  the  solid  as  quickly  as  possible 
and  concentrated  by  evaporation.  During  evaporation  chloride 
and  sulphate  of  sodium  contained  as  impurities  separate  out ;  they 
are  "  fished "  out  with  perforated  ladles,  and  hence  are  termed 
"fished  salts;"  while  the  solution  is  concentrated,  freed  from 
carbonate  by  addition  of  lime,  and  finally  evaporated  in  hemi- 
spherical iron  pots  till  fused  caustic  soda,  NaOH,  remains.  It  is 
then  run  into  iron  drums  and  brought  to  market.  The  principle 
of  the  manufacture  of  caustic  potash  is  similar. 

Properties. — The  hydroxides  of  the  metals  lithium,  sodium, 
potassium,  rubidium,  and  caesium  of  the  general  formula  MOH 
have  been  termed  "  caustic "  lithia,  soda,  &c.,  owing  to  their 
corrosive  and  solvent  properties  (/ca/w,  T  burn).  They  are  all 
white  soluble  solids  melting  at  a  red  heat  and  volatilising  at  a 
white  heat.  When  dissolved  in  water,  great  heat  is  evolved  owing 
to  combination.  When  fused,  they  attack  glass  and  porcelain,  dis- 
solving the  silica  of  the  glass  and  the  silica  and  alumina  of  the 
porcelain  ;  they  act  on  metals,  converting  them  into  oxides,  with 
exception  of  nickel,  iron,  silver,  and  gold.  Caesium  hydroxide  is 
most,  and  lithium  hydroxide  least  volatile. 

Sodium  and  potassium  hydroxides  usually  contain  as  impuri- 
ties sulphates,  carbonates,  and  chlorides.  A  partial  purification 
may  be  effected  by  treatment  with  absolute  alcohol  in  which  the 
hydroxides  dissolve,  while  the  salts  are  insoluble.  The  clear  solu- 
tion is  decanted  from  the  undissolved  salts,  the  alcohol  is  removed 
by  distillation,  and  the  residue  fused. 

If  absolutely  pure  hydroxides  are  required,  however,  they  are 
best  prepared  from  the  metals  by  throwing  small  pieces  into  water, 
and  subsequently  evaporating  the  solution  of  hydroxide  in  a  silver 
basin. 


MANUFACTURE   OF  SODIUM  AND   POTASSIUM.  217 

The  hydrosulphides  are  white  crystalline  bodies,  which  fuse  to 
black  liquids,  but  turn  white  again  on  solidification.  They  may 
be  obtained  in  solution  by  saturating  solutions  of  the  hydroxide 
with  hydrogen  sulphide,  thus  : — 

NaHO.Aq  +  S2S  =  ISTaHS.Aq  +  H20. 

The  hydroxides  volatilise  as  such  when  heated  ;  but  hydrosulphides 
lose  hydrogen  sulphide,  and  leave  the  sulphides. 

Ammonium  hydrosulphide  dissociates  into  ammonia  and  hydro- 
gen sulphide  at  50°,  and  above,  and  on  cooling,  the  constituents 
re-unite.*  It  forms  colourless  crystals. 

Appendix. — Manufacture  of  sodium  and  potassium.  An  indication  of  the 
method  of  preparing  these  metals  was  given  on  p.  30.  As  they  are  now  pre- 
pared from  the  hydroxides,  by  a  process  devised  by  Mr.  Castner,f  a  short 
sketch  of  the  manufacture  is  here  appended. 

The  following  reaction  takes  place  at  a  red  heat  between  carbon  and  the 
hydroxide :— GNaOH  +  2C  =  2Na2CO3  +  3H2  +  2Na.  But  if  carbon  is 
heated  with  caustic  soda,  the  hydroxide  melts,  and  the  carbon,  which  is  lighter 
than  the  soda,  floats  to  the  surface,  and  is  for  the  most  part  unacted  on.  Hence 
it  is  necessary  to  weight  the  carbon  so  as  to  cause  it  to  sink,  or  else  to  add  some 
substance  to  prevent  the  caustic  alkali  fusing  completely,  so  that  the  carbon 
may  remain  mixed  with  it.  The  old  plan  consisted  in  adding  lime ;  but  the 
temperature  at  which  the  metal  distilled  off  was  rendered  so  high  that  the  yield 
was  small,  and  the  destruction  of  the  wrought-iron  tubes  used  as  stills  was 
enormous.  The  new  method  is  to  heat  a  mixture  of  pitch  and  finely-divided 
iron  (spongy  iron)  to  redness.  Compounds  of  hydrogen  and  carbon  distil  off, 
and  an  intimate  mixture  of  iron  and  carbon  is  left  in  a  porous  state.  This 
mixture  is  introduced  along  with  caustic  soda  into  cast-iron  crucibles  provided 
with  tight  lids,  from  each  of  which,  a  tube  conveys  the  metallic  vapour  to  the 
condensers,  which  themselves  are  tubes  about  5  inches  in  diameter  and  3  feet 
long,  and  which  are  placed  in  a  sloping  position  so  that  the  melted  metal  runs 
down  into  a  small  pot  through  a  hole  about  20  inches  from  the  nozzle.  The 
crucibles  are  heated  by  means  of  gas  to  about  1000°;  and  when  the  distillation 
is  over,  in  about  an  hour  and  a  quarter,  the  crucible  is  lowered  in  the  furnace, 
so  as  to  separate  it  from  the  lid  which  is  stationary;  it  is  then  withdrawn,  emptied, 
recharged  while  still  hot,  and  replaced.  It  is  next  lifted  by  hydraulic  power 
till  it  again  meets  its  lid,  and  the  operation  again  commences.  The  mixture  of 
sodium  carbonate  and  spongy  iron  emptied  from  the  crucible  after  each  distil- 
lation is  treated  with  water,  the  iron  is  recharged  with  carbon,  and  the  sodium 
carbonate  is  converted  by  means  of  lime  into  caustic  soda  to  be  used  in  a 
subsequent  operation. 

The  metals  potassium  and  rubidium  can  be  similarly  prepared  ;  but  lithium 
and  caesium  must  be  obtained  by  electrolysis. 


*  Engel  and  Moitessier,  Comptes  rend.,  88,  1353. 
t   Chem.  News,  54,  218. 


218 


CHAPTEE  XVII. 

OXIDES,  SULPHIDES,  SELENIDES,  AND  TELLURIDES  OF  THE  BERYLLIUM 

GROUP. HYDROXIDES  AND  HYDROSULPHIDES. DOUBLE  COMPOUNDS 

WITH  HALIDES. OXIDES,  SULPHIDES,  SELENIDES,  AND  TELLURIDES 

OF  THE  MAGNESIUM  GROUP. — HYDROXIDES  AND  HYDROSULPHIDES. — 
DOUBLE  COMPOUNDS. 

Oxides,  Sulphides,   Selenides,  and  Tellurides  of 
Beryllium,  Calcium,  Strontium,  and  Barium. 

The  compounds  of  beryllium  differ  from  those  of  the  other 
metals  ;  those  of  calcium,  strontium,  and  barium  strongly  resemble 
each  other. 

Sources. — These  compounds  are  never  found  free ;  but  the 
oxides  occur  in  combination  with  carbon  dioxide,  silica,  and  sulphur 
trioxide,  as  carbonates,  silicates,  and  sulphates. 

List.               Oxygen.                     Sulphur.  Selenium.  Tellurium. 

Beryllium..  BeO.                                 BeS.  (?)  BeSe.              ? 

Calcium CaO;  CaO2.  CaS;  CaS2;   CaS5.*  CaSe.               ? 

Strontium..  SrO;    SrO2.  SrS;                 SrS4.  SrSe.                ? 

Barium....  BaO;  BaO2.  BaS;  BaS3;  BaS3.f  BaSe.              ? 

Preparation. — 1.  By  direct  union. — All  of  these  metals 
readily  oxidise  when  exposed  to  air,  and  burn  when  heated  in  air 
or  oxygen,  producing  monoxides.  They  would  also  in  all  proba- 
bility combine  with  sulphur,  selenium,  and  tellurium. 

Barium  dioxide  is  produced  when  the  monoxide  is  heated  to 
450°  in  a  current  of  pure  dry  air;  the  polysulphides  of  these 
metals  are  also  formed  when  the  hydrosulphides  are  boiled  with 
sulphur,  thus: — Ca(SH)2.A.q  +  S  =  CaS2.Aq  +  H2S;  and  similarly 
with  others;  also  by  heating  the  monosulphides  with  sulphur. 

2.  By  heating  hydroxides,  nitrates,  or  carbonates. — 
These  compounds  may  be  viewed  as  compounds  of  the  oxides 
with  oxides  of  hydrogen,  nitrogen,  carbon,  or  iodine,  thus : 

*  Chem.  Soc.,  47,  478. 
t  Ibid.,  49,  369. 


OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES.          219 

CaO.H.O;  CaO.N2O5;  CaO.CO2.  At  a  red  or  white  heat,  the 
water,  nitrogen  pentoxide  (which  splits  into  lower  oxides  of 
nitrogen  and  oxygen),  or  carbon  dioxide,  are  evolved  as  gas, 
while  the  non-volatile  oxide  of  the  metal  remains.  The  loss  of 
water  takes  place  readily  with  beryllium  hydroxide ;  slowly, 
beginning  at  100°,  or  even  lower,  with  calcium  hydroxide,  and  at 
a  very  high  temperature  with  strontium  and  barium  hydrox- 
ides. The  loss  of  N^Os  takes  place  at  a  red  heat  in  all  cases. 
This  method  is  adopted  as  the  only  practical  one  in  preparing: 
barium  oxide,  which  is  now  made  on  a  large  scale.  To  ensure 
thorough  expulsion  of  oxides  of  nitrogen,  the  partially  decomposed 
oxide  is  heated  in  a  vacuum.*  Beryllium  carbonate  is  decom- 
posed at  low  redness ;  calcium  carbonate  begins  to  decompose 
below  400° ;  and  provided  the  carbon  dioxide  be  removed  by  a 
current  of  air  or  steam,  so  that  recombination  cannot  take  place,  the 
decomposition,  if  sufficient  time  be  given,  is  complete  at  that 
temperature. 

The  decomposition  of  calcium  carbonate  (limestone)  by 
heat,  termed  "lime-burning"  is  carried  out  in  "lime-kilns," 
towers  open  above,  with  a  door  below,  into  which  alternate  layers 
of  lime  and  coal  are  introduced  from  above.  The  coal  is  set  on 
fire,  and  the  "  burnt  "  or  "  quick  "  lime  is  withdrawn  below,  after 
all  carbon  dioxide  has  been  expelled,  and  when  cold.  Strontium 
and  barium  oxides  may  also  be  produced  from  their  carbonates,  but 
at  a  higher  temperature ;  it  is  well  to  mix  them  with  a  little  coal, 
which  reduces  the  carbon  dioxide  to  monoxide,  so  that  no  recom- 
bination takes  place. 

Calcium  sulphide  is  similarly  formed  by  heating  calcium  hydro- 
sulphide,  Ca(SH)2  =  CaS.H2S,  in  a  current  of  hydrogen  sul- 
phide. Strontium  and  barium  sulphides  could  no  doubt  be 
obtained  in  an  analogous  manner. 

The  monoxides  of  calcium,  strontium,  and  barium  are  also 
obtainable  by  heating  the  dioxides  to  450°  under  reduced  pressure, 
or  to  a  higher  temperature.  This  process  is  made  use  of  in  pro- 
ducing oxygen  on  a  large  scale  (see  p.  65). 

Calcium  dioxide  is  also  said  to  be  produced  in  small  amount 
when  the  carbonate  is  heated  to  low  redness.  The  hydrated 
dioxides  may  be  dried  by  moderate  heat. 

3.  By  double  decomposition.  Monoxides. — Barium  mon- 
oxide is  prepared  by  heating  together  barium  sulphide  and  copper 
or  zinc  oxide.  On  treatment  with  water,  barium  hydroxide  goes 
into  solution. 

*  Boussingault,  Annales  (5),  19,  464. 


220      THE  OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES 

Sulphides.  —  The  hydroxides,   when  heated  in    a  current   of 
hydrogen  sulphide  yield  the  monosulphides,  thus  :  — 


Ca(OH)2  +  H*S  =  CaS  +  2H,0. 

4.  By  removing  oxygen  from  the  sulphates,  selenates,  or 

selenites  by  heating  to  redness  with  carbon  or  carbon  monoxides; 
tue  sulphides  or  selenides  are  left.  The  sulphides  of  calcium, 
strontium,  and  barium  are  thus  prepared.  The  selenides  are 
similarly  prepared  by  heating  selenates  or  selenites  to  dull  redness 
in  a  current  of  hydrogen.  It  is  in  this  way  that  barium  com- 
pounds are  produced  from  the  insoluble  sulphate,  which  is  mixed 
with  bituminous  coal  and  heated  to  redness.  The  sulphide  thus 
produced  is  converted  into  the  chloride  by  treatment  with  hydro- 
chloric acid,  or  into  the  oxide,  by  heating  with  copper  or  zinc  oxide. 
The  soluble  hydroxide  is  produced  o-n  treatment  with  water. 

Properties.  —  Monoxides.  —  These  are  white  powdters,  or  hard, 
white,  or  greyish-white  masses.  They  all  unite  with  water  with 
evolution  of  much  heat.  Beryllium  oxide  forms  the  least  stable, 
and  barium  oxide  the  most  stable  compound.  Beryllium  oxide  is 
said  to  volatilise  at  a  high  temperature  ;  calcium  oxide  melts 
only  in  the  electric  arc,  while  strontium  and  barium  oxides  melt 
at  a  white  heat.  The  oxides  are  crystalline  when  prepared  by 
heating  the  nitrates  in  covered  porcelain  crucibles  Beryllium 
oxide  crystallises  from  its  solution  in  fused  sulphate  of  beryllium 
and  potassium,  or  in  fused  boron  oxide. 

The  dioxides  are  white  substances,  which  evolve-  oxygen  when 
heated,  calcium  dioxide  most  readily,  barium  dioxide  at  a  bright- 
red  heat  ;  barium  dioxide  is  said  to  fuse  before  evolving  oxygen  (?). 
They  dissolve  in  water  with  moderate  ease,  forming  compounds. 

The  monosulphides  are  white  amorphous  powders,  very 
sparingly  soluble  in  water,  but  reacting  with  it  (see  below). 

The  monoselenides  are  also  white,  sparingly  soluble  powders, 
which  turn  red  on  exposure  to  air,  owing  to  the  expulsion  of 
selenium  by  oxygen  ;  the  monosulphides  turn  yellow,  owing  to 
the  formation  of  poly  sulphides.  The  tellurides  have  not  been 
examined. 

The  polysulphides  are  yellow  solids,,  soluble  in  water. 
Barium  monosulphide,  when  heated  in  a  current  of  steam,  decom- 
poses it,  hydrogen  being  evolved,  and  barium  sulphate  remaining. 
The  impure  monosulphides,  produced  by  heating  the  powdered 
carbonates  with  sulphur,  or  the  sulphate  with  carbon,  possess  the 
curious  property  of  remaining  luminous  in  the  dark,  after  having 
been  exposed  to  light.  Such  substances  used  to  be  caMzd  phos- 


OF  BEKYLLIUM,   CALCIUM,  STRONTIUM,  AND  BARIUM.        221 

pJwri.  The  calcium  compound  used  to  be  known  as  "  Canton's 
phosphorus,"  and  the  barium  compound  as  "  Bolognian  phos- 
phorus." The  modern  "  luminous  paint  "  owes  its  property  to  this 
peculiarity. 

All  these  oxides  are  converted  into  chlorides  when  heated  in  a 
current  of  chlorine. 

Uses. — Calcium  oxide  (lime)  when  heated  to  whiteness  in  the 
oxy-bydrogen  flame  evolves  a  brilliant  light  (Drummond's  light)  ; 
barium  oxide  and  dioxide  are  employed  in  the  commercial  manu- 
facture of  oxygen. 

Physical  Properties. — The  melting  and  boiling-points  of  these  bodies  are 
unknown. 


Mass  of  one  cubic  centimetre — 

BeO.  CaO.       Sr(X        BaO. 

3-18  at  14°        3-25        475        5'72 


BaO,. 
4-96 


Heats  of  formation: — 

Ca      +  O  =  CaO  +  1310K ;    +  H2O  =  155K ;    +  Aq  =  30K. 
Sr      +  O  =  SrO    +  1284K ;    +  H2O  =  177K;   +  Aq  =  116K. 
Ba      +  O  =  BaO  +  1242  (?)K;    +  H2O  =  223K;    +  Aq  =  122K. 
BaO  +  O  =  Ba02  +  172  K;    +  H2O2  =  102K. 
Ca      +  S  =  CaS  +  869K. 
Sr      +  S  =  SrS   +  974K. 
Ba     +  S  =  BaS  +  983  (?)K. 


Double  Compounds. 

(a.)  With  water,  &c.     The  following  bodies  are  known : — 


Oxides  with  water. 
Beryllium. .      *3BeO.10H-2O.     #2BeO.3H.:O. 

*Be0.4H.20.  BeO.H26. 

Calcium  ...      CaO.H2O.  =  Ca(HO)2. 
Strontium..      SrO.HoO     =  Sr(OH)2. 

Sr0.9H,0  =  Sr(OH)o.8H,0. 
Barium....      BaO.H2O    =  Ba(OH)2. 

Ba0.9H20  =  Ba(OH)2.8H20. 


Dioxides 
with  water. 


CaO2.8H2O. 
SrO,.8H20. 


Dioxide  with 

hydrogen 

dioxide. 


BaO2.8H2O.       BaO^.H.O, 


Sulphides  with 


Sulphides  with  water. 

hydrogen  sulphide. 

Beryllium  . 

BeS  (?)H20. 

p 

Calcium  .  .  . 

CaS.H20  =  Ca(SH)(OH). 

CaS.H2S  =  Ca(SH)2.f 

CaS.4H20  =  Ca(SH)(OH).3HoO. 

Strontium.  . 

SrS.HoO  =  Sr(SH)(OH).  ? 

SrS.H2S  =  Sr(SH)2  ? 

Barium  .... 

BaS.H,0  -  Ba(SH)(OH)? 

BaS.H2S  =  Ba(SH)2? 

*  The  existence  of  these  compounds  is  doubtful, 
t  Chem.  Soc.,  45,  271  and  696. 


222      THE   OXIDES,    SULPHIDES,   SELENIDES,    AND    TELLURIDES 

Sulphide  with  water  and  hydrog-en  sulphide — 

Calcium CaS.H2S.6H2O  =  Ca(SH)2.6H2O. 

Hydrated  polysulphides.— Ca2S2.3H2O  ;   SrS4.6H2O,  and  others. 


Preparation. — Hydrated  oxides,  and  hydroxides.  1.  By 
direct  addition. — All  of  these  oxides  unite  with  water  directly ; 
beryllium  oxide  shows  least  tendency ;  calcium  oxide  unites  with 
great  evolution  of  heat ;  the  water  is  at  first  absorbed,  and  then 
the  lumps  of  lime  grow  so  hot  as  to  evolve  clouds  of  steam,  and 
break  up  into  a  bulky  white  powder.  This  is  the  familiar  opera- 
tion of  "slaking  lime."  The  product  is  termed  "slaked  lime." 
Barium  oxide  unites  with  water  with  so  great  an  evolution  of  heat 
as  to  turn  red  hot  when  thrown  into  water.  Calcium  hydroxide  is 
sparingly  soluble  in  water,  and  the  solubility  diminishes  with  rise 
of  temperature.  At  15°,  1  gram  of  calcium  oxide  dissolves  in 
779  grams  of  water ;  at  20°,  in  791  grams  ;  and  at  95°,  in  1650  grams. 
It  would  thus  appear  that  calcium  hydroxide  loses  water  when 
heated  even  in  contact  with  water,  and  hence  shows  no  tendency 
towards  further  hydration.  Strontium  and  barium  hydroxides,  on 
the  other  hand,  dissolve  to  some  extent  in  hot  water,  and  on 
cooling,  crystals  of  Sr(OH)2.8H2O,  or  Ba(OH)2.8H,O  separate. 
At  15°,  1  gram  of  barium  hydroxide  dissolves  in  about 
20  grams  of  water ;  and  at  100°,  in  2  grams.  Strontium  hydroxide 
is  less  soluble.  Calcium  hydroxide,  Ca(OH)2,  separates  in  crystals 
when  its  solution  is  evaporated  in  vacuo.  The  hydrated  peroxides 
are  also  formed  by  dissolving  the  peroxides  in  water  and  crystal- 
lising. The  compound  BaOj.HgOj,  separates  from  a  solution  of 
Ba02  in  H202  containing  water.  A  possible,  though  improbable, 
view  of  the  constitution  of  the  compound  Ca(SH)(OH).3HaO  is 
that  it  consists  of  CaO.H2S. 4H,,O.  It  is  produced  by  passing 
sulphuretted  hydrogen  into  a  paste  of  calcium  hydroxide  and 
water. 

2.  By  double  decomposition. — (a.)  By  addition  of  a  soluble 
hydroxide  (e.g.,  of  lithium,  sodium,  potassium,  &c.,  or  ammonia 
and  water)  to  a  soluble  compound  of  beryllium,  calcium,  strontium, 
or  barium,  thus  : — 

CaCl2.Aq  +  2KOH.Aq  =  Ca(OH)2  +  2KCl.Aq. 

No  doubt  this  change  always  takes  place  to  a  greater  or  less 
extent.  But  as  strontium  and  barium  hydroxides  are  fairly  soluble 
in  water,  they  separate  only  when  the  solution  is  a  concentrated 
one.  With  beryllium,  the  hydroxide  produced  by  heating  any 


OF   BERYLLIUM,   STRONTIUM,   CALCIUM,   AND   BARIUM.        223 

oluble  salt,  such  as  the  chloride,  sulphate,  or  nitrate,  with  potas- 
sium hydroxide,  thus  :—  BeCl2.Aq  +  2KOH.Aq  =  Be(OH)2.2H2O 
+  2KC1.  Aq,  redissolves  in  excess  of  the  potassium  hydroxide,  doubt- 
less producing  a  soluble  double  oxide  of  beryllium  and  potassium  ; 
but  the  solution  of  this  substance,  when  boiled,  decomposes  into 
beryllium  hydroxide,  Be  (OH)2,  which  precipitates,  and  potassium 
hydroxide,  which  remains  in  solution. 

Solutions  of  strontium  and  barium  hydroxides  give  precipitates 
with  soluble  salts  of  beryllium  and  calcium,  owing  to  the  greater 
insolubility  of  the  hydroxides  of  the  latter  metals. 

The  hyd  rated  peroxides  may  be  similarly  produced  by  addition 
of  some  dioxide,  such  as  hydrogen  or  sodium  dioxide,  to  a  solution 
of  the  hydroxide  of  the  metal,  thus  :  — 

Ca(OH)2.Aq  +  H202.Aq  =  CaO2.8H2O  +  Aq. 

As  they  are  sparingly  soluble  they  are  precipitated. 

(6.)  By  the  action  of  hydrogen  sulphide  on  the  hydroxides, 
the  hydrated  sulphides  are  formed,  and  in  presence  of  excess  of 
hydrogen  sulphide  the  sulphydrated  sulphides.  With  calcium,  for 
example,  the  action  is  as  follows  :  — 

Ca(OH)2.Aq  +  H2S  =  Ca(SH)(OH).Aq  +  H20;  or 
CaO.H2O.Aq  +  HZS  =  CaS.Aq  +  H20  ; 

and  further, 

Ca(SH)(OH).Aq  +  H*S  =  Ca(SH)2.Aq  +  H,0. 
If  the  solutions  are  strong  and  cold,  the  substances— 

Ca(SH)(OH)3H2O  (=  CaS.4H3O)  and  Ca(SHV6H8O 

(=  CaS.H2S.6H,O) 

separate  in  crystals. 

The  calcium  compounds  are  the  only  ones  which  have  been 
carefully  investigated  as  regards  their  behaviour  with  hydrogen 
sulphide  ;  similar  compounds  no  doubt  exist  with  beryllium, 
strontium  and  barium,  and  also  with  hydrogen  selenide  and 
telluride. 

The  hydrosulphide,  Ca(SH)2,  when  heated  with  water  (as  it 
cannot  be  obtained  free  from  the  six  molecules  of  water  with  which 
it  crystallises,  this  water  reacts),  gives  off  hydrogen  sulphide,  and 
the  hydroxy-hydrosulphide  remains,  thus  :  — 


Ca(SH),.Aq.  +  H20  =  Ca(SH)(OH).Aq 
The  hydrosulphide,  when  treated  with  sulphur,  evolves  hydrogen 


224      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLUEIDES 

sulphide  with  formation  of  a  polysulphide.  Such  polysulphides 
are  known  only  in  solution. 

Properties. — The  hydroxides  are  white  powders ;  that  of 
beryllium  is  insoluble  in  water,  but  dissolves  in  a  solution  of 
ammonium  carbonate,  and  is  reprecipitated  on  boiling.  This 
reaction  serves  to  separate  it  from  aluminium  hydroxide,  which  is 
insoluble  in  aqueous  ammonium  carbonate.  The  hydroxide  of 
calcium  is  sparingly  soluble  in  water  (see  p.  222),  that  of  strontium 
more  soluble,  and  barium  hydroxide  easily  soluble.  The  hydrates 
of  strontium  and  barium,  Sr(OH)2.8H2O,  and  Ba(OH)2.8H2O,  are 
white  crystalline  bodies,  rapidly  turning  opaque  on  exposure  to 
air,  owing  to  absorption  of  carbon  dioxide.  When  heated  to  75°, 
7  molecules  of  water  are  lost,  and  the  eighth  only  at  a  red  heat. 
From  this  it  would  appear  that  the  compound  BaO.2H3O  is  not 
much  inferior  in  stability  to  BaO.H2O,  and  that  the  formula 
Ba(OH)2  for  the  latter  does  not  express  any  exceptionally  stable 
form  of  combination  between  water  and  oxide. 

The  hydrated  dioxides  are  crystalline  powders,  which  may  be 
dried  in  vacua  to  the  dioxides.  That  of  barium,  indeed,  may  be 
heated  to  over  300°,  without  loss  of  oxygen. 

The  hydrosulphides  are  very  unstable  bodies,  capable  of  exist- 
ence only  when  cooled  by  ice  in  presence  of  hydrogen  sulphide. 
When  placed  in  water  at  the  ordinary  temperature,  hydrogen  sul- 
phide is  evolved,  and  the  hydroxy-hydrosulphide, 

Ca(SH)(OH).3H30, 
is  left. 

There  appear  to  be  various  compounds  of  oxides  and  sulphides 
of  these  metals  (the  existence  of  which,  however,  requires  further 
proof),  e.g.,  2CaO.CaS2,  3CaO.CaS2,  3CaO.CaS3,  &c.,  in  com- 
bination  with  water. 

On  boiling  solutions  of  the  hydroxides,  calcium,  strontium,  or 
barium,  with  sulphur,  polysulphides  are  formed,  together  with 
thiosulphates,  thus : — 

3Ca(OH)3.Aq  +  28  -h  wS  =  CaS203.Aq  +  2CaS»/a. 

The  polysulphide  formed  depends  on  the  amount  of  sulphur  pre- 
sent. A  deep  yellow  solution  is  obtained  from  which  the  thio- 
sulphate  separates  in  crystals. 

(The  slaking  of  lime,  the  precipitation  of  calcium  hydroxide  with  sodium 
hydroxide,  the  crystallisation  of  barium  hydroxide  from  a  hot  solution  ;  the 
preparation  of  calcium  sulphide  by  the  action  of  hydrogen  sulphide  or  calcium 
hydroxide ;  the  formation  of  polysulphides  of  calcium  on  boiling  "  milk  of 


OF   MAGNESIUM,  ZINC,  AND   CADMIUM.  225 

lime"  with  sulphur;  and  the  precipitation  of  "milk  of  sulphur"  on  addition 
of  sulphuric  acid  to  the  orange  solution  form  suitable  lecture  experiments.) 

(c.)  Double  compounds  with  halides. — These  are  few  in  number. 
BeCL>.BeO,  is  said  to  be  obtained  on  evaporating  an  aqueous  solution  of  beryl- 
lium chloride.  CaCl^.SCaO.lSI^O  is  prepared  by  boiling  calcium  hydroxide 
in  a  solution  of  calcium  chloride,  and  filtering  while  hot ;  BaCl2.BaO.5H2O, 
BaBriBaO.5H2O,  and  BaI2.BaO.5H2O  are  similarly  prepared. 

There  appear  also  to  be  indications  of  similar  calcium  and  strontium 
compounds,  SrCl2.SrO.9H2O  having  been  prepared. 

It  is  possible  to  regard  these  compounds  as  hydroxychlorides, 
thus  : — Ba<5ly.2H2O,  &c.  Although  somewhat  similar  formulae 

could  be  constructed  for  more  complex  compounds,  as,  for  example, 
Cl— Ca— O— Ca— O— Ca— O— Ca— C1.15H2O  ;  yet,  inasmuch 
as  similar  double  halides  exist  in  number,  which  cannot  in  reason 
be  similarly  represented,  it  appears  advisable,  in  the  present  state 
of  our  knowledge,  to  adhere  to  the  simpler  and  older  methods  of 
representation. 

Oxides,  Sulphides,  Selenides,  and  Tellurides  of 
Magnesium,  Zinc,  and  Cadmium. 

As  many  of  these  compounds  are  unaffected  by  air  and  carbon 
dioxide,  and  do  not  react  or  combine  with  water,  they  occur 
native. 

Sources. — Magnesium  oxide  occurs  as  periclase ;  also,  in  com- 
bination with  water,  Mg(OH)2,  or  magnesium  hydroxide,  as 
brucite,  in  white  rhombohedra.  It  also  occurs  in  combination  with 
carbon  dioxide,  silicon  dioxide,  &c.  Zinc  oxide,  ZnO,  is  named 
zincite  or  red  zinc  ore ;  it  is  red  owing  to  its  containing  ferric  oxide 
in  small  quantity ;  it  is  also  found  in  combination  with  oxides  of 
iron  and  manganese  as  franklinite.  Zinc  sulphide  occurs  as  blende, 
associated  with  many  other  sulphides,  both  in  crystalline  and  in 
sedimentary  rocks.  It  is  the  chief  ore  of  zinc.  It  has  usually  a 
black  colour,  but  is  white  when  pure.  Cadmium  sulphide,  CdS, 
occurs  as  the  rare  mineral  greenockite.  Zinc  oxide  also  occurs  in 
combination  with  carbon  dioxide  and  with  silica. 

List.  Oxygen.  Sulphur.  Selenium.  Tellurium. 

Magnesium..  MgrO.  MgS.  M*Se?  M&Te? 

Zinc ZnO ;  ZnO2  P  ZnS ;  ZnS5  P         ZnSe.  ZnTe  P 

Cadmium CdO ;  CdO2  P  CdS.  CdSe.  CdTe. 

Preparation.—!.  By  direct  union.— These  elements  all  burn 
in  oxygen,  or  when  heated  to  a  high  temperature  in  air.  Magne- 
sium burns  with  a  brilliant  white  flame,  but  if  the  supply  rf  air  is 

Q 


226      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES 

limited,  the  nitride,  Mg3N2,  is  simultaneously  produced.  The 
metal  is  sold  in  the  form  of  thin  ribbon  for  purposes  of  signalling, 
photographing  dark  chambers,  &c. ;  and  in  fine  dust,  for  signalling. 
A  little  powder,  when  thrown  into  a  flame,  gives  a  brilliant  flash 
of  light.  Zinc  burns  with  a  green  flame,  giving  off  filmy  clouds  of 
oxide.  Cadmium  also  burns  to  a  brown  oxide. 

The  sulphides  are  also  produced  by  throwing  sulphur  on  to 
the  red-hot  metals.  Zinc  and  cadmium  do  not  readily  combine  with 
selenium ;  if  the  metal  be  fused  with  selenium,  the  latter  distils 
off,  leaving  the  metal  coated  with  a  crust  of  selenide.  But  with 
tellurium,  tellurides  are  produced,  the  boiling-point  of  that 
element  being  higher. 

2.  By  heating   a  compound. — The  hydroxides,  carbonates, 
nitrates,  or  sulphates  of  these  metals,  when  heated,  leave  the  oxide. 
The  hydroxides  and  carbonates  are  decomposed  at  a  low  red  heat ; 
the  nitrates  and  sulphates  require  a  higher  temperature. 

3.  By  double  decomposition. — Sulphides  of  these  metals  are 
produced  by  heating  the  oxides  in  a  current  of  hydrogen  sulphide 
or  carbon  disulphide,  thus  : — 

MgO  4-  H2S  =    MgS  +  HZ0 ;  and 
2MgO  +  CS2  =  2MgS  +  COZ. 


Zinc  and  cadmium  selenides  have  been  similarly  prepared. 

Inasmuch  as  the  sulphides,  selenides,  and  tellurides  of  zinc  and 
cadmium  are  insoluble  in  water,  they  may  be  produced  by  precipi- 
tation, viz.,  by  passing  a  current  of  hydrogen  sulphide  through  a 
solution  of  a  soluble  salt  of  the  metals  ;  thus  :  — 


ZnS04.Aq  +  H2S  =  ZnS  -f  H2S04.Aq. 

There  appear  good  grounds  for  believing  that  this  reaction 
gives  not  a  sulphide  such  as  ZnS,  but  a  hydrosulphide,  ZnS.^H2S. 
The  body  produced  contains  more  sulphur  than  corresponds  to  the 
formula  ZnS,  and  gives  off  hydrogen  sulphide  on  heating.  The 
precipitate  produced  as  above  is  soluble  in  many  acids  ;  hence,  to 
ensure  thorough  precipitation,  the  acid  must  be  neutralised  by  an 
alkali,  e.g.,  by  soda  or  ammonia.  Acetic  acid,  however,  has  no 
solvent  action  ;  hence  precipitation  is  complete  from  a  solution  of 
zinc  acetate.  Cadmium  sulphide,  prepared  in  a  similar  manner,  is 
also  probably  a  hydrosulphide.  It  is,  unlike  zinc  sulphide,  in- 
soluble in  dilute  acids  ;  but  dissolves  in  moderately  strong  hydro- 
chloric acid. 

Magnesium  sulphide  cannot  be  thus  prepared  ;  if  the  hydr- 
oxide is  employed  the  hydrosulphide  is  produced. 


OF   MAGNESIUM,  ZINC,   AND   CADMIUM.  '    227 

The  selenides  and  tellnrides  of  zinc  and  cadmium  may  be 
similarly  obtained. 

Zinc  and  cadmium  peroxides,  and  probably  also  magnesium 
peroxide,  are  formed  by  addition  of  hydrogen  dioxide  to  the 
hydroxides.  They  appear  to  be  compounds  of  dioxide  with  mon- 
oxide in  proportions  as  yet  unascertained.  The  pentasulphide  of 
zinc  is  produced  when  a  zinc  salt  is  treated  with  a  solution  of 
potassium  pentasulphide. 

Properties. — Magnesium  and  zinc  oxides  and  sulphides  are 
white;  cadmium  oxide  brown,  and  its  sulphide  yellow.  When 
prepared  by  the  union  of  the  metal  with  oxygen,  magnesium  oxide 
is  dense,  and  has  the  specific  gravity  3*6.  Magnesia  usta,  or 
calcined  magnesia,  is  a  very  loose  white  powder  produced  by 
gently  glowing  the  hydroxycarbonate,  known  as  magnesia  alba. 
When  produced  from  the  native  carbonate,  magnesite,  it  is  dense 
and  hard,  and  is  made  use  of  as  a  lining  for  the  interior  of 
Bessemer  converters.  It  is  known  as  "  basic  lining."  It  is  very 
sparingly  soluble  in  water,  50,000  parts  of  water  dissolving  only 
one  parfc  of  oxide ;  it  probably  dissolves  as  hydroxide.  It  unites 
slowly  with  water,  when  it  has  not  been  strongly  ignited ;  and  also 
attracts  carbon  dioxide  from  the  air,  if  moist.  It  is  soluble  in  all 
~acids. 

Zinc  oxide  is  also  a  soft  white  powder.  When  produced  by 
burning  zinc,  it  is  sometimes  named  "  lana  philosophical  on 
account  of  its  woolly  texture.  When  heated  it  turns  yellow,  but 
its  white  colour  returns  on  cooling.  It  is  insoluble  in  and  does 
not  combine  directly  with  water,  nor  does  it  unite  with  carbon 
dioxide. 

Cadmium  oxide  is  a  soft  brown  powder. 

None  of  these  bodies  are  easily  volatilised,  nor  do  they  melt 
easily. 

Magnesium  sulphide  reacts  with  water,  giving  hydroxyhydro- 
sulphide  (?)  or  hydroxide  and  hydrosulphide.  It  is  an  amorphous 
pinkish  body,  infusible,  and  burning  when  heated  in  air  to  oxide 
and  sulphur  dioxide. 

Zinc  sulphide,  as  blende,  forms  compact  masses  of  various 
colours  due  to  impurities ;  it  is  usually  black,  and  is  known  to 
miners  as  "  black-jack."  It  is  translucent  and  crystalline.  When 
"  roasted "  or  heated  in  air,  it  changes  to  oxide  and  sulphur 
dioxide.  Prepared  artificially,  by  precipitation  and  subsequent 
heating,  it  forms  a  white  infusible  powder.  It  is  employed  as  a 
pigment  under  the  name  of  "  zinc-white."  Its  "  covering  power  " 
is  not  so  great  as  that  of  white  lead  (see  Carbonates,  p. 

Q  2 


228      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLUEIDES 

but  it  has  the  advantage  of  not  turning  black  on  exposure  to 
hydrogen  sulphide  as  white  lead  does,  zinc  sulphide  being  white. 
Cadmium  sulphide,  as  greenockite,  occurs  in  yellow  transparent 
crystals ;  prepared  by  precipitation,  it  is  a  yellow  powder,  and 
is  used  as  an  artist's  colour,  under  the  name  of  "cadmium 
yellow,"  or  "jaune  brittawt."  It  is  not  permanent,  being  easily 
oxidised  by  moist  air.  When  heated  to  redness  it  turns  first 
brownish,  then  carmine-red.  It  fuses  at  a  white  heat,  and  crys- 
tallises in  scales  on  cooling. 

The  oxygen  of  these  oxides  is  displaced  at  a  red  heat  by 
chlorine. 

The  peroxides  of  zinc,  magnesium,  and  cadmium  are  white 
powders.  They  do  not  contain  enough  oxygen  to  correspond  to 
the  formulae  Mg02,  &c.,  and  are  either  mixtures  or  compounds  of 
higher  oxides  with  the  monoxides. 

Zinc  pentasulphide  is  a  flesh-coloured  precipitate,  which,  on 
treatment  with  hydrochloric  acid,  dissolves  with  effervescence  of 
hydrogen  sulphide,  sulphur  being  deposited. 

Zinc  selenide,  ZnSe,  is  a  yellow  amorphous  powder,  which 
changes  into  yellow  crystals  when  heated  in  a  current  of  hydrogen. 
Cadmium  selenide  forms  deep  reddish-black  crystals.  The  amorph- 
ous telluride  has  metallic  lustre,  but  forms  a  red  powder.  When 
heated  in  hydrogen  it  forms  ruby-red  crystals ;  cadmium  telluride 
is  also  a  metallic-looking  substance  giving  black  crystals.  These 
bodies  are  probably  decomposed  by  hydrogen  into  the  elements, 
which  recombine  in  the  cooler  part  of  the  tube.  It  is  improbable 
that  they  are  volatile  as  compounds. 

Physical  Properties. 
Mass  of  one  cubic  centimetre  : — 

Oxygen.  Sulphur.           Selenium.          Tellurium. 

Magnesium....      3 '636*  ?                        ?                           ? 
(crystallised) 

Zinc 5 -78  at  15°  4  "05            5 -4  at  15°         6 '34  at  15° 

Cadmium  8  '11  4  -5              5  '8  at  15°         6  '2  at  15° 

(crystalline)  (precipitated) 
Heats  of  formation  :  — 


Kg 

+ 

0 

=  MgO 

+ 

1440K; 

+  H2O  =  50K. 

Zn 

+ 

0 

=  ZnO 

+ 

853K; 

+  H2O  =  -26K. 

Cd 

+ 

0 

=  CdO 

+ 

755K; 

+  H2O  =  -  98K. 

Ms 

+ 

S 

=  MgS 

+ 

776K. 

Zn 

+ 

S 

=  ZnS 

+ 

396K. 

Cd 

+ 

S 

-  CdS 

+ 

324K. 

*  The  density  increases  on  calcination;  magnesia  produced  by  igniting 
carbonate  has  the  density  3  '19  at  0°. 


OF    MAGNESIUM,   ZINC,  AND   CADMIUM.  229 

Double  compounds. — (a.)  With  water :  hydrates  or  hydr- 
oxides.— The  mineral  brucite,  MgO.H2O,  or  Mg(OH)2,  occurs 
native,  usually  in  masses  of  serpentine.  It  crystallises  in  rhombo- 
hedra.  Magnesium  oxide,  when  prepared  from  the  nitrate  or 
carbonate  at  a  low  red  heat,  unites  with  water,  forming  a  solid 
translucent  substance  harder  than  marble.  After  being  heated  to 
whiteness,  it  loses  the  property  of  combination  with  water.  Zinc 
and  cadmium  oxides  do  not  combine  with  water  directly. 

Soluble  salts  of  magnesium,  zinc,  and  cadmium,  on  treatment 
with  hydroxides  of  sodium,  potassium,  or  barium  give  gelatinous 
precipitates  of  the  hydrates.  Ammonia  in  water  (equivalent  to  am- 
monium hydroxide)  also  produces  precipitates,  but  redissolves 
them  if  added  in  excess.  Magnesium  hydroxide  does  not  react  with 
excess  of  sodium  or  potassium  hydroxides,  whereas  zinc  and  cad- 
mium hydroxides  are  soluble  in  excess  of  the  precipitant,  forming 
double  compounds  (see  infra). 

Crystals  of  ZnO.H2O  and  of  CdO.H2O  are  produced  after  some 
time  by  placing  a  stick  of  zinc  or  cadmium  in  aqueous  ammonia,  in 
contact  with  iron,  lead,  or  copper.  The  zinc  compound  forms 
rhombic  prisms,  of  2'68  specific  gravity.  And  octahedral  crystals 
of  ZnO.2H2O  have  been  formed  by  allowing  a  solution  of  Zn02K2 
to  stand  for  some  months.  The  following  bodies  are  thus 
known : — 

MgO.H2O  =  Mg(OH)2;   ZnO.H2O  =  Zn(OH)2; 
CdO.H2O  =  Cd(OH)2;  ZnO.2H2O. 

(6.)  With  hydrogen  sulphide. — Zinc  and  cadmium  sulphides 
do  not  appear  to  combine  with  hydrogen  sulphide.  But  if  a  stream 
of  that  gas  is  led  through  water  in  which  magnesium  oxide  or 
carbonate  is  suspended,  a  soluble  compound  is  formed,  which  has 
not  been  obtained  solid,  but  which  is  supposed  to  have  the  formula 
MgS.H2S  =  Mg(SH)2,  and  to  be  magnesium  hydrosulphide. 
When  gently  warmed,  this  solution  evolves  hydrogen  sulphide, 
thus:— Mg(SH)2.Aq  +  2H20  =  Mg(OH)2.Aq  +  2H2S.  This 
solution  dissolves  sulphur  with  a  yellow  colour,  and  may  then 
contain  polysulphides  of  magnesium. 

The  selenides  and  tellurides  have  not  been  investigated. 

(c.)  Compounds  of  oxides  with  oxides. — White  crystals  of 
ZnO.K2O  and  ZnO.Na,2O  [=  Zn(OK)2,  and  Zn(ONa)2] 
separate  from  solutions  of  zinc  hydroxide  in  caustic  alkali. 
Metallic  zinc  dissolves  in  boiling  caustic  potash  or  soda,  with  evo- 
lution of  hydrogen,  thus  :— Zn  +  2NaOH.Aq=Zn(ONa)2.Aq-r#2. 
A  similar  cadmium  compound  is  formed  by  dissolving  cadmium 


230      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLUPJDES 

oxide  in  fused  potassium  hydroxide.  On  treating  a  solution  of 
zinc  hydroxide  in  caustic  soda  with  alcohol,  the  compound 
ZnO.Na2O.8H2O  is  thrown  down  in  crystals.  These  bodies  cor- 
respond to  the  hydroxides,  the  hydrogen  being  wholly  or  partially 
replaced  by  sodium  or  potassium. 

(d.)  Compounds  of  sulphides  with  sulphides.  —  Zinc 
sulphide  is  said  to  be  wholly  dissolved  when  added  to  a  solution 
of  sodium  sulphide  containing  a  weight  of  sulphur  equal  to  that 
contained  in  the  zinc  sulphide.  The  inference  is  that  the 
compound  ZnS.Na2S  is  produced.  Cadmium  sulphide  is  also 
sparingly  soluble  in  excess  of  alkaline  sulphides. 

Cadmium  sulphide  is  supposed  to  polymerise  when  boiled  with 
acids  or  with  sodium  sulphide;  and  the  sulphide  produced  by 
treating  with  hydrogen  sulphide  cadmium  hydroxide  which  has 
been  boiled  with  water  is  vermilion-coloured.  Cadmium  sul- 
phide may  also  be  obtained  dissolved  in  water  by  washing  the 
precipitated  sulphide  thoroughly,  and  treatment  with  solution  of 
hydrogen  sulphide.  A  yellow  solution  is  produced,  which  coagu- 
lates on  treatment  with  weak  solutions  of  salts,  especially  those  of 
cadmium. 

(e.)  Compounds  of  sulphides  with  oxides.  —  Magnesium 
oxide  heated  in  a  mixture  of  carbon  dioxide  and  disulphide  is 
converted  into  MgO.MgS.  The  corresponding  zinc  compound  has 
been  prepared  by  heating  zinc  sulphate,  ZnSO4,  in  hydrogen  ;  and 
the  cadmium  compound,  CdO.CdS.H2O,  is  thrown  down  as  a  red 
precipitate  when  hydrogen  sulphide  is  passed  through  a  boiling 
solution  of  a  cadmium  salt.  The  compound  4ZnO.ZnS  has  been 
found  in  zinc  furnaces. 

(/.)  Compounds  of  oxides  with  halides.  —  The  following 
"  basic  "  halides  have  been  prepared  by  the  reaction  of  water  at  a 
high  temperature  on  the  halides  :  — 


2M<rCl2.MirO  ;  Mg-CUMgO  ;  MgCl^MgO  ;  M&C12.9M&O  ;  MgCLUOMg-O. 
ZnCl2.3ZnO  ;  ZnCl2.6ZnO  ;  ZnCl2.9ZnO. 


2M<rCl2.MirO  ;  Mg-CUMgO  ;  MgCl 
ZnCl2.3ZnO  ;  ZnCl2.6ZnO  ;  ZnCl2.9 
CdCLj.CdO  ;  CdBr2.CdO. 


These  bodies  crystallise  with  varying  amounts  of  water  ;  thus  crystals  of 
MgCl2.5MgO  have  been  obtained  with  17,  14,  8,  and  6H2O.  Zinc  oxychlorides 
possess  the  property  of  dissolving  silk,  but  not  wool  or  cotton,  and  their 
solutions  are  employed  as  a  means  of  separating  the  constituents  of  mixed 
fabrics.  The  zinc  oxychlorides  are  used  by  dentists  as  a  stopping  for  teeth. 


OF  MAGNESIUM,  ZINC,  AND   CADMIUM. 


231 


Physical  Properties. 
Mass  of  1  cubic  centimetre  :— 


o  

Be. 
3'02 

Ca. 
3-16—  3-32* 

Sr. 
4'5  —  475* 

Ba. 
5-32—  5'72* 

(OH),.. 

s 

2-8 

3-63 

4-49 

Se  
Te  

— 

— 

— 

— 

O 3-20—3-75* 

(OH)2..  2-36* 


Se. 
Te 


Zn. 

5.47—5.78* 
2  -68—3  -05 
3-92—4-07* 

5-40 

6-34 


Cd. 
6-95—8-11* 

4-79 

4-50 — 4-91* 

5-8—8-9 

6-20 


The  asterisked  higher  numbers  usually  refer  to  the  crystallised  varieties, 
but  are  sometimes  the  results  of  different  experimenters. 


Heats  of  formation  :  — 


Ca 

+ 

0 

= 

CaO  -t 

-    1310K; 

Sr 

+ 

o 

= 

SrO    H 

-  1284K; 

Ba 

+ 

0 

mi 

BaO  4 

-  1242K; 

Mg 

••4- 

0 

= 

Mg-0  H 

-  1440K; 

Zn 

+ 

0 

= 

ZnO  4 

-    853K; 

Cd 

+ 

0 

.. 

.. 

Ca 

+ 

s 

• 

CaS  + 

896K; 

Sr 

+ 

s 

= 

SrS    -f 

974K. 

Ba 

4* 

s 

= 

BaS  + 

983K; 

-I-  H2O  =  Ca(OH)2  +  155K. 
+  H«O  =  Sr(OH)2  +  177K. 
+  H2O  =  Ba(OH)2  +  223K. 
+  H2O  =  Mg(OH)2  +  50K. 
+  H2O  =  Zn(OH)2  -  26K. 
+  H2O  =  Cd(OH)2  +  657K. 

Mg-  +  S  -  Mg-S  +  776K. 
Zn  +  S  =  ZnS  +  396K, 
Cd  +  S  =  CdS  +  324K. 


232 


CHAPTEE   XVIII. 

OXIDES  AND  SULPHIDES  OF  ELEMENTS  OF  THE  BORON  GROUP. — DOUBLE 
COMPOUNDS  WITH  WATER  AND  OXIDES  ;  BORACIC  ACID  AND  BORATES  ; 
HYDROXIDES  OF  SCANDIUM,  YTTRIUM,  LANTHANUM,  AND  YTTERBIUM. 

OXYHALIDES  ;  FLUOBORATES. — OXIDES  AND  SULPHIDES  OF  ELEMENTS 

OF  THE  ALUMINIUM  GROUP. — HYDROXIDES,  HYDROSULPHIDES  ;  DOUBLE 
OXIDES  AND  SULPHIDES. — OXYHALIDES. 

Oxides   and   Sulphides   of  Boron,    Scandium, 
Yttrium,  Lanthanum,  and  Ytterbium. 

Of  these,  boron  oxide  and  sulphide,  and  the  oxides  of  the 
remaining  elements  of  the  group  have  alone  been  investigated. 
The  selenides  and  tellurides  are  unknown. 

Sources. — These  compounds  do  not  occur  native.  Boron 
oxide  is  found  in  combination  with  water,  as  B2O3.3H2O,  as 
sassolite;  with  sodium  oxide  as  borax,  2B2O3.Na2O.10H2O  ;  with 
magnesium  oxide  and  chloride  as  boracite,  8B2O3.6MgO.MgCl2 ; 
and  with  silicon  and  calcium  oxides  as  datolite, 

3SiO2.B2O3.2CaO.H2O. 

Scandium,  yttrium,  and  ytterbium  oxides  are  found  in  combination 
with  silica  in  gadolinite,  and  with  niobium  and  tantalum  oxides  in 
yttrotantalite,  samarskite,  and  euxenite ;  wjiile  lanthanum  oxide 
accompanies  cerium  and  didymium  oxide  in  cerite,  in  combination 
with  silica. 

List.  Boron.    Scandium.        Yttrium.         Lanthanum.        Ytterbium. 

Oxygen..      B2O3.        Sc2O3.        Y2O3;  Y4O9.  La2O3;  La4O9.         Yb2O3 
Sulphur  .     B2S3. 

Preparation. — 1.  By  direct  combination. — Boron  burns  in 
oxygen  or  nitric  oxide,  NO.  Yttrium  is  also  oxidised  when 
heated  in  air,  and  lanthanum  becomes  covered  with  a  steel-blue 
film.  When  strongly  heated  it  takes  fire  and  burns.  The  other 
elements  of  this  group  have  not  been  prepared.  Boron  unites 
with  sulphur  at  a  white  heat. 


OXIDES  AND   SULPHIDES   OF  BORON,  ETC.  233 

2.  By  heating  the  hydroxides,  &c. — This  is  the  usual  method 
of  preparation.     These  substances  part  with  water  at  a  red  heat, 
leaving  the  oxides.      The   oxalates,  carbonates,  and   nitrates   of 
scandium,   yttrium,   lanthanum,   and   ytterbium    also    yield    the 
oxides  when  heated  to  redness. 

3.  By  double    decomposition. — Boron    oxide  mixed  with 
uarbon,  and  heated  to  redness  in  a  stream  of  carbon  disulphide  gas, 
yields  the  sulphide. 

Properties. — Boron  trioxide,  B,O3,  is  a  non-volatile  glass, 
melting  to  a  viscid  liquid  at  a  red  heat.  It  reacts  with  and 
dissolves  in  alcohol  and  in  water.  When  fused  with  the  oxides  of 
metals  they  are  dissolved,  forming  borates,  i.e.,  double  oxides  of 
boron  and  the  metal.  The  sulphide,  BoS3,  is  a  whitish-yellow 
substance,  volatile  when  heated  in  a  stream  of  hydrogen  sulphide, 
and  melting  at  a  red  heat.  It  is  decomposed  by  water,  yielding 
boracic  acid  and  hydrogen  sulphide. 

The  oxides  of  scandium,  yttrium,  lanthanum,  and  ytterbium 
are  white  powders,  insoluble  in  water,  and  soluble  with  difficulty  in 
acids.  They  do  not  react  with  alkaline  hydroxides,  nor  do  they 
fuse  in  the  oxyhydrogen  flame.  The  peroxides  of  yttrium  and 
lanthanum  ate  also  white  powders,  which  part  with  the  excess  of 
oxygen  when  heated. 

Mass  of  1  cubic  centimetre  : — B2O3,  1'85  grams  at  14'4°  ;  Sc2O3,  3'8  grams  ; 
Y2O3,  5'03  grams  at  22°  ;  La2O3,  6'5  grams  at  17° ;  Yb2O3,  9'2  grams. 
Heat  of  formation  :—B2  -f-  3O  =  B2O3  +  3172K;  +  Aq  =  180K. 

Double  compounds. — (a.)  With  water.  Preparation.— 
Boron  trioxide  dissolves  in  water  with  evolution  of  heat,  com- 
bining with  it  to  form  the  compound  B2O3.3H2O,  or  H3BO3, 
commonly  called  boracic  acid.  The  same  compound  can  also  be 
prepared  by  addition  of  sulphuric  acid  to  a  solution  of  borax  or 
some  other  borate  in  water,  when  the  sodium  of  the  borax  is 
replaced  by  hydrogen,  thus  : — 

Na^BA.Aq  +  H2S04.Aq  +  5H3O  =  4H3BO3  +  Na,S04.Aq. 

The  boracic  acid  separates  in  pearly-white  scales,  which  have 
a  bitterish  cooling  taste.  Boracic  acid  is  also  obtainable  by  the 
action  of  moist  air  on  boron ;  also  by  boiling  boron  with  nitro- 
hydrochloric  acid,  when  it  unites  simultaneously  with  oxygen  and 
water. 

The  hydrated  oxides  of  scandium,  ytterbium,  lanthanum,  and 
didymium,  are  produced,  like  those  of  magnesium,  by  adding 
sodium  hydroxide  or  any  soluble  hydroxide  to  solutions  of  the 


234      THE   OXIDES,   SULPHIDES,  SELENIDES,  AND    TELLUEIDES. 

chlorides,  or  any  other  soluble  compounds  of  the  metals.  They 
are  insoluble  in  and  do  not  combine  with  these  hydroxides  to 
form  compounds  undecomposed  by  water. 

Boracic  acid  is  a  natural  product,  obtained  in  volcanic 
districts,  especially  in  Tuscany,  and  in  the  Lipari  Islands.  The 
native  form  is  named  sassolite.  Steam  containing  vapour  of 
boracic  acid  issues  from  jets  in  the  ground  called  soffioni.  The 
steam  from  these  jets  is  made  to  blow  into  artificial  basins  or 
lagoni,  where  the  boracic  acid  condenses  along  with  the  steam. 
The  solution  is  concentrated  by  causing  it  to  flow  over  long  sheets 
of  lead,  heated  by  the  waste  steam  of  the  sojftoni.  It  finally  runs 
into  crystallising  tanks,  where  the  boracic  acid  separates  out  on 
cooling.  The  crude  product  contains  about  76  per  cent,  of  boracic 
acid;  it  is  purified  by  recrystallisation.  Other  compounds  of 
boron  trioxide  with  water  are  produced  by  heating  H3BO3 ;  these 
are  BZO3.IIZO  and  2BoO3.H2O.  The  first  remains  on  heating  to 
100°;  the  second  is  left  at  160°;  while  at  270°  the  compound 
8B2O3.H2O  is  said  to  remain. 

Properties. — Boracic  acid,  H3BO3  (B2O3.3H2O)  crystallises  in 
nacreous  laminae ;  the  other  compounds  are  glassy  substances. 
The  hydrates  of  scandium,  &c.,  are  white  gelatinous  precipitates. 
Their  exact  composition  has  not  been  ascertained.  Boracic  acid  is 
volatile  with  steam ;  and  it  reacts  also  with  ethyl  and  especially 
with  methyl  alcohol,  forming  volatile  compounds.  It  is  estimated 
by  distilling  with  sulphuric  acid  and  methyl  alcohol ;  the  distillate 
is  evaporated  to  dryness  with  a  known  weight  of  lime.  It  is  used 
as  an  antiseptic,  and  is  employed  as  a  preservative  of  milk,  fish, 
&c.  A  flame  held  in  the  steam  evolved  from  a  boiling  solution  is 
tinged  green ;  if  alcohol  be  present,  it  burns  with  a  green  flame. 
This  constitutes  the  usual  qualitative  test  for  boron. 

(b.)  With  hydrogen  sulphide.— None  of  these  possible  com- 
pounds has  been  investigated. 

(c.)  Compounds  of  oxides  with  oxides.— No  compounds  of 
scandia,  &c.,  are  known  with  the  oxides  of  elements  preceding 
them  in  the  periodic  table.  They  combine  with  sulphur  trioxide, 
forming  sulphates,  colourless  crystalline  bodies ;  with  nitric  pent- 
oxide,  forming  nitrates,  <fec.  These  compounds  are  considered  later. 

Boron  trioxide  combines  with  other  oxides  when  they  are 
heated  together.  The  resulting  compounds  are  termed  borates. 
The  most  important  of  these  is  borax,  sodium  borate.  The  follow- 
ing is  a  list  of  the  more  typical  of  these  compounds  ;  in  this  classi- 
fication the  combined  water  has  not  been  included,  as  there  is  no 
evidence  that  it  replaces  either  oxide  of  boron  or  oxide  of  the  com- 


THE  BORATES. 


235 


bined  raetal.  The  ratios  are  very  numerous  and  complex.  The 
metal,  in  the  following  table,  has  been  considered  analogous  to 
calcium  oxide,  CaO,  and  has  been  termed  MO  in  the  heading.  It 
would  correspond  to  JM203,  or  to  M20.  The  amount  of  water  in 
the  salts  which  have  been  prepared  has  been  placed  in  brackets  ; 
if  another  classification  is  adopted  (see  Silicates,  p.  308),  it  often 
becomes  an  integral  portion  of  the  formula.  The  question  of  these 
formulae  will  be  treated  of  further  on,  under  silicates,  phosphates, 
&c.  The  ratio  given  is  that  of  the  oxygen  in  the  boron  trioxide  to 
the  oxygen  in  the  metallic  oxide,  the  water,  as  before  stated,  being 
neglected. 


2B203.6MgO.3Pe.03. 

2B2O3.4A12O3  (6H2O  ;  also  anhydrous). 
2B203.3A1203.(7H20). 

B203.3CaO.CaCl2; 


Katio2 

„      2 
„     2 

»      1 

5  (2B2O3.15MO). 
4  (2B2O3.12MO). 
3  (2B2O3.9MO). 
1  (2B2O3.6MO). 

",      3 
»     2 
»     3 

5  (2B2O3.5MO). 
2  (2B2O3.4MO). 
1  (2B2O3.3MO). 
1  (2B203.2MO). 

2B203.5BaO. 

B203.2BaO;  B203.2MgO. 

2B2O3.3CaO;  2B2O3.3SrO  ;  2B2O3.3CoO(4H2O). 

B203.Na20(3H20,  also4H2O)  ;  K.2O;  CaO(2H2O, 

also  anhydrous)  ;  SrO  ;  BaO  (10H2O,  also  H2O) 
MgO(4H2O,  also  8H2O)  ;  CdO  ; 

3B203.Fe203.(3H20)  ; 

B203.NiO(2H20);  PbO(H20);  Ag2O(H2O)  ; 
also  B2O3.PbO.PbCl2(H2O). 
4B2O3.3Ag-2O. 
5B203.3SrO(7H20). 

2B203.Li20.5H20;  2B2O3.Na2O(10H2O,  borax; 
6H2O  ;  5H2O  ;  also  SHoO). 
K20(5H20)  ;   (NH4)20(3H20,  also  4H2O)  ;   " 
BaO.(H2O)  ;  SrO(4H2O,  also  anhydrous)  ; 
BaO(5H2O,  also  anhydrous)  ;  PbO(4H2O). 
3B203.Li20.6H20;  3B2O3.K2O(8H:2O)  ; 
BaO(14H2O)  ;  MgO(8H2O). 
4B2O3.Li2O.10H2O  j  4B2O3.Na2O(10H:2O)  ; 
(NH4)20(6H20)  ;  CaO(9H20);  SrO(6H2O); 
Mg-O(llH2O). 

5B2O3.Na2O(10H2O)  ;   (NH4),O(6H2O). 
6B203.K20(9H20);   (NH4)20(9H20)  ; 
MgO.(18H20). 

This  list  comprises  nearly  all  the  known  borates.  They  are  prepared  by  one 
of  three  methods  :  —  (1.)  By  mixing  a  solution  of  boracic  acid  with  the  hy- 
droxide or  carbonate  of  the  metal,  evaporating,  and  crystallising.  This  metho* 
applies  only  to  the  borates  of  the  elements  of  the  sodium  group  ;  their  Ky- 
droxides  and  carbonates,  as  also  their  borates,  are  soluble.  (2.)  By  heating  the 
oxide  or  carbonate,  or  even  the  nitrate  or  sulphate,  of  the  metal  with  /boron 
trioxide  to  a  high  temperature.  The  mass  often  crystallises  on  cooliugi  The 


4  :  1  (4B203.3MO). 

5  :  1  (5B2O3.3MO). 

6  :  1  (2B203.MO). 


„  9:1  (3B2O3.MO). 

„  12  :  1  (4B203.MO). 

„  15  :  1  (5B203.MO). 

„  18  :  1  (6B2O3.MO). 


236      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND    TELLURIDES. 

borates  of  many  oxides  such  as  those  of  copper,  nickel,  &c.,  are  coloured.  Few 
of  them  have  been  analysed.  (3.)  By  adding  a  soluble  borate  such  as  sodium 
borate  to  a  soluble  salt  of  the  metal.  A  precipitate  is  formed  with  all  elements 
except  those  of  the  sodium  group.  These  precipitates,  when  washed  with 
water,  are  decomposed,  the  boracic  acid  being  washed  out,  and  the  hydroxide  of 
the  metal  remaining  behind.  They  are  thus  unstable  compounds,  largely  or 
wholly  decomposed  by  water. 

The  compounds  containing  water  are  almost  always  crystalline  ;  those  pro- 
duced by  fusion  are  also  often  crystalline,  but  are  sometimes,  like  glass,  amor- 
phous ;  those  produced  by  precipitation  are  of  doubtful  existence,  inasmuch 
as  a  mixture  of  hydroxide  and  borate  might  on  analysis  give  numbers  which 
would  lead  to  a  definite  formula. 

The  most  important  of  these  bodies  is  borax.  It  occurs  as  an 
incrustration  on  the  soil  of  districts  in  Central  Asia,  and  is  known 
as  tincdl ;  it  is  found  most  abundantly,  however,  in  lakes  in 
California,  450  miles  S.E.  of  San  Francisco,  the  most  impor- 
tant of  which  is  12  miles  in  length  and  8  miles  broad ;  the  greater 
part  of  "  Borax  Lake "  is  dry,  and  the  surface  is  charged  with 
borax,  common  salt,  sodium  and  magnesium  sulphates,  and  salts 
of  ammonium.  These  salts  are  collected  and  purified  by  recrystal- 
lisation.  A  solution  of  borax  dissolves  many  substances  insoluble 
in  water,  such  as  stearic  acid,  resins,  arsenious  oxide,  &c.  It  is 
chiefly  employed  for  glazing  porcelain  and  for  soldering  metals ; 
the  film  of  oxide  coating  the  heated  metal  dissolves  in  melted 
borax,  and  clean  surfaces  of  the  metal  can  thus  be  brought  in 
contact.  It  has  also  considerable  antiseptic  and  detergent 
properties. 

(d.)  Double  compounds  of  sulphides,  selenides,  and  tellu- 
rides  are  unknown,  also  (e.)  compounds  of  sulphides  and 
oxides. 

(/.)  Compounds  of  oxides  with  halides. — The  only  com- 
pounds which  have  been  prepared  are  the  double  fluorides  and  oxides 
of  boron  and  rnetals,  and  an  oxychloride.  Boron  trioxide  dissolves 
in  hydrofluoric  acid,  and  the  solution,  when  concentrated  by  stand- 
ing over  sulphuric  acid,  is  a  syrup,  which  contains  B203  and  HF  in 
the  ratio  B203.6HF.H20  ;  it  has  been  named  fluoboric  acid.  The 
same  liquid  is  obtained  by  saturating  water  with  boron  fluoride, 
BF3,  and  distilling.  The  existence  of  this  body  as  a  definite  sub- 
stance appears  to  be  questionable.  It  is  decomposed  by  water  into 
boracic  and  hydrofluoric)  acids.* 

The  oxychloride,  BOC1,  is  produced  by  heating  to  150°  a  mix- 
ture of  B2O3  and  2BC13.  It  is  a  fuming  liquid.  With  water  it 
yields  boracic  and  hydrochloric  acids. 

*  Bassarow,  Comptes  rend.,  78,  1698. 


237 


Oxides,  Sulphides,   Selenides,  and  Tellurides  of 
Aluminium,  Gallium,  Indium,  and  Thallium. 

These  are  as  follows  :  — 

Oxygen.  Sulphur.        Selenium.  Tellurium. 

Aluminium  ......      A1.:O;(.  AL2S3.  ?  ? 

Gallium  ........      GaO(?)  ;  Ga^.  Ga,2S3  (?),  ?  ? 

Indium  .........      In.,O3?  ;  In2O3.  In2S3.  ?  ? 

Thallium  .......      TL>O  ;  TL>OZ-  (T1O2)*.     Tl^S  ;  Tl^.  TLjSe.  ? 


Sources.  —  Aluminium  oxide,  A12O3,  occurs  native  in  a  pure 
state  as  corundum;  contaminated  with  ferric  oxide  as  emery; 
coloured  blue  by  cobalt  oxide  as  sapphire;  coloured  red  by  chromium 
oxide  as  ruby;  coloured  purple  by  manganese  sesqui  oxide,  as  ame- 
thyst; and  yellow  by  ferric  oxide,  as  topaz.  It  also  occurs  in  com- 
bination with  water,  with  silica,  and  with  other  oxides  (see  below  ; 
Silicates,  p.  303;  and  Spinels,  p.  241).  Gallium  and  indium  sulph- 
ides accompany  zinc  in  some  blendes  ;  and  thallium  is  found  in  the 
"  flue-  dust  "  of  pyrites  burners,  being  contained  in  certain  samples 
of  iron  pyrites,  FeS2. 

Preparation.—  1.  By  direct  union.  —  The  metals  all  oxidise 
when  heated  in  air,  but  not  very  readily.  Fused  aluminium 
becomes  coated  with  a  film  of  its  oxide,  A12O3  ;  gallium,  too, 
oxidises  only  on  its  surface,  even  when  strongly  heated  ;  indium 
forms  a  film  of  pale-yellow  In2O3,  and  thallium  becomes  covered 
with  a  layer  of  a  mixture  of  T12O  and  T12O3.  The  sulphides  and 
selenides  may  also  be  prepared  by  direct  union;  T12S3  can  be 
prepared  only  thus. 

2.  By  heating  compounds.  —  (1.)  The  hydrates,  when  heated. 
yield  the  oxides.     Aluminium  hydrate  loses  all  its  water  at  360°  ; 
indium  hydrate  at  655°  ;  and  thallium  hydrate  at  230°.     (2.)  The 
compound   of  indium  sulphide,    In2S3,    with   hydrogen   sulphide 
loses  hydrogen  sulphide  when  heated.     (3.)  Aluminium  oxide  has 
been  prepared  by  heating  potash  alum,  I^SOi.A^SOJg,  to  white- 
ness;   a   mixture   of    potassium   sulphate   and  alumina  remains, 
sulphuric  anhydride  escaping  ;  the  potassium  sulphate  is  dissolved 
out  with  water,   leaving  the  alumina.      (4.)    Gallium  oxide   has 
been  prepared  by  heating  the  nitrate. 

3.  By  double  decomposition.  —  Gallium  sulphide,  Ga^,  is 
produced  by  addition  of  a  soluble  sulphide  (ammonium  sulphide 
has  been   used)   to  a  soluble    salt  of   gallium  ;  indium  sulphide, 
In2S3,  is  precipitated  by  hydrogen  sulphide.     Solutions  of  thallous 

*  In  combination. 


238      THE  OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLTJRIDES 

salts,  such  as  T1N03,  or  T12S04,  give  with  hydrogen  sulphide  a 
precipitate  of  T12S.  If  a  thallic  salt  be  used,  it  is  first  reduced  to 
a  thallous  salt  by  the  hydrogen  sulphide,  with  separation  of 
sulphur,  and  thallous  sulphide  is  then  precipitated,  thus  : — 

TlCl3.Aq  +  H2S  =  T1C1  4-  2H01.Aq  +  S  ; 
2TlCl.Aq  +  H2S  =  T12S  +  2H01.Aq. 

When  carbon  disulphide  gas  is  passed  over  red-hot  alumina, 
some  of  the  oxide  is  converted  into  sulphide.  A  similar  action 
takes  place  with  hydrogen  sulphide.  Indium  sulphide,  In2S3,  may 
be  produced  in  scales  like  mosaic  gold,  by  fusion  of  indium 
trioxide,  In2O3,  with  sodium  carbonate  and  sulphur.  No  doubt 
sodium  sulphate  is  formed  at  the  expense  of  the  oxygen  of  the 
indium  oxide,  and  the  indium  combines  with  the  excess  of 
sulphur. 

4.  By  the  action  of  heat,  in  a  current  of  hydrogen,  gallium 
trioxide  gives  a  bluish-grey  sublimate,  supposed  to  be  monoxide ; 
and  indium  trioxide,  In>O3,  similarly  treated,  gives  a  mixture  of 
oxides,  one  of  which  is  said  to  have  the  formula  IntO3.     It  is 
probably  a  mixture  or  a  compound  of  In2O  with  In>O3.     When 
thallic  oxide,  T12O3,  is  heated  to  360°  it  begins  to  lose  oxygen, 
giving  the  compound  3T12O3.T12O,  which  is  perfectly  stable  up  to 
565° ;  at  higher  temperatures,  np  to  815°,  T120  volatilises  away ; 
and  the  residue  T12O3  is  stable  in  presence  of   air   above   that 
temperature.    The  monoxide,  T12O,  when  heated  in  air  is  partially 
oxidised  to  T12O3. 

By  removing  oxygen  from  thallous  sulphate,  TL,SO4,  thallous 
sulphide  is  left.  This  action  is  analogous  to  the  loss  of  oxygen 
which  sodium,  and  barium  sulphates,  &c.,  suffer  when  heatsd  in 
hydrogen  or  with  carbon.  In  the  case  of  thallium,  the  sulphate  is 
heated  with  potassium  cyanide,  KCN",  which  is  doubtless  con- 
verted into  cyanate,  KCNO. 

5.  Special  methods. — Crystalline  alumina  has  been  produced 
by  fusing  the  amorphous  variety  in  the  oxyhydrogen  flame  ;  by 
heating  the  oxide  along  with  aqueous  hydrochloric  acid  to  350°  in 
a  sealed  tube ;  and  by  melting  together  at  a  white  heat  aluminium 
oxide  with   lead   monoxide  (litharge),  or  with  barium  fluoride. 
The  last  two  processes  yield  artificial  corundum  ;  and  if  a  trace  of 
cobalt  oxide  or  chromium  oxide  be  added,  artificial  sapphires  or 
rubies  are  produced.* 

Properties. — Trioxides. — Aluminium  and   gallium  trioxides 
are  white  powders,  or  friable  masses ;  indium  trioxide  has  a  tinge 
*  Compt.  rend.,  104,  737. 


OF   ALUMINIUM,   GALLIUM,   INDIUM,   AND   THALLIUM.          230 

of  yellow,  especially  when  hot ;  and  thallium  trioxide  is  a  brown 
powder.  Crystalline  aluminium  trioxide  is  exceedingly  hard,  and 
is  insoluble  in  acids.  The  amorphous  trioxide,  when  ignited, 
appears  also  to  alter  its  structure,  probably  polymerising  (i.e., 
several  molecules  unite  to  one),  for  it  is  then  almost  unattacked 
by  acids.  It  can  still  be  dissolved,  however,  by  boiling  sulphuric 
or  strong  hydrochloric  acid,  forming  the  sulphate  or  chloride  ;  the 
crystalline  variety  is  totally  insoluble.  All  the  trioxides  are 
without  action  on  water. 

Trisulphid.es,  &C. — Aluminium  trisulphide  forms  yellow 
crystals,  which  turn  dark  when  heated  ;  the  selenide  and  telluride 
are  black  non- volatile  powders ;  gallium  trisulphide  has  not  been 
described ;  indium  trisulphide  is  a  brown  powder,  or  gold-coloured 
scales ;  and  thallium  trisulphide,  a  black,  ropy  substance,  brittle 
below  12°.  Aluminium  sulphide  is  decomposed  by  water,  giving 
the  hydrate  and  hydrogen  sulphide,  thus  : — 

A12S3  +  3H2O.Aq  =  Al2O3.wH2O  +  3JGT2S. 

The  other  three  are  unchanged  by  water,  but  decompose  when 
boiled  with  acids. 

Other  oxides  and  sulphides. — There  are  no  lower  oxides  or 
sulphides  of  aluminium  ;  the  lower  oxide  of  gallium,  produced  by 
heating  the  trioxide  in  hydrogen,  is  a  bluish-grey  substance.  The 
lower  oxides  of  indium  are  black  powders. 

Thallium  monoxide  is  a  reddish-black  substance,  melting  about 
300°,  and  is  volatile  between  585°  and  800°.  When  heated  with 
sulphur,  the  oxygen  is  replaced  by  sulphur.  Ifc  combines  directly 
with  water,  forming  the  hydrate,  T12O.H2O,  and  absorbs  carbon 
dioxide  from  moist  air.  It  has  thus  some  resemblance  to  the 
hydroxides  of  the  metals  of  the  sodium  group.  Thallous  sulphide, 
when  precipitated,  forms  greyish  or  brownish  flocks ;  from  a  hot, 
slightly  acid  solution  it  comes  down  in  blue-black  crystals.  It 
may  be  fused  to  a  black  lustrous  mass  like  plumbago.  The 
selenide  is  a  black  crystalline  body. 

Physical  Properties. 

1.  Mass  of  1  cubic  centimetre  :—AL2O3 :    3'98  grains  at  14°;   In.2O3  :  7'18  ; 

TL2S:  8-0. 

2.  Melting-point :— T1.2O3 :  759°. 

3.  Heats  of  formation  :— 2A1  +  3S  =  Al.^  +  1224K. 

2T1  +  O    =  T^O    +  423K;   +  H2O  =  33K. 
2T1  +  S     =  TL2S    +  197K. 

Double  compounds.— (a.)  With  water :  hydrates  or  hydr- 
oxides.— The  hydrated  trioxides  are  produced  by  addition  of  a 


240      THE   OXIDES,   SULPHIDES,  SELENIDES,  AND   TELLURIDES 

soluble  hydroxide,  such  as  that  of  sodium,  potassium,  or  barium, 
or  even  of  thallium  (T10H),  to  solutions  of  soluble  salts  of  the 
metals.  A  solution  of  ammonia  in  water  acts  in  a  similar  manner, 
as  if  it  contained  ammonium  hydroxide,  NH4.OH.  The  reaction 
is  as  follows,  e.g.,  with  aluminium: — 

Al,C]..Aq  +  GKOH.Aq  =  Al2O3rcH2O  +  GKCl.Aq. 

Excess  of  precipitant  (except  ammonia)  dissolves  the  hydrates 
of  aluminium  and  gallium  ;  gallium  hydroxide  is  soluble  even  in 
solution  of  ammonia.  Solution  takes  place  owing  to  the  formation 
of  soluble  double  compounds  (see  below). 

Aluminium  hydroxide  may  also  be  produced  by  passing  a 
current  of  carbon  dioxide  into  a  solution  of  potassium  aluminate 
(A1203.K20).  Potassium  carbonate  is  formed,  and  the  hydrate  of 
aluminium  precipitated.  Aluminium  sulphide,  A12S3,  reacts  with 
water,  giving  the  hydrate  and  hydrogen  sulphide.  Hence,  when 
solution  of  ammonium  sulphide  is  added  to  a  soluble  aluminium 
compound,  the  hydrate  is  precipitated,  whilst  sulphuretted 
hydrogen  is  evolved. 

The  sulphides  are  not  known  to  form  compounds  with  water. 

Thallium  monoxide,  T12O,  dissolves  in  water,  and  on  cooling, 
or  on  evaporation,  the  solution  deposits  yellow  needles  of 
TLO.H2O  =  2T1OH.  Its  solution  absorbs  carbon  dioxide  from 
the  air.  Aluminium  hydrate,  prepared  by  precipitation,  forms 
gelatinous  flocks,  and  when  dried  at  ordinary  temperature  in 
air,  has  approximately  the  formula  ALOg.SHaO.  This  is  a 
ha.rd,  horny  mass  ;  when  heated  it  gives  up  its  water.  Up 
to  65°  the  loss  is  rapid,  and  at  that  temperature  the  hydrate 
has  approximately  the  formula  A12O3,3H2O.  The  rate  of  loss 
of  water  diminishes  as  the  temperature  rises  to  150°,  and 
increases  up  to  160°,  diminishing  again  up  to  200°.  The  com- 
position of  the  hydrate  between  lbO°  and  200°  is  nearest  the 
formula  A12O3.2H2O.  From  200°  to  250°  the  rate  of  loss  of  water 
is  rapid,  but  is  much  slower  between  250°  and  290°,  and  here  the 
formula  approximates  to  ALO3.H2O.  Complete  dehydration  does 
not  occur  till  850°  is  reached.  It  is  probable  that  there  are  many 
hydrates  of  alumina,  but  that  no  one  is  stable  over  any  consider- 
able range  of  temperature. 

The  action  of  excess  of  water,  however,  on  aluminium 
amalgam  yields  a  crystalline  hydrate  of  the  formula  A1(OH)3 
=  A12O3.3H2O. 

Three  natural  hydrates  are  known,  giblsite,  A12O3.3H2O, 
bauxite,  A12O3.2H2O,  and  diaspore,  A12O3.H2O.  Artificial  crystals 


OF  ALUMINIUM,  GALLIUM,   INDIUM,  AND   THALLIUM.         241 

of  gibbsite  have  been  produced  by  the  slow  action  of  the  carbonic 
acid  of  the  air  on  a  solution  of  aluminate  of  potassium  ;  and  by 
boiling  aluminium  acetate  or  hydroxide  for  a  long  time  with  water, 
the  dihydrate  is  said  to  be  precipitated. 

Indium  hydrate  is  a  gelatinous  white  precipitate,  which  when 
air-dried  has  approximately  the  formula  In2O3.6H2O.  When 
heated,  it  loses  water  gradually  up  to  150°.  The  rate  of  loss  then 
increases  to  160°,  again  to  slacken.  The  composition  between  150° 
and  160°  nearly  corresponds  to  the  formula  In2O3.3H2O.  It  is  not 
dehydrated  till  655°  ;  and  there  are  no  signs  of  other  hydrates. 

Air-dried  hydrate  of  thallium  has  the  formula  T12O3.H2O.  At 
higher  temperatures  it  is  dehydrated. 

(6.)  With  hydrogen  sulphide. — Indium  sulphide,  In.S-,, 
when  precipitated  from  soluble  compounds  of  indium  with 
hydrogen  sulphide,  has  a  deep  yellow  colour.  It  can  be  dried  in 
air,  but  when  heated  it  evolves  hydrogen  sulphide,  leaving  the 
sulphide.  It  is  probably  a  compound  of  the  nature  of  a  hydrate  : 
In2S3.nH>S.  The  white  precipitate  produced  by  ammonium 
sulphide  with  salts  of  indium  is  also  probably  of  this  nature.  It 
is  soluble  in  solution  of  ammonium  sulphide. 

(c.)  Compounds  of  oxides  with  oxides.— On  adding  a 
solution  of  potassium  hydroxide  to  aluminium  hydrate,  complete 
solution  occurs  when  the  ratio  of  the  alumina  to  the  potash 
is  as  A1203  :  K20 ;  the  same  compound  is  precipitated  when  a 
solution  in  excess  of  hydroxide  is  mixed  with  alcohol,  in 
which  caustic  potash  is  soluble,  but  not  the  aluminate.  It  has 
the  formiila  A12O3.K2O  =  2KA1O2.  A  similar  sodium  compound 
has  been  prepared.  The  compounds  Al203.2Na20  and  Al203.3NaoO 
are  also  said  to  have  been  prepared.  By  dissolving  hydrate  of 
alumina  in  solution  of  barium  hydroxide  and  evaporating,  crystals 
of  Al2O3.BaO.6H2O,  Al2O3.2BaO.5H,O,  and  Al,O3.3BaO.IlH2O 
are  successively  deposited.*  These  bodies  may  be  compared  with 
the  borates. 

The  mineral  named  spinel  is  a  compound  of  alumina  with 
magnesium  oxide,  Al2O3,MgO.  It  crystallises  in  octahedra,  and 
has  been  prepared  artificially.  Gahnite  is  a  similar  compound 
with  zinc  oxide  of  the  formula  Al2O3.ZnO,  and  chrysoberyl  with 
beryllium  oxide  Al2O3.BeO. 

Two  compounds  with  barium  oxide  and  chloride  are  also  known, 
viz.,  Al2O3.BaO.BaCl2  and  Al.Oa.BaO.SBaCk 

Gallium  oxide  would,  no  doubt,  enter  into  similar  combinations, 
but  these  have  not  been  investigated. 

*  Berichte,  14,  2151  j  J.  praJct.  Chem.,  26,  385,  474 ;   Chem.  News,  42,  29. 

E 


242      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

A  higher  oxide  of  thallium  in  combination  with  barium  oxide  is 
produced  bypassing  a  rapid  current  of  chlorine  through  potassium 
hydroxide,  in  which  thallic  hydrate  is  suspended.  The  solution 
turns  violet,  and  with  barium  nitrate  gives  a  violet  precipitate 
which  contains  the  oxide  T103.* 

(d.)  Compounds  of  sulphides  with  sulphides. — Indium  sul- 
phide forms  with  potassium  and  sodium  sulphides  red  crystalline 
compounds  of  the  formulae  In>S3.ILS,  and  In2S3.Na2S.  A  silver 
compound  of  similar  formula  is  produced  on  addition  of  silver 
nitrate  to  their  solutions.  Thallic  sulphide,  T12S3,  also  unites  with 
thallous  sulphide,  T12S,  giving  black  crystalline  bodies. 

(e.)  No  compounds  of  oxides  with  sulphides  are  known. 

(/.)  Compounds  with  halides.— On  evaporating  an  aqueous 
solution  of  aluminium  chloride,  it  is  probable  that  oxychlorides  are 
produced,  inasmuch  as  hydrogen  chloride  is  evolved.  On  repeated 
evaporation,  all  aluminium  remains  as  hydroxide.  Similar  com- 
pounds, but  somewhat  indeBnite,  have  been  produced  by  the  action 
of  aluminium  chloride  on  aluminium  in  presence  of  air.  Gallium 
chloride,  on  addition  of  wa.ter,  gives  a  white  precipitate  of  oxy- 
chloride,  the  formula  of  which  is  unknown. 

Uses. — The  chief  use  of  alumina  is  as  a  mordant.  When  a  salt 
of  aluminium  in  solution  is  boiled  in  contact  with  animal  or  vege- 
table fibre,  it  splits  into  acid,  and  hydrate  of  alumina,  the  latter 
depositing  on  the  fibre.  The  fibre  has  the  power  of  absorbing 
and  "  fixing  "  colouring  matters,  when  boiled  with  their  solutions, 
If  the  colouring  matter  be  dissolved  in  water  along  with  a  salt  of 
aluminium,  and  the  solution  be  boiled,  the  hydrated  alumina  often 
comes  down  in  combination  with  the.  colour,  giving  a  "lake." 
Such  lakes  are  made  use  of  as  paints. 

Physical  Properties. 
Mass  of  1  cubic  centimetre  : — 

B.       Sc.     Y.      La.    Yb.          Al.  Ga.       In.       Tl. 

0 1-85    3-8    5-0    6-5    9 '2    3 '90— 4-0      —      7 '18 

OH 1-49     —      —      -  2'39f 

S —  __ 

Heats  of  formation. 

2B  +  3O  =  B203  +  2  x  1586K;    +  3H2O  =  2B(OH)3  +  2  x  60K. 

2A1  +  30  +  3H2O  =  2A1(OH)3  +  2  x  1945K. 

2T1  +  O  =  T12O  +  423K;   +  H2O  =  2T1OH  +  33K;  +  Aq  =  -  32K 

2T1  +  3O  +  3H2O  =  2T12(OH)3  +  2  x  432K. 

2A1  +  3S  =  A12S3  +  2  x'  612K. 

2T1  -f  S  =  T12S  +  2  x  98-5  K. 

*   Gazzetta,  17,  450. 

f  Gibbsite,  A1(OH)3.     Diaspore,  AIO(OH)  =  3 '4. 

' 


243 


CHAPTEK  XIX. 

OXIDES,  SULPHIDES,  SELE^IDES,  AND   TELLURIDES    OF    ELEMENTS    OF   THE 

CHROMIUM    GROUP. HYDROXIDES. DOUBLE    OXIDES  AND    SULPHIDES. 

THE  SPINELS. — OXYHALIDES. CHROMATES,  FERRATES,  AND  MANGA- 

NATES. PERMANGANATES. CHROMYL    AND     MANGANYL     CHLORIDES; 

CHLORO-CHBOMATES. 

Oxides,  Sulphides,  Selenides,   and  Tellurides  of 

Chromium,  Iron,  Manganese,  Cobalt,  and 

Nickel. 

These  compounds  may  be  divided  into  five  well-defined  groups  : 
(1)  the  monoxides,  monosulphides,  &c.,  such  as  FeO,  FeS, 
&c. ;  (2)  the  sesquioxides,  sequisulphides,  &c.,  for  example, 
Fe,O3,  Pe2S3,  &c. ;  (3)  the  dioxides,  such  as  MnO2 ;  (4)  the 
trioxides,  of  which  CrO3  is  an  instance ;  and  (5)  the  heptoxides, 
of  which  compounds  are  known  in  the  case  of  manganese,  Mn2O7. 
The  double  compounds  will  be  considered  in  connection  with  each 
group.  As  these  bodies  or  their  compounds  are  very  numerous,  it 
is  advisable  to  consider  them  in  the  order  of  the  above  groups.  It 
may  be  noticed  generally  that  in  formula,  preparation,  and  proper- 
ties, the  monoxides,  &c.,  show  a  certain  resemblance  to  those  of 
magnesium,  zinc,  and  cadmium ;  while  the  sesquioxides,  &c.,  are 
comparable  with  those  of  aluminium.  The  trioxides  find  their 
closest  analogues  in  the  sulphur  group ;  and  the  compounds  of 
manganese  heptoxide  have  the  same  crystalline  form  as  the  per- 
chlorates. 

I.  Monoxides,  monosulphides,  monoselenides,  and  mono- 
tellurides : — 

List.  Oxygen.  Sulphur.  Selenium.  Tellurium. 

Chromium  ...  —  CrS.                 CrSe. 

Iron FeO.  (Fe-^FeS.                FeSe.  FeTe  P 

Manganese...  MnO.  MnS.                   ?  ? 

Cobalt CoO.  CoS.                CoSe.  ? 

Nickel NiO.  (Ni^NiS.                NiSe.  ? 

Sources. — CrO  is  said  to  exist  in  combination  with  Cr2O3  in 
some  chrome  ores.  FeO  exists  io  combination  with  C02  as  carbo- 

E  2 


24Jt      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES 

nate  in  spathic  iron  ore,  and  with  Fe2O3  in  magnetite.  MnO  has 
been  found  native.  It  forms  crystals  which  reflect  green,  and 
transmit  red  light.  NiO  is  also  found  native.  FeS  is  sometimes 
found  in  meteoric  iron,  in  combination  with  dinickel  sulphide, 
Ni2S,  as  2FeS.Ni2S.  Manganous  sulphide,  MnS,  occurs  as  man- 
ganese blende,  or  alabandine,  in  iron-black  lustrous  cubes  or  octa- 
hedra.  Native  cobalt  sulphide  is  known  as  syepoorite.  It  forms 
8teel-grey  to  yellow  crystals,  and  is  used  by  Indian  gold  workers 
to  give  a  rose-colour  in  burnishing  gold.  Nickel  sulphide,  NiS, 
occurs  in  nature  as  long  brass-yellow  needles,  and  is  named  capillary 
pyrites,  or  millerite.  Nickel  oxide,  NiO,  along  with  magnesium 
oxide,  occurs  as  a  silicate  in  the  ore  from  New  Caledonia.  The  ore 
contains  about  18  per  cent,  of  nickel  oxide. 

Preparation. — 1.  By  direct  union. — Higher  oxides  are  pro- 
duced by  the  union  of  chromium,  iron,  manganese,  and  cobalt  with 
oxygen;  but  nickel  burns  to  NiO.  Iron,  manganese,  cobalt,  and 
nickel  unite  directly  with  sulphur,  selenium,  and  probably  tellu- 
rium, forming  monosulphides,  &c. 

The  union  with  sulphur  may  be  illustrated  by  heating  an  intimate  mixture 
of  iron  filings  with  sulphur  in  a  test  tube  ;  the  mixture  glows  throughout,  and 
is  conver*  ed  into  ferrous  sulphide. 

2.  By  heating  double  compounds. — Iron,  manganese,  cobalt, 
and  nickel  oxideis  may  be  obtained  by  heating  the  oxalates,  thus  : — 

FeC2O4  =  FeO  +  CO  +  C02. 

Manganese,  cobalt,  and  nickel  monoxides  are  produced  when  their 
carbonates  or  hydroxides  are  heated,  thus :  MnCO3  =  MnO  + 
(702;  Ni(OH),  =  NiO  +  HZ0.  Air  must  be  excluded,  except 
in  the  case  of  nickel.  Nickel  monoxide  alone  is  produced  on 
igniting  the  nitrate ;  with  the  other  metals  higher  oxides  are 
formed.  We  here  see  a  proof  of  the  comparative  stability  of 
the  higher  oxides ;  those  of  chromium  being  most,  and  those  of 
nickel  least  stable. 

3.  By  reducing  a  higher  oxide  or  sulphide. — Iron  sesqui- 
oxide,  Fe^O3,  heated  in  a  mixture  of  carbon  monoxide  and  dioxide, 
such  as  is  produced  by  the  action  of  sulphuric  acid  or  oxalic  acid, 
is  reduced  to  the  monoxide.     It  is  also  produced  in  a  crystalline 
form  by  heating  iron  to  redness  in  a  current  of  carbon  dioxide ; 
and  by  heating  the  sesquioxide,  Fe2O3,  in  hydrogen ;  between  the 
temperatures  330°  and  440°  magnetic  oxide,  Fe3O4,  is  produced ; 
but  from  500°  to  600°  the  product  is  FeO.     At  still  higher  tem- 
peratures metallic  iron  is  formed.*     The  higher  oxides  of  cobalt 

*  Chem.  Soc.,  33,  1,  506 ;  37,  790. 


OF  CHROMIUM,   IKON,   MANGANESE,   COBALT,   AND   NICKEL.      245 

and  nickel  lose  oxygen  when  heated  alone,  the  former  at  a  white 
heat,  the  latter  at  a  red  heat. 

Chromium  monosulphide  and  rnonoselenide,  CrS  and  CrSe,have 
been  produced  by  heating  the  sesquisulphide  or  selenide  to  redness 
in  hydrogen.  Ferric  sulphate,  Fe2(SO4)3,  heated  in  hydrogen  is 
said  to  give  Fe8S ;  and  ferrous  sulphate,  FeSO4,  heated  in  sulphur 
vapour,  Fe2S.  As  both  these  bodies  are  strongly  magnetic,  there 
appears  reason  to  suspect  that  they  contain  metallic  iron;  they 
are  blackish-grey  powders.  When  heated  with  carbon,  FeSO4  is 
said  to  yield  FeS ;  cobalt  sulphate  behaves  similarly. 

Ferrous  sulphide,  FeS,  is  produced  by  heating  to  redness  the 
disulphide,  iron  pyrites,  FeS2,  or  magnetic  pyrites,  Fe.Sj.3FeS ; 
sulphur  volatilises ;  it  may  also  be  formed  by  heating  pyrites, 
FeS2,  with  metallic  iron.  Cobalt  sulphate,  CoSO4,  heated  in 
hydrogen,  gives  an  oxysulphide,  CoO.CoS  (see  below)  ;  but  nickel 
sulphate  yields  dinickel  sulphide,  Ni2S. 

4.  By  double  decomposition. — Manganous  oxide  is  most 
easily  prepared  by  heating  the  dichloride,  MnCL,  with  sodium 
carbonate,  Na2CO3,  and  a  little  ammonium  chloride.  The  reaction 
is  as  follows,  MnCl2  +  Na2CO3  =  MnO  +  2NaCl  +  C02.  The 
oxide  is  really  formed  by  decomposition  of  the  carbonate  produced 
by  double  decomposition.  The  fused  mass  is  deprived  of  sodium 
chloride  by  treatment  with  water.  Higher  oxides  of  iron  or  man- 
ganese, when  heated  with  sulphur  to  a  high  temperature,  yield  the 
monosulphide ;  the  sulphur  combining  with,  as  well  as  replacing 
oxygen.  Thus  Fe2O3  and  FeaO4,  Mn2O3  and  MnO3  yield  mono- 
sal  phides,  and  sulphur  dioxide ;  both  reduction  and  double  de- 
composition proceed  simultaneously.  Manganese  dioxide  is  also 
converted  into  sulphide  when  it  is  heated  in  vapour  of  carbon 
disulphide,  the  carbon  removing  oxygen  while  manganese  and 
sulphur  unite.  Cobalt  and  nickel  sulphides  have  also  been  pro- 
duced by  heating  the  oxides  in  a  current  of  hydrogen  sulphide  or 
sulphur  gas.  All  monosulphides  (and  probably  also  monoselenides 
and  tellurides)  are  precipitated  on  adding  to  a  soluble  chromous, 
ferrous,  manganous,  cobalt,  or  nickel  compound  a  soluble  sulphide 
(selenide  or  telluride).  Ammonium  sulphide  is  commonly  em- 
ployed. Manganese,  cobalt,  and  nickel  sulphides  are  also  precipi- 
tated from  solutions  of  their  acetates  by  hydrogen  sulphide.  The 
typical  equations  are : — 

FeS04.Aq  +  (NH4)2S.Aq  =  FeS  +  (NH4)2S04.Aq ; 
Mn(C2H302)2.Aq  +  HZ8  =  MnS  +  2C2H402.Aq. 

Properties. — Ferrous  oxide  is   a  black   amorphous  powder, 


246      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES 

pyrophoric,  i.e.,  igniting  and  glowing  like  tinder  on  exposure  to  air 
it  decomposes  water,  slowly  at  the  ordinary  temperature,  quickly 
on  boiling,  liberating  hydrogen.  When  prepared  by  the  action  of 
carbon  dioxide  on  metallic  iron,  it  forms  small  black  lustrous 
crystals.  Manganous  oxide  is  a  greyish-green  powder,  melting  about 
1500°  to  a  green  mass.  When  heated  to  redness  in  a  current  of 
hydrogen  chloride  it  is  converted  into  transparent  emerald-green 
octahedra.  Cobalt  monoxide  is  an  olive-green,  and  nickel  monoxide 
a  greyish-green,  powder.  The  latter  has  been  obtained  in  crystals 
by  fusing  a  mixture  of  nickel  sulphate  and  potassium  sulphate ; 
sulphur  trioxide  and  its  decomposition  products,  sulphur  dioxide 
and  oxygen  escape,  and  crystals  of  nickel  oxide  remain  disseminated 
through  the  potassium  sulphate,  the  latter  of  which  can  be  re- 
moved by  solution  in  water.  These  bodies  are  all  insoluble  in 
water,  and  are  not  easily  attacked  by  acids. 

Chromous,  ferrous,  cobaltous,  and  nickelous  sulphides  when 
prepared  by  precipitation  are  black  flocculent  masses ;  manganous 
sulphide,  similarly  obtained,  is  pale  yellowish-pink.  Very  tinely 
divided  iron  sulphide  is  green  when  suspended  in  water.  Pink 
manganous  sulphide  when  heated  in  a  sealed  tube  with  yellow 
ammonium  sulphide  (polysulphide)  changes  to  green,  owing  prob- 
ably to  some  molecular  change.  When  prepared  in  the  dry  way, 
chromous  and  cobalt  sulphides  are  grey,  ferrous  aad  nickel  sul- 
phides brass-yellow,  and  the  native  form  of  manganous  sulphide 
iron-black.  They  all  exhibit  dull  metallic  lustre.  Manganous 
sulphide  changes  to  yellow-green  hexagonal  prisms  when  heated 
to  redness  in  a  current  of  hydrogen  sulphide.  The  selenides  are 
white,  yellow,  or  grey  bodies,  also  with  dull  metallic  lustre.  All 
these  substances  are  insoluble  in  water ;  they  react  with  acids, 
giving,  for  example,  with  hydrochloric  or  sulphuric  acids,  the 
chloride  or  sulphate  of  the  metal  and  hydrogen  sulphide.  Hydro- 
chloric acid,  if  dilute,  does  not  attack  nickel  or  cobalt  sulphides 
unless  it  is  heated.  The  action  of  dilute  hydrochloric  or  sulphuric 
acid  on  ferrous  sulphide  is  the  usual  method  of  preparing  hydrogen 
sulphide. 

A  wet  mixture  of  iron  filings,  sulphur,  and  ammonium  chloride 
turns  hot,  owing  to  the  combination  of  the  iron  and  sulphur.  Such 
a  mixture  is  employed  in  cementing  iron,  for  example  in  the  con- 
struction of  submarine  piers  for  bridges.  The  sulphides  can  all 
be  fused  at  a  white  heat.  Dinickel  sulphide,  Ni2S,  can  even  be 
melted  in  glass  vessels. 

Double  compounds.— (a.)  With  water.— Hydrates  or  hy- 
droxides. These  substances  are  prepared,  as  usual,  by  the 


OF  CHROMIUM,   IRON,  MANGANESE,  COBALT,  AND   NICKEL.      247 

action  of  a  soluble  hydroxide  or  of  ammonia  dissolved  in  water 
on  some  soluble  compound  of  the  metal,  e.g.,  the  chloride  or 
sulphate.  With  chromium,  iron,  and,  in  a  less  degree,  man- 
ganese and  cobalt,  great  care  mast  be  taken  to  exclude  oxygen ; 
the  water  in  which  the  precipitant  is  dissolved  must  be  boiled 
in  vacuo,  to  remove  dissolved  oxygen,  and  the  precipitation, 
filtration,  &c.,  conducted  in  an  atmosphere  of  hydrogen.  Chro- 
mous  compounds  are  best  prepared  from  the  acetate,  which  is 
made  by  the  action  of  nascent,  hydrogen  from  zinc  and  hydro- 
chloric acid  on  a  solution  of  chromium  trichloride.  On  adding 
potassium  acetate,  chromous  acetate  is  precipitated  as  a  red 
powder.  On  treatment  with  potassium  hydroxide,  it  yields 
chromous  hydrate,  2CrO.H2O,  as  a  substance  yellow  when  wet, 
turning  brown  when  dried.*  When  boiled  with  water,  hydrogen 
is  evolved,  and  chromic  hydrate  is  produced.  The  water  which  it 
contains  cannot  be  removed  by  heat,  for  the  reaction  takes  place 
2CrO.H2O  =  Cr2O3  +  H*. 

Ferrous  hydrate,  FeO.H2O  (?),  is  a  white  precipitate,  which 
becomes  much  denser  on  standing  in  a  solution  of  potassium 
hydroxide.  It  is  sparingly  soluble  in  water  (1  in  150,000).  It 
absorbs  carbon  dioxide  from  air;  and  when  dry  it  turns  hot  and 
oxidises  on  exposure  to  air.  The  wet  hydrate,  on  atmospheric 
oxidation,  turns  first  green,  then  rust  coloured. 

Manganous  hydrate  is  also  white,  and  turns  brown  on  exposure 
to  air.  It  is  said  to  contain  24  per  cent,  of  water,  and  hence  must 
have  approximately  the  formula  3MnO.4H2O.  It  can  be  produced 
by  boiling  manganous  sulphide,  MnS,  with  caustic  potash.  Co- 
baltous  hydrate  is  a  dingy- red  powder,  prepared  by  boiling  a  solu- 
tion of  cobalt  di chloride  with  caustic  potash,  and  collecting  and 
drying  the  precipitate.  In  the  cold,  a  blue  oxychloride  is  precipi- 
tated. The  hydrate  of  nickel,  NiO.2H2O,  occurs  native,  in  small 
emerald-green  prisms  ;  andNiO.H2O  =  Ni(OH)2isan  apple-green 
precipitate.  By  leaving  a  solution  of  nickel  carbonate  in  excess 
of  ammonia  to  crystallise,  this  hydrate  separates  in  green 
crystals. 

It  appears  probable  that  the  precipitated  sulphides  of  these 
metals  are  in  reality  compounds  of  the  sulphides  with  water. 

(6.)  No  hydrosulphides  are  known  ;  and  (c.)  No  doable  oxides 

(rf.)   Compounds  of  Sulphides  with  Sulphides  : — 

2FeS.Ko8  ;  obtained  by  igniting  Fe.2S&'K2S  in  hydrogen. 

SMnS.KoS ;    dark    red    scales,   produced    by  heating   together  man- 

*  Annales  (5),  25,  416;   Comptes  rend.,  92,  792,  1051. 


248   THE  OXIDES,  SULPHIDES,  SELENIDES,  AND  TELLURIDES 

ganese  sulphate,  MnSO4,  with  potassium  sulphide  and 
carbon,  and  dissolving  out  the  excess  of  potassium  tul- 
phide  with  water. 

3MnS.Na2S.     Light  red  needles,  similarly  prepared.     Also 
MnS.2Na2S. 
NiS.2FeS.     A  double  sulphide  of  nickel  and  iron,  named  pentlandite, 

which  forms  bronze-yellow  crystals. 
FeS.2ZnS,  known  as  christophite,  occurs  native ;    also  CoS.CuS,  carro- 

lite. 
(e.)  Compound  of  oxide  and  sulphide. — CoS.CoO,  a  dark  grey  sintered  mass, 

produced  by  heating  cobalt  sulphate,  CoSO4,  in  hydrogen. 
(f) .  Compounds  with  halides. — Chromous  chloride  is  said  to  give  a  light  grey 
oxychloride ;  and  cobalt  chloride  heated  with  water  a  greenish-blue 
oxychloride.  Similar  bodies,  green  and  insoluble,  are  produced,  when 
nickel  chloride  or  iodide  is  heated  with  nickel  hydroxide.  Their 
formulse  are  unknown. 

II.  Sesquioxides,  sesquisulphides,  sesquiselenides  (the 
tellurides  have  not  been  investigated). 

List.  Oxygen.  Sulphur.  Selenium. 

Chromium Cr2O3.  Cr2S3.  Cr2Se3. 

Iron Fe2O3.  Fe2S3.  Fe;Se3. 

Manganese Mn2O3.  — 

Cobalt Co2O3.  Co2S3. 

Nickel Ni203. 

Sources. — Chromium  sesquioxide  exists  in  combination 
with  ferrous  oxide  in  rhrome  iron  ore  or  chromite,  the  chief  source 
of  chromium.  It  occurs  in  veins  in  serpentine  rock.  As  chrome- 
ochre  it  forms  a  yellow-green  earthy  deposit,  which  is  found  in 
Shetland.  Iron  sesquioxide  is  very  widely  distributed,  and 
occurs  as  red  hcematite  or  specular  ore  in  large  deposits  in  Cumber- 
land and  Lancashire  in  early  formations ;  in  carboniferous  strata 
as  brown  hcematite  or  Umonite  in  the  Forest  of  Dean,  in  Glamor- 
ganshire, or  associated  with  oolitic  rocks  as  the  earthy  haematite 
of  Northamptonshire  and  Lincolnshire.  More  recent  deposits  of 
Umonite  occur  as  bog-iron-ore  in  Ireland  and  North  Germany. 
Magnetic  ore,  or  magnetite,  Fe2O3.FeO,  is  also  very  widely  dis- 
tributed. It  is,  perhaps,  the  purest  form  of  iron  ore.  and  occurs 
as  sand  in  Sweden.  From  it  the  celebrated  Swedish  iron  is  made. 
Magnetic  pyrites,  Fe2S3.FeS,  and  2Fe2S3.FeS,  and  copper  pyrites, 
Fe2S3.CuaS,  are  made  use  of  as  sources  of  sulphur.  Manganese 
sesquioxide,  Mn2O3,  occurs  zsbrannite,  andhydrated,  Mn2O3.H,O, 
as  grey  maganese  ore.  Wad  is  a  mixture  of  oxides  of  manganese, 
probably  consisting  largely  of  Mn2O3.  In  combination  with  MnO, 
it  forms  hausmannite,  Mn,O3.MnO  (see  Spinels).  Cobalt  and 


OF   CHROMIUM,   IRON,   MANGANESE,   COBALT,   AND   NICKEL.      249 

nickel  sesquioxides  do  not  occur  native,  but  Co.S  .CoS  is  known 
as  linnoeite. 

Preparation. — 1.  By  direct  union. — Chromium,  heated  in 
air,  forms  Cr^O3 ;  but  iron,  manganese,  and  cobalt  burn  to  com- 
pounds of  the  sesquioxides  and  monoxides,  depending  on  the  tem- 
perature. A  steel  watch-spring  set  on  fire  by  being  tipped  with 
burning  sulphur,  burns  in  oxygen  with  brilliant  scintillations  to 
Fe3O3.FeO,  or  magnetic  oxide,  which  fuses  and  drops  from  the 
wire, 

FIG.  32. 


This  forms  a  telling  experiment,  and  illustrates  well  the  direct  union  of 
metals  of  this  group  with  oxygen.  The  jar  in  which  the  combustion  takes 
place  should  stand  in  an  iron  tray,  or  in  a  plate  full  of  water,  for  the  fused 
oxide  is  certain  to  crack  any  glass  tray  on  which  it  falls. 

Iron  filings,  heated  to  dull  redness  in  a  current  of  sulphur  gas, 
forms  Fe2S3 ;  and  the  corresponding  selenide,  Fe2Se3,  has  been 
similarly  made. 

2.  By  reducing  a  higher  compound. — Chromium  trioxide, 
CrO>,  when  strongly   ignited,  loses   oxygen,  forming  the  sesqui- 
oxide.     Compounds  of  the  trioxide,  such  as  mercurous  chromate, 
HgoCrO4,   ammonium  dichromate,  (NH^CraOr,  and  others  also 
yield  the  sesquioxide  on  ignition.     Chromates,  such  as  bichrome, 
ILCr2O7,    at    a  white  heat    give    neutral    chromate,    chromium 
sesquioxide,   and  oxygen,  thus : — 2K2Cr2O7  =  2K2CrO4  +  Cr,O3 
4-30.     Manganese  dioxide,   at  a   dull-red   heat,    likewise   loses 
oxygen,  giving  Mn3O3. 

3.  By    oxidising    a   lower  compound. — Ferrous   sulphate, 
FeSO4,  when  distilled  for  the  manufacture  of  anhydrosulphuric 
acid  (see  p.  433),  leaves  a  residue  of  sesquioxide.     It  may  be  sup- 
posed that  the  ferrous  oxide  decomposes  water-gas,  arising  from 
water  still   combined  with   the  ferrous  sulphate,   producing  the 
sesquioxide.     Ferrous  carbonate  heated  gently  in  air  yields  ferrous 
oxide,  FeO,  which  unites  with  oxygen,  forming  the  sesquioxide. 


250      THE   OXIDES,    SULPHIDES,    SELENIDES,   AND    TELLURIDES 

It  is  also  produced  by  heating  ferrous  sulphate  with  a  little  nitre, 
KNO3,  to  supply  oxygen.  Ferrous  oxalate,  FeC2O4,  yields  the 
monoxide  on  ignition,  and  in  air  the  sesquioxide  is  produced.  The 
lower  oxides  of  manganese,  MnO  and  Mn3O4,  when  heated  in 
oxygen  give  the  sesquioxide,  when  the  pressure  of  oxygen  is 
greater  than  O26  of  an  atmosphere.  As  the  pressure  of  the 
oxygen  in  ordinary  air  is  approximately  one-fifth  of  an  atmo- 
sphere, such  oxidation  does  not  occur  in  air,  unless  it  be  com- 
pressed. The  nitrates  of  these  metals,  when  heated,  yield 
the  sesquioxides.  This  is  a  case  of  simultaneous  decomposition 
and  oxidation.  The  nitrate  is  decomposed  into  monoxide  and 
nitric  pentoxide,  thus  : — Fe(NO3)2  =  FeO  +  NtO*  ;  but  the 
pentoxide  parts  with  its  oxygen,  being  itself  converted  into  lower 
oxides  of  nitrogen,  NO  and  NOZ,  thus :  2FeO  +  N205  =  Fe2O3 
+  2JV02;  and  6FeO  +  2V206  =  3Fe2O3  +  2JVO.  And  similarly 
with  the  other  metals. 

4.  By  the  action  of  heat  on  a  compound. — The  hydrates  of 
these  metals  when  heated  leave  the  oxides.  Ferric  hydrate,  when 
boiled  for  a  long  time  in  water,  is  ultimately  dehydrated,  and  dry 
ferric  oxide  settles  out.  The  nitrates  and  sulphates,  &c.,  are  also 
decomposed  by  heat,  and  also  the  borates.  The  excess  of  boracic 
acid  is  removed  by  weak  hydrochloric  acid. 

5.  By  double  decomposition. — Ferric  oxide  is  produced  in 
a  crystalline  form  when  ferric  chloride  and  lime  are  heated  to 
redness,  or  when  ferrous  sulphate  and  sodium  chloride  are  heated 
together  in  air.  The  ferrous  oxide  is  oxidised  by  the  air,  and  crys- 
tallises from  the  salt.  The  sulphides  are  generally  prepared  by 
double  decomposition.  Chromium  sesquisulphide  is  obtained  when 
chromium  trioxide  is  heated  to  whiteness  in  a  current  of  carbon 
disulphide  gas  ;  heated  in  sulphur  gas  or  in  hydrogen  sulphide,  it 
suffers  no  change ;  but  the  chloride  is  converted  into  sulphide  or 
selenide  by  hydrogen  sulphide  or  selenide  at  a  red  heat,  and  the 
hydrate,  when  heated  to  440°  in  sulphur  gas,  or  to  a  higher  tem- 
perature in  selenium  vapour,  yields  the  sulphide  or  selenide. 
Cobaltic  hydrate  gently  heated  in  hydrogen  sulphide  also  gives 
cobalt  sesquisulphide.  Nickel  sesquisulphide  is  unknown. 

Properties. — Oxides. — Chromium  sesquioxide  is  an  amorph- 
ous green  powder;  when  crystalline  it  forms  green  tablets,  or,  if 
produced  at  a  high  temperature,  brown  crystals.  The  amorphous 
variety,  if  it  has  not  been  exposed  to  a  high  temperature  during  its 
formation,  becomes  incandescent  when  gently  heated,  no  doubt 
owing  to  polymerisation,  several  molecules  uniting  to  form  one. 
It  is  then  practically  insoluble  in  acids.  This  behaviour  is 


OF  CHROMIUM,  IRON,  MANGANESE,  COBALT,  AND  NKfflL.      251 

also  seen  with  aluminium,  manganese,  and  iron  sesquioxides.  The 
crystalline  varieties  of  chromium  oxide  are  produced  in  presence 
of  chlorine,  or  by  some  solvent  for  the  oxide.  Thus  chromium 
oxychloride,  CrOzCh,  when  passed  through  a  red-hot  tube,  de- 
posits crystalline  oxide ;  similarly,  potassium  dichromate,  heated 
in  chlorine,  gives  a  mixture  of  crystalline  oxide  and  potassium 
chloride,  the  excess  of  oxygen  being  expelled.  Iron  sesqui- 
oxide  may  be  obtained  in  crystals  by  fusing  the  amorphous 
variety  with  calcium  chloride,  or  by  heating  it  in  a  current  of 
hydrogen  chloride.  It  would  appear  that  in  such  cases  the 
volatile  chloride  is  formed  ;  and  that  it  is  decomposed  by  oxygen, 
yielding  oxide,  which  is  deposited  in  crystals.  Crystalline 
varieties  of  the  sesquioxides  of  cobalt  and  nickel,  owing  to  their 
easy  decomposition,  have  not  been  obtained.  That  of  manganese 
has  not  been  prepared  artificially.  Amorphous  ferric  sesquioxide 
is  brown-red  or  red,  according  to  the  method  of  preparation.  If 
prepared  from  ignited  ferrous  sulphate  it  has  a  fine  colour,  and  is 
used  as  a  paint,  under  the  name  "  Venetian  red."  It  is  also  used 
under  the  name  of  "  rouge  "  for  grinding  and  polishing  glass  objects, 
such  as  the  lenses  of  telescopes,  &c.,  and  as  "  crocus"  to  produce 
shades  from  purple-red  to  yellow,  according  to  the  amount,  on 
porcelain,  in  combination  with  silica.  The  crystalline  variety  is 
black.  When  native,  as  specular  ore,  it  forms  very  lustrous 
rhombohedra  ;  another  crystalline  variety,  martite,  occurs  in  octa- 
hedra ;  while  hcematite  consists  of  kidney-shaped  (botryoidal) 
masses,  with  a  radiated  crystalline  structure.  Manganese 
sesquioxide,  when  amorphous,  is  a  black  powder ;  as  braunite  it 
forms  brownish-black  lustrous  quadratic  pyramids.  Cobalt 
sesquioxide,  prepared  by  heating  the  hydrated  compound  to 
600 — 700°,  is  a  black  powder,  as  is  also  nickel  sesquioxide. 

These  bodies  show  different  degrees  of  stability.  While 
chromium  sesquioxide  can  be  fused  at  a  white  heat  without  change, 
iron  sesquioxide  is  converted  into  Pe3O4,  and  at  a  bright-red  heat, 
manganic  sesquioxide  gives  Mn3O4.  Cobalt  and  nickel  sesqui- 
oxide lose  oxygen  at  a  dull-red  heat,  giving  Co3O4  and  NiO 
respectively.  Cobaltic  oxide,  as  borate,  is  made  use  of  as  a  black 
pigment  in  enamel  painting.  Chromium  sesquisulphide  and 
sesquiselenide  form  brilliant  black  plates;  iron  sulphide  and 
selenide  are  yellowish- grey  with  metallic  lustre;  and  cobalt 
sesquisulphide  forms  a  dark  iron-grey  mass. 

Double  compounds. — (a.)  With  water :  hydrates  or  hydr- 
oxides.— These  are  produced  as  usual  from  a  soluble  salt  of  the 
hydroxide.  Those  of  cobalt  and  nickel  are  formed  by  the 


252      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES 

action  of  an  alkaline  solution  of  sodium  or  potassium  hypo- 
chlorite  on  a  salt  of  the  metal.  Hydrated  monoxide  is  produced 
and  further  oxidised  by  the  hypochlorite,  thus  : — 

2CoO.*H2O  +  NaClO.Aq  =  Co2O3.nH2O  +  NaCl.Aq. 

Cobalt  is  more  easily  oxidised  than  nickel,  for  chlorine  water 
converts  the  hydrated  monoxide  into  the  sesquioxide,  thus  : — 

2CoO.wH2O  +  Cl2.Aq  +  H30  =  Co2O3jzH2O  +  2HCl.Aq. 

Hydrated  chromium  sesquioxide  is  dissolved  by  excess  of  cold 
caustic  potash  or  soda,  but  is  precipitated  on  warming  (see 
below). 

There  are  two  varieties  of  chromic  salts,  which  are  respectively 
green  and  violet.  Both  varieties  give  with  alkalis  a  grey-green 
precipitate.  By  varying  the  conditions,  the  following  hydrates 
have  been  prepared  : — 

Cr2O3.9H2O.     Grey- violet  powder. 

Cr3O3.7H2O.     Greyish-green;     soluble    in    alkali    with   violet 
colour. 

Cr2O3.6H2O.     Green,  gelatinous,  drying  to  a  hard  black  mass. 

Cr2O3.5H2O.     Similar  to  last. 

Cr-jO3. 411^0.     Green ;  by  boiling  chromic  chloride  and  caustic 
alkali. 

Cr2O3.2H2O.  Guignet's  or  Pannetier's  green ;  produced  by  heat- 
ing bichrome,  K2Cr2O7,  and  borax.  Oxygen  is  lost,  and  a  borate 
of  chromium  and  alkali  is  formed.  On  treatment  with  water,  the 
borate  is  decomposed,  leaving  the  hydrate.  This  body  is  a  fine 
green  pigment. 

These  hydrates  dissolve  in  cold  acids,  giving  violet  salts,  the 
solutions  of  which  turn  green  when  warmed,  most  probably  owing 
to  the  formation  of  a  basic  salt.  Thus  chromic  sulphate, 
Cr2(S04)3.Aq  (or  Cr203.3S03.Aq),  when  warmed,  is  supposed  to 
give  Cr20.(S04)2.Aq  (or  Cr203.2S03.Aq),  losing  the  elements  of 
sulphuric  anhydride. 

No  native  form  of  chromium  hydrate  is  known. 
Ferric  hydrates  are  found  native.  Brown  or  yellow  clay  iron 
ore  is  supposed  to  be  the  trihydrate,  Fe2O3.3H26  or  Fe(OH)3; 
xanthosiderite  is  Fe,O3.2H2O,  or  Fe2O(OH)± ;  and  gotliite  or  needle 
iron  ore,  Fe2O3.H2O  or  FeO.(OH).  Limonite  is  2Fe2O3.3H2O  ; 
and  turgite,  2Fe2O3.H2O.  Precipitated  hydrate,  dried  in  air, 
possesses  the  approximate  formula  Fe2O3.5H2O ;  when  heated, 
water  is  gradually  lost,  no  sign  of  formation  of  intermediate 
hydrates  being  found.  It  is  probable  that  there  are  many 


OF   CHROMIUM,   IRON,   MANGANESE,   COBALT,   AND   NICKEL.      253 

hydrates,  each  of  which  is  stable  within  a  very  limited  range  of 
temperature;  hence,  on  drying,  indefinite  mixtures  are  produced.* 
By  prolonged  boiling  in  water,  the  hydrate  PeaOa.H^O  is  produced, 
and  after  a  long  time  the  precipitate  consists  of  anhydrous  sesqui- 
oxide ;  it  appears,  therefore,  that  the  hydrate  may  lose  water  even 
in  presence  of  great  excess  of  water  at  100°.  Hydrate  of  iron  is 
used  as  a  mordant  (see  aluminium  hydrate,  p.  242).  It  produces 
stains  of  "  iron-mould  "  on  linen  ;  these  can  be  removed  by  oxalic 
acid,  and  a  little  metallic  tin  to  reduce  the  iron  from  sesquioxide 
to  monoxide,  which  is  more  easily  soluble. 

Hydrated  manganese  sesquioxide  occurs  native  as  manganite 
or  grey  manganese  ore ;  its  formula  is  Mn2O3.H2O.  Wad,  a 
mixture  of  oxides  of  manganese,  probably  contains  some  other 
hydrates.  Both  ferrous  and  manganous  hydrates,  suspended  in 
water,  when  shaken  with  oxygen  or  air,  are  converted  into 
hydrated  sesquioxides.  That  of  iron  is  rust-brown,  and  of  man- 
ganese dark-brown. 

Hydrated  sesquioxides  of  cobalt  and  nickel  are  black 
precipitates.  That  of  nickel  is  said  to  have  the  formula 
Ni2O3.3H2O. 

It  is  probable  that  the  sesquisulphides,  produced  by  precipita- 
tion, are  also  hydrated.  A  green  flocculent  precipitate  is  pro- 
duced by  addition  of  a  polysulphide  of  ammonium,  (NH4)2SM 
(yellow  sulphide),  to  a  solution  of  ferric  chloride,  to  which  a  small 
quantity  of  chlorine  water  or  solution  of  bleaching  powder  has 
been  added.  With  excess,  it  is  oxidised  and  dissolved.  This 
green  precipitate  is  soluble  in  ammonia  with  a  green  colour, 
possibly  giving  a  double  sulphide.  Its  formula  is  said  to  be 
2Fe2S3.3H2O.  A  cobaltic  salt  gives,  with  hydrogen  sulphide,  a 
dark-grey  precipitate  of  cobalt  sesquisulphide,  also  probably 
hydrated.  No  similar  nickel  compound  has  been  prepared. 

(6.)  No  compounds  with  hydrogen  sulphide  are  known. 

(c.)  Compounds  of  oxides  with  oxides. — As  has  been  stated, 
hydrated  chromium  sesquioxide  dissolves  in  cold  solutions  of  the 
hydroxides  of  potassium  of  sodium,  but  is  reprecipitated  on 
warming.  This  behaviour  is  so  far  analogous  to  that  of  alumi- 
nium hydrate ;  the  double  oxide  of  aluminium  and  alkali-metal, 
however,  is  more  stable  than  that  formed  by  chromium,  for  its 
solution  can  be  boiled  without  change.  The  other  hydrates  of 
this  group  are  insoluble  in  alkalis. 

The  Spinels.— Compounds  of  these  sesquioxides  with  mon- 
oxides of  dyad  metals  form  a  very  important  group  of  minerals, 
*  Chem.  Soc.,  53,  50. 


254      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES 

crystallising  in  octahedra,  or  in  rhombic  dodeeahedra,  named 
spinels,  the  name  spinel  being  generally  applied,  but  being 
specially  applicable  to  the  oxide  of  aluminium  and  magnesium, 
Al2O3.MgO.  The  following  is  a  list  :— 

Cr2O3.FeO  ;  chromite,  or  chrome-iron  ore.         Al2O3.ZnO;  gahnite. 
Fe2O3.FeO  ;  magnetite,  or  magnetic  iron  ore.  Al0O3.FeO  ;    zeilanite. 
'Fe2O?.T£.gQ;magnesio-ferrite.  Al2O3.BeO  ;    chrysoberyl. 

Fe2O3.ZnO  ;  franTclinite.  Mn2O3.ZnO  ;  Tietaerolite. 

;    spinel.  Mn2O3.MnO  ;  hausmannite. 


Besides  these,  Cr2O3.ZnO,  Cr2O3.CrO,  Cr2O3.MnO,  Fe2O3.CaO,  Co2O3.CoO, 
and  Ni2O3.NiO  have  been  made  artificially.* 

Chromous  hydrate,  Cr(OH)2,  made  by  addition  of  caustic 
soda  to  chromium  dichloride,  when  exposed  to  air,  changes  to  a 
snuff-coloured  powder,  of  the  formula  Cr2O3.CrO.  It  has  not 
been  obtained  crystalline.  When  iron  wire  and  lime  are  heated  to 
whiteness  in  presence  of  air,  black  crystals  of  Fe2O3.CaO  are  pro- 
duced ;  the  same  compound  is  formed  by  strongly  igniting  a 
mixture  of  haematite  and  chalk.  Franklinite,  Fe>O3.ZnO,  has 
been  produced  by  strongly  igniting  a  mixture  of  iron  sesquioxide, 
zinc  sulphate,  and  sodium  sulphate.  The  zinc  oxide  remaining 
after  decomposition  of  the  sulphate  combines  with  the  oxide  of 
iron.  The  sodium  sulphate  may  act  as  a  solvent.  Iron,  man- 
ganese,  and  cobalt  sesquioxides  lose  oxygen,  the  first  at  a  white 
heat,  the  second  at  bright  redness,  the  last  at  a  dull-red  heat, 
giving  these  complex  oxides.  That  of  iron  is  the  important  magnetic 
iron  ore,  occurring  largely  in  Sweden.  Manganoso-manganic 
oxide  is  a  reddish-brown  powder,  which  turns  black  when  heated, 
but  recovers  its  red  colour  on  cooling.  Cobaltoso-cobaltic  and 
nickeloso-nickelic  oxides  form  grey  octahedra  with  metallic 
lustre.  That  of  cobalt  may  be  produced  by  heating  the  nitrate 
or  oxalate  to  redness,  and  boiling  the  residue  with  hydrochloric 
acid  ;  and  that  of  nickel  by  heating  nickel  dichloride,  NiCl2, 
to  350  —  400°  in  a  current  of  moist  oxygen.  Manganese  dichloride, 
on  exposure  to  moist  air,  is  also  changed  into  the  crystalline  oxide  ; 
and  it  may  also  be  produced  by  heating  manganous  oxide,  MnO, 
to  redness  in  water-gas. 

These  bodies  are  also  known  in  a  hydrated  condition. 

The  snuff-coloured  powder,  obtained  as  described,  from  chrom- 
ous  oxide  in  air,  is  probably  hydrated.  A  dingy  green  hydrate  of 
ferroso-  ferric  oxide  is  produced  by  oxidation  of  ferrous  hydrate  ; 
and  black  hydrates  are  precipitated  by  addition  of  an  alkali  to  a 

*  Comptes  rend.,  104,  580. 


OF  CHROMIUM,  IRON,  MANGANESE,   COBALT,  AND  NICKEL.      255 

mixture  in   molecular   proportions   of   a   ferrous   and  ferric  salt, 
thus  : — 

FeCl2.Aq  +  2FeCl3.Aq  +  SKOH.Aq  =  SKCl.Aq  +  Fe3O4.nH2O. 

Like  the  anhydrous  oxide,  Fe3O4,  these  hydrates  are  magnetic. 
A  solution  of  manganoso- manganic  oxide  in  phosphoric  acid  gives 
a  brown  precipitate  with  potash,  doubtless  of  hydrate. 

A  few  other  double  compounds  are  known,  in  which  the  sesqui- 
oxide  and  protoxide  are  present  in  different  ratios.  Thus,  by 
addition  of  ammonia  solution  to  a  solution  of  a  mixture  of  calcium 
chloride  and  chrominm  trichloride,  the  body  Cr2O3.*2CaO  is  pre- 
cipitated. A  somewhat  similar  compound,  but  containing  calcium 
chloride  in  addition,  of  the  formula  Pe2O3.2CaO.CaCl2,  crystal- 
lises from  a  solution  of  iron  sesquioxide  and  lime  in  fused  calcium 
chloride,  in  shining  black  prisms.  And  lastly,  by  heating  a 
mixture  of  hydrated  ferric  oxide,  potassium  carbonate,  and  potas- 
sium chloride,  till  the  latter  is  volatilised,  ferric  oxide,  in  combina- 
tion with  a  small  quantity  of  water  and  potassium  oxide,  remains 
as  transparent  red-brown  crystals. 

"  Smithy  scales  "  are  produced  by  heating  iron  to  redness  in 
air.  Two  layers  are  formed  ;  the  outer  layer  has  approximately 
the  composition  Fe3O4 ;  the  inner  layer  forms  a  blackish-grey, 
porous,  brittle  mass,  and  has  the  formula  Pe2O3.6FeO.  Ferroso- 
ferric  oxide  is  produced  also  when  iron  burns  in  oxygen,  when 
iron  is  heated  in  water-gas,  or  when  the  monoxide  is  heated  in  a 
current  of  hydrogen  chloride. 

It  is  possible  to  take  two  views  of  the  constitution  of  these 
oxides  ;  the  first  is  that  the  sesquioxides  are  chemical  individuals, 
derived  from  the  corresponding  trichlorides  ;  and  there  appears 
little  doubt  that  this  is  the  case  with  chromium  and  iron  sesqui- 
oxides, Cr2O3  and  Fe2O3,  being  easily  derived  from  and  convertible 
into  Cr.Cle  and  Pe2Cl6  respectively.  Similarly,  their  compounds 
with  the  protoxides  would  justly  have  the  formulae  Cr2O3.CrO  and 
Pe2O3.FeO.  But  in  the  case  of  manganese  there  appears  to  be 
some  evidence  of  the  existence  of  two  bodies  of  like  formula,  but 
of  different  properties,  implying  different  constitution.  There  is 
little  doubt  that  the  fact  that  such  bodies  become  much  more 
dense  and  insoluble  in  acids  on  ignition,  sometimes,  indeed,  them- 
selves evolving  heat  when  gently  warmed,  is  due  to  polymerisa- 
tion, i.e.,  the  association  of  several  simple  molecules  to  form,  a 
more  complex  one.  But  the  evidence  as  regards  manganese 
sesquioxide  points  to  a  different  cause.  That  body  may  be  regarded 
as  either  a  chemical  individual,  Mn^Oa,  and  the  derived  manganoso- 


256      THE  OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES 

manganic  oxide  as  Mn2O3.MnO  ;  or  it  may  be  conceived  to  be 
MnCX.MnO,  a  compound  of  dioxide  and  monoxide,  or  a  manganite 
of  manganese  ;  and  the  substance,  Mn3O4,  might  be  MnO2  2MnO. 
Now  manganese  sesquioxide,  when  treated  with  dilute  nitric  acid, 
gives  a  solution  of  manganous  nitrate,  Mn(N03)2,  and  a  residue  of 
MnO2.  With  sulphuric  acid  oxygen  is  evolved,  and  manganous 
sulphate,  MnS04,  dissolves.  The  acetate,  phosphate,  &c.,  of 
Mn203  can,  however,  be  prepared  ;  and  it  is  very  unlikely  that 
such  bodies  are  mixtures  of  manganous  salts  and  salts  of  manga- 
nese dioxide  ;  salts  of  the  latter  being  almost  unknown.  On 
addition  of  alkali  to  such  salts  a  brown  precipitate  is  produced, 
soluble  in  acids  with  formation  of  salts  of  the  sesquioxide  ;  whereas 
the  hydrated  sesquioxide,  Mn(OH)3,  produced  by  oxidation  in  air 
of  manganous  hydrate  is  split  by  nitric  acid  into  manganous 
nitrate  and  insoluble  hydrated  dioxide,  MnO2.wH2O  ;  and  it  is 
insoluble  in  dilute  sulphuric  acid.  These  facts  would  lead  us  to 
conclude  that  two  bodies  of  the  formula  Mn.O3  exist,  one  of 
which,  however,  has  the  constitution  MnO2.MnO.  The  oxides 
would  well  repay  study  in  this  direction. 

(d.)  Compounds  of  oxides  with  sulphides.  —  Iron  sesqui- 
oxide, heated  in  sulphur  gas,  gives  the  compound  Fe2O3.3Fe2S3. 
No  other  compounds  of  this  nature  have  been  prepared  in  this 
group. 

(e.)  Compounds  of  sulphides  with  sulphides.—  The  follow- 
ing is  a  list:  —  * 


brick-red  powder.  Cr2S3.MnS  :  chocolate-coloured  powder. 

Cr.2S3.CrS:  grey-black  powder.  Fe2S3.Cu2S.     Copper-pyrites. 

Cr2S3.ZnS  :  dark  brown  powder.  Co2S3.CoS.      Linnceite. 

Cr2S3.FeS:  Daubreelite  ;  black.  Ni2S3.NiS.      Berychite. 

In  these  compounds,  as  in  the  spinels,  one  metal  may  replace 
another  without  reference  to  atomic  weight.  If  any  one  molecule 
he  considered,  it  of  course  possesses  a  definite  formula,  such  as 
Co2S3.CoS.  But  the  mineral  named  nickel-linnceite  contains  some 
Ni2S3.NiS  ;  or,  perhaps,  CoJ33.NiS,  along  with  the  former.  The 
atomic  ratio  of  metal  to  sulphur  is  a  constant  one,  but  as  these 
bodies  have  the  same  crystalline  form,  and  as  their  molecules 
occupy  approximately  the  same  volume,  they  can  replace  one 
another  in  any  crystal.  The  usual  way  of  denoting  such  replace- 
ment in  any  proportion  is  to  write  the  formula,  for  example,  of 
nickel-linncBite,  thus:  (Co,Ni)3S4. 

*   Wien.  Akad.  Ser.  (2),  81,  531  ;  Monatsh.  f.  Chcm.,  2,  266. 


OF   CHROMIUM,  IRON,  MANGANESE,   COBALT,  AND   NICKEL.      257 

The  same  peculiarity  is  noticeable  in  the  spinels,  where  alu- 
minium, chromium,  iron,  and  manganese  may  replace  each  other 
as  sesquibxides,  and  beryllium,  magnesium,  zinc,  &c.,  as  monoxides. 
This  will  be  again  referred  to  in  treating  of  the  silicates. 

The  double  sulphides  which  have  been  prepared  artificially 
have  been  obtained  by  passing  hydrogen  sulphide  over  a  heated 
mixture  of  the  hydrates  of  the  respective  metals  ;  thus,  a  mixture 
of  chromic  hydrate  and  zinc  hydrate  thus  treated,  gives  a  mass 
which,  when  boiled  with  hydrochloric  acid,  leaves  a  dark  brown 
powder  of  the  formula  Cr2S3.ZnS. 

More  complex  sulphides  of  iron  are  found  native,  and  are  generally 
termed  magnetic  pyrites.  They  have  the  formula?  FeJ33.3MS, 
Fe2S3.4MS,  Fe2S3.5MS,  and  Fe2S3.6MS,  M  representing  iron, 
cobalt,  or  nickel.  They  form  yellow  crystals  with  metallic  lustre, 
Copper  pyrites,  barnhardiite,  and  chalcopyrrhotite  are  similar 
bodies,  containing  copper,  and  have  respectively  the  formulas 
Fe2S3.Cu,S,  Fe,S3.2Cu.,S,  and  Fe,S3.2CuS.FeS.  Purple  copper  ore 
is  a  similar  compound  of  uncertain  formula.  By  fusing  iron  with 
sulphur  and  potassium  carbonate,  purple-brown  needles,  of  the 
formula  KFeS2,  are  formed.  By  ignition  in  hydrogen  it  yields 
2FeS.K2S. 

(/.)  Compounds  with  halides. — These  bodies,  as  usual,  are 
formed  either  by  evaporating  or  heating  an  aqueous  solution  of  the 
trichlorides,  or  by  heating  a  mixture  of  chloride  and  hydrate. 

The  following  have  been  prepared  : — 

Cr203.8CrCl3.24H_,0. 
Cr.2O3.4CrCl3.8H.2O,  and  3H.,Q. 
CroO3.2CrCl3.2H.2O. 
Cr2O3.CrCl3  3H.O. 

The  corresponding  compounds  of  iron  are  not  so  definite. 
Weak  solutions  of  ferric  chloride,  when  heated,  give  1,  soluble 
ferric  hydrate  and  hydrogen  chloride,  which  recombine  slowly  on 
cooling. 

2.  From  stronger  solutions  mixtures  of  oxy chlorides  separate. 

3.  At  high  temperatures  the  ferric  hydrate  loses  water,  and 
ferric  oxide  is  deposited. 

Dark  red  plates,  of  the  formula  9Fe3O3.FeCl3,  separate  from  a 
strong  solution  of  ferric  hydrate  in  ferric  chloride  on  evaporation 
in  vacuo. 

Oxychlorides  are  also  produced  when  solutions  of  ferrous 
chloride  are  exposed  to  air. 

Oxychlorides  of  manganese,  cobalt,  and  nickel  are  unknown. 

s 


258      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES 

III.  Dioxides  and  disulphides. 

List.         Chromium.      Iron.      Manganese.          Cobalt.        Nickel. 
Oxygen....      CrO2.  MnO2.  (CoO2).*       (NiO2).* 

Sulphur . . .  FeS2.  NiS2. 

Sources. — Manganese  dioxide,  or  pyrolusiie  (from  7rt>/>,  fire, 
and  Xveti/,  to  loose,  refeiring  to  its  action  in  removing  the  green 
and  brown  tints  of  glass  coloured  by  iron,  owing  to  the  comple- 
mentary action  of  its  purple  colour),  is  one  of  the  chief  ores  of 
manganese.  It  is  an  iron-black  or  grey  mineral,  very  hard,  and 
somewhat  brittle,  with  fibrous  texture.  It  is  largely  employed  for 
making  chlorine. 

Nodules  containing  manganese  dioxide  are  of  common  occur- 
rence on  the  sea-bottom  ;  they  have  been  dredged  from  the  bed  of 
the  Pacific  and  Atlantic  Oceans,  and  are  found  in  the  Firth  of 
Clyde. 

Iron  pyrites  or  mundic,  FeS2,  is  a  golden-yellow  mineral 
crystallising  in  cubes.  It  is  very  hard  and  brittle,  and  was 
formerly  used  as  a  m-eans  of  striking  fire,  whence  its  name. 
Marcasite  is  a  whitish  mineral  with  metallic  lustre,  of  the  same 
formula,  crystallising  in  the  trimetric  system.  Both  of  these 
minerals  occur  in  slate,  coal,  shale,  &c.  They  oxidise  on  exposure 
to  moist  air,  and  furnish  the  sulphuric  acid  necessary  for  alum  in 
alum  shale.  They  are  used  as  a  source  of  sulphur. 

Preparation. — 1.  By  direct  union. — Hydrated  chromium 
sesquioxide,  Cr2O3.?/H2O,  heated  in  air  to  200°,  is  oxidised  to  the 
hydrated  dioxide,  CrO2.H2O  ;  the  hydrated  compound  is  dried  at 
253°.  Iron  and  sulphur  combine  below  redness  to  form  FeS2 ;  and 
lower  sulphides  of  iron  unite  with  sulphur  when  gently  heated  in 
a  current  of  hydrogen  sulphide. 

2.  By  heating  a  compound. — The  hydrated  dioxides  can  be 
dried   at  200 — 250°,  yielding  the  dioxides.       Chromium  nitrate, 
when  heated,  yields  the  dioxide,  and  manganese  dioxide  is  produced 
by  heating  manganous  nitrate,  or  manganous  carbonate  and  potas- 
sium chlorate.     The  oxygen  is  derived  from  the  nitric  anhydride, 
or  from  the  potassium  chlorate. 

3.  By  double    decomposition. — Oxides   of   iron,  heated   in 
hydrogen  sulphide  to  above  100°,  are  converted  into  disulphide; 
and   an   alkaline    poly  sulphide    reacts    with   ferrous    chloride   or 
sulphate    at    180°,    yielding    disulphide.      Nickel    disulphide    is 

*  In  combination,  as  2CoO2.CoO  and  2NiO2.NiO.     See  also  Cobalt-amines. 


OF  CHROMIUM,   IRON,   MANGANESE,    COBALT,   AND   NICKEL.      259 

produced   by  heating  a  mixture  of    nickel   carbonate,  potassium 
carbonate,  and  sulphur  to  dull  redness. 

Properties.— Chromium  dioxide  is  a  black  powder,  giving 
off  oxgen  at  350°.  It  is  insoluble  in  water,  but  soluble  in  acids, 
and  reprecipitated  from  its  solution  as  hydrate  by  ammonia. 
Manganese  dioxide  is  a  black  powder  when  prepared  artificially. 
It  dissolves  in  strong  sulphuric  acid,  yielding  a  yellow  sulphate, 
MnO2.2S03.  On  diluting  this  solution,  the  hydrated  dioxide  is 
precipitated.  Iron  disulphide  when  prepared  artificially  is  a 
black  powder,  or  sometimes  yellow  cubes  like  the  native  form, 
insoluble  in  acids ;  and  nickel  disulphide  is  a  steel-grey  powder. 

Double  compounds,  (a.)  With  water. — Hydrated  chromium 
dioxide  is  produced,  as  before,  mentioned,  by  the  spontaneous  oxida- 
tion of  the  hydrated  sesquioxide  at  200° ;  and  also  by  reducing 
chromium  trioxide  or  its  compounds.  Thus,  by  passing  a  current 
of  nitric  oxide,  NO,  through  a  dilute  solution  of  potassium 
dichromate,  K>Cr2O7,  it  is  deprived  of  part  of  its  oxygen,  and 
gives  a  flocculent  brown  precipitate  of  the  hydrated  dioxide.  The 
reduction  may  be  effected  by  ammonia,  as  when  a  solution  of  am- 
monium dichromate,  (NH4)2Cr2O7.Aq,  is  boiled,  the  oxygen  going 
to  oxidise  the  hydrogen  of  the  ammonia ;  or  by  means  of  a  chromic 
compound,  e.g.,  by  heating  together  a  solution  of  chromium  tri- 
chloride, CrCI3,  with  potassium  dichromate,  K2Cr207  or  K20.2Cr03 ; 
chromium  hydrate  may  be  supposed  to  be  formed  by  the  action  of 
water  on  chromium  trichloride,  thus: — 2CrCl3.Aq  +  3H20  = 
Cr203.Aq  +  GHCl.Aq ;  and  the  hydrate  then  acts  on  the  trioxide 
combined  with  potassium  oxide  in  the  dichromate,  thus : — 
Cr203.Aq  +  Cr03.Aq  =  3Cr02.?iH20.  The  complete  equation  is  : — 
4CrCl3.Aq  +  5H,0  4-  K,O207.Aq  =  2KCl.Aq  +  6OO,.wH20  + 
lOHCl.Aq.  Heat  alone  expels  oxygen  from  chromium  trioxide, 
but  the  resulting  substance  is  said  to  be  3CrO^Cr2O>  Oxalic 
acid,  H2C204,  or  alcohol  may  also  be  used  to  effect  the  reduction. 

It  is  still  a  question  whether  this  body  is  not  a  chromate  of 
chromium,  Cr03.O2O3.  Against  this  view,  it  may  be  stated  that 
while  chromates,  when  distilled  with  sodium  chloride  and  strong 
sulphuric  acid,  give  chromyl  dichloride,  Cr02Cl2  (see  p.  268), 
this  substance  does  not  do  so ;  and  that  it  dissolves  in  acids  as  a 
whole,  and  is  reprecipitated  by  alkalis,  as  it  would  be,  were  it  a 
definite  individual.  Yet,  on  boiling  with  alkalies,  hydrated 
chromium  sesquioxide  is  precipitated,  and  the  trioxide  combines 
with  the  alkali,  forming  a  chromate. 

The  compounds  MnO,.2H,O,  MnO,.H2O,  2MnO,.H2O, 
3MnO,.H2O  and  4MnO2.H2O  are  known.  They  are  all 

s  2 


260       THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES 

brownish-black  or  black  powders.  The  last  of  these  is  produced 
by  treating  Mn3O4  'or  Mn2O3  with  strong  nitric  acid,  whence 
the  conclusion  that  these  bodies  are  compounds  of  Mn02  with 
2MnO  and  MnO  respectively.  The  monohydrate,  MnO2.H2O,  is 
formed  by  the  spontaneous  decomposition  of  a  solution  of  potassium 
permanganate,  KMn04  or  K2O.Mn207,  or  by  the  action  of  chlorine 
on  manganous  carbonate  suspended  in  water.  The  compound 
2MnO2.H2O  is  precipitated  by  addition  of  potassium  hypochlorite 
to  a  manganous  salt  in  presence  of  excess  of  ferric  chloride ;  and 
the  compound  3MnO2.H^O  by  evaporating  a  solution  of  manganous 
bromate.  The  dihydrate,  MnO2.2H,O,  is  precipitated  on  addition 
of  water  to  the  sulphate  Mn02.2S03 ;  the  existence  of  this 
sulphate  appears  to  lend  support  to  the  theory  that  the  dioxide  is 
a  chemical  individual,  and  not  a  manganate  of  manganese, 
MnO3.MnO.  It  need  hardly  be  pointed  out  that  the  molecular 
weights  of  all  these  bodies  are  unknown. 

(6.)  Double  oxides. — Several  manganese  compounds  are 
known,  viz  .— MnO2.MnO,  MnO2.CaO,  2(MnO>).K,O, 
2(MnO2).CaO.  These  substances  are  formed. by  the  action  of 
air  on  (1)  warm  hydrated  manganese  monoxide  precipitated  from 
the  dichloride  MnCl2  by  its  equivalent  of  calcium  hydrate ;  (2)  by 
the  same  process,  twice  the  equivalent  of  lime  being  added, 
thus :— MnCl2.Aq  +  2Ca(OH)2  +  0  -  MnO,.CaO  +  CaCL.Aq 
+  2H20,  and  (3)  by  the  action  of  manganese  dichloride  on  the 
former  compounds,  thus  : — 

2(MnO2.CaO)  +  MnCl2Aq  =  2(MnO2).CaO  +  Mn(OH)2  + 

CaCl2Aq. 

These  bodies  are  all  hydrated,  but  the  amount  of  com- 
bined water  is  unknown.  Their  formation  is  the  principle  of 
"  Weldon's  manganese-recovery  process "  whereby  manganese 
dioxide  which  has  been  used  for  the  manufacture  of  chlorine,  and 
converted  into  dichloride,  is  restored  to  the  state  of  dioxide,  and 
thereby  again  rendered  available  for  preparing  chlorine  (see  p.  75). 
Such  bodies  as  MnCX.CaO  are  termed  manganites.  The  com- 
pound 2(MnOj).K2O  is  a  black  powder;  others  containing  less 
oxide,  e.g.,  12(MnO,).Na2O,  5(MnO2).Na,O,  &c.,  are  produced  by 
heating  manganous  chloride  with  sodium  hydrate  and  sodium 
chloride.* 

Compounds  of  the  formula  5 (MnO2)M"O,  where  M"  stands  for 
calcium,  strontium,  zinc,  or  lead,  may  be  produced  by  heating 

*  Sull.  Soc.  CUm.  (2),  30, 110;  Dingl.  polyt.  Jour.,  129,  51 ;  Chem.  Soc.  J., 
37,  22;  591;  Compt.  rend.,  101,  167;  103,  261. 


OF   CHROMIUM,   IRON,   MANGANESE,   COBALT,   AND    NICKEL.      261 

chlorides  of  these  metals  with  potassium  permanganate.  They 
form  black  crystals.  At  higher  temperatures,  2(MnO2).M"O  and, 
at  still  higher,  MnO2.M"O  are  produced. 

Similar  cobalt  and  nickel  compounds,  2(CoO2).CoO  and 
7CoO2.4CoO  (with  water  of  hydration  from  4H2O  to  H20),  also 
3NiO2.5NiO.9H2O  are  produced  by  adding  sodium  hypochlorite, 
NaCIO,  to  a  mixture  of  the  hydrate  of  cobalt  or  nickel  and  excess 
of  soda.  A  cobalt  compound  of  the  formula 

3(2Co02.3CoO).K20.3H20 

is  produced  by  heating  the  monoxide  with  caustic  potash  in 
presence  of  air.  No  doubt,  double  compounds  with  other  metals 
could  be  prepared. 

(c.)  Oxyhalides.— An  oxjfluoride  of  the  formula  MnO2.MnP4 
or  MnOF2  is  said  to  be  produced  by  adding  manganese  tetra- 
chloride  to  a  boiling  solution  of  potassium  fluoride.  It  is  a  rose- 
coloured  powder,  and  combines  with  potassium  fluoride,  forming  the 
compound  MnOF2.2KF.  The  trifluoride  is  said  to  yield  similar 
double  salts,  e.g.,  Mn2F4O.4KF.  These  bodies  are  produced  by 
treating  potassium  permanganate,  KMn04,  with  aqueous  hydrogen 
fluoride. 

IV.  Trioxides. — (a.)  The  only  trioxides  known  in  the  free  state 
are  chromium  trioxide,  or  chromic  anhydride,  CrO3,  and  man- 
ganese trioxide,  MnO3.  Iron  trioxide  exists  in  combination 
with  potassium  monoxide  in  potassium  ferrate,  and  that  of  man- 
ganese in  potassium  manganate. 

Preparation. — By  double  decomposition. — Chromyl  fluoride 
(see  p.  268),  led  into  a  crucible  slightly  damp  and  loosely  covered 
with  damp  paper,  reacts  with  the  water,  depositing  long  needles 
of  the  trioxide  ;  thus : — 

Cr02F2  +  EZ0  =  CrO3  +  2HF. 

By  the  action  of  sulphuric  acid  on  a  chromate,  a  sulphate  and 
chromic  anhydride  are  formed.  On  pouring  1  volume  of  a  saturated 
solution  of  potassium  dichromate,  K2Cr2O7,  into  If  volumes  of  strong 
sulphuric  acid,  long  needles  of  chromic  anhydride  hydride  deposit  on 
cooling.  They  are  difficult  to  free  from  sulphuric  acid ;  and  the 
present  method  of  preparing  the  trioxide  for  commercial  use  is  by 
adding  to  strontium  chromate  exactly  enough  sulphuric  acid  to 
precipitate  the  strontium  as  sulphate,  to  decant  the  solution  of 
trioxide  from  the  insoluble  sulphate,  and  to  evaporate  to  dryness.* 

Manganese    trioxide   is   obtained   by    dropping   a   solution   of 

*  The  autlior  has  tried  the  process,  but  without  success. 


262       THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES 

potassium  permanganate  in  strong  sulphuric  acid  on  to  sodium 
bicarbonate ;  Mn03  is  liberated,  and  is  carried  on  in  the  solid  state 
by  the  carbon  dioxide. 

Properties. — Chromium  trioxide  forms  a  red  crystalline 
powder,  a  mass  of  loose  woolly  crystals,  or  scarlet  crystals.  It 
melts  at  190°,  and  begins  to  decompose  at  250°,  losing  oxygen.  It 
is  soluble  in  water,,  and  the  solution  contains  chromic  acid, 
Cr03.H20,  or  H2Cr04,*  or  H2Cr207.  Its  compounds  with  other  oxides 
are  called  chromates.  The  blue  solution  obtained  by  shaking  a 
dilute  solution  of  chromium  trioxide  with  hydrogen  dioxide,  and 
extracting  with  ether,  is  said  to  be  a  compound  of  the  formula 
Cr03.H202.  On  evaporation  of  the  ether,  it  remains  as  a  blue  oil.f 

Manganese  trioxide  is  a  reddish,  amorphous,  deliquescent  sub- 
stance, unstable  at  the  ordinary  temperature. 

(6.)  Compounds  with  other  oxides. — Chromates,  ferrates, 
and  manganates.  Of  these  the  chromates  are  the  most  stable,  and 
have  been  best  investigated.  They  may  be  divided  into  four  classes : — 

1.  Basic  chromates;  those  in  which  the  number  of  atoms  of 
oxygen  in  the  base  exceeds  one-third  of  that  in  the  chromic  anhy- 
dride. These  compounds  are  orange,  red,  or  brown  in  colour. 
They  are  produced  by  double  decomposition,  a  solution  of  a  soluble 
chromate,  such  as  potassium  chromate,  K2Cr04,  being  added  to  a 
soluble  salt  of  the  metal ;  in  such  a  case,  un combined  chromic 
anhydride  exists  in  solution;  or  by  digesting  a  chromate,  such  as 
PbCrO4  =  PbO.CrO3with  alkali,  or  with  excess  of  base.  They 
are  as  follows  : — 

Ratio,  3  :  9  :— Cr03.3Bi203.     Ratio,  6  :  9  :— 2CrO3.3Bi2O3. 
„      3:4  :— CrO3.4ZnO,3H2O  :  CrO3.4CuO. 
„      3  :  3  :— CrO3Al2O3 ;    CrO3.Cr.2O3(?)(this  body  is   CrO2)  ;    CrO3.Fe2O3; 

CrO3.3NiO.3H2O;  CrO3.Bi2O3;  CrO3.3CuO;  CrO3.3Hg-O. 
„      6  :  5:— 2CrO3.5NiO.l2H2O.     Ratio,  21  :  9 :— 7CrO:i.3Bi2O3. 
„      3  :  2 :— CrO3.2ZnO.H2O  ;        CrO3.2CdO.H2O  ;        CrO3.2MnO.2H2O  ; 

CrO3.2CoO.2H2O;    CrO3.2NiO.6H2O;    CrO3.2PbO; 

Cr03.2CuO;    CrO3.2HgO ;    CrO3.2Hg-2O ; 

2CrO3.3CuO.K2O.3H2O. 
„      6  :  3  :—  2CrO3.3PbO  ;  2CrO3.Bi2O3;  2CrO3.CuO.2PbO. 

These  compounds  are  orange,  red,  or  brown  powders,  and  are 
insoluble  in  water,  or  nearly  so  ;  they  dissolve  in  acids,  being  con- 
verted into  chromates  containing  a  larger  proportion  of  trioxide 
of  chromium.  The  most  important  of  them  is  the  chromate 
CrO3.2PbO;  it  is  named  "chrome-red  "  or  "  Persian-red."  It  is  pro- 

*   Comptes  rend.,  98,  1581. 
t  Ibid.,  97,  96. 


OF    CHROMIUM,   IRON,   MANGANESE,   COBALT,   AND   NICKEL.      263 

duced  by  addition  of  lead  oxide  to  the  monoplumbic  chromate, 
PbCrO4,  or  CrO.^.PbO  ;  or  with  a  purer  shade  by  heating  that 
body  with  potassium  nitrate;  the  potassium  oxide  withdraws 
chromic  anhydride,  and  on  washing  with  water,  excess  of  potas- 
sium nitrate  and  chromate  are  withdrawn  and  the  basic  chromate 
is  left  as  a  red  powder.  Cloth  on  which  a  precipitate  of  yellow 
PbCrO4  has  been  formed,  may  be  changed  to  a  brown-red  by 
plunging  it  into  a  bath  of  boiling  milk  of  lime  (Ca(OH)2.Aq), 
which  withdraws  half  the  chromic  anhydride.  2CrO3.3PbO 
occurs  in  scarlet  crystals  as  melanochroite  ;  and  2CrO3.CuO.2PbO 
as  a  yellowish-brown  mineral  named  vauquelinite. 

2.  The  second  class  of  chromates  is  often  termed  "neutral." 
This  name  was  originially  applied  to  those  substances  incapable  of 
affecting  the  colour  of  litmus.  But  most  of  these  chromates  are 
insoluble  ;  moreover,  the  typical  "neutral  "  chromate  of  potassium, 
K2Cr04(Cr03.K20)  has  an  alkaline  reaction  and  turns  red  litmus 
blue.  It  is  better  therefore  to  discard  the  misleading  name. 
The  oxygen  of  the  chromic  anhydride  bears  to  that  of  the  base 
the  ratio  3:1.  The  following  is  a  list  :  — 

Ratio  3:1.— 

CrO3.H2O  (chromic  acid)  ;  CrO3.Li2O.2H2O;  CrQ3.Na2O.10H2O  (crystal- 
lised above  30°,  this  body  is  anhydrous)  ;  CrO3.K2O  ;  CrO3.K(NH4)O 
(=KNH4CrO4);  CrO3M:gO.7H2O  ;  CrO3.CaO.4H2O  ;  CrO3.SrO  ; 
CrO3.BaO;  CrO3.Tl2O;  CrO3.PbO;  CrO3.CuO;  CrO3.Ag2O;  CrO3.HgO; 


Of  these,  the  hydrogen,  lithium,  sodium,  potassium,  magnesium, 
calcium,  copper,  and  mercuric  compounds  are  soluble  in  water. 
Hydrogen  chromate,  H2CrO4,  is  produced  by  dissolving  chro- 
mium trioxide  in  water,  and  cooling  with  melting  ice.  It  forms 
small  red  deliquescent  crystals,  which  readily  part  with  water. 
Potassium  chromate,  K,CrO4,  has  a  light-yellow  colour,  and  a 
bitter,  cooling  taste  ;  it  is  exceedingly  poisonous  ;  it  is  insoluble  in 
alcohol,  but  soluble  in  water  (100  grams  of  water  at  15°  dissolve 
48'3  grams  of  chromate).  Lt  melts  at  a  low  red  heat,  and  crystal- 
lises in  double  hexagonal  pyramids.  Strontium  chromate, 
SrCrO4,  is  sparingly  soluble.  It  is  the  one  from  which  chromic 
anhydride  is  now  made  commercially  by  addition  of  sulphuric 
acid.  It  is  found  to  be  the  only  available  chromate  from  which 
the  chromium  trioxide  is  completely  expelled  by  its  equivalent  of 
sulphur  trioxide,  by  the  action  of  sulphuric  acid  ;  hence  its  use. 
Barium  chromate,  BaCrO4,is  an  insoluble  yellow  powder,  used  as 
a  pigment  under  tne  name,  "  yellow  ultramarine."  Lead  chromate, 
PbCrOi,  is  found  native,  as  red  lead-ore  or  croco'isite.  It  crystal- 


264      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

lises  in  monoclinic  prisms.  It  is  a  translucent  yellow  body,  and 
occurs  in  decomposed  granite  or  gneiss.  Prepared  by  addition  of 
potassium  chromate  or  dichromate  to  a  soluble  salt  of  lead,  it  is  a 
yellow  powder,  and  is  known  as  "  chrome-yellow  "  and  used  as  a 
pigment.  It  fuses  to  a  brown  liquid,  and  solidifies  to  a  brown- 
yellow  mass.  It  is  made  use  of  in  estimating  carbon  and  hydrogen 
in  carbon  compounds.  It  is  practically  insoluble  in  acids,  but 
dissolves  easily  in  potassium  hydrate,  forming  chromate  and  plum- 
bite  of  potassium.  Silver  chromate,  Ag2CrO4  is  a  deep-red 
precipitate,  crystalline  in  structure  ;  the  individual  crystals  trans- 
mit green  light. 

3.  Bichromates. — These    bodies    are    often    called    "  acid  " 
chromates,  and  their  solutions  have  an  acid  reaction  with  litmus. 
They  are  produced  by  adding  some  acid,  e.g.,  chromic  acid,  or  more 
often  nitric  acid  to  the  monochromates.     They  are  as  follows : — 

Eatio6:l.  2CrO3.I,i2O;  2CrO3.Na2O.2H2O ;  2CrO3.K2O  ;  2CrO3.(NH4)2O ; 
2Cr03.Ca0.3H20;  2CrO3.BaO ;  2CrO3.TloO ;  2CrO3.PbO ; 
2Cr03.Ag-oO, 

The  most  important  of  these  is  potassium  dichrorc  ate,  or 
"  bichrome,"  which  is  prepared  on  a  manufacturing  scale.  It 
is  produced  by  acidifying  the  monochromate,  K2Cr04,  with  sulph- 
uric acid,  thus:— 2K2O04.Aq  -f  H2S04.Aq  =  K2S04.Aq  + 
K2Cr20-.Aq  +  H20.  It  forms  deep  orange-red  tables  or  prisms.  It 
is  insoluble  in  alcohol,  but  soluble  in  water  (100  grams  dissolve  at 
20°  12'4  grams  of  bichrome) .  It  melts  at  a  dull  red  heat,  and  decom- 
poses at  a  white  heat  into  potassium  chromate,  chromium  sesqui- 
oxide,  and  oxygen.  It  is  affected  by  light,  and  has  the  curious 
property  of  rendering  gelatine  impregnated  with  it  insoluble  in 
water  after  exposure  to  light,  and  it  thus  finds  an  application 
in  photography.  It  is  largely  used  as  an  oxidising  agent,  and  for 
making  chrome-yellow,  &c. 

The  dichromates  are  decomposed  by  much  water,  excepting 
those  of  sodium,  potassium,  and  ammonium. 

The  name  anhydrochromates  is  sometimes  applied  to  these  bodies, 
the  view  being  taken  that  they  are  compounds  of  monochromate 
and  anhydride,  thus  :— K.CrO4.CrO3. 

4.  Polychromates ;  tri-,  tetra-,  &c. 

Eatio9  :2.  3CrO3.2ZnO,  soluble,  crystalline;  3CrO3.2Tl2O. 
Ratio  9:1.  3CrO3.K2O;  3CrO3.(NH4)2O ;  3CrO3.Tl2O. 

These  bodies  are  deep-red  crystals,  formed  on  crystallising  the  dichromates 
from  strong  nitric  acid. 

Ratio  12  :  1. — 4CrO3.K2O,  similarly  prepared.     The  polychromates  decom- 
pose on  treatment  with  much  water. 


FERRATES  AND   MANGANATES.  265 

Ferrates. — Of  these,  only  the  potassium,  sodium,  and  barium 
salts  are  known.  Their  formulas  are  supposed  to  be  Fe03.K20 ; 
Fe03.Na20  ;  and  Fe03.BaO ;  but  the  potassium  and  sodium  salts 
are  stable  only  in  presence  of  a  large  excess  of  alkali,  and  the 
barium  salt  has  not  been  analysed.  The  ratio  of  oxygen  to  iron  in 
the  iron  tri oxide  has  been  determined ;  hence  the  deduction  of 
the  formula,  Fe03. 

Sodium  or  potassium  ferrate  is  formed  by  heating  iron- filings 
and  sodium  or  potassium  nitrate  to  dull  redness ;  by  igniting  iron 
sesquioxide  with  sodium  or  potassium  hydrates  in  an  open  crucible, 
better  with  addition  of  sodium  or  potassium  nitrate ;  by  passing 
chlorine  through  a  very  strong  solution  of  sodium  or  potassium 
hydrates  in  which  ferric  hydrate  is  suspended ;  the  ferrate,  being 
insoluble  in  the  strong  alkali,  is  precipitated  as  a  black  powder ; 
and  by  electrolysing  a  strong  solution  of  potash  or  soda  with  iron 
poles  ;  the  ferrate  crystallises  on  the  positive  pole.  The  produc- 
tion of  ferrate  may  be  shown  as  a  lecture  experiment  by  adding 
a  few  lumps  of  potassium  hydrate  to  some  solution  of  ferric  chloride, 
and  adding  bromine  and  warming. 

The  potassium  ferrate  may  be  dried  on  a  porous  plate ;  it 
cannot  be  filtered  through  paper,  as  it  at  once  loses  oxygen.  It 
forms  a  fine  cherry-red  solution,  but  it  soon  decomposes  with  loss 
of  oxygen.  Barium  ferrate  is  a  purple  precipitate  produced  by 
adding  a  solution  of  barium  hydroxide  to  the  solution  of  potas- 
sium ferrate.  The  ferrates  at  once  lose  oxygen  on  addition  of 
an  acid. 

Manganates. — Of  these,  only  the  sodium,  potassium,  calcium, 
and  barium  salts  are  known.  They  are  prepared  by  heating  man- 
ganese dioxide  with  sodium  or  potassium  hydroxides  or  carbonates  ; 
manganate  and  a  lower  oxide  of  manganese  are  formed  ;  or  nitrate 
or  chlorate  of  calcium  or  barium  with  manganese  dioxide.  The 
yield  may  be  increased  by  adding  sodium  or  potassium  nitrate  to 
the  hydroxides.  On  treatment  with  cold  water,  they  form  a  deep 
green  solution,  and  when  it  is  evaporated  in  a  vacuum,  crystals 
are  deposited.  These  crystals  have  the  formula  KaMnOj  = 
MnO3.K2O;  the  barium,  calcium,  and  sodium  manganates  are 
supposed  to  have  similar  formulae.  On  leaving  a  strong  solution 
of. potassium  manganate  exposed  to  air,  crystals  of  dimanganate 
have  been  formed,  2MnO3.K2O.H2O,  the  carbon  dioxide  of  the  air 
having  withdrawn  half  the  potash. 

Potassium  manganate  is  stable  only  in  presence  of  excess  of 
alkali,  and  is  decomposed  by  pure  water  with  formation  of  per- 
manganate and  dioxide,  thus  : — 


266      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND  TELLURIDES. 

3(Mn03.K30)  +  2H20  +  Aq  =  Mn207.K2O.Aq  +  4KOH.Aq  + 

MnO2.nH2O. 

Owing  to  this  change  of  colour  from  green  to  purple,  the  old 
name  for  potassium  manganate  was  "  mineral  chameleon." 

Manganate  of  barium  is  known  as  "  baryta-green."  Potassium 
manganate  having  been  produced  by  gradually  adding  manganese 
dioxide  to  a  fused  mixture  of  two  parts  of  potassium  hydrate  and  one 
part  of  potassium  nitrate,  the  cooled  mass  is  treated  with  water 
and  filtered.  On  addition  of  barium  nitrate  to  the  nitrate,  a  violet 
precipitate  of  barium  manganate  is  produced,  which  is  heated  to 
redness  with  solid  barium  hydrate  till  it  assumes  a  bright-green 
colour.  It  is  then  treated  with  water  to  remove  barium  hydrate. 
The  green  colour  is  in  all  cases  probably  due  to  basic  man- 
ganates. 

Perchromates  and  permanganates. — These  bodies  are  com- 
pounds of  oxides  with  the  heptoxides  of  chromium  or  manganese, 
Cr207,  or  Mn207.  Those  of  chromium  are  very  unstable,  if,  indeed, 
they  are  capable  of  existence.  If  hydrogen  dioxide,  H202,  be 
added  to  a  solution  of  chromic  acid,  or  of  potassium  chromate  and 
sulphuric  acid,  a  dark- brown  colour  is  produced.  On  shaking  the 
solution  with  ether,  the  upper  layer  of  ether  has  a  fine  blue  colour; 
on  evaporation  at  — 20°,  a  deep  indigo-blue  oily  liquid  is  left;  this 
is  possibly  perchromic  anhydride,  or  chromium  heptoxide,  Cr207, 
but  is  also  said  to  be  a  compound  of  the  formula  Cr03.H202. 
Its  salts  are  unknown.  This  reaction  affords  a  very  delicate 
test  both  for  chromium  trioxide  and  for  hydrogen  dioxide  (sec 
p.  197). 

Potassium  permanganate,  Mn»O7.K,O,  or  KMnO4,  is  pro- 
duced by  acidifying  potassium  manganate.  It  may  be  supposed 
that  the  manganic  acid,  Mn03.H2O,  decomposes  at  the  moment  of 
its  liberation,  yielding  manganese  dioxide  and  permanganic  acid, 
thus:— 3Mn03.H2O.Aq  =  Mn207.H2O.Aq  +  MnO2.?/H2O.  The  same 
change  is  produced  by  boiling  a  solution  of  potassium  manganate, 
or  by  treating  sodium  manganate  with  magnesium  sulphate,  thus  : — 
3(Mn03.Na2O)Aq  +  2(S03.MgO)Aq  +  2H20  -.  Mn2O7.Na2O.Aq  + 
2(S03.Na20)Aq  +  2(MgO.H2O)  +  MnO2.wH2O;  magnesium  man- 
ganate being  unstable.  Manganate  may  also  be  converted  into 
permanganate  without  separation  of  dioxide  by  means  of  chlorine, 
thus:— 2(Mn03.K20)Aq  +  (7/2  =  2KCl.Aq  +  Mn207.K2O.Aq. 

The  following  permanganates  are  known : — 

Mn2O7.H2O.Aq,   or    HMn04.Aq;     Mn2O7.K2O,   or   KMnO4 ; 
NH4MnO4;  Ba(MnO4)2;  Pb(MnO4)2;  and  AgMnO4. 


PERMANGANATES.  267 

The  barium  salt  is  made  by  the  action  of  carbon  dioxide  on 
barium  manganate ;  and  from  it  the  free  acid,  HMnO4,  may  be 
separated  by  addition  of  monohydrated  sulphuric  acid,  H2SO4.H2O. 
It  forms  a  greenish -yellow  solntion,  and  deposits  slowly  a  dark, 
reddish-brown  liquid,  not  solidifying  at  — 20°;  it  is  said  to  be 
manganese  heptoxide,  or  permanganic  anhydride,  Mn207.  It  is 
non- volatile.*  This  liquid  dissolves  in  strong  sulphuric  acid  with 
a  yellow-green  colour ;  it  explodes  when  strongly  heated.  The 
yellow-green  solution  contains  (MnO3)2S04.  On  adding  water  the 
colour  changes  to  violet — that  of  permanganic  acid. 

The  silver  and  lead  salts  are  formed  br  adding  soluble  salts 
of  silver  or  lead  to  potassium  permanganate.  They  are  dark- 
coloured  precipitates.  The  ammonium  salt  is  made  by  mixing 
the  silver  salt  with  ammonium  chloride.  Potassium  permanganate, 
with  excess  of  potassium  hydrate,  turns  green  with  formation 
of  manganate,  oxygen  being  evolved,  thus : — 2KMn04.Aq  + 
2KOH.Aq  =  2K2MnO4.Aq  +  H20  +  0. 

Potassium  permanganate  forms  dark-red,  almost  black,  crystals, 
with  greenish  reflection  ;  its  solution  is  sold  as  a  disinfectant  under 
the  name  of  "  Condy's  fluid,"  and  has  a  splendid  purple  colour. 
The  dichromate  and  permanganate  of  potassium  are  used  as  means 
of  oxidising  substances  in  presence  of  water.  Bichrome  does  not 
readily  part  with  its  oxygen,  even  to  an  easily  oxidisable  body, 
unless  an  acid  be  present ;  when  it  does,  chromium  dioxide  is  pro- 
duced. Thus  : — 

2Cr03.K2O.Aq  +  H20  =  2CrO2.nH2O  +  2KOH.Aq  +  20, 
Potassium  permanganate  acts  similarly,  thus : — 

Mn207.K2O.Aq  +  H20  =  2MnO2.^H2O  4-  2KOH.Aq  +  30. 

In  presence  of  an  acid  (usually  sulphuric  acid)  a  salt  of  chromium 
or  manganese  is  produced,  thus  : — 2Cr03  =  Cr203  +  30  ;  and 
Cr203  +  3H2S04  =  O2(S04)3  +  3H2O.  AlsoMn2O7  =  2MnO  + 
5O  ;  and  MnO  +  H3S04  =  HnSO4  +  H20.  The  complete  equa- 
tions are : — 

K2O207.Aq  +  4H2S04  =  K2S04.Aq  +  O2(S04)3.Aq  +  4H20  +  30; 
and  2KMn04.Aq  +  3H2S04.Aq  =  K2S04.Aq  +  2MnS04.Aq 
+  3H20  +  5O. 

The  oxygen,  being  in  the  nascent  or  atomic  state,  is  available  for 
oxidation  of  compounds  of  carbon,  &c. 

*  SeeChem.  Soc.,  53,  175. 


268      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

Compounds  of  oxides  with  halides.—  These  are  as  fol- 
low: —  Cr02Cl2,  chromyl  dichloride;  Cr02F2,  chromyl  difluoride,  and, 
possibly,  Mn02Cl2,maiiganyl  chloride.  They  are  formed  by  distilling 
a  mixture  of  sodium  chloride  or  fluoride,  potassium  dichromate  or 
permanganate,  and  strong  sulphuric  acid.  The  reaction  takes 
place  between  the  liberated  chromium  trioxide  or  manganese 
heptoxide  and  the  hydrogen  halide,  the  sulphuric  acid  combining 
with  the  water  produced,  which  would  otherwise  decompose  the 
chromyl  or  manganyl  halide,  thus  :  — 

Cr03  +  2HC1  +  H2S04  =  Cr02Cl2  +  H2S04.H20. 

Chromyl  dichloride  may  indeed  be  obtained  by  the  direct  action 
of  dry  hydrogen  chloride  on  pure  chromium  trioxide.  Hydrogen 
bromide  and  iodide  are  decomposed  with  liberation  of  bromine  or 
iodine.  Chromyl  chloride  is  a  deep-red  liquid,  closely  resembling 
bromine  in  appearance  ;  it  boils  at  118°,  and  gives  a  deep-red 
vapour.  It  mixes  in  all  proportions  with  carbon  disulphide  and 
with  chloroform.  The  manganese  compound  is  said  to  be  a  purple 
vapour,  condensing  at  a  very  low  temperature  ;  but  it  requires  re- 
investigation.  Chromyl  fluoride  may  be  made  by  a  similar  pro- 
cess. Chromyl  chloride  reacts  with  water,  forming  chromium 
trioxide  or  chromic  acid,  thus  :  — 

cl       H-OH  --  fvn^OH       HCI 
C1  ""  H.OH  ~         °2<OH  ""  HCI. 


As  its  vapour-  density  shows  it  to  have  the  formula  Cr02Cl2,  it  is 
concluded  that  chromic  acid  is  analogously  constituted,  and  may 
be  represented  by  the  structural  formula  CrO*(OH)2,  and  chio- 
mates  as  Cr02(OM')2.  It  is  obvious  that  an  intermediate  com- 
pound between  Cr02Cl2  and  Cr02(OM')2  should  exist  of  the 

formula  Cr02<Q,     .     Such   a   body  is  known,  and  is   termed  a 

chloro-chromate.  The  potassium  salt  is  produced  by  saturating  a 
hot  solution  of  dichromate  of  potassium  with  hydrogen  chloride 
and  leaving  it  to  crystallise.  Flat  rectangular  prisms  of  the 

OK 
compound  CrO^Qi     are  deposited  ;  on  treatment  with  water  they 

decompose.  The  mercuric  salt  is  also  known.  Compounds  have 
also  been  prepared  of  the  formulas  2CrO3.KP  and  2CrO3.NH4F  ; 
they  are  produced  by  adding  aqueous  hydrofluoric  acid  to  potas- 
sium or  ammonium  dichromates  ;  they  may  be  constituted  thus  :  — 


OXYCIILOR1DES   OF   CHROMIUM.  269 

On  heating  chromyl  dichloride  to  180 — 190°  in  a  sealed  tube 
chlorine  separates,  and  the  compound  Cr3Cl2Ofi  remains  as  a  black 
powder.  Its  constitution  may  be  thus  represented  : — 

Cl—  CrOi— Cr02— Cr02—  Cl. 

The  corresponding  potassium  salt  is  produced  by  saturating  potas- 
sium chlorochromate  with  ammonia,  and  the  ammonium  salt  by 
saturating    a  solution  of    chromyl  dichloride  in  chloroform  with 
ammonia.     Their  constitutional  formulae  may  be  : — 
KO— Cr02— O02— O02— OK ;  and 

,  (NH4)0-  Cr02— Cr02—  Cr02— 0(NH4). 

Such  constitutional  formulas  will  be  further  referred  to  in  treating 
of  silicates,  phosphates,  and  sulphates. 

No  compounds  of  bromine  or  iodine  analogous  to  chromyl  chlo- 
ride are  known  ;  bromine  or  iodine  are  invariably  liberated.  The 
volatility  of  the  chlorine  compound  serves  to  identify  chlorine  in 
presence  of  bromine  or  iodine  ;  on  distilling  a  mixture  of  halides 
with  bichrome  and  sulphuric  acid,  if  chromium  is  found  in  the 
distillate,  the  presence  of  chlorine  in  the  mixture  is  proved. 

Physical  Properties. — 1.   Weight  of  1  cubic  centimetre. 

MnO,  5-1 ;  CoO,  5-6;  NiO,  5'6;  6'8  (crystallised). 

FeS,  4-8;  MnS,  4'0 ;     NiS,  5'6. 

Cr2O3,  6'2  (crys.);  Fe2O3,  5'3  (native) ;  Mn2O3  (braunite),  4'75;  Co2O3,  4'8. 

Cr.S3, 4-1 ;  Fe2S3,  4'3 ;  Co2S3,  4'8. 

Ni.203,  4-8. 

Cr5O9,  4-0 ;  Fe3O4  5'12  (magnetite')  ;  Mn3O4,  4'85  (native) ;   Co3O4,  6'3. 

Mn02,  4  83 ; 

MnS2,  3  46;  FeS2,  5-04  (pyrites};  4'8  (marcasite) . 

Cr03,  2-8. 

Heats  of  formation. 

Cr203  +  30  =  2Cr03  +  143K.  Mn  +   O  +  2H2O  =  Mn(OH2) 

+  948K. 
Fe  +  O  +  H2O  =  Fe(OH)2  +  683K.        Mn  +  2O  +  H2O  =  MnO2.H2O 

+  1164K. 
2Fe  +  30  +  3H2O  =  Fe(OH)3  +  1912K.  Mn  +  S  +  »F2O  =  MnS.wHoO 

+  444K. 
3Fe  +  40  =  Fe304  +  2647K.  Co  +  O  +  H2O  =  Co  (OH).,  + 

634K. 

Fe  +  S  +  »H2O  =  FeS.«H2O  +  23  3K. 

2Co(OH)2   +    O    +  H2O  =  Co2O3.3H2O    Co  +  S  +  wH2O   =   CoS.wHnO 
+  223K  +  197K. 

Ni  +  O  +  H2O  =  Ni(OH),,  + 

608K. 

2Ni(OH)2   +    O  +  H2O  =  Ni203.3H20     Ni  +  S  +  wH2O  = 
+  13K.  +  174K. 


270 


CHAPTER  XX. 

OXIDES,  SULPHIDES,  SELENIDES,  AND  TELLURIPES  OF  ELEMENTS  OF  THE 
CARBON  GROUP  ;  FORMIC  AND  OXALIC  ACIDS  ;  CARBONATES,  TITANATES, 
ZIRCONATES,  AND  THORATES  ;  SULPHOCARBONATES  AND  OXYSULPHO- 
CARBONATES,  OXYHALIDES,  AND  SULPHOHAL1DES. 

Oxides,    Selenides,    and    Tellurides    of    Carbon, 
Titanium,  Zirconium,  Cerium,  and  Thorium. 

This  group  gives  representatives  of  monoxides,  sesquioxides, 
dioxides,  and  peroxides.  The  monoxides  show  little  tendency 
towards  combination;  the  dioxides  form  compounds  with  the 
oxides  of  other  elements,  which  are  named  carbonates,  titanates, 
and  zirconates.  Some  similar  compounds  of  the  sulphides  have 
also  been  prepared. 

Carbon.  Titanium.  Zirconium. 

Oxygen....      CO;  CO2.       TiO;*  Ti2O3;  TiO2;TiO3.   ZrO2;  Zr2O5. 
Sulphur...      CS;  CS2.        TiS;  Ti2S3;  TiS2.  ZrS2P 

Cerium.  Thorium. 

Oxygen Ce2O3;  CeO2 ;  CeO;j.          ThO2;  Th2O7. 

Sulphur Ce2S3 ;  ThS2. 

1.  Monoxides  and  monosulphides  (selenides  and  tellurides 
have  not  been  prepared). 

Sources. — Carbon  monoxide  is  produced  by  the  decay  of 
organic  matter,  and  by  the  incomplete  combustion  of  fuel. 

Preparation.— By  direct  union. — Carbon  is  said  to  combine 
with  oxygen  to  form  monoxide ;  it  appears  more  likely  that  the 
dioxide  is  first  formed,  and  by  its  contact  with  red-hot  carbon  is 
converted  into  monoxide,  thus  C02  +  C  =  2GO. 

2.  By  replacement. — Steam,  led  over  white-hot  carbon,  yields 
a  mixture  of  hydrogen  and  carbon  monoxide.     This  mixture  is  well- 
adapted  for  heating  purposes,  and  is  commercially  termed  "  water- 
gas."     It  is  frequently  employed  in  driving  gas-engines.     Carbon 

*  As  hydrate,  Ti(OH)2. 


CARBON   MONOXIDE.  271 


withdraws  oxygen  from  sodium  sulphate,  NaaSO^  forming  mon- 
oxide and  sodium  sulphide.  Carbon  withdraws  oxygen  from 
many  oxides,  carbon  monoxide  being  formed. 

3.  By  reduction.  —  Zinc   or   copper  withdraws   oxygen  from 
carbon  dioxide,  producing.  monoxide  ;   heating  a  mixture  of  mag- 
nesium carbonate  and  zinc  dust  is   an  available  method  of  pre- 
paration.     Carbon   monosulphide   is  deposited   from   carbon   di- 
sulphide,  after  long  exposure  to  light  ;    and  titanium  monosulphide 
is  produced  by  the  action  of  hydrogen  on  the  red-hot  disulphide. 

4.  By  decomposition  of   a    compound.  —  The  oxide  C203 
appears  to  be  incapable  of  existence,  but  oxalic  acid,  C2O4H2,  may 
be  viewed  as  its  compound  with  water.     On  depriving  oxalic  acid 
of  water  by  the  action  of  concentrated  sulphuric  acid,  a  mixture  of 
carbon  monoxide  and  dioxide  is  evolved,  thus  — 

C2O4H2  +  H2S04  =  CO  +  C02  +  H2S04.H20. 

Similarly,  if  the  elements  of  water  are  withdrawn  from  formic  acid, 
C02H2,  by  strong  sulphuric  acid,  carbon  monoxide  is  produced. 
This  is  by  far  the  most  convenient,  though  not  the  cheapest,  method 
of  preparation,  and  yields  perfectly  pure  monoxide. 

5.  By  double  decomposition.  —  Hydrocyanic  acid,  HCN"  (see 
p.  559),  liberated  in  presence  of  fairly  strong  sulphuric  acid,  takes 
up  water,  forming  carbon  monoxide,  and  ammonia  which  combines 
with  the  sulphuric  acid,  thus  — 

HCN  +  H3S04.H20  =  CO  +  (NH4)HSO4. 

The  hydrocyanic  acid  is  conveniently  produced  from  potassium 
ferrocyanide. 

Properties.  —  Carbon  monoxide  is  a  colourless  gas  at  ordi- 
nary temperatures;  it  condenses  to  a  liquid  at  —190°,  and  the 
white  solid  produced,  by  its  evaporation  melts  at  —199°.  Its  critical 
temperature  is  about  —  139'5°;  and  its  critical  pressure  is  35'5 
atmospheres.  It  is  soluble  in  alcohol  ;  100  volumes  dissolve  about 
20  volumes  ;  but  it  is  very  sparingly  soluble  in  water,  100  volumes 
dissolving  only  3  volumes  of  the  gas.  It  has  a  faint  smell,  but  no 
taste.  It  is  poisonous,  forming  a  compound  with  the  haemoglobin 
of  the  blood  which  gives  a  spectrum  closely  resembling  that  of 
oxyhasmoglobin  ;  but,  while  the  latter  is  at  once  altered  by  ammo- 
nium sulphide,  the  spectrum  due  to  carbon  monoxide  lasts  after 
such  treatment  for  several  days.  It  is  absorbed  by  potassium 
(see  below),  and  by  compounds  of  silver,  and  gold  ;  also  by  cuprous 
chloride.  When  left  long  in  contact  with  potassium  or  sodium 
hydroxide  it  combines,  forming  formate  of  potassium  or  sodium. 


272      THE   OXIDES,   SULPHIDES,   SELEXIDES,  AND  TELLURIDES 

Carbon  monosulphide  is  a  red  powder,  sparingly  soluble  in 
carbon  disulphide  and  in  ether  ;  it  dissolves  in  solution  of  potassium 
hydrate,  and  is  reprecipitated  by  acids  ;  it  decomposes  at  200°  into 
carbon  and  sulphur.  It  is  probably  a  polymeride  of  CS.  Tita- 
nium monosulphide  is  a  black  insoluble  substance,  decomposed 
only  by  fusion  with  alkalis. 

Compounds  with  water.— It  is  sometimes  stated  that  carbon 
monoxide  is  the  anhydride  of  formic  acid,  C02H2,  and  if  their 
formulae  alone  be  considered  such  might  be  the  case.  But  there 

0 

can  be  no  doubt  that  formic  acid  has  the  constitution  H — C — OH, 
and  that  it  is  partly  a  carbide  of  hydrogen,  and  is  derived  from 
tetrad  carbon.  The  true  acid  derived  from  carbon  monoxide  is 
unknown  ;  its  formula  should  be  HO — C — OH.  Hence  carbon 
monoxide  reacts  slowly  with  potassium  hydroxide,  a  molecular  re- 
arrangement being  effected  in  order  to  produce  potassium  formate, 
O 

H — C — OK.  The  explosive  grey  compound  produced  by  direct 
combination  of  carbon  monoxide  with  potassium,  which  has  the 
formula  K«CW0W  is  probably  also  partly  a  carbide  of  potassium. 

Ti(OH)2  is  said  to  be  produced  by  the  action  of  sodium  amalgam 
on  the  tetrachloride,  TiCl4,  in  presence  of  water.  Titanium  di- 
chloride,  TiCl2,  decomposes  water,  giving  a  mixture  of  trichloride 
and  sesquioxide.  No  compounds  of  these  monoxides  with  oxides 
or  sulphides  are  known. 

Compounds  with  chlorides. — Carbon  monoxide  combines 
directly  with  platiiious  chloride,  to  form  the  body  PtCL  2CO, 
with  platinic  chloride  to  form  PtCl4.3CO,  and  with  cuprous 
chloride  to  form  Cu2Cl2.2CO.  These  are  insoluble  crystalline 
compounds.  The  last  is  formed  when  carbon  monoxide  is  shaken 
with  a  solution  of  cuprous  chloride  in  hydrochloric  acid,  and  is 
used  as  a  means  of  separating  carbon  monoxide  from  other  gases 
with  which  it  may  be  mixed. 

A  compound  of  the  formula  TiO.TiCl3  is  also  known ;  it  is 
produced  by  the  action  of  oxygen  on  titanium  tetrachloride,  TiCl4, 
at  a  red  heat.  2CeO.CeCl2  is  formed  by  the  action  of  steam  and 
nitrogen  ou  a  mixture  of  cerium  and  sodium  chlorides ;  it  forms 
silvery  scales. 

II.  Sesquioxides  and  sssquisulphides. — Carbon  sesqui- 
oxide is  unknown;  its  compound  with  water  is  oxalic  acid. 
Carbon  sesquisulphide  is  said  to  be  produced  by  the  action  of 
sodium  amalgam  on  the  disulphide ;  it  is  a  red-brown  powder. 


OF   CARBON,   TITANIUM,   ZIRCONIUM,    CERIUM,   AND   THORIUM.    273 

Titanium  sesquioxide  is  formed  when  the  dioxide  is  heated  in 
hydrogen,  or  during  the  preparation  of  the  trichloride  (see  page  145) 
due  to  the  action  of  air.  It  forms  copper-coloured  crystals,  and 
has  the  same  crystalline  form  as  specular  iron,  Pe2O3.  Titanium 
sesquisulphide  is  produced  by  the  action  of  a  moist  mixture  of 
hydrogen  sulphide  and  carbon  disulphide  on  the  dioxide,  TiO2,  at 
a  bright  red  heat.  It  is  a  black  powder.  Cerium  sesquioxide  is 
produced  by  heating  the  oxalate  in  a  current  of  hydrogen.  It  is  a 
grey  solid,  reacting  with  acids  forming  salts.  The  sesqui- 
sulphide,* produced  by  the  action  of  dry  hydrogen  sulphide  on 
red  hot  cerium  dioxide,  or  by  passing  that  gas  over  a  fused 
mixture  of  cerium  trichloride  and  sodium  chloride,  is  a  crystalline 
vermilion  or  black  compound,  according  to  the  temperature.  It 
is  slowly  decomposed  by  warm  water.  Similar  compounds  of 
zirconium  and  thorium  have  not  been  prepared. 

Compounds  with  water. — Oxalic  acid  may  be  regarded  as 
the  hydrate  of  the  unknown  carbon  sesquioxide.  It  has  the 
formula  C204H2,  and  not  C02H,  as  can  be  shown  by  the  following 
synthesis  : — Ethylene  is  known  to  possess  the  formula  Q-Jli  from 
its  vapour-density.  On  bringing  ethylene  and  bromine  together, 
direct  addition  takes  place,  and  ethylene  dibromide,  C2H4Br2,  is 
formed.  This  body,  on  treatment  with  silver  hydroxide,  exchanges 
bromine  for  hydroxyl,  thus :— C2H4Br2  +  2AgOH  =  C2H4(OH)2 
+  2AgBr.  Glycol,  as  the  substance  C2H4(OH)2  is  named,  on 
oxidation  yields  oxalic  acid,  thus  :— C2H4(OH)3  +  4O  =  C202(OH)2 
-f  2H20.  It  is  therefore  concluded  that  oxalic  acid  contains 
two  atoms  of  carbon.  Its  constitutional  formula  is  written 
0=C— OH 

,  and  it  would  thus  appear  that  the  atom  of  carbon  is 
0=C— OH 

here  capable  of  combining  with  four  monads,  and  is  a  tetrad. 
As  carbon  tetrachloride  possesses  the  formula  CC14,  and  carbon 
hexachloride  is  C2C16  (see  p.  155),  it  is  seen  that  two  atoms 
of  carbon  possess  the  property  of  combining  with  each  other. 
Now,  in  contrasting  this  with  the  behaviour  of  members  of 
the  previous  group,  such  as  iron,  it  must  be  remembered  that 
ferric  chloride  possesses  the  formula  FeCl3,  as  shown  by  its 
vapour- density  at  high  temperatures.  At  low  temperatures,  its 
formula  is  Fe2Cl6,  and  it  has  been  supposed  that  iron  at  low  tem- 
peratures, like  carbon  under  almost  all  circumstances,  is  a  tetrad. 
The  hydroxide,  Pe2O3.H2O,  has  probably  a  high  molecular  weight, 
for  the  sesquioxide,  Fe2O3,  has  the  power  of  combining  with  a 

*  Comptes  rend.,  100,  1461. 

T 


274      THE   OXIDES,   SULPHIDES,    SELENIDES,   AND    TELLURIDES. 

large  number  of  molecules  of  other  oxides,  and  presumably  com- 
bines with,  itself  to  form  considerable  molecular  aggregates.  But 
ignoring  this,  the  formula  of  this  hydroxide  may  be  O— Fe — OK, 
or  it  may  have  a  constitution  analogous  to  that  of  oxalic  acid,  viz., 

jjQ^>Fe — ^e<\QH'    in   which   case   the   atoms   of    iron    would 

be  tetrad.  At  present  there  is  no  means  of  deciding  the  point, 
though  the  opinion  of  chemists  favours  the  triad  nature  of  the 
atom  of  iron. 

The  study  of  oxalic  acid  and  its  compounds  belongs  to  the 
domain  of  Organic  Chemistry;  and  these  are  so  numerous  that 
their  formation  and  relationship  would  occupy  too  large  a  space  in 
such  a  book  as  this. 

Titanium  tetrachloride  on  treatment  with  metallic  copper  or 
silver  in  a  state  of  fine  division  yields  the  hexachloride,  Ti2Cl6 ; 
and  on  addition  of  an  alkali,  to  its  solution  in  water,  a  brown  pre- 
cipitate of  the  hydroxide,  Ti2O3.3H2O,  is  produced.  It  is  soluble  in 
acids  giving  violet  salts. 

Hydrated  cerium  sesquioxide  is  formed  by  addition  of  an 
alkali  to  a  solution  of  the  trichloride.  It  rapidly  oxidises  on 
exposure  to  air. 

Compounds  with  halides. — On  treating  trichloride  of  titanium 
with  a  little  water,  the  body  Ti202Cl2  is  produced.  Supposing 
it  to  be  constituted  like  oxalic  acid,  its  formula  would  be 

Cl^Ti — Ti<^£j,.     It  is  also  formed  by  the  action  of  a  mixture  of 

hydrogen  and  titanium  tetrachloride  on  the  red  hot  dioxide,  thus  : — 
TiCli  +  H2  +  TiO2  =  2HC1  +  Ti2O2Cl2.  It  forms  reddish- 
brown  laminae. 

A  compound  of  the  formula  CeiO3.Ce>Cl6  is  produced  by  the 
action  of  sodium  hydroxide,  and  subsequently  of  water  on  the  tri- 
chloride, or  of  a  mixture  of  steam  and  nitrogen  on  the  trichloride. 
It  is  an  insoluble  dark  purple  powder. 

III.  Dioxides. — Sources. — All  of  these  dioxides,  that  of  cerium 
excepted,  are  found  native.  Carbon  dioxide  occurs  in  air. 
Ordinary  country  air  contains  somewhat  under  4  volumes  per 
10,000  of  air ;  in  cities,  owing  to  its  evolution  from  chimneys  and 
from  respiration,  it  is  present  in  somewhat  higher  amount,  and  in  fogs 
may  amount  to  6  volumes.  It  issues  from  the  ground  in  volcanic 
districts.  The  "  Grotto  del  Cane,"  near  Naples,  is  well  known  in 
this  respect ;  the  gas  in  the  depression  in  the  ground  contains  from 
60  to  70  per  cent,  of  carbon  dioxide.  It  is  a  frequent  constituent  of 


DIOXIDES  OF  CARBON,  TITANIUM,  ZIRCONIUM,  AND  THORIUM.  275 

mineral  waters,  and  is  present  in  small  quantity  in  all  natural 
water,  including  sea- water.  It  is  the  source  from  which  plants  de- 
rive their  carbon,  and  is  produced  by  the  decay  of  all  organic  matter. 
Some  specimens  of  quartz  contain  cavities  filled  with  liquid  carbon 
dioxide.  In  combination  with  other  oxides,  especially  with  lime, 
as  carbonate,  it  forms  a  great  portion  of  the  earth's  crust. 
Titanium  dioxide  seems  native  in  dimetric  prisms,  as  rutile,  in 
granite,  gneiss,  or  mica  slate  ;  also  as  anatase,  in  acute  rhombo- 
hedra  ;  and  as  broolcite  in  trimetric  crystals. — 'Zirconium  dioxide 
occurs  in  combination  with  silica  as  zircon,  or  hyacinth,  ZrO2.SiO2, 
and  as  malacone,  in  some  granites.  Thorium  dioxide  occurs  as 
thorite,  3(ThO2.SiO2).4H3O,  and  is  also  combined  with  niobic  and 
tantalic  pentoxides  in  euxenite. 

Preparation. — In  considering  the  methods  of  preparation  of 
these  compounds  it  must  be  remembered  that  carbon  dioxide  is  a  gas, 
while  the  dioxides  of  the  other  elements  are  non- volatile  solids. 

1.  By  direct  union. — The  elements  all  burn  in  oxygen,  forming 
dioxides,  with  exception  of  cerium.  In  presence  of  excess  of  the 
element,  carbon  forms  monoxide,  and  titanium  forms  sesquioxide. 
Cerium  yields,  not  dioxide,  but  sesquioxide.  Compounds  of  carbon 
also  burn,  giving  carbon  dioxide.  Carbon  unites  with  sulphur  at  a 
red  heat,  forming  disulphide  ;  but  it  does  not  combine  directly  with 
selenium  or  tellurium ;  and  zirconium  and  thorium  also  form 
disulphides  when  heated  in  sulphur  gas.  The  selenides  and  tellurides 
of  the  other  elements  have  not  been  prepared. 

The  combustion  of  carbon  in  oxygen  may  be  shown  by  heating  a  piece  of 
charcoal  to  redness  in  a  Bunsen's  flame,  and  plunging  it  into  oxygen  gas,  as  shown 
in  fig.  33.  The  charcoal  continues  to  burn  brightly,  and  the  product  is  carbon 

FIG.  33. 


T  2 


276      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES 

dioxide.  The  combustion  of  a  diamond  may  also  be  shown,  as  in  fig.  34,  by 
wrapping  up  a  fragment  of  diamond  in  a  small  spiral  of  thin  platinum  wire 
connected  with  two  stout  copper  wires  which  pass  through  an  indiarubber  cork 
closing  the  end  of  a  wide  test-tube.  The  test-tube  is  filled  with  oxygen,  and 
by  means  of  an  electric  current  from  four  Bunsen's  cells,  the  thin  platinum  wire 

FIG.  34. 


is  heated  to  whiteness.  The  diamond  is  thus  raised  to  its  point  of  ignition, 
and  on  discontinuing  the  current  it  continues  to  glow  until  it  is  finally  totally 
consumed.  That  carbon  dioxide  is  the  product  of  combustion  may  be  shown  by 
shaking  the  contents  of  the  tube  with  a  little  baryta-water  (Ba(OH)2.Aq),  when 
a  white  precipitate  of  barium  carbonate,  BaC03,  is  formed.  Another  instructive 


FIG.  35. 


OF   CARBON,   TITANIUM,   CERIUM,   ZIRCONIUM,   AND   THORIUM.     27? 

experiment  is  devised  to  show  that  the  volume  of  carbon  dioxide  produced  by  the 
union  with  carbon  of  a  known  volume  of  oxygen  is  equal  to  that  of  the  oxygen. 
The  oxygen  is  contained  in  the  bulb,  and  confined  over  mercury.  The  carbon 
is  wrapped  in  a  piece  of  platinum  wire,  and,  as  in  the  case  of  the  diamond, 
heated  to  its  point  of  ignition.  The  gas  expands  at  first,  of  course,  owing  to 
its  temperature  being  raised,  but  on  cooling,  the  mercury  in  the  two  limbs  of 
the  U-tube  returns  to  its  original  level,  showing  that  the  volume  of  gas  is  the 
same  after  it  has  been  converted  into  carbon  dioxide.  (See  fig.  35.) 

Carbon  also  withdraws  oxygen  from  its  compounds  with  other 
elements,  combining1  with  it,  a  mixture  of  monoxide  and  dioxide 
being  usually  formed.  Carbon  heated  to  bright  redness  in  steam 
gives  a  mixture  of  monoxide,  dioxide,  and  hydrogen  ("  water-gas  ") 
There  is  little  doubt  that  the  oxides  of  the  other  elements  of  this 
group  could  be  similarly  formed. 

Compounds  of  carbon  with  hydrogen  and  oxygen  also  burn  in 
oxygen  forming  dioxide.  Thus  when  a  candle,  consisting  chiefly  of 
carbon  and  hydrogen,  burns,  both  its  carbon  and  hydrogen  unite 
with  oxygen.  The  union  takes  place  more  rapidly  in  oxygen  gas 
than  in  air,  but  the  total  amount  of  heat  evolved  is  the  same  which- 
ever be  employed.  But  owing  to  the  greater  rapidity  of  combina- 
tion, the  temperature  is  higher  during  combustion  in  oxygen  than 
in  air.  The  oxidation  of  the  blood  of  animals  is  also  a  slow  com- 
bustion, taking  place  in  the  capillary  bloodvessels,  the  oxygen  being 
derived  from  the  inspired  air. 

2.  By  union  of  a  lower  oxide  or  sulphide  with  oxygen 
or  sulphur. — Carbon  monoxide  burns  in  air  or  oxygen  to  form 
dioxide.     A  mixture  of  the  two  gases  explodes  on  passing  a  spark, 
provided  they  are  moist.     No  explosion  takes  places  when  they  are 
dry,  although  combination  occurs  in  the  space  through  which  the 
spark   passes.      Carbon   monoxide    also    withdraws   oxygen  from 
oxides  of  many  other  elements,  such  as  those  of  iron,  copper,  &c., 
to  form  dioxide.     When  heated  to  whiteness  with  steam,  a  portion 
is  converted  into  dioxide.    Titanium  sesquioxide  and  sesquisulphide 
readily  unite  with  oxygen  or  sulphur,  forming  dioxide  or  disul- 
phide. 

3.  By  the  action  of  heat  on  a  compound. — All  carbonates, 
those  of  lithium,  sodium,  potassium,  rubidium,  and  caesium  ex- 
cepted,  lose  carbon  dioxide  when  heated.      Barium  carbonate  re- 
quires a  white  heat ;  strontium  carbonate  a  bright  red  heat,  and 
calcium  carbonate  a  red  heat.     These  carbonates  decompose  more 
readily  if  heated  in  a  cnrrent  of  some  indifferent  gas,  such  as  air  or 
steam.      Compounds  of  the  other  dioxides   have   not   been  thus 
decomposed,  owing  to  the  non-volatility  of    the   dioxides.      But 
the   sulphocarbonates,   like    the   carbonates,   are   decomposed   by 


278      THE    OXIDES,   SULPHIDES,   SELENIDES,  AND  TELLUEIDES 

heat  into  sulphides  and  carbon  disulphide.  Calcium  compounds, 
for  example,  decompose  thus — 

CaCO3  =  CaO  +  C02;  CaCS3  =  CaS  +  G8Z. 

The  dioxides  of  titanium,  zirconium,  cerium,  and  thorium  are 
produced  by  heating  their  hydrates  or  sulphates,  and  that  of  thorium 
by  heating  its  oxalate. 

4.  By  displacement. — This  method,  as  a  rule,  yields  the 
hydrates ;  but  as  carbonic  acid  (the  hydrate  of  carbon  dioxide)  is 
very  unstable,  it  is  produced  thus :  for  example,  a  carbonate, 
treated  with  sulphuric  acid,  yields  a  sulphate,  carbon  dioxide,  and 
water  :— ISTa^COg.Aq  +  H2S04.Aq  =  Na2SO4.Aq  +  C02  +  H20  ; 
or  the  reaction  may  be  thus  written : — C02.Na20  +  S03.H2O  = 
S03.Na20  +C02  +  H20.  There  is  no  tendency  to  form  a  compound 
between  carbon  dioxide  and  sulphur  trioxide. 

In  actual  practice,  carbon  dioxide  is  prepared  on  a  large  scale 
by  burning  carbon  in  air,  or  by  treating  calcium  carbonate  with 
sulphuric  or  hydrochloric  acid.  When  the  last  acid  is  used,  some 
spray  of  hydrogen  chloride  is  apt  to  be  carried  over  with  the  carbon 
dioxide,  hence  it  is  advisable  to  wash  it  by  leading  it  through  a 
solution  of  hydrogen  sodium  carbonate.  If  sulphuric  acidis  employed, 
the  calcium  carbonate  must  be  in  the  state  of  fine  powder,  else  it 
becomes  coated  with  an  insoluble  layer  of  sulphate  which  hinders 
further  action.  It  is  by  this  method  that  carbon  dioxide  is  usually 
made  in  the  manufacture  of  "  aerated  water." 

Cerium  tetrafluoride,  when  heated  in  air,  loses  fluorine,  and 
yields  the  dioxide.  This  is  probably  due  to  the  moisture  in  the 
air,  forming  hydrogen  fluoride,  and  would  come  under  the  next 
heading 

5.  By  double  decomposition. — Carbon  disulphide  has  been 
produced  by  heating  carbon  tetrachloride  to  200°  with  phosphorus 
pentasulphide ;  substituting  selenium  for  sulphur,  a  liquid  was 
produced  containing  about  2  per  cent,  of  diselenide. 

Special  method. — Carbon  dioxide  is  produced  by  the  de- 
composition of  grape-sugar,  CeH^Oe,  under  the  action  of  the  yeast 
ferment  (Saccharomyces  cerevisice),  when  ethyl  alcohol,  C2H5.OH, 
and  carbon  dioxide  are  the  chief  products. 

The  starch  contained  in  grain  is  converted  during  the  process  of  "  malting," 
or  incipient  germination,  during  which  the  grain  is  kept  warm  and  moist  on 
the  "  malting- floors,"  into  grape-sugar,  by  aid  of  the  ferment  diastase,  con- 
tained in  the  grain.  The  growth  is  then  stopped  by  heating  the  malt ;  it  is 
crushed,  and  is  known  as  "grist;"  it  is  transferred  to  the  "mash-tun,"  a 
large  cask  or  vat,  where  it  is  treated  with  warm  water.  The  solution  of  grape- 


OF   CARBON,   TITANIUM,   ZIRCONIUM,   CERIUM,   AND   THORIUM.    279 

sugar  thus  obtained  is  called  the  "  wort ;  "  it  is  mixed  with  yeast,  and  left  to 
ferment,  when  the  change  already  mentioned  takes  place.  The  carbon  dioxide 
fills  the  vat  and  escapes  into  the  air.  The  equation  is — C6H12O6  =  2C2H5.OH 
f  2CO2. 

Properties. — At  the  ordinary  temperature  carbon  dioxide  is  a 
gas.  Its  boiling  point  under  normal  pressure  is  about  —79°.  Its 
melting  point  is  nearly  the  same  as  its  boiling  point ;  it  is  given  as 
—  78*5°,  hence  the  liquid  easily  freezes  by  its  own  evaporation.  It 
may  be  condensed  to  a  liquid  at  a  pressure  of  about  36  atmospheres 
at  10°.  The  gas  is  colourless,  has  a  faint  sweetish  smell  and  taste, 
and  is  much  heavier  than  air,  hence  it  is  best  collected  by  down- 
ward displacement.  Its  great  density  (22,  compared  to  air=14'47) 
permits  of  its  being  poured  from  one  vessel  to  another  without 
much  loss.  Its  density  is  easily  shown  by  pouring  it  into  a  light 
beaker,  suspended  from  the  beam  of  a  balance,  and  counterpoised. 


FIG.  36. 


Carbon  dioxide  supports  the  combustion  of  the  elements  potas- 
sium, sodium,  and  magnesium.  They  deprive  it  of  a  portion  of  its 
oxygen,  forming  oxides  and  carbon  monoxide,  as  well  as  some  free 
carbon  ;  the  oxide  then  unites  with  excess  of  carbon  dioxide,  forming 
a  carbonate.  Carbon  may  also  be  said  to  burn  in  carbon  dioxide,  inas- 
much as  when  the  dioxide  is  led  over  red  hot  carbon,  the  monoxide 
is  formed :  but  because  the  heat  evolved  by  this  reaction  is  com- 


280      THE   OXIDES,    SULPHIDES,    SELENIDES,   AND   TELLURIDES. 

paratively  small,  the  carbon  is  not  thereby  kept  at  its  temperature 
of  incandescence,  and  action  ceases,  unless  a  supply  of  heat  be 
added  from  without.  When  carbon  burns  in  oxygen,  therefore,  the 
whole  of  the  oxygen  is  not  converted  into  carbon  dioxide  ;  the  action 
ceases  when  the  dioxide  formed  bears  a  certain  proportion  to  the 
total  gas  present ;  the  reverse  action  then  tends  to  begin.  Hence 
a  candle,  burning  in  air,  goes  out  when  the  carbon  dioxide  formed 
reaches  a  certain  proportion  of  the  total  gas ;  and  for  the  same 
reason,  an  animal  dies  when  breathing  a  confined  atmosphere,  long 
before  it  has  completely  deprived  it  of  oxygen.  A  man  can  breathe, 
however,  for  some  time  in  an  atmosphere  in  which  a  candle  refuses 
to  burn,  as  was  shown  by  the  late  Dr.  Angus  Smith.  Carbon  di- 
oxide is  decomposed  by  the  green  colouring  matter  of  plants  in 
sunshine ;  the  exact  nature  of  this  decomposition  is  not  known ; 
there  are  grounds  for  supposing  that  it  consists  in  a  reaction 
occurring  between  carbon  dioxide  and  water,  as  follows  : 

COa  +  H20  =  H2CO  +  02. 

The  substance  H2CO  is  named  formic  aldehyde,  and  it  has  been 
recently  shown  to  be  easily  transformable  into  a  kind  of  sugar, 
C6H1206,  named  formose.  There  may  be  some  connection  between 
this  transformation  and  the  formation  of  sugar  in  plants.  The 
carbon  dioxide  is  absorbed  by  the  stomata  or  "  small  mouths  "  in 
the  under  surface  of  the  leaves  of  plants,  and  oxygen  is  evolved. 
This  may  be  experimentally  shown  by  placing  some  blades  of  grass 
in  a  jar  of  water  inverted  over  a  trough.  The  oxygen  gas  collects 
in  the  upper  portion  of  the  jar  during  several  days'  exposure  to 
sunlight,  and  may  be  recognised  by  the  usual  tests. 

Liquid  carbon  dioxide  is  heavier  than  water,  and  does  not  mix 
with  it.  It  is  a  non-conductor  of  electricity.  Above  the  temperature 
30'9°,  the  critical  point  of  carbon  dioxide,  the  gas  cannot  be  made  to 
assume  the  liquid  state  by  compression.  The  solid  dioxide  is  a 
loose  white  powder,  like  snow,  produced  by  allowing  the  liquid  to 
escape  into  a  thin  flannel  bag;  the  liquid  absorbs  heat  during  its 
conversion  into  gas,  and  a  portion  solidifies,  owing  to  its  being 
thus  cooled.  A  mixture  of  solid  carbon  dioxide  with  ether  gives 
a  temperature  of  —100°. 

It  has  been  recently  shown  that  carbon  and  carbonic  oxide  do 
not  unite  with  perfectly  dry  oxygen,  unless  they  be  kept  exposed 
to  a  very  high  temperature.  The  presence  of  water  or  some 
other  compound  containing  hydrogen  being  necessary,  it  is  sup- 
posed that  the  carbon  or  carbonic  oxide  reacts  with  the  water 
liberating  hydrogen,  thus—  CO  +  HZ0  =  002  +  2fl~,  or  C  +  H20 


PROPERTIES   OF   CARBON   DIOXIDE. 


281 


=  CO  +  21Z,  and  that  the  hydrogen  then  unites  with  the  oxygen, 
to  form  water,  which  is  again  acted  on.* 

The  test  for  carbon  dioxide  is  its  combination  with  calcium  or 
barium  oxide,  when  shaken  with  a  solution  of  the  respective  hydr- 
oxide, to  form  carbonate,  in  either  case  a  white  powder,  which 
effervesces  with  acids. 

The  presence  of  carbon  dioxide  in  expired  air  may  be  demonstrated  by  the 
arrangement  shown  in  the  figure  : — 

FIG.  37. 


The  air  entering  the  lungs  passes  through  lime-water  in  the  bottle  on  the 
right  hand  side ;  as  ordinary  air  contains  only  4  volumes  of  carbon  dioxide 
in  10,000,  a  turbidity  is  not  seen  for  some  time.  The  exhaled  air  passes 
through  the  lime-water  in  the  left  hand  bottle  and  soon  turns  it  turbid. 

The  amount  of  carbon  dioxide  in  atmospheric  air  may  be  esti- 
mated comparatively  by  measuring  the  amount  required  to  produce 
incipient  turbidity  in  baryta  water. 

The  little  apparatus  is  shown  in  fig.  38.  The  indiarubber  ball  is  squeezed, 
the  air  escaping  through  the  opening.  The  opening  is  then  closed  with  the 
finger,  and,  on  allowing  the  ball  to  expand,  air  is  drawn  through  the  baryta 

FIG.  38. 


Dixon,  Chem.  Soc.,  49,  94. 


282      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLUKIDES. 

water.  On  removing  the  finger  the  ball  is  again  squeezed  empty,  and  air  is  again 
drawn  through  the  baryta  water.  Having  found  the  number  of  charges 
of  the  ball  which  must  pass  through  the  baryta  water  to  produce  a  turbidity 
with  ordinary  air,  it  may  be  assumed  with  fair  correctness  that  the  normal 
amount  is  present,  viz.,  4  volumes  in  10,000.  On  applying  the  same  test  to 
vitiated  air,  fewer  charges  are  required,  and  the  amount  of  carbon  dioxide  may 
be  calculated  by  simple  proportion. 

Carbon  dioxide  rapidly  combines  with  the  hydroxides  of  sodium 
and  potassium,  as  well  as  with  those  of  calcium  and  barium.  The 
method  of  absorbing  it  from  gaseous  mixtures  is  to  shake  them 
with  a  strong  solution  of  potassium  hydroxide.  It  may  also  easily 
be  absorbed  by  passing  it  through  a  solid  mixture  of  hydroxides  of 
calcium  and  sodium,  commonly  termed  "  soda-lime." 

Carbon  disulphide  is  a  limpid  colourless  liquid,  heavier  than 
water  and  not  mixible  with  it,  melting  at  —110°  and  boiling  at 
4tr04°.  In  the  crude  state  it  contains  hydrogen  sulphide  and  dis- 
agreeably-smelling sulphur  compounds.  It  may  be  purified  from 
hydrogen  sulphide  by  shaking  it  with  a  solution  of  potassium 
permanganate,  which  oxidises  that  impurity,  and  from  sulphur- 
compounds  and  sulphur  by  shaking  it  with  mercuric  chloride  and 
mercury  and  distilling  it.  When  pure  it  has  a  not  unpleasant 
ethereal  odour.  Its  vapour  is  very  poisonous  when  breathed.  Its 
vapour  ignites  very  easily  when  mixed  with  air  (at  149°),  hence  it 
must  be  kept  away  from  a  flame  and  distilled  by  aid  of  a  water- 
bath.  It  is  decomposed  by  light,  acquiring  thereby  a  disagreeable 
smell.  It  is  slightly  soluble  in  water.  Its  vapour  explodes  when 
exposed  to  the  shock  of  decomposing  f  alminate  of  mercury,  being 
resolved  into  the  elements  carbon  and  sulphur.  It  is  formed  with 
absorption  of  heat,  hence  its  instability ;  heat  is  evolved  when  it  is 
exploded.  It  mixes  easily  with  alcohol,  ether,  and  oils,  and  is  used 
for  extracting  oils  and  fats  from  acids,  animal  refuse,  wool,  &c., 
and  as  a  solvent  for  sulphur  chloride  in  vulcanising  caoutchouc. 

It  unites  with  sulphides,  giving  sulphocarbonates  (see  below), 
and  when  passed  through  a  hot  tube  with  chlorine  it  yields 
sulphur  chloride  (S2C12)  and  carbon  tetrachloride  (see  p.  145). 

In  preparing  the  pure  dioxides  of  titanium,  zirconium,  cerium,  and 
thorium,  the  chief  difficulty  is  the  separation  from  the  oxides  of  other  elements, 
especially  from  silica.  The  process  is,  fusion  with  a  mixture  of  potassium  and 
sodium  carbonates  (fusion-mixture),  which  yields  in  each  case  silicate,  titanate, 
zirconate,  or  thorate  of  the  alkaline  metals,  and  the  oxides  of  the  other  metals, 
if  these  are  present.  In  the  case  of  titanium,  hydrogen  fluoride  is  added  to  the 
solution  of  the  fused  mass  in  water,  and  the  titanium  thrown  down  as  double 
fluoride  of  titanium  and  potassium,  TiF4.2KF.  These  crystals  are  afterwards 
dissolved  in  water,  and  on  addition  of  ammonia  the  titanium  is  thrown  down  as 


DIOXIDES   OF   TITANIUM,   ZIRCONIUM,   CERIUM,  AND   THORIUM.   283 

hydrate.  With  zirconium,  the  fused  mass,  consisting  of  silicate  and  zirconate 
of  sodium  and  potassium,  is  mixed  with  excess  of  hydrochloric  acid,  and  evapo- 
rated to  dryness.  This  gives  a  mixture  of  silica  and  oxychlorides  of  zirconium. 
On  treatment  with  hydrochloric  acid,  the  silica,  not  being  thus  converted 
into  chloride,  does  not  dissolve,  but  the  zirconium  dissolves  as  chloride, 
along  with  iron,  &c.  The  solution  is  boiled  with  thiosulphate  of  sodium,  which 
precipitates  the  zirconium,  leaving  the  iron  in  solution.  On  ignition  of  the 
thiosulphate  of  zirconium,  pure  zirconia,  ZrO2,  is  left. 

Cerium  is  similarly  separated,*  but  it  is  precipitated  as  oxalate,  and  on 
ignition  the  oxide  Ce2O3  is  left.  Thorium  is  precipitated  as  oxalate,  from  its 
solution  in  hydrochloric  acid,  after  separation  of  silica  ;  and  from  a  solution  of 
the  oxalate  in  hydrochloric  acid  by  a  strong  solution  of  potassium  sulphate, 
with  which  it  combines,  forming  a  double  sulphate  of  thorium  and  potassium 
see  p.  428). f  It  also  yields  an  insoluble  thiosulphate. 

Titanium  dioxide,  native  as  rutile,  forms  reddish-brown 
crystals ;  artificially  prepared  it  is  a  reddish-brown  powder.  It  is 
insoluble  in  water  and  does  not  react  with  acids,  except  with 
strong  sulphuric  acid  or  fused  bisulphates. 

It  melts  in  the  oxyhydrogen  flame.  It  has  been  artificially 
crystallised  by  passing  vapours  of  titanium  tetrachloride  and 
steam  through  a  red-hot  tube. 

Zirconia,  or  zirconium  dioxide,  is  a  white  powder;  it  is 
obtained  in  small  quadratic  prisms  by  crystallisation  from  fused 
borax. 

Cerium  dioxide  is  a  pale-yellow  insoluble  substance,  which 
also  crystallises  from  fused  borax  in  tesseral  crystals.  On  boiling 
with  hydrochloric  acid,  chlorine  is  evolved,  and  the  trichloride  is 
produced,  CeCl3.  With  sulphuric  acid  it  also  dissolves,  the  sul- 
phate Ce2(S04)3.Ce(S04)2  being  formed^with  evolution  of  oxygen. 
It  is  soluble  in  nitric  acid. 

Thorium  dioxide,  or  thoria,  is  a  white  powder,  separating 
from  its  solution  in  borax  in  transparent  quadratic  crystals. 

Compounds  with  water  and  hydrogen  sulphide. — Carbon 
dioxide  as  gas  dissolves  to  some  extent  in  water;  100  volumes 
of  water  at  20°  dissolve  about  90  volumes,  and  at  15°  about 
100  volumes.  The  solution  has  a  pleasant  sharp  taste,  and  is 
usually  called  "  soda-water."  The  carbon  dioxide  is,  however, 
forced  in  under  a  pressure  of  several  atmospheres.  The  gas 
escapes  quickly  if  the  pressure  is  decreased  immediately;  but 
after  some  days  or  weeks  it  appears  to  have  entered  into  combina- 
tion to  some  extent  with  the  water,  and  does  not  then  escape  so 

*  For  details  regarding  cerium  compounds  see  Brauner,  Chem.  Soc.,  47, 
879  ;  references  to  other  papers  are  given, 
t  Cleve,  Sull.  Soc.  CUm.  (2),  21,  115. 


284      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLUEIDES. 

readily.  The  solution  turns  litmus  solution  claret  coloured.  It  acts 
on  zinc,  iron,  and  magnesium,  forming  carbonates  and  liberating 
hydrogen.  Itjprobably  consists  of  a  weak  solution  of  carbonic  acid, 
H2C03,  with  carbon  dioxide  uncombined  but  mixed  with  the  water. 

Carbon  disulphide  does  not  unite  directly  with  hydrogen  sul- 
phide, but  sulphoearbonie  acid,  as  the  compound  is  named, 
H2CS3,  is  produced  on  addition  of  weak  hydrochloric  acid  to  a 
solution  of  a  sulphocarbonate,  e.g.,  Na2CS3  (see  below).  It  is  a 
dark-yellow  oil,  with  a  pungent  odour,  and  on  rise  of  temperature 
it  rapidly  decomposes  into  carbon  disulphide,  CS2,  and  hydrogen 
sulphide,  HZS. 

Many  hydrates  of  titanium  dioxide  have  been  described, 
but  the  data  regarding  them  are  as  a  rule  contradictory.  On 
heating  titanic  hydrate  thrown  down  from  its  chloride  by  an  alkali 
it  loses  water  gradually,  with  rise  of  temperature,  and  shows  no 
sign  of  any  definite  hydrates.  It  is  probable  that  there  are  many, 
and  that  no  one  is  stable  over  any  large  range  of  temperature. 

The  hydrates  of  zirconium  dioxide  appear  also  to  be  numer- 
ous. The  only  sudden  break  in  drying  the  hydrate  precipitated 
from  the  chloride  by  ammonia  is  at  400°.  On  reaching  this  tem- 
perature the  body  suddenly  turns  incandescent,  and  all  water  is 
expelled.  It  has  then  become  difficult  to  dissolve  in  acids,  and  it 
is  believed  that  sudden  polymerisation  has  occurred,  many  mole- 
cules of  ZrO2  having  united  to  form  one  complex  molecule. 

Cerium  hydrate  at  600°  has  the  formula  CeO2.2H2O.  At 
lower  temperatures  it  is  brownish-yellow,  but  at  that  temperature 
and  above  it  is  bright  yellow  ;  as  it  dries  further,  its  colour  changes 
to  a  salmon -pink.  It  is  produced  by  the  action  of  sodium  hypo- 
chlorite  on  Ce2O3. 

Thorium  hydrate  is  a  gelatinous  mass ;  it  probably  resembles 
titanium  hydrate. 


Compounds  with  Oxides  and  Sulphides — Carbon- 
ates, Titanates,  Zirconates,  Thorates— Carbon 
Oxysulphide,  Oxysulphocarbonates,  and  Sul- 
phocarbonates. 

These  compounds  maybe  divided  into  two  classes  :  (1)  normal 
compounds,  those  in  which  the  ratio  of  the  number  of  oxygen 
atoms  in  the  dioxide  to  that  of  the  oxide  of  the  metal  is  as 
2:1;  and  (2)  basic  compounds,  those  in  which  the  ratio  is 
less  than  2:1;  no  acid  compounds,  those  in  which  the  ratio  is 


CARBON   OXYSULPHIDE  ;  CARBONATES.  285 

greater  than  2:1,  are  known.  The  normal  compounds  are  most 
numerous. 

But  before  considering  these  bodies  it  is  advisable  to  describe 
carbon  oxysulphide,  of  which  the  formula  is  COS*  as  shown  by 
its  gaseous  density.  This  body,  therefore,  cannot  be  regarded  as  a 
compound  of  carbon  dioxide  and  carbon  disulphide,  C02.CS2,  but 
as  carbon  dioxide,  of  which  one  atom  of  oxygen  is  replaced  by  sul- 
phur. It  may  be  produced  by  leading  a  mixture  of  carbon  dioxide 
and  carbon  disulphide  gases  through  a  tube  filled  with  platinum 
black,  i.e.,  finely-divided  platinum,  or  by  the  union  of  carbon 
monoxide  with  sulphur.  But  it  is  most  easily  produced  by  the 
reaction  between  sulphocyauide  of  hydrogen  and  water.  The 
compound  KCNS,  on  treatment  with  sulphuric  acid,  yields  the 
acid  HCNS.  If  the  sulphuric  acid  be  moderately  strong  and 
warm,  it  combines  with  the  ammonia  produced  by  the  decom- 
position of  the  acid,  thus  :—  HCNS  +  H2O  =  NH3  +  COS.  Car- 
bon oxysulphide  is  a  not  infrequent  constituent  of  mineral  springs, 
but,  as  a  rule,  it  has  for  the  most  part  reacted  with  water  to  form 
carbon  dioxide  and  hydrogen  sulphide,  thus  :  —  COS  +  H20  = 
COz  +  HtS.  It  is  a  colourless  gas,  without  odour  or  taste  when 
pure,  somewhat  soluble  in  water,  and  combustible  to  dioxides  of 
carbon  and  sulphur.  It  is  hardly  affected  by  aqueous  potash,  but 
is  easily  absorbed  by  an  alcoholic  solution.  Its  physiological 
effects  resemble  those  of  nitrous  oxide.f 

There  are  thus  three  bodies,  all  of  which  form  compounds  with 
oxides  and  sulphides,  viz.  :  (702,  carbon  dioxide  ;  COS,  carbon 
oxysulphide  ;  and  CS2,  carbon  disulphide. 

Compounds  of  Carbon  Dioxide  with  Oxides. 

1.  Normal  carbonates.  —  Ratio  of  oxygen  in  carbon  dioxide 
to  oxygen  in  combined  oxide,  2:1. 

The  following  is  a  list  of  the  known  compounds  :  — 


Simple   carbonates:  —  "Li^CO3;   Na^COa  with  15,  10,  8,  7,  6,   5,  2,  and 
1H20  ;  K2C03  with  2H2O  and  H2O  ;  Rb2CO3.H2O  ;  Cs2CO3  ; 
(NH4)2C03.H20. 

Complex    carbonates  :  —  HNaCO3  ;    H2Na4(CO3)3.3H2O  ;    HKCO3.H.,O  ; 
HRbC03;  HCsC03;  HNH4CO3  ;  H2(NH4)4(CO3)3.2H2O. 

These  carbonates  are  all  made  by  the  action  of  carbon  dioxide  on 
a  solution  of  hydroxide  of  the  metal,  thus  :  —  2NaHO.Aq  -+-  C0a  = 
H20. 

*  Than,  Annalen,  Suppl,  1,  236. 
t  J.praJct.  Chem.  (2),  36,  64. 


286      THE   OXIDES,    SULPHIDES,    SELENIDES,   AND   TELLURIDES. 

Of  these,  lithium  carbonate,  Li2C03,  occurs  in  mineral  waters  ; 
it  is  sparingly  soluble  in  water  (about  1*4  grams  in  100  of 
water  at  20°),  and  may  be  produced  by  addition  of  a  concen- 
trated solution  of  sodium  carbonate  to  a  soluble  salfc  of  lithium. 
For  the  preparation  of  sodium  and  potassium  carbonates,  see 
p.  671. 

Sodium  carbonate  is  a  constituent  of  certain  "  soda-lakes  "  in 
Egypt  and  Hungary ;  it  also  occurs  in  volcanic  springs. 

The  ordinary  name  for  the  carbonate  Na2CO3  is  soda-asli;  for 
the  crystalline  salt,  Na2CO3.10H2O,  soda  crystals  or  "washing- 
soda;"  and  for  hydrogen  sodium  carbonate  HNaCO3,  bicarbonate, 
or  "  baking-soda."  The  latter  is  produced  by  treating  the  normal 
carbonate  (crystals)  with  carbon  dioxide,  thus  : — Na2CO3  +  (702  + 
H20  =  2NaHCO3.  Hydrogen  sodium  carbonate  is  less  soluble 
than  sodium  carbonate. 

Carbonate  of  sodium  melts  at  about  818°,  and  of  potassium 
at  about  830°.  On  heating  hydrogen  sodium  carbonate  it  loses 
water  and  carbon  dioxide,  and  yields  sodium  carbonate,  thus : — 
2HNaCO3  =  HZ0  +  C02  +  Na2CO3.  The  simple  carbon- 
ates, except  those  of  ammonium  (see  p.  533),  volatilise  un- 
changed at  a  bright  red  or  white  heat,  and  are  not  decomposed 
into  carbon  dioxide  and  metallic  oxide.  It  is  probable  that  a  car- 
bonate of  sodium  and  potassium  also  exists,  of  the  formula 
NaKCO3;  a  mixture  of  the  two  is  named  "fusion  mixture,"  and 
is  used  in  the  decomposition  of  silicates,  &c.  It  has  a  much  lower 
melting  point  than  either  of  the  pure  salts.  The  compound 
H2Na4(CO3)3.3H2O  occurs  native,  and  is  known  as  trona  or  urao ; 
in  old  times  it  used  to  be  an  important  source  of  soda.  These  bodies 
have  all  an  alkaline,  cooling  taste ;  the  ammonium  compound 
smells  of  ammonia,  owing  to  its  decomposing,  on  exposure,  into 
ammonia,  carbon  dioxide,  and  water.  Hydrogen  ammonium  car- 
bonate is  found  in  guano  deposits. 

Simple     carbonates  : — BeCO3.4H2O  ;       CaCO3,    also    5H2O  ;       SrCO3  ; 

BaCO3 ;  MgCO3 ;  also  3H2O  and  5H2O  ;  ZnCO3 :  CdCO3. 
Complex  carbonates : — H2Ca(CO3)2.Aq  (?)  ;  Na2Ca(CO3)2.5H2O  ; 

H2Mg(CO3)2.Aq ;  Na2Mg(C03)2;  HKMg-(CO3)2.4H2O  ; 

(NH4)2M&(C03)2.4H20;  H2K8Zn6(C03)u.7H20:  Na6~Zn8(CO3)n.8H2O. 
Na6Zn8(C03)n.8H20. 

These  carbonates  are  all  white  solids.  They  are  decom- 
posed by  heat  (see  the  respective  oxides),  barium  carbonate 
requiring  the  highest  temperature.  The  following  are  found 
native  : — Calcium  carbonate,  CaC03,  as  calcspar  or  Iceland-spar, 
in  hexagonal  rhombohedra  ;  as  arrayonite  in  trirnetric  rhombic 


THE   CAKBONATES.  287 

prisms  ;  as  marble,  limestone,  chalk  ;  a  constituent  of  shells, 
bones,  &c.  It  may  be  produced  in  the  form  of  calcspar  by 
crystallisation  from  a  mixture  of  fused  sodium  and  potassium 
chlorides  ;  by  precipitation  from  solution  below  30°  ;  and  as 
arragonite  by  precipitation  above  90°.*  Between  these  tempera- 
tares  mixtures  of  microscopic  crystals  of  the  two  are  precipitated 
by  addition  of  sodium  or  ammonium  carbonate  to  a  solution  of  a 
soluble  salt  of  calcium.  When  heated  to  redness  in  a  closed  iron 
tube,  calcium  carbonate  fuses,  and  then  yields  a  crystalline  mass 
resembling  marble.  The  carbonates  of  calcium,  strontium,  and 
barium  are  formed  by  direct  union  of  oxide  with  carbon  dioxide  ; 
the  union  is  attended  with  great  evolution  of  heat,  causing  the 
oxide  to  become  incandescent  ;  the  product  with  lime  has  the 
formula  CO2.2CaO.  The  compound  Na3Ca(CO3)2.5H2O  is  named 
gaylussite  ;  strontium  carbonate,  SrCO3,  is  found  native  as  stron- 
tianite  ;  and  barium  carbonate,  BaCO3,  as  wiiherite.  MgCO3  is 
magnesite,  and  a  double  carbonate  of  calcium  and  magnesium,  in 
which  indefinite  amounts  of  both  metals  are  present,  is  dolomite  ; 
it  forms  large  mountain  ranges,  named  "  The  Dolomites,"  in 
northern  Italy.  Zinc  carbonate,  ZnCO3,  occurs  native  as  calamine, 
and  is  accompanied  .by  cadmium  carbonate,  CdCO3. 

The  so-called  acid  carbonates,  e.g.,  H2Ca(C03)2,  H2Mg(C03)2, 
and  similar  compounds  of  barium,  strontium,  &c.,  have  not  been 
isolated.  Their  existence  is  assumed  because  the  normal  car- 
bonates dissolve  freely  in  a  solution  of  carbonic  acid.  On  warm- 
ing the  solution,  they  are  decomposed  with  evolution  of  carbon 
dioxide  and  precipitation  of  the  simple  carbonates. 

Carbonates  of  boron  and  scandium  are  unknown  ;  of  this  group 
only  Y2(CO3)3.12H2O,  and  2H2O  ;  and  La,(CO3)2,  found  native 
as  lanthanite,  are  known.  The  existence  of  a  carbonate  of  alu- 
minium is  doubtful  ;  carbonate  of  gallium  is  unknown.  In,(CO2)3, 
however,  has  been  prepared.  These  are  insoluble  white  bodies, 
which  lose  carbon  dioxide  when  heated,  leaving  the  oxides. 

Thallium  forms  no  thallic  carbonate,  but  thallous  carbonate, 
T12CO3,  is  produced  by  precipitation.  There  is  some  evidence  of 
a  hydrogen  thallium  carbonate,  HT1(CO3). 

Chromic,  ferric,  and  manganic  carbonates  are  unknown.  On 
addition  of  a  soluble  carbonate  to  their  soluble  salts,  e.g.,  chlorides, 
the  hydrates  are  precipitated,  and  carbon  dioxide  escapes, 
thus  :  — 


2CrCl3.Aq  +  3NasC03.Aq  =  Cr203.Aq  +  6NaCl.Aq  +  3C03. 
*  Comptes  rend.,  92,  189. 


288      THE   OXIDES,   SULPHIDES,    SELENIDES,   AND   TELLURIDES. 

The  carbonates  derived  from  the  monoxides  of  these  metals  are 
as  follows : — 

Simple  carbonates  : — CrCO3  ;  FeCO3 ;  MnCO3  ;  CoCO3  ;  NiCO3. 
Complex  carbonates :— HKCo(CO3)2.2H2O ;  H2NaoCo(CO3)3.4H2O  ; 

Na2Co(C03)2.10H20;  HKNi(CO3)2.4H2O  ;  K2Ni(CO3)2.4H2O  ;" 

Na2NiCo(CO3)3.10H2O. 

Of  these,  chromous  carbonate  is  produced  by  mixing  a  solu- 
tion of  chromous  chloride  with  sodium  carbonate  ;  FeCO3  is  found 
native,  and  named  spathic  iron  ore  or  siderite ;  in  an  impure  state, 
mixed  with  clay  or  shale,  it  is  termed  clay -band  or  black-band,  and 
forms  one  of  the  most  important  ores  of  iron.  When  pure  it  is  a 
whitish  crystalline  rock.  It  is  soluble  in  water  containing  carbon 
dioxide  ;  such  a  solution  may  contain  hydrogen  ferrous  carbonate, 
H2Fe(C03)2,  which,  however,  has  not  been  isolated.  It  is  in  this 
form  a  constituent  of  iron  springs,  and,  on  exposure  to  air,  it  loses 
carbon  dioxide,  and  the  iron  oxidises  to  ferric  hydrate,  and  deposits 
on  the  bed  of  the  stream.  A  hydrated  carbonate,  FeCO3.H2O, 
also  occurs  native.  Manganese  carbonate,  MnCO3,  occurs  native 
as  manganese  spar. 

No  carbonates  of  titanium,  or  zirconium  are  known. 

Cerium  hydrate,  however,  on  exposure  to  air,  absorbs  carbon 
dioxide,  yielding  Ce2(CO3)3.9H2O.  Silicon  and  germanium  do 
not  yield  carbonates,  but  tin  forms  a  basic  carbonate  (see  below). 
Lead  carbonate,  PbCO3,  occurs  native,  and  is  known  as  cerussite. 
Lead  oxide  sometimes  replaces  calcium  oxide  in  native  calcium  car- 
bonate, to  the  extent  of  3  or  4  per  cent. ;  the  compound  is  called 
plumbocalcite.  Pluinbo-arragonite  has  also  been  found  native  at 
the  lead  hills  in  Lanarkshire.  A  chlorocarbonate,  of  the  formula 
PbCO3.PbCl2,  may  be  produced  by  boiling  lead  carbonate  and 
chloride  together  in  water.  It  is  an  insoluble  white  substance. 
It  also  occurs  native  as  corneous  lead.  When  heated,  it  loses 
carbon  dioxide,  leaving  PbO.PbCl2. 

Carbonates  of  nitrogen,  vanadium,  niobium,  and  tantalum  are 
unknown,  and  also  carbonates  of  phosphorus,  arsenic,  and  anti- 
mony ;  a  basic  carbonate  of  bismuth  has  been  prepared  (see 
below). 

Carbonates  of  molybdenum  and  tungsten  do  not  appear  to  exist, 
but  several  double  carbonates  of  uranyl  (U02)  (see  p.  407) 
have  been  prepared.  These  are  Na4(UO2)(CO)3,  K4(UO2XCO3)3, 
and  (NH4)4(UO2)(CO3)3.  A  calcium  compound  occurs  native  ;  its 
formula  is  Ca(UO2XCO3)2.10H2O.  It  is  seen  that  the  group  U02j 
or  uranyl,  acts  like  a  dyad  metal. 


THE  CARBONATES.  289 

Normal  carbonate  of  copper  is  unknown.  The  only  known 
normal  compound  has  the  formula  Najd^CO^.GH-O.  Silver 
carbonate,  Ag2CO3,  is  a  yellowish-white  powder,  produced  by 
precipitation;  it  loses  carbon  dioxide  at  200°  ;  KAgCO3  is  formed 
if  HKCO3  be  used;  it  is  white.  Mercurous  carbonate,  Hg2CO3, 
is  a  very  unstable  brown  precipitate.  Carbonates  of  gold  and  of 
the  metals  of  the  palladium  and  platinum  groups  are  too  unstable 
to  exist. 

Considering  these  carbonates  as  a  whole,  it  may  be  noticed 
(L)  that  with  exception  of  those  of  the  sodium  group  of  metals  all 
are  decomposed  by  heat  into  oxide  and  carbon  dioxide ;  (2)  those 
of  the  sodium,  calcium,  and  magnesium  groups,  and  thallons  and 
cerium  carbonates  are  formed  by  direct  union  of  the  hydroxides 
and  carbon  dioxide ;  (3)  that  the  oxides,  except  those  of  the 
sodium  group,  do  not  combine  directly  with  carbon  dioxide ;  cal- 
cium oxide,  however,  begins  to  combine  at  415° ;  and  (4)  that  the 
carbonates  of  calcium,  stiontium,  barium,  and  silver,  are  the  only 
normal  ones  produced  by  precipitation  by  addition  of  a  soluble 
carbonate  to  a  soluble  salt  of  the  metals.  In  all  other  cases,  basic 
carbonates  are  precipitated.  These  will  now  be  considered. 

2.  Basic  carbonates. — These  bodies  contain  a  greater  proportion  of  the  oxide 
of  the  metal  than  is  represented  by  the  ratio  given  before.  The  oxygen  of  the 
metallic  oxide  bears  a  larger  ratio  to  that  of  the  carbon  dioxide  than  1:2.  Their 
formulae  are  most  conveniently  stated  as  addition-formulae ;  the  relations  then 
appear  most  clearly.  They  are  unknown  in  the  sodium  group  of  elements. 

CO2.5BeO.5H2O  ;  6CO2.3K.2O.4BeO  ;  CO2.2CaO.H.2O  ;  CO,.2CaO  (produced 
by  heating  CaCO3 ;  by  heating  CaO  in  CO2,  the  mass  turning  incandescent 
during  union ;  or  by  exposure  of  Ca(OH)2  to  air)  ;  3CO2.4CaO,  also  produced 
by  direct  union ;  CO2.2SrO ;  CO2.2BaO ;  4CO2.5MgrO  (precipitated  hot)  ; 
3CO2.4MgO  (native ;  hydromagnesite)  ;  COo.2ZrLO.H.2O ;  CO.,.3ZnO.3H.,O 
(native  ;  zinc-bloom)  •  CO.,.5ZnO.6H2O  ;  2CO2.3ZnO.H2O  ;  2CO2.5ZnO.5H2P  ; 
4CO2.5ZnO.H2O ;  4CO2.°ZnO.6H2O ;  CO2.3CdO.  These  substances  (the 
cadmium,  strontium,  and  barium  compounds  excepted)  are  produced  by  pre- 
cipitation under  various  conditions  of  temperature  and.  dilution. 

2CO2.4ThO.:.SH2O  appears  to  exist,  but  there  are  no  corresponding  com- 
pounds of  tin  or  lead.  CO2.2SnO,  however,  is  thrown  down  on  addition  of 
sodium  carbonate  to  stanncus  chloride,  SnCl2,  as  a  white  precipitate. 

The  substance  known  as  white-lead  is  probably  a  mixture  of  basic  carbonates 
of  lead.  Seen  under  the  microscope,  it  consists  of  small  spherical  masses,  each 
of  which  is  opaque  and  reflects  white  light.  Hence  its  use  as  a  paint. 
It  possesses  great  "  covering  power,"  owing  to  its  not  transmitting  light. 
It  is  produced  by  the  action  of  acetic  acid,  carbon  dioxide  and  water  on 
metallic  lead;  similar  basic  carbonates,  which  however,  have  not  the  same 
opaque  quality,  are  produced  by  precipitation.  The  following  have  been 
analysed :: — 


290      THE   OXIDES,   SULPHIDES,  SELENIDES,  AND   TELLURIDES. 

2C02.3PbO.H20  ;  3C02.4PbO.H20  ;  5CO2.6PbO.H2O  ;  6CO2.7PbO.2H2O  ; 
and  5CO2.8PbO.3H2O. 

Ferrous  salts,  on  treatment  with  a  soluble  carbonate,  give  a  white  precipitate 
of  presumably  basic  carbonate.  This  precipitate  rapidly  turns  green,  absorbing 
oxygen  :  it  has  not  been  analysed.  With  manganese,  cobalt  and  nickel  the 
following  compounds  are  known: — CO2.3CoO.3H2O;  2CO2.5CoO.4H.)O  ; 
CO2.3NiO.6H2O  (found  native,  and  named  emerald  nicJceT)  •  2CO2.5NiO.7H2O. 

Copper  and  mercury  also  form  basic  carbonates.  CO2.2CuO.H2O  occurs 
native  as  malachite,  a  beautiful  green  mineral,  and  2CO2.3CuO.H2O,  as 
azurite,  which  has  a  splendid  blue  colour.  By  precipitation  CO2.6CuO  and 
CO2.8CuO.5H2O  are  formed  as  light  blue  precipitates.  Mercuric  salts  with 
soluble  carbonates  give  a  reddish  precipitate  of  CO2.4Hg-O. 

Titanates,  zirconates,  and  thorates. — These  have  been  little  investigated. 
The  compounds  which  have  been  prepared  are  :  — 

NaaTiOj, ;    K2TiO3  ;    MgTiO3 ;  FeTiO3 ;  CaTiO3  ;   and  ZnTiO3  ;  also 
TiO2.2ZnO;  2TiO2.3ZnO  ;  5TiO2.4ZnO. 

The  titanates  of  sodium  and  potassium  are  yellowish,  fibrous  masses,  pro- 
duced by  heating  titanic  oxide  with  excess  of  carbonate  of  sodium  or  potassium. 
On  treatment  with  water  they  decompose,  a  sparingly  soluble  (acid  ?)  salt 
being  precipitated,  while  a  (basic  ?)  salt  remains  in  solution.  Obviously  these 
compounds  have  little  stability.  Magnesium  and  iron  titanates  are  produced 
by  heating  titanium  oxide  with  magnesium  chloride,  or  with  a  mixture  of  ferrous 
fluoride  and  sodium  chloride.  The  iron  titanate  forms  long  thin  steel-grey 
needles.  It  is  formed  native  as  ilmenite  :  it  is  isomorphous  with  and  crystal- 
lises along  with  iron  sesquioxide.  The  compounds  TiO2.2MgrO  and  TiO2  2FeO 
are  similarly  prepared.  Calcium  titanate,  CaTiO3,  occurs  native  as  perowskite. 

By  igniting  together  zirconia  and  sodium  carbonate,  the  compound  Na2ZrO;J 
is  formed.  It  is  decomposed  by  water  into  zirconium  hydrate  and  sodium 
hydrate.  A  larger  amount  of  carbonate  yields  Zr02.2Na2O  ;  it  is  also  decom- 
posed by  water,  and  deposits  hexagonal  crystals  of  a  salt  of  the  formula 
8ZrO2.Na2O.12H2O.  Magnesium  zircon  ate  has  also  been  prepared  by  fusing 
zirconium  dioxide  and  magnesium  oxide  in  presence  of  ammonium  chloride.  It 
is  a  powder  consisting  of  transparent  crystals. 

Although  thorium  dioxide  dissolves  in  alkalies,  and  probably  unites  with 
oxides,  no  thorates  have  been  analysed. 

Compounds  of  sulphides  with  sulphides. — These  bodies 
have  been  investigated  only  in  the  compounds  of  carbon.  They  are 
named  sulphocarbonates  or  thiocarbonates,  from  the  Greek  word  for 
sulphur,  Oeiov.  They  are  produced  by  the  action  of  carbon  disul- 
phide  on  sulphides,  which  is  analogous  to  that  of  carbon  dioxide 
on  oxides.  Those  which  have  been  prepared  and  analysed 
are: — 

LiCS3;  NaCS3;  K2CS3 ;  (NH4)2CS3 ;  MgCS3;  CaCS3;  SrCS3 ;  BaCS;,. 

Precipitates  are  produced  by  potassium  sulphocarbonate  in 
solutions  of  zinc,  cadmium,  chromium,  iron,  manganese,  cobalt, 


SULPHOCARBONATES.  —  CARBON  YL   CHLORIDE.  291 

nickel,  tin,  lead,  bismuth,  platinum,  silver,  gold,  and  mercury. 
These  require  further  investigation. 

Potassium  sulphocarbonate  consists  of  yellow  deliquescent 
crystals  ;  it  is  formed  by  digesting  an  aqueous  or  alcoholic  solution 
of  potassium  sulphide,  K2S,  with  carbon  disulphide  ;  the  crystals 
contain  water,  which  is  expelled  at  80°,  leaving  a  brown-  red  solid. 
On  heating  it,  potassium  trisulphide,  K3S3,  remains,  mixed  with 
carbon.  The  ammonium  salt  is  produced  along  with  ammonium 
sulphocyanide,  by  digesting  carbon  disulphide  with  alcoholic 
ammonia,  thus  :—  2CS,  +  4NH3  =  (NH4)2CS3  4-  NH4CNS.  It 
forms  yellow  crystals,  insoluble  in  alcohol,  but  soluble  in  water. 
The  calcium  and  barium  salts  are  prepared  like  the  potassium  salt. 
Milk  of  lime  and  carbon  disulphide  give  an  orange-red  basic  salt, 
CaCS3.2CaO.8H2O  ;  at  30°  it  melts  to  a  red  liquid,  from  which 
CaCS3.3CaO.10H2O  separates.  The  action  of  carbon  oxysulphide 
on  sulphides  requires  investigation. 

Compounds  of  oxides  with  halides.  —  It  has  already  been 
stated  that  carbon  monoxide  and  chlorine  combine  directly  ;  the 
product  is  carbonyl  chloride,  or  carbon  oxy  chloride,  COCk-  Its 
vapour-density  shows  it  to  have  that  formula,  and  not  to  be  a 
compound  of  C02  and  CCU.  It  is  produced  on  exposing  a  mixture 
of  the  two  gases  to  sunlight,  hence  its  old  name,  phosgene  gas,  a 
gas  produced  by  light  (0ujs).  It  is  more  easily  prepared  by  passing 
carbon  monoxide  through  hot  antimony  peritachloride,  SbCl5,  which 
loses  two  atoms  of  chlorine  ;  or  by  passing  a  mixture  of  the  gases 
through  a  tube  filled  with  hot  animal  charcoal.  It  condenses  to  a 
liquid  boiling  at  8'4°.*  When  treated  with  water  it  produces  carbon 
dioxide  and  hydrogen  chloride.  Assuming  the  carbon  dioxide  to 
remain  in  combination  with  water,  as  carbonic  acid,  the  change 
may  be  thus  represented:  — 


Cl        H.OH        m^OH        HC1 
C1  "  H.OH  -'  CO<OH  +  HC1. 

Light  is  thus  thrown  on  the  constitution  of  carbonic  acid. 
It  appears  to  consist  of  carbon  monoxide  in  combination 
with  hydroxyl  ;  and  the  normal  carbonates  may  be  similarly 

represented  ;     for    example,    sodium    carbonate    as 


OTT 

hydrogen  sodium  carbonate  as  CO<          ;  calcium  carbonate  as 


CO<Q>Ca  ;  basic  copper  carbonate  as  CO<Q  ~QU>0,  each  atom 
*  For  sulpliochlorides,  see  P.  Klason,  Berichte,  20,  2376. 


292      THE    OXIDES,    SULPHIDES,   SELENIDES,  AND   TELLUKIDES. 

of  copper  being  half  oxide,  half  carbonate.  The  more  complex  basic 
carbonates  may  also  be  similarly  represented  ;  e.g.,  basic  lead  car- 

CO<OPb\0 
bonate  may  be  written  QQ^O          Q>Pb.     But  such  complicated 

formulae  are  not  confirmed  by  any  other  considerations,  and  should 
be  sparingly  used  ;  moreover,  it  is  impossible  to  represent  the 
various  amounts  of  water  in  combination  with  such  compounds  in 
any  way  but  by  simple  addition. 

The  oxychlorides  of  titanium  have  recently  been  investigated, 
and  their  formulae  appear  capable  of  similar  modes  of  expression. 
Titanium  tetrachloride  may  be  supposed  to  react  with  water  form- 
ing the  hydroxide  Ti(OH)4,  which,  however,  appears  to  be  unstable 
(see  p.  284).  The  corresponding  carbon  hydroxide,  C(OH)4,  is 
certainly  incapable  of  existence,  but  if,  instead  of  hydrogen,  it 
contain  certain  hydrocarbon  groups,  such  as  ethyl,  C2H5,  it 
becomes  stable.  For  example,  the  body  C(OCJE[5)4  is  known,  and 
is  named  ethyl  orthocarbonate,  the  name  orthocarbonic  acid  being 
applied  to  the  unknown  C(OH)4.  If  water  containing  hydrogen 
chloride  in  solution  (36  per  cent.  HC1)  be  mixed  with  titanium 
chloride,  a  violent  reaction  occurs,  and  a  yellow,  spongy,  very 
deliquescent  mass  is  produced,  which  has  the  formula  Ti(OH)Cl3. 
It  is  tolerably  stable  in  aqueous  solution.  On  adding  titanium 
tetrachloride  to  very  cold  water  in  theoretical  amount,  the  dihy- 
droxydichloride,  Ti(OH)2Cl2,  is  produced.  It  is  a  yellow  deli- 
quescent substance ;  and  may  also  be  mixed  with  water.  On 
exposing  the  di-  or  tri-chloride  to  moist  air  for  some  time,  the 
trfhydroxymonochloride  is  formed,  Ti(OH)3Cl.  It  has  been 
obtained  in  a  crystalline  form.  It  is  insoluble  in  water,  but  soluble 
in  weak  hydrochloric  acid.  We  have  thus  the  series  : — 

TiCl4;  Ti(OH)Cl3;  Ti(OH)2Cl2;  Ti(OH)3Cl;  and  Ti(OH)4. 

All  of  these  compounds,  when  heated  alone,  evolve  titanium 
tetrachloride  or  hydrogen  chloride,  leaving  a  residue  of  dioxide. 

Oxychloride  of  zirconium,  ZrOCl2,  separates  in  tetragonal 
crystals  from  a  hydrochloric  solution  of  the  oxy chloride  in  water ; 
a  similar  bromide  is  known. 

A  higher  oxide  of  titanium  is  produced  on  treating  titanium  hydrate  with 
hydrogen  dioxide.*  It  is  a  yellow  substance,  the  formula  oF  which  approxi- 
mates to  TiO3.3H2O.  It  appears  to  form  compounds  with  TiO2  in  the  ratios 
4Ti02.Ti03;  3Ti02.Ti03;  2TiO2.TiO3;  and  TiO2.TiO3. 

*  Chem.  Soc.,  49,  150,  484. 


OXYHALIDES   OF   TITANIUM.  293 

Certain  fluorine  derivatives  of  this  body  in  combination  are  also  known. 
They  are  as  follows  :  — 


;     2TiO2F2.3BaF2  ;    TiOF4.BaF2; 
and  TiO2F2.3NH4F. 

Attempts  to  prepare  similar  zirconium  compounds  yielded  Zr2O5wH2O,  as  a 
white  precipitate  ;*  and  cerium  trioxide  has  been  thus  prepared  as  an  orange- 
red  precipitate.f  Thorium  yields  an  oxide  of  the  formula  Th2O7  by  similar 
treatment. 

Physical  Properties. 
Mass  of  1  cubic  centimetre  :  — 

C.  Ti.  Zr.  Ce.  Th. 

Monoxides  .......  ?  — 

Dioxides  ........      1'2—  1«6J  4  25§  5'85    6'93—  7  09    10'22 

Hydrated  dioxides          —  — 

Monosulphides  .  .  .          T66  5'1|| 

Bisulphides  ......          1-29(0°)  -  8'29 

Carbonates.    Li.       Na.       K.       Ca.        Sr.      Ba.     Mg.      Zn.      Cd. 
1-79       2-4      2-1       2'9        3-6      4'3       3'0      4'4      43 

Tl.        Pb.     Mn.     Fe.        Ag. 
7'2        6-5      3-6      3-8        6'0 

Heats  of  formation  :  — 

C  +  O  =  CO  +  290K;   CO  +  O  =  C02  +  680Kj  C  +  2O  =  C02  + 

970K. 
CO  +  C12  =  COC12  +  261K;  C  +  O  +  S  =  COS  +  370K;  C  +  2S  = 

CS2  -  260K. 
2XaOH.Aq  +  CO,  =  NaaCOg.Aq  +  261K;  2KOH.Aq  +  C02  =  K2CO3.Aq 

+  261K. 
CaO  +  C02  =  CaC03  +  308K  (?)  ;  SrO  +  CO2  =  SrCO3  +  958K  ; 

BaO  +  CO2  =  BaC03  +  622K. 
.O  +  CO2  =  Agr2C03  +  200K;  PbO  +  CO2  =  PbCO3  -  744K. 


*  Berichte,  15,  2599. 

f  Comptes  rend.,  100,  605. 

J  Solid. 

§  Artificial;  Sutile,  4'42j  Broolcite,  3'89-4'22;  Anatase,  3'75-4'06. 

I!  Ce2S3. 


294 


CHAPTEE  XXL 

OXIDES,    SULPHIDES,    SELENIDES,  AND   TELLURIDES    OF   MEMBERS    OF   THE 

SILICON     GROUP. — SILICATES,      STANNATES,     AND     PLUMBATES. OXY- 

HAL1DES. 

Oxides,   Sulphides,  Selenides,  and  Tellurides  of 
Silicon,  Germanium,  Tin,  and  Lead. 

The  formulae  of  the  compounds  of  this  group  of  elements 
resemble  those  of  carbon  and  titanium.  There  are  monoxides, 
sesquioxides,  dioxides,  and  intermediate  combinations,  but  no  per- 
oxides have  been  prepared.  But  a  noticeable  difference  is  that  the 
monoxides,  except  that  of  silicon,  form  compounds ;  the  com- 
pounds of  the  dioxides  are  very  numerous ;  and  we  again  meet 
with  resemblances  between  the  first  number  of  the  previous  group 
with  that  of  this  group ;  i.e.,  between  compounds  of  carbon  and 
silicon,  as  we  do  between  those  of  beryllium  and  mag'nesium,  and 
of  boron  and  aluminium. 

I.  Monoxides,  monosulphides,  selenides,  and  tellurides. 

Silicon.      Germanium.  Tin.  Lead. 

Oxygen SiO  (?).         GeO.*  SnO.  PbO. 

Sulphur SiS.  GeS.  SnS.  PbS. 

Selenium ?  ?  SnSe.  PbSe. 

Tellurium —  PbTe. 

Sources. — Lead  monoxide  occurs  as  lead  ochre,  a  yellow  earthy 
mineral  found  sparingly  among  lead  ores.  The  sulphide  is  the 
chief  ore  of  lead.  It  is  named  galena.  It  occurs  in  crystals 
derived  from  the  cubical  system,  usually  rhombic  dodecahedra. 
It  has  a  very  distinct  cubical  cleavage,  and  forms  leaden-coloured 
masses  with  brilliant  metallic  lustre.  It  is  found  in  the  Isle  of 
Man,  at  the  lead  hills  in  Lanarkshire,  in  Cornwall,  in  the  moun- 
tain limestone  of  Derbyshire,  and  in  the  lower  silurian  strata  of 
Cardiganshire  and  Montgomeryshire.  It  is  also  found  in  combina- 

*  J.praJct.  Chem.  (2),  34.  177;  36,  177;  Clem.  Centralll.,  1887,  329. 


OXIDES  AND   SULPHIDES  OF  SILICON,  GERMANIUM,  ETC.      295 

tion  with  the  sulphides  of  arsenic,  antimony,  and  copper.     Lead 
selenide  occurs  as  claustlialite,  and  the  telluride  as  altaite. 

Preparation. — 1.  Direct  union. — The  only  monoxide  obtain- 
able thus  is  that  of  lead.  It  is  prepared  as  massicot  by  heating 
lead  in  a  reverberatory  furnace  to  dull  redness,  taking  care  that 
the  resulting  oxide  shall  not  fuse,  and  raking  it  away  as  it  is 
formed.  If  the  oxide  fuses,  it  forms  litharge.  The  monosulphides 
of  tin  and  lead  are  also  produced  directly,  by  melting  the  metal 
and  adding  sulphur.  In  the  case  of  lead,  the  mixture  becomes 
incandescent  owing  to  the  heat  liberated  during  combination. 
Lead  selenide  is  similarly  prepared. 

2.  By  heating  a  compound. — Germanous,  stannous,  and  lead 
hydrates,  heated  in  a  current  of  carbon  dioxide,  lose  water,  leaving 
the  monoxides.     If  heated  in  hydrogen,  the  temperature  must  not 
exceed  80°,  else  reduction  to  metal  takes  place.     The  dehydration 
of  stannous  hydrate  takes  place  on  boiling  water  in  which  it  is 
suspended,  the  condition  being  the  absence  of  ammonia.     Lead 
hydrate  suspended  in  water  loses  water  on  exposure  to  sunlight, 
forming  crystalline   monoxide.      Tin   oxalate   and   lead   oxalate, 
carbonate,  or  nitrate,  when  heated,  yield  monoxides. 

3.  By  reducing  a  higher  compound. — Silicon  monoxide  is  said 
to  have  been  formed  as  one  of  the  products  of  heating  silica  in  the 
Cowles'  electric  furnace,  which  is  lined  with  carbon.     No  doubt  it 
would  be  possible  to  prepare  germanium  and  tin  monoxides  from 
the  dioxides  by  careful  heating  in  hydrogen  gas  ;  but  the  reduc- 
tion is  apt  to  go  too  far,  and  to  produce  metal.     Lead  dioxide  and 
its  compounds,  when  strongly  heated,  yield  monoxides. 

Silicon  disulphide,  when  heated  to  whiteness,  loses  sulphur, 
and  yields  monosulphide ;  and  germanium  disulphide  is  reduced  to 
monosulphide  by  heating  in  hydrogen. 

Stannic  sulphide,  SnS2,  loses  sulphur  at  a  red  heat,  forming 
monosulphide  ;  also  the  sesquisulphide,  Sn2S3. 

4.  By  double  decomposition. — Tin  and  lead  monoxides  are 
produced  by  heating  their  corresponding  chlorides,  SnCl2  or  PbCl2, 
with  sodium  carbonate.     It  may  be  supposed  that  the  carbonates 
first  formed  are  decomposed,  leaving  the  monoxides. 

The  sulphides  are  produced  by  heating  the  oxides  in  vapour  of 
carbon  disulphide,  or  in  the  case  of  germanium,  tin,  and  lead,  by 
treating  a  solution  of  a  salt  of  the  metal  or  of  the  hydroxide  in 
potassium  hydroxide  with  hydrogen  sulphide  or  some  other  soluble 
sulphide. 

Stannous  selenide  is  best  prepared  by  the  action  of  selenium  on 
hot  stannous  chloride. 


296       THE  OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES 

Properties. — Silicon  monoxide  is  said  to  be  an  amorphous 
greenish  powder ;  those  of  germanium  and  of  tin  blackish  powders. 
Tin  monoxide  may  be  obtained  crystalline  by  heating  a  mixture  of 
the  hydroxide  and  acetate  to  133° ;  and  of  a  vermilion  colour  by 
evaporating  a  solution  of  ammonium  chloride  in  which  the  hydrate 
is  suspended.  Lead  monoxide,  in  the  form  of  massicot,  is  lemon- 
yellow;  it  may  be  prepared  pure  by  strongly  heating  lead  car- 
bonate or  nitrate  ;  and  in  the  form  of  litharge  as  a  yellowish-red 
laminated  mass  of  crystals.  A  red  variety  is  produced  by  heating 
the  hydroxide  to  110°.  It,  too.  can  be  obtained  crystalline  by  fusion 
with  caustic  potash ;  it  separates  out  in  cubes  on  slow  cooling ;  if  it  is 
allowed  to  deposit  from  an  aqueous  solution  of  potassium  hydroxide 
it  separates  first  in  yellow  laminae,  and  afterwards  in  red  scales. 

Of  these  oxides,  lead  oxide  is  the  only  one  soluble  in  water  ;  it 
requires  7000  times  its  weight  of  water  for  solution. 

The  monoxides  of  silicon,  germanium,  and  tin  appear  to  have 
very  high  melting  points ;  lead  oxide  melts  at  a  red  heat. 

Silicon  monosulphide  is  a  volatile  yellow  body ;  that  of 
germanium,  when  obtained  by  precipitation,  forms  a  reddish- 
brown  amorphous  powder ;  but  when  prepared  in  the  dry  way 
it  consists  of  thin  plates,  transparent  and  transmitting  red  light ; 
but  grey,  opaque,  and  exhibiting  metallic  lustre  by  reflected  light. 
Its  vapour-density  is  normal,  corresponding  to  the  formula  GeS. 
It  volatilises  easily. 

Tin  monosulphide  is  a  leaden-grey  crystalline  substance, 
exhibiting  metallic  lustre.  It  has  also  been  prepared  by  electro- 
lysis of  a  solution  in  alkaline  sulphide,  and  then  forms  metallic- 
looking  cubes.  The  precipitated  variety  is  brown  and  amorphous, 
and  is  sparingly  soluble  in  alkaline  sulphides.  It  dissolves  in  and 
crystallises  from  fused  stannous  chloride,  SnCl2.  The  selenide 
forms  steel-grey  prisms. 

The  appearance  of  lead  sulphide  as  galena  has  been  already 
described.  When  heated  it  melts,  and  volatilises  at  a  high  tem- 
perature. Prepared  by  precipitation,  it  is  a  black  amorphous 
powder  if  the  solution  be  cold ;  and  if  warm,  greyish  and  crys- 
talline. 

Lead  sulphide  and  oxide  react  together  when  heated,  yielding 
metallic  lead  and  sulphur  dioxide,  thus — 

PbS  +  2PbO  =  3Pb  +  SO,. 

This  reaction  is  made  use  of  in  the  extraction  of  lead  from  its  ores. 
The  sulphide  when  roasted  is  converted  partially  into  the  oxide  ; 
and  on  raising  the  temperature,  metallic  lead  is  produced. 


OF  SILICON,   GERMANIUM,  TIN,  AND   LEAD.  297 

The  selenide  is  a  grey  porous  mass  when  artificially  prepared ; 
native  as  clausthallite  it  forms  leaden  grey  crystals  with  metallic 
lustre. 

Compounds  of  the  monoxides,  &c.  (a.)  With  water. — 
Silicon  monoxide  has  not  been  obtained  in  combination  with  water. 
The  hydrate  of  germanium  monoxide  has  not  been  analysed ;  it  is 
a  white  precipitate  produced  on  boiling  germanium  dichloride  with 
caustic  potash.  That  of  tin  monoxide  is  produced  by  adding 
sodium  carbonate  to  a  solution  of  tin  dichloride  ;  this  precipitate 
is  also  said  to  consist  of  a  basic  carbonate  of  the  formula 
CO2.2SnO  (see  p.  289). 

Hydrate  of  lead  monoxide,  prepared  by  precipitation  and  dried 
in  air,  has  the  formula  2PbO.H2O;  and  after  standing  for  some 
weeks  over  sulphuric  acid,  so  as  further  to  dry  it,  its  formula  is 
3PbO.H,O.  The  first  of  these  hydrates  forms  microscopic  crystals, 
and  the  second,  lustrous  octahedra. 

A  mixture  of  lead  hydrate  and  basic  carbonate  is  produced  on 
exposing  metallic  lead  to  the  action  of  water  and  air.  Water  alone 
has  no  effect  on  lead,  nor  has  oxygen ;  but  together  they  attack  it, 
and  as  the  metal  lead  is  commonly  used  for  water-pipes,  the  slight 
solubility  of  the  oxide  is  apt  to  cause  it  to  contaminate  the  water. 
It  is  found  that  the  presence  of  sulphates,  carbonates,  and  chlorides 
stops  this  action. 

(6.)  Compounds  with  oxides. — No  compounds  have  been  pre- 
pared with  silicon  or  germanium  monoxides ;  but  hydrated  tin  and 
lead  monoxides  are  soluble  in  sodium,  potassium,  calcium  and 
barium  hydroxides,  no  doubt  forming  compounds.  The  calcium 
compound  is  said  to  form  sparingly  soluble  needles.  A  yellow 
precipitate  of  the  formula  2PbO.Ag2O  is  produced  by  adding 
caustic  potash  to  a  mixture  of  two  soluble  lead  and  silver  salts ;  it 
is  probably  analogous  to  the  compounds  with  the  former  oxides. 
On  boiling  a  solution  of  stannous  hydrate  in  caustic  potash, 
metallic  tin  is  deposited,  and  a  stannate  (see  below)  is  formed. 

(c.)  Compounds  of  sulphides  with  sulphides.— Mono- 
sulphides  of  silicon,  germanium,  tin,  and  lead  are  insoluble  in 
solutions  of  monosulphides  of  the  alkalies,  and  no  compounds 
are  known.  Compounds  of  lead  sulphide  with  those  of  arsenic 
and  antimony  occur  in  nature,  and  will  be  described  later  on. 

(d.)  Compounds  with  halides. — No  compounds  of  silicon  or 
germanium   monoxides  with   halides    are   known ;    but    stannous 
chloride,  SnCl2,  if  dissolved  in  much  water,  deposits  a  white  pow- 
der of  the  formula  SnO.SnCl2.2H2O,  according  to  the  equation — 
2SnC'2.Aq  +  3H30  =  SnO.SnCl2.2H3O  +  2HCl.Aq. 


298      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES 

The  same  compound  is  produced   by   the  action  of   atmospheric 
oxygen  on  a  solution  of  stannous  chloride — 

3SnCl2.Aq  +  0  =  SnCl4.Aq  +  SnO.SnCl2.2H2O. 

The  decomposition  may  be  prevented  by  addition  of  a  soluble 
chloride,  such  as  hydrogen  or  ammonium  chloride,  which  forms  a 
double  salt  with  stannous  chloride  not  decomposed  by  air,  and  not 
altered  by  water  (see  p.  154). 

The  oxyhalides  of  lead  are  pretty  numerous.  A  fusible  oxy- 
fluoride  is  produced  by  heating  together  fluoride  and  oxide.  Five 
oxychlorides  are  known,  viz. : — 

PbO.3PbCl2,  a  laminar  pearl-grey  substance,  obtained  by  fusion 
of  oxide  with  chloride,  and  treatment  with  water. 

PbO.PbCl.,  found  native  as  matlockite  in  yellowish  translucent 
crystals  ;  and  produced  by  fusing  together  lead  chloride  and  carbon- 
ate, or  by  heating  lead  chloride  in  air.  It  is  manufactured  as  a 
pigment  by  adding  to  a  hot  solution  of  lead  chloride,  lime  water 
in  quantity  sufficient  to  remove  half  the  chlorine  as  calcium  chloride. 
It  has  a  white  colour,  and  good  covering  power. 

2PbO.PbCL,  a  mineral  known  as  mendipite,  forming  white, 
translucent  crystals. 

3PbO.PbCl>,  prepared  by  fusion ;  or  by  adding  a  solution  of 
sodium  chloride  to  lead  oxide.  It  is  a  yellow  substance,  and  is 
used  as  a  pigment  under  the  name  of  Turner's  yellow. 

5PbO.PbCl2,  produced  by  fusion,  is  a  deep  yellow  powder,  and 
7PbO.PbCL,  prepared  by  heating  together  litharge  and  ammonium 
chloride,  forms  cubical  crystals.  It  is  a  fine  yellow  pigment,  and  is 
known  as  Cassel  yellow. 

Two  oxybromides  have  also  been  produced,  by  decomposition  of 
the  double  bromide  of  lead  and  ammonium  (see  p.  154)  with 
water,  viz.,  PbO.PbBr2.H2O,  and  2(PbO.PbBr2)3H2O.  The  same 
compounds  are  produced  by  the  action  of  atmospheric  oxygen  on 
fused  lead  bromide,  PbBr2,  but  anhydrous.  Oxyiodides  of  the 
formulae  PbO.PbI2,  2PbO.PbI2.H,O,  3PbO.PbI2.2H2O,  and 
5PbO.PbI2,  are  produced  by  similar  reactions.  The  first  of  these, 
when  prepared  by  the  action  of  hydrated  lead  peroxide  on  potas- 
sium iodide  in  contact  with  air,  combines  with  the  potassium 
carbonate  produced  by  the  action  of  the  carbon  dioxide  of  the  air 
on  the  resulting  potassium  hydroxide,  giving  compounds  of  the 
formulae  PbO.PbI2.K2CO32H2O,  2(PbO.PbL)3K2CO3.2H2O,  and 
PbI2.2KI.K>CO3.3H2O  ;  and  by  mixing  together  potassium 
iodide  and  lead  carbonate,  the  compound  PbO.Pb^.CO^  is  pro- 
duced. 


OF  SILICON,  GERMANIUM,  TIN,  AND  LEAD.  299 

It  appears  possible  also  to  obtain  mixed  halides ;  one  of  these 
produced  by  the  action  of  lead  oxide  on  zinc  chloride  has  the 
formula  PbO.ZnCL. 

II.  Sesquioxides  and  sesquisulphides. — Of  these  compounds, 
hydrated  sesquioxides  of  silicon  and  tin,  sesquioxide  of  lead,  and  tin 
sesquisulphide  are  the  only  representatives.  Their  formulae  are 
Si,O3.H2O,  Sn,O3nH2O,  Pb2O3,  and  Sn2S3.  The  first,  Si3O3.H2O, 
from  its  analogy  to  the  corresponding  carbon  compound,  oxalic  acid, 
is  sometimes  named  silico-oxalic  acid.  The  constitution  of  oxalic 
acid  has  been  noticed  on  p.  273,  and  it  is  probable  that  the 
analogous  silicon  compound  is  similarly  constituted.  It  is  pro- 
duced by  the  action  of  ice-cold  water  on  silicon  hexachloride  ;  and 
its  formation  may  be  represented  graphically  thus  : — 

Si^Cl  +  °<H        Si<°  2H(? 

IXGI     H.OH  =    *  OH      HC1 

'n!       H'°w~    Q-^OH         HC1 
&1^0  2HC1 


four  atoms  of  chlorine  being  replaced  by  two  atoms  of  oxygen, 
and  two  byhydroxyl  (OH)'.  It  is  a  white  mass;  but  unlike  oxalic 
acid  the  remaining  hydrogen  of  the  hydroxyl  cannot  be  replaced 
by  metals.  It  is,  therefore,  said  to  be  "  devoid  of  acid  properties." 
When  treated  with  any  soluble  hydroxide,  it  gives  a  silicate  with 
evolution  of  hydrogen.  The  compound  is,  however,  of  considerable 
interest,  inasmuch  as  it  displays  the  analogy  between  silicon  and 
carbon. 

Hydrated  sesquioxide  of  tin  is  said  to  be  produced  by  boiling 
together  hydrated  ferric  sesquioxide,  Fe2O3.nH2O,  and  stannous 
chloride,  SnCl2.  It  is  a  slimy  grey  precipitate. 

Lead  sesquioxide,  Pb2O3,  is  produced  by  the  action  of  sodium 
hypochlorite,  NaOCl.Aq,  en  salts  of  lead,  or  on  a  solution  of  lead 
hydrate  in  caustic  soda ;  and  also  by  the  action  of  alkalies  on  a 
solution  of  red  lead  in  acetic  acid.  The  last  action  will  be  noticed 
below,  in  treating  of  red  lead.  The  sesquioxide  is  a  reddish-yellow 
insoluble  powder ;  it  dissolves  for  a  moment  in  hydrochloric  acid, 
but  almost  at  once  chlorine  is  evolved,  and  the  dichloride  precipi- 
tated. No  double  compounds  of  sesquioxides  are  known. 

Tin  sesqui sulphide  is  produced  by  heating  three  parts  of  the 
monosulphide  with  one  part  of  sulphur  to  dull  redness.  It  has  a 
greyish-yellow  metallic  lustre,  and  at  high  temperatures  decom- 
poses into  monosulphide  and  sulphur. 


300      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND  TELLUR1DES 


III.  Dioxides,  disulphides,  diselenides,  and  ditellurides. 

List.                  Oxygen.  Sulphur.  Selenium.  Tellurium. 

Silicon SiO2  SiS2  SiSe2?  SiTe2 

Orermanium    GeO2  GeS2  ?  ? 

Tin SnO2                SnS2  SnSe2  ? 

Lead    PbO2                 —  —  — 


These  are  the  most  stable  compounds  with  silicon,  germanium, 
and  tin ;  lead  dioxide,  however,  easily  loses  oxygen. 

Sources. — Silicon  dioxide  occurs  native  in  hexagonal  prisms, 
capped  by  hexagonal  pyramids,  as  rock-crystal,  bog-diamond,  or  Irish 
diamond.  When  coloured  yellow  or  orange  by  sesquioxide  of  iron 
it  is  named  cairngorm;  it  also  also  occurs  with  an  amethyst 
colour  due  to  manganese  sesquioxide  ;  and  of  a  rose-red  colour  (rose- 
quartz).  It  is  very  hard,  easily  scratching  glass.  It  frequently  con- 
tains small  cavities,  filled  with  liquid  carbon  dioxide,  often  contain- 
ing a  minute  cubical  crystal  of  sodium  chloride.  Quartz  is  a  name 
applied  to  less  perfectly  crystalline  silica,  and  usually  occurs  in 
white  translucent  masses.  When  perfectly  transparent  it  is  used 
for  the  lenses  of  spectacles,  being  harder  and  less  easily  scratched 
than  glass.  It  is  cut  into  slices  by  a  copper  disc,  moistened  with 
emery  and  oil,  then  ground  and  polished.  Flint  and  chert  are 
forms  of  silica  found  embedded  in  chalk,  or  older  limestones,  and 
are  due  to  the  siliceous  spicules  of  sponges,  now  extinct.  It  has 
usually  a  dull  grey-brown  colour,  owing  probably  to  its  containing 
some  free  carbon,  derived  doubtless  from  the  animal  matter  of  the 
shell-fish,  the  remains  of  which  constitute  the  chalk,  for  it  turns 
white  on  ignition.  Chalcedony  is  a  variety  of  quartz,  not  display- 
ing definite  crystalline  structure,  but  showing  a  fibro-radial  struc- 
ture, and  occurring  in  kidney-shaped,  translucent  masses.  Varieties 
of  chalcedony  are  named  agate,  hornstone,  onyx,  carnelian,  catseye, 
chrysoprase,  &c.  Sandstone  consists  mainly  of  water-  or  air-rolled 
grains  of  quartz,  bound  together  by  a  little  lime. 

Silica  also  occurs  in  combination  with  many  other  oxides,  as 
silicates.  With  water,  it  occurs  as  opal,  an  amorphous  translucent 
substance,  which  has  been  deposited  in  thin  layers.  This  pro- 
duces in  some  specimens  a  brilliant  play  of  colours,  owing  to  the 
refraction  and  interference  of  the  light  which  it  reflects.  Opal 
is  soluble  in  a  hot  solution  of  potassium  hydrate ;  it  is  thus  dis- 
tinguished from  quartz.  The  other  silicates  will  be  considered 
later. 


.OF   SILICON,  GERMANIUM,   TIN,  AND   LEAD.  301 

Germanium  disulphide,  in  combination  with  silver  snlphide, 
forms  the  mineral  argyrodite,  found  in  the  Himmelsfiirst  mine  at 
Freiberg.  It  is  almost  the  only  mineral  in  which  germanium  has 
been  found. 

Tin  dioxide,  named  cassiterite,  or  tinstone,  is  the  only  important 
source  of  tin.  It  occurs  in  veins,  traversing  the  primitive  granite 
and  slate  of  Cornwall ;  it  is  also  exported  from  Melbourne.  It 
forms  translucent  white,  grey,  or  brownish  quadratic  crystals.  Its 
crystalline  form  is  the  same  as  that  of  anatase,  one  of  the  forms  of 
titanium  dioxide. 

Stannic  sulphide,  SnS2,  occurs  in  combination  with  sul- 
phides of  iron  and  copper,  and  is  named  tin  pyrites. 

Preparation. — 1.  By  direct  union. — Silicon  dioxide,  or  silica, 
is  formed  when  silicon  barns  in  air  or  oxygen.  Germanium 
dioxide  and  stannic  oxides  are  similarly  produced.  The  oxides  thus 
prepared  are  amorphous.  Lead  unites  with  oxygen  to  form  mon- 
oxide, PbO,  as  already  mentioned.  The  highest  stage  of  oxida- 
tion produced  directly  is  that  of  red  lead,  Pb304  =  PbO2.2PbO. 
Stannous  oxide  also  unites  directly  with  oxygen  to  produce  the 
dioxide. 

2.  By  decomposing  a  double  compound. — All  these  oxides 
remain  on  heating  to  redness  their  various  hydrates ;  germanium 
dioxide  has  also  been  prepared  from  its  sulphate,  Ge(SO4)2,  which 
loses  sulphur  trioxide  at  a  red  heat. 

3.  Prom  lower  compounds. — Lead  monoxide  heated  to  dull 
redness  with  potassium  chlorate  is  oxidised  to  the  dioxide.     The 
potassium  chloride  and  excess  of   chlorate  are  dissolved  out  by 
water.     It  is  also  formed  by  fusing  lead  monoxide  with  potassium 
hydroxide.     Hydrogen  is  evolved,  and  potassium  plumbate  is  pro- 
duced;   on  treatment  with  water   the  dioxide  remains   in  black 
hexagonal  tables. 

Tin  disulphide  and  diselenide  are  prepared  by  a  somewhat 
curious  method.  When  tin  and  sulphur  are  heated  together,  the 
sesquisulphide  is  the  highest  sulphide  formed.  But  if  ammonium 
or  mercuric  chloride  be  heated  in  a  glass  retort  with  the  mixture 
of  tin  and  sulphur  the  disulphide  is  produced.  It  is  supposed 
that  a  double  chloride  of  tin  and  ammonium,  or  of  tin  and  mercury, 
is  first  formed,  and  that  this  reacts  with  sulphur,  thus : — 
2(SnCl2.2NH4Cl)  +  2S  =  SnS2  +  SnCl4.2NH4Cl  +  2NH4C1. 
Diselenide  of  tin  is  produced  by  the  action  of  iodine  on  the 
monoselenide,  in  presence  of  carbon  disulphide,  thus  : — 2SnSe  + 
2I2  =  SnLi  +  SnSe2 ;  at  the  same  time  some  selenium  is  liberated, 
according  to  the  equation,  SnSe  +  2I3  =  SnI4  +  Se.  The  tin 


302       THE  OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES 

tetriodide  dissolves  in  the  carbon  disulphide,  leaving  the  di- 
selenide,  which  is  insoluble. 

4.  By  double  decomposition. — Tin  dioxide  is  produced  in  a 
crystalline  form  by  passing  the  vapours  of  stannic  chloride,  SnCU, 
and  water  through  a  red-hot  tube.  The  crystals  produced  are  of  the 
same  form  as  brookite  (Ti02)  :  quadratic  crystals  are  formed  by 
the  action  of  hydrogen  chloride  on  the  red-hot  dioxide.  The  di- 
sulphides  of  silicon  and  germanium  are  both  produced  by  double 
decomposition.  To  prepare  the  former,  silica,  or  a  mixture  of 
carbon  and  silica,  is  exposed  at  a  white  heat  to  the  action  of 
carbon  disulphide ;  the  monosulphide  is  simultaneously  produced, 
probably  owing  to  the  decomposition  of  the  disulphide.  The 
disulphides  of  germanium  and  of  tin  are  precipitated  from  solutions 
of  the  dioxides  by  hydrogen  sulphide.  Tin  disulphide  is  also 
produced  by  passing  a  mixture  of  hydrogen  sulphide  and  gaseous 
tin  tetrachloride  through  a  tube  heated  to  dull  redness. 

Properties. — The  properties  of  native  silica  have  been  already 
described.  It  fuses  at  a  white  heat  in  the  oxyhydrogen  flame  to  a 
p;lassy  mass,  which  can  be  drawn  into  threads.  In  this  form  it 
furnishes  one  of  the  besb  insulators  for  electricity,  and  has  been 
used  to  suspend  the  needles  of  galvanometers.  Such  threads  have 
great  tenacity  and  are  very  elastic.  Even  when  moist  they  do  not 
conduct.  Amorphous  silica,  produced  by  heating  the  hydrate,  is 
a  loose  white  powder;  it  is  said  to  volatilise  when  heated  to 
whiteness  in  water-vapour,  resembling  boron  oxide  in  this  respect. 
While  the  crystalline  form  is  not  attacked  by  solutions  of  potas- 
sium or  sodium  hydroxide,  the  amorphous  variety  dissolves 
slowly.  Crystalline  silica  is  attacked  only  by  hydrofluoric  acid. 

Germanium  dioxide  is  a  dense,  gritty,  white  powder, 
sparingly  soluble  in  water,  and  crystallising  from  it  in  small 
rhombohedra.  Its  solubility  is  : — 1  gram  of  Ge02  dissolves  in 
247'1  grams  of  water  at  20°,  and  in  95'3  grams  at  100°. 

Tin  dioxide  is  a  white  or  yellowish  powder,  insoluble  in 
water.  It  turns  dark  yellow  when  heated,  but  again  becomes 
white  on  cooling.  Under  the  name  "  putty  powder "  it  finds 
commercial  use  in  polishing  stone,  glass,  steel,  &c. 

Lead  dioxide  is  a  soft  brown  powder,  insoluble  in  water; 
when  heated  to  redness  it  loses  oxygen,  leaving  a  residue  of 
monoxide. 

Silicon  disulphide  forms  long  white  volatile  needles.  It  is 
remarkable  that  the  oxide  is  so  non- volatile,  while  the  sulphide 
can  be  sublimed ;  it  leads  to  the  supposition  that  while  the 
sulphide  has  the  formula  assigned  to  it,  SiS2,  the  formula  of  the 


OF   SILICON,  GERMANIUM,  TIN,  AND  LEAD.  303 

oxide,  as  we  know  it,  is  really  a  high  multiple  of  Si02.  And  on 
comparing  the  silicon  and  carbon  compounds,  this  conclusion  is 
strengthened.  For  while  the  boiling-points  of  carbon  dioxide, 
disulphide,  and  tetrachloride  are  respectively  —  78'5°,  46°,  and  76'7°, 
an  ascending  series,  we  have  with  silicon,  the  dioxide  melting  at 
a  white  heat,  the  sulphide  easily  volatile,  and  the  chloride  boiling 
at  58°.  The  order  of  volatility  is  reversed.  And  as  it  is  found 
with  compounds  of  carbon  and  hydrogen,  that  the  more  complex 
the  molecule,  the  higher  the  boiling-point,  we  may  conclude  that 
the  non-volatility  of  silica  is  due  to  its  molecular  complexity. 
There  is  at  present,  however,  no  means  of  ascertaining  how  many 
molecules  of  Si02  are  contained  in  the  complex  molecule  of  ordi- 
nary silica,  the  formula  of  which  must  therefore  be  written 

(Si02)». 

Germanium  disulphide  is  described  as  a  white  precipitate, 
sparingly  soluble  in  221 '9  parts  of  water,  and  also  soluble  in 
sulphides.  It  appears  not  to  decompose  on  solution  ;  but  silicon 
disulphide  reacts  with  water,  forming  hydrogen  sulphide  and  a 
hydrate  of  silica. 

Tin  disulphide,  prepared  by  precipitation,  is  a  buff-yellow 
powder,  insoluble  in  water.  When  obtained  by  the  dry  process 
it  forms  golden-yellow  scales,  and  is  named  "  mosaic  gold."  The 
diselenide  is  a  red-brown  crystalline  powder. 

Double  compounds. — It  is  convenient  to  group  these  as 
follows : — (a)  Compounds  of  the  oxides  with  water  and  oxides  ; 
(b)  oxyhalides  and  sul  phohalides ;  (c)  compounds  of  sulphides 
with  other  sulphides ;  and  (d)  oxy sulphides. 

(a.)  Compounds  with  water  and  oxides. — The  most  im- 
portant of  these  compounds  are  the  silicic  acids  and  the  silicates ; 
allied  to  them  are  the  stannates  and  plumbates,  and  there  appears 
to  be  indications  of  the  existence  of  germanates. 

General  Remarks  on  the  Silicates. — The  ratios  between  the 
oxygen  of  the  silica  and  the  oxygen  of  the  metallic  oxides  com- 
bined with  it  are  very  numerous.  The  silicates  form  a  very  large 
portion  of  the  crust  of  the  earth,  and  they  have  very  varied  com- 
position. Among  the  native  silicates  the  ratio  of  oxygen  in  silica 
to  that  in  oxide  of  metal  may  vary  for  monad  and  dyad  metals, 
such  as  potassium  or  calcium,  between  2  :  4  and  4:1;  or  to  take 
hypothetical  specific  instances, — between  SiO2.4K2O,  or  Si02.4CaO 
and  2SiO2.K20,  or  2Si02.CaO  ;  and  for  silicates  of  triad  metals,  such 
as  aluminium  or  iron,  between  2  :  6,  as  in  Si02.2Al203,  and  12  to 
3,  as  in  6Si02.Al203.  It  must  be  remembered  that  the  native 
silicates  have  almost  always  been  formed  in  a  matrix  containing 


304      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

compounds  of  many  elements ;  hence  it  is  rare  to  find  among  the 
silicates  pare  compounds  such  as  those  of  which  the  formulae  have 
been  given  above.  For  instance,  it  is  not  unusual  to  tin d  a  silicate 
containing  both  the  metals,  potassium  and  calcium,  as  oxides  com- 
bined with  silica  ;  or  the  oxides  of  the  metals,  iron  and  aluminium, 
or  of  calcium  and  aluminium,  and  that  not  in  atomic  proportion ; 
for  we  may  have  a  silicate  of  aluminium  containing  only  a  trace  of 
iron,  or  a  silicate  of  calcium  containing  only  a  trace  of  magnesium 
or  ferrous  iron,  the  crystalline  form  of  which  does  not  differ  from 
that  of  the  pure  silicate.  It  is  not  to  be  conceived  that  in  such 
instances  any  given  molecule  has  not,  as  is  usual  among  compounds, 
a  perfectly  definite  formula ;  but  it  would  appear  that  it  is  possible 
for  an  apparently  homogeneous  crystal  to  be  made  up  of  molecules 
of  silicate  of  aluminium  and  silicate  of  iron,  or  of  silicate  of  mag- 
nesium and  silicate  of  calcium  in  juxtaposition  ;  so  that,  to  take  a 
suppositious  case,  a  crystal  containing  1000  molecules  might 
consist  of  999  molecules  of  magnesium  silicate  and  one  molecule 
of  calcium  silicate,  or  of  998  molecules  of  magnesium  silicate  and 
two  molecules  of  calcium  silicate,  and  so  on;  oxides  of  magnesium 
and  calcium  being  mutually  replaceable  in  any  proportion  what- 
ever. And  similarly  with  the  compounds  of  silica  with  the  sesqui- 
oxides  of  iron  and  aluminium.  But  all  oxides  are  not  capable  of 
mutually  replacing  each  other.  While  beryllium,  calcium,  mag- 
nesium, iron,  manganese,  nickel,  cobalt,  sodium,  and  potassium 
monoxides  mutually  replace  one  another,  and  while  the  sesqui- 
oxides  of  aluminium,  iron,  manganese,  chromium,  &c.,  are  also 
mutually  replaceable,  it  is  found  that  the  place  of  a  monoxide  is 
not  taken  by  a  sesquioxide,  and  vice  versa.  But  a  silicate  may 
contain  at  once  a  mixture  of  sesquioxides  and  a  mixture  of  mon- 
oxides in  combination  with  silica. 

To  deduce  the  formula  of  a  natural  silicate  from  its  percentage 
composition  is  a  problem  of  some  difficulty.  It  is  solved  by  ascer- 
taining the  ratio  of  all  the  oxygen  combined  with  dyad  metals, 
whatever  they  may  be,  to  that  combined  with  triad  metals,  and 
to  that  contained  in  the  silica.  An  example  will  render  this  clear. 

On  analysis,  a  specimen  of  the  felspar  named  orthoclase  (which  is 
essentially  a  silicate  of  aluminium  and  potassium,  but  which  may 
contain  iron  sesquioxide  replacing  alumina,  and  sodium,  magnesium, 
and  calcium  oxides  replacing  potassium  oxide)  gave  the  following 
numbers : — 

SiO2.          A12O3.  CaO.  K2O.  Na2O. 

65-69         17-97  T34         L3'99  1-01  =  lOO'OO  per  cent. 


FORMULA   OF  SILICATES.  305 

These  constituents  contain  oxygen  in  the   following   propor- 
tions : — 

32  48  16  16  16 


OV33  102-02  6b'-u8  94-28  62'09, 

the  denominators  being  the  molecular  weights  of  the  oxides,  and 
the  numerators  the  oxygen  contained  in  these  weights.  The  ratios 
are,  therefore,  as  follows  : — 


SiO,.  A12O3.  CaO.  K2O. 

65-69  x  32    17-97  X  48    1'34  x  16    13-99  x  16    1-Q1  X  16 
60-33  102-02  5b'-o8  94'28  62-09 

or  34-84  +  8'45   +  0'38  +  2'37  +  0'26  =  46*30  per  cent,  of 
oxygen. 

We  have,  therefore,  the  ratio  : — 

Oxygen  in  silica.         Oxygen  in  alumina.          Oxygen  in  lime,  potash,  and  soda. 
34-84  :  8-45  0'38  +  2'37  +  0'26  =  3'01* 

or       12  :  3  :  1,  nearly. 

Hence  the  formula  is  6Si02.Al203.M20,  where  M  stands  for 
calcium,  potassium,  or  sodium.  It  is  usually  written  thus  : — 
6Si02.Al203.(Ca,  K2,  Xa2)0,  the  comma  between  those  symbols  en- 
closed within  brackets  signifying  that  they  are  mutually  replaceable 
in  any  proportions.  Had  iron  sesquioxide  been  present,  the  oxygen 
contained  in  it  would  have  been  added  to  that  of  the  alumina,  and 
the  formula  would  then  have  been  written, 

6Si02(Al,Fe)203(Ca,  K2,  Na2)0. 

As  with  the  borates,  chromates,  and  carbonates,  there  are 
two  methods  of  representing  the  formulae  of  the  silicates.  The 
first  method  is  to  consider  them  as  addition  compounds  cf 
silica  with  other  oxides,  and  the  formula  of  orthoclase,  as  written 
above,  is  constructed  on  that  principle.  It  must,  however,  clearly 
be  understood  that,  inasmuch  as  we  know  almost  nothing  regard- 
ing the  internal  constitution  of  such  compounds,  we  can  only  guess 
at  their  structure  from  analogy  with  the  hydrocarbons  and  their 
derivatives. 

The  method  of  writing  given  above  does  not  imply  that  the 
compound  contains  as  such  the  molecular  group  Si02  united  with 

*  The  calculated  ratio  of  oxygen  in  the  above  compound  is — 

Si02.  A1203.  M20. 

34-39  :  869  :  2'87. 


306      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLUKIDES. 

molecular  groups  A1203  and  K20.  It  is  merely  a  method  of  show- 
ing the  proportions  of  ingredients  which  the  compound  contains 
in  an  orderly  manner,  and  is  better  than  if  we  were  to  write  the 
formula,  Al2K2Si6Oi6. 

The  second  method  starts  from  the  fact  that  in  such  compounds 
silicon  is  a  tetrad  element;  that  analogous  to  its  compounds 
with  fluorine  or  chlorine,  SiF4  or  SiCl4,  the  typical  silicic  acid 
has  the  formula  Si(OH)4.  This  substance  is  named  orthosilicic 
acid.  Its  salts  may  be  supposed  to  be  formed  by  'replacing  the 
hydrogen  of  the  hydroxyl  groups  by  metals  ;  thus  the  potassium  salt 

/0>Ca 
has  the  formula  Si(OK)4,  the  calcium  salt.'Si04Cair2,  or  Si 


and  the  aluminium  salt,  3(Si04)IVAl4m.  These  are  the  same  as 
Si02.2K20,  Si02.2CaO,  and  3Si02.2Al203,  and  are  named  ortho- 
silicates. 

Silicates  of  the  formula,  Si02.K20,  Si02.CaO,  &c.,  are  also 
known,  and  in  them  the  oxygen  of  the  silica  bears  the  ratio  to  that 
of  the  oxide  as  2:1.  These  may  be  supposed  to  be  derived  from 
the  hydroxide  Si02.H20,  which  is  named  metasilicic  acid,  and 
which  may  be  regarded  as  orthosilicic  acid  deprived  of  a  mole- 

^O 
cule  of  water;  its  constitution  maybe  represented  Si\OH,  and  its 

XOH 

^0  .0 

potassium  and  calcium  salts  as  Si^OK,  and  Si\~(X   ~ 

XOK  \0>0a. 

It  will  be  remembered  that  an  analogy  was  drawn  between 
chromyl  dichloride  Cr02Cl2,  and  chromic  acid  CrO2(OH)2  (see 

p.  268),  and  it  was  pointed  out  that  the  substance  Cr02<QL 
might  be  regarded  as  partaking  of  the  nature  both  of  the 

OT£~ 

dichlovide  and  of  potassium  chromate,  Cr02<Qg-,  being,  in  fact, 

an  intermediate  stage.  We  should  expect,  therefore,  intermediate 
compounds  between  silicon  tetrachloride,  SiCl4,  and  silicon  tetra- 
hydroxide,  Si(OH)4.  Only  one  such  body  is  known,  viz.,  SiCl3.SH, 
in  which  hydrosulphuryl  replaces  hydroxyl.  But  derivatives  of  the 
elements  of  this  group  are  known,  which  represent  similar  com- 
pounds connected  with  metasilicic  acid,  SiO(OH)2.  Although  the 
corresponding  chloride  SiOCl2  is  unknown,  yet  it  is  represented 

^0 

by  GeOCl2  ;    and  although   Si^OH  is  also  unknown,  it  finds  a  re- 

XC1 


THE  SILICATES.  307 


preservative  in  the  compound  of  tin,  Sn\  OH.  This  method  of  repre- 

XC1 

sentation,  which  may  be  termed  the  method  of  substitution,  is,  there- 
fore, justified. 

But  we  may  go  still  further  Hitherto  we  have  been  dealing 
with  compounds  containing  only  one  atom  of  silicon.  It  is,  how- 
ever, conceivable  that  two  molecules  of  orthosilicic  acid  may  form 
an  anhydride,  water  being  lost  between  them,  thus  :  — 


-H20  =  (1)          Q     ;  and  further  (2) 
.OH  /OH 

./OH 


OH 

Si^OH 

and  (3)       >0    . 
SiOH 


The  compound  (1)  is  termed  disilicic  acid;  (2)  is  the  first,  and 
(3)  the  second  anhydride  of  disilicic  acid.  A  representative  of 
(1)  is  serpentine,  2Si02.3MgO  ;  wollastonite,  2Si02.2CaO,  may  be 
a  representative  of  (2),  although  its  formula  may  equally  well  be 
the  simpler  one,  SiO2.CaO,  or  SiO(O2)Ca;  and  okenite,  2Si02.CaO, 
may  represent  the  calcium  salt  of  (3). 

A  chlorine-derivative  of  (1),  however,  is  known,  viz.,  Si2OCl6, 
in  which  all  hydroxyl  is  replaced  by  chlorine.  That  it  possesses 
that  simple  formula  is  shown  by  its  vapour-density. 

In  a  similar  manner,  a  trisilicic  acid  may  be  derived  from 
three  molecules  of  orthosilicic  acid,  by  loss  of  two  molecules  of 
water  ;  it  in  its  turn  will  yield  three  anhydrosilicic  acids  ;  and  a 
tetrasilicic  acid  may  be  supposed  to  exist,  of  which  four  anhydro- 
acids  are  theoretically  capable  of  existence.  Of  this  tetrasilicic 
acid  three  chlorine-derivatives  have  been  prepared  of  the  formula, 
Si403Clio,  Si404Cl8,  and  Si4O5Cl6,  corresponding  to  the  respective 
acids,  Si4O3(OH)10,  Si404(OH)8,  and  Si4O5(OH)6,  as  shown  by  their 
vapour-densities.  The  first  is  tetrasilic  acid  itself  ;  the  second  and 
third  its  first  and  second  anhydrides  respectively.  Salts  of  even 
more  condensed  silicic  acids  may  exist. 

Many  silicates  are  known,  containing  more  base  than  that 

x  2 


308      THE   OXIDES,  SULPHIDES,   SELEXIDES,  AND  TELLURIDES. 

contained  in  orthosilicates,  in  which  the  ratio  is  Si02.2M''0.  For 
example,  colly  rite  has  the  formula  SiO2.2Al203,  the  ratio  of  oxygen 
in  the  silica  to  that  in  the  oxide  being  2  :  6.  Such  silicates  are 
termed  basic.  Their  formulae  may  be  written  in  an  analogous 
manner,  on  the  supposition  that  the  metal  exists  partly  as  oxide, 
partly  as  silicate.  Thus  the  above  compound  may  be  represented 
thus  :  — 

0—  AlZZO 

—  AlzzO 

—  AlzzO  ; 

—  AlzzO 


each  atom  of  aluminium  being  one-third  ortho-silicate,  and  two- 
thirds  oxide.  And  so  with  other  instances. 

These  remarks  must  be  held  to  apply  also  to  the  titanates, 
zirconates,  stannates,  and  plumbates  ;  but  similar  compounds  of 
tin  and  lead  are  not  numerous. 

One  point  must  still  be  noticed  before  proceeding  with  a 
description  of  the  silicates,  viz.,  the  question  as  to  whether  or  not 
water,  occurring  in  combination  with  a  silicate  or  stannate,  should 
be  included  in  the  formula.  For  example,  by  including  water,  a 
compound  of  the  formula  Si02.CaO.H20  may  be  represented  as 
OH 

an  orthosilicate,  SiXQ^Ca,  or,  excluding  the  water,  as  a  meta- 

SOH 

^o 

silicate,  Sir-CK   r  .H20,   the  water  being   regarded   as   water   of 


crystallisation.  There  is  no  rule  for  guidance  in  discriminating 
water  of  crystallisation  from  combined  water  ;  and  indeed  we  have 
no  reason  to  regard  water  of  crystallisation  as  combined  in  any 
other  fashion  than  other  oxides.  At  present,  however,  no  satis- 
factory theory  has  been  devised  whereby  water  of  crystallisa- 
tion can  be  rendered  a  part  of  the  formula,  like  the  molecule  of 
water  in  the  first  example  given  above  ;  and  in  the  present  state  of 
our  knowledge  the  only  course  is  to  exercise  discretion  as  regards 
its  inclusion  or  exclusion. 


THE   SILICATES,   STANNATES,   AND  PLUMBATES.  309 


Silicates,  Stannates,  and  Plumbates. 

8iO2.2H2O  (?)  =  Si(OH)4 ;  SiO2.H2O  =  SiO(OH)2.— 
SnO2.4H2O   (?)  =  Sn(OH)4;     SnO2.H2O   (?)  =  SnO(OH)2 

7SnO2.2H2O  ;  5SnO2.5H2O. 
PbO2.H2O  j  3PbO2.H2O. 

These  compounds  are  very  inde finite.  On  addition  of  dilate 
hydrochloric  acid  to  a  dilute  solution  of  sodium  or  potassium  sili- 
cate, no  precipitate  is  produced.  Placing  this  solution  in  a 
dialyser — a  circular  frame,  like  a  tambourine,  covered  with  parch- 
ment or  parchment  paper  or  bladder,  and  floated  on  water — the 
crystalline  sodium  chloride  passes  through  the  diaphragm,  while 
the  colloid  (glue-like)  non-crystalline  silicic  acid  remains  behind 
for  the  most  part.  It  was  suggested  by  Graham,  the  discoverer  of 
this  method  of  separation,  that  the  molecules  of  the  colloid  body  are 
much  more  complicated  and  larger  than  those  of  the  crystalline 
substance,  and  hence  pass  much  more  slowly  through  the  very 
minute  pores  of  the  dialyser.  To  such  passage  Graham  gave  the 
name  osmosis,  and  the  general  phenomenon  is  termed  diffusion. 
Recent  researches  appear  to  confirm  this  view,  and  to  show  that 
the  molecules  of  colloid  bodies  are  very  complex.  It  is  supposed 
that  the  silicic  hydrate  thus  remaining  soluble  is  orthosilicic  acid, 
Si(OH)i,  inasmuch  as  it  is  produced  from  an  orthosilicate.  To 
obtain  it  pure,  the  water  outside  the  dialyser  must  be  frequently 
renewed.  A  solution  of  silicic  acid  containing  5  per  cent,  of  Si02 
may  thus  be  prepared  ;  and  by  placing  it  in  a  dry  atmosphere  over 
sulphuric  acid,  it  is  slowly  concentrated  until  it  reaches  a  strength 
of  14  per  cent. 

It  forms  a  limpid  colourless  liquid,  with  a  feeble  acid  reaction. 
When  warmed,  it  gelatinises ;  this  change  is  retarded  by  the 
presence  of  a  small  amount  of  hydrochloric  acid,  or  of  caustic  soda 
or  potash  ;  but  is  furthered  by  the  presence  of  a  carbonate. 

Similar  results  were  obtained  from  a  stannate  mixed  with 
dilute  hydrochloric  acid,  and  also  from  a  titanate.  The  solutions 
have  similar  properties. 

It  is  supposed  that  the  gelatinous  .substance  produced  from 
orthosilicic  acid  is  metasilicic  acid,  SiO(OH)2.  When  dried  for 
several  months  over  strong  sulphuric  acid,  it  corresponds  with 
that  formula.  This  hydrate  is  also  supposed  to  be  produced  when 
a  halide  of  silicon  reacts  with  water.  A  convenient  method  of 
preparation  consists  in  leading  silicon  fluoride  into  water  (see 
p.  153).  It  is  said  to  have  been  obtained  in  crystals  of  the 


310      THE   OXIDES,   SULPHIDES,  SELENIDES,   AND   TELLURIDES. 

formula  SiO(OH)2.3H2O,  by  the  action  of  hydrochloric  acid  on  a 
siliceous  limestone. 

On  drying  precipitated  silica  for  five  months  over  sulphuric 
acid,  it  had  the  approximate  formula  3SiO2.4H2O.  When  the 
temperature  was  raised,  it  lost  water  gradually,  but  no  evidence  of 
any  definite  hydrate  was  obtained ;  no  point  could  be  found  at 
which  a  small  rise  of  temperature  did  not  produce  a  further  loss  of 
water.  The  same  remarks  apply  to  stannic  hydrate.  But  about 
360°,  the  substance,  which  had  the  composition  3SnO2.H2O,  and  a 
dirty  brown  colour,  displayed  a  sudden  change  of  colour  to  pale 
yellow,  and  had  then  the  formula  7SnO2.2H...O. 

When  metallic  tin  is  treated  with  strong  nitric  acid,  it  is 
oxidised  ;  copious  red  fumes  are  evolved,  and  a  white  powder  is 
produced.  While  ordinary  hydrate,  prepared  by  precipitation,  is 
soluble  in  acids,  this  white  substance  is  not ;  and  after  drying  in  a 
vacuum  or  at  100°  it  has  the  formula  5SnO2.5H2O  (see  below). 

Hydrated  lead  peroxide,  dried  in  air,  has  the  formula 

3PbO,.H20. 

On  further  heating1,  water  and  then  oxygen  are  lost. 

By  passing  a  current  of  electricity  between  two  lead  plates, 
dipping  in  dilute  sulphuric  acid,  hydrated  peroxide  of  lead  is 
formed  on  the  positive,  while  hydrogen  is  evolved  at  the  negative 
plate.  This  hydrate  has  the  formula  PbO2.H2O.  Such  an 
arrangement  gives  a  very  powerful  current,  lead  peroxide  being 
very  strongly  electro-positive ;  and  it  is  made  use  of  for  "  storage 
batteries." 

SiO2.2Li2O;   SiO2.Li2O  ;  5SiO2.:Li2O.—  SiO2.2Na2O(?)  ;  SiO2.Na2O.8H2O  ; 

5SiO2.2Na2O  ;  4SiO2  Na2O.—   SiO2.2K2O(?) ;    SiO2.K2O  ;    9SiO2.2K2O, 

or  perhaps  4SiO2.K2O. 
SnO2.Na2O.3,  8,  9,  and  10H2O  :  SnO2.K2O.3H2O  ;  2SnO2.(NH4)2O.wH2O. 

5SnO2.Na2O.4H2O  ;  5SnO2.K2O.4H2O  ;  7SnO2.K2O.3H2O. 
PbO2.K2O.3H2O,  and  others. 

When  silica  is  fused  with  a  carbonate  or  hydroxide  of  lithium , 
sodium,  or  potassium,  a  glass  is  formed  of  indefinite  composition, 
depending  on  the  proportions  taken.  The  lithium  glass,  however, 
dissolves  in  fused  lithium  chloride,  and  crystallises  out  on  cooling. 
The  lithium  chloride  withdraws  lithia  from  the  silicate,  forming 
oxychloride ;  and  by  keeping  the  mass  fused  for  different  times, 
the  three  compounds  given  above  are  formed. 

Soluble  glass,  or  water-ylass,  is  a  silicate  of  sodium  or  potassium. 
It  is  prepared  as  mentioned ;  or  by  heating  silica  (quartz,  flint, 


SILICATES  AND   STANNATES.  311 

sand,  &c.)  with  solution  of  caustic  soda  or  potash,  under  pressure. 
The  proportion  of  silica  and  potash  usually  corresponds  with  the 
formula  4SiO2.K2O  ;  on  treating  the  solution  with  alcohol,  a  sub- 
stance of  that  formula  is  thrown  down;  it  is  suggested  that  the 
more  probable  formula  is  9SiO2.2K2O.  It  is  probably  a  mixture. 
If  the  sodium  silicate  be  saturated  with  silica,  4SiO2.Na2O,  is 
produced. 

Soluble  glass  is  a  syrupy  liquid,  obtained  by  dissolving  the 
product  of  fusion  in  water,  or  by  evaporating  the  solution  of  silica 
in  alkaline  hydroxide.  It  is  used  to  form  artificial  stone ;  for  it 
reacts  with  calcium  hydrate  or  carbonate,  giving  insoluble  calcium 
silicate,  which  may  be  used  to  bind  together  large  amounts  of  sand 
into  a  coherent  mass.  It  is  also  employed  in  mural  painting  ;  and 
it  is  added  to  cheap  soaps. 

Hydrated  silica  dissolves  to  some  extent  in  solution  of  am- 
monia, but  no  solid  compound  has  been  obtained. 

Decomposition  of  silicates. — The  usual  method  of  decomposing  insoluble 
silicates  is  by  fusing  them  with  a  mixture  of  sodium  and  potassium  carbonates, 
named  "  fusion-mixture."  Carbonates  or  oxides  of  the  metals  remain,  and  the 
silica  combines  with  the  sodium  and  potassium  oxides,  forming  a  mixture  of 
silicates.  This  mixture  is  now  treated  with  water,  when  the  silicates  of  the 
alkalies  pass  into  solution,  and  may  be  removed  from  the  insoluble  oxides  by 
filtration.  But  as  it  is  usually  required  to  separate  the  silica,  it  is  more  common 
to  add  hydrochloric  acid,  which,  if  the  solution  be  strong,  precipitates  gelatinous 
silicic  acid,  and  converts  the  oxides  of  the  metals  into  chlorides.  On  evapora- 
tion to  dryness  and  heating,  the  silicic  acid  is  decomposed  into  water  and  silica, 
and  after  re-evaporation  with  a  little  hydrochloric  acid,  it  is  insoluble  in  dilute 
hydrochloric  acid,  which  dissolves  the  chlorides  of  the  metals,  and  thoy  may  then 
be  separated  by  filtration.  On  ignition,  the  silica  remains  as  a  white  loose 
powder,  and  if  required  it  may  be  weighed. 

The  corresponding  stannates  are  prepared  by  fusing  tin 
dioxide  with  hydroxide,  sulphide,  nitrate,  or  chloride  of  sodium  or 
potassium ;  or  by  heating  metallic  tin  with  a  mixture  of  hydroxide 
and  nitrate,  from  the  latter  of  which  it  derives  its  oxygen.  On 
treatment  with  water  the  mass  dissolves,  and  on  evaporation 
deposits  crystals  containing  3,  8,  9,  or  10  molecules  of  water, 
according  to  circumstances.  The  salt  with  3H20  may  also  be 
precipitated  by  adding  alcohol. 

Stannic  hydrate  is  soluble  in  ammonia,  forming  a  jelly,  in 
which  the  ratio  of  Sn02  to  ammonia  corresponds  with  the  formula 
2Sn02.(N"H4)20. 

Metastannates. — By  boiling  the  product  of  the  action  of  nitric 
acid  on  tin,  5SnO2.oH2O,  with  sodium  or  potassium  hydroxide,  a 


312      THE  OXIDES,  SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

solution  is  obtained,  from  which,  if  caustic  soda  be  used,  granular 
white  crystals  deposit  on  cooling,  of  the  formula 
5SnO2.Na.O.4H2O. 

If  potash  be  used,  a  similar  compound,  5SnO2.K2O.4HaO,  is  pre- 
cipitated by  addition  of  excess  of  potash,  in  which  it  is  insoluble. 
It  is  a  gummy  non-crystalline  substance.  Both  of  these  com- 
pounds are  decomposed  by  boiling  water  into  alkali  and  meta- 
stannic  acid.  It  is  the  fact  that  one-fifth  of  the  water  is  replaced 
by  sodium  or  potassium  oxide,  which  leads  to  the  formula 
5SnO2.5H2O  for  metastannic  acid,  instead  of  SnO2.H2O,  which 
would  more  simply  represent  its  percentage  composition. 

On  mixing  metastaunic  acid,  dissolved  in  hydrochloric  acid,  with 
caustic  potash,  until  the  precipitate  at  first  produced  redissolves, 
and  then  adding  alcohol,  a  precipitate  of  the  formula 

7Sn02.K20.3H,0 

is  produced.  There  appear  also  to  be  other  analogous  substances. 
Plumbates. — By  fusing  lead  dioxide  with  excess  of  caustic 
potash,  it  dissolves ;  the  solution  of  the  product,  in  a  little  water, 
deposits  octahedral  crystals  of  the  formula  PbO2.K3O.3H2O 
analogous  to  the  stannate.  By  fusing  litharge  with  potassium 
hydroxide,  the  compounds  PbO2.K.O  and  3PbO2.2K2O,  are  formed 
with  absorption  of  oxygen.  These  salts  are  decomposed,  on  treat- 
ment with  water,  into  potassium  hydroxide  and  hydrated  lead 
dioxide  ;  they  are  stable  only  in  presence  of  excess  of  alkali. 

SiO2.2BeO      (phenacite,      beryl,      emerald)  ;       SiOo.CaO      (wollastonite)  ; 

2SiO2.CaO.2H2O    (oTcenite)  •    3SiO2.2CaO.H2O    (gyrolHe)  ; 
SnO2.CaO,  also  5H2O ;  2SnO2.:  SrO.10H2O  ;  SnO2.2BaO.10H2O.* 

These  silicates  are  found  native ;  they  are  well  crystallised 
minerals.  By  adding  to  solutions  of  calcium,  strontium,  or  barium 
chlorides  a  solution  of  sodium  or  potassium  silicate,  white  curdy 
insoluble  precipitates  are  produced  of  the  respective  silicates,  the 
composition  of  which  is  analogous  to  that  of  the  alkaline  silicate 
from  which  they  are  produced. 

Of  the  native  silicates,  phenacite  is  an  orthosilicate  ;  icollastonite 
probably  a  metasilicate  ;  okenite  a  salt  of  disilicic  acid,  Si20(OH)6 ; 
and  gyrolite,  of  the  second  anhydride  of  trisilicic  acid,  Si304(OH)4. 
And  with  the  stannates,  we  have  barium  orthostannate  ;  calcium 
metastannate  (rejecting  the  water)  ;  and  the  strontium  salt  of 
distannic  acid. 

*  Comptes  rend.,  96,  701. 


SILICATES  AND   STANNATES.  313 

Two  compounds  are  known,  the  first  occurring  native,  a 
titanate  and  silicate  of  calcium,  named  sphene  •  and  the  second,  of 
similar  crystalline  form  (monoclinic  prisms)  produced  by  heating 
a  mixture  of  silica  and  tin  dioxide  with  excess  of  calcium  chloride 
to  bright  redness  for  eight  hours.  These  bodies  are  derived  from 
a  compound  analogous  to  the  second  anhydride  of  disilicic  acid. 
Their  formulae  are  probably — 

Ca<°>Si<°>Ti<°>Ca,  and  Ca<°>Si<°>Sn<°>Ca, 

Similar  silico-zirconates  occur  native. 

Ordinary  Mortar  is  made  by  mixing  sand  with  slaked  lime.  The  rapid 
setting  of  the  mortar  is,  however,  not  due  to  the  combination  of  the  calcium 
and  silicon  oxides,  but  to  the  formation  of  the  compound  CO2.2CaO,  by  absorp- 
tion of  carbon  dioxide  from  the  air.  But,  after  the  lapse  of  years,  combination 
of  the  silica  does  take  place,  and  very  old  mortars  contain  much  calcium 
silicate. 

Hydraulic  mortars,  as  those  mortars  are  named  which  "  set "  under  water, 
on  the  other  hand,  cannot  be  produced  from  anhydrous  silica.  A  mixture  of 
precipitate  silica  or  of  crushed  opal  and  lime  hardens  under  water ;  but  the  best 
hydraulic  mortars  are  made  from  hydrated  silirates  of  alumina.  The  celebrated 
pozzolana  of  Xaples  is  such  a  substance.  When  mixed  with  lime,  there  is 
formed  a  silicate  of  aluminium  and  calcium,  which  is  rapidly  produced,  and 
perfectly  insoluble  in  water.  Tufa,  pumice,  and  clay-slate  form  similar  insoluble 
mortars.  Marl,  a  mixture  of  clay  and  calcium  carbonate,  after  ignition,  sets 
when  moistened.  This  is  probably  in  the  first  instance  due  to  hydration,  and 
subsequently  to  the  formation  of  a  silicate  of  aluminium  and  calcium. 

SiO2.2(Mg,  Fe)O  (chrysolite,  olivine)  ;  SiO.2.(THLg,  Fe",  Mn",  Ca)O  (augite 
and  hornblende ;  these  differ  in  crystalline  form,  but  are  both  monoclinic)  ; 
2SiO2.3(Mgr,  Fe")O.2H.2O  (serpentine,  sometimes  containing  Na2,  Mn",  and 
Ni");  3SiO2.2Mg-O.2H.:O,or4H.2O  (meerschaum);  5SiO2.4M:g-O  (talc;  contains 
a  little  water.— SiO2.2ZnO.EL2O  (siliceous  calamine)  :  SiO2.2ZnO  (urillemite).— 
2SnO2.3ZnO.10H2O. 

These  silicates  are  all  found  native  and,  as  a  rule,  crystalline. 
Chrysolite  and  willemite  are  orthosilicates ;  siliceous  calamine 
possibly  a  basic  metasilicate  of  the  formula  SiO.(OZnOH)2  ; 
augite  and  hornblende  are  metasilicates,  but  one  is  probably  a 
polymeride  of  the  other,  possibly  a  derivative  of  the  disilicic  acid, 

HO  O  OH 

TTQ>Si<Q>Si<[QTT»  like  sphene,  with  which,  however,  neither  is 

isomorphous.      Serpentine    is    a    derivative   of   disilicic  acid,  and 
meerschaum  and  talc  of  tri-  and  penta-silicic  acids  respectively. 

The  silicates  of  boron,  aluminium,  ferric  iron,  &c.,  are  very 


314      THE   OXIDES,   SULPHIDES,    SELEXIDES,   AND    TELLURIDES. 


numerous,  and  it  is  here  impossible  to  do  more  than  give  a  sketch 
of  their  nature. 

Datolite  has  the  formula  Si02.B203.CaO  ;  and  botryolite  contains, 
in  addition,  two  molecules  of  water.  They  are  doubtless  derived 
silicates  of  boron  and  calcium,  and  may  be  constituted  thus  :  — 


\0 

f(X  Q.  .<       p 

\0>Sl<0>Ca 


,and 
' 


'\X>si< 


0— CaOH 
OH. 


Xenolite  is  aluminium  orthosilicate,  3Si02.2Al203,  A  number 
of  minerals,  including  fibrolite,  topaz,  muscovite,  paragonite  and 
eucryptite  (varieties  of  mica),  dumortierite,  grossularite  (a  lime 
alumina  garnet),  prehnite,  and  natrolite  (or  soda  mesotype),  may  be 
simply  derived  from  it ;  the  following  structural  formulae  show 
their  relations  (Clarke)  : — 


SiO»=Al 


XSiO,=Al 
Xenolite. 

/Si04=(A10)3 


/Si04=(A10)3 
Al-Si04=Al 
xSi04=Al 
Fibrolite. 

/Si04=KH2 


Si04=(AlF2)3 


Si04=Al 

Topaz. 


Si04=Al 
Dumortierite. 


Si04=Al 
Muscovite. 


Paragonite. 


Alf  Si04EEAl. 
Eucryptite. 


XSi04=Al 
Natrolite. 

,OH 


Grossularite. 

,vo* 


Si04=Al 
Prehnite. 


-43. 
XSi04=R3 


Kaolin. 


Kaolin  or  china-clay,  is,  it  will  be  seen,  partly  hydrate  of 
aluminium.  R  in  the  last  formula  may  be  calcium,  iron  (dyad), 
magnesium,  sodium,  or  potassium,  or  generally  a  mixture. 

The  metasilicates  may  be  similarly  represented.  Among  these 
are  pyrophyllite,  4SiO>.Al203.H20  and  spodumene,  jade,  and  leucite 
containing  lithium,  sodium,  and  potassium  respectively.  They  may 

all  be  represented  by  the  formulae  A1<J<^Q3     -p ,  where  R  stands 
forH,Li,  Na,  or  K. 


NATURAL   SILICATES.  315 

There  are  at  least  two  other  silicic  acids,  2Si02.H20,  or 
Si2O3(OH)2,  the  second  anhydride  of  disilicic  acid,  and  3Si02.2H2O, 
or  Si304(OH)4,  the  second  anhydride  of  trisilicic  acid,  which  yield 
salts.  Petalite,  (Si203)2Al.Li,  is  a  salt  of  the  first,  and  the  felspars  albite, 


. 

and    orthoclase,     Si304</\          °f    the    second' 


N)/  C 

By  trebling  these  formulae  we  obtain  groups  analogous  to  those  of 
the  orthosilicates  ;  and  this  shows  a  striking  analogy  between 
these  and  other  minerals,  otherwise  difficult  to  classify.  Thus 

/Si04EE  /Si306EE 

analogous  to  Al^~Si04:=rAl,  we  have  Ak  Si30^=:Al.   The  calcium 

XSi04=Al  XSi308^Al 

salt  corresponding  to  the  first  formula  and  the  sodium  salt  of  the 
second  are  respectively  the  minerals  — 

/SiO^  Gag  =Si04\  /SisO^Nas 

Al£SiO,=AlAl=Si047Al,    Al^Si308=Al  ,  and 
xSi04=Al  Al=SiO 

Anorthite.  Albite. 

/Si308=(Al(OM)2)3 


Ldbradorlte» 

If  potassium  replaces  the  sodium  of  albite,  the  mineral  is  orthoclase, 
or  potash  felspar.* 

Lastly,  an  instructive  analogy  is  pointed  out  by  Clarke,  which 
promises  to  throw  light  on  a  curious  compound  of  a  brilliant  blue 
colour,  found  native,  and  named  lapis  lazuli,  which  is  now  manu- 
factured in  large  quantities  as  a  paint  under  the  name  of  ultra- 
marine, by  heating  together  sodium  sulphate,  sulphur,  felspar,  and 
some  carbon  compound  such  as  resin.  The  mineral  sodalite  has 
the  formula 

4Si02.4Al203.2Na2O.ISTaCl. 

Ultramarine  may  be  represented  as  the  sodo-sulphuryl  (SNa)  com- 
pound of  which  sodalite  is  a  chloride  ;  and  the  analogy  is  streng- 
thened inasmuch  as  the  constitution  of  another  mineral,  nosean, 
closely  allied  to  ultramarine,  is  thereby  represented.  The  formula 
are  :  — 


*  F.  W.  Clarke,  Amer.  Jour,  of  Science,  NOT.,  1886 ;  Aug.,  1887 :  Amer. 
Chem.  J.,  10,  120  ;  38,  384. 


316      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLUR1DES. 

Si04=Na3  /SiO^Naa 

Al  Al-Si04=Al  Al 


AlSi04=Al.  AlSi04=Al  Al~Si04=Al 

XC1  NSO4—  Na.  XS—  Na, 

Sodalite.  Nosean.  Ultramarine. 

Such  are  some  of  the  attempts  which  have  been  made  to 
classify  these  complex  silicates.  Whether  they  are  justified  or 
not,  if  they  serve  to  connect  together  bodies  resembling  each  other, 
and  to  point  the  way  to  new  researches,  they  have  their  use, 

A  few  other  silicates  have  still  to  be  mentioned. 

SiO2.2MnO  (tephroite)  ;  SiO2.MnO  (rhodonite)  ;  SiO2.CuO.2H2O  (chryso- 
col?a)  ;  3SiO2.2Ce2O3  (cerite)  ;  3SiO2.2(Y,  Ce,  Fe,  Mn,  &c.)2O3  (gadolinite)  ; 
3(SiO2.ThO2)4H2O  (thorite). 

After  what  has  been  said,  these  may  easily  be  grouped  in  their 
respective  classes.  Other  stannates  have  also  been  prepared,  for 
example  — 

SnO2.NiO.5H2O  ;  SnO2.CuO.6H2O  ;  SnO2.CuO.4H2O  j 
Sn02.CuO(NH4)20.2H20  ;   SnO2.A&2O. 

The  germanates  have  not  been  investigated.  But  as  dioxide  of 
germanium  is  soluble  in  excess  of  caustic  alkali,  they  are,  without 
doubt,  capable  of  existence.  It  has  lately  been  announced  that 
germanium  exists  in  small  amount  in  euxenite  ;  and  it  is  present, 
no  doubt,  in  the  form  of  a  germanate. 

Double  Compounds  of  the  Sulphides  and  Selenides. 

Those  of  tin  alone  have  been  investigated. 

Stannous  sulphide,  SnS,  when  treated  with  a  very  strong 
solution  of  potassium  sulphide,  K2S,  dissolves  ;  while  tin  precipi- 
tates in  the  metallic  state.  The  equation  is  — 

2SnS  +  K2S.Aq  =  SnS2.K3S.Aq  +  Sn. 
By  further  action,  hydrogen  is  evolved,  thus  — 
Sn  +  3K2S.Aq  +  4H20  =  SnS3.K2S.Aq  +4KOH.Aq  +  2/4 

The  same  compound  is  also  produced  by  warming  stannous 
sulphide  with  the  polysulphide  of  an  alkali,  e.g.,  K2S5.Aq,  or 
(NH4)2S5.Aq  ;  the  monosulphide  is  then  converted  into  the  di- 
sulphide  which  dissolves  in  the  solution  of  sulphide  ;  or,  more 
simply  still,  tin  disulphide  may  be  dissolved  in  a  solution  of  potas- 
sium sulphide. 

The  hydrogen  salt  of  sulphostannic  acid,  SnS,.H,S.  or 
SnS(SH)2  (it  will  be  noticed  that  this  is  a  meta-acid),  is  produced 
on  adding  an  acid  to  a  sulphostannate,  as  a  yellow  precipitate,  which 


SULPHOSTANNATES.  —  OXYCHLORIDES   OF   SILICON.  317 

becomes  dark  -coloured  on  exposure  to  air.      The  following  salts 
exist  ;  they  are  all  prepared  thus,  and  are  soluble  in  water  :  — 

SnS(SNa)2.3H20,  also  2H2O  ;   SnS(SK)2.10H2O,  also  SH^O  ; 
3SnS2.(NH4)2S.6H2O;  SnS(S2)Ba.l4H2O  ;  SnS(S2)Sr.l2H2O  ; 
and  SnS(S2)Ba.8H2O. 

SnSe(SeK)2.3H2O  has  been  analysed  ;  and  a  mixed  componnd 
obtained  by  digesting  potassium  sulphide  with  tin  and  selenium 
has  the  formula  SnSe2.K2S.3H2O.*  It  would  appear  that  two  iso- 

d^"K"  C&ATJT 

merides  might  here  exist,  viz.,  SnSe<^g«  ,  and  SnS<a   j,  ;  but 

they  have  not  been  identified. 

A  native  sulphostannate  of  copper,  iron,  and  zinc  is  known  as 
tin-pyrites.  Its  formula  is  SnS2.(Cu2,  Pe,  Zn)S.  It  is  also  a 
me  ta-  com  pound  . 

(6.)  Compounds  with  halides.  —  These  are,  as  a  rule,  difficult 
to  prepare,  for  almost  all  are  acted  on  by  water.  No  compound  of 
the  formula  SiOCl2  is  known.  The  corresponding  germanium 
compound,  GeOCl2,  is  produced  by  distilling  germanium  tetra- 
chloride  in  contact  with  air.  It  is  a  colourless,  fuming,  oily  liquid 
boiling  above  100°.  By  passing  a  mixture  of  silicon  tetrachloride 
and  hydrogen  sulphide  through  a  red-hot  tube  the  substance 
SiCl3.SH  is  formed.  It  boils  at  196°.  The  sulphochloride, 
SiSCl2,  is  said  to  be  formed  by  the  same  process  ;  probably  the 
former  compound  dissociates  at  a  high  temperature  into  hydrogen 
chloride  and  the  latter. 

Silicon  tetrachloride,  SiCl4,  led  over  fragments  of  felspar  con- 
tained in  a  white-hot  porcelain  tube,  deprives  the  felspar  of 
oxygen,  and  yields  the  oxychloride  (SiCl3)2O.  It  is  a  liquid  boiling 
at  136  —  139°  ;  and  this  compound,  passed  through  a  hot  glass  tube 
along  with  oxygen,  yields  a  liquid  from  which,  on  fractional  on,  the 
following  compounds  have  been  isolated  :  —  Si2OCl<5  (136  —  139°)  ; 
SiiOsClio  (152—154°);  SiACU  (198—202°).  These  substances 
give  vapour-densities  which  lead  to  the  formulae  ascribed.  A  fourth 
is  formed  which,  on  analysis,  gives  the  numbers  for  Si^OsClg  ;  the 
molecular  weight  of  such  a  body  should  be  405  ;  that  deduced  from 
its  vapour-density  was  614  ;  its  formula  is  therefore  doubtful.  It 
boiled  at  a  very  high  temperature.t 

A  somewhat  analogous  body  to  the  compound  SiCl3(SH)  is  the 
substituted  orthostannic  acid  produced  by  the  action  of  water  on 

OTT 
stannic  chloride.     Its  formula  is   SnO<^^n    .    It  may  be  regarded 


«  Comptes  rend.,  95,  641. 

f  Troost  and  Hautefeuille,  Annales  (5),  7,  453. 


318      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

as  metastannic  acid,  with  one  hydroxyl-group  replaced  by  chlorine. 
On  treatment  with  ammonia  it  yields  the  salt  SnO<p,       4. 

In  conclusion,  a  set  of  curious  compounds  of  carbon  and  silicon 
with  oxygen  and  sulphur  may  be  mentioned,  which  require  further 
investigation.*  The  first  of  these  is  a  greenish-white  mass  pro- 
duced by  the  action  of  carbon  dioxide  on  white-hot  silicon.  Its 
formula  is  SiCO.  Vapours  of  hydrocarbons  passed  over  silicon, 
heated  in  a  porcelain  tube,  yield  a  bottle-green  substance  of  the 
formula  SiC02,  the  oxygen  being  derived  from  the  tube.  By  sub- 
stituting a  mixture  of  carbon  dioxide  and  hydrogen  the  substance 
Si2C3O  is  produced  ;  and  by  the  action  of  silicon  and  carbon  at  a 
white  heat  on  porcelain,  a  body  of  the  formula  Si2C302  is  formed. 
No  clue  has  been  obtained  regarding  the  constitution  of  these 
bodies. 

Here  also  may  be  mentioned  a  very  remarkable  compound  of 
carbon  monoxide  with  nickel,  produced  by  passing  that  gas  over 
hot  finely-divided  nickel,  and  condensing  by  means  of  a  freezing 
mixture.  ]t  has  the  empirical  formula  Ni(CO)4,  and  is  a  colour- 
less liquid,  boiling  about  45°.  Its  vapour  density  corresponds 
with  the  formula  given.  It  deposits  metallic  nickel  when  heated 
to  180°,  as  a  brilliant  mirror,  j 

Physical  Properties. 

Weights  of  1  cubic  centimetre  : — 

Si.  Gre.         Sn.                   Pb.                                  Si.  Ge.     Sn.      Pb. 

O..    2-89            6-0—6-6  8-74*— 9'29§  O2  ..  2'65||  -  6'7       8'9 

S  ..                             5-0                   7-5  S2     .       —  —  4-6       6-3lf 

Se..     —  —          6-2                   8-1  Se2..      —  —  5 '1 

Te..  —         6-5                  8-1  Te2..  —  — 

Heats  of  formation : — 

Si    +  20  +  Aq  =  SiO2.Aq  +  1779K  (?). 

Sn  +  20  =  SnO2  +  1400K  (?). 

Sn  +     O  =  SnO  +  700K  (?) . 

Sn  +     O  +  H2O  =  Sn02H2   +  681K. 

Pb  +     O  =  PbO  ...  3  ....      I  +  503K. 
Pb  +     S  =  PbS  +  184K. 


*  Comptes  rend.,  93,  1508.       f  Chem.  Soc.,  57,  749.       J  Red.       §  Yellow. 
||  Rock  crystal  at  10°  :—  Tridyinite,  2  '3  ;  fused  to  glass,  2  -22.          f  Pb2S3. 


319 


CHAPTER  XXII. 

OXIDES,  SULPHIDES,  &C.,  OF  ELEMENTS  OF  THE  NITROGEN  GROUP. — 
THE  PENTOXIDES  AND  PENTASULPHIDES,  AND  THEIR  COMPOUNDS  ; 
NITRATES,  VANADATES,  SULPHOVANADATES,  NIOBATES,  AND  TANTAL- 

ATES. — TETROXIDES. TRIOXIDES  ;    NITRITES  AND  VANADITES. NITRIC 

OXIDE   AND    SULPHIDE. — NITROUS    OXIDE    AND    HYPONITRITES. 

Oxides,  Sulphides,   Selenides,  and  Tellurides  of 
Nitrogen,  Vanadium,  Niobium,  and  Tantalum. 

These  are  very  numerous.  The  compounds  of  nitrogen  are  not 
formed  by  direct  union,  for  heat  is  absorbed  during  their  formation 
and  they  therefore  are  easily  decomposed.  Those  of  vanadium 
niobium,  and  tantalum,  on  the  other  hand,  are  very  stable. 

,.  List  of  Oxides. 

Nitrogen.  Yanadium.     Niobium.       Tantalum. 

Monoxides   N^O 

Dioxides NO  VO*              NbO 

Trioxides N2O3  V2O3 

Tetroxides NO^ ;  N2O4    VO2*  NbO2            TaO2 

Pentoxides N2O5  V2O5               Nb2O5          TaoOs 

Hexoxide N2O6 

List  of  sulphides,  selenides,  and  tellurides: — 

NS;  NSe;  VS2;  V2S5;  TaS2(?). 

Sources. — None  of  these  bodies  occurs  native.  The  pentoxides 
occur  in  combination  with  the  oxides  of  metals  in  the  nitrates, 
vanadates,  niobates,  and  tantalates,  which  will  be  described  later. 
Among  the  most  important  are  nitrates  of  sodium  and  of  potas- 
sium, named  respectively  Chili  saltpetre  and  saltpetre  or  nitre; 
vanadinite,  a  vanadate  and  chloride  of  lead ;  pyrochlore,  a  niobate 
of  calcium,  cerium,  &c.  ;  euxenite,  a  niobate  and  tantalate  of 
cerium,  yttrium,  &c.  ;  and  tantalite,  a  tantalate  of  iron  and  man- 
ganese. 

Preparation. — The  starting-point  for  the  preparation  of  all 

*  As  the  molecular  weight  of  these  bodies  is  unknown  their  simplest  formulae 
are  given.  j 


320      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

the  oxides  of  the  members  of  this  group  is  the  compounds  of  the 
pentoxides  with  other  oxides.  For  nitrogen  oxides,  the  nitrates  of 
potassium  and  sodium  ;  for  vanadium  oxides,  the  vanadate  of  lead  ; 
for  the  oxides  of  niobium  and  tantalum,  the  niobates  and  tantal- 
ates  of  yttrium,  lanthanum,  iron,  manganese,  &c.  On  treatment 
of  these  compounds  with  strong  sulphuric  acid,  hydrates  of  the 
pentoxides  are  set  free.  This  may  be  regarded  as  the  displace- 
ment of  an  oxide  by  another  oxide,  viz.,  S03.  As  nitric  acid, 
N2O5.H20,  or  as  its  vapour-density  shows  us,  HN03,  is  a  liquid,  vola- 
tile without  decomposition,  it  can  be  distilled  away  from  the  solid 
sulphate  of  sodium  or  potassium  ;  the  vanadate  of  lead,  on  treat- 
ment with  sulphuric  acid,  or,  better,  on  fusion  with  hydrogen 
potassium  sulphate,  HKS04,  is  decomposed,  lead  sulphate,  which 
is  insoluble  in  water,  being  left  behind  ;  and  on  treatment  with 
water  vanadate  of  potassium  is  dissolved,  from  which  strong  nitric 
acid  sets  free  vauadic  acid,  V205.H30,  as  a  reddish  precipitate. 
The  pentoxides  of  niobium  and  tantalum  are  also  produced  by  fusing 
the  ores  with  hydrogen  potassium  sulphate,  and  after  cooling, 
boiling  the  fused  mass  with  water  ;  the  iron,  yttrium,  &c.,  all  go 
into  solution  as  sulphates,  and  the  pentoxides  remain  as  insoluble 
hydrates. 

We  shall  begin  —  reversing  the  usual  order  —  with  the  pent- 
oxides,  because  they  form  the  sources  of  the  lower  oxides. 

Pentoxides.  —  Nitrogen  pentoxide  is  produced  by  the  action 
on  nitric  acid  of  phosphoric  anhydride,  P2O5,  a  body  which  has  a 
great  tendency  to  combine  with  water,  and  which,  therefore,  with- 
draws it  from  nitric  acid.  The  acid  cannot  be  dehydrated  by  heat 
alone,  for  the  pentoxide  easily  decomposes  into  the  tetroxide,  losing 
oxygen.  Phosphorus  pentoxide  is  gradually  added  to  ice-cold, 
pure  nitric  acid,  and  the  syrupy  liquid  is  distilled  at  a  low  tem- 
perature. The  liquid  distillate  consists  of  two  layers,  the  upper 
one  being  the  pentoxide,  mixed  with  a  little  of  the  compound 
2N»O5.H2O  ;  the  lower  consisting  of  the  latter  compound.  The 
upper  layer  is  separated,  and  cooled  with  a  freezing  mixture,  when 
the  pentoxide  deposits  in  crystals.  The  equation  is  :  — 

P205  =  2HP03  +  Na05. 


This  substance  may  also  be  prepared  by  heating  silver  nitrate, 
AgNO3,  to  58  —  68°  in  a  current  of  perfectly  dry  chlorine.  This  reac- 
tion should  yield  a  hexoxide,  N206,  thus,  AgNO3  4-  C12  =  2AgCl 
-f  •  N-»O6  ;  but  the  hexoxide  is  unstable,  and  decomposes  at  the  moment 
of  liberation  into  pentoxide  and  oxygen.  The  hexoxide  is  said, 
however,  to  be  produced  by  passing  an  electric  discharge  through 


OF  NITROGEN,  VANADIUM,  NIOBIUM,  AND   TANTALUM.       321 

a  mixture  of  nitrogen  and  oxygen  at  — 23°,  and  to  form  a  volatile 
crystalline  powder. 

Another  method,  which  appears  to  act  well,  is  to  pass  a  mixture 
of  nitric  peroxide,  N02,  and  chlorine  over  dry  silver  nitrate  at 
60—70°.  The  equation  is  A702  -f.  Cl  +  AgNO3  =  AgCl  +  NZ0,. 

The  pentoxide  must  be  condensed  in  a  (J  -tube,  surrounded  by  a 
freezing  mixture ;  and  the  most  scrupulous  care  must  be  taken  to 
exclude  moisture,  by  drying  the  apparatus  and  materials  perfectly 
before  use,  and  by  preventing  the  access  of  moist  air. 

Vanadium,  niobium,  and  tantalumpentoxid.es  are  produced 
(1)  by  burning  the  elements  in  air,  or  by  the  oxidation  of  the  lower 
oxides  when  heated  in  air.  (2)  By  heating  their  hydroxides 
(acids),  or  in  the  case  of  vanadium  by  heating  ammonium  vanadate, 
2NH4VO3  =  2NH3  +  H,0  +  V2O5;  or  by  heating  a  solution  of 
the  oxide  V02  in  strong  sulphuric  acid ;  the  first  reaction  is  the 
formation  of  the  sulphate,  V2O5.'2SO3.H2O,  a  portion  of  the  sul- 
phuric arid  losing  oxygen  to  oxidise  the  tetroxide  to  pentoxide, 
thus  2VO2  +  H2S04  =  V2O5  4-  H20  +  S02 ;  the  pentoxide  then 
forms  the  above  sulphate ;  V2O5  +  2H2S04  =  VZOS.2SO3  +  2H20. 
The  sulphate  is  decomposed  on  further  ignition  into  Y205  and  SO3. 
(3)  By  the  action  of  water  on  the  pentahalide  or  oxyhalides.  This 
yields  the  hydroxides,  from  which  the  oxides  are  obtainable. 

Properties.— Nitric  pentoxide  forms  brilliant,  colourless, 
transparent  rhombic  prisms;  it  melts  at  30°,  and  boils  about  45°. 
It  is  very  unstable,  forming  nitric  peroxide  with  loss  of  oxygen,  but 
can  be  preserved  for  several  days  at  10°  in  a  dry  atmosphere.  It 
hisses  when  dropped  into  water,  forming  hydrated  nitric  acid. 

Vanadium  pentoxide  is  a  reddish-yellow  solid,  sparingly 
soluble  in  water,  to  which  it  imparts  a  yellow  colour.  The  solution 
is  tasteless,  but  has  an  acid  reaction.  It  melts  when  heated  to 
redness,  and  on  solidifying  it  turns  incandescent,  probably  display- 
ing the  phenomenon  of  superfusion.  . 

Niobium  pentoxide  is  a  white  insoluble  solid,  turning  yellow 
when  heated,  but  regaining  its  whiteness  on  cooling.  It  has  been 
fused  at  a  white  heat.  After  ignition  it  is  insoluble  in  acids. 

Tantalum  pentoxide  is  also  a  white  insoluble  powder,  which 
has  not  been  fused.  It  is  also  insoluble  in  acids. 

Vanadium  is  the  only  element  of  which  a  pentasulphide  is 
known.  It  is  pioduced  by  adding  ammonium  sulphide  to  a  solution 
of  the  pentoxide,  and  precipitating  with  hydrochloric  acid.  It  is 
a  brown  precipitate,  which  turns  black  on  drying.  It  is  soluble  in 
sulphides  of  sodium  and  potassium,  forming  sulphovanadates  (see 
below). 


322      THE  OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

Compounds  with  water  and  oxides.—  Of  these  oxides  that 
of  nitrogen  is  the  only  one  which  readily  dissolves  in  water,  forming 
a  compound.  That  of  vanadium  is  slightly  soluble  ;  but  the  pent- 
oxides  of  niobium  and  tantalum  do  not  combine  with  water.  The 
name  "  acid  n  is  applied  to  the  hydrates  of  these  oxides,  because 
the  hydrogen  of  the  combined  water  is  replaceable  by  metals,  when 
the  compound  in  solution  is  treated  with  hydroxides  of  the  metals, 
or  heated  with  the  carbonates.  These  acids  are  as  follows  :  — 

2N205.H20;  1ST205.H20,  or  HN03  ;  Y205.H20,  or  HVO3; 
(this  body  contains  another  molecule  of  water,  which  is  easily  ex- 
pelled by  heat,  and  which  is  therefore  not  regarded  as  essential  to 
its  composition)  ;  Nb205.^H20,  and  Ta2O5.nH20,  the  value  of  n  being 
unknown. 

There  are  two  classes  of  nitrates,  the  ordinary  nitrates,  and 
the  basic  nitrates  ;  and  many  classes  of  vanadates,  niobates,  and 
tantalates. 

Nitric  acid  and  nitrates.—  Preparation.—  The  method  of 
preparation  of  nitric  acid  is  by  distillation  of  sodium  or  potassium 
nitrate  with  excess  of  sulphuric  acid.  The  reaction  is  as  follows  — 

KNO3  +  H2S04  =  HKSO4 


It  would  appear  as  if  economy  of  sulphuric  acid  might  be  attained 
by  using  the  proportions  2KN03  +  H2S04  =  K2S04  +  2HN"03; 
but  at  the  temperature  at  which  hydrogen  potassium  sulphate 
attacks  a  nitrate,  nitric  acid  is  largely  decomposed.  On  the  small 
scale,  the  distillation  is  carried  out  in  a  glass  retort  (see  Fig.  39)  ; 
on  the  large  scale  in  one  of  iron.  The  iron  is  protected  by  a  film 


FIG.  39. 


of  ferroso-ferric  oxide,  Pe3O4,.  which  is  at  once  formed  on  the 
surface,  and  on  which  nitric  acid  is  without  action.  The  worm  of 
the  condenser  and  the  receivers  are  usually  made  of  stoneware. 

Nitric  acid  is  also  produced  along  with  nitrous  acid  by  tbe 
action  of  water  on  nitric  peroxide,  Na04  or  N03,  thus — N204  +  H20 


NITRIC,  VANADIC,   NIOBIC,   AND  TANTAIJC  ACIDS.  323 

=  HN03  +  HNO2;   also  by  heating  a  solution  of   nitrous  acid, 
3HNO8  =  HN03  +  H2O  +  2NO. 

When  prepared  by  distillation  it  usually  has  a  yellow  colour, 
owing  to  its  containing  peroxide,  NO2,  in  solution.  This  substance 
is  easily  volatile,  and  may  be  removed  by  passing  a  current  of  air 
through  the  acid  for  some  hours. 

Properties. — Nitric  acid,  when  pure,  is  a  colourless  liquid, 
fuming  slightly  in  the  air,  being  somewhat  volatile  at  the  ordinary 
temperature.  It  freezes  at  —55°.  and  boils  at  86°,  partially  de- 
composing into  tetroxide,  N204,  oxygen  and  water,  a  weaker  acid 
remaining  behind.  It  is  completely  decomposed  when  heated  in  a 
sealed  tube  to  256°.  Its  density  corresponds  with  the  formula 
HN03.  It  absorbs  water  from  the  air,  forming,  no  doubt,  a 
hydrate,  which,  however,  has  not  been  isolated,  although  it  is 
stated  to  have  the  formula  2HN03.3H2O,  or  N206.5H20. 

The  hydrate  2N205.H2O  is  produced  during  the  preparation  of 
nitric  anhydride,  N205,  by  use  of  phosphorus  pentoxide.  It  is  the 
lower  layer,  into  which  the  distillate  separates,  and  it  crystallises 
out  when  cooled  by  a  freezing  mixture  ;  and  it  can  also  be  prepared 
by  adding  nitric  anhydride  to  nitric  acid.  At  the  ordinary  tem- 
perature it  is  a  liquid,  but  it  turns  solid  at  about  —5°. 

A  solution  of  vanadium  pentoxide  in  water  perhaps  contains 
the  compound  Y2O5  3H2O,  or  H3V04;  but  the  hydrate  best  known 
is  V2O5.H2O,  or  HVO3,  corresponding  to  nitric  acid.  This  sub- 
stance is  a  brown-red  powder,  prepared  by  adding  nitric  acid  to  a 
solution  of  one  of  its  salts,  e.g.,  V2O5.K2O,  or  KVO3.  It  is  also 
formed  by  heating  a  mixture  of  solutions  of  copper  sulphate  with 
vanadic  acid  and  a  large  excess  of  ammonium  chloride  to  75°.  The 
copper  vaiiadate  decomposes,  depositing  golden-yellow  scales  of 
metavanadic  acid.  It  contains  a  molecule  of  water  in  additioa, 
V2O5.2H2O,  but  as  the  second  molecule  is  lost  when  it  is  dried  over 
strong  sulphuric  acid,  it  must  be  very  loosely  combined.  It  is  also 
produced  by  the  action  of  water  or  vanadium  pentachloride,  or 
oxychloride,  VOC13.  It  is  a  reddish-yellow  powder  or  golden- 
yellow  scales  ;  it  is  very  hygroscopic. 

Niobic  and  tantalic  acids  are  precipitated  as  white  powders 
on  adding  hydrochloric  acid  to  a  solution  of  sodium  or  potassium 
niobate  or  tantalate;  or  by  the  action  of  water  on  the  penta- 
chloride of  niobium  or  tantalum.  When  heated  they  lose  water, 
and  leave  the  pentoxide. 

Nitrates,  vanadates,  niobates,  tantalates. — These  salts  are 
all  produced  by  the  action  of  nitric,  vanadic,  niobic  or  tantalic 
acid,  in  presence  of  water,  on  hydrates,  oxides,  or  carbonates,  or 

Y  2 


324      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND    TELLURIDES. 

by  fusion  of  the  pentoxides  of  the  three  last  with  hydrates  or 
carbonates  of  lithium,  sodium,  potassium,  &c.  The  following 
equations  may  be  taken  as  typical : — 

HNO3.Aq    +  KOH.Aq  =  KNO3.Aq  +  H2O; 
2HNO3.Aq  +  CuO  -  Cu(NO3)2.Aq  +  H2O. 
2HN03Aq  +  CaCO3  =  Ca(NO3)2.Aq  +  H2O  +  C0.2. 
V205  +  2KOH.Aq  =  2KVO3.Aq  +  H2O  ;  " 
V205  +  3Na2C03  =  2Na3V04  +  3<7O2. 

These  equations  are  rendered  more  simple  by  the  older  method  of 
representation,  thus  : — 

N2O5.Aq  +  K2O.Aq  =  ]ST2O5.E:2O.Aq ; 
N205.Aq  +  CuO  =  N2O5CuO.Aq. 
N2O5.Aq  +  C02  CaO  =  N2O5.CaO.Aq  +  C0.2. 
V2O5  +  KsO.HsO  =  V2O5.E:2O  +  H20 : 
V205  +  3C02.Na20  =  V2O5.3Na2O  +  3CO2. 

All  nitrates  are  soluble,  and  hence  cannot  be  produced  by  precipita- 
tion, unless  the  solution  be  a  concentrated  one.  It  is  possible  to 
prepare  certain  nitrates,  however,  such  as  those  of  lead,  silver, 
and  barium,  by  addition  of  much  nitric  acid  to  a  soluble  salt  of 
such  metals;  for  the  nitrates  produced  are  sparingly  soluble  in 
nitric  acid.  Thus  : — 

BaCl2  +  2HNO3  =  Ba(NO:{)2  +  2HC1; 
Ag2S04  +  2HN03  =  2AgNO3  +  H2S04. 

The  nitrate  of  barium  or  silver  is  precipitated  as  a  crystalline 
powder.  Many  vanadates,  niobates,  and  tantalates  are  produced 
by  precipitation,  e.g.,  those  of  lead  and  silver. 


Nitrates,  vanadates,  niobates,  and  tantalates. 

LiN03  ;  below  10°,  2LiNO3.3H2O  ;  NaNO3  ;  KNO3 ;  KNO3.2HNO3 

melting  at  —3°. 
BbN03:  BbN03.5HN03.     CsNO3.     NH4NO3;  NH4NO3.2HNO3 : 

NH4NO3.HNO3. 

These  are  all  white,  soluble  salts.  Those  containing  excess  of 
nitric  acid  are  made  by  mixture  and  cooling.  With  the  exception 
of  ammonium  nitrate,  the  action  of  heat  on  which  is  peculiar,  and 
will  be  fully  treated  of  later  in  this  chapter,  these  salts  when 
heated  to  bright  redness  fuse  and  give  off  oxygen,  forming  at  lirst 
the  corresponding  nitrites  MNO3 ;  at  very  high  temperatures  they 
give  off  nitrogen  and  oxygen,  and  leave  oxides  and  peroxides.  They 


THE   NITRATES.  325 

cannot  be  strongly  ignited  even  in  gold,  silver,  or  platinnm  vessels 
without  attacking  them,  forming  oxides. 

Two  of  them,  sodium  and  potassium  nitrates,  are  commercially 
important.  Sodium  nitrate,  named  "  Chili  saltpetre,"  does  not 
occur  in  Chili,  hut  forms  immense  beds,  several  feet  thick,  at 
Tarapaca,  in  Northern  Peru.  Its  local  name  is  "  caliche."  Its 
crystalline  form  is  nearly  cubic,  but  in  reality  it  forms  very  obtuse 
rhombohedra ;  it  is  often  erroneously  named  "  cubic  saltpetre." 
One  gram  of  the  salt  dissolves  in  1*4  grams  of  water  at  15° ;  it  is 
also  soluble  in  alcohol.  It  is  largely  used  as  a  manure. 

Potassium  nitrate,  also  called  "  nitre "  or  "  saltpetre,"  is 
present  in  most  soils,  being  especially  abundant  in  chalk  or  marl. 
It  also  occurs  in  the  leaves  of  many  plants,  especially  in  those  of 
the  tobacco-plant.  It  is  found  as  an  efflorescence  on  the  soil  of 
hot  countries,  being  formed  by  the  action  of  a  ferment  or  ammonia 
in  presence  of  bases,  the  ammonia  being  derived  from  decomposing 
animal  or  vegetable  matter.*  The  nitrate  ferment  is  a  minute 
organism  similar  to  those  which  produce  fermentation.  Nitrifica- 
tion, as  the  process  of  transformation  of  ammonia  into  nitric  acid 
is  called,  goes  on  beneath  the  surface  of  the  soil,  the  necessary 
conditions  being  apparently  presence  of  air  and  absence  of  light. 
It  ceases  and  does  not  recommence  if  the  soil  be  kept  for  some 
time  at  100°,  the  organism  being  destroyed  ;  but  after  exposure  to 
the  atmosphere  fresh  germs  enter,  and  it  again  proceeds.  The 
manufacture  of  nitre  by  this  process  has  been  carried  out  for  ages 
in  Upper  India ;  stable-manure  and  limestone  are  exposed  to  air 
for  several  months,  and  the  resulting  nitrate  of  calcium  is  con- 
verted  into  nitrate  of  potassium  by  treatment  with  potassium 
carbonate  or  sulphate  ;  the  soluble  potassium  nitrate  is  easily 
separated  from  the  insoluble  calcium  carbonate  or  sulphate.  The 
process  is  also  carried  out  in  France  and  elsewhere. 

Potassium  nitrate  is  now  largely  prepared  from  the  Peruvian 
sodium  nitrate  by  mixing  the  latter  with  potassium  chloride. 
Sodium  chloride  is  formed,  and,  as  it  is  much  less  soluble  in  hot 
water  than  potassium  nitrate,  it  separates  out  on  evaporation.  The 
mother-liquor,  after  removal  of  most  of  the  salt,  deposits  crystals 
of  nitre. 

Potassium  nitrate  crystallises  in  two  forms  :  in  trimetric  prisms, 
and  in  rhombohedra,  like  calcspar.  It  has  a  cooling  taste ;  it  is 
soluble  in  3J  parts  of  water  at  18°,  but  insoluble  in  alcohol.  It 
melts  at  339°.t 

*  Chem.  Soc.,  35,  454. 

t  For  lists  of  melting  points,  see  Carnelley  and  Williams,  Chem.  Soc.,  33,  279. 


326      THE   OXIDES,   SULPHIDES,   SELENIDES,   AKD   TELLUEIDES. 

Ammonium  nitrate  is  prepared  by  mixing  nitric  acid  and 
ammonia,  and  evaporating  till  the  water  is  expelled.  It  dissolves 
in  half  its  weight  of  water  at  18°,  and  is  also  soluble  in  alcohol.  It 
melts  at  108°,  and  can  be  distilled  at  180°,  splitting  into  nitric  acid 
and  ammonia,  which  recombine  on  cooling  (?).  At  a  higher  tem- 
perature it  decomposes  into  nitrous  oxide  and  water.  It  is  formed 
in  solution  by  the  action  of  dilute  nitric  acid  on  some  metals,  espe- 
cially on  tin. 

Orthovanadates  :  Na3VO4  ;  K3VO4  ;  also  with  3H2O  and  2H2O.  Pyro- 
vanadate  :  V2O5.2K2O.3H2O.  Metavanadates  :  LiVO3  ;  NaVO3  ;  also  with 
2H20  ;  KV03  2H20  ;  NH4.VO3.  Acid  Vanadates  :  2V,O5.LJUO  ;  also  with 
9H2O;  2V2O5.Na2O;  2V2O5.K2O.3,  4,  and  7H2O;  2V2O5  iNH4)2O.4H2O  ; 
3V205.2Na20.9H20  ;  3V2O5.K2O.6H2O  (insoluble);  3V2O5.Na2O.9H2O  ; 
3V205.(NH4)20.6H20;  4V2O5.6Na2O. 

The  Orthovanadates  are  produced  by  fusing  vanadium  pent- 
oxide  with  carbonates  in  theoretical  proportions.  With  sodium 
carbonate  the  pyrovanadate,  Na4V2O7,  is  formed  first.  They  are 
soluble  in  water,  but  decompose  slowly  at  the  ordinary  tempera- 
ture, rapidly  on  warming,  into  sodium  or  potassium  hydroxides 
and  pyro  vanadates  or  metavanadates.  They  are  yellowish  solids. 

The  metavanadates  are  white,  soluble,  earthy  bodies  which, 
on  acidifying  with  acetic  acid,  turn  orange,  and  on  evaporation 
deposit  orange-yellow  crystals  of  the  acid  vanadates.  Ammonium 
metavanadate  is  produced  by  addition  of  ammonia  in  excess  fco 
vanadic  acid;  the  acid  vanadate,  2V2O5.(NH4)2O,  by  saturating 
ammonia  with  vanadic  acid  ;  and  on  acidifying  with  acetic  acid 
the  body  3V2O5.(NH4)2O  is  produced. 


Niobates.—  8Nb205.4K20.16H20  ;  7Nb.:O5.3B:2O.32H2O  ; 

2Nb2O5.3K2O.13H2O  ;  3Nb2O5.K2O.5H2O  ;  4Nb2O5.2K2O.l]H2O 
Nb205  2K20.11H26  ;  Nb2O5.Na2O.6H26  ;  3Nb265.2Na2O.9H26. 


The  first  of  these  is  obtained  by  fusion  of  niobic  pentoxide  with 
potassium  carbonate  solution  in  water,  and  crystallisation  ;  the 
solution  also  deposits  crystals  of  the  second  compound  ;  and  the 
third  is  formed  by  addition  of  potassium  hydroxide  to  one  of  the 
former,  and  crystallisation.  The  fourth  is  produced  by  boiling 
potassium  fluoxyniobate,  NbOF3.2KF.H20,  with  hydrogen  potas- 
sium carbonate;  it  is  nearly  insoluble  in  water.  These  compounds 
are  all  white,  and  crystallise.  The  sodium  salts  are  easily  decom- 
posed by  water  into  hydrated  niobic  pentoxide  and  sodium 
hydroxide. 


NITRATES,   VANADATES,  NIOBATES,  AND   TANTALATES.          327 
Tantalates.—  3Ta205.4Na20.25H,0  ;    3Ta2O5.4K2O.16H2O  ; 


On  fusing  tantalum  pentoxide  with  excess  of  caustic  potash  or 
soda,  and  washing  out  excess  of  the  alkali  with  alcohol,  the  salts  of 
the  formula  3TaoO5.4M2O  remain  as  crystalline  powders.  Their 
solutions,  when  warmed,  deposit  the  other  salts  of  the  formula 
Ta2O3.MoO  as  insoluble  precipitates. 

Be(N03)2.3H20;    Be^OH).NO3.H2O  ;    Ca(NO3)2.4H2O  ;    Sr(NO3)2.5H2O  ; 
Ba(N03)2. 

These  are  also  white  soluble  salts.  The  basic  beryllium 
nitrate  is  produced  by  digesting  a  solution  of  the  ordinary  nitrate 
with  beryllium  hydrate.  Calcium  nitrate  often  occurs  as  an 
efflorescence  on  caverns  frequented  by  bats  and  birds,  and  in  stables, 
&c.,  where  animal  matter  decomposes  in  presence  of  calcium 
carbonate.  It  is  easily  soluble  in  water,  and  in  alcohol,  and  may 
be  fused  without  decomposition.  Strontium  nitrate  is  also  an 
easily  soluble  salt  ;  it  is  used  to  produce  red  fire  in  pyrotechny. 
Barium  nitrate  is  one  of  the  important  salts  of  barium.  It  is 
formed  by  dissolving  barium  sulphide  (q.v.)  or  carbonate  in  dilute 
nitric  acid,  or  on  account  of  its  sparing  solubility  (1  part  in  11*7 
of  water  at  20°)  by  addition  of  potassium  nitrate  to  a  strong 
solution  of  barium,  chloride.  It  is  insoluble  in  strong  nitric  acid 
and  also  in  alcohol.  These  nitrates,  when  heated,  yield  nitrites, 
and  then  oxides  at  a  bright  red  heat. 

Ca(V03)2;       Sr(V03)2;      Ba(VO3)2.H2O  ;      2Ca2V2O7.5H2O  j     Ba^O?; 
2V205.CaO;  2V205.BaO;  2V2O5.3BaO.19H2O. 

The  three  first  are  yellowish-white  gelatinous  precipitates 
formed  by  adding  ammonium  metavanadate  to  soluble  salts  of  the 
metals;  the  three  last  are  orange-coloured,  and  are  produced  by 
acidifying  the  former  with  acetic  acid.  The  other  vanadates  are 
insoluble  and  are  formed  on  adding  to  a  soluble  salt  of  the  metal 
potassium  orthovanadate.  They  haTe  not  been  analysed.  The 
pyrovanadates  are  produced  by  precipitation. 

N"b2O5.2CaO;  Nb2O5.CaO. 

These  are  prepared  by  fusing  niobium  pentoxide  with  calcium 
chloride,  or  with  calcium  fluoride  and  potassium  chloride.  They 
are  insoluble.  Other  niobates  and  tantalates  are  formed  as  in- 
soluble precipitates  on  adding  a  soluble  niobate  or  tantalate  to  a 
soluble  salt  of  calcium,  strontium,  or  barium.  They  have  not  been 
analysed. 


328      THE   OXIDES,    SULPHIDES,    SELENIDES,   AND   TELLUEIDES. 

Mgr(NO3)2.6H2O  ;      Zn(NO3)2.6H2O  ;     Cd(NO3)2.4H.2O.— Basic    nitrates :— 
3N205.4Zn0.3H20  ;  N2O5.2ZnO.3H2O  ;  N2O5.2CdO.3HoO  ;  and  N2O5.8ZnO. 

Magnesium,  zinc,  and  cadmium  nitrates  are  white  deliquescent 
crystals,  soluble  in  alcohol.  The  basic  nitrates  of  zinc,  produced 
by  digesting  the  ordinary  nitrate  with  zinc  hydrate,  are  non- 
crystalline  soluble  masses.  NboO5.4MgO  and  Nb2O5.3MgO  are 
also  known. 

Sc(NO3)3 ;  Y(NO3)3.4H2O  and  12H2O;  La(NO3)3.6H2O  and  4H2O. 

These  are  colourless  soluble  deliquescent  salts.  A  crystalline 
vanadate  of  boron  has  been  produced  by  fusion. 

A1(N03)3.9H20  ;  Ga(N03)3;  In(NO3)3.3HoO  ;  T1NO3 ;  T1NO3.3HNO3 
Aluminium    nitrate  is   deliquesent ;    when  digested   with  hy- 
droxide,  or  when  heated,  it  forms  basic  salts,  similar  to  those  of 
zinc.     Indium  also  forms  basic  nitrates. 

Thallous  nitrate  is  insoluble  in  a.lcohol ;  the  acid  salt  crystal- 
lises from  strong  nitric  acid.  All  these  salts  are  colourless. 

T13V04  ;  T14V207  ;  T1V03  ;  also  4V2O5.T12O  ;  5V2O5.6T12O  ;  7V2O5.6T12O. 
The  first  of  these,  prepared  by  fusion,  is  a  red  substance ;  the 
second  is  precipitated  by  addition  of  or tlio vanadate  of  sodium, 
NasVOi  to  a  thallous  salt,  as  a  yellowish  powder ;  and  the  third 
is  produced  by  fusion ;  it  forms  dark  scales.  The  pyrovanadate 
is  formed  with  liberation  of  alkali ;  if  it  be  warmed  with  water, 
more  and  more  alkali  goes  into  solution,  and  the  other  acid  vana- 
dates  are  produced. 

Cr(N03)3.9H20 ;  Fe(NO3)3.9H2O.— Basic  salts,  2N2O5.Cr2O3 ;  3N2O5.2Cr2O3 ; 
also  many  basic  ferric  salts.  Two  basic  salts  of  chromium  should  be  here 

/N03  /N03 

included,  viz.  :  Cr— OH,  and  Cr^-NO3,  produced  by  treating  the  compound 

\C1  \C1 

Cr(OH)2Cl  with  nitric  acid. 

Chromium  nitrate  is  a  violet  crystalline  substance ;  and  the 
ferric  salt  lavender- blue ;  both  are  very  soluble.  The  basic  salts 
of  chromium  are  green ;  those  of  iron  orange-yellow. 

Fe(N03)2.6H20  ;        Mn(NO3)2.6H2O,       and      3H2O ;       Co(NO3)2.6H2O ; 
Ni(NO3)2.6H2O.— Basic  salt .— N2O5.6CoO.5H2O. 

The  solution  of  ferrous  nitrate  must  be  evaporated  in  the  cold ; 
when  heated,  oxygen  from  the  nitric  group  oxidises  the  iron  to 
ferric  nitrate,  and  a  basic  substance  is  formed.  The  ordinary 
nitrate  of  iron  is  green  ;  that  of  manganese,  pink ;  that  of  cobalt, 
red ;  and  of  nickel,  grass-green.  They  are  all  soluble  in  alcohol. 


NITRATES,  VAXADATES,   NIOBATES,   AND   TANTALATES.       329 

Basic  cobalt  nitrate  is  produced  as  a  blue  precipitate  by  adding  a 
solution  of  ammonia  to  the  normal  nitrate ;  and  nickel  nitrate, 
similarly  treated,  gives  a  green  basic  salt. 

Hydrated  titanium  and  zirconium  dioxides  are  soluble  in  nitric 
acid  ;  but  on  warming  the  solution  of  the  former,  the  hydrate 
separates  out.  Zirconium  nitrate  can  be  evaporated  to  dryness ;  it 
leaves  a  gummy  mass.  Cerium  sesquioxide  dissolves  in  nitric  acid, 
and  on  evaporation  a  crystalline  mass  of  Ce(N03)3.6H20  is  left. 
The  dioxide  also  forms  an  orange-yellow  solution  in  nitric  acid. 

Thorium  nitrate,  Th(NO3)4,  is  a  crystalline  salt ;  it  also  forms 
a  double  salt  with  potassium,  nitrate  Th(NO3)4.KNO3. 

Silica,  recently  precipitated,  is  sparingly  soluble  in  nitric  acid. 
The  nitrate  of  germanium  has  not  been  prepared;  that  of  tin, 
Sn(NO3)4,  is  obtained  by  dissolving  stannic  hydrate,  Sn(OH)4,  in 
dilute  nitric  acid  ;  on  rise  of  temperature  it  easily  decomposes  into 
metastannic  acid,  5SnO2.5H2O,  and  nitric  peroxide,  N02.  If  am- 
monium nitrate  be  present,  the  decomposition  does  not  occur, 
probably  because  it  forms  a  double  salt. 

Stannous  nitrate,  Sn(NO3)2,  is  produced  by  dissolving  tin  in 
dilute  cold  nitric  acid.  It  also  is  easily  decomposed  when  heated, 
giving  metastannic  acid.  Lead  nitrate,  Pb(NO3)2.,  forms  octa- 
hedra  ;  when  crystallised  below  16°,  it  contains  2H20  ;  it  is  in- 
soluble in  alcohol.  By  digesting  it  with  lead  hydrate,  or  by  adding 
ammonia  to  ordinary  lead  nitrate,  the  basic  salts,  N2O5.2PbO.H2O 
(=NO3-Pb-  OH);  N2O5.2PbO;  2N2O5.3PbO.3H2O ;  and 
3N2O5.10PbO.4H2O,  are  formed.  The  last  three  are  nearly  in- 
soluble in  water. 

Two  vanadates  of  lead  are  found  native,  viz.,  Pb(VO3)2,  lead 
metavanadate,  or  dechenite,  and  Pb2V2O7,  lead  pyrovanadate,  or 
de-sdoizite.  Lead  orthovanadate,  Pb3(VO4)2,  has  also  been  prepared  ; 
it  is  a  yellow  precipitate.  An  orange-coloured  acid  salt  is  also 
produced  on  treating  one  of  these  vanadates  with  acetic  acid ;  'it 
has  the  formula  2V2O5.PbO.  The  mineral  vanadinite, 
3Pb3(VO4)2.PbCl2,  is  a  compound  of  lead  orthovanadate  and 
chloride. 

Nitrates,  vanadates,  &c.,  of  members  of  the  vanadium  group  do 
not  appear  to  exist.  The  compound  nitric  peroxide,  N2O4,  has  been 
viewed  as  nitrate  of  nitrosyl,  NO,  thus,  NO(N03)  ;  but  of  the 
justice  of  this  view  there  is  no  proof.  A  nitrate  of  the  oxide  V2O4 
appears  to  exist ;  and  V2Q6  is  soluble  in  acids,  but  the  hydrates  of 
tantalum  and  niobium  pentoxides  are  insoluble  in  nitric  acid. 

Similarly,  although  the  oxides  of  phosphorus  and  arsenic  dis- 
solve in  nitric  acid,  no  compound  has  been  isolated.  But  with 


330      THE   OXIDES,   SULPHIDES,   SELENIDES,   AXD   TELLUEIDES. 

antimony,   N2O5.Sb4O6,  has   been  prepared  ;    and  the  pentoxide, 
Sb2O5,  is  slightly  soluble  in  nitric  acid. 

Bismuth  nitrate,  Bi(NO3)3.5H2O,  is  a  well  crystallised  salt. 
On  treatment  with  water  it  gives  a  mixture  of  three  salts, 
each  of  which  may,  however,  be  prepared  fairly  pure  by  careful 
attention  to  temperature  and  dilution.  These  are  N2Os.Bi2O3.I:LO 
=  2{BiO(NO3)}.H2O;  2N2O5.Bi2O3  H2O  =  Bi(OH)(NO3)2;  and 
N2O5.2Bi2O3.H2O  These  basic  nitrates  are  insoluble  in  water. 

Molybdenum  trioxide  is  soluble  in  nitric  acid  ;  so  too  is  oxide  of 
tungsten,  but  no  compounds  are  known.  Uranium  forms  yellow 
nitrates  of  uranyl  of  the  formulae  UO2(NO3)2.3H2O  and  6H2O. 

Samarskite  consists  chiefly  of  niobates  of  uranyl,  iron,  and 
yttrium. 

A  nitrate  of  tellurium  of  the  formula  N2O5.4TeO2  is  produced 
on  dissolving  tellurium  in  nitric  acid,  and  evaporating. 

Rhodium  oxide  is  soluble  in  nitric  acid,  but  the  nitrate  is 
unstable.  But  on  adding  sodium  nitrate  the  stable  double  salt 
Rh(NO3)3.NaNO3  may  be  obtained  in  crystals.  Palladium  nitrate, 
Pd(NO3)2  is  easily  prepared  by  dissolving  palladium  monoxide,  or 
the  metal,  in  nitric  acid.  It  is  a  brown  compound  ;  and  on  evapo- 
ration a  basic  salt  is  produced. 

Osmium  oxide  is  also  soluble  in  nitric  acid.     Platinic  nitrate, 
Pt(NO3)j,  is  unstable,  but  as  with  rhodium  the  addition  of  potas- 
sium nitrate  yields  a  stable  double  salt  of  the  formula 
Pt(N03)4.KN03. 

Cu(N03)2.3H20  ;  Cu3(V04)2.H20  ;  V2O5.4CuO.3H2O,  also  H2O.  The 
latter  is  possibly  VO.(OCu.OH).(O2)Cu.  It  is  found  native,  and  named 
volborthite. 

Cu(N03)2.NH4NO3. 

Copper  nitrate  is  a  soluble  blue  salt,  crystallising  well.  It 
is  the  source  of  copper  oxide  for  the  analysis  of  organic  sub- 
stances, for,  like  almost  all  the  nitrates,  it  yields  the  oxide  on 
ignition.  The  vanadates  are  brown  substances. 

AgN03;  Ag-NO3.KN03;  AgrNO3.NH4NO:1 ;  2Ag-NO3.Pb(NO3)2. 
Agr3V04;  Agr4V207;  AsV03. 

The  first  nitrate  is  an  important  substance.  Great  use  is  made 
of  it  in  photography,  electro  typing,  &c.,  and  under  its  old  name 
"  lunar  caustic"  (luna  =•  silver),  it  is  employed  as  a  caustic,  being 
cast  into  sticks  for  medical  use.  It  is  a  white  easily  fusible  salt 
(m.  p.  218°)  ;  it  is  soluble  in  about  its  own  weight  of  cold  water, 
and  in  about  four  times  its  weight  of  alcohol.  It  crystallises  with 
sodium  and  lithium,  to  form  double  salts  like  those  of  potassium 


NITRATES,   VAN  ABATES,   NIOBATES,   AND   TANTALATES.        331 

and  ammonium,  but  not  in  molecular  proportions.     A  number  of 
double  nitrates  and  halides  are  known  ;  e.g., 


4AgN03.Pb(N03)2.2AgI  ;  2A&NO3.Pb(NO3)2.2AgI. 

These  are  sparingly  soluble  salts  prepared  by  mixture. 

The  mercurous  nitrates  are  numerous,  many  basic  compounds 
being  known.     They  are  as  follows  :  — 


;  3N205.4Hg-2O.H20  ;  3N2O5.5Hg2O.2H2O  ; 

Others  are  said  to  have  been  obtained,  but  their  existence  is 
questionable.  Mercurous  nitrate  is  formed  by  digesting  mercury 
with  cold  dilute  nitric  acid.  The  basic  nitrates  are  produced  by  the 
action  of  water  on  the  ordinary  salt.  Double  salts  with  strontium, 
barium,  and  lead  nitrates  are  also  known,  of  formulas  such  as 
3N2O5.2PbO.2Hg2O.  All  these  salts  are  crystalline  and  soluble. 

By  dissolving  mercuric  oxide,  HgO,  in  excess  of  nitric  acid 
and  evaporating,  crystals  of  the  salt  2Hg(NO3)2.H.,O,  are  deposited. 
Crystals  with  8H2O  may  also  be  produced  by  cooling  the  solution. 
These  crystals,  when  fused,  deposit  a  basic  salt,  N2O3.2HgO.3H2O  ; 
and  with  water  they  yield  N2O5.3HgO.H2O.  Like  silver  nitrate, 
mercuric  nitrate  combines  with  mercury  halides,  forming  colour- 
less crystalline  compounds,  e.g.,  Hg(NO3)2.HgI2  ;  2Hg(NO3)2.HgI2; 
Hg(NO3)2.2HgI2;  and  2Hg(NO3)2.3HgI2.  These  are  all  decom- 
posed by  water.  The  compound  2Hg(NO3)2.4AgI.Hv!O  is  also 
known. 

Oxide  of  gold  dissolves  in  nitric  acid,  but  the  solution  decom- 
poses spontaneously  at  the  ordinary  temperature,  again  depositing 
gold  oxide. 

Compounds  of  vanadium  pentasulphide.  —  This  body  is 
soluble  in  sulphides  of  the  alkalies.  On  adding  alcohol  to  its 
solution  in  potassium  sulphide,  a  scarlet  precipitate  is  produced, 
consisting  of  potassium  sulphovanadate  ;  it  has  probably  the 
formula  V2S5.K2S  =  KVS3,  and  is  a  meta-compound.  A  solution 
of  this  substance  gives  brown  precipitates  with  soluble  salts  of 
other  elements,  but  the  formulas  of  the  compounds  are  unknown. 

Compounds  containing  halogens. 
VOF3;  YOC13;  YOBr3;  NbOF3;  NbOCl3  ;  NbOBr3  ;  TaOF3. 

No  corresponding  nitrogen  compound  is  known,  although  a 
mixture  of  nitrosyl  chloride,  NOC1,  and  chlorine  reacts  with  water 
as  if  it  consisted  of  NOC13. 


332      THE   OXIDES,   SULPHIDES,    SELENIDES,   AND   TELLURIDES. 

Yanadyl  trifluoride  is  known  in  combination  (see  below). 

Vanadyl  chloride,  VOC13,  is  produced  by  heating  the  oxide, 
V202  (or  VO  ?)  in  a  current  of  chlorine,  when  direct  union  ensues. 
The  higher  oxides,  mixed  with  carbon  and  heated  in  chlorine,  also 
yield  it.  The  bromide,  VOBr3,  is  similarly  prepared ;  also  by  pass- 
ing bromine  over  the  heated  trioxide,  V2O3,  but  no  corresponding 
iodide  seems  capable  of  existence. 

Niobium  oxyfluoride  (niobyl  fluoride),  oxychloride,  and 
oxybromide  are  volatile  white  crystalline  bodies.  The  chloride 
has  a  vapour  density  corresponding  to  the  formula  NbOCl3.  They 
are  prepared  along  with  the  pentahalides  by  the  action  of  chlorine 
on  a  mixture  of  the  pentoxide  with  charcoal  at  a  bright  red  heat. 
The  trichloride  at  a  red  heat  decomposes  carbon  dioxide,  pro- 
ducing carbon  monoxide  and  the  oxychloride.  Tantalum  oxy- 
fluoride  is  produced  by  the  action  of  air  or  water- vapour  on  the 
pentafluoride ;  the  oxychloride  and  oxybromide  could  probably  be 
similarly  produced. 

Yanadyl  chloride  is  a  golden-yellow  liquid,  boiling  at  127°.  Its 
density  leads  to  the  usual  formula.  The  oxybromide  forms  a  dark 
red  liquid  boiling  at  about  130°  under  a  pressure  of  100  mms.,  but 
it  is  decomposed  at  180°  into  the  dibromide  YOBr2. 

These  oxyhalides  form  the  following  compounds  with  the 
halides  of  other  elements  : — 

Fluoxyvanadates  : — 

V205.2VOF3.6KF.2H20  ;     V2O2.2VOF3.6NH4F.2H2O  ; 
V2O5.2VOF3.12NH4F. 

Vanadoxyfiuorides  : — 

2VOF3.3KHF2 ;  2VOF3.3NH4.HF2 ;  2VOF3.ZnF2.ZnO.14H2O. 

NioboxyfLuorides : — 

NbOF3.2KF.H20  ;  NbOF3.2NH4F.H2O  ;  NbOF3.3KF  ;  NbOF3.3NH4F  j 
3NbOF3.5KF.H2O  ;     3NbOF3.5NH4F.H2O  ;     NbOF3.3KF.HF  ; 
3NbOF3.4KF.2H20  ;     NbOF3.NH4F  ;     NbOF3.NbF5.3NH4F  ; 
NbOF3  ZnF2.6H20. 

Tantaloxyfluoride  : — TaOF3.3NH4F. 

These  bodies  are  produced  by  direct  union.  They  are  crystal- 
line salts.  The  tantaloxyfluorides  react  with  water,  forming 
hydrated  tantalum  pentoxide  and  tantalinuorides,  such  as  TaF52KF, 
hence  they  have  been  little  investigated.  The  corresponding 
chlorides  and  bromides  of  these  elements  are  also  easily  decom- 
posed by  water,  hence  their  derivatives  have  not  been  prepared. 


TETROXIDES   OF   NITBOGEX   AND   VANADIUM.  333 

Tetroxides,  or  dioxides. — These  are  as  follows : — 

2VO2  and  N2O4  ;  VO2  or  V2O4  ;  NbO2  or  N"b2O4  ;  TaO2  or  Ta.,O4  ; 
VS2  or  V2S4. 

The  formula  of  nitric  peroxide,  as  this  substance  is  usually 
called,  depends  on  the  temperature.  In  the  liquid  state  it  is  a 
tetroxide,  N2O4.  The  gas,  at  the  lowest  possible  temperature, 
also  approximates  to  this  formula:  but  on  raising  the  temperature, 
dissociation  ensues,  the  extent  of  dissociation  depending  on  the 
temperaiure  and  pressure,  until,  at  140°,  at  atmospheric  pressure, 
the  more  complex  molecules  of  N204  are  entirely  resolved  into  mole- 
cules of  N02.  At  higher  temperatures  the  compound  NO  disso- 
ciates in  its  turn  into  NO  and  0,  and  at  620°  the  gas  contains  no 
molecules  of  peroxide.  On  cooling,  recombination  takes  place, 
and  the  phenomena  are  reversed.  It  is  possible  to  trace  these 
changes  by  the  alteration  of  colour  of  the  gas ;  N204  is  an  almost 
colourless  substance  when  solid ;  N02  is  dark  reddish-black  ;  and 
a  mixture  of  NO  and  O  is  also  colourless.  On  heating  a  tube  of 
hard  glass  filled  with  the  gas,  it  turns  dark  at  first,  and  then 
lightens  in  colour,  turning  nearly  colourless  at  the  temperature  at 
which  the  glass  begins  to  soften.  As  we  have  the  two  substances, 
one  of  which  is  a  polymeride  of  the  other,  it  is  convenient  to  give 
them  different  names.  The  first,  N02,  we  shall  call  nitric  peroxide, 
reserving  the  name  tetroxide  for  the  compound  N204. 

Alternative  formulae  have  been  ascribed  to  the  oxides  of  vana- 
dium, niobium,  and  tantalum.  They  are  non- volatile  solids,  and 
nothing  is  known  regarding  their  molecular  complexity. 

Preparation.— 1.  By  the  union  of  the  lower  oxides  with 
oxygen. — Nitrous  oxide,  N20,  does  not  combine  directly  with 
oxygen;  but  nitric  oxide,  NO,  mixed  with  half  its  volume  of 
oxygen,  at  once  combines,  forming  a  mixture  of  peroxide  and 
tetroxide.  Nitrogen  trioxide,  N203,  which  is  a  blue  liquid,  is  also 
slowly  converted  into  peroxide  and  tetroxide  when  kept  in  presence 
of  oxygen  or  air. 

Vanadium  tetroxide  is  formed  when  the  trioxide  is  heated 
in  air ;  but  on  prolonged  heating  it  is  oxidised  to  the  pent- 
oxide. 

2.  By  depriving  a  higher  oxide  of  oxygen. — It  has  been 
already  remarked  that  nitrogen  pentoxide  decomposes  spon- 
taneously into  peroxide  and  oxygen.  Nitric  acid  is  more  stable ; 
but  when  its  vapour  is  led  through  a  red-hot  tube,  a  large  propor- 
tion is  decomposed.  It  is  more  convenient,  however,  to  deprive 
nitric  acid  of  oxygen  by  distilling  it  with  arsenious  anhydride. 


334      THE   OXIDES,   SULPHIDES,   SKLENIDES,   AND   TELLURIDES. 

The  reaction  is :— 4N"205.H20  +  As406  =  4^04  +  2As205  +  4H20. 
The  water,  however,  reacts  with  the  tetroxide,  thus : — !3N204  -f 
2H20  =  4HN03  +  2 NO ;  and  a  mixture  of  tetroxide,  peroxide, 
and  nitric  oxide  is  produced.  On  condensing  the  product,  these 
combine  to  form  trioxide,  thus,  NOy  +  NO  =  N203.  Hence,  in 
order  to  remove  water  from  the  sphere  of  action,  a  considerable 
quantity  of  strong  sulphuric  acid  or  phosphorus  pentoxide  is  added. 
The  product  is  then  pure  peroxide  and  tetroxide.  To  remove 
nitric  acid,  some  of  which  is  apt  to  distil  over,  the  liquid  is  again 
distilled,  with  addition  of  a  little  more  arsenic  trioxide  and  phos- 
phorus pentoxide. 

The  tetroxide  may  also  be  formed  by  the  action  of  nitric  pent- 
oxide  on  the  trioxide.  The  blue  liquid  containing  trioxide  may  be 
rendered  orange  by  addition  of  a  mixture  of  nitric  acid  and  phos- 
phoric anhydride,  which  must  contain  ]ST205. 

When  a  nitrate  is  heated,  it  decomposes  into  an  oxide  and  oxides 
of  nitrogen.  If  the  pentoxide  were  not  so  unstable,  one  would 
expect  that  it  would  be  formed,  but,  as  a  rule,  the  peroxide  resolved 
by  heat  into  nitric  oxide  and  oxygen  is  produced  by  its  decomposi- 
tion. On  cooling  the  resulting  gases  they  re-combine  to  form 
tetroxide  and  peroxide.  The  most  convenient  nitrate  t&  employ  is 
that  of  lead.  The  equation  is  : — 

Pb(NO3)3  =  PbO  +  2A702  +  0. 

Metallic  tin  may  also  be  used  to  withdraw  oxygen  from  nitric 
acid.  The  equation  is  : — 

Sn  +  4HN03  =  SnO2  +  2^204  +  2H,0. 

Nitric  and  nitrous  oxides,  NO  and  N20,  are,  however,  produced 
simultaneously.  The  nitric  acid  must  be  strong  and  somewhat 
warm.  It  will  be  remembered  that  the  tin  is  oxidised  to  meta- 
stannic  acid,  5SnO2.5H2O. 

The  compound,  VO,C1,  decomposes  when  heated  in  carbon 
dioxide  into  VO2  and  chlorine. 

Niobium  pentoxide  is  reduced  to  tetroxide  by  heating  it  to 
whiteness  in  hydrogen,  and  tantalum  pentoxide  when  heated  to 
whiteness  in  a  crucible  lined  with  carbon  loses  oxygen,  leaving  the 
tetroxide. 

Properties. — Nitrogen  tetroxide  is  a  colourless  solid  below 
— 10'14°.  At  that  temperature  it  melts,  but  the  liquid  has  a  pale 
straw  colour,  owing  to  incipient  dissociation.  As  the  temperature 
rises  its  colour  changes  to  yellow  and  then  orange-red;  it  boils  at 


TETEOXIDES   AND   TETR  A  SULPHIDES   OF   NITROGEN",   ETC.         335 

22°,  giving  cff  a  brown-red  gas,  which  consists  largely  of  the  per- 
oxide. The  peroxide  is  not  known  in  the  solid  form,  but  the 
liquid  tetroxide  apparently  contains  some,  judging  from  its  colour. 
The  liquid  compound  is  heavier  than  water  (1*45  at  15°).  It 
reacts  with  ice-cold  water,  forming  nitrous  and  nitric  acids, 
N204  +  H20  =  HNO3  +  HNO2;  and  at  higher  temperatures 
forming  nitric  acid  and  nitric  oxide,  3N204  +  2H20  =  4HNO3  -f 
2NO.  It  dissolves  in  strong  nitric  acid,  forming  the  red  fuming 
acid  often  employed  for  oxidation  of  sulphides,  &c. ;  and  in  sul- 
phuric acid,  giving  salts  of  nitrosyl,  NO  (see  sulphates).  It  acts 
violently  on  cork  and  indiarubber,  hence,  in  preparing  it,  all  the 
joints  should  be  of  sealed  glass. 

Vanadium  tetroxide,  V2O4  or  VO2,  is  a  dark  green  amorphous 
powder,  insoluble  in  water,  but  soluble  in  hydroxides  of  sodium 
and  potassium,  forming  hypovanadates,  and  in  acids,  forming  salts 
of  vanadyl  (VO). 

Niobium  tetroxide  is  a  dense  black  insoluble  powder,  which 
on  ignition  in  air  yields  the  pentoxide ;  and  tantalum  tetroxide 
is  a  dark  substance,  which  acquires  metallic  lustre  under  the  bur- 
nisher. 

Tetrasulphides  of  vanadium,  V2S4,  and  tantalum,  Ta^Si  (?) 
are  known.  The  first,  produced  by  heating  the  tetroxide  in  a 
stream  of  hydrogen  sulphide,  is  a  black  powder,  insoluble  in  water, 
alkalies,  or  alkaline  sulphides ;  the  second,  which  may  be  an  oxy- 
sulphide,  is  produced  by  heating  tantalum  pentoxide  in  vapour  of 
carbon  disulphide  or  tantalum  pentachloride  in  hydrogen  sulphide. 
It  is  a  black  powder,  which  when  burnished  acquires  a  brass-yellow 
lustre. 

Compounds  with  oxides  and  sulphides. — Nitric  peroxide 
does  not  combine  with  water,  but  is  decomposed  (see  above).  It 
combines,  however,  with  lead  oxide,  producing  a  compound  of  the 
formula  PbN2O5,  which  may  be  a  salt  of  the  hypothetical  acid, 

HoN205,  or  may  be  a  double  nitrite  and  nitrate  of  lead,  Pb<t^Q2. 

Similar  compounds,  but  containing  more  lead  oxide,  are  produced 
by  heating  lead  nitrate  with  metallic  lead. 

Vanadium  tetroxide  dissolves  in  alkalies,  forming  hypo- 
vanadates. On  addition  of  a  hydroxide  to  its  solution  in  hydro- 
chloric or  sulphuric  acids,  its  hydrate,  V2O4.7H2O,  is  thrown  down 
as  an  amorphous  black  precipitate,  which  may  be  viewed  as 
hydrated  hydrogen  hypovanadate.  An  arbitrary  division  is  usually 
drawn  between  the  compounds  called  hypovanadates  and  those 
termed  vanadyl  salts.  They  are  here  considered  as  chemically 


336      THE   OXIDES,   SULPHIDES,    SELENIDES,    AND   TELLUEIDES. 

similar ;  both  contain  vanadium  tetroxide  in  combination  with 
other  oxides.  They  are  as  follows  : — 

2V2O4.K2O.7H2O  ;  2V2O4.Na2O.7H2O  ;  2V2O4.(NH4)2O.3H2Oj  2V2O4.BaO  ; 
2V2O4.PbO  ;  2V2O4.Ag-2O. 

These  are  termed  hypovanadates.  There  are  also  V2O4.3SO3.4HUO 
and  15H2O;  V2O4.^SO3  7H2O  and  10H2O.  These  are  termed 
vanadyl  sulphates,  and  will  be  considered  among  the  sulphates. 

Potassium  hypovanadate,  2V2O4.K2O.7H>O,  forms  dark  brown 
crystals,  soluble  in  water,  but  nearly  insoluble  in  caustic  potash, 
and  quite  insoluble  in  alcohol.  The  sodium  salt  is  similar.  The 
barium,  lead,  and  silver  salts  are  brown  or  black,  and  are  produced 
by  precipitation. 

Hydrated  vanadium  tetrasulphide  is  precipitated  on  addi- 
tion of.  an  acid  to  a  solution  of  the  tetroxide  in  sulphides  of  the 
alkalies.  It  is  a  brown  powder.  It  dissolves  in  sulphides  of  the 
alkalies,  forming  the  hyposulphovanadates.  These  have  been 
little  studied ;  they  are  black  solids  dissolving  with  a  brown 
colour.  Those  of  the  alkalies  are  soluble,  and  give  precipitates 
with  solutions  of  the  metals. 

Compounds  with  halides. — Compounds  of  the  formulae 
NOCla  and  N02C1,  though  it  has  been  stated  that  they  are  formed 
by  various  reactions,  have  been  proved  to  consist  of  solutions  of 
chlorine  in  nitrosyl  chloride,  NOC1,  or  in  nitrogen  tetroxide.  Nor 
is  any  compound  known  of  the  formula  NOC12. 

But  vanadium  oxytrichloride,  VOC13,  when  heated  to  400°  with 
metallic  zinc  is  converted  into  VOC1>,  a  light  green  crystalline 
solid,  deliquescent,  and  soluble  in  alkalies.  The  corresponding 
bromide  is  a  yellow-brown  deliquescent  solid,  produced  by  heating 
the  tribromide  to  180°.  The  corresponding  fluoride,  VOF2,  is 
known  in  combination  with  ammonium  fluoride,  in  the  blue  mono- 
clinic  crystals  of  VOF2.2NH4F,  produced  by  adding  hydrogen 
ammonium  fluoride,  HNH4F2,  to  a  solution  of  tetroxide,  V204,  in 
hydrofluoric  acid. 

Trioxides,  N203 ;  V2O3. — Preparation. — Nitrogen  trioxide, 

or  nitrous  anhydride,  is  produced  by  the  union  of  nitric  peroxide, 
N02,  with  nitric  oxide,  NO.  It  is  apparently  formed  by.  all 
reactions  involving  these  products  ;  but  as  it  cannot  exist  in  the 
gaseous  state,  it  is  formed  only  on  cooling  the  mixture  of  its 
products  of  decomposition.*  Such  a  gaseous  mixture  is  liberated 
on  treating  a  nitrite  with  sulphuric  acid,  thus  : — 

*  Chem.  Sue.,  47,  187. 


NITRITES  AND  VANADITES.  337 

2KN02  +  H2S04  =  KsSO*  +  H20  +  N02  +  NO; 
or  by  adding  water  to  hydrogen  nitrosyl  sulphate  :  — 

2H(NO)S04  +  Aq  =  2H2S04.Aq  +  NO,  +  NO. 

When  fairly  pure  it  is  a  mobile  blue  liquid,  stable  only  at  a  very 
low  temperature.  It  does  not  solidify  even  on  cooling  it  to  about 
—90°.  If  warmed,  it  decomposes  into  its  constituents  ;  and  as  more 
nitric  oxide  escapes  than  peroxide,  the  colour  of  the  remaining 
portion  changes  to  green,  and  subsequently  to  dirty  red  :  for  the 
colour  of  the  remaining  peroxide  is  changed  by  that  of  the  blue 
trioxide.  It  is  also  formed  by  the  action  of  a  small  quantity  of 
water  on  nitrogen  tetroxide,  thus  :  —  2N204  +  H20  =  2HN03  + 
N203  ;  and  this  is  one  of  the  easiest  methods  of  preparing  it. 
A  mixture  of  nitric  oxide,  NO,  and  oxygen,  even  if  the  oxygen 
be  in  excess,  combines  to  some  extent  to  form  the  trioxide  when 
cooled  in  a  freezing  mixture. 

Vanadium  trioxide  is  produced  by  heating  vanadium  pent- 
oxide  in  a  current  of  hydrogen  or  with  carbon.  It  is  also  formed 
when  V2O2  is  heated  gently  in  air.  It  is  a  black  insoluble  powder, 
possessing  semi-metallic  lustre.  It  is  insoluble  in  acids.  When 
heated  to  redness  in  air,  it  glows  and  burns  to  the  pentoxide.  It 
is  a  conductor  of  electricity.  Like  nitrogen  trioxide,  it  combines 
with  oxides,  forming  the  vanadites. 

No  trioxide  of  niobium  or  tantalum  has  been  prepared. 

Compounds  with  oxides.  —  Nitrites  and  vanadites.  —  It  is 
probable  that  two  sets  of  nitrites  exist,  having  the  same  formulae 
but  different  constitution  ;  these  may  be  regarded  as  derivatives  qf 

two  hypothetical  nitrous  acids,  HN<^Q,  and  HO  —  N=O. 

It  is  probable  that  the  silver  and  mercury  salts  are  derivatives 
of  the  first,  and  the  potassium  and  calcium  salts  of  the  second. 
The  reason  for  this  view  is  as  follows  :  — 

The  compound  of  carbonr  hydrogen,  and  iodine,  known  as 
methyl  iodide,  has  the  formula  CH3I.  When  heated  with  silver 
nitrite  in  a  sealed  tube,  silver  iodide  is  produced,  along  with  the 
compound  CH3.N02,  named  nitromethane.  Now,  on  exposing  this 
liquid  to  the  action  of  nascent  hydrogen,  produced,  for  example,  by 
the  action  of  tin  on  hydrochloric  acid,  the  following  reaction 
occurs  :  — 

6H  =  CH3.NH2  +  2H20  ; 


the    oxygen   is   replaced   by   hydrogen,   forming    the    compound 


338      THE   OXIDES,    SULPHIDES,    SELENIDES,   AND    TELLUEIDES. 

(CH3).]SrH>,  analogous  to  ammonia,  NH3  ;  and  it  is  argued  that  the 
nitrogen  and  the  carbon  must  be  combined  with  each  other. 

On  heating  methyl  iodide,  CH3I,  with  potassium  nitrite,  on  the 
other  hand,  a  compound  of  the  same  formula  is  produced,  viz., 
CH3.N02,  along  with  potassium  iodide.  But  this  body,  which  is 
named  methyl  nitrite,  differs  entirely  in  properties  from  its 
isomeride,  nitromethane.  And  on  treatment  with  nascent  hydro- 
gen, this  reaction  takes  place  :  — 


CH3.N02  +  6H  =  CH^OH  +  NH3  +  H20. 

The  body  CH3.OH  is  named  methyl  alcohol,  and  it  is  certain 
that  carbon  and  oxygen  are  here  combined.  Hence  the  formula 
CH3O—  NO  is  attributed  to  it,  and  KO—  NO  to  the  nitrite  from 
which  it  is  derived  ;  whereas  silver  nitrite  has  apparently  the 
formula  Ag  —  NO2. 

These  conclusions  are  confirmed  by  a  study  of  the  action  of 
caustic  potash  on  these  bodies.  For  while  nitromethane  reacts 
thus  :  — 

CH3.N02  +  KOH  =  CH2.KN02  +  H20, 

methyl  nitrite  is  decomposed,  thus  :  — 

CH3.ONO  +  KOH  =  CH3.OH  4-  KONO, 

the  original  potassium  nitrite  being  reproduced. 

While,  therefore,  silver  nitrite  should  probably  be  regarded  as 
a  nitride  of  silver  and  oxygen,  and  should  be  considered  among 
the  nitrides,  and  potassium  nitrite  as  a  derivative  of  nitrous 
anhydride,  yet  we  do  not  know  which  bodies  to  place  in  one  class 
and  which  in  the  other  ;  and  as  we  are  not  sure  whether  some  of 
the  compounds  named  nitrites  are  not  mixtures  of  both  com- 
pounds, it  is  more  convenient  to  include  both  varieties  at  present 
in  one  class.* 

Preparation.  —  The  nitrites  are  prepared  :  1.  By  reducing  the 
nitrates.  This  is  best  done  by  fusing  them  with  metallic  lead. 
For  instance,  three  parts  of  potassium  nitrate  fused  with  two  parts 
of  metallic  lead  with  constant  stirring  yield  potassium  nitrite  and 
lead  monoxide,  thus  :  — 

KN03  +  Pb  =  KNOa  +  PbO. 

Potassium  sulphite  may  also  be  employed  as  a  reducing  agent. 
2.  By  the  action   of   a  mixture  of  NO2   and    NO  on 

*  Che  m.  800.,  47,  203,  205,  631. 


THE   NITRITES   AND  VANADITES.  339 

hydroxides. — Those  reactions  which  produce  snch  mixtures  in 
correct  proportions  are  to  be  preferred.     An  example  is — 

NO  +  N02  +  2KOH.Aq  =  2KN02.Aq  +  H2O. 

3.  By  passing  a  mixture  of  oxygen  and  ammonia  over 
heated  platinum  black  (finely  divided  platinum),  ammonium 
nitrite  is  formed,  thus  : — 

2NH.  +  30=  NH4N02  +  H20. 

The  nitrites  of  lead  and  silver  are  nearly  insoluble,  whereas 
the  nitrates  are  very  soluble  salts ;  hence,  on  adding  to  a  nitrite  a 
soluble  salt  of  one  of  these  metals  (nitrates),  the  respective 
nitrites  are  precipitated.  They  may  be  converted  into  other 
nitrites  by  digestion  with  a  soluble  chloride  in  the  case  of  silver,  or 
a  sulphate  in  the  case  of  lead. 

List  of  Nitrites.— The  following  have  been  prepared  :— 
NaN02;  KN02;  NH4NO2.H.2O. 

White  deliquescent  salts.  That  of  sodium  is  soluble  in  alcohol. 
The  ammonium  salt  is  produced  by  addition  of  nitrous  anhydride, 
N203,  to  ammonia,  keeping  it  cold ;  or  by  mixing  solutions  of  lead 
nitrite  and  ammonium  sulphate,  filtering  off  insoluble  lead  sul- 
phate, and  evaporating  in  a  vacuum  to  crystallisation.  When 
heated,  even  in  solution,  it  undergoes  the  curious  decomposition 
NH4N02  =  N2  +  2H20. 

This  forms  a  convenient  method  of  preparing  pure  nitrogen. 
It  may  be  carried  out  more  conveniently  by  heating  a  mixture  of 
potassium  nitrite  and  ammonium  chloride,  best  after  addition  of 
copper  sulphate. 

The  corresponding  vanadites  have  not  been  analysed.  They 
are  produced  by  dissolving  vanadium  trioxide  in  alkalies.  They 
are  red  when  hydrated,  but  green  when  anhydrous. 

Ca(N02)2.H20  ;  Sr(N02)2.H20  ;  Ba(NO2)£.H2O  ;  Ba(NO2)2.KNO2.H2O. 

These  salts  may  be  formed  by  heating  a  nitrate  of  one  of  these 
metals,  dissolving  the  product  in  water,  and,  in  order  to  separate 
oxide,  passing  carbon  dioxide  to  remove  it  as  carbpnate.  The  fil- 
trate is  evaporated  and  crystallised.  Calcium  nitrite  is  insoluble 
in  alcohol.  These  are  all  soluble  white  salts. 

Mg(N02)2.3H20  and  2H2O  ;  Zn(NO2)2.3H2O  ;  Cd(NO2)2.H2O.  Also  basic 
salts  :—N2O3.2ZnO,  and  N2O3.2CdO;  and  double  salts,  Cd(NO2)2.2KNO2, 
and  Cd(NO2)2.4KNO2. 

These  are  all  white  soluble  salts. 

Nitrites  of   chromium   and  iron   have  not  been   investigated. 

z  2 


340      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

Manganous  nitrite  is  a  pink  deliquescent  salt  ;  that  of  cobalt  is 
rose-coloured,  and  of  nickel  green. 

The  double  nitrates  of  the  last  two  metals  are  better  known. 
They  are  as  follows  :  — 

3(Co(NO2)2.2KNO2).H2O,  also  with  other  amounts  of  water. 
Ni(NO2)2.Ca(NO2)2.KNO2  ;  also  similar  strontium  and  barium  salts. 

These  contain  the  metals  as  dyads,  and  are  derivatives  of  CoO, 
and  NiO. 

2Co(NO2)3.4NaNO2.H2O  ;   also  6NaNO2.H2O  ;    2Co(NO2)3.4K2O. 

These  compounds  are  produced  by  boiling  a  cobalt  salt  with 
acetic  acid  and  nitrite  of  sodium  or  potassium.  The  cobalt  is 
here  triad,  as  in  Co2O3.  Nickel  forms  no  corresponding  com- 
pounds, and  as  the  double  nitrite  of  cobalt  and  potassium  is  nearly 
insoluble  in  water,  its  formation  is  used  as  a  means  of  separating 
cobalt  from  nickel.  It  has  a  bright  yellow  colour,  and  is  therefore 
used  as  a  pigment. 

The  following  compounds  of  lead  are  known:  — 
Pb(NO2)2;  N2O3.2PbO.HoO,  and  3H.2O  ;  N2O3.3PbO.H2O  ;  N2O3.4PbO.H2O. 

The  last  three  are  yellow  bodies,  and  are  made  by  boiling 
a  solution  of  lead  nitrate  with  metallic  lead;  the  first,  by 
passing  a  current  of  carbon  dioxide  through  one  of  the  latter 
suspended  in  water  ;  the  excess  of  lead  oxide  is  removed  as  car- 
bonate. When  lead  nitrate  solution  is  boiled  with  lead,  a  double 

nitrate  and  nitrite  is  also  formed.     Its  formula  is  4Pb<        2. 


a  basic  salt  is  also  produced,  viz.,  N2O3.N2O5.9PbO.3H2O.  The  first 
of  these  has  been  viewed  as  a  salt  of  the  anhydride  N204  ;  as  N204.PbO 
(see  p.  335)  ;  but  the  formula  given  is  more  probably  correct. 

Copper  nitrite,  Cu(NO2)2  is  an  apple-green  crystalline  salt; 
and  silver  nitrite,  AgNO2,  forms  long  needle-shaped  pale-yellow 
crystals,  sparingly  soluble  in  cold  water, 

Some  interesting  double  nitrites  of  platinum  have  been  pre- 
pared (see  pp.  485  and  544). 

Compounds  with  halides.—  NOC1  ;*  YOGI.  The  first  of 
these  bodies  has  the  molecular  weight  given  by  the  formula.  It 
is  prepared  (1)  by  passing  a  mixture  of  nitric  peroxide  and  chlorine 
through  a  red-hot  tube.  The  nitric  peroxide  is  doubtless  dis- 
sociated into  nitric  oxide  and  oxygen,  and  the  former  combines 
with  the  chlorine.  It  is  also  produced  by  direct  combination  of 
nitric  oxide  with  chlorine  at  a  red  heat.  (2)  By  the  action  of  salt 
(NaCl)  on  hydrogen  nitrosyl  sulphate,  H(NO)S04,  produced  by 
*  Chem.  Sot-.,  27,  630  ;  49,  222. 


NITRIC  OXIDK  341 

saturating  strong  sulphuric  acid  with  N02  and  NO,  thus : 
H(NO)SO4  +  NaCl  =  HNaS04  +  NOCl.  (3)  Along  with  free 
chlorine,  by  heating  a  mixture  of  hydrochloric  and  nitric  acids, 
thus  :— 3HC1  +  HNO3  =  2H2O  +  NOCl  +  Git ;  and  probably  by 
the  action  of  hydrogen  chloride  on  nitrogen  tetroxide,  which  may 
be  regarded  as  nitrate  of  nitrosyl,  NO(N03),  thus  : — 

HC1  +  NO(N03)  =  NOCl  +  HN03. 

A  mixture  of  nitric  and  hydrochloric  acids  has  been  long  known 
under  the  name  "aqua  regia."  Owing  to  the  nascent  chlorine,  it 
has  the  property  of  dissolving  gold  and  platinum,  converting  them 
into  chlorides.  It  is  a  powerful  oxidising  agent,  the  chlorine  re- 
acting with  water  forming  nascent  oxygen  and  hydrogen  chloride. 

The  corresponding  vanadosyl  chloride,  VOC1,  is  a  brown 
powder  formed  by  heating  the  trichloride,  VOC13,  to  redness  in  a 
current  of  hydrogen.  At  the  same  time  the  compound  V2O2C1  is 
formed  as  a  heavy  shining  powder  like  mosaic  gold,  and  also  the 
oxide  V2O2  or  VO.  With  vanadium  we  have  thus  the  series, 
VOC13,  VOC12,  VOC1,  and  V,O2C1. 

Nitric  oxide  and  vanadium  dioxide,  NO  and  V2O2.  The 
first  of  those  is  often  erroneously  named  nitrogen  dioxide.  Its 
formula,  however,  even  at  —100°,  is  NO,  as  shown  by  its  vapour- 
density.  No  tendency  towards  increased  density  has  been  noticed  ; 
the  gas  contracts  paripassu  with  hydrogen.  The  molecular  weight 
of  the  vanadium  compound  is  unknown,  but  as  it  is  derived  from 
V2O,C1,  it  is  possibly  V2O2. 

Nitric  oxide  is  produced  in  an  impure  state  by  the  action  of 
nitric  arid  on  certain  metals.  It  is  probable  that  the  normal  action 
of  nitric  acid  is  similar  to  that  of  other  acids ;  that  a  nitrate  is 
produced  with  liberation  of  hydrogen.  But  nascent  hydrogen 
(i.e.,  hydrogen  in  the  state  of  being  liberated,  when  it  consists  in 
all  probability  of  single  uncombined  atoms)  cannot  exist  in 
presence  of  nitric  acid,  but  deprives  it  of  oxygen.  In  theory,  the 
following  reactions  are  possible  : — 


+  M"  =  M(N03)2  +  2H, 


The  conditions  determining  the  prevalence  of  any  one  of  these 
reactions  are  temperature,  presence  of  water,  and  of  the  products  of 
reaction.  But  the  oxides  of  nitrogen  produced  may  themselves 
react  with  water  or  with  nitric  acid.  For  example,  if  N204  be 


342      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

liberated  in  presence  of  water,  the  reaction  described  on  p.  337 
will  take  place,  and  a  mixture  of  nitric  oxide  and  nitric  acid  will 
be  produced.  But  some  peroxide  may  escape  along  with  nitric 
oxide.  The  gases  NO,  N^O,  and  nitrogen,  not  being  affected  by 
water,  will  be  liberated  as  such,  if  formed. 

Nitric  acid  diluted  with  its  own  volume  of  water,  acts  on 
copper  at  15°  and  on  aluminium  at  60 — 65°,  producing  a  mixture 
containing  98  and  97  per  cent,  respectively  of  nitric  oxide,  along 
with  a  small  amount  of  nitrous  oxide  and  nitrogen.  With  silver, 
acid  of  the  same  strength  at  15°  gives  31  per  cent  of  nitric  oxide 
and  60  per  cent,  of  nitrous  oxide,  N^O,  while  iron  with  nitric  acid 
of  any  dilution,  gives  chiefly  nitric  oxide  (from  86  to  91  per  cent.).* 

The  action  of  nitric  acid  on  copper  therefore  forms  the  most 
convenient  method  of  preparing  nitric  oxide.  The  equation  is  :  — 
3Cu  +  8HNO3.Aq  =  3Cu(N03)2.Aq  +  4H20  +  2NO.  To  prepare 
the  pure  compound,  this  gas  is  passed  through  a  strong  cold  solu- 
tion of  ferrous  sulphate,  FeS04,  with  which  nitric  oxide  combinesf 
(see  p.  428).  On  warming  the  solution,  the  compound  is  decom- 
posed, and  pure  nitric  oxide  is  liberated.  It  is  a  colourless,  nearly 
insoluble  gas,  which,  when  mixed  with  air  or  oxygen,  gives  red 
fumes  of  nitric  peroxide.  It  condenses  to  a  colourless  liquid  at 
—  11°  under  a  pressure  of  104  atmospheres.  Under  normal 
pressure,  it  boils  at  — 153*6°,  and  begins  to  solidify  when  the 
pressure  is  reduced  to  138  mms.  at  —167°.  It  does  not  support 
combustion,  but  like  other  gases  containing  oxygen,  it  is 
decomposed  at  a  high  temperature,  and  thus  glowing  charcoal 
or  phosphorus  burn  in  it.  With  the  vapour  of  carbon  disulphide 
it  forms  a  mixture  which,  when  set  on  fire,  burns  rapidly  with  a 
brilliant  blue-white  flame.  When  mixed  with  hydrogen,  it  can 
bo  exploded  by  a  powerful  spark. 

The  corresponding  oxide  of  vanadium,  V2O2,  may  be  formed 
by  the  action  of  potassium  on  a  higher  oxide  of  vanadium,  and 
used  to  be  considered  to  be  metallic  vanadium.  It  is  also  pro- 
duced when  a  mixture  of  vanadyl  trichloride,  VOC13,  and  hydrogen 
are  passed  through  a  tube  full  of  red-hot  charcoal.  It  is  a  light- 
grey  powder  with  metallic  lustre,  difficult  of  fusion,  and  insoluble 
in  water  and  acids.  When  heated  in  air,  it  burns  to  higher  oxides. 

It  may  be  produced  in  solution  by  reducing  a  solution  of 
vanadium  pentoxide  in  sulphuric  acid  by  means  of  zinc.  Such  a 
solution  has  a  lavender  colour,  and  is  one  of  the  most  powerful 
reducing  agents  known. 

*  Chem.  SOP.,  28,  828 ;  32,  52. 
t  Compt.  rend.,  89,  410. 


XITROSO-SULPHIDES.      NITROUS  OXIDE.  343 

Nitrogen  sulphide  and  selenide,  NS  and  NSe. — The  first 
is  produced  by  the  action  of  ammonia  on  sulphur  chloride  dissolved 
in  carhon  disulphide,  thus :— SNH3  +  3S2C12  =  6NH4C1  4-  2NS  + 
4S  ;  the  ammonium  chloride,  being  insoluble  in  carbon  disulphide, 
is  removed  by  nitration,  and  the  ca.rbon  disulphide  on  evaporation 
deposits  nitrogen  sulphide  in  yellow  rhombic  prisms.  The  corre- 
sponding selenium  compound,  produced,  however,  from  selenium 
tetrachloride,  is  an  amorphous,  orange-coloured,  insoluble  substance. 
Both  of  these  bodies  explode  by  percussion. 

When  mixed  with  chloroform  and  treated  with  chlorine,  sulphur- 
yellow  crystals  of  the  formula  NSC1  are  deposited,  analogous  to 
nitrosyl  chloride,  NOC1.  A  second  chloride  (NS)3C1  is  also  formed  ; 
it  deposits  in  copper- coloured  needles. 

Nitroso-siilphides. — A  curious  set  of  compounds  of  nitric 
oxide  with  sulphide  of  iron  and  of  a  metal  has  been  produced* 
by  dropping  a  solution  of  ferric  chloride  into  a  mixture  of  solutions 
of  potassium  nitrite  and  ammonium  sulphide,  when  black  crystals  of 
Fe3S1(NO)4.H2S  are  deposited.  When  the  solution  of  these  crystals 
is  heated  with  caustic  soda,  they  yield  large  black  crystals  of  the 
compound  Fe2S3(NO)2.3Na2S;  and  with  an  acid,  a  black  precipitate 
of  "  nitrososulphide  of  iron,"  Fe2S3(NO)2  separates.  The  first 
compound,  heated  to  100°  with  sodium  sulphide,  deposits  red  prisms 
of  the  body  Fe2S3(NO)2.Na>S.H2O. 

The  constitution  of  these  bodies  is  unknown ;  but  they  appear 
to  be  related  to  the  nitroferricyanides  (see  p.  566).  It  is  sug- 
gested that  a  corresponding  amido-compound  has  the  formula 
Fe(NO2).SNH2,  and  the  last  nitroso -sulphide  may  be  analogously 
represented  Fe(SNa).SNO. 

Nitrons  oxide,  N20,  is  produced  (1)  by  the  action  of  metals 
on  nitric  acid.  Zinc  and  pure  nitric  acid  at  15°  yield  a  mixture 
consisting  of  1  per  cent,  of  nitric  oxide,  78  per  cent,  of  nitrous 
oxide,  and  21  per  cent,  of  nitrogen.  Nickel  and  cobalt,  too,  with 
acid  diluted  with  its  own  volume  of  water,  yield  a  mixture  contain- 
ing about  80  per  cent. ;  and  tin,  at  ordinary  temperatures,  furnishes 
a  mixture  containing  from  67  to  85  per  cent.,  with  acids  of  all  con- 
centrations. (2)  The  simplest  method  of  preparation  is  to  heat 
a  mmonium  nitrate  to  above  185°,  when  it  decomposes  like  the  nitrite, 
thus :— NH,NO3  =  N20  +  2£T20.  (3)  Nitrous  oxide  is  also  formed 
by  the  action  of  an  acid  or  an  hyponitrite  (see  below). 

*  Serichte,  16,  2600. 


344      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES 

Nitrous  oxide,  or  hyponitrous  anhydride,  as  it  is  sometimes 
named,  is  a  colourless  gas,  possessing  a  faint  sweetish  smell  and 
taste.  It  is  somewhat  soluble  in  water,  and  is  best  collected  over 
hot  water,  or  by  downward  displacement.  When  exposed  to  a 
sudden  shock,  as,  for  instance,  the  detonation  of  a  fulminate,  it 
explodes  into  its  constituents  ;  this  is  a  property  common  to  bodies 
produced  with  absorption  of  heat.  It  is  condensed  by  pressure  to  a 
liquid,  boiling  at  —88°  to  —92°,  and  when  the  liquid  is  evaporated 
by  a  current  of  air  some  of  it  freezes  to  a  white  solid,  melting  at 
—99°.  Its  most  striking  property  is  its  action  on  the  nervous 
system  when  breathed,  which  has  gained  for  it  the  name  "  laughing- 
gas."  When  pure,  it  produces  insensibility,  and  is  used  as  an 
anaesthetic  in  minor  surgical  operations  and  in  dentistry  ;  but  when 
diluted  with  air  it  causes  excitement  and  intoxication.  It  easily 
decomposes  when  heated,  hence  a  candle  burning  brightly  con- 
tinues to  burn  more  brightly  in  the  gas.  But  if  the  candle  is 
burning  feebly  it  is  extinguished. 

Compounds  with  oxides.  —  Hyponitrites.*  —  A  solution  of 
potassium  nitrate  or  nitrite,  exposed  to  nascent  hydrogen  generated 
from  sodium  amalgam  (an  alloy  of  sodium  and  mercury)  loses  oxygen, 
and  potassium  hyponitrite,  KNO,  is  produced,  about  15  per  cent. 
of  the  nitrate  or  nitrite  suffering  change.  The  same  compound  is 
formed  by  fusing  iron  filings  with  potassium  nitrate.  The  sodium 
salt  forms  white,  needle-shaped  crystals,  and  has  the  formula 
NaNO.3H2O.  With  silver  nitrate,  in  presence  of  acetic  acid,  the 
silver  salt  is  precipitated  ;  it  is  a  pale  yellow  body,  of  the  formula 
AgNO.  On  addition  of  hydrochloric  acid  to  the  silver  salt  sus- 
pended in  water,  the  acid,  presumably  HNO,  is  liberated.  It 
reduces  potassium  permanganate  ;  and  on  standing,  decomposes 
into  water  and  nitrous  oxide.  No  other  salts  have  been  analysed  ; 
but  a  solution  of  the  sodium  salt  gives  precipitates  with  soluble 
salts  of  most  metals,  almost  all  of  which  are  insoluble  in  acetic  acid. 

We  have  thus  a  series  of  oxides  and  acids  of  nitrogen,  vanadium, 
niobium,  and  tantalum  :  — 


,  nitrous  oxide  or  hyponitrous  anhydride.    HNO  acid. 
NO,  nitric  oxide. 

N2O3,  nitrogen  trioxide  or  nitrous  anhydride.      HNO2  acid. 
N204,  NOZ,  nitrogen  tetroxide  and  peroxide. 
N2O5,  nitrogen  pentoxide  or  nitric  anhydride.      HNO3  acid. 

H2N4On  acid. 
N2O6,f  nitrogen  hexoxide. 

*  Divers,  Proc.  Hoy.  Soc.,  19,  425;  33,  401;   Chem.  Soc.,  45,  78;  47,  361. 
f  The  hexoxide  has  been  formed  by  passing  sparks  through  a  mixture  of 


OF  NITROGEN,  VANADIUM,  NIOBIUM,   AND  TANTALUM.       345 

Similarly : — 

V202  — 

V203  HV02(?) 

V204         Nb204         Ta204         H2V4O9(?) 

rH3V04  -I 
V,05         Nb205         Ta^jOs      <  H4V2O7  I 

IHVO,  J 


Physical  Properties. 

Mass  of  1  cubic  centimetre. 

Nitrogen.         Vanadium.        Niobium.  Tantalum. 

Monoxides    .....      See  below. 

Dioxides  .......  3'64  at  20° 

Trioxides  .......  472  at  16° 

Tetroxides  ......      T49  at  0° 

Pentoxides  .....  3'5  at  20°         4'37—  4'53        7'35—  8'01 

Mass  of  1  c.c.  N2O. 

Temp.  -20-6°    -11'6°    -5*5°    -2'2°    +  6'6°    +  117°    +  19'8°    +  237°. 
Mass.       1-002      0-952      0'930    0'912    0*849      0*810      0758       0'698 
NS,  2-22  at  15°  ;  VS2,  47  at  21°  ;  ¥385,  3'0. 

HN03,  1-552,  at  15°.    2N2O6.H2O,  1'642  at  18°.     VOC12,  2'88  at  13°  ; 

VOC13,  1-865  at  0°. 

Heats  of  Combination. 

2^  +  O  =  N30  -  180K.     2^  +  3O  +  Aq  =  N2O3.Aq  -  68K. 

N  +  O  =  NO    -  215K.     N  +  20  =  NO2  -  77K. 
2NO2  =  NiOt  +  129K.     2N  +  4O  =  -^2O4  -  26K. 
2N  +  5O  =  N205  +  131K  ;   +  Aq  =  2HNO3.Aq  +  167K. 
N204  -  N2O4  -  31K.     N205  =  N2OS  -  83K. 


Specific  heat 

of  gaseous  N2O4  or  NO2.* 

Temp  

f  26-5° 
\  66-7° 

f   27-7° 
1  103-1° 

f   28-9° 
1150-6° 

/   29-0° 
1  198-5° 

f   29-2° 
1253-1° 

f  27-6° 
1289-5° 

Spec.  |heat 

0-747 

0-663 

0-513 

0-395 

0-319 

0-298. 

oxygen  and  nitrogen,  cooled  to  —23°.  From  volumetric  measurements  the 
compound  produced  —  a  volatile  crystalline  powder  —  is  declared  to  have  the 
formula  NO3  (Comptes.  rend  ,  94,  1306). 

.  *  This  great  change  is  due  to  absorption  of  heat  in  the  conversion  of  N2O4 
into  NO2  (Compt.  rend.,  64,  237). 


346 


CHAPTEE  XXIII. 

OXIDES,  SULPHIDES,  SELENIDES,  AND  TELLURIDES  OF  ELEMENTS  OF  THE 
PHOSPHORUS  GROUP.— CONSTITUTION  OF  PHOSPHORIC  ACID,  ETC. — THE 
PHOSPHATES,  ARSENATES,  ANTIMONATES,  SULPHOPHOSPHATES,  SULPH- 
ARSENATES,  AND  SULPHANTIMONATES  ;  PTROPHOSPHATES,  METAPHOS- 
PHATES,  AND  ANALOGOUS  COMPOUNDS. 


Oxides,  Sulphides,  Selenides,  and  Tellurides  of 
Phosphorus,  Arsenic,  Antimony,  and  Bismuth. 

List  of  Oxides,  Sulphides,  Selenides,  and  Tellurides. 


Bi202. 

P406.       As406.       Sb406.       Bi406. 
P2O4.  Sb2O4.       Bi2O4. 

P205.       As205.       Sb205.       Bi205. 


P4S3.         — 

—  As2S2.         —  Bi2S2. 

—  As2S3.       Sb2S3.       Bi2S3. 
P2S4.         - 

P2S5.  As2S5.       Sb2S5.          — 


Selenides  and  tellurides.  —  P2Se5  ;  'AsSeS2  ; 
SbTe;  Sb2Te3  ;  Bi2Se3  ;  Bi3Te;  Bi3Te2;  Bi2Te3. 


As2Te3  ;   Sb2Se3  ; 


Sources.  —  Pentoxide  of  phosphorus  occurs  in  combination 
with  oxides  of  metals,  especially  calcium  and  aluminium,  as  apatite, 
phosphorite,  wavellite,  &c.  Arsenious  oxide,  As406,  is  found  as 
arsenite,  or  arsenic  bloom  ;  and  Sb4O6  as  antimony  bloom  in  trimetric 
prisms,  and  as  senarmontite  in  regular  octahedra.  The  oxide,  Sb2O4, 
is  named  antimony  ochre. 

The  sulphides  As2S2  (realgar)  AB»S»(orptm«ti),  Sb2S3  (stibnite), 
and  BLSs  (bismuthine)  also  occur  native  ;  as  well  as  in  combination 
with  many  other  sulphides. 

Preparation.—  1.  By  direct  union.  —  When  phosphorus  is 
burned  in  excess  of  air  or  oxygen,  the  pentoxide  is  formed. 
Arsenic  and  bismuth  burn  to  trioxides  ;  and  antimony  to  trioxide 
and  tetroxide.  In  a  limited  supply  of  air,  and  at  moderately  high 
temperature,  phosphorus  gives  P4O,  P2O4,  and  P2O5  ;  by  careful 
regulation  of  air  a  considerable  amount  of  P4O6  is  produced,  even 
as  much  as  50  per  cent.,  the  other  oxide  being  mainly  P2O5. 

The  process  of  preparing  phosphorus  pentoxide  is  to  drop  pieces  of  dry 
phosphorus  through  a  tube  passing  through  a  cork  closing  the  neck  of  a  glass 


OXIDES  OF  PHOSPHORUS  AND  ARSENIC.        347 

balloon,  while  a  current  of  air,  dried  by  passing  through  a   U-tube  filled  with 
pumice-stone   moistened   with  sulphuric   acid,  is  blown  in.       The  fumes   are 


.  40. 


condensed  partly  in  the  balloon,  partly  in  the  bottle  communicating  with  it  by 
a  wide-mouthed  tube. 

By  the  glowing  of  phosphorus  in  dry  air  the  pentoxide  is  the  only  product. 

Arsenious  oxide,  As4O6,  is  usually  produced  by  condensing 
in  brick  chambers  the  fumes  resulting  from  the  roasting  in  muffles 
of  arsenical  ores  of  tin,  cobalt,  and  nickel,  or  arsenical  pyrites.  To 
purify  it,  the  condensed  product  is  sublimed  in  cast-iron  pots. 

By  limiting  the  supply  of  air,  antimony  burns  to  Sb4O6,  but 
with  free  access  of  air,  to  Sb2O4. 

The  sulphides,  selenides,  and  tellurides  of  all  these  elements  are 
produced  by  direct  union. 

2.  By  decomposition  of  other  oxides.  —  Phosphorus  tetr- 
oxide,  P>O4,*  is  produced  by  distilling  in  a  vacuum  the  product  of 
the  combustion  of  phosphorus  in  a  slow  current  of  air.  Bright 
orthorhombic  crystals  sublime,  of  the  formula  P2O4,  arising  from 
the  decomposition  of  the  phosphorous  oxide,  thus  :  — 

7P4O6  =  10P2O4  +  2P4O. 

Arsenic  pentoxide  loses  oxygen,  forming  trioxide  at  a  dull  red 
heat  ;  antimony  pentoxide  yields  tetroxide  at  temperatures  above 
275°  ;  and  bismuth  pentoxide,  heated  to  250°,  is  converted  into 

*  Chem.  Soc.,  49,  833. 


348      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND  TELLURIDES. 

tetroxide,  and  over  305°  into  trioxide.     No  known  rise  of  tempera- 
ture, however  great,  deprives  phosphorus  pentoxide  of  oxygen. 

3.  By  oxidation  in  the  wet  way. — This  method  in  reality 
yields  hydrates  or  acids.     The  usual  oxidising  agents  are  a  mix- 
ture of  nitric  and  hydrochloric  acids  (aqua  regia,  see  p.  341),  or 
caustic  potash  and  chlorine  or  bromine.    Water  cannot  be  expelled 
by  heat  from  phosphoric  acid,  P2O5.HoO  =  HPO3 ;    but  arsenic 
acid,  As2O5.H2O,  is  dehydrated  at  a  dull  red  heat,  antimonic  acid, 
Sb2O5.H2O,  by  heating  not  above  275°,    and   hydrated   bismuth 
pentoxide  at  120°. 

4.  By  decomposition   of   compounds. — The  hydrates,   as 
remarked  above,  lose  water;    and  the  nitrates  and  sulphates  of 
antimony  and  bismuth  decompose,  when  strongly  heated,  leaving 
trioxides.     Phosphoryl  chloride,  POC13,  when  heated  with  metallic 
zinc,  yields  zinc  chloride  and  tetraphosphorns  oxide,  P4O  ;  and  the 
same  body  is  formed  by  heating  phosphoryl  chloride  with  phos- 
phorus, thus  : — 

POC13  +  P4  =  PC13  +  P40. 

5.  By  double  decomposition. — As  a  rule,  this  process  yields 
the  hydroxides  or  acids,  for  example  :   PC13  +  3H20  =  H3P03  + 
3HC1 ;  POC13  +  3H20  =  H3P04  +  3HC1 ;  2SbOCl  +  2KOH.Aq 
=   Sb2O3.Aq    +    2KCl.Aq    +    H20 ;     2BiCl3    +    GKOH.Aq    = 
Bi2O3.H2O  +  6KClAq  -f  2H20 ;  and,   with  the  exception  of  the 
compounds  of  phosphorus,   these  yield  oxides  when  heated.     It 
forms,  however,   the  usual   method   of  preparing   the    sulphides, 
excepting  those  of  phosphorus:  e.g.,  2AsCl3.Aq  +  3H%S  =  As2S3 
+  6HCl.Aq ;  2SbC13.Aq  +  3H2S  =  Sb2S3  +  GHCl.Aq,  Ac. 

Properties. — P4O  is  a  light  red  or  orange  powder  resembling 
red  phosphorus,  for  which  it  was  formerly  taken  ;  when  prepared 
by  oxidation  of  phosphorus,  it  possesses  reducing  properties  ;  but 
when  by  depriving  POC13  of  chlorine,  it  does  not  reduce  salts  of 
mercury,  silver,  or  gold. 

Phosphorous  oxide  or  anhydride,  P406,  forms  feathery 
crystals,  melting  at  22'5°,  and  boiling  at  173'3°.  It  is  decomposed 
by  heat  thus  : — 

2P406  =  3P304  +  P2. 

It  is  slowly  attacked  by  cold  water,  with  formation  of  phosphorous 
acid,  H3P03,  and  immediately  and  with  violence  by  hot  water.  It 
is  luminous  in  the  dark  in  presence  of  oxygen  at  a  less  pressure 
than  that  of  the  air ;  and  when  heated  gently  in  air,  it  burns  to 
P2O5.  It  also  burns  in  chlorine,  forming  POC13  and  P02C1. 

The  tetroxide  forms  orthorhombic  crystals.      It  is  soluble  in 


OXIDES  OF  ARSENIC  AND   ANTIMONY.  349 

water,  giving  a  mixture  of  phosphorous  and  phosphoric  acids, 
thus  :— P2O4  +  3H2O  =.  H3P04  +  H3P03.  Ifc  is,  therefore,  sup- 
posed to  have  the  formula  P204  or  PO(P03)  ;  it  would  then  be 
named  phosphorjl  metaphosphate.  But  of  this  there  is  no  other 
proof. 

The  pentoxide  or  phosphoric  anhydride  is  a  snow-white 
powder,  volatile  below  redness.  It  has  a  great  tendency  to  com- 
bine with  water,  and  is,  therefore,  used  as  a  dehydrating  agent, 
e.g.,  in  the  preparation  of  nitrogen  pentoxide  and  sulphur  tri- 
oxide.  When  heated  with  carbon,  it  yields  carbon  monoxide  and 
phosphorus. 

Arsenious  oxide  or  anhydride,  sometimes  called  arsenic 
trioxide,  exists  in  three  forms.  When  condensed  at  high  tem- 
peratures, it  is  an  amorphous  porcelain-like  mass ;  its  specific 
gravity  is  then  3"  74.  When  cooled  quickly,  or  when  it  crystallises 
trom  solution,  it  forms  colourless  regular  octahedra,  the  specific 
gravity  of  which  is  nearly  the  same,  viz.,  3' 70.  But  when  crys- 
tallised at  low  temperatures,  or  when  it  separates  from  its  saturated 
solution  in  caustic  potash,  it  forms  rhombic  crystals  of  the  specific 
gravity  4'25. 

Arsenious  oxide  is  sparingly  soluble  in  water  (vitreous,  4  in 
100  ;  crystalline,  1'2  or  1'3  parts  in  100  of  water).  It  does  not 
combine  with  water,  but  crystallises  out  from  its  solution  in  the 
anhydrous  state.  It  is  sparingly  soluble  in  alcohol.  Its  vapour- 
density  at  a  white  heat  corresponds  to  the  formula  As406.*  It 
sublimes  without  fusion,  but  when  heated  under  pressure  it  can  be 
fused. 

It  is  both  an  oxidising  and  a  reducing  agent,  tending  with 
certain  oxides — nitric  acid,  chromic  acid,  &c.,  to  remove  their 
oxygen,  while  it  is  itself  reduced  by  carbon,  phosphorus,  sodium,  <fcc. 
It  is  exceedingly  poisonous  ;  less  than  0'4  gram  has  been  known  to 
cause  death  ;  but  by  continually  increasing  doses,  the  system  may 
become  inured  to  as  much  as  0'2  gram  at  a  time.  The  antidote  is 
a  mixture  of  hydrated  ferric  oxide  and  magnesium  chloride,  pro- 
duced by  adding  magnesium  oxide  or  carbonate  in  excess  to  tri- 
chloride of  iron ;  such  a  mixture  forms  an  insoluble  arsenite  of 
iron,  while  the  magnesium  chloride  and  oxide  act  as  a  purgative. 

Arsenic  pentoxide  is  a  white  mass,  dissolving  in  water  to 
produce  arsenic  acid.  It  is  poisonous,  but  is  not  so  deadly  as  the 
trioxide. 

AntimonioTis  oxide  is  found   native  in  trimetric  prisms  as 
antimony -bloom,  and  in  regular  octahedra  as  senarmontile.      It  is  a 
*  EericMe,  12,  1112. 


350      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

white  powder,  turning  yellow  when  heated,  but  white  again  on 
cooling.  It  melts  at  a  red  heat,  and  volatilises  at  1550°.  Its 
vapour-density  points  to  the  formula  Sb406,  like  arsenious  oxide.* 
It  is  insoluble  in,  and  does  not  combine  with  water.  One  of  the 
best  solvents  is  a  solution  of  tartrate  of  hydrogen  and  potassium 
(cream  of  tartar) .  HKCJI^Oe-Aq  ;  it  forms  the  potassium  salt  of 
the  acid  Sb(OH)C4H406,  a  substituted  antimonious  acid. 

Antimony  tetroxide,  Sb2O4,  also  occurs  native  as  antimony 
ochre.  It  is  a  white  powder  when  cold,  and  yellow  when  hot.  It 
has  not  been  melted  or  volatilised.  It  is  possibly  metantimonate 
of  antimonyl,  SbO(SbO3). 

The  pentoxide,  Sb2O5,  is  an  insoluble  lemon-coloured  powder. 

Bismuth  dioxide,  Bi2O2,  is  a  black  crystalline  powder,  ob- 
tained by  the  reduction  with  tin  dichloride  of  the  trioxide  sus- 
pended in  alkali  ;  it  must  be  dried  out  of  contact  with  air.  On 
treatment  with  acid,  it  gives  a  salt  of  the  oxide  Bi2O3,  and  a  pre- 
cipitate of  metallic  bismuth.  It  oxidises  at  180°. 

The  trioxide,  Bi2O3,  is  a  yellow- white  solid,  which  crystallises 
from  fused  potassium  hydroxide.  No  compound  with  an  oxide  is 
known,  but  it  is  not  impossible  that  such  a  hot  solution  contains 
an  easily  decomposible  bismuthite. 

The  tetroxide,  Bi2O4,  is  a  brown-yellow  solid,  produced  by 
treating  the  trioxide  suspended  in  a  cold  solution  of  potash  with 
chlorine:;  and  the  pentoxide,  Bi2O5,  is  a  red  powder,  similarly 
prepared,  the  solution  of  potash  being  kept  boiling  during  passage 
of  chlorine.  The  pentoxide  combines  with  water,  forming  the 
hydrate  Bi,O5.H2O. 

As  hydrogen  sulphide  has  no  action  on  a  solution  of  a  phos- 
phate, the  sulphides  of  phosphorus  are  prepared  by  direct 
union.  There  appear  to  be  only  three  definite  compounds. f  Phos- 
phorus and  sulphur  may  be  melted  together,  but  combination  takes 
place  only  above  130C'.  Owing  to  the  great  violence  of  the  action 
and  the  inflammability  of  phosphorus  in  presence  of  air,  a  large 
quantity  of  sand  is  added  to  the  melted  mixture,  and  the  retort  is 
filled  with  carbon  dioxide.  If  phosphorus  is  in  excess,  the  com- 
pound produced  is  P4S3.  This  substance  is  reddish-yellow,  melts 
at  ]  67°,  and  boils  constantly  about  380°.  If  sulphur  is  in  excess, 
the  pentasulphide,  P2S5,  is  formed,  melting  at  210°  and  boiling  at 
519°.  Phosphorus  and  sulphur  both  dissolve  in  these  compounds, 
but  apparently  without  altering  them.  On  heating  a  solution  of 
the  body  P4S3  in  carbon  disulphide,  however,  with  sulphur,  yellow 

*  Berichte,  12,  1282. 

f  Bull.  Soc.  Chim.,  41,  433 ;   Comptes  rend.,  102,1386. 


SULPHIDES   OF  ARSENIC   AND  ANTIMONY.  351 

crystals  of  the  compound  P2S4  are  deposited  ;  and  intermediate 
indistinct  crystals  are  said  to  have  been  obtained  of  the  formula 
P8SU  =  P4S,.2P2S4. 

The  selenides  of  phosphorus  are  somewhat  doubtful  in  com- 
position. The  bodies  P4Se,  P2Se,  P2Se3,  and  P2Se5,  are  said  to 
have  been  prepared,  but,  except  perhaps  the  last,  they  are  probably 
mixtures  of  compounds  analogous  to  the  sulphides.  Phosphorus 
and  tellurium  apparently  mix  in  all  proportions  ;  no  definite  com- 
pounds have  been  isolated. 

Arsenic  disulphide,  As^,  is  found  native  as  realgar,  in  mono- 
clinic  prisms.  It  is  a  reddish-orange  body,  and  may  be  produced 
by  heating  arsenic  and  sulphur  together  in  the  right  proportions. 
The  trisulphide,  A  8283,  similarly  produced,  occurs  native  in 
trimetric  prisms  as  orpiment  ;  it  forms  translucent  lemon-yellow 
crystals.  Prepared  by  double  decomposition,  it  is  a  yellow  powder, 
which  is  easily  melted  and  volatilised.  When  hydrogen  sulphide 
is  passed  into  an  aqueous  solution  of  the  trioxide  no  precipitate  is 
produced,  but  the  solution  turns  yellow.  The  substance  in  solution 
is  probably  a  hydrate  and  hydrosulphide  ;  on  addition  of  hydro- 
chloric acid,  the  trisulphide,  As,S3,  or  more  probably  its  compound 
with  hydrogen  sulphide,  is  thrown  down.  It  is  soluble  in  solu- 
tions of  hydroxide  or  hydrosulphide  of  sodium  or  potassium, 
forming  oxysulpharsenites  and  sulpharsenites  (see  below).  The 
pentasulphide  is  an  easily  fusible  yellow  powder  ;  it  is  formed  by 
direct  union  ;  by  addition  of  an  acid  to  a  sulpharsenate  ;  and  by 
the  action  of  a  rapid  current  of  hydrogen  sulphide  on  a  solution 
of  arsenic  acid.  It  is  easily  soluble  in  solutions  of  sulphides  of 
the  alkalies,  forming  sulpharsenates  (see  below).  The  action  of 
a  slow  current  of  hydrogen  sulphide  on  a  solution  of  arsenic  pent- 
oxide  is  first  to  reduce  it,  thus  :  — 


As205.Aq  +  2H2S  =  As203.Aq  +  .2H20  +  2S  ; 

and  then  to  precipitate  the  trisulphide.* 

Selenides  of  arsenic  have  not  been  prepared  ;  but  two  double 
sulphoselenides  have  been  obtained  by  direct  union,  viz.,  As.2SeSo, 
and  As.,SSe2.  They  are  red  bodies  ;  the  latter  may  be  distilled 
unchanged.  The  tellurides,  also  directly  prepared,  have  the 
formulae  As.2Te2  and  A&,Te3. 

Antimony  trisulphide,  Sb2S3,  occurs  native  in  trimetric  grey 

metallic-looking  or  in  orange-coloured  prisms,  as  stibnite.    It  can  be 

prepared  by  direct  union,  or  by  the  action  of  hydrogen  sulphide  on 

a  soluble  salt  of  antimony.     The  former  method  yields  crystals  ; 

*  Bunsen,  Annalen,  192,  305  ;  Brauner,  Chem.  Soc.,  53,  145. 


352      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

the  latter,  an  orange-red  powder,  which,  until  dried,  appears  to  be 
a  hydrosulphide  ;  it  dries  to  a  brown  powder.  It  turns  grey  at 
200—220°,  and  melts  easily.  The  selenide,  Sb2Se3,  is  a  greyish, 
metallic-looking  solid,  produced  by  direct  union ;  the  telluride, 
SbTe,  is  iron-grey;  and  Sb2Te3,  silver- white.  The  penta- 
sulphide  is  not  produced  by  direct  union,  but  by  decomposition  of 
a  sulphantimoiiate  (see  below)  by  an  acid.  It  is  a  dark  orange- 
coloured  powder.  The  pentaselenide  is  a  brown  precipitate, 
similarly  prepared. 

Bismuth  trisulphide,  Bi2S3,  is  found  in  nature  as  bismuth- 
glance,  or  bismuthine,  in  rhombic  crystals,  with  steel -grey  metallic 
lustre.  A  body  of  similar  appearance  is  prepared  by  direct  union, 
which  becomes  crystalline  when  heated  with  an  alkaline  sulphide. 
The  brown-black  precipitate,  obtained  by  passing  hydrogen  sulphide 
through  an  acid  solution  of  bismuth  nitrate  or  chloride,  is  a  com- 
pound of  bismuth  sulphide  with  water  and  hydrogen  sulphide. 
The  action  of  hydrogen  sulphide  on  an  alkaline  solution  of  bismuth 
trioxide  is  said  to  yield  the  disulphide,  Bi2S2,  in  combination  with 
water.  The  triselenide  is  a  black  lustrous  powder,  similarly  pre- 
pared; and  the  telluride  is  indefinite.  The  mineral  telluric  bismuth, 
Bi2S3.2Bi2Te3,  occurs  native. 


Compounds  with  Water  and  Oxides ;  with  Hydro- 
gen Sulphide  and  Sulphides ;  with  Selenides ; 
and  with  Tellurides. 

The  constitution  of  the  acids  derived  from  the  pent- 
oxides/  pentasulphides,  &c.,  of  phosphorus,  arsenic,  and 
antimony. — Phosphorus,  it  will  be  remembered,  forms  two 
chlorides,  PC13  and  PC15  (see  p.  160).  When  the  pentachloride  is 
treated  with  a  small  quantity  of  water,  an  oxychloride,  of  the 
formula  POC13  is  produced  (see  below).  The  equation  is  : — 

PC16  +  H20  =  POC13  +  2HCI. 

It  is  probable  that  this  oxychloride,  which  corresponds  to  those  of 
vanadium,  VOC13,  and  niobium,  NbOCl3,  and  to  tantalum  oxy- 
fluoride,  TaOF3,  is  in  reality  the  decomposition  product  of  a 
dihydroxy  trichloride,  P(OH)2C13,  the  reaction  taking  place  thus : — 

PC15  +  2H20  =  P(OH)2C13  +  2HC1; 
but  that  body  beiug  unstable  forms  an  anhydride,  thus  : — 
P(OH)2C13  =  H20  +  POC13. 


CONSTITUTION   OF  THE  PHOSPHORIC  ACIDS.  353 

The  action  of  water  on  phosphoryl  chloride,   POC13,   is  to  yield 
orthophosphoric  acid,  PO.(OH)3,  thus:  — 

POC13  +  3H20  =  PO(OH)3  +  3HCI. 
We  have  thns  the  series  :  — 

01       /Cl       HOX      /Cl  .01  /OH 

>P^C1  ;  >P^-C1  ;       O=P^Cl  ;    and    0=Pf  OH. 

OK     XC1       KG/    XC1  XC1  \)H 


The  density  of  the  vapour  of  phosphoryl  chloride,  POC13,  shows 
it  to  have  the  molecular  weight  corresponding  to  that  formula  ; 
and  the  fact  that  the  hydrogen  in  orthophosphoric  acid  is  replace- 
able in  three  stages  by  snch  a  metal  as  potassium  is  a  strong 
argument  in  favour  of  the  analogy  between  phosphoryl  chloride 
and  phosphoryl  hydroxide,  or  phosphoric  acid  ;  such  phosphates 
are  :  — 

PO(OH)2OK;  PO(OH)(OK)2,  and  PO(OK)3. 

It  would  thus  appear  that  phosphoric  hydroxide,  or  the  true 
orthophosphoric  acid,  should  possess  the  formula  P(OH)5;  but 
of  this  body,  the  first  anhydride,  PO(OH)3,  is  the  one  to  which  the 
name  orthophosphoric  acid  is  applied. 

By  heating  the  first  anhydride,  PO(OH)3,  the  elements  of  water 
are  expelled,  and  the  second  anhydride,  metaphosphoric  acid, 
PO2(OH),  is  produced,  thus  :— 

PO(OH)3  =  H20.+  PO2(OH). 

This  substance  is  usually  a  monobasic  acid,  that  is,  its  hydrogen  is 
replaceable  in  one  stage;  hence  its  formula  (see,  however,  p.  369). 
The  analogous  compound  P02C1  has  also  been  prepared. 

But  intermediate  between  PO(OH)3  and  PO2(OH),  there 
exists  an  acid  of  the  formula  HjP2O7,  named  pyrophosphoric  acid. 
And  corresponding  to  this  hydroxide,  P2O3(OH)4,  a  chloride, 
PaOsCU,  exists,  which,  however,  has  not  been  gasified,  inasmuch  as 
it  decomposes.  But  arguing  from  the  relation  of  the  chloride 
POC13  to  the  acid  PO(OH)3,  the  analogy  of  pyrophosphoric  acid 
to  pyrophosphoryl  chloride  appears  justified,  for  its  hydrogen  is 
replaceable  in  fourths.  And  just  as  in  the  case  of  the  silicic  acids, 
acids  are  derived  from  two  molecules  of  the  ortho-acid  with  loss  of 


0=p  . 

/     ^ 

water,  so  here.      We  have    therefore  the  series   0\         ^^    and 


0=P=0 

o/ 


QJJ»  the   second   member  of  which  has  the  same  compo- 
°=P<OH 

2  A 


354      THE   OXIDES,   SULPHIDES,    SELENIDES,   AND   TELLURTDES. 

sition  as  metaphosphoric  acid,  but  is  a  poljmeride.  Salts  of  this 
acid  are  called  dimetaphosphates ;  the  acid  is  dibasic.  Salts  of  the 
unknown  acid,  H6P4013,  are  also  known.  Such  an  acid  would  be 
the  fourth  anhydride  of  tetraphosphoric  acid,  Hi4P4O17,  also  un- 
known. And  salts  of  the  hypothetical  acid,  H]2Pio03l,  are  also 
known,  which  would  be  similarly  derived.  There  are  also  tri-, 
tetra-,  and  hexa-metaphosphates,  apparently  corresponding  to 
condensed  acids. 

Such  compounds  can  be  also  represented  as  formed  by  union 
of  phosphoric  anhydride  with  oxides.  We  have,  for  example,  the 
series : — 

P2O5.M2O     =  2PO2(OM),  monometaphosphates. 
P2O6.2M2O   =   P2O3(OM)4,  pyrophosphates. 
P2O5.3M2O   =   2PO(OM)3,  orthophosphates. 

2P2O5.2M2O    =   2P204(OM)2,  dimetaphosphates. 

2P2O5.3M2O   =   P4O7(OM)6,  a-phosphates. 

3P2O5.3M2O   =  2P3O6(OM)3,  trimetaphosphates. 

4P2O5.4M2O    =  2P4O8(OM)4,  tetrametaphosphates. 

5P2O5.6M2O    =   P10O19(OM)12,  j8-phosphates. 

6P2O5.6M2O   =   P6Oj2(OM)6,  hexametaphosphates. 

Such  compounds  are,  as  a  rule,  soluble  in  water  without  decom- 
position. The  sodium  salts  like  ex.-  and  (3-,  however,  named  "  Fleit- 
inann  and  Henneberg's  phosphates,"  are  decomposed  by  much  hot 
water  into  mixtures  of  other  salts.  But  the  corresponding  pyro- 
and  meta-arsenates  are  converted  into  ortho- arse  nates  on  treat- 
ment with  water,  unless  they  happen  to  be  insoluble.  For  example, 
the  ortho-arsenate,  Na^HAsOi,  is  a  well-known  body ;  on  ignition, 
ifc  loses  water  and  yields  Na4As2O7,  corresponding  to  the  pyro- 
phosphate,  Na4P2O7 ;  but  on  treatment  with  water,  while  sodium 
pyrophosphate  dissolves  as  such,  sodium  pyro-arsenate  reacts  with 
the  water,  thus : — Na4As2O7  +  H20  =  SNaaHAsC^.  No  ortho- 
antimonates  are  known  except  that  of  hydrogen,  SbO(OH)3; 
some  pyroantimonates  and  many  metantimonates  have  been  pre- 
pared, and  these  have  the  formulae  M4Sb2O7  and  MSbO3.*  The 
Hydrate  of  bismuth,  Bi2O5.H2O,  is  analogous  to  a  meta-acid ;  it 
appears  to  be  incapable  of  combination  with  other  oxides. 

Compounds  analogous  to  the  orthophosphates  have  been  pre- 
pared, in  which  the  oxygen  of  the  phosphate  is  partially  replaced 
by  sulphur,  such  as  K3PSO3,  Na,PS2O2,  and  possibly  Na3PS:iO. 
These  bodies  are  termed  thiophosphates  or  sulphophosphates. 
With  selenium,  compounds  analogous  to  the  pyrophosphates  have 

*  Ifc  is  unreasonable  to  name  compounds  of  the  general  formula  M4Sb2O7 
"  metantimonates,"  as  is  usually  done.  These  bodies  have  here  been  named 
systematically  "  pyroantimonates." 


ORTHOPHOSPHORIC   ACID.  355 

been  prepared,  e.g.,  K4P2Se7.  Orthothioarsenic  acid,  AsS(SH)3,  is 
said  to  have  been  prepared ;  and  ortho-,  pyro-,  and  meta-thioarsenates 
are  known.  Similarly,  orthothioantimo nates  are  known:  bat  no 
pyro-  or  meta-derivatives  have  been  prepared,  nor  are  there  any 
thiobismuthates. 

Double  compounds  of  the  pentoxides,  &c.;  phosphates 
and  similar  compounds. — Ortho-acids. 

Orthophosphoric  acid  is  formed  by  the  oxidation  of  phos- 
phorus with  boiling  nitric  acid,  best  in  presence  of  a  little  iodine; 
by  treating  an  orthophosphate  with  some  acid  which  forms  an  in- 
soluble compound  with  the  metal ;  and  by  the  action  of  a  penta- 
halide  or  an  oxytrihalide  on  water.  If  the  first  method  be  employed, 
the  first  product  is  phosphorous  acid.  The  nitric  acid  should  have 
the  specific  gravity  1'2,  and  should  be  employed  in  considerable 
excess  ;  and  at  the  last,  stronger  acid  may  be  employed  to  oxidise 
the  phosphorous  to  phosphoric  acid.  The  second  method  is  the  one 
employed  on  a  large  scale ;  calcium  orthophosphate,  Ca^PO^,  is 
mixed  with  sulphuric  acid,  and  the  precipitated  calcium  sulphate 
removed  by  subsidence.  The  equation  is  : — 

Ca3(P04)2  +  3H3S04.Aq  =  3CaSO4  +  2H3P04.Aq. 

It  is  common  to  use  calcined  bones  or  apatite  (see  p.  358)  as 
the  source  of  calcium  phosphate.  The  third  method  is  the  most 
convenient  for  preparing  phosphoric  acid  in  the  laboratory,  and  it 
may  be  coupled  with  the  preparation  of  hydriodic  acid.  Red 
phosphorus  and  iodine  in  the  proportions  equivalent  to  the  formula 
PI5  are  placed  in  a  retort ;  excess  of  water  is  added,  and  the  mix- 
ture is  distilled.  Water  distils  over  first,  and  then  an  aqueous 
solution  of  hydrogen  iodide,  while  phosphoric  acid  remains  in  the 
retort.  It  is  advisable  then  to  evaporate  the  viscid  residue  with 
nitric  acid. 

Orthophosphoric  acid  is  also  produced  by  dissolving  phosphorus 
pentoxide  in  cold  water,  and  boiling  the  solution  of  the  resulting 
metaphosphoric  acid ;  and  also  by  oxidation  with  nitric  acid  of 
hypophosphorous.  phosphorous,  and  hypophosphoric  acids. 

By  spontaneous  evaporation  of  its  aqueous  solution,  it  crystal- 
lises in  long  colourless  prisms,  melting  at  41 '75°,  and  has  the 
formula  H3PO4.  From  the  mother  liquor  of  these  crystals  fresh 
crystals  deposit  on  cooling,  of  the  formula  2H3PO4.H2O  ;  these 
melt  at  about  27°.  Commercial  phosphoric  acid  is  a  mixture  of 
these  two  compounds. 

The  solution  of  phosphoric  acid  is  very  sour;  the  acid  may  be 

2  A  2 


356      THE   OXIDES,  SULPHIDES,   SELENIDES,   AND   TELLtl RIDES. 

heated  to  160°  without  alteration,  but  at  212°  it  is  largely  con- 
verted into  pyrophosphoric  acid. 

By  similar  processes  orthoarsenic  acid  is  produced.  The  most 
convenient  plan  is  to  boil  elementary  arsenic,  or  arsenious  oxide,  with 
nitric  acid,  or  to  pass  chlorine  through  water  with  which  powdered 
arsenious  oxide  is  mixed.  The  solution  is  evaporated  to  dryness, 
and  heated  for  some  time  to  100°  ;  water  is  then  added,  and  on 
spontaneous  evaporation  the  hydrated  acid  2H3AsO4.H2O  deposits 
in  small  needle-shaped  crystals ;  and  on  heating  to  150°  ortho- 
arsenic  acid,  H3AsO4,  remains. 

Orthoantimonic  acid  has  been  produced  by  treating  potas- 
sium metantimonate,  KSbO3,  with  nitric  acid.  It  forms  an  in- 
soluble  white  precipitate.  The  usual  product  of  this  action, 
however,  is  metantimonic  acid,  HSbO3. 

The  only  corresponding  sulphur  compound  is  orthosulph- 
arsenic  acid,  H3AsS4,  which  is  precipitated  by  addition  of  hydro- 
chloric acid  to  a  solution  of  sodium  sulpharsenate,  Na3AsS4.Aq. 
Thiophosphates,  on  similar  treatment,  give  off  hydrogen  sulphide, 
and  yield  phosphates. 

List  of  Ortho-phosphates  and  Orthoarsenates. — The  follow- 
ing have  been  prepared  : — 

Simple  salts  : — 

2Li3P04.H20  ;  Na3P04.12H20  ;  K3PO4 ;   (NH4)3PO4. 
2Li3AsO4H2O;  Na3AsO4.12H2O  ;   K3AsO4  ;   (NH4)3AsO4.3H2O. 

Mixed  salts  :— 

H2LiPO4;   H2NaPO4.H2O  ;  H2KPO4 ;  H2(NH4)PO4. 
3H2L,iAs04.2H20  ;   H2NaAsO4.H2O,   and  2H2O  ; 

H2KAsO4  ;  H2(NH4)AsO4. 
HNa2PO4.12  and  7H2O  ;   H(NH4)2PO4. 
HNa2As04.12  and  7H2O  ;  HK2AsO4  ;  H(NH4),AsO4. 
(Li,Na)3PO4  ;   HNaKPO4  ;  HNa(NH,)PO4.4H2O  ; 

Na(NH4)2P04.4H20;  HNaKAsO4.7H2O. 
Na3P04.2NaF. 

These  bodies  are  all  white  salts.  They  are  prepared  by  the 
action  of  hydroxide  or  carbonate  of  lithium,  sodium,  or  potassium, 
ov  of  ammonia,  on  phosphoric  or  arsenic  acid.  The  simple 
salts  are  produced  only  by  the  action  of  hydroxide,  if  in  solution, 
for  carbonic  acid  decomposes  them,  giving  a  carbonate  and  a 
phosphate  or  arsenate  containing  an  atom  of  hydrogen.  But  the 
carbonates  ignited  with  the  theoretical  amount  of  phosphoric  acid 
yield  simple  phosphates.  The  phosphates  containing  one  and  two 
atoms  of  hydrogen,  however,  cannot  be  made  by  fusion. 

Hydrogen  di-lithium  phosphate  has   not  been  obtained  pure. 


PHOSPHATES,  ARSENATES,  AND   SULPHAKSENATES.          357 

On  adding  hydrogen  disodium  phosphate  to  a  concentrated  solution 
of  a  soluble  lithium  salt,  a  precipitate  is  produced  of  the  formula 
(Li>HPO4.LiH2PO4)H2O.  It  is  a  sparingly  soluble  salt  (1  in 
200  parts  of  water).  The  other  salts  are  easily  soluble. 

Hydrogen  disodium  phosphate,  HNa3POi.l2H2O,  is  the 
ordinary  commercial  "phosphate  of  soda;"  the  corresponding 
arsenate  is  also  a  commercial  product ;  they  crystallise  in  mono- 
clinic  prisms.  The  salt  HNa(NH4)PO4.4H2O  is  known  as  "  micro- 
cosmic  salt,"  because  it  occurs  in  urine ;  the  human  organism 
used  to  be  known  as  the  "  microcosm."  It  is  used  as  a  blowpipe 
reagent  (see  Metaphosphoric  Acid). 

The  following  thiophosphates  are  similar  in  composition : — * 

Na3P03S.12H20  ;  Na3PO2S2.llH2O  ;   (NH4)3PO2S2.2H2O. 

Salts  of  potassium  have  been  obtained  in  solution;  and  also 
sodium  tritbiophosphate,  NaaPOS3.  These  bodies  are  produced 
by  the  action  .of  sodium  hydroxide  on  powdered  phosphorus  penta- 
sulphide.  They  are  unstable,  especially  the  trithiophosphate, 
which  decomposes  when  the  solution  is  heated  to  50°  ;  a  tempera- 
ture of  90°  destroys  the  dithiophosphates,  and  they  are  precipitated 
by  addition  of  alcohol  to  their  aqueous  solutions.  They  resemble 
the  phosphates  in  appearance. 

Analogous  oxythioarsenates  have  been  made  by  dissolving 
arsenious   oxide   in   a   solution    of   sodium   sulphide.       They   are 
separated  by  fractional  crystallisation.     Their  formulas  are  : — • 
Na3AsO3S.12H2O  ;  Na,2H:AsO3S.8H:2O  ;  and  Na3AsO3S.2H2O. 

Analogous  to  these  are  the  thioarsenates,  2Na3AsS4.15H2O  ; 
K;3AsS4 ;  (NH4)3AsS4 ;  and  Na3(NH4)3(AsS4)2.  They  are  pro- 
duced along  with  pyro-  and  me fca- thioarsenates  by  digesting  arsenic 
pentasulphide,  As2S5,  with  alkaline  sulphides,  and  evaporating 
the  solution  until  crystals  separate  ;  or  by  dissolving  arsenic  tri- 
sulphide,  As2S3,  in  the  solution  of  a  polysulphide.  They  may  also 
be  produced  by  fusion.  If  arsenic  pentasulphide  be  dissolved  in 
solution  of  sodium  or  potassium  hydroxide,  a  mixture  of  aryenate 
and  thioarsenate  is  produced.  They  form  yellowish  crystals,  and 
are  very  soluble  in  water.  The  solution  of  arsenic  sulphide  in 
ammonium  polysulphide,  a  process  used  in  qualitative  analysis  in 
order  to  separate  sulphide  of  arsenic  from  sulphides  of  copper,  lead, 
bismuth,  mercury,  and  cadmium,  depends  on  the  formation  of 
these  bodies.  The  sulphides  of  antimony  and  of  tin  form  similar 
compounds,  and  may  be  separated  in  the  same  manner  from  sul- 
phides of  lead,  copper,  &c. 

*  J.  prakt.  CJiem.  (2),  31,  93. 


358      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND  TELLUKIDES. 

The  thioantimonates  may  be  classed  with  the  preceding  salts. 
The  following  are  known: — 

Na3SbS4.9H20  ;  2K3SbS4.9H2O. 

They  are  prepared  by  boiling  a  mixture  of  caustic  alkali,  sul- 
phur, and  antimony  trisulphide ;  they  form  yellowish  crystals. 
The  sodium  salt  has  been  long  known  as  "  Schlippe's  salt."  The 
compound  Na3SbSe4.9H2O  forms  orange-red  tetrahedra  ;  it  is  pro- 
duced by  fusing  together  sodium  carbonate,  antimony  triselenide, 
sulphur,  and  carbon.  Trisodium  trithioseleno-antimonate, 

Na3SbS3Se.9H3O, 

is  formed  by  boiling  the  tetrathioantimonate  with  selenium.     It 
forms  yellow  crystals. 

Simple  salts : — 

jBe3(P04)2.7H20;    Ca3(PO4)2  ;     Ba3(PO4>2.H2O. 

I  Ca3(As04)2;  Ba3(AsO4)2. 

Mixed  salts  :— 

f  HCaP04.4,  3,  and  2H2O  ;  HSrPO4 ; 
I  HCaAsO4  ;  HSrAsO4  • 

Ca3(P04)2.2CaHP04 ;    Ba3(PO4)2.2BaHPO4. 

r  Ca(H2P04)2  ;  Ba(H2P04)2  ; 
I  Ba(H2As04)2 ; 

fLiCaP04;  KCaP04;  NaSrPO4;  KSrPO4 ;  NaBaPO4 ; 
I  KBaPO4 ;  NaSrAsO4 ;  2NH4CaAsO4.H2O,  also  of  Ba  ; 

H2(NH4)2Ca(As04)2  ;   also  of  Ba. 

3Ca3(PO4)o.CaF2  (apatite}  ;  3Ca3(PO4)2.CaCl2  (apatite). 
7{Ca(H2PO4)2}CaCl2.14H2O ;  4{Ca(H2PO4)2}CaCl2.8H2O ; 
Ca(H2P04)2  CaCl2.H26. 

The  simple  salts  are  produced  by  addition  of  the  chloride  of 
the  metal  to  trisodium  phosphate  or  arsenate.  They  are  inso- 
luble white  powders.  The  salts  containing  an  atom  of  hydrogen 
are  also  insoluble,  and  are  similarly  precipitated  with  hydrogen 
disodium  phosphate  or  arsenate.  By  boiling  with  water  these  are 
decompcsed,  giving  the  insoluble  simple  phosphate,  while  the 
soluble  salt  containing  one  atom  of  hydrogen  goes  into  solution. 
The  simple  salt  may  also  be  precipitated  by  addition  of  excess  of 
ammonia,  or  of  caustic  soda  or  potash,  to  the  mono-  or  di-hydrogen 
salts.  These  compounds  are  soluble  in  acids,  the  soluble  di-hydric 
salts  being  formed  ;  but  are  reprecipitated  as  simple  salts  on  addi- 
tion of  alkaline  hydroxide. 

Calcium  phosphate  is  the  chief  mineral  constituent  of  bones  ; 
bone-ash,  or  calcined  bones,  contains  about  93  per  cent,  of 


PHOSPHATES  AND  ARSENATES.  359 

Ca3(P04)2.  It  is  also  widely  distributed  in  soil.  •  When  found 
native  in  combination  with  calcium  chloride  or  fluoride,  it  is 
known  as  phosphorite,  or  apatite  (see  above)  ;  the  chlorine  and 
fluorine  are  mutually  replaceable.  Coprolites  consist  of  the  remains 
of  the  excreta  of  extinct  animals,  and  are  found  in  the  Lias.  They 
contain  from  80  to  90  per  cent,  of  phosphates.  These  bodies  are 
largely  used  for  artificial  manure. 

To  render  the  tricalcium  phosphate  soluble,  so  that  its  phosphorus  may  bo 
easily  assimilated  by  plants,  it  is  treated  with  sulphuric  acid  in  sufficient  amount- 
to  convert  it  into  monocalciuin  phosphate,  thus: — Ca^PO^  +  2H2SO.j  = 
Ca(H2PO4)2  +  2CaSO4. 

The  mixture  of  monocalcium  phosphate  and  sulphate  is  applied  to  the  soil, 
usually  mixed  with  organic  matter  containing  nitrogen.  The  old  plan  of  allow- 
ing land  periodically  to  lie  fallow  had  the  effect  of  promoting  a  similar  decom- 
position by  aid  of  the  carbon  dioxide  of  the  air.  It  appears  that  one  part  of 
tricalcium  phosphate  dissolves  as  monocalcium  phosphate  in  from  12,000  to 
100,000  parts  of  water  saturated  with  carbon  dioxide.  At  the  same  time  the 
carbon  dioxide  decomposes  silicates,  rendering  their  potash  available  for  the  use 
of  plants  ;  and  nitrogen  in  the  form  of  ammonia  collects  on  the  soil,  being 
brought  down  by  rain.  In  the  modern  system  of  agriculture,  artificial  manure 
is  applied  to  the  soil,  containing  these  substances  in  a  soluble  form ;  the  phos- 
phorus as  monocalcium  phosphate,  the  potash  as  chloride  or  carbonate,  and  the 
nitrogen  as  salts  of  ammonia,  or  as  sodium  nitrate;  or  in  the  form  of  animal 
matter,  from  which  ammonia  is  formed  by  putrefaction,  such  as  manure,  guano, 
dried  blood,  &c. 

Calcium  arsenate,  CaHAsO4,  is  found  native  as  pharmacolite. 

The  double  phosphates  and  arsenates  are  produced  by  mixture. 
A  arsenato-chloride,  corresponding  to  apatite,  has  been  produced 
artificially. 

The  monothiophosphates  of  calcium,  strontium,  and  barium 
are  all  insoluble  white  precipitates ;  the  dithiophosphates  of 
strontium  and  barium,  and  the  trithiophosphate  of  barium,  are 
also  insoluble. 

Thioarsenates  of  beryllium  and  of  strontium  have  been  pre- 
pared, but  not  analysed;  these  of  calcium  and  barium  have  the 
formulae  Ca3(AsS±)2,  and  Ba3(AsS4)2 ;  they  are  insoluble  yellow 
precipitates,  produced  by  adding  alcohol  to  the  product  of  the 
action  of  hydrogen  sulphide  on  HBaAsO4.  The  resulting  thio- 
arsenate,  HBa(AsS4),  decomposes  thus: — 

3HBaAsS4.Aq  =  Ba3(AsS4)2  +  BaAsS3.Aq  +  H*S\ 

the  metathioarsenate  remains  dissolved.  The  corresponding  thio- 
antimonate,  Ba3(SbS4)2,  has  also  been  obtained  from  the  corre- 
sponding sodium  salt  by  precipitation. 


360      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

Simple  salts  :  — 

Mg3(P04)2;  Zn3(P04)2.5H40  ;    Cd3(PO4)2  ; 

Mg3(As04)2;  Zn3(As04)2.3H20;  Cd2(AsO4)2.3H2O  ; 
Mixed  salts:— 

HMg:PO4.7H2O  ;  HZnPO4.H2O  ;  Zn(H2PO4)2.2H2O. 

HMgAs04.7H20  ;  HZnAs04;  H2Cd5(AsO4)4  4H2O. 

NaMg-PO4;  KMg-PO4  ;  H2(NH4)2Mg-(PO4)2.3H2O  ; 
NH4MgP04.6H20  ;  NH4ZnPO4.2H2O. 

KMgrAsO4  ;  NaMgAsO4.6H2O. 

(wagnerite)  =  PO 


Similar  arsenates  have  been  prepared  artificial^. 

Trimagnesium  orthophosphate  is  a  constituent  of  the  ash  of 
seeds,  especially  of  wheat.  It  and  the  corresponding  arsenate  are  in- 
soluble in  water.  The  other  salts  are  produced  by  precipitation,  and 
are  sparingly  soluble.  The  most  important  are  ammonium  mag- 
nesium phosphate  and  arsenate.  The  former  is  a  constituent 
of  certain  urinary  calculi,  and  is  formed  by  the  putrefaction  of 
urine,  and  separates  in  crystals.  Both  of  these  salts  are  very 
sparingly  soluble  in  water  (about  1  in  13,000),  and  are  used  in  the 
estimation  of  magnesium,  and  of  phosphoric  and  arsenic  acids. 
They  are  produced  by  adding  a  solution  of  magnesium  chloride 
and  ammonium  chloride,  commonly  called  "  magnesia  mixture," 
along  with  ammonia,  to  a  soluble  phosphate  or  arsenate.  On  igni- 
tion they  leave  a  residue  of  pyrophosphate  or  pyroarsenate. 

Thioarsenates  of  magnesium,  zinc,  and  cadmium  have  also  been 
prepared  :  they  are  soluble  crystalline  salts, 

BPO4  ;  2YPO4.5H2O  (xenotime)  ;  LaPO4. 
YAs04 

Boron  phosphate  is  an  insoluble  white  substance  produced  by 
heating  boron  hydrate  with  orthophosphoric  acid.  Yttrium  phos- 
phate and  arsenate  and  lanthanum  phosphate  are  white  gelatinous 
precipitates  produced  by  double  decomposition.  Yttrium  phos- 
phate occurs  native,  and  that  of  lanthanum  occurs  in  several  rare 
minerals. 

A1P04.3  and  4H2O  ;  AlAsO4.2H2O. 

Phosphates  of  aluminium  and  hydrogen:  —  A1(H.;PO4)3  and 
A12H9(P04)5  H.,0. 

Basic  phosphates  of  aluminium  :—  6A1PO4  A12O3.18H2O  ; 
4A1PO4A12O3.12H2O  ;  P2O5.2A13O3.8,  6,  and  5H2O. 

Thallous  phosphates  :—  T13PO4  ;  HT1£PO4.H2O  ;  H2T1PO4. 

Aluminium  phosphate,  produced  by  precipitation,  is  a  white 
bulky  precipitate,  closely  resembling  hydrated  alumina,  from  which 
it  is  dim  cult  to  distinguish  and  to  separate.  The  arsenate  closely 


PHOSPHATES  AND  ARSENATES.  361 

resembles  the  phosphate.  The  compound  A1PO4.4H2O  occurs 
native  as  gibbsite ;  it  is  also  produced  on  boiling  a  solution  of 
hydrogen  aluminium  phosphate.  The  first  basic  phosphate  is  pro- 
duced by  adding  ammonia  to  a  solution  of  the  orthophosphate  in 
hydrochloric  acid  ;  the  second  is  wavellite.  The  third,  with  5H2O, 
is  turquoise,  which  owes  its  blue  colour  to  a  trace  of  copper  ;  with 
6H2O  it  is  peganite,  and  with  8H2O  it  forms  crystals  of  fisclierite. 

Thallic  arsenate  is  a  flocculent,  insoluble  precipitate;  the 
thallous  phosphates  are  nearly  insoluble,  and  separate  from  dilute 
solutions  in  crystals. 

CrP04.7,  6,  5,  and  3H2O  ;  FePO4. 

The  chromic  salt  exists  in  two  forms  :  the  violet  modification, 
with  7H2O,  which  is  soluble  and  crystalline,  and  is  produced  by 
treating  a  solution  of  violet  chromic  chloride  with  silver  phos- 
phate ;  and  the  green  modification,  precipitated  by  addition  of  a 
soluble  phosphate  to  a  green  chromium  salt.  The  violet  variety, 
when  heated,  changes  into  the  green  one;  and  the  green  precipi- 
tate becomes  violet  and  crystalline  on  standing.  Ferric  phosphate 
is  a  white  precipitate  produced  in  a  neutral  solution  of  a  ferric  salt 
by  hydrogen  disodium  phosphate,  or  by  exposing  ferrous  phosphate 
to  air.  Arsenates  give  similar  precipitates  with  chromium  and 
iron  salts. 

Iron  also  forms  the  following  double  phosphates  with  hydro- 
gen:— 

Fe(H2P04)3  ;  FeH3(PO4)2 ;  Fe6H3(PO4)7  ;  Fe8H3(PO4)9  ;  and  Fe4H3(PO4)5. 
Also  the  basic  phosphates  :— P2O5.2Fe2O3.12H.2O  (cacoxene)  j  5H.2O  (dvfrenite 
or  green  iron  ore)  ;  and  12H.2O  or  18H2O  (delvauxite) . 

Basic  ferric  phosphate  is  also  a  frequent  constituent  of  bog- 
iron  ore.  Manganic  and  cobaltic  orthophosphates  and  arsenates 
are  unknown. 

Simple  salts  : — 

Cr3(P04)2  (?)  ;  Fe3(P04)2  8H,0  ;  Mn3(PO4)2.7H2O  ;  Co^PO^SH.^  ; 
Ni3(PO4)2.7H2O  ;   Fe3(AsO4)2  ;   Co3(AsO4)2.8H.2O  and  Ni3(AsO4)2.8H.2O 
(cobalt-  and  nickel-bloom). 

Mixed  salts  :— 

Fe(H.,PO4)2.2H2O  ;  Mn(H2PO4)2.2H2O  ;  HMnPO4.3B:2O  ; 

(NHJFe(P04).H20  ;   (NH4)Mn(PO4).H.2O. 
AJso  the  arsenates,  Co(H.2AsO4)2  ;  Mn(H2AsO4)2 ;  MnHAsO4. 
And  the  minerals  childrenite,   a  phosphate  of  aluminium,  iron,  and  man- 
ganese :  triplite,  (Fe,Mn)3(PO4)2,  and  triphylline,  (Li2,Mg,Fe3Mn)3(PO4)2. 

Chromous  phosphate  is  a  blue  precipitate ;  ferrous  phosphate 
is  white  and  insoluble  ;  it  occurs  native  as  vivianite  or  blue  iron 
earth  ;  the  hydrogen  manganous  salts  and  the  double  ammonium 


362      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLUKIDES. 

salts  are  obtained  by  mixture  and  crystallisation,  e.g.,  Mn3(PO4)2  + 
H3P04.  Aq  =  3HMnPO4  4-  Aq ;  Mn3(PO4)2  +  (NH4)3P04.  Aq  = 
3NH4MnPO4  +  Aq.  The  cobalt  salt  is  reddish-blue,  and  the  nickel 
salt  light-green.  Arsenates  of  cobalt  and  nickel  occur  native  ; 
cobalt-bloom  forms  red,  and  nickel-bloom  green,  crystals. 

Elements  of  the  carbon-group  form  no  normal  phosphates. 
Carbon  phosphate  is  unknown ;  titanium  forms  the  compound 
Ti2Na(PO4)3  when  titanium  dioxide  is  fused  with  hydrogen  sodium 
ammonium  phosphate  (microcosmic  salt)  ;  and  sodium  thorium 
phosphate,  Th2Na(PO4)3,  is  similarly  prepared  ;  zirconium  salts  by 
precipitation  give  the  basic  phosphate  (ZrO)3(PO4)2 ;  thorium 
phosphate  is  a  white  precipitate  ;  cerous  phosphate,  CePO4,  occurs 
native  as  cryptolite  and  phosphocerite ;  prepared  artificially,  it  forms 
a  white  precipitate.  Arsenates  of  titanium,  zirconium,  and  thorium 
have  been  prepared ;  also  cerous  arsenate,  CeAsO4  (?)  and  sulph- 
arsenate,  CeAsS4(?),  which  require  investigation. 

SiH2(PO4)2.3H2O  is  deposited  from  a  solution  of  silica  in 
phosphoric  acid  kept  at  125°  for  several  days.  It  is  soluble  in, 
and  decomposed  by  contact  with,  water.  Germanium  phosphate 
has  not  been  prepared  ;  a  basic  phosphate  of  tin,  P2O5.2SnO2.10H2O, 
is  deposited  on  treatment  of  tin  dioxide  (metastannic  acid)  with 
phosphoric  acid;  this  compound  is  insoluble  in  nitric  acid,  and  is 
therefore  used  in  separating  phosphoric  acid  from  solutions  con- 
taining it.  Corresponding  arsenates  are  unknown.  By  fusing 
stannic  oxide  with  borax  and  microcosmic  salt,  crystals  of 
the  formula  Na2Sn(PO4)2  are  produced.  With  microcosmic 
salt  alone,  the  body  NaSn,(PO4)3  is  formed  in  microscopic 
crystals. 

Stannous  phosphato-chloride,  Sn3(PO4)2.SnCl7,  is  precipitated 
by  adding  a  solution  of  ordinary  sodium  phosphate  to  excess  of  tin 
dichloride ;  but  with  excess  of  sodium  phosphate  the  precipitate 
has  the  formula  Sn  (PO4)2.2SnHP(X.3H2O.  The  arsenates, 
similarly  produced,  are  said  to  have  the  formulas  2HSnAsO4.H>O 

and  C1|£>As04.H20. 

Lead  orthophosphate,  Pb3(PO4)2,  produced  by  precipitation,  is 
a  white  amorphous  substance,  fusible,  and  crystallising  on  cooling. 
By  adding  phosphoric  acid  to  a  dilute  boiling  solution  of  lead 
nitrate,  the  compound  Pb(H2PO4)2  is  thrown  down  in  sparkling 
white  laminae.  In  the  cold,  a  phosphato-nitrate,  of  the  formula 
Pb(NO3)2.Pb3(PO4)a.2HaO,  is  precipitated.  It  is  decomposed  by 


PHOSPHATES   AND   ARSENATES.  363 

boiling  water.  By  employing  a  boiling  solution  of  lead  chloride 
and  excess  of  sodium  phosphate,  the  compound 

Pb3(PO4)2.PbCL.H2O 

is  precipitated.  With  excess  |of  lead  chloride  the  precipitate  con- 
sists of  2Pb3(PO4)2.PbCL  (?).  Pyromorphite,  another  phosphate- 
chloride,  3Pb3(PO4)2.PbCl2,  occurs  native  in  hexagonal  prisms, 
usually  of  a  green  colour.  The  corresponding  arsenate, 

3Pb3(As04),.PbCL, 

is  also  found  in  nature,  and  is  named  mimetesite.  Crystals  in 
which  arsenic  and  phosphorus  replace  each  other  partially  are 
common.  The  arsenates  Pb3(AsO4)3  and  HPbAsO4  have  been 
produced  by  precipitation,  and  also  the  sulpharsenate,  Pb,AsS4. 

(VO)P04.7H20  ;   (VO)As04.7H20  ;   (VO)2H3(PO4)3.3H:;O. 
These  are  the  simpler  phosphates  and  arsenates  of  elements  of 
the  nitrogen  group.    They  are  brilliant  yellow  or  red  crystals.    It 
is  to  be  noticed  that  these  bodies  may  equally  well  be  conceived  as 
vanadates  of  phosphoryl  and  arsenyl,  thus : — 

(PO)  V04.7H20  ;  (AsO)V04.7H,0 ;  and  (PO.OH)3(VO4)2.3H2O. 

Tantalum  pentoxide,  dissolved  in  hydrochloric  acid,  forms  a  jelly 
with  phosphoric  acid,  due  probably  to  a  combination  between  them. 

A  curious  compound  of  the  formula  4MgHPO4.NO2  is  produced 
by  boiling  magnesium  pyrophosphate  with  strong  nitric  acid,  and 
heating  it  in  a  paraffin-bath  until  it  ceases  to  emit  fumes.  It  is 
a  crystalline  whitish-yellow  powder,  which  gives  off  nitric  per- 
oxide when  strongly  heated. 

The  vapour-density,  and  consequently  the  molecular  weight,  of 
phosphorus  pentoxide  is  unknown.  If  its  formula  be  P2O5,  it 
may  perhaps  be  regarded  as  phosphoryl  phosphate,  (PO)PO4, 
O=PEEO3:EEP— O  ;  and  arsenic  pentoxide  and  the  other  pentoxides 
might  be  similarly  regarded. 

Many   very  complicated   compounds   of   the    pentoxides   with 
each  other  have  recently  been  discovered.     Among  these  are 
P2O5.V2O5.(NH4)2O.H>O  ;  4P2O5.6V2O5.3K2O.2lHaO  ; 
P2O5.20V2O5.69H2O ;  5A&,O5.8V2O5.27H2O. 

Some  also  contain  vanadium  dioxide,  for  example, 

2P203.V02.18V2Q6.7(NH4)20.50H20. 

Compounds  of  arsenious  and  arsenic  oxides  are  also  known  ; 
thus  : — 
2As2Oa.3As3Oj.H2O  ;  As,O3.2As2O3.H2O  ;  and  As2Os.As2O3.H,O. 


364      THE   OXIDES,   SULPHIDES,   SELEN1DES,  AND   TELLURIDES. 

They  are  produced  by  partial  oxidation  of  arsenious  oxide, 
As4O6,  by  nitric  acid,  and  are  definite  crystalline  bodies.*  The 
bismuth  phosphate  corresponding  to  the  last  of  these,  BiPO4  = 
P2O5.Bi2O3  is  produced  by  precipitation.  The  corresponding 
arsenate,  BiAsO4.H2O  is  a  yellowish-white  precipitate  ;  they  may, 
however,  equally  well  be  regarded  as  metaphosphate  and  met- 
arsenate  of  bismuthyl,  (BiO)PO3  and  (BiO).AsO3. 

The  compounds  with  the  elements  molybdenum  and  tungsten 
are  exceedingly  complicated.  Molybdenum  trioxide,  MoO3,  and 
tungsten  trioxide,  WO3,  combine  with  phosphorus  tri-  and  pent- 
oxides,  and  with  many  other  oxides ;  these  compounds  will  be 
described  among  the  oxides  of  molybdenum  and  tungsten.  The  only 
one  to  be  mentioned  here  is  ammonium  phosphomolybdate,  which 
is  produced  by  adding  ammonium  molybdate  to  any  warm  solu- 
tion containing  an  orthophosphate.  It  is  a  bright  yellow  precipitate, 
insoluble  in  nitric  acid,  and  is  used  as  a  test  for  phosphoric  acid. 
Several  compounds  of  uranyl,  (U02),  are  known.  The  normal  salt 
has  not  been  prepared,  but  double  salts  are  known,  for  example, 

(U02)3(P04)2.2  (U02)HP04.H20, 

which  is  formed  by  precipitation  as  a  light  yellow  powder.  By 
digestion  with  phosphoric  acid,  the  salts  (UO2)HPO4,  and 
(UO2)(H2PO4)2  are  formed  ;  corresponding  arsenates  have  been 
prepared.  Uranyl  sodium  salts,  (UO2)NaFO4  and  (UO2)NaAsO4, 
are  produced  by  addition  of  sodium  phosphate  in  excess.  The 
calcium  salt,  (UO2)2Ca(PO4)2.8H2O,  is  found  native  as  uranite ; 
and  a  similar  copper  salt,  (UO2)2Cu(PO4)2.8H2O,  occurs  as  chalco- 
lite. 

Phosphates  and  arsenates  of  the  palladium  and  platinum 
groups  of  metals  require  investigation.  No  compound  has  been 
analysed  (except  HJRh(PO4)2.H2O),  although  salts  of  these  metals 
give  precipitates  with  phosphates  and  arsenates.  Compounds  of 
gold  are  unstable. 

Copper  orthophosphate,  Cu^(PO4)2,  is  a  blue-green  precipitate  ; 
or,  when  prepared  by  heating  the  pyrophosphate  with  water, 
yellowish-green  crystals  with  3H2O.  The  salt  HCuPO4  is  also  a 
blue-green  precipitate.  Many  basic  compounds  occur  native,  e.g., 

P2O5.4CuO.H2O,   2H2O,   and   3H.O ;    P2O5.5CuO.2H2O  and 
3H2O ;  and  P,O5.6CuO.3H2O. 

The  last  is  the  most  important,  and  is  named  phosphocltalcite. 
*  Comptes  rend.,  100,  1221. 


PYKOPHOSPHOKIC  ACID.  365 

The  arsenates,  CTl3(AsO4)2  and  H2Cu2(AsO4) ,H2O,  are  green 
and  blue  powders  respectively. 

Silver  phosphate,  AgtPO4,  is  a  yellow  precipitate,  produced  by 
adding  any  soluble  phosphate  to  a  solution  of  silver  nitrate.  It  is 
used  as  a  test  for  phosphoric  acid.  Hydrogen  disilver  phosphate, 
HAg2PO4,  produced  by  digesting  the  former  with  phosphoric  acid, 
forms  colourless  crystals ;  it  is  at  once  decomposed  by  water  into 
Ag5PO4  and  H3P04.  The  arsenate,  Ag;AsO4,  is  a  red  precipitate. 
It  is  formed  by  adding  an  arsenate  to  a  solution  of  silver  nitrate, 
and  cautiously  adding  ammonia.  It  serves  as  a  test  for  arsenic 
acid,  and  distinguishes  it  from  arsenious  acid. 

Mercurous  phosphate,  Hg;jPO4,  and  mercuric  phosphate, 
Hg;5(PO4}2,  are  white  crystalline  powders.  A.  phosphato-nitrate, 
Hg}PO4.HgNO3.H,O,  is  also  known.  The  arsenate  Hg,HAsO4  is 
an  orange  precipitate. 

Pyro-compounds.  —  Pyrophosphoric  acid,  H4P2O7  = 
P2O5(OH)4,  is  produced  by  heating  orthophosphoric  acid  to  215*. 
The  change  begins  at  160°,  but  is  not  complete  at  215°,  for  the  mass 
still  contains  unchanged  orthophosphoric  acid.  If  a  higher  tem- 
perature be  employed,  meta  phosphoric  acid  begins  to  be  formed. 
Similarly,  pyroarsenic  acid  is  formed  by  heating  the  ortho-acid 
to  140—160°.  Pyroantimonic  acid,  unlike  the  corresponding 
acids  of  phosphorus  and  arsenic,  is  produced  by  the  action  of 
water  on  the  pentachloride.  When  SbCl5  is  mixed  with  a  little 
water,  crystals  of  the  formula  SbCl5.4H2O  are  deposited. 
Addition  of  more  water  to  the  cold  solution  of  this  body  produces 
the  insoluble  oxy chloride,  SbOCl3 ;  on  warming  this  antimonyl 
chloride  with  much  water,  the  sparingly  soluble  pyroantimonic 
acid,  HiSb2O7.2H2O  is  formed.  The  water  of  crystallisation  may 
be  expelled  at  100°.  No  corresponding  compound  of  bismuth  is 
kno^vn. 

These  bodies  may  also  be  prepared  by  replacing  some  metal 
such  as  lead,  in  the  pyro-salts,  by  hydrogen,  by  the  action  of 
hydrogen  sulphide,  thus  : — 

PbJP207  +  2H2S  +  Aq  =  H4P207.Aq  +  2PbS. 

The  lead  pyrophosphate  is  insoluble,  and  is  suspended  in  water. 
Pyroarsenic  acid,  however,  cannot  be  thus  prepared,  for  it  reacts 
with  hydrogen  sulphide,  giving  arsenic  pent asulp hide.  But  as 
pyrantimonic  acid  is  sparingly  soluble,  it  is  precipitated  on  adding 
aa  acid  to  a  solution  of  a  pyroantimonate ;  e.g., 

q  +  4HCl.Aq  =  H4Sb2O7  +  4KCl.Aq. 


366      THE  OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLUKIDES. 

On  standing,  even  in  contact  with  water,  it  loses  water,  changing 
to  HSbO3,  thus  :— 

H4Sb2O7  =  2HSbO3  +  H20. 

No  pyrosulpho-  or  pyroselenio-acids  are  known. 

Pyrophosphoric  acid  is  usually  a  soft  colourless  glass-like 
body ;  it  has,  however,  been  obtained  in  opaque  indistinct  crystals. 
Pyroarsenic  acid  forms  hard  shining  crystals ;  it  unites  with  water 
at  once,  giving  out  heat,  and  forming  a  solution  of  orthoarsenic 
acid. 

Pyroantimonic  acid  is  a  white  powder,  soluble  in  a  large 
quantity  of  water,  from  which  it  is  precipitated  by  addition  of 
acids. 

Pyrophosphates,  &C. — The  pyrophosphates  and  pyroarsenates 
are  produced  by  heating  the  mono-hydrogen  or  mono-ammonium 
orthophosphates  to  redness,  thus  :— 

2HNa2PO4  =  Na4P2O7  +  #20; 
2NH4MgP04  =  Mg.P207  +  2NH,  +  H,0. 

The  pyroarsenates  require  investigation.  It  is  possible  that  on 
treatment  with  water  di metallic  orthoarsenates  are  again  formed, 
but  this  has  not  been  proved.  The  pyroantimonates  are  produced 
by  heating  the  metantimonates  with  water,  or  with  an  oxide, 
thus : — 

2MSbO,  +  M20  =  M4Sb207,  and  2MSb03  +  H20  =  M2H2Sb207. 

The  pyrophosphates  may  also  be  produced  by  action  of  pyro- 
phosphoric  acid  on  oxides,  hydroxides,  or  carbonates. 

Pyrothioarsenates  are  the  salts  usually  produced  by  dissolving 
arsenic  pentasulphide  in  solutions  of  soluble  sulphides,  or  hydrosul- 
phides,  or  the  trisulphide  in  solutions  of  polysulphides  ;  or  by  the 
action  of  hydrogen  sulphide  on  solutions  of  the  arsenates ;  or  by 
fusing  the  sulphides  of  arsenic  and  metal  together.  Many  are 
insoluble,  and  are  precipitated  on  additio'n  of  the  sodium  salt  to  a 
solution  of  a  compound  of  the  element.  On  treatment  with 
alcohol,  they  are  often  decomposed  into  orthothioarsenates,  which 
are  precipitated,  while  the  nieta-salts  dissolve. 

List  of  Pyrophosphates,  &c. 
Simple  salts : — 

Na4Po07.10H20 ;  K4P207.3H20;  (NH41I4P2O7.— Li4As2S- ;   Na4As2S7 ; 
K4As2S7;   CNH4)4As2S7.— K4Sb207. 

Mixed  salts:— 

H;Na2P207 ;  Na2(NH4)2P2Or  5H,O  ;  H2K2P2O7  ;  2HK2(NH4)P2O7.H2O ; 
Na.KsP.O7.l2H.jO  j  H2(NH4)  JP2O;.— H2Na2Sb2O7  ;  H2K2Sb2O7. 


PYROPIIOSPHATES  AND   PYROANTIMONATES.  367 

The  pyrophosphates  are  produced  by  addition  of  a  hydr- 
oxide or  carbonate  to  the  acid;  many  of  them  are  precipitated 
by  alcohol.  They  are  white  deliquescent  salts,  and  they  are  not 
altered  by  boiling  with  water;  but,  on  boiling  with  acids,  they 
combine  with  water,  forming  orthophosphates.  The  double  salts 
are  produced  by  mixture  and  crystallisation.  On  heating  dihydro- 
gen  raonosodium  orthophosphate,  H2NaPO4,  to  200°,  it  loses  water, 
giving  dihydrogen  disodium  pyro phosphate,  thus  : — 2H2NaPO4  = 
H>NaoP2O7  +  H20.  Potassium  pyroantimonate,  K4Sb2O7,  is  pro- 
duced by  fusing  the  metantimonate,  KSbO3,  with  caustic  potash, 
and  subsequent  crystallisation  from  water.  Dihydrogen  dipotas- 
sium  pyrantimonate  is  formed,  along  with  potassium  hydroxide,  by 
warming  the  tetrapotassium  salt  with  water.  The  corresponding 
sodium  salt  is  very  sparingly  soluble  in  water — it  is  one  of  the 
few  nearly  insoluble  salts  of  sodium — and  the  formation  of  a  pre- 
cipitate in  a  solution  free  from  other  metals  on  addition  of  a  solu- 
tion of  the  potassium  salt  indicates  the  presence  of  sodium,  owing 
to  the  formation  of  H2Na2Sb2O7. 

Simple  salts  : — 

Be.;,P207.5H20  ;  Ca^O^^O  ;  ST<F2O7  H2O  ;  Ba^O^O  ;  Ca^As^  ; 
and  others. 

Mixed  salts  :— 

Na2CaP2O7.4H2O  ;  and  insoluble  white  pyrantimonates. 

Hydrogen  pyrophosphate  gives  no  precipitate  with  the 
chlorides  of  these  metals ;  but  with  sodium  pyrophosphate 
these  pyrophosphates  are  precipitated.  The  calcium  salt  fuses  to 
a  transparent  glass,  which  may  be  substituted  for  ordinary  glass 
for  many  purposes. 
Simple  salts  : — 

Mg2P2O7  3H2O  ;  2Zn2P2O7.H2O  and  10H2O  ;  Cd^O^ELjO  ;  Mg-jAs.^,-. 
Mixed  salts  :— 

Na2ZnP2O7,  also  with  4H2O  ;  Na2CdP2O7. 

The  anhydrous  magnesium  pyrophosphate  is  left  as  a  white 
raked  mass  on  igniting  ammonium  magnesium  orthophosphate, 
NH4MgPO4.  These  anhydrous  salts  are  soluble  in  sulphurous 
acid,  and  crystallise  from  the  solution  on  evaporation.  The  double 
salts  crystallise  from  solutions  of  oxides  in  sodium  metaphosphate. 
The  sulpharsenate  of  magnesium  is  a  very  soluble  yellow  salt,  also 
soluble  in  alcohol. 

Pyrophosphates,  &c.,  of  the  boron  group  of  elements  have  not 
been  prepared. 

A14(P2O7)3.10H2O  is   a  white  precipitate,  differing  from  the 


368      THE   OXIDES,   SULPHIDES,   SELEXIDES,   AND   TELLURIDES. 

orthophosphate  by  its  solubility  in  ammonia.  The  salts  of  gallium, 
indium,  and  thallium  have  not  been  prepared.  The  double  salt, 
NaAlP2O7,  crystallises  from  a  solution  of  A12O3  in  fused  sodium 
metaphospbate. 

Pyrophosphate  of  carbon  is  unknown ;  titanium,  zirconium,  and 
tin  pyrophosphates,  TiP2O7,  ZrP2O7,  and  SnP2O7,  are  prepared  by 
dissolving  the  dioxides  in  fused  orthophosphoric  acid. 

Silicon  pyrophosphate,*  SiP2O7,  crystallises  in  octahedra  from 
a  solution  of  silica  in  fused  metaphosphoric  acid,  and  lead  pyro- 
phosphate, Pb2P2O7.H2O,  produced  by  precipitation,  is  a  bulky 
white  powder.  Pb2As2S7  is  also  known. 

Cr4(P207)3 ;  Fe4(P207)3.9H20.— 2Na4P207.Fe4(P207)3.7H20 ;  F84(As2S;)3. 

These  salts  are  produced  by  precipitation ;  that  of  chromium 
is  green,  and  those  of  iron  nearly  white.  They  are  soluble  in 
excess  of  sodium  pyrophosphate,  and  doubtless  form  salts  like 
the  double  salt  of  iron  of  which  the  formula  is  given  above.  Ammo- 
nium sulphide  does  not  precipitate  chromium  or  iron  from  solu- 
tions of  these  double  salts.  NaCrP2O7  crystallises  from  a  solution 
of  chromium  sesquioxide  in  sodium  raetaphosphate. 

Fe2P207 ;  Mn2P207.3H20  ;  Co2P2O7;  Ni2P2O7.6H2O ;  NaNH1MnP2O7.3HiO ; 

Fe..As.,S7  ;  Mn2As2S7 ;  and  Co2As2S7  are  produced  by  precipitation. 

Of  the  nitrogen  and  phosphorus  groups,  the  only  pyrophos- 
phate known  is  that  of  bismuth,  Bi4(P2O7)3,  which  is  a  white  pre- 
cipitate. It  crystallises  from  a  solution  of  bismuth  trioxide  in 
fused  sodium  metaphosphate.  But  hydrogen  sodium  pyrophos- 
phate dissolves  antimony  trioxide.  The  pyro phosphates  of  elements 
of  the  palladium  and  platinum  groups  have  not  been  prepared. 

Cupric  pyrophosphate,  Cu2P2O7.H2O,  is  a  greenish- white 
powder  produced  by  precipitation.  Silver  pyrophosphate,  Ag4P2O7, 
is  a  white  curdy  precipitate.  Its  formation  serves  to  distinguish 
pyrophosphates  from  orthophospbates,  which  give  a  yellow  pre- 
cipitate of  Ag3PO4  with  silver  nitrate.  A  double  pyrophosphate  of 
gold  and  sodium,  of  the  formula  2Na4P2O7.Au4(P2O7)3.H2O,  is 
formed  by  mixing  gold  trichloride  with  sodium  pyrophosphate  and 
evaporation ;  the  sodium  chloride  separates  in  crystals,  leaving  the 
above  salt.  Mercuric  pyrophosphate,  Hg2P2O7,  and  mercurous 
pyrophosphate,  Hg,P2O7,  are  white  precipitates. 

It  is  to  be  noticed  that  while  there  are  many  double  pyrophos- 
phates in  which  the  two  atoms  of  hydrogen  of  pyrophosphoric  acid 
are  replaced  by  one  metal,  and  two  by  another,  such  as  H3Na2P2O7,' 

'*  Comptes  rend.,  963  1052  ;  99,789;  102,1017. 


METAPHOSPHATES.  369 

Na>CaP2O7,  &c.,  there  are  few  in  which  the  hydrogen  is  replaced 
in  fourths.  Yet  instances  are  known,  for  example,  NaNH4MnP2O7, 
HKoNH4P2O7,  and  one  or  two  others.  The  conclusion  is  therefore 
justified  that,  inasmuch  as  such  compounds  are  known,  there  are 
four  atoms  of  hydrogen  in  hydrogen  pyrophosphate.  With  the 
pyrothioarsenates  and  pyroantirnonates,  such  double  compounds 
are  unknown  :  the  only  double  salts  being  those  of  the  pyroanti- 
monates  of  hydrogen  and  a  metal  such  as  H2Na>Sb2O7. 

Meta-compounds. — Metaphosphates,  etc. — It  cannot  be  said 
with  certainty  that  more  than  one  metaphosphoric  acid  is  known, 
although,  as  mentioned  on  p.  354,  there  are  grounds  for  infer- 
ring the  existence  of  at  least  five  sets  of  metaphosphates :  mono-, 
di-,  tri-,  tetra-,  and  hexa-metaphosphates,  derived  from  condensed 
acids.*  When  phosphoric  anhvdride  is  dissolved  in  cold  water,  and 
the  resulting  solution  evaporated,  or  when  orthophosphoric  acid  is 
heated  above  213°,  a  transparent  glassy  soluble  substance  remains, 
the  simplest  formula  of  which  is  HPO3.  The  same  body  is  pro- 
duced by  (1)  heating  inicrocosmic  salt  to  redness,  when  sodium 
metaphosphate  is  produced,  thus:— HNaNH4PO4  =  NaPO3  +  H20 
+  NH3 ;  (2)  dissolving  this  metaphosphate  in  water,  and  adding  lead 
nitrate,  when  lead  metaphosphate  is  formed,  thus: — 2NaP03.Aq  + 
Pb(X03)2. Aq  =  2NaN03.  Aq  +  Pb(PO3)2 ;  and  (3)  suspending  the 
insoluble  lead  metaphosphate  in  water,  and  passing  through  the 
liquid  a  current  of  hydrogen  sulphide,  when  lead  sulphide  and 
hydrogen  metaphosphate  are  produced,  thus : — Pb(PO3)j  +  Aq  + 
II2S  =  2HP03.Aq  +  PbS.  On  evaporating  the  filtered  liquid 
to  dryness,  the  same  glassy  soluble  body  is  obtained.  It  is 
probably  a  hexametaphosphoric  acid,  for  it  forms  salts  in  which 
one-sixth  of  the  hydrogen  is  replaceable. 

But  it  has  been  noticed  that  during  the  preliminary  stage  of 
phosphorus  manufacture,  in  evaporating  orthophosphoric  acid  with 
charcoal  or  coke,  and  igniting  the  residue,  the  black  powder  of 
carbon  and  metaphosphoric  acid  gives  up  nothing  to  water;  an 
insoluble  variety  is  in  fact  produced.  This  variety  differs  therefore 
from  the  other,  and  is  possibly  monometaphosphoric  acid,  for  that 
body  gives  insoluble  salts. 

On  boiling  metaphosphoric  acid  with  water,  orthophosphoric 
acid  is  formed,  thus :— HP03.Aq  +  H2O  =  H3P04.Aq.  The  meta- 
acid,  when  added  to  a  solution  of  albumen  (white  of  egg)  in  water, 
coagulates  it,  producing  a  curdy  precipitate;  the  silver  salt  is 
white,  and  is  not  produced  on  adding  silver  nitrate  to  a  solution  of 

*  See  also  Zeitschr.f.physik.  Chem.,  6,  122. 

2   B 


370      THE   OXIDES,    SULPHIDES,   SELENIDES,   AND    TELLURIDES. 

metaphosphoric  acid ;  and  it  gives  no  yellow  precipitate  when 
warmed  with  ammonium  molybdate  and  nitric  acid.  But,  after 
boiling  with  water,  the  resulting  orthophosphoric  acid  does  not 
coagulate  albumen,  gives  a  yellow  precipitate  of  silver  ortho- 
phosphate,  AgyPO,,  with,  silver  nitrate,  and  a  bright  yellow 
precipitate  with  ammonium  molybdate.  The  two  acids  are  there- 
fore obviously  distinct  bodies.  They  are  distinguished  from 
pyrophosphoric  acid  by  the  fact  that  silver  pyrophosphate  is  white 
and  curdy. 

Metaphosphoric  acid  is  volatile  at  a  high  temperature,  but  it 
does  not  lose  water  to  give  phosphorus  pentoxide. 

Metarsenic  acid,  HAsO3,  is  likewise  produced  by  heating 
ortho-  or  pyroarsenic  acid  to  200 — 206°.  It  is  a  white  nacreous 
substance  sparingly  soluble  in  cold  water ;  but  its  solution  exhibits 
no  properties  differing  from  those  of  a  solution  of  orthoarsenic 
acid,  and  it  appears,  therefore,  to  combine  with  water  to  form  the 
latter  body.  The  metarsenates,  too,  are  only  known  as  solids; 
they  may  be  obtained  from  the  appropriate  hydrogen  or  ammonium 
orthoarsenates,  e.g.,  HNaNH4AsO4  =  NaAsO3  +  H20  +  NHZ', 
but  on  treatment  with  water  they  combine,  forming  dihydrogen 
metallic  ortho-arsenates. 

The  metathioar senates  are  produced  by  the  action  of  alcohol 
on  solutions  of  the  pyrothioarsenates,  thus : — 

K4As2S7.Aq  +  Ale  =  K3AsS4  +  KAsS3.Aq.Alc. 

The  orthosulpharsenate  is  precipitated,  while  the  metasulph- 
arsenate  remains  in  solution.  The  acid  is  unknown.  They  have 
been  little  investigated. 

Metantimonic  acid,  HSbO3,  results  from  the  spontaneous 
decomposition  of  H4Sb207  dissolved  in  water ;  it  is  also  produced 
when  the  pyro-acid  is  heated,  or  when  a  metantimonate  is  treated 
with  an  acid.  It  is  also  formed  by  the  action  of  nitric  acid  on 
antimony.  It  is  a  soft  white  sparingly  soluble  powder.  This 
compound  and  its  salts  are  usually  inconsistently  named  "  anti- 
monic  acid  "  and  "  antimonates."  Hydrated  pentoxide  of  bismuth, 
Bi2O5.H2O  (see  p.  350)  may  be  classed  here. 

(a.)  Hexametaphosphates. — These  are  the  salts  prepared  by 
the  usual  methods  from  ordinary  metaphosphoric  acid  :  Na6P6Oi8 ; 
(NH4)6P6O18;  Na-jCa^PeO^ ;  Agf;P6O18;  and  others. 

The  sodium  salt  is  produced  by  strongly  igniting  dihydrogen 
sodium  orthophosphate  until  it  fuses,  and  then  rapidly  cooling  the 
fused  mass.  It  is  an  amorphous  colourless  deliquescent  glass, 
easily  soluble  in  water  and  in  alcohol.  It  gives  gelatinous  preci- 


METAPHOSPHATES.  371 

pitates  with  salts  of  most  metals;  its  hexa-basic  character  is 
deduced  from  the  formulae  of  double  salts  such  as  the  one  given 
above,  Na2Ca5P6O18.  The  ammonium  salt  is  produced  by  saturating 
ordinary  metaphosphoric  acid  with  ammonia,  and  evaporating. 

(6.)  Tetrametaphosphates.  —  Lead  oxide,  heated  with  excess 
of  phosphoric  acid,  yields  large  transparent  prisms  of  an  insoluble 
salt.  The  salt  is  powdered,  and  digested  with  sodium  sulphide  ; 
lead  sulphide  and  sodium  tetrametaphosphate  are  formed.  It  is 
diluted  with  much  water,  and  filtered.  On  adding  alcohol,  an 
elastic  ropy  mass,  like  caoutchouc,  is  precipitated.  Its  solution  in 
water  gives  ropy  precipitates  with  salts  of  other  metals.  Its 
tetra-basicity  is  inferred  from  the  existence  of  double  salts  such  as 


(c.)  Trimetaphosphates.  —  When  a  considerable  mass  of 
sodium  metaphosphate  is  slowly  cooled,  the  mass  acquires  a 
beautiful  crystalline  structure  ;  and  on  treatment  with  warm 
water  the  solution  separates  into  two  layers,  the  larger  stratum 
containing  the  crystalline,  and  the  smaller  the  ordinary  vitreous, 
salt.  The  solution  of  the  crystalline  variety  gives  crystalline 
precipitates  with  salts  of  many  metals,  the  silver  salt,  for  example, 
depositing  in  crystals  of  the  formula  Ag^O^HoO.  The  sodium 
salt  deposits  in  large  crystals  of  the  formula  Na3P;<O9.6H2O.  Its 
tri-  basicity  is  inferred  from  formulae  such  as  2NaBaP3O9.H2O. 
The  salts  of  this  acid  uniformly  crystallise  well. 

(d.)  Dimetaphosphates.—  By  heating  copper  oxide,  CuO, 
with  a  slight  excess  of  phosphoric  acid  to  350°,  an  insoluble 
crystalline  powder  is  formed.  On  digestion  with  sulphides  of 
sodium,  potassium,  &c.,  the  corresponding  dimetaphosphates  are 
formed,  and  separate  in  crystals  on  addition  of  alcohol.  Double 
salts  are  produced  by  mixture,  such  as  NaNH4P2OH.HoO  ; 
NaKP2O6.H2O;  NaAgP2O6,  &c.  These  salts,  like  the  trimeta- 
phosphates,  are  crystalline  bodies  sparingly  soluble  in  water. 

(e.)  Monometaphosphates.  —  These  bodies  are  insoluble  in 
water.  They  are  produced  by  igniting  together  the  oxides  and 
phosphoric  acid  in  molecular  proportions  ;  or,  by  adding  excess  of 
phosphoric  acid  to  solutions  of  nitrates  or  sulphates,  evaporating, 
and  heating  the  residues  to  350°  or  upwards.  They  are  crystalline 
and  anhydrous,  and  form  no  double  salts  ;  even  the  salts  of  the 
alkalies  are  nearly  insoluble  in  water.  The  solution  of  the  potassium 
salt  in  acetic  acid  gives  precipitates  with  salts  of  barium,  lead,  and 
silver. 

Metantimonates.—  These  salts  are  produced  by  fusing  anti- 
mony or  its  trioxide  with  nitrates,  or  the  acid  HSbO3  with 

2  B  2 


372       THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

carbonates ;  or  by  double  decomposition  from  the  potassium  salt, 
KSb03.Aq.     The  chief  compounds  are : — 

LiSbO3  ;  2NaSbO3.7H2O  ;  NaSbO3.3H2O  ;  KSbO3  ;  also  2KSbO3  5H2O  and 
3H20;  NH4Sb03.2H20  ;  Ca(SbO3)2;  Sr(SbO3)2.<  H2O;  Ba(SbO3)2.5H2O ; 
Mgr(SbO3)2.12H2O  ;  Zn(SbO3)2;  Co(SbO3)2;  Ni(SbO3)2.6H2O  ; 
Sn(Sb03)2.2H20  ;  Pb(SbO3)2;  Cu(SbO3)2  ;  Hgr(SbO3)2. 

All  these  salts,  with  exception  of  the  lithium,  sodium, 
potassium,  and  ammonium  salts,  are  sparingly  soluble  in  water,  and 
crystalline.  The  compounds  2NaSbO3.7H2O  and  2KSbO3.5  and 
3H2O  are  gummy,  and  may  possibly  be  derived  from  a  poly- 
metantimonic  acid.  When  boiled  with  water  they  are  decomposed, 
giving  a  residue  of  3Sb2O5.K2O.10H2O. 

"Naples  yellow"  is  a  basic  antimonate  of  lead,  produced  by 
heating  2  parts  of  lead  nitrate,  1  part  of  tartar- emetic,  and 
4  parts  of  common  salt  to  such  a  temperature  that  the  salt  fuses ; 
the  mass  is  then  treated  with  water,  which  dissolves  the  salt, 
leaving  the  "Naples  yellow  "  in  the  form  of  a  fine  yellow  powder. 
Another  basic  antimonate  of  lead  occurs  native  as  Meinerite, 
Sb2O5.3PbO.4H2O. 

Certain  complex  phosphates  have  been  prepared  by  fusing 
tetrasodium  pyrophosphate  with  me ta phosphate  in  the  proportion 
Na4P207  to  2NaPO3.  The  product  is  soluble  without  decomposi- 
tion in  a  small  quantity  of  hot  water,  and  crystallises  from  the 
solution  ;  but  it  is  decomposed  by  much  water.  With  solutions  of 
salts  of  the  metals,  it  gives  precipitates  ;  the  silver  salt,  for  example, 
has  the  formula  Ag6P4O13.  Another  salt  has  been  produced  by 
fusing  together  the  same  constituents  in  the  proportion  Na4P207 
to  8NaP03..  The  resulting  salt  is  very  sparingly  soluble  ;  the  silver 
salt  derived  from  it  has  the  formula  Ag12Pi0O31.  These  phosphates 
go  by  the  name  of  Meitmann  and  Henneberg,  their  discoverers. 


373 


CHAPTER  XXIV. 

OXIDES,    ETC.,    OP    ELEMENTS    OF    THE    PHOSPHORUS    GROUP. COMPOUNDS 

OP  TETROXIDES  ;  HTPOPHOSPHATES  AND  HYPOANTIMONATES. CONSTI- 
TUTION OF  PHOSPHITES,  ETC. — THE  PHOSPHITES,  ARSENITES,  AND 
ANTIMONITES,  THIOARSENITES  AND  THIOANTIMONITES.—  THE  HYPO- 
PHOSPHITES. — OXYHALIDES  AND  SULPHOHALIDES. 

Oxides,  Sulphides,  Selenides,  and  Tellurides  of 
Phosphorus,  Arsenic,  Antimony,  and  Bismuth, 
continued. 

Compounds  of  tetroxides. — It  has  been  already  stated  that 
the  oxide  P2O4,  when  treated  with  water,  gives  a  mixture  of  phos- 
phorous and  phosphoric  acids,  thus : — P2O4  -f  3H2O  -f  Aq  = 
H3P04.Aq  4-  H3P03. Aq.  It  is  therefore  concluded  to  be  a  phosphite 
of  phosphoryl,  thus : — (PO)'"(PO.j).  But  a  tetrabasic  acid  is  known, 
of  the  formula  P2O4.2H2O  =  P2O2(OH)4.  which  forms  distinct 
salts,  and  possesses  properties  differing  from  those  of  such  a  mix- 
ture. The  sodium  salt,  P2O2(ONa)4,  is  converted  by  bromine  and 
water  into  dihydrogen  disodium  pyrophosphate,  and,  as  the  acid 
has  no  marked  reducing  properties,  it  may  possibly  have  the  con- 
stitution— 

0=P(OH)2  0=P(OH)2 

,  that  of  pyrophosphoric  acid  being          >  0 
0=P(OH)2  0=P(OH)2. 

Hypophosphoric  acid,*  as  the  acid  P2O2(OH)4  is  called,  is 
produced  along  with  orthophosphoric  and  phosphorous  acids,  by 
the  oxidation  of  phosphorus  exposed  to  water  and  air.  About  one- 
sixteenth  of  the  phosphorus  is  converted  into  hjpophosphoric  acid. 
On  addition  of  sodium  carbonate,  the  dihydrogen  disodium  salt 
separates  out,  owing  to  its  sparing  solubility  in  water.  To  prepare 
the  pure  acid,  the  barium  salt  is  treated  with  the  theoretical 

*  Annalen,  87,  322  ;  19  i,  23;  JBericAte,l6,  749  ;  Comptesrend.,  101,  1058  ; 
102,  110. 


374      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

.amount  of  sulphuric  acid  ;  insoluble  barium  sulphate  is  formed, 
and  the  acid  remains  in  solution.  On  evaporation  in  a  vacuum, 
the  acid  H4P2O6.2H2O  separates  out  in  large  rectangular  tables, 
melting  at  about  62°.  On  standing  in  a  dry  vacuum,  these 
crystals  lose  water,  and  gradually  change  to  needles  of  the  pure 
a-jid  H4P2O6.  This  body,  at  70°,  suddenly  decomposes  into  phos- 
phorous and  metaphosphoric  acids:  —  H4P2O6  =  H3PO3  +  HPO3. 
The  following  salts  are  known  :  — 


;  K4P2O6.5H2O  ;  (NH4)4P2O6.H2O  ;  Mg-2P2O6.12H2O  ; 
Ca2P2O6.2H2O  ;  Ba2P2O6  ;  Pb2P2O6  ;  and  Ag4P2O6  ;  and  the  double  salts 
H3NaP2O6.2H2O  ;  H2Na2P2O6  ;  HNa3P2O6.9H2O  ;  H3Na5(P2O6)2.20H2O  ; 
H3KP206  ;  "H2K2P206  3H20  ;  HK3P2O6.3H2O  ;  H3(NH4)P2O6  ; 
H2(NH4)2P2O6;  H2M:&P2O6.4H2O  ;  H2CaP2O6.6H2O  ;  H2BaP2O6.2H2O. 

With  lithium  salts,  sodium  hypophosphate  gives  a  white  pre- 
cipitate. 

The  tetra-metallic  salts  of  the  alkalis  are  easily  soluble  in 
water  ;  the  dihydrogen  disodium  salt  is  sparingly  soluble,  and  is 
used  to  separate  the  acid  from  its  mixture  with  phosphorous  and 
orthophosphoric  acid.  The  dibarium  salt  is  produced  by  precipi- 
tation ;  it  is  nearly  insoluble  in  water,  as  are  most  of  the  other 
salts.  When  the  salts  are  heated  they  give  products  of  decomposi- 
tion of  phosphorous  acid  (hydrogen  phosphide  and  metaphosphate) 
and  metaphosphate  of  the  metal. 

The  silver  salt  may  be  prepared  directly  by  dissolving  6  grams 
of  silver  nitrate  in  100  grams  of  nitric  acid  diluted  with  100  grams 
of  water,  and  while  it  is  kept  hot  on  a  water-bath  adding 
8  or  9  grams  of  phosphorus.  The  mixture  must  be  cooled  as  soon 
as  the  violent  evolution  of  gas  ceases,  and,  on  standing,  tetrargentic 
hypophosphate  crystallises  out.  The  silver  salt  is  not  reduced  to 
metallic  silver  on  boiling,  as  is  silver  phosphite  ;  and  the  sodium 
salt  does  not  reduce  salts  of  mercury,  gold,  or  platinum. 

No  similar  compounds  of  arsenic  are  known  ;  but  antimony 
tetroxide,  when  fused  with  potassium  hydroxide  or  carbonate, 
yields  a  mass  from  which  cold  water  extracts  excess  of  alkali; 
the  residue,  dissolved  in  boiling  water  and  evaporated  to  dryness 
gives  a  yellow  non-crystalline  mass  which  has  the  composition 
Sb2O4.KoO.  On  treatment  with  hydrochloric  acid,  it  is  con- 
verted into  2Sb2O4.K2O  ;  and  excess  of  acid  liberates  the  com- 
pound Sb2O4.H2O. 

Compounds  of  trioxides  and  trisulphides  :  —  Constitution 
of  the  acids,  hydroxides,  and  salts  derived  from  the  trioxides 
and  trisulphides  of  phosphorus,  arsenic,  antimony,  and  bis- 


CONSTITUTION   OF   PHOSPHOROUS   ACID,  ETC.  37.") 

muth. — It  will  be  remembered  that  phosphoryl  chloride,  POC13, 
on  treatment  with  water,  yields  orthophosphoric  acid,  PO(OH)3, 
and  it  may  be  supposed  that  phosphorus  trichloride,  PC13,  yields 
a  similar  acid,  P(OH)3.  Such  an  acid  ought  to  be  tribasic,  like 
orthophosphoric  acid,  and  should  yield  three  double  salts,  e.g., 
r(OHXONa),  P(OH)(ONa)2,  and  PO(ONa)3.  Bat  the  last  of 
these  is  formed  only  when  the  second  is  mixed  with  great  excess  of 
a  strong  solution  of  sodium  hydroxide,  and  left  for  some  time  ;  it 
is  then  thrown  down  on  addition  of  alcohol.  It  appears  not  im- 
probable, therefore,  that  a  change  has  taken  place  during  this 

TT 

time,    and    that    the    compound    O^P^/  has    changed    to 


PO(H)3.  And  it  is  also  to  be  noticed  that  when  water  acts  on  phos- 
phorus trichloride,  some  orthophosporic  acid  and  free  phosphorus 
are  formed;  this  might  take  place  during  the  change  of  P(OH)3  to 
its  isomeride  O=P(OH)2H.  Moreover,  an  acid  is  known,  named 
ethyl-phosphinic  acid  (produced  by  the  oxidation  of  the  compound 
ethyl -phosphine),  analogous  to  hydrogen  phosphide  (see  p.  532), 
which  is  certainly  dibasic,  and  in  which  the  phosphorus  is  doubt- 
less in  direct  union  with  carbon.  The  formulas  are :  — 

/H  K  OH 

P^-H  P^H  O=Pf  OH  . 

XH  XC2H5  XC2H5 

Hydrogen  phosphide.  Ethyl  phosphine.  Ethyl-phosphinic  acid. 

There  are  therefore  good  reasons  for  believing  that,  although 
two  phosphorous  acids  might  exist,  the  one  known  is  0=P(OH)oH, 
and  not  P(OH)s.  The  isomerism  is  analogous  to  that  of  the  two 
nitrous  acids  (see  p.  337),  0=N— OH,  and  O2=N— H.  The  anhy- 
dride of  the  acid  0=P(OH)2H  would  be  therefore  not  P2Oa,  but 
O2PH,  an  unknown  substance.  As  with  orthophosphoric  acid  pj'ro- 
phosphates  are  known,  so  pyrophosphites  exist,  e.g.,  Na4P205. 
Such  substances  also  find  representatives  among  the  arsenites  and 
thioarsenites,  all  these  series  of  salts  being  known,  viz.,  MAs02, 
and  MAsS2,  metarsenites  and  thioarsenites  ;  M4As205  and  MiAs^So, 
pyroarsenites  and  thioarsenites ;  and  M3As03  and  M3AsS3,  ortho- 
arsenites  and  thioarsenites.  The  corresponding  metaphosphites  are 
unknown.  A  few  antimonites  and  sulphantimonites  have  also  been 
prepared. 

Phosphorous  acid,  etc. 

H3PO3  ;  H4Sb->O5  =  Sb2O3.2H2O  ;  H3SbO3  =  Sb2O3.3H2O. 

To  prepare  crystalline  phosphorous  acid,  H3PO3,  a  current  of 
dry  air  is  passed  through  phosphorus  trichloride  heated  to  60°  and 


376      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

passed  into  water  cooled  to  0°.  When  the  water  is  saturated,  the 
crystals  which  separate  are  washed  with  ice-cold  water,  and  dried 
in  a  vacuum.  It  is  also  slowly  formed  by  union  of  the  anhydride 
with  water;  or  along  with  orthophosphoric  acid  by  the  action  of 
water  on  the  tetroxide  ;  or  along  with  phosphoric  and  hypophos- 
phoric  acids  by  the  oxidation  of  phosphorus  in  air,  in  contact 
with  water.  Phosphorus  also  abstracts  oxygen  from  a  solution  of 
copper  sulphate,  depositing  copper,  thus  :  —  3CuS04.Aq  +  6H2O 
+  2P  =  3H,S04.Aq  4-  2H3PO3.Aq  +  3Cu.  The  sulphuric  acid 
may  be  removed  as  barium  sulphate  by  cautious  addition  of  solu- 
tion of  barium  hydroxide. 

Pyroantimonious  acid,  H4Sb2O5,  is  produced  by  addition  of 
copper  sulphate  to  a  solution  of  antimony  trisulphide  in  caustic 
potash.  Copper  sulphide  is  formed,  and  potassium  antimonite  ; 
and  on  addition  of  an  acid  to  the  filtered  liquid,  the  antimonite  is 
decomposed,  pyroantimonious  acid  being  precipitated. 

Orthoantimonious  acid  is  formed  by  the  spontaneous  de- 
composition of  the  peculiar  compound  acid  of  which  tartar-emetic 
is  the  potassium  salt.  This  acid  is  liberated  from  the  barium  salt 
corresponding  to  tartar-  emetic,  by  the  action  of  sulphuric  acid,  and 
has  the  formula  (C4H4O6)"Sb.OH.  With  water  it  yields  Sb(OH)3, 
and  tartaric  acid,  C4H606.Aq.  From  this  it  would  appear  that  tartar- 
emetic  is  not,  as  hitherto  supposed,  atartrate  of  potassium  and  anti- 
monyl,  K(SbO)C4H406,  but  a  tartaro-antimonite  (C4H406)"Sb.OK, 
two  hydroxyl  groups  of  antimonious  acid,  Sb(OH)3,  being  replaced 
by  the  dyad  group  (C4H406). 

Phosphorous  acid  forms  deliquescent  white  crystals,  melting 
at  74°.  When  heated  it  decomposes  into  hydrogen  phosphide  and 
phosphate  :  — 

4H3PO3  =  3H3PO4 


Zinc  and  iron  dissolve  in  it,  and  the  liberated  gas  is  hydrogen 
phosphide  ;  this  action  is  somewhat  similar  to  that  of  nitric  acid 
on  certain  metals,  whereby  ammonia  is  produced.  It  is  a  powerful 
reducing  agent,  tending  to  combine  with  oxygen  to  form  ortho- 
phosphoric  acid  ;  hence,  when  added  to  solutions  of  salts  of  silver, 
gold,  and  mercury,  the  metals  are  deposited.  It  also  reduces 
sulphurous  acid  to  hydrogen  sulphide,  thus  :  — 

3H3P03.Aq  +  H2S03.Aq  =  3H2P04.Aq  +  HtS. 

The  antimonious  acids  are  white  powders,  insoluble  in  water, 
but  soluble  in  hot  solutions  of  hydroxides  of  sodium  and  potassium, 


PHOSPHITES,   ARSENITES,  AND  ANTIMONITES.  377 

forming  anfcimonites.  The  corresponding  hydroxides  of  bismuth 
have  no  acid  properties.  The  three  hydrates,  Bi(OH)3,  Bi2O(OH)4, 
and  BiO(OH),  are  all  known.  They  are  produced  by  heating 
solutions  of  bismuth  salts  with  potash  or  ammonia. 

Phosphites.  —  NaaPOa  is  the  only  trimetallic  phosphite  known. 
It  is  produced  by  addition  of  a  large  excess  of  a  strong  solution  of 
sodium  hydroxide  to  disodium  phosphite,  HNa2P03.Aq,  and  after 
two  hours  adding  alcohol.  The  trisodium  salt  settles  down  as  a 
viscid  syrup,  which  is  stirred  with  alcohol,  and  finally  dried  in  a 
vacuum  over  sulphuric  acid. 


HK(HP03);  and  2H4Na,2(H:PO3)3H:2O  ;  and 

These  bodies  form  soluble  crystals,  and  are  produced  by  addition 
of  phosphorous  acid  to  hydroxides  or  carbonates. 

Ca(HP03).H20  j  2Sr(HP03).H20  ;  2Ba(HPO3).H2O  ;  and  H^XHPO^.H^O  j 
H2Ba(HPO3)2.H2O. 

White  sparingly  soluble  salts. 

Mg(HP03)  ;  Cd(HP03)  (?)  ;  2Zn(HP03).5H20. 

These  and  an  ammonium  magnesium  phosphite  are  produced  by 
precipitation.  They  are  white,  crystalline,  and  sparingly  soluble. 

Phosphites  of  aluminium,  chromium,  and  iron  have  been  pre- 
pared, but  not  analysed.  They  are  sparingly  soluble  precipitates. 

Mn(HPO2)  ;  Co(HPO2).2H2O,  and  Ni(HPO3).3H2O. 

Coloured  precipitates. 

Sn(HPO3)  and  phosphites  of  tin  dioxide  and  of  titanium  have 
also  been  prepared  ;  they  are  white  precipitates.  Pb(HPO3)  is  also 
white,  and  is  formed  by  precipitation.  It  is  nearly  insoluble.  When 
digested  with  ammonia,  the  basic  phosphate,  P2O3.4PbO.2H2O,  is 
produced.  Bismuth  phosphite  is  a  white  precipitate;  and  copper 
phosphite,  Cll(HPO3).2H2O,  forms  sparingly  soluble  blue  crystals  ; 
when  boiled,  metallic  copper  is  precipitated. 

All  these  phosphates  decompose  when  heated,  evolving  hydro- 
gen and  a  little  hydrogen  phosphide,  and  leaving  a  phosphate. 

It  is  stated  that  when  the  compound  2HNa(HPO3).5H2O  is 
heated  to  160°  it  loses  six  molecules  of  water,  forming  a  pyrophos- 
phite,  Na2H2P2O5.*  Data  concerning  the  phosphites  are  exceed- 
ingly meagre,  and  the  whole  series  of  salts  requires  reinvestigation. 

*  Comptes  rend.,  106,  1400. 


378      THE   OXIDES,    SULPHIDES,    SELENIDES,   AND   TELLURIDES. 

Some  oxythiophosphites*  have  been  prepared  by  the  action  of 
a  solution  of  sodium  hydroxide  on  phosphorus  trisulphide  (pre- 
sumably P4S3).  Hydrogen,  mixed  with  hydrogen  phosphide,  is 
evolved,  and  on  evaporation  crystals  are  deposited  of  the  composi- 
tion Na4P2O3S2.6H2O,  analogous  to  a  pyrophosphite.  With  sodium 
hydrosulphide,  NaSH,  hydrogen  phosphide  and  sulphide  are  evolved, 
and  the  solution,  evaporated  in  a  vacuum,  deposits  crystals  of 
Na4P2OS4.6H2O.  These  crystals  lose  hydrogen  sulphide  at  the 
ordinary  temperature,  probably  forming  the  salt  previously  men- 
tioned. With  ammonium  hydrosulphide,  crystals  of  the  formula 
(NH4)4P2S5.3H2O  are  deposited,  which,  when  dried  at  100°  in  a 
current  of  hydrogen  sulphide  lose  hydrogen  sulphide,  giving  the 
compound  (NH4)4P2O3S3.2H2O. 

From  the  mother  liquor  of  these  crystals  the  compound 
(NH4)4P2O3S2.2H2O,  analogous  to  the  potassium  salt  has  been 
obtained.  Solutions  of  these  salts  when  boiled  lose  hydrogen  sul- 
phide, and  yield  phosphites. 

Arsenites  and  thioarsenites. — KAsO2  and  NH4AsO2  are 
white  soluble  salts,  produced  by  dissolving  arsenious  oxide  (As406) 
in  caustic  potash  or  ammonia.  They  are  apparently  metarsenites. 
By  similarly  treating  arsenic  trisulphide  with  potassium  sulphide, 
either  by  solution  or  by  fusion,  the  corresponding  thioarsenite, 
KAsS2,  is  produced.  It  decomposes  when  treated  with  warm  water. 

By  adding  alcohol  to  a  solution  of  a  large  amount  of  arsenic 
trioxide  in  caustic  potash,  the  pyroarsenite,  H3KAs2O5,  is  produced. 
When  digested  with  caustic  potash,  the  salt  K4As2O5  is  formed,  and 
may  be  precipitated  with  alcohol.  A  similar  ammonium  salt  is 
produced  by  direct  addition,  (NH4)4As2O5.  The  sodium  salts  are 
all  very  soluble,  and  have  not  been  isolated.  The  corresponding 
pyrothioarsenites  are  unknown;  but  orthothioarsenites  of  potas- 
sium and  ammonium,  K3AsS3  and  (NH4)3AsS3,  are  precipitated  on 
adding  alcohol  to  a  solution  of  arsenic  trisulphide  in  excess  of 
colourless  ammonium  sulphide. 

Ca(AsO2)2;  Ca2As2O5;  Ca3(AsO3)2;  Sr(AsO2)2;  Ba(AsO2)2;  Ba2As2O5.4H2O ; 

H4Ba(As03)2. 

These  are  white  sparingly  soluble  salts,  produced  by  addition 
of  arsenious  oxide  to  the  hydroxides,  or  arsenites  of  potassium  or 
ammonium  to  salts  of  the  metals. 

Corresponding  to  these  are  Ca3(AsS3)a.l5H3O  ;  Ba2As2S3 ;  and 
Ba3(AsS3)2 ;  they  are  soluble  substances  precipitated  by  alcohol. 

*   Comptex  rend.,  93,  489  ;  98,  43. 


THE   ARSENITES   AXD   AXTLMOXITES.  379 

Mg;3(AsO3)2 ;  MgHAsO. ;  Mg,As,O3 ;  Mg,As,S5 ;  and  Zn2As.2S5 
are  produced  by  double  decomposition. 

Arsenites  of  the  boron,  and  ahi minium  groups  have  not  been 
prepared. 

Various  basic  arsenites  of  iron  are  known.  These  are  insoluble, 
and  are  produced  by  addition  of  a  ferric  salt  and  an  alkali  to 
solutions  of  arsenious  oxide,  and  for  this  reason  a  mixture  of  ferric 
hydrate  and  magnesia  is  employed  as  an  antidote  in  cases  of  arsenical 
poisoning.  Among  these  are  FeAsO3.Fe2O3;  2PeAsO3.Fe2O3.7H2O, 
and  5H,O. 

Ferrous  pyroarsenite,  Pe^A^Og,  is  a  greenish  precipitate ; 
Mn3H6(AsO3)4.H,O  and  Co3H6(AsO3)4.H2O  are  rose-red  precipi- 
tates ;  the  corresponding  nickel  salt,  Ni3H6(AsO3)4.H2O,  is  a 
greenish- white  precipitate  which  yields  Ni3(AsO4)2  on  ignition. 
The  sulpharsenites  of  these  metals  are  all  pyro-derivatives,  viz., 
FeoAs,S5,  Mn,As2S5,  Co2As,S5,  and  Ni2As2S5. 

Stannous  and  stannic  arsenites  and  sulpharsenites  have  been 
prepared,  but  not  analysed.  The  three  lead  arsenites,  Pb(AsO2)2, 
PboASoOa,  and  Pb3(AsO3)2,  are  all  white  precipitates.  The  com- 
pound Pb(AsS2)2  is  a  mineral  named  sartorite ;  Pb2As2S5  is 
named  duj'renoysite,  and  Pb3(AsS3}>,  guittermannite.  All  these  are 
crystals  with  metallic  lustre,  and  occur  native. 

The  arsenite  of  hydrogen  and  copper,  HCuAsO3,  is  obtained 
by  adding  to  a  solution  of  copper  sulphate  a  solution  of  potassium 
arsenite,  a  solution  of  arsenious  oxide,  and  a  small  amount  of 
ammonia.  It  is  a  fine  green  powder,  and  is  named,  from  its  dis- 
coverer, "  Scheele's  green."  The  arsenite  Cu(AsO2)2  is  produced 
by  digesting  copper  carbonate  with  arsenious  oxide  and  water. 

Copper  sulpharsenite,  Cu2As>S5,  is  formed  by  precipitation; 
and  some  minerals  exist  which  appear  to  be  compounds  of  copper 
sulpharsenite  and  sulphide,  e.g.,  Cu4AsS4,  julianite,  Cu6As4S9,  bin- 
nite,  and  011^82 S7,  tennantite. 

Silver  arsenite,  Ag3AsO3,  is  a  yellow  precipitate  produced  by 
adding  to  silver  nitrate  a  solution  of  arsenious  oxide  in  ammonia. 
It  is  soluble  in  excess  of  ammonia.  It  serves,  along  with  Scheele's 
green,  as  a  distinctive  test  between  arsenious  and  arsenic  oxides ; 
it  will  be  remembered  that  copper  arsenate  is  blue,  and  silver, 
arsenate  red.  The  corresponding  sulpharsenite,  Ag3AsS3,  occurs 
native  as  proustite ;  and  the  mineral  xanthoconate,  AggASgSjo 
appears  to  be  a  double  sulpharsenite  and  sulpharsenate  of  silver. 

Only  two  antimonites  are  known,  viz.,  NaSbO2.3H2O,  which 
forms  octahedra,  and  is  obtained  by  dissolving  antimonious  oxide, 
(Sb4O6)  in  caustic  soda ;  and  an  acid  compound,  NaSbO2.2HSbO2, 


— ..  »  ««>  «a  vi  r*  T  m 


380      THE   OXIDES,    SULPHIDES,    SELENIDES,   AND   TELLUKIDES. 

similarly  prepared.  The  corresponding  thioantimonite,* 
NaSbS2,  separates  on  addition  of  alcohol  to  a  solution  of  Sb2S3  in 
sodinm  hydroxide  ;  and  copper-coloured  crystals  of  2NaSbS2.H2O 
deposit  from  a  concentrated  solution  of  the  same  substances.  Many 
sulphantimonites  occur  native;  among  them  are  Fe(SbS2)2, 
berthierite  ;  Pb(SbS2)2,  zinkenite;  Pb2Sb2S5,  jamesonite ;  Pb3Sb2S6, 
boulangerite;  Pb,iSb2S7,  meneghinite ;  PbsSb2S8,  geocronite;  CuSbS2, 
chalcostiUte ;  Cu2Sb4S7,  guejarite;  CuPbSbS3,  lournonite;  Ag3SbS3, 
pyrargyrite ;  AgSbS2,  miargyrite ;  Ag5SbS4,  stepJianite ;  Ag9SbS6, 
polybasite;  and  Hg(SbS2)2,  livingstonite.  Besides  these,  similar  com- 
pounds of  bismuth  are  known,  e.g.,  AgBiS2,  silver  bismuth  glance; 
Pb(BiS2)2,  galenobismuthite  ;  Pb2Bi2S6,  cosalite  ;  Pb6Bi2S9,  beeger- 
ite  ;  CuBiSo,  emplectite ;  Cu3BiS3,  wittichenite ;  and  others.  These 
double  sulphides  of  bismuth  have  not  been  made  artificially ;  but 
the  compound  KBiS2,  produced  by  fusing  bismuth  with  sulphur 
and  sodium  carbonate,  forms  steel-grey  shining  needles. 

Hypophosphites.f— Hydrogen  hypophosphite,  H3P02,  is  a 
monobasic  acid ;  and  it  is  therefore  concluded  that  its  constitution  is 
somewhat  analogous  to  that  of  phosphorous  acid,  inasmuch  as  it 
may  be  regarded  as  a  hydroxyl-derivative  of  an  oxidised  hydrogen 
phosphide,  thus,  0=P(OH)H2.  It  is  only  the  hydrogen  of  the 
hydroxyl  which  can  be  replaced  by  metals.  The  anhydride  of 
such  an  acid  would  not  be  the  oxide  P2O,  but  the  unknown  com- 
pound 0=PH2— O— PH2=O  =  H4P203.  Such  a  body  might  be 
expected  to  be  devoid  of  acid  properties. 

Hypophosphorous  acid,  H3PO2,  is  produced  by  decomposing 
a  solution  of  the  barium  salt,  Ba(H2P02)2,  with  its  equivalent  of 
sulphuric  acid.  The  dilute  solution  is  boiled  down,  and  finally 
evaporated  at  105°,  the  temperature  being  gradually  raised  to  130°. 
It  is  then  cooled  to  0°,  and  on  shaking  it  crystallises.  It  melts  at 
17'4°.  When  heated,  it  decomposes  into  phosphoric  acid  and 
hydrogen  phosphide,  thus  : — 

2H3P02  =  H3P04  +  PH3. 

It  yields  salts  on  neutralisation  with  hydroxides  or  oxides. 
But  sodium,  potassium,  and  barium  hypophosphites  are  easily  pre- 
pared by  boiling  phosphorus  with  their  hydroxides.  The  hydrogen 
phosphide  which  is  evolved  is  spontaneously  inflammable,  owing 
to  its  containing  a  trace  of  liquid  hydride,  P2H4.  The  reaction  is  : — 
4P  +  3KOH.Aq  +  3H20  =  PJT3  +  3KH2P02.Aq. 

*  See  also  Ditte,  Comptes  rend.,  102,  168,  for  pyrothioantimonites. 
f  Rammelsberg,  Chem.  Soc.,  26,  1. 


HYPOPHOSPHITES.  381 

It  is  from  the  barium  salt,  thus  prepared,  that  the  acid  is 
obtained. 

Hypophosphites. 

LiH.,P02.HoO  ;  NaH2P02.H20  ;  KE^PO*  ;  (NH^B^PO,,. 

These  salts  are  white  crystalline  bodies,  produced  as  described. 
Those  containing  water  may  be  rendered  anhydrous  at  200°.  They 
decompose,  when  more  strongly  heated,  as  follows  :  — 

5NaH2PO2  =  Na4P2O7  +  NaPO3  +  2PH3  +  2HZ. 
The  ammonium  salt  undergoes  a  different  change,  thus  :  — 
7NH4H2PO2  =  H4P2O7  +  2HPO3  +  H20 


White  soluble  salts.     When  heated  they  decompose,  thus  :  — 
7Sr(H2PO,)3  =  3Sr2P2O7  +  Sr(PO3)2  +  6PH3  +  H20  +  4H2. 

Mg(H2PO2)2.6H2O  ;  Zn(H2PO2)2.6H2O  ;  and  Cd(H2PO2)2. 

These  are  also  soluble  crystalline  salts,  which  can  be  dried  at 
200°.     When  heated  they  decompose,  thus  :  — 

5Zn(H2PO2)2  =  2Zn2P2O7  +  Zn(PO3)2  +  4P#3  +  4£T2. 

Aluminium  and  chromium  hypophosphites  are  gummy  solids  ; 
the  ferric  salt  is  a  white  sparingly  soluble  powder  (?). 


Fe(H2P0.2).6H20  ; 

The  ferrous  salt  has  been  prepared  by  dissolving  iron  in  the 
acid  ;  the  others  by  neutralisation.  They  can  be  dried  at  200°.  They 
are  all  crystalline  and  soluble.  They  change  thus,  when  heated  :  — 

6Co(H2PO2)2  =  4Co(PO3)2  +  2CoP  +  2PH3  +  9^. 

Pb(H2PO2)2  is  crystalline  and  sparingly  soluble;  when  heated, 
it  decomposes,  thus  :  — 

9Pb(H2PO2)2  =  4Pb2P2O7  +  Pb(PO3)2  +  8PH3  +  2HZ0  +  4ff2. 

Thallous  hypophosphite,  T1H2PO2,  forms  soluble  white  crystals. 
It  decomposes  like  the  sodium  salt  when  heated.  The  uranyl  salt, 
UO2(H2PO2)2.H2O,  is  a  sparingly  soluble  yellow  crystalline  salt. 

Like  the  phosphites,  the  hypophosphites  possess  great  power 
of  reduction  ;  the  reaction,  for  example,  with  silver  nitrate,  is 
Ba(H2P02)2.Aq  +  6AgN03.Aq  +  4H20  =  2H3P04.Aq  +  4HN03.Aq 
-r  Ba(N03)2.  Aq  +  6Ag  +  Hz.  The  free  hydrogen  further  reduces  the 


382      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLUKIDES. 

nitric  acid.  With  solutions  of  cupric  salts,  cuprous  salts  are  first 
produced,  and  then  a  reddish  precipitate  of  copper  hydride,  CuH, 
is  formed.  Hypophosphorous  acid  also  withdraws  oxygen  from 
sulphur  dioxide,  liberating  sulphur. 

Double  compounds  with  halogens.  —  With  phosphorus, 
compounds  of  the  type  POC13  are  best  known. 

Arsenic  forms  only  one  compound  of  this  nature,  viz., 
AsOF3.KF.H2O  ;  its  characteristic  compound  is  AsOCl  ;  and 
antimony  and  bismuth  resemble  arsenic;  the  compound  SbOCl3 
is,  however,  known. 


POFS  ;  PSF^  j  POC13  ;  PSC13  ;  POBr3  ;  PSBr3  ;  POCl2Br  ;  PSCl2Br. 
SbOCl3;  SbSCl3. 

These  compounds  have  the  formulae  assigned,  inasmuch  as  their 
vapour-  densities  have,  in  almost  all  cases,  been  determined.  Their 
constitution  is,  without  doubt,  analogous  to  0=PEEC13;  and  it  will 
be  remembered  that  when  treated  with  water  or  alkalies  they  give 
rise  to  orthophosphoric  or  orthothiophosphoric  acid.  The  corre- 
sponding antimony  compound,  SbOCl3,  on  treatment  with  water, 
yields  the  more  stable  pyrantimonic  acid,  H4Sb2O7.2H2O. 

POF3,  phosphoryl  trifluoride,  is  a  colourless  gas,  liquid  at 
—  50°,  or  at  16°  under  a  pressure  of  15  atmospheres.  By  evapora- 
tion of  the  liquid  a  portion  solidifies  to  a  snow-like  solid.  It  is 
produced  by  direct  combination  of  phosphorus  trifluoride  and 
oxygen,  which  takes  place  with  explosion  on  passing  a  spark 
through  the  mixed  gases.  It  is  more  easily  produced  by  distilling 
powdered  cryolite,  AlF3.3NaP,  with  P2O5. 

PSFs,  the  corresponding  sulphur  compound,  is  a  spontaneously 
inflammable  gas,  liquefying  under  pressure  of  10'3  atmospheres  at 
13  '8°.  It  is  best  prepared  by  heating  a  mixture  of  phosphorus 
pentasulphide  and  lead  fluoride,  thus  :  — 

P2S5  +  5PbP2  =  5PbS  +  2PF,  ;  and  3PF5  +  P2S5  =  5PSF3. 

The  density  of  this  gas  shows  that,  like  the  other  similar  com- 
pounds, it  cannot  be  regarded  as  the  compound  3PF6.PzS6t  but  as 
the  simpler  body  P!SF3. 

POC13,  phosphoryl  trichloride,  is  produced  by  the  action  of 
water  on  the  pentachloride,  thus  :  — 

PC15  +  H20  =  POC13  +  2JET0Z  (see  p.  353). 

But,  as  it  quickly  reacts  with  water,  it  is  convenient  to  use  com- 
bined water,  in  the  form  of  boracic  acid,  H3BO3,  in  its  formation. 
It  is  easily  obtained  by  distilling  a  mixture  of  phosphorus  penta- 


OXY-    AND    SULPHO-HALIDES   OF   PHOSPHORUS.  383 

chloride  and  boracic  acid  in  theoretical  proportions.  It  can  also 
be  produced  by  heating  together  the  pentachloride  and  pentoxide 
of  phosphorus,  thus  : — 

3PC15  +  P,05  =  5POC13, 

It  is  a  colourless  liquid,  heavier  than  water  (1'7),  boiling  at  110°. 
It  fumes  in  the  air,  forming  phosphoric  and  hydrochloric  acids. 
It  may  be  solidified,  and  melts  at  2*5°.  It  combines  with  some 
other  chlorides,  forming,  for  example  : — 

POC13.BC13  ;  a  white  solid,  melting  at  1]°. 

POC13.A1C13 ;  a  white  solid,  melting  and  boiling  without  decomposition  (?). 

POCl3.M:g-C1.2 ;  a  white  solid,  decomposed  when  heated. 

POCLj.ZnCLj;  white  rhombic  crystals. 

POCl3.SnCl4 ;  a  liquid,  boiling  at  180°. 

It  also  forms  gelatinous  compounds  with  sodium  and  potassium 
chlorides. 

PSC13,  sulphophosphoryl  trichloride,  is  also  a  colourless 
fuming  liquid,  heavier  than  water,  boiling  at  124'25°.  It  could 
doubtless  be  prepared  by  heating  phosphorus  pentachloride  with 
pentasulphide ;  but  it  is  more  readily  obtained  by  the  action  of 
hydrogen  sulphide  on  phosphoryl  trichloride,  thus  : — POC13  +- 
#2$  =  PSC13  +  H20 ;  or  by  distilling  phosphoric  chloride  with 
antimony  trisulphide,  thus  : — 

6PC15  +  5Sb2S3  =  3P2S5  +  10SbCls ;  and 
3PC15  +  P2S5  =  5PSC13. 

The  easiest  method  of  preparation  is  to  distil  phosphorus  with 
sulphur  chloride,  S2C12 ;  the  reaction  is  : — 

2P  +  3S2C12  =  4S  +  2PSC13. 

A  compound  of  this  body,  with  sulphur  dichloride,  PSC13.SC12, 
is  produced  by  the  action  of  sulphur  on  phosphoric  pentachloride. 
It  is  a  colourless  liquid,  boiling  at  100°.  Its  molecular  weight  has 
not  been  determined. 

POBr3  and  PSBr3  are  crystalline  solids,  similarly  prepared. 
The  former  melts  at  45°  and  boils  at  195°  ;  the  latter  is  yellow,  and 
cannot  be  distilled  without  partial  decomposition.  POCl2Br  and 
PSCl2Br  are  also  known. 

Analogous  compounds  of  arsenic  are  unknown  ;  but  two  com- 
pounds of  arsenyl  fluoride,  of  the  formulae  AsOF3.KF.H2O  and 
AsOFj.AsF5.4KF.3H2O,  have  been  prepared  by  treating  arsenate 
of  potassium  with  much  hydrofluoric  acid.  They  are  colourless 
crystalline  bodies. 


3S4      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

Antimonyl  trichloride,  SbOCl3,  is  produced  by  the  action 
of  a  trace  of  water  on  the  pentachloride,  SbCl5.  Another  state- 
ment is  that  this  body  has  the  formula  SbCl5.H20  ;  it  might  well 
be  SbOCl3.2HCl.  It  crystallises  from  chloroform.  The  corre- 
sponding compound  SbSCl3  forms  white  crystals ;  it  is  produced 
by  the  action  of  hydrogen  sulphide  on  the  pentachloride.  It  is 
said  to  decompose  when  heated  into  SbCl3  aud  S2C12  (?). 

Pyrophosphoryl  chloride,  P203C14,  corresponding  to  pyro- 
phosphoric  acid,  P203(OH)4,  has  been  produced  by  the  action  of 
nitrogen  tetroxide,  N204,  on  phosphorus  trichloride.  It  is  a  colour- 
less liquid,  boiling  between  210°  and  215°.  On  treatment  with 
water  it  yields  orthophosphoric  acid.  Pyrosulphophosphoryl 
bromide  is  produced  by  dissolving  phosphorus  trisulphide,  P2S3  (a 
mixture  ?),  in  carbon  disulphide,  and  adding  the  necessary  quantity 
of  bromine.  The  carbon  disulphide  is  distilled  off,  and  the  residue 
is  extracted  with  ether,  which  dissolves  the  compound  P2S3Br4.  A 
light  yellow  oily  liquid  remains  on  evaporating  the  ether.  When 
heated  with  phosphorus  pentabromide,  this  substance  yields  the 
orthosulphophosphoryl  bromide,  PSBr3 ;  and  when  distilled  alone, 
the  compound  P2SBr6,  which  may  be  regarded  as  corresponding  to 
the  unknown  thiodiphosphoric  acid,P2S(OH)6,  with  hydroxyl  re- 
placed by  bromine  (see  p.  353). 

This  substance  is  a  white  solid,  melting  at  —5°  to  a  yellow 
liquid. 

Metaphosphoryl  chloride,  P02C1,  is  said  to  have  been 
obtained  by  heating  in  a  sealed  tube  for  six  hours  a  mixture  of 
phosphorus  pentoxide  and  phosphoryl  trichloride,  thus  : — 

P2O5  +  POC13  =  3P02C1. 

It  is  a  viscid  colourless  substance.  The  corresponding  sulpho- 
phosphoryl  bromide,  PS2Br,  is  the  insoluble  residue  after  dissolving 
out  the  compound  P2S3Br4  with  ether  (see  above).  The  analogous 
metantimonyl  chloride,  SbO2Cl,  is  produced  by  the  action  of  much 
water  on  SbCl5. 

No  chlorine  derivatives  of  the  oxide  or  sulphide,  P203  or  P2S3, 
are  known.  But  the  bismuth  haloid  compounds  and  almost  all 
those  of  arsenic  and  antimony  are  thus  composed. 

Arsenosyl  chloride,  or  arsenyl  monochloride,  AsOCl,  is 
a  hard  white  translucent  fuming  solid,  formed  by  the  action  of  a 
small  amount  of  water  on  arsenic  trichloride.  It  forms  the  follow- 
ing compounds : — 

AsOCl.As.jO.,  ;  AsOCl.NH4Cl ;  and  AsOCl.H2O. 


OXYHALIDES   OF  ARSENIC,   ANTIMONY,   AND   BISMUTH.          385 

The  last  of  these  may  be  viewed  as  orthoarsenious  acid,  with  one 
hydroxyl  gronp  replaced  by  chlorine,  thus  : — As(OH)2Cl.  Arsen- 
osyl  bromide,  AsOBr,  is  a  brown  waxy  solid  similarly  prepared. 
It  forms  the  compound  2AsOBr.3H2O,  which  may  perhaps  be  con- 
ceived as  As2O(OH)2Br2.2H20,  a  derivative  of  pyroarsenkms  acid, 
two  hydroxyl  groups  being  replaced  by  bromine. 

By  similarly  treating  arsenic  tri-iodide  with  water,  the  com- 
pound AsOI.As4O6  crystallises  out  in  thin  plates. 

Sulpharsenosyl  iodide,  AsSI,  is  said  to  be  formed  by  the  action 
of  iodine  on  arsenic  trisulphide;  and  on  addition  of  powdered 
arsenic  to  a  solution  of  sulphur  and  bromine  in  carbon  disulphide, 
the  compound  AsSBr.SBr,  separates  in  dark-red  crystals. 

Antimony  trifluoride,  SbF3,  deliquesces  on  exposure  to  moist 
air,  forming  the  compound  3SbOF.SbF3;  and  bismuth  oxyfluoi id  j, 
BiOF,  remains  as  a  white  powder  on  heating  the  crystalline  com- 
pound BiOF.2HF,  obtained  by  the  action  of  concentrated  hydro- 
fluoric acid  on  bismuthous  oxide,  Bi2O3. 

Antimonosyl  chloride,  SbOCl,  and  bismuth  oxyehloride, 
BiOCl,  are  produced  by  the  action  of  water  on  the  trichlorides 
SbCl3  and  BiCl3.  The  former  is  obtained  in  crystals  by  mixing 
10  parts  of  the  trichloride  with  17  of  water,  and,  after  allowing  to 
stand  for  some  days,  filtering,  and  washing  the  precipitate  with 
ether.  The  corresponding  bismuth  compound  is  used  as  a  pigment 
and  cosmetic  under  the  name  "  pearl-white."  When  heated  in  air, 
it  changes,  giving  the  body  3BiOC1.2Bi2O3.  Many  other  com- 
pounds are  produced  by  the  action  of  water  on  antimony  tri- 
chloride ;  among  these  are — 

SbOC1.7SbCl3  ;  2SbOClSb2O3;  20SbOC1.10Sb:2O3  SbCl3,  &c. 
These   bodies   all   dissolve  in  concentrated  hydrochloric  acid, 
giving  the  trichloride. 

Similar  bromides  are  known,  similarly  prepared ;  for  instance — 

2SbOBr.Sb.,O3  ;  20SbOBr.lOSb.,O3  SbBr3 ;  BiOBr  ;  7BiOBr.2Bi2O3. 
SbOI ;  2SbOI.Sb.2O3  ;  ~BiOI ;  and  3BiOI.4Bi2O3. 

Compounds  of  sulphantimonosyl  chloride  are  also  known,  pro- 
duced by  the  action  of  the  trichloride  on  trisulphide  of  antimony. 
Crystals  of  SbSCl.SbCl3  are  produced,  and  on  washing  them  with 
alcohol,  2SbSC1.3Sb2S3  remains. 

Sulphantimonosyl  iodide,  SbSI,  is  the  product  of  the  action  of 
antimony  tri-iodide  on  the  trisulphide ;  it  is  a  brown-red  powder ; 
when  boiled  with  zinc  oxide  and  water,  the  oxysulphide,  Sb2OS2,  is 
formed. 

2  c 


386      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

The  compounds  BiSCl  and  BiSI  are  similarly  produced  ;  and 
a  selenochloride,  BiSeCl,  is  formed  as  steel -grey  nee  die- shaped 
crystals  on  adding  bismuth  triselenide,  Bi2Se3,  to  molten 
BiCl3.2NH4Cl. 

No  halogen  compounds  derivable  from  or  connected  with  hypo- 
phosphorous  acid  are  known ;  dry  hydrogen  iodide  acts  on  that 
acid  violently,  producing  phosphorous  acid  and  phosphonium 
iodide  (see  p.  517),  thus  : — 

3H3P02  +  HI  =  2H3P03  +  PH4I. 


Physical  Properties. 

Mass  of  1  cubic  centimetre — 

P2O5,  2-387  ;  As4O6  (amorphous),  374  ;   (crystalline)  370. 
As2O5,  4'0;  Sb4O6  (octahedral),  511  ;   (prismatic)  572. 
Sb205,  378;  Sb204,  4'07  ;  Bi2O5,  5'1  ;  Bi2O4,  5'6  ;  Bi2O3,  8'08. 
P4S3,  2-00  ;  As2S2,  3-55  ;  As2S3,  3'45  ;  Sb2S3,  4'22  ;   (stibnite)  4'6. 

Bi2S3,  7-00. 

As2Se3,  475  ;  Bi2Se3,  6 '25  ;  Sb2Te3,  6  5  ;  Bi2Te3,  7'23— 7'94. 
POC13,  1711  at  0°:  P2O3C14,  1-58  at  7°;  Sb4O5Cl2,  5'0;  BiOCl,  7'2. 
POBr3,  2-82 ;  PSBr3,  2'87 ;  AsSBr3,  279  ;  BiOBr,  670  at  20°. 

Heats  of  formation — 

P  =  P  -  T51K.      2P  +  50  =  P205  +  3700K  +  Aq  =  2H3PO4.Aq  + 

360K. 

2P  +  30  +  Aq  =  2H3PO3.Aq  +  2   x   1252K. 
2P  +   O  +  Aq  =  2H3PO2.A.q  +  2  x   373K. 

P  +  O  +  3CI  =  POC13  +  1460K  ;  P  +  O  +  3Br  =  POBr3  +  1056K. 
2As  +  5O  =  As205  +  2194K  ;    +  Aq  =  60K. 
2As  +  30  =  As2O3  +  1547K;    +  Aq  =-7GK. 
2Sb  4-  50  +  3H2O  =  2H3Sb04  +  2  x   1144K. 
2Sb  +  30  =  Sb2O3  +  IGtiOK.     Sb  +   0  +  Cl  =  SbOCl  +  897K. 
2Bi  -4-  30  -r  3H2O  =  2H3BiO3  +  2   x   691K ;  Bi  +   O  +  Cl  = 
BiOCl  +  882K. 


387 


CHAPTER  XXV. 

OZONE  (OXIDE  OF  OXYGEN). — OXIDES,  SULPHIDES,  SELENIDES,  AND  TEL- 

LURIDES  OF  MOLYBDENUM,  TUNGSTEN,  AND  URANIUM. MOLYBDATES, 

TUNGSTATES,   AND    UEANATES. SULPHOMOLYBDATES,    ETC. — OXYHA- 

LIDES. 

Ozone. 

Ozone. — It  has  long  been  known  that  oxygen  throngh  which 
electric  sparks  have  been  passed  acquires  a  peculiar  smell,  and  acts 
rapidly  on  mercury.  This  behaviour  is  due  to  the  conversion  of 
the  oxygen  into  an  allotropic  modification,  to  which  the  name 
ozone  (from  o£eii>,  to  smell)  has  been  given.*  In  this  instance 
the  molecular  weight  is  known,  and  consequently  the  formula  of 
ozone,  03;  and  it  appears  advisable,  therefore,  to  regard  it  as  an 
oxide  of  oxygen.  It  is  true  that  ordinary  oxygen,  which  possesses 
the  molecular  formula  02,  might  also  thus  be  regarded ;  but,  inas- 
much as  ozone  is  the  only  allotropic  modification  of  an  element 
(except  perhaps  sulphur  gas  at  a  low  temperature,  which  may 
possess  the  formula  Ss)  which  is  fairly  stable  and  possesses  a  known 
molecular  weight  at  the  ordinary  temperature,  it  has  been  given  a 
prominent  position. 

Sources. — Ozone  occurs  in  small  amount  in  the  atmosphere, 
especially  of  the  country.  It  may  be  recognised  by  its  power  of 
turning  red  litmus  paper  soaked  in  a  solution  of  potassium  iodide 
blue,  owing  to  the  liberation  of  potassium  hydroxide  (see  below). 
Country  air  contains  at  most  about  one  seven-hundred-thousandth 
of  its  volume  of  ozone.  It  appears  to  contain  more  ozone  in  spring 
than  in  summer,  and  more  in  summer  than  in  autumn  or  winter ; 
and  it  is  more  abundant  on  rainy  than  on  fine  days.  Its  presence 
appears  also  to  be  favoured  (in  the  northern  hemisphere)  by  west 
or  south-west  winds ;  and  its  existence  has  been  shown  to  be 
largely  dependent  on  the  prevalence  of  atmospheric  electricity,  for 
its  amount  is  greatly  increased  during  and  after  thunderstorms. 
Its  presence  in  country  air  in  greater  amount  than  in  town  air  may 

*  Schonbein,  Pogg.  Ann.,  50,  616 ;  Andrews,  Chen.  Soc.  J.t  0,  168. 

2  C  2 


388      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

be  due  to  the  fact  that  the  oxygen  evolved  from  plants  contains 
small  traces  of  ozone,  and  that  in  the  neighbourhood  of  towns  the 
ozone  is  destroyed  by  its  action  on  organic  particles,  and  on  the 
sulphurous  acid  produced  during  the  combustion  of  coal. 

Preparation. — Ozone  is  formed,  as  mentioned  above,  by  the 
passage  of  electric  sparks  through  oxygen  ;  and  it  is  also  pro- 
duced during  the  oxidation  by  free  oxygen  of  various  substances, 
such  as  phosphorus  in  contact  with  water,  ether  vapour,  benzene 
and  other  hydrocarbons,  and  also  by  the  combustion  of  hydrogen  ; 
by  the  action  of  sulphuric  acid  on  barium  dioxide,  potassium  per- 
manganate, and  other  substances  which  evolve  oxyg-en  in  the  cold 
on  being  thus  treated;  and,  lastly,  by  the  electrolysis  of  dilute 
sulphuric  acid.  It  is  never  obtained  pure.  By  the  first  process  a 
quarter  of  the  oxygen  present  has  been  converted  into  ozone,  but 
by  the  other  processes  a  much  smaller  proportion  undergoes 
change. 

These  processes  of  formation  may  be  illustrated  as  follows : — 

1.  By  slow  oxidation. — (a.)  A  few  sticks  of  pho°phorus  are  placed  in  a 
large  bottle  and  partly  covered  with  water.     After  standing  for  about  an  hour, 
the  air  in  the  bottle  is  aspirated  through  a   (J'tu^e  containing  a  solution  of 
potassium  iodide  mixed  with  a  little  boiled  starch.     The  solution  will  turn  blue 
owing  to  the  liberation  of  iodine  and  the  formation  of  blue  iodide  of  starch. — 
(5.)  A  few  drops  of  ether  are  poured  into  a  large  dry  beaker,  covered  with  a 
plate,  and  the  beaker  is  shaken  so  as  to  mix  the  ether  vapour  with  the  air.    The 
gaseous  mixture  is  then  stirred  with  a  glass  rod  heated  over  a  flame  till  too  hot 
to  touch.     On  pouring  a  little  solution  of  potassium  iodide  and  starch  into  the 
beaker  and  shaking,  a  blue  colour  will  be  produced.     It  has  been  observed  that 
this  reacl ion  is  also  shown  by  the  air  in  a  bottle  containing  a  little  petroleum, 
frequently  opened  and  shaken,  especially  if  it  has  been  exposed  to  sunshine  for  a 
few  days. 

2.  During-  combustion. — If  a  small  jet  of  hydrogen  be  burned  below  a 
funnel,  and  the  products  be  drawn  through  a  solution  of  potassium  iodide  and 
starch,  the  blue  colour  is  produced ;  but,  besides  ozone,  hydrogen  peroxide  and 
ammonium  nitrite  are  produced,  both  of  which  have  the  property  of  liberating 
iodine  from  such  a  solution.     The  method  of  distinguishing  these  bodies  from 
ozone  is  described  below. 

3.  Dilute  sulphuric  acid,  electrolysed  by  eight  Grove  cells,  each  electrode 
consisting  of  six  thin  platinum  wires,  yields  oxygen  rich  in  ozone.     In  one  ex- 
periment at  9°,  about  one  quarter  of  the  oxygen  collected  was  in  the  form  of 
ozone.     Persu'phuric  acid  is  also  formed  in  the  liquid  by  this  process. 

4.  The  most  convenient  method  of  producing  ozone  is  by  the  passage  of  the 
"silent  discharge"  through  oxygen.     This  "  silent  discharge  "  appears  to 
consist  of  a  rain  of  small  sparks,  and  is  best  produced  between  two  surfaces  of 
glass  placed  very  near  each  other,  with  conducting  coatings  on  their  exterior 
surfaces.     A  KuhmkorfC  coil  or  an  electrical  machine  may  be  used  as  a  source 
of  the  electricity  of  the  high  potential  required.     The  apparatus,  of  which  a 


OZONE. 


389 


cut  is  given  in  fig.  41,  serves  well  for  the  purpose,  and  by  its  means  the  rela- 
tion between  the  alteration  in  volume  of  the  oxygen  during  conversion  into 
ozone  and  the  volume  of  the  ozone  produced  may  be  shown.  It  consists  of  a 


FIG.  41. 

wide  glass  tube,  standing  on  a  foot,  and  constricted  about  2  inches  from  its 
lower  end.  At  its  lower  end  a  paraffined  cork,  or  a  glass  stopper  lubricated  with 
vaseline,  is  inserted  in  the  tubulus,  and  on  the  opposite  side  to  the  tubulus  a 
vertical  tube,  provided  with  a  stopcock,  ending  in  a  (J-^be,  is  sealed  on.  A 
narrower  tube,  which  should  fit  the  wider  one  very  closely,  but  without  touching, 
is  sealed  through  its  upper  end.  At  the  top  of  the  wide  tube  a  gauge,  like 
that  shown  in  the  figure,  is  attached  by  sealing.  The  outer  tube  is  covered  with 
tinfoil  where  it  surrounds  the  inner  tube. 

As  ozone  is  destroyed  by  grease,  the  stopcock  should  be  lubricated  with  vase- 
line, and  no  india-rubber  connections  should  be  placed  in  contact  with  ozone, 
for  it  at  once  attacks  india-rubber. 

To  illustrate  the  formation  of  ozone  with  this  apparatus,  a  slow  current  of 
oxygen  is  passed  through  the  tube,  entering  through  the  gauge-tube,  which  should 
contain  no  liquid.  A  platinum  wire  connected  with  one  pole  of  a  coil  is  dipped 
in  dilute  sulphuric  acid  contained  in  the  inner  tube,  while  the  outer  coating 
of  tinfoil  is  connected  with  the  other  pole  of  the  coil.  The  JJ-tUDe  having  been 
filled  with  a  solution  of  potassium  iodide  and  starch,  a  blue  colour  is  produced 
as  soon  as  the  current  passes.  The  characteristic  smell  may  be  noticed  before 
the  solution  is  poured  into  the  U'^UDe- 

Properties. — At  ordinary  pressure  and  temperature,  ozone  is  a 
gas,  colourless  in  thin  layers;  but  by  looking  through  a  tube 
several  metres  in  length,  filled  with  ozonised  oxygen,  it  is  seen  to 
have  a  blue  colour.  When  compressed,  this  blue  colour  becomes 
more  apparent,  and  at  low  temperatures  it  increases  in  intensity. 
A  current  of  ozonised  oxygen,  cooled  to  —180°  by  liquid  oxygen 
boiling  at  atmospheric  pressure,  deposits  its  ozone  as  a  dark-b^e 
liquid,  while  the  oxygen  passes  on.  The  blue  liquid  boils  at 
-106°.* 

*  Comptes  rend.,  94,  1249  ;  Monatshrft  Chem.,  8,  69. 


390      THE   OXIDES,   SULPHIDES,   SELEN1DES,  AND   TELLURIDES. 

When  heated  to  250 — 300°,  ozone  is  reconverted  into  ordinary 
oxygen,  and  the  volume  of  the  gas  is  found  to  have  permanently 
increased.  Ozone  liberates  iodine  from  a  solution  of  potassium 
iodide,  forming  potassium  hydroxide  and  free  iodine  ;  it  oxidises 
silver  and  mercury,  which  are  unaffected  by  ordinary  oxygen  at 
the  atmospheric  temperature,  and  at  once  converts  black  lead 
sulphide  into  white  lead  sulphate.  It  reacts  with  hydrogen  per- 
oxide, but  only  slowly  in  presence  of  free  acid  ;  the  action  is  rapid 
in  presence  of  an  alkali ;  oxygen  gas  is  evolved.  It  bleaches 
indigo  and  other  vegetable  colouring  matters.  It  is  very  sparingly 
soluble  in  water,  although  nearly  ten  times  more  soluble  than 
oxygen.  It  provokes  coughing,  irritating  the  bronchial  tubes.  It 
is  poisonous  when  breathed  in  a  concentrated  form  ;  and,  curiously, 
the  blood  of  animals  killed  by  it  is  found  to  have  the  dark  colour 
of  venous  blood  ;  death  appears  to  be  produced  by  asphyxia. 

Proof  of  the  formula  of  ozone. — That  ozone  has  the  formula 
03  is  rendered  probable  by  the  following  experiments  : — 1.  Oxygen, 
when  ozonised,  undergoes  contraction.  This  may  be  proved  by 
placing  the  apparatus  shown  in  fig.  41,  filled  with  oxygen,  in 
water  so  as  to  maintain  a  constant  temperature,  for  on  passing  the 
discharge  the  gas  would  become  heated,  and  changes  of  volume, 
not  dependent  on  the  conversion  of  oxgyen  into  ozone,  would  then 
occur.  Some  strong  sulphuric  acid,  coloured  with  indigo,  is  intro- 
duced into  the  gauge,  and  the  stopcock  connecting  the  apparatus 
with  the  U'tube  is  shut.  On  passing  a  current,  a  momentary 
expansion  will  take  place  at  first,  due  for  the  most  part  to  heating 
of  the  gas  ;  it  is,  however,  followed  by  a  contraction  shown  by  the 
rise  of  the  liquid  in  the  gauge.  Its  level  is  observed. 

2.  The  apparatus  is  then  removed  from  the  water,  and  by  a 
rapid  shake,  a  small  thin  bulb  filled  with  oil  of  turpentine  contained 
in  the  lower  part  of  the  tube  is  broken.  The  apparatus  is  again 
placed  in  water,  and  allowed  to  stand  for  a  few  minutes,  so  as  to 
regain  its  original  temperature.  A  further  contraction  will  have 
taken  place,  amounting  to  twice  that  originally  observed.  The 
U-tube  is  washed  out  and  filled  with  fresh  iodide  of  potassium 
and  starch  ;  the  contents  of  the  apparatus  are  then  expelled 
through  the  U"tu^e  by  a  current  of  oxygen  ;  no  coloration  is  pro- 
duced, showing  that  the  ozone  has  been  completely  removed. 

The  relation  of  the  volume  of  the  ozone  to  that  of  the  oxygen 
from  which  it  has  been  produced,  can  be  inferred  from  these  experi- 
ments. To  take  a  suppositions  case  :—  Suppose  the  total  volume 
of  the  oxygen  before  electrification  is  100  c.c.  After  partial  con- 
version into  ozone,  the  volume  may  be  imagined  to  be  reduced  to 


OZONE.  391 

99  c.c. ;  and  after  absorption  of  the  ozone  by  turpentine,  the  con- 
traction is  twice  as  great  as  the  original  one,  and  the  volume  is 
further  reduced  to  97  c.c.  We  have  thus :  — 

Volume  of  original  gas    100  c.c. 

Volume  of  oxygen  plus  ozone 99  c.c. 

Volume  of  oxygen  after  removal  of  ozone 97  c.c. 

Hence  oxygen  converted  into  ozone 100  —  97  c.c.  =  3  c.c. 

Volume  of  that  ozone    93  —  97  c.c.  =  2  c.c. 

We  see,  therefore,  that  three  volumes  of  oxygen  are  converted  into 
two  volumes  of  ozone. 

The  density  of  ozone  should,  therefore,  be  that  of  03/2  =  24. 

No  direct  experiments  on  its  density  have  been  made ;  but 
corroborative  evidence  is  furnished  by  experiments  in  which  the 
rate  of  diffusion  of  ozone  mixed  with  oxygen  was  compared  with 
that  of  chlorine  mixed  with  oxygen.*  The  rate  of  diffusion  of  two 
gases,  as  shown  by  Graham,  is  inversely  as  the  square  roots  of 
their  respective  densities.  Now,  the  density  of  chlorine  is  35*5, 
the  square  root  of  which  is  5'96 ;  and  that  of  ozone  is  presumably 
24,  the  square  root  of  which  is  4'90  ;  hence,  for  every  4*90  grams 
of  chlorine  escaping  into  air  by  diffusion,  5'96  grams  of  ozone 
should  escape.  The  ratio  between  these  numbers  is 

5-96  :4-90  :  100  :  82-2; 

the  rate  of  diffusion  should  be,  therefore,  the  100/82  of  that  of 
chlorine  ;  it  was  experimentally  found  to  be  the  100/84th  part,  a 
sufficiently  close  approximation.  A  similar  set  of  experiments 
proved  it  to  have  nearly  the  same  rate  of  diffusion  as  carbon  di- 
oxide, CO2,  the  density  of  which  is  22.  It  may  be  regarded,  there- 
fore, as  a  compound  of  three  atoms  of  oxygen,  and  it  possesses  the 
formula  O3,  with  the  molecular  weight  4*. 

Many  substances,  such  as  potassium  iodide,  mercury,  and  silver, 
convert  ozone  into  ordinary  oxygen,  but  remove  only  the  third 
atom  of  the  oxygen  of  ozone.  The  equations  are  : — 

2KI  Aq  +  03  +  H2O  =  2KOH.Aq  +  l2.Aq  +  02 ; 
2Ag  +  03  =  Ag,O  +  02 ;  and  Hg  +  03  =  HgO  +  02. 

Other  bodies,  such  as  the  dry  dioxides  of  lead  and  manganese,  and 
copper  oxide,  decompose  it  without  themselves  suffering  any  per- 
manent change.  And  in  some  cases  it  has  a  reducing  action ;  for 
example,  silver  oxide  is  reduced  to  metallic  silver,  thus  : — Ag-2O  + 
03  =  2Ag  +  202  ;  moist  dioxide  of  lead  is  also  reduced  : — 

*  Soret,  Annales  (4),  7,  113  ;    13,  2,7. 


392       THE   OXIDES,    SULPHIDES,   SELENIDES,   AND   TELLUEIDES 

PbO2  +  03  =  PbO  -I-  202.  And  in  alkaline  or  neutral  solution  it 
reduces  hydrogen  dioxide,  H2O2.Aq  -f-  03  =  H2O.Aq  +  202.  It  is 
probable  that  the  decomposing  action  which  silver,  mercury,  &c., 
have  on  ozone  is  due  to  a  double  chang;e,  for  instance  :  2Ag  +  03 
=  Ag2O  -f  02,  and  Ag2O  +  03  =  2Ag  +  20,.  These  changes 
may  be  regarded  as  due.  to  the  action  of  atomic  oxygen,  a  body 
incapable  of  more  than  a  momentary  existence  at  the  ordinary 
temperature,  but  one  which  we  should  suspect  to  display  great 
chemical  activity.  In  this  connection  it  may  be  noted  that  at  the 
moment  when  the  electric  discharge  begins  to  pass  through  pure 
dry  oxygen,  a  sudden  expansion  occurs,  too  sudden  to  be  regarded 
as  due  to  rise  of  temperature;  an  equally  sudden  contraction 
ensues.  It  may  be  supposed  that  the  first  action  of  the  discharge 
is  to  partly  dissociate  the  ordinary  oxygen,  O2,  into  atoms,  many 
of  which  then  combine  in  groups  of  three,  forming  ozone,  03. 

Tests  for  Ozone. —Ozone  liberates  iodine  from  potassium 
iodide,' with  formation  of  potassium  hydroxide.  If,  therefore,  half 
of  a  strip  of  red  litmus  paper  be  moisbened  with  a  solution  of 
potassium  iodide  and  starch,  the  moist  portion  will  become  blue, 
owing  to  the  liberated  alkali.  This  effect  is  not  produced  by 
nitrous  acid,  hydrogen  peroxide,  chlorine,  or  other  substances 
which  have  also  the  power  of  liberating  iodine  from  potassium 
iodide. 

Another  test  is  the  power  which  ozone  possesses  of  oxidising 
a  .thallous  salt  to  hydrate d  thallic  oxide.  Paper  moistened  with  a 
solution  of  colourless  thallous  hydroxide  therefore  changes  to  the 
brown  tint  of  thallic  hydrate  on  exposure  to  ozonised  oxygen. 


Oxides  and  Sulphides  of  Molybdenum,  Tungsten, 
and  Uranium. 

No  selenides  or  tellurides  of  the  elements  of  this  group  have 
been"  prepared.  The  following  is  a  list  of  the  oxides  and  sul- 
phides:— 

List.  Molybdenum.  Tungsten.  Uranium. 

Oxygen  !Mo2O3;  MoO2 ;  MoO3.  WO2 ;  WO3.       TTO2  ;  TJO3;  UQ4.  .- 

U209(?)*;   TJ06.* 
Sulphur     —         MoS2;  MoS3;  MoS4.       WS2 ;   WS3.       TJS2;  TJS3  (?).* 

Besides  these,    the   following   oxides   are   known;    they   may   be 
regarded  as  compounds  of  the  simpler  ones  with  each  other: — 

*  Possibly  exist  in  combination  with  other  oxides  or  sulphides. 


OF  MOLYBDENUM,  TUNGSTEN,  AND   URANIUM.  393 

Mo,O5    (in    combination    with    water)    =    MoO2.MoO3 ;    U2O5  ; 
Mo~O8  =  MoCMMoO3;  U3O8  =  UO2.2UO3. 

Sources. — Molybdenum  and  tungsten  trioxides  occur  native 
as  molybdic  ochre  and  tiwgstic  or  wolfram  ochre;  the  former  often 
coats  the  surface  of  the  native  sulphide  as  an  earthy  powder; 
and  the  latter  forms  a  bright  yellow  or  yellowish -green  powder, 
sometimes  occurring  crystallised  in  cubes.  The  oxide  U3O8  is  the 
chief  constituent  of  pitchblende,  the  chief  source-of  uranium.  It  is 
a  hard  greyish,  greenish,  or  reddish-black  mineral,  sometimes 
crystallising  in  regular  octahedra.  It  usually  accompanies  lead 
and  silver  ores.  Molybdenum,  tungsten,  and  uranium  also  occur 
as  trioxides,  in  combination  with  other  oxides.  Among  such 
compounds  are  wulfenite,  or  yellow  lead  ore,  lead  molybdate^ 
PbMoO4 ;  calcium  tungstate,  CaWO4,  named  scheelite  or  tungsten 
(from  the  Swedish  words  twig,  heavy,  and  sten,  stone;  its  specific 
gravity  is  6)  ;  ferrous-manganous  tungstate,-  (Fe,Mn)WO4,  or  wol- 
fram, the  chief  ore  of  tungsten ;  and  scheeletine  or  lead  tungstate, 
PbWO4.  Uranium  occurs  as  carbonate  in  liebigite,  Ca(UO2XCO3)2 ; 
as  phosphate  in  uranium  vitriol ;  also  in  uranite, 

2(UO2).Ca(PO4)2.8H2O, 

and  in  chalcolite,  in  which  copper  replaces  calcium. 

Uranium  also  occurs  in  the  rare  minerals  samarskite,fergusonite, 
pyrochlore,  euxenite,  &c.,  in  combination  with  oxides  of  niobium, 
tantalum,  yttrium,  and  other  elements. 

-Disulphide  of  molybdenum,  MoS2,  occurs  native  as  molyb- 
denite, or  molybdenum  glance,  in  soft,  grey,  elastic,  flexible 
laminae,  resembling  lead  in  colour  and  lustre,  and  graphite  in  its 
touch. 

Preparation. — 1.  By  direct  union. — Molybdenum  and  tungs- 
ten, when  finely  divided,  burn  when  heated  in  air  to  the  trioxides, 
MoO3  and  WO3;  uranium  yields  the  oxide  U3O8.  The  trfoxide 
of  molybdenum  is  also  obtained  by  heating  the  metal  in  water- 
vapour,  or  with  potassium  hydroxide.  The  sulphides,  MoSk, 
WS2,  and  US2,  are  also  produced  directly,  by:  heating  the  finely- 
divided  metals  with  sulphur. 

.  2.  By  heating  double  compounds. — The  oxides  Mo2O3,- 
MoO2,  MoO3,  WO3,  UO2,  UO3,  and-  UO4  are  left  anhydrous 
when  their  hydrates  are  heated.  With  Mo2O3  and  MoO2,  air 
must  be  excluded,  else  oxidation  occurs.  The  hydrate  of  the 
oxide  UO2  becomes  anhydrous  when  boiled  with-  water  I  -To 
dehydrate  UO4.2H2O,  the  temperature  must  not  be  allowed  to  rise 
much  above  100°,  else  loss  of  oxygen  ensues. 


394       THE   OXIDES,   SULPHIDES,    SELENIDES,   AND   TELLUKIDES 

Molybdates,  tungstates,  and  uranates  of  ammonium  and  of 
mercury  leave  the  tri oxides  when  heated  to  redness,  the  volatile 
bases  being  expelled.  Uranyl  nitrate,  UO2(NO3)Z,  at  250°  yields 
the  trioxide.  When  more  strongly  ignited,  U3O8  is  produced  ; 
and  at  an  intense  heat,  U2O5. 

3.  By  reducing  a  higher  oxide  or  sulphide. — Molybdenum 
sesquioxide  is  produced    by  treating   the   trioxide  with   nascent 
hydrogen   from    zinc   and    hydrochloric    acid.     Molybdenum    and 
tungsten  dioxides  are  produced  when  the  trioxides  are  heated  to 
low  redness  in  hydrogen;  at  high  temperatures   the  oxides   are 
reduced  to  metal.     Uranium  dioxide  is  produced  by  heating  the 
complex  oxide  U3O8  to  whiteness  with  carbon,  or  in  a  current  of 
hydrogen.     It  has   also  been   prepared   by   heating   the   oxalate, 
(UO2)C2O4,  or  the   double   oxychloride,  UO2C12.2KC1.2H2O,  to 
redness  in  a  current  of  hydrogen.    Molybdenum  dioxide  is  obtained 
in  a  crystalline  form,    by  fusing  sodium   molybdate,   Na2MoO4, 
with   metallic   zinc,  which   deprives   the  trioxide,   MoO3,  of   its 
oxygen.     Uranium  tetroxide,  UO4,  loses  oxygen  when  heated  to 
250°,  leaving  the  trioxide,  and  at  higher  temperatures  gives  the 
oxide  U3O8,  which  loses  more  oxygen  on  intense  ignition,  leaving 
Ua05. 

The  higher  sulphides  of  molybdenum  and  tungsten,  US4,  US3, 
and  WS3,  likewise  lose  sulphur  at  a  red  heat,  yielding  the 
disulphides. 

4.  By  oxidation  of  a  lower  oxide.— The  oxides  MoO3,  WO3, 
and  U3O8  are -produced  when  the  lower  oxides  are  ignited  in  air. 
The  higher  sulphides,   however,  are  not  formed  by  heating  the 
lower  ones  with  sulphur. 

5.  By  replacement,  or  by  double  decomposition. — The 
only  oxide  produced  by  this  method  is  uranium  tetroxide ;  it  is 
formed    when   a    mixture    of    solutions    of    uranyl    nitrate    and 
hydrogen  dioxide,  in  presence  of  a  large  excess  of  sulphuric  acid, 
are  allowed  to  stand  for  some  weeks,  thus: — 

U02(N03)2.Aq  +  H202.Aq  =  UO4  +  2HN03.Aq. 

This  is,  however,  a  method  of  preparing  the  sulphides.  Molyb- 
denum or  tungsten  trioxide,  heated  with  sulphur,  yields  sulphur 
dioxide,  and  the  disulphide.  Bisulphide  of  tungsten  is  also  pro- 
duced by  heating  any  oxide  in  a  current  of  hydrogen  sulphide  or 
carbon  disulphide  ;  and  uranium  disulphide  has  been  obtained  by 
heating  uranium  tetrachloride,  UC14,  in  a  current  of  hydrogen 
Bulphide. 


OF   MOLYBDENUM,  TUNGSTEN,   AND   URANIUM.  395 

The  higher  sulphides  are  also  prepared  by  this  method. 
Molybdenum  and  tungsten  trisulphides  are  formed  by  addition  of 
hydrogen  sulphide  or  ammonium  sulphide  to  the  solution  of  a 
moljbdate  or  a  tungstate,  and  subsequent  addition  of  an  acid. 
They  are  then  precipitated.  Uranium  trisulphide  is  produced 
by  heating  the  tribromide  in  a  current  of  hydrogen  sulphide. 
Molybdenum  tetrasulphide  is  precipitated  on  addition  of  an  acid 
to  a  solution  of  a  sulphopermolybdate,  such  as  Na^MoSs.Aq. 

Properties. — Molybdenum  sesquioxide  was  believed  by 
Berzelius  to  be  the  monoxide,  MoO.  It  is  a  black  powder,  when 
obtained  by  igniting  the  hydrate;  but  when  produced  by  the 
action  of  nascent  hydrogen  from  zinc  and  hydrochloric  acid  on  the 
trioxide,  a  dark  brass-yellow  precipitate.  Molybdenum  dioxide, 
from  the  trioxide  with  hydrogen,  is  a  dark-brown  powder ;  when 
prepared  from  sodium  molybdate  by  fusion  with  zinc,  it  forms 
blue-violet  prisms.  Dioxide  of  tungsten  forms  brilliant  copper- 
red  plates,  insolable  in  water  and  acids ;  and  uranium  dioxide 
also  possesses  metallic  lustre ;  prepared  from  the  oxalate,  it  is  a 
cinnamon- brown  powder ;  but  when  obtained  from  the  double 
chloride,  it  crystallises  in  lustrous  octahedra.  The  amorphous 
form  glows  when  heated  in  air,  burning  to  UaOg. 

Molybdenum  trioxide  forms  a  light  porous  white  mass  of 
silky  scales ;  it  melts  at  a  red  heat  to  a  dark-yellow  liquid,  which, 
when  cooled  slowly,  solidifies  in  needles.  It  is  volatile  in  a  current 
of  air,  but  not  alone;  this  is  perhaps  due  to  the  transient  forma- 
tion of  a  dissociable  and  more  volatile  higher  oxide.  It  is  insoluble 
in  water,  but  dissolves  in  acids.  Trioxide  of  tungsten  is  a 
lemon-  or  sulphur-yellow  powder,  turning  darker  when  heated. 
It  may  be  obtained  in  transparent  trimetric  tables  by  crystallisa- 
tion from  fused  borax,  or  in  octahedra  by  heating  it  in  a  current 
of  hydrogen  chloride.  It  melts  at  a  bright- red  heat.  Uranium 
trioxide  is  a  buff- coloured  powder.  Uranium  tetroxide  forms 
a  heavy,  white,  crystalline  precipitate.  The  more  complex  oxide, 
Mo3O8  is  a  blue  insoluble  powder ;  U3OP,  when  prepared  artificially, 
is  a  dark-green  velvety  powder  ;  and  U2O5  a  black  powder.  When 
the  glaze  on  porcelain  is  mixed  with  the  oxide  U3O8,  and  baked, 
an  intense  black  colour  is  produced,  and  it  is  conjectured  that 
during  firing,  the  oxide  UsO8  is  converted  into  U2O5. 

Molybdenum  disulphide,  prepared  artificially,  is  a  black 
lustrous  powder ;  disulphide  of  tungsten  forms  slender  black 
needles;  and  that  of  uranium  is  a  greyish-black  amorphous  body, 
becoming  crystalline  at  a  white  heat.  Molybdenum  trisulphide 
is  a  blackiah-brown  powder;  and  that  of  tungsten  forms  black 


396      THE   OXIDES,    SULPHIDES,    SELENIDES,   AND   TELLUKIDES 

lumps  which  yield  a  liver-coloured  powder.  Both  of  these  bodies 
dissolve  in  solutions  of  sulphides  of  the  alkalis  ;  that  of  tungsten 
is  slightly  soluble  in  water,  but  is  precipitated  on  addition  of 
ammonium  chloride.  It  becomes  denser  when  boiled  with  hydro- 
chloric acid.  Uranium  trisulphide  is  a  black  powder.  Molyb- 
denum tetrasulphide  forms  dark-red  flocks,  drying  to  a  dark- 
green  mass  with  metallic  lustre ;  when  triturated,  it  gives  a  red 
powder. 

Double  compounds. —  (a.)  With  water. — The  hydrates 
are  mostly  prepared  by  double  decomposition ;  those  of  the 
trioxides,  and  of  uranium  tetroxide,  may  be  termed  acids,  inasmuch 
as  they  correspond  in  formula  to  numerous  double  oxides.  Double 
oxides  corresponding  to  the  other  oxides  of  these  elements  have 
not  been  prepared. 

Hydrated  molybdenum  sesquioxide  is  produced  by  adding 
potassium  hydroxide  to  a  solution  of  a  molybdate  previously 
exposed  for  some  time  to  the  action  of  nascent  hydrogen  from  zinc 
and  hydrochloric  acid,  or  better,  sodium  amalgam.  It  is  a  black 
precipitate,  soluble  in  acids,  forming  dark-coloured  or  purple 
molybdous  salts;  in  dilute  solution  they  have  a  brownish-red 
colour. 

Hydrated  molybdenum  dioxide  is  produced  by  adding 
ammonia  solution  to  a  solution  of  molybdenum  tetrachloride.  It 
is  a  rusty-coloured  precipitate,  sparingly  soluble  in  water,  in 
which  it  dissolves  to  a  dark  red  solution ;  hence  it  should  be 
washed  with  alcohol.  Its  solution  gelatinises  011  standing.  It  is 
soluble  in  acids,  forming  reddish-brown  solutions. 

Hydrated  dioxide  of  tungsten  is  unknown;  that  of  uranium 
is  precipitated  in  red-brown  flocks  from  uranous  salts  by  addition 
of  an  alkali.  It  is  soluble  in  acids,  forming  green  solutions. 

Molybdenum  trioxide  is  sparingly  soluble  in  water  (I  in 
500).  By  dialysing  it,  Graham  prepared  a  stronger  solution, 
possessing  a  yellow  colour  and  an  acid  taste.  This  soluble  modi- 
fication has  also  been  prepared  by  addition  of  the  theoretical 
amount  of  sulphuric  acid  to  barium  molybdate  suspended  in  water, 
and  filtering  off  the  precipitated  barium  sulphate.  On  evaporation 
it  forms  a  transparent  blue-green  mass,  which  slowly  dries  to  the 
anhydrous  oxide.  The  hydrate,  or  acid,  2MoO3.H2O  =  H2Mo2O7, 
has  been  prepared  by  drying  the  residue  for  two  months  over 
strong  sulphuric  acid;  and  a  hydrate,  or  acid,  MoO3.H2O,  once 
separated  in  prisms,  after  long  standing,  from  a  solution  of  the 
magnesium  salt  which  had  been  mixed  with  nitric  acid  equivalent 
to  the  magnesium. 


OF  MOLYBDENUM,  TUNGSTEN,  AND  URANIUM.  397 

The  hydrated  double  oxide,  Mo2O5.3H2O.  forms  a  blue  pre- 
cipitate on  mixing  a  solution  of  the  dioxide  with  a  solution  of  the 
trioxide  in  hydrochloric  acid.  It  may  be  regarded  as  MoO2.MoO3, 
molybdyl  molybdate.  Similarly,  the  oxide  Mo3O8  may  be  viewed 
as  MoO2.2MoO3,  or  molybdyl  dimolybdate. 

Hydrated  tungsten  trioxide,  or  tungstic  acid,  WO3.H2O, 
=  H2WO4,  forms  a  yellow  precipitate  on  adding  an  acid  to  a  hot 
solution  of  a  tungstate.  It  crystallises  without  alteration  of  com- 
position from  hydrofluoric  acid.  By  similar  treatment  of  a  cold 
solution,  a  white  gelatinous  precipitate  of  WO3.2H2O  is  formed. 
It  is  also  produced  when  water  is  added  to  a  solution  of  tungsten 
chloride  or  oxychloride. 

A  soluble  modification  of  tungstic  acid,  named  metatungstic 
acid,  is  produced  by  action  of  sulphuric  acid  on  barium  tungstate 
suspended  in  water.  On  evaporation,  the  solution  deposits  yellow 
crystals  of  4(WO3.H2O).31H2O  =  H2W4O13.31H2O.  This  hydrate 
is  easily  soluble  in  water  and  forms  soluble  salts.  On  heating  its 
concentrated  solution,  ordinary  tungstic  acid  separates  out. 

Hydrated  uranium  trioxide,  UO3.2H2O,  has  not  been  ob- 
tained pure  by  precipitation,  for  alkali  is  always  carried  down. 
But  by  heating  a  weak  alcoholic  solution  of  the  nitrate,  oxidation 
products  of  alcohol  are  suddenly  evolved  ;  the  hydrated  oxide  re- 
mains as  a  buff-coloured  mass.  It  is  also  formed  by  exposing 
moist  U3O8  to  air.  When  dried  in  vacua  it  forms  UO3.H2O  = 
H2UO4,  a  lemon-yellow  powder. 

The  hydrated  tetroxide,  UO4.2H2O,  is  a  yellow-white  powder 
obtained  by  mixing  a  solution  of  a  uranyl  salt  with  hydrogen  di- 
oxide. On  treatment  with  potash,  uranic  hydrate,  UO3.2H2O,  is 
precipitated,  and  the  potassium  salt  of  an  acid  dissolves  which 
may  be  conceived  to  have  the  formula  H8UOi0.  The  hydrated 
tetroxide  may  therefore  be  viewed  as  UO6.2UO3.6H2O.  Attempts 
to  prepare  the  hydrated  oxide  U06  were,  however,  unsuccessful  ; 
on  addition  of  hydiogen  dioxide  to  a  nitric  acid  solution  of  uraninm 
nitrate,  the  ratio  of  uraninm  to  oxygen  in  the  precipitate  corre- 
sponded approximately  to  the  formula  U2O9. 

(b.)  No  hydrosulphides  are  known. 

(c.)  Double  oxides  and  sulphides;  salts  of  molybdic, 
tungstic,  and  uranic  acids ;  also  of  corresponding  sulpho- 
acids. — A  compound  of  tungsten  dioxide  and  sodium  oxide  has 
been  prepared,  by  dissolving  in  fused  sodium  tungstate  as  much 
trioxide  as  it  will  take  up,  and  heating  the  mixture  to  redness  in 
hydrogen.  On  treatment  with  water,  the  compound  2WO2.NaoO 
=  Na,W2O5  remains  in  golden-yellow  scales  and  cubes  possessing 


398      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

metallic  lustre.  It  cannot  be  prepared  by  direct  union  of  the 
oxides.  No  similar  compounds  of  molybdenum  or  uranium  are 
known. 

Molybdates,  tungstates,  and  uranates.  —  These  are  among 
the  most  complex  of  compounds  known.  Owing  to  their  com- 
plexity, the  formulae  of  many  are  somewhat  uncertain,  different 
investigators  drawing  different  conclusions  from  their  analytical 
data.  There  can  be  no  doubt  that,  of  all  oxides,  these  show  most 
tendency  to  polymerise,  especially  when  in  union  with  others.  It 
will  be  convenient,  in  writing  the  formulae  of  these  complex  bodies, 
to  represent  them  as  compounds  of  oxides  with  oxides,  e.g., 
mM2O.nR03,  where  M  stands  for  any  element,  and  R,  for  molyb- 
denum, tungsten,  or  uranium.  As  nothing  is  known  regarding 
the  constitution  of  these  bodies,  the  water  frequently  contained  in 
them  will  be  written  separately. 

5(Mo03.Li20).3H20;  3(Mo03.Li2O).8H2O  ;  MoO3.Na2O.H2O,  and  2H2O  ; 
2(MoO3.K2O).H2O;  MoO3.K2O.5H2O  ;  MoO3.(NH4)2O.—  WO3.Li2O; 
W03.Na20;  WO^O-H^O,  2H2O,  and  5H2O  ;  WO3.(NH4)2O.— 
TJO3.Na2O.6H2O  ;  TJO3.(NHt)2O. 

The  lithium,  sodium  and  potassium  salts  are  obtained  by 
fusing  the  respective  trioxides  with  the  carbonates.  The  molyb- 
dates  and  tungstates  are  colourless  ;  the  uranates  yellow.  The 
ammonium  salts  crystallise  from  solutions  of  trioxides  in  am- 
monia; they  are  precipitated  by  alcohol;  the  neutral  ammonium 
tuiigstate  is,  however,  unstable,  and  yields  crystals  of 
3WO3.2(NH4)2O.3H2O.  Ammonium  molybdate  is  employed  as  a 
reagent  for  orthophosphoric  acid. 

The  double  salt  3MoO3.K2O.2Na2O.HH2O  is  also  known,  and 
is  produced  by  mixture.  Sodium  tungstate,  Na2WO4,  is  used  as 
a  mordant  in  dyeing,  and,  as  it  fuses  at  a  red  heat,  it  is  employed 
to  render  linen  and  cotton  cloth  uninflammable. 

2MoO..Na20;  2MoO3.(NH4)2O.—  2WO3.Na2O.2H2O  and  6H2O  ; 
2O  and  3H2O—  2TJO3.Na2O  ;  2UO3.K2O. 


These  are  crystalline  salts  obtained  by  acidifying  the  former,  or 
by  adding  trioxide  in  theoretical  proportion  to  their  solutions. 
The  uranium  salts  are  also  produced  by  addition  of  excess  of 
solution  of  potassium  hydroxide  to  a  uranyl  salt,  such  as  the 
nitrate,  U02(N03)2.Aq.  They  are  light  orange  powders. 


MOLYBDATES,  TUNGSTATES,  AND  URANATES.  399 


7Mo03.3Na20.22H20  ;  7MoO.3K2O.4H2O  ;  7MoO3.3(NH4)2O.22H8O.— 
7W03.3Iii0.19H20;  7WO3.KoO.6H2O. 

These  molybdates  are  produced  by  evaporation  to  dryness  of 
solutions  of  the  trioxide  in  solutions  of  carbonates.  From  the 
potassium  salt  the  curious  compound  16MoO3.6K2O.4H2O2  has 
been  obtained  with  hydrogen  dioxide.  The  tungstates  are  obtained 
by  the  action  of  carbonic  acid  on  the  former  salts. 

5Mo03.2(NH4)20.3H20.—  5W03.2Na20.11H20 


These  salts,  and  those  which  follow,  are  produced  by  acidifying 
those  in  which  the  number  of  molecules  of  the  two  oxides  are  more 
nearly  equal. 

12W03.5Na20.28H20jl2W035K2O.HH20;  12WO3.5(NH4)2O.5H2O  and 

11H20. 
12W03.Na20.4K,0.15H20  ;  12WO3.Na2O.4(NH4)2O.12H2O;  and  others. 

3MoO3.Na.2O.4H2O  and  7H2O  ;  3MoO3.K2O.3H2O;  3MoO3.Rb2O.2H2O. 

3WO3.Na2O.4Hp  ; 


Molybdates  of  the  following  types  are  also  known  ;  they  are  all 
produced  by  addition  of  acid  to  those  containing  less  trioxide  :  — 


4MoO3.Na2O.6H2O  ; 

10Mo03.Na,20.21H20; 

A  corresponding  tetratungstate,  4WO3  Na-jO,  remains  insoluble 
on  digesting  the  fused  salt,  12WO3.5Na2O,  with  water;  the  salt 
oWO3.2Na.2O  dissolves.  A  hexuranate,  6UO3.K2O,  is  also 
known;  it  is  produced  by  fusion  of  uvanyl  sulphate,  UO2.SO4, 
with  potassium  chloride.  All  these  bodies  are  crystalline,  and 
apparently  definite  chemical  compounds. 

The  tetratungstates,  or,  as  they  have  been  termed,  the 
metatungstates,  form  a  separate  class,  inasmuch  as  the  tung- 
stic  acid  produced  from  them  is  soluble.  They  are  produced  by 
boiling  solutions  of  ordinary  tungstates  with  hydrated  tungstic 
acid,  WO3.2H2O,  or  by  adding  phosphoric  acid  to  a  solution  of  a 
tungstate  until  the  precipitate  at  first  formed  redissolves.  They 
are  also  obtained  by  adding  carbonates  to  metatungstic  acid,  pro- 
duced from  the  barium  salt  with  sulphuric  acid.  They  form  well- 
defined  colourless  crystals.  Those  of  the  first  group  have  the 
formulae  4WO3.Na,O.4H,O  and  10H2O  ;  4WO3.K2O.8H2O  ;  and 
4WO3.(NH4),O  8H2O. 

The  sulpho-compounds  are  less  complicated.  They  are  as 
follows  :  — 


400      THE   OXIDES,   SULPHIDES,    SELENIDES,   AND   TELLURIDES. 


MoS3  Na2S  ;       MoS3  K2S  ;        MoS3.(NH4)2S.—  WS3.Na2S  ; 
•WS3(NH4)2S.—  Also    2MoS3.Na2S  ;     2MoS3.K2S.—  2WS3.Na2S  ;* 
The  analogous   oxysulphides    have    also   been  prepared  :—  MoO2S.(NH4)2S.  — 
WO2S.K2S.—  2MoO2S.Na2S.—  WO3.K2S.H.O. 

No  similar  uranium  compounds  are  known. 

The  sulphomolybdates  and  sulphotungstates  are  prepared  by 
dissolving  the  triaulphides  of  these  elements  in  sulphides  of  the 
alkalis,  and  crystallising  ;  or  those  of  potassium  by  fusing 
together  potassium  carbonate,  sulphur,  carbon,  and  molybdenum 
or  tungsten  trisulphide.  Potassium  sulphomolybdate  forms  deep- 
red  prisms,  which  reflect  green  light.  The  sulphomolybdates 
yield  deep-red  solutions  ;  the  sulphotuiigstates  are  yellowish-red. 
The  disulphomolybdates  and  tungstates  are  produced  by  adding 
acetic  acid  to  the  mono-salts  ;  they  are  precipitated  by  alcohol. 
The  oxysulphomolybdates  and  tungstates  are  produced  by  mixture, 
or  by  adding  the  hydrosulphide  of  the  metal  to  a  solution  of  a 
molybdate  or  tungstate,  and  evaporating  to  crystallisation.  They 
form  golden-red  or  yellow  needles. 

These  bodies  form  well  crystallised  double  salts  with  potassium 
nitrate,  e.g.,  MoS3.K2S.KNO3  and  WS3.K2S.KNO3. 

Mo03.2Be0.3H20;  MoO3CaO;  MoO3.SrO  ;  MoO3.BaO.—  WO3.CaO;WO3.SrO; 
WO3  BaO.—  2TJO3.CaO  ;  2TJO3.SrO  ;  2UO3.BaO.—  7WO3.3BaO.8H2O  ; 
12WO3.2BaO.3Na2O.24H2O. 

These  molybdates  and  tungstates  are  prepared  by  fusing  the 
chloride  of  the  metal  with  molybdenum  or  tungsten  trioxide  and 
sodium  chloride,  or  by  precipitation.  They  are  sparingly  soluble 
white  crystalline  bodies.  The  uranates  are  reddish-yellow,  and  are 
produced  by  precipitation. 

Calcium  tungstate  occurs  native  as  scheelite  or  tungsten  in 
white  quadratic  pyramids,  associated  with  tin-stone  and  apatite. 
The  mineral  is  insoluble  in  water. 

Metatungstates  :—  4WO3.CaO  ;  4WO3.SrO.8H2O  ;    4WO3,BaO.9H2O, 

are  soluble  salts,  prepared  by  dissolving  the  carbonate  in  the  acid. 

MoS3.CaS;  MoS3.SrS  ;  MoS3  BaS.—  WS3.CaS  :  WS3.SrS;  WS3.BaS. 
3MoS3.CaS;  3MoS3SrS;  3MoS3.BaS. 

The  trisulphomolybdates  are  produced  by  boiling  the  trisulphide 
with  solutions  of  the  sulphides  ;  and  the  monosulphomolybdates 
deposit  from  the  mother  liquor.  They  are  dark-red  substances. 
The  sulphotuiigstates  are  produced  by  treating  the  tungstates  with 
hydrogen  sulphide. 

*  Annalen,  232,  214. 


MOLYBDATES,  TUNGSTATES,  AND  URANATES.       401 


oO  ;  MoO3.ZnO  ;  MoO3.CdO.—  WO3.MgO  ;  WO3.ZnO  ; 
WO3.CdO.-2TJO3.M:eO  ;  2TJO3.ZnO.—  Also  7WO3.2MffO.(NH4)2O.10H2O  ; 
12WO3.3Mg:O.2(NH4)2O.24H2O  ;  7WO3.ZnO.(NH4)2O.3H2O. 

These  molybdates  and  tungstates  are  produced  by  fusing  together 
the  chloride  of  the  metal  with  sodium  molybdate  and  chloride.  They 
form  colourless  crystals.  The  uranates  are  produced  by  igniting 
the  doable  acetate  of  uranyl  and  the  metal.  They  are  not  crystal- 
line. The  double  ammonium  salts  are  obtained  by  mixture. 

Metatungstates  :—  4WO3.MgO.8H2O  ;  iWO^ZnO^OHjO  ; 
4W03.Cd0.10H20. 

These  are  all  colourless  crystalline  salts,  and  are  prepared  from 
the  carbonates. 

The  sulpho  molybdates  of  zinc  and  cadmium  are  dark-brown 
precipitates.  The  neutral  magnesium  salt  is  soluble,  as  is  also  the 
yellow  sulphotungstate.  The  sulphotungstates  of  zinc  and 
cadmium  are  sparingly  soluble  yellow  bodies. 

Simple  boron  and  yttrium  molybdates  have  not  been  prepared. 
Boron  tungstate  is  also  unknown;  but  double  compounds  of 
WO3,  B2O3,  an  oxide,  and  water  are  very  numerous.  They  are 
soluble  colourless  salts,  crystallising  well.  Owing  to  their  high 
molecular  weights,  too  great  confidence  must  not  be  placed  in  the 
formulae  given  ;  but  they  appear  to  belong  to  the  following  classes  :  — 

10WO3.B2O3.2BaO.20HoO. 

9W03.B203.Na20.3H,0. 

9W03.B203.2Ba0.20H20  ;  9WO3.B2O3.2CdO.15H2O. 

14WO3.B2O3.3K2O.22H2O  ;  (the  barium  and  silver  salts  are  also  known)  — 

12WO3.B2O3.4K.2O.21H2O. 

7W03.B263.Na20.11H20. 

The  solution  of  the  cadmium  salt  has  the  exceedingly  high  specific 
gravity  3  '6.  The  acid  corresponding  to  the  nonotungstate  has  been 
prepared  from  the  barium  salt.  It  is  a  syrup,  and  gives  insoluble 
precipitates  with  solutions  of  alkaloids,  and  may  be  used  to  separate 
quinine,  strychnine,  &c.,  from  solutions.  It  may  be  regarded  as 
boron  tungstate.  These  bodies  are  all  prepared  by  mixture. 

Aluminium  tungstate  has  the  formula  7WO3.A12O3.9H2O  ;  it  is 
obtained  by  precipitation.  3WO3.Y2Oa.6H2O  is  also  known.  Salts 
of  gallium  and  indium  have  not  been  prepared.  —  MoO3.Tl2O  is  a 
crystalline  powder. 

MoO3.FeO;  MoO3.MnO.H.,O  ;  MoO3.CoO;  MoO3.NiO.— 
W03.FeO;    WO3.MnO  ;  WO3.CoO;  WO3NiO  ;  WO3.(Fe,Mn)O. 

Sulphomolybdates   and    sulphotungstates   of    similar   formula 

2  D 


402      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

have  also  been  prepared.  They  are  produced  by  precipitation, 
or  by  fusion  of  the  trioxide  with  chloride  of  the  metal  and  common 
salt.  Ferrous  manganous  tungstate  is  wolfram,  the  chief  ore  of 
tungsten.  It  is  a  hard  dark-grey  or  brownish  mineral,  asso- 
ciated with  tin-ores  and  galena.  7WO3.3MnO.llH2O  and 
7WO3.3NiO.14H3O  are  produced  by  precipitation. 

The  metatungstates  known  are  4WO3.MnO.10H2O  ;  4WO3.CoO.9H2O  ;  and 
4WO3.NiO.8H2O.  They  are  soluble.  4MoO3.Fe2O3.7H2O  ;  also  double  salts  of 
ammonium  with  chromium  and  with  ferric  iron  of  the  general  formulae 
10MoO3.M2O3.3K2O.6H2O,  where  M  may  be  aluminium,  chromium,  ferric  iron, 
or  triad  manganese.  A  manganic  salt  is  also  known  of  the  formula 

16Mo03.Mn203.5K20.12H20. 

3W03.Cr203.13H20  ;  7WO3.Cr2O3.9H2O  ;  5WO3.Fe2O3.5(NH4)2O.H2O; 

the  double  salt  is  soluble. 

The  uranates  have  been  little  studied.  Double  molybdates 
and  chromates  have  been  prepared,  of  which  an  example  is 
Mo03.Cr03.K2O.Mg0.2H20. 

These  oxides  do  not  combine  with  oxides  of  carbon  ;  but  with 
titanium  dioxide,  compounds  similar  to  these  with  boron  oxide  have 
been  prepared.  Among  them  are  12WO3.TiO2.4K2O  and 
10WO3.TiO2.4K2O.  Zirconium,  cerium,  and  thorium  compounds 
appear  to  exist,  but  have  not  been  investigated. 

The  silicomolybdates  and  tungstates  are  also  numerous. 
Silicomolybdic  acid  has  the  formula  12MoO3.SiO2.13H2O  ;  it 
forms  fine  yellow  crystals.  It  gives  precipitates  with  salts  of 
rubidium  and  caasium,  affording  a  means  of  separating  these  metals 
from  sodium  and  potassium.  The  corresponding  tungstates  of 
silicon  and  their  derivatives  have  the  formulas 

12WO3.SiO2.4H2O.nAq  and  10WO3  SiO2.4H2O.»Aq. 

There  are  two  isomerides  having  the  first  formula.  The  potassium 
salt  of  the  first  is  produced  by  boiling  gelatinous  silica  (SiO. (OH).) 
with  ditungstate  of  potassium.  This  yields  a  precipitate  with 
mercurous  nitrate,  from  which  the  acid  may  be  liberated  with 
hydrochloric  acid.  The  salts  are  produced  by  its  action  on  carbon- 
ates. The  ammonium  salt  of  silicodecitungstic  acid, 

10W03.Si02.4(NH4)20, 

is  produced  similaily  from  ammonium  ditungstate.  This  acid  also 
yields  numerous  salts.  It  is  unstable,  and,  on  evaporation,  is  con- 
verted into  the  isomeric  acid  of  the  first  formula,  which  has  been 


COMPLEX  MOLYBDATES   A^D   TUNGSTATES.  403 

named  decitungstosilicic  acid.  These  acids  and  their  salts  as  a 
rule  crystallise  well. 

The  salts  of  tin  have  not  been  caref  ally  examined. 

Lead  molybdate,  MoO3.PbO,  occurs  native  as  wulfenite  or 
yellow  lead  ore.  It  is  a  heavy  orange-yellow  mineral,  occurring  in 
veins  of  limestone.  It  may  also  be  obtained  as  a  white  precipitate, 
or  in  crystals  by  fusing  sodium  molybdate  with  lead  chloride  and 
common  salt. 

Lead  tungstate,  WO3.PbO,  also  occurs  native  as  scheeletine,  in 
quadratic  crystals  isomorphous  with  the  molybdate.  It  has  a 
greenish  or  brown  colour.  It  can  be  prepared  artificially  like  the 
molybdate,  and  is  then  white.  The  salt  7WO3.3PbO.10H2O  is 
produced  by  precipitation.  The  metatungstate,  4WO3.PbO.6H2O, 
crystallises  in  needles.  2UO3.PbO  is  yellowish-red  and  insoluble. 
MoS3.PbS  and  WS3.PbS  are  dark  coloured  precipitates. 

The  oxides  of  the  elements  of  the  vanadium  and  phosphorus 
groups  form  exceedingly  complex  compounds  with  the  trioxides  of 
molybdenum  and  tungsten,  and  with  the  oxides  of  other  elements.* 
To  these  names  vanadimolybdates,  vanaditungstates,  &c.,  are 
applied,  the  number  of  molecules  of  trioxide  being  denoted  by  a 
numerical  prefix.  The  chief  compounds  are  as  follows  ;  they  are 
produced  by  mixture,  and  are  well-  crystallised  bodies  :  — 

5W03.V205.4(NH4)20.13H20.  18MoO3.As,O5.30H2O. 


6Mo03.P205.Aq.  20MoO3.P2O5.2BaO.24H2O. 

6WO3.As2O5.3K.2O.3H2O.  20MoO3.P2O5.6BaO.42H2O. 

6W03.As.205.4K20.2H20.  20MoO3.P2O5.7K20.28H2O. 

10WO3.V2O5.22H2O.  20MoO3.P2O5.8K2O.18H2O. 

14WOa.2P206.6(NH4)20.42H20.  20WO3.P2O5.6BaO.48:H2O. 

16Mo03.P205.3(NH4)20.14H20.  22MoO3.P2O5.3(NH4)2O.?H2O. 

16MoO3.2V2O5.5BaO.28H2O.  22WO3.P2O5.2K2O.6H:2O. 

16W03.P205.Ca0.5H20.  22WO3.P2O5.3(NH4)2O.21H2O. 

16WO3.P2O5.4K.2O.2H2O.  22WO3.P,O5.4BaO.32H2O. 

16W03.P205.6(NH4)20.1f  H20.  24MoO3.P2O5.62H2O. 

16WO3.As2O5.6Ag2O.11  H2O.  24WO3.P2O5.53H2O. 

18Mo03.  V2~05.8(NH4)20.  15H2O.  24MoOs.PoO5.2K2O.4H2O. 

18WO3.P2O5.K20.  19H.2O.  24WoO:4.P2O5.2K2O.6BL>O. 

18W03.V205.36H20.  24W03.P205.3K20.21H20. 
18W03.P205.6K20.23H20. 

24Mo03.P203.5  (NH4)20.20H20. 
24Mo03.6P20.6(NH4)20.7H20. 

It  is  to  be  noticed  that  the  ratios  of  the  molecules  of  trioxide 

*  Wolcott  Gibbs,  Amer.  Jour.  Sci.  (3),  14,  61  ;  Amer.  Chem.  Jour.,  2,  217, 
281  ;  5,  ,  361,  391  ;  7,  209,  313,  392;  Chem.  Mus,  45,  29,  50,  60;  48,  135. 

2  D  2 


404      THE   OXIDES,    SULPHIDES,   SELENIDES,   AND    TELLURIDES. 

to  pentoxide  are  5  :  1,  6  :  1,  7  :  1,  8  :  1,  10  :  1,  10  :  1,  18  :  1, 
20  :  1,  22  :  1,  and  24  :  1 ;  that  the  number  of  molecules  of  the 
alkaline  oxide  varies  from  1  to  8  ;  and  that  phosphorus  trioxide 
and  monoxide  (the  hypothetical  anhydride  of  hypophosphorous 
acid)  appear  also  to  be  capable  of  union  with  these  trioxides. 

Still  more  complex  bodies  have  been  prepared,  containing  two 
or  more  pentoxides  of  different  elements  ;  or  a  pentoxide  of  one 
and  a  trioxide  of  another  element,  for  example : — 

14Mo03.8V205.P205.8(NH4)20.50H20 ;  48MoO3.  V2O5.2P2O5.7(NH4)2O.30H2O  ; 
60W03.V205.3P205.10(NH4)20.6H20;  16WO3.3V2O5.P2O5.5(NH:4)2O.37H2O. 

Apparently  arsenic,  antimonic,  niobic,  and  tantalic  oxides,  and 
the  trioxides  of  boron,  phosphorus,  vanadium,  arsenic,  and  anti- 
mony, are  capable  of  forming  similar  compounds.  A  quaternary 
compound  has  even  been  obtained  of  the  formula 

60WO3.8P2O5.V2O5.VO2.18BaO.15()H:2O, 

Some  complex  uranium  compounds  occur  native,  resembling  to 
some  extent  those  mentioned  above.  They  are  : — 

Frogerite  ..  ..  3TJO3.As2O5.12H2O  ; 

Walpurgin          ..  ..  3TJO3.5Bi2O3.2As2O5.10H2O  ; 

Zeunerite  . .  . .  2TJO3.As2O5.CuO.8H2O  : 

Uranospinite       ..  . .  2TTO3.  As2O5.BaO.8H2O,  and 

UranospTicerite   ..  ,.  UO3.Bi2O3.H2O. 

They  are  yellowish  or  green  crystalline  minerals. 

Indications  also  appear  to  exist  of  complex  molybdotungstates, 
but  they  have  not  been  investigated. 

Uranyl  tungstate,  WO3.UO;.H2O,  is  a  brown  precipitate. 
Triple  compounds  have  also  been  prepared  of  the  trioxides  of 
molybdenum  or  tungsten,  one  of  the  oxides  of  sulphur,  and  the 
oxide  of  an  alkaline  metal,  but  at  present  there  are  no  precise  data 
as  to  their  formulae. 

Oxides  of  the  platinum  group  of  metals  also  form  similar  com- 
pounds. Among  the  few  which  have  been  prepared  are  : — 

10MoO3.PtO2.4Na2O.29H2O  and  10WO3.PtO2.4K2O.9H2O. 

They  are  analogous  to  the  titani-  and  silici-decimolybdates  and 
tungstates. 

The  compounds  of  copper  are  : — 

3MoO3.4CuO.5H2O  ;  the  metatungstate,  4"WO3.CuO.llH2O  ;  the  sulplio- 
molybdate,  MoS3.CuS  ;  and  the  sulpkotungstate,  WS3.CuS. 

They  are  obtained  by  precipitation. 


MOLYBDATES,  TUNGSTATES,  AND  URANATES.       405 

The  silver  salts  are  : — 

MoO3.Ag:2O  ;  2WO3.A&2O ;  the  metatungstate,  4WO3.Ag2O.3H2O  ;  the 
uranate,  2TJO3.Agr2O ;  and  the  sulphomolybdate  and  sulphotungstate, 
MoS3.As2S,  and  WS^Ag^S. 

They  are  all  insoluble,  except  the  metatungstate.  The  action 
of  hydrogen  at  the  ordinary  temperature  on  silver  molybdate 
or  tungstate  is  said  to  produce  sub-argeiitous  salts,  containing 
the  oxide  Ag40,  but  in  the  light  of  recent  researches  this  action 
is  improbable. 

The  following  mercury  compounda  have  been  prepared : — 

Mo03.Hg20  ;  2Mo03.Hs,0  ;  WO3.Hg2O  ;  2WO3.3HgO;  3WO3.2Hg-O;  the 

metatungstate,  4WO3.Hg>2O.25H2O  ;  and  the  sulpho-compounds,  MoS3.Hg2S, 
MoS3.Hg-S,  WS3.Hg:2S  and  WS3.Hg-S. 

These  are  all  produced  by  precipitation  ;  even  the  metatung- 
state is  insoluble.  Mercurous  tungstate,  WO3.HgoO,  is  completely 
insoluble  in  water,  and  on  ignition,  leaves  tungsten  trioxide  ;  hence 
tungsten  trioxide  is  usually  separated  from  other  metals  and 
estimated  by  precipitation  with  inercurous  nitrate. 

The  tungstates  and  molybdates  generally  resemble  the  sul- 
phates in  their  formulas;  and  these  might  with  reason  be  written 
from  analogy  M2Mo04  and  M2W04 ;  and  a  few  uranates  appear 
also  to  possess  similar  formulae.  Salts  analogous  to  anhydro-  or 
di-sulphates  are  also  known,  such  as  M2Mo207  =  2Mo03.M2O  and 
M2VV"207  =  2WO3.M20  ;  the  uranates,  as  a  rule,  are  thus  constituted. 
But  as  nothing  is  known  of  the  constitution  of  the  more  complex 
salts,  which,  as  has  been  seen,  are  very  numerous,  the  provisional 
method  of  writing  the  formulae  of  the  oxides  separately  has  uni- 
formly been  adopted. 

Peruranates. — It  has  been  stated  that  the  solution  of  a  uranyl 
salt  yields  a  white  compound  of  the  formula  UO4.2H2O3  on  treat- 
ment with  hydrogen  dioxide.  This  compound  when  mixed  witb 
solution  of  potassium  hydroxide  gives  a  precipitate  of  the  hydrated 
trioxide,  UO3.2H2O,  while  the  salt  UO6.2K2O.10H2O,  goes  into 
solution,  and  may  be  separated  as  a  yellow  or  orange  precipitate 
on  addition  of  alcohol.  It  may  also  be  produced  by  adding  hydro- 
gen dioxide  to  a  solution  of  hydrated  uranium  trioxide  in  caustic 
potash.  The  sodium  salt,  similarly  prepared,  has  the  formula, 
UO6.2Na2O.8HoO ;  and  by  using  a  smaller  amount  of  alkalii;^ 
hydroxide,  the  compound  UO6.UO3.Na2O.6H2O  is  formed,  and 
separates  on  addition  of  alcohol.  The  analogous  ammonium  com- 
pound has  also  been  prepared.  These  compounds  would  lead  to 
the  inference  that  an  oxide  of  the  formula  UO6  is  capable  of 
existence  ;  but  it  has  been  suggested,  apparently  on  insufficient 


406      THE    OXIDES,   SULPHIDES,    SELENIDES,   AND   TELLURIDES. 

evidence,  that  they  are  in  reality  compounds  of  uranium  tetroxide 
with  peroxides  of  the  metals,  thus  :— UO4.2K,O2.10H2O  ; 
UO4.2Na2O2.8H,O  ;  and  2UO4.Na2O2.6H2O.  They  readily  part 
with  oxygen,  forming  uranates.  Similar  permolybdates  and  per- 
tungstates  are  said  to  be  capable  of  existence  at  low  temperatures. 

Persulphomolybdates.— Potassium  dimolybdate  on  treatment 
in  solution  with  hydrogen  sulphide  yields  a  mixture  of  potassium 
sulphomolybdate,  MoS3  K2S,  and  molybdenum  trisulphide,  MoS3. 
Such  a  mixture,  when  boiled  with  water  for  some  hours,  gives  off 
hydrogen  sulphide,  and  forms  a  copious  precipitate  ;  it  is  collected 
and  washed  with  water  until  the  washings  give  a  red  precipitate  of 
Mo S4  with  hydrochloric  acid.  Water  extracts  potassium  persul- 
phomolybdate,  MoS4.K2S  from  the  residue,  leaving  the  disulphide, 
MoS,.  On  treatment  with  hydrochloric  acid,  the  tetrasulphide  is 
precipitated,  and  from  it  the  salts  may  be  obtained  by  treatment 
with  sulphides.  The  alkali  and  ammonium  salts  are  soluble  with 
a  red  colour  ;  they  yield  precipitates,  usually  red  or  reddish-brown, 
with  soluble  salts  of  the  metals.  The  magnesium  salt  is  an  in- 
soluble red  precipitate. 

(d.)  Compounds  with  halides. — No  simple  oxyfluorides  of 
molybdenum  are  known.  But  by  dissolving  molybdates  in  hydro- 
fluoric acid  and  evaporating  the  solutions,  compounds  isomorphous 
with  stannifluorides,  SnF4.2MF.H2O,  and  titani-  and  zirconi- 
fluorides  of  corresponding  formulae  are  produced.  Molybdoxy- 
fluorides  of  the  general  formula  MoO2F2.2MP.H2O  have  been 
prepared  with  potassium,  sodium,  ammonium,  and  thallium  ;  of  the 
formula  MoO2F2.2MF.2H2O  with  rubidium  and  ammonium;  and 
with  6H2O  with  zinc,  cadmium,  cobalt,  and  nickel. 

Tungstoxyfluorides  have  been  similarly  prepared ;  also  one  of 
the  formula  WO3.3NH4F.  They  are  isomorphous  with  the  former 
salts.  The  oxyfluoride  itself  is  known  with  uranium,  UO2F2.  It 
is  a  white  substance  produced  by  evaporating  a  solution  of  the 
trioxide  in  hydrofluoric  acid  ;  and  has  been  obtained  in  crystals 
by  subliming  the  tetrafluoride,  UF4  in  air.  It  also  forms  double 
salts  on  mixture ;  for  example,  UO2F2.NaF.4H,O  ;  UO2F2.3KF  ; 
UO2F2.5KF  ;  and  2UO2F2.3KF.2H2O.  They  are  crystalline  yellow 
bodies.  The  salt  UO2F2.KF  is  a  yellow  crystalline  precipitate 
obtained  by  adding  a  solution  of  potassium  fluoride  to  uranyl 
nitrate,  UO2(NO3)2.Aq. 

Oxychlorides  and  oxybromides  of  all  these  elements  are  known, 
viz. :  MoO2Cl2,  WO2C12,  UO2C12 ;  and  MoO2Br2,  WO2Br2,  and 
UO2Br2.  They  are  all  produced  by  the  action  of  the  halogen  on 
the  heated  dioxides  or  by  heating  the  trioxides  in  a  current  of 


OXYHALIPES  OF  MOLYBDENUM,  TUNGSTEN, 

hydrogen  chloride  or  bromide.  They  may  also  be  formed  by  passing 
the  halogen  over  a  hot  mixture  of  the  trioxide  with  charcoal ; 
and  one,  MoO2Br2,  has  been  prepared  by  heating  a  mixture  of  the 
trioxide  with  boron  trioxide  and  potassium  bromide  : — MoO3  -f- 
B2O3  +  2KBr  =  2KBO3  +  MoO,Br2.  Molybdyl  dichloride, 
MoO2Cl2,  forms  square  reddish-yellow  plates  ;  it  volatilises  without 
fusion.  The  bromide  also  volatilises  in  crystalline  yellow  scales. 
They  are  soluble  in  water,  alcohol,  and  ether.  Tungstyl  dichloride, 
WO>C12  forms  lemon-yellow  scales ;  and  the  bromide  consists  of 
scales  like  mosaic  gold.  They  decompose  when  heated.  Uranyl 
dichloride,  UO2CL,  is  a  yellow  crystalline  fusible  body,  volatile  with 
difficulty ;  the  bromide  forms  yellow  needles.  An  oxyiodide  is  said 
to  have  been  made. 

Molybdyl  and  uranyl  dichlorides  form  compounds  with  water, 
MoO2Cl2.H2O  and  UO2C12.H2O.  The  first  of  these  is  a  white 
crystalline  substance,  very  volatile  in  a  current  of  hydrogen 
chloride ;  it  is  produced,  along  with  the  anhydrous  body,  by 
passing  hydrogen  chloride  over  molybdenum  trioxide  at  150 — 200°. 
Uranyl  dichloride  unites  with  chlorides  of  the  alkalies,  forming 
bodies,  such  as  UO2C12.2KC1.2H2O,  similar  to  the  fluorides ;  the 
corresponding  bromide  also  gives  salts,  e.gr.,  UO2Br2.2KBr.7H2O. 

Molybdenum  and  tungsten  also  form  other  oxyhalides,  MoOCl4, 
WOCli,  and  WOBr4.  These  may  be  named  molybdanosyl  and 
tungstosyl  tetrachlorides,  respectively.  The  first  is  produced, 
along  with  molybdyl  dichloride,  by  the  action  of  chlorine  on  a 
heated  mixture  of  the  trioxide  with  charcoal.  It  forms  green 
easily  fusible  crystals,  which  melt  and  sublime  below  100° ;  it  is 
soluble  in  alcohol  and  in  ether.  The  corresponding  tungsten 
compound  is  produced  when  tungstyl  chloride  is  quickly  heated 
above  140°.  It  forms  red  transparent  needles ;  it  melts  at  210'4°, 
and  boils  at  227'5°.  Its  vapour  density  corresponds  with  the 
formula  WOCl*.  The  bromide  is  similarly  prepared  by  heating 
tungstyl  dibromide  ;  it  forms  light-brown  woolly  needles. 

Molybdenum  forms  some  other  oxyhalides.  The  action  of 
chlorine  on  a  mixture  of  molybdenum  trioxide  and  carbon  gives, 
besides  the  compounds  already  mentioned,  two  others  :  Mo2O3Cl<;, 
which  forms  dark  violet  crystals,  ruby-red  by  reflected  light,  and 
volatile  without  decomposition ;  and  Mo4O5Cli0,  forming  large 
blackish-brown  crystals,  volatile  in  a  current  of  hydrogen.  The 
first  points  to  a  dimolybdic  acid,  Mo2O3(OH)6,  but  the  second  is  a 
derivative  of  a  lower  oxide. 

Molybdous  bromide,  MoBr2,  on  treatment  with  alkali,  yields  a 
solution  from  which  carbonic  or  acetic  acid  throws  down  the 


408      THE   OXIDES,   SULPHIDES,    SELENIDES,   AND    TELLURIDES. 

hydroxybromide,  Mo3Br4(OH)2,  as  a  yellow  sparingly  soluble 
precipitate.  This  body  acta  as  a  base,  yielding  a  crystalline 
sulphate,  Mo3Br4.SO4,  chromate,  Mo3Br4.CrO4,  molybdate, 
Mo3Br4.MoO4,  oxalate,  Mo3Br4.C>O4,  and  phosphate, 
Mo3Br4.2PO(OH)2. 

The  oxycblorides,  such  as  MoOoCL  and  MoOCl4,  point  to 
hydroxides  like  MoO2(OH)2  and  MoO(OH)4;  these  are  known 
with  all  three  elements  and  are  the  respective  acids. 

No  sulphohalides  are  known. 


Physical  Properties. 

Mass  of  one  cubic  centimetre  : — 

MoO2,6'44  grams  at  16°.  MoO3,  4'39  grams  at  21°.  Mo&j,  4-44— 4'59  grains. 
WO2,  12-11  grams.     WO3,  7'23  grams,  at  17°.     WS2,  G  26  grams  at  20°. 
UO2,  10'15  grams;  TI3O8,  7'19  grams  ;  UO3,  5-02—5 '26  grams. 
The  heats  of  formation  are  xxnknown. 


409 


CHAPTER  XXVI. 

COMPOUNDS  OF  OXYGEN,  SULPHUR,  SELENIUM,  AND  TELLURIUM  WITH 

EACH  OTHER. ACIDS  AND  SALTS  OF  SULPHUR,  SELENIUM,  AND 

TELLURIUM  ;  SULPHATES,  SELENATES,  AND  TELLURATES. 

These  compounds  are  most  conveniently  divided  into  the  two 
classes: — (1)  the  oxides  and  their  compounds;  and  (2)  the 
compounds  of  sulphur,  selenium,  and  tellurium  with  each 
other. 

The  following  is  a  list  of  the  oxides : — 

Sulphur.  Selenium.  Tellurium. 

S2O3*;  S02;  SO3;  S20rf.        SeO2.          TeO2;  TeO3. 

Besides  these,  the  double  oxides  SSeO3,  STeO3,  and  SeTeO3  are 
known,  analogous  to  the  oxide  S2O3. 

Sources. — Sulphur  dioxide  is  the  only  one  of  these  compounds 
occurring  native.  It  is  present  in  the  air  in  the  neighbourhood  of 
volcanoes,  being  produced  by  the  combustion  of  sulphur,  and  also 
in  the  air  of  towns,  where  its  presence  is  due  to  the  combustion  of 
coal,  which  almost  always  contains  small  quantities  of  iron  pyrites. 
Air  in  the  neighbourhood  of  furnaces  where  sulphides  are  roasted 
also  contains  this  gas.  It  is  very  injurious  to  vegetation,  and  the 
prevention  of  its  presence  in  the  atmosphere  in  large  quantities 
should  engage  the  attention  of  manufacturers. 

Sulphur  trioxide  exists  in  abundance  in  combination  with  other 
oxides  in  sea-water,  or  on  the  earth's  surface,  as  sulphates,  and 
selenium  trioxide  has  been  found  native  in  combination  with  lead 
oxide.  The  more  important  of  the  natural  sulphates  are  Glauber's 
salt,  or  sodium  sulphate,  Na^SOj.lOHoO,  which  is  contained  in 
sea-water  and  in  many  mineral  wraters,  and  when  solid,  in  efflor- 
escent crusts,  is  named  thenardite ;  glaserite,  ILSO^  in  sea- water 
and  spring- water ;  schonite,  KJVEg^SO^.fil^O,  anhydrite,  CaSO4, 
and  gypsum,  CaSO4.2H2O  ;  celestin,  SrSO4 ;  heavy  spar,  or 
barytes,  BaSO4 ;  Epsom  salt,  MgSO4.7H2O;  feather  alum, 

*  Poff  %  Ann.,  156,  531. 

f  Comptes  rend.,  86,  20,  277 ;  90,  269. 


410      THE   OXIDES,    SULPHIDES,    SELENTDES,   AND    TELLURIDES. 

A12(SO4)3.18H2O  ;  alum  stone,  A1KSO4.2A1(OH)3;  copperas,  or 
green  vitriol,  FeSO4.7H2O;  cobalt  vitriol,  CoSO4.7HoO;  anglesite, 
PbSO4;  lanarkite,  a  double  carbonate  and  sulphate  of  lead,  and 
leadhillite,  PbSO4.PbO  ;  and  blue  vitriol,  CuSO4.5H2O.  Lead 
selenate,  PbSeO4.  has  also  been  found  native. 

Preparation.  —  1.  By  direct  union.—  Sulphur,  selenium,  and 
tellurium  burn  with  a  faint  blue  flame  when  heated  in  air,  forming 
the  dioxides.  Heated  in  oxygen,  the  flame  of  burning  sulphur  is 
much  more  brilliant,  and  of  a  fine  lilac  colour.  Its  combustion 
forms  a  telling  experiment.  About  3  or  4  per  cent,  of  the  product 
of  the  combustion  consists  of  sulphur  trioxide,  S03.  The  sulphides 
of  many  metals,  when  roasted  in  air,  give  the  oxide  of  the  metal 
and  sulphur  dioxide.  Iron  pyrites  containing  from  2  to  4  per  cent. 
of  copper  is  made  use  of  in  its  commercial  preparation,  the  copper 
being  extracted  from  the  residue.  The  sulphur  dioxide  is  em- 
ployed directly  in  the  preparation  of  sulphuric  acid.  It  is  also 
a  by-product  in  the  roasting  of  zinc  sulphide,  in  the  smelting 
of  lead  ores  (see  p.  429),  and  in  various  other  metallurgical 
processes. 

2.  By  oxidation  of  a  lower  oxide.  —  Sulphur  trioxide  is 
thus  prepared  on  a  commercial  scale.  In  the  laboratory  it  may 
be  prepared  by  the  following  method  :  — 

A  dry  mixture  of  gaseous  sulphur  dioxide  and  oxygen,  the 
dioxide  being  made  to  bubble  through  the  wash-bottle  containing 
strong  sulphuric  acid  twice  as  quickly  as  the  oxygen,  is  led  through 
a  tube  of  hard  glass,  heated  to  redness,  filled  with  asbestos,  pre- 
viously coated  with  metallic  platinum  by  moistening  it  with 
platinum  tetrachloride,  and  igniting  it.  Under  the  influence  of  the 
finely-divided  platinum,  the  sulphur  dioxide  and  the  oxygen  com 
bine,  and  the  sulphur  trioxide  produced  is  condensed  in  a  flask. 
To  obtain  the  pure  trioxide,  water  must  be  rigorously  excluded, 
and  corks  should  not  be  exposed  to  its  action,  for  they  are  at  once 
attacked. 

By  passing  an  electric  discharge  of  high  potential  through  a 
mixture  of  perfectly  dry  sulphur  dioxide  and  oxygen,  combination 
takes  place  between  4  vols.  of  sulphur  dioxide  and  3  vols.  of 
oxygen  to  form  persulphuric  anhydride  or  disulphur  heptoxide, 


3.  By  reducing  a  higher  oxide.  —  The  trioxides  of  sulphur 
and  of  tellurium,  at  a  red  heat,  decompose  into  the  dioxides  and 
oxygen.  The  vapour  of  sulphuric  or  selenic  acid  also,  at  a  red 
heat,  gives  water,  sulphur  or  selenium  dioxide,  and  oxygen,  and  it 
is  by  this  method  that  a  mixture  in  the  requisite  proportion  of 


SULPHUR  TRIOXIDE  AND   DIOXIDE.  411 

sulphur  dioxide  and  oxygen  is  obtained  on  a  large  scale  for  the 
manufacture  of  sulphur  trioxide.  The  sulphuric  acid  is  decom- 
posed by  causing  it  to  flow  on  to  red-hot  bricks  ;  and  the  mixed 
gases  are  dried  by  passage  upwards  through  a  tower  filled  with 
coke,  kept  moist  by  strong  sulphuric  acid.*  The  mixture  is  then 
passed  over  asbestos  coated,  with  platinum,  as  on  the  small  scale 
(see  previous  page). 

The  reduction  may  also  be  effected  by  chemical  agency.  On 
heating  sulphur  and  sulphuric  acid,  the  dioxide  and  water  are  the 
sole  products,  thus  :—  2(SO3.H20)  +  S  =  3S02  +  2H20.  Carbon 
may  be  used  in  the  form  of  charcoal  ;  in  this  case  a  mixture  of 
carbon  dioxide  and  sulphur  dioxide  is  produced,  from  which  it  is 
not  easy  to  separate  the  carbon  dioxide:  —  2(S03.H20)  -f  C  = 
2S02  +  COZ  +  2H20.  Almost  all  metals,  when  heated  with  strong 
sulphuric  acid,  yield  sulphur  dioxide,  a  sulphate  and  sulphide  of  the 
metal,  hydrogen  sulphide,  free  sulphur,  and  water.  For  example, 
with  copper,  the  metal  most  frequently  employed  in  the  form  of 
foil  or  turnings  in  the  ordinary  laboratory  process  for  preparing 
sulphur  dioxide  :f  — 


(1.)  Cu  +  2H2SO4  =  CuS04  +  SO2  +  2H2O 
(2.)  4Cu  +  5H2SO4  =  4CuSO4  +  H2S  +  4H2O  ; 
(3.)  3Cu  +  4H2SO4  =  3CuS04  +  CuS  +  4H2O  ; 
(4.)  4Cu  +  4H2SO4  =  3CuSO4  +  Cu2S  +  4H2O;  and 
(5.)  SO2  +  2H.2S  -  2H2O  +  3S. 

Reaction  (1)  is  that  which  predominates  ;  but  the  other  reactions 
doubtless  take  place,  for  the  products  are  found  in  the  residue. 

It  is  probable  that  these  reactions  are  due  to  the  action  of  hot 
nascent  or  atomic  hydrogen  on  sulphuric  acid.  Thus,  the  eqna- 
tions  may  also  be  written  :  — 


(1.)  Cu  +  H2SO4  =  CuS04  +  2H;  ~B£O4  +  2H  =  2H2O  +  S02; 

(2.)  H2S04  +  SH=  4H20  +  H^S  ; 

(3.)  CuS04  +  H^S  =  CuS  +  H2SO4;  and 

(4.)  2CuSO4  +  WH  =  Cu2S  +  H2SO4  +  4H2O. 

The  metals  osmium,  iridinm,  platinum,  and  gold  are  the  only 
ones  which  withstand  the  action  of  boiling  sulphuric  acid;  but 
strong  acid  may  be  evaporated  in  iron  pans,  for  the  iron  becomes 
protected  by  a  coating  of  sulphate,  which  is  insoluble  in  oil  of 
vitriol. 

Gold  is,  however,  attacked  by  selenic  acid  ;  the  acid  is  reduced 
by  it  and  other  metals  to  the  dioxide.  Selenic  acid  is  also  converted 

*  Divgl.  polyt.  J.,  218,  128. 
t  Chem.  Soc.t  33,  112. 


412      THE   OXIDES,   SULPHIDES,    SELENIDES,   AND   TELLURIDES. 

into  selenious  acid,  with  evolution  of  cblorine,  by  boiling  it  with 
hydrochloric  acid,  thus  : — 

H2Se04  +  2HCl.Aq  =  H8Se03.Aq  +  H20  +  Clv 

The  oxides  S203,  SSe03,  STe03>  and  SeTe03  are  also  formed 
by  reduction.  They  are  produced  by  dissolving  sulphur  in  fused 
sulphur  trioxide ;  selenium  in  sulphur  trioxide ;  and  tellurium  in 
strong  selenic  acid. 

4.  By  heating  compounds. — Both   sulphites  and  sulphates, 
and  probably  also  selenites,  selenates,  tellurites,  and  tellurates,  when 
heated  to  a  high  temperature  decompose,  leaving  the  oxide  of  the 
metal  with  which  the  oxide  of  sulphur,  selenium,  or  tellurium  was 
combined.     But  the  dioxides  are  usually  produced,  for  the  tem- 
perature at  which  decomposition  occurs  is  almost  always  so  high 
as  to  partially,  at  least,  decompose   the  trioxides.       Anhydrosul- 
phates,  such  as.  Na2S2O7,  however,  give  off  half  their  trioxide  when 
heated,    leaving    the    monosulphate,    Na2SO4.       The    compounds 
with  water,  however,  in  every  case,  except  that  of  selenic  acid,  are 
decomposed  by  heat,  yielding  the  respective  oxide. 

Thus  a  solution  of  sulphur  dioxide  in  water,  presumably  con- 
taining sulphurous  acid,  H2S03,  loses  the  oxide  when  boiled; 
selenious  and  tellurous  oxides  remain  on  evaporating  their  aqueous 
solutions ;  the  latter,  indeed,  separates  out  on  warming  its  solution 
to  40°;  sulphuric  acid,  H2S04,  when  gasified  has  the  density  44'5, 
proving  it  to  have  split  into  its  constituent  oxides,  which,  however, 
recombine  on  cooling ;  the  trioxide  is  prepared,  moreover,  by  dis- 
tilling anhydrosulphuric  acid,  H2S207,  which  decomposes  thus: — 
H2S207  =  H2S04  +  SOZ ',  and  tellurium  trioxide  is  produced  by 
heating  the  hydrate  to  a  temperature  below  redness. 

5.  By  double   decomposition. — As  this  process  is   usually 
carried  out  in  the  presence  of  water,  the  hydrates   (acids)  are  the 
usual  products. 

6.  By  displacement. — This   is  a    convenient  method  of  pre- 
paring   sulphur  trioxide.       Strong  sulphuric    acid  is  mixed  with 
phosphoric  anhydride,  care  being  taken  to    keep    the   acid   cold 
during   mixing.      It    is  then  distilled,   when  the  trioxide  passes 
over,  the  phosphoric  anhydride  having  abstracted  water  from  the 
sulphuric  acid,  thus: — 

H2SO4  +  P205  =  803  +  2HP03. 

A  sulphate  also,  when  strongly  ignited  with  silicon  dioxide, 
or  with  phosphorus  pentoxide,  yields  sulphur  trioxide,  or  its  pro- 
ducts of  decomposition,  the  dioxide  and  oxygen.  This  process 


PROPERTIES   OF  THE   OXIDES   OF   SULPHUR,  ETC.  413 

finds  practical  application  in  the  manufacture  of  glass,  where 
silica  in  the  form  of  sand  is  heated  with  sodium  sulphate,  lime, 
and  carbon.  The  addition  of  carbon  causes  the  conversion  of  the 
sulphate  into  sulphite  ;  the  silica  replaces  the  sulphur  dioxide  at  a 
lower  temperature  than  it  would  replace  the  trioxide  of  the 
sulphate.  A  double  silicate  of  sodium  and  calcium  is  thus 
formed,  which  constitutes  one  variety  of  glass.  The  method,  it 
will  be  seen,  is  not  available  for  the  preparation  of  the  oxides  of 
sulphur. 

Properties. — Sulphur  dioxide  is  a  gas  at  the  ordinary  tem- 
perature, but  it  may  be  easily  condensed  to  a  liquid  by  passing  it 
first  through  a  tube  filled  with  calcium  chloride,  to  dry  it,  and 
then  through  a  leaden  worm  cooled  by  a  mixture  of  salt  and 
crushed  ice. 

It  boils  at  —8°  under  normal  pressure,  and  melts  at  about 
-  79°.  The  liquid  oxide  is  mobile  and  colourless,  and  heavier  than 
water  (1*45).  It  forms  a  white  crystalline  solid  when  sufficiently 
cooled  by  its  own  evaporation.  The  gas  has  the  familiar  smell  of 
burning  sulphur;  it  is  irrespirable ;  it  supports  the  combustion  of 
potassium,  tin,  and  iron,  which  combine  both  with  its  oxygen  and 
its  sulphur.  It  is  readily  soluble  in  water ;  one  volume  of  water 
absorbs  about  fifty  times  its  volume  of  the  gas  at  the  ordinary 
temperature,  probably  with  formation  of  sulphurous  acid,  H2S03. 
Hence  it  cannot  be  collected  over  water ;  but,  as  its  density  is 
high  (32),  it  is  easy  to  collect  it  in  a  jar  by  downward  displace- 
ment. 

Selenium  dioxide  is  a  white  solid,  volatilising  to  a  yellow- 
vapour  without  melting,  at  a  heat  somewhat  below  redness,  and 
condensing  in  white  quadrangular  needles.  Its  vapour  has  a 
sharp  acid  odour.  It  is  soluble  in  water,  producing  selenious 
acid. 

Tellurium  dioxide  is  a  white  solid,  sometimes  crystallising 
in  octahedra.  It  melts  to  a  deep-yellow  liquid,  and  at  a  high 
temperature  it  volatilises.  It  is  sparingly  soluble  in  water,  and 
does  not  appear  to  form  the  acid. 

Sulphur  trioxide  crystallises  in  long  colourless  prisms, 
arranged  in  feathery  groups  ;  it  somewhat  resembles  asbestos.  It 
melts  at  15°,  and  boils  at  46°,  producing  dense  white  fumes  with 
the  moisture  of  the  air.  Its  molecular  weight,  as  shown  by  its 
vapour  density,  is  80.  It  unites  with  water  with  great  violence, 
hissing  like  a  red-hot  iron.  It  is  made  in  considerable  quantity, 
being  used  in  the  manufacture  of  alizarine  or  turkey-red,  and 
other  artificial  dyes. 


414      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

When  this  body  is  kept  for  some  time  at  a  temperature 
below  25°,  it  changes  into  another  modification  which  crystallises 
in  thin  needles.  When  heated  above  50°  it  gradually  liquefies, 
and  changes  into  the  first  modification.  It  is  distinguished 
from  the  first  modification  by  the  difficulty  with  which  it  dis- 
solves in  HaSO*.  and  by  its  crystallising  out  of  the  solution  un- 
changed. 

There  appear  to  be  indications  of  the  existence  of  an  oxide 
S205 ;  for  sulphur  trioxide  dissolves  the  dioxide  in  large  amount, 
and  the  solution  is  stable  up  to  5°. 

No  attempts  to  prepare  selenium  trioxide  have  succeeded. 
The  acid,  when  heated,  decomposes  into  selenium  dioxide,  oxygen, 
and  water.  Selenious  anhydride  is  the  only  product  of  the  action 
of  oxygen,  even  in  the  state  of  ozone,  on  selenium. 

Tellurium  trioxide  is  an  orange-yellow  insoluble  substance, 
which  does  not  dissolve  even  in  hydrochloric  or  nitric  acid. 
When  strongly  heated,  it  loses  oxygen,  producing  tellurium 
dioxide. 

Sulphur,  selenium,  and  tellurium  dissolved  in  pure  melted 
sulphur  trioxide  give  respectively  blue,  green,  and  red  substances. 
The  sulphnr  and  tellurium  compounds  have  been  isolated,  and 
have  been  shown  to  have  the  formula  S2O3  and  STeO3 ;  it  is  pre- 
sumed that  the  others  are  similarly  constituted.  Selenium  and 
tellurium  also  dissolve  in  concentrated  selenic  acid,  doubtless  form- 
ing similar  compounds.  The  sulphur  compound  is  insoluble  in 
perfectly  pure  sulphuric  anhydride,  and  may  be  separated  from  it 
by  decantation.  It  decomposes,  on  exposure  to  air  at  ordinary 
temperatures,  into  sulphur  dioxide  and  sulphur.  It  dissolves  in 
strong  sulphuric  acid,  and,  on  diluting  the  acid,  it  is  decomposed. 
The  tellurium  compound  appears  to  exist  in  two  modifications,  a 
red  one,  and  a  buff-coloured,  obtained  by  heating  the  red  variety 
to  90°. 

Persulphuric  anhydride,  S207,  at  the  ordinary  temperature 
forms  an  oily  liquid  ;  when  cooled  to  0°,  it  solidifies  in  long  thin 
transparent  flexible  needles.  It  sublimes  easily,  and  decomposes 
spontaneously  on  standing  for  a  few  days.  It  dissolves  in  strong 
sulphuric  acid  ;  it  is  immediately  decomposed  by  heat. 

A.  Compounds  with  water  and  oxides;  acids  and  salts 
of  sulphur,  selenium,  and  tellurium.  I. — Compounds  of  the 
trioxides;  sulphuric,  selenic,  and  telluric  acids;  sulphates, 
selenates,  and  tellurates. 

The  trioxide  of  sulphur  dissolves  in  water  with  evolution  of 
great  heat,  forming  various  hydrates,  according  to  the  relative 


SULPHURIC   ACID.  415 

proportion    of    oxide    and     water.       The    following    have    been 
isolated : — 

SO3.5H,O;  S03.3H20;  SO3.2H2O ;  S03.H20  =  H2S04; 
2SO3.H2O  =  H2S2O7. 

Those  containing  less  water  than  ordinary  sulphuric  acid  are 
more  conveniently  produced  by  dissolving  sulphur  trioxide  in  the 
ordinary  acid;  those  containing  more,  by  pouring  ordinary  sul- 
phuric acid  into  water.  Salts  have  been  produced  corresponding 
to  the  acids  H2S04  and  H2S207 ;  they  are  named  sulphates,  and 
pyrosulphates  or  arihydrosulphates  respectively. 

On  boiling  a  solution  of  sulphuric  acid  in  water,  the  water 
evaporates,  and  the  acid  becomes  more  and  more  concentrated, 
until  it  acquires  nearly  the  composition  expressed  by  the  formula 
H2S04 ;  on  further  heating,  this  compound  dissociates  into  trioxide, 
or  anhydride,  $03,  and  water,  both  of  which  evaporate  together. 

Some  of  these  hydrates  may  be  dismissed  in  a  few  words.  The 
hydrate,  S03.5H20  =  H2S04.4H2O,  crystallises  out  on  cooling  sul- 
phuric acid  containing  the  correct  amount  of  water  to  a  very  low 
temperature.  It  melts  at  —25°.  H2S04.2H2O  is  the  point  of 
maximum  contraction  of  sulphuric  acid  and  water,  but  has  not 
been  obtained  in  a  solid  state;  and  H2SO4.H2O  is  also  obtained 
by  cooling  a  mixture  in  the  correct  proportion.  It  melts  at  8°. 
The  corresponding  selenic  acid,  H2SeO4.H2O,  melts  at  25°.  The 
monohydrate  requires  particular  attention. 

Sulphuric  acid,  "oil  of  vitriol,"  H2S04.— Sulphur  trioxide, 
as  has  been  mentioned,  is  decomposed  by  heat,  and  hence  it  cannot 
be  produced  in  quantity  by  the  combustion  of  sulphur  in  air  or 
oxygen,  for  the  temperature  of  burning  sulphur  is  higher  than  that 
at  which  the  trioxide  decomposes.  Hence  an  indirect  method  of 
preparation  must  be  chosen.  It  can  be  prepared  in  aqueous 
solution  by  oxidising  sulphur;  for  example,  when  boiled  with 
nitric  acid,  that  acid  parts  with  its  oxygen,  oxidising  the  sulphur 
to  sulphuric  acid,  while  oxides  of  nitrogen  are  liberated.  Sulphur 
may  also  be  oxidised  on  treatment  with  chlorine  and  water, 
thus : — 

S  +  3C12  +  4H20  =  H2S04  +  6HC1. 

It  will  be  remembered  that  the  halogen  acids  may  be  prepared 
by  the  action  of  the  halogens  in  presence  of  water  on  hjdrogeii 
sulphide  (see  p.  106)  ;  and,  similarly,  an  aqueous  solution  of  sulphur 
dioxide  is  oxidised  to  sulphuric  acid  by  their  action.  Chromic 
acid  and  other  oxidising  agents  also  effect  such  oxidation. 


416      THE   OXIDES,   SULPHIDES,    SELENIDES,   AND    TELLUEIDES. 

But  such  processes  are  too  expensive  to  be  used  in  manufacture. 
The  main  outlines  of  the  process  actually  in  use  are  givren  here  ; 
the  details  and  the  connection  of  this  with  other  manufactures 
will  be  described  later  (see  p.  667). 

Sulphur  dioxide  at  once  attacks  nitrogen  peroxide,  N02.  With- 
out discussing  intermediate  products,  which  will  be  afterwards 
•considered,  the  final  reaction,  in  presence  of  water  at  least,  is 
80Z  +  NOZ  +  jff20  =  S03.H20  4-  NO.  In  presence  of  air,  as 
has  been  seen  on  p.  333,  nitric  oxide  is  oxidised  to  a  mixture  of 
peroxide  and  tetroxide,  JV02  and  N^O*.  These  gases  again  part  with 
their  oxygen  when  brought  in  contact  with  a  fresh  supply  of  sulphur 
dioxide.  In  theory,  then,  a  small  amount  of  nitrogen  dioxide  is 
capable  of  converting  an  indefinite  amount  of  sulphur  dioxide,  in 
presence  of  oxygen  and  water,  into  sulphuric  acid.  The  nitrogen 
dioxide  required  for  this  process  is  derived  from  nitric  acid,  pre- 
pared in  the  usual  manner,  i.e.,  from  sodium  nitrate  and  sulphuric 
acid.  On  bringing  it  into  contact  with  sulphur  dioxide,  it  is 
reduced,  and  gives  an  effective  mixture  of  oxides  of  nitrogen. 
This  process  may  be  illustrated  by  the  following  experiment : — 
D  is  a  flask  containing  copper  turnings  and  strong  sulphuric 


FIG.  42. 

acid,  from  which,  on  applying  heat,  sulphur  dioxide  is  generated. 
B  is  a  similar  flask  containing  copper  turnings  and  dilute  nitric 
acid,  and  yields  a  supply  of  nitric  oxide  when  warmed.  E  is  a 
flask  containing  water.  The  delivery  tubes  of  these  flasks  all 
enter  the  large  balloon,  A,  through  a  large  perforated  cork;  a 
crlass  tube  passes  to  the  bottom  of  the  globe  through  a  fourth  hole 
in  the  cork,  and  serves  as  an  exit  tube  for  any  excess  of  gas. 
Nitric  oxide  is  first  passed  into  the  globe.  It  unites  with  the 


SELEXIC  AXD   TELLURIC   ACIDS.  417 

oxygen  of  the  air,  forming  a  mixture  of  the  dioxide  and  peroxide, 
which  are  at  once  notfcefcble  as  red  fumes.  Sulphur  dioxide  is 
passed  in  next,  and  reacts  with  the  peroxide ;  it  will  be  noticed 
that  the  sides  of  the  globe  soon  become  covered  with  radiating 
crystals.  These  are  described  later;  they  consist  of  hydrogen 
nitrosyl  sulphate,  SO2(OH)(ONO),  and  are  known  as  "chamber 
crystals."  Steam  is  then  passed  into  the  globe  by  boiling  the  water 
in  the  flask,  E.  The  crystals  disappear  and  the  liquid  which 
collects  in  the  globe  is  dilute  sulphuric  acid.  It  may  be  concen- 
trated by  evaporation  in  a  porcelain  or  platinum  basin,  till  its 
strength  is  little  below  that  indicated  by  the  formula  H2S04. 

Selenic  acid*  may  be  prepared,  like  sulphuric  acid,  by  the 
action  of  chlorine  water  on  selenium,  or,  better,  on  selenious  acid ; 
but  on  concentration,  the  selenic  acid  is  reduced  by  the  hydro- 
chloric acid  with  evolution  of  chlorine.  A  better  plan  is  to 
saturate  a  solution  of  selenious  acid  with  chlorine  gas,  thereby 
converting  that  acid  into  selenic  acid;  to  saturate  the  mixed 
selenic  and  hydrochloric  acids  with  copper  carbonate,  forming  a 
mixture  of  copper  selenate  and  chloride ;  to  evaporate  to  dryness, 
and  extract  with  alcohol,  which  dissolves  the  copper  chloride, 
leaving  the  selenate  ;  and,  finally,  to  dissolve  the  selenate  in  water, 
and  liberate  the  selenic  acid  by  precipitating  the  copper  as  sul- 
phide by  a  current  of  hydrogen  sulphide.  After  filtering  off  the 
copper  sulphide,  the  selenic  acid  is  concentrated  by  evaporation. 
It  can  be  obtained  nearly  anhydrous  by  evaporation  in  a  vacuum 
at  180°.  The  acid  has  then  the  formula  H2Se04.  A  higher  tem- 
perature decomposes  it  into  selenium  dioxide,  water,  and  oxygen. 
One  other  hydrate  of  selenium  trioxide  has  been  prepared  by  cool- 
ing a  solution  of  the  acid  of  the  requisite  strength  to  —32°.  It 
has  the  formula  H2Se04.H20,  and  melts  at  25°.  Attempts  to 
prepare  other  hydrates  in  the  solid  state  have  not  been  successful. 

Telluric  acid  is  produced  in  solution  by  treating  the  barium 
salt  (obtained  by  heating  tellurium  with  barium  nitrate)  sus- 
pended in  water,  with  the  requisite  amount  of  sulphuric  acid,  and, 
after  filtration,  concentrating  the  acid  by  evaporation.  Colourless 
hexagonal  prisms  of  the  formula  H2TeO4.2H>O  separate  out  on 
cooling.  It  loses  its  water  a  little  above  100°,  leaving  the  acid 
H2TeO4  as  a  white  solid. 

These  acids  are  also  produced  by  the  action  of  water  on  the 
chlorides,  S02C12,  Se02Cl2,  and  Te02Cl2. 

Sulphuric    and    selenic    acids    are    dense,    viscid,    colourless 

*  Proc.  Soy.  Soc.,  46,  13. 


418      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

liquids,  exceedingly  corrosive,  inasmuch  as  they  abstract  the 
elements  of  water  from  many  organic  substances  containing  carbon, 
hydrogen,  and  oxygen.  A  piece  of  wood  placed  in  strong  sul- 
phuric acid  is  blackened  and  charred,  and  suga.r  placed  in  contact 
with  it  is  converted  into  a  tumefied  mass  of  impure  carbon.  Pure 
anhydrous  sulphuric  acid,  H2SO4,  is,  however,  a  solid,  melting  at 
10'5°,  and  selenic  acid,  H2SeO4,  melts  at  58°.  The  presence  of  a 
mere  trace  of  water  greatly  lowers  the  melting  points  of  these 
bodies. 

The  hydrate  of  telluric  acid,  H2TeO4.2H2O,  dissolves  slowly, 
but  to  a  considerable  extent  in  water.  The  anhydrous  acid, 
H2TeO4,  can  be  dissolved  only  by  prolonged  boiling  with  water. 

These  acids  cannot  be  said  to  boil,  in  the  purely  physical 
sense  of  the  word.  At  the  ordinary  temperature,  sulphuric  acid, 
if  perfectly  pure,  gives  off  sulphur  trioxide,  hence  the  only  method 
of  obtaining  an  acid  precisely  corresponding  to  the  formula  H2S04, 
is  to  add  sulphuric  anhydride  to  ordinary  oil  of  vitriol.  When 
concentrated  by  evaporation  as  far  as  possible,  the  acid  contains 
about  98  per  cent,  of  H2S04.  On  further  heating  to  327°,  this  acid 
dissociates  with  apparent  ebullition  into  water  and  trioxide,  which 
recombine  on  cooling,  forming  an  acid  of  the  same  composition. 
By  taking  advantage  of  the  different  rates  of  diffusion  of  water- 
gas  and  sulphuric  anhydride,  which  possess  respectively  the 
densities  9  and  40,  and  whose  ratio  of  diffusion  is  therefore  as 
-v/9,  a  much  stronger  acid  has  been  obtained.  Acid  con- 


FJG.  43. 


SULPHATES,   SELEXATES,  AND  TELLURATES.  419 

tabling  5  per  cent,  of  water  was  boiled  in  a  flask,  while  a  gentle 
current  of  air  passed  downwards  through  a  tube,  sealed  on  to 
the  bottom  of  the  other  flask  ;  after  an  hour,  the  composition  of 
the  remaining  acid  was  approximately  60  per  cent,  of  H2S04,  and 
40  per  cent,  of  S03.  This  process  of  concentration  is  not  applied 
on  a  large  scale. 

Pure  selenic  acid  begins  to  decompose  into  dioxide,  oxygen,  and 
water  at  about  200°.  On  distilling  dilute  selenic  acid,  water  passes 
over  up  to  205° ;  a  little  dilute  acid  then  begins  to  distil  over,  and, 
at  260°,  white  fumes  appear,  containing  a  little  trioxide,  but  for 
the  most  part  consisting  of  selenium  dioxide. 

Telluric  acid  is  non- volatile,  and  parts  with  its  water  below  a  red 
heat,  leaving  the  anhydride,  TeO3. 

A  great  rise  of  temperature  is  produced  by  the  action  of  water 
on  sulphuric  and  selenic  acids,  due  to  their  combination  with  it  to 
form  hydrates. 

The  specific  gravity  of  ordinary  sulphuric  acid  is  approximately 
1'84  at  15°;  that  of  selenic  acid,  2'61  at  15°;  and  of  telluric  acid, 
3-42  at  18-8°. 

Sulphates,  selenates,  and  tellurates.— These  salts  are  ob- 
tained by  the  action  of  the  acids  on  aqueous  solutions  of  the 
hydroxides  or  carbonates  of  the  metals ;  by  the  action  of  the  con- 
centrated acids  at  a  high  temperature  on  most  metals,  with  evolu- 
tion of  the  dioxides  ;  by  the  action  of  aqueous  solutions  of  the 
acids  on  many  of  the  metals  themselves,  on  the  oxides,  or  hydroxides, 
and  on  some  of  the  sulphides  ;  and  by  heating  a  mixture  of  the 
acid  and  a  halide,  nitrate,  or  acetate  of  a  metal,  or,  in  short,  with 
any  salt  containing  a  volatile  or  decomposable  oxide.  Thus,  for 
example  : — 

H2S04.Aq  +  2KOH.Aq  =  K2S04.Aq  +  2H2O; 

Te03  +  Na2CO3.Aq  =  Na<,TeO4.Aq  +   CO2; 

H2SO4.Aq  +  Zn  =  ZnSO4.Aq  +  JT2; 

H2SeO4.Aq  +  CuO  =  CuSeO4.Aq  +  H2O; 

H2SO4.Aq  +  FeS  =  FeSO4.Aq  +  H2S ; 

H2SO4  +  2NaCl  =  Na2SO4  +  2HCI; 

H2SO4.Aq  +  CaSO3  =  CaSO4  +  SO2  +  Aq; 

H2SO4  +  CaSi03  =  CaSO8  +  H2SiO3. 

The  salts  of  calcium,  strontium,  barium,  and  lead  are  insoluble, 
or  nearly  insoluble,  and  may  therefore  be  produced  by  addition  of 
a  soluble  sulphate,  selenate,  or  tellurate,  to  the  solution  of  a  soluble 
salt  of  one  of  these  metals,  thus  : — 

CaCl2.Aq  +  NagSOi-Aq  .=  CaSO4  +  2NaCl.Aq; 
Pb(N03)2.Aq  +  K2Se04.Aq  =  PbSO4  +  2KNO8.Aq. 

2  E  2 


420      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

The  other  sulphates  and  selenates  are  soluble  in  water.  Many 
of  the  tellurates  are  insoluble,  and  may  be  produced  by  precipita- 
tion. The  sulphates  are  also  formed  by  the  oxidation  of  sul- 
phides by  boiling  with  nitric  acid  ;  by  the  action  of  chlorine 
water  ;  or  by  the  action  of  air. 


Li2S04.H20;  Na2S04.7,  and  10H2O  ;  ILjSO^  K,b2SO4;  Cs2SO4;  (NH4)2SO4.— 
Na2Se04.10H20;  I^SeO4;  (NH4)2SeO4.—  K2TeO4.5H2b;  (NH,)2TeO4. 

Lithium  sulphate  crystallises  in  flat  tables,  easily  soluble  in 
water  and  alcohol.  Sodium  sulphate  occurs  anhydrous  as  thenar- 
dite  ;  and  when  crystallised  with  10H2O  it  is  known  as  Glauber's 
salt.  It  is  prepared  in  immense  quantity  from  common  salt  and 
sulphuric  acid,  as  a  preliminary  to  the  manufacture  of  sodium  car- 
bonate, and  is  then  termed  "  salt-cake."  It  is  also  produced  by 
passing  a  mixture  of  steam,  air,  and  sulphur  dioxide  through 
sodium  chloride,  heated  to  dull  redness  (Hargreave's  process).  It, 
is  obtained  as  a  residue  in  the  preparation  of  nitric  and  of  acetic 
acid  ;  of  ammonium  chloride  ;  and  of  common  salt  by  the  evapora- 
tion of  sea-  water.  It  crystallises  in  an  anhydrous  state  from  water 
at  40°  in  rhombic  octahedra.  It  is  insoluble  in  alcohol,  but  very 
soluble  in  water  ;  100  parts  of  water  dissolve  12  parts  at  0°,  and 
48  parts  at  18°.  It  crystallises  with  10H20  in  large,  colourless, 
monoclinic  prisms.  Crystals  with  7H20  are  deposited  below  18°. 
On  raising  the  temperature  of  a  saturated  solution  above  33°,  the 
anhydrous  salt  deposits,  hence  it  appears  to  possess  a  lower  solu- 
bility at  high  than  at  low  temperatures.  This  apparent  abnor- 
mality is  doubtless  explained  by  the  dissociation  of  the  solution 
of  the  decahydrate,  Na2S04.10H20,  as  the  temperature  rises. 
Sodium  selenate  is  isomorphous  with  and  closely  resembles  the 
sulphate.  The  tellurate  has  not  been  carefully  examined. 

Potassium  sulphate  crystallises  from  the  aqueous  extract  of 
kelp  (burned  seaweed),  in  trimetric  prisms  or  pyramids.  It  is 
among  the  least  soluble  of  the  potassium  salts,  100  parts  of  water 
dissolving  8'36  parts  at  0°.  It  is  insoluble  in  alcohol.  Both 
sodium  and  potassium  sulphates  have  a  saline  bitter  taste,  and  a 
purgative  action.  Potassium  selenate  is  produced  by  fusing 
selenium  or  potassium  selenite  with  nitre,  and  crystallisation  from 
water;  it  resembles  the  sulphate.  The  tellurate  forms  rhombic 
crystals  ;  they  deliquesce  in  air',  becoming  converted  by  carbon 
dioxide  and  water  into  carbonate  and  ditellurate.  Rubidium  and 
oaBsium  sulphates  resemble  that  of  potassium,  but  are  much  more 
soluble  in  water.  Ammonium  sulphate,  selenate,  and  tellurate  are 
isomorphous  with  potassium  sulphate,  but  are  more  soluble.  The 


SULPHATES,   SELENATES,  AND   TELLURATES.  421 

sulphate,  when  heated,  decomposes  above  280°,  yielding  ammonia 
water,   and  nitrogen,  and   a    sublimate    of  hydrogen    ammonium 
sulphate;  the  selenate  gives,  first,  hydrogen  ammonium  selenate, 
and  then  selenium,  its  dioxide,  water,  and  nitrogen.     These  salts, 
with  the  exception  of  lithium  sulphate,  are  all  insoluble  in  alcohol. 

Double  salts  :—HLiS04  ;  HNaSO4;  HKSO4  ;  H(NH4)SO4.—  HKSeO4  ; 
H(NH4)Se04.—  HNaTe04;  2HKTeO4.3H2O.-HNa,(SO4)2  ;  H3Na(SO4)2  ; 
HK3(S04)2;  H3K(,S04)2;  LiKSO4;  NaK3(SO4)2;  H2K4(SO4)3;  Li4(NH4)2(SO4)3; 
Li,K4(S04)3;  NaK^SO^g;  HK3(TeO4)2. 


These  substances  are  white  crystalline  bodies,  very  soluble  in 
water,  and  also,  as  a  rule,  in  alcohol.  They  are  produced  by 
mixture  and  crystallisation.  Bisulphate  of  potassium,  as  hydrogen 
potassium  sulphate  is  generally  named,  is  used  in  decomposing 
various  minerals,  which  are  for  that  purpose  reduced  to  fine 
powder,  mixed  with  the  salt,  and  fused.  When  carefully  heated 
it  loses  water  and  yields  the  anhydrosulphate,  or  true  disalphate, 
K2S207.  Sodium  tri  potassium  sulphate  is  technically  named  plate- 
salt,  from  its  crystallising  in  hexagonal  plates;  it  deposits  on 
cooling  an  aqueous  extract  of  kelp. 

The  existence  of  the  more  complex  double  sulphates  leads  to 
the  conclusion  that  the  molecular  formulae  of  the  ordinary  sul- 
phates are  not  so  simple  as  they  are  usually  written.  Such 
formula  as  HaK^SC^):,  and  NaK5(S04)3,  lead  to  the  conclusion 
that  the  formula  of  potassium  sulphate  is  probably  at  least 
K6(S04)3.  Double  salts  with  other  acids  are  also  known;  e.g., 
KoSOi.H^TOa  and  K2S04.H3P04  separate  from  solutions  of  potas- 
sium sulphate  in  nitric  or  phosphoric  acid.  They  are,  however, 
decomposed  by  water.  The  existence  of  such  salts  would  also 
favour  the  supposition  of  greater  complexity  of  molecule. 


BeSO4.2,  4,  and  GE^O;  CaSO4.2H2O  ;  2CaSO4.H2O  ;  SrSO4.    BaSO4.  — 
BeSeO4.4H2O  ;  CaSeO4.2H2O  ;  SrSeO4  ;  BaSeO4.— 
CaTeO4  ;  SrTeO4  ;  BaTeO4.3H2O. 

With  the  exception  of  beryllium  sulphate,  which  is  soluble, 
all  these  compounds  may  be  prepared  by  precipitation.  Beryllium 
sulphate  forms  quadratic  octahedra  ;  it  is  insoluble  in  alcohol  but 
very  soluble  in  water.  On  evaporation  with  beryllium  carbonate, 
it  yields  gummy  basic  salts  of  the  formulas 

SO3.2BeO.3H2O  ;  SO3.3BeO.4H2O  ;  SO3.6BeO.3H2O. 

Calcium  sulphate  occurs  abundantly  in  the  native  form  in  salt 
mines.  When  anhydrous,  it  forms  trimetric  prisms,  and  is  named 
anhydrite  ;  and  with  two  molecules  of  water  it  is  gypsum  ;  indivi- 


422      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

dual  varieties  of  gypsum  are  named  selenite,  alabaster,  and  satin- 
spar  ;  selenite  forms  transparent  colourless  monoclinic  crystals ; 
the  massive  variety  is  alabaster ;  and  satin-spar  is  fibrous.  When 
gypsum  is  heated  and  ground  it  forms  "  plaster  of  Paris,"  a 
material  much  employed  in  taking  casts,  and  as  a  cement.  The 
dihydrated  calcium  sulphate  becomes  anhydrous  and  falls  to  a 
powder  when  heated  ;  on  mixing  the  powder  with  water,  a  pasty 
mass  is  produced  with  which  casts  may  be  taken.  After  a  few 
minutes  it  hardens,  expanding  slightly  at  the  same  time,  and 
forms  a  fine  white  material.  Plaster  of  Paris,  mixed  with  a 
saturated  solution  of  potassium  sulphate,  gives  a  paste  which 
solidifies  more  rapidly  than  ordinary  plaster  of  Paris,  and  has  a 
nacreous  lustre ;  for  certain  purposes  this  mixture  is  to  be 
preferred  to  the  ordinary  one.  A  double  salt  K2Ca(SO4)2.H2O,  is 
produced.  Hydrated  calcium  sulphate  is  very  sparingly  soluble 
in  water,  and  is  more  soluble  in  cold  than  in  hot  water  (1  in  420 
at  20°).  This  is  probably  due  to  the  solution  containing  the 
dihydrated  compound,  which  loses  water,  becoming  insoluble  as 
the  temperature  rises.  It  is  much  more  soluble  in  weak  hydro- 
chloric or  nitric  acid;  or  in  presence  of  common  salt,  or  of  sodium 
thiosulphate.  Its  solubility  in  the  last  affords  a  method  of  sepa- 
rating calcium  from  barium.  Calcium  sulphate  melts  at  a  red 
heat.  The  selenate  closely  resembles  the  sulphate  in  preparation 
and  properties,  and  is  isomorphous  with  it.  It  is  reduced  to  the 
selenite,  however,  when  boiled  with  hydrochloric  acid,  chlorine 
being  evolved. 

Calcium  tellurate  is  a  white  precipitate,  soluble  in  hot  water. 

Strontium  sulphate,  SrS04,  occurs  native  as  ccelestin  in  tri- 
metric  crystals.  It  is  soluble  in  about  7,000  parts  of  cold  water ; 
it  fuses  at  a  bright  red  heat.  The  selenate  resembles  it. 

Barium  sulphate  occurs  as  heavy-spar  or  barytes,  in  large 
quantity ;  it  forms  trimetric  crystals.  A  solution  of  barium 
chloride  or  nitrate  is  the  common  reagent  for  sulphuric  acid.  On 
adding  it  to  a  sulphate,  a  dense  white  precipitate  is  produced, 
practically  insoluble  in  water  and  acids.  Its  insolubility  serves  to 
distinguish  it  from  most  other  bodies  of  similar  appearance.  In 
estimating  sulphuric  acid,  it  is  always  weighed  in  the  form  of 
barium  sulphate.  It  is  unaltered  by  ignition ;  when  heated  with 
charcoal  or  coke,  however,  it  yields  barium  sulphide  ;  and  this  is 
the  usual  process  of  preparing  compounds  of  barium,  since  the 
sulphide  dissolves  in  acids.  Barium  sulphate  reacts  to  a  limited 
extent  when  boiled  with  a  solution  of  sodium  carbonate ;  a 
portion  is  converted  into  carbonate,  thus  : — 


SULPHATES,  SELENATES,   AND   TELLURATES.  423 


BaSO4  +  Na^COg.Aq  =  BaCO3  +  Na2S04.Aq. 

But  the  reaction  is  incomplete.  It  is  only  after  removal  of  the 
sodium  sulphate  and  replacement  by  fresh  sodium  carbonate  that 
further  decomposition  takes  place.  On  fusion  with  excess  of  sodium 
or  potassium  carbonate,  however,  it  is  completely  converted  into 
carbonate.  Barium  sulphate  has  been  used  as  a  pigment  under  the 
name  permanent  white  ;  it  has  too  little  body,  and  hence  it  is 
generally  mixed  with  white-lead  or  zinc-  white  (ZnS).  Barium 
selenate  closely  resembles  the  sulphate,  but  it  is  decomposed  on 
boiling  with  hydrochloric  acid,  selenious  acid  and  chlorine  being 
formed.  This  serves  to  distinguish  it,  and  to  separate  it  from 
the  sulphate.  The  tellurate  is  fairly  soluble  in  warm  water. 

Double  sulphates,  selenates,  and  tellurates.  —  K2Be(SO4)2;  H.2Ca(SO4V2; 
H2Sr(SO4)2;    H2Ba(SO4)2,    also    with    2H,O  ;    H6Ca(SO4)4;    Na.2Ca(SO4)2; 
;  Na4Ca(S04)3.2HoOj  K.2Ca2(SO4)3.3H:2O  ;   H2Ba(TeO4)2.2H2O. 


Hydrogen  calcium  and  barium,  sulphates  are  crystalline  bodies 
produced  by  dissolving  the  ordinary  sulphates  in  strong  sulphuric 
acid  and  crystallising.  They  are  decomposed  by  water.  The 
tellurate  is  soluble  in  water.  The  double  salts  are  prepared  by 
digesting  the  simple  salts  with  sodium  or  potassium  sulphate  ; 
that  of  calcium  crystallises  out  with  2H20,  but  at  a  higher 
temperature  loses  water,  and  is  then  identical  with  the  mineral 
glauberite,  crystallising  in  rhombic  prisms. 

Mg-SO4.7,  6,  and  1H2O;  ZnSO4.7,  6,  5,  2,  and  1H2O;  CdSO4.4H.:O, 
also  1H2O,  and  3CdSO4.8H2O.—  MgSeO4.7H2O  ;  ZnSeO4.7,  6,  and  2H2O  ; 
CdSeO4.2H2O.—  M&TeO4  ;  CdTeO4. 


These  salts  are  all  easily  soluble  in  water,  except  magnesium 
and  cadmium  tellurates,  which  are  produced  by  precipitation  from 
concentrated  solutions.  Magnesium  sulphate,  as  Epsom  salt, 
MgSO4.7H2O,  and  as  kieserite,  MgSO4.H2O,  occurs  native  in 
caves  in  magnesium  limestone  and  in  the  salt-beds  of  Stassfurth. 
It  is  a  frequent  constituent  of  mineral  waters.  It  has  a  bitter 
taste  and  a  purgative  action.  It  is  made  on  the  large  scale  by 
treating  dolomite,  a  carbonate  of  magnesia  and  calcium,  or  serpentine, 
a  hydrated  silicate,  with  sulphuric  acid.  The  hepta-hydrated  sul- 
phates and  selenates  of  magnesium  and  zinc  are  isomorphous,  and 
crystallise  in  four-sided  right  rhombic  prisms.  When  heated  to 
150°  they  lose  6H30,  but  retain  tbe  seventh  molecule  even  at  200°. 
Anhydrous  magnesium  sulphate  melts  at  a  red  heat  ;  the  cadmium 
and  zinc  salts  lose  trioxide,  leaving  the  oxides.  These  salts  are 
insoluble  in  alcohol.  Zinc  sulphate,  digested  with  hydroxide, 


424      THE   OXIDES,   SULPHIDES,  SELENIDES,  AND  TELLURIDES. 

yields  several  basic  sulphates:  SO3.2ZnO ;  SO3.4ZnO.10  and 
2H2O  ;  SO3.6ZnO.10H2O  ;  and  SO,.8ZnO.2H2O.  With  excep- 
tion of  the  first,  they  are  crystalline  bodies. 

Mixed  salts.— 

H2Mg(S04)2;  H6Mgr(S04>>4;  Na2Mg-(SO4)2.6H2O; 
K2Mg-(SO4)2.6H2O ;  K2CaoMg-(SO4)4.2H2O ; 
Na2Zn(S04)2.4H2O  ;   (NH4)2Zn(SO4)2.6H2O ; 
Mg-Zn(S04)214H20;  Na2Cd(SO4)2.6H2O, 

and  other  similar  salts.  These  are  all  soluble,  and  are  prepared  by 
mixture. 

.  •       B2(S04)3.H20  :  Sc2(S04)3.6H20  ;  Y2(SO4)3.8H2O  ;  La2(SO4)3.9H2O.— 

Seleiiates  and  tellurates  have  not  been  prepared.  Boron  sulphate 
is  a  white  mass,  produced  by  evapora.ting  boron  trioxide  with  sul- 
phuric acid.*  It  is  decomposed  by  water.  The  other  salts  of  the 
group  are  white  and  crystalline. 

Double  salts. — 

H3B(S04)3;   (NH4)Sc(S04)2;  K4Sc2(SO4)5;  Na3Sc(SO4)3.6H2O  ; 
K3Y(S04)3.wH20;  Na3Y(S04)3.2H20;  (NH4)La(SO4)2.4H2O;  K3La(SO4)3. 

These  salts  are  sparingly  soluble,  and  are  produced  by  mixture. 

A12(S04)3.18H20 ;  Ga2(S04)3;  In2(SO4)3.9H2O;  T12(SO4)3.7H2O.— 
Al2(SeO4)3.wH2O;  and  the  frhallous  salts  T12SO4 ;  HT1SO4  ;  and  Tl2SeO4. 

Sulphate  of  aluminium,  containing  18H20,  occurs  native  as 
alunogen,  or  feather  alum ;  it  forms  delicatQ  fibrous  masses  or 
crusts.  It  is  known  in  commerce  as  "  concentrated  alum,"  and 
is  prepared  by  heating  finely  ground  clay  with  strong  sulphuric 
acid  until  the  latter  begins  to  volatilise.  After  lying  some  days, 
it  is  treated  with  water ;  the  solution  is  freed  from  iron  by  pre- 
cipitating it  as  ferrocyanide,  or  by  addition  of  certain  peroxides, 
such  as  those  of  lead  or  manganese ;  it  is  then  evaporated  to 
dryness  and  fused.  It  crystallises  with  difficulty,  being  exceed- 
ingly soluble  (1  in  2  parts  of  water)  ;  its  crystallisation  may  be 
furthered  by  addition  of  alcohol,  in  which  it  is  insoluble.  Basic 
salts  are  known,  produced  by  the  action  of  hydrated  alumina  on 
the  ordinary  sulphate,  by  incomplete  precipitation  with  ammonia, 
or  by  the  action  of  zinc  on  a  solution  of  ordinary  sulphate.  These 
are  said  to  have  the  formulae  3SO32A12O3;  3SO3.3A12O3.9H2O 
(occurring  native  as  aluminite)  •  3SO3.4A12O3.36H2O ;  and 
3SO3.5ALO3.20H2O.  The  selenate  closely  resembles  the  sulphate, 

*  J.  PraJct.  Chem.  (2),  38,  118. 


SULPHATES,  SELEXATES,  AND  TELLUKATES.       425 

and  yields  corresponding  basic  salts.  The  tellurate  is  a  white  pre- 
cipitate. Gallium  sulphate,  Ga^SO^s,  is  very  soluble,  and  crystal- 
lises in  nacreous  scales  ;  indium  sulphate  has  been  obtained  only  as 
a  gummy  mass  ;  and  thallic  sulphate  forms  thin  colourless  laminae, 
which  are  decomposed  by  water  into  the  hydrated  trioxide  and  sul- 
phuric acid. 

Thallous  sulphate  and  selenate  crystallise  in  anhydrous  rhom- 
bic prisms  isomorphous  with  potassium  sulphate.  They  are  soluble 
in  water.  They  establish  a  link  between  the  aluminium  and  the 
potassium  groups. 

Double  salts. — The  alums. — These  bodies  are  very  numerous. 
They  all  crystallise  in  regular  octahedra,  are  soluble  in  water,  and 
have  the  general  formula  M']V["'RO4.12H2O,  where  M'  stands  for 
lithium,  sodium,  potassium,  rubidium,  cesium,  ammonium,  thal- 
lium (as  a  thallons  compound),  or  silver;  M'"  for  aluminium, 
gallium,  indium,  chromium,  ferric  iron,  manganic  manganese,  or 
cobaltic  cobalt;*  and  R  for  sulphur  or  selenium.  Tellurium 
alums  do  not  seem  to  have  been  prepared.  The  number  of  possible 
different  alums  is  therefore  96 ;  of  these  some  25  have  been  pre- 
pared. Alums  containing  aluminium,  gallium,  and  indium  are 
colourless ;  chromium  alums  are  very  deep  purple ;  iron  alums, 
pink ;  and  manganese  alums,  brownish-red.  As  they  are  all  iso- 
morphous, they  crystallise  together.  For  example,  an  alum  con- 
taining aluminium  and  potassium  placed  as  a  nucleus  in  a  solution 
of  chromium  alum  becomes  covered  with  a  regular  deposit  of  the 
latter,  and  a  coating  of  iron  alum  may  be  deposited  on  the 
exterior. 

Alums  are  prepared  by  mixing  solutions  of  the  sulphates  or 
selenates  of  the  two  metals,  and  crystallising.  The  most  important 
are  potassium  aluminium  sulphate,  and  ammonium  alumi- 
nium sulphate,  KA1(SO4)2.12H2O,  and  NH4A1(SO4)2 12H2O. 
Ammonium  alum,  which  also  occurs  native  as  tchermigite,is  prepared 
by  mixture  ;  100  parts  of  water  dissolve  5*22  parts  at  0°,  and  421'9 
parts  at  100°.  Potassium  alum  is  prepared  on  a  very  large  scale 
by  calcining  aluminous  schists,  which  are  essentially  impure  sili- 
cate of  aluminium  containing  quantities  of  iron  pyrites  and  car- 
bonaceous matter.  The  pyrites  on  ignition  forms  ferrous  sulphate, 
FeSO4,  and  free  sulphuric  acid.  The  ignited  mineral  is  methodi- 
cally extracted  with  water,  and  the  liquors  are  concentrated  in 
leaden  pans,  giving  an  acid  solution  of  aluminium  sulphate  con- 
taining ferrous  or  ferric  sulphates.  To  this  liquor,  a  concentrated 

*  Proc.  Roy.  Soc.  Ed.,  123,  203. 


426      THE    OXIDES,    SULPHIDES,   SELENIDES,    AND   TELLURIDES. 

solution  of  potassium  chloride  is  added.  It  is  preferable  to  the 
Bulphate,  for  it  forms,  with  the  iron  sulphate,  uncrystallisable 
ferric  chloride  along  with  potassium  sulphate.  After  settling,  it 
is  run  into  coolers  to  crystallise.  The  confused  crystals  which 
separate  are  washed,  drained,  dissolved  in  fresh  water,  and  re- 
crystallised  in  casks.  It  is  sometimes  freed  from  iron  before  the 
second  crystallisation  by  one  of  the  methods  already  described 
(p.  424). 

The  chief  use  of  alum  is  as  a  mordant  in  dyeing ;  the  sulphate 
and  acetate  of  aluminium  are  used  for  the  same  purpose.  When 
cloth  or  any  mineral  or  vegetable  fibre  is  boiled  in  such  a  solution, 
it  becomes  impregnated  with  hydrated  alumina ;  and  when  treated 
with  a  dye,  a  triple  combination  appears  to  take  place  between  the 
fibre,  the  alumina,  and  the  colouring  matter. 

Some  basic  sulphates  of  aluminium  occur  native.  These  are 
alunite,  4SO3.K2O.^A12O3  3H2O,  found  at  Tolfa,  near  Civita 
Vecchia,  at  Solfatara,  near  Naples,  and  at  Puy  de  Garcy,  in  the 
Auvergne.  It  forms  rhombohedral  crystals,  and  is  used  for  the 
manufacture  of  Roman  alum,  which  has  been  prepared  from  it 
from  very  early  times.  When  it  is  calcined  at  a  moderate  heat, 
the  hydrated  alumina  loses  water,  and  on  lixiviation,  alum  dis- 
solves, and  may  be  crystallised  as  usual.  The  basic  sulphate,  lowigite, 
4SO3.K2O.3A12O3.H2O,  is  also  a  natural  product. 

The  difference  of  solubility  of  potassium  alum  from  that  of  ru- 
bidium and  caesium  alums  has  afforded  a  means  of  separating  from 
each  other  these  elements,  which  almost  always  occur  together. 
Rubidium  and  caesium  alums  are  insoluble  in  a  cold  saturated  solu- 
tion of  potassium  alum ;  hence,  on  concentrating  such  a  mixture, 
the  first  portions  of  the  crystals  consist  chiefly  of  the  former. 
Caesium  alum  is  likewise  insoluble  in  a  saturated  solution  of 
rubidium  alum,  and  may  be  separated  from  the  latter  in  a  similar 
manner. 

Mn(SO4)2. — Produced  by  dissolving  potassium  permanganate, 
KMnO4,  in  a  mixture  of  500  grams  of  sulphuric  acid  and  150  of 
water.  It  is  a  yellow  substance,  which  deposits  a  basic  sulphate 
as  a  black  powder  of  the  formula  MnO.SO4. 

Cra(SO4)8.15  and  5  H2O;  Pez(SO4)3.9H2O;  Mn2(SO4)3.— There 
are  two  hydrated  varieties  of  chromium  sulphate,  a  green  and  a 
violet.  The  green  salt  is  produced  when  the  sulphate  is  pro- 
duced by  the  ordinary  methods  above  50°,  or  by  heating  the  violet 
variety  to  that  temperature  ;  it  is  soluble  in  alcohol.  The  violet 
variety  is  produced  in  the  cold ;  it  is  also  formed  when  the  green 
modification  is  allowed  to  stand.  It  is  precipitated  by  alcohol, 


SULPHATES,   SELENATES,  AND  TELLURATES.  427 

and  crystallises  best  from  a  mixture  of  alcohol  and  water.  On 
heating  either  variety  with  excess  of  sulphuric  acid  to  above  190°, 
a  light  yellow  mass  of  anhydrous  sulphate  is  obtained,  insoluble  in 
water,  and  with  difficulty  in  acids.  Several  basic  salts  are  known, 
produced  by  digesting  a  solution  of  the  ordinary  salt  with 
chromium  hydrate,  or  by  incomplete  precipitation.  Among  these 
are  2SO3.Cr2O3 ;  2SO3.3Cr2O3;  and  3SO3.2Cr.iO3.  They  are 
insoluble  and  amorphous.  Ferric  sulphate,  Pe2(SO4)3.9H2O, 
seems  native  as  coquimbite.  It  is  produced  by  oxidising  ferrous 
sulphate  with  nitric  acid  in  presence  of  strong  sulphuric  acid  : 
2FeSO4  +  H2S04  -I-  O  =  Pe,(SO4)3  +  H20.  It  forms  small  pink 
scales,  and  is  very  difficult  to  dissolve  in  water.  Manganic  sulphate 
is  a  non-crystalline  green  substance  produced  by  heating  the 
hydrated  dioxide  with  sulphuric  acid.  Many  basic  sulphates  of 
iron  and  manganese  are  known,  which  resemble  those  of  chromium. 
The  double  salts  of  these  oxides,  or  alums,  have  already  been 
noticed.  A  sulphato-nitrate  of  chromium,  Cr2(SO4)(NOa)4is  pro- 
duced by  dissolving  the  hydrated  basic  sulphate,  Cr2(SO4)(OH)4. 
in  strong  nitric  acid.  The  salt  Cr2(SO4)2(NO3)2  is  also  known. 

CrSO4.Aq;   FeSO4.7,  5,  3,  2,  and  1H2O  ;    MnSO4.7,  6,  5,  4,  and  2^0; 

CoSO4.7,  6,  and  4H2O  ;  NiSO4.7  and  6H2O. 
FeSe04.7  and  5H2O  j  CoSeO4.7H2O  ;  Ni2SeO4.7  and  6BL>O. 
FeTeO4;  MnTeO4;  CoTeO4;  NiTeO4. 

Chromous  sulphate  has  been  obtained  as  a  blue  solution,  by 
dissolving  the  metal  in  dilute  acid.  Like  all  chromous  salts,  it 
has  powerful  reducing  properties.  Ferrous  sulphate  occurs  native 
as  green  vitriol  or  copperas,  produced  by  the  atmospheric  oxidation 
of  iron  pyrites.  It  usually  crystallises  with  7H20,  in  light-green 
monoclinic  crystals,  which  absorb  oxygen  slowly  in  moist  air, 
forming  a  basic  ferric  sulphate  (said  to  be  2(SO3.Pe2O3). H>O), 
but  in  dry  air  they  are  permanent.  When  heated  to  redness  it 
evolves  sulphur  dioxide,  and  a  basic  sulphate  remains,  which,  on 
further  heating,  leaves  a  residue  of  ferric  oxide,  and  yields  a  dis- 
tillate of  sulphur  trioxide.  This  residue  is  named  rouge,  and  used 
to  be  known  as  "  colcothar  vitrioli,"  or  "  caput  mortuum"  ;  it  is  used 
as  a  pigment.  Ferrous  sulphate  has  been  obtained  with  different 
amounts  of  water,  according  to  the  temperature  at  which  it  is 
crystalised ;  the  hydrates  with  3  and  2H20  are  formed  in  presence 
of  sulphuric  acid.  That  with  1H30  is  produced  by  drying  the 
salt  at  114°;  the  last  molecule  is  retained  at  280°,  and  is  some- 
times termed  "  water  of  constitution."  Ferrous  sulphate  absorbs 
nitric  oxide  (see  p.  342)  ;  but  the  composition  of  the  resulting 


428      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLUR1DES. 

compound  depends  on  the  pressure  and  temperature,  varying  from 
3FeSO4.2NO  to  6FeS04.2NO.  Manganous  sulphate  is  a  pink 
salt ;  cobalt  sulphate  rose-red,  and  nickel  sulphate  grass-green. 
The  anhydrous  salts  are  colourless.  The  hydrated  sulphates  of 
these  metals,  containing  the  same  number  of  molecules  of  water  of 
crystallisation  are  isomorphous  with  each  other;  those  with 
5H20  resemble  copper  sulphate,  CuSO4.5H2O,  in  crystalline 
form. 

The  selenates  closely  resemble  the  sulphates ;  the  tellurates  are 
insoluble  precipitates.  FeTeOt  occurs  native,  and  has  been  named 
ferrotellurite. 

A  large  number  of  double  salts  of  the  general  formula, 
M'2R04.M''R,04.6H20,  are  known,  where  M'  stands  for  Li,  Na,  K, 
Eb,  Cs,  IT  and  NH4 ;  M",  for  Mg,  Zn,  Cd,  Cr",  Fe",  Mn",  Co", 
Ni",  and  Cu" ;  and  R  for  S  or  Se.  They  all  crystallise  in  mono- 
clinic  crystals,  and  are  isomorphous  with  each  other.  They  are 
produced  by  mixture.  The  double  salts  of  hydrogen, 

H2Mn(S04)2,  and  H6Mn(SO4)4 

have  also  been  prepared. 

Sulphate  of  carbon  is  unknown.  Both  the  monoxide  and 
dioxide  of  carbon  are  insoluble  in  sulphuric  acid. 

Ti2(S04)3;  Ce2(S04)3.5,  6,  8,  9,  and  12H2O. 
Double  salts:— Ce2(SO4)3.2K2SO4.2H2O;  Ce2(SO4)3.5K2SeO4,  and  others. 

The  titanous  sulphate  is  violet ;  the  cerous  salts  colourless. 

Ti(SO4)2;  Zr(SO4)2;  Ce(SO4)2.4H2O  ;  Th(SO4)2.4H2O.— Also  double  salts, 
such  as  K2Ti(S04)3;   (NH4)6Ce(SO4)5.4H2O  ;  K4Th(SO4)4.2H2O. 

The  cerium  salt  is  yellow ;  the  others  colourless.  Cerium  also 
forms  a  double  salt,  containing  the  metal  in  two  states  of  oxida- 
tion ;  it  is  called  ceroso-ceric  sulphate.  It  has  a  brown-red  colour 
and  the  formula  2Ce(SO4)2.Ce2(SO4)3.25H2O.  These  bodies, 
especially  titanium,  zirconium,  and  cerium,  also  yield  basic  sul- 
phates. The  formation  of  titanium  sulphate  serves  as  a  means 
of  separating  titanium  from  silica.  The  mixture  is  fused  with 
hydrogen  potassium  sulphate,  dissolved  in  water,  and  filtered  from 
silica;  on  boiling  with  water  the  titanium  sulphate  is  decomposed 
into  hydrate  and  sulphuric  acid. 

Silica  is  insoluble  in  sulphuric  acid ;  and  germanium  does  not 
appear  to  form  a  sulphate. 


SULPHATES,  SELEXATES,  AND   TELLURATES.  429 


SnSO4  ;     PbSO4 ;     PbSeO4  ;     PbTeO4.— Double     salts  :— K2Sn(SO4)2  ; 
4X.2Sn(S04)2.SnCl2 ;  (NH4)2Pb(SO4)2. 

Stannous  sulphate  is  colourless  and  crystalline.  The  double 
salts  are  obtained  by  mixture.  Lead  sulphate  occurs  native  in 
trimetric  crystals  as  angle»ite,  isomorphons  with  those  of  heavy 
spar  (barium  sulphate).  The  crystalline  variety  may  be  obtained 
by  fusing  lead  chloride  with  potassium  sulphate.  The  selenate 
has  also  been  found  native.  As  lead  sulphate  and  selenate  are 
nearly  insolubl  e,  they  may  be  produced  by  precipitation  ;  they 
form  dense  white  powders,  more  easily  dissolved  by  water  than  by 
the  dilate  acid ;  but  they  are  soluble  to  a  small  extent  in  strong 
acids.  They  dissolve  in  larger  quantity  in  solutions  of  sulphate, 
nitrate,  acetate,  or  tartrate  of  ammonium,  and  easily  in  caustic 
alkali,  and  in  thiosulphates.  Lead  sulphate  also  dissolves  in  sul- 
phuric acid  ;  the  solution  deposits  crystals  of  H2Pb(SO4)2.H2O. 
These  bodies  melt  at  a  red  heat. 

Lead  sulphate,  heated  with  the  sulphide,  as  in  lead  smelting, 
yields  metallic  lead  and  sulphur  dioxide,  thus  : — PbSO4  +  PbS  = 
2Pb  +  2S02;  or  the  oxide  and  metal :— 2PbSO4  +  PbS  =  3S02  + 
2PbO  +  Pb. 

Lead  tellurate  is  also  a  white  precipitate,  but  is  more  easily 
soluble  in  water.  Basic  sulphates  and  selenates  of  tin  and  lead 
have  also  been  prepared ;  stannic  hydrate  dissolves  in  sul- 
phuric acid,  but  stannic  sulphate  is  an  indefinite  non-crystalline 
body. 

Compounds  of  nitrogen  and  vanadium  usually  contain  the 
nitrosyl,  or  vanadyl  groups.  Compounds  of  the  pentoxides  with 
sulphuric  anhydride  are,  however,  known.  The  compound, 
SO3.N2Oa.4H2SO4,  a  white  crystalline  body,  is  produced  by  cool- 
ing a  mixture  of  sulphur  trioxide  and  nitric  acid;  it  is  at  once 
decomposed  by  water,  and,  when  heated,  evolves  red  fumes,  yielding 
a  sublimate  supposed  to  be  SO3.N2O3.  This  would  be  nitrosyl 
sulphate,  SO,(ONO)2,  to  be  alluded  to  later.  The  first  may  be 
viewed  as  a  compound  of  nitryl  sulphate,  S04(NO2)2  with  sul- 
phuric acid.  The  compound,  2(SO3).N2O5,  is  also  known.  It  is  a 
snowy  crystalline  mass,  produced  by  the  action  of  induction  sparks 
on  a  mixture  of  sulphur  dioxide,  oxygen  and  nitrogen ;  it  may  be 
regarded  as  nitryl  anhydrosulphate,  S207(N02)2. 

Vanadyl  sulphate,  3SO3.V2O5,  is  prepared  by  dissolving 
vanadium  pentoxide  in  cold  sulphuric  acid,  and  expelling  excess 
of  sulphuric  acid  by  heat.  It  may  be  regarded  as  (VO)"/2(SOJ)S. 


430      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLUEIDES. 

It  is  red  and  crystalline.  During  evaporation,  the  green  compound 
of  V2O4,  2SO3.V2O4  =  (VO)"2(SO4)2  separates  as  a  crust.  By 
heating  the  first  compound  to  the  temperature  of  melting  lead, 
the  basic  sulphate,  (VO)2O.(SO4)2,  is  obtained  as  a  red  crystalline 
mass.  A  double  sulphate  of  the  formula,  2SO3.K2O.V2O5.6H2O, 
is  also  known. 

These  bodies  are  mostly  derivatives  of  the  pentoxides  of 
nitrogen  and  vanadium.  Niobium  and  tantalum  are  said  also  to 
form  sulphates,  but  these  compounds  have  not  been  investigated. 

Nitrosyl  sulphate,  (NO)2S04,  may  be  the  substance  alluded  to  on 
the  previous  page.  Hydrogen  nitrosyl  sulphate,  H(NO)SO4,  is 
better  known,  and  is  produced  by  the  action  of  nitrogen  trioxide 
on  sulphuric  acid,  thus  :— N203-f-2H2S04  =  2H(NO)SO4  +  H20. 
Excess  of  sulphuric  acid  must  be  present  to  combine  with  the  water. 
The  same  substance  is  produced  by  the  action  of  sulphur  dioxide 
on  nitric  acid,  or  by  passing  the  vapours  from  a  heated  mixture  of 
nitric  and  hydrochloric  acids  (nitrosyl  chloride  and  chlorine,  see 
p.  341)  through  strong  sulphuric  acid.  It  forms  long,  thin,  trans- 
parent crystals  melting  at  85-87°.  It  is  the  substance  known  as 
"chamber  crystals,"  and  its  solution  in  sulphuric  acid  is  produced 
in  the  "  Gay-Lussac  tower,"  in  which  the  escaping  gases  from  the 
vitriol  chambers  are  brought  in  contact  with  strong  sulphuric 
acid.  On  treatment  with  water,  it  is  at  once  decomposed  into  oxides 
of  nitrogen  (NO  and  NOz  +  NzOt)  ;  this  change  takes  place  in  the 
"  Glover  tower,"  where  the  sulphuric  acid  containing  hydrogen 
nitrosyl  sulphate  is  diluted ;  the  oxides  of  nitrogen  are  liberated, 
and  again  pass  into  the  chambers  (see  p.  416).  (See  also  nitrosyl 
anhydrosulphate,  p.  434). 

(FO)"'2(SO4)3,  phosphoryl  sulphate,  is  produced  by  mixture;  it 
forms  thin  transparent  scales,  and  is  decomposed  at  30°,  and  by 
water;  the  corresponding  compounds  of  arsenic,  antimony,  and 
bismuth  are  unknown,  the  groups  (AsO)',  (SbO)'  and  (BiO)' 
tending,  as  a  rule,  to  replace  only  one  atom  of  hydrogen. 

By  dissolving  arsenious  oxide,  As406,  in  sulphuric  acid  of 
different  concentrations,  which  must  not,  however,  be  more  dilute 
than  corresponds  with  the  formula,  H2S04.H20,  various  white 
crystalline  sulphates  of  arsenic  have  been  obtained.  They  appear 
to'have  the  formulae  8(SO3).As2O3;  4(SO3).As2O3;  3(SO3).As2O3(?); 
2(SO3).As2O3;  and  SO3.As2O3.  The  body,  3(SO3).As2O3,  would 
correspond  to  As2(SO4)3;  2(SO3)As2O3  may  be  written 
SO4 — As — O— As — SO4;  and  SO3.As2O3  may  represent  arsenosyl 
sulphate,  (AsO)'2SO4,  corresponding  in  formula  to  nitrosyl  sul- 


SULPHATES,   SELENATES,   A^   TELLURATES.  431 

phate.  These  bodies  are  all  decomposed  by  water,  and  are  all 
very  unstable. 

The  sulphates  of  antimony  are  similar  but  more  stable.  The 
compounds,  4(SO3).Sb2O3,  3(SO3).Sb2O3,  2(SO3).Sb2O3,  and 
SO3.Sb,O3,  have  been  prepared.  The  normal  salt,  Sb2(SO4)3  = 
3(SO3).Sb2O3,  is  produced  by  boiling  antimony  with  strong  sul- 
phuric acid.  It  crystallises  in  needles. 

With  bismuth,  the  compounds,  3(SO3).Bi2O3,2(SO3).Bi2O3,  and 
SO3.Bi2O3,  are  known.  Bismuth  dissolves  in  hot,  strong  sul- 
phuric acid,  with  evolution  of  sulphur  dioxide  forming  the  first;  it 
is  decomposed  by  water,  giving  the  third.  Double  salts  with 
hydrogen,  HBi(SO4)2.H2O;  with  ammonium,NH4Bi(SO4)2.4H2O; 
and  with  potassium.  K3Bi(SO4)3  are  also  known.  The  selenates 
and  tellurates  have  scarcely  been  examined.  Bismuth  tellurate, 
however,  has  been  found  native.  Its  formula  is  TeO3.Bi2O3 ;  it 
has  been  named  montanite, 

Hydrated  molybdenum  sesquioxide  forms  a  dark-coloured  solu- 
tion with  sulphuric  acid,  which  may  contain  Mo2(S04)3.  The  di- 
oxide gives  a  red-solution,  supposed  to  contain  Mo(SO4)2. 

UjaBtfus  sulphate,  U(SO4)2.4  and  8H2O,  forms  green  crystals, 
and  is  produced  by  dissolving  hydrated  uranium  dioxide  in 
sulphuric  acid.  A  basic  sulphate,  SO3.UO2.3H2O,  is  also  known  ; 
and  also  the  double  salt  K2U(SO4)3.HiO.  They  are  green, 
soluble  bodies. 

MoO2(SO4)  and  UO2(SO4),  molybdyl  and  uranyl  sulphates, 
are  yellow  crystalline  bodies,  obtained  from  the  hydrated  trioxides. 
This  sulphate  of  molybdenum,  when  boiled  with  water,  decomposes, 
depositing  the  hydrated  oxide,  5(MoO3).H2O.  Double  salts  of 
uranyl  sulphate  are  known,  e.g.,  H,(UO2)(SO4)2,  and 

K2(U02)(S04)2.2H20. 
The  selenates  and  tellurates  are  little  known. 

Tellurium  dioxide  dissolves  in  hot  dilute  sulphuric  acid,  and 
deposits  crystals  of  SOa.2TeO2.  It  is  decomposed  by  warm  water. 

Ru(S04)2;  Bh2(S04)3.12H20;  PdSO4.2H,O.— Also  KHh(SO4)2. 
Ruthenium  and  rhodium  sulphates  are  orange- brown  and  red 
solutions,  drying  respectively  to  a  yellow-brown  amorphous  mass, 
and  to  a  brick-red  powder ;  they  are  produced  by  oxidation  of  the 
sulphide.  Palladium  dissolves  in  sulphuric  acid,  mixed  with  a 
little  nitric  acid  ;  the  solution,  when  evaporated,  deposits  brown 
crystals. 

OsS04;  Os(S04)2;  IrS04;  IrO.SO4 ;  PtSO4; 


432      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

These  are  all  yellow  syrups,  drying  to  brown  non-crystalline 
masses  ;  they  are  all  produced  by  oxidising  the  respective  sulphides 
with  nitric  acid,  with  the  exception  of  platinous  sulphate,  PtS04, 
which  is  produced  when  the  chloride,  PtCl2,  is  dissolved  in 
sulphuric  acid. 


4;  HAgS04;  H3As(SO4)2.H2O;  H6Ag2(SO4)4;  Hg:2SO4  ;  Hg:2SeO4; 
Agr2TeO4  ;  cuprous  and  aurous  sulphates  are  unknown.  Auric  sulphate, 
however,  can  be  prepared  in  solution  by  dissolving  auric  oxide  in  dilute 
acid.  It  decomposes  on  standing. 

Sulphates  of  silver  and  mercury  are  sparingly  soluble  white 
salts,  produced  by  precipitation,  or  by  dissolving  the  metals  in 
sulphuric  acid.  The  silver  salt  is  isomorphous  with  anhydrous 
sodium  sulphate.  The  tellurate  is  a  dark-yellow  powder.  It  has 
been  found  native,  and  named  magnolite. 

CuSO4.5H2O;  CuSeO4.5H2O  ;  HgSO4.—  Basic  salts  :—SO3.2CuO.H2O  ; 
SO3.3CuO.3H2O;  SO3.4CuO.3H2O  ;  SO3.3HgO.  Double  salts  :—  Those 
of  copper  belong  to  the  class  M2'M"(SO4)2.6H2O  ;  those  of  mercury  re- 
semble 3K2Hgr(S04)2.2H20.  Also  HgSO4.HgI2  ;  2Hg-S04.Hg-S. 

Copper  sulphate,  or  blue  vitriol,  is  produced  on  a  large  scale  by 
the  spontaneous  oxidation  of  copper  pyrites,  or  by  the  action  of 
air  on  ignited  cuprous  sulphide,  Cu2S,  whereby  cupric  oxide  is 
produced  at  the  same  time.  It  crystallises  with  water  in  large 
blue  monoclinic  prisms,  isomorphous  with  ferrous  sulphate  of  the 
same  degree  of  hydration.  Indeed,  copper  sulphate,  if  present  in 
excess  in  a  solution  containing  ferrous  sulphate,  induces  the  latter 
to  adopt  its  crystalline  form  ;  and,  similarly,  ferrous,  zinc,  mag- 
nesium, or  nickel  sulphate  in  excess,  causes  copper  sulphate  to 
assume  their  special  form.  When  heated  to  100°,  CuSO4.5H2O 
loses  four  molecules  of  water;  the  last  molecule  is  retained 
up  to  200°,  and  is  regarded  as  "  water  of  constitution."  It  is 
easily  soluble  in  water,  but  insoluble  in  alcohol.  The  tetra- 
basic  salt  occurs  native  as  brochantite.  The  selenate  closely  re- 
sembles the  sulphate.  Mercuric  sulphate  is  decomposed  by  water 
into  a  soluble  acid  salt,  3SO3.HgO.wH2O,  and  the  basic  salt, 
SO3.3HgO,  a  lemon-yellow  powder,  which  used  to  be  called  tur- 
peth  mineral.  The  compound,  2HgSO4.HgS,  is  precipitated  by 
the  action  of  a  moderate  quantity  of  hydrogen  sulphide  on  a  solu- 
tion of  the  sulphate.  It  is  a  white  precipitate. 

Anhydro-  or  pyrosulphuric  acid,  H,S2O7.—  This  substance 
is,  as  will  appear  hereafter,  an  analogue  of  pyrophosphoric  acid, 


ANHYDROSULPHATES.  433 

inasmuch  as  it  maybe  regarded  as  constituted  of  two  molecules  of 
sulphuric  acid,  minus  a  molecule  of  water,  thus . — 

HO— (S02)-0—  (SO,)—  OH. 

But  it  cannot  be  prepared  by  heating  ordinary  sulphuric 
acid,  for  that  acid,  as  already  remarked,  distils  as  a  whole. 
It  may  be  obtained  by  dissolving  sulphur  trioxide  in  ordinary 
sulphuric  acid,  thus : — H2S04  +  SO3  =  H2S2O7.  The  old  method 
of  preparation,  which  gained  for  this  acid  the  name  "Nord- 
hausen  sulphuric  acid,"  is  still  carried  out  at  Nordhausen  in. 
Saxony;  it  consists  in  distilling  partially  dried  ferrous  sulphate 
from  tube-shaped  retorts  of  very  refractory  fire-clay.  The 
products  are  sulphur  dioxide  and  anhydrosulphuric  acid,  while 
ferric  oxide  of  a  tine  red  colour  remains  in  the  retort,  and  is  made 
use  of  as  a  pigment  under  the  name  of  "Venetian  red"  or 
"  rouge."  This  method  of  manufacture  is  a  very  ancient  one. 
When  ferrous  sulphate,  FeSO4.7H2O,  is  dried,  it  loses  six  mole- 
cules of  water,  retaining  the  seventh.  On  distilling  the  mono- 
hydrated  salt,  sulphur  dioxide  and  water  are  evolved  first,  leaving 
basic  ferric  sulphate,  thus  : — 

2FeS04.H20  =  SO,  +  H20  +  Fe2O2(SO4)(=  SO3.Fe2O3). 

The  sulphur  dioxide  escapes ;  the  temperature  is  then  raised, 
when  sulphur  trioxide  distils  over,  and  combines  with  the  water, 
leaving  iron  sesquioxide  in  the  retort. 

Anhydrosulphuric  acid  is  a  white  solid,  crystallising  in  needles, 
and  melting  at  35°.  It  gives  off  sulphur  trioxide  when  heated.  It 
hisses  when  dropped  into  water,  evolving  great  heat. 

It  is  probable  that  still  more  condensed  sulphuric  acids  are 
formed  when  more  sulphur  trioxide  is  added  to  sulphuric  acid; 
but  they  have  been  little  investigated.  Corresponding  compounds 
of  selenium  and  tellurium  are  unknown. 

Pyrosulphates  and  polytellurates. — The  pyrosulphates  are 
produced  (1)  by  the  action  of  pyrosulphuric  acid  on  the  oxides; 
(2)  in  a  few  cases  by  heating  the  double  salts  of  hydrogen  and  a 
metal ;  and  (3)  by  the  action  of  sulphur  trioxide  on  the  normal 
sulphate.  The  following  salts  are  known  : — 

No2S2O7 ;  K.2S2°7  5  Ba2S2O7  ;  Ag2S2O7 ;  also  the  double  salt  HKS2O7. 

The  sodium  and  potassium  salts  may  be  prepared  by  all  these 
methods.  They  are  crystalline  salts,  which  combine  with  water, 
forming  hydrogen  metallic  sulphates.  Hydrogen  potassium  pyrosul- 
phate  crystallises  from  a  solution  of  the  anhydrosulphate  in  strong 
sulphuric  acid;  the  other  salts  are  best  prepared  by  method  (3). 

2  F 


434      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

Nitrosyl  anhydrosulphate,  S207(NO)2,  is  produced  as  a  white 
crystalline  substance  by  the  action  of  sulphur  dioxide  on  nitric 
peroxide.  It  is  at  once  decomposed  by  water  into  sulphuric  acid 
and  the  products  of  decomposition  of  nitrous  anhydride. 

Several  polysulphates  of  arsenic,  antimony,  &c.,  have  already 
been  described  among  the  sulphates. 

Di-  and  tetra-tellurates  are  also  known.  The  ditellurates  prob- 
ably correspond  to  the  anhydrosulphates  ;  and  the  tetratellurates 
are  produced  by  the  action  of  water  on  the  monotellurates.  The 
formulae  of  the  following  have  been  ascertained  :  — 


7;  (NH4)2Te2O7  ;  PbTe2O7;  Ag:2Te2O7  ;  also  4TeO3.K.O  ; 
4Te03.(NH4)20;  4TeO3.BaO  ;  4TeO3.PbO;  and  4TeO3.Ag:2O. 

These  bodies  are  more  soluble  than  the  ordinary  tellurates. 


435 


CHAPTER  XXVII. 

COMPOUNDS  OF  OXYGEN,  SULPHUR,  SELENIUM,  AND  TELLURIUM  WITH 

EACH  OTHER  (CONTINUED). SULPHITES,  SELENITES,  AND  TELLURITES  ; 

HYPOSULPHITES,  THIONATES,  THIOSULPHATES,  ETC. — OXYHAL1DES. 

Compounds  with  Water  and  with  Oxides  (continued):— 
(2)  Compounds  of  the  Dioxides ;  Sulphurous,  Selenious, 
and  Tellurous  Acids;  Sulphites,  Selenites,  and  Tel- 
lurites. 

Sulphurous,  selenious,  and  tellurous  acids,  in  aqueous  solu- 
tion, are  produced  either  by  direct  combination  of  the  anhydrides 
with  water,  or  by  displacement. 

Water  absorbs  at  15°  about  45  times  its  volume  of  sulphur 
dioxide ;  and  on  cooling  the  solution  several  definite  hydrates  have 
been  obtained. 

By  passing  a  current  of  the  gas  through  a  solution  cooled  to 
—6°,  white  crystals,  fusing  at  4°,  of  the  formula  H2SO3.8H2O, 
were  produced.  By  a  similar  process,  crystals  melting  at  14°,  of 
the  formula  H2SO3.6H2O,  were  obtained ;  and  it  is  also  stated  that 
the  compound  H>SO3  has  been  thus  isolated  in  cubical  crystals.  A 
solution  of  sulphurous  acid  may  also  be  produced  by  adding  almost 
any  acid  to  a  dilute  solution  of  a  sulphite ;  if  the  solution  be  strong, 
the  anhydride,  S02,  is  evolved.  On  boiling  a  solution  of  sulphur 
dioxide  the  gas  is  evolved  ;  but  it  does  not  wholly  escape,  except 
the  boiling  be  considerably  prolonged.  The  solution  possesses  the 
smell  and  taste  of  the  gas,  and,  like  many  other  similar  solutions, 
it  doubtless  contains  the  free  anhydride  as  well  as  the  acid. 
When  heated  to  180 — 200°  in  a  sealed  tube,  an  aqueous  solution  of 
sulphur  dioxide  yields  sulphuric  acid  and  free  sulphur. 

It  shows  a  great  tendency  to  absorb  oxygen.  On  exposure 
to  air,  it  is  gradually  converted  into  sulphuric  acid ;  and  this 
conversion  may  be  effected  by  the  addition  of  a  solution 
of  a  halogen,  or  of  a  chromate,  of  a  manganate  or  perman- 
ganate, &c.,  which  readily  yields  oxygen.  A  convenient  test 
for  a  sulphite  consists  in  boiling  it  with  a  solution  of  potassium 

2  F  2 


436      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

dichromate,  acidified  with  hydrochloric  acid  ;  the  orange  colour  of 
.the  dichromate  changes  to  the  green  colour  of  a  chromic  salt,  and 
the  solution  then  contains  a  sulphate,  which  yields  a  precipitate 
•with  barium  chloride. 

This  power  of  reduction  has  led  to  the  employment  of  sulphur 
dioxide  in  bleaching  animal  fibres,  such  as  silk  and  wool.  The 
colouring  matters,  which  are  insoluble,  are  converted  into  colour- 
less substances  by  exposure  in  a  moist  state  to  the  fumes  of 
burning  sulphur  It  also  finds  use  as  a  disinfectant,  and  in  the 
form  of  sulphites  is  used  in  brewing  for  checking  fermentation. 

Sulphurous  acid  at  once  reacts  with  hydrogen  sulphide,  giving 
a  deposit  of  sulphur  :—2H^8  +  H2S03.Aq  =  2H20  +  Aq  +  3S 
(see  Pentathionic  Acid,  p.  451). 

Selenious  acid,  HaSeO3,  is  produced  by  direct  union  of  the 
dioxide  with  water,  or  by  boiling  selenium  with  nitric  acid.  It 
deposits  in  colourless  prismatic  crystals  when  its  solution  is  cooled. 
The  crystals  lose  water  on  exposure  to  air,  and  when  gently  heated 
they  yield  the  dioxide.  When  a  current  of  sulphur  dioxide  is  passed 
through  its  solution,  it  is  decomposed,  depositing  selenium,  thus  : 
H2Se03.Aq  +  H20  4-  2S02  =  2H2S04.Aq  +  Se.  This  is  the  usual 
method  of  separating  selenium  from  its  compounds.  The  solution 
of  selenious  acid  has  a  very  acid  taste.  It  is  not  altered  by  boiling 
with  hydrochloric  acid,  but  may  be  oxidised  to  selenic  acid  by  the 
usual  oxidising  agents  ;  not,  however,  by  nitric  or  nitrohydro- 
chloric  acid  (see  p.  417). 

Tellurous  acid,  H2TeO3,  is  precipitated  by  pouring  strong 
nitric  acid,  in  which  tellurium  has  been  boiled,  at  once  into  water, 
or  by  the  action  of  water  on  tellurium  tetrachloride.  It  is  a  white 
bulky  precipitate,  drying  to  a  white  powder,  only  sparingly  soluble 
in  water.  It  dissolves  in  acids,  but  is  reprecipitated  on  dilution. 

The  sulphites,  selenites,*  and  tellurites  are  prepared  by 
the  usual  methods  of  preparing  salts.  They  are  all  decomposed 
by  such  acids  as  sulphuric  or  phosphoric,  with  liberation  of  the 
respective  acid.  They  are  also  all  decomposed  by  heat.  Like  the 
sulphates,  they  form  two  main  classes,  the  normal  salts,  such  as 
M2S03,  and  the  anhydro-  or  pyro-salts,  such  as  M2S205  (compare 
also  Phosphates).  The  latter  are  known  only  in  a  few  instances. 


Li2SO3.6H2O;  Na2SO3.8,  and  7H2O;  KjSQ^B^O;  (NH4)2SO3.—  LiSeO3.H2O; 
Na2Se03;  K^SeOg;  Rb2SeO3;  Cs.2SeO3;  (NH4)2SeO3.—  I^TeO-,  ; 
Na2TeO3.»H2O  ;  ^TeOg. 

These  are  all  white  soluble  salts.     At  a  dull  red  heat  potassium 
*  Bull.  Soc.  Chim.  (5),  23,  260,  335. 


SULPHITES,   SELENITES,   AND   TELLURITES.  437 

sulphite  gives  sulphate  and  sulphide,  thus  : — 4KoSO3  =  3K2SO4  + 
K2S 

Double    salts.— HNaS03;     HKSO3 ;     H(NH4)SO3  ;     NaKSO3.2H2O  ;* 

KNaS03.H20.*— HLiSe03 ;  HNaSeO3;  HKSeO3;  also  H3Li(SeO3)2; 

H3Na(Se03)2;  H3K(SeO3)2  ;  and  H2(NH4)4(SeO3)3.— 

H3Na(Te03)2.H20  ;  H^TeO-j^B^O  ; 

H3(NH4)(Te03)2.H20. 

These  are  produced  by  mixture.  When  heated,,  the  acid  sulphites 
give  off  water,  and  leave  a  residue  of  sulphate  and  thiosulphate. 

They  are  all  white  and  soluble,  and  smell  of  sulphur  dioxide. 

The  normal  sulphites  of  potassium  and  ammonium  form 
compounds  with  nitric  oxide,  NO,  named  nitrososulphites  (see 
p.  455). 


BeSO;.  ;     CaSO3.2H2O  ;     SrSO3  ;     BaSO3.— BeSeO3.2H2O  ; 
SrSe03.2H20;  BaSeO3.H2O.— CaTeO3 ;  SrTeO3; 

With  the  exception  of  beryllium  sulphite,  these  salts  are 
sparingly  soluble  in  water,  and  may  be  produced  by  precipitation, 
when  they  come  down  in  small  crystals.  The  tellurites  are  also 
produced  by  fusion  of  the  respective  carbonate  with  tellurons 
anhydride.  They  are  all  white  bodies,  and  the  sulphites  decom- 
pose, when  heated,  into  sulphate  and  sulphide. 

Little  is  known  of  the  double  sulphites  of  these  metals.  Solu- 
tions of  the  neutral  salts  absorb  sulphur  dioxide,  but  the  neutral 
salts  again  crystallise  out  on  evaporation  over  sulphuric  acid.  Such 
a  solution  of  calcium  sulphite  is  made  use  of  in  sugar  refining  to 
prevent  fermentation. 

Double  salts.—  H,Be(SeO3)2;  H2Ca(SeO3)2.H2O;  H2Sr(SeO3)2. 
These  are  white  soluble  salts,  obtained  by  mixture  and  crystal- 
lisation.    The  existence  of  corresponding  tellurites  is  doubtful. 

Mg:SO3.6  and  3H2O  :  ZnSO3.5H2O  ;  and  CdSO3.H2O. 
These  are  sparingly  soluble  white  salts. 

MgSe03.6H20  ;  ZnSeO3.H.:O  ;  and  CdSeO3. 

These  are  sparingly  soluble  salts,  which  dissolves  in  selenious 
acid,  forming  double  salts  with  hydrogen,  which  have  the  formulae 
H  M&(SeO3)2 ;  H4Mg(SeO3)3.3H2O;  H2Cd2(SO3)3.B:2O  ;  andH2Cd3(SeO3)4. 
MgTeO3 ;  ZnTeO3 ;  and  CdTeO3. 

These  are  also  obtained  by  precipitation. 

No  sulphite,  selenite,  or  tellurite  of  boron  is  known.     Scandium 

*  These  salts  are  isomeric  (see  p.  453).  They  are  formed  respectively  thus  : — 
2HNaS03. Aq  +  K2CO3.Aq  =  2KXaSO3.Aq  +  C02  +  H2O ;  and  2HKS03.Aq  + 
Lq  =  2XaKSO3.Aq  +  C0.2  +  H2O. 


438      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

forms  a  selenite  of  the  formula  10SeO2.3Sc2O3.4H2O.  Yttrium 
sulphite,  Y2(SO3)3,  and  selenite,  Y2(SeO3)3.12H2O,  are  white  in- 
soluble powders.  Yttrium  tellurite  is  a  white  precipitate.  The 
compounds  of  this  group  have  scarcely  been  examined. 

Aluminium  sulphite  is  basic:  SO2.A12O3.2H2O.  The  selenite, 
however,  Al2(SeO3)3,  is  normal.  These  salts,  and  the  tellurite,  are 
white  and  insoluble ;  but  the  selenite  dissolves  in  selenious  acid. 

Indium  sulphite,  In2(SO3)3.8H3O,  is  a  white  insoluble  powder. 
Its  formation  is  made  use  of  in  separating  indium  from  traces  of 
copper,  lead,  zinc,  and  iron.  The  gallium  salts  have  not  been  pre- 
pared. The  compounds  9SeO2.4Al2O3.36H2O  and  the  double  salts 
H3Al(SeO3)3.4H2O  and  H3In(SeO3)3.6H2O  have  been  prepared. 

Thallous  sulphite,  selenite,  and  tellurite  are  nearly  insoluble. 

Cr2(SO3)3.16H2O  is  a  yellow  precipitate,  thrown  down  by 
alcohol.  Fe2(S03)3  may  exist  as  a  red  solution,  but  is  rapidly 
changed  by  reduction  into  ferrous  sulphate ;  but  if  alcohol  be 
added  at  once,  a  yellow-brown  basic  salt,  3SO2.2Fe2O3,  is  pre- 
cipitated. On  treatment  with  water  it  decomposes,  yielding  the 
salt  SO2.Fe2O3.6H2O.  On  addition  of  caustic  potash  to  the 
original  red  solution,  the  basic  double  salt  3SO2.2K2O.Pe2O3.5H2O 
is  precipitated.  A  double  salt  of  cobalt,  KCom(SO3)2,  is  produced 
by  digesting  cobaltic  hydrate  with  hydrogen  potassium  sulphite. 

Cr2(SeO3)3  and  Fe2(SeO3)3  are  insoluble  powders.  The 
tellurates  are  also  insoluble. 

FeS03.3H20;  MnSO3.2H2O  ;  CoSO3;  NiSO3.6H2O. 
FeSeO3;  MnSeO3.2H2O  ;  CoSeO3.2H2O  ;  NiSeO3.2H2O. 

These  salts  are  sparingly  soluble,  but  crystallise  from  dilute 
solutions.  The  tellurites  are  insoluble.  A  double  selenite,  of  the 
formula  H2Ni(SeO3)2.'2H2O,  has  been  prepared. 

The  sulphites  and  tellurites  of  cerium,  zirconium,  and  thorium 
are  said  to  be  white  insoluble  powders.  The  selenites, 
Ce2(SeO3)3.12H2O  ;  Th(SeO3)4  8H2O  ;  and  the  acid  salts 
H2Ce2(Se03)4.5H20,  H2Th(Se03)3.6H2O  and  H6Th(SeO3)5.5H2O 
have  been  prepared. 

Salts  of  silicon  and  germanium  are  unknown.  Stannic  selenite 
is  said  to  be  an  insoluble  precipitate.  PoSO3,  PbSeO3,  and 
PbTeO3  are  nearly  insoluble  white  precipitates. 

Compounds  of  nitrogen,  vanadium,  niobium,  tantalum,  phos- 
phorus, arsenic,  and  antimony  are  unknown.  Bismuth  sulphite, 
SO,.Bi2O3,  is  basic,  and  sparingly  soluble. 

Compounds  of  molybdenum  and  tungsten  have  not  been  pre- 
pared. But  uranyl  sulphite,  (UO2)(SO3).3H,O,  is  known;  and 


SULPHITES,  SELENITES,   AND  TELLURITES.  439 

doable  sulphites,  of  the  general  formula  (UO2)HM'(SO3)2,  where 
M'  is  Na,  K,  or  NH4,  are  produced  by  mixture.  They  are  yellow, 
sparingly  soluble,  crystalline  precipitates.  Osmous  sulphite, 
OsSO3,  is  produced  by  dissolving  the  tetroxide,  OsO4,  in  sul- 
phurous acid.  It  forms  a  double  sulphite  with  potassium, 
K6Os(S03)4.5H20. 

Double  sulphites  of  palladium,  rhodium,  iridium,  and  platinum 
with  the  alkalies  are  known.  That  of  palladium,  Na6Pd(SO3)4.2H2O, 
is  produced  by  add  ing  sulphurous  acid  to  palladium  dichloride,  and 
precipitating  with  caustic  soda.  The  precipitate  gradually  becomes 
yellow  and  crystalline.  The  iridium  compound  has  a  similar 
formula.  Other  double  salts  are  also  formed  at  the  same  time, 
viz.,  H2Na6Ir(SO3)5.4H2O  and  10H2O.  They  form  whitish- 
yellow  scales.  A  double  salt,  which  crystallises  well,  is  produced 
by  the  action  of  sulphurous  acid  on  ammonium  iridi  chloride, 
Ir2Cl6.6NH4Cl,  viz.,  IrCL.H2SO3.4NH4Cl,  which  reacts  with 
carbonates,  yielding  salts,  such  as  IrCl2.K,SO3.2NH4C1.4IT>O. 

Platinons  compounds  are  also  known.  Sulphur  dioxide,  passed 
through  water  in  which  platinic  hydrate  is  suspended,  reduces 
and  dissolves  it  ;  and  on  addition  of  a  sodium  salt,  a  precipitate  of 
the  formula  Na6Pt(SO3)4.3H2O  is  produced.  The  action  of  sul- 
phurous acid  on  ammonium  platinochloride  is  to  form  the  com- 
pound H(PtCl)SO3.2NH4Cl,  in  which  <,be  group  (PtCl)  functions 
as  a  monad.  The  hydrogen  in  this  body  may  be  replaced  by  metals. 
Substituting  potassium  platinochloride  for  the  ammonium  salt, 
the  corresponding  compound  H(PtCl)SO3.2KCl  is  obtained. 
And  by  the  action  of  excess  of  a  sulphite  on  such  compounds, 
bodies  such  as  H(PtCl)SO3.K2SO3.3H2O  are  formed.  Lastly,  by 
the  action  of  hydrogen  ammonium  sulphite  on  ammonium  platino- 
chloride, PtCl2.2NH4Cl,  both  atoms  of  chlorine  are  replaced,  and 
the  compound  Pt(SO3H)2.2NH4Cl.H2O  is  obtained  in  crystals. 
Possibly  selenious  acid  would  form  similar  combinations. 


Cu2SO3;  Cu^Oj.H-.O  ;  A?2SO3  ;  HgoSO3.  —  Cu^eOa;  Ag2SeO3;  Hgr2SeO3. 
These  salts  are  insoluble,  and  are  produced  by  precipitation,  or 
by  the  action  of  sulphurous  acid  on  the  hydrates.    Cuprous  sulphite 
forms  red  microscopic  quadratic  prisms  ;  silver  sulphite  is  white. 

Double  Salts.—  NaCuSO3.H2O  ;   (NH4)Cu(SO3)  ;  K4Cuo(SO3)3,  and 

perhaps  more  complex  salts,  e.g.,  8K2SO3.CuSO3.16H2O  ; 

5Na.2S03.CuS03.38H20,  &c. 

These  are  produced  by  mixture.  Double  sulphites  of  gold 
are  also  known,  such  as  3Na2SO3.Au.,SO3.3H2O  ;  this  compound 
has  a  purple  colour,  and  from  it  other  double  salts  may  be  pre- 


440      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

pared.    Normal  cupric  sulphite  is  unknown  ;   CllSeO3.2H2O  forms 
blue  needles.     The  tellurite  is  green. 

A  basic  cupric  sulphite,  SO2.4CTlO.7H2O,  is  precipitated  on 
addition  of  cupric  hydrate  to  a  solution  of  sulphur  dioxide  in 
absolute  alcohol ;  and  also  several  cuprous-cupric  sulphites,  e.g., 
Cu2SO3.CuSO3.2H2O,  produced  by  warming  a  solution  of  cupric 
sulphite  with  hydrogen  potassium  sulphite.  They  are  red  crys- 
talline powders. 

Hydrogen  cupric  selenite,  H2Cll(SeO3)2.2H2O,  is  prepared 
by  mixture.  HgS03  does  not  exist.  The  selenite,  HgSeO3,  is 
a  white  precipitate,  and  the  tellurite,  a  brown  precipitate.  A 
basic  salt,  SO2.2HgO,  is  produced  by  precipitation.  It  is  a  heavy 
white  crystalline  body.  H2Hg(SO3)2,  Na2Hg(SO3)2,  K2Hg(SO3)2, 
and  (NH4)2Hg(SO3)2  have  also  been  prepared.  They  are  soluble. 
Ammonium  sulphite  unites  with  mercuric  chloride,  forming  the 
salt  2(NH4)2S03.3HgCl2. 

A  double  auric  sulphite,  5K2SO3.Au2(SO3)3.5H2O,  is  produced 
by  adding  potassium  sulphite  to  a  solution  of  potassium  aurate. 
It  forms  yellow  needles. 

Polysulphites,  selenites,  and  tellurites. — The  compounds 
analogous  to  the  anhydrosulphates,  and  to  the  pyrophosphates, 
are  not  very  numerous.  Those  which  have  been  prepared  are  as 
follows : — 

Na2S2O5;  K2S2O5 ;  (NH4)2S2O5.— CaSe2O5 ;   BaSe2O5 ;    CdSe2O5;   MnSe2O5 ; 
CoSe2O5;  PbSe2O5.— Li2Te2O5  ;  Na^^Os ;  K2Te2O5  ;  CaTe2O5. 

Sodium  and  potassium  anhydrosulphites  are  produced  by 
passing  a  current  of  sulphur  dioxide  through  hot  soluiions 
of  the  respective  carbonates;  they  separate  in  crystals.  The 
ammonium  compound  is  formed  when  the  normal  sulphite  is 
heated.  The  corresponding  selenites  and  tellurifces  are  formed  by 
warming  solutions  of  the  normal  salts  with  the  requisite  excess  of 
acid  or  anhydride  ;  and  some  of  the  tellurites  have  been  prepared 
by  fusing  the  dioxide  with  the  required  amount  of  the  carbonate. 
They  are  almost  all  soluble. 

Three  salts  are  known  which  contain  a  smaller  excess  of  di- 
oxide over  the  normal  salt,  viz.,  4SO2.3HgO  ;  4SeO2.3HgO  ;  and 
3SeO2.CoO.H2O. 

One  tetraselenite,  4SeO2.NiO.H2O,  which  may  be  regarded  as 
hydrogen  nickel  anhydroselenite,  H2Ni(Se2O6)2.  and  the  follow- 
ing tetratellurites,  4TeO2.Li2O,  4TeO2.K2O,  4TeO2.CaO,  and 
4TeO2.BaO  have  been  prepared ;  the  tellurites  are  formed  when 
excess  of  anhydride  is  added  to  the  normal  salts. 

Compounds  of  oxides  and  halides.— As  these  compounds 


OXYHALIDES   OF  SULPHUR,   SELENIUM,  AND   TELLURIUM.        441 

are  related  solely  to  the  dioxides  and  trioxides  of  sulphur,  selenium, 
and  tellurium,  it  appears  advisable  to  consider  them  here,  before 
treating  of  the  other  compounds  of  these  elements. 

Sulphuryl,  selenyl,  and  telluryl  compounds.— These  con- 
tain the  groups  (S02)",  (Se02)",  and  (Te02)".  They  are  as 
follows:— S02C12;  SeO2Cl2  (?)  ;  SO2Br2. 

Sulphury  1  chloride  is  produced  by  the  direct  combination  of 
sulphur  dioxide  and  chlorine  in  sunlight,  or  in  presence  of  charcoal 
at  a  moderate  temperature.  It  is  more  easily  prepared  by  passing 
a  current  of  sulphur  dioxide  through  hot  antimony  pentachloride, 
which  parts  with  two  atoms  of  chlorine  ;  and  it  is  likewise  obtained 
by  distilling  sulphuric  acid  with  phosphorus  pentachloride,  thus  : — 
4SO2(OH)2  +  2PC13  =  2PO(OH)3  +  4S02C12  +  2HC1.  This 
action,  however,  yields  other  products.  It  is  a  colourless  liquid, 
boiling  at  77° ;  its  vapour-density  is  normal ;  but  it  decomposes  at 
440°  into  sulphur  dioxide  and  chlorine.  The  corresponding 
bromide  forms  white  crystals,  volatile  at  the  ordinary  temperature. 
These  bodies  rapidly  react  with  water,  forming  sulphuric  acid  and 
the  halogen  acid,  e.g., 

S02C12  +  2H.OH  =  S02(OH)2  +  2HCL 

It  is  this,  and  analogous  actions,  which  lead  to  the  conclusion 
that  sulphuric  acid  may  be  regarded  as  analogous  to  suiphuryl 
chloride,  and  that  their  formulae  are  comparable  : — 

S02<°},  S02<g|          .;',,...'   ' 

(see  p.  268).  But  we  are  ignorant  of  the  molecular  weight 
of  sulphuric  acid ;  and  the  existence  of  double  sulphates  such  as 
those  mentioned  on  p.  421  would  lead  to  the  belief  that  the 
molecular  weight  is  higher  than  that  expressed  by  the  formula 
H2S04. 

Chlorosulphonic  acid. — The  existence  of  two  bodies  related 
like  S02C12  and  S02(OK)2  would  lead  to  the  inference  that  an  in- 
termediate compound  is  possible  ;  a  body  containing  one  atom  of 
chlorine  and  one  hydroxyl  group.  This  body  is  chlorosulphonic 
acid,  S02(OH)C1.  It  is  produced  by  the  action  of  dry  hydrogen 
chloride  on  sulphur  trioxide,  thus :— SO3  +  HCl  =  S02(OH)C1 ; 
or  on  anhydrosulphuric  acid,  H2S2O7.  It  is  also  formed  when 
sulphuric  acid  is  distilled  with  phosphorus  pentachloride,  thus  : — 
S02(OH)2  +  PC15  =  POC13  +  S02(OH)C1  +  HCl;  or  with 
phosphoryl  chloride:— 4S02(OH)2  +  2POC13  =  4S02(OH)C1  + 
2HP03  +  2HCI.  It  is  a  fuming  colourless  liquid,  boiling  at 


442      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

158'4°  (another  statement  gives  151°)  ;  its  density  is  178.  At 
200°,  it  decomposes  into  sulphuric  acid,  sulphuryl  chloride,  and 
other  products.  Near  its  boiling  point  its  density*  corresponds 
with  the  formula  S02(OH)C1;  but  at  higher  temperatures  it  is 
lower,  owing  to  decomposition. 

A  few  salts  of  this  acid  are  known. f  Dry  nitrosyl  chloride, 
NOCl,  acts  on  sulphur  trioxide,  giving  nitrosyl  chlorosulphonate, 
SO2(O.NO)C1  ;  it  is  a  white  crystalline  mass  which  can  be 
melted,  but  which  decomposes  on  raising  the  temperature.  A  salt 
derived  from  sulphur  tetrachloride,  SC14,  is  produced  by  its  action 
on  sulphur  chloride,  S2C12,  in  presence  of  chlorine,  thus  :  -  S2C12  -f- 
2S02(OH)C1  +  3C72  =  2SO2(OSC13)C1  +  2HCL  The  group 
(SC13)'  behaves  in  this  case  like  a  monad  metal.  This  chloro- 
sulphonate is  a  white  crystalline  substance,  subliming  at  57° ;  it  is 
converted  by  heating  in  a  sealed  tube  into  a  mixture  of  sulphuryl 
and  sulphurosyl  chlorides,  SO2(OSC13)C1  =  S02CJ2  +  SOC12. 
Similar  bodies  are  produced  by  the  action  of  chlorosulphonic  acid 
on  selenium  and  on  titanium  tetrachlorides  at  100°.  The  first, 
SO2(OSeCl3)Cl,  is  a  yellow  amorphous  powder;  the  second, 
SO2(O.TiCl3)Cl,  melts  at  165°  and  boils  at  183°.  Both  of  these 
bodies  decompose  when  heated.  Salts  of  the  ordinary  kind  are 
unknown,  because  the  acid  is  at  once  energetically  attacked  by 
water,  yielding  sulphuric  and  hydrochloric  acids  : — 

SO,(OH)C1  +  H20  =  S02(OH)2  +  HCL 

(compare  Chlorochromates,  p.  2(8). 

Anhydrosulphuryl  chloride,  S205C12,  corresponding  to  an- 
hydrosulphuric  acid,  S205(OH)2,  is  also  known.  It  is  produced 
by  distilling  phosphorus  pentachloride  with  sulphur  trioxide  : — 
PC15  +  2SO3  =  POC13  +  S208C12 ;  or  with  chlorosulphuric  acid, 
PC15  +  2S02(OH)C1  =  S205C12  +  POC13  +  2HCL  It  is  also 
formed  when  phosphoryl  chloride  and  sulphur  trioxide  are  heated 
in  a  sealed  tube  to  160°  :-2POCl3  +  6SO3  =  3S205C12  +  P2O5. 
It  is  a  colourless  liquid,  of  density  1'82,  boiling  at  153°.  Its 
density  is  normal  at  184°,  but  at  250°  it  decomposes,  giving  chlo- 
rine, and  sulphur  dioxide  and  trioxide. 

No  direct  compounds  of  sulphur  dioxide  with  halogen  acids  are 
known.  But  selenium  and  tellurium  dioxides  form  the  follow- 
ing :  — SeO2.HCl,  an  amber-coloured  liquid,  stable  below  26°; 
Se02.2HCl,  stable  at  -20°  ;  Se02.2HBr,  stable  below  55°  ; 
2Se02.5HBr,  stable  at  —25°  ;  Te02.HBr,  a  brown  solid,  stable 

*   ComptesrenJ.,96,  616;   Berichte,I6,  479,  602. 
t  Annalen,  196,  265;   Chem.  Soc.,  41,  297. 


OXYHALIDES   OF   SULPHUK,   SELENIUM,   AND   TELLURIUM.        443 

at  15°;  Te02.2HBr,  stable  at  14°,  and  decomposed  at  40° 
into  Te02.2HBr,  which  on  further  heating  yields  water  and 
black^  needles  of  tellurosyl  bromide,  TeOBr2.  The  compound 
2Te02.3HCl  is  stable  at  —10°;  on  rise  of  temperature  it  yields 
TeO2.HCl,  which  at  110°  gives  a  white  mass  of  TeOCl2.  There 
is  some  reason  to  doubt  the  definite  nature  of  these  so-called 
compounds. 

Sulphurosyl  (thionyl),  selenosyl,  and  tellurosyl  halides, 
SOC12;  SeOCl2;  TeOCl2;  SeOBr2;  TeOBr,.— No  fluorides  or 
iodides  are  known. 

Sulphurosyl  chloride  is  prepared  by  passing  sulphur  dioxide 
over  heated  phosphorus  pentachloride  : — $02  +  PC15  =  POC13  + 
SOC12 ;  or  by  distilling  calcium  sulphite,  CaSO3,  with  phosphoryl 
chloride.  It  is  also  obtained  by  distilling  a  mixture  of  sulphur 
chloride,  S2C13,  and  sulphur  trioxide,  through  which  chlorine  is 
being  passed :— SC14  +  SO3  =  SOC12  +  80Z  +  Ck.  It  is  a 
colourless  liquid,  boiling  at  82°  ;  it  bears  to  sulphurous  acid  the 
same  relation  as  sulphuryl  chloride  to  sulphuric  acid,  as  is  shown 
by  its  action  on  water  :—SOCl2  +  2H.OH  =.  SO(OH)2  +  2HCL 
The  sulphurous  acid,  however,  decomposes  into  water  and  the 
dioxide. 

Selenosyl  chloride,  SeOCl2,  is  produced  by  heating  together 
selenium  tetrachloride  and  selenium  dioxide :— SeCl^  +  SeO2  = 
2SeOCl2 ;  by  the  action  of  water  on  selenium  tetrachloride ;  or, 
most  readily,  by  distilling  selenium  dioxide  with  sodium  chloride, 
thus : — 2SeO2  +  2NaCl  =  NaoSeO3  -I-  SeOCl2.  It  is  a  yellowish 
substance,  melting  at  10°  and  boiling  at  179'5°.  Its  specific 
gravity  is  2v44.  The  corresponding  tellurium  compounds  have 
been  obtained,  as  described,  by  heating  the  compounds  of  the 
dioxide  with  the  halides  of  hydrogen. 

Other  acids  of  sulphur  and  selenium. — The  following  is 
a  list : — 

(1.)  Thiosulphuric  acid,*f  H2S2O3.  (7.)  Tetrathionic  acid,  H2S4O6. 

(2.)  Seleniosulphuric  acid,*  H2^SeO3.  (8.)  Pentathionic  acid,  H2S5O6. 

(3.)  Hyposulphurous  acid,*  H2S2O4.  (9.)  Hexathionic  acid(?),  H2S6O6. 

(4.)  Bithionic  acid,}  H2S2O6.  (10.)  Persulphuric  acid  (?),  H2S2O8. 

(5.)  Trithionic  acid,  H2S3O6.  (11.)  Dithiopersulphuric  acid,*§ 
(6.)  Seleniotrithionic  acid,*  H2S2SeO6.                     H2S4O8. 

*  These  acids  are  unknown  in  the  free  state ;  but  their  salts  have  been  pre- 
pared. 

t  Formerly  named  hyposulphurous  acid. 
£  Also  named  hyposulphuric  acid. 
§  This  name  is  a  provisional  one. 


444      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

1.  Thiosulphuric  acid,  H2S203. — On  adding  dilute  hydro- 
chloric or  sulphuric  acid  to  a  weak  solution  of  the  sodium  salt,  the 
acid  appears  to  be  liberated  ;  but  it  decomposes  almost  immediately. 
Sulphur  separates  and  sulphurous  acid  is  formed,  thus  : — H2S203  = 
H2S03  +  S.  But  a  secondary  reaction  appears  to  take  place  at 
the  same  time,  for  hydrogen  sulphide  may  be  recognised  at  first 
by  its  smell :— H2S203  =  H2S  +  0  +  <S02.  This  may  indeed  be 
the  first  stage  of  the  decomposition,  the  nascent  oxygen  reacting 
with  the  hydrogen  sulphide,  giving  water  and  sulphur. 

Na2S203.5H20 ;  K2S2O3.2H2O  ;  3{(NH4)2S2O3}H2O. 

Sodium  thiosulphate  is  produced  by  boiling  a  solution  of 
sodium  sulphite  with  sulphur,  thus  : — 

Na^SOg.Aq  +  S  =  Na2S203.Aq, 

or  by  boiling  sulphur  in  a  solution  of  sodium  hydroxide : — 
CNaOH.Aq  +128  =  2Na2S5.Aq  +  Na2S203.Aq  +  3H20 ;  the 
potassium  salt  is  prepared  similarly ;  and  they  may  be  obtained  by 
adding  a  solution  of  the  respective  carbonate  to  a  solution  of 
calcium  thiosulphate,  CaS203.Aq  +  M2C03.Aq  =  M2S203.Aq  + 
CaCO3 ;  insoluble  calcium  carbonate  is  precipitated,  and  the 
soluble  thiosulphate  remains  dissolved. 

These  are  very  soluble  white  salts.  The  sodium  salt  forms 
large  monoclinic  crystals.  It  is  made  use  of  as  an  "  antichlore  ;  " 
cloth  bleached  with  chloride  of  lime  its  dipped  in  its  solution  to 
remove  adhering  chlorine,  which  might  attack  the  fibre.  It  reacts 
with  the  halogens,  thus  :— 2^"a2S203.Aq  +  OZ2  =  2NaCl.Aq  + 
Na2S406.Aq ;  sodium  tetrathionate  is  formed.  It  is  also  used  in 
*  fixing"  photographic  negatives  or  prints  (see  Silver  Thiosul- 
phate). 

When  heated,  sodium  thiosulphate  yields  sulphate  and  penta- 
sulphide,  4Na2S2O3  =  SNa^SC^  +  Na^. 

CaS2O3.6H2O  ;  SrS2O3.6H2O ;  BaS2O3.H2O. 

Calcium  thiosulphate  is  prepared  on  a  large  scale  from  "  soda- 
waste,"  which  is  essentially  a  sulphide  of  calcium,  It  is  exposed 
to  the  air  in  a  moist  state  for  some  days,  when  the  sulphide  is 
partially  converted  into  sulphite,  CaS03.  At  the  same  time 
sulphur  is  liberated,  probably  by  the  action  of  atmospheric  car- 
bonic acid  and  oxygen,  and  it  reacts  with  the  sulphite,  forming 
thiosulphate.  On  treating  the  oxidised  waste  with  water,  a  solu- 
tion of  sulphite  and  thiosulphite  is  obtained.  The  sulphite 
deposits  in  crystals  on  evaporation  ;  they  are  removed,  and  the 
thiosulphate  crystallises  from  the  mother  liquor.  Calcium  thio- 


THIOSULPHATES.  445 

sulphate  is  the  usual  source  of  the  thiosulphates  generally.      It 
crystallises  in  large  clear  triclinic  prisms. 

Strontium  and  barium  thiosulphates  are  precipitated  on  mixing 
solutions  of  the  respective  chlorides  with  sodium  thiosulphate. 
The  precipitation  is  completed  by  adding  alcohol.  They  are  white, 
sparingly  soluble  salts. 

The  double  salt  CaNa2(S2O3)2.wH2O  is  produced  by  treating 
calcium  sulphate  with  a  solution  of  sodium  thiosulphate.  It  is  a 
soluble  salt.  Barium  and  strontium  sulphates  do  not  give  this 
reaction,  and  it  therefore  affords  a  means  of  separating  calcium 
from  the  sulphates  of  these  metals. 

MgrS.:O.,,.6H.:O  ;  ZnS.2O3.nH2O  :   CdS:O  ./<H  O. 

These  are  very  soluble  salts.  The  two  last  may  be  produced 
along  with  sulphite  by  passing  sulphur  dioxide  through  water  in 
which  the  sulphides  are  suspended  :—  ZnS  +  H2S03.Aq  =  ZnSO 
+  H2S.Aq;  2H2S  +  S02  =  2H2O.Aq  +  3S  ;  ZnSO3  +  Aq  4-  S  = 
ZnS203.Aq.  Solutions  of  the  zinc  and  cadmium  salts  are  decom- 
posed by  heat  into  sulphuric  and  sulphurous  acids  and  zinc  sul- 
phide and  sulphate.  The  double  salt,  K2Mg(S2O3)2.6H2O,  is 
prepared  by  mixture. 

The  thiosulphates  of  the  boron  group  of  elements  are  unknown, 
as  are  also  those  of  the  aluminium  group,  with  one  exception  ;  a 
double  thiosulphate  of  thallium  and  sodium,  Na6Tl4(S2O3)5.10H2O, 
is  produced  by  mixture  ;  it  forms  fine  silky  needles. 

Chromic  and  ferric  thiosulphates  are  unknown. 

2FeS2O3.5H2O  ;  CoS^O3.6H2O  ;  NiS2O3.6H2O. 

The  manganese  salt  has  not  been  obtained  solid  ;  it  decom- 
poses on  concentration  into  sulphur,  sulphur  dioxide,  and  man- 
ganous  sulphide.  The  ferrous  salt  is  formed,  along  with  sulphite, 
by  dissolving  iron  in  sulphurous  acid.  On  evaporation,  the  less 
soluble  sulphite  crystallises  first  ;  the  thiosulphate  separates  on 
concentrating  the  mother  liquor.  These  salts  are  all  soluble  and 
unstable. 

The  only  known  thiosulphates  of  an  element  of  the  carbon 
group  are  those  of  zirconium  and  thorium.  The  former  is  precipi- 
tated as  thiosulphate,  Zr(S2O3)2  (?),  by  boiling  a  solution  of  its 
chloride  with  sodium  thiosulphate.  This  precipitation  serves  as  a 
means  of  separating  zirconium  from  yttrium,  the  cerium  metals, 
and  iron.  On  ignition  of  the  white  precipitate,  pure  zirconia  is 
left.  Thorium  thiosulphate  is  also  a  white  precipitate. 

Thiosulpbates  of  tfie  elements  of  the  silicon  group  are  unknown, 
with  the  exception  of  that  of  lead,  PbS2O3.  It  is  a  wl 


15  r 


446      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

cipitate,  very  sparingly  soluble  in  water,  but  dissolving  in  solutions 
of  thiosulphates  of  other  metals,  forming,  for  example,  K2Pb(S2O3)2, 
BaPb(S2O3)2,  &c. 

Thiosulpbates  of  elements  of  the  nitrogen  and  phosphorus 
groups  have  not  been  prepared,  with  the  exception  of  the  double 
salts  with  bismuth,  which  have  formulae  such  as  K3Bi(S2O3)3.H2O. 
They  are  very  soluble  in  water  and  also  in  alcohol,  in  which  the 
simple  salts  are  nearly  insoluble ;  they  are  thrown  down  on  adding 
a  solution  of  potassium  chloride. 

No  thiosulphate  of  molybdenum,  tungsten,  or  uranium  is 
known. 

Platinum  forms  a  double  thiosulphate  with  sodium,  of  the 
formula  Na6Pt"(S2O3)4.10H2O.  It  is  precipitated  by  alcohol  from 
a  mixture  of  ammonium  platinochloride  and  sodium  thiosulphate. 
It  forms  yellow  crystals. 

Double  salts  of  copper,  silver,  and  gold  with  sodium  thiosul- 
phate are  also  known.  KCu'S2O3.H2O  precipitates  on  adding 
potassium  thiosulphate  to  cupric  sulphate,  as  a  yellow  precipitate, 
which  rapidly  changes  to  cuprous  sulphide.  With  more  potassium 
thiosulphate,  the  salt  K3Cu  (S2O3)2  is  precipitated  on  addition  of 
alcohol.  Similar  sodium  salts  are  known.  Silver  thiosulphate  is 
exceedingly  unstable,  giving  sulphide ;  but  two  varieties  of  double 
salt  are  known,  produced  by  dissolving  silver  oxide  in  a  solution 
of  a  thiosulphate,  or  by  dissolving  silver  chloride,  nitrate,  &c.,  in 
a  solution  of  an  alkaline  thiosulphate.  These  are  R4Ag3(S2O3)3 
and  RAgS2O3,  R  standing  for  a  monad  metal.  Such  a  double  salt  is 
formed  during  the  "  fixing  "  of  photographic  negatives  and  prints. 
That  portion  of  the  silver  bromide  or  iodide  not  exposed  to  light, 
and  not  reduced  to  the  metallic  state  by  treatment  with  the 
"  developer,"  is  removed  from  the  plate  or  paper  by  immersion  in 
a  solution  of  sodium  thiosulphate,  or,  as  it  is  familiarly  termed, 
"hypo."  Salts  of  the  first  series  are  easily  soluble  in  water; 
hence  the  necessity  of  using  excess  of  thiosulphate  in  fixing,  else  a 
salt  of  the  second  series  is  formed,  which  is  insoluble. 

A  double  thiosulphate  of  gold  and  sodium  is  prepared  by  mixing 
solutions  of  auric  chloride  and  sodium  thiosulphate  and  adding 
alcohol ;  the  barium  salt,  BaAu2(S2O3)4,  is  insoluble,  and  is 
formed  from  the  sodium  salt,  NaAu(S2O3)2,  by  double  decompo- 
sition. 

A  double  mercuric  salt,  KioHg"3(S2O3)8,  is  produced  by  dissolv- 
ing mercuric  oxide  in  a  solution  of  potassium  thiosulphate.  It 
forms  sparingly  soluble  white  prisms. 

The  chief  insoluble  thiosulphates  are  those  of  barium  and  lead. 


HYPOSULPHUROUS  ACID.  4-1-7 

The  tendency  of  copper,  silver,  gold,  and  mercury  to  form  donble 
thiosnlphates  should  be  remarked. 

The  estimation  of  a  thiosulphate  depends  on  its  action  on  free 
iodine  dissolved  in  a  solution  of  potassium  iodide,  whereby  an  iodide 
and  a  tetrathionate  are  produced,  thns  : — 2Na2S203.Aq  +  I2  = 
Xa2S406.Aq  +  2NaI.Aq.  The  amount  of  thiosulphate  is  easily 
calculated  from  the  amount  of  iodine  employed. 

2.  Closely  allied  to  the  thiosulphates  are  the  selenio-sulphates, 
formed  by  boiling  a  sulphite  with  selenium.     The  potassium  and 
sodium  salts  are  crystalline  bodies  thus  prepared;  on  addition  of 
a  cadmium  salt  insoluble  cadmium  selenio-sulphate,  CdSSeO3,  is 
precipitated;  but  most  selenio-sulphates  of  metals  decompose,  a 
selenide  or  selenium  being  precipitated.     Thioselenates,  which  it 
might  be  supposed  would  be  formed  on  boiling  sulphur  with  a 
solution  of  a  selenite,  do  not  appear  to  exist  (see  below,  Constitu- 
tion of  Sulphur  Acids). 

3.  Hyposulphurous  acid,  H2S204. — This  acid  is  said  to  be 
produced  by  the  action  of  zinc  on  an  aqueous  solution  of  sulphur- 
ous acid.     No  hydrogen  is  evolved,  and  the  solution  acquires  a 
brownish-yellow  colour  and  great  reducing  power.    Its  tendency  to 
unite  with  free  oxygen  is  such  that  it  turns  warm  on  exposure  to 
air.     The  sodium    salt   is    better  known.     It  is  prepared   by  di- 
gesting in  a  closed  vessel  in  the  cold  finely-divided  zinc  with  a 
concentrated  solution  of  hydrogen  sodium  sulphite,  HNaS03.     Its 
formation  is  expressed  by  the  equation : — 

Zn  +  4HNaS03.Aq  =  Na2Zn(SO3)2  +  Na^S^.Aq  +  2H2O. 

The  zinc-sodium  snlphite  separates  out  on  addition  of  alcohol, 
and  on  cooling  the  remaining  liquid  slender  needles  separate,  still 
containing  a  little  zinc,  from  which  they  may  be  freed  by  dissolv- 
ing in  water  and  again  mixing  the  solution  with  alcohol. 

M.  Schiitzenberger,  the  discoverer  of  these  compounds,  believed 
them  to  have  the  formulae  H2S02  and  HNaS02  respectively.*  But 
the  formulas  appear  to  be  H2S204  and  Na^S^,  for  the  following 
reasons : — The  action  of  a  dilute  solution  of  the  sodium  salt  on  a 
solution  of  copper  sulphate  in  ammonia  is  to  yield  sodium  sulphite 
and  a  cuprous  compound.  Now  it  has  been  shown  that  for  every 
two  atoms  of  sulphur  contained  in  sodium  hyposulphite,  two 
molecules  of  copper  sulphate  are  reduced.  This  implies  the  gain 
of  owe,  not  two,  atoms  of  oxygen  for  every  two  atoms  of  sulphur. 
If,  for  instance,  the  formula  were  HNaSO2,  the  oxidation  by  means 

*  Suit.  Soc.  Chim.,  12,  121 ;  19,  152 ;  20,  145 ;  Bernthsen,  Berichte,  14, 
438  ;  Annalen,  211,  285. 


443      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

of  cupric  oxide  would  be  expressed  by  the  equation  HNaS02  + 
2CuO  =  HNaS03  +  Cu20.  But  then  two  atoms  of  copper  would 
be  equivalent  to  one  atom  of  sulphur.  The  reaction  is  in  fact 
Na2S204  +  2CuO  +  H20  =  Cu20  +  2NaHS03. 

Again,  iodine  in  presence  of  water  converts  this  salt  into  sul- 
phate ;  and  if  its  formula  were  HNaS02  four  atoms  of  iodine 
would  be  required  for  each  atom  of  sulphur,  thus : — HNaS02 
+  2H2O  +  2I2  =  HNaS04  +  4HI.  But  it  is  found  that  in  actual 
fact  three  atoms  of  iodine  for  each  atom  of  sulphur  are  necessary ; 
hence  the  equation  Na2S204  +  3I2  +  4H20  =  2NaI  +  4HI  + 
2H2S04.  The  formula  of  the  acid  must  therefore  be  H2S204,  and 
not  H2S02.  Other  salts  have  not  been  investigated. 

The  sodium  salt  when  added  in  excess  to  copper  sulphate  gives  a 
precipitate  of  copper  hydride,  Cu2H2  (see  pp.  382  and  577).  A  solu- 
tion of  the  sodium  salt,  as  has  been  remarked,  absorbs  free  oxygen, 
and  on  this  fact  is  founded  a  method  of  estimating  oxygen  dissolved 
in  water,  the  end  point  of  the  reaction  being  denoted  by  the  action 
of  the  sodium  salt  on  indigo,  used  as  an  indicator.  A  quantity  of 
indigo  solution  is  decolorised  by  addition  of  hyposulphite  solution 
of  known  reducing  power,  ascertained  by  its  reaction  with  ammo- 
niacal  copper  sulphate;  the  solution  of  free  oxygen  is  then  added, 
the  indigo-white  being  thereby  partially  reconverted  into  indigo- 
blue  ;  and  the  unoxidised  indigo  is  again  decolorised  by  addition  of 
hyposulphite  solution. 

The  impure  calcium  salt  in  aqueous  solution  is  employed  in 
the  arts,  in  dyeing  with  indigo.  Insoluble  indigo-blue  is  by  its 
means  combined  with  hydrogen,  and  thereby  converted  into  soluble 
indigo-white.  The  goods  are  then  dyed,  and,  on  exposure  to  air, 
the  indigo  is  again  oxidised,  and  changes  to  insoluble  blue.  The 
dye-bath  is  named  the  "  hyposulphite  vat." 

4.  Dithionic  or  hyposulphuric  acid,  H2S206. — The  man- 
ganous  salt  of  this  acid,  MnS2O6.6H2O,  is  produced  by  passing 
.a  current  of  sulphur  dioxide  through  water,  kept  cold,  and  con- 
taining manganese  dioxide  in  suspension.  Dithionate  and  sulphate 
of  manganous  are  produced,  thus  : — 

MnO2  +  2S02.Aq  =  MnS206.Aq;  MnO2  +  S02.Aq  =  MnS04.Aq. 

To  separate  the  dithionate  and  sulphate,  a  solution  of  barium 
hydroxide  is  added  to  the  solution.  White  barium  sulphate  and 
manganese  hydrate  are  precipitated  as  insoluble  powders,  while 
barium  dithionate  goes  into  solution  : — MnS206.Aq  +  Ba(OH)2  = 
BaS206.Aq  +  Mn(OH)2.  From  the  barium  salt  a  solution  of  the 
acid  may  be  obtained  by  careful  addition  of  dilute  sulphuric  acid. 


DITHIONATES.  449 

It  may  be  concentrated  in  a  vacuum  over  sulphuric  acid  till  it 
acquires  the  specific  gravity  1'35  ;  if  an  attempt  be  made  to  con- 
centrate further,  it  decomposes  into  sulphuric  acid  and  sulphur 
dioxide. 

Dithionic  acid  is  a  syrupy  strongly  acid  liquid.  Its  salts  are 
prepared  by  addition  of  the  required  sulphate  to  the  barium  salt. 
They  are  as  follows  :  — 


;  NaAO,.2H,0;  K&A,  ;  Rb2S2O6; 

These  are  all  colourless  soluble  crystals,  insoluble  in  alcohol. 

CaS206.4H20  ;  SrS206.H20;  BaS.2O6.2  and  4^0  ;  and  the  double  salts 
Na2Ba(S2O6)2.4  and  P.EUO. 

These  salts  are  all  soluble. 

.—  MgrBa(S2O6)2.4H2O. 


Yttrium  dithionate  has  been  prepared  ;  and  also  the  aluminium 
salt,  A12(S2O6)3.18H2O. 

^Oe  forms  crystals  isomorphous  with  K2S2O6. 


the  ferric  salt  is  basic. 
FeS206.5  and  7H2O  ;  *LnS.2O6.6B^O  ;  CoS^S  and  SE^O  ;  Ni2S2O6.6H2O. 

Ceric  hydrate  is  insoluble  in  dithionic  acid.  Th(S2O6)2.4H2O 
is  very  unstable.  Lead  dithionate,  PbS2O6.4H^O,  and  the  basic 
salt,  (Pb2O)S2O6,  are  crystalline. 

No  compounds  of  the  elements  of  the  nitrogen  group  are 
known  ;  and  bismuthyl  dithionate,  (BiO)2S2O8,  is  the  only  repre- 
sentative of  the  phosphorus  group. 

Three  basic  uranyl  salts,  6UO2.S,O5.10H2O;  7UO2.S2O5.8H2O  ; 
and  8UO2.S2O5.2IH2O,  have  also  been  made.  No  salts  of  metals 
of  the  palladium  or  platinum  groups  are  known. 

Ag-oS206.2H20  ;      NaAgS206.2H20     and     Tl4Ag2(S2O6)3,    are     all     soluble. 
CuS2O6.4H2O  ;  HgS2O6.4H2O  ;  and  basic  eupric  and  mercuric  salts  exist. 

The  dithionates  are  almost  all  crystalline  and  soluble  in  water.* 
5.  Trithionic  acid.—  The  potassium  salt  of  this  acid  is  pro- 
duced by  digesting  at  a  gentle  heat  a  solution  of  hydrogen  potas- 
sium sulphite  with  sulphur  :—  6HKS03.Aq  +  S2  =  2K2S3Ofl.Aq  + 
K2S203.Aq  -f  3H20.  The  warm  filtered  solution  deposits  the  tri- 
thionate  in  crystals.  Also,  by  passing  sulphur  dioxide  through  a 
saturated  solution  of  potassium  thiosulphate  mixed  with  alcohol  :  — 

2K2S203.Aq  +  3S02  =  2K2S306.Aq  +  S. 

*  Annalen,  246,  179  and  284. 

2   Q 


450      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLUEIDES. 

It  is  crystallised  from  dilute  alcohol.  Also  by  passing  sulphur 
dioxide  through  a  mixture  of  solution  of  hydrogen  potassium  sul- 
phite and  potassium  sulphide  :—  4HKS03.Aq  +  K2S.Aq  +  4S02 
=  3K2S306.Aq  +  2H2O. 

The  acid  is  produced  by  substituting  hydrogen  for  the  potas- 
sium in  the  potassium  salt  by  addition  of  hydrosilicifluoric  acid, 
H2SiF6.Aq,  which  forms  an  insoluble  salt  of  potassium,  K,SiP6. 
When  dilute  the  acid  is  stable  ;  but  on  attempting  to  concentrate 
it,  even  at  0°,  it  evolves  sulphur  dioxide,  deposits  sulphur,  and 
sulphuric  acid  remains  insolation  :  —  H2S:iO6  =  H2S04  -\-  $02  -f-  S. 

Potassium  trithionate,  in  aqueous  solution,  soon  decomposes 
into  pentathionate,  sulphate,  and  sulphur  dioxide. 

The  trithionates  are  very  unstable,  and  appear  to  be  all  soluble 
in  water.  The  following  have  been  prepared  :  — 


(NH4)2S306  ;  BaS3O6.2H2O;  ZnS3O6  ;  T12S3O6,  and  KCuS3O6. 

The  sodium  salt  cannot  be  prepared  like  that  of  potassium. 
6.  Seleniotrithionic  acid,  H2S2Se06.  The  potassium  salt  of 
this  acid  is  formed  by  digesting  selenium  with  potassium  sulphite, 
or  with  hydrogen  potassium  sulphite  ;  or  by  evaporating  together 
a  mixture  of  solutions  of  hydrogen  potassium  sulphite  and 
potassium  seleniosulphate,  K2SSe03.  It  is  most  easily  obtained 
by  mixing  a  solution  containing  hydrogen  potassium  sulphite 
and  thiosulphate  with  selenious  acid.  The  liquid  becomes  warm, 
and  the  potassium  salt  then  crystallises  out  in  needles  on  cooling. 
The  salt  K2S2Se06  is  stable  in  solution  for  some  time,  but  gradually 
decomposes,  forming  partly  potassium  dithionate  and  free 
selenium,  and  partly  selenium,  potassium  sulphate,  and  sul- 
phurous acid. 

7.  Tetrathionic  acid,  H2S406.  —  Tetrathionates  are  produced 
by  adding  iodine  in  small  successive  portions  to  the  solution  of 
thiosulphates,  thus  :—  2N"a2S203.Aq  +  I2  =  2NaI.Aq  +  NaoS406.Aq. 
They  are  precipitated  by  addition  of  alcohol.  In  this  manner 
tetrathionates  of  sodium,  potassium,  strontium,  and  barium  have 
been  prepared.  Also,  by  adding  dilute  sulphuric  acid  to  a  mix- 
ture of  lead  thiosulphate  and  lead  peroxide  :  —  2PbS203.  Aq  +  Pb(X 
+  2H2S04.Aq  =  PbS406.Aq  +  2PbSO4  +  2H2O.  The  acid  is 
obtained  by  treating  the  solution  of  the  lead  salt  with  dilute  sul- 
phuric acid,  filtering  from  the  precipitated  lead  sulphate,  and 
evaporating  in  a  vacuum.  When  heated,  it  decomposes  into 
sulphuric  and  sulphurous  acids  and  free  sulphur.  Its  solution  is 
colourless,  and  has  a  strong  acid  taste.  When  heated  with  hydro- 
chloric acid,  it  gives  off  hydrogen  sulphide. 


PENTATHIONIC   ACID.  451 

The  tetrathionates  are  all  soluble,  but  are  precipitated  by 
alcohol  from  their  aqueous  solutions.  They  crystallise  well ;  and 
when  heated  they  give  a  sulphate  or  a  sulphide,  sulphur  dioxide, 
and  free  sulphur.  The  solution  of  the  potassium  salt,  on  standing, 
contains  a  mixture  of  trithionate  and  pentathionate.  Those  pre- 
pared are  as  follows  : 

Na2S406.nH20 ;    ^S4O6  •    SrS4O6.6H,O  ;    BaS,O6. 2H.2O ;    CdS4O6 ;    FeS4O6 ; 
NiS4O6 ;  PbS4Os ;  and  Cu2S4O6. 

The  last  is  obtained  when  a  solution  of  barium  thiosulphate  is 
digested  with  copper  sulphide. 

8.  Pentathionic  acid,  H2S506.* — On  passing  a  slow  current 
of  hydrogen  sulphide  through  a  weak  solution  of  sulphurous  acid 
at  0°,  sulphur  is  deposited,  and  a  solution  is  obtained  containing 
liquid  sulphur,  sulphuric  acid,  a  trace  of  trithionic  acid,  tetra-, 
penta-,  and  an  acid  containing  still  more  sulphur,  probably  hexa- 
thionic  acid.  It  is  also  said  to  contain  dissolved  sulphur,  which 
can  be  precipitated  by  a  solution  of  potassium  nitrate.  Such  a 
solution  is  known  as  "  Wackenroder's  solution."  It  may  be  con- 
centrated over  sulphuric  acid.  To  prepare  a  pentathionate  from 
it,  very  dilute  potash  is  added  with  constant  stirring ;  potassium 
pentathionate  is  at  once  decomposed  by  excess  of  alkali ;  but  it 
is  stable  in,  and  may  be  recrystallised  from,  acid  solution.  Salts 
may  also  be  prepared  by  mixing  the  concentrated  Wackenroder's 
solution  with  acetates,  and  leaving  to  evaporate.  The  acetic  acid 
evaporates  away,  leaving  the  thionate  in  a  crystalline  condition. 
The  potassium  and  the  copper  salts  have  been  analysed  ;  the  former 
has  the  formula  2K2S5O6.3H2O  ;  the  latter  CuS566.4H2O.  They 
crystallise  well. 

The  first  action  between  hydrogen  sulphide  and  sulphurous 
acid  appears  to  result  in  the  formation  of  tetrathionic  acid:  — 
3SO2.Aq  +  HZS  =  H2S4Ofi.Aq.  Tetrathionic  acid  and  free  sul- 
phurous acid  form  trithionic  and  thiosnlphuric  acids,  thus  : — 
H2S406.Aq  +  H2S03.Aq  =  H2S306.Aq  +  H2S203.Aq.  The  thio- 
sulphuric  acid,  being  unstable,  gives  up  its  sulphur;  the  nascent 
sulphur  adds  itself  to  the  trithionic  acid,  forming  pentathionic 
acid,  while  much  of  the  sulphur  separates  in  the  free  state.  By 
the  action  of  excess  of  hydrogen  sulphide  for  a  long  time,  the 
equation  2H2S  +  S02  =  2HZ0  +  3S  is  realised.  The  action  of 
the  nascent  sulphur  from  the  decomposing  thiosulphuric  acid 
appears  also  to  give  rise  to 

*  Debus,  Chem.  Soc.,  53,  278. 

2  G  2 


452      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

9.  Hexathionic  acid,  H3S606,  the  potassium  salt  of   which 
separates  from  the  mother  liquors  of  the  pentathionate  in  a  nearly 
pure  state,  in  white  wart-like  masses. 

10.  The  sodium  salt  of  dithiopersulphuric  acid,  H2S408,*  is 
said  to  be  produced    by  saturating    a    solution  of  sodium  thio- 
sulphate,  containing  more  sodium  thiosulphate  than  it  can  dissolve, 
with  sulphur  dioxide.     The  process  is  repeated  for   several  days, 
the  solution  being    occasionally  allowed  to    stand  at  rest.      On 
evaporation  over  sulphuric  acid,  anhydrous  crystals  of  NagSjOg 
separate  out.     They  crystallise  from  water  with  2H20.     The  equa- 
tion suggested  is  2Na2S203  +  5S02  =  2Na2S408  +  S.     It  may  be 
noticed  that  such  a  body  is  the  analogue  of  hexathionic  acid,  two 
atoms  of  sulphur  being  replaced  by  oxygen. 

Constitution  of  the  acids  of  sulphur  and  selenium.  —  The 
constitution  of  the  sulphates  and  pyrosulphates  has  already  been 
discussed.  It  is  probable  that  that  of  the  selenates  and  tellurates 
is  similar  ;  and  it  now  remains  to  discuss  the  other  compounds 
which  have  not  yet  been  considered. 

Just  as  there  are  probably  two  nitrous  acids  (see  p.  337)  and 
two  phosphorous  acids  (see  p.  375),  so  theory  leads  to  the  sug- 
gestion that  two  sulphurous  acids  are  also  capable  of  existence.f 

Their  formulae  should  be  — 


n     q^  , 

=S  and 


Now  sulphurosyl  chloride,  SOC12,  cannot  be  conceived  other 
than  0=S=C12;  on  treating  it  with  water,  it  would  naturally 
follow  that  0—  S(OH)2  should  be  formed.  And  if,  instead  of 
acting  on  it  with  water,  alcohol  or  ethyl  hydroxide,  (C2H5)OH  be 
chosen,  the  corresponding  sulphite  of  ethyl  (C2H5)',  viz., 
O=S(OC2H5)2,  should  result  4  This  is,  in  fact,  the  case.  And, 
moreover,  ethyl  sulphite  reacts  with  boiling  caustic  potash,  pro- 
ducing potassium  sulphite  and  ethyl  hydroxide,  thus  :  — 

0=S(OC2H5)2  +  2HOK  =  2HOC2H5  +  K2SO3. 

It  might  be  expected  that  the  same  compound,  ethyl  sulphite, 
would  be  produced  by  heating  a  sulphite  with  iodide  of  ethyl, 
(C2H5)I,  thus  :— 

2  +  2I(C2H5)  =  2NaI  +  0=S(OC2H5)2. 


*  Compt.  rend.,  106,  851,  1354. 

t  Divers,  Chem.  Soc.,  47,  205  ;  49,  533.     Eohrig,  J.  praJct.  Chem.  (2),  37, 
217. 

$  The  compound  actually  used  is  sodium  elhoxide,  C2H6ONa. 


CONSTITUTION   OF  THE   ACIDS   OF  SULPHUR.  453 

Bnt  the  product  is  a  different  body.  It  has  a  higher  boiling 
point  than  ethyl  sulphite,  and,  moreover,  on  boiling  with  an  alkali, 
a  different  change  occurs  ;  only  one  ethyl  group  is  replaced  by  the 
alkaline  metal,  and  a  salt  termed  an  ethyl-sulphonate  is  produced. 

The  conclusion  follows,  therefore,  that  sodium  sulphite  has  a 
constitution  different  from  that  of  ethyl  sulphite.  The  alternative 
formula,  (Ot)^S(0  H)H,  is  therefore  adopted,  and  the  formulae  for 
these  bodies  are,  therefore  :  — 


^Q^25  o^  ,       ^<,  . 

0>    <(C2H5)     >       0>    <(C2H5)''and    0>S<H 

Ethyl-sulphonate  of       Ethyl-sulphonate  of  Sulphurous  acid. 

ethyl.  sodium. 

This  view  of  the  constitution  of  ethyl-sulphonate  of  sodium  is 
confirmed  by  the  relation  of  this  body  to  ethyl  hydrosulphide, 
(C2H5)SH,  a  compound  analogous  to  alcohol,  which  is  ethyl 
hydroxide,  (C2H3)OH.  On  oxidising  ethyl  hydrosulphide,  ethyl- 
sulphonic  acid  is  produced  :  — 

(C2H5)SH  +  30  =  (C2H5)S03H. 

And,  conversely,  by  reducing  ethyl  sulphonyl  chloride, 
(C2H5)S02C1,  with  nascent  hydrogen,  ethyl  hydrosulphide  is 
formed,  thus:  — 

(C2H5)S(02)IVC1  +  6H  =  (C2H5)SH  +  2H20  +  HC1. 

Other  considerations  lead  to  the  same  conclusion,  but  the  proof 
given  is  the  most  important,  because  it  is  the  most  direct.  It 
must  then  be  concluded  that,  when  sulphurosyl  chloride  is  decom- 
posed by  water,  the  sulphurous  acid  originally  formed,  O=S(OH)2, 
undergoes  molecular  rearrangement,  and  changes  into  sulphonie 
acid,  (O2)S(OH)H.  It  has  also  been  ascertained  that  two  sodium 
potassium  sulphites,  NaKSO3,  exist.  These  areKO.S02Na  and 
NaO.S02K,  and  they  differ  in  properties.* 

Seleiiious  acid,  on  the  contrary,  appears  to  have  the  formula 
O—  Se(OH)2;f  for  by  acting  on  selenosyl  chloride,  O=SeCl2, 
with  ethyl  hydroxide,  or  by  heating  together  sodium  selenite  and 
ethyl  iodide,  the  same  product  is  obtained,  viz.,  O=Se(OC2H5)2  ; 
this  is  known  because  it  reacts  with  caustic  soda,  forming  selenite 
again,  thus  :  O=Se(OC2H5)2  -f  2HONa  =  0=Se(ONa)2  + 
2HO(C2H5).  There  appears,  therefore,  to  be  only  one  selenious 
acid,  O=Se(OH)2. 

The  constitution  of  tellurous  acid  has  not  been  investigated.    • 

*  Berichte,  22,  1729. 
f  Ibid.,  13,  656. 


454      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

Thiosulphuric  acid  is  thus  named  because  it  may  be  regarded 
as  sulphuric  acid,  H2S04,  of  which  one  atom  of  oxygen  has  been 
replaced  by  an  atom  of  sulphur,  Ot-lov.  Here  again  alternative 
formulae  are  possible.  The  oxygen  may  be  replaced  in  the  group 
(S02)",  or  in  one  of  the  hydroxyl  groups.  The  alternative  for- 
mulae are  :  — 


^x-  rl 

0>S<OH'and 

Preference  is  given  to  the  latter  formula,  for  this  among  other 
reasons  :  an  aqueous  solution  of  sodium  thiosulphate,  when  boiled 
with  ethyl  bromide,  forms  sodium  ethyl  thiosulphate,*  thus  :  — 

Na2S203.Aq  +  (C2H5)Br  =  Na(C2H5)S203.Aq  +  NaBr.Aq. 

On  mixing  this  salt  with,  barium  chloride,  it  is  to  be  presumed 
that  barium  ethyl  thiosulphate  is  produced.  This  compound  is 
unstable,  and  in  a  few  hours  decomposes  into  barium  dithionate, 
BaS206,  and  ethyl  disulphide,  thus  showing  that  the  ethyl  group, 
(C2H5),  was  attached  to  sulphur,  not  to  oxygen,  thus  :  — 

=  BaS206  +  (C3H5)2S2.f 

As  regards  hyposulphurous  acid,  too  little  is  known  regarding 

it  to  establish  any  formula  as  probable;  the  formula  02S^—  -  —  ^S02 
has  been  suggested. 

The  constitution  of  dithionic  acid  follows  from  the  decomposi- 
tion of  barium  ethyl-thiosulphate.  It  may  be  regarded  as  certain 
that  ethyl,  once  attached  to  sulphur,  will  not  readily  leave  it  ;  the 
constitution  of  barium  dithionate  is  therefore, 

,0—8(00 

,  and  probably 


although  the  smooth  decomposition  of  this  body  into  barium  sul- 
phate and  sulphur  dioxide  might  lead  to  the  conjecture  that  the 
two  sulphuryl  groups  are  united  by  virtue  of  their  oxygen  atoms. 
But  this  argument  may  have  little  value. 

Seleniosulphuric  acid,  H2SSe03,  has  doubtless  the  constitution 

OTT  OTT 

for  the  isomeric  acid,  02Se<gjj,  cannot  be  prepared  by 

*  Berichte,  7,  646. 
f  Chem.  Soc.,  28,  687. 


NITROSOSULPHATES.  455 

the  action  of  sulphur  on  sodium  selenite,  which,  as  has  been 
pointed  out,  has  the  constitution  SeO(OH)2. 

It  is  useless,  in  the  present  state  of  our  knowledge,  to  construct 
constitutional  formulae  for  the  remaining  thionic  acids.  The  pos- 
sible formulas  are  discussed  by  Debus  (Transactions  of  the  Chemical 
Society,  1888,  p.  354)  ;  but  no  decided  reason  has  yet  been  adduced 
for  giving  preference  to  one  formula  over  others. 

The  relation  between  the  so-called  dithiopersulphuric  acid  and 
hexathionic  acid  has  already  been  suggested  (p.  452). 

Nitrososulphates.  —  By  passing  a  current  of  nitric  oxide,  NO, 
through  a  cooled  solution  of  ammonium  or  potassium  sulphites, 
two  molecules  of  the  oxide  unite  with  each  molecule  of  the  sulphite, 
forming  crystalline  compounds,  possessing  respectively  the  formulae 
(NH4)2SO3(NO)2  and  K2SO3(NO)2.  The  method  of  formation 
would  suggest  an  analogy  with  the  thiosulphates.  It  has  been 
suggested  that  because,  when  exposed  to  the  action  of  nascent 
hydrogen  from  sodium  amalgam  in  strong  alkaline  solution,  these 
salts  yield  a  hyponitrite  and  a  sulphite,  they  are  constituted  simi- 

O  R" 
larly  to  thiosulphates,  viz.,  0=S<,,      .      The  equation   re- 


presenting their  reduction  would  therefore  be  :  — 

(KS03)(N"0)2K  +  2Na  =  (S03K)Na  +  NaNO  +  KNO. 

But  that  the  reduction  of  nitric  oxide  in  alkaline  solution  should 
yield  a  hyponitrite  is  to  be  expected,  and  the  argument  is  of  little 
value.  These  compounds  would  repay  further  investigation. 

Compounds  of  sulphur,  selenium,  and  tellurium  with 
each  other.  —  It  is  questionable  whether  the  bodies  produced  by 
fusing  sulphur  and  selenium  together  are  mixtures  or  compounds. 
A  yellow  compound  or  mixture  is  produced  by  passing  a  current  of 
hydrogen  sulphide  through  a  solution  of  selenious  acid.  It  is 
probable  that  this  reaction  is  analogous  to  that  of  hydrogen  sul- 
phide on  sulphurous  acid,  and  if  so  it  must  be  a  very  complicated 
one.  A  brick-red  solid  is  formed  when  selenium  and  sulphur  are 
fused  together  in  the  proportion  of  SeSs.  Sulphur  and  selenium 
crystallise  together  from  hot  benzene  in  orange  crystals,  but  the 
ratio  between  the  two  is  indefinite. 

Similarly,  an  iron-grey  mass  is  formed  when  selenium  and 
tellurium  are  melted  together. 

The  compounds  of  sulphur  with  tellurium  are  more  definite. 
Hydrogen  sulphide  produces  in  acidified  solutions  of  tellurites  a 
dark-brown  precipitate  of  TeS2,  soluble  in  solutions  of  sulphides  of 
the  alkalies,  forming  sulphotellurites.  These  bodies  are  also 


456      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

formed  when  hydrogen  sulphide  is  passed  through  a  solution  of  a 
tellurite.  The  sodium  and  lithium  salts  are  amorphous  pale-yellow 
masses.  The  potassium  salt,  K6TeS5,  separates  in  pale  yellow  needles 
when  its  solution  is  evaporated  in  a  vacuum.  The  ammonium 
salt,  (NH4)6TeS5,  crystallises  in  pale  yellow  quadratic  prisms. 
The  salts  of  calcium,  strontium,  and  barium  are  prepared  by  boil- 
ing solutions  of  the  corresponding  sulphides  with  tellurium  disul- 
phide.  The  barium  salt  crystallises  well. 

The  other  sulphotellurites  are  obtained  by  precipitation. 

The  following  have  been  analysed  : — 

Zn3TeS5  ;  Pt3(TeS5)2  ;  A&6TeS5  ;  Au2TeS5  ;  Hgr6TeS5  ;  and  Hgn3TeS5. 

They  are  brown  or  black  insoluble  bodies. 

Tellurium  trisulphide,  TeS3,  is  deposited  in  lustrous  dark- 
grey  spangles  from  telluric  acid  saturated  with  hydrogen  sulphide. 
The  sulphotellurates  are  produced  by  substituting  a  tellurate  for 
telluric  acid,  and  filtering  off  the  precipitated  trisulphide.  The 
salts  of  sodium  and  potassium  are  yellow  and  crystalline.  Their 
formulae  are  unknown,  but  it  is  probable  that  their  investigation 
would  throw  light  on  the  constitution  of  sulphuric,  selenic,  and 
telluric  acids. 

Ortho-acids. — Analogy  with  orthocarbonic  acid  (see  p.  292), 
orthosilicic  acid  (see  p.  306),  and  phosphoric  acid  (see  p.  353) 
would  lead  to  the  supposition  that  orthosulphuric  acid  should 
possess  the  formula  S(OH)6,  corresponding  to  the  theoretical 
P(OH)5  and  C(OH)4  (of  which,  however,  the  ethyl  salt  is  known), 
and  the  known  Si(OH)4.  It  is,  indeed,  possible  that  the  acid  con- 
taining two  molecules  of  water,  H2S04.2H20,  may  be  hydrogen 
orthosulphate.  But  no  other  salts  are  known.  The  first  anhydride 
of  such  an  acid  would  be  the  crystalline  monohydrated  acid, 
H2S04.H20  =  SO(OH)4;  but,  again,  metals  do  not  appear  to 
replace  hydrogen.  The  second  anhydride,  S02(OH)2,  is  the 
ordinary  acid,  which  forms  numerous  salts. 

Similarly,  orthosulphurous  acid  would  correspond  with  the 
unknown  orthosilicoformic  acid,  H.Si(OH)3,  and  the  likewise 
unknown  orthoformic  acid,  H.C(OH)3,  of  which,  however,  the 
ethyl  salts  are  in  both  cases  known.  The  formula  of  orthosul- 
phurous acid  would,  therefore,  be  H.S(OH)5.  It  is  unknown,  nor 
have  any  derivatives  been  prepared.  But  the  sulphotellurites  may 
be  its  sulphur-tellurium  analogues,  and  have  the  constitution 
M.Te(SM)5.  It  is  not  improbable  that  the  sulphotellurates,  on 
further  investigation,  should  supply  the  link  missing  in  ortho- 
sulphates. 


PHYSICAL   PROPERTIES. 


457 


It  is  thus  evident  that  a  systematic  study  of  the  rarer  elements 
is  greatly  to  be  desired,  inasmuch  as  light  is  thereby  thrown  on 
the  relations  of  atoms  with  each  other;  in  other  words,  on  the 
structure  of  compounds. 

Physical  Properties. 


Mass  of  one  cubic  centimetre : — 
SO2.  Temp.   -20 '5°    -9 '9°    -2'1°      0° 


Mass 

SO2.  Temp. 
Mass 


21-7° 

1  -491  1  '461  1  '438  1  '434  1'376 
102-4°  120-4°  130-3°  140 '8° 
1-104  1-017  0-956  0-869 

Temp.     155-05°     156 '0°. 

Mass         0-637        0'52.     Critical  temp.,  156°. 


35-2°      52°      62°  82 -4° 

1  -337  1  '287  1-252  T184 

146-6°      151-7°  154  -3° 

0-806       0-732  0-671 


S03,  1-936  gram  at  20°.  SeO2,  3'954.  TeO2,  5784  at  14°.  TeO3,  5'112  at 
11°.  H2SO4,  1-839  at  15° ;  1*836  at  20°  ;  1-833  at  25°.— H2SO4.H2O,  1778  at 
15°.— H2SO4.2H2O,  1-651  at  15°. -H2SO4.3H2O,  1'551  at  15.°— H2S2O7,  1'9.— 
H2SeO4,  2-62. 

Li,S04.        Na2S04.        K2S04.       Rb2SO4.       Cs2SO4.    (NH4)2SO4. 

2  -21  2-68  2-66  3 '64  4' 10  1 '76 

Se    —  3-21  3-08  3 -90  4 -34  2 '20 


BeSO,. 
2-44 

Se    — 


CaSO4. 
2-97 
2-93 


SrS04. 
3-97 
4-23 


BaSO,. 
4-48 
4-75 


2-71 


ZnS04. 
3-62 


CdS04. 
4-45 


803(804)3.  Y2(S04)3.     AL,(S04)3.  In2(S04)3.    Ce2(SO4)3.    (T12SO4). 
2-58  2-61  271  3  44  3'91  6 '80 

ge    

Cr2(S04)3.       Fe2(S04)3.       FeSO4.       MnSO4.       CoSO4.       NiSO4. 


3-01 

Se       — 

PbSO4.      CuSO4. 

6-00          3-61 
Se     6-22  — 


3-01 


6-47 


3-35 

A&2S04. 
5-49 
5-92 

Tl2TeO4. 
675 


3-28 


7-56 


BaTeO4. 
4-54 


3-47 
4-03 


3-42 


H2Te04,     (NH4)2Te04. 


3-42 


3-00 


Heat  of  combination  :  — 

*S  +  O  +  Aq  =  SOAq  +  109K. 

S  +  2O  =  S02  +  710K;    +  Aq  =  77K.     SOZ 

S  +  30  =  S03  +  1033K;    +  Aq  =  H2SO4.Aq 

2H2SO4.Aq  +  O  =  H2S2O8.Aq  -  283K. 

2S  +  20  +  Aq  =  H2S2O3.Aq  +  689K. 

2S  +  2ff  +  6O  +  Aq  =  H2S2O6.Aq  +  2796K. 


SO2  4 
392K. 


62K. 


Ehombic ;  monoclinic  23K  more. 


458      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

4S  +  5O  +  Aq  =  H284O6.Aq  +  1928K. 

S  +  O  +  2CI  =  SOCJ2  +  498K  ;  SO2  +  2CI  =  SO2C12  +  187K. 

2S  +  5O  +  2CI  =  S2O5C12  +  1630K. 

Se  +  20  =  Se02  +  572K  ;    +  Aq  ==  H2Se03.Aq  -  9K. 

Se  +  3O  +  Aq  =  H2SeO4.Aq   +  768K. 

Te  +  2O  +  H2O  =  H2TeO3  i-  773K. 

Te  +  3O  +  Aq  =  H2TeO4.Aq  +  985K. 

2XaOH.Aq  +  H2SO4.Aq  =  Na2SO4.Aq  +  314Z.     Similarly  for— 


Li2S04.     K2S04.     T12S04.     CaS04.     SrSO4.     BaS04.     (NH4)28O4  all  with  Aq. 
313K.       313K.      311K.       311K.      307K.      3B9K.  282K. 

MgSO4.Aq.  ZnSO4.Aq.  CdSO4.Aq.  FeSO4.Aq.  MnS04.Aq.  CoSO4.Aq.  NiSO4.Aq. 
ailK.          235K.          238K.          249K.          266K.  247K.          263K. 

CuS04.Aq.         Al2(S04)3.Aq.        Cr2(SO4)3Aq.         Fe2(SO4)3.Aq. 
184K.  632K.  493K.  338K. 


459 


CHAPTEE  XXVIII. 

COMPOUNDS    OF     THE     HALOGENS     WITH     OXYGEN,     SULPHUR,     SELENIUM, 

AND    TELLURIUM. OXY-ACIDS    OF   THE     HALOGENS  ;     HYPOCHLORITES, 

CHLORITES,    CHLORATES,.    AND     PERC.HLORATES ;    BROMATES,    IODATES, 
AND    PERJODATES. 

In  this  group,  as  in  the  preceding,  the  compounds  with  oxygen 
present  marked  difference  in  most  points  from  those  with  sulphur, 
selenium,  and  tellurium,  which  have  already  been  described  as 
halides  on  p.  167. 

While  fluorine  forms  no  compound  with  oxygen,  those  of 
chlorine,  bromine,  and  iodine  are  numerous ;  and  the  compounds 
of  their  oxides  with  other  oxides  are  well  denned,  and  have  long 
been  known.  The  following  is  a  list  of  the  oxides  : — 

Chlorine.  Bromine.  Iodine. 

Cl^O;  C102.*  (?)  I203(?)t ;  I205. 

Sources. — Iodine  pentoxide  occurs  in  combination  with  sodium 
oxide  as  sodium  iodate  in  caliche,  the  crude  sodium  nitrate  found  in 
Peru  (see  p.  325). 

Preparation. — Chlorine  monoxide  is  produced  by  passing  a 
current  of  dry  chlorine  over  dry  precipitated  mercuric  oxide,  con- 
tained in  a  tube  cooled  with  ice.  The  chlorine  combines  with  the 
mercury,  forming  an  oxychloride,  and  with  the  oxygen,  forming 
chlorine  monoxide,  thus  :— 2HgO  +  2Ck  =  Hg2Cl2O  +  Cl*0.  The 
gaseous  monoxide  is  condensed  in  a  freezing  mixture  of  finely- 
powdered  ice"  and  salt.  If  a  lower  temperature  can  be  obtained  for 
condensation  it  should  be  employed,  for  the  yield  is  thereby  much 
increased. 

Ordinary  red  oxide  of  mercury,  owing  to  its  compact  nature, 
cannot  be  used  in  this  preparation ;  the  yellow  variety,  produced 
by  addition  of  caustic  soda  to  mercuric  chloride,  and  dried  at  400°, 
must  be  employed. 

Compounds  of  the  formulae  CIO  and  C1203  are  unknown. 

Chlorine  peroxide,  C102,  is  formed  by  heating  chloric  acid, 
HC103  (see  p.  464). 

*  Annalen,  177,  1 ;  213,  113.    Berichte,  14,  28. 
f   Compt.  rend.,  85,  957. 


460      THE   OXIDES,   SULPHIDES,    SELENIDES,   AND   TELLUKIDES. 

The  reaction  is  expressed  by  the  equation  :  —  3HC103  =  HC104 
+  2(7/02  4-  H2O  ;  perchloric  acid  being  formed  simultaneously.  It 
is  more  convenient  to  prepare  it  from  potassium  chlorate  and  con- 
centrated sulphuric  acid,  yielding  chloric  acid,  which  decomposes 
as  above.  The  temperature  should  not  exceed  40°,  else  a  danger- 
ous explosion  will  result. 

No  oxides  of  bromine  have  been  isolated. 

Iodine  trioxide,  I203,  is  said  to  be  produced  by  the  action  of 
ozone  on  iodine. 

Iodine  pentoxide,  I2O5,  is  produced  by  heating  iodic  acid, 
HIO3,  to  170°.  It  is  the  anhydride  of  this  acid  :—  2HIO3  =  I2O5 


Properties.—  Chlorine  monoxide,  CkO,  is  a  yellowish-brown 
gas,  condensing  to  a  dark  brown  liquid,*  which  boils  at  5°  under  a 
pressure  of  738  mm.  (about  6°  under  normal  pressure).  It  is 
soluble  in  water,  forming  a  yellow  solution  of  hypochlorous  acid  ; 
hence  it  is  sometimes  named  hypochlorous  anhydride.  It  is 
inadvisable  to  collect  more  than  a  drop  or  two  in  a  test-tube,  for  it 
is  exceedingly  explosive.  The  gas  can  be  exploded  by  gentle  heat, 
by  throwing  into  it  a  pinch  of  flowers  of  sulphur,  or  by  contact 
with  organic  matter.  Its  density  at  10°  is  normal. 

Chlorine  trioxide  does  not  exist.  The  gas,  formerly  believed  to 
be  this  substance,  produced  by  the  mutual  action  of  nitric  acid, 
potassium  chlorate,  and  arsenic  trioxide,  has  been  shown  to 
consist  of  the  peroxide  mixed  with  variable  amounts  of  free 
chlorine. 

Chlorine  peroxide,  C102  (comp.  nitric  peroxide,  N02),  is  a 
dark  red  liquid,  boiling  at  9°  under  a  pressure  of  730  mm.  (about 
10'6°  at  760  mm.).  It  forms  a  reddish-brown  gas,  which  explodes 
when  heated,  often,  indeed,  at  the  atmospheric  temperature.  Its 
density  at  10'7°  and  718  mm.  was  found  to  correspond  with  the 
formula  C702;  it  does  not  appear,  therefore,  to  resemble  nitric 
peroxide  in  forming  a  polymeride.  With  water  it  forms  a  mixture 
of  chlorous  and  chloric  acids. 

Chloric  acid  and  hydrogen  chloride  decompose  one  another  to 
a  great  extent,  giving  a  mixture  of  chlorine  peroxide  and  free 
chlorine.  This  mixture,  which  is  evolved  by  the  action  of  hydro- 
chloric acid  diluted  with  its  own  volume  of  water  on  potassium 
chlorate,  or  by  distilling  a  mixture  of  potassium  chlorate,  salt, 
and  dilute  sulphuric  acid,  was  long  believed  to  be  a  definite  oxide 
of  chlorine,  and  was  named  by  Sir  Humphrey  Davy,  its  discoverer, 

*  Serichte,  16,  2998  ;  17,  157.     Annalen,  230,  273. 


HYPOCHLORITES,  HYPOBROMITES,  AND  HYPOIODITES.        461 

euchlorine.  The  equation  expressing  complete  decomposition 
would  be  HC103  +  5HC1  =  3H2O  +  30^;  but  the  reaction  is  only 
a  partial  one,  the  chloric  acid  yielding  perchloric  acid  and  chlorine 
peroxide,  as  already  described,  mixed  with  variable  quantities  of 
chlorine. 

Iodine  pentoxide,  I205,  is  a  white  solid,  crystallising  in  the 
trimetric  system.  When  heated  to  180 — 200°  it  decomposes,  with- 
out explosion,  into  iodine  and  oxygen.  It  combines  with  water, 
forming  iodic  acid. 

Iodine  forms  no  other  oxides  capable  of  free  existence. 

Compounds  with  water  and  other  oxides. — The  oxides 
described  combine  with  water,  forming  compounds  termed  acids. 
They  are  as  follows : — 

(1.)  HC1O,*  hypochlorous  acid.        MBrO,  hypobromite.  MIO,  hypoiodite. 
(2.)  HC1O2,*  chlorous  acid. 

(3.)  HC1O3,  chloric  acid.  MBrO3,  bromate.          HIO3,  iodic  acid. 

(4.)  HC1O4,  perchloric  acid.  H5IO5,  periodic 

acid. 

It  is  to  be  noticed  that  the  perchloric  and  hypobromons  acids 
and  salts  of  bromic  and  hypoiodous  acids  are  known,  whereas  the 
free  oxides  have  not  been  prepared,  owing  to  their  instability. 

1.  Hypochlorites,  hypobromites,  and  hypoiodites  of  the 
metals  of  the  sodium  and  calcium  groups  are  produced  by  the 
action  of  the  halogen  on  solutions  of  the  respective  hydroxides, 
thus  :— Clz  +  2KOH.Aq  =  KCl.Aq  +  KOCl.Aq  +  H20 ;  2C72  + 
2Ca(OH)2.Aq  =  CaCl2.Aq  +  Ca(OCl)2.Aq  +  2H20  ;  and  the 
hypochlorites  are  also  formed  by  acting  on  the  hydroxides  with 
hypochlorous  acid. 

Hypochlorous  acid  is  easily  prepared  in  dilute  solution  by 
shaking  precipitated  mercuric  oxide  with  chlorine-water,  and 
filtering  from  the  precipitated  mercuric  oxychloride,  thus : — 
2HgO  +  2Cl2.Aq  =  HgCl2.HgO  +  2HC10.Aq.  It  forms  a  pale 
yellow  solution,  with  a  pleasant  smell  of  seaweed ;  it  possesses 
very  powerful  oxidising  and  bleaching  properties.  It  reacts  at 
once  with  hydrochloric  acid,  forming  chlorine  and  water,  thus  : — 
HClO.Aq  +  HCLAq  =  H20  +  Ck  +  Aq.  It  cannot  be  obtained 
in  concentrated  solution,  for  it  decomposes  into  chlorine  and 
oxygen.  It  can  also  be  produced  by  passing  chlorine  through 
water  containing  calcium  carbonate  in  suspension,  thus  : — CaCO3 
+  Aq  -I-  Clt  =  CaCl2.Aq  +  COZ  +  2HC10.Aq.  By  distillation  the 
hypochlorous  acid  may  be  separated  from  the  calcium  chloride ; 

*  Known  only  in  solution. 


462      THE   OXIDES,   SULPHIDES,    SELENIDES,   AND    TELLURIDES. 

it  comes  over,  along  with  water,  in  the  first  portion  of  the  distillate. 
A  similar  action  takes  place  with  solution  of  sodium  carbonate. 
When  a  current  of  chlorine  is  passed  through  it,  a  mixture  of 
chloride  and  hypochlorite  is  formed  at  first,  thus  : — 

JSTaaCOg.Aq  +  Ok  =  NaCl.Aq  +  NaClO.Aq  +  (702; 
further  action  of  chlorine  liberates  hypochlorous  acid,  thus : — 
NaClO.Aq  +  CZ2  +  H20  =  NaCl.Aq  +  2HC10.Aq. 

Hypobromous  acid  may  be  obtained  in  dilute  aqueous  solu- 
tion, by  shaking  precipitated  mercuric  oxide  with  bromine -water. 
It  is  a  yellow  liquid,  with  a  smell  closely  resembling  that  of  hypo- 
chlorous  acid. 

Hypoiodous  acid  has  not  been  obtained  in  the  free  state. 

Hypochlorites,  hypobromites,  and  hypoiodites. — Only  one 
salt,  viz.,  calcium  hypochlorite,  Ca(OCl)2.4H20,  has  been  prepared 
in  an  approximately  pure  state. 

It  has  been  stated  that  when  a  hydroxide,,  dissolved  in  water, 
is  saturated  with  chlorine  in  the  cold,  a  mixture  of  a  hypochlorite 
and  chloride  is  formed.  Thus  with  sodium  hydroxide  : — 

2NaOH.Aq  +  C12  =  NaCl.Aq  +  NaOCl.Aq  +  H20. 

But  sodium  hypochlorite,  owing  to  its  instability,  has  never  been 
isolated.  Such  a  solution  has,  however,  great  oxidising  power,  and 
is  .named  "  Labarroque's  disinfecting  liquid."  A  similar  mixture 
of  potassium  chloride  and  hypochlorite  used  to  be  known  as  "  Eau 
de  Javelle,"  and  was  formerly  used  for  bleaching. 

The  most  important  compound  of  this  acid  is  a  double  chloride 
and  hypochlorite  of  calcium,  known  commercially  as  bleaching  - 
powder  or  "chloride  of  lime."*  It  is  produced  on  the  large 
scale  by  passing  chlorine  over  slaked  lime  (calcium  hydroxide), 
spread  in  thin  layers  on  slate  shelves,  in  a  building  specially  con- 
structed for  the  purpose  (see  Alkali-manufacture,  p.  670).  The 
reaction  which  takes  place  is  : — 

Ca(OH)2  +  013  =  Ca(OCl)Cl  +  H80. 

That  this  body  really  is  a  definite  compound  of  the  formula 

OC1 
Ca</-n    ,   and  not   a   mixture  of    chloride    and   hypochlorite   of 

calcium,   is    shown   by   the    fact   that   calcium    chloride   is    deli- 

*  Gay-Lussac,  Annales,  26,  163;  Odling,  Manual,  1861,  I,  56;  Kopfer, 
Chem.  Soc.,  28,  713  j  Kingzett,  ibid.,  28,  404 ;  Stahlschmidt,  Dingl.  polyt.  J., 
221,  243,  335. 


HYPOCHLORITES.  463 

qnescent,  soon  liquefying  by  attracting  moisture  from  air  ; 
but  bleaching- powder  '  does  not  deliquesce.  Moreover,  calcium 
chloride  and  hypochlorite  are  both  exceedingly  soluble  in 
water  ;  but  1  part  of  bleaching-powder  requires  about  20  parts 
of  water  to  effect  solution  ;  it  usually  leaves  a  slight  residue 
consisting  of  calcium  hydroxide,  some  of  which  it  almost  always 
retains  in  the  uncombined  state.  But  this  compound,  Ca(OCl)Cl, 
is  decomposed  by  water.  For  on  cooling  a  saturated  solution, 
or  on  evaporating  it  over  sulphuric  acid,  calcium  hypochlorite, 
Ca(OCl)2,  crystallises  out,  in  transparent,  very  unstable  crystals, 
while  calcium  chloride,  which  is  more  soluble,  remains  in  solution. 
Bleaching-powder  is  a  white  non-crystalline  powder,  smelling 
of  hypochlorous  acid.  Its  solution  bleaches,  owing  to  its  parting 
with  oxygen,  thus :— Ca(OCl)2.Aq  =  CaCl2.Aq  +  20.  This 
change  is  greatly  facilitated  by  addition  of  an  acid,  whereby 
hypochlorous  acid  is  liberated,  which  gives  up  its  oxygen,  being 
converted  into  hydrochloric  acid.  Hence,  goods  to  be  bleached 
are  first  run  through  an  aqueous  solution  of  bleaching-powder, 
and  then  through  a  bath  of  dilute  sulphuric  acid. 

Calcium  hypochlorite  gives  no  precipitate  with  silver  nitrate, 
for  silver  hypochlorite  is  very  soluble.  Metallic  mercury  is 
converted  by  hypochlorous  acid  into  oxychloride,  but  by  chlorine 
into  chloride ;  hence  it  is  possible  to  distinguish  the  one  from  the 
other  in  aqueous  solution. 

When  distilled  with  dilute  sulphuric,  nitric,  phosphoric,  or 
even  hydrochloric  acid,  if  the  last  is  not  in  excess,  hypochlorous 
acid  is  found  in  the  distillate.  Excess  of  hydrochloric  acid 
produces  the  decomposition: — HClO.Aq  +  HCl.Aq  =  H2O  + 
Clz  +  Aq  ;  but,  if  only  enough  hydrochloric  acid  is  used  to  liberate 
hypochlorous  acid,  the  latter  distils  over. 

The  action  of  a  cobalt  salt  on  a  solution  of  chloride  of  lime  is 
to  form  hydrated  cobalt  sesquioxide.  On  boiling,  even  a  minute 
proportion  of  this  oxide  causes  evolution  of  oxygen  from  the  solu- 
tion of  bleaching-powder.  It  is  supposed  that  the  black  hydrated 
oxide  of  cobalt  is  further  oxidised  to  an  oxide,  the  formula  of 
which  is  unknown,  and  that  this  higher  oxide  is  simultan- 
eously decomposed,  liberating  oxygen.  Such  an  action  is  termed 
"  catalytic."  The  final  reaction  is  2CaCl(OCl).Aq  =  2CaCJ2.Aq 

+  Of 

Chlorine  acts  on  silver  hydroxide  suspended  in  water,  forming 
silver  chloride  and  hypochlorous  acid.  If  the  oxide  be  present  in 
large  excess,  and  if  the  solution  be  shaken,  the  odour  of  hypo- 
chlorous  acid  disappears,  and  the  solution  contains  the  very  solu- 


464      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

ble    silver   hypochlorite.      But   on    standing,  decomposition  soon 
ensues,  chlorate  and  chloride  of  silver  being  produced : — 

6AgC10.Aq  =  5AgCl  +  AgC103.Aq. 

The  only  other  known  compound  of  chlorine  monoxide  is  a  red 
body,  crystallising  in  needles,  produced  by  its  action  on  sulphur 
trioxide.  It  has  the  formula  C12O.4SO3.  It  melts  at  about  50°, 
and  is  at  once  resolved  by  water  into  sulphuric  and  hypochlorous 
acids. 

Hypobromites  and  hypoiodites  have  not  been  obtained  free 
from  admixture  with  bromides  and  iodides.  They  are  even  less 
stable  than  hypochlorites,  and  are  similarly  produced.  Both 
bromine  and  iodine  dissolve  in  caustic  soda  or  potash  solution, 
forming  yellowish  liquids,  which  possess  a  fragrant  chlorous  smell. 
They  presumably  contain  in  solution  the  respective  hypobromite 
or  hypoiodite.  They  rapidly  decompose  on  standing  into  bromide 
or  iodide,  and  bromate  or  iodate,  thus  : — 

6KBrO.  Aq  =  SKBr.Aq  +  KBr03.Aq ; 
GKIO.Aq  =  5KI.Aq  +  KI03.Aq. 

Chlorous  acid  and  chlorites. — When  chlorine  peroxide, 
C102,  is  added  to  water,  it  yields  a  mixture  of  chlorous  acid,  pre- 
sumably HC102,  and  chloric  acid,  HC103,  thus  :— 2C102  +  H20  + 
Aq  =  HC102.Aq  +  HC103.Aq.  But  chlorous  acid  has  not  been 
examined.  The  reaction  is  strictly  analogous  to  that  between 
nitric  peroxide  and  water  (see  p.  334). 

Similarly,  the  addition  of  chlorine  peroxide  to  an  aqueous 
solution  of  a  hydroxide  yields  a  mixture  of  a  chlorite  and 
a  chlorate.  Potassium  chlorite  is  more  soluble  than  the 
chlorate,  and  may  be  obtained  crystallised  in  thin  needles.  It  has 
the  formula  KC1O2.  The  lead  and  silver  salts  are  sparingly 
soluble,  and  may  be  precipitated.  They  crystallise  from  a  warm 
solution  in  thin  yellow  plates. 

Chloric,  bromic,  and  iodic  acids  :— chlorates,  bromates, 
and  iodates. — These  compounds  may  be  viewed  as  combinations 
of  the  unknown  chlorine  and  bromine  pentoxides,  and  of  the 
known  iodine  pentoxide,  with  water  and  oxides. 

Chloric  acid,  HC103,  is  best  prepared  by  adding  the  requisite 
amount  of  dilute  sulphuric  acid  to  barium  chlorate  (see  below), 
filtering  from  the  precipitated  barium  sulphate,  and  concentrating 
by  evaporation  in  vacuo  over  sulphuric  acid.  It  is  a  colourless  syrupy 
liquid,  which  is  at  once  decomposed  at  100°  into  perchloric  acid, 


BROMIC  AND  IODIC  ACIDS.  465 

water,  and  chlorine  peroxide,  which  itself  explodes  into  chlorine 
and  oxygen.  Ic  oxidises  organic  matter  with  great  energy,  often 
igniting  it.  '  .  - 

Bromic  acid,  HBr03.Aq,  is  similarly  prepared.  It  is  even 
more  unstable  than  chloric  acid,  and  decomposes,  giving  off 
bromine  and  oxygen,  before  it  can  be  rendered  syrupy  by  evapora- 
tion. 

lodic  acid  may  be  similarly  prepared  from  barium  iodate. 
But  it  is  more  conveniently  prepared  by  direct  oxidation  of  iodine 
by  means  of  strong  nitric  acid.  Convenient  proportions  are 
5  grams  of  iodine  and  200  grams  of  strong  nitric  acid;  the 
mixture  is  kept  at  60°  for  an  hour.  lodic  acid  separates  out ;  and  a 
further  quantity  may  be  obtained  by  distilling  off  the  nitric  acid. 

The  oxidation  may  also  be  effected  by  means  of  chlorine  and 
water,  or  of  potassium  chlorate  and  hydrochloric  acid,  which 
yield  nascent  oxygen.  Iodine  suspended  in  about  ten  times  its 
weight  of  water  is  treated  with  a  current  of  chlorine  till  the  iodine 
is  completely  dissolved.  Sodium  carbonate  is  then  added,  which 
throws  down  a  portion  of  the  iodine,  to  be  collected  and  treated 
as  before.  The  liquid  is  then  mixed  with  barium  chloride,  which 
throws  down  barium,  iodate,  which  is  collected  and  decomposed  by 
boiling  with  the  requisite  quantity  of  sulphuric  acid.  The  solu- 
tion is  filtered  from  the  insoluble  barium  sulphate,  and  boiled 
down,  when  the  iodic  acid  separates  in  crystals. 

The  acid  HIO3  is  a  white,  easily  soluble  substance,  crystal- 
lising in  hexagonal  tables.  At  130°,  or  when  digested  with  abso- 
lute alcohol,  it  loses  water,  forming  the  less  hydrated  compound, 
HI3O8  =  3I2O5.H2O.  At  170°,  this  body  forms  the  anhydride, 
LO5 ;  and  the  acid  may  again  be  produced  by  dissolving  the  anhy- 
dride in  water. 

Another  hydrate,  I2O5.5H2O  =  2H6IC>6,  has  also  been  ob- 
tained, crystallising  in  hexagonal  tables. 

lodic  and  hydriodic  acids  cannot  exist  in  the  same  solution ; 
they  react  forming  iodine  and  water,  thus  : — 

SHI.Aq  +  HI03.Aq  =  3I2  +  3H20  +  Aq. 

Chlorates,  bromates,  and  iodates.— These  bodies  are  pro- 
duced (1)  by  heating  the  hypochlorites,  hypobromites,  or  hypo- 
iodites,  thus  :— 3MXO  =  MXO3  +  2MX  ;  (2)  by  treating  the  acids 
with  hydroxides  or  carbonates ;  or  (3)  by  acting  on  barium  chlorate, 
bromate,  or  iodate  with  the  solution  of  a  sulphate.  Some  are 
produced  by  precipitation,  e.g.,  lead,  mercurous,  and  silver 
bromates?  and  many  iodates. 

2  H 


466     THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

2LiC103.H20;    NaClO3;    KC1O3;    RbClO3;    NH4C1O3.— L,iBrO3 ;    NaBrO3; 
KBrO3;  NH4BrO3.— LiIO3 ;  NaIO3.H2O  and  5H2O  ;   KIO3;  NH4IO3. 

These  salts  are  white,  soluble  crystalline  bodies,  all  of  which 
are  decomposed  by  heat,  giving  off  oxygen,  and  leaving  the  halide, 
thus :— 2MX03  =  2MX  +  302.  If  a  chlorate  be  employed,  part 
of  the  oxygen  converts  chlorate  into  perchlorate,  thus  : — MC103 
-r  O  =  MC104.  But  there  appears  to  be  no  definite  ratio  between 
the  amount  of  perchlorate  formed  and  the  amount  of  oxygen 
evolved.  The  application  of  heat  should  be  continued  nntil  a 
sample  of  the  residue  gives  no  yellow  coloration  on  addition  of 
hydrochloric  acid.  Perbromates  and  periodates  do  not  appear  to 
be  thus  produced.  The  ammonium  salts  decompose  with  explosive 
violence,  giving  nitrogen,  water,  and  the  halide  of  hydrogen. 

Potassium  chlorate  is  the  most  important  of  these  salts.  It 
is  formed  by  boiling  a  solution  of  the  hypochlorite,  thus  : — 
SKClO.Aq  =  KC103.Aq  +  2KCl.Aq.  As  the  chlorate  is  much 
less  soluble  than  the  chloride,  it  crystallises  out  on  evaporation. 
The  preparation  of  the  chlorate  may,  however,  be  carried  out  at 
one  operation.  Chlorine  passed  into  a  cold  solution  of  potassinm 
hydroxide  yields  chloride  and  hypochlorite ;  if  the  solution  be 
heated  during  passage  of  the  chlorine,  the  chlorate  is  produced, 
^he  complete  reaction  is  :— 6KOH.Aq  +  3C72  =  5KCl.Aq  + 
KC103.Aq  4-  3H20  (see  also  p.  462).  Potassium  carbonate  may 
be  substituted  for  the  hydroxide ;  in  this  case  carbon  dioxide  is 
evolved. 

Potassium  chlorate  crystallises  in  monoclinic  six-sided  plates 
often  of  considerable  size.  It  is  insoluble  in  alcohol,  and  sparingly 
soluble  in  water,  1  part  of  the  salt  requiring  at  15°  about  15  parts 
of  water  for  solution.  When  heated,  it  fuses  at  388°,  and  at  a  some- 
higher  temperature  begins  to  evolve  oxygen.  If  manganese  di- 
oxide be  mixed  with  the  chlorate,  a  much  lower  temperature 
suffices  to  cause  evolution  of  oxygen,  while  a  little  chlorine  is  also 
evolved.  It  is  suggested  that  the  nature  of  the  change  which 
takes  place  is  the  temporary  formation  of  potassium  permanga- 
nate, according  to  the  equation  2MnO2  +  '2KC1O3  =  2KMnO4  -f 
Cl%  +  02,  an(^  ^nat  *ne  permanganate  is  further  decomposed  into 
oxygen  and  peroxide  of  manganese,  ready  to  undergo  further 
oxidation.  The  reaction  would  then  to  some  sense  be  analogous 
to  that  of  cobalt  sesquioxide  on  a  hot  solution  of  bleaching-powder 
(see  p.  463).  As  has  been  already  mentioned,  the  decomposition 
of  potassium  and  other  chlorates  probably  occurs  in  two  stages  : — * 

*  Spring  and  Prost,  Suit.  Soc.  CJiim.  (3),  1,  340. 


CHLORATES,   BROMATES,   AND   IODATES.  467 


(1.)  The  chlorine  pentoxide  of  the  chlorate  K2O.Cl2O5  is  decom- 
posed into  chlorine  and  oxygen  ;  and  (2)  the  nascent  chlorine  dis- 
places oxygen  from  the  potassium  oxide,  K20.  That  this  is  the  case, 
appears  to  follow  from  the  behaviour  of  other  chlorates,  in  which 
the  oxygen  of  the  metallic  oxide  is  only  partially  displaced  by 
chlorine;  such  chlorates  yield  a  mixture  of  oxygen  -and  free 
chlorine.  For  example,  100  grams  of  barium  chlorate  yield 
0*28  gram  of  free  chlorine  ;  of  mercuric  chlorate,  3*7  ;  of  lead 
chlorate,  8'0  ;  of  copper  chlorate,  12'5  ;  and  of  zinc  chlorate, 
14'4  grams.  In  such  cases  the  oxygen  of  the  metallic  oxide 
remains  behind  in  part,  while  chlorine  is  evolved  in  greater  or  less 
quantity,  according  to  the  conditions  of  the  reaction.  If  potassium 
chlorate  be  perfectly  pure,  no  chlorine  is  evolved  ;  the  displacement 
of  oxygen  is  perfect. 

The  bromates,  when  heated,  yield  up  oxygen,  but  no  per- 
bromate  is  formed.  Experiments  as  regards  free  bromine  have 
not  been  made.  The  iodates  likewise  decompose  into  iodides  and 
oxygen,  no  periodates  being  formed  ;  but  iodine  is  liberated  along 
with  oxygen  from  sodium  iodate. 

Double  salts.—  HNa(IO3)2;  H2Na(IO3}3;  HK(IO3)2,  H^IO^. 

These  salts  are  prepared  by  acidifying  the  ordinary  salts  with 
hydrochloric,  nitric,  or  iodic  acid,  which  practically  amounts  to 
mixture  of  the  constituents.  They  form  white  soluble  crystals. 
Their  existence  would  lead  to  the  conjecture  that  the  formula  of 
iodic  acid  is  a  multiple  of  HI03. 


NaIO3.2NaBr.9H2O; 

HK(IO3)2.KC1.—  KIO3.HKSO4. 

These  soluble  crystalline  salts  are  obtained  by  mixture. 


Ca(C103)2.2H:20;  Sr(C103)2.5H20  ;  Ba(ClO3)2.— 
Sr(BrO3)2.H.2O; 


These  are  sparingly  soluble  white  crystalline  salts,  best  pro- 
duced by  mixing  potassium  chlorate  with  the  acetate  or  chloride 
of  calcium,  strontium,  or  barium,  and  evaporating  to  crystallise. 
The  more  soluble  acetate  or  chloride  of  potassium  remains  dis- 
solved, while  the  halate  crystallises  out.  Beryllium  iodate  is  said 
to  be  a  gummy  mass. 


Mg(C103)2.6H20  ;     Zn(C103)2.6H20.—  Mg(Br03)2.6H20  ;    Zn(BrO3)2.6H2O  ; 
.—  Mg(I03)2.4EL20  ;  Zn(IO3)  2.2^0. 

2  H   2 


468      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES. 

The  chlorates  and  bromates  and  the  iodate  of  magnesium  are 
easily  soluble  in  water  ;  zinc  iodate  dissolves  sparingly.  They  are 
all  white  and  crystalline. 


Y(C103)3.—  Y(Br03)3;  La(BrO3)3.9H2O.—  Y(IO3)3; 
These  are  sparingly  soluble  crystalline  white  salts. 

A1(C103)3  (P),  Al(Br03)3  (?),  A1(IO3)3  (P). 

These  are  deliquescent  syrups  ;  the  iodate  appears  to  crystal- 
lise. The  gallium  and  indium  salts  have  not  been  prepared. 
T1C1O3,  TlBrO3,  and  T1IO3  are  white  sparingly  soluble  crystals. 

The  salts  of  chromium  and  ferric  iron  are  indefinite.  A  basic 
iodate  of  the  formula  2I2O6.Pe2O3.8H2O,  or  4Fe(IO3)3Fe2O3.24H2O, 
has  been  prepared. 

Fe(Br03)2;  Fe(IO3)2;  Co(ClO3)2.6H2O  ;  Ni(ClO3)2.6H2O.—  Co(BrO3)2.6H2O  ; 
Ni(Br03)2.6H20.—  Mn(IO3)2.H2O  ;  Co(IO3)2.H2O  ;  Ni(IO3)2.H2O. 

These  are  coloured  crystalline  salts.  The  chlorate  and  bromate 
of  manganese  are  known  in  solution.  They  all  readily  decompose, 
the  metal  being  oxidised  to  a  higher  oxide. 


Ce(ClO3)3.wH2O  ; 
White  salts  ;  the  iodate  is  sparingly  soluble. 

Pb(ClO3)2.H2O  ;  Pb(BrO3)2.H2O  and  Pb(IO3)2. 

Sparingly  soluble  salts.  No  compounds  of  the  other  elements 
of  this  group  have  been  prepared. 

The  compound  SO3.I2O5  is  said  to  be  obtained  in  granular 
crystals  by  the  action  of  sulphur  trioxide  on  iodine  pentoxide  at 

100°.* 

2Bi(IO3)3.H2O,  and  a  basic  bromate,  2Br2O5.3Bi2O3.6H2O,  haye  been  pre- 
pared. They  are  insoluble.  (VO2)(IO3)2.5H2O  is  a  yellow  precipitate.  It  is 
the  only  known  compound  of  this  group. 

No  compounds  of  the  palladium  or  platinum  groups,  or  of  gold, 
have  been  prepared. 


A&C1O3;  AgBrO3;  Ag-IO3;  H&C1O3;  HgBrO3;  HgrIO3. 

Chlorate  of  silver  is  soluble  ;  the   other  salts  given  above  are 
sparingly  soluble  white  bodies,  produced  by  precipitation. 

*  J.  praJct.  Cbem.,  82,  72. 


PERCHLORATES   AND   PERIODATES.  469 

Cu(ClO3K6H,O;  Cu(BrO.,)2.5H2O;  2CuIO3.3H2O.— 
Hg(C103)2;  Hg(Br03)2.2H20; 


Chlorate  and  bromate  of  copper  and  mercuric  chlorate  are 
easily  soluble  ;  the  remaining  bodies  are  nearly  insoluble. 

It  will  be  noticed  that  as  a  rule  the  chlorates  become  more 
soluble,  the  bromates  and  iodates  less  soluble,  as  the  elements 
follow  in  the  periodic  order.  It  would  be  advisable  to  attempt  to 
prepare  double  salts  of  the  chlorates  and  bromates,  and  also  of 
such  iodates  as  those  of  calcium  and  magnesium. 

Double  iodates.  —  Chromiodates.*  —  By  dissolving  chromium 
trioxide  in  iodic  acid,  and  evaporating  over  sulphuric  acid,  ruby- 
red  rhombic  crystals  of  chromiodic  acid,  IO2.O.CrO2.OH,  are 
deposited.  With  iodates,  corresponding  chromiodates  have  been 
prepared,  viz.,  IO2.O.CrO2.OLi.H,O,  IO2.O.CrO2.ONa.H2O, 
IO2.O.CrO2.OK,  and  IO2.O.CrO2.ONH4.  Manganese,  cobalt, 
and  nickel  salts  have  also  been  prepared.  These  compounds  have 
a  brilliant  red  colour,  and  are  decomposed  by  water  into  chromates 
and  iodates. 

Perchloric  and  periodic  acids,  perchlorates,  and  per- 
iodates.  —  Perbromic  acid  and  perbromates  are  unknown.  These 
acids  and  salts  may  be  regarded  as  compounds  of  the  unknown 
heptoxides,  C1207  and  I207,  with  water  and  oxides.  Perchlorate  of 
potassium  is  the  starting  point  for  the  perchlorates.  It  is  pro- 
duced by  heating  the  chlorate,  some  of  the  nascent  oxygen  com- 
bining with  the  chlorate  and  oxidising  it;  or  by  heating  the 
chlorate  with  nitric  acid,  thus  :  — 


3KC103  +  2Htf  03  =  KC104  -f  2KNO3  +  H20  +  Ck  +  202. 

By  the  first  method,  a  mixture  of  chloride  and  perchlorate  of 
potassium  is  produced  ;  by  the  second,  a  mixture  of  perchlorate 
and  nitrate.  They  are  separated  by  crystallisation,  the  perchlorate 
being  much  less  soluble  than  the  chloride  or  nitrate.  Prom  potas- 
sium perchlorate,  perchloric  acid  is  produced  by  distillation 
with  sulphuric  acid  ;  it  comes  over  at  203°  as  an  oily  liquid  con- 
taining  70*3  per  cent,  of  HClOj.  On  mixing  this  hydrate  with 
twice  its  volume  of  oil  of  vitriol  and  again  distilling,  anhydrous 
perchloric  acid  distils  as  a  yellowish  strongly  fuming  liquid.  On 
further  distillation,  the  oily  hydrate  passes  over,  and  when  it 
comes  in  contact  with  the  anhydrous  acid  they  combine  to  form  a 
hydrate,  HC1O4.H2O  ;  a  little  sulphuric  acid  also  distils  over.  The 

*  Compt.  rend.,  104,  1514. 


470      THE  OXIDES,   SULPHIDES,   SELEN1DES,  AND  TELLUKIDES. 

crystals,  collected  and  distilled  alone,  yield  pure  perchloric  acid  in 
the  first  portions  of  the  distillate. 

The  anhydrous  acid,  HC104,  is  a  colourless  very  volatile  liquid 
Its  specific  gravity  is  1*782  at  15'5°.  It  explodes  violently  when 
brought  in  contact  with  any  oxidisable  matter,  and  hisses  when 
dropped  into  water.  It  decomposes  when  boiled,  leaving  a  black 
explosive  residue.  It  also  decomposes,  frequently  with  explosion, 
at  the  ordinary  temperature.  The  monohydrate,  HC1O4.H2O,  pro- 
duced by  addition,  is  a  white  solid,  melting  at  50°,  and  decompo- 
sing at  110°  into  pure  acid  and  the  oily  hydrate  mentioned  above, 
which  resembles  sulphuric  acid  in  appearance,  and  distils  un- 
changed at  203°.  An  aqueous  solution  of  perchloric  acid  does  not 
bleach,  and  reddens  litmus.  It  is  also  not  reduced  by  hydrogen 
sulphide  or  sulphur  dioxide. 

Periodic  acid,  H5IO6  (=  HIO4.2H2O),  is  prepared  from 
a  periodate.  The  starting  point  is  sodium  iodate,  NaIO3,  which 
is  oxidised  by  sodium  hypochlorite.  A  mixture  of  sodium  iodate 
and  caustic  soda  is  saturated  with  chlorine,  when  the  reaction 
occurs :— NaI03.Aq  +  SNaOH.Aq  +  Clz  =  H3Na2.I06.Aq  + 
2NaCl.Aq ;  or  1  part  of  iodine  and  7  parts  of  sodium  carbonate  are 
dissolved  in  100  parts  of  water  and  saturated  with  chlorine.  The 
iodate  at  first  formed  is  converted  into  periodate,  which  crystal- 
lises out,  being  sparingly  soluble  in  water.  This  periodate  is  dis- 
solved in  nitric  acid  free  from  nitrous  acid,  and  silver  nitrate  is 
added ;  the  precipitated  trihydrogen  diargentic  periodate  is  dis- 
solved in  hot  dilute  nitric  acid  and  evaporated  until  monoargentic 
periodate,  AgIO4,  crystallises  out.  On  treatment  with  water,  this 
salt  undergoes  the  change  2AgIO4  +  4H20  =  HaAg2IO6  +  H5IO6. 
The  silver  salt  is  removed  by  filtration,  and  the  filtrate  on  evapo- 
ration deposits  crystals  of  periodic  acid. 

Periodic  acid,  H5IOfi,  forms  white,  oblique,  rhombic  prisms 
which  melt  between  130°  and  136°  with  decomposition  into  iodine 
pentoxide,  water,  and  oxygen.  It  is  easily  soluble  in  water,  and 
sparingly  in  alcohol  and  in  ether.  Unlike  perchloric  acid,  it  is  at 
once  reduced  by  hydrochloric  or  sulphurous  acids  and  by  hydro- 
gen sulphide. 

The  perchl orates  and  periodates  are  produced  in  the  usual 
manner. 

NaC104;  KC1O4;  NH4C1O4;  LiIO4;  NaIO4;  KIO4. 

The  sodium  salts  are  very  soluble ;  potassium  perchlorate  is 
one  of  the  least  soluble  of  potassium  salts ;  hence  perchloric  acid 
may  be  used  as  a  means  of  precipitating  potassium.  It  is  almost 
insoluble  in  alcohol.  The  iodate  is  also  sparingly  soluble. 


PERCHLORATES  AND  PERIOD  ATES.  471 

CaCClO^;  Ba(C104)2. 

These   are   very   soluble.     No   periodates   are   known,  except 

Ca(I04)2. 

Zn(C104)2;  CdCClO^s.—  Mgr(IO4)2.10H20  ;  Cd(IO4)2. 


These  are  white  soluble  salts. 

The  remaining  perchlorates  which  have  been  prepared  are  :— 


;    Mn(ClO4)2;    PD(C1O4)2.3H2O;    (Pb-2O)(ClO4)2.H2O; 
Cu(C104)2;  AgC104;  HgrC104.3H,0; 


They  are  all  soluble  in  water  and  crystalline,  except  the  silver 
salt,  which  is  a  white  powder. 

Only  a  few  corresponding  periodates  are  known,  viz.,  Fe(IO4)3, 
a  bright  yellow  powder;  AgIO4,  crystallising  in  orange-yellow 
crystals  ;  and  Pb(IO4)2,  an  amorphous  red  salt. 

Many  complex  periodates  are  known,  which  may  be  best 
explained  by  reference  to  the  conception  of  a  normal  hydroxide, 
as  follows:—  Sodium  and  elements  of  that  group  tend  to  form  only 
a  monohydroxide,  M.OH;  those  of  the  magnesium  and  calcium 
groups,  dihydroxides,  MU(OH)2;  those  of  the  boron  and  aluminium 
groups,  trihydroxides,  MUI(OH)3;  silicon,  and  possibly  other  mem- 
bers of  the  carbon  and  silicon  groups,  tetrahydroxides,  MIY(OH)4  ; 
but  here  we  notice  instability,  so  that  the  first  anhydrides  of  such 
bodies,  MIV0(OH>>,  are  more  stable  ;  the  pentahydroxides  of  ele- 
ments of  the  nitrogen  and  phosphorus  groups  are  non-existent; 
but  their  first  anhydrides  are  known  with  phosphorus,  arsenic,  <fcc., 
in  phosphoric  and  arsenic  acids,  PVO(OH)3  and  AsvO(OH)3. 
Hexahydroxides  may  be  inferred  in  the  case  of  normal  sulphuric, 
selenic,  and  telluric  acids  ;  again,  their  existence  is  doubtful  in  any 
definite  cases  ;  but  their  second  anhydrides,  such  as  S^O^OH)?, 
are  well-known  bodies  ;  and  it  would  follow  that  the  elements  of 
the  chlorine  group  should  produce  heptahydroxides,  MVU(OH)7. 
Such  substances  are  unknown  with  chlorine,  but  the  assumption 
of  their  existence  affords  a  means  of  representing  systematically 
many  of  the  compounds  of  periodic  acid. 

The  perchlorates,  which  possess  the  general  formula  MC104, 
may  be  regarded  as  the  metallic  derivatives  of  the  third  anhydrides 
of  the  hypothetical  heptahydroxides,  thus  :  — 

Normal  salt  ......  C1(OM)7  ; 

First  derivative  .  .  C1O(OM)5  ; 

Second  derivative.  C102(OM)3; 

Third  derivative.  .  C103(OM).     (Ordinary  perchlorate.) 


472      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

Such  derivatives  are  known  with,  the  periodates.  Those  of  the 
last  class  have  already  been  considered ;  it  remains  to  describe  and 
classify  the  derivatives  of  the  first  and  second  anhydrides  of  the 
normal  acid,  H7I07,  which,  however,  is  unknown  as  such.  The 
acid  HI04  is  unknown;  the  known  acid  H5IO6,  which  has  been 
described,  is  the  first  anhydride  of  the  theoretical  normal  acid, 
H7I07.  It  has  been  suggested  that  derivatives  of  the  type  M'I04 
should  be  named  meta-periodates,  as  the  phosphates  of  the  type 
MP03  are  termed  meta-phosphates ;  derivatives  of  the  formula 
M3I06  have  been  termed  meso-  (middle)  periodates  j  of  the  type 
M5I06,  para-periodates ;  and  of  the  type  M7I07,  ortho-perio- 
dates.  Besides  these  derivatives,  some  of  a  still  more  condensed 
type  are  known. 

Single  Salts,  containing  only  one  Metal. 

Para-periodates.— H5I06 ;  Li5IO6;    Ba5(IO6)2;    FeTI5(IO6)2;    Agr5IO6 ; 

Hir5I06  j   Cu5(I06)2.5H20  ;  Hgr5(I06)2. 
Meso-periodates.— Ni3(I05)2;  Pb3(IO5)2;  Ag3IO5. 

Double  Salts. 

Ortho-periodates.—  H6NaIO7;    H5K2lO7.2H2O ;    H4(NH4)MgIO7.H:O  ; 
(M7IO7).  2H5ZnIO7.H2O;      H5CaIO7.2H2O ;      H5SrIO7.H2O; 

H5BaI07.H20;  HFeni2IO7.20H2O. 

Para-periodates.— H3L,i2IO6  ;    H3Na2IO6 ;    H2Na3IO6  ;    H3(NH4)2IO6 ; 
(M5IO6) .  H3Mg-IO6.9H:2O ;  HZn2IO6 ;  HCd2lO6.H2O ;  H3CaIO6 ; 

£H3SrIO6.H2O ;       H3BaIO6,    anhydrous,     and    with 
4H20;     H3FeI06;     H4Pb3(IO6)2  ;     H3Ag2IO6  ; 
H2Ag-3IOc ;  HCun2IO6,  anhydrous,  and  with  3H»O. 

Meso-periodates. — HCdIO5,    anhydrous    and   with   4H2O  ;    H2AgIO5 ; 
(M3106).  HA&2I05. 

This  classification  must  be  regarded  as  merely  provisional ;  it 
is,  as  a  rule,  impossible  to  decide  whether  hydrogen  should  be 
included  in  the  formula,  or  should  belong  to  water  of  crystallisation. 
For  example,  the  salt  HCdI05  is  a  meso-periodate  when  thus 
written  ;  but  it  has  also  been  prepared  of  the  formula  HCdl05.4H20. 
If  one  molecule  of  this  water  be  inclnded,  it  becomes  a  para-perio- 
date,  thus  : — H3CdI06.3H20 ;  if  two  molecules  of  water  be  included, 
its  formula  is  that  of" an  ortho-periodate,  thus  : — H5CdI07.2H20. 
'Lastly,  the  salt  HCdIO5  still  contains  hydrogen  ;  by  doubling  its 
formula,  and  subtracting  the  elements  of  water,  we  have 
2HCdI05  —  H20  =  Cd2I2O9,  a  diperiodate.  To  form  any  definite 
conclusion  is  difficult,  for  the  individuality  of  each  of  the  four 
classes  of  compounds  is  not  well  marked,  as  in  the  case  of  the 
analogous  phosphates. 

Derivatives  of  condensed  periodic  acids  are  also  known.     These 


PERIODATES.  473 

may  be  viewed  as  derived  from  a  hypothetical  diperiodic  acid, 
analogous  to  pyrophosphoric  and  phosphoric  acid  and  to  anhydro- 
sulphuric  acid,  of  the  formula  I20(OH)12,  from  which  there  are 
deducible  the  five  anhydro-  acids,  (1)  I202(OH)10;  (2)  I203(OH)8; 
(3)  I204(OH)6;  (4)  I205(OH)4;  and  (5)  I206(OH)2.  Derivatives 
of  the  dodeca-,  of  the  deca-,  and  of  the  hexa-hydroxyl  acids, 
I20(OH)12,  I202(OH)10,  and  I204(OH)6,  are  unknown;  the  others 
may  be  classified  as  follow  :  — 


Octohydroxyl  acid.—  Mgr4I2On  ; 
Tetrahydroxyl  acid.  —  K4l2O9  ;  HB^L,O9  ;  Mgr2I2O9  ;  HFeI2O9  ; 
Ag:4I2O9,  anhydrous,  also  with  "H^Q  and 


The  salt  Ag4I2O9.H2O  is  not  identical  with  the  para-peri  odate 
of  similar  percentage  composition,  HAg2rO5;  they  differ  in  ap- 
pearance, and  while  the  molecule  of  water  in  the  first  salt  is  lost  at 
100°,  no  change  occurs  on  heating  the  second  salt  until  the  tem- 
perature rises  to  300°.  And  the  two  compounds  H3Ag2IO6  and 
Ag1I2O9.3H2O  are  also  quite  different  from  each  other  in  chemical 
and  physical  properties. 

Formation.  —  To  describe  the  method  of  formation  of  each 
individual  salt  would  occupy  too  much  space.  The  general 
methods  are  :  — 

Meta-periodates  (MI04)  are  produced  by  boiling  di-,  meso-, 
or  para-periodates  with  nitric  acid  ;  thus,  for  example  :  — 


H3Ag2I06  +  HN03  =  AgI04.H20  +  H20  +  AgNO3. 

Di-periodates  are  changed  to  para-periodates  by  treatment  with 
silver  nitrate:  — 

KJ209.Aq  +  4AgN03.Aq  +  3H20  =  2H3Ag2IO6  +  4KN03.Aq. 

Para-periodates  yield  meso-periodates  when  their  double  salts 
with  hydrogen  are  heated  :  — 

H4Pb3(I06)2  =  Pb3(I05)2 


Meso-periodates    may   in   analogous   manner    yield  di-period- 
ates  :  — 

2HAg2IO5  =  AgJ2O9  +  H20. 

Meta-periodates  are  often  decomposed  by  water,  yielding  para- 
periodates,  e.g.  :  — 

2AgIO4  +  4H20  =  H3Ag2IO6  +  H5I06. 


474      THE   OXIDES,  SULPHIDES,   SELENIDES,  AND   TELLURIDES. 
Derivatives  of  a  few  still  more  condensed  types  are  known, 

Ba5I4019:  Agr10I4019;  Cd10I6O3l,15H2O. 

A  remarkable  compound  of  the  formula  N2O6.C1;;O7  = 
N2O5(C1O4)2,  or  C12O7(NO3)2,  has  been  produced  by  passing  a 
silent  electric  discharge  through  a  mixture  of  chlorine,  nitrogen, 
and  oxygen.*  It  is  a  white  solid,  easily  volatile  in  a  vacuum;  it 
deliquesces  in  air,  giving  a  mixture  of  nitric  and  perchloric  acids. 

Physical  Properties. 

Mass  of  one  cubic  centimetre  : — 

I2O5,  4-8  grams  at  9°.    HIO3,  4'87  grams  at  0°. 
Seats  of  combination  : — 

201  +  O  =  Ct2O  -  178K;   +  Aq  =  2HOCl.Aq  +  94K. 

2CI  +  5O  +  Aq  =  2HClO3.Aq  -  204K. 

2CI  +  7O  +  Aq  =  2HClO4.Aq  +  42K. 

2Br  +   O  +  Aq  =  2HOBr.Aq  -  -162K. 

2Br  +  5O  +  Aq  =  2HBrO3.Aq  -  436K. 

21  +  5O  =  I205  +  453K;    +  H2O  =  2HIO3  +  26K. 

21  +  7O   h  Aq  =  2H5IO6.Aq  +  268K. 

*  Comptes  rend.,  98,  626. 


475 


CHAPTEE  XXIX. 

OXIDES,  SULPHIDES,  AND  SELENIDES  OF  RHODIUM,  RUTHENIUM,  AND 
PALLADIUM  : — OF  OSMIUM,  IRIDIUM,  AND  PLATINUM  ;  PLATING- 
NITRITES,  AND  PLATINOCHLOROSULPHITES  ;  CARBONTL  COMPOUNDS, 
AND  PLATINOPHOSPH1TES  ;  OXIDES,  SULPHIDES,  SELENIDES,  AND 

TELLURIDES     OF    COPPER,    SILVER,     MERCURY,     AND    GOLD. OXYHA- 

LTDES. — CONCLUDING   REMARKS    ON   OXIDES    AND    SULPHIDES. 

No  tellurides  of  metals  of  the  palladium  or  platinum  groups  are 
known.  The  following  is  a  list  of  the  compounds  which  have  been 
prepared: — 

Note. — The  following  method  may  be  advantageously  employed  in  separating 
the  inetals  of  the  palladium  and  platinum  groups  from  each  other : — The  ore  is 
treated  with  aqua  regia  under  pressure.  The  solution  contains  platinum, 
palladium,  rhodium,  ruthenium;  the  residue,  osmium,  iridium,  and  some 
rhodium  and  ruthenium.  The  solution  is  boiled  with  caustic  soda,  and  mixed 
with  a  solution  of  potassium  chloride  and  alcohol ;  the  sparingly  soluble  platini- 
chloride  of  potassium  separates  out.  On  ignition,  it  is  converted  into  metallic 
platinum.  A  sheet  of  zinc  is  placed  in  the  solution  from  which  the  platinum 
has  been  removed  ;  the  remaining  metals  are  precipitated. 

The  insoluble  residue  is  heated  in  a  platinum  retort  in  a  current  of  oxygen, 
when  osmium  tetroxide  volatilises.  The  residue  in  the  retort,  and  the  metals 
precipitated  with  zinc  are  melted  with  four  times  their  weight  of  zinc  under  a 
layer  of  zinc  chloride.  The  alloy  is  heated  with  hydrochloric  acid  until  pal- 
ladium begins  to  dissolve  with  a  brown  colour.  The  black  residue  is  boiled  with 
aqua  regia  ;  a  residue  of  a  portion  of  the  rhodium  and  ruthenium  still  remains. 
From  the  solution,  palladium  di-iodide  is  precipitated  with  potassium  iodide. 
The  solution  is  treated  with  a  current  of  hydrogen,  which  precipitates  all  the 
remaining  metals  except  iridium.  The  precipitate  is  mixed  with  the  rhodium 
and  ruthenium,  and  heated  with  barium  chloride  in  a  current  of  chlorine  to 
volatilise  any  remaining  osmium  as  dichloride.  The  residue,  consisting  of 
barium  rhodiochloride,  is  dissolved  in  water,  and  the  barium  removed  with 
sulphuric  acid.  The  rhodium  is  then  thrown  down  with  sodium  hydrogen 
sulphite,  which  precipitates  the  insoluble  compound  3Na2O.Bli2O3.6SO2.  The 
ruthenium,  ajain  precipitated  from  the  filtrate  with  zinc,  is  boiled  with  potas- 
sium hydroxide  and  chromate,  treated  with  excess  of  potash,  and  boiled  with 
sodium  sulphate.  The  precipitate  contains  only  ruthenium. — See  also  Iron, 
1879,  13,  654. 


476      THE   OXIDES,  SULPHIDES,   SELENIDES,  AND   TELLUKIDES 

Oxygen. 

Ehodium —        RhO;  Rh2O3;  RhO2;  RhO3;        — 

Kuthenium —         RuO;  Ru2O3;  B.uO2;  RuO3;*  RuO4 

Palladium Pd2O ;    PdO         —        PdO2        — 

Sulphur.  Selenium. 

Khodium —        B,hS ;  E-hoSg        — 

Ruthenium —          —       B,u2S3 ;  RuS2.  — 

Palladium Pd2S;     PdS ;       —  PdS2.  PdSe. 

None  of  these  compounds  occurs  native. 

Preparation.  —  1.  By  direct  union.  —  Finely-divided 
rhodium,  prepared  by  heating  the  double  chloride  RhCl3.3NH4Cl 
to  redness,  when  heated  to  dull  redness  in  oxygen,  yields  the  mon- 
oxide, RhO  ;  powdered  ruthenium  is  oxidised  to  Ru2O3 ;  pal- 
ladium yields  dark-grey  Pd2O.  Ruthenium  tetroxide,  RuO4,  is 
formed  by  direct  union  at  about  1000°,  but  decomposes  on  cooling. 
This  is  a  most  curious  result,  for  the  tetroxide  is  decomposed 
violently  when  heated  to  108°,  and  it  is  only  by  rapid  cooling,  by 
means  of  an  inside  tube  through  which  cold  water  circulates, 
which  passes  through  the  centre  of  the  outside  tube,  heated  to 
bright  redness,  that  it  is  possible  to  isolate  some  of  the  tetroxide 
without  decomposition.  If  allowed  to  cool  slowly,  the  body  dis- 
sociates again  into  ruthenium  and  oxygen.f 

Rhodium  and  palladium  monosulphides,  and  palladium  mono- 
selenide  are  formed  with  incandescence  when  the  metals  are  heated 
with  sulphur  or  selenium. 

2.  By    decomposing    a    higher    compound    by   heat. — 
Rhodium   sesquioxide,   when  heated,   yields   the   monoxide ;  and, 
similarly,  the  sesquisulphide  yields  the  monosulphide. 

3.  By  the  action  of   heat    on    a    double  compound. — 
Rhodium  nitrate,  when  heated  to  dull  redness,  leaves  a  residue  of 
Rh2O3 ;  ruthenic  sulphate,  Ru(SO4)2,  yields  the  dioxide  RuO2  on 
ignition ;  and  palladous   nitrate,  Pd(NO3)2,    moderately    heated, 
yields  the  monoxide,  PdO.     The  hydrates,  when  they  exist,  yield 
the  oxides  when  heated. 

4.  By    replacement.  —  Sulphur    displaces    chlorine    when 
heated  with  the  compound  RhCl3.3NH4Cl ;  and  oxygen,  when  a 
mixture  of  the  sesquioxide    and  sulphur   are  heated  in  a  current 
of  carbon  dioxide.     In  each  case  the  monosulphide,  RhS,  is  formed. 

*  Known  only  in  combination. 

t  Debray  and  Joly,  Comptes  rend.,  106,  100,  and  328.  See  also  ibid.,  84, 
946. 


'  OF  RHODIUM,  RUTHENIUM,   AND   PALLADIUM.  477 

Conversely,  the  sulphides,  roasted  in  air,  are   converted  into  the 
more  stable  of  the  oxides. 

5.  By  double  decomposition. — Ruthenium  dichloride,  RuCls, 
calcined  with  sodium  carbonate  in  an  atmosphere  of  carbon  di- 
oxide, yields  the  monoxide;  the   excess   of   sodium  carbonate  is 
removed  by  washing  with  water.     Palladium  monoxide,  PdO,  is 
similarly  prepared.     On   boiling   a   solution   of  palladium  tetra- 
chloride   with   a   solution   of   sodium   carbonate,    the    anhydrous 
dioxide  is  precipitated. 

Rhodium  sesquisulphide  is  produced  by  heating  the  trichloride, 
RhCl3,  in  a  current  of  hydrogen  sulphide  to  360°  ;  ruthenium 
sesquisulphide  and  disulphide  are  produced  by  passing  hydrogen 
sulphide  through  solutions  of  the  respective  chlorides.  Palladium 
monosulphide,  PdS,  is  formed  by  the  action  of  hydrogen  sulphide 
on  the  dichloride,  and  the  disulphide  by  the  action  of  hydrochloric 
acid  on  sodium  sulphopalladate.  Na2PdS3. 

6.  By  oxidation  of  the  metal  or  of  a  lower  oxide  by  nascent 
oxygen.     This  process  yields  the  higher  oxides.     When  rhodium 
or  an  oxide  is  fused  with  a  mixture  of  potassium  hydroxide  and 
nitrate,  the  dioxide,  RhO2,  is  formed,  and  may  be  separated  from 
the  excess  of   soluble   salts  by  boiling  with   dilute   nitric   acid. 
Chlorine   acts   on   rhodium   sesquioxide   in   presence    of    caustic 
potash  (forming  hypochlorite  of  potassium)  giving  a  green  preci- 
pitate of  the  hydrated  dioxide,  and  a  violet-blue  solution,  from 
which  a  green  powder  deposits  on  standing.     On  warming  with 
nitric   acid,   this  powder  leaves   the    anhydrous   trioxide,  RhO3. 
Similarly,  when   ruthenium  is  heated  with  nitre  and  potassium 
hydroxide,  a  soluble  yellow  mass  is  obtained,  believed  to  contain 
the  trioxide  in  combination  with  potassium  oxide.     On  saturating 
its  hot  solution  in  aqueous  caustic  potash  with  chlorine,  a  sublimate 
is  formed  of  RuO4. 

Palladium  hemisulphide,  Pd2S,  is  formed  by  a  method  which 
cannot  easily  be  classified.  A  mixture  of  the  monosulphide,  PdS, 
sodium  carbonate,  ammonium  chloride,  and  sulphur  is  heated  to 
redness  for  twenty  minutes.  On  digesting  with  water,  sodium 
sulphopalladite,  NaPdS3  (see  below),  goes  into  solution,  while 
the  hemisulphide  remains  as  a  fused  mass. 

Properties. — The  monoxides  are  dark-grey,  insoluble  powders, 
with  semi-metallic  lustre.  Those  of  ruthenium  and  rhodium  are  not 
attacked  by  acids ;  palladium  monoxide  dissolves.  Monoxides  of 
rhodium  and  palladium  are  reduced  to  metal  by  hydrogen  at  a 
dull-red  heat;  that  of  ruthenium  at  the  ordinary  temperature. 
The  monosulphides  of  rhodium  and  palladium  are  bluish-white 


478      THE   OXIDES,   SULPHIDES,  SELENIDES,  AND   TELLURIDES 

substances  with  metallic  lustre.  The  latter  melts  at  about  1000°. 
Palladium  selenide  resembles  the  sulphide,  but  has  not  been 
fused. 

Rhodium  sesquioxide  is  a  grey  porous  mass,  with  metallic 
iridescence  ;  and  that  of  ruthenium,  a  dark  blue,  insoluble  powder. 
Rhodium  sesquisulphide  forms  brownish-black  crystalline  plates  ; 
the  ruthenium  compound  is  a  brown  powder. 

Rhodium  dioxide  is  a  dark-brown  insoluble  powder  ;  ruthenium 
dioxide  prepared  by  roasting  the  disulphide  in  a  blackish-blue 
powder  ;  prepared  by  heating  the  sulphate,  it  is  a  greyish  metallic- 
looking  substance,  showing  a  blue  iridescence.  When  heated  in 
oxygen  to  the  melting-point  of  copper,  it  crystallises  in  quadratic 
prisms,  isomorphous  with  cassiterite,  SnO2,  and  with  rutile,  TiO2. 
Anhydrous  palladium  dioxide  is  a  black  powder,  soluble  in  acids, 
even  in  strong  hydrochloric  acid  ;  but,  curiously,  with  dilute 
hydrochloric  acid,  chlorine  is  evolved. 

Ruthenium  disulphide  is  a  brownish-  yellow  precipitate;  and 
palladium  disulphide  a  blackish-brown  crystalline  powder. 

Rhodium  trioxide  is  a  blue  flocculent  precipitate. 

Ruthenium  tetroxide  forms  volatile  golden-yellow  rhomboidal 
prisms,  melting  at  25  '5°  when  pure,  and  decomposing  rapidly  at 
106°.  It  is  sparingly  soluble  in  water.  Its  vapour  density  cor- 
responds with  the  formula  RuO^.  Its  aqueous  solution  is  said  to 
yield  an  oxysulphide  with  hydrogen  sulphide. 

Compounds  with  water  and  oxides,  and  with  hydrogen 
sulphide  and  sulphides.  —  The  following  have  been  prepared  :  — 


PdO.wH2O.—  Bh2O3.3  and  5H2O;  Bu2O3.3H2O  ;  Bh2S3.3H2S  ; 
BhO2.2H2O  ;  BuO2.2H2O;  PdO2.»H2O.—  PdS2.Na2S  ; 
PdS2.Ag-2S;  PdS^PdsS.KsS  ;  |PdS2.2PdS  ;  PdS2.PdS.Ag-2S  ;  BuO3.Na2O  ; 
RuOg.KsO;  BuO3.MgO  ;  BuO3.CaO  ;  BuO3.SrO;  BuO3.BaO;  BuO3.Ag-2O. 
Complex  oxides.  —  Bu2O5.2H2O;  BtLjOj.^O  ;  and  Bu4O9.2H2O.  — 


PdO.wH2O.  —  A  dark-brown  precipitate,  produced  by  addition  of 
solution  of  sodium  carbonate  to  solution  of  palladous  chloride, 
PdCl2.Aq.  It  reacts  with  acids,  forming  palladous  salts. 

Rh2O3.3H2O.  —  A  gelatinous  precipitate,  produced  by  adding 
an  alcoholic  solution  of  potash  to  a  solution  of  the  double  chloride 
RhCl3.3NaCl.  It  is  nearly  insoluble  in  acids,  though  a  red  solu- 
tion is  formed  when  it  is  digested  with  hydrochloric  acid.  By  use 
of  aqueous  solution  of  potash,  the  pentahydrate  is  thrown  down  as 
a  somewhat  soluble  yellow  precipitate. 

Rh2S3.3H2S   and  Rh2S3.3Na2S  are  produced  by  addition    of 


OF  EHODIUM,  RUTHENIUM,  AND   PALLADIUM.  479 

hydrogen  or  sodium  sulphide  respectively  to  a  solution  of  the 
trichloride,  RhCl3.Aq.  The  first  is  a  brownish-black  insoluble 
precipitate;  the  second  a  dark-brown  crystalline  body.  The 
former  compound  is  noticeable  as  being  one  of  the  very  few  hydro- 
sulphides  known. 

Ru2O3.3H2O  is  a  dark  precipitate  produced  by  sodium  carb- 
onate in  a  solution  of  ruthenium  trichloride.  It  is  soluble  in  acids, 
forming  ruthenic  salts. 

RhO2.2H2O  is  a  green  precipitate  formed  by  the  action  of 
chlorine  on  a  solution  of  the  hydrate,  Rh2O3.5H2O.  It  is  somewhat 
soluble  in  water,  with  a  violet-blue  colour ;  and  with  hydrochloric 
acid  it  evolves  chlorine,  dissolving  to  BhCl3. 

RuO2.2H2O  is  a  yellow  precipitate  produced  by  treating  a 
solution  of  potassium  ruthenichloride,  RuCl4.2KCl.Aq,  with 
sodium  carbonate.  It  dissolves  in  acids  with  a  yellow  colour, 
forming1  ruthenic  salts  ;  and  in  alkalies  with  a  light-yellow  colour. 

PdO2.??H2O  is  similarly  prepared,  but  it  appears  to  be  impos- 
sible to  obtain  it  free  from  admixed  alkali. 

Sulphopalladites. — By  fusing  together  palladium  monosul- 
phide,  sodium  carbonate,  ammonium  chloride,  and  sulphur,  a 
whitish-grey  metallic-looking  button  of  Pd2S,  is  formed.  The  fused 
mass  of  salts  covering  this  button,  when  washed  with  alcohol,  gives 
a  residue  of  sodium  sulphate,  and  the  compound  Na^PdSs,  forming 
reddish-grey  metallic- looking  needles.  With  silver  nitrate,  a 
blackish -brown  precipitate  of  Ag,PdS3  is  formed.  If  potassium 
carbonate  be  employed  in  the  above  fusion,  the  residue  on  treat- 
ment with  alcohol  contains  the  sub-palladous  salt  K2PdS3.Pd2S, 
which  forms  blue  metallic-looking  hexagonal  laminae.  It  is  in- 
soluble ;  when  heated  in  hydrogen,  palladium  is  produced,  along 
with  the  soluble  salt  K4PdS4,  thus  :— 2K2Pd3S4  +  4fl"2  =  4H2S  + 
5Pd  +  PdS2.2K2S  The  salt  K2PdS3.Pd2S  when  treated  with 
hydrochloric  acid  yields  the  hydrogen  salt  H2PdS3.PdoS,  which, 
on  oxidation  in  air,  yields  the  compound  Pd3S4,  thus : — 
H2PdS3.Pd2S  +  0  =  H20  +  Pd3S4.  When  heated  in  air,  Pd3S4 
is  converted  into  PdS.  The  silver  compound,  Ag2PdS3.Pd2S, 
forms  whitish-grey  plates. 

Ruthenates  and  pernithenates. — Ruthenium  tetroxide  fused 
under  water  and  added  to  strong  potash  solution  at  60°  evolves 
oxygen,  and  on  cooling  deposits  blackish-brown  quadratic  octa- 
hedra  of  potassium  perruthenate,  KRuO4.  The  mother  liquor 
from  this  salt  on  evaporation  gives  crystals  of  potassium  ruthenate, 
ILRuOi.H^O,  crystallising  in  rhombic  prisms,  and  soluble  in  a 
little  water,  with  a  yellow  colour.  On  diluting  its  solution  it 


480      THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES 

decomposes,  thus :— 4K2Ru04.Aq  +  5H20  =  2KRu04.Aq  + 
Ru2O5.2H2O  +  GKOH.Aq.  Diruthenium  pentoxide,  Ru2O5.2H2O, 
is  a  crystalline  body  ;  the  substance  KRllO3,  which  may  be  named 
hyporuthenite  of  potassium,  is  its  compound  with  potassium  oxide. 
Ru2O5.K2O.  This  oxide,  Ru2Os,  heated  in  a  vacuum  to  260°,  loses 
oxygen,  depositing  black  scales  of  Ru4O9 ;  the  same  substance 
is  produced  when  a  solution  of  the  tetroxide  is  heated  with  water 
to  100°. 

From  potassium  ruthenate  the  following  bodies  have  been 
prepared: — Na2RuO4.2H2O,  MgRuO4,  and  CaRuO4,  black  pre- 
cipitates ;  BaRuO4,  a  vermilion  precipitate ;  and  Ag,RuO4,  a 
dense  black  precipitate. 

The  formulae  of  potassium  hyporuthenite,  KRuO3,  is  analogous 
to  that  of  potassium  chlorate ;  and  those  of  potassium  ruthenate, 
K2RuO4,  and  of  potassium  perruthenate,  KRuO4,  to  potassium 
manganate  and  permanganate  respectively ;  but  the  crystalline 
forms  are  not  the  same.  We  have  at  present  no  certain  know- 
ledge regarding  the  constitution  of  these  bodies. 


Oxides,  Sulphides,  and  Selenides  of  Osmium, 
Iridium,  and  Platinum. 

List  :— 

Oxygen. 

Osmium OsO  ;    Os2O3 ;    OsO2 ;    OsO3  ;*    OsO4. 

Iridium IrO  ;     Ir2O3 ;     IrO2 ;     IrO3 

Platinum PtO         —         PtO2        — 

Sulphur. 

Osmium OsS,  &c.  (?)      —         —  OsS4. 

Iridium IrS ;  Ir2S3 ;  IrS2 ;  IrS3.       — 

Platinum PtS      —       PtS2       —          — 

The  oxide  Pt3O4  has  also  been  prepared.  The  selenides  and 
tellurides  require  investigation ;  they  have  not  been  analysed. 

None  of  these  compounds  occurs  in  nature. 

Preparation.— 1.  By  direct  union.— Osmium  tetroxide  is 
formed  when  finely-divided  osmium  is  heated  to  bright  redness 
in  oxygen  or  in  air.  Platinum  monosulphide  is  also  directly 
formed. 

2.  By  decomposing  a  higher  compound  by  heat.— Platinum 
dioxide,  gently  heated,  is  converted  into  the  oxide  Pt3O4 ;  and 
platinum  disulphide  yields  the  monosulphide  at  a  low  red  heat. 
Iridium  monosulphide  is  also  produced  when  higher  sulphides  are 

*  Known  only  in  combination. 


OF   OSMIUM,   IRIDIUM,   AND    PLATINUM.  481 

heated.  As  a  rule,  however,  the  oxides  or  sulphides,  when  heated, 
give  off  oxygen  or  sulphur,  leaving  the  metals.  The  compound 
OsO3  appears  to  be  incapable  of  separate  existence.  When  liberated 
from  its  compound  with  potassium  oxide,  K2OsO4,  by  dilute  nitric 
acid,  it  decomposes  into  dioxide  and  tetroxide,  thus : — 2OsO3  = 
OsO4  +  OsO>. 

3.  By  the  action  of  heat  on  a  double  compound. — Osmium 
dioxide,  iridium  dioxide,  and   platinum  mono-  and  di-oxides  are 
produced   by   gently  heating  the  hydrates.       Osmium   monoxide 
is  formed  when  the  sulphite,   OsSO3  (see  p.  439),  is  heated   in 
hydrogen. 

4.  By  double  decomposition.— This  method  serves  for  the 
preparation  of  most    of  these  compounds.     Osmium  sesquioxide, 
Os2O3,  is  produced  from   potassium  osmochloride,   OsCl3.3KCl ; 
the   dioxide,    OsO2,    from  potassium    osmichloride,  OsClt.2KCl ; 
iridium  monoxide,  IrO,  from  the  compound  IrS2O5.6KCl;  and 
iridium   sesquioxide    from   potassium  iridochloride,   IrCl3.3KCl ; 
by   gently   heating  these   salts    with  potassium  carbonate,    in   a 
current  of  carbon  dioxide.    In  aqueous  solution,  with  caustic  potash, 
the  hydrates  are  generally  formed,  which,  on  heating,  leave  the 
oxides. 

The  sulphides  of  osmium  are  said  to  be  produced  from  solutions 
of  the  corresponding  compounds  by  the  action  of  hydrogen  sul- 
phide, and  those  of  iridium  and  platinum  have  been  similarly 
obtained.  As  a  rule,  sulphides  of  the  alkalies  may  also  be  used  as 
precipitants,  but  the  resulting  sulphides  are  soluble  in  excess. 
Iridium  disulphide,  IrS2,  has  been  prepared  by  igniting  ammonium 
iridichloride,  IrCl4.2NH4Cl,  with  sulphur. 

5.  By  oxidation  of  the  metal  by  means  of  nascent  oxygen. 
— Finely-divided  osmium  distilled  with  nitrohydrochloric  acid  is 
oxidised  to  the  tetroxide,  which  volatilises.      Iridium  fused  with 
potassium  and   barium   nitrate  is  oxidised  to  the  trioxide  IrO3, 
which  to  some  extent  remains  combined  with  the  potassium  or 
barium.       Compounds     of     platinum     dioxide     (platinates)     are 
similarly  formed. 

Properties. — Osmium  monoxide,  sesquioxide,  and  dioxide, 
iridium  monoxide  and  sesquioxide,  and  platinum  monoxide  and 
dioxides  are  black  amorphous  powders,  insoluble  in  water  and  in 
acids.  Osmium  dioxide,  prepared  by  heating  the  hydrate,  forms 
copper-red  lumps.  Iridium  trioxide  is  black  and  crystalline. 
Osmium  trioxide  is  said  to  be  formed  as  a  waxy  substance,  in 
combination  with  the  tetroxide  when  the  latter  is  distilled  from 
strong  sulphuric  acid.  Osmium  tetroxide  forms  large  crystals ;  it 

2  i 


482      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES. 

is  very  volatile  ;  it  melts  below  100°,  and  volatilises  at  a  somewhat 
higher  temperature.  It  has  an  exceedingly  pungent,  disagreeable 
smell,  strongly  irritating  the  eyes,  and  is  very  poisonous  when  its 
vapour  is  inhaled.  An  antidote  is  said  to  be  hydrogen  sulphide 
well  diluted  with  water.  It  is  soluble  in  water,  and  also  in  alcohol 
and  in  ether:  the  solution  in  the  latter  two  menstrua  deposit 
metallic  osmium  on  standing.  It  also  dissolves  in  alkalies  to  red 
or  yellow  solutions ;  these,  when  heated,  part  with  it  to  some 
extent,  and  to  some  extent  lose  oxygen,  retaining  an  osmite  in 
solution.  It  is  best  obtained  pure  by  saturating  the  first  third  of 
the  distillate  obtained  from  osmiridium  (a  native  alloy  of  iridium 
and  osmium)  and  nitrohydrochloric  acid  with  caustic  potash,  and 
again  distilling.  Part  of  the  tetroxide  volatilises  over  in  crystals, 
and  a  portion  dissolves  in  the  distillate.  It  is  made  use  of  as  a 
means  of  hardening  animal  preparations  for  the  microscope. 

The  sulphides  of  osmium  are  black  insoluble  substances.  The 
one  best  known  is  OsS4,  which  is  a  black  precipitate  obtained 
in  saturating  a  solution  of  the  tetroxide  in  hydrochloric  acid  with 
hydrogen  sulphide. 

Iridium  monosulphide  is  a  blackish-blue  insoluble  substance  ; 
the  sesquisulphidc,  brownish-black,  and  sparingly  soluble ;  the  di- 
sulphide  a  yellow-brown  powder,  and  the  trisulphide  has  a  dark 
yellow-brown  colour ;  it  is  difficult  to  precipitate.  All  the  sul- 
phides of  iridium  dissolve  in  solutions  of  alkaline  sulphide,  no 
doubt  forming  compounds ;  none  of  which,  however,  have  been 
investigated. 

Platinum  mono-  and  disulphides  are  also  black  and  insoluble. 
The  disulphide  is  soluble  in  alkaline  sulphides,  forming  double 
compounds,  regarding  which  there  are  no  data.  Platinum  selen- 
ide,  directly  prepared,  is  a  grey  infusible  mass.  Its  formula  is 
unknown. 

Double  compounds.— 1.  With  water:  hydrates. 

Hydrated  osmium  monoxide,  OsO.wH2O  ;  sesquioxide,  Os2O3.wH2O  ;  di- 
oxide, OsO2.2H2O ;  iridium  sesquioxide,  Ir2O3.2H2O,  and  5H2O  ;  dioxide, 
IrO2.2H2O  ;  platinum  monoxide,  PtO.H2O  ;  and  dioxide,  PtO2.wH2O. 

These  are  all  prepared  by  acting  on  solutions  of  corresponding 
compounds  with  sodium  or  potassium  hydroxide.  Thus :  — 
OsO.wH.O,  from  OsS03  and  KOH  in  a  closed  vessel; 
Os2O3.nH2O,  from  OsCl3.3KCl;  OsO2.2H2O,  from  OsCl^NaCl ; 
Ir.O3.2H2O  from  IrCl3,  with  KOH  and  alcohol ;  Ir2O3.5H2O,  from 
IrCl3.3KCl  and  a  little  potash  ;  IrO2.2H2O,  from  IrCl4.2KCl  with 
boiling  potash ;  or  from  IrCl3.3KCl  and  potash,  with  subsequent 


HYDRATES   OF   OSMIUM,  IRIDIUM,  AND    PLATINUM.  483 

exposure  to  oxygen ;  PtO.H2O,  from  PtCl2  and  warm  KOH ; 
some  remains  dissolved,  but  is  precipitated  on  addition  of  dilute 
sulphuric  acid ;  and  PtO2.nH2O,  by  the  action  of  potassium 
hydroxide,  or  finely  divided  calcium  carbonate,  or  a  solution  of 
platinic  nitrate  or  sulphate,  Pt(N"03)4,  or  Pt(S04)2. 

Hyd rated  osmium  monoxide  is  a  blue-black  powder,  soluble 
with  a  blue  colour  in  hydrochloric  acid;  it  rapidly  oxidises  on 
exposure  to  air.  The  hydrated  sesquioxide  is  a  brown-red  pre- 
cipitate, soluble  in  acids ;  the  hydrated  dioxide  is  a  gummy-black 
precipitate,  insoluble  in  acids. 

Hydrated  iridium  sesquioxide,  Ir2O3.2H2O,  is  a  black  pre- 
cipitate: the  compound  Ir2O3.5H2O  is  yellow,  and  easily  oxidised. 
It  dissolves  in  excess  of  potassium  hydroxide.  The  hydrated 
dioxide,  IrO2.2H2O  is  an  indigo-coloured  precipitate  soluble  in 
acids  with  a  dark-brown  colour. 

Hydrated  platinum  monoxide  is  a  black  powder,  soluble  in 
acids,  forming  unstable  salts ;  the  hydrated  dioxide,  PtO2.nH2O, 
is  also  a  black  powder,  soluble  in  acids,  forming  platinic  salts. 

2.  Compounds  with  other  oxides : — Of  these  only  the 
osmites,  and  platinates  have  been  investigated. 

Potassium  osmite,  K2OsO4.2H2O,  is  prepared  by  dissolving  the 
tetroxide  in  potassium  hydroxide,  and  adding  alcohol,  which  re- 
duces the  tetroxide  to  trioxide  in  presence  of  the  potash.  Thus 
prepared,  it  is  a  brick-red  powder.  If  the  reduction  be  effected 
more  slowly  by  potassium  nitrite,  KNO2,  the  osmite  crystallises  in 
octahedra.  The  sodium  salt  is  more  soluble.  No  other  salts  have 
been  investigated.  These  salts  are  composed  of  the  oxide  Os03, 
unknown  in  the  free  state.  Although  osmium  tetroxide  dissolves 
in  alkalies,  yet  the  solution,  when  distilled,  yields  free  tetroxide 
again  ;  hence  the  combination,  if  there  is  one,  must  be  very  unstable. 

Hydrated  iridium  sesquioxide,  Ir2O3.5ILO,  dissolves  in  alkalies, 
possibly  forming  compounds  ;  but  none  have  been  isolated.  The 
trioxide,  prepared  by  fusing  finely  divided  iridium  with  potassium 
nitrate,  is  mixed  or  combined  with  a  variable  amount  of  potassium 
oxide,  from  which  it  cannot  be  freed  by  washing. 

Platinites,  compounds  of  platinum  monoxide  with  oxides  of 
the  alkaline  metals,  appear  to  be  formed  when  platinum  is  heated 
with  caustic  alkalies.  They  are  uninvestigated.  Platinates  are 
produced  by  the  action  of  excess  of  alkali  on  a  solution  of 
platinum  tetrachloride.  The  following  have  been  analysed : — 
3PtO2.Na^O.6H2O ;  a  reddish-yellow  crystalline  precipitate 
formed  by  exposing  a  solution  containing  platinum  tetrachloride 
and  sodium  carbonate  to  sunlight ;  3PtO2.K2O,  produced  by  heat- 

2  J  2 


484      THE   OXIDES,   SULPHIDES,    SELENIDES,   AND  TELLURIDES. 

ing  potassium  platinichloride  with,  caustic  potash  to  dull  redness, 
and  exhausting  with  water  ;  it  is  a  rust-coloured  substance  ;  and 
SPtO.BaO,  formed  by  exposing  a  mixture  of  platinum  tetrachloride 
and  barium  hydroxide  to  sunshine.  These  compounds  all  require 
investigation.  The  sulphides  of  osmium,  iridium,  and  platinum 
dissolve  in  solutions  of  sulphides  of  the  alkalies,  no  doubt  forming 
compounds,  none  of  which,  however,  have  been  investigated. 

Oxysulphides.  —  Osmium  tetrasulphide  on  oxidation  yields  a 
body  of  the  formula,  Os3S7O5.2H2O  ;  and  on  further  oxidation, 
OsSO3.3H3O.  The  latter  is  not  a  sulphite,  but  hydrated  osmium 
tetroxide,  in  which  one  atom  of  oxygen  has  been  replaced  by 
sulphur;  it  differs  from  osmous  sulphite,  OsSO3,  produced  by 
dissolving  the  tetroxide  in  sulphurous  acid.  A  somewhat  similar 
body  is  said  to  be  formed  when  platinum  disulphide  is  boiled  with 
nitric  acid. 

Double  compounds  of  platinum.  —  Platinonitrites.—  Solu- 
tions of  potassium  nitrite  and  potassium  platinichloride  mixed, 
deposit  crystals  of  potassium  platinonitrite,  the  empirical  formula 
of  which  is  ILPt(NO2)4.  This  compound  contains  dyad  platinum, 
for  on  treatment  with  chlorine,  two  atoms  add  themselves  on,  con- 
verting the  compound  into  one  containing  tetrad  platinum.  The 
potassium  salt  gives  with  silver  nitrate  a  precipitate  of  silver  pla- 
tinonitrite, Ag2Pt(NO2)4,  from  which  the  barium  salt,  BaPt(NO2)4, 
is  produced  by  the  action  of  barium  chloride.  From  the  barium 
salt  many  others  have  been  produced  by  the  action  of  solutions  of 
sulphates  of  the  metals.  The  platinonitrites  are  uniformly  soluble, 
and  crystallise  well.  The  following  have  been  prepared  :  — 


Li2Pt(N02)4.3H20  ;    Na2Pt(N02)4  ;  K2Pt(NO2)4.2II2O  ;  Rb2Pt(NO2)4.2H,O  ; 

Cs2Pt(N02)4  ;   (NH4)2Pt(N02)i.2H20. 

MgPt(N02)4.5H20;  ZnPt(N02)4.8H20;  CdPt(NO2)4.3H2O. 

CaPt(N02)4.5H20;  SrPt(NO2)4.3H2O  ;  BaPt(NO3)4.3H2O. 

Y2{Pt(N02)4}3.9H20;  Al2{Pt(NO2)4}3.14H2O  ;  TLjPtCNO^. 

MnPt(N02)4.8H20  ;  CoPt(NO2)4.8H2O  ;  NiPt(NO2)4.8H2O. 

Ce2{Pt(N02)4}3.18H20  ;  PbPt(NO2)4.3H2O. 

CuPt(N02)4.3H20  ;  A&2Pt(NO3)4  ;  and  Hgr2Pt(NO3)4.Hg:2O.H2O. 

Salts  of  erbium,  lanthanum,  and  didymium  are  also  said  to  have  been  pre- 


These  salts,  treated  with  an  alcoholic  solution  of  iodine,  form 
iodoplatininitrites,  containing  two  atoms  of  iodine  in  excess  of 
the  above  formulae,  e.g.,  K2(PtI2).(NO2)4.  The  hydrogen,  lead,  and 
silver  salts  are  insoluble,  and  are  thrown  down  from  the  potas- 


PLATINONITRITES   AND   PLATINOCHLOROSULPHITES.  485 

sium  salt  by  adding  nitrate  of  hydrogen,  lead,  or  silver  to  its  solu- 
tion. These  salts  are,  as  a  rule,  amber  coloured,  and  crystallise 
well.  The  platinum  is  not  thrown  down  by  hydrogen  sulphide, 
nor  is  the  iodine  removed  by  silver  nitrate,  but  on  addition  of  a 
mercuric  salt,  mercuric  iodide  separates. 

Attempts  to  prepare  platinonitrites  of  beryllium,  iron,  or  in- 
dium, by  addition  of  the  sulphates  of  these  metals  to  the  barium 
salt  result  in  the  formation  of  diplatinonitrites,  or  more  correctly 
diplatinoxynitrites,  the  products  of  decomposition  of  nitrogen 
trioxide  being  evolved,  thus  : — 

2BePt(N02)4.Aq  =  Be(Pt20)(NO2)4.Aq  +  Be(NO2)2.Aq  +  NO 

+  N02. 

The  beryllium,  aluminium,  indium,  chromic,  ferric,  and  silver 
salts  have  been  prepared. 

A  third  compound,  still  more  condensed,  named  triplatino- 
nitrous  acid,  is  produced  when  a  solution  of  platinonitrous  acid 
is  allowed  to  evaporate  spontaneously,  thus  : — 

3H2Pt(N"02)4.Aq  =  H4(Pt30)(]Sr02)8.Aq  4-  2NO  +  2NOZ  +  H2O. 

The  potassium  salt  has  been  prepared  ;  it  is  a  yellow,  well-crystal- 
lised substance  which  may  be  heated  to  130°  without  change. 
It  is  suggested  that  these  compounds  have  formulae  such  as 

TH^O— NO=NO—  OK          l^      ^Q— NO=NO— OK 
T^0— NO=NO— OK'         ix>-"\o— NO=NO— OK J 

0^Pt— O— NO  =NO— OK 
J^Pt— O— NO=NO— OK 

It  is  possible  that  these  bodies  may  be  in  some  measure  ana- 
logues of  the  nitrosulphides,  described  on  p.  343 ;  but  too  little 
is  still  known  of  these  compounds. 

Platintmolybdates  and  platinitungstates,  analogous  to  the 
silicitungstates,  have  already  been  briefly  described  on  p.  404. 

Chloroplatinosulphites,  of  the  general  formula  ClPtSO3M,  are 
produced  by  the  action  of  sulphurous  acid  on  ammonium  platini- 
chloride.  These  compounds  have  been  already  described  on  p.  439. 

Carbonyl,  the  group  CO,  also  enters  into  combination  with 
platinum  and  halogens,  to  form  platinicarbonyl  compounds. 
They  are  produced  by  direct  union  of  platinum  dichloride  with  car- 
bon monoxide.  Three  compounds  are  thus  formed, 

XCO— PtCla 
CL2=Pt=CO  ;  Cl2=Pt=(CO)2;  and  Cl2=Pt<^  | 

\CO-CO 


486       THE   OXIDES,   SULPHIDES,   SELENIDES,  AND   TELLURIDES 

On  heating  the  mixture  to  150°,  the  second  and  third  give  off 
carbon  monoxide ;  and  on  raising  the  temperature  to  240°  in  a 
stream  of  carbon  dioxide,  platinicarbonyl  chloride,  C12  =  Pt  =  CO, 
sublimes  in  golden-yellow  needles,  melting  at  195°.  It  also  crys- 
tallises from  carbon  tetrachloride,  CC14.  The  original  crude  pro- 
duct heated  to  150°  in  a  current  of  carbon  monoxide  yields  a  sub- 
limate of  platinidicarbonyl  chloride,  Cl2Pt(CO)2 :  it  forms  white 
needles  melting  at  142°.  The  third  compound,  diplatinitricar- 
bonyl  tetrachloride  is  extracted  from  the  crude  product  by  boiling 
carbon  tetrachloride,  from  which  it  crystallises  in  slender  yellow 
needles,  melting  at  130°.  The  two  latter  compounds  sublime 
if  heated  in  a  current  of  carbon  monoxide,  whereas  they  decompose 
if  heated  alone. 

Platinous  chloride  also  forms  double  compounds  with  phos- 
phorous acid.  The  combination  does  not  take  place  directly,  but 
by  the  action  of  water  on  monophosphoplatinic  chloride  (see  p. 
174),  thus :— Cl2Pt=PCl3  +  3#20  =  3HC1  +  Cl2=:Pt=P(OH)3. 
Dichloroplatini-phosphonic  acid  forms  deliquescent  orange- 
red  prisms.  The  silver  and  lead  salts  have  been  prepared ;  the 
acid  is  decomposed  by  alkalies. 

Diphosphoplatinic  chloride,  produced  by  dissolving  monophos- 
phoplatinic chloride  in  phosphorus  trichloride,  forms  yellow 
crystals.  It  yields  with  water  cooled  with  ice,  dichloro- 
platinidiphosphonic  acid,  thus : — 

P(OH)3 
Cl2Pt=P2Cl6   +    6H20    =    6HCI    +    Cl2Pt<  | 

P(OH)3 
which  consists  of  yellow,  very  deliquescent  needles.     If  the  tem- 

O 

/  \ 

perature  rises  to  10°  or  12°,  the  body  ClPt=P2(OH)5  is  formed; 
it  is  a  colourless  crystalline  acid,  which  at  150°  loses  water,  leaving  ; 

/\ 
ClPt=P2O(OH)3,  a  light  yellow  powder. 

Platinum  alloys  easily  with  tin,  forming  a  compound  of  the 
formula  Pt^na.  This  substance  burns  when  heated  in  air,  forming 
an  oxide,  Pt2Sn3O3.  It  also  forms  a  black  compound  when  treated 
with  hydrochloric  acid,  which  appears  to  be  the  corresponding 
chloride.  This  body  with  dilute  ammonia  yields  a  hydroxide, 
Pt2Sn3O2(OH)2,  as  a  brownish-black  insoluble  body.  When  it  is 


OF   COPPEE,  SILVER,  GOLD,   AND  MERCURY.  487 

gently  heated  in  a  current  of  dry  oxygen,  the  oxide  Pt2Sn3O4  is 
formed.* 

Oxides,  Sulphides,  Selenides,  and  Tellurides  of 
Copper,  Silver,  Gold,  and  Mercury. 


iur. 


List : —  Oxygen.  Sulph 

Copper. .  . .  Cu2O  ;  CuO  ;     Cu2O3  ;f  CuO2.  Cu2S  ;  CuS  ; 

Silver Agr2O ;  AgrO ;        —     ;       —     ;  Ag2S ;    —    ;     — 

Gold Au20;  AuO(?);  Au203§;  -        .  Au2S;    — 

Mercury  . .  Hg2O  j  HgO  ;  ;   -  -    ;  HgfS ;     — 

List : —  Selenium.  Tellurium. 

Copper   Cu2Se ;  CuSe.  ? 

Silver Ag2Se ;  A&Se.  Agr2Te. 

Gold AtLjTe. 

Mercury —         HgrSe. 

Cu40  is  also  said  to  have  been  prepared,  and  there  is  also  some 
doubtful  evidence  of  the  existence  of  a  similar  suboxide  of  silver, 

AgA: 

Sources. — Many  of  these  bodies  occur  native.  Cuprous  oxide, 
Cu2O,  occurs  as  red  copper  ore  in  regular  octahedra,  and  as  copper 
bloom  in  trimetric  needles.  Cu2S  is  known  as  copper  glance ;  it 
forms  trimetric  hexagonal  prisms  ;  it  is  also  a  constituent  of  copper 
pyrites  and  of  purple  copper  ore  (see  p.  257).  Silver  salphide, 
Ag3S,  occurs  as  silver  glance,  or  argyrose,  in  dark  grey  masses  with 
dull  metallic  lustre.  Argentiferous  copper  glance,  or  stromeyerite, 
has  the  formula  ClloS.AgaS.  Cuprous  selenide,  CllaSe,  forms  the 
rare  mineral,  berzelianite,  occurring  in  silver  white  crusts.  Hessite, 
or  telluric  silver,  Ag2Te,  and  the  double  telluride,  Au2Te.4Ag2Te, 
also  occur  native. 

Cupric  oxide,  CuO,  forms  the  important  black  copper  ore,  or 
melaconite;  it  crystallises  in  cubes.  The  sulphide,  CuS,  is  known 
as  indigo  copper  or  corellin,  crystallising  in  hexagonal  plates. 
Mercuric  sulphide,  HgS,  when  found  native  is  named  cinnabar ;  it 
has  a  dull  red  colour ;  it  is  the  chief  ore  of  mercury ;  it  usually 
occurs  in  heavy  earthy  lumps,  but  is  occasionally  found  crystal- 
lised in  acute  hexagonal  rhombohedra.  The  crystals  are  sometimes 
bright  red  and  transparent.  Mercuric  selenide,  HgSe,  also  occurs 
native. 

*  Comptes  rend.,  98,  985.  f  Known  only  in  combination, 

t  As  regards  the  existence  of  Ag4O,  see  CAem.  Soc.,  51,  416;  Serichte,  20, 
1458;  2554. 

§  Serichte,  19,  2541. 


488       THE   OXIDES,    SULPHIDES,   SELENIDES,  AND   TELLURIDES 

One  oxyhalide  also  occurs  in  nature.  Atacamite  is  a  native 
oxychloride  of  copper,  3CuO.CuCl2.5H2O  ;  it  crystallises  in  green 
rhombic  crystals. 

Preparation. — 1.  By  direct  union. — Copper  heated  in  air 
becomes  covered  with  scales ;  these  consist  on  the  exterior  of  black 
cupric  oxide,  CuO,  and  on  the  interior  of  red  cuprous  oxide,  Cu2O. 
Silver  does  not  combine  with  oxygen  at  the  ordinary  pressure,  but 
under  an  increased  pressure  of  15  atmospheres,  a  portion  of  the 
silver  oxidises  at  300°,  forming  argentous  oxide,  Ag2O  ;  mercury 
slowly  oxidises  when  kept  boiling  in  an  atmosphere  of  oxygen  or  air 
for  several  weeks.  This  fact  was  discovered  by  Boyle,  and  it  will  be 
remembered  that  by  means  of  the  oxidation  of  mercury  Lavoisier 
made  his  all-important  discovery  of  the  nature  of  oxygen  (see  p.  11). 
The  red  powder  which  slowly  gathers  on  the  surface  of  the  boiling 
mercury  used  to  be  termed  "  mercurius  prcecipitatus  per  se." 

Silver  (argentic)  oxide,  AgO,  is  produced  by  the  direct  oxida- 
tion of  silver  by  means  of  ozone,  or  by  nascent  oxygen,  when  a  solu- 
tion of  silver  nitrate  is  electrolysed  with  silver  poles.  Gold  does 
not  directly  unite  with  oxygen. 

The  sulphides  may  all  be  prepared  by  direct  union.  Cuprous 
sulphide,  Cu2S,  is  formed  when  finely  divided  copper  and  sulphur 
are  rubbed  together  in  a  mortar.  The  mass  grows  red  hot,  great 
heat  being  evolved  during  the  union.  Bed  hot  copper  burns  in 
sulphur-gas,  yielding  the  same  compound.  Silver  and  sulphur 
also  unite  directly  to  form  argentous  sulphide,  Ag2S.  Gold  and 
sulphur  do  not  unite  when  heated  together,  because  the  sulphides 
easily  decompose  by  heat ;  but  on  heating  a  mixture  of  geld  and 
silver  with  sulphur,  dark  grey  crystals  of  the  formula  2Au2S3.5Ag2S 
are  produced.  Mercuric  sulphide,  HgS,  is  formed  as  a  black 
amorphous  mass  by  rubbing  together  mercury  (200  parts)  and 
sulphur  (32  parts).  After  sublimation  it  is  brilliant  red,  and  is 
known  as  vermilion,  and  used  as  a  paint. 

Cuprous  and  cupric  selenides,  Cu2Se  and  CuSe  ;  argentous  and 
argentic  selenides,  Ag>Se  and  AgSe,  and  mercuric  selenide,  HgSe ; 
also  argentous  and  aurous  tellurides,  Ag2Te  and  Au2Te,  and  copper 
telluride,  are  formed  by  heating  the  elements  together  in  the 
required  proportions. 

2.  By  reducing  a  higher  compound. — Cuprous  oxide  is 
produced  by  heating  a  mixture  of  cupric  oxide,  CuO,  or  better 
copper  sulphate,  CuSO4,  with  metallic  copper  to  an  intense 
red  heat.  The  sulphate  loses  S03,  forming  oxide,  which  is 
reduced  by  the  metallic  copper.  Cuprous  oxide  is  also  produced 
by  boiling  cupric  hydroxide  with  grape  sugar  and  caustic  soda, 


OF   COPPER,   SILVER,   GOLD,   AND   MERCURY.  489 

better  in  presence  of  tartaric  acid,  which  keeps  the  hydroxide  in 
solution  as  double  tartrate.  The  grape  sugar  is  oxidised,  while  the 
copper  oxide  loses  oxygen.  Five  molecules  of  grape  sugar,  C6Hi206, 
are  capable  of  reducing  one  molecule  of  cupric  oxide.  This  is  the 
basis  of  Pehling's  process  for  estimating  sugar.  Copper  dioxide, 
CuO2,  and  argentic  oxide,  AgO,  are  very  unstable  bodies,  yielding 
cupric  oxide,  CuO,  and  argentous  oxide,  Ag2O,  on  gentle  heating. 

3.  By  decomposing  a  double  compound. — The  hydroxides 
yield  the  oxides  when  gently  heated.     Silver  oxide  is  formed  from 
the  carbonate,  Ag2CO3,  at  200°.     Cnpric  oxide  is  produced  from 
cupric  sulphate,  CuSO4,  at  a  white  heat,  and  from  cupric  nitrate 
or  carbonate  at  a  red  heat.     Gold  sesquioxide,  Au2O3,  is  produced 
by  addition  of  an  acid  to  an  aurate,  e.g.,  AUjjO^KjO,  with  sul- 
phuric acid.     Compounds  of  gold  trioxide  with  oxides  are,  as  a 
rule,  decomposed  by  water.     The  oxide  dissolves  in  strong  nitric 
acid,  doubtless  forming  auric  nitrate,  but  on  addition  of  water  the 
oxide  is  again  deposited.      The    same   change   takes   place  with 
argentic  oxide.     It  dissolves  in  moderately  strong  nitric  acid,  but 
the  nitrate  decomposes  on  dilution,  the  oxide  being  precipitated. 
Mercuric  oxide,  HgO,  like  cupric  oxide,  is  usually  produced  by 
heating  the  nitrate ;    mercurous  nitrate,  HgNO3,  also  leaves  mer- 
curic oxide  when  heated. 

Cuprous  sulphide,  Cu2S,  is  formed  when  cupric  sulphate  is 
heated  to  whiteness  in  a  crucible  lined  with  carbon;  and  aurous 
telluride  remains  on  heating  sulphotellurate  of  gold,  TeS2.Au2S3. 

4.  By  double  decomposition.— This  process,  as  a  rule,  yields 
hydroxides,  but   as   these  bodies  are  unstable   in   this   group  of 
elements,  the  oxides  are  formed. 

ClljO. — Heating  together  cuprous  chloride,  Cl^CL,  and  sodium 
carbonate,  or  boiling  together  cuprous  chloride  and  solution  of 
caustic  soda. 

Ag2O. — Solution  of  silver  nitrate,  AgN03,  and  hot  barium 
hydroxide  (used  because  commercial  sodium  or  potassium  hydr- 
oxide almost  always  contains  chloride);  boiling  together  silver 
chloride,  AgCl.  and  strong  caustic  potash. 

Au2O. — Aurous  chloride,  AuCl,  and  cold  potash  solution. 

Hg2O. — Mercurous  chloride  or  nitrate,  and  cold  caustic  potash 
in  the  dark. 

CuO. — Cupric  nitrate,  or  sulphate,  and  hot  caustic  soda  or 
potash  solution.  In  the  cold  the  hydrate  is  precipitated. 

AuO. — Adding  solution  of  hydrogen  potassium  carbonate  to  a 
solution  of  gold  in  aqua  regia,  gold  being  present  in  excess ;  it  pre- 
cipitates when  the  temperature  is  raised  to  50°. 


490      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES 

The  sulphides  are  generally  prepared  by  passing  hydrogen 
sulphide  through  a  solution  of  a  suitable  salt  of  the  metal,  thus : — 
Cu2S  from  Cu2Cl2  suspended  in  water  ;  Ag2S  from  AgN03.  Aq ; 
Au2S  from  KAu(CN)2.Aq  (see  p.  572)  ;  Hg2S  appears  not  to  be 
formed  from  a  mercurous  salt  and  hydrogen  sulphide ;  the  precipi- 
tate produced  consists  of  mercuric  sulphide,  HgS,  mixed  with  free 
mercury ;  Cu2Se  and  Ag2Se  have  been  similarly  formed  with  aid 
of  H2Se ;  CuS  from  CuS04.Aq,  &c. ;  AuS  appears  to  be  the  for- 
mula of  the  precipitate  produced  in  a  cold  dilute  solution  of  auric 
chloride  (?) ;  HgS  from  HgCl2.Aq,  &c.  With  mercury,  inter- 
mediate sulphochlorides  are  formed  (see  below).  Cupric  selenide, 
CuSe,  has  been  similarly  obtained. 

Properties. — Cuprous  oxide,  Cu2O,  is  a  bright  red,  or  a 
yellow  red,  powder,  according  to  the  method  of  preparation;  it 
can  be  fused  at  a  very  high  temperature.  Argentous  oxide,  Ag2O, 
is  a  dense  black  powder,  which  decomposes  above  200°  into  silver 
and  oxygen.  Aurous  oxide,  Au2O,  is  also  a  black  powder,  soluble 
in  alkalies.  On  standing  it  changes  to  auric  oxide,  Au2O3,  and 
metallic  gold.  Mercurous  oxide  is  also  black,  and  is  even  more 
easily  decomposed  into  mercuric  oxide,  HgO,,  and  mercury ;  the 
change  is  brought  about  by  sunlight,  or  even  by  trituration  in  a 
mortar. 

Cuprous  sulphide,  Cu2S,  is  a  black  substance.  When  heated 
to  redness  in  air,  it  burns  to  cupric  oxide  and  sulphur  dioxide.  It 
undergoes  a  reaction  when  heated  with  cupria  oxide,  whereby 
metallic  copper  and  sulphur  dioxide  are  formed  : — Cu3S  +  2CuO  = 
4Cu  +  802-  This  reaction  takes  place  during  the  preparation  of 
metallic  copper  (compare  the  action  of  lead  sulphate  and  oxide  on 
the  sulphide,  p.  429).  Argentous  sulphide  is  a  leaden  grey 
body  with  dull  metallic  lustre ;  when  produced  by  precipitation  it 
is  black.  When  heated  in  air  it  is  oxidised  to  sulphate,  AgoSO^. 
Aurous  sulphide  is  a  dark  brown  precipitate,  which  loses  its  sul- 
phur when  strongly  ignited. 

Cuprous  selenide,  prepared  by  fusion,  is  a  silver  white  sub- 
stance ;  by  precipitation  it  is  a  black  powder.  Argentous 
selenide  is  a  black  precipitate,  grey  when  dry,  and  melting  at  a  red 
heat  to  a  silver- white  button.  Argentous  telluride  forms  leaden 
grey  granules,  and  aurous  telluride  is  a  grey  brittle  substance. 

Cupric  oxide  is  black.  It  melts  at  a  bright  red  heat  and 
crystallises  from  fused  potassium  hydroxide  in  tetrahedra.  Ar- 
gentic oxide,  AgO,  is  a  white  substance  ;  it  dissolves  in  cold 
nitric  acid  with  a  deep  brown  colour  (forming  argentic  nitrate 
Ag(N03)2  ?) ;  but  on  dilution  it  is  precipitated  unchanged. 


OF   COPPER,   SILVER,   GOLD,   AND   MERCURY.  491 

Auric  monoxide,  AuO,  is  a  black  substance,  soluble  in  hydro- 
chloric acid  to  a  dark  green  solution;  and  mercuric  oxide, 
produced  in  the  dry  way,  is  a  brownish-red  or  red  crystalline 
powder;  when  heated  it  becomes  bright  red,  and  then  turns 
black  and  begins  to  decompose. 

Auric  sesquioxide,  Au-jOa,  prepared  by  decomposing  an  aurate 
with  an  acid,  still  retains  alkali.  To  purify  it,  it  is  dissolved  in 
strong  nitric  acid,  and  on  dilution  the  oxide  is  precipitated  pure. 
It  is  a  brownish-black  powder,  soluble  in  nitric  or  sulphuric  acids, 
but  the  nitrate  and  sulphate  are  decomposed  by  addition  of  water. 
It  is  very  unstable,  being  decomposed  by  light. 

Copper  dioxide,  CuO2,  produced  by  adding  dilute  hydrogen 
dioxide  at  0°  to  cupric  hydroxide,  Cu(OH)2,  is  a  yellowish-brown 
substance,  very  unstable,  yielding  oxygen  and  cupric  oxide. 

Cupric  sulphide,  CuS,  produced  by  precipitation,  is  black. 

Auric  monosulphide,  AuS,  is  yellow,  and  loses  sulphur  when 
gently  heated,  giving  aurous  sulphide.  Mercuric  sulphide  is  a 
velvety-black  powder,  when  produced  by  direct  union  or  by  pre- 
cipitation. When  sublimed,  or  when  warmed  in  contact  with  an 
alkaline  sulphide,  or  when  heated  with  excess  of  sulphur  and 
solution  of  potassium  hydroxide  to  45 — 50°  for  10  hours,  it  acquires 
a  brilliant  red  colour  ;  it  is  by  one  or  other  of  these  methods  that 
vermilion  is  prepared. 

Cupric  selenide,  CuSe,  is  a  black  precipitate,  acquiring 
metallic  lustre  when  rubbed  in  a  mortar  ;  it  loses  half  its  selenium 
by  heat.  Argentic  selenide,  AgSe,  is  a  white  lustrous  substance, 
and  mercuric  selenide,  HgSe,  is  also  white,  with  metallic  lustre. 

Auric  sesquisulphide,  Ai^Ss,  is  a  black  precipitate.* 

Copper  disulphide  is  known  only  in  combination. 

Double  compounds.  1.  With  water. — Cuprous,  mercurous, 
and  gold  oxides  do  not  form  hydrates :  silver  hydroxide,  AgOH, 
produced  by  precipitation  in  the  cold,  is  a  grey  flocculent  sub- 
stance, losing  water  at  60°,  and  leaving  the  oxide.  It  is  sparingly 
soluble  in  water. 

Cupric  hydroxide,  Cu(OH)2,  is  a  pale  blue  precipitate,  dry- 
ing to  greenish- blue  lumps.  It  has  a  metallic  taste,  hence  it  must 
be  slightly  soluble  in  water.  It  loses  water  below  100°,  even  in 
presence  of  water,  leaving  the  black  oxide.  Hydrated  auric 
dioxide  is  an  olive-green  precipitate,  which  cannot  be  dried 
without  loss  of  water  and  conversion  into  the  black  oxide,  AuO. 

Mercuric  hydrate,  Hg(OH)2,  produced  by  precipitation,  is  a 
*  See  Berichte,  20,  2369,  and  2704. 


492       THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLURIDES 

yellow  powder,  which  may  be  heated  to  100°  without  decomposi- 
tion. At  a  higher  temperature  it  loses  water,  leaving  the  yellow 
oxide.  It  has  also  a  strong  metallic  taste,  hence  it  must  be 
somewhat  soluble. 

Hydrated  auric  sesquioxide,  Au2O3.H2O,  is  a  dark-brown 
powder,  thrown  down  from  a  solution  of  auric  chloride,  AuCl3.Aq, 
mixed  with  a  solution  of  hydrogen  potassium  carbonate,  on  addition 
of  sodium  sulphate.  If  dilute  potash  be  used  for  precipitation,  the 
trihydrate,  Au2O3.3H2O  =  Au(OH)3,  is  produced.  Both  of  these 
substances  loses  water  with  great  readiness. 

2.  With  oxides. — These  bodies  are  produced  by  direct  union. 
They  are  as  follows: — HgO.K2O. — Formed  by  heating  mercuric 
oxide  with  fused  potash.     It  consists  of  white  crystals. 

Cu2O3.?zCaO.  This  substance  forms  rose  coloured  crystals,  and 
is  produced  by  the  action  of  a  solution  of  calcium  hypochlorite 
(bleaching  powder,  Cl — Ca — OC1)  on  cupric  nitrate.  This  sub- 
stance is  so  unstable  that  the  ratio  between  sesquioxide  of  copper 
and  oxide  of  calcium  has  not  been  ascertained ;  but  it  appears  to 
be  proved  that  the  copper  and  oxygen  bear  to  one  another  the 
proportion  indicated  by  the  formula  Cu203. 

3.  Aurates. — These  are  analogous  compounds  of  gold  sesqui- 
oxide.      Only     one     has     been     carefully    investigated,     viz.  : — 
Au2O3.K2O.6H2O  =  KAuO2.3H2O.    It  crystallises  011  evaporation 
from  a  solution  of  auric  hydrate  in  caustic  potash.    It  forms  yellow 
crystals,  arid  its  solution,  mixed  with  solutions  of  the  salts  of  other 
metals  gives  precipitates,  no  doubt  of  analogous  composition.     On 
mixing  its  solution  with  hydrogen  potassium  sulphite,  yellow  needles 
are  formed,  of  the  formula  KAuO2.4HKSO3,  which  are  nearly  in- 
soluble in  dilute  alkali,  but  dissolve  in  water  with  decomposition.* 

4.  Double  sulphides.— 4Cu2S.K2S  and  Au2S.K2S,  are  soluble 
substances  crystallising  from  solutions  of  the  respective  sulphides 
in  a  strong  solution  of  potassium  sulphide. 

(CuS2)2(NH4)2S  crystallises  in  soluble  red  needles  from  a  solu- 
tion of  cupric  sulphide,  CuS,  in  yellow  polysulphide  of  ammonium. 
Mercuric  sulphide,  precipitated,  also  dissolves  in  a  mixture  of  solu- 
tions of  potassium  monosulphide  and  hydroxide,  giving  crystals  of 
HgS.KoS.5H2O,  which  are  decomposed  by  water.  The  com- 
pound 5HgS.K2S,  is  also  produced  by  mixture  ;  it  crystallises  in 
golden-yellow  plates,  with  one  molecule  of  water;  in  colourless 
crystals  with  7H2O  ;  and  when  anhydrous  in  black  needles. 

*  As  regards  the  "  Purple  of  Cassius,"  see  J.  prakt.  Chem.,  121,  30,  252. 
This  substance,  used  as  a  test  for  gold,  and  produced  by  addition  of  stannous 
chloride  to  a  compound  of  gold,  owes  its  colour  to  finely  divided  metallic  gold. 


OF   COPPER,   SILVER.   GOLD,   AND   MERCURY.  403 

5.  With     halides.— CuO.CuFo.HoO,    and    HgO.HgP2    are 

formed  by  heating  solutions  of  the  respective  fluorides.  The  first 
is  green  and  insoluble  ;  the  second,  an  orange-yellow  powder. 

2CuO.CuClo.4H2O  is  produced  by  addition  of  a  small  amount 
of  potash  to  CuClo.Aq  ;  2HgO.HgCl2  is  a  brick-red  powder. 

3CuO.CuClo.5HoO  occurs  native  in  green  rhombic  crystals  as 
atacamite;  prepared  by  the  action  of  ammonium  chloride  on 
metallic  copper  in  presence  of  air,  it  forms  the  pigment  Brunswick 
green,  with  4  or  6H2O.  3HgO.HgCl2,  produced  by  heating 
mercuric  chloride  with  solution  of  hydrogen  potassium  carbonate, 
forms  yellow  crystals  ;  4HgO.HgCl2  crystallises  in  brown  crusts 
from  the  filtrate.  3CuO.CuCl2  is  a  green  hydrated  substance 
produced  by  the  action  of  water  on  the  compound  CuCl2.N2H4 
(see  p.  545).  The  following  oxyhalides  of  mercury  are  produced 
by  mixture  :—HgO.2HgCl2,  white  and  soluble;  2HgO.HgBr2, 
yellow  soluble  needles ;  3HgO.HgI2,  a  yellow  brown  powder. 

Similar  sulphohalides  of  mercury  are  known,  viz. : — 
2HgS.HgClo_;  HgS.HgBr2;  2HgS.HgI2,  all  yellowish- white 
substances,  produced  by  the  action  of  a  limited  amount  of 
hydrogen  sulphide  on  the  respective  halide  of  mercury.  From 
the  nitrate  and  the  sulphate,  corresponding  compounds, 
2HgS.Hg(NO3)2  and  2HgS.HgSO4  are  produced.  The  com- 
pounds 3HgS.HgCl2  and  4HgS.HgClo.  have  also  been  prepared. 
Lastly,  by  boiling  mercuric  sulphide  with  a  solution  of  cupric 
chloride,  a  brilliant  orange- coloured  substance  is  formed,  viz., 
HgS.CuCl,  sulphur  separating  at  the  same  time. 

Physical  Properties. 

Mass  of  one  cubic  centimetre. 

Cu20,  6-13  grams;  CuO,  6'40;  A&2O,  7'52  ;  Hgr2O,  10'7;  HgO,  H'30. 
Pd.2S,  7-30;  PtS,  8-85;  PtS2,  7-22.— CusS,  5'79  ;  CuS,  4'64;  As2S,  7'36 ; 
HgrS,  8'10  (cinnabar). 

Heats  of  formation : — 

Pd  +  O  +  H2O  =  Pd(OH)2  +  227K—  Pd  +  20  +  2H2O  =  Pd(OH)4  + 

304K. 

Pt  +  O  +  H2O  =  Pt(OH)2  +  179K. 
2Cu  +  O  =  Cu2O  +  408K.— Cu  +  O  =  CuO  +  372K.— 2Cu  +   S  = 

Cu2S  +  183  K. 
Cu  +  S  =  CuS  +  81K.-— 2Agr  +  O  =  Agr2O  +  59K.— 2Ag-  +  S  =  A&,S 

+  33K. 

2Au  +  3O  +  3H2O  =  2Au(OH)3  -  132K.— 2Hgr  +  O  =  Hg.,O  +  422K. 
S.S  +  O  =  HgO  +  302K.— Hg  +  S  =  HgS  +  149K. 


494      THE   OXIDES,   SULPHIDES,   SELENIDES,   AND   TELLUEIDES. 


Concluding  Remarks  on  the  Oxides,  Sulphides,  &c. 

In  concluding  the  description  of  oxides,  sulphides,  selenides,  and 
tellurides  it  may  be  pointed  out  that  the  available  data  as  regards 
compounds  of  selenium  and  tellurium  are  very  scanty.  A  com- 
plete theory  of  chemistry  can  only  be  constructed  by  supplementing 
deficiencies  in  one  set  of  compounds  by  examples  from  others ;  and  it 
would  follow  that  in  spite  of  their  want  of  commercial  importance, 
the  selenides  and  tellurides  greatly  require  exhaustive  study.  The 
existence  of  hydrosulphides,  analogous  to  the  hydroxides,  for 
example,  is  possible.  But  few  of  these  appear  to  be  stable,  at 
least  at  the  ordinary  temperature,  although  the  precipitated 
sulphides  usually  contain  a  small  amount  of  sulphur  in  excess  of 
that  required  by  their  formulae,  denoting  the  presence  of  a  trace  of 
undecomposed  hydrosulphide.  In  this  connection  it  may  be  noted 
that  the  sulphides  of  many  elements,  such  as  arsenic,  copper,  lead, 
silver,  gold,  &c.,  when  produced  in  dilute  neutral  solution  are 
soluble  in  water,  and  are  precipitated  only  on  addition  of  an  acid 
or  salt.  Such  solutions,  however,  do  not  contain  appreciable 
amounts  of  hydrosulphides  ;  and  it  is  probable  that  they  are  either 
hydroxy-hydrosulphides,  or  colloidal  and  soluble  varieties  of 
sulphides. 

The  physical  properties  of  the  oxides,  sulphides,  &c.,  still 
require  investigation ;  our  knowledge  in  this  respect  greatly  falls 
short  of  our  acquaintance  with  the  halides.* 

Classification  of  the  oxides. — It  has  been  customary  to 
divide  the  oxides  into  three  classes : — basic  oxides,  acid- 
forming  oxides,  and  peroxides,  to  which  may  perhaps  be  added 
a  fourth  class,  suboxides.  This  classification  is  founded  partly 
on  the  behaviour  of  these  oxides  towards  water,  towards  each 
other,  and  when  exposed  to  heat.  It  cannot  be  strictly  maintained, 
and  indeed  it  has  tended  to  obscure  the  relations  between  different 
families  of  oxides.  Yet  as  this  nomenclature  is  still  in  vogue,  it 
is  advisable  to  insert  a  short  sketch  here  of  the  nature  of  the 
division. 

A  suboxide  is  one  which  shows  no  tendency  towards  the  for- 
mation of  double  compounds  ;  and  which,  when  treated  with  acids,  is 
either  indifferent  to  their  action,  or  if  attacked,  decomposes  into 
element,  and  a  higher  oxide,  which  combines  with  the  distinctive 
oxide  of  the  acid.  Thus,  suboxide  of  lead,  or  lead  dross,  of  some- 

*  For  a  list  of  double  sulphides,  see  Pogg.  Ann.,  149,  381,  and  153,  588. 
The  individual  compounds  have  been  described  in  their  place. 


CLASSIFICATION   OF   OXIDES.  495 

what  indefinite  composition,  when  treated  with  acetic  acid,  for 
example,  yields  metallic  lead,  while  lead  acetate  passes  into 
solution. 

A  basic  oxide  is  one  which,  when  treated  with  an  acid,  com- 
bines with  the  distinctive  oxide  of  the  acid,  forming  a  salt,  with 
liberation  of  water.  Thus  calcium  oxide  aud  nitric  acid  give 
calcium  nitrate  and  water,  and  so  with  a  multitude  of  instances. 
Such  bodies  are  often  soluble  in  water,  and  it  is  at  present  a 
disputed  point  whether  they  are  resolved  by  water  into  their  con- 
stituents, basic  oxide  and  acid  oxide.  This,  however,  is  certain, 
that  in  most  cases,  on  evaporating  the  water,  they  remain,  as  a 
rule,  in  an  anhydrous  state.  We  have  seen,  however,  that  many 
so-called  basic  oxides  are  capable  of  entering  into  combination 
with  each  other;  and  in  such  cases,  it  is  a  matter  of  opinion 
which  to  term  the  basic  and  which  the  acid  oxide.  An  acid  oxide, 
conversely,  is  defined  as  one  which  combines  with  a  basic  oxide, 
forming  a  salt.  It  is  noticeable  that,  as  a  rule,  such  acid  oxides 
contain  more  than  one  atom  of  oxygen.  But,  again,  many 
examples  of  compounds  of  acid  oxides  with  each  other  have  been 
noticed,  and,  as  with  basic  oxides,  it  is  impossible  to  ascribe  to 
each  its  peculiar  function. 

A  peroxide  is  defined  as  one  which  on  treatment  with  certain 
acids  (especially  with  strong  sulphuric  acid)  gives  off  oxygen ;  or, 
which  on  treatment  with  an  aqueous  solution  of  a  halogen  acid 
evolves  halogen.  Such  bodies,  as  a  rule,  are  also  decomposed  by 
moderate  heat  into  a  lower  oxide  and  oxygen.  Here  again,  how- 
ever, we  notice  that  almost  all  so-called  peroxides,  when  suitably 
treated,  yield  compounds  both  with  basic  and  with  acid-forming 
compounds.  Such  compounds,  however,  are  not  usually  stable, 
and  lose  oxygen  readily  when  heated. 


Constitutional  formulae. — In  the  foregoing  chapters  on  the 
oxides,  constitutional  formulae  have  been  adopted,  when  the 
molecular  weight  of  the  compound  has  been  determined  from  its 
vapour- density ;  as,  for  example,  S02C12 ;  or,  where  the  formula  can 
be  directly  deduced  from  such  compounds  by  simple  and  direct 
connection,  as,  for  instance,  S02(OH)2.  But  the  latter  formulae 
are  by  no  meant  so  well  vouched  for  as  the  former,  and  we  have 
seen  (p.  421)  reason  to  believe  that  the  simple  formula  of  sulphuric 
acid  does  not,  in  all  probability,  represent  its  true  molecular 
weight.  Where  such  evidence  is  not  at  hand,  the  double  com- 
pounds have  been  classified  as  addition  products.  This,  how- 


496      THE   OXIDES,   SULPHIDES,   SELENIDES,    AND   TELLURIDES. 

ever,  by  no  means  precludes  the  ascribing  to  them  constitutional 
formulas,  when  data  sufficient  to  warrant  this  course  have  been 
accumulated;  and,  in  some  cases,  we  have  been  guided  to  such 
formulas  by  analogy  with  compounds,  the  proof  of  whose  consti- 
tutional formulas  is  fairly  satisfactory. 

Constitution  of  the  double  halides  and  oxyhalides.  —  But 
having  in  many  cases  seen  reasons  for  giving  constitutional 
formulas  to  certain  double  oxides,  it  may  not  be  amiss  to  inquire 
whether  the  double  halides,  which  have  uniformly  been  treated  as 
additive  compounds,  should  not  also  have  constitutional  formulas 
ascribed  to  them. 

It  has  been  suggested  that  such  combination  occurs  by  virtue 
of  the  halogen  elements,  which  in  such  compounds  function  as 
triads  towards  each  other.  We  are  acquainted,  for  example,  with 
the  compound  IC13,  in  which  iodine  acts  as  a  triad.  Now,  if  this 
supposition  be  granted,  it  becomes  possible  to  represent  any  double 
halides  whatever  constitutionally. 

For  example,  the  compounds  KF.HP,  KP.2HF,  and  KF.3HF, 
are  known.     They  may  be  written  :  — 

JF—  H  FH 

K—  F=  F—  H;  K—  F<  |  ;    and   K—  F<        \F—  H. 

XF—  H  XFHX 


We  have  also  : 

^Cl.H          JWKF 

nr     .01     CIX^          B^F 
Zn<cl=ci;>Zn;          \p 

and  so  on.  Given  the  hypothesis,  all  double  halides  may  be  thus 
represented  by  a  little  ingenuity. 

It  is  an  ascertained  fact  that  the  vapour-  densities  of  many 
simple  halides  increase  with  rise  of  temperature.  For  example,  the 
formula  of  gaseous  stannous  chloride  at  temperatures  not  far  above 
its  boiling  point,  601°,  is  Sn2Cl4,  but  with  rise  of  temperature  it 
falls,  until  at  a  high  temperature  its  formula  is  SnCl2.  It  might  be 
conceived  that  such  bodies  are  analogously  constituted,  thus  :  — 

pi  _  /-n 

Sn<pj~p,^>Sn;  but  we  shall  see  reason  to  doubt  this  explana- 

tion in  considering  compounds  of  such  elements  with  hydrocarbon 
radicles  (see  p.  506).  And  if  such  an  explanation  is  unsatis- 
factory for  bodies  in  the  gaseous  state,  it  appears  inadvisable  to 
apply  it  to  solid  and  liquid  substances,  about  whose  molecular 
weights  we  can  only  speculate. 


497 


PART  V.— THE  BORIDES ;   THE  CARBIDES 
AND   SILICIDES. 


CHAPTEE  XXX. 

BORIDES. — CARBIDES   AND    SILICIDES. ORGANO- METALLIC     COMPOUNDS.— 

CONSTITUTION   OF  DOUBLE   COMPOUNDS. 

Borides. 

Very  few  of  these  compounds  are  known.  The  list  which  follows 
comprises  all  that  have  been  investigated  : — JBT3JB ;  Mg3B2 ;  A1B  ; 
A1B6 ;  Mn3B2 ;  B3C ;  BN ;  Ag3B ;  also  borides  of  iron,  pal- 
ladium, indium,  and  platinum.  The  compound  of  boron  with 
nitrogen  will  be  considered  under  the  heading  "  Nitrides." 

Hydrogen  boride,  HJ$*  is  produced  by  gradual  addition  of 
strong  hydrochloric  acid  to  magnesium  boride,  Mg3B2,  contained 
in  a  flask.  A  colourless  gas,  consisting  of  more  than  99  per  cent, 
by  weight  of  hydrogen  and  less  than  1  per  cent,  of  hydrogen 
boride  is  evolved.  It  has  a  disagreeable  smell,  and  produces  head- 
ache and  nausea.  It  is  sparingly  soluble  in  water,  but  its  solution 
is  permanent,  retaining  its  smell  for  several  years.  The  gas  is 
decomposed  into  boron  and  hydrogen  at  a  red  heat.  Hydrogen 
boride  communicates  a  brilliant  green  colour  to  the  flame  of  the 
burning  hydrogen. 

Its  formula  was  determined  by  comparing  the  weight  of  water 
obtained  by  passing  a  known  volume  of  the  gas  over  red-hot  copper 
oxide  with  that  obtained  from  an  equal  volume  of  hydrogen.  Had 
its  formula  been  H3B,  occupying  the  same  volume  as  the  hydrogen 
it  contains,  the  weight  of  water  should  have  been  identical  in  both 
cases  ;  had  its  formula  been  HB,  a  less  amount  of  water  would 
have  been  produced.  Actual  experiment  showed  that  a  somewhat 
greater  amount  was  formed ;  hence  the  conclusion  that  it  contains 
more  hydrogen  than  H2B ;  and  the  probable  conjecture  that  its 
formula  is  H3B. 

*  Jones,  Chem.  Soc.,  35,  41 ;  39,  215. 

2  K 


498  THE  BORIDES,   CARBIDES,   AND   SILICIDES. 

Magnesium  boride,  Mg3B2,  is  a  grey  semifused  mass,  pro- 
duced by  direct  union ;  or  when  formed  by  the  action  of  boron 
chloride  on  hot  magnesium,  an  almost  black  substance.  It  is  most 
easily  obtained,  although  in  an  impure  state,  by  heating  together 
to  redness  in  a  covered  crucible  a  mixture  of  boron  trioxide  and 
magnesium  dust.  It  is  insoluble  in  water. 

Aluminium  borides,  A1B,  and  A1B6,*  are  produced  when 
aluminium  and  boron  trioxide  are  heated  together.  The  first  forms 
golden-yellow  hexagonal  laminae  ;  the  latter  large  black  laminae. 
At  the  same  time  boron  carbide  is  formed,  due  to  the  carbon  of 
the  furnace,  probably  of  the  formula  B3C,  in  hard  black  crystals 
with  metallic  lustre,  insoluble  in  nitric  acid. 

Manganese  boride,  Mn3B2,  forms  grey-violet  crystals,  pro- 
duced by  heating  manganese  carbide  to  redness  with  boron  tri- 
oxide. They  are  decomposed  by  water  at  100°,  and  by  acids, 
hydrogen  alone  being  evolved. 

Silver  boride,  possibly  Ag3B,  is  a  black  precipitate  produced 
when  hydrogen,  containing  hydrogen  boride,  is  passed  through  a 
solution  of  silver  nitrate.  It  reacts  with  hot  water,  evolving 
hydrogen  boride. — Boride  of  iron,  a  substance  with  white  metal- 
lic lustre,  is  formed  by  heating  ferrous  borate  in  a  stream  of 
hydrogen,  or  by  the  action  of  boron  trichloride  on  red-hot  iron. 

The  remaining  borides  have  been  little  investigated. 

Carbides  and  Silicides. 

Compounds  of  carbon  with  hydrogen  have  been  very  fully  in- 
vestigated, and  those  containing  hydrogen  and  other  elements  (the 
"  organo-metallic  "  compounds)  are  also,  in  many  instances,  known. 
To  describe  the  "  hydrocarbons  "  is  beyond  the  province  of  this 
book,  as  the  subject  is  fully  treated  in  text-books  of  organic 
chemistry.  Some  of  the  more  important,  however,  will  be  con- 
sidered here. 

Methane  or  marsh-gas,  CH±. — Sources. — As  its  name  implies, 
this  compound  is  formed  in  marshes,  where  it  is  produced  by 
the  decomposition  of  carbon  compounds  such  as  woody  fibre,  out 
of  contact  with  air,  at  the  bottom  of  stagnant  pools.  When  the 
mud  is  stirred,  the  marsh-gas  comes  to  the  surface  in  large  bubbles 
mixed  with  carbon  dioxide,  also  arising  from  the  decay  of  the 
organic  matter,  and  with  nitrogen  dissolved  in  the  water.  Methane 
is  also  known  as  "fire-damp"  by  miners,  and  occurs  in  coal  mines. 
When  the  pressure  of  the  atmosphere  diminishes,  as  shown  by  a 
*  Comptes  rend.,  97,  456. 


METHANE,   OR  MARSH-GAS.  499 

falling  barometer,  methane  issues  from  cracks  in  the  coal,  mixing 
with  the  air  of  the  mine,  and  forming  an  exceedingly  dangerous 
explosive  mixture,  by  the  ignition  of  which  many  lives  a  re  annually 
lost.  Methane  requires  for  complete  combustion  to  carbon  di- 
oxide and  water  twice  its  volume  of  oxygen,  corresponding  to 
approximately  ten  times  its  volume  of  air.  But,  in  order  to  fire 
such  a  mixture,  the  temperature  must  be  high.  Sir  Humphrey 
Davy  took  advantage  of  this  fact  in  his  invention  of  the  "  Davy 
Safety  Lamp,"  an  oil  lamp  completely  surrounded  with  copper 
gauze  ;  the  copper  conducts  away  the  heat,  so  that,  even  if  a  mix- 
ture of  methane  and  air  penetrates  to  the  interior  of  the  lamp,  the 
heat  it  evolves  is  distributed  over  a  considerable  mass  of  copper, 
and  the  temperature  is  thereby  lowered  below  the  point  of  ignition 
of  the  mixture  of  methane  and  air  in  the  mine.  When  such  com- 
bustion takes  place  in  the  interior  of  the  lamp,  however,  the  miner 
should  withdraw. 

Methane  issues  from  borings  in  the  ground,  in  the  vicinity  of 
the  oil-springs  of  Pennsylvania,  in  enormous  quantity,  and  it  is 
utilised  as  a  fuel. 

Methane  is  also  one  of  the  chief  constituents  of  coal-gas,  formed 
by  the  destructive  distillation  of  coal  ;  London  gas  contains  from 
35  to  42  per  cent,  by  volume. 

Preparation.  —  When  carbon  and  hydrogen  combine  directly 
in  the  intense  heat  of  the  arc-light,  they  form  not  methane,  but 
acetylene,  CZH2.  From  this  compound,  however,  methane  can  be 
produced  by  the  action  of  nascent  hydrogen. 

Methane  is  also  obtainable  by  double  decomposition.  1.  When 
a  mixture  of  hydrogen  sulphide  and  carbon  disulphide  vapour, 
produced  by  passing  a  current  of  the  former  through  a  wash-bottla 
containing  liquid  carbon  disulphide,  is  led  through  a  red-hot  tube 
of  hard  glass  filled  with  copper  turnings,  the  copper  withdraws 
sulphur,  and  hydrogen  and  carbon  combine,  thus  :  — 

2HZS  +  G82  +  8Cu  =  4CU2S  +  CHi. 

2.  Pure  methane  is  formed  by  the  action  of  water  or  am- 
monia on  zinc-  methyl  (see  p.  503)  ;  the  zinc  is  converted  into 
hydroxide  or  into  zinc-amide,  and  its  place  is  filled  by  hydrogen, 
thus  :  — 

Zn(CH3)2  +  2H20  =  Zn(OH)2  +  2CH,  • 
Zn(CH3)2  +  2NH3  =  Zn(NH2)2 


The  decomposition  of  a  mixture  of  sodium  acetate  and  hydr- 
oxide by  heat  also  yields  impure  methane.     It  is  better  to  sub- 

2  K  2 


500  THE   BORIDES,   CARBIDES,   AND    SILICIDES. 

stitute  for  pure  caustic  soda,  "soda-lime,"  produced  by  slaking 
lime  with  caustic  soda  solution.  Sodium  acetate  may  be  regarded 
as  sodium  carbonate,  one  sodoxyl  group  ( — ONa)  of  which  is  re- 
placed by  methyl,  i.e.,  methane  minns  an  atom  of  hydrogen.  When 
heated  with  sodium  hydroxide,  its  sodoxyl  replaces  the  methyl- 
group,  which  combines  with  the  hydrogen  of  the  caustic  soda, 
forming  methane,  thus  :  — 

CH3— CO.ONa  +  H— ONa  =  CH,  +  CO<ONa 

A  flask  of  hard  glass  should  be  used,  and  the  mixture  of  acetate 
and  soda-lime  should  be  thoroughly  dried  before  it  is  placed  in  the 


Properties. — Methane  is  a  colourless  gas,  without  smell, 
almost  insoluble  in  water.  When  pure  it  burns  with  a  non- 
luminous  flame.  It  decomposes,  when  strongly  heated,  into 
other  hydrocarbons  and  hydrogen.  It  is  unattacked  by  acids 
or  alkalies ;  with  chlorine  in  direct  sunlight,  however,  it  gives  a 
series  of  substitution -products,  in  which  one,  two,  three,  or  four 
atoms  of  hydrogen  are  successively  replaced  by  chlorine.  The 
names  and  formulae  of  these  bodies  are  as  given  below  : — 

Chloromethane,  or  methyl  chloride,  CH^Cl; 
Dichloromethane,  or  methylene  dichloride,  CH2C12  ; 
Trichloromethane,  or  chloroform,  CHC13 ; 
Tetrachloromethane,  or  carbon  tetrachloride,  CC14. 

These  bodies  may  have  their  chlorine  replaced,  atom  by  atom, 
by  the  action  of  nascent  hydrogen,  yielding  methane  as  a  final 
product.  The  existence  of  this  series  of  compounds  strongly 
corroborates  the  conclusions  drawn  from  the  vapour-density  of 
methane,  that  it  contains  four  atoms  of  hydrogen,  inasmuch  as  its 
hydrogen  is  replaceable  in  fourths. 

Methane  boils  at  —164°,  and  solidifies  to  a  white  snow-like 
mass  about  — 185'8°. 

Hydrogen  silicide,  SiH^  the  corresponding  compound  to 
methane,  is  also  a  colourless  gas.  It  does  not  occur  free  in 
nature. 

Preparation. — 1.  By  direct  combination. — Nascent  hydro- 
gen, evolved  by  electrolysing  a  solution  of  common  salt  by  a 
battery,  the  negative  pole  of  which  consists  of  aluminium  contain- 
ing silicon,  unites  with  the  silicon,  and  spontaneously  inflammable 
bubbles  of  hydrogen  containing  hydrogen  silicide  are  evolved 
2.  By  double  decomposition. — Magnesium  silicide,  produced 
by  heating  to  redness  magnesium  powder  and  sand  in  a  small 
crucible,  is  treated  with  dilute  hydrochloric  acid.  The  magnesium 


HYDEOGEN   SILICIDES  ;    ETHANE.  501 

silicide  yields  magnesium  chloride  and  siliciuretted  hydrogen,  as 
hydrogen  silicide  is  often  called,  thus  : — 

Mg2Si  +  4HCl.Aq  =  H,8i  +  2MgCl2.Aq.    (Compare  BH3,  p.  497.) 

This  forms  a  convenient  lecture  experiment. 
A  third  method  is  to  heat  the  compound  SiH(OC2H5)3  with, 
sodium,  which  is  itself  unchanged,  but  which  induces  the  follow- 
ing decomposition  :— 4SiH(OC2H5)3  =  SiH*  +  3Si(OC2H5)3. 

Properties. — Hydrogen  silicide  is  a  colourless,  spontaneously 
inflammable  gas,  insoluble  in  water,  burning  to  water  and  silica. 
It  also  burns  in  chlorine,  producing  hydrogen  and  silicon  chlorides. 
It  is  decomposed  at  400°  into  amorphous  silicon  and  hydrogen.  It 
liquefies  under  a  pressure  of  50  atmospheres  at  —11°,  70  atmo- 
spheres at  —5°,  and  100  atmospheres  at  —1°. 

A  liquid  compound  analogous  to  chloroform,  of  the  formula 
SiHCl3,  is  produced  by  heating  silicon  to  redness  in  a  current  of 
hydrogen  chloride.  It  boils  at  55 — 60°.  With  water,  it  yields 
SiH2O3,  or  silicoformic  anhydride.  The  corresponding  iodide  is 
also  known ;  it  boils  at  220°. 

Ethane,  C2H6. — When  methyl  iodide,  CH3I,  is  treated  with 
sodium,  sodium  iodide  and  di-methyl  or  ethane  is  produced, 
thus : — 

CH3|I ~"Naj  Na    I|CH3,  or  2CH3I  +  2Na  =  2NaI  +  G2H6. 

From  this  synthesis  it  is  argued  that  the  constitution  of  ethane 
is  represented  by  the  formula  H3C — CH3.  This  compound  differs 
in  formula  from  methane  by  containing  the  group  (CH2)  in 
addition ;  and  many  other  hydrocarbons  are  known  of  the  general 
formula  CnH2«+2.  To  treat  of  such  compounds  is  the  province  of 
Organic  Chemistry  ;  but  it  may  be  here  stated  that  such  a  series 
of  compounds  is  termed  a  homologous  series.  Thus  we  have  : — 
Methane,  CH± ;  ethane,  CZR6 ;  propane,  C^Es ;  butane,  C^HW  • 
pentane,  C5H^  and  so  on.  Like  methane,  ethane  is  a  colourless 
insoluble  gas,  devoid  of  taste  or  smell;  it  issues,  along  with 
methane,  from  the  soil  in  parts  of  Pennsylvania. 

Hexahydrogen  disilicide,  or  silicon-ethane,  Si2H6. — When 
an  electric  discharge  is  passed  through  hydrogen  silicide,  a  yellow 
compound  encrusts  the  tube,  having  the  composition  of  silicon- 
ethane.  It  burns  in  the  air,  and  ignites  on  percussion ;  like  the 
tetrahydride,  it  burns  in  chlorine.*  This  compound  is  analogous 
to  the  hexachloride  described  on  p.  151,  and  its  formula  is  deduced 
by  analogy,  for  its  molecular  weight  is  unknown.  No  other  mem- 

*  Comptes  rend.,  89,  1068. 


502  THE   BORIDES,   CARBIDES,  AND   SUICIDES. 

her  of  the  homologous  series  is  known  with  silcon,  but  a  com- 
pound containing  both  carbon  and  silicon,  named  silico-nonane, 
has  been  produced  by  treating  zinc  ethyl  (see  p.  503),  Zn(C2H5)2, 
with  silicon  tetrachloride.  Its  formula  is  Si(C2H5)4,  and  it  is  note- 
worthy as  the  analogue  of  the  corresponding  carbon  compound 
nonane,  C9H2o. 

For  other  compounds  displaying  analogy  between  carbon  and 
silicon,  a  text-book  of  Organic  Chemistry  must  be  consulted. 

Double  compounds  of  methyl  and  ethyl  ;  "  Organo- 
metallic  compounds."  —  This  name  is  given  to  compounds  in 
which  the  metallic  elements  replace  the  hydrogen  of  methane, 
ethane,  and  similar  hydrocarbons  ;  or  they  may  be  regarded  as 
compounds  of  groups  such  as  (CH3)',  methyl,  or  (C2H5y,  ethyl, 
with  the  elements.  As  these  compounds  are  usually  capable  of  exist- 
ence in  the  gaseous  state,  and  as  their  vapour-densities  are,  as  a 
rule,  known,  they  are  well  adapted  to  throw  light  on  the  formulae 
of  other  compounds  of  the  elements.  They  will  be  considered  in 
their  order. 

Preparation.  —  1.  By  the  action  of  methyl  or  ethyl  iodide 
(iodomethane,  or  iodoethane),  CH3I,  or  C2H5T,  on  the  elements, 
or  on  their  alloys  with  potassium  or  sodium,  thus  :  — 

ZnNa2  +  2C2H5I  =  Zn(C2H5)2  +  2NaI  ; 
SbK3  +  3C2H5I  =    Sb(C2H5)3  +  SKI. 

2.  By  heating  the  halides  of  some  elements  with  zinc- 
ethyl,  Zn(C2H5)2,  thus  :— 

HgCl2  +  Zn(C2H5)2  =  Hg(C2H5)2  +  ZnCl3; 
Sn(C2H5)2I2  +  Zn(C2H5)2  =  Sn(C2H5)4  +  ZnI2. 

3.  By  replacing  zinc  in  zinc-ethyl  by  another  metal  by 
direct  action,  e.g.  :— 

Zn(C2H5)2  +  2Na  =  2Na(C2H5)  +  Zn. 


Properties.  —  These  compounds  are  colourless  or  yellow  liquids 
with  nauseous  smell,  heavier  than  water,  and  with  few  exceptions 
(Bi(C2H5)3,  Pb2(C2H5)6,  and  Sn2(C2H5)4),  volatile  without  decom- 
position at  comparatively  low  temperatures.  Hence  their  vapour- 
densities  have  in  most  cases  been  determined.  They  are  almost 
all  decomposed  by  water,  yielding  the  hydroxide  of  the  element 
and  ethane,  thus  :—  Zn(C2H5)2  +  2H.OH  =  Zn(OH)2  +  2GZH6. 
Most  of  them  react  energetically  with  oxygen,  and  inflame  spon- 
taneously in  air.  By  cautious  oxidation  they  yield  either  organo- 


COMPOUNDS   OF  METHYL  AND   ETHYL.  503 

metallic  oxides  or  double  oxides  of  metal  and  ethyl  or  methyl,  for 
example:— Sb(C2H5)3  +  O  =  O=Sb(C2H5)3;   Sn2(C2H5)6  +  O  = 

^^S    fCH^3'    zin(>etnyl   gives   a   double   oxide,    named   zinc- 

ethylate  or  ethoxide,  thus:— Zn(C2H6)2  +  2O  =  Zn(OC2H5)2. 

In  many  cases  they  form  addition-products  with  halogens,  as 
for  example,  Sb(C2H5)3  +  la  =  I2Sb(C2H5)3 ;  in  other  instances, 
the  compound  is  split,  forming  an  iodide  of  the  organo-metal  and 
ethyl  iodide,  thus  : — 

Hg(C2H5)2  +  I2  =  I.Hg.C2H5  +  C2H5I ; 
(C2H5)3Sn-Sn(C2H5)3  +I2  =  2ISn(C2H5)3. 

But  halogen  compounds,  if  they  contain  two  atoms  of  halogen, 
yield  oxides  on  treatment  with  hydroxides  of  the  alkalies;  for 
example,  I2Sn(C2H5)2  yields  O=Sn(C2H5)2 ;  and  the  compounds 
OSn2(C2H5)6,  and  O=Sb(C2H5)3,  are  produced  by  direct  oxida- 
tion. 

Hydroxides  are  similarly  produced  from  the  monohalides, 
thus :— C2H5HgI  +  KOH.Aq  =  KI.Aq  +  C2H5.Hg.OH ;  and, 
similarly,  (C2H5)3T1.OH,  (C2H5)3Sn.OH,  and  (C2H5)4Sb.OH 
have  been  prepared.  These  are  soluble  compounds,  which,  on  treat- 
ment with  acids  form  definite  salts,  such  as  nitrate,  C2H5.Hg.ONO2 ; 
sulphate,  {(C2H5)2T10}2SO2,  &c. 

List. — Na(C2H5)  ;  K(C2H5)  ;  these  bodies  have  been  produced 
only  in  combination  with  zinc  ethyl,  by  acting  on  that  substance 
with  metallic  sodium  or  potassium.  The  compounds  have  the 
formulae  Na(C2H5).Zn(C2H5)2,  and  K(C2H5).Zn(C2H5)2,  and  con- 
sist of  large  clear  crystals. 

Be(C2H5)2;  from  beryllium  and  mercury  ethyl,  Hg(C2H5)2, 
b.  p.  287°. 

Mg(C2H5)2 ;  from  magnesium  and  ethyl  iodide.     Not  volatile. 

Zn(CH3)2  (b.p.46°),  and  Zn(C2H5)2  (b.  p.  118°) ;  from  an  alloy 
of  zinc  and  sodium  and  the  respective  iodide. 

B(C2H5)3  (b.  p.  95°)  ;  from  boron  trichloride  and  zinc  ethyl. 
This  body  is  analogous  to  hydrogen  boride  ;  with  oxygen  it  yields 
the  ethyl  salts  of  ethyl  boracic  acid,  C2H5.B(OC2H5)2,  and  of 
diethyl  boracic  acid,  (C2H5)2.B(OC2H5).  These  substances  are 
more  easily  produced  by  the  action  of  zinc  ethyl  on  ethyl  borate, 
B(OC2H5)3,  formed  by  the  action  of  ethyl  hydroxide  (ordinary 
alcohol)  on  boron  trichloride,  thus  : — 

JSC13  -f  3CoH5OH  =  B(OC2H5)3  +  ZHCL 
The  reactions  of  this  substance  with  zinc  ethyl  are  as  follows : — 


504  THE  BORIDES,   CARBIDES,  AND   SILICIDES. 

B(OC2H5)3  -f  Zn(C2H5)2  =  B<  +  Zn<  ;  and 


•R^25  f7nfc^  TT  ^k    .- 

*<(OC2H5)2  +  ^n  (OC2H5)  . 

The  analogy  of  the  compound  Zn(OC2H5)2,  also  known,  with 
the  hydroxides,  will  be  perceived. 

On  treatment  of  ethyl  borate  of  ethyl,  and  of  diethyl  borate  of 
ethyl  with  water,  ethyl  and  diethyl  boracic  acids  are  produced, 
thus  :  — 


These  compounds,  it  will  be  noticed,  are  the  analogues  of  com- 
pounds occupying  an  intermediate  position  between  boron  hydride 

and   hydroxide,    such   compounds   being   incapable   of   existence, 

TT  -Fl- 

owing to  their  instability,  thus  :~B<J/:r\     and  B<JT  ;   and, 


P  TT 

similarly,  the  compound  Zn<%Ap5TT  \   is    analogous  to   a   mixed 

hydride  and  hydroxide,  H  —  Zn  —  OH. 

A1(CH3)3;  A1(C2H5)3;  A12(CH3)6;  A12(C2H5)6.—  A  great  deal 
of  interest  attaches  to  these  compounds.  They  are  produced  by 
the  action  of  metallic  aluminium  on  mercury  methide  or  ethide. 
The  methide  boils  at  130°  ;  the  ethide  at  194°. 

The  first  point  which  a  study  of  their  vapour-densities  is  able 
to  decide  is  the  precise  constitutional  formulae  of  the  halides  of 
such  elements  as  aluminium,  chromium,  iron,  &c.  We  have 
seen,  on  page  143,  that  while  dichloride  of  chromium,  in  the 
state  of  gas,  appears  to  exist  partly  as  CrCl2,  at  1600°  its  high 
vapour-  density  shows  the  presence  of  molecular  aggregates,  prob- 
ably of  the  complexity  Cr2Cl4.  Iron  dichloride,  at  1400  —  1500°, 
possesses  the  simple  formula  FeCl2.  Chromic  chloride,  about  1060°, 
has  the  simple  formula  CrCl3,  while  ferric  chloride,  below  620°, 
has  a  complex  formula,  probably  Fe2Cl6,  but  at  higher  temperatures 
(750°  and  upwards)  it  has  the  simpler  formula  FeCl3.  The 
densities  of  aluminium  halides,  and  their  bearing  on  the  molecular 
weights  of  these  compounds,  has  been  discussed  on  p.  135,  with 
similar  conclusions. 

Precisely  similar  results  are  obtained  with  the  methide  and 
ethide  of  aluminium.  The  following  tables  give  a  summary  of  the 
results  obtained  :  — 


CONSTITUTION  OF  THE  ETHIDES  AND   HALIDES.  505 

Ethide.—Temperatures:  —  234°        235°        258°        310°        350° 
Densities:—        65'1(?)    121  (?)     87'4        36'2        36'2 

The  theoretical  density  of  the  compound  A1(C2H5)3  is  57,  and 
of  A12(C2H5)6  is  114. 

Methide.—  Temperatures  :—  130°          163°          220°          240° 
Densities:—         63'1          59'3          40'7          40'5 

Theoretical  density  of  A1(CH3)3,  36'0  ;  of  A12(CH3)6,  72. 

Two  different  sets  of  observers  are  responsible  for  the  densities 
of  the  ethide  at  234°,  viz.,  Gay-Lussac,  and  Buckton  and  Odling  ; 
and  at  235°,  Victor  Meyer,  and  Louise  and  Roux.  At  310°  and 
350°  the  substance  is  wholly  decomposed.  All  that  can  be 
gathered  from  these  results  is  that,  at  low  temperatures,  the 
formula  appears  to  be  Al2(C2H5)6,  and  at  higher  temperatures,  the 
molecular  formula  is  a  simpler  one.  With  the  methide  the  results 
show  more  symmetry.  The  density  at  130°,  63'1,  approaches  the 
theoretical  density  of  A12(CH3)6,  and  at  240°,  the  number  40*5  is 
not  far  removed  from  36,  the  density  of  A1(CH3)3.  These  results 
generally  confirm  those  obtained  with  the  chloride,  given  on  p.  135  ; 
and  it  may,  consequently,  be  concluded,  that  at  high  temperatures 
all  these  bodies  have  the  simpler  formulae,  and  at  lower  tempera- 
tures, more  complex  formulae,  probably  due  to  association  of  two 
simpler  molecules. 

But  a  second  question  arises,  which  involves  a  point  of  extreme 
theoretical  importance.  It  is  :  What  is  the  nature  of  the  com- 
bination which  exists  in  the  double  molecular  formulae  ?  To  this 
question  there  are  three  possible  answers. 

First,  from  analogy  with  the  carbon  compounds  C2H6  and  C2C16, 
the  former  of  which  betrays  its  constitution  by  its  synthesis  from 
methyl  iodide  and  sodium  (p.  501)-,  such  compounds  as  A12C16, 
A12(C2E[5)6,  &c.,  may  be  regarded  as  thus  constituted  :  — 

C13A1—  A1C13. 

Second.  The  complex  halides,  A12C16,  &c.,  may  be  regarded  as 
analogous  to  double  halides,  such  as  have  been  discussed  on 

C1=C1 
p.  496,   constituted  thus  :   Al(-Cl=Cl-^Al. 


Third.  They  may  be  regarded  as  purely  additive  compounds, 
groups  such  as  A1C13  being  capable  of  associating  in  twos,  threes, 
&c. 

The  second  hypothesis  may  be  at  once  disposed  of  by  noticing 
that  such  a  constitution  as  (A1C13)(C13A1)  is  completely  excluded, 
from  the  fact  that  no  such  formula  can  be  applied  to  the  methides 


506  THE  BORIDES,  CARBIDES,  AND   SILICIDES. 

and  ethides,  for  the  ethyl  and  methyl  groups  have  no  further 
power  of  combination  ;  no  addition  compounds  of  methane  and 
ethane  are  known.  This  of  itself  forms  a  strong  argument 
against  the  proposed  graphic  formulae  for  the  halides,  mentioned 
on  p.  496.  Hence  we  are  confined  to  the  first  and  third  hypo- 
theses. Against  the  first,  which  looks  plausible  from  the  analogy 
between  A12C]6  and  C2C16,  it  may  be  urged  that  while  compounds 
of  carbon,  in  which  it  functions  as  a  tetrad,  as  in  CH4,  CC14,  &c., 
are  the  rule,  such  compounds  of  aluminium  are  wholly  unknown. 
Moreover,  none  of  the  elements  of  the  aluminium  group  form  such 
compounds  ;  those  of  manganese,  which  presents  some  slight 
analogy  with  aluminium,  such  as  MnF4,  are  exceedingly  unstable. 

We  are,  therefore,  obliged  to  accept  the  third  hypothesis  that 
two  classes  of  chemical  compounds  can  exist  ;  the  substitutive,  of 
which  we  have  had  many  examples,  and  the  additive.  It  is  im- 
possible to  class  compounds  containing  water  of  crystallisation 
otherwise  than  as  additive  compounds,  and  there  appears  no 
reason  to  believe  that  double  halides  are  otherwise  constituted. 
Moreover,  the  uncertainty  attaching  to  molecular  formulae,  such  as 
A12C16,  which  appear  to  be  constant  over  a  very  small  range  of  tem- 
perature, and  the  consideration  of  the  molecular  weight  of  hydro- 
gen fluoride,  and  similar  bodies,  would  lead  to  the  supposition  that 
the  molecular  aggregation  is  not  necessarily  restricted  to  that  of 
twice  the  simpler  molecule.  But  these  considerations  should  not 
lead  us  to  exclude  substitutive  formulae,  for  which,  as  has  been 
shown  repeatedly,  we  have  abundant  evidence;  it  would  merely 
lead  to  the  conclusion  that  it  is  impossible  to  represent  all  forms 
of  chemical  combination  by  their  aid. 

Si(C2H5)4,  from  SiCl4  and  Zn(C2H5)2,  and  the  derivatives, 
ClSi(C2H5)3,  Cl2Si(C2H6)2,  Cl3Si(C2H5),  confirm  and  exemplify  the 
compounds  SiH4,SiHCl3,  and  SiCl4.  Besides  these,  the  existence  of 
compounds 

Si(OC2H5)4;  0=Si<25;  0=Si(C2H5)2;  and  HO—  Si(C2H5)3, 


justify  the  views  expressed  on  p.  306,  regarding  the  constitution 
of  orthosilicic  acid. 

Si2(C2H5)6,  from  disilicon  hexiodide  Si2I6,  and  zinc  ethyl,  con- 
firms the  formula  of  the  hexahydride,  Si2H6,  and  renders  likely 
the  suggested  formulae  for  the  polysilicic  acids,  described  on 
p.  307. 

The  compounds  of  tin,  Sn(C2H5)4,  from  SnCl4  and  Zn(C2H5)2, 
or  from  Sn(C.H5)2I  and  Zn(C2H5)2;  Sn2(C2H5)6,  from  an  alloy  of 


ETHYLENE,   OR  OLEFIANT   GAS.  507 


tin  and  sodinra  in  the  proportion  expressed  by  the  formula 
and  zinc  ethyl  ;  and  of  Sn2(C2H5)4,  from  an  appropriate  alloy  by 
the  same  reaction,  confirm  the  relationship  between  silicon  and 
tin.  The  last  compound  is  analogous  to  the  chloride, 

=Cl2, 


in  the  state  of  vapour  at  low  temperatures. 

The  relations  of  lead  to  silicon  and  tin  are  exemplified  by  the 
existence  of  the  compounds  Pb(C2H5)4,  and  Pb2(C2H5)6. 

It  will  be  remembered  that  lead  tetrachloride  is  a  very  unstable 
compound,  and  that  diplumbic  hexachloride  is  unknown  (see 
p.  153). 

The  similar  compounds  of  the  nitrogen  and  phosphorus  groups 
will  be  alluded  to  later,  in  discussing  the  nitrides  and  phosphides 
of  hydrogen. 

Lastly,  dyad  compounds  of  mercury,  Hg(CH3)2,  Hg(C2H5)2,  and 
others,  are  known,  the  vapour-densities  of  which  establish  the 
formulae  of  the  dihalides  of  mercury,  although  it  is  not  improbable 
that  the  latter  may  have  more  complex  formulae  in  the  solid 
state. 

Ethylene,  C2H4.  —  Like  methane,  this  hydrocarbon  forms  the 
first  member  of  a  homologous  series  ;  it  is  termed  the  olefine 
series,  from  the  old  name  for  ethylene,  "  olefiant  gas,"  due  to  the 
fact  that  ethylene  and  chlorine  combine  directly  to  form  a  dichlo- 
ride,  C2H4C12,  which  is  an  oily  body. 

Preparation.  —  Ethylene  is  one  of  the  products  of  the  distilla- 
tion of  wood  and  coal,  being  probably  formed  by  the  action  of 
heat  on  methane,  thus  :  —  2C  JJ*  =  (72ff4  +  2HZ.  It  is  usually  pre- 
pared by  the  action  of  sulphuric  acid  on  alcohol  (ethyl  hydroxide), 
C2H5.OH.  The  first  action  is  the  formation  of  hydrogen  ethyl 
sulphate,  HO—  S02—  OC2H5,  thus  :—  C2H5OH  +  HO—  S02—  OH 
=  HO  —  S02  —  OC2H5  +  H20.  On  raising  the  temperature,  the  sul- 
phate is  decomposed,  thus  :—  HO—  SO2—  OC2H5  =  HO—  S02—  OH 
+  (72£T4.  The  operation  should  be  performed  with  a  large  excess 
of  sulphuric  acid  in  a  large  flask,  for  the  mixture  is  very  apt  to 
froth  up.  Ethylene  and  homologous  hydrocarbons  are  also  formed 
by  the  action  of  acids  on  carbide  of  iron,  or  cast  iron  ;  this  mode 
of  formation  is  analogous  to  that  by  which  hydrogen  bo  ride  and 
silicide  are  prepared. 

Properties.  —  Ethylene  is  a  colourless  gas,  without  odour, 
almost  insoluble  in  water.  It  may  be  condensed  to  a  liquid  boiling 
at  -102-3°,  and  when  frozen  it  is  a  solid  melting  at  —169°.  It 


508  THE  BORIDES,   CARBIDES,  AND   SILICIDES. 

combines  directly  with  the  halogens,  forming  oily  bodies,  which 
may  be  regarded  as  substitution  products  of  ethane,  C2H6.  From 
this  and  other  reactions  it  is  assumed  that  the  formula  of  ethylene 
is  H2C=CH2,  analogous  to  the  Cl2Sn=SnCl2,  and  other  similar 
compounds. 

Ethylene  burns  with  a  luminous  flame,  and  is  one  of  the  con- 
stituents of  coal-gas  which  cause  it  to  burn  brightly.  The  lumi- 
nosity is  due  to  the  presence  of  solid  white-hot  particles  of 
carbon.  That  this  is  the  case  is  proved  by  the  fact  that  solar 
light  reflected  from  a  candle  or  coal-gas  flame  shows  when  viewed 
through  the  spectroscope  its  characteristic  vertical  black  lines ; 
now  gases  cannot  reflect  light,  hence  the  presence  of  a  solid  in 
the  flame  is  demonstrated.  By  mixing  with  excess  of  air,  so  as  to 
supply  sufficient  oxygen  to  wholly  consume  the  carbon  within  the 
flame,  a  non-luminous  and  hotter  flame  is  obtained ;  this  is  the 
principle  of  the  Bunsen's  burner,  so  necessary  in  our  labora- 
tories. 

Acetylene,  C2H2. — This  hydrocarbon  is  formed  along  with 
ethylene  during  the  distillation  of  wood,  coal,  &c.,  and  hence  it 
forms  one  of  the  constituents  of  coal-gas.  It  has  been  prepared 
by  exposing  methane  or  ethylene  to  a  red  heat,  probably  according 
to  the  equations :— 2  (7fl~4  =  GZHZ  +  3H2;  C^  =  CZH2  +  Hz. 
One  of  the  easiest  methods  of  preparing  acetylene  is  to  partially 
burn  methane ;  or  coal-gas,  the  methane  in  which  is  sufficient  for 
the  purpose.  When  a  Bunsen's  burner  "burns  below,"  a  disagree- 
able smell  is  perceived,  due  to  this  gas.  It  may  be  still  more 
conveniently  prepared  by  burning  air  in  coal-gas,  by  means  of  the 
arrangement  shown  in  Fig.  44.  The  air  enters  by  a  small  tube 
into  an  atmosphere  of  coal-gas,  where  it  burns  in  excess  of  the 
latter.  The  acetylene  is  drawn  off  by  means  of  an  aspirator  and 
after  being  cooled  it  is  passed  through  an  ammoniacal  solution  of 
cuprous  chloride,  with  which  it  reacts,  forming  a  red  insoluble 
compound. 

It  is  also  formed  by  the  direct  union  of  carbon  with  hydrogen 
at  an  intensely  high  temperature,  produced  by  the  electric  arc  in 
an  atmosphere  of  hydrogen. 

Acetylene  is  a  colourless  gas  with  a  disagreeable  smell;  it 
liquefies  at  1°  under  a  pressure  of  48  atmospheres.  It  unites 
directly  with  chlorine,  &c.,  forming  a  tetrachloride,  and  it  is  there- 
fore concluded  that  it  possesses  the  constitutional  formula 
HC=CH.  When  passed  over  heated  sodium,  one  or  both  atoms 
of  hydrogen  are  replaced  by  the  metal,  forming  HCEECNa  and 
NaCEECNa,  solid  bodies  which  on  treatment  with  water  at  once 


HYDROCARBONS. 


509 


yield  sodium  hydroxide  and  acetylene,  thus  : — HC:r=CNa  +  HOH 
=  HCEECH  +  NaOH.  With  ammoniacal  solutions  of  cuprous  or 
argentous  chloride  it  yields  red  or  yellowish -white  precipitates 

FIG.  44. 


of  H— C=C— Cu— CuOH  and  H— Cz=C — Ag,  which  are  ex- 
ceedingly explosive  when  dry,  and  which,  on  treatment  with  acids, 
yield  acetylene,  e.g.,  H— C=C— Ag  +  ClH.Aq  =  H—C^C—H 
4-  AgCl  +  Aq.  Homologues  of  acetylene  are  also  known  which 
give  similar  metallic  compounds. 

This  scanty  notice  of  the  hydrocarbons  must  here  suffice. 
Enough  has  been  said  to  show  the  relations  of  these  bodies  to 
the  silicon  compounds,  and  to  throw  some  light  on  the  nature 
of  the  compounds  of  other  elements.  The  hydrocarbons  may  be 
termed  the  "  elements  "  of  Organic  Chemistry,  and  their  deriva- 
tives are  as  numerous  as,  and  more  complex  than,  those  of  almost 
all  other  elements  together. 

The  remaining  carbides  and  silicides  have  been  little  investi- 
gated, but  appear  worthy  of  more  careful  study. 


510  THE   BORIDES,   CARBIDES,   AND   SILICIDES. 

Iron  carbide  exists  in  pig-iron,  the  crude  iron  produced  by 
smelting  iron  ore  in  a  blast  furnace  with  coal  and  lime.  The 
greater  part  of  the  carbon  is,  however,  uncombined.  If  finely- 
divided  iron  be  kept  fused  with  charcoal  in  a  crucible  until  it  has 
united  with  its  maximum  of  carbon,  a  dark-grey  mass  is  obtained, 
exceedingly  brittle,  and  containing  94*36  per  cent,  of  iron  and 
5'64  per  cent,  of  carbon.  Dividing  94'36  by  the  atomic  weight  of 
iron,  56*02,  and  5'64  by  12'0,  the  atomic  weight  of  carbon,  the 
ratio  of  the  number  of  atoms  of  iron  to  that  of  carbon  is  ascer- 
tained ;  it  is  T68  Fe  to  0'47  C.,  or  approximately  Fe7C2,  which 
would  require  5' 7  per  cent,  of  carbon. 

Some  specimens  of  pig-iron  when  broken  are  seen  to  have  a 
grey,  and  some  a  white  colour.  The  grey  specimens  contain  car- 
bide of  iron  and  free  carbon,  for  when  treated  with  acid,  carbon  is 
left  in  the  form  of  graphite,  while  hydrocarbons  like  ethylene, 
CzHt,  are  evolved.  From  this  it  may  perhaps  be  concluded  that 
the  carbide  of  iron  present  has  the  formula  Fe2C2,  corresponding 
to  C2H4.  But  such  a  body  has  not  been  obtained.  The  amount  of 
"  combined  carbon  "  in  white  pig-iron  is  about  2*5  per  cent.,  and 
of  graphite  0*9  per  cent.,  and  in  grey  pig-iron  the  "  combined 
carbon  "  amounts  to  about  1*0  per  cent.,  and  the  graphite  to  2'6 
per  cent.  If  the  iron  contains  manganese,  its  capacity  for  retain- 
ing carbon  in  combination  is  much  increased.  An  iron  containing 
10  per  cent,  of  manganese  retains  as  much  as  4  per  cent,  of  car- 
bon in  chemical  combination,  and  is  known  as  "  spiegel  iron." 
Steel  is  also  a  mixture  of  iron  with  its  carbide.  If  the  proportion 
of  carbon  does  not  exceed  0'3  per  cent.,  the  steel  is  comparatively 
soft;  if  it  contain  from  TO  to  1'2  per  cent.,  the  steel  is  hard,  and 
is  employed  for  cutting  instruments ;  1'4  cent,  of  combined  carbon 
renders  it  like  white  cast  iron,  more  fusible,  and  very  brittle. 

The  effect  of  adding  silicon  to  iron  is  to  modify  its  proper- 
ties very  considerably.  Samples  have  been  obtained  containing 
as  much  as  10  per  cent,  of  silicon,  but  the  iron  has  at  the  same 
time  contained  1'12  per  cent,  of  free  carbon  and  0'69  per  cent,  of 
combined  carbon,  besides  phosphorus,  manganese,  and  sulphur. 
"  Silicon  pig,"  as  this  mixture  is  termed,  forms  better  castings 
than  ordinary  cast  iron.  The  best  results,  most  free  from  air-holes, 
are  obtained  with  from  1*5  to  3  per  cent,  of  silicon.  The  iron  is 
usually  bluish,  and  has  a  close-grained  fracture,  but  with  10  per  cent, 
of  silicon  the  colour  is  nearly  white,  and  the  fracture  shows  large 
silvery  facets.  No  definite  compound  has,  however,  been  isolated. 

Like  iron,  nickel  unites  with  carbon,  forming  a  brittle  carbide 
of  unknown  formula. 


CARBIDES   AND    SILICIDES.  511 

Compounds  of  tin  and  lead  with  silicon  appear  to  be  formed 
y  direct  union. 

On  dissolving  a  large  amount  of  pig-iron  containing  titanium 
in  dilute  hydrochloric  acid,  a  number  of  minute  cubes  with  metal- 
lic lustre  were  obtained,  having  the  composition  TiC. 

A  carbide  of  palladium  is  produced  by  fusing  palladium  in 
a  crucible  filled  with  lampblack.  It  is  so  brittle  that  if  struck 
with  a  hammer  when  red-hot  it  falls  to  powder  and  gives  off  a 
white  fume.  A  piece  of  palladium  heated  in  an  alcohol  flame 
unites  with  carbon  (?)  before  it  becomes  red-hot,  and  when  re- 
moved from  the  flame  it  glows  until  the  carbon  is  consumed. 
Iridium  behaves  similarly. 

Certain  carbon  compounds  containing  platinum  are  said  to  leave 
a  carbide  on  gentle  ignition.  It  may  be  a  mixture,  however,  for 
on  treatment  with  nitro-hydrochloric  acid  the  platinum  dissolves, 
leaving  carbon. 

Platinum  and  silicon  readily  combine,  forming  a  white  me- 
tallic looking  mass. 

Copper  and  silver  also  unite  with  silicon,  and  three  carbides 
of  silver  are  said  to  exist,  viz.,  Ag4C,  Ag3C,  and  AgC,  produced 
by  heating  certain  compounds  of  carbon  containing  silver.  Their 
existence,  however,  is  doubtful. 


512 


PART  VI.— THE  NITRIDES,  &c. 


CHAPTER  XXXI. 

NITRIDES,    PHOSPHIDES,    AKSENIDES,    AND    ANTIMONIDES     OF    HYDROGEN  : 
DOUBLE    COMPOUNDS  :    AMINES    AND   AMIDES. 

THE  compounds  of  nitrogen,  phosphorus,  arsenic,  and  antimony 
with  hydrogen  are  best  known.  Many  combinations  containing 
nitrogen  and  hydrogen  have  been  prepared ;  the  nitrides  of  the 
other  elements  are  but  little  investigated.  The  phosphides,  gene- 
rally produced  by  direct  union,  require  investigation.  A  con- 
siderable number  of  arsenides  and  antimonides  are  found  native. 

1.  Compounds  with  hydrogen;  hydrogen  nitrides  (am- 
monia  and  hydrazine),  phosphides  (phosphines),  arsenides 
(arsines),  and  antimonide  (stibine). 

List  :-- 

Nitrogen.  Phosphorus.  Arsenic.  Antimony. 

NHt',  NZH,.    PH3;  P2H4;  P4H2.     AsH,;  (AsH),.        8bHa. 

Sources. — Ammonia  occurs  in  the  atmosphere  in  very  small 
proportion  (3  or  4  parts  per  million) .  But  its  presence  is  essential 
to  the  life  of  plants,  and  indirectly  of  animals.  It  is  washed  down 
by  the  rain  into  the  soil,  whence  it  is  absorbed  as  food  by  vegeta- 
tion, probably  after  oxidation  to  nitrates.  It  is  produced  by  the 
putrefaction  of  nitrogenous  organic  matter,  especially  by  the 
decomposition  of  a  constituent  of  urine,  urea,  CON2H4,  under  the 
influence  of  a  ferment  named  bacillus  urece.  The  change  produced 
is  represented  thus  :— CON2H4  +  H20  =  002  +  2NH3.  Although 
it  is  exceedingly  soluble  in  water,  yet  it  is  retained  by  soil,  and 
is  available  for  plant-food.  Some  ammonia,  however,  is  washed 
down  by  streams,  and  hence  natural  water  always  contains  traces. 

Ammonium  chloride  is  found  encrusting  the  soil  in  the  neigh- 
bourhood of  volcanoes.  The  ammonia  prepared  from  this  source 
is  named  "  volcanic  ammonia." 

The  remaining  hydrides  do  not  occur  free  in  nature. 

Preparation. — By  direct  union. — Although  the  decomposi- 
tion of  ammonia  is  attended  by  absorption  of  heat,  showing  that 


HYDROGEN  PHOSPHIDES,   ARSENIDES,  AND  ANTIMONIDES.      513 

its  formation,  as  usual  in  the  case  of  stable  compounds,  should 
take  place  with  evolution  of  heat,  yet  there  is  insufficient  evidence 
that  ammonia  has  been  produced  by  direct  union  of  its  elements. 
But  if  one  of  the  two  constituent  elements  is  in  the  nascent  state, 
union  occurs.  This  may  be  effected  (1)  by  the  action  of  the 
induction  discharge  on  a  mixture  of  the  gases  ;  and  (2)  by  leading 
a  mixture  of  moist  hydrogen  and  nitrogen  over  red-hot  iron  filings. 
It  is  to  be  assumed  in  the  first  case  that  the  induction  discharge 
dissociates  molecules  of  nitrogen  and  of  hydrogen  into  atoms, 
which  then  combine  ;  and  in  the  second  that  a  hydride  or  nitride 
(most  probably  the  latter)  of  iron  is  formed,  which  is  then 
attacked  by  the  nitrogen  or  hydrogen.  In  both  cases,  however, 
mere  traces  are  produced.  (3.)  Moist  nitric  oxide  passed  over 
hot  iron  filings  yields  ammonia  ;  here  both  hydrogen  and  nitrogen 
are  nascent.  (4.)  By  the  action  of  nascent  hydrogen  from  zinc 
and  sodium  hydroxide  (see  p.  229)  on  oxygen  compounds  of 
nitrogen,  such  as  nitric  oxide,  nitrites,  or  nitrates. 

Hydrogen  arsenide  and  antimonide  are  also  obtained  by  this 
process.  A  solution  of  chloride  of  arsenic  or  antimony  is  placed  in 
a  flask  containing  hydrochloric  acid  and  pure  zinc.  The  nascent 
arsenic  or  antimony,  liberated  from  the  chloride,  unites  with  the 
nascent  hydrogen,  forming  arsenide  or  antimonide  of  hydrogen. 

2.  By  the  decomposition  of  their  compounds  by  heat. 
—  All  ammonium  and  phosphonium  salts  dissociate  when  heated, 
and  with  the  exception  of  the  nitrite,  nitrate,  chlorate,  and  a  few 
others,  they  yield  acid  and  ammonia.      Thus  ammonium  chloride 
yields  ammonia  and  hydrogen  chloride  ;  phosphonium  iodide,  phos- 
phine  and  hydrogen  iodide,  thus  :  — 

NH4C1  =  NH3  +  HCl;  PHJ  =  PH3  +  HI. 

Recombination  takes  place  on  cooling;  hence  this  process  cannot  be 
practically  applied. 

3.  By   double   decomposition.—  Nitrides  of    boron,  silicon, 
magnesium,  titanium,  &c.,  when  heated  in  a  red-hot  tube  in  a 
current  of  steam,  or  with  an  alkali,  yield  ammonia,  thus  :  — 


2BN  +  3HiO  =  B2O3  +  2NH3. 

Attempts  have  been  made  to  utilise  this  reaction,  but  without 
commercial  success. 

Hydrogen  phosphides,  arsenides,  and  antimonide  are  also 
similarly  produced  by  the  action  of  hydrochloric  acid  or  of  water 
on  phosphides,  arsenides,  or  antimonide  of  sodium  or  calcium. 
These  bodies,  prepared  by  direct  union  of  the  elements  in  the 

2  L 


514  THE  NITRIDES,   PHOSPHIDES,   ETC. 

desired  proportion,  undergo  a  change  such  as  this:  —  Na3As  + 
BHCl.Aq  =  3NaCl.Aq  +  AsHz. 

As  ammonia  does  not  combine  with  hydroxides  or  with  warm 
chlorides  of  sodium,  potassium,  calcium,  &c.,  it  is  usually  prepared 
by  heating  its  hydrochloride  (ammonium  chloride)  with  excess  of 
calcium  oxide,  or  with  caustic  soda,  thus  :  — 

NH;C1  +  NaOH  =  NH3  +  NaCl  +  TT20  ; 
2NH4C1  +  CaO  =  2NH3  +  CaCl2 


Similarly,  phosphine,  P-ET3,  may  be  produced  from  phosphonium 
iodide  and  a  caustic  alkali. 

4.  Hydrogen  phosphide,  PH9,  is  formed  when  phosphorus  is 
boiled  with  a  solution  of  potassium  or  sodium  hydroxide.  This 
may  be  regarded  as  a  union  of  the  phosphorus  both  with  the 
hydrogen  of  the  water,  forming  PH3l  and  with  oxygen,  the 
hydroxyl  and  hydrogen  forming  hypophosphorous  acid  ;  the  latter 
afterwards  may  be  supposed  to  react  with  the  alkali,  forming 
water  and  a  hypophosphite.  The  complete  reaction  is  — 

P4  -f-  3H20  +  3NaHO.Aq  '=  PHZ  -t-  3NaH2P02.Aq. 
It  may  be  regarded  as  occurring  in  the  two  stages  :  — 

P4  +  6H.OH  =  3H2PO(OH)  +  H3P  ; 
and       3H2PO(OH)  +  SNaOH.Aq  =  3H2PO(ONa).Aq  +  3HS0. 

(see  Hypophosphorous  Acid,  p.  380).  This  reaction  is  essentially 
analogous  to  that  of  sulphur  on  sodium  hydroxide  ;  only  in  this 
case  a  further  change  occurs,  whereby  sulphur  dioxide  and  hydro- 
gen sulphide  mutually  decompose  each  other,  yielding  sulphur, 
which  further  reacts  on  the  undecomposed  sulphite. 

Hypophosphorous  acid,  H3P02,  and  phosphorous  acid,  H3P03, 
when  heated,  yield  phosphoric  acid  and  hydrogen  phosphide.  It 
will  be  remembered  that  hypophosphorous  acid  is  probably  two- 
thirds  hydrogen  phosphide,  and  phosphorous  acid  one-third  hydro- 
gen phosphide,  thus  :  — 

H2=P(OH)     and     H—  P(OH)2. 

ii  H 

O  O 

When  heated,  these  bodies  decompose,  thus  :  — 

2H3P02  =  H3P04  +  PHZ;  4H3P03  =  3H3P04  +  PH3. 


5.  The  usual  source  of  ammonia  is  the  "  gas-liquor," 
produced  by  causing  coal  gas  to  pass  through  water  in  the 
"  scrubbers."  The  nitrogen  and  hydrogen  of  the  coal  unite, 


HYDRAZINE   AND   AMMONIA.  515 

forming  ammonia,  which  escapes  with  the  coal  gas,  but  is  retained 
in  the  water,  owing  to  its  high  solubility.  The  gas-liquor  is 
neutralised  with  hydrochloric  acid,  the  water  expelled  by  evapora- 
tion, and  the  ammonium  chloride  is  then  sublimed  in  hemi- 
spherical iron  pots,  covered  by  hemispherical  lids.  Ammonia  is 
produced  from  the  chloride  by  the  action  of  quicklime. 

6.  Hydrazine,  N^H^* — The  method  of  producing  this  sub- 
stance involves  the  use  of  carbon  compounds,  and  can  hardly  be 
understood  without  a  knowledge  of  their  nature  and  reactions. 
But,  for  completeness'  sake,  the  method  will  be  indicated  here. 

The  hydrochloride  of  ethyl  amidoacetate, 

NH2.CH2.COOC2H5.HC1, 

is  treated  with  a  solution  of  sodium  nitrite.  The  following  change 
takes  place : — 

KB2— CH2— COOC2H5.HC1  +  NaNO2.Aq  =  NaCl.Aq  +  2H20  + 
|t\CH.COOC2H6. 

The  last  compound,  diazoacetate  of  ethyl,  when  heated  with 
caustic  soda,  polymerises,  forming  a  triple  group,  while  the  ethyl 
group  is  replaced  by  hydrogen.  This  group,  on  treatment  with 
acids,  reacts  with  water,  forming  oxalic  acid  and  hydrazine, 
thus : — 

{(N"2)=CH.COOH}3  +  6H20  =  3(COOH)2  +  3N2H4. 

An  acid,  named  hydrazoic  acid,  has  been  prepared  by  Curtius,  of  the  formula 
H(X3).  It  is  a  soluble  gas,  with  a  penetrating  smell,  forming  salts.  The  silver 
salt,  Ag^N"3,  is  an  insoluble,  explosive  powder ;  the  barium  salt,  BaN6,  forms  large, 
transparent  crystals.  It  is  derived  from  benzoyl-azo-imide, 

Jf. 

Properties. — Ammonia,  NH3,  is  a  colourless  gas,  with  a 
pungent  odour,  very  soluble  in  water,  1  volume  of  water  dis- 
solving more  than  800  volumes  of  the  gas.  This  solution  is  the 
liquor  ammonice,  or  "  spirit  of  hartshorn  "  of  the  shops,  so  called 
because  it  used  to  be  obtained  by  distilling  stags'  or  harts'  horns. 
In  reality,  this  yields  the  carbamate,  which,  however,  is  easily  con- 
verted into  ammonia  by  quicklime. 

Liquid  ammonia  boils  at  —40°,  and  solidifies  to  a  white  crys- 
talline solid  at  about  —80°. 

Owing  to  its  solubility  in  water,  the  gas  must  be  collected  over 
mercury,  or,  as  it  is  very  light  (8'5  times  as  heavy  as  hydrogen), 

*  Curtius,  Berichte,  20,  1062. 

2   L   2 


516  THE  NITRIDES,  PHOSPHIDES,  ETC. 

by  upward  displacement.  As  it  is  absorbed  by  the  usual  drying 
agents,  sulphuric  acid  or  calcium  chloride,  it  must  be  dried  by 
passage  through  a  tube  filled  with  calcium  or  barium  oxide. 

A  considerable  rise  of  temperature  occurs  when  ammonia  gas 
is  passed  into  water,  owing  partly  to  the  liquefaction  of  the  gas, 
and  partly,  no  doubt,  to  chemical  combination  with  the  water.  It 
appears  probable  that  a  solution  of  ammonia  contains,  besides 
liquid  ammonia  mixed  with  water,  a  small  amount  of  the  com- 
pound NH4OH.  But  of  this  there  is  no  satisfactory  proof  as  yet. 
The  solution,  however,  reacts  as  if  it  contained  such  a  body  ;  like 
caustic  soda  and  potash,  it  has  a  strong .  alkaline  reaction  and  a 
caustic  taste.  But  the  ammonia  is  easily  expelled  by  boiling  the 
solution  ;  hence  ammonium  hydroxide,  if  it  exists,  must  be  very 
unstable. 

When  heated  to  a  few  degrees  above  500°.  ammonia  decom- 
poses; but  at  that  temperature  the  rate  of  decomposition  is 
exceedingly  slow.  As  there  is  no  recombination  between  its 
constituents,  a  sufficiently  long  exposure  to  that  temperature 
ultimately  completely  decomposes  it.  Decomposition  takes  place 
more  rapidly  the  higher  the  temperature,  and  is  aided  by  porous 
surfaces.* 

Ammonia  does  not  evolve  sufficient  heat  by  burning  to  con- 
tinue ignited  in  air,  for  a  considerable  amount  of  heat  is  absorbed 
to  effect  its  decomposition  before  free  hydrogen  is  produced, 
which  will  unite  with  oxygen.  But  it  burns  in  oxygen  with  a 
yellowish  flame,  giving  nitrogen  and  water.  It  instantly  reacts 
with  halogens,  forming  halogen  substitution  products  if  halogen 
is  in  excess,  and  nitrogen  if  excess  of  ammonia  be  present  (see 
pp.  54  and  158). 

It  unites  with  very  many  compounds ;  these  substances  will  be 
considered  later.  Its  heat  of  formation  is  N  +  3B"  =  NHS  + 
120K  +  Aq  =  204K. 

Phosphoretted  hydrogen,  as  tri hydrogen  phosphide,  PH3j 
is  usually  called,  is  also  a  colourless  gas,  possessing  a  disagreeable 
smell  of  garlic.  Unlike  ammonia,  it  is  nearly  insoluble  in  water. 
The  liquid  boils  at  —85°,  and  solidifies  at  — 132'5°.t  ^  is  exceed- 
ingly poisonous,  air  containing  one  ten-thousandth  of  its  volume 
of  the  gas  speedily  producing  death.  When  contaminated  with 
the  liquid  phosphide,  P2H4,  it  is  spontaneously  inflammable ;  such 
a  mixture  is  produced  by  every  method  of  preparation  except 
that  of  decomposing  phosphonium  iodide,  PH4I,  with  caustic 

*   Chem.  Soc.,  45,  92. 

f  Monatsh.  Chem.,  7,  371. 


PHOSPHONIUM   SALTS.  517 

alkali,  or  by  boiling  phosphorus  with  an  alcoholic  solution  of  soda 
or  potash.  In  preparing  such  an  inflammable  compound,  care 
must  be  taken  to  expel  air  from  the  flask  in  which  it  is  generated 
by  means  of  a  current  of  coal-gas,  or  of  carbon  dioxide.  When  it 
is  allowed  to  bubble  through  water,  each  bubble  takes  fire 

Fio.  45. 


spontaneously  as  it  bursts,  and  produces  a  beautiful  vortex  ring 
of  finely  divided  phosphoric  acid. 

The  heat  of  formation  of  PH3  is  P  +  3B"  =  PH,  +  43K. 

Like  ammonia,  hydrogen  phosphide  unites  directly  with  hydro- 
gen chloride,  bromide,  iodide,  and  sulphate,  but  compounds  with 
other  acids  have-not  been  prepared.  The  "phosphonium"  salts, 
as  these  compounds  have  been  named,  from  their  analogy  with 
ammonium  compounds,  have  the  formulae  PH4C1,  PH4Br,  and 
PH4I ;  the  formula  of  the  sulphate  has  not  been  ascertained. 

Phosphonium  chloride,  PH4C1,  is  produced  by  mixing  equal 
volumes  of  phosphuretted  hydrogen  and  hydrogen  chloride,  and 
compressing  the  mixture.  At  20  atmospheres,  small  white  crys- 
tals deposit  on  the  side  of  the  tube.  The  same  substance  is  pro- 
duced by  cooling  the  mixture  to  —30°  or  —35°. 

Phosphonium  bromide,  PH4Br,  is  produced  when  the  gases 
are  mixed  and  cooled ;  or  by  the  action  of  a  strong  solution  of 
hydrobromic  acid  on  phosphorus  at  100 — 120°  in  a  sealed  tube. 
It  forms  white  crystals  resembling  the  chloride. 

Phosphonium  iodide,  PH4I,  is  produced  by  mixing  hydrogen 
phosphide  and  hydrogen  iodide  at  the  ordinary  temperature.  A 
more  convenient  method  of  preparation  is  to  dissolve  400  grams 
of  yellow  phosphorus  in  its  own  weight  of  carbon  disulphide,  and 


518  THE  NITRIDES,  PHOSPHIDES,  ETC. 

to  add  very  gradually  680  grams  of  iodine,  keeping  the  solution 
cold.  The  carbon  disulphide  is  then  completely  distilled  off  by 
means  of  a  water- bath.  The  product  is  a  mixture  of  iodides  of 
phosphorus  with  free  phosphorus.  While  carbon  dioxide  is  passed 
through  the  retort,  240  grams  of  water  are  slowly  added,  the  tem- 
perature still  being  kept  low.  The  following  reaction  takes 
place :— 13P  +  91  +  21H20  =  3H4P207  +  7PHJ  +  2fll.  The 
condenser  is  then  removed  and  a  long  wide  tube  adapted  to  the 
neck  of  the  retort,  closed  at  its  further  end  by  a  perforated  cork, 
through  which  a  narrow  tube  is  inserted  leading  to  a  draught. 
On  careful  heating  over  a  sand-bath,  the  phosphonium  iodide 
sublimes  into  the  wide  tube,  the  current  of  carbon  dioxide  being 
maintained.  It  forms  a  white  crystalline  crust,  which  on  careful 
resublimation  crystallises  in  perfect  lustrous  cubes.  It  is  interest- 
ing to  note  that  the  crystalline  form  of  these  bodies  is  identical 
with  that  of  the  halides  of  sodium,  potassium,  &c. 

All  these  substances,  on  passing  into  vapour,  decompose  into 
their  constituents,  thus  resembling  ammonium  chloride.  Their 
vapour  densities  correspond  to  this  change,  and  are  half  what  they 
would  be  were  the  compounds  to  volatilise  unchanged. 

Phosphonium  sulphate  is  formed  by  passing  hydrogen  phos- 
phide into  strong  sulphuric  acid  at  —35°,  It  forms  a  white 
crystalline  mass,  which  decomposes  as  temperature  rises,  the  sul- 
phuric acid  being  reduced  to  hydrogen  sulphide,  sulphur,  and 
sulphur  dioxide,  while  acids  of  phosphorus  are  produced.  No 
nitrate  is  formed  under  similar  circumstances.  The  nitric  acid  is 
reduced,  and  inflammable  hydrogen  phosphide  is  formed. 

Hydrogen  arsenide,  arsine,  or  arseniuretted  hydrogen, 
H3As,  and  hydrogen  antimonide,  stibine,  or  antimoniuretted 
hydrogen,  H3Sb,  usually  written  AsH3  and  SbH3,  are  colourless 
gases,  exceedingly  poisonous.  They  have  very  disagreeable  smells  ; 
that  of  AsH3  resembling  garlic:  liquid  AsH3  boils  at  —  54'8°,  and 
the  solid  melts  at  — 113-5° ;  and  solid  SbH3  melts  at  — 91'5°,  but 
decomposes  before  its  boiling  point  is  reached.*  They  are  very 
sparingly  soluble  in  water.  As  ordinarily  prepared,  they  are 
mixed  with  large  quantities  of  hydrogen.  Stibine,  indeed,  cannot 
be  obtained  pure,  except  at  a  very  low  temperature  ;  even  at  —60° 
a  tube  containing  liquid  stibine  becomes  coated  with  metallic 
antimony.  They  do  not  unite  with  acids. 

This  means  of  recognising  arsenic  and  antimony  is  taken  advantage  of  in 
"  Marsh's  test."  Compounds  of  arsenic  or  antimony,  placed  in  a  flask  contain- 

*  Olzewski,  Monatsh.  Ckem.,  5,  127;  7,  371. 


MARSH'S  TEST. 


519- 


ing  zinc  and  acid,  which  yield  nascent  hydrogen,  unite  with  the  hydrogen,  pro- 
ducing arsine  or  stibine.  As  commercial  zinc  often  contains  arsenic  and 
antimony,  specially  purified  zinc  must  be  employed.  The  gas,  after  being  dried 
by  passage  through  a  tube  containing  calcium  chloride,  is  set  on  fire  at  the  exit 
tube,  which  should  be  drawn  out  into  a  jet,  as  shown  in  the  figure.  On  holding 

Fm.  46. 


the  lid  of  a  porcelain  crucible  in  the  flame,  arsenic  or  antimony  is  deposited,  the 
former  with  a  grey,  and  the  latter  with  a  black,  colour.  These  deposits  may  be 
distinguished  from  each  other  by  their  behaviour  with  a  solution  of  calcium 
hypochlorite.  While  the  grey  deposit  of  arsenic  is  easily  oxidised  and  dissolved, 
the  black  stain  of  antimony  remains  unaffected. 

If  the  exit  tube  be  heated  to  redness,  the  arsine  or  stibine  is  decomposed, 
and  deposits  of  arsenic  and  antimony  are  obtained,  which  may  be  dissolved  and 
tested  by  the  usual  means.  This  process  is  well  adapted  for  testing  for  these 
poisons  in  complex  organic  mixtures,  such  as  the  contents  of  the  stomach,  &c. 
For  further  details  concerning  this  process,  a  work  on  analytical  chemistry  must 
be  consulted. 

Hydrazine,  N^H^  is  a  gas,  with  an  exceedingly  sharp  pungent 
smell,  somewhat  resembling  that  of  ammonia.  It  is  very  hygro- 
scopic and  difficult  to  free  from  water.  Like  ammonia,  it  unites 
with  acids  to  form  salts  ;  its  hydrochloride,  for  example,  having 
the  formula  N>H4.HC1.  Its  name  is  derived  from  the  French  terra 
for  nitrogen,  azote. 

Tetrahydrogen  diphosphide,  PaH4,  commonly  termed  liquid 
phosphoretted  hydrogen,  is  produced  along  with  the  gaseous  phos- 
phine  by  most  of  the  reactions  which  serve  to  prepare  the  latter. 
It  may  be  separated  by  passing  the  gaseous  spontaneously  inflam- 
mable product  through  a  \J  -tube  cooled  by  a  freezing  mixture. 
It  is  a  colourless  mobile  refractive  liquid,  which,  on  standing, 


520 


THE  NITRIDES,   PHOSPHIDES,   ETC. 


decomposes  into  phosphine  and  dihydrogen  tetraphosphide,  P4H2, 
a  red  solid.  Liquid  phosphoretted  hydrogen  is  spontaneously  in- 
flammable. No  compounds  with  acids  are  known. 

A  velvety  brown  substance,  said  to  have  the  empirical  formula 
AsH,  is  produced  when  sodium  or  potassium  arsenide  is  treated 
with  water. 

Composition  of  ammonia. — The  volume  relations  of  the  constituents  of 
ammonia  may  be  shown  by  the  following  experiments  :— 

1.  To  prove  that  ammonia  gas  contains  half  its  volume  of  nitrogen. — The 
principle  of  the  operation  is  to  place  gaseous  ammonia  in  contact  with  some 
substance  capable  of  removing  its  hydrogen  by  oxidation,  and  to  compare  the 
volume  of  the  ammonia  taken  with  that  of  the  residual  nitrogen.  For  this 
purpose  a  dry  graduated  tube,  about  40  cm.  in  length,  is  filled  with  ammonia  by 
upward  displacement ;  the  ammonia  may  be  prepared  for  this  purpose  by 
warming  a  strong  solution,  in  a  flask,  through  a  cork  in  the  neck  of  which  issues 
a  long  vertical  tube,  as  shown  in  figure  47.  When  full,  the  graduated  tube  is 

Fm.  47. 


slowly  raised,  and  when  free  from  the  vertical  tube  conveying  the  ammonia,  it  is 
closed  with  the  thumb.  It  is  then  transferred  to  a  basin  containing  a  strong  solu- 
tion of  sodium  hypobromite,  NaBrO  (Fig.  48).  Some  of  the  solution  will  enter  : 
the  tube  is  now  shaken,  and  its  open  end  is  again  dipped  into  the  solution  of  hypo- 
bromite. The  reaction  SNaBrO.Aq  +  2NHZ  =  SNaBr.Aq  +  3H2O  +  Nz  takes 
place.  On  removing  the  graduated  tube  to  a  jar  of  water,  and  equalising  the  lev  el 


COMPOSITION  OF   AMMONIA. 


521 


of  the  liquid  inside  the  tube  with  that  of  the  water  in  the  jar,  it  will  be  found 
that  the  nitrogen  occupies  half  the  space  originally  occupied  by  the  ammonia.  It 
is  thus  seen  that  two  volumes  of  ammonia  yield  one  volume  of  nitrogen. 


FIG.  48. 


FiG.  49. 


522 


THE   NITRIDES,   PHOSPHIDES,   ETC. 


2.  To  prove  that  for  every  three  volumes  of  hydrogen  contained  in  ammonia, 
it  contains  one  volume  of  nitrogen. — A  tube,  provided  with  a  stopcock  at  each 
end,   is   filled  with  chlorine  (Fig.   49).     It   is  divided  into  three  equal  parts 
by  two   indiarubber  rings.      A   solution    of    ammonia   is    then   poured   into 
the   funnel    at    one    end,    and    the   upper   stopcock    is    opened,   when   some 
ammonia  solution  enters  the  tube.     A  flame  is  seen  to  run  down   the  tube. 
It    is    now   shaken,   when    dense    white    fumes    of    ammonium    chloride    are 
formed.     More  ammonia  solution  is  passed  in,  and  the  tube  is  again  shaken. 
Finally  the  funnel   is  rinsed   out,  and  some  weak  sulphuric  acid   is    passed 
into  the  tube,  to  combine  with  the  excess  of  ammonia.     On  placing  the  tube  in 
a  jar  of  water,  opening  the  lower  stopcock,  and  equalising  levels,  it  is  seen  that 
the  remaining  nitrogen  occupies  one-third  of  the  volume  originally  occupied  by 
the  chlorine.     But,  as  equal  volumes  of  chlorine  and  hydrogen  combine  to  form 
hydrogen  chloride,  it  is  evident  that  the  three  volumes  of  chlorine  must  cor- 
respond to  three   volumes   of  hydrogen:    hence,  for  every  three  volumes  of 
hydrogen  in  ammonia,  one  volume  of  nitrogen  is  present. 

3.  To  show  that,  on  decomposing  ammonia  by  heat,  the  resultant  gases  occupy 
twice  the  volume  of  their  compound. — Pass  electric  sparks  from  a  Ruhmkorff 's 
coil  through  ammonia  contained  in  a  tube  standing  in  a  mercury  trough.     The 
ammonia  will  be  completely  decomposed  in  about  three-quarters  of  an  hour, 
and  it  will  be  seen  that  its  volume  has  doubled  (Fig.  50) . 


FIG.  50. 


It  is  thus  shown  that  two  volumes  of  ammonia  when  decom- 
posed yield  a  mixture  consisting  of  three  volumes  of  hydrogen 
with  one  of  nitrogen.  And  it  may  be  concluded,  conversely,  that 
if  combination  could  be  induced  between  nitrogen  and  hydrogen, 
one  volume  of  the  former  would  unite  with  three  of  the  latter,  to 
produce  two  volumes  of  ammonia. 


HYDROXYLAMINE.  523 

It  may  also  be  shown  by  weighing  a  vacnons  flask  of  known 
volume,  filling  it  with  ammonia,  and  weighing  again,  that  ammonia 
is  8'5  times  as  heavy  as  hydrogen.  This  corresponds  to  a  mole- 
cular weight  of  17,  implying  the  formula  NH3. 

The  formulae  of  phosphine  has  been  deduced  from  analysis, 
aud  from  its  density ;  that  of  arsine  from  analogy,  and  that  of 
stibine  from  the  formula  of  the  compound  it  forms,  A&Sb,  when 
passed  into  a  solution  of  silver  nitrate. 

Compounds  of  hydrogen  nitride,  phosphide,  arsenide, 

and  antimonide.  The  halogen  substitution  compounds  of  am- 
monia have  already  been  described  on  p.  158.  Analogous  to 
NH2C1,  which  may  be  named  monochloramine,  is  the  compound — 

Hydroxylamine,  NE2OE* — It  is  produced  by  the  reduction 
of  nitric  oxide  or  nitric  acid  by  means  of  nascent  hydrogen,  gene- 
rated by  the  action  of  hydrochloric  acid  on  tin,  zinc,  cadmium, 
aluminium,  or  magnesium.  To  prepare  it,  nitric  oxide  is  passed 
through  a  mixture  of  tin  and  hydrochloric  acid,  to  which  a  few 
drops  of  chloride  of  platinum  have  been  added,  to  promote  galvanic 
action  and  facilitate  the  evolution  of  the  hydrogen.  The  solution 
then  contains  stannous  chloride,  SnCl2,  and  hydroxylamine  hydro- 
chloride,  NH2.OH.HC1.  The  tin  is  removed  as  sulphide,  SnS,  by 
the  passage  of  hydrogen  sulphide  through  the  solution.  The 
filtrate  from  the  sulphide  is  evaporated  to  dryness,  and  extracted 
with  absolute  alcohol,  in  which  ammonium  chloride,  also  produced 
by  reduction  of  the  nitric  oxide,  is  insoluble,  but  in  which  hydr- 
oxylamine hydrochloride  dissolves.  On  filtering  from  the  undis- 
solved  ammonium  chloride,  and  again  evaporating  to  dryness, 
hydroxylamine  hydrochloride  remains  as  a  white  crystalline  mass. 

From  the  hydrochloride,  the  sulphate  is  produced  by  evapora- 
tion with  weak  sulphuric  acid ;  and  from  a  solution  of  the  sulphate 
hydroxylamine  may  be  liberated  by  addition  of  the  requisite 
amount  of  baryta- water. 

If  the  solution  is  distilled,  a  considerable  portion  of  the  hydr- 
oxylamine passes  over  with  the  steam,  but  most  of  it  is  decomposed 
thus  :—3NH2OH  =  NH3  +  N2  +  3H20.     The  heat  of  formation  o* 
hydroxylamine  is :— 3^V  +  H  +  0  +  Aq  =  KB3O.Aq  +  181  E 
(Thomsen  gives  +  243  K). 

Hydroxylamine  is  a  powerful  reducing  agent.  When  added  tt 
solutions  of  salts  of  silver  or  mercury,  the  metals  are  precipitated ; 
and  when  boiled  with  copper  sulphate,  cuprous  oxide,  Cu2O,  is 
thrown  down. 

*  Chem.  Soc.,  43,  443 ;  47,  71 ;  51,  50,  659. 


524  THE  NITRIDES,  PHOSPHIDES,  ETC. 

The  following  salts  of  hydi-oxylamine  have  been  prepared  :  —  NH2OH.HC1  ; 
2NH2OH.HC1  ;  3NH2OH.HC1  ;  NH2OH.HNO3  ;  2NH2OH.H2SO4  ; 
3NH2OH.H3PO4  ;  2NH2OH.H2C2O4  (oxalate).  Some  double  salts  have  also 
been  prepared,  which  in  crystalline  form  resemble  those  of  ammonium, 
e.g.,  (NH2OH).HA1(S04)2.12H20  ;  (NH2OH).HCr(SO4)2.12H2O  ;  and 
(NH.2OH).HFe(SO4).12H2O;  corresponding  to  the  alums;  and 
(NH2OH)2  H2SO4.Mg:SO4.6H2O,  corresponding  to  the  double  sulphates  of  dyad 
metals  (see  pp.  425  and  428). 

The  constitution  of  hydroxylamine  is  doubtless  H2N  —  OH. 

No  similar  compound  of  phosphorus  is  known  ;  but  attention 
may  be  directed  to  hypophosphorous  acid,  the  oxidised  analogue  of 

/H 
hydroxylamine,    0=P^-H      (p.   380)  ;  and  the  somewhat  analo- 

XOH 

gous  constitution  of  hyponitrous  acid,  0=N  —  H  (see  p.  344). 
Phosphorous  and  nitrous  acids  may  also  be  compared  (see  pp.  337 
and  345).  Arsenic  and  antimony  do  not  form  similar  combina- 
tions ;  but  these  bodies  may  be  compared  with  0=As  —  Cl, 
0=Bi—  01,  described  on  pp.  384,  385. 

Amido-compounds  or  amines.  —  As  the  group  named  hydr- 
oxyl,  —  OH,  may  be  regarded  as  capable  of  entering  into  combina- 
tion with  the  elements,  forming  hydroxides  and  acids  ;  so  the 
group  —  NH2,  named  the  "  amido-group  "  or  "amine"  enters 
into  similar  combinations.  And  such  compounds  may  be  regarded 
as  substituted  ammonia,  just  as  the  hydroxides  and  acids  may  be 
viewed  as  substituted  water.  Thus  we  have  Na  —  OH,  sodium 
hydroxide,  to  which  corresponds  Na  —  NH2,  sodamide  ;  and 

r,    zinc    hydroxide,    with    its    analogue    ZiK^---2,     zinc- 


amide.  But  few  of  these  simpler  compounds  are  known  ;  because 
the  nitrogen  still  retains  its  power  of  combining  with  haloid  and 
other  acids  to  form  salts.  Such  bodies  are  so  numerous  that  only 
an  incomplete  sketch  can  be  given  here.  We  shall  begin  with  the 
simpler  compounds,  considering  the  salts  subsequently. 

Simple  compounds  :  — 

NaNH2;  KNH2;  Zn(NH2)2;  ZnPH  ;  P(NH2)3. 

Sodamide  and  potassamide*  are  produced  by  passing  am- 
monia over  gently  heated  sodium  or  potassium.  They  are  olive- 
green  substances,  transmitting  brown  light  when  in  thin  scales. 
They  melt  a  little  above  100°,  and  when  heated  to  dull  redness 

*  Annalen,  108,  88. 


THE   AMIDES.  525 


give  nitride  of  potassium  or  sodium,  K3N  or  NaaN,  and  ammonia. 
With  water  they  yield  hydroxide  and  ammonia,  thus  establishing 
their  constitution  ;  thus  :  KNH2  +  H.OH  =  KOH  +  H.NH*. 

Zinc-amide,*  Zn(NH2)2,  is  a  white  powder,  insoluble  in 
ether,  produced  along  with  methane  or  ethane  by  treating  zinc- 
methyl  or  zinc-ethyl  with  ammonia.  When  heated  to  redness  it 
yields  the  nitride,  Zn3N2.  The  compound  ZnPH  forms  a  yellow 
mass;  it  is  produced  by  passing  a  current  of  phosphine  into 
zinc-ethyl,  Zn(C2H5)2. 

Phosphorosamide,  P(NH2)3,  appears  to  be  produced  by  the 
action  of  ammonia  on  phosphorus  trichloride,  PC13,  thus  :  —  PCla  -f- 
SHNHo  =  P(NH2)3  -|-  3HCI.  The  hydrogen  chloride  combines 
with  the  excess  of  ammonia,  forming  ammonium  chloride,  from 
which  the  phosphorosamide  has  not  been  separated.  The  mixture 
is  a  white  crystalline  mass. 

The  carbon  compound,  C(NH2)4,  appears  incapable  of  exis- 
tence; a  body  differing  from  it  by  the  elements  of  ammonia  is 
however  known;  it  is  named  guanidine,  and  its  formula  is 
HN=C(NH2)2. 

Double  compounds.—  Halides,  and,  generally  speaking,  salts 
of  such  amides,  are  formed  by  the  action  of  ammonia  on  most  com- 
pounds of  the  metals  ;  but  here  a  difficulty  in  classification  meets 
us,  for  a  considerable  number  of  molecules  of  ammonia  very  fre- 
quently add  themselves  to  such  compounds,  and  it  is  at  present  as 
impossible  in  many  cases  to  assign  reasonable  constitutional  for- 
mulae to  such  bodies,  as  it  is  to  understand  in  what  manner  of 
combination  water  of  crystallisation  exists  in  salts  which  contain 
it.  We  shall,  therefore,  assume  that,  where  it  appears  reasonable 
to  suppose  so,  an  amide  is  formed  ;  and  any  further  molecules  of 
ammonia  which  add  themselves  on  to  such  compounds  will  often 
be  represented  as  if  they  were  merely  additive  molecules.  At  the 
same  time  there  are  compounds,  such  as  those  of  cobalt  and  of 
platinum,  where  such  additive  molecules  of  ammonia  appear  to 
form  an  essential  portion  of  the  total  molecule.  Where  such  is  the 
case,  attention  will  be  drawn  to  the  fact. 

The  elements  will,  as  usual,  be  considered  in  their  periodic 
order. 

NH4C1.3NH3;  NH4C1.6NH3;  NH4Br.3NH3. 

The  first  of  these  melts  at  7°,  the  second  at  —18°.  They  are 
produced  by  heating  ammonium  chloride  with  excess  of  ammonia, 
and  allowing  it  to  cool  in  contact  with  the  gas.f  The  compound 

*  Annalen,  134,  52.  f  Comptes  rend.,  88,  578. 


526  THE  NITRIDES,  PHOSPHIDES,  ETC. 


is  also  formed  by  direct  union,  ammonium  nitrate 
liquefying  in  contact  with  dry  ammonia.* 

Ca(NH2)2.2HC1.6NH3  and  *Sr(NH2)2.2HC1.6NH3. 

White  substances  produced  by  saturating  calcium  or  strontium 
chloride  with  ammonia.  When  warmed  the  original  constituents 
are  re-formed.  The  corresponding  barium  compound  is  unknown. 

ClZn(NH2).HCl;  HO.CO.O.Zn(NH2)  ;  HO.SO2Zn(NH2).— 

Zn(NH2)2.2HCl;  Cd(NH2)2.2HCl  ;  Zn(NH2)2.2HC1.2  and  3NH3; 
Zn(NH2)2.2HI.2  and  3NH3;"  Zn(NH2)2.H2SO4.H2O;  Zn(NH2)2.H2S2O3; 
Zn(NH2)2.H2S04.2  and  3NH3.4H2O  ;  Cd(NH2)2.H2CrO4.2NH3; 

3(Zn(NH2)2.2HI03).2NH3  ;  2Zn(NH2)2.Zn(OH)2.12H2O  ; 
2(Zn(NH2)2.H4P207)Zn(OH)2.8H20. 

These  compounds  are  all  made  by  treating  the  respective  salts 
with  ammonia. 

BF3.3NH3;  BF3.2NH3;  BF3.NH3. 

Produced  by  the  action  of  dry  ammonia  on  boron  trifluoride, 
BF3.  The  last  of  these  might  be  written  BN.3HF.  But  boron 
nitride,  BN,  when  treated  with  aqueous  hydrofluoric  acid,  yields 
BF3.NH4F,  ammonium  borofluoride,  which,  it  may  be  supposed,  is 
not  BN.4HF.  The  formula  is  more  probably  F2B(NH2)HF.  It 
may  be  volatilised  without  decomposition.  The  formula  of  the 
second  may  be  written  FB(NH2)2.2HF,  and  of  the  first 
B(NH2)3.3HF.  The  first  and  second,  when  heated,  lose  ammonia, 
leaving  the  third.  Boron  chloride,  BC13,  is  said  to  yield  2BC13.3NH3, 
which  may  possibly  be  a  mixture  of  C1B(NH2)2.2HC1  and 
C12B(NH2).HC1. 

Compounds  of  scandium,  yttrium,  and  lanthanum  have  not 
been  examined. 

The  compounds  of  aluminium  are  similar  to  those  of  boron, 
A1(NH2)3.3HC1  and  C1A.1(NH2)2.2HC1  having  been  prepared. 
It  is  interesting  to  note  a  similar  compound  of  aluminium  chloride 
with  phosphuretted  hydrogen,  3A1C13.PH3.  Compounds  of  gal- 
lium and  indium  have  not  been  examined.  But  thallium  tri- 
chloride reacts  with  ammonia  in  presence  of  ammonium  chloride, 
giving  a  dense  white  precipitate  of  the  trihydrochloride  of 
thallamide,  T1(NH2)3.3HC1. 

The  chromium  compounds  are  somewhat  complex.  Chro- 
mium hydrate,  digested  with  ammonium  chloride  and  ammonia, 
dissolves  with  a  deep  red  colour  ;  and  on  exposing  the  solution  to 
air,  a  violet  powder  precipitates  ;  this  powder  dissolves  in  hydro- 

*  Proc.  Hoy.  Soc.,  21,  1091  ;  Comptes  rend.,  94,  1117. 


CHROMAJVIINES.  527 

•chloric  acid,  forming  the  salt  CrCls.4NH3.H2O.  This  compound 
might  be  regarded  as  Cr(NH2)3.3HCl.NH3.H20  ;  but  while  it  loses 
its  water  of  crystallisation  at  100°,  ammonia  is  retained  up  to  200°, 
which  would  lead  to  the  conclusion  that  even  the  fourth  molecule 
is  in  intimate  relation  to  the  chromium.  These  compounds  may 
be  supposed  to  contain  the  group  — (N2H5) — ,  or  — NH3 — NH2 — ,  a 
group  which  may  be  named  the  diamido-group  ;  it  might,  perhaps, 
preferably  be  termed  the  ammonium-amido-group. 

Such  a  supposition  would  bring  such  compounds  into  con- 
formity with  those  of  cobalt  and  of  other  elements ;  but  the 
heptamines  cannot  be  classified  thus,  unless  a  further  condensation 
of  the  ammonia  molecule  is  supposed  possible. 

There  are  five  series  of  these  compounds  :  the  triamines,  the 
tetramines,  the  pentamines,  the  hexamines,  and  the  hept- 
amines. 

Of  the  triamines,  the  oxalate,  Cr2O3.3C2O3.6NH3.3H2O,  has  been  prepared. 
Of  the  tetramines,  the  compound  CrCl3.4NH3.H2O  is  an  example;  the  bromide, 
CrBr3.4NH3.H2O ;  the  iodide,  CrI3.4NH3.H2O ;  the  chlorodibromide, 
CrClBr2.4NH3.H2O ;  the  dichlorobromide,  CrBr2C1.4NH3.H2O ;  the  chlorodi- 
iodide,  CrClI2.4NH3.H2O ;  the  bromosulphate,  CrBr(SO4).4NH3.H2O;  the 
'  chlorochromate,  CrCl(CrO4).4NHa.H2O,  and  the  chloronitrate, 

CrCl(N03)2.4NH3.H20, 
have  been  prepared.     They  hare  a  deep  red  colour. 

The  starting  point  for  the  pentamines  is  chromous  chloride, 
CrCl2,  produced  by  the  action  of  hydrogen  on  red-hot  chromic 
chloride,  CrCl3  (see  p.  138).  It  is  added  to  a  solution  of  ammo- 
nium chloride  in  strong  ammonia,  in  which  it  dissolves  with  a 
blue  colour.  Air  is  then  passed  through  the  liquid  until  oxidation 
is  complete.  Excess  of  hydrochloric  acid  is  added,  and  the 
mixture  is  boiled,  when  the  hydrochloride  of  the  pentamine  is 
precipitated.  It  is  purified  by  solution  in  weak  sulphuric  acid, 
and  filtering  into  a  large  excess  of  strong  hydrochloric  acid, 
washing  ,with  water  and  alcohol,  and  drying  in  air.  Its  formula 
is  CrCl3.5NH3.  It  is  a  red  crystalline  powder.  Numerous  salts 
have  been  obtained,  the  composition  of  all  of  which  is  analogous 
to  that  of  the  chloride.  These  bodies  have  been  named  purpureo- 
chromium  compounds. 

If,  instead  of  treating  with  hydrochloric  acid,  dilute  hydro- 
bromic  acid  be  used,  the  hydroxy bromide  of  the  dipentamine, 
HO-  -Cr2Br5.10NH3.H2O,  crystallises  out  in  carmine  needles.  On 
digestion  with  hydrochloric  acid,  the  chloride  is  formed,  from 
which,  by  suitable  means,  other  salts  can  be  prepared.  They  all 
crystallise  well,  and  have  a  carmine-red  colour.  On  treatment 


528  THE   NITRIDES,   PHOSPHIDES,   ETC. 

with  silver  hydroxide,  the  chloride  yields  the  hydroxide,  a  blue 
solution,  which  rapidly  changes  to  red.  These  hydroxy- derivatives 
have  been  named  rhodochromium  salts.  Isomeric  with  these 
are  the  erythrochromium  compounds,  produced  by  digesting 
the  former  with  dilute  ammonia.  While  solutions  of  the  former 
have  a  blue  colour,  the  latter  are  red. 

The  roseochromium  compounds,  containing  two  hydroxy  l- 
groups,  are  produced  by  precipitating  purpureo-  compounds  with 
sodium  dithionate  after  boiling  with  dilute  ammonia. 

By  digesting  roseo-  or  purpureo-salts  with  ammonia  in  a  close 
vessel,  luteo-salts  are  produced,  in  which  six  molecules  of 
ammonia  are  in  combination  with  chromium  trichloride. 

Two  heptamines  have  also  been  prepared  as  double  salts.  It 
should  be  stated  that  these  formulae  are  usually  doubled,  chromium 
trichloride  being  assumed  to  have  a  molecular  weight  corre- 
sponding to  the  formula  Cr2Cl6 ;  but,  with  respect  to  this  view,  see 
the  statements  on  p.  505. 

Supposing  the  halogen  compounds  of  all  these  amines  to  exist, 
and  the  atom  of  halogen  to  be  represented  by  X,  the  chromamines 
may  be  classified  as  follows  : — 

Triamines  :  CrX3.3NH3,  possibly  Cr(NH2)3.3HX. 
Tetramines:  OX3.4NH3,  possibly  Cr(NH2)2.(F2H5).3HX. 
Pentamines :  CrX3.5NH3  (purpureo-chromic  compounds)  ;  possibly 

Cr(NH2)(N2H5)2.3HX. 
Hydroxydipentamines :  Cr2X5(OH).10NH8  (rliodo-  and  ery  thro -chromic 

compounds). 

Hydroxypentamines  :  CrX2(OH).5NH3. 
Hexamines:  CrX3.6NH3;  possibly  Cr(N2H5)3.3HX. 
Heptamines :  CrX3.7NH3. 

Ferric  chloride  combines  with  dry  ammonia  to  form 
PeCl3.NH3,  or  Cl2==.Fe(NH2).HCl,  a  red  mass,  volatilising 
when  heated,  leaving  a  residue  of  ferrous  chloride. 

The  manganamines  have  not  been  examined. 

Cobaltamines.  —  These  compounds  closely  resemble  the 
chromamines.  They  fall  into  the  following  classes : — 

Diamines:  CoX3.2NH3. 

Triamines:  CoX3.3NH3;  also  CoCl3.2NH3.NO2H. 

Tetramines:  CoX3.4NH3;  also  CoX(NO2)2.4NH3,  and  Co2O(NO2)4.8NH3. 

Pentamines:  CoX3.5NH3;  also  CoX(NO2)2.5NH3  and  CoX2(N02).5NH3. 

Hexamines:  CoX3.6KH3. 

Diamines. — These  are  prepared  from  the  pentamines  (purpureo- 
cobaltamines  (see  below)  by  adding  a  solution  of  hydrogen 
ammonium  sulphite,  HNH4S03,  until  the  liquid  smells  of  sulphur 


COBALTAMINES.  529 

dioxide.  Sparingly  soluble  brown  octahedra  of  the  sulphite, 
COo(SO3)3.4NH3.5H2O,  are  deposited.  In  this  case  the  sulphite  is 
the  only  salt  known. 

Triamines. — If  more  free  ammonia  be  present,  and  if  the 
addition  of  hydrogen  ammonium  sulphite  is  stopped  as  soon  as 
the  smell  of  ammonia  disappears,  insoluble  yellow  needles  of  the 
triamine  sulphite,  Co2(SO3)3.6NH3.H2O,  are  deposited.  Here, 
again,  other  salts  have  not  been  prepared. 

A  series  of  compounds,  in  which  one  molecule  of  ammonia  of 
the  triamines  is  replaced  by  the  group  HN02,  nitrous  acid,  are 
formed  by  the  action  of  ammonium  nitrite  on  neutral  ammoniacal 
solutions  of  cobalt  salts.  The  salt  Co(NO2)3.2NH3.NH4NO2 
crystallises  out;  and  the  ammonium  group  is  replaceable  by 
other  metals.  Thus  the  salts  Co(NO2)3.2NH3.TlNO2  and 
Co(NO2)3.2NH3.Hg'NO2  and  others  have  been  prepared  by  preci- 
pitation, the  groups  NH4N02,  T1NO,,  Hg]Sr02,  &c.,  being  substi- 
tuted for  one  molecule  of  ammonia,  while  the  three  groups  of  NO2 
are  in  combination  with  the  cobalt.  These  may  also  be  regarded 
as  ammoniacal  double  nitrites  of  cobalt  and  ammonium,  &c. 

Tetramines. — These  substances  are  known  as  fuscocobalt- 
amines.  They  are  produced  by  the  action  of  water  on  the  oxycobalt- 
amines,  which  are  also  tetramines.  The  nitrate  has  the  formula 
Co,O(NO3)4.8NH3;  the  chloride,  Co2OCl4.8NH3,  &c.  The  croceo- 
cobaltamines  are  closely  allied  to  the  fuscocobaltamines ;  they 
are  produced  by  the  action  of  nitrites  on  ammoniacal  solutions  of 
cobalt  salts.  The  nitrate,  Co(NO2)2.(NO3).4NH3,  forms  sparingly 
soluble  sherry-coloured  crystals.  It  is  produced  by  mixing  a 
solution  of  cobalt  chloride  with .  ammonium  nitrite,  and  then 
adding  a  solution  of  ammonium  nitrate  containing  much  ammonia; 
the  equation  showing  its  formation  is 

2CoCl2.Aq  +  2NH4NO3.Aq  +  6NH3.Aq  +  4NH4]ST02.Aq  +  O  = 

4NH4Cl.Aq   +   H2O   +   2{Co(NO2)2NO3.4NH3}. 

The  sulphate  is  similarly  prepared  from  cobalt  sulphate,  ammonia, 
and  potassium  nitrate.  The  chloride,  iodide,  chromate,  and  di- 
chromate  have  been  prepared.  A  tri-iodide  is  also  known : 

Co(N02)2.I3.4NH3. 

It  appears  possible  for  the  ammonia  in  the  tetramine  to 
exchange  with  the  group  N02.  By  acting  on  cobalt  chloride  with 
potassium  nitrite  in  presence  of  a  large  excess  of  ammonium 
chloride,  the  body  Co(NH3)2C1.4NO2  is  produced.  It  will  be 

2  M 


530  THE   NITRIDES,   PHOSPHIDES,  ETC. 

observed  that  this  formula  is  strictly  analogous  to  that  of  the 
croceocobaltamines,  Co(NO2)2C1.4NH3. 

Pentamines. — There  are  two  isomeric  series  of  pentamines:  the 
roseocobaltamin.es  and  the  purpureocobaltamines.  The  for- 
mula of  both  is  CoX3.5NH3.  The  first  are  produced  by  exposing  a 
brown  ammoniacal  solution  of  cobalt  sulphate,  CoS04,  to  air, 
when  it  turns  cherry-red,  and  deposits  a  brownish-black  powder. 
On  addition  of  hydrochloric  acid,  care  being  taken  to  keep  the 
mixture  cold,  a  brick-red  powder  is  precipitated,  which  is  collected, 
and  washed,  first  with  strong  hydrochloric  acid,  then  with  ice-cold 
water.  The  formula  of  this  substance  is  CoCl3.5NH3.H2O.  The 
nitrate  is  similarly  prepared,  and  is  a  yellow  precipitate.  The 
sulphate  and  other  salts  have  been  obtained.  From  the  sulphate, 
by  addition  of  solution  of  barium  hydroxide,  an  alkaline  liquid  is 
produced,  probably  containing  the  hydroxide;  it  absorbs  carbon 
dioxide  from  the  air,  and  from  it  other  salts  may  be  produced. 
The  roseocobaltamines  all  contain  water  of  crystallisation. 

By  allowing  the  temperature  to  rise  during  the  neutralisation 
of  an  ammoniacal  solution  of  cobalt  sulphate  with  hydrochloric 
acid,  violet-red  anhydrous  prisms  of  purpureocobaltamine 
chloride,  CoCl3.5NH3,  are  deposited.  The  same  compound  is 
produced  by  heating  fuscocobaltamine  chloride,  CoCl3.4NH3,  in  a 
sealed  tube  with  aqueous  ammonia.  The  nitrate,  acid  sulphate, 
chromate,  and  pyrophosphate,  and  other  salts  have  been  prepared ; 
the  hydroxide  and  sulphite  are  also  known.  The  purpureocobalt- 
amines  are  all  anhydrous. 

Closely  connected  with  these  are  the  xanthocobaltamines,  in 
which  one  atom  of  chlorine  is  replaced  by  one  molecule  of  the 
nitro-group,  N02,  thus  : — Co(NO2)Cl2.5NH3.  They  are  produced 
by  mixing  cobalt  nitrate  with  excess  of  an  alcoholic  solution  of 
ammonia,  and  passing  in  a  mixture  of  nitric  oxide  and  peroxide, 
produced  by  the  action  of  nitric  acid  on  starch,  care  being  taken 
to  keep  the  mixture  cold.  Yellow-brown  prisms  of 
Co(N02)(N03)2.5NH3 

are  deposited.  The  sulphate  is  similarly  prepared,  and  from  it 
the  chloride,  hydroxide,  and  carbonate  have  been  made.  The 
xanthocobaltamines,  when  digested  with  hydrochloric  acid  and 
ammonium  chloride,  lose  the  nitro-group,  which  is  replaced  by 
chlorine;  the  purpureocobaltamine  is  formed,  CoCl3.5NH3. 

The  flavoeobaltamines  are  similar  to  the  xanthocobaltamines, 
but  in  these  two  atoms  of  chlorine  are  replaced  by  two  nitro- 
groups.  They  are  produced  by  treating  a  purpureocobaltamine, 


COB  ALT  AMINES.  531 

e.g.,  CoCl3.5NH3,  with  potassium  nitrite,  and  adding  a  little  acetic 
acid.  The  formula  of  the  chloride  is  Co(NO2)2C1.5NH3.  The 
nitrate,  iodide,  and  other  salts  have  been  prepared. 

The  trinitropentamine,  Co(NO2)3.5NH3,  is  produced  by 
treating  the  trichloropentamine,  CoCl3.5NH3  (purpureo  cobalt  - 
amine)  with  silver  nitrite.  It  forms  brown-orange  octahedra. 

Hexamines. — These  are  named  luteocobalt amines.  The 
chloride,  CoCl3.6NH3,  is  formed  by  digesting  cobalt  chloride  with 
solid  ammonium  chloride  and  ammonia.  On  shaking,  the  liquid 
turns  brown.  Lead  or  manganese  dioxide  is  then  added,  and 
after  heating,  the  liquid  is  filtered  and  saturated  with  hydrogen 
chloride ;  yellow-brown  crystals  are  deposited.  The  bromide, 
iodide,  carbonate,  nitrate,  pyrophosphate  (insoluble),  phosphate,  and 
sulphate  are  among  the  salts  which  have  been  prepared. 

Derivatives  of  the  unknown  chloride  CoCl4  have  also  been 
obtained  as  pentamines.  The  general  formula  of  these  bodies  is 
ColvOX2.5NH3.  They  are  formed  by  direct  oxidation  of  ammoniacal 
cobalt  solutions.  They  are  decomposed  by  water,  with  evolution 
of  oxygen,  and  formation  of  the  usual  pentamines  (purpureo- 
cobaltamines).  They  form  olive-brown  crystals. 

Here,  again,  the  usual  formulae  have  been  halved ;  for  there 
appears  to  be  no  valid  reason  for  supposing  that  the  formula  of 
cobalt  trichloride  is  Co2Cl6  in  preference  to  CoCl3.  Where  the 
actual  molecular  weight  is  unknown,  preference  is  always  given  to 
the  simplest  formulae.  The  additive  formulae  given,  however, 
certainly  do  not  express  the  constitution  of  these  bodies.  But  it 
is  possible  to  represent  them  all  as  derivatives  of  ammonia, 
NH3,  if  it  can  be  supposed  that  a  di-ammonia  is  capable  of 
existence,  — NH3 — H3N" — ,  a  reasonable  enough  supposition,  inas- 
much as  ammonia  can  combine  directly  with  hydrogen  halides  to 
form  bodies  such  as  H — NH3 — Cl.  If  this  be  granted,  then,  the 
formulae  of  the  cobaltamines  may  be  thus  represented : — 

Diamines :— Cl— Co(NH2)2.2HCl. 
Triamines  :— Co(NH2)3.3HCl. 
Tetramines:— Cl— Co(NH3— NH2)2.2HC1. 
Pentamines:— NH2— Co  (NH3.NH2)2.3HC1. 
Hexamines :— Co(NH3.NH2)3.3HCl. 

Or,  again,  it  may  be  supposed  that  they  are  thus  constituted : — 

Cl 

2  M  2 


532  THE   NITRIDES,    PHOSPHIDES,   ETC. 


&c.,  the  group  —  NH2<  having  the  power  of  combination  with  the 
monad  element  chlorine,  and  with  the  monad  group  (1STH4).  But 
these  formulas  are  speculative  and  have  little  to  support  them. 

Chromosamines,  derivatives  of  CrX2,  are  unknown. 

Ferrosamines,  manganosamines,  cobaltosamines,  and  nickelos- 
amines  have  been  prepared.  They  are  as  follows  :  — 

FeCl2.6NH3;  Fe2P2O7.NH3.—  MnCl2.6NH3(?);  MnSO4.4NH3  (?). 
NiCl2.6NH3;  NiBr2.6NH3;  NiI2.4NH3;  NiI2.6NH3. 
Ni(N03)2.4NH3.H26  ;  Ni(NO2)2.4  and  6NH3  ;  Ni(BrO3)2.2NHs; 
Ni(IO3)2.4NH:3  ;   NiSO4.4NH3.2H2O  ;  2NiSO4.10NH3.7H2O  ; 
NiS04.6NH3;  NiS203.4NH3.6H20  ;  NiS2O6.NH3. 

These  salts  are  all  crystalline,  and  are  produced  by  direct 
addition. 

One  of  the  amido-  compounds  of  carbon  has  already  been 
mentioned  (see  Guanidine,j).  525).  Others  are  known  in  which  one 
or  more  of  the  hydrogen  atoms  of  the  hydrocarbons  is  replaced  by 
the  amido-group.  Thus  we  have  methylamine,  CH3.NH2,  di- 
methylamine,  (CH3)ZNH,  and  trimethylamine,  (OH^^N,  all 
forming  salts  resembling  those  of  ammonium.  Here,  too,  similar 
phosphines  are  met  with,  viz.,  CH^PH2,  (CH3)2PH,  and 
(CH?)3P,  monomethyl,  dimethyl,  and  trimethyl  phosphines, 
respectively,  as  well  as  many  others,  in  which  ethyl,  propyl,  and 
other  paraffin  radicles  replace  the  hydrogen  of  phosphoretted 
hydrogen.  Similar  derivatives  are  known  of  arsine,  but  in  this 
case  hydrogen  is  no  longer  in  combination  with  the  arsenic,  but 
chlorine,  oxygen,  sulphur,  &c.  For  example,  we  know  the  com- 
pounds :—CH3AsCl2  ;  (CH3)2AsCl;  (CH3)3As;  and  these  bodies, 
and  similar  compounds  containing  oxygen,  such  as  CH3AsO,  or 
sulphur,  CH3AsS,  &c.j  have  the  power  of  combining  with  other  two 
atoms  of  chlorine,  or  with  another  atom  of  oxygen  forming  such 
compounds  as  CH3AsCl4,  (CH3)2AsCl3,  (CH3)3AsCl2,  (CH)4AsCl, 
and  even  (CH3)5As.  The  last  of  these  compounds  is  specially 
interesting  as  a  representative  of  the  unknown  NH5. 

The  stibines,  derivatives  of  SbH3,  are  similarly  constituted  ; 
but  for  detailed  accounts  of  these  bodies  a  treatise  on  carbon 
compounds  must  be  consulted. 

Corresponding  to  guanidine,  C(NH)"(NH2)2,  is  — 

Carbamide,  or  urea,  CO(NH2)2,  which  may  be  regarded  as 
carbonic  acid,  the  hydroxyl-groups  of  which  have  been  replaced 
by  amido-  groups.  It  exists  in  urine  (from  2  to  3  per  cent.),  and 
is  the  form  in  which  most  of  the  nitrogen  consumed  in  food  is 


UREA  AND   SULPHOCARBAMIDE.  o33 

eliminated  from,  the  organism.  It  may  be  separated  from  urine 
after  evaporation,  to  about  one  quarter  of  its  original  volume  by 
addition  of  nitric  acid,  which  precipitates  the  sparingly  soluble 
nitrate.  From  the  nitrate,  carbamide  may  be  separated  by  addition 
of  the  requisite  amount  of  potassium  hydroxide,  evaporation  to 
dryness,  and  extraction  with,  alcohol,  from  which  it  crystallises  on 
cooling  in  white  prisms. 

It  may  also  be  produced  by  treating  carbonyl  chloride,  COC12, 
with  ammonia,  thus:— COCk  +  2HNH2  =  CO(NH2)2  +  2HCI; 
also  by  heating  solutions  of  ammonium  carbonate  or  carbamate  to 
140—150°  in  sealed  tubes :— CO (ONH4)2  =  CO(NH2)2  +  2H20  ; 
NH2— CO(ONH4)  =  CO(NH2)2  -f  H2O.  Urea  unites  with  acids ; 
thus  the  hydrcchloride  has  the  formula  CO(NH2)2.HC1 ;  the  nitrate 
CO(NH2)2.HNO3.  It  is  decomposed  by  a  solution  of  potassium 
hypochlorite  or  hypobromite,  thus : — CO(NH2)2.Aq  +  SKBrO.Aq 
=  SKBr.Aq  -f  C02  -f  2H20  +  N2.  By  measuring  the  volume 
of  nitrogen  liberated,  the  amount  of  urea  in  such  a  liquid  as  urine 
may  be  estimated. 

Sulphocarbamide,  CS(NH2)3,  resembles  carbamide. 

HO — CO — NH2,  or  carbamic  acid,  is  unknown  in  the  free 
state.  Its  ammonium  salt  is  produced  by  the  union  of  one 
volume  of  carbon  dioxide  with  two  volumes  of  ammonia,  thus : — 
002  +  2NH3  =  NH4O.CO.NH2,  or  by  digesting  a  strong  solution 
of  ammonium  carbonate  with  saturated  aqueous  ammonia.  It  is 
completely  decomposed  at  60°  into  its  constituents.  The  follow- 
ing salts  of  the  acid  have  been  prepared  : — 

NaO.CO.NH2;  KO.CO.NH2;  Ca(O.CO.NH2>k;  Sr(O.CO.NH2)2; 
Ba(6.CO.NH2)2. 

Those  of  calcium,  strontium,  and  barium  are  soluble,  thus  dif- 
fering from  the  carbonates. 

Carbamates  are  attacked  by  hypobromites,  but  not  by  hypo- 
chlorites  ;  they  may  be  thus  distinguished  from  ammonium  carbo- 
nate, which  is  decomposed  by  both. 

The  hydrochlorides  of  titanamine,  Ti(NH2)4.4HCl,  and  of 
zirconamine,  Zr(NH2)4.4HCl,  are  produced  by  heating  the 
chlorides  in  a  current  of  ammonia  gas.  They  form  white  deli- 
quescent crystals. 

Difluosilicamine  dihydrofluoride,  F2=Si(NH2)2.2HF ; 
iodostannamine  trihydriodide,  I— Sn(NH2)3.3HI,  and  the  com- 
pounds Sn(NH2)4.4HI  and  SnI4.6NH3,  are  all  produced  by 
direct  addition.  The  monophosphine  of  stannic  chloride, 
Cl3Sn(PHo).HCl,  and  probably  the  monamine  are  also  known. 


534  THE   NITRIDES,   PHOSPHIDES,   ETC. 

The  known  stannous  compounds  are  SnCl2.3NH3;  SnI2.4NH3; 
and  also  the  plumbous  compound,  PbI2.2NH3.  The  hydroxide, 
Pb(OH)2.2NH3,  has  also  been  [prepared,  and  a  chloride  of  the 
formula  2PbCl2.3NH3. 

Vanadium  trichloride  combines  with  ammonia ;  niobium  and 
tantalum  chlorides  have  not  been  examined  in  this  respect. 

Phosphorus  triamide  has  already  been  described. 

The  acids  of  phosphorus,  also,  form  compounds  in  which  the 
amido-group  replaces  hydroxyl,  more  or  less  completely.  They  are 
as  follows  : — 

Orthophosphamide,  PO(NH2)3,  is  produced  by  the  action  of 
dry  ammonia  gas  on  phosphoryl  chloride,  thus  : — POC13  -f  3HNH> 
=  PO(NH2)3  +  3HC1.  The  excess  of  ammonia  combines  with  the 
hydrogen  chloride,  forming  ammonium  chloride,  which  is  removed 
by  washing  with  water,  in  which  phosphamide  is  insoluble.  It  is  a 
white  powder,  not  acted  on  by  boiling  water,  but  decomposed  by  hot 
sulphuric  a.cid  into  ammonium  sulphate  and  phosphoric  acid.  A 
similar  body,  sulphophosphamide,  PS(NH2)3,  is  obtainable  from 
sulphophosphoryl  chloride,  PSC13. 

When  heated,  phosphamide  gives  rise  to  substances  containing 
less  nitrogen,  and  corresponding  to  the  anhydrophosphoric  acids, 
so  far  as  the  analogy  between  the  amido-gronp  and  hydroxyl  will 
permit.  Phosphorylamide-imide  (the  group  =NH  is  named 
the  "imido-group  ")  and  phosphoryl  nitride,  thus  produced,  are 
white  insoluble  powders.  These  three  bodies  have  the  formulae 
O=P.(NH2)3;  NH=(OP)— NH2;  and  N=(OP),  the  first  two 
of  which  correspond  to  O=P(OH)3,  and  O=(OP)— OH. 

Orthophosphamic  acid  is  unknown  ;  but  its  sulphur  ana- 
logue, PS(.NH2)(OH)2,  is  produced  by  treating  sulphophosphoryl 
chloride,  PSC13,  with  strong  aqueous  ammonia.  It  forms  soluble 
salts.  The  anhydride  of  phosphamic  acid,  in  which  two  hydroxyl- 
groups  are  replaced  by  the  imido-group,  NH,  may  be  termed 
phosphimic  acid.  Its  formula  is  O(NH)"P(OH).  It  is  a  pasty 
soluble  mass,  produced  by  the  action  of  dry  ammonia  on  phos- 
phoric anhydride,  thus : — 

P205  +  2NH.  =  20(NH)P(OH)  -|-  H20. 

It  is  monobasic,  and  forms  white  crystalline  salts,  of  which  those 
of  sodium,  potassium,  ammonium,  calcium,  ferrous,  manganous, 
nickel,  cadmium,  zinc,  lead,  silver,  and  mercury  have  been  prepared. 
This  acid  may  be  regarded  as  metaphosphoric  acid,  O2P(OH),  with 
one  atom  of  oxygen  replaced  by  the  imido-group,  (NH)". 


PHOSPHAMIC   ACIDS.  535 

Phosphodiamic  acid,  OP(NH2)2.OH,  is  also  unknown,  but  its 
sulphur  analogue,  SP(NH2)2.OH,  is  produced  by  treating  sulpho- 
chloride  of  phosphorus  with  ammonia,  and  digesting  the  resulting 
solid  product  with  water.  It  may  be  supposed  that  the  inter- 
mediate body  S.PC1(NH2)2  is  formed.  The  free  acid  has  not  been 
obtained,  but  its  zinc,  lead,  copper,  and  silver  salts  are  insoluble 
precipitates,  and  establish  its  formula. 

Pyrophosphamic  acids  are  also  known,  and  correspond  to 
pyrophosphoric  acid,  P203(OH)4,  in  which  one,  two,  three,  or  four 
hydroxyl-groups  are  replaced  by  the  amido-group. 

Pyrophosphamic  acid,  P2O3(NH2)(OH)3,  is  produced  by 
heating  a  solution  of  pyrophosphodiamic  acid  (see  below) ;  the 
amido-group  of  the  latter  is  exchanged  for  hydroxyl,  thus : — 
P203(NH2)2(OH)2  +  H.OH  =  P203(NH2)(OH)3  +  HNH,. 

Pyrophosphodiamic  acid,  P2O3(NH2)2(OH)2,  is  produced  by 
adding  phosphoryl  chloride,  POCl3,to  a  cold  saturated  solution  of  am- 
monia, thus :— 2POC13  +  2NH3.Aq  +  3H2O  =  P2O3(NH2XOH)2.Aq 
-f  GHCl.Aq.  It  is  also  formed  by  boiling  phosphoryl  amide- 
imide,  PO(NH)(NH2),  with  dilute  sulphuric  acid,  thus: — 
2PO(NH)(NH2)  +  H2S04.Aq  +  3H20  =  P2O3(NH2)2(OH)2.Aq  + 
NH^SO^.Aq.  It  is  soluble  in  water,  yielding  salts. 

Pyrophosphotriamic  acid  should  have  the  formula 
P2O3(NH2)3(OH),  and  should,  therefore,  be  a  monobasic  acid.  But 
the  body  of  that  formula  is  tetrabasic,  and  hence  is  more  probably 
tri-imido-pyrophosphoric  acid,  P2(NH)"3(OH)4.  It  is  produced 
by  the  action  of  ammonia  on  phosphoryl  chloride,  with  subsequent 
treatment  with  water,  thus  :— 2POC13  +  9NH3.Aq  +  2H2O  = 
P2(NH)3(OH)4  -f  6NH4Cl.Aq.  It  is  a  white,  amorphous,  sparingly- 
soluble  powder,  forming  salts ;  those  of  potassium  and  ammonium 
are  monobasic,  thus  : — P2(NH)3(OH)3(OK) ;  they  are  white  and 
insoluble.  Mono-,  di-,  and  tri-basic  lead  salts  have  been  prepared, 
and  a  tetrabasic  mercuric  salt. 

Other  more  complex  compounds,  probably  amido-derivatives  of 
still  more  condensed  phosphoric  acids,  are  produced  by  the  action 
of  ammonia  on  phosphoryl  chloride.  Among  them  are  P4N5OnH17 ; 
P4N4O9H]0 ;  and  P4N5O7H9. 

Closely  connected  with  these  bodies  is  phospham,  PN2H, 
produced  by  the  action  of  ammonia  on  phosphoric  chloride, 
PC15.  The  intermediate  product  is  phosphorus  trichlorodiamide, 
PC13(NH2)2,  which  when  heated  evolves  hydrogen  chloride,  thus  : — 
PC13(NH2)2  =  PN2H  +  3HCL  The  constitution  of  phospham 
may  be  taken  as  N=EP=(NH).  It  is  a  white  insoluble  powder, 
unattacked  by  chlorine  or  by  sulphur  gas.  If  boiled  with  alkalies, 


536  THE   NITRIDES,    PHOSPHIDES,   ETC. 

it  yields  a  phosphate  and  ammonia,  thus  : — NEEP=(NH)  -f-  OIL 
+  3H— OK.Aq  =  0=P(OK)3.Aq  +  2NH3. 

Phosphorus  trichloride,  similarly  treated  with  ammonia,  yields, 
as  has  been  mentioned  on  p.  525,  phosphorus  triamide,  P(NH2)3,  as 
a  white  mass.  When  heated  out  of  contact  with  air,  a  whitish- 
yellow  residue  is  left,  probably  containing(HN)=P(NH2)  and  PEEN. 

Compounds  are  produced  by  treating  halides  of  arsenic,  anti- 
mony, and  bismuth  with  ammonia.  They  have  not  been  ex- 
haustively studied  ;  but  the  following  are  known  : — 

2AsCl3.7NH:3;  2AsI3.9NH3;  As2ClNH:6O4 ;  SbCl3.NH3 ;   SbCl5.6NH3 ; 
2BiCl3.NH3;  BiCl3.2NH3;  BiCl3.3NH3;  BiBr3.2NH3;  2BiBr3. 5NH3 ; 
BiBr3.2NH3. 

These  compounds  are  all  formed  by  direct  addition.  The  body 
As2ClNH6O4  is  produced  by  the  action  of  water  on  the  amine 
2AsCl3.7NH3,  and  it  appears  possible  that  their  constitution  is 
closely  related.  Perhaps  the  formlss  may  be  adopted : — 

(NH2)2.2HC1  A  /022'HC1 

NH  .2NH4C1  and   As\U 

(NH2),2HC1  As<foH)2 

The  formulas  of  the  remaining  compounds  are  easily  repre- 
sented as  chloramine  hydrochlorides,  with  the  exception  of 
2AsI3.9NH3,  which  requires  further  investigation. 

Amido-compounds  of  molybdenum  are  unknown.  The  action 
of  ammonia  at  a  high  temperature  on  the  chloride  yields  the 
nitride,  Mo3N2,  as  a  grey  powder. 

Complicated  compounds  are  produced  by  the  action  of  am- 
monia on  tungsten  hexachloride.  One  of  these  compounds  is 
said  to  have  the  formula  W7N9O4H4 ;  another,  W5N6O5H3 ;  a  third, 
W2N2O3;  while  W2N3  is  formed  from  WO2C12,  and  also  from  WC16. 
As  regards  the  constitution  of  these  bodies,  no  conclusions  can  be 
suggested  until  they  are  further  investigated. 

Uranium  tetrachloride  absorbs  ammonia,  producing 

3UC14.4NH3. 

Sulphur  dichloride,  treated  with  ammonia  gas,  yields  the 
compounds  S(NH2)2.2HC1  and  SC12.4NH3 ;  disulphur-dichloride, 
S2C12,  yields  S2C12.4NH3.  They  are  fairly  stable  crystalline 
bodies.  No  similar  compounds  of  selenium  have  been  pro- 
duced ;  but  tellurium  tetrachloride,  TeCl4,  with  ammonia  yields 
Te(NH2)4.4HCl. 

Compounds   containing   oxygen  have    been   more   closely  ex- 


SULPHAMIDES.  537 

amined.  Sulphurosyl  chloride,  SOCL,  with  ammonia  yields 
sulphurosamine,  SO(NH2}>,  and  hydrogen  chloride.  It  is  notice- 
able that  with  compounds  of  phosphorus  and  sulphur  the  basic 
character  of  the  amido-group  appears  to  be  neutralised  by  the 
acid  functions  of  the  groups  (SO)"  or  (PO)'" ;  hence  the  hydro  - 
chlorides  are  not  formed,  but  hydrogen  chloride  is  liberated.  Such 
alteration  in  the  functions  of  an  amide,  produced  by  the  entry  of 
groups,  which,  when  combined  with  water,  give  rise  to  acids,  is 
of  common  occurrence  among  the  amido-derivatives  of  the  carbon 
compounds. 

Sulphur  dioxide  mixed  with  its  own  volume  of  ammonia  yields 
sulphurosamic  acid,  HO— (SO) — NH2;  and  with  twice  its  volume 
of  ammonia,  ammonium  sulphurosamate,  NH4O — (SO) — NIL,  is 
produced.  No  other  compounds  of  this  acid  have  been  prepared. 

Sulphuryl  chloride,  S02C12,  with  ammonia,  does  not  yield 
sulphuramine,  S02(NH2)2,  as  might  be  expected,  but  the  reac- 
tion takes  place  with  formation  of  ammonium  sulphamate, 
NH2 — (SO2) — ONH4,  and  ammonium  chloride ;  but  it  is  impossible 
to  represent  such  a  change  without  the  interposition  of  a  molecule 
of  water.  The  reaction  requires  further  investigation.  Ammonium 
sulphamate  is  however  easily  obtained  by  the  action  of  ammonia 
on  sulphur  trioxide,  thus :— SO3  +  2NHS  =  NH4O— (SO2)— NH2 ; 
if  less  ammonia  be  used,  sulphamic  acid  is  formed,  thus : — 
SO3  +  NH3  =  HO — (SO2)— NH2.  Ammonium  sulphamate  is 
crystalline,  and  is  sparingly  soluble  in  water,  and  yields,  with 
barium  chloride  and  ammonia,  a  white  precipitate  of  a  basic 
barium  sulphamate,  from  which  the  neutral  salt  may  be  pre- 
pared by  cautious  addition  of  sulphuric  acid.  Its  formula  is 
Ba(OSO2NH2)2;  and  from  it  the  potassium  and  other  salts  have 
been  produced  by  treatment  with  sulphates. 

Similar  compounds  of  selenium  and  tellurium  are  unknown. 

Compounds  with  oxides  of  chlorine,  bromine,  and  iodine  are 
unknown.  The  amido-derivatives  of  these  elements  have  been 
described  among  the  halogen  compounds  of  nitrogen  (see  p.  158). 

The  amines  of  ruthenium,  rhodium,  and  palladium  differ 
in  character  from  each  other.  Those  of  ruthenium  occupy  a 
unique  position;  those  of  rhodium  closely  resemble  the  chrom- 
amines  and  cobaltamines ;  while  those  of  palladium  are  more 
closely  related  to  the  nickelamines  and  similar  bodies.  They  are 
all  specially  stable. 

The  compounds  of  ruthenium  are  produced  by  the  action  of 
solution  of  ammonia  on  ammonium  ruthenichloride,  (NH4)2RuCl6. 


538  THE   NITRIDES,   PHOSPHIDES,   ETC. 

The  mixture  is  heated,  evaporated  to  dryness,  and  extracted  with 
alcohol,  which  leaves  a  pale  yellow  crystalline  powder  of  the 
formula  RuCl2.4NH3.3H2O.  It  is  to  be  observed  that  the  ruthe- 
nium is  not  said  to  be  reduced  by  this  action  ;  hence  the  formula 
usually  assigned,  Ru"(N2H5)2.2HCl,  is  obviously  inapplicable.  On 
treatment  with  silver  hydroxide,  the  chloride  yields  a  hydroxide 
in  solution,  from  which  several  salts  —  the  carbonate,  nitrate,  sul- 
phate, &c.  —  have  been  prepared. 

When  the  hydroxide  is  heated  it  loses  two  molecules  of  am- 
monia, leaving  the  hydrate  of  the  diamine,  Ru(NH3)2(OH)2.4H2O, 
in  the  solid  state.  From  this  body  salts  have  been  prepared, 
which  have  a  darker  yellow  colour  than  those  of  the  diamine.  As 
ruthenium  dichloride  is  blue,  compounds  derived  from  it  would 
almost  certainly  not  have  the  colour  of  the  ammonium  rutheni- 
chloride,  in  which  the  tetrachloride,  Ru014,  is  contained,  unless 
there  were  some  close  connection  between  them. 

The  rhodium  amines  are  similar  to  the  purpureo-  and 
roseocobaltamines.  The  compounds  may  be  thus  classified  :  — 

E,li(NH3)5.X3  ;  roseorhodamines,  or  rhodamines  ; 

Cl—  K,li(NH:3)5.X2;  purpureorhodamines,  or  chlororhodamines  ; 

(NO3)  —  Rli(NH3)5.X2  ;  nitratorhodamines  ; 

(NO2)  —  B,h(NH3)5.X2;  nitrorhodamines,  or  xanthorhodamines. 

In  the  first  set  of  compounds  X3  is  replaceable  ;  in  the  remain- 
ing three  sets,  X2.  Hence  these  bodies  confirm  the  suggested 
formulae  for  the  cobaltamines.  For  the  first  set  we  may  suggest 
the  formula  :  — 


H5)2  2HX'  and  for  the  second>  X—  Rh(NH3)5.2HX. 

The  roseorhodamines  are  obtained  by  digesting  rhodochloride 
of  ammonium,  RhCl3.2NH4Cl,  with  ammonia.  This  yields  the 
chloride,  RhCl3.5NH3,  from  which  the  hydrate  is  obtainable  by 
the  action  of  silver  hydroxide  ;  and  from  it  the  carbonate,  oxalate, 
sulphate,  &c. 

The  purpureorhodamines  are  formed  from  rhodium  tri- 
chloride and  ammonia  ;  that  they  contain  one  atom  of  chlorine  in 
more  intimate  combination  than  the  other  two  is  proved  by  the 
fact  that  on  treatment  with  silver  nitrate,  sulphate,  &c.,  only  two 
atoms  of  chlorine  are  exchanged  for  the  groups  (N03)2,  (S04),  &c. 
Corresponding  bromine  and  iodine  compounds  are  produced  from 
the  roseorhodamines,  in  which  all  the  halogen  atoms  are  replace- 
able, by  keeping  the  bromides  and  iodides  at  a  high  temperature 
for  some  time.  The  nitrato-  and  nitro-compounds  may  be  similarly 


PALLADAM1NES.  539 

prod  need.     All  these  bodies  form  series  of  salts,  such  as  hydroxide, 
nitrate,  snlphate,  &c. 

Three  series  of  palladium  componnds  are  known,  two  derived 
from  the  dichloride,  PdCl3,  and  the  third  from  the  trichloride, 
PdCl3.  They  are  as  follows : — 

PdX-,.2NH3  =  Pd(NH2)2.2HX,  palladamine  dihydrohalide ; 
PdX2.4NH3  =  Pd(N2H5)2.2HX,  palladodiamine  dihydrohalide ; 
1  PdX3.2NH3  =  X — Pd(NH2)2.2HX,  halopalladamine  dihydrohalide. 

The  hydrochloride  of  the  palladamine  is  produced  by  digest- 
ing palladium  dichloride  with  a  slight  excess  of  ammonia  solution. 
It  has  a  red  colour,  but  at  100°  it  turns  yellow,  possibly  owing  to 
isomeric  change.  The  fluoride,  the  bromide,  the  iodide,  the  hydr- 
oxide (which  is  crystalline  and  a  strong  base),  and  several  other 
salts,  such  as  the  carbonate,  nitrite,  sulphite,  and  sulphate,  have 
been  prepared  by  the  usual  methods.  All  crystallise  well. 

By  digesting  palladium  dichloride  with  a  greater  excess  of 
ammonia  solution,  the  hydrochloride  of  palladodiamine  is  pro- 
duced. Of  this  series,  the  fluoride,  bromide,  iodide,  hydroxide, 
silicifluoride,  carbonate,  nitrate,  sulphite,  and  sulphate  are  known. 
When  heated  to  100°,  these  salts  lose  ammonia,  being  converted 
into  compounds  of  the  first  series. 

The  hydrochloride  of  the  third  series  is  produced  by  oxidising 
that  of  the  first  with  nitrohydrochloric  acid,  or  by  exposing  its 
solution  to  the  action  of  chlorine.  It  and  the  other  salts  are  dark 
red  crystalline  compounds. 

Osmamines,  Iridamines,  and  Platinamines. 

The  Osmamines  are  derived  from  tetrad  osmium,  as  in  OsCLi. 
They  are  as  follows  : — 

Cl2=Os(NH2)2.2HCl.wH2O ;  O=Os(NH2)2.(OH)2;  and  OsCl2(NH3)4. 

The  second  of  these  is  formed  by  the  action  of  excess  of 
ammonia  on  osmium  tetroxide,  OsO4;  it  is  a  blackish-brown 
powder,  soluble  in  hydrochloric  acid,  yielding  the  first. 

The  third,  supposed  by  its  discoverer,  Glaus,  to  be  analogous 
to  the  ruthenamines  of  similar  formula,  is  produced  by  the  action 
of  ammonium  chloride  on  potassium  osmate,  K20s04.  On  treat- 
ment with  silver  hydroxide,  it  yields  a  hydroxide.  This  compound 
evidently  also  contains  tetrad  osmium  ;  but,  like  the  correspond- 
ing compounds  of  ruthenium,  it  requires  reinvestigation,  for  its 
formula  implies  that  it  is  a  derivative  of  dyad  osmium.  It  is 
probable  that  there  is  error  in  supposing  it  to  contain  twelve 
atoms  of  hydrogen. 


540  THE   NITRIDES,   PHOSPHIDES,   ETC. 

The  compound  Os2N2O5K2  is  produced  by  the  action  of  am- 
monia and  potassium  hydroxide  on  osmium  tetroxide,  thus : — 
6OsO4  +  SNHS  +  6KOH  =  3Os2N2O5K2  +  JV2  +  15H20.  From  the 
barium  salt  the  acid  has  been  obtained.  Many  salts  are  known, 
of  which  those  of  sodium,  potassium,  ammonium,  barium,  and 
zinc  are  soluble ;  and  those  of  lead,  silver,  and  mercury  insoluble. 
They  explode  when  heated. 

The  iridamines  are  derived,  first,  from  iridium  dichloride. 
Such  are  iridosamine  hydrochloride,  Ir(NH2)2.2HCl,  and  its 
derivatives,  and  iridosodiamine  hydrochloride, 

Ir(NH2.NH3)2.2HCl; 

the  nitrate  and  sulphate  have  also  been  prepared.  The  first 
is  produced  by  cautiously  heating  iridium  trichloride  till  it 
changes  to  the  dichloride,  dissolving  the  brown  residue  in  solution 
of  ammonium  carbonate,  and  adding  a  slight  excess  of  hydrochloric 
acid.  It  is  a  yellow-orange  substance.  The  sulphate  is  produced 
by  evaporating  the  hydrochloride  with  the  requisite  amount  of 
sulphuric  acid.  When  the  hydrochloride  is  boiled  with  excess  of 
ammonia,  the  diamine  hydrochloride,  Ir(N2H6)2.2HCl,  is  produced 
as  a  whitish  precipitate.  The  nitrate  and  sulphate  are  crystalline. 

Second,  from  iridium  trichloride,  IrCl3.  The  hydrochloride, 
IrCl3.5NH3,  is  analogous  to  that  of  the  purpureocobaltamines 
and  the  rhodamines.  It  is  produced  by  gently  heating,  for  some 
weeks,  ammonium  iridichloride,  IrCl3.3NH4Cl,  with  excess  of 
ammonia  solution,  then  neutralising  with  hydrochloric  acid,  and 
washing  the  flesh-coloured  precipitate  with  water.  With  silver 
hydroxide  it  yields  the  hydroxide,  from  which  the  nitrate,  sulphate, 
&c.,  may  be  prepared  by  neutralisation. 

Third,  from  iridium  tetrachloride,  IrCl^.  By  heating  iridos- 
amine hydrochloride,  Ir(NH2)2.2HCl,  with  strong  nitric  acid,  the 
nitrate  of  dichloroiridodiamine  is  produced.  When  evaporated 
with  hydrochloric  acid,  violet  crystals  of  the  hydrochloride  are 
formed.  This  compound  is  known  to  have  the  constitution 
Cl2=Ir(N2H5)2.2HCl,  because  silver  nitrate  removes  only  half  its 
chlorine,  forming  the  dinitrate.  If  its  formula  were  Ir(N"H2)4.4HCl, 
all  the  chlorine  would  be  then  removed.  The  sulphate,  produced 
by  evaporating  the  hydrochloride  with  the  requisite  amount  of 
sulphuric  acid,  forms  greenish  needles. 

The  amido  -  derivatives  of  platinum  have  been  very 
thoroughly  investigated,  and  are  very  numerous.  They  are 
divisible  into  three  main  groups,  according  as  they  are  derived 
from  PtX2,  PtX3,  or  PtX4,  where  X  represents  a  halogen,  &c. 


PLATINAMINES.  541 

1.  Platinous  derivatives  (from  PtX2). 

1.  Pt"(NH2)2.2HX  ;*  salts  of  platinosamine. 

2.  X—  Pt"(N2H5).HX;t   salts  of  haloplatinosodiamine  (the    name   di- 
amine  may  be  given  to  the  group  (  —  NH2  —  NH3  —  ). 

These  compounds  are  isomeric  with  those  of  group  1. 


3.  ^Xnam*5  salts  of  platinosomonamine-diamine. 

4.  Pt//(N2H5)2.2HX;§  salts  of  platinosodiamine. 

1.  The  hydrochloride  of  platinosamine,  Pt(NH2)2.2HCl,  is 

produced  by  heating:  the  hydrochloride  of  platinosodiaraine, 
Pt(N2H5)2.2HCl,  to  220—270°  ;  or  by  boiling  platinum  dichloride 
with  solution  of  ammonium  carbonate,  filtering,  and  crystallising. 
It  forms  yellow  rhombohedra.  Silver  salts  remove  all  the  chlorine  ; 
and  in  this  way  many  of  the  salts  have  been  prepared.  Among 
these  are  the  bromide,  iodide,  oxide,  oxalate,  nitrite,  nitrate,  sul- 

NH  Cl 

phite,    sulphate,    chlorosulphite,    Pt<  jrjr2  QQ  TT>  an(^    sulphite, 


QO  TT 

gQ3TT'  wnich  have  replaceable  hydrogen,  and  furnish 

series  of  metallic  derivatives. 

2.  By   the   action   of    ammonia    on   a   solution    of    platinous 
chloride  in  hydrochloric  acid,   a  precipitate  (the  "  green   salt  of 
Magnus  ")  is  formed,  and  the  filtrate,  on  cooling,  deposits  yellow 
prisms  of  chloroplatinosodiamine  hydrochloride, 

ClPt(N2H5).HCl. 

From  its  solution  silver  salts  remove  only  half  the  total  chlorine, 
yielding  corresponding  salts,  among  which  are  the  bromide,  iodide, 
cyanide,  nitrite,  nitrate,  sulphate,  chlorosulphite,  and  sulphite. 
The  two  last  retain  hydrogen,  like  the  compounds  of  group  1, 
and  yield  metallic  derivatives.  With  caustic  soda  the  chloride 
yields  hydroxyplatinosodiamine  hydroxide,  HO  —  Pt  —  (N2H6).OH. 

3.  The    action  of  a  small  amount  of   ammonia   on   platinum 
dichloride   yields    a    double   compound   of    the    dichloride    with 
platinosomonamine-diamine    hydrochloride,    of    the    formula 

|V  -.  JTQ,  .PtCl2.    When  treated  with  nitric  acid,  the  nitrate 


*  Reiset,  Annales  [3],  11,  426;  Peyronne,  ibid.,  16,  462  ;  Cleve,  Bull.  Soc. 
Chim.,  16,  203. 

t  Cleve,  ibid.,  16,  207. 

J  Cleve,  ibid.,  16,  21. 

§  Peyronne,  Annales  [3],  12,  193  ;  Cler^,  Bull.  Soc.  Chim.,  7,  12. 


542  THE   NITRIDES,   PHOSPHIDES,   ETC. 

NH  HNO 

is  produced,  Pt<  /j~  Jr  \  TTNO  '  anc^  ^rom  ^  *ne  chloride,  sul- 


phate, &c. 

4.  When  the  hydrochloride  of  the  monamine,  Pt(NH2)2.2HCl, 
is  digested  with  ammonia,  or  when  its  isomeride  (the  "  green  salt 
of  Magnus,"  see  below)  is  similarly  treated,  the  compound 
Pt(N2H5)2.2HCl,  is  formed,  and  deposits  in  large  yellow  crystals. 

Its  platinochloride,  Pt(N2H5)o.2HCl.PtCl2,  is  the  green  salt  of 
Magnus*  (the  first  discovered  of  these  amido-derivatives),  as  is 
proved  by  its  formation  by  direct  addition  of  platinum  dichloride 
to  the  hydrochloride  of  platinosodiamine.  This  platinochloride 
forms  insoluble  needles  of  a  deep  green  colour.  It  was  originally 
produced  by  addition  of  ammonia  to  a  mixture  of  platinum  tetra- 
chloride  with  sulphur  dioxide  ;  a  mixture  containing  platinum  di- 
chloride, owing  to  the  reduction  of  the  tetrachloride  by  the  sulphur 
dioxide. 

Of  the  diamiue,  the  bromide,  iodide,  hydroxide,  carbonate, 
oxalate,  nitrate,  chromate,  dichromate,  sulphate,  hydrogen  sul- 
phate, hydrogen  phosphate,  and  other  salts  have  been  prepared. 

Two  series  of  double  salts  of  the  di-diamine  are  known, 
produced  by  addition.  The  first  of  these  (Buckton's)  have  the 
formula  Pt(N2H5)32HCl.MCl2,  where  M  stands  for  a  dyad  metal  ; 
the  second  (Thomson's),  M(N2H5)2.2HCl.PtCl2.  This  second 
series  really  forms  the  platinochlorides  of  the  diamines  of  other 
metals.  The  salt  of  Magnus  is  the  platinochloride  of  this  series, 
where  M  stands  for  platinum,  thus  :—  Pt(N2H5)2.2HCl.PtCl2. 

II.  Compounds  of  platinum  trichloride,  PtCl3  (or,  as  PtCl3  is 
unknown,  possibly  of  Pt2Cl6;  but,  as  there  is  as  little  reason  to 
suppose  the  existence  of  the  latter  body,  the  simpler  formulae  are 
adopted).  Derivatives  of  the  following  series  are  known. 

1.  X—  Pt(NH2)2.2HX;t  haloplatinodimonamine. 

2.  X—  Pt(N2H5)22HX;J  haloplatinodi-diamine. 

3.  X2—  Pt(N2H5)  ;§  dihaloplatinodiamine. 

1.  The  first  of  these  is  produced  as  iodoplatinodimonamine 
hydriodide,   by  the   action  of   ammonia  on  di-iodoplatinidiamine 
hydriodide    (see   below),    I2PtIV(KE2)2.2HL     It    is   a   crystalline 
powder,  and  is  the  only  compound  of  the  series  known. 

2.  The   starting  point  for   salts  of   the   second    series    is    the 
nitrate   of   platinosodiamine    (I  4).     On   treatment    with    iodine, 

*  Magnus,  Pogg.  Ann.,  14,  242. 

f  Cleve,  Bull.  Soc.  Chim.,  17,  100. 

£  Cleve,  ibid.,  15,  168. 

§  Clave,  ibid.,  17,  100;  Blomstrand,  BericUe,  1871,  639. 


PLATINAMINES.  543 

it  yields  the  nitrate  of  di-iodoplatini-di-diamine  (see  below), 
l2=Pt(N2H5)2.2HNO3.  This  substance,  with  ammonia,  loses  iodine, 
and  is  converted  into  the  oxide  of  iodoplatino-di-diamine  nitrate, 


T     ™-^o5.5  HNO3.N,H5.  ,,.     T       ,  .  ,      ,. 

I  —  P'  O—       -N~H  >^  —  *'    wnica    forms    micro- 


scopic yellow  needles.  With  nitric  acid,  it  yields  the  nitrate  of 
iodoplatinodi-diamine,  I  —  Pt(N2H5)2.2HNO3,  a  soluble  orange 
powder,  crystallising  in  small  prisms.  From  the  nitrate,  the  sul- 
phate, phosphate,  and  oxalate  have  been  made. 

By  boiling  the  oxide  of  iodoplatino-di-diamine  nitrate  with 
silver  nitrate,  hydroxyplatino-di-diamine  nitrate  is  produced, 
HO—  Pt(N2H5)2.2HN03,  and  from  this  salt  the  chloride,  sulphate, 
orthophosphate,  dichromate,  and  oxalate  have  been  prepared,  the 
hydroxyl-group  retaining  its  position. 

By  further  treatment  with  nitric  acid,  the  hydroxyl-group  is 
replaced  by  the  group  CN"03y,  yielding  NO3.Pt(N2H5)2.2HNO3,  a 
body  resolved  by  water  into  the  hydroxy-compound. 

The  bromochloride,  bromonitrate,  bromosulphate,  and  brom- 
oxalate  have  also  been  prepared,  of  the  formula 

Br—  Pt(N2H5)2.2HX. 

3.  The  chloride  alone  is  known,  Cl2=Pt(N2H5)  :  it  is  an 
amorphous  yellow  powder,  produced  by  the  action  of  nitrohydro- 
chloric  acid  on  a  base  of  the  formula  HO  —  Pt(N~2H5),  which, 
nevertheless,  differs  from  the  salt  I  2.  Opinions  differ  (Blom- 
strand,  Cleve)  as  to  the  composition  of  the  compound 

HO-Pt—  (N2H5)  ; 

it  and  its  derivatives  are  amorphous  explosive  black  substances, 
produced  by  boiling  chloroplatinosodiamine  hydrochloride  with 
soda. 

III.  Platinic  amines,  derived  from  PtX4.  These  compounds 
fall  into  the  following  classes  :  — 

1.  X2=Ptiv(NH:2)2.2HX.*     Dihaloplatinamine  diliydrohalide. 

2.  X3=Ptiv(NH2).HX.t     Trihaloplatinamine  hydrohalide. 

3.  X2=Ptiv<N"H2'I^x  •     Dihaloplatinimonodiamine  hydrohalide. 

4.  X2=Pt(N2H5)2.2HX.§     Dihaloplatimdi-diaminehydrohalide. 


*  Gerhardt,  Rev.  Sclent.,  28,  273 ;  Clere,  Bull.  Soc.  Chim.,  17,  100. 
t  Ibid.,  17,  105. 
J  Ibid.,  17,  107. 

§  G-ros,  Annales  [2],  69,  204;  Eaewsky,   ibid.  [3],  22,  273;  Cleye,  Bull. 
Soc.  Chim.,  7,  19 ;  and  15,  162. 


544  THE   NITRIDES,    PHOSPHIDES,   ETC. 

1.  These  compounds    are  prepared   from  the   chloride,  which 
is  formed  by  the  action  of  chlorine   on  platosamine  hydrochloride 
(I    1),    suspended   in   water.      It   forms    small    yellow    quadratic 
octahedra,    and   is    sparingly   soluble   in   water.     Its    formula   is 
Cl2=Pt(NH2)2.2HCl.     From  it  many  other  salts  have  been  pre- 
pared, among  which  are  the  dibromodihydrobromides,  the  di-iodo- 
dihydriodide,  the  dihydroxydihydroxide,  the  dinitrato-dinitrates, 
the  dihydroxydinitrate,  the   dinitrato-dinitrite,  the  nitrato-chloro- 
dinitrite,  the  dichlorodinitrite,  &c.     The  formula  of  the  last  may 
be  given  to  illustrate  the  nomenclature.     It  is 

CL=Pt(NH2)2.2HN02. 

2.  Compounds    containing  the  groups  EEPt(N2H5)  —  are  simi- 
larly formed  by  the  action  of  chlorine  on  chloroplatinosodiamine 
(I    2).      They    are    isomeric    with    the    former.       The    chloride 
forms    sparingly   soluble    yellow   laminae,    and   has    the    formula 
Cl3EEPt(N2H5).HCl.     From  it  the  tribromohydrobromide,  the  tri- 
hydroxy-nitrate,  the  dichloro-nitro-nitrite, 

(NO2)Cl2=Pt(N2H5).H]TO2, 


com- 


the  dihydroxy-sulphate,    (HO)2=Pt<^2H5HS04,  and  other 
pounds  have  been  prepared  by  the  usual  methods. 

TU"   TT 

3.  Derivatives    of    =Pt<^-jj  5  are  prepared,  like  those  of  the 

former  two  groups,  by  the  action  of  chlorine  on  the  hydrochloride 
of  platinoso-mono-diainine,  Pt(NH2)(N2H5).2HCl.  Its  hydro- 
chloride  forms  yellow  rhombic  scales.  The  dihydroxy-dinitrate, 
the  dibromo-dinitrate,  and  the  dibromo-sulphate  have  been  pre- 
pared. 

4.  Derivatives  of  =Pt(N2H5)2,  are  similarly  prepared  by  the 
action    of   chlorine    on   a   solution    of  platinosodi-diamine  hydro- 
chloride  (I  4)  ;    or  by  dissolving  the  hydrochloride  of  dichloro- 
platinamine    (IV    1)    in    ammonia.       The    hydrochloride    of    the 
dichloride   forms   sparingly   soluble   yellow   transparent    regular 
octahedra.      Many  derivatives  of  this  amine  are  known  ;  among 
others,  the   dibromo-hydrobromide,  the  hydroxybromo-dibromide, 
the  di-iodo-hydriodide,  the  chlorobromo-hydrochloro-hydrobromide 
(ClBr=Pt(NoH5)2.HCl.HBr),  &c.,  &c. 

Some    similar    compounds    with    hydroxylamme    have    been 
prepared.* 

*  Chem.  CentralbL,  1887,  1254. 


CUPKOSAMINES  AND  CUPRAMINES.  545 

Cuprosamines  and  Cupramines;  Argentamines,  Auramines, 
Mercurosamines,  and  Mercuramines. 

The  amido-derivatives  of  copper  are  divisible  into  two 
classes  : — 

I.  Those  containing  cuprous  copper,  as  in  cuprous  chloride, 

II.  Those   containing  cuprie   copper,    as   in  cupric   chloride, 
CuCl2. 

But  this  difference  is  to  be  noted  between  these  compounds 
and  those  of  the  previous  palladium  and  platinum  groups,  viz., 
that  on  treatment  with  halogen  acids  they  give  double  halides,  such 
as  CuCl.NH4Cl;  CuCl2.2NH4Cl,  &c.  They  are  not  so  stable  as 
the  compounds  of  the  preceding  groups,  but  rather  resemble  the 
zinc  and  cadmium  compounds. 

I.  Cuprous  compounds.*f — 

1.  Cu2Cl2.NH3  =  Cu2=NH.2HCl,  dicuprosamine  dihydro- 
chloride,  produced  by  direct  action  in  a  gentle  heat,  is  a  black 
powder. 

2.  CuCl.NH3  =  Cu — NH2.HC1,  cuprosamine  hydrochloride, 
is  a  non-crystalline  substance,  produced  by  the  action  of  ammonia 
on  copper  monochloride,  in  the  cold.     After  long  continued  action 
of  ammonia,  it  appears  probable  that  the  compound  CuC1.2NH3  is 
formed. 

3.  CuI.2NH3  =  CuNH2.NH4I  forms  white  crystalline  plates. 
It    is   produced   by  digesting  copper   with   cupric   chloride,    and 
then  adding  a  solution  of  potassium  iodide. 

II.  Cupric  compounds.^ — 1.  Cupramine  hydrochloride, 
Cu(NH2j2.2HCl,  is  produced  by  the  action  of  ammonia  on 
cupric  chloride,  CuCl2,  at  140°.  The  corresponding  carbonate, 
Cu(NH2)2.H2CO3,  and  sulphate,  Cu(NH2)2.H2SO4,  have  been 
prepared  by  direct  addition.  They  are  apple-green  compounds. 

NH 

2.  Cu<  ,^  Jj  y2HBr  is  precipitated  by  alcohol  from  a  mixture 

of  ammonia  with  cupric  bromide. 

3.  Cu(N2H5)2.2HI.H2O   is   formed   by   the    action    of    atmo- 
spheric oxygen  on  a  solution  of  cuprous  iodide,  Cul,  in  ammonia. 
This  body  is  of  special  interest,  for  cnpric  iodide,  CuI2,  is  unstable. 

*  Delierain,  Compt.  rend.,  55,  807;  Leval,  J.  Pharm.  (3),  4,  328. 
f  As  we  are  ignorant  of  the  molecular  weight  of  combined  cuprous  chloride, 
the  simple  formula  is  given. 

I  Kammelsberg,  Pogg.  Ann.,  48,  162 ;  55,  246. 


TJHIVIRSIT7 


546  THE  NITRIDES,  PHOSPHIDES,   ETC. 

'The  hydroxide  is  also  known,  Cu(N2H5),H2.(OH)2.2H3O,  forming 
blue  octahedra ;  also  the  sulphate,  dithionate,  and  iodate. 

4.  Cu(N2H5)2.(HBr)(NH4Br)  is  produced  by  direct  union. 

5.  Cu(N2H5)2.2NH4Cl  is  similarly  produced.     It  is  blue  and 
amorphous. 

Argentamines. — These  appear  to  be  very  numerous,  inasmuch 
as  almost  all  salts  of  silver  are  soluble  in  ammonia,  and  presumably 
unite  with  it.  But  only  a  few  have  been  isolated.  These  are  all 
argentous  compounds. 

1.  Argentamine.  Ag(NH2)   (?),  is  a  black  explosive  powder, 
commonly  called  "fulminating  silver,"  produced  by  the  action  of 
ammonia  solution  on  silver  hydroxide 

2.  (AgNH2.HI).AgI.      A  double  salt,   formed  by  the  action 
of  gaseous  ammonia  on  dry  silver  iodide  which  has  not  been  fused. 

3.  Ag(NH2).HNO3  and  the  corresponding  chlorate,  sulphate, 
and   chromate,    are   soluble   crystalline  bodies,  formed  by  direct 
union. 

4.  (AgNH2.HCl).2NH4Cl,   is   a   double    salt,    formed  by  the 
action  of  ammonia  on  silver  chloride,  suspended  in  water.     It  is 
very  soluble,  and  crystallises  ont  on  concentration.     Silver  bromide 
does  not  absorb  ammonia.     The  corresponding  nitrate  has  been 
prepared. 

Auranrines.* — Aurous  oxide,  Au2O,  dissolves  in  strong  am- 
monia, giving  NAu3.NH3.  When  boiled  with  water,  ammonia  is 
evolved,  and  gold  nitride,  Au3N,  remains.  Gold  monoxide,  AuO, 
on  similar  treatment,  yields  a  similar  compound,  but  the  gold  is 
present  as  hydroxide;  its  formula  is  N(AllOH)3.NH3.  It  is  a 
very  explosive  substance,  which,  when  boiled  with  water,  under- 
goes a  similar  decomposition,  the  product  being  N(AllOH)3. 
Auric  chloride,  AuCl3,  digested  with  ammonia,  yields  "  fulminat- 
ing gold,"  a  mixture  of  HN=AuCl,  and  HN=Au— NH2.  The 
latter,  digested  with  sulphuric  acid,  yields  a  salt  of  the  formula 
Au(N2H5)2.H2SO4.  These  compounds  are  all  very  unstable. 

Mercurosamines  and  mercuramines.t — Of  these  many  are 
known ;  and  a  few  examples  of  corresponding  phosphorus  and 
arsenic  compounds  have  also  been  prepared,  which  will  be  con- 
sidered along  with  their  analogues. 

I.  Mercurosamines. — Of  these  there  are  three  classes;  the 

*  Dumas,  Annales  (2),  44,  167;  Easchig,  Annalen,  235,  341. 

f  The  chief  references  on  this  subject  are  : — Mitscherlich,  Fogg.  Ann.,  9, 
387;  16,41;  55,248;  Kane,  Annales  (2),  72,  215;  Millon,  ibid.  (3),  18,  392; 
Plantancour,  Annalen,  40,  115;  Hirzel,  ibid.,  84,  258;  Schruieder,  J.  prakt. 
Chem.,  75,  128. 


MEKCUBAMINES.  547 

first  contains  the  group  (NH)2f  ;  the  second  the  group  (NH)", 
and  the  third  the  triad  atom  (N)'".  These  are  analogous  to  the 
monamimes,  diamines,  and  triamines,  where  the  hydrogen  of  a 
molecule  of  ammonia  is  replaced  successively  by  one,  two,  and 
three  hydrocarbon  groups,  snch  as  methyl,  ethyl,  &c.,  as  NH2CH3, 
NH(CH3)2,  and  N(CH3)3. 

1.  HgNH2.HP,    a    black    substance,    decomposed    by    water, 
produced  by  the  action  of  gaseons  ammonia  on  mercurous  fluoride. 
A     double    salt    of     the     chloride,    with     ammonium     chloride, 
HgNH2.NH4Cl  (or  possibly  Hg(N2H5)HCl),  is  formed  when  dry 
ammonia  is  absorbed  by  dry  mercurous  chloride.     When  warmed 
this  body  loses  ammonia,  leaving  the  hydrochloride,  HgNEL.HCl. 
The  iodide  is  unstable. 

2.  The  compounds  Hg,NH.HCl  and  HgoNH.HBr  are  black 
substances,  produced  by  treating  mercurous  chloride  or  bromide 
with   solution   of  ammonia.     The   formation   of   this   precipitate 
serves  to  distinguish  mercurous  chloride  from  that  of  silver  or 
lead,  both  of  which  are  also  insoluble.     Mercurous  nitrate,  with 
ammonia  solution,  gives  a  corresponding  compound, 

2(Hg2NH.HN03).H20, 

as  a  greyish-black  powder,  decomposed  by  light. 

The  action  of  hydrogen  arsenide  on  mercuric  chloride  is  to 
produce  an  analogous  compound,  in  the  form  of  a  double  salt, 
HgoAsCl.HgCL,  as  a  brownish-yellow  precipitate.  Here  hydrogen 
is  replaced  by  chlorine  ;  and  it  may  be  remembered  that  compound 
arsines  containing  hydrogen  in  union  with  arsenic  are  also 
unknown. 

3.  2(Hg3N.HNO3).3H2O,  trimercurosamine  nitrate,  is  also 
formed  by  treating  mercurous  nitrate  with  ammonia  solution. 

II.  Mercurarnines. — These  may  be  divided  into  four  classes: — 
1.  Those  in  which  the  mercury-atom  shares  its  two  powers  of 
combination  with  the  amido-group,  and  with  some  other  group. 

Cl — Hg — NH2,  chloromercuramine,  is  a  white  precipitate, 
formed  by  adding  a  slight  excess  of  ammonia  to  a  cold  solution  of 
mercuric  chloride,  HgCl2.Aq.  When  gently  heated,  its  bydro- 
chloride,  Cl  — Hg — NH2.HCl,  sublimes,  leaving  the  compound 
C.Hg — N=Hg.HgCl2  (see  below).  Chloromercuramine  is 
named  "infusible  white  precipitate."  The  hydrochloride  may 
also  be  produced  by  acting  on  dry  mercuric  chloride  with  gaseous 
ammonia,  or  by  digesting  mercuric  oxide,  HgO,  with  ammonium 
chloride.  It  resembles  mercuric  chloride  in  appearance,  and  may 
be  sublimed  without  sensible  decomposition. 

2  N  2 


548  THE  NITRIDES,   PHOSPHIDES,   ETC. 

Bromomercuramine,  BrHgNH2,  and  its  hydrobromide  re- 
semble the  chloro-  compounds  in  properties  and  reactions. 

lodomercuramine  hydriodide,  produced  by  evaporating  a 
solution  of  mercuric  iodide  in  ammonia,  forms  small  white  needles. 
A  double  salt'  of  oxymercuramine  nitrate  with  ammonium  nitrate, 

O  <C  Trf  _        2  ^^4^^3'  *s  ^orme^  by  mixing  solutions  of 


mercuric  nitrate  and  ammonia,  and  evaporating  the  filtered  liquid. 
When  boiled  with  water,  its  solution  deposits  yellow  needles  of 
the  simple  nitrate. 

2.  Mercur  amines.  —  Mercuramine  hydrochloride, 

Hg(NHa)2.2HCl, 

or  "fusible  white  precipitate,"  is  produced  by  adding  a  solution 
of  mercuric  chloride  to  a  boiling  mixture  of  solutions  of  ammonium 
chloride  and  ammonia  as  long  as  the  precipitate  at  first  formed 
redissolves  ;  also  by  boiling  chloromercuramine,  ClHgNH2,  with 
solution  of  ammonium  chloride.  It  forms  white  rhomboidal  dodeca- 
hedra.  The  hydriodide  is  a  substance  of  a  dull-  white  colour, 
produced  by  the  action  of  ammonia  gas  on  mercuric  iodide.  In 
presence  of  water,  crystals  of  Hg(NH2)2.2HI.3H2O  are  formed.  A 
double  salt  of  the  oxide  with  mercuric  nitrate, 


is  produced  by  adding  ammonia  in  small  quantity  to  a  slightly 
acid  solution  of  mercuric  nitrate.  It  deposits  slowly  as  a  white 
precipitate. 

3.  The  third  group  resembles  the  first,  in  having  halogen  or 
similar  groups  directly  connected  with  the  mercury  ;  but  two 
hydrogen-atoms  of  the  ammonia  are  thereby  replaced. 

The  fluoride,  (FHg)2.NH.H2O,  is  a  gelatinous  precipitate  pro- 
duced by  treating  mercuric  fluoride  with  ammonia.  —  Dichloro- 
xnercuramine  hydrochloride.  (ClHg)2.NH.HCl,  is  formed  as  a 
white  insoluble  precipitate  by  the  action  of  great  excess  of  am- 
monia on  mercuric  chloride.  —  Hydroxy  chloromercuramine, 

° 


;  is  produced  when  chloromercuramine  hydrochloride, 

Cl—  Hg—  NH2.HC1,  is  boiled  with  water,  thus  :—  2ClHgNH2  HC1 
+  H20  +  Aq  =  NH4Cl.Aq  +  2HCl.Aq  +  (HOHg).(ClHg).NH. 
It  is  a  dense  yellow  powder.  With  solution  of  potassium  iodide  it 
gives  the  corresponding  hydroxyiodide,  which  is  also  formed  as  a 
brown  precipitate  by  the  action  of  ammonia  on  mercuric  iodide.  — 


MERCURAMINES.  549 

The  hydroxyoxide,  O<Hg(NH)— Hg  OH'  is  Produced  b7  the 
action  of  strong  ammonia  solution  on  yellow  mercuric  oxide.  It 
is  a  brown  insoluble  substance,  turning  white  on  exposure  to 
air  owing  to  absorption  of  carbon  dioxide.  Many  salts  of  this 
body  are  known. 

Oxydimercuramine  nitrate,  O<TTd>NH.HNO3,  is  a  granu- 
lar white  powder,  formed  by  boiling  oxymercuramine  mercuric 
nitrate,  O(HgNH2)2.HgNO3  (see  2),  with  water ;  ammonium  nitrate 
is  also  formed.  The  mercuro-hydroxy nitrate  of  oxydimercur- 

TT.J  OTT 

amine,  O<jr5>NH.Hg<[j,.Q  »  is  produced  by  adding  a  great 
excess  of  ammonia  to  mercuric  nitrate  ;  it  is  a  whitish-yellow  pre- 
cipitate. 

Compounds  such  as  these  are  very  numerous.  Carbonates, 
chromates,  sulphites,  phosphates,  arsenates,  iodates,  and  other 
compounds  have  been  prepared.  Their  methods  of  preparation, 
constitution,  and  properties  may,  however,  be  inferred  from  those 
of  the  halides  and  nitrates  described  above. 

4.  The  last  series  of  compounds  is  one  in  which  the  hydrogen 
of  ammonia  is  entirely  replaced  by  mercury.  Trimercuramine, 
N2(Hg")3,  or  more  correctly  mercuric  nitride,  is  a  dark-brown 
powder,  produced  by  passing  ammonia  over  hot  mercuric  oxide  at 
130°.  It  is  exceedingly  explosive.  The  action  of  liquefied  ammonia 
on  mercuric  iodide  yields  the  compound  IHg — N=Hg  ;  and  the 
hydrate  HO.Hg — N— Hg  is  formed  by  digesting  mercuric  oxide 
with  aqueous  ammonia.  It  may  be  heated  to  100°,  and  yields  the 
oxide  Hg— N — Hg — O — Hg — N=Hg  as  a  deep-brown  explosive 
powder.  From  the  oxide  the  chloride,  ClHg — N=Hg,  is  produced 
by  treatment  with  hydrochloric  acid.  A  compound  of  this  chloride 
with  mercuric  chloride,  ClHg — N=Hg.HgCl2,  forms  small  red 
crystalline  laminae,  and  is  left  as  a  residue  when  the  hydrochlo- 
ride  of  chloromercuramide,  ClHgNH2.HCl,  is  sublimed  from 
chloromercuramide,  ClHgNH2.  Similar  to  this  last  compound  is 
one  produced  by  the  action  of  hydrogen  phosphide  on  a  solution 
of  mercuric  chloride  ;  its  formula  is  2(ClHg — P=Hg).HgCl2.  It 
is  a  yellow  powder.  The  corresponding  bromide  has  also  been 
prepared.* 

*  Rose,  Pogg.  Ann.,  40,  75. 


550 


CHAPTER  XXXII. 

NITRIDES,    PHOSPHIDES,    ARSENIDES,  AND   ANTIMON1DES    (CONTINUED)  ; 
CYANIDES   AND   DOUBLE    CYANIDES. 


Na3N;*  Na3Pjf  Na3As  £  Na3Sb.t—  K3N  j*  K3Pf  (?)  ; 

Sodium  nitride  is  a  greenish  mass,  produced  by  heating  sod 
amide  (seep.  524)  to  redness,  thus  :—  3NaNH2  =  Na,N  +  2NK3. 
Potassium  nitride  is  similarly  produced.  These  compounds 
burn  brilliantly  when  heated  in  air,  and  are  decomposed  by  water. 
—  Sodium  and  potassium  phosphides  are  produced  by  direct 
union,  best  under  a  layer  of  xylene,  C8Hi0  ;  the  union  is  exceed- 
ingly energetic,  and  is  accompanied  by  evolution  of  heat  and  light. 
Excess  of  phosphorus  is  dissolved  out  by  treatment  with  carbon 
disulphide,  and  the  blackish  powder  remaining  is  dried  in  a  cur- 
rent of  dry  carbon  dioxide.  —  Arsenide  and  antimonide  of 
sodium  and  potassium  are  metallic-looking  substances,  of  crys- 
talline fracture,  produced  by  direct  union  at  a  red  heat  j  the  union 
takes  place  with  incandescence.  With  water,  these  bodies  yield 
hydrogen  arsenide  or  antimonide. 

No  nitrides  of  beryllium,  calcium,  strontium,  or  barium  have 
been  prepared  ;  beryllium  is  said  to  combine  directly  with 
phosphorus:  but  the  compound  obtained  was  impure.  Calcium 
and  barium  phosphides  have  been  produced  mixed  with  pyro- 
phosphates§  by  the  action  of  phosphorus  gas  on  the  oxides,  thus  : 
7BaO  +  12P  =  5BaP2  +  Ba^O?.  The  mixture  is  a  brownish- 
black  lustrous  substance,  giving  with  water  phosphine  and  barium 
hypophosphite.  Arsenides  appear  to  be  similarly  produced.  No 
antimonides  have  been  prepared. 

*  G-ay-Lussac   and    Thenard,    Eech.   physico-chim.,   1,   354;   Beilstein   and 
G-euther,  Annalen,  108,  88. 

f  Vigier,  Bull.  Soc.  Chim.,  1861,  6.^ 
J  Landolt,  Annalen,  89,  201. 
§   Dumas,  Annales,  32,  364. 


NITRIDES  AND   PHOSPHIDES.  551 


.:—  Zn3N2  ;f  Zn,P2;§  ZnP;  ZnP2;(?) 
ZnP6;(?)  Zn3As2;  Cd3As2iJ.  —  Nitride?  of  cadmium  have  not  been  prepared; 
but  that  metal  unites  directly  with  phosphorus,  forming  Cd3P2  and  Cd.2P- 
The  arsenide  is  said  to  have  the  formula  Cd2As. 

Magnesium  nitride  is  a  greenish-yellow  amorphous  mass, 
produced  by  direct  union  of  nitrogen  with  red-hot  magnesium,  or 
even  by  burning  magnesium  in  a  limited  supply  of  air  ;  it 
reacts  with  water,  forming  ammonia.  —  Zinc  nitride  is  produced 
by  heating  zincamine,  Zn(NH2)2,  to  redness  (see  sodium  nitride)  ; 
it  is  a  grey  powder,  reacting  violently  with  water,  yielding  am- 
monia and  zinc  hydroxide.  Magnesium  phosphide,  produced 
by  direct  union  at.  a  red  heat,  is  a  steel-grey,  crystalline  substance 
with  metallic  lustre.  The  compound  Zn3P2  is  produced  by  direct 
union  of  the  vapours  of  zinc  and  phosphorus,  either  directly  or 
when  zinc  phosphate  is  strongly  heated  with  charcoal.  It  forms 
iridescent  prismatic  crystals,  or  a  grey  mass.  It  volatilises  at  a 
higher  temperature  than  zinc.  The  phosphide,  ZnP,  is  said  to  form 
brilliant  needles  ;  it  is  probable  that  the  compounds  ZnP2  and 
ZnP6  are  mixtures  of  amorphous  Zn3P2  and  red  phosphorus.^ 
Cadmium  phosphide,  Cd3P2,  is  a  crystalline  body  with  grey 
metallic  lustre.  The  phosphide,  Cd,P,  is  said  to  be  formed  at  the 
same  time.^[  These  bodies  require  further  study.  —  Magnesium 
arsenide  is  a  brown  slightly  lustrous  substance,  produced  by 
direct  union  ;  zinc  and  arsenic  combine  with  incandescence,  giving 
brilliant  grey  octahedra,  which,  when  heated,  yield  a  brittle  grey 
button  of  Zn3As;  and  cadmium  arsenide,  a  bright  metallic- 
looking  substance  with  a  reddish  tinge,  is  produced  by  the  action 
of  potassium  cyanide,  KCN,  at  a  red  heat  on  cadmium  arsenate. 
Compounds  of  these  elements  with  antimony  may  be  prepared  by 
fusion;  two  crystalline  antimonides  of  zinc,  of  the  formulae 
ZnSb  and  Zn3Sba,  are  known  ;  they  appear  to  be  definite  com- 
pounds. They  decompose  water  at  the  ordinary  temperature. 

BN.**  —  No  other  compounds  of  the  elements  of  this  group  have 
been  prepared.  —  Boron  nitride  is  produced  by  direct  union  ;  by 
the  action  of  ammonium  chloride  on  boron  oxide  at  a  red  heat; 
and  by  passing  the  product  of  the  action  of  boron  chloride  on 

*  Brieglieb  and  Geuther,  Chem.  News,  38,  39  ;  Annalcn,  123,  228. 

t  Phil.  Mag.  (4),  15,  149. 

I  Parkinson,  Chem.  Soc.  (2),  5,  117. 

§  Vigier,  Bull.  Soc.  Chim.,  1861,  5. 

|j  Compt.  rend.,  86,  1022,  1065. 

f  Renault,  Annales  (4),  9,  162. 

•*  Wohler,  Annalen,  74,  70  ;  Martius,  ibid.,  109,  80. 


552  THE  NITRIDES,  PHOSPHIDES,   ETC. 

ammonia  through  a  red  hot  tube.  It  is  a  soft  white  amorphous 
infusible  powder.  It  is  very  stable  ;  but  when  heated  in  steam  it 
yields  boron  oxide  and  ammonia  (see  p.  513). 

A1N  ;*  the  phosphide  and  arsenide  have  been  prepared,  but 
not  analysed.  The  only  other  compound  of  the  group  which  has 
been  prepared  in  a  definite  form  is  TISb.  —  Aluminium  nitride 
was  prepared  by  heating  aluminium  with  sodium  carbonate  to  an 
exceedingly  high  temperature  (the  nitrogen  is  evidently  derived 
from  air)  ;  it  forms  yellow,  lustrous  crystals,  becoming  dull  on 
exposure  to  moist  air,  and  finally  evolving  ammonia,  leaving  a 
residue  of  aluminium  hydroxide.  —  The  phosphide  and  arsenide 
are  grey  masses,  produced  by  direct  union.  —  Thallium  anti- 
monide,  also  produced  directly,  is  brittle,  and  possesses  metallic 
lustre. 


CrP.—  Fe3N2  (?)  ;f  Fe3P4;  PeP;  Fe2P  ;f—  Fe3As2;  FeAs  ; 
t  Fe2As3;  FeAs2  ;  FeAs4.—  Mn3P2(?);  MnAs.—  Co3P2  ; 
CoAs3.—  Ni2P;  Ni3P2;  Ni3As;  Ni2As;  Ni-jAss;  NiAs;  NiAs2;  NiSb. 

Many  of  these  compounds  occur  native  ;  among  them  are  leucopyrite  or 
arsenosiderite,  Fe2As3  ;  lolinflite,  FeAs2  ;  Jcaneite,  MnAs  ;  smaUite,  CoAs.,  ; 
sJcutterudite,  CoAs3  ;  kupfernickel,  or  niccolite,  NiAs  ;  rammelsbergite,  NiAs2  ; 
,and  breithauptite,  NiSb. 

Chromium  nitride  has  been  obtained  by  heating  anhydrous 
chromium  trichloride  in  ammonia.  It  is  an  insoluble  brown 
powder,  burning  in  air  to  chromium  sesquioxide  and  nitrogen. 
The  phosphide,  similarly  prepared,  is  a  black  powder,  insoluble 
in  water,  and  not  attacked  by  acids.  Phosphides  of  cobalt  and 
•nickel,  Co3P2,  and  Ni3P2,  are  grey  powders,  produced  by  heating 
-the  dichlorides  in  a  current  of  phosphine.  Iron  at  a  red  heat  is 
•hardly  attacked  by  molecular  nitrogen.  But  if  the  nitrogen  is 
nascent,  as,  for  instance,  if  ammonia  be  passed  over  red-hot  iron, 
a  white  brittle  substance  is  formed,  and  the  gain  in  weight  corre- 
sponds to  the  formula  Fe2N.  A  similar  substance  is  formed  by 
heating  ferrous  chloride,  PeCl2,  in  a  current  of  ammonia  ;  but  its 
composition  appears  to  correspond  with  Pe3N2.  At  a  higher  tempe- 
rature it  loses  nitrogen,  and  is  converted  into  Fe3N.  Iron  nitrides 
burn  in  air,  and  when  heated  in  hydrogen  yield  ammonia  and 
metallic  iron  ;  with  steam,  iron  oxide  and  ammonia  are  the 
products. 

Many   phosphides   of   iron   have   been    obtained,  §    but   the 

*  Mallet,  Chem.  Soc.,  30,  349. 
t  Stahlschmidt,  Fogg.  Ann.,  125,  37. 
I   Compt.  rend.,  86,  1022  and  1065. 
§  Freese,  Pogg.  Ann.,  132,  225. 


PHOSPHIDES  AND  ARSENIDES  OF  IRON,  MANGANESE,  ETC.      553 

separate  existence  of  many  of  them  as  distinct  chemical  individuals 
is  doubtful.  Those  which  appear  best  established  are  Fe3P4,  pro- 
duced as  a  black  powder  by  heating  the  disulphide,  PeS2,  in  a 
current  of  phosphine ;  PeP,  a  grey  tumefied  mass,  obtained  by  the 
action  of  phosphorus  vapour  on  finely  divided  iron,  reduced  from 
its  oxide  by  hydrogen  ;  and  Pe2P,  a  hard  brittle  mass  with  metallic 
lustre,  produced  by  throwing  phosphorus  on  to  red-hot  iron  filings. 
These  substances  are  insoluble,  and  are  attacked  with  difficulty  by 
acids.  A  phosphide  of  manganese,  which  appears  to  approxi- 
mate in  composition  to  the  last  mentioned  phosphide  of  iron,  is 
produced  similarly,  or  by  reducing  manganous  pyrophosphate, 
Mn2P2OT,  by  charcoal  at  an  intense  heat.  Corresponding  phos- 
phides of  nickel  and  cobalt  are  similarly  prepared,  and  have 
similar  properties.  The  arsenides  of  iron  are  whitish-grey 
brittle  substances  with  metallic  lustre,  which  are  either  found 
native,  or  have  been  prepared  by  direct  union.  A  white  hard 
magnetic  alloy  is  also  formed  when  antimony  and  iron  are 
heated  together.  The  native  arsenide  of  manganese  is  a  hard 
grey  substance,  approximating  in  composition  to  the  formula 
MnAs.  Cobalt  diarsenide  or  smaltine  is  the  most  abundant  of 
cobalt  ores,  and  is  found  native  in  silver-white  regular  crystals. 
When  heated,  a  portion  of  the  arsenic  is  evolved,  and  a  fusible 
brittle  metallic-looking  mass  remains.  Skutterudite,  or  modumite, 
CoAs3,  forms  regular  crystals  of  a  grey-white  metallic  appearance, 
which  evolve  arsenic  when  heated.  Chloranthite,  or  white  nickel, 
NiAs2,  forms  tin- white  regular  crystals,  or  as  rammelsburgite,  tri- 
metric  prisms,  which  oxidise  in  moist  air  to  arsenate  of  nickel. 
Copper  nickel  or  niccolite,  NiAs,  usually  forms  compact  masses  of 
a  copper-red  colour,  and  sometimes  hexagonal  prisms ;  it  is  one  of 
the  chief  ores  of  nickel.  The  rare  mineral  breithauptite,  NiSb, 
eccurs  in  thin,  copper-coloured,  hexagonal  plates.  Speiss  is  a 
deposit  formed  in  the  pots  when  roasted  arsenide  of  cobalt,  mixed 
with  copper  nickel,  is  fused  with  potassium  carbonate  and  silica  in 
the  preparation  of  smalt,  a  blue  glass  containing  cobalt.  It  con- 
tains cobalt,  manganese,  iron,  antimony,  bismuth,  and  sulphur, 
but  consists  mainly  of  nickel  arsenide ;  and  the  proportions  of 
these  constituents  correspond  best  with  the  formula  Ni3As2.  It  is 
sometimes  found  in  dimetric  crystals,  but  is  generally  a  white 
metallic-looking  substance  with  a  reddish  tinge.  The  arsenide, 
Ni2As,  has  been  produced  by  direct  union. 

Double  compounds. — These  are  found  native,  and  uniformly 
contain  sulphur ;  the  most  important  of  the  double  sulphides  and 
arsenides  are : — 


554  THE  NITRIDES,  ARSENIDES,  ETC. 

Mispiclcel,  or  arsenopyrites,  FeSAs;  pacite,  Pe5S2As8;  glaucopy rites, 
3?ej3S2As24 ;  glaucodot  (Fe,Co)SAs;  cobaltite,  CoSAs;  gersdorffite,  NiSAs  ; 
ullmannite,  NiSSb ;  corynite,  NiS(As,Sl>)  ;  and  ulloclasite,  Co3S4As6Bi4. 

These  have  a  yellow  or  grey  colour,  and  possess  metallic 
lustre. 

Nitride  of  carbon  or  cyanogen,  C2N2,  is  such  a  remarkable 
substance,  and  forms  so  many  double  compounds,  that  it  is  prefer- 
able to  consider  it  apart.  It  will  therefore  be  treated  of  after  the 
other  nitrides  have  been  described. 

Titanium  forms  two  well- denned  nitrides,  which  for  long 
were  mistaken,  owing  to  their  metallic  lustre,  for  titanium  itself. 
Wohler  was  the  first  to  show  their  true  nature.*  Their  formulae 
are  TiN  and  Ti3N4,  the  first  corresponding  to  the  oxide,  Ti2O3, 
and  the  latter  to  TiOa.  TiN  is  produced  by  heating  titanium 
dioxide  in  a  current  of  ammonia;  Ti3N4,  by  similarly  treating 
TiCl4 ;  on  heating  it  to  a  high  temperature  for  a  sufficiently  long 
time,  it  loses  nitrogen,  yielding  TiN.  Titanium  mononitride  forms 
golden-yellow  crystals,  and  trititanic  tetranitride  forms  crystals  of 
a  copper-red  colour  with  metallic  lustre.  The  existence  of  other 
nitrides,  described  by  Wohler,  appears  to  be  disproved.  When 
heated  in  steam  these  nitrides  yield  titanium  oxide  and  ammonia. 
Titanium  easily  unites  directly  with  nitrogen,  forming  a  mixture 
of  these  compounds. 

Zirconium  also  forms  nitrides  when  the  element  or  its  tetra- 
chloride  is  heated  in  ammonia ;  yellow  crystals  have  been  obtained 
also  by  the  action  of  atmospheric  nitrogen  on  zirconium  at  an 
intense  heat.j  Their  composition  is  unknown,  but  they  are  decom- 
posed by  steam,  yielding  ammonia.  Cerium  and  thorium  com- 
pounds are  unknown. 

No  phosphide  of  carbon  is  known.  Titanium  phosphide  has 
been  prepared  by  heating  the  phosphate  with  carbon.  Its  formula 
is  unknown ;  but  it  is  said  to  form  white  brittle  fragments. 
Phosphides  of  cerium,  zirconium,  and  thorium  have  not  been 
prepared;  nor  are  arsenides  or  antimonides  of  these  elements 
known. 

Nitride  of  silicon  is  a  white  amorphous  mass,  of  the  formula 
SLN3,  infusible,  and  unoxidisable  by  heating  in  air,  and  insoluble 
in  all  acids  but  hydrofluoric.  It  is  produced  by  heating  silicon  in 
a  current  of  nitrogen ;  the  action  of  ammonia  on  silicon  tetra- 
chloride  yields  a  chloride,  Si6N6CL,  a  white  powder,  which  when 

*  Annales  (3),  29,  175;  and  52,  92;  also  Friedel  and  GKierin,  Compt.  rend., 
82,  972,  and  Annales  (5),  7,  24. 

f  Mallet,  Sill.  Amer.  J.,  28,  346. 


PHOSPHIDES  AND  ARSENIDES   OF   TIN,  ETC.  555 

heated  in  ammonia  loses  hydrogen  chloride,  leaving  Si2N3H.*  It 
slowly  evolves  ammonia  on  exposure  to  moist  air.  Compounds  of 
silicon  with  phosphorus,  arsenic,  and  antimony  are  unknown.  The 
germanium  compounds  have  not  been  investigated  ;  and  nitrides 
of  tin  and  lead  are  unknown.  Tin  combines  with  phosphorus 
directly,  forming  a  brilliant  crystalline  mass  which  appeal's  to 
have  the  formula  SnaP2.  It  is  less  fusible  than  tin,  but  white, 
softer,  and  more  malleable.  Another  phosphide  is  produced  by 
the  action  of  phosphine  on  stannic  chloride  ;  on  treatment  with 
water,  a  yellow  powder  remains  which  has  the  formula  SnP3. 
Phosphides  of  tin,  heated  in  a  current  of  hydrogen,  leave  a  residue 
of  tin,  while  phosphorus  sublimes.  Lead  dissolves  about  15  per 
cent,  of  phosphorus.  The  product  is  like  lead,  and  may  be  cut 
with  a  knife  ;  but  it  breaks  when  hammered.  Excess  of  phos- 
phorus crystallises  from  the  lead  in  the  form  of  "red"  (black 
metallic)  phosphorus  (see  p.  59).  Phosphine  is  said  to  throw 
down  a  brown  precipitate  of  lead  phosphide  from  a  solution  of  the 
acetate. 

Arsenides  of  tin  and  lead  appear  to  be  of  the  nature  of  alloys. 
They  form  metallic-looking  masses,  and  lose  arsenic  on  distilla- 
tion. An  arsenide  of  tin  containing  1  part  of  arsenic  to  15  parts 
of  tin  crystallises  in  large  leaves  ;  it  is  less  easily  fused  than  tin. 
The  compound  Sn>As3  has  also  been  prepared.  The  alloy  of  lead 
and  arsenic  is  also  crystalline  and  brittle;  PbAs,  Pb3As4,  and 
Pb2As  are  known.  f  Lead  shot  contains  O'l  to  0'2  per  cent,  of 
arsenic  ;  its  presence  makes  the  lead  assume  the  form  of  drops, 
and  renders  it  harder.  The  antimonides  will  be  treated  of  in  the 
next  chapter,  for  they  are  of  the  nature  of  alloys. 


PN  (?)  ;  VN  ;  VN2.—  AsP  ;  SbP.—  SbjjAs  ; 

The  product  of  the  action  of  ammonia  on  phosphorus  trichloride 
is  probably  P(NH2)3  (see  p.  525).  When  heated,  a  residue  is  left 
which  may  contain  phosphorus  nitride,  PN,  but  this  subject 
requires  further  investigation.  Vanadyl  trichloride,  VOC13,  or 
vanadium  trioxide,  V2O3,+  when  heated  to  a  high  temperature  in 
a  current  of  ammonia,  yield  a  greyish-brown  powder  mixed  with 
small  plates  with  metallic  lustre,  possessing  the  formula  VN.  The 
first  product  of  the  action  of  ammonia  on  vanadyl  trichloride  is 
the  dinitride,  VN2,  a  brown  powder,  which  loses  nitrogen  at  a 
white  heat,  leaving  the  mononitride,  VN.  The  phosphide, 

*  Compt.  rend.,  93,  1508. 

f  Ibid.,  86,  1022  and  1068. 

X  Roscoe,  Annalen,  Suppl.,  6,  314,  and  7,  70. 


556  THE   NITRIDES,   PHOSPHIDES,   ETC. 

which  has  not  been  analysed,  is  said  to  be  formed  by  the  action  of 
carbon  at  a  white  heat  on  vanadyl  phosphate,  and  to  form  a  grey 
porous  mass.  Similar  compounds  of  niobium  and  tantalum  have 
not  been  prepared,  nor  have  arsenides  and  antimonides  of 
vanadium. 

Nitrides  of  arsenic,  antimony,  and  bismuth  are  unknown.  It 
would  be  advisable  to  investigate  the  action  of  a  high  temperature 
on  the  compounds  of  the  trichlorides  with  ammonia. 

The  action  of  arsine  on  phosphorus  trichloride,  or  of  phosphine 
on  arsenic  trichloride,  yields  phosphide  of  arsenic,  as  a  red- 
brown  solid,  soluble  in  carbon  disulphide,  of  the  formula  AsP.  It 
is  changed  by  water  into  an  oxide,  As3P2O2.  When  heated  in 
carbon  dioxide  phosphorus  sublimes,  and  then  arsenic.  A  similar 
red  phosphide  of  antimony,  SbP,  is  produced  by  the  action  of 
phosphorus,  dissolved  in  carbon  disulphide,  on  a  solution  of 
antimony  bromide  in  carbon  disulphide.  Antimony  and  arsenic 
combine  when  heated  together,  forming  a  crystalline  substance  of 
the  formula  Sb2As ;  and  the  mineral  allamontite  has  the  formula 
Sb2As3. 

Mo3N2;  "W2N3;*  TJ3N2(?).— MoP;  W3P4;  W2P.— Arsenides  and  anti- 
monides unknown. 

Mo3N2  is  produced  by  the  action  of  ammonia  at  a  red  heat  on 
molybdenum  chloride ;  it  is  a  grey  powder.  Tungsten  nitride  is 
a  black  powder,  produced  by  the  action  of  ammonia  at  a  red  heat 
on  W02C12,  or  on  WC16  (see  p.  536).  Similarly,  uranium  penta- 
chloride,  heated  in  a  current  of  ammonia,  yields  a  black  powder  of 
doubtful  formula.  Molybdenum  phosphide  is  a  grey  metallic- 
looking  mass,  formed  by  heating  a  mixture  of  molybdenum  pent- 
oxide,  metaphosphoric  acid,  and  charcoal  to  whiteness ;  one 
phosphide  of  tungsten,  W3P4,  is  produced  by  direct  union  at  a 
red  heat,  and  is  a  dark-grey  powder ;  and  the  other  phosphide, 
W2P,  forms  fine  hexagonal  steel-grey  crystals  with  metallic  lustre, 
produced  by  reducing  with  charcoal  a  mixture  of  metaphosphoric 
acid  and  tungsten  pentoxide.  Phosphides  of  uranium  have  not 
been  prepared. 

Although  ruthenium,  rhodium,  and  palladium  combine  with 
phosphorus,  arsenic,  and  antimony,  no  compounds,  except  PdP2, 
have  been  investigated.  No  simple  nitrides  of  these  metals  are 
known.  The  same  remark  may  be  made  of  osmium.  The  phos- 
phides, arsenides,  and  antimonides  are  much  more  easily  fusible 
than  the  metals  themselves. 

*  Wohler,  Annalen,  108,  258. 


NITRIDES,  PHOSPHIDES,   ETC.,  OF  PLATINUM.  557 

Platinum  nitride,  PtsN2,  is  produced  by  heating  the  oxide  of 
platinosodiamine,PtlI(NH2)2.H2Oto2800,thns:  3Pt(NH2)2.H2O  = 
3H2O  +  4>NH3  +  Pt3N2.  It  is  a  greyish  substance,  decomposing 
suddenly  at  290°  into  platinum  and  nitrogen. 

The  phosphide,  PtgP5,  is  a  white  substance,  with  metallic  lustre, 
much  more  easily  fusible  than  platinum,  produced  by  direct  union, 
and  crystallising  in  cubes.  When  heated  in  a  muffle,  the  residue 
Pt,P  is  left.  A  corresponding  iridium  compound  is  similarly 
formed,*  and  is  known  as  "  cast  iridium."  The  arsenide,  PtASj, 
also  formed  by  direct  union,  resembles  the  phosphide,  and  the 
antimonide  is  also  white,  brittle,  and  easily  fused.  A  hydroxy- 
arsenide,  Pt.AsOH,  is  formed  by  passing  a  current  of  arsine 
through  a  solution  of  platinic  chloride  ;  it  forms  black  scales. 


Cu3N;t   Cu3P;t    CU3P2;    CuP  ;    CtlgAs;   Cu6As  ; 
—  A&3N(?);     AgT3P;     Ag3P2;     A&P2  ;     Ag3As  ;      Ag^As,  ;     AgAs  ; 

Ag3Sb2.—  Au3N  ;  AtuPa;  Au4As3.—  Hg3N2  ;  Hg-3P2;  H^As^  HgAs. 


The  nitride,  Cu3N,  is  produced  by  passing  ammonia  over 
cuprous  oxide  heated  to  250°  ;  it  is  a  brown  substance,  decomposing 
about  360°.  It  has  been  suggested  that  fulminating  silver  (see 
p.  546)  is  in  reality  a  nitride,  but  it  appears  more  probable  that  it 
is  silver  amide,  AgNH2.  Gold  nitride  has  already  been  mentioned 
(p.  546).  Mercuric  nitride,  Hg3N2,  is  a  black  substance,  pro- 
duced by  the  action  of  ammonia  on  mercuric  oxide  at  130°,  which 
detonates  when  heated  or  struck. 

Cuprous  phosphide,  Cu3P,  is  a  grey  powder,  produced  by 
heating  cuprous  chloride,  Cu,Cl2,  in  a  current  of  phosphine. 
Cupric  phosphide,  Cu3P2,  is  similarly  prepared  from  cupric 
chloride,  CuCl2,  and  forms  a  black  powder.  It  is  attacked  by 
hydrogen  chloride,  yielding  spontaneously  inflammable  phosphine. 
At  a  high  temperature,  in  a  current  of  hydrogen,  it  yields  the 
phosphide,  CuP2,  as  a  grey  crystalline  powder.  Phosphides  of 
silver  are  formed  by  direct  union.  The  formulae  given  above 
have  been  ascribed  to  them,  but  are  not  certain.  A  compound  of 
the  formula  Ag3P.3AgNO3,  and  a  similar  compound,  Ag3As,3HNO3, 
are  produced  in  yellow  crystals  by  saturating  a  strong  solution  of 
silver  nitrate  with  phosphine  or  arsine  at  0°.  They  are  very 
unstable,  almost  at  once  depositing  metallic  silver.  There  appears 
also  to  be  a  similar  compound  of  antimony. 

Gold  phosphide,  AuP,  is  produced  by  direct  union  between 

*   Chem.  News,  48,  285. 

t  Schrotter,  Annalen,  37,  131. 

J  Rose,  Pogg.  Ann.,  4,  110;  6,  209;  14,  188;  24,  328. 


558  THE   NITRIDES,   PHOSPHIDES,   ETC. 

spongy  gold  and  phosphorus ;  it  is  a  grey  mass,  more  fusible  than 
gold,  with  metallic  lustre.  The  phosphide,  A.U3P2,  is  produced  by 
precipitation  with  phosphine,  and  is  a  black  powder;  it  is  mixed 
with  metallic  gold.  Mercury  phosphide,  probably  Hg3P2,  is  a 
black  compound,  formed  when  mercuric  oxide  or  chloride  is  heated 
with  phosphorus  ;  it  is  also  formed  in  brown  flakes  when  a  mercuric 
salt  is  treated  with  phosphine,  or  as  a  yellow  sublimate  when 
mercnric  chloride  is  heated  in  a  current  of  phosphine.  Along  with 
this  phosphide,  a  yellow  powder  of  the  formula  Hg3P2.3HgCl2  is 
produced,  which  decomposes  thus  when  boiled  with  water: — 
Hg3P2.3HgCl2  +  6H20  +  Aq  =  6HCl.Aq  +  2H3PO3  +  CHg. 

Mercuric  phosphide  also  forms  double  compounds  with 
basic  mercuric  nitrate  and  sulphate,  Hg3P2.3Hg2O(NO3)2  and 
Hg3P2.3Hg3O(SO4)2.4H2O,  formed  by  he  action  of  phosphine  on 
the  nitrate  or  sulphate. 

The  arsenides,  Cu3As  and  Ag3As,  occur  native  as  arsenical 
copper,  or  domeykite,  and  arsenical  silver,  or  huntilite.  The  other 
arsenides  are  formed  directly,  as  is  also  arsenide  of  gold.  Mercury 
and  arsenic  do  not  easily  combine  directly,  but  when  arsine  is 
passed  into  a  solution  of  mercuric  chloride,  the  compound 
Hg3As2.3HgCl2  is  precipitated.  It  is  a  yellowish-brown  powder, 
and  when  in  contact  with  water  slowly  decomposes  into  arsenious 
oxide,  As4O6,  mercury,  and  hydrogen  chloride. 

Further  investigation  of  all  these  compounds  is  much  to  be 
desired.  Data  concerning  most  of  them  are  very  meagre,  and 
many  have  not  been  examined  since  the  time  of  Berzelius. 


Nitride  of  Carbon,  or   Cyanogen,   C2N2,  and  its 
Compounds. 


Cyanogen,  (CN)z,*  is  not  formed  by  direct  union.  It  is  best 
prepared  by  heating  cyanide  of  silver,  gold,  or  mercury,  preferably 
the  last,  thus  :—  Hg(CN)2  =  Hg  +  (CN)Z.  It  may  be  more  con- 
veniently prepared  by  heating  a  mixture  of  mercuric  chloride  with 
dry  potassium  ferrocyanide,  or  better  with  potassium  cyanide  (see 
below). 

Cyanogen  is  a  colourless  gas  with  a  sharp  smell,  resembling 
that  of  bitter  almonds.  It  is  exceedingly  poisonous.  It  burns 
with  a  blue-purple  flame,  forming  carbon  dioxide  and  nitrogen. 
Water  at  the  ordinary  temperature  dissolves  about  four  and  a  half 
times,  and  alcohol  twenty-three  times,  its  volume  of  cyanogen.  In 

*  Gay-Lussac,  Annales,  77,  128;  95,  136. 


CYANIDES.  559 

the  liquid  state  it  is  colourless,  and  boils  at  —20°,  and  at  a  lower 
temperature  it  freezes  to  a  white  solid  melting  at  — 34'4°. 

Its  formula  is  shown  to  be  (GN)2  by  its  vapour  density,  and  it 
may  be  regarded  as  similar  to  molecular  chlorine,  hydrogen,  or 
oxygen,  Ck,  IT2,  or  02,  or  to  ethane  (dimethyl),  ((7j6T3)2,  (see  p.  501)  ; 
and  it  has  been  shown  to  contain  its  own  volume  of  nitrogen  by 
decomposing  a  known  volume  by  means  of  an  electric  spark.  Its 
heat  of  formation  is  :  2C  +  2N  =  CZN2  —  65  7K. 

Cyanides. — The  starting  point  for  preparing  the  cyanides  is 
potassium  cyanide,  produced  by  heating  the  ferrocyanide, 
K4Pe(CN)6  (see  p.  562). 

Hydrogen  cyanide,  hydrocyanic  acid,  or  prussie  acid, 
HCX.* — Hydrogen  and  cyanogen  do  not  combine  directly,  but 
hydrogen  cyanide  is  produced  when  the  electric  arc  passes  through 
moist  air,  by  the  union  of  carbon,  hydrogen,  and  nitrogen.  Anhydr- 
ous hydrogen  cyanide  may  be  prepared  by  heating  mercuric  cyanide, 
better  mixed  with  ammonium  chloride,  with  strong  hydrochloric 
acid,  passing  the  vapours  over  powdered  marble  to  remove  excess 
of  hydrogen  chloride,  and  through  a  tube  filled  with  ignited  calcium 
chloride,  to  dry  the  gas.  Or  by  decomposing  mercuric  cyanide  at 
30°  or  40°  in  a  tube  with  hydrogen  sulphide,  and  causing  the 
resulting  gases  to  pass  through  a  layer  of  lead  carbonate  to  remove 
excess  of  hydrogen  sulphide.  The  pure  compound  should  never  be 
prepared  without  the  utmost  precautions  being  taken  against  its 
escape  into  the  air  of  the  laboratory,  as  it  is  an  intense  poison. 
The  anhydrous  compound  may  also  be  prepared  by  distilling  its 
strong  aqueous  solution  with  fused  calcium  chloride  dropped  into 
the  acid  in  small  pieces  at  a  time,  to  abstract  water.  It  must  be 
condensed  tn  a  receiver,  best  in  a  \J  -tube,  cooled  by  a  freezing 
mixture,  and  the  exit  from  the  receiver  should  lead  away  to  a  good 
draught. 

An  aqueous  solution  of  the  acid  may  be  prepared  by  distilling 
potassium  cyanide  with  dilute  sulphuric  acid : — KCN.Aq  + 
H*S04.Aq  =  HCN.Aq  +  KHS04.Aq.  Or  ferrocyanide  of  potassium 
may  be  employed  (10  parts,  water  30  parts,  sulphuric  acid  6  parts), 
thus : — 

2K4Fe(CN)6.Aq  +  3H2S04.Aq  =  3K2S04.Aq  +  ILFe2(CN)6  + 

6HCN.Aq. 

Hydrogen  cyanide  is  a  colourless  liquid,  boiling  at  27° ;  it 
freezes  to  a  solid,  which  melts  at  —15°.  It  has  a  strong  odour  to 

*  Qay-Lussac,  Annales,  77,  128 ;  95.  136. 


560  THE  NITRIDES,   PHOSPHIDES,  ETC. 

those  who  can  smell  it,  but  about  one  person  out  of  every  five  is 
incapable  of  perceiving  it.  It  can  always  be  detected  by  the 
choking  sensation  which  it  produces  in  the  glands  of  the  throat. 
It  is  miscible  with  water  in  all  proportions.  It  burns,  forming 
water,  carbon  dioxide,  and  nitrogen. 

It  is  exceedingly  poisonous  ;  a  few  drops  of  the  strong  aqueous 
solution  cause  immediate  death.  It  is  employed  medicinally  in  a 
2  per  cent,  solution.  It  may  be  produced  by  distilling  crushed 
peach-stones  or  laurel  leaves  with  water,  and  it  is  known  that 
such  preparations  were  used  in  the  middle  ages  by  professional 
poisoners. 

The  heat  of  formation  of  hydrogen  cyanide  is : — H  +  C  +  N  = 
HOT"  -  275K. 

The  analogy  between  chlorine  and  cyanogen,  and  between 
hydrogen  chloride  and  cyanide,  is  a  striking  one.  The  cyanides  in 
many  respects  resemble  the  chlorides,  but  while  hydrogen  chloride 
is  not  easily  produced  from  its  salts  except  by  the  action  of 
acids  like  sulphuric,  phosphoric,  &c.,  even  carbonic  acid  expels 
hydrogen  cyanide  from  some  cyanides.  Hence,  solid  potassium 
cyanide  always  smells  of  hydrogen  cyanide. 

The  cyanides  and  double  cyanides  are  very  numerous.  It  is 
only  possible  here  to  give  a  partial  sketch  of  these  compounds. 

LiCN;  NaCN;  KCN;  RbCN;  CsCN;  NH4CN. 

These  salts  are  produced  by  the  action  of  hydrocyanic  acid  on 
the  hydroxides  of  the  metals,  or  by  direct  combination  of  cyanogen 
with  the  metals  ;  that  of  ammonium  by  direct  combination  of  equal 
volumes  of  hydrogen  cyanide  and  ammonia,  or  by  distilling  a 
mixture  of  potassium  cyanide  and  ammonium  chloride  in  requisite 
proportions.  Cyanides  are  also  produced  by  passing  cyanogen 
into  solutions  of  the  hydroxides;  a  cyanate  and  cyanide  are 
formed  thus :— 2KOH.Aq  +  (CN)2  =  KCKAq  +  KCNO.Aq. 
This  reaction  is  exactly  analogous  to  that  which  takes  place 
between  chlorine  and  caustic  alkali  (see  p.  462).  An  interesting 
synthesis  of  potassium  cyanide  is  carried  out  by  passing  nitrogen 
over  a  red-hot  mixture  of  carbon  and  potassium  carbonate,  pro- 
duced by  igniting  the  tartrate,  citrate,  or  some  similar  salt;  it 
may  be  formulate d  :—K2CO3  +  4C  +  JV2  =  2KCN  +  SCO. 
Sodium  cyanide  is  also  formed  when  any  nitrogenous  carbon 
compound  is  heated  with  sodium ;  this  affords  a  means  of  testing 
for  nitrogen  in  carbon  compounds.  It  is  also  produced  in  a 
blast  furnace,  where  iron  ores  are  smelted  with  coal  and  lime ; 


THE   CYANIDES.  561 

the  sodium  is  contained  in  the  coal  ash  and  the  limestone  ;  the 
carbon  is  derived  from  the  coal,  and  the  nitrogen  from  the  air.  It 
may  be  separated  from  the  escaping  gases  by  passing  it  through 
scrubbers  filled  with  water,  as  in  the  extraction  of  ammonia  from 
coal-gas. 

Potassium  cyanide  is  most  conveniently  prepared  by  heating 
the  ferrocyanide,  K4Pe(CN)6,  previously  dried,  in  an  iron  crucible. 
It  decomposes,  giving  an  indefinite  carbide  of  iron  and  the  cyanide. 
Sometimes  potassium  carbonate  is  added  to  increase  the  yield.  It 
may  be  purified  by  crystallisation  from  alcohol.  If  required  per- 
fectly free  from  cyanate,  KCNO,  it  is  best  produced  by  passing 
the  vapour  of  hydrogen  cyanide  into  an  alcoholic  solution  of 
potassium  hydroxide,  when  it  is  precipitated. 

These  cyanides  are  all  white  deliquescent  solids,  crystallising  in 
the  regular  system;  they  smell  of  prussic  acid.  They  are  very 
soluble  in  water,  and  somewhat  soluble  in  alcohol.  They  are  all 
poisonous. 

Although  cyanogen  and  hydrogen  cyanide  are  produced  with 
absorption  of  heat,  potassium  cyanide  is  formed  with  heat  evolu- 
tion:—  K  +  C  +  N  =  KCN  +  325K. 

Ca(CN)2;  Sr(CN)2,  and  Ba(CN)2. 

White  deliquescent  solids.  Barium  cyanide  may  be  prepared 
by  the  action  of  the  nitrogen  of  the  air  on  a  red  hot  mixture  of 
barium  carbonate  and  carbon  ;  when  heated  to  300°  in  a  current 
of  water-vapour,  it  yields  its  nitrogen  in  the  form  of  ammonia, 
thus  :—  Ba(CN)2  +  4^0  =  BaCO3  4-  2NH3  +  CO  +  Hz.  This 
process  has  been  proposed  as  a  method  of  producing  ammonia 
from  atmospheric  nitrogen,  but  is  not  commercially  successful. 


;  Zn(CN)2;  Cd(CN)2. 
Double  compounds:—  2(Zn(CN)2).NaCN.5H20;  Zn(CN)2.KCN; 
Zn(CN)2.2NH4CN;  Zn(CN)2.Ba(CN)2. 

Magnesium  cyanide  is  soluble  ;  the  cyanides  of  zinc  and  cad- 
mium are  white  precipitates,  thrown  down  from  solutions  of  their 
soluble  salts  by  addition  of  potassium  cyanide.  The  double 
cyanides  are  soluble,  and  are  obtained  by  mixture. 

Yttrium  cyanide  is  soluble.     Aluminium  cyanide  appears  to 
be  incapable  of  existence.     Gallium  and  indium  cyanides  have  no;tx 
been  prepared.     Thallous  cyanide,  T1CN,  is  thrown  down  from 
a  solution  of  thallous  hydroxide  in  hydrocyanic  acid  by  addition 
of  alcohol  and  ether  as  a  white  precipitate.     It  crystallises  from  a 

2  o 


562  THE   NITRIDES,  PHOSPHIDES,   ETC. 

hot  solution,  and  is  readily  soluble  in  water.  It  forms  the  double 
cyanides  2TlCN.Zn(CN)2 ;  also  T1(CN)3.T1CN,  produced  by  the 
action  of  hydrocyanic  acid  on  moist  thallic  oxide ;  the  latter  crys- 
tallises from  strong  hydrocyanic  acid,  but  is  decomposed  by  water. 

Cr(CN)3.  Ferric  cyanide  is  unknown  in  the  solid  state;  nor  are  simple 
manganic  or  cobaltic  cyanides  known.  Nickelicyanides  are  unknown  even  in 
combination. 

Chromic  cyanide,  Cr(CN)3,  is  said  to  be  the  formula  of 
the  bluish-grey  precipitate,  produced  on  adding  a  solution  of 
chromium  trichloride  to  a  solution  of  potassium  cyanide.  Its 
formula  is  doubtful. 

Cr(CN)2;  F8(CN)2;  Mn(CN)2(?);  Co(CN)2,  and  Ni(CN)2. 

Prepared  by  addition  of  solution  of  potassium  cyanide  to  solu- 
tions of  chromous,  ferrous,  manganous,  cobaltous,  or  nickelous 
salts.  Chromous  cyanide,  prepared  from  chromous  chloride,  is 
white;  ferrous  cyanide,  the  formula  of  which  is  doubtful,  is 
yellowish-red ;  that  of  manganese  is  reddish-white ;  of  cobalt, 
flesh-coloured  ;  and  of  nickel,  apple-green. 

Double  cyanides. — The  double  cyanides  of  this  group  of 
elements  are  very  numerous.  They  may  be  divided  into  three 
classes : — 1,  those  containing  the  elements  in  dyad  forms  of  com- 
bination ;  2,  those  containing  the  elements  as  triads ;  and 
3,  those  in  which  the  iron,  &c.,  exists  in  both  dyad  and  triad 
states. 

1.  Chromocyanides  are  unknown;  they  are  probably  capable 
of  existence,  for  chromium  dicyanide  dissolves  in  excess  of  solution 
of  potassium  cyanide.  So  also  do  cyanides  of  manganese  and 
cobalt. 

Perrocyanides  are  compounds  containing  ferrous  cyanide, 
Fe(CN)2,  in  combination  with  four  molecules  of  an  alkaline 
cyanide,  as  in  K4Pe(CN)6  =  Pe(CN)2.4KCN  ;  or  with  two  mole- 
cules of  the  cyanide  of  a  dyad  metal,  as  in 

Ba2Pe(CN)6  =  Pe(CN)22Ba(CN)2. 

The  starting  point  for  the  ferrocyanides  is  the  potassium 
salt,  K4Pe(CN)6.  It  is  produced  on  the  large  scale,  by  heating 
together  in  a  shallow  iron  pan  nitrogenous  animal  matter,  such  as 
chips  of  horn,  hair,  fragments  of  skin,  woollen  rags,  &c.,  with 
crude  potassium  carbonate  and  iron  filings.  Cyanide  of  potas- 
sium and  ferrous  sulphide  are  produced,  the  latter  deriving  its 
sulphur  partly  from  the  organic  matter,  partly  from  the  sulphate 


FERROCYANIDES.  563 

present  as  impurity  in  the  crude  carbonate  of  potassium.*  Only 
one-sixth  to  one-tenth  of  the  nitrogen  present  in  the  animal  matter 
is  utilised.  On  treatment  with  water,  the  potassium  cyanide 
and  ferrous  sulphide  react,  thus  : — 6KCKAq  +  FeS  =  K£>  + 
K4Fe(CN")6.Aq.  The  liquors  are  then  evaporated,  and  the  impure 
crystals  which  separate  out  are  recrystallised. 

The  formula  of  the  crystals  is  K4Fe(CN)6.3H2O ;  they  are 
truncated  dimetric  pyramids  of  a  lemon-yellow  colour,  easily 
soluble  in  water,  and  not  poisonous.  When  heated,  iron  carbide 
and  potassium  cyanide  are  produced  (see  p.  560).  When  distilled 
with  strong  sulphuric  acid  carbon  monoxide  is  evolved,  thus  : — 

K4Fe(CN)6  +  6H2S04  +  6H20  =  2K2SO4  +  FeSO4  + 
3(NH4)2SO4  +  6(70. 

It  may  be  supposed  that  the  hydrogen  cyanide  at  first  liberated 
combines  with  water,  forming  ammonium  formate,  HCO.ONH4, 
which  is  decomposed  by  the  sulphuric  acid,  liberating  carbon  mon- 
oxide. But  such  stages  cannot  be  recognised  in  the  decomposition. 

On  adding  to  a  strong  solution  of  potassium  ferrocyanide, 
previously  boiled  to  expel  air,  strong  hydrochloric  acid,  also  boiled 
and  cooled,  and  a  little  ether,  thin  white  scales  of  hydrogen 
ferrocyanide,  H4Fe(CN)6,  separate  out.  They  may  be  collected 
on  a  filter,  washed  with  a  mixture  of  alcohol  and  ether,  and  dried 
over  sulphuric  acid  in  a  vacuum.  Hydroferrocyanic  acid  is  easily 
soluble  in  water  and  alcohol,  but  insoluble  in  ether. 

Barium  ferrocyanide,  Ba.,Fe(CN)6,  may  be  produced  by 
action  on  barium  cyanide  (obtained  from  the  carbonate,  carbon,  and 
nitrogen)  of  ferrous  sulphate,  thus :—  3Ba(CN)2.Aq  +  FeS04.Aq 
=  BaS04  +  BaoFe(C!N")6.Aq ;  also  by  precipitating  a  boiling 
solution  of  potassium  ferrocyanide  with  great  excess  of  barium 
chloride,  and  boiling  the  resulting  precipitate  with  solution  of 
barium  chloride.  It  crystallises  in  flattened  yellow  monoclinic 
prisms  with  six  molecules  of  water. 

The  other  ferrocyanides  are  prepared  either  by  treating  the 
hydroxide  or  carbonate  of  the  metal  with  a  solution  of  hydrogen 
ferrocyanide ;  by  mixing  a  solution  the  sulphate  of  the  metal  with . 
solution  of  barium  ferrocyanide ;  or  by  precipitation,  many  ferro- 
cyanides being  insoluble. 

The  following  is  a  list  of  the  more  important  ferrocyanides':— 


Liebig,  Annalen,  38,  20. 

2  0  2 


564  THE  NITRIDES,   PHOSPHIDES,  ETC. 

Li4Fe(CN)6;  Na4Fe(CN)6.12H2O  ;  K4Fe(CN)6.3H2O  ; 
(NH4)4Fe(CN6).3H:20;  also  L,i2K2Fe(CN)6.6H2O  ;  NaK3Fe(CN)6; 
K2(NH4)2Fe(CN)6  ;     K3(NH4)Fe(CN%  ;      and    the    double    salts 
(NH4)4Fe(CN)6.2NH4C1.3H2O,  and  (NH4)4Fe(CN)6.2NH4Br.3H2O. 
Ca2Fe(CN)6.12H20;  Ba2Fe(CN)6.6H2O  ;  also  K2CaFe(CN)6.3H2O  ;   and 


(The  last  two  double  salts  are  produced  by  precipitation.) 


Mg-2Fe(CN)6.12H20;  Zt^e(GS)6.3H^O  ;  K2Mg-Fe(CN)6. 

Al4{Fe(CN)6}a;  Fe4"'{Fe''(CN)J3.18H20  (Prussian  blue)  ;  also 

KFe///Fe(CN)6. 

The  aluminium  compound  and  the  ferric  compound  are  pro- 
duced by  precipitation.  The  latter  is  prepared  industrially  as  a 
blue  pigment,  by  precipitation,  thus  :  — 

4FeCl3.Aq  +  3K4Fe(CN)6.Aq  =  Pe4'"{Fe(CN)6}3  +  12KCl.Aq  ; 

or  by  the  oxidation  by  air,  or  other  oxidising  agents  of  potassium 
ferrous  ferrccyanide,  probably  thus  :  —  6K2Fe{Fe(CN)6}.Aq  +  3O 
=  Fe203n.H80  +  3K4Fe(CN)6.Aq  +  Fe4{Fe(CN)6}3.  It  is  by  this 
last  method  that  it  is  usually  prepared  commercially.  At  the 
same  time,  potassium  ferric  ferrocyanide,  KFe'"Fe"(CN)6,  is 
produced,  which  is  soluble  in  water.  It  appears  to  be  formed,  if 
the  ferrocyanide  of  potassium  is  present  in  insufficient  quantity, 
thus  :  — 

K4Fe(CN)6.Aq  +  FeCl3.Aq  =  KFe"'Fe"(OT)6.Aq  +  3KCl.Aq. 

When  digested  with  more  ferrocyanide,  it  is  converted  into 
Prussian  blue.  This  compound  may  also  be  regarded  as  potassium 
ferrous  ferricyanide,  KFe"Fe'"(CN)6  (which  see). 

Ferrous  ferrocyanide,  Fe2"Fe"(CN)6  (white),  has  the  same 
percentage  composition  as  ferrous  cyanide,  Fe(CN)2.  But  as 
ferrocyanides  of  manganese  (white),  cobalt  (pale  blue),  and 
nickel  (light  green),  with  corresponding  formulas,  are  known,  it 
is  probable  that  the  formula  is  the  more  complex  one.  By 
addition  of  solution  of  potassium  ferrocyanide  to  a  solution  of  iron 
wire  in  aqueous  sulphurous  acid,  the  potassium  ferrous  salt, 
K2Fe"Fe''(CN)6,  is  thrown  down  as  a  white  precipitate.  This 
compound  is  also  produced  when  potassium  ferrocyanide  is  dis- 
tilled with  dilute  sulphuric  acid,  as  in  the  preparation  of  hydrocy- 
anic acid,  thus  :—  2K4Fe"(CN)6.Aq  +  3H2S04.Aq  =  3K2S04.Aq  + 
QHCN  +  K2Fe"'Fe"(CN)6.  With  a  ferrous  salt  containing,  as  it 
usually  does,  a  little  ferric  salt,  this  precipitate  is  light  blue,  and 
serves  for  the  detection  of  ferrous  iron.  It  also  rapidly  turns  blue 
an  exposure  to  air,  owing  to  oxidation. 


CHROMICYANIDES,  FERRICYANIDES,   ETC.  565 

Lead  ferrocyanide  is  white  ;  that  of  bismnth  also  white ;  of 
monad  copper,  white,  Cu4Fe(CN)6;  potassium  cuprous  ferro- 
cyanide, K2Cu2Fe(CN)6,  forms  deep  brown  crystals;  potassium 
cupric,  K2CuFe(CN)6,  is  the  brown-red  precipitate  produced  by 
a  solution  of  potassium  ferrocyanide  in  solutions  of  copper  salts  ; 
with  great  excess  of  ferrocyanide  of  potassium  a  reddish-purple 
precipitate  of  Cu2Fe(CN)6  is  produced.  The  silver  salt  is  white, 
and  is  not  acted  on  by  hydrochloric  acid  ;  the  mercuric  salt  is  also 
white.  Ferrocyanides  of  cupramine  and  of  mercuramine  are  also 
known. 

The  mangano cyanides  are  analogous  to  the  ferrocyanide s, 
and  are  also  produced  by  dissolving  manganous  cyanide  in  excess 
of  an  alkaline  cyanide.  The  potassium  salt  forms  deep  violet 
tabular  crystals  of  the  formula  K4Mn(CN)6.  It  would  be  in- 
teresting to  compare  the  salts  K2MnFe(CN)6  and  K2FeMn(CN)6 
with  a  view  of  seeing  whether  or  not  they  are  identical. 

The  double  cyanides  of  nickel  have  formulas  differing  from 
the  ferro-  and  manganocyanides.  The  potassium  salt,  K2Ni(CN)4, 
produced  by  mixture,  forms  yellow  oblique  rhomboidal  prisms. 
Ammonium,  calcium,  and  barium  compounds  have  also  been  pre- 
pared. 

Chromicyanides,  ferricyanides,  manganicyanides,  and 
cobalticyanides. — Chromicyanide  of  potassium,  K3Cr'"(CN)6, 
produced  by  dissolving  chromium  hydrate  in  solution  of  potassium 
cyanide  in  presence  of  potassium  hydroxide,  forms  brown  crystals, 
from  which  the  red  silver  salt  may  be  produced  by  precipitation. 
The  silver  salt  with  hydrogen  sulphide  gives  the  hydrogen  salt 
H3Cr'"(CN)6,  which  is  a  crystalline  body.  Ferrous  chromicyanide 
is  a  brick-red  powder. 

The  starting  point  for  ferricyanides  is  potassium  ferrocyanide. 
When  a  current  of  chlorine  is  passed  through  its  solution,  the  fol- 
lowing reaction  takes  place:— 2K4Fe"(CN)6.Aq  +  01,  —  2KCl.Aq 
+  2K3Fe'"(CN)6.Aq.*  A  still  better  methodf  is  to  digest  potas- 
sium ferric  ferrocyanide  with  a  solution  of  potassium  ferrocyanide, 
thus  :— KFe'"Fe(CN)6.Aq  +  K4Fe(CN)6.Aq  =  K3Fe'"(CN)6.Aq 
+  K2Fe"{Fe"(CN)6}.  The  insoluble  potassium  ferrous  ferro- 
cyanide is  removed  by  nitration,  and  may  be  reconverted  into 
potassium  ferric  ferrocyanide  by  digestion  with  nitric  acid,  and 
thus  rendered  available  for  a  second  operation.  The  filtrate  on 
evaporation  yields  dark  orange-red  crystals  of  ferricyanide.  The 
sodium  salt  is  similarly  prepared.  The  double  salt  of  sodium  aud 

*  Gmelin,  Handbook,  7,  468. 
f  Williamson,  Annaleny  57,  2«j7. 


5G6  THE   NITRIDES,   PHOSPHIDES,   ETC. 

potassium  has  the  formula  Na3K3{Fe(CN)6}2  ;  hence  the  formula 
of  the  simple  salts  is  often  written  Na6Fe2'"(CN)12.  The  lead 
salt  is  sparingly  soluble  in  water,  and  crystallises  in  brown-  red 
plates.  From  it  the  hydrogen  salt  is  produced  by  the  action  of 
the  requisite  amount  of  dilute  sulphuric  acid  ;  the  filtrate  from  the 
lead  sulphate  is  evaporated,  and  deposits  brownish  needles  of 
H3Fe(CN)6. 

The  iron  salts  are  specially  interesting.  Ferrous  ferricyanide, 
Fe"3{Fe'"(CN)6}2,  is  a  deep-blue  precipitate,  known  as  Turnbull's 
blue,  which  shows  on  its  fractured  surfaces  a  copper-red  lustre.  It 
is  extensively  used  in  calico-printing,  and  is  produced  by  addition 
of  solution  of  ferrous  sulphate  to  potassium  ferricyanide,  thus  :  — 


3Fe"SO,.Aq+  2K3Fe'"(CN)6.Aq  =  Fe,"{Fe"'(CN)e}2  +  6KCl.Aq. 

Potassioferrous  ferricyanide,  KFe"Fe'"(CN)6,  is  a  bine-  violet 
compound,  produced  by  boiling  white  potassium  ferrous  ferro- 
cyanide,  K2Fe"Fe"(CN)6,  with  dilute*  nitric  acid.  When  digested 
with  a  ferrous  salt,  it  yields  Turnbull's  blue,  thus  :  — 

2KPe"Pe'"(CN)e  +  FeS04.Aq  =  Fe3"{Fe'"(CN)6}2  +  K2S04.Aq; 
with  a  ferric  salt  Prussian  blue  is  formed  :  — 

3KFe"Fe'"(CN)6  +  FeCl3.Aq  =  SKCl.Aq  + 

Fe"'Fe3"{Fe'"(CN)6}3  =  Fe4'"{Fe"(CN)6}3. 

By  the  action  of  excess  of  chlorine  on  a  solution  of  potassium 
ferro-  or  ferricyanide,  Prussian  green  is  formed.  It  is  a  green 
ferricyanide  of  the  formula  Fe3"Fe4'"}Fe(CN)6}6. 

With  ferric  chloride,  potassium  ferricyanide  gives  a  brown 
solution,  which  may  contain  ferric  ferricyanide,  Fe'"Fe(CN)6.  or 
perhaps  ferric  cyanide,  Fe(CN)3. 

Nitro.pmssides.  —  A  class  of  compounds  containing  nitric 
oxide  is  produced  by  the  action  of  nitric  acid  mixed  with  its  own 
volume  of  water  on  ferro-  or  ferricyanides  ;*  the  mixture  after 
standing  is  heated  in  a  water-bath,  when  gases  are  evolved. 
When  it  no  longer  gives  a  blue  precipitate  with  ferrous  sulphate  it 
is  cooled,  when  nitre  and  oxamide  crystallise  out.  The  mother 
liquor  is  neutralised  with  sodium  carbonate  and  again  filtered. 
The  filtrate  on  evaporation  deposits  first  crystals  of  nitre,  and 
afterwards  deep-red  crystals  of  sodium  nitroferricyanide, 
NaoFe'"(CN)5.NO.  Many  salts  have  been  prepared.  The  most 
striking  reaction  of  the  nitroprussides  is  that  with  a  soluble 

*  Playfair,  Phil.  Mag.  (3),  36,  197,  271,  348.  Roussin,  Annales  (3),  52, 
285.  Pavel,  Berichte,  16,  2600. 


THE   CYANIDES.  567 

sulphide ;  a  splendid  purple  colour  is  produced,  which,  however,  is 
transient. 

It  is  suggested  that  these  compounds  are  closely  allied  to  the 
nitrosulphides  of  iron  (see  p.  343) ;  for  on  adding  mercuric 
cyanide  to  sodium  ferrinitrosulphide,  hydrogen  sodium  nitroferri- 
cyanide  is  formed,  thus  :  — 

2NaFeS2.NO.Aq  +  H20  +  5Hg(CN)2.Aq  = 

2HNaFe(CN)5.NO.Aq  +  4HgS  +  HgO  ; 
and,  conversely, 

2Na2Fe(CN)5.NO.Aq  +  Na^S.Aq  = 

2NaFeS,.NO.Aq  +  lONaCKAq. 

At  present,  however,  there  are  not  data  sufficient  to  make  it 
possible  to  suggest  constitutional  formulas  for  these  compounds. 

Manganicyanide  of  potassium,*  K3Mn'"(CN)r,,  is  formed  by 
exposing  the  manganocyanide  to  air.  It  is  amorphous  with  the 
ferricyanide,  and  forms  reddish-brown  crystals.  The  ferrous  salt 
is  cobalt-blue,  but  is  unstable. 

Cobalticyanide  of  potassiumf  is  similarly  prepared.  The 
hydrogen  salt,  produced  from  the  lead  salt  with  sulphuretted 
hydrogen,  H3Co(CN)6,  forms  colourless  needles.  Ferrous  cobalti- 
cyanide,  Fe3"{Co(CN)6}2,  is  a  white  precipitate,  analogous  in 
formula  to  Turnbull's  blue.  The  corresponding  cobaltous  salt 
is  a  light- red  precipitate. 

Nickelicyanides  are  unknown. 

Cyanide  of  titanium  has  not  been  investigated.  But  a  double 
nitride  and  cyanide,  Ti(CN)3.3Ti3N2,J  occurs  in  copper-coloured 
crystals  in  the  beds  of  blast-fu maces,  and  was  formerly  believed 
to  be  the  element  titanium.  It  may  be  produced  by  heating  to  a 
high  temperature  a  mixture  of  titanium  dioxide  and  potassium 
ferrocyanide.  When  heated  in  steam  these  crystals  yield  ammonia, 
hydrogen,  and  hydrocyanic  acid,  leaving  a  residue  of  titanium 
dioxide ;  and  in  chlorine,  titanium  chloride  and  crystals  of  a  double 
compound  of  the  chlorides  of  titanium  and  cyanogen,  TiCl4.CNCl. — 
Cerium  cyanide  is  said  to  be  a  white  precipitate;  cyanides  of 
zirconium  and  of  thorium  have  not  be  piepared. 

Cyanides  of  silicon  and  of  germanium  are  also  unknown ;  tin 
appears  not  to  form  a  cyanide ;  and  lead  yields  only  a  white  pre- 
cipitate of  a  hydroxycyanide,  HO — Pb — CN,  in  presence  of  am- 
monia. 

*  Eaton  and  Fittig,  Annalen,  145, 157  ;  Descampe,  Bull.  Soc.  CMm.,  9,  443. 
t  Zwenger,  Annalen,  62,  137. 
J  Wohler,  Chem.  Soc.,  2,  352. 


568  THE  NITKIDES,  PHOSPHIDES,  ETC. 

Cyanides  of  elements  of  the  nitrogen-group  have  not  been 
prepared. 

Phosphorous  cyanide,  P(CN)3,*  forms  long,  white  needles, 
which  catch  fire  when  touched  with  a  warm  glass  rod.  It  is  pro- 
duced by  heating  to  130°  in  a  sealed  tube  a  mixture  of  silver 
cyanide  and  phosphorus  trichloride,  and  subsequent  sublimation 
in  a  current  of  carbon  dioxide.  It  melts  at  200°— 203°.  Cyanide 
of  arsenic  may  be  similarly  prepared.  Cyanides  of  antimony  and 
bismuth  are  unknown. 

Cyanides  of  molybdenum,  tungsten,  and  uranium  have  not 
been  examined. 

(CN)20  is  unknown.  The  corresponding  sulphide,  (CN)2S,  is 
produced  by  the  action  of  a  solution  of  cyanogen  iodide  in  ether 
on  silver  sulphocyanide,  thus : — AgSCN  -f-  ICN.  eth.  =  Agl  -f 
(CJN")2S.  eth.  It  forms  volatile,  colourless,  rhombic  tables. 

Cyanogen  hydroxide,  or  cyanic  acid,  (CN)OH,  and  the 
corresponding  (CN)SH,  sulphocyanic  acid  form  numerous 
compounds  in  which  the  hydrogen  is  replaced  by  metals.  The 
potassium  salts  are  produced  by  oxidation  of  potassium  cyanide, 
with  atmospheric  oxygen,  or  better,  by  lead  oxide  or  man- 
ganese dioxide;  and  by  direct  combination  of  potassium  cyanide 
with  sulphur.  For  an  account  of  their  salts,  a  text- book  on 
the  carbon  compounds  must  be  consulted.  Ferric  sulpho- 
cyanide, Pe(CNS)3,  a  blood-red,  soluble  salt,  is  produced  by  the 
action  of  an  aqueous  solution  of  potassium  or  ammonium  sulpho- 
cyanide on  ferric  salts  ;  it  is  noticeable  as  a  test  for  iron  in  the 
ferric  condition  ;  ferrous  sulphocyanide  being  colourless.  Selenio- 
cyanic  anhydridet  or  selenium  cyanide,  and  seleniocyanides  J 
are  similarly  prepared  to  the  sulphur  compounds.  They  are 
unstable,  decomposing  easily  with  separation  of  selenium.  Tel- 
lurium compounds  have  not  been  prepared. 

Fluoride  of  cyanogen  will  no  doubt  soon  be  prepared  by 
Moissan.  Cyanogen  chloride,  CNC1,  bromide,  CNBr,  and 
iodide,  CNI,  are  produced  by  the  action  of  the  halogen  on  mer- 
curic cyanide.  Chlorine  in  the  dark ;  bromine  on  the  cyanide,  cooled 
by  ice  ;  and  iodine  at  a  gentle  heat,  yield  the  respective  halides. 
The  chloride  is  a  colourless  gas,  liquefying  at  —12°  to  —16°,  and 
solidifying  at  —18°  to  long,  transparent  prisms.  It  forms  a 
hydrate  with  water.  The  bromide  forms  long,'  colourless  needles 
which  soon  change  to  minute  cubes.  It  melts  above  40°,  but 

*  Hiibner  and  Wehrhahne,  Annalen,  128,  254  ;  132,  277. 
t  Linnemann,  Annalen,  120,  36. 
J  Crookes,  Chem.  Soc.  J.,  4,  12. 


THE  CYANIDES.  569 

volatilises  rapidly  at  15°.  The  sublimed  iodide  also  forms  long, 
white  needles,  but  crystallises  from  alcohol  or  ether  in  four-sided 
tables.  It  boils  above  100°,  but  volatilises  at  the  ordinary  tempe- 
rature. All  these  bodies  are  very  poisonous. 

Some  double  compounds  of  the  chloride  are  known,  produced 
by  direct  union,  e.g.,  BC13.CNC1;  PeCl3.CNCl;  TiCl4.CNCl; 
and  SbCLj.CNCl.  The  boron  and  antimony  compounds  form 
white  crystals;  the  titanium  compound  is  a  yellow,  crystalline 
mass  ;  and  the  iron  compound  is  black,  and  apparently  amorphous. 

Ruthenium  forms  ruthenocyanides,  similar  in  formula  to  the 
ferrocyanides,  and  isomorphous  therewith.*  The  potassium  salt 
is  formed  by  fusing  chloride  of  ruthenium  and  ammonium  with 
potassium  cyanide;  the  nitrate  deposits  it  in  small,  colourless 
tables  of  the  formula  K4Ru(CN)6.  On  warming  this  compound 
with  hydrochloric  acid,  a  violet  precipitate  of  ruthenous  cyanide, 
Ru(CN)2,  is  produced.  The  hydrogen  salt  is  liberated  from  the 
potassium  salt  in  presence  of  ether,  like  hydrogen  ferrocyanide  ; 
it  forms  white  lamin®.  Buthenic  cyanides  have  not  been  iso- 
lated. 

Rhodocyanides,  on  the  other  hand,  are  unknown.  Rhodium 
tricyanide,  Rh(CN)3,  formed  by  addition  of  acetic  acid  to  a  solu- 
tion of  rhodicyanide  of  potassium,  is  a  red  powder,  soluble  in 
potassium  cyanide  solution,  forming  rhodicyanides.  The  rhodi- 
chloride  of  potassium,  K3RhCl6,  fused  with  potassium  cyanide, 
yields  potassium  rhodicyanide,  K3Rh(CN)6,  analogous  to  ferri- 
cyanide.  It  forms  large,  anhydrous,  easily-soluble  crystals. 

The  cyanides  of  palladium  require  investigation.  Palladium 
dicyanide  is  said  to  be  a  white  precipitate,  produced  on  adding 
palladium  dichloride  to  mercuric  cyanide.  It  dissolves  in  a  solution 
of  potassium  cyanide,  giving  crystals  of  K3Pd(CN)4,  analogous  to 
the  double  cyanides  of  nickel.  The  tetracyanide,  Pd(CN)4,  is  said 
to  be  a  rose-colcured  precipitate  produced  by  mercuric  cyanide  in 
a  solution  of  potassium  palladichloride,  K2PdCl6.A.q. 

Potassium  osmocyanide,f  K4Os(CN)6,  analogous  to  the  fer- 
rocyanide, is  produced  by  adding  solution  of  potassium  cyanide  to 
a  solution  of  osmium  tetroxide,  OsO4,  in  aqueous  caustic  potash. 
The  solution  is  evaporated  to  dryness,  and  heated  to  dull  redness. 
On  treatment  with  water  osmocyanide  of  potassium  dissolves,  and 
may  be  purified  by  crystallisation.  It  forms  yellow,  quadratic 

*  Claus,  Jahresb.,  1855,  446. 

t  Claus,  Seitrdge  zur  Chemie  der  Platinmetalle,  Dorpat,  1854;  Martius, 
Jahresb.,  1860,  233. 


570  THE   NITRIDES,   PHOSPHIDES,   ETC. 

crystals  isomorphous  with,  the  ferrocyanides.  Its  solution  gives  a 
light-blue  precipitate  with  ferrous  salts,  which  is  oxidised  by  nitric 
acid  into  a  violet  compound  analogous  to  Turnbull's  blue,  probably 
Fe3"{Os(CN)6}2.  A  violet  compound,  said  to  have  the  same 
formula,  is  produced  by  addition  of  a  ferric  salt  to  potassium 
osmocyanide.  Barium  osmocyanide,  Ba2Os(CN)6,  crystallising  in 
reddish-yellow  prisms,  is  produced  by  treating  this  compound  with 
baryta-water,  which  separates  ferric  hydrate.  The  acid  is  also 
known,  and  is  prepared  in  the  same  manner  as  hydroferrocyanic 
acid.  When  boiled,  the  solution  of  the  acid  gives  a  violet  pre- 
cipitate of  osmium  dicyanide,  Os(CN)2. 

The  iridicyanides,*  of  which  the  potassium  salt  is  produced 
by  fusing  ammonium  iridichloride,  IrCl3.3NH4Cl,  with  potassium 
cyanide,  or  metallic  iridium  with  potassium  ferrocyanide,  are 
analogous  to  the  f  erricyanides  and  also  resemble  the  rhodicyanides. 
The  hydrogen,  potassium,  and  barium  salts  are  white  and  crystal- 
line ;  the  zinc,  ferrous,  lead,  and  mercurous  salts  are  white  and 
insoluble ;  the  ferric  salt  yellow;  and  the  cupric  salt  blue. 

Platinum  forms  two  series  of  cyanides ;  1,  those  analogous 
to  the  double  cyanides  of  nickel,  for  example,  K2Pfc(CN)4  ;  and 
2,  dihalo-platinocyanides,  such  as  I2Pt(CN)4.K2.  The  potassium 
salt  of  the  first  series  is  produced  by  heating  platinum  with 
cyanide  or  ferrocyanide  of  potassium,  or,  better,  by  dissolving 
ammonium  platini chloride,  mixed  with  caustic  potash,  in  a  strong 
solution  of  potassium  cyanide,  boiling  until  ammonia  is  expelled, 
and  crystallising.  It  forms  rhombic  prisms,  yellow  by  trans- 
mitted, and  blue  by  reflected,  light.  The  copper  salt  is  a  green 
precipitate,  produced  by  adding  solution  of  copper  sulphate  to  a 
solution  of  potassium  platinocyanide ;  and  from  it  the  hydrogen 
salt  may  be  prepared  by  the  action  of  hydrogen  sulphide;  the 
barium  salt,  by  the  action  of  barium  hydroxide ;  and  from  the 
barium  salt  the  platinocyanides  of  other  metals  may  be  produced 
by  adding  the  requisite  amounts  of  sulphates  of  other  metals.  The 
platinocyanides  all  exhibit  rema.rkable  dichroism ;  the  magnesium 
salt  is  one  of  the.  most  beautiful;  it  forms  square-based  prisms, 
deep  red  by  transmitted  light;  the  sides  of  the  prisms  reflect 
brilliant  metallic  green,  and  the  extremities  are  purple-blue. 

As  regards  the  products  of  their  oxidation  by  nitric  acid, 
chlorine  and  bromine  in  presence  of  water,  lead  dioxide,  &c.,  con- 
siderable doubt  still  exists.  On  the  one  hand,  they  are  stated  to 
have  formulae  such  as  K2Pt(CN)5;  and  analyses  of  many  such 

*  Martius,  Annalen,  117,  357. 


THE   CYANIDES.  571 

compounds  are  given  by  several  well-known  chemists.*  On  the 
other  hand,  the  compounds  produced  by  the  action  of  chlorine 
are  said  to  have  formula  such  as  6(K2Pt(CN)4).Cl2.(H20).t  And 
recently,  the  formula  [K2Pt(CN)4.3H20]3Cl  has  been  ascribed  to 
the  potassium  compound,  and  that  of  [K2Pt(CN)4.3H2O]3HClJ  to 
a  similar  compound  produced  by  the  action  of  hydrogen  chloride. 
Regarding  the  action  of  excess  of  halogen,  only  one  view  exists ; 
such  compounds  have  the  formulae  like  the  one  already  given, 
viz.,  Cl2.Pt(CN)4.KLj.  Compounds  containing  chlorine,  bromine, 
the  nitro-group,  N02,  the  group  S04,  &c.,  have  been  prepared. 
They  all  display  remarkable  dichroism. 

CuCN;  AgCN;  AuCN. — Double  cyanides. — Cuprosocyanides,  such  as 
KCu(CN)2;  K2Cu3(CN)5;  and  K3Cu(CN)4.— Argentocyanides,  such  as 
KAg(CN)2;  K2NaAg3(CN)6.—  Auro  cyanides,  such  as  KAu(CN)2. 

Cuprous  and  argentous  cyanides  are  white  powders.  The 
first  is  obtained  by  adding  a  solution  of  potassium  cyanide  to  a 
solution  of  cuprous  chloride,  Cu2Cl2,  in  hydrochloric  acid.  It  may 
be  obtained  in  crystals  by  treating  with  hydrogen  sulphide  lead 
cuproso-cyanide,  PbCu(CN3}3,  suspended  in  water ;  the  compound 
HCu(CN)2  appears  to  be  formed,  which,  when  filtered  from  the 
lead  sulphide  and  evaporated,  decomposes,  depositing  crystals  of 
cuprous  cyanide. 

Silver  cyanide  is  easily  produced  by  adding  to  a  solution  of 
silver  nitrate  a  solution  of  the  requisite  amount  of  potassium 
cyanide ;  excess  of  cyanide  redissolves  the  precipitate,  producing 
the  double  cyanide  KAg(CN)2,  which  separates  in  crystals  on 
evaporation.  Aurous  cyanide  is  produced  by  decomposing 
potassium  aurocyanide,  KAu(CN)2,  with  nitric  acid.  It  is  a 
yellow  crystalline  powder. 

Mercurous  cyanide  does  not  exist.  On  addition  of  a  soluble 
cyanide  to  a  mercurous  salt,  metallic  mercury  is  precipitated,  and 
mercuric  cyanide  goes  into  solution. 

The  double  cyanides  are  produced  by  the  action  of  potassium 
cyanide  in  excess  on  the  cyanides,  or  on  the  chlorides,  oxides,  &c. 
From  the  potassium  salts  other  derivatives  may  be  prepared. 
Those  of  silver  and  of  gold  are  largely  used  in  electro-plating.  A 
double  nitrate  and  cyanide  of  silver  is  known,  AgCN.AtNO3, 
crystallising  from  a  solution  of  silver  cyanide  in  a  solution  of 
silver  nitrate. 

*  Knop,  J.  prakt.  Chein.,  37, 461 ;  Wiselsky,  ibid.,  69,  276 ;  Martius,  loc,  cit. 
t  Hadow,  Chem.  Soc.  J.,  14,  106. 
J  Wilm,  Berichte,  19,  959. 


572  THE  NITRIDES,  PHOSPHIDES,  ETC. 

Cu(CN)2 ;  Hgr(CN)2.— Double  salts,  such  as  K2Cu(CN)4,  and  K2Hg(CN)4.— 
Cu(CN)2.2CuCN ;  Cu(CN)2.4CuCN.  Mercuric  cyanide  also  forms  numerous 
compounds  with  other  salts,  such  as  Hg(CN)2.KCl ;  2Hg-(CN)2.CaCl2.6H2O ; 
Hg-(CN)2.2CoCl24H2O ;  and  similarly  with  bromides  and  iodides  ;  also 
Hg:(CN)2.K2CrO4;  Hg-(CN)2.Ag2Cr2O7;  2Hg-(CN)2.Ag-2SO4;  2Hg(CN)2.K2S2O3; 
Hg>(CN)2.Ag-NO3,  and  many  others. 

Cupric  cyanide  is  very  unstable,  giving  off  cyanogen.  It  is 
a  yellow-green  precipitate,  produced  by  adding  copper  sulphate  to 
excess  of  potassium  cyanide.  It  dissolves  rapidly,  giving  a 
double  salt.  When  allowed  to  stand  it  changes  into  the  double 
compound,  Cu(CN)2.2CuCN,  which  forms  green  granular  crystals, 
or  the  other  cuprous-cupric  cyanide,  Cu(CN)2.4CuCN.  These 
bodies  rapidly  decompose,  forming  cuprous  cyanide. 

Mercuric  cyanide  is  produced  by  boiling  mercuric  sulphate 
with  a  solution  of  potassium  ferrocyanide,  or  by  digesting  mercuric 
oxide  with  hydrocyanic  acid.  It  forms  colourless  dimetric  crystals. 
The  double  compounds  crystallise  well,  and  are  produced  by 
mixture. 

Au(CN)3  is  unknown  in  the  free  state.  Potassium  auricyanide, 
KAu(CN)4,  is  produced  by  crystallising  a  mixture  of  auric 
chloride,  AuCl3,  with  potassium  cyanide.  It  forms  large  colour- 
less tables.  The  silver  salt,  produced  by  precipitation  with  silver 
nitrate,  yields,  on  treatment  with  hydrochloric  acid,  the  hydrogen 
salt,  which,  after  evaporation  over  sulphuric  acid,  separates  from 
its  solution  in  large  colourless  tables  of  the  formula 

2HAu(CN)4.3H2O. 

Constitution  of  the  cyanides. — Two  formulae  are  possible 
for  hydrogen  cyanide;  either  H — CEEN,  representing  it  as 
methane  with  one  atom  of  nitrogen  replacing  three  atoms  of 
hydrogen;  or  H — NC,  representing  it  as  ammonia,  in  which 
carbon  replaces  two  atoms  of  hydrogen.  These  are  suggested  by 
the  following  considerations  among  others : — Compounds  are 
known,  in  which  the  hydrogen  of  hydrogen  cyanide  is  replaced  by 
methyl,  CH3.  One  of  those,  when  treated  with  nascent  hydrogen, 
yields  an  ammonia,  ethylamine,  C2H5.NH2,  the  constitution  of 
which  has  been  proved  to  be  CH3.CH3.NH2;  this  cyanide  is  not 
easily  attacked  by  hydrochloric  acid,  but  when  boiled  with  caustic 
potash  it  assimilates  the  elements  of  water,  yielding  ammonia  and 
potassium  acetate,  thus :— CH3CN  +  H20  +  H.OH  =  CH3.COOH 
4-  NH3,  the  nitrogen  being  replaced  by  oxygen  plus  hydroxyl. 
The  other  compound,  CH3.NC,  is  not  easily  reduced,  but  at  once 
decomposes  on  treatment  with  hydrochloric  acid,  giving  methyl- 


THE   CYANIDES.  573 

amine  and  formic  acid,  thus :— CH3NC  +  H20  4-  H.OH  = 
CH3.NH2  +  HCO.OH.  Compounds  of  the  first  class  are  not 
specially  poisonous,  and  have  a  not  unpleasant  smell ;  compounds 
of  the  second  class  are  exceedingly  poisonous,  and  have  an  unbear- 
able odour.  Both  are  produced  together  by  the  reactions : — 
CH3I  -f  Ag(CN)  =  CH3(CN)  +  Agl;  and  CH3KSO4  +  KCN 
=  K2SO4  +  CH3(CN).  Thus  it  would  appear  that  either 
potassium  and  silver  cyanides  are  mixtures  of  two  such  salts 
as  AgCN"  and  AgNC  ;  or  that  the  compound  CH3CN,  which  is 
a  more  stable  body  than  CH3NC,  is  produced  when  heated, 
owing  to  molecular  change  during  the  reaction.  The  latter 
view  appears,  on  the  whole,  the  most  tenable ;  and  it  would  there- 
fore follow  that  the  cyanides  belong  to  the  class  represented  by 
HNC.  This  may  also  be  inferred  from  their  very  poisonous 
nature. 

It  is  also  noticeable   that  the  cyanides  show  great  tendency 

towards  the  formation  of  complex  compounds.     Cyanogen  itself 

polymerises ;  the  chloride  C3N3C13,  is  known  as  cyanuric  chloride ; 

and  it  has  been  suggested  that  the  grouping  of  the  cyanogen  is  in 

Cl— C— N=C— Cl 

II  I 

such  cases  N — C=N         .     The  group  C3N"3,  therefore,  may 

Cl 

be  regarded  as  a  triad-group  ;  and  potassium  ferrocyanide  may  be 
thus  represented  as  Fe"(C3N3K2)2.  Similarly,  dicyanogen  com- 
pounds are  known,  in  which  the  grouping  has  been  supposed  to  be 
— C=N 

|      ;    this  is  a   dyad-group ;  and  ferricyanide  of  potassium 
N=C— 

on  this  theory  would  be  Ee'"(C2N2K)3,  and  potassium  nickelo- 
cyanide  and  similar  salts  Ni"(C2N"2K)2.  But  it  must  be  remem- 
bered that  such  methods  of  representation,  however  suggestive, 
have  little  to  recommend  them  except  inasmuch  as  they  may  prove 
to  be  working  theories. 


574 


PART  VII.— ALLOYS. 

CHAPTER  XXXIII. 

ALLOYS  appear  to  form  three  distinct  classes :  (1.)  Mixtures  in 
which  no  chemical  combination  has  occurred,  and  which 
may  be  regarded  as  solidified  solutions ;  (2.)  Chemical  com- 
pounds with  definite  formulae;  and  (3)  substances  inter- 
mediate between  these  two  classes,  which  contain  the 
elements  partly  in  a  state  of  mixture,  partly  as  compounds.* 
But  in  the  present  state  of  our  knowledge,  we  can  seldom  dis- 
criminate between  these  three  classes,  and  hence,  in  the  following 
chapter,  attention  will  be  drawn  to  cases  of  definite  combination, 
wherever  suspected,  while  the  elements  will,  as  usual,  be  taken 
mainly  in  the  periodic  order. 

It  frequently  happens  that  two  elements  will  not  mix,  or  that 
one  will  mix  with  a  minimal  quantity  of  another.  Thus,  while 
copper  and  silver,  or  lead  and  tin,  mix  in  all  proportions,  iron  and 
silver  do  not ;  a  little  silver,  it  is  true,  enters  the  iron,  considerably 
modifying  its  properties ;  and  a  little  ii-on  enters  the  silver ;  but 
mixtures  in  any  desired  proportion  cannot  be  prepared.  It  has  been 
suggested  that  alloys  often  contain  one  or  more  of  their  constituent 
metals  in  an  allotropic  condition ;  the  alloy  of  zinc  and  rhodium, 
when  freed  from  zinc  by  treatment  with  acid,  leaves  the  rhodium 
in  an  allotropic  state ;  and  this  modification  is  converted  into 
ordinary  rhodium  with  slight  explosion  at  300°  (see  p.  78). 

A  new  method  of  investigating  alloys  has  recently  been  devised,f 
and  it  has  been  applied  to  determining  the  constitution  of  alloys 
of  copper  and  zinc,  and  of  copper  and  tin.  The  principle  of  the 
method  is  as  follows : — If  a  battery  be  constructed  containing, 
instead  of  a  plate  of  any  single  metal,  a  compound  plate  made 
of  two  metals,  the  electromotive  force  of  the  circuit  is  that  of  the 
more  positive  metal.  If  an  alloy  of  two  metals  is  used  as  material 
for  a  plate,  the  electromotive  force  is  still  that  of  the  more  electro- 

*  Matthiessen,  'Brit.  Assn.  Reports,  1863,  37;  Chem.  Soc.  J.,  1867,  201. 
t  Laurie,  Chem.  Soc.  J.,  1888,  104. 


HYDRIDES.  67  O 

positive  metal,  if  the  alloy  is  a  mere  mixture  ;  bat  if  a  compound, 
it  has  its  own  electromotive  force,  differing  from  that  of  the 
more  electropositive  element  of  the  compound.  If  the  alloy 
consists  of  both  a  mixture  and  a  compound,  then,  as  the  plate 
dissolves  away,  the  more  electropositive  element  will  disappear 
first,  and  the  electromotive  force  will  fall  suddenly  to  that  due 
to  the  compound.  In  this  way  the  existence  of  definite  com- 
pounds of  the  formulae  CuZn2  and  Cu3Sn,  have  been  rendered 
probable. 

By  extension  and  development  of  such  experiments  as  these, 
we  may  hope  soon  to  enlarge  our  knowledge  of  alloys. 

The  alloys  will  now  be  described  in  their  order. 

Hydrides. — Sodium  and  potassium  heated  in  a  current  of 
hydrogen  yield  hydrides,  of  which  the  sodium  compound  has  the 
formula  Na»H.  Sodium  hydride*  is  a  soft  substance  like  wax, 
which  becomes  brittle  at  a  temperature  somewhat  below  its  melt- 
ing point.  It  is  formed  at  300°,  and  dissociates  at  421°.  Its 
melting  point  lies  below  that  of  sodium.  When  treated  with 
mercury,  the  sodium  and  mercury  unite,  and  hydrogen  is  expelled. 
The  potassium  compound  is  white,  brittle,  and  shows  crystalline 
structure.  Lithium  absorbs  only  seventeen  times  its  volume  of 
hydrogen. 

No  other  hydrides  are  met  with  till  the  metal  iron  is  reached. 
The  action  of  zinc  ethyl,  Zn(C2H5)2,  on  ferrous  iodide  in  presence 
of  ether,  is  represented  by  the  equation : — Zn(C2H5)2  +  PeI2  = 
ZnL  +  2(72Ht  +  FeH2.  The  product  is  a  black  powder,  resembl- 
ing finely-divided  iron,  which  evolves  hydrogen  when  gently 
heated,  or  on  treatment  with  water.  Its  composition  is  con- 
jectural, for  it  has  not  been  analysed,  and  apparently  some 
hydrogen  is  evolved  along  with  the  ethylene. 

Metallic  iron  absorbs  a  small  quantity  of  hydrogen  gas  if 
exposed  to  it  in  a  finely-divided  condition.  Meteoric  iron  has  been 
found  to  contain  2 '85  times  its  volume  of  gas,  containing  86  per 
cent,  of  hydrogen.  Similar  results  have  not  been  obtained 
with  chromium,  manganese,  or  cobalt ;  but  nickel,  in  the  porous 
state,  if  made  the  negative  electrode  of  a  battery,  absorbs  about 
165  times  its  volume  of  hydrogen,  losing  it  gradually  in  the 
course  of  a  few  days.  If  it  be  recharged  several  times,  it  falls  to 
powder.f 

*  Troost  and  Hautefeuille,  Comptes  rendus,  78,  807. 
t  Raoult,  Comptes  rendus,  69,  826. 


576  ALLOYS. 

Vanadium  absorbs  about  13  per  cent,  of  its  weight  of  hydrogen, 
forming  a  compound  which  oxidises  easily  in  air. 

A  hydride  of  niobium,  of  the  formula  NbH,  is  formed  by  the 
action  of  sodium  on  niobifluoride  of  potassium.  It  is  a  black 
powder,  soluble  only  in.  hydrofluoric  acid  and  in  fused  hot  potas- 
sium hydroxide.* 

Rhodium  and  ruthenium  do  not  appear  to  combine  with 
hydrogen;  but  palladium  may  be  made  to  absorb  as  much  as 
936  times  its  volume,  or  4'68  per  cent,  of  hydrogen,  when  made 
the  negative  pole  of  a  battery  by  which  dilute  sulphuric  acid  is 
being  electrolysed.  The  specific  gravity  of  the  palladium  is 
thereby  reduced  from  12'38  to  11'79;  and  it  becomes  magnetic, 
implying  that  solid  hydrogen  is  magnetic.  This  affords  a  means 
of  determining  the  specific  gravity  of  solid  hydrogen,  on  the 
assumption,  which  is  nearly  true  in  most  instances,  that  the 
specific  gravity  of  an  alloy  is  the  mean  of  that  of  its  constituents. 
It  is  0'62  at  15°.  From  the  sodium  alloy,  Na2H.  it  is  0'63.f  The 
specific  heat  of  solid  hydrogen  can  also  be  calculated  on  a  similar 
assumption.  The  following  results  were  obtained : — 

Sp.ht.  4-49;  8-87;  4'99;  8'31 ;  4'08;  4'96;  5'76  ;  4'06;  4'46;  9'10;  4'58; 
6-02 ;  4-82  ;  6-55  ;  4-34. 

The  mean  result  is  5*7. J  It  will  be  seen  that  the  atomic  heat 
of  hydrogen  may  lie  near  that  of  other  elements — about  6 '2. 

This  alloy, §  which  has  been  supposed  to  contain  the  metal 
"  hydrogenium,"  as  it  was  termed  by  Graham,  resembles  palla- 
dium in  colour.  It  loses  its  hydrogen  when  heated,  best  in  a 
vacuum.  The  hydrogen  possesses  very  active  properties,  resembl- 
ing those  which  it  possesses  in  the  nascent  state  ;  thus  it  combines 
directly  in  the  dark  with  bromine  and  with  iodine ;  reduces 
mercuric  chloride  to  mercurous  chloride,  ferric  to  ferrous  salts, 
&c.  The  alloy  approximates  in  composition  to  that  expressed  by 
the  formula  Pd2H,  but  it  appears  to  absorb  hydrogen  in  excess, 
which  is  not  chemically  combined,  but  in  a  state  of  mixture.  To 
this  phenomenon  Graham  gave  the  name  "  occlusion."  The  metal 
platinum  has  also  the  power  of  occluding  gases.  "  Platinum 
black,"  produced  by  dissolving  platinous  chloride,  PtCl2,  in  caustic 
potash,  adding  alcohol  gradually  to  the  hot  liquid,  and  washing 
the  precipitated  metallic  powder  successively  with  alcohol,  hydro- 

*  Kriiss,  Berichte,  20,  169. 

f  Troost  and  Hautefeuille,  ibid.,  78,  968;  also  Dewar,  Phil.  Mag.  (4),  47, 
324. 

J  Koberts  and  Wright,  CJiem  Soc.,  26,  112. 

§  Graham,  Roy.  Soc.  Proc.,  16,  422;  17,  212,  500. 


ALLOYS   OF  H,  Li,  NA,  K,  AND  (NH4).  577 

chloric  acid,  canstic  potash,  and  distilled  water,  so  as  to  remove  all 
foreign  substances,  has  the  power  of  absorbing  hydrogen  in  greater 
quantity  than  compact  platinum.  It  also  absorbs  about  250  times 
its  volume  of  oxygen,  and  when  introduced  into  a  mixture  of  these 
gases,  it  causes  their  combination.  "  Spongy  platinum,"  pre- 
pared by  igniting  ammonium  platinichloride,  (NH4)2PtCl6,  has  a 
similar  power  in  less  degree.  If  a  jet  of  hydrogen  be  directed  on 
it,  it  grows  red  hot,  and  inflames  the  hydrogen.  A  recent 
application  of  this  power  of  causing  the  combination  of  such  gases 
has  been  applied  to  the  detection  of  fire-damp  (mainly  CH4)  in 
mines.  The  bulb  of  a  thermometer,  coated  with  finely-divided 
platinum,  or  better,  palladium,  registers  a  sudden  rise  of  tempera- 
ture when  it  is  brought  into  a  mixture  of  marsh  gas  and  air. 

CuH,  or  Cu,H2,  copper  hydride,*  is  a  brown  powder,  pro- 
duced by  adding  to  a  strong  solution  of  copper  sulphate  a  solution 
of  hydrogen  hypophosphite,  H3P02,  made  by  adding  sulphuric  acid 
to  a  solution  of  barium  hypophosphite.  It  decomposes  rapidly 
between  55°  and  60° ;  it  is  attacked  by  hydrochloric  acid,  giving 
cuprous  chloride  and  hydrogen,  thus  : — 

CuH  +  2HCl.Aq  =  CnCLHCLAq  +  H2. 
Alloys  of  lithium,  sodium,  potassium,  and  ammonium. — 

Lithium,  sodium,  and  potassium  mix  with  each  other  in  all  pro- 
portions. Alloys  of  sodium  and  potassium,  containing  10  to  30  per 
cent,  of  the  latter,  are  liquid  at  0°,  and  have  very  high  surface 
tension. 

Sodium  dissolves  in  liquid  ammonia,  forming  an  opaque  liquid, 
with  coppery  metallic  lustre,  said  to  have  the  formula  Natalie  ;f 
it  has  been  named  sodammonium,  and  is  supposed  to  be  the 
analogue  of  the  undiscovered  N2H8,  diammonium.  With  excess  of 
ammonia  a  blue  liquid  is  formed.  This  substance,  released  from 
pressure,  deposits  sodium ;  it  can  hardly  be  a  simple  solution  of 
that  metal  in  liquid  ammonia,  for,  if  so,  it  is  the  only  instance  of  a 
metal  dissolving  in  a  compound  without  chemical  action. 

The  following  alloys  of  the  elements  have  been  examined  (to 
economise  space,  symbols  are  here  employed;  where  indices  are 
given  formulae  have  been  ascribed) : — 

Na,  Zn. — Zinc  is  insoluble  in  sodium  ;  but  they  may  be  mixed 

together. 

Na,  Cd. — Sodium  dissolves  about  3  per  cent,  of  cadmium. 
Na,  In.— Mix  easily.     Na,  Tl.— Mix  easily. 

*  Wurtz,  Annales  (3),  11,  251. 

f  Weyl,Poffff.Ann.,  121,  607  j  123,  365  j  also,  Seeley,  Chem.  New,  22,  317. 

2  P 


578  ALLOYS. 

KFe2,  and  KFe3. — More  fusible  than  iron  ;  produced  by  heat- 
ing iron  sesquioxide  with  potassium  tartrate.  Sodium 
alloys  are  similarly  made. 

Na,  Pb ;  K,  Pb. — Similarly  produced ;  Na,  Pb  alloys  are 
malleable  and  bluish  ;  those  of  K,  Pb  are  white,  brittle,  and 
granular.  Lead  is  insoluble  in  melted  sodium. 

Na,  Sn  ;  K,  Sn. — Similarly  prepared  ;  white  and  brittle. 

Na,  Bi ;  K,  Bi. — Similarly  prepared ;  white  and  brittle. 

Na,  Pt;  &c. — Metals  of  the  platinum  group  are  attacked  at  a 
red  heat  by  sodium  or  potassium. 

Na,  Ag. — Silver  is  insoluble  in  melted  sodium. 

Na,  Au. — Sodium  dissolves  about  one-third  of  its  weight  of 
spongy  gold;  the  alloy  is  white,  and  harder  than  sodium. 

Li,  Hg. — Lithium  amalgam  is  produced  by  mixing  the  metals, 
or  by  electrolysing  a  concentrated  solution  of  lithium 
chloride  with  mercury  as  the  negative  pole.  It  crystallises 
in  needles,  and  is  at  once  acted  on  by  water. 

Na,  Hg. — Prepared  by  mixture ;  best  under  a  layer  of  heavy 
paraffin  ;  much  heat  is  evolved  by  the  union.  When  it 
contains  under  1'5  percent,  of  sodium,  it  is  liquid;  over 
that  percentage,  solid.  It  is  much  employed  as  a  source  of 
nascent  hydrogen  in  alkaline  solution.  It  is  slowly  attacked 
by  water ;  but  quickly  by  dilute  acids. 

K,  Hg;  Rb,  Hg. — Similarly  prepared,  and  similar  in  proper- 
ties. Both  crystallise  in  needles.  Rb,  Hg  may  be  pre- 
pared like  Li,  Hg. 

NH4,  Hg  (?). — A  buttery  metallic  mass,  produced  by  the  action 
of  Na,  Hg  on  ammonium  chloride.  Its  difference  in  pro- 
perties from  metallic  mercury  would  lead  to  the  supposition 
that  it  contains  the  ammonium  group  ;  but  it  is  very  un- 
stable, and  splits  quickly  into  mercury,  and  ammonia  and 
hydrogen,  which  are  evolved.  It  may  be  frozen,  and  then 
forms  a  solid  bluish-grey  brittle  metal.  A  similar  spongy 
bismuth  compound  may  be  prepared. 

Ca,  Zn. — A  white  alloy,  containing  from  2'6  to  6*4  per  cent,  of 
calcium,  produced  by  heating  together  calcium  chloride, 
zinc,  and  sodium.  It  does  not  decompose  cold  water,  and  is 
not  appreciably  tarnished  by  air. 

Ca,  Al. — Similarly  prepared ;  white ;  contained  8'6  per  cent, 
of  calcium. 

Ba,  Al. — Similarly  prepared ;  white ;  contained  24  to  36  per 
cent,  of  barium.  It  easily  decomposes  cold  water. 


ALLOYS.  579 

Ba,  Pe. — Lead- col oured ;  prepared  by  direct  union;  very 
oxidisable. — Ba,  Pd ;  white. 

Ba,  Ft. — Bronze  metal  falling  to  red  powder. 

Ca,  Hg ;  Sr,  Hg ;  Ba,  Hg.— Produced  by  electrolysis,  like 
lithium  amalgam.  The  first  contains  very  little  calcium, 
the  second  is  somewhat  richer,  and  the  third  may  easily  be 
obtained  crystalline.  Barium  amalgam  is  also  produced  by 
shaking  a  solution  of  barium  chloride  with  sodium  amalgam; 
it  is  pasty  and  crystalline.  Even  at  a  white  heat  it  retains 
77  per  cent,  of  mercury.  Ba,  Sn  and  Ba,  Bi  have  been 
similarly  prepared.  f 

Mg,  Zn;  Mg,  Cd;  Mg,  Al;  Mg,  Tl;  Mg,  Pfaf;  Mg,  Sn; 
Mg,Sb;  Mg,Bi;  Mg,Pt;  Mg,Ag;  Mg,Au;  and  Mg,  Pt 
have  been  prepared.  They  are  brittle,  harder  than  the 
constituent  metals,  and  have  a  granular  fracture.  They 
are  all  easily  oxidised.  Iron  and  cobalt  are  said  not  to  alloy 
with  magnesium,  but  the  addition  of  a  little  magnesium  to 
nickel  lowers  its  melting  point,  and  renders  it  ductile  and 
malleable.  This  discovery  has  greatly  increased  the  uses  of 
nickel.  Magnesium  dissolves  in  mercury. 

Zn,  Cd. — Zinc  and  cadmium  mix  in  all  proportions. 

Zn,  Tl. — A  soft  white  alloy. 

Zn,  Fe. — Iron  and  zinc  do  not  easily  unite.  But  iron  may  be 
"  galvanized,"  that  is,  coated  with  zinc,  by  passing  it  through 
a  bath  of  zinc  kept  melted  under  a  coating  of  ammonium 
chloride.  The  iron  must  be  first  scrupulously  cleaned  with 
acid,  and  polished  first  with  sand,  then  with  bran.  "Gal- 
vanized iron  "  is  used  for  roofing,  and  for  utensils  of  various 
kinds.  The  zinc  does  not  easily  oxidise,  but  if,  owing  to 
imperfect  coating,  oxidation  takes  place,  the  zinc  oxidises 
and  not  the  iron. 

Some  iron  dissolves  in  the  zinc,  which  is  then  known 
as  "hard  spelter;"  it  is  purified  by  distillation. 

Zn,  Sn. — An  alloy  of  91*5  per  cent,  of  tin  with  8'3  per  cent,  of 
zinc  is  permanent;  other  alloys  "liquate,"  that  is,  when 
heated  on  a  sloping  bed,  the  more  easily  fusible  tin  melts 
and  runs  down,  leaving  the  less  fusible  zinc  behind. 

Zn,  Sn9,  Pb2. — An  alloy  made  in  these  proportions  melts  at 
168°. 

Zn,  Pb. — Harder  than  lead.  Lead  dissolves  only  1*2  per  cent, 
of  zinc  ;  and  zinc  only  1'6  per  cent,  of  lead.  A  process  for 
desilverising  lead  is  based  on  this  fact.  The  lead  contain- 
ing silver  is  mixed  mechanically  with  zinc,  and  the  mixture 

2  p  2 


580  ALLOYS. 

is  stirred.  The  silver  is  carried  up  by  the  zinc,  which  floats. 
The  zinc  solidities  at  a  higher  temperature  than  the  lead, 
and  the  cake  of  zinc  is  removed  and  distilled ;  the  silver 
remains  behind.  The  lead  is  easily  freed  from  zinc  by 
oxidation  ;  the  zinc  is  removed  as  dross.  (Parke's  process 
for  desilverising  lead.) 

Zn,  Pb,  Bi. — An  alloy  containing  equal  parts  by  weight  of 
each  melts  under  boiling  water. 

Zn,  Bi. — Zinc  dissolves  2*4  per  cent,  of  bismuth ;  bismuth 
from  8'6  to  14*3  per  cent,  of  zinc. 

Zn,  Ru. — Hexagonal  prisms,  burning  when  heated  in  air. 

Zn,  Rh. — Rhodium  melted,  zinc  added,  and  excess  of  zinc 
removed  by  treatment  with  hydrochloric  acid.  A  white 
crystalline  compound. 

Zn,  Pt. — -Similarly  prepared.  Zinc  and  platinum  unite  with 
incandescence.  The  compound  is  very  hard,  and  bluish- 
white  in  colour.  It  fuses  easily. 

Zn,  Cu. — Brass,  pinchbeck,  Muntz  metal,  tombac.  Produced 
by  melting  copper  and  adding  zinc.  Copper  may  be 
superficially  coated  with  brass  by  exposing  it  to  zinc- vapour. 
The  colour  of  brass  and  tombac  is  yellow,  resembling  gold. 
Brass  tarnishes  in  air,  but  it  may  be  protected  by  "  lacquer- 
ing," that  is,  coating  it  with  a  varnish  made  of  shellac 
dissolved  in  alcohol,  and  coloured  with  gamboge.  It  is 
harder,  not  so  tough,  and  more  easily  fusible  than  copper, 
and  is  ductile  and  malleable.  English  brass  contains  usually 
70  per  cent,  of  copper  and  30  per  cent,  of  zinc ;  pinchbeck, 
86  per  cent.  Cu  and  14  per  cent.  Zn ;  Muntz  metal,  used 
for  castings,  axle-bearings,  &c.,  66  per  cent.  Cu  and  34  per 
cent.  Zn ;  tombac,  86  per  cent.  Cu  and  14  per  cent.  Zn ; 
and  bronze  powder,  for  imparting  the  appearance  of  bronze 
to  castings,  &c.,  83  per  cent.  Cu  and  17  per  cent.  Zn. 

Zn,  Cu,  Ni. — "  German  silver."  A  white  alloy,  hard,  malle- 
able, and  ductile.  Contains  Cu,  62  per  cent.,  Zn,  23  per 
cent.,  Ni,  15  per  cent.  Used  for  coins. 

Zn,  Ag. — A  malleable,  permanent  alloy. 

Zn,  Au. — Zinc  alloys  easily  with  gold.  An  alloy  of  11  parts 
of  gold  to  1  part  of  zinc  is  greenish-yellow  and  brittle ;  of 
equal  parts  is  white  and  hard ;  and  of  2  parts  of  zinc  with 
1  part  of  gold,  hard,  and  whiter  than  zinc. 

Zn,  Hg. — Easily  prepared.  It  is  not  attacked  by  dilute  sul- 
phuric acid;  hence  zinc  battery  plates  are  amalgamated. 
Until  they  are  made  the  negative  pole  of  the  battery,  hydro- 


ALLOYS.  .581 

gen  is  not  evolved.  The  compound  Zn3Hg  is  produced 
bj  electrolysing  a  solution  of  zinc  chloride  with  a  mercury 
electrode ;  and  by  squeezing  a  saturated  zinc  amalgam  the 
compound  Zn2Hg  is  said  to  remain. 

Cd,  Pb ;  Cd,  Sn.— Malleable  white  alloys.— CdaTI,  white  and 
crystalline. 

Cd2Pt. — A  white  granular  very  brittle  compound,  prepared 
like  the  compound  ZnPt. 

Cd,  Cu. — Brittle  and  whitish-red.  Cd,  Ag. — An  alloy  of  2 
parts  of  cadmium  with  1  part  of  silver  is  malleable  and 
tenacious;  with  1  part  of  cadmium  with  2  of  silver,  is 
brittle.  Cd,  Hg. — Cadmium  amalgamates  easily.  An 
amalgam  containing  21  per  cent  of  cadmium  is  brittle ; 
alloys  with  more  cadmium  are  malleable  and  very  tenacious. 

Al,  Tl. — A  soft  dull-coloured  alloy. 

Al,  Pe. — An  alloy  containing  as  much  as  1T5  per  cent,  of 
aluminium  is  made  by  the  Cowle's  process  of  heating  corun- 
dum (native  oxide  of  aluminium)  by  the  electric  arc  in  a 
chamber  along  with  charcoal,  previously  soaked  in  lime- 
water  and  dried,  so  as  to  prevent  its  conducting ;  scrap  iron 
is  present,  which  boils  at  the  enormously  high  temperature 
of  the  arc,  and  washes  down  the  aluminium,  forming  an 
alloy.  It  has  been  shown  that  this  process  does  not  depend 
on  electrolysis,  because  an  alternating  current,  which  is 
incapable  of  electrolysing,  yields  equally  good  results.  The 
alloy  is  named  "  ferro-alnminium,"  and  is  employed  as 
follows :  a  quantity  of  nearly  pure  iron  (fine  wrought  iron, 
containing  but  little  carbon)  is  heated  to  its  point  of  fusion, 
and  enough  ferro-aluminium  is  added  to  give  a  percentage 
of  about  O'l  of  aluminium  to  the  total  mass  of  iron  employed. 
The  melting  point  of  the  iron  is  thereby  greatly  lowered,  it 
is  said  as  much  as  500°,  and  the  iron  is  then  directly  em- 
ployed for  castings.  Another  noteworthy  point  is  that  iron 
containing  even  such  a  small  proportion  of  aluminium 
retains  the  carbon  in  combination  until  it  is  just  on  the 
point  of  solidifying,  and  then  rejects  it  almost  completely  to 
the  outside.  Castings  made  thus  are  very  fine  grained,  and 
show  no  porosity.  Such  iron  is  named  "  mitis-iron."  An 
alloy  possessing  the  approximate  composition  AlPe4  is  very 
hard,  and  may  be  forged. 

Al:3Mn. — This  alloy  is  apparently  of  definite  composition ;  it 
forms  square-based  prisms. 


582  ALLOYS. 

Al  Ni6. — Large  shining  crystals,  also  of  definite  composition. 

Al,  Ti. — Brilliant  brown  iridescent  crystals. 

Al3Zr;  or  including  silicon  (Al3Zr)2Si. — Crystalline  laminae. 

Al,  Sn. — Aluminium  and  tin  alloy  in  all  proportions  ;  it'  the 
alloy  contains  from  7  to  19  per  cent,  of  aluminium  it  is 
ductile,  if  over  30  per  cent.,  it  is  brittle. 

Al,  Pb. — Aluminium  and  lead  do  not  alloy. 

Al3Nb  and  Al3Ta. — Crystals  with  metallic  lustre ;  hard  and 
brittle. 

A14W. — Hard  brittle  grey  ortho-rhombic  crystals. 

Al,  Cu. — "  Aluminium  bronze."  These  alloys  are  blue- white 
when  they  contain  little  copper,  and  gold-coloured  to  red 
when  the  copper  predominates.  That  with  60 — 70  per  cent, 
of  aluminium  is  brittle,  very  hard,  and  crystalline ;  with  30 
per  cent.,  soft ;  with  under  30,  it  again  becomes  hard ;  an 
alloy  with  20  per  cent,  is  so  brittle  that  it  may  be  powdered 
in  a  mortar.  Alloys  containing  from  11  to  If  per  cent,  of 
aluminium  possess  great  tenacity,  malleability,  and  ductility, 
and  may  be  easily  worked.  They  resemble  gold  in  colour. 

Tl2Sn.— White,  difficult  to  fuse.  Tl2Pb.— Soft  and  non-crys- 
talline ;  lead-coloured.  Tl4Sb. — Hard,  and  not  permanent 
in  air.  Tl,  Bi. — Greyish-red,  soft,  and  fusible.  Tl,  Cu, — 
Brass  coloured,  soft ;  may  be  cut  with  a  knife.  TLHg. — 
Of  butter-like  consistence. 

Cr,  Fe. — "  Ferro- chrome."  Produced  by  simultaneous  reduc- 
tion of  a  mixture  of  the  oxides,  e.g.,  of  a  mixture  of  chrome 
iron  ore  and  haematite.  The  alloy  resembles  iron  in  appear- 
ance. It  is  used  for  addition  to  iron,  which  it  renders  very 
hard,  and  especially  adapted  for  cutting  instruments,  as  it 
can  be  easily  tempered. 

Cr,  Mn. — Very  hard,  and  only  slowly  attacked  by  nitre-hydro- 
chloric acid. 

Mn,  Fe. — "  Ferro-manganese."  Produced  by  simultaneous 
reduction  of  oxides  of  iron  and  manganese ;  resembles  iron 
in  appearance.  It  is  used  for  addition  to  metallic  iron,  to 
which  it  communicates  valuable  properties.  An  iron  con- 
taining about  10  per  cent,  of  manganese  crystallises  in  large 
brilliant  plates,  and  is  known  as  "  spiegel  iron,"  or  "  specular 
iron."  The  presence  of  manganese  in  steel  causes  it  to  harden, 
however  slowly  it  is  cooled  ;  and  if  much  manganese  be 
present,  the  iron  loses  its  magnetic  properties.  "  Hadfield's 
manganese  steel,"  containing  from  7  to  20  per  cent,  of  man- 


ALLOYS.  583 

ganese,  is  so  hard  that  it  cannot  be  filed ;  yet  it  is  ductile, 
and  may  be  drawn  into  fine  wire.     It  is  very  tenacious. 

Fe,  Co. — A  hard,  very  compact  alloy. 

Fe,  Ni. — The  presence  of  3  to  10  per  cent,  of  nickel  in  iron 
renders  it  harder  and  more  brittle. 

Fe,  Ti. — Is  present  in  some  pig-irons. 

Fe,  Sn. — A.  very  brittle  alloy.  Six  parts  of  tin  and  one  of 
iron  forms  a  hard  white  metal.  Iron  is  "  tinned "  by 
plunging  scrupulously  clean  plates  (see  Zn,  Fe)  into 
molten  tin,  kept  liquid  under  a  layer  of  grease.  It  is  left 
for  some  time,  withdrawn,  passed  through  rollers,  and 
passed  quickly  through  a  fresh  bath  of  tin,  to  destroy  the 
crystalline  foliated  appearance  of  the  first  coating.  Where 
such  a  "moire"  effect  is  required,  it  may  be  produced  by 
brushing  the  surface  of  the  "  tin  plate  *"'  "with  weak  nitro- 
hydrochloric  acid.  Such  tinned  iron  resists  the  action  of 
moist  air  ;  but,  as  the  coating  of  tin  is  seldom  quite  perfect, 
galvanic  action  begins  after  some  time,  and  the  iron  is 
oxidised.  Hence  "  tinned  iron  "  does  not  last  so  well,  and 
is  not  so  generally  applicable  as  "  galvanised  iron."  An 
alloy  of  5  per  cent,  of  iron,  6  per  cent,  of  nickel,  and 
89  per  cent,  of  tin  is  used  under  the  name  "polychrome  " 
for  tinning  copper.  It  adheres  easily  to  iron. 

Fe,  Pb. — Iron  may  be  similarly  coated  with  lead.  Cubes  of 
the  formula  FePb2i  of  a  brass  yellow  colour,  have  be«n 
found  in  cracks  in  the  hearth  of  a  blast  furnace.  Iron  ana 
lead  alloy ;  the  product  is  very  hard  ;  and  may  be  fused  at 
a  white  heat. 

Fe,  Ta. — Very  hard ;  scratches  glass.     Not  ductile. 

Fe,  Sb. — "  Reaumur's  alloy."  Very  hard,  melting  at  a  white 
heat.  It  is  produced  by  melting  together  under  charcoal 
70  per  cent,  of  antimony  and  30  per  cent,  of  iron. 

Fe,  Mo. — Greyish-blue,  brittle,  with  granular  fracture. 
Difficult  to  fuse. 

Fe,  W. — Whitish-brown,  and  compact.  Alloys  with  more 
than  10  per  cent,  of  tungsten  do  not  fuse.  An  alloy  has, 
however,  been  prepared  with  80  per  cent,  of  tungsten.  It 
is  very  hard,  and  contains  5  per  cent,  of  carbon.  Tung- 
sten is  sometimes  added  to  steel,  in  order  to  render  it 
hard. 

Fe,  Rh.  —  These  metals  alloy  easily.  Steel,  containing  a  little 
rhodium,  is  greatly  improved  in  quality.  An  alloy  con- 
taining more  rhodium  takes  a  high  polish. 


584  ,        ALLOYS. 

Fe,  Pd. — One  per  cent,  of  palladium  in  steel  renders  it  very 

brittle. 
Fe,  Pt. — Easily  formed.     The  alloy  takes  on  a  high  polish,  and 

is  very  unalterable.      One  containing  9  parts  of  steel  to 

4  of  platinum  is  ductile  and  hard. 
Fe,  Cu. — Iron  alloys  with  copper  in  all  proportions.     An  alloy 

of  2  parts  of  copper  and  1  part  of  iron  is  of  a  greyish-red 

colour  and  very  tenacious.      The  presence  of   1  or  2  per 

cent,  of  copper  in  steel  renders  it  brittle. 
Fe,  Ag. — A  small  quantity  of  silver  in  steel  renders  it  hard. 
Fe,  All. — The  metals  alloy  easily.     An  alloy  containing  1  part 

of  iron  and  12  parts  of  gold  has  a  pale-yellow  colour,  and  is 

very  ductile.     One  containing  1  part  of  iron  to  6  of  gold  is 

known  as  "  grey  gold,"  and  is  used  by  jewellers. 
Fe,  Hg. — Mercury  and    iron   do  not  unite   directly.     But  in 

presence  of  sodium,  mercury  alloys  with  iron.    The  amalgam 
•    may  also  be  prepared  by  electrolysis  (see  Zn,  Hg).     It  is 

insoluble  in  mercury,  and  soon  splits  into  its  constituents. 

The  residue,  after  squeezing  the  excess  of  mercury  through 

chamois  leather,  is  said  to  have  the  formula  FeHg. 
Mn,  Pb. — Hard  and  ductile. 
Mn,  Sn;  Mn,  Cu;  Mn,  Ag;   Mn,  Au.— Manganese  easily 

forms    these    alloys.       They    resemble  the    corresponding 

alloys  of  iron.     That  with    copper  is  reddish-white,  and 

malleable. 
Mn,  Hg. — Produced  by  shaking  a  strong  solution  of  manganese 

dichloride  with   sodium  amalgam,  or  by  electrolysis.     It  is 

grey  and  crystalline,  and  soluble  in  mercury. 
Co,  Ni. — The  metals    alloy    easily,    forming   a  brittle  white 

metal. 
Co,  Pb. — This  alloy  is  brittle  ;  when  fused  it  separates  into 

two  layers. 

Co,  Sn. — Bluish- white,  somewhat  ductile. 
Co,  Sb. — Easily  prepared  ;  grey   and  brittle. 
Co,  Pt.— A  fusible  alloy.     Co,  Cu. — Brittle  dull-red  alloy. 
Co,  Ag. — Brittle  ;  when  fused,  separates  into  two  layers. 
Co,  Au. — An  alloy  of  I  part  of  cobalt  and  19  of  gold  is  very 

brittle,  and  has  a  deep-yellow  colour ;  even  1  part  in  130  of 

gold  renders  it  brittle. 
Co,   Hg. — Prepared  like  manganese    amalgam.       White  and 

magnetic. 
Ni,  Sn.— Hard  white    brittle   alloy.      Ni,  Pb.— Grey  brittle 

lamina).     Ni,  Bi. — Ditto. 


"ALLOYS.  585 

Ni,  Pd.— A  brilliant  alloy,  capable  of  bigh  polisli ;  very  malle- 
able. It  absorbs  70  times  its  volume  of  hydrogen. 

Ni,  Pt. — Whitish- yellow  ;  as  fusible  as  copper. 

Ni,  Cll. — An  alloy  containing  10  parts  of  copper  to  4  of 
nickel  is  silver- white.  The  alloy  containing  zinc  in  addi- 
tion is  German  silver  (see  Zn,  Ni,  Cu). 

Ni,  Ag.— A  malleable  alloy.  Ni,  An.— Hard,  .very  malleable, 
and  ductile,  yellowish-white,  and  capable  of  a  good  polish. 

Ni,  Hg. — Like  cobalt  amalgam. 

Sn,  Pb. — "  Solder,"  "  Pewter." — Alloys  of  tin  and  lead  are 
harder  than  tin.  Plumbers'  solder,  for  soldering  lead 
pipes,  &c.,  contains  66  per  cent,  of  lead  and  33  per  cent,  of 
tin;  tinsmiths'  solder  consists  of  equal  weights  of  both. 
Lead  and  tin  may  be  mixed  in  all  proportions.  Pewter, 
much  used  for  drinking  vessels,  taps,  &c.,  consists  of 
80  per  cent,  of  lead  and  20  per  cent,  of  tin.  The  tin  pro- 
tects the  lead  from  the  action  of  acid  liquors.  Pewter 
sometimes  consists  almost  entirely  of  tin,  with  a  little 
copper  to  give  it  hardness.  "  Britannia  metal "  consists 
of  equal  parts  of  brass,  tin,  antimony,  and  bismuth; 
"  Queen's  metal "  of  one  part  each  of  antimony,  lead,  and 
bismuth,  and  9  parts  of  tin. 

Sn,  Pb,  Bi. — Alloys  of  these  metals,  to  which  cadmium  is  some- 
times added,  have  very  low  melting-points,  and  are  hence 
termed  "  fusible  alloys."  The  following  is  a  list : — 


Sn 
Pb 
Bi 

Cd 


They  are  nsed  for  safety  taps,  to  prevent  excess  of  pressure  in 
boilers,  or  to  melt  and  allow  the  escape  of  water  in  case  of 
fire. 

Sn,  Sb. — A  hard  white  sonorous  alloy;  when  composed  of 
1  part  antimony  to  3  parts  of  tin,  it  is  somewhat  malleable, 
but  is  apt  to  crack. 

Sn,  Bi. — A  hard,  brittle  alloy. 

Sn3Ru. — Prepared  like  the  rhodium  alloy. 

Sn2Ru. — Produced  by  direct  union;  cubical  crystals,  re- 
sembling bismuth. 

Sn3Rh. — Brilliant  crystals  left  on  treating  tin  containing 
3  per  cent,  of  rhodium  with  hydrochloric  acid. 


Newton's. 
3 

Darcet's. 
1 

Rose's. 
207 

Wood's.  : 

2 

Lipowitz's. 
4 

5 

1 

236 

2 

8 

-     .       8 

2 

420 

7  to  8 

15 

1  to  2 

3 

p..,          .    945° 

93° 

80—90° 

66—71° 

60° 

586  ALLOYS. 

SnRh. — Brilliant  black  crystals  of  the  formula  given. 

SnPd. — Brilliant  scales,  corresponding  to  the  formula. 

Sn3Ir. — Similar  to  the  rhodium  alloy. 

SnJr. —  Cubical  crystals. 

SlljPt. — Dilute  hydrochloric  acid  on  an  alloy  of  tin  and 
platinum,  containing  not  more  than  2  per  cent,  of  the 
latter. 

Sn3Pt2. — White  brilliant  fusible  laminae,  consisting  of  small 
cubes. 

Sn,  Cu. — Bronze,  speculum  metal. — This  alloy  has  been 
known  for  ages,  and  was  produced  by  reducing  copper  and 
tin  ores  at  one  operation.  For  bells,  8  to  11  parts  of  tin 
and  100  parts  of  copper  are  employed.  With  more  than 
11  per  cent,  of  tin,  the  alloy  is  malleable  if  quickly  cooled, 
and  may  be  fused  at  a  red  heat.  A  common  alloy  consists 
of  22  parts  of  tin  and  78  parts  of  copper.  The  hardness 
of  bronze  is  greatly  increased  by  the  addition  of  a  small 
amount  of  phosphorus,  as  copper  phosphide.  Speculum 
metal  for  astronomical  mirrors  consists  of  32  per  cent,  of 
tin,  67  of  copper,  and  1  of  arsenic.  It  is  susceptible  of 
very  high  polish.  The  tin  may  be  "  liquated "  out 
of  such  alloys.  Copper  cooking  vessels  are  often  protected 
against  corrosion  by  "  tinning."  The  copper  is  cleaned 
by  scouring  with  ammonium  chloride,  or  better  with  the 
double  chloride  of  zinc  and  ammonium.  The  tin  is  then 
run  over  it,  and  the  excess  poured  out.  A  thin  coherent 
coating  covers  the  copper. 

Sn,  Ag. — Tin  alloys  in  all  proportions  with  silver,  forming 
hard  white  alloys ;  on  liquation,  however,  the  tin  is 
removed. 

Sn,  Au. — This  alloy  is  whitish-yellow  and  brittle. 

Sn,  Hg. — An  amalgam  of  1  part  of  tin  with  10  of  mercury  is 
liquid  ;  one  with  1  part  of  tin  and  3  of  mercury  crystallises 
in  cubes.  This  alloy  is  employed  in  silvering  mirrors ;  also 
for  coating  the  rubbers  of  fractional  electrical  machines. 

Pb,  Sb.—Typs-metaL— Type-metal  consists  of  lead  containing 
17  to  18  per  cent,  of  antimony.  It  is  a  dull-grey  alloy, 
much  harder  than  lead  ;  and  it.  is  rendered  still  harder  by 
addition  of  8  to  10  per  cent,  of  tin. 

Pb,  Bi.— White  brittle  lamirea. 

Pb,  W. — An  alloy  of  lead  and  tungsten  is  brown,  spongy,  and 
ductile. 

Pb,   Cu. — Lead  and  copper    do    not  alloy    easily ;    the  alloy 


ALLOYS.  587 

separates  into  two  layers  when  left  in  repose.  When 
stirred,  however,  castings  can  be  made.  They  have  a  dull 
reddish-grey  colonr,  and  are  said  to  withstand  the  action  of 
sulphuric  acid.  Two  or  three  per  cent,  of  lead  added  to 
brass  makes  it  less  fibrous  and  more  easily  worked. 
Pb,  Ag. — Most  commercial  lead  contains  silver.  When  allowed 
to  cool  slowly,  nearly  pare  lead  crystallises  out,  the  silver 
remaining  in  the  melted  portion.  By  a  systematic  procedure 
of  this  nature,  the  crystals  being  separated  from  the  still 
liquid  portion,  silver  is  separated  from  lead  (Pattinson's 
process  for  desilverising  lead).  The  alloy  is  white,  and 
harder  than  lead.  It  may  be  freed  from  lead  by  cupella- 
lation ;  that  is,  by  melting  the  alloy  in  a  cupel  or  shallow 
vessel  made  of  bone-ash  in  a  current  of  air.  The  lead  is 
oxidised,  and  the  oxide  is  absorbed  by  the  porous  cupel, 
leaving  metallic  silver. 

Pb,  All. — Lead  makes  gold  very  brittle ;  even  1  part  in  2000 
greatly  alters  its  malleability  and  ductility.  This  alloy  is 
produced  in  the  process  of  cupelling  gold. 

Pb,  Hg. — Lead  amalgam  is  easily  obtained.  From  a  strong 
solution  of  lead  in  mercury,  crystals  separate,  which  are 
said  to  possess  the  formula  Pb2Hg3. 

Sb,  Bi. — Antimony  and  bismuth  mix  in  all  proportions.  The 
alloy,  like  bismuth,  expands  on  solidification. 

Sb,  Cu. — Antimony  renders  copper  brittle;  even  0'00015  of  its 
weight  produces  the  effect.  The  alloy  of  the  formula 
SbCu2  used  to  be  known  as  "  Regulus  of  Venus,"  and  has  a 
purple  metallic  lustre.  When  melted  with  lead  and  cooled 
slowly,  the  upper  layer  has  approximately  the  formula 
SbCu4,  and  is  nearly  white,  with  vitreous  fracture. 

Sb,  Ag. — Antimony  and  silver  alloy  easily,  forming  a  similar 
alloy.  Silver  displaces  copper  from  the  copper-antimony 
alloy. 

Sb,  Au, — One  part  of  antimony  to  nine  parts  of  gold  yields  a 
brittle  white  alloy;  even  0'05  per  cent,  of  antimony 
renders  gold  brittle. 

Sb,  Hg. — Antimony  dissolves  in  boiling  mercury,  but  not  to  a 
great  extent.  Crystals  separate  on  cooling. 

Bi,  W. — A  porous  brittle  alloy,  with  dull  metallic  lustre. 

Bi,  Rh. — A  white  brittle  alloy,  completely  dissolved  by  nitric 
acid. 

Bi,  Pd, — Grey,  as  hard  as  steel. 

Bi,  Pt. — Bluish  brittle  fusible  Iamina3. 


588  ALLOYS. 

Bi,  Cu.— Pale  red  and  brittle. 

Bi,  Ag. — White,  brittle,  and  crystalline. 

Bi,  Au. — Greenish-yellow,  granular,  and  brittle ;  0'05  per 
cent,  of  bismuth  renders  gold  quite  brittle. 

Bi,  Hg. — Bismuth  easily  dissolves  in  mercury  :  a  concentrated 
solution  deposits  crystals  on  cooling. 

Mo,  Pt. — Hard,  grey,  and  brittle. 

W,  Cu. — Spongy  and  somewhat  ductile. 

W,  Ag. — Brownish- white,  somewhat  malleable. 

Rh,  Pt. — Platinum  containing  30  per  cent,  of  rhodium  is  more 
fusible  than  rhodium,  and  easily  worked. 

Rh,  Cu. — Alloy  easily;  the  alloy  is  completely  soluble  in 
nitric  acid. 

Rh,  Ag. — Very  malleable. 

Rh,  Au. — Rhodium  containing  4  or  5  per  cent,  of  gold  is  gold- 
coloured,  very  ductile,  and  difficult  of  fusion. 

Pd,  Pt. — Grey,  hard,  somewhat  ductile. 

Pd,  Cu. — The  metals  unite  with  incandescence.     An  alloy  ol 

4  parts  of  copper  to  1  of  palladium  is  white  and  ductile ; 
one  with  equal  parts  is  pale-yellow  and  susceptible  of  high 
polish.- 

Pd,  Ag. — Used  for  dentists'  enamel ;  contains  1  part  of  silver 
to  9  of  palladium.  It  is  grey  and  harder  than  iron. 

Pd,  Au. — The  metals  unite  with  incandescence.  With  the 
proportion  of  1  part  of  palladium  to  6  of  gold,  the  alloy  is 
almost  white  ;  with  1  to  4,  it  is  white,  hard,  and  ductile ; 
with  equal  parts,  bright  grey. 

Os,  Ir. — Osmiridium  :  found  native,  containing  other  metals 
of  the  platinum-group.  It  forms  white  scales,  is  exceed- 
ingly hard,  and  is  used  for  pointing  gold  pens,  for  the 
bearings  of  small  wheels,  &c. 

Os,  Cu. — Os,  Ag. — Os,  Au. — Ductile  alloys.  Os,  Hg  adheres 
to  glass. 

Ir,  Pt. — Harder  than  platinum  and  less  easily  fusible.  An 
alloy  containing  about  10  per  cent,  of  iridium  is  used  for 
crucibles,  &c. 

Ir,  Ag. — Ductile  and  white.     Ir,  Au. — Ductile  and  yellow. 

Pt,  Cu. — A  ductile  alloy,  with  the  colour  and  density  of  gold. 
It  is  used  in  ornamental  jeweller's  work  ;  the  alloy  contains 

5  per  cent,  of  copper  and  95  per  cent,  of  platinum. 

Pt,  Ag. — Less  ductile  and  harder  than  silver,  sometimes  used 

for  jewellery.     Its  colour  is  white. 
Pt,  Au. — With  2  parts  of  platinum  to  1  of  gold,  the  alloy  is 


ALLOYS.  589 

brittle ;  with  equal  parts,  gold-coloured ;  with  3  of  pla- 
tinum, grey.  Gold  is  used  for  soldering  platinum  vessels. 

Pt,  Hg. — Produced,  like  iron  amalgam,  in  presence  of  sodium. 
If  squeezed  through  leather,  the  definite  compound  PtHg2 
remains.  When  treated  with  nitric  acid,  it  gives  a  residue 
retaining  7  to  8  per  cent,  of  mercury,  which  behaves  like 
platinum-black. 

Cu,  Ag. — White  ;  if  copper  predominates,  gold- coloured.  All 
alloys  liquate,  except  one  of  the  composition  Cu2Ag3. 
The  alloys  take  a  much  higher  polish  than  pure  silver. 
This  alloy  is  extensively  used  for  coinage.  English 
"silver"  contains  7'5  per  cent,  of  copper;  its  specific 
gravity  is  10' 20.  French  money  contains  copper  and  zinc. 
Silver-copper  alloys,  if  cooled  slowly,  do  not  remain  homo- 
geneous ;  the  metals  separate  partially.  Silver  solder, 
used  for  soldering  jewellery,  contains  66  per  cent,  of  silver, 
with  copper  and  zinc. 

Cu,  Au. — This  alloy  is  used  for  coins,  watches,  jewellery,  &c., 
owing  to  its  greater  hardness  than  gold.  The  English 
standard  is  11  parts  of  gold  to  1  of  copper ;  in  France  and 
the  United  States,  9  parts  of  gold  to  1  of  copper.  The 
alloys  are  more  fusible  than  gold  itself.  Gold  solder 
consists  of  5  parts  of  gold  to  1  part  of  copper.  The  rich- 
ness of  a  gold  alloy  is  estimated  in  "  carats  ;"  24-carat  gold 
is  pure ;  23-carat  gold  contains  -^th.  of  copper. 

CUj  Hg. — Prepared  by  boiling  copper  in  mercury;  by  tritu- 
rating finely-divided  copper,  first  with  mercurous  nitrate, 
and  then  with  mercury.  When  heated,  it  exudes  drops  of 
mercury ;  and  if  then  ground  up,  it  is  so  soft  as  to  be 
moulded  by  the  fingers ;  but  it  speedily  becomes  hard.  By 
pressing  through  leather,  the  alloy  CuHg  remains. 

Ag,  Au. — Pale  greenish-yellow.  Found  native,  and  known  as 
"  electrum."  Sometimes  used  for  jewellery.  It  is  harder 
and  more  fusible  than  gold ;  that  containing  1  part  of  silver 
to  2  of  gold  is  the  hardest. 

Ag,  Hg. — By  placing  mercury  in  a  mixture  of  2  parts  of 
mercuric  nitrate  with  three  of  silver  nitrate,  a  crystalline 
growth  of  silver  amalgam  takes  place,  which  is  sometimes 
called  the  "Tree  of  Diana."  Silver  amalgamates  readily 
with  mercury  ;  the  amalgam  deprived  of  excess  of  mercury 
by  squeezing  through  leather .  has  the  formula  AgHg2. 
Silver  amalgam  is  nearly  insoluble  in  mercury. 

Au,  Hg. — Gold  amalgamates  readily.     Crystals  separate  which 


590  ALLOYS. 

are  said  to  possess  the  formula  AuHg4.     They  are  white, 
and  dissolve  sparingly  in  mercury. 

It  is  seen  that  very  few  alloys  have  definite  formulae,  and  some 
of  those  which  appear  to  be  definite  chemical  compounds  do  not 
possess  marked  metallic  lustre.  It  is  very  difficult  to  determine 
whether  or  not  an  alloy  contains  a  definite  compound  in  solution. 
In  a  mixture  of  two  or  more  metals,  that  alloy  which  possesses  the 
lowest  melting  point  has  not  a  definite  formula.  The  lowering  of 
the  melting  point  of  a  metal  appears  to  be  proportional,  at  all 
events  for  dilute  solutions,  to  the  absolute  amount  of  the  metal 
present  in  smallest  quantity,  and  inversely  proportional  to  its 
molecular  weight.  Hence,  by  determining  the  lowering  of  the 
melting  point  of  a  metal  such  as  sodium  due  to  the  addition  of 
small  amounts  of  other  metals,  the  relative  molecular  weights  of 
the  dissolved  metals  may  be  ascertained ;  and  it  appears  that, 
assuming  the  molecule  of  mercury  to  be  monatomic,  an  assumption 
which  is  justified  on  other  grounds,  the  molecular  weights  of  most 
of  the  other  metals  are  also  identical  with  their  atomic  weights. 

Alloys  are  not  electrolysed  into  their  constituents  by  the 
passage  of  an  electric  current ;  they  are  all  good  conductors  ;  but 
the  conductivity  of  those  which  conduct  best,  such  as  silver, 
copper,  and  gold,  is '  greatly  diminished  by  the  presence  of  small 
amounts  of  other  metals. 

It  has  been  already  remarked  that  one  of  the  elements  of  an 
alloy  appears  in  some  cases  to  be  present  in  an  allotropic  condition. 
It  is  noteworthy  that,  by  dissolving  out  the  zinc  from  an  alloy  of 
zinc  and  rhodium,  the  latter  metal  should  be  left  in  an  allotropic 
condition,  so  unstable,  that  on  rise  of  temperature  a  slight  ex- 
plosion takes  place,  and  the  allotropic  rhodium  returns  to  its 
usual  form.  It  appears  not  improbable  that  metallic  iron  is 
capable  of  existing  in  two  allotropic  states  :  one  soft  and  not 
capable  of  permanent  magnetisation  ;  while  the  other  form,  steel, 
is  hard,  can  be  tempered,  and  remains  magnetic  for  a  long  time 
after  magnetisation.  This  change  is  apparently  induced  by  the 
presence  of  a  small  amount  of  carbon. 

Altogether,  our  knowledge  of  the  chemical  nature  of  alloys  is 
very  scanty ;  but  the  attention  of  chemists  is  again  turning  to  this 
subject,  so  important  both  from  a  scientific  as  well  as  from  a 
practical  standpoint. 


591 


PART  VIII. 

CHAPTER  XXXIV. 

THE  RARE  EABTHS. — ENERGY  RADIATED  PROM  MATTER;  SPECTROSCOPY; 
CONNECTION  OF  THE  SPECTRA  OF  THE  ELEMENTS  WITH  ATOMIC 
WEIGHT. — APPLICATION  OF  SPECTRUM  ANALYSIS  TO  THE  ELUCIDA- 
TION OF  THE  RARE  EARTHS. — SKETCH  OF  SOLAR  AND  STELLAR 
SPECTRA. 

THE  elements  and  their  compounds  have  now  been  classified ;  and 
it  has  been  seen  that  the  arrangement  adopted,  that  of  the  periodic 
table,  has  been  fairly  justified,  inasmuch  as  elements  displaying 
similarity,  although  always  offering  a  regular  gradation  of  pro- 
perties with  increase  of  atomic  weight,  have  fallen  into  the  same 
groups. 

But  a  number  of  rare  elements,  comprising  those  contained  in 
snch  scarce  minerals  as  orthite,  euxenite,  cerite,  samarskite,  and 
gadolinite,  have  been  only  cursorily  alluded  to ;  these  elements  are, 
yttrium,  lanthanum,  ytterbium,  terbium,  didymium,  erbium, 
and  samarium ;  and  to  this  list  a  number  of  others  might  be 
added  of  even  more  doubtful  individuality,  to  which  the  names 
neodymium,  praseodymium,  decipium,  phillipiam,  holmium, 
thulium,  dysprosium,  and  gadolinium  have  been  given.  The  state 
of  our  knowledge  of  these  rare  bodies  is  such  that  it  appears 
advisable  to  consider  them  in  a  separate  chapter ;  moreover,  it  is 
the  opinion  of  Lecoq  de  Boisbaudran  and  Crookes,  two  of  the  chief 
authorities  on  such  bodies,  that  they  do  not  find  their  place  in  the 
periodic  system  of  the  elements. 

Before  they  are  described,  it  is  necessary  to  have  some  acquaint- 
ance with  the  methods  of  spectroscopy,  and  with  the  nature  of  the 
vibrations  emitted  from  matter. 

Spectrum  analysis.* — General  considerations. — It  has  already 
been  mentioned  (see  p.  92)  that  all  matter  is  in  a  state  of  mole- 
cular motion.  This  motion  is  of  two  kinds.  Gases,  which  inhabit 
space  great  in  comparison  with  the  actual  volume  of  their  con- 

*  See  Roscoe's  Spectrum  Analysis  ;  Schellen's  Spectral- Analyse,  and  the 
original  papers  to  which  reference  is  made  in  notes  to  this  chapter. 


592  SPECTRUM  ANALYSIS. 

stituent  molecules,  have  great  freedom  of  motion,  or,  as  it  is 
termed,  great  "free  path;"  the  duration  of  time  in  which  their 
molecules  are  in  a  state  of  unimpeded  motion  is  great  in  com- 
parison with  that  in  which  they  are  in  collision  with  neighbouring 
molecules,  or  with  the  sides  of  the  containing  vessel.  But  besides 
this  "  translatorj  "  motion,  or  motion  through  space,  the  molecules 
are  permanently  in  a  state  of  vibratory  motion.  The  true  nature 
of  this  vibrational  motion  is,  however,  as  yet  uncertain.  They  are 
capable  of  communicating  this  vibratory  motion  to,  and  receiving 
it  from,  a  medium  which  pervades  all  space,  termed  "  ether."  To 
discuss  the  nature  of  "  ether  "  would  lead  us  beyond  our  province  ; 
it  may,  however,  be  stated  that  no  form  of  matter  is  impermeable 
to  ether;  and  that  it  does  not  appear  to  be  comparable  in  nature  or 
properties  with  the  usual  forms  of  matter  with  which  we  are 
acquainted.  The  necessity  for  inferring  its  existence  is  obvious, 
however,  when  we  consider  that  such  vibrations  are  transferred 
across  a  vacuum,  and  that  they  spend  time  in  passing.  Light  and 
radiant  heat  are  special  kinds  of  such  vibrations;  and  it  is  known 
that  light  is  not  instantaneously  transmitted  across  empty  space, 
but  travels  at  the  rate  of  185,000  miles  per  second.  There  must 
be  something  to  convey  this  motion — something  set  into  vibration 
by,  and  communicating  its  vibration  to,  material  bodies— and  this 
medium  is  called  ether. 

The  molecules  of  a  gas,  being  far  apart,  do  not  materially  inter- 
fere with  each  other's  vibrations ;  hence  each  single  molecule 
assumes  such  rates  and  modes  of  vibration  as  are  compatible  with 
its  structure;  and  such  modes  of  vibration  are  transmitted  through 
the  ether  to  surrounding  objects,  which  in  their  turn  generally 
take  up  and  exhibit  vibrations  of  similar  rates  and  modes  to  those 
of  .the  gaseous  molecules  which  incite  them. 

Such  vibrations  are,  however,  of  varying  frequency ;  each  dif- 
ferent kind  of  vibrating  molecule  having  its  own  special  rate  or 
rates  of  vibration.  When  a  vibrating  molecule  causes  waves  in 
the  ether  which  pass  any  stationary  point  at  a  rate  greater  than 
20  million-million  per  second,  it  produces  effects  of  sensation,  of 
expansion,  &c.,  which  we  term  heat.  If  they  pass  at  a  rate  greater 
than  392  million-million  per  second,  they  affect  chemically  the 
compounds  composing  the  lining  membrane  of  the  retina  of  the 
eye,  and  we  have  then  light ;  and  it  is  possible  to  recognise  vibra- 
tion as  frequent  as  4000  million- million  per  second,  by  their  effect 
on  certain  other  compounds,  notably  the  salts  of  silver,  and  to 
vibration  of  such  wave-lengths  is  given  the  name  "  actinic."  To 
refract  such  exceedingly  rapid  vibrations,  quartz  prisms  must  be 


SPECTRUM  ANALYSIS.  593 

used,  for  they  are  absorbed  by  glass.  But  it  must  not  be  supposed 
that  there  is  any  difference  in  kind,  bat  only  in  frequency,  between 
vibrations  to  which  we  give  these  different  names. 

Oar  eyes,  then,  are  capable  of  distinguishing  as  light- 
vibrations  whose  number  lies  between  392  million-million  and 
757  million-million  per  second.  Now,  as  we  know  the  velocity 
of  light,  and  the  number  of  vibrations  per  second, 'the  length  of  a 
wave  capable  of  exciting  any  definite  vibration  is  easily  calculated  ; 
it  is,  expressed  in  millimetres,  the  velocity  of  light  in  millimetres 
per  second,  divided  by  the  number  of  waves  per  second.  Thus 
the  wave-length  of  the  slowest  visible  vibration  is  766'7  millionths 
of  a  millimetre ;  and  of  the  fastest  visible,  about  397  millionths  of 
a  millimetre.  Waves  of  ether  of  different  lengths  produce  on  us  the 
effect  of  colour.  Red  light,  for  example,  is  caused  by  waves  of 
about  686  millionths  of  a  millimetre  in  length ;  yellow  light,  by 
waves  of  589  millionths  of  a  millimetre  long ;  green,  by  waves  of 
527  millionths  of  a  millimetre  ;  and  blue,  by  waves  of  486  millionths 
of  a  millimetre ;  while  waves  of  405  millionths  of  a  millimetre 
produce  the  impression  of  violet  light.  The  result  of  the  im- 
pinging on  the  retina  of  waves  of  all  visible  wave-lengths  is  to 
produce  what  we  term  white  light.  We  can  give  no  corresponding 
names  to  waves  capable  only  of  inciting  a  rise  of  temperature,  or 
of  only  producing  chemical  action ;  they  must  be  distinguished  by 
the  number  indicating  the  particular  wave-length  referred  to. 

Such  waves  are  propagated  more  quickly  through  some  media 
than  through  others ;  they  pass  more  rapidly  through  gases,  such 
as  air,  than  through  glass,  or  quartz,  or  liquids.  If  they  fall  on 
thick  plates  with  parallel  surfaces  at  right  angles  to  that  direction 
of  their  propagation,  they  merely  undergo  retardation,  while  they 
pass  through  the  medium ;  but  if  they  fall  on  such  plates  at  any 
angle  (not  a  right  angle)  to  the  surface,  the  ray  is  bent  or  refracted 
during  its  passage  through  the  plate,  returning  to  its  original 
direction  on  issuing  from  its  other  surface.  If,  however,  they  fall 
obliquely  on  a  prism,  that  is,  a  block  of  glass  or  other  transparent 
material  of  triangular  section,  they  are  doubly  bent,  both  on  enter- 
ing and  on  issuing. 

But  white  light,  or,  to  speak  more  generally,  radiant  energy, 
consists  of  vibrations  of  all  conceivable  rates ;  and  it  is  known  that 
those  waves  whose  frequency  is  most  rapid  are  more  refracted 
during  their  passage  through  a  prism  than  waves  of  less  frequent 
vibrations ;  and  they  are  therefore  bent  through  a  more  acute 
angle,  or,  to  express  it  in  the  usual  language,  they  are  more  power- 
fully refracted  than  those  of  less  frequency.  Hence  it  happens 

2  Q 


594  SPECTRUM  ANALYSIS. 

that  white  light,  when  passed  through  a  prism,  is  sorted  oat  into 
coloured  lights  ;  violet  light  with  its  rapid  vibrations  being  more 
bent  than  red  light.  Now,  if  the  ray  of  light  passing  through  the 
prism  comes  from  a  circular  aperture,  say  in  a  window  shutter, 
and  is  homogeneous,  that  is,  consists  of  waves  of  some  definite 
frequency,  the  result  will  be  that  an  image  of  the  circular  aperture 
will  be  projected  on  a  screen  placed  to  receive  it.  If  white  light 
conies  from  a  circular  aperture,  then  a  number  of  coloured  circles 
must  appear  on  the  screen.  But  the  number  is  practically  infinite ; 
hence  these  circles  will  overlap  each  other,  except  at  the  ends  of 
the  image ;  there  the  light  will  appear  coloured,  the  outside  colour 
being  red  at  one  end,  and  violet  at  the  other  (see  Fig.  51)  ;  but  the 


FIG.  51. 

major  part  of  the  image  will  appear  white,  owing  to  the  over- 
lapping of  the  coloured  light.  To  obviate  this,  a  slit  is  used  as  the 
aperture  ;  and  an  infinite  number  of  narrow  parallelograms  are  thus 
thrown  on  the  screen.  The  finer  the  slit,  the  less  the  mixture  of 
waves  of  different  frequency  on  the  screen ;  and  though  overlapping 
cannot  entirely  be  avoided,  it  may  be  greatly  reduced.  The 
resulting  image  is  termed  a  spectrum,  and  is  shown  in  Fig.  52. 

It  has  been  stated  that  when  the  molecules  of  a  gas  are  so  hot 
as  to  emit  radiant  energy  which  can  be  observed,  the  vibrations 
which  they  perform  are  of  certain  definite  frequencies,  inasmuch 
as  they  are  seldom  interfered  with  by  collision.  It  is  otherwise 
with  a  solid,  or  with  a  liquid.  In  them  the  molecules  are  so  closely 
packed  as  to  leave  little  room  for  independent  motion — they  possess 


SPECTRUM   ANALYSIS.  595 

small  free  path.     It  therefore  happens  that  no  molecule  is  free  to 
oscillate  or  vibrate  without  interference  from  its  neighbour  mole- 


FIG.  52. 

cules  ;  hence,  while  each  molecule  tends,  no  doubt,  to  execute  vibra- 
tions of  such  frequency  and  character  as  correspond  with  its  indi- 
vidual nature,  it  is  forced  to  execute  vibrations  of  different  periods. 
Hence  (to  confine  ourselves  to  light)  an  incandescent  solid  or  liquid 
emits  light  of  all  visible  wave-frequency,  that  is,  of  every  visible 
colour.  But,  at  temperatures  at  which  they  first  become  luminous 
(about  550°),  they  emit  dark-red  light,  and  are  said  to  be  "  dull  red- 
hot."  With  rise  of  temperature,  they  emit  yellow  along  with  red 
light,  and  are  said  to  be  "  bright  red-hot;"  at  still  higher  tempera- 
tures green  and  blue  light  is  emitted,  and  they  are  then  "  white-hot ; " 
and  it  may  be  noticed  that  the  electric  arc-light  is  blue  in  colour, 
owing  to  its  intensely  high  temperature.  The  spectrum  of  most 
radiating  solids  is  a  "  continuous  "  one,  that  is,  it  is  composed  of 
light  of  ail  possible  wave-lengths.  The  solar  spectrum,  due  to  that 
immense  mass  of  incandescent  matter,  the  Sun,  is  mainly  of  this 
character,  but  it  is  crossed  by  various  dark  lines,  implying  absence 
of  waves  where  they  occur,  the  nature  of  which  will  be  afterwards 
described. 

Such  spectra  appear  to  depend  on  the  complexity,  as  well  as  on 
the  near  neighbourhood,  of  the  molecules.  It  is  probable,  from 
what  we  know  of  dissociation,  that  a  high  temperature  will  split 
complex  molecules  into  simpler  ones,  and  that  the  spectra  of  the 
simpler  molecules  will  themselves  be  simpler.  But  just  as  it  is 

2  Q  2 


596 


SPECTRUM   ANALYSIS. 


SPECTRUM    ANALYSIS. 


597 


598  SPECTRUM   ANALYSIS. 

possible  to  touch  a  stretched  wire,  like  a  piano-wire,  so  that  its 
fundamental  vibration  alone  is  audible,  or  to  cause  it  to  vibrate 
strongly,  when  unpleasing  over-tones  or  higher  notes  are  per- 
ceived, so  it  is  probable  that  a  high  temperature  may  cause  vibra- 
tions in  a  simple  molecule,  which  are  unperceived,  owing  to  their 
small  intensity,  at  lower  temperatures  ;  and  certain  spectra  become 
more  complex  when  the  gaseous  bodies  emitting  them  are  strongly 
heated. 

The  spectra  of  the  elements  lithium,  sodium,  potassium,  rubi- 
dium, caesium,  calcium,  strontium,  barium,  boron,  gallium,  thal- 
lium, and  some  others,  become  visible  when  a  compound  of  the 
metal  (preferably  the  chloride,  owing  to  its  volatility)  is  heated  in 
a  Bunsen's  flame  in  a  loop  of  platinum  wire.  The  accompanying 
woodcut*  (pp.  596  and  597)  reproduces  some  of  these  spectra  in 
black  and  white;  the  wave-lengths  in  millionths  of  a  millimetre 
are  given,  and  also  the  letters  which  are  employed  to  denote  the 
principal  lines  of  the  spectra. 

If  the  temperature  be  higher,  that  of  the  electric  spark  for 
example,  different  spectra  are  produced.  To  render  such  spectra 
visible,  one  of  the  secondary  wires  from  a  Riihmkorff's  coil  is 
connected  with  a  platinum  wire,  which  is  placed  about  O2  mm. 
above  the  surface  of  a  solution  of  the  chloride  of  the  element  to 
be  tested,  while  the  other  wire,  also  with  a  platinum  terminal,  dips 
in  the  liquid.  Sparks  pass  from  wire  to  liquid,  and  vice  versa,  and 
some  of  the  dissolved  solid  is  volatilised  and  heated  to  a  high  tem- 
perature. The  spectra  may  then  be  observed.  They  are  shown 
in  Fig.  54. 

(For  convenience  of  reference,  the  colours  corresponding  to 
certain  wave-lengths  are  given  f: — Bed,  686  yu,;  yellow,  589  ya; 
green,  527  ^t;  blue,  486  fi ;  violet,  405  /*.) 

It  is  seen  that,  while  in  some  cases  the  spectrum  is  more  com- 
plex, in  other  cases  it  is  simpler. 

Method  of  determining  atomic  weights  by  means  of 
spectra. — By  means  of  the  spark  spectra,  it  has  been  found 
possible  by  Lecoq  de  Boisbaudran  to  predict  the  atomic 
weights  of  certain  elements.};  The  method  of  calculation  will 
be  shown  for  that  of  the  recently  discovered  element  germanium. 

There  are  two  brilliant  lines  in  the  spark  spectrum  of  silicon, 
and  also  of  its  fellow  elements  germanium  and  tin  ;  and  also  in 

*  Copied  from  Spectres  lumineux,  by  M.  Leeoq  de  Boisbaudran,  Paris, 
1874. 

f  /i  denotes  one  millionth  of  a  millimetre. 
J  Chem.  News,  1886  (2),  4. 


SPECTRUM   ANALYSIS. 


599 


600 


SPECTRUM  ANALYSIS. 


SPECTKUM  ANALYSIS.  601 

those  of  aluminium,  gallium,  and  indium,  three  corresponding 
elements  belonging  to  the  previous  group  of  the  periodic  table. 
Their  wave-lengths  are  as  follows  (X  =  wave-length  in  millionths 
of  a  millimetre)  : — 

Si.  Ge.  Sn.          Al.  Ga.          In. 

Istline....      A  =  412-9      468'0      563  '0         — 
2nd  line . .       X  =  389  '0      422  '6      452  -4         —  —  — 


Mean  wave-length      401  "0      445 '3      507 '7      395 '2      410-1      430  '6 

The  atomic  weights  of  these  elements  of  which  that  constant  is 
known  are,  Si  =  28;  Ge  ? ;  Sn  =  118;  Al  =  27'5 ;  Ga  =  69'9  ; 
In  =  113'5.  Comparing  the  differences  between  the  atomic 
weights  of  the  members  of  both  series  with  those  between  the 
mean  wave-lengths  of  their  two  characteristic  rays,  the  following 
table  results : — 

Atomic  weights.  A.       Variations.  A(mean).  A.  Variations. 

Si 28     ]  401-0  40  "51 

Ge   ....         ?       ^  90  445-3  100 

Sn 118     J  507-7 

Al 27-5  ,9  A       2-8302        395-2  37 '584 

Ga 69-9      2f-2         10°  410'1  9n-*  100 

In 113-5  430-6 

Under  the  heading  "  Variations  "  is  stated  the  percentage  of 
the  first  difference  which  must  be  added  to  it  to  obtain  a  number 

2-8303  x  42-4 


equal   to  the   second   difference;    thus,  42*4 


100 


43-6 ;  and  44*3  +  40'51.^144'3  =  62'4.     The  ratio  which  follows 
1UU 

gives  a  means  of  determining  what  the  values  of  A  for  the  atomic 
weights  of  silicon  and  germanium,  and  for  germanium  and  tin, 
should  be : — 

Al-2Ga -f  In      :       Al-2Ga  +  In      ::       Si-2Ge  +  Sn.        :     Si-2Ge  +  Sn 

(A)  (at.  wt.).  (A)  (at.  wt.). 

37-584  2-8302  ::  40 '51  :  3 '051 

The  number  3'051  is  the  percentage  of  the  difference  between 
the  atomic  weights  of  silicon  and  germanium,  by  which  this  differ- 
ence must  be  increased  to  make  it  equal  to  the  difference  between 
the  atomic  weights  of  germanium  and  tin.     The  first  difference, 
therefore,  is  90/2'03051  =  44'32.     Hence  we  have  the  series- 
Si    =    28-00 
Ge  =     72-32 
Sn  =  118-00 


602  SPECTRUM  ANALYSIS. 

The  atomic  weight  subsequently  found  by  Winkler,  the  dis- 
coverer of  germanium,  was  72*3. 

It  is  thus  seen  that  there  exists  a  close  relation  between  the 
atomic  weights  of  allied  elements  and  certain  lines  of  their 
spectra.  This  subject  has,  however,  as  yet  been  very  little 
studied. 

To  render  gases  luminous  which  do  not  emit  light  at  the  tem- 
perature of  a  Bunsen's  flame,  such  as  hydrogen,  oxygen,  &c.,  a 
discharge  of  electricity  of  high  potential  is  passed  through  them 
when  rarefied  to  a  pressure  of  under  5  millimetres.  The  gases 
are  confined  in  tubes,  generally  called  "  vacuum  tubes,"  through 
which  platinum  wires,  or  sometimes  wires  of  aluminium,  are 
sealed.  These  wires  are  connected  with  the  secondary  coil  of  a 
E/iihmkorff's  induction  coil,  and  on  passing  an  alternating  cur- 
rent of  high  potential  the  gas  in  the  tube  is  raised  to  a  high 
temperature  and  emits  light.  By  directing  a  spectroscope  on 
the  narrow  capillary  portion  of  the  tube,  the  spectrum  may  be 
observed. 

Many  solid  bodies  exposed  to  an  electric  discharge  of  high 
potential  in  vacuum  tubes  also  emit  coloured  light.  Such  sub- 
stances are  said  to  "  phosphoresce,"  The  form  of  tube  em- 
ployed by  Mr.  Crookes,  the  discoverer  of  this  property,  is  shown 
in  Fig.  55.  Among  such  substances  are  pTienakite  (beryllium  sili- 


FIG.  55. 

cate),  which  emits  a  blue  glow  ;  spodumene  (lithium  aluminium 
silicate),  which  shines  with  a  rich  golden-yellow  light ;  the  ruby, 
which  exhibits  a  very  brilliant  crimson  phosphorescence ;  and  the 
diamond,  the  light  of  which  is  exceptionally  brilliant  and  of  a 
greenish-white  colour. 

The  rare  earths. — Seen  through  a  spectroscope,  such  coloured 
lights  resolve  themselves  into  bands  of  greater  or  less  brilliancy 
at  various  parts  of  the  spectrum.  The  oxides  of  the  rare 
elements  previously  mentioned  when  examined  in  vacuum  tubes 
by  an  inductive  discharge  are  particularly  rich  in  such  lines  and 
bands,  and  it  is  by  this  means  that  Crookes  has  investigated  their 
nature,  while  Lecoq  de  Boisbaudran,  Cleve,  Delafontaine, 


THE  RARE  EARTHS.  603 

Marignac,  Soret,  Nilson,  Brauner,  and  others  have,  as  a  rule, 
employed  the  spark  spectrum. 

These  elements  are  divisible  into  three  main  groaps,  the  di- 
dymium  group,  comprising  bodies  to  which  the  names  neodymium, 
praseodymium,  samarium,  and  dysprosium  have  been  given ;  the 
erbium  group,  members  of  which  have  been  named  scandium, 
ytterbium,  terbium,  erbium,  holmium,  and  thulium ;  and  the 
yttrium  group,  to  individual  members  of  which  names  have  not 
yet  been  given.* 

The  main  lines  of  separation  are  as  follows ;  but  it  should  be 
mentioned  that  many  other  processes  have  been  adopted: — The 
mineral  is  finely  powdered,  and  boiled  for  some  hours  with  hydro- 
chloric acid  (gadolinite,  thorite),  or  mixed  with  strong  sulphuric 
acid,  and  gently  heated  (cerite,  euxenite)  ;  or  fused  with  hydrogen 
sodium  sulphate;  or  treated  with  hydrofluoric  acid  (samarskite, 
&c.).  The  product  is  then  treated  with  cold  water  and  filtered, 
and  the  residue  is  again  treated  similarly.  To  this  solution 
ammonium  oxalate  is  added,  which  precipitates  the  metals  as 
oxalates.  The  precipitate  is  dissolved  in  hydrochloric  acid ;  then 
thrown  down  with  ammonia  to  remove  lime,  and  next  ignited,  thus 
leaving  a  residue  of  oxides,  usually  of  a  reddish-brown  colour. 
The  oxides  are  dissolved  by  long  boiling  with  nitric  acid;  the 
excess  of  acid  is  evaporated,  and  solid  potassium  sulphate  is  added 
until  the  solution  is  saturated.  Double  sulphates  of  members  of 
the  cerium,  lanthanum,  and  didymium  groups  with  potassium 
separate  out,  and  are  removed  by  filtration,  while  sulphates  of  the 
yttrium  group  remain  in  solution.  The  elements  of  both  groups  are 
then  precipitated  as  oxalates  ;  to  separate  cerium,  the  oxalates  are 
dissolved  in  nitric  acid  and  heated  to  incipient  decomposition,  and 
the  solution  is  poured  into  a  large  excess  of  hot  water.  Basic 
cerium  nitrate  separates  as  a  whitish-yellow  precipitate.  By  two 
or  three  repetitions  of  this  process,  cerium  may  finally  be  obtained 
free  from  lanthanum  and  didymium.  The  residues  are  submitted  to 
repeated  fractionation,  either  by  addition  of  an  amount  of  ammonia 
insufficient  to  precipitate  more  than  a  fraction  of  the  total  amount 
of  element  present ;  or  by  treating  the  mixed  oxides  with  an  amount 
of  nitric  acid  insufficient  for  complete  solution  ;  or  by  heating  the 
mixed  nitrates  cautiously,  so  as  to  produce  partial  conversion  into 
oxides,  and  treatment  with  water,  in  which  the  undecomposed 
nitrates  alone  are  soluble;  or  by  other  processes  comparable  with 

*  Brauner,  Chem.  Soc.,  41,  68 ;  also  numerous  papers  by  Cleve,  Nilson,  and 
others. 


604 


SPECTRUM  ANALYSIS. 


the  above.  It  should  be  understood  that  such  processes  must  be 
repeated  methodically  thousands  of  times  before  any  definite 
elements  are  isolated.  And  it  is  also  remarkable  that  minerals 
from  different  sources  yield  very  different  results,  nature  having 
often  performed  a  partial  separation. 

Elements  of  the  didymium  group  have  been  investigated  by 
means  of  the  absorption  spectra  seen  when  a  solution  of  one  of  the 
compounds  of  the  elements  in  water  is  examined  through  a  spectro- 
scope. The  old  "didymium  "  has  the  spectrum  shown  below  (A). 


1000 


Fm.  56  (B). 

The  absorption  spectrum  of  bodies  separated  from  didymium  by 
processes  of  fractional  crystallisation,  precipitation,  &c.,  are  shown 
at  (B).  The  thin  line  at  320,  the  line  at  400,  the  band  between 
420  and  440,  the  narrow  band  between  460  and  470,  and  lines  at 
575,  620,  715,  765,  and  845  form  together  the  spectrum  of  the 
so-called  samarium,  a  pseudo-element  separated  from  what  was  at 
one  time  believed  to  be  the  pure  element  didymium  by  Delafon- 
taine*  in  1878,  and  by  Lecoq  de  Boisbaudran.  In  1885,  Carl 

*  Ckem.  News,  38,  223 ;  40,  99.     This  description  is  largely  taken  from 
Mr.  Crookes'  address  to  the  Chemical  Society,  Chem.  Soc.,  55,  256. 


THE  RARE  EARTHS.  605 

Auer*  succeeded  in  isolating  two  new  bodies  by  fractionally 
crystallising  the  double  nitrates  of  elements  of  this  group  with 
ammonium  nitrate.  Of  these,  one  had  pink  salts,  and  he  named 
it  neodymium ;  the  other  green,  and  to  it  he  gave  the  name  praseo- 
dymium. The  absorption  spectrum  of  the  former  includes  the 
lines  at  187,  207,  the  three  faint  lines  at  250,  the  broad  band  at 
300,  the  thin  line  at  355,  the  band  at  365,  and  the  two  bands  about 
385 ;  while  the  exceedingly  fine  line  at  549  is  strengthened  to  a 
distinct  band.  The  latter  has  the  other  part  of  the  thick  band  at 
287,  one  at  430,  the  band  at  455,  and  the  thick  band  between  497 
and  515.  There  are  still  two  bands  unclaimed,  viz.,  those  at  462 
and  475,  which  might  lead  to  the  supposition  that  a  third  substance 
is  present  which  has  not  been  identified.  But  Mr.  Crookes  states 
that  by  other  methods  of  fractionation  he  has  obtained  evidence 
of  other  cleavages;  for  it  must  be  noticed  that  treatment  with 
any  one  reagent  will  effect  a  separation  into  only  two  groups ;  and 
that  the  particular  results  obtained  by  Auer  depend  on  the  nature 
of  the  process  which  he  adopted.  Kriiss  and  Nilsonf  believe  the 
old  didymium  to  contain  at  least  nine  separate  components.  But 
it  is  dangerous  to  draw  any  definite  conclusion  from  such  results ; 
for  Brauner  has  shownj  that  on  mixing  a  dilute  solution  of  a  salt 
of  samarium  with  one  of  didymium,  the  three  bands  at  430 — 460 
disappear,  while  samarium  bands  do  not  take  their  place  until  a 
large  proportion  of  a  salt  of  the  latter  has  been  added. 

In  an  exactly  similar  manner,  the  original  "  erbium  "  has  been 
resolved  into  fractions  giving  absorption  spectra  corresponding  in 
part  with  that  of  their  parent  earth.  The  investigations  of 
Delafontaine,  Marignac,  Soret,  Nilson,  Cleve,  Brauner,  and  others, 
have  pointed  towards  at  least  six  different  earths,  three,  scandia, 
ytterbia,  and  terbia,  having  no  absorption  spectrum,  while  others, 
viz.,  the  new  erbia,  holmia,  and  thulia  give  absorption  spectra.  The 
earth  called  philltpia  has  been  proved  by  Roscoe  to  be  a  mixture 
of  yttria  and  terbia. 

Elements  of  the  yttrium  group  do  not  give  absorption  spectra ; 
hence  they  have  been  investigated  by  Lecoq  de  Boisbaudran 
chiefly  by  spark  spectra,  and  by  Crookes,  by  means  of  phosphor- 
escence spectra.  The  old  "yttrium,"  by  a  system  of  fractionation 
repeated  many  thousand  times,  has  been  separated  into  a  number 
of  portions.  The  spectra  of  the  extreme  ends  of  the  fractions 
differ  from  that  of  the  original  yttrium  by  showing  new  bands, 

*  MonatsJi.  Chem.,  6,  477. 
t  Berichte,  20,  2134. 
j  Chem.  Soc.,  43,  286. 


606  SPECTRUM  ANALYSIS. 

and  by  the  disappearance  of  some  of  the  old  ones.  And  a  gradual 
transition  may  be  noticed  from  fraction  to  fraction,  the  new  band 
appearing  dimly,  and  gaining  strength  as  the  separation  proceeds ; 
or  the  old  band  becoming  fainter,  finally  to  vanish.  The  spectra 
of  the  fraction  to  which  the  names  "samarium,"  "yttrium  a," 
"  mosandrium,"  and  "yttrium"  have  been  given  are  shown  in 
Fig.  56  (B),  as  well  as  the  result  of  continuing  the  fractionation  to 
the  other  side,  and  separating  these  substances  as  far  as  practicable. 
It  is  right  to  observe,  however,  that  de  Boisbaudran  does  not  agree 
with  Crookes  in  such  conclusions;  he  maintains  that  there  are 
three  perfectly  characterised  earths,  to  which  the  provisional  symbols 
Za,  Z/3,  and  27  have  been  given,  which  Crookes  has  not  succeeded 
in  separating.  He  regards  it  as  probable  also  that  the  oxide  of  Z/3 
is  identical  with  a  deep-brown  oxide  obtained  from  the  so-called 
terbium.  Crookes  has  also  found  that  the  addition  of  foreign 
elements,  for  instance,  lime  or  alumina,  has  a  profound  influence 
in  modifying  such  phosphorescence  spectra. 

We  see  therefore  that  there  is  great  reason  to  believe  that  such 
substances  are  mixtures.  Crookes  has  revived  the  bold  specula- 
tion of  Marignac,  that  not  all  the  molecules  of  any  given  element 
are  uniform  in  mass  or  other  properties,  and  that  what  we  name 
an  element  is  simply  the  mean  result  of  a  number  of  atoms  or 
molecules,  closely  approximating  to  each  other  in  properties,  but 
not  identical ;  and  he  suggests  that,  provided  suitable  methods, 
such  as  the  various  plans  of  fractionation,  be  made  use  of,  it  may 
be  possible  to  effect  a  separation  of  more  or  less  complete  nature. 
Whether  this  view  is  a  correct  one,  or  whether  the  rare  elements 
of  which  he  treats  are  merely  mixtures  of  some  eight  or  ten  new 
bodies,  which,  owing  to  their  similar  behaviour,  are  very  difficult 
to  separate,  must  be  left  to  the  future  to  determine.  He  suggests, 
indeed,  that  there  may  be  different  degrees  of  elemental  rank.  But 
the  fact  that  the  presence  of  one  element  tends  to  modify,  and 
sometimes  to  thoroughly  alter,  the  spectrum  of  another  should  lead 
to  great  caution  in  accepting  the  help  of  spectroscopy  in  identi- 
fying elements. 

It  may  here  be  mentioned  that  Brauner  has  succeeded  in 
obtaining  elements  from  tellurium,  or  at  least  from  what  usually 
passes  under  that  name.  Further  research  will  doubtless  throw 
light  on  the  question  of  its  elementary  nature. 

Solar  and  stellar  spectra. — One  other  application  of  spec- 
troscopy remains  to  be  mentioned.  It  has  led  to  the  identification 
of  many  elements  existing  in  the  sun,  the  fixed  stars,  nebulae,  and 
comets  with  those  existing  on  our  earth.  The  principle  underlying 


SPECTRUM  ANALYSIS.  607 

this  discovery  is  as  follows : — Matter  not  only  radiates  energy,  it 
also  absorbs  energy.  We  see  a  wall  coloured  because  the  paint 
with  which  it  is  covered  absorbs  vibrations  of  certain  wave-lengths 
from  the  white  light  which  illumines  it,  while  reflecting  vibrations 
of  other  wave-lengths. 

A  gaseous  molecule  can  be  made  to  oscillate  by  the  impinge- 
ment of  ether  waves  of  the  same  period  of  oscillation,  and 
not,  as  a  rale,  by  waves  of  a  different  period ;  and  if  ether  vibra- 
tions of  some  definite  periods  impinge  on  a  large  number  of 
molecules  all  capable  of  vibrating,  to  the  same  period,  then  it  will 
cause  them  to  vibrate.  But  it  may  be  that  the  intensity,  that  is, 
the  amplitude,  of  the  vibration  of  the  ether  is  not  sufficient  to 
cause  so  many  molecules  themselves  to  vibrate  with  an  amplitude 
great  enough  to  be  perceived  by  our  senses ;  the  ether  vibrations 
are  then  practically  extinguished,  because  they  distribute  their 
energy  through  such  a  large  number  of  molecules. 

Now  the  light  given  out  by  an  incandescent  gas  is,  as  we  have 
seen,  generally  composed  of  waves  of  a  few  definite  lengths.  And 
if  its  waves,  propagated  through  the  ether,  be  caused  to  impinge 
on  a  quantity  of  the  same  gas,  the  molecules  of  that  gas  will  be  set 
in  vibratory  motion;  but  that  motion,  being  distributed  over  a 
large  number  of  molecules,  will  be  so  weakened  in  amplitude  as 
not  to  be  perceptible.  To  confine  ourselves  to  light :  if  the  yellow 
light  emitted  from  incandescent  sodium  gas  be  caused  to  impinge 
on  a  sufficient  quantity  of  sodium  gas,  which  is  not  at  so  high  a 
temperature  as  to  incandesce,  it  will  be  completely  absorbed,  and 
the  sodium  light  will  not  pass  through  the  sodium  gas;  or,  more 
correctly  speaking,  the  vibrations  of  the  second  portion  of  gas  will 
be  too  small  in  amplitude  to  affect  our  eyes. 

The  sun  is  a  vast  mass  of  incandescent  matter,  sending  forth 
energy  of  all  conceivable  wave-lengths.  Among  these  vibrations 
are  some  which  coincide  in  period  with  those  given  out  by  incan- 
descent sodium.  But  the  sun  is  surrounded  by  an  atmosphere  of 
sodium  gas  ;  hence  these  vibrations  will  not  be  transmitted  through 
the  sodium  vapours  to  the  ether  with  amplitude  sufficient  to  be 
perceived.  It  is  for  this  reason  that  we  see  in  the  solar  spectrum 
a  dark  line,  or  more  correctly,  two  dark  lines  very  near  together, 
in  the  yellow  part  of  the  spectrum.  This  doable  line  is  named 
"  the  D  line,"  and  its  position  is  absolutely  identical  with  that  of 
the  bright  line  visible  when  the  light  of  incandescent  sodium  gas 
is  viewed  through  a  spectroscope.  It  is  therefore  legitimate  to 
conclude  that  the  phenomenon  which  can  be  produced  on  a  small 
scale  is  identical  with  that  occurring  in  the  sun  and  its  atmosphere  ; 


608  SPECTRUM  ANALYSIS. 

and  it  follows  that  the  sun  is  surrounded  by  an  atmosphere  con- 
sisting partly  of  gaseous  sodium. 

By  similar  means,  by  comparing  the  dark  lines  seen  in  the  solar 
spectrum  and  in  the  spectrum  of  the  fixed  stars  with  the  bright 
lines  produced  by  incandescent  gases,  it  has  been  discovered  that 
many  of  our  elements  are  present  in  these  heavenly  bodies.  The 
following  is  a  list  of  those  which  have  been  identified  in  the  sun ; 
with  the  number  of  lines  which  have  been  observed  coinciding 
with  the  ordinary  spectra  : — 

Element H.   Na.    K.   Ca.   Sr.   Ba.   Mg.   Zn.  Cd.   Al.   Or.  Fe.    Mn.   Co. 

Lines 4       2      2      75      4      11       4       22       2      18    450   57      19 

Element..      Ni.  Ti.   Ce..Pb.  V.  Mo.  U.  Pd. 
Lines  ....      33   118    2     3     4      8      2      5 

There  are  also  present,  lithium,  iridium,  and  copper. 

The  following  are  doubtful : — In,  Bb,  Cs,  Bi,  Sn,  Ag,  Be,  La, 
Y,  C,  Si,  Th,  and  the  halogens,  F,  Cl,  Br,  and  I  are  absent. 

Oxygen  has  been  lately  observed ;  but  it  gives  bright  bands,  and 
not  absorption  lines. 

Prominences  are  continually  observed  on  the  disc  of  the  sun. 
These  appear  to  be  enormous  outbursts  of  the  gaseous  atmo- 
sphere ;  they  have  been  examined,  and  appear  to  consist  of 
hydrogen,  and  of  the  vapours  of  magnesium  and  iron,  besides 
other  elements. 

The  moon  reflects  the  solar  spectrum  without  alteration, 
adding  nothing  and  absorbing  nothing.  This  affords  an  argument 
for  the  non-existence  of  a  lunar  atmosphere,  borne  out  by  other 
considerations. 

The  fixed  stars  may  be  divided  into  four  classes  :  — 

(I.)  White  stars,  such  as  Sirius ;  they  have  been  found  to  con- 
tain hydrogen,  sodium,  magnesium,  and  iron. 

(2.)  Yellowish  stars,  such  as  Arcturus  ;  they  possess  a  complex 
spectrum  like  the  sun,  and  no  doubt  our  sun  belongs  to 
this  class. 

(3.)  lied  stars,  like  a-Orionis  and  a-Herculis  ;  these  show  sets 
of  bands  resembling  those  caused  by  the  solar  spots.  It 
has  been  suggested  that  they  are  surrounded  with  a  thick 
atmosphere. 

(4.)  Stars  usually  of  small  magnitude,  such  as  fy-Cassiopeiae. 
They  show  lines  of  hydrogen  and  of  sodium. 

Nebulae  and  comets  show  a  faint  continuous  spectrum,  together 
with  certain  lines  which  are  identical  with  those  of  certain  hydro- 


fi   UNIVERSITY    1 

V  OF  J 

SPECTRUM  ANALYSIS.    >£dU F O R NA£=^D 0 9 

carbons  when  exposed  to  an  electric  discharge  under  low  pressure 
in  vacuum  tubes. 

It  is  probable  that  some  of  them,  at  least,  consist  of  incan- 
descent solid  matter,  accompanied  by  a  gaseous  hydrocarbon. 

This  short  sketch  will  suffice  to  give  an  idea  of  the  manner  in 
which  we  have  acquired  a  knowledge  of  the  chemical  composition 
of  the  heavenly  bodies.  A  large  number  of  facts  has  been  accu- 
mulated, but  it  cannot  be  doubted  that  improved  methods,  and  the 
extension  of  observations  to  the  invisible  parts  of  the  spectrum 
TV  ill  greatly  add  to  our  conceptions  of  the  nature  of  the  galaxy  of 
suns  with  which  we  are  surrounded. 

The  nature  of  the  vibrations  which  are  transmitted  to  us 
through  the  ether  is  not  as  yet  understood,  and  the  sciences  of 
chemistry  and  spectroscopy  touch  at  only  a  few  points  as  yet ; 
but  it  is  evident  that  further  research  will  greatly  increase  our 
knowledge  of  the  atomic  and  molecular  constitution  of  matter. 
Already  it  has  afforded  a  means  in  the  hands  of  Bunsen  and 
Kirchhoff,  of  Crookes,  of  Lecoq  de  Boisbaudran,  and  of  Reich 
and  Richter,  of  detecting  the  presence  of  undiscovered  elements 
in  minerals  and  in  waste  products ;  the  spectrum  lines  have  been 
shown  to  be  in  close  relationship  with  the  atomic  weights  of  the 
elements ;  and  some  success  has  been  met  with  in  applying  spec- 
troscopy to  quantitative  analysis.  These  are  great  achievements  ; 
but  there  are  undoubtedly  greater  to  follow. 


2  R 


610 


CHAPTEE  XXXV. 

THE  ATOMIC  AND  MOLECULAR  WEIGHTS  OF  ELEMENTS  AND  COMPOUNDS. — 
THE  KINETIC  THEORY  OF  GASES. — THE  STANDARD  OF  MOLECULAR 
WEIGHTS. — THE  VAPOUR-DENSITY  OF  ELEMENTS  AND  COMPOUNDS. — 
DISSOCIATION  OF  MOLECULES  OF  ELEMENTS  AND  COMPOUNDS. — 

ATOMIC    AND    MOLECULAR    HEATS. REPLACEMENT. — ISOMORPHISM. — 

MOLECULAR    COMPLEXITY. MONATOMIO    STATE    OF    MERCURY   GAS. 

IN  stating  the  objects  of  the  science  of  chemistry,  in  the  first 
pages  of  this  book,  the  composition,  nature,  synthesis,  and  classi- 
fication of  different  kinds  of  matter  were  first  noticed;  for  it  is 
obviously  necessary  that  they  should  be  known  in  order  that  the 
further  objects  of  the  science,  viz.,  the  nature  of  the  changes  which 
matter  undergoes,  and  the  classification  of  these  changes,  may  be 
understood.  To  discuss  the  nature  of  such  changes  from  a  physical 
point  of  view  is  not  within  our  province  here  ;  but  if  has  been  seen 
that,  in  order  to  obtain  a  connected  view  of  the  relations  between 
various  classes  of  compounds,  certain  conceptions  must  be  enter- 
tained regarding  the  ultimate  nature  and  the  constitution  of 
matter.  These  conceptions  depend  on  the  behaviour  of  gaseous 
matter  when  exposed  to  different  conditions  of  pressure,  temper- 
ature, &c.,  and,  for  the  most  part,  our  classification  is  one  strictly 
applicable  only  to  gases.  To  assign  formulae  to  liquids  and  solids, 
as  has  been  frequently  remarked,  is  usually  an  extension,  not 
warranted  by  our  knowledge,  of  the  principles  which  represent 
our  conceptions  only  of  gaseous  matter. 

It  is  therefore  advisable  to  consider  in  detail  four  classes  of 
constants,  all  of  which  are  indispensable  to  correct  classification ; 
these  are : — 

1.  The  atomic  weights  of  the  elements; 

2.  The  molecular  weights  of  the  elements  ; 

3.  The  molecular  weights  of  compounds ;  and 

4.  The  structure  of  compounds. 


DENSITY  OF  GASES.  611 

The  atomic  and  molecular  weights  of  elements  and  the 
molecular  weights  of  compounds. — (a.)  Density  in  the  state 
of  gas. — It  has  been  told  in  Chapter  II  what  led  Dalton  to  assign 
certain  atomic  weights  to  the  elements  which  he  investigated. 
Having  ascertained  the  equivalents  of  certain  elements,  he  was 
gnided  by  the  principle  of  "  simplicity  "  and  "  similarity  ;"  that  is, 
the  atomic  weight  of  an  element  was  taken  to  be  that  multiple  of 
its  equivalent  which  gives  the  simplest  proportions  between  the 
numbers  of  atoms  contained  in  all  known  compounds  of  the  element ; 
and  like  compounds  were  assigned  like  formula}.  This  scheme  was 
also  followed  oat  by  Berzelius.  We  have  seen  again  in  Chapter  VIII, 
p.  109,  how  the  atomic  weights  of  elements  may  be  deduced  from 
the  densities  of  their  gaseous  compounds  ;  the  history  of  the 
discovery  is  as  follows  : — In  1805,  Gay-Lussac  and  Humboldt,  in 
investigating  the  volume  composition  of  water,  found  that  two 
volumes  of  hydrogen  unite  with  one  volume  of  oxygen  to  form  two 
volumes  of  water-gas  (see  p.  193).  This  led  Gay-Lussac  to  make 
further  researches  on  the  relative  volumes  in  which  gases  combine, 
and  he  discovered  that  two  volumes  of  nitrous  oxide  consist  of  one 
volume  of  oxygen  and  two  volumes  of  nitrogen  ;  that  one  volume  of 
chlorine  unites  with  one  volume  of  hydrogen  to  form  two  volumes 
of  hydrogen  chloride;  that  two  volumes  of  ammonia  consist  of  three 
volumes  of  hydrogen  and  one  of  nitrogen ;  and  that  one  volume  of 
carbon  monoxide  unites  with  one  volume  of  chlorine  to  form  two 
volumes  of  carbonyl  chloride,  or,  as  it  was  then  termed,  "  phosgene 
gas."  Towards  the  end  of  1808  he  made  the  important  generali- 
sation in  the  Memoires  de  la  Societe  d'Arpueil,  2,  207,  that — (1) 
"  there  is  a  simple  relation  between  the  volumes  of  gases 
which  combine  j "  and  (2)  "  a  similar  simple  relation  exists 
between  the  volumes  of  the  combining  gases  and  that  of  the 
resulting  gaseous  compound."  And  from  these  statements  it 
follows :— "  The  weights  of  equal  volumes  of  both  simple  and 
compound  gases  (or  in  other  words,  their  densities),  are  either 
proportional  to  their  combining  weights,  or  are  a  simple 
multiple  thereof." 

As  a  sequel  to  Gay-Lussac's  discovery,  Avogadro  announced 
in  1811  (Journal  de  Physique,  73,  58)  that  equal  volumes  of  gases 
contain  equal  numbers  of  particles  (molecules  int  eg  r  antes),  but  that 
these  are  not  of  the  nature  of  atoms,  indivisible,  but  consist  of 
several  atoms.  Otherwise  stated,  the  molecular  weights  are  pro- 
portional to  the  densities.  The  relation  between  the  relative 
masses  and  rates  of  motion  of  gases  has  been  since  worked  out  by 
Clerk  Maxwell,  Sir  William  Thomson,  Clausius,  and  others, 

2  E  2 


612  STANDARD   OF  MOLECULAR  WEIGHTS. 

and  starting  with  the  assumption  that  the  expansive  tendency 
of  gases  is  due  to  the  motion  of  their  molecules,  they  deduced 
the  kinetic  theory  of  gases,  for  an  account  of  which  the  reader  is 
referred  to  Maxwell's  Theory  of  Heat,  pp.  289,  et  seq.,  or  to  the 
article  on  "  Heat  "  in  Watt's  Dictionary  of  Chemistry,  3,  p.  131. 

By  means  of  a  mechanical  conception,  viz.,  that  the  pressure  of 
a  gas  is  due  to  the  impacts  of  its  molecules  on  the  walls  of  the 
containing  vessel ;  and  that  its  temperature  is  due  to  the  motion  of 
its  molecules ;  it  is  shown  that  Avogadro's  law  is  true,  viz.,  that 
the  number  of  molecules  in  equal  volumes  of  all  gases  is  equal, 
provided  the  gases  be  compared  under  similar  conditions  of  tem- 
perature and  pressure. 

Standard  of  molecular  weights. — We  know  by  experiment 
the  relative  weights  of  many  molecules.  We  know  that  the 
relative  densities  of  hydrogen  and  chlorine  are  as  1  :  3§'4;  that 
is,  the  molecule  of  chlorine  is  35*4  times  as  heavy  as  the  molecule 
of  hydrogen.  But  still  the  question  is  not  answered,  what  are  their 
relative  atomic  weights  ?  In  other  words,  how  many  atoms  are 
contained  in  a  molecule  of  hydrogen  and  in  a  molecule  of  chlorine  ? 
We  have  seen  on  pp.  158,  159,  and  160  that  if  hydrogen  chloride 
consist  of  1  atom  of  hydrogen  in  combination  with  1  atom  of 
chlorine,  it  is  a  reasonable  deduction  that  a  molecule  of  hydrogen 
contains  also  2  atoms  of  hydrogen,  and  a  molecule  of  chlorine 
2  atoms  of  chlorine,  although  the  possibility  is  not  excluded  that 
it  may  consist  of  more  than  2,  This  leads  us  to  consider  the 
densities  of  gaseous  elements  in  so  far  as  these  have  been  de- 
termined, so  that  we  may  ascertain  whether  they  correspond 
with  hydrogen  and  with  chlorine  in  the  complexity  of  their  mole- 
cules. 

Density  of  Elements  in  the  Gaseous  State. 

Hydrogen. ...  1  (unit  of  density). 

Sodium 12*7*  (Victor  Meyer's  method,  in  platinum  vessel). 

Potassium. . . .      18'8*  (  „  „  „  ). 

Zinc 34-15  at  1400°.f 

Cadmium 57'01  at  1040°,{ 

Mercury 10O94  at  446°  ;§  101'3  at  about  1730°. || 


*  Scott,  Proc.  Hoy.  Soc.  Ed.,  14. 

f  Mensching  and  Meyer,  Berichte,  19,  3295. 

£  Deville  and  Troost,  Annales,  113,  46. 

§  Dumas,  Annales,  33,  337. 

||  Biltz  and  Meyer,  Zeitschr.fiir  Phys.  Chem.,  4,  265. 


MOLECULAR  WEIGHTS  OF   GASEOUS  ELEMENTS.  61& 

Thallium  ....    206-2  at  1730°:* 

Nitrogen   ....      14'08  at  atmospheric  temperature- ;f  not  altered  at  highest 

temperatures. 
Phosphorus  . .      63'96  at  313°  £  55'7  at  800—900°;  53'65  at  1200—1300°  j 

52-45  at  1500°;  46'59  at  1680°;  45'58  at  1708.  § 

Arsenic 154'2  at  644°  and  860P ;  ||  79'5  above  1700°.^ 

Antimony. .  . .    155'5  at  1572° ;  141'5  at  1640°. If 

Bismuth 146'5  at  1640°.f 

Oxygen 15*99  at  atmospheric  temperature;**  not  altered  at  the 

highest  temperature. 
Sulphur 114-9  at  468°  ;ff  94'8  at  about  500°  ;JJ  39'1  at  714—743° ; 

34-7  at  800—900°;     31'8  at   1100— 1160°  ;ff  31'8  at 

1719°.f 

Selenium  ....    lll'O  at  860°;  92'2  at  1040°;  82'2  at  8420°.  §§ 
Tellurium  . . .    130'2  at  1390— 1439°. §§ 

Fluorine 18*3  at  atmospheric  temperature.  ||  || 

Chlorine 35'90  at  20°  ;<ft[  35*45  at  200° ;  35'31  at  630°  ;***  31'83  at 

800°;  27-06  at  1000°;  24'02  at  1200°;  23'3  at  1560°. 
Bromine 80  -16fth    82  "77  at  102  "6°;   81 '03  at  175 '6;   79 '93  at 

2281H;  52'7atl500°.§§§ 
Iodine 127-66   at  253°;    127'37  at  580°;   98'4  at  840°;    82.5  at 

1000°;||||||  63-7  at  1500°  under  low  pressure.im 

The  list  given  above  does  not  include  all  determinations ;  but 
the  more  important  researches  are  referred  to  in  the  notes. 

These   results   lead   to    a    division   of   the    elements  into  two 
groups: — (1)  Those  which  undergo  no  .change  in  density  on 


*  Biltz  and  Meyer,  Zeitschr.  jur  Phys.  Chem.,  4,  265. 
f  Eegnault,  corrected  by  Jolly,  Wied.  Ann.,  6,  536. 
"I  Dumas,  Annales,  49,  210. 

§  Meyer  and  Biltz,  Zeitschr.  phys.  Chem.,  4^  259. 
|!  Mitscherlich  ;  and  Deville  and  Troost. 
f  Meyer  and  Biltz,  loc.  cit.,  263. 
**  Regnault,  corrected  by  Jolly,  loc.  cit. 

ft  Bineau.     See   also   Biltz,    Zeitschr.  phys.    Chem.,   2,    920,  and   3,   228; 
Ramsay,  ibid.,  3,  67. 

J J  Dumas,  Annalex,  50,  178 ;  Mitscherlich,  Fogg.  Ann.,  29,  217. 
§§  Deville  and  Troost,  Annales,  58,  273. 
IJII  Moissan,  Compt.  rend.,  1889,  Dec.  2nd. 
11F  Ludwig,  Berichte,  1,  232. 

***  Meyer,  Berichte,  12,  1428   (the  chlorine  was  produced  from  platinous 
chloride,  and  was  nascent;  it  mixed  at  once  with  nitrogen), 
tft  Mitscherlich.' 

Ill  Jahn,  Monatsh.  Chem.,  1882,  176. 
§§§  Meyer  and  Ziiblin,  Berichte,  13,  405  (from  PtBr4). 
IIIHI  Meyer,  Berichte,  13,  394. 

Crafts  and  Meier,  Compt.  rend.,  92,  39. 


614  MOLECULAK  WEIGHTS   OF   COMPOUNDS. 

rise  of  temperature ;  that  is,  those  of  which  the  co-efficient  of 
expansion  remains  equal  to  that  of  hydrogen.  Such  are  mercury, 
nitrogen,  oxygen;  and,  although  experiments  in  this  direction 
have  not  been  made,  probably  sodium,  potassium,  zinc,  cadmium, 
thallium,  and  tellurium  (?).  (2)  Those  of  which  the  vapour 
density  decreases  with  rise  of  temperature ;  among  these  ^are 
phosphorus,  arsenic,  antimony,  bismuth  (?),  sulphur,  selenium, 
fluorine  (?),  chlorine,  bromine,  and  iodine. 

Now,  we  can  calculate  the  maximum  atomic  weights  of  many 
of  these  elements  from  the  vapour  densities  of  their  volatile 
compounds,  generally  of  their  halides,  or  of  their  hydrides.  An 

example  of  each  will  be  given. 

Constituents. 
Parts  by  weight  of 

Compound.  Density  x  2.  Mol.  wt.  f * N 

Water 9  "0          18-00  H  =      1  '00    O    =    16  -CO 

Sodium  '(forms  no  sufficiently  volatile  compound). 

Potassium  iodide 168  '9        165  -99  Z  =    39  -14    I     =  126  -85 

Zinc  chloride 133 '4         136'22  Zn  =     65  "3       C12  =     70'92 

Cadmium  bromide. 267  '1         272  "00  Cd  =  112  -1       Br  =  159  •  90 

Mercuric  chloride 283 '0         271' '12  Hg=200'2       C12  =    70'92 

Thallium  monochloride. .      236  "7         239  "66  Tl  =  204 "2       Cl  =     35  -46 

Ammonia 17  "2  17'03  N=     14'03     H3  =       3 '00 

Phosphine 33 '1  34-03  P    =     31  -03     H3  =       3 'GO 

Arsine.... 77  "8          78'09  As  =     75'09     HJ  =      3'00 

Antimony  trichloride  ...     :224'7         226 '68  Sb  =  120  '30     C13=  lOfi'38 

Bismuth  trichloride 327 '7         314 '48  Bi-208'JO     C13=  106 '38 

Nitric  oxide 30 -0  30 '03  O    =     1000      N=     14'03 

Hydrogen  sulphide 34 '4  34 '06  S     =     3206     H2  -       2 "00 

Selenium  dioxide 116'0      /"ill '00  Se  =     7i) '0       O5  =     32'00 

Methyl  fluoride 34'76    '     34*00  F    =    19 -0     CH.3=     15  '00 

Hydrogen  chloride 36 '0  36 '46  01=     3.Y-46     II  =       1 '00 

Mercuric  bromide 351 '0         360'1  Br2=159'9       Hg=  200'2 

Hydrogen  iodide 128 '0         127 '85  I     =12685     11=       1 -00 

From  these  examples,  it  will  be  seen  that  the  smallest  weight  of 
element  which  enters  into  the  molecule  -of  one  of  the  above- 
mentioned  compounds,  and  which  therefore  is  the  maximum  atomic 
weight,  is  as  follows  (in  whole  numbers)  : — 

H.    Na.       K.    Zn.    Cd.     Hg.     TL     K     P.    As.    Sb.      Bi.     O.     S.     Se 
1     23(?)     39    65     112    200    206     14    31     79     120    208     16     32     79 

T«J.      F.       Cl.      Br.       I. 
125      19      35-5      79      126 

while  the  vapour  densities  are  sometimes  equal  to  these  numbers, 
as  in  the  case  of  hydrogen,  nitrogen,  and  oxygen  (thallium  and 
fluorine)  at  all  temperatures ;  sometimes  equal  at  low  temperatures, 


MOLECULAR  WEIGHTS   OF  ELEMENTS.  615 

and  half  at  high  temperatures,  as  is  the  case  with  chlorine, 
bromine,  and  iodine  ;  sometimes  half  at  all  available  temperatures, 
as  with  sodium,  potassium,  zinc,  cadmium,  and  mercury;  some- 
times twice  as  great  at  low  temperatures,  and  becoming  equal 
with  rise  of  temperature,  as  with  phosphorus,  arsenic,  and 
antimony ;  and  sometimes  a  greater  multiple  than  twice,  as  with 
sulphur. 

It  is  necessary  to  postulate  the  inviolable  nature  of  Avogadro's 
law  that  equal  volumes  of  gases,  under  similar  conditions  of 
temperature  and  pressure,  contain  the  same  number  of  molecules, 
and  the  above  apparently  capricious  data  become  clear.  To  take 
an  example  from  each  class  : — 

1.  The  atomic  weight  of  hydrogen,  is  accepted  as  unity.     The 
molecular  weight  of    hydrogen,   equal   to  2,  is  the  standard    of 
molecular  weight ;  and   2  grams  of  hydrogen  inhabit,^  at  0°  and 
760  mm.  pressure,  22'32  litres.      The  same  volume   is  inhabited 
by  28  grams  of  nitrogen  under  similar  conditions  of  temperature 
and  pressure.     The  molecular  weight  of  nitrogen  is  therefore  28, 
and  28  is  twice  14,  the  atomic  weight.     Hence  the  molecule  of 
free  nitrogen  contains  2  atoms,  and  its  molecular  formula  is  N2. 
It  appears  to  be  unaltered  by  rise  of   temperature.      The  same 
reasoning  holds  with  oxygen,  and  also  with  thallium  and  fluorine, 
and  with  chlorine,  bromine,  and  iodine  at  low  temperatures,  also 
with  arsenic  at  1700°,  with  sulphur  above  1100°,  with  selenium 
at  1420°,  and  with  tellurium  at  1439°. 

2.  Considering  mercury  as   an  instance  of  the  second  class,  we 
find  that  200    grams  of   its  vapour  inhabit   the  same   space   as 
2  grams  of  hydrogen  under  similar  conditions  of  temperature  and 
pressure.     But  from  the  density  of  its  chloride,  283  (as  nearly 
271     as    can    be     expected   from    the    experimental    error),    an 
atom  of  mercury  is  seen  to  be  at  most  200  times  as  heavy  as 
an  atom  of  hydrogen,  for,  on  subtracting  (2  X  35'4)  from  271,  the 
remainder,  200,  represents  the  maximum  atomic  weight  of  mercury. 
But  if  the  molecule  of  mercury  were  represented  by  the  formula 
Hg2,  it  should  weigh  400  times  as  much  as  an  atom  of  hydrogen, 
or  200  times  as  much  as  a  molecule.    But  it  weighs  only  100  times 
as   much    as   an   equal    volume  of   hydrogen.      Hence,  we   must 
conclude  either  that  the  formula  of  mercuric  chloride  should  be 
written  Hg2Cl2,  mercury  having  the  atomic  weight  100,  or  that 
the  molecule  of  mercury  consists  of  1  atom,  inhabiting  the  same 
space   as  a  molecule  of    hydrogen,   which   consists   of   2    atoms. 
We  shall  see  that  the  specific  heat  of  mercury  confirms  the  latter 
view.     So  with  zinc,  cadmium,  sodium,  and  potassium. 


616  MOLECULAR   WEIGHTS   OF  ELEMENTS. 

3.  The  justice  of  this  view  is  borne  out  bj  the  behaviour  of 
the  elements  chlorine,  bromine,  and  iodine  at  high  temperatures. 
With  rise   of  temperature  the   density  diminishes  progressively, 
until  with  iodine  at  1500°  the  density  is  63' 7,  that  is,  equal  to  half 
the  atomic  weight   of   iodine,  as    deduced   from  the  formula   of 
hydrogen   iodide.      The  molecules  of   these    elements  appear   to 
consist   of  2  atoms   within  a  wide  range    of  temperature ;    but, 
finally,  they  gradually  dissociate  into  monatomic  molecules  ;  and 
the  gradual  decrease  of  density  is  caused  by  the  gradual  transition 
from  diatomic  to  monatomic  molecules.      Bismuth,  from  the  one 
observation  available,  appears  to  be  undergoing  this  transition  ; 
but  not  to  have  reached  the  final  monatomic  stage. 

4.  Lastly,  phosphorus  at  313°  is  64  times  as  heavy  as  hydro- 
gen ;  its  molecules  are  therefore  128  times  as  heavy  as  an  equal 
number  of  atoms  of  hydrogen.       But  its  maximum  atomic  weight, 
from  the  density  of  phosphirie,  PH3,  is  31  ;    hence  we  must  con- 
clude that  its  molecules  are  tetratomic.     With  rise  of  temperature 
they  tend  to  become  diatomic  ;  but,  even  at  the  very  high  tempera- 
ture 1708°,  the  vapour  contains  many  tetratomic  molecules.      The 
molecules  of  arsenic,  tetratomic  up  to  860°,  become  diatomic  at 
1700°  ;  and  those  of  antimony  have  not  become  wholly  diatomic  at 
1640°.     The  molecular  weight  of  sulphur  is  especially  anomalous, 
as  shown  by  its  vapour-density.      At  464°,  it  has  been  found  by 
Biltz  as  high  as  230,  implying  a  molecular  formula  of  about  S8 ;  it 
decreases  in    density  without  a  halt  til]    at   1100°  its  molecular 
formula   is    S2;    but   above  that  temperature,  up   to    1719°,    no 
further  change  occurs.     We  may,  therefore,  conclude  that  at  high 
temperatures  its  vapour-density  shows   its   molecular    complexity 
to  be  S2 ;  leaving  undecided  the  precise  molecular  complexity  at 
low  temperatures.     With  selenium  and  tellurium  there  is  evidence 
of  similar  change,  but  over  a  much  smaller  range  of  temperature  ; 
these  substances  become  gaseous  at  temperatures  so  high  that  the 
more  complex  molecules  are  already  decomposed.. 

In  the  last  two  classes,  we  have  phenomena  similar  to  those 
observed  during  the  dissociation  of  a  compound  ;  but,  for  example, 
while  phosphorus  pentachloride,  PC15,  dissociates  into  unlike 
molecules,  viz.,  PC13  and  C12,  iodine,  I2,  dissociates  into  like 
molecules,  viz.,  I  and  I.  There  is  no  reason  to  suggest  different 
causes  for  these  similar  phenomena  ;  and  we  are,  therefore, 
justified  in  regarding  the  vapours  of  elements,  with  the  few  excep- 
tions of  sodium,  potassium,  zinc,  cadmium,  and  mercury,  as  con- 
sisting of  complex  molecular  groups,  which  become  more  simple  as 


SPECIFIC   HEATS   OF  ELEMENTS*  617 

temperature  rises.  It  is  indeed  possible,  knowing  the  complexity 
of  two  molecular  states,  to  calculate  the  proportion  of  dissociated 
and  undissociated  molecular  groups  by  means  of  the  formula 


where  p  represents  the  number  of  molecules  decomposed  per  100 
undecomposed  molecules  originally  present,  d,  the  theoretical 
density  of  the  undecomposed  substance  ;  and  D,  the  found  density 
of  the  partially  dissociated  gas.  The  rate  of  increase  of  dissocia- 
tion with  rise  of  temperature  and  fall  of  pressure  may  thus  be 
followed.  Bat  the  end  result  alone  concerns  us  here. 

(6.)  Specific  heats  of  elements  and  compounds.—  A  deter- 
mination of  the  specific  heats  of  elements  furnishes  an  arbitrary 
law,  discovered  by  Dulong  and  Petit*  in  1819,  which  has  been 
already  explained  on  p.  126,  viz.,  that  "the  atoms  of  all  ele- 
ments in  the  solid  state  have  equal  capacity  for  heat  ;"  the 
specific  heats  of  elements  are  therefore  inversely  proportional  to 
their  atomic  weights,  and,  as  the  theoretical  specific  heat  of  solid 
hydrogen  is  apparently  6'0,  compared  with  water  as  unity  (see  pp. 
128  and  576),  the  approximate  atomic  weights  of  the  elements  may 
be  ascertained  by  dividing  that  number  by  the  found  specific  heat. 

Attention  has  already  been  drawn  to  the  exceptions  to  this  law 
in  the  case  of  beryllium,  boron,  carbon,  and  silicon  (see  p.  155), 
and  to  the  fact  that  at  high  temperatures  their  atomic  heats 
approximate  to  those  of  other  elements  at  lower  temperatures  ;  but 
it  is  not  so  well  known  that  many  other  elements  show  similar,  if 
not  so  great,  deviations.  The  following  table  shows  the  specific 
heats  of  some  elements  at  50°  and  at  3000.f 

Specific  heat  Specific  heat 


Element. 
Cadmium.  ..... 

at  50°. 
0  0551 

Atomic  heat. 
6-18 

at  300°. 
0  -0617 

Atomic  heat.  J 
6-92 

Zinc  

0  '0929 

6  08 

0-1040 

6-81 

Iron    ....... 

0-1113 

6'23 

0-1376 

7'71 

Silver            .  . 

0-0556 

6'00 

0-0609 

6-57 

0-0932 

5-90 

0  -0985 

6-24 

Nickel  

0  -1090 

6'43 

0-1327 

7-83 

Antimony  
Lead  

0-0495 
0-0304 

5-95 
6-29 

0-0537 
0  -0338 

6-46 
7-00 

Aluminium  .... 

0  -2164 

5-87 

0-2401 

6-51 

*  Annales,  10,  395. 

f  Gazzetta,  18,  13  ;  also  Chem.  Soc.,  54,  1237. 

t  The  atomic  heat  is  the  product  of  specific  heat  into  atomic  weight,  i.e., 
the  heat  in  calories  required  to  raise  the  temperature  of  the  atomic  weight  of 
an  element  taken  in  grams  through  1°. 


618  SPECIFIC  HEA.TS   OF   COMPOUNDS. 

The  increase  is  very  remarkable,  amounting  in  the  case  of  iron 
to  nearly  25  per  cent,  of  its  amount  at  50° ;  and  it  is  also  to  be 
noticed  that  it  is  not  of  equal  rate  for  all  the  elements  investigated. 
It  must  be  remembered  that  the  specific  heat  of  solids,  as  we  deter- 
mine it,  is  the  sum  of  very  different  actions ;  first,  the  temperature 
of  the  body  is  increased ;  second,  internal  work,  due  to  the  separa- 
tion of  molecules  and  increasing  their  rate  of  motion,  is  done  ;  and, 
third,  external  work,  due  to  the  expansion  of  the  body,  forms  a 
portion  of  that  for  which  heat  is  expended.  The  last,  however,  is 
so  small  that  it  may  be  neglected.  We  cannot,  therefore,  attempt 
to  explain  the  true  nature  of  the  specific  heat  of  solids,  and  we  must 
therefore  accept  Dulong  and  Petit's  law  as  an  empirical  statement 
of  facts,  which  has,  however,  proved  of  great  service  to  chemical 
theory. 

In  1831,  Neumann  extended  Dulong  and  Petit's  law  to  com- 
pounds. His  statement  is* : — "  The  specific  heats  of  similar  com- 
pounds is  inversely  as  their  molecular  weights :"  or,  otherwise 
expressed,  "  the  molecules  of  similar  compounds  have  equal 
capacities  for  heat."  As  examples,  the  following  instances  may 
be  quoted : — 

Molecular  Calculated 

Compound.        weight.  Specific  heat.  Product,  specific  heat. 

CaCO3 100-08                 0-2044  20'46  0*2057 

MgCO3 94-30                0-2161  20 '38  0  "2211 

ZnCO3 125-3                  0 '1712  21'45  0'1669 

BaS04 233-0  0-1068  24 -88  0'1061 

CaSO4 136-14  0  '1854  25  '24  0  '1804 

SrSO4 183-5  0-130  23 '85  0'1346 

MgO  .........       40-3  0-276  11-12  0270 

HgO 216-2  0  -049  10  -59  0  '051 

ZnO 81-3  0-132  10  "73  0'138 

HgS 232-3  0-052  12'08  0'052 

PbS 239-0  0  -053  12  -67  0  -051 

ZnS 97-36  0 '112  10-90  0-125 

Neumann's  extension  of  Dulong  and  Petit's  law  was  confirmed 
by  Regnault,  in  1840;  and  Kopp,  in  1864, t  made  numerous 
determinations  of  the  specific  heats  of  compounds,  which  led  to 
the  conclusion  that  the  atomic  heat  of  chlorine  in  its  compounds 
varies  from  6'1  in  some  double  chlorides  to  6'4  in  chlorides  such 

*  Fogg.  Ann.,  23,  1. 

f  Annalen,  Suppl.,  3,  1  and  289. 


REPLACEMENT.  619 

as  MCI;  of  bromine,  from  6'5  to  6'9 ;  of  iodine  from  6'5  to  6'7. 
In  the  case  of  compounds  containing  oxygen,  however,  the  specific 
heat  of  oxygen,  deduced  by  subtracting  the  known  specific  heat  of 
the  element  in  the  compound  from  the  molecular  heat  of  the  com- 
pound, is  in  general  about  4;  similarly  combined,  hydrogen  has 
the  approximate  specific  heat  2*3  ;  carbon,  1'8  ;  boron,  2' 7 ;  silicon, 
3'8 ;  and  phosphorus  and  sulphur,  each  5'4. 

If  it  is  required  to  calculate  the  molecular  heat  of  such  a  com- 
pound as  ferric  oxide,  Fe203,  we  have — 

Atomic  heat  of  iron,  6'16 ;  mean  atomic  heat  of  oxygen,  4'0 ; 

hence  (6-16  x  2)  +  (4  x  3)  =  24'32;  found,  25'1  (Kopp). 

It  must  be  noticed  here  that  a  determination  of  the  specific 
heat  of  a  compound  throws  no  light  on  its  molecular  weight.  For 
the  molecular  heat  is  the  product  of  specific  heat  and  molecular 
weight,  and  this  product  evidently  depends  on  the  particular 
molecular  weight  chosen.  Thus  in  the  above  example  the  mole- 
cular weight  has  been  assumed  to  correspond  to  the  formula  Fe2O3; 
had  we  assumed  the  formula  as  Fe406,  which  may  be  true,  the 
molecular  heat  would  have  been  doubled. 

By  means  of  these  laws,  the  atomic  weights  of  elements  can  be 
deduced  with  great  probability.  First,  analysis  of  a  compound 
furnishes  the  equivalent  of  the  element;  second,  the  vapour 
density  of  a  compound  of  the  element  reveals  the  maximum  number 
for  its  atomic  weight;  third,  the  specific  heat  of  the  element  shows 
whether  its  true  atomic  weight  is  this  maximum  number,  or  some 
fraction  thereof. 

(c.)  Replacement. — The  law  of  replacement  is  also  adduced 
as  a  means  of  determining  formulae,  and,  taken  in  conjunction  with 
the  methods  previously  described,  it  often  furnishes  a  valuable  aid. 
It  may  be  best  understood  by  a  concrete  instance.  It  is  argued 
that  ethane,  C2H6,  contains  six  atoms  of  hydrogen,  because  it  is 
possible  to  replace  them  by  sixths  by  chlorine ;  the  series  of  com- 
pounds, C2H6,  C2H5C1,  C3H4C13,  C2H3C13,  C2H2C14,  C2HC15,  and 
C2C16,  is  known.  Selenium  tetrachloride  is  regarded  as  containing 
four  atoms  of  chlorine,  because  they  are  replaceable  by  fourths ; 
the  series  SeClBr3,  SeCl3Br,  and  SeBr4  being  known.  It  is  by  this 
means  that  the  basicity  of  acids  is  usually  ascertained ;  thus  sul- 
phuric acid,  H2S04,  is  generally  taken  as  dibasic,  because  its 
hydrogen  may  be  easily  replaced  by  halves  ;  but  here  the  existence 
of  such  sulphates  as  H3ftra(S04)2  and  NaK3(S04)2  would  lead  to 
the  inference  that  the  molecule  of  sulphuric  acid  is  expressible  by 
the  more  complex  formula  H4S208,  while  the  definite  crystalline 


620  ISOMORPHISM. 


compounds,  H2K4(S04)3  and  ISTaK^SOOs,  would  cause  us  to  regard 
the  molecule  of  sulphuric  acid  as  H6S3Oi2.  It  must  be  remembered 
that  the  molecular  weight  of  gaseous  sulphuric  acid  is  unknown, 
and  that  to  deduce  its  molecular  complexity  from  the  apparently 
analogous  compound,  S02C12,  which  has  undoubtedly  that  formula 
in  the  gaseous  state,  is  not  permissible. 

(d.)  Isomorphism.—  The  law  of  isomorphism  also  furnishes 
data  whereby  atomic  weights  may  sometimes  be  deduced.  As 
stated  by  Mitscherlich,  its  discoverer,  in  1818,  it  is,  "  substances 
of  similar  chemical  constitution  possess  similar  crystalline 
form."*  This  statement  is  by  no  means  reversible  ;  it  is  not 
true  that  similar  crystalline  form  implies  similar  chemical  con- 
stitution. But  if  two  bodies  form  "  mixed  crystals  ;  "  that  is,  if  a 
mixture  of  solutions  of  two  compounds  deposits  crystals  contain- 
ing both  compounds  in  indeterminate  amount,  of  similar  crystal- 
line form  to  that  which  either  salt  assumes  when  pure,  they  may 
be  taken  to  possess  similar  constitution.  The  following  is  a  list 
of  elements  which,  as  a  rule,  replace  each  other  in  such  a  manner, 
and  which  are  therefore  said  to  form  isomorphous  compounds. 

I.  F,  Cl,  Br,  I  ;  Mn  (in  permanganates)  . 

II.  S,  Se  ;  Te  (in  tellurides)  ;  Or,  Mn,  Fe  (in  chromates,   manganates, 
and  ferrates)  ;  As  and  Sb  in  arsenides  and  antimonides  of  the  for- 
mula ME2. 
III.  As,  Sb,  Bi;  Te  (as  element)  ;  P,  Y  (in  salts);    N,  P  in  ammonium 

and  phosphonium  compounds. 
IT.  Li,  Na,  K,  Eb,  Cs  ;  Tl,  Ag. 
Y.  Sr,  Ba,  Pb,  Cu;  Mg,  Zn,  Fe,  Mn;  Ni,  Co,  Cu;  Ce,  La,  Di,  Er,  and  Y 

with  Ca;  Cu,  Hg  with  Pb  ;  Be,  Cd,  In  with  Zn;  Tl  with  Pb. 
VI.  Al,  Or,  Mn,  Fe;  Ce,  U  in  sesquioxides. 
VII.  Cu,  Ag  in  cuprous  and  argentous  oxides  ;  Au. 
VIII.  Eh,  Eu,  Pd,  Os,  Ir,  Pt;  Fe,  Ni,  Au;  Sn,  Te. 
IX.  C,  Si.Ti,  Zr,  Sn,  Th;  Ti,  Fe. 
X.  Nb,  Ta. 
XI.  Cr,  Mo,  W. 

Those  elements  separated  from  the  others  by  a  semicolon  dis- 
play only  partial  isomorphism. 

As  an  application  of  isomorphism  to  the  determination  of  an 
atomic  weight,  the  case  of  gallium  may  be  cited.  Before  this 
constant  had  been  determined  by  the  vapour  density  of  its  chlor- 
ide, or  by  the  specific  heat  of  the  element,  f  it  was  found  that  the 
69  parts  by  weight  of  gallium  replaced  27  parts  by  weight  of 

*  Annales,  14,  172,  and  19,  350. 

f  Lecoq  de  Boisbaudran,  Compt.  rend.,  83,  824;  Berthelot,  ibid.,  86,  786. 


MOLECULAR  COMPLEXITY. 


621 


aluminium,  in  a  gallium  alum,  crystallising  in  the  usual  form  of 
alums,  the  octahedron,  with  twelve  molecules  of  water.  Its 
equivalent  had  been  found  from  the  analysis  of  its  chloride  to  be 
23,  approximately.  Knowing  that  the  atomic  weight  of  alu- 
minium is  three  times  its  equivalent,  the  conclusion  was  drawn  that 
gallium  also  is  a  triad  element  in  such  compounds,  and  that  its 
atomic  weight  is  23  x  3  =  69. 

Further  reference  to  this  principle  will  be  made  in  treating  of 
the  periodic  arrangement  of  the  elements. 

(e.)  The  method  devised  by  Lecoq  de  Boisbaudran,  and  de- 
scribed in  the  previous  chapter,  should  not  be  omitted  in  stating  the 
methods  of  determining  atomic  weights. 

(/.)  Lastly,  the  atomic  weight  may  be  deduced  from  the  posi- 
tion of  the  element  in  the  periodic  table,  allocated  to  it  by  a 
consideration  of  the  nature  of  its  compounds.  This  is  discussed 
on  p.  639. 

The  complexity  of  the  molecules  of  those  substances  which  can- 
not be  obtained  in  the  gaseous  state  has  been  fully  considered  by 
Henry.*  He  discusses  the  chlorides  and  oxides,  but  the  argu- 
ments which  he  deduces  in  favour  of  molecular  complexity  would 
apply  to  other  compounds. 

Let  us  contrast  first  the  volatility  of  chlorides  and  oxides; 
some  instances  are  given  in  the  following  table  : — 


Volatile  oxides. 

^on-volatile  oxides. 

Compound. 
JO  O       .... 

Mol.  wt. 
32 
87 
64 
119 
80 
135 
44 
99 
154 
182 
237 
153-5 
208-5 
342 
395 

Boiling- 
points. 
-186° 
+      6° 
-     8° 
-1-   82° 
+   46° 
+  77° 
-  79° 
+      8° 
-I-   76° 
+  118° 
+  182° 
+  110° 
+  148°t 
+  227° 
+  346° 

Compoun 
fB203     . 

IBGV  . 
rsio2.  . 

\SiCl4.   . 
TTi02    . 

lTici4  . 

Nb205  . 
NbCl5  . 
Cr203.. 
CrUl3  . 
As406  . 
AsCls.. 
Sb4O6  . 
SbCl3.  . 

I.     Mol.  wt. 
»x70 
117 
nx60 
.        170 
nx82 
192 
.     n  x  174 
271-5 
.      n  x  153 
159 
396 
181-5 
564 
228  -5 

Boiling- 
points. 

17° 
59° 
135° 
240-5° 

volatile 
200° 
134° 
1500° 
225° 

1  OC1,  .  . 

r  SO,   

\SOC12  

rso,  . 

tso2ci2.... 

{COo 

COC12  

CCL  . 

rc2ci4o.... 

IC2C16  
JPC130  
1  PCL   . 

JWC14O  ... 
IWCle  

*  Phil.  Mag.,  Aug.,  1885. 

t  Decomposes  inta  PC13  +  C13. 


622  MOLECULAR   COMPLEXITY. 

Such  a  table  might  be  greatly  extended ;  but  it  suffices  to  show 
that  while  the  oxides  in  the  first  column  have  invariably  lower 
boiling-points  than  the  corresponding  chlorides,  those  in  the 
second  column  are,  as  a  rule,  non-volatile,  while  the  chlorides  are 
volatile  and  have  simple  molecular  formulae,  as  shown  by  their 
vapour-densities.  Now  it  is  noticeable  that  the  volatility  of  a 
halide  depends  on  the  atomic  weight  of  the  halogen  it  contains. 
The  chlorides  volatilise  at  lower  temperatures  than  the  bromides, 
and  the  bromides  at  a  lower  temperature  than  the  iodides.  It 
may  therefore  be  expected  that  the  oxides,  containing  the  still  more 
volatile  element  oxygen,  should  have  lower  volatili  sing-points 
than  the  chlorides.  That  this  is  the  case,  when  the  substance 
exists  in  a  simple  molecular  state,  is  proved  by  the  first  column. 
The  high  volatilising-points  of  the  oxides  of  arsenic  and  antimony, 
the  molecular  weights  of  which  are  known  to  correspond  to  the 
formulae  As4O6  and  Sb406,  shows  that  they  are  connected  with 
increased  molecular  complexity.  It  is  a  fair  inference,  there- 
fore, that  the  non- volatility  of  many  of  the  oxides  is  due  to  their 
complex  molecules.  Examples  of  the  same  kind  may  be  found  in 
great  number  among  the  compounds  of  carbon. 

The  progessive  nature  of  the  dehydration  of  hydrated  oxides 
points  to  the  same  conclusion.  Thus  boracic  acid — 

Dried  at  ordinary  temperature,  has  the  formula. .  H3B03 ; 

Dried  at  100°, V, H2B204; 

Dried  at  160°, H2B407 ; 

Dried  at  270°, H2B16O25. 

It  appears  to  be  a  legitimate  conclusion  that  the  anhydrous  oxide 
is  (B203)»,  where  n  is  a  high  number. 

Similar  arguments  may  be  adduced  from  the  density  of  the 
oxides  compared  with  that  of  the  chlorides. 

It  is  also  noticeable  that  one  oxide  forms  double  compounds  with 
others  ;  and  it  is  a  fair  inference  to  draw  that,  in  default  of  a 
different  oxide,  it  combines  with  itself. 

The  fluorides  occupy  an  abnornal  position  as  regards  the 
chlorides  ;  here  also  their  volatility  is  as  a  rule  not  so  great ;  and 
they  form  more  numerous  and  more  stable  double  compounds  than 
the  chlorides  do.  It  may  therefore  be  equally  well  inferred  that 
the  molecular  weights  of  the  fluorides  of  most  elements  are  not  re- 
presented by  the  simple  formulae  which  it  is  customary  to  ascribe 
to  them. 

It  would  follow  from  these  arguments  that  the  molecular  weight 
of  liquid  water  is  not  represented  by  the  simple  formula  H20,  for 


MOLECULAR  COMPLEXITY.  623 

it  boils  at  a  higher  temperature  than  hydrogen  sulphide  ;  a  change 
in  the  molecular  complexity  has  not  been  observed  in  steam  at  a 
low  temperature ;  but  such  a  change  undoubtedly  takes  place  with 
hydrogen  fluoride  before  the  liquid  state  is  reached  (see  p.  115). 

Although  we  may  therefore  assume  the  complexity  of  most 
of  the  oxides,  no  method  has  yet  been  devised  whereby  the  pre- 
cise value  of  the  molecular  weight  may  in  all  cases  be  determined. 

The  operation  of  solution  appears  in  many  instances  to  exercise 
a  dissociating  action  on  molecular  aggregates.  It  has  been 
proved  experimentally,  by  Raoult,*  that  the  depression  of  the 
freezing-point  of  a  solvent,  produced  by  the  presence  of 
dissolved  substance,  is  approximately  inversely  propor- 
tional to  the  molecular  weight  of  the  latter,  and  directly 
proportional  to  its  absolute  weight.  Raoult's  experimental 
proof  has  been  substantiated  by  a  theory  of  the  nature  of  matter  in 
solution,  devised  by  Van't  Hoff,f  depending  on  certain  thermo- 
dynamical  relations  which  cannot  be  explained  here.  Hence  a 
measurement  of  the  depression  of  the  freezing-point  of  a  solution 
containing  a  known  percentage  of  dissolved  substance  may  be 
made  to  yield  data  regarding  its  molecular  weight.  The  method 
has  been  applied  with  great  success  to  the  determination  of  the 
molecular  weights  of  carbon  compounds,  dissolved  in  liquids  which 
are  also  compounds  of  carbon  ;  but  data  derived  from  the  lowering 
of  the  freezing-point  of  water,  due  to  the  presence  of  a  dissolved 
salt,  point  to  the  dissociation  of  the  salt  into  the  ions  of  which 
it  is  composed,  that  is,  the  products  which  are  obtained  from  it 
under  the  influence  of  an  electric  current. 

The  method  of  application  is  as  follows: — The  observed  lower- 
ing of  freezing-point  of  100  grams  of  water  or  other  solvent, 
caused  by  the  presence  of  P  per  cent,  of  a  dissolved  compound,  is 
termed  C  ;  Raoult  terms  the  ratio  C/P  the  co-efficient  of  lowering  of 
freezing-point  for  the  dissolved  compound.  If  M  be  the  molecular 
weight  of  the  compound,  the  ratio  MC/P,  or  the  lowering  of  freezing- 
point  per  molecule  of  the  dissolved  substance,  is  constant  for  com- 
pounds of  similar  nature.  The  value  of  this  number  for  com- 
pounds which  do  not  dissociate,  or,  what  corresponds  therewith, 
which  do  not  conduct  electrolytically,  is  19,  water  being  the  solvent 
in  each  case. 

Until  this  method  has  been  more  carefully  investigated,  it  is 
premature  to  give  an  extended  statement  oi  results ;  it  may,  how- 
ever, be  mentioned  that  Paterno  and  NasiniJ  have  thereby  deter  - 

*  Annales  (6),  8,  317.  t  PM.  Mag.,  August,  1888. 

J  Berichte,  21,  2153. 


624  MOLECULAR   COMPLEXITY. 

mined  the  molecular  weights  of  sulphur,  phosphorus,  bromine,  and 
iodine.  For  sulphur  dissolved  in  benzene,  the  freezing-point  of 
benzene  was  found  to  be  depressed  about  O26°  for  each  part  per 
cent,  of  dissolved  sulphur.  The  theoretical  molecular  depression 
of  its  freezing-point,  calculated  by  Van't  Hoff  on  theoretical 
grounds,  is  53;  now  0'26  x  192  =  50;  but  192  =  6  X  32  ;  and 
it  would  follow  that  the  molecule  of  sulphur  dissolved  in  benzene 
has  the  formula  S6,  a  probable  conclusion  from  its  vapour-density 
(see  p.  614).  Similar  experiments  with  bromine  dissolved  in 
water  and  in  acetic  acid  led  to  the  formula  Br2 ;  for  iodine,  I2 
mixed  with  I ;  and  for  phosphorus,  P2  mixed  with  P4. 

The  depression  in  the  vapour-pressure  of  a  liquid  produced  by 
the  presence  of  dissolved  substances  was  also  found  by  Raoult  to 
be  approximately  inversely  proportional  to  the  molecular  weight  of 
the  latter ;  and  Van't  Hoff  has  also  shown  that  thermodynamical 
considerations  lead  to  a  similar  conclusion  (loc.  cit.).  This  method 
has  not  been  so  widely  applied  as  that  depending  on  the  lowering 
of  freezing-point ;  but  by  its  help  Loeb*  has  determined  the  mole- 
cular weight  of  iodine  dissolved  in  ether  and  in  carbon  disulphide; 
his  conclusion  is  that  the  brown  solution  in  ether  contains  mostly 
molecules  of  I4,  while  the  violet  solution  in  carbon  disulphide 
contains  a  large  proportion  of  I2  molecules.  This  conclusion,  it 
will  be  observed,  does  not  agree  with  that  of  Paterno  and  Nasini. 
Ramsay  has  also  applied  this  method  to  determine  the  molecular 
weights  of  some  metals,  the  solvent  being  mercury ;  and  the  evi- 
dence is  in  favour  of  a  monatomic  molecular  state.f  Experiments 
by  Heycock  and  Neville  on  the  depression  of  the  freezing-point  of 
tin  and  of  sodium  used  as  solvents  for  metals  appear  to  point  to  a 
similar  conclusion. J  From  the  vapour- densities  of  these  metals, 
which  have  been  volatilised,  the  conclusion  would  seem  to  be 
justified.  But  our  knowledge  is  as  yet  too  immature  to  allow  of 
positive  conclusions. 

The  monatomic  nature  of  mercury  gas. — Before  dismissing 
the  subject  of  molecular  weights,  very  valuable  experiments  of 
Kundt  and  Warburg§  must  be  mentioned,  which  lend  great  sup- 
port to  the  view  that  the  molecules  of  mercury  consist  of  single 
atoms ;  and,  consequently,  that  molecules  of  hydrogen,  nitrogen, 
oxygen,  chlorine,  &c.,  consist  each  of  two  atoms.  The  argument  is 
as  follows  : — Assuming  that  the  pressure  of  a  gas  on  the  walls  of 

*  CJtem.  Soc.,  53,  405. 

t  Ibid.,  55,  251. 

J  Ibid.,  55,  666. 

§  Pogg.  Ann.,  127,  497 ;  135,  337  and  527. 


MOLECULAK  COMPLEXITY.  625 

the  vessel  containing  it  is  due  to  the  impacts  of  its  molecules  on 
the  walls  ;  and  that  the  effect  of  a  rise  of  temperature  of  a  gas  is 
to  increase  the  number  of  impacts  in  unit  of  time,  and  hence 
its  pressure,  it  is  possible  to  calculate  the  increase  of  kinetic 
energy  given  to  a  gas  by  raising  its  temperature  through  1°. 
The  amount  of  heat  required  to  raise  through  1°  the  molecular 
weight  expressed  in  grams  of  any  gas  has  been  calculated  to  be 
3'00  calories,  provided  the  gas  be  not  allowed  to  expand  ;  if  it  be 
allowed  to  expand,  it  must  overcome  the  pressure  of  the-  air ;  or  if  it 
be  supposed  to  be  confined  in  a  vertical  cylinder  with  a  piston  it  must 
lift  a  column  of  air  through  some  height ;  and,  in  order  that  it  may 
be  able  to  accomplish  this  work,  more  heat  must  be  communicated 
to  it  than  that  which  produces  merely  a  rise  of  temperature.  This 
may  be  shown  to  amount  to  2'00  calories  more  per  gram  molecule 
of  the  gas.  The  first  of  these  quantities  of  heat,  3*00  calories, 
represents  the  molecular  heat  of  the  gas  at  constant  volume ;  the 
second,  5'00  calories,  the  molecular  heat  at  constant  pressure. 
The  ratio  between  these  numbers  is  1  :  1*66.  The  actual  specific 
heat  of  mercury  vapour  has  not  been  determined ;  but  it  has 
been  found  by  Kundt  and  Warburg  that  this  ratio  actually 
exists  between  the  specific  heat  of  mercury  vapour  at  constant 
volume  and  at  constant  pressure.  But  with  oxygen,  hydrogen, 
nitrogen,  carbon  monoxide,  nitric  oxide,  and  other  gases, 
the  molecules  of  which  are  presumably  diatomic,  the  molecular 
heat  at  constant  volume  is  for  02,  4'96  ;  for  H2,  4'82  ;  for  N2,  4'82  ; 
for  CO,  4'86 ;  for  NO,  4'95  ;  instead  of  3'00,  the  calculated  mole- 
cular heat.  The  specific  heat  at  constant  pressure  is  found  by 
adding  2'00  calories  to  each  of  these  numbers;  thus  02,  6*96;  H2, 
6'82;  N2,  6-82;  CO,  6'8b' ;  NO,  6'95.  The  ratio  between  these 
numbers  is  as  1  :  1'41  approximately.  Why  does  a  gas  such  as 
oxygen  require  more  heat  to  raise  its  temperature  at  constant 
volume  than  mercury  gas  ?  The  answer  is,  that  the  heat  is  not 
wholly  utilised  in  causing  molecular  motion,  but  is  partly  employed 
in  causing  the  atoms  in  the  molecule  to  rotate,  or  oscillate ;  while 
with  mercury  vapour  the  monatomic  nature  of  its  molecules  makes 
such  an  expenditure  of  energy  impossible. 

Granting  that  mercury  gas  consists  of  monatomic  molecules,  it 
follows  from  the  density  of  mercury  gas  compared  with  those  of 
hydrogen  and  oxygen,  &c.,  that  the  molecules  of  the  latter  consist 
of  two  atoms ;  and  from  this  we  can  deduce  the  molecular  weights 
of  all  bodies  obtainable  in  the  gaseous  state  without  decomposition.* 

*  For  a  detailed  account  of  this  subject,  see  Clerk-Maxwell's  Theory  of 

2   S 


626  MERCURY   GAS. 

The  structure  of  compounds  has  been  dealt  with  as  opportunity 
arose  during  their  classification ;  and  little  can  be  added  with 
advantage  to  what  has  already  been  said.  Our  knowledge  of  the 
structure  of  carbon  compounds,  which  forms  the  basis  of  organic 
chemistry,  is  in  a  much  more  advanced  state  than  that  of  com- 
pounds of  other  elements ;  and  further  investigation  of  the 
compounds  of  carbon  containing  other  elements  besides  carbon, 
hydrogen,  and  oxygen  is  likely  to  shed  light  on  the  subject. 

Heat,  Third  Edit.,  chap.  XI ;  also  Naumann's  Thermochemie  (1882),  71  et  seq. ; 
also  Ostwalds'  Allgemeines  Chemie,  1,  266  (1885). 


627 


CHAPTEK  XXXVI. 


'  THE    PERIODIC    ARRANGEMENT    OF   THE    ELEMENTS. 

THE  relation  between  the  atomic  weights  of  the  elements 
has,  almost  since  the  announcement  of  the  atomic  hypothesis  by 
Dalton,  been  a  subject  of  speculation.  The  first  conjecture,  pub- 
lished by  Prout  (1815),  and  shortly  afterwards  by  Meinecke 
(18  L7),  was  that,  as  it  was  conceivable  that  the  ancient  doctrine  of 
the  uniformity  of  matter  was  true,  the  primary  material  mast  be 
hydrogen,  and  the  atomic  weights  of  the  other  elements  should 
therefore  be  multiples  of  that  of  hydrogen.  This  hypothesis  was 
warmly  advocated  by  Thomas  Thomson,  in  whose  text  book 
Dalton's  discovery  was  first  formally  announced;  but  Berzelius 
pronounced  against  it,  relying  on  his  own  determinations  of  atomic 
weights.  But  in  1842  it  was  discovered  by  Liebig  and  Redten- 
bacher,  and  confirmed  by  Dumas  and  Stas,  and  by  Erdmann  and 
Marchand,  that  Berzelius  had  made'an  error  in  his  determination  of 
the  atomic  weight  of  carbon,  and  that  the  correct  value  was  12  ;  and 
shortly  afterwards  Dumas  determined  with  great  precautions  the 
ratio  of  the  weights  of  hydrogen  and  oxygen  in  water,  obtaining  the 
value  16  for  oxygen,  and  by  similar  work  the  value  14  for  nitrogen  ; 
and  Prout's  hypothesis  was  accordingly  resuscitated,  not  in  its 
original  form,  however ;  but  it  was  supposed  that  the  atomic  weights 
of  the  elements  were  multiples  of  0'5,  half  the  atomic  weight  of 
hydrogen.  This  change  was  necessitated  by  Berzelius's  determina- 
tion of  the  atomic  weight  of  chlorine,  which  is  approximately  35'5, 
confirmed  by  Penny,  by  Marignac,  and  by  Pelouze ;  it  was  ulti- 
mately disproved,  however,  by  Stas's  determinations  of  the  atomic 
weights  of  silver,  chlorine,  bromine,  iodine,  potassium,  sodium, 
lithium,  sulphur,  nitrogen,  and  lead,  which  were  executed  with  a 
precision  not  to  be  surpassed. 

In  1817  Dobereiner  pointed  out  that  the  atomic  weight  of 
strontium  is  the  arithmetical  mean  of  those  of  calcium  and  barium. 
This  is  not  actually  the  case,  but  the  number  87'5  closely  ap- 
proaches 88'5,  the  true  arithmetical  mean.  Many  similar  "  triads  " 

2  s  2 


628  THE   PERIODIC   LAW. 

exist,  as  will  afterwards  be  shown ;  Zeuner,  in  1857,  tried  to 
arrange  all  the  atomic  weights  then  known  as  "  triads." 

In  1850  Pettenkofer  suggested  that  the  atomic  weights  of 
similar  elements  formed  arithmetical  series.  This  view  was 
adopted  and  extended  by  Bremers,  Gladstone,  and  Dumas. 

The  first  fruitful  attempt  to  introduce  order  into  the  seem- 
ing chaos  of  numbers  was  due  to  Newlands  in  18*33  and  1864. 
It  has  recently  been  pointed  out  that  de  Chancourtois,*  Pro- 
fessor of  Geology  at  the  Ecole  des  Mines  in  Paris,  had  indepen- 
dently anticipated  Newlands  by  about  a  year  ;  but  his  suggestions 
were  encumbered  with  untenable  theories,  and  met  with  no  atten- 
tion. Newlands  arranged  all  the  elements  then  known  in  the 
order  of  their  atomic  weights,  and  observed  that  every  eighth 
element,  as  a  general,  but  uot  absolute,  rule,  belonged  to  the  same 
class,  manifesting  similar  properties.  He  termed  this  relation 
the  "  law  of  octaves." 

In  1869  D.  Mendeleeff,  Professor  at  St.  Petersburg,  and 
Lothar  Meyer,  now  Professor  at  Tubingen,  in  Wurtemburg', 
simultaneously  published  on  the  subject,  both  pointing  out,  inde- 
pendently of  the  other,  that  "  the  properties  of  the  elements  are 
periodic  functions  of  their  atomic  weights."  The  methods  of 
representation,  though  the  idea  was  essentially  the  same,  differed 
slightly  from  each  other.  Meyer's  scheme  was  as  follows  :f — 


Li 

Be 

B 

C 

N 

0 

F. 

Ma 

Mg 

Al 

Si 

P 

S 

Cl. 

K 

Ca 

Sc 

Ti 

V 

Cr 

Mn 

Fe, 

Co,  Ni. 

Cu 

Zn 

Ga 

Ge 

As 

Se 

Br. 

Rb 

Sr 

Y 

Zr 

Nb 

Mo 

— 

Ru, 

Rh,  Pd. 

Ag 

Cd 

In 

Sn 

Sb 

Te 

I 

Cs 

Ba 

La,  Di 

Ce 

— 

— 

— 

— 





Yb 



Ta 

W 

— 

Os, 

Ir,  Pt. 

Au 

Hg 

Tl 

Pb 

Bi 

— 

— 

_  _  _  Th  —  U 


Mendeleeff's  table  is  somewhat  differently  constructed,  although 
essentially  the  same.  It  may  be  regarded  as  Meyer's  table  turned 
through  a  right  angle  : — 


*  Nature,  41,  986. 

f  The  table  has  been  given  as  published  in  the  last  edition  of  his  " 
Theorien ;"  see  also   the   translation    by   Bedson   and   Williams,    1888.     The 
portion  of  cerium  has  been  altered  to  the  carbon  group. 


ros 

I  IT 

IP* 


THE  PERIODIC   IAW.  629 

E.:O  I Li  K           Eb  Cs        —  —                EC1. 

EO  II Be  Ca          Sr  Ba                                       EC12. 

E203  III B  Sc          Y  La       Yb                          EC13. 

EO2IV C  Ti           Zr  Ce        —  Th                EC14. 

EaOs  v"(ni)....  N  V           Nb  Di       Ta                   EC13EC15. 

EO3VI   (II)....  O  Cr          Mo  —        W  U       EC12(EC16). 

B.2O7  VII  (I) . . . .  F  Mn  —  —  —        ECI(EC17). 

fFe  fRu 

E04  VIII  <{  Co  4  Eh 

[Ni  [Pd  [Pt 

E2O  I Na  Cu         Ag  —        An                           EC1. 

EO  II Mg  Zn         Cd  Hg                           EC12. 

E5O3  III Al  Ga         In  —       Tl                           EC13. 

E02IV Si  Ge         Sn  —        Pb  —                EC14. 

EoOs  V  (III)....  P  As         Sb  Bi                   EC13,EC15. 

E03VI  (II)  ....  S  Se  Te  —  —      EC12,(EC16). 

EsOjYIII  (I)...      Cl  Br         I  —  -       ECI.(EC17). 

While  in  L.  Meyer's  table  the  alternate  elements  show  analogy 
with  each  other,  in  Mendeleeff's  table  the  elements  are  divided 
into  two  classes. 

We  shall  consider:  1,  the  numerical  relations  of  the 
numbers  expressing  atomic  weights ;  2,  some  of  the  physical 
properties  of  the  elements  and  their  compounds,  varying 
with  atomic  weight ;  3,  a  comparison  of  the  formulae  of  com- 
pounds of  the  elements;  and  4,  the  fulfilment  of  predic- 
tions  of  the  atomic  weights  and  properties  of  undiscovered 
elements,  and  the  changes  in  recognised  atomic  weights,  due  to 
the  periodic  arrangement. 

1.  Numerical  relations. — These  are  best  seen  by  reference 
to  Lothar  Meyer's  arrangement. 

(a.)  Vertical  columns. — It  is  to  be  noted  that  the  atomic 
weights  of  the  elements  of  the  Na,  Mg,  Al,  Si,  P,  S,  and  Cl 
columns  are  nearly  the  mean  of  those  of  the  nearest  elements  of 
the  Li,  Be,  B,  C,  N",  O,  and  P  columns.  Thus,  for  example,  the 
mean  of  the  atomic  weights  of  Li  and  K=J(7'03  +  39-14)  =  23'08 ; 
the  atomic  weight  of  sodium  is  23*06.  Calculating  in  this  manner, 
we  have  the  following  numbers  : — 

Na.  Mg.  Al.  Si.  P.  S.  Cl. 

Calculated 23'08  24'5  27'5  30'0  32 '6  34'2  37  "0 

Found 23-06  24 '4  27 '1  28-4  31 '0  32"  1  35 '5 

Difference    +0*02  +0'1  40 '4  +1'6  + 1 '6  +2'1  +2 '5 

Here  there  is  a  constantly  increasing  difference. 

Cu.           Zn.         Ga.         GTe.         As.  Se.  Br. 

Calculated 62  "3        63 '7      66 -4      69 '4      72 '7  74-1  — 

Found 63-3         65" 5       69 '9       72 '3       75 '0  79 -1  — 

Difference -I'D       -1'8     -3'5     -2'9     -2'3  -5*0  — 


630  THE  PERIODIC   LAW. 

We  note  that  tlie  negative  difference  shows  signs  of  increase ; 
but  it  is  irregular. 

Ag.  Cd.  In.  Sn. 

Calculated 109  "15  112 '2  113  -6  115  -4 

Found 107-94  112 -1  113'7  118  "1 

Difference +  l'2l  -fO'l  -O'l  -2'7 

There  are  no  data  for  further  calculations;  it  is  to  be  noticed, 
however,  that  the  difference  is,  to  begin  with,  a  positive  one, 
becoming  negative.  It  would  be  possible,  however,  to  calculate, 
with  some  probability  of  correctness,  the  atomic  weight  of  the 
element  succeeding  niobium,  in  the  nitrogen  group,  in  the  follow- 
ing manner  : — The  difference  between  the  calculated  and  the  found 
values  of  silicon  and  phosphorus  is,  in  each  case,  -j-  1*6  ;  that 
between  the  calculated  and  found  values  of  germanium  is  — 2'9, 
and  of  arsenic  —  2*3  ;  it  is,  therefore,  to  be  expected  that  the  differ- 
ence will  be  approximately  —2' 7  between  the  calculated  and  found 
values  of  antimony,  for  it  is  approximately  the  same  for  the 
members  of  the  fourth  and  fifth  groups.  The  atomic  weight  of 
antimony  is  120'3  ;  subtracting  from  it  2' 7,  we  have  117'6  ;  multi- 
plying by  2,  we  obtain  235'2,  as  the  sum  of  the  atomic  weights 
of  niobium  and  the  element  immediately  following  it,  and  preced- 
ing tantalum.  Subtracting  from  235'2  the  atomic  weight  of 
niobium,  94' 2,  we  obtain  141 '0  as  the  probable  number  for  the 
element  "  eka-niobium."  Whether  this  is  identical  with  neo- 
dymium,  one  of  the  products  into  which  the  element  didymium  was 
split  up  by  Auer  von  Welsbach  in  1885,*  and  to  which  he  assigns 
the  atomic  weight  140'8,  time  must  determine.  The  properties  of 
its  compounds,  so  far  as  they  have  been  investigated,  hardly  lend 
support  to  the  view ;  but  it  is  probable  that  it  has  not  yet  been 
obtained  in  a  state  of  sufficient  purity  to  allow  of  definite 
conclusions. 

Another  method  of  averaging  may  be  tried  for  the  atomic 
weights  of  elements  of  the  Li,  Be,  B,  C,  N,  0,  and  F  groups.  It 
is  seen  at  once  that  the  atomic  weight  of  calcium,  for  example, 
which  is  40'0,  differs  greatly  from  the  mean  atomic  weights  of 
magnesium,  24'4,  and  zinc,  65'5  =  44'9.  But  a  closer  approxima- 
tion may  be  obtained  in  some  instances  by  taking  the  average  of 
the  atomic  weights  of  the  two  nearest  elements  in  the  same 
vertical  row.  We  thus  obtain  the  "  triads."  to  which  attention 
was  directed  by  Dobereiner.  This  method  is  not  available  for 

*  Monatfth.f.  Chem.,  6,  477.  The  author  lias  been  verbally  informed  by 
C.  M.  Thompson,  that  he  has  conQrmed  von  Welsbach's  work. 


THE  PERIODIC   LAW.  631 

potassium,  calcinm,  scandium,  &c.  ;  for  example,  Li  7'03  +  Rb  85'4 
=  92-43,  and  J(92-43)  =  46'21  ,  a  number  very  far  from  K  =  39*14. 
But  Rb  =  85'4  is  approximately  the  mean  of  K  =  39'14  and 
Cs  =  132-9,  viz.,  86-02  ;  Sr  =  87'5  is  nearly  the  mean  of  Ca  =  40'0 
and  Ba  =  137'0,  viz.,  88'5  ;  Y  =  887  does  not  greatly  differ  from 
i(Sc  =  44-]  +  La  =  138*5)  =  91*3  ;  and  Zr  9O7  may  be  com- 
pared with  i(Ti  =  48*1  +  Ce  =  140'2)  =  94'1.  The  difference,  it 
will  be  noticed,  is  an  increasing  one. 

Applying  the  same  method  to  Ca,  Zn,  Gra,  Ge,  As,  Se,  and  Br, 
i.e.,  Cu  =  i(Na  +  Ag),  Zn  =  J(Mg  +  Cd),  &c.,  we  obtain  :— 


Cu.  Zn.  Ga.  Ge.         As.  Se.          Br. 

r  Calculated  ____        65'5  68  '2  70'4  73  '2  757  78'5  81*15 

1  Found  .......        63-3  65  "5  69  "9  72  '3  75  '0  79  "1  79  '96 

I  Difference  ____       +2*2  +  2'7  +  0'5  +0'9  +  07  -0'6  +1'19 

Here,  too,  the  approximation  is  fair,  but  the  differences  are 
irregular. 

(6.)  Horizontal  rows.  —  The  question  here  is  as  regards  the 
position  of  the  atomic  weight  of  an  element  with  respect  to  those 
immediately  preceding  and  succeeding  it  in  numerical  order.  The 
comparison  is  as  follows  :  — 


Be. 

9'02 

B. 
10-55 

C. 
12-52 

K. 

14-00 

0. 
16'5 

F. 
19  5 

•s  Found    ..... 

9-10 

11  -01 

12-00 

14'04 

16  -0 

19  '0 

1  Difference  
f  Calculated  

-0-08 

Mg. 
25-08 

-0-46 

Al. 

26  '39' 

+  0-52 

Si. 
29-06 

-0-04 

P. 
30-93 

+  0-5 

S. 
33  '24 

+  0-5 

CL 

35  -go 

J  Found 

24-38 

27  -I 

28-4 

31  '03 

32  '06 

35  -45 

L  Difference  
r  Calculated  

+  0-7O 

Ca. 
41  '6 

-0-72- 

Sc. 
44-0 

+  0-66 

Ti. 
47-6 

-0-80' 

V. 

50  -2 

+  1-18 

Cr. 
53  '1 

-1-0  -15 

J  Found    

40'0 

44-1 

48  '1 

51  '2 

52  '3 

+  1'6 

—  0-1 

—0-5 

—  1  '0 

+  0'8 

Zn. 
66*6 

Ga. 
68-9 

Ore. 
72-4 

As. 
75-7 

Se. 
77-5 

J  Found    ...      ... 

65-5 

69  '9 

72-3 

75  '0 

79  '1 

L  Difference  

+  1-1 

—  1-0 

+  0-15 

+  0-7 

—  1-6 

r  Calculated  

Sr. 
87-0 

Y. 

89-1 

Zr. 

91-4 

Nb. 
93-3 

Mo. 

?.* 
99-6 

-|  Found    

87'5 

887 

90-7 

94-2 

—  0-5 

+  0*4 

+  0*7 

—0-9 

*  This  atomic  weight  has  been  calculated  on  the  assumption  that  the  average 
number  would  be  I'O  too  small. 


632                                        THE  PERIODIC  LAW. 

Cd.           In.  Sn.  Sb.  Te. 

(•Calculated 110 "8       115 '1  117  "0  121-5  123  "6 

4  Found 112-1       113-7  118'1  120  "3  125-0 

I  Difference ..              -1'32     +  1*4  -1-1  +1'2  -1'4 


Ba.  La. 

r  Calculated 135  '7  138  "6 

i  Found 137*0  138 '5 

[Difference..  -1'3  +  0'1 


Hg.  Tl.  Pb. 

200  -6  203  -6  206  "0 

200-4  201-1  206-9 

+  0-2  -0-5  -0-9 


It  has  not  been  thought  permissible  to  take  the  mean  of  the 
second  last  member  of  one  row  and  the  first  member  of  the  next, 
so  as  to  obtain  the  atomic  weight  of  the  last  member ;  hence,  the 
atomic  weights  of  the  first  and  last  members  of  the  rows  are,  as  a 
rule,  omitted.  The  results,  however,  show  that,  although  it  is 
possible  to  approximate  to  the  atomic  weights  of  unknown 
elements,  the  numbers  are  too  irregular  to  allow  of  accurate  pre- 
diction. 

Various  attempts  have  been  made  to  devise  some  scheme  which 
should  reduce  these  numbers  to  order.  One  which  holds  out 
hopes  of  ultimate  success  is  due  to  G.  Johnstone  Stoney.*  Until 
more  accurate  numbers  have  been  obtained  in  all  cases,  there  is 
little  to  be  done.  It  may  be  stated,  however,  that  the  variations 
from  a  mean  curve  passing  among  points  representing  atomic 
weights  appear  themselves  to  vary  periodically. 

To  discover  the  true  relations  between  these  numbers  must 
remain  one  of  the  problems  of  chemistry  ;  and  its  discovery  will, 
in  all  probability,  prove  a  key  to  many  problems  at  present 
unsolved. 

As  an  example  of  attempts  which  have  frequently  been  made 
to  assign  some  cause  for  the  periodic  arrangement,  a  recent  note 
by  A.  M.  Stapley  will  be  here  quoted.  His  table  is  given  on  the 
next  page.f 

These  results  are  obtained  by  taking  (as  a  rule)  the  first 
member  of  a  column,  and  adding  to  it  16,  or  multiples  thereof, 
for  elements  on  the  left,  and  the  product  of  the  first  member 
by  2,  adding  to  it  16,  or  multiples  thereof,  for  the  elements 
on  the  right  of  each  column.  There  is,  generally  speaking, 
a  certain  concordance  between  the  numbers  obtained  and  the 
true  atomic  weights ;  but  there  are  many  wide  discrepancies, 
especially  in  the  row  containing  Os,  Ir,  Pt,  Au,  &c.  The  author 

*  "  The  logarithmic  law  of  atomic  weights,"  Chem.  Soc.  Abstr.,  1888-89, 
55. 

f  Nature,  41,  57. 


THE   PERIODIC   LAW. 


633 


YII. 

VIII. 

I. 

H  .  1. 

R'   =  3. 

RH  =  4 

R«>  =  5 

Riv  =  6 

Li  7 

3  +  16  F. 



— 

— 

7  +  16  Na 

Cl  3  +  32 







K   7  +  32 

6+  48  Mn. 

8  +  48  Fe 

10  +  48  Co 

12  +  48  Ni 

14  +  48  Cu 

Br  3  +  80 





— 

Rb7  +  80 

6+96? 

8  +  96  Ru 

10  +  96  Rh 

12  +  96  Pd 

14.  +  96  Ag 

13+  128 

— 

— 

— 

Cs  7  +  128 

6+  144? 



— 

— 

— 

?3+  176 

— 

— 

— 

— 

6+  192? 

8  +  1920s 

10  +  192  Ir 

12  +  192  Pt 

14  +  192  Au 

?  3  +  224 

— 

— 

— 

~ 

II. 

III. 

IY. 

Y. 

YI. 

Be  9 

B  11 

C  12 

N  14 

O  16 

9  +  16  Mg 

11  +  16  Al 

12  +  16  C 

14  +  16P 

16  +  16S 

Ca  9  +  32 

Sell  +  32 

K  12  +  32 

Y  14  +  32 

Cr  16  +  32 

18  +  48  Zn 

22  +  48  Ga 

12  +  48Ge 

14  +  48  As 

32  +  48  Se 

Sr  9  4  80 

Y  11  +  80 

Zr  12  +  80 

Nbl4  +  80 

Mol6  +  80 

18  +  96  Cd 

22  +  96  In 

24  +  96  Sn 

28  +  96  Sb 

32  +  96  Te 

Ba  9  +  128 

La  11  +  128 

Cel2  +  128 

Dil4  +  328 

— 



22  +  144  Er 

— 

— 

— 



— 

— 

— 

W  16  +  176 

18+  192  Hg 

22  +  192  Tl 

24  +  192  Pb 

28  +  92  Bi 

— 

2 

Th  12  +  224 

U  16  +  224 

of  this  suggestion  compares  these  figures  with  those  of  the  oxides, 
i.e.,  MO,  M02,  M2O3,  MO5,  &c.  This  has  no  real  significance,  but 
only  typifies  the  fact  that  16  is  an  average  difference.  The 
scheme  has  little  to  recommend  it,  and  is  adduced  merely  as  a 
sample  of  numerous  attempts  of  the  kind. 

2.  Physical  properties. — (a.)  Volumes  and  their  connec- 
tion with  atomic  weights. — The  specific  volume  of  a  substance 
expressed  in  units  is  the  volume  of  one  gram ;  the  specific 
gravity  is  the  weight  of  one  cubic  centimetre ;  and  it  is  obvious 
that  the  one  is  reciprocal  to  the  other.  The  atomic  weight,  multi- 
plied by  the  specific  volume,  or  divided  by  the  specific  gravity, 
gives  the  atomic  volume  of  an  element ;  that  is,  the  number  of 
cubic  centimetres  occupied  by  its  atomic  weight  expressed  in 
grams.  If  it  were  certain  that  the  space  between  the  atoms  of 
liquids  and  solids  were  equal  in  all  cases,  the  resulting  numbers 
would  give  the  comparative  volumes  of  the  atoms ;  but,  as  this  is 
probably  not  the  case,  the  numbers  represent  merely  the  volume 


634 


THE   PERIODIC   LAW. 


of  the  atom  plus  the  space  it  inhabits.  That  such  constants  bear 
definite  relations  to  the  periodic  arrangement  of  the  elements  is 
seen  from  the  following  table  : — * 


1. 

2. 

3. 

1 

Li 

=  11-9 

K 

= 

45-5 

Eb 

= 

56-3 

2 

Be 

=    4-3 

Ca 

= 

25-3 

Sr 

= 

34-5 

3 

B 

=    4-1 

Sc 

= 

? 

Y 

= 

? 

4 

C 

=    3-4 

Ti 

= 

p 

Zr 

= 

21-9 

5 

N 

— 

V 

= 

9-3 

Nb 

= 

14-5 

6 

O 

— 

Cr 

= 

77 

Mo 

= 

11-1 

~ 

F 

— 

Mn 

= 

7-4 

— 

rFe 

_ 

6-6 

Eu 

= 

9-2 

8 

— 

1  Co 

iNi 

= 

67 
67 

Eh 
Pd 

I 

9-5 
9-3 

1 

Na 

=  23-7 

Cu 

= 

7-2 

Ag 

= 

10-3 

2 

Mg 

=  13-3 

Zn 

= 

95 

Cd 

as 

13-0 

3 

Al 

=  10-1 

G-a 

= 

11-8 

In 

= 

15-3 

4 

Si 

=  11-3 

Oe 

= 

13-2 

Sn 

=. 

16-1 

5 

P 

=  13-5 

As 

= 

13-3 

Sb 

=* 

17-9 

6 

8 

=  15-7 

Se 

= 

18-5 

Te 

= 

20-3 

7 

Cl 

=  25-6 

Br 

= 

25-1 

I 

— 

257 

5. 


6. 


4. 

Cs  -  70-6 
Ba  =  36  5 
La  =  22-9 

Ce  ~  21-0  Th  =  29  9 

Ta  =  17-0 
W  =  9 "6  U  =  13  0 

Os  =  8-9 
Ir  =  8-6 
Pt  =  9-1 
Au  =  10-2 
Hg  =  14  8 
Tl  =17-2 
Pb  =  18-2 
Bi  =  21-2  — 


Similar  regularities  are  observable  in  the  molecular  volumes  of 
the  oxides  ;f  those  of  the  lithium  and  sodium  groups  are  taken  as 
M20 ;  those  of  the  beryllium  and  magnesium  groups  as  M202 ; 
those  of  the  boron  and  aluminium  groups  as  M>O3 ;  of  the  carbon 
and  silicon  groups  as  M204 ;  of  the  nitrogen  and  phosphorus 
groups  as  M205;  and  of  the  chromium  and  sulphur  groups  as  M206. 
The  volumes  are  those  of  oxides  supposed  to  contain  1  atom  of 
element. 


1 

2 
3 

4 
5 
6 

1. 
Li20 
BeoO2 
B263 
C204 
N 
0 

7 
7 
19 
46 

2. 
K20 

Ca2O2 

Ti204 
V205 
Cr206 

17 
18 
18 
20 
26 
37 

3. 

Eb2O    21 
Sr2O2    22 
Y2O3     23 
Zr2O4    25 
Nb2O5  30 
Mo2O6  33 

4.                   5. 
Cs2O   25 
Ba2O228 

C12O4  26 
Ta^Og  31 
W206  37 

6. 

Th2O4  27 
U2O6    56 

7 

F 

— 

Mn 

— 

— 

— 

—                 — 

— 

1 

Na20 

11 

Cu2O 

12 

Ag20 

14 

Au2O  18 

— 

2 

Mg202 

12 

Zn2Os 

:14 

Cd202 

16 

Hg2O219 

— 

3 

A12O3 

13 

Ga20; 

,17 

In2O3 

19 

T12O3  23 

— 

4 

Si204 

23 

G-e2O. 

,22 

Sn2O4 

22 

Pb2O4  27 

— 

5 

P2O3 

30 

As2O5 

31 

BbjOj 

42 

—                  — 

— 

6 

S2O6 

41 

Se 

— 

Te 

— 

Bi,O5  42 

— 

7 

— 

•~ 

Br 

~ 

I 

— 

__                  _ 

— 

*  Somewhat  altered  from  that  given  by  L.  Meyer,  Annalen,  Szippl.,  7,  354. 
f  Brauner  and  Watts,  Berichte,  14,  48. 


THE  PERIODIC   LAW. 


635 


(6.)  Melting-points.* — These,   so  far  as  they  are  known,  are 
on  the  absolute  scale  as  follows  : — 

6. 


Th? 


U   2008? 


1. 

2. 

3. 

4. 

5. 

1 

Li 

453 

K 

335 

Eb 

311 

Cs  300 

— 

2 

Be 

1230  + 

Ca 

+ 

Sr 

+ 

Ba748  • 

— 

:j 

B 

+  + 

Se 

p 

Y 

? 

La+  + 

— 

4 

C 

00 

Ti 

00 

Zr 

+  + 

Ce  •+•  + 

— 

* 

N 

59 

V 

00 

Nb 

00 

— 

Ta 

00 

6 

0 

59- 

Cr 

2270  + 

Mo 

00 

'  — 

W 

+  + 

7 

F 

— 

Mn 

2170 





— 

8 

— 

fFe 

{m 

[CO 

2080 
2070 
1870 

fEu2070] 
\  Eh  2270  \ 
(.Pd  1775  J 

ros 

2770] 
2220  }• 
2050  J 

1 

Na 

369 

Cu 

1330 

Ag 

1230 

— 

Au 

1310 

2 

Mg 

1023 

Zn 

690 

Cd 

590 

— 

Hg 

234 

3 

Al 

1123 

G-a 

303 

In 

449 

— 

Tl 

563 

4 

Si 

+  + 

Ge 

1173 

Sn 

503 



Pb 

599 

5 

P 

528 

As 

773  + 

Sb 

710 

— 

Bi 

540 

6 

S 

388 

Se 

490 

Tl 

728 

— 

7 

Cl 

198 

Br 

266   • 

I 

387 

— 

The  signs  +  and  —  affixed  to  a  number  signify  that  the  melting- 
point  is  above  or  below  the  number  given.  The  sign  +  standing 
alone  means  that  the  melting-point  is  higher  than  the  one  imme- 
diately above.  The  sign  oo  means  that  the  element  has  not  been 
melted.  Similar  relations  have  been  traced  for  the  halides  and 
ethides  by  Carnelleyf  for  boiling-points,  showing  similar  regu- 
larity. 

The  periodic  arrangement  also  shows  analogies  between  the 
refraction-equivalents  and  the  conductivity  for  heat  and  elec- 
tricity of  the  elements,  and  also  heats  of  formation  of  halides, 
oxides,  &c.,  which  lack  of  space  will  not  allow  us  to  discuss  here. 
Enough  has  been  given,  however,  to  fully  justify  the  statement 
that  the  properties  of  elements  are  functions  of  their  atomic 
weights. 

3.  Comparison  of  the  elements  and  their  compounds.  — 
These  must  be  very  summarily  discussed.  Beginning  with  halides, 
it  is  to  be  noticed  that  elements  of  the  lithium  group  form  only 
halides  of  the  formula  MX;  while  sodium  resembles  them  in 
this  respect.  The  bodies  are  not  soluble  in,  and  do  not  react 
with,  water  ;  or,  to  speak  more  correctly,  water  may  be  expelled 
from  their  solutions  without  decomposing  them.  Of  the  sodium 
group,  the  elements  copper,  silver,  and  gold  more*  closely  re- 


*  Lothar  Meyer. 

f  PAH.  Mag.,  July,  1884  ;  Sept.,  1385.     Chem  News,  Nos.  1375-1378. 


636  COMPARISON   OF   COMPOUNDS. 

semble  those  of  the  iron,  palladium,  and  platinum  groups  than 
they  do  sodium.  Their  monohalides  are  insoluble ;  and  they 
form  soluble  dihalides,  which  connect  them  with  the  elements 
of  the  magnesium  group  ;  while  gold  forms  trihalides.  The  halides 
of  the  beryllium  group  are,  without  exception,  dihalides,  as  are 
also  those  of  the  magnesium  group,  with  exception  of  mercury, 
which  harks  back,  as  it  were,  to  the  sodium  group,  forming  mono- 
halides closely  resembling  those  of  copper,  silver,  and  gold. 
Trihalides  of  elements  of  the  boron  group  are  the  only  ones  known  ; 
the  elements  of  the  aluminium  group,  also,  all  form  trihalides  ; 
but  a  dihalide  of  aluminium  is  known  in  combination;  also  a 
dihalide  of  gallium  ;  and  indium  forms  both  a  di-  and  a  mono- 
halide.  The  dihalides  are  wanting  with  thallium,  but  the  mono- 
halides are  the  more  stable  compounds.  The  elements  of  the 
carbon  group  form  only  tetrahalides ;  the  compounds  such  as 
M2X6,  which  might  pass  for  trihalides,  are,  without  doubt,  com- 
binations in  which  two  atoms  of  the  element  M  are  conjoined ; 
cerium,  however,  may  form  a  genuine  trihalide.  The  silicon- 
group  of  elements  also  forms  tetrahalides,  those  of  lead  being 
unstable;  while  silicon,  germanium,  and  tin  also  form  dihalides. 

Elements  of  the  nitrogen  group,  nitrogen  itself  excepted,  form 
more  than  one  halide  ;  those  of  vanadium  being  specially  numerous  ; 
but,  while  niobium  forms  two,  tantalum  forms  only  one.  This 
order  is  reversed  with  the  phosphorus  group  ;  for,  while  phosphorus 
is  capable  of  uniting  with  as  many  as  eleven  atoms  of  halogen,  but 
not  with  less  than  three,  bismuth  appears  incapable  of  combining 
with  more  than  three  atoms  of  a  halogen,  and  also  forms  a  dihalide. 
The  elements  chromium,  manganese,  iron,  cobalt,  and  nickel  form 
halides  much  more  closely  resembling  each  other  than  the  halides  of 
chromium  and  manganese  resemble  those  of  the  oxygen  and  fluorine 
groups  ;  while  molybdenum,  tungsten,  and  uranium  are  again 
noted  for  the  great  number  of  their  halogen  compounds.  Sulphur, 
selenium,  and  tellurium  appear  to  combine  with  two  and  with 
four  atoms  of  halogen ;  although  the  compounds  are  not  all  re- 
presented. Iodine  forms  a  mono-  and  a  tri-chloride.  The 
halides  of  the  iron  and  of  the  palladium  groups  correspond  to  the 
formulae  MX2,  MX3,  and  MX4;  and  those  of  the  platinum  group 
are  similar. 

The  capacity  for  forming  double  halides  appears  to  increase,  as 
a  rule,  with  rise  in  atomic  weight ;  but  it  must  be  remarked  that 
the  investigation  of  these  bodies  is  closely  connected  with  their 
stability  in  presence  of  water;  few  compounds  having  been 
isolated  which  are  unable  to  resist  the  action  of  that  agent. 


COMPARISON   OF   COMPOUNDS.  637 

Taking  next  in  order  the  alkides,  for  example,  the  ethides,  we 
have  as  the  only  representative  of  the  lithium  group  the  double 
ethide  of  zinc  and  potassium,  K(C2H5).Zn(C2H5)2,  and  of  the 
sodium  group,  the  corresponding  compound  Na(CjH§).Zn(C»H»)», 
corresponding  with  the  halides  of  sodium  and  potassium.  The 
beryllium  group  is  represented  by  Be(CaH5)2,  corresponding  to 
the  halides;  and  we  have  next  Mg(C2H5)2  and  Zn(C.H5)2,  repre- 
senting the  dibalides.  The  mercury  compound,  Hg(C2H6)2,  also 
corresponds  to  its  dihalide;  of  the  boron-group,  B(C2H5)3  is  the 
only  ethide  known  ;  but  with  aluminium  the  two  compounds, 
A1(C2H5)3  and  A12(C2H5)6,  have  been  prepared;  the  theoretical 
consequences  of  the  existence  of  these  bodies  have  been  alluded  to 
on  p.  504.  With  silicon,  Si(C2H5)4  and  Si2(C2H6)6  are  known ; 
with  tin,  Sn(C2H5)4,  Sn2(C2H5)6,  and  Sn,(C2H5)4;  and  with  lead, 
Pb(C2H5)4  and  Pb2(C2H5)6. 

Of  the  nitrogen  group,  we  have  N(C2H5)3  and  N2(C2H5)4 ;  and 
of  the  phosphorus  group,  P(C2H6)3  and  P.,(C2H5)4;  also  As(C2H3)3, 
As^JIs^,  and  As2(C2H5)i.  Similarly,  with  antimony,  the  com- 
pound Sb(C2H5)3  is  known. 

The  hydroxides  in  general  correspond  to  the  halides;  but  it 
may  be  pointed  out  again  here  that  C(OH)4,  P(OH)5,  and  S(OH)6 
are  unstable,  and  hence  unknown,  although  their  derivatives 
CO(OH)2,  PO(OH)3,  and  SO,(OH)2  lead  us  to  infer  their  possi- 
bility. 

The  oxides,  sulphides,  selenides,  and  tellurides  are  much  more 
numerous  and  complex.  For  with  elements  of  the  lithium  and 
sodium  groups  we  have  not  merely  what  we  may  term  normal 
oxides,  such  as  Li2O  and  NaoO,  but  also  such  bodies  as  K2O2, 
K204,  K2S5,  &c.  If  we  include  copper,  silver,  and  gold,  we  have 
also  M2O,  MO,  M203,  and  M02;  but  it  is  doubtful  whether  these 
elements  are  not  really  members  of  the  iron,  palladium,  and  platinum 
groups.  With  the  beryllium  group,  we  have  Ca02,  Sr02,  and 
Ba02,  besides  BaS,  BaS2  BaS3,  SrS4,  and  BaS5.  In  the  magnesium 
group,  however,  the  existence  of  dioxides  is  doubtful ;  but  its  last 
member,  mercury,  forms  an  oxide,  Hg20,  corresponding  to  its 
monochloride ;  and  in  the  boron  group  the  only  known  oxides  are 
trioxides,  except  with  yttrium  and  lanthanum,  where  evidence  of 
higher  oxides,  Y409  and  La4O9  has  been  obtained.  Here,  too,  we 
notice  a  well-marked  tendency  to  form  double  oxides  with  those  of 
other  elements.  The  borates,  although  indefinite,  contain  the 
oxide  B^03  as  their  "acidic"  constituent.  Elements  of  the  alu- 
minium group,  thallium  excepted,  iorm  exclusively  sesquioxides 
and  sulphides ;  aluminium,  too,  forms  many  double  oxides, 


()38  COMPARISON  OF   COMPOUNDS. 

among  others,  the  spinels.  Both  a  monoxide  and  monosulphide 
and  sesquioxide  and  sesquisulphide  of  thallium  are  known,  and 
also  a  dioxide  in  combination  with,  other  oxides,  where  it  plays  an 
"acidic"  part. 

With  the  carbon  group,  the  oxides  become  more  numerous.  We 
know  those  of  the  general  formulae  MO,  M203,  MO2,  M205,  M03,  and 
M207,  the  dioxides,  M02,  exhibiting  definite  acid  characters,  and 
the  greatest  stability,  except  with  cerium.  Silicon  and  its 
"  homologues  "  form  monoxides  and  monosulphides,  sesquioxides 
and.  sesquisulphides,  and  dioxides  and  disulphides.  Again,  those 
of  the  formula  MR2  are  most  stable,  and  display  "acidic" 
characters. 

The  elements  of  the  nitrogen  group  also  form  numerous  oxides 
and  sulphides.  We  know  M20,  MO,  M203,  M02,  M205,  and  M03. 
Those  of  the  formula  M206  are  best  characterised,  and  their  com- 
pounds are  most  stable.  The  closely  analogous  phosphorus  group 
is  characterised  by  compounds  of  the  formulae  P40,  P4S3,  BiO, 
PA,  P204,  P205. 

The  compounds  of  phosphorus  and  arsenic  of  the  formula? 
P205  and  As205  are  the  most  stable  ;  those  of  antimony  and  bismuth 
find  their  most  stable  stage  in  Sb406  and  Bi4O6. 

Of  the  group  of  which  oxygen  is  the  first  member,  we  have 
chromium  with  derivatives  such  as  MO  ;  chromium  and  molyb- 
denum forming  compounds  such  as  Cr203,  Mo203 ;  chromium, 
molybdenum,  tungsten,  and  uranium  giving  dioxides,  M02,  and 
trioxides,  M03 ;  while  molybdenum  forms  a  tetrasulphide,  MoS4, 
and  uranium  a  tetroxide,  U04.  Still  higher  oxides  of  uranium 
appear  to  exist  in  combination.  Those  of  the  type  M03  appear  to  be 
best  characterised.  Oxides  of  elements  of  the  sulphur  group  are  not 
as  a  rule  stable,  except  in  combination;  but  S02,  S03,  Se02,  Te02, 
and  Te03  are  known.  Compounds  of  S202,  S203,  and  S^,  besides 
others  more  complex,  are  known  as  hyposulphites,  thiosulphates, 
and  persulphates.  Perhaps  the  oxides  M03  may  be  regarded  as 
most  characteristic. 

The  oxides  of  manganese  are  very  numerous,  resembling  those 
of  aluminium  and  chromium  on  the  one  hand,  and  those  of  iron, 
nickel,  and  cobalt  on  the  other.  We  are  acquainted  with  MnO, 
Mn203,  Mn02,  and  with  Mn03  and  Mn207  in  combination.  The 
most  stable  oxide  is  MnO ;  that  characterising  the  position  of 
manganese  in  the  periodic  table  isMn207.  The  sulphides  are  fewer 
in  number. 

The  oxides  of  the  halogens,  taken  together,  furnish  representa- 
tions of  M2O,  M203,  M02,  M205,  and  M207.  The  second  and  fifth  are 


COMPARISON   OF  COMPOUNDS.  639 

known  only  in  combination.  The  sulphides  range  from  Cl4Se  to 
C12S2.  The  oxide  M207  is  regarded  as  characteristic. 

Proceeding  to  the  iron  group,  we  have  iron  itself,  with  oxides 
FeO,  Fe203,  and  Fe03:  the  last  in  combination;  and  the  sulphide 
FeS3 ;  cobalt,  with  CoO  and  Co2O3;  and  nickel,  with  the  sulphide 
Ni3S,  and  the  oxides  NiO  and  Ni203. 

The  palladium  group  contains  compounds  representing  MO, 
M2O3,  M02,  and  M03 ;  and  the  platinum  group  MO,  M203,  MO2, 
M03,  and  MO4. 

The  reason  for  inserting  the  general  formnlaB  of  the  oxides  and 
chlorides  at  the  beginning  and  end  of  the  table  on  p.  629  will  now 
be  seen.  These  oxides  and  chlorides  certainly  exist  in  most  cases, 
either  free  or  in  combination.  But  the  elements  do  not  form  such 
compounds  exclusively.  It  is  possible  that  when  we  know  more 
about  the  temperature  of  maximum  stability  of  such  compounds, 
we  shall  have  light  thrown  on  the  subject ;  for  the  present,  all  that 
can  be  said  is  that  there  is  certainly  a  definite  order  visible  in  the 
periodic  arrangement  of  the  elements,  in  which,  in  the  main, 
elements  possessing  similar  properties  are  grouped  together ;  and 
we  must  trust  to  experiment  to  give  us  knowledge  of  the  true 
meaning  of  all  its  apparent  inconsistencies  and  anomalies. 

The  borides,  carbides,  nitrides,  phosphides,  &c.,  do  not  throw 
any  further  light  on  the  periodic  arrangement.  They  have  as  yet 
been  too  little  investigated. 

4.  Prediction  of  undiscovered  elements. — When  Men- 
deleeff  gave  its  present  form  to  the  periodic  table,  the  element 
indium  was  believed  to  possess  the  atomic  weight  76,  twice  its 
equivalent,  which  is  38 ;  the  formula  of  its  most  stable  chloride 
was,  therefore,  accepted  as  InCl2,  and  of  its  corresponding  oxide, 
InO.  The  properties  and  reactions  of  the  element  and  its  com- 
pounds forbade  it  having  a  place  in  the  potassium  or  calcium 
groups ;  moreover,  there  was  no  vacant  place  for  it :  its  atomic 
weight  could  not,  therefore,  be  38.  With  the  then  accepted  atomic 
weight  76,  it  would  have  fallen  between  arsenic  and  selenium,  a 
position  for  which  it  showed  no  analogy,  and,  again,  one  occupied 
fully.  With  the  atomic  weight  38  x  3  =  114,  it  falls  in  the 
aluminium  group ;  and  its  specific  heat,  shortly  afterwards  deter- 
mined, confirmed  its  right  to  that  position. 

The  element  uranium  was  supposed  to  possess  the  atomic 
weight  120.  The  formula  of  the  uranyl  compounds,  which  are 
very  characteristic,  contained  the  group  (U2O2)U,  and  its  stable 
oxide  was  regarded  as  U203.  But  with  the  atomic  weight  120,  its 
place  is  among  elements  such  as  tin,  antimony,  and  tellurium, 


640  PREDICTION   OF   UNDISCOVERED    ELEMENTS. 

with  which  it  has  no  connection  ;  and,  again,  these  places  were 
already  filled.  Hence  it  was  decided  to  double  the  atomic  weight ; 
assigning  the  formula  (UOo)11  to  the  uranyl  group,  and  U03  to 
its  oxide.  It  then  fell  into  its  true  position  as  the  analogue  of 
molybdenum  and  tungsten.  This  conclusion  was  afterwards 
ratified  by  Zimmerman. 

The  element  with  the  approximate  atomic  weight  44,  in  the 
boron  group,  was  then  unknown.  Mendeleeff  predicted  its  exist- 
ence. Belonging  to  the  boron  group,  "  eka-boron,"  as  he  named 
the  element,  should  have  an  oxide  of  the  formula  M203,  without 
very  marked  tendencies  towards  combination,  inasmuch  as  it  lies 
between  calcium  and  titanium  ;  its  sulphate  should  display  analogy 
with  that  of  calcium,  and  be  sparingly  soluble ;  it  should  accom- 
pany the  next  member  of  the  group,  yttrium,  and  should  be 
difficult  to  separate  from  that  element.  "  The  oxide  will  be  in- 
soluble in  alkalies  ;  "  it  will  give  gelatinous  precipitates  with  potas- 
sium hydroxide  and  carbonate,  sodium  phosphate,  &c.,  &c.  Ten 
years  later,  "scandium"  was  discovered  by  Nilson,  possessing 
these  identical  characteristics. 

At  the  same  time,  Menieleeff  predicted  the  existence  of  two 
other  elements,  also  then  unknown,  viz.,  "  eka-aluminium  "  and 
"  eka-silicon."  Eka-aluminium  should  have  the  atomic  weight 
68  ;  its  compounds  should  resemble  those  of  aluminium  in  formula. 
It  should  be  easily  reduced,  stable,  of  sp.  gr.  about  5'9,  and 
should  decompose  water  at  a  red  heat.  All  these  predictions 
were  subsequently  fulfilled  by  <-  gallium,"  discovered  in  1875 
by  Lecoq  de  Boisbaudran.*  Eka-silicon  was  not  discovered  till 
much  later.  It  is  the  element  "  germanium,"  discovered  by 
Winkler  in  1886.  As  with  gallium,  it  fulfils  all  that  Mendeleeff 
predicted. 

Among  other  points  to  be  mentioned  are  the  correction  of  the 
atomic  weight  of  beryllium,  long  maintained  to  be  three  times  its 
equivalent  4'6,  instead  of  twice  (see  p.  128)  ;  the  placing  in  their 
true  position  the  elements  osmium,  iridium,  and  platinum, 
since  confirmed  by  the  re-determination  of  their  atomic  weights,  by 
Seubert  (Os  =  190-8;  Ir=192'64;  and  Pt  =  194-46)  ;  also  of 
gold  by  Thorpe  and  Laurie  (197'34),  confirmed  by  Kriiss  (197'12)  ; 
the  numbers  previously  accepted  were  Os  =  200;  Ir,  197;  and 
Pt,  197  to  198,  while  gold  was  taken  as  197*1,  differing  little  from 
those  more  recently  obtained. 

Brauner  announced,  in  1889,f  that  he  has  for  six  years  been 

*  Mendeleeff,  Compt.  rend.,  81,  969. 
f  Chem.  Soc.,  1889,  382. 


PREDICTION  FROM  THE  PERIODIC  LAW.  641 

engaged  in  determining  the  atomic  weight  of  tellurium.  At  pre- 
sent, the  data  represent  it  with  the  atomic  weight  128.  But  it 
must  obviously  lie  between  antimony,  on  the  one  hand,  with  the 
atomic  weight  120- 3,  and  iodine,  126P86.  Mendeleeff  assigned  it 
the  atomic  weight  125  in  his  earliest  table.  Brauner  finds  that 
the  element  named  tellurium  is  a  mixture  of,  at  least,  three 
elements,  and  he  is  at  present  engaged  in  their  separation.  It  is 
not  improbable  that  his  work  will  result  in  the  discovery  of 
elements  of  higher  atomic  weight,  for  which  there  are  vacant 
places  in  the  antimony  group,  and  also  following  tellurium  in  the 
sulphur  group. 

The  rare  elements,  described  in  Chapter  XXXIY,  now  being 
investigated  by  Crookes,  Cleve,  Nilsson,  and  others,  present  a 
problem  difficult  to  solve.  Should  it  appear,  as  believed  by  Crookes, 
that  these  elements  are  capable  of  resolution  into  an  almost 
infinite  variety  of  others,  the  conclusion  will  be  difficult  to  recon- 
cile with  the  periodic  arrangement ;  but  should  it  finally  prove,  as 
the  author  believes  to  be  more  likely,  that  they  supply  the  places 
wanting  between  the  atomic  weights  141  and  172  inclusive,  com- 
prising in  all  15  undiscovered,  or,  at  least,  unidentified,  elements, 
the  periodic  table  will  be  nearly  completed.  Time  alone  will  show 
\vhich  of  these  surmises  is  the  correct  one. 


2  T 


642 


PART  IX. 


CHAPTEE  XXXVII. 

PROCESSES   OF   MANUFACTURE. 

VARIOUS  processes  of  manufacture  will  now  be  discussed,  for  they 
cannot  be  correctly  understood  in  all  their  bearings  without  a 
previous  knowledge  of  scientific  chemistry.  In  a  work  of  this 
extent,  the  treatment  must  necessarily  be  incomplete;  and  atten- 
tion will  be  drawn  to  the  chemical  nature  of  the  changes  involved 
in  manufactures,  rather  than  to  the  mechanical  appliances  and 
plant  requisite  to  carry  them  out.  For  detailed  information  on 
such  questions,  special  treatises  must  be  consulted. 

The  matter  will  be  arranged  under  three  main  heads  : — 

1.  Combustion ;  and  means  for  generating  high  temperatures. 

2.  The  metals  :  their  extraction  from  their  ores. 

3.  Other  processes  of  chemical  manufacture  arranged,  so 
far  as  is  possible,  as  the  operations  are  carried  out  on  a  large 
scale,  those  manufactures  which  are  carried  on  under  one 
roof  being  grouped  together. 

1.  Combustion. — For  practical  purposes,  combustion  is  the 
union  of  carbon,  or  of  gases  containing  hydrogen  and  hydro- 
carbons, with  the  oxygen  of  the  air.  It  is  true  that  other  sub- 
stances burn,  and  evolve  heat,  and  that  combustion  may  take 
place  in  gases  other  than  air  ;  but  economy  prevents  the  employ- 
ment of  such  processes,  except  in  one  or  two  unimportant  in- 
stances. 

The  substance  burned  is  termed  "  fuel."  In  using  fuel,  there 
are  two  objects  which  may  be  sought  for: — (a)  to  obtain  the 
maximum  heating  effect ;  and  (&)  to  produce  the  highest  possible 
temperature.  The  maximum  amount  of  heat  obtainable  from  a 
fuel  is  termed  its  heating -power.  The  highest  temperature  which 
can  be  produced  by  burning  fuel,  under  favourable  circumstances, 
is  termed  its  calorific,  intensity. 

(a.)  Heating -power. — The  theoretical  heating-power  of  a  fuel  is 
approximately  calculable  from  its  elementary  composition.  It  is 
calculable  absolutely  in  the  theoretical  case  of  the  fuel  consisting 


HEATING-POWER  OF  FUEL.  643 

of  a  pure  element,  or  of  a  mixture  of  pure*  elements  and  pure 
combustible  compounds  in  known  proportions;  or  if  the  impurity 
itself  is  non-combustible,  and  of  known  specific  heat. 

1.  The  fuel  is  pure  carbon. — The  thermal  equation  with  pure 
wood  charcoal  is  :— C  +  02  =  C02  +  969'8K ;  whence  it  foUows 
that  I  gram  of  carbon  in  burning  to  C03  evolves  8080  cal.     This  is 
its  heating-power. 

If  the  carbon  contain  ash,  the  heating-power  relative  to  that  of 
pure  carbon  is  represented  by  the  percentage  of  carbon.  Thus,  if 
a  specimen  of  wood  charcoal  or  coke  contain  2  per  cent,  of  ash,  its 
heating-power  is  98  per  cent,  of  8080  =  7920  calories. 

2.  The  fuel   is    pure   hydrogen.  —  Hydrogen    burns   to   form 
gaseous  water,  and  the  water  is  seldom  or  never  restored  to  the 
liquid  state  by  condensation,  for  a  temperature  of  over  100°  in  the 
flue  is  required  to  keep  up  the  draught.     Hence  the  equation  is 
H2  +  0  =  H20  +  587K ;  and  multiplying  by  100  and  dividing  by 
2,  one  gram  of  hydrogen  gives  29,350  calories  when  burned.     This 
is  its  heating-power. 

3.  The  fuel  is   carbon  monoxide. — The   thermal  equation   for 
CO,    burning    to    C02,   is  :—  CO  +  0  =  C02  +  680K;    whence, 
multiplying  by  100  and  dividing  by  28,  1  gram  of  carbon  mon- 
oxide, in  burning  to  dioxide,  has  a  heating- power  of  2428  calories. 

4.  A   mixture  containing  hydrogen  and  carbon  monoxide  has 
a  heating-power  depending  on  their  relative  proportion,  and  on 
their  several  heating-powers.     Thus,  a  mixture  containing  50  per 
cent,  of  each  has  the  heating-power 

{(50  X  29,350)  +  (50  x  2428)}/100  =  15,890  calories. 

5.  The  fuel  is  a  hydrocarbon. — Suppose  the  hydrocarbon  to  be 
methane  (marsh-gas) ,  CH4.     Its  composition  is  C  =  75  per  cenl . ; 
H  =  25  per  cent.     Calculated  as  in  (4),  the  heating-power  should 
be,  were  the  carbon  and  hydrogen  free, 

{(75  x  8089)  +  (25  x  29,000)}/100  =  13,400  calories. 

It  actually  amounts  to  only  12,030  calories.  The  difference, 
1370  calories,  is  absorbed  in  decomposing  methane  into  its  elem3nts, 
and  is  lost,  so  far  as  heating-power  is  concerned. 

The  following  table  gives  the  heating-power  of  the  hydro- 
carbons up  to  C6HU  in  100  calories  =  K,  for  molecular  weights  : — 

CH4.        C2H3.      C'3H5.      C4H10.     C3H12.     C6H14. 
1925         3413        4904        6387        7889        9313        /^\^ 
A  =          1488        1491         1483         1502         1424 


644  CALORIFIC  INTENSITY. 

The  difference  is  a  nearly  regular  one  ;  hence  it  is  possible  to 
calculate  the  heat  of  combustion  of  any  paraffin,  of  which  the 
molecular  weight  is  known,  by  adding  to  1925  some  number 
approximating  to  1480  for  every  group  CH2  above  methane ; 
multiplying  by  100,  and  dividing  by  its  molecular  weight.  In 
this  manner  the  heating-power  of  liquid  fuel,  which  is  now  coming 
into  use,  may  be  calculated  with  fair  accuracy. 

6.  The  f uel  is  coal,  wood,  or  peat.  —  Only  roughly  approxi- 
mate results  can  be  calculated  from  a  knowledge  of  the  percentage 
composition  of  the  fuel,  since  the  data  are  wanting  for  the  heat  of 
union  of  the  carbon,  hydrogen,  and  oxygen  in  the  fuel.  It  is 
customary,  but  incorrect,  to  suppose  that  the  oxygen  is  already 
combined  with  hydrogen  as  water,  and  to  calculate  the  heat  of 
combustion  of  the  residue  as  if  it  consisted  of  a  mixture  of  free 
carbon  and  gaseous  hydrogen.  Hence  it  is  found  by  the  formula : 
Heating-power  =  8080C  +  29,850 (H  -  J0)/100.  For  such  com- 
plex fuels  a  practical  essay  is  best. 

(&.)  Calorific  intensity. — The  highest  temperature  theoretically 
obtainable  from  a  fuel  may  be  calculated  ;  but  here  the  values 
obtained  are  usually  far  from  the  truth.  The  calorific  intensity 
depends  on  the  heat  of  combustion  of  the  fuel,  and  as  the  heat  is 
employed  in  raising  the  temperature  of  the  products  of  combustion, 
it  also  depends  on  their  specific  heat ;  and  as  air  is  almost  always 
used  to  promote  combustion,  a  quantity  of  inert  gas,  viz.,  nitrogen, 
has  also  to  be  heated;  nor  is  this  all;  for  more  air  must  be 
admitted  than  can  be  wholly  utilised  ;  hence  the  excess  of  air  has 
also  to  be  heated.  We  must  know,  therefore,  in  order  to  make  an 
approximate  calculation,  the  heating- power  of  the  fuel ;  the 
amount,  and  the  specific  heat  of  the  products  of  combustion ;  the 
specific  heat  of  nitrogen  and  that  of  air. 

1.  Suppose  the  fuel  to  be  pure  carbon  burned  in  oxygen. 
The  heating-power  of  12  grams  of  carbon  is  97,000  calories.  It 
forms  44  grams  of  carbon  dioxide,  the  specific  heat  of  which  is 
usually  taken  as  0'2164.  Now,  12  grams  of  carbon,  in  burning  to 
carbon  dioxide,  would  raise  the  temperature  of  97,000  grams  of 
water  through  1°.  It  would  raise  the  temperature  of  44  grams  of 
water  through  97,000/44  =  2204°.  But  as  the  specific  heat 
of  carbon  dioxide  is  0'2614,  it  should  raise  the  temperature  of 
44  grams  of  C02,  its  product  of  combustion,  through  2204/0  2164 
=  10,184°.  Now  it  has  been  shown  by  E.  Wiedemann  that  the 
specific  heat  of  carbon  dioxide  is  not  constant,  being  at  100° 
0-2169,  and  at  200°  0'2387 ;  hence  the  assumption  that  it  is  a  con- 
stant is  unwarranted,  and  the  temperature  calculated  above  is 


PYROMETERS.  645 

certainly  too  High.  Bat  for  another  reason  the  result  is  totally 
fallacious.  Carbon  dioxide  dissociates  long  before  such  a  tempera- 
ture is  reached;  it  begins  to  dissociate,  indeed,  at  1200 — 1300°. 
It  is,  therefore,  improbable  that  the  temperature  as  as  high  as 
2000°. 

2.  As  a  further  example  of  the  method  of  calculation,  an 
instance  is  chosen  where  the  fuel  is  a  hydrocarbon,  viz.,  methane, 
CH4 ;  it  is  supposed  to  be  burnt  in  twice  as  much  air  as  is 
necessary  for  complete  combustion.  The  data  are  as  follows  : — 

16  grams  of  methane  evolve,  on  burning,  192,500  calories, 
and  produce  carbon  dioxide,  „  44  grams, 

and  water-gas,  „  36       „ 

consuming  oxygen  ,,  64       „ 

equivalent  to  air,  containing  nitrogen        256       „ 
but  also  part  with  heat  to  320       „ 

of  air.     The  heat  evolved  is,  therefore,  utilised  in  raising  the  tem- 
perature of  a  mixture  of  carbon  dioxide,  water-gas,  nitrogen,  and 
air.     Their  specific  heats  are  given  as  CO2  =  0'2164 ;  H20  gas  = 
0-475  ;  X  =  0-244 ;  and  air  =  0-238. 
The  temperature  is,  therefore, 

T 192,500 

"  (44  x  0-2164)  +  (36  x  0'475)  +  (256  x  0'244)  +  (320  x  0'238) 

This  is  a  probable  result,  as  the  amount  of  dissociation  at  1167° 
can  be  but  small ;  but  it  is  still  inaccurate,  owing  to  the  assump- 
tion that  the  specific  heats  of  carbon  dioxide  and  water-gas  are 
constant  between  200  and  1200°. 

Apparatus  for  measuring  high  temperatures :  pyrometers. 

— For  detailed  description  of  such  instruments,  a  treatise  on  Techni- 
cal Chemistry  must  be  consulted  ;  the  principles  involved  depend 
on  the  following  considerations  : — 

1.  The  expansion  of  a  gas.  A  cylindrical  bulb  of  porcelain,  or 
of  platinum,  provided  with  a  long  capillary  neck,  the  capacity  of 
which  is  small  in  comparison  with  that  of  the  bulb,  is  heated  in 
the  furnace  of  which  the  temperature  is  to  be  measured.  The 
escaping  air  is  collected  and  measured.  By  this  means  tempera- 
tures as  high  as  1700°  have  been  measured.  A  similar  method 
consists  in  confining  the  air  or  other  gas  at  constant  volume,  and 
noting  the  rise  of  pressure  produced  by  the  increased  tempera- 
tures. Both  of  these  methods  involve  calculation,  but  are  subject 


646  -FUELS. 

to    errors    small     in    comparison    with    the    total    temperature 
measured. 

2.  Water  is  caused  to  circulate  through  a  spiral  tube  exposed  to 
the  heat.     Its  temperature  on  entering  the  tube  is  read  by  means 
of  a  thermometer,  as  also  its  temperature  on  leaving.     Compara- 
tive measurements  are  thus  possible,  the  rate  of  flow  being  main- 
tained constant. 

3.  Siemens'    pyrometer  consists  of  a   platinum  wire,  through 
which  a  current  is  passed,  exposed  to  the  high  temperature.     Its 
resistance  is  increased  by  rise  of  temperature,  and  the  increase  is 
measured.     A  formula    having    been    obtained  showing  the  ratio 
between  the  rise  of  resistance  and  the  temperature,  the  latter  can 
be  calculated. 

4.  The  fusing-points  of  a  number  of  salts  have  been  determined 
with  fair  accuracy  by  Carnelley  and  Williams  up  to  about  900°. 
By  noting  the  particular  salts  which  fuse,  or  which  remain  unfused, 
at  the  temperature  to  be  measured,  an  estimation  may  be  made  to 
within  10—20°.* 

5.  For  higher  temperatures,  cones  are  sold  by  the  Jena  Glass 
Company,    composed    of   various    silicates,    by   means   of    which 
approximate  estimations  may  be  made  in  a  similar  manner. 

The  first  is  the  standard  method,  but  is  sometimes  inconvenient 
of  application.  Siemens'  pyrometer  gives  good  results ;  and  a 
sixth  method,  depending  on  the  communication  of  heat  from  an 
iron  ball  heated  in  the  furnace  in  a  clay  tube  to  water,  into  which 
it  is  dropped,  also  yields  fairly  accurate  results. 

Varieties  of  fuel. — Coal  consists. of  carbon,  hydrogen,  oxygen, 
nitrogen,  and  ash  composed  of  silicates,  sulphates,  and  phosphates 
of  alumina,  iron,  lime,  and  magnesia.  It  usually  contains 
some  iron  pyrites.  The  varieties  of  coal  may  be  classified  as 

follows-: — 

Oxygen  and 

Carbon,  p.  c.  Hydrogen,  p.  c.  Nitrogen,  p.  c. 

1.  Caking  coal 83'0— 88'0  5'0— 5'2  3'0— 5'5 

2.  Splint  coal 75'0— 83'0  6'3— 6'5  5'0— 10'5 

3.  Cherry,  or  soft  coal     81'0— 85'0  5'0— 5'5  8'5— 12'0 

4.  Cannelcoal 83'0— 86'5  5'4— 57  8'0— 12'5 

5.  Anthracite 90'0— 94'0  1'5— 4  0  3'0— 4'8 

The  first,  as  its  name  implies,  "  cakes  "  readily,  and  undergoes  a 
semifusion  when  heated,  which  causes  it  to  become  spongy.  The 
.second  ioes  not  cake,  but  burns  brightly.  The  third  does  not 
cake,  b  it  is  easily  broken  ;  it,  as  well  as  the  second,  is  much 

*  For  a  list  of  such  salts,  see  Chem.  Soc.,  33,  273-281. 


FUELS.  647 

used  for  household  purposes.  The  fourth  is  used  for  gas  manu- 
facture, as  it  evolves  much  more  gas  and  oils  when  distilled  than 
any  of  the  other  varieties.  It  is  hard,  and  does  not  soil  the  fingers. 
"  Jet "  is  a  special  variety  of  cannel  coal. 

Coke  is  produced  by  charring  or  distilling  coal,  either  by  heat- 
ing the  coal  in  open  heaps,  covered  to  prevent  too  free  access  of 
air,  or  by  distilling  coal  in  coke  ovens.  It  consists  almost  entirely 
of  carbon  and  ash.  During  its  formation,  gases  escape,  consist- 
ing mainly  of  compounds  of  carbon  and  hydrogen,  some  of  which 
may  be  liquefied,  and  of  ammonia,  most  of  which  is  now  recovered 
by  "  scrubbing "  with  water,  i.e.,  by  causing  the  gases  to  pass 
through  water  contained  in  [J  -shaped  iron  tubes.  The  amount  of 
coke  prod  lined  from  different  varieties  of  coal  varies  within  wide 
limits.  From  some  coals  80  per  cent,  of  coke  may  be  obtained, 
while  others  yield  as  little  as  56  per  cent.  Anthracite  furnishes 
from  85  to  92  per  cent,  of  coke. 

Gaseous  fuels. — These  are  produced  in  one  of  two  ways. 
Either  the  coal  is  distilled  in  a  special  form  of  apparatus  termed  a 
*'  producer,"  by  the  combustion  of  a  portion ;  or  steam  is  led 
through  white-hot  coke.  If  produced  by  the  latter  method,  the 
product  is  termed  "  water-gas,"  The  Siemens  gas  producer  has 
been  found  to  yield  the  following  mixture  of  gases : — 

CO2.  CO.  N.  H.         Hydrocarbons. 

4—6        21-5—24        60—64,        5'2— 9'5         1-3—2-6    p.  c.  by  volume. 

Produced  by  the  latter  method,  the  gases  have  been  found  to 
consist  of — 

CO.  H.  N.  CO2. 

28-6  14-6  53-0  4'0 

The  nitrogen  is  due  to  the  air  forced  into  the  fuel  along  with 
the  steam. 

Liquid  fuels. — These  consist  of  natural  oils,  consisting  mainly 
of  hydrocarbons.  The  fuel  is  burnt  by  injection  by  means  of  com- 
pressed air  against  a  plate,  or  a  bed  of  coke ;  by  percolation 
upwards  through  a  bed  of  heated  fire  bricks  ;  by  vaporisation  in  a 
separate  still,  the  products  of  distillation  being  burned ;  or  by  in- 
jection by  means  of  superheated  steam.  The  last  plan  is  said  to 
yield  the  best  results. 

To  ensure  complete  combustion  of  solid  fuels,  such  as  coal,  a 
regular  supply  of  combustible  must  be  introduced  into  the 
furnace.  The  stoking  is  now-a-days  often  performed  mechanically, 
sometimes  by  travelling  fire-bars,  sometimes  by  the  introduction 
at  regular  intervals  of  time  of  known  amounts  of  fuel  below  the 


648  USE  OF  FUEL. 

ignited  mass,  so  that  the  gases  distilled  off  by  the  heat  may  travel 
upwards  through  the  incandescent  upper  layer,  and  so  be  com- 
pletely burned  at  the  surface,  where  they  mix  with  air, 

Uses  of  fuel. — The  chief  uses  to  which  fuel  is  put  is  (1)  in 
evaporation;  the  flame  and  hot  gases  are  either  allowed  to  pass 
over  the  surface  of  the  liquid  to  be  evaporated  (surface  evapora- 
tion), which  is  contained  in  long  tanks  ;  or  they  impinge  at  the 
bottom  of  flat  shallow  pans  filled  with  the  solution  to  be  evapo- 
rated. The  "Yaryan"  system,  which  is  now  coming  largely  into 
use,  and  which  is  a  very  economical  one,  consists  in  the  use  of  a 
number  of  straight  tubes  passing  from  end  to  end  of  a  shell,  arid 
coupled  to  each  other  at  their  ends  by  connecting  tubes.  The 
liquid  flows  through  these  tubes,  which  are  kept  vacuous  by  a 
pump  and  heated  with  steam.  Three  or  more  such  sets  of  tubes 
are  worked  in  concert,  the  vacuum  being  maintained  at  the  exit 
from  the  last  set.  The  steam  from  the  first  set  serves  to  heat  the 
tubes  in  the  second,  and  that  from  the  second  heats  the  third  set 
of  pipes.  The  temperature  is  thus  kept  low,  for  the  liquid  boils 
under  reduced  pressure;  the  surface  for  evaporation  is  large  and 
constantly  renewed,  and  the  heat  is  economised,  since  the  steam 
derived  from  the  first  set  of  pipes  is  utilised  in  heating  the  second, 
and  that  from  the  second  goes  to  heat  the  third. 

2.  Distillation. — This  operation  is  not  frequently  practised  in 
the  manufacture  of  compounds  other  than  those  of  carbon.     The 
apparatus  is  usually  of   the    simplest    description ;    the    heat    is 
applied  by  an  open  fire  to  a  retort  connected  with  a  condensing 
worm,  as  in  the  manufacture  of  nitric  acid  ;  by  the  products  of 
combustion  of  coal,  as  in  distilling  zinc,  sodium,  phosphoruSj  &c., 
from  cJay  retorts ;  or  a  large   Bunsen  burner  is  used  as  source  of 
heat,  as  in  the  evaporation  of  sulphuric  acid  in  glass  vessels,  which 
is  in  reality  effected  by  distillation.     For  carbon  compounds,  such 
as  alcohol,  hydrocarbons,  &c.,  more  complicated  forms  of  apparatus 
are  used  ;  but  the  method  of  heating  is  of  the  simplest  kind  ;  either 
a  direct  flame  or  a  steam  jacket  is  employed. 

3.  Reverberatory  furnaces. — In  such  furnaces  the  products    of 
combustion    come  into  direct  contact  with    the  substances  to  be 
heated.     Such  furnaces  serve  for  the  calcination  of  ores,  for  firing 
porcelain  and  bricks,  and  in  glass  making  ;  in  the  last  instance, 
the  glass  is  contained  in  fire-clay  pots,  which   are  exposed  to  the 
products  of  combustion  of  coal  burned  in  a  separate  compartment. 

In  other  operations,  the  solid  fuel  comes  into  direct  contact 
with  the  object  to  be  heated,  as  in  lime-burning,  in  lead-smelting, 
and  in  iron-smelting.  In  some  cases  combustion  is  furthered  by  a 


REGENERATIVE  FURNACES.  649 

blast  of  air ;  and  if  the  blast  be  heated,  a  great  saving  in  fuel  is 
effected,  for  the  temperature  in  the  furnace  is  higher,  less  heat 
being  withdrawn  from  the  furnace  in  heating  the  air.  This 
process  is  made  use  of  in  iron-smelting  ;  and  the  Siemens 
regenerative  furnace  is  constructed  on  a  similar  principle ;  but  in 
the  latter  case  ifc  is  extended,  so  that  the  gaseous  fuel  employed  is 
also  heated.  The  "regenerators"  are  large  chambers  constructed 
of  fire-clay  bricks,  and  filled  loosely  with  bricks.  The  products  of 
combustion  pass  from  the  chamber  in  which  the  combustion  takes 
place  through  these  chambers,  before  escaping  into  the  flues.  The 
gases  part  with  their  heat  to  the  bricks  ;  and,  after  a  certain  time, 
a  second  pair  of  similar  chambers  is  brought  into  operation.  The 
current  is  then  reversed,  by  opening  appropriate  valves,  and  the 
air  enters  through  one  of  the  already  hot  chambers,  while  the 
"  producer  "  gas  is  heated  by  the  other.  As  before,  the  products 
of  combustion  pass  through  the  second  pair  of  chambers.  When 
the  first  pair  has  grown  cool,  and  the  second  pair  hofc,  the  current 
is  again  reversed.  By  this  means  a  great  saving  in  heat  is 
effected ;  for  the  heat  of  the  escaping  gases,  instead  of  being  dissi- 
pated, is  to  a  great  extent  trapped  by  the  brick  chambers  and 
utilised. 

Such  furnaces  are  employed  in  iron-smelting,  in  glass  making, 
and,  indeed,  in  most  chemical  operations  where  economy  of  fuel  is 
an  object.  It  is  also  possible,  in  using  such  regenerators,  to 
render  the  flame  oxidising  or  reducing  as  required,  by  regulating 
the  relative  amounts  of  air  and  producer-gas.  The  air  and  gas 
mix  and  burn  at  the  spot  where  the  high  temperature  is  required. 

For  certain  operations  where  a  sudden  intense  and  uniform  rise 
of  temperature  is  required,  the  heat  radiated  from  flame  is  made 
use  of.  Before  describing  the  device  adopted  to  secure  such 
flames,  the  subject  of  flame  must  be  itself  considered. 

The  cause  of  the  luminosity  of  flame  has  long  been  a  question 
under  discussion.  It  has  been  urged  on  the  one  hand,  that  the 
presence  of  solid  particles  rendered  incandescent  by  a  high  tem- 
perature is  essential  to  light;  and  the  luminosity  of  the  flame  of 
a  candle  or  of  burning  hydrocarbons  has  been  ascribed  to  the 
presence  in  the  flame  of  particles  of  white-hot  carbon.  In  a  candle 
flame  there  are  three  separate  regions  or  zones ;  first  the  faintly 
blue  interior  cone,  where  the  compound  of  carbon  with  hydrogen, 
or  of  carbon  with  hydrogen  and  oxygen,  is  being  partly  distilled, 
partly  decomposed  into  other  hydrocarbons  and  free  carbon  by  the 
heat  radiated  towards  the  wick  by  the  luminous  zone.  Next 
follows  the  luminous  zone,  to  which  the  oxygen  of  the  air  has  some 


650  RADIANT-HEAT   FURNACES. 

access,  but  is  yet  not  present  in  quantity  sufficient  for  complete 
combustion  ;  and  last,  there  is  the  indefinite  hazy  bluish-pink  zone, 
surrounding  the  luminous  zone,  where  the  combustion  is  com- 
pleted. In  a  candle  flame  it  has  been  conclusively  proved  that 
incandescent  solid  particles  are  present ;  because  if  the  sun's  rays 
be  focussed  on  the  flame  by  a  lens,  the  light  emitted  from  the 
brilliant  spot  is  seen  to  yield  the  absorption-bands  peculiar  to  the 
solar  spectrum  when  viewed  through  a  spectroscope.  Now,  gases 
cannot  reflect  light,  but  only  solids  and  liquids.  It  is  unlikely 
that  liquids  are  present ;  but  it  is  exceedingly  probable  that 
unburnt,  yet  white-hot,  particles  of  carbon  are  present.  Of 
course  if  a  plate  be  held  over  the  flame  of  a  candle,  it  will  be 
smoked ;  this  would  appear  to  favour  such  a  conclusion  ;  yet  it  is 
not  inconceivable  that  the  presence  of  a  cold  body,  such  as  a  plate, 
should  produce  that  separation  of  carbon  for  which  it  is  intended 
as  a  test.  Such  presence  is,  however,  proved  indubitably  by  the 
reflection  of  the  solar  spectrum.  Yet  it  has  been  shown  that  a  gas, 
such  as  hydrogen,  burning  under  high  pressure,  gives  a  luminous 
flame ;  and  the  Bunsen  flame,  non-luminous  because  of  the  com- 
plete combustion  of  the  gas,  may  be  rendered  luminous  if  its 
temperature  be  raised  by  heating  the  tube  through  which  it  issues. 
The  luminosity  of  a  coal-gas  flame  is  caused  by  the  presence  in  it  of 
solid  carbon  particles,  produced  by  the  incomplete  combustion  of 
hydrocarbons  of  the  ethylene  and  acetylene  series,  and  by  the 
vapours  of  benzene,  C6H6,  and  naphthalene,  C10H8,  the  vapour- 
pressures  of  which  are  sufficiently  high  at  the  ordinary  tempera- 
ture to  permit  of  their  existing  as  gases,  when  mixed  with  such 
gases  as  hydrogen,  methane,  and  carbon  monoxide,  which  are  the 
other  chief  constituents  of  coal-gas. 

By  regulating  the  supply  of  producer  gas  and  air,  and  by  a 
special  construction  of  furnace,  whereby  the  flame  is  allowed  to 
pass  without  striking  the  arch  of  the  combustion  chamber,  Siemens 
has  succeeded  in  producing  a  luminous  flame,  the  radiating  power 
of  which  is  very  great.  While  non-luminous  flames  give  up  their 
heat  by  contact,  luminous  particles  lose  heat  chiefly  by  radiation. 
Hence  the  temperature  of  such  a  flame  is  very  intense  ;  it  may  be 
so  adjusted  as  to  be  evenly  distributed ;  and  by  its  means  large 
sheets  of  cold  plate  glass  may  be  heated  to  the  softening  point 
without  cracking  in  less  than  two  minutes.  Such  flames  are 
capable  of  other  applications. 


651 


CHAPTEE  XXXVIII. 

COMMERCIAL   PREPARATION   OF  THE    ELEMENTS. 

THE  preparation  of  many  of  those  elements  which  are  of  commer- 
cial importance  has  already  been  indicated ;  the  reactions  by  which 
some  are  obtained  are,  however,  somewhat  complicated,  and  their 
manufacture  is  best  described  here. 

1 .  Sodium. — The  process  which  has  now  superseded  all  others 
is  that  of  Castner.*  It  consists  in  heating  to  bright-redness  a 
mixture  of  iron,  carbon,  and  caustic  soda.  Its  advantages  over 
the  older  method,  in  which  a  mixture  of  lime,  sodium  carbonate, 
and  coke  was  heated,  is  that  the  carbon,  being  weighted  by  the 
iron,  sinks,  and  is  thus  brought  in  contact  with  the  fused  caustic 
soda  ;  whereas,  by  the  older  process,  contact  between  the  reacting 
materials  was  by  no  means  so  perfect.  The  iron  in  a  spongy, 
finely-divided  state,  reduced  from  its  oxide  without  fusion  by 
carbon  monoxide  or  hydrogen,  is  impregnated  with  tar  and  heated 
to  redness.  The  hydrocarbon  is  decomposed,  and  a  mixture  of 
70  per  cent,  of  iron  with  30  per  cent,  of  carbon  is  left.  This  mix- 
ture is  ground  and  mixed  with  such  a  quantity  of  caustic  soda  as 
to  correspond  with  the  equation 


6NaOH  +  2(Fe,C2)  =  6Na  +  ^Fe  +  2CO  +  2C03  +  3H2; 

this  corresponds  to  22  Ibs.  of  carbon  to  every  100  Ibs.  of  caustic 
soda.  The  mixture  is  placed  in  large  cast-iron  crucibles,  each  of 
which  stands  on  a  circular  platform,  which,  when  raised,  is  flush 
with  the  hearth  of  the  furnace,  but  which  can  be  lowered  by  aid  of 
hydraulic  power,  the  platform  and  crucible  then  sinking  into  a 
chamber  below  the  furnace.  The  crucibles,  when  raised,  fit  a 
retort-head,  also  of  iron,  an  asbestos  collar  being  interposed  to 
secure  better  junction.  The  heat  is  derived  from  a  Siemens  gas 
furnace.  When  the  crucibles  reach  1000°  C.,  sodium  distils  freely, 
and  passes  through  the  tube  projecting  from  the  crucible  cover, 
whence  it  falls  into  heavy  oil.  As  soon  as  an  operation  is  finished, 

*  Chem.  News,  54,  218. 


652  METALLURGY   OF   ALUMINIUM. 

the  crucible  is  lowered,  seized  with,  travelling  tongs,  emptied,  re- 
filled, and  before  its  temperature  has  had  time  to  fall,  replaced  in 
position.  The  residue  consists  of  a  little  sodium  carbonate  and 
the  iron  of  the  so-called  "  carbide."  It  is  treated  with  warm 
water,  and  the  soluble  carbonate  is  afterwards  causticised  with 
lime  ;  while  the  iron  is  dried,  mixed  with  tar,  and  re-coked,  to 
serve  for  another  operation.  A  crucible  is  charged  every  two 
hours,  which  is  the  length  of  time  occupied  by  a  distillation. 

2.  Magnesium. — The  process  is  sufficiently  described  on  p.  35. 
The  equation  is  KCl.MgClo  +  2Na  =  KC1  +  2NaCl  +  Mg. 

3.  Zinc. — The  ore,  consisting  of  a  mixture  of  blende  (black- 
jack),   ZnS,    calamine,     ZnCOs,    calamine-stone,    ZnSiOa.HoO,    and 
gahnite,  ZnO.Al203,  is  roasted  on  a  flat  hearth  at  a  dull  red  heat, 
to  expel  sulphur  as  sulphur  dioxide,  and  also  water  ;  the  resulting 
oxide  and  silicate  of  zinc  is  then  mixed  with  coke  and  distilled 
from  tubular  retorts  of  fire-clay,  and  condensed  in  tubes  of  sheet- 
iron,  secured  to  the  mouths  of  the  retorts  by  fire-clay  ;  or  it  is  dis- 
tilled downwards,  as  with  magnesium  (see  p.  34,  Fig.  4).     The 
reaction  is: — ZnO  +C  =  CO  +  Zn. 

4.  Aluminium. — There  are  three  processes  in  operation  for  the 
commercial  preparation  of  aluminium — (a.)  Reduction  of  the  chlor- 
ide by  means  of  sodium.     The  double  chloride  of  aluminium  and 
sodium,  prepared  by  passing  chlorine  over  a  bright  red-hot  mixture 
of  clay,  finely  ground  charcoal,  lamp-black,  oil,  and  salt,  is  volatile, 
and  sublimes  in  crystals.     It  always  contains  a  little  chloride  of 
iron,  which  even  in    small   quantity  impairs  the   quality  of  the 
aluminium  obtained.     The  iron  is  removed  by  fusing  the  double 
chloride,  and  introducing  a  little  metallic  aluminium,  which  dis- 
places metallic  iron  from  its  chloride.     The  metallic  iron  sinks, 
leaving  perfectly  white  double  chloride,  which  is  much  less  deli- 
quescent than  the  impure  substance.     This  double  chloride,  of  the 
formula  3NaCl.AlCl3,  is  mixed  with  finely  cut  sodium,  in  a  wooden 
agitator,  and  placed  on   the  hearth   of   a    Siemens'   regenerative 
furnace ;  a  brisk  action  takes  place  at  once,  and  the  aluminium  is 
run  off  into  moulds.     The  residue  is  treated  with  water  to  recover 
the  salt,  together  with  any  undecomposed  chloride,  from  which  the 
alumina  is  recovered  by  precipitation  as  hydrate. 

(b.)  Reduction  of  m/o/^e(sodium  aluminiumflnoride,3N"aF.AlF3) 
by  means  of  sodium. — The  furnace  is  a  flat  chamber,  in  the  upper 
surface  of  which  there  are  holes,  through  which  crucibles  contain- 
ing melted  cryolite  and  salt  may  be  reached.  An  iron  rod,  with  a 
hollow  cylinder  at  one  end,  is  made  use  of  for  the  purpose  of  con- 
veyirg  the  sodium  into  the  melted  mass.  The  hollow  cylinder  is 


METALLURGY  OF  ALUMINIUM.  653 

filled  with  sodium,  and  plunged  by  a  workman  into  the  crucible ; 
at  the  high  temperature  of  the  fused  cryolite,  the  sodium  gasifies, 
and  its  vapour  passing  upwards  through  the  molten  cryolite, 
deprives  it  of  its  fluorine,  metallic  aluminium  being  produced. 
The  metal  sinks  to  the  bottom  of  the  crucible,  and  after  a  sufficient 
quantity  has  been  reduced,  it  is  poured  out  of  the  crucible  into 
moulds. 

(c.)  By  means  of  the  electric  furnace. — This  process  is  not  suc- 
cessful in  producing  metallic  aluminium,  for  it  remains  mostly 
disseminated  through  the  carbon ;  but  it  is  well  adapted  for  the 
manufacture  of  alloys.  The  furnace  consists  of  an  oblong  fireclay 
box,  into  which  project  at  each  end  thick  rods  of  gas-carbon,  con- 
nected by  means  of  copper  cables  with  a  powerful  dynamo-electric 
machine.  The  furnace  is  charged  with  a  mixture  of  corundum, 
(A1203),  metallic  copper,  and  fine  particles  of  charcoal  coated  with 
lime  to  render  it  non-conducting.  On  passing  the  current,  an 
enormously  high  temperature  is  produced ;  the  carbon  poles,  which 
at  first  are  almost  in  contact,  are  gradually  drawn  apart,  and  the 
electric  arc  leaps  between  them.  The  alumina  is  deprived  by  the 
carbon  of  its  oxygen,  and  the  copper  boils  ;  the  separated  aluminium 
is  washed  down  by  the  liquid  copper  and  the  aluminium  bronze, 
as  the  alloy  is  termed,  which  contains  over  15  per  cent,  of  alumi- 
nium, collects  on  the  bottom  of  the  furnace,  and  is  removed  by 
tapping  a  hole.  That  the  process  is  a  true  reduction,  and  not 
dependent  on  the  electrolysis  of  alumina,  is  proved  by  the  fact  that 
an  alternating  current  may  be  employed ;  and  such  a  current  is 
incapable  of  electrolysing  a  compound. 

Magnesium  and  aluminium  are  obtained  by  the  use  of  sodium. 
The  remainder  of  the  metals  industrially  prepared  are  reduced  by 
aid  of  carbon. 

5.  Iron. — A  list  of  the  ores  of  iron  is  given  on  pp.  244,  248, 251, 
and  288.  The  ores  are  roasted  to  remove  water,  carbon  dioxide,  and 
carbonaceous  matter  ;  to  render  them  more  dense  ;  and  to  oxidise 
any  ferrous  iron  (as  in  spathic  ore,  black  band,  and  clay-band)  into 
ferric  oxide.  The  roasted  ore  is  then  stamped  or  crushed  into  frag- 
ments as  large  as  a  fist.  It  is  then  introduced  into  a  blast  furnace 
along  with  alternate  layers  of  coal  and  limestone.  The  blast  furnace, 
which  is  often  80  feet  in  height,  consists  of  an  outer  wall  of  brick, 
an  inner  space,  fitted  with  loose  scoriae,  or  refractory  sand,  to  allow 
for  expansion  ;  and  an  inner  wall  of  firebrick.  The  upper  portion  of 
the  furnace  is  termed  the  "  shaft ;"  the  cup-shaped  part  of  t  ;e  fur- 
nace is  named  the  "  boshes,"  and  the  lower  cylindrical  part  is  named 
the  "  throat,"  or  "  tunnel-hole,"  terminating  in  the  "  crucible,"  or 


654  METALLURGY   OF  IRON. 

"  hearth."  The  combustion  of  the  fuel  is  furthered  by  a  blast  of 
hot  air  (at  200— 400°  C.)  through  the  "tuyeres,"  or  "  twyers," 
forced  in  under  a  pressure  of  3  or  4,  or  even  10,  Ibs.  per  square 
inch.  It  is  usual  now,  instead  of  allowing  the  furnace  gases  to 
escape,  to  cause  a  conical  cover,  which  can  be  depressed  into  the 
mouth  of  the  furnace,  to  force  the  products  of  combustion  through 
':  scrubbers,"  or  iron  absorbing  vessels,  containing  water,  whereby 
potassium  cyanide  and  other  products  are  condensed.  Although 
pure  iron  has  a  very  high  fusing-point,  iron  containing  3  to  4  per 
cent,  of  carbon  melts  at  about  1100°,  and  hence  it  is  possible  to 
smelt  it  in  such  a  furnace. 

The  reactions  occurring  are  very  complicated.  The  coal  burns 
to  carbon  monoxide  and  dioxide ;  it  also  contains  nitrogen  and 
salts  of  potassium,  and  yields  potassium  cyanide,  which  has  a 
reducing  action ;  the  reduced  iron  acts  on  the  oxides  of  carbon, 
reproducing  carbon,  and  re-forming  oxides  of  iron.  The  following 
equations  express  the  changes  which  occur  : — 

1.  Fe2O3  +  CO  =  2FeO  +  CO2.          7.  2CO  =  C  +  C02. 

2.  FeO  +  CO  =  Fe  +  CO2.  8.  Fe2O3  +  C  =  2FeO  +  CO. 

3.  Fe  +  CO2  =  FeO  +  CO.  9.  2Fe2O3  •+  C  =  4FeO  +  C02. 

4.  2  FeO  +  C02  =  Fe2O3  +  CO.  10.  FeO  +  C  =  Fe  +  CO. 

5.  2FeO  +  CO  =  Fe2O3  +  C.  11.  C  +  CO2  =  2CO. 

6.  Fe  +  CO  =  FeO  +  C. 

Many  of  these  equations,  it  will  be  noticed,  are  the  converse  of 
others;  the  reactions  take  place  in  an  inverse  sense  in  different 
parts  of  the  furnace.  Besides  these  changes,  others  take  place  in 
which  potassium  cyanide  plays  a  part : — 

12.  2KCN  +  3FeO  =  K2O  +  2CO  +  N2  +  3Fe. 

13.  2CO  =  C  +  CO2;  and  14.  K2O  +  CO2  =  K2CO3. 

The  carbonate  is  carried  down  and  reconverted  into  cyanide  in 
the  throat  of  the  furnace.  The  actual  reduction  takes  place  near 
the  tuyeres  ;  only  one  half  or  one  quarter  of  the  carbon  monoxide 
is  utilised ;  carbon  deposits,  however,  in  the  middle  of  the  furnace, 
about  25  feet  above  the  hearth. 

When  a  sufficient  amount  of  iron  has  collected  in  the 
crucible,  a  workman  makes  a  hole  in  the  clay  plug  which  confines 
the  iron,  and  allows  it  to  flow  into  wide  channels  termed  "  sows," 
whence  it  diverges  into  narrower  moulds,  named  "pigs;"  hence 
the  name  "  pig  iron."  The  slag  which  is  formed  by  the  combina- 
tion of  the  silica  existing  as  an  impurity  in  the  ore  with  the  lime, 
and  with  some  of  the  iron  oxide,  is  lighter  than  iron,  and  floats  on 


METALLURGY  OF  IRON.  655 

its  surface.  It  fuses,  and  runs  off  after  the  iron  has  flowed  away. 
This  slag  is  sometimes  made  use  off  for  coarse  glass. 

There  are  two  main  varieties  of  pig  iron,  grey  and  white ;  and 
there  are  intermediate  varieties  known  as  "  mottled."  These  all 
contain  carbon,  often  as  much  as  6  per  cent. ;  but  while  the  carbon 
in  the  white  pig  is  in  combination  with  the  iron  forming  a  carbide, 
of  which  the  formula,  however,  has  not  been  determined,  that  in 
the  grey  pig  is  partly  present  in  the  free  state  as  graphite.  On 
treatment  with  acids,  the  combined  carbon  escapes  in  combination 
with  hydrogen,  chiefly  in  the  form  of  hydrocarbons  of  the  ethylene 
series ;  while  the  free  carbon  remains  unaffected  by  acids.  But 
both  varieties  are  left  if  the  iron  is  treated  with  a  solution  of 
copper  sulphate,  which  dissolves  the  iron  as  sulphate,  leaving 
copper  in  its  place.  The  specific  gravity  of  the  white  iron  is  the 
higher,  varying  between  7'58  and  7'68;  that  of  grey  pig  has  a 
specific  gravity  of  about  7.  The  production  of  one  or  other  variety 
depends  on  the  temperature  of  the  furnace.  The  white  cast  iron 
is  produced  at  the  lower  temperature,  while  the  grey  pig  is  formed 
as  the  temperature  rises.  If  the  grey  pig  be  melted  and  suddenly 
cooled,  it  solidifies  as  white  pig,  the  carbon  being  retained ;  but  if 
heated  strongly  and  cooled  slowly,  the  carbon  has  time  to  separate. 
For  castings,  a  mixed  pig  is  best,  being  more  fluid,  and,  when  it 
solidifies,  closer-grained.  The  iron  is  remelted  in  a  cupola,  a 
cylindrical  furnace  about  9  or  12  feet  high,  cased  in  iron-plate,  and 
the  iron  is  run  into  moulds  made  of  a  mixture  of  sand  and  pow- 
dered charcoal  with  a  little  clay,  or  of  loam,  or  of  iron.  If  iron 
moulds  are  used,  the  casting  is  rapidly  cooled  on  the  exterior,  and 
is  said  to  be  case-hardened. 

The  operation  of  removing  carbon  and  other  impurities  from 
the  iron  is  termed  "  refining."  This  is  accomplished  either  by 
heating  the  iron  on  a  hearth,  a  blast  of  air  being  directed  on  to  the 
melted  iron.  The  carbon  is  oxidised  to  carbon  monoxide ;  the 
silicon  in  the  oxide  iron  is  converted  into  silica,  which  combines 
with  ferrous  oxide  resulting  from  the  oxidation  of  the  iron  to 
form  ferrous  silicate  ;  this  forms  a  slag  and  protects  the  iron. 
This  slag  is  subsequently  mixed  with  forge- scales  (oxides  of  iron), 
and  made  use  of  in  refining  a  further  charge  of  crude  iron ;  the 
oxygen  of  the  iron  oxides  unites  with  the  carbon  of  the  crude  iron 
forming  carbon  monoxide,  which  escapes,  while  malleable  iron  is 
left.  The  "bloom"  of  iron,  a  spo-igy  semifused  mass,  is  placed 
under  a  steam  hammer,  and  the  enclosed  slag  removed  by  repeated 
blows.  Another  plan  of  refining,  which  has  much  similarity  with 
the  one  described,  is  termed  "puddling."  The  flame  of  a  rever- 


656  STEEL. 

beratory  furnace  plays  on  the  white  cast  iron,  placed  on  a  hearth 
of  slag  containing  iron-scales ;  when  the  iron  has  melted  it  is 
spread  over  the  hearth  by  means  of  a  rake,  and  continually  stirred 
about;  this  is  the  operation  termed  "puddling."  Flames  of 
burning  carbon  monoxide  appear  on  the  surface  of  the  iron,  due 
to  the  action  of  the  oxide  of  iron  in  the  slag  on  the  carbon  of  the 
crude  iron;  the  mass  becomes  pasty,  and  is  finally  scraped 
together  into  lumps  (blooms)  ;  these  are  placed  under  the  steam- 
hammer,  and  forged  into  bars. 

The  Bessemer  process — The  third  plan  of  producing  soft  iron 
(wrought  iron)  is  by  the  Bessemer  process.  This  consists  in 
running  the  molten  cast  iron  from  the  blast-furnace  into  pear- 
shaped  vessels  of  iron -plate,  termed  converters  ;  the  lining  of  such 
converters  used  to  be  of  "ganister,"  a  variety  of  very  siliceous 
clay  ;  but  of  late  years  the  magnesia  bricks  introduced  by  Messrs. 
Thomas  and  Gilchrist  ("  basic  lining  ")  have  supplanted  ganister. 
Fire-clay  tubes  lead  to  the  bottom  of  the  converter,  through  which 
a  blast  of  air  can  be  forced  into  the  molten  iron.  When  the 
lining  is  of  ganister  the  phosphorus  and  sulphur  are  not  wholly 
removed,  for  the  free  oxides  are  reduced  by  molten  iron,  pro- 
ducing phosphide  and  sulphide  of  iron.  But  with  a  magnesia 
lining,  lime  may  be  thrown  on  to  the  surface  of  the  molten  iron ; 
it  combines  with  the  oxides  of  phosphorus  and  sulphur,  forming 
phosphate  and  sulphate  of  calcium,  which  then  escape  reduction. 
With  a  siliceous  lining,  it  is  impossible  to  make  use  of  lime,  for 
an  easily  fusible  slag  is  at  once  produced,  and  the  lining  of  the 
f urnace  is  destroyed,  owing  to  the  formation  of  an  easily  fusible 
silicate  of  calcium  and  iron. 

Flames  issue  from  the  mouth  of  the  converter ;  the  carbon, 
silicon,  sulphur,  phosphorus,  and  manganese  burn  to  oxides ;  and 
when  the  flames  cease,  the  iron,  approximately  pure,  may  be  run 
oat  into  moulds.  Such  iron  is  the  purest  form  of  commercial  iron. 

Steel. — The  difference  between  steel,  wrought  iron,  and  cast 
iron  consists  in  the  amount  of  carbon  which  they  contain.  To 
convert  wrought  iron  into  steel,  it  is  necessary  to  add  carbon. 
This  is  done  in  the  Bessemer  converter  by  throwing  into  the 
fused  wrought  iron  a  known  quantity  of  a  variety  of  iron  contain- 
ing a  known  amount  of  manganese  and  carbon,  named  spiegel- 
iron  (i.e.,  mirror- iron),  owing  to  the  bright  crystalline  facets 
which  it  shows  when  broken.  The  spiegel-iron  mixes  with  the 
decarbonized  iron,  and  the  mixture  is  completed  by  turning  on  the 
blast  for  a  few  seconds.  The  converter  is  then  tilted,  and  the 
steel  is  poured  out  into  moulds. 


STEEL.  657 

It  is  also  possible  to  prepare  steel  by  adding  wrought  bar  iron 
nearly  free  from  carbon,  to  pig-iron  kept  melted  in  the  hearth  of 
a  Siemens  furnace.  This  is  the  principle  of  Martin's  process. 
Steel  produced  by  the  Bessemer  or  by  the  Martin  process  is  use- 
ful for  rails,  ship-  plates,  and  ordnance. 

For  cutting  instruments  steel  is  chiefly  made  by  the  "  cemen- 
tation-process.'" The  best  qualities  of  bar  iron  are  employed. 
They  are  placed  in  fire-clay  boxes,  and  packed  in  charcoal ;  the 
boxes  are  then  kept  at  a  red  heat  for  six  or  seven  days.  A  sample 
bar  is  withdrawn  from  time  to  time  and  tested ;  when  a  sufficient 
amount  of  carbon  has  been  absorbed,  the  boxes  are  allowed  to 
cool,  and  when  cold  the  bars  are  removed  and  forged  under  a  steam 
hammer.  It  has  long  been  a  matter  of  speculation  as  to  the 
manner  in  which  the  iron  absorbs  the  carbon.  In  view  of  the 
recent  discovery  of  the  compound  of  nickel  with  carbon  monoxide, 
Ni(CO)4,  a  compound  which  is  decomposed  into  nickel,  carbon,  and 
a  mixture  of  carbon  monoxide  and  dioxide  at  a  low  temperature,  it 
may  be  conjectured  that  iron  also  possesses  some  tendency  to  form 
a  similar  compound,  which,  however,  is  too  dissociable  to  be 
isolated,  but  which  is  formed  and  decomposed  during  the  process 
of  the  conversion  of  bar  iron  into  steel,  and  which  serves  to  convey 
carbon  into  the  interior  of  the  iron. 

The  steel,  thus  made,  is  refined  by  rolling  or  hammering  out 
the  bars,  placing  a  number  of  the  rods  together,  and  welding  them 
into  a  compact  whole.  Such  steel  goes  by  the  name  of  shear  stee'l, 
owing  to  its  imployment  for  cutting  instruments. 

Cast  steel  is  made  by  fusing  such  bars  in  crucibles  made  of  a 
mixture  of  graphite  and  fire-clay,  and  then  casting  the  steel  in 
moulds. 

It  is  also  possible  to  convert  the  surface  of  objects  made  of 
soft  iron  into  steel,  by  heating  them  to  redness  and  then  sprinkling 
them  with  powdered  ferrocyanide  of  potassium.  This  process  is 
termed  surface-hardening. 

Steel  has  a  fine  granular  fracture,  and  does  not  exhibit  the 
coarse  crystalline  structure  of  cast  iron,  nor  the  fibrous  appearance 
of  wrought  iron.  It  contains  amounts  of  carbon  varying  from  0*6  to 
1*9  per  cent.,  according  to  the  use  for  which  it  is  intended ;  the  hard- 
ness, toughness,  and  tenacity  increase  with  the  amount  of  carbon. 

Tempering,  hardening,  and  annealing  of  steel. — The  result  of 
rapidly  cooling  strongly  heated  steel  is  to  harden  it ;  by  raising 
it  to  a  much  lower  temperature,  and  cooling  it  quickly,  it  is 
tempered ;  and  it  is  annealed  by  heating  it  to  a  temperature  higher 
than  that  required  to  temper  it,  and  cooling  it  slowly. 

2  u 


658  STEEL. — NICKEL. 

Ifc  appears  that  there  is  some  evidence  of  the  existence  in  steel 
and  white  cast  iron  of  a  carbide,  of  the  formula  Fe2C ;  and  also 
that  at  a  temperature  of  850°  a  change  takes  place  in  metallic 
iron,  whereby  it  is  changed  into  an  allotropic  modification.  The 
specific  heat  of  iron  undergoes  at  that  temperature  a  sudden 
change  ;  and  it  allso  alters  its  electromotive  force  at  that  tempera- 
ture ;  and  these  changes  imply  some  change  in  molecular  aggrega- 
tion or  structure.  And  it  is  suggested  by  Osmond,  who  has 
investigated  this  change,  that  the  molecular  arrangement  or  aggre- 
gation which  exists  at  a  high  temperature  may  remain  permanent 
if  the  iron  contain  carbon,  and  if  it  be  rapidly  cooled. 

This  capacity  of  retaining  the  molecular  structure,  which  it 
possesses  at  temperatures  above  850°,  is  much  influenced  by  the 
presence  of  foreign  ingredients.  If  manganese  be  present  to  the 
amount  of  7  per  cent.,  no  sudden  change  of  specific  heat,  &c., 
occurs ;  and  if  present  in  smaller  proportions,  it  exerts  a  like 
influence,  though  to  a  less  degree.  Tungsten  has  an  even  greater 
effect.  The  effect  of  suddenly  cooling  steel  containing  these 
elements  is  to  harden  it. 

In  annealing,  the  carbide  of  iron  becomes  diffused  through  the 
iron  in  small  crystals,  and  the  iron  itself  develops  a  finely  granu- 
lar crystalline  structure.  It  thereby  becomes  tougher,  and  at  the 
same  time  softer. 

The  hardness  of  steel  varies  also  with  the  temperature  to  which 
it  is  heated  before  being  cooled,  as  well  as  on  the  suddenness  of 
the  cooling.  If  cooled  rapidly  from  a  high  temperature,  it  is 
harder  than  glass,  and  brittle ;  if  cooled  from  a  comparatively  low 
temperature,  it  is  elastic  ;  and  at  intermediate  temperatures,  it 
displays  hardness  and  elasticity  in  various  degrees. 

6.  Nickel. — The  chief  ore  of  nickel  is  the  double  silicate  of 
nickel  and  magnesium,  named  garnierite,  which  contains  from  8  to 
10  per  cent,  of  the  metal,  and  is  exported  in  large  quantity  to 
France  from  New  Caledonia.  Almost  all  the  nickel  in  the  market 
is  now  produced  from  this  ore,  and  the  process  of  extraction  is  a 
metallurgical  one. 

The  finely  ground  ore  is  mixed  with  about  half  its  weight  of 
alkali- waste  (calcium  sulphide)  or  of  gypsum,  and  about  5  per  cent,  of 
ground  coal,  moistened,  and  made  into  bricks.  These  are  then  smelted 
in  a  reverberatory  furnace,  or  in  a  small  cupola,  the  reduction  of  iron 
being  as  much  as  possible  prevented.  A  "  matt "  is  obtained,  con- 
taining about  60 — 70  per  cent,  of  nickel  and  12  per  cent,  of  iron, 
together  with  sulphur  and  graphite.  As  iron  has  a  greater  affinity 
for  oxygen  thar  nickel,  while  nickel  combines  more  readily  with 


NICKEL. — TIN. — LEAD.  659 

sulphur  than  iron  does,  the  iron  in  the  ground  regulus,  which  is 
roasted  at  a  dull  red  heat,  is  converted  into  oxide.  To  convert 
this  oxide  into  silicate  or  iron  slag,  the  roasted  mass  is  then 
thoroughly  mixed  with  fine  sand,  and  fused  in  a  small  reverbera- 
tory  furnace.  The  sulphide  of  nickel  forms  a  fused  layer  under 
the  molten  slag.  The  process  is  repeated,  sometimes  as  often  as 
five  times,  to  remove  iron  as  thoroughly  as  possible.  The  slags  all 
contain  nickel ;  they  are  ground  and  re-smelted  with  sand  and 
gypsum,  when  they  yield  a  regulus  poor  in  nickel  and  a  slag  prac- 
tically free  from  that  metal.  The  poor  regulus  is  then  crushed, 
mixed  with  gypsum  and  sand,  and  again  fused.  The  calcium 
sulphate  is  attacked  by  the  silica,  giving  oxygen,  which  oxidises 
the  iron  in  the  regulus,  and  the  resulting  oxide  forms  an  easily 
fusible  slag  with  the  lime  and  silica. 

The  sulphide  of  nickel,  freed  as  described  from  iron,  is  crushed 
and  exposed  to  a  dull -red  heat  on  the  hearth  of  a  reverberatory 
furnace.  This  oxidises  both  the  sulphur  and  the  nickel;  a  little 
nitre  is  sometimes  added  towards  the  end  of  the  operation.  The 
resulting  oxide  is  finally  reduced  by  making  it  into  cakes  with 
powdered  wood  charcoal,  and  heating  it  in  crucibles  to  a  bright-red 
heat. 

7.  Tin. — The  only  available  ore  is  tin-stone,  Sn02.     The  ore  is 
purified  by  "  dressing"  and  washing,  in  which  it  is  to  some  extent 
freed  from  gangne.    It  is  then  roasted  in  reverberatory  furnaces  to 
expel  arsenic  and  sulphur,  present  as  arsenical  pyrites;  it  is  again 
washed  to  remove  copper  sulphate  and,  after  drying,  it  is  mixed 
with  slag  from  former  operations  and  with  anthracite  coal,  and 
smelted;    occasionally  fluor-spar  is   added  to  flux  the  silica  still 
present;    the   tin    collects   in   a    compartment   analogous   to   the 
crucible  of  a  blast  furnace,  from  which  it  overflows  into  a  second 
receptacle.     To  free  it  from  iron  and  arsenic,  its  usual  impurities, 
it  is  ''  liquated,"  i.e.,  heated  to  its  fusing  point  on  a  sloping  bed  ; 
the  pare  tin  melts  and  runs  down,  leaving  a  less  fusible   alloy 
with  iron  and  arsenic  behind.     It  then  undergoes  a  process  known 
as  "  boiling  "  :  it  is  stirred  with  a  log  of  wet  wood,  and  the  steam 
rising  to  the  surface  carries  with  it  impurities.     The  metal  thus 
prepared  is  known  as  refined  tin,  and  is  very  nearly  pure. 

For  a  sketch  of  the  methods  of  tinning  iron  and  copper,  see 
pp.  583  and  586. 

8.  Lead. — The  chief  source  of  lead  is  galena,  PbS.     There  are 
two  chief  systems  of  extraction;   the  first,  by  use  of  the  "Scotch 
hearth,"  consisting  in  effecting  the  reactions  between  lead  oxide, 

2  u  2 


660  LEAD. — ANTIMONY. 

sulphate,  and  sulphide  (see  pp.  296  and  429)  at  as  low  a  tempera- 
ture as  possible,  while  in  certain  recent  processes  the  temperature 
is  raised  by  means  of  a  blast. 

The  hearth  of  the  furnace  used  in  the  first  method  is  con- 
structed of  slag,  and  slopes  towards  one  side.  The  powdered  galena 
is  spread  on  the  hearth  and  heated  by  a  charge  of  coal.  Lime  is 
raked  in  small  quantity  into  the  ore  to  separate  silica,  with  which 
it  combines.  The  galena  is  partly  oxidised  to  oxide  and  to  sul- 
phate, sulphur  dioxide  escaping  along  with  fumes  of  lead  sulphate 
and  oxide.  To  condense  and  trap  such  fumes  is  very  difficult,  and 
long  flues  are  often  employed,  debouching  here  and  there  into 
chambers,  and  provided  with  bafflers,  i.e.,  wooden  spars  kept  wet 
by  an  intermittent  flow  of  water.  In  spite  of  all  precautions,  much 
fume  escapes. 

When  the  lead  sulphide  is  partially  oxidised,  the  temperature 
is  raised  and  the  reactions  occur : — 

PbS  +  2PbO  =  3Pb  +  S02;  and  PbS  +  PbS04  =  2Pb  +  2SO2. 

The  lead  runs  off",  and  is  cast  into  pigs. 

If  the  second  method  be  employed,  the  ore  is  spread  on  a 
hearth  with  coal  and  lime,  and  exposed  to  a  high  temperature  by 
means  of  a  hot  blast.  The  reactions  already  mentioned  occur,  but 
much  fume  escapes ;  it  is  drawn  off  through  a  hood  above  the 
furnace  by  means  of  a  fan,  through  wide  iron  tubes,  in  which  it 
is  cooled.  After  passing  the  fan,  it  is  forced  into  woollen  bags 
stretched  from  top  to  bottom  of  large  chambers.  The  solid  matter 
is  trapped  in  the  flannel,  while  the  gaseous  products  of  combustion 
escape  through  the  pores.  The  fume  is  shaken  out  of  the  bags 
and  again  heated  with  coke,  a  blast  being  again  employed.  A 
further  yield  of  metallic  lead  is  obtained,  and  the  fume,  which  is 
quite  white,  finds  some  market  as  a  paint. 

Lead  usually  contains  silver,  and  sometimes  a  trace  of  gold. 
The  silver  is  extracted  by  Pattinson's  process,  or  by  Parkes's 
process  (see  p.  579,  587,  and  663). 

9.  Antimony. — The  sulphide,  Sb2S3,  or  grey  antimony  ore,  is  the 
principal  ore.  It  is  easily  fused,  and  is  liquated  from  the  gangue 
with  which  it  is  associated  by  heating  it  in  a  hearth  provided  with 
an  opening  below,  through  which  the  fused  sulphide  is  run  off. 
The  metal  is  obtained  from  the  sulphide  by  roasting  it  in  a  rever- 
beratory  furnace  until  it  is  converted  into  the  oxide,  SbzO*.  This 
oxide,  still  mixed  with  some  sulphide,  is  transferred  to  crucibles, 
mixed  with  a  little  crude  tartar  or  argol  (hydrogen  potassium  tar- 


ANTIMONY.  —BISMUTH. — COPPER.  661 

trate,  HKC4Hi06),  or  with  charcoal  and  sodium  carbonate,  and 
heated.  Reduction  to  metal  takes  place,  partly  owing  to  the 
mutual  action  of  oxide  on  sulphide,  and  partly  to  the  reduction  of 
the  oxide  by  the  carbon. 

It  is  also  possible  to  prepare  antimony  directly  from  the 
sulphide  by  heating  it  with  scrap  iron  and  a  little  sodium  carbon- 
ate or  sulphate  to  promote  fusion.  The  antimony  settles  to  the 
bottom  of  the  crucible. 

To  purify  antimony  from  arsenic,  it  is  fused  under  a  layer  of 
potassium  nitrate.  A  considerable  loss  of  antimony  occurs. 

10.  Bismuth. — Bismuth  is  generally  found  native,  and  is  freed 
from  gangue  by  liquation.     When  obtained  as  a  bye-product  from 
cobalt  and  other  ores,  it  is  precipitated  as  bismuthyl  chloride,  and 
reduced  by  fusion  with  charcoal  and  sodium  carbonate. 

11.  Copper. — The   extraction  of  copper  from  its  ores  varies 
according   to   the  nature  of   the   ore.     If  it  is  an  oxide,  simple 
reduction  with  coal  is  sufficient ;    but  as  the  ore  almost    always 
contains  sulphide,   other  processes  have  to  be   employed.      The 
sulphide  may  be  treated  in  the  "  dry  way,"  i.e.,  in  a  furnace,  or 
in  the  "  wet  way,"  i.e.,  by  precipitation  on  iron. 

1.  The  ores  are  calcined  in  order  to  volatilise  a  portion  of  the 
arsenic,  antimony,  and  sulphur ;  some  sulphate  of  copper  is  thereby 
formed.    The  calcined  ore  is  then  heated  with  a  flux  in  a  reverbera- 
tory  furnace.     The  effect  of  this  is  to  reduce  any  oxide  present  to 
metallic  copper ;  to  reduce  sulphate  to  oxide,  which  reacts  with 
sulphides  of  copper  and  iron,  giving  metallic  copper,  oxide  of  iron, 
and  sulphur  dioxide,  in  the  same  manner  as  the  similar  compounds 
of  lead  react ;  and  to  separate  some  of  the  iron  as  a  silicate  in 
combination   with   the   constituents   of   the   flux.      But   metallic 
copper  is  miscible  with  copper  sulphide,  and  the  resulting  regulus 
is  re-smelted  in  a  similar  manner.     The  product  consist  of  metallic 
copper  mixed  with  cuprous  oxide,  Cu2O.     To  finally  convert  the 
remaining  oxide  into  metallic  copper,  the  "  rose-copper  "  is  rapidly 
melted  under  a  layer  of  charcoal,  and  stirred  with  a  birch- wood 
pole.     It  is  then  cast  into  cakes. 

2.  The  "  wet "  method  of  extracting  copper  from  its  sulphidt. 
consists  in  allowing  the  ore  to  lie  in  heaps  exposed  to  the  air  and 
rain.     The  sulphide  is  oxidised  to  sulphate,  which  dissolves,  and 
its  solution  runs  into  ponds  or  tanks.     Scrap  iron  is  then  added, 
and  the  copper  precipitates  as  a  mud  on  the  surface  of  the  iron, 
mixed  with  basic  feme  sulphate.     The  copper,  being  specifically 


602  COPPER. — SILVER. 

heavier,  is  freed  from  the  basic  sulphate  by  washing,  and  is  then 
smelted. 

Large  quantities  of  iron  pyrites,  containing  about  4  per  cent, 
of  metallic  copper,  are  now  imported  into  this  country.  It  is 
delivered,  first  to  the  sulphuric  acid  manufacturer,  where  the 
sulphur  is  burned  in  "pyrites-kilns."  The  ore,  then  consisting  of 
ferric  oxide  and  oxide  and  sulphide  of  copper,  is  then  transferred 
to  the  copper  works.  It  is,  roasted,  at  a  low  red  heat,  with  salt ; 
the  copper  is  thus  converted,  first  into  sulphate,  and  then,  by 
means  of  the  salt,  into  chloride,  and  on  treatment  with  water  it 
passes  into  solution.  The  residue  of  iron  oxide,  after  drying,  is 
passed  on  to  the  iron-smelters.  As  such  ores-  usually  contain 
some  silver,  it,  too,  is  converted  into  chloride,  and  as  silver 
chloride  forms  a  soluble  double  chloride  with  sodium  chloride,  ii<  is 
dissolved  along  with  the  copper  chloride.  The  silver  is  removed 
by  careful  addition  of  solution  of  potassium  iodide,  which  con- 
verts it  into  the  insoluble  iodide,  which  is  allowed  to  settle,  and 
removed.  The  solution  of  cupric  chloride  is  treated,  as  already 
described,  with  scrap  iron,  and  the  copper  precipitated  in  the 
metallic  state.  It  is  separated,  mechanically,  from  the  precipitated 
basic  sulphate  of  iron,  and  is  then  smelted. 

12.  Silver.^ — Silver  occurs  chiefly  as  sulphide  and  as  thio-anti- 
mouate.  If  the  ores  are  rich,  they  are  ground  to  a  very  fine 
powder,  moistened  with  salt  water,  and  treated  with  roasted  iron 
and  copper  pyrites,  i.e.,  with  a  mixture  of  ferrous  and  cupric  sul- 
phate and  sulphide,  and  with  mercury.  The  sulphates  are  con- 
verted partly  into  chlorides,  the  silver  also  becoming  changed  into 
chloride,  and  dissolving  in  the  excess  of  salt  as  double  chloride  of 
silver  and  sodium.  The  silver  chloride  reacts  with  the  mercury, 
forming  calomel,  HgCl,  and  an  amalgam  of  silver,  which  is  pressed 
in  canvas  bags.  As  silver  amalgam  is  solid,  and  only  sparingly 
soluble  in  mercury,  it  remains  behind  for  the  most  part ;  it  is  then 
distilled,  and  the  recovered  mercury  is  used  in  a  subsequent 
operation.  This  process  is  very  wasteful,  inasmuch  as  mercury 
equivalent  to  the  silver  is  lost  as  calomel. 

By  another  process,  the  sulphides  are  reduced  to  powder  and 
roasted ;  the  sulphides  are  converted  into  sulphates.  As  silver 
sulphate  withstands  a  higher  temperature  than  the  other  sulphates, 
it  remains  unchanged,  while  the  other  sulphates  are  decomposed. 
On  treatment  with  a  solution  of  salt,  the  silver  passes  into  solution 
as  double  chloride,  and  is  precipitated  on  metallic  copper.  It  is 
also  possible  to  omit  treatment  with  salt,  and  to  dissolve  the  silver 


S1LYEK. — GOLD.  663 

sulphate  and    precipitate  silver  from   the   solution    by   metallic 
copper. 

The  ores  are  also  sometimes  treated  with  melted  lead,  which 
decomposes  the  sulphide,  forming  lead  sulphide  and  metallic  silver, 
which  dissolves  in  the  excess  of  lead,  and  is  extracted  therefrom 
by  cupellation. 

If  silver  is  contained  in  metallic  lead,  it  is  separated  by  frac-- 
tional  crystallisation,  a  process  invented  in  1833  by>  Mr.  H-.  L. 
Pattinson ;  this  method  depends  on  the  fact  that  when  a  dilute^ 
solution  is  cooled,  the  pure  solvent  crystallises  out  at  a  tern-, 
perature  below  the  usual  freezing-point,  while  the  remaining 
solution  has  a  lower  freezing-point,  and  remains  liquid.  By  a 
series  of  fractional  crystallisations,  the  lead  is  divided  into  two. 
portions,  one  pure  and  free  from  silver,  and  a  quantity  of  lead, 
very  rich  in  silver  is  obtained,  which  is  then  cupelled. 

Another  process,  due  to  Mr.  Parkes,  is  to  add  to  the  molten 
lead  about  one-twentieth  of  its  weight  of  zinc,  and  to  mix  the  two, 
as  well  as  possible,  by  stirring.  The  zinc  dissolves  the  silver,  and 
as  zinc  and  lead  do  not  appreciably  mix  to  form  an  alloy,  the  zinc, 
floats  to  the  surface,  bringing  the  silver  with  it.  The  zinc  solidifies 
at  a  higher  temperature  than  the  lead,  and  the  solid  cake,  is 
removed.  The  zinc  is  separated  from  the  silver  by  distillation 
from  an  iron  crucible,  similar  to  that  employed  in  producing 
sodium,  which  may  be  raised  to  fit  its  lid ;  the  condensing- tube 
issues  from  the  lid.  The  silver  is  left,  along  with.  a.  little  lead, 
which  is  dissolved  by  the  zinc. 

To  refine  the  silver,  it  is  cupelled.  The  lead  containing  silver 
is  fused  in  a  good  draught  on  a  hearth  of  bone-ash,  pressed,  tightly 
into  an  iron  grating  of  an  oval  shape,  depressed  in  the  middle. 
The  lead  and  other  metals  oxidise ;  the  oxides  soak  into  the  porous 
bone-ash,  and  at  a  certain  point  the  dull  appearance  of  the  metal 
changes:  a  brilliant  display  of  iridescent  colours  appears  on  its 
surface,  due  to  diffraction  colours,  caused  by  a  thin  film  of  lead 
oxide ;  and  suddenly  the  brilliant  metallic  lustre  of  the  pure 
molten  silver  is  seen.  The  metal  is  cooled  by  water,  and  removed. 
The  resulting  litharge  is  reconverted  into  lead. 

13.  Gold. — Gold  usually  occurs  native.  It  may  be  associated 
with  quartz,  in  which  case  its  extraction  is,  for  the  most  part, 
mechanical ;  or  with  sulphides  and  tellurides  of  zinc,  bismuth, 
lead,  and  other  metals,  from  which  it  must  be  separated  chemically. 

1.  If  associated  with  quartz,  the  rock  is  stamped  to  powder, 
and  washed,  by  allowing  a  stream  of  water  to  carry  away  the 


604  GOLD. — MERCURY. 

gangue.  But  the  smaller  particles  of  gold  are  apt  to  be  carried 
away ;  hence  the  washings  are  generally  caused  to  traverse  an 
amalgamated  copper  runnel,  small  bridges  being  placed  at  intervals 
across  the  channel,  to  act  as  traps.  Much  of  the  gold  sticks  to  the 
mercury ;  and  it  is  found  of  advantage  to  add  a  small  percentage 
of  sodium  to  the  mercury,  the  effect  of  which  is  to  keep  its  surface 
clean. 

The  mercury  is  scraped  from  the  copper  runnel  with  india- 
rubber  scrapers,  and  squeezed  through  leather ;  the  solid  amalgam 
is  distilled  when  a  sufficient  quantity  has  been  collected. 

2.  Many  processes  have  been  proposed  for  the  extraction  of 
gold  from  ores  containing  sulphides.  The  ores  are,  in  every  case, 
roasted  to  oxidise  the  sulphides ;  they  may  then  be  treated  with 
chlorine  water,  or  with  a  solution  of  bleaching-powder,  best  under 
pressure,  which  dissolves  the  gold  as  chloride ;  the  oxides  are  not 
thereby  attacked.  The  gold  is  precipitated  from  its  solution  by 
boiling  it  with  a  solution  of  ferrous  sulphate  or  oxalic  acid. 

A  recent  process  for  extracting  gold  or  silver  from  very  poor 
ores  consisted  in  treating  the  crushed  ore  with  a  5  per  cent,  solu- 
tion of  potassium  cyanide.  The  gold  and  silver  dissolve  with 
evolution  of  hydrogen,  while  the  sulphides,  &c.,  are  unattacked. 
To  separate  the  noble  metals  from  the  cyanide  solution,  which 
contains  them  as  double  cyanides  (see  p.  571),  the  liquid  is 
filtered  through  zinc  turnings.  The  metals  deposit  in  a  film  on 
the  surface  of  the  zinc,  and  are  easily  removed  by  washing.  The 
cyanide  is  available  for  a  second  extraction. 

14.  Mercury. — The  only  available  ore  of  mercury  is  cinnabar, 
HgS. 

Two  methods  of  extraction  are  practised.  The  first  consists 
of  calcining  the  ore  in  a  shaft-furnace,  and  condensing  the  mer- 
curial vapours  in  vessels  of  boiler-plate,  or  in  brick  chambers  ;  or 
in  the  old  form  of  condensers,  named  "  aludels,"  which  consist  of 
earthenware  bottles  open  at  both  ends,  and  fitted  together  like 
drain  pipes.  The  second  method  is  to  distil  the  ore  with  lime,  or 
v  ith  forge-scales. 

The  first  method  depends  on  the  equation: — 

HgS  +  02  =  Hg  +  S02. 

The  second  involves  the  formation  of  calcium  sulphide  and 
thiosulphate,  from  the  action  of  the  lime  on  the  sulphur  (see 
p  444),  or  of  iron  sulphide,  while  the  mercury  distils  off,  and  is 
condensed  by  passing  the  vapour  through  water. 


PHOSPHORUS.  665 

Mercury  is  sold  in  iron  bottles  containing  about  80  Ibs. 

15.  Phosphorus. — The  present  process  for  tlie  commercial  pre- 
paration of  phosphorus  is  to  prepare  phosphoric  acid  from  apatite, 
phosphorite,  or  bone-ash,  all  of  which  mainly  consist  of  calcium 
orthophosphate.  This  is  carried  out  by  adding  "  chamber- acid  " 
(i.e.,  aqueous  sulphuric  acid,  as  it  comes  from  the  chambers)  to 
the  ground  mineral,  in  such  proportion  as  to  correspond  to  the 
equation  : — 

Ca3(P002  +  3H2S04  =  3CaS04  +  2H3P04. 

The  solution  of  phosphoric  acid  is  decanted  from  the  precipitated 
calcium  sulphate ;  the  precipitate  is  washed ;  and  the  solution  of 
orthophosphoric  acid  is  evaporated.  During  evaporation,  coke,  or 
charcoal,  in  coarse  powder,  is  added,  and  the  mixture  is  dried  and 
heated  to  dull  redness.  The  product  is  a  mixture  of  carbon  with 
metaphosphoric  acid,  the  insoluble  variety  (probably  mono-meta- 
phosphoric  acid)  being  produced.  Cylinders  of  Stourbridge  clay 
are  charged  with  the  mixture ;  they  are  placed  in  tiers  in  a 
furnace,  preferably  heated  by  regenerator  gases.  To  the  mouths 
of  the  cylinders  are  attached  copper  tubes  through  which  the 
phosphorus  gas,  carbonic  oxide,  and  hydrogen  issue.  These  tubes 
dip  below  the  surface  of  warm  water  in  pots  provided  with  lids. 
The  temperature  is  raised  to  bright  redness,  and  the  phosphorus 
distils  over.  The  equation  representing  the  change  is  : — 

4HP03  +  12C  =  2H2  +  6CO  +  P4. 

The  phosphorus  is  then  in  greyish-coloured  lumps  ;  to  purify  it, 
it  is  usually  redistilled ;  it  is  subsequently  melted,  and  moulded 
into  sticks  by  causing  it  to  flow  into  horizontal  tubes,  cooled  by 
cold  water. 

It  is  possible  to  prepare  phosphorus  by  distilling  calcium  ortho- 
phosphate  with  charcoal  or  coke,  but  the  temperature  required 
is  a  very  high  one,  and  it  appears  to  be  impossible  to  construct 
retorts  of  a  sufficiently  infusible  material.  Even  the  so-called 
"  graphite  "  crucibles  liquefy  at  the  necessary  temperature.  It  is 
generally  stated  that  the  calcium  orthophosphate  is  converted  into 
dihydrogen  calcium  orthophosphate,  Ca(H2PO4)2,  and  that  a  solu- 
tion of  this  substance  is  evaporated  in  contact  with  carbon,  pro- 
ducing calcium  metaphosphate ;  and  that,  on  distilling  the  meta- 
phosphate  with  carbon,  orthophosphate  remains  in  the  retort, 
while  phosphorus  distils.  Such  a  process  is  certainly  possible, 
but  it  is  not  practised,  owing  to  the  exceedingly  high  temperature 
required,  and  the  destructive  action  on  the  retorts. 


666  PHOSPHORUS. 

A  process  has  recently  been  patented  whereby  phosphorus  is 
produced  directly  from  apatite,  or  from  any  substance  containing 
calcium  orthophosphate,  by  distilling  it  with  carbon.  To  produce 
the  enormously  high  temperature  required,  an  electric  furnace, 
somewhat  similar  to  that  employed  in  the  manufacture  of  alu- 
minium alloys  by  the  Cowles  process,  is  made  use  of.  The  floor  of 
the  furnace  consists  of  a  bed  of  cast  iron,  which  serves  as  one  of 
the  electrodes  ;  the  other  electrodes,  as  in  the  Cowles'  furnace, 
consist  of  rods  of  gas-carbon.  The  cast  iron  becomes  charged 
up  to  8  or  9  per  cent,  with  phosphorus,  forming  a  phosphide ;  but 
its  conductivity  is  not  thereby  impaired.  The  phosphorus  distils 
over,  and  is  condensed  and  purified  as  usual.  This  ingenious 
method  has  not  as  yet  been  carried  out  on  a  scale  sufficiently  large 
to  render  its  success  certain,  but  it  is  at  present  in  operation. 

The  preparation  of  chlorine,  bromine,  iodine,  and  sulphur  is 
intimately  connected  with  that  of  various  compounds  ;  hence  a 
description  of  the  methods  employed  is  reserved  to  the  next 
chapter. 


667 


CHAPTEK  XXXIX. 

PROCESSES    OF   MANUFACTURE. 

1.  Utilisation  of  sulphur  occurring  as  sulphur  dioxide 
in  furnace  gases,  &c. — If  more  than  4  per  cent,  by  volume  of  the 
furnace  gas  consists  of  sulphur  dioxide,  it  is  most  profitable  to 
pass  it  into  sulphuric  acid  chambers.     But  below  that  amount  the 
operation  is    unprofitable.     Hence  various   expedients   have  been 
suggested  for  absorbing  the  dioxide  by  some  substance  which  will 
permit  of  its-  recovery  in  the  form  of  sulphur,  or  as  dioxide  free 
from  admixed  gases.     As   sulphur  dioxide  is  produced  in  large 
amount  by  the  calcination  of  sulphides,  which  is  the  usual  pre- 
liminary to  the  extraction  of  metals  from  their  ores,  the  problem 
of  utilising  it,  or  of  preventing  nuisance,  is  one  of  great  import- 
ance. 

Two  methods  are  in  practical  operation.  One  of  these  depends 
on  the  absorption  of  the  gas  by  water.  The  furnace  gases,  having 
been  cooled,  are  passed  into  a  tower  filled  with  coke,  down  which 
cold  water  flows.  If  the  gases  contain  I  per  cent,  of  sulphur 
dioxide,  1  cubic  metre  of  water  dissolves  3  or  4  kilograms  ;  if 
2^  per  cent.,  8  to  10  kilograms.  The  aqueous  solution  is  boiled  to 
expel  the  dioxide  (an  operation  which  must  obviously  be  performed 
by  heat  which  would  otherwise  be  wasted),  and  the  gas  is  either 
utilised  for  the  manufacture  of  sulphuric  acid,  or  condensed  by 
cold  and  pressure,  or  it  may  be  converted  into  sulphites. 

The  other  process  consists  in  passing  the  furnace  gases,  cooled 
to  100°,  through  milk  of  magnesia  (magnesium  oxide  mixed  with 
water).  A  sparingly  soluble  sulphite  is  formed,  which  is  collected. 
On  heating  it  to  200°,  magnesia  is  regenerated,  the  sulphite  evolv- 
ing from  30  to  33  per  cent,  of  its  weight  of  dioxide.  The  magnesia 
serves  for  a  further  operation. 

2.  Manufacture  of  sulphuric  acid. — The  sources  of  sulphur 
for  sulphuric  acid  are  :   (a)  Sicilian  sulphur ;  (6)  sulphur  recovered 
from  alkali-waste  (see  below) ;  (c)  hydrogen  sulphide,  also  from 
alkali-waste ;  or  (d)  copper  pyrites.    If  the  last  source  be  employed, 


668  PROCESSES   OF   MANUFACTURE. 

the  pyrites,  after  being  burned  for  the  sulphur  which  it  contains, 
is  passed  on  to  the  copper  works,  where  the  copper  is  extracted  by 
the  wet  process,  described  on  p.  661. 

The  sulphur  or  the  pyrites  is  burnt  in  kilns  especially  con- 
structed for  the  purpose,  usually  rectangular  boxes  of  fire-brick, 
into  which  the  necessary  amount  of  air  may  be  admitted  by 
dampers.  Too  little  air  causes  sublimation  of  sulphur  ;  too  much 
causes  an  increase  in  the  consumption  of  nitre,  and  lowers  the 
yield  of  sulphuric  acid.  Iron  pots  containing  sodium  nitrate  and 
sulphuric  acid  stand  on  the  floor,  or,  better,  in  the  flue,  of  the  fur- 
nace; nitric  acid  is  thereby  generated,  and  its  products  of  reaction, 
along  with  sulphur  dioxide  and  a  little  trioxide,  pass  up  flues  lead- 
ing from  the  kilns.  These  flues  enter  a  dust  chamber,  where  dust 
is  deposited  if  pyrites  be  burned,  which  contains  sand,  arsenious 
and  lead  and  iron  oxides,  sulphuric  acid,  and  sometimes  a  little 
thallium  oxide. 

The  mixture  of  sulphur  dioxide,  sulphur  trioxide  (3 — 10  per 
cent.),  nitrous  fumes,  some  excess  of  oxygen,  and  nitrogen  then 
passes  into  a  tower,  named  from  its  inventor  the  "  Glover's  tower," 
where  it  meets  a  descending  current  of  sulphuric  acid  and  water 
from  which  nitrous  fumes  have  been  liberated.  The  source  of  this 
acid  will  afterwards  be  described  ;  the  hot  gases  evaporate  some  of 
the  water,  and  are  themselves  cooled  thereby  ;  the  mixture  of  gases 
is  now  richer  in  nitrous  fumes,  and  contains  water-vapour  in 
addition. 

The  gases  now  enter  the  "  chambers."  These  consist  of  large 
rectangular  boxes,  made  of  lead,  the  joints  in  which  are  fused 
together,  not  soldered.  As  lead  is  a  soft  metal,  the  leaden  cham- 
bers are  supported  on  frameworks  of  wood  at  some  distance  from 
the  ground.  A  number  of  such  chambers  (from  three  to  five)  are 
placed 'in  a  double  row;  they  communicate  by  means  of  wide 
leaden  pipes.  The  bottoms  of  the  chambers  are  covered  with  about 
2  inches  of  water,  and  are  provided  with  valves,  through  which  the 
weak  acid  is  drawn  off  from  time  to  time.  Sometimes,  when  nitre- 
pots  are  not  used  for  generating  nitric  acid  in  the  burners,  nitric 
acid  is  introduced  into  the  first  chamber,  falling  on  an  erection  of 
earthenware  pots,  over  which  it  flows,  and  is  exposed  to  the  action 
of  sulphur  dioxide.  Steam  is  passed  from  a  boiler  into  each 
chamber  by  a  jet  at  one  end,  and  a  draught  is  produced  through 
the  whole  set  of  chambers,  usually  by  connecting  the  Gay-Lussac 
tower  (afterwards  to  be  described)  with  a  chimney ;  the  issuing 
gas  should  contain  5  to  6  per  cent,  of  free  oxygen,  together  with 
the  nitrogen  equivalent  to  the  oxygen  in  the  air  admitted  into  the 


SULPFUE1C  ACID.  669 

burners.  Before  passing  into  the  chimney,  however,  these  gases, 
which  should  always  contain  excess  of  oxides  of  nitrogen,  are 
made  to  pass  up  a  tall  tower  constructed  of  lead  and  packed 
with  hard  coke.  Down  this  tower,  which  is  called  after  its  in- 
ventor, Gay-Lussac  (1827),  a  regular  supply  of  strong  sulphuric 
acid  trickles ;  it  absorbs  the  nitrons  fumes,  forming  hydrogen 
nitrosyl  sulphate.  H.(NO)SO4,  which  dissolves  in  the  excess  of 
sulphuric  acid.  The  reaction  is 

2NO  +  0  +  2H.S04  =  2H(NO)S04. 

The  "  2NO  +  0  "  may  consist  of  N02  +  NO ;  the  gas  is  pale 
orange.  The  issuing  "  nitrous  vitriol  "  runs  into  an  egg-shaped 
iron  vessel,  from  which  it  is  forced  up  a  stout  leaden  tube  to  a 
tank  at  the  top  of  the  Glover's  tower.  Generally  about  half  of 
the  whole  of  the  sulphuric  acid  made  is  passed  down  the  Gay- 
Lussac  tower. 

The  object  of  the  Glover  tower  is  the  opposite  of  the  Gay- 
Lussac  tower,  viz.,  to  denitrate  the  sulphuric  acid,  and  to  return 
the  nitrous  fumes  to  the  chambers.  The  Glover  tower  is  also  con- 
structed of  lead,  but  it  is  lined  with  brick  and  packed  with  flints, 
for  coke  soon  becomes  disintegrated  by  the  hot  gases.  The  gases 
from  the  pyrites- burners  enter  the  tower  at  its  base,  and  meet  on 
their  ascent  with  a  stream  of  nitrous  vitriol  diluted  with  ordinary 
chamber  acid.  The  degree  of  dilution  depends  on  the  temperature 
of  the  gases  from  the  kilns,  and  on  the  amount  of  nitrous  com- 
pounds in  the  nitrous  vitriol.  The  gases  are  themselves  cooled  by 
their  passage  through  the  tower,  and  at  the  same  time  the  diluted 
nitrous  vitriol  is  concentrated,  and  passes  out  below  in  a  concen- 
trated form  at  a  temperature  of  120°  to  130°.  The  steam  evapo- 
rated from  the  diluted  acid  passes,  along  with  the  sulphur  dioxide 
and  nitrous  fumes,  into  the  chambers.  The  reaction  which  takes 
place  in  the  Glover  tower  is 

2H(NO)S04  4-  S0a  +  2H20  =  3H3S04  +  2NO. 

As  nitrogen  trioxide,  N203,  cannot  exist  in  the  gaseous  state,  it 
cannot  be  present  in  the  chambers  as  such  ;  hence  the  active  gases 
must  consist  of  nitric  peroxide,  nitric  oxide,  sulphur  dioxide,  an'd 
steam.  There  can  be  little  doubt  that  the  sulphur  dioxide  reacts 
with  the  peroxide  and  some  of  the  water-gas  to  form  hydrogen 
nitrosyl  sulphate,  thus  : — 

2S02  +  3N02  +  H20  =  2H(NO)S04  +  NO. 
The  hydrogen  nitrosyl  sulphate,  however,  has  only  an  ephemeral 


670  PROCESSES   OF   MANUFACTUKE. 

existence,  being  decomposed  by  the  steam  into  sulphuric  acid  and 
nitric  peroxide  and  nitric  oxide,  the  latter  of  which  is  reoxidised 
by  the  oxygen  present  to  peroxide,  again  to  react  with  a  further 
quantity  of  sulphur  dioxide  and  steam.  There  is,  however,  always 
a  certain  loss  of  oxides  of  nitrogen,  partly  caused  by  some  nitric 
oxide  escaping  through  the  Gay-Lussac  tower,  and  partly,  as  some 
suppose,  owing  to  a  further  reduction  to  -nitrous  oxide,  which  is 
not  recoverable. 

The  acid  from  pyrites  usually  contains  arsenic,  from  which  it 
is  purified,  if  desired,  by  precipitating  the  arsenic  as  sulphide, 
either  with  sulphuretted  hydrogen  or  with  a  sulphide  of  sodium 
or  barium.  Nitrous  compounds  are  generally  removed  by  the  addi- 
tion of  a  little  ammonium  sulphate  during  the  concentration  of  the 
acid.  The  escaping  gas  is"nitrogen.  To  prepare  pure  acid,  the 
concentrated  acid  must  be  distilled  from  glass  retorts. 

Should  the  Glover  tower  not  be  employed,  the  chamber  acid 
must  be  concentrated  by  heating  it  in  leaden  pans,  best  from 
above.  It  may  thus  be  concentrated  until  it  has  the  specific  gravity 
1'72,  containing  about  79  per  cent,  of  acid,  and  boiling  at  200°. 
Up  to  that  point,  only  water  evaporates,  and  the  acid  does  not 
appreciably  attack  the  lead. 

Further  concentration  is  carried  out  in  vessels  of  platinum  or 
glass,  in  the  form  of  stills ;  it  may  even  be  boiled  down  in  iron 
basins,  provided  the  top  portion  of  the  iron  is  protected  from  the 
hot  weak  acid.  It  is  then  filled  into  carboys,  and  brought  to 
market.  The  strong  acid  is  known  as  "oil  of  vitriol." 

The  method  of  manufacturing  sulphur  trioxide,  or  sulphuric 
anhydride,  is  described  on  p.  411.  Chlorosulphonic  acid, 
Cl — S02OH,  is  produced  by  passing  gaseous  hydrochloric  acid 
over  the  hot  sulphur  trioxide ;  and  anhydrosulphuric  acid  by 
mixing  trioxide  with  oil  of  vitriol. 

Alkali  manufacture. — A  large  number  of  processes  are  con- 
nected with  the  manufacture  of  sodium  carbonate,  Na2C03,  among 
the  more  important  of  which  are  the  preparation  of  caustic 
soda;  of  chlorine,  with  its  concomitants  bleaching  powder  and 
potassium  chlorate  ;  of  sulphuric  acid  ;  of  hydrochloric  acid ;  of 
pure  sulphur  from  pyrites  ;  and  of  sodium  thiosulphate. 

As  the  object  of  the  manufacturer  is  to  make  use  of  the 
cheapest  materials,  the  choice  of  a  starting  point  is  limited. 
Two  compounds  of  sodium  occur  in  enormous  quantity  on 
the  earth's  surface,  viz.,  salt,  or  sodium  chloride,  and  caliche, 


THE  LEBLANC   SODA-PKOCESS.  671 

or  sodium  nitrate  from  Pern.  The  latter  is  made  use  of  chiefly 
as  a  manure  ;  but  it  also  serves  as  a  source  of  nitric  acid,  which 
is  employed  in  the  manufacture  of  sulphuric  acid,  and,  conse- 
quently, of  sodium  sulphate. 

Carbon  dioxide  is  a  product  of  combustion ;  but,  as  it  is 
thereby  largely  diluted  with  nitrogen  and  with  unburned  oxygen, 
it  is  not  generally  available  -when  obtained  from  fuel. 

The  chief  available  source  is  limestone,  or  calcium  carbonate. 

If  it  were  possible  to  cause  salt  to  react  quantitatively  with 
limestone,  so  as  to  realise  the  equation  CaC03  +  2NaCl  =  CaCl2  + 
Na2C03,  the  alkali  maker's  business  would  be  a  simple  one.  It  is 
true  that  limestone  moistened  with  a  solution  of  salt  does  yield 
calcium  chloride  and  sodium  carbonate  after  some  weeks,  but  only 
a  small  proportion  of  the  whole  mass  reacts ;  hence  it  is  necessary 
to  introduce  secondary  reactions,  so  as  to  obtain  a  reasonable  yield 
of  the  desired  product  from  the  raw  materials. 

There  are  two  methods  of  achieving  this  object  which  are 
practically  successful.  These  are  : — 

1.  The  Leblanc  soda-process ;  and 

2.  The  ammonia  soda-process. 
We  shall  consider  these  in  their  order. 

1.  The  Leblanc  soda-process. 

The  equation  to  be  realised  is,  as  already  mentioned, 

CaC03  +  2NaCl  =  CaCl2  +  Na2C03. 
In  fact,  an  attempt  is  made  to  realise  the  still  simpler  equation, 

2NaCl  +  H20  +  CO2  =  Na2C03  +  2HC1 ; 
or,  if  caustic  soda  is  required,  the  corresponding  equations, 

Ca(OH)2  +  2NaCl  =  CaCl2  +  2NaOH,  or 
H20  4-'NaCI  =  HC1  +  NaOH. 

The  operations  in  the  Leblanc  process  consist — 

A.  In  preparing  sodium  sulphate  from  salt. 

B.  In  converting  the  sulphate  into  sulphide   of   calcium  and 
sodium  carbonate  by  heating  with  lime  and  coal. 

C.  In   crystallising  out   the    decahydrated   sodium  carbonate, 
Na2C03.10H20  (soda-crystals),  or  in  producing  dry  sodium  carbon- 
ate or  soda-ash. 

To  these  are  added  : — 

D.  The    causticising    of    the    sodium    carbonate,    producing 
sodium  hydroxide ;  and 

E.  The  recovery  of  the  sulphur  from  the  calcium  sulphide. 

A.  The  preparation  of  sodium  sulphate.— This  is  achieved 


672  PROCESSES   OF  MANUFACTUKE. 

either  (a)  by  exposing  salt  to  the  action  of  sulphur  dioxide,  steam, 
and  air  (Hargreaves'  process)  ;  or  (6)  by  treating  salt  with  sul- 
phuric acid. 

(a.)  The  Hargreaves'  process  for  manufacturing  sodium 
sulphate  and  hydrochloric  acid. — The  gases  obtained  by  the  com- 
bustion of  sulphur,  or  more  usually  of  pyrites,  are  passed  downwards 
through  salt  contained  in  cast-iron  cylinders  enclosed  in  a  fire- 
brick casing,  and  provided  with  fire-places  and  flues.  Much 
depends  on  the  physical  state  of  the  salt.  It  should  be  poroup, 
and  yet  not  too  closely  packed.  It  is  moistened  and  moulded  by 
pressure  into  cakes,  and  they  are  broken  up  and  packed  in  the 
cylinders,  which  are  furnished  with  perforated  shelves,  or  grids,  so 
that  the  pressure  of  the  salt  in  the  cylinder  may  not  consolidate 
the  lower  layers.  The  sulphur  dioxide  produced  in  pyrites-kilns 
should  contain  the  requisite  excess  of  oxygen  to  convert  it  into 
trioxide,  and  is  mixed  with  steam,  which  is  blown  into  the  pipes 
leading  from  the  pyrites-burners.  The  temperature  of  the  cylinders 
should  be  maintained  as  close  as  possible  to  500 — 550°.  At  first 
external  heat  is  required,  but  the  heat  developed  by  the  reaction 
is  afterwards  sufficient.  Each  cylinder  is  capable  of  holding  40 
tons  of  salt,  and  eight  cylinders  form  a  set.  The  reaction  is  a 
slow  one,  and  takes  several  weeks. 

The  issuing  gases  are  drawn  off  by  means  of  a  fan ;  they  con- 
sist of  hydrogen  chloride  and  nitrogen,  along  with  the  excess  of 
oxygen.  The  hydrogen  chloride  is  condensed  in  coke  towers,  as 
will  afterwards  be  described. 

The  reaction  is  of  the  simplest  kind,  and  is  shown  by  the 
equation : — 

2S02  +  02  +  2H20  -f  4NaCl  =  2Na,S04  +  4HC1. 


(6.)  Sulphate  from  salt  and  sulphuric  acid. — This  is  the 
original  process  for  manufacturing  sodium  sulphate.  Coarse- 
grained salt  is  mixed  with  sulphuric  acid  of  70 — 80  per  cent. 
(140°  Tw.),  in  spoon-shaped  iron  pans,  covered  by  a  close  arch  of 
brick,  through  which  a  stoneware  pipe  passes.  The  sulphuric 
acid  is  mixed  hot.  When  action  has  ceased,  the  salt  is  converted 
into  hydrogen  sodium  sulphate,  thus  : — NaCl  -f  H2S04  =  HC1  + 
HNaSO*.  The  hydrogen  chloride  passes  off  through  the  stone- 
ware pipe  in  the  arch  of  the  furnace  to  a  tower  filled  with  coke, 
down  which  water  flows.  It  is  dissolved,  and  runs  out  at  the 
foot  of  the  tower  in  a  saturated  condition.  The  hydrogen  sodium 
sulphate,  containing  excess  of  salt  (for  the  total  quantity  of  salt 
corresponding  to  the  equation  2NaCl  +  H2S04  =  NaaS04  +  2HC1 


SODIUM   CARBONATE.  673 

is  added  at  the  commencement),  is  raked  from  the  pan  into  the 
"  roaster,"  a  trap  being  lifted  to  permit  of  the  transfer.  Some- 
times a,  "blind  roaster,"  i.e.,  a  furnace  heated  from  outside,  is 
made  use  of ;  but  such  furnaces  are  difficult  to  keep  tight ;  it  is 
more  usual  to  employ  an  open  roaster,  where  the  products  of  the 
combustion  of  coke  play  directly  on  the  mixture  of  salt  and  acid 
sulphate.  The  gases  are  then  condensed  in  a  separate  coke-tower, 
and  furnish  a  weaker  acid,  which  is  made  use  of  instead  of  water 
for  the  coke-tower  connected  with  the  u  pan."  When  all  action 
has  ceased,  the  "  salt-cake  "  is  raked  out  of  the  furnace. 

It  is  now  common  to  use  a  mechanical  furnace,  consisting  of  a 
rotating  disc  of  brick- work  on  an  iron  frame,  covered  by  a 
stationary  hood,  and  provided  with  mechanical  stirrers.  The  heat 
is  supplied  from  a  furnace  at  the  side,  the  products  of  combustion 
playing  directly  on  the  mixture  of  salt  and  sulphuric  acid.  This 
mixture  enters  from  a  hopper  at  the  top  of  the  hood,  and  is  distri- 
buted slowly  towards  the  side  of  the  disc  by  the  mechanical 
stirrers ;  it  is  from  time  to  time  dropped  through  traps  into  trucks 
placed  to  receive  it.  The  gases  pass  out  through  the  top  of  the 
hood,  entering  an  iron  pipe,  for  iron  is  not  attacked  by  gaseous 
hydrogen  chloride  above  a  certain  temperature;  As  the  gas  cools, 
it  enters  pipes  of  stoneware  or  glass,  which  lead  it  to  the  condens- 
ing tower. 

Manufacture  of  sodium  carbonate  by  the  Leblanc  pro- 
cess.— The  materials  are,  salt-cake,  which  should  be  porous  and 
spongy ;  limestone,  or  roughly  crushed  chalk,  as  free  as  possible 
from  magnesia  or  silica ;  and  small-coal,  or  "  slack,"  as  free  from 
ash  as  possible,  so  as  to  avoid  formation  of  calcium  silicate.  These 
materials  are  crushed  and  mixed  together,  usually  in  the  propor- 
tion of  100  parts  of  sulphate,  80  of  limestone,  and  40  of  coal. 

When  hand-furnaces  are  used.. the  materials  are  heated  directly 
by  the  gases  of  combustion  and  stirred,  by  means  of  rakes ;  the 
mixture  sinters,  but  does  not  quite  fuse.  It  is  moved  about,  and 
finally  gathered  into  balls  of  *'  blackrash."  These  are  withdrawn 
from  the  furnace  and  allowed,  to  cool. 

Mechanical  revolving  furnaces  are  now  common  ;  a  cylinder  of 
iron  plate,  lined  with  fire-brick,  lies  horizontally  on  rollers,  so  that 
it  caii  be  made  to  revolve  on  its  axis.  One  end  of  the  cylinder 
abuts  on  a  furnace,  of  which  the  combustion^products  pass  through 
the  cylinder,  escaping  through  a  flue,  similarly  abutting  on  its 
other  end.  The  cylinder  is  charged  through  an  opening  in  the 
middle,  through  which  it  can  be  filled  when  the  opening  is  above, 

2  x 


674  PROCESSES   OF  MANUFACTURE. 

or  emptied  when  the  cylinder  is  turned  ronnd.  This  hole  is  closed 
with  a  door,  luted  on  with  clay,  after  filling  the  cylinder  with  its 
charge,  which  consists  usually  of  100  parts  of  sulphate,  72  of  lime- 
stone, and  40  of  coal.  The  cylinder  is  made  slowly  to  rotate,  and 
the  charge  is  thereby  mixed  and  tossed,  while  the  flames  from  the 
furnace  play  through.  After  2J  to  2|  hours  the  operation  is 
ended.  The  opening  is  brought  to  the  top,  and  10  parts  of  quick- 
lime mixed  with  12  to  16  parts  of  cinders  are  thrown  in.  The  door 
is  replaced,  and  for  a  few  minutes  the  cylinder  is  rapidly  rotated, 
so  as  to  mix  the  black-ash  with  these  additions.  The  object  of 
adding  them  is  that,  on  subsequently  lixiviating  the  ash,  the  lime 
may  slake  and  burst  up  the  lumps,  and  thus  allow  the  water 
quickly  to  dissolve  the  carbonate.  It  is  also  customary  to  add  some 
fresh  sodium  sulphate  at  the  end  of  the  operation,  in  order  to 
decompose  cyanide,  thus:— Na2S04  +  4NaCN  =  Na2S  +  4NaCNO. 
The  rotation  of  the  cylinder  is  finally  stopped,  the  door  removed, 
and  the  charge  emptied  into  iron  trucks,  brought  successively 
below  the  opening.  The  charge  of  black-ash  in  the  trucks  sends 
off  from  all  parts  of  its  surface  flames  of  carbon  monoxide, 
coloured  yellow,  of  course,  by  sodium. 

The  action  which  takes  place  in  hand- furnaces  is  believed  to 
consist  of  the  reduction  of  the  sulphate  in  the  upper  portion  of  the 
mixture  to  sulphide,  and  the  expulsion  of  carbon  dioxide  from  the 
limestone.  But  the  lime  is  recarbonated  by  the  carbon  dioxide 
produced  by  the  reduction  of  sulphate  in  the  lower  layers  by  the 
coal.  When  all  the  sulphate  is  reduced,  the  temperature  rises,  and 
calcium  carbonate  is  decomposed,  reacting  with  the  sodium 
sulphide.  The  escape  of  carbon  monoxide  takes  place  only  at  the 
end  of  the  operation,  and  renders  the  mass  porous.  The  reactions 
in  a  hand-furnace  are  probably  represented  by  the  equations : — 

5Na,S04  +  IOC  =  5Na,S  +  10C02; 

5Na2S  +  5CaC03  =  5Na2C03  +  5CaS;  and,  at  the  end, 

2CaC03  +20  =  2CaO  +  4CO. 

The  black-ash,  when  nearly  cold,  is  broken  into  lumps,  and 
placed  in  the  lixiviating  tanks,  so  arranged  that  the  strongest 
liquor  comes  in  contact  with  the  fresh  black-ash,  and  is  drawn  off 
saturated,  while  the  ash  already  partially  extracted  is  exposed  to 
the  action  of  the  weakest  liquors.  The  ash  must  not  remain  too 
long  in  contact  with  the  water,  nor  must  the  temperature  be  high, 
else  back  action  commences,  and  the  calcium  sulphide  and  sodium 
carbonate  react  to  form  calcium  carbonate  and  sodium  sulphide. 
The  liquor,  when  drawn  off,  is  turbid,  and  has  a  green  colour,  due 


CAUSTIC   SODA.  675 

to  a  trace  of  sodium  ferrous  sulphide.  It  is  allowed  to  settle,  and 
transferred  to  pans  heated  by  the  waste  heat  from  the  black-ash. 
furnace,  preferably  from  above.  On  evaporation,  salts  separate, 
which  are  "  fished  "  out  with  perforated  ladles.  They  consist  at 
first  of  sodium  chloride  and  sulphate.  The  liquor  contains  carb- 
onate of  soda,  and  an  equal  quantity,  or  even  more,  caustic.  On 
further  concentration,  Na2C03.H20  separates  and  is  removed. 
The  red  liquor,  as  the  mother  liquor  is  termed,  is  often  made  into 
caustic,  but  often  it  is  evaporated  to  dryness  and  calcined  with 
sawdust;  or,  better,  treated  before  boiling  down  with  carbon 
dioxide,  either  from  furnace  gases  or  from  lime-kilns,  in  order  to 
carbonate  the  caustic.  A  special  advantage  of  the  last  process  is 
that  sulphide  of  sodium  is  thereby  converted  into  carbonate, 
whereas  by  ignition  with  sawdust  it  remains  unaffected  ;  it  is 
sometimes  converted  into  sulphate  by  ignition  in  air  after  carb- 
onation. 

The  carbonate  is  sometimes  purified  by  redissolving,  settling. 
evaporating,  fishing,  and  igniting.  It  is  then  ground  and 
packed. 

Crystal  soda,  Na^CO-j.lOHaO,  is  made  from  the  impure  yellow 
carbonate.  It  is  dissolved,  and  after  settling,  it  is  run  into  tanks, 
and  allowed  to  cool.  The  mother  liquor  is  boiled  down  ;  it  con- 
tains sulphate,  but  is  useful  for  glass-making. 

The  "  bicarbonate,"  or  hydrogen  sodium  carbonate,  HN"aC03, 
is  produced  by  treating  the  crystals  with  carbon  dioxide  made 
from  limestone  and  acid.  The  water  of  the  hydrated  carbonate 
drops  away,  and  masses  of  bicarbonate  are  left,  which  retain  the 
form  of  the  original  crystals. 

Caustic  soda.  —  To  prepare  "caustic,"  the  tank  liquors,  which 
already  contain  much  caustic,  are  run  into  iron  tanks  and  mixed 
with  lime.  The  calcium  carbonate  is  filtered  off  through  cloth 
filters,  and  returned  to  the  black  -ash  furnace.  The  liquors  are 
concentrated  in  a  "  boat-pan,"  i.e.,  a  pan  shaped  like  a  boat,  of 
which  the  sides  alone  are  heated  from  below,  and  the  salts  deposit 
on  the  bottom.  They  are  fished,  and  returned  to  the  black-ash 
furnace.  A  little  sodium  nitrate  is  then  added  to  oxidise  the 
sulphide,  thus  :  — 


2Na2S  +  NaN03  +  3H20  =  Na.SA  +  3NaOH  +  NH3. 
3NaOH  +  NaN03  =  4N%S03  +  NH3. 
NaN03  +  2H20  =  4Na*S04  +  NaOH  +  NH3. 

2x2 


676  PROCESSES   OF  MANUFACTURE. 

The  sulphide  is  thus  ultimately  converted  into  sulphate  and 
caustic,  with  escape  of  ammonia. 

The  liquors,  after  concentration,  are  then  transferred  to  the 
"  finishing  pans,"  thick  hemispherical  iron  pots,  where  the  final 
water  is  removed.  At  a  certain  stage  graphite  separates,  owing  to 
the  decomposition  of  the  cyanide,  and  even  here  a  little  sodium 
nitrate  is  added  to  remove  the  last  trace  of  sulphide.  The  fused 
caustic  is  then  poured  into  iron  drums,  in  which  it  is  brought  to 
market. 

Utilisation  of  tank- waste.— The  recovery  of  sulphur  from 
the  calcium  sulphide  in  the  tank- waste  would,  if  complete,  cause 
the  manufacture  of  sodium  carbonate  ultimately  to  resolve  itself 
into  a  reaction  between  calcium  carbonate  and  sodium  chloride,  if 
calcium  carbonate  is  the  final  waste  product;  or  between  water 
and  sodium  chloride,  if  the  calcium  be  recovered  as  carbonate  and 
returned  to  the  soda-ash  furnace.  The  latter  is  the  more  perfect 
theoretically. 

As  a  sample  of  the  first,  Schaffner's  process  may  be  cited.  la 
it  the  muddy  deposit,  after  lixiviation  of  the  black-ash  and  re- 
moval of  the  sodium  carbonate,  was  allowed  to  lie  exposed  to  air ; 
Mond  introduced  a  blast  of  air  for  oxidation ;  and  the  oxidised 
waste,  consisting  largely  of  calcium  thiosulphate  mixed  with  a 
portion  of  unoxidised  material,  was  treated  with  hydrochloric 
acid.  A  reaction  similar  to  the  following  took  place  : — 

CaS2O3.  Aq  +  2CaS,  +  6HCl.Aq  =  3CaCl2.Aq  +  3H20  +  (2x  +  2)S. 

The  sulphur  sludge  was  allowed  to  deposit,  or,  better,  the  sulphur 
was  melted  by  heating  under  pressure,  and  recovered ;  the  calcium 
chloride  was  run  to  waste.  Were  the  Leblanc  process  theoretically 
perfect,  such  recovery  of  sulphur  would  dispose  of  all  the  hydro- 
chloric acid  made,  leaving  no  surplus  for  the  manufacture  of 
bleaching  powder. 

Schaffner  and  Helwig  are  the  inventors  of  another  process, 
which,  however  ingenious,  has  not  succeeded  commercially.  In  it 
the  waste  was  treated  with  magnesium  chloride,  calcium  chloride 
and  magnesium  sulphide  (or  hydrosulphide)  being  obtained,  thus : — 

CaS  +  MgCI2.Aq  =  CaCl2.Aq  +  MgS.Aq. 

The  solution  of  magnesium  sulphide  (or  hydrosulphide)  when 
heated  to  80°  yielded  oxide  and  hydrogen  sulphide,  thus  : — 

MgS  +  H20  =  MgO  +  H2S. 
The   hydrogen   sulphide  was   stored   in  gas-holders,  leakage, 


RECOVERY   OF   SULPHUR.  677 

owing  to  diffusion  through  water,  being  prevented  by  sealing  the 
gasometers  with  heavy  petroleum  oil.  The  sludge  of  calcium 
chloride  and  magnesium  oxide  was  treated  with  carbon  dioxide 
under  pressure,  and  yielded  calcium  carbonate  and  magnesium 
chloride,  the  latter  being  utilised  for  further  treatment  of  waste, 
thus : — 

CaCl2.Aq  +  MgO  +  C02  =  CaC03  +  MgCl2.Aq. 

The  precipitated  calcium  carbonate  was  returned  in  a  dry  state  to 
the  black-ash  furnace.  The  hydrogen  sulphide  was  utilised  in  the 
manufacture  of  sulphuric  acid  by  direct  burning,  or,  by  mixing 
with  sulphurous  acid,  made  to  yield  up  its  sulphur. 

Chance's  recovery  process  promises  better  results.  It  con- 
sists in  saturating  with  carbon  dioxide  the  waste,  mixed  with 
water,  and  contained  in  a  series  of  vertical  cylinders.  In  the  first 
cylinder  into  which  the  carbon  dioxide  enters,  a  portion  of  the 
calcium  sulphide  is  converted  into  carbonate,  while  the  hydrogen 
sulphide  converts  the  remainder  into  calcium  hydrosulphide 
thus  : — 

2CaS  +  H2C03.Aq  =  CaC03  +  Ca(SH)2.Aq. 

The  further  action  of  the  carbon  dioxide  is  to  decompose  the 
hydrosulphide,  the  sulphuretted  hydrogen  passing  into  the  second 
cylinder,  thus  : — 

Ca(SH)2.Aq  -|-  H2C03.Aq  =  CaC03  +  2H2S  +  Aq. 

The  waste  in  the  second  cylinder  is  thus  converted  into  soluble 
hydrosulphide  of  calcium,  in  its  turn  to  be  decomposed  by  the 
carbon  dioxide.  The  hydrogen  sulphide  is  thus  driven  from  cylin- 
der to  cylinder,  until  finally  it  is  expelled.  When  the  first  cylinder 
is  exhausted  of  hydrogen  sulphide,  it  is  thrown  out  of  circuit,  to 
be  recharged  with  fresh  waste  ;  it  then  becomes  the  end  cylinder 
of  the  circuit.  The  resulting  calcium  carbonate  may,  when  dried, 
be  returned  to  the  black-ash  furnace. 

The  hydrogen  sulphide  may  be  utilised  in  the  manufacture  of 
sulphuric  acid,  but  it  pays  better  to  recover  it  in  the  form  of 
sulphur.  This  is  done  by  Glaus*  s  process.  The  sulphuretted 
hydrogen  is  burned  below  a  layer  of  ferric  oxide,  air  being  care- 
fully regulated,  so  that  one-third  of  the  total  gas  is  converted  into 
dioxide.  The  dioxide  reacts  with  the  hydrogen  sulphide,  in  con- 
tact with  the  hot  and  porous  ferric  oxide,  yielding  sulphur  and 
water,  thus : — 

2H2S  +  S02  =  2H20  +  3S. 


678  PROCESSES   OF  MANUFACTURE. 

The  sulphur  distils  over,  and  is  condensed  in  suitable  brick 
chambers,  the  nitrogen  of  the  air  passing  on.  The  sulphur  is 
melted  under  hot  water  at  a  high  pressure,  and  brought  to  market. 

Manufacture  of  chlorine. — The  manufacture  of  chlorine  is 
intimately  connected  with  the  Leblanc  soda  process,  for  hydrogen 
chloride  is  thereby  produced  in  large  amount.  There  are  two 
remunerative  processes  for  the  manufacture  of  chlorine  :  the  usual 
one,  viz.,  the  treatment  of  manganese  dioxide  with  hydrochloric 
acid;  and  the  mutual  action  of  air  and  hydrogen  chloride  at  a 
high  temperature,  in  presence  of  some  material  (best,  copper 
chlorides)  capable  of  inducing  their  action.  The  last  process  is 
generally  called  the  "  Deacon  chlorine  process,"  for  Mr.  Deacon 
was  the  first  to  make  it  a  commercial  success.  The  first  process 
is  always  worked  so  as  to  recover  the  manganese  ;  this  improvement 
is  due  to  the  late  Mr.  Weldon. 

1.  The  manganese  chlorine  process.-— The  chief  source  of 
the  manganese  ore  is  the  Spanish  province  of  Huelva;  the  ore 
consists  essentially  of  dioxide.  It  is  broken  into  fragments  smaller 
than  a  hen's  egg,  and  placed  in  "  chlorine  stills,"  built  of  sandstone 
boiled  in  tar  ;  .such  stills  are  sometimes  cut  from  a  single  block  of 
sandstone.  They  are  circular  or  octagonal  troughs,  covered  with  a 
block  of  sandstone,  the  junction  between  the  cover  and  the  trough 
being  made  tight  by  a  circular  band  of  india-rubber,  on  which  the 
cover  rests.  The  acid  is  admitted  and  the  chlorine  evolved 
through  holes  cut  in  the  cover.  The  ore  (6  to  10  cwt.)  is  placed 
on  a  grating  or  table  standing  in  the  still,  and  acid  is  run  in  till 
the  still  is  three-quarters  full.  The  first  reaction  takes  place 
quickly;  it  consists  probably  in  the  formation  of  MnCl3,  thus  : — 
k2Mn02  +  8HC1  =  2MnCl3  +  4H20  +  C12.  When  the  first  action 
has  ceased,  steam  is  blown  in  for  about  10  minutes,  so  as  to  com- 
plete the  reaction — 2MnCl3  =  MnCl2  +  C12;  fresh  steam  is  intro- 
duced at  successive  periods  of  an  hour.  Only  a  portion  of  the 
hydrochloric  acid  is  used ;  6  to  10  per  cent,  remains  free  after  the 
action  is  completed,  and  the  chlorine  produced  amounts  to  only 
about  one-third  of  that  contained  in  the  acid  used. 

Weldon's  manganese -recovery  process. — The  manganese 
chloride  from  the  stills  is  run  oft'  and  mixed  in  a  covered  tank 
with  calcium  carbonate  to  neutralise  the  free  acid,  and  to  precipi- 
tate the  iron  from  the  ore  as  ferric  hydroxide.  The  precipitate  is 


RECOVERY   OF   MANGANESE.  679 

allowed  to  settle,  and  the  clear  liquor  is  mixed  with  milk  of  lime 
free  from  magnesia.  This  precipitates  manganese  hydroxide,. 
Mn(OH)2,  and  the  object  of  the  process  is  to  convert  this  hyd] - 
oxide  into  hydrated.  dioxide  by  meanssof  a  blast  of  air.  If  air 
were  blown  through  such  moist  hydroxide  at  a  high  temperature,, 
only  one-third  of  the  manganese  would  be  oxidised,  the  product 
being  hydrated  Mn304,  which  may  be  viewed  as  Mn02.2MnO  ;  at 
the  ordinary  temperature  the  action  would  be  very  slow,  and. 
would  lead  to  the  formation  of  Mn203  =  Mn02.MnO.  But  if 
excess  of  lime  be  added  in  addition  to  that  required  to  precipitate 
manganous  hydroxide,  and  if  the  mud  of  hydroxides  of  manganese 
and  calcium  be  exposed  to  air  in  a  hot  state,  a  mixture  of  man- 
ganites  of  calcium,  of  the  formulae  Ca0.2Mn02  and  CaO.Mn02,  is 
formed,  in  which  all  manganese  is  in  the  state  of  peroxide.  The 
presence  of  calcium  chloride  in  the  liquid  is  desirable,  inasmuch 
as  it  is  then  better,  able  to  dissolve  lime,  and  to  bring  about  its 
combination  with  the  peroxide. 

The  mud  is  placed  in  tall  iron  cylinders  and  heated  by  blowing 
in  steam ;  air  is  then  forced  in.  The  temperature  should  not  exceed 
65°,  else  Mn304  and  Mn203  are  formed.  The  manganese  rapidly 
oxidises,  and  the  colour  of  the  mud  changes  to  black.  When  the 
amount  of  dioxide  no  longer  increases,  manganous  chloride  is  run 
in,  when  the  reaction  occurs  : — 

2(CaO.MnO2)  +  MnCla.+  H20  =  Ca0.2Mn02  +  Mn(OH)2 

+  Cade. 

The  mud  is  then  run  into  tanks  and  the  calcium  chloride  drawn 
off  from  the  precipitated  sludge. 

A  different  form  of  chlorine  still,  taller  in  proportion  to  its 
diameter,  and  unprovided  with  a  grating,  is  made  use  of.  It  is 
charged  with  hydrochloric  acid,  and  the  mud  is  run  in  as  long  as 
chlorine  is  evolved ;  the  mixture  grows  hot,  and  nearly  all  the 
hydrochloric  acid  may  be  utilised,. only  \  to  1  per  cent,  remaining 
free  at  the  end  of  the  reaction.  It  is  advisable  to  employ  the  acid 
liquor  from,  the  stills  charged  with  manganese  ore  along  with, 
fresh  hydrochloric  acid  in  the  mud.  stills;  the  free  acid  is  thus 
saved. 

Another  process  of  manganese  recovery,  practised  on  a  limited \ 
scale,  is  due  to  Mr.  Dunlop.  It  consists  in  converting  the  man- 
ganous chloride  into  carbonate  by  heating  its  solution  under 
pressure  with  chalk;  the  calcium  chloride  is  removed,  and  the 
precipitated  manganous  carbonate,  while  still  moist,  heated  in  a 


680  PROCESSES   OF  MANUFACTURE. 

current  of  air.     It  is  thus  converted  into  dioxide,  which  is  used  for 
a  subsequent  operation,  as  in  the  Weldon  process. 

2.  The  Deacon  chlorins  process. — The  fundamental  reaction 
of  this  process  is  expressed  by  the  equation  4HC1  +  02  = 
2H30  +  2C13.  But  the  action  is  a  very  incomplete  one  unless 
some  porous  substance  be  present,  and. even  then  it  would  amount 
to  only  a  small  fraction  of  the  theoretical  product.  The  presence 
of  copper  chlorides  causes  it  to  take  place,  and  on  the  small  scale 
as  much  as  90  per  cent,  of  the  hydrogen  chloride  has  been  thus 
decomposed.  The  cuprous  chloride  effects  the  reaction  2Cu2Cl2  -f 
4HC1  +  02  =  4CuCl,  +  2H20,  and  the  cupric  chloride  evolves 
chlorine,  regenerating  cuprous  chloride,  thus  : — 2CuCl2  = 
2Cu2Cl2  +  C12.  The  reaction  can  take  place  only  at  such  a  tem- 
perature that  the  absorption  and  evolution  of  chlorine  are  at  a 
balance ;  it  begins  a't  204°,  and  is  most  active  between  373°  and 
400°.  At  417°,  cupric  chloride  volatilises.  The  reaction  depends 
not  on  the  amount,  but  on  the  surface,  of  the  copper  chlorides, 
and  to  increase  surface,  fragments  of  brick  soaked  in  copper  sul- 
phate are  employed.  The  sulphate  is  rapidly  converted  into 
chloride. 

In  this  process  the  hydrogen  chloride  may  be  taken  directly 
from  the  salt-cake  pans  or  the  decomposing  furnace.  It  enters  a 
set  of  pipes,  in  which  its  temperature  is  raised  to  400° ;  it  then 
passes  into  a  cylindrical  chamber,  filled  with  prepared  brick,  and 
surrounded  by  a  non-condncting  jacket  to  prevent  heat  escaping. 
At  the  commencement,  this  chamber  is  heated  by  the  waste  heat 
from  the  fire  employed  to  heat  the  gas,  but  it  maintains  its  own 
temperature  after  a  short  time.  The  temperature  must  be  care- 
fully regulated  during  the  whole  operation.  The  exit  from  the 
brick-chamber  leads  to  a  series  of  glass  or  earthenware  pipes,  in 
which  the  mixture  of  escaping  gases — chlorine,  hydrogen  chloride, 
nitrogen,  excess  of  oxygen,  and  steam — is  cooled;  hydrogen 
chloride  is  removed  by  passing  the  gases  upwards  through  a  coke- 
tower,  down  which  water  flows ;  and,  if  required  for  the  manufac- 
ture of  bleaching  powder,  the  gases  are  dried  by  passing  through 
a  similar  tower  fed  with  oil  of  vitriol.  They  then  pass  through  a 
Root's  blower;  this  blower  ensures  the  entry  of  sufficient  air  from 
leakage  in  the  decomposing  furnace,  pipes,  &c.,  to  supply  oxygen 
for  the  hydrogen  chloride. 

The  cuprous  bricks  become  exhausted  after  some  time,  probably 
losing  their  porosity,  and  one  of  the  disadvantages  of  the  process 
is  the  necessity  of  frequently  replacing  them  by  freshly  prepared 


BLEACHING   POWDEK.  681 

ones.     The  amount  of  decomposed  hydrogen  chloride  on  the  large 
scale  seldom  exceeds  45  per  cent,  of  the  total  amount  present. 

Bleaching  powder.  —  The  chief  use  of  chlorine  is  in  the  manu- 
facture of  bleaching  powder,  "bleach,"  or  "chloride  of  lime." 
The  upshot  of  many  researches  on  the  formula  of  bleaching  powder 
has  been  to  show  that  it  undoubtedly  consists  of  the  compound 

PI 

,  with  a  little  free  lime  mechanically  protected  from  the 


action  of  chlorine,  and  about  15  per  cent,  of  water.  It  has  been 
proved  to  contain  no  calcium  chloride,  because  all  chlorine  is  ex- 
pelled by  passing  over  it  a  current  of  carbon  dioxide  ;  calcium 
chloride  treated  thus  of  course  remains  unaltered  (see  also  p.  463). 

For  the  manufacture  of  good  bleaching  powder,  the  lime  must 
be  specially  pure,  well  slaked,  and  free  from  lumps,  and  it  should 
contain  no  magnesia.  It  is  exposed  to  the  action  of  chlorine,  made 
by  the  manganese  process,  and  therefore  nearly  pure,  spread  on  the 
floors  of  chambers  of  brickwork  or  lead  or  cast-iron,  six  feet  high, 
and  of  considerable  area  ;  these  chambers  are  protected  internally 
by  a  layer  of  cement  and  tar.  The  gas  is  introduced  in  the  roof, 
and  descends,  owing  to  its  weight.  The  progress  of  the  operation 
is  seen  through  windows  in  the  cast-iron  doors;  when  the 
chambers  are  seen  to  be  green,  admission  of  chlorine  is  stopped. 
The  chlorine  being  forced  in  under  a  slight  pressure,  some  fresh 
lime  is  thrown  in  to  absorb  that  remaining  in  the  chambers  ; 
workmen  then  enter,  their  mouths  protected  by  bandages  of  wet 
cloth,  and  rake  the  powder  so  as  to  expose  fresh  surfaces.  Chlorine 
is  again  introduced,  and  when  absorption  again  ceases,  the  powder 
is  removed  and  packed  in  casks.  The  amount  of  available  chlorine, 
i.e.,  the  amount  which  is  capable  of  liberating  iodine,  acting  as  an 
oxidiser,  &c.,  is  usually  37  to  38  per  cent.,  but  may  in  exceptional 
circumstances  rise  to  43  per  cent.  During  the  whole  operation  the 
temperature  is  kept  as  low  as  possible. 

Should  the  chlorine  be  made  by  the  Deacon  process,  and  be  con- 
sequently diluted  with  nitrogen  and  oxygen,  a  larger  surface  of 
lime  may  be  exposed,  because  there  is  less  danger  of  heating,  and 
because  the  chlorine  is  not  so  greedily  absorbed.  The  chambers 
are  filled  by  a  series  of  slate  shelves,  distant  from  each  other  about 
a  foot,  and  so  arranged  that  the  gas  zig-zags,  passing  over  shelf 
after  shelf  on  its  way  from  the  top  of  the  chamber  to  the  ground. 
The  weaker  chlorine  is  brought  into  contact  with  fresh  lime,  and 
the  fresh  chlorine  with  lime  already  partially  charged.  By  this 
method  the  bleaching  powder  contains  a  less  percentage  of  avail- 


682  PROCESSES   OF  MANUFACTURE. 

able  chlorine  than  if  purer  chlorine  be  used ;  the  amount  seldom 
exceeds  36  per  cent. 

Potassium  chlorate. — The  chlorine  may  also  be  utilised  in 
the  manufacture  of  potassium  chlorate,  though  for  this  substance 
there  is  only  a  limited  demand.  To  prepare  chlorate,  the  chlorine 
is  led  into  a  closed  leaden  tank,  filled  with  milk  of  lime,  continually 
agitated  and  splashed  by  a  mechanical  stirrer.  It  is  rapidly  ab- 
sorbed, with  great  evolution  of  heat ;  the  hypochlorite  of  calcium  first 
formed  is  rapidly  changed  into  chlorate.  The  reaction  occurs  : — 

6Ca(OH)2.Aq  +  6C12  =  5CaCl2.Aq  +  Ca(C103)2.Aq  +  6H20. 

In  actual  practice  it  is  found  that  the  ratio  of  chlorine  in 
chloride  to  that  in  chlorate  is  5 '5  to  I,  instead  of  5  to  1,  as  required 
by  theory ;  some  oxygen  is  said  to  escape  (?).  After  the  lime  mud 
has  settled,  potassium  chloride  equivalent  to  the  calcium  chlorate 
is  added  to  the  liquor  drawn  off  from  the  sediment,  and  the 
mixture  is  evaporated  in  iron  pans.  On  cooling,  the  less  soluble 
potassium  chlorate  crystallises  out,  leaving  the  very  soluble  calcium 
chloride  in  the  mother  liquor.  On  cooling  the  mother  liquor, 
a  fresh  crop  of  crystals  of  chlorate  separates.  The  potassium 
chlorate  is  rendered  sufficiently  pure  by  a  second  crystallisation 
from  hot  water. 

Sodium  chlorate  is  made  from  potassium  chlorate  by  treating 
a  solution  of  the  latter  with  hydrosilicifluoric  acid,  prepared  by 
passing  silicon  fluoride  into  water;  the  insoluble  silicifluoride  of 
potassium  is  removed,  and  the  liquid  is  evaporated  till  crystals 
separate. 

All  these  operations  are  often  concurrently  carried  out  in  an 
alkali-work  employing  the  Leblanc  soda  process.  It  is  a  matter 
of  choice  whether  the  manganese  chlorine  process  or  that  of 
Deacon  be  employed,  but  most  works  prefer  the  former.  It  will 
be  seen  that  with  recent  improvements  most  of  the  by-products 
are  utilised.  The  sulphur  is  recovered;  the  carbon  dioxide 
required  to  decompose  the  waste  may  be  obtained  from  the  lime- 
kilns ;  the  calcium  carbonate  produced  from  the  waste  is  returned 
to  the  black-ash  furnace;  but  of  the  chlorine  of  the  salt,  two- 
thirds  are  rejected  as  calcium  chloride  by  the  manganese  chlorine 
process,  whereas,  by  Deacon's  process,  one  half  is  at  least  utilised. 
The  manganese  dioxide  employed  in  the  manufacture  of  chlorine  is 
regenerated,  but  here  again  with  an  expenditure  of  lime. 


THE  AMMONIA-SODA  PROCESS.  683 

The  other  important  process  for  the  manufacture  of  alkali  is 
theoretically  more  perfect,  but  up  to  the  present  it  has  not  been 
found  possible  to  combine  it  with  the  profitable  manufacture  of 
chlorine. 

2.  The  ammonia-soda  process. — The  fundamental  reaction 
involved  by-  this  process  is  : — 

NaCl.Aq  +  NH3.Aq  +  H20  +  C02  =  HNaC03  +  NH4Cl.Aq. 

It- was  first  made  successful  by  M.  Solvay,  about  1864. 

Brine  from  a  salt-mine,  purified  from  salts  of  magnesium  by 
the  addition  of  a  little  milk  of  lime,  and  of  the  added  lime  by 
ammonium  carbonate,  is  filtered  and  cooled;  it  is  brought  up  to 
saturation  by  addition  of  solid  salt,  and  saturated  with  ammonia, 
produced  by  heating  ammonium  chloride  with  calcium  hydrate. 
It  is  then  introduced  into  vertical  cylinders  of  considerable  height 
(36  to  63  feet),  provided  with  perforated  shelves ;  or,  more 
usually,  it  is  placed  in  a  set  of  shorter  cylinders,  arranged  in  a 
vertical  column,  their  united  height  being  equal  to  that  mentioned. 
Carbon  dioxide  from  the  lime-kiln  in  which  the  lime-stone  is 
burned  in.  order  to  provide  lime  to  decompose  the  ammonium 
chloride,  after  being  washed  and  cooled,  is  pumped  in  at  the 
bottom  of  the  lowest  cylinder,  in  a  series  of  jerks,  by  a  powerful 
pump.  This  carbon  dioxide  is  necessarily  dilute,  containing  about 
25  per  cent.  C02.  Towards  the  end,  as  the  liquid  becomes 
saturated,  purer  carbon  dioxide,  obtained  by  heating  sodium 
hydrogen  carbonate,  is  made  use  of.  Crusts  of  hydrogen  sodium 
carbonate  deposit  on  the  perforated  shelves ;  when  the  operation 
is  complete,  the  liquid  containing  undecomposed  salt,  ammonium 
chloride,  and  excess  of  ammonia,  is  run  off ;  it  enters  the  stills, 
where  it  is  treated  with  milk  of  lime  and  where  the  ammonia  is 
recovered.  During  the  passage  of  carbon  dioxide,  heat  is  generated 
in  the  cylinders,  but  they  are  cooled  from  the  outside  by  cold 
water,  and,  moreover,  the  expansion  of  the  carbon  dioxide  on  its 
passage  upwards  absorbs  heat,  so  that  the  temperature  does  not 
rise  greatly.  The  escaping  dioxide  is  -passed  through  fresh  brine, 
so  as  to  deprive  it  of  ammonia. 

Water  is  then  run  into  the  cylinders  and  steam  is  blown  in. 
The  crusts  of  bicarbonate  of  soda  dissolve,  and,  on  cooling,  separate 
in  crystals.  It  is  collected,  dried  at  60°,  and  heated  in  closed 
vessels  to  expel  carbon  dioxide,  which  again  passes  into  the  decom- 
posing cylinders. 

This  process  should  theoretically  realise  the  equation  2XaCl  -f- 


684  PROCESSES   OF  MANUFACTURE. 

CaC03  =  CaCL  -f  Na2C03,  if  the  ammonia  were  perfectly  re- 
covered ;  but  in  practice  the  loss  of  ammonia  amounts  to  about 
6  to  8  per  cent,  of  the  carbonate  of  soda  formed. 

The  product  is,  of  course,  free  from  sulphides  and  caustic  soda, 
but  it  is  less  dense  than  that  obtained  by  the  Loblanc  process.  A 
very  large  amount  of  carbonate  is  now  made  by  this  process ;  it 
may  be  causticised  in  the  usual  way  if  caustic  soda  is  required,  or 
ferrate  of  sodium,  Na2Fe03,  may  be  made  by  heating  it  with  ferric 
oxide  with  free  access  of  air,  and  then  decomposed  by  water,  the 
ferric  oxide  being  precipitated,  while  caustic  soda  remains  in  the 
liquor. 

A  modification  of  this  process  which  is  also  worked  consists  in 
the  preparation  of  solid  hydrogen  ammonium  carbonate  by  the 
action  of  carbon  dioxide  on  ammonia  solution.  This  solid  is  filtered 
on  to  cloth  filters  and  then  watered  with  a  solution  of  salt ;  it  is 
thereby  converted  into  bicarbonate  of  soda,  while  liquor  containing 
ammonium  chloiide,  one-third  of  the  salt  used,  and  one-third  of 
undecomposed  ammonium  hydrogen  carbonate,  runs  through.  Ifc  is, 
however,  difficult  to  prevent  considerable  loss  of  ammonia,  and  the 
large  mass  of  material  on  the  filters  is  difficult  to  handle.  It  is  then 
ignited  in  a  reverberatory  furnace,  the  carbon  dioxide  being  lost. 

These  are  among  the  most  important  chemical  processes  carried 
out  on  a  large  scale.  For  detailed  information  the  reader  is 
advised  to  consult  Lunge's  Sulphuric  Acid  and  Alkali  Manufacture  ; 
Richardson  and  Watts'  Technical  Dictionary;  Thorpe's  Dictionary 
of  Applied  Chemistry ;  and,  above  all,  the  Journal  of  the  Society  of 
Chemical  Industry. 


INDEX. 


MINERALS    AND    ORES. 


Agate,  49,  300. 
Alabandine,  244. 
Alabaster,  422. 
Albito,  29,  315. 
Allamontite,  556. 
Altaite,  295. 
Aluminite,  424. 
Alum  stone,  410. 
Al unite,  426. 
Alunogen,  424. 
Amethyst,  237. 
Anatase,  44,  275,  300. 
Anglesite,  410,  429. 
Anhydrite,  31,  409. 
Anorthite,  315. 
Antimony  bloom,  349. 
Antimony  ochre,  57. 
Apatite,  31,  57,  358. 
Aquamarine,  31. 
Argyrodite,  49,  301. 
Argyrose,  487. 
Arragonite,  286. 
Arsenical  pyrites,  57. 
Arsenopy  rites,  554. 
Arsenosid^rite,  552. 
Asbestos,  33. 
Atacarnite,  483,  493. 
Augite,  33,  313. 
Azurite,  79,  290. 

Barnhardite,  257. 

Barytes,  31,  409. 

Basalt,  49. 

Bauxite,  240. 

Beegerite,  380. 

Berthierite,  380. 

Berychite,  256. 

Beryl,  31,  312. 

Berzelianite,  487. 

Biotite,  33. 

Black  band  iron  ore,  40,  288. 

Black  copper  ore,  487. 

Black  lead,  43. 

Blende,  33,  62,  225. 

Blue  iron  ore,  351. 

Bog  diamond,  49,  300. 


Bog  iron  ore,  40,  248. 
Boracite,  35,  232. 
Borax,  35,  232. 
Boronatrocalcite,  35. 
Botryolite,  314. 
Boulangerite,  380. 
Bournonite,  380. 
Braunite,  41,  248,  251. 
Breithauptite,  552. 
Brochanite,  432. 
Bromargyrite,  174. 
Brookite,  44,  275. 
Brown  haematite,  2i8. 
Brown  iron  ore,  40. 
Brucite,  225. 

Cacoxene,  361. 
Cairngorm,  300. 
Calamine,  33. 

„         siliceous,  313. 
Calcspar,  31,  286. 
Caliche,  325. 

Capillary  pyrites,  41,  24  L 
Carbon,  43. 
Carbonado,  43,  47. 
Carnallite,  33,  123. 
Carnelian,  300. 
Carrolite,  248. 
Cassiterite,  50,  301. 
Castor  and  pollux,  29. 
Catseye,  300. 
Celestine,  31,  409. 
Cerite,  36,  44,  232,  316. 
Cerussite,  50,  288. 
Chalcedony,  49,  300. 
Chalcolite,  393. 
Chalcopyrrhotite,  257. 
Chalcostibite,  380. 
Chalk,  31,  287. 
Chert,  300. 
Childrenite,  361. 
Chili  saltpetre,  72,  319. 
China  clay,  37,  314. 
Christophite,  248. 
Chrome  iron  ore,  248,  251. 
Chrome  ochre,  248. 


686 


INDEX.      MINERALS   AND    ORES. 


Chrysoberyl,  31,241. 

Chrysocolla,  316. 

Chrysoprase,  300. 

Chrysorite,  313. 

Cinnabar,  62,  79,  487. 

Clausthalite,  295. 

Clay,  49. 

Clay  band,  40,  288. 

Clay  iron  stone,  4'J,  252. 

Cobalt  bloom,  361. 

Cobaltite,  554. 

Collyrite,  308. 

Columbite,  36. 

Copperas,  410,  427. 

Copper  bloom,  487. 

Copper  glance,  79,  487. 

Copper-nickel,  41. 

Copper  pyrites,  79,  218,  256,  257. 

Coprolites,  57. 

Corellin,  487. 

Corneous  lead,  148,  288. 

Corundum,  37,  237. 

Corynite,  554. 

Cosalite,  380. 

Crocoisite,  263. 

Cryolite,  29,  37,  72,  115,  133. 

Cryptolite,  362. 

Cuprite,  79. 

Datolite,  36,  232,  314. 
Daubreelite,  256. 
Dechenite,  329. 
Derbyshire  spar,  31. 
Delvauxite,  361. 
Descloisite,  329. 
Diamond,  43,  46. 
Diaspore,  240. 
Dolomite,  33,  287. 
Dolorite,  31. 
Dumortierite,  314. 

Emerald,  31,  312. 

Emerald  nickel,  290. 

Emery,  57,  237. 

Emplectite,  380. 

Epsom  salts,  423,  409,  33. 

Eucryptite,  314. 

Euxenite,  36,  44,  49,  54,  275,  319. 

Feather  alum,  409,  424. 
Felspar,  29,  37. 
Fergusonite,  393. 
Ferrotellurite,  428. 
Fibrolite,  314. 
Fischerite,  361. 
Flint,  300,  49. 
Fluocerite,  144. 
Fluorspar,  31,  72,  120. 
Franklinite,  254,  225. 
Frogerite,  404. 


Gadolinite,  316,  36,  44,  232. 
Gahnite,  241.      . 
Galena,  50,  62,  294. 
Galenobismuthite,  380. 
Garnierite,  316. 
Geooronite,  380. 
Gibbsite,  240,  361. 
Glance-cobalt,  41. 
Glaserite,  409. 
Glauber's  salt,  29,  409,  420. 
Glaucodot,  554. 
Glaucopyrites,  554. 
Gothite,  40,  252. 
Granite,  49. 
Graphite,  43,  47. 
Green  iron  ore,  361. 
Greenockite,  33,  228. 
Green  vitriol,  410,  427. 
Grey  iron  ore,  248,  252. 
Grossularite,  314. 
Guejarite,  380. 
Gypsum,  421,  409. 
Gyrolite,  312. 

Hsematite,  48,  251,  402. 
Hausmannite,  41,  248,  254. 
Heavy- spar,  409,  31. 
Hessite,  487. 
Hetserolite,  254. 
Hornblende,  313,  33,  37. 
Horn  quicksilver,  175. 

„     silver,  79. 
Hornstone,  300. 
Hyacinth,  275. 
Hydromagnesite,  289. 

Icelarid-spar,  286,  31. 
Ilmenite,  290. 
Indigo-copper,  487. 
lodargyrite,  174. 
Iron  pyrites,  258,  41,  62. 

Jade,  314. 
Jamesonite,  380. 

Kaneite,  552. 
Kaolin,  37,  314. 
Kerargyrite,  174. 
Kidney  ore,  40. 
Kieserite,  423. 
Ktipfer-nickel,  552,  41,  57. 

Labradorite,  315. 
Lake  ore,  40. 
Lanarkite,  410. 
Lanthanite,  287. 
Leadhillite,  410. 
Lead  ochre,  294. 
Lepidolite,  28,  29. 
Leucite,  314. 


INDEX.      MINERALS   AND   ORES 


687 


Leueopyrite,  552. 
Liebigife,  393. 
Limestone,  287,  31. 
Limonite,  248. 
Linnolite,  252,  256,  499. 
Livingstonite,  380. 
Loadstone,  40. 
Lolingite,  552. 
Lourgite,  426. 

Magnesioferrite,  254. 

Magnesite,  287,  33. 

Magnetic  iron  ore,  40,  244,  254. 

pyrites,  257,  248. 
Magnetite,  40,  244,  254. 
Malacone,  275. 
Manganese  blende,  244. 
Marble,  281,  31. 
Marcasite,  258. 
Martite,  251. 
Matlockite,  298. 
Meerschaum,  313,  33. 
Melaconite,  487. 
Melanochroite,  263. 
Mendipite,  293. 
Meneghinite,  380. 
Miargyrite,  380. 
Mica,  314,  29,  37. 
Millerite,  24*. 
Mimetesite,  363. 
Mispickel,  57,  553. 
Molybdenum  glance,  393. 
Molybdic  ochre,  393. 
Mottramite,  54. 
Mundic,  258. 
Muscovite,  314. 

Natrolite,  314. 
Needle  iron  ore,  252. 
Niccolite,  552,  41. 
Nickel  bloom,  361. 
Niobite,  54. 
Nitre,  29,  325. 
Nosean,  315. 

Okenite,  307,  312. 
Olivine,  313,  33. 
Onyx,  300. 
Opal,  300,  49. 
Ores,  33. 

Orpiment,  57,  346. 
Orthite,  36,  44. 
Orthoclase,  304,  315. 

Pacite,  554. 
Paragonite,  314. 
Pegmatite,  43,  361. 
Pentlandite,  248. 
Perowskite,  44,  290. 
Petalite,  28,  315. 


Pharmacolite,  359. 
Phenacite,  31. 
Phenavite,  3 1 2. 
Phosphocalcite,  364. 
Phosphocerite,  362. 
Phosphorite,  31,  57. 
Pitchblende,  60,  393. 
Plumbago,  43. 
Plumboarragonite,  288. 
Plumbocalcite,  288. 
Polybasite,  380. 
Porphyry,  49. 
Potash  alum,  425. 
Potash-felspar,  29. 
Prehnite,  314. 
Proustite,  79. 
Psilomelane,  41. 
Purple  copper,  257,  487. 
Pyrargyrite,  79,  380. 
Pyrites,  37,  41. 
Pyrochlore,  319,  393. 
Pyrolusite,  41,  258. 
Pyromorphite,  363. 
Pyrophyllite,  314. 

Q.uartz,  300,  49. 

Eammelsbergite,  552. 
Realgar,  57,  346. 
Red  haematite,  248. 

„    lead  ore,  263. 

„    zinc  ore,  225. 
Rhodonite,  316. 
Rock-crystal,  300,  49. 
Rock  salt,  72. 
Rose  quartz,  300. 
Ruby,  37,  237. 
Rutile,  275,  44. 

Saltpetre,  29,  319,  325. 
Samarskite,  36,  232,  330,  393. 
Sandstone,  49. 
Sapphire,  37,  237. 
Sassolite,  35,  232,  234. 
Satin-spar,  422. 
Scheeletine,  393. 
Soheelite,  393,  60. 
Schist,  49. 
Schonite,  409. 
Selenite,  421,31. 
Senarmontite,  349. 
Serpentine,  307,  33,  313. 
Siderite,  288. 
Silica,  302,  49. 
Silver  bismuth  glance,  380. 

„      copper  glance,  79. 

„      glance,  79,  487. 
Skutterudite,  552. 
Smaltite,  552,  41,  57. 
Soap  stone,  33. 


688 


INDEX.   MINERALS  AND  ORES. 


Sodalite,  315. 

Spathic  iron  ore,  40,  244,  288. 

Specular  iron  ore,  40,  248,  251. 

Speiss,  553. 

Sphene,  213,  44. 

Spinel,  241,  254. 

Spinels,  253. 

Spodumene,  314. 

Steatite,  33. 

Stephanite,  380. 

Stibnite,  346,  57. 

Stromeyerite,  487. 

Stroutianite,  287,  31. 

Syepoorite,  244. 

Sylvin,  29. 

Talc,  313,  33. 
Tantalite,  54,  319. 
Tchermigite,  425. 
Telluric  bismuth,  352. 

silver,  487. 
Tephroite,  316. 
Thenardite,  409. 
Thorite,  316,  44,  275. 
Tincal,  35. 

Titaniferous  ore,  40,  44. 
Topaz,  237,  314. 
Trap,  49. 

Triphylline,  28,  361. 
Triplite,  361. 
Trona,  286. 
Tungstic  ochre,  393. 
Turgite,  252. 
Turpeth  mineral,  432. 
Turquoise,  361. 
Tysonite,  144. 

Uilmannite,  554. 


Ultoclasite,  554. 
Uranite,  393. 
Uranosphaerite,  404. 
Uranospinite,  404. 

Vanadinite,  329,  319. 
Vauquelinite,  263. 
Vivianite,  361. 
Volborthite,  330. 

Wad,  248,  41. 
Wagnerite,  360. 
Walpurgin,  404. 
Wavellite,  361,  57. 
White  nickel,  553. 
Willemite,  313. 
Witherite,  31,  287. 
Wittichenite,  380. 
Wolfram,  393,  60. 

„         ochre,  393. 
Wollastonite,  31 2,  307. 
Wulfenite,  393,  60. 

Xanthosiderite,  252. 
Xenolite,  314. 
Xenotime,  360. 

Yellow  lead  ore,  393. 
Yttrotantalite,  36,  232. 

Zeilanite,  254. 

Zeunerite,  404. 

Zinc  blende,  325,  33,  62. 

„     bloom,  289. 
Zincite,  225. 
Zinckenite,  380. 
Zircon,  275,  44. 


GENERAL    INDEX. 


XOTE. — Fluorides,   chlorides,   bromides,   and   iodides  are    included  under  the 

head  halides. 

Sulphides,  selenides,  and  tellurides,  under  the  head  sulphides. 
Nitrides,   phosphides,   arsenides,   and    antimonides,    under   the    head 

nitrides. 


Acetylene,  508. 

Acid  chromates,  264. 

Acids,  89,  108.     See  also  Hydrogen. 

Acids.     See  Hydrogen  salts. 

Air,  70,  3,  6,  8,  12,  88,  274,  281. 

Alchemy,  4. 

Alkali  manufacture,  670. 

Allotropy,  43,  67,  78,  125,  141,  349. 

Alloys,  574,  577. 

Alum,  38,  425. 

Aluminium,  37. 

bronze,  582. 
„  halides,  133. 

„  manufacture,  652. 

„  nitrate,  328. 

„  ,        nitride,  &c.,  552. 
„  orthophosphate,  360. 

oxide,  sulphide,  237. 
pyrophosphate,  367. 
silicate,  314. 
sulphate,  424. 
Alums,  425. 
Amalgams,  32,  578. 
Amines,  524. 
Ammonia,  512. 

„          composition  of,  520. 
Ammonia-soda  process,  671,  683. 
Ammonium,  117. 

„  alum,  425. 

„  amalgam,  578. 

carbamate,  533. 
halides,  117. 
magnesium       phosphate, 

360. 

„  molybdate,  398. 

nitrate,  326. 
nitrite,  339. 
orthophosphate,  361. 
sulphate,  420. 
sulphides,  211. 
tribromide,  119. 


Amorphous  condition,  89. 
Analysis,  14. 

„         qualitative,  14. 
„         quantitative,  10,  14. 
Andrews,  387. 
Anhydrochromates,  264. 
Antimonates,  254. 
Antimonious  acid,  376. 
Antimonites,  379. 
Antimoniuretted  hydrogen,  518. 
Antimony,  56. 

„  amido-compounds,  536. 

halides,  160. 
manufacture,  650. 
,,  oxides,  346. 

„  phosphide,  556. 

„  sulphates,  431. 

,,  sulphides,  selenides,  tellur- 

ides, 352. 
,,  tetroxide,    compounds    of, 

374. 

Antimonosyl  halides,  385. 
Antimonyl  trichloride,  38  i. 
Aqua-regia,  341. 
Argentamines,  546. 
Arsenamines,  536. 
Arsenates,  354. 
Arsenic,  56. 

cyanide,  568. 
halides,  160. 
oxides,  346. 
„  „       double       compounds 

of,  363. 

„         phosphide,  556. 
„         sulphates,  430. 
„         sulphides,  351. 
Arsenites,  378. 
Arseniuretted  hydrogen,  518. 
Arsenyl  monochloride,  384. 

„        trifluoride,  383. 
Arsine,  518. 

2   Y 


690 


GENERAL  INDEX. 


Arsines,  532. 
Atmosphere,  70,  88. 
Atomic  heat,  127,  617. 
Atomic  theory,  3,  15. 
Atomic  weights,  17,  598,  610. 

„  „         deduction  from  spc. 

tra,  598. 

weights,  table  of,  23. 
Atoms,  109. 
Auramines,  546. 
Aurates,  492. 
Avogadro's  law,  96,  611. 

Bacon,  Roger,  5. 
Barium,  31,  120. 
,.         dioxide,  218. 
halides,  120. 
nitrate,  327. 
„         nitrite,  339.x 
,r         orthophospnate,  358. 
„         oxides,  sulphides,  218. 
„         phosphide,  550. 
sulphate,  421. 
sulphide,  218. 
Barometer,  92. 
Bases,  89. 

Basic  carbonates,  289. 
Basic  lining,  221. 
Basic  silicates,  308. 
Bassarow,  236. 
Becher,  10. 
Beetroot,  29. 
Bergman,  10. 
Bernthsen,  447. 
Berthollet,  14. 
Beryllium,  31. 

halides,  120. 
„  nitrate,  327. 

,,  orthophosphate,  358. 

rr  oxides,  218. 

sulphate,  421. 
sulphides,  218. 

Berzelius,  19,  36,  45,  144,  206,  627. 
Bessemer  process,  656. 
Bismuth,  56. 

„         halides,  160. 

„         manufacture,  661. 

nitrate,  330. 

„         orthophosphate,  364. 
oxides,  346,  350. 
oxyhalides,  385. 
,,         pyrophosphate,  368. 

sulphates,  431. 
„         sulphide,  350. 
Bismuth  amines,  536. 
Bismuthine,  346. 
Black,  10. 
Black  ash,  673. 
Black  Jack,  227,  33. 
Black  lead,  43. 


Bleaching  powder,  462,  681. 
Blue  vitriol,  410. 
Boisbaudran,  Lecoq  de,  598. 
Bone  black,  44. 
Boracic  acid,  233. 
Borates,  234. 
Borax,  232,  35. 
Borides,  497. 
Borofluorides,  13?. 
Boron,  35. 

ethyl,  50^. 
halides,  131. 

„       nitride,  551. 

„       phosphate,  360. 

„       sulphate,  424. 

„       tungstate,  401. 
Boyle,  7,  92. 
Boyle's  law,  92. 
Brass,  580. 
Brauner,  605. 

„         and  Tomicek,  351. 
Britannia  metal,  585. 
Bromates,  465. 
Bromic  acid,  465. 
Bromine,  72. 

halides,  169. 
Bronze,  586. 
Brunswick  green,  493. 
Bunsen,  29,  115,  351. 
Burnett's  disinfecting  fluid,  124. 

Cadmium,  33. 

„          halidea,  123. 
nitrate,  328. 
nitrite,  339. 
oxides,  225. 
phosphates,  360. 
phosphide,  551. 
sulphate,  423. 
„          sulphide,  225. 

yellow,  228. 
Ca&sium,  29. 

„         halides,  115. 
„         oxides,  211. 
„         sulphate,  420. 
sulphide,  211. 
Cailletet,  28. 
Calcium,  31. 

halides,  120. 
„         nitrate,  327. 
nitrite,  339. 
,,         orthophosphate,  358. 

oxide,  218. 
„         phosphide,  550. 
„         sulphate,  421 . 
„         sulphides,  218. 
Caliche,  325. 
Calorific  intensity,  642. 
Caput  mortuum,  427. 
Carbamic  acid,  533. 


GENERAL  INDEX. 


691 


Carbamide,  532. 
Carbides,  498. 
Carbon,  43. 

„       dioxide,  274,  10,  14,  16,  43. 

„       disulphide,  275,  282.   . 

„       halides,  144. 

„       monosulphide,  270. 

„       monoxide,  270. 

„       oxysulphide,  285. 

„       phosphate,  362. 

„       sesquioxide,  272. 

„       sesquisulphide,  272. 

„       sulphate,  428. 
Carbonates,  normal,  285. 

basic,  289. 
Carbonic  acid,  284. 

„         oxide,  16,  270. 
Carbonyl  chloride,  291. 
„        sulphide,  285. 
Carnelley  and  Williams,  325. 
Caron,  50. 
Cassel  yellow,  298. 
Castner's  process,  217,  651. 
Cast  steel,  657. 
Catalytic  action,  463. 
<  atseye,  300. 

Caustic  soda  manufacture,  675. 
Cavendish,  10. 
Cementation  process,  657. 
Cerium,  43. 

dioxide,  274,  283. 
halides,  144. 

„        nitrate,  329. 

„        orthophosphate,  362. 

„        sesquioxide,  273. 

„        sesquisulphide,  273. 

„        sulphates,  428. 

„       trioxide,  270. 
Chalk,  31,  287. 
Chamber  crystals,  417. 
Chance's  recovery  process,  677. 
Chemistry,  objects  of,  1. 
Chili  saltpetre,  72,  319. 
Chlorine,  72. 

halides,  169. 
hydrate,  76. 
manufacture,  678. 
oxides,  459. 
sulphides,  166. 
Chlorosulphonic  acid,  441. 
Chromamines,  526. 
Chromates,  262. 
Chrome  red,  262. 

„        ochre,  248. 
Chromic  acid,  262. 
Chromicyanides,  565. 
Chromium,  40. 

„          dioxide,  258. 
halides,  137. 
„          monosulphide,  243. 


Chromium  monoxide,  243. 
nitrate,  328. 
nitride,  552. 
orlhophosphate,  361. 
sesquioxide,  248. 
sesquisulphide,  248. 
sulphate,  426. 
trioxide,  261. 
Chromyl  dichloride,  268. 
„  '    difluoride,  268. 
Clark,  315. 

Claus's  recovery  process,  677. 
Clay,  49. 
Cleve,  603. 
Cobalt,  41. 

„       dioxide,  258. 
„      halides,  137. 

monosulphide,  243. 
monoxide,  243. 
nitrate,  328. 
nitrite,  340. 
orthophosphate,  361. 
phosphide,  552. 
sesquioxide,  248. 
sesquisulpliide,  248.J 
sulphate,  427. 
vitriol,  410. 
Cobaltamines,  528. 
Cobalticyanides,  567. 
Cobaltosamines,  532. 
Coke,  441. 

Colcothar  vitrioli,  427. 
Colloids,  309. 
Columbium,  53. 
Combustion,  8—12,  67. 

„  (in  manufacture),  642. 

Compounds,  88. 
Condy's  fluid,  2^7. 
Constitutional  formulae,  207. 
Cooke  and  Eichards,  202. 
Copper,  79. 

„        cyanides,  5^1, 
„       halides,  174. 
„        hydride,  577. 
„        manufacture,  661. 
„        nitrate,  330. 
„        nitride,  557. 
nitrite,  340. 
„        orthophosphate,  364. 

oxides,  487. 

„        pyrophosphate,  368. 
„        sulphate,  432. 
„        sulphides,  487. 
Coprolites,  57,  359. 
Cotton   goods,   fraudulent   weighting, 

124. 

Croceocobaltamines,  529. 
Cruokes,  87,  602. 
Cubic  saltpetre,  325. 
Cupramines,  545. 


VJ'2 


GENERAL   INDEX. 


Cuprosamines,  545. 
Cyanic-acid,  568. 
Cyanides,  560. 

„         constitution  of,  572. 
Cyanogen,  558,  554. 

.,  bromide,  568. 
chloride,  568. 
sulphide,  568. 

Dalton,  15. 

Davy,  29,  206,  499. 
lamp,  499. 

Debray,  61,  78. 

Debus,  451. 

Density  of  gaseous  elements,  612. 

Deville,  36,  37,  50. 

Diamond,  combustion  of,  276. 

Dichromates,  264. 

Didymium,  53,  603. 

Diffusion,  91,  309. 

Dissociation,  616. 

Dithionates,  449. 

Dithionic  acid,  448. 

Dithiopersulphuric  acid,  452. 

Ditte,  380. 

Divers,  344.  . 

Double  compounds,  of  ha'ides,  119, 
123, 125, 132, 136, 140, 142,  147, 153, 
160, 164,  166,  168, 171, 173, 179, 187. 

Double  compounds,  of  oxides,  214, 221, 
229,  246,  251,  259,  272,  297. 

Double  decomposition,  81,  121. 

Dross,  51. 

Dualistic  theory,  206. 

Dulong  and  Petit' s  law,  127,  617. 

Dumas,  99,  202,  207,  550. 

Dysprosium,  603. 

Earths,  38. 
Earths,  alkaline,  31. 

„       rare,  602. 
Ebullition,  91. 
Ekaaluminium,  640. 
Ekaboron,  640. 
Ekasilicon,  640. 
Electrolysis,  29,  74,  85. 
Electrum,  589. 
Elements,  3—13,  25. 

„         atomic  weights  of,  610. 

,,         general  remarks  on,  83. 

„         molecular  weights  of,  612. 

„         specific  volumes  of,  633. 

„         vapour  density  of,  612. 
Empedocles,  3. 
Empirical  formulae,  209. 
Epsom  salts,  423,  33,  409. 
Equations,  110. 
Equivalents,  19. 
Erbium,  56,  603. 
„        halides,  160. 


Erdmann  and  Marchand,  202. 
Erythrochromium  salts,  528. 
Ethane,  501. 
Ethylene,  507. 
Ethylphosphinic  acid,  375. 

Fehling's  process,  439. 
Fermentation,  278. 
Ferrates,  265. 

Ferric  compounds.     See  Iron. 
Ferricyanic  acid,  566. 
Ferri cyanides,  565. 
Ferroaluminium,  581. 
Ferrocyanic  acid,  563. 
Ferrocyanides,  562. 
Ferromanganese,  582. 
Ferrosamines,  532.. 
Ferrous  compounds.     See  Iron. 
Flavocobaltamines,  530. 
Fleitmann    and     Henneberg's     phos- 
phates, 372. 
Fluoboric  acid,  132. 
Fluorine,  65,  72. 

halides,  31,  72,  120,  169. 
Flux,  122. 
Formulae,  21. 

„         constitutional,  207. 

„         molecular,  126,  612,  et  seq. 
Free  path,  92. 
Friedel  and  Guerin,  146. 
Fritsche,  51. 
Fuels,  646. 

Fuscocobaltamines,  529. 
Fusible  alloys,  585. 

Galvanised  iron,  579. 
Gallium,  37. 

halides,  133. 

nitrate,  328. 

oxides,  237. 

sulphate,  424. 

sulphides,  237. 


Gas 
Gas 


97. 

carbon,  44. 


Gases,  91,  97. 

Gay-Lussac,  36,  94,  287,  462,  559. 
Gay-Lussac's  law,  94. 
Gay-Lussac  and  Thenard,  550. 
Gay-Lussac  and  Humboldt,  611. 
Geber,  4. 
Germanates,  316. 
Germanium,  49. 

dioxide,  300. 

disulphide,  300. 

halides,  148. 

monosulphide,  294. 

monoxide,  294. 

orthophosphate,  362. 
German  silver,  580. 
Gibbs,  403. 


GENERAL   INDEX. 


693 


Glatzel,  42. 

Glauber's  salt,  420,  29,  409. 

Glucinum,  31. 

Gold,  79. 

cyanides,  571. 

halides,  174. 

manufacture,  663. 

nitrate,  331. 

nitride,  557. 

oxides,  487. 

pyro phosphate,  368. 
„     sulphide,  487. 
Graham,  309,  391,  396,  576. 
Greek  fire,  58. 
Grey  gold,  584. 
Guanidine,  525. 
Guignet's  green,  252. 

Hales,  9. 
Halides,  88,  84. 

„         constitution  of,  504. 

„        double  compounds  of.     See 

Double  compounds. 
„        molecular  formulae  of,   126, 

135,  154. 

„        of  halides,  169. 
„         of  hydrogen,  112. 
„  „          composition  of, 

113. 

„         preparation  of,  182. 
„        properties  of,  184. 
„         sources  of,  181. 
Hard  spelter,  579. 
Hargreare's  process,  672. 
Heating  power,  642. 
Helmont,  ran,  10. 
Henry,  621. 

Hexametaphosphates,  370. 
Hexathionic  acid,  452. 
Hillebrand  and  Norton,  46. 
Hofmann,  100. 
Holmium,  603. 
Hydraulic  mortars,  313. 
Hydrazine,  515,  519. 
Hydrides,  575. 
Hydriodic  acid,  107. 
Hydroboric  acid,  497. 
Hydroborofluoric  acid,  133. 
Hydrobromic  acid,  107. 
Hydrochloric  acid,  108. 
Hydrocyanic  acid,  559. 
Hydrogen,  25,  10,  40. 

antimonate,  365. 
antimonide,  518. 
arsenates,  356. 
arsenide,' 518. 
arsenite,  378. 
borate,  233. 
boride,  497. 
borofluoride,  133. 


Hydrogen  bromate,  465. 
„          bromide,  104. 

„         hydrate  of,  112. 
„          carbonate,  284. 
,,          chlorate,  464. 
„          chloride,  104. 
„  „         composition     of, 

113. 

„  chloride,  hydrate  of,  112. 

,,  chlorosulphonate,  441. 

chromate,  263. 

cyanate,  568. 

cyanide,  559. 

dilithium  phosphate,  356. 

disodium  phosphate,  357. 

dithionate,  448. 

dithiopersulphate,  452. 

ferricyanide,  566. 

ferrocyanide,  563. 

fluoborate,  132. 

fluoride,  104. 

halides,  112. 

„       composition      of, 
113. 

hexathionate,  452. 

hypobromite,  462. 

hypochlorite,  461. 

hyponitrite,  344. 

hypophosphate,  373. 
.  hypophosphite,  447. 

hyposulphate,  448. 

hyposulphite,  447. 

hypovanadate,  335. 

iodate,  465. 

iodide,  104. 

metaphosphate,  369. 

molybdate,  396. 

niobate,  323. 

nitrate,  322. 

nitrides,  512. 

orthoantimonate,  356. 

orthoarsenate,  356. 

orthophosphate,  355. 

orthosulpharsenate,  356. 

oxalate,  273. 

oxides,  191. 

pentathionate,  451. 

perchlorate,  469. 

periodate,  469. 

permanganate,  267. 

phosphates,  352. 

phosphides,  514,  519. 

phosphite,  375. 

py roan timon ate,  365. 

pyroarsenate,  365. 

pyrophosphate,  365. 

pyrosulphate,  432. 

selenate,  417. 

selenide,  191. 

seleniotrithionate,  450. 

2  Y  2 


694 


GENERAL  INDEX. 


Hydrogen  selenite,  436. 

„         silicates,  303,  306,  309. 
,„         silicide,  500. 
„         sulphate,  415. 
sulphide,  191. 
,,         sulphite,  435. 
„         sulphocarbonate,  284. 
,,         sulphocyanate,  568. 
sulphostannate,  316. 
tellurate,  417. 
telluride,  191. 
tellurite,  436. 
tetrathionate,  450. 
thiosulphate,  444. 
trisulphide,  196. 
trithionate,  449. 
turigstate,  397. 
vanadate,  323. 
Hydrogenium,  576. 
Hydroxylamine,  523. 
Hypobromites,  461. 
Hypobromous  acid,  462. 
Hypochlorites,  462. 
Hypochlorous  acid,  461. 
Hypochlorous  anhydride,  460. 
Hypoiodites,  462. 
Hyponitrites,  344. 
Hypophosphites,  380,  381. 
Hypophosphoric  acid,  373. 
Hypophosphorous  acid,  380. 
Hyposulphuric  acid,  448. 
Hype-sulphurous  acid,  447. 

„  „     constitution  of, 

447. 
Hyporanadates,  335. 

Indium,  37. 

halides,  ]33. 
nitrate,  328. 
oxides,  237. 
sulphate,  424. 
sulphide,  237. 
Iodine,  72. 

halides,  169. 
oxides,  459. 
lodoplatininitrites,  484. 
Iridamines,  540. 
Iriclicyanides,  570. 
Iridium,  77. 

halides,  177. 
„         oxides,  480. 
„         sulphate,  431. 
sulphide,  480. 
Iron,  40. 

carbide,  510. 
disulphide,  258. 
halides,  137. 
manufacture,  653. 
monosulphide,  243. 
monoxide,  243. 


Iron  nitride,  552. 

,,     orthophosphate,  361. 

,,     sesquioxide,  248. 

„     sesquisulphide,  248. 

„     sulphates,  426. 

„     trinitrate,  328. 

„     trioxide,  261. 

„     valency  of,  273. 
Isomorphism,  law  of,  620. 

Jaune  brillant,  228. 

Keiser,  203. 

Kelp,  116. 

Kirchhoff,  115. 

Klason,  291. 

Kopp,  618. 

Kriiss  and  Nilson,  605. 

Kundt  and  Warburg,  624. 

Lagoni,  234. 
Lampblack,  45. 
Lana  philosophica,  227. 
Lanthanum,  36. 

halides,  131. 

„  orthophosphate,  360. 

„  sulphate,  424. 

Laurent  and  Grerhardt,  207. 
Lavoisier,  11,  206. 
Lead,  49. 

„      dioxide,  300. 

halides,  148. 

manufacture,  659.       ' 

monosulphide,  294. 

monoxide,  294. 

nitrate,  329. 

nitrite,  340. 

orthophosphate,  362. 

phosphatochloride,  363. 

phosphatonitrate,  362. 

phosphide,  555. 

sesquioxide,  299. 

sulphate,  429. 
Leblanc  soda  process,  671. 
Limited  reaction,  58. 
Liquids,  91. 
Litharge,  295. 
Lithium,  28. 

„       halides,  115. 

oxide,  211. 
„        sulphate,  420. 
„        sulphide,  211. 
Liver  of  sulphur,  43. 
Lunar  caustic,  330. 
Luteochromium  salts,  528. 
Luteocobaltamiiies,  531. 

Magnesia  alba,  33,  227. 
Magnesia  usta,  227. 
Magnesium,  33. 


GENERAL   INDEX. 


695 


Magnesium  boride,  498. 
ethyl,  503. 
halides,  123. 
„  nitrate,  328. 

„  nitride,  226. 

„  nitrite,  333. 

„          ortkophosphate,  360. 
„  oxide,  225. 

„  pyrophosphate,  367. 

sulphate,  423. 
sulphide,  225. 
Manganates,  265. 
Manganese,  41. 

dioxide,  258. 
halides,  137. 
„  heptoxide,  267. 

„  monosulphide,  243. 

„  monoxide,  243. 

„  nitrate,  328. 

„          nitrite,  340. 
„          orthophosphate,  361. 
„  phosphide,  553. 

„  sesquioxide,  248. 

„  silicate,  41. 

„  sulphate,  426. 

„  trioxide,  261. 

Manganicyanides,  567. 
Manganocyanides,  565. 
Manganosamines,  532. 
Manganosomanganic  oxide,  254. 
Manganyl  chloride,  268. 
Marsh  gas,  498,  16. 
Marsh's  test,  518. 
Massicot,  295. 
Matter,  states  of,  91. 
Mayo,  8. 
Meinecke,  627. 
Mendeleeff,  201,  628. 
Mercuramines,  546. 
Mercury,  79.-' 

cvanides,  571. 
ethyl,  507. 

halides,  174.  s 

manufacture,  664.  ^ 
nitrates,  331.  ~~  ? 
nitride,  549,  557. 
orthophosphates,  365. 
oxides,  487-K1 
„        pyrophosphates,  368. 
„        sulphates,^432.> 
„        vapour  density,  615. 
„        vapour,  monatomic,  624. 
Metals  of  the  earths,  38. 
Metantimonates,  371. 
Metantimonic  acid,  370. 
Metaphosphates,  369,  370. 
Metaphosphoric  acid,  369. 
Metaphosphoryl  chloride,  384. 
Metarsenic  acid,  370. 
Metatungstates,  399. 


Methane,  16,  498. 

Methylamines,  532. 

Meteorites,  40. 

Meyer,  L.,  20,  628. 

Meyer,  V.,  102. 

Microcosmic  salt,  357. 

Mitis  iron,  581. 

Mitscherlich's  law,  620. 

Mixtures,  88.  . 

Moire,  583. 

Moissan,  74,  146. 

Molecule,  16. 

Molecular  complexity,  621. 

Molecular  compounds,  209. 

Molecular  formulae,  126, 162,  612. 

Molecular  heat,  618. 

Molecular  weights,  612,  et  se^. 

Molybdates,  398. 

Molybdenum,  60. 

halides,  406. 

nitride,  556. 

oxides,  392,  395. 

oxyhalides,  406. 

phosphates,  364. 

sulphates,  431. 

sulphides,  392. 
Molybdic  acid,  408. 
Mortars,  313. 
Muntz  metal,  580. 

Naples  yellow,  372. 
Nascent  state,  141. 
Neodymium,  603. 
Neumann,  618. 
Newlands,  20,  628. 
Nickel,  40. 

dioxide,  258. 

disulphide,  258. 

halides,  137. 

manufacture,  658. 

monosulphide,  243. 

monoxide,  243. 

nitrate,  328. 

nitrite,  340. 

orthophosphate,  361. 

phosphide,  552. 
„      sesquioxide,  248. 
„      sulphate,  427. 
Nickelosamines,  532. 
Nickel-plating,  41. 
Nilson,  46,  122. 
Niobates,  323. 
Niobic  acid,  323. 
Niobium,  53. 

„        dioxide,  333. 
halides,  157. 
„        hydride,  576. 
„        pentoxide,  320. 
Niobyl  halides,  332. 
Nitrates,  323. 


696 


GENERAL  INDEX. 


Nitre,  29,  325. 
Nitric  acid,  322. 
Nitric  oxide,  341. 
Nitric  peroxide,  333. 
Nitrification,  325. 
Nitrites,  337. 
Nitrogen,  53. 

dioxide,  341. 

halides,  157. 

hexoxide,  344. 

monoxide, 

pentoxide,  320. 

sulphates,  429. 

sulphides,  343. 

tetroxide,  333. 

trioxide,  336. 
Nitroprussides,  566. 
Nitrosulphides,  343. 
Nitrosulphates,  429. 
Nitrosyl  chloride,  340. 
„       sulphate,  430. 
Nitrous  acid,  337. 
Nitrous  anhydride,  336. 
Nitrous  oxide,  343. 
Nitroxyl  chloride,  336. 
Nomenclature,  89. 

Odling,  462. 
Oil  of  vitriol,  415. 
Ores,  33. 

Organometallic  compounds,  502. 
Orthoacids,  456. 
Orthoantimonic  acid,  356. 
Orthoantimonious  acid,  376. 
Orthoarsenates,  356. 
Orthoarsenic  acid,  356. 
Orthophosphates,  356. 
Orthophosphoric  acid,  356. 
Orthosilicic  acid,  306. 
Orthosulpharsenic  acid,  356. 
Orthovanadates,  326. 
Osmamines,  539. 
Osmiridium,  77,  588. 
Osmites,  483. 
Osmium,  77. 

„        halides,  172. 
„        oxides,  480. 
„        sulphate,  431. 
sulphide,  480. 
Osmocyanides,  569. 
Osmosis,  309,  91. 
Oxalic  acid,  273. 
Oxidation,  140. 
Oxides,  84,  191. 

action  of  heat  on,  63. 

and    sulphides,    &c.,    general 
remarks,  494. 

classification  of,  205,  494. 

dualistic  theory  of,  206. 

molecular  formulce  of,  621. 


Oxygen,  60,  61,  9-11. 

„        halides,  166. 

„        oxide,  387. 
Oxyhydrogen  blowpipe,  193. 
Ozone,  387. 

„      formula  of,  390. 

Palladamines,  539. 
Palladium,  77. 

cyanides,  569. 

halides,  170. 

hydride,  576. 

oxides,  476. 

phosphate,  364. 

phosphide,  556. 

sulphate,  431. 

sulphides,  476. 
Pannetier's  green,  252. 
Paracelsus,  6. 
Pattin son's  process,  587. 
Peligot,  61. 

Pentathionic  acid,  451. 
Pentoxides,  double  compounds  of,  363. 
Perchlorates,  471. 
Perchloric  acid,  469. 
Perchromates,  266. 
Periodates,  470. 
Periodic  acid,  469. 
Periodic  law,  627. 
„        table,  20. 
Permanganates,  266. 
Permanganic  acid,  267. 
Persian  red,  262. 
Persulphomolybdates,  406. 
Persulphuric  anhydride,  414. 
Peruranates,  405. 
Petterssen,  122. 
Pewter,  585. 
Phlogiston,  10. 
Phosgene,  291. 
Phospham,  535. 
Phosphamic  acids,  534. 
Phosphamide,  534. 
Phosphate  of  soda,  357. 

„  „          manures,  359. 

Phosphines,  532. 
Phosphites,  377. 
Phosphomolybdates,  403. 
Phosphoniuni  salts,  317. 
Phosphoric  acids,  352. 
Phosphorosamide,  525. 
Phosphorous  acid,  375. 
Phosphorus,  56. 

cyanide,  568. 
halides,  160. 
manufacture,  665. 
nitride,  555. 
oxides,  346. 

pentoxide,   double    com- 
pounds of,  363. 


GENERAL   INDEX. 


097 


Phosphorus  sulphides,  350. 

„  vapour  density,  616. 

Phosphoryl  amidomride,  531. 

metaphosphate,  349,  373. 

nitride,  534. 

sulphate,  430. 

tribronride,  383. 

trichloride,  382. 

trifluoride,  382. 


Pictet 


28. 


Pinchbeck,  580. 
Plaats,  van  der,  202. 
Plants,  respiration  of,  280,  388. 
Piaster  of  Paris,  422. 
Piatiiiamiues,  543. 
Platinates,  483. 

Platinicarbonyl  compounds,  485. 
Platinimolybdates,  485. 
Platinitungstates,  485. 
Platinochlorosulphites,  485. 
Platinodiamines,  542. 
Platinonitrites,  484. 
Piatinophosphorous  acid,  486. 
Platinosamines,  541. 
Platinum,  77. 

„         cyanides,  570. 
.,         halides,  172. 
„        nitrate,  330. 
„         nitride,  557. 
oxides,  480. 
phosphate,  364. 
„         sulphate,  431. 
sulphides,  480. 
Plato,  2,  3. 
Plumbates,  312. 
Polychromates,  264. 
Polymerides,  333. 
Polyselenites,  440. 
Polysulphites,  440. 
Polytellurites,  440. 
Potassamide,  524, 
Potassium,  28. 

alum,  425. 
chlorate,  64. 

„        manufacture,  682. 
cyanide,  561. 
halides,  115. 
hydride,  575. 
hyponitrite,  344. 
nitrate,  325. 
nitride,  550. 
nitrite,  337,  339. 
oxides,  211. 
selenide,  211. 
sulphate,  420. 
„  sulphides,  211. 

„  triiodide,  119. 

Pozzolana,  313. 
Praseodymium,  603. 
Prehnite,  314. 


Priestley,  11,  64. 
Proust,  15.     '.   • 
Prout,  627. 
Prussian  blue,  566. 

„        green,  566. 
Prussic  acid,  559. 
Purple  of  Casius,  492. 
Purpureochromium  compounds,  527. 
Purpureocobaltamines,  530. 
Py-roantimonic  acid,  365. 
Pyroantimonious  acid,  376. 
Pyroarsenic  acid,  365. 
Pyrometers,  645. 
Pyrophorism,  246. 
Pjrophosphates,  366. 
Pyrophosphoric  acid,  365,  368,  353. 
Pyrophosphoryl  chloride,  384. 
Pyrosulphates,  433. 
Pyrosulphuric  acid,  432. 
Pyrotellurates,  433. 

Queen's  metal,  585. 

Rammelsherg,  380. 
Raoult's  method,  623. 
Rayleigh,  202. 
Reaction,  limited,  58. 
Reduction,  41. 
Regnault,  202,  618. 
Regulus  of  Venus,  587. 
Reverberatory  furnaces,  648. 
Rhodamines,  538. 
Rhod  cyanides,  569. 
Rhodium,  77. 

cyanide,  569. 

halides,  170. 

nitrate,  330. 

oxides,  476. 

phosphate,  364. 

sulphates,  431. 
„  sulphides,  476. 

Rhodochromium  salts,  528. 
Richter,  15. 
Roasting,  227. 
Roscoe,  55,  60. 
Roseochromium  salts,  528. 
Roseocobaltainines,  530. 
Rouge,  427. 
Rubidium,  29. 

halides,  115. 
„          oxide,  211. 
„          sulphate,  420. 
„          sulphide,  211. 
Ruthenamines,  537. 
Ruthenates,  479. 
Ruthenium,  77. 

halides,  170. 
„  oxides,  476. 

„  sulphates,  431. 


698 


GENERAL  INDEX. 


Ruthenium  sulphides,  476. 
Ruthenocyanides,  569. 

Salt,  6,  28. 
Salt-cake,  420,  673. 
Saltpetre,  29,  319,  325. 
Salts,  89. 

„     double,  89. 
Samarium,  603. 
Scandium,  36,  603. 

„          halides,  131. 
„          oxides,  232. 
„          sulphate,  424. 
Schaffner  and  Helwig's  process,  676. 
Scheele,  11. 
Schlippe's  salt,  358, 
Schonbein,  387. 
Schiitzenberger,  447. 
Scott,  202. 
Sea-water,  115,  409. 
Sea-weed,  72. 
Selenates,  419. 
Selenic  acid,  417. 
Seleniotrithionic  acid,  450. 
Selenious  acid,  435. 
Selenites,  43B. 
Selenium,  61. 

„         acids,  constitution  of,  452. 
„         halides,  166. 
„         oxide,  409. 
„         sulphide,  455. 
Selenosyl  compounds,  443. 
Selenyl  compounds,  441. 
Sesquioxides,  constitution  of,  255. 
Setterberg,  29. 
Shear  steel,  657. 
Silicamine,  533. 
Silicates,  303. 

„         decomposition  of,  311. 
Silicic  acids,  303,  306,  309. 
Silicides,  498. 
Silicoethane,  501. 
Silicomolybdates,  402. 
Silicon,  49. 

dioxide,  300. 
disulphide,  300. 
ethyl,  506. 
halides,  14S. 
monosulphide,  295. 
monoxide,  295. 
nitride,  554. 
orthophosphate,  362. 
oxy carbides,  318. 
pyrophosphate,  368. 
sesquioxide,  2b>9. 
sulphate,  428. 
Silicon  pig,  510. 
Silicooxalic  acid,  299. 
Silicotungstates,  402. 
Silver,  79. 


Silver  coin,  589. 
„      cyanides,  571. 
halides,  174. 
hyponitrite,  344. 
manufacture,  662. 
nitrate,  330. 
nitrite,  337. 
oxides,  487. 
orthophosphate,  365. 
solder,  589. 
sulphates,  432. 
sulphides,  487. 
Smithy  scales,  255. 
Soda  ash,  286. 
„     crystals,  286. 
„     mesotype,  314. 
Sod  amide,  524. 
Sodammonium,  577. 
Sodium,  28. 

,,        chlorate,  manufacture,  682. 

halides,  115. 
,,        hydrides,  575. 
„        hyponitrite,  344. 
nitrate,,325. 
nitride,  550. 
nitrite,  339. 
,,        orthophosphates,  357. 

oxides,  211. 
,,        phosphites,  377. 
„        pyrophosphate,  366. 
silicate,  310. 
sulphate,  420. 
sulphides,  211. 
Soffioni,  234. 
Solder,  585. 
Solids,  91. 
Soluble  glass,  310. 
Solution,  107. 
Soret,  391. 
Specific  heat,  123,  617. 

„       volume,  633. 
Spectrum  analysis,  591. 
Speculum  metal,  586. 
Spongy  platinum,  577. 
Stahl,  11. 
Stannamine,  533." 
Stannates,  311. 
Star  spectra,  608. 
Stas,  81,  202. 
Steel,  656. 
Stibine,  518. 
Stibines,  532. 
Strontium,  31. 

halides,  120. 
nitrate,  327. 
nitrite,  339. 
oxides,  218. 
sulphates,  419. 
sulphides,  218. 
sulphites,  436. 


GENERAL   INDEX. 


699 


Sublimation,  152. 
Sulphides,  84,  191. 
Sulpho-.     See  also  Thio-. 
Sulphocarbamide,  533. 
Sulphostannates,  316. 
Sulphostannic  acid,  316. 
Sulphur,  65. 

acids,  constitution  of,  452. 

amines,  536. 

from  furnace  gases,  667. 

halides,  166. 

oxides,  409. 

selenide,  455. 

sesquioxide,  414. 

trioxide,  412,  14,  15. 
Sulphuric  acid,  415. 

„  „      manufacture,  41 G,  667. 

Sulphurosyl  compounds,  443. 
Sulphurous  acid,  435. 
Sulphuryl  compounds,  441. 
Surface-tension,  91. 
Symbols,  20,  110. 
Sympathetic  inks,  139. 
Synthesis,  14. 

Tank  waste,  676. 
Tantalates,  323. 
Tantalic  acid,  323. 
Tantalum,  53. 

„          dioxide,  333. 
halides,  157. 

„          phosphate,  363. 

.,          pentoxide,  320. 

„          tetrasulphide,  335. 
Telluramines,  536. 
Tellurates,  419. 
Telluric  acid,  417. 
Tellurites,  436. 
Tellurium,  61,  606. 

halides,  166. 

„          nitrate,  330. 

„  oxides,  409. 

„  sulphates,  431. 

„          sulphide,  455. 
Tellurosyl  compounds,  443. 
Tellurous  acid,  435. 
Telluryl  compounds,  441. 
Terbium,  49,  603. 

halides,  148. 
Tetrathionic  acid,  450. 
Tetratungstates,  399. 
Thallium,  37. 

„         antimonide,  552. 

„         halides,  133. 

„         nitrate,  328. 

„         orthophosphate,  360. 

„         oxides,  237. 

„         sulphate,  424. 

„         sulphides,  237. 
Than,  285. 


Thenard,  36,  195. 
Thioantimonates,  358. 
Thioarsenates,  355. 
Thioarsenites,  378. 
Thiocarbonates,  290. 
Thiocyanates,  568. 
Thiopalladites,  479. 
Thicphosphates,  354. 
Thiophosphoryl  halides,  382. 
Thiosulphates,  444. 
Thiosulphuric  acid,  444. 
Thorates,  290. 
Thorium,  43. 

dioxide,  275. 
disulphide,  275. 
halides,  144. 
heptoxide,  293. 
nitrate,  329. 
orthophosphate,  362. 
sulphate,  428. 
Thulium,  603. 
Tin,  49. 

„     dioxide,  300. 
„     disulphide,  300. 
„     halides,  148. 
,,     manufacture,  659. 
.,     monosulphide,  294. 
„     monoxide,  294. 
„     nitrates,  329. 
,,     orthophosphates,  362. 
„     phosphatochloride,  362. 
,,     phosphide,  555. 
„     salt,  151. 
„     sesquioxide,  299. 
„     sesquisulphide,  299. 
„     sulphate,  429. 
Titanamines,  533. 
Titanates,  290. 
Titanium,  43. 

„         cyanonitride,  567. 
dioxide,  275. 
disulphide,  277. 
halides,  144. 
monosulphide,  270. 
monoxide,  270. 
nitrides,  554. 
orthophosphates,  362. 
oxychloride,  292. 
sesquioxide,  273. 
sesquisulphide,  273. 
sulphate,  428. 
Tobacco-ash,  28. 
Tombac,  580. 
Traces,  influence  of,  82. 
Transmutation,  3,  4. 
Tree  of  Diana,  589. 
Trithionic  acid,  449. 
Troost,  42,  45. 

Troost  and  Hautefeuille,  317. 
Tungstates,  398. 


'00 


GENERAL    INDEX. 


Tungsten,  60,  393. 

„         ammonia  compounds,  536. 
halides,  164. 

„         nitride,  556. 
oxides,- 392. 

„         oxyhalides,  406. 

„         phosphates,  364. 

„         sulphides,  392. 
Tungstic  acid,  397. 
Turnbull's  blue,  566. 
Turner's  yellow,  298. 
Type  metal,  586. 

Ultramarine,  315. 
Uranates,  398,  405. 
Uranium,  60. 

,,         ammonium  compounds,  53G. 
„         halides,  3  64. 
„         oxides,  392. 

oxyhalides,  406. 
„         sulphates,  431. 
„         sulphides,  392. 
Uranyl  nitrates,  480. 
,,       phosphates,  364. 
,,       tungstate,  404. 
Urea,  532. 
Urine,  357,  360. 

Valency,  129,  504. 
Valentine,  6. 
Vanadates,  323. 
Vanadic  acid,  323. 
Vanadimolybdates,  403. 
Vanadites/337. 
Vanadium,  53. 

dioxide,  341. 
halides,  157. 
hydride,  576. 
nitrides,  555. 
pentasulphide,  321. 
pentoxide,  320. 
tetrasulphide,  321. 
tetroxide,  333. 
trioxide,  337. 
Yanadyl  dihalides,  336. 

monohalides,  340. 
orthophosphate,  363. 
sulphate,  429. 
trihalides,  332. 
Vapour,  97. 

„        density,  97. 
„        pressure,  91. 


Venetian  red,  433. 
Vermilion,  488. 

Water,  191,  11. 

„      composition  of,  201. 

„      physical  properties  of,  199 
Water-glass,  310. 
Weber,  36,  49,  52,  154. 
Weldon's  process,  678. 
Wenzel,  15. 
White  lead,  289. 
Williamson,  565. 
Winkler,  49,  87. 
Wohler,  36,  37,  45,  551,  567. 
Wood  charcoal,  44. 
Wurtz,  577. 

Xanthocobaltamines,  530. 

Ytterbium,  36,  603. 

halides,  131. 
„          oxide,  232. 
Yttrium,  36,  603. 

halides,  131. 

,,       orthophosphate,  360. 
„       oxide,  232. 
„       sulphate,  424. 

Zinc,  33. 

ethyl,  503. 
halides,  123. 
manufacture,  652. 
nitrate,  328. 
nitride,  551. 
nitrite,  339. 
oxides,  225. 
phosphate,  360. 
sulphate,  423. 
sulphides,  225. 
Zincamide,  525. 
Zirconamine,  533. 
Zirconates,  290. 
Zirconium,  43. 

„  dioxide,  275. 

„  disulphide,  275. 

halides,  144. 
„  nitrate,  329. 

„  nitrides,  554. 

„  orthophosphate,  362. 

„  pentoxide,  293. 

sulphate,  428. 


HARRISON    AND   SOKP,    PRINTERS    IN    OKIHNARY    JO    Ul.H   MAJESTY     ST.    WAR  UN's    LANK,    I,OM>oN 


OVERDUE. 

MAtTa    1933 
MAR    4  1933 


m  30  1937 


JAN    21940 


Mffi 


KtC'D  LD 

OCT    5*65 -11  AN 


«ayU'49Rf 

j9 


X 


21-50m-l,'3'. 


YC  21939 


UNIVERSITY  OF  CALIFORNIA  LIBRARY