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A 

HISTORY  OF  CHEMISTRY 

FROM    EARLIEST   TIMES    TO 
THE    PRESENT    DAY 


BEING    ALSO 


AN  INTRODUCTION  TO  THE  STUDY  OF  THE 

SCIENCE 


BY 

ERNST    VON    MEYER,    PH.D. 

PROFESSOR   OF   CHEMISTRY   IN   THE   TECHNICAL   HIGH   SCHOOL,    DRESDEN 

TRANSLATED   WITH    THE   AUTHOR'S    SANCTION 

BY 

GEORGE   McGOWAN,   PH.D. 


SECOND  ENGLISH   EDITION,   TRANSLATED   FROM   THE  SECOND 

GERMAN    EDITION,  WITH   NUMEROUS   ADDITIONS 

AND  ALTERATIONS 


MACMILLAN    AND    CO.,    LIMITED 

NEW  YORK  :  THE   MACMILLAN  COMPANY 
1898 

The  Right  of  Translation  and  Reproduction  is  Reserved 


RICHARD  CLAY  AND  SONS,  LIMITED, 

LONDON   AND   BUNG  AY. 


First  Edition  1891. 
Second  Edition  1898. 


PREFACE    TO    THE    FIEST    GERMAN    EDITION 

NEARLY  five  decades  have  passed  by  since  Hermann  Kopp's 
classical  Geschichte  der  Chemie  1  began  to  appear,  and  it  is 
now  fifteen  years  since  this  was  followed  by  the  same 
indefatigable  author's  Entwickelung  der  Chemie  in  der 
neueren  Zeit?- 

The  publication  of  these  comprehensive  works,  in  con- 
junction with  which  Hofer's  Histoire  de  la  Chimie  must  be 
named,  and  the  further  descriptions  of  the  growth  of 
chemistry  within  particular  periods  given  both  by  Kopp 
himself  and  by  other  writers,  might  lead  one  to  suppose  that 
there  was  no  pressing  need  for  further  work  in  the  same 
direction  at  the  present  time. 

This  point  can,  the  author  thinks,  be  best  discussed  by 
his  making  a  few  remarks  here  with  respect  to  the  aim  and 
plan  of  the  present  volume. 

In  this  History  of  Chemistry  the  attempt  has  been  made 
to  describe  within  short  compass  the  development  of 
chemical  knowledge,  and  especially  of  the  general  doctrines 
of  chemistry  which  have  thus  been  gradually  evolved,  from 
their  earliest  beginnings  up  to  the  present  day.  After  a 

1  "History  of  Chemistry." 

2  "  The  Development  of  Chemistry  in  Recent  Times." 

85421 


vi  PREFACE  TO  THE  FIRST  GERMAN  EDITION 

general  account  of  the  main  directions  followed  by  chemistry 
in  the  various  ages,  the  growth  of  particular  branches  of  the 
science  has  been  more  or  less  minutely  detailed. 

In  the  general  descriptions  great  emphasis  has  been  laid 
upon  the  genesis  of  particular  ideas,  and  their  expansion  into 
important  dogmas  or  comprehensive  theories.  At  the  same 
time,  in  order  that  a  vivid  picture  of  the  various  periods  and 
their  distinguishing  characteristics  might  be  presented  to 
the  reader,  short  accounts  have  been  given  of  the  works,  and 
in  some  cases  of  the  lives,  of  the  men  who  originated  and 
developed  such  views. 

In  the  special  sections,  on  the  other  hand,  the  attempt 
has  been  made  to  collect  together  fundamental  facts,  which 
have  been  sifted  and  relegated  to  their  proper  branch  of  the 
science,  and  thus  to  offer  as  clear  a  description  as  possible  of 
the  state  of  chemical  knowledge  at  the  time  in  question. 

That  neither  in  this  nor  in  the  history  of  the  develop- 
ment of  theoretical  views  could  completeness  be  thus 
achieved,  hardly  requires  to  be  stated.  But  the  author  has 
at  all  events  endeavoured  to  give  a  fair  synopsis  of  the  most 
important  theories  and  facts  which  constitute  the  foundation 
of  chemistry  as  we  now  know  it. 

The  growth  of  chemical  knowledge  during  recent  times, 
since  Boyle,  and  especially  since  Lavoisier,  naturally  forms 
the  principal  subject  of  the  following  chapters.  The  author 
is  fully  aware  of  the  many  difficulties  which  have  to  be  met 
here,  difficulties  which  increase  in  extent  the  nearer  we 
approach  to  the  history  of  our  own  period.  We  stand  too 
close  to  the  development  of  the  theoretical  views  of  these 
latter  days  to  feel  certain  of  always  preserving  the  unbiassed 


PREFACE  TO  THE  FIRST  GERMAN  EDITION  vii 

temperament  which  is  essential  to  the  true  historian.  But, 
notwithstanding  this,  the  author  has  ventured  the  attempt 
to  carry  the  record  of  the  history  of  chemistry  up  to  the 
present  day. 

In  this  task  he  has  done  his  best  to  preserve  throughout 
an  objective  attitude ;  and  he  has  further  been  guided  by 
the  earnest  desire  to  contribute  effectively  towards  shedding 
a  clear  light  upon  the  opposing  views  held  with  respect 
to  the  development  and  the  importance  of  the  chemical 
doctrines  of  to-day.  It  has  also  been  his  duty  as  an 
historian  to  endeavour  to  apply  to  the  services  rendered  by 
eminent  investigators  of  quite  recent  years  a  calmer  and 
j  uster  criticism  than  has  hitherto  in  many  cases  been  meted 
out  to  them. 

ERNST  VON   MEYER. 

LEIPZIG,  7th  October,  1888. 


TRANSLATOR'S    PEEFACE    TO   THE   FIRST 
ENGLISH    EDITION 

THE  author,  in  his  preface  to  the  original  German  edition, 
discusses  the  question  whether  there  is  any  necessity  for 
a  new  history  of  chemistry  in  his  own  language  at  the 
present  day.  That  there  is  full  room  for  one  in  this  country 
will  be  admitted  upon  all  hands.  It  is  therefore  hoped  that 
the  appended  history  will  prove  not  only  useful  to  the  student, 
but  also  interesting  to  the  general  reader  who  is  desirous  of 
gaining  some  idea  of  the  development  of  chemical  science. 

The  translator  has  done  his  best  to  reproduce  clearly  the 
sense  of  the  German  original.  And,  since  Professor  von 
Meyer  has  been  so  kind  as  to  read  over  the  first  corrected 
proofs,  as  well  as  to  answer  a  great  many  queries,  it  is  hoped 
that  this  has  been  achieved. 

A  considerable  number  of  small  alterations  and  additions 
have  been  made  for  this  edition,  most  of  them  by  the  author, 
but  some  by  the  translator  with  the  author's  concurrence. 
While  these  may  reasonably  be  supposed  to  have  improved 
the  book,  they  have  not  altered  its  character  in  the  slightest 
degree.  The  translator  has  further  added  a  number  of 
duplicate  references  to  English  journals  (to  such  papers  as 
were  published  both  in  German  and  English),  and  also  a  few 
new  ones,  for  the  greater  convenience  of  English  readers. 


TRANSLATOR'S  PREFACE 


In  conclusion,  he  would  express  his  indebtedness  to  the 
various  gentlemen  who  have  been  kind  enough  to  give  him 
the  benefit  of  their  criticism  and  advice  upon  different  points, 
with  regard  to  which  his  own  special  knowledge  was  insuffi- 
cient, and  also  to  those  others  who  have  assisted  him  in  the 
matter  of  references,  etc. 

UNIVERSITY  COLLEGE  OF  N.  WALES,  BANGOR, 
March,  1891. 


AUTHOR'S   NOTE   TO   THE   FIRST   ENGLISH 
EDITION 

It  was  a  great  satisfaction  to  me  that  the  translation  of 
this  history  was  undertaken  by  my  former  pupil,  Dr.  McGowan, 
and  I  desire  to  express  here  my  appreciation  of  the  manner 
in  which  he  has  entered  into  the  spirit  of  the  work,  and  to 
offer  him  my  hearty  thanks  for  all  his  trouble  in  the  matter. 

May  the  book  find  many  friends  among  the  English- 
speaking  peoples,  and  help  to  stimulate  the  interest  of  its 
readers  in  the  development  of  our  science. 

ERNST   VON   MEYER. 

LEIPZIG,  February,   1891. 


TRANSLATOR'S  PREFACE  TO  THE  SECOND 
ENGLISH   EDITION 

THE  present  edition  is  a  translation  of  the  second  German 
edition  (published  in  1895),  with  a  number  of  further  addi- 
tions and  alterations,  most  of  these  latter  having  been  made 
by  the  author,  but  a  good  many  of  them  by  myself,  with  his 
approval ;  and,  as  in  the  case  of  the  previous  edition,  the 
proof  sheets  had  the  benefit  of  the  author's  revision  after  my 
own  corrections  were  made. 

In  his  preface  to  the  second  German  edition  Professor 
von  Meyer  expresses  his  gratification  at  the  success  of 
the  English  version,  and  then  goes  on  to  speak  of  the 
additional  sources  of  information  on  subjects  of  historical 
chemistry  which  have  during  the  last  few  years  become 
available  for  reference.  Among  these  are  the  Berzelius- 
Liebig  and  the  Liebig-Wb'hler  Letters,  the  Letters  and 
Journals  of  Scheele,  Priestley's  Letters,  and  the  autobio- 
graphical fragment  which  Liebig  left  behind  him.  In 
addition,  there  are  the  recently  published  and  valuable  his- 
torical researches  of  Berthelot  on  the  chemistry  of  the  early 
Middle  Ages,  and  the  writings  of  Ladenburg,  Schorlemmer, 
Thorpe,  Grimaux,  and  others  on  the  development  of  chem- 
istry within  certain  definite  periods,  or  on  the  life  and  work 
of  particular  chemists. 


TRANSLATOR'S  PREFACE 


I  may,  perhaps,  be  permitted  to  add  my  word  of  appreci- 
ation to  what  the  author  has  said  with  regard  to  the  friendly 
reception  of  the  first  English  edition  both  in  this  country 
and  in  America,  and  to  express  the  hope  that  the  present 
edition  may  be  found  at  least  equally  acceptable. 


GEORGE  McGOWAN. 


BALING,  LONDON,  W. 
July,  1898. 


TABLE    OF    CONTENTS 


PAGE 


LIST  OF  ABBREVIATIONS         ....  .  xxiii 

INTRODUCTION  1 

p 

CHAPTER  I 

FROM  THE  EARLIEST  TIMES  TO  THE  BIRTH  OF  ALCHEMY    .        .          5 

Theoretical  Views  upon  the  Composition  of  Substances,  and 
especially  upon  the  elements,  6.  Aristotle's  Elements,  7. 

The  Empirical  Chemical  Knowledge  of  the  Ancients,  9. 
Metallurgy  of  the  Older  nations— Gold,  11  ;  Silver,  Copper, 
Iron,  13  ;  Lead,  Tin,  etc.,  14;  Mercury,  15.  The  Manufacture 
of  Glass,  16.  Pottery,  17.  The  Manufacture  of  Soap,  17.  Dye- 
ing, 17.  The  beginnings  of  Pharmacy,  18. 

CHAPTER   II 

THE  AGE  OF  ALCHEMY 21 

General  History  of  Alchemy 23 

Origin  and  First  Signs  of  Alchemistic  Efforts,  23.  The  Alex- 
andrian Academy,  27.  The  A  Ichemy  of  the  A  rabians— Geber  and 
his  Disciples,  28-30.  Alchemy  among  the  Western  Nations,  30. 
Albertus  Magnus,  Roger  Bacon,  31.  Arnaldus  Villanovanus,  32. 
Raymundus  Lullus,  33.  Basilius  Valentinus,  36. 

,    Special  History  of  Alchemy 37 

Theories  and  Problems  of  the  Alchemistic  Period,  37.  The 
pseudo-Geber,  39-41.  Views  of  Basilius  Valentinus,  etc.,  41. 
The  Philosopher's  Stone,  42. 

Practical -Chemical  Knowledge  of  the  Alchemists,  45. 

Technical  Chemistry — Gold,  46.  Silver,  46.  Copper  and 
other  metals,  47.  Pottery,  Glass,  Dyeing,  47-48.  Pharma- 
ceutical Chemistry,  48. 


CONTENTS 


Knowledge  of  the  Alchemists  with  regard  to  Chemical  Com- 
pounds, 49.  Alkalies,  50,  Acids,  51.  Salts,  52.  Preparations 
of  Antimony,  etc. ,  54.  Organic  Compounds,  56. 

The  Fortunes  of  Alchemy  during  the  last  Four  Centuries,  58. 

A  Short  Review  of  Alchemistic  Efforts,  63. 


CHAPTER   III 

PAGE 

HISTORY  OP  THE  IATRO-CHEMICAL  PERIOD 65 

General  History  of  this  Period    .  67 

Paracelsus  and  his  school,  67.  The  latro-chemical  Doctrines 
of  Paracelsus,  69.  Turquet  de  Mayerne,  73.  Libavius,  74. 
Van  Helmont  and  his  Contemporaries,  75.  The  work  of  van 
Helmont,  73.  Sala  and  Sennert,  80.  Sylvius  and  Tachenius, 
80.  Georgius  Agricola,  80.  Palissy,  85.  Glauber,  86. 

Special  History  of  the  latro-chemical  Period   ....        87 

Technical  Chemistry,  87.  Metallurgy,  88.  Pottery  and 
Glass  Manufacture,  89.  Dyeing,  etc.,  90. 

Development  of  Pharmacy  and  of  the  Knowledge  of  Chemical 
Preparations,  91.  Inorganic  Compounds,  91.  Organic  Com- 
pounds, 96. 

CHAPTER   IV 

HISTORY  OF  THE  PERIOD  OF  THE  PHLOGISTON   THEORY,  FROM 

BOYLE  TO  LAVOISIER 100 

INTRODUCTION 100 

General  History  of  the  Phlogistic  Period          ....  103 

Robert  Boyle,  103.  Mayow,  107.  Lemery  and  Homberg,  107. 
Kunkel  and  Becher,  109.  Stahl  and  the  Phlogiston  Theory,  110. 
Fr.  Hoffmann  and  Boerhave,  113. 

The  development  of  Chemistry,  and  particularly  of  the 
Phlogiston  Theory,  after  StahVs  Time,  115.  Neumann,  Eller, 
Pott,  Marggraf,  115-116.  Geoffrey,  Duhamel  de  Monceau, 
Rouelle,  Macquer,  117-119.  Black,  119.  Cavendish,  121. 
Priestley,  122.  Bergman  and  Scheele,  124-125. 

Special  History  of  the  Phlogistic  Period 128 

Pneumatic  Chemistry  and  its  Relations  to  the  Doctrine  of 
Phlogiston,  128.  The  Discovery  of  Oxygen  and  the  Composition 
of  Air,  130. 

Development  of  Theoretical  Vieivs  in  the  Phlogistic  Period,  134, 
Views  regarding  Elements  and  Chemical  Compounds,  135. 


CONTENTS 


Views  regarding  Chemical  Affinities  and  its  Causes,  137. 
Geoffrey's  Tables  of  Affinities,  138. 

Practical  Chemical  Knowledge,  in  the,  Phlogistic  Age,  140. 
The  Development  of  Analytical  Chemistry,  141.  Boyle,  141. 
Fr.  Hoffmann,  Marggraf,  Scheele,  142-143.  Bergman,  143.  The 
beginnings  of  Gas  Analysis,  145. 

Technical  Chemistry  in  the  Phlogistic  Age — Metallurgy,  146. 
The  Ceramic  Industry,  Dyeing,  147. 

Technico-chemical  Preparations — Acids  and  Alkalies,  147. 
The  Discovery  of  Elements,  149.  Inorganic  and  Organic  Com- 
pounds, 150-151. 

Pharmaceutical  Chemistry,  154. 

Concluding  Remarks  upon  this  Period,  155. 

CHAPTER   V 

PAGE 

HISTORY  OF  THE  MOST  RECENT  PERIOD   (FROM  THE  TIME   OF 

LAVOISIER  UP  TO  NOW) 158 

Introduction  .        . 158 

General  History  of  Chemistry  during  this  Period  .        .      160 

Lavoisier  and  the  Antiphlogistic  Chemistry,  160.  Lavoisier's 
Life  and  Work,  160  et  seq.  His  Combustion  Theory,  164-167. 
Triumph  of  the  Antiphlogistic  Chemistry,  168.  Beginnings  of 
a  Rational  Chemical  Nomenclature,  170.  Guyton  de  Morveau, 
172.  Berthollet,  173.  Fourcroy,  174.  Vauquelin,  176.  %\ 

The  State  of  Chemistry  in   Germany  at  the   end    of    the     1\ 
Eighteenth  Century,  177.     Klaproth,  178.     The  State  of  Chemistry 
in  England,  Scotland  and  Sweden,  180. 

Development  of  the  Doctrine  of  Chemical  proportions,  181. 
Richter,  182.  His  law  of  Neutralisation,  183.  The  Beginnings 
of  Stdchiometry,  185.  Proust,  185.  Hi  scon  test  with  Berthollet, 
186.  Recognition  of  Constant  Combining  Proportions,  187. 

Dalton's  Atomic  Theory 188 

Law  of  Multiple  Proportions,  189-190.  Dalton's  Attempts  to 
determine  the  relative  Atomic  Weights  of  the  Elements,  191. 
His  Atomic  Weights  and  Chemical  Symbols,  193-194. 

Further  Development  of  the  Atomic  Theory,  194.  Thomas 
Thomson,  194.  Wollaston,  195.  Humphry  Davy,  his  Life  and 
most  important  Work,  195-199.  Gay-Lussac,  199.  His  Law  of 
Volumes  and  Work  generally,  200-201 .  Front's  Hypothesis  and  its 
Effects,  Wl. 

Berzelius — A  Survey  of  his  Work 203 

Biographical  Notice,  204.     His  Influence  upon  the  Develop- 


CONTENTS 


ment  of  Analytical  and  Organic  Chemistry,  205-207.  His 
Experimental  Researches,  205-207.  Berzelius  as  a  Teacher  and 
Writer,  207-209.  His  general  Character,  209. 

Development  of  the  Atomic  Theory  by  Berzelius,  210.  His 
Determinations  of  relative  Atomic  Weights,  211  et  seq.  His 
Oxygen  Law,  212. 

Influence  of  Gay-Lussac's  Law  of  Volumes  upon  the  Atomic 
Theory,  214.  Avogadro's  Hypothesis,  215.  Application  of  the 
Law  of  Volumes  by  Berzelius,  216.  The  Position  of  the  Atomic 
Theory  in  1818,  217.  Dulong  and  Petit's  Law,  220.  Influence 
of  the  Doctrine  of  Isomorphism  upon  the  Atomic  Theory,  221. 
Mitscherlich,  222. 

The  Atomic  Weight  System  of  Berzelius  from  1821  to  1826, 223. 
Dumas'  Attempt  to  alter  the  Atomic  Weights,  225.  Failure  of 
this  Attempt,  227.  Faraday,  227.  His  Law  of  Definite 
Electrolytic  Action,  228. 

The  Electro- Chemical  Theories  of  Davy  and  Berzelius,  229  et 
seq.  The  Dualistic  System  of  Berzelius,  233.  His  Chemical 
Nomenclature  and  Notation,  234-237. 

Manifestations  against  Dualism,  237.  Discovery  of  the 
Alkali  Metals,  238.  Recognition  of  the  Elementary  Nature  of 
Chlorine,  240.  Theory  of  the  Hydrogen  A  cids  (Davy  and  Dulong), 
241.  Doctrine  of  the  PolybasicA  cids  (Liebig),  243.  Graham,  244. 

Development  of  the   Dualistic  Doctrine  in  the   Domain  of 
Organic  Chemistry,    246.     The   Growth  of  Organic   Chemistry 
previous  to  1811,  246.     The  Position  of  Berzelius  with  regard  to 
Organic  Chemistry,    248.      Development   of  Views    respecting 
Radicals,  249. 

Isomerism  and  its  Influence  on  the  Development  of  Organic 
Chemistry,  250.  Observations  of  Liebig,  Wohler,  Faraday,  and 
Berzelius,  251.  Clearer  Definition  of  the  terms  Isomerism, 
Polymerism,  and  Metamerism  by  Berzelius,  252. 

The  older  Radical  Theory,  253.  The  Etherin  Theory, 
(Dumas  and  Boullay),  253-254.  Liebig  and  Wohler's  Work  upon 
Benzoyl  Compounds,  254.  The  Ethyl  Theory  of  Berzelius  and 
Liebig,  256.  Position  of  the  Radical  Theory  in  1837,  258. 
Definition  of  the  term  Radical,  260.  Bunsen,  260.  His  Work 
upon  the  Cacodyl  Compounds,  261.  The  significance  of  the 
Radical  Theory,  261. 

Liebig,  Wohler,  and  Dumas — A  Survey  of  their  more  import- 
ant Work,  262.  Justus  Liebig,  his  Life  and  Work,  262.  Liebig  as 
a  Teacher,  265.  His  Literary  Activity,  266.  His  experimental 
Researches,  267.  Friedrich  Wohler,  270.  Wohler  as  a  Teacher 
and  Writer,  271.  His  services  to  Science,  272.  Dumas,  his  Life 
and  Work,  272-275. 

The  Development  of  Unitary  Views  in  Organic  Chemistry,  275. 


CONTENTS 


Substitution  Theories,  275.  Dumas'  Laws  of  Substitution,  276. 
Laurent's  Substitution  or  Nucleus  Theory,  278.  Criticism  of  the 
same,  279.  Dumas'  Type  Theory,  280.  His  Unitary  System, 
281.  The  Overthrow  of  Berzelius'  Dualistic  Doctrine,  282. 
Berzelius'  Fight  against  the  Substitution  Theory  and  his  Defeat, 
282  et  seq. 

Fusion  of  the  older  Theory  of  Types  with  the  Radical  Theory 
by  Laurent  and  Gerhardt,  286.  Laurent  and  Gerhardt,  a  Sketch 
of  their  Lives,  286.  Gerhardt's  Theory  of  Residues,  287.  His 
Law  of  Basicity,  289.  Gerhardt' s  first  Classification  of  Organic 
Compounds,  289.  His  Reform  of  the  Atomic  Weight  System,  290. 
The  distinguishing  between  the  terms  Molecule,  Atom,  and  Equival- 
ent by  Laurent  and  Gerhardt,  293.  Work  preparatory  to  the  new 
Type  Theory— Wurtz  and  A.  W.  Hofmann,  295-298.  Williamson's 
Experiments  on  the  Formation  of  Ethers,  298.  His  Opinions 
with  regard  to  the  "Typical"  View,  299.  Gerhardt' s  new 
Theory  of  Types,  300.  Work  preparatory  to  this,  301.  Deriva- 
tion of  Organic  Compounds  from  Types,  303.  Gerhardt's  Views 
upon  Chemical  Constitution,  304.  Criticisms  upon  his  Type 
Theory,  306.  Extension  of  the  Type  Theory  by  Kekule, 
307.  Kekule,  308.  Mixed  Types,  308.  Marsh  Gas  as  a  Type, 
309.  Position  of  the  Type  Theory  in  1858,  310. 

Development  of  the  Newer  Radical  Theory  by  Kolbe — A  Survey 
of  Kolbe' s  Life  and  Work,  311.  The  Re-animation  of  the  Radical 
Theory  by  him — Frankland's  Co-operation,  313.  Copulated  or 
Conjugate  Compounds,  315.  Setting  aside  of  the  Notion  of 
Copulation  by  Frankland,  316.  Kolbe's  Carbonic  Acid  Theory, 
317.  The  Derivation  of  Organic  Compounds  from  Inorganic,  317. 
Kolbe's  most  important  Experimental  Researches,  319.  His  Atti- 
tude towards  the  older  and  the  newer  Chemistry,  320.  Kolbe's 
real  Types,  321. 

PAGE 

The  founding  of   the  Doctrine  of   the  Saturation-Capacity 

of  the  Elements  by  Frankland 322 

Preparatory  steps  towards  this  Doctrine,  322.  Frankland's 
services  here,  322  et  seq.  Assumption  of  a  varying  Saturation- 
Capacity,  325.  Discussions  on  the  Subject  by  Odling,  William- 
son, and  Wurtz,  326-327. 

The  Recognition  of  the  Valency  of  Carbon,  327.  Kekul6's 
services  here,  329.  Kolbe  and  Frankland's  share  in  the  Matter, 
329. 

Development   of   Chemistry   under    the   Influence    of    the 

Doctrine  of  Valency  during  the  last  Thirty  Years    .        .      331 

Beginnings  of  the  Structure  Theory — Kekule  and  Couper,  332. 
Establishment  of  the  true  Atomic  Weights  by  Cannizzaro,  335. 

b 


xviii  CONTENTS 


Discussions  regarding  the  Nature  of  "  Structure  "  by  Butlerow 
and  Erlenmeyer,  336. 

Controversies  respecting  constant  and  varying  Valency  of  the 
Elements,  337.  Views  upon  varying  Valency  held  by  Frankland, 
Kolbe,  etc.,  337-338;  by  Erlenmeyer,  Wurtz,  and  Naquet,  338. 
Kekule's  Theory  of  a  Constant  Valency,  338  ;  Grounds  for  the 
Assumption  of  a  varying  Valency,  340  et  seq. 

The  further  Development  of  the  Structure  Theory — The  chief 
Directions  taken  by  Organic  Chemistry  during  the  last  Thirty 
Years,  342.  Views  upon  the  linking  of  Atoms,  343.  Constitu- 
tion of  Organic  Compounds  according  to  the  Structure  Theory,  344. 
Saturated  and  Unsaturated  Compounds,  344.  Kekule's  Theory 
of  the  Aromatic  Compounds,  346.  Modifications  in  this  Theory 
proposed  by  Ladenburg,  Glaus,  and  Baeyer,  348-349.  Constitu- 
tion of  pyridine,  pyrrol,  etc.,  350-351.  Victor  Meyer's  more  pre- 
cise Conception  of  the  term  Aromatic  Compounds,  351.  Applica- 
tion of  Structural -chemical  Conceptions  to  the  Investigation  of  Iso- 
merism,  351.  Position-isomerism,  353.  Tautomerism  or  Desmo- 
tropism,  354-355.  Geometrical  isomerism  (Wislicenus),  356. 
Allo-isomerism  (Michael),  356.  The  supposed  Spacial  Arrangement 
of  atoms,  357  et  seq.  The  Development  of  Important  Methods  for 
investigating  the  Constitution  of  Organic  Compounds,  361. 
Synthetic  Methods  (Wohler,  Kolbe,  Frankland,  Baeyer,  Kekule, 
Ladenburg,  Fittig,  W.  H.  Perkin  sen.,  and  others),  361. 
Chemical  Behaviour  of  Organic  Compounds,  365. 

The  Main  Currents  in  Inorganic  and  General  Chemistry  during 
the  last  Thirty  Years,  367.  Application  of  the  Structure  Theory 
to  Inorganic  Compounds,  368.  Important  Researches  in  In- 
organic Chemistry,  369.  The  Periodic  System  of  the  Elements 
(Newlands,  L.  Meyer,  Mendelejeff),  370.  Crookes'  Hypothesis 
of  a  Primary  Material,  374.  General  Significance  of  Physico- 
chemical  Investigations,  375.  Ostwald,  377.  Van  't  Hoff,  377. 


CHAPTER   VI 

PAGE 

SPECIAL  HISTORY  OF  THE  VARIOUS  BRANCHES  OF  CHEMISTRY 

FROM  LAVOISIER  TO  THE  PRESENT  DAY          .        .        .      379 

Introduction  381 

History  of  Analytical  Chemistry 384 

Qualitative  Analysis  of  Inorganic  Substances,  384.  Use  of 
the  Spectroscope  for  this  purpose,  385.  Quantitative  Analysis  of 
Inorganic  Substances,  386.  Kaproth,  Vauquelin,  386.  Lavoisier, 
Proust,  Berzelius,  387.  Dumas,  Erdmann  and  Marchand, 
Marignac,  and  Stas,  388.  H.  Rose,  Wohler,  Fresenius,  389. 


CONTENTS 


Docimacy,  390.  Volumetric  Analysis,  390.  Its  Development 
by  Gay-Lussac,  Bunsen,  Mohr,  etc.,  391.  Development  of 
Methods  of  Gas  Analysis,  392.  The  Analysis  of  Organic 
Substances  (Lavoisier,  Gay-Lussac  and  Thenard,  Berzelius, 
Liebig),  393-397.  Legal-chemical  Analysis,  397.  Technico- 
chemical  Methods,  398. 

PAGE 

The   Progress   in   Pure   Chemistry   from   Lavoisier  to   the 

Present  Time 400 

Special  History  of  Inorganic  Chemistry 400 

The  Discovery  of  Elements,  and  the  Determination  of  their 
Atomic  Weights,  401.  Oxygen,  Nitrogen  and  Hydrogen,  401-402. 
The  Halogens,  402.  Selenium,  Tellurium,  etc.,  403.  Boron  and 
Carbon,  404.  Allotropy,  405.  The  Metals  of  the  Alkalies  and 
Alkaline  Earths,  407-408.  Beryllium,  Cadmium,  Thallium, 
Aluminium,  Indium,  Gallium,  408-409.  Metals  of  the  Cerium 
Group,  409.  Nickel  and  Cobalt,  410.  Chromium,  Titanium, 
Germanium,  etc.,  410-411.  Vanadium  and  allied  Elements,  412. 
Metals  of  the  Platinum  Group,  413.  Argon,  Krypton,  Metar- 
gon,  Neon  and  Helium,  414-417.  Rayleigh,  414.  Ramsay,  415. 
Supposed  new  Elements,  417. 

Inorganic  Compounds,  418.  Hydrogen  Compounds  of  the 
Halogens,  418.  Oxygen  Compounds  of  Hydrogen  and  of  the 
Halogens,  418.  Sulphur,  Selenium  and  Tellurium  Compounds,  J. 
420.  Compounds  of  Nitrogen,  Phosphorus,  etc.,  421-424.  Com- 
pounds of  Boron,  Silicon,  and  Carbon,  424.  Compounds  of  the 
Alkali  and  Alkaline  Earth  Metals,  426.  Compounds  of  the 
Metals  of  the  Iron  Group,  etc.,  427.  Compounds  of  Tin,  Vana- 
dium, etc.,  429.  Compounds  of  Gold,  Platinum,  etc.,  430. 

Special   History  of   Organic   Chemistry   in  the  Nineteenth 

Century 432 

Hydrocarbons  and  their  Derivatives,  433.  The  Alcohols  and 
Analogous  Compounds,  437.  Carboxylic  Acids,  441.  Acid  Chlor- 
ides, Anhydrides,  and  Amides,  444.  Oxy-  and  Amido- Acids,  446. 
Aldehydes,  448.  Ketones  and  Ketonic  Acids,  451.  Carbohy- 
drates and  Glucosides,  454.  Haloid  Derivatives  of  the  Hydro- 
carbons, etc.,  457.  Nitro-  and  Nitroso-Compounds,  460. 
Sulphur  Compounds,  462.  Organic  Nitrogen  Compounds 
(Amines,  etc.),  465.  Phosphines,  Arsines,  Stibines,  469.  Azo- 
Compounds,  470.  Diazo-Compounds,  470.  Hydrazines,  Cyano- 
gen Compounds,  472-478.  Pyridine  and  Quinoline  Bases,  478. 
Their  Relation  to  Vegetable  Alkaloids,  482.  Pyrrol  and  Analo- 
gous Compounds,  484.  Organo-metallic  Compounds,  486. 

b  2 


CONTENTS 


History  of  Physical  Chemistry  in  Recent  Times       .        .        .      488 

Determination  of  Vapour  Density  and  the  Application  of  this, 
490.  Dissociation,  492.  The  Liquefaction  of  Gases,  492.  The 
Kinetic  Theory  of  Gases,  493.  Spectrum  Analysis,  494.  Atomic 
Volumes  of  Solids  and  Liquids,  495.  Laws  regulating  the  Boiling 
Temperature,  496.  Specific  Heat  of  Solid  Bodies,  497.  Optical 
Behaviour  of  Solids  and  Liquids  (Refraction,  Circular  Polarisa- 
tion), 498.  Diffusion,  etc.,  500.  Theory  of  Solution  ;  Electrolytic 
Dissociation,  501.  The  Electrolysis  of  liquid  or  of  dissolved  Sub- 
stances, 503.  Isomorphism,  etc.,  505.  Thermo- Chemistry,  507.- 
Julius  Thomsen  ;  Berthelot,  508.  Photo- Chemistry,  509. 

Development  of  the  Doctrine  of  Affinity  since  the  Time  of 
Bergman,  512.  Bergman's  Doctrine  of  Affinity,  512.  Berthollef  s 
Doctrine  oj  Affinity,  513.  The  Supplanting  of  Bertholletf  s  Opinions 
by  other  Doctrines,  515.  The  Revival  of  Berthollef  s  Doctrines, 
517.  The  latest  Development  of  the  Doctrine  of  Affinity,  519. 

Sketch  of  the  History  of   Mineralogical  Chemistry  during 

the  last  Hundred  Years        .  .522" 

Its  Earlier  History,  522.  The  Chemical  Mineral  System  of 
Berzelius,  524.  Other  Mineral  Systems,  525.  The  more  recent 
Development  of  Mineral  Chemistry,  525-526.  The  Artificial 
Production  of  Minerals — Beginnings  of  Geological  Chemistry,  527. 

Development  of  Agricultural  and  of  Physiological  Chemistry     530 

Agricultural  Chemistry  and  Vegetable  Physiology,  531.  The 
Humus  Theory,  531.  Reform  of  Agricultural  Chemistry  by 
Liebig,  532.  Its  further  Development  by  Liebig  and  his  School, 
533.  Nitrification  and  the  Assimilation  of  free  Nitrogen  by 
plants,  534-535. 

The  Development  of  Phy  to -Chemistry,  536.  Important 
Phyto-Chemical  Researches,  537-538. 

The  Development,  of  Zoo-Chemistry,  539.  Researches  upon 
the  Constituents  of  the  Animal  Body,  539.  The  Chemistry  of 
the  Animal  Secretions — Saliva,  Gastric  Juice,  Bile,  Blood,  541  ; 
Milk,  Urine,  542.  Metabolism,  544. 

Fermentation;  Putrefaction,  546.  Views  regarding 
Fermentation,  546  et  seq.  Organised  and  Unorganised  Fer- 
ments, 548.  The  Phenomena  of  Putrefaction,  548.  The 
Ptomaines,  549. 

The  Relation  of  Chemistry  to  Pathology  and  Therapeutics^ 
549.  Bacteriology,  550.  Antiseptics,  Anaesthetics,  and  Anti- 
pyretics, 550-551. 

The  Relation  of  Chemistry  to  Pharmacy,  552. 


CONTENTS  xxi 


History   of  Technical  Chemistry  during  the  last  Hundred 

Years 554 

Introduction,  554.  Development  of  Technical  Instruction, 
556.  Literature  on  Technical  Chemistry,  556. 

The  Progress  of  Metallurgy ,  557.  Iron  and  Steel,  557.  Nickel, 
Silver,  the  Galvano-Plastic  Process,  Aluminium,  558-559. 
Mineral  Pigments,  560. 

Development  of  the  Great  Chemical  Industries,  561. 

Sulphuric  Acid,  561.  The  Soda  Industry,  562-564.  Hydro- 
chloric Acid,  Chlorine,  and  Bleaching  Powder,  565-566. 
Bromine  and  Iodine,  566.  Nitric  Acid,  Gunpowder,  566-567. 
Other  Explosives,  Matches,  568. 

The  Manufacture  of  Soap,  etc.,  569.  Ultramarine,  570. 
Glass,  Earthenware,  and  Pottery,  570,  571.  Mortar,  Paper, 
571,  572.  Starch,  Beet-Sugar,  572-574. 

Fermentation  Processes,  574.  The  Manufacture  of  Spirits, 
575.  The  Quick  Vinegar  Process,  575. 

The  Aniline  Colours  and  other  similar  Dyes,  576.  Phthal- 
e'ins,  Azo-Dyes,  578.  Alizarine,  the  Safranines,  Indigo  Blue, 
579.  Dyeing,  580.  Tanning,  580. 

Various  Chemical  Preparations,  581.  Various  Products 
from  Coal-tar  ;  Illuminants,  582.  Heating  Materials,  584. 

The  Growth   of   Chemical   Instruction   in  the  Nineteenth 

Century,  more  especially  in  Germany       ....      586 

The  State  of  Education  in  Science  at  the  end  of  the 
Eighteenth  Century,  586.  Experimental  Lectures,  587.  The 
Development  of  Practical  Instruction  (Berzelius,  Liebig),  587- 
588.  The  Erection  of  Laboratories  for  General  Instruction  in 
Germany,  588  et  seq.  Erdmann,  590.  The  State  of  Scientific 
Education  in  France,  Great  Britain,  etc.,  591.  Improvements 
in  the  Construction  of  Chemical  Laboratories,  593. 

Chemical  Literature,  594.  Text-books,  594.  Larger 
Treatises  and  Encyclopedias,  595.  Periodical  Journals,  596. 
Yearly  Reports  (Jahresberichte),  597.  The  Necessity  for 
Criticism  in  Chemical  Literature,  598.  The  Study  of  Original 
Memoirs,  598. 

INDEX  OF  AUTHORS'  NAMES .      601 

INDEX  OF  SUBJECTS  613 


ABBREVIATIONS  OF  THE  NAMES  OF  MOST  OF 

THE  JOURNALS  TO  WHICH  REFERENCE 

HAS  BEEN  MADE 

Ann.   Chem.      .     .    Liebig's  Annalen  der  Chemie  und  Pharmacie  (begun 

1832). 
Ann.  Chim.      .     .    Annales  de  Chimie  et  de  Physique  (begun  1816 ;  five 

series). 

Ami.  de  Chimie     .    The  same  journal  from  1789  to  1815. 
Ann.  des  Mines     .    Annales  des  Mines. 
Ann.  of  Philosophy  Annals   of  Philosophy   (edited  by  Thomas  Thomson, 

1813-26).     This  journal  was  subsequently  merged 

in  the  Philosophical  Magazine. 

Ann.  Phys.       .     .    The  new  Series  (Neue  Folge)  of  Poggendorff's  Annalen. 
Archiv.  Pharm.    '.    Archiv  der  Pharmacie  (begun  1832). 
Bayer.   Akad.   .     .    Sitzungsberichte  der  Bayerischen  Akademie  der  Wiss- 

enschaften. 
Ber Berichte  der  Deutschen  chemischen  Gesellschaft  (begun 

1868). 

Bull.  Soc.  Chim.    .    Bulletin  de  la  Societe  Chimique  de  Paris  (begun  1864). 
Chem.  Centr.     .     .    Chemisches  Centralblatt  (begun  1848). 
Chem.  News      .     .    Chemical  News  (begun  1860). 
Compt.  Rend.    .     .   Comptes  Rendus  des  Seances  de  1' Academic  des  Sciences 

(begun  1835). 

Crell's  Ann.       .     .    Chemische  Annalen  von  L.  v.  Crell  (1784-1805). 
Dingl.  Journ.    .     .    Dingler's  Polytechnisches  Journal  (begun  1820). 
Gazz.  Chim.  Ital.   .    Gazzetta  Chimica  Italiana  (begun  1871). 
Gilb.  Ann.    .     .     .    Annalen  der  Physik  von  Gilbert  und  Gr en  (1798-1824). 

/Bericht  iiber  die  Entwickelung  der  Chemischen  Indus-  m 
Hofmanrfs  *r^e  wahrend  des  letzten  Jahrzehnts  von  Hofmann 

Bericht   etc.   .  (began  1875,  but  ceased  after  the  publication  of 

\         two  volumes). 
Jahres.  Berz.     .     .    Jahresberichte  iiber  die  Fortschritte  der  Chemie  und 

Mineralogie  von  Berzelius  (1821-47). 

Jahres.    d.    Chemie   Jahresberichte  iiber  die  Fortschritte  der  Chemie  von 
Liebig  und  anderen  (begun  1847). 


LIST  OF  ABBREVIATIONS 


Journ.  Chem.  Ind.  Journal  of  the  Society  of  Chemical  Industry  (begun 
1882). 

Journ.  Chem.  Soc.  Journal  of  the  Chemical  Society  (Memoirs  and  Pro- 
ceedings, vols.  i.-iii.,  1841-47  ;  Journal  begun  1848). 

Journ.  de  Phys.     .    Journal  de  Physique  (1778-94  ;  1798-1823). 

Journ.    pr.    Chem.    Journal  fiir  praktische  Chemie  (begun  1834 ;  the  new 
series  begun  1870). 

Mon.  Sclent.  .  .  Moniteur  Scientifique  (edited  by  Quesneville,  begun 
1857). 

Phil.  Mag.        .     .    Philosophical  Magazine  (begun  1798). 

Phil.  Trans.  .  .  Philosophical  Transactions  of  the  Roya)  Society  (begun 
1666). 

Phil.  Trans.  E.  .  Philosophical  Transactions  of  the  Royal  Society  of 
Edinburgh  (begun  1788). 

Pogg.  Ann.  .  .  Annalender  Physikund  Chemie  von  PoggendorfF  (begun 
1824  ;  new  series  begun  1877). 

Proc.  JR.  S.  .  .  Proceedings  of  the  Royal  Society  [begun  1800.  Vols. 
i.  -iv.  (1800-1843)  are  entitled  "Abstracts  of  the 
Papers  printed  in  the  Philosophical  Transactions  of 
the  Royal  Society  of  London,"  and  vols.  v. ,  vi. 
(1843-1854)  "  Abstracts  of  Papers  communi- 
to  the  Royal  Society."  The  final  form  of  title, 
"Proceedings  of  the  Royal  Society  of  London," 
begins  with  vol.  vii.,  published  in  1856]. 

Proc.  JR.  S.  E.  .  Proceedings  of  the  Royal  Society  of  Edinburgh  (begun 
1845). 

Rec.  Trav.  Chim.  .  Recueil  des  Travaux  Chimiques  (begun  1882). 

Schiveigg.  Journ.  Journal  fiir  Chemie  und  Physik  von  Schweigger 
(1811-33). 

Wagner's  Jahresber.  Jahresbericht  iiber  die  Leistungen  der  chemischen 
Technologic  von  Wagner  (begun  1856). 

Wiener  Monatshefte  Monatshefte  fiir  Chemie  und  verwandte  Theile  anderer 
Wissenschaften  (begun  1880). 

Ztschr.  anal.  Chem.  Zeitschrift  fiir  analytische  Chemie  von  Fresenius  (begun 

1862). 

Ztschr.  Chem.  .  Zeitschrift  fiir  Chemie  (1865-71);  this  was  a  continua- 
tion of  the  Kritische  Zeitschrift  (begun  1858). 

Ztschr.  phys.  Chem.  Zeitschrift  fiir  physikalische  Chemie,  Stochiometrie, 
und  Verwandtschaftslehre  (edited  by  Ostwald  and 
van  't  Hoff ;  begun  1887). 


ERRATA. 

Page    27,  line  18,  from  top,  for  "Synesius"  read  "Synesios." 

„  357,    ,,      2,  from  top,  for  "  Lebel  "  read  "  Le  Bel." 

„  386,    , ,      2,  from  top,  for  ' '  Kirchoff  "  read  ' <  Kirchhoff. " 

,,  407,     ,,     19,  from  top,  for  "  Matth lessen  "  read  "Mathiessen." 

,,  *46,    ,,     17,  from  top,  for  "  R.  Hofmann  "  read  "  R.  Hoffmann." 

„  481,    ,,      5,  from  foot,  for  ' '  Huisberg  "  read  "  Hinsberg." 

,,  499,    ,,      5,  from  foot,  for  "Lebel"  read  "  Le  Bel." 

,,  502,    ,,     11,  from  foot,  for  "Eykman"  read  "Eykmann." 

, ,  505,    , ,    11,  from  foot,  for  ' '  Scherer ' '  read  ' '  Scheerer. " 

,,  537,    ,,       7,  from  top,  for  "formic  acid"  read  "formic  aldehyde. 

,,  543,    ,,    11,  from  foot  for  "Scherer"  read  "Scheerer." 

,,  558,    ,,      7,  from  foot,  for  "Pattison"  read  "Pattinson." 

„  575,  note  4,  for  "  Schiizenbach  "  read  "  Schiitzenbach." 


A  HISTOKY  OF  CHEMISTEY 


INTRODUCTION 

CHEMISTRY  has  for  the  last  two  hundred  years  or  so  been 
defined  as  the  study  of  the  composition  of  substances.  Its 
first  task,  therefore,  lies  in  ascertaining  the  constituents  of 
which  the  material  world  surrounding  us  is  composed,  in 
reducing  these  constituents  to  their  elements,  and  in  building 
up  new  chemical  compounds  from  the  latter.  Hand  in  hand 
with  these  analytic  and  synthetic  problems  there  goes  the 
further  task  of  determining  the  laws  which  regulate  the 
chemical  combination  of  matter. 

The  problems  just  indicated  occupy,  in  the  widest  sense 
of  the  word,  the  attention  of  chemists  to-day.  The  prob- 
lems of  chemistry  were,  however,  different  in  former  times, 
and  it  is  precisely  these  differences  in  aim  which  characterise 
the  various  epochs  into  which  the  history  of  the  science  may 
therefore  be  divided. 

The  oldest  nations  with  regard  to  which  we  possess 
reliable  information — the  Egyptians,  Phoenicians,  Jews  and 
others — did  indeed  possess  a  certain  disjointed  knowledge  of 
chemical  processes  acquired  accidentally;  but  these  were 
applied  for  their  practical  results  alone,  and  not  with  the 
object  of  deducing  any  comprehensive  scientific  explanation 
from  them.  We  meet  with  similar  conditions  among  the 
earliest  cultured  European  nations,  the  Greeks  and  Romans, 
who  owed  most  of  their  knowledge  of  chemical  facts  to  the 
peoples  just  named.  Nowhere  do  we  find  in  antiquity  the 
endeavour  to  gain  an  insight  into  chemical  processes  by 


2  A  HISTORY  OF  CHEMISTRY  INTRO. 

means  of  definitely  planned  experiments.  Although  the 
Ancients  were  wholly  without  such  data,  furnished  by  exact 
research,  as  are  nowadays  held  to  be  indispensable,  this 
did  not  prevent  them  from  speculating  as  to  the  nature  of 
the-  universe;  indeed,  those  theoretical  views  upon  the 
nature  of  matter,  on  the  "  elements "  of  which  the  world 
was  composed,  have  given  to  the  earliest  age  of  chemistry 
its  own  particular  stamp.  Some  of  these  systems — especi- 
ally Aristotle's  system  of  the  elements — continued  to  hold 
sway  for  many  centuries,  and  influenced  more  especially  the 
whole  teaching  of  the  Middle  Ages. 

From  the  above-mentioned  doctrine  of  the  nature  of  the 
elements  was  developed  the  theory  of  the  transmutation  of 
metals,  or  rather  the  fixed  belief  that  one  element  can  be 
transformed  into  another.  Even  so  far  back  as  the  beginning 
of  our  own  era,  at  first  in  Egypt,  there  began  the  striving  to 
transmute  the  base  metals  into  the  noble,  to  "  create  "  gold 
and  silver. 

The  art  by  which  this  was  to  be  achieved  was  termed 
chemia  (^/W<z),  a  name  dating,  so  far  as  actual  proof  goes, 
from  the  fourth  century,  but  in  reality  probably  from  an 
earlier  period.1 

There  are  many  indications  that  this  conception  of  the 
aim  of  chemistry  and  of  the  problems  which  it  had  to  solve 
predominated  for  centuries  following,  e.g.  it  lies  at  the 
root  of  the  definition  giverHby-Suidas,  the  author  of  an 
encyclopedia,  who  lived  in  the  eleventh  century:  "Chem- 
istry, the  artificial  preparation  of  silver  and  gold ;  "  further, 
"  XPV(707rol/^a "  was  a  very  commonly  used  designation  for 
chemistry  over  a  long  period. 

This  task,  the  solution  of  which  was  the  aim  of  the 

1  This  word  is  of  Egyptian  origin  and  is  probably  founded  on  the  North 
Egyptian  word  CMmi,  the  name  for  Egypt.  It  also  means,  however, 
"black,"  and  hence  there  is  still  some  doubt  whether  the  word  x^M6*0  °f 
that  period  denotes  Egyptian  art  or,  as  Hoffmann  in  the  article  "  Chemie," 
in  the  Dictionary  of  Chemistry  edited  by  A.  Ladenburg,  endeavours  to 
prove,  the  employment  of  a  black -coloured  preparation  valuable  for  al- 
chemistical  purposes.  The  mode  of  writing  x^6'0*  and  ^ne  derivation  of 
this  word  from  xvP-&s>  mav  ^e  regarded  as  incorrect. 


INTRO.  INTRODUCTION 


so-called  Alchemy,1  characterises  the  •  alchemistic  period,  a 
period  extending  from  at  least  the  fourth  century  of  our  era 
to  the  first  half  of  the  sixteenth.  It  is  impossible  to  state 
with  perfect  exactitude  the  date  at  which  alchemy  took  its 
rise,  its  origin  being  lost  in  the  mists  of  the  past.  The 
labours  of  the  alchemists,  who  strove  by  all  imaginable 
methods  to  attain  to  the  philosopher's  stone  (by  the  aid  of 
which  not  only  were  the  noble  metals  to  be  produced  from 
the  base,  but  also  the  life  of  man  to  be  prolonged),  had  the 
effect  of  largely  extending  the  area  of  the  then  existing 
knowledge  of  chemical  facts. 

In  the  first  half  of  the  sixteenth  century,  almost  contem- 
poraneously with  the  Reformation,  i.e.  with  the  birth  of  a 
new  epoch  in  the  world's  history,  chemistry  began  to  develop 
in  a  new  direction,  without,  however,  losing  all  at  once  its 
alchemistic  tendencies.  Chemistry,  which  had  already 
proved  itself  a  valuable  helpmeet  to  medicine  in  the 
preparation  of  active  remedies,  came  to  be  looked  upon  as 
the  basis  of  the  whole  medical  art.  Health  and  illness  were 
reduced  to  chemical  processes  in  the  human  body ;  only  by 
means  of  chemical  preparations  could  an  unhealthy  body  be 
restored  to  its  normal  condition ;  in  short,  the  absorption  of 
medicine  in  chemistry,  the  fusion  of  both  together,  was  the 
cry  which  emanated  from  Paracelsus.  Van  Helmont,  de  le 
Boe  Sylvius,  Tachenius  and  others  were  the  chief  exponents 
of  this  doctrine,  which  characterises  the  period  of  Medical  or 
latro-Chemistry.  The  fact  that  technical  chemistry  was 
advanced  at  the  same  time,  through  the  labours  of  indi- 
viduals such  as  Georgius  Agricola,  was  without  influence  on 
the  prevailing  tendency  of  the  science  of  that  age. 

From  the  middle  of  the  seventeenth  century  on,  the 
iatro-chemical  current  gradually  underwent  substitution  by 
another.  After  that  date  chemistry  strove  hard  to  becpme  a 
self-supporting  branch  of  natural  science,  quite  independent 
of  every  other.  Indeed,  the  history  of  chemistry  proper 
begins  with  Robert  Boyle,  who  taught,  as  its  main  object, 
the  acquisition  of  a  knowledge  of  the  composition  of  bodies. 

The  conception  of  this  aim  marks  the  date  from  which 

1  This  term  with  the  Arabic  prefix  "al"  became  naturalised  very  early. 

B    2 


4  A  HISTORY  OF  CHEMISTRY  INTRO. 

chemistry  may  be  regarded  as  a  science  striving  towards 
an  ideal  goal  along  the  paths  of  exact  research,  without 
regard  to  practical  results,  and  solely  with  the  object  of 
arriving  at  the  truth. 

The  most  important  problem,  whose  solution  occupied  all 
the  chemists  of  note  at  that  day,  was  the  question  of  the 
chemical  reasons  underlying  the  phenomena  of  combustion. 
Since  Stahl's  attempt  to  explain  the  latter,  the  hypothetical 
fire  stuff  Phlogiston — which  was  supposed  to  escape  during 
every  combustion — was  regarded  as  the  universal  principle  of 
combustibility.  This  doctrine  held  sway  over  chemists  at 
the  end  of  the  seventeenth  and  during  the  greater  part  of 
the  eighteenth  centuries  to  such  an  extent  that  we  are 
justified  in  characterising  this  period  (after  the  death  of  iatro- 
chemistry)  as  the  period  of  the  Phlogiston  Theory. 

The  fall  of  the  latter,  and  its  replacement  by  the  anti- 
phlogistic system  of  Lavoisier,  bring  us  to  the  commencement 
of  the  chemical  era  in  which  we  are  still  living.  For,  upon 
the  foundation  laid  by  Lavoisier  and  his  co-workers,  and 
firmly  fixed  by  Dalton,  Berzelius  and  others,  the  structure  of 
the  new  chemistry  rises.  The  founding  and  developing  of 
the  chemical  atomic  theory,  and  its  extension  to  all  parts  of 
chemical  science,  characterise  this  latest  epoch,  to  which  the 
period  of  Lavoisier's  reform  of  chemistry  was  a  necessary 
stepping-stone ;  it  is,  therefore,  to  be  designated  as  the 
period  of  the  Chemical  Atomic  Theory.  An  insight  into 
the  conditions  which  it  involved  being  only  possible  by 
careful  quantitative  researches,  the  balance  has  been,  since 
the  time  of  Lavoisier;  the  most  valuable  instrument  of  the 
chemist.  H.  Kopp  is,  therefore,  fully  justified  in  naming 
the  epoch  which  begins  with  the  French  savant  the  period  of 
quantitative  research.  Of  late  years  the  first  aim  of  chem- 
istry, i.e.  the  exact  determination  of  the  composition  of 
substances,  has  been  accompanied  by  the  investigation  of 
the  relations  which  exist  between  their  physical  properties 
and  chemical  composition.  But  the  light  of  the  atomic 
theory  permeates  the  whole,  so  that  one  is  forced  to  regard 
it  as  the  guiding  star  of  modern  chemistry. 


CHAPTER   I 

FROM  THE  EARLIEST  TIMES  TO  THE  BIRTH  OF 
ALCHEMY 

THE  characteristics  of  this  period,  which  have  been  already 
referred  to,  justify  one  in  designating  it  the  period  of  crude 
empiricism  with  regard  to  chemical  facts.  In  sharp  contrast 
with  the  disinclination  of  the  Ancients  towards  experiment, 
through  which  alone  the  secrets  of  nature  are  to  be  un- 
ravelled, stood  their  great  love  of  speculation,  by  means  of 
which  they  did  not  hesitate  to  attempt  an  explanation  of  the 
ultimate  reasons  of  all  things.  Aristotle,  to  whom  the  natural 
sciences  owed  the  direction  which  they  followed  for  a  very 
long  time,  pointed  to  deduction  as  the  road  which  should 
lead  to  the  goal.  Instead  of  drawing  general  conclusions 
from  accurately  observed  facts,  the  Ancients  preferred  to 
advance  from  the  general  to  the  particular.  The  position  of 
all  the  natural  sciences  in  far-back  times,  especially  that  of 
chemistry,  is  sufficient  to  prove  how  the  most  mischievous 
errors  crept  in  and  became  firmly  established  in  consequence 
of  following  the  purely  deductive  method. 

The  philosophical  writings  of  the  Ancients,  especially  those 
of  the  Greeks  and  Romans,  give  us  a  tolerably  distinct  idea 
of  their  theoretical  views.  Certain  writings  of  Aristotle,  and 
also  the  "  Trepl  \l6wv "  of  his  pupil  Theophrastus,  are  of 
especial  value  for  the  criticism  of  the  empirical  chemical 
knowledge  of  these  times.  The  works  of  Dioscorides  on 
Materia  Medica  and  particular  chapters  of  the  Historia 
Naturalis  of  the  elder  Pliny  give  us  an  exceptionally  clear 
insight  into  the  knowledge  of  the  Ancients.  Dioscorides,  who 


6        FROM  EARLIEST  TIMES  TO  THE  BIRTH  OF  ALCHEMY      CH. 

was  born  about  the  middle  of  the  first  century  at  Anazarbos, 
enlarged  his  acquirements,  already  great,  by  experiences 
collected  on  long  journeys.  His  fame  as  a  physician  holds 
good  among  the  Turkish  doctors  to  this  day.  The  work  of 
Pliny  above-mentioned  contains  exceedingly  valuable  records 
of  the  state  of  scientific  knowledge  in  his  time ;  it  also  ^hows, 
however,  that  the  author  was  by  no  means  master  of  the 
immense  amount  of  material  which  he  had  collected l  from 
tradition,  but  which  he  had  not  really  assimilated. 


Theoretical  Views  upon  the  Composition  of  Substances,  and 
upon  the  Elements? 


The  question  of  the  ultimate  constituents  of  bodies,  i.e.,  of 
the  elements  which  go  to  build  up  the  world,  occupied  the 
minds  of  the  oldest  nations.  To  give  an  exhaustive  description 
of  their  speculations  on  the  point  does  not  come  within  the 
scope  of  this  work ;  what  is  wanted  is  rather  to  call  special 
attention  to  those  views  which  have  exercised  a  permanent 
influence  upon  the  chemical  ideas  of  later  times. 

This  applies  in  a  particular  degree  to  the  doctrine  of  the 
elements,  which  originated  with  Empedoclfis,  although  it 
usually  bears  Aristotle's  name;  also,  but  to  a  much  lesser 
extent,  to  the  ideas  of  the  older  Greek  philosophers  regarding 
the  original  material  of  which  the  world,  according  to  them, 
was  built  up.  Views  like  that  of  Thales^  (in  the  sixth  cen- 
tury B.C.),  that  water  is  the  ground  material,  or  those  of 
Anaximenes  and  Heraclitna  (in  the  same  century),  who 
ascribed  to  air  and  fire  respectively  the  same  role,  have  had 
no  influence  upon  the  development  of  chemical  knowledge. 

1  Pliny  the  younger  characterised  the  work  of  his  uncle  as  "  opus  diffusum, 
eruditum,  nee  minus  varium,  quam  ipsa  natura,"  and  similar  admiration 
of  it  was  expressed  by  other  authors  of  the  day.     Our  thanks  are  due  to 
E.  O.  von  Lippmann,  who  has  recently  published  a  memoir  entitled  Die 
chemischen  Kenntnisse  des  Plinius  ("Pliny's  Knowledge  of  Chemistry"),  in 
which  the  whole  subject  is  treated  in  lucid  style  (vide  Mittheilungen  aus  dem 
Osterlande,  vol.  v.,  p.  370). 

2  Cf.  Kopp,  Geschichte  der  Chemie,  vol.  i.   p.   29 ;  vol.  ii.   p.   267 ;  also 
Hofer,  Histoire  de  la  Chimie,  vol.  i.  p.  72. 


THE  ELEMENTS  OF  ARISTOTLE 


Democritus  (in  the  fifth  century  B.C.)  also  took  a  ground 
material  as  the  basis  of  his  speculations,  but  subdivided  this 
further  in  that  he  imagined  it  to  be  made  up  of  the  smallest 
possible  particles,  of  atoms,  which  differed  from  one  another 
\in  form  and  size,  but  not  in  the  nature  of  their  substance. 
All  tie  changes  in  the  world  consisted,  according  to  him,  in 
the  separation  and  recombination  of  these  atoms,  which  were 
supposed  to  be  in  a  state  of  continual  motion.  This  doc- 
trine, which  at  first  sight  appears  to  accord  with  our  present 
chemical  atomic  theory,  but  which  in  reality  has  nothing  in 
common  with  the  latter,  was  further  developed  by  Epicurus, 
as  may  be  well  seen  in  the  didactic  poem  of  Lucretius,  De 
Rerum  Natura. 

The  four  so-called  "elements" — air,  water,  earth  and 
fire — were  regarded  by  that  intellectually  great  philosopher, 
Empedocles  of  Agrigent  (about  440  B.C.),  as  the  basis  of  the 
world ;  but  neither  he  himself  nor  Aristotle,  who  adopted  these 
into  his  system  of  natural  philosophy,  looked  upon  them  as 
different  kinds  of  matter,  but  as  different  properties  carried 
about  by  one  original  matter.1  Their  chief  qualities  (the 
primce  qualitates  of  the  later  scholastics)  he  held  to  be  those 
apparent  to  the  touch,  viz.,  warm,  cold,  dry,  and  moist.  Each 
of  the  four  so-called  elements  is  characterised  by  the  pos- 
session of  two  of  these  properties,  air  being  warm  and  moist, 
water  moist  and  cold,  earth  cold  and  dry,  and  fire  dry  and 
warm.  The  differences  in  the  material  world  were,  therefore, 
to  be  ascribed  to  the  properties  inherent  in  matter.  From 
the  assumption  that  these  latter  can  alter,  there  necessarily 
follows  the  immediate  conviction  that  substances  can  be 
transformed,  one  into  the  other.  It  is  easy  to  see  how,  when 
based  upon  speculations  of  this  nature,  the  belief  in  the 
transformation  of  water  into  air  should  establish  itself,  for 
both  have  the  property  of  moistness  in  common,  while  cold, 
the  individual  property  of  water,  can  be  converted  by  the 
addition  of  heat  into  the  second  chief  property  of  air.  And 
it  is  not  surprising  that  considerations  of  this  kind  on  the 

1  Cf.  the  ingenious  exposition  by  Th.  Gomperz  in  his  work  "  Griechische 
Denker,"  p.  183  (Leipzig,  Veit  and  Co.). 


8        FROM  EARLIEST  TIMES  TO  THE  BIRTH  OF  ALCHEMY     CH. 

states  of  aggregation  of  matter  should  lead  to  the  idea  of 
transforming  one  kind  of  matter  into  another.  It  was  doubt- 
less by  the  generalisation  of  such  views  that  the  belief  in  the 
possibility  of  the  transmutation  of  metals,  which  formed  the 
chief  feature  of  the  alchemistic  period,  grew  to  the  extent 
that  it  did. 

Aristotle  considered  that  his  four  elements  were  insufficient 
in  themselves  to  explain  the  phenomena  of  nature ;  he  there- 
fore assumed  a  fifth  one,  termed  ovcria,  which  he  imagined 
to  possess  an  ethereal  or  immaterial  nature  and  to  permeate 
the  whole  world.  As  the  "  quinta  essentia "  this  played  an 
immense  rdle  among  the  followers  of  the  Aristotelian  doctrine 
in  the  Middle  Ages,  and  gave  rise  to  endless  confusion,  from 
the  endeavours  of  many  (who,  unlike  Aristotle,  supposed  it  to 
be  material)  to  isolate  it. 

There  seems  to  be  a  high  degree  of  probability  in  the 
assumption  that  Empedocles  and  Aristotle  did  not  themselves 
deduce  their  theory  of  the  elements,  but  derived  it  from 
other  sources ;  thus  the  oldest  writings  of  India  teach  that 
the  world  consists  of  the  four  elements  mentioned  above,1 
together  with  ether,2  which  last  is  most  likely  related  to 
Aristotle's  overt  a. 

It  is  unnecessary  to  point  out  how  widely  the  above  views 
of  the  Greek  philosophers  with  regard  to  the  elements  de- 
viate from  the  conceptions  of  modern  chemistry. 

With  respect  also  to  the  meaning  of  the  term  "  chemical 
combination,"  one  meets,  even  if  only  occasionally,  with 
opinions  diametrically  opposed  to  those  obtaining  at  the 
present  day ;  the  formation  of  a  substance  by  the  interaction 
of  others  was  looked  upon  as  the  creation  of  a  new  matter, 
and  the  destruction  of  the  original  substances  from  which  it 
was  produced  was  assumed.  Everywhere  men  were  contented 
with  theoretical  explanations,  without  attempting  to  prove 
their  correctness  by  actual  experiment.  This  want  shows 

1  Instead  of  air,  the  element  wind  is  given. 

2  So  teaches  Buddha  (as  Dr.  Pfungst  has  been  good  enough  to  inform 
me) ;   see  the  Anguttara  Nikdja,  vol.  i.  fol.  c.e.     Here  consciousness  is 
named  as  the  sixth  element. 


i    EMPIRICAL  CHEMICAL  KNOWLEDGE  OF  THE  ANCIENTS    9 

itself  very  markedly  in  the  manner  in  which  the  Ancients 
regarded  the  numerous  chemical  facts  which  they  had  learned 
by  empirical  methods,  and  mostly  by  accident. 

The  Empirical  Chemical  Knowledge  of  the  Ancients.1 

The  Egyptians  stand  out  prominently  from  among  the 
earlier  civilised  nations  as  having  usefully  applied  their 
knowledge  of  chemical  processes,  acquired  by  chance  observa- 
tions, to  useful  purposes ;  the  needs  of  everyday  life  and  the 
desire  to  make  that  life  a  comfortable  one  were  the  incentives. 

Their  country  formed  a  kind  of  focus  in  which  was  con- 
centrated the  chemical  knowledge  of  the  time,  if  one  may  so 
designate  an  acquaintance  with  technical  processes.  The 
Egyptians  already  possessed  at  a  very  early  date  a  large 
experience  in  the  production  of  metals  and  alloys,  in  dyeing, 
in  the  manufacture  of  glass,  and  also  in  the  making  and 
application  of  pharmaceutical  and  antiseptic  preparations. 
The  chemical  art  proper,  revered  as  "  holy  "  (ayia  re^vrj),  was 
jealously  guarded  by  the  priesthood  as  a  treasure  at  once 
precious  and  profitable.  Only  the  elect  might  penetrate  its 
mysteries.  That  laboratories,  in  which  chemical  operations 
of  various  kinds  were  carried  out,  actually  formed  adjuncts 
to  the  temples,  is  clearly  proven  by  the  inscriptions  found  in 
such  chambers,  e.g.  at  Dendera  and  Edfu. 

There  can  scarcely  be  a  doubt  that  the  Phoanicians  and 
Jews  obtained  their  knowledge  of  the  manufacture  of  import- 
ant technical  products  from  the  Egyptians.  In  like  manner, 
and  to  an  even  greater  extent,  was  there  a  wealth  of  chemical 
experience  laid  open  to  the  Greeks,  and  afterwards  to  the 
Romans,  by  reason  of  their  close  relations  with  the  ancient 
country  Chemi  (see  p.  2,  note  1).  The  writings  of  such 
eminent  Greek  philosophers  as  Solon,  Pythagoras,  Demo- 
critus  and  Plato,  who  succeeded  in  gaining  the  confidence  of 
the  Egyptian  priesthood,  contributed  in  no  small  degree  to 
the  spread  of  such  practical  knowledge. 

1  Cf.  Kopp,  Gesch.  d.  Chemie,  vols.  iii.  and  iv.  ;  Hofer,  Hist.,  vol.  i.  p. 
106  et  seq. 


10      FROM  EARLIEST  TIMES  TO  THE  BIRTH  OF  ALCHEMY     CH. 

But  all  the  knowledge  so  gained  was  purely  empirical ;  long 
ages  were  to  pass  before  the  various  items  of  which  it  was  com- 
posed were  brought  together  under  a  general  scientific  stand- 
point. In  this  section  of  the  book  merely  those  portions  of 
applied  chemistry  which  were  known  to  the  Ancients  will  be 
treated  of.  That  a  people,  so  gifted  as  the  Greeks  were,  should 
have  failed  to  understand  how  to  group  together  the  numerous 
observations  in  those  subjects  which  lay  ready  to  their  hand, 
and  to  draw  conclusions  from  them,  can  only  be  explained  by 
the  whole  tendency  of  their  thought,  and  particularly  by  their 
undervaluing  the  inductive  method.  Aristotle's  opinion  that 
"industrial  work  tends  to  lower  the  standard  of  thought" 
was  certainly  of  influence  here.  In  accordance  with  this 
dictum  the  educated  Greeks  held  aloof  from  the  observation 
and  practice  of  technical  chemical  processes;  a  theoretical 
explanation  of  the  reactions  involved  in  these  lay  outside 
their  circle  of  interests.  To  this  want  of  sympathy  is  cer- 
tainly to  be  ascribed  the  fact  that  the  discovery  of  even  the 
most  important  chemical  processes  is  but  very  seldom  to  be 
connected  with  the  names  of  distinct  historical  persons; 
while,  on  the  other  hand,  the  old  historians  give  detailed 
records  of  those  men  who  advanced  untenable  opinions  on  the 
constitution  of  the  world. 

Before  giving  an  account  of  the  state  of  practical  chemical 
knowledge  in  early  times,  it  may  be  remarked  in  passing 
that  much  uncertainty  often  prevailed  in  consequence  of 
different  products  being  called  by  one  and  the  same  name. 
Substances  were  not  distinguished  according  to  their  chemi- 
cal behaviour,  the  investigation  of  which  possessed  no  interest 
for  the  Ancients,  but  were  classified  according  to  their  out- 
ward appearance  and  source,  a  confounding  of  similar  or 
identification  of  dissimilar  substances  thus  frequently  result- 
ing. Two  samples  of  one  and  the  same  compound — soda,  for 
instance — were  looked  upon  as  different,  if  the  external 
appearance  seemed  to  indicate  a  dissimilarity.  Much  dis- 
crimination has  been  found  to  be,  and  still  is,  requisite  in 
order  to  clear  up  the  indistinct  points  in  the  records  of  the 
old  historians. 


METALLURGY  OF  THE  OLDER  NATIONS  11 


Metallurgy  of  the  Old  Nations}- 

We  find  in  the  earliest  records  of  the  civilised  nations  (the 
Egyptians,  Jews,  Indians,  etc.)  an  acquaintance  with  the 
working  of  different  metals.  By  the  younger  of  those  nations 
mythical  personages  were  held  to  have  taught  this  art,  e.g. 
Prometheus,  Cadmus,  etc.,  by  the  Greeks.  If  the  translations 
of  the  Hebrew  words  in  the  Old  Testament  signifying 
"  metals "  are  correct,  then  the  Jews  were  acquainted  with 
six,  viz.  gold,  silver,  copper,  iron,  lead  and  tin ;  this  may  be 
considered  certain  as  regards  the  first  four,  which  either 
occur  native  or  are  readily  reduced  from  their  ores.  They 
are  recorded  in  the  Old  Testament  in  the  order  just  given. 

The  name  "  metals  "  is  derived,  according  to  Pliny,  from 
the  fact  of  their  never  occurring  separately  but  in  veins 
together,  /-ter'  d\\a.2  Even  at  that  early  period  glance,  duc- 
tility and  hardness  were  held  to  be  characteristics  of  a  metal. 
With  regard  to  the  origin  of  metals  and  ores  in  the  interior 
of  the  earth,  the  Ancients  had  formed  the  most  extravagant 
conceptions ;  they  believed,  on  the  ground  of  Aristotle's 
weighty  testimony,  that  they  were  produced  by  the  penetra- 
tion of  air  into  the  vitals  of  the  earth,  and  consequently 
assumed  that  the  amount  of  metal  or  ore  increased  as  the 
mine  proceeded  inwards. 

The  Greeks,  and  especially  the  Romans,  were  intimately 
acquainted  with  many  metallurgical  processes ;  Dioscorides, 
Pliny  and  later  historians  give  fairly  exact  data  for  the 
obtaining  and  smelting  of  ores,  but  not  the  slightest  attempt 
is  made  to  explain  the  chemical  processes  which  this 
involves. 

The  noble  metals  gold  and  silver,  whose  stability  in  the 

1  The  following  works  have  been  used  for  reference : — R.  Andree,  Die 
Metalle  bei  denNatiirvdlkem(Veitund  Co.,  Leipzig,  1884) ;  Beck,  Geschichte 
des  Eisens  (Vieweg,  Braunschweig,   1884  ;  2nd.    ed.    1891) ;   0.   Schrader, 
Sprachvergleichung  und  Urgeschichte  (Jena,  1883) ;  and  also  various  treatises 
by  K.  B.  Hofmann,  to  whom  the  author  is  greatly  indebted  for   much 
information  on  the  subject. 

2  Herodotus  gives  ^iraXKov  as  signifying  a  mine. 


12      FROM  EARLIEST  TIMES  TO  THE  BIRTH  OF  ALCHEMY      CH. 

fire  had  not  escaped  the  Ancients,  were  those  earliest  known 
(in  prehistoric  times),  and  were  highly  valued;  the  fact  of 
their  occurring  native,  and  the  ease  with  which  they  can  be 
worked,  afford  a  sufficient  explanation  of  this.1  The  exceed- 
ing malleability  of  gold  excitec^  the  astonishment  of  the 
older  nations  in  a  high  degree^  and  rendered  possible 
the  gilding  of  objects  by  covering  them  with  thin  plates  of 
the  metal.  The  later  discovery  of  affixing  a  layer  of  gold  by 
means  of  the  amalgamation  process  was  known  considerably 
before  the  time  of  Pliny. 

In  the  second  century  B.C.  we  meet  with  the  first  records  2 
of  a  cupellation  process,  by  which  gold  was  freed  from 
admixtures;  in  fact,  an  operation  similar  to  the  so-called 
lead  process  was  then  carried  out,  gold  dust  being  melted 
with  lead  and  salt  for  a  number  of  days.  The  purification  of 
gold  by  means  of  mercury  was  also  well  known  in  Pliny's 
time. 

Silver,  which  the  enterprising  Phoenicians  are  supposed  to 
have  supplied  to  the  other  civilised  nations  from  Armenia 
and  Spain,  where  rich  silver  ores  occur,  was,  according 
to  the  record  of  Strabo,  i.e.  at  the  begining  of  our  era, 
purified  in  a  precisely  similar  manner  to  gold,  viz.  by 
fusion  with  lead.  The  separation  of  silver  from  gold  does 
not  appear  to  have  been  known  before  our  era,  at  any  rate 
an  extant  record  3  states  that  Archimedes  was  not  possessed 

1  The  gold  mines  of  Nubia  (the  Egyptian  name  nub,  i.e.  gold,  is  perhaps 
connected  with  the  designation  of  that  country)  were  worked  very  ex- 
tensively by  the  Egyptians.     According  to  the  records  of  Agatharchides 
and  of  Diodorus  Siculus,  in  which  pity  is  expressed  for  the  slaves  employed 
in  the  work,  the  finely  ground  gold  ore  was  washed  out  and  the  heavy  residue 
melted.     In  the  time  of  Rameses  II.  the  mines  yielded  gold  to  the  value  of 
£125,000,000  sterling  per  annum.     The  gold-producing  land  of  Ophir,  from 
which  the  Pho3nicians  obtained  the  precious  metal,  is  supposed  to  have 
been  in  India,  Midian  (Arabia),  or  on  the  east  coast  of  Africa.     The  same 
energetic  trading  nation  opened  up  for  the  Greeks  the  first  gold  mines  on 
the  island  of  Thasos. 

2  This  record,  which  originated  with  Agatharchides,  is  to  be  found  in 
Diodorus. 

3  Archimedes  attempted  to  determine  whether  the  crown  of  King  Hiero 
contained  silver,  and,  if  so,  how  much  ;  this  problem  he  tried  to  solve  by 
taking  the  specific  gravity,  not  by  chemical  means. 


i  METALLURGY  OF  THE  OLD  NATIONS  13 

of  the  means  to  accomplish  this.  From  indications  which 
Pliny  gives,  however,  it  appears  that  in  his  time  a  kind  of 
cementation  process  was  practised,  which  probably  consisted 
in  the  treatment  of  silver  containing  gold  with  salt  and 
alum  shale.  Moreover,  an  amalgam  of  gold  and  silver  was 
regarded  in  ancient  times  as  a  particular  individual  metal, 
being  termed  asem  by  the  Egyptians,  and  rfXe/crpos  by  the 
Greeks  (amber  being  distinguished  as  TO  r)\eK.rpov).  From 
this  also  it  may  be  concluded  that  at  that  time  no  method 
was  known  of  separating  the  metals. 

The  data  concerning  copper  (termed  %d\/c6<;,  aes 1),  which 
has  been  known  from  very  primitive  times  (being  first  found 
in  the  neolithic  stone  age),  frequently  refer  to  its  alloys  with 
other  metals,  especially  to  bronze ;  the  latter,  as  is  well  known, 
was  very  early  used  for  making  weapons,  ornaments  and 
utensils.  Copper,  which  was  universally  employed  in  pre- 
historic times,  was  found  native  in  many  places  (e.g.  in  Egypt), 
or  was  readily  smelted  from  malachite  or  similar  copper  ores. 
All  the  civilised  nations,  which  have  been  named,  were 
acquainted  with  bronze  before  they  had  learnt  to  prepare  its 
other  constituent,  metallic  tin,  no  mention  of  which  is  made 
in  old  Egyptian  records.  With  regard  to  the  smelting  pro- 
cesses by  which  the  "  aes "  of  the  Ancients  was  obtained, 
nothing  certain  is  known. 

Iron,  the  extraction  and  working  of  which  was  not  dis- 
covered till  after  that  of  copper  and  bronze,  but  which,  never- 
theless, goes  back  to  very  ancient  times  also,2  was  prepared 
in  smelting  furnaces ;  the  old  authors  do  not,  however,  give 
any  particulars  as  to  the  actual  process.3  The  ores  used  are 

1  The  Roman  aes  has  the  same  stem  as  the  Sanscrit  word  ayas,  signify- 
ing ore  ;  the  latter  designation  cuprum  for  copper  is  an  abbreviation  of  aes 
cyprium  (so  called  because  of  its  occurrence  in  Cyprus). 

2  According  to  Lepsius,  iron  has  been  in  use  in  Egypt  for  more  than 
5000  years,  having  served  primarily  for  the  manufacture  of  hard  instru- 
ments, while  utensils  of  all  kinds  were  made  from  bronze. 

3  Old  Roman  smelting  furnaces  with  their  appurtenances  have  recently 
been  excavated  near  Eisenberg  in  the  Pfalz.   The  form  of  apparatus  used  by 
the  Egyptians  for  the  smelting  of  iron  can  be  arrived  at  approximately  from 
inscriptions,  etc.  ;  it  is  worthy  of  note  that  bellows  of  the  same  shape  as 
those  of  Ancient  Egypt  are  in  use  in  the  interior  of  Africa  at  the  present  da}\ 


14      FROM  EARLIEST  TIMES  TO  THE  BIRTH  OF  ALCHEMY      CH. 

supposed  to  have  been  brown  iron  ore  and  magnetite ;  that 
meteoric  iron  was  first  employed  is  an  improbable  and  un- 
proven  assumption.  The  tempering  of  iron  was  early  learnt 
in  Ancient  Egypt;  even  in  the  time  of  Pliny  the  un- 
desirable property  of  impure  iron,  which  we  now  term 
brittleness,  was  known,  and  its  capability  of  assuming  the 
peculiarity  of  the  magnet  stone  when  brought  into  contact 
with  the  latter,  was  also  observed. 

Lead  *  was  likewise  known  from  very  early  times,  having 
been  prepared  and  turned  to  good  account,  by  the  Greeks 
and  Romans  more  especially.  Little,  however,  is  known 
with  regard  to  the  smelting  processes  for  it,  Pliny's  records 
on  the  subject  being  indistinct ;  but  the  smelting  was 
probably  carried  out  on  a  refining  hearth.  On  the  other 
hand  we  have  many  details  as  to  the  use  of  lead  for  making 
water  pipes,  writing  tablets,  coins,  etc.  Soldering  with  lead 
or  with  an  alloy  of  lead  and  tin  was  also  well  known.  Since 
cooking  utensils  were  often  made  of  lead,  symptoms  of  lead 
poisoning  occurred  frequently ;  but  notwithstanding  this,  the 
metal  was  prized  as  a  medecine. 

Recent  discoveries  in  Egyptian  tombs  have  brought  to 
light  the  fact  that  tin  also  was  prepared  fairly  pure  in  olden 
times,  and  that  it  found  numerous  applications.  Among  the 
Romans  lead  and  tin  were  distinguished  from  one  another  as 
plumbum  nigrum  and  plumbum  candidum.2  The  alloy  of 
the  two  together,  i.e.  solder,  played,  as  already  mentioned,  an 
important  part  in  technical  work.  Still  older  and  of  even 
greater  significance  was  the  use  of  bronze,3  which  one  meets 
with  among  the  most  ancient  civilised  nations. 

1  Cf.  K.  B.  Hofmann's  Das  Blei  bei  den  Volkern  des  Alterthums  (Berlin, 
1885). 

2  The  word  stannum,  which  now  denotes  tin,  appears  in  Pliny's  time 
to  have  signified   an  alloy   of   tin    and    lead.      Whether  the  Kaffo-irepos 
of  the  Iliad  stood  for  tin  is  likewise  highly  problematical.     It  is  equally 
uncertain  from  whence  the  Phoenicians  obtained  this  metal  (or  an  alloy  of 
it) ;  whether  from  India,  with  which  they  had  commercial  relations,  or 
from  Britain  and  Iberia.  The  similiarity  between  the  Sanscrit  word  Jcastira 
and  the  Greek  word  KO.O O(T epos  has  been  used  as  an  argument  in  favour  of 
the  former  assumption  (cf.  A.  v.  Humboldt,  Kosmos,  ii.  §  409). 

3  K.  B.  Hofmann  considers  that  the  name  bronze,  with  regard  to  the 


i  METALLURGY  OF  THE  OLD  NATIONS  15 

Zinc,1  as  an  individual  metal,  was  certainly  not  known  to 
the  Ancients,  but  its  alloys  with  copper  (^aX/eo?,  ope^aX/eo<?) 
found  the  widest  application. 

Brass,  the  first  description  of  which  is  given  by  Aristotle 
as  the  "  metal  of  the  Mosynoeci "  (from  which  the  German 
word  Messing,  signifying  brass,  is  undoubtedly  derived),  was 
for  long  regarded  as  copper  which  had  been  coloured  yellow 
by  fusing  it  with  an  earth  (cadmia) ; 2  it  was  only  recognised 
as  an  alloy  at  a  much  later  date.  The  change  in  colour 
produced  in  copper  by  certain  additions  to  it  played — in  the 
transmutation  of  metals — an  important  part  in  the  alchemistic 
age. 

The  first  records  as  to  mercury  are  to  be  found  in 
Theophrastus  (about  300  B.C.),  who  gives  its  preparation 
from  cinnabar  by  means  of  copper  and  vinegar,  and  terms  it 
"liquid  silver."  Dioscorides  describes  the  production  of 
mercury,  which  he  at  first  termed  vSpdpyvpos,  from  cinnabar 
and  iron,  i.e.  by  a  process  of  simple  elective  affinity,  without, 
however,  making  the  slightest  attempt  to  explain  the  process. 
For  the  carrying  out  of  this  operation,  an  exceedingly  im- 
perfect distilling  apparatus  was  used.  Pliny  makes  mention 
both  of  the  purification  of  the  metal,  by  squeezing  it  through 
leather,  and  also  of  its  poisonous  nature.  It  did  not  escape 
the  Ancients  that  other  metals,  gold  in  especial,  were  altered 
by  mercury  (cf.  p.  12);  indeed  Vitruvius  gives  a  minute 
recipe  for  the  recovery  of  gold  in  worn-out  sewn  draperies 
by  means  of  it. 

An  account  will  be  given  later  on  of  several  metallic  com- 
pounds known  in  ancient  times. 

origin  of  which  there  has  been  much  dispute,  is  probably  derived  from  the 
word  ftpovit'fiffio}',  meaning  an  alloy,  a  word  possibly  borrowed  from  the 
Persian.  The  view,  held  even  so  early  as  in  Pliny's  time,  that  "bronze" 
was  derived  from  (aes)  Brundusinum,  has  been  proved  untenable. 

1  Cf .  K.  B.  Hofmann's  paper  in  the  Zeitschriftfur  Berg-  und  Huttenwesen, 
vol.  xli.  Nos.  46—51. 

2  Even  so  early  as  300  B.C.,  "  cadmia"  was  famous  as  a  medicine.     The 
word  likewise  means  "  tutty  "  (oxide  of  zinc),  or  also  rich  zinc  ore.  Accord- 
ing to  K.  B.  Hofmann,  it  is  not  improbable  that  galmei  (cadmia,  calamine) 
is  derived  from  cadmia  ;  i.e.  those  three  terms  appear  to  be  synonymous. 


16      FROM  EARLIEST  TIMES  TO  THE  BIRTH  OF  ALCHEMY     CH. 


Beginnings  of  Technical  Chemistry  among  the  Ancients. 

The  Manufacture  of  Glass. — The  art  of  making 
vessels  from  glass  originated  in  China  and  Egypt,  and  had 
for  a  long  time  its  chief  habitat  in  Thebes ;  from  there  it 
spread  to  the  Phoenicians  and  other  Eastern  nations,  the 
Greeks  first  acquiring  it — so  far  as  actual  proof  goes — in  the 
fifth  century  B.C.  Pliny  is  the  first  to  give  a  distinct 
account  of  the  preparation  of  glass  by  fusing  sand  and  soda 
together.1 

The  artificial  colouring  of  glass  by  metallic  oxides, 
especially  oxide  of  copper,  was  very  early  discovered.  Many 
of  the  remains  which  have  been  found  in  Ancient  Egypt 
indicate  that  the  manufacture  of  glass  must  at  that  time 
have  attained  to  a  high  degree  of  perfection,  methods  for 
producing  enamels  and  artificial  gems  being  then  known. 
Pliny  states  that  beryl,  opal,  sapphire,  amethyst,  etc.,  could  be 
imitated,  but  that  at  the  same  time  these  imitations  were 
distinguishable  from  the  real  stones  through  being  softer  and 
lighter. 

The  first  preparation  of  glass  presupposes  in  any  case 
an  acquaintance  with  soda  or  potash ;  the  former  of  these 
was  found  as  a  natural  product  on  the  shores  of  certain 
lakes,  e.g.  in  Macedonia  and  Egypt,  while  carbonate  of 
potash  was  obtained  from  a  very  early  period  by  lixiviating 
the  ashes  of  plants,  and  also,  according  to  Dioscorides,  by 
igniting  tartar.  These  two  salts 2  were  frequently  mistaken 
for  one  another  on  account  of  their  similar  action.  They 
were  largely  used  for  the  preparation  of  soap,  and  also 
directly  for  washing  clothes,  cleansing  the  skin  and  the  teeth 
(just  as  the  ash  of  tobacco,  which  is  rich  in  carbonate  of 
potash,  is  often  employed  as  a  tooth-powder  at  the  present 

1  The  discovery  of  glass  in  Egypt  was  undoubtedly  accidental,  soda 
having  been  added  as  a  flux  to  sand  containing  gold  for  the  purpose  of 
extracting  the  latter. 

2  The  Hebrew  neter  probably  denotes  soda,  while  the  Latin  nitrum  is 
employed  by  Pliny  for  both  alkaline  salts.     The  designation  alkali  came 
originally  from  the  Arabs. 


i  MANUFACTURE  OF  POTTERY  AND  SOAP  17 

day),  and  also  as  ingredients  of  medicines.  Lastly,  the 
ashes  of  plants  and  saltpetre  were  much  prized  as  effective 
manures. 

To  the  art  of  pottery  must  be  ascribed  an  age  at  least 
as  great  as  that  of  the  preparation  of  the  nobler  metals  and 
of  glass.  Even  the  old  Egyptians  understood  how  to  coat 
their  originally  simple  earthen  vessels  with  coloured  enamel. 
At  a  later  date  the  ceramic  industry  prospered  among  the 
Etruscans,  and  also  in  many  towns  of  Southern  Italy  and 
Asia  Minor.  Porcelain,  which  was  discovered  and  employed 
by  the  Chinese,  remained  entirely  unknown  to  the  older 
civilised  European  nations. 

The  Manufacture  of  Soap. — Of  no  slight  interest  is 
the  fact  that  the  saponification  of  fats  by  means  of  alkalies, 
with  the  object  of  preparing  soap — that  is  to  say,  a  com- 
plicated process  of  organic  chemistry — ,  was  already  practised 
in  ancient  times.  Pliny's  records  on  the  subject  make  it 
probable  that  in  Germany  and  Gaul  soap  was  prepared  from 
animal  fat  and  the  aqueous  extract  of  ashes,  the  latter 
being  strengthened  (rendered  caustic)  by  the  addition  of 
lime.  Further,  there  was  a  distinction  drawn  between  soft 
and  hard  soaps,  according  as  potash  or  soda  (the  latter  being 
obtained  from  the  ashes  of  shore  plants  in  Gaul)  was  used 
in  the  preparation.1 

Dyeing  likewise  belongs  to  the  arts  which  the  Egyptians, 
Lydians,  Phoenicians  and  Jews  greatly  developed.  They 
knew  how  to  fix  certain  dyes  on  cloth  by  means  of  mordants, 
alum 2  playing  an  important  part  here  ;  indeed  the  dyeing  of 
purple  had  attained  to  a  high  state  of  perfection  among  the 
Phoenicians.  Pliny  mentions  the  application  both  of  madder 
dye  and  of  litmus  (the  gatulian  purple).  Indigo  blue  seems 
to  have  been  more  used  at  that  time  for  painting  than  for 

1  From  K.  B.  Hofmann's  researches  it  appears  to  be  doubtful  whether 
the  sapo  of  the  Romans  meant  soap,  and  not  rather  a  depilatory. 

2  Under  ffTvirrripia  or  alumen  of  the  Ancients  must  be  understood  sub- 
stances of  astringent  properties  generally,  although  alum  itself  is  what  is 
usually  meant ;  being  prepared  from  alum  shale,  it  contained  green  vitriol 
as  an  impurity. 

C 


18    FROM  EARLIEST  TIMES  TO  THE  BIRTH  OF  ALCHEMY  CHAP, 

dyeing,  but  with  this  exception  mineral  substances  were 
employed  as  paints.  The  principal  of  these  in  Pliny's  time 
were  white  lead,  cinnabar,  vermilion,  smalt,1  verdigris,  red 
oxide  of  iron  and  soot.  This  last,  mixed  with  gum,  also 
served  as  ink.  Numerous  recent  researches 2  have  proved 
that  sulphide  of  lead  (galena)  formed  the  basis  of  the  much- 
used  old  Egyptian  cosmetic  mesdem, — and  not  native  sulphide 
of  antimony,  as  was  at  one  time  supposed.  Mesdem  was 
also  a  highly  prized  medicine.  The  use  of  preparations  of 
antimony  belongs  to  a  later  period. — The  sulphides  of 
arsenic,  realgar  and  orpiment,  served  both  as  pigments  and  as 
medicines,  although  their  poisonous  action  was  known.  In 
short,  the  Ancients  had  access  to  a  considerable  number 
of  colouring  chemical  compounds,  some  of  these  being  the 
earliest  chemical  preparations  to  be  manufactured  on  a  large 
scale. 

As  has  been  already  indicated,  the  use  of  such  arti- 
ficially prepared  products  in  medicine  also  extends  to  a 
period  very  far  back,  even  although,  in  referring  to  this, 
one  can  only  speak  of  the  first  beginnings  of  a  pharma- 
ceutical chemistry.  But  a  connection  between  the  chemical 
art  and  pharmacy  established  itself  very  early  indeed,  e.g. 
among  the  Egyptians,  who  were  doubtless  the  first  to  employ 
actual  chemical  preparations  for  medicinal  purposes.  Thus 
verdigris,  white  lead,  litharge,  alum,  soda  and  saltpetre 
served  for  the  making  of  salves  and  other  medicaments, 
while  the  preparation  of  lead  plaister  from  litharge  and  oil 
was  much  practised  in  the  time  of  Dioscorides.  Iron  rust 
was  a  very  old  medicine,  its  use  being  ascribed  to  ^Escula- 
pius,  while  sulphur  and  copper  vitriol  containing  iron  (chal- 
canthum)  were  valuable  ingredients  of  the  medical  treasury 

1  Davy  found  cobalt  in  certain  antique  glasses,  and  assumed  from  this 
that  smalt  had  been  used  in  their  manufacture.  Accbrding  to  Fouque  (Compt. 
Rend.,  vol.  cviii.  p.  325)  Egyptian  glass  contained  only  oxide  of  copper  as  the 
colouring  material ;  but  vitrifiable  pigment  containing  cobalt  has  been  again 
found  recently  in  small  Egyptian  statuary. 

2  Collected  and  critically  examined  by  K.  B.  Hofmann  in  his  paper  : — 
Ueber  Mesdem  (Mittheilungen  des  Vereins  der  Arzte  in  Steiermark,  1894, 
Nos.  1  and  2). 


i        ORGANIC  SUBSTANCES  KNOWN  IN  ANCIENT  TIMES       19 

before  our  era ;  but  the  important  preparations  of  antimony 
and  mercury  can  be  proved  to  have  first  come  into  notice  in 
the  alchemistic  period. 

Most  of  the  officinal  compounds  just  referred  to  were 

also  used  for  other  purposes,  as  has  already  been  mentioned 

\  in  a  few  cases.      The  combustion-product   of  sulphur,   for 

\instance,  was  employed  for  fumigation  (vide  Homer),  for  the 

purification  of   clothes,  the  conservation   of  wine,  and   for 

'  destroying  impure  colours  (Pliny),  while  copper  vitriol  and 

alum  were  used  in  dyeing  operations. — In  closing  this  short 

account  of  the  knowledge  possessed  by  the  Ancients  with 

regard  to  chemical  compounds,  the  following  substances  may 

be  mentioned,  substances  whose  practical  application  dates 

from  a  very  early  period.     In  ancient  times  lime  was  burnt, 

and  after  being  slaked,  was  used  for  preparing  mortar,  and 

also,  as  already  stated,  for  causticising  soda  (cf.  p.  17).      Of 

Ithe  acids,  acetic  acid 1  in  the  form  of  crude  wine  vinegar  was 
bhe  earliest  known,  its  presence  being  assumed  in  all  acid 
plant  juices.  The  mineral  acids,  which  are  of  such  import- 
ance in  technical  chemistry,  were  only  discovered  in  the 
succeeding  epoch. 

Other  organic  compounds  known  at  the  beginning  of  our 
era,  and  doubtless  even  before  then,  were  sugar  (from  the 
sugar-cane),  starch2  (from  wheat),  many  fatty  oils  (from 
seeds  and  fruits,  the  oil  being  extracted  either  by  pressing 
or  by  boiling  with  water),  petroleum,  and  oil  of  turpentine, 
which  last  was  obtained  by  the  distillation  of  pine  resin  in 
very  imperfect  apparatus.3  Of  the  fatty  oils,  olive,  almond 
and  castor  oils,  etc.,  were  known  and  used  for  a  variety  of 
purposes,  the  first-named — e.g. — for  extracting  perfumes  from 

1  The  Ancients  had  the  most  extravagant  ideas  with  regard  to  the 
solvent  power  of  vinegar  upon  mineral  substances,  as  may  be  gathered  from 
the  concordant  statemants  of  Livy  and  Plutarch  that  Hannibal,  in  his  pass- 
age across  the  Alps,  cleared  the  way  of  rocks  by  means  of  it.     The  story  •• 
which  Pliny  tells  of  Cleopatra  may  also  be  recalled  here, — how  she,  in  ful- 
filment of  her  wager  to  consume  a  million  sesterces  at  one  meal,  dissolved 
costly  pearls  in  vinegar  and  drank  the  solution. 

2  &/j.v\ov,  so  called  from  its  being  prepared  without  millstones,  and  the 
production  of  which  is  described  by  Dioscorides. 

3  Prof.  K.  B.  Hofmann  kindly  tells  me  that  the  earliest  account  of  a 
destillatio  per  decensum  is  to  be  found  in  Ae'tius  (Aldine  Ed.,  fol.  10). 

c  2 


20  FROM  EARLIEST  TIMES  TO  THE  BIRTH  OF  ALCHEMY  CHAP,  i 

flowers,  leaves,  etc.  Ethereal  oils  were  also  known  and 
employed  in  large  number. — The  animal  fats  played  an 
important  part  in  medicine,  and  Pliny's  mention  of  sheeps- 
wool  grease,  among  other  things,  is  noteworthy  here,  seeing 
that  it  has  recently  been  brought  into  use  again  in  the  form 
of  lanoline. — Pliny  does  not  seem  to  have  been  acquainted 
with  cane  sugar ;  but  one  frequently  comes  across  passages 
in  his  writings  referring  to  the  occurrence  and  remarkable 
actions  of  vegetable  poisons  (alkaloids). 

Such  compounds  as  spirits  of  wine,  carbonic  acid,  etc., 
which  are  formed  in  many  processes  of  fermentation,  e.g.  in 
the  making  of  wine,  beer  and  bread,  remained  unknown  to 
the  Ancients.  It  is  true  that  they  noticed  in  these  cases 
and  also  in  others — natural  emanations  of  gas,  for  instance — 
the  presence  of  a  kind  of  air  prejudicial  to  breathing  and 
even  under  certain  circumstances  fatal  to  life,  but  it  did  not 
occur  to  them  to  recognise  in  this  a  gas  different  from 
atmospheric  air. 

This  lack  of  the  gift  of  observation,  this  disinclination  to 
go  to  the  root  of  any  phenomenon,  in  fact,  a  certain  in- 
difference with  regard  to  natural  events,  are  characteristics 
of  the  attitude  of  the  Ancients  towards  nature.  Instead  of 
experimenting  with  natural  products,  they  infinitely  preferred 
to  call  speculation  to  their  aid,  so  that  the  most  superficial 
observations  gave  rise  to  opinions  which,  when  uttered  by 
high  authorities,  attained  to  the  dignity  of  dogmas.  How 
otherwise  than  from  an  extreme  lack  of  the  desire  of 
observation  can  one  explain  Aristotle's  assertion  that  a  vessel 
filled  with  ashes  will  contain  as  much  water  as  one  which  is 
empty  ?  A  further  instance  of  the  credulity  of  that  time  is 
given  in  the  conviction  expressed  by  Pliny,  and  universally 
held,  that  air  can  be  transformed  into  water,  and  vice  versa, 
that  earth  is  produced  from  water,  and  that  rock-crystal  also 
proceeds  from  the  latter.  The  assumption  that  water  can 
be  transformed  into  earth  has  often  come  up  again  at  later 
periods,  having  exercised  the  minds  of  people  even  in  com- 
paratively recent  times ;  as  it  subsequently  assumed  the 
form  of  an  important  question  of  dispute,  it  will  be  referred 
to  in  detail  later  on. 


CHAPTER  II 
THE  AGE  OF  ALCHEMY 

IN  the  introduction  to  this  book  Egypt  is  spoken  of  as  the 
mother-land  of  Alchemy.  The  University  of  Alexandria  was 
especially  instrumental  in  the  propagation  of  the  latter  during 
the  first  centuries  of  our  era ;  it  was  the  carrier  and  inter- 
mediary for  the  alchemistic  doctrines,  more  particularly  at 
the  time  of  the  fall  of  the  Western  Roman  Empire. 

The  attempts  to  convert  the  base  metals  into  the  noble 
ones  had  their  origin  in  superficial  observations,  which  ap- 
peared to  give  a  strong  support  to  the  belief  in  this  trans- 
mutation. Among  such  accidental  observations  was  that  of 
the  deposition  of  copper  upon  iron  utensils  left  in  copper 
mines  from  the  waters  which  accumulated  there.  What 
more  natural  than  to  conclude  that  a  transmutation  of  iron 
into  copper  had  occurred  ?  For  the  production  of  gold  or 
silver  from  copper,  the  transformation  of  the  latter  into 
yellow  or  white  alloys  by  means  of  earthy  substances  such 
as  calamine  or  arsenic  appeared  to  give  warrant.  Finally, 
the  fact  that  a  residue  of  gold  or  silver  remained  behind 
when  an  alloy  with  lead  or  an  amalgam  with  mercury  was 
strongly  heated,  indicated  the  generation  of  those  noble  metals. 

To  these  considerations  of  a  practical  nature,  which 
strengthened  the  conviction  as  to  the  transmutation  of 
metals,  but  which  inferred  a  gross  self-deception  on  the 
part  of  the  observer  himself — to  say  nothing  of  their  being 
turned  to  good  account  by  crafty  knaves — there  came  to  be 
allied,  in  this  epoch  for  the  first  time,  the  tendency  to  group 
together  chemical  facts  from  common  points  of  view. 


22  THE  AGE  OF  ALCHEMY  CHAP. 

It  was  precisely  in  the  mode  in  which  it  was  attempted 
to  explain  the  composition  of  the  metals  that  there  lay  a 
powerful  and  ever-active  charm,  leading  to  the  belief  in  the 
ennobling  of  the  baser  metals  and  to  continually  repeated 
efforts  to  achieve  this.  The  first  beginnings  in  an  experi- 
mental direction,  which  we  meet  with  early  in  the  alchemistic 
period,  although  very  incomplete,  indicate  nevertheless  a 
distinct  step  in  advance  as  compared  with  the  deductive 
method  which  had  hitherto  reigned  supreme,  and  whose  fruits 
consisted,  for  the  most  part,  in  the  setting  up  of  mystic  cos- 
mogonies. The  few  observations  which  were  made  remained, 
however,  isolated — that  is,  were  not  grouped  together  in  a 
connected  manner. 

That  the  attempts  to  attain  to  a  knowledge  of  the 
processes  of  nature  by  the  inductive  method  were  but  slight 
at  best  in  the  alchemistic  period,  is  explained  by  the 
supremacy  of  the  Aristotelian  doctrine,  which,  amalgamated 
with  the  Neo-Platonic  philosophy,  trammelled  the  minds  of 
men  throughout  almost  the  whole  of  the  Middle  Ages.  Even 
the  Christian  theology  had  to  compromise  with  this  system, 
the  product  of  the  joint  work  being  scholasticism,  which 
imprinted  its  stamp  upon  all  the  mental  efforts  of  that 
time  and  prevented  their  free  development.  The  relation  of 
the  alchemistic  tendencies  to  the  Aristotelian  philosophy  has 
been  already  indicated  (p.  7). 

The  limitation  of  this  epoch  between  the  first  appearance 
of  alchemistic  conceptions  (in  the  fourth  century)  and  the 
bold  attempt  of  Paracelsus  to  call  in  chemistry  to  the  aid 
of  medicine  (in  the  beginning  of  the  sixteenth  centurv)  is 
thus  a  natural  one,  since,  during  the  whole  of  this  time,  one 
and  the  same  keynote  runs  through  all  the  questions  bearing 
upon  chemistry,  viz.  the  idea  of  ennobling  the  metals. 
People  were  so  convinced  of  the  practicability  of  this  for  many 
centuries,  that  almost  every  one  who  devoted  himself  to 
chemistry,  and  many  others  besides,  strove  hopefully  towards 
this  long-desired  goal.  The  early  mixing  up  of  astrological 
and  cabalistic  nonsense  with  these  alchemistic  endeavours 
marks  very  distinctly  the  degeneration  of  the  latter. 


ii  ORIGIN  AND  FIRST  SIGNS  OF  ALCHEMY  23 

Alchemy  by  no  means  ceased  to  exist  on  the  appearance 
of  the  new  iatro-chemical  doctrines,  but  gradually  receded 
as  chemistry  became  more  of  a  science.  True,  its  seductive 
problems  are  often  seen  to  throw  a  weird  lightning  flash  on 
the  chemists'  camp,  and  to  exercise  upon  even  the  most 
eminent  of  them  an  undoubted  influence  ;  but  upon  the  main 
lines  which  chemistry  has  followed  ever  since  the  time  of  Boyle, 
the  phantasies  of  alchemy  have  had  no  appreciable  effect. 
Notwithstanding,  however,  that  this  influence  was  but  slight, 
a  short  account  of  the  position  of  alchemy  during  the  last 
four  centuries  cannot  properly  be  omitted,  and  will  therefore 
be  added  as  an  appendix  to  this  section  of  the  book. 


GENERAL  HISTORY  OF  ALCHEMY.1 

Origin'2'  and  First  Signs  of  Alchemistic  Efforts. 

The  sources  from  which  the  belief  in  the  practicability  of 
the  transmutation  of  metals  was  nourished,  and  which  in  the 
course  of  centuries  gradually  expanded  into  a  broad  stream 
of  the  most  mischievous  errors,  have  their  origin  in  the  gray 
mists  of  antiquity.  No  actual  proof  of  these  must  be 
looked  for :  we  depend,  with  regard  to  them,  upon  mythical 
and  mystical  traditions.  The  first  historical  sources,  too, 
are  small  in  number  and  very  obscure.  But  we  find  among 
various  nations  distinct  signs  of  alchemy  having  been  pursued 
as  a  secret  science  and  having  been  held  in  honour. 

When  one  recalls  to  mind  that  Ancient  Egypt   was  a 

1  Cf.  Kopp,  Gesch.  d.  Chemie,  vol.  i.  p.  40,  et  seq.  ;  also  his  work,  Die 
Alchemie  in  dlterer  und  neuerer  Zeit  (Heidelberg,  1886). 

2  Cf.  particularly  M.  Berthelot's  Les  Origines  de  rAlchimie  (Paris,  1885) 
and  his  Introduction  d  I'jZtude  de*la  Chimie  des  Anciens  et  du  Moyen-dge 
(Paris,   1889) ;  also  H.  W.  Schaefer's  admirable  treatise : — Die  Alchemie  ; 
ihr    aegyptisch-griechischer     Ursprung,    efcc.     (Fleusburg,    1887  ;     School- 
calendar).     M.  Berthelot  has  indeed  rendered  signal  service  by  his  publica- 
tion and  critical  revision  of  old  alchemistic  works,   such  as  the  Leyden 
papyrus,    and  Greek  and  Arabic  MSS.     Quite   recently,   in   conjunction 
with  certain  philologists,  he  has  given  to  the  world  the  Collection  des  Anciens 
Alchimistes  Grecs  and  La  Chimie  en  Moyen-dge. 


24  THE  AGE  OF  ALCHEMY  CHAP. 

centre  of  the  higher  culture,  and,  especially,  that  it  was  a 
country  where  the  chemical  art  was  practised,  one  feels  no 
surprise  that  the  earliest  reliable  records  of  alchemy  are  to 
be  found  there.  /  Egyptian  sources,  partly  such  as  have  been 
preserved  to  us  by  the  Leyden  papyrus  (about  300  A.D.),  and 
partly  the  writings  of  the  Alexandrians  from  the  third  to  the 
seventh  century  A.D.,  constitute  the  most  valuable  aids  at  our 
disposal  for  a  historical  proof  of  the  origin  of  alchemy.  The 
influence  of  the  doctrines  and  practical  recipes  contained  in 
these  works  upon  the  alchemy  of  the  entire  Middle  Ages  is 
easily  demonstrable. 

The  tradition  according  to  which,  among  other  know- 
ledge, the  art  of  ennobling  metals  had  been  brought  from 
heaven  to  earth  by  demons,  was  universally  diffused  in  the 
first  centuries  of  our  era ;  Zosimos  of  Panopolis  states  that 
the  mystical  book  from  which  this  art  was  to  be  learned  was 
termed,  xfifiev  and  the  art  itself  ^fieia.  This  myth  doubt- 
less sprang  from  one  exactly  similar  which  is  to  be  found  in 
the  apocryphal  book  of  Enoch ;  indeed  indications  of  it 
are  to  be  met  with  even  in  Genesis.  The  later  alchemists 
were  inclined  to  refer  the  origin  of  alchemy  to  the  time 
before  the  flood,  thinking  that  a  special  sanctity  would  accrue 
to  their  art  from  this  great  age.  Moreover,  they  wrote  down 
various  biblical  characters  as  alchemists,  on  the  authority 
of  certain  passages  in  Holy  Writ,  for  instance,  Moses  and  his 
sister  Miriam,  and  the  Evangelist  John.  When  legends 
such  as  these  found  credence  in  the  Middle  Ages,  it  is  hardly 
surprising  that  the  records  as  to  the  origin  of  this  art, 
which  remain  to  us  from  ancient  times,  should  have  upheld 
their  authority  over  a  very  long  period. 

The  first  personality  with  which  the  origin  of  alchemy 
is  associated  is  that  of  Hermes  Trismegistos,1  "  the  three  times 
great,"  who  was  said  to  have  been  the  author  of  books  upon 
the  holy  art ;  he  was,  moreover,  generally  reverenced  as  the 
discoverer  of  all  the  arts  and  sciences.  The  then  popular 
expressions  "  hermetic,"  "  hermetic  writings  "  and  "  hermetic 

1  This  designation  is  probably  first  found  in  Tertullian  (end  of  the  second 
century  of  our  era).  Of.  Schaefer,  p.  4,  &c. 


ii  ALCHEMY  AMONG  THE  EGYPTIANS  25 

art "  l  recalled  this  undoubtedly  mythical  personage  even  so 
recently  as  in  the  present  century.  In  Romish  Egypt  pillars 
were  erected  in  honour  of  this  Hermes,  upon  which  alchemistic 
inscriptions  were  cut  in  hieroglyphics. 

Who  then  was  this  Hermes  ?  One  has  to  seek  in  him,  as 
ancient  traditions  indicate  almost  certainly,  the  personified 
idea  of  strength,  i.e.  the  old  Egyptian  godhead  Thot  (or 
Theuth),  which,  when  endowed  with  the  serpent-staff  as  the 
symbol  of  wisdom,  was  compared  by  the  Greeks  with  their 
Hermes,  the  latter  designation  being  thus  transferred  to  the 
Egyptian  god.2  Alchemy,  as  a  holy  and  divine  art,  whose 
special  task  consisted  in  tHe  prej^afioli~ofTHe"metals,  was 
kept  secret  and  fostered  by  the  priesthood,  the  sons  of  kings 
alone  being  permitted  to  penetrate  its  mysteries.  The  esti- 
mation in  which  it  was  held  rose  in  exact  proportion  with 
the  belief  that  Egypt  owed  to  alchemy  its  riches. 

When  and  in  what  way  the  influence  of  other  nations 
made  itself  felt  upon  the  alchemy  of  the  Egyptians,  it  is 
difficult  to  determine.  The  Babylonish  astrologers,  without 
doubt,  undertook  the  fusion  of  astrology  and  magic;  in 
particular,  the  mutual  relations  between  the  sun  and  planets 
and  the  metals,  which  were  taken  for  granted  for  so  many 
centuries,  were  of  old  Babylonish  origin.  According  to  the 
account  of  the  Neo-Platonist  Olympiodor  (in  the  fifth  century 
A.D.),  gold  corresponds  to  the  sun,  silver  to  the  moon,  copper 
to  Venus,  iron  to  Mars,  tin  to  Mercury,  and  lead  to  Saturn.3 

Certain  passages  in  the  works  of  Dioscorides,  Pliny,  and 
the  Gnostics  enable  us  to  conclude  that  the  transmutation 
of  copper  into  silver  and  gold  was  regarded  as  an  as- 
certained fact  during  the  first  centuries  of  our  era.4  The 

1  The  designation  "spagiric  art"  (from  (nrdw,  to  separate,  and  ayfipw, 
to  unite)  occurs  for  the  first  time  in  the  sixteenth  century. 

2  This  identity  is  confirmed  by  the  fact  that,  in  the  inscriptions  on  the 
temple  of  Dakke  on  the  Nile  dedicated  to  Thot,  the  three  names  Thot, 
Hermes  and  Mercurius  occur,   the  first  in   hieroglyphics,   the  second  in 
Greek,  and  the  third  in  Latin  (cf.  Schaefer,  p.  7). 

3  Even  in  Galen  are  to  be  found  statements  with  regard  to  the  influence    ' 
of  the  planets  upon  the  metals. 

4  The  Chinese  also  busied  themselves  with  alchemy  at  that  time,  the 


26  THE  AGE  OF  ALCHEMY  CHAP. 

"  duplication  of  the  metals,"  which  is  to  be  found  in  the 
writings  of  first-century  authors,  and  which  also  plays  a  part 
in  the  Leyden  papyrus,  likewise  refers  to  the  transmutation 
of  metals.  The  designation  of  this  art  as  "  Chemia  "  probably 
appears  for  the  first  time  in  an  astrological  treatise  of  Julius 
Firmicus  (in  the  fourth  century). 

Berthelot  has  made  a  careful  study  of  the  Leyden  papyrus 
(found  in  Thebes  in  the  third  century  A.D.),  and  has  com- 
pared it  with  later  alchemistic  writings.  This  has  led  him 
to  the  conclusion  that  an  intimate  connection  existed  between 
the  industrial  production  of  the  noble  metals,  the  dyeing  of 
fabrics,  and  the  colouration  of  glass  (whence  the  frequent 
expressions : — Tingiren  der  Metalle ;  Tincturen,  etc.).  The 
alleged  processes  of  transmutation,  which  were  currently 
believed  for  hundreds  of  years,  consisted  in  artifices  for  de- 
basing the  noble  metals,  but  at  the  same  time  imitating 
their  appearance  as  nearly  as  possible  in  less  costly  alloys. 
It  is  quite  likely  that,  as  time  went  on,  the  idea  took 
possession  of  many  kinds  that  the  gold  and  silver  were  newly 
created  by  some  supernatural  aid.  It  would  thus  seem  as  if 
alchemy  originated  in  the  fraudulent  practices  of  gold- workers. 

The  records  of  the  study  of  alchemy  go  on  increasing  from 
the  4th  century,  much  information  regarding  it  being  found 
in  the  writings  of  the  Alexandrian  savants  of  that  time, 
especially  in  those  of  Zosimos,  Synesios  and  Olympiodor.  In 
addition  to  these,  various  pseudo-authors,  especially  pseudo- 
Democritus,  are  cited  here  as  witnesses  to  the  spread  of 
alchemy ;  the  philological-historical  critic  is  not  yet,  however, 
in  a  position  to  fix  the  dates  at  which  these  works  were  written. 
In  the  Middle  Ages  people  did  not  hesitate  to  accept  the 
writings  of  the  false  Democritus,  and  also  those  of  a  pseudo- 
Aristotle,  as  originating  from  the  ancient  philosophers 
Democritus  and  Aristotle  themselves.  The  later  alchemists 
also  fathered  counterfeit  writings  upon  Thales,  Heraclitus 
and  Plato,  in  order  to  make  use  of  the  great  authority  of 
those  names  for  their  own  ends. 

transformation  of  tin  into  silver,  and  of  the  latter  into  gold,  being  held  to 
have  been  actually  accomplished. 


ii  ALCHEMY  AMONG  THE  EGYPTIANS  27 

Zosimos  of  Panopolis,  a  voluminous  author  of  the  fifth 
century,  who  was  looked  upon  as  one  of  the  greatest  authori- 
ties among  alchemists  both  of  that  date  and  of  later  times, 
is  said  to  have  written  twenty- eight  books  treating  of  alchemy, 
of  which,  however,  only  small  fragments  remain.  His  mysti- 
cal recipes  are  quite  unintelligible,  and  yet  he  distinctly 
speaks  of  the  fixation  of  mercury,  of  a  tincture  l  which  changes 
silver  into  gold,  and  also  of  a  divine  water  (panacea).  Refer- 
ence is  frequently  made  to  the  work  of  the  pseudo-Democri- 
tus,  (frvarifca  KOI  fjuvo-Tifca.  The  graphic  and  mysterious 
language  of  Zosimos  appears  to  have  exercised  a  permanent 
influence  upon  the  works  of  the  later  Alexandrians,  and  also, 
subsequently,  upon  those  of  the  alchemists  of  the  Middle 
Ages. 

The  end  of  the  fourth  century  and  the  beginning  of  the 
fifth  constitute,  without  doubt,  the  period  in  which  the  study 
of  alchemy  reached  its  zenith  among  the  Alexandrians; 
but  the  works  of  Synesius  upon  alchemy  and  magic,  and 
those  of  Olympiodor,  who  bore  the  surname  of "  TTO^T???," 
operator,  do  not  yield  much  certain  information  with  regard 
to  definite  operations  or  to  the  knowledge  of  chemical  facts. 
How  many  works  which  would  have  been  valuable  for  the 
history  of  chemistry  were  lost  through  the  destruction  of  the 
Serapeum,  which  marked  the  completion  of  the  overthrow  of 
Hellenic  culture  in  Egypt,  cannot  at  this  distance  of  time 
be  estimated.  That  all  acquaintance  with  chemical  opera- 
tions, and  chemical  knowledge  and  skill  generally,  were  not 
thereby  quite  exterminated  was  due  to  the  relations  which 
were  before  that  developed  between  the  Alexandrians  and 
the  Byzantine  savants ;  for,  from  the  sixth  century  on,  applied 
chemistry,  which  may  also  be  said  to  include  alchemy,  found 
-a  foothold  at  Byzantium.  Even  in  Egypt  itself  the  know- 
ledge of  chemistry  was  not  completely  extirpated  by  that 
catastrophe,  but  continued  to  exist  by  fostering  certain 
branches  of  industry,  which,  without  it,  could  never  have 
been  developed.  Lastly,  the  conviction  that  metals  could 

1  The  term  "  mercurius  philosophorum,"  which  is  often  found  in  later 
writings,  was  first  used  by  Synesius. 


28  THE  AGE  OF  ALCHEMY  CHAP 

be  transmuted  had  fixed  its  roots  too  deeply  to  allow  of  this 
art,  by  which  endless  riches  were  to  be  attained,  dying  a 
natural  death. 

The  Alchemy  of  the  Arabians. 

The  germs  of  chemical  knowledge,  which  had  lain  hidden 
in  the  brains  of  a  few  philosophers,  attained  to  a  marvellous 
growth  among  the  Arabians,  who  overran  and  conquered 
Egypt  in  the  seventh  century ;  it  might  have  appeared  much 
more  likely  that  they  would  crush  the  arts  and  sciences 
rather  than  be  the  instruments  of  their  resurrection.  It  was 
certainly  curious  that  this  people,  originally  strangers  to 
science,  should  assume  the  care  of  it  and  cause  it  to  flourish 
in  an  undreamt-of  degree,  at  a  time  when  culture  remained 
at  its  lowest  ebb  in  most  European  countries,  and  everything 
had  to  give  way  to  the  pressure  of  the  conditions  produced 
by  the  migration  of  the  nations.1 

The  first  appearance  of  the  Arabians  in  Egypt,  where  they 
destroyed  much  priceless  literary  treasure  by  fire,  did  not 
seem  to  herald  any  such  change  of  opinion.  They  very  soon 
learnt,  however,  to  assimilate  the  elements  of  the  education 
of  the  conquered  peoples,2  so  that  we  find  (especially  after 
the  conquest  of  Spain,  in  the  beginning  of  the  eighth 
century)  many  cities  of  learning  springing  up ;  to  these  in 
the  following  centuries  the  European  nations — especially 
France,  Italy  and  Germany — sent  crowds  of  earnest  students, 

1  Alex,  von  Humboldt  gives  expression  to  this  point  in  the  following 
words  :   "  The  Arabians,  an  original  Semitic  stock,  partially  drove  away  the 
barbarism  which  had  overwhelmed  Europe  for  two  centuries,  convulsed  as 
it  had  been  by  revolutions.     They  turned  to  the  everlasting  springs  of 
Greek  philosophy,  and  thereby  assisted  not  only  in  preserving  the  culture 
of  science,  but  in  widening  it  and  opening  out  new  paths  to  the  investigators 
of  nature." 

2  Reference  may  just  be  made  here  to  the  important  part  played  by  the 
Nestorians  in  engrafting  the  scientific  spirit  upon  the  Arabians,  and  in 
enriching  them  with  practical  chemical  knowledge.     The  latest  researches 
of  Berthelot  and  others  leave  no  doubt  that  the  Arabians  derived  from  the 
Syrians  much— if  not  indeed  the  greater  part — of  their  knowledge  of 
chemistry. 


ii  ALCHEMY  AMONG  THE  ARABIANS  29 

who  applied  themselves,  for  the  most  part,  to  the  study  of 
medicine,  mathematics  and  optics.  From  the  Arabian  uni- 
versities of  Cordova  and  other  Spanish  cities,  where  alchemy 
was  also  ardently  studied,  it  made  its  way  to  the  other 
western  nations,  among  which  it  attained  to  its  full  develop- 
ment in  the  thirteenth  century. 

A  renown  quite  unexampled,  and  an  authority  which  con- 
tinued all  through  the  Middle  Ages,  were  attained  by  the 
physician  and  alchemist  Dschafar,  afterwards  known  to 
western  nations  by  the  name  of  Geber.  About  his  life  (he 
is  supposed  to  have  lived  in  the  ninth  and  tenth  centuries) 
nothing  is  known.  It  is  possible,  too,  that  Geber  himself 
has  been  sometimes  confused  with  his  pupil  Dschabir  of 
Tharsis. 

There  can  indeed  be  no  dispute  that  with  the  name  Geber 
was  propagated  the  memory  of  a  personality,  with  which  the 
chemical  knowledge  of  the  time  was  bound  up.  But  Berthe- 
lot's  recent  researches l  have  proved  that  the  Latin  writings 
hitherto  ascribed  to  Geber  cannot  have  come  from  him.  The 
oldest  of  these — the  celebrated  Summa  Perfectionis  Magisterii 
— was  not  written  before  the  middle  of  the  fourteenth  cen- 
tury ;  and  the  De  Investigations  Veritatis  and  De  Investiga- 
tione  Perfectionis  Metallorum,  formerly  regarded  as  genuine, 
belong  to  an  even  later  date.  In  fact,  the  whole  of  what 
were  supposed  to  be  Geber's  writings  are  apocryphal. 

The  Arabic  MSS.  of  the  real  Geber,  which  Berthelot's 
investigations  have  now  brought  to  light,  prove  that  he  did 
not  really  profess  the  knowledge  and  the  opinions  with 
which  he  has  been  credited.  On  the  contrary,  we  find  Geber 
adhering  closely  to  the  Grseco-Alexandrian  alchemists,  and 
bringing  forward  many  mystical  views,  e.g.,  the  belief  in 
the  influence  of  the  planets  upon  the  metals.  There  is  no 
distinct  indication  in  his  writings  of  the  theory  of  the  metals 
hitherto  ascribed  to  him  (see  below).  Geber  can  therefore 
no  longer  be  regarded  as  the  author  of  the  Latin  treatises 
with  which,  up  to  now,  his  name  has  been  associated.  These 

1  See  p.  23,  Note  2.     Of.  also  two  papers  by  Berthelot  in  the  Revue  des 
deux  Mondes,  Sept.  15th  and  Oct.  1st,  1893. 


30  THE  AGE  OF  ALCHEMY  CHAP, 

writings  contain,  in  fact,  the  collected  knowledge  of  the  four 
or  five  centuries  after  his  time. 

The  disciples  of  Geber,  famous  Arabian  physicians  like 
Maslema,  Rhazes,  Avicenna,  Avenzoar,  Abukases  and  Averr- 
hoes,  may  possibly  have  exercised  a  retarding  influence  upon 
the  development  of  medical  science  and  of  pharmacy.  And 
it  is  extremely  doubtful  whether  they  advanced  chemistry  in 
any  material  degree.  It  is  worthy  of  note  that  Rhazes  dis- 
tinctly assumes  the  transmutation  of  metals,  while  Avicenna 
disputes  it. 


Alchemy  among  the  Christian  Nations  of  the   West  during 
the  Middle  Ages. 

The  doctrines  of  the  Egypto-Greek  and  Arabian  alchemists 
gradually  penetrated  into  France,  Italy  and  Germany,  certain 
Byzantine  savants — Michael  Psellus  among  them — also  con- 
tributing to  the  spread  of  alchemistic  ideas.  Eastern  in- 
fluence is  recognised  distinctly  for  the  first  time  in  the 
earliest  appearance — of  which  there  is  clear  proof — of  an 
alchemist  in  Germany  at  the  court  of  Adalbert  von  Bremen 
(about  1063),  as  recorded  by  Adam  von  Bremen ;  a  baptised 
Jew  named  Paul  gave  out  that  he  had  learnt  in  Greece  the 
art  of  transmuting  copper  into  gold,  and  he  appears  to  have 
imposed  upon  the  above-named  ecclesiastical  prince.  The 
next  certain  records  of  alchemistic  endeavours  in  Germany 
date  from  the  thirteenth  century,  at  which  period  alchemy 
was  studied  by  men  famous  for  their  learning,  and  was  conse- 
quently developed  in  a  high  degree. 

The  transformation  of  the  base  metals  into  the  noble  by 
means  of  the  philosopher's  stone  formed  at  that  date  the 
cardinal  point  towards  which  all  chemical  knowledge  was 
directed.  Vinzenz  of  Beauvais1  (in  the  first  half  of  the 
thirteenth  century)  and,  after  him,  men  like  Albertus 
Magnus,  Roger  Bacon,  Arnaldus  Villanovanus  and  Ray- 
mund  Lully,  whose  chief  works  belong  to  the  same  century. 

]  Vincentius  Bellovacensis. 


ii  ALCHEMY  DURING  THE  MIDDLE  AGES  31 

regarded  the  transmutation  of  metals  as  an  incontrovertible 
fact.  These  maintained  that  the  philosopher's  stone  did 
exist,  and  was  endowed  with  the  most  marvellous  powers 
(see  below),  their  dogmas  being  based  upon  those  of  the 
Aristotelians  and  of  the  Egypto-Greek  alchemists.  In  ad- 
dition to  these,  the  most  distinguished  representatives  of 
chemistry,  all  of  whom  belonged  to  the  priestly  class,  must 
be  mentioned  the  famous  Thomas  Aquinas ;  the  latter  did  not 
indeed  materially  advance  the  knowledge  of  chemistry,  but 
he  stood  up  at  various  times  for  the  truth  of  the  doctrine 
of  transmutation  of  metals. 

The  influence  of  the  four  men  above-mentioned  upon 
the  history  of  chemistry  renders  biographical  notices  of 
them  desirable;  their  views  upon  the  alchemistic  problem, 
and  also  their  very  considerable  practical  knowledge,  will  be 
treated  of  under  special  sections.  Their  writings  have  to  be 
criticised  with  some  caution,  since  many  of  the  alchemistic 
treatises  of  later  times  were  given  out  to  the  world  under 
their  names. 

Albertus  Magnus,  or,  more  properly,  Albert  von  Bollstadt. 
born  at  Lauingen  on  the  Danube  in  1193,  taught  philo- 
sophy, grammar,  alchemy,  etc.,  publicly  as  a  Dominican  in 
Hildesheim,  Regensburg,  Cologne  and  Paris,  and  became 
Bishop  of  Regensburg  in  1260.  He  retired,  however,  to 
the  cloister  five  years  later,  and  died  in  the  Dominican 
convent  of  Cologne  after  having  devoted  himself  for  fifteen 
years  to  scientific  work.  Albertus  Magnus  was  held,  both 
by  his  contemporaries  and  still  more  during  the  later  Middle 
Ages,  as  a  man  of  the  greatest  erudition  and  widest  acquire- 
ments, the  degrees  of  which  are  given  by  Tritheim,  an 
author  of  the  fifteenth  century,  in  the  following  words  : 
Magnus  in  magia  natural*,  major  in  philosophia,  maximus 
in  theologia.  His  noble  character  also  earned  for  him  the 
highest  respect.  Of  his  numerous  memoirs,  the  two — De 
Alchymia  and  De  Rebus  Metallicis  et  Mineralibus  are  of 
the  most  value  for  adjudging  his  position  with  regard  to 
alchemy. 

Roger  Bacon  was  born  in  Somersetshire  in  1214,  and 


32  THE  AGE  OF  ALCHEMY  CHAP. 

studied  science,  as  well  as  theology,  both  at  Oxford  and 
Paris.  The  veneration  felt  by  posterity  for  his  marvellous 
and  many-sided  knowledge  is  shown  by  the  title  which  it 
conferred  upon  him  of  Doctor  Mirabilis.  Since  he  did  not 
hesitate  to  oppose  in  many  points  the  orthodox  beliefs  of  his 
day,  he  was  subjected  to  bitter  persecution  and  penalties. 
His  death  probably  occurred  in  the  year  1294. 

His  firm  belief  in  the  power  of  the  philosopher's  stone, 
not  only  to  transform  a  million  times  its  own  weight  of 
base  metal  into  gold,  but  also,  to  prolong  life,  seems  to 
us  incomprehensible  when  contrasted  with  the  otherwise 
enlightened  views  which  he  held  and  propagated.  This 
undisguised  recognition  of  miracle-working,  and  this  bias 
towards  the  marvellous,  are  directly  opposed  by  the  fact 
that  Roger  Bacon  taught  the  working  out  of  carefully 
devised  experiments  as  a  special  kind  of  research,  by  which 
new  data  for  the  knowledge  of  nature  should  be  acquired. 
He  is  to  be  regarded  as  the  intellectual  originator  of 
experimental  research,  if  the  departure  in  this  direction  is 
to  be  coupled  with  any  one  name — a  direction  which, 
followed  more  and  more  as  time  went  on,  gave  to  the 
science  its  own  particular  stamp,  and  ensured  its  steady 
development.  The  most  important  works  of  Roger  Bacon 
are  the  following: — Opus  Majus;  Speculum  Alchemice ;  and 
Breve  Breviarium  de  Dono  Dei.  He  did  not  apparently  do 
much  towards  the  spread  and  development  of  practical 
chemical  knowledge. 

In  the  life  and  work  of  the  two  notable  alchemists, 
Arnaldus  Villanovanus  and  Raymundus  Lullus,  the  alchem- 
istic  tendencies  of  their  century  are  clearly  reflected,  although 
much  uncertainty  exists  as  to  many  points,  especially  in  the 
life  of  the  latter,  and  also  with  regard  to  the  works  ascribed 
to  Lully.  Both  of  them  at  all  events  were  held  in  high 
esteem,  not  only  during  their  lives,  but  also-  in  the  centuries 
following.  Arnaldus  Villanovanus,  whose  birthplace  is  un- 
certain, practised  as  a  physician  in  Barcelona  in  the  second 
half  of  the  thirteenth  century.  His  opinions,  however, 
causing  great  offence  to  the  priests,  he  was  obliged  to 


ii    ARNALDUS  VILLANOVANUS  AND  RAYMUNDUS  LULLUS     33 

flee  from  there,  and  after  vainly  endeavouring  to  escape 
persecution  in  Paris  and  in  various  towns  of  Italy,  he  at 
last  found  an  asylum  in  Sicily  with  King  Frederick  II. 
Summoned  to  Avignon  by  Pope  Clement  V.,  then  seriously 
ill,  he  lost  his  life  by  shipwreck  on  the  way  thither,  about 
the  year  1313.  He  had  special  opinions  of  his  own  as  to 
the  nature  and  efficacy  of  the  philosopher's  stone,  and  also 
with  regard  to  the  noble  metals  obtained  through  its  means. 
Among  his  writings  may  be  mentioned :  Rosarius  Philosoph- 
orum ;  DC  Vinis ;  and  De  Venenis. 

A  similarly  restless  life  was  foreordained  for  Raymund 
Lully,  a  life  which  comprised  in  itself  the  greatest  contradic- 
tions and  eccentricities.  Shortly  after  his  death  the  object  of 
a  traditional  glorification,  Lully  possessed  among  alchemists 
the  fame  of  having  attained  to  the  highest  which  it  was  in 
the  power  of  their  art  to  achieve.  The  historical  critic  has 
a  difficult  task  in  dealing  with  him ;  for  while,  on  the  one 
hand,  many  of  the  writings  ascribed  to  him  are  obviously 
counterfeit,  there  are,  on  the  other,  no  sufficient  data  for 
deciding  as  to  which  of  the  remainder  are  really  genuine. 
Thus  there  is  very  great  uncertainty  whether  the  alchemist 
Raymund  Lully  is  identical  with  the  famous  grammarian  and 
dialectician  of  the  same  name,  who  was  called  by  his  admirers 
Doctor  Ulumindtissimus ;  for  this  view,  which  has  been  held 
by  many,  is  strongly  opposed  by  the  fact  that  criticisms  of 
alchemy  are  to  be  found  in  many  of  the  works  of  the  latter. 

Most  of  the  records  which  we  possess  of  the  life  of  Ray- 
mund Lully  agree  in  stating  that  he  was  descended  from  a 
noble  Spanish  family,  and  was  born  in  the  year  1235. 
After  leading  a  dissipated  life  at  the  court  of  Aragon,  he 
abjured  the  pleasures  of  the  world  in  his  thirtieth  year  and 
devoted  himself  to  science.  It  was  probably  Bacon  and 
Villanovanus  who  initiated  him  into  the  secrets  of  alchemy. 
When  somewhat  aged,  he  gave  himself  up  to  the  conversion 
of  the  heathen,  undertaking  several  journeys  to  Africa  for 
this  purpose ;  his  reception  there,  however,  was  more  than 
once  of  the  worst,  and  he  was  at  last  stoned  to  death  in 
the  year  1315.  Tradition  has  it  that  he  lived  for  several 

D 


34  THE  AGE  OF  ALCHEMY  CHAP. 

years  after  that  date  in  the  unresting  study  of  alchemy, 
but  there  can  be  no  doubt  as  to  the  untenability  of  this 
report. 

His  alchemistic  doctrines  were  very  obscure;  and  still 
more  incomprehensible  and  hidden  in  deep  mystic  darkness 
are  his  recipes  for  the  ennobling  of  the  metals.  Certainly 
none  of  the  alchemists  who  preceded  him  have  ascribed  to 
the  philosopher's  stone  such  powers  as  he  did ;  for  he  was 
able  to  cry  out  presumptuously :  "  If  the  sea  were  of 
mercury,  I  would  change  it  into  gold."1  And  not  only 
gold,  but  also  all  precious  stones,  and  that  highest  good — 
health, — together  with  long  life,  were  to  be  obtained  through 
its  means.  Of  the  writings  which  are  attributed  to  him, 
the  Testamentum,  Codicillus  sen  Vademecum,  and  Experimenta 
are  regarded  as  genuine. 

The  earliest  of  the  Latin  writings  formerly  ascribed  to 
Geber  (e.g.,  the  Summa,  mentioned  on  p.  29)  may  possibly 
have  come  into  circulation  soon  after  Lully's  death.  It  is 
worthy  of  note,  and  also  important  for  fixing  with  more  or 
less  accuracy  the  date  at  which  they  lived,  that  neither 
Albertus  Magnus  nor  Raymund  Lully  refer  to  these  writ- 
ings, which  grew  in  repute  from  the  close  of  the  fourteenth 
century  onwards.  The  information  which  one  finds  in  the 
works  of  the  pseudo-Geber  is  by  no  means  inconsiderable. 
Great  progress  is  apparent  in  the  recipes  given  for  the 
making  of  preparations ;  in  the  use  of  apparatus  such  as 
the  water-bath,  the  ash-bath,  and  improved  furnaces ;  and  in 
the  description  of  chemical  operations  like  sublimation, 
filtration,  crystallisation,  distillation,  &c.,  &c.  All  this 
leaves  no  doubt  on  the  mind  as  to  the  high  standard  of 
practical  chemical  knowledge  which  the  pseudo-Geber 
possessed.  The  important  question  of  the  constitution  of 
•the  metals  out  of  mercury  and  sulphur  will  be  discussed 
later  on. 

The  history  of  alchemy  in  the  fourteenth  and  first  half 
of  the  fifteenth  centuries  contains  no  single  name  which 
will  compare  in  eminence  with  those  of  the  above-mentioned 

1  Mare  tingerem,  si  mercurius  esset. 


ii  ALCHEMY  IN  THE  UTH  AND  15TH  CENTURIES  35 

philosophers,  as  the  alchemists  themselves  preferred  to  be 
called. 

This  must  not  be  taken  as  meaning  that  the  supposed 
art  of  making  gold  had  died  out ;  on  the  contrary,  it  bore 
its  strangest  fruit  during  that  period.  If  it  be  desired  to 
connect  specific  names  with  the  study  of  alchemy  at  that 
time,  then  the  Frenchman  Nicolas  Flamel,  Isaac  Hollandus 
the  elder  and  the  younger,  Count  Bernardo  da  Trevigo,  and 
Sir  George  Ripley  may  be  mentioned  as  among  those  who 
were  supposed  to  be  in  possession  of  the  wonder-working 
philosopher's  stone.  These  men  did  nothing,  however,  to 
materially  advance  the  knowledge  of  chemistry. 

Alchemy  was  at  this  time  fostered  and  protected  at 
many  of  the  European  courts,  for  nothing  appeared  to  be 
more  simple  than  to  recuperate  embarrassed  finances  by 
means  of  artificial  gold.  Many  documents  in  the  history 
of  that  century  bear  record  to  the  frequent  disappoint- 
ments which  were  certain  to  come  about  sooner  or  later, — 
decrees  against  the  practice  of  alchemy,  threatenings  of 
those  who  contravened  these  with  the  severest  punishments, 
and  accounts  of  discoveries  of  the  most  bare-faced  imposi- 
tions. Alchemy  found  especial  protection  at  the  court  of 
Henry  VI.  of  England,  in  spite  of  the  fact  that  the  kings 
preceding  him  had  had  to  pay  heavily  for  their  leaning 
towards  the  hermetic  art,  and  that  a  stringent  law  against 
it  had  been  promulgated  by  Henry  IV.  The  consequence  of 
the  favour  shown  to  it  by  these  monarchs  was  the  production 
of  large  quantities  of  counterfeit  gold  which,  in  the  form  of 
coinage,  inundated  neighbouring  countries.  Charles  VII.  of 
France,  who  was  then  at  war  with  England,  was  seduced  by 
an  alchemist,  Le  Cor,  into  a  similar  experiment,  and  thereby 
materially  increased  the  debt  of  his  country ;  to  the  alche- 
mistic  gold  which  he  set  in  circulation  were  added  the 
English  "  Rose  nobles."  Counterfeit  coining,  carried  out  on 
such  a  large  scale,  was  hardly  calculated  to  raise  the  reputa- 
tion in  which  alchemy  was  held. 

Chemistry,  not  being  enriched  during  that  time  by  any 
facts  of  importance,  likewise  suffered  from  this  depreciation  ; 

D  2 


36  THE  AGE  OF  ALCHEMY  CHAP. 

it  first  received  new  life  from  the  work  of  BasiLYalentine, 
whose  acquirements  in  practical  chemistry  even  now  excite 
our  wonder.  This  remarkable  man  was  the  real  precursor 
of  the  iatro-chemical  period,  even  although  he  was  unable 
to  free  himself  from  the  fetters  of  the  alchemistic  faith. 
Of  his  life  practically  nothing  is  known ;  from  his  writings 
we  learn  his  name  and  the  time,  approximately,  in  which  he 
lived,  viz.  the  second  half  of  the  fifteenth  century,  and 
also  that  he  was  a  Benedictine  monk  of  Southern  Germany. 
The  most  important  of  his  works  were  published  in  the 
beginning  of  the  seventeenth  century  by  a  city  chamberlain 
Tolde  in  Frankenhausen,  Thuringia ;  whether  foreign  matter 
has  become  mixed  up  with  them  cannot  now  be  deter- 
mined. So  much  is  certain,  that  Basil  Valentine  was  re- 
garded as  an  oracle  by  alchemists  so  early  as  the  end  of 
the  fifteenth  and  beginning  of  the  sixteenth  centuries,  and 
was  held  in  higher  honour  than  Geber,  higher  even  than 
Raymund  Lully,  besides  being  admired  by  many  who  had 
nothing  to  do  with  alchemy.  His  works  were  spread 
abroad  by  means  of  copies,  and  excited  the  interest  of 
the  Emperor  Maximilian  I.  to  such  a  degree  that  he 
caused  a  searching  inquiry  to  be  made  in  the  year  1515  as  to 
which  Benedictine  convent  the  famous  author  had  dwelt  in ; 
but  unfortunately  his  efforts  in  this  direction  were  without 
result,  as  were  also  all  later  ones. 

An  account  will  be  given  further  on  both  of  his  theoretical 
views  and  of  his  wide  acquaintance  with  practical  chemistry. 
Among  the  writings  which  are  presumably  his,  and  which 
are  at  the  same  time  of  the  most  importance,  are  the  follow- 
ing : — Triumphwagen  des  Antimonii  ("  Triumphal  Car  of 
Antimony  ") ;  Von  dem  grossen  Stein  der  Uralten  Weisen  ("  On 
the  Great  Stone  of  the  Ancient  Philosophers  ")  ;  OJfenbarung 
der  verborgenen  Handgriffe  ("Revelation  of  the  Hidden  Key") ; 
Letztes  Testament  ("  Last  Testament ") ;  Schlussreden  ("  Con- 
cluding Words  "). 

In  the  first-mentioned  work  we  possess  what  for  that 
time  was  a  marvellous  description  of  an  element  -and  its 
compounds,  the  knowledge  of  these  being  due  mainly  to 


ii  ALCHEMISTIC  THEORIES  AND  PROBLEMS  37 

Basil  Valentine  himself.  The  language  which  he  employs 
is  frequently  obscured  by  mystical  pictures  and  alchemistic 
ideas;  but,  while  he  thus  appears  as  a  visionary  on  the 
one  hand,  he  excites  on  the  other  our  highest  admiration 
from  the  fulness  of  his  temperate  and  conscientious  obser- 
vations, as  well  as  from  the  rational  views  he  takes  of 
subjects  which  were  then,  for  the  most  part,  judged 
erroneously.  The  rich  experiences  in  practical  chemistry 
which  he  made  his  own  cause  him  to  stand  out  as  the 
most  distinguished  chemist  of  the  whole  alchemistic  period. 
His  boldness,  too,  in  proposing  the  use  of  chemical  prepara- 
tions for  medicinal  purposes  led  the  way  in  a  direction 
which  soon  after  his  time  became  the  prevailing  one,  viz. 
the  iatro-chemical,  which  dominated  the  succeeding  age. 
Notwithstanding  all  this,  Basil  Valentine  was  an  out-and-out 
alchemist,  holding,  as  such,  the  most  exaggerated  ideas  as  to 
the  power  of  the  philosopher's  stone ;  just  as  the  tendency 
towards  alchemy  and  the  firm  belief  in  the  possibility 
of  transmuting  metals  and  of  prolonging  life  continued 
engrained  in  many  of  the  iatro-chemists. 


SPECIAL  HISTORY  OF  ALCHEMY. 

Theories  and  Problems  of  the  Alchemistic  Period. 

The  alchemistic  ideas,  with  the  transmutation  of  metals  as 
their  leading  principle,  have  been  proved  (as  already  men- 
tioned) to  have  originated  and  to  have  been  first  systemati- 
cally fostered  in  Egypt.  The  first  attempt  to  explain  this 
assumed  transmutation,  by  a  theoretical  conception  of  the 
nature  of  metals,  was  made  very  early.  From  a  similar 
endeavour,  i.e.  from  regarding  transmutation — then  looked 
upon  as  an  incontrovertible  fact — as  a  consequence  of  the 
constitution  of  the  metals,  there  sprang  the  doctrine  con- 
tained in  the  works  ascribed  to  Geber,  which  in  its  essentials 
predominated  during  the  alchemistic  period.  It  was  thus 
always  the  metals  which  gave  rise  to  the  early  chemical 
theories. 


38  THE  AGE  OF  ALCHEMY  CHAP. 

If  we  penetrate  to  the  kernel  of  the  doctrines  of  the 
Alexandrians  through  the  veil  of  mysticism  which  envelops 
it,  we  see  that  these  philosophers  were  permeated  with  the 
idea  that  the   metals  were  alloys  of  varying   composition. 
From  this  it  necessarily   followed  that  the  transformation 
of  one  metal  into  another  was  possible,  either  through  the 
addition   of  new   metallic    substances    or   the  expulsion  of 
some  already  present.     Such  transformations  of  similar  sub- 
stances into  one  another  appear  much  less  wonderful  than 
those  of  dissimilar  ones  like  air,  water  and  earth,  which  were 
mutually   convertible,   according    to   the    teaching    of    the 
Platonists  and  Aristotelians.     The  means  for  bringing  about 
these  changes  in  the  metals,  the  substances  which  it  was 
necessary  to  add  to  them,  and  the  operations  which  had  to 
be  gone  through,  were   either  kept   secret  or  obscured  by 
indistinct  figurative  language.     The  various  colours  of  the 
metals,  and  their  alteration  by  melting  them  with  others, 
played  a  prominent  part  in  alchemistic  processes ;  in  impart- 
ing thereby  the  colour  of  a  noble  metal  to  a  base  one,  much 
was  supposed  to  have  been  attained.     For  the  Alexandrians, 
therefore,  and  also  for  the  alchemists  of  the  Middle  Ages, 
the  colouring  of  metals  was  synonymous  with  their  trans- 
mutation.    The  chief  operations  were  the  so-called  Xantkosis, 
Leukosis  and  Melanosis,  which  were  compared  with  the  pro- 
cesses followed  in  the  dyeing  of  cloth.     The  old  designation 
of  tinctures  for  the  media  by  which  this  transformation  was 
brought  about,  gives  expression  to  the  idea  that  the  latter 
consisted  in  a  dyeing  operation. 

As  may  be  imagined,  no  trace  can  be  found  of  any  distinct 
chemical  conception,  or  of  any  knowledge  of  the  actual  opera- 
tions which  take  place  in  these  transmutations.  At  the  root, 
however,  of  these  endeavours  of  the  Alexandrian  alchemists 
to  produce  noble  metals  from  base,  lay  speculations  purely 
philosophical,  which  strongly  excited  and  strengthened  the 
belief  in  the  transmutation  of  metals.  These  were  partly 
taken  from  the  writings  of  Plato,  especially  from  his  Timceus, 
which  was  highly  esteemed  by  the  Alexandrians,  and  partly 
from  the  philosophy  of  Aristotle.  Both  of  these  Greeks  held 


«  DOCTRINES  OF  THE  PSEUDO-GEBER  39 

the  opinion  that  the  (so-called)  elements  in  general  were 
capable  of  transformation  into  one  another,1  and  an  extension 
of  this  idea  led  to  the  assumption  that  the  same  applied  to  the 
metals.  The  observations  of  the  supposed  generation  of  noble 
metals  from  base,  which  have  been  already  discussed,  were 
looked  upon  as  proofs  of  the  correctness  of  this  supposition. 

In  the  writings  hitherto  attributed  to  Geber,  but  which, 
according  to  Berthelot,  are  not  of  earlier  date  than  the  four- 
teenth century,  we  find  a  specific  chemical  theory  of  the  metals, 
a,  theory  which,  supported  by  the  great  authority  of  Geber's 
name,  found  universal  recognition  in  the  later  Middle  Ages. 
This  theory  looks  upon  classes  of  bodies  from  a  chemical 
point  of  view,  and  seeks  to  explain  the  difference  between  the 
substances  comprising  these  by  assuming  a  peculiar  chemical  j 
composition.  The  metals  consist  of  sulphur  and  mercury,  / 
which  are  present  in  them  in  different  proportions  and  in 
different  degrees  of  purity.2 

The  transmutation  of  metals  consists,  according  to  him,  in 
an  arbitrary  alteration  of  their  composition ;  the  ennobling 
of  them,  specially,  in  a  purification  and  fixation  of  the  mer- 
cury. The  idea  of  creating  a  metal  anew,  which  we  find 
highly  developed  among  Western  alchemists,  is  not  to  be 
found  in  the  pseudo-Geber's  writings.  This,  together  with 
the  application  of  his  theory,  is  proved  by  the  following 
sentences,  which  comprise  in  themselves  his  theoretical  and 
practical  chemical  programme  :  "  To  assert  that  one  substance 
can  be  produced  from  another  which  does  not  contain  it,  is 

1  This  idea  comes  out  very  clearly  in  the  following  passage  from 
Timceus : — "  We  believe  from  observation  that  water  becomes  stone  and 
earth  by  condensation,  and  wind  and  air  by  subdivision ;  ignited  air  be- 
comes fire,  but  this,  when  condensed  and  extinguished,  again  takes  the 
form  of  air,  and  the  latter  is  then  transformed  into  mist,  which  dissolves 
into  water.     From  this,  lastly,  are  produced  rocks  and  earth." 

2  The  pseudo-Geber  sometimes  added  arsenic  to  the  above-named  con- 
stituents of  the  metals  as  a  third  possible  one,  without  however  laying 
emphasis  upon  this  extension.     Here  and  there,  also,  Aristotle's  doctrine 
of  the  four  different  states  of  matter  appears  to  get  mixed  up  with  his  views 
upon  the  composition  of  the  metals,  the  "four  elements"  being  regarded 
to  some  extent  as  subsidiary  constituents,  sulphur  and  mercury  being  the 
princit)al  ones. 


40  THE  AGE  OF  ALCHEMY  CHAP. 

folly.  Since,  however,  all  metals  consist  of  sulphur  and  mer- 
cury, we  can  add  to  them  the  constituent  in  which  they  are 
deficient,  or  abstract  the  one  which  is  present  in  excess.  In 
order  to  achieve  this,  make  use  of  the  art :  calcination,  subli- 
mation, decantation,  solution,  distillation,  coagulation  (crys- 
tallisation), and  fixation.  The  active  agents  are  the  salts, 
alums,  vitriols,  borax,  the  strongest  vinegar  and  fire." 

The  varying  origin  of  the  works  hitherto  ascribed  to  Geber 
explains  why  in  many  passages  of  these  writings  no  distinc- 
tion is  drawn  between  the  supposed  two  constituents  of  the 
metals  and  natural  sulphur  and  mercury,  while  we  frequently 
find  him  expressing,  in  others,  the  opinion  that  the  former 
are  not  identical  with  the  latter.  The  mercury  and  sulphur 
present  in  the  metals  were,  in  this  second  case,  looked  upon 
as  being  of  an  abstract  nature;  thus  mercury  conferred 
glance,  malleability,  fusibility,  and  what  we  consider  metallic 
properties  generally,  while  sulphur,  on  account  of  its  com- 
bustibility, was  regarded  as  being  present  because  of  the 
alteration  of  many  metals  in  the  fire.  The  noble  metals, 
those  which  withstood  the  fire,  therefore  consisted  of  almost 
pure  mercury,  which  however  could  not  be  identical  with  the 
ordinary  substance  of  that  name,  since  the  latter  was  volatile ; 
this  property  was  ascribed  to  the  fact  of  ordinary  mercury 
containing  sulphur.  By  means  of  these  and  similar  assump- 
tions, contradictions  between  theory  and  facts  were  easily  set 
aside,  the  alchemists  of  later  times  especially  distinguishing 
themselves  in  this  way. 

For  the  solution  of  the  possible  problem  of  the  transmuta- 
tion of  metals — possible,  that  is,  in  the  sense  of  the  above 
theory, — so-called  "  medicines  "  are,  according  to  the  pseudo- 
Geber,  requisite,  these  being  distinguished  as  possessing 
different  power  and  virtue.  The  medicines  of  the  first  order 
do  indeed  produce  changes  in  the  base  metals,  but  these 
changes  are  not  permanent.  Those  of  the  second  order  parti- 
ally alter  the  properties  of  such  metals  into  those  of  the 
noble  ones,1  but  the  transmutation  proper  is  only  effected  by 

1  The  Particulars  of  the  later  alchemists  appear  to  have  corresponded 
to  medicines  of  the  second  order. 


ii  VIEWS  OF  THE  LATER  ALCHEMISTS  41 

the  medicine  of  the  third  order,  which  is  variously  designated 
as  the  Philosopher's  Stone,  the  Grand  Elixir,  or  the  Magistermm 
(masterpiece).1  The  accounts  which  the  pseudo-Geber  gives 
of  the  preparation  of  the  medicines  of  higher  order  are  wholly 
unintelligible ;  it  should,  however,  be  emphasised  that  there 
is  a  wide  difference  between  these  and  the  incredible  ex- 
aggerations of  which  other  alchemists  were  guilty,  when 
speaking  of  the  efficacy  of  such  secret  preparations. 

One  cannot  but  feel  surprised  that  the  alchemists  of  the 
thirteenth  and  fourteenth  centuries,  possessing  as  they  did  a 
fairly  extensive  knowledge  of  chemistry,  should  have  re- 
mained satisfied  with  such  speculations  as  to  the  constitution 
of  the  metals,  without  actually  trying  to  isolate  the  sub- 
stances that  they  assumed  as  being  present  in  these  and 
other  bodies.  Instead  of  endeavouring  to  gain  an  insight 
into  their  composition  by  experiment,  they  brought  forward 
fresh  hypotheses  to  controvert  obvious  objections,  e.g.,  that 
the  above-mentioned  constituents  (mercury,  &c.)  were  not 
identical  with  the  substances  commonly  so  named. 

The  above  theory  of  the  metals  underwent  an  extension 
by  Basil  Valentine,  who  assumed  the  presence  in  them  of  a 
third  constituent,  viz.  salt.2  By  the  term  salt  he  did  not 
mean  a  definite  chemical  compound,  such  as  common  salt, 
but  rather  the  principle  of  solidification  and  power  of  with- 
standing fire,  just  as  sulphur  determined  the  combustibility 
or  change  in  the  fire  and  also  the  colour,  and  mercury  the 
metallic  character  and  volatility.  Basil  Valentine  generalised 
his  opinion  in  this  way,  that  he  assumed  these  three  essential 
principles  in  all  substances,  an  assumption  which  Paracelsus 
appropriated  later  on,  and  made  the  basis  of  his  iatro-chemical 
doctrine. 

Their  views  upon  the  composition  of  the  elementary  bodies 
being  so  very  obscure  and  so  utterly  wrong,  one  sees  how 
impossible  it  was  for  the  alchemists  to  explain  chemical 

1  At  a  later  period  the  great  elixir  was  distinguished  from  the  small  one, 
which  only  transmuted  the  base  metals  into  silver. 

2  Isaac  Hollandus  had  before  this  spoken  of  the  saline  principle  of  the 
metals. 


42  THE  AGE  OF  ALCHEMY  CHAP. 

processes  rightly,  connected  as  these  are  with  the  formation 
of  compounds.  Some  very  incomplete  attempts  were  made 
to  give  a  theoretical  explanation  of  isolated  observations, 
but  these  only  led  to  gross  errors  creeping  in ;  the  calcina- 
tion of  the  metals,  for  instance,  was  supposed  to  depend 
upon  the  escape  of  moisture  or  of  some  other  constituent, 
an  idea  which  reappeared  in  another  form  in  the  later  theory 
of  phlogiston.  The  above  theory  of  the  composition  of 
metals  is  sufficient  evidence  of  the  small  amount  of  trouble 
which  was  taken  to  find  out  the  true  chemical  constituents 
of  bodies. 

We  may  safely  say  that  scientific  chemistry  only  really 
began  with  the  fruitful  endeavours  to  discover  the  real  com- 
position of  substances.  It  is  out  of  the  question  to  speak  of 
this  as  applying  to  a  time  when  it  was  considered  as  proved 
that  the  formation  of  a  chemical  compound  was  identical 
with  the  annihilation  of  its  original  components,  a  new 
substance  being  created.  This  view  was  the  almost  sole 
predominating  one  during  the  later  alchemistic  period, 
although  in  the  works  of  the  pseudo-Geber  we  find  some 
indications  o£  more  correct  opinions  on  the  composition  of 
many  chemical  compounds  (the  recognition  of  mercury  and 
sulphur,  for  instance,  as  constituents  of  cinnabar). 

Contemporaneously  with  the  holding  of  such  theories 
based  upon  no  facts  whatever,  the  Western  alchemists 
strove  in  every  imaginable  way  to  obtain  the  philosopher's 
stone, — mercurius  philosophorum.1  Those  of  them  who  were 
in  happy  possession  of  the  means  for  transmuting  metals, 
attributed  to  it  the  most  astounding  powers.  In  order  to 
give  some  idea  of  the  aberration  of  mind  caused  by  the 
alchemistic  problem,  a  few  of  the  extraordinary  assertions  of 
well-known  alchemists  with  regard  to  the  preparation  and 
efficacy  of  the  philosopher's  stone  may  be  mentioned  here. 

For  its  preparation  (we  are  now  speaking  more  particu- 
larly of  the  thirteenth  century  onwards)  a  materia  prima 
was  requisite,  to  obtain  which  was  the  hardest  task  of  all. 
The  most  incredible  substances,  natural  products  of  every 
1  Cf.  the  Engler  lecture  :— Der  Stein  der  Weisen  (Carlsruhe,  1889). 


ii  THE  PHILOSOPHER'S  STONE  43 

kind,  were  taken  as  raw  materials  for  the  manufacture  of 
this  preparation,  and  worked  up  in  every  conceivable  way. 
Those  who  laid  claim  to  the  possession  of  the  philosopher's 
stone  took  very  good  care  to  keep  the  secret  of  their  materia 
prima  to  themselves.  They  described  all  kinds  of  operations 
with  it 1  in  the  most  enigmatical  recipes,  employing  at  the 
same  time  mystical  drawings,  such  as  those  of  the  dragon,  the 
red  or  green  lion,  the  lily,  the  white  swan,  &c.,  and  well  knew 
how  to  keep  their  imitators,  of  whom  there  were  formerly  shoals 
(isolated  cases  being  found  even  in  this  century),  in  a  state 
of  continual  tension.  That  this  was  possible  is  explained 
by  the  immovable  and  almost  universal  belief  in  the  trans- 
mutation of  metals,  by  means  of  the  philosopher's  stone, 
during  the  Middle  Ages. 

To  the  latter  the  greatest  miracles  were  ascribed ;  thus, 
Roger  Bacon  does  not  hesitate  to  say  that  it  was  able  to 
transform  a  million  times  its  weight  of  base  metal  into  gold 
(millies  millia  et  ultra).  Others,  e.g.  Arnaldus  Villanovanus, 
were  more  modest  in  their  estimate  of  its  powers,  stating 
that  it  could  convert  into  gold  one  hundred  times  its  weight 
of  mercury.  Others,  again,  surpassed  even  Bacon,  as  the 
following  passage  from  the  Testamentum  Novissimum,  ascribed 
to  Lully,  proves :  "  Take  of  this  precious  medicine  a  small 
piece,  as  large  as  a  bean.  Throw  it  upon  a  thousand  ounces 
of  mercury,  and  this  will  be  changed  into  a  red  powder. 
Put  one  ounce  of  the  latter  upon  one  thousand  ounces  of 
mercury,  which  will  thereby  be  transformed  into  a  red 
powder.  Of  this,  again,  an  ounce  thrown  upon  a  thousand 
ounces  mercury,  will  convert  it  entirely  into  medicine. 
Throw  an  ounce  of  this  on  a  thousand  ounces  of  fresh 
mercury,  and  it  will  likewise  turn  into  medicine.  Of  this 
last  medicine,  throw  once  more  an  ounce  upon  a  thousand 
ounces  of  mercury,  and  this  will  be  entirely  changed  into 
gold,  which  is  better  than  gold  from  the  mines."  One  sees 
clearly,  from  these  and  other  fraudulent  assertions,  that  the 
simple  standpoint  which  the  Egypto-Greek  alchemists 

1  The  process  of  fixation,  a  term  which  indicated  the  solidification  of 
mercury  by  the  transmutation,  was  of  special  importance. 


44  THE  AGE  OF  ALCHEMY  CHAP. 

assumed  with  regard  to  the  question  of  the  transmutation 
of  metals,  was  departed  from  in  the  later  Middle  Ages. 

In  view  of  such  excesses,  which  are  an  insult  to  the 
human  understanding,  it  causes  no  surprise  to  find  attributed 
to  the  philosopher's  stone  other  results  which  are,  if  possible, 
/  \even  more  incredible;  being  a  universal  medicine,  health 
and  life  were  to  be  preserved  and  ensured  by  it.  State- 
ments as  to  the  power  of  prolonging  life  possessed  by  the 
elixir  were  also  rife  in  the  later  Middle  Ages,  and  it\was  no 
unusual  assertion  that  adepts,  the  fortunate  possessors  of 
the  panacea,  had  been  able  to  prolong  their  lives  to  400  years 
and  more.  The  long  lives  of  the  patriarchs  were  explained 
by  the  assumption  that  they  were  acquainted  with  this 
universal  medicine.  In  the  time  of  the  Arabian  alchemists 
healing  properties  were  ascribed  to  gold  prepared  artificially 
and  brought  into  the  potable  form  (aurum  potabile),  and 
from  this  the  belief  in  the  medicinal  power  of  the  philoso- 
pher's stone  appears  to  have  originated. 

Alchemistic  ideas  produced  their  most  absurd  results 
towards  the  end  of  the  Middle  Ages  and  in  still  more  recent 
times,  the  creation  of  living  beings  by  means  of  the  philo- 
sopher's stone  being  not  merely  held  as  possible,  but  being 
actually  taught ;  this  marks  the  acme  of  the  mental  aber- 
ration they  induced. 

The  melancholy  picture,  which  the  condition  'of  alchemy 
presents  to  us  at  various  periods,  becomes  still  more  sombre 
and  involved  in  deeper  shadow  from  the  fact  that  men 
did  not  hesitate  to  affirm  the  Divine  assistance  and  to  claim 
predestination,  in  order  to  explain  the  marvellous  effects  of 
the  philosopher's  stone.  Gross  abuse  was  made  in  this  way 
of  the  name  of  the  Deity,  and  also  of  prayers  and' biblical 
quotations,  by  the  alchemists  of  the  thirteenth  century,  and 
still  more  by  their  successors.  There  is  no  need  to  go  into 
further  details  upon  this  point  here,  but  it  is  necessary  to 
mention  it  in  order  that  the  methods  by  which  the  problems 
of  alchemy  were  treated  at  different  periods  may  appear  in 
their  proper  light. 

Upon  the  development  of  chemistry  as  a  science,  the 


ii  PRACTICAL-CHEMICAL  KNOWLEDGE  45 

alchemistic  doctrines — especially  the  theories  of  the  composi- 
tion of  metals — had  only  a  slight  and  an  indirect  influence. 
The  excesses  to  which  they  gave  rise  have — as  aberrations 
of  mind,  enchaining  a  large  portion  of  the  educated — a 
higher  value  for  the  history  of  civilisation  than  for  that  of 
chemistry.  The  main  significance  of  alchemy  for  the  latter 
lies  in  this, — that  the  endeavours  to  solve  the  problem  of  the 
transmutation  of  metals  were  the  cause  of  actual  work 
with  materials  of  every  kind ;  and  the  result  of  this  was 
a  not  inconsiderable  increase  in  the  knowledge  of  applied 
chemistry  during  the  alchemistic  age.  The  following  section 
will  be  devoted  to  an  account  of  the  latter. 


Practical- Chemical  Knowledge  in  the  Alchemistic  Period.1 

When  one  considers  upon  what  superficial  observations 
the  conviction  of  the  transmutability  of  metals  was  based, 
and  how  readily  wholly  untenable  theories  upon  the  com- 
position of  bodies  were  brought  forward  and  accepted,  one 
feels  no  surprise  that  comparatively  little  progress  was 
made,  during  the  succeeding  epochs,  towards  explaining  the 
numerous  chemical  processes  already  known  to  the  Ancients. 
The  acquirements  in  chemistry  during  these  centuries  them- 
selves likewise  'remained,  for  the  most  part,  empirical;  it 
was  but  seldom  that  the  composition  of  chemical  compounds 
was  even  in  some  degree  correctly  indicated.  The  fantastic 
treatment  of  chemistry — a  treatment  wholly  foreign  to  the 
exact  sciences — has  been  sufficiently  detailed  in  the  preceding 
section.  We  must  not  omit  to  mention,  however,  that  the 
addition  of  new  facts  to  those  already  known,  and  the  gain 
of  experience  in  the  fields  of  technical  and  pharmaceutical 
chemistry  and  in  the  manufacture  of  chemical  preparations, 
were  not  inconsiderable. 

1  Cf.  Kopp,  Gesch.  d.  Chemie,  vols.  iii.  and  iv.  ;  Hofer,  Histoire,  etc., 
vol.  i.  p.  317,  et  seq.;  Gmelin,  Gesch.  d.  Chemie.;  and  Berthelot,  La  Trans- 
mission de  la  Science  Antique  du  Moyen-dge. 


46  THE  AGE  OF  ALCHEMY  CHAP. 

Technical  Chemistry. — Metallurgy,  upon  which  the 
infant  powers  of  an  early  developed  technique  were  expended, 
shows,  upon  the  whole,  but  little  progress.  Towards  the  end 
of  the  alchemistic  period  certain  other  metals  were  indeed 
added  to  those  already  known,  viz.,  the  semi-metal  antimony, 
together  with  bismuth  and  zinc  ;  but  these  can  only  lay  claim 
to  a  subordinate  position  in  the  circle  of  metallurgical  processes 
generally.  From  the  eleventh  century  on,  mining  increased 
among  the  Western  nations,  in  Germany  especially  in  the 
Harz,  Nassau  and  Schlesien.  So  far  as  our  present  in- 
formation goes,  only  trifling  alterations  were  made  in  the 
preparation  and  purification  of  the  metals.1 

Gold  was  obtained  and  purified  from  other  metals  and 
admixtures  by  the  old  method  of  cupellation  (working  with 
lead),  already  accurately  described  by  the  pseudo-Geber.  The 
latter  knew  that  the  desired  result  was  ensured  and  its  pro- 
gress hastened  by  the  addition  of  saltpetre,  and,  further,  that 
copper  and  tin,  but  not  silver,  could  be  separated  from  gold 
in  this  way.  In  the  fifteenth  century  there  was  added  to 
this  the  process  of  purifying  gold  by  fusing  it  with  antimony 
trisulphide  ore  (Spiessglanzerz),  a  method  which  is  given  in 
detail  by  Basil  Valentine.  Alloys  of  gold  were  often  fraudu- 
lently prepared  of  set  purpose. 

The  extraction  of  silver  from  its  ores  was  accomplished, 
as  in  Pliny's  time,  by  fusion  with  lead,  an  operation 
first  termed,  "  Aussaigern"  by  Basil  Valentine.  The  only 
means  of  separating  gold  from  silver  which  was  known  up 
to  a  comparatively  recent  date,  was  the  cementation -process 
of  the  Ancients.  The  wet  process  with  nitric  acid  appears 
to  have  been  first  successful  in  the  time  of  Albertus  Magnus, 
at  least  he  is  the  earliest  to  indicate  it ;  an  absolutely 

1  The  work  entitled  Schedula  Diversarum  Artium,  which  was  written  by 
Theophilus  Presbyter,  a  Benedictine  of  the  eleventh  century,  gives  a  true 
picture  of  the  state  of  technical  industry  in  his  time,  particularly  of  the 
working  up  of  metals,  something  being  also  said  about  their  production 
from  the  ores.— A  tenth-century  manuscript,  Mappce  Clavicula,  edited  by 
Berthelot,  contains  an  essay  on  the  noble  metals,  and  by  its  agreement 
with  recipes  found  in  the  Leyden  papyrus,  conclusively  shows  the  close 
connection  with  the  Egypto-Greek  alchemy. 


METALLURGY  4T 


certain   acquaintance  with  the  process  is  first  to  be  found 
in  Agricola. 

From  the  importance  which  was  attached  to  the  successful 
working-up  of  gold  and  silver  ores,  one  understands  how  the 
closest  attention  was  given  from  an  early  period  to  the  definite 
quantitative  yield  of  the  noble  metals.  Accurate  balances 
came  into  use,  their  employment  in  cupellation  and  cementa- 
tion processes  being  made  obligatory  by  law ;  one  thus  meets 
here  with  the  first  beginnings  of  a  docimacy. 

With  regard  to  the  metallurgy  of  iron,  lead,  tin  and 
copper  in  the  alchemistic  period,  there  are  no  particular 
improvements  to  record.  Basil  Valentine  (fifteenth  century) 
states  that  the  last  metal  was  also  obtained  by  the  wet 
process  as  the  so-called  cement  copper,  by  precipitating  a 
solution  of  copper  vitriol  with  iron.  The  changes  undergone 
by  these  metals  on  being  heated  and  on  treatment  with 
chemical  reagents,  especially  acids,  were  closely  studied, 
and  thereby  the  knowledge  of  metallic  preparations  decidedly 
enlarged.  (See  p.  52.) 

Mercury,  which  played  such  an  important  part  in  the 
theoretical  views  of  the  alchemists,  was  prepared  on  a  large 
scale  for  technical  purposes  by  roasting  quicksilver  ores  in 
improved  furnaces,  especially  after  the  opening  up  of  the 
rich  Idrian  mines  in  the  fifteenth  century.  The  prepara- 
tion of  the  metal  by  distilling  a  mixture  of  sublimate  and 
caustic  lime  was  well  known  to  Basil  Valentine.  For  its 
purification  he  gives  various  processes,  some  of  which  had 
been  already  described  by  the  pseudo-Geber.  Mercury  was 
much  used,  particularly  for  the  extraction  of  gold  and  silver 
(by  the  so-called  amalgamation  process)  and  for  gilding. 

Metallic  zinc  and  bismuth,  and  also  cobalt  ore,  are  like- 
wise mentioned  by  Basil  Valentine,  but  the  metals  themselves 
do  not  seem  to  have  been  employed  technically;  some 
preparations  of  zinc,  however,  were.  A  special  place  among 
chemical  preparations  is  to  be  assigned  to  antimony  and  its 
compounds,  the  knowledge  of  which  is  due  to  Basil  Valentine 
himself.  (See  p.  54.) 

In  pottery  and   glass  manufacture,  important  improve- 


48  THE  AGE  OF  ALCHEMY  CHAP. 

ments  in  single  points  were  made  during  the  alchemistic 
period ;  but  it  is  also  noticeable  here  that  the  interest  in 
the  chemical  processes  remains  a  purely  external  one,  no 
attempt  being  made  to  give  a  scientific  explanation  of  the 
facts  empirically  arrived  at.  The  general  use  of  glazes  con- 
taining lead  and  tin  for  earthenware  vessels  is  worthy  of 
mention,  as  is  also  the  burning  of  colours  into  glass  (the 
whole  mass  having  formerly  been  coloured  by  the  addition  of 
metallic  oxides  during  fusion). 

Dyeing  remained  stationary  on  the  whole,  so  far  as  the 
chemical  media  for  fixing  the  colour  on  the  fibre  were  con- 
cerned ;  alum  was  universally  employed  as  a  mordant,  being 
manufactured  on  a  large  scale  in  different  places.  The 
introduction  of  the  kermes  dye  (cochineal)  into  European 
countries  by  the  Arabians,  that  of  orchilla,  already  known  in 
ancient  Rome  (from  the  East  in  the  thirteenth  century), 
and,  lastly,  the  gradual  supplanting  of  the  (blue)  dye  from 
woad  by  indigo,  are  the  most  important  technico-chemical 
events  in  the  domain  of  dyeing. 


Condition  of  Pharmaceutical  Chemistry. 

Although  the  Arabians  and  the  later  Western  savants 
busied  themselves  with  chemical  operations,  and  thereby 
arrived  at  preparations  of  the  most  various  kinds,  the  pharma- 
ceutical chemistry  of  that  period  only  profited  slightly  by 
this ;  it  was  Basil  Valentine  who  inaugurated  a  new  era  by 
his  bold  attempts  to  apply  chemical  preparations  to  medicinal 
purposes.  The  opening  up  of  the  intimate  connection  exist- 
ing between  chemistry  and  medicine,  which  led  to  the  high 
development  of  pharmacy,  was  reserved  for  the  period  of  iatro- 
chemistry.  The  Arabians  prepared  their  medicines  strictly 
according  to  the  recipes  of  Galen,  Andromachus  and  others, 
which  were  transmitted  to  them,  according  to  Leo  Africanus, 
by  the  Nestorians.1  Apothecaries'  shops,  in  which  the 
remedies  were  almost  exclusively  prepared  from  vegetable 

1  For  their  influence  upon  the  Arabians  see  note  2,  p.  28. 


ii  KNOWLEDGE  OF  CHEMICAL  COMPOUNDS  49 

substances,  sprang  up  at  an  early  date.  To  the  Arabians 
belongs  the  credit  of  having  improved  and  rendered  the 
process  of  distillation  serviceable  for  this  purpose  :  distilled 
water,  ethereal  oils,  and  other  products  (especially  spirit 
of  wine)  obtained  by  distillation,  to  which  the  most  wonder- 
ful results  were  ascribed,  soon  came  into  general  use. 

These  apothecaries'  shops  with  their  fittings  then  spread 
into  Spain,  Southern  Italy  (into  Salerno  in  the  eleventh  cen- 
tury) and,  somewhat  later,  into  Germany.  The  recipes  of 
that  time  for  the  preparation  of  medicines,  the  imperfect 
pharmacopeias,1  show  that  the  doctrines  and  axioms  of  Galen 
and  the  Arabian  physicians  remained  the  standards  up  to  the 
end  of  the  fifteenth  century.  The  position  of  the  physician 
with  regard  to  the  apothecary  was  early  fixed  by  legal  statute, 
it  being  considered  advisable  to  draw  a  sharp  distinction  be- 
tween the  man  who  had  to  prescribe  the  medicines  and  the 
man  who  had  to  make  them. 

With  respect  to  chemical  preparations  proper,  a  few  new 
ones  were  added  to  those  already  used  in  medicine,  e.g.  salt- 
petre, mercury  in  the  form  of  grey  ointment,  and — towards 
the  end  of  the  fifteenth  century,  at  the  instigation  of  Basil 
Valentine — various  mercurial  and  antimonial  preparations 
(see  p.  54).  Almost  all  the  physicians  of  that  time  took  up, 
however,  an  antagonistic  position  with  regard  to  the  last  of 
these,  being  of  opinion  that  the  undoubted  poisonous  properties 
of  antimony  compounds  were  incompatible  with  their  internal 
use. 

Knowledge  of  the  Alchemists  with  regard  to  Chemical 
Compounds. 

It  has  already  been  mentioned  that  the  knowledge  of  the 
true  composition  of  chemical  compounds  was  but  slightly 
extended  during  this  period ;  we  have  therefore  to  deal  here 
with  the  state  of  empirical  knowledge  as  affecting  substances 
prepared  artificially,  together  with  a  few  occurring  naturally. 

1  The  first  German  pharmacopeia  (Arzneibuch)  was  drawn  up  by  Ortholph 
von  Baierland  and  appeared  in  1477. 

E 


50  THE  AGE  OF  ALCHEMY  CHAP. 

The  tendency  to  group  together  observed  facts  under  a 
common  point  of  view  showed  itself  at  an  early  date  with 
respect  to  salts,  of  which  a  large  number  were  known.  The 
pseudo-Geber  regarded  solubility  in  water  as  a  general  charac- 
teristic ;  later  on  the  generic  name  sal  was  made  to  include  a 
variety  of  substances,  e.g.  the  vitriols,  potash,  soda,  saltpetre, 
alum,  etc.  Other  chemical  compounds  of  totally  different 
nature,  viz.  the  alkalies  and  acids,  were  added  to  the  class  of 
salts  by  many  alchemistic  writers,  the  term  sal  being  thus 
widely  extended  and  distorted ;  it  was  reserved  for  a  later 
century  to  fix  it  without  any  ambiguity.  In  addition  to  the 
common  designation  sal  for  a  number  of  heterogeneous  bodies, 
we  find  in  the  writings  of  that  time  the  generic  name  spiritus 
for  the  volatile  acids,  e.g.  spiritvis  salis  for  hydrochloric  acid  ; 
also  the  name  spiritus  urince  for  volatile  alkaline  salt  (car- 
bonate of  ammonia).  The  individual  salts  are  distinguished 
by  the  word  which  follows  sal,  for  instance,  sal  petrce,  sal 
maris,  etc. ;  for  alkalies,  such  as  caustic  potash,  the  expression 
nitrum  alcalisatum  is  frequently  used.  One  seldom  meets 
in  the  alchemistic  age  with  a  strict  distinction  between 
potash  and  soda,  or  between  their  carbonates,  while,  on  the 
other  hand,  preparations  of  carbonate  of  potash  obtained  in 
different  ways  were  regarded  as  dissimilar  products.1 

This  acquaintance  with  the  carbonates  of  soda  and  potash 
was  accompanied  by  a  knowledge  of  the  lyes  obtained  from 
them  by  the  addition  of  lime,  the  strongly  alkaline  and  solvent 
power  of  these  lyes  being  largely  made  use  of,  e.g.  in  the  pre- 
paration of  milk  of  sulphur.  Tjhe  name  "  alkali "  is  first  met 
with  in  the  writings  ascribed  to  Geber,  while  the  designation 
"caustic"  had  been  already  employed  by  Dioscorides  for 
burnt  lime,  and  at  a  later  period  for  lyes.  The  question  of 
the  occurrence  of  alkalies  in  plants  was  frequently  discussed 
among  the  alchemists ;  although  it  did  not  escape  some  of 
them  that  different  amounts  of  ash  and  of  alkali  were  found 
in  different  parts  of  a  plant,  only  a  few  held  the  opinion 
that  the  alkali  was  really  present  in  the  plant  itself,  most  of 

1  The  salt  from  the  ashes  of  plants  was  termed  sal  vegetabile,  and  that 
from  tartar,  sal  tartari. 


if         SULPHURIC,  NITRIC,  AND  HYDROCHLORIC  ACIDS         51 

them  believing  that  it  was  first  produced  during  the  inciner- 
ation of  the  latter. 

It  was  formerly  taken  for  granted  that  the  Arabians 
possessed  a  very  considerable  knowledge  of  the  acids,  in  com- 
parison with  that  of  the  Ancients,  who  were  totally  unac- 
quainted with  the  mineral  acids.  This  assumption  was  based 
upon  the  fact  that  in  the  treatise  De  Inventione  Veritatis,  at- 
tributed to  Geber,  he  explained  the  method  of  obtaining 
nitric  acid  by  distilling  a  mixture  of  saltpetre,  copper  vitriol, 
and  alum  in  certain  proportions;  it  was  designated  aqua 
dissolutiva  or  aqua  fortis.  We  know  now,  however,  that  this 
manuscript  does  not  date  further  back  than  the  fourteenth 
century.  The  preparation  of  nitric  acid  from  saltpetre  and 
sulphuric  acid  was  known  to  alchemists  of  a  later  date ;  and 
we  find  Basil  Valentine  speaking  of  it  as  a  process  which  had 
been  in  operation  for  a  long  time. 

Sulphuric  acid  was  certainly  obtained  by  the  pseudo-Geber, 
for  he  mentions  as  noteworthy  that  when  alum  is  strongly 
heated,  a  spirit  distils  over  which  possesses  a  high  degree  of 
solvent  power ;  he  does  not,  however,  appear  to  have  investi- 
gated its  properties  more  closely.  The  writings  of  Basil 
Valentine  show  that  the  preparation  of  sulphuric  acid  by  dis- 
tilling a  mixture  of  iron  vitriol  and  pebbles,  and  also  by  setting 
fire  to  sulphur  after  the  addition  of  saltpetre  to  it,  was  known 
not  only  to  himself  but  also  to  his  predecessors.  An  aqueous 
solution  of  sulphurous  acid,  the  combustion  product  proper 
of  sulphur,  was  frequently  confounded  with  sulphuric  acid. 

Basil  Valentine  is  the  first  to  describe  the  preparation  of 
aqueous  hydrochloric  acid,  which  he  terms  spiritus  salis,  by 
heating  a  mixture  of  common  salt  and  green  vitriol,  and  also 
its  behaviour  towards  many  of  the  metals  and  their  oxides. 
He  likewise  knew  that  a  mixture  of  this  acid  with  aquafortis 
was  the  so-called  aqua  rrgis,  now  termed  aqua  regia,  which 
the  pseudo-Geber  had  already  made  use  of,  obtaining  it  by 
the  solution  of  salmiac  in  nitric  acid. 

Nitric  acid  and  aqua  regia l  (so-called  because  it  dissolved 

1  Albertus  Magnus  terms  them  respectively  aqua  prima  and  aqua 
stcunda. 

E    2 


52  THE  AGE  OF  ALCHEMY  CHAP. 

gold,  the  king  of  metals)  were  highly  prized  by  the  alchemists 
of  the  West.  The  observation  that  almost  nothing  was 
able  to  withstand  this  aqua  regia,  even  sulphur  being  "con- 
sumed" by  it,  strengthened  the  conviction  that  in  it  they 
possessed  a  liquid  which  very  nearly  approximated  to  the 
long-sought-for  "alkahest,"  the  universal  solvent.  On  the 
same  grounds  oil  of  vitriol  was  greatly  valued,  many  indeed 
regarding  it  as  the  sulphur  philosophorum,  or,  at  least,  as  a 
substance  which  would  lead  to  the  acquirement  of  the  materia, 
prima. 

Among  the  salts  which  were  already  known  in  Pliny's 
time,  and  whose  properties  were  carefully  investigated  by 
the  alchemists,  alum  and  some  of  the  vitriols  deserve  special 
mention,  the  former  being  obtained  in  various  places  from 
alum  shale.  The  pseudo-Geber  tells  us  how  to  purify  it  by 
recrystallisation  from  water,  and  terms  it  alumen  de  rocca 
(from  the  name  of  its  chief  source,  the  town  Roccha),  a  term 
which  long  remained  in  vogue  in  France  as  alun  de  roche. 
The  fact  that  alum  contained  an  alkaline  salt  was  overlooked, 
and  its  true  composition  remained  unknown.  Iron  and 
copper  vitriols  were  lagely  employed  in  different  chemical 
operations.  The  pseudo-Geber  describes  the  preparation  of 
the  pure  products  by  crystallisation,  and  Basil  Valentine  the 
production  of  iron  vitriol  by  dissolving  iron  in  sulphuric 
acid,  a  method  which  indicated  the  composition  of  the  salt, 
although  he  did  not  explain  this  correctly. 

The  important  salts,  saltpetre,  salmiac  and  carbonate  of 
ammonia,  first  became  known  and  used  for  chemical  purposes 
in  the  alchemistic  period.  The  author  of  the  works  ascribed 
*^to  Geber  was  well  acquainted  with  potash  saltpetre,  as  it 
served  him  for  the  preparation  of  nitric  acid ;  and  there  is 
every  reason  to  suppose  that  it  was  used  in  even  earlier 
times  for  the  production  of  fire-works  and  such  like  things, 
after  its  property  of  deflagrating  with  red-hot  carbon  had 
oeeu  recognised.  The  oldest  designations  for  it  were  sal 
Vetrce  and  sal  petrosum.  Ray m und  Lully  also  termed  it  sal 
nitri,  but  distinguished  between  it  and  nitram,  the  fixed 
alkali  of  the  older  writers;  in  the  sixteenth  century  this 


ii  SALTS  OF  AMMONIA  AND  OF  THE  METALS  53 

latter  word  was  converted  into  natron,  while  the  name  nitrum 
was  given  to  potash  saltpetre. 

The  same  applies  to  the  term  salmiac,  sal  ammoniacum, 
as  to  that  of  nitrum,  in  so  far  that  both  of  them  had  originally 
a  different  meaning  from  what  they  now  possess ;  for  the  sal 
ammoniacum  of  the  Ancients  was  without  doubt  rock-salt. 
At  the  time  when  the  pseudo-Geber's  works  were  written, 
on  the  other  hand,  this  name,  which  is  also  metamorphosed 
into  sal  armeniacum  (Armenian  salt),  could  only  mean 
salmiac.  The  sal  armoniacum  of  Basil  Valentine  led  to  the 
contraction  salmiac.  At  first  this  salt  appears  to  have  been 
partly  prepared  from  dung,  and  partly  to  have  been  found 
as  a  natural  product  of  volcanic  origin. 

Carbonate  of  ammonia,  well  known  to  the  alchemists  of 
the  thirteenth  century  as  volatile  alkaline  salt  (spiritus  urince) 
was  obtained  by  distilling  putrefied  urine.  Basil  Valentine 
taught  how  to  prepare  it  from  salmiac  and  fixed  (carbonated) 
alkali,  a  method  which  led  a  long  time  afterwards  to  the 
proper  recognition  of  the  composition  of  the  salt.  The 
pharmaceutical  use  of  these  two  ammonia  compounds,  just 
named,  probably  belongs  to  a  later  date. 

The  knowledge  of  the  metallic  salts  was  very  decidedly 
increased  during  the  alchemistic  period.  A  special  interest 
attached  to  a  solution  of  gold  in  aqua  regia,  since  from  this 
aurum  potabile  the  most  wonderful  medicinal  effects  were 
expected.  The  pseudo-Geber  was  the  first  to  become 
acquainted  with  nitrate  of  silver  in  the  crystalline  state,  and 
to  observe  the  precipitation  of  its  solution  by  one  of  common 
salt,  a  reaction  which  came  to  be  applied  as  a  test  both  for 
silver  and  for  salt.  The  alchemists  were  also  aware  of  the  \ 
beautiful  precipitation  of  metallic  silver  from  a  solution  of  its  J 
nitrate  by  means  of  mercury  or  copper. 

Compounds  of  mercury  early  attracted  the  interest  of 
those  who  carried  out  chemical  operations.  The  pseudo-Geber 
described  the  preparation  of  mercuric  oxide  by  calcining  the 
metal,  and  that  of  sublimate  (mercuric  chloride)  by  heating 
a  mixture  of  mercury,  common  salt,  alum  and  saltpetre ;  he  also 


54  THE  AGE  OF  ALCHEMY  CHAP. 

taught  how  to  prepare  various  amalgams.1  Basil  Valentine 
was  acquainted  with  basic  mercuric  sulphate,  and  also  with 
mercuric  nitrate.  Being  an  advocate  of  heroic  treatment, 
he  recommended  the  medicinal  use  both  of  the  latter  and  of 
sublimate. 

Preparations  of  zinc  and  bismuth  (e.g.  zinc  vitriol)  were 
well  known  towards  the  end  of  the  fifteenth  century,  but 
detailed  records  are  wanting  both  of  their  formation  and 
their  properties.  Antimony  and  its  compounds,  on  the  other 
hand,  were  the  object  of  unwearied  labours  on  the  part  of 
Basil  Valentine,  as  his  treatise  Triumphwagen  des  Antimonii 
("  Triumphal  Car  of  Antimony  ")  sufficiently  testifies.  He 
shows  how  to  prepare  antimony  itself  from  the  native 
sulphide  (which  was  termed  antimonium  or  stibium  and  was 
known  to  the  Ancients),  by  fusing  it  with  iron.  In  his 
treatise,  WiederJiolung  des  grossen  Steins  der  Uralten  Weisen 
("  Recovery  of  the  Great  Stone  of  the  Ancient  Philosophers  ") 
he  writes :  "  If  one  adds  some  iron  to  the  fused  Spiessglas,2 
there  is  produced  by  a  particular  manipulation  a  curious 
star,  which  the  wise  men  before  me  called  the  signet  star  of 
philosophy."  Basil  Valentine  was  well  aware  that  antimony 
did  not  possess  the  properties  of  a  metal  in  full  degree,  and 
so  he  regarded  it  as  a  variety  of  one,  especially  as  a  variety  of 
lead;  he  sometimes  talks  of  it  as  the  lead  of  antimony. 
Even  in  his  time  antimony  was  employed  for  alloys,  which 
served  for  the  manufacture  of  printer's  type,  mirrors  and 
bells.  It  did  not  escape  him,  either,  that  Spiessglas  con- 
tained sulphur,  and  he  was  also  acquainted  with  amorphous 
sulphide  of  antimony  and  sulphur  auratum  (a  mixture  of 
Sb2S3  and  Sb2S5).  He  gives  distinct  recipes  for  the  prepara- 
tion of  antimony  trichloride  (butter  of  antimony),  of  powder 
of  algaroth  (basic  chloride  of  antimony),  of  antimony  trioxide, 

1  This  word  is  first  found  in  the  writings  of  Thomas  Aquinas.     The  part 
played  by  amalgams  in  the  transmutation   of  metals  has  been  already 
considered. 

2  This  designation  of  Basil  Valentine's  for  native  sulphide  of  antimony 
became  altered  later  on  into  Spiessglanz. 


ii  METALLIC  OXIDES  ;   SULPHUR  55 

and  of  potassic  antimoniate,  and  there  can  hardly  be  a  doubt 
that  he  recommended  and  applied  those  preparations  for 
internal  use.  With  regard  to  the  composition  of  these,  he 
only  appears  to  have  had  a  tolerably  clear  idea  of  that  of 
the  sulphide. 

Arsenic,  which  is  so  closely  allied  chemically  to  antimony, 
and  with  whose  sulphides  the  Ancients  were  acquainted,  was 
first  prepared  by  the  Western  alchemists  in  the  thirteenth 
century ;  Basil  Valentine  regarded  it  as  a  "  bastard  metal  " 
analogous  to  antimony.  Arsenious  acid  is  first  distinctly 
spoken  of  by  the  pseudo-Geber,  having  been  obtained  by  the 
roasting  of  realgar ;  it  was  known  as  white  arsenic,  in  contra- 
distinction to  the  red  and  yellow  varieties  (realgar  and 
orpiment).  Its  occurrence  in  the  smoke  from  pyrites  burners 
was  also  noticed  by  the  observant  Basil  Valentine.  Mention 
has  already  been  made  of  the  important  part  which  was  played 
in  alchemistic  operations  by  the  property  which  arsenic  pos- 
sessed of  turning  copper  white;1  indeed,  this  contributed 
materially  to  the  belief  in  the  possibility  of  the  transmutation 
of  copper  into  silver. 

In  addition  to  the  metallic  oxides  which  have  been 
already  spoken  of  (those  of  mercury,  antimony,  etc.),  and  the 
early  known  oxide  of  copper  and  oxides  of  lead  (PbO  and 
Pb3O4),  oxide  of  zinc  and  peroxide  of  iron  may  be  specially 
mentioned.  The  former  of  these,  which  separated  in  woolly 
flakes  when  zinc  was  burnt,  and  which  was  therefore  termed 
lana  philosophica,  appears  to  have  been  known  to  Dioscorides, 
but  it  is  in  the  alchemistic  period  that  we  first  come  across 
an  intimate  acquaintance  with  it.  The  alchemists  of  the 
Middle  Ages  were  familiar  with  peroxide  of  iron  in  the 
different  forms,  red  and  yellow ;  the  designation  colcothar,  for 
the  ignited  oxide,  is  to  be  found  for  the  first  time  in  Basil 
Valentine's  writings. 

The  theoretical  importance  which,  from  early  times,  was 
ascribed  to  sulphur  as  a  constituent  of  the  metals,  and  also  of 
other  bodies,  leads  to  the  question — How  was  the  actual  know- 

1  On  account  of  this  behaviour,  the  pseudo-Geber  calls  arsenic  medicina 
Venerem  decdbans. 


56  THE  AGE  OF  ALCHEMY  CHAP. 

ledge  of  this  element  and  of  its  compounds  acquired  ?  The 
property  possessed  by  sulphur  of  dissolving  in  aqueous  alkalies, 
and  of  being  thrown  down  from  such  a  solution  as  sulphur  milk 
upon  the  addition  of  acids,  is  described  by  the  pseudo-Geber 
in  his  treatise  De  Inventions  Yeritatis  ;  the  disappearance  of 
sulphur,  when  acted  upon  by  aqua  regia,  was  likewise  re- 
garded as  solution.  Basil  Valentine  is  the  first  to  give 
definite  details  regarding  flowers  of  sulphur,  and  also  re- 
garding the  taking  up  of  the  element  by  many  oils,  a 
property  upon  which  the  preparation  of  sulphur  balsam 
depended. 

Mention  has  already  been  made  of  various  sulphur  com- 
pounds, the  sulphides  of  mercury  and  antimony  among  others 
which  were  the  most  valuable  materials  for  the  production 
not  only  of  sulphur  itself,  but  also  of  other  bodies.  These 
had  already  been  grouped  together  as  forming  a  particular 
variety  of  compounds,  under  the  name  oimarcasitce  (Albertus 
Magnus),  zinc  blende,  galena,  and  iron  and  copper  pyrites 
being  included  among  them.  The  peculiarity,  which  these 
substances  had  in  common,  of  giving  off  a  product  of  such 
characteristic  odour  as  sulphurous  acid  when  roasted,  may 
not  unlikely  have  formed  the  main  reason  for  thus  gathering 
them  into  one  group.  It  must  not  be  forgotten,  how- 
ever, that  the  formation  of  several  metallic  sulphides  from 
their  components  had  been  observe^,  (e.g.  that  of  cinnabar 
from  quicksilver  and  sulphur),  and  this  may  be  supposed 
to  have  contributed  materially  to  a  knowledge  of  their 
composition. 

In  spite  of  many  unequivocal  observations  to  the  con- 
trary, people  still  held  to  the  assumption  that  the  metals 
and  almost  all  other  substances  contained  sulphur.  Organic 
bodies,  too,  had  to  conform  to  this  hypothesis;  their  real 
constituents  remained  hidden,  no  sharp  general  distinction 
being  drawn  between  them  and  inorganic  compounds.  The 
meagre  attempts  made  to  explain  the  formation  of  organic 
substances,  e.g.  in  fermentation  processes,  only  give  evidence 
of  confused  and  untenable  views.  The  organic  preparations 
which  were  known  in  the  alchemistic  age  were  but  few  in 


ii  SPIRIT  OF  WINE,  VINEGAR,  ETC.  57 

number.  Among  them  spirit  of  wine l  takes  a  prominent 
place,  its  manufacture  being  gradually  simplified  and  im- 
proved after  more  perfect  apparatus  had  been  introduced  by 
the  Alexandrians.  In  accordance  with  its  importance  for 
medicinal  and  alchemistic  purposes,  it  was  usually  termed  aqua 
vitce,  the  name  alcohol  being  first  met  with  in  Libavius  (end 
of  the  sixteenth  century).  The  preparation  of  concentrated 
spirit  of  wine — as  an  excellent  solvent  for  many  things — by 
repeated  distillation,  and  also  by  dehydration  with  fused 
potashes,  was  already  known  to  Raymund  Lully.  To  test  its 
strength,  Basil  Valentine  recommends  that  a  portion  be 
burnt,  in  order  to  see  whether  any  water  remains  behind  or 
not.  The  latter  alchemist  was  also  acquainted  with  various 
chemical  transformations  of  alcohol,  although  he  did  not 
obtain  the  resulting  compounds  in  a  state  of  purity ;  among 
these  were  the  production  of  common  ether  by  the  action  of 
sulphuric  acid,  and  of  nitric  and  hydrochloric  ethers  by  the 
action  of  nitric  and  hydrochloric  acids  respectively.  By  the 
"  sweetening  "  ( Versilssung)  of  alcohol  is  to  be  understood 
our  term  etherification.  That  alcohol  is  only  formed  during 
the  various  processes  of  fermentation,  which  yield  wine,  beer 
and  spirits,  was  not  perceived  even  by  the  most  acute  ob- 
servers of  that  time;  its  pre-existence  in  unfermented 
materials  was  thus  taken  for  granted. 

Increasing  attentio..  was  likewise  paid  to  the  product  of 
the  acetic  fermentation.  The  alchemists  of  the  later  Middle 
Ages  taught  how  to  concentrate  vinegar  by  distillation,  and 
they  also  prepared  various  salts  of  acetic  acid,  e.g.  basic 
acetate  and  sugar  of  lead.  Other  organic  acids,  too,  were 
noticed  in  different  plant  juices,  but  they  were  mostly  mis- 
taken for  acetic  acid.  The  addition  to  the  medical  treasury 
of  various  resins  and  oils,  especially  ethereal  oils,  which  were 
obtained  from  plants  by  distillation  in  improved  apparatus, 

1  Berthelot  (Ann.  Chim.,  (6),  vol.  xxiii.,  p.  433)  has  traced  with  great 
care  the  history  of  the  discovery  of  spirit  of  wine,  and  has  found  that  the 
preparation  of  alcohol  by  distilling  wine  was  accurately  known  so  far  back 
as  the  time  of  Marcus  Graecus  (eighth  century,  A.D.). 


58  THE  AGE  OF  ALCHEMY  CHAP. 

is  no  evidence  of  scientific  progress;  this  really  begins  for 
organic  chemistry  with  the  discovery  of  methods  for  arriving 
at  the  composition  of  organic  compounds. 


The  Fortunes  of  Alchemy  during  the  last  Four  Centuries. 

After  the  labours  of  Basil  Valentine,  and  especially  after 
the  beginning  of  the  iatro-chemical  period,  alchemy  gradu- 
ally became  separated  from  chemistry,  which  was  raising 
itself  to  the  rank  of  a  science.  Although,  therefore,  a  record 
of  the  alchemistic  aims  or  rather  errors  of  the  last  few  centuries 
does  not  properly  come  within  the  scope  of  a  short  history 
of  chemistry,  they  cannot  be  passed  over  in  complete  silence  ; 
the  justification  for  this  lies  in  the  relations  in  which  the  most 
eminent  chemists  of  the  sixteenth  and  seventeenth  centuries 
stood  with  regard  to  alchemy.  The  support  given  by  such 
men  to  the  latter  undoubtedly  accounts  to  a  large  extent 
for  the  belief  in  the  transmutation  of  metals  as  an  incon- 
trovertible fact  being  but  seldom  affected,  and  this,  notwith- 
standing the  great  increase  in  chemical  knowledge.  Another 
effective  means  by  which  the  life  of  alchemy  was  prolonged, 
consisted  in  the  favour  with  which  it  was  regarded  by  many 
princes;  the  seductive  prospect  of  easily  acquired  treasure 
often  rendered  the  latter  a  prey  to  designing  alchemists. 

The  actual  decay  of  alchemy,  for  which  the  numberless 
disappointments  of  honest  workers  and  the  exposure  of 
numerous  frauds  paved  the  way,  may  be  dated  from  the  first 
half  of  the  eighteenth  century,  when  the  conviction  of  the 
practicability  of  transmuting  metals  began  to  die  out  among 
most  chemists.  Even  up  to  the  present  century,  however, 
we  find  able  and  educated  men  in  the  thralls  of  alchemistic 
chimeras,  and  directly  opposing  the  simplest  rules  of 
reason. 

A  distinction  must  be  drawn  during  the  iatro-chemical 
period  between  alchemists  and  chemists,  inasmuch  as  the 
latter  aimed  at  the  solution  of  a  scientific  problem,  viz.  the 


ii         ALCHEMY  DURING  THE  LAST  FOUR  CENTURIES          59 

knowledge  of  the  relations  between  chemistry  and  medicine. 
At  the  same  time  this  distinction  must  not  be  taken  as 
meaning  that  the  most  eminent  among  the  iatro-chemists 
were  not  firmly  convinced  that  the  ennobling  of  metals  was 
a  fact,  indeed  some  of  them  maintained  that  they  were  in 
possession  of  the  most  powerful  alchemistic  specifics ;  it  was 
but  seldom,  however,  that  chemists  were  at  the  same  time 
practical  alchemists. 

Paracelsus,  who  was  greatly  given  to  romantic  exaggera- 
tions, claimed  for  himself  the  widest  knowledge  of  alchemy. 
Van  Helmont,  whose  authority  was  especially  weighty,  went 
so  far  as  to  describe  in  detail  the  transmutation  of  mercury 
into  gold  and  silver,  as  effected  by  himself  with  the  aid 
of  a  very  small  quantity  of  a  gold-  and  silver-producing  philo- 
sopher's stone.  The  opinion  -held  by  the  highly  esteemed 
Libavius  respecting  alchemy  and  what  it  could  effect  is 
equally  significant  of  the  judgment  of  that  period  upon  the 
subject ;  he  regarded  the  transmutation  of  metals  as  an 
accomplished  fact.  Other  influential  physicians  of  the  six- 
teenth century,  such  as  Agricola — famed  as  an  observant  and 
accomplished  metallurgist, — Sennert,  and  Angelus  Sal  a,  were 
more  cautious  in  their  assertions  with  respect  to  alchemy, 
but  they  never  seriously  contended  against  the  possibility 
of  transmutation.  Tachenius  alone,  the  last  iatro-chemist 
of  note,  took  up  a  sceptical  position  with  regard  to  the 
alchemistic  problem ;  he  considered  the  evidence  adduced  in 
favour  of  the  ennobling  of  metals  as  insufficient,  notwith- 
standing that  his  famous  teacher  Sylvius  had  given  himself 
up  unreservedly  to  the  belief  in  their  transmutation. 

The  power  of  this  belief  was  still  so  great  at  that  time, 
when  the  phlogistic  period  was  just  beginning  and  chemistry 
was  striving  to  develop  itself  independently,  that  it  took 
firm  root  in  the  minds  of  even  the  most  discerning  men, 
with  Boyle  at  their  head.  The  latter  was  firmly  convinced 
of  the  possibility  of  transmuting  individual  metals  into  one 
another,  as  were  also  many  of  his  contemporaries  and 
successors,  e.g.  Glauber,  Homberg,  Kunkel,  Stahl  and  Boer- 
have,  of  whose  earnest  desire  to  arrive  at  the  truth  there 


60  THE  AGE  OF  ALCHEMY  CHAP. 

can  be  no  doubt  whatever.  That  the  wished-for  goal  was 
never  reached  in  spite  of  the  most  unwearied  efforts,  did  not 
shake  their  belief  in  the  correctness  of  the  assumptions  of 
alchemy ;  Stahl  alone  began  to  doubt  these  towards  the 
end  of  his  life,  and  warned  his  brethren  against  alchemistic 
frauds.  The  vitality  of  the  belief  in  transmutation  depended 
chiefly  on  the  theoretical  opinions  which  these  men  held  re- 
garding the  composition  of  metals ;  the  primal  error  of  the 
pseudo-Geber  and  his  disciples  was  thus  propagated  for 
centuries  through  the  alchemistic  age. 

Boerhave  was  the  last  distinguished  chemist  to  support 
with  his  great  authority  some  of  the  alchemistic  views, 
while  he  failed  to  criticise  others  of  the  fraudulent  asser- 
tions with  sufficient  sharpness.  After  his  time  no  notable 
exponent  of  chemistry — which  had  now  attained  to  the 
rank  of  a  science — spoke  in  their  favour;  but  all  the 
greater  was  the  number  of  cheats  and  swindlers  who  culti- 
vated the  lucrative  field  of  gold-making  even  during  the 
eighteenth  century.  The  conviction  of  the  impossibility  of 
transmutation,  which  was  at  that  time  establishing  itself 
among  scientific  chemists,  made  its  way  but  slowly  into 
outer  circles.  Credulity,  and  the  hope  of  obtaining  riches 
for  nothing,  were  the  means  of  leading  many  into  very 
doubtful  paths  even  so  late  as  the  end  of  last  century  and 
the  beginning  of  this  one.1  The  final  echoes  of  the  alche- 
mistic problem,  which  had  for  so  long  a  period  of  time 
held  the  cultured  of  every  nation  in  a  state  of  tension,  and  had 
even  blinded  eminent  scientific  men,  only  appear  to  die 
away  during  the  last  decades  of  our  own  century. 

Seeing  the  marvellous  results  which  alchemy  produced, 
it  is  but  natural  to  inquire  more  closely  into  the  supposed 
evidence  in  favour  of  the  ennobling  of  metals,  and  to  ask 
what  kind  of  observations  led  to  this  being  regarded  as  a 
matter  of  fact.  If  most  weight  is  to  be  laid  upon  the 

1  For  details  on  these  points,  especially  for  an  account  of  the  interesting 
relations  of  the  Rosicrucians  to  alchemy,  and  of  secret  alchemistic  as- 
sociations, etc.,  see  H.  Kopp's  Die  Alchemie  in  dlterer  und  neuerer  Zeit,  a 
book  which  gives  us  a  clear  insight  into  the  workings  of  the  alchemists. 


ii  POWER  OF  THE  PHILOSOPHER'S  STONE  61 

statements  of  men  who  had  established  their  claim  as 
practised  observers,  then  first  place  must  be  given  to  the 
records  of  the  great  physician  and  chemist  van  Helmont 
(towards  the  middle  of  the  seventeenth  century),  respecting 
transmutation  as  carried  out  by  himself;  these  records 
afford  the  most  remarkable  testimony  to  the  power  of  alche- 
mistic  illusions.  Van  Helmont  had  received  from  an 
unknown  source  a  small  specimen  of  the  philosopher's  stone, 
and  with  this  he  states  that  he  transformed  several  portions 
of  mercury  into  pure  gold,  giving  the  exact  proportions 
by  weight ;  one  part  of  this  preparation  sufficed  to  trans- 
mute 2000  parts  of  mercury. 

Soon  after  the  death  of  van  Helmont,  Helvetius,  body- 
physician  to  the  Prince  of  Orange,  published  a  detailed 
account  of  the  transmutation  of  lead  into  gold,  by  means  of 
a  trifling  quantity  of  a  preparation  which  had  come  to  him 
from  the  hand  of  a  stranger.  It  appeared  impossible  to 
doubt  the  testimony  of  such  men,  who  were  held  in  high 
esteem  by  all  the  scientific  investigators  of  that  time. 

More  palpable  proof  of  the  actual  transmutation  of  metals 
was  held  to  be  furnished  by  the  coins  or  ornaments  prepared 
from  alchemistic  gold  up  to  and  in  the  eighteenth  century.1 
The  evidence,  which  came  for  the  most  part  too  late,  that 
these  consisted  of  worthless  alloys  (e.g.  bronze  gilt  over), 
was  all  too  soon  forgotten.  The  findings  of  courts  of  justice, 
too,  in  favour  of  alchemistic  operations,  were  looked  upon  as 
proofs  of  transmutation  having  been  actually  accomplished. 

As  has  been  already  mentioned,  a  large  number  of 
German  princes  gave  unremitting  support  to  the  efforts  of 
the  alchemists,  being  induced  to  do  so  by  the  hope  of  large 
gains.  Many  of  them  worked  zealously  at  transmutation 
themselves,  among  others  John,  Burgrave  of  Niirnberg,  who 
received  the  surname  of  "  the  Alchemist " ;  the  Emperor 
Rudolph  II.,  the  most  powerful  protector  of  the  makers  of 
gold;  the  Elector  Augustus  of  Saxony,  the  Elector  John 
George  of  Brandenburg,  etc.  etc.  The  courts  of  these 
princes  were  the  field-grounds  of  adepts,  who  for  long 
1  Cf.  H.  Kopp's  Alchemic,  vol.  i.,  p.  90,  et  seq. 


62  THE  AGE  OF  ALCHEMY  CHAP. 

succeeded,  by  means  of  clever  experiments,  in  maintaining  a 
belief  in  their  art  among  these  Maecenases,  until,  as  usually 
happened,  they  were  unmasked  as  cheats  and  generally 
severely  punished,  after  having  been  the  cause  of  excessive 
expenditure  on  the  part  of  their  patrons. 

It  is  impossible  to  enter  here  into  details  of  the 
romantic  lives  of  alchemists  like  Leonhard  Thurneysser, 
physician  at  the  court  of  John  George  of  Brandenburg, 
Sendivogius,  Caetano  (on  whom  the  title  of  Count  was 
bestowed),  St.  Germain,  Cagliostro,  etc.  The  two  last  named 
lived  at  a  time  when  chemistry  was  strong  enough  as  a 
science  to  protect  itself  against  the  frauds  of  alchemy.  The 
opposition  to  the  latter  which  was  raised  in  the  course  of 
the  preceding  century  by  chemists  of  repute,  e.g.  Geoffroy 
the  elder  (the  earlier  warnings  of  Erasmus  of  Rotterdam, 
Athanasius  Kircher  and  Palissy  having  had  no  effect),  led 
to  its  ultimate  fall,  which  even  the  amalgamation  of  alche- 
mistic  aims  with  those  of  the  secret  societies  (Rosicrucians, 
Illuminates,  etc.)  was  powerless  to  retard.  The  belief  in 
the  possibility  of  the  transmutation  of  metals  received  its 
actual  deathblow  from  the  new  chemistry  which  began  with 
Lavoisier.1  At  the  same  time,  however,  (i.e.  about  the  year 
1790),  the  Hermetic  Society  endeavoured  to  foster  and  main- 
tain the  alchemistic  illusion  in  Germany.  It  has  only  recently 
come  to  light  that  the  leaders  of  this  undertaking  were. 
Kortum  (the  poet-author  of  the  Jobsiade  and  a  practising 
physician  in  Bochum,  Westphalia)  and  a  Dr.  Bahrens, 
a  clergyman.  But  Wiegleb,  a  chemist  and  pharmacist  of 
merit,  combated  those  belated  efforts  with  entire  success. 

The  melancholy  errors  which  arose  from  the  introduction 
of  the  mystical  religious  element  into  alchemy  can  but  be 
indicated  here ;  the  assertion,  frequently  made  by  adepts, 

1  Schmieder,  who  published  a  history  of  alchemy  in  1832  (in  Halle),  did 
not  hesitate  to  accept  the  transmutation  of  metals  as  having  been  actually 
accomplished  by  various  adepts.  He  expresses  himself  with  more  caution 
regarding  the  assumed  efficacy  of  the  philosopher's  stone  as  a  medicine  and 
a  means  of  prolonging  life.  Even  in  quite  recent  times  we  find  the  study 
of  alchemy  carried  on,  ostensibly  with  result,  e.g.,  in  Paris  in  1844  (cf. 
Baudrimont,  Traite  de  Chimie,  vol.  i. ). 


ii         GENERAL  EFFECT  OF  ALCHEMY  ON  CHEMISTRY          63 

that  the  secret  of  making  gold  was  revealed  to  them  through 
the  grace  of  God,  only  excites  feelings  of  repugnance.1 
Other  frauds,  which  were  likewise  the  products  of  alchemistic 
effort  during  the  eighteenth  century,  to  go  no  further  back, 
merely  provoke  satire ;  among  these  may  be  mentioned  the 
endeavours  to  prepare  from  the  air  the  so-called  ' '  substance 
of  shooting  stars  "  (the  alga  Nostoc  commune,  which  is  found 
in  wet  ground,  was  so  regarded),  and  the  materia  prima 
from  "air-salt." 

The  benefits  which  have  accrued  to  chemistry  during 
the  last  four  centuries  from  the  mania  for  producing 
gold  from  the  base  metals,  can  only  be  estimated  as  very 
slight.  It  was  but  very  seldom  that  a  discovery  of  technical 
importance,  like  that  of  the  making  of  porcelain  by  Bottger, 
sprang  from  alchemistic  work.  On  the  other  hand,  it  did  a 
vast  amount  of  harm  during  that  period,  for  it  crippled  the 
usefulness  of  many  able  men  who  would  undoubtedly 
have  advanced  science  had  they  not  been  influenced  by 
chimeras  of  an  exciting  nature ;  as  it  was,  they  were  led 
away  into  the  most  tortuous  paths. 

We  are  thus  forced  to  the  above  unfavourable  criticism 
of  the  work  of  the  alchemists  on  their  problem  of  the 
transmutation  of  metals,  in  spite  of  the  striking  and 
seemingly  incontestable  evidence  in  favour  of  the  latter ;  in 
spite,  also,  of  a  strong  inclination  at  the  present  time  to  a 
belief  in  the  mutual  convertibility  of  elements  chemically 
similar — a  belief  grounded  upon  speculations  which  do  not 
seem  to  be  without  foundation.  But  in  no  single  case,  as 
yet,  has  there  been  any  positive  evidence  brought  forward  in 
support  of  this  idea. 

If,  therefore,  we  review  the  work  of  the  alchemists  during 

1  Had  such  misuse  of  the  name  of  God  and  of  the  Bible  been  made  in 
the  time  of  Luther,  as  was  later  the  case,  or  had  he  been  aware  of  it,  his 
opinion  of  alchemy  would  have  been  a  much  lower  one  ;  as  a  matter  of  fact 
he  valued  it  because  of  its  bearing  upon  religious  feeling.  In  contradis- 
tinction to  this  stands  Melanchthon's  criticism  of  alchemy,  a  criticism 
which  testifies  to  the  sobriety  of  his  judgment  (he  called  it  imposturam 
qvandam  sophisticam). 


64  THE  AGE  OF  ALCHEMY  CHAP,  n 

the  last  fifteen  centuries,  we  arrive  at  the  conclusion  that  it 
was  based  upon  a  series  of  falsely  interpreted  chemical 
problems.  The  expectation  of  the  easy  acquirement  of 
boundless  riches,  the  auri  sacra  fames  to  which  it  led,  formed 
the  powerful  stimulus  to  the  useless  and  yet  continually 
renewed  efforts  of  an  unsatisfied  mankind. 


CHAPTER  III 
HISTORY  OF  THE  IATRO-CHEMICAL  PERIOD 

INTRODUCTION. — Traditional  belief,  which  dominated  every 
branch  of  science  during  the  Middle  Ages,  exercised 
its  power  not  least  in  the  domain  of  alchemy,  for  almost 
every  one  engaged  in  chemical  pursuits  was  deluded  by 
the  idea  that  gold  and  other  bodies  could  be  artificially 
prepared.  In  the  course  of  the  fifteenth  century,  however, 
this  yoke,  which  had  hindered  the  development  of  free 
inquiry,  was  in  many  quarters  cast  off.  The  sciences, 
hitherto  studied  almost  alone  in  the  cloister,  now  found  a 
foothold  in  the  universities  of  France,  England,  Germany 
and  other  countries,  which  were  then  both  increasing  in 
number  and  expanding  rapidly ;  the  free  interchange  of 
ideas  among  these  seats  of  learning  rendered  a  development 
of  the  sciences  possible,  as  it  had  never  been  before.  That 
the  discovery  and  spread  of  the  art  of  printing  contributed 
materially  to  this,  hardly  requires  to  be  stated;  for  new 
ideas,  which  were  opposed  to  those  prevalent  up  till  then, 
and  which  had  hitherto  been  restricted  to  a  narrow  circle, 
became  quickly  disseminated  by  its  aid.  Any  one  could 
inform  himself  as  to  the  range  of  any  particular  science  by 
means  of  the  encyclopedias  and  special  memoirs  which  were 
being  printed  in  increasing  numbers.  As  a  consequence  of 
this,  the  capacity  for  independent  criticism  spread,  one  of 
the  most  effectual  of  remedies  against  the  domination  of 
the  scholastics  being  thereby  created.  A  further  aid  to 
controverting  scholastic  principles  was  found  in  the  in- 

F 


THE  IATRO-CHEMICAL  PERIOD  CHAP. 


ductive  method,  then  gradually  forcing  itself  forward,  by 
means  of  which  the  experimental  sciences  were  called  into 
life. 

In  addition  to  these  impulses  of  a  freer  spirit,  chemistry 
received  a  powerful  impetus  from  the  increase  in  scientific 
knowledge  which  resulted  from  the  discovery  of  the  New 
World  and  of  the  ocean  route  to  the  East  Indies.  All  these 
events  testified  to  the  birth  of  a  new  era,  which  found 
its  most  powerful  expression  in  the  works  of  the  Reforma- 
tion. 

At  that  time  chemistry  strove  to  free  itself  from  the 
exclusive  domination  of  the  alchemistic  idea.  And  even 
although  the  latter  was  not  totally  supplanted,  still  another 
aim  came  into  prominence,  an  aim  to  which  a  scientific 
character  could  not  be  denied ;  the  chemical  knowledge  of 
that  day  was,  however,  so  very  imperfect  that  a  solution  of 
this  new  problem  was  not  to  be  expected.  Chemistry  was, 
in  fact,  to  be  intimately  conjoined  with  medicine ;  each  (so 
many  opined)  was  to  help  the  other.  The  chemist  was  to 
discover  the  medicines,  prepare  them  carefully,  and  investi- 
gate them  chemically,  while  the  physician  was  to  examine 
and  explain  their  action ;  or,  better  still,  both  things  were  to 
be  united  in  one  person.  The  mutual  interaction  of  chemistry 
and  medicine  is  the  main  idea  which  runs  through  the  iatro- 
chemical  age,  and  which  gives  to  the  latter  its  own  particular 
stamp. 

What  benefit,  then,  accrued  to  both  of  them  from  this  ? 
The  answer  is,  a  mutual  enrichment,  which  did  almost  more 
for  chemistry  than  for  medicine  :  for  the  former  was  raised 
to  a  higher  level  through  being  transferred  from  the  hands 
of  laboratory  workers,  who  were  mostly  uneducated,  to  those 
of  men  belonging  to  a  learned  profession  and  possessing  a 
high  degree  of  scientific  culture.  The  iatro-chemical  age 
thus  formed  an  important  period  of  preparation  for  chemistry, 
a  period  during  which  the  latter  so  extended  her  province  that 
she  was  enabled  in  the  middle  of  the  seventeenth  century  to 
stand  forth  as  a  young  science  by  the  side  of  her  elder  sister 
physics.  That  period  was  for  chemistry  an  apprenticeship  in 


in  LIFE  AND  WORK  OF  PARACELSUS  67 

the  fullest  sense  of  the  word,  during  which  she  laboriously 
acquired  the  capacity  to  see  that  the  iatro-chemical  doctrines 
were  untenable,  and  to  apply  herself  to  her  true  vocation. 


GENERAL  HISTORY  OF  THE  IATRO-CHEMICAL  PERIOD 
AND  PARTICULARLY  OF  ITS  THEORETICAL  VIEWS.1 

The  main  currents  of  the  iatro-chemical  age  emanated 
from  Paracelsus,  van  Helmont  and  de  le  Boe  Sylvius,  with 
whose  name  must  be  coupled  that  of  his  most  distinguished 
pupil,  Tachenius,  their  doctrines  being  spread  by  schools 
of  greater  or  lesser  importance.  Besides  these  there  were 
some  men  who  worked  independently,  or  who  at  least  did 
not  entirely  subordinate  themselves  to  their  authority,  of 
whom  Libavius,  Glauber  and  Sala  may  be  mentioned.  Other 
men  like  Agricola,  Palissy,  etc.,  employed  their  energies  in 
a  totally  different  direction,  giving  all  their  attention  to 
technical  chemistry. 

Paracelsus  and  his  School.2 — Paracelsus  was  the  man 
who,  in  the  first  half  of  the  sixteenth  century,  opened  out 
new  paths  for  chemistry  and  medicine  by  joining  them 
together.  To  him  is  undoubtedly  due  the  merit  of  freeing 
chemistry  from  the  restrictive  fetters  of  alchemy,  by  a  clear 
definition  of  scientific  aims.  He  taught  that  "  the  object 
of  chemistry  is  not  to  make  gold  but  to  prepare  medicines." 
True,  chemical  remedies  had  been  employed  now  and  again 
before  his  time,  Basil  Valentine  in  particular  having  sug- 
gested their  use  ;  but  Paracelsus  differed  from  his  predecessor 
in  the  theoretical  motives  which  led  him  to  employ  them. 

1  Cf.  Kopp,  Geschichte  der  Chemie,  vol.  i.  p.  84. 

2  The  recent  researches  upon  Paracelsus — more  especially  Fr.  Mook's 
Theophrastus  Paracelsus  (Wurzburg,  1876)  ;  E.  Schubert  and  K.  Sudhoff's 
Paracelsus- Forschungen  (Frankfurt,  1887-9)  ;  and  Aberle's  Grabdenkmat, 
Schddel  und  Abbildungen  des  Theophrastus  Paracelsus,  etc.  (Salzburg,  1891) 
("The  Gravestone,  Skull,  and  Portraits  of  Theopbrastus Paracelsus,  etc.") 
— have  thrown  much  light  upon  the  life  and  works  of  this  truly  eccentric 
man.     They  materially  enhance  our  appreciation  of  the  real  services  which 
he  rendered. 

F   2 


68  THE  IATRO-CHEMICAL  PERIOD  CHAP. 

He  regarded  the  healthy  human  body  as  a  combination  of 
certain  chemical  matters ;  when  these  underwent  change 
in  any  way,  illnesses  resulted,  and  the  latter  could  therefore 
only  be  cured  by  means  of  chemical  medicines.  The  fore- 
going sentence  contains  the  quintessence  of  Paracelsus' 
doctrine ;  the  principles  of  the  old  school  of  Galen  were 
quite  incompatible  with  it,  these  having- — indeed — had 
nothing  to  do  with  chemistry. 

Paracelsus  entered  the  lists  with  great  boldness  and  with 
a  marvellous  vigour,  to  combat  the  old  doctrines  long  accepted 
by  all  physicians.  Although  his  exaggerations  here  are 
distinctly  to  be  condemned,  still  he  effectually  obviated  by 
his  action  the  growing  stagnation  of  medicine,  and  partly 
carried  through  valuable  innovations,  partly  incited  others 
to  do  so. 

His  career  was  not  calculated  to  raise  him  in  the  esteem 
of  his  opponents,  that  is,  of  nearly  all  the  physicians  of  the 
time.  Paracelsus  (his  full  name  was  Philippus  Aureolus 
Paracelsus  Theophrastus  Bombastus)  was  born  at  Einsiedeln1 
in  Switzerland  in  1493,  and  returned  to  his  native  country 
about  1525  as  a  physician  celebrated  for  his  wonderful 
oures,  after  an  extremely  unsettled  life  and  the  most  roman- 
tic wanderings  in  almost  every  country  in  Europe.  The 
chair  of  Medical  Science  (therapeutics)  at  Basle  was  conferred 
upon  him,  and  this  position,  together  with  his  fame  as  a 
doctor,  he  made  use  of  to  spread  the  iatro-chemical  doctrine, 
.and  to  fight  against  the  old  medical  school  with  every 
possible  dialectic  weapon.  He  discredited  the  hitherto 
undisputed  authority  of  Galen  and  Avicenna,  and  succeeded 
by  means  of  popular  lectures  given  in  German,  as  well  as 
by  his  rude  originality,  in  gaining  a  large  number  of 
adherents.  A  quarrel  with  the  Basle  Municipal  Council 
soon  compelled  him,  however,  to  leave  that  town  (in  1527), 
and  after  moving  about  restlessly  in  Alsace,  Bavaria,  Austria 
and  Switzerland,  he  at  last  came  to  Salzburg  in  the  Tyrol, 
where  he  died  in  1541  in  wretched  circumstances.  The 

1  The  name  Eremita  (Hermit)  which  was  given  to  him  by  many,  recalled 
that  of  his  native  town  (the  verb  einsiedeln  means  "  to  live  like  a  hermit "). 


in  THE  SYSTEM  AND  VIEWS  OF  PARACELSUS  69 

assertion  that  Paracelsus  was  done  to  death  by  the  hirelings 
of  physicians  who  were  his  enemies,  has  been  proved  to  be 
unfounded  (Cf.  Aberle,  loc.  cit.). 

There  has  at  all  times  been  much  difference  of  opinion 
in  criticising  this  gifted  man,  whose  life  offered  such  a  rude 
contrast  to  his  mental  capacity.  Rated  too  high  and  even 
extolled  by  his  disciples,1  and  also  by  many  who  disapproved 
of  his  doctrines,  he  was,  on  the  other  hand,  disparaged  by 
his  opponents  and  by  chemists  who  criticised  him  as 
historians.  The  good  to  which  he  incited  by  his  reforming 
labours  seldom  found  the  recognition  it  deserved,  from  its 
being  so  much  mixed  up  with  charlatanism  and  coarseness, 
while  the  overweening  estimation  in  which  he  held  himself 
helped  to  make  him  ridiculous  in  the  eyes  of  thoughtful 
physicians. 

At  the  root  of  his  iatro-chemical  doctrines,  which  he 
imagined  were  based  upon  ample  experience,  lay  the 
idea  already  mentioned, — that  the  operations  which  go 
on  in  the  human  body  are  chemical  ones,  and  that  the 
state  of  health  depends  upon  the  composition  of  the  organs 
and  the  juices.  With  respect  to  the  constituents  of  organic 
bodies,  Paracelsus  adhered  to  Basil  Valentine's  assumption 
that  the  latter  were  composed  of  mercury,  sulphur  and  salt. 
Indeed,  in  spite  of  many  contradictions  in  the  details  of  his 
theoretical  views,  this  hypothesis  forms  the  foundation  of 
his  whole  system.2  When  one  of  these  elements  predomi- 
nates or  when  it  falls  below  its  normal  amount,  illnesses 
ensue.  This  idea  is  expressed  in  the  most  fantastic  manner 
in  the  writings  of  this  strange  man,  as  the  following  sentences- 
show  : — 

An  increase  of  the  sulphur  gives  rise  to  fever  and  the  plague, 
an  increase  of  mercury  to  paralysis  and  depression,  and  an  in- 
crease of  salt  to  diarrhoea  and  dropsy.  By  the  elimination  of 

1  Cf.  A.  N.  Scherer's  memoir  Theophrastus  Paracelstus  (St.  Petersburg, 
1821).    Francis  Bacon  criticised  him  more  reasonably,  praising  his  endeav 
ours  to  get  at  the  truth  through  the  light  of  experience. 

2  Medicine  rests,  according  to  the  confused  statement  of   Paracelsus, 
upon  four  pillars,  of  which  chemistry  forms  one ;  the  three  others  are 
philosophy,  astronomy  and  virtue. 


70  THE  IATRO-CHEMICAL  PERIOD  CHAP. 

the  sulphur,  gout  results,  and  by  distilling  it  from  one  organ 
into  another,  delirium,  and  so  on. — However  unfounded  such 
opinions  are,  it  is  possible  to  find  a  certain  sense  in  them ; 
on  the  other  hand,  his  utterances  upon  the  relations  of  the 
individual  organs  and  the  secretions  of  the  human  body  to  the 
metals  and  planets,  to  both  of  which  he  ascribes  a  mystical 
influence,  are  quite  unintelligible.  Not  less  incomprehensible 
is  his  assumption  of  a  connection  between  the  plague  and 
shooting  stars.  He  designates  tartarus  as  the  cause  of 
various  illnesses,  meaning  by  this  expression  precipitates  from 
juices  which  in  the  healthy  state  contain  no  solid  particles. 
The  deposition  of  concretionary  matter,  which  he  may  have 
observed  in  the  affected  organs  during  many  diseases  (such 
-as  gout,  stone  in  the  kidneys  and  gall-stones),  no  doubt  led 
him  to  this  partially  sound  conclusion.  The  comparison  of 
such  secretions  with  known  sediments,  particularly  with 
tartar,  led  to  the  general  designation  tartarus ;  the  word 
had  possibly  also  a  double  meaning,  recalling  the  severe  pains 
which  people  afflicted  with  these  ailments  had  to  endure. 

While  Paracelsus  endeavoured  in  this  semi-rational,  if  also 
fantastic,  manner  to  reduce  pathological  processes  to 
chemical  causes,  he  assumed  nevertheless  for  his  iatro- 
chemical  doctrine  the  action  of  particular  forces  in  certain 
cases,  which  forces  he,  in  his  drastic  manner,  pictured  to 
himself  as  personified.  Digestion,  in  especial,  was  regulated 
by  the  action  of  Archeus,  who — as  a  good  genius — rendered 
the  nutriment  consumed  digestible,  effected  the  separation 
of  indigestible  matters,  and  provided  generally  for  the 
preservation  of  a  proper  equilibrium.  Diseases  in  the 
stomach  were  produced  by  Archeus  becoming  ill.  In  this 
interpretation  of  such  a  specific  chemical  process  as  digestion, 
Paracelsus  was  disloyal  to  his  own  principles.  It  fell  to  the 
later  iatro-chemists  to  clear  their  doctrinal  system  from 
this  incongruity. 

Diseases  were  to  be  cured  by  medicines  (arcana),  the 
preparation  of  which,  as  we  have  already  seen,  was — 
according  to  Paracelsus — the  aim  of  chemistry.  Due 
recognition  must  be  given  here  to  the  fact  that  this 


in  SERVICES  RENDERED  BY  PARACELSUS  71 

axiom  infused  new  life  into  the  effete  medical  doctrines. 
Paracelsus  enriched  medicine  with  a  large  number  of 
valuable  preparations.  The  manner  in  which  he  applied 
most  of  these  must  remain  unknown  to  us  ;  but  it  is  certain 
that  he  effected  numerous  brilliant  cures  in  cases  of  serious 
illness.  With  regard  to  the  preparations  which  he  employed, 
we  know  that  he  was  the  first  to  stamp  copper  vitriol,  corrosive 
sublimate,  sugar  of  lead  and  various  antimony  compounds 
as  medicines,  these  metallic  compounds  having  hitherto  been 
looked  upon  with  dread,  on  account  of  their  poisonous 
properties.  Further,  he  brought  into  use  dilute  sulphuric 
acid,  "  sweetened  oil  of  vitriol "  (sweetened  by  spirit  of  wine, 
and  which  was  known  at  a  later  date  as  Haller's  acid), 
tinctures  of  iron  and  iron  saffron ;  and  he  also  introduced 
better  methods  for  preparing  and  utilising  various  essences 
and  extracts.  He  appears  to  have  attained  great  success  by 
the  judicious  prescription  of  laudanum. 

That  Paracelsus  gave  a  tremendous  impetus  to  the  higher 
development  of  the  apothecary's  calling  by  such  generous 
additions  to  the  medical  treasury  goes  without  saying ;  for 
before  his  time  apothecaries'  shops  were  nothing  more  than 
stores  for  roots,  herbs,  syrups  and  confections  of  every  kind, 
the  preparation  of  the  latter  being  carried  out  exclusively 
in  them.  The  making  of  new  medicines  presupposed  an 
acquaintance  with  chemical  facts  and  processes ;  pharmacists 
had  therefore  to  be  continually  striving  to  attain  to  this 
knowledge,  pharmacy,  in  the  proper  sense  of  the  word, 
taking  its  beginning  here.  The  service  which  Paracelsus 
rendered  in  instigating  physicians  and  apothecaries  to  busy 
themselves  with  chemistry  was  a  great  one,  but  Scherer  goes 
too  far  when  he  says  that  "  pharmacy  owes  everything  to 
Paracelsus."  l 

The  trenchant  innovations  which  Paracelsus  strove  to 
introduce  gave  rise  to  violent  agitations  among  his  contem- 
poraries, agitations  which  were  continually  receiving  new 
food  from  his  numerous  memoirs,  circulated  in  various 
languages,  and  dating  the  most  part  from  the  time  after 

1  Loc.  tit. 


72  THE  IATRO-CHEMICAL  PERIOD  CHAP. 

his  departure  from  Basle.  These  gave  frequent  opportunity 
for  vehement  contradictions  on  the  part  of  the  old  medical 
school.  So  far  as  their  composition  goes,  his  writings  stand 
upon  a  very  low  level,  faithfully  reflecting  as  they  do  the 
unsettled  life  and  rude  attitude  of  their  author.  Every 
one  of  them  shows  an  illimitable  self-conceit,  many  indeed 
being  written  in  a  manner  quite  unworthy  of  an  educated 
man.  His  chemical  knowledge  and  his  views  with  regard 
to  the  origin  of  diseases  are  best  seen  in  the  following 
works : — Arclidioxa ;  De  Tinctura  Physicorum  ;  De  Morbis  ex 
Tartaro  Oriundis ;  Paramirum  ;  Grosse  Wundarznei. 

The  results  of  the  labours  of  Paracelsus  were  not 
long  in  manifesting  themselves.  His  pupils,  inspired  by 
the  new  doctrines,  glorified  him  as  the  reformer  of 
medicine;  while  the  adherents  of  the  old  school,  on  the 
other  hand,  resisted  desperately  the  innovations  and  attacks 
which  undermined  their  views.  A  violent  contest  ensued  and 
continued  for  a  long  time,  until  it  was  decided,  if  not  in 
favour  of  Paracelsus,  at  least  in  that  of  the  more  moderate 
iatro-chemists.  It  does  not  lie  within  the  scope  of  this 
work  to  enter  minutely  into  these  controversies,  sufficing 
as  it  does  to  indicate  here  the  significance  of  the  new 
medico-chemical  views  for  the  development  of  chemistry./ 
But  we  may  mention  that  the  Swiss  physician  Erastus 
(whose  German  name  was  Lieber),  who  remained  faithful 
to  the  doctrines  of  Galen,  was  Paracelsus's  chief  opponent, 
and  was  especially  instrumental  in  exposing  the  mischievous 
contradictions  which  were  accumulated  in  his  later  writings. 
The  medical  world  was  agitated  during  the  sixteenth  century 
by  polemical  writings  on  both  sides.  Of  the  disciples  of 
Paracelsus,  who,  less  gifted  than  their  master,  paraphrased 
his  ideas  and  imitated  his  less  amiable  peculiarities, 
especially  his  charlatanism,  but  who  fell  short  of  him  as 
scientists,  Leonhard  Thurneysser1  (called  zum  Thurm)  was 

1  A  good  account  of  Thurneysser' s  performances  is  to  be  found  in 
Mochsen's  admirable  work,  Beitrage  zur  Geschichte  der  Wissenschaften  in  der 
Mark  Brandenburg,  etc.  (Berlin  and  Leipzig,  1783).  Cf.  also  A.  W.  Hof- 
mann's  admirable  lecture,  Berliner  Alchemisten  und  Chemiker  (1882). 


in  TURQUET  DE  MAYERNE;  LIBAVIUS;  CROLL  73 

the  best  known.  The  latter  achieved  nothing  of  any  note 
for  chemistry,  but  his  unsuccessful  appearance  as  an 
adept  ensures  for  him  a  place  in  the  history  of  alchemy 
cf.  (p.  62). 

The  acts  of  men  of  this  calibre,  who  wrought  immense 
mischief  by  the  reckless  use  of  poisonous  preparations, 
render  intelligible  the  attempts  which  were  made  to  put  a 
stop  to  their  excesses  by  legal  statute.  This  is  seen,  for 
instance,  by  the  parliament  of  Paris  prohibiting  the 
prescription  of  antimonial  preparations,  and  by  the  sentence 
of  condemnation  which  the  medical  faculty  of  Paris  hurled 
against  every  attempted  innovation  in  the  healing  art. 

But  there  belonged  also  to  the  school  of  Paracelsus  men  of 
scientific  eminence  who  did  not  subscribe  to  all  his  doctrines, 
but  rather  regarded  them  from  a  critical  point  of  view,  and  who 
endeavoured  in  a  rational  manner  to  extract  the  good  which 
they  contained.  The  most  prominent  of  these  at  the  end  of 
the  sixteenth  and  beginning  of  the  seventeenth  centuries  were 
Turquet  de  Mayerne  and  Libavius,  Oswald  Croll  and  Adrian 
van  Mynsicht.  These  were  for  some  time  contemporaries 
of  van  Helmont,  and  formed  the  connecting  link  between 
Paracelsus  and  that  remarkable  man.  They  greatly  enriched 
not  only  medicine  but  also  chemistry. 

Turquet  de  Mayerne  was  born  at  Geneva  in  1573, 
and  became  a  noted  physician  in  Paris.  Holding,  however, 
as  he  did,  that  the  antimonial  preparations  now  in  ill- 
repute  were  necessary,  and  therefore  prescribing  them,  he 
found  it  impossible  to  keep  on  good  terms  with  his  professional 
brethren  in  that  city,  and  preferred  to  become  body-physician 
to  the  King  of  England,  in  which  country  he  died  in  1655. 
His  knowledge  of  chemistry  was  very  highly  developed  for 
that  age,  as  a  consequence  of  which  he  laboured  earnestly 
for  the  rational  application  of  chemical  remedies,  without 
falling  into  the  exaggerations  of  Paracelsus  on  the  one  hand, 
or  rejecting  all  the  medicines  of  the  school  of  Galen  on  the 
other. 

The  physicians  Croll  and  van  Mynsicht  busied  them- 
selves in  a  similar  manner  and  at  about  the  same  time. 


74  THE  IATRO-CHEMICAL  PERIOD  CHAP. 

Having  a  good  knowledge  of  chemistry,  they  brought  into 
vogue  many  of  the  medicaments  of  Paracelsus,  together  with 
other  new  preparations;  among  the  latter,  Croll  was  the 
first  to  recommend  the  use  of  sulphate  of  potash  and  of 
volatile  salt  of  amber  (succinic  acid),  and  van  Mynsicht  that 
of  tartar  emetic. 

Andreas  Libavius  (Libau)  attracts  our  attention  in  a 
high  degree  by  the  critical  position  which  he  took  up  with 
regard  to  the  gross  errors  of  the  school  of  Paracelsus,  and 
especially  also  by  many  new  observations  which,,  he  con- 
tributed to  chemistry.  He  was  the  first  chemist  of  note  in 
Germany  who  stood  up  manfully  against  the  excesses  of 
Paracelsus,  and  who  vigorously  combated  the  defects  in 
his  doctrines,  the  obscurities  in  his  writings,  his  phantasies 
and  sophisms,  and  the  employment  of  "secret  remedies." 
Originally  a  physician,  Libavius  attained  to  a  wide  knowledge 
of  chemistry,  which  he  helped  to  extend,  although  latterly  he 
devoted  himself  chiefly  to  historical  and  philological  studies. 
He  died  in  1616  as  director  of  the  gymnasium  at  Coburg, 
having  previously  worked  with  great  success  as  a  physician  and 
at  the  same  time  as  head  of  the  "  Latin  School "  at  Kothenburg 
on  the  Tauber  from  1591  to  1607.  Thanks  to  his  medical 
knowledge  and  to  his  thorough  general  education,  Libavius 
was  able  to  appreciate  better  than  his  contemporaries  the 
influence  which  chemistry  ought  to  exercise  upon  medicine  ; 
he  took  up  a  position  midway  between  those  of  Paracelsus 
and  his  opponents,  the  latter  of  whom  wished  nothing  less 
than  to  banish  chemistry  from  medical  science.  Notwith- 
standing his  sound  judgment,  however,  of  which  he  gave 
many  proofs,  he  could  not  quite  free  himself  from  the 
predilection  of  his  time  towards  alchemy. 

Libavius  did  chemistry  a  real  service  in  writing  his 
text-book,  which  was  published  in  1595  under  the  title 
Alchymia,  and  which  contained  all  the  most  important  facts 
and  theories  germane  to  the  subject  at  that  date.  His 
other  writings,  in  which  he  combated  the  weak  points  of 
the  Paracelsian  school  (as  indicated  above),  and  also 
described  new  chemical  observations,  appeared  in  three 


in  VAN  HELMONT'S  LIFE  AND  WORK  75 

volumes  shortly  before  his  death,  under  the  title  Opera 
Omnia  Medico-chymica.  We  shall  still  have  frequent 
occasion  to  refer  to  his  practical  chemical  knowledge,  which 
was  attested  by  the  discovery  of  important  facts. 

It  is  worthy  of  note  that  Libavius  made  a  vigorous 
effort  to  establish  chemical  laboratories,  in  which  scientific 
work  should  be  carried  out.  From  the  proposals  which  he 
brought  forward  with  this  end  in  view,  it  is  evident  that  he 
was  desirous  to  provide  plenty  of  accommodation  in  these 
laboratories,  and  to  furnish  them  with  fittings  of  the  most 
varied  kind.1 


Johann  Baptist  van  Helmont  and  his  Contemporaries. 

A  distinguished  place  and  a  detailed  notice  in  the 
history  of  the  iatro-chemical  period  is  due  to  van  Helmont, 
one  of  the  most  eminent  and  independent  chemists  of  his 
time.  Endowed  with  rich  acquirements  and  experiences  in 
medicine  and  chemistry,  he  surpassed  those  of  his  con- 
temporaries who  worked  in  the  same  field.  His  life  was 
for  the  most  part  that  of  a  scholar  working  in  quiet, 
although  his  brilliant  outward  circumstances  (he  belonged 
to  a  noble  Brabantine  family)  were  hardly  in  keeping  with 
this.  Born  in  Brussels  in  the  year  15*77,  he  applied  him- 
self at  an  unusually  early  age  to  the  study  of  philosophy 
and  theology;  but  finding  no  satisfaction  in  these,  he 
renounced  them  to  devote  himself  to  medicine.  At  first 
an  adherent  of  the  old  school  of  the  Galenites,  he  soon 
recognised  its  deficiencies  and  turned  to  the  doctrines  of 
Paracelsus,  accepting  them,  however,  only  in  part.  With  a 
growing  enthusiasm  for  his  physician's  calling,  he  fought 
against  the  old  medical  system,  and  materially  contributed 
by  his  brilliant  services  in  bringing  about  its  fall.  Without 
van  Helmont,  iatro-chemistry  would  never  have  attained  to 

1  For  an  account  of  the  life  and  work  of  Libavius,  cf.  Ottmann's  lecture 
in  the  Verhandlungen  der  Gesetlschaft  Deutscher  Naturforscher,  etc.,  1894, 
vol.  ii.  p.  79. 


76  THE  IATRO-CHEMICAL  PERIOD  CHAP. 

the  height  to  which  it  was  raised  later  on  by  Sylvius  and 
Tachenius.  In  addition,  he  enriched  pure  chemistry  by  a 
very  great  number  of  valuable  observations.  So  attached 
did  he  become  to  his  scientific  pursuits  that  he  declined 
the  tempting  offers  of  princes,  preferring  to  investigate  the 
secrets  of  nature  in  his  laboratory  at  Brussels,  in  which  city 
he  died  in  1644. 

In  van  Helmont  wonderful  contradictions  were  united. 
In  contrast  with  his  gift  of  sharp  and  temperate  observation, 
there  was  an  intense  inclination  towards  the  supernatural, — 
possibly  the  result  of  his  mystical  and  magical  studies,  to 
which,  as  well  as  to  theology,  he  had  applied  himself.  Thus 
this  same  man,  who  laid  the  foundation  of  the  first  know- 
ledge of  gases,  and  showed  thereby  a  keenness  of  perception 
unapproached  before  his  time  by  any  other  observer,  defended 
the  transmutation  of  the  base  metals  into  gold  with  the 
utmost  vigour  (cf.  p.  61) ;  his  belief  in  this  was  grounded  so 
firmly  that  illusions  arose  from  it  which  are  to  us  incompre- 
hensible. 

After  this  it  is  easy  to  understand  that  van  Helmont 
was  not  free  from  fantastic  ideas  of  a  less  questionable 
nature.  His  theoretical  views  upon  the  elements  and  his 
iatro-chemical  doctrines  yield  many  proofs  of  this ;  but,  on 
the  other  hand,  much  of  his  knowledge  was  so  sound,  and' 
he  was  able  to  expound  it  so  much  better  than  any  of  his 
predecessors,  that  the  good  service  which  he  rendered  far 
outweighed  the  bad  effect  of  any  of  his  mistakes. 

Van  Helmont  had  his  own  opinion  with  regard  to  the 
primary  substances  of  which  matter  was  composed ;  he 
neither  accepted  all  the  four  Aristotelian  elements1  nor 
those  which  were  assumed  by  Basil  Valentine,  but  looked 
upon  water  as  the  chief  constituent  of  all  matter.  That  it 
was  present  in  organic  bodies  he  concluded  from  the  fact  of 
invariably  finding  it  as  a  product  of  their  combustion.  He 
imagined  that  he  contributed  a  strong  proof  of  this  by  an 

1  With  respect  to  air,  it  is  uncertain  whether  van  Helmont  looked  upon 
it  as  an  element  or  not.  He  denied  altogether  that  fire  could  be  of  a  material 
nature,  which  is  evidence  of  his  extraordinary  clearness  of  perception. 


in  VAN  HELMONT'S  CHEMICAL  KNOWLEDGE  77 

experiment  which  showed  that  plants  could  be  made  to  grow 
luxuriantly  in  pure  water  alone,  which,  he  believed,  was 
their  only  nutriment  under  the  circumstances.  That  he  was 
thereby  convinced  of  the  transformation  of  water  into  earthy 
matter  is  therefore  quite  intelligible. 

Whilst  van  Helmont  thus  subscribed  to  the  same  error 
that  held  possession  of  many  minds  both  before  and  after  his 
time,  he  nevertheless  recognised  much  more  clearly  than  his 
contemporaries  the  unchangeableness  of  matter  in  numerous 
instances ;  thus  he  contributed  more  than  any  one  else 
to  do  away  with  the  belief  that  the  copper  thrown  down  from 
a  solution  of  copper  vitriol  by  means  of  iron  was  newly 
created.  He  further  showed  that  the  same  substance  con- 
tinued to  exist  in  many  of  its  compounds,  e.g.,  silver  in  its 
salts,  and  silica  in  water  glass,  the  latter  yielding,  on 
decomposition  with  acids  (according  to  his  own  memorable 
observations),  the  same  amount  of  silicic  acid  as  was  originally 
used  to  prepare  it.  These  were  views  and  observations  of 
the  greatest  moment;  for,  in  place  of  the  former  obscure 
conceptions  as  to  the  formation  of  chemical  compounds,  he 
substituted  the  doctrine  that  the  original  substance,  even 
after  undergoing  chemical  changes,  remains  present  in  the 
new  products.  He  had  therefore  clearly  grasped  the 
fundamental  idea  of  the  conservation  of  matter  in  particular 
cases. 

Van  Helmont  thus  stands  out  as  unique  in  those  ideas, 
which  pointed  out  new  paths  to  chemistry.  The  relations 
between  chemistry  and  medicine  too,  the  latter  of  which  he 
also  ardently  fostered,  led  him  to  views  which  likewise 
possess  a  partial  originality,  since  he  endeavoured  to  decide 
theoretical  questions  by  means  of  experiments  with  juices 
and  other  secretions  of  the  animal  body.  The  reactions 
which  go  on  in  the  liquids  of  the  body  were  in  his  opinion  of 
especial  importance,  for,  according  as  the  latter  were  acid  or 
neutral,  they  regulated  its  most  important  functions.  Besides 
the  chemical  nature  of  the  juices,  fermentation  was,  according 
to  him,  the  principal  cause  of  the  organic  processes ;  but  he 
expresses  himself  less  clearly  upon  this  point  than  upon  the 


78  THE  IATRO-CHEMICAL  PERIOD  CHAP. 


significance  of  the  chemical  reactions.  Indeed,  he  could  not 
quite  free  himself  from  the  idea  of  Archeus  governing  diges- 
tion and  the  processes  connected  with  it.  On  the  other 
hand,  he  stood  on  solid  ground  in  his  explanation  of  vital 
processes,  when  he  took  into  account  the  chemical  nature  of 
the  juices.  He  held  that  the  acid  of  the  gastric  juice 
brought  about  digestion,  but  this,  if  present  in  excess,  gave 
rise  to  discomfort  and  illnesses,  which  were  the  more  serious 
the  more  acid  there  was ;  and  the  latter  could  not  then,  as 
under  normal  conditions,  be  neutralised  by  the  alkali  of  the 
bile,  which  mixes  with  the  gastric  juce  in  the  duodenum. 
To  cure  any  of  the  ailments  produced  in  this  way,  van 
Helmont  declared  that  medicines  of  an  alkaline  nature 
(alkaline  salts)  must  be  used ;  while  those  of  an  opposite 
kind,  which  arose  from  a  deficiency  of  acid,  were  to  be 
treated  by  medicines  of  an  acid  nature.  He  also  recom- 
mended the  latter  in  cases  of  gout,  stone  and  similar  diseases, 
which  likewise  originated  (in  his  opinion)  from  an  insufficient 
or  irregular  admixture  of  the  juices.  These  views  show  a 
distinct  advance  upon  those  of  Paracelsus.  For,  while  the 
latter  assumed  the  presence  of  arbitrary  constituents — in- 
capable of  preparation — in  organic  matter,  van  Helmont 
searched  for  the  actual  substances  themselves,  and  compared 
the  interactions  of  the  various  juices  which  mingle  with  one 
another  with  similar  reactions  of  solutions  outside  the  organs ; 
a  procedure  which  laid  the  first  foundation,  however  insecure, 
of  chemical  physiology. 

Van  Helmont  proved  himself  an  original  investigator  of 
the  first  rank,  who  opened  out  new  ground  for  chemical 
science  by  his  researches  on  gases — researches  which  con- 
stitute him  the  real  founder  of  pneumatic  chemistry ;  though 
this  indeed  only  attained  to  a  considerable  development  a 
century  after  his  time,  when  the  discoveries  connected  Avith 
it  brought  about  the  great  reform  of  the  science.  If  we 
consider  that  before  van  Helmont's  time  the  most  various 
gases,  such  as  hydrogen,  carbonic  acid  and  sulphurous  acid, 
were  looked  upon  as  not  differing  materially  from  ordinary 
air,  and  that  he  was  the  first  to  characterise  gaseous  sub- 


in  VAN  HELMONT'S  INFLUENCE  ON  CHEMISTRY  79 

stances  as  different,  by  investigating  their  properties,  we 
gain  some  idea  of  the  immense  services  which  he  rendered. 
He  it  was  who  gave  to  them  the  generic  name  of  "  gas," l 
and  he  further  distinguished  them  from  vapours,  in  so  far 
that  the  latter  were  condensed  to  liquids  upon  cooling,  while 
the  former  were  not. 

Van  Helmont  specially  examined  carbonic  acid,  and 
showed  how  it  was  produced  from  limestone  or  potashes 
with  acids,  from  burning  coal,  and  in  the  fermentation  of 
wine  and  beer ;  he  also  pointed  out  its  presence  in  the 
stomach,  and  its  occurrence  in  mineral  waters  and  in  many 
natural  cavities  in  the  earth.  He  usually  termed  it  gas 
sylvestre?  To  the  want  of  suitable  apparatus  for  collecting 
gases  are  to  be  ascribed  the  imperfections  in  many  of  his 
observations,  and  also  the  confounding  of  carbonic  acid  with 
other  gases  which  were  non-supporters  of  combustion  like 
itself;  nevertheless  he  described  the  two  combustible  gases 
—hydrogen  and  marsh  gas — as  peculiar  varieties  of  air. 
His  collected  works  were  published  in  1648  by  his  son 
under  the  title,  Ortus  Medicince  ml  Opera  et  Opuscula  Omnia. 

Van  Helmont's  influence  upon  his  contemporaries  and 
upon  the  development  of  the  iatro-chemical  doctrines  must 
be  rated  very  high.  By  his  introduction  of  chemical  ideas 
into  medical  science,  the  latter  was  advanced,  because  the 
use  of  chemical  medicines  seemed  natural  from  thence- 
forth; moreover,  in  his  Pharmacopolium  ac  Dispensatorium 
Modernum,  he  published  suitable  prescriptions  for  the  pre- 
paration of  medicines.  The  scientific  spirit  which  he 
endeavoured  to  introduce  into  the  healing  art  tended  to 
its  more  healthy  development,  in  contrast  with  the  crude 
empiricism  of  the  Paracelsian  school. 

In  a  similar  manner,  if  in  lesser  degree,  various  other 
physicians  of  that  time  were  also  active.  Well  equipped 

1  In  choosing  this  designation,  van  Helmont  had  Chaos  in  his  mind, — 
possibly  also  the  process  of  fermentation  (the  Dutch  word  for  the  verb  "  to 
ferment"  is  gisteri). 

2  By  the  designation  sylvestre,  he  doubtless  meant  to  indicate  the  im- 
possibility of  condensing  the  gas ;  at  least  he  says  in  one  passage :  Gas 
sylvestre,  sive  inco'ercibile,  quod  in  corpus  cogi  non  potest  visibile. 


80  THE  IATRO-CHEMICAL  PERIOD  CHAP. 

with  chemical  knowledge,  they  pursued  the  practice  of  their 
calling,  and  were  enabled  by  their  clearness  of  vision  to  re- 
cognise and  combat  many  evils,  e.g.  those  which  arose  from 
the  use  of  secret  remedies ;  among  them  we  must  mention 
Angelus  Sala  and  Daniel  Sennert.  Sala,  who  practised  as 
body-physician  at  the  Mecklenburg  Court  in  the  first  half  of 
the  seventeenth  century,  awakens  our  surprise  by  his  able  criti- 
cisms both  of  the  Paracelsian  and  of  the  old  medical  schools, 
and  also  by  his  (for  that  time)  wide  knowledge  of  chemistry. 
This  knowledge,  conjoined  with  his  solid  medical  experience, 
was  of  the  utmost  value  not  only  to  pharmacy  but  also  to 
pure  chemistry;  for  he  formed  correct  ideas  with  regard  to 
the  composition  and  reactions  of  many  chemical  compounds, 
such  as  had  never  been  advanced  before  his  time.  Thus  he 
tells  us  that  salmiac  consists  of  hydrochloric  acid  and  car- 
bonate of  ammonia  (fluchtiges  Laugensalz),  and  he  also  knew 
that  sulphuric  acid  was  able  to  drive  out  nitric  acid  from  its 
salts, — and  so  on. 

Sennert,  who  taught  as  professor  at  Wittenberg  in  the 
first  quarter  of  the  seventeenth  century,  devoted  his  energies 
chiefly  to  proving  to  the  medical  world  the  wonderful 
efficacy  of  chemical  remedies,  when  these  were  properly  applied. 
It  is  true  that  he  was  never  able  to  disentangle  himself 
from  many  of  the-  erroneous  conceptions  of  Paracelsus,  for 
instance,  from  the  doctrine  of  the  three  primary  elements ; 
but  he  worked  effectively  against  the  serious  abuses 
which  had  crept  into  medicine  through  the  influence  of 
the  last-named,  especially  against  the  so-called  universal 
remedies. 

^Sylvius  and  Tachenius. — F.  de  le  Boe  (Dubois) 
Sylvius  was  born  at  Hanau  in  1614,  and,  after  a  thorough 
grounding  in  scientific  and  medical  studies,  practised  with 
great  success  as  a  physician,  and  later  on,  until  his  death  in 
1672,  was  famous  as  professor  of  medical  science  in  Leyden. 
In  his  knowledge  of  medicine  he  far  surpassed  most  of  his 
contemporaries.  He  was  aware  of  the  difference  between 
arterial  and  venous  blood,  and  ascribed  the  red  colour  of  the 


in  SYLVIUS  AND  TACHENIUS  81 

former  to  the  air  absorbed  in  breathing.  Combustion  and 
respiration  were  in  his  view  precisely  similar  phenomena. 
He  directed  all  his  efforts,  as  instanced  in  this  latter  case, 
to  proving  that  the  processes  which  go  on  in  the  human  body 
— whether  they  be  normal  or  pathological — were  purely 
chemical  ones.  The  spiritualistic  element  which  was  mingled 
with  the  doctrines  of  Paracelsus  and  van  Helmont  was  to 
be  entirely  set  aside.  Digestion,  for  instance,  which  only 
appeared  possible  to  the  two  latter  by  the  intervention  of 
a  spirit  (Archeus),  was  regarded  by  Sylvius  as  a  chemical 
process  in  which  the  saliva  primarily,  but  also  the  gastric 
and  pancreatic  juices  and  the  bile,  were  the  most  important 
acting  agents.  To  the  acid,  alkaline,  or  neutral  reactions  of 
the  juices  of  the  body  he  ascribed  an  equal,  if  not  a  higher, 
significance  than  van  Helmont  himself,  following  the  latter 
in  this  as  in  similar  questions.  Sylvius  had  a  predilection  for 
comparing  chemical  with  physiological  and  pathological  pro- 
cesses, which  frequently  led  him  into  error.  Medicine  as  a 
whole,  he  considered,  ought  simply  to  be  applied  chemistry. 
That  these  one-sided  endeavours  were  bound  to  miscarry, 
considering  the  state  of  chemical  knowledge  at  that  time, 
requires  no  demonstration.  And  it  is  equally  easy  to 
understand  why  his  chemical  doctrines  brought  less  benefit 
to  medicine  than  to  chemistry,  seeing  that  educated  physicians, 
if  they  wished  to  comprehend  them,  were  compelled  to  go 
minutely  into  the  study  of  chemical  questions.  This  applied 
in  a  very  special  degree  to  the  new  remedies,  the  prepara- 
tion and  rational  application  of  which  presupposed  a  know- 
ledge of  chemistry.  Sylvius,  addicted  as  he  was  to  the  use 
of  heroic  medicines,  did  not  hesitate  to  prescribe  lapis 
infernalis  (nitrate  of  silver),  sublimate  and  zinc  vitriol  for 
internal  use;  and  he  was  particularly  enthusiastic  about 
antimonial  and  mercurial  preparations. 

While  there  are  but  few  discoveries  in  pure  chemistry 
by  Sylvius  himself  to  chronicle,  his  pupil  Otto  Tachenius 
proved  himself  an  independent  investigator,  to  whom  the 
science  is  indebted  both  for  extremely  valuable  observations 
and  for  speculations  deduced  from  these.  Of  his  life  we 

G 


82  THE  IATRO-CHEMICAL  PERIOD  CHAP. 

only  know  that  he  was  born  at  Herford  in  Westphalia,  and 
that,  after  moving  about  from  place  to  place  as  an  apothecary's 
assistant,  he  applied  himself  to  the  study  of  medicine  in 
Italy  towards  the  middle  of  the  seventeenth  century,  and 
practised  in  Venice  as  a  physician.  Although  he  attached  the 
greatest  weight  to  clear  relations  between  chemistry  and 
medicine,  he  had  no  hesitation  in  working  mischief  with 
secret  remedies.  Tachenius  was  the  last  iatro-chemist  of 
note  who  followed  the  doctrines  of  Sylvius  with  enthusiasm. 
In  addition  to  him  may  be  mentioned  here  the  famous 
English  physician  Willis  (pb.  1675),  who  likewise  advocated 
similar  views. 

Tachenius,  among  his  other  valuable  observations,  con- 
tributed materially  to  elucidating  that  problem  which  Boyle 
considered  the  most  important  of  all,  viz.  a  knowledge  of 
the  composition  of  bodies.  It  was  with  him  that  the  first 
serviceable  definition  of  the  term  "  salt,"  as  a  compound  of  an 
acid  and  an  alkali,  originated.  His  statements  on  the  com- 
position of  various  compounds  show  great  acuteness,  which  is 
also  seen  in  the  value  he  attached  to  certain  reactions  as 
tests  for  different  substances.  While  Tachenius  thus  laid  the 
foundations  of  qualitative  analysis  in  a  more  systematic  manner 
than  his  predecessors,  his  attention  was  also  directed  to  the 
quantitative  proportions  in  which  substances  react  chemically 
— a  point  to  which  hardly  any  attention  had  hitherto  been 
paid ;  and  this  he  exemplified  with  tolerable  accuracy  by  noting 
the  increase  in  weight  which  took  place  when  lead  was 
transformed  into  minium.  His  writings,  and  also  those 
of  his  master  Sylvius,  treat  for  the  most  part  of  subjects 
of  chiefly  medical  interest,  but,  as  we  have  just  seen,  facts 
and  opinions  of  importance  to  chemistry  are  also  recorded 
in  them. 

If  we  wish  to  arrive  at  the  main  result  which  the  iatro- 
chemical  doctrines  produced  upon  the  development  of  chem- 
istry, we  must  particularly  bear  in  mind  the  point  already 
touched  upon,  viz.  that  the  study  of  chemistry  by  physicians 
who  had  had  a  thorough  education  helped  materially  to  shape 
its  course  on  scientific  lines.  Notwithstanding  the  numerous 


in  DEVELOPMENT  OF  CHEMISTRY  83 

errors  and  fantastic  conceptions  in  which  the  iatro-chemists 
were  involved,  we  come  across  many  very  striking  views, — 
views  which  exercised  a  marked  influence  upon  the  whole 
tendency  of  the  succeeding  epoch.  Of  these  we  would 
mention  here:  (1)  the  recognition  of  the  more  intimate 
components  of  salts,  and  the  clearer  comprehension  of  what 
was  meant  by  the  terms  "chemical  compound"  and  "chem- 
ical affinity,"  by  a  knowledge  of  which  the  chief  aim  of 
chemistry,  i.e.  the  investigation  of  the  true  composition  of 
bodies,  was  effectively  advanced;  and  (2)  the  recognition 
of  the  analogy  between  the  processes  of  combustion  and  the 
calcination  of  the  metals  on  the  one  hand,  and  respiration  on 
the  other.  These  were  doctrines  of  very  great  weight  indeed. 
The  phlogistic  hypothesis,  too,  which  predominated  during  the 
greater  portion  of  the  eighteenth  century,  was  indicated  by 
many  of  the  iatro-chemists ;  i.e.  many  of  the  latter  had  ideas 
upon  combustion  which  approximated  to  those  of  the  phlo- 
gistonists.  Lastly,  van  Helmont's  work  upon  gases  exercised 
the  greatest  influence  on  the  development  of  pneumatic 
chemistry,  from  which  the  impulse  to  the  great  reform  of  our 
science  at  the  end  of  last  century  sprang. 

It  is  thus  evident  that  many  of  the  aims  of  the  phlo- 
gistonists  were  intimately  connected  with  the  observations 
and  opinions  proper  of  the  iatro-chemists.  And  while  the 
medico-chemical  opinions  of  the  latter  were  rudely  upset 
after  the  middle  of  the  seventeenth  century,  their  facts  and 
theories  appertaining  to  chemistry  were  the  means  of  guiding 
the  latter  into  scientific  paths. 


Agricola,  Palissy,  and  the  other  Promoters  of  Applied  Chemistry 
during  the  latro-chemical  Age.1 

Independently  of  the  main  iatro-chemical  current,  chem- 
istry in  its  applications  to  industries  was  fostered  by  men 
who  possessed,  for  their  time,  sound  chemical  knowledge. 

1  Cf.  Kopp,  Gesch.  d.  Chem.,  vol.  i.  pp.  104,  128;  and  Hofer,  Histoire 
de  la  Chimie,  vol.  ii.  pp.  38,  67  e.t  seq. 

G   2 


84  THE  IATRO-CHEMICAL  PERIOD  CHAP. 

The  chief  of  these  were  Georgius  Agricola,  who  directed  his 
attention  specially  to  metallurgy;  Bernard  Palissy,  who 
developed  the  ceramic  art;  and  Joahnn  Rudolf  Glauber,  who, 
without  ceasing  to  be  an  iatro-chemist,  devoted  his  powers 
for  the  most  part  to  technical  chemistry.  The  following 
paragraphs  give  a  few  details  explanatory  of  the  services 
rendered  to  the  science  by  the  knowledge  and  experiences  of 
those  men ;  but  what  we  are  chiefly  concerned  with  here  is 
their  significance  from  a  more  general  point  of  view. 

Georgius  Agricola l  was  born  at  Glauchau  in  1494,  and  be- 
came a  noted  physician ;  he  died  while  mayor  of  Chemnitz 
in  1555.     He  was  thus  a  contemporary  of  Paracelsus.     Al- 
though, like  the  latter,  a  medical  man,  he  followed  totally  differ- 
ent lines.     Without  troubling  himself  about  the  storms  which 
raged  round  medicine  in  his  day,  he  devoted  himself  by  choice 
to  the  study  of  mineralogy  and  metallurgy,  being  impelled 
thereto  by  the  flourishing  mining  and  smelting  industry  of 
Saxony,  while  at  the  same  time  he  continued  to  practise  as 
a  doctor.     His  chemical  knowledge  and  wide  experiences  are 
detailed  by  him  in  his  principal  work :  De  Re  Metallica,  libri 
XII,  which  remained  for  a  long  time  the  most  important 
text-book  of  mineralogy.     Through  this,  as  well  as  through 
his  other  writings — of  which  De  Natura  Fossilium,  libri  Jf, 
and  De  Ortu  et  Causis  Subterraneorum  were  also  of  especial 
mineralogical  value, —  there  runs  quite  a  different  tone  from 
what   we  find  in  Paracelsus.     They  are  characterised  by  a 
clearness  of  expression,  a  temperate  conception  of  the  opera- 
tions  described,   and   a  distinct    description    both    of    the 
apparatus  employed  and  the   processes   followed, — qualities 
which  stamp  Agricola  as  a  true  investigator.     It  was  through 
his  writings,  especially  through   the   first   of  those   named 
above,  that  the  more  important  operations  in  the  working 
up   of  ores  for  their  metals  first  became  generally  known ; 
and   he  was   likewise  the   first   to   explain   intelligibly  the 

1  Cf.  G.  H.  Jacobi's  dissertation : — Der  Mineralog  Georgius  Agricola 
und  sein  Verhattniss  zur  Wissenschaft  winer  Zeit  (Leipzig,  1889).  ("The 
Mineralogist,  Georgius  Agricola,  and  his  relation  to  the  Science  of  his 
Time.") 


in  GEORGIUS  AGRICOLA,  PALISSY  AND  GLAUBER  85 

manufacture  of  other  products  obtained  by  smelting,  and 
of  various  preparations  of  technical  importance.  His  works 
are  indispensable  to  the  history  of  metallurgy. 

His  quiet  objective  modes  of  thought  and  investigation 
did  not,  however,  prevent  him  in  his  more  mature  age  from 
attributing  a  certain  degree  of  liklihood  to  the  alchemistic 
problem,  to  which  he  had  devoted  himself  warmly  in  his 
youth;  at  the  same  time  he  had  no  sympathy  with  the 
wild  exaggerations  which  even  then  prevailed. 

Working  on  lines  similar  to  those  of  Agricola,  and  at  about 
the  same  period,  the  Italian  Biringuiccio  of  Siena  busied 
himself  with  the  processes  of  metallurgy,  as  detailed  in  his 
work  Pirotechnia,  which  appeared  in  1540.  This  too  is 
marked  by  the  clearness  and  exactitude  with  which  various 
technical  procedures  are  described.  Biringuiccio  held  aloof 
from  the  iatro-chemical  questions  and  the  alchemistic  doc- 
trines of  his  day. 

Bernard  Palissy  became  distinguished  as  an  investigator, 
and  as  a  man  who  allowed  himself  to  be  guided  solely  by  the 
results  of  experiment,  at  a  time  before  the  inductive  method 
was  commonly  recognised  as  the  means  of  attaining  to  the 
truth.  It  was  in  the  domain  of  ceramic  art  that  his  principal 
work  lay ;  and,  although  frequently  disappointed  in  the  results 
he  obtained,  his  untiring  efforts  at  improvment  in  it  were 
ultimately  followed  by  success.  The  simple  and  clearly 
written  works  of  Palissy  enable  us  to  appreciate  the  labours 
and  struggles  of  this  remarkable  and  steadfast  man,  who, 
beginning  as  a  common  potter  destitute  of  the  higher  educa- 
tion, became  the  great  authority  on  his  subject.1  He  took  his 
first  lessons  from  the  book  of  nature,  as  he  himself  tells  us ;  2 
putting  observation  and  experiment  in  the  foreground,  he 
combated  every  speculation  which  was  not  based  upon  these, 
especially  such  doctrines  as  had  merely  the  stamp  of  authority 
to  back  them.  There  could  hardly  have  been  any  man  of  his 

1  Hofer,  who  was  the  first  to  recognise  the  services  of  Palissy  as  they 
deserved,  speaks  of  him  as  "  un  des  plus  grands  hommes  dont  la  France 
puisse  s'enorgueillir  "  (Histoire  de  la  Chimie,  vol.  ii.  p.  92). 

2  "  Je  rial  point  eu  d'autre  livre,  que  le  del  et  la  terre,  lequel  est  connu  de 
tons  et  est  donnd  cl  tons  de  connoistre  et  lire  ce  beau  livre." 


86  THE  IATRO-CHEMICAL  PERIOD  CHAP. 

time  more  free  from  prejudice ;  his  clear  understanding  and 
circumspect  criticism  enabled  him  to  cast  aside  the  doctrines 
o  f  Paracelsus,  and  to  make  use  of  the  weapons  of  ridicule 
against  the  mistaken  beliefs  of  alchemy.  His  life  extended 
over  nearly  the  whole  of  the  sixteenth  century,  and  might  be 
said  to  consist  of  a  series  of  vicissitudes.  Along  with  Agricola 
he  maybe  looked  upon  as  the  chief  exponent  of  experimental 
chemistry  in  his  time.  His  acuteness  was  further  evidenced 
in  the  domains  of  mineralogy  and  agricultural  chemistry,  to 
the  founding  of  which  branches  of  science  he  largely  con- 
tributed. 

Johann  Rudolf  Glauber,  who  was  born  at  Karlstadt  in 
Franken   (Bavaria)    in    1604,    and   who   died   in   1668    at 
Amsterdam,  fostered  applied  chemistry  ardently,  and  enriched 
it  by  valuable  observations.     It  was  in  this  direction  that 
he  chiefly  worked,  his  iatro-chemical  labours  holding  but  a 
secondary  place.     His  life  was   an   extremely  restless   one, 
which  may  not   improbably  account  for   the  unsettled  and 
almost  discontented  tone  which  runs  through  many  of  his 
writings.     Without  a  classical  education,  and  imbued  with 
the  prejudices  of  his  age,  he  has  been  well  designated  the 
Paracelsus  of  the   seventeenth  century.      He  was,  in  fact, 
addicted  to  fantastic  and  superstitious  ideas,  and  therefore 
also  to  the  extravagances  of  alchemy ;  on  the  other  hand,  he 
possessed  exceptional  talents  of  observation  and  invention, 
regarding  which  some  details  will  be  given  in  the  next  section 
of  this  book.     In  theoretical  points  of  chemistry,  too,  he  gave 
proof  of  his  clear-sightedness,  explaining,  for  example,  many 
of  the  effects  of  chemical  affinity  in  the  decomposition  of  salts 
by  acids  or  bases, — and  so  on.     He  was  the  first  to  explain  a 
case   of  what  we   call   double  decomposition, — the  mutual 
action  of  mecuric  chloride  and  antimony  trisulphide  upon  one 
another.     Mention  must  also  be  made  here  of  his  perspica- 
city in  questions  of  national  economy,  his  writings  upon  which 
are  to  be  found  mixed  up  with  his  chemical  papers,  especially 
in  the  six-volume  work  Teiitschland's  Wohlfarth  ("  The  Weal 
of  Germany  ").     Time  after  time  Glauber  sought  to  demon- 
strate that  his  country  should  work  up  and  improve  its  own 


in  ADVANCES  IN  TECHNICAL  CHEMISTRY  87 

products,  and  not  leave  this  for  other  nations  to  do ;  instead 
of  buying  at  a  dear  rate  manufactured  articles  whose  raw 
material  was  obtained  from  Germany,  that  country  ought  to 
make  and  export  them  herself. 

With  Glauber  and  Tachenius  the  iatro-chemical  period 
closes.  Both  of  them  belonged  in  many  of  their  chemical 
ideas  and  also  in  point  of  time  (during  the  last  years  of  their 
lives)  to  the  succeeding  era,  between  which  and  the  previous 
one  it  is  impossible  to  draw  an  absolutely  sharp  line.  Both 
aided  chemistry  by  observations  of  extreme  value,  and 
materially  advanced  the  experimental  method,  which  became 
from  thenceforth  the  sure  guiding  star  of  chemical  research. 


EXTENSION  OF  PRACTICAL   CHEMICAL  KNOWLEDGE  IN 
THE  IATRO-CHEMICAL  AGE.1 

As  was  to  be  expected  from  the  whole  tendency  of  this 
period,  during  which  chemistry  became  so  intimately  united 
to  medicine,  the  gain  of  knowledge  lay  chiefly  in  respect  to 
chemical  preparations,  which  it  was  hoped  to  apply  as  medi- 
cines. The  efforts  to  discover  new  remedies  had  the  result  of 
causing  chemical  compounds,  whether  novel  or  already  known, 
to  be  investigated  more  carefully  and  scientifically  than  had 
ever  been  done  before.  The  products  of  the  animal  body 
were  zealously  studied,  and  a  small  beginning  was  made  in 
physiological  chemistry  by  the  examination  of  milk,  blood, 
saliva,  etc.,  which  in  its  turn  increased  the  interest  felt  in 
organic  compounds.  In  technical  chemistry  less  progress  was 
made  than  in  chemistry  which  was  related  to  medicine.  An 
advance  in  the  knowledge  of  the  composition  of  substances 
and  in  the  observation  of  reactions,  i.e.  in  qualitative  analysis, 
first  became  noticeable  towards  the  end  of  the  iatro-chemical 
period. 

Technical  Chemistry. — The  most  eminent  exponents 
in  this  direction,  chief  among  whom  were  Agricola  and  Palissy, 

1     Cf.  Kopp,  Gesch.   d.   Chemie,  vol.  ii.  pp.  Ill,  126  ;  vols.  iii.  and  iv. 
passim. 


88  THE  IATRO-CHEMICAL  PERIOD  CHAP. 

have  been  already  referred  to.  In  their  works,  as  also  in 
the  writings  of  Biringuiccio,  Caesalpin  and  others  which  are 
devoted  to  technical  chemistry,  special  weight  is  laid  on  the 
particular  operations  by  which  technical  products  are  ob- 
tained, these  operations  being  minutely  described. 

In  Metallurgy  Agricola  and  Libavius  were  the  first  to 
point  out  a  method  by  means  of  which  it  was  possible  to 
estimate  approximately  the  amount  of  metal  in  an  ore ; 
the  science  of  testing  thus  gradually  developed  itself  from 
such  beginnings.  The  more  scientific  treatment  of  applied 
chemistry  is  further  shown  by  the  fact  that  by-products 
began  to  be  used  which  had  previously  been  neglected,  e.g.  the 
sulphur  which  escaped  during  the  partial  roasting  of  pyrites 
was  condensed,  the  tutty  from  zinc  ores  was  utilised  for 
brass,  and  so  on. 

A  knowledge  of  the  individual  metals,  and  of  the  methods 
by  which  they  could  be  obtained  and  worked  up,  became 
extended  in  the  sixteenth  century  by  Agricola  and  other 
authors  making  into  common  property  what  had  hitherto 
been  only  known  to  the  few ;  e.g.  the  separation  of  gold  from 
silver  by  means  of  nitric  acid,  which  was  first  carried  out  on 
a  large  scale  in  Venice  towards  the  end  of  the  fifteenth 
century,  and  the  amalgamation  process,  first  applied  in 
Mexico  about  the  middle  of  the  sixteenth  century  for  ex- 
tracting silver  from  its  ores,  but  only  introduced  into  Europe 
towards  the  end  of  the  eighteenth.  It  is  in  the  sixteenth 
century  that  we  find  the  first  reliable  observations  on  the 
production  of  ruby  glass  by  means  of  gold.  Salts  of  the 
latter  metal  and  also  of  silver  were  more  carefully  investi- 
gated, with  reference  particularly  to  their  medical  applica- 
tion ;  and  some  of  their  characteristic  reactions — by  which  it 
became  possible  to  distinguish  them  from  other  substances — 
were  also  noticed. 

With  respect  to  copper  and  its  precipitation  from  a 
solution  of  copper  vitriol  by  means  of  iron,  we  find  even 
chemists  of  discernment  like  Libavius  holding  fast  to  the 
old  idea  that  a  transmutation  had  occurred ;  but  others,  e.g. 
van  Helmont  and  Sala,  recognised  the  pre-existence  of  the 


in     METALLURGY  ;  POTTERY  AND  GLASS  MANUFACTURE    89 

copper.  The  metallurgical  operations  necessary  for  obtaining 
iron  became  generally  known  through  Agricola's  writings,1 
thus  the  production  of  steel  by  the  puddling  process  was 
first  described  by  him.  Steel  was  at  that  time  regarded  as 
a  very  pure  iron.  Of  the  other  metals,  a  knowledge  of  zinc 
and  bismuth  was  gradually  acquired,  although  there  was 
often  uncertainty  about  them,  and  they  were  frequently  con- 
founded with  antimony.  Tin,  lastly,  was  much  used  in  the 
sixteenth  century  for  tinning  iron.  But  the  iatro-chemical 
age  interested  itself  less  in  the  metals  themselves  than  in 
the  salts  prepared  from  them,  since  there  was  always  the 
chance  of  these  proving  useful  in  medicine.  (See  under 
Preparations.) 

Pottery  and  Glass  Manufacture. — The  ceramic  in- 
dustry in  particular  made  considerable  progress,  thanks  to 
the  untiring  efforts  of  Palissy;  his  only  guide  was  the  ex- 
perience gained  from  innumerable  trials,  but  he  succeeded 
in  affixing  beautiful  and  durable  enamels  on  earthenware 
vessels,  especially  on  those  of  Fayence  pottery.  His  obser- 
vations on  this  point,  and  also  on  the  application  of  different 
clays  for  ceramic  purposes,  and  the  burning-in  of  colours,  are 
given  in  his  work  L'Art  de  Terre,  which  at  the  same  time  aims 
at  showing  the  value  of  the  experimental  method  as  opposed 
to  theory  alone.  Porta  was  also  busy  in  Italy  about  the 
middle  of  the  sixteenth  century  with  work  similar  to  Palissy 's. 

The  manufacture  of  glass  did  not  lag  behind  that  of 
pottery.  From  the  Venetian  factories,  whose  sixteenth- 
century  productions  still  astonish  and  delight  the  con- 
noisseur, the  art  of  making  glass  of  the  most  various  colours 
and  of  different  degrees  of  refrangibility  spread  to  other 
countries.  The  work  of  the  Florentine  Antonio  Neri,  en- 
titled De  Arte  Vitraria,  which  appeared  in  1640,  not 
improbably  contributed  materially  to  spreading  a  knowledge 
of  special  operations,  his  large  experience  on  the  subject 
being  detailed  in  this  book.  Great  skill  was  also  attained 

1  The  significance  of  Agricola's  work  in  this  field  is  clearly  seen  in  the 
account  given  by  L.  Beck  in  his  Geschichte  des  Eisens,  vol.  ii.  p.  22,  etc. 


90  THE    ATRO-CHEMICAL  PERIOD  CHAP. 

even  at  that  date  in  the  imitation  of  precious  stones,  as 
Porta's  recipes  show.  One  of  the  most  important  discoveries 
of  the  time  was  that  of  cobalt  blue  by  Christoph  Schurer,  a 
Saxon  glass-blower,  who  obtained  it  on  fusing  the  cobalteous 
residue  from  the  manufacture  of  bismuth  with  glass ;  it  soon 
became  a  much-prized  article  of  commerce,  being  known 
under  the  names  zaffre  (from  sapphire),  and,  later  on,  smalt. 

Dyeing. —  One  of  the  results  of  the  discovery  of 
America  and  of  the  ocean  route  to  the  East  Indies  was  seen 
in  the  increased  importation  of  indigo  and  cochineal,  which 
gave  a  fresh  impetus  to  the  dyeing  industry.  Many  im- 
proved methods  of  fixing  these  and  other  colours  upon  cloth — 
e.g.  the  use  of  a  solution  of  tin,  the  judicious  mordanting  of 
the  stuffs  with  alum,  iron  solution,  etc. — were  found  out  in 
the  sixteenth  century.  The  dyer  of  that  time  might  consult 
the  first  text-book  on  this  subject,  written  by  the  Venetian 
Rosetti,  which  appeared  in  1540.  Glauber,  too,  made  numer- 
ous observations  on  dyeing  processes,  and  aided  not  a  little 
in  advancing  a  knowledge  of  these. 

A  new  industry  sprang  up  towards  the  end  of  the 
fifteenth  century  in  the  rapidly  extending  distillation  of 
brandy ;  up  to  that  time  spirit  of  wine  was  looked  upon  as 
a  medicine  only,  but  now  it  began  to  be  more  and  more 
used,  sufficiently  diluted,  as  a  drink.  The  development 
of  this  branch  of  trade  resulted  in  great  improvements  in 
distilling  apparatus,  which  also  came  to  be  of  service  in 
laboratories.  The  interest  which  this  industry  excited  is 
seen  from  the  numerous  works  upon  the  art  of  the  distiller 
which  appeared  at  that  time. 

The  applications  of  chemistry  were  in  fact  extended  in 
the  most  various  directions,  among  others  to  agriculture,  if 
only  in  a  modest  degree;  thus  we  find  the  gifted  Palissy 
calling  attention  to  the  importance  of  soluble  salts  in  man- 
ures, and  recommending  the  addition  of  mineral  substances, 
e.g.  marl,  to  these.  Here  we  have  the  earliest  beginnings  of 
a  rational  chemistry  of  agriculture. 


KNOWLEDGE  OF  INORGANIC  COMPOUNDS  91 


Development  of  Pharmacy  and  of  the  Knowledge  of  Chemical 
Preparations. 

Pharmaceutical  chemistry  is  most  distinctly  a  creation 
of  the  iatro-chemical  age,  during  which  it  was  taught  that 
the  chief  aim  of  chemistry  lay  in  the  discovery  of  medicines 
that  could  be  prepared  artificially.  In  accordance  with  this 
dictum,  not  only  were  the  preparations  already  known,  but 
also  those  others  which  had  been  newly  discovered  after 
much  seeking,  tested  for  their  action  upon  the  organism. 
The  circle  of  chemical  facts  was  thus  greatly  widened  by 
these  iatro-chemical  labours.  The  influence  of  the  latter 
upon  chemistry  was  made  further  apparent  by  the  fact  of 
the  drug- shops  in  which  artificial  preparations  were  made, 
becoming  the  nurseries  of  hard-working  chemists,  who,  espe- 
cially in  the  succeeding  generation,  played  an  important  part 
in  the  building  up  of  the  scientific  system. 

Inorganic  Compounds. — The  preparation  of  mineral 
acids  showed  improvements,  and  their  investigation  was 
marked  by  advances  which,  however,  only  became  of  prac- 
tical value  later  on,  when  the  acids  began  to  be  employed 
technically.  Glauber  taught  how  to  prepare  hydrochloric 
acid  from  rock-salt  and  oil  of  vitriol,  and  also  fuming  nitric 
acid  from  saltpetre  and  white  arsenic. 

To  Libavius  belongs  the  merit  of  simplifying  the  mode 
of  preparing  sulphuric  acid,  and  of  proving  that  the  acid 
obtained  in  various  ways — from  alum,  vitriol  (sulphate  of 
iron),  or  sulphur  and  nitric  acid — was  one  and  the  same  sub- 
stance. The  behaviour  of  the  acids  just  named  to  metals, 
salts  and  organic  compounds  led  to  a  knowledge  of  a  great 
number  of  bodies  which  had  been  either  unknown  hitherto, 
or  at  least  had  never  been  produced  in  this  particular  way  : 
and  thus,  from  their  modes  of  preparation,  deductions  as  to 
their  composition  often  became  possible.  Among  such  sub- 
stances were  the  chlorides  formed  by  the  action  of  hydrochloric 
acid  upon  many  of  the  metals,  which  up  to  then  had  been 


92  THE  IATRO-CHEMICAL  PERIOD  CHAP, 

prepared  by  heating  the  latter  with  sublimate,  and  hence 
the  presence  of  mercury  in  the  resulting  products  was  as- 
sumed. Glauber,  to  whom  we  owe  a  knowledge  of  many  of 
them, — e.g.  zinc,  stannic,  arsenious  and  cuprous  chlorides — 
disproved  this  erroneous  assumption ;  he  and  his  contempo- 
raries regarded  these  salts  as  compounds  of  the  metal  and 
hydrochloric  acid. 

Salts  were  destined  to  play  a  very  great  part  in  medi- 
cine. Especial  interest  was  taken  in  the  alkaline  salts,  both 
from  a  theoretical  point  of  view — their  composition  being  a 
frequent  theme  of  discussion — and  also  from  a  practical,  on 
account  of  their  technical  and  officinal  applications. 

Potash  saltpetre,  which  was  prepared  on  a  large  scale 
on  account  of  its  increasing  use  in  the  manufacture  of  gun- 
powder,1 was  also  prized  as  a  medicine  when  fused.  The 
observation  made  by  the  pseudo-Geber — so  important  for 
a  knowledge  of  its  composition — that  saltpetre  results  on 
saturating  potashes  with  nitric  acid,  was  first  made  use  of 
technically  in  the  iatro-chemical  age.  Sulphate  and  chloride 
of  potash,  which  were  prepared  by  many  different  methods 
and  known  under  various  names,  were  employed  as  medi- 
cines,— the  former  by  Paracelsus,  and  the  latter  by  Sylvius 
and  Tachenius  (as  sal  febrifugum  Sylvii).  Carbonate  of 
potash,  too,  prepared  from  tartar  and  the  ashes  of  plants, 
was  another  medicament.  Even  iatro-chemists  of  eminence 
like  Tachenius  believed  in  a  chemical  difference  between 
various  potashes,  according  to  their  modes  of  preparation, — 
an  error  which  Boyle  was  the  first  to  correct;  still  more 
frequently  do  we  meet  with  a  confounding  of  potash  salts 
with  those  of  soda,  e.g.  their  carbonates  and  chlorides. 
Glauber's  sulphate  of  soda,  obtained  from  the  residue  left  in 
the  manufacture  of  hydrochloric  acid,  and  known  under  the 
name  of  sal  mirabile,  was  highly  prized  by  physicians. 
Whether  borax,  which  was  used  in  soldering  during  the 
iatro-chemical  period,  was  also  employed  as  a  medicine  is 
doubtful. 

1  Agricola  describes  the  preparation  of  saltpetre  in  his  work  De  Re 

Metallica. 


in  SALTS  OF  AMMONIA  AND  OF  THE  EARTHS  93 

Salts  of  ammonia  were  largely  used,  both  officinally  and 
technically,  especially  sal  ammoniac,  whose  manufacture  was 
attempted  in  Europe  so  early  as  the  seventeenth  century ; 
its  artificial  formation  from  volatile  alkaline  salt  and 
hydrochloric  acid  was  known  to  the  iatro-chemists  of  that 
time  (Sylvius,  Tachenius,  Glauber),  but  it  was  only  at  a 
much  later  date  that  its  true  composition  was  indicated. 
The  near  relation  thus  found  to  exist  between  carbonate  of 
ammonia  and  salmiac  led  conversely  to  the  preparation  of 
the  former  from  the  latter  by  means  of  carbonate  of  potash ; 
from  the  apparently  different  action  of  samples  of  volatile 
alkaline  salt  of  diverse  origin  (from  blood,  urea  and  salmiac), 
it  was  supposed  that  they  were  different  compounds,  but 
this  error  was  recognised  by  Tachenius.  Of  other  salts  of 
ammonia  we  may  mention  the  sulphate,  discovered  by 
Libavius,  the  nitrate,  by  Glauber,  and  the  acetate ;  the 
last,  known  as  spiritus  Mindereri  (from  its  discoverer,  the 
physician  Raymund  Minderer),  was  much  valued  as  a  medicine 

But  few  of  the  salts  of  the  earths  were  known,  and 
there  was  uncertainty  as  to  their  composition.  Lime  and 
alum  earth  (alumina),  for  instance,  were  supposed  to  be 
pretty  much  the  same.  Of  their  salts,  alum — prepared  by 
adding  putrefied  urine  to  the  crude  alum  lye  (the  aqueous 
extract  from  roasted  aluminous  shale) — was  much  prized 
for  its  technical  value,  and  was  manufactured  in  large 
quantity ;  the  alum  of  that  day  was  thus  essentially  ammonia 
alum.  Agricola  himself  characterised  gypsum  as  a  compound 
of  lime,  while  chloride  and  nitrate  of  calcium  were  known 
in  the  seventeenth  century,  and  possibly  even  before  then. 
Agricola  and  his  contemporaries  were  also  aware  that  silica 
(i.e.  pure  sand) — which  was  for  long  reckoned  as  one  of  the 
earths — fused  with  potashes  to  a  glass  which  was  soluble  in 
water,  and  the  clear-sighted  Tachenius  saw  in  this  behaviour 
an  indication  of  the  acid  nature  of  the  substance. 

The  salts  of  the  heavy  and  of  the  noble  metals,  and 
various  preparations  of  the  semi-metals  (arsenic,  antimony  and 
bismuth)  were  of  much  importance  for  iatro-chemistry,  and 
therefore  also  for  the  development  of  the  chemical  know- 


94  THE  IATRO-CHEMICAL  PERIOD 


ledge  of  that  time.  Basil  Valentine,  as  we  have  alreacty 
seen,  had  worked  up  a  large  number  of  antimonial  pre- 
parations and  had  recommended  them  for  internal  use  prior 
to  the  appearance  of  Paracelsus  and  his  school.  And 
although,  in  consequence  of  the  abuses  resulting  from  secret 
medicines  containing  antimony,  sharp  edicts  were  issued 
prohibiting  their  employment,  preparations  of  antimony  came 
notwithstanding  more  and  more  into  favour,  this  being  greatly 
due  to  the  efforts  of  Sylvius.  Metallic  antimony  itself  was 
prescribed  in  pills,  which  were  called  "  the  everlasting,"  since 
it  was  believed  that  they  acted  merely  by  contact,  and  that 
therefore,  after  passing  through  the  body,  they  could  be  used 
again  and  again.1 

It  was  during  this  period  that  "  Kermes "  mineral, 
sulphur  auratum,  and  powder  of  algaroth2  were  added  to 
the  medical  treasury;  antimoniate  of  potash — prepared  by 
detonating  antimony  trisulphide  with  saltpetre — was  also 
much  used  as  a  medicine.  To  Glauber  more  than  any  one 
else  is  due  a  clearer  knowledge  of  the  chemistry  of  this  and 
other  antimony  compounds. 

There  was  still  great  obscurity  with  regard  to  white 
arsenic  and  the  metal  prepared  from  it,  and  also  with  respect 
to  other  arsenic  compounds;  among  the  latter  we  may 
mention  arseniate  of  potash,  which  was  prepared  by  fusing 
the  trioxide  with  saltpetre,  and  for  which  Paracelsus  appears  to 
have  had  a  great  predilection  as  a  medicine  (arsenicum  fixum). 
Glauber  was  the  first  to  prepare  chloride  of  arsenic  (AsCl3). 
Preparations  of  bismuth  were  less  used  for  medicinal  pur- 
poses, although  the  similarity  between  bismuth  and  antimony, 
which  often  led  to  confusing  the  one  with  the  other,  did  not 
escape  the  iatro-chemists.  Basic  nitrate  of  bismuth  was  much 
prized  as  a  cosmetic,  while  the  oxide,  according  to  Agricola, 
was  used  as  a  paint. 

1  Lemery  in  his  Cours  et  Chimie  (1675)  remarks  upon  the  use  of  these 
pills  as  follows  :  ' '  LorsqiCon  avale  la  pillule  perpettielle,  die,  est  entrainee  par 
sa  pesanteur,  et  elle  purge  par  bas  ;  on  la  lave  et  on  la  redonne  comme  devant, 
et  ainsi  perpetiiellement." 

2  So  called  after  the  Veronese  physician  Victor  Algarotus,  who  praised 
it  as  pulvis  angelicus. 


COMPOUNDS  OF  ZINC,  MERCURY,  ETC.  95 


Of  the  compounds  of  zinc,  the  oxide,  zinc  vitriol  (which 
Agricola  terms  chalcanthum  candidum),  and  the  chloride 
became  better  known ;  the  last  of  these  was  prepared  by 
Glauber  by  heating  calamine  strongly  with  hydrochloric 
acid,  and  it  therefore  contained  basic  salt.  From  tin 
Libavius  obtained  its  tetrachloride,  by  distilling  it  with 
sublimate ;  assuming  in  this  the  presence  of  mercury,  he 
termed  it  spiritus  argenti  mm  sublimati,  but  later  on  it  was 
commonly  known  as  spiritus  fumans  Libavii.  The  solution 
of  this  compound,  obtained  by  treating  tin  with  aqua  regia, 
began  to  be  applied  by  Drebbel  in  many  dyeing  operations 
about  the  year  1630. 

The  discovery  and  investigation  of  ferric  and  plumbic 
chlorides,  the  latter  of  which  was  used  instead  of  white  lead 
as  a  paint,  is  likewise  due  to  Glauber.  The  methods  of  pre- 
paring many  metallic  salts  already  known  were  also  much 
improved,  as  is  seen,  for  instance,  in  the  description  given 
by  Agricola  of  the  preparation  of  iron  and  copper  vitriols. 

The  iatro-chemists  devoted  much  attention  to  the 
production  and  medical  application  of  quicksilver  compounds. 
It  was  given  to  Paracelsus  to  overcome  the  prejudices  of 
many  against  mercurial  medicines,  although  most  of  the 
physicians  of  the  old  school  would  have  nothing  to  do  with 
them.  Paracelsus  and  his  disciples  had  no  hesitation  in 
making  use  of  metallic  mercury — finely  divided  in  pills, — 
sublimate,  and  the  so-called  turpeth  mineral  (i.e.  basic  mer- 
curic carbonate  or  sulphate,  both  of  which  went  under  this 
name).  In  this  way  a  much  better  knowledge  of  various 
mercury  compounds  was  gradually  arrived  at,  some  of  these 
compounds  being  already  known  and  some  newly  discovered. 
Among  the  latter  were  calomel  and  white  precipitate  (from 
sublimate  and  ammonia),  both  of  which  were  prized  as 
medicines.  It  was  during  this  period  that  chemists  gradually 
learnt  that  cinnabar  consisted  of  mercury  and  sulphur,  and 
that  mercury  itself  belonged  to  the  true  and  not  to  the  half- 
metals. 

Of  the  compounds  of  silver,  lapis  infernalis  (the  nitrate) 
was  found  useful  in  medicine,  principally  through  Sala's  re- 


96  THE  IATRO-CHEMICAL  PERIOD  CHAP. 

commendation,  and  the  sulphate  and  chloride  of  silver  were 
also  known.  The  production  of  the  latter  on  precipitating 
a  solution  of  silver  with  hydrochloric  acid  or  common  salt 
dissolved  in  water,  was  made  use  of  analytically  as  a  test  both 
for  silver  and  for  chlorides. 

Indeed  the  beginnings  of  qualitative  analysis  in  the  wet 
way  are  to  be  sought  for  in  .the  iatro-chemical  age,  in  so  far 
that  conclusions  regarding  the  presence  of  one  or  another 
constituent  were  drawn  from  the  appearance  and  behaviour 
of  precipitates,  and  of  salts  which  crystallised  out  from  solu- 
tion. Tachenius  laid  especial  weight  on  distinguishing  such 
precipitates  by  their  colours,  and  he  was  himself  able  to 
detect  several  metals  in  solution  together  by  means  of  certain 
reagents,  such  as  tincture  of  galls,  the  carbonates  of  potash 
and  ammonia,  caustic  potash,  etc. 

Organic  compounds  became  known  in  rapidly  aug- 
menting numbers,  in  consequence  of  the  increasing  attention 
paid  to  the  products  of  vegetable  and  animal  assimilation ; 
the  actual  knowledge  of  such  bodies  continued,  however,  very 
superficial  and  incomplete,  since  their  composition  remained 
quite  obscure.  Of  the  acids,  acetic  acid  became  better 
known,  and  several  of  its  salts  were  used  in  medicine  with 
good  effect.  It  did  not  escape  Glauber  that  the  distillate 
from  wood  contained  an  acid  which  strikingly  resembled 
that  of  vinegar.  The  iatro -chemists  taught  how  to  prepare 
concentrated  acetic  acid  by  the  distillation  of  verdigris, 
whence  it  was  known  as  copper  spirit  or  radical  vinegar  ;  and 
this  latter  substance  Tachenius  was  inclined  to  regard  as  van 
Helmont's  alkahest.  The  two  acetates,  sugar  of  lead  and  the 
basic  acetate,  were  also  examined  more  accurately  by 
Libavius,  and  employed  as  medicines.1 

Salts  of  tartaric  acid,  of  which  tartar  had  been  known 
for  a  long  time,  came  to  be  valued  as  medicines  in  the  sixteenth 
century ;  the  discovery  of  the  free  acid  itself  belongs  to  a 

1  The  liquid  which  distils  over  on  heating  sugar  of  lead  and  which  we 
now  know  to  contain  acetone,  was  investigated  repeatedly  ;  from  its  desig- 
nation of  quintessence,  a  specially  high  value  seems  to  have  been  put  upon  it. 


in  KNOWLEDGE  OF  ORGANIC  COMPOUNDS  97 

much  later  date.  The  designation  tartarus,  applied  to  tartar, 
was  likewise  the  generic  name  in  the  iatro-chemical  age  for 
other  very  different  salts,  e.g.  for  the  salts  of  potash,  in  so  far 
as  they  were  prepared  from  tartar,  and  also  for  sediments 
from  solutions,  especially  those  from  animal  secretions.  The 
part  which  tartarus  played  in  the  theoretical  considerations 
of  iatro-chemistry  has  already  been  spoken  of.  The  salts  of 
other  vegetable  acids  were  also  frequently  termed  tartarus, 
e.g.  salt  of  sorrel,  which  appears  to  have  been  often  confused 
with  tartar.  Neutral  tartrate  of  potash,  known  as  tartarus 
tartarisatus,  from  its  preparation  from  tartar  and  salt  of  tartar 
(K2C03),  and  the  double  tartrate  of  potash  and  soda,  called 
Seignette  salt  after  the  man  who  accidentally  discovered  it, 
likewise  became  known  to  chemists. 

A  compound  of  even  greater  importance  to  the  medical 
treasury  than  the  tartrates  just  mentioned  was  tartar  emetic, 
the  preparation  of  which  from  oxide  of  antimony  and  tartar 
was  described  by  the  Dutch  physician  Mynsicht,  and  after- 
wards more  accurately  by  Glauber.1  A  tartar  containing 
iron  (tartarus  ckalybeatus)  became  known  through  Sala's 
Tartarologia.  Paracelsus  also  made  use  of  the  distillate  from 
tartar — which  is  now  known  to  contain  pyro-tartaric  acid 
besides  other  substances — as  a  medicine  (spiritus  tartari). 

Succinic  acid,  the  near  relation  of  which  to  tartaric  has 
only  become  clear  in  our  own  time,  is  described  by  Libavius 
and  Croll  under  the  name  of  Bernsteinsalz  (flos  succini),  what 
they  referred  to  being  the  distillation  product  of  amber ; 
Lemery  was  the  first  to  recognise  its  acid  nature,  about  1675. 
The  acid  juice  of  the  apple  and  other  fruits  was  employed  for 
preparing  various  medicines  (e.g.  the  tinctura  martis  pomata), 
before  any  attempt  was  made  to  isolate  the  acid  itself.  Free 
benzoic  acid,  however,  obtained  by  subliming  gum  benzoin, 
was  discovered  and  minutely  described  by  the  French 
physician  Blaise  de  Vigenere  (1522-96)  towards  the  end 
of  the  sixteenth  century,  while  Turquet  de  Mayerne  described 

1  It  may  just  be  mentioned  here  that  the  taking  of  small  quantities  of 
tartar  emetic,  prepared  by  allowing  wine  to  stand  in  goblets  made  of  anti- 
mony, had  been  a  common  practice  long  .before  this. 

H 


98  THE  IATRO-CHEMICAL  PERIOD  CHAP. 

the  improved  method  of  preparing  it  in  the  dry  way,  which 
is  still  practised  at  the  present  time.  The  juice  of  gall 
apples,  which  contains  tannic  acid,  and  the  extract  of  oak 
bark  were  used  by  many  iatro-chemists  from  the  time  of 
Paracelsus  to  test  for  iron  in  solutions,  especially  in  mineral 
waters ;  but  no  one  succeeded  in  isolating  either  tannic  or 
gallic  acid  itself. 

Although  the  old  observation — that  the  fats  were  altered 
chemically  by  the  alkalies  and  metallic  oxides — did  not 
lead  the  iatro-chemists  to  a  knowledge  of  the  fatty  acids, 
it  guided  many  of  them,  the  acute  Tachenius  in  particular, 
to  the  correct  assumption  that  "  oil  or  fat  contains  a  hidden 
acid."  It  was  only  one  hundred  and  sixty  years  later  that 
Chevreul's  work  upon  fats  laid  the  firm  foundation  for  the 
present  views  upon  their  chemical  constitution. 

Spirit  of  wine — the  aqua  mice  of  the  alchemists — con- 
tinued to  grow  in  importance  during  the  iatro-chemical  age, 
as  it  had  done  in  the  alchemistic.  This  applied  to  it  not 
merely  from  a  theoretical  point  of  view,  as  being  a  product 
of  various  fermentation  processes  to  which  much  attention 
was  paid,  but  also  from  a  practical,  since  Paracelsus  and  his 
disciples  used  it  largely  in  the  preparation  of  essences  and 
tinctures.1 

To  the  German  physician  Valerius  Cordus  is  due  the 
first  exact  knowledge  of  the  ether  produced  from  alcohol  by 
acting  upon  it  with  sulphuric  acid,  although  his  instructions 
for  preparing  it  were  only  published  after  his  death,  and  the 
ether  then  accepted  in  the  Pharmacopeias  as  oleum  mtrioli 
dulce  verum  (about  1560).  His  work,  however,  became  for- 
gotten so  soon,  that  we  find  even  such  an  accomplished 
chemist  as  Stahl  unaware  of  it.  A  mixture  of  alcohol  and 
ether,  which  later  on  enjoyed  a  wide  popularity  under  the 
name  of  Hoffman's  drops,  had  probably  been  employed  by 
Paracelsus  as  a  medicament.  The  knowledge  of  compound 

1  The  name  alcohol  (cdcool)  for  spirit  of  wine,  which  has  been  in  common 
use  since  the  time  of  Libavius,  had  formerly  quite  another  meaning,  having 
been  applied  indifferently  to  antimony  sulphide,  vinegar  and  various  other 
compounds. 


in  KNOWLEDGE  OF  ORGANIC  COMPOUNDS  99 

ethers  remained  very  fragmentary,  scarcely  any  addition  hav- 
ing been  made  to  it  since  the  observations  of  Basil  Valentine 
(p.  57). 

The  work  done  upon  other  organic  substances  led  to  their 
practical  application  in  medicine  and  in  daily  life,  and  also 
to  improvements  in  the  modes  of  preparing  them,  e.g.  in  the 
extraction  of  sugar  from  the  sugar-cane,  the  juice  being 
clarified  by  white  of  egg  and  lime;  but  scientific  know- 
ledge with  regard  to  such  bpdies  remained  at  the  lowest 
level. 


H  2 


CHAPTER  IV 

HISTORY   OF   THE   PERIOD    OF    THE    PHLOGISTON 
THEORY,  FROM  BOYLE  TO  LAVOISIER 

Introduction. — The  reasons  for  naming  this  period  of  about 
one  hundred  and  twenty  years  the  period  of  the  phlogiston 
theory,  or  of  phlogistic  chemistry,  have  been  already  stated 
shortly  (p.  4).  For  the  first  portion  of  this  era  the  designa- 
tion is  in  truth  not  absolutely  fitting,  since  Robert  Boyle — 
the  man  who  above  all  others  gave  a  new  direction  to 
chemistry  at  the  time — did  not  concur  in  the  phlogistic  views. 
The  development  proper  of  the  phlogiston  theory  really  took 
place  after  his  death.  Nevertheless  the  period  from  Boyle  to 
Lavoisier  may  be  so  named,  because  the  most  important 
part  of  chemical  research  during  that  time  had  to  do  with 
the  phenomena  of  combustion  and — what  was  recognised  as 
analogous — the  calcination  of  the  metals.  All  the  eminent 
chemists  of  that  day  directed  their  attention  to  this  problem 
both  theoretically  and  experimentally.  It  formed,  especially 
towards  the  end  of  this  period,  the  centre  around  which  the 
whole  of  chemistry  circled ;  it  became  a  stumbling-block  to  the 
adherents  of  the  old  doctrines,  and  led  to  a  reform  of  the 
science  so  fundamental  and  far-reaching  that  the  chemistry 
of  to-day  still  lives  under  it. 

The  iatro-chemical  theories  strove  after  the  impossible, 
and  therefore  quickly  succumbed;  the  marked  one-sided- 
ness  apparent  in  them,  the  gratuitous  explanations  of 
life-processes,  and  the  total  neglect  of  the  anatomy  and 
morphology  of  the  organs,  made  their  decline  inevitable. 
An  opportunity  was  thus  given  to  chemistry  to  loosen  and 


CHAP,  iv    GENERAL  CHARACTERISTICS  OF  THIS  PERIOD       101 

finally  break  the  bands  which  medicine  had  wound  around 
her,  and  to  take  up  an  independent  position  of  her  own. 
She  still  remained  for  a  time  under  the  protection  of  the 
healing  art,  to  which  she  was  indeed  an  indispensable  aid ; 
but  from  the  time  of  Boyle  onwards,  the  great  aim  of 
chemistry  was  recognised  as  being  the  discovery  of  new 
chemical  facts,  for  the  sake  of  arriving  at  the  truth  alone. 

The  spirit  of  true  investigation  which  penetrated  the 
natural  sciences  at  the  end  of  the  sixteenth  and  beginning 
of  the  seventeenth  centuries  also  began  to  extend  itself  to 
chemistry,  the  development  of  physics  exerting  an  especially 
powerful  influence  upon  the  younger  sister-science.  The  in- 
ductive method,  too,  acquired  a  continually  growing  and 
a  lasting  influence  as  a  guide,  the  nature  of  which  was 
indicated  by  Francis  Bacon 1  substantially  as  follows  : — 

"  The  true  kind  of  experience  is  not  the  mere  groping  of 
a  man  in  the  dark,  who  feels  at  random  to  find  his  way, 
instead  of  waiting  for  the  dawn  or  striking  a  light.  ...  It 
begins  with  an  ordered — not  chaotic — knowledge  of  facts, 
deduces  axioms  from  these,  and  from  the  axioms  again  designs 
new  experiments."  Equipped  with  such  axioms,  chemistry 
might  enrol  itself  among  the  exact  sciences. 

The  learned  societies  which  came  into  existence  in  the 
second  half  of  the  seventeenth  and  beginning  of  the  eighteenth 
centuries,  and  whose  periodicals  spread  abroad  the  results  of 
chemical  investigations,  aided  materially  towards  the  healthy 
development  of  the  science.  The  incitement  they  gave  to 
researches,  which  could  then  be  submitted  to  verification  by 
other  workers,  was  also  of  great  value.  Finally,  they  promoted 
the  reciprocal  action  of  chemistry  and  allied  branches  of 
science  upon  each  other,  an  action  so  fruitful  in  its  results, 
by  bringing  their  respective  exponents  into  closer  connection. 

1  Novum  Organon,  Aphorism  82,  paragraph  3.  Bacon  in  the  above  para- 
graph gave  expression  to  no  new  idea,  but  merely  called  special  attention 
to  the  value  of  experience,  a  point  already  recognised  by  his  predecessors 
Palissy,  Leonardo  da  Vinci,  Paracelsus  and  others.  Liebig  in  a  series  of 
essays  has  proved  conclusively  how  unjustifiable  it  is  to  designate  Bacon  as 
the  originator  of  the  inductive  method,  and  how  little  he  was  permeated  by 
the  spirit  of  true  research  (see  Liebig's  Reden  und  Abfiandlungen,  1874). 


102  THE  PHLOGISTIC  PERIOD  CHAP. 

The  Royal  Society,  which  was  formed  about  the  middle 
of  the  seventeenth  century  by  the  amalgamation  of  the  two 
smaller  scientific  societies  of  Oxford  and  London,  and  which 
began  to  publish  the  Philosophical  Transactions  in  1665, 
furnishes  a  good  instance  of  what  has  just  been  said.  The 
Italian  academies,  especially  the  Academia  del  Cimento  of 
Florence  (1657),  devoted  themselves  mostly  to  physical  and 
mathematical  studies.  In  Vienna  the  Academia  Naturae 
Ouriosorum  was  started  in  1652,  taking  the  name  of  Ccesarea 
Leopoldina  in  honour  of  its  patron  Leopold  I.  The  Acade'mie 
Roy  ale  originated  in  Paris  in  1666  out  of  friendly  meetings 
which  were  held  at  the  house  of  the  physicist  Mersenne ; 
the  Mtmoires  de  VAcaddmie  des  Sciences  began  to  appear  in 
1699.  The  Berlin  Academy  was  founded  in  1700  by 
Frederick  I.,  Leibniz  being  its  first  president;  and  during 
the  earlier  half  of  the  eighteenth  century  the  northern 
countries  followed  suit  with  similar  learned  societies,  that  of 
St.  Petersburg  being  started  in  1725,  that  of  Stockholm  in 
1739,  and  that  of  Copenhagen  in  1743. 

That  an  extraordinary  interest  was  felt  at  this  time  in 
scientific  questions  is  readily  seen  from  the  literature  of  the 
day,  which  reflects  the  excitement — sometimes  feverish  in 
its  intensity — raised  by  isolated  discoveries,  like  that  of  phos- 
phorus, or  by  disputed  problems,  such  as  the  question  of  the 
cause  of  combustion. 

The  modes  in -which  chemical  questions  were  treated  did 
indeed  approximate  to  the  methods  followed  in  recent  times, 
but  in  one  respect  there  was  a  striking  distinction  between 
them.  The  chemical  investigation  of  the  phlogistic  period 
took  very  little  note  (and  then  only  incidentally)  of  the  propor- 
tions by  weight  in  which  substances  entered  into  reaction ;  it 
turned  its  attention  almost  alone  to  the  qualitative  side  of 
the  phenomena.  The  introduction  and  subsequent  develop- 
ment of  the  phlogistic  doctrines  were  only  possible  because  of 
the  utter  neglect  of  quantitative  relations.  Even  acute  ob- 
servers who  noticed  that  metals  increased  in  weight  upon 
calcination,  and  thus  came  into  direct  conflict  with  the 
phlogistic  view,  evaded  the  only  correct  explanation  of  this, — 


iv  ROBERT  BOYLE  103 

and,  with  it,  of  the  phenomena  of  combustion — by  far-fetched 
conceptions.  This  blinding  of  the  understanding  by  an 
erroneous  theory,  consequent  upon  the  refusal  to  look  into  all 
the  conditions  which  might  have  helped  to  clear  up  the  ques- 
tion, is  peculiar  to  the  period  of  phlogistic  chemistry. 

In  spite,  however,  of  the  fundamental  error  which  ran 

through  it,  the  period  was  a  highly  fruitful  one  for  chemistry ; 

1  it  forms  the  indispensable  introduction  to  the  most  recent 

\phase  of  development  of  the  science.     And  although  it  was 

itself  fettered  by  many  erroneous  ideas,  still  the  phlogistic 

age  contributed  largely  to  the  refutation  of  mischievous  errors, 

e.g.  those  belonging  to  the  iatro-chemical  doctrines  and  the 

false  beliefs  of  alchemy. 


GENERAL  HISTORY  OF  THE  PHLOGISTIC   PERIOD1 

Robert  Boyle  and  his  Contemporaries. 

Boyle  has  been  rightly  spoken  of  as  the  investigator  who, 
by  his  creative  genius,  pointed  out  the  new  path  to  the 
period  just  then  beginning;  it  would  be  even  better  to  say 
that  with  him  this  new  path  originated.  The  spirit  of  pure 
investigation,  free  from  the  fetters  of  alchemistic  and  iatro- 
chemical  conceptions,  animated  this  remarkable  man,  whom 
chemistry  has  to  thank  for  teaching  her  the  real  aims  which 
she  should  pursue.  The  leading  ideas  of  his  scientific  pro- 
gramme, which  are  laid  down  in  the  Preliminary  Discourse 
(in  Shaw's  edition  of  Boyle's  works,  three  vols.,  1725),  deserve 
to  be  quoted  here  : — 

P.  xxvi.  " '  *  '  I  saw  that  several  chyjnaists  had,  by  a 
laudable  diligence,  obtain'd  various  productions,  and  hit 
upon  many  more  phenomena,  considerable  in  their  kind, 
than  could  well  be  expected  from  their  narrow  principles ; 
but  finding  the  generality  of  those  addicted  to  chymistry, 
to  have  had  scarce  any  view,  but  to  the  preparation  of 

1  Cf.  H.  Kopp,  Gesch.  d.  Chemie,  vol.  i.  p.  146  et  seq. ;  Hofer,  Hist,  de  la 
Chimie,  vol.  ii.  p.  146  et  seq. 


104  THE  PHLOGISTIC  PERIOD  CHAP. 

medicines,  or  to  the  improving  of  metals,  I  was  tempted  to 
consider  the  art,  not  as  a  physician  or  an  alchymist,  but  a 
philosopher.  And,  with  this  view,  I  once  drew  up  a  scheme 
for  a  chymical  philosophy  ;  which  I  shou'd  be  glad  that  any 
experiments  or  observations  of  mine  might  any  way  con- 
tribute to  complete." 

P.  xviii.  ".  .  .  And,  truly,  if  men  were  willing  to  regard 
the  advancement  of  philosophy,  more  than  their  own  reputa- 
tions, it  were  easy  to  make  them  sensible,  that  one  of  the 
most  considerable  services  they  could  do  the  world  is,  to 
set  themselves  diligently  to  make  experiments,  and  collect 
observations,  without  attempting  to  establish  theories  upon 
them,  before  they  have  taken  notice  of  all  the  phenomena 
that  are  to  be  solved." 

Experimental  methods,1  taken  in  conjunction  with  the 
careful  observation  of  actual  phenomena,  form  therefore, 
according  to  Boyle,  the  only  sure  foundation  for  specula- 
tions. To  have  made  this  the  common  property  of  chemistry, 
which  from  thenceforth  strove  to  work  out  its  fundamental 
principles  by  means  of  experiment,  is  the  undying  service 
rendered  by  Boyle. 

His  life  2  was  devoted  to  fostering  the  natural  sciences, 
especially  chemistry.  The  seventh  son  and  fourteenth  child  of 
the  Earl  of  Cork,  he  was  born  on  the  25th  of  January,  1626. 
After  an  exceptionally  careful  training  at  Eton,  he  became  a 
student  at  Geneva,  and  continued  his  studies  in  the  quiet  of 
his  estate  of  Stalbridge  until  1654,  when  he  settled  at 
Oxford,  carrying  on  there  a  constant  intercourse  with  other 
eminent  men  of  learning.  While  at  Oxford,  he  belonged  to 
a  society  called  The  Invisible  College,  the  stimulating  effect  of 
which  doubtless  led  to  the  formation  of  the  Royal  Society. 
From  1668  he  lived  in  London,  where  he  continued  to  work 
actively,  as  he  had  done  at  Oxford,  for  the  Royal  Society, 
which  had  been  founded  in  1663  ;  he  became  its  president 

1  Thus  he  says  that  from  these  alone  can  we  look  for  progress  in  all 
useful  knowledge. 

2  For  a  pleasant  account  of  Boyle's  life  and  works  cf.  Thorpe's  Essays  in 
Historical  Chemistry,  p.  1  et  seq. 


iv  BOYLE'S  VIEWS  UPON  THE  ELEMENTS  105 

in  1680  and  held  that  office  until  his  death  in  1691.  His 
noble  and  unpretentious  character,  with  its  accompanying 
modesty,  and  his  simple  religious  tone,  called  forth  astonish- 
ment and  admiration  both  from  his  contemporaries  and  his 
successors.  Wh^^^-Ciontrast Jbetween  this  modesty  and  the 
rude  assumption  of  Paracelsus,  or  the  self-appreciation  of 
van  Helmont  and  many  other  savants  of  the  iatro-chemieal 
age! 

The  services  whichr  Boyle  rendered  in  the  development 
of  chemistry  stretch  over  tlje  most  various  provinces  of  the 
sctencej  Isolated  observations  of  importanc^  by  which  he 
enricne^— indeed,  fundamentally  extended— /applied  chem- 
istry, fche\  knowledge  of  chemical  compounds  >and  their 
analysis,  the  chemistry  of  gase^,  and  pharmacy;  will  be 
treate^  of  in,  the  special  part  of  "this  bo6k.  We  have  at 
present  only  to  do  with  the  general  significance  of  his  work 
and  of  his  theoretical  views  for  chemistry. 

The  term  "  element,"  which  before  Boyle's  time  was 
a  very  fluctuating  and  therefore  uncertain  one,  received 
through  him  a  more  positive  meaning.  In  his  work, 
Chemista  Scepticus  (1661),  he  criticises  the  Aristotelian  and 
the  alchemistic  elements,  which  were  still  accepted  by  many 
in  the  iatro-chemical  age.  He  enunciated  the  axiom  that 
only  what  can  be  demonstrated  to  be  the  undecomposable 
constituents  of  bodies  are  to  be  regarded  as  elements ;  and 
he  considered  it  hazardous  to  advance  opinions  as  to  the 
properties  of  the  elements  in  general,  without  having  first 
obtained  a  firm  foundation  in  their  actual  properties  in- 
dividually. With  a  far-seeing  glance  he  looked  forward  to  the 
discovery  of  a  much  greater  number  of  elements  than  was  at 
that  time  assumed,  at  the  same  time  contending  that  many  of 
the  substances  then  held  to  be  elementary  were  not  really  so. 

Hand  in  hand  with  this  wholesome  simplification  of  views 
upon  the  elements,  there  went  fruitful  ideas  upon  the 
union  of  the  elements  to  compounds,  and  also  upon  affinity 
as  the  cause  of  chemical  combination,  l^oyle  was  the  first 
to  state  with  perfect  clearness  that  a  chemical  compound 
results  from  the  combination  of  two  constituents,  and  that 


106  THE  PHLOGISTIC  PERIOD  CHAP. 

|  it  possesses  properties  totally  different  from  those  of  either 
of  its  constituents  alone.  This  definite  opinion  enabled  him 
to  draw  a  sharp  distinction  between  mixtures  and  chemical 
compounds. 

In  order  to  explain  the  formation  or  decomposition  of 
compounds,  Boyle  advanced  a  corpuscular  theory^which 
gave  evidence  of  his  acuteness  and  showed  how  far  he 
was  ahead  of  his  contemporaries.  In  his  opinion  all 
substances  consisted  of  minute  particles,  and  chemical 
combination  took  place  when  particles  of  different  matter 
which  mutually  attracted  each  other  came  together.  If 
another  substance  interacted  with  this  new  body,  whose 
particles  possessed  a  greater  affinity  for  those  of  one  of  the 
components  of  the  latter  than  these  components  had  for 
each  other,  then  decomposition  ensued.  In  such  simple 
manner  did  Boyle  endeavour  to  explain  the  formation  and 
decomposition  of  chemical  compounds. 

No  one  before  him  had  grasped  so  clearly  and  treated  so 
successfully  the  main  problem  of  chemistry, — the  investigation 
of  the  composition  of  substances.  In  doing  this  he  had  the 
solid  ground  of  experience  and  experiment  under  his  feet, 
and  could  always  bring  forward  evidence  for  the  probability 
of  his  views.  His  endeavours  to  get  at  the  root  of  the 
composition  of  bodies  gave  a  refreshing  impetus  to  analytical 
chemistry,  which  indeed  before  his  time  could  hardly  be  said 
to  exist ;  and  we  are  at  the  same  time  indebted  to  him  for 

/fixing  the  meaning  of  a  "  chemical  reaction."  Boyle  appears 
to  have  been  the  first  to  make  use  of  the  term  analysis,  in  the 
sense  in  which  it  has  since  been  employed  by  chemists. 
.  Boyle  likewise  devoted  much  attention  to  the  question  of 
the  cause  of  combustion  and  other  similar  phenomena,  and 
although  his  attempts  at  explaining  these  were  not  very 
successful,  his  remarkable  experiments  on  the  part  played  by 
air  in  combustion  helped  materially  to  the  later  solution  of 
the  problem.  His  work  on  air  and  gases  led  him  in  1660 
to  the  memorable  discovery  of  the  now  well-known  law  that 
x  "the  volume  of  a  gas  varies  inversely  with  the  pressure" 
(Mariotte  found  this  out  independently  seventeen  years  later). 


iv  BOYLE'S  WRITINGS  ;  LEMERY  AND  HOMBERG          107 


Boyle's  writings,  which  were  already  widely  read"  in  his 
,  are  characterised  by  simplicity  of  style  and 


clearness  of  expression  ;  they  offer  an  agreeable  contrast  to 
the  works  of  many  of  the  other  chemists  of  his  time,  who 
sought  to  hide  their  deficiencies  in  clear  thought  and  accurate 
knowledge  by  metaphorical  and  mysterious  language.  In 
addition  to  other  papers  published  in  the  Philosophical 
Transactions,  the  following  works  of  his,  which  were  brought 
out  both  in  English  and  Latin,  are  to  be  especially  men- 
tioned :  —  The  Sceptical  Chymist  (Chemista  Scepticus)  first  pub- 
lished anonymously  in  1661,  and  afterwards  in  numerous 
editions  with  Boyle's  name  as  author  ;  Tentamina  qucedam 
Physiologica  (1661);  and  Experimenta  et  Consider  utiones  de 
Coloribus  (1663). 

Among  the  contemporaries  of  Boyle  who  also  advanced  the 
natural  sciences,  especially  chemistry,  and  of  whom  Willis, 
Hooke,  Wren  and  Hawksbee  must  be  mentioned  here,  there 
was  one  in  particular  who,  although  a  practising  physician 
himself,  rendered  good  service  to  chemistry  by  his  observa- 
tions on  combustion  and  calcination,  viz.  John  Mayow 
(born  1645).  His  assumption  —  that  atmospheric  air 
contained  a  substance1  (also  present  in  saltpetre)  which 
combined  with  metals  when  they  were  calcined,  and  which 
sustained  respiration  and  converted  the  venous  blood  into 
arterial  —  was  bound  to  result  in  the  right  interpretation  of 
the  phenomena  of  combustion,  when  the  observations  which 
had  led  to  it  were  sufficiently  extended.  Mayow's  early 
death  in  1679  was  perhaps  the  reason  why  this  did  not 
come  about,  the  development  of  the  new  chemistry  being 
greatly  retarded  in  consequence. 

Lemery  and  Homberg.  —  The  Academic  Royale  rfes 
Sciences  formed  in  France  the  centre  of  union  for  chemists 
in  that  country,  the  chief  exponents  of  the  science  in 
Boyle's  time,  particularly  during  the  last  quarter  of  the 
seventeenth  century,  being  Wilhelm  Homberg  and  Nicolas 
Lemery.  Both  of  them  being  good  observers,  their  work 

1  Mayow  termed  this  substance  spiritus  igno-aereus  or  nitro-a&reus. 


108  THE  PHLOGISTIC  PERIOD  CHAP. 

tended  chiefly  to  the  development  of  practical  chemistry, 
which  was  especially  indebted  to  Homberg  for  many  valuable 
contributions.  In  the  scientific  explanation  of  technical 
processes  they  come  a  long  way  after  Boyle ;  Homberg,  in 
particular,  was  still  trammelled  by  alchemistic  views,  and 
held  fast  to  the  idea  that  substances  consisted  of  sulphur, 
mercury  and  salt. 

Lemery,  born  in  1645,  hardly  did  any  independent 
work  on  the  treatment  of  theoretical  questions,  but  he  well 
knew  how  to  sift  and  put  together  the  facts  already  known. 
This  is  shown  in  his  Cours  de  CJiymie1  brought  out  in  1675, 
which  was  for  long  held  to  be  the  best  text-book  of  chemistry, 
and  was  so  widely  used  that  the  author  himself  lived  to  see 
thirteen  editions  of  it  published. 

In  addition  to  this  literary  work  Lemery  was  exceedingly 
active  as  a  teacher,  the  last  thirty  years  of  his  life  being 
taken  up  in  that  way ;  in  his  earlier  years  he  was  much 
involved  in  religious  polemics,  and  hence  was  unable  to  turn 
his  chemical  knowledge  to  the  best  account  during  that 
period. 

Lemery  designated  chemistry  a  "  demonstrative  science," 
and  therefore  sought  to  elucidate  chemical  operations  by  suit- 
able experiments.  In  theoretical  questions,  e.g.  in  his  views 
upon  combustion  and  upon  the  composition  of  substances,  he 
was  for  the  most  part  an  adherent  of  Boyle. 

While  Lemery  was  chiefly  exercised,  then,  about  the 
effective  propagation  of  his  science,  Homberg — born  in  1652 
and  permanently  settled  in  Paris  after  a  restless  life  and 
multifarious  study — found  particularly  good  opportunity,  as 
body-physician  and  alchemist  to  the  Duke  of  Orleans,  of 
making  numerous  and  sometimes  important  observations 
in  practical  chemistry.  Some  of  his  researches,  e.g.  that  upon 
the  saturation  of  acids  by  bases,  contained  fruitful  germs 

1  Shortly  before  the  publication  of  the  Cours  de  Chymie,  two  other  text- 
books appeared  in  Paris,  both  entitled  Traite  de  Chymie,  by  Lefevre  (1660) 
and  Chr.  Glaser  (1663),  under  the  latter  of  whom  Lemery  had  begun  his 
studies.  Glaser's  book  treats  chiefly  of  pharmaceutical,  and  Lefevre's  of 
theoretical  chemistry,  which  latter,  however,  was  not  much  advanced  by  it. 


iv  KUNKEL  AND  BECHER  109 

which  became  developed  later  on  in  the  hands  of  other 
workers.  Most  of  the  writings  of  these  two  men,  both  of 
whom  died  in  the  same  year  (1715),  were  published  in  the 
Memoirs  of  the  French  Academy. 

Kunkel  and  Bee  her. — The  most  eminent  German 
chemist  in  Boyle's  time  was  Kunkel,  in  conjunction  with 
whom  Becher  must  also  be  named.  Closely  connected  with 
the  latter  was  Stahl,  the  originator  of  the  phlogiston  theory, 
of  which  the  germs  are  to  be  seen  in  the  views  of  both  of  the 
men  first  mentioned. 

Johann  Kunkel,  born  at  Rendsburg  in  1630,  did  excellent 
service  to  practical  chemistry  as  an  able  experimenter  and 
acute  observer.  Originally  a  pharmacist,  he  early  showed  the 
leaning  towards  alchemy  which  was  decisive  and  fateful  as 
regarded  the  whole  course  of  his  life ;  he  was  too  honest 
not  to  see  through  many  of  the  frauds  of  adepts,  but  at  the 
same  time  was  so  firmly  convinced  of  the  possibility  of  the 
transmutation  of  metals  that  he  gave  his  life-work  to 
solving  the  problem.  Employed  as  an  alchemist  by  various 
princes  (among  whom  were  the  Dukes  of  Lauenburg,  the 
Elector  John  George  of  Saxony,  and  the  great  Elector  of 
Brandenburg),  whose  desires  he  was  unable  to  gratify,  he  led 
a  restless  life  which  came  to  a  close  at  Stockholm  in  1702, 
where,  by  the  favour  of  Charles  XL,  he  had  found  a  more 
honourable  position  than  any  previously  allotted  to  him. 
Kunkel's  preconceived  opinions  caused  his  writings  to  be  per- 
meated by  mischievous  errors,  and  to  contain  work  bearing 
upon  alchemy.  What  a  contrast  between  him  and  Boyle ! 
While  the  latter  was  seeking  to  ascertain  the  real  composition 
of  substances,  and  to  get  at  their  demonstrable  constituents, 
the  former  still  held  to  the  tenet  that  all  metals  contained 
mercury.  Nevertheless,  as  a  promoter  of  experimental 
chemistry,  and  therefore  of  practical  chemical  knowledge, 
Kunkel  deservedly  holds  a  high  place. 

Johann  Joachim  Becher,  who  was  born  at  Speyer  in 
1635  and  died  in  London  in  1682,  worked  almost  contem- 
poraneously with  Kunkel,  but  more  for  the  theoretical 


110  THE  PHLOGISTIC  PERIOD  CHAP. 

explanation  of  already  observed  facts  than  for  the  practical 
side  of  the  subject ;  in  his  unsettled  life  and  his  propensity 
towards  new  projects,  he  resembled  the  latter.  He  worked 
as  an  alchemist  at  various  courts  (in  Mainz,  Munich  and 
Vienna),  but  he  was  too  honourable  to  deceive  his  patrons, 
and  too  candid  to  allow  of  his  remaining  long  in  any  one  place. 
His  bold  technical  projects  almost  always  came  to  nothing ; 
they  show  only  too  clearly  their  author's  deficiency  in  practical 
chemical  knowledge.  In  theoretical  questions  as  to  the  com- 
position of  substances  Becher  attempted  to  revive  the  old  ideas 
of  Basil  Valentine  and  Paracelsus  in  another  form.  In  place 
of  mercury,  sulphur  and  salt,  he  set  up  three  "  earths,"  of 
which  all  inorganic  ("  sub-terrestrial ")  bodies  should  consist, 
viz.  the  mercurial,  the  vitreous  and  the  combustible  (terra 
pinguis).  The  nature  of  any  material  depended  upon  the 
proportions  in  which  these  three  fundamental  earths  were 
contained  in  it.  Of  especial  importance  w:as  Becher's 
assumption  that,  when  substances  were  burnt  or  metals 
calcined,  the  terra  pinguis  escaped,  and  that  in  this  escape 
lay  the  explanation  of  combustion ;  it  was  from  this  concep- 
tion that  Stahl's  phlogiston  theory  originated.  The  opinions 
of  Becher  upon  the  production  of  salts  and  acids  from 
these  earths  were  also  received  with  approbation  by  his 
disciples. 

These  theoretical  views  are  to  be  found  in  Becher's 
first  work,  Physica  Subterranea  (1669),  and  in  his  last, 
Theses  Chymicce  (1682).  His  doctrines  acquired  great 
celebrity  through  Stahl,  whose  work  belongs  for  the  most 
part  to  the  eighteenth  century,  on  which  he  conferred  a 
character  of  its  own  by  his  development  of  the  phlogiston 
theory. 

Stahl  and  the  Phlogiston  Theory. 

The  theory  of  the  phenomena  of  combustion  and  other 
analogous  processes,  which  were  to  be  explained  by  the 
assumption  of  the  hypothetical  phlogiston,  was  the  point  round 
which  chemists  in  general  gravitated  during  the  eighteenth 


iv  STAHL'S  PHLOGISTON  THEORY  111 

century;  until  the  appearance  of  Lavoisier  the  phlogiston 
theory  received  the  assent  of  most  investigators. 

Georg  Ernst  Stahl,  born  at  Anspach  in  1660,  devoted 
himself  to  the  study  of  medicine,  and  acquired,  first  at  Jena 
and  later  on  at  Halle — to  whose  university  he  had  been  called 
as  professor  of  medicine  and  chemistry  in  1693 — ,  the  reputa- 
tion of  a  distinguished  physician  and  academic  teacher. 
Appointed  physician  to  the  king  in  1716,  he  removed  to 
Berlin,  where  he  laboured  with  success  for  the  extension  of 
chemical  knowledge  until  his  death  in  1734.  He  worked 
at  chemistry  in  the  true  scientific  spirit ;  himself  guided  by 
the  ardent  desire  to  discover  the  truth,  he  was  able  to  draw 
around  him  pupils  animated  by  a  similar  aim.  The  most 
eminent  among  the  Berlin  chemists  of  the  succeeding 
generation  studied  under  him. 

Even  in  his  own  lifetime  the  doctrines  which  he  taught, 
togetherwith  a  number  of  valuable  detached  observations,  were 
widely  disseminated  by  means  of  his  writings,  and  especially  by 
his  lectures,  the  latter  of  which  were  published  by  several  of 
his  pupils.1  Stahl,  however,  exercised  his  greatest  influence 
both  upon  his  contemporaries  and  upon  the  succeeding  genera- 
tion by  his  phlogiston  theory,  which  eclipsed  all  his  other 
chemical  work. 

Stahl  himself  freely  recognised  the  close  connection 
between  his  views  upon  combustion  and  calcination  and  the 
original  ones  of  Becher ;  he  went  to  work,  however,  quite 
differently  from  the  latter,  although  his  doctrine  was  grounded 
upon  Becher's  idea  regarding  the  combustible  constituent. 
This  assumption  of  a  constituent  common  to  combustible 
bodies  (a  "  fire  material,"  a  "  sulphur,"  and  so  on)  was  indeed 
of  older  date  than  that  of  Becher's  terra  pinguis,  which  Stahl 
at  once  utilised,  in  order  to  build  up  his  phlogiston  theory 
thereon.  This  rests  upon  the  hypothesis  that  combustible 
substances — among  which  the  metals  capable  of  calcination 

1  Among  Stahl's  writings  we  may  name  the  Zymotechnia  Fundamentally, 
etc.  (1697);  Specimen  Becherianum,  etc.  (1702);  and  Zufallige  Gedanken  uber 
den  Streit  von  dem  sogenannten  Sulphure  ("Occasional  Thoughts  on  the 
Dispute  regarding  the  so-called  Sulphur"),  (1718).  Of  his  pupils,  Juncker 
was  especially  active  in  propagating  the  views  of  his  master. 


112  THE  PHLOGISTIC  PERIOD  CHAP. 

were  reckoned — contain   phlogiston   as   a  common   constit- 
uent, which  escapes  on  combustion  or  calcination.     Since, 
as  was  then  held,  every  phenomenon  bearing  upon  this  could 
be  readily  explained  by  the  aid  of  such  an  assumption,  it 
was  considered  unnecessary  to  prove  the  actual  existence  of 
phlogiston  itself  directly.     Stahl  was  able  by  means  of  it 
to  group  uniformly  together  and  to  explain  a  large  number 
of  chemical  reactions.     The  more  violently  the  combustion  of 
any  substance  went  on — so  he  taught, — the  richer  it  was  in 
phlogiston ;  coal,  which  can  be   almost  entirely  consumed, 
was  therefore  to  be  regarded  as  nearly  pure  phlogiston.     In 
order  to  reproduce  the  original  substance,  its  combustion- 
products  had  to  be  added  to  it  again;  in  this  manner  the 
metals  were  "  revived "    from    their   calces,   which,   accord- 
ing to  Stahl's  notion,  had  resulted  from  the  former  through 
the  escape  of  the  phlogiston.     When  a  metallic   calx  was 
heated  along  with  coal,  the  phlogiston  so  abundantly  con- 
tained in  the  latter  combined  with  it,  the  metal  being  thus 
reproduced ;  consequently  a  metallic  calx  was  a  constituent 
of  a  metal.     Upon  a  like  sophism  rested  Stahl's  assumption 
that  sulphur  consisted  of  sulphuric  acid  and  phlogiston.     He 
saw  in  the  production  of  sulphur,  on  heating  sulphuric  acid 
or   a   sulphate  with   coal   (phlogiston),  a   synthesis   of  the 
former,  and  therefore  a  proof  that  sulphur  was  a  compound 
body.     Upon  the  further  logical  conclusion, — that  the  pro- 
ducts of  combustion  of  any  substance  must  be  lighter  than 
that  substance  itself,  seeing  that  they  are  constituents  of  it, 
no  importance  was  placed.     And  no  attention  was  paid  to 
the  numerous  observations  which  showed  that  this  was  not  the 
case? — that,  indeed,  a  calcination  of  the  metals  was  accom- 
panied by  an  increase  in  weight.     It  was  facts  like  those 
just  named  which,  after  a  prolonged  struggle,  brought  about 
the  overthrow  of  the  phlogiston  theory. 

To  Stahl  belongs  the  merit  of  grouping  together  the 
phenomena  of  oxidation  and  reduction,  as  we  now  term 
these,  albeit  by  the  aid  of  a  false  hypothesis.  The  addition' 
of  phlogiston  is  equivalent  to  reduction,  and  its  withdrawal 
or  escape  to  oxidation.  The  analogy  between  respiration 


iv  HOFFMANN  AND  BOERHAVE  113 

and  the  decomposition  of  animal  matters  on  the  one 
hand,  and  combustion  on  the  other,  did  not  escape  Stahl, 
who  likewise  assigned  the  chief  role  in  these  processes  to 
phlogiston. 

The  value  of  his  theory  lay  therefore  in  the  interpretation 
which  it  afforded  of  a  variety  of  processes  from  one  common 
point  of  view.  The  simplicity  of  this  explanation  blinded 
both  himself  and  the  generation  which  followed  him  to  such 
a  degree  that  they  left  unnoticed  all  the  glaring  contradic- 
tions between  actual  facts  and  the  phlogistic  doctrine. 
Notwithstanding  this,  however,  the  latter  was  not  an 
obstacle  to  the  development  of  chemistry,  seeing  that 
chemists  like  Black,  Cavendish,  Marggraf,  Scheele,  Bergman 
and  Priestley,  who  so  greatly  extended  the  science  by  their 
wide-reaching  discoveries,  were  phlogistonists  in  the  full 
sense  of  the  word. 

Hoffmann  and  Boer  have. — Before  speaking  of  the 
further  destinies  of  the  phlogiston  theory,  and,  in  connec- 
tion with  this,  of  the  state  of  chemistry  at  that  date,  the 
work  of  two  of  Stahl's  contemporaries  who  contributed 
materially  to  the  advancement  of  the  science  must  be 
considered,  viz.  Friedrich  Hoffmann  and  Hermann  Boerhave. 
Both  of  these  men  were  eminent  physicians  and  accomplished 
chemists,  but  they  were  not  exactly  adherents  of  Stahl's 
phlogiston  doctrine,  although  they  held  similar  views  with 
regard  to  combustion. 

Hoffmann,  born  at  Halle  in  1660,  i.e.  in  the  same  year 
as  Stahl,  after  acquiring  a  thorough  knowledge  of  medicine, 
mathematics  and  the  natural  sciences,  practised  first  as  a 
physician  and  then  became  professor  of  the  science  of  medicine 
in  Halle,  where  he  ultimately  died  in  1742,  after  an  inter- 
regnum spent  in  Berlin.  His  most  important  work  was  done 
in  medicine  and  in  pharmaceutical  and  analytical  chemistry. 
He  combated  with  success  the  iatro-chemical  doctrines  of 
Sylvius  and  Tachenius,  which  still  held  their  ground  with 
many  physicians,  exposing  their  absurdities  and  showing 
to  what  nonsensical  deductions  such  exaggerations  led. 

I 


114  THE  PHLOGISTIC  PERIOD  CHAP. 

Many  of  his  investigations  and  discoveries  in  pharmaceuti- 
cal and  analytical  chemistry  will  be  touched  upon  in  the 
special  history  of  this  time.  Hoffmann's  views  on  com- 
bustion were  very  similar  to  those  of  Stahl.  With  respect 
to  the  calcination  of  the  metals  and  the  reduction  of  their 
oxides,  however,  he  expressed  opinions  which  approximate 
to  those  held  at  the  present  day,  believing,  as  he  did, 
that  metallic  calces  contained  a  sal  acidum'  in  addition  to  a 
metal,  the  former  of  which  escaped  when  the  calces  were 
reduced.  This  assumption  did  away  with  the  similarity 
between  combustion  and  calcination  ;  these  phenomena 
became  indeed  rather  opposed  to  one  another  thereby,  and 
with  this  the  special  use  of  the  phlogiston  theory  vanished. 
Hoffmann  was  a  very  voluminous  author,  and  his  collected 
works,  entitled  Opera  Omnia  Pkysico-medica.  show  clearness 
of  style  and  precision  of  expression. 

Hermann  Boerhave,  born  in  1668  at  Voorhout  near 
Leyden,  was  originally  destined  for  the  study  of  theology, 
but  devoted  himself  to  medicine,  gaining  at  the  same  time 
an  excellent  knowledge  of  the  natural  sciences,  and  especi- 
ally of  chemistry.  From  the  year  1709  onwards,  he  was  able 
to  utilise  his  catholic  education  to  advantage  as  professor  of 
medicine,  botany  and  chemistry  in  Leyden,  and  attained  to 
the  highest  distinction;  he  died  there  in  1738. 

Boerhave's  place  in  the  history  of  chemistry  is  due  not 
to  any  striking  experimental  researches,  but  to  the  excep- 
tional acuteness  which  he  showed  in  noting  and  collating 
chemical  phenomena  from  one  common  point  of  view.  His 
large  text-book  Elementa  Chemiw  (1732) x  was  intended  to 
contain  all  the  most  important  work  done  in  chemistry, 
and  for  a  long  time  it  remained  by  far  the  best  guide  to 
the  study  of  the  science.  His  estimate  of  the  latter  as 
an  absolutely  independent  science,  subordinate  to  no  other, 

1  The  admirable  English  editions  of  Boerhave's  text-book  were  edited 
with  great  care  and  success  by  Dr.  Peter  Shaw.  As  a  writer  in  the 
Saturday  Review  has  pointed  out,  the  third  edition  of  Shaw's  translation, 
which  appeared  in  1753  in  two  quarto  volumes,  contains  a  mass  of  original 
notes  of  great  value  and,  especially,  some  detailed  catalogues  of  early 
Greek  writings  upon  alchemy. 


iv  BOERHAVE'S  PLACE  IN  CHEMICAL  HISTORY  115 

and  whose  aim  should  be  the  investigation  and  perception 
of  chemical  facts,  was  at  once  a  beneficial  and  an  elevated 
one.  In  accordance  with  this  view  we  find  him  condemning 
the  abuses  which  the  iatro-chemists  had  introduced  into 
chemistry.  The  work  of  the  alchemists  he  did  not  criticise 
sharply  enough  ;  in  his  endeavours  to  test  the  assertions 
which  they  made,  he  believed  that  he  found  here  and  there 
some  corroboration  of  them,  and  was  thus  probably  not  dis- 
inclined to  decide  in  favour  of  the  adepts  in  cases  where 
experience  had  not  as  yet  spoken  her  last  word.  On  the  other 
hand,  he  refuted  many  statements,  such  as  those  which  told 
of  the  fixation  of  mercury  and  of  the  production  of  the  latter 
from  lead  salts,  and  thus  contributed  to  clear  up  and  rectify 
alchemistic  opinions  and  assertions. 

Boerhave  appears  to  have  concurred  in  the  phlogiston 
theory  in  many  points,  at  least  he  expressed  no  opinions 
contrary  to  Stahl's  fundamental  views,  although  he  did  not 
agree  in  regarding  the  calces  of  the  metals  as  the  earthy 
elements  of  these  latter.  Like  many  other  investigators,1 
Boerhave  studied  the  processes  involved  in  calcination,  and 
to  him  is  due  the  valuable  experimental  contradiction  of  the 
view  put  forth  by  Boyle  and  others, — that,  during  calcina- 
tion, a  ponderable  fire-stuff  is  taken  up,  and  thus  the  increase 
in  weight  of  the  metals  explained. 


The  Development  of  Chemistry,  and  particularly  of  the 
Phlogiston  Theory,  after  Stahl's  time. 

The  influence  of  Stahl's  doctrine  manifested  itself  more 
immediately  in  Germany,  where  it  received  the  almost 
unqualified  support  of  chemists,  Berlin  remaining  the 
centre  point  of  this  theory.  Among  the  men  who  upheld 
and  sought  to  propagate  it,  Marggraf  was  the  most  eminent. 
Kaspar  Neumann  (born  1683)  and  Johann  Theodor  Eller 
(born  1689),  contemporaries  of  Stahl,  were  also  active 
adherents  of  the  doctrine  in  the  capital  city  of  Prussia. 
Both  of  them,  as  professors  at  the  medico-chirurgical  institute, 

I  2 


116  THE  PHLOGISTIC  PERIOD  CHAP. 

were  in  a  high  degree  active  in  maintaining  and  spreading  a 
knowledge  of  chemistry.  Their  own  observations  were, 
however,  of  little  importance ;  those  of  Eller  were  chiefly 
upon  subjects  of  medical  physiology,  and  are  full  of  untenable 
speculations.  Stahl's  disciple  and  pupil  Johann  Heinrich 
Pott  (born  1692)  enriched  chemistry  by  many  valuable 
observations,  but  he  was  unfortunate  in  his  explanation  of 
these,  regarding  boracic  acid,  for  instance, — a  substance 
which  he  had  himself  investigated  carefully — as  consist- 
ing of  copper  vitriol  and  borax.  The  results  which  he 
achieved  were  not  at  all  commensurate  with  his  untiring 
perseverance,  which  he  showed,  among  other  ways,  in  his  en- 
deavours to  prepare  porcelain.  Although  an  adherent  of  the 
phlogistic  doctrine,  Pott  did  not  bring  forward  anything 
new  in  its  favour ;  with  regard  to  the  nature  of  phlogiston 
itself,  he  could  only  express  the  opinion  that  it  was  "  a  variety 
of  sulphur." 

Andreas  Sigismund  Marggraf1  (1709-1782)  was  the 
last  and  most  eminent  adherent  of  phlogistic  views  in 
Germany.  Destined  originally  for  an  apothecary,  he 
acquired  a  knowledge  and  practical  experience  of  chemistry, 
pharmacy  and  metallurgy  as  assistant  to  Neumann  at  Berlin, 
and  by  sedulous  study  at  the  high  schools  of  Frankfurt  on 
the  Oder,  Strasburg  and  Halle,  and  finally  at  the  Freiberg 
School  of  Mines  ;  this  knowledge,  accompanied  as  it  was  by  ex- 
ceptional gifts  of  observation,  put  him  in  a  position  to  carry 
out  researches  of  the  greatest  value.  One  has  only  to  think, 
of  the  observations  made  by  him  in  his  work  on  phosphoric 
acid, — observations  which,  considering  the  highly  defective 
state  of  chemical  analysis  at  that  date,  fill  us  with  admira- 
tion ;  of  the  proof  which  he  furnished  of  the  difference  be- 
tween alum  and  the  so-called  bitter  earth  (magnesia),  sub- 
stances which  had  hitherto  been  generally  confounded  ;  and, 
above  all,  of  his  investigation  of  the  juice  of  the  red  beet,  in 
which  he  discovered  cane  sugar  (see  special  section  of  this 
book).  It  was  during  this  research  that  Marggraf  introduced 

1  For  an  account  of  his  life  and  works  see  A.  W.  Hofmann's  charming 
Erinnerungen  aus  der  Berliner  Vergangenheit,  p.  10  et  seq. 


iv  THE  FRENCH  PHLOGISTONISTS  117 

the  microscope  into  chemistry,  as  a  valuable  aid  in  distin- 
guishing between  different  substances. 

With  this  great  talent  for  observation  he  united  the  gift 
of  drawing  what  were  generally  sound  conclusions  from  his 
work.  In  one  point,  however,  Marggraf,  like  all  phlogis- 
tonists,  was  not  in  a  position  to  do  this ;  although  he  had 
himself  proved  that  phosphorus  increases  in  weight  by 
conversion  into  phosphoric  acid,  he  could  not  free  himself 
from  the  idea  that  phlogiston  escaped  during  this  process  of 
combustion.  And  he  could  never  be  brought  to  see  that 
this  conception  was  an  erroneous  one,  although  the  anti- 
phlogistic doctrine  was  brought  out  several  years  before  his 
death.  Marggraf 's  papers  are  almost  all  contained  in  the 
Memoirs  of  the  Berlin  Academy ;  most  of  them  were 
published  during  his  lifetime  in  two  volumes,  under  the 
title  Chemische  Schriften. 

The  French  Phlogistonists. — The  chief  exponents  of 
chemistry  in  France  during  the  eighteenth  century  until 
the  downfall  of  the  phlogistic  system  were  Geoffroy, 
Duhamel,  Rouelle  and  Macquer,  who  concurred  essentially 
in  Stahl's  views.  They  enriched  the  science  not  only  by 
important  facts,  but  also  now  and  again  by  useful  working 
theories. 

Stephan  Frangois  Geoffroy  (the  elder,  to  distinguish  him 
from  his  less  celebrated  younger  brother,  Claude  Joseph, 
whose  work  was  chiefly  pharmaceutico-chemical)  was  born 
in  Paris  in  1672,  and  helped  for  some  time  in  his  father's 
drug  shop;  he  gave  himself  up,  however,  to  chemical  and 
medical  studies,  and  laboured  with  great  success  as  professor 
of  medicine  in  the  Jardin  des  Plantes  from  the  year  1712 
until  his  death  in  1731.  Geoffroy  made  himself  a  name 
throughout  the  scientific  world  by  his  researches  upon 
chemical  affinity  ;  his  Tables  des  Rapports  (tables  of  affinity), 
in  which  the  results  of  his  most  important  observations  are 
collected,  exercised  a  great  influence  upon  the  doctrine  of 
affinity.  His  theoretical  views  were  less  happy,  e.g.  he  looked 
upon  the  iron  found  in  the  ashes  of  plants  as  having  been 


118  THE  PHLOGISTIC  PERIOD  CHAP. 

produced  artificially  during  the  process  of  ignition.  In  the 
questions  of  combustion  and  calcination  he  approximated 
very  closely  to  Stahl's  view ;  the  metals,  for  example,  he  re- 
garded as  composed  of  earths  and  a  species  of  sulphur. 
Geoffroy  rendered  a  real  service  by  the  energy  with  which  he 
attacked  alchemistic  frauds,  subjecting  these  as  he  did  to 
critical  examination  in  the  memoir  Des  Supercheries  concernant 
la  Pierre  Philosophale,  presented  to  the  French  Academy. 

Geoffroy 's  treatises  were  published  partly  in  the 
Memoirs  of  the  French  Academy,  and  partly  in  the 
Philosophical  Transactions.  His  long-celebrated  work,  Trac- 
tatus  de  Materia  Medica,  shows  what  a  high  value  he  placed 
upon  chemistry  as  a  sister  science  and  aid  to  medicine. 

Duhamel  de  Monceau  (born  1700,  died  1*781),  of  the 
school  of  Lemery  and  Geoffroy,  spent  his  entire  life  in  Paris, 
where  his  versatility  gained  for  him  a  high  reputation. 
His  sterling  work  was  not  by  any  means  in  pure  chemistry 
alone,  but  also  in  physics,  meteorology,  physiology,  botany, 
and — particularly — in  chemistry  as  applied  to  agriculture. 
We  must  make  especial  mention  here  of  the  fact  that  he 
furnished  definite  proof  of  the  difference  between  potash  and 
soda,  by  preparing  the  latter  pure ;  he  also  showed  that  it 
was  the  base  of  rock-salt,  borax  and  Glauber's  salt.  The 
first  proposals  to  prepare  soda  artificially  from  rock-salt 
came  from  him,  a  fact  which  shows  his  far-sightedness. 

Whilst  Duhamel  worked  purely  as  an  academician, 
Guillaume  Frai^ois  Rouelle  (born  1703,  died  1770)  was 
mainly  occupied  in  teaching,1  in  which  he  greatly  excelled ; 
some  of  his  pupils,  particularly  Lavoisier  and  Proust,  arrived  at 

1  The  numerous  records  of  Rouelle' s  activity  as  a  teacher,  which  have 
come  down  to  us,  enable  us  to  form  a  clear  picture  of  the  conditions  of 
chemical  teaching  in  those  days,  and  at  the  same  time  to  appreciate  the 
remarkable  personality  of  the  man.  The  lectures  on  chemistry  were  de- 
livered by  two  professors,  one  of  them  treating  the  theory  of  chemical  pro- 
cesses, whilst  the  other,  in  conjunction  with  him,  showed  and  explained 
how  they  were  carried  out  practically.  While  the  former  (Bourdelin) 
fatigued  his  audience  by  abstract  reasonings,  Rouelle  inspired  the  students 
of  practical  chemistry  by  the  vivacity  of  his  discourse,  during  which  he 
frequently  became  so  excited  as  to  throw  off  his  periwig  and  some  of  his 
articles  of  clothing  (cf.  Hofer,  Hist,  de  la  Chimie,  vol.  ii.  p.  378). 


iv  THE  BRITISH  PHLOGISTONISTS— BLACK  119 

the  highest  eminence.  At  the  same  time  he  was  also  busy  as  an 
investigator,  as  many  admirable  observations  and  conclusions 
drawn  from  these  show.  Rouelle  fixed  the  meaning  of  the  term 
"  salt  "  (in  the  Memoirs  of  the  Academy  for  1 745)  from  a  far 
more  general  point  of  view  than  van  Helmont  or  Tachenius 
had  done.  The  composition  of  a  substance  alone  was  sufficient 
to  tell  him  whether  it  belonged  to  the  class  of  salts  or  not. 
Salts  were  produced  by  the  combination  of  acids  of  every  kind 
with  the  most  various  bases ;  and,  in  addition  to  neutral  salts, 
he  drew  a  distinction  between  acid  and  basic  ones.  With  views 
so  clear  as  these,  Rouelle  was  far  ahead  of  his  contemporaries. 

Among  the  latter  was  Pierre  Josephe  Macquer  (born 
1718,  died  1784),  who  was  likewise  an  active  and  successful 
teacher  at  the  Jardin  des  Plantes,  and  who  also  aided 
effectively  in  the  spread  of  chemical  knowledge  by  means  of 
his  text-books.1  His  own  individual  work  lay  less  in 
theoretical  than  in  applied  chemistry,  to  which  he  made 
valuable  contributions  (especially  in  the  manufacture  of 
pottery  and  in  dyeing). 

From  the  beginning  of  his  career  to  its  end  Macquer 
was  a  phlogistonist,  and  did  all  that  he  could  to  reconcile 
the  continually  augmenting  discrepancies  between  theory 
and  facts ;  he  paid  no  heed  to  proportions  by  weight,  for  it 
was  only  in  this  way  that  he  could  maintain  the  phlogistic 
hypothesis.  And  even  although  it  was  proved  to  be 
erroneous  and  untenable  several  years  before  his  death,  he 
was  still  unable  to  renounce  it. 

TheEnglish, Scotch  and  Swedish  Phlogistonists.— 
Joseph  Black,  professor  of  chemistry  in  the  Universities  of 
Glasgow  and  Edinburgh  successively,  who  was  born  in  1728 
and  died  in  1799,  advanced  chemistry  in  an  exceptional 
degree  by  his  splendid  experimental  researches,  which  were 
published  in  the  Philosophical  Transactions  ;  in  especial  by  his, 
for  that  time,  masterly  investigations  on  carbonic  acid  and 
its  compounds  with  the  alkalies  and  alkaline  earths,  which 

1  The  principal  of  these  were  :  Elements  de  Chymie  Thevrique  (1749)  ; 
Elements  de  Chymie  Pratique  (1751) ;  and  his  Dictionnaire  de  Chymie  (1778). 


120  THE  PHLOGISTIC  PERIOD  CHAP. 

were  planned  and  carried  out  with  the  utmost  ingenuity.  His 
observations  led  to  a  clear  knowledge  of  processes  which 
had  formerly  been  explained  quite  wrongly,  and  they  drew 
the  attention  of  investigators  in  a  special  manner  towards 
gases ;  the  work  done  with  these  had  the  effect  of  causing 
chemistry  to  proceed  on  new  lines,  and  was,  in  fact,  the 
necessary  forerunner  of  the  latest  epoch  of  the  science. 
In  addition  to  this  Black  threw  open  a  new  field  to  physics 
by  the  discovery  of  latent  heat  in  1 7  6  2,  in  which  his  wonder- 
ful gift  of  experimenting  came  to  his  aid.1 

In  order  to  appreciate  his  labours  at  their  true  value, 
and  to  compare  them  with  those  of  other  chemists  who 
busied  themselves  with  similar  questions,  we  have  only  to 
fix  our  attention  on  his  researches  upon  the  alkaline  earths 
and  the  alkalies.  The  carbonates  of  these  were  before 
Black's  time  regarded  as  simple  substances  ;  and  it  was 
further  assumed  that  when  limestone  was  burnt  fire-stuff 
was  taken  up,  and  that  this  went  over  into  potashes  or  soda 
when  these  were  causticised  by  means  of  lime.  Black,  on 
the  contrary,  proved  by  his  researches  that  when  limestone 
or  Magnesia  alba  was  calcined,  something  escaped  which  led 
to  a  loss  of  weight  and  which  was  identical  with  van 
Helmont's  gas  sylvestre.  This  gas — which  he  termed  fixed 
air,  because  of  its  being  held  bound  by  caustic  alkalies, 
lime,  etc. — he  proved  to  be  also  present  in  the  mild 
alkalies ;  and  these  latter  became  caustic  when  deprived  of 
their  carbonic  acid  by  lime  or  magnesia.  In  this  truly 
classical  research  we  meet  with  methods  which  bear  the 
impress  of  an  entirely  new  departure.  That  Black  devoted 
great  attention  to  the  proportions  by  weight  of  the  com- 
pounds which  entered  into  the  reaction  is  seen  in  all  his 
investigations ;  and  it  is  thus  easy  to  understand  how  he 
gave  up  the  phlogiston  theory  and  concurred  in  the  doctrine 
of  Lavoisier  when  the  correct  explanation  of  combustion 
and  similar  processes  became  possible  through  the  discovery 
of  oxygen. 

1  The  Swedish  physicist,  J.   C.   Wilcke,  also  discovered  latent  heat 
about  the  same  time  and  independently  of  Black. 


iv  CAVENDISH'S  LIFE  AND  WORK  121 

Black,  by  his  fundamental  labours,  did  away  with  many 
errors,  and  thereby  prepared  the  way  for  the  definite  know- 
ledge of  the  true  composition  of  important  chemical  com- 
pounds. Notwithstanding  this,  the  evident  conclusions 
which  followed  from  his  researches  on  causticity  were  un- 
favourably criticised  by  many  of  the  chemists  of  his  time, 
and  indeed  their  correctness  disputed ;  it  is  strange  to  find 
that  even  Lavoisier  could  not  bring  himself  candidly  to 
recognise  Black's  services  in  this  respect,  and  that  he  rather 
ranged  himself  on  the  side  of  the  latter 's  antagonists,  who 
were  in  reality  unable  to  weaken  one  of  his  arguments. 

In  his  countryman,  Henry  Cavendish,  Black  had  a  most 
distinguished  co-worker,  who,  while  investigating  quite 
independently  of  him,  did  so  upon  similar  lines,  and  to  the 
great  benefit  of  chemistry.  Cavendish,  born  at  Nice  in  1731, 
devoted  himself  very  quietly  but  not  the  less  efficiently  to 
the  natural  sciences,  which  he  studied  thoroughly,  especially 
to  physics  and  chemistry ;  he  died  in  London  in  18 10.1 

There  is  but  little  to  be  said  about  his  life,  for  his 
unsociable  and  retiring  nature  led  him  to  shun  anything  like 
publicity,  and  indeed  it  was  only  with  reluctance  that  he 
was  induced  to  publish  the  results  of  his  remarkable  work ; 
for  this  reason  many  valuable  observations  of  his  remained 
unknown  for  some  decades.  Although  Cavendish  inherited 
a  large  patrimony,  he  adhered  throughout  to  a  severely 
simple  style  of  living. 

His  masterly  researches — so  important  both  from  a 
physical  and  from  a  chemical  standpoint — upon  hydrogen 
(inflammable  air),  which  he  was  the  first  to  distinguish  as  a 
peculiar  gas  differing  from  all  others,  and  also  those  upon 
carbonic  acid,  constitute  him  one  of  the  founders  of 
pneumatic  chemistry  and  one  of  the  originators  of  the  new 
era.  To  him  we  owe  the  proof,  of  what  value  need  not  be 
said,  that  water  consists  of  hydrogen  and  oxygen ;  further, 

1  The  details  of  Cavendish's  life  and  a  picture  of  his  peculiar  disposition 
are  to  be  found  in  Wilson's  Life  of  the  Honourable  H.  C.  Cavendish  (1848). 
Compare  also  Thorpe's  clever  memoir  in  his  Essays  in  Historical  Chemistry, 
p.  70  et  seq. 


122  THE  PHLOGISTIC  PERIOD  CHAP. 

the  proofs  that  atmospheric  air  is  a  mixture  of  nitrogen  and 
oxygen  in  constant  proportions,  and  that  nitric  acid  can  be 
produced  by  the  chemical  combination  of  these  two  latter 
gases  in  presence  of  water.  All  these  were  discoveries  of 
the  greatest  moment.  In  them  Cavendish  himself  forged 
the  most  powerful  weapon  for  the  overthrow  of  the  phlogiston 
theory,  notwithstanding  which  we  find  him  still  faithful  to 
the  latter.  His  opposition  to  the  antiphlogistic  doctrine, 
which  he  himself  helped  to  found  by  his  own  investigations, 
can  only  be  explained  by  the  fact  that  he  did  not  pay 
enough  attention  to  the  proportions  by  weight  in  the  pro- 
cesses of  combustion,  but  explained  the  latter  in  a  way 
which  appeared  to  him  sufficiently  convincing,  viz.  by  regard- 
ing hydrogen  as  identical  with  phlogiston. 

Besides  this  Cavendish  showed  an  absolutely  marvellous 
exactitude  in  his  researches  upon  gases,  whose  specific 
gravities  and  volume-ratios  in  chemical  reactions  he  estab- 
lished. With  what  ingenuity  he  thought  out  and  carried 
through  physical  experiments  is  well  exemplified  in  his  work 
on  the  specific  heats  of  metals,  and  in  his  attempt — the  first 
one  which  was  successful — to  determine  the  specific  gravity 
of  the  earth.  Another  instance  will  be  fresh  in  the  memory 
of  most  readers,  viz.  Cavendish's  surmise,  from  the  results  of 
his  own  experiments  on  the  combination  of  oxygen  and 
nitrogen,  that  there  was  possibly  still  another  gas  present  in 
the  air  in  small  quantity  (argon).  When  one  considers  this 
wonderful  versatility  and  remembers  the  thorough  mathe- 
matical training  that  Cavendish  had  gone  through,  one 
can  but  wonder  the  more  that  he  laid  too  little  stress  upon 
proportions  by  weight  in  chemical  reactions. 

The  most  zealous  champion  for  the  phlogistic  idea  at 
that  time  was  Joseph  Priestley,  to  whom  the  chemistry  of 
gases  owes  an  extraordinarily  large  number  of  new  observa- 
tions and  important  discoveries.  In  Priestley  were  united 
an  eccentric  mind,  in  which  fantastic  speculations  found  a 
place,  and  a  simple  and  child-like  disposition.  He  combated 
the  antiphlogistic  doctrines  until  his  death  (in  1804)  as  no 
other  man  did,  although  his  own  researches  often  went  to 


iv  JOSEPH  PRIESTLEY  123 

strengthen,  even  to  lay  the  foundations  of,  the  latter.  In 
contrast  with  the  quiet  existence  of  Black  and  Cavendish, 
wholly  devoted  to  science,  a  wandering  life  full  of  vicissitudes 
and  even  of  persecutions  was  destined  for  Priestley,1  doubt- 
less for  the  most  part  because  of  his  relations  to  the  English 
Church  and  his  own  intolerance.  Theology  was  his  own 
special  subject,  and  he  was  already  a  minister  when  he  first 
carne  more  closely  into  contact  with  scientific  questions. 
Born  at  Fieldheads  near  Leeds  in  1733,  and  acquainted 
with  poverty  in  his  early  years,  he  afterwards  earned  a 
modest  living  as  a  teacher  of  languages  (he  taught  Latin, 
Greek,  French,  Italian  and  Hebrew),  and  then  as  a  minister 
of  the  Gospel.  His  versatility  was  further  shown  by  the 
fact  that  he  also  occasionally  gave  lectures  in  logic,  history, 
law,  anatomy,  etc.  The  numerous  philosophical  and  theo- 
logical books  which  he  wrote,  some  of  them  very  com- 
prehensive, are  probably  now  altogether  forgotten,  although 
Priestley  himself  considered  these  his  best  work.  A  per- 
sonal acquaintance  with  Benjamin  Franklin  led  him  to  make 
scientific  researches,  an  early  result  of  which  was  his 
History  of  Electricity.  Later  on,  in  the  comparative  leisure 
of  librarian  to  Lord  Shelburne,  he  found  time  for  chemical 
investigations,  his  most  important  work  being  done  at  this 
period  (1772—9). 

After  some  years  spent  as  minister  of  a  meeting-house 
in  Birmingham,  Priestley  was  obliged  to  leave  the  latter 
town  for  London  in  1791,  an  attack  on  Burke's  writings  upon 
the  French  Revolution  having  raised  popular  opinion  against 
him,  and  indeed  resulted  in  open  mob-riot.  A  few  years 
later  he  emigrated  to  America,  and  settled  at  Northum- 
berland near  Philadelphia,  where  he  died  in  1804.  Although 
there  is  much  of  dilettantism  in  the  mode  in  which  Priestley 
treats  scientific  problems,  he  rivets  our  attention  by  the 
charm  of  his  intense  originality  and  perspicacity. 

Endowed  with  an  unusual  gift  for  experimenting  and 

1  Thorpe's  admirable  paper  (Essays,  p.  28)  gives  a  graphic  account  of 
Priestley's  life  and  many-sided  activity.  Compare  also  Priestley's  Scientific 
Correspondence,  edited  by  H.  C.  Bolton  (Ne^  York,  1892). 


124  THE  PHLOGISTIC  PERIOD  CHAP. 

observing,  he  was  able  to  treat  the  most  difficult  problems  of 
pneumatic  chemistry,  although  lacking  a  thorough  scientific 
education.  He  prepared  and  investigated  a  large  number 
of  gases  which,  with  the  exception  of  carbonic  acid  and 
hydrogen,  were  practically  unknown  before  his  time.  Of 
all  his  discoveries,  that  of  oxygen  (in  1774)  was  the  most 
important ;  it  will  be  treated  of  later  on.  It  is  true,  as  we  now 
know,  that  Scheele  had  indeed  preceded  Priestley  in  many  of 
these  observations,  but  he  had  omitted  to  publish  his  results  soon 
enough.  Priestley's  beautiful  researches  on  this  gas  did  not, 
however,  lead  him  to  the  correct  explanation  of  combustion ; 
he  remained,  on  the  contrary,  true  to  the  doctrine  of  phlo- 
giston. But  his  mistaken  ideas  respecting  this  and  similar 
processes  did  not  prevent  him  drawing  from  his  own  ob- 
servations sagacious  conclusions  with  regard  to  the  series  of 
recurrent  changes  which  oxygen  undergoes  in  animal  and 
vegetable  metabolism, — a  far  more  complicated  process 
than  that  of  combustion,  which,  tied  as  he  was  by  a  false 
hypothesis,  he  was  unable  to  explain. 

Contemporaneously  with  the  three  last-named  British 
chemists,  two  most  distinguished  investigators,  Torbern  Olof 
Bergman  and  Karl  Wilhelm  Scheele,  were  labouring  in 
Sweden  as  upholders  of  the  phlogistic  theory,  which  their 
brilliant  discoveries  and  observations  only  served  so  deeply 
to  undermine,  that  its  supersession  was  inevitable.  Bergman 
had  acquired  such  a  wide  knowledge  of  the  natural  sciences 
that  he  taught  with  eminent  success  as  professor  of  physics, 
mineralogy  and  chemistry  at  Upsala.  Born  in  the  year  1735, 
he  died  at  the  early  age  of  forty-nine,  doubtless  from  the 
effect  of  overwork  upon  a  weak  constitution.  |  His  chief 
services  to  chemistry,  to  which  from  1767  he  principally 
devoted  himself,  were  in  the  domain  of  analysis,  which  he 
treated  systematically  and  enriched  by  valuable  methods. 
He  knew  well  how  to  make  his  chemical  experiences  useful 
for  the  definition  and  classification  of  minerals,  and  thereby 
laid  the  foundation  of  mineralogical  chemistry  and  chemical 
geology.  The  current  views  upon  chemical  affinity  thus 
gained  through  him  precision  and  clearness;  the  scientific 


TV  BERGMAN  AND  SCHEELE  125 

character  of  chemistry  was  materially  raised  by  such  observa- 
tions, and  a  general  survey  of  chemical  processes  rendered 
much  easier.  His  papers  appeared  originally  in  the  Memoirs 
of  the  Academies  of  Stockholm  and  Upsala;  later  on  they 
were  collected  together,  and  published  in  five  volumes  in 
1779-1788,  under  the  title  Opuscula  Physica  et  Chemica. 

Karl  Wilhelm  Scheele  will  remain  for  all  time  one  of  the 
most  distinguished  of  chemists ;  and  his  fame  is  not  lessened 
by  the  fact  that  he  continued  all  his  life  through  a  zealous 
supporter  of  the  phlogistic  doctrine.  In  spite  of  this  fact,  of 
the  unfavourable  conditions  under  which  he  lived,  and  of  the 
short  span  of  his  life,  he  contributed  to  chemistry  a  wealth  of 
new  observations — many  of  them  discoveries  of  supreme 
value — which  furnished  a  rich  mine  for  the  experimental 
work  and  theoretical  discussions  of  future  generations. 

Much  new  light  has  been  thrown  on  Scheele's  life  and 
scientific  work  by  A.  E.  Nordenskiold's  recently  published 
book:  Karl  Wilhelm  Scheele:  Nachgelassene  Brief e,  und 
Aufzeichnungen  ("  Karl  Wilhelm  Scheele :  His  Letters  and 
Journals  ")  (Stockholm,  1892).  This  materially  supplements 
the  earlier  biographies  of  Crell,  Sjosten-Wilcke,  etc.,  and 
gives  us  more  especially  a  clear  account  of  the  genesis  and  of 
the  dates  of  Scheele's  magnificent  discoveries,  while  at  the 
same  time  we  learn  what  a  number  of  his  observations,  of 
great  importance,  have  hitherto  remained  unknown. 

Scheele,  born  on  the  9th  of  December,  1742,  at  Stralsund, 
the  capital  of  Pomerania,  which  at  that  time  belonged  to 
Sweden,  began  at  fourteen  years  of  age  his  apprenticeship  in 
Gothenburg  with  Apothecary  Bauch,  who  soon  recognised 
and  appreciated  the  boy's  remarkable  gifts.  Restricted 
almost  entirely  to  a  few  antiquated  text-books,  together  with 
the  fairly  good  chemical  inventory  of  the  apothecary's  shop, 
Scheele,  by  his  unwearied  experimenting,  acquired  such  a 
knowledge  of  the  properties  and  reactions  of  many  substances 
that,  by  the  time  he  went  to  Malmo  (in  1765)  he  had, 
although  still  only  an  apprentice,  gained  more  experience 
than  the  majority  of  the  chemists  of  the  time.  At  Malmo, 
and  also  in  the  succeeding  posts  he  held  (Stockholm,  1768- 


126  THE  PHLOGISTIC  PERIOD  CHAP. 

1770,  and  Upsala,  1770-1775),  he  increased  his  knowledge  of 
the  most  important  branches  of  chemistry  without,  however, 
becoming  so  well  known  at  the  time  as  he  deserved.  It  was 
only  when,  through  Gahn's  good  offices,  he  came  into  close 
relation  with  Bergman — a  connection  which  began  in  a 
misunderstanding  and  coolness,  but  which  developed  into  a 
friendship — that  Scheele  continued  to  gain  steadily  in  repu- 
tation. After  taking  over  the  pharmacy  at  Koping  in  1775, 
he  was  able  to  devote  himself  more  closely  to  scientific  work, 
and  with  still  more  brilliant  results.  The  records  of  his 
researches  followed  one  another  rapidly  in  the  Transactions 
of  the  Stockholm  Academy,  into  which  he  had  been  received 
as  Studiosus  Pharmacies  in  1775.  In  1777  he  published  the 
results  of  his  investigation  on  air,  oxygen,  combustion  and 
respiration  in  a  volume  entitled  Chemische  Alhandlung  von 
der  Luft  und  dem  Feuer  ("A  Chemical  Essay  on  Air  and 
Fire").  After  his  early  death  at  barely  forty-four  years  of 
age — a  death  undoubtedly  hastened  by  a  too  close  devotion 
to  science — his  collected  works  were  published  in  two  volumes 
in  German  by  Hermbstadt  (Berlin,  1793),  under  the  title : 
Sammtliche  Physische  und  Chemische  Werke. 

It  is  not  merely  as  an  investigator  and  discoverer,  but  as 
a  high-principled  and  unassuming  man,  that  Scheele  merits 
our  warmest  admiration.  His  aim  and  object  was  the  dis- 
covery of  the  truth.  The  letters  of  the  man  reveal  to  us  in 
the  pleasantest  way  his  high  scientific  ideal,  his  genuinely 
philosophic  temper,  and  his  simple  mode  of  thought.  "  It  is 
the  truth  alone  that  we  desire  to  know,  and  what  joy  there  is  in 
discovering  it  /"  With  these  words  he  himself  characterises 
his  own  efforts. 

It  is  not  proposed  to  enter  minutely  at  this  point 
into  his  varied  investigations ;  a  general  account  only 
of  his  services  to  science  will  be  given  here,  and  the  more 
important  parts  of  his  work  will  be  referred  to  in  short  detail 
later  on. 

Endowed  with  a  most  wonderful  gift  of  observation 
Scheele  was  able  to  bring  to  a  successful  conclusion 
researches  carried  on  with  but  very  limited  means  at  com- 


iv  SCHEELE'S  GREAT  ACHIEVEMENTS  127 

mand.  A  brilliant  proof  of  this  is  given  in  his  investigations 
upon  black  oxide  of  manganese  (De  Magnesia  Nigra),  which 
many  competent  workers  before  him  had  studied  without 
succeeding  in  making  its  nature  clear.  During  this  research 
Scheele  discovered  in  rapid  succession  four  new  substances 
— chlorine,  oxygen,  manganese  and  baryta — of  which  the 
two  first  especially  were  of  the  utmost  importance  for  the 
proper  understanding  of  chemical  processes. 

The  way  in  which  he  isolated  and  noted  the  characteristics 
of  oxygen  and  also,  previous  to  this,  of  a  long  series  of  hitherto 
unknown  gases,  prove  him  to  have  been  a  magnificent  ex- 
perimenter. And  similarly  we  see  him  as  an  incomparable 
observer  in  the  discovery  of  analytical  methods  and  in  the 
opening  out  of  entirely  new  fields  of  inorganic  chemistry  (see 
special  section).  Scheele  was  the  first  to  note  the  fact  that 
there  are  various  stages  in  the  oxidation  of  such  metals  as 
iron,  copper  and  mercury,  notwithstanding  that  he  still 
adhered  to  the  phlogistic  hypothesis  in  explaining  the  com- 
position of  those  products.  With  this  knowledge  he  was  far 
ahead  of  Lavoisier,  Proust  and  others. 

In  a  manner  nothing  short  of  marvellous  Scheele  brought 
his  inventive  genius  to  bear  upon  organic  chemistry,  which 
had  till  then  been  left  almost  untouched;  working  out  in 
every  direction  new  methods  for  isolating  the  products  of 
vegetable  and  animal  metabolism,  he  prepared  a  large 
number  of  acids  and  other  organic  compounds  hitherto 
unknown.  Scheele  was  a  pioneer  in  nearly  every  branch 
of  chemistry,  being  unique  in  power  of  observation  and  in 
the  quick  comprehension  of  facts,  although,  it  is  true,  not 
always  happy  in  his  interpretation  of  these,  fettered  as  he 
was  by  the  phlogiston  theory.  Scheele's  discoveries  will  be 
referred  to  separately  in  the  various  sections  of  the  Special 
History  of  Chemistry. 

In  order  to  properly.,  appreciate  the  condition  of  the 
phlogiston  theory  in  the  seventh  and  eighth  decades  of  the 
eighteenth  century — that  is,  shortly  before  its  downfall, — the 
development  up  to  that  date  of  a  special  section  of  chem- 
istry, viz.  pneumatic,  must  be  considered.  The  work  done 


128  THE  PHLOGISTIC  PERIOD  CHAP. 

with  gases,  and,  more  especially,  the  knowledge  acquired  of 
their  properties  and  behaviour,  had  led  finally  to  the  correct 
interpretation  of  combustion.  The  special  history  of  the 
phlogistic  period  thus  falls  to  be  treated  of  now. 


DEVELOPMENT  OF  PARTICULAR  BRANCHES  OF  THEO- 
RETICAL AND  PRACTICAL  CHEMISTRY  IN  THE 
PHLOGISTIC  PERIOD. 

Pneumatic  Chemistry  and  its  Relations  to  the 
Doctrine  of  Phlogiston. — The  influence  which  the  in- 
vestigation of  gases,  especially  of  oxygen,  exercised  in  shaping 
chemistry  is  sufficiently  well  known.  Oxygen  forms  to  some 
extent  the  centre-point  of  chemical  research  during  the  last 
quarter  of  the  eighteenth  century,  for  the  knowledge  of  the 
part  which  it  played  in  combustion  and  similar  processes  led 
to  the  setting  aside  of  a  doctrine  that  had  dominated  all 
theoretical  views  for  a  hundred  years ;  and,  further,  because 
results  of  the  greatest  importance  were  conjoined  with  its 
study,  inasmuch  as  this  contributed  materially  to  the  develop- 
ment of  the  atomic  theory. 

The  services  of  the  men  whose  observations  did  most 
towards  building  up  the  chemistry  of  gases  have  already 
been  mentioned  generally;  it  will  suffice  here  to  treat  in 
more  detail  certain  of  these  observations  together  with  a  few 
others.  Boyle's  researches  show  a  marked  advance  over 
those  of  van  Helmont  in  the  mode  in  which  he  collected 
gases  and  worked  with  them ;  at  the  same  time  neither  he 
nor  his  contemporaries  felt  quite  sure  whether  carbonic  acid 
and  hydrogen,  whose  characteristic  properties  he  knew, 
differed  materially  from  atmospheric  air.  This  uncertainty 
is  also  seen  in  the  work  of  later  investigators,  e.g.  Hales ;  the 
erroneous  idea  that  gases  were  ordinary  air  with  various 
admixtures,  had  fixed  itself  firmly  in  the  minds  of  chemists. 
To  Black  is  due  the  merit  of  proving  the  precise  difference 
between  carbonic  acid  and  air,  by  showing  the  "  fixation  "  of 
the  former  by  caustic  alkalies.  Cavendish,  who  recognised 


iv  PNEUMATIC  CHEMISTRY  129 

in  hydrogen  a  peculiar  gas,  likewise  helped  to  do  away  with 
the  misconception.  That  Scheele  had  already  discovered 
numerous  gases  by  the  year  1770,  and  had  proved  them  to  be 
individual  substances,  is  clearly  shown  in  his  letters  and 
journals  (cf.  pp.  124 — 5).  Finally,  we  would  mention  here  the 
remarkable  supplemental  researches  of  Bergman  on  carbonic 
acid  (17  7  4). 

"The  methods  of  collecting  gases  had  improved  consider- 
ably since  Hales — and,  before  him,  the  little-known  Moitrel 
d'^Ilement — had  effected  a  separation  of  the  generating 
vessel  from  the  receiver.  Air  was  found  to  be  a  fluid  capable 
of  measurement  which  possessed  weight,  and  which,  like  all 
other  fluids,  could  be  transferred  from  one  vessel  to  another. 
The  apparatus  which  Black,  Priestley,  Scheele  and  others 
used,  and  those  which  we  employ  at  the  present  day, 
gradually  developed  themselves  from  that  of  Hales.  Priestley 
was  the  first  to  describe  the  collection  of  gases  over  mercury, 
and  he  succeeded  by  this  device  in  discovering  gaseous 
ammonia,  hydrochloric  acid,  silicon  fluoride  and  sulphurous 
acid, — all  of  which  had  been  overlooked  so  long  as  water  only 
was  used  for  this  purpose.  Scheele  had  anticipated  Priestley 
in  the  isolation  of  some  of  these,  as  well  as  of  nitric  oxide 
and  sulphuretted  hydrogen  (about  1770),  but  had  not  pub- 
lished his  observations. 

The  discovery  of  so  many  gaseous  substances  of  such 
different  character  greatly  excited  the  chemical  world.  The 
properties  of  each  gas  were  carefully  examined ;  and,  after 
Mayow's  researches,  and  especially  after  the  more  exact 
determinations  by  Cavendish,  the  density  was  taken  as  the 
criterion  of  one  gas  differing  from  another  and  from  atmo- 
spheric air.  Due  regard  was  also  paid  to  the  greater  or 
lesser  absorption  of  gases  by  water,  as  a  distinct  test  for 
some  of  them  ;  Bergman,  for  instance,  determined  with  fair 
accuracy  the  solubility  of  carbonic  acid  in  water.  But  the 
true  composition  of  gaseous  bodies  remained  unknown  during 
this  epoch,  great  uncertainty  prevailing  even  about  the 
simplest  of  them  until  Lavoisier  had  pronounced  his  opinion 
as  to  the  elementary  nature  of  oxygen  and  hydrogen.  How 

K 


130  THE  PHLOGISTIC  PERIOD  CHAP. 

could  this  indeed  be  otherwise,  so  long  as  the  presence  of 
phlogiston  was  assumed  in  most  gases  ?  Hydrogen  was 
considered  identical  with  phlogiston  by  many  chemists  soon 
after  the  middle  of  the  eighteenth  century,  Cavendish  and 
Kirwan  setting  the  precedent  for  this  ;  others  looked  upon 
coal  as  being  rich  in  phlogiston,  if  not  as  the  latter  itself. 
The  most  various  and  often  confused  opinions  were  expressed 
regarding  the  composition  of  carbonic  acid,  carbonic  oxide, 
nitric  oxide,  sulphurous  acid,  sulphuretted  hydrogen  and 
other  gases,  these  opinions  being  made  to  fit  in  with  the 
views  of  the  phlogistic  doctrine  prevalent  at  that  time. 

Of  greater  moment  than  these  varying  opinions  upon 
the  constitution  of  the  gases  just  named  were  the  long 
unsettled  questions  :  "  Is  atmospheric  air  a  simple  or  a  com- 
pound body,  and — if  the  latter — what  are  its  constituents 
or  ingredients  ?  "  These  questions  were  solved  experimen- 
tally by  chemists  belonging  to  the  phlogistic  era,  more  par- 
ticularly by  S'cheele  and  Priestley  ;  but  it  was  left  to  Lavoisier 
to  interpret  their  observations  correctly.  We  must  now 
speak  of  the  most  important  of  the  facts  then  brought  to 
light,  which  bore  upon  the  composition  of  the  air.1 

The  first  observation  which  aided  in  overthrowing  the 
old  assumption  of  air  being  a  simple  substance,  was  the  be- 
haviour of  an  enclosed  volume  to  a  body  burning  and  to 
metals  heated  in  it.  Boyle  was  -forced  by  his  researches 
in  this  direction  to  the  supposition  that  one  ingredient  of 
the  air  was  necessary  to  respiration  and  combustion,  and 
to  the  calcination  of  the  metals ;  but  he  was  unable  to 
isolate  this  ingredient,  as  was  also  Mayow,  who,  with  his 
assumption  of  a  spiritus  ingo-aereus,  which  brought  about 
combustion  (cf.  p.  107),  came  pretty  near  to  the  right  in- 
terpretation. It  was,  however,  only  a  hundred  years  later, 
after  oxygen  and  nitrogen  had  been  prepared  successfully, 
that  the  question  approached  its  solution.  Nitrogen,  which 
various  investigators  had  already  worked  at,  was  first  isolated 
by  Scheele ;  but  Rutherford,  who  discovered  it  independently 
in  1772,  by  the  absorption  of  the  carbonic  acid  produced  by 
1  Cf.  Ramsay's  recent  volume,  The  Gases  of  the  Atmosphere  (Macmillan 
.and  Co.,  1896). 


iv    DISCOVERY  OF  OXYGEN  BY  SCHEELE  AND  PRIESTLEY    131 

combustion  or  respiration  in  an  enclosed  volume  of  air,  pre- 
ceded Scheele  in  publication.  It  followed  from  their  observa- 
tions that  this  gas,  which  was  incapable  of  sustaining  either 
combustion  or  respiration,  must  be  one  of  the  ingredients  of 
the  atmosphere.  The  other  was  isolated  and  examined  by 
Scheele  and  Priestley.  The  journals  already  alluded  to  make 
it  clear  that  as  early  as  1771 — 1773,  i.e.  during  the  years  of 
his  sojourn  at  Upsala,  Scheele  prepared  oxygen  by  heating 
black  oxide  of  manganese  with  sulphuric  or  arsenic  acid,  and 
also  from  nitrates  and  from  the  oxides  of  mercury  and  silver, 
and  noted  its  characteristics  clearly.  Priestley,  who  likewise 
observed  the  gas  at  about  the  same  time,  without,  however, 
recognising  its  peculiar  nature,1  first  isolated  it  for  certain 
on  August  1st,  1774,  by  heating  red  oxide  of  mercury ;  and, 
as  he  published  his  results  earlier  than  Scheele,  he  has 
hitherto  been  regarded  as  the  first  discoverer  of  oxygen, 
whereas  we  now  know  the  converse  to  be  the  case.  Both 
observed  that  this  gas  was  capable  of  supporting  combustion 
and  respiration  in  an  intensified  degree.  Priestley  named  it 
"  dephlogisticated  air,"  and  Scheele  at  first  aer  vitriolicus,  later 
"  fire  air  "  and  also  "  life  air." 

The  momentous  discovery  of  oxygen  enabled  both  of  them 
to  recognise  air  as  being  a  mixture  of  two  kinds  of  gas ; 2 
Priestley  calls  nitrogen  "  phlogisticated  air,"  and  Scheele 
terms  it  "  spent  air."  They  both  found  substances  which 
absorbed  the  one  constituent  of  the  air  (oxygen).  Here,  again, 
Scheele  showed  the  greater  versatility,  for  while  Priestley 
employed  for  this  purpose  saltpetre  gas  (nitric  oxide),  Scheele 
made  use  of  phosphorus,  hydrate  of  protoxide  of  iron,  mix- 
tures of  iron  and  sulphur,  and  moist  iron  filings.  They  made 
the  further  important  observation  that,  upon  burning  a  candle 
in  an  enclosed  volume  of  air,  exactly  as  much  "  fixed  air  " 
(carbon  dioxide)  was  generated  as  oxygen  had  vanished. 

Notwithstanding  all  this  they  did  not  get  at  the  right 

1  Hales  and  Bayen,  too,  had  observed  oxygen  previous  to  this,  but  also 
without  recognising  its  peculiar  nature. 

2  Scheele,  in  his  treatise  Von  Luft  und  Feuer("  On  Air  and  Fire"),  puts 
as  the  heading  to  a  series  of  his  investigations  this  sentence : — "  The  air 
must  be  made  up  of  elastic  fluids  of  two  kinds." 

K   2 


132  THE  PHLOGISTIC  PERIOD  CHAP. 

explanation  of  combustion,  respiration  and  calcination,  whose 
analogy  to  one  another  they  clearly  saw  :  so  prejudiced  were 
they  by  the  idea  that  phlogiston  escaped  during  these  pro- 
cesses, that  the  path  distinctly  marked  out  by  their  own  ob- 
servations was  left  for  another  to  tread.  Lavoisier  was 
destined  to  do  this,  as  he  easily  threw  aside  the  trivial 
phlogistic  prepossessions  that  he  cherished  at  the  beginning 
of  his  scientific  career.  The  others,  indeed,  upheld  a  con- 
tradictory explanation  of  combustion  and  analogous  processes, 
in  order  to  remain  loyal  to  the  phlogistic  doctrine.  But  that 
it  was  Priestley  and  Scheele  who,  by  their  exhaustive  re- 
searches on  oxygen  and  the  part  which  it  played  in  the  pro- 
cesses just  mentioned,  furnished  the  experimental  material 
for  the  correct  understanding  of  these,  and  not  Lavoisier,  is 
beyond  all  question. 

After  the  discovery  of  oxygen  and  of  its  chief  properties 
the  days  of  the  phlogistic  theory  were  numbered,  although 
many  of  the  most  eminent  chemists  still  held  to  it  in  spite 
of  accumulating  contrary  evidence.  The  greatest  difficulty 
in  the  way  of  the  old  doctrine  was  the  fact,  already  known 
for  a  long  time,  that,  in  those  cases  where  phlogiston  was 
supposed  to  escape,  the  products  became  heavier  instead  of 
decreasing  in  weight.  The  exact  researches  on  the  calcina- 
tion of  the  metals,1  had  their  results  been  studied  without 
any  preconceived  opinions,  ought  to  have  led  to  the  correct 
explanation,  viz.  that  one  ingredient  of  the  air  combines 
with  the  metals  to  form  calces;  for  not  only  was  the  increase 
in  weight  observed,  but  also  the  disappearance  of  a  portion 
of  the  air.  But  instead  of  drawing  from  this  the  conclusion 
that  the  phlogistic  hypothesis  was  untenable,  chemists  en- 
deavoured to  make  the  observed  facts  fit  in  with  the  latter 
by  putting  a  strained  interpretation  on  them.  Even  Boyle, 
acute  as  he  was,  tried  to  help  himself  by  the  false  assumption 

1  The  earliest  of  such  investigations,  which  yielded  extremely  valuable 
observations  on  the  increase  in  weight  of  the  metals  and  the  part  played  by 
the  air  in  their  calcination,  were  undertaken  by  Jean  Rey,  Hooke,  Mayow 
and  Boyle  in  the  seventeenth  century.  Rey  and  Mayow  came  very  near  to 
explaining  the  results  of  their  experiments  correctly. 


iv  RESULTS  OF  THE  DISCOVERY  OF  OXYGEN  133 

that  the  increase  in  weight  was  due  to  a  ponderable  fire-stuff.1 
It  was  sought  to  show  by  pure  philosophy  alone,  without  the 
faintest  shadow  of  proof,  that  air  was  essential  to  calcination 
and  similar  processes,  by  assuming  that  it  must  be  present 
in  order  to  take  up  the  escaping  phlogiston.  This  expedient, 
first  brought  forward  by  Becher  and  Stahl,  was  made  use  of 
again  and  again  by  later  phlogistonists. 

While  these  latter  imagined  that  they  had  thus  correctly 
interpreted  the  part  played  by  the  air,  they  followed  Stahl's 
example  in  paying  no  heed  to  the  observed  alteration  in 
weight,  either  regarding  this  as  accidental  or  making  the 
most  unhappy  attempts  at  explaining  it.  Thus  we  find 
Juncker,  a  pupil  of  Stahl's,  pointing  out  that  the  metallic 
calces  were  denser  than  the  metals,  and  therefore  heavier, — 
an  utter  confounding  of  the  absolute  weight  with  the  specific 
gravity,  and  also  a  wrong  assertion,  since  Boyle  had  already 
shown  in  certain  instances  that  the  calces  were  specifically 
lighter  than  their  corresponding  metals.  Equally  unscientific 
was  the  assumption  that  the  phlogiston  which  escaped  in 
these  processes  possessed  a  negative  weight,  and  that,  there- 
fore, the  residual  product  must  be  the  heavier ;  even  Guyton 
de  Morveau  and  Macquer  fell  into  this  gross  error.  True,  the 
most  able  chemists  of  the  phlogistic  period  did  not  concur  in 
these  untenable  views,  but  maintained  that  it  was  the  business 
of  physicists  to  investigate  such  points.2  As  a  matter  of 
fact,  it  remained  for  the  physicist  Lavoisier  to  give  the  right 
explanation  of  this,  and,  with  it,  that  of  combustion  and 
similar  processes. 

1  Boerhave  showed  the  weakness  of  such  an  assumption  by  proving  that 
the  weight  of  certain  metals,  e.g.  silver,  remained  the  same,  whether  they 
were  at  the  ordinary  temperature  or  at  a  red  heat.     He,  therefore,  ex- 
pressed the  opinion  that  an  increase  in  weight  on  calcination  depended  upon 
the  addition  of  a  "saline  ingredient"  (salziges  Theilchen)  from  the  air. 

2  Some  chemists  there  were  who  did  not  regard  the  above  observations 
on  the  increase  in  weight  of  metals  when  calcined  as  meaningless  ;  Tillet, 
for  example,  who  made  a  communication  to  the  French  Academy  in  1762 
upon  the  increase  in  weight  of  lead,  calling  special  attention  at  the  same 
time  to  the  fact  that  a  fit  explanation  of  this  had  still  to  be  given. 


134  THE  PHLOGISTIC  PERIOD  CHAP. 


Development  of  some  particular  Theoretical   Views  in  the 
Phlogistic  Period. 

It  is  necessary  to  make  one's  self  acquainted  with  the 
growth  of  the  more  important  chemical  ideas  of  this  time, 
in  order  to  properly  appreciate  the  advances  which  they 
show  upon  those  of  the  preceding  periods,  and  also  in  order 
to  comprehend  the  connection  existing  between  the  theo- 
retical views  of  the  phlogistic  era  and  of  that  new  one  which 
begins  with  Lavoisier.  We  have  to  deal  here  with  the 
meanings  attached  to  the  terms  "  element "  and  "  chemical 
compound,"  and  also  with  the  ideas  of  the  phlogistonists 
upon  chemical  affinity. 

Views  regarding  Elements  and  Chemical  Com- 
pounds.— The  position  which  Boyle  took  up  with  respect  to 
the  question  of  the  elements  has  been  already  spoken  of;  he 
it  was  who  established  the  scientific  term  "  element,"  in  that 
he  regarded  as  elements  those  actual  constituents  of  com- 
pound bodies  which  were  capable  of  isolation  and  which 
could  not  themselves  be  broken  up  into  simpler  substances. 
With  the  increase  of  means  for  deciding  the  question 
whether  any  substance  is  in  this  sense  an  element  or  not, 
the  boundary  line  between  elements  and  chemical  compounds 
became  more  and  more  altered  in  position,  but  at  the  same 
time  sharper.  Boyle  further  cherished  the  idea  that  the 
elements  attainable  by  chemists  were  not  the  ultimate 
constituents  of  matter. 

Notwithstanding  the  clearness  with  which  Boyle  set 
forth  the  conditions  which  an  element,  according  to  his 
view,  must  fulfil,  we  find  among  his  contemporaries  and 
their  successors  a  tendency  to  go  back  to  the  alchemistic 
elements,  and  even  to  the  Aristotelian.  Willis,  Lefevre  and 
Lemery  associated  earth  and  water  with  the  three  elements 
of  Basil  Valentine  and  Paracelsus ;  Becher  also  adhered  to 
those  three  under  other  names,  adding  water  to  them ;  and 
even  Stahl  was  unable  to  free  himself  from  ideas  of  this  kind. 


iv        VIEWS  REGARDING  ELEMENTS  AND  COMPOUNDS        135 

The  erroneous  assumption  of  the  phlogiston  theory— 
that  the  products  of  combustion  and  calcination,  i.e.  acids 
and  metallic  oxides,  were  simple,  and  the  original  substances 
compound — had  the  most  serious  consequences  in  keeping 
back  a  knowledge  of  the  true  elements.  While  Boyle 
appeared  inclined  to  reckon  the  metals  among  the  latter, 
their  compound  nature  was  never  questioned  from  the  time 
of  Stahl  until  the  fall  of  the  phlogistic  doctrine;  and, 
conversely,  the  metallic  calces  and  compounds  produced  in 
an  analogous  manner  (e.g.  sulphuric  acid,  phosphoric  acid 
and  water)  were  regarded  as  elements.  Sulphur  and 
phosphorus  belonged  of  course  to  the  compounds.  Phlogiston 
itself,  the  supposed  existence  of  which  was  due  to  this  in- 
version of  actual  relations,  was  regarded,  on  the  other  hand, 
as  an  element.  Only  after  this  purely  hypothetical  state 
of  matters  had  been  set  aside  by  the  proof  that  instead  of 
the  escape  of  phlogiston  the  absorption  of  oxygen  must 
be  allowed,  and  instead  of  the  assimilation  of  phlogiston  the 
withdrawal  of  oxygen,  did  Lavoisier  bring  light  into  the 
prevailing  confusion — a  confusion  which  was  being  continu- 
ally increased  by  the  addition  of  contradictory  facts. 

With  respect  to  the  term  "  chemical  compound,"  and  the 
formation  of  such,  ideas  were  developed  during  this  period 
which  contained  much  that  was  sound,  and  which  indicated 
an  advance  over  previous  ones ;  this  is,  of  course,  apart  from 
the  erroneous  assumption  that  those  bodies  which  were 
afterwards  recognised  as  being  simple  (many  metals  and 
some  non-metals)  were  compounds  of  their  oxides  with 
phlogiston.  By  the  clearness  of  his  views  Boyle  contributed 
materially  to  an  insight  into  the  nature  of  chemical  com- 
pounds, and  to  a  recognition  of  their  dissimilarity  to  simple 
substances.  Boyle,  Mayow  and  especially  Boerhave  gave 
utterance  to  the  weighty  tenet  that  the  characteristic 
properties  of  substances  which  combine  together  chemically 
do  indeed  disappear  after  such  combination,  but  that  never- 
theless the  latter  are  not  lost,  but  are  still  present  in  the 
compound.  At  that  time  it  was  necessary  to  defend  this 
truth,  which  became  more  distinctly  formulated  later  on  in 


136  THE  PHLOGISTIC  PERIOD  CHAP. 

the  law  of  the  Conservation  of  Matter,  against  the  old 
delusion  that  the  formation  of  a  compound  was  synonymous 
with  the  creation  of  a  new  substance.  How  clearly  the 
investigators  just  named  had  grasped  the  meaning  of  the 
term  "  chemical  compound,"  is  shown  by  the  sharp  distinction 
which  they  drew  between  it  and  a  mixture  of  its  components. 

Analytical  chemistry,  which  was  meantime  gradually 
developing,  aided  towards  a  better  understanding  of  the  com- 
position of  substances,  for  by  its  means  certain  constituents  of 
salts  and  of  other  compounds  could  be  distinguished  from  one 
another.  So  long,  however,  as  analysis  remained  merely 
qualitative,  and  no  account  was  taken  of  the  proportions 
by  weight  in  which  substances  combined,  any  considerable 
development  of  the  meaning  of  the  term  "chemical  com- 
pound "  was  impossible ;  this  was  reserved  for  the  succeeding 
age. 

The  defective  knowledge  of  the  quantitative  composition 
of  substances  forced  chemists  back  upon  conclusions  drawn 
from  analogy,  when  they  wished  to  obtain  a  survey  of  the 
compounds  known.  It  was  to  the  endeavour  to  explain 
similar  phenomena  by  the  assumption  of  a  common  prin- 
ciple that  the  phlogistic  theory  owed  its  origin.  Acids, 
salts  and  metallic  calces  were  looked  upon  as  being  of 
analogous  composition,  both  because  of  their  behaviour 
and  their  modes  of  formation.  The  distinct  recognition  of 
the  fact  that  salts  were  produced  by  the  combination  of  acids 
with  bases  was  one  of  the  greatest  achievements  of  the 
phlogistic  period.  Before  the  term  "  salt  "  assumed  such  a 
definite  form,  indistinct  ideas  on  the  subject  were  very 
prevalent ;  we  have  only  to  recall  that  even  such  a  man  as 
Stahl  used  the  word  for  acids  and  alkalies  as  well  as  for 
salts  proper.  After  Boerhave,  Geoffroy  and  Duhamel 
had  succeeded  in  giving  greater  precision  to  the  con- 
ceptions regarding  these  classes  of  compounds,  Rouelle  was 
able  (in  1*745)  to  define  salts  once  for  all  as  the  products 
of  the  union  of  acids  with  bases, — and  he  further  drew  a 
sharp  distinction  between  neutral  salts  (sels  neutres  par/aits') 
on  the  one  hand,  and  basic  and  acid  salts  on  the  other. 


iv         VIEWS  WITH  REGARD  TO  CHEMICAL  AFFINITY          137 


The  characteristics  of  salts  which  formerly  obtained — 
their  solubility  in  water  and  their  taste, — therefore  fell  to  the 
ground,  seeing  that  Kouelle  included  the  insoluble  silver  and 
mercurous  chlorides  among  them. 

But  while  Rouelle's  views  regarding  the  alkaline  salts 
were  perfectly  sound,  he  could  not  throw  off  the  old  idea 
that  the  vitriols  and  other  metallic  salts  consisted  of  metal 
and  acid ;  it  fell  to  Bergman  to  show  that  this  was  erroneous, 
by  the  proof  that  it  is  the  metallic  calces  and  not  the  metals 
themselves  which  combine  with  acids  to  salts.1  What  an 
advance  is  shown  by  those  definite  conceptions  on  the  com- 
position of  salts,  as  compared  with  the  vague  ideas  that  even 
Stahl  not  long  before  had  given  utterance  to,  viz.  that  salts 
were  made  up  of  an  earth  and  water ! 

Views  regarding  Chemical  Affinity  and  its  Causes. 
—The  old  assumption  that  those  bodies  have  an  affinity  for 
one  another  which  have  something  in  common,  that  affinity, 
in  fact,  is  conditioned  by  this,  according  to  the  axiom  similia 
similibm,  held  its  ground  in  speculative  minds  even  into  the 
eighteenth  century.  The  word  affinitas,  which  expresses  this 
idea,  and  which  was  already  employed  by  Albertus  Magnus, 
presupposes  therefore  the  similarity  of  substances  which 
interact  with  one  another.  Boerhave,  on  the  contrary, 
stoutly  maintained  that  it  is  unlike  substances  which  show 
the  greatest  tendency  to  combine  with  each  other ;  and, 
notwithstanding  that  the  reason  given  for  the  combination 
of  bodies  is  exactly  the  opposite  of  what  was  originally 
taught  as  such,  viz.  their  dissimilarity,  the  name  "  chemical 
affinity"  or  "affinity"  for  this  force  has  been  generally 
retained.2 

After  the  time  of  Glauber,  and  especially  after  that  of 
Boyle,  much  attention  was  paid  to  the  processes  in  which 
the  forces  of  affinity  manifest  themselves.  Cases  of  so- 

1  The  following  passage  from  the  pseudo-Geber's  Testamentum  shows 
that  even  then  people  were  on  the  way  towards  the  true  explanation  of 
this.     The  passage  is  :  Ex  metallisfiunt  sales  post  ipsorum  calcinationem. 

2  These   terms  were  temporarily    replaced    by   others,    e.g.    rapport 
(Geoffroy),  attractio  (Bergman). 


138  THE  PHLOGISTIC  PERIOD  CHAP. 

called  simple  elective  affinity  (aUractio  electiva  simplex,  a 
term  which  originated  with  Bergman)  were  interpreted 
correctly  by  both  the  chemists  just  named,  and  also  by 
Mayow;  for  instance,  the  expulsion  of  ammonia  from 
salmiac  by  fixed  alkali,  by  the  assumption  that  the  attraction 
of  the  latter  for  hydrochloric  acid  was  greater  than  that  of 
this  acid  for  the  ammonia  (fliicTitiges  Laugensalz).  Observa- 
tions of  this  kind  on  the  expulsion  or  precipitation  of  bases 
or  acids  from  salts,  by  substances  endowed  with  stronger 
powers  of  affinity,  soon  induced  chemists  to  work  out  the 
order  in  which  analogous  bodies  were  separated  from  their 
compounds  by  others.  The  observations  on  the  precipitation 
of  metals  and  on  the  expulsion  of  various  acids  from  salts 
by  means  of  sulphuric  and  nitric  acids,  among  others,  may 
have  tended  in  an  especial  degree  to  make  clear  the  different 
strengths  of  affinity  in  analogous  bodies.  The  collation  of 
the  results  of  numerous  investigations  on  the  behaviour  of 
acids  and  bases  to  salts,  and  of  metals  to  metallic  salts, 
yielded  tables  of  affinity,  Tables  des  rapports  (first  published 
by  Geoffroy  in  1718  in  the  Memoirs  of  the  Paris  Academy), 
in  which  similar  substances  were  so  arranged  that  their 
affinity  to  the  dissimilar  ones  placed  outside  the  table 
gradually  decreased. 

The   following   table   will    serve  to  elucidate  Geoffrey's 
principle : — 


SULPHURIC  ACID. 

Fixed  alkali 

Volatile  alkali 

Absorptive  earth 

Iron 

Copper 

Silver. 


FIXED  ALKALI. 

Sulphuric  acid 
Nitric  acid 
Hydrochloric  acid 
Vinegar 
Sulphur. 


These  tables  of  affinity  remained  in  use  for  a  considerable 
period,  although  it  was  apparent  that  they  stood  in  need  of 
amendment,  and  were  frequently  modified  and  enlarged.  Their 
deficiencies  became  especially  obvious  when  chemists  began 
to  recognise  more  fully  the  influence  of  heat  upon  the 


iv  GEOFFROY'S  TABLES  OF  AFFINITY  139 

progress  of  chemical  reactions,  and  observed  that  some,  whose 
course  under  ordinary  conditions  was  perfectly  well  known, 
proceeded  in  an  exactly  opposite  direction  at  a  higher 
temperature ;  Stahl,  for  instance,  had  noted  this  correctly  in 
the  interaction  of  calomel  and  silver  at  a  lower,  and  of 
chloride  of  silver  and  mercury  at  a  higher  temperature. 
Such  reciprocal  reactions  led  to  the  proposal  to  prepare 
tables  of  affinity  for  medium  and  high  temperatures,  both 
for  wet  and  dry  (i.e.  fusion)  reactions.  Bergman  made  the 
attempt  in  1775  to  work  out  this  proposal  of  Baume's  by 
investigating  the  mutual  behaviour  of  a  very  large  number 
of  compounds,  with  the  result  that  the  doctrine  of  chemical 
affinity  was  materially  advanced,  in  so  far  as  this  was 
possible  by  such  empirical  work. 

The  results  of  his  extended  researches  were  utilised  by 
Bergman  for  setting  up  a  theory  of  affinity,  which  will  be 
most  conveniently  considered  in  conjunction  with  Berthollet's 
doctrine  of  affinity  (see  the  history  of  the  doctrine  of  affinity 
in  recent  times).  But  even  prior  to  the  efforts  of  both  of 
these  men,  the  cause  of  this  affinity  was  a  subject  of  frequent 
reflection  and  of  far-reaching  speculation.  Boyle's  lucid 
conception — that  the  small  particles  (of  which,  in  his  view, 
different  bodies  were  made  up)  attract  each  other — has 
been  already  mentioned.  The  greater  or  lesser  degree  of 
this  mutual  attraction  of  heterogeneous  substances  depended 
upon  the  form  and  position  of  each  small  particle.  He  did 
not,  however,  specially  work  out  this  idea,  which  lay  at  the 
root  of  his  corpuscular  theory,  doubtless  because  he  was  so 
sagacious  as  to  see  that  he  could  not  possibly  arrive  at  any 
knowledge  with  regard  to  the  shape  of  atoms.  Lemery,  on 
the  other  hand,  gave  a  loose  rein  to  his  fancy  upon  this 
question.  According  to  him,  the  combination  of  two  sub- 
stances— e.g.  of  an  acid  with  a  base — depended  upon  one  of 
the  small  particles  being  sharp  and  the  other  porous ;  by  the 
fitting  of  the  points  into  the  cavities,  combination  was 
effected.  He  further  attempted  to  explain  the  throwing 
down  of  precipitates,  the  solution  of  metals  in  acids,  etc.,  in 
a  similar  manner. 


140  THE  PHLOGISTIC  PERIOD  CHAP. 

The  force  which  the  mutual  attraction  of  the  particles 
calls  forth  was  regarded  by  many,  e.g.  by  Buffon  (who 
occasionally  took  part  in  the  discussion  of  theoretical 
chemical  questions),  as  identical  with  that  of  gravitation. 
But  Bergman,  who  was  also  inclined  to  this  assumption, 
justly  pointed  out  that,  since  these  particles  act  upon  one 
another  at  the  smallest  possible  distances,  this  force  must 
be  exerted  differently  from  that  of  gravity ;  and  Newton,  who 
also  turned  his  attention  to  the  point,  likewise  assumed  a 
difference  between  affinity  and  gravitation. 

It  was,  however,  impossible  that  this  subject  which  dealt 
with  the  phenomena  of  affinity  could  develop  greatly  in  the 
phlogistic  period,  since  the  proportions  by  weight  in  chemical 
processes  were  hardly  thought  of  at  all.  But  the  purely 
qualitative  investigation  of  a  large  number  of  reactions,  from 
whose  outcome  conclusions  were  to  be  drawn  regarding  the 
interaction  of  individual  components,  had  the  effect  of  matur- 
ing much  good  fruit,  so  that  the  unresting  efforts  of  chemists 
to  enlighten  themselves  upon  such  questions  turned  out  by 
no  means  useless. 

This  indeed  applies  generally  to  the  attempts  of  that 
age  in  questions  of  theoretical  chemistry — attempts  which 
were  on  the  whole  unhappy.  The  chief  gain  was  on  the 
practical  side,  in  the  rich  material  accumulated  by  observa- 
tion, the  complete  application  of  which  was  reserved  for  the 
new  era. 

The  most  important  achievements  in  practical  chemistry 
during  this  period  will  be  touched  upon  briefly  in  the 
following  section,  in  so  far  as  they  have  not  already  been 
described  in  the  general  part. 


History  of  Practical  Chemical  Knowledge  in  the  Phlogistic  Age. 

The  question  of  the  composition  of  substances  —  that 
problem  which  had  been  recognised  as  fundamental  from 
the  time  of  Boyle — could  only  be  solved  by  the  experimental 
method ;  it  was  analytical  chemistry,  which  had  developed 


iv  DEVELOPMENT  OF  ANALYTICAL  CHEMISTRY  141 

since  that  time,  that  was  to  lead  to  this  knowledge.  This 
indispensable  branch  of  the  science  proved  itself  especially 
useful  to  applied  chemistry,  whose  growth  also  falls  to  be 
recorded  here.  The  products  of  technical  importance  lead 
us,  lastly,  to  those  chemical  compounds,  a  knowledge  of 
which  was  of  moment  at  that  time,  and  therefore  also  to  the 
pharmaceutical  preparations  and  to  a  description  of  the  state 
of  pharmacy  during  the  phlogistic  period. 

Development  of  Analytical  Chemistry. — Although 
the  question  of  the  composition  of  chemical  compounds  was 
still   in   a   rudimentary  stage,  and  a  solution  of  it  in  such 
a   sense   as  we   understand  that   word   to-day  was   not   to 
be   expected,   yet   great   attention    was    paid    during    the 
phlogistic  period  to  those  reactions  by  which  it  was  possible 
to  detect  substances  with  certainty.     Qualitative  analysis, 
of  which  we  had  only  the  small  beginnings  to  record  in  the 
iatro-chemical  age,  was  developed  by  the  labours  of  Boyle, 
Hoffmann,  Marggraf,  and  especially  Scheele  and  Bergman,  in 
such  a  way  that  the  observations  of  antiphlogistic  chemistry 
which  bore  upon  it  could  be  accepted  as  valuable  contribu- 
tions.    When   we   take   into   account   the   then   prevailing 
neglect  of  the  proportions  by  weight  of  reacting  substances, 
it   causes    us   no    surprise    that    methods   of    quantitative 
analysis  were  but  seldom  applied ;  and  yet,  in  spite  of  this, 
we  meet  with  several  notable  advances  in  the  analysis  both 
of  solid  and  gaseous  bodies. 

The  analytical  investigation  of  substances  in  the  wet 
way  was  greatly  advanced  by  Boyle,  and  this  in  a  systematic 
manner  as  compared  with  the  more  scattered,  although 
valuable,  observations  of  Tachenius.  Boyle  it  was  who 
introduced  the  word  analysis  for  those  chemical  reactions  by 
which  individual  substances  could  be  recognised  in  presence 
of  one  another.  For  the  carrying  out  of  such  reactions  he 
employed  certain  reagents,  of  which  he  possessed,  for  his 
time,  an  extensive  knowledge.  It  was  with  him  that  the 
systematic  employment  of  plant  juices  as  indicates  originated, 
either  in  solution  or  fixed  upon  paper,  for  the  recognition  of 


142  THE  PHLOGISTIC  PERIOD  CHAP. 

acids,  bases  and  neutral  substances,  and  for  this  purpose  he 
studied  and  made  particular  use  of  the  colouring  matters  in 
the  juices  of  litmus,  violets  and  corn-flowers.  Besides  these 
general  reagents,  which  served  to  distinguish  important 
classes  of  compounds,  Boyle  introduced  many  other  character- 
istic ones  which  allowed  of  the  recognition  of  individual  sub- 
stances in  the  form  of  precipitates.  For  the  detection  of 
sulphuric  and  hydrochloric  acids,  respectively,  he  used  solu- 
tions of  calcium  and  silver  salts,  and  vice  versa.  Ammonia  he 
recognised  by  the  production  of  a  cloud  when  it  came  in 
contact  with  hydrochloric  or  nitric  acid;  copper  salts  by 
the  blue  solution  which  they  gave  with  excess  of  volatile 
alkaline  salt;  solutions  containing  iron  by  the  black 
colouration  they  yielded  with  infusions  of  tanning  stuffs1 
(from  gall  apples,  oak  leaves,  etc.).  He  was  also  sometimes 
happy  in  the  way  in  which  he  applied  careful  observations 
on  the  precipitation  of  certain  metals  by  others,  as  tests 
for  these. 

The  salt  solutions  found  in  nature,  mineral  springs  in 
particular,  had  before  this  time  stimulated  the  iatro-chemists 
to  search  out  the  substances  which  they  contained.  Some 
advances  in  the  analysis  of  mineral  waters  became  noticeable 
at  the  end  of  the  seventeenth  and  in  the  eighteenth  centuries, 
and  we  find  at  the  same  time  the  chemists  engaged  on  the 
subject  inspired  with  the  wish  to  prepare  those  natural 
products  artificially ;  but  the  knowledge  requisite  for  doing 
this,  i.e.  a  knowledge  of  the  true,  and  especially  of  the 
quantitative,  composition  of  these  waters,  was  wanting  even 
at  the  end  of  last  century.  Hoffmann  investigated  a  large 
number  of  mineral  waters,  and  proved  the  presence  in  them 
of  carbonic  acid,  iron,  common  salt,  and  salts  of  magnesia 
and  lime,  showing  at  the  same  time  how  to  test  for  these ; 
he  also  pointed  out  the  characteristics  of  alkaline  and  sulphur 
waters.  In  addition  to  this,  he  demonstrated  the  incorrect- 
ness of  previous  statements  as  to  the  presence  of  gold,  silver 
and  arsenic  in  such  waters,  and  explained  the  connection 

1  The  prescription  for  preparing  black  iron  ink  from  gall  apples  and 
iron  vitriol  is  due  to  Boyle. 


iv  PROGRESS  IN  CHEMICAL  ANALYSIS  143 

between  the.  occurrence  of  such  exceptional  salts  as  alum  and 
copper  vitriol  and  the  nature  of  the  soil  at  those  places.  He 
frequently  made  use  of  crystalline  form  to  distinguish  different 
salts. 

The  observations  made  by  Marggraf  materially  enlarged 
the  acquaintance  with  reagents  suitable  for  the  detection  of 
substances,  and  also  the  knowledge  of  the  composition  of 
many  compounds.  He  used,  for  instance,  a  solution  of 
prussiate  of  potash  to  test  for  iron,  and  applied  the  different 
colourations  which  the  salts  of  potash  and  soda  impart  to  a 
flame  for  their  detection — a  point  that  had  also  been  observed 
independently  by  Scheele.  The  behaviour  of  many  salts  to 
caustic  potash  enabled  Marggraf  to  arrive  at  their  composition : 
thus  he  proved  that  gypsum  consisted  of  lime  and  sulphuric 
acid,  and  that  this  acid  was  also  present  in  heavy  spar.  As 
already  mentioned,  he  made  use  of  the  microscope  for  getting 
at  the  crystalline  forms  of  different  substances. 

That  Scheele  owed  his  mastery  in  the  discovery  of  new 
substances  to  the  gift  of  deducing  their  presence  from 
certain  reactions,  and  that  he,  therefore,  greatly  extended 
analytical  chemistry  by  a  multitude  of  observations,  hardly 
requires  to  be  stated.  But,  although  in  his  knowledge  of 
the  chemical  behaviour  of  bodies  he  was  equalled  by  no  one 
of  his  contemporaries,  he  unfortunately  did  not  apply  this 
knowledge  systematically,  as  Bergman  did,  thereby  laying  the 
firm  foundation  for  the  methodical  use  of  reagents,  and,  with 
it,  of  qualitative  analysis.  The  reactions  which  the  latter 
made  use  of  as  tests  for  baryta,  lime,  copper,  sulphuretted 
hydrogen,  and  sulphuric,  oxalic,  arsenious  and  carbonic  acids, 
etc.,  are  those  in  vogue  at  the  present  day.  Bergman  also 
drew  attention  to  the  general  application  of  the  fixed 
alkalies  for  precipitating  solutions  of  metals  and  earths ;  to 
many  other  reagents,  such  as  sublimate,  sugar  of  lead,  and 
liver  of  sulphur;  and  also  to  modes  for  estimating  pre- 
cipitates and  separating  salts.  The  first  methods,  by  which 
it  was  possible  to  test  minerals  and  especially  ores  completely, 
were  due  to  him,  viz.  their  digestion  with  hydrochloric  or 
nitric  acid,  or  their  fusion  with  carbonate  of  potash.  There 


144  THE  PHLOGISTIC  PERIOD  CHAP. 


can  be  no  doubt,  however,  that  he  was  indebted  to  Scheele 
for  many  observations;  the  latter,  for  instance,  fused  up 
minerals  with  alkalies  so  early  as  1*772-3,  perceived  the  dif- 
ference between  soluble  and  insoluble  silicic  acid,  and  carried 
through  the  separation  of  iron  and  manganese  by  means  of 
acetic  acid. 

Qualitative  analysis  in  the  dry  way  made  considerable 
advances  in  the  eighteenth  century  by  the  increasing  use  of 
the  blowpipe,  the  value  of  which  in  the  examination  of  ores 
was  recognised  more  especially  in  Sweden.  Gahn  and 
Bergman,  together  with  the  mineralogist  Cronstedt,  were 
chiefly  instrumental  in  introducing  it  into  chemistry ; l  in  their 
tests  they  employed  borax,  soda,  cobalt  solution  and  other  re- 
agents, and  also  made  use  of  the  difference  between  the 
inner  and  outer  flames,  though  Scheele  was  manifestly  the 
first  to  recognise  and  explain  correctly  the  reason  of  this  dif- 
ference. But  it  was  through  Berzelius  that  the  blowpipe  be- 
came universally  employed  and  felt  to  be  an  almost  indis- 
pensable aid  in  analysis. 

Attempts  not  merely  to  test  for  substances  qualitatively, 
but  also  to  determine  their  quantity,  were  few  in  number 
up  to  the  time  of  Lavoisier,  and  yet  it  is  evident  from  many 
statements  made  by  Boyle,  Homberg,  Marggraf,  Scheele, 
Bergman  and  others,  that  they  sometimes  endeavoured  to 
take  the  proportions  by  weight  into  account.  How  otherwise 
is  it  possible  to  explain  Marggraf  s  accurate  determination  of 
the  weight  of  the  precipitate  obtained  by  dissolving  a  given 
quantity  of  silver  and  precipitating  the  solution  with  common 
salt ;  or  Black's  estimation  of  the  weight  of  the  precipitate 
obtained  by  adding  carbonate  of  soda  to  a  solution  of  sulphate 
of  magnesia  which  corresponded  to  a  definite  amount  of 
magnesia  alba,  in  order  to  prove  the  constant  proportion  of 
fixed  air  in  the  latter  ?  Mention  must  also  be  made  here  of 

1  After  investigating  the  point  with  great  care,  J.  Landauer  (Ber.  xxvi, 
p.  898)  has  brought  forward  proof  to  show  that  it  was  Cronstedt  who  really 
rendered  the  chief  service  here,  and  not  Anton  Swab,  as  has  recently  been 
contended.  G.  v.  Engestrom  was  the  author  of  the  first  manual  on  the  use 
of  the  blow-pipe ;  this  was  published  in  1770  as  an  appendix  to  a  work  on 
mineralogy. 


iv  THE  BEGINNINGS  OF  GAS  ANALYSIS  145 

the  determination  of  the  weights  of  metallic  precipitates  (i.e- 
the  metals  themselves)  by  Bergman  and  others.  Bergman 
was  probably  the  first  to  proceed  on  the  principle  that  an 
element  should  not  be  itself  isolated  and  estimated  according 
to  its  own  weight,  but  separated  in  the  most  convenient 
form  as  an  insoluble  precipitate,  e.g.  lime  earth  as  oxalate 
of  lime,  and  sulphuric  acid  as  sulphate  of  baryta. 

In  pneumatic  chemistry,  too,  the  necessity  became 
strongly  felt  of  being  able  to  detect  different  gases  in 
presence  of  one  another  by  means  of  reagents,  and  to 
estimate  their  relative  volumes  quantitatively.  For  this 
purpose  special  absorptives  were  used,  by  the  action  of 
which  the  differences  in  the  gases  had  first  been  noticed. 
Thus  caustic  potash  was  found  to  be  suitable  for  the  absorp- 
tion and  measurement  of  carbonic  acid,  and  saltpetre  gas 
(nitric  oxide),  hydrate  of  protoxide  of  iron,  moist  sulphuret 
of  iron,  or  phosphorus,  for  that  of  oxygen.  Of  course  the 
results  of  such  quantitative  analysis  were  very  inexact.1  But 
Cavendish  succeeded  in  making  an  extremely  accurate 
determination  of  the  oxygen  in  air  by  the  method  suggested 
by  Volta,  viz.  by  exploding  with  hydrogen.  Unlike  previous 
experimenters,  he  found  the  composition  of  the  air  constant, 
the  oxygen  amounting  on  the  average  to  20*85  per  cent. ; 
the  mean,  as  determined  at  the  present  day,  is  20'9  per  cent. 

As  the  foregoing  short  account  shows,  a  great  deal  of 
preparatory  work,  which  chiefly  required  perfecting  in  the 
quantitative  direction,  stood  ready  to  hand  at  the  period 
which  began  with  Lavoisier.  The  most  important  features 
and  principles  of  chemical  analysis  were  contained  in  these 
preparatory  researches,  and  only  waited  for  development. 

1  As  the  result  of  very  imperfect  methods,  Priestley  and  Scheele  found 
that  the  proportion  of  oxygen  in  air  varied  between  18  and  25  per  cent. 
The  term  "  eudiometry "  (>i;5tos,  fine  (applied  to  weather),  and  /xerpou, 
a  measure]  came  into  use  then,  because  it  was  supposed  that  the  purity  of 
the  air  was  arrived  at  by  the  determination  of  its  oxygen  ;  and  it  has 
continued  to  be  employed  in  gas  analysis  in  spite  of  its  inaptness. 


146  THE  PHLOGISTIC  PERIOD  CHAP. 


The  State  of  Technical  Chemistry  in  the  Phlogistic  Period. 

Many  chemists  of  the  time,  among  whom  we  may  mention 
Boyle,  Kunkel,  Marggraf,  Macquer  and  Duhamel,  frequently 
directed  their  efforts  to  applying  their  scientific  experience  of 
chemical  processes  to  the  advancement  of  particular  branches 
of  industry.  Technical  chemistry  thus  made  good  progress 
during  this  period.  We  come  across  the  beginnings  of  great 
chemical  industries,  and  are  able  to  perceive  the  development 
of  a  knowledge  of  technically  important  chemical  preparations,, 
whose  manufacture  has  increased  during  this  century  in  an 
undreamt-of  degree. 

The  distinction  between  applied  and  pure  chemistry  was 
luniversally  recognised  towards  the  middle  of  the  eighteenth 
century.  Serviceable  text-books,  treating  of  particular 
branches  of  technical  chemistry,  were  not  wanting,  the 
conjunction  of  theory  and  practice  so  necessary  for  the 
i  Ifare  of  the  latter  being  thus  cared  for.  Analysis  was 
also  successfully  brought  into  the  service  of  chemistry, 
especially  in  the  working-up  of  ores.  Even  so  early  as  168(> 
Charles  XL  of  Sweden  had  recognised  the  value  of  such 
investigations,  and  had  caused  a  technical  laboratory  to  be 
built.  Here,  under  Hiarne's  superintendence,  all  sorts  of 
natural  products  (such  as  ores  and  other  minerals,  soils,  etc.) 
were  examined,  and  researches  were  instituted,  with  the 
object  of  rendering  chemical  products  of  practical  use,  and  of 
applying  in  daily  life  the  various  results  obtained. 

In  metallurgy  the  several  modes  of  procedure  underwent 
only  slight  changes,  but,  as  a  consequence  of  the  clearer  com- 
prehension of  chemical  reactions,  light  was  thrown  upon 
many  processes  which  had  hitherto  been  wrongly  explained. 
The  results  of  the  researches  of  Bergman,  Gahn  and  Rinman 
came  to  be  used  in  the  manufacture  of  iron  and  steel,  the 
difference  between  these  being  traced  to  its  true  reason  only 
at  the  end  of  the  phlogistic  period.  Marggraf  taught  an 
easier  mode  of  preparing  zinc  from  calami  ne  in  closed  chambers, 
with  exclusion  of  air  as  far  as  possible,  and  thus  made  this. 


iv  ADVANCES  IN  TECHNICAL  CHEMISTRY  147 


useful  metal  more  available.  The  manufacture  of  brass  was 
materially  improved  by  Duhamel  de  Monceau,  and  that  of 
cast-iron  and  steel  by  the  versatile  Reaumur.  The  produc- 
tion and  working-up  of  particular  metals,  e.g.  the  engraving, 
tinning  and  gilding  of  iron,  the  silvering  of  copper,  etc.,  were 
developed  in  many  ways  by  Boyle  and  Kunkel. 

A  highly  productive  field  was  opened  up  for  the  ceramic 
industry  by  the  accidental  discovery  of  porcelain,  the  manu- 
facture of  which,  although  carried  out  on  a  large  scale  at 
Meissen,  remained  a  secret  until  it  was  successfully  solved  at 
Sevres  in  1769  by  the  carefully  planned  experiments  of 
Reaumur  and  other  later  chemists,  notably  Macquer.  Im- 
provements and  novelties  in  the  manufacture  of  glass  were 
introduced  by  Kunkel  and  Boyle,  e.g.  in  the  preparatior 
of  ruby  glass  and  in  glass  painting.  Dyeing  was  likewise 
enriched  by  the  experiences  of  various  chemists.  New 
colours,  chief  among  which  was  Prussian  blue  (discovered 
quite  accidentally  by  the  dyer  Diesbach  in  1710),  together 
with  paints,  such  as  mosaic  gold  and  Scheele's  green,  were 
made  available  for  industrial  purposes.  And  chemists,  among 
whom  Stahl,  Hellot  and  Macquer  must  be  particularly  men- 
tioned, endeavoured  not  only  to  prepare  and  apply  colours  by 
practical  recipes,  but  also  to  aid  the  manufacturer  by  specula- 
tions upon  the  modes  in  which  dyeing  processes  are  brought 
about.  Dyes  were  divided  by  them  into  two  classes,  accord- 
ing as  they  were  capable  of  being  fixed  upon  cloth  with  or 
without  mordants,  and  Bancroft  (in  1794)  distinguished 
these  as  adjective  and  substantive  dyes.  Scheele  was  the  first 
to  give  a  correct  explanation  of  the  formation  of  lead  white,  a 
substance  much  prized  as  a  white  paint. 

Those  technically  important  preparations,  of  which  an 
intimate  knowledge  was  first  gained  in  the  phlogistic  age, 
constituted  a  valuable  introduction  to  the  chemical  industries 
of  to-day.  At  that  time  the  tendency  of  chemists  was  to 
inquire  whether  this  or  that  substance  was  technically 
useful,  just  as  in  the  preceding  period  they  had  tested 
chemical  compounds  for  their  application  to  medicine.  The 
manufacture  of  acids  and  alkalies,  the  chemical  industry 

L  2 


148  THE  PHLOGISTIC  PERIOD  CHAP. 

which  constitutes  the  basis  of  nearly  all  others,  was  last 
century  only  in   its   infancy,  although  even   then  some  of 
these  products  began  to  be  made  in  considerable  quantities. 
Thus  Boyle  tells  us  that  nitric  acid  was  manufactured  from 
saltpetre   in    special   "  distilleries "   (Brennereien)    to   more 
advantage  than  was  the  case  before,  by  improved  methods 
worked   out   by   Stahl   and   others.     Rouelle  was  the  first 
to  show  how  it  could  be  concentrated  by  distilling  it  with 
oil  of  vitriol.     Sulphuric  acid  was  first  manufactured  on  the 
large  scale  in  England  (by  Ward  of  Richmond)  about  the 
middle  of  the  eighteenth  century,  by  burning  sulphur  with 
the  addition  of  saltpetre.     The  perishable  and  at  the  same 
time  costly  glass  balloons  in  which  the  process  was  carried 
out  were  soon  replaced — at  first  in  Birmingham — by  leaden 
chambers,  which  are  still  indispensable  for  this  manufacture ; 
the  continuous  working  of  these  chambers  is  an  achievement 
of  our  own  century.     The  preparation  of  fuming  sulphuric 
acid  from  "weathered"  iron  vitriol  had  been  known  long 
before  that   of  oil   of  vitriol   itself,  which    last,   moreover, 
received  its  name  because  of  its  production  from  this  salt. 
The  manufacture  of  the  fuming  acid,  based  upon  the  old 
observations  of  the  pseudo-Geber  and  Basil  Valentine,  was 
first  carried  on  at  Nordhausen  in  the  Harz  (whence  its  name 
of  Nordhausen  sulphuric  acid,  still  in  vogue),  being  removed 
subsequently  to  Bohemia.     The  time  for  the  technical  ap- 
plication of  hydrochloric  acid  and  the  chlorine  generated  from 
it  was  not  yet  come  ;  hydrofluoric  acid,  however,  was  used  for 
etching  glass  by  Schwanhardt  of  Ntirnberg  so  far  back  as  the 
seventeenth  century. 

The  alkalies  and  their  carbonates  were,  as  in  ancient 
times,  obtained  from  the  ashes  of  plants,  carbonised  tartar 
and  incrustations  on  the  soil,  to  be  used  for  the  production 
of  soap,  glass,  etc.  The  discovery  of  the  practical  prepara- 
tion of  soda  from  common  salt,  which  revolutionised  in- 
dustrial chemistry,  was  reserved  for  the  beginning  of  the 
present  epoch ;  but  even  so  early  as  the  first  half  of  the 
eighteenth  century  some  remarkable  observations  were  made 
which  showed  that  it  was  possible  to  convert  salt  first  into 


iv  ELEMENTS  DISCOVERED  DURING  THIS  PERIOD          149 

sodic  sulphate,  and  then  the  latter  into  soda — reactions  which, 
as  he  himself  tells  us,  were  turned  to  use  by  Leblanc,  the 
gifted  originator  of  the  soda  industry.1 

Duhamel  de  Monceau,  one  of  those  who  showed  how  to 
transform  common  salt  into  soda,  deserves  praise  for  intro- 
ducing suitable  processes  for  the  preparation  of  various 
products  of  technical  importance, — salmiac,  starch,  soap,  etc. 
We  find,  in  fact,  the  clearer  knowledge  of  chemical  reactions 
resulting  in  improvements  in  old  processes  generally,  and 
many  new  manufactures  created  or  at  least  prepared  for,  e.g. 
the  now  enormous  beet  sugar  industry  by  Marggrafs  dis- 
covery. 

Knowledge  of  other  important  Compounds  during  the 
Phlogistic  Period. 

The  increase  in  the  knowledge  of  the  elements  and  of 
chemical  compounds — which,  although  of  no  special  technical 
value  then,  were  partly  destined  to  become  so — was  quite 
remarkable  in  the  phlogistic  period,  so  that  it  is  worth  while 
to  take  a  short  survey  of  these  here.  To  the  elements 
known  at  that  time  (although  they  were  not  regarded  as 
such)  various  new  ones  were  added,  of  which  we  may 
mention  phosphorus,  chlorine,  manganese  (isolated  by  Gahn 
in  1774),  cobalt  (Brandt,  1742),  nickel  (Cronstedt,  1750),  and 
platinum  (Watson,  1750).  The  discovery  of  these  was  usually 
preceded  by  a  thorough  investigation  of  their  compounds, 
although  chance  sometimes  came  into  play,  e.g.  in  the 
isolation  of  phosphorus.  This  last  discovery  excited  chemists 
in  an  unwonted  degree  and  produced  an  extraordinary  sensa- 
tion among  educated  circles  in  Germany,  England  and 
France,  on  account  of  the  marvellous  properties  of  the  new 
body.  Brand,  a  Hamburg  alchemist,  succeeded  in  1669  in 
obtaining  phosphorus  by  distilling  the  residue  from  evapor- 

1  A  notable  observation  made  by  Scheele  about  the  year  1770  deserves 
mention  here,  viz. ,  that  soda  can  be  prepared  by  treating  a  solution  of  salt 
with  oxide  of  lead,  filtering,  and  passing  carbonic  acid  through  the  filtrate. 
This  process  was  patented  by  Turner  in  1787. 


150  THE  PHLOGISTIC  PERIOD  CHAP. 

ated  urine,  and  gave  it  the  same  name  as  the  Bologna  stone 
or  phosphor  (which  was  sulphide  of  barium,  prepared  by 
heating  the  sulphate  with  carbon),  already  known.  The  two 
leading  chemists  of  the  day,  Boyle  and  Kunkel,  endeavoured 
for  years  to  discover  the  secret  of  its  preparation,  and 
ultimately  succeeded,  contributing  thereby  at  the  same  time 
to  a  better  knowledge  of  the  element. 

Of  the  chemical  compounds  prepared  artificially,  it  was 
the  combustion-  and  calcination-products  of  the  elements, 
i.e.  acids  and  metallic  oxides,  which  awakened  the  most 
interest,  in  accordance  with  the  tendency  of  the  age ;  and 
accompanying  this,  the  salts  formed  from  these  bodies  were 
carefully  studied.  A  good  deal  has  already  been  said  with 
regard  to  the  knowledge  of  these  substances.  Although  the 
views  as  to  their  composition  were  quite  erroneous,  the 
correct  interpretation  which  "came  later  was  materially  aided 
by  the  accurate  investigation  of  their  behaviour. 

Of  acids  as  combustion  products,  phosphoric  acid  deserves 
the  first  mention.  It  was  discovered  by  Boyle,  and  its 
nature  elucidated  by  an  admirable  research  of  Marggraf  s, 
who  showed  how  it  was  produced  by  burning  phosphorus, 
and  also  by  treating  the  latter  with  nitric  acid  ;  he  likewise 
explained  its  production  from  urine.  Further,  that  the 
amount  of  phosphorus  present  in  the  latter  depended  upon 
the  nutriment  taken,  was  distinctly  stated  by  him.  Scheele 
and  Gahn  were  the  first  to  prove  the  presence  of  phosphoric 
acid  in  bones.  It  has  already  been  mentioned  that  the 
earliest  accurate  knowledge  of  the  combustion-products  of 
sulphur,  coal,  and  of  gases  containing  oxygen  generally, 
belongs  to  the  second  half  of  the  eighteenth  century. 
Cavendish  proved  the  composition  of  nitric  acid  by  its 
synthesis  from  nitrogen  and  oxygen  (in  presence  of  water), 
but  the  clear  result  of  his  researches  was  obscured  by  phlo- 
gistic accessories.  The  discovery  and  accurate  examination 
of  nitrous  acid — "  volatile  nitric  acid  " — was  due  to  Scheele 
in  1768  ;  his  able  treatise  on  the  subject  was  only  published 
recently  along  with  his  letters  (loc.  cit.,  p.  9). 

The  many  investigations  which  were  made  on  the  pro- 


iv  INORGANIC  AND  ORGANIC  PREPARATIONS  151 

ducts  of  calcination  of  the  metals  and  semi-metals  greatly 
advanced  the  knowledge  of  these.  We  may  mention  here  the 
recognition  by  Scheele  of  white  arsenic  as  the  calx  of  the 
metallic  arsenic  and  the  oxidation  of  the  former  to  arsenic 
acid  in  1775,  his  discovery  of  molybdic  and  tungstic  acids, 
and  the  investigation  of  the  behaviour  of  quicksilver  calx 
upon  heating — so  pregnant  in  its  results. 

The  knowledge  that  a  salt  consisted  of  an  acid  and  a 
base  facilitated  the  survey  of  many  compounds  widely 
apart  from  one  another.  Marggraf,  for  instance,  showed 
that  sulphate  of  potash  had  an  analogous  composition  to 
gypsum  and  heavy-spar,  although  it  was  so  unlike  these. 
The  definite  distinction  of  alum  earth  from  lime  earth,  of  the 
latter  from  magnesia 1  (Hoffmann  and  Black),  and  of  potash 
from  soda  (Duhamel,  Scheele,  and  others)  belonged,  with 
many  other  discoveries,  to  the  phlogiston  theory  in  its 
prime,  and  was  of  great  service  to  the  succeeding  period. 
A  large  number  of  new  salts  became  known,  among  others 
salts  of  manganese  and  bismuth  (including  the  basic  nitrate 
of  bismuth,  so  much  valued  as  a  cosmetic),  compounds  of 
cobalt,  nickel,  platinum,  etc.  And  the  qualitative  composi- 
tion of  many  salts,  whose  nature  had  hitherto  been  quite 
misunderstood,  was  correctly  explained,  e.g.  that  of  alum, 
borax,  calamine  and  other  compounds. 

Organic  Preparations. — The  knowledge  of  organic 
compounds  was  likewise  much  advanced,  especially  by 
Scheele,  who  devised  methods  for  discovering  and  isolating 
organic  acids.  While  new  fields  were  thus  opened  up  at 
the  close  of  the  phlogistic  period,  those  organic  substances 
which  were  already  known  were  also  further  investigated. 
It  is  true  that  the  real  composition  (even  qualitative)  of  all 
these  carbon  compounds  remained  unrecognised,  and  this 
complete  ignorance  hid  itself  behind  meaningless  expressions 
-and  periphrases ;  thus  oil  and  water,  or  a  combustible  and 

1  Silicic  acid,  which  had  for  long  been  reckoned  among  the  earths  as 
*'  vitrifiable  earth,"  was  first  characterised  by  Scheele  as  a  fire-proof  acid 
in  the  year  1773  (Letters,  p.  69). 


152          --.-'„£**-;   THE  PHLOGISTIC  PERIOD  CHAP. 


a  mercurial  principle,  were  assumed  as  the  constituents  of 
alcohol.  It  was  again  Lavoisier  who  pointed  out  the  right 
path  here,  by  proving  that  carbon,  hydrogen  and  oxygen 
were  the  constituents  of  this  as  of  most  other  organic 
substances,  and  by  indicating  modes  for  determining  the 
proportions  by  weight  of  the  elements  just  named. 

Spirit  of  wine  and  the  ethers  which  could  be  obtained 
from  it,  together  with  common  ether  itself,  were  the 
subjects  of  frequent  investigation,  so  that  they  came  to 
be  prepared  fairly  pure.  Spirit  of  wine  especially  was 
employed  in  analysis  for  the  separation  of  different  salts, 
and  attempts  were  made  to  deduce  the  amount  of  alcohol 
in  aqueous  solutions  of  it  from  its  specific  gravity;  the 
beginnings  of  alcoholometry  are  to  be  found  with  Reaumur 
in  1733  and  Brisson  in  1768.  With  respect  to  its  forma- 
tion in  spirituous  fermentations  opinions  were  very  confused ; 
many,  indeed,  disputed  this  formation,  assuming  its  pre-exist- 
ence  in  the  wine  must,  etc. 

Ether,  which  was  termed  spiritus  vini  vitriolatus  or 
cethereus,  became  known  through  the  labours  of  Frobenius 
(about  1730),  Hoffmann,  Pott,  Baume  and  others,  and  was 
used  medicinally  admixed  with  spirit  of  wine  (Hoffmann's 
drops).  The  erroneous  idea  that  it  contained  sulphur 
prevailed  for  a  long  time,  until  this  was  finally  done  away 
with  by  the  investigation  of  Valentin  Rose  the  younger 
(in  1800).1  The  name  "sulphur  ether"  arose  from  this. 
At  that  time  any  pungent  volatile  liquid  was  termed  an 
ether. 

Nitrous2  ether,  muriatic  ether,  and  acetous3  ether,  so 
named  because  of  their  respective  origins,  were  likewise 
carefully  investigated,  and  were  valued  as  officinal  prepara- 
tions. Scheele's  acuteness  of  observation  is  well  shown  by 
the  fact  that  he  recognised  the  necessity  for  having  a 
mineral  acid  present  during  the  formation  of  ethers  of  weak 

1  Prior  to  this  date,  Hoffmann  and  Macquer  correctly  assumed  that 
ether  was  formed  from  alcohol  by  the  elimination  of  water. 

3     Our  present  nitrous  ether,  admixed  with  a  little  nitric  ether,  aldehyde, 
etc.  3  Ethyl  acetate. 


iv  KNOWLEDGE  OF  ORGANIC  ATMTT    ^  153 

acids,  such  as  acetic  and  benzoic,  a  point  which  had  been 
overlooked  before  his  time. 

The  knowledge  of  the  organic  acids  was  materially  ex- 
tended during  the  phlogistic  period,  especially  towards  its 
close.  Acetic  acid,  which  had  been  longest  known  of  any, 
was  now  prepared  in  the  concentrated  pure  state  as  the  glacial 
acid,  and  its  combustibility  was  observed  by  Lauraguais. 
Kunkel,  Boyle  and  others  believed  in  the  identity  of  the 
acetic  acids  prepared  by  fermentation  and  by  the  distilla- 
tion of  wood,  without,  however,  being  able  to  adduce  definite 
proof  of  this ;  the  latter  was  furnished  by  Thenard  in  1802. 
The  resemblance  between  formic  acid,  discovered  by  Wray 
in  1760,  and  acetic  acid  was  early  noticed,  and  led  to  con- 
founding the  one  with  the  other,  until  Marggraf  definitely 
proved  their  dissimilarity. 

Scheele  showed  how  to  prepare  a  large  number  of  acids 
from  plant  juices,  by  first  forming  their  lime  or  lead  salts, 
and  then  decomposing  these  with  suitable  mineral  acids, 
usually  sulphuric.  In  this  way  he  discovered  tartaric  acid, 
which  had  hitherto  been  overlooked  in  spite  of  the  fact  that 
tartar  had  been  known  for  a  long  time ;  also  citric,  malic  and 
oxalic  acids,  the  last  of  which  he  prepared  by  acting  upon 
sugar  with  nitric  acid,  and  which  he  recognised  as  being 
identical  with  the  acetosellic  acid  he  had  obtained  from  wood- 
sorrel.  By  treating  milk  sugar  with  nitric  acid  he  was  led  to 
the  discovery  of  mucic  acid,  and  by  investigating  sour  milk 
to  that  of  lactic  acid,  while  he  found  uric  acid  in  (bladder) 
stones.  For  other  acids,  already  known,  he  devised  improved 
methods  of  preparation,  e.g.  for  gallic  and  benzoic.  Lastly, 
his  discovery  of  prussic  acid  in  1782,  by  decomposing  yellow 
prussiate  of  potash  with  sulphuric  acid,  is  worthy  of  note. 
The  masterly  investigation  of  it  which  he  made  enabled  him 
to  give  its  qualitative  composition  with  accuracy ;  one  only 
requires  to  translate  his  phlogistic  language  into  modern 
chemical  terms. 

The  fatty  oils  and  animal  fats  were  frequent  subjects  of 
investigation,  without  their  composition  and  chemical  be- 
haviour, especially  towards  the  alkalies,  becoming  any  clearer ; 


154  THE  PHLOGISTIC  PERIOD  CHAP. 

and  this  in  spite  of  an  important  observation  made  by  Scheele 
in  the  discovery  of  glycerine,  or  Oelsiiss,  as  he  termed  it,  by 
acting  upon  a  fatty  oil  with  litharge.  The  importance  of  this 
observation  was  only  recognised  at  a  much  later  date.  Only 
the  rudiments  of  preparatory  researches  are  to  be  seen  in 
the  chemistry  of  the  sugars  and  of  other  products  of  animal 
and  vegetable  metabolism,  such  as  the  ethereal  oils,  albumens, 
etc. 

Condition  of  Pharmaceutical  Chemistry. 

The  interests  which  chemistry  and  pharmacy  had  in 
common  resulted  in  their  exercising  a  beneficial  action  upon 
one  another.  A  large  number  of  famous  investigators  owed 
to  the  practice  of  pharmacy  their  stimulus  to  the  study  of 
purely  chemical  phenomena ;  of  these  we  may  mention 
Kunkel,  the  Lemerys  (father  and  son),  Geoffrey,  Kouelle, 
Neumann,  Marggraff  and  Scheele.  While  they  themselves 
and  others  contributed  a  wealth  of  the  most  valuable  obser- 
vations, indeed  of  fundamental  discoveries,  to  chemistry, 
pharmacy  was  at  the  same  time  materially  advanced,  not  only 
by  those  discoveries,  but  also  by  special  pharmaceutical  re- 
searches. The  chief  gain  for  pharmacy  lay  in  its  intimate 
fusion  with  pure  chemistry.  On  the  other  hand,  the  work 
required  in  apothecaries'  shops  proved  itself  the  best  pre- 
paratory training  for  future  chemists.  The  scientific  taste 
was  nourished  by  excellent  text-books  on  pharmaceutical 
chemistry,  e.g.  Baume's  ttttrnents  de  Pharmacie  Thdorigue  et 
Pratique  (l762),Hagen's  Lehrbuclider  Apotliekerkunst  (Hagen's 
Text-Book  of  Pharmacy),  and  was  firmly  established  by  the 
founding  of  pharmaceutical  laboratories ;  the  growth  of  the 
latter  belongs,  however,  more  to  the  present  epoch. 

Many  additions  were  made  during  this  period  to  the 
medical  treasury  by  pharmaceutical  chemistry.  Of  the  new 
medicines  which  then  came  into  vogue,  and  whose  nature 
was  often  involved  in  mystery  until  they  ceased  to  be  secret 
remedies,  the  following  important  ones  may  be  mentioned  > — 
Carbonate  of  ammonia,  which  was  contained  in  the  famous 


iv  PHARMACEUTICAL  CHEMISTRY  155 

"  English  drops  " ;  sulphate  of  potash,  valued  under  Glaser's 
designation  of  sal  polychrestum,  which  was  obtained  by 
detonating  sulphur  with  saltpetre;  sulphate  of  magnesia, 
first  prepared  from  the  Epsom  (spring)  water  by  Grew  in 
1695,  and  termed  sal  anglicum,  and,  later  on,  bitter  salt; 
and  magnesia  alba,  obtained  from  the  mother  liquors  in  the 
preparation  of  saltpetre  by  means  of  carbonate  of  potash. 
Among  the  preparations  of  antimony,  the  Kermes  minerale, 
whose  composition  was  only  arrived  at  correctly  during  the 
present  century,  came  into  repute.  Ferric  chloride  in 
alcoholic  solution  was  a  favourite  secret  medicine  in  the 
first  half  of  the  eighteenth  century  under  the  name  of 
"  gold  drops  "  or  nerve  tincture ;  its  nature,  however,  soon 
became  recognised.  Hoffmann's  drops  and  the  compound 
ethers  were  likewise  used  officinally.  Goulard  introduced 
basic  acetate  of  lead  after  the  middle  of  the  last  century  as 
a  remedy  for  external  use,  and  it  is  called  by  his  name  to 
this  day. 

Many  observations  were  made  with  regard  to  substances 
of  special  antiseptic  action,  Kunkel  pointing  to  the  mineral 
acids  for  this.  The  antiseptic  properties  of  iron  vitriol  and 
alum  were  made  use  of  in  the  impregnation  of  wood  with 
these  salts,  according  to  the  proposal  of  the  Swede,  Faggot. 
In  1782,  Scheele  recommended  the  conservation  of  vinegar 
by  boiling  it  in  closed  vessels ;  he  was  thus  the  discoverer 
of  the  sterilisation  method,  now  of  such  supreme  import- 
ance. 

Concluding  Remarks. — The  period  of  phlogistic  chem- 
istry must  be  looked  upon  as  the  indispensable  forerunner  of 
the  new  era  which  began  with  Lavoisier.  The  erroneous 
conception  which  underlay  the  important  phenomena  of  com- 
bustion and  calcination,  and  which  spread  itself  over  many 
other  processes,  most  assuredly  did  not  prevent  the  young 
science  of  chemistry  from  developing  in  a  healthy  manner. 
Without  doubt  it  was  the  experimental  method  which  con- 
tributed most  to  this.  Hand  in  hand  with  this  development 
we  find  an  increasing  improvement  in  the  means  for  observ- 


156  THE  PHLOGISTIC  PERIOD  CHAP. 

ing  chemical  processes  and  for  establishing  the  properties  of 
substances.  These  advances  were  due  partly  to  improved  ap- 
paratus (for  instance,  the  apparatus  required  for  collecting  and 
measuring  gases),  and  partly  to  the  use  of  physical  methods 
of  research ;  and  here  we  may  note  the  more  frequent  deter- 
minations of  the  specific  gravity  of  bodies  in  different  states 
of  aggregation,  and  the  use  of  the  microscope.  The  time  had 
not  yet  arrived  when  the  balance  was  to  be  employed  with 
such  great  advantage  for  the  exact  determination  of  propor- 
tions by  weight  in  chemical,  reactions,  although  a  number  of 
noteworthy  beginnings  of  quantitative  analysis  are  to  be 
found. 

It  is  especially  to  be  noted  as  characteristic  of  this  period 
that  chemistry  now  became  fully  awake  to  her  own  proper 
task,  which  was  to  investigate  the  composition  of  substances, 
and  to  find  out  the  constituents  from  which  they  could  be 
prepared.  Analytical  chemistry  was  to  aid  in  solving  this 
problem ;  but  useful  and  important  results  were  achieved  by 
the  synthetic  method  also. 

The  independent  scientific  character  of  chemistry  showed 
itself  in  the  forms  which  its  relations  to  other  sciences 
assumed.  The  previous  dependence  upon  medicine  and 
pharmacy  ceased ;  instead  of  being  their  servant,  chemistry 
became  their  helper  and  adviser.  It  also  came  into  close 
contact  with  physics,  mineralogy  and  botany,  which  resulted 
in  mutual  advantage  to  all  of  them,  and  made  chemistry 
the  indispensable  helpmeet  of  the  others.  We  have  only  to 
think  of  the  services  rendered  to  those  'sciences  by  chemists, 
e.g.  to  physics  by  Boyle,  and  to  physics  and  mineralogy  by 
Bergman.  This  coalition  with  the -various  other  sciences  had 
the  effect  of  opening  up  new  common  ground  both  for  these 
individually  and  for  chemistry.  We  find  the  first  scientific 
treatment  of  mineralogical  and  physical  chemistry  during  the 
phlogistic  period,  and  the  advances  made  in  organic  prepared 
the  ground  for  physiological  chemistry. 

Nothing  is  less  justifiable,  therefore,  than  to  assert  that 
chemistry  was  at  that  time  no  science,  and  that  it  was 
Lavoisier  who  created  one  out  of  what  was,  before  his 


iv  CONCLUDING  REMARKS  157 

time,  a  science  only  in  name.  The  record  of  the  services  of 
Boyle,  Stahl,  Black,  Bergman,  Scheele,  Cavendish,  Priestley, 
Marggraf  and  others,  is  sufficient  to  prove  the  error  of  such 
an  assumption.1  In  spite  of  the  false  hypothesis  which  lay 
at  the  root  of  the  phlogiston  theory,  it  was  the  latter  itself, 
together  with  the  work  which  resulted  from  it,  that  formed 
the  necessary  foundation  for  the  correct  standpoints  and  the 
numerous  researches  of  the  succeeding  period. 

1  Cf.  Dumas' s  Lemons  sur  la  Philosophic  Chimique  (1837),  p.  137;  and 
also  the  sentence  with  which  Wurtz  began  his  Histoire  des  Doctrines 
Chimiques  (1868) :  "  La  chimie  est  line  science  franchise  ;  elle  fat  constitute 
par  Lavoisier,"  etc.  Volhard  investigated  this  statement  and  so  completely 
overthrew  it  (Journ.  pr.  Chem.,  N.  F.,  vol.  ii.  p.  1  et  seq.),  that  recent  at- 
tempts to  minimise  the  force  of  his  criticism  have  not  only  missed  their 
mark,  but  are  unjustified  in  their  form  and  style  (see  especially  Grimaux' 
Lavoisier  (1888),  pp.  128  and  363).  The  sentence  by  Grimaux  (p.  128) : 
"  Toute  la  science  modernerfest  que  le  developpement  de  Pceuvre  de  Lavoisier" 
can  only  be  regarded  as  an  extravagant  exaggeration,  exceeding  even  that 
of  Wurtz,  just  quoted.  The  most  eminent  among  the  antiphlogistonists, 
moreover,  never  thought  of  calling  in  question  the  scientific  tendency  of 
the  chemical  views  which  they  themselves  combated. 


CHAPTER  V 

HISTORY  OF   THE  MOST  RECENT  PERIOD  (FROM 
THE  TIME  OF  LAVOISIER  UP  TO  NOW) 

THE  beginning  of  the  latest  period  of  chemistry,  to  which 
the  present  generation  of  investigators  still  belongs,  is  rightly 
associated  with  Lavoisier's  reforms,  which  turned  the  chemi- 
cal science  of  his  day  into  new  paths ;  he  demonstrated  the 
supreme  importance  of  the  proportions  by  weight  in  chemical 
reactions,  which  were  wrongly  interpreted  when  these  were 
disregarded.  This  applied  in  an  especial  degree  to  the 
processes  of  combustion  and  similar  phenomena,  which 
Lavoisier  was  the  first  to  explain  correctly.  Of  course 
this  explanation  only  became  possible  after  Scheele's  and 
Priestley's  discovery  of  oxygen.  If  we  desire,  therefore,  to 
associate  the  commencement  of  the  new  era  with  any  par- 
ticular event,  it  must  be  with  the  latter  important  discovery, 
which  has  been  already  described  in  the  history  of  the  pre- 
ceding period. 

Lavoisier's  combustion  theory,  with  oxygen  as  its  centre- 
point,  now  stepped  into  the  place  of  the  phlogistic  doctrine, 
which  had  attained  to  the  dignity  of  a  dogma ;  the  chemistry 
dominated  by  the  latter  was  thus  changed  info  the  so- 
called  antiphlogistic  system.  A  complete  transformation  of 
all  the  ideas  respecting  combustion  and  calcination,  and 
therefore  respecting  the  composition  of  the  most  important 
substances,  took  place, — truly  a  reform  in  the  fullest  sense 
of  the  word.  For,  all  the  reactions  in  which  the  escape  of 
phlogiston  had  hitherto  been  assumed  depended,  as  Lavoisier 
taught,  upon  the  taking  up  of  oxygen ;  and,  conversely, 


CHAP,  v  THE  MODERN  CHEMICAL  PERIOD  159 

those  processes  which  had  been  explained  by  assuming  the 
absorption  of  phlogiston,  depended  upon  the  separation  of 
oxygen. 

Lavoisier  showed  that  substances  like  sulphuric  and 
phosphoric  acids  and  the  metallic  calces,  which  according 
to  the  phlogistic  doctrine  were  looked  upon  as  elements, 
were  really  compounds  :  while  those  regarded  as  compounds, 
e.g.  the  metals,  sulphur  and  phosphorus,  he  assumed  to  be 
elementary. 

It  will  be  appropriate  here  to  enter  shortly  again  into 
the  chief  points  of  dispute  in  which  the  phlogistic  doctrine 
became  involved  at  the  time  of  the  discovery  of  oxygen 
(about  1775),  and  by  which  its  fall  was  accelerated.  The 
facts  to  which  the  phlogiston  theory  was  unable  to  accommo- 
date itself  were  many  in  number.  To  chemists  who  regarded 
hydrogen  as  phlogiston — a  frequent  assumption — the  great 
difficulty  arose  of  proving  whence  the  phlogiston  came  which 
escaped  during  the  calcination  of  the  metals,  and  the  combus- 
tion of  sulphur,  phosphorus  and  coal  in  closed  vessels.  The 
reduction  of  the  metallic  oxides  by  hydrogen  did  indeed 
appear  to  allow  of  a  perfect  explanation  from  the  phlogistic 
standpoint,  if  one  paid  no  heed  to  the  simultaneous  forma- 
tion of  water  and  the  diminution  in  weight  of  the  oxides. 
But  how  could  a  reduction  of  the  metallic  calx  take  place 
without  the  presence  of  phlogiston  (hydrogen)  ?  This  occurred 
in  the  case  of  those  calces  which  were  converted  into  metal 
when  heated  alone  in  closed  vessels.  For  the  production  of 
quicksilver  from  red  oxide  of  mercury  and  of  silver  and  gold 
from  their  oxides  by  heat,  the  phlogistic  doctrine  was  able  to 
offer  no  explanation.  It  was,  indeed,  those  reactions  which 
led  to  the  discovery  of  oxygen  that  brought  about  the  col- 
lapse of  the  theory,  and  rendered  possible  the  establishment 
of  the  antiphlogistic  system.  And  a  few  years  later  the 
keystone  was  added  to  the  latter  by  the  proof  that  water, 
which  had  hitherto  been  looked  upon  as  an  element,  was  a 
compound  of  oxygen  and  hydrogeu. 


160  THE  MODERN  CHEMICAL  PERIOD  CHAP. 


GENERAL   HISTORY   OF    CHEMISTRY   DURING  THIS 
PERIOD. 

Lavoisier  and  the  Antiphlogistic  Chemistry  {from  1775 
to  the  end  of  the  Eighteenth  Century). 

Lavoisier's  great  achievement  consisted  in  abolishing  old 
prejudices,  and  in  the  masterly  application  of  scientific  prin- 
ciples to  the  explanation  of  chemical  processes.  A  wealth  of 
important  facts  was  handed  down  to  him  by  the  phlogisto- 
nists;  he  himself  did  not  add  much  to  this  in  the  way  of 
new  chemical  observations,  but  he  sifted  and  collated,  from  a 
point  of  view  hitherto  unattained,  that  which  was  ready  to 
hand,  giving  at  the  same  time  the  correct  explanation  of 
many  processes.  We  shall  not  be  wrong  if  we  place  such 
services  to  the  credit  of  his  highly-trained  physical  and 
mathematical  mind,  which  early  freed  itself  from  the  bonds 
of  the  phlogistic  hypothesis.  As  a  physicist  Lavoisier  was 
bound  to  take  into  account  alterations  in  weight,  e.g.  in  the 
calcination  of  metals ;  the  properties  of  the  products  obtained 
interested  him  in  a  lesser  degree.  This  explains  why  he 
himself  made  no  independent  chemical  discoveries ;  but  the 
unique  service  which  he  rendered  in  being  the  first  to  give  a 
comprehensive  and  correct  explanation  of  the  observations  of 
others  remains  incontestable. 

Lavoisier  lived  to  see  his  work  appreciated  in  the  highest 
degree;  he  saw  the  fruit  of  his  labours,  the  antiphlogistic 
system,  come  out  victorious  in  the  fight  with  the  phlogistic, 
and  propagate  itself  beyond  France.  —  Anton  Laurent 
/"Lavoisier  was  born  on  August  26th,  1743,  a  year  after 
Scheele,  but  how  different  were  the  outward  circumstances 
of  the  two !  While  the  latter  was  early  thrown  upon  his 
own  resources,  and  was  in  the  fullest  sense  of  the  word  ap 
self-educated  man,  Lavoisier,  the  son  of  a  distinguished 
barrister,  had  a  splendid  training  given  him,  and  enjoyed 
special  opportunities  for  acquiring  a  thorough  knowledge  of 
mathematics  and  physics,  which  exercised  a  permanent 


v  LAVOISIER'S  LIFE  AND  WORK  161 , 

influence  upon  the  whole  tendency  of  his  thoughts  and 
methods  of  investigation.  In  botany,  too,  in  mineralogy  and 
geology,  meteorology  and  anatomy  he  was  well  versed.  Of 
his  teachers,  the  mathematician  La  Caille,  the  botanist  B.  de 
Jussieu,  and  the  mineralogist  Guettard  may  be  mentioned, 
while  it  was  Rouelle  who  initiated  him  into  chemistry. 
Even  whilst  still  very  young,  Lavoisier  gained  great  repute 
by  his  scientific  investigations,  so  that  we  find  him  received 
(as  Associate)  into  the  French  Academy  in  1768,  the  imme- 
diate cause  of  this  being  a  prize  essay  upon  the  most  suitable 
method  of  street-lighting  for  large  towns. 

His  earliest  chemical  work1 — particularly  the  research 
upon  the  supposed  transformation  of  water  into  earth,  the 
results  of  which  he  published  in  1770 — afford  clear  evidence 
of  his  physical  methods.  In  this  he  proved  that  the  total 
weight  of  the  closed  glass  vessel  plus  that  of  the  water  which 
had  for  a  long  time  been  boiling  in  it  remained  unaltered, 
but  that  the  weight  of  the  earth  produced  was  exactly 
equivalent  to  the  loss  in  weight  of  the  vessel ;  the  logical 
conclusion  to  be  drawn  from  this  was  that  the  earth  came 
from  the  glass  and  not  from  the  water.  What  this  earth 
was  he  did  not  investigate;  on  the  other  hand,  Scheele 
was  led  to  the  same  conclusions  as  Lavoisier  by  examining 
it  qualitatively. 

The  latter  here  recognised  and  laid  stress  on  the  use  of 
the  balance  as  a  reliable  guide  in  chemical  work.  Soon 
after  this  he  busied  himself  with  investigating  the  reactions, 
involved  in  the  combustion  of  substances  and  in  the  calcina- 
tion of  the  metals,  making  use  here  of  some  previous  obser- 

1  With  regard  to  Lavoisier's  writings,  the  reader  is  referred  to  the 
(Euvres  de  Lavoisier  (piibliees  par  les  soins  du  Ministre  de  V Instruction 
Publique),  which  were  published  in  Paris  in  1862 ;  and  to  the  analyses  of 
his  most  important  papers,  given  by  H.  Kopp  in  his  Chemie  in  der  neueren 
Zeit  (1874),  and  by  Hofer  in  his  Histoire  de  la  Chimie,  vol.  ii.  p.  490  et  seq. 
In  addition  to  these,  Grimaux'  book,  Lavoisier,  1743 — 1794  (published  in 
1888),  is  a  valuable  authority  on  Lavoisier's  life  and  work,  even  allowing 
for  the  fact  that  the  laudation  of  the  famous  chemist  is  overdone  in  it  (cf. 
note,  p.  157).  This  circumstance,  together  with  the  criticism  meted  out  to 
opponents,  and  exaggerations  of  various  kinds,  seriously  detracts  from  the 
value  of  what  is  in  itself  a  great  historical  treatise. 

M 


162  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

vations  by  others  on  the  increase  in  weight  during  such 
€alcination.  With  the  aid  of  an  exceedingly  delicate  balance 
he  sought,  in  the  first  instance,  to  estimate  exactly  the 
alterations  in  weight  which  occurred  during  these  processes, 
and  to  get  at  the  reason  for  this.  The  results  of  these 
labours,  materially  amplified  by  Priestley's  and  Scheele's 
observations  on  oxygen  and  its  chemical  behaviour,  formed 
the  foundation  of  Lavoisier's  theory  of  combustion. 

His  position  had,  in  the  meantime,  become  a  brilliant  one ; 
as  Farmer-general  (he  began  in  1768  by  being  an  assistant 
— adjoint),  and,  shortly  after,  as  chief  director  of  the  saltpetre 
industry,  of  which  the  Government  had  a  monopoly,  he  had 
plenty  of  leisure  to  devote  to  his  own  investigations,  and 
to  assist  the  State  both  by  his  advice  and  by  the  introduc- 
tion of  valuable  improvements  (e.g.  in  the  manufacture  of 
potash  saltpetre,  gunpowder,  etc.).  His  numerous  reports 
on  technical  questions  are  evidence  of  his  industry,  his 
versatility,  and  his  wide-reaching  influence.  For  such  kind 
of  work  he  had  ample  opportunity  as  member  of  various 
Commissions,  e.g.  of  the  Socitte1  d' Agriculture,  the  Bureau 
de  Consultation,  the  Commissions  des  Poids  et  MSsures,  and 
so  on. 

Closely  related  to  his  work  upon  combustion  were  the 
important  researches  which  he  carried  out  in  conjunction 
with  Laplace  upon  the  latent  heat  of  ice  and  the  specific 
heats  of  various  bodies.  It  was  his  clear  physical  conception 
of  the  nature  of  heat,  as  opposed  to  that  of  many  phlogisto- 
nists  (who  were  unable  to  get  rid  of  the  assumption  of  a 
ponderable  caloric),  which  enabled  Lavoisier  to  interpret 
correctly  those  chemical  reactions  in  which  heat  was  evolved, — 
the  phenomena  of  combustion  in  particular. 

Notwithstanding  the  extraordinary  services  which  La- 
voisier rendered  to  science,  and,  through  the  latter,  to  his 
country,  by  applying  his  knowledge  and  experience  with 
never-flagging  zeal  for  her  benefit,  he  did  not  escape  the  fate 
which  befell  so  many  of  his  fellow-citizens.  Impeached  under 
the  Reign  of  Terror,  he  was  condemned  to  death,  and 
executed  together  with  twenty-eight  other  Fermiers-ge'ndraux, 


v  LAVOISIER'S  LIFE  AND  WORK  163 

on  the  8th  of  May,  1794.1  Amongst  all  his  numerous  friends 
and  admirers,  only  a  few,  including  Hauy  and  Borde,  and 
only  one  chemist,  Loysel,  had  the  courage  to  protest  against 
this,  but  without  effect.  His  more  influential  colleagues, 
like  Guy  ton  de  Morveau,  Monge,  and  especially  Fourcroy,2 
who  took  part  in  politics,  and  who  had  assuredly  been  able 
during  his  five  months'  imprisonment  to  do  something  for 
his  deliverance,  did  not  dare  to  offer  any  opposition  to  this 
terrible  crime. 

Lavoisier  published  most  of  his  works  in  the  Memoirs  of 
the  French  Academy,  over  sixty  papers  by  him  being  con- 
tained in  its  volumes  for  the  years  1768-87  ;  some  others 
are  to  be  found  in  the  Journal  de  Physique  and  in  the 
Annales  de  Clnwiie?  His  projected  plan  of  publishing  an 
edition  of  his  collected  works  was  only  carried  out  long 

1  Much  light  has  been  thrown  upon  this  sad  event  by  documents  pub- 
lished by  Ed.  Grimaux,  which  relate  to  the  death  of  Lavoisier.    It  has  been 
conjectured  that  Marat  hastened  the  proceedings  against  him  from  a  feeling 
of  petty  revenge,  because  of  Lavoisier  having  unfavourably  criticised  a 
treatise  of  his,  entitled  Recherches  Physiques  sur  le  Feu,  which  appeared  in 
1780.     For  Marat,  in  his  infamous  Ami  du  Peuple,  had  repeatedly  de- 
nounced Lavoisier  and  had  brought  about  the  impeachment,  although  he 
did  not  himself  survive  to  see  the  arrest  of  Lavoisier  and  his  colleagues.    In 
the  sentence,  which  was  passed  after  an  imprisonment  and  inquiry  extend- 
ing over  five  months,  it  was  stated  that  he  was  condemned  to  death  "  as 
convicted  of  originating  or  participating  in  a  plot  against  the  French 
nation,  the  aim  of  which  was  to  aid  the  enemies  of  France ;  especially  in 
that  he  had  practised  every  kind  of  extortion  upon  the  people,  and  had 
caused  tobacco  to  be  admixed  with  water  and  pernicious  substances,  to  the 
detriment  of  the  health  of  the  citizens  who  used  it." — Cf.  Grimaux'  work, 
Lavoisier,  1743-94,  d'apres  sa  Correspondance,  ses  Manuscripts,  etc.  (Paris, 
1888). 

2  Grimaux'  publication,  just  cited,  and  also  Berthelot's  Notice  Historique 
sur  Lavoisier  (Mon.  Scient.,  1890,  p.  125),  reflect  seriously  upon  the  indif- 
ference to  Lavoisier's  fate  shown  by  Fourcroy,  de  Morveau  and  others. 

3  The  dates  upon  which  Lavoisier's  papers  appeared  are  of  importance 
for  their  criticism  ;  we  have  especially  to  remember  here  that  the  yearly 
volumes  of  the  Memoires  de  PAcaddmie  did  not  correspond  with  the  dates 
of  their  publication,  but  that  they  were  usually  brought  out  several  years 
afterwards  (e.g.  the  Mdmoires  for  1772  in  1776,  and  those  for  1782  in  1785). 
The  effect  of  this  disarrangement  has  been  great  confusion  with  regard  to 
the  actual  time  at  which  this  and  the  other  treatise  was  written  by  Lavoisier, 
because  of  subsequent  alterations  in  the  papers.     But,  so  far  as  it  has  been 
found  possible  to  verify  them,  those  dates  are  given  here. 

M    2 


164  THE  MODERN  CHEMICAL  PERIOD  CHAP, 

after  his  death  (1862-1892).  His  Opuscules  Physiques  et 
Chymiques,  which  appeared  in  1774,  contained  his  ideas 
upon  the  nature  of  gases  and  his  views  upon  the  processes 
of  combustion.  In  his  Traitd  EUmentaire  de  Cliimie  (pr£sent6 
dans  un  ordre  nouveau  et  d'apres  les  dfoouvertes  modernes), 
published  in  1789,  he  gave  a  summary  of  the  most  important 
facts  of  chemistry,  and  explained  them  according  to  the  anti- 
phlogistic theory,  which  thus  received  its  first  text-book ; 
by  means  of  translations  of  this  book  the  new  doctrine  was 
materially  propagated. 

The  researches  of  Lavoisier  which  were  of  greatest  moment 
for  the  development  of  chemistry  were  those  which  contri- 
buted to  the  founding  of  the  antiphlogistic  system,  and 
which  led  to  the  overthrow  of  the  phlogistic ;  those,  namely, 
which  treated  of  the  phenomena  of  combustion,  calcination 
and  respiration.  The  chief  work  of  his  life  consisted  in  his 
recognising  and  explaining  the  part  played  by  oxygen  in 
these  processes,  and  in  this  lies  his  abiding  service. 

The  previous  observations  of  Rey,  Mayow  and  others, 
who  had  attributed  the  increase  in  weight  of  the  metals 
during  their  calcination  to  an  absorption  of  air,  contained 
only  the  first  germs  of  the  correct  explanation  of  these  pro- 
cesses. From  the  year  1772  Lavoisier  busied  himself  with 
investigations  bearing  upon  this  subject,  the  first  results  of 
which  he  delivered  in  a  sealed  note  to  the  French  Academy 
on  November  1st  of  that  year.  This  note  stated  that  by  the 
combustion  of  sulphur  and  phosphorus,  and  by  the  calcina- 
tion of  the  metals,  the  weight  of  these  substances  increased 
from  the  absorption  of  a  large  amount  of  air ;  and  that,  by 
the  reduction  of  litharge  with  coal  in  an  enclosed  space,  a 
considerable  quantity  of  air — a  thousandfold  the  volume  of 
the  litharge — was  generated.  Lavoisier  was  at  this  time 
in  the  same  position  as  Mayow  had  been,  that  is,  still  quite 
uncertain  as  to  which  portion  of  the  air  caused  this  increase 
in  weight,  as  to  the  air  itself  being  a  mixture  of  gases,  and 
especially  as  to  the  nature  of  the  process  which  went  on  in 
the  reduction  of  the  litharge  ;  he  was  inclined  to  regard  the 
generated  gas  (carbonic  acid)  as  the  fluid  originally  combined 


v  BEGINNINGS  OF  HIS  COMBUSTION  THEORY  165 

with  the  lead.  This  uncertainty  was  brought  about  by  his 
paying  too  little  heed  to  the  qualitative  side  of  the  chemical 
reactions. 

By  repeating  these  and  similar  researches,  however, 
Lavoisier  soon  arrived  at  a  clearer  perception  of  the  matter, 
and  he  especially  recognised  his  error  with  regard  to  the  re- 
duction of  the  oxide  of  lead.  In  1774  he  gave  further  details 
of  these  observations,  in  particular  of  the  calcination  of  tin  ;x 
the  investigation  was  in  its  main  points  a  repetition  of 
Boyle's,  but  Lavoisier  was  able  to  draw  more  correct  con- 
clusions from  it  than  Boyle  had  done.  A  sealed  retort,  in 
which  some  tin  had  previously  been  placed,  was  weighed 
both  before  and  after  being  heated,  and  found  equally  heavy 
each  time,  whence  the  conclusion  was  drawn  that  no  fire- 
stuff  had  been  absorbed ;  on  the  retort  being  opened  after 
cooling,  air  rushed  in,  and  the  whole  apparatus  showed  an 
increase  in  weight  exactly  equal  to  that  which  the  tin  had 
undergone  by  calcination.  Lavoisier  concluded  from  this 
that  calcination  depends  upon  the  absorption  of  air,  i.e.  that 
the  latter  is  the  cause  of  the  increase  in  weight. 

But  although  we  find  in  these  results  the  beginnings  of 
his  combustion  theory,  there  was  still  wanting  the  definite 
knowledge  as  to  which  portion  of  the  air  combined  with  the 
metals  and  the  combustible  substances.  Oxygen  was  in  the 
meantime  discovered  independently  by  Scheele  and  Priestley, 
and  they  recognised  in  it  the  constituent  of  the  air  which 
was  necessary  for  combustion ;  but  Lavoisier  held  the  key  to 
the  explanation  of  his  researches  as  soon  as  he  received  news 
of  this  discovery.  How  he  turned  this  to  advantage  is  shown 
in  a  paper  written  in  1775,2  in  which  the  role  of  oxygen  for 
the  general  explanation  of  the  reactions  in  question  is  fully 
appreciated ;  it  was  this  gas  which  combined  with  the  metals, 
sulphur,  phosphorus,  coal,  and  so  on.  The  production  of  car- 
bonic acid  from  saltpetre  and  coal  led  him  to  the  conclusion 
that  oxygen  must  likewise  be  present  in  this  salt — a  point 
that  Mayow  indeed  recognised  a  hundred  years  before  this, 

1  (Eitvres  de  Lavoisier,  vol.  ii.  p.  105. 

2  Cf.  (Euvres,  vol.  ii.  p.  125. 


166  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

only  that  the  latter  terms  it  spiritus  nitro-aereus  instead  of 
oxygen.  Strangely  enough,  no  reference  is  made  by  Lavoisier 
to  the  influence  which  Priestley's  discovery  of  oxygen  (com- 
municated to  him  by  Priestley  himself)  exercised  upon  his 
researches  with  oxide  of  mercury  and  upon  his  explanation 
of  previous  experiments.1 

Lavoisier  in  due  course  arrived  at  perfect  clearness  in  his 
explanations,  for  instance,  with  regard  to  the  composition  of 
atmospheric  air ;  it  was  in  1776  that  he  observed  that  the 
combustion-product  of  the  diamond  consisted  of  carbonic 
acid  alone,  and  in  the  following  year  he  showed  that,  by 
burning  phosphorus  in  a  closed  vessel,  one-fifth  of  the  volume 
of  air  in  the  latter  was  used  up,  and  non-respirable  air 
remained  behind.  The  results  of  these  researches,  together 
with  the  observations  made  by  Scheele  and  Priestley,  of 
which  he  had  in  the  meantime  obtained  fuller  knowledge, 
and  the  investigations  which  he  made  in  1777  on  the  com- 
bustion of  organic  substances,  the  products  of  which  he 
proved  to  be  carbonic  acid  and  water,  enabled  Lavoisier  to 
establish  the  main  points  of  his  Combustion  or  Oxidation 
Theory  as  follows2 : — 

1  The  attitude  which  Lavoisier  sometimes  took  up  with  respect  to  the 
observations  and  discoveries  of  others  awakens  painful  feelings  ;  it  is 
melancholy  to  see  an  investigator  of  such  splendid  gifts  so  unjust  regarding 
the  services  of  others.  Thus  Lavoisier  makes  no  mention  in  his  first 
chemical  paper,  on  the  composition  of  gypsum,  of  Marggraf's  important 
researches,  although  these  were  among  the  best  known  of  any,  while  more 
than  their  due  recognition  was  awarded  to  the  other  chemists  who  had 
worked  at  the  same  subject.  In  a  similar  manner  he  ignored,  in  the 
account  of  his  researches  on  the  composition  of  water,  those  of  Cavendish 
which  proved  the  same  point  (i.e.  its  composition),  and  of  whose  results  he 
had  positive  knowledge  through  Blagden's  information.  Black's  splendid 
investigations  upon  fixed  air,  from  which  Lavoisier  without  doubt  received 
the  greatest  assistance  towards  his  conception  of  the  fixation  of  gases,  he 
treated  in  a  cold  and  depreciatory  manner,  whilst  the  most  trivial  objec- 
tions raised  against  Black  were  examined  with  the  utmost  minuteness  and 
care.  These  are  unfortunately  blots  upon  Lavoisier's  reputation,  notwith- 
standing the  lustre  with  which  it  has  become  surrounded  through  the 
idealistic  historical  writings  of  Dumas,  Wurtz,  Grimaux  and  others.  Cf. 
also  Thorpe's  Essays,  p.  87,  and  especially  p.  110  et  seq.,  in  which  many  of 
the  disputed  points  in  question  are  cleared  up. 

2  (Euvres,  vol.  ii.  p.  226,  in  the  Memoire  sur  la  Combustion  en  gdndral. 


v  LAVOISIER'S  OXIDATION  THEORY  167 

(1)  Substances  burn  only  in  pure  air  (air  eminemment 
pur). 

(2)  This  air  is  consumed  in  the  combustion,  and  the  increase 
in  weight  of  the  substance  burnt  is  equivalent  to  the  decrease  in 
weight  of  the  air. 

(3)  The  combustible  body  is,  as  a  rule,  converted  into  an 
acid  by  its  combination  with  the  pure  air,  but  the  metals,  on  the 
other  hand,  into  metallic  calces. 

The  last  sentence  contains  an  idea  of  great  moment, 
which  Lavoisier  developed  later  into  his  theory  of  the  com- 
position of  acids,  according  to  which  these  latter  contain 
oxygen  as  the  oxygenating  or  acidifying  principle  (principe 
oxygine  ou  acidiftant).  To  establish  this  assumption,  he 
both  made  investigations  himself  and  referred  to  and  utilised 
those  of  others ;  in  this  way  he  states  that  sulphuric  acid 
consists  of  sulphur  and  oxygen,  phosphoric  acid  of  phosphorus 
and  oxygen,  and  nitric  acid  of  saltpetre  gas  (nitric  oxide) 
and  oxygen.  The  true  composition  of  the  last  acid  was 
first  determined  by  Cavendish,  through  its  synthesis  from 
nitrogen  and  oxygen  in  presence  of  water.  Hydrochloric 
acid  being  a  powerful  acid,  likewise  contained  oxygen, 
according  to  Lavoisier's  assumption,  and  this  applied  in  still 
stronger  degree  to  the  chlorine  produced  by  its  oxidation. 
Lavoisier  further  occupied  himself  with  the  question — What 
kind  of  oxygen-compound  does  hydrogen  yield?  without, 
however,  arriving  at  the  correct  explanation  of  this  inde- 
pendently ;  for  he  expected  to  find  an  acid  as  the  product 
of  its  combustion,  and  therefore  looked  for  one.  It  is  the  un- 
disputed merit  of  the  phlogistonist  Cavendish  to  have  proved 
that  water  alone  is  produced  by  the  combustion  of  hydrogen.1 

This  fundamental  observation  first  proved  itself  fruitful, 

1  With  regard  to  this  point  and  also  to  Watt's  share  in  recognising  the 
composition  of  water,  cf .  H.  Kopp's  detailed  memoir  :  Ueber  die  Entdeclcung 
der Zusammensetzung  des  Wassers  (Braunschweig,  1875).  See  also  Berthelot's 
essay  on  Lavoisier  (Mon.  Sclent.,  1890,  p.  138),  and  Thorpe's  Essays,  p.  110. 
Berthollet's  testimony  (Ibid.,  note,  p.  139)  leaves  no  doubt  whatever  that 
even  Lavoisier's  own  friends  admitted  without  any  reservation  Cavendish's 
priority  in  this  discovery. 


68  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

however,  in  the  hands  of  Lavoisier,  who  was  thus  enabled 
to  give  at  once  the  real  composition  of  water  (out  of  hydro- 
gen and  oxygen),  while  at  the  same  time  estimating  the 
relative  proportions  of  these  approximately.  He  also 
correctly  interpreted  the  decomposition  of  water  by  red-hot 
iron,  and  its  formation  from  the  reduction  of  metallic  oxides 
by  means  of  hydrogen.  The  generation  of  the  latter  gas 
on  dissolving  metals  in  acids  was  likewise  satisfactorily 
explained.  It  was  precisely  this  reaction  which  had 
strengthened  the  phlogistonists  in  their  opinion  that  the 
metals  contained  phlogiston,  which,  being  identical  with 
hydrogen,  escaped  on  dissolving  these  in  acids.  The  com- 
position of  water  having  been  arrived  at,  Lavoisier  now  saw 
that  the  hydrogen  came  from  the  water,  and  that  the  oxygen 
of  the  latter  united  with  the  metal  to  oxide,  which  then  in 
its  turn  combined  with  the  acid.1 

With  the  knowledge  of  this,  which  came  in  the  year 
1783,  the  last  obstacles  with  which  the  antiphlogistic 
system  had  to  contend  were  overcome :  the  phlogistic  theory 
could  maintain  itself  no  longer,  but  collapsed.  Up  to  this 
date  Lavoisier  was  almost  alone  in  the  fight  against  it, 
having  only  received  material  aid  from  eminent  physicists 
and  mathematicians,  like  Laplace,  Monge,  Cousin,  etc.  But 
now  chemists  of  standing  began  to  apply  his  ideas,  at  first  in.' 
France  (Berthollet  1785,  de  Morveau  1786,  and  the  diplo- 
matically cautious  Fourcroy  not  until  1787),  and  very  soon 
in  other  countries  also  (Kirwan,  e.g.,  in  1792).  Lavoisier's 
critical  treatises,  which  were  directed  to  showing  the  un- 
tenability  of  the  phlogistic  theory,  conjoined  with  his  Trcdtt 
de  Chimie,  gave  the  final  blow  to  that  doctrine. 

The  main  features  of  Lavoisier's  work,  which  was  the 
means  of  leading  chemistry  into  new  paths,  have  now  been 
described ;  but  some  of  his  observations  and  speculations,  e.g. 
his  researches  on  the  composition  of  organic  compounds,  and 
his  comprehensive  ideas  regarding  metabolism  in  the  organic 
world,  will  be  treated  of  in  the  special  history  of  this  time. 
The  systematic  application  of  quantitative  methods  of  re- 
1  Laplace  and  Meusnier  took  an  active  share  in  these  investigations. 


v  TRIUMPH  OF  ANTIPHLOGISTIC  CHEMISTRY  169 

search,  and  the  unbiased  treatment  of  chemical  processes 
from  a  rather  physical  point  of  view,  led  him  to  interpret 
correctly  the  most  important  phenomena  of  chemistry,  the 
explanation  of  which  had  been  sought  for  in  vain  by  several 
generations  of  investigators,  fettered  as  they  were  by  the 
phlogiston  theory.  The  material  which  these  latter  had 
collected  together,  especially  the  observations  of  Black, 
Scheele,  Priestley  and  Cavendish,  were  indispensable  to 
Lavoisier ;  we  have  only  to  recollect  that  the  discoveries  of 
most  importance  for  his  system — of  oxygen,  and  of  the  true 
composition  of  water — were  not  made  by  himself.  But  his 
genius,  far  transcending  that  of  any  of  his  contemporaries, 
enabled  him  to  get  at  the  root  of  phenomena  which  they 
failed  to  comprehend.  After  recognising  that  phlogiston 
had  no  existence,  and  that  oxygen  was  the  gas  necessary 
for  combustion,  calcination  and  respiration,  he  translated  the 
obscure  and  wholly  erroneous  reactions  in  which  phlogiston 
was  assumed  into  simple  antiphlogistic  language. 

Although  the  quantitative  method  of  research  was  followed 
and  duly  valued  by  individual  chemists  both  before  and 
during  the  time  of  Lavoisier,  e.g.  by  Boyle,  Black,  Marggraf, 
Cavendish,  Scheele,  and  especially  Bergman,  still  none  of  these 
investigators  made  use  of  the  balance  as  an  aid  to  chemical 
work  with  such  a  definite  aim  and  perfect  conviction  of  its 
significance  as  he.  Lavoisier  was  penetrated  by  the  truth 
that  no  matter  is  lost  during  chemical  reactions,  and  he 
gave  admirable  expression  to  this  conviction  of  the  conserva- 
tion of  matter  by  indicating  chemical  reactions  by  equations, 
writing  down  as  equal  the  substances  before  their  interaction 
with  each  other  and  the  products  of  this  interaction.1  What 

1  In  his  Trait^  de  Chimie  (1789)  there  is  the  following  notable  passage  in 
connection  with  his  researches  on  fermentation  :  "  Rien  ne  se  cree,  ni  dans 
les  operations  de  I'art  ni  dans  celles  de  la  nature,  et  Von  peut  poser  en  principe 
que,  dans  toute  operation,  il  y  a  une  egale  quantite  de  matiere  avant  et  apres 
V  operation  y  que  la  qualite  el  la  quantite  des  principes  est  la  meme,  et  qu'il 
n'y  a  que  des  changements,  des  modifications.  C  'est  sur  ce  principe  qu'est 
fonde  tout  Part  defaire  des  experiences  en  chimie.  On  est  oblige  de.  sxpposer, 
dans  toutes,  une  veritable  egalite"  ou  Equation  entre  les  principes  des  corps 
qiCon  examine  et  ceiix  qiion  retire  par  I 'analyse." 


170  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

many  others  accepted  as  being  correct,  without  emphasising 
it  particularly,  was  for  him  a  law  upon  which  he  based  his 
speculations  and  researches.  The  weight  of  a  compound 
body  was  equal'  to  the  aggregate  weights  of  its  constituents. 
Although  this  last  sentence  now  sounds  so  simple  and  self- 
evident,  it  had  to  be  proved  to  those  who  regarded  heat  as 
material ;  for  the  evolution  of  heat  which  took  place  during 
chemical  combination  was  bound  to  be  accompanied  by  a 
decrease  in  weight,  if  a  caloric  was  assumed.  Lavoisier  was 
kept  from  falling  into  this  grievous  error  by  his  conception 
of  the  nature  of  heat.  His  mati&re  de  chaleur  had  no  weight ; 
this  he  concluded  from  experiments  in  which  he  burnt  sub- 
stances in  closed  vessels,  proving  thereby  that  no  diminution 
in  weight  occurred.  Many  of  his  expressions  show  that  his 
views  upon  its  nature  approximate  to  the  '  Mechanical 
Theory  of  Heat.1  The  phlogistonists,  on  the  other  hand, 
who  saw  in  heat  a  ponderable  substance,  were  bound  to 
suffer  shipwreck  with  such  a  false  basis  to  start  from. 

The  antiphlogistic  system,  the  outcome  of  the  proper 
interpretation  of  those  processes  which  were  designated  com- 
bustion, calcination,  reduction,  etc.,  meant,  in  fact,  a  complete 
reform  of  chemistry.  The  more  important  of  the  changes 
which  the  latter  underwent  have  been  already  detailed,  but 
it  will  be  convenient  here  to  refer  shortly  to  the  most 
striking  alterations  thus  effected  in  the  views  regarding 
elements  and  chemical  compounds.  Contemporaneously 
with  the  definite  formation  of  these  opinions  went  the  attempts 
to  introduce  a  scientific  nomenclature,  which  likewise  fall  to 
be  treated  of  now. 

Boyle's  view  with  respect  to  the  term  "  element "  was 
retained  by  Lavoisier ;  the  latter,  therefore,  regarded  as 
elements  those  substances  which  could  not  be  decomposed 
into  simpler  ones.  But  then  what  immense  alterations  he 
made  in  details  here  !  The  metals  and  the  most  important 
non-metals  were  ranked  among  the  elements;  compound 
bodies  like  the  alkalies,  ammonia  and  the  earths  were  indeed 
numbered  among  these  also,  but  not  without  great  doubt 
1  Cf.  (Euvres,  vol.  ii.  p.  285. 


v  BEGINNINGS  OF  A  RATIONAL  NOMENCLATURE         171 

being  expressed  as  to  their  elementary  nature.  Oxygen, 
also  recognised  as  an  element,  became,  on  account  of  its  part 
in  combustion  and  its  capacity  for  combining  with  so  many 
other  elements,  the  centre  point  of  the  antiphlogistic  system, 
which  indeed  owed  its  inception  to  the  knowledge  of  the 
behaviour  of  other  elements  towards  oxygen.  The  im- 
portance which  Lavoisier  attached  to  this  gas  is  clearly  shown 
in  his  theory  of  acids,  just  mentioned,  and  in  the  statement 
that  the  bases  which  combine  with  acids  likewise  contain 
oxygen.  The  composition  of  a  large  number  of  com- 
pounds— oxides,  acids  and  salts — was  thus  now  rightly 
interpreted,  the  phlogistic  hypothesis  having  regarded  as 
simple  the  substances  belonging  to  the  first  two  of  these 
classes. 

The  extent  of  Lavoisier's  knowledge  and  that  of  his  dis- 
ciples, and  especially  their  views  with  respect  to  elements 
and  compounds,  is  to  be  seen  in  the  work  entitled  Mtthode  de 
Nomenclature  Chimiqtw,  which  was  published  by  the  former 
in  1787  in  conjunction  with  Guy  ton  de  Morveau,  Berthollet 
and  Fourcroy.  The  three  last  were  the  first  French  chemists 
of  note  to  give  up  the  phlogiston  theory  and  to  follow  the 
"  new  chemistry."  To  Guyton  de  Morveau  belongs  the  credit 
of  making  the  first  attempt  towards  a  convenient  chemical 
nomenclature,  and  thereby  of  inciting  to  the  publication  of 
the  above  book. 

In  this  work  all  substances  are  divided  into  elements  and 
compounds.  To  the  former  belonged — in  addition  to  light 
and  heat — oxygen,  hydrogen  and  nitrogen ;  these  formed  the 
first  class.  The  second  group  contained  the  acid-forming 
elements, — sulphur,  phosphorus  and  carbon,  to  which  were 
added  the  hypothetical  radicals  of  hydrochloric,  hydrofluoric 
and  boracic  acids.  The  third  class  comprised  the  metals,  the 
fourth  the  earths,  and  the  fifth  the  alkalies ;  but  Lavoisier 
considered  the  elementary  nature  of  the  last  of  these  as  so 
improbable  that  in  his  Traite'  de  Chimie  (1789)  he  no  longer 
included  them  among  the  elements.  For  the  nomenclature 
of  the  latter,  the  old  names  of  the  metals  and  of  some  of  the 
non-metals  (e.g.  soufre,  phosphore,  etc.)  were  retained,  while 


172  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

Lavoisier's  new  names  for  others  of  the  non-metallic  elements 
{e.g.  oxygene,  Jiydrogene,  azote)  were  introduced. 

Compounds  were  classified  as  binary  and  ternary,  and  these 
designations  were  to  a  great  extent  retained  later  on,  although 
it  was  found  necessary  to  extend  their  meaning  as  chemistry 
developed.  To  the  binary  compounds  belonged,  in  the  first 
instance,  the  acids,  whose  names  were  composed  of  two  words, 
one  of  which  (acide)  was  common  to  all,  the  other  being 
special  to  each  acid,  e.g^  acide  carbonique,  sulphurique,  azotique. 
In  the  case  of  two  acids  of  one  and  the  same  element,  the 
name  of  that  one  which  contained  the  less  oxygen  ended  in 
eitx,  e.g.  acide  sulpkureux.  The  second  group  of  binary  com- 
pounds embraced  the  oxygen  compounds  of  the  metals,  which, 
as  bases,  were  placed  opposite  the  acids ;  they  were  given  the 
generic  name  of  oxydes,  that  of  the  particular  metal  in  ques- 
tion being  added  (e.g.  oxyde  de  plomb,  etc.)  The  sulphur es 
(e.g.  sulphuretted  hydrogen  and  the  metallic  sulphides),  phos- 
phures  and  carbures  likewise  belonged  to  the  class  of  com- 
pounds of  two  elements,  as  did  also  the  compounds  of  the 
metals  with  one  another. 

The  principal  ternary  compounds  were  the  salts,  produced 
by  the  combination  of  bases  with  acids ;  their  generic  name 
was  derived  from  the  latter,  with  the  addition  in  each  case  of 
that  of  the  metal,  alkali,  or  earth  in  question  (e.g.  nitrate  de 
plomb,  sulfate  de  baryte,  etc.). 

The  advance  which  is  shown  by  this  classification  of 
chemical  compounds  is  very  great.  In  place  of  false  assump- 
tions and  designations  devoid  of  any  system,  we  find  a  correct 
idea  of  the  qualitative  composition  of  substances,  and  a 
rational  nomenclature  corresponding  to  this.  The  develop- 
ment of  the  latter,  and  the  international  form  which  was 
given  to  it  by  Berzelius,  will  be  treated  of  below. 

Guyton  de  Morveau,  Berthollet  and  Fourcroy. 

These  three  investigators,  who,  along  with  Lavoisier,  laid 
the  foundation  of  a  scientific  chemical  nomenclature,  exercised 
a  further  influence  on  the  development  of  chemical  doctrines 


v  GUYTON  DE  MORVEAU :  BERTHOLLET  173 

by  their  other  work,  the  most  important  of  which  falls  to  be 
considered  here. — Guyton  de  Morveau,  born  at  Dijon  in  1 737, 
began  life  as  a  lawyer  (avocat),  but  gave  up  this  career  in  order 
to  devote  himself  wholly  to  chemistry.  His  first  attempt  at 
a  chemical  nomenclature  brought  him  into  close  contact 
with  the  French  Academy,  and  in  particular  with  Lavoisier, 
the  outcome  of  which  was  the  book  cited  above.  Elected  a 
deputy  in  1791,  Guy  ton  de  Morveau  did  his  best  to  render 
his  chemical  knowledge  and  its  practical  application  of  use 
to  his  country;  we  have  only  to  recall  here  his  efforts  to 
employ  the  air-balloon  for  strategic  purposes  in  the  battle  of 
Fleurus,  his  activity  in  helping  to  found  the  ficole  Polytech- 
nique,  in  which  he  subsequently  became  a  professor,  and  his 
services  as  Director  of  the  Mint,  etc.  The  part  which  he 
played  in  politics  was  less  beneficial — it  was,  in  fact, 
pernicious ;  for,  although  an  influential  member  of  the 
National  Assembly  and  of  the  Convention,  he  did  nothing 
which  could  tend  to  lessen  the  excesses  of  the  Revolution. 
He  died  in  Paris  in  1 8 1 6. 

To  the  main  service  which  he  rendered,  viz.  that  of  having 
been  efficacious  in  introducing  a  rational  system  of  nomencla- 
ture for  chemical  compounds,  in  place  of  the  unmeaning  names 
and  confusing  synonyms1  hitherto  in  use,  he  added  the 
further  one  of  developing  this  system  by  experimental 
researches  in  analytical  and  technical  chemistry.  He  also 
aided  in  spreading  abroad  a  knowledge  of  the  labours  of 
Bergman,  Scheele  and  Black,  by  making  good  translations  of 
their  works. 

Claude  Louis  Berthollet,  born  at  Talloire  in  Savoy  in 
1748,  had  his  home  in  Paris  from  the  year  1772,  and 
showed  a  wonderful  activity  in  the  most  various  branches 
of  chemistry,  especially  after  the  year  1780,  when  he  was 

1  Thus  sulphate  of  potash  had  five  different  names,  most  of  which  were 
unintelligible,  viz.  sal  polychrestum  Glaseri,  tartars  vitriolatus,  vitriolum 
potassce,  sal  de  duobus,  and  arcanum  duplicatum.  A  large  number  of  the 
names  in  common  use  at  that  time  for  gases,  salts,  acids  and  bases  have 
been  grouped  together  by  Nordenskiold  in  an  appendix  to  Scheele's  Letters 
(p.  467). 


174  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

elected  to  the  French  Academy.  He  found  vent  for  his 
great  organising  talents  as  a  teacher  in  the  Normal  and 
Polytechnic  Schools  (after  1794),  in  Napoleon's  historical 
expeditions  to  Italy  and  Egypt,  in  which  he  took  part,  and 
in  undertakings  for  the  public  benefit.  He  attained  to  the 
highest  honours  both  under  the  Empire  and  after  the  Re- 
storation, and  died  at  Argeuil,  near  Paris,  in  1822.  During 
the  last  years  of  his  life,  regular  meetings  attended  by 
eminent  savants  were  held  at  his  house,  their  proceedings 
being  published  in  the  Mdmoires  de  la  Sotiete  d'  Argeuil 
(1807-1817).  At  first  a  phlogistonist,  Berthollet  frankly 
declared  for  Lavoisier's  doctrine  in  1785. 

His  experimental  researches  were  especially  valuable  and 
fruitful  during  this  period,  i.e.  from  1785  until  his  death. 
Mention  may  be  made  here  of  those  upon  ammonia,  prussic 
acid,  sulphuretted  hydrogen  and  chlorate  of  potash,  and  upon 
the  practical  application  of  chlorine ;  he  worked  out  with 
substantial  correctness  the  composition  of  the  three  hydrogen 
compounds  just  named.  But  his  researches  and  speculations 
upon  chemical  affinity  were  of  more  general  and  far-reaching 
significance  his  Essai  de  Statigue  Ckimique  exercised  at  that 
time  and  st  exercises  a  most  powerful  influence '  upon  this 
question.  The  cardinal  points  of  his  doctrine  of  affinity  will 
be  given  in  detail  in  conjunction  with  the  results  obtained 
by  Proust  (whose  work  arose  from  Berthollet's),  the  latter  of 
which  led  to  the  knowledge  of  definite  chemical  proportions, 
and  therefore  belong  to  the  history  of  the  development  of 
the  Atomic  Theory. 

Anton  Francois  Fourcroy  (born  1755,  died  1809)  under- 
stood as  a  teacher  how  to  inspire  his  pupils  with  enthusiasm, 
and  worked  in  this  way  with  quite  remarkable  vigour  for  the 
propagation  of  the  antiphlogistic  system,  aiding  the  latter 
also  by  his  writings.  The  chemical  articles  which  he  wrote 
(after  1797)  for  the  Encydope'die  Mtthodique  contain  pane- 
gyrics upon  the  antiphlogistic  chemistry  which,  in  his  excess 
of  patriotic  zeal,  and  possibly  not  without  an  egotistical 
arri&re  pensee,,  he  termed  cliimie  frangaise.  Fourcroy  ex- 


v  ANTON  FRANCOIS  FOURCROY  175 

pounded  the  antiphlogistic  doctrine  in  larger  works  also, 
among  others  in  his  Systeme  des  Connaissances  Chimiques,  and 
his  Philosophic  Chimique,  etc. 

Born  one  of  an  impoverished  family,  he  had  to  earn  the 
money  required  for  his  studies  under  the  most  pressing 
circumstances.  His  work  in  medicine  and  natural  history 
led  to  the  honour  of  his  inclusion  in  the  French  Academy  in 
1 785,  a  year  after  he  had  succeeded  Macquer  as  professor  at 
the  Jardin  des  Plantes.  Later  (especially  after  the  Reign  of 
Terror),  when  Fourcroy  was  on  the  Public  Education 
Committee,  he  found  an  opportunity  of  utilising  the 
experiences  which  he  had  gained  as  a  teacher.  Under 
Buonaparte  (then  Consul)  he  became  himself  Minister  of 
Public  Instruction,  the  education  of  the  country  being 
reorganised  for  the  most  part  according  to  his  views,  and 
special  regard  paid  to  scientific  studies.  It  was  certainly  due 
indirectly  to  him  that  chemistry  bore  such  wonderful  fruit 
in  France  during  the  succeeding  decades.  Lastly,  he  took 
the  leading  part  in  founding  the  Polytechnic  and  Medical 
Schools,  the  ficole  Centrale,  and  the  Natural  History 
Museum. 

Fourcroy 's  great  merit  lay  in  his  activity  as  an  organiser 
and  teacher.  And  although  his  experimental  investigations 
yielded  no  results  of  great  general  significance,  they  served 
as  preparatory  work  in  many  branches,  e.g.  in  those  of 
physiological  and  pathological  chemistry.  His  conjoint 
researches  with  Vauquelin,  in  which  the  latter  undoubtedly 
had  the  principal  share,  were  of  special  importance  with 
regard  to  organic  compounds,  which  had  been  but  little 
worked  with  up  to  that  time. 

The  results  of  most  of  these  researches  were  published 
in  the  Annales  de  Ghimie,  which  was  founded  at  Lavoisier's 
instigation  by  Fourcroy,  Berthollet  and  Guyton  de  Morveau. 
This  journal,  which  started  into  life  during  the  first  year  of 
the  Revolution  (1789),  lived  through  the  storms  of  the  period 
and  formed  the  point  of  union  for  French  chemists ;  it  was 
at  the  same  time  the  organ  of  the  new  doctrine,  as  opposed 
to  the  older  Journal  de  Physique,  in  which  the  last  adherents 


176  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

of  the  phlogiston  theory  endeavoured  to  uphold  the  latter. 
The  Me'moires  of  the  French  Academy  appeared  in  1789  for 
the  last  time  ;  the  Academy  itself  ceased  to  exist  four  years 
after  that  date,  to  be  replaced  in  1 7  9  5  by  the  Institwt  National 
out  of  which  the  present  Academic  Fran$aise  originated  in 
1815,  shortly  after  the  Restoration. 

After  Lavoisier's  death  the  chief  representatives  of 
chemistry  in  France  were  the  three  men  just  named, 
together  with  Vauquelin  the  younger.  The  latter  had  won 
by  his  researches  the  right  of  being  numbered  among  those 
who  gave  effective  aid  in  firmly  establishing  the  antiphlogistic 
system.  Vauquelin,  born  at  Hebertot  in  1763,  was  first 
brought  into  contact  with  chemistry  as  an  apothecary's 
apprentice;  a  fortunate  destiny  led  him  to  Fourcroy's 
laboratory,  in  which  he  found  employment  as  assistant.  He 
soon  became  Fourcroy's  collaborates,  and  attracted  the 
attention  of  chemists  in  general  by  his  brilliant  work.  From 
1793  onwards  he  filled  various  posts  of  distinction,  and 
laboured  with  success  in  many  different  directions,  succeeding 
Fourcroy  as  Professor  of  Chemistry  to  the  Medical  Faculty 
after  the  death  of  the  latter;  he  died  in  1829.  Vauquelin 
did  not  content  himself  with  merely  teaching  chemistry  by 
lectures,  but  gave  systematic  practical  instruction  in  his 
laboratory  to  young  men  who  were  desirous  of  it,  and  thus 
trained  many  chemists  who  afterwards  rose  to  fame. 

Vauquelin's  work,  which  is  characterised  by  great  care- 
fulness and  exactitude,  extended  over  the  most  various 
branches  of  chemistry.  His  investigations  of  minerals 
promoted  the  development  of  mineralogical  chemistry,  and 
led  him  to  the  discovery  of  new  bodies,  e.g.  chromium  and 
beryllia.  His  splendid  gifts  of  observation  likewise  showed 
themselves  in  organic  chemistry,  in  the  discovery  of  quinic 
acid,  asparagine,  camphoric  acid  and  other  substances.  His 
papers  are  to  be  found  for  the  most  part  in  the  Annales  de 
Chimie,  of  which  he  was  one  of  the  editors  after  1791,  but 
some  of  them  are  contained  in  the  Annales  des  Mines  and 
other  journals.  An  "  Introduction  to  Chemical  Analysis," 
which  appeared  in  the  Annales  de  Chimie  in  1799,  may  be 


v  STATE  OF  CHEMISTRY  IN  GERMANY  177 

mentioned  here;  a  German  translation  of  this  led  to  its 
becoming  better  known  and  appreciated  than  would  other- 
wise have  been  the  case.  In  1812  Vauquelin  published  his 
Manuel  de  I'Essayeur. 

Fourcroy's  contemporary  and  Berthollet's  celebrated 
opponent,  Josephe  Louis  Proust,  belongs — in  virtue  of  his 
chief  work,  which  helped  materially  to  found  the  doctrine  of 
chemical  proportions — to  the  succeeding  period,  under  which 
he  will  therefore  be  spoken  of.  Other  French  chemists,  e.g. 
Pelletier,  Gengembre,  Bayen,  Parmentier,  etc.,  who  gave  in 
their  adhesion  to  the  doctrine  of  Lavoisier  during  the  lifetime 
of  the  latter,  were  also  active  in  chemical  research,  but  they 
produced  no  work  of  general  significance;  some  of  the 
observations  made  by  them  will  be  referred  to  in  the  special 
history  of  the  chemistry  of  the  time. 


The  State  of  Chemistry  in  Germany  at  the  End  of  the 
Eighteenth  Century. 

German  chemists  proved  themselves  much  less  accessible 
to  the  antiphlogistic  doctrines  than  Lavoisier's  own  country- 
men. The  more  eminent  among  them  only  began  to  slacken 
in  their  warfare  against  the  new  views,  and  to  accommodate 
themselves  to  these,  during  the  last  decade  of  the  eighteenth 
century.  Of  those  who  lived  during  that  period,  and  who 
were  active  both  as  investigators  and  teachers,  Klaproth 
deserves  the  first  mention.  Richter  likewise  participated  in 
the  working  out  of  a  most  important  question  for  general 
chemistry,  in  that  he  was  the  originator  of  "  stochiometry" ; 
his  investigations  are  to  be  looked  upon  as  valuable  prepara- 
tory work  for  the  chemical  atomic  theory,  and  they  will  be 
referred  to  under  this.  None  of  the  other  German  chemists 
of  that  time  produced  work  of  general  importance,  although 
they  laboured  with  success  in  particular  departments  of  the 
science.  Some  of  the  most  noteworthy  of  these  efforts  will 
find  their  place  in  the  special  history  of  certain  branches  of 
chemistry ;  Buchholz,  Trommsdorff,  Wiegleb  and  Westrumb 

N 


178  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

may  be  named  here  as  having  enriched  pharmaceutical  and 
technical  chemistry  by  valuable  observations.  Hermbstadt 
and  Girtanner  were  among  the  German  chemists  who  first 
frankly  recognised  the  antiphlogistic  system,  and  they 
effectively  aided  in  propagating  it  in  their  own  country  by 
means  of  their  writings, 

Martin  Heinrich  Klaproth,  born  at  Wernigerode  in  174B 
(i.e.  in  the  same  year  as  Lavoisier),  only  began  to  teach 
chemistry — at  the  Berlin  School  of  Artillery — when  some- 
what advanced  in  life,  as  he  continued  true  to  his  apothecary's 
calling  till  1787;  but  this  did  not  prevent  him  from  carrying 
out  in  his  earlier  years  investigations  of  the  utmost  value,  at 
first  under  the  guidance  of  Valentin  Rose,  and  later  on, 
independently.  It  was  to  these  latter  researches  that  he 
owed  his  reception  into  the  Berlin  Academy.  When  the 
University  was  founded  in  the  Prussian  capital,  he — although 
sixty-seven  years  of  age — was  elected  its  first  Professor  of 
Chemistry  in  1810,  and  in  this  post  he  continued  until  the 
beginning  of  1 8 1 7 — the  year  of  his  death. 

Klaproth  was  distinguished  by  the  care  and  thoroughness 
with  which  he  carried  out  all  his  work;  the  quantitative 
method  of  research  was  materially  developed  and  improved 
by  him,  and  he  thereby  helped  on  the  recognition  of  the 
cardinal  principles  advocated  by  Lavoisier.  After  Klaproth 
had  convinced  himself  of  the  correctness  of  the  antiphlogistic 
doctrine,  by  thoroughly  testing  the  reactions  which  took 
place  in  combustion  and  calcination,  he  became  one  of  its 
truest  adherents;  and  his  example  led  many  other  German 
chemists  in  the  same  direction.  Other  scientists,  too,  who 
were  not  precisely  chemists,  took  a  part  in  the  contest  to 
which  these  theories  gave  rise ;  thus  we  find  Alexander  von 
Humboldt  publicly  declaring  for  Lavoisier's  doctrine  in 
1793. 

Klaproth's  researches  in  analytical  chemistry  were  rightly 
looked  upon  at  that  time  as  patterns  for  the  younger  gene- 
ration of  chemists.  Like  Vauquelin's  efforts,  they  aimed 
at  establishing  the  composition  of  minerals  by  means 
of  improved  analytical  methods,  and  thereby  laying  the 


v  KLAPROTH'S  LIFE  AND  WORK  179 

foundation  for  a  chemical  classification  of  these.  His 
observations  were  so  exact  as  to  result  in  the  discovery  of 
various  elements  and  earths — e.g.  uranium,  titanium,  cerium 
and  zirconia — while,  at  the  same  time,  he  corrected  and 
amplified  results  which  had  been  arrived  at  by  others  upon 
many  new  substances — e.g.  tellurium,  chromium  and  beryllium. 
We  shall  frequently  have  occasion  to  refer  to  Klaproth's 
meritorious  work  in  the  history  of  analytical  and  mineralo- 
gical  chemistry.  His  conscientiousness  further  showed  itself  in 
the  way  in  which,  contrary  to  the  custom  prevalent  among 
chemists  at  that  day,  he  published  the  results  of  his  analysis ; 
instead  of  merely  stating  the  conclusions  presumably  arrived 
at  from  his  experiments,  he  gave  the  actual  figures  of  these, 
and  so  made  it  possible  to  subject  them  to  a  minute  criticism 
or  correction. 

The  above  sketch  of  Klaproth's  work  may  be  fitly 
concluded  by  quoting  the  following  sentence  of  A.  W. 
Hofmann's1 : — "  Endued  with  a  modesty  totally  alien  to 
all  presumption,  recognising  to  their  full  extent  the  services 
of  others,  and  tender  of  his  fellow-men's  weaknesses  but 
unsparing  in  the  criticism  of  his  own  work,  Klaproth  will 
remain  to  us  for  all  time  the  model  of  a  true  investigator 
of  science." 

Klaproth's  experimental  researches  were  published  in 
various  journals,  e.g.  in  the  "Memoirs"  of  the  Berlin  Academy 
and  in  Crell's  Chemische  Annalen  ;  he  himself  collected  these 
scattered  papers  together  into  a  five-volume  work,  entitled 
Beitrage  zur  chemischen  Kenntnis  der  Mineralkorper  (1795- 
1810),  to  which  a  sixth  volume,  Chemische  Abhandlungen 
gemischten  Inhalts,  was  added  in  1815.  His  literary 
activity  was  further  shown  in  the  publication  of  the 
Chemisches  Worterbuch  (1807-1810),  and  in  the  revision 
of  the  works  of  others,  e.g.  B.  Gren's  Handbuch  der  Chemie 
(1806). 

That  chemistry  in  general  was  carefully  fostered  in 
Germany  during  the  two  last  decades  of  the  eighteenth 
century  is  also  proved  by  the  fact  that  various  journals  were 

1  Chemische  Erinnerungen. 

N   2 


180  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

started  during  that  period,  whose  main  object  was  the 
publication  of  papers  on  chemistry.  Among  these  were  L. 
von  Crell's  Chemische  Annalen — whose  editor  merits  our 
praise, — which  were  a  continuation  of  the  Chemischcs  Journal, 
begun  in  1778  ;  Scherer's  Allgemeines  Journal  der  Chemie, 
which  was  incorporated  with  Crell's  Annalen  after  1803  ; 
and  the  Annalen  der  Physik,  founded  by  Gren  and  Gilbert  in 
1798,  and  which  since  1825  have  appeared  as  Poggendorffs 
Annalen  der  Physik  und  Chemie. 


The  State  of  Chemistry  in  England,  Scotland  and  Sweden 
towards  the  End  of  the  Eighteenth  Century. 

The  most  distinguished  chemists  in  England  and  Sweden 
at  the  time  of  Lavoisier's  attack  upon  the  phlogiston  theory, 
viz.  Black,  Cavendish,  Priestley,  Scheele  and  Bergman,  were 
avowed  opponents  of  the  new  doctrine.  Black  alone  among 
them,  after  considerable  hesitation,  frankly  recognised  its 
truth.  Cavendish,  whose  own  discoveries  contributed  in  great 
degree  to  the  downfall  of  the  phlogistic  view,  could  not  bring 
himself  fairly  to  renounce  it.  The  others,  whose  brilliant 
work  had  likewise  forged  the  best  weapons  for  its  overthrow, 
died  without  being  convinced  of  its  untenability.  Other 
English  chemists,  for  instance  Henry,  Kirwan,  and  Hatchet, 
also  tried  to  hold  fast  by  the  phlogistic  hypothesis  so  long  as 
it  appeared  possible  to  say  anything  in  its  favour.  Kirwan 
especially,  who  was  one  of  those  who  believed  phlogiston  to 
be  identical  with  hydrogen,  continued  the  fight  against  the 
new  doctrine  till  1792,  in  which  year  he  subscribed  to  it 
himself.  Its  first  adherent  in  England  was  Lubbock,  who 
concurred  in  Lavoisier's  views  so  early  as  1784.  The  four 
chemists  just  named,  being  representatives  of  their  science 
at  that  day,  merit  this  brief  mention ;  they  advanced  par- 
ticular branches  of  chemistry  by  their  work,  but  did  not 
influence  its  general  tendency.  Thus  their  countryman, 
John  Dalton,  who  soon  after  this  made  such  a  wonderful  step 
in  advance,  showed  only  the  greater  individuality  in  pointing 


v       WORK  PREPARATORY  TO  DALTON'S  ATOMIC  THEORY    181 

out  the  new  path,  by  following  which  chemical  research  has 
since  made  such  enormous  strides. 

After  the  deaths  of  Bergman  and  Scheele,  Sweden  had  at 
the  close  of  the  eighteenth  century  no  chemist  who  enriched 
the  science  with  facts  of  general  importance,  though  Ekeberg 
and  Gahn  worked  energetically  at  analytical  and  mineralogical 
chemistry.  It  was  only  at  the  dawn  of  this  century  that 
Berzelius'  star  arose,  the  light  from  which  was  to  illumine 
nearly  every  branch  of  chemistry  during  its  first  four  decades. 
A  period  singularly  rich  in  scientific  facts  for  chemistry  thus 
began  with  him,  while  in  his  contemporaries,  Davy  and  Gay- 
Lussac,  the  science  possessed  two  other  workers  of  the  highest 
power.  Dalton's  Atomic  Theory,  founded  as  it  was  upon  the 
doctrine  of  chemical  proportions,  formed  the  basis  of  all  their 
efforts. 


Development  of  the  Doctrine  of  Chemical  Proportions. 
Dalton  s  Atomic  Theory. 

The  idea  of  atoms  as  forming  the  ultimate  constituents  of 
matter  often  arose  of  old  in  speculative  minds,  without,  however, 
an  exact  chemical  atomic  theory  being  evolved  from  it. 
Boyle's  corpuscular  theory  was  and  remained  merely  a  product 
of  ingenious  speculation,  which  ended  in  the  assumption  of  a 
primary  material,  and  therefore  bore  no  fruit.  Only  after 
a  series  of  proven  facts  had  led  to  the  presupposition  of 
atoms,  and  after  this  assumption  had  enabled  those  facts 
to  be  satisfactorily  explained,  could  there  be  any  talk  of 
founding  a  chemical  atomic  theory.  The  merit  of  estab- 
lishing this  is  without  a  shadow  of  doubt  due  to  John  Dalton. 
But  before  it  could  be  brought  to  completion,  the  meaning  of 
the  term  "  chemical  proportions,"  according  to  which  simple 
substances  united  to  form  compound  ones,  had  to  be  firmly 
fixed ;  and  an  important  part  of  this  problem  was  worked  out 
by  two  chemists  before  Dalton,  viz.  Richter  and  Proust. 

Richter,  whose  work  was  to  all  intents  and  purposes  un- 
known to  Dalton  at  the  time  when  he  conceived  his  atomic 


182  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

theory1,  founded  the  doctrine  of  chemical  proportions  without, 
perhaps,  seeing  its  great  importance  himself,  while  Proust 
proved  that  the  ratio  in  which  two  elements  combine 
chemically  with  one  another  is  constant,  or,  if  there  is  more 
than  one  compound  of  these  elements,  the  ratio  alters 
by  definite  increments.  If  we  but  consider  that  the 
atomistic  hypothesis,  from  which  the  chemical  atomic  theory 
sprang,  originated  with  an  observation  by  Dalton  which 
followed  from  Proust's  demonstrations,  and  which  was  com- 
prised within  the  law  of  multiple  proportions,  we  see  how 
intimate  was  the  connection  between  the  latter  and  these 
preparatory  labours  (cf.  note  1,  p.  189). 

Jeremias  Benjamin  Richter,  born  at  Hirschberg  in 
Schlesien  in  1762,  became  a  mining  official  (Bergsekretar) 
at  Breslau,  and  then  chemist  (Bergassessor  and  Arkanist2)  in 
the  porcelain  manufactory  at  Berlin,  in  which  city  he  died 
in  1807.  His  researches — from  which  the  doctrine  of  pro- 
portions by  weight  was  mainly  established,  and  which  showed 
that  acids  combined  with  bases  to  form  salts — together  with 
the  conclusions  which  he  drew  from  them,  were  published 
by  him  in  his  Anfangsgrunden  der  Stochiometrie  oder  Mess- 
kunst  Chemischer  Elemente  ("Rudiments  of  Stochiometry,  or 
the  Art  of  Measuring  Chemical  Elements"),  (1792-1794), 
and  in  his  work  entitled,  Ueber  die  neueren  Gegenstande  in 
der  Chemie  ("  Upon  recent  Discoveries  in  Chemistry  "),  which 
was  published  in  eleven  parts  at  irregular  intervals  between 
1792  and  1802;  this  latter  was  in  great  part  a  continua- 
tion of  the  first-mentioned  book. 

Many  chemists  before  him  had  busied  themselves  with 
the  same  task — the  determination  of  the  amounts  of  acid 
and  base  in  salts ;  in  addition  to  Kunkel,  Lemery,  Stahl 
and  Homberg,  special  mention  must  be  made  here  of  Wenzel 
(who  was  born  at  Dresden  in  1740,  and  died  while  director 
of  the  Freiberg  foundries  in  1793),  who  placed  beyond  a 

1  Angus  Smith,  Memoir  of  John  Dalton  and  History  of  the  Atomic- 
Theory,  p.  214. 

2  Arkanist,  meaning  literally  "  secret  chemist,"  was  the  German  title  in 
use  at  that  time. 


v  JEREMIAS  BENJAMIN  RICHTER  183 

doubt  the  fact  that  acids  and  bases  combine  in  constant 
proportions,  grounding  this  conclusion  upon  the  results  of 
numerous  and,  for  the  most  part,  thoroughly  serviceable 
analyses.  Richter  was  in  a  position  to  deduce  the  important 
"  law  of  neutralisation "  (Neutralitatsgesetz)  from  his  own 
researches  upon  the  quantities  of  bases  and  acids  which 
combine  to  form  neutral  salts — researches  carried  out  with 
great  circumspection.  Translated  from  his  writings,  ob- 
scured as  these  were  by  much  phlogistic  verbiage,1  into  the 
chemical  language  of  to-day,  this  runs  somewhat  as  follows : 
"  When  equal  amounts  of  one  and  the  same  acid  are  rendered 
neutral  by  different  amounts  of  two  or  more  bases,  the  latter 
are  equivalent  to  one  another,  and  vice  versa."  It  follows 
quite  clearly  from  his  statements  that  he  regarded  those 
quantities  of  oxides  which  contain  equal  amounts  of  oxygen 
as  equivalent  to  one  another,  i.e.  as  requiring  like  quantities 
of  a  given  acid  to  neutralise  them.  Richter  had  come  to  the 
right  conclusion  as  to  the  capacity  of  iron  and  quicksilver 
to  unite  with  oxygen  in  two  proportions,  from  the  composi- 
tion of  the  corresponding  salts.  With  these  weighty 
observations  he  thus  anticipated  the  precisely  similar  ones 
of  Proust.  Scheele  had  previously  attained  to  the  same 
knowledge  (cf.  p.  127). 

Notwithstanding  that  Richter's  work  contained  such  far- 
reaching  discoveries,  these  remained  almost  unnoticed,  their 
value  being  manifestly  not  recognised.  This  was  partly  due 
to  the  peculiar  phlogistic  language — obscure  and  clumsy 
— in  which  he  clothed  the  results  of.  his  researches.  A 
curious  speculation  in  which  he  indulged  may  also  have 
caused  his  whole  work  to  be  unfavourably  criticised, — 
his  assumption,  namely,  that  a  definite  arithmetical  relation 
existed  between  the  combining  weights  of  the  bases  and 
acids.2  Judicious  as  he  was  in  other  points,  he  believed  that 
he  had  found  a  proof  that  the  combining  weights  of  the  bases 

1  Although  he  had  ceased  to  be  a  phlogistonist,  Richter  still  made  fre- 
quent use  of  phlogistic  expressions,  which  often  obscured  his  writings. 

2  Even  before  his  scientific  career  had  begun,  Richter  was  animated  with 
the  conviction  that  "  chemistry  was  a  branch  of  applied  mathematics." 


184  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

and  acids  form  approximately  regular  series, — the  former 
arithmetical,  and  the  latter  geometrical.  The  importance 
which  he  assigned  to  his  "law  of  progression,"  and  his 
continuous  efforts  to  furnish  proofs  in  support  of  it,  mani- 
festly prevented  him  from  perceiving  the  significance  and 
range  of  his  law  of  neutralisation;  indeed,  he  held  this 
speculation  as  being  the  more  important  of  the  two. 

The  chemical  world  was  to  a  certain  extent  made 
acquainted  with  the  truths  lying  dormant  in  Richter's  papers 
by  G<  E.  Fischer,  who  put  his  countryman's  observations 
into  intelligible  language;  he  collected  together  in  a  clear 
manner  the  scattered  numerical  values  which  Richter  had 
arrived  at  as  representing  the  amounts  of  bases  and  acids 
which  combined  with  one  another,  and  thus  prepared  the 
first  table  of  equivalent  weights.1  Notwithstanding  that 
the  attention  of  chemists  was  in  this  way  drawn  to  Richter's 
researches,  it  was  a  long  time  before  they  became  thoroughly 
known  and  estimated  at  their  true  value.  It  was  thus  that 
facts  proved  by  him  were  rediscovered  by  others  much  later, 
e.g.  the  combination  of  bases  which  contain  equal  amounts  of 
oxygen  with  equal  quantities  of  the  same  acid,  by  Gay-Lussac, 
who  was  without  doubt  unacquainted  with  this  portion  of 
Richter's  work.  As  Kopp  pertinently  remarks  in  his  Ent- 
wickehong  der  Chemie  in  der  neueren  Zeit,  S.  152  ("  Development 
of  Chemistry  in  Recent  Times,"  p.  152):  "The  history  of 
our  science  affords  few  examples  of  important  and  well-proven 
facts  being  overlooked  for  so  long  a  time  and  to  such  an 
extent;  and,  further,  when  the  appreciation  of  these  facts 
did  finally  come,  of  the  merit  of  their  discovery  being 
minimised  so  far  as  the  discoverer  himself  was  concerned, 
and  the  credit  given  in  great  part  to  another." 

It  was  only  long  after  his  death  that  Richter's  services 
were   recognised   to  their  full  extent.2     Starting  from  the 

1  This  table  was  published  by  Fischer  in  his  translation  of  Berthollet's 
Recherches  sur  Us  Lois  de  VAffinitd.     The  fact  that  the  latter  adopted 
Fischer's  grouping  in  his  work,  Essai  de  Statique  Chimique,  vol.  i.  p.  134, 
made  Richter's  labours  known  in  France  also. 

2  Cf.   especially  C.   Lowig's  memoir,  Jeremias  Benjamin  Richter,  der 


v  JOSEPHE  LOUIS  PROUST  185 

observation  that  the  neutrality  is  not  disturbed  by  the 
mutual  decomposition  of  two  neutral  salts,  he  created  the 
doctrine  of  equivalents ;  he  was  the  originator  of  "  Stb'chio- 
metry," 1 — "  the  art  of  chemical  measurement,  which  has  to 
deal  with  the  laws  according  to  which  substances  unite  to 
form  chemical  compounds." 

Josephe  Louis  Proust. — The  work  of  this  investigator, 
who,  independently  of  Richter,  also  partially  proved  the 
validity  of  the  law  of  chemical  proportions,  fell  later  in  point 
of  time  than  the  most  important  of  Richter's  researches. 
Born  at  Angers  in  1755,  Proust  went  through  Rouelle's 
course  of  study,  and  then  applied  his  knowledge  of  pharmacy 
and  chemistry  in  the  first  instance  as  manager  of  the 
apothecary's  shop  attached  to  the  Salpetriere  Hospital  in 
Paris,  and  later  as  a  teacher  in  different  Spanish  universities. 
It  was  in  Madrid,  where  he  settled  after  1791,  that  he 
carried  out  his  most  celebrated  investigations.  The  war 
deprived  him  both  of  his  post  and  of  his  splendidly  equipped 
laboratory  in  1808,  and  it  was  only  towards  the  end  of  his 
life  that  his  necessities  were  relieved  by  a  pension,  while 
he  was  at  the  same  time  received  into  the  Paris  Academy ; 
he  died  at  his  native  town  of  Angers  in  1826. 

His  most  important  work  was  the  result  of  a  series  of 
questions  which  Berthollet  had  propounded.  At  the  end  of 
the  eighteenth  century  (i.e.  from  1798  onwards),  the  latter's 
Kccherches  sur  les  Lois  de  VAffinitt,  which  he  collected  together 
in  1803  in  his  Essai  d'une  Statique  Chimique,  created  an 
extraordinary  sensation.  Grounding  his  objections  upon 

Entdecker  der  chemischen  Proportioned,  (Breslau,  1874)  ["  Jeremias  Benjamin 
Richter,  the  Discoverer  of  Chemical  Proportions  "  (Breslau,  1874)].  Ac- 
cording to  Fischer,  Richter's  work  was  particularly  emphasised  by  Gehlen, 
Schweigger  and  Berzelius.  The  discovery  of  the  law  of  neutralisation  was 
ascribed  by  Berzelius  to  Wenzel,  in  consequence  of  a  misunderstanding  on 
the  part  of  the  former ;  and  it  was  left  to  H.  Hess  of  St.  Petersburg  to 
point  out  this  error,  thirty-three  years  after  Richter's  death. 

1  Richter  himself  says  that  he  was  unable  to  devise  a  better  name  for 
this  than  the  word  "  Stb'chiometrie,  from  ffroix^ov,  signifying  something 
which  cannot  be  further  divided,  and  /leTpe^,  which  denotes  the  finding  out 
of  relative  proportions. " 


186  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

speculations  apparently  well  founded,  this  gifted  writer  dis- 
puted the  fact  that  constant  proportion  was  the  rule  with 
regard  to  the  constituents  of  chemical  compounds.  His 
ideas  upon  chemical  affinity,  by  which  the  combination  of 
substances  with  one  another  is  regulated,  will  be  treated  of 
in  detail  in  the  special  history  of  this  part  of  our  science. 
Suffice  it  to  say  here  that,  starting  from  the  axiom  that 
chemical  processes  are  dependent  upon  the  relative  masses 
of  the  reacting  bodies,  he  arrived  at  the  conclusion  that,  in 
a  chemical  compound  which  results  from  the  union  of  two 
substances,  so  much  the  more  of  the  one  substance  must 
enter  into  it,  the  more  of  that  substance  there  is  available, 
always  supposing  that  no  exceptional  circumstances  stand  in 
the  way  of  this  mass-action.  Berthollet's  great  reputation 
may  have  been  the  reason  why  none  of  the  other  leading 
chemists  of  the  day  raised  any  objections,  although  they 
certainly  did  not  concur  in  this  view.  For,  with  respect 
to  many  compounds,  salts  especially,  the  constancy  of  the 
combining  proportions  of  their  constituents  was  a  fact  be- 
yond all  doubt  to  men  like  Richter,  Wenzel,  Klaproth, 
Vauquelin  and  others. 

Proust  took  up  the  cudgels  against  Berthollet,  and,  by 
means  of  exact  experiment,  overthrew  one  by  one  the 
theoretical  conclusions  of  his  opponent.  This  memorable 
controversy,  which,  beginning  in  IT 9 9,  was  continued  for 
eight  years,  and  which  was  conducted  on  both  sides  with 
consummate  ingenuity  and  supplemented  by  laborious  in- 
vestigations, ended  in  the  conclusive  proof  of  constant 
combining  proportions. 

To  what  extent  Dalton  was  influenced  by  Proust's  labours 
in  his  researches  in  a  similar  direction,  it  is  hard  to  say ;  but 
they  were  certainly  not  without  some  effect  upon  him,  the 
dispute  between  Berthollet  and  Proust  being  followed  with  the 
keenest  interest  in  scientific  circles. 

So  early  as  the  year  1799  Proust  had  proved  the  con- 
stant composition  both  of  natural  and  of  artificial  carbonate 
of  copper,1  and  had  called  special  attention  to  the  unvarying 
1  Ann.  de  Chimie,  vol.  xxxii.  p.  30. 


v      THE  PROUST- BERTHOLLET  CONTROVERSY       187 

proportions  by  weight  in  true  chemical  compounds,  as  opposed 
to  the  varying  ones  in  mixtures.  Still  more  important  than 
these  were  observations — to  be  supplemented  later  on  by 
himself  and  others — upon  the  two  stages  of  oxidation 
which  tin  shows,1  and  upon  the  two  compounds  which 
iron  forms  with  sulphur;2  for  he  particularly  emphasised 
the  point  that  not  only  were  the  proportions  between 
the  metals  and  oxygen  or  sulphur  constant  in  the  in- 
dividual compounds,  but  also  that  the  combining  pro- 
portions increase  by  leaps,  and  not  gradually,  when  two 
elements  unite  to  form  more  than  one  compound.  Ber- 
thollet  thought  that  he  had  proved  exactly  the  opposite  in 
his  researches  on  the  formation  of  oxides  and  salts3  (e.g. 
the  nitrates  of  mercury),  viz.  that  metals  can  form  oxides 
with  gradually  increasing  amounts  of  oxygen.  But  Proust 4 
showed  that  his  experiments  were  wrong,  and  that  he  had 
deduced  his  conclusions  from  the  analysis  of  mixtures  and 
not  of  definite  compounds.  The  superiority  of  Proust  in 
experimental  points  was  clearly  manifested,  since  he  proved 
to  Berthollet  that  many  of  the  substances  which  the  latter 
regarded  as  oxides  contained  chemically-combined  water; 
it  was  Proust  who  first  classed  the  hydrates  among  chemical 
compounds.  In  fact,  he  succeeded  by  generalisation  and  by 
firmly  establishing  his  view — that  combination  between  the 
other  elements  and  oxygen  or  sulphur  only  takes  place  in 
one  or,  at  most,  in  a  few  proportions — in  completely  routing 
the  weak  arguments  of  his  opponent,  many  of  which  were 
advanced  without  any  experimental  proof  to  support  them.5 
Proust  had  repeatedly  laid  stress  upon  the  validity  of 
combining  proportions,  without  however  trying  to  get  clearly 
at  the  reasons  for  this.  How  near  he  was  to  recognising 
the  law  of  multiple  proportions,  which  Dalton  deduced  from 
his  own  researches — researches  similar  to  Proust's,  and  not 
excelling  these  in  exactitude !  One  is  led  to  the  surmise 

1  Journ.  de  Phys.,  vol.  li.  p.  174.         2  Ibid.,  vol.  liv.  p.  89. 

3  Cf.  Essai  de  Statique  Chimique,  vol.  ii.  p.  399  et  seq. 

4  Joum.  de  Phys.,  vol.  lix.  pp.  260,  321. 
6  Ibid.,  vol.  Ixiii.  pp.  364,  438. 


188  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

that  if  Proust  had  calculated  the  results  of  his  experiments 
on  the  composition  of  binary  compounds  otherwise  than  he 
did,  he  would  have  discovered  that  law.  The  happy  idea 
occurred  to  Dalton  of  reckoning  the  amounts  of  one  element, 
which  combined  in  different  proportions  with  another,  in 
terms  of  a  given  chosen  quantity  of  the  latter ;  the  result  of 
this  was  that  the  multiple  proportions  became  manifest,  and 
these  he  explained  by  the  aid  of  the  atomic  hypothesis. 


DALTON'S  ATOMIC  THEORY. 

John  Dalton,1  the  eldest  son  of  a  poor  weaver,  was 
born  at  Eaglesfield  in  Cumberland  on  September  6th,  1766, 
and  had  to  make  his  own  living  at  an  early  age  as  an 
elementary  teacher.  Endowed  with  a  strong  bent  towards 
mathematics  and  physics,  he  acquired  a  sound  knowledge  of 
these  subjects,  and  was  thus  enabled  to  carry  out  indepen- 
dent investigations  in  them,  and  to  take  the  post  of  mathe- 
matical and  physical  master  in  a  college  at  Manchester  in 
1793.  It  was  there,  in  1794,  that  he  made  the  important 
discovery  of  colour-blindness,  which  he  noticed  in  the  first 
instance  in  himself;  as  a  consequence  of  this  the  phenomenon 
goes  by  the  name  of  Daltonism  to  the  present  day.  He  soon 
included  chemistry  also  in  his  studies,  the  most  important 
problem  of  which  he  was  destined  to  solve.  In  his  modesty 
Dalton  had  no  thought  of  acquiring  for  himself  a  brilliant 
position  in  life,  and  a  wide  sphere  of  action ;  after  1 7  9  9,  in 
fact,  he  supported  himself  by  taking  private  pupils.  The 
highest  reward  for  his  truly  philosophic  mind  consisted  in 
the  elucidation  of  the  truth.  He  died  at  Manchester  in 
1844. 

Dalton's  earlier  researches  on  the  physical  behaviour  of 
gases  (their  expansion  by  heat  and  absorption  by  liquids) 

1  For  Dalton's  life  and  work,  compare  the  Memoirs  of  the  Life  and 
Scientific  Researches  of  John  Dalton,  by  W.  C.  Henry,  M.D.  (Cavendish 
Society,  London,  1854),  and  Lonsdale's  Li fe  of  Dalton  ;  the  latter  author  has 
preserved  to  us  a  number  of  traits  which  were  characteristic  of  Dalton's 
simple  and  kindly  nature. 


JOHN  D ALTON  189 


were  of  great  influence  upon  his  later  chemical  labours.  For 
it  was  through  them  that  he  acquired  the  experimental 
dexterity  which  stood  him  in  such  good  stead  when  analysing 
those  gases,  whose  composition  led  him  to  the  law  of  multiple 
proportions. 

The  discovery  of  this  law,  and  the  conception  of  the  atomic 
theory  which  arose  from  it,1  date  from  about  1802-1803. 
After  that  time  Dalton  applied  himself  to  the  task  of  building 
up  a  firm  foundation  for  these  by  amplifying  his  observa- 
tions; he  only  published  his  discovery  in  1808,  when  the 
first  volume  of  his  New  System  of  Chemical  Philosophy  appeared. 
But  the  outlines  of  the  atomic  theory  had,  with  Dalton's 
concurrence,  been  made  public  by  Thomas  Thomson — an 
enthusiastic  admirer  of  Dalton — in  his  System  of  Chemistry 
a  year  before  this,  so  that  the  first  influence  of  this  great 
scientific  event  upon  the  chemical  world  is  to  be  dated  from 
then.  The  second  volume  of  Dalton's  above-mentioned 
work,  with  material  additions  to  the  researches  originally 
published,  appeared  in  1810,  and  the  third  volume  so  late 
as  18 27,  by  which  time  its  contents  were  mostly  out  of  date. 

The  first  of  Dalton's  observations  which  formed  the 
starting  point  for  the  atomic  theory  consisted  in  the  deter- 
mination of  the  composition  of  oil-forming  gas  (ethylene), 

1  Interesting  details  respecting  the  steps  by  which  Dalton  was  led  to 
the  formulation  of  his  atomic  theory  have  recently  been  given  in  H.  Debus's 
Die  Genesis  von  Dalton's  Atomtheorie,  Parts  I  and  II  [Ztschr.  phys. 
Chem.,  xx,  3  (1896);  xxiv,  2  (1897)],  and  Roscoe  and  Harden's  A  New 
View  of  the  Origin  of  Dalton's  Atomic  Theory,  a  Contribution  to  Chemical 
History,  etc.  (MacmillanandCo.,  1896).  Cf.  Also  H.  Debus's  pamphlet : — 
Ueber  einige  Fundamentalsdtze  der  Chemie,  insbesondere  das  Dalton- 
Avogadro'sche  Gesetz  (1894).  According  to  these  authors,  Dalton  arrived 
at  the  atomic  hypothesis  deductively  about  the  year  1801,  and  not  from 
the  result  of  his  researches  on  the  composition  of  gases.  The  discovery  of 
the  law  of  multiple  proportions  was  thus  not  the  cause  of  the  atomic  theory 
being  brought  forward,  but,  on  the  contra'ry,  succeeded  the  latter. — This 
is  a  point  which  is  obviously  of  the  first  importance  in  the  history  of 
chemistry.  But  the  author  feels  that  before  he  can  himself  express  a 
definite  opinion  on  the  subject,  a  more  minute  re-examination  of  the  whole 
question  is  required  than  the  time  at  his  disposal  permits,  before  the  issue 
of  the  present  edition.  In  the  meantime,  therefore,  the  different  views  are 
merely  placed  before  the  reader. 


190  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

and  light  carburetted  hydrogen  (methane).  From  his  ana- 
lyses of  these  two  gases  he  concluded  that,  for  the  same 
quantity  of  carbon,  twice  as  much  hydrogen  was  contained 
in  the  latter  as  in  the  former,  i.e.  that  the  proportions  of 
hydrogen  were  as  2:1.  This  regularity  induced  him  to 
investigate  other  compounds  in  the  same  direction;  thus, 
in  the  case  of  carbonic  oxide  and  carbonic  acid,  he  found 
that,  for  the  same  amount  of  carbon,  the  ratios  of  oxygen 
present  in  these  were  again  respectively  as  1  :  2.  His 
conviction  that  there  must  be  a  law  underlying  these  so 
simple  relations  hardly  required  any  further  strengthening 
after  he  had  met  with  similar  simple  numerical  proportions 
in  the  results  of  his  analysis  of  nitrous  oxide,  nitric  oxide, 
nitrous  acid  and  nitric  acid  (i.e.  the  anhydrides  of  the  two 
last).1  He  had,  therefore,  proved  that  when  different  quan- 
tities of  one  element  combined  chemically  with  one  and 
the  same  quantity  of  another,  these  amounts  stood  in  a 
simple  relation  to  one  another — a  relation  which  could  be 
expressed  by  whole  numbers.  The  law  of  multiple  pro- 
portions was  thus  discovered;  it  had,  indeed,  been  deduced 
from  experiments  which  were  of  necessity  not  very  exact,  as 
was  to  be  expected  from  the  state  of  chemical  analysis  at 
that  time. 

Dalton,  however,  did  not  remain  content  with  this 
important  result,  but  sought  an  explanation  of  the  numerical 
relations  which  he  had  discovered.  This  was  afforded  him 
by  the  atomistic  hypothesis,  in  the  assumption,  not  new  in 
itself,  that  substances  consist  of  ultimate  particles  not 
further  divisible — of  atoms.  This  hypothesis  gave  a  satis- 
factory explanation  of  the  facts  comprised  within  the  law  of 
multiple  proportions,  for  one  now  only  required  to  substitute 
absolute  numbers  for  the  relative  ones,  i.e.  to  assume  that  in 
carbonic  oxide  (for  instance)  one  atom  of  carbon  was  com- 
bined with  one  of  oxygen,  and  in  carbonic  acid  one  atom  of 
carbon  with  two  of  oxygen,  and  so  on.  Upon  the  firm  basis 
of  this  assumption  Dalton  erected  his  Atomic  Theory,  the 

1  Dalton  was,  however,  wrong  in  his  analysis  of  nitric  acid,  which  he 
made  out  to  consist  of  nitrogen  and  oxygen  in  the  proportions  of  1  atom  to  2. 


v  DALTON'S  ATOMIC  THEORY  191 

essence   of   which   is   given   in    the   two   succeeding   para- 
graphs : — 

(1)  Every    element    is    made  up   of  homogeneous  atoms 
whose  iveight  is  constant. 

(2)  Chemical    compoimds   are  formed    ~by   the    union    of 
the   atoms   of  different    elements    in    the   simplest   numerical 
proportions. 

His  speculations  upon  the  atoms  themselves,  which 
Dalton  assumed  for  the  sake  of  simplicity  to  be  spherical  in 
shape,  and  also  the  hypothesis  that  they  do  not  come  into 
direct  contact  with  one  another  but  are  separated  by  a  heat 
zone,  have  but  a  merely  subordinate  significance  as  compared 
with  the  above  two  sentences ;  they  exercised  no  influence 
on  the  development  of  the  chemical  atomic  theory. 

Dalton  now  sought  to  deduce  the  relative  atomic  weights 
from  the  proportions  by  weight  in  which  the  elements  unite 
to  form  compounds,  proceeding  to  this  task,  which  consti- 
tuted the  main  feature  l  of  his  New  System,  with  wonderful 
confidence.  Since  he  had  no  certain  means  of  arriving  at 
these  numeric  proportions  of  the  combining  atoms,  assump- 
tions had  to  be  made,  and  these  were  of  the  simplest  kind. 
The  following  statements  by  Dalton  refer  solely  to  compounds 
of  two  elements. 

When  only  one  compound  of  two  elements  A  and  B  is 
known,  we  must  assume  that  it  is  made  up  of  one  atom  of 
the  one  and  one  atom  of  the  other  :  A  +  B  (binary  compound, 
or  atom  of  the  second  order.  Dalton  spoke  of  an  elementary 
atom  as  .an  atom  of  the  first  order). 

If  two  compounds  of  two  elements  A  and  C  are  known, 
their  composition  is  expressed  by  the  symbols  A  +  C  and 
A -{-20  (ternary  compound,  or  atom  of  the  third  order). 

When    the    composition    of    three    compounds   of    two 

1  Dalton's  own  words  are  : — (to  ascertain)  the  relative  weights  of  the 
ultimate  particles,  both  of  simple  and  compound  bodies,  the  number  of  simple 
elementary  particles  which  constitute  one  compound  particle,  and  the  number 
of  less  compound  particles  which  enter  into  the  formation  of  one  more  com- 
pound particle. 


192  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

elements  A  and  D  had  to  be  decided,  then,  according  to 
Dalton,  the  following  combinations  were  the  probable  ones : 
A+  D,  A  +  2D,  and  2.4 +  Z>.  Atoms  of  the  fourth  order 
(e.g.  A  +  3E),  etc.,  were  also  allowed  by  Dalton,  although 
he  favoured  the  more  simple  proportions.  Compounds  whose 
atomic  numbers  were  as  2  :  3  or  2  :  5,  he  explained  as  result- 
ing from  two  atoms  of  a  higher  order  than  the  elementary 
atom  (e.g.  nitrous  acid  from  one  atom  of  nitric  oxide  and 
one  of  nitric  acid).1 

Dalton's  statement  that  the  atomic  weight  of  a  compound 
is  equal  to  the  sum  of  the  atomic  weights  of  its  constitu- 
ent elements  appears  to  us  nowadays  self-evident ;  but  we 
must  not  forget  that  at  that  period,  in  spite  of  Lavoisier's 
energetic  protest,  the  false  idea  of  heat  being  material  had 
by  no  means  been  discarded  by  all  chemists,  many  of  them 
still  believing  that  a  loss  of  matter  occurred  when  heat  was 
evolved  from  the  combination  of  two  elements. 

Setting  out  then  from  the  above  premises,  Dalton  en- 
deavoured to  determine  the  relative  atomic  weights  of  the 
elements  as  follows : — Starting  with  water,  as  the  only  com- 
pound of  hydrogen  and  oxygen  (peroxide  of  hydrogen  being 
at  that  time  unknown),  he  estimated  the  proportions  in  which 
both  of  these  were  present,  and  then  took  hydrogen  as  the 
unit  to  which  oxygen  and  other  elements  were  to  be  referred. 

1  Dalton's  precise  words,  as  given  in  his  New  System,  second  edition, 
vol.  i.  p.  213,  are  as  follows  : — 

"If  there  are  two  bodies,  A  and  B,  which  are  disposed  to  combine,  the 
following  is  the  order  in  which  the  combinations  may  take  place,  beginning 
with  the  most  simple,  namely  : 

"  1  atom  of  A  + 1  atom  of  B=  1  atom  of  C,  binary, 

"  1  atom  of  A  +  2  atoms  of  B  =  l  atom  of  D,  ternary,"  etc. 

Again,  at  p.  214  : — 

"  1st,  When  only  one  combination  of  two  bodies  can  be  obtained,  it  must 
be  presumed  to  be  a  binary  one,  unless  some  cause  appear  to  the  contrary. 

"2d,  When  two  combinations  are  observed,  they  must  be  presumed  to 
be  a  binary  and  a  ternary. 

"3d,  When  three  combinations  are  obtained,  we  may  expect  one  to  be 
a  binary  and  the  other  two  ternary. 

"4th,  When  four  combinations  are  observed,  we  should  expect  one 
binary,  two  ternary,  and  one  quaternary,  etc." 


v  DALTON'S  ATOMIC  WEIGHTS  193 

The  relative  values  of  the  latter,  as  deduced  from  the  com- 
position of  their  oxygen  and  hydrogen  compounds,  were 
according  to  his  view  their  atomic  weights.  In  this 
way  he  determined  the  relative  atomic  weight  of  nitrogen 
from  the  composition  of  ammonia,  which,  as  the  only  com- 
pound of  hydrogen  and  nitrogen,  consisted  of  one  atom  of 
each  of  those  elements ;  and  that  of  carbon  from  the  analyses 
of  carbonic  oxide  and  carbonic  acid,  using  in  this  case  the 
value  he  had  obtained  for  oxygen  in  the  analysis  of  water. 

As  the  analytical  methods  which  he  employed  were  liable 
to  many  sources  of  error,  it  was  impossible  that  his  results 
could  be  accurate ;  but  the  great  merit .  belongs  to  Dalton 
of  having  propounded  the  principle  of  the  determination 
of  the  relative  atomic  weights,  or,  to  speak  more  correctly, 
of  the  combining  weights  of  the  elements.  How  far  his 
first  "  atomic- weight  numbers,"  as  published  by  Thomson  in 
1805,  differ  from  the  values  current  to-day,  is  seen  from  the 
following  table : — 


"  Relative  Atomic  Weights." 

According  to 
Dalton. 

Their  current 
Values. 

Hydrogen  .... 
Oxygen       .... 

1 
6-5 

1 

7-98 

Nitrogen    .... 

5 

4-66 

Carbon       .... 

5-4 

6 

Dalton  published  a  greatly  extended  and,  to  some  extentr 
improved  table  of  "  relative  atomic  weights "  in  the  first 
volume  of  his  work  (1808),  in  which  7  is  the  value  given  for 
oxygen ;  the  numbers  which  he  obtained  are  too  low  through- 
out, and  deviate  from  the  true  values  by  several  units  in  the 
case  of  the  elements  of  higher  atomic  weight.1  His  attempt 
to  apply  the  atomic  hypothesis  to  organic  compounds  must 

1  This  table  of  atomic  weights  shows  his  endeavours  to  round  off  the 
numerical  values,  from  his  perception  of  the  insufficiency  of  the  methods 
employed,  as  is  seen  in  the  following  instances ;  the  figures  appended  below 
in  brackets,  after  those  of  Dalton,  give  the  correct  combining  weights  : 
sulphur  13  (16),  iron  38  (56),  zinc  56  (64'9),  copper  56  (63'3),  silver  100  (108),. 
mercury  167  (200). 

O 


194  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

also  be  mentioned  here,  although  it  turned  out  unsuccessful, 
the  results  of  his  organic  analyses  being  far  from  exact. 

Nor  must  we  forget  Dalton's  efforts  to  build  up  a  system 
of  notation  which  should  illustrate  atomic  composition. 
The  atoms  of  the  elements  were  represented  by  various 
circular  symbols,  e.g.  oxygen  by  an  empty  circle  O, 
hydrogen  by  0,  nitrogen  by  0  ,  and  sulphur  by  ®. 
These  signs,  placed  conveniently  near  to  each  other, 
indicated  the  supposed  constitution  of  chemical  compounds ; 
for  water  the  symbol  0O  was  used,  for  ammonia  00, 

for  sulphuric  acid  1  ^  y  ^ ,  and  so  on. 
CJ^pU 

But  the  simpler  and  easily  decipherable  system  of  nota- 
tion which  Berzelius  introduced  some  time  after  this,  pre- 
vented Dalton's  from  ever  coming  into  general  use. 


Further  Development  of  the  Atomic  Theory. 

The  reception  which  Dalton's  atomic  theory  found 
among  chemists  was  almost  wholly  favourable,  although 
there  were  not  wanting  a  few  to  depreciate  the  new  doctrine, 
and  even  to  ascribe  the  merit  of  its  origination  to  others. 
In  Great  Britain  it  found  from  the  beginning  an  enthusiastic 
adherent  in  Thomas  Thomson,2  who,  however,  rather  did  it 
harm  than  good  by  his  excess  of  zeal,  a  fatal  tendency  to 
speculation  sometimes  causing  him  to  quit  the  sure  ground 
of  exact  experiment.  It  was  of  particular  importance,  at  the 

1  Dalton  did  not  know  the  compound   S03,  but  supposed   that   this 
formula  gave  the  composition  of  sulphuric  acid. 

2  Thomas  Thomson  (born  1773,  died  1852)  exercised  no  slight  influence 
on  the  growth  of  theoretical  chemical  views,  especially  in  England,  both  by 
his  experimental  researches  in  chemistry,  and  by  his  text-books.     That  it 
was  he  who  first  gave  to  the  public  the  principles  of  Dalton's  atomic  theory 
has  been  mentioned  already.    As  a  historian  of  chemistry  he  was  also  active, 
his  History  of  Chemistry  appearing  in  1830-31.     Most  of  his  papers  were 
published  in  the  Annals  of  Philosophy,  which  he  himself  edited.     As  pro- 
fessor in  the  University  of  Glasgow  (1818-1841)  he  was  eminently  success- 
ful, founding  there  the  first  chemical  laboratory  for  general  instruction  in 
Great  Britain. 


FURTHER  DEVELOPMENT  OF  THE  ATOMIC  THEORY  195 

time  a  theory  so  far-reaching  was  set  up,  that  the  facts  on 
which  it  rested  (still  few  in  number)  should  be  amplified  and 
deepened  by  reliable  observations. 

The  estimations  made  by  Thomson  of  the  relative  atomic 
weights  of  elements  and  compounds  were  still  more  defective 
than  Dalton's,  and  became  influenced  subsequently  in  an  in- 
excusable manner  by  Prout's  erroneous  hypothesis, — and 
that,  too,  after  Berzelius  had  begun  his  long  series  of  classical 
labours  with  the  accurate  determination  of  atomic  weights. 
On  the  other  hand,  Thomson's  investigation  of  the  potash 
salts  of  oxalic  acid  helped  to  confirm  the  atomic  doctrine, 
since  they  showed  that  the  quantities  of  potash  which 
reacted  with  a  given  amount  of  oxalic  acid  were  to  each 
other  as  1 :  2  : 4  by  weight.  An  analogous  observation  was 
made  by  Wollaston,1  who  found  that  in  the  neutral  and  acid 
carbonates  of  potash  the  proportions  of  carbonic  acid  rela- 
tively to  the  same  weight  of  potash  were  as  1:2.  The 
applicability  of  the  law  of  multiple  proportions  was  thus  also 
proved  for  salts. 

The  position  which  from  that  time  (about  1808)  the 
most  distinguished  investigators  of  the  day — Davy,  Berzelius 
and  Gay-Lussac — took  up  with  regard  to  Dalton's  atomic 
theory,  renders  an  account  of  their  most  important  work 
and  their  general  services  appropriate  at  this  point.  The  re- 
searches of  Gay-Lussac  upon  gases,  and  even  more  the  un- 
resting efforts  of  Berzelius  to  work  out  sure  foundations  for 
the  determination  of  the  true  atomic  weights,  had  the  deepest 
influence  on  the  development  of  the  atomic  doctrine,  which 
is  now  the  basis  of  chemistry. 

Davy  and  Gay-Lussac;  their  life  and  work. — Davy 
was  at  first  sceptical  with  regard  to  Dalton's  rights  as  theorigin- 

1  W.  H.  Wollaston  was  born  in  1766  (the  same  year  as  Dalton),  and  died 
in  1828.  Originally  a  physician,  he  soon  gave  himself  up  to  the  study  of 
physics  and  chemistry,  enriching  the  former  especially  by  important  ob- 
servations. At  the  same  time  he  became  favourably  known  by  his  chemical 
researches,  particularly  by  his  work  on  the  platinum  metals.  Most  of  his 
papers  are  to  be  found  in  the  Philosophical  Transactions,  but  a  few  of  them 
in  the  A  nnals  of  Philosophy. 

o  2 


196  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

ator  of  the  atomic  theory,  and  indeed,  in  1809,  he  claimed  for 
Higgins  the  priority  for  this  doctrine,  the  latter  having  made 
use  of  the  atomic  hypothesis  to  explain  chemical  facts  so- 
early  as  1*789  (in  his  work,  A  Comparative  View  of  the 
Phlogistic  and  Antiphlogistic  Theories).  Higgins  certainly 
expressed  opinions  which,  on  a  superficial  glance,  appeared 
similar  to  those  of  Dalton,  stating  as  he  did  that  the  smallest 
particles  combine  in  simple  numerical  proportions  to  form 
chemical  compounds.  But  these  views  were  brought  forward 
without  any  internal  organic  connection,  and,  moreover,  they 
were  not  based  upon  experiment.  It  became  clear  to  Davy 
later  on  that  Higgins  had  no  claim  to  be  regarded  as  the 
originator  of  the  atomic  theory,  and  he  then  frankly  recog- 
nised Dalton's  service. 

Humphry  Davy,  born  at  Penzance  in  Cornwall  in  1778, 
was  destined  for  a  distinguished  career,  to  be  cut  short  by  an 
early  death,  his  creative  genius  being  impaired  during  the 
last  years  of  his  life  by  prolonged  illness.  So  early  as  1813, 
when  only  thirty-five  of  age,  he  had  to  leave  off  work  and 
seek  renewed  health  on  the  Continent,  in  Italy  for  the  most 
part.  From  that  time  he  travelled  a  good  deal.  After  1820 
he  lived  and  worked  again  in  England,  but  left  it  in  1827,  never 
to  return,  for  he  died  in  1829  at  Geneva  on  his  homeward 
journey. 

While  only  a  surgeon's  assistant,  Davy  acquired  by  his 
own  energy  such  a  wide  knowledge  of  chemistry  and  the 
natural  sciences,  that  at  twenty  years  of  age  he  was  able  to 
take  the  post  of  chemist  in  the  newly- founded  Pneumatic 
Institution  at  Bristol.  The  aim  which  this  institution  had 
set  before  itself  was  to  test  the  various  artificially  prepared 
gases  for  their  physiological  and  medical  action.  It  was 
here  that  Davy  carried  out  his  researches  on  nitrous  oxide, 
whose  intoxicating  and  stupefying  action  he  discovered,  and 
on  the  effect  of  other  gases  (admixed  with  nitrogen)  on  the 
organism,  e.g.  hydrogen  and  carbonic  acid  ;  in  this  way  he 
laid  the  foundation  of  his  fame  as  a  great  experimenter. 
So  early  as  1801  we  find  him  assistant  professor  at  the  Royal 
Institution  of  London  (very  soon  to  become  professor),  and 


HUMPHRY  DAVY  197 


shortly  afterwards  a  member  of  the  Royal  Society,  whose 
president  he  became  in  1820. 

His  most  memorable  work,  which  effected  a  complete 
transformation  in  many  branches  of  chemistry,  was  accom- 
plished during  the  first  thirteen  years  of  this  century.  We 
need  only  mention  here  the  isolation  of  the  metals  of  the 
alkalies  and  alkaline  earths  by  the  galvanic  current,  through 
which  a  whole  series  of  hitherto  undecomposed  substances 
were  recognised  as  compound.  An  almost  still  more  im- 
portant result  of  these  observations  was  the  discovery  of 
the  elementary  nature  of  chlorine,  which  up  till  then  was 
held  to  be  a  compound ;  this  opened  out  entirely  new  stand- 
points, which  led  to  a  transformation  of  the  views  upon  the 
constitution  of  acids.  When  it  was  proved  that  there 
were  acids  which  did  not  contain  oxygen,  a  material  altera- 
tion in  Lavoisier's  theory  became  for  the  first  time  necessary. 
Discoveries  of  such  range  as  this  characterise  the  period  in 
which  Davy  developed  his  wonderful  activity.  His  most 
important  experimental  researches  will  be  described  partly  in 
the  further  course  of  the  general  history  of  this  period,  and 
partly  in  the  synopsis  of  the  progress  of  particular  branches 
of  chemistry. 

Davy  contributed  greatly  by  his  popular  lectures,  es- 
pecially by  those  given  for  the  Board  of  Agriculture,  to 
heighten  the  public  interest  in  chemistry  during  the  first 
decade  of  this  century.  He  it  was,  too,  who  showed  in  what 
high  degree  chemistry  could  and  should  meet  the  require- 
ments of  technical  industries  and  of  daily  life  ;  we  have  only 
to  think  in  this  connection  of  the  miner's  safety  lamp  which  he 
constructed. 

Davy's  genius  in  grasping  chemical  relations  was  especially 
apparent  in  his  efforts  to  discover  the  connection  between 
electricity  and  chemical  affinity,  both  of  which  he  regarded 
as  resulting  from  a  common  cause.  He  was  the  first  to  set 
up  an  electro-chemical  theory  grounded  upon  experiments, 
which  were  devised  and  carried  out  in  a  masterly  manner, 
and  in  this  way  he  opened  out  the  province  in  which 


198  THE  MODERN  CHEMICAL  PERIOD  CHAP, 

Berzelius   was   to   work   with    such    effect   in   the    decade 
following.1 

Wherever  Davy,  with  his  aptitude  for  experiment  and 
acuteness  of  mind,  treated  chemical  problems,  he  achieved 
great  results.  Within  the  narrower  limits  of  special  research 
also,  e.g.  in  his  invesigations  on  ammonium  amalgam,  phosgene, 
eu chlorine,  iodine,  solid  phosphuretted  hydrogen,  and  the 
phenomena  of  combustion,  the  fruits  of  his  labours  were  at 
once  perceptible  ;  his  work  always  left  a  deep  mark.  After 
the  year  1801  Davy  published  his  most  important  papers  in 
the  Philosophical  Transactions,  but  some  are  to  be  found  in  the 
Annales  de  Chimie  and  in  the  Journal  de  Physique.  Of  his 
few  larger  works,2  the  Elements  of  Chemical  Philosophy 
(1810-12)  became  best  known,  especially  as  it  was  soon 
translated  into  French  and  German.  After  his  death  all  his 
works  were  collected  together  and  published  by  his  brother 
John  Davy. 

In  addition  to  the  interest  which  Davy's  wonderful 
services  to  science  call  forth,  there  is  to  be  added  the  purely 
human  interest  in  his  personality.  The  nobility  and  poetry 
of  his  nature  are  shown  both  in  the  journals  which  he  kept 
during  his  extended  journeyings  in  France,  Germany  and 
Italy,  in  his  letters,  and  his  Memoirs.2'  The  inventions  made 
by  him  for  the  public  good  raise  still  higher  our  regard  for 
this  remarkable  investigator. 

1  Davy's  electro-chemical  theory  of  affinity  will  be  described  along  with 
that  of  Berzelius  in  one  of  the  succeeding  paragraphs. 

2  The  judgment  which  Berzelius  passed  upon  Davy's  literary  activity, 
in  a  letter  written  to  Wohler  in  1831,  is  of  much  interest  (cf.  Ber.,  vol.  xv. 
p.  3166).     The  latter  had  been  deploring  that  he  was  overwhelmed  with 
literary  work,  whereupon  Berzelius  replied  as  follows:  "Had  Davy  been 
forced  to  occupy  himself  as  much  with  writing  as  you  have  to  do  now,  I  am 
convinced  that  he  would  have  advanced  chemistry  by  a  hundred  years  ;  but 
he  remained  only  a  '  brilliant  fragment '  (ylanzendes  Bruchstiick),  because  he 
was  not  compelled  from  the  beginning  to  initiate  himself  thoroughly  into 
every  part  of  the  science  as  into  one  organic  whole." 

3  Memoirs  of  the  Life  of  Sir  Humphry  Davy,  by  J.  Davy  (London, 
1839). — A  delightful  monograph  on  Davy,  based  for  the  most  part  on  Dr. 
John  Davy's  work,  has  recently  been  written  by  T.  E.  Thorpe  (Century 
Science  Series,  Cassell  and  Co.,  1896). 


DAVY  ;  GAY-LUSSAC 


Davy's  historico-critical  attitude  towards  Dalton's  atomic 
doctrine  has  been  already  spoken  of.  But  although  he 
subsequently  gave  the  latter  credit  for  originating  this 
theory,  he  continued  sceptical  with  regard  to  Dalton's  con- 
clusions.1 He  would  not  admit  that  Dalton's  atomic  weights 
were  really  such  ;  in  his  view  these  were  merely  the  proportion 
numbers  of  the  elements,  for  the  determination  of  whose 
atomic  weights  there  was  no  sure  basis  to  go  upon. 
Wollaston  had  before  this  given  utterance  to  a  similar 
circumspect  criticism  of  Dalton's  bold  speculations,  having 
published  in  1808  his  opinion  that  the  numbers  arrived  at 
by  Dalton  gave,  not  the  atomic  weights,  but  the  chemical 
equivalents  of  the  elements.  Gay-Lussac,  too,  whose  labours 
began  at  that  time  to  exercise  such  a  powerful  influence 
on  the  development  of  chemistry,  rejected  the  assumption  of 
atomic  weights,  and  merely  allowed  that  the  ratio  (rapport) 
of  one  element  (e.g.  hydrogen,  nitrogen,  or  iodine)  to  another 
(e.g.  oxygen)  was  established  by  analytical  and  synthetical 
determinations. 

Gay-Lussac,  whose  critical  attitude  to  Dalton's  atomic 
theory  has  just  been  touched  upon,  helped  on  the  latter  in 
a  quite  exceptional  degree  by  his  wide-reaching  discovery  of 
the  so-called  "  Law  of  volumes  " — more,  indeed,  than  he  was 
willing  to  confess. 

Josephe  Louis  Gay-Lussac,  born  in  1 7  7  8  at  St.  Leonard 
in  the  old  province  of  Limousin,  after  acting  as  Fourcroy's 
demonstrator  became  in  1809  professor  of  chemistry  at  the 
Ecole  Polytechnique  (at  which  he  had  been  a  pupil  up  to  the 
year  1800),  and  at  the  same  time  held  the  chair  of  physics 
at  the  Sorbonne.  In  1832  he  resigned  his  chair  at  the 
Sorbonne  to  fill  that  of  general  chemistry  at  the  Jardin  des 
Plantes ;  he  died  in  1850.  After  his  initiation  into  science 
by  Berthollet,  and  while  still  very  young,  Gay-Lussac  aroused 
the  marked  attention  of  his  contemporaries  by  his  physical 
investigations  on  the  behaviour  of  gases — investigations 
which  touched  more  or  less  on  the  province  of  chemistry. 
Brief  mention  may  also  be  made  here  of  his  bold  balloon 
1  Cf.  particularly  his  Elements  of  Chemical  Philosophy. 


200  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

-ascents  in  1804,  undertaken  at  first  along  with  Biot  and 
afterwards  alone.  His  researches  made  after  1805,  upon 
the  laws  deducible  from  the  combining  volumes  of  gases 
which  unite  chemically  with  one  another,  had  most  incisive 
results.  What  rich  fruit  this  yielded  for  chemistry  as  a 
whole,  and  not  merely  for  the  chemistry  of  gases,  will  be 
shown  later  on.  Gay-Lussac's  name  is  further  associated 
with  the  discovery  of  the  definite  relation  which  exists 
between  the  volume  of  a  gas  and  its  temperature ;  it  was 
only  after  this  law  had  been  worked  out,  a  law  which 
supplemented  that  of  Boyle  and  Mariotte,  that  reliable 
measurements  of  gases  could  be  made. 

In  his  work  which  bore  upon  special  branches  of  chemistry 
Oay-Lussac  likewise  proved  himself  a  masterly  investigator ; 
to  exactitude  in  observing,  and  acuteness  in  explaining  his 
observations,  he  added  a  wonderful  lucidity  in  expounding 
his  researches  and  the  conclusions  at  which  he  arrived.  His 
work  on  iodine  and  cyanogen  and  their  compounds  would 
-alone  suffice  to  ensure  him  a  place  among  the  most  dis- 
tinguished chemists.  How  stimulating  and  full  of  matter 
were  his  papers  !  The  one  upon  cyanogen,  especially,  was 
the  basis  on  which  the  radical  theory  was  afterwards 
developed,  for  cyanogen  was  characterised  by  Gay-Lussac  as 
the  first  compound  radical.  Even  his  minor  work  bears  the 
-classical  stamp ;  of  it  we  may  mention  here  his  researches 
•on  the  compounds  of  sulphur,  and  on  the  various  stages  of 
oxidation  of  nitrogen,  and  his  conjoint  work  with  Thenard1 
upon  the  alkali  metals.  Together  with  Liebig  he  investigated 
the  fulminates.  Hidden  in  many  of  these  pieces  of  work 

1  L.  J.  Thenard,  born  in  1777,  a  pupil  of  Vauquelin  and  Berthollet, 
became  professor  at  the  JiJcole  Polytechnique  and  in  the  College  de  France, 
and  worked  energetically  for  the  promotion  of  the  study  of  natural  sciences 
in  France.  His  name  is  indissolubly  united  with  that  of  Gay-Lussac, 
their  conjoint  work  leading  to  a  knowledge  of  many  chemical  processes, 
and  contributing  to  the  improvement  of  important  methods.  Thenard's 
Traitd  de  Chimie  ^Jlementaire,  a  text-book  which  was  most  widely  used, 
thanks  to  the  happy  synoptical  arrangement  of  its  contents,  was  of  great 
merit ;  the  first  French  edition  of  it  was  published  in  1813-16,  and  the  first 
German  edition  (translated  from  the  fifth  French  by  Fechner)  in  1825-33. 
Thenard  died  in  1857. 


v  <:AY-LUSSAC'S  WORK;  PROUT'S  HYPOTHESIS  201 

there  lay  germs  which  were  to  expand  into  important 
discoveries ;  for  example,  his  observation  on  the  action  of 
chlorine  upon  wax  laid  the  foundation  for  subsequent 
researches  upon  substitution  reactions. 

By  his  work  on  technical  subjects,  Gay-Lussac  proved 
that  he  understood  how  to  bring  his  results  in  analytical 
chemistry  to  bear  upon  these.  He  is  to  be  regarded  as  the 
originator  of  volumetric  analysis;  and  the  improved  ana- 
lytical methods  which  he  thus  introduced,  and  which  have 
since  come  intc  general  use,  have  helped  materially  to  ad- 
vance chemical  industries.  We  shall  meet  with  his  work  in 
almost  every  important  branch  of  chemical  investigation, — 
in  analytical,  technical,  physical  and  pure  chemistry. 

Gay-Lussac  published  most  of  his  experimental  results 
in  the  Annales  de  Chimie,1  but  a  few  of  them  are  to  be 
found  in  the  Memoirs  de  la  Socie'te'  d'Ar$euil  and  in  the 
Comptes  Rendus.  Of  his  papers  which  appeared  separately, 
mention  may  be  made  here  of  a  number  upon  methods  of 
investigating  and  testing  commercial  products,  silver  ores, 
etc.,  which,  as  a  member  of  various  commissions,  he  worked 
out;  also  of  the  Recherches  Physiques  et  Chimiques  (1811), 
which  he  edited  conjointly  with  Thenard. 


Prout's  Hypothesis  and  its  Effects. 

During  the  period  in  which  Davy  and  Gay-Lussac  were 
carrying  on  their  brilliant  work,  and  before  the  star  of 
Berzelius  had  attained  to  its  full  lustre,  a  literary-chemical 
event  occurred  which  made  a  profound  impression  upon  nearly 
all  the  chemists  of  that  day,  viz.  the  advancement  of  Prout's 
hypothesis.  This  was  one  of  those  factors  which  materially 
depreciated  the  atomic  doctrine  in  the  eyes  of  many 
eminent  investigators.  On  account  of  its  influence  upon  the 
further  development  of  the  atomic  theory,  this  hypothesis 
must  be  discussed  here,  although  it  has  happened  but  seldom 

1  After  the  year  1816  this  journal  was  edited  by  Arago  and  himself 
under  the  title  Annales  de  Chimie  et  de  Physique. 


202  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

that  an  idea  from  which  important  theoretical  conceptions 
sprang,  originated  in  such  a  faulty  manner  as  it  did. 

In  the  year  1 8 1 5  a  paper1  appeared  in  which  the  relation 
between  the  atomic  weights  of  elements  and  the  specific 
gravities  of  their  vapours  was  treated  of  ;  in  this  paper,  and 
still  more  positively  in  a  second,2  published  in  the  following 
year,  the  tenet  was  set  up  by  their  anonymous  author  that 
the  atomic  weights  of  the  elements — taking  that  of  hydrogen 
as  unity — were  expressible  by  whole  numbers,  i.e.  that  they 
were  multiples  of  the  atomic  weight  of  the  lightest  element.3 
From  this  there  followed  the  hypothesis  proper  of  Prout 
(who  had,  in  the  meantime,  become  known  as  the  author  of 
the  above  two  papers), — that  hydrogen  may  be  regarded  as 
the  primary  matter  from  which  all  other  elements  are  formed 
by  various  condensations. 

This  idea,  so  lightly  thrown  out.  and  which  adapted  itself 
so  usefully  to  the  incomplete  investigations  of  others,4 
possessed  both  then  and  at  various  later  periods  a  great 
charm  for  many  chemists.  Even  before  these  papers  had 
been  published,  Dalton's  friend  Thomson  had  alluded  to 
the  fact  that,  according  to  his  own  experiments  and  those 
of  others,  the  atomic  weights  of  several  of  the  elements  were 
multiples  of  those  of  oxygen.  He  endeavoured,  indeed,  to 
establish  the  same  point  several  years  after  this,  without 
considering  that  the  numbers  which  Berzelius  had  found 
in  the  meantime  differed  widely  from  his  own,  which  had 
therefore  become  of  very  doubtful  value.  Thomson  was 
the  victim  of  this  preconceived  opinion ;  he  went  so  far  as 
to  see  in  Prout 's  assumption  a  fundamental  law  of  chemistry, 

1  Annals  of  Philosophy,  vol.  vi.  p.  321. 

2  Ibid.,  vol.  vii.  p.  111. 

3  The  author  altered  the  numerical  values  of  the  atomic  weights  in  a 
highly  arbitrary  manner,  so  that  they  should  not  merely  be  whole  numbers, 
but  should  also  show  regular  differences  among  each  other,  as  is  seen  from 
the  following  examples  : — 

Calcium  20  Iron  28  Chlorine    36 

Sodium  24  Zinc  32  Potassium  40. 

4  Prout  himself  was  a  physician,  and  his  own  investigations  were  few 
in  number  and  anything  but  conclusive. 


BERZELIUS  203 


Although  Berzelius  and,  later,  Turner  and  others  proved 
the  untenability  of  Prout's  hypothesis,  many  chemists  still 
inclined  towards  it.  In  his  text-book  of  1827,  L.  Gmelin 
gave  the  "  mixture  weights "  (Mischungsgewichte)  as  far  as 
possible  in  whole  numbers,  which  he  was  assuredly  not 
justified  in  doing  after  Berzelius'  classical  researches.  Later 
still,  about  the  year  1840,  Dumas  and  Stas,  who  had 
determined  the  atomic  weights  of  carbon,  oxygen,  chlorine 
and  calcium  with  great  exactitude,  and  also  Erdmann  and 
Marchand  in  their  numerous  investigations  in  a  like  direc- 
tion, betrayed  a  strong  inclination  to  this  hypothesis,  the 
weakness  of  which  was  afterwards  proved  by  Stas  himself 
and  by  Marignac.  The  predilection  shown  by  many  chemists 
for  this  conception,  which  led  to  such  far-reaching  deduc- 
tions, helped  to  discredit  the  whole  atomic  doctrine  in  the 
minds  of  thoughtful  investigators. 

Like  Davy  and  Gay-Lussac,  who,  it  is  true,  did  not 
specially  occupy  themselves  with  the  problem  of  determining 
the  atomic  weights  of  the  elements,  Berzelius  kept  himself 
entirely  free  from  those  prepossessions ;  and,  since  even  at 
that  time  he  devoted  all  his  energies  to  the  solution  of  ques- 
tions allied  to  this,  his  opinions  possessed  the  very  greatest 
value.  Firm,  and  not  led  away  by  the  alluring  simplicity^of 
Prout's  hypothesis,  he  held  fast  to  his  aim, — the  accurate, 
purely  experimental  determination  of  the  atomic  weights, 
and  by  his  masterly  work  he  firmly  established  the  then 
unsteady  edifice  of  the  atomic  doctrine. 


BERZELIUS— A  SURVEY  OF  HIS  WORK. 

The  life  of  this  investigator,  who  developed  and  enriched 
chemistry  in  its  most  important  branches  as  hardly  any 
other  man  has  done,  was  the  quiet  and  uneventful  one  of  a 
student.  He  was  guided  in  his  work  by  the  great  and  com- 
prehensive aims, — to  investigate  carefully  the  composition  of 
chemical  compounds,  and  to  arrive  at  the  laws  according  to 
which  they  are  formed. 


204  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

Jakob  Berzelius  was  born  at  the  little  town  of  Westerlosa 
in  Ostergotland,  Sweden,  where  his  father  was  a  schoolmaster, 
on  the  2  9th  of  August,  1779.  A  love  for  chemistry  appears 
to  have  developed  itself  in  him  at  a  very  early  date,  but  his 
desire  to  devote  himself  to  its  study  at  Upsala  was  only 
attained  (in  179  8)  under  many  difficulties  and  disappoint- 
ments. The  lectures  and  instruction  given  by  his  teachers 
Afzelius  and  Ekeberg  were  uninspired  by  the  spirit  after 
which  Berzelius  strove.  We  therefore  find  him  turning  to 
the  study  of  medicine,  without,  however,  losing  sight  of 
chemistry  as  an  important  aid  to  the  latter.  His  early  work, 
especially  that  which  he  carried  out  along  with  Hisinger 
upon  the  action  of  the  galvanic  current  on  salts,  made  him 
known  in  his  own  country,  so  that  in  1802  he  was  appointed 
assistant  professor  in  medicine,  botany  and  pharmacy  at  the 
University  of  Stockholm,  and,  five  years  later,  professor  of 
medicine  and  pharmacy.  In  1815  he  was  called  to  the 
chair  of  chemistry  in  the  newly-founded  Chirurgico-Medical 
Institute  there.  His  lectures,  which  were  at  first  purely 
theoretical,  according  to  the  established  custom,  he  began  to 
enliven  by  judiciously  chosen  experiments ;  while  a  very  im- 
perfectly equipped  laboratory  enabled  him  to  carry  through  the 
exact  experiments  which  were  to  firmly  establisththe  doctrine 
of  chemical  proportions.  In  those  modest  rooms  were  accom- 
plished the  famous  researches,  most  of  them  by  himself  alone, 
but  some  in  conjunction  with  specially  gifted  pupils.  The 
names  of  those  latter  are  sufficient  in  themselves  to  show 
the  wonderful  results  which  he  achieved  by  his  teaching ; 
among  them  we  may  mention  here  Heinrich  and  Gustav 
Rose,  Mitscherlich,  Wohler,  Chr.  Gmelin,  Magnus  and 
Mosander. 

From  the  year  1818,  when  he  was  nominated  permanent 
secretary  to  the  Stockholm  Academy,  of  which  he  had  been 
a  member  since  1808,  and  still  more  after  1832,  when 
Mosander  succeeded  him  in  his  chair,  Berzelius  devoted 
himself  to  literary  work  with  an  effectiveness  which  has 
hardly  been  equalled  by  any  chemist  either  before  or  after 
him.  His  energetic  life  came  to  a  close  on  the  7th  of 


v  BERZELIUS'  MORE  IMPORTANT  WORK  205 

August  1848.     In  1818  he  was  ennobled  by  King  Charles 
XIV.,  and  in  1835  made  a  baron  by  the  same  monarch. 

To  give  a  short  and  at  the  same  time  succinct  account  of 
the  great  scientific  achievements  of  Berzelius  is  no  easy 
task,  for  these  did  not  merely  touch  upon  the  main  points 
of  chemistry,  but  penetrated  deeply  into  them,  and  gave 
rise  to  weighty  reforms.  After  occupying  himself  for  the 
first  seven  years  of  his  independent  scientific  work  with 
researches  in  various  branches  of  the  science,  especially 
physiological  chemistry,  and  proving  himself  thereby  to  be 
an  exceptional  observer,  his  efforts  rose — from  1807 — to  a 
higher  level.  For,  from  that  date,  his  entire  energy  was 
devoted  to  one  great  aim;  the  minute  investigation  of 
chemical  proportions  and,  with  that,  the  development  of  the 
atomic  doctrine  he  looked  upon  as  his  life-task.  At  the  time 
when  he  began  his  work  upon  the  combining  proportions  of 
the  elements,  the  atomic  doctrine  was  unknown  to  him.  His 
first  researches  were  inspired  by  J.  B.  Richter's  papers  and 
then  by  Davy's  discoveries,  before  he  was  aware  of  the 
results  of  Dalton's  labours  which  had  led  to.  the  atomic 
theory.  How  Berzelius  built  up  the  doctrine  of  proportions 
by  improving  analytical  methods  and  by  the  clear-sighted 
interpretation  of  his  own  researches  and  those  of  others, 
and  how  he  created  solid  foundations  for  the  determination 
of  atomic  weights,  will  be  described  in  the  following  section. 

But  we  must  just  mention  here  that  he  greatly  enriched 
analytical  chemistry  by  the  discovery  of  new  methods.  These 
were,  indeed,  indispensable  to  him  for  the  attainment  of  his 
great  aim,  for  it  was  only  by  means  of  the  most  accurate  pos- 
sible analyses  that  the  constancy  of  combining  proportions 
could  be  definitely  proved.  This  was,  however,  by  no  means 
the  only  branch  of  chemistry  which  was  indebted  to  him,  for 
analysis  in  his  hands  was  made  to  open  up  other  and  larger 
domains.  His  first  attempt  to  work  out  the  composition  of 
minerals  on  the  basis  of  the  atomic  theory,  i.e.  with  the  aid 
of  'the  law  of  multiple  proportions,  was  made  so  early  as  the 
year  1812,  and  his  establishment  of  a  chemical  mineral 
system  created  an  extraordinary  interest. 


206  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

Of  still  more  far-reaching  effect  were  his  successful  en- 
deavours to  show  that  organic  compounds  were  likewise 
subject  to  the  law  of  multiple  proportions.  After  materially 
improving  the  methods  of  analysis  of  organic  bodies,  he  was 
able  to  demonstrate  in  1814  that  simple  atomic  relations 
prevail  among  the  constituents  of  organic  acids  and  of  their 
salts.  The  atomic  theory  thus  became  the  guiding  star  both 
for  Berzelius  and  for  the  whole  science. 

Berzelius  assumed  that  atoms  were  electrically  polarised, 
-and  looked  upon  this  as  the  cause  of  the  combination  of 
elements  in  definite  proportions.  His  electro-chemical 
theory,  developed  from  this  assumption,  and  his  dualistic 
system,  which  was  the  immediate  result  of  this  theory,  will 
be  described  in  detail  along  with  other  similar  attempts  at 
explaining  the  phenomena  of  affinity. 

Experiment  formed  the  basis  of  his  speculations.  By 
connected  observations  on  the  chemical  behaviour  of  simple 
and  compound  bodies,  he  extended  the  most  important 
branches  of  his  science  in  a  marvellous  degree. 
,  Of  his  numerous  researches  on  inorganic  substances,  that 
upon  selenium  is  a  classical  model,  worthy  to  rank  alongside 
of  Gay-Lussac's  upon  iodine.  We  may  also  call  to  mind 
here  his  remarkable  investigations  upon  ferro-cyanogen  com- 
pounds, sulpho-salts  and  fluorine  compounds,  among  many 
others.  All  his  experimental  work  shows  the  originality  of 
a  master  mind ;  and  although  his  inventive  genius  was  not 
so  great  as  that  of  Davy,  his  strict  methods  of  procedure 
and  conscientious  observations  led  him  to  discoveries  of  the 
first  importance. 

The  work  of  Berzelius  in  organic  chemistry  is  less  imposing 
than  that  which  has  just  been  sketched,  but  we  have  only 
to  recall  his  discovery  of  racemic  acid,  and  his  important 
investigations  on  its  isomerism  with  tartaric  acid,  to  see  that 
here,  too,  he  made  a  deep  mark.  As  he  was  the  first  to 
apply  the  principles  of  the  atomic  theory  to  organic  sub- 
stances, so  he  sought  to  introduce  his  electro-chemical  and 
dualistic  views  here  also.  These  efforts  of  his  to  simplify 
complex  relations  were  not  however  in  this  instance  per- 


BERZELIUS  AS  A  TEACHER  AND  WRITER  i2«»7 


manently  successful,  for,  although  his  radical  theory  had 
a  fruitful  influence  for  a  time,  it  was  unable  to  hold  its 
ground  against  the  unitary  conception.  Much  of  his  work  in 
mineralogical  and  physiological  chemistry  was  fundamental 
in  its  nature,  and  was  even  that  of  a  pioneer,  since  it  had  as 
its  immediate  result  (especially  in  mineralogical  chemistry) 
the  setting  up  of  entirely  new  points  of  view  and  new  aims. 

The  grand  creative  genius  of  Berzelius  and  the  joy  he  had 
in  his  work  are  not  only  apparent  in  his  experimental 
researches,  but  show  themselves  also  in  his  activity  as  a 
teacher,  whether  as  manifested  in  personal  intercourse  with 
his  pupils  or  as  finding  expression  in  writing.  In  his  little 
laboratory  there  assembled  young  men  from  far  and  near, 
most  of  them  already  well  versed  in  chemical  knowledge,  to 
learn  from  his  experience  and  then  to  further  propagate  his 
doctrines.  From  Germany  especially,  where  at  that  time 
there  was  hardly  any  provision  for  practical  chemical  work, 
came  aspiring  students,  who  subsequently  advocated  the 
principles  of  his  school  and  extended  its  influence. 

Berzelius'  literary  activity  is  most  strikingly  shown  in  his 
Lehrluch  der  Chemie,1  of  which  five  editions,  each  of  them 
completely  revised,  appeared.  Along  with  the  absolute 
thoroughness  which  we  also  admire  in  his  experimental  work, 
clearness  of  description  is  united  in  this  book  with  precision 
of  expression.  He  did  not  merely  confine  himself  to  the 
simple  exposition  of  known  facts,  but  criticised  with  absolute 
impartiality  the  experiments  from  which  these  were  deduced. 
His  text-book  remained  a  model,  unapproached  by  any  other, 
during  succeeding  decades.  The  many-sidedness  of  Berzelius 
and  his  power  of  work  were  also  strikingly  shown  in  the 
Jahresbericht  uler  die  Fortschritte  in  der  Physik  und  Chemie 
("  Annual  Report  on  the  Progress  of  Physics  and  Chemistry  "), 

1  This  book  came  out  for  the  first  time  in  1808-1818  in  three  volumes 
(Swedish) ;  the  second  Swedish  edition  (four  vols.,  1825-31)  was  translated 
into  German  by  Wohler,  while  the  subsequent  editions  were  printed 
in  German  only.  The  third  (four  vols.,  1833-35)  and  the  fourth  (four  vols., 
1835-41)  were  done  into  German  by  Wohler  "from  the  Swedish  MSS.  of 
the  author,"  while  the  fifth  "original  edition"  (five  vols.,  1843-48)  was 
written  by  Berzelius  himself  with  Wohler's  co-operation. 


208  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

twenty-seven  volumes  in  all,  which  were  published  by  him 
in  Swedish  from  the  year  1821  until  his  death  ;  these  were 
also  brought  out  in  German  by  Gmelin  for  the  first  three 
years,  and  subsequently  by  Wohler  (in  Tubingen).  He  had 
undertaken  to  report  to  the  Stockholm  Academy  upon  the 
work  published  on  those  subjects,  a  task  which  he  performed 
with  diligence  and  perspicacity.  With  regard  to  work  which 
came  at  all  within  his  own  province,  he  knew  to  perfection 
how  to  fill  the  role  of  critic,  although  on  some  occasions  he 
was  led  by  the  characteristics  of  particular  experimental  re- 
searches to  express  a  judgment  which  betrays  a  certain  prepos- 
session. Notwithstanding  this,  however,  his  Jahresberichte  are 
and  will  remain  indispensable  sources  of  information  for  any 
one  who  wishes  to  understand  the  currents  and  changes  of 
opinion  in  the  chemistry  of  that  time. 

The  experimental  researches  of  Berzelius  were  as  a  rule 
first  published  in  Swedish  in  the  Transactions  of  the  Stockholm 
Academy,  but  most  of  them  were  afterwards  given  out  in 
German,  and  a  few  in  English  and  French  (in  Gilbert's, 
Poggendorff's,  and  Lielig's  Annalen.  the  Annales  de  Chimie, 
Annals  of  Philosophy,  etc.).  They  are  characterised  by  the 
same  excellences  as  his  text-book. 

The  above  sketch  of  his  main  achievements  is  sufficient  to 
indicate  the  qualities  which  distinguished  Berzelius  as  a 
classical  investigator.  Thoroughness  and  perseverance  in 
everything  which  he  undertook  ;  exactness  in  all  his  observa- 
tions, and  the  capacity  for  arranging  these  distinctly  and  ex- 
plaining them  clearly ;  inviolable  adherence  to  the  results  of 
experience  (which  was  his  guide  before  everything  else),  and 
an  equally  firm  adherence  to  results  which,  in  his  opinion,  had 
been  correctly  arrived  at  from  a  number  of  data  ;  these  were 
the  characteristics  which  distinguished  this  great  man. 

The  desire  to  retain  whatever  of  good  the  science  possessed 
was  developed  in  him  in  an  exceptional  degree  ;  indeed,  in  sus- 
taining this  conservative  attitude  he  went  so  far  as  to  see  a 
danger  to  the  steady  development  of  chemistry  in  every  in- 
novation which  called  in  question  views  already  proved  and 
found  useful.  Hence  his  fervent  opposition  to  many  new 


v  REVIEW  OF  BERZELIUS'  WORK  209 

hypotheses  which  he  had  in  the  end  to  recognise  as  correct 
His  great  services  in  furthering  chemistry  were,  however,  not 
lessened  by  this  peculiarity,  which  had  its  real  cause  in  a  pro- 
found sense  of  justice  ;  on  the  contrary,  by  a  prudent  adherence 
to  approved  opinions,  Berzelius  often  prevented  the  confusion 
to  which  the  views  he  combated  might  probably  have  given 
rise,  had  they  been  accepted  without  reservation.  Not  that 
he  was  averse  to  healthy  reform.  But  against  anything 
violent — to  his  mind  revolutionary — he  fought  with  all  his 
energy  he  did  not  shun  even  hot  polemics l  when  anything 
that  he  regarded  as  sound  was  at  stake. 

His  pupil  Heinrich  Rose  gave  a  comprehensive  review  of 
his  general  character  in  the  "  Memorial  Speech  of  Berzelius,  "2 
— a  speech  of  great  beauty  and  with  a  pleasant  warmth  of  tone 
running  through  it.  At  the  close  of  it  (p.  5  9)  Rose  says : 
"  The  irresistible  captivation  which  Berzelius  exercised  over 
those  who  enjoyed  the  privilege  of  a  lengthened  intercourse 
with  him  was  only  partly  due  to  the  lofty  genius,  whose 
sparks  flashed  from  all  his  work,  and  only  partly  to  the 
clearness,  the  marvellous  wealth  of  ideas,  and  the  untiring 
care  and  great  industry  that  gave  everything  with  which  he 
had  to  do  the  stamp  of  the  highest  perfection.  It  was  also — 
and  every  one  who  knew  him  intimately  will  agree  with  me 
in  this, — it  was  also  those  qualities  which  placed  him  so  high 
as  a  man  :  it  was  his  devotion  to  others,  the  noble  friendship 
which  he  showed  to  all  whom  he  deemed  worthy  of  it,  the 
great  unselfishness  and  conscientiousness,  the  perfect  and  just 
recognition  of  the  services  of  others, — in  short,  it  was  all  those 
qualities  which  spring  from  an  upright  and  honourable 
character. "  3 

1  His  controversies  with  Dumas,   Laurent,    Liebig  and  others  have 
often  been  harshly  and  unfairly  criticised,   in  that  a  false  light  has  been 
thereby   thrown   upon    his    whole    work.       The  younger  generation  of 
chemists,  in  especial,  quickly  forgot  after  his  death  the  debt  which  was  due 
to  him  for  the  imperishable  services  which  he  had  rendered  in  the  building 
up  of  the  science.     Indeed,  derision  and  cheap  ridicule  of  the  mistakes  he 
made  are  still  to  be  found  in  recent  works  which  treat  of  the  development 
of  chemical  theories. 

2  Delivered  at  a  public  meeting  of  the  Berlin  Academy,  3rd  July,  1851. 

3  The  recently  published  letters  of  Berzelius  and  Liebig  to  each  other, 

P 


210  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

We  may  close  this  section  with  the  following  words, 
in  which  the  same  chemist  portrays  in  a  few  lines  the 
wonderful  work  of  his  master :  "  When  a  man  who  is  endowed 
with  exceptional  talents  as  an  investigator  enriches  every 
branch  of  his  science  Vith  the  most  pregnant  facts,  distin- 
guishes himself  equally  in  empirical  and  speculative  research, 
and  grasps  the  whole  subject  in  a  philosophic  sprit ;  when  he 
arranges  each  detail  systematically  and  clearly,  and  gives  the 
whole  to  the  world  in  a  doctrinal  system,  critically  sifted  and 
put  in  as  perfect  a  form  as  possible  ;  lastly,  when  he  proves 
himself  a  noble  example  of  a  practical  and  theoretical  teacher 
to  a  circle  of  pupils  eager  for  knowledge, — that  man  so  fulfils 
the  highest  demands  of  his  science,  that  he  will  continue  to 
shine  forth  as  a  brilliant  model  for  ages  to  come.  " 


The  Firm  Establishment  of  the  Doctrine  of  Chemical  Propor- 
tions and  the  Development  of  the  Atomic  Theory  by 
Berzelius ;  together  .with  the  share  taken  in  these  Toy 
Gay-Lussac,  Dulong  and  Petit,  and  Mitscherlich. 

It  has  been  already  stated  in  the  preceding  section  that 
Berzelius  regarded  the  investigation  of  chemical  proportions, 
and  of  the  laws  which  regulate  these,  as  his  life  task.  Com- 
pounds of  oxygen  formed  the  starting-point  for  his  researches 
and  for  the  deductions  which  he  drew  from  them,  this  element 
being  indeed,  after  the  time  of  Lavoisier,  the  centre  round 
which  the  whole  of  chemistry  ranged  itself.  Even  in  the 
first  investigations,  which  he  began  to  publish  in  1810  in 
Swedish,  and  in  1811  in  German  (in  Gilbert's  Annalen,  vols. 
xxxvii.,  xxxviii.,  and  xl.),  Berzelius  furnished  powerful  proofs 

which  embrace  the  years  1831-1845,  confirm  in  the  most  absolute  manner 
the  above  kindly  critique.  This  book,  edited  by  Liebig's  grandson,  J. 
Carriere,  and  published  by  Lehmann  (Munich  and  Leipzig)  in  1893,  will 
be  welcomed  as  one  of  the  best  contributions  that  has  been  made  to  the 
history  of  chemistry  of  late  years.  It  will  assuredly  help  towards  a  truer 
criticism  not  merely  of  Berzelius  and  Liebig  themselves,  but  also  of  many 
other  eminent  men,  and  at  the  same  time  assist  towards  a  clearer  view  of 
various  important  points. 


v       DEVELOPMENT  OF  THE  ATOMIC  THEORY      211 

of  the  existence  of  chemical  and,  more  particularly,  of  mul- 
tiple proportions  in  the  oxygen  compounds  of  the  elements.  If 
we  consider  that  he  carried  out  this  great  work  and  the  sub- 
sequent investigations  connected  with  it  (for  which  entirely 
new  methods  had  to  be  devised),  almost  altogether  by  himself, 
we  shall  gain  some  idea  of  the  wonder  which  such  achieve- 
ments created  anong  his  contemporaries.1 

A  true  scientist,  Berzelius  knew  how  to  advance  from 
the  particular  to  the  general ;  he  first  collated  a  number  of 
important  facts  which,  taken  together,  rendered  possible  the 
gradual  but  firm  establishment  of  the  atomic  theory.  Among 
these  were  the  proofs  that  the  proportion  of  sulphur  to  metal 
in  the  metallic  sulphides  was  the  same  as  that  in  the  cor- 
responding sulphates ;  that  the  amounts  of  oxygen  in  the 
equivalents  of  bases  were  likewise  the  same ;  and  that  in 
salts  of  every  kind  the  ratios  between  the  quantities  of  base, 
acid  and  water  were  simple  ones, — and  so  on. 

In  the  years  1812  to  1816  Berzelius  investigated  the 

1  Many  passages  in  the  works  of  Berzelius  proved  that  he  looked  upon 
the  firm  establishment  of  the  doctrine  of  chemical  proportions,  and,  in  con- 
nection with  this,  the  determination  of  the  atomic  weights  of  the  elements 
and  the  constitution  of  chemical  compounds,  as  his  chief  task.  His  own 
words  may  be  quoted  here  to  show  how  he,  impressed  as  he  was  with  the 
incompleteness  of  previous  work  on  the  subject,  strove  to  improve  upon  it : 
' '  I  soon  convinced  myself  by  new  experiments  that  Dalton's  numbers  were 
wanting  in  that  accuracy  which  was  requisite  for  the  practical  application 
of  his  theory.  I  now  perceived  that  if  the  light  which  had  arisen  upon 
the  whole  science  was  to  be  propagated,  the  atomic  weights  of  as  large  a 
number  of  elements  as  possible,  and,  above  all,  of  the  most  commonly 
occurring  ones,  must  be  determined  with  the  greatest  accuracy  attainable  ; 
and,  together  with  this,  the  proportions  according  to  which  compound 
atoms  (zusammengesetzte  Atome)  combine  among  each  other,  as,  for  instance, 
in  salts,  with  the  analysis  of  which  I  had  been  occupied  for  some  time. 
Without  work  of  this  kind  no  day  could  follow  the  morning  dawn.  This 
was,  therefore,  the  most  important  point  for  chemical  research  at  the  time, 
and  I  devoted  myself  to  it  with  unresting  energy.  Several  of  the  more 
important  atomic  weights  I  subjected,  after  lengthened  intervals,  to  a 
closer  scrutiny,  making  use  of  improved  experimental  methods.  After 
work  extending  over  ten  years,  the  results  of  which  have  been  published 
in  the  scientific  journals,  I  was  able  in  1818  to  publish  a  table  which  con- 
tained the  atomic  weights,  as  calculated  from  my  experiments,  of  about 
2000  simple  and  compound  substances." — Lehrbuch  der  Chemie,  vol.  iii.  p. 
1161,  fifth  edition. 

p  2 


212  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

stages  of  oxidation  of  most  of  the  metals  and  metalloids  then 
known  (to  use  his  own  term  for  the  non-metals),  and,  by  deter- 
mining the  composition  of  these  oxides,  confirmed  the  law 
of  multiple  proportions.  And,  notwithstanding  that  he  some- 
times proceeded  from  erroneous  premises,  e.g.  from  the 
assumption  that  chlorine  and  ammonia  contained  oxygen, 
his  grasp  of  the  subject  was  so  complete  that  he  was  able 
to  keep  the  main  conclusions  drawn  from  his  experiments 
free  from  error. 

Of  special  significance  for  the  sound  development  of  the 
atomic  doctrine  were  his  efforts  (intimately  connected  with 
the  work  just  mentioned)  to  deduce  the  relative  atomic 
weights  of  the  elements,  and  also  of  compounds,  from 
the  composition  of  chemical  compounds  as  determined  by 
analysis.  He  went  about  this  with  great  circumspection, 
showing  wonderful  tact  in  the  selection  of  proper  footholds 
from  which  to  approach  the  difficult  task.  Already  in  one 
of  his  earlier  papers 1  we  meet  with  the  first  statement  of 
the  "  oxygen  law,"  according  to  which  the  amount  of  oxygen 
in  the  acid  of  a  salt  stands  in  a  simple  numerical  proportion 
to  that  in  the  base, — a  statement  which  was  the  result  of 
experience,  and  which  Berzelius  followed  in  many  atomic 
weight  determinations. 

The  propositions  which  Dalton  had  brought  forward  with 
a  view  of  arriving  at  the  atomic  numbers  of  the  constituents 
of  chemical  compounds  were  rightly  designated  by  Berzelius 
as  arbitrary.  Among  them,  for  example,  was  the  assumption 
that  the  atomic  proportion  of  two  elements  to  one  another, 
when  only  one  compound  of  these  was  known,  must  be  1  :  1. 
Berzelius,  too,  set  out  from  simple  premises,  and  had  to 
exercise  all  his  ingenuity  in  order  to  find  further  support 
for  such  assumptions.  One  of  these  latter  (advanced  at  the 
beginning  of  his  work  on  the  subject)  was — that  1  atom  of 
one  element  A.  combines  with  1,  2,  3,  or  4  atoms  of 
another  element  B.  The  less  simple  combining  proportions 
2 A  :  3J?  or  2 A  :  SB  were  first  allowed  by  Berzelius  about 
the  year  1819,  and  without  any  reservation  only  in  1827. 

1  Gilbert's  Annalen,  vol.  xxxviii.  p.  161. 


v  RELATIVE  ATOMIC  WEIGHTS  213 

With  such  propositions  as  a  basis,  even  when  including 
the  definitely  expressed  "  oxygen  law "  (which  had  been 
worked  out  in  the  meanwhile),  Berzelius  would  have  been 
hardly  more  successful  in  solving  the  question  of  the  number 
of  elementary  atoms  in  a  compound  than  Dalton  and  his 
immediate  successors,  had  he  not  known  how  to  appreciate 
the  value  of  Gay-Lussac's  important  discovery  of  the  "  law 
of  volumes "  for  clearing  up  the  points  in  question.  By 
making  use  of  this,  the  simplest  combining  proportions  in 
which  different  elements  unite  became  all  at  once  apparent, 
and,  by  applying  it  further,  Berzelius  was  able  to  bring  his 
experimental  work  to  its  first  conclusion.  His  Versuch  uber 
die  Theorie  der  chemischen  Proportioned,  und  uber  die  ckemischen 
Wirkungen  der  Elektrizitdt  ("  Essay  upon  the  Theory  of 
Chemical  Proportions  and  upon  the  Chemical  Action  of 
Electricity  ")  appeared  first  in  1814  in  Swedish,  in  1 8 1 9  in 
French,  and  in  1820  in  German.1  In  this  memorable 
work  for  the  history  of  chemistry  he  developed  his  concep- 
tion of  the  atomic  doctrine,  and  his  ideas  upon  the  relations 
between  chemical  affinity  and  electric  polarity.  His  dualistic 
views  stood  out  clearly  here,  and  at  the  same  time  he  devised 
a  new  language  and  nomenclature  for  his  system.  Of  special 
importance  was  the  collection  of  the  results  of  his  arduous 
investigations  in  tables  of  the  atomic  weights  of  elements 
and  compounds ;  he  was  able  to  give  original  figures  for 
about  2000  substances.  In  order  to  become  thoroughly 
acquainted  with  the  grounds  which  influenced  Berzelius  in 
his  choice  of  these  values,  we  must  take  into  account  the 
law  of  volumes  above  all  other  things,  because,  as  has  already 
been  mentioned,  he  not  only  drew  important  inferences 
from  it,  but  used  it  almost  from  the  beginning  of  his 
researches  as  the  basis  of  his  atomic  weight  system. 

1  Edited  by  K.  A.  Blode. 


214  THE  MODERN  CHEMICAL  PERIOD  CHAP. 


Influence  of  the  Law  of  Volumes  upon  the  Atomic  Theory. 

Among  the  greatest  of  the  services  rendered  by  Gay- 
Lussac  was  the  research  which  he  published  towards  the  end 
of  1808  in  the  Mtmoires  de  la  Socie'te'  d'Argeuil,  vol.  ii.  p.  20*7 x. 
Having  three  years  previously,  in  conjunction  with  Alexander 
von  Humboldt,  observed  that  exactly  two  volumes  of 
hydrogen  unite  with  one  volume  of  oxygen  to  form  water, 
he  showed  by  comprehensive  investigations  that  similar 
simple  volumetric  relations  exist  between  all  gases  which 
combine  chemically  with  one  another,  and  further,  that  the 
gaseous  products  formed  also  stand  in  a  simple  volumetric 
relation  to  their  components.  He  proved  this,  for  example, 
in  the  formation  of  two  volumes  of  carbonic  acid  from  two 
of  carbonic  oxide  and  one  of  oxygen,  and  in  the  combination 
of  hydrogen  and  chlorine  and  of  ammonia  and  hydrochloric 
acid  in  equal  volumes ;  he  likewise  showed  that  two  volumes 
of  ammonia  were  composed  of  three  volumes  of  hydrogen 
and  one  of  nitrogen,  and  two  volumes  of  (anhydrous)  sul- 
phuric acid  of  two  volumes  of  sulphurous  acid  and  one  of 
oxygen.  Several  of  these  proportions  he  was  able  to  deduce 
from  the  results  of  other  workers,  e.g.  Dalton,  Davy  and 
Vauquelin,  who  had  determined  the  volumes  with  fair 
accuracy  in  their  experiments  on  gaseous  compounds,  with- 
out, however,  recognising  the  underlying  law. 

Having  concluded  from  their  similar  behaviour  with 
regard  to  changes  of  pressure  and  temperature  that  all  gases 
possess  a  like  molecular  constitution,  Gay-Lussac  deduced 
from  his  researches,  just  quoted,  the  following  important 
}aw . — The  weights  of  equal  volumes  of  both  simple 
and  compound  gases,  and  therefore  their  densities, 
are  proportional  to  their  empirically  found  combin- 

1  In  his  Classiker  der  Exakten  Wissenschaften,  W.  Ostwald  has  put 
within  every  one's  reach  these  papers  of  Gay-Lussac  and  of  A.  von  Hum- 
boldt, as  well  as  the  fundamental  researches  of  Dalton  and  Davy  already 
referred  to.  A  like  service  as  regards  chemical  classics  has  been  rendered 
to  English-speaking  chemists  in  the  Alembic  Club  Reprints,  edited  by  Dr. 
Leonard  Dobbin,  and  published  by  W.  F.  Clay,  Edinburgh. 


v  GAY-LUSSAC'S  LAW  OF  VOLUMES  ;  AVOGADRO          215 

ing  weights,  or  to  rational  multiples  of  the  latter. 
In  this  sentence  the  old  idea — that  certain  definite 
relations  exist  in  nature  between  the  weight  and  mass 
(pondere  et  mensura)  of  compounds — first  found  distinct 
expression. 

Gay-Lussac  was  himself  inclined  to  connect  his  law  of 
volumes  with  the  atomic  theory, — indeed,  he  recognised  in  it 
a  support  for  the  latter.  But  he  was  unable  to  set  aside 
certain  difficulties  which,  in  spite  of  the  simplicity  of  the 
known  volume-relations,  came  in  the  way,  and  he  therefore 
adhered  to  his  empirical  standpoint. 

The  assumption  obviously  so  closely  related  to  the  above, 
viz.  that  equal  volumes  of  different  gases  contain  equal 
numbers  of  smallest  particles,  and  that,  in  the  case  of  the 
simple  gases,  these  are  not  undecomposable  but  consist  of 
several  atoms,  was  made  so  early  as  1811  by  Avogadro.1 
From  such  an  assumption  it  followed  that  the  masses  of 
these  smallest  particles,  i.e.  the  molecular  weights  of  the 
gases,  were  proportional  to  the  vapour  densities.  The  par- 
ticles were  termed  by  him  molecules  inttgrantes,  and  their 
constituents  (i.e.  our  atoms),  molecules  e'le'mentaires.  Not- 
withstanding the  fruitfulness  of  those  conceptions,  and  the 
ease  with  which  by  their  aid  the  mutual  relations  between 
the  volumes  of  gases  and  the  atoms  could  be  explained, 
they  remained  almost  unnoticed.  The  reason  for  this  may 
to  some  extent  have  been  that  Avogadro  generalised  too 
boldly,  extended  his  hypothesis  to  non-volatile  substances, 
and  brought  forward  no  new  facts  in  support  of  it. 

But  although  the  conclusions  drawn  from  the  law  of 
volumes  by  the  scientist  just  named  remained  unheeded  at 
the  time,  the  law  itself  bore  rich  fruit  for  the  atomic 
doctrine.  Dalton  himself  showed  a  disinclination  to  agree 
with  the  results  of  Gay-Lussac's  researches,  indeed,  he  doubted 

1  Journ.  de  Phys.,  vol.  Ixxiii.  p.  58.  (This  paper  forms  No.  8  of 
Ostwald's  Classiker;  cf.  also  No.  4  of  the  Alembic  Club  Reprints. )  Amadeo 
Avogadro,  born  1776,  died  while  still  professor  of  physics  at  Turin  in  1856. 
It  is  through  the  treatise  just  mentioned  that  his  name  will  always  remain 
famous. 


216  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

their  correctness.  Thomson  and  Davy  too  did  not  perceive 
that  the  law  of  volumes  had  any  special  significance  from 
the  atomic  point  of  view,  as,  although  they  frequently  made 
use  of  the  volume-relations  of  gases  to  arrive  at  their  com- 
position, at  other  times  they  interpreted  these  relations 
wrongly;  thus  they  assumed  that  a  volume  of  hydrogen 
contained  only  half  as  many  atoms  as  an  equal  one  of 
oxygen. 

Berzelius,  however,  recognised  in  the  law  of  volumes  a 
welcome  corroboration  of  the  atomic  theory,  and  allowed 
himself  to  be  guided  by  it  in  his  views  upon  the  number  of 
atoms  in  chemical  compounds,  and,  consequently,  upon  the 
numerical  values  of  the  atomic  weights.  His  "  volume 
theory"  (Volumtheorie)  contained  the  attempt  to  combine 
Gay-Lussac's  law  with  the  atomic  theory.  He  set  forth  the 
atomistic  view,  which  he  had  himself  put  into  shape  under 
the  influence  of  the  law  of  volumes,  definitely  and  con- 
clusively in  two  papers.1  He  started  with  the  assumption 
that  in  the  case  of  every  simple  substance,  when  it  was 
in  the  gaseous  form,  one  volume  corresponded  with  one 
atom,  and  therefore  made  use  of  the  designation  "volume 
atoms"  (Volumatome)  for  those  smallest  particles.  Where- 
ever  it  was  practicable,  he  endeavoured  to  measure  the 
volumes  of  the  combining  substances,  and  from  these  deduced 
the  atomic  numbers.  The  analysis  of  the  compound,  in 
which  the  volumes  of  the  elementary  constituents  were 
known,  led  him  to  the  true  determination  of  the  atomic 
weights  of  the  latter.  Thus,  from  the  fact  that  water  con- 
sists of  two  volumes  of  hydrogen  and  one  of  oxygen,  he 
deduced  the  atomic  composition  of  water  which  holds  at  the 
present  day,  together  with  the  relative  atomic  weights  of 
oxygen  and  hydrogen;  and  from  the  (volumetric)  mode  of 
formation  of  carbonic  oxide  and  carbonic  acid  he  arrived  at 
the  true  composition  of  these  compounds,  and  at  the  atomic 
weight  of  carbon,  etc. 

But,  however  much  Berzelius  was  convinced  at  that  date 
(1813)  of  the  superiority  of  this  conception  over  the  "cor- 
1  Ann.  of  Philos.,  vol.  ii.  pp.  359,  443  (1813). 


v  THE  ATOMIC  WEIGHTS  OF  BERZELIUS  IN  1818          217 

puscular  theory,"  which  took  no  account  of  volume-relations, 
he  did  not  fail  to  recognise  the  limits  of  application  of  his 
volume  theory.  To  extend  to  non- volatile  bodies  the  con- 
ceptions which  he  had  gained  from  gases  seemed  to  him 
hazardous;  in  fact,  his  doubts  as  to  the  possibility  of 
regarding  all  elements  and  chemical  compounds  from  the 
standpoint  of  the  volume  theory  grew  rapidly,  as  is  easily 
seen  in  his  Essay  upon  the  Theory  of  Chemical  Proportions, 
etc.  (cf.  p.  230),  which  was  published  a  few  years  after  this- 
But  he  had,  at  any  rate,  found  in  the  law  of  volumes  a 
valuable  aid  towards  the  determination  of  the  atomic  com- 
position of  numerous  substances,  and  the  deduction  from  this 
of  the  atomic  weights  of  many  of  the  elements. 

A  glance  at  the  table  of  atomic  weights  which  he  pub- 
lished in  1818  shows  how  reliable  the  values  found  by  him 
are,  comparing  favourably  as  they  do  with  those  of  other 
observers.  A  later  table  given  out  by  him  in  1827  contained 
marked  improvements  on  the  former  one.  and  brought  his 
atomic  weights  still  nearer  to  those  current  at  the  present 
day.  But  great  uncertainty  still  prevailed  with  regard  to  the 
proportional  numbers  of  many  of  the  atomic  weights,  as  com- 
pared with  that  of  hydrogen  or  oxygen.  Berzelius  took  oxygen 
(as  the  most  important  element,  the  "  pole  of  chemistry ") 
for  the  basis  of  his  other  atomic  weights,  making  that  of 
oxygen  =  100.  His  ground  for  this  preference1  was  that 
oxygen  was  capable  of  combining  chemically  with  every  other 
element ;  in  fact,  oxygen  compounds  were  almost  the  only 
ones  made  use  of  at  that  time  for  the  derivation  of  the  atomic 
weights. 

If  we  calculate  his  values  upon  that  of  hydrogen,  which 
is  now  the  customary  unit,  we  obtain  numbers  that  can  be 
compared  with  those  in  use  to-day.  The  following  selection 
of  such  atomic  weights  from  the  year  1818  will  serve  to 

1  In  his  text-book  (first  edition,  vol.  iii.  p.  99)  he  expresses  himself  as 
follows  :  "To  refer  the  other  atomic  weights  to  that  of  hydrogen  offers 
not  only  no  advantages,  but  has,  in  fact,  many  inconveniences,  seeing  that 
hydrogen  is  very  light  and  is  seldom  a  constituent  of  inorganic  compounds. 
Oxygen,  on  the  other  hand,  unites  all  the  advantages  in  itself.  It  is,  so  to 
speak,  the  centre-point  round  which  the  whole  of  chemistry  revolves." 


218  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

corroborate  what  has  just  been  said  (the  current  values  are 
those  in  brackets) : — 

Carbon  12'12  (12)  Lead        416     (207)  Sodium      93.5    (23) 

Oxygen  16       (15'96)  Mercury  406    (200)  Potassium  157. 6  (39) 

Sulphur  32-3    (32)  Copper    129     (63'3)  Silver         433 '7  (108). 

Iron        109-1(56) 

The  question  now  forces  itself  upon  us — What  were  the 
grounds  which  led  Berzelius  to  assume  twice  as  high  a  value 
for  many  metals  (e.g.  iron,  lead,  mercury,  copper,  chromium, 
tin,  etc.),  and  four  times  as  high  a  value  for  potassium,  sodium 
and  silver,  as  are  now  assigned  to  them  ?  The  reason  lay  in 
his  presupposition  of  the  simplest  possible  combining  pro- 
portions, for  at  that  time  such  proportions  as  2:3,  2:5, 
3 : 4,  etc.,  appeared  to  him  too  complex ;  only  one  atom  of 
an  element  was,  in  his  then  view,  present  in  (a  molecule 
of)  a  compound.  The  compounds  formed  by  the  oxidation 
of  iron,  for  example,  in  which  the  proportions  of  oxygen 
were  as  2:3,  and  which  we  now  express  by  the  formulse 
FeO  and  Fe203,  had  for  him  the  composition  expressed  by 
the  formulae  Fe02  and  FeO3,  whence  the  atomic  weight  of 
iron  came  out  double  what  we  now  have  it.  An  analogous 
composition  was  attributed  to  other  metallic  oxides  corre- 
sponding to  the  protoxide  and  sesquioxide  of  iron,  so  that 
the  atomic  weights  of  their  metals  were  doubled.  In  like 
manner  Berzelius  was  led,  by  the  assumption  that  the  ratio 
of  oxygen  in  potassic  peroxide  and  oxide  was  as  3 : 2,  to  the 
erroneous  conclusion  that  the  latter  contained  one  atom  of 
potassium  combined  with  two  of  oxygen,  and  the  peroxide 
one  of  potassium  combined  with  three  of  oxygen ;  hence  for 
potassium  and  the  analogous  monovalent  elements  sodium, 
lithium  and  silver,  whose  oxides  have  in  reality  the  general 
formula  Me2O,  atomic  weights  four  times  higher  than  the 
true  ones  were  deduced. 

Thus,  in  spite  of  Berzelius'  gigantic  labours,  many  points 
attaching  to  his  system  of  atomic  weights  still  remained  un- 
certain ;  there  were  as  yet  too  few  reliable  and  comprehen- 
sive data  to  allow  of  the  true  relations  of  the  values  found 
to  that  of  hydrogen  or  oxygen  being  firmly  established. 


v  DULONG  AND  PETIT  219 

Berzelius  himself  was  convinced  of  the  insufficiency  of  the 
methods  by  which  he  had  determined  the  atomic  composi- 
tion of  compounds,  and,  from  this,  the  atomic  weights  of  the 
elements.  Apart  from  his  somewhat  arbitrary  suppositions, 
he  had  merely  found  in  the  physical  behaviour  of  gases— 
in  the  relation  of  their  specific  gravities  to  the  combining 
weights — a  good  basis  upon  which  to  work  out  the  question 
of  the  magnitudes  of  the  relative  atomic  weights. 

The  year  1819  brought  with  it  two  important  dis- 
coveries in  physical  chemistry  which  helped  to  clear  up  the 
above  uncertainties;  attention  was  called  almost  simul- 
taneously by  Dulong  and  Petit1  to  the  relations  between 
the  atomic  weights  of  the  elements  and  their  specific  heats, 
and  by  Mitscherlich  to  the  connection  between  similarity  of 
crystalline  form  and  analogous  constitution.  The  latter 
discovery  and  the  doctrine  of  isomorphism  which  grew  out 
of  it  were  largely  made  use  of  by  Berzelius  for  determining 
relative  atomic  weights;  but  to  Dulong  and  Petit 's  state- 
ment he  paid  much  less  heed,  as  it  still  required  extension 
and  corroboration.  Both  of  these  discoveries  have  exercised 
such  a  profound  influence  on  the  development  of  the  atomic 
weight  system  that  they  must  be  discussed  shortly  here,  in 
so  far  as  they  refer  to  the  latter  (cf.  section  devoted  to  the 
history  of  Physical  Chemistry). 

1  P.  L.  Dulong,  who  was  born  in  1785  at  Rouen,  and  died  in  1838  while 
Director  of  the  Polytechnic  School  at  Paris,  rendered  imperishable  service, 
more  especially  by  his  physico-chemical  investigations.  But,  apart  from 
these,  his  purely  chemical  labours — e.g.  that  upon  chloride  of  nitrogen,  in 
discovering  which  compound  he  lost  an  eye  and  several  fingers  (in  1811), 
that  upon  the  oxygen  compounds  of  phosphorus  and  nitrogen,  and  his 
fruitful  speculations  upon  the  constitution  of  acids — ensure  him  an  honour- 
able place  in  the  history  of  the  natural  sciences. 

T.  A.  Petit  was  born  in  1791,  and  died  while  Professor  of  Physics  at 
the  Polytechnic  School  so  early  as  1820.  To  chemists  he  is  known  by  his 
conjoint  work  with  Dulong  on  the  atomic  heats  of  the  elements  (see  above), 
his  other  researches  being  purely  physical. 


220  THE  MODERN  CHEMICAL  PERIOD  CHAP, 


Dulong  and  Petit's  Law. 

From  researches 1  carried  out  in  part  with  substances  not 
quite  pure,  and  in  part  by  methods  upon  which  not  much 
reliance  could  be  placed,  those  two  investigators  drew  the 
important  conclusion  that  the  specific  heats  of  a  number  of 
the  solid  elements,  the  metals  in  particular,  were  nearly 
inversely  proportional  to  their  atomic  weights.  But,  how- 
ever bold  these  deductions  were,  deductions  which  they 
expressed  in  the  sentence:  "The  atoms  of  simple  sub- 
stances have  equal  capacities  for  heat,"  or,  "The 
atomic  heats  of  the  elements  are  equal,"  their  confi- 
dence in  them  was  on  the  whole  justified  by  later  and  more 
accurate  experiments;  at  any  rate  most  of  the  metallic 
elements  fulfilled  the  Dulong -Petit  law  approximately. 
The  exceptions  to  it,  shown  by  many  of  the  non-metals  in  a 
greater  or  lesser  diminution  of  the  atomic  heats,  have  only 
in  some  measure  been  explained  in  recent  years  by  the  proof 
that  the  specific  heats  of  such  elements  vary  greatly  with  the 
temperature.  In  the  case  of  simple  chemical  compounds,  too, 
a  relation  was  soon  found  between  their  specific  heats  and 
atomic  weights  (by  Neumann,  in  1831). 

When  once  its  validity  had  been  proved,  the  significance 
of  the  Dulong-Petit  law  for  the  determination  of  the  relative 
atomic  weights  of  the  elements  became  immediately  apparent. 
One  had  merely  to  determine  the  specific  heat  of  an  element 
in  order  to  arrive  at  its  atomic  weight  from  this,  taken  in 
conjunction  with  the  atomic  heat  (which  was  assumed  to  be 
a  constant),  i.e.  the  product  of  the  specific  heat  into  the 
atomic  weight.  Dulong  and  Petit  at  once  went  on  to  apply 
their  law  to  this  problem,  and  came  to  the  conclusion — a  con- 
clusion which  was  later  recognised  as  correct — that  the  atomic 
weights  ascribed  by  Berzelius  to  several  of  the  metals  must 
be  halved. 

There  was,  however,  as  yet  no  pressing  reason  why  the 
latter,  on  a  dispassionate  review  of  Dulong  and  Petit's 

1  Ann.  Chim.  Phys.,  vol.  x.  p.  395  (1819). 


v  ISOMORPHISM  AND  THE  ATOMIC  THEORY  221 

results,  should  at  once  agree  to  this  demand.  That  those 
results  were  of  great  importance  for  theoretical  chemistry 
he  willingly  admitted,  but  he  maintained  that  they  had  not 
yet  been  proved  to  be  of  such  general  application  that  a  law 
could  be  formulated  from  them.  He  especially  opposed  any 
fundamental  alterations  of  his  own  atomic  weights,  as  he 
held  that,  if  this  were  done,  improbable  atomic  proportions 
would  have  to  be  assumed  for  the  compounds  of  some  of  the 
elements.  This  attitude  towards  the  Dulong-Petit  law  was 
only  gradually  abandoned  by  Berzelius,  after  further  proofs 
bearing  on  the  point  had  been  adduced. 


Influence  of  the  Doctrine  of  Isomorphism  upon  Atomic 
Weight  Determinations. 

After  the  founding  and  development  of  crystallography 
by  Rome  de  1'Isle  and  Hauy,  various  experimenters  had 
observed  that  substances  of  different  chemical  composition 
crystallise  together  in  one  and  the  same  crystalline  form. 
As  instances  of  this  may  be  mentioned  Gay-Lussac's  ob- 
servation that  crystals  of  potash  alum  grow  in  a  solution 
of  ammonia  alum,  while  still  retaining  their  original  crystal- 
line form,  and  Beudant's,  that  copper  vitriol  is  obtained 
in  the  same  form  as  iron  vitriol  when  a  small  quantity  of 
the  latter  is  added  to  a  solution  of  the  former,  and  so  on. 
But  neither  this  observation  nor  the  definite  statement 
by  Fuchs  upon  the  replacement  of  certain  substances  in 
minerals  by  others  [his  doctrine  of  "vicariating  con- 
stituents" (Vikariierenden  Bestandtheilen1)']  led  to  the  re- 
cognition of  the  relation  between  crystalline  form  and 
chemical  constitution. 

This  important  discovery  2  was  reserved  for  E.  Mitscher- 

1  This  means  substitution  without  any  accompanying  change  of  crystal- 
line form  ;  thus,  to  give  one  or  two  examples,  Fe"  can  replace  Ca",  and  Al'" 
can  replace  Fe'"  or  Cr'"  in  this  way. 

2  Berl.  Akad.  Abhandlungen  der  phys.  Klasse,  1818-19,  p.  426;  also 
Ann.  Chim.  Phys.,  vol.  xiv.  p.  172;  xix.  p.  350. 


222  THE  MODERN  CHEMICAL  PERIOD  CHAP, 

lich,1  who  explained  the  occurrence  of  isomorphous  crystals 
in  substances  of  different  nature  by  proving  that  they 
possessed  a  similar  chemical  composition.  Thus  he  found, 
on  examining  the  salts  of  phosphoric  and  arsenic  acids,  that 
only  those  of  analogous  composition  and  containing  equal 
amounts  of  water  of  crystallisation  were  isomorphous.  His 
subsequent  investigations  of  selenates  and  sulphates,  of  the 
isomorphism  of  magnesium,  and  zinc  oxides,  and  of  iron, 
chromium  and  aluminium  salts,  confirmed  the  intimate 
connection  existing  between  crystalline  form  and  chemical 
composition.  At  first,  after  making  those  observations, 
Mitscherlich  was  of  opinion  that  isomorphism  depended 
chiefly  on  the  number  of  the  elementary  particles  (in  the 
molecule),  but  he  soon  convinced  himself  that  the  chemical 
nature  of  these  had  also  to  do  with  it. 

Berzelius,  who  regarded  the  discovery  of  isomorphism  as 
"  the  most  important  since  the  establishment  of  the  doctrine 
of  chemical  proportions,"  endeavoured  to  arrive  at  the 
atomic  weights  of  the  elements  by  the  aid  of  isomorphous 
compounds.  For,  according  to  him,  isomorphism  meant 
similarity  in  atomic  constitution ;  chemists  only  required  to 
know  the  composition  of  one  compound  in  order  to  deduce 

1  Eilhard  Mitscherlich  was  born  in  1794  in  Oldenburg,  and  died  in  1863 
at  Berlin,  where  he  worked  as  Klaproth's  successor  in  the  University  from 
the  year  1821 ;  he  enriched  chemistry  by  beautiful  discoveries,  and  especi- 
ally advanced  it  very  greatly  in  the  physical  direction.  At  the  beginning 
of  his  career  he  devoted  himself  to  oriental  and  linguistic  studies,  only 
taking  up  the  natural  sciences  incidentally  ;  but,  after  circumstances  had 
compelled  him  to  turn  wholly  to  medicine  and  its  allied  subjects,  his 
intercourse  with  Berzelius,  to  whom  he  went  in  Stockholm  in  1819,  was 
decisive  as  to  his  future  course.  His  work  will  frequently  be  referred  to 
in  the  special  section  of  this  book  ;  but  mention  may  be  made  here  of 
his  important  investigation  of  manganic  and  permanganic  acids,  his  work 
upon  selenic  acid,  and  that  upon  benzene  and  its  derivatives.  His  success- 
ful attempts  to  prepare  minerals  artificially  and  his  varied  studies  in  geo- 
logical chemistry  give  further  proof  of  the  many-sidedness  of  the  man,  his 
greatest  achievement  of  all  being  the  discovery  of  isomorphism,  mentioned 
above.  His  Lehrbuch  der  Chemie  is  marked  by  originality  both  of  form 
and  contents.  For  an  account  of  Mitscherlich's  life  and  work,  see  Hofmann's 
Chemische  Erinnerungen,  etc.,  p.  30,  and  the  Erinnerung  an  Eilhard  Mit- 
scherlich ("  Memorial  of  Eilhard  Mitscherlich,"  by  Alexander  Mitscherlich, 
Berlin,  1894). 


v  THE  ATOMIC  THEORY  IN  1826  223 

that  of  the  remaining  isomorphous  ones  from  it.  The 
quantities  of  the  isomorphous  elements  which  replaced  one 
another,  referred  to  a  definite  unit, — say  oxygen  or  hydrogen 
— were  regarded  by  Berzelius  as  the  relative  atomic  weights. 
He  made  extensive  use  of  this  new  aid  to  confirm  the  cor- 
rectness of  his  atomic  weight  determinations. 

The  Atomic  Weight  System  of  Berzeliiis,  1821—1826. 

At  first,  in  1821,  Berzelius  did  not  consider  that  any 
change  [in  the  atomic  weights  was  called  for,  as  the  new 
facts  could  be  made  to  accord  with  his  determinations  and 
deductions.  But  five  years  later  he  resolved,  after  minute 
consideration,  upon  certain  modifications,  which  chiefly  con- 
sisted in  halving  the  atomic  weights  of  many  of  the  elements. 
The  grounds  which  weighed  with  him  in  this  he  set  forth  in 
a  conclusive  manner.1  What  mainly  necessitated  the  abandon- 
ment of  his  former  assumptions  was  the  composition  of  chromic 
oxide  and  chromic  acid.  The  amount  of  oxygen  in  the 
latter  (so  he  writes)  was  to  that  of  the  base  as  3:1  in 
neutral  salts,  whence  the  composition  CrO3  followed  for 
chromic  acid ;  while  in  chromic  oxide  the  proportion  was  as 
Cr2 : 03.  But,  in  order  to  concede  this  last,  he  had  to  give 
to  ferric  and  aluminic  oxides  (oxygen  compounds  iso- 
morphous with  and  capable  of  replacing  chromic  oxide)  the 
analogous  compositions  F203  and  A12O3,  and  to  their  metals, 
as  a  consequence,  only  half  as  large  atomic  weights  as  he 
had  previously  done.  Iron  protoxide  received  the  simplified 
formula  FeO,  and  the  oxides  of  magnesium,  zinc,  nickel, 
cobalt,  etc.,  which  were  isomorphous  with  it,  were  regarded 
as  similarly  constituted.  The  necessary  result  of  all  this 
was,  as  already  stated,  the  halving  of  the  atomic  weights 
hitherto  in  use,  so  that  these  now  conformed  to  Dulong 
and  Petit's  law.  With  the  atomic  weights  of  sodium, 
potassium  and  silver,  which  Berzelius  likewise  halved,  the 
circumstances  were  peculiar.  He  had  arrived  at  the  con- 
clusion, with  respect  to  basic  oxides,  that  the  strong  bases 
1  Pogg.  Ann.,  vol.  vii.  p.  397;  vol.  viii.  pp.  1,  177. 


224  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

(such  as  oxide  of  potassium)  contained  metal  and  oxygen  in 
the  proportion  1:1,  and  therefore  gave  potassium,  sodium 
and  silver  double  their  proper  atomic  weights  ;  for,  according 
to  our  present  ideas,  two  atoms  of  the  metal  are  combined  in 
these  bases  with  one  of  oxygen.  The  following  list  by  him 
of  the  atomic  weights  of  some  of  the  more  important  elements, 
with  hydrogen  as  the  unit,  shows  the  approximation  of  the 
numbers  to  those  in  use  to-day,  and  also  the  amendment l 
which  some  of  them  had  undergone  during  the  years  1818-26 
<cf.  table,  p.  218)— 

Carbon        .         12  "25      (12)  Lead  .      207 '4       (207) 


Oxygen 

16          (15-96) 

Mercury 

202-8       (200) 

Sulphur 

32-24      (32) 

Copper 

63-4      (63-3) 

Nitrogen     . 

14-18      (14) 

Iron 

54-4      (56) 

Chlorine 

35-47      (35-4) 

Sodium 

46-6       (23) 

Phosphorus 

31-4       <31) 

Potassium    . 

78-5      (39) 

Arsenic 

75-3       (75) 

Silver 

216-6      (108) 

The  figures  in  brackets  indicate  the  current  values. 

In  this  table  of  the  year  1826  we  find  for  the  first  time 
the  atomic  weights  of  nitrogen  and  chlorine  as  simple  sub- 
stances. Berzelius  held  longer  than  any  other  chemist  to 
his  assumption  that  they  contained  oxygen;  the  grounds 
which  necessitated  his  giving  up  this  hypothesis  are  entered 
into  further  on. 

If  we  review  these  efforts  of  Berzelius  at  determining 
the  atomic  weights  of  the  elements,  we  see  that  he  was 
mainly  guided,  in  the  case  of  non-volatile  bodies,  by  the 
composition  of  the  oxygen  compounds,  i.e.  by  the  deter- 
mination of  the  proportion  of  element  to  oxygen,  and 

1  Berzelius,  who  had  devoted  his  whole  energies  to  perfecting  analytical 
methods  and  amending  the  atomic  weight  numbers,  had  afterwards  to 
suffer  harsh  criticism  from  others  who,  by  reason  of  improvements  in  such 
methods,  attained  to  still  more  exact  results  ;  this  applied  in  an  especial 
degree  to  Dumas  (cf.  Ann.  Chem.,  vol.  xxxviii.  p.  141  et  seq.),  who  deter- 
mined the  equivalent  of  carbon  "with  every  imaginable  precaution,"  and 
found  its  value  to  be  6.  The  difference  between  this  number  and  that 
which  Berzelius  had  found,  viz.  6 '12,  caused  Dumas  to  utter  the  most  severe 
reproaches  against  the  great  master  of  analysis  (cf.  Berzelius'  mild  reply, 
Lehrb.  d.  Chem.,  vol.  iii.  p.  1165,  and  Liebig's  admirable  protest  against 
Dumas'  procedure,  Ann.  Chem.,  vol.  xxxviii.  p.  214  et  seq.}. 


DUMAS  AND  THE  ATOMIC  WEIGHTS 


then,  secondly,  by  the  doctrine  of  isomorphism,  while  to  the 
Dulong-Petit  law  he  allowed  only  a  slight  influence.  In 
those  cases  where  the  elements  or  simple  compounds  of 
the  elements  were  known  in  the  gaseous  state,  his  volume 
theory  came  in  as  a  help  towards  deducing  the  desired  values. 
Berzelius  still  held  fast  to  the  idea  that  the  amounts  of  the 
elements  contained  in  equal  gaseous  volumes  were  propor- 
tioned to  their  atomic  weights.  But  this  assumption  was 
soon  overthrown  by  the  remarkable  results  of  an  investiga- 
tion which  exercised  such  a  profound  influence  on  the  views 
of  many  chemists  that  it  must  be  described  at  this  point. 


Dumas'  Attempt  to  alter  the  Atomic  Weights. 

In  the  year  1827  a  young  chemist,  J.  B.  A.  Dumas  (cf. 
p.  272  et  seq.\  who  had  already  made  himself  favourably 
known  by  other  work,  published  a  research,1  the  great  merit 
of  which  lay  in  the  working-out  of  an  admirable  method  for 
the  determination  of  vapour  densities.  By  this  method  he 
succeeded  in  estimating  the  specific  gravity  of  the  vapours 
of  several  elements ;  and  the  relation  existing  between  these 
comparable  values  was,  according  to  Dumas  (who  took  up 
here  the  same  standpoint  as  Berzelius  in  his  volume  theory), 
that  of  the  relative  atomic  weights.  The  elements  which  he 
adduced  were  iodine  and  mercury,  and  to  these  he  added 
phosphorus  and  sulphur  a  little  later.2  The  result  of  this 
was  that  he  obtained  different  numerical  values  from  those 
assumed  by  Berzelius  for  the  atomic  weights  of  the  above 
elements,  which  had  been  held  for  a  year  past.  Taking  the 
atomic  weight  of  hydrogen  as  1,  and  that  of  oxygen  as  16 
(Berzelius'  numbers),  the  above  vapour  densities  gave  the 
values  123  for  iodine,  101  for  mercury,  6 2 '8  for  phosphorus, 
and  96  for  sulphur.  Further,  Mitscherlich  determined  the 
vapour  density  of  arsenic  in  1833,  and  calculated  from  this 
the  atomic  weight  150.  True,  these  numbers  bore  a  simple 

1  Ann.  Chim.  Phys.,  vol.  xxxiii.  p.  337. 

2  Ibid.,  vol.  xlix.  p.  210;  vol.  1.  p.  170. 


226  THE  MODERN  CHEMICAL  PERIOD  CHAP. 


relation  to  the  atomic  weights  of  Berzelius,  that  of  the  latter 
for  mercury  (200)  being  double,  those  for  phosphorus  and 
arsenic  (31  and  75)  half,  and  that  for  sulphur  (32)  one-third 
as  great  as  the  values  deduced  by  Dumas  from  his  vapour- 
density  determine '  ;ons,  and  held  by  him  to  be  the  correct 
ones.  The  result  ( :.  this  alteration  of  the  atomic  weights  by 
the  latter  was  great  confusion.  Wh'le  Berzelius  remained 
true  to  his  own  numbers,  holding  n  ^r  uric  oxide,  for  ex- 
ample, to  be  composed  of  mercury  and  oxyg^r  '^  atomic 
proportions,  Dumas  assumed  in  it  two  atoms  of  ury  to 
one  of  oxygen,  and  gave  it  the  composition  ana  formula 
which  Berzelius  ascribed  to  mercurous  oxide,  viz.  Hg2O. 
Again,  to  phosphuretted  hydrogen,  in  which  Berzelius  quite 
rightly  assumed  the  proportions  of  three  atoms  of  hydrogen 
to  one  of  phosphorus,  on  account  of  its  analogy  to  ammonia, 
Dumas  gave  twice  as  many  atoms  of  hydrogen,  and  therefore 
the  formula  PH6. 

In  making  the  above  alterations  Dumas'  procedure  was 
quite  without  method,  and  only  served  to  complicate  matters 
further.  He  drew  a  theoretical  distinction  between  smallest 
physical  and  chemical  particles,  bearing  Avogadro's  specu- 
lations in  mind;  but  this  attempt  at  separating  molecule 
from  atom  remained  not  only  unfruitful,  but  resulted  in  con- 
fusion. The  manner  in  which  Dumas  spoke  of  half  an  atom 
of  oxygen,  and  of  hydrochloric  acid  as  composed  of  half  atoms 
of  hydrogen  and  chlorine,  must  have  been  unintelligible  at 
that  time,1  and  was  sharply  criticised  by  Berzelius. 

A  comparison  of  the  atomic  weights  of  Berzelius  and 
Dumas  with  those  of  to-day  shows  us  how  fully  justified 
the  former  was  in  adhering  to  his  own,  which  he  had 
arrived  at  after  the  most  mature  consideration ;  Berzelius' 
values  have  proved  to  be  the  right  ones.  In  view  of  recent 
experience,  however,  he  became  more  cautious  in  the  use  of 
his  volume  theory,  and  from  henceforth  only  applied  the 
law — that  the  atomic  weights  of  the  elements  are  propor- 

1  If  Dumas  had  been  fully  acquainted  with  Avogadro's  ideas,  he  would 
have  expressed  himself  more  distinctly,  and  have  cleared  up  the  opposing 
points  which  remained  unsolved. 


MICHAEL  FARADAY  227 


tional  to  the  densities  of  their  vapours — to  the  permanent 


The    mighty   reform   which   Dumas    aimed    at    in   this 
section  of  theoretical  chemistry  remained  without  result ; 
and  there  is  justification  for  the  reproa^  brought  against 
him  by  many,  and  more  especially  by  Jferzelius,  of  having 
introduced  obscurity  ,\jnd  disorder  into1"  the  atomic  weight 
system  of  the  latter. <:  For  the  sake  of  an  unproven  hypo- 
thesis ™     t.^  neglected  the  most  striking  chemical  analogies 
(e.g.  th       :etween  ammonia  and  phosphuretted  hydrogen), 
and  frequently  confused  things  which  were  perfectly  clear. 
In  consequence  of  the  objections  which  he  raised  to  Berzelius' 
atomic  weights  of  the  elements,  the  distrust  of  these  latter 
by  contemporary  chemists  grew  in  extent,  so  that  we  find 
even  the  most  distinguished  investigators  like  Gay-Lussac 
•and  Liebig  doubting  whether  it  was  possible  to  determine 
the  relative  weights  of  the  atoms  with   certainty.      They 
would  have  satisfied  themselves  with  establishing  the  equi- 
valents, and  leaving  the  atomic  weights  quite  out  of  account. 
The  opposition  to  the  atomic  weight  system  of  Berzelius  was 
at  its  height  towards  the  end  of  the  third  and  beginning  of 
the  fourth  decade  of  the  century.     In  Germany,  especially, 
L.    Gmelin   advocated    the    establishment    of  the   simplest 
"  combining  weights";   but  the  certainty  of  being  able  to 
determine  the  true  equivalents  of  the  elements  was  not  in 
itself  sufficient,  although  Faraday's  discovery  of  the  electro- 
lytic law  in  1834  appeared  to  guarantee  a  solid  basis  for 
this  (see  second  paragraph  below). 

Michael  Faraday,  who  was  born  in  London  in  1794,  was 
endowed  with  such  exceptional  inclination  for  the  study  of 
the  natural  sciences  and  such  experimental  aptitude  that  he 
worked  his  way  up  from  humble  circumstances,  although  he 
had  received  no  systematic  training  previous  to  his  con- 
nection with  Davy.  Davy  immediately  recognised  the 
extraordinary  talents  of  the  youth,  and  got  him  to  assist  him 
in  his  work.  Faraday's  most  important  discoveries  belong 
to  the  domain  of  physics  (his  investigations  on  induction 

Q  2 


228  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

currents,  electro-magnetism  and  diamagnetism).  His  electro- 
lytic law,  which  was' of  such  supreme  importance  for  the  electro- 
chemical theory,  is  touched  upon  below.  He  made  himself 
known  to  the  chemical  world  more  particularly  by  his 
beautiful  investigations  on  the  liquefaction  of  gases,  by  his 
work  on  the  hydrocarbons  from  oil-gas  (when  he  proved  the 
isomerism  of  butylene  with  ethylene),  and  by  that  on  the 
chlorides  of  carbon.  He  was  one  of  the  earliest  to  promote 
the  study  of  physical  chemistry,  which  owed  to  him  its  first 
great  advance  since  the  investigations  of  Dulong  and  Petit 
on  specific  heat,  and  those  of  Mitscherlich  on  isomorphism. 
The  results  of  most  of  his  experimental  work  were  published 
in  the  Philosophical  Transactions,  but  some  in  Poggendorff's 
Annalen  and  other  journals.  During  the  greater  part  of 
his  life  (he  died  in  1867)  he  worked  at  the  Royal  Institu- 
tion, in  which  he  became  professor  in  1828.  In  addition  to. 
his  wonderful  gifts  as  an  investigator,  Faraday  possessed  in 
an  exceptional  degree  the  power  of  clear  and  pleasant  ex- 
position ;  the  memory  of  his  "  Lectures  to  Children  "  at  the 
Royal  Institution  still  survives  (see  his  delightful  little  book, 
The  Chemical  History  of  a  Candle).  In  private  life  the 
simplicity  and  amiability  of  his  character  made  him  greatly 
beloved.1 

Faraday  made  the  memorable  observation  (see  above)  that 
the  same  galvanic  current  decomposed  electrolytes,  e.g.  water, 
hydrochloric  acid  and  metallic  chlorides,  in  such  a  manner 
that  equivalent  amounts  of  hydrogen  or  metal  were  separated 
at  the  negative  pole,  and  the  corresponding  quantities  of 
oxygen  or  chlorine  at  the  positive.2  He  grouped  those  facts 
together  under  the  title  of  "The  Law  of  definite  Electrolytic 
Action."  In  the  determination  of  electro-chemical  equiva- 
lents he  saw  a  sure  auxiliary  means  for  fixing  chemical 
atomic  weights  in  doubtful  cases.  Berzelius,  however,  did 
not  recognise  any  necessity  in  this  case  either  for  departing 

1  A  pleasant  account  of  his  life  is  given  by  Thorpe  in  his  Essays,  p.  142 
et  seq. ,  as  a  critique  upon  Bence  Jones's  Life  and  Letters  of  Faraday. 

2  Phil.  Trans,  for  1834,  or  Pogg.  Ann.,  vol.  xxxiii.  p.  301. 


v  DAVY'S  ELECTRO-CHEMICAL  THEORY  229 

from  his  own  atomic  weights,  but — obviously  because  of  a 
misconception — disputed  the  correctness  of  the  numbers 
obtained  by  the  electrolytic  method. 

The  time  for  a  clear  grasp  of  the  terms  equivalent,  atom 
and  molecide,  and  for  drawing  a  sharp  distinction  between 
these,  was  not  yet  come.  Berzelius  was  therefore  perfectly 
justified  in  adhering  to  his  relative  atomic  weights,  the  best 
proof  for  which  was  to  be  furnished  later.,  But,  as  already 
remarked,  he  now  only  made  use  of  his  volume-theory  in  a 
greatly  modified  degree,  in  consequence  of  the  results  obtained 
by  Dumas  and  Mitscherlich.  With  regard  to  vapours,  he 
foresaw  (in  1835)  the  possibility  of  the  relation  between 
volume  and  atomic  weight  being  a  variable  one  (he  drew  a 
distinction  between  gases  and  vapours,  and  only  strictly 
applied  the  law  of  volumes  to  the  latter). 

How,  in  the  course  of  the  succeeding  decades,  Gmelin's 
combining  weights  became  gradually  replaced  by  the  atomic 
weights  now  in  use  (most  of  which  had  been  brought  forward 
by  Berzelius),  will  be  detailed  later  on.  The  reader's  atten- 
tion will  be  chiefly  directed  in  the  following  sections  to 
Berzelius'  energy  in  a  speculative  direction,  as  shown  in  the 
setting  up  of  his  dualistic  system  ;  this  last  was  the  fruit  of 
an  electro-chemical  theory  which,  along  with  Davy's,  now 
falls  to  be  briefly  considered. 


The  Electro-Chemical  Theories  of  Davy  and  Berzdim. 

The  perception  that  a  close  relation  existed  between 
electrical  force  and  chemical  reaction  spread  rapidly  at  ttie 
beginning  of.  the  century,  after  the  decomposition  of  water 
into  its  constituents  by  the  galvanic  current  had  been- 
proved  by  Nicholson  and  Carlisle  (in  1800),  and  that  of  salts 
into  their  bases  and  acids  by  Berzelius  and  Hisinger  (in  1803). 
The  first  fruit  of  the  many  and  varied  observations  on  .the 
action  of  the  current  on  chemical  compounds,  and  on  the 
accompanying  electromotive  force  in  chemical  reactions,  was 


230  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

Davy's  Electro-Chemical  Theory,1  which  he  thought  that  he 
had  founded  on  a  firm  basis  by  his  ingeniously  devised 
researches,  begun  in  the  year  1800.  He  took  as  his 
starting-point  the  proved  experimental  fact  that  different 
substances,  capable  of  combining  chemically  with  one 
another,  e.g.  copper  and  sulphur,  became  oppositely  electri- 
fied upon  contact  when  insulated.  Heating  intensified  the 
resulting  difference  of  potential,  until  it  vanished  in 
consequence  of  the  chemical  combination  of  the  substances. 
This  latter,  Davy  then  reasoned,  is  simultaneous  with  the 
equalisation  of  the  potentials.  The  greater  the  difference 
between  these  before  combination,  the  greater  must  be 
the  chemical  affinity  of  the  different  substances  for  one 
another.  By  the  addition  of  electricity  to  the  compounds > 
their  constituents  receive  the  same  electric  polarities  which 
they  possessed  before  combination ;  the  positive  constituents 
go  to  the  negative  pole,  and  the  negative  ones  to  the 
positive. 

Davy  inclined  to  the  assumption  that  electrical  processes 
and  the  phenomena  of  chemical  affinity  arose  from  a  common 
cause.  His  electro-chemical  theory  was  characterised  by  the 
axiom  that  the  small  particles  of  substances  which  have  an 
affinity  for  one  another  only  become  oppositely  electrified 
upon  contact.  But  later  researches,  especially  those  of 
Berzelius,  led  to  the  abandonment  of  this  principle,  while, 
otherwise,  many  of  Davy's  original  icjeas  were  retained. 

Berzelius  brought  forward  the  main  outlines  of  his 
electro-chemical  theory  in  1812,2  after  having  already  at 
various  times  expressed  his  views  upon  the  indissolubility  of 
chemical  and  electrical  processes,  upon  combustion  as  an 
electro-chemical  phenomenon,  and  on  the  probability  of  the 
small  particles  being  polarised.  But  the  theory  as  a  whole, 
with  its  far-reaching  conclusions,  was  first  published  in  his 
Versuch  uber  die  Theorie  der  Chemischen  Proportionen,  etc., 

1  Phil.  Trans.,  1807,  p.  1  ;  cf.  also  his  Elements  of  Chemical  Philosophy. 
Die  Electrochemischen  Untersuchungem  Davys,  with  Annotations,  constitutes 
No.  45  of  W.  Ostwald's  Klassiker. 

2  Schweigger's  Journ.,  vol.  vi.  p.  119. 


v  BERZELIUS'  ELECTRO-CHEMICAL  THEORY  231 

already  mentioned  at  p.  213.  In  this  we  see  clearly  how  he 
deduced  his  theory  from  facts,  and  then  how,  from  the 
standpoint  so  obtained,  he  succeeded  in  penetrating  and 
dominating  with  it  the  whole  domain  of  chemistry.  His 
doctrine,  developed  in  this  way  from  the  electro-chemical 
point  of  view,  continued  the  prevailing  one  for  the  next 
twenty  years,  until  it  had  to  yield  to  the  pressure  of  facts 
with  which  it  could  not  be  reconciled. 

Berzelius  started  with  the  primary  assumption  that  the 
atoms  of  elements  were  in  themselves  electric ;  electric 
polarity,  therefore,  was  an  essential  property  of  these 
smallest  particles,  which  further  possessed  at  least  two 
poles,  whose  quantities  of  electricity  were  in  most  cases 
different,  so  that  either  positive  or  negative  electricity 
predominated  in  the  particle  as  a  whole.  Thus  elements 
were  divided  into  positive  and  negative,  according  to  which- 
ever of  these  electricities  prevailed ;  and  this  last  point  was 
easily  solved  by  noting  whether  the  element  in  question 
was  separated  at  the  negative  or  positive  pole  of  the  gal- 
vanic battery  upon  electrolysis.1  In  like  manner  Berzelius 
assumed  a  polarity  for  compounds  as  well  as  for  elements, 
although,  in  consequence  of  the  neutralisation  of  the 
opposite  electricities  by  one  another  in  the  formation  of 
compounds,  this  polarity  was  thereby  weakened.  The 
intensity  of  the  polarity  was,  according  to  him,  a  measure  of 
the  excess  of  one  or  the  other  kind  of  electricity.  The 
dissimilar  polar  intensity  of  the  small  particles  was  regarded 
as  the  cause  of  their  various  affinities  (der  verschiedenen 
Affinitatswirkungeri).  And,  as  the  forces  of  affinity  were 
found  to  be  dependent  on  the  temperature,  so  polarity  was 
also  to  be  regarded  as  a  function  of  heat. 

Chemical  combination  of  the  elements  or  compounds 
consisted,  according  to  Berzelius,  in  the  attraction  of  the 
dissimilar  poles  of  the  small  particles,  and  in  the  consequent 
neutralisation  of  the  different  electricities.  If  positive 

1  At  first  Berzelius  designated  the  elements  after  the  poles  at  which 
they  were  separated,  i.e.  he  called  the  metals  negative,  and  the  metalloids 
positive. 


232  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

electricity  predominated  in  the  original  substance,  then  an 
electro-positive  compound  resulted,  and  vice  versa.  If  the 
electricities  neutralised  one  another,  then  an  electrically 
indifferent  product  was  the  result.  Oxygen,  as  the  most 
electro-negative  element,  served  Berzelius  here  (as  it  had 
done  in  his  atomic  weight  estimations)  as  the  standard  by 
which  to  determine  the  kind  of  polarity  of  the^  various 
elements.  Those  elements  which  yielded  basic  compounds 
with  oxygen,  even  although  only  their  lowest  oxides  were 
basic,  were  classed  as  electro-positive,  and  those  whose 
oxides  were  acids  as  electro-negative.  Following  this 
principle  he  arranged  the  simple  substances  in  a  series,  in 
which  oxygen  as  the  first  member  was  followed  by  the  other 
metalloids,  while  hydrogen  formed  the  bridge  between  the 
latter  and  the  metals,  the  whole  ending  with  sodium  and 
potassium.  In  referring  to  this,  Berzelius  frequently  stated 
that  many  elements  which  were  positively  polar  with  regard 
to  some  were  negatively  polar  with  regard  to  others,  e.g. 
sulphur  was  positive  to  oxygen,  but  negative  to  the  metals 
and  hydrogen, — and  so  on.  Oxygen  alone  he  held  to%& 
an  absolutely  negative  element,  because  in  no  case  did  it 
behave  as  a  positive  one  with  respect  to  any  other. 

By  the  aid  of  such  conceptions,  which  formed  the 
substance  of  his  electro-chemical  theory,  Berzelius  was  en- 
abled to  give  a  satisfactory  interpretation  of  the  facts  which 
were  at  that  time  considered  of  greatest  moment.  The  electro- 
lytic processes,  i.e.  the  separation  of  the  positive  and  negative 
constituents  of  compounds  at  the  negative  and  positive  poles 
respectively,  were  explained  in  a  simple  manner  by  the 
assumption  that  the  galvanic  current  reinvested  the  small 
particles  of  compound  bodies  with  their  original  polarity. 
The  many  and  various  manifestations  of  affinity  could  in 
this  way  be  referred  back  to  a  common  cause. 

Proceeding  from  this  one  hypothesis, — that  electric 
polarity  was  a  property  of  the  atoms  of  substances, — Berzelius 
was  able  to  bring  y  light  and  order  into  the  province  of 
inorganic  chemistry,  which  was  at  that  time  (1819)  almost 
the  only  branch  of  the  science  to  be  considered.  His 


v  THE  DUALISTIC  SYSTEM  OF  BERZELIUS  233 

electro-chemical  theory  led  him,  in  the  first  instance,  to  a 
perfectly  definite  conception  of  the  "  constitution  or  rational 
composition  of  chemical  compounds,"  and  then  to  a  nomen- 
clature and  corresponding  system  of  formulae  developed 
from  this.  His  efforts  in  this  direction  were  crowned  with 
the  greatest  success.  Even  at  the  present  day  we  cannot 
do  without  the  chemical  language  which  he  introduced, 
although,  on  the  other  hand,  his  dualistic  views  on  the  com- 
position of  chemical  compounds  have  not  survived  so  long. 
He  was,  however,  the  first  to  draw  a  precise  distinction 
between  the  empirical  and  rational  composition  of  chemical 
compounds.  The  constitution  of  the  latter  was,  according  to 
him,  arrived  at  by  investigating  their  proximate  constituents 
(such  being,  for  instance,  Cu2O,  CuO,  and  (C2H5)2O  in  copper 
salts,  ethers,  etc.),  and  this  task  he  regarded  as  one  of  the 
most  important  which  falls  to  the  lot  of  the  chemist.  He 
himself  devoted  his  whole  energies  to  its  solution,  the 
electro-chemical  theory  serving  as  a  means  whereby  he 
might  attain  to  this  great  end. 

The  Dualistic  System  of  Berzelius. 

The  necessary  consequence  of  the  electro-chemical  view- 
was  the  assumption  that  every  compound  body  consisted  of 
two  parts,  which  were  electrically  different;  without  such 
difference  a  chemical  compound  could  not  be  formed. 
Further,  the  constitution  of  the  latter  was  known  when  its 
positive  and  negative  constituents  were  demonstrated.  It 
was  again  compounds  of  oxygen, — acids,  bases  and  salts, — 
by  means  of  which  Berzelius  developed  this,  his  dualistic 
doctrine.  The  elements  which  were  combined  with  oxygen 
were  the  positive  constituents,  e.g.  the  metals  in  oxides, 
and  the  metalloids  in  acids.  The  electro-chemical  antithesis 
was  illustrated  by  the  following  formulae  : — 

+-  +- 

FeO  BaO 

Iron  Barium  Sulphuric  Carbonic 

protoxide  oxide  acid  acid. 


234  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

The  anhydrous  bases  are  the  positive  constituents  of  salts, 
and  the  acids  —  in  which  negative  polarity  predominates  — 
the  negative  ones,  as  is  shown  by  the  formulae  — 

+   -  + 

BaO-S03  ZNOC02. 

Berzelius  considered  that  the  strongest  proof  of  the  correct- 
ness of  this  theory  lay  in  the  electrolytic  decomposition  of 
compounds,  especially  of  salts,  into  the  above-mentioned  two 
portions,  which  were  separated  at  the  poles  of  opposite 
electricity  to  their  own.  He  further  sought  to  explain  the 
composition  of  double  salts  according  to  the  dualistic 
hypothesis,  giving,  for  example,  sulphate  of  potash  as  the 
positive,  and  sulphate  of  alumina  as  the  negative  constituent 
of  alum. 

In  the  year  1819,  when  Berzelius  published  a  detailed 
exposition  of  his  electro-chemical  theory,  he  was  convinced 
that  all  acids  contained  oxygen.  In  his  view  water  played 
in  hydrated  acids  the  part  of  a  weak  electro-positive  con- 
stituent, and  in  metallic  hydroxides  that  of  a  weak  electro- 
negative one  ;  the  hydrates  of  sulphuric  acid  and  of  cupric 
oxide  therefore  received  the  formulae  — 


H2OS03  CuO-H20. 

The  binary  conception,  which  had  already  been  applied  by 
Lavoisier  to  acids  and  bases,  and  even  by  Rouelle  to  salts, 
thus  received  the  strongest  support  from  the  electro-chemical 
theory,  and  was  materially  developed  in  consequence.  It 
will  be  shown  in  the  next  section  how  Berzelius  was  obliged 
to  give  up  Lavoisier's  one-sided  theory  of  the  oxygen  acids. 

The  efforts  of  Berzelius  to  introduce  a  rational  and 
generally  applicable  nomenclature  go  back  to  the  year 
181  1.1  His  nomenclature  is  a  continuation  of  that  of 
Lavoisier,  de  Morveau  and  Berthollet,  which  however  he 
greatly  extended  and  amplified,  his  first  efforts  in  this 
direction  having  been  published  in  the  Versuch  iller  die 

1  Journ.  de  Phys.,  vol.  Ixxiii.  p.  257. 


v  BERZELIUS'  SYSTEM  OF  NOTATION  235 

Theorie  der  Chemischen  Proportioned,  etc.,  already  frequently 
mentioned.  The  division  of  the  elements  into  metalloids 
and  metals,  according  to  their  electro-chemical  character; 
that  of  the  positive  oxygen  compounds  into  suboxides, 
oxides  and  peroxides ;  and  the  corresponding  division  of  the 
acids  (which  were  designated  according  to  their  degree  of 
oxidation),  have  been  found  to  be  so  convenient  that  only 
very  trifling  alterations  have  had  to  be  made  in  them. 
In  like  manner  he  designated  the  chlorine  compounds 
corresponding  to  the  oxides  by  adding  different  final 
syllables  or  prefixes,  e.g.  sub-chloride  (Chlorur),  chloride,  per- 
chloride,  etc.  In  the  nomenclature  of  the  oxygen  salts  the 
name  of  the  acid  constituent  preceded  that  of  the  basic,  e.g. 
sulphate  of  oxide  of  copper. 

He  also  endeavoured  to  apply  similar  principles  in 
naming  organic  compounds,  whose  constitution  had  been 
determined  on  his  own  lines.  But  the  time  had  not  yet 
come  when  it  was  possible  to  devise  a  rational  nomenclature 
for  these. 

Berzelius  next  established  a  system  of  chemical  notation,1 
connected  in  the  most  intimate  possible  manner  with  his 
chemical  nomenclature,  which  had  given  expression  in  clear 
language  to  the  electro-chemical  views  on  the  composition 
of  substances ;  this  notation  was  to  attain  the  same  end  in  a 
more  concise  manner.  In  doing  this  he  rendered  an  immense 
service,  for  it  thus  became  possible,  by  the  aid  of  simple 
symbols,  not  merely  to  express  the  composition  of  chemical 
compounds,  but  to  picture  even  complicated  reactions  in  an 
easily  intelligible  manner.  He  gave  to  each  element  a  symbol, 
which  was  usually  the  first  or  the  first  two  letters  of  its  Latin 
name,  less  often  of  the  Greek  one ;  thus  the  symbol  jET stands 
for  hydrogen  (hydrogenium),  S  for  sulphur  (sulphur),  0  for 
oxygen  (oxygenium),  C  for  carbon  (carlo),  Ag  for  silver 
(argentum),  Hg  for  mercury  (hydrargyrum),  and  so  on. 
These  symbols  denote  at  the  same  time  the  atomic  weights 
of  the  elements  in  question,  referred  to  a  definite  unit. 

1  Cf.  particularly  the  Versuch  uber  die  Theorie  der  Chemischen  Propor- 
tionen,  p.  116,  et  seq. 


236  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

By  placing  the  symbols  alongside  of  one  another,  and 
adding  a  figure  to  indicate  the  number l  of  atoms  when  the 
latter  amounted  to  more  than  one,  the  formulae  of  chemical 
compounds  was  obtained :  e.g.  H20  for  water,  S02  for 
sulphurous  acid,  C02  for  carbonic  acid,  Na2OC02  for 
carbonate  of  soda,  etc. 

What  an  advance  upon  Dalton's  attempts  towards  the 
same  end,  his  figures  only  serving  to  illustrate  the  simplest 
of  compound  substances  !  Dalton's  notation  was  soon  for- 
gotten, never  having  indeed  met  with  general  approval, 
while  that  of  Berzelius  became  indispensable  to  chemists, 
and  still  remains  so. 

Berzelius  attached  a  special  meaning  to  the  symbols 
with  a  bar  drawn  across  them,  these  being  employed  by  him 
to  indicate  that  the  elements  in  question  were  in  the  state 
of  double  atoms,  or,  as  he  put  it,2  that  "  they  remain 
c  onnected  together ; " 3  this  applied,  for  example,  to  the 
hydrogen  in  water,  JtO,  to  the  chlorine  in  anhydrous  per- 
chloric acid,-G107J  and  to  the  iron  in  the  sesquioxide,:Fe03. 
This  mode  of  notation,  which  had  exceedingly  bad  results, 
arose  from  Berzelius  taking  oxygen  as  his  unit,  and  using 
it  as  the  standard  for  the  saturation-capacities  of  other  ele- 
ments.4 He  was  thus  led  to  the  assumption  of  the  double 
atom  constituting  a  chemical  unit,  and  the  above  symbols 
with  bars  served  him  to  give  expression  to  this ;  at  a  later 
period,  however,  he  gave  up  using  them,  and  reverted  to  the 
true  atomic  weights.  There  were  nevertheless  many  chemists 
who  would  not  concur  in  this  view,  cherished  by  Berzelius 
for  a  time,  of  the  atoms  of  certain  elements  being  only 
present  as  pairs  in  compounds ;  these  chemists  assumed 

1  Berzelius  at  first  denoted  the  number  of  oxygen  atoms  by  dots,  and 
that  of  sulphur  atoms  by  commas,  e.g.  calcium  oxide,  Ca  ;  iron  bisulphide, 
Fe  ;  this  system  remained  longest  in  use  among  mineralogists. 

2  Lehrb.  d.  Chemie,  fifth  edition,  vol.  i.  p.  121. 

3  "  .    .    .  dass  sie  zusammenhdngend  bleiben. " 

4  Berzelius  designated  oxygen  as  "the  measure  of  the  relative  weight 
according  to  which  an  element  entered  into  combination  "  (dass  Mass  der 
relativen   Gewichtsmenge,   nach   ivelcher   ein   Grundstoff  vorzugsweise    Ver- 
bindiingen  eingeht). 


v  MANIFESTATIONS  AGAINST  DUALISM  237 

simple  instead  of  double  atoms  and,  with  this,  equivalents 
instead  of  atoms.  Blomstrand,  who  has  shown  in  his  admi- 
rable work,  Die  Chemie  der  Jetztzeit  ("  The  Chemistry  of  the 
Present  Time  "),  the  close  connection  which  exists  between 
the  views  of  Berzelius  and  those  held  to-day,  describes  the 
results  of  the  system  of  notation  and  of  the  views  just  men- 
tioned in  the  following  eloquent  words :  "  This  erroneous 
conception  was  without  doubt  the  almost  sole  reason  why 
Berzelius'  atomic  theory  found  so  little  acceptance ;  it 
acted  like  a  restraining  curb  in  preventing  the  free  develop- 
ment of  the  latter,  and  led  little  by  little  to  a  peculiar 
confusion  with  regard  to  the  fundamental  principles  of 
chemistry,  the  distinction  between  atomic  weight  and 
equivalent  becoming  by  degrees  nearly  effaced,  until  at  last 
the  volume-atomic  weights  and  the  whole  atomic  theory 
of  Berzelius  were  almost  forgotten  by  the  great  majority  of 
the  chemists  of  his  school." 

Like  every  innovation,  the  admirable  system  of  notation 
which  Berzelius  recommended  met  with  most  violent  opposi- 
tion from  many  chemists,  especially  in  England.  People 
spoke  of  "  abominable  symbols  "  which  were  more  calculated 
to  introduce  confusion  than  clearness. 

In  1820,  then,  the  dualistic  system,  with  the  electro- 
chemical theory  for  its  basis,  stood  fully  equipped,  and  was 
soon  utilised  by  the  vast  majority  of  chemists  as  a  guide  in 
the  confusion  which  resulted  from  the  daily  accumulation 
of  new  facts.  Berzelius  further  attempted  to  apply  the 
dualistic  hypothesis  in  organic  chemistry,  which,  from  the 
third  decade  of  the  century,  was  more  and  more  attracting 
the  attention  of  chemists.  How  it  came  into  collision  here 
with  the  unitary  theory,  and  had  finally  to  succumb  to  the 
latter,  will  be  described  further  on. 

Manifestations  against  Dualism — Theory  of  the  Hydrogen 
and  of  the  Poll/basic  Acids. 

The  tenet  which  was  set  up  by  Lavoisier,  and  which 
Berzelius  defended  with  all  his  power, — that  the  character 


238  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

of  acids  depends  upon  their  containing  oxygen,  and  that 
consequently  this  element  is  an  unfailing  constituent  of  their 
salts, — this  theory  of  the  oxygen  acids  was  already  greatly 
shaken  towards  the  end  of  the  first  decade  of  the  present 
century,  and  was  abandoned  by  most  chemists  during  the 
second,  as  a  knowledge  of  facts  opposed  to  it  increased. 
Finally  Berzelius,  who  remained  longest  true  to  the  older 
idea,  convinced  himself  of  the  existence  of  acids  free  from 
oxygen.  The  gradual  transformation  of  chemistry  which 
resulted  from  the  setting  aside  of  this  dogma  (that  all  acids 
contained  oxygen)  was  a  thorough  one,  for  the  unadaptable 
dualistic  system  was  thereby  battled  with,  and  its  fall  pre- 
pared for. 

In  order  to  thoroughly  understand  this  change  of  views, 
it  is  necessary  that  a  clear  light  should  be  thrown  upon  the 
facts  which  brought  it  about.  The  discovery  of  the  alkali 
metals  by  Davy  and  the  allied  researches  which  he  made 
on  the  nature  of  chlorine  must  be  regarded  as  the  starting- 
points  from  which  the  light  of  the  new  knowledge  radiated. 
Before  Davy,  who  had  recognised  in  the  galvanic  current 
a  powerful  means  for  decomposing  chemical  compounds, 
isolated  potassium  and  sodium  from  the  alkalies  by  its  aid,1 
the  latter  were  regarded  as  undecomposable ;  and  this 
even  although,  from  the  time  of  Lavoisier,  it  was  con- 
sidered probable  that  they  were  constituted  analogously  to 
the  metallic  oxides,  and  were  therefore  oxygen  compounds. 
This  view  was  also  held  at  an  even  earlier  date 
by  Scheele,  as  his  recently  published  journals  show. 
The  many  fruitless  experiments  which  Davy  had  made  with 
the  alkalies  in  solution  were  finally  crowned  with  success 
when  he  exposed  these  substances,  only  slightly  moistened, 
to  the  action  of  a  strong  current.  His  correct  assumption, 
that  the  metals  separated  at  the  negative  pole  were  true 
elements,  did  not  indeed  find  immediate  acceptance  ;  in  fact 
he  himself  was  temporarily  in  doubt  as  to  whether  they  did 
not  contain  hydrogen,  especially  after  the  presence  of  the 
latter  •  element  in  the  alkalies  had  been  proved  by  Gay- 
1  Phil  Tram,  for  1808,  p.  1. 


v  DAVY'S  DISCOVERY  OF  THE  ALKALI  METALS          239 

Lussac  and  Thenard,  both  of  whom  from  this  point  took  an 
active  part,  by  their  researches,1  in  the  solution  of  the 
problems  in  question.  The  idea  that  the  alkali  metals 
might  be  hydrogen  compounds  had  crept  in  from  an  analogy 
drawn  between  them  and  ammonia ;  at  that  time  the  latter 
was  supposed  to  contain  oxygen,  which  was  withdrawn  from 
it  in  the  formation  of  ammonium  amalgam.  The  erroneous 
conclusion  that  the  above  metals  contained  Jhydrogen,  which 
resulted  from  this  false  interpretation,  was  however  put 
right  by  Gay-Lussac  and  Thenard,  who  explained  the  point 
correctly.  (Cf.  "below.  It  was  mainly  upon  the  three  re- 
actions specified  towards  the  end  of  the  next  paragraph  that 
Gay-Lussac  and  Thenard  relied  here ;  from  these  the 
elementary  nature  of  the  alkali  metals,  as  well  as  of  chlorine, 
followed.)  Consequently,  from  the  year  1811,  potassium 
and  sodium  were  regarded  as  metals  and  therefore  as 
elements. 

With  the  elucidation  of  the  above  points,  the  question 
as  to  whether  chlorine  was  really  a  compound  substance, 
and  not  rather  a  simple  one,  rapidly  approached  its  solution. 
According  to  the  assumption  of  Berthollet  and  Lavoisier, 
hydrochloric  acid  contained  oxygen  combined  with  a  radical 
muriatique,  and  the  chlorine  which  was  liberated  by  its 
oxidation  was  looked  upon  as  oxidised  hydrochloric  acid, 
and  was  therefore  named  so  (oxy -muriatic  acid).  At  the 
time  when  Davy2  and  Gay-Lussac  and  Thenard3  began 
their  memorable  investigations,  hydrochloric  acid  gas  was 
generally  held  to  contain  chemically  combined  water.  But 
even  with  the  most  powerful  reducing  agents  these  chemists 
were  unable  to  prove  the  presence  of  oxygen  either  in  per- 
fectly dry  hydrochloric  acid  or  chlorine,  and  this  of  itself 
made  them  incline  to  the  belief  that  chlorine  was  an  element 
and  hydrochloric  acid  its  hydrogen  compound.  The  idea, 
however,  of  oxygen  being  a  necessary  constituent  of  all  acids 
had  taken  such  firm  root  that  numerous  fresh  investigations 

1  Ann.  de  Chimie,  vol.  Ivi.  p.  205 ;  vol.  Ixv.  p.  325. 

2  Phil.  Trans,  for  1810,  p.  231. 

3  Memoires  de  la  Societed'Arwuil,  vol.  ii.  p.  339. 


240  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

were  required  before  it  could  be  got  rid  of.  The  most 
important  of  the  observations  which  led  to  this  were  the 
following  : — Hydrogen  and  chlorine  unite  to  form  anhydrous 
hydrochloric  acid,  which  is  decomposed  by  sodium  with  the 
liberation  of  half  its  volume  of  hydrogen  and  the  formation 
of  sodium  chloride,  while  the  latter  also  results  directly  from 
the  combination  of  sodium  and  chlorine. 

Upon  the  ground  of  those  facts  Davy  was  the  first  to 
express  the  distinct  opinion  that  chlorine  was  an  element, 
suggesting  for  it  the  name1  by  which  it  has  since  been 
known.  At  first  Gay-Lussac  and  Thenard  had  misgivings 
about  agreeing  to  this,  fearing  to  disturb  the  uniformity  of 
the  chemical  system.  But,  after  the  former  had  completed 
his  famous  investigation  upon  iodine,  both  he  and  Thenard, 
as  well  as  other  French  chemists,  were  obliged  to  concur  in 
Davy's  view.  Iodine  and  fluorine  now  received  a  place 
among  the  elements,  next  to  their  analogue  chlorine. 

Berzelius  did  not  allow  himself  to  be  convinced  all  at 
once  of  the  necessity  for  this  thorough  innovation,  which 
entailed  the  abandonment  of  the  theory  of  oxygen  acids. 
The  unity  of  chemical  theory  went  with  him  before  every- 
thing else ;  he  saw  in  the  projected  reform  an  overthrow  of 
the  principles  which  had  governed  the  older  chemical  system. 
After  having  given  eloquent  expression  to  his  ideas  on  the 
subject  in  letters  to  Marcet,  Gilbert,  Thomson  and  others, 
he  collected  together  the  arguments  in  favour  of  the  older 
view  in  a  treatise 2  entitled :  Versucli  einer  Vergleicliung 
der  d/teren  und  der  neueren  Meinungen  uber  die  Natur  der 
oxydierten  Salzaure,  zur  Beurtheilung  des  Vorzuges  der  einen 
v&r  der  anderen  ("  An  attempt  to  compare  the  Old  and  New 
Opinions  with  regard  to  the  Nature  of  the  Oxidised  Muri- 
atic Acid,  and  to  estimate  the  Advantages  of  the  One  over 
the  Other").  His  standpoint  is  clearly  set  forth  in  the 
following  words  :  "  I  decline  to  give  in  my  adhesion  to  the 
new  doctrine  until  it  has  been  made  perfectly  consistent 
and  uniform  with  the  new  theoretical  science  which  its 

1  Phil.  Trails,  for  1811,  p.  1. 

2  Gilbert's  Annahn,  vol.  1.  p.  356. 


v  THEORY  OF  THE  HYDROGEN  ACIDS  241 

authors  claim  to  have  built  upon  the  ruins  of  the  chemical 
theory  that  they  have  demolished.  For  I  demand  un- 
compromisingly from  any  chemical  theorem  that  it  shall 
agree  with  the  rest  of  chemical  theory  and  be  capable  of 
incorporation  in  it ;  if  this  be  not  the  case,  then  I  must 
reject  it,  unless,  indeed,  the  evidence  in  its  favour  is  of  such 
an  incontrovertible  nature  as  to  necessitate  a  revolution  in 
the  chemical  theory  with  which  it  is  at  variance." 

In  one  point,  however,  Berzelius  soon  gave  up  the 
opinion  that  every  acid  must  contain  oxygen,  by  recognising 
sulphuretted  and  telluretted  hydrogens  as  hydrogen  acids ; 
this  latter  nomenclature  (hydracides)  was  first  made  use  of  by 
Gay-Lussac.  At  that  time  Berzelius  still  held  that  oxygen 
was  present  in  chlorine,  iodine  and  fluorine,  even  after  Gay- 
Lussac's  famous  research  upon  the  salts  of  hydrocyanic  acid 
had  proved  that  these  last  were  free  from  it.  It  was  only  after 
he  had  been  able  to  make  the  results  of  his  own  investigations 
on  ferro-cyanogen  and  sulpho-cyanogen  compounds  agree 
with  the  theory  of  non-oxygenated  acids  that  he  resolved  to 
include  chlorine  and  iodine  among  the  elements.  About 
the  same  time  (1820)  he  gave  up  the  idea  that  nitrogen 
and  ammonia  contained  oxygen ;  but  it  was  not  until  1825 
that  he  abandoned  what  remained  of  his  old  view,  by 
including  fluorine  with  chlorine  and  iodine  among  the  salt- 
forming  elements  or  halogens ; *  he  drew  a  sharp  distinction 
between  the  haloid  salts,  i.e.  the  salts  produced  by  the 
combination  of  the  above  elements  with  the  metals,  and  the 
amphid  salts,  or  those  containing  oxygen. 

Theory  of  the  Hydrogen  Acids. 

Several  years  before  Berzelius  had  given  up  the  oxygen- 
acid  theory,  Davy,2  and  almost  at  the  same  moment  Dulong,3 
made  the  attempt  to  bridge  over  the  gap  between  the 
oxygen  and  hydrogen  acids  by  a  uniform  interpretation  of 

1  Jahresber.,  vol.  vi.  p.  185  ;  also  in  his  Lehrb.  d.  Chemie. 

2  Phil.  Trans,  for  1815,  p.  203. 

3  Schweigger's  Journal,  vol.  xvii.  p.  229. 

R 


242  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

their  constitution.  In  these  efforts  we  see  the  beginnings  of 
the  hydrogen-acid  theory,  which  was  to  become  of  such 
great  importance  a  few  decades  later  on.  From  his  observa- 
tion that  iodic  anhydride  was  devoid  of  acid  properties,  but 
acquired  them  after  combination  with  water,  Davy  drew  the 
conclusion  that  hydrogen  and  not  oxygen  was  the  acidifying 
principle  in  the  latter  compound ;  hydrogen,  in  his  opinion, 
was  an  essential  constituent  of  all  acids.  The  assumption,, 
that  hydrated  acids  and  salts  contained  water  or  metallic 
oxides  together  with  acid  anhydrides,  he  held  to  be  un- 
proven  and  unnecessary.  Dulong  expressed  himself  in  a 
similar  sense  after  an  investigation  of  oxalic  acid  and  its 
salts;  the  former  he  regarded  as  a  compound  of  hydrogen 
with  carbonic  acid,  while  in  the  latter  he  assumed  an 
analogous  combination  of  the  metals  with  the  elements  of 
carbonic  acid.  In  these  discussions  a  dualistic  conception 
of  acids  and  salts  was  still  apparent,  hydrogen  and  the 
metals  being  placed  opposite  salt-forming  radicals ;  but  the 
way  was  now  opened  for  a  unitary  theory  of  acids  and  salts. 

Berzelius'  criticism  of  those  attempts  to  explain  the 
constitution  of  important  classes  of  compounds  was  un- 
usually mild ;  but  at  the  same  time  he  adhered  to  his 
dualistic  view,  since  he  laid  special  weight  upon  the  possi- 
bility of  preparing  the  immediate  constituents  (of  the  acids), 
the  radicals  of  the  hydrogen-acid  theory  being  but  seldom 
capable  of  isolation. 

As  his  electro-chemical  theory  became  better  known,  and 
was  received  with  approbation,  the  opposing  views  of  Davy 
and  Dulong  lost  ground ;  it  was  only  in  the  thirties  that 
they  reappeared,  with  fresh  arguments  to  back  them  up, 
after  which  they  were  gradually  accepted.  The  following 
observation  by  Daniell  (in  the  year  1840)  upon  the  electrolysis 
of  salts  was  brought  forward  as  an  argument  in  their  favour : 
"  When  galvanic  currents  are  passed  through  different  electro- 
lytes, e.g.  acidified  water,  fused  chloride  of  lead,  or  a  solution 
of  sulphate  of  potash,  amounts  of  hydrogen,  lead  and 
potash  are  set  free  at  the  negative  pole,  which  stand  to 
one  another  in  the  ratios  of  their  chemical  equivalent- 


v  LIEBIG'S  THEORY  OF  POLYBASIC  ACIDS  243 

numbers."  This  is  in  accordance  with  Faraday's  "  Electro- 
lytic Law,"  excepting  that  in  the  case  of  the  sulphate  of 
potash  an  equivalent  of  hydrogen  is  liberated  in  addition  to 
an  equivalent  of  the  base.  The  current  therefore  appears  to 
do  double  work  here,  in  spite  of  the  law  just  mentioned ; 
for,  if  it  be  assumed  that  the  immediate  constituents  of  one 
equivalent  of  the  salt  are  potash  and  sulphuric  acid,  then 
only  one  equivalent  of  potash — as  the  electro-positive 
portion — should  result,  and  not  one  of  potash  plus  one  of 
hydrogen.  But  this  apparent  contradiction  is  done  away 
with  by  adopting  the  view  of  Davy  and  Dulong,  i.e.  by 
assuming  potassium  as  the  positive,  and  the  radical  SO4 
(oxy-sulpliion)  as  the  negative  constituent.  The  two 
equivalents  of  potash  and  hydrogen  are  then  seen  to  be 
secondary  products  of  the  decomposition  of  one  equivalent 
of  water  by  the  potassium  originally  separated  at  the 
negative  pole.  The  conclusion  drawn  from  this  observation 
on  the  constitution  of  salts  was  then  of  course  extended  to 
that  of  acids,  in  which  hydrogen  was  assumed  as  the  one 
constituent,  and  a  radical — either  containing  oxygen,  or 
free  from  it — as  the  other. 

The   theory   of  the   hydrogen-acids   became   still   more 
clearly  denned  after  Liebig  had  brought  forward  his : — 


Doctrine  of  the  Polybasic,  Acids.1 

This  we  shall  consider  here,  although  it  only  dates  from 
1834,  because  of  its  close  connection  with  the  above  views 
of  Davy  and  Dulong.  Many  chemists  at  that  time,  Gay- 
Lussac  and  Gmelin  in  especial,  inclined  to  the  assumption 
that  the  atoms  of  the  various  metallic  oxides  contained  one 
atom  of  oxygen  to  one  atom  of  metal,  and  combined  with 
one  atom  of  acid  to  form  neutral  salts ;  Berzelius  too,  after 
1826,  was  of  opinion  that  this  combining  proportion  was 
the  rule.  But  a  view  of  such  simplicity  as  this,  according 
to  which  almost  every  acid  was  regarded  as  monobasic,  could 
1  Ann.  Chem.,  vol.  xxvi.  p.  113. 

R  2 


244  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

no  longer  hold  its  ground  after  Graham's 1  famous  investi- 
gation of  the  phosphoric  acids.2  For  this  chemist  showed 
that  ordinary,  pyro-,  and  meta-phosphoric  acids  contained 
different  amounts  of  "  basic  water "  to  1  atom  of  P2O5,  viz. 
3,  2  and  1  atoms  of  water,  these  latter  being  replaceable  by 
metallic  oxides.  The  different  saturation-capacities  of  those 
acids  were  in  this  way  demonstrated,  being  held  to  depend 
upon  the  amounts  of  basic  water  which  entered  into  their 
constitution. 

Liebig  built  upon  the  ground  which  Graham  had 
prepared,  and  with  such  success  that,  by  the  aid  of  his 
own  admirable  and  comprehensive  researches  upon  a  large 
number  of  acids,  he  was  able  to  firmly  establish  his  theory 
of  polybasic  acids.  By  his  investigations  on  citric,  tartaric, 
cyanuric,  comenic  and  meconic  acids,  he  convinced  most 
chemists  that  these  resembled  phosphoric  acid  in  basicity  (i.e. 
were  polybasic).  He  distinctly  and  definitely  resisted  the 
application  to  them  of  the  arbitrary  tenet  that  the  atoms  of 
all  acids  are  equivalent  to  one  another,  and  he  gave  as  the 
criterion  of  a  polybasic  acid  its  capability  of  forming  com- 
pound salts  with  different  metallic  oxides  (e.g.  such  a  salt  as 

PO4  -j    J^2  V       Liebig  was  the  first  to  distinguish  between 

mono-,  di-,  and  tri-basic  acids. 

In  order  to  express  the  facts,  he  still  made  use  of  the  de- 
finition of  acids  in  the  dualistic  sense,  according  to  which 

1  Thomas  Graham,  born  in  Glasgow  in  1805,  became  in  1830  Professor 
of  Chemistry  at  Anderson's  College  of  that  city,  and  then  in  1837  at  Uni- 
versity College,  London.     In  1855  he  resigned  this  post  on  being  appointed 
Master  of  the  Mint ;  he  died  in  1869.     His  admirable  text-book,  Elements 
of  Chemistry,  was  used  not  only  in  England,  but  was  recast  and  translated 
into  German  by  J.  Otto  and  H.  Kolbe.     Graham's  originality  was  shown 
by  his  valuable  physico-chemical  investigations  on  the  diffusion  of  gases, 
osmose,  etc. ,  which  opened  out  new  paths  in  the  science,  while  at  the  same 
time  he  enriched  general  chemistry,  especially  inorganic,  by  his  purely 
chemical  work.     Thanks  to  the  generosity  of  Graham's  old  friend,  the  late 
James  Young  of  Kelly,  his  collected  researches  have  been  published  in  one 
large  volume,  entitled  Chemical  and  Physical  Researches  (Edinburgh,  1876). 
A  full  account  of  Graham's  life,  and  of  the  great  services  which  he  rendered 
to  chemistry,  is  given  by  Thorpe  in  his  Essays,  p.  160,  et  seq. 

2  Phil.  Trans,  for  1833,  p.  253 ;  or  Ann.  Chem.,  vol.  xii.  p.  1. 


v  LIEBIG'S  THEORY  OF  POLYBASIC  ACIDS  245 

these  were  regarded  as  compounds  of  one  atom  of  acid  anhy- 
dride with  one,  two  or  three  atoms  of  water.  But  this  he 
felt  to  be  unsatisfactory,  since  it  did  not  permit  acids  and 
salts  to  be  regarded  from  a  uniform  standpoint.  He  pointed  out 
with  great  acuteness  the  contradictions  which  were  involved 
in  the  retention  of  this  view,  summing  up  his  criticism  as 
follows  :  "  In  order  to  explain  one  and  the  same  phenomenon 
we  make  use  of  two  different  methods.  We  are  obliged  to 
ascribe  to  water  the  most  various  properties,  calling  it  basic 
water,  water  of  hydration  and  water  of  crystallisation,  while 
at  the  same  time  we  see  it  enter  into  compounds  in  which 
it  assumes  no  one  of  these  forms.  And  all  because  we  have 
chosen  to  draw  a  sharp  line  of  demarcation  between  haloid 
and  oxygen  salts — a  line  not  observable  in  the  compounds 
themselves,  seeing  that  in  all  their  relations  they  show 
similar  properties." 

Liebig  was  led  to  the  theory  of  hydrogen  acids  from 
grounds  of  probability,  and  still  more  from  grounds  of  con- 
venience. The  sentences  in  which  he  enunciates  this 
doctrine  explain  his  standpoint  so  clearly  and  tersely  that 
they  must  be  quoted  here. 

"  Acids  are  particular  compounds  of  hydrogen,  in  which 
the  latter  can  be  replaced  by  metals." 

"  Neutral  salts  are  those  compounds  of  the  same  class  in 
which  the  hydrogen  is  replaced  by  its  equivalent  in  metal. 
The  substances  which  we  at  present  term  anhydrous  acids 
only  become,  for  the  most  part,  capable  of  forming  salts  with 
metallic  oxides  after  the  addition  of  water,  or  they  are  com- 
pounds which  decompose  these  oxides  at  somewhat  high 
temperatures."1 

Those  sentences  distinctly  show  us  the  influence  which  the 
accumulating  observations  on  the  substitution  of  hydrogen 
by  other  elements  had  exercised  upon  Liebig.  This  inclina- 
tion of  the  latter  to  a  unitary  hypothesis  was  keenly  felt 

1  Liebig  here  formulates  sulphates  as  S04  +  Me.     The  decomposition  of 
the  metallic  oxides  to  which  he  refers  is  their  reduction,  thus — 


246  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

by  Berzelius,1  who  to  the  end  of  his  life  described  Liebig's 
theory  of  the  polybasic  acids  as  one  which  "  has  led  to  the 
confusion  of  ideas,  and  has  stood  in  the  way  of  a  more  per- 
fect knowledge."  But  in  thus  criticising  views  of  such  great 
importance,  and  which  served  in  quite  an  exceptional  degree 
to  clear  up  the  uncertain  notions  with  respect  to  the  term 
"  equivalent,"  Berzelius  stood  almost  alone. 


Development  of  the  Dualistic  Doctrine  in  the  domain  of 
Organic  Chemistry — The  Older  Radical  Theory. 

During  the  second,  and  still  more  during  the  third  decade 
of  our  century,  organic  chemistry  emerged  from  its  modest 
beginnings,  to  play  an  important  part  even  so  early  as  in  the 
forties.  It  was  destined  to  be  the  medium  for  the  develop- 
ment of  important  views  and  of  doctrines  evolved  from  these, 
thereby  reacting  beneficially  upon  its  elder  sister  inorganic 
chemistry.  At  first  it  continued  on  pretty  much  the  same 
lines  as  the  latter,  the  dualistic  hypothesis,  which  had  kept 
its  place  so  well  with  inorganic,  being  applied  to  organic 
compounds  also.  Here  again  Berzelius  struck  in  as  a 
reformer  with  all  his  accustomed  energy,  and  guided  for  a 
time  the  fortunes  of  organic  chemistry.  A  glance  at  the 
earlier  history  of  the  latter  will  show  us  how  imperfect  was 
the  knowledge  of  this  branch  of  our  science  before  the  second 
decade  of  the  nineteenth  century. 


The  Growth  of  Organic  Chemistry  previous  to  1811. 

So  early  as  at  the  close  of  the  seventeenth  century 
mineral  substances  were  classed  apart  from  vegetable  and 
animal,  the  three  being  treated  separately  in  text-books  of 

1  The  letters  between  Berzelius  and  Liebig,  already  referred  to,  give  in- 
structive and  at  the  same  time  interesting  details  upon  this  point,  and  upon 
the  genesis  and  critical  examination  of  Liebig's  view ;  they  also  show  us 
how  the  estrangement  with  Berzelius  came  about  (cf.  especially  pp.  154, 
159  etseq.,  and  166). 


v        EARLIER  DEVELOPMENT  OF  ORGANIC  CHEMISTRY     247 

chemistry,  in  that  of  Lemery,  for  instance ;  this  division  was 
in  accordance  with  the  classification  of  natural  substances 
according  to  the  three  "  kingdoms  of  nature,"  which  was 
even  then  in  vogue.  It  was  from  this  empirical  standpoint 
that  the  chemistry  of  organic  compounds  developed  itself, 
after  Lavoisier  had  proved  qualitatively  that  the  main 
constituents  of  these  were  carbon,  hydrogen,  oxygen  and 
sometimes  nitrogen,  occasionally  together  with  sulphur  and 
phosphorus.  How  he  sought  to  utilise  this  quantitatively 
also,  by  working  out  a  method  of  organic  analysis,  will  be 
described  under  the  history  of  analytical  chemistry.  He  it 
was  at  all  events  who  laid  the  foundation  for  a  thorough 
knowledge  of  the  subject;  for,  before  scientific  investiga- 
tion in  this  branch  could  become  possible,  the  composition 
of  organic  compounds  had  to  be  established.  Notwith- 
standing that  but  very  little  was  known  at  that  time  about 
the  chemical  constitution  of  these,  Lavoisier  tried  to  form 
an  opinion  on  the  subject  in  particular  cases.  A  point 
worthy  of  special  mention  was  his  view — a  view  which  for 
long  exercised  great  influence — that  the  organic  acids  were 
oxides  of  compound  radicals,  while  he  supposed  that  most  of 
the  mineral  acids  contained  oxygen  united  with  an  element ; 
this  had  indeed  a  distinct  resemblance  to  the  conceptions  of 
the  radical  theory  adopted  at  a  later  period. 

While  Lavoisier  and  other  chemists  after  him  remained 
true  to  the  old  classification  of  substances,  Bergman  began 
about  the  year  1780  to  distinguish  organic  from  inorganic 
bodies.  But,  in  spite  of  the  simplicity  which  this  proposal 
had  to  recommend  it,  the  line  which  remained  drawn  between 
vegetable  and  animal  substances  was  only  gradually  removed 
as  the  knowledge  increased  that  the  same  chemical  com- 
pounds occurred  both  in  vegetables  and  animals,  as  proved, 
e.g.  in  the  case  of  several  fats,  formic  acid,  benzoic  acid,  etc. 
Still  it  was  generally  felt  to  be  necessary  to  strictly  separate 
organic  from  inorganic  bodies,  it  being  represented  as  an 
infallible  distinction  that  the  former  could  not  be  prepared 
directly  from  their  elements.  But  even  this  barrier  was 
destined  to  fall  before  very  long,  and  both  classes  of  com- 


248  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

pounds   to   be   regarded   henceforth   from  the  same  stand- 
points. 

The  Position  of  Berzelius  with  regard  to  Organic  Chemistry. 

At  the  beginning  of  this  century  chemists  of  such 
eminence  as  Dalton,  de  Saussure,  Proust,  and  especially  Gay- 
Lussac  and  Thenard,  exercised  all  their  ingenuity  in  trying 
to  work  out  a  reliable  method  for  determining  the  quantita- 
tive composition  of  organic  compounds,  but  the  results  of 
their  experiments  only  partly  approximated  to  the  truth. 
Before  Berzelius  (1811),  no  one  had  attempted  to  give  a 
definite  answer  to  the  question  whether  the  composition  of 
organic  substances  was,  like  that  of  inorganic,  subject  to  the 
law  of  multiple  proportions ;  whether,  therefore,  the  former 
were  to  be  looked  upon  as  chemical  compounds  in  the  sense 
of  the  atomic  theory.  He  himself  had  so  far  elaborated  a 
method  of  analysing  the  salts  of  organic  acids  that  he  was 
able  to  deduce  with  tolerable  certainty  from  his  results  the 
existence  of  simple  chemical  proportions  between  the  ele- 
mentary constituents  of  an  acid  and  the  oxygen  of  the  base.1 
This  first  successful  attempt  to  bring  organic  compounds 
under  the  atomic  theory,  in  the  same  way  as  inorganic,  was 
followed  in  1813  and  1814  by  investigations 2  carried  on 
with  improved  processes,  which  strengthened  his  conviction 
that  the  law  of  multiple  proportions  applied  in  the  fullest 
degree  to  organic  compounds  also.  In  determining  these 
atomic  weights,  he  recommended,  as  a  principle  to  be 
followed  wherever  possible,  that  the  substances  in  question 
should  be  analysed  in  the  form  of  their  compounds  with 
inorganic  bodies  (e.g.  acids  as  metallic  salts). 

But  even  although  these  researches — the  first  made  in 
this  direction — led  to  the  recognition  of  an  analogy  between 
the  two  classes  of  substances,  still  Berzelius  did  not 
immediately  make  up  his  mind  to  regard  organic  com- 
pounds as  constituted  exactly  like  inorganic  (i.e.  with 

1  Gilbert's  Annalen,  vol.  xl.  p.  247. 

2  See  especially  Annals  of  Philosophy,  vols.  iv.  and  v. 


v   THE  VIEWS  OF  BERZELIUS  UPON  ORGANIC  CHEMISTRY  249 

respect  to  the  arrangement  of  their  constituent  elements). 
On  the  contrary,  he  considered  it  necessary  to  draw  a  sharp 
distinction  between  the  latter  as  binary,  and  organic  com- 
pounds as  ternary  and  quaternary;  for  these,  as  he  stated 
in  1813,  contain  more  than  two  elements.  As  a  con- 
sequence of  this,  compounds  like  marsh  gas,  cyanogen  and 
the  hypothetical  oxalic  anhydride  were  classified  as  inorganic, 
an  arrangement  which  was  long  retained  (and  still  is,  to 
some  extent)  on  grounds  of  convenience,  Gmelin  being 
especially  strong  in  his  recommendation  of  it.  But  this 
empirical  separation  of  the  two  series  of  substances  soon 
proved  to  be  quite  inadequate,  particularly  after  various  oils 
had  been  recognised  as  binary  compounds  of  carbon  and 
hydrogen  of  complex  composition. 

Berzelius  himself  made  the  attempt,  in  his  treatise1 
referred  to  above,  to  bridge  over  the  gap  between  inorganic 
and  organic  bodies  by  assuming  that  the  latter,  like  the 
former,  are  constituted  binarily,  but  contain  compound  radi- 
cals in  place  of  elements. 

Gay-Lussac's  beautiful  researches  on  cyanogen  had 
without  doubt  a  powerful  effect  in  reviving  this  idea,  which 
had  already  been  advanced  by  Lavoisier,  for  they  proved  the 
important  fact  that  cyanogen,  as  a  compound  radical,  can 
play  the  part  of  an  element  perfectly.  This  in  its  turn  gave 
rise  to  further  efforts  to  search  for  similar  atomic  complexes 
(Atomkomplexe)  in  other  organic  compounds.  Gay-Lussac 
himself  expressed  the  opinion  that  alcohol  consisted  of  ethyl- 
ene  and  water,  and,  as  its  vapour  density  proved,  of  equal 
volumes  of  these ;  while  he  assumed  carbon  and  water  as  the 
immediate  constituents  of  sugar.  Hydrochloric  ether  was 
regarded  by  Robiquet  as  a  compound  of  ethylene  with 
hydrochloric  acid,  and  anhydrous  oxalic  acid  by  Dobereiner 
as  one  of  carbonic  acid  with  carbonic  oxide. 

These  efforts  to  look  upon  compound  radicals  as  the 
immediate  constituents  of  organic  substances  may  be 
regarded  as  the  beginnings  of  the  radical  theory.  The 

1  Versuch  uber  die  Theorie  der  chemischen  Proportionen,  etc.  (Dresden,, 
1820). 


250  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

above  attempts  at  a  solution  were,  however,  disapproved  of 
by  Berzelius,  who  raised  a  warning  voice  and  declared  them 
incompatible  with  the  electro-chemical  views.  In  accordance 
with  the  latter,  the  electro-negative  oxygen  was  placed  op- 
posite to  a  compound  radical  as  the  positive  constituent  of 
a,  compound,  thus  showing  that  at  that  date  Berzelius  did  not 
believe  in  radicals  containing  oxygen.  At  that  time  also 
he  conceded  the  variability  (Veranderlichkeit  durch  Substi- 
tution) of  radicals,  but  went  back  from  this  later  on,  thereby 
putting  an  obstacle  in  the  way  of  the  healthy  development 
of  the  radical  theory. 

The  time  for  the  completion  of  this  doctrine  was  not  yet 
come;  but  the  theorising  upon  tlie  proximate  constituents 
of  organic  compounds  was  of  much  benefit,  in  that  it  gave  a 
stimulus  to  the  study  of  the  latter.  To  the  first  task  of 
determining  their  empirical  composition  was  added  the  far 
higher  one  of  investigating  their  chemical  constitution  by 
getting  at  the  proximate  constituents,  as  these  were  under- 
stood by  Berzelius.  The  discovery  of  the  first  case  of 
isomerism  in  the  third  decade  of  the  century  gave  a  power- 
ful impetus  to  this,  and  caused  the  great  importance  of  the 
task  to  be  better  appreciated,  and  a  more  correct  idea  of  it 
to  be  formed.  If  we  try  to  picture  to  ourselves  the  stand- 
point of  the  chemists  of  that  day,  we  see  how  such  startling 
observations  of  compounds  having  the  same  chemical  com- 
position, but  differing  totally  in  their  properties,  forced  them 
of  necessity  to  the  conclusion  that  the  cause  of  this 
phenomenon  (termed  isomerism)  was  to  be  sought  for  in  a 
dissimilarity  of  the  proximate  constituents  of  the  compounds 
in  question.  What  a  powerful  and  continually  renewed 
-charm  was  thereby  given  to  the  search  for  those  different 
radicals  of  organic  compounds  ! 

Isomerism  and  its  Influence  on  the  Development  of 
Organic  Chemistry. 

Up  to  about  the  year  1820  it  was  considered  an  axiom 
in  chemistry  that  substances  of  the  same  qualitative  and 


v  THE  FIRST  OBSERVED  CASE  OF  ISOMERISM  251 

quantitative  composition  must  possess  the  same  properties. 
Even  then,  it  is  true,  cases  were  known  which  appeared  to 
contradict  this  natural  assumption,  viz.  the  different  modi- 
fications of  chromic  oxide  and  of  silicic  acid,  and,  in  especial, 
the  proof  given  by  Berzelius  of  the  two  varieties  of  tin 
dioxide.  But  little  weight,  however,  was  placed  upon  these 
observations;  they  were  simply  looked  upon  as  exceptions 
to  the  general  rule,  and  considered  merely  as  indicating 
physical  differences,  as  in  cases  of  dimorphism,  of  which  a 
number  were  known. 

So  little  were  chemists  prepared  for  the  existence  of 
substances  of  the  same  composition,  but  of  different  chemical 
and  physical  properties,  that  most  of  them  considered  the 
first  observed  case  of  isomerism  in  organic  chemistry  as  due 
to  an  error.  In  1823  Liebig  had  found,  on  comparing  his 
analysis  of  silver  fulminate  with  that  of  silver  cyanate,  which 
Wohler  had  investigated  a  year  before,  that  the  results  of 
the  analyses  of  both  salts  were  alike.1  Satisfied  of  the  cor- 
rectness of  his  own  work,  he  thought  that  Wohler  had  probably 
made  some  mistake,  but  became  convinced  that  this  was  not 
the  case  upon  repeating  the  investigation  himself.  From 
that  date,  accordingly,  two  compounds,  which  differed  as 
widely  as  possible  from  one  another  chemically,  were  recog- 
nized as  having  the  same  composition. 

While  Berzelius  attached  full  significance  to  the  above 
observation,  he  did  not  immediately  give  in  his  adhesion  to  it,2 
but  rather  waited  for  further  confirmation  of  the  point ;  Gay- 
Lussac,  on  the  other  hand,  felt  no  doubt  whatever  as  to  the 
correctness  of  the  discovery,  and  explained  the  differences  in 
the  above  salts  by  assuming  a  difference  in  the  manner  in 
which  their  constituent  elements  were  combined.  After 
Faraday's  discovery,3  in  1825,  of  a  hydrocarbon  in  oil  gas 
which  had  the  same  composition  as  ethylene,  but  which 

1  Ann.  Chim.  Phys.,  vol.  xxiv.  p.  264. 

2  At  first  Berzelius  was  of  opinion  that  an  error  had  probably  been 
made  on  one  side  or  the  other  (cf.  Jahresbericht,  vol.  iv.  p.  110 ;  vol.  v.  p. 
85). 

3  Annals  of  Philosophy,  vol.  xi.  pp.  44  and  95. 


252  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

showed  a  totally  different  behaviour,  and  after  Wohler  in 
1828  had  obtained  urea  from  the  transformation  of  the 
similarly  composed  cyanate  of  ammonium,  chemists  became 
more  conversant  with  the  existence  of  isomeric  compounds. 
Berzelius  only  accepted  those  facts  after  hesitation,  but 
ultimately  convinced  himself  of  their  absolute  correctness  by 
experiments  of  his  own.  He  proved  that  racemic  acid  had 
the  same  composition  as  tartaric,1  and  thereupon  proposed  the 
term  isomeric  for  those  substances  which,  with  the  same 
chemical  composition,  possess  different  properties.  The 
general  designation  isomerism  has  since  then  been  retained. 
Berzelius  soon  saw  himself  necessitated  to  define  more  strictly 
the  meaning  to  be  attached  to  this  word;  2  he  distinguished 
between  polymerism  and  metamerism,  as  special  cases  of 
isomerism,  in  essentially  the  same  manner  as  we  still  do  to- 
day.3 His  power  of  generalising,  even  with  but  a  scanty 
number  of  facts  to  go  upon,  was  shown  here  in  a  very  high 
degree. 

The  ideas  of  Berzelius  with  regard  to  the  probable  cause 
of  isomerism  in  organic  compounds  are  clearly  shown  in  many 
of  his  utterances  ;  in  his  view  isomeric  compounds  are  those 
in  which  the  atoms  of  the  elementary  constituents  have 
grouped  themselves  differently  into  compound  radicals. 
"  The  isomerism  of  compounds  in  itself  presupposes  that  the 
positions  of  the  atoms  in  them  must  be  different."  To 
conclude  from  this  sentence  that  Berzelius  looked  upon  the 
problem  of  elucidating  the  relative  positions  of  the  atoms 
in  space  as  one  which  was  soluble,  is  certainly  not  justifiable; 
what  he  no  doubt  had  in  his  mind  was  the  determining  of 
the  mutual  relations  of  atoms  in  their  compounds,  and, 
especially,  the  establishment  of  the  mode  in  which  atoms  are 
combined  to  form  the  proximate  constituents  or  compound 
radicals  of  compounds.  The  accumulating  observations  of 

1  Berzelius1  Jahresber.,  vol.  xi.  p  44  (1832). 

2  Ibid.,  vol.  xii.  p.  63  (1833). 

3  Berzelius  regarded  the  different  modifications  of  elements  as  a  par- 
ticular case  of  isomerism  ;  the  designation  allotropy,  now  employed  for 
this,  only  dates  from  1841. 


v  DUMAS  AND  BOULLAY'S  ETHERIN  THEORY  253 

cases  of  isomerism  quickly  brought  the  question  of  chemical 
constitution  in  this  sense  to  the  stage  at  which  an  experi- 
mental solution  of  it  was  deemed  possible,  and  this  was 
attempted  by  grouping  together  a  number  of  organic  com- 
pounds on  the  basis  of  the  hypothesis  of  definite  common 
radicals.  The  outcome  of  this  attempt  was  the  Radical 
Theory,  in  the  shaping  of  which  Berzelius  and  Liebig  had 
the  greatest  share.  To  distinguish  it  from  the  more  recently 
revived  form  of  views  of  a  similar  character,  it  is  known  as 
the  older  Radical  Theory. 


The  older  Eadical  Theory. 

Prior  to  1830,  as  has  been  already  stated,  efforts  were 
not  wanting  to  explain  the  constitution  of  particular  com- 
pounds by  the  assumption  of  compound  radicals.  The 
chief  incitement  to  those  efforts  lay  in  the  proof  that 
cyanogen  acted  like  an  element  in  its  numerous  compounds, 
besides  being  known  in  the  free  state  itself.  The  observation 
that  alcohol  is  easily  transformed  into  ether  and  ethylene 
may  have  given  rise  to  the  supposition  that  ethylene  was  a 
constituent  of  both  of  these. 

This  idea,  which  was  held  by  Gay-Lussac,  had  new  life 
imparted  to  it  for  the  time  being  by  Dumas  and  Boullay's 
attempt1  to  generalise  it  by  extending  it  to  derivatives  of 
-alcohol  and  ether.  The  radical  "  etherin/' 2  C2H4,  was  assumed 
by  them  to  be  present  in  what  afterwards  became  known  as 
ethyl  compounds,  and  was  compared  with  an  inorganic 
compound,  ammonia.  Like  the  latter,  etherin  was  regarded 
as  a  base,  capable  of  forming  a  hydrate  with  water,  and 
ethers  (analogous  to  salts)  with  acids.  The  following 
table  will  help  to  explain  the  endeavours  to  establish 
an  analogy  between  organic  and  inorganic  compounds 

1  Ann.  Chim.  Phys.,  vol.  xxxvii.  p.  15  (1838). 

2  The  radical  C2H4  had,  at  Berzelius'  suggestion,  received  the  name 

^Etherin. 


254  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

(some  of  the  latter  not  having  been  isolated,  as  a  matter 
of  fact)  :— 

Etherin,  C2H4 Ammonia,  H3N 

Alcohol,  C2H4  +  H2O 

Ether,  2C2H4  +  H2O 

Hydrochloric  ether,  C2H4  +  HC1     .        .    |  Chloride  ^ammonia, 

Acetic  ether,  2C2H4  +  C8H6O3  +  H2O      . 

This  attempt,  which  is  known  under  the  name  of  the 
etherin  theory,  was  so  far  the  precursor  of  the  true  radical 
theory  in  that  it  had  the  comparison  of  organic  with  inorganic 
substances  in  common  with  the  latter.  In  criticising  it 
Berzelius  was  thoroughly  justified  in  emphasising  the  point 
that  it  was  quite  admissible  to  group  the  above  compounds 
in  tabular  form  alongside  of  one  another,  while  at  the  same 
time  he  expressed  the  opinion  that  their  presumed  constitution 
was  highly  doubtful. 

But  the  real  development  of  the  existing  idea  that  organic 
compounds  owe  their  characteristics  to  the  radicals  which 
they  contain,  was  mainly  brought  about  by  Liebig  and 
Wohler's  memorable  research,  entitled  Ueber  das  Eadikal 
der  Benzoesaure  ("  Upon  the  Radical  of  Benzoic  Acid  ").2  In 
this  they  proved  incontestably  that  in  numerous  transforma- 
tions of  oil  of  bitter  almonds,  and  of  chlorine  and  bromine 
compounds  prepared  from  it,  a  radical  of  the  composition 
C14H10O2,3  which  they  termed  Benzoyl,  remained  unaltered. 
They  showed  by  convincing  experiments  that  this  radical 
may  be  assumed  as  present  in  benzoic  acid,  benzoyl  chloride 
and  bromide,  benzamide,  benzoic  ether  and  benzoyl  sulphide, 
and  that  it  comports  itself  in  these  compounds  like  an 
element.  This  piece  of  work  was  not  only  of  profound  signi- 
ficance for  the  radical  theory,  but  it  has  also  exercised  a  most 

1  Dumas'  atomic  weights,  taking  H=l,  were  C  =  6,  and  0  =  16. 

2  Ann.   Chem.,  vol.  iii.  p.    249  (1832).     The  correspondence  between 
Liebig  and  Wohler  (edited  in  1888  by  A.  W.  v.  Hofmann  and  E.  Wohler) 
gives  a  welcome  insight  into  the  origin  of  this  pioneering  piece  of  work, 
while  at  the  same  time  it  constitutes  the  best  memorial  of  the  close  friend- 
ship existing  between  the  two  men. 

3  Berzelius'  atomic  weights  were  :  H  =  l,  C  =  12,  O  =  16. 


v  BERZELIUS  AND  LIEBIG'S  ALKYL  THEORY  255 

powerful  influence  on  the  development  of  organic  chemistry 
generally,  the  new  methods  given  in  it  for  the  preparation  of 
particular  compounds  having  proved  applicable  to  whole  classes 
The  authors  laid  greatest  stress  upon  the  proof  of  a  "com- 
pound element,  benzoyl,  in  a  series  of  organic  compounds." 

Berzelius  was  so  convinced  by  these  astonishingly  clear 
results  of  the  correctness  of  their  interpretation,  that  he 
concurred  enthusiastically  in  the  assumption  of  the  radical 
benzoyl ; 1  the  facts  were  so  strongly  in  its  favour  that  he 
felt  himself  compelled  to  give  up  his  axiom, — that  oxygen 
cannot  be  a  constituent  of  a  radical.  But  unfortunately 
this  was  only  for  a  short  time,  as  he  soon  reverted  to  the 
opinion  that  the  existence  of  oxygenated  radicals  was  abso- 
lutely incompatible  with  his  electro-chemical  theory. 

Most  chemists  of  that  day  held  that  the  radicals  which 
were  proved  to  be  present  in  several  compounds  were  to- 
be  regarded  as  atomic  groups  capable  of  existing  separately, 
and  that  their  isolation  should  therefore  be  striven  after. 
Although  benzoyl  itself  had  not  been  isolated,  as  little  doubt 
was  felt  with  respect  to  its  separate  existence  as  with  respect 
to  that  of  calcium  or  of  nitric  anhydride,  neither  of  which 
had  yet  been  obtained.  The  natural  result  of  Liebig  and 
Wohler's  investigation  was  a  strong  incitement  to  chemists 
to  search  for  the  atomic  groups  peculiar  to  different  series 
of  compounds,  whose  modes  of  formation  and  behaviour 
pointed  to  a  probable  connection  between  them. 

The  radical  theory  proper,  in  the  establishment  of  which 
Berzelius  and  Liebig  took  part  during  the  ensuing  years,, 
arose  out  of  such  endeavours.  A  series  of  organic  compounds, 
closely  related  to  alcohol,  furnished  the  most  suitable  object 
for  such  a  view,  these  compounds  being  even  at  that  date 
among  the  most  carefully  investigated  of  organic  substances. 
In  1833  Berzelius2  emphasised  the  necessity  of  assuming  a 

1  In  his  letter  to  Liebig  and  Wohler  (Ann.  Chem.,  vol.  iii.  p.  282), 
Berzelius  proposed  the  name  Proin  or  Orthrin  (from  irpa>ta,nd  6p6pos  respec- 
tively, meaning  "morning  blush  "),  because  with  this  research  a  new  day 
had  dawned  for  organic  chemistry. 

2  Jahresber.,  vol.  xiii.  p.  190  et  seq.  The  Berzelius-Liebig  Letters  (pp. 
55  et  seq.  and  67)  give  many  details  as  to  the  origin  of  this  view. 


256  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

binary  structure  for  all  organic  as  for  all  inorganic  compounds 
renouncing  at  the  same  time  the  idea  of  oxygenated  radicals. 
Benzoyl  he  explained  as  being  the  oxide  of  the  complex 
C4H10,  the  peroxide  of  this  being  anhydrous  benzoic  acid. 
Ether  he  regarded  as  the  sub-oxide  of  ethyl,  and  he  gave  to 
it  the  formula  (C2H5)20 ;  this  last  corresponded  to  the 
inorganic  bases,  and  was  combined  with  acids  in  ethers 
exactly  as  the  metallic  oxides  were  in  salts.  Alcohol,  on  the 
other  hand,  which  is  so  nearly  related  to  ether,  was  looked 
upon  by  him  as  the  oxide  of  a  radical  C2H6,  a  view  which 
entirely  effaced  the  connection  between  the  two  compounds.1 
Liebig,2  noting  this  error,  published  in  the  following 
year  his  opinion  that  alcohol,  as  well  as  ether  and  its  deriva- 
tives, were  compounds  of  one  and  the  same  radical  ethyl,  to 
which,  however,  he  gave  the  formula  C4H10  (in  place  of  C2H5 
by  Berzelius).  His  view  is  apparent  from  the  following 
table  :— 

Ether,  C4H10O Ethyl  iodide,  C4H10I2 

A  i     i,  i    n  TT   r»  TT  rk  f  Nitrous  ether  (Saltpeterdther). 

Alcohol,  C4H10O.H20        .       .       .  {C4Hioo>N2o3  V 

Ethyl  chloride,  C4H10C12  .       .       .      Benzoic  ether,  C4H10O.C14H10O3. 

He  accordingly  designated  ether  as  ethyl  oxide,  and 
alcohol  as  hydrate  of  ethyl  oxide,  comparing  the  former  with 
potassic  oxide,  and  the  latter  with  potassic  hydroxide.  Not- 
withstanding, however,  his  recognition  of  the  fact  that  the 
same  radical  is  common  to  both,  he  fell  into  an  error  which 
Berzelius  had  avoided,  viz.  he  attributed  to  alcohol  and  the 
corresponding  compounds  twice  the  atomic  weight  that  they 
really  possess.  But  apart  altogether  from  these  mistakes  .of 
Liebig  and  Berzelius,  the  advantages  of  their  ethyl  theory 
were  at  once  apparent.  A  broad  pathway  was  opened  out 

1  Berzelius  conceived  himself  obliged  to  take  this  view  of  the  atomic 
composition  of  alcohol  and  ether  on  account  of  their  vapour  densities  ;  from 
these  he  deduced  the  correct  molecular  formulae,  without,  however,  being 
able  to  arrive  at  the  true  constitution  of  alcohol,  as  he  did  at  that  of 
ether. 

2  Ann.  Chem.,  vol.  ix.  p.  1,  Ueber  die Konstitutiondes  Aethers und  seiner 
Verbindungen  ("On  the  Constitution  of  Ether  and  its  Compounds "). 


v  LIEBIG'S  SHARE  IN  THE  RADICAL  THEORY  257 

for  the  conception  that  organic  compounds  were  constituted 
analogously  to  inorganic.  Ethyl  played  in  a  large  number  of 
compounds  the  same  part  as  potassium  or  ammonium l  did  in 
others.  Liebig  finally  extended  this  comparison  to  mercaptan 
and  ethyl  sulphide,  then  just  discovered.  It  was  due  in  a  high 
degree  to  his  eloquent  advocacy  of  the  assumption  of  "  com- 
pound elements"  that  the  radical  theory  found  such  wide 
recognition.2 

The  leading  chemists  of  that  day  held  firm  to  their 
expressed  opinions  regarding  radicals: — Dumas  to  the 
assumption  that  etherin  was  the  radical  of  alcohol,  etc. ; 
Berzelius  to  the  view  that  alcohol  and  ether  had  different 
constitutions,  although  he  did  not  absolutely  deny  the 
admissibility  of  the  extended  ethyl  theory;  while  Liebig 
remained  true  to  the  latter.  He  differed  most  from  Berzelius 
upon  the  question  of  oxygenated  radicals,  which  were  in  his 
opinion  indispensable ;  thus  he  had  no  doubt  that  carbonic 
oxide  was  a  constituent  of  carbonic  and  also  of  oxalic  acid. 
But  in  one  point  those  chemists  were  all  agreed,  viz.  that 
compound  radicals  existed  as  distinct  constituents  in  their 
compounds. 

Liebig  by  degrees  took  up  another  and  broader  view  of  the 
nature  of  radicals  than  Berzelius,  who  inclined  more  and 
more  to  the  opinion  that  they  were  unalterable.  In  Liebig, 
on  the  other  hand,  we  get  frequent  glimpses  of  the  idea  that 
the  grouping  of  the  elements  to  radicals  must  prove  of 
essential  service  to  a  better  understanding  of  the  modes  of 
decomposition  and  formation  of  compounds.  This  conception 
appears  to  have  forced  itself  upon  him  from  the  result  of  an 

1  In  the  place  of  the  assumption  that  ammonia  itself  is  combined  with 
acids  in  its  salts,  the  view — originally  held  by  Ampere  (in  1816)  and  which 
had  now  the  authority  of  Berzelius  to  back  it — gradually  spread,   that  in 
those  salts  ammonium,  NH4,  acts  analogously  to  the  metals. 

2  We  must  not  omit  to  state  here  that  Kane,  independently  of  Berzelius 
and  Liebig,  pointed  out  the  analogy  between  a  radical  Athereum,  i.e.  ethyl, 
which  was  to  be  assumed  in  ether,  alcohol,   etc.,  and  the  hypothetical 
ammonium  ;  the  paper,  however,  in  which  he  expressed  this  view  (which 
was  published  in  1833  in   The  Dublin  Journal  of  Medical  and  Chemical 
Science,  vol.  ii.  p.  348)  remained  quite  unnoticed. 


258  THE  MODERN  CHEMICAL  PERIOD  CHAP 

investigation1  which  Regnault2  had  undertaken  at  his 
suggestion.  The  latter  had  obtained  a  substance  of  the 
composition  C4H6C12,  which  he  termed  chloro-aldehyde, 
by  decomposing  ethylene  chloride  with  alcoholic  potash. 
Liebig  3  thereupon  expressed  his  opinion  that  the  radical  C4H6 
was  a  constituent  of  this  chloride  and  of  numerous  other 
compounds;  this  radical  he  named  acetyl,  and  he  placed 
it  parallel  to  the  hypothetical  amidogen  (Amid),  and  its 
hydrogen  compounds,  ethylene  and  ethyl,  to  ammonia  and 
ammonium,  thus: — 

C4H6,  acetyl,  corresponds  toN2H4,  amidogen 
C4H8,  ethylene,       ,,  ,,N2H6,  ammonia 

C4H10,  ethyl,  ,,  ,,N2H8,  ammonium. 

Liebig  laid  especial  weight  upon  finding  an  expression 
for  the  constitution  of  aldehyde  and  acetic  acid;  these  he 
looked  upon  as  the  protoxide  and  hydrated  oxide  of  the 
acetyl  radical,  and  he  gave  them  the  formulae  C4H6O.H20 
and  C4H6O3.H2O.  This  conception  paved  the  way  for  the 
explanation  of  the  conversion  of  alcohol  into  aldehyde  and 
acetic  acid,  while  at  the  same  time  it  raised  up  doubt  as  to 
the  rigid  unchangeability  of  a  radical. 

The  year  1837  may  be  looked  upon  as  that  in  which 
the  older  radical  theory  attained  to  its  zenith  and  stood 
out  most  securely,  in  spite  of  the  many  attacks  which  it  had 
to  undergo.  Liebig  and  Dumas,  who  were  convinced  of 
the  untenability  of  the  etherin  theory,  joined  together  to 
make  a  thorough  investigation  of  organic  compounds  with 


1  Ann.  Chem.,  vol.  xv.  p.  60. 

2  H.  V.  Regnault,  who  was  born  at  Aix-la-Chapelle  in  1810  and  died  at 
Auteuil  near  Paris  in  1878,  was  a  pupil  of  Liebig.     Up  to  1840  he  gave  his 
attention  to  organic  chemistry,  which  he  enriched  by  valuable  work,  but 
after  that  devoted  himself  to  physico-chemical  researches  which  will  ensure 
him  a  distinguished  place  in  the  history  of  the  science.     His  many-sided- 
ness is  shown  in  his  admirable  investigations  on  the  respiration  of  animals, 
undertaken  conjointly  with  Reiset.     By  means  of  translations,  his  Cours 
j&ttmentaire  de  Chimie  (1847-49)  became  well  known  and  appreciated  in 
other  countries  besides  France. 

3  Ann.  Chem.  vol.  xxx.  p.  229. 


v  THE  RADICAL  THEORY  IN  1837  259 

respect  to  the  radical  theory.  In  a  paper1  given  out  jointly 
in  his  own  name  and  Liebig's,  Dumas  set  forth  his  altered 
opinions  and  described  the  problems  to  be  solved.  Organic 
chemistry  was  regarded  by  both  as  the  Chemistry  of  Com- 
pound Radicals,  and  was  denned  accordingly.2  These  radi- 
cals were  compared  with  the  elements,  e.g.  ethyl,  methyl 
(whose  existence  in  wood  spirit  was  deduced  from  Dumas 
and  Peligot's  memorable  research),  and  amyl*  with  the 
metals,  acetyl  with  sulphur,  and  so  on;  and  their  com- 
pounds with  the  corresponding  compounds  of  the  elements, 
e.g.  ethyl  sulphide  (C2H5)9S,  with  sulphide  of  potassium, 
K2S,  etc.4 

The  chemists  of  that  day  did  not,  however,  remain 
content  with  simply  contrasting  organic  with  inorganic  com- 
pounds as  an  aid  to  getting  at  their  formulae;  on  the 
contrary,  they  applied  in  the  happiest  manner  to  the  investi- 
gation of  organic  compounds  the  principles  which  they 
knew  to  hold  good  in  inorganic  chemistry,  faithful  to  the 
axiom  enunciated  by  Berzelius  in  1817 :  "  The  application 
of  what  is  known  regarding  the  combination  of  the  elements 
in  inorganic  nature,  to  the  critical  examination  of  their  com- 
pounds in  organic,  is  the  key  by  which  we  may  hope  to 

1  Comptes  Rendm,  vol.  v.  p.  567.     That  this  union  of  the  two  investiga- 
tors was  of    short  duration   is    easily  intelligible  when   one    considers 
the  different  modes  of  thought  and  dispositions  of  the  two  men.     The 
criticism  with  respect  to  Dumas,  which  we  find  in  the  correspondence  be- 
tween Berzelius  and  Liebig,  shows  such  a  separation  to  have  been  inevitable. 
Gay-Lussac  throws  a  clear  light  on  the  occurrence  in  a  letter  to  Liebig 
which  begins  with  the  words  : — Maintenant,  mon  cher  Liebig,  je  vous  felicite 
d'etre  sorti  de  la  galere  ou   vous  dtiez  entre.      Je  ne   concevais  pas  votre 
mariage.  .  .  .,  etc.  (The  Berzelius- Liebig  Letters,  p.  171). 

2  Cf.  Liebig's  Handb.  d.  organ.  Chemie,  p.  1. 

3  Cf.  Cahours'  investigation  of  fusel  oil,  Ann.  Ghent.,  vol.  xxx.  p.  228. 

4  The  following  quotation  from  the  paper  cited  above  (note  1)  shows 
the  then  standpoint  of  Dumas  and  Liebig  :  "  Organic  chemistry  possesses 
its  own  elements,  which  sometimes  play  the  part  of  chlorine  or  oxygen, 
sometimes  that  of  a  metal.     Cyanogen,  amidogen,  benzoyl  and  the  radicals 
of  ammonia,  of  the  fats,  and  of  alcohol  and  its  derivatives,  constitute  the 
true  elements  of  organic  nature,  while  the  simplest  constituents,  such  as 
carbon,  hydrogen,  oxygen  and  nitrogen,  only  appear  when  the  organic  sub- 
stance is  destroyed." 

s  2 


260  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

arrive  at    true    ideas    with    respect    to    the  composition  of 
organic  substances." 

As  the    presence  of    such  atomic  complexes  in  organic 
compounds  came  to  be  assumed  with  more  confidence,  the 
term  radical  became  more  sharply  defined.     Liebig  himself 
enunciated  in  1838  three  characteristics  by  which  a  com- 
pound radical  was  distinguished.      In  bringing  forward  his 
view  he  made  use  of  cyanogen  as  an  instance,  and  spoke 
as    follows : 1  "  We   term  cyanogen  a  radical  because  (1)  it 
is  the  unchanging    constituent   of  a  series    of  compounds ; 
(2)  because  it  is  capable  of  replacement  in  these  by  simple 
substances;  and    (3)    because,    in    those    cases  where    it   is 
combined  with  one  element,  this    latter  can  be  exchanged 
for  its  equivalent  of  another  element."     At  least  two  of  the 
conditions    here   adduced   had  to  be  fulfilled  in  order  that 
an  atomic  complex  might  be  stamped  as  a  radical.       The 
existence  of    these    conditions,    moreover,   could    only    be 
established  by  the  most  minute  investigation  of  the  chemical 
behaviour  of  organic  bodies.      That  is  to  say,  the  nature  of 
the    radicals  assumed   in   the   latter  could  only  be  arrived 
at    from   the   study  of    their   reaction-  and  decomposition- 
products. 

The  radical  theory  gave  such  a  powerful  impulse  to  the 
science  that  its  influence,  even  when  it  fell  into  error, 
cannot  be  too  greatly  prized.  Chemists  of  the  highest 
eminence  were  attracted  to  the  task  of  investigating  the 
constituents  of  compounds  which  were  related  to  one 
another.  Among  the  most  fruitful  of  those  efforts  were  a 
series  of  admirable  researches  upon  the  cacodyl  compounds2 
by  Robert  Bunsen,  begun  in  the  year  1839  (see  below). 

Robert  Wilhelm  Bunsen,  born  at  Gottingen  on  March  31st, 
1811,  became  assistant-professor  at  the  University  there, 
then  succeeded  Wohler  at  Cassel,  and  was  appointed  pro- 
fessor in  the  University  of  Marburg  in  1838.  His  next 
post  (only  occupied  for  a  short  time)  was  at  Breslau,  after 

1  Ann.  Chem.,  vol.  xxv.  p.  3. 

2  Ann.  Chem.,  vol.  xxxi.  p.  175 ;  vol.  xxxvii.  p.  1.  ;  vol.  xlii.  p.  14 ;  vol. 
xlvi.  p.  1. 


v  ROBERT  WILHEL&L  BUNSEN  261 

which  he  was  called  (in  1851)  to  Heidelberg,  of  whose 
University  he  remained  a  bright  ornament  until  his  resig- 
nation in  1889.  Chemistry  is  indebted  to  him  for  a 
vast  number  of  the  most  important  researches  in  every 
branch  of  the  science ;  his  name  will  therefore  be  very  often 
referred  to  in  the  special  history  of  its  various  sections. 
Beginning  with  work  in  inorganic  chemistry,  he  soon  turned 
his  attention  to  the  organic  compounds  of  arsenic,  by 
investigating  which  he  raised  up  a  powerful  support  for  the 
radical  theory.  His  work  upon  gases  led  him  to  devise  new 
methods,  by  sifting  and  combining  which  he  created  the 
gas  analysis  of  to-day.  The  discovery  of  spectrum  analysis 
by  him  and  Kirchhoff — one  of  the  grandest  and  most  fruitful 
of  the  last  fifty  years — is  fresh  in  every  one's  recollection. 
His  labours  in  other  branches  of  physical,  analytical,  in- 
organic and  mineralogical  chemistry  will  be  referred  to  in 
the  detailed  description  of  these.  Throughout  he  has  shown 
himself  an  investigator  of  the  most  marked  originality  and 
a  pioneer  in  the  science;  while  his  career  as  a  teacher, 
extending  over  more  than  half  a  century,  has  been  singularly 
successful  in  its  results. 

Bunsen's  researches  on  the  cacodyl  compounds  resulted 
in  the  proof  that  the  so-called  alkarsin,  the  product  of  the 
distillation  of  acetate  of  potash  with  arsenious  acid,  con- 
tained the  oxide  of  an  arseniuretted  radical  As2C4H12 
(H  =  l,  C  =  12,  As  =  75),  this  radical  remaining  unchanged 
in  a  long  series  of  reactions  of  that  oxide,  and  being  even 
itself  capable  of  isolation.  This  "  compound  element "  con- 
taining arsenic  (an  unusual  constituent  of  organic  bodies)  was 
thus  shown  to  be  a  true  radical. 

The  investigations  of  Gay-Lussac  upon  cyanogen,  of 
Liebig  and  Wohler  upon  benzoyl  compounds,  and  of  Bunsen 
upon  the  compounds  of  cacodyl,  have  been  justly  termed  the 
three  pillars  of  the  radical  theory.  The  assumption  of 
radicals  gained  so  immensely  in  probability  from  the  results 
of  these  researches,  that  the  hypothesis  which  lay  at  the 
root  of  the  theory  might  now  be  regarded  as  well  established. 
In  any  case  the  older  radical  theory  formed  an  indispensable 


262  THE  MODERN  CHEMICAL  PERIOD  CHAP 


link  in  the  chain  of  theoretical  views,  and  marked  an  extra- 
ordinary advance  upon  the  previous  unconnected  opinions. 
And  even  although  this  theory  (as  it  then  stood)  exercised 
no  very  permanent  effect  directly,  being  soon  overthrown  by 
opposing  currents,  it  showed  itself  in  a  high  degree  capable 
of  further  development.  For,  shortly  after  the  catastrophe 
which  came  upon  it,  it  was  able  to  throw  off  a  few  restraining 
fetters  and  to  start  again  into  fresh  life. 

Before  proceeding  to  describe  the  development  of  the 
hypotheses  directed  against  the  older  radical  theory,  it  will 
be  convenient  to  give  a  short  account  here  of  the  lives  and 
chief  labours  of  the  three  chemists  who  were  mainly  in- 
strumental in  changing  the  direction  of  organic  chemistry 
during  the  third  and  fourth  decades  of  the  nineteenth 
century,  and  who  furthermore  exercised  a  powerful  influence 
upon  our  science  up  to  a  very  much  more  recent  date. 


Liebig,   Wohler  and  Dumas — A  Survey  of  their  more 
important  Work. 

Liebig  and  Wohler,  who  were  guided  by  similar  scientific 
aims,  and  were  at  the  same  time  close  personal  friends,  must 
be  spoken  of  together  in  the  history  of  the  science;  the 
portrait  of  the  one  is  incomplete  unless  supplemented  by  the 
characteristic  features  of  the  other.  The  fruit  of  their 
common  labour  is  among  the  richest  in  the  whole  of 
chemistry.  The  selection  of  their  letters,  extending  from  1829 
to  1873,  which  was  edited1  by  the  late  A.  W.  v.  Hofmann, 
with  E.  Wohler 's  co-operation,  is  a  memorial  to  the  steadfast 
friendship  that  existed  between  the  two  men,  and  at  the  same 
time  a  most  important  contribution  to  the  history  of 
chemistry. 

Justus  Liebig,2  whose  influence  in  shaping  the  radical 

1  Published  by  Vieweg,  Brunswick,  1888. 

2  Cf.  the  Memoirs  by  H.  Kolbe,  Journ.  pr.  Chem.  (2),  vol.  viii.  p.  428  ; 
by  A.  W.  v.  Hofmann,  Ber. ,  vol.  vi.  p.  465 ;  and  especially  the  various 
memorial  papers  (partly  by  A.  W.  v.  Hofmann)  on  Liebig  and  Wohler,  Ber. , 
xxiii.  Ref.  p.  785  et  seq.       These  last  include,  in  an  appendix,  a  fragment 


v  LIEBIG,  WOHLER,  AND  DUMAS  263 

theory  and  upon  organic  chemistry  in  general  has  just  been 
touched  upon,  earned  by  his  scientific  work  the  right  to  be 
regarded  as  one  of  the  most  distinguished  investigators  of 
the  century.  Born  at  Darmstadt  on  12th  May  1803,  his 
early  years  did  not  seem  to  give  any  special  promise  of  the 
fiery  spirit  which  he  later  developed,  although  it  was 
not  long  before  he  felt  himself  drawn  towards  chemistry 
with  irresistible  power.  He  has  himself  given  us  a  graphic 
description,  in  the  autobiographical  sketch  already  mentioned, 
of  the  way  in  which  he  gained  a  knowledge  of  chemical  facts 
and  phenomena,  having  determined  at  an  early  age  to  make 
chemistry  a  study,  to  the  utter  astonishment  of  his  teachers 
and  fellow  pupils.  He  relates  in  pleasant  manner  how 
"  that  disposition  developed  in  myself,  which  is  found  in 
chemists  more  than  in  students  of  other  sciences,  viz., 
to  think  in  phenomena  "  (in  Erscheinungen  zu  denken.)  It 
was  this  capacity  which  caused  "  all  that  I  saw,  whether  in- 
tentionally or  unintentionally,  to  remain  fixed  in  my  memory 
with  photographic  accuracy." 

He  soon  forsook  the  calling  of  apothecary,  through 
which  alone  it  was  possible  at  that  time  to  gain  a  practical 
knowledge  of  chemistry,  in  order  to  devote  himself  to 
academic  studies.  Relying  on  himself  alone,  he  continued 
his  early-begun  investigations  upon  fulminate  of  silver,  which 
he  hoped  would  give  him  a  certain  definite  position  in  science. 
But  however  independent  the  youth  thus  showed  himself  in 
this  direction,  he  was  unable  to  resist  the  influence  of  the 
natural  philosophy  (or,  as  it  might  be  better  expressed  in 
English,  physio-philosophy)  current  at  that  day.  At  a  later 
period  we  find  him  speaking  with  bitterness  of  the  two  years 
that  he  had  lost  by  it,  during  which  time  he  studied  under 


of  an  autobiography  of  Liebig's.  Compare  also  the  Letters  between  Liebig 
and  Wohler,  and  Liebig  and  Berzelius.  In  1895,  W.  A.  Shenstone  wrote  a 
short  Life  of  Liebig  for  the  Century  Science  Series  (Cassell  and  Co. ),  which 
gives  in  brief  compass  an  excellent  picture  of  the  man  and  the  chemist, 
though — from  want  of  space — too  little  is  said  of  his  purely  scientific 
work. 


204  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

Schelling  at  Erlangen.1      But  he  rescued   himself  from  this 
by  going  in  search  of  his  science  to  where,  at  that  time,  it 
nourished   most   brilliantly, — to   Paris,    where    Gay-Lussac, 
Thenard,  Dulong,  Chevreul,  Vauquelin  and  others  were  hard 
at   work.      With    recommendations    from    Alexander    von 
Humboldt  to  Gay-Lussac  and  other  influential   chemists,  he 
recovered  himself  in  those  surroundings  (as  he  has  himself  so 
delightfully  described),  and  soon  became  closely  associated 
with  Gay-Lussac,  the  result  of  which  was  their  important 
investigation  of  the  fulminates.      This  piece  of  work  paved  a 
way  for  him  ;  in  1824  he  was  called  as  professor  to  Giessen, 
where  he  remained  for  twenty-eight  years,  but  where  at  first 
he  had  to  fight  hard   and  continuously  in  order  to  maintain 
his  position,  his  youth  being  a  source  of  offence  to  the  older 
professors.2      In  1852  he  accepted  a  call  to  the  University  of 
Munich,  being  led  to  this  by  the  desire  to  throw   off  the 
fatigues  of  laboratory  teaching  and   to   live    all  the    more 
ardently  for  research.     His  magnificent  labours  were  brought 
to  a  close  there  by  death,  on  18th  April,  1873,  but  the  genius 
which  inspired  them,  and  which  had  acted  with  such  powerful 
effect  upon  his  contemporaries,  continued  to   influence  man- 
kind.    How  powerful  an  influence  he  exercised — as  shown  in 
his   greatness  as  a  teacher,  in   the  transformation  of  whole 
branches  of  the  science,  and  in  the  setting  aside  of  firmly 
rooted  views  which  in  his  opinion  were  erroneous — we  shall 
now  attempt  shortly  to  describe. 

1  In  an  essay  entitled    Ueber  das  Studium    der  Naturwissenschaften 
("  On  the  Study  of  the  Natural  Sciences  "),  published  in  1840,  Liebig  ex- 
pressed himself  as  follows  :  "I  myself  spent  a  portion  of  my  student  days 
at  a  university  where  the  greatest  philosopher  and  metaphysician  of  the 
century  charmed  the  thoughtful  youth  around  him  into  admiration  and 
imitation  ;  who  could  at  that  time  resist  the  contagion  ?    I  too  have  lived 
through  this  period — a  period  so  rich  in  words  and  ideas  and  so  poor  in 
true  knowledge  and  genuine  studies  ;  it  cost  me  two  precious  years  of  my 
life." 

2  G.   Weihrich,   in  his  pamphlet,  Beitrdge  zur  Geschichte  des  chemis- 
chen   Unterrichts  an  der  Universitdt  Giessen  (1891),  has  given  a  full  and 
careful  account  of  Liebig's  academic  work  and  of  his  relations  to  the  Uni- 
versity. 


v  LIEBIG'S  LIFE  AND  WORK  265 

As  a  teacher  Liebig  stands  almost  alone.  Berzelius,  the 
great  master,  only  drew  around  himself  pupils  who  had 
already  a  considerable  knowledge  of  the  subject,  and  worked 
(directly)  in  a  comparatively  narrow  circle.  Liebig,  on  the 
other  hand,  founded  a  real  school  of  chemistry,  by  sparing  no 
pains  in  instructing  his  pupils  individually  from  the  com- 
mencement of  their  course  of  study.  He  was  the  first  to  give 
systematic  teaching  in  chemistry,  for  up  to  that  time  there 
was  no  laboratory  in  existence  which  was  devoted  solely  to 
that  purpose.  And  he  was  also  the  first  to  recognise  the 
necessity  for  having  chemical  institutes  which  should  further 
not  merely  the  science  itself,  but  also  the  many  other 
branches  dependent  upon  it.  His  laboratory  in  Giessen 
served  as  a  pattern  upon  which  numerous  others  were  in  the 
course  of  years  modelled,  at  first  slowly  but  afterwards  in  more 
rapid  succession.  By  the  charm  of  his  own  personality  Lie- 
big  stimulated  his  pupils  and  inspired  them  with  enthusiasm, 
especially  when  the  solution  of  a  scientific  question  came  up. 
Kolbe  has  described  for  us  his  unique  character  as  a  teacher 
in  the  following  striking  sentences: — "  Liebig  was  not  a  teacher 
in  the  ordinary  sense  of  the  word.  Scientifically  productive 
himself  in  an  unusual  degree,  and  rich  in  chemical  ideas,  he 
imparted  the  latter  to  his  more  advanced  pupils,  to  be  put 
by  them  to  experimental  proof;  he  thus  brought  his  pupils 
gradually  to  think  for  themselves,  besides  showing  and 
explaining  to  them  the  methods  by  which  chemical  problems 
might  be  solved  experimentally." 

In  addition  to  this  Liebig  gave  a  new  form  and  meaning 
to  his  experimental  lectures,  so  that  here  also  he  set  up  a 
standard.  His  pupils  were  legion  ;  many  of  them  afterwards 
spread  abroad  the  doctrines  of  their  master  in  universities, 
polytechnic  institutes,  technical  schools,  etc.  Out  of  a 
long  list  of  them  which  might  be  given  here,  the  following 
may  be  mentioned : — A.  W.  v.  Hofmann,  Strecker,  Fresenius, 
Will,  H.  Buff,  Fehling,  Henneberg,  Schlossberger,  Rochleder, 
Schlieper,  Scherer,  Redtenbacher,  v.  Bibra,  Varrentrapp, 
Th.  Poleck,  Playfair,  Muspratt,  Stenhouse,  Brodie,  Gerhardt, 
Williamson,  Wurtz,  Frankland  and  Volhard. 


266  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

The  mental  vigour  which  was  shown  in  the  results  of 
Liebig's  teaching  is  also  seen  in  his  literary  activity,  which 
awakens  a  feeling  of  astonishment  by  its  many-sidedness, 
embracing  as  it  does  the  most  various  branches  of  the 
science.  Throughout  it  all  we  see  the  capacity  of  the  true 
investigator  to  state  points  correctly  and  clearly,  to  grasp 
the  connection  between  different  processes  distinctly,  and  to 
draw  able  and  ingenious  conclusions.  These  merits  impart 
to  Liebig's  writings  a  great  and  ever-renewed  charm.  His 
numerous  experimental  researches,  together  with  the  joint 
ones  with  Wohler,  were  mostly  published  in  the  Annalen* 
which  he  began  to  give  out  in  1832.  His  extended 
investigations  in  physiological  chemistry,  which  were  begun 
in  1837,  led  him  on  to  the  grand  achievement  of  setting  forth 
the  applications  of  chemistry  to  agriculture,  physiology  and 
pathology  in  three  separate  works.2  In  these  he  combated 
the  current  doctrines  which  were  held  with  regard  to  the 
nutrition  of  plants  and  animals,  basing  his  arguments  upon 
exact  experiments.  Notwithstanding  the  great  excitement 
which  those  publications  produced,  Liebig  found  leisure  to 
write  his  Chemische  Brief e  ("Chemical  Letters,"  1844),  by 
which  he  proved  that  chemistry  might  be  treated  popularly, 
and  yet  at  the  same  time  scientifically.  It  is  almost 
inconceivable  how  he  still  found  time  remaining  to  devote  to 

1  Till  1840  this  journal  was  termed  Annalen  der  Pharmacie,  and  after 
that  date  (with   Wohler  as  joint  editor)  Annalen  der  Chemie  und  Phar- 
macie. 

2  Die  Chemie  in  ihrer  Anwendung  auf  Agrilcultur  und  Physiologic,  1840 
("  Chemistry  in  its  Application  to  Agriculture  and  Physiology,"  1840); 
Die  Thierchemie  oder  organische  Chemie  in  ihrer  Anwendung  auf  Physiologic 
und  Pathologie,  1842  ("  Animal  or  Organic  Chemistry  in  its  Application  to 
Physiology  and  Pathology,"  1842) ;  Der  chemische  Prozess  der  Erndhrung 
der  Vegetabilien  und  die  Naturgesetze  des  Feldbaues,  1862  ("  The  Chemical 
Processes  in   the  Nutrition   of  Vegetables,    and  the  Natural    Laws    of 
Tillage,"  1862).     In  one  of  his  letters  to  Berzelius  (Letters,  p.  210)  Liebig 
tells  us  how  and  why  he  was  led  to  take  up  this  last  branch  of  applied 
chemistry.     An  "insurmountable  distaste  and  repugnance  to  this  dispu- 
tation in  chemistry  had  taken  hold  of  him  ;  he  was  tired  out  (auf  die  Spitze 
gestellt)  by  the  controversy  about  the  substitution  theory,"  etc.   Whereupon 
he  developed  in  broad  lines  the  programme  of  his   agricultural  chemical 
work. 


v  LIEBIG'S  LITERARY  ACTIVITY  267 

the  ffandwdrterbuck  der  reinen  und  angewandten  Chemie 
("  Dictionary  of  Pure  and  Applied  Chemistry  "),  founded  by 
Wohler,  Poggendorff  and  himself,  and,  after  the  death  of  Ber- 
zelius  in  1848,  to  the  Jahresbericht  uber  die  Fortschritte  der 
Chemie.  In  addition  to  all  these  there  are  still  to  be  men- 
tioned his  occasional  papers,1  some  of  which  exercised  a 
powerful  effect ;  this  applied  in  an  especial  degree  to  the 
two  essays  upon  the  state  of  chemistry  in  Austria  and 
Prussia.  In  these,  as  in  other  papers  devoted  to  questions 
of  theoretical  chemistry  (e.g.  in  his  writings  directed  against 
the  views  of  Dumas,  and  of  Laurent  and  Gerhardt),  is  shown 
the  sparkling  critical  vein  of  this  gifted  man,  who,  from  his 
rectitude  and  love  of  truth,  never  palliated  what  he  felt  to 
be  erroneous  or  insincere.  Occasionally  Liebig  may  have 
gone  too  far  in  his  critical  utterances  upon  particular  men ; 
but  the  mainspring  of  his  decided  attitude  with  respect  to 
them  was  always  the  boundless  love  of  science  and  of  truth, 
and  an  inflexible  sense  of  justice. 

As  an  investigator  Liebig  shows  all  his  individuality. 
To  organic  chemistry  he  had  devoted  the  full  powers  of  his 
mind  from  the  very  beginning,  without  however  neglecting 
any  important  part  of  inorganic.  His  very  first  work — that 
upon  the  fulminates — led  to  valuable  results ;  for,  through  it 
the  isomerism  of  cyanic  and  fulminic  acids  became  recognised, 
a  new  field  for  investigation  being  thereby  opened  up. 
Another  result  of  this  laborious  research  upon  these  easily 
decomposable  substances  was  the  perfecting  of  organic 
analysis,  to  which  Liebig  gave  its  present  form.  By  means 
of  methods  improved  by  himself,  he  established  the  com- 
position of  numerous  organic  compounds,  especially  of 
various  acids.  His  work  upon  these  last  led  him  to  a  distinct 
conception  of  the  term  basicity ;  from  this  he  developed  his 
doctrine  of  polybasic  acids  (already  touched  upon),  doing 
more  to  clear  up  the  points  involved  here  than  any  other 
chemist  before  him. 

1  These  were  published  by  M.  Carriere  under  the  title  JReden  und 
Abhandlungen  ("  Speeches  and  Essays"),  by  Justus  von  Liebig.  (In  1845 
he  was  made  a  baron  by  the  Grand  Duke  of  Hesse.) 


268  THE  MODERN  CHEMICAL  PERIOD  CHAP, 

His  previous  admirable  researches  upon  compounds 
closely  related  to  alcohol  and  acetic  acid,  e.g.  ethyl-sulphuric 
acid,  aldehyde,  acetal,  chloral,  etc.,  rendered  him  specially 
capable  of  developing  the  radical  theory  and  infusing  fresh 
life  into  it.  The  work  which  he  did  upon  sulphocyanogen 
compounds  and  upon  the  decomposition  products  of  am- 
monium sulphocyanide  showed  him  as  a  brilliant  experi- 
menter in  all  his  many-sidedness. 

But  his  most  remarkable  achievements  were  the  re- 
searches carried  out  conjointly  with  Wohler,  which  bring  them 
both  before  us  in  their  full  freshness  and  power,  and  which 
will  long  continue  to  call  forth  the  admiration  of  chemists. 
Wohler's  work  upon  cyanic  acid  and  Liebig's  upon  the  ful- 
minates drew  them  together;  their  friendship  is  beautifully 
shown  by  the  investigations  which  they  undertook  in  common, 
during  which  each  animated  the  other,  while  striving  at  the 
same  time  to  do  his  best  himself.1  And  how  strikingly  was 
the  one  man  the  complement  of  the  other !  Liebig — fiery, 
restless,  and  always  advancing,  able  to  utilise  his  rich 
experiences  gained  in  the  preparation  and  analysis  of  organic 
compounds  for  overcoming  the  hardest  difficulties.  Wohler, 
on  the  other  hand,  quiet,  almost  prosaic,  but  not  less  conscious 
of  his  aim  than  Liebig  himself,  exercising  patience  in  clearing 
up  obscure  points  to  which  too  little  attention  had  been 
paid.  The  memorable  research  upon  the  radical  of  benzoic 
acid  has  been  already  detailed.  The  investigations  upon 
amygdalin  cleared  up  the  difficult  point  as  to  how  bitter 
almond  oil  was  formed,  and  those  upon  uric  acid,  published 
in  the  same  year  (1837),  enriched  organic  chemistry  to  an 
undreamt-of  extent  with  a  wealth  of  the  most  remarkable 
compounds, — compounds  which  have  quite  recently  proved 
objects  of  the  greatest  interest  to  chemists.  We  are  indeed 
not  wrong  in  asserting  that  the  organic  chemistry  of  to-day 
is  grounded  mainly  upon  the  pioneering  labours  of  Liebig, 
and  of  Liebig  and  Wohler  together. 

1  Cf.  the  letters  of  both  quoted  in  A.  W.  v.  Hofmann's  Memoir  of 
Wohler,  Ber.,  vol.  xv.  p.  3127  etseq.,  and  also  the  Correspondence  already 
frequently  referred  to. 


v  LIEBIG  AS  AN  INVESTIGATOR  269 

In  addition  to  all  this,  inorganic  chemistry  was  anything 
but  neglected  by  Liebig,  who  enriched  it  by  valuable  obser- 
vations on  the  most  various  subjects ;  we  have  only  to  recall 
his  work  upon  the  compounds  of  alumina,  antimony  and 
silicic  acid,  and  many  analytical  methods  which  he  worked 
out,  e.g.  the  separation  of  nickel  from  cobalt.  The  results 
obtained  by  him  in  the  laboratory  were  often  of  great 
service  for  technical  chemistry;  for  instance,  the  improved 
preparation  of  cyanide  of  potash  for  the  galvano-plastic 
process,  and  the  reduction  of  a  solution  of  silver  by  aldehyde 
for  the  production  of  mirrors. 

Liebig's  share  in  the  development  of  organic  chemistry, 
especially  with  regard  to  the  views  which  had  come  to  be 
accepted  in  it,  became  less  marked  towards  the  end  of  the 
thirties,  as  from  that  time  he  gave  all  his  energies  to  the 
solution  of  a  great  question  which  had  only  an  indirect 
bearing  upon  chemistry.  The  nutrition  of  plants  and 
animals,  the  transformations  of  matter  in  animated  nature 
—these  were  the  grand  problems  which  he  strove  to  solve 
by  experimental  researches  in  an  entirely  new  direction. 
The  influences  which  emanated  from  him,  the  setting  right 
of  erroneous  views,  the  ingenious  interpretation  of  natural 
processes  investigated  by  himself  and  his  pupils,  and  the 
stimulus  which  invariably  accompanied  his  labours  and 
the  deductions  drawn  from  them, — all  these  can  but  be 
referred  to  here.  The  most  important  results  of  those 
researches  will  be  spoken  of  under  the  history  of  physio- 
logical chemistry.  Liebig's  experiments  on  the  nutrition 
of  animals  led  him  to  distinguish  clearly  between  nutrient 
substances  among  themselves,  and  between  these  and 
other  substances  which,  though  not  directly  nutrient,  bring 
about  metabolic  changes  in  the  organism.1  By  getting 
at  the  relative  nutritive  values  of  these  materials  he 
was  enabled  to  introduce  improved  systems  of  feeding, 
and  so  to  further  the  laws  of  health;  we  have  only  to 
recall  here  his  extract  of  meat  and  his  "children's  food." 

1  "...    Unterscheidung  der  Ndhrstqffe  unter  sich  und  von  den  Genust- 
mitteln. " 


270  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

He  was  thus  in  this  respect  a  general  benefactor  of 
mankind. 

We  may  close  this  attempt  at  depicting  within  narrow 
limits  the  scientific  achievements  of  Liebig  with  the  follow- 
ing eloquent  words  of  A.  W.  v.  Hofmann : — "  If  we  sum  up 
in  our  minds  all  that  Liebig  did  for  the  good  of  mankind — 
in  industries,  in  agriculture,  and  in  the  laws  of  health,  we 
may  confidently  assert  that  no  other  man  of  learning,  in  his 
course  through  the  world,  has  ever  left  a  more  valuable 
legacy  behind  him." 

Friedrich  Wohler,1  whose  work  blended  so  happily  with 
that  of  Liebig,  also  proved  himself  by  his  own  individual 
researches  a  master  in  his  science.  By  far  the  greater 
portion  of  his  work  lay  in  the  domain  of  inorganic  chemistry 
which  he  furthered  in  a  remarkable  degree. 

Wohler's  life  may  be  sketched  in  a  few  sentences.  Born 
in  the  village  of  Eschersheim,  near  Frankfort  on  the  Main, 
on  July  31st,  1800,  he  received  in  the  latter  city  a  splendid 
education  at  the  hands  of  such  eminent  teachers  as  Karl 
Bitter,  Grotefend,  and  F.  C.  Schlosser.  There,  too,  he  first 
made  acquaintance  with  chemistry,  to  which  he  remained 
faithful,  thanks  to  the  influence  of  L.  Gmelin,  notwith- 
standing that  he  went  through  the  medical  curriculum  at 
Marburg  and  Heidelberg.  It  was  Gmelin,  too,  who  re- 
commended the  young  doctor  of  medicine  to  Berzelius,  the 
latter  receiving  him  with  open  arms.  After  barely  a  year's 
stay  in  Stockholm, — a  year,  however,  rich  in  experiences 
and  uneffaceable  impressions,  and  of  which  he  himself  has 
given  us  such  a  clear  picture2 — Wohler  returned  to  Germany 
in  the  autumn  of  1824,  to  become  shortly  afterwards  a 
teacher  in  the  Technical  School  (Gewerbeschule)  at  Berlin. 
In  1831  he  had  to  leave  the  pleasant  and  stimulating 
society  of  his  friends  there  (among  whom  we  may  mention 
Mitscherlich,  the  brothers  Rose,  PoggendorfF  and  Magnus) 
to  fill  the  post  of  professor  in  the  newly-founded  Higher 
Technical  School  at  Cassel ;  while  in  1836  he  accepted  a 

1  Cf.  A.  W.  v.  Hofmann's  Memoir  of  Wohler,  Ber.,  vol.  xv.  p.  3127  et 
seq.,  and  Ber.,  vol.  23,  Ref.  p.  833.  2  Ber.,  vol.  viii.  p.  838  et  seq. 


v  WOHLER'S  SCIENTIFIC  WORK  271 

call  to  Gb'ttingen  as  successor  to  Stromeyer,  where,  till  his 
death  on  23rd  September  1882,  he  remained  a  bright 
ornament  of  the  Georgia- Augusta  (the  university  of  that 
town). 

Wohler's  influence  as  a  teacher,  especially  after  his  re^ 
moval  to  Gottingen,  may  be  described  as  enormous.  Like 
his  friend  Liebig,  he  laid  the  greatest  weight  upon  a  thorough 
grounding  in  the  rudiments  of  chemistry.  The  advantages 
which  he  had  gained  from  his  analytical  work  under  Berzelius 
he  now  imparted  to  his  pupils.  Out  of  a  long  list  of  these, 
a  few  may  be  named  who  themselves  subsequently  continued 
to  teach  in  the  spirit  of  their  master: — Th.  Scherer,  H. 
Kolbe,  Henneberg,  Knop,  Stadeler,  Geuther,  Limpricht, 
Fittig,  Beilstein,  Hiibner  and  Zoller. 

Wb'hler  was  especially  active  in  a  literary  sense  during 
the  earlier  portion  of  his  life,  as  is  shown  by  his  co-operation 
in  the  Dictionary  of  Chemistry,  already  mentioned,  and  his 
translations  of  the  Text-Book  and  Annual  Reports  (Jahres- 
lerichte)  of  Berzelius.  The  first  edition  of  his  Grundriss  der 
anorganischen  Chemie  ("  Outlines  of  Inorganic  Chemistry ") 
occupying  about  150  pages,  appeared  in  1831,  the  Organic 
following  in  1840 ;  both  of  these  went  through  numerous 
editions.1  His  results  in  the  investigation  of  minerals  he 
collected  together  in  1853  in  the  valuable  work,  Praktische 
Ubungen  in  der  chemischen  Analyse  ("  Practical  Exercises  in 
Chemical  Analysis  ").2  His  experimental  researches — most 
of  which  he  published  in  the  Annalen  der  Chemie,  but  some 
of  the  earlier  ones  in  Poggendorff's  and  in  Gilbert's  Annalen 
— embrace  almost  every  branch  of  inorganic  chemistry. 
Some  of  them  also  led  to  the  opening  up  of  important 
branches  of  organic,  e.g.  his  splendid  work  upon  cyanic  acid 
and  its  salts,  the  discovery  of  urea,  and  also  the  investi- 
gations carried  on  along  with  Liebig.  In  all  of  them,  as 

1  From  its  sixth   edition  the  Organic  Chemistry  has  been  admirably 
edited  by  Rudolf  Fittig  ;  the  fourteenth  and  fifteenth  (the  last)  editions  of 
the  Inorganic  were  given  out  by  H.  Kopp. 

2  The  second  edition  appeared  in  1861  under  the  title  Die  Miner alanalyse 
in  Beispielen  ("The  Analysis  of  Minerals,  illustrated  by  Examples"). 


272  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

also  in  his  later  labours,  his  remarkable  gifts  as  an  observer 
are  apparent. 

We  cannot  enter  into  details  at  this  point  either  with 
regard  to  his  work  in  analytical  chemistry,  which  he  enriched 
by  admirable  methods,  or  to  that  in  inorganic.  But  a  few 
investigations  in  the  latter  branch  must  just  be  mentioned, 
viz.  those  upon  aluminium,  boron,  silicon  and  titanium, 
and  their  remarkable  compounds,  by  which  the  resemblance 
between  the  two  last-named  elements  and  carbon  was  clearly 
brought  to  light. 

The  papers  in  which  Wohler  describes  the  results  of  his 
experiments  are  written  in  a  clear,  forcible  and  simple 
manner,  and  attract  our  attention  not  merely  by  those 
characteristics — now-a-days  somewhat  rare, — but  above  all  by 
the  depth  of  their  contents.  That  he  had  plenty  of  humour 
at  command  is  proved  by  his  letters  to  Liebig,  and  by  the 
delicious  satires l  which  he  wrote  when  Dumas  allowed  him- 
self to  be  carried  too  far  by  the  deductions  that  he  drew 
from  the  doctrine  of  substitution.  Wohler  never  rushed  of 
his  own  accord  into  discussions  upon  important  questions  of 
theoretical  chemistry, — a  trait  characteristic  of  his  quiet 
disposition,  and  one  which  distinguishes  him  from  Liebig, 
the  born  reformer,  who  looked  upon  this  as  a  matter  of  duty. 

As  has  been  already  said,  the  two  investigators  will 
remain  inseparable  in  the  history  of  chemistry.  Liebig 
himself  gives  expression  to  this  in  one  of  his  last  letters  to 
Wohler,  dated  December  31st,  1871,  in  the  following 
beautiful  terms  : — "  Even  after  we  are  dead  and  our  bodies 
long  returned  to  dust,  will  the  ties  which  united  us  in  life 
keep  our  memory  green,  as  an  instance — not  very  frequent — 
of  two  men  who  wrought  and  strove  in  the  same  field 
without  envy  or  ill-feeling,  but  who  continued  in  the  closest 
friendship  throughout." 

Jean  Baptiste  Andre  Dumas,2  who  was  born  at  Alais  in 
1800,  and  died  at  Cannes  in  1884,  rendered  to  his  science 

1  Ann.  Chem.,  vol.  xxxiii.  p.  309  (see  alsobelow,  p.  282) ;  also  the  Liebig 
Berzelius  Letters,  p.  211,  note. 

2  Cf.  A.  W.  v.  Hofmann's  Memoir,  Ber.,  vol.  xvii.  fief.  p.  629  et  seq. 


v  DUMAS  :  A  SURVEY  OF  HIS  WORK  273 

extraordinary  services,  to  which  we  shall  frequently  have 
occasion  to  refer.  Beginning  life  as  apprentice  to  an 
apothecary  in  his  native  town,  he  found  this  calling  uncon- 
genial, and  set  out  on  foot  for  Geneva  in  the  autumn  of 
1816.  Coming  in  contact  there  with  such  distinguished 
men  as  Pictet,  Decandolle,  de  la  Rive  and  others,  he  was 
stimulated  to  scientific  researches  which  quickly  attracted 
the  attention  of  the  savants  just  named.  He  made  him- 
self known  particularly  by  the  active  part  which  he  took  in 
the  physiologico-chemical  investigations  of  Prevost.  With 
the  versatility  which  distinguished  him,  he  soon  began  to 
take  up  problems  in  organic  as  well  as  in  physical  chemistry. 
In  1823,  acting  on  A.  v.  Humboldt's  advice,  Dumas  betook 
himself  to  Paris,  finding  there  the  most  friendly  reception 
at  the  hands  of  the  eminent  chemists  of  that  city.  At 
Paris  he  spent  the  rest  of  his  life,  filling  various  posts  as  a 
teacher  and  also  other  offices;  he  lectured  with  striking 
effect  at  the  Athenceum,  the  ficole  Centrale  des  Arts  et  Manu- 
facticres,  the  Sorbonne,  and  the  polytechnic  and  medical 
schools. 

No  laboratory  having  been  placed  at  his  disposal,  he 
established  one  at  his  own  expense  in  1832.  After  the 
year  1848  Dumas  was  frequently  called  into  the  public 
service,  being  for  a  long  time  minister  of  state,  besides  having 
to  fill  other  offices,  so  that  his  work  as  a  teacher  was  often 
interrupted.  The  keen  interest  which  he  felt  in  public 
affairs  was  shown  in  many  cases  by  his  active  co-operation, 
e.g.  in  furnishing  Paris  with  a  water  supply  and  in  devis- 
ing means  to  remedy  the  diseases  of  the  silkworm  and 
vine,  etc.  In  1 8  6  8  he  was  further  nominated  permanent 
secretary  of  the  Academy,  of  which  he  had  long  been  a 
member. 

We  have  still  to  make  mention  of  the  more  important 
of  Dumas'  literary  labours.  The  first  of  the  larger  works 
by  which  he  became  known  was  his  Traitd  de  Chimie  apliqude 
aux  Arts  (1828);  in  its  treatment  of  the  matter,  and 
especially  its  arrangement,  this  remained  a  model  for  many 
subsequent  text -books  on  technology.  The  whole  in- 

V 


274  THE  MODERN  CHEMICAL  PERIOD  CHAP, 

dividuality  of  the  man  comes  out  in  his  Lemons  sur  la 
Philosophic  Chimique  (published  in  1837  by  Bineau  from 
Dumas'  lectures),  in  which  he  treats  the  development  of 
chemical  theories  with  great  clearness  and  with  a  rare 
charm  of  style ;  this  work,  however,  cannot  be  regarded  as 
a  strictly  historical  one.  The  numerous  panegyrics  which 
Dumas  delivered  are  in  their  form,  down  to  the  minutest 
detail,  carefully  elaborated  works  of  art ;  among  them  may 
be  mentioned  those  upon  Pelouze,  Balard,  Regnault  and 
Faraday. 

The  Essai  de  Statique  Chimique  des  ~Etres  Organists,  par 
MM.  Dumas  et  Boussingault  (1841),  became  especially  well 
known ;  in  this  the  life  of  plants  and  animals  and,  more 
particularly,  the  processes  of  metabolism,  were  treated  from 
the  chemical  point  of  view.  The  opinions  expressed  here 
were  in  part  instigated  by  the  pioneering  work  of  Liebig,  whose 
influence  however  was  not  sufficiently  recognised  by  the 
authors,  so  that  he  felt  himself  called  upon  to  draw  atten- 
tion to  his  perfectly  justifiable  claims  in  very  distinct 
language.1  A  debt  of  gratitude  is  due  to  Dumas  for  the 
pious  service  which  he  rendered  in  editing  the  reissue  of 
Lavoisier's  works.2 

Most  of  the  numerous  experimental  researches  which 
we  owe  to  Dumas  were  published  by  him  in  the  Annahs  de 
Chimie  et  de  Physique,  of  which  he  was  one  of  the  editors 
after  1840.  In  recalling  his  most  important  and  productive 
labours,  emphasis  must  be  laid  upon  the  great  service  which 
he  rendered  in  working  out  various  methods  of  general 

1  Ann.  Chem.,  vol.   xli.  p.  351.     In  this  as  well  as  in  other  instances 
Dumas  unfortunately  did  not  show  in  a  favourable  light.     The  historian  is 
bound  to  notice  such  facts,  since  they  cannot  be  erased  from  the  scientific 
character  of  so  eminent  an  investigator.  Liebig  criticised  these  peculiarities 
of  Dumas  with  great  severity  (cf.  Ann.  Chem.,  vol.   ix.   pp.  47,  129  ;  also 
Kolbe's  claim  of  priority,  Journ.  pr.  Chem.  (2),  vol.  xvi.  p.  30 ;  and  the 
Berzelius-Liebig  Letters,  pp.  6,  7,  11,  34,  43,  45,  171,  238,  etc.).    Such  occur- 
rences are,  to  quote  Liebig,  "black  leaves  in  the  book  of  chemical  history, — 
black,  because  they  absorb  the  rays  of  light  without  thereby  becoming 
luminous  themselves. "     Dumas  was  unable  to  disprove  or  even  to  minimise 
the  heavy  charges  which  Liebig  brought  against  him, 

2  Cf.  p.  161,  note. 


BEGINNINGS  OF  UNITARISM  IN  ORGANIC  CHEMISTRY   275 

application.  His  mode  of  determining  vapour  densities 
and  that  of  estimating  nitrogen  have  found  universal 
appreciation.  His  admirable  investigations  in  organic 
chemistry  shed  a  brilliant  light  over  wide  branches  of  it, 
and  guided  many  chemists  for  a  time  as  to  the  direction  in 
which  they  should  work.  Mention  must  be  made  too  of 
his  conjoint  researches  with  Peligot l  upon  wood  spirit  and 
upon  sethal(from  spermaceti), — compounds  whose  analogy 
to  alcohol  he  proved  ;  and  of  his  discovery  and  investigation 
of  trichloracetic  acid,  which  crowned  the  edifice  of  the  sub- 
stitution theory.  The  general  character  of  his  work  naturally 
led  Dumas  to  take  an  active  share  in  the  discussion  of 
problems  in  theoretical  chemistry.  His  rather  unhappy 
participation  in  the  question  of  the  values  of  the  atomic 
weights  has  been  already  noticed.  The  determinations 
which  (partly  in  conjunction  with  Stas)  he  made  of  the 
atomic  weights  of  carbon,  oxygen  and  other  elements  deserve 
to  be  recorded  as  experimental  work  carried  out  with  the 
utmost  care  and  circumspection. 

Apart  from  the  shadow  thrown  upon  Dumas'  achieve- 
ments by  some  of  the  incidents  in  his  scientific  life,  his 
services  will  long  continue  to  excite  the  highest  admira- 
tion as  evidences  of  a  powerful  and  comprehensive  mind. 
The  immense  influence  which  he  exercised  upon  the  form 
assumed  by  organic  chemistry,  and,  in  particular,  upon  the 
development  of  general  views  opposed  to  dualism,  will  be 
detailed  in  the  following  section. 


The  Development  of  Unitary    Views  in  Organic 
Chemistry. — Substitution  Theories. 

At  the  time  when  Dumas  brought  forward  his  own  as 
well  as  previous  observations  upon  the  substitution  of 
hydrogen  by  chlorine  and  other  elements  as  a  basis  for 

1  E.  M.  Peligot,  born  in  1811,  was  for  a  long  time  Professor  of  Chemistry 
at  the  Conservatoire  desArts  et  Metiers,  and  distinguished  himself  by  much 
admirable  work  in  inorganic,  organic  and  technical  chemistry  (beet  sugar 
industry) ;  he  died  in  April  1890.  Cf.  Mon.  Scient.  1890,  p.  885. 

T   2 


276  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

theoretical  statements,  the  electro-chemical  doctrine  of  Ber- 
zelius,  and  the  radical  theory  which  fitted  in  with  it,  were  in 
high  repute.  The  idea  (deduced  as  it  was  from  numerous 
facts)  that  electro-positive  elements  like  hydrogen  could 
be  replaced  by  electro-negative  ones  like  chlorine,  oxygen 
and  others,  was  bound  to  become  a  stumbling-block  for  the 
dualistic  hypothesis,  which  could  no  longer  after  this  be  main- 
tained in  its  integrity.  The  various  attempts  to  explain  the 
phenomena  of  substitution  from  general  standpoints,  which 
now  fall  to  be  detailed,  were  at  the  same  time  the  significant 
utterances  of  a  struggling  unitarism  against  the  binary  view. 
In  connection  with  this,  one  has  to  recall  to  mind  that, 
according  to  the  position  of  Berzelius'  dualistic  doctrine  at 
that  time,  the  radicals  were  looked  upon  as  unalterable 
atomic  complexes.  The  consequence  of  the  electro-chemical 
view  was  the  assumption  that  negative  elements  like  chlorine, 
bromine  and  oxygen  could  not  enter  into  the  composition  of  a 
radical.  That  the  observations  on  the  substitution  of  hydro- 
gen atoms  in  organic  compounds  by  those  other  elements 
was  in  direct  contradiction  to  this  assumption,  appears  to 
us  now  self-evident. 


Dumas'  Laws  of  Substitution. 

Some  isolated  facts,  which  proved  that  a  substitution  of 
this  kind  could  go  on  among  the  elements,  were  already 
known  when  Dumas  turned  his  whole  attention  to  the 
subject.  Thus  Gay-Lussac  had  established  the  formation  of 
cyanogen  chloride  from  hydrocyanic  acid,  Faraday  that  of 
sesquichloride  of  carbon  (C2C16)  from  ethylene  chloride,  and 
Liebig  and  Wohler  the  conversion  of  bitter  almond  oil  into 
benzoyl  chloride.  It  had  not  escaped  these  chemists  that 
when  the  above  compounds  were  subjected  to  the  action  of 
chlorine,  an  amount  of  hydrogen,  equivalent  to  the  chlorine 
which  entered  into  them,  was  separated ;  indeed,  the  opinion 
was  expressed  (by  some,  if  not  all,  of  them)  that  the  one 
element  had  replaced  the  other. 


v  DUMAS'  LAWS  OF  SUBSTITUTION  277 

In  the  year  18341  Dumas,  a  propos  of  an  investigation 
on  the  mutual  action  between  chlorine  and  oil  of  turpentine, 
but  more  especially  of  his  work  upon  the  production  of 
chloral  from  alcohol,  condensed  into  two  empirical  rules  the 
facts  with  regard  to  substitution,  for  which  he  proposed  the 
designation  metalepsy  (i.e.  exchange,  /^eraX^i/rt?).  These 
were  not  intended  to  comprise  a  theory  of  substitution,  as 
his  first  utterances  on  the  subject  show,  but  only  to  give 
expression  to  the  facts.  They  were  as  follows: — 

"  When  a  compound  containing  hydrogen  is  exposed  to 
the  dehydrogenising  action  of  chlorine,  bromine,  or  iodine,  it 
takes  up  an  equal  volume  of  chlorine,  bromine,  etc.,  for  each 
atom  of  hydrogen  that  it  loses. 

"  If  the  compound  contains  water,  it  loses  the  hydrogen 
of  this  without  replacement." 

The  second  of  these  rules  was  deduced  from  the  trans- 
formation of  alcohol  into  chloral,  and  was  thus  intended  to 
explain  the  mode  of  formation  of  the  latter,  and  at  the  same 
time  to  support  Dumas'  view  of  the  constitution  of  alcohol, 
the  latter  being  regarded  by  him  as  a  compound  of  ethylene 
and  water. 

Dumas  soon  extended  his  statement  to  one  of  great 
significance,  viz.  that  in  chemical  reactions  generally  an 
exchange  of  equivalents  of  one  element  for  equivalents  of 
others  takes  place.  It  was  from  this  standpoint  that  he 
regarded  the  oxidation  of  alcohol  to  acetic  acid,  and  that  of 
bitter  almond  oil  to  benzoic  acid,  etc.  etc.,  and  he  emphasised 
the  point  that  each  atom  of  hydrogen  was  here  replaced  by 
half  an  atom  of  oxygen.  Those  views,  which  gave  evidence 
of  great  clearness  of  vision,  were  however  obscured  by 
certain  additions  which  could  not  fail  to  create  confusion 
with  regard  to  the  constitution  of  the  compounds  in  question; 
thus,  to  give  one  instance  only,  formic  acid  was  looked  upon 
as  a  "  metaleptic  product "  of  alcohol,  although  such  a  rela- 
tion could  not  be  proved  in  this  case. 

1  Of.  Ann.  Chim.  Phys.  (2),  vol.  Ivi.  pp.  113,  140. 


278  THE  MODERN  CHEMICAL  PERIOD  CHAP. 


Laurent's  Substitution  or  Nucleus  Theory. 

Dumas  limited  himself  at  that  time  (1835)  to  condensing 
the  known  facts  into  the  two  above-mentioned  laws.  But 
his  countryman  Laurent  went  further,  in  that  he  took  into 
consideration  the  nature  of  the  compounds  produced  by  sub- 
stitution, and  compared  them  with  the  original  ones.  He  was 
thus  led  to  the  proposition1  that  the  structure  and  chemical 
character  of  organic  compounds  are  not  materially  altered  by 
the  entrance  of  chlorine  and  the  separation  of  hydrogen. 
This  law,  when  taken  in  conjunction  with  the  view  that 
chlorine  assumes  the  role  of  the  substituted  hydrogen,  is  the 
kernel  of  the  Substitution  Theory  proper,  of  which  Laurent 
must  be  regarded  as  the  author ;  for  Dumas  denied  at  that 
time  the  analogy  between  substitution  derivatives  and  the 
original  compounds,  and  in  reply  to  Berzelius,  who  attacked 
him  for  this  assumption,  threw  the  responsibility  for  it  upon 
Laurent.2 

The  latter  then  strove  to  erect  a  system  by  developing 
the  above  doctrine,  the  result  of  his  efforts  being  the  so- 
called  Nucleus  Theory,3  which  was  published  in  the  year 
1836;  a  short  account  of  this  must  be  given  here,  even 
although  it  never  met  with  very  hearty  approval.4  According 
to  Laurent,  organic  compounds  contained  nuclei  (radicaux), 
and  he  distinguished  between  original  nuclei  (radicaux 
fondamentaux),  composed  of  carbon  and  hydrogen  in  simple 
atomic  proportions,  and  derived  nuclei  (radicaux  derives), 
which  were  produced  from  the  first-named  either  through  the 
substitution  of  hydrogen  by  other  elements  or  by  the  taking 
up  of  additional  atoms.  He  further  stated  that  compound 

1  Laurent  frequently  enunciated  this(cf.  Ann.  Chim.  Phys.  (2),  vol.  Ix. 
p.  223;  vol.  Ixi.  p.  125  ;  vol.  Ixvi.  p.  326). 

2  Comptes  Rendus,  vol.  vi.  pp.  647,  695.     Laurent  stood  up  for  his  own 
view  (Ann.  Chim.  Phys.  (2),  vol.  Ixvii.  p.  303). 

3  Cf.  Ann.  Chim.  Phys.  (2),  vol.  Ixi.  p.  125. 

4  L.  Gmelin  did,  it  is  true,  make  use  of  the  subdivision  of  organic  com- 
pounds, according  to  different  nuclei,  as  a  basis  in  his  well-known  text- 
book, and  helped  in  this  way  to  spread  Laurent's  views. 


v  LAURENT'S  NUCLEUS  THEORY  279 

radicals  like  amidogen  or  nitroxyl  might  substitute  in  place 
of  elements.  This  attempted  classification  of  organic  com- 
pounds, under  the  name  of  the  neucleus  theory,  shows  a 
distinct  connection  with  the  radical  theory ;  but  the  one- 
sided view  of  the  latter — that  the  radicals  were  unalterable 
— has  here  disappeared.  While  this  change  in  principle 
marks  an  advance,  the  abandonment  of  the  relation  between 
organic  and  inorganic  compounds  was  undoubtedly  a  great 
defect,  since  it  involved  the  loss  of  a  support  indispensable 
for  a  natural  classification  of  organic  substances. 

It  was  not  difficult  for  the  chief  exponents  of  the  radical 
doctrine  to  prove  the  insufficient  basis  of  the  nucleus  theory, 
the  more  so  that  Laurent  laid  himself  open  to  criticism  not 
merely  as  a  theoriser  but  also  as  an  experimenter.  His 
work  was  severely  handled  by  Liebig,  who  came  to  the 
conclusion  that  Laurent's  theory  was  unscientific  and  there- 
fore pernicious.  Berzelius  likewise  raised  his  voice  ener- 
getically against  it,  and  indeed  went  so  far  as  to  say  that  he 
considered  a  detailed  criticism  of  it  superfluous.  But,  as  a 
matter  of  fact,  Laurent  was  too  much  depreciated  from  this 
side ;  for,  however  much  we  may  dissent  from  many  of  his 
untenable  speculations,  his  effort  to  classify  organic  com- 
pounds on  uniform  principles,  and  to  show  their  connection 
with  one  another,  was  not  without  merit.  In  addition  to 
this  he  had  effectively  aided  in  overthrowing  the  dogma  of  the 
unchangeability  of  radicals.  And,  finally,  we  are  indebted 
to  him  for  the  proof  that  Dumas'  empirical  rules  of  substitu- 
tion are  by  no  means  always  applicable. 

Before  Laurent,  in  conjunction  with  Gerhardt,  had  again 
brought  forward  his  ideas  in  a  more  perfect  form,  Dumas1 
entered  the  lists  to  do  battle  against  the  radical  theory,  and, 
with  this,  against  the  dualistic  idea  in  general.  His  beautiful 
discovery  of  "  chloracetic  acid  "  afforded  him  the  immediate 
occasion  for  this,  and  he  now  gave  in  his  adhesion  to 
Laurent's  opinions,  which  formerly  he  would  have  nothing  to 
do  with.  The  substituting  atoms,  e.g.  the  halogens,  take  up 
the  role  of  the  expelled  hydrogen  atoms,  and  the  resulting 
1  Ann.  Chim.  Phys.  (2),  vol.  Ixxiii.  p.  73  et  seq. 


280  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

halogen  compounds  must  therefore  show  an  analogy  to  the 
original  ones, — this  was  for  Dumas  the  clear  result  of  his 
work  upon  trichloracetic  acid ;  and  he  drew  the  same  con- 
clusion from  the  similar  relations  existing  between  aldehyde 
and  chloral.  To  put  his  ideas  into  a  more  permanent  form, 
he  referred  such  related  compounds  to  definite  types,  from 
which  they  were  derivable. 

Dumas    Type  Theory  (1839). 

This  effort,  which  reminds  us  strongly  of  Laurent's 
nucleus  theory  (since  in  this  case  also  whole  series  of  com- 
pounds were  referred  to  fixed  atomic  complexes),  bears  in 
the  history  of  chemistry  the  name  of  the  Older  Type  Theory, 
to  distinguish  it  from  the  newer  one  of  Laurent  and 
Gerhardt.  Dumas  was  led  to  establish  his  theory  of  types l 
from  the  behaviour  of  trichloracetic  acid,  as  observed  by  him- 
self; he  laid  stress  upon  the  fact  that,  in  spite  of  the 
entrance  of  six  atoms  of  chlorine  in  place  of  six  atoms  of 
hydrogen,2  the  character  of  this  derivative  remained  essentially 
the  same  as  that  of  acetic  acid  itself.  Both  compounds  are 
monobasic  acids,  and  both  yield  products  of  analogous  com- 
position with  alkalies.  From  all  this  he  concluded  that 
"  there  are  in  organic  chemistry  certain  types  which  remain 
unchanged,  even  when  their  hydrogen  is  replaced  by  an 
equal  volume  of  chlorine,  bromine,  or  iodine."  Acetic  and 
trichloracetic  acids,  aldehyde  and  chloral,  marsh  gas  and 
chloroform,  belong  severally  to  the  same  chemical  types. 
According  to  Dumas,  one  such  type  embraced  compounds 
which  contained  the  same  number  of  equivalents  combined 
in  a  like  manner,  and  whose  properties  were  in  the  main 
similar.  We  see  here  that  the  mutual  relations  of  com- 
pounds belonging  to  one  chemical  type  are  the  same  as 

1  Ann.  Chim.,  vol.  xxxiii.  pp.  179  and  259;  cf.  also  M.  Berthelot's  recent 
work,  Introduction  &  Fjfaude  de  la  Chimie  des  Anciens  et  du  Moyen  Age 
(1889). 

2  Dumas  assigned  to  acetic  acid  the  formula  C4H8O4,  and  to  (tri)chlor- 
acetic  acid  that  of  C4H2C16O4. 


v  DUMAS'  UNITARY  SYSTEM  281 

those  which  Laurent  assumed  between  his  original  and  derived 
nuclei. 

But  the  term  "  chemical  type  "  did  not  satisfy  Dumas ; 
he  allowed  it  to  merge  into  that  of  "  mechanical  type,"  1  this 
latter  comprising  all  compounds  which  might  be  supposed  to 
be  formed  from  one  another  by  substitution,  even  if  they 
differed  totally  in  properties.  Acting  on  this  idea,  Dumas 
quite  rightly  classified  alcohol  and  acetic  acid  under  the  same 
mechanical  type  ;  but,  on  the  other  hand,  he  brought  together 
compounds  which  had  no  sort  of  connection  with  one 
another,  e.g.  formic  acid  and  methyl  ether.  The  ultimate 
result  was  that  an  empty  scheme  of  formulation  carried 
the  day  over  what  was  really  good  in  this  doctrine — a 
doctrine  developed  from  Laurent's  nucleus  theory.  The 
endeavour  to  arrange  organic  compounds  upon  certain 
types  outweighed  and  pushed  aside  the  higher  problems 
which  Berzelius  had  sketched  out  for  chemical  science. 
The  idea  of  definite  atomic  complexes  or  radicals,  which  was 
meant  to  pave  the  way  for  a  knowledge  of  the  chemical 
constitution  of  compounds,  was  superseded  by  the  setting  up 
of  mechanical  types,  and  thus  the  link  intended  to  connect 
organic  with  inorganic  compounds  was  completely  snapped. 

This  total  abandonment  of  the  principles  put  forward 
by  Berzelius,  and  found  by  him  to  be  so  serviceable, 
could  not  fail  to  arouse  his  liveliest  opposition.  Dumas  had 
characterised  Berzelius' electro-chemical  doctrine  as  erroneous ; 
the  unitary  conception  was  to  step  into  the  place  of  the 
dualistic  which  the  latter  theory  involved.  Every  chemical 
compound  forms  a  complete  whole,  and  cannot  therefore  consist 
of  two  parts.  Its  chemical  character  is  dependent  primarily 
upon  the  arrangement  and  number  of  the  atoms,  and  in  a  lesser 
degree  upon  their  chemical  nature.  These  propositions  of 
Dumas  stood  in  the  sharpest  opposition  to  the  doctrine  of 
Berzelius;  they  proclaimed  a  one-sided  unitarism,  which 
was  therefore  combated  by  Berzelius  with  every  force  at 
his  command. 

1  Regnault  had  already  (in  1838)  spoken  in  a  similar  sense  of  molecular 
types,  which  remain  unchanged  in  chemical  reactions. 


282  THE  MODERN  CHEMICAL  PERIOD  CHAP. 


The  Overthrow  of  Berzelius'  Ducdistic  Doctrine. 

Dumas  did  not  scruple  to  say  plainly  that  the  dualistic 
doctrine  was  harmful  and  retarded  the  development  of 
organic  chemistry,  and  he  made  every  effort  to  set  it  aside 
and  to  supplant  it  by  the  unitary  theory.  His  attack  upon 
Berzelius'  doctrine  (at  that  time  held  in  high  repute  by 
most  chemists)  was  vigorously  answered  both  by  the  latter 
and  by  Liebig.  Liebig x  indeed  admitted  many  points  which 
were  disputed  by  Berzelius,  e.g.  the  fact  of  substitution,  but 
he  protested  against  Dumas'  wide  extension  of  this  principle 
(of  substitution).  The  assertion  of  the  latter  that  every 
element  of  a  compound  might  be  replaced  by  another,  and 
yet  the  type  be  retained,  was  characterised  by  Liebig  as 
entirely  unproven,  and  met  with  an  ironical  rejoinder.2 
Berzelius,  who  saw  his  whole  system  based  upon  the  electro- 
chemical theory  threatened,  directed  his  criticism  in  the 
Jahresberichten  for  1838  and  the  next  five  years  or  so  against 
the  theory  of  types.  In  opposition  to  Dumas'  unitary  view 
he  set  up,  as  sharply  as  it  was  possible  to  do,  the  electro- 
chemical and  therefore  dualistic  theory  as  the  fundamental 
principle ;  he  adhered  indeed  essentially  to  his  former  stand- 
point, according  to  which  electro-negative  elements  could  in 
no  case  enter  into  the  composition  of  radicals. 

Berzelius  sought  to  get  over  the  difficulties  which  the 
substitution  of  hydrogen  by  chlorine  and  other  elements 
involved,  by  arguing  that  compounds  formed  in  this  manner 
must  have  a  constitution  different  from  that  of  the  original 
ones.  But  here  he  entered  upon  dangerous  ground,  and  was 
thereby  led,  prudent  investigator  as  he  was,  into  the  most 
utter  contradictions  of  the  principles  which  he  had  formerly 
held  to  be  inviolable. 

Berzelius  first  expressed  himself  upon  the  composition 
of  acetic  and  trichloracetic  acids.  While  the  former  (i.e.  the 

1  Ann.  Chem.,  vol.  xxxiii.  p.  301. 

2  Cf.  Ann.  Chem.,  vol.  xxxiii.  p.  308.     The  satirical  letter  given  here 
was  composed  by  Wohler  and  published  by  Liebig. 


v  BERZELIUS'  FIGHT  AGAINST  THE  SUBSTITUTION  THEORY  283 

anhydrous  acid) l  was  regarded  by  him  as  the  oxide  of  the 
radical  acetyl,  and  given  the  formula  C4P3  +  O3,  he  looked 
upon  trichloracetic  acid  as  a  so-called  "copulated  compound" 
or  "  conjugate  compound  "  (gepaarte  Verbindung"2)  of  quite 
different  constitution,  viz.  as  a  chloride  of  carbon  copulated 
with  oxalic  acid,  of  the  formula  Cg-Gig  +  CgOg.3  But  he  could 
not  at  that  time  make  up  his  mind  to  follow  this  to  its 
logical  conclusion,  and  to  ascribe  to  acetic  acid  an  analogous 
composition  (i.e.  to  write  it  down  as  methyl  copulated  with 
oxalic  acid),  manifestly  from  the  apprehension  that  he  would 
in  so  doing  surrender  a  principle  of  his  electro-chemical 
doctrine.  He  attempted  similarly  to  explain  the  constitu- 
tion of  other  chlorine  organic  derivatives,  by  assuming 
copulse  (Paarlinge)  containing  chlorine,  with  the  result  that 
a  different  rational  formula  was  assigned  to  the  mother 
substance  from  that  given  to  its  derivatives. 

These  unfortunate  attempts  to  explain  by  the  speculative 
method  the  constitution  of  chemical  compounds,  that  prob- 
lem which,  in  his  own  opinion,  was  the  most  important  in 
the  science,  led  Berzelius  completely  astray.  In  order  to 
carry  through  his  doctrine  of  copulse,  he  had  to  assume 
arbitrary  radicals  in  organic  compounds,  without  being  able 
to  adduce  the  least  evidence  in  favour  of  such  assumptions. 
Above  all,  he  did  not  see  what  these  really  led  to,  for  he 
overlooked  the  fact  that  his  chlorinated  copulae  could  only 
be  formed  by  the  substitution  of  the  hydrogen  atoms  of  the 
radical  by  chlorine. 

Melsens'4  important  observation,  made  in  the  year  1842, 

1  Berzelius  formulated  acetic  acid  as  hydrate,  C4j=t3-03  +  j*0,  i.e.  as  a 
compound  of  the  anhydride  (at  that  time  unknown)  with  water. 

2  The  idea  that  certain  organic  compounds  are  copulated  or  conjugated 
(gepaart)  was  definitely  expressed  for  the  first  time  in  one  of  the  earliest 
of  Gerhardt's  papers  (Ann.  Chim.   Phys.  (2),  vol.  Ixxii.  p.   184).     In  this 
paper  he  used  the  word  copulation  (accouplement)  to  signify  the  combination 
of  organic  substances  with  inorganic.     The  one  portion  of  such  compounds 
he  termed  the  copula  (copule),  e.g.  the  organic  substance  which  is  copulated 
with  an  inorganic  acid. 

3  For  an  explanation  of  these  "  crossed  "  symbols,  see  p.  236. 

4  Ann.  Chim.  Phys.  (3),  vol.  x.  p.  223. 


284  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

that  chloracetic  acid  is  reconverted  into  acetic  by  the  action 
of  potassium  amalgam,  convinced  Berzelius1  that  his  view  of 
the  two  acids  having  different  constitutions  was  no  longer 
tenable.  He  therefore  decided  to  regard  acetic  acid  in  the 
same  way  as  its  chlorine  derivative,  i.e.  as  a  copulated  oxalic 
acid  with  the  copula  C2Jt3,  formulating  the  two  compounds 
thus  — 

C2F3  +  C2O3.  jtO      .       .       .      Acetic  acid. 

s.tO      .        .       .      Chloracetic  acid. 


But  in  doing  this  he  made  the  important  admission  of  the 
substitution  of  hydrogen  by  chlorine  in  the  copula.  And 
even  although  he  did  emphasise  the  point  that  the  latter 
exercised  no  particular  effect  upon  the  compound  to  which 
it  belonged,  he  none  the  less  recognised  hereby  a  funda- 
mental principle  of  the  doctrine  of  substitution. 

But,  notwithstanding  this  admission,  Berzelius  remained 
to  the  end  of  his  life  an  opponent  of  the  theory  of  types,  and 
endeavoured  to  uphold  the  dualistic  view  by  every  means  in 
his  power.  He  had  to  undergo  the  pain,  however,  of  finding 
his  hitherto  faithful  adherents  no  longer  able  to  follow  him 
in  this,  and  indeed  of  hearing  them  dissent  publicly  from 
his  treatment  of  the  question  as  to  how  the  constitution  of 
organic  compounds  was  to  be  explained.  Liebig,  who  had 
already  before  this  taken  the  facts  of  substitution  into 
account,2  declared  openly  against  Berzelius'  far-fetched 
attempts  at  explanation,3  the  more  so  since  the  chlorine 
and  bromine  derivatives  of  aniline  had  been  investigated  in 
the  Giessen  laboratory  by  A.  W.  v.  Hofmann,  and  had  been 
accepted  as  evidence  that  the  chemical  character  of  a  com- 
pound depends  to  a  not  inconsiderable  extent  upon  the 
arrangement  of  its  atoms.  Liebig  therefore  turned  himself 
to  the  unitary  theory.  The  following  words  4  show  us  the 

1  Lehrb.  d.  Chemie  (fifth  edition),  vol.  i.  p.  709. 

2  Ann.  Chem.,  vol.  xxxi.  p.  119  ;  vol.  xxxii.  p.  72. 

3  Ibid.,  vol.  1.  p.  295  ("Berzelius  und  die  Probabilitatstheorien").     The 
correspondence  between  Berzelius  and  Liebig,  which  has  been  so  often  re- 
ferred to  already,  shows  us  in  a  truly  dramatic  way  the  gradual  estrange- 
ment of  the  two  men.  4  Ibid.  ,  vol.  1.  p.  297. 


v  OVERTHROW  OF  THE  DUALISTIC  DOCTRINE  285 

attitude  taken  up  by  Liebig,  and  we  may  be  sure  by  others 
also,  towards  Berzelius  at  that  time :  "  During  the  last 
years  (of  his  life)  Berzelius  ceased  to  take  an  experimental 
share  in  the  solution  of  the  problems  of  the  time,  and  turned 
the  whole  force  of  his  mind  to  theoretical  speculations ;  but 
these,  not  being  the  result  of  his  own  observations  or 
supported  by  them,  found  no  echo  or  approval  in  the 
science." 

This  much  is  certain,  that,  by  carrying  his  speculations 
too  far,  Berzelius  had  not  only  shaken  the  edifice  of  his  own 
doctrine,  but  had  also  greatly  injured  the  radical  theory, 
more  particularly  by  heaping  up  one  unproven  hypothesis 
upon  another.  His  opponents  went  so  far  as  to  assert  that 
he  had  by  his  arbitrary  assumptions  "made  a  theory 
regarding  substances  which  had  no  existence  "  in  organic 
chemistry.  It  almost  seemed  as  if  his  whole  system  was 
doomed  to  fall.  One  result  of  all  this  was  that  many 
chemists  became  visibly  discouraged,  and,  holding  all  specu- 
lation as  dangerous,  either  applied  themselves  to  the 
empirical  side  of  the  science,  or  turned  to  other  subjects. 
And  yet,  in  spite  of  the  slight  regard  in  which  the  radical 
theory  was  held  in  many  quarters,  it  soon  became  evident 
that,  for  the  investigation  of  chemical  constitution,  the 
assumption  of  radicals,  which  had  displaced  the  theory  of 
types,  was  indispensable.  In  the  course  of  the  forties  a 
fusion  of  the  radical  theory  with  the  older  doctrine  of  types 
took  place  on  the  unitary  side;  from  the  joint  work  of 
Laurent  and  Gerhardt  there  resulted  the  new  theory  of  types. 
Upon  the  other  side,  at  the  same  time,  the  much-derided 
copulse  were  brought  back  to  fresh  life  by  H.  Kolbe ;  with 
Frankland's  aid  a  clearer  notion  of  the  meaning  of  copulated 
compounds  was  arrived  at,  and  thus  the  way  was  smoothed 
for  the  establishment  of  the  new  radical  theory  and  the 
doctrine  of  valency. 


286  THE  MODERN  CHEMICAL  PERIOD 


Fusion  of  the  older  Theory  of  Types  with  the  Radical  Theory 
by  Laurent  and  Gerhardt. 

Of  the  two  investigators  whose  joint  work  effected  a 
transformation  of  the  old  into  the  new  theory  of  types, 
Laurent — as  mentioned  above — had  been  already  active  as 
the  originator  of  the  substitution  theory  proper.  Although 
both  of  them  were  resolute  opponents  of  the  dualistic  view, 
they  had,  nevertheless,  no  objection  to  make  use  of  the  con- 
ception of  radicals,  though  to  these  latter  they  attached  a 
meaning  of  their  own.  Besides  Laurent  and  Gerhardt  other 
chemists  contributed  materially  to  the  establishment  of  the 
new  theory  of  types,  both  by  the  ideas  to  which  they  gave 
expression  and  by  the  observations  that  they  made.  The 
stimulus  thus  given  by  Wurtz,  Hofmann  and  Williamson 
thus  falls  to  be  recorded  here  also. 

Laurent  and  Gerhardt  exercised  a  strong  mutual  in- 
fluence upon,  and  undoubtedly  supplemented  one  another. 
Gerhardt  was  endowed  with  the  special  gift  of  bringing 
together  isolated  facts  under  one  common  point  of  view,  and 
of  drawing  general  conclusions  therefrom.  Laurent  too  was 
happy  in  perceiving  the  great  importance  involved  in  par- 
ticular ideas,  and  he  kept  himself  freer  from  prepossessions 
upon  many  points  than  his  colleague. 

A  few  sentences  may  be  added  here  with  regard  to  the 
lives  of  these  two  men.  Auguste  Laurent,  born  at  La  Folie 
near  Langres  in  1807,  was  initiated  into  chemistry  by 
Dumas,  thus  acquiring  a  special  knowledge  of  the  organic 
part  of  it,  to  which  with  a  certain  one-sidedness  he  sub- 
sequently remained  faithful.  His  work  upon  naphthalene 
and  carbolic  acid,  together  with  their  derivatives,  is  evidence 
of  this.  After  filling  various  posts,  the  last  of  which  was  a 
chemical  professorship  at  Bordeaux,  Laurent  became  Warden 
of  the  Mint  at  Paris,  where  he  remained  in  intimate  con- 
nection with  Gerhardt  until  his  early  death  in  1853. 

Charles  Gerhardt  was  born  at  Strasburg  in  1816,  and 
began  his  scientific  career  well  equipped  with  a  wide  general 


v  LAURENT  AND  GERHARDT  287 

education ;  he  studied  chemistry  at  various  places  in 
Germany,  finally  under  the  stimulating  guidance  of  Liebig, 
to  whom  he,  like  so  many  others,  was  so  greatly  indebted. 
After  working  for  several  years  in  Paris,  he  became  Pro- 
fessor of  Chemistry  at  Montpellier  from  1844  to  184 8,  and 
after  another  prolonged  residence  in  the  first-named  city 
(where  he  opened  a  school  for  chemistry,  which  however 
was  not  commercially  a  success),  was  called  in  1855  to  fill 
the  chemical  chair  in  the  Faculty  of  Sciences  at  Strasburg, 
where  he  died  in  the  following  year.  His  important  services 
in  the  development  of  organic  chemistry,  together  with  the 
joint  theoretical  views  of  Laurent  and  himself,  are  detailed 
below. 

Gerhardt' s  Theory  of  Residues. 

At  the  time  that  Gerhardt  brought  out  his  first  scientific 
work,  the  fight  between  the  radical  and  substitution  theories 
was  at  its  height.  The  latter  found  pronounced  expression 
in  Dumas'  theory  of  types,  and  was  opposed  not  merely  to 
the  dualistic  views  upon  which  the  older  radical  theory  was 
based,  but  to  radicals  in  general.  Gerhardt  doubtless  felt 
the  disadvantages  which  the  abandonment  of  the  proximate 
constituents  of  organic  compounds  involved.  Without  for- 
saking the  strict  unitary  standpoint  of  Dumas,  he  attempted 
to  reintroduce  the  disdained  radicals  into  chemistry  under 
another  name  and  with  an  altered  meaning, — he  set  up  the 
theory  of  residues  (thdorie  des  rdsidus).1 

According  to  him,  residues  are  atomic  complexes  which 
remain  over  from  the  interaction  of  two  compounds,  as  the 
result  of  the  stronger  affinity  of  particular  elements  for  one 
another,  and  which  combine  together  because  they  are 
incapable  of  existing  separately.  Thus  Gerhardt  explained 
the  formation  of  nitro-benzene  from  benzene  and  nitric  acid, 
and,  generally,  the  production  of  those  bodies  which  he  termed 
"  copulated  compounds  "  (gepaarte  Verbindungen)  in  the  fol- 
lowing simple  manner  : — "  When  two  substances  react  with 

1  Ann.  Chim.  Phys.  (2)  vol.  Ixxii.  p.  184. 


288  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

one  another,  an  element  (e.g.  hydrogen)  present  in  the  one 
combines  with  another  element  (oxygen)  present  in  the  other 
to  produce  a  stable  compound  (water),  while  the  residues 
unite  together."  The  latter  he  did  not  look  upon  as  being 
actual  atomic  groups  present  in  the  compound  in  question, 
but  as  imaginary  quantities ;  they  were  in  his  view  absolutely 
distinct  from  the  compounds  of  the  same  composition  which 
were  known  in  the  free  state,  e.g.  sulphurous  acid  (S02)  or 
nitrogen  peroxide  (NO2).  Gerhardt  gave  expression  to  this 
difference  by  assuming  the  residues  as  being  present  in  the 
"  substitution-form."  Further,  the  supposition  of  different 
residues  in  one  and  the  same  compound,  according  either 
to  its  mode  of  formation  or  decomposition,  was  also 
brought  forward  by  him  at  that  time.1 

If  we  examine  this  conception  of  Gerhardt's  more  closely, 
we  see  that  his  views  upon  substitution  are  expressed  in  the 
same  breath  with  those  upon  radicals  as  variable  atomic 
complexes.  He  endeavoured,  in  fact,  to  explain  the  pro- 
cesses of  substitution  by  the  aid  of  this  idea,  in  teaching  that 
an  eliminated  element  is  replaced  by  an  equivalent  of  another 
element  or  residue  of  the  reacting  substance. 

Dumas  and  Laurent  too  had  already  said  the  same  thing 
in  a  different  way.  But  Gerhardt  knew  how  to  draw  im- 
portant conclusions  from  his  theory  with  regard  to  the 
chemical  nature  of  "  copulated  compounds " ;  it  did  not 
escape  him  that  the  saturation-capacities  of  the  latter  with 
respect  to  bases  were  quite  different  from  those  of  the 
original  acids  before  these  had  been  "  copulated  "  with  an 
alcohol  or  a  hydrocarbon.  Thus  nitro-benzene,  an  indifferent 
substance,  was  produced  from  nitric  acid  and  benzene,  and 
the  monobasic  ether-sulphuric  acids  from  sulphuric  acid  and 
the  alcohols.  Gerhardt  concluded  from  these  and  similar 
observations  that  "  the  basicity  of  a  copulated  compound  is 

1  It  must  be  mentioned  here  that  the  founders  of  the  radical  theory, 
Berzelius  and  Liebig,  had  expressed  at  one  time  (the  former  in  1834,  and 
the  latter  in  1838)  perfectly  similar  views  as  to  the  possibility  of  assuming 
different  radicals  in  the  same  compound  (cf.  Berzelius'  Jahresbericht,  vol. 
xiv.  p.  348 ;  Ann.  Ohem.,  vol.  xxvi.  p.  176). 


v  GERHARDT'S  CLASSIFICATION  OF  ORGANIC  COMPOUNDS  289 

equal  to  the  sum  of  the  basicities  of  the  copulating  sub- 
stances minus  1."  By  means  of  this,  his  "  Law  of  Basicity  " 
(Basizitdtsgesetz}^  he  was  able  to  determine  the  chemical 
nature  of  acids  about  whose  saturation-capacities  doubt  still 
prevailed  at  that  time.  With  absolute  definiteness  he 
stated  acetic  acid  to  be  monobasic,  although  it  forms  an  acid 
sodium  salt,  and  the  same  with  regard  to  hydrochloric  and 
nitric  acids,  because  all  these  yield  only  neutral  ethers  ; 
while  sulphuric  and  oxalic  acids  were  dibasic  because,  on 
copulation  with  an  alcohol,  they  yield  in  the  first  instance 
monobasic  ether-acids. 


Gerhardt' s  first  Classification  of  Organic  Compounds. 

Even  before  Gerhardt  had  attained  to  such  clearness  in 
this  important  question,  he  had  directed  his  endeavours  to 
the  classification  of  organic  compounds.  His  first  attempt 
at  this  is  contained  in  the  Precis  de  Chimie  Organigue 
(1842).  Here  we  find  him  strongly  influenced  by  Dumas 
and  his  type  theory ;  like  the  latter,  he  avoided  the  use  of 
any  formulae  which  might  appear  to  indicate  the  proximate 
or  rational  composition  of  chemical  compounds.  These  he 
arranged  in  an  ascending  series  according  to  their  empirical 
formulae,  in  such  a  manner  that  substances  containing  equal 
amounts  of  carbon  constituted  one  group.  Inclined  to 
express  himself  in  figurative  language,  he  compared  this 
classification  of  organic  compounds  to  a  ladder,  whose 
lowest  steps  were  formed  of  the  substances  of  simplest,  and 
whose  highest  of  those  of  most  complex  composition.  And 
since,  from  the  oxidation  of  compounds  rich  in  carbon, 
others  which  contain  fewer  atoms  of  that  element  are 
produced,  he  gave  his  arrangement  the  name  of  "  combustion 
ladder  "  (echelh  de  combustion). 

There  was  nothing  of  an  unconstrained  and  natural 
classification  here;  on  the  contrary,  the  most  diverse 

1  Cf.  Comptes  Rendus,  vol.  xvii.  p.  312 ;  Comptes  rendus  des  Travaux 
Chimiques  par  Laurent  et  Gerhardt  (1845),  p.  161. 

U 


290  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

substances  were  collected  into  one  class,  provided  only  they 
fulfilled  the  necessary  condition  of  containing  the  same 
number  of  carbon  atoms.  Not  the  slightest  heed  was  paid 
to  their  chemical  nature ;  acetic  ether  was  placed  alongside 
of  butyric  acid,  and  ethyl-oxalic  acid  alongside  of  succinic, 
solely  for  the  reason  given  above.  We  note  distinctly  here 
the  influence  of  Laurent,  who  not  long  before  had  made  a 
mechanical  classification  of  organic  substances  in  a  precisely 
similar  manner  (this,  however,  had  made  no  impression). 

Indeed,  it  is  hardly  conceivable  to  imagine  how  the 
older  radical  theory  could  have  sustained  a  more  severe  blow 
than  it  did  by  the  undue  exaggeration  of  Dumas'  theory  of 
types.  Gerhardt  himself  quickly  felt  this;  his  attempt  at 
classification,  which  found  its  final  and  most  definite  ex- 
pression in  the  new  theory  of  types,  showed  distinctly  that 
he  had  found  a  point  of  connection  with  the  views  of  the 
radical  theory,  and  that  he  strove  to  amalgamate  the  latter 
with  the  doctrine  of  substitution. 

Before  setting  forth  in  detail  these  labours  of  Gerhardt, 
the  efforts  which  he  made — partly  in  conjunction  with 
Laurent — to  bring  about  uniformity  of  view  with  regard  to 
the  atomic  weights  of  elements  and  compounds  must  be 
touched  upon.  The  great  and  lasting  service  which  those 
two  men  rendered  in  clearly  defining  what  is  meant  by  the 
term  "  molecule,"  and  therewith  reviving  Avogadro's  hypo- 
thesis, especially  deserves  our  fullest  recognition. 


Gerhardt's  "Equivalents" 

At  the  beginning  of  the  forties  the  uncertainty  as  to 
what  atomic  weights  should  be  ascribed  to  the  elements,  and 
what  atomic  (i.e.  molecular)  weights  to  chemical  compounds, 
had  become  one  of  great  moment.  The  doubt  which  Gay- 
Lussac,  Davy  and  others  had  previously  urged  against  the 
assumption  of  definite  atomic  weights  was  again  brought 
forward  by  Gmelin  and  his  school.  The  atomic  weight  system 
of  Berzelius,  that  work  which  he  had  accomplished  after  such 


v  GERHARDT'S  EQUIVALENTS  291 

immense  labour,  came  very  near  to  being  given  up,  or  at 
least  greatly  altered.  In  place  of  his  atomic  weights,  based 
as  they  were  upon  solid  foundations,  "  combining  weights  " 
were  to  be  introduced,  i.e.  those  values  which  were  expressed 
by  the  simplest  proportions  of  the  substances  entering  into 
combination.  All  speculations  upon  relative  atomic  values 
were  to  be  banished,  and  only  the  most  sober  possible 
formulation  of  chemical  compounds  attempted.  The  imme- 
diate result  of  this  reaction  was  the  halving  of  a  large 
number  of  the  atomic  weights  which  Berzelius  had  intro- 
duced into  the  science.  In  place  of  the  values  assumed  by 
him  for  carbon,  oxygen,  sulphur  and  most  of  the  metals, 
other  values  only  half  as  great  were  taken ;  these  equivalents 
were:  C  =  6,  O  =  8,  S  =  16,  Ca  =  20,  Mg=12,  and  so  on. 

Gerhardt  began  to  oppose  these  equivalents  in  the  year 
1842,  and  was  able  to  prove  by  cogent  arguments  that  their 
assumption  was  inadmissible.1  He  showed,  namely,  that 
the  amounts  of  water,  carbonic  acid,  carbonic  oxide  and 
sulphuric  acid,  which  were  separated  during  the  reactions 
of  organic  compounds,  were  never  expressible  by  what  was 
known  as  one  equivalent,  but  by  two  or  some  multiple  of 
two.  The  smallest  equivalent  formulae  for  those  com- 
pounds, according  to  Gmelin's  view,  were  H2O2,  C204> 
C2O2  and  S2O4.  But,  argued  Gerhardt,  there  must  be 
an  error  underlying  this :  "  the  symbols  H2O2  and  C2O4 
either  express  one  equivalent,  or  they  express  two."  If  we 
assume  the  former  of  these,  then  the  formulae  of  the  in- 
organic compounds  must  be  doubled ;  if  the  latter,  then  the 
"  organic  formulae "  must  be  halved.  Gerhardt  did  away 
with  the  contradiction  which  existed  in  the  formulation  of 
organic  and  inorganic  compounds  by  reinstating  Berzelius' 
atomic  weights  for  the  elements  carbon,  oxygen  and  sulphur, 
which  were  the  ones  of  greatest  moment  here  ;  i.e.  taking 
H  =  l,  then  0  =  12,0  =  16,  and  S  =  32.2  But  he  earned 

1  Cf .  Journ.  pr.  Chem. ,  vol.  xxvii.  p.  439 ;  also  his  Precis  de  Chimie 
Organique,  vol.  i.  p.  49. 

2  Cf.  Journ.  pr.  Chem.,  vol.  xxx.  p.  1.       It  is  very  extraordinary  that 
Gerhardt  should  have  made  no  reference  here  to  the  identity  of  the  atomic 
weights  which  he  proposed  with  those  of  Berzelius. 

u  2 


292  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

this  reform  only  half  way ;  for,  while  he  gave  the  proper 
values  for  the  elements  just  named,  he  was  led  by  special 
considerations  to  assume  values  for  most  of  the  metals  which 
were  only  half  as  great  as  those  proposed  by  Berzelius. 
Unlike  the  latter,  who  began  by  assuming  that  most  of  the 
metallic  oxides  had  the  composition  indicated  by  the 
general  formula  MeO,  Gerhardt  compared  these  oxides 
with  water,  giving  them  therefore  the  formula  Me9O.  He 
thus  arrived  at  the  correct  atomic  weights  of  the  monovalent 
metals,  but  at  incorrect  ones  for  the  divalent :  e.g.  for  calcium 
the  value  20  instead  of  40,  for  lead  that  of  103*5  instead  of 
207,  and  so  on. 

Apart  from  this  incompleteness  there  was  an  obscurity  in 
Gerhardt 's  views  with  respect  to  atomic  weights  which  could 
not  fail  to  produce  confusion ;  he  both  called  the  atomic 
weights  just  mentioned  equivalents,  and  at  the  same  time 
made  use  of  this  term  for  those  amounts  of  chemical  com- 
pounds which  corresponded  to  their  molecular  weights,  i.e. 
speaking  generally,  for  quantities  which  are  by  no  means 
necessarily  equivalent  chemically.  Thus  the  quantities  of 
hydrochloric,  sulphuric  and  acetic  acids  represented  by  the 
formulae  HC1,  H2SO4  and  C2H402,  were  in  his  mind  equi- 
valent to  one  another.  We  must  here  emphasise  the  point 
that  Gerhardt  attached  another  meaning  to  this  word  to 
what  we  now  do;  equivalents  of  chemical  compounds  were 
for  him  merely  the  comparable  quantities  of  these. 

Absolute  clearness  in  the  above  points  was  only  arrived 
at  through  Laurent's  assistance.  The  latter  definitely  grasped 
the  distinctions  between  molecular,  atomic  and  equivalent 
weights,  the  correct  determination  of  whose  values  constitutes 
the  basis  of  our  present  views  upon  molecule  and  atom ;  it 
was  he  who  brought  Avogadro's  hypothesis  back  to  life  again, 
and  prepared  the  way  for  its  development,  so  vitally  im- 
portant for  chemical  science. 


v        MEANING  OF  MOLECULE,  ATOM  AND  EQUIVALENT     293 

The  distinguishing  between  the  terms  Molecule,  Atom,  and 
Equivalent  by  Laurent  and  Gerhardt. 

Gerhardt's  most  memorable  efforts  had  for  their  aim  the 
expression  of  the  composition  of  all  chemical  compounds  by 
means  of  formulae  based  upon  one  common  standard,  i.e. 
formulae  comparable  with  one  another.  The  formulae  of 
volatile  compounds  ought,  according  to  him,  invariably  to 
indicate  those  quantities  which  occupy  two  volumes  when  in 
the  gaseous  state,  taking  the  volume  of  one  atom  of  hydrogen 
as  equal  to  1.  This  sound  principle  has  ever  since  been  fully 
recognised. 

Acting  upon  this,  he  altered  the  four-volume  formulae  of 
many  organic  compounds  into  tioo-volume  ones  by  halving 
them.  The  false  conception,  much  current  at  that  time, 
according  to  which  acetic  acid  (for  example)  received  the 
formula  C4H8O4,  alcohol  that  of  C4H12O2,  and  ethylene  that 
of  C4H8,  had  grown  up  as  the  result  of  the  dualistic  views 
upon  the  composition  of  organic  compounds,  and  also  of  the 
use  of  several  incorrect  atomic  weights.1  It  was  precisely 
to  organic  compounds — most  of  them  volatile  without  de- 
composition— that  Gerhardt's  law  could  be  most  extensively 
applied,  the  law,  namely,  that  their  formulae  depend  upon 
the  amounts  by  weight  which  are  contained  in  equal 
volumes. 

Much  of  Gerhardt's  indistinctness,  e.g.  that  produced  by 
his  using  the  word  "  equivalent "  in  a  totally  mistaken  sense, 
was  put  right  by  Laurent.  The  latter  pointed  out  with 
emphasis  and  clearness 2  that  Gerhardt's  equivalents  were 
not  even  comparable  with  those  of  compounds,  let  alone  of 
equal  value  with  them  ;  he  showed  that  Gerhardt's  equi- 
valents of  the  elements  must  be  regarded  as  their  atomic 
weights,  and  the  equivalents  of  compounds  as  their  molecular 

1  For  deducing  the  atomic  composition  of  organic  acids,  the  silver  salts 
of  the  latter  were  chiefly  made  use  of  ;  for  acetate  of  silver  Berzelius  had 
arrived  at  the  formula  C4H603.AgO  (Ag  =  216),  from  which  the  composition 
of  the  acid,  as  given  above,  followed.     Alcohol  was  regarded  by  Liebig  as 
the  hydrate  of  ethyl  ether,  and  consequently  formulated  as  C4H100-H2O, 
whence  the  composition  C4H8  was  ascribed  to  ethylene,  and  so  on. 

2  Ann.  Chim.  Phys.  (3),  vol.  xviii.  p.  266. 


294  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

weights.     Laurent's  merit  consisted  in  clearly  grasping  the 
meanings  to  be  attached  to  these  terms. 

Laurent  understood  the  molecular  weight  of  an  element 
or  chemical  compound  as  meaning  that  quantity  which, 
under  like  conditions,  occupies  the  same  volume  as  two 
atoms  of  hydrogen ;  the  quantity  represented  by  the  latter 
he  looked  upon  as  a  molecule  of  hydrogen.  For  him,  there- 
fore, the  molecular  weights  of  chlorine,  oxygen,  nitrogen 
and  cyanogen  were  expressed  by  the  formulae  C1.2,  O2,  N2 
and  (CN)2,  and  the  molecular  weights  of  hydrochloric  and 
acetic  acids  by  the  formulae  HC1  and  C2H4O2,  because  the 
quantities  indicated  by  those  symbols  filled,  when  in  the 
state  of  vapour,  the  same  space  as  two  parts  by  weight  of 
hydrogen.  The  agreement  between  his  ideas  and  those  of 
Avogadro  is  plainly  evidenced  here ;  but  to  Laurent  belongs 
the  further  merit  of  developing  these  in  a  high  degree.  He 
defined  the  molecule  as  "  the  smallest  quantity  which  can  be 
employed  in  order  to  produce  a  compound."  And  he  saw  a 
proof  of  the  correctness  of  this  view  in  the  fact  that  the 
atoms  of  chlorine,  bromine,  hydrogen,  etc.,  always  act 
chemically  in  pairs. 

The  atom,  according  to  Laurent,  is  the  smallest  quantity 
of  an  element  which  can  be  present  in  a  compound;  for 
atomic  weights  he  adopted  the  values  proposed  by  Gerhardt, 
which  agreed  to  a  great  extent  with  those  of  Berzelius. 
Equivalents,  lastly,  signified  for  him  the  "  equivalent 
amounts  of  analogous  substances  "  (die  gleichwertliigen  Mengen 
analoger  Korper).  This  last  definition  led  logically  to  the 
assumption  that  one  and  the  same  element  has  more  than 
one  equivalent,  if  it  reacts  with  others  in  varying  combining 
proportions.1 

The  joint   work   of  Laurent   and    Gerhardt   upon   this 

1  "The  idea  of  an  equivalent  includes  in  itself  the  view  of  a  similar 
function  ;  we  know  that  one  and  the  same  element  can  fill  the  role  of  two 
or  of  several  others,  whence  it  must  follow  that  different  weights  also 
correspond  to  those  different  functions.  On  the  other  hand,  we  find 
different  weights  of  the  same  metal,  e.g.  iron,  copper,  mercury,  etc.,  re- 
placing the  hydrogen  of  acids,  and  thus  forming  salts  which  contain  the 
same  metal  but  possess  different  properties.  These  metals  have  therefore 
various  equivalents"  (cf.  Comptes  rendusdes  Travaux  Chimiques  par  Laurent 
et  Gerhardt  (1849),  p.  1.  et  seq.). 


v        WORK  PREPARATORY  TO  THE  NEW  TYPE  THEORY    295 

question — so  excessively  important  for  theoretical  chemistry 
—found  very  little  acceptance  amongst  chemists;  indeed, 
many  of  them  actively  opposed  such  a  conception  as  that  of 
variable  equivalent  values.  The  sound  but  not  yet  sufficiently 
grounded  views  of  Laurent  upon  the  magnitude  of  the  mole- 
cules (i.e.  molecular  weights)  of  elements  and  compounds  did 
not,  however,  succeed  in  making  their  way  at  that  time 
—towards  the  end  of  the  forties.  Gmelin's  combining  weights 
were  still  for  the  most  part  adhered  to,  and  at  the  date  of  the 
appearance  of  Gerhardt's  Lehrfawh  der  Chemie  (1853)  were 
in  such  general  use  that  the  author,  against  his  better  judg- 
ment, used  Gmelin's  numbers  for  the  chemical  symbols  in 
his  first  three  volumes,  i.e.  he  employed  equivalent  formula?.1 
Stronger  proof  than  that  given  by  Laurent  and  Gerhardt 
had  to  be  adduced  in  order  to  convince  people  that  the 
atomic  and  molecular  weights  which  they  employed  were 
the  correct  ones.  It  was  the  researches  of  Williamson, 
published  at  the  beginning  of  the  fifties,  which  were  especially 
instrumental  in  leading  to  this.  The  true  perception  was 
again  arrived  at  here  from  experience  collected  in  the  field 
of  organic  chemistry. 


Influence  of  the  Researches  of  Wurtz,  Hofmann  and  William- 
son upon  the  Development  of  the  Theory  of  Types  (1848-51). 

The  discovery  by  Wurtz  2  and  Hofmann  of  organic  deri- 
vatives  of  ammonia  was  of  great  importance  for  the  firm 

1  Gerhardt  gave  his  reasons  for  using  this  notation  in  the  preface  to  his 
book  (vol.  i.  pp.  1,  2)  as  follows  :  "  J*y  ai  memefait  le  sacrifice  de  ma  nota- 
tion, pour  m'en  tenir  aux  formules  anciennes,  afin  de  mieux  ddmontrer  par 
Vexemple,  combien  Vusage  de  ces  dernieres  est  irrational,  et  de  laisser  au 
temps  le  soin  de  consacrer  une  reforme  que  les  chimistes  n'ont  pas  encore 
ge'ne'ralment  adopte'e." 

2  C.  A.  Wurtz,  who  was  born  at  Strassburg  in  1817  and  died  at  Paris 
in  1884,  was  a  pupil  of  Liebig,  Balard  and  Dumas  ;  his  life  and  works  have 
been  described  very  fully  by  A.  W.  v.  Hofmann  (Ber.,  vol.  xx.p.815  et  seq. ), 
and  by  Friedel  (Notice  sur  la  Vie  et  les  Travaux  de    Wurtz).     From  the 
year  1845  onwards,  Wurtz  filled  the  post  of  professor  at  various  teaching 
institutions  in  Paris  (including  the  Ecole  de  Medicine  and  the  Sorbonne),  his 
influence  becoming  very  great  as  time  went  on.     The  lucidity  and  general 


296  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

establishment  of  the  views  finally  comprised  in  Gerhardt's 
theory  of  types.  In  1849  Wurtz  observed  the  remarkable 
decomposition  of  cyanic  ether  by  means  of  caustic  potash, 
whereby  he  discovered  methylamine  and  ethylamine,  com- 
pounds so  closely  resembling  ammonia.1  Before  this 
Berzelius  had  already  expressed  the  view  that  the  organic 
nitrogenous  bases  in  general  might  be  looked  upon  as  sub- 
stances which  were  copulated  with  ammonia.  Liebig,  on 
the  other  hand,  regarded  these  as  amido-compounds  analo- 
gous to  the  ethers.  Wurtz  fluctuated  between  these  two 
opinions,  besides  also  suggesting  the  possibility  of  the 
organic  bases  being  substitution  products  of  ammonia,  e.g. 
of  "  methyliak  "  (our  methylamine)  being  ammonia  in  which 
one  hydrogen  atom  was  replaced  by  methyl.  At  first,  how- 
ever, he  appears  to  have  given  the  preference  to  the  older 
view  of  Berzelius,  according  to  which  ethylamine,  for  example, 
was  "  ammonia  copulated  with  etherin." 

The  "  typical "  view  of  these  bases  was  first  arrived  at 
through  A.  W.  v.  Hofmann's  brilliant  researches  upon  amine 
bases;  the  production  of  these  from  ammonia  and  haloid 
compounds  of  the  alkyls  furnished  a  splendid  proof  of  the 
correctness  of  the  view  that  those  compounds  were  formed 
from  ammonia  by  the  exchange  of  one  or  more  hydrogen 
atoms  for  alcohol  radicals.2  The  constitution  of  the  imide 
and  nitrite  bases,  like  that  of  di-  and  tri-ethylamine,  could 

form  of  his  lectures  were  such  as  to  make  it  a  pleasure  to  listen  to  them. 
From  1866  to  1875  he  was  Dean  of  the  Medical  Faculty,  and  in  this  position 
materially  aided  in  raising  the  standard  of  instruction  in  practical  chemistry 
and  physiology  for  medical  students.  Among  his  writings  were  the  Lemons 
de  Philosophic  Chimique  (1864)  and  La  Thdorie  Atomique  (1879),  works  which 
treated  of  questions  in  theoretical  chemistry  and  which  found  much  accept- 
ance because  of  their  clearness  and  the  charming  style  in  which  they  were 
written ;  also  his  Traite  Elementaire  de  Chimie  Medicale  (1864),  and  the 
Dictionnaire  de  Chimie  Pure  et  Appliquee  (edited  by  him).  His  admirable 
experimental  researches,  by  which  he  acted  as  a  pioneer  in  opening  up 
particular  branches  of  organic  chemistry,  will  be  spoken  of  under  the  special 
history  of  the  subject.  Most  of  his  work  was  published  in  the  Annales  de 
Ghimie  et  de  Physique,  of  which  he  became  one  of  the  editors  in  1852,  and 
in  the  Comptes  Rendus. 

1  Comptes  Rendus,  vol.  xxviii.  p.  223  et  seq. 

2  Ann.  Chem.,  vol.  Ixxiv.  p.  174. 


v  AUGUST  WILHELM  VON  HOFMANN  297 

scarcely  be  explained  in  any  other  way  than  by  their  deriva- 
tion from  ammonia,  through  the  substitution  of  hydrogen 
atoms  by  alkyl  radicals.  Before  continuing  this  subject,  a 
short  account  must  be  given  here  of  Hermann's  life  and  work. 

August  Wilhelm  von  Hofmann,  born  at  Giessen  on  8th 
April  1818,  after  several  years  of  philosophical  and  juris- 
tical studies  devoted  himself  to  chemistry  under  the  guidance 
of  Liebig,  whose  assistant  he  soon  became.  After  filling 
for  a  short  time  the  post  of  assistant-professor  (Privatdocent) 
at  Bonn,  he  accepted  in  1845  a  call  (made  at  Prince  Albert's 
instigation)  to  the  newly  founded  College  of  Chemistry  in 
London,  which  became  a  government  institution  in  1853; 
in  1855  he  was  also  made  a  non-resident  Assayer  of  the 
Mint  (these  appointments,  which  were  held  by  eminent 
chemists,  otherwise  unconnected  with  the  Mint,  were 
abolished  in  1870).  He  likewise  taught  at  the  School  of 
Mines.  In  1864  he  removed  back  again  to  Bonn,  and  in 
1865  was  called  to  Berlin,  as  successor  to  Mitscherlich, 
where  he  continued  to  work  with  quite  exceptional  brilliancy 
until  his  death  on  May  5th,  1892. 

Hofmann's  work  as  a  teacher  was  in  every  respect 
extraordinarily  fruitful,  the  most  striking  proof  of  this  being 
shown  by  the  large  number  of  his  pupils  who  have  since 
attained  to  eminence.  His  organising  talent  found  scope  in 
the  building  and  fitting  up  of  two  admirable  laboratories  for 
general  instruction  at  Bonn  and  Berlin.  To  success  as  a 
teacher  there  was  also  added,  in  a  marked  degree  in  his  case, 
success  as  an  author ;  here  he  showed  the  power  of  represent- 
ing facts,  and  chemical  doctrines  founded  upon  them,  in  a 
delightfully  clear  and  perspicuous  manner.  As  an  instance 
of  this  we  may  mention  his  Einleitung  in  die  moderne  Chemie 
("  Introduction  to  Modern  Chemistry ").  The  Obituary 
Memoirs  (upon  Liebig,  Wohler,  Dumas,  Sella  and  Wurtz)  by 
him  are  characterised  by  the  loving  care  with  which  he  enters 
into  the  life  and  works  of  the  men  whom  he  extols,  besides 
being  written  in  a  most  fascinating  style. 

As  an  investigator  in  experimental  chemistry  Hofmann 
meets  us  at  every  step ;  organic  chemistry,  more  especially 


298  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

the  field  of  nitrogen  and  phosphorus  compounds,  was 
thoroughly  studied  by  him,  and  in  part  exhausted.  Finally, 
reference  must  be  made  here  to  the  wonderful  influence 
which  he  exerted  upon  the  coal  tar  colour  industry,  an  industry 
which  to  a  great  extent  arose  out  of  his  scientific  studies. 
Most  of  Hofmann's  papers  were  published  in  the  Annalen 
der  Chemie  and  in  the  Berichte  of  the  German  Chemical 
Society  (at  Berlin),  which  was  founded  by  him  in  1868,  and 
of  which  he  was  for  a  long  time  President.  In  November, 
1892,  F.  Tiemann  delivered  before  the  German  Chemical 
Society  a  sympathetic  and  appreciative  address  upon  his 
life  and  work  (Ber.,  vol.  xxv.  p.  3377). 

It  was  only  after  these  important  investigations  by 
Hofmann  on  the  constitution  of  the  organic  ammonia  bases 
that  Wurtz  clearly  perceived  that  this  relationship  to 
ammonia  was  the  only  conclusive  explanation  of  those  com- 
pounds. He  (Wurtz)  condensed  the  result  of  the  above 
researches  into  the  words :  "  It  was  thus  that  the  ammonia 
type  was  created." 

To  this  Williamson,1  by  his  distinguished  researches,2 
added  the  water  type,  thereby  with  Wurtz  and  Hofmann 
providing  the  foundation  for  Gerhardt's  theory  of  types.  In 
his  experiments  Williamson  started  with  the  idea  of  replac- 
ing hydrogen  in  known  alcohols  by  hydrocarbons,  so  as  to 
obtain  homologues  of  the  former.  The  action  of  ethyl  iodide 
upon  potassium  ethylate  yielded  him,  however,  ethyl  ether, 
and  not  the  expected  ethylated  alcohol.  This  result  induced 
him  to  try  whether,  by  the  action  of  potassium  ethylate 
upon  methyl  iodide,  a  mixture  of  ethyl  and  methyl  ethers  or 
only  one  homogeneous  compound  would  be  produced.  The 
latter  was  found  to  be  the  case ;  methyl- ethyl  oxide,  a  "  mixed 

1  A.  W.  Williamson,  born  in  1824,  was  a  pupil  of  Liebig  and  afterwards 
filled  for  a  long  time  the  chair  of  chemistry  in  University  College,  London, 
retiring  from  this  post  in  1887.     Especially  in  the  years  between  1850-60 
did  he  enrich  organic  chemistry  with  valuable  observations,  which  led  to 
deductions  of  general  application.     His  work  upon  the  formation  and  con- 
stitution of  ethers,  more  particularly,  was  of  the  first  importance. 

2  Cf.  especially  Ann.  Chem.,  vol.  Ixxvii.  p.  37  ;  vol.  Ixxxi.  p.  73.       Or 
Journ.  Chem.  Soc.,  vol.  iv.  pp.  106  and  229. 


v  WILLIAMSON'S  RESEARCHES  ON  ETHERS  299 

ether,"  was  obtained,  and  with  this  the  much-discussed  and 
at  that  time  burning  question  of  the  molecular  weights  of 
ether  and  ethyl  alcohol,  and  also  that  of  the  atomic  weight  of 
oxygen,  were  solved.1  Liebig's  idea  that  alcohol  was  the 
hydrate  of  ether  had  to  be  given  up  ;  on  the  other  hand, 
Williamson's  researches  proved  that  the  molecular  formulae 
of  both  compounds  which  had  been  assumed  "by  Berzelius 
were  the  correct  ones.  The  formation  of  ether  by  the 
interaction  of  alcohol  and  sulphuric  acid,  a  process  which 
had  so  greatly  exercised  the  minds  of  the  most  eminent 
chemists,  was  thus  now  made  perfectly  clear  by  Williamson. 
Alcohol  and  ether  he  regarded  as  analogous  to  and  built 
up  on  the  type  of  water,  as  his  definitions  and  formulae 
show  :  — 

0,  Water  ;  °25O>  Alcoho1  J  0'  Ether' 


This  view  (a  view  of  which  Laurent  and  other  chemists 
had  previously  spoken  favourably  as  being  an  admissible  one) 
Williamson  then  proceeded  to  extend  to  many  other  sub- 
stances, organic  and  inorganic,  endeavouring  at  the  same 
time  to  make  its  advantages  evident.  Thus  he  compared 
the  acids,  ketones  (of  whose  true  composition  he  had 
furnished  beautiful  experimental  proof  by  a  process  similar 
to  that  mentioned  above),  and  other  compounds  with  water, 
i.e.  he  derived  from  water  the  compounds  just  named,  by  the 
substitution  of  one  or  both  atoms  of  hydrogen  by  compound 
radicals  or  elements.  The  following  examples  will  serve  to 
illustrate  his  "  typical  "  theory  :  — 

P  FT  O  "FT  "NTi 

°2g3vO,  Acetic  acid  ;  gO,  Potassic  hydrate  ;  g  2O,  Nitric  acid  ; 

p  R  n     Acetic  anhydride    K  ^n        „..,  . 


K 

known)  ; 

Williamson  expressed  himself  as  follows  with  regard  to 
the  applicability  of  the  typical  view  :  2    "  The  method  here 

1  Chancel  arrived  in  a  similar  manner  at  the  same  result,  independently 
of  Williamson  (cf.  Comptes  Rendus,  vol.  xxxi.  p.  521). 

2  Journ.  Chem.  Soc.,  vol.  iv.  p.  239. 


300  THE  MODERN  CHEMICAL  PERIOD  CHAP, 

employed  of  stating  the  rational  constitution  of  bodies  by 
comparison  with  water,  seems  to  me  to  be  susceptible  of 
great  extension;  and  I  have  no  hesitation  in  saying  that 
its  introduction  will  be  of  service  in  simplifying  our  ideas, 
by  establishing  a  uniform  standard  of  comparison  by  which 
bodies  may  be  judged  of." 

His  confidence  in  the  possibility  of  extending  the 
"  typical "  idea  came  out  still  more  strongly  upon  another 
occasion,1  when  he  expressed  the  opinion  that  reference  to 
the  one  type  of  water  sufficed  for  all  inorganic  and  for  the 
best-known  organic  compounds ;  only  that  in  the  case  of 
many  substances,  e.g.  dibasic  acids,  the  formula  of  water 
must  be  taken  doubled.  The  views  expressed  here  are  also 
to  be  found  for  the  most  part  in  Gerhardt's  theory  of  types. 
The  most  important  result  of  Williamson's  researches  con- 
sisted, however,  not  in  the  one-sided  typical  mode  of  ex- 
plaining the  constitution  of  chemical  compounds,  but  rather 
in  the  determination  of  the  true  molecular  values  of  organic 
substances.  The  methods  which  he  made  use  of  in  order  to 
attain  this  end  very  soon  proved  themselves  exceptionally 
productive ;  they  led  Gerhardt  to  the  discovery  of  the  acid 
anhydrides,  and  Wurtz  to  that  of  mixed  hydrocarbon  radicals, 
the  investigation  of  both  of  which  has  finally  settled  the 
controversy  as  to  the  molecular  formulae  of  whole  series  of 
organic  compounds. 


Grerhardt's  new  Theory  of  Types.2 

What  has  just  been  said  is  sufficient  to  show  how  effec- 
tively the  "  typical  "  view  of  organic  compounds  was  furthered 
by  the  experimental  researches  of  Wurtz,  Hofmann  and 
Williamson.  Numerous  nitrogenous  compounds  were  re- 
ferred to  the  ammonia  type,  and  a  still  larger  number  of 
oxygenated  ones  to  the  water  type.  Gerhardt  consummated 

1  Journ.  Chem.  Soc.,  vol.  iv.,  p.  350  (1851). 

'J  Cf.  Ann.  Chim.  Phys.  (3),  vol.  xxxvii.  p.  331 ;  also  Traite  de  Chimie, 
vol.  iv.  (1856). 


v       FIRST  STEPS  TOWARDS   GERHARDT'S  TYPE  THEORY    301 

his  work  by  adding  to  these  the  hydrogen  and  hydro- 
chloric acid  types,  and  then  he  made  the  attempt  to  include 
all  organic  compounds  under  those  few  forms. 

The  endeavour  to  compare  organic  with  inorganic  bodies, 
which  was  already  so  strongly  marked  in  the  radical  theory, 
was  again  distinctly  apparent  here ;  and  here  again  it  was 
ethyl  compounds  which  mainly  gave  rise  to  the  setting  up 
of  inorganic  types  as  models  for  organic  compounds.  So 
early  as  1846  Laurent *  had  thrown  out  the  suggestion  which 
was  established  in  full  detail  by  Williamson  later  on, — that 
alcohol  and  ether  might  be  looked  upon  as  derivatives  of 
water,  thus — 

H2O,  Water  ;  ^O,  Alcohol  ;  |£o,  Ether.2 

The  inorganic  acids  and  oxides  too  might  be  viewed 
(according  to  Laurent)  as  substitution-products  of  water. 
These  compounds,  so  various  in  their  natures,  were  regarded 
as  built  up  after  the  same  pattern. 

In  and  after  1848  the  American  chemist  Sterry  Hunt 
published  several  papers,3  in  which  he  gave  a  wide  extension 
to  the  typical  view  by  showing  how  large  numbers  of  oxy- 
genated compounds,  inorganic  as  well  as  organic,  might  be 
pictured  as  derived  from  water,  and  how  hydrocarbons  belong 
to  the  hydrogen  type.  But  his  work,  being  unknown  in 
Europe,  did  not  in  any  way  quicken  the  growth  of  the  similar 
ideas  then  running  through  many  other  minds.  On  the 
other  hand,  the  above  definite  utterances  of  Williamson 
upon  the  reference  of  many  organic  compounds  to  water  (as 
the  form  of  compound  of  most  general  application)  un- 
doubtedly brought  about  a  more  rapid  development  of  the 
doctrine  of  types.  Not  merely  oxygenated  bodies,  but  also 
non-oxygenated  ones  like  amines,  were  without  any  hesita- 
tion taken  as  derived  from  water.  Although  Williamson 
thus  lost  his  firm  standing  ground  in  consequence  of  the  all 
too  great  elasticity  of  his  formulae,  he  gained,  on  the  other 

1  Ann.  Chim.  Phys.  (3),  vol.  xviii.  p.  266  et  seq. 

2  Of.  also  Berzelius'  view  with  regard  to  Ether,  p.  256. 

3  Amer.  Journ.  of  Science  (2),  vols.  v.,  vi.,  vii.  and  viii. 


302  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

hand,  marked  advantages  from  the  extension  of  the  type 
idea.  He  referred  many  compounds  to  the  double  or  triple 
water  type,  and  thereby  introduced  the  notion  of  polyatomic 
radicals  into  chemistry.  Sulphuric  acid,  for  example,  he 
referred  to  two  molecules  of  water  in  which  two  atoms  of 
hydrogen  are  replaced  by  sulphuryl  (SO2) — 


O 


2  Mol.  water  ;  SO 


•>O2     Sulphuric  acid  ; 
H  ° 


while  phosphoric  acid  was  derived  in  a  like   manner    from 
three  molecules  of  water,  and  so  on. 

Stimulated  especially  to  it  by  his  own  important  dis- 
covery of  the  anhydrides  of  monobasic  organic  acids,1 
Gerhardt  collected  the  accumulated  mass  of  "  typical "  ideas 
and  condensed  them  into  uniformity.  Before  everything 
else  he  desired  to  classify  the  large  number  of  organic 
compounds  in  a  synoptical  manner,  and  for  this  the  water, 
ammonia,  hydrogen  and  hydrochloric  acid  types  were  to  serve 
as  models.  In  addition  to  this  he  made  use  of  a  principle 
for  the  co-ordination  of  organic  substances,  which  had  indeed 
been  already  applied  by  other  chemists,  but  never  in  such  a 
general  manner,  viz.,  he  arranged  them  in  different  series, 
the  members  of  each  series  belonging  to  the  same  type. 
His  first  classification  of  organic  compounds  (cf.  p.  289) 
did  not  possess  the  advantages  which  such  a  grouping  in 
series  offered.  Since  then  Schiel 2  had  established  the  con- 
ception of  homology  by  directing  attention  to  the  equal 
differences  in  the  composition  of  analogous  bodies,  more 
particularly,  of  the  alcohols,  while  Dumas  had  proved  the 
same  thing  for  the  acids.  And  the  researches  of  Kopp  had 
further  shown,  with  the  utmost  clearness,  not  only  the 
chemical  but  also  the  physical  resemblance  of  homologous 
compounds. 

1  Ann.  Chem.,  vol.  Ixxxii.  p.  128.     Those  bodies,  whose  existence  had 
been  predicted  by  Williamson,  were  formerly  supposed  by  Gerhardt  to  be 
incapable  of  preparation. 

2  Ann.  Chem.,  vol.  xliii.  p.  107  (1842). 


v        DERIVATION  OF  ORGANIC  COMPOUNDS  FROM  TYPES     303 

Gerhardt  now  collated  the  results  of  those  preparatory 
labours  with  great  ingenuity,  and  associated  with  the  series 
of  homologous  bodies,  which  differed  in  composition  by  the 
increment  (CH2)W,  other  series  of  isologous  and  heterologous 
compounds.  The  former  of  these  were,  according  to  him, 
chemically  analogous  substances  which  show  another  com- 
position-difference from  homologous  ones,  e.g.  ethyl  alcohol, 
C2H6O,  and  phenol,  C6H6O ;  propionic  acid,  C3H6O2,  and 
benzoic  acid,  C7H602, — compounds  which  differ  from  one 
another  by  the  increment  C4.  Heterologous  series  contain 
such  substances  as  are  chemically  dissimilar,  but  show  a 
close  connection  with  one  another  in  their  modes  of  forma- 
tion. To  such  a  series  belong,  for  instance,  ethyl  alcohol, 
C2H6O,  and  acetic  acid,  C2H402 ;  amyl  alcohol,  C5H120,  and 
valeric  acid,  C6H10O2. 

As  already  mentioned,  Gerhardt  looked  upon  the  members 
of  such  series  as  derivatives  of  one  of  his  four  types,  resulting 
from  these  by  the  partial  or  complete  substitution  of  their 
hydrogen  atoms  by  residues.  From  the  water  type  were 
derived  (as  Williamson  had  already  taught)  most  of  the 
organic  compounds,  including  the  alcohols,  acids,  simple 
and  compound  ethers,  acid  anhydrides,  ketones,  aldehydes 
and  salts.  Alongside  of  water  the  analogously  constituted 
sulphuretted  hydrogen  was  placed  as  an  auxiliary  type,  and 
from  it  the  sulphur  compounds  corresponding  to  the  oxygen 
compounds  just  mentioned  were  derived,  e.g.  the  sulphides, 
mercaptans,  thio-acids,  etc.  The  following  examples  will 
serve  to  illustrate  what  has  just  been  said : — 


H90  H  C,H,0  C9HR  H 


Water      Methyl  alcohol      Acetic  anhydride      Acetic  ether     Aldehyde. 

Under  the   ammonia   type   were   classified  the  amines, 
amides  and  imides,  phosphines,  arsines,  etc.,  thus — 

(C2H5)3P 


Methylamine    Acetamide     Succinimide  Triethyl-phosphine. 

The  hydrogen  type  included  the  hydrocarbons,  together 


304  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

with    the  organo-metals ;    and   the    analogous    hydrochloric 
acid  type  the  chlorides,  iodides,  cyanides,  etc.,  thus — 

H        CH3          CH3          C2H5.  H          CH,          C2H5 

H          H          C2H5  Zn    '  Cl  Cl  CN  ' 

Gerhardt  was  quite  justified  in  terming  this  classification 
of  organic  compounds  according  to  types  a  syst&me  unitaire, 
for  all  assumption  of  an  opposite  within  the  chemical  com- 
pounds themselves,  or  of  a  binary  structure,  was  here  entirely 
eliminated.  Each  compound  was  looked  upon  as  a  complete 
whole ;  even  in  those  cases  where  the  dualistic  conception 
appeared  to  be  indicated  (especially  in  that  of  salts),  deriva- 
tives of  water  alone  were  seen. 

The  question  now  arises, — did  Gerhardt  himself  believe 
that  he  would  get  nearer  to  the  solution  of  that  problem, 
which  Berzelius  had  designated  as  being  of  supreme  import- 
ance to  chemistry,  by  setting  up  those  types  and  referring 
organic  compounds  to  them  ?  Did  he  consider  that  he  had 
thereby  materially  advanced  the  solution  of  the  chemical 
constitution  of  organic  bodies  ?  The  answer  to  this  must  be 
in  the  negative,  if  we  mean  "  constitution  "  in  Berzelius'  sense. 
Gerhardt  repeatedly  expressed  the  opinion  that  it  was 
impossible  to  arrive  at  the  true  constitution  of  these  com- 
pounds, meaning  by  this  the  arrangement  of  their  atoms 
(V arrangement  des  atomes).  In  his  view  no  strictly  rational 
formulae  for  organic  compounds  could  be  brought  forward 
which  would  satisfy  this  demand,  since  several  formulae 
showing  different  proximate  constituents  or  residues  might 
be  looked  upon  as  equally  correct,  according  to  the  modes  of 
formation  or  decomposition  of  the  compounds.  Grounds  of 
expediency  alone  must  decide  whether  one  formula  was  to 
be  preferred  to  another ;  that  formula  which  explained  the 
larger  number  of  methods  of  formation  and  decomposition 
of  the  particular  compound  in  question  was  to  be  chosen. 
This  elastic  view  was  brought  prominently  forward  by  Ger- 
hardt at  every  opportunity,  especially  in  the  fourth  volume 
of  his  text-book,  and  he  emphasised  the  point  that  the  con- 
stitution of  compounds,  according  to  the  type  theory,  was  not 


v      GERHARDT'S  VIEWS  UPON  CHEMICAL  CONSTITUTION  305 

the  same  thing  as  their  rational  composition  in  Berzelius' 
sense. 

Formulae  were  for  Gerhardt  merely  pictures  of  the 
changes  which  chemical  compounds  underwent ;  they  simply 
illustrated  the  modes  of  formation  and  decomposition  of  the 
latter.  Types,  on  their  part,  even  when  their  composition 
is  exceedingly  simple,  "  do  not  in  any  respect  show  how  the 
atoms  are  grouped,  but  only  the  analogies  of  their  meta- 
morphoses. The  type  is  the  unit  with  which  are  compared 
all  those  compounds  which  show  analogous  decompositions, 
or  which  are  the  products  of  analogous  decompositions." 

After  this  exposition  of  Gerhardt's  system  in  its  main 
points,  it  will  be  intelligible  why  it  has  been  spoken  of  as 
resulting  from  the  fusion  of  the  type  theory  of  Dumas  with 
the  older  radical  theory.  Gerhardt  had  made  use  of  par- 
ticular parts  in  both  of  these,  and  had  recast  them  slightly 
for  incorporation  into  his  syst&me  unitaire.  The  idea  that 
organic  compounds  are  constructed  on  certain  models,  to 
which  they  can  be  referred,  originated  essentially  in  the 
older  type  doctrine,  but,  although  hidden,  it  was  also 
contained  in  the  radical  theory;  in  the  latter,  groups  of 
organic  substances  had  been  directly  compared  with 
analogously  constituted  inorganic  ones.  Now  it  was  of 
fundamental  importance  for  the  success  of  the  new  type 
theory  that  it  borrowed  from  the  radical  theory  the  concep- 
tion of  atomic  groups  which  behaved  like  simple  substances ; 
these  groups  could  not,  however,  exist  in  the  free  state,  as 
had  formerly  been  supposed,  but  could  only  act  in  place  of 
elements  in  compounds.  This  conception,  coupled  with  that 
of  the  alterability  (by  substitution)  of  these  atomic  com- 
plexes, has  proved  to  be  absolutely  correct,  and  at  the  same 
time  of  the  greatest  value.  The  question  of  the  proximate 
composition  of  the  above  groups  was  left  unanswered,  and 
indeed  untouched,  by  Gerhardt,  the  key  to  its  solution  being 
supplied  from  quite  another  quarter,  i.e.  by  Kolbe  and 
Frankland. 

While  the  older  type  theory  of  Dumas  ascribed  no 
appreciable  influence  to  the  chemical  nature  of  the  con- 

x 


306  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

stituents  of  a  compound  upon  the  character  of  the  latter, 
Gerhardt  showed  his  greater  insight  in  this  point  also  by 
recognising  certain  principles  of  Berzelius'  school,  even 
when  he  appeared  mainly  intent  on  opposing  their  spirit. 
He  pointed  out  that  the  elements  or  atomic  groups,  which 
take  the  place  of  hydrogen  in  his  types,  determine  according 
to  their  electro-chemical  nature  the  nature  of  the  result- 

•tcr 

ing  compounds.      Thus   he   represented   potash,  rrO,  as   a 

NO 
basic,  and  nitric  acid,    TT2O,  as  an  acid  body,  because  the 

hydrogen  of  the  neutral  water  was  replaced  respectively  in 
these  by  an  electro-positive  and  an  electro-negative  radical ;. 

O  TT 

but  alcohol,     |    5Q,  as  an  almost  neutral  compound,  ethyl 
M 

being  of  pretty  much  the  same  nature  as  hydrogen  itself. 
This  return  to  views,  which  had  formerly  been  combated  so 
vigorously  by  that  side,  deserves  to  be  especially  noted. 

The  criticisms  passed  upon  Gerhardt's  type  theory  at 
that  time  varied  very  much.  Many  chemists,  especially 
the  younger  ones,  greeted  it  as  an  important  conquest  on 
the  part  of  research.  But,  as  a  matter  of  fact,  the  favourable 
reception  given  to  the  typical  view  was  due  to  grounds  of  a 
practical  nature ;  men  gave  it  as  their  opinion  quite  frankly, 
that  the  chief  advantage  which  the  reference  of  organic 
compounds  to  a  few  inorganic  types  brought  with  it,  con- 
sisted in  its  thereby  simplifying  the  study  of  organic 
chemistry.  Liebig,  who  had  criticised  Gerhardt's  earlier 
efforts  at  classifying  organic  compounds  most  severely,1 
acknowledged  later  on2  the  "  utility  of  the  so-called  type 
theory";  but  at  the  same  time  he  laid  stress  upon  the 
point  that  it  left  the  weighty  question  of  the  formation 
of  organic  compounds  untouched.  Kolbe  took  up  a  more 
drastic  attitude  than  this;  he  designated  the  grouping  of 
organic  compounds  into  the  above  four  types  a  mere  playing 
with  formulae.  His  own  efforts  he  directed  to  replacing 

1  Ann.  Chem.,vol.  Ivii.  p.  93,  Herr  Gerhardt  unddie  organische  Chemie. 

2  Ann.  Chem.,  vol.  cxxi.  p.  163. 


v  EXTENSION  OF  THE  TYPE  THEORY  BY  KEKULE        307 

these  purely  formal  types  by  real  ones,  which  should  stand 
in  a  natural  connection  to  the  compounds  derived  from 
them.  Indeed,  there  was  a  serious  danger  that  a  door  would 
be  opened  for  empty  formulation.  We  have  only  to  recall 
that  Odling  and  also  Wurtz1  endeavoured  to  simplify 
Gerhardt's  types  by  referring  those  of  water  and  ammonia 
to  the  double  and  triple  hydrogen  ones.  With  this  the 
momentous  question  of  the  chemical  constitution  of  organic 
compounds  was  diverted  appreciably  from  the  direction 
which  had  been  given  to  it  by  the  school  of  Berzelius  and 
Liebig.  The  term  "  constitution,"  already  very  elastic  in 
Gerhardt's  theory,  threatened  to  lose  all  meaning  by  formu- 
lation so  exaggerated. 

Extension  of  the  Type  Theory  ~by  KekuU. 

Gerhardt  did  not  live  to  enjoy  the  cordial  reception 
which  was  given  by  many  chemists  to  the  opinions  laid 
down  by  him  in  the  fourth  volume  of  his  text-book.  His 
type  theory  underwent  a  not  inconsiderable  extension  the 
year  after  his  death  (in  1857),  by  the  assumption  of  the 
so-called  mixed  types,  which  aimed  at  making  clear  the 
relations  of  many  organic  compounds  to  two  or  more  types. 
The  more  general  application  of  this  by  Kekule2  was 
preceded  by  Williamson's  idea  that  certain  organic  com- 
pounds might  be  derived  from  multiplied  or  condensed  types. 
Just  as  chemical  compounds  proceeded  from  these  through 
the  substitution  of  several  hydrogen  atoms  by  polybasic 
radicals,  so  different  types  like  water  and  ammonia,  or  water 
and  hydrogen,  etc.,  were  conjoined  in  order  to  derive  from 
them  those  substances  which  had  previously  been  known 
as  copulated  compounds  (gepaarte  Verbindungen),  to  distin- 
guish them  from  others  which  were  readily  classified  under 
one  type.3  Kekule  recognised  in  the  removal  of  this 

1  Cf.  Ann.  Chim.  Phys.  (3),  vol.  xliv.  p.  305. 

2  Ann,  Chem.,  vol.  civ.,  p.  129. 

3  The  same  idea  which  Kekule  generalised  later  on  had  indeed  occurred 
to  Gerhardt,  in  so  far  that  he  had  referred  the  aminic  acids  (for  example)  to 
the  mixed  ammonia- water  type. 

x  2 


380  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

barrier  the  main  advantage  which  was  to  be  derived  from 
the  assumption  of  mixed  types,  as  is  apparent  from  the 
following  extract :  "  The  so-called  copulated  compounds 
are  not  constituted  differently  from  other  chemical  com- 
pounds; they  can  in  like  manner  with  these  be  referred 
to  types  in  which  hydrogen  is  replaced  by  radicals ;  and,  in 
respect  to  formation  and  saturation-capacity,  they  follow 
the  same  laws  which  hold  good  for  all  chemical  com- 
pounds."1 

Before  continuing  the  subject,  a  short  account  must  be 
given  of  the  career  and  labours  of  the  famous  chemist  just 
named. — August  Kekule,  born  at  Darmstadt  on  7th  Sep- 
tember, 1829,  became  assistant  professor  of  chemistry  at 
Heidelberg  in  1856,  and  then  professor  at  Ghent  from  1858 
to  1 8  6  5  ;  in  the  latter  year  he  was  called  to  the  University 
of  Bonn,,  where  he  continued  to  labour  until  his  death  on 
the  13th  of  July,  1896.  There  could  be  no  stronger 
testimony  of  his  profound  and  wide-reaching  influence  as  a 
teacher  than  in  the  large  number  of  his  pupils  who  have 
attained  to  eminence  in  their  science.  By  his  Lehrluck  der 
organischen  Ghemie  ("  Text-Book  of  Organic  Chemistry," 
Erlangen,  begun  to  be  published  in  1859),  in  which  he 
endeavoured  to  work  out  the  typical  view  and  subsequently 
the  structural  doctrine  to  their  logical  conclusions,  he 
exercised  an  immense  influence  upon  the  chemists  of  his 
time.  More  especially,  by  his  happy  conception  of  benzene 
(the  basis  of  the  "  aromatic"  hydrocarbons)  as  a  hexamethine, 
he  furnished  the  direction  for  one  of  the  most  important  and 
wide-spreading  branches  of  chemical  research ;  and  this  still 
holds  with  undiminished  force  at  the  present  moment.  His 
researches  on  fulminate  of  mercury,  unsaturated  dibasic  acids, 
and  the  condensation  of  aldehyde  (to  name  only  a  few)  proved 
him  to  be  an  admirable  investigator.  Mention  may  also  be 
made  here  of  his  share  in  the  editing  of  a  former  journal,  the 
Kritische  Zeitschrift  fur  Chemie,  etc.,  and  of  the  present 
Annalen  der  Chemie,  in  the  latter  of  which  most  of  his 
experimental  work  was  published.  A  warm  tribute  to  his 
1  Ann.  Chem.,  vol.  civ.  p.  139. 


v  SETTING  UP  OF  MIXED  TYPES  309 

memory,  from  the  pen  of  H.  Landolt,  is  to  be  found  in  the 
JBerichte,  vol.  xxix.  p.  1971 ;  and  the  KekuM  memorial  lecture 
by  F.  R.  Japp,  delivered  before  the  Chemical  Society  on 
December  15th,  1897,  is  reprinted  in  the  Journ.  Ckem.  Soc. 
for  February,  1898. 

A  few  examples  of  formulae  will  serve  to  make  the  use 
of  the  mixed  types  intelligible  : — 

Cso6  H 

j|  O,  Benzene-sulphonic  acid,  referred  to  — ; 

H 

H2N 

°2  O,  Carbamic  acid,  referred  to  S£ 

H  fy 
H° 

Almost  simultaneously  with  the  above  extension  of  the 
type  theory,  a  suggestion  was  made  by  Kekule'  which,  thanks 
to  special  circumstances,  was  destined  to  give  this  theory  a 
far  more  extended  application.  2.  propos  of  his  researches 
upon  fulminate  of  mercury,1  he  had  expressed  the  opinion 
that  the  methyl  compounds  and  the  numerous  bodies  derived 
from  them  might  be  referred  to  the  type  of  marsh  gas,  to 
which  he  gave  the  equivalent  formula  C2H4.  He  illustrated 
the  connection  of  several  compounds  to  the  new  type  by  the 
following  examples : — 

C2H4  C2H3C1  C2HC13        C2H3CN       C2C13(NO4) 

Methyl  hydride  Methyl  chloride     Chloroform  Aceto-nitrile  Chloro-picrin. 

Kekule's  formulation'  here  is  noteworthy,  in  that  he 
uses  atomic  weights  which  he  had  formerly  regarded  as 
incorrect,  i.e.  H  =  l,  C  =  6,  and  0  =  8.  And  a  remark  that 
he  makes  strikes  one  as  strange — viz.  that  the  new  type  was 
not  to  be  taken  in  the  sense  of  Gerhardt's  unitary  theory, 
but  in  that  of  Dumas'  types.  From  this  one  might  infer 
that  marsh  gas  was  not  intended  to  be  placed  alongside  of 
Gerhardt's  four  types ;  but,  notwithstanding  this,  to  give  it 
a  place  by  itself  does  not  seem  to  have  been  meant  by 
Kekule,  since  he  adds,  quite  in  the  spirit  of  the  newer  type 
1  Ann.  Chem.,  vol.  ci.  p.  200. 


310  THE  MODERN  CHEMICAL  PERIOD  CHAP' 

theory,  that  what  he  mainly  wishes  to  indicate  by  his 
formulae  are  the  relations  in  which  the  compounds  enume- 
rated stand  to  one  another. 

In  the  following  year  (1858),  however,  the  meaning 
which  he  attached  to  methane  as  the  mother  substance  of 
a  large  number  of  compounds  became  more  clear.  But  a 
detailed  account  of  his  views  upon  this  must  be  reserved  for 
a  later  section  of  the  book,  when  the  transition  of  the  type 
theory  into  the  structure  theory  will  come  to  be  discussed. 

Before,  however,  this  development  of  chemical  hypotheses 
could  be  consummated,  much  work  had  to  be  done  in  order 
to  get  nearer  to  a  knowledge  of  the  chemical  constitution  of 
organic  compounds.  The  types  themselves  could  not  aid 
in  the  solution  of  this  problem  without  their  own  nature 
being  first  elucidated.  The  key  to  the  explanation  of  these 
relations  was  forged  by  the  labours  and  speculations  of 
Frankland  and  Kolbe.  To  these  two  investigators  is 
primarily  due  the  more  profound  insight  into  the  constitu- 
tion of  organic  substances  as  opposed  to  the  typical  and 
therefore  superficial  view  (der  typisch  schematischen).  Their 
researches  contributed  more  than  any  others  to  bring  about 
the  change  in  direction  taken  by  the  type  theory;  they 
were,  in  fact,  the  indispensable  preliminary  to  that  trans- 
formation of  theoretical  opinions  which  completed  itself 
towards  the  end  of  the  fifties.  The  correctness  of  this 
statement  will  be  seen  from  what  follows  in  the  succeeding 
sections. 

It  is  true  that  the  typists  place  quite  another  estimate 
upon  the  services  of  Frankland  and  Kolbe.  The  influence 
exercised  by  these  two  men  on  the  remodelling  of  the  type 
theory  has  not  only  been  greatly  minimised,  but  even  the 
exact  contrary  has  been  asserted,  viz.  that  "  typical "  hypo- 
theses influenced  them.1 

1  Such  erroneous  conceptions  are  always  long  of  being  dispelled.  Thus, 
in  the  description  of  "the  theories  of  to-day"  in  Wurtz's  Histoire  des 
Doctrines  Chimiques,  the  influence  of  the  above  two  scientists  is  very  much 
neglected.  It  seems  hardly  credible  that  Frankland,  the  real  originator  of 
the  doctrine  of  valency,  should  scarcely  be  mentioned  in  this  publication. 
The  same  applies  to  the  general  section  of  Kekule's  Lehrbuch  der  organischen 


KOLBE'S  LIFE  AND  WORK  311 


Development  of  the  Newer  Radical  Theory  by  Kolbe — 
A  Survey  of  his  Principal  Work. 

Before  speaking  of  Kolbe's  scientific  labours,  which  pro- 
duced a  deep  and  lasting  effect  on  the  development  of 
theoretical  chemistry,  a  short  sketch  of  his  life  may  be  fitly 
appended  here.1 

Hermann  Kolbe,  son  of  the  Pastor  of  Elliehausen  near 
Gottingen,  was  born  in  1818,  and  applied  himself  to  the 
study  of  chemistry  under  Wohler's  stimulating  guidance  in 
1838.  The  results  of  his  first  research  were  published  in 
1842,  and  for  the  next  forty-two  years  he  continued  to 
enrich  his  science  with  a  long  succession  of  the  most 
valuable  experimental  and  theoretical  work.  His  outward 
life,  if  we  except  perhaps  the  first  few  years  immediately 
following  his  university  curriculum,  was  that  of  a  German 
scientist.  From  1842-47  he  was  assistant  to  Bunsen  at 
Marburg  and  then  to  Playfair  in  London,  during  which 
time  he  occupied  himself  mainly  with  practical  chemical 
work;  after  this  came  the  years  of  his  literary  apprentice- 
ship (1847-51)  in  Brunswick,  where  he  had  gone  at  the 
request  of  the  well-known  publishers,  Fr.  Vieweg  and  Son 
to  take  up  the  editorship  of  the  Dictionary  of  Chemistry 
started  by  Liebig.  This  work  not  being  of  such  a  nature  as 
to  satisfy  him  permanently,  he  willingly  accepted  in  1851  a 
call  to  Marburg,  where,  as  Bunsen's  successor,  he  developed 
exceptional  powers  as  a  teacher,  especially  in  the  years 
following  1858.  In  1865  he  was  called  to  the  University 
of  Leipzig,  and  worked  there  with  marked  success  until  his 
death  on  25th  November  1884. 

Chemie  ;  there  the  debt  due  to  Frankland  is  absolutely  ignored,  while  the 
share  in  the  development  of  organic  chemistry  taken  by  Dumas,  Gerhardt, 
Laurent  and  Kekule  himself  is  minutely  detailed.  At  a  later  date  (cf.  Ber. 
for  1880,  p.  7)  Wurtz  unreservedly  acknowledged  Frankland's  service  by 
stating  that  he  was  the  first  to  put  forward  the  idea  of  the  saturation- 
capacity  of  elementary  atoms. 

1  Cf.  the  memoirs  which  appeared  shortly  after  Kolbe's  death  by  E.  v. 
Meyer,  Journ.  pr.  Chem.  (2),  vol.  xxx.  p.  417  ;  Voit,  Bayer.  Acad.,  1885 ; 
and  A.  W.  v.  Hofmann,  Ber.,  vol.  xvii.  p.  2809. 


312  THE  MODERN  CHEMICAL  PERIOD  CHAP, 

The  great  influence  which  Kolbe  exercised  upon  chemical 
science  depended  to  an  unusual  degree  upon  his  experimental 
work,  which  will  be  discussed  later  on,  but  at  the  same 
time  also  upon  his  eminence  as  a  teacher,  in  which  respect  he 
may  be  spoken  of  along  with  Liebig.  His  method  of  teaching 
was  very  like  that  of  the  latter  and  had  the  best  results ;. 
the  student  of  practical  chemistry  was  taught  to  observe 
and  think  for  himself.  Kolbe's  gifts  as  a  teacher  were 
greatly  enhanced  by  his  sound  common-sense  and  organising 
talent,  which  showed  themselves  in  a  marked  degree  in  the 
building  and  fitting  up  of  the  new  Leipzig  laboratory  (in. 
1868). 

In  addition  to  his  work  as  a  teacher,  based  as  this  was 
upon  oral  instruction,  Kolbe  was  also  extremely  active  in  a 
literary  sense.  Apart  from  his  numerous  scientific  papers, 
valuable  articles  for  the  ffandworterbuch  der  Chemie  ("  Dic- 
tionary of  Chemistry"),  and  occasional  pamphlets,  he  pub- 
lished a  large  Lehrbuch  der  organischen  Chemie  ("  Text- 
Book  of  Organic  Chemistry,"  Braunschweig,  1854-65),  and 
smaller  text-books  both  of  inorganic  and  organic  chemistry 
(1877-83).  These  books  are  distinguished  by  clearness  in 
arrangement,  precision  of  expression,  a  delightful  style,  and 
perspicacity  and  acuteness  in  discussion. 

In  his  writings  upon  questions  of  theoretical  chemistry> 
published  for  the  last  fourteen  years  of  his  life  in  the 
Journal  fur  praktische  Chemie  (of  which  he  succeeded 
Erdmann  as  editor  in  1870),  Kolbe  gave  play  to  a  keen 
criticism,  which  became  intensified  as  time  went  on,  upon 
the  defects  and  extravagances  which  he  considered  were 
due  to  the  direction  taken  by  modern  chemistry.  If  those 
critiques  were  often  strongly  polemical  and  did  not  altogether 
avoid  the  danger  of  introducing  the  personality  of  many  a 
brother  chemist,  still  his  only  aim  in  them  was  the  welfare 
of  his  beloved  science,  which  he  believed  to  be  in  serious 
danger.  His  efforts  at  exposing  error  were  often  wrongly 
interpreted  by  many  of  his  contemporaries,  just  as  Liebig's 
polemical  writings  were  often  perversely  criticised. 


KOLBE  AND  FRANKLAND'S  PIONEERING  WORK         31S 


The  Re-animation  of  the  Radical  Theory  by  Kolbe — 
Frarikland's  Co-operation. 

At  the  time  when  Kolbe  published  the  first  of  his  more 
important  researches,1  the  doctrine  advocated  by  Berzelius, 
that  organic  compounds  contain  definite  radicals  which  act 
similarly  to  elements  in  inorganic  compounds,  had  been 
driven  into  the  background  by  the  attack  of  unitarism. 
Many  chemists  were  of  opinion  that  the  partly  arbitrary 
supposition  of  hypothetical  radicals  could  not  advance  the 
science  any  further.  The  assumption  of  copulae  (Paarlinge) 
in  the  so-called  copulated  compounds  satisfied  very  few.  In 
short,  the  old  radical  theory  in  its  original  form  was  held  to 
be  no  longer  capable  of  existence.  The  preference  given  by 
the  school  of  Gmelin  to  the  simplest  views  which  were 
possible  is  sufficient  evidence  of  this  sense  of  discouragement. 
Facts  alone  were  to  decide ;  any  intelligent  grouping  of 
these  facts  together  was  deemed  useless. 

Kolbe  now  united  the  conclusions  deduced  from  his 
first  researches  with  the  declining  theory  of  Berzelius ;  he 
endued  the  latter  with  new  life  by  casting  aside  whatever 
of  it  was  dead  and  replacing  this  by  vigorous  principles. 
From  his  own  and  other  investigations  he  came  to  the 
conclusion  that  the  unalterability  of  radicals,  as  taught  by 
Berzelius,  could  no  longer  be  maintained,  since  the  facts  of 
substitution  had  to  be  taken  into  account.  He  did,  indeed, 
adopt  Berzelius'  hypothesis  of  copulse,  but  attached  another 
meaning  to  these,  since  he  allowed  that  they  exercised  a  not 
inconsiderable  influence  upon  the  compounds  with  which 
they  were  copulated.2 

If  we  desire  to  sum  up  the  main  results  of  his  labours 
just  cited,  and  of  his  synthesis  of  trichloracetic  acid,  so 
immediately  connected  with  them,  we  may  do  so  as  follows : 
Trichloro-methyl-hyposulphuric  acid  (our  present  trichloro- 
methyl-sulphonic  acid),  discovered  by  him,  and  trichlor- 

1  Ann.  Chem.,  vol.  xlv.  p.  41  ;  vol.  liv.  p.  145. 

2  Cf.  Ann.  Chem.,  vol.  liv.  p.  156. 


314  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

acetic  acid,  together  with  the  compounds  free  from  chlorine 
obtained  from  these  by  reduction,  were  analogously  consti- 
tuted acids,  copulated  respectively  with  trichloro-methyl  and 
methyl,  thus — 

C2C13 + S2O6 + HO  C2H3 + S2O5  +  HO 

C2C13 + C203+H0  C2H3  +  C203 + HO 

True,  the  mode  in  which  these  two  radicals  were 
combined  with  the  acids  was  not  yet  known,  but  the  germ 
of  the  correct  explanation  with  regard  to  the  constitution 
of  carboxylic  and  sulphonic  acids,  which  was  given  by  Kolbe 
at  a  later  date,  was  already  present  here. 

This  germ  was  soon  to  undergo  further  development  by 
investigations  carried  out  at  first  by  Kolbe  alone,  and 
afterwards  together  with  Frankland  in  London.  From  their 
beautiful  researches  on  the  transformation  of  the  alkyl 
cyanides  into  fatty  acids,1  they  concluded  with  perfect 
precision  that  methyl,  ethyl,  and  similar  radicals  were 
immediate  constituents  of  acetic  acid  and  its  homologues. 
Kolbe  himself  was  led  to  the  same  conclusion  by  his 
important  work  upon  the  electrolysis  of  salts  of  the  fatty 
acids ; 2  he  saw  in  the  methyl  and  butyl,  separated  at  the 
positive  pole  from  acetic  and  valerianic  acids  respectively, 
the  proof  of  the  correctness  of  this  assumption.  He  believed, 
indeed,  that  he  had  isolated  the  radicals  themselves;  and 
even  although  he  was  wrong  in  so  thinking  (the  hydro- 
carbons obtained  by  him  having  double  the  molecular 
weight  that  the  radicals  would  possess),  this  affected  but 
little  the  question  of  the  constitution  of  the  carboxylic  acids. 
The  chief  goal  of  his  endeavours,  i.e.  the  discovery  of  the 
true  composition  of  the  above  and  similar  acids,  was  still  kept 
in  view  by  him,  notwithstanding  this  mistake. 

The  outcome  of  this  work  of  his  was  that  the  view  pre- 
viously held  with  regard  to  these  organic  acids  no  longer 
satisfied  him.  He  did  not,  however,  abandon  this  all  at 
once,  but  rather  developed  from  it  a  theory  which  approxi- 

1  Ann.  Chem.,  vol.  Ixv.  p.  288. 

2  Ibid.,  vol.  Ixix.  p.  258. 


v  KOLBE'S  DOCTRINE  OF  CONJUGATE  COMPOUNDS       315 

mated  to  the  truth,  and  which  soon  showed  itself  capable  of 
further  improvement.  Even  so  early  as  when  writing  the 
articles  upon  Formulae  and  Copulated  Compounds  for  his 
Dictionary  (in  1848),  he  expressed  and  gave  reasons  for  the 
view  that  the  fatty  acids  were  oxygen  compounds  of  the 
radicals  hydrogen,  methyl,  ethyl,  &c., combined  with  the  double 
carbon  equivalent  C2.1 

Acetic  acid  contained  as  its  immediate  constituent  an 
atomic  complex  constituted  similarly  to  that  of  the  cacodyl 
compounds.  Cacodyl  itself,  which  was  here  for  the  first 
time  interpreted  as  being  arsenic  copulated  with  two  methyl 
radicals,  corresponded  to  the  so-called  acetyl  of  acetic  acid, 
i.e.  C2H3C2  (not  to  be  confounded  with  the  radical  acetyl  of 
to-day,  which  at  that  time  was  known  as  acetoxyl). 

Even  at  this  early  date  Kolbe  expressed  the  significant 
opinion  that  in  the  acetyl  (C2H3C2)  of  acetic  acid,  "  the  last 
C2  alone  forms  the  connecting-link  for  the  oxygen,  the 
methyl  being  in  some  sort  only  an  appendage."  This  idea, 
which  recalls  Berzelius'  doctrine  of  copulse,  was  based 
upon  the  point  that  it  was  unessential  for  the  nature  of 
the  acids  whether  hydrogen  or  methyl,  ethyl,  etc.,  was  copu- 
lated with  the  C2. 

He  entered  into  these  important  ideas  in  detail  in  a 
treatise  entitled,  Ueber  die  chemische  Konstitution  und  Natur 
der  organischen  Eadikale  ("  Upon  the  Chemical  Constitu- 
tion and  Nature  of  the  Organic  Radicals").2  Taking  his 
stand  upon  the  basis  of  the  older  radical  doctrine,  he  built 
this  up  into  a  living  theory  by  eliminating  from  it  all  those 
principles  which  stood  in  contradiction  to  the  facts.  But  at 
the  same  time  he  did  not  remain  stationary  upon  the  point 
of  vantage  he  had  thus  gained. 

Under    the   influence   of    the   admirable  researches    of 

1  Kolbe,  like  many  others,  made  use  at  this  time  of  Gmelin's  equivalent 
weights,  in  which  H=l,  C  =  6,  0  =  8,  S  =  16,  etc.     His  formulae  were,  not- 
withstanding this,  molecular  formulas ;  thus  he  gave  carbonic  acid,  acetic 
acid,  alcohol,  aldehyde  and  acetone  the  same  atomic  (i.e.  molecular)  weights 
as  we  employ  for  these  substances  to-day. 

2  Ann.  Chem.,  vol.  Ixxv.  p.  211  ;  vol.  Ixxvi.  p.  1. 


316  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

Frankland  l  upon  the  alcohol  radicals  and  the  organo-metallic 
compounds,  which  were  begun  at  that  time,  Kolbe  advanced 
step  by  step.  With  regard  to  this  period,  he  stated  de- 
finitely himself,2  that  "  the  want  of  clearness  in  (my)  con- 
ception of  the  mode  in  which  the  so-called  copulae  were 
combined,  was  a  great  weakness  in  the  hypothesis  of 
copulated  radicals.  .  .  .  It  is  Frankland's  merit  to  have 
been  the  first  to  throw  light  upon  this,  and  therewith  to 
have  thereby  completely  done  away  with  the  idea  of  copula- 
tion, by  recognising  the  fact  that  the  various  elements  possess 
definite  saturation-capacities." 

Kolbe  readily  embraced  his  friend's  views,  and  copulse 
thus  received  a  totally  different  meaning  from  what  they 
had  formerly  done;  henceforth  they  were  to  be  regarded 
as  integral  parts  of  organic  compounds  and  not  as  mere 
appendages. 

This  change  in  his  opinions  was  not  long  of  bearing 
fruit.  And  here  it  was  again  the  fatty  acids  whose 
constitution  he  undertook  to  work  out.  In  1 8  5  5  3  he  first 
gave  definite  expression  to  the  view  that  the  acids,  con- 
sidered as  anhydrous,  were  derivatives  of  carbonic  acid ; 

1  Sir  Edward  Frankland,   born  at  Churchtown,    near  Lancaster,   on 
January  18th,  1825,  studied  chemistry  at  the  Museum  of  Practical  Geology 
in  London,  then  with  Liebig  and  Bunsen,  and  also  under  Kolbe' s  stimulus 
in  Germany.     He  afterwards  filled  successively  the  chairs  of  chemistry  in 
the  Owens  College,'  Manchester   (1851-7),    St.    Bartholomew's   Hospital, 
London  (1857),  Royal  Institution  (1863),  Royal  School  of  Mines  (1865),  and 
Normal  School  of  Science,  South  Kensington  (1881).     This  last  chair  he 
resigned  in  1885,  retiring  then  from  professorial  work.    Frankland  attracted 
the  attention  of  chemists  even  by  his  earliest  work,  which  led  him  to  the 
discovery  of  the  organo-metals,  and  also  by  his  joint  researches  with  Kolbe. 
The  chief  share  which  he  took  in  the  development  of  our  present  views 
upon  the  valency  of  the  elements  will  be  discussed  in  detail  later  on,  while 
his  other  memorable  investigations  in  organic  chemistry  will  often  have  to 
be  referred  to  under  the  special  history  of  this  branch.    Frankland's  papers 
have  mostly  been  published  in  the  English  journals  and  the  Annalen  der 
Chemie  ;  in  1877  they  were  collected  into  one  volume,  entitled  Researches 
in  Pure,  Applied  and  Physical  Chemistry.     He  is  also  the  author  of  the 
text-book,  Lecture  Notes  for  Chemical  Students. 

2  Cf.   Das  chem.  Laboratorium  der  Universitcit  Marburg,  etc.  (Braun- 
schweig, 1865),  p.  32. 

3  Handwb'rterbuch  der  Chemie,  vol.  vi.  p.  802. 


v  DERIVATION  OF  ORGANIC  COMPOUNDS  FROM  INORGANIC  317 

for  instance,  acetic  was  methyl-carbonic  acid,  i.e.  C2O4,  in 
which  one  oxygen-equivalent  was  replaced  by  methyl,  C2H3. 
The  hydrated  acids  he  still  regarded  dualistically  as  com- 
pounds of  the  anhydrides  with  water. 

The  assumption  that  those  acids  were  substitution- 
products  of  carbonic  acid  had  developed  itself  from  the 
views  held  regarding  the  organo-metallic  compounds.  Just 
as  Frankland  explained  cacodylic  acid  as  arsenic  acid  with 
two  methyls  in  the  place  of  two  equivalents  of  oxygen, 
and  stanno-ethyl  oxide  as  the  corresponding  tin  derivative, 
so  did  Kolbe  happily  interpret  the  constitution  of  other 
organic  compounds.  He  soon  advanced  beyond  the  field 
of  the  organic  acids,  and  developed  the  idea,  similar  to 
that  mentioned  above,  that  many  organic  substances  are 
to  be  regarded  as  derivatives  of  carbonic  acid,  and  many 
others  as  derivatives  of  sulphuric.  How  this  idea  expanded 
into  a  perfect  whole  is  seen  from  his  writings  in  the  years 
185  7-5  8,1  and  also  from  those  portions  of  his  text-book  which 
were  written  both  at  that  time  and  shortly  before  it.  These 
theoretical  considerations  and,  with  them,  the  revived  radical 
theory"  attained  to  their  completed  form  in  a  treatise  pub- 
lished in  1859,  entitled,  Ueber  den  naturlichen  Zusammen- 
hang  der  organischen  mit  den  unorganischen  Verbindungen, 
die  wissenschaftliche  Grundlage  zu  einer  naturgemdssen  Klassi- 
fikation  der  organischen  chemischen  Korper  ("Upon  the 
Natural  Connection  existing  between  Organic  and  Inor- 
ganic Compounds,  being  the  Scientific  Basis  of  a  Rational 
Classification  of  Organic  Chemical  Substances  ").2 

The  main  outcome  of  Kolbe's  speculations  is  given  in 
the  following  sentence :  "  Organic  compounds  are  all  de- 
rivatives of  inorganic,  and  result  from  the  latter — in  some 
cases  directly — by  wonderfully  simple  substitution-processes." 
This  idea  runs  through  the  whole  treatise,  and  is  illustrated 

1  Ann.  Chem.,  vol.  ci.  p.  257  ;  this  paper  is  a  joint  one  with  Frankland, 
i.e.  Kolbe  lays  emphasis  on  the  point  that  he  is  here  giving  utterance  both 
to  his  own  and  Frankland's  views.    Cf.  also  Kolbe's  pamphlet  (1858),  Ueber 
die  chemische  Konstitution  organischer  Verbindungen  ("On  the  Chemical 
Constitution  of  Organic  Compounds  "). 

2  Ann.  Chem.,  vol.  cxiii.  p.  293. 


318  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

with  the  most  convincing  clearness  by  numerous  examples 
taken  from  the  wide  field  of  organic  chemistry. 

The   alcohols,   carboxylic  acids,   ketones   and   aldehydes 
were    derived,    according    to    Kolbe,    from    carbonic    acid, 

(C2O2)O2,   and   its   hydrate,   C2O2.y  ^,   respectively.      The 

polybasic  carboxylic  acids  proceeded  in  the  same  way  from 
two  or  three  molecules  of  the  hydrated  carbonic  acid,  through 
the  entrance  of  polyatomic  radicals,  just  as  the  monobasic 
did  from  one  molecule.  Similar  definite  views  were  ex- 
pressed by  Kolbe  with  regard  to  other  classes  of  organic 
compounds,  e.g.  the  phosphinic  and  arsenic  acids,  amines 
and  amides,  and  the  organo-metals,  which  he  derived  in  the 
simplest  manner  from  inorganic  compounds.  He  laid  the 
utmost  emphasis  upon  his  formulae  being  the  unambiguous 
expression  of  precise  opinions ;  with  Gerhardt's  assumption 
that  various  constitutional  formulae  might,  with  equal  justice, 
be  set  up  for  one  and  the  same  compound,  he  had  absolutely 
nothing  in  common. 

Kolbe  himself  gave  a  striking  proof  in  the  treatise 
above  mentioned  of  the  capacity  for  development  of  his 
views  respecting  the  constitution  of  organic  compounds. 
He  comprised  in  his  survey  not  merely  those  classes  of 
compounds  which  were  known,  but  advanced  beyond  them 
to  others  at  that  time  unknown.  From  the  relations  so 
clearly  recognised  by  him  as  existing  between  the  alcohols 
and  the  carboxylic  acids,  he  deduced  the  possibility  of  pre- 
paring new  varieties  of  alcohols ;  he  predicted  the  existence 
both  of  secondary  and  of  tertiary  alcohols,1  and  even  went 
so  far  as  to  indicate  a  probable  method  for  preparing  and 
decomposing  the  first  of  these.  No  such  brilliant  deduc- 
tive treatment  of  chemical  questions  had  as  yet  been  seen 
in  organic  chemistry.  And  the  discovery  of  those  classes 
of  compounds  which  he  had  prognosticated  had  not  to  be 
waited  for  long ;  Friedel  isolated  secondary  propyl  alcohol 
in  1862,  and  Butlerow  tertiary  butyl  alcohol  in  1864. 

The    comprehensive    speculations    of    Kolbe    upon    the 

1  Cf.  Ann.  Chem.,  vol.  cxiii.  p.  307. 


v  KOLBE'S  EXPERIMENTAL  RESEARCHES  319 

constitution  of  organic  compounds  could  not  have  attained  to 
the  firm  hold  and  the  wide  significance  which  they  did,  had 
they  not  been  conjoined  throughout  with  admirable  experi- 
mental work.  We  shall  frequently  have  occasion,  in  the 
special  history  of  organic  chemistry,  to  refer  to  those  labours, 
through  which  the  rational  composition  of  important  classes 
of  compounds  was  first  arrived  at  with  certainty.  Thus  it 
was  his  researches  upon  lactic  acid  which  showed  ifc  to  be 
oxy-propionic,  and  the  corresponding  alanin  to  be  amido- 
propionic  acid.  Glycollic  acid  and  glycocoll  were  likewise 
shown  by  Kolbe  to  belong  to  the  same  class,  the  one  being 
proved  to  be  oxy-,  and  the  other  amido-acetic  acid ;  he  also 
recognised  salicylic  acid  as  oxybenzoic,  and  the  so-called 
benzamic  acid  (Benzaminsdure)  as  amido-benzoic.  He  was 
thus  in  a  position  to  clear  up  the  constitution  of  compounds 
upon  whose  investigation  chemists  of  such  eminence  as 
Kekule  and  Wurtz  had  laboured  in  vain.  Numerous  sub- 
stances, the  names  (Trivialbezeichnungeri)  given  to  which 
showed  how  little  was  known  with  respect  to  their  constitu- 
tion, received  from  Kolbe  their  proper  place  among  other 
compounds.  The  conversion  of  malic  and  tartaric  acids  into 
succinic,  which  was  carried  out  by  Schmitt1  at  his  suggestion, 
revealed  at  one  stroke  the  hitherto  unknown  relations  exist- 
ing between  the  two  first  of  these  acids  and  the  last.  By 
his  researches  upon  taurine,  which  he  taught  how  to  prepare 
artificially,  he  proved  how  both  it  and  the  isethionic  acid 
produced  from  it  were  constituted  analogously  to  alanin 
and  lactic  acid.  And  the  same  clearness  shed  itself  over 
the  rational  composition  of  asparagine  and  aspartic  acid, 
which  he  was  the  first  to  interpret  correctly. 

The  above  are  merely  the  results  of  work  performed 
within  a  short  period  of  time,  but  they  are  amply  sufficient 
to  prove  what  undying  service  he  rendered  in  investigating 
the  chemical  constitution  of  organic  compounds.  And  no 

1  Rudolf  Schmitt,  born  in  1830,  filled  the  chair  of  chemistry  at  the 
Dresden  Technische  Hochschuleirom  1871  to  1893,having  previously  occupied 
other  chemical  posts  at  Marburg,  Cassel  and  Niirnberg.  His  admirable 
experimental  researches  extend  over  many  branches  of  organic  chemistry, 
but  deal  more  especially  with  the  aromatic  compounds. 


320  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

mention  has  been  made  here  of  a  large  number  of  other 
researches  carried  out  at  his  suggestion  and  with  his  co- 
operation; among  these  were  the  work  of  Griess  upon  the 
class  of  diazo-compounds,  Oefele's  discovery  of  the  sulphines, 
and  Volhard's  synthesis  of  sarcosine. 

In  order  to  round  off  in  some  degree  this  short  record  of 
Kolbe's  achievements,  we  ought  further  to  recall  several 
investigations  made  in  the  years  following,  i.e.  after  1863, 
in  which  he  was  guided  throughout  by  the  aspiration  to 
gain  the  furthest  possible  insight  into  the  constitution  of 
organic  compounds.  Among  these  we  may  refer  to  his  proof 
of  malonic  acid  resulting  from  cyan-acetic,  and  being  there- 
fore carboxyl-acetic  acid,  the  discovery  of  nitro-me thane, 
the  series  of  memorable  researches  upon  salicylic  and  para- 
oxybenzoic  acids,  and  lastly,  that  upon  isatoic  acid,  which 
was  cut  short  by  his  death. 


Kolbe's  Attitude  towards  the  older  and  the  newer  Chemistry. 

In  all  Kolbe's  investigations,  whether  speculative  or 
experimental,  we  feel  the  salutary  historic  method  by  which 
they  are  characberised.  He  built  upon  the  edifice  already 
existing,  and  remained  in  his  scientific  efforts  in  continuity 
with  the  chiefs  of  the  classical  school.  He  was  always  glad 
to  acknowledge  that  his  success  as  a  chemist  was  due 
primarily  to  Berzelius,  and,  after  him,  "  to  the  great  exem- 
plars Liebig,  Wohler  and  Bunsen,  who,  to  use  a  phrase  of 
Berzelius,  were  true  workers  in  chemistry  "  (wahre  Bearleiter 
der  Chemie  gewesen  sind). 

The  criticisms  passed  upon  Kolbe  by  his  contemporaries, 
in  so  far  as  regarded  his  attitude  to  organic  chemistry, 
differed  very  greatly.  The  exponents  of  the  earlier  period 
appreciated  his  services  better  than  the  disciples  of  the 
type  theory, — a  theory  which  he  himself  did  not  value  at  its 
true  worth.  A  few  remarks  upon  the  relation  between 
Kolbe's  views  and  those  of  the  typists  will  be  in  place  here. 
As  already  stated,  he  spoke  of  the  type  theory  as  being  un- 


KOLBE'S  REAL  TYPES  321 


scientific ;  he  saw  in  it  not  a  real  theory  but  merely  a  play 
upon  formulae.  In  spite  of  his  definite  utterances  upon  this 
point,  however,  it  has  been  frequently  asserted  that  he  took 
Gerhardt's  doctrine  of  types  as  his  basis,  and  that  therefore 
his  derivation  of  organic  compounds  from  carbonic  acid, 
carbonic  oxide,  sulphuric  acid,  sulphurous  acid,  etc.,  coin- 
cided with  that  from  the  three  types  of  hydrogen,  water 
and  ammonia.  Kolbe  did  indeed  connect  organic  with 
inorganic  compounds,  but  he  repeatedly  emphasised  the 
point l  that  these  latter  were  real  types,  as  opposed  to  the 
formal  ones  of  the  type  theorists.  His  most  ardent  wish 
was  to  fathom  the  chemical  constitution  of  organic  com- 
pounds ;  but  to  merely  classify  the  latter  upon  certain  models 
or  to  go  so  far  as  to  force  them  into  arbitrary  types,  was 
in  the  highest  degree  distasteful  to  him.  Kolbe  attached 
special  weight  to  the  relations  actually  existing  between 
organic  and  inorganic  bodies,  whence  the  emphasis  laid  in 
the  title  of  his  treatise,  spoken  of  above,  upon  the  "  natural 
connection  between  these  as  forming  a  scientific  basis  for  a 
rational  classification  of  organic  substances."  Hence,  also, 
his  attempts,  begun  at  an  early  date,  to  prepare  organic  com- 
pounds artificially  from  simple  inorganic  ones,  with  the  object 
of  thus  gaining  an  insight  into  their  chemical  constitution. 

We  thus  see  Kolbe  pursuing  his  own  way,  not  led  aside 
by  the  criticisms  of  his  contemporaries,  but  working  with 
wonderful  effect,  more  particularly  in  advancing  a  knowledge 
of  the  rational  composition  of  organic  compounds.  The 
older  radical  theory  acquired  through  him  new  life,  and  the 
radicals  themselves  received  a  more  profound  meaning. 
While  in  the  type  theory  the  latter  were  looked  upon  as 
residues  whose  nature  could  be  no  further  investigated, 
Kolbe  devoted  his  whole  energies  to  breaking  up  the 
radicals  into  their  immediate  constituents.  To  give  but  a 
few  examples, — he  showed  cacodyl  to  be  arsene-dimethyl, 
acetyl  to  be  a  compound  of  methyl  and  carbonyl,  and  the 
alkyls  to  be  derivatives  of  methyl.  These  and  other  results 
of  his  investigations,  together  with  the  rich  fruits  of  Frank  - 
1  Cf.  (e.g.)  Journ.  pr.  Chem.  (2),  vol.  xxviii.  p.  440. 

Y 


322  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

land's  labours,  were  undoubtedly  of  the  first  importance, 
indeed  indispensable,  for  the  development  of  the  new  type 
doctrine  into  the  structure  theory. 

These  two  men,  the  workers  of  greatest  originality  in  the 
field  of  organic  chemistry  during  the  storm-and-stress  period 
of  the  fifties,  thus  contributed  most  materially  by  their 
labours  to  the  recognition  of  the  fact  th.at  the  peculiarity  of 
Gerhardt's  types  rested  upon  the  different  saturation-capa- 
cities of  the  elements  which  they  contained.  The  chief 
merit  of  having  worked  as  a  pioneer  in  this  direction  belongs 
to  Frankland. 


THE  FOUNDING  OF  THE  DOCTRINE  OF  THE  SATURATION- 
CAPACITY  OF  THE  ELEMENTS  BY  FRANKLAND. 

In  the  foregoing  section  the  influence  exercised  by 
Frankland  on  the  views  developed  by  Kolbe  with  regard 
to  the  constitution  of  organic  compounds  has  been  already 
distinctly  emphasised.  It  was  Frankland  who,  in  his 
memorable  paper, — On  a  New  Series  of  Organic  Compounds 
containing  Metals 1 — furnished  the  proof  that  the  copulation 
of  radicals  with  elements  (e.g.  carbon,  arsenic  and  sulphur), 
as  taught  by  Kolbe,  depended  upon  a  property  inherent  in  the 
elementary  atoms  of  the  compounds  just  named.  The 
notion  of  copulation  was  recognised  by  Frankland  as  being 
one-sided,  and  the  misconception  which  had  crept  in  from 
its  use  was  done  away  with  by  him, — the  idea,  namely, 
that  the  radicals  present  as  so-called  copulse  in  organic 
substances  exercised  no  appreciable  influence  upon  those 
compounds  with  which  they  were  supposed  to  be  copulated. 

From  his  experiences  gained  from  the  organo-metallic 
compounds,  Frankland  developed  the  doctrine  of  the  valency 
of  the  elements.  If,  freeing  our  minds  from  all  prepossession, 
we  turn  our  glance  backward,  we  recognise  the  germ  of  this 
doctrine  as  being  already  present  in  the  law  of  multiple 

1  Phil.  Trans.,  vol.  cxlii.  p.  417;  Ann.  Chem.,  vol.  Ixxxv.  p.  329.  This 
paper  was  read  before  the  London  Chemical  Society  in  1852. 


v  THE  DOCTRINE  OF  SATURATION-CAPACITY  323 

proportions,  which  stated  that  the  elements  show  different, 
but  at  the  same  time  perfectly  definite  stages  in  their 
combinations.  Among  the  facts  known  at  a  very  early 
period  was,  for  instance,  that  of  one  atom  of  phosphorus 
combining  with  three  and  five  atoms  of  chlorine  to  definite 
compounds ;  but  the  expression  for  this  and  other  similar 
observations,  viz.  that  phosphorus  and  many  other  elements 
were  possessed  of  more  than  one  valency,  i.e.  could  manifest 
varying  saturation-capacities,  had  yet  to  be  found.  Further, 
no  one  had  any  clear  conception  of  a  limit  to  the  saturation- 
capacities  of  elements,  and,  what  was  of  the  first  importance, 
a  sharp  distinction  between  the  terms  "  atom  "  and  "  equiva- 
lent "  was  still  wanting.  With  regard  to  this  latter  point, 
the  experiences  gained  respecting  the  substitution  of  the 
hydrogen  of  organic  compounds  by  chlorine,  oxygen,  etc., 
and  the  deductions  drawn  from  these  had  tended  to  elucidate 
matters.  So  early  as  1834  Dumas  had  pointed  out  that 
1  atom  of  hydrogen  was  replaced  by  1  atom  of  chlorine, 
but  only  by  J  an  atom  of  oxygen;  those  quantities  were 
therefore  equivalent  to  1  atom  of  hydrogen.  The  idea  of 
the  "  replaceable  value "  of  certain  metals  also  came  more 
distinctly  into  prominence  through  the  doctrine  of  polybasic 
acids,  already  spoken  of;  this  was  exemplified,  for  instance, 
in  Liebig's  statement  that  1  atom  of  antimony  was  equiva- 
lent to  3  atoms  of  hydrogen,  but  one  of  potassium  only  to  1 
atom  of  hydrogen.  Notwithstanding  this,  however,  a  precise 
expression  for  such  facts  as  these  had  not  yet  been  found. 
In  the  course  of  the  forties  the  conception  of  a  chemical 
equivalent  as  distinguished  from  an  atom,  a  conception 
which  had  been  arrived  at  after  so  much  labour,  completely 
died  out ;  the  growing  influence  at  that  time  of  the  Gmelin 
school  affords  us  eloquent  testimony  of  this  backward 
step. 

It  is  a  remarkable  fact  that,  for  establishing  the  doctrine 
of  valency,  it  was  not  the  simple  compounds  of  inorganic 
chemistry  but  the  more  complicated  ones  of  organic  that  were 
called  into  service.  The  relations  which  in  the  former 
found  clear  expression,  and  were  easily  read  in  the  law  of 

Y  2 


324  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

multiple  proportions,  had  to  be  first  laboriously  deciphered 
here  from  organic  compounds. 

As  stated  already,  it  was  the  organo-metals  from  which 
Frankland  deduced  the  results  which  constitute  the  kernel 
of  our  present  theory  of  valency.  He  acted  as  pioneer  in 
this  branch  more  than  any  other  man,  and  distinguished 
himself  by  his  admirable  investigations.  Before  him  (more 
particularly)  Bunsen  had  accomplished  his  memorable  work 
on  the  cacodyl  compounds,  and  cacodyl  itself  had  been 
designated  by  Kolbe  as  arsene-dimethyl.  Relying  upon  his 
own  observations  on  the  stanno-ethyl  compounds,  and  on  the 
behaviour  of  the  cacodyl  derivatives  and  other  bodies,  Frank- 
land  proved  with  convincing  clearness  that  the  theory  of 
copulse  was  untenable.  Frankland's  train  of  reasoning  was 
somewhat  as  follows : — If  we  start  with  the  latter  theory,  we 
must  assume  that  the  power  of  the  metals  to  combine  with 
oxygen  is  not  altered  by  their  being  copulated  with  radicals. 
But  facts  tell  against  such  an  assumption,  as  is  seen  at  a 
glance  from  the  following  examples: — Tin-ethyl  (SnC4H5; 
C  =  6)  ought,  according  to  that  theory,  to  unite  with  oxygen 
in  two  proportions,  but  in  reality  it  is  only  capable  of  taking 
up  one  equivalent  of  this  element,  and  not  two,  like  tin  itself. 
Cacodyl,  which  is  arsenic  copulated  with  two  methyls,  does 
indeed  form  two  oxides,  from  which  it  might  be  argued  that 
the  one  with  one  equivalent  of  oxygen  corresponded  to 
arsenic  sub-oxide,  and  the  other  with  three  equivalents  to 
arsenious  acid ;  but  this  hypothesis  affords  no  explanation 
whatever  of  the  fact  that  the  latter  compound  is  very 
readily  oxidisable,  whereas  its  supposed  analogue  cacodylic 
acid  cannot  be  oxidised  by  any  means. 

These  and  similar  contradictions  were  done  away  with  by 
Frankland  in  the  simplest  manner,  by  the  assumption  that 
the  so-called  copulated  compounds  were  derivatives  of  in- 
organic bodies  in  which  oxygen  had  been  replaced  by  its 
equivalent  of  hydrocarbon  radicals.  Stanno-ethyl  oxide  was 
explained  as  tin  dioxide,  Sn02,  in  which  one  equivalent  of 
oxygen  was  replaced  by  ethyl,  and  cacodyl  oxide  as  arsenious 
acid,  in  which  two  equivalents  of  oxygen  had  been  sub- 


y          THE  SATURATION-CAPACITY  OF  THE  ELEMENTS        325 

stituted  by  two  methyls.  Frankland  then  proceeded  to 
extend  this  conception  to  other  compounds  in  the  most 
felicitous  manner,  and — what  was  especially  important — 
thus  brought  the  laws  which  are  shown  in  the  composition 
of  organic  and  inorganic  substances  into  relation  with  the 
fundamental  properties  of  the  elements  which  these  contain. 

He  expressed  his  views  upon  this  point  in  the  following 
sentences,1  which,  from  their  great  importance,  have  a  claim  to 
a  special  place  in  a  history  of  chemistry :  "  When  the  formulae 
of  inorganic  chemical  compounds  are  considered,  even  a  super- 
ficial observer  is  impressed  with  the  general  symmetry  of  their 
construction.  The  compounds  of  nitrogen,  phosphorus,  anti- 
mony, and  arsenic,  especially,  exhibit  the  tendency  of  these 
elements  to  form  compounds  containing  3  or  5  atoms  of  other 
-elements ;  and  it  is  in  these  proportions  that  their  affinities 
are  best  satisfied :  thus  in  the  ternal  group  we  have  NO3 
NH3,  NI3,  NS3,  PO3,  PH3,  PC13,  SbO3,  SbH3,  SbCl3,  AsO3. 
AsH3,  AsCl3,  etc. ;  and  in  the  five-atom  group,  N05,  NH4O, 
NH4I,  P05,  PH4I,  etc.  Without  offering  any  hypothesis 
regarding  the  cause  of  this  symmetrical  grouping  of  atoms, 
it  is  sufficiently  evident, from  the  examples  just  given,  that  such 
a  tendency  or  law  prevails,  and  that,  no  matter  what  the 
character  of  the  uniting  atoms  may  ~be,  the  combining  power  of 
the  attracting  element,  if  I  may  be  allowed  the  term,  is 
•ahoays  satisfied  ~by  tine  same  number  of  these  atoms" 

In  this  way  was  established  the  doctrine  that  a  varying, 
but  at  the  same  time,  within  certain  limits,  definite  satura- 
tion-capacity appertains  to  the  atoms  of  the  elements.  For 
the  ones  which  have  just  been  named  this  was  expressed 
by  the  numbers  3  and  5;  Frankland  did  not  assume  any 
higher  stage  of  saturation  for  them.  By  this  treatise  of 
his,  so  rich  in  ideas  and  facts,  he  opened  up  a  new  field  in 
theoretical  chemistry,  which,  assiduously  cultivated  as  it  has 
been  ever  since,  has  served  both  as  the  centre-  and  the 
starting-point  for  all  chemical  investigations.  Under  the 
influence  of  the  theory  of  valency  all  theoretical  chemical 
views  thenceforth  developed  themselves,  as  will  be  clearly 

Phil  Trans.,  vol.  cxlii.  p.  417  ;  Ann.  Chem.,  vol.  Ixxxv.  p.  368. 


326  THE  MODERN  CHEMICAL  PERIOD  CHAP, 

seen  from  the  following  sections.  The  happy  interpretation 
of  the  constitution  of  the  so-called  copulated  compounds  was 
the  immediate  cause  of  this  great  advance,  in  so  far  that 
Frankland  proved  copulation  to  be  a  consequence  of  satura- 
tion-capacity. 

After  the  definite  valency  of  particular  elements  had 
bqen  established  by  Frankland,  it  might  have  been  imagined 
that  every  chemist  could  have  deduced  for  himself  the 
saturation-capacities  of  other  elements  from  their  behaviour. 
Frankland's  pioneering  work  did  not,  however/ produce  fruit 
with  such  rapidity.  How  slowly  his  views  found  acceptance 
among  chemists  is  proved  by  a  paper  of  Odling's,  published 
in  1854,  and  entitled  On  the  Constitution  of  Acids  and  Salts.1 
The  latter  chemist  still  adhered  firmly  to  the  type  theory. 
He  argued  that  salts  and  acids,  especially  those  containing 
oxygen,  can  be  referred  to  the  simple  or  multiple  water  type 
in  such  a  way  that  the  hydrogen  of  the  latter  is  partially 
or  completely  substituted  by  elementary  or  compound 
radicals  of  definite  replaceable  value.  This  latter  term  was 
used  by  Odling  to  express  what  Frankland  had  done  by 
the  word  atomic.  Iron  and  tin  had,  according  to  Odling, 
two  replaceable  values,  whose  magnitudes  he  indicated  by 
the  dashes  which  have  since  then  been  so  largely  employed, 
thus :  Fe"  and  Fe'",  Sn'  and  Sn".  Thus  far  he  followed 
Frankland's  conception  of  the  saturation-capacity  of  the 
elements.  For  the  polybasic  acids  he  accepted  Williamson's 
views,  in  that  he  assumed  in  them  oxygenated  radicals  of 
definite  replaceable  value,  which  were  introduced  into  the 
type  (H2O)n.  Just  as  sulphuric  acid  was  built  up  on  the 
double  water  type  by  the  entrance  of  the  diatomic  radical 
SO2,  so  he  derived  phosphoric  and  arsenic  acids  from  the 
triple  water  type  (3H20)  by  introducing  the  atomic  groups 
(PO)'"  and  (AsO)'" ;  while  in  the  carbonates  the  radical  CO, 
with  a  replaceable  value  of  2,  was  assumed,  and  so  on.  But 
mischievous  obscurations  now  began  to  be  mixed  up  with 
this.  As  a  result  of  his  one-sided  typical  conception,  Odling 
did  not  hesitate  to  assume  that  the  diatomic  radical  S02  acted 
1  Journ.  Chem.  Soc.,  vol.  vii.  p.  1. 


v  VALENCY  OF  ELEMENTS  AND  RADICALS  327 

as  monatomic  in  dithionic  acid,1  and  the  diatomic  radical 
CO  as  monatomic  in  oxalic  acid ;  and  this  last  (for  example) 

he  referred  to  the  double  water  type,  thus:  (CO)'^p  1  20". 

But,  with  all  this,  Odling  deserves  credit  for  being  instru- 
mental in  causing  a  constant  replaceable  value  to  be  ascribed 
to  particular  elements,  to  hydrogen  and  oxygen  in  especial, 
whereby  the  atomic  weights  of  these  two  latter  served  as 
standards  for  fixing  the  replaceable  values  of  other  elements 
and  compound  radicals.  Williamson  afterwards  helped  most 
materially  to  clear  up  the  meaning  of  Odling's  formulae,  and 
to  bring  about  a  more  intelligent  conception  of  the  constitu- 
tion of  chemical  compounds.2 

-  The  utterances  of  Wurtz  3  and  of  Gerhardt  4  upon  the 
saturation-capacity  of  the  nitrogen  atom  also  showed  that 
Frankland's  ideas  acted  but  slowly ;  for  the  last-named  had 
expressed  himself  on  this  point  in  almost  exactly  the  same 
sense  three  years  previously.  In  many  cases  chemists  were 
content  with  merely  the  notion  of  compound  radicals,  with- 
out investigating  the  influence  of  the  contained  elements 
upon  the  saturation-capacities  of  .  these  complexes ;  this 
applied  in  an  especial  degree  to  the  radicals  composed 
of  carbon  and  hydrogen,  with  whose  replaceable  value  (that 
of  the  radicals)  various  eminent  investigators  occupied 
themselves. 


The  Recognition  of  the  Valency  of  Carbon. 

A  considerable  time  elapsed  before  any  definite  utter- 
ance was  made  with  regard  to  the  valency  of  the  carbon  of 
alcohol  radicals — the  organic  element  in  the  true  sense  of  the 
term.  Instead  of  deducing  this  fundamental  property  from 
its  oxygen  compounds,  carbon  monoxide  and  dioxide,  a  more 

1  This  he  formulated  :— (S02)'(S02)'  \  2Q 

2  Cf.  Journ.  Chem.  Soc.,  vol.  vii.  p.  137  ;  or  Ann.'Chem.,  vol.  xci.  p.  226. 

3  Ann.  Chim.  Phys.  (3),  vol.  xliii.  p.  492  (1855).  ' 

4  TraM  de  Chimie,  vol.  iv.  pp.  595  and  602  (1856). 


328  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

tedious  method  was  adopted;  it  was  the  investigation  of 
carbon-containing  radicals  which  led  to  the  final  solution 
of  the  question.  Among  the  researches  which  were  of 
effective  service  here,  we  must  first  mention  that  by  Kay,1 
made  at  Williamson's  suggestion,  upon  "tribasic  formic 
ether " ;  this  compound,  which  resulted  from  chloroform 
and  sodium  ethylate,  was  regarded  as  a  derivative  of  three 
atoms  of  ethyl  alcohol,  in  which  the  three  atoms  of  basic 
hydrogen  had  been  replaced  by  the  "tribasic  radical  of 
chloroform,  CH."  Ranking  alongside  of  this  important 
piece  of  work  came  that  of  Berthelot  upon  glycerine.2 
Aided  materially  by  Wurtz's  expositions,  Berthelot  charac- 
terised this  compound  as  a  triatomic  alcohol,  since  he 
assumed  in  it  a  tribasic  radical,  C6H5  (C  =  6),  replacing  three 
atoms  of  hydrogen  in  the  triple  water  type.  To  the  alkyls 
which  took  the  place  of  three  atoms  of  hydrogen,  diatomic 
ones  were  soon  added,  ethylene  being  so  designated  by 
H.  L.  Buff.3  The  brilliant  discovery  by  Wurtz  of  the  first 
known  diatomic  alcohol,  glycol,4  served  as  a  corroboration  of 
this  view. 

Chemists  were,  it  is  true,  upon  the  track  of  the  cause 
of  the  different  replacing  values  of  those  radicals  (CH)'", 
(C6H5)'",  and  (C2HJ",  for  we  find  utterances  by  Gerhardt 
and  Wurtz  to  the  effect  that  ethylene  was  dibasic,  because 
one  atom  of  hydrogen  had  been  withdrawn  from  the  mono- 
basic ethyl,  and  glyceryl  tribasic,  because  it  contained  two 
atoms  of  hydrogen  less  than  the  corresponding  propyl.  But 
no  one  had  attained  to  a  complete  explanation  of  these 
radicals ;  their  saturation-capacities  had  never  been  distinctly 
referred  back  to  that  of  carbon. 

In  a  paper  entitled,  Ueber  die  Konstitution  und  die 
Metamorphosen  der  chemischen  Verbindungcn  und  uber  die 
chemische  Natwr  des  Kohlenstoffs  ("  On  the  Constitution  and 
Metamorphoses  of  Chemical  Compounds,  and  on  the  Chemi- 

1  Journ.  Chem.  Soc.,  vol.  vii.  p.  224. 

2  Ann.  Chim.  Phys.  (3),  vol.  xli.  p.  319. 

3  Ann.  Chcm.,  vol.  xcvi.  p.  302. 

4  Comptes  Rendus,  vol.  xliii.  p.  199. 


v  VALENCY  OF  CARBON  329 

cal  Nature  of  Carbon"),1  which  was  published  in  1858, 
Kekule  drew  the  following  nearly  allied  conclusion.  He 
applied  to  carbon  what  had  already  for  a  long  time  been 
recognised  with  regard  to  other  elements, — to  nitrogen  and 
its  chemical  analogues  in  the  first  instance.  The  reasons 
given  by  him  for  carbon  being  tetravalent  are  contained  in 
the  following  sentences : — "  If  we  look  at  the  simplest  com- 
pounds of  this  element,  CH4,  CH3C1,  CC14,  CHC13,  COC12, 
CO2,  CS2  and  CHN,  we  are  struck  by  the  fact  that  the 
quantity  of  carbon  which  is  considered  by  chemists  as  the 
smallest  amount  capable  of  existence — the  atom — always 
binds  four  atoms  of  a  monatomic  or  two  of  a  diatomic 
element,  so  that  the  sum  of  the  chemical  units  of  the  ele- 
ments combined  with  one  atom  of  carbon  is  always  equal  to 
four.  We  are  thus  led  to  the  opinion  that  carbon  is  tetra- 
tomic."  This  train  of  thought  is  almost  the  same  as  that 
which  led  Frankland  to  deduce  the  tri-  and  penta-valence 
of  nitrogen,  phosphorus,  arsenic  and  antimony,2  the  latter 
chemist  having  also  arrived  at  the  saturation-capacities  of 
these  elements  from  a  study  of  their  simplest  compounds.  It 
follows  from  this  that  the  above  utterance  of  Kekule  cannot 
be  regarded  as  a  thoroughly  original  achievement,  all  the 
more  since  the  tetravalence  of  carbon  had  already  been 
recognised  both  by  Kolbe  and  Frankland,  and  especially  as 
it  formed  the  basis  of  the  latter's  statements  upon  the 
constitution  of  organic  compounds.3  In  curious  contrast 

1  Couper,  too,  independently  of  Kekule,  and  shortly  after  the  appearance 
of  the  paper  just  cited,  expressed  the  view  that  the  atom  of  carbon  was 
tetravalent  (cf.  Comptes  Rendus,  vol.  xlvi.  p.  1157). 

2  Cf.  p  325. 

3  Cf.    Kolbe's  publication    entitled    Zur    Entwickelungsgeschichte    der 
theoretischen  Chemie  ("Contribution  to  the  History  of  the  Development  of 
Theoretical   Chemistry"),  Leipzig,   1881,  p.   26  et  seq.,  especially  p.  33. 
Others,  too,  have  claimed  for  Kolbe  the  merit  of  being  the  first  to  perceive 
the  tetravalence  of  carbon,  e.g,  Blomstrand,  who  thus  expresses  himself  in 
his  Chemie  der  Jetztzeit  ("Chemistry  of  the  Present  Time"),  p.  110  :  "No 
other  chemist  can  lay  the  same  claim  as  Kolbe  to  be  regarded  as  the  origin- 
ator of  the  doctrine  of  the  saturation -capacity  of  carbon.    Alongside  of  him 
must  be  placed  Frankland,  whose  uninterrupted  researches,  conceived  and 
carried  out  with  equal  felicity,  continually  furnished  new  supports  in  aid  of 
the  doctrine  mentioned  above, — a  doctrine  which  comprises  in  itself  every- 


330  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

with  the  high  value  which  most  chemists  have  placed  upon 
this  service  of  Kekule's  is  the  depreciatory  way  in  which 
he  talks  of  it  himself.1 

Kekule's  service  in  this  point  must  be  sought  for  in  the 
fact  that  he  endeavoured  to  get  at  the  root  of  the  problem 
as  to  how  two  or  more  carbon  atoms  combine  with  one 
another,  and  how  their  mutual  affinities  are  satisfied.  The 
immediate  result  of  these  speculations  was  the  doctrine  of 
the  "  linking  of  atoms  "  (  Verkettung  der  Atome)  in  chemical 
compounds.  Indirectly,  Kolbe's  and  Frankland's  views  had 
a  most  material  share  in  developing  this  crowning  edifice  of 
the  structure  theory. 

thing  that  relates  to  saturation,  and  which  has  found  in  Kolbe's  carbonic 
acid  theory  by  far  its  most  important  application."  A.  Glaus  (Journ.  pr. 
Chem.  (2),  vol.  iii.  p.  267)  has  written  in  a  similar  sense.  Kekule  is  there- 
fore not  justified  in  claiming  for  himself  the  merit  "of  having  introduced 
the  idea  of  the  atomicity  of  the  elements  into' chemistry  "  ("  den  Begrijf  der 
Atomigkeit  der  Elemente  in  die  Chemie  eingefiihrt  zu  haben  "),  (cf.  Kekule, 
Ztschr.  Chem.  for  1864,  p.  689).  This  idea  was  without  doubt  primarily 
due  to  Frankland,  who  expresses  himself  clearly  and  unequivocally  on  the 
point  hi  his  Experimental  Researches  (1877),  p.  145,  as  follows  :  "  This  hypo- 
thesis which  was  communicated  to  the  Royal  Society  in  the  second  of  the 
following  papers"  (cf.  p.  325  of  this  book),  "on  10th  May  1-852,  constitutes 
the  basis  of  what  has  since  been  called  the  doctrine  of  atomicity  or  equiva- 
lence of  elements  ;  and  it  was,  so  far  as  I  am  aware,  the  first  announcement 
of  that  doctrine." 

1  Thus  Kekule  says,  at  the  close  of  his  above-mentioned  treatise,  p. 
109  :  "Lastly,  I  feel  bound  to  emphasise  the  point  that  I  myself  attach  but 
a  subordinate  value  to  considerations  of  this  kind.  But  since  in  chemistry, 
when  there  is  a  total  lack  of  exact  scientific  principles  to  go  upon,  we  have 
to  content  ourselves  for  the  time  being  with  conceptions  of  probability  and 
expediency,  it  appears  appropriate  that  those  views  should  be  published, 
because  they  seem  to  me  to  furnish  a  simple  and  tolerably  general  expression 
precisely  for  the  latest  discoveries,  and  because  therefore  their  application 
may  perhaps  conduce  to  the  finding  out  of  new  facts." 


CHEMISTRY  DURING  THE  LAST  FORTY  YEARS          331 


DEVELOPMENT  OF  CHEMISTRY  UNDER  THE  INFLUENCE 
OF  THE  DOCTRINE  OF  VALENCY  DURING  THE  LAST 
FORTY  YEARS. 

The  chemical  atomic  theory  had  been  in  existence  for 
nearly  fifty  years  before  the  natural  inference  was  drawn 
with  sufficient  exactitude  from  it  that  each  elementary  atom 
possesses  a  definite  saturation-capacity,  and  that  this  is 
expressible  in  some  cases  by  a  constant  factor,  but  in  most- 
cases  by  a  varying  one/  In  recognising  this  a  great  advance 
was  made, — an  advance  which  showed  itself  particularly  in  the 
fact  that,  after  the  establishment  of  the  valency  theory  by 
Frankland,  people  attained  to  a  more  definite  conception  of 
the  chemical  constitution  of  inorganic,  and  more  especially 
of  organic  compounds.  From  thenceforth  continuous  efforts 
were  made  to  solve  this  problem,  first  recognised  in  its 
fullest  signification  by  JSerzelius,  by  the  aid  of  the  ideas 
which  Frankland  had  either  himself  expressed  or  had 
induced  in  others.  Chemists  endeavoured,  by  breaking  up 
compound  bodies  (in  part  actually  and  in  part  on  paper 
only)  and  distributing  the  elementary  atoms  according 
to  their  supposed  saturation-capacities,  to  work  out  the 
mutual  relations  of  these  ultimate  constituents.  In  this 
way  there  shone  forth  from  valency  a  light  which  now 
illumines  the  whole  field  of  chemistry. 

The  theory  of  the  linking  of  atoms  was  considered 
by  most  chemists  as  the  necessary  result  of  the  idea 
that  a  saturation-capacity  (with  respect  to  other  ele- 
ments), expressible  by  figures,  belonged  to  the  atoms  of  each 
individual  element.  With  the  development  of  this  view,  in 
organic  as  well  as  in  inorganic  chemistry,  many  brains 
have  been  busily  engaged  for  the  last  forty  years.  The 
idea  of  a  definite  saturation-capacity  for  each  element  has 
formed  a  necessary  aid  in  the  solution  of  numerous  important 
points  which  have  come  up  during  this  period,  e.g.  the 
question  of  the  nature  of  valency,  the  reasons  for  many  cases 
of  isomerism  hitherto  unexplained,  etc.,  and  it  still  remains 
an  indispensable  guide  in  all  scientific  chemical  investigations. 


332  THE  MODERN  CHEMICAL  PERIOD  CHAP. 


Beginnings  of  the  Structure  Theory — KekuU  and  Couper. 

The  theory  of  types,  according  to  which  all  organic 
compounds  were  referred  to  a  few  simply  constituted  bodies, 
had  been  rendered  objectless  by  Frankland's  conception  of 
that  property  of  elements  which  we  now  term  valency. 
The  types  now  presented  themselves  as  hydrogen  compounds 
of  mono-,  di-,  tri-,  and  tetra-valent  elements.  Had  Frank- 
land's  ideas  at  once  received  the  attention  which  they 
merited,  the  detailed  development  of  the  theory  of  types, 
as  given  by  Gerhardt  in  the  fourth  volume  of  his  text-book, 
could  have  been  entirely  dispensed  with. 

Out  of  Frankland's  idea  of  saturation-capacity  there 
grew  the  further  notion  that  the  elementary  atoms  could  be 
combined  among  themselves  by  one  or  more  affinities, 
according  to  their  nature,  and  that  a  disappearance  of 
individual  affinities  took  place  as  the  result  of  this.  This 
idea  was  first  advanced  by  Kekule,  and  shortly  after  by 
Couper,  in  the  treatises  already  referred  to  (in  1858). 
These  therefore  contain  the  beginnings  of  the  structure 
theory.1 

After  having  deduced  the  "  tetratomicity "  of  carbon 
from  the  composition  of  a  number  of  simple  compounds  of 
that  element,  Kekule  expressed  himself  upon  the  constitu- 
tion of  compounds  which  contain  more  than  one  atom  of 
carbon  as  follows : 2  "  In  the  case  of  substances  containing 
several  carbon  atoms  we  must  assume  that  at  least  some  of 
the  atoms  (of  the  other  elements  present)  are  held  bound  by 
the  affinities  of  the  carbon  atoms,  and  that  the  latter  are 
themselves  linked  together,  whereby  a  part  of  the  affinity 
of  the  one  (carbon  atom)  is  necessarily  tied  by  an  equally 
large  part  of  the  affinity  of  the  other." 

"The  simplest  and  therefore  the  most  probable  case  of 

1  The  term  "structure"  (Struktur)  was  first  introduced  by  Butlerow 
(Ztschr.  IChem.    for   1861,   p.   553);   through  it  he  quite  unintentionally 
awakened  the  erroneous  idea  that  the  actual  spacial  arrangement  of  the 
atoms  could  be  arrived  at  by  the  aid  of  the  above  hypothesis. 

2  Ann.  Chem.,  vol.  cvi.  p.  154. 


v  BEGINNINGS  OF  THE  STRUCTURE  THEORY  333 

such  a  combination  (Aneinanderlagerung)  of  two  carbon 
atoms  is  that  in  which  one  affinity  of  the  one  atom  is  tied 
by  one  affinity  of  the  other.  Of  the  four  affinity  units  of 
each  of  the  two  carbon  atoms,  two  are  thus  taken  up  in 
keeping  both  atoms  together  ;  six  consequently  remain  over, 
to  be  available  for  atoms  of  other  elements." 

Here,  therefore,  there  was  set  up  the  hypothesis  that  the 
carbon  atoms  join  together,1  and  lose  in  consequence  a 
portion  of  their  affinities.  Starting  with  the  assumption 
that  more  than  two  atoms  of  carbon  can  coalesce  in  the  same 
manner,  Kekule  generalised  this  particular  case  by  establish- 
ing the  value  2n  +  2  for  the  saturation-capacity  of  the 
complex  Cn.  He  did  not,  however,  remain  stationary  at 
this  point,  but  represented  further  that  "a  more  compact 
combination  of  the  carbon  atoms"  might  be  assumed  in 
other  organic  compounds,  e.g.  benzene  and  naphthalene.  As 
the  "  next  most  simple  coalition  of  carbon  atoms  "  he  con- 
ceived the  case  of  the  mutual  interchange  of  two  affinity- 
units.  The  relations,  too,  of  other  polyvalent  elements  to 
the  carbon  atoms  were  taken  into  account  by  him,  and  he 
gave  illustrations  to  show  that  these  were  bound  either  by 
all  their  affinities  or  by  a  portion  of  them  to  the  affinities 
of  the  carbon.2  The  main  features  of  the  doctrine  of  the 
"  Linking  of  Atoms  "  (Bindung  der  Atome)  were  contained  in 
those  sentences  of  Kekule's. 

Almost  at  the  same  time  Couper,3  independently  of  Kekule, 
arrived  at  similar  views  with  respect  to  the  mutual  linking 
of  several  carbon  atoms.  Being  definitely  of  opinion  that 
Gerhardt's  doctrine  of  types  did  not  satisfy  the  claims  required 
by  a  theory,  he  made  the  attempt  to  get  at  the  constitution 
of  chemical  compounds  by  falling  back  upon  the  elementary 
atoms.  He  laid  stress  upon  the  point  that,  in  addition  to  the 
affinity  proper  (Wahherwandtschaff),  the  degree  of  that 
affinity  (Gradveiwandtschaft)  of  the  small  particles  came  into 

1  Sick  aneinander  lagern. 

-  Cf.,  for  instance,  Ann.  Chem.,  vol.  cvi.  p.  155. 

3  Comptes  Rendm,  vol.  xlvi.  p.  1157  ;  Ann.  Chim.  Phys.  (3)  vol.  liii. 
p.  469. 


334  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

play  in  the  formation  of  chemical  compounds.  For  the  atom 
of  carbon  the  highest  power  of  combination  was  expressible 
by  the  number  4.  In  general  he  adopted  Frankland's 
doctrine  of  the  varying  saturation- capacities  of  the  elements. 
Couper  further  laid  great  emphasis  upon  the  capacity  of  the 
carbon  atoms  to  unite  with  one  another,  and  this  in  such  a 
manner  that  a  part  of  their  own  individual  power  of  com- 
bination was  thereby  neutralised.  This  linking  of  the  atoms, 
he  illustrated  by  bars  drawn  between  the  chemical  symbols  of 
the  combining  particles  ;  he  thus  laid  the  foundation  of  the 
so-called  "  structural  formulae."1  The  following  examples  will 
serve  to  illustrate  this : — 

CH3  CH3  C0-OH 

Alcohol :  I  ^    Acetic  acid  :  I  r?        Oxalic  acid. 

n^2  nu2 

0-OH  °0-OH  C0-OH 

Both  Kekule  and  Couper  expressed  with  absolute  de- 
fmiteness  the  axiom  that  the  "  atomicity  of  the  elements"  was 
to  be  made  use  of  for  arriving  at  the  constitution  of  chemical 
compounds.  The  idea  of  the  term  "  atomicity  "  had  without 
any  doubt  been  introduced  by  Frankland  six  years  previous 
to  this.  The  further  development  of  the  above  axiom  and 
its  utilisation  in  the  theory  of  the  linking  of  atoms  was 
carried  out  mainly  by  Kekule,  and  in  the  succeeding  years 
also  by  Butlerow  and  Erlenmeyer. 

Before  an  absolutely  certain  knowledge  of  the  atomicity 
or,  better,  the  valency  of  the  elements  could  be  attained, 
perfect  clearness  has  to  be  arrived  at  with  respect  to  the 
magnitudes  of  the  atomic  weights ;  and,  more  particularly, 
the  distinction  between  the  atom  and  equivalent  of  polyvalent 
elements  had  to  be  clearly  grasped.  That  was,  however,  by 
no  means  the  case  at  this  time.  In  writing  the  formulae  of 
chemical  compounds,  most  chemists  employed  Gmelin's 
equivalents  from  force  of  habit ;  but,  in  making  use  of  these, 

1  Wurtz  manifestly  forgot  Couper's  paper  in  the  Anncdes  de  Chimie  et  de 
Physique,of  which  he  (Wurtz)  was  one  of  the  editors,  for  he  took  credit  to 
himself  as  being  the  first  to  make  use  of  these  linking-bars  (see  his  Atomic 
Theory,  fourth  English  edition,  p.  214,  note). 


v  THE  ATOMIC  WEIGHTS  :  CANNIZZARO  335 

the  true  chemical  values  of  the  atoms  remained  indistinct 
and  only  became  apparent  after  the  conversion  of  the 
equivalents  into  atomic  weights.  For  instance,  the  functions 
of  the  simple  atoms  C  and  S  were  ascribed  to  the  double 
equivalents  C2  and  S2  in  the  formulas  employed  by  Kolbe, 
while  for  hydrogen,  chlorine,  nitrogen  and  other  elements, 
the  equivalents  were  identical  with  the  atomic  weights.1 
And  the  disorder  was  increased  by  many  chemists,  Couper 
among  the  number,  giving  to  carbon  its  correct  atomic  weight 
(12),  while  retaining  the  equivalent  (8)  for  oxygen.  It  is 
true  that  Gerhardt  had  already  attempted  to  bring  order  into 
the  prevailing  confusion,  but  his  mode  of  procedure  had  not 
been  logical  enough.2 

Thanks  to  the  efforts  of  the  Italian  chemist  Cannizzaro,  a 
way  was  prepared  in  1858  for  the  clearing  up  of  this  un- 
satisfactory state  of  matters,  although  those  efforts  received 
only  tardy  recognition.  It  was  he  who,  by  his  criticism  in  a 
paper  entitled  Sunto  di  un  Corso  de  Filosofia  Chimica 
•("  Outlines  of  a  Course  of  Chemical  Philosophy  "),3  threw 
light  upon  the  methods  employed  for  arriving  at  the  relative 
atomic  weights  of  the  elements.  He  recognised,  as  especi- 
ally reliable,  the  deduction  of  these  values  from  the  vapour 
densities  of  chemical  compounds, — a  method  now  in  uni- 
versal use.  And  he  further  showed  to  what  extent  the 
specific  heats  of  the  metals  might  be  regarded  as  a  trust- 
worthy aid  in  the  determination  of  their  atomic  weights, 

1  The  meaning  of  this  is  at  once  apparent  if  we  take  Kolbe's  old  formula 
for  acetic  acid,  C2H3.  C202.  OHO,  and  convert  it  into  our  present  formula, 
CH3.  CO.  OH,  by  changing  the  double  atoms  C2  and  Oa  into  the  single  ones 
C  and  0. 

2  Cf.  p.  295. 

3  Nuovo  Cimento,  vol.  vii.  p.  321.     This  paper  was  edited,  with  notes, 
by  the  late  Lothar  Meyer  for  Ostwald's  Classiker  (German  by  Miolati)  in  1891. 
Stanislao  Cannizzaro,  born  in  1826,  first  studied  medicine,  then  chemistry 
under  Piria,  and  subsequently  filled  in  succession  the  chairs  of  chemistry  in 
Genoa,  Palermo,  and  (since  1871)  in  Rome.     This  last  he  still  holds,  while 
he  is  at  the  same  time  a  Senator  and  a  member  of  the  High  Court  of  Public 
Education  (Mitglied  des  obersten  Rathes  des  tiffentlichen  Unterrichts).     His 
experimental  researches,  e.g.  those  on  benzyl  alcohol  and  on  santonine  and 
allied  compounds,  are  of  a  very  high  order. 


336  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

wrong  values  for  many  of  these  having  come  to  be  accepted 
as  the  result  of  Gerhardt's  statements. 

After  the  correct  atomic  weights  of  the  elements  had 
been  established  in  this  way,  it  became  possible  to  build  up 
the  doctrine  of  the  chemical  values  of  the  elements  from  a 
more  general  point  of  view  than  before.  First  it  was 
applied  to  the  compounds  of  carbon,  whose  constitution 
became  the  subject  of  the  most  ardent  investigation. 
Kekule  in  his  text-book  (begun  to  be  published  in  1 8  5  9), 
and  Butlerow  and  Erlenmeyer  in  various  papers  and  subse- 
quently in  text-books  also,  endeavoured  to  explain  the 
connection  existing  between  the  elementary  atoms  within 
the  molecules,  by  setting  out  with  the  conception  that 
a  definite  atomicity  appertained  to  each  element;  carbon, 
hydrogen,  oxygen  and  nitrogen  came  primarily  into  question 
here. 

Butlerow  was  the  first  to  express  himself  clearly  upon 
the  principle  which  underlay  these  efforts,  and,  with  this, 
upon  the  nature  of  the  Structure  Theory  (which  received  its 
name  from  him).1  We  must  premise  here  that  he  took  up 
his  position  on  the  valency  theory  founded  by  Frankland, 
according  to  which  many  of  the  elements  possess  a  varying 
saturation-capacity.  Butlerow  defined  the  structure  of  a 
chemical  compound  as  the  "  manner  of  the  mutual  linking  of 
the  atoms  in  a  molecule;"  he -decisively  rejected  the  idea 
that  it  afforded  any  information  as  to  the  position  of  the 
individual  atoms  in  space.  He  advanced  the  opinion  that 
the  chemical  character  of  a  compound  depended  first  upon 
the  nature  and  quantity  of  its  elementary  constituents,  and 
then  upon  its  chemical  structure.  The  latter  had,  to  his 
mind,  but  one  meaning ;  he  could  not  agree  with  Gerhardt 
that  several  rational  formulae  might  be  proposed  for  one  and 

1  Ztschr.  Chem.  for  1861,  p.  549  et  seq. — Alexander  Butlerow,  who  was 
born  in  1828  and  died  a  few  years  ago,  became  professor  of  chemistry  in  the 
University  of  Kasan  in  1858,  and  in  that  of  St.  Petersburg  in  1868.  He 
contributed  materially  to  the  development  of  organic  chemistry  by  many 
admirable  experimental  researches,  and  in  a  very  special  manner  by  his 
Text-book  of  Organic  Chemistry  ;  this  latter,  which  appeared  first  in  1864 
in  Russian  and  in  1868  in  German,  has  had  a  far-reaching  influence. 


v  DISCUSSIONS  ON  THE  NATURE  OF  VALENCY  337 

the  same  chemical  compound,  one  formula  only  appearing 
possible  to  him. 

The  more  that  the  former  adherents  of  the  type  theory 
came  to  feel  the  necessity  for  abandoning  it,  and,  free  from 
the  yoke  of  this  doctrine,  of  basing  all  considerations  with 
respect  to  chemical  constitution  upon  the  "  atomicity  "  of  the 
elements,  the  more  definitely  ought  the  views  upon  the 
nature  of  this  property  of  the  elements  to  have  shaped 
themselves. — The  conclusion,  deduced  from  numerous  ex- 
periments, that  the  atoms  of  certain  elements  show  a  con- 
stant combining  value  and  the  atoms  of  others  a  varying 
one,  came  at  that  time  into  opposition  with  the  opinion  that 
this  capacity  of  the  elements  was  invariable. 


Controversies  respecting  constant  and  varying  Valency  of 
the  Elements. 

Frankland,  the  originator  of  the  doctrine  of  the  satura- 
tion-capacity of  elementary  atoms,  held  aloof  from  the  lively 
discussions  to  which  it  gave  rise,  more  especially  after  the 
year  1870.  This  in  all  probability  accounts  for  his  service  in 
developing  such  an  important  doctrine  having  been  forgotten 
by  many  chemists,  and  precisely  by  those  who  have  taken 
the  most  active  share  in  the  above  discussions.1  About  the 
year  1860  Frankland's  views  regarding  a  saturation-capacity 
peculiar  to  the  elements,  which,  under  certain  circumstances, 
might  be  a  varying  one,  were  accepted  either  tacitly  or 
expressly  by  most  chemists  of  standing.  Even  so  early  as 
1856  Gerhardt  had  stated  in  his  text-book  that  nitrogen 
was  sometimes  triatomic,  sometimes  pentatomic, — a  view 
which  coincided  exactly  with  that  of  Frankland.  Wurtz, 
Williamson  and  Couper  also  held  this  opinion,  and  not  for 
nitrogen  and  its  analogues  alone,  but  also  as  being 
characteristic  of  many  other  elements ;  that  Kolbe  likewise 
agreed  with  Frankland  on  this  point  has  been  stated 
already.  In  the  assumption  that  a  constant  valency  was 
1  See  Note  ],p.  310. 

z 


338  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

characteristic  of  a  few  elements  and  a  varying  one  character- 
istic of  many  more,  Kolbe  merely  saw  another  expression 
for  the  law  of  multiple  proportion ;  this  conception,  as 
corresponding  with  facts,  he  considered  necessary,  because 
nothing  was  known  of  the  real  cause  of  valency. 

This  view,  then,  which  had  so  many  observations  to  sup- 
port it,  led  to  the  conclusion  that  each  element  possessed  a 
maximum  saturation-capacity;  but  that  lower  stages  of  satura- 
tion might  coexist  along  with  this ;  Kolbe  had  expressed  him- 
self in  this  sense  so  far  back  as  the  year  1 854.1  Towards  the 
beginning  of  the  sixties,  several  chemists  who  took  an  active 
part  in  developing  the  structure  theory  gave  utterance  to  the 
same  opinion  in  a  more  definite  manner.  Erlenmeyer,  in  par- 
ticular, maintained  in  various  papers,2  and  afterwards  in  his 
Lehrbuck  der  organischen  Chemie,  that  each  element  possesses  a 
maximum  valency,  or  that  each  is  furnished  with  a  definite 
number  of  Affinivalenten  or  affinity-points  (Ajjinitdtspunkten), 
only  part  of  these,  however,  being  in  many  cases  combined 
with  the  affinity-points  of  other  elements.  In  ammonia, 
for  instance,  only  three  of  the  five  equivalents  of  the 
nitrogen  atom  come  into  play,  while  in  chloride  of  ammonium 
all  five  are  satisfied.  Following  this  out,  Erlenmeyer  dis- 
tinguished between  saturated  and  unsaturated  compounds. 
Strickly  speaking,,  this  is  nothing  else  than  Frankland's 
view. 

At  about  the  same  time  a  lively  discussion  with  respect 
to  the  atomicity  of  the  elements  went  on  between  Wurtz 
and  Naquet3  on  the  one  hand,  and  Kekule4  on  the  other. 
The  two  former  declared  for  the  assumption  of  a  varying 
valency  in  the  case  of  many  of  the  elements,  while  Kekule, 
on  the  other  hand,  expressed  his  opinion  more  definitely 
than  before  that  the  "  atomicity  of  the  elements  is  a  funda- 
mental property  of  the  atoms,  quite  as  unalterable  as  their 
atomic  weights." 

1  Cf.  Lehrbuch  der  organischen  Chemie,  vol.  i.  p.  22. 

2  Ztschr.  Chem.  for  1863,  pp.  65,  97,  and  609 ;  for  1864,  pp.  1,  72,  and 
628.  3  Ibid.,  p.  679. 

4  Ibid.,  p.  689 ;  Comptes  Rendus,  vol.  Iviii.  p.  510. 


CRITICISM  OF  KEKULE'S  THEORY 


In  order  to  confirm  this  theorem  of  absolute  or  constant 
valency,  and  to  reconcile  it  with  conflicting  facts,  Kekule 
was  obliged  to  have  recourse  to  hypotheses  which  laid  them- 
selves strongly  open  to  criticism.  A  few  examples  may  be 
given  here  to  illustrate  his  view  of  the  valency  of  each 
element  being  constant.  According  to  him,  nitrogen  and  its 
chemical  analogues  acted  only  as  trivalent,  sulphur,  like 
oxygen,  only  as  divalent,  and  chlorine,  bromine  and  iodine 
as  monovalent.  In  order,  therefore,  to  explain  the  consti- 
tution of  compounds,  in  which,  upon  the  assumption  of 
a  varying  valency,  the  elements  just  named  had  a  higher 
saturation-value  than  he  assigned  to  them,  Kekule  had  to 
presuppose  a  fundamental  difference  as  existing  between 
compounds  of  one  and  the  same  element.  To  his  first 
hypothesis  of  absolutely  constant  valency  he  added  the 
further  one,  that  those  compounds,  in  which  the  elements 
are  present  in  their  supposed  normal  values,  are  distinguished 
from  the  others  by  a  more  compact  structure ;  the  former  he 
termed  atomic,  and  the  latter  molecular  compounds.  The 
components  of  the  latter,  e.g.  ammonia  and  hydrochloric  acid 
in  salmiac,  phosphorus  trichloride  and  chlorine  in  phosphorus 
pentachloride,  were,  according  to  his  view,  held  together  by 
forces  of  another  kind  to  those  which  acted  in  the  atomic 
compounds.  In  order  to  give  expression  to  the  looser  con- 
nection between  the  molecules  of  these  substances,  he  placed 
their  components  dualistically  alongside  of  one  another  in 
writing  the  formulae ;  thus  he  gave  PC13 .  C12  as  the  formula 
of  phosphoric  chloride,  and  H3N .  H2S  as  that  of  ammonium 
hydrosulphide.  He  would  not  admit  a  variation  in  the 
saturation-values  of  nitrogen  and  phosphorus  in  compounds 
like  those  just  named. 

Other  chemists  were  thus  justified  in  asking  what  his 
grounds  were  for  assuming  such  a  distinction  between  the 
forces  by  which  chemical  constitution  was  conditioned ;  for, 
in  both  kinds  of  compounds  the  same  atomic  laws  held  good. 
Kekule  regarded  the  breaking  up  of  compounds  into  their 
components  at  a  somewhat  high  temperature  as  a  criterion 
of  their  being  molecular  compounds,  while  atomic  compounds 

z  2 


340  THE  MODERN  CHEMICAL  PERIOD  CHAP. 


were  those  which  could  be  converted  into  the  gaseous  state 
without  decomposition.  But  this  distinction  between  the 
two  categories  could  not  be  maintained  in  the  face  of  known 
facts ;  it  soon  became  evident  that  such  an  artificial  partition 
only  served  to  introduce  confusion  and  bring  about  contra- 
dictions which  were  irreconcilable. 

This  theory  of  the  constant  valency  of  the  elements  could 
not  therefore  long  withstand  the  critical  examination  to 
which  it  was  subjected  by  Kolbe,1  and  more  especially  by 
Blomstrand,2  not  to  mention  others.  The  known  facts  could 
not  by  any  possibility  be  brought  into  accordance  with  the 
assumption  of  saturation-capacity  being  invariable,  and  this 
helped  more  than  anything  else  to  cause  the  theory  to  be 
abandoned  by  its  most  zealous  adherents.  How,  for  instance, 
could  the  existence  and  behaviour  of  the  organic  ammonium 
bases,  the  sulphones  and  sulphoxides,  perchloric  and  periodic 
acids,  and  many  other  compounds  be  explained  by  the  aid 
of  the  above  hypothesis  ?  Other  weighty  arguments  have 
recently  been  brought  forward  which  must  be  regarded  as 
incompatible  with  those  urged  shortly  after  the  setting  up 
of  Kekule's  theory;  to  take  compounds  of  one  element 
only,  we  may  refer  here  to  the  discovery  of  the  isomeric 
triphenyl-phosphine  oxides,  in  one  of  which  the  phosphorus 
must  be  pentavalent,  and  also  to  the  proof  given  of  phos- 
phorus pentafluoride  existing  in  the  gaseous  state.  Such 
facts  are  not  to  be  reconciled  with  the  assumption  of  phos- 
phorus being  only  trivalent. 

1  Cf.  Joum.  pr.  Chem.  (2),  vol.  iv.  p.  241. 

2  In  his  work,  Die  Chemie  der  Jetztzeit,  Blomstrand  went  carefully  into 
the  doctrine  of  the  saturation-capacity  of  the  elements,  and  by  his  compre- 
hensive treatment  of  the  question  materially  lightened  the  labours  of  other 
critics  as  to  the  share  taken  by  different  workers  in  its  development. — C. 
Wilhelm  Blomstrand,  born  in  1826,  filled  the  chair  of  chemistry  in  the 
University  of  Lund  in  Sweden  from  1854  until  1895  ;  he  died  in  1897.     His 
eminent  researches  in  various  branches  of  mineralogical  and  also  of  organic 
chemistry  are  distinguished  by  their  thoroughness,  and  show  the  influence 
of  Berzelius,  whose  doctrines  Blomstrand  endeavoured,  in  his  book  men- 
tioned above,  to  reconcile  and  bring  into  close  connection  with  the  more 
recent  views.     From  the  electro-chemical  basis,  in  especial,  he  was  able  to 
throw  light  upon  the  valency  question,  and  to  gain  for  it  new  points  of  view. 


v          GROUNDS  FOR  ASSUMING  A  VARYING  VALENCY       341 

We  may  assert  that  in  the  course  of  the  last  thirty 
years  the  majority  of  chemists  have  adopted  the  opinion 
that  the  atoms  of  most  of  the  elements  possess  a  varying 
saturation-capacity,  varying  according  to  the  conditions. 
The  idea  prescribed  as  essential  at  the  time  the  theory  of 
an  unchanging  valency  was  set  up,  viz.  that  this  was  a 
fundamental  property  of  atoms,  may  be  fully  recognised 
without  our  being  thereby  forced  to  the  conclusion  that  the 
valency  of  the  elementary  atoms  must  therefore  be  constant. 

In  connection  with  these  weighty  discussions  upon  the 
nature  of  valency,  reference  may  be  made  here  to  a  problem 
nearly  related  to  it,  which  has  given  rise  of  recent  years  to 
frequent  debate,  and  also  to  important  experimental  work, 
viz. — the  question  whether  the  individual  affinity-units  or 
valencies  of  one  element  are  alike  or  different.  If  we  only 
took  into  consideration  some  isolated  facts,  such  as  the  dis- 
similar functions  of  the  two  atoms  of  oxygen  or  sulphur  in 
carbonic  acid  and  carbon  disulphide  respectively,  we  might  be 
inclined  to  favour  the  assumption  of  a  difference  in  two 
affinities  of  the  carbon  atom  with  respect  to  the  other  two. 
But  the  numerous  investigations  which  have  been  made  by 
Popoff,  Schorlemmer,  L.  Henry,  Rose  and  others,  with  the 
object  of  deciding  this  point  so  far  as  regards  carbon,  have  led 
to  the  conclusion  that  its  four  affinities  are  alike. 

The  equality  or  inequality  of  the  affinities  of  the 
sulphur  and  nitrogen  atoms  is  still  undecided,  notwith- 
standing ^hat  many  facts  bearing  on  the  point  have  been 
collected  together.  Among  other  researches  we  may  men- 
tion the  work  of  Krtiger,  which  appeared  to  prove  a 
difference  in  the  valencies  of  sulphur ;  but,  while  his 
results  have  been  corroborated  on  one  side,  they  have  been 
doubted  on  the  other.  The  remarkable  isomerism  in  the 
derivatives  of  hydroxylamine,  which  has  been  worked  out 
by  Lossen,  seems  quite  compatible  with  the  assumption  of 
the  affinities  of  nitrogen  being  different;  more  recent 
researches  by  Lessen,  Beckmann,  Behrend  and  Werner, 
however,  point  to  another  solution  of  the  question  on 
stereo-chemical  lines. 


342  THE  MODERN  CHEMICAL  PERIOD  CHAP. 


The  main  directions  which  chemical  investigation  has 
taken,  since  these  discussions  with  regard  to  valency  came 
up,  are  characterised  by  the  endeavour  to  gather  from  the 
chemical  behaviour  of  compounds  an  insight  into  their  con- 
stitution, by  the  aid  of  the  assumption  that  the  elements 
have  a  definite  saturation-capacity ;  while  at  the  same  time 
efforts  are  being  made  to  arrive  at  the  mutual  relations 
between  the  physical  properties  of  compounds  and  their  con- 
stitution as  determined  by  chemical  means.  To  this  problem, 
which  has  only  recently  been  assiduously  attacked,  although 
it  has  been  projected  for  a  long  time,  an  analogous  one  has 
been  added,  viz.  the  elucidation  of  the  connection  which 
obviously  exists  between  the  relative  atomic  weights  of  the 
elements  and  their  chemical  and  physical  properties. 


The  further  Development  of  the  Structure  Theory — The  chief 
Directions  taken  l>y  Organic  Chemistry  during  the  last 
thirty  Years. 

At  a  first  glance  it  strikes  one  as  strange  that  organic 
chemistry  in  particular  should  have  been  made  the  field  for 
speculations  as  to  the  composition  of  chemical  compounds, 
speculations  which  had  the  valency  theory  as  their  basis. 
The  reason  for  this  preference  is  undoubtedly  to  be  sought 
for  in  the  peculiarity  of  that  element  which  is  never 
wanting  in  the  so-called  organic  compounds,  carbon,  even  if 
we  allow  for  the  fact  that  it  was  from  compounds  of  carbon — 
the  organo-metallic  ones — that  the  idea  of  the  saturation- 
capacity  of  elements  developed  itself. 

From  the  tendency  of  the  atoms  of  carbon  to  unite  with 
one  another  according  to  different  degrees  of  affinity 
(Gradvenvandtschaft),  i.e.  by  the  interchange  of  one,  two, 
or  three  affinities,  the  production  of  the  variously  com- 
posed carbon  compounds  could  be  explained  without 
difficulty.  The  addition  of  elements  like  hydrogen,  oxygen, 
sulphur,  nitrogen  and  chlorine  to  the  complexes  of  carbon 
atoms  was  rendered  intelligible  in  a  similar  manner  by 


v  VIEWS  UPON  THE  LINKING  OF  ATOMS  343 

assuming  that  the  individual  affinities  of  the  elements  named 
were  satisfied  by  a  like  number  of  affinities  of  carbon.  The 
combination  of  the  carbon  atoms  among  themselves  or  with 
other  elementary  atoms,  as  illustrated  in  this  way,  was 
termed  "  linking  "  (  Verkettung).  From  thenceforth  the  ad- 
herents of  the  structure  theory  came  to  grasp  more  clearly 
the  problem  of  chemical  investigation.  They  sought  to 
combine  the  atoms  of  the  various  elements  in  question 
suitably  with  one  another,  according  to  their  saturation- 
capacities,  directing  their  efforts  mainly  to  investigating  the 
structure  of  the  compounds  of  carbon,  since  inorganic  sub- 
stances, as  being  of  much  simpler  composition,  seemed  to 
offer  few  or  even  no  difficulties  to  the  application  of  the 
above  principle.  The  conceptions  thus  gained  of  the 
structure  of  organic  substances  were  then  tested  with  more 
or  less  minuteness  by  actual  experiment,  with  the  object  of 
seeing  whether  the  modes  of  formation  and  decomposition  of 
the  compounds  in  question,  and  their  chemical  behaviour 
generally,  agreed  with  the  theoretical  hypotheses. 

The  readiness  with  which  many  chemists  took  to  the 
construction  of  formulae  which  were  meant  to  express  the 
mutual  relations  existing  between  the  atoms  of  a  compound, 
i.e.  the  structure  of  the  latter,  may  in  some  cases  have  given 
rise  to  the  belief  that  by  the  aid  of  such  symbols  an  insight 
into  the  actual  arrangement  of  the  atoms  in  space  might  be 
obtained.  Some  investigators  of  eminence  may  have  in- 
cited to  such  daring  hopes  and  expectations  by  indistinct 
modes  of  expression  and  unhappily  chosen  comparisons  and 
illustrations.  In  the  minds  of  younger  chemists,  especially, 
it  was  easy  for  erroneous  ideas  regarding  the  problems  of 
chemistry  to  effect  a  lodgment.  We  may  recall  here  that 
Kekule  spoke  of  the  carbon  atoms  as  sliding  over  and 
adhering  to  one  another,1  and  of  the  other  side  of  a  molecule, 
etc. ;  that  in  his  text-book  he  brought  forward  graphic 
formula,  in  which  the  elementary  atoms  have  different  forms 
according  to  their  saturation-capacities ;  and,  further,  that 

1  "  Von  einem  Zusammenschieben  oder  Aneinanderleimen  der  Kohlenstojf- 
atome." 


344  THE  MODERN  CHEMICAL  PERIOD  CHAP. 


the  smallest  particles  of  an  element  have  been  pictured  by 
Naquet  and  Baeyer  as  furnished  with  small  hooks,  by  which 
they  catch  hold  of  one  another.  Metaphors  such  as  these 
tended,  at  any  rate,  to  an  over-estimation  of  the  capabilities 
of  the  structure  theory. 

The  more  prudent  advocates  of  the  latter,  with  Butlerow 
at  their  head,  dissented  all  along  from  the  idea  that  such 
formulae  could  furnish  any  picture  of  the  arrangement  of  the 
atoms  in  space.  On  the  other  side  Kolbe,  in  particular,  pro- 
tested with  all  his  critical  acumen  against  such  exaggerations, 
as  leading  easily  to  error.  He  remained  staunch  to  the  point 
of  view  which  he  had  laid  down  in  1854,1  believing  that  no 
clear  conception  could  ever  be  arrived  at  as  to  how  the  atoms 
of  a  compound  were  thus  arranged. 


Constitution  of  Organic  Compounds  according  to  the 
Structure  Theory. 

Although  the  structure  theory  was  unable  to  realise  the 
highly-pitched  expectations  which  aimed  at  a  knowledge  of 
the  spacial  arrangement  of  the  atoms,  it  possessed  none  the 
less  great  practical  value.  The  development  of  organic 
chemistry  since  the  middle  of  the  sixties  shows  in  fact  that, 
through  the  aid  of  the  structural  hypothesis,  the  discovery 
of  new  modes  of  formation  and  decomposition  of  compounds, 
the  recognition  of  the  relations  existing  between  various 
classes  of  bodies,  and,  especially,  the  interpretation  of  the 
constitution  of  numerous  organic  substances  became  possible. 
Kekule's  theory  of  the  aromatic  compounds  (see  below)  forms 
the  most  striking  proof  of  this. 

The  working  out  of  the  constitution  of  the  so-called 
saturated  compounds  offered  fewer  difficulties  than  that 
of  the  compounds  poorer  in  hydrogen, — the  unsaturated 
ones.  Kekule  was  the  first  to  express  the  definite  opinion 
that  in  all  fatty  compounds  the  carbon  atoms  were  united 
to  one  another  by  an  affinity  of  each,  a  point  which  might 

1  Lehrb.  d.  organ.  Chemie,  vol.  i.  p.  13. 


v  CONSTITUTION  OF  UNSATURATED  COMPOUNDS         345 

have  been  deduced  from  Couper's  and  also  from  Kolbe's 
rational  formulae,  had  the  equivalents  used  by  them  been 
converted  into  the  atomic  symbols.  The  expositions  given 
by  Kekule  and  also  by  Erlenmeyer,  Butlerow,  Glaus  and 
others  in  text-books  of  organic  chemistry  and  occasional 
papers,  with  regard  to  the  constitution  of  such  compounds 
soon  became  the  common  property  of  nearly  all  chemists. 

More  difficult  was  the  question — What  was  the  function 
of  the  carbon  atoms  in  organic  compounds  poorer  in 
hydrogen  ?  With  respect  to  the  constitution  of  these, 
Kolbe,  Couper  and  Wurtz  had  already  expressed  the  view 
that  in  them — e.g.  ethylene,  acrylic  acid,  acetylene,  etc. — one 
or  several  atoms  of  carbon  acted  as  divalent.  Kekule* 
hesitated  at  first  between  two  opinions.  He  was,  on  the 
one  hand,  inclined  to  assume  a  "  more  compact,"  i.e.  a  double 
or  treble,  linking  of  particular  pairs  of  carbon  atoms  in  the 
substances  in  question  ;  while,  on  the  other,  his  experimental 
researches  upon  unsaturated  organic  acids  led  him  to  prefer 
the  idea  that  the  affinities  of  certain  of  their  carbon  atoms 
were  not  completely  saturated,  and  that  these  therefore 
show  gaps  (Luckeri),  by  means  of  which  the  capability  of 
further  combination  which  such  compounds  possess  can  be 
explained.  The  latter  of  the  two  views  coincided  in  the 
main  with  the  one  mentioned  above,  in  which  divalent 
carbon  atoms  were  presupposed.  Kekule,  it  is  true,  never 
definitely  admitted  that  he  regarded  the  saturation-capacity 
of  carbon  as  a  varying  quantity.  Of  recent  years  preference 
has  been  given  to  the  conception  of  a  double  or  treble 
linking  of  the  carbon  atoms,  although  the  other  view  does 
not  want  for  eminent  adherents.  Thus  Fittig,1  from  his 

1  Rudolf  Fittig,  born  6th  December,  1835,  after  working  for  several 
years  on  the  teaching  staff  of  the  University  of  Gottingen,  became  Professor 
of  Chemistry  at  Tubingen  in  1869,  and  was  called  from  thence  to  the  Uni- 
versity of  Strasburg  in  1876,  where  he  still  continues  ;  the  beautiful 
laboratory  there  was  planned  by  him.  His  name  will  often  be  mentioned 
in  the  special  history  of  organic  chemistry,  which  he  has  greatly  enriched 
by  most  admirable  researches,  more  especially  upon  aromatic  and  un- 
saturated compounds.  Wohler's  Grundriss  der  organischen  Chemie  ("  Out- 


346  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

work  upon  unsaturated  acids,  has  expressed  himself  in  favour 
of  the  assumption  of  carbon  being  divalent  in  some  of  these 
compounds.1  But  the  question  of  the  constitution  of  such 
compounds  has  not  yet  been  conclusively  answered ;  for 
numerous  observations  have  been  made  which  appear  to 
show  that  the  complete  solution  of  this  problem  by  the  aid 
of  structural-chemical  hypotheses  alone  is  impossible. 


Theory  of  the  Aromatic  Compounds. 

In  Kekule's  hands  the  structure  theory  scored  by  far 
its  greatest  victory,  in  the  deciphering  of  the  constitution  of 
the  so-called  aromatic  compounds.2  These  were  defined  by 
him  as  derivatives  of  benzene ;  his  first  task  therefore  con- 
sisted in  elucidating  the  structure  of  this  long-known  hydro- 
carbon, i.e.  in  explaining  how  the  six  carbon  and  the  six 
hydrogen  atoms  were  combined  together.  Here  Kekule 
took  up  again  his  previously  expressed  idea  of  a  more 
compact  linking  of  the  carbon  atoms,  and  discussed  the 
possible  cases  of  how  the  six  in  benzene  could  be  connected 
together,  setting  out  with  the  assumption  that  the  carbon 
acted  as  tetravalent  and  the  hydrogen  as  monovalent.  While 
the  compounds  of  the  fatty  series  contained — in  the  language 
then  and  now  current — an  open  chain,  Kekule  assumed  in 
benzene  a  closed  one,  and  pictured  each  of  the  six  carbon 
atoms  present  in  the  molecule  as  being  united  to  two  others. 
The  structural  formula  which  followed  from  this  was  the 
hexagon,  since  then  so  widely  made  use  of,  whose  angles 
were  formed  of  carbon  atoms  linked  alternately  to  each 
other  by  one  and  two  bonds,  and  also  combined  in  every 
case  with  one  atom  of  hydrogen,  thus — 

lines  of  Organic  Chemistry"),  entirely  recast  by  him  and  published  under 
the  same  title,  has  run  through  numerous  editions  ;  he  supplemented  it  in 
1872  by  the  companion  volume,  Grundriss  der  anorganischen  Chemie. 

1  Cf.  Ann.  Chem.,  vol.  clxxxviii.  p.  95. 

2  Bull.  Soc.  Chim.  for  1865,  p.  104;  Ann.  Chem.,  vol.  cxxxvii.  p.  129. 


v      KEKULE'S  THEORY  OF  THE  AROMATIC  COMPOUNDS     347 


H 

C 


HC  CH 

HC  CH 


Kekule  and  his  pupils,  together  with  many  other  chemists 
who  had  busied  themselves  with  the  derivatives  of  benzene 
after  this  view  had  been  published,  now  directed  their  efforts 
to  comparing  all  the  known  and  rapidly  increasing  observa- 
tions bearing  upon  this  class  of  bodies  with  the  deductions 
drawn  from  the  above  formula,  and  therewith  to  proving  by 
actual  experiment  the  admissibility  of  the  assumptions  on 
which  the  formula  was  based.  An  almost  boundless  number 
of  facts  were  thus  collected  together,  which,  taken  as  a  whole, 
were  found  to  agree  readily  with  Kekule's  hypothesis.  The 
first  inference  to  be  drawn  from  it,  viz.  that  the  six  hydrogen 
atoms  which  were  distributed  similarly  among  the  six  carbon 
ones  were  in  every  respect  equal  to  one  another,  was  con- 
firmed by  the  observation,  made  over  and  over  again,  that 
only  one  and  the  same  product  resulted  from  the  replacement 
of  any  one  of  the  hydrogen  atoms  of  benzene  by  a  mono- 
valent  radical  or  element,  and  never  a  second  isomeric 
compound.  When  two  or  three  atoms  of  hydrogen  became 
substituted,  the  case  was  otherwise.  From  his  formula 
Kekule  deduced  the  number  of  isomers  which  were  then  to 
be  expected ;  he  stated  his  opinion  that  three  isomeric  com- 
pounds, and  not  more,  would  result  in  both  cases  through 
the  replacement  of  two  or  three  of  the  hydrogen  atoms  of 
benzene  by  the  same  substituent.  If  two  dissimilar  radicals 
took  the  place  of  two  atoms  of  hydrogen,  the  number  of 
possible  isomers  was  not  increased;  these  did  augment, 
however,  to  a  definite  number  when  three  hydrogen  atoms 
were  replaced  by  two  or  three  different  substituents.  The 
truth  of  these  and  of  other  prognostications  by  Kekule  has 


•  348  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

since  been  verified  in  the  most  brilliant  manner  by  a  vast 
number  of  observations. 

This  happy  interpretation  of  the  constitution  of  benzene 
shed  a  great  light  over  a  hitherto  neglected  branch  of  the 
science.  Not  merely  the  immediate  derivatives  of  benzene, 
but  also  substances  much  more  distantly  related  to  it,  like 
naphthalene  and  anthracene,  and  more  recently  phenanthrene, 
fluorene  and  many  other  hydrocarbons,  together  with  their 
numberless  and  often  important  derivatives,  had  their 
chemical  constitution  successfully  investigated  by  the  aid  of 
Kekule's  hypothesis. 

This  hypothesis  did  not,  however,  completely  satisfy 
a  number  of  chemists,  who  considered  modifications  in  it 
necessary.  We  need  not  enter  here  into  the  reasons  which 
led  to  such  modifications,  but  may  just  mention  Ladenburg's  1 
prism  formula  and  Claus's2  diagonal  one  (see  appended  figures), 
which  were  brought  forward  by  those  investigators  as  explain- 
ing more  completely  than  Kekule's  hexagon  formula  the 
chemical  behaviour  of  benzene. 

1  JBer.,  vol.  ii.  p.  140  ;  also  his  pamphlet,  Theorie  der  aromatischen  Ver- 
bindungen. — Albert  Ladenburg,  born  at  Mannheim  on  July  2nd,  1842,  has 
been  a  notable  contributor  to  organic  chemistry  by  his  excellent  experi- 
mental work.     His  chief  researches  have  been  upon  the  organic  compounds 
of  silicon,  the  benzene  derivatives,  and  more  particularly  the  derivatives 
of  pyridine  and  piperidine.  His  Vortrdge  uber  die  Entivickelungsgeschichte  der 
Chemie  in  den  letzten  100  Jahren  (1st  edition,  1869,  2nd  edition,  1887),  is 
well  known  as  a  genuine  historical  work.     He  is  editor  of  the  chemical 
section  of  the  EncyUopddie  der  Naturwissenschaften  (published  by  Trewendt). 
Since  1890  Ladenburg  has  held  the  chair  of  chemistry  at  Breslau,  having 
previously  taught  at  Heidelberg  and  Kiel. 

2  Theoretiache  Betrachtungen  und  deren  Anwendung  zur  Systematik  der 
organischen  Chemie  (1867),  ("  Theoretical  Considerations  and  their  Appli- 
cation to  the  Systematising  of  Organic  Chemistry  ").     Adolph  Glaus,  born 
June  6th,  1840,  studied  under  Kolbe  and  Wohler,  and  now  holds  the  pro- 
fessorship of  chemistry  at  the  University  of  Freiburg-im-Breisgau.     His 
experimental  work  has  been  mainly  in  organic  chemistry,  of  which  he  has 
systematically  investigated  various  branches, — e.g.  the  derivatives  of  quino- 
line,  the  fatty-aromatic  ketones,  etc.     He  has  further  from  time  to  time 
published  papers  giving  his  views  on  many  important  points  of  chemical 
theory  (cf.  the  Grundziige  der  modernen  Theorie  in  der  organischen  Chemie, 
Freiburg,  1871  ;  and  also  the  Journal  fiir  praktische  Chemie  since  1888). 


CONSTITUTION  OF  THE  AROMATIC  COMPOUNDS        349 


1IC  CH 

\/ 

CH 

CH 

HC/ 

\CH 

HC-I-CH 

\                    X 

HC/ 

SloH 

H 

Ladenburg's  formula.  Claus's  formula. 

The  discussions  upon  this  point  still  continue  ;  thus,  the 
results  of  recent  admirable  investigations  on  the  hydro- 
phthalic  acids,  etc.,  by  A.  von  Baeyer l  had,  he  considered, 
given  him  grounds  for  disputing  all  the  above  hypotheses  on 
the  constitution  of  benzene,  while  Glaus  2  maintained — and 
not  without  cause — that  Baeyer's  view  was  identical  with 
his  own.  The  latter  has  quite  lately  acknowledged 3  that 
Claus's  formula  agrees  best  with  known  facts,  including  those 
which  cannot  be  made  to  harmonise  with  either  Kekule's  or 
Ladenburg's  hypothesis.  The  most  recent  discussions  upon 
the  constitution  of  benzene,  naphthalene,  quinoline,  etc.,  can 
only  be  indicated  here.4 

But,  notwithstanding  all  this,  the  fact  must  be  fully 
recognised  that  Kekule's  conception,  even  although  it  by  no 
means  affords  a  complete  picture  of  the  constitution  of 
benzene,  has  borne  many  and  rich  fruits.  Through  the 
stimulus  which  was  given  by  his  theory  of  the  aromatic 
compounds,  the  work  of  numberless  chemists  with  this  class 
of  substances,  work  extending  over  a  long  period  of  time, 
received  a  particular  stamp  of  its  own ;  their  chemical  labours 
have  been  carried  out  entirely  under  the  influence  of  the 
benzene  theory. 

The  meaning  of  the  term  Aromatic  Compmwids  has  of 

1  Ann.  Chem.,  vol.  ccxlv.  p.  103;  vol.  cell.  p.  257;  vol.  cclviii.  pp.  1 
and  145. 

2  Journ.  pr.  Chem.  (2),  vol.  xxxvii.  p.  455. 

3  Ann.  Chem.,  vol.  cclxix.  p.  177. 

4  Cf.  especially,  in  addition  to  the  papers  cited  in  note  3,  p.  351,  Ad. 
Glaus,  Journ.  pr.  Chem.  (2),  vol.  xlviii.  p.  576 ;  vol.  xlix.  p.  505  ;   W. 
Marckwald,  Ann.  Chem.,  vol.  cclxxiv.  p.  331;  Briihl,  Journ.  pr.  Chem.  (2), 
vol.  xlix.  p.  201  ;   E.  Bamberger,  Ann.  Chem.,  vol.  cclvii.  p.  1  ;  Collie, 
Journ.  Chem.  Soc.,  vol.  Ixxii.  p.  1013. 


350  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

late  years  undergone  a  wide  extension  since  the  near  relation 
of  pyridine,  quinoline  and  iso-quinoline  and  their  derivatives 
to  benzene  has  come  to  be  recognised.  The  ardour  shown  in 
the  investigation  of  these  nitrogenous  bodies,  with  their 
endless  derivatives,  has  gone  on  increasing  in  proportion  with 
the  increasing  surmise  of  a  close  connection  existing  between 
them  and  the  vegetable  alkaloids,  and  with  the  actual  proof 
of  this  in  some  particular  cases.  .  Kb'rner  was  the  first  to 
propound  the  important  idea  that  pyridine  may  be  regarded 
as  benzene  in  which  a  methine  (CH'")  is  replaced  by  the 
trivalent  nitrogen  atom.1  The  inferences  drawn  from  this 
with  respect  to  the  derivatives  of  pyridine,  like  those  deduced 
from  the  structure  of  benzene,  have  formed  the  subject  of 
numberless  experimental  researches  and  theoretical  dis- 
cussions which  are  still  proceeding.  Reference  will  be  made 
to  some  of  the  more  important  results  of  these  investigations, 
and  of  others  upon  the  nitrogen  compounds  termed  poly- 
azines,  in  the  special  history  of  organic  chemistry. 

The  efforts  to  gain  a  clear  conception — in  the  widest  sense 
of  the  word — of  the  structure  of  benzene  and  its  derivatives 
have  also  been  of  use  in  the  case  of  other  classes  of  com- 
pounds, especially  for  those  analogous  substances  furfurane, 
thiophene  and  pyrrol,  which  are  now  universally  regarded 
as  being  characterised  by  a  closed  five-membered  ring 
containing  four  carbon  atoms  together  with  an  atom  of 
oxygen,  an  atom  of  sulphur,  or  the  imido-group  (NH) 
respectively.  Victor  Meyer's 2  splendid  and  thorough  re- 

1  Dewar  was  the  first  to  publish  this  view  (Journ.  Chem.  Soc.,  vol.  xxiv. 
p.  145  ;  or  Ztsc.hr.  Chem.  for  1871,  p.  117),  Korner  having  however  already 
given  utterance  to  it  in  his  lectures. 

2  Viktor  Meyer,  born  8th  September,  1848,  after  filling  the  post  of  pro- 
fessor of  chemistry  at  Stuttgart  and  at  Zurich,  was  called  to  the  chief  chem- 
istry chair  at  Gottingen  on  Wohler's  death  in  1885,  and  removed  from  there 
in  1889,  to  succeed  Bunsen  at  Heidelberg  ;  he  died  suddenly  on  August  8th, 
1897.     His  comprehensive  researches  upon  nitro-compounds  of  the  fatty 
series,  upon  iso-nitroso  compounds,  and  upon  thiophene  are  among  the 
very  first  of  our  time,  and  have  contributed  largely  to  increase  our  know- 
ledge of  organic  chemistry.     The  method  devised  by  him  for  vapour-density 
determinations  has  become  a  standard  one,  and  has  also  been  successfully 
applied  to  the  solution  of  important  theoretical  questions  (e.g.  to  that  of 


v        CHARACTERISTICS  OF  THE  AROMATIC  COMPOUNDS      351 

searches  on  thiophene  and  its  derivatives  l  have  before  all 
others  led  conclusively  to  the  recognition  of  the  analogous 
composition  of  the  above  substances,  and  also  to  a  more  pre- 
cise conception  of  the  term  aromatic  compounds.  According 
to  Meyer,2  it  is  the  chemical  behaviour  of  a  substance  with 
regard  to  nitric  acid,  sulphuric  acid,  bromine,  and  acid 
chlorides  (in  the  presence  of  chloride  of  aluminium)  which 
decides  whether  it  has  a  claim  to  be  ranked  among  those 
compounds.  He  lays  here  the  greatest  weight  upon  facts, 
whereas  in  previous  determinations  of  the  nature  of  this  class 
of  substances  the  existence  of  a  closed  ring  of  six  carbon 
atoms  was  held  to  be  a  fundamental  condition. 

Those  chemists 3  who  have  made  a  special  study  of  the 
constitution  of  benzene,  naphthalene,  quinoline,  etc.,  are  at 
present  inclined  to  think  that  the  reciprocal  linking  of  the 
carbon  atoms  may  vary  with  the  metamorphoses  of  the  com- 
pounds in  question,  in  such  a  way  that  the  "  central  "  bonds 
change  into  the  so-called  double  bonds,  and  vice  versa',  an 
interchange  of  linkage  is  thus  assumed.  And  although  we 
have  as  yet  no  knowledge  of  the  actual  nature  of  these  modes 
of  linking,  such  speculations  have  a  certain  value,  serving  as 
they  may  do  to  a  better  understanding  of  many  curious  facts. 


Application  of  Structural-chemical  Conceptions  to  the 
Investigation  of  Isomerism. 

Detailed  reference %  has  already  been  made  to  the  sig- 
nificance which  the  investigation  of  the  isomeric  relations  of 
organic  compounds  has  for  the  question  of  their  chemical 

the  valency  of  aluminium).  Among  his  most  recent  researches  were  those 
on  the  iodo-  and  iodoso-  compounds,  and  on  the  laws  governing  the  esteri- 
fi cation  of  aromatic  acids.  Lastly,  Victor  Meyer  and  Jacobsen's  large 
Lehrbuch  der  organischen  Chemie  is  a  work  of  very  great  value.  A 
short  but  appreciative  memorial  address  on  Victor  Meyer  by  Liebermann 
is  to  be  found  in  the  Berichte,  vol.  xxx,  p.  2157. 

1  Cf.  his  work,  Die  Thiophengruppt  ("The  Thiophene  Group"),  Braun- 
schweig, 1888.  2  Ibid,}  p  276. 

3  Cf.  especially  Ad.  Claus,  Journ.  pr.  Chem.  (2),  vol.  xlii.  pp.  24,  260, 
458 ;  vol.  xliii.  p.  321. 


352  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

constitution.1  Indeed,  the  efforts  made  during  the  last  thirty 
years  to  prepare  as  large  a  number  of  isomers  as  possible, 
and  to  establish  their  structure,  is  a  main  feature  of  the  mode 
in  which  organic  chemistry  has  been  and  still  is  being  studied. 
Before  the  derivatives  of  benzene  had  acquired  that  pre- 
dominating interest  for  chemists  which  they  afterwards  came 
to  do,  the  constitution  of  metameric  substances  was  held  to 
be  sufficiently  explained  by  a  difference  in  the  grouping  of 
the  atoms  of  the  radicals.  We  have  only  to  recall  here  the 
proof  given  of  the  rational  composition  of  trimethylamine  as 
opposed  to  that  of  the  isomeric  propylamine;  the  reason 
assigned  for  the  metamerism  of  diethyl  oxide  and  methyl- 
propyl  oxide  ;  and,  lastly,  to  think  of  the  secondary  and 
tertiary  alcohols  or  acids,  whose  constitution  was  predicted 
with  perfect  definiteness  before  they  had  been  discovered 
(i.e.  of  the  metamerism  of  dimethyl-carbinol  with  ethyl- 
carbinol,  and  that  of  trimethyl-carbinol  with  propyl-,  iso- 
propyl-,  or  methyl-ethyl-carbinol),2  &c. 

To  such  satisfactorily  explained  cases  of  metamerism  as 
these,  the  investigation  of  the  aromatic  compounds  now 
added  numerous  others  which,  however,  unlike  the  former, 
could  not  be  referred  back  to  a  different  grouping  of  the 
atoms  in  the  radicals.  Kekule  therefore  sought  to  explain 
the  similar  composition  of  various  benzene  substitution  pro- 
ducts (e.g.  of  the  three  dibromo-benzenes,  the  three  phenylene- 

1  Cf.  p.  250  et  seq. 

2  The  rational  formulae  will  serve  to  illustrate  the  above  cases  of  meta- 
merism — 

CH3) 

C3H7  )  x  CH3  [  N  C2H5  1  0  CH3 

CH  j 


Propylamine        Trimethylamine      Diethyl  oxide        Methyl-propyl  oxide 
C(CH3)2(()H)  CH2(C2H5)  (OH) 

Dimethyl-carbinol  Ethyl-carbinol 

CH3 

pCaH7/^-rr»  CC2H5(OH) 

C(CH3)OH  H2(0]  H 


Trimethyl-carbinol          Propyl-carbinol         Methyl-ethyl-carbinol 


v  EXPLANATION  OF  POSITION-ISOMERISM  353 

dicarboxylic  acids,  &c.)  from  his  conception  of  the  struc- 
ture of  benzene,  by  assuming  different  relative  positions 
of  the  substituents  to  one  another.  Such  compounds  were 
termed  position-isomers.  The  question  of  the  relative  positions 
occupied  by  the  entering  substituents,  or,  as  it  was  also 
called,  the  determination  of  the  chemical  position  of  the  latter, 
was  ardently  studied  from  different  sides,  after  the  problem 
had  been  raised  by  Kekule.  Among  the  investigations  which 
helped  in  a  special  degree  towards  the  solution  of  this  were 
those  of  Baeyer  upon  the  constitution  of  mesitylene  and  its 
derivative  isophthalic  acid,  those  of  Graebe  upon  naphthalene 
and  phthalic  acid,  and  that  of  Ladenburg  on  terephthalic 
acid.  By  the  ingenious  conclusions  drawn  from  these  and 
many  other  researches,  the  structure  of  the  so-called  Ortho-, 
Para-,  and  Meta-compounds  was  arrived  at  with  considerable 
certainty.  Some  errors,  however,  did  creep  in  here, — for 
instance,  the  wrong  interpretation  of  the  constitution  of 
quinone  from  theoretical  considerations,  a  point  which  gave 
rise  to  very  great  confusion  before  the  mistake  was  finally 
put  right.  Korner's  researches x  have  been  of  immense 
value  for  the  determination  of  position;  he  introduced  a 
new  method  here. 

The  investigation  of  these  metameric  relations  among 
the  derivatives  of  benzene  materially  lightened  that  of  the 
still  more  complicated  phenomena  among  the  pyridine  and 
quinoline  bases  which  were  referable  to  similar  causes.  The 
metamerism  of  the  pyridine-carboxylic  acids  and  other 
derivatives,  which  had  been  predicted  on  theoretical  grounds 
from  conceptions  as  to  the  structure  of  pyridine,  was 
beautifully  confirmed  later  on  by  the  comprehensive  re- 
searches of  Weidel,  Skraup  and  others ;  while  considerations 
of  the  same  kind  have  proved  equally  fruitful  in  the  investi- 
gation of  the  derivatives  of  thiophene  and  pyrrol,  and  also 
of  indole  and  other  aromatic  compounds,  such  as  the  poly- 
azines  and  poly-azoles. 

But  the  certainty  with  which  the  constitution  of  meta- 
meric substances  was  supposed  to  have  been  established  left 
1  Gazz.  Chim.  ItaL,  vol.  iv.,  p.  305. 

A  A 


354  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

much  to  be  desired  in  many  cases.  The  symbols  employed 
to  express  the  structure  of  such  compounds  were  intended 
to  have  but  one  definite  meaning ;  Gerhardt's  view,  that 
several  formulae  might  be  used  indifferently  to  picture  the 
reactions  of  the  bodies  in  question,  was  entirely  abandoned. 
On  the  other  hand,  more  organic  compounds  became  known 
whose  constitution  could  be  illustrated  equally  well  by 
two  totally  different  formulae,  according  to  their  chemical 
behaviour  in  different  circumstances.  Many  of  the  reactions 
of  aceto-acetic  ether,  for  instance,  cause  us  to  give  to  it  the 
constitution  which  is  apparent  in  its  name,  but  in  others  it 
behaves  like  the  ether  of  an  oxy-crotonic  acid;  indeed 
L.  Claisen1  has  just  proved  that  its  sodium  compound  is 
derivable  from  the  latter  ether.  Phloroglucin,  which  has 
been  for  long,  and  justly,  looked  upon  as  trioxy -benzene, 
may  also  be  indicated,  from  some  of  its  reactions,  as  a  meta- 
meric  tricarbonyl  compound.2 

The  constitution  of  these,  as  well  as  of  certain  other 
compounds,  e.g.,  isatin,  oxindole,  carbostyril,  cyanamide,  etc., 
is  therefore  capable  of  two  explanations.  Opinions  are  still 
divided  among  chemists  who  have  busied  themselves  with 
this  question  as  to  which  of  the  two  possible  structural 
formulae  is  the  correct  one  for  such  compounds.  Baeyer 
distinguishes  between  a  stable  (stabile)  modification  and  an 
unstable  (Mile)  one,  the  latter  being  termed  the  pseudo-form  ; 
for  isatin,  e.g.,  the  formula  containing  hydroxyl  is  the  stable 


1  Ann.  Chem.,  vol.  ccxcvii.  p.  92. 

2  The  tautomerism  of  the  above  compounds  is  seen  from  the  following 
formulae : — 

CH2-CO-CH3  CH  =  C(OH)CH3 

>-OC2H5  CO'OCoH5 


CO- 


C(OH)  CO 

A  A 

HC        CH  H2C        CH2 


(OH)C        C(OH)  OC        CO 

\  /  V 

CH  OH2 


v  TAUTOMERISM  OR  DESMOTROPISM  355 

modification,  while  pseudo-isatin  is  unknown  in  the  free 
(or  unstable)  state,  only  derivatives  of  it  being  capable  of 
existence. 

C.  Laar,1  who  has  discussed  this  question  minutely,  applies 
the  name  tautomerism  to  these  phenomena.     A  "  change  in 
combination  or  position  of  hydrogen  atoms  "  2  is  always  in- 
volved here,  as  is  readily  seen  in  what  is  doubtless  the  simplest 
case   of   such  a   tautomerism — in   hydrocyanic   acid.      The 
chemical  behaviour  of  this  acid  leads  on  the  one  hand  to  the 
structural  formula  H  — C=N,  and  on  the  other  to  that  of 
C  =  N  —  H  (in  which  the  carbon  is  divalent) ;  in  the  former 
case  the  hydrogen  is  linked  with   carbon,  and  in  the  latter 
with  nitrogen.     Laar  imagines  oscillatory  conditions  within 
the  hydrocyanic  acid  molecule,  which  cause  the  hydrogen 
atom  to  take  up  the  one  and  the  other  position  alternately  ;. 
he  therefore  presupposes  the  simultaneous  existence  of  both 
modifications.     Since  all  cases  of  tautomerism  depend  upon 
a  change  in  the  linking  of  the  atoms  of  carbon,  nitrogen  and 
oxygen  with  respect  to  hydrogen,  Victor  Meyer  and  Jacobsen 
have  proposed  to  replace  the  above  indefinite  term  by  the 
better  one  of  desmotropism. 

During  the  last  few  years  experimental  and  speculative 
work  have  added  largely  to  the  number  of  known  tautomeric 
compounds.  In  a  lecture  entitled  "  Ueber  Tautomerie" 
delivered  at  Stuttgart  last  year  (1897),  W.  Wislicenus  gave 
an  excellent  resumt  of  the  most  important  investigations  in 
this  field.  Of  special  interest  are  those  still  rare  cases  in- 
which  the  two  tautomeric  forms  of  a  compound  have 
actually  been  observed,  by  W.  Wislicenus  himself  and  by 
L.  Claisen.  Under  these  circumstances  the  former  is  justified 
in  concluding  that  tautomeric  phenomena  are  reversable 
intra-molecular  changes  which  only  lend  themselves  to  ob- 
servation in  exceptional  instances.  According  to  F.  Traube,3 
"  tautomerism  is  a  particular  kind  of  isomerism  in  which  we 
have  to  do  with  a  state  of  equilibrium,  excessively  sensitive 

1  Ber.,  vol.  xviii.  p.  648  ;  vol.  xix.  p.  730. 

2  Ein  " Bindungs-  oder  Platzwechsel  von  Wasserstqffatomen." 

3  Ber.,  vol.  xxix.  p.  1723. 

A   A   2 


356  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

to  outward  conditions,  of  two  isomers  that  change  very 
readily  the  one  into  the  other." 

Here  then  we  have  an  instance  of  the  constitution  of  one 
and  the  same  compound  being  expressible  by  two  structural 
formulae,  either  one  of  them  apparently  as  correct  as  the 
other.  In  another  group  of  me  tamers  we  find  just  the 
opposite  conditions,  i.e.,  one  and  the  same  structural  formula 
applying  to  two  totally  different  chemical  compounds  of  the 
same  composition.  J.  Wislicenus 1  was  the  first  to  establish 
such  an  identity  in  structure  (Strulduridentaf)  for  two  different 
substances — the  fermentation-  and  para-lactic  acids.2  The 
structure  theory  is  therefore  insufficient  to  explain  such 
cases  of  metamerism  as  this.  Further  instances  of  the  same 
kind  are  found  in  crotonic  and  iso-crotonic,  fumaric  and 
maleic,  and  mesaconic  and  citraconic  acids.  Wislicenus 
designated  this  species  of  metamerism  geometrical  isomerism, 
and  Michael,  who  has  likewise  occupied  himself  for  a  long 
time  with  the  study  of  this  branch,  allo-isomerism.  These 
phenomena  are  now  grouped  under  the  term  Stereo-isomerism, 
and  the  rapidly  growing  Stereo-chemistry  now  forms  a  distinct 
branch  of  the  science. 

J.  Wislicenus3  has  attempted  to  explain  phenomena  of 

1  Johannes  Wislicenus,  born  at  Klein-Eichstedt,  near  Querfurt  in  Thiir- 
ingen,  on  24th  June,  1835,  became  in  1885  professor  of  chemistry  and  head 
of  the  chief  chemical  laboratory  in  the  University  of  Leipzig,  after  filling 
from  1872-85  the  corresponding  post  at  Wtirzburg,  before  which  he  taught 
at  Ziirich.     After  the  death  of  Strecker,  whom  he  succeeded  at  Wiirzburg, 
he  re-edited  the  former's  text-book  of  chemistry.     His  experimental  re- 
searches, most  of  which  have  been  published  in  the  Annalen  der  Chemie, 
pertain  almost  exclusively  to  the  domain  of  organic  chemistry,  in  the  special 
history  of  which  we  shall  frequently  have  occasion  to  refer  to  them.     The 
very  important  work  which  he  did  on  the  lactic  acids  impelled  him  even  so 
early  as  1873  to  the  conclusion  that  the  cause  of  the  difference  between  two 
of  them  must  be  sought  for  in  the  spacial  relations  of  the  atoms  in  the  mole- 
cule.    His  quite  recent  speculations  upon  geometrical  isomers  are  referred 
to  above. 

2  Ann.  Chem.,  vol.  clxvii.  p.  343. 

3  Cf.  Die   rdumliche  Anordnung  der  Atome  in  organischen  Molekiilen 
(Leipzig,  1887),  ("  The  Spacial  Arrangement  of  the  Atoms  in  Organic  Mole- 
cules ") ;  also  the  Tageblatt  der  Naturforscherversammlung  zu  Wiesbaden, 
1887  ("  Journal  of  the  Assembly  of  Scientists  at  Wiesbaden,  1887  "). 


v  VAN  'T  HOFF  AND  LE  BEL'S  HYPOTHESIS  357 

this  kind  by  the  aid  of  an  hypothesis  propounded  by  van 
't  Hoff  and  Lebel.1  According  to  this  hypothesis,  which  was 
designed  with  the  object  of  explaining  the  optical  activity  of 
isoraeric  compounds,  the  centre  of  gravity  of  an  atom  of 
carbon  is  supposed  as  in  the  middle  of  a  tetrahedron,  and 
its  four  affinities  as  at  the  four  corners.  When  two  atoms 
of  carbon  become  linked  together,  with  the  subsequent 
neutralisation  of  one  affinity  of  each,  then  van  't  Hoff  and, 
after  him,  Wislicenus  assume  that  both  are  capable  of 
rotating  in  opposite  directions  about  a  common  axis;  and 
the  possibility  of  such  rotation  is  supposed  to  cease  with  the 
double  or  triple  linking  of  the  carbon  atoms.  Wislicenus 
has  made  this  hypothesis  the  basis  of  his  discussions  and  his 
later  experimental  researches.  An  important  aid  to  this 
conception  is  added  in  the  supposition  that,  in  the  rotation 
of  systems  with  carbon  atoms  linked  together  by  one  affinity 
of  each,  "  specially  directed  forces,  the  affinity-energies," 
come  into  play,  which  regulate  the  spacial  relations  of  the 
atoms  to  one  another.  Wislicenus  believes  that  in  these 
suppositions  he  possesses  a  means  whereby  "  the  establishing 
of  the  spacial  arrangement  of  atoms  in  particular  cases  may 
be  arrived  at  by  experiment." 

The  theory  which  is  based  upon  the  presence  of  asym- 
metric carbon  atoms  in  chemical  compounds  is  in  point  of 
fact  supported  by  many  important  observations.  In  the 
first  place  it  is  to  be  noted  that  all  optically  active  organic 
compounds,  whose  constitution  is  established,  contain  one  or 
more  asymmetric  carbon  atoms.  The  observations  which 

1  Cf.  van  't  HofFs  pamphlet,  Dix  Annies  dans  Vhistoire  d'une  Theorie 
(1887).  Van  't  Hoff  first  published  his  views  on  the  subject  in  the  small 
volume,  La  Chimie  dans  VEspace,  in  1875  (English  edition  by  Marsh, 
under  the  title  Chemistry  in  Space,  1891  ;  and  German,  by  Herrmann,  1877 
and  1894).  Le  Bel  also  brought  out  the  same  hypothesis,  independently 
of  van  't  Hoff,  in  the  Bull.  Soc.  Chim.  (2),  vol.  xxii.  p.  337.  Messrs.  Long- 
mans and  Co.  have  just  published  (1898)  a  second  revised  and  enlarged 
English  edition  of  van  't  HoflPs  The  Arrangement  of  the  Atoms  in  Space, 
with  a  preface  by  Johannes  Wislicenus,  and  an  appendix  entitled  "  Stereo- 
Chemistry  among  Inorganic  Substances,"  by  Alfred  Werner.  The  book  is 
translated  and  edited  by  Arnold  Eiloart,  who  has  made  a  special  study  of 
this  branch. 


358  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

have  been  made  upon  racemic,  malic,  mandelic  and  lactic 
acids,  and  upon  a  number  of  other  substances,  are  in  perfect 
accord  with  the  above  theory.  The  plan  of  breaking  up 
inactive  into  active  modifications,  which  was  first  followed 
by  Pasteur x  with  such  striking  success,  has  since  been  applied 
in  many  other  cases  with  equally  good  results.  The  theory  has 
proved  especially  fruitful  during  the  last  decade,  as  applied 
by  Emil  Fischer2  in  his  brilliant  researches  on  the  sugars. 

Further,  A.  von  Baeyer's  important  work  upon  the  hydro- 
phthalic  acids,3  whose  isomerism  is  without  doubt  due  to 
differences  in  the  spacial  arrangement  of  the  atoms,  con- 
stitutes a  strong  support  for  the  theory  of  the  asymmetric 
carbon  atom  in  "  ring-shaped  "  structures. 

The  investigation  of  the  isomerism  of  certain  compounds, 
in  which  the  so-called  "  double  linkage  "  of  carbon  is  to  be 
found,  has  proved  exceptionally  fruitful.  The  work  under- 
taken by  Johannes  Wislicenus  and  his  pupils  4  upon  fumaric 
and  maleic,  crotonic  and  iso-crotonic,  angelic  and  tiglic  acids, 
and  their  halogen  derivatives,  with  the  object  of  getting  at 
the  root  of  these  phenomena,  has  led  to  surprising  results, 
which  however  do  not  harmonise  with  theory  in  many 
respects.  In  fact  the  investigations  of  A.  Michael 5  and 

1  Louis  Pasteur  (born  at  Dole  on  December  27th,  1822,  died  at  Paris  on 
September  28th,  1895)  has  proved  a  great  pioneer  in  chemical  as  well  as  in 
the  biological  sciences.     It  was  indeed  his  systematic  work  upon  optically 
active  compounds,  especially  the  tartaric  acids,  which  led  him  on  to  the 
treatment  of  biological  questions, — to  the  isolation  and  artificial  culture  of 
pure  ferments.     His  researches  upon  the  alcoholic,  lactic  and  acetic  fermen- 
tations constituted  him  a  chief  founder  of  the  new  zymo-chemistry  and 
bacteriology.     The  brewing  industry  is  deeply  indebted  to  him  for  the  im- 
provements which  he  brought  about  in  it.     Following  on  those  researches 
we  have  his  great  work  on  inoculation  against  splenic  fever,  dysentery  and 
hydrophobia.     He  belongs  truly  to  the  great  benefactors  of  mankind. 

2  Ber.,  vol.    xxiii.  p.  2114,  vol.  xxiv.  p.  3997.     See  also  the   Special 
History  of  Organic  Chemistry. 

3  Ann,   Chem.,  vol.  ccxlv.  p.  103 ;  vol.  ccli.  p.   257  ;   vol.  cclvi.  p.   1  ; 
vol.  cclviii.  pp.  1  and  145  ;  vol.  cclxvi.  p.  169 ;  vol.  cclxix.  p.  145. 

4  Seethe  pamphlet  already  quoted ;  also  Ann.   Chem.,  vol.  ccxlvi.  p. 
-53  ;  vol.  ccxlviii.  pp.  1  and  281 ;  vol.  ccl.  p.  224. 

5  Cf.  especially  Journ.  pr.  Chem.  (2),  vol.  xlvi.  p.  400,  besides  preceding 
numbers. 


v  GEOMETRIC-CHEMICAL  ISOMERISM  359 

others 1  have  shown  that  contradictions  occur  in  them  which 
throw  doubt  upon  some  of  the  theoretical  hypotheses. 

This  idea  of  referring  the  cause  of  many  cases  of  iso- 
merism  to  the  different  geometrical  arrangement  of  the 
atoms  has  had  a  most  stimulating  effect,  and  has  led  to  the 
discovery  of  many  hitherto  overlooked  relations  existing 
between  isomeric  substances.  The  work  done  upon  the 
dichlorides  of  tolane,  the  butylenes,  the  isomeric  cinnamic 
acids,  erucic  and  brassidic  acids,  and  upon  the  alkyl-succinic 
acids  deserve  mention  here.2  Of  recent  years  there  have 
been  numerous  speculations  advanced  with  the  object  of  bring- 
ing conflicting  phenomena  into  accord  with  theory,  e.g.  Victor 
Meyer  and  Kiecke's3  ideas  upon  the  "constitution  of  the 
carbon  atom,"  and  Bischoff's4  "dynamic  hypothesis"  of  certain 
cases  of  isomerism. 

All  this  work  is  due  to  the  circumstance,  of  which  there 
can  no  longer  be  any  doubt,  that  geometric-chemical  isomers 
do  really  exist.  During  the  last  few  years  there  have  been 
similar  observations  with  regard  to  various  nitrogen  com- 
pounds, and  efforts  have  been  made  to  trace  these  cases  of  iso- 
merism back  to  spacial  relations, — to  the  configuration  of  the 
nitrogen  atom.  It  is  more  especially  in  those  compounds  in 
which  we  have  a  double  linkage  between  the  carbon  and 
nitrogen,  i.e.  =C:=N — ,  that  such  isomers  have  been  noticed. 
The  theory  of  the  stereo-isomerism  of  nitrogen  compounds, 
— a  theory  due  to  a  great  extent  to  Werner  and  Hantzsch,5 
— is  based  upon  the  work  of  the  late  Victor  Meyer  and 
Auwers,  of  Beckmann,  and  particularly  of  A.  Hantzsch 
himself  on  the  oximes  of  aldehydes  and  ketones,  together 

1  Skraup,  Wiener  Moiiatshefte,  etc,  vol.  xii.  p.   119;   Anschiitz,  Ann. 
Chem.,  vol.  ccliv.  p.  175. 

2  Cf.  Special  History  of  Organic  Chemistry. 

3  Ber.,  vol.  xxi.  p.  951.  4  Ber.,  vol.  xxiii.  p.  1467. 

5  Ber.,  vol.  xxiii.  pp.  1  and  1243.  For  the  literature  on  the  subject,  see 
Hantzsch's  Grundriss  der  Stereochemie  (Breslau,  1893).  On  p.  106  the  vital 
part  of  this  theory  is  expressed  as  follows: — "In  the  language  of  the 
valency  theory,  the  geometrical  isomerism  of  nitrogen  compounds  .... 
depends  upon  the  three  valencies  of  the  nitrogen  atom  not  being  in  the 
same  plane  in  certain  of  these  compounds." 


360  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

with  quite  recent  observations  on  the  hydrazones  and  the 
carbo-di-imides  by  Overton  and  others.  There  is  no  question 
that  a  large  number  of  important  cases  of  isomerism  have 
been  in  a  way  explained  by  the  assumption  of  spacial 
differences  in  the  relation  of  the  nitrogen  to  the  carbon 
atom.  But  whether  stereo-isomerism  is  to  be  assumed  in  as 
many  cases  as  Hantzsch  is  inclined  to  believe,  is  for  the 
present  doubtful  (compare  the  diazo-compounds  in  the 
Special  History  of  Organic  Chemistry). 

It  is  impossible  to  give  a  definite  answer  to  the  question 
whether  the  spacial  arrangement  of  the  atoms  within  a  mole- 
cule actually  corresponds  with  the  configurations  assumed 
by  the  above-named  scientists,  for  no  proof  can  be  furnished 
of  the  correctness  of  these  conceptions.  The  expectations 
raised  by  them — of  obtaining  a  deeper  insight  into  the 
mode  in  which  the  atoms  are  arranged  in  a  compound — are 
possibly  pitched  too  high.  Criticism  has  indeed  begun — 
as  already  indicated — to  busy  itself  with  the  explanation 
of  geometrical  isomerism  in  particular  cases,1  but  stereo- 
chemical  theories2  are  not  yet  sufficiently  advanced  to  give 
us  a  clear  view  of  the  whole  subject.  The  time  has  not  yet 
come  for  an  objective  historical  account  of  stereo-chemistry, 
in  which  theory  and  fact  shall  have  their  true  values 
assigned  to  them ;  the  subject  is  but  in  its  infancy. 

1  Ad.  Glaus  has  been  especially  active  in  disputing  the  correctness  of 
the  stereo-chemical  view  as  applied  to  the  isomeric  oximes  ;  cf.  Journ.  pr. 
Chem.,  vol.  xliv.  p.  312 ;  vol.  xlv.  pp.  1,  556 ;  vol.  xlvi.  p.  544. 

2  Hantzsch's  Grundriss  der  Stereochemie  gives  a  good  summary  of  the 
work  done  in  this  branch  of  chemistry  up  to  the  year  1893.     Compare  also 
Auwers'  Die  Entwickelung  der  Stereochemie  (Heidelburg,  1890),  and  C.  A. 
Bischoff  and  P.  Walden's  Handbuch  der  Stereochemie  (vol.  i,  1894),  which 
goes  minutely  into  the   subject.     In  English  there  is  Eiloart's  book    A 
Guide  to  Stereo- Chemistry. 


DEVELOPMENT  OF  SYNTHETIC  METHODS  361 


The  Development  of  Important  Methods  for  investigating 
the  Constitution  of  Organic  Compounds. 

The  above-mentioned  discussions  upon  isomers  are  suffi- 
cient to  show  us  how  materially  these  have  aided  the 
development  of  organic  chemistry  since  the  subject  was 
zealously  taken  in  hand.  Hardly  any  other  group  of 
phenomena  has  furthered  the  solution  of  the  question  of 
chemical  constitution  in  a  more  lasting  manner,  for  the 
attempts  to  establish  the  constitution  of  isomeric  bodies 
have  coincided  with  those  whose  aim  was  to  fathom  the  cause 
of  isomerism.  The  methods  followed  during  the  last  decade 
for  investigating  the  rational  composition  of  organic  com- 
pounds have  in  great  part  developed  themselves  from  others 
previously  in  use.  The  paths  which  have  led  towards  the 
wished-for  goals  were  smoothed  by  the  indispensable 
preparatory  labours  of  Liebig,  Wohler,  Bunsen,  Kolbe, 
Frankland,  Dumas,  Williamson,  Gerhardt,  Hofmann,  Wurtz 
and  others. 


Synthetic  Methods. 

The  mode  of  attaining  to  a  knowledge  of  the  constitu- 
tion of  organic  compounds,  which  had  been  least  worked 
out  of  any,  was  their  artificial  preparation  from  others 
of  simpler  composition.  After  Wohler  had  published  his 
memorable  observation  on  the  production  of  urea  from  its 
elements,  and  had  therewith  furnished  a  complete  synthesis 
of  it,  years  elapsed  before  any  further  successful  work  in 
this  direction  fell  to  be  recorded.  Referring  the  reader  to 
the  special  history  of  organic  chemistry,  we  need  merely 
recall  here  the  important  discoveries  during  the  fifties  by 
Kolbe  and  Frankland, — the  synthesis  of  acetic  acid  by  the 
former,  and  the  building  up  of  hydrocarbons  from  substances 
of  simpler  composition  by  the  latter. 

The  importance  of  synthetic  research  was  from  thence- 


362  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

forth  recognised  in  an  increasing  degree;1  indeed,  it  was 
from  artificial  modes  of  preparation  that  the  constitution  of 
many  organic  substances  could  first  be  deduced  with  cer- 
tainty. Thus  (to  give  only  one  or  two  instances)  the  rational 
composition  of  acetic  acid  was  arrived  at  from  its  production 
from  the  methyl  compounds — methyl  cyanide  and  sodium- 
methyl.  The  constitution  of  hydrocarbons  was  inferred 
from  their  synthesis  from  halogen-alkyls  with  zinc  or 
sodium,  and  that  of  the  ketones  through  their  formation 
from  acid  chlorides  and  zinc-alkyls.  Light  was  thrown 
upon  the  true  composition  of  the  oxy-acids  by  their 
synthesis  from  aldehydes  or  ketones  and  hydrocyanic  acid, 
and  also  from  phenates  and  carbonic  acid.  And  to  what  a 
wealth  of  synthetic  reactions  and  discoveries  of  new  com- 
pounds have  not  the  sodium  derivatives  of  certain  acid 
ethers — e.g.  aceto-acetic  and  malonic  ethers — led  !2 

In  every  section  of  the  wide  field  of  organic  chemistry, 
great  success  has  followed  the  application  of  synthetic 
methods;  and  the  worth  of  these  latter  is  not  to  be 
measured  merely  by  the  vast  number  of  new  compounds  to 
which  they  have  given  rise,  but  by  their  own  intrinsic 
value,  which  has  shown  itself  in  the  knowledge  thereby 
gained  of  the  chemical  constitution  of  organic  compounds. 
The  so-called  condensation  syntheses  have  proved  themselves 
of  especial  value  in  this  direction.  This  term  "  condensa- 
tion" has,  since  Baeyer's  explanation  on  the  subject,  been 
employed  generally  for  those  reactions  in  which  several 
similar  or  dissimilar  molecules  coalesce  together,  with 
elimination  of  water,  in  such  a  manner  that  the  carbon 
atoms  become  linked  to  one  another.  A  classical  instance 
of  it  (observed  a  long  time  ago  by  Kane,  but  first  explained 
by  Baeyer,  as  above)  is  given  in  the  transformation  into 
mesityl  oxide — or  into  phorone — and  then  into  mesitylene 

1  In  1889  chemical  literature  was  enriched  by  an  admirable  systematic 
"  Textbook  of  Syntheses  "  on  a  historical  basis,  in  K'.  Elb's  Die  Synthetischen 
Darstellungsmethoden  der  Kohlenstoffverbindungen. 

2  With  reference  to  these  and  other  syntheses,  cf.  the  special  history 
of  organic  chemistry. 


v  "CONDENSATION"  SYNTHESES  363 

which  acetone  experiences  under  the  influence  of  sulphuric 
acid.  Similar  reactions  go  on  in  the  case  of  other  ketones 
and  of  aldehydes — e.g.  the  condensation  of  acetic  to  crotonic 
aldehyde  (Kekule) — and  that  of  a  mixture  of  acetic  and 
benzoic  aldehydes  to  cinnamic  aldehyde.  Through  these 
and  other  processes  a  bridge  was  thrown  over  the  gap 
between  the  saturated  and  unsaturated  compounds,  while 
at  the  same  time  light  was  shed  upon  the  constitution  of  the 
latter.  The  reaction  discovered  by  and  called  after  W.  H. 
Perkin,  sen.,  which  depends  on  the  condensation  of  aldehydes 
with  fatty  acids,  formed  the  basis  of  some  notable  researches 
by  Fittig,  Claisen  and  others,  while  it  likewise  aided  in 
clearing  up  the  rational  composition  of  unsaturated  acids. 

A.  von  Baeyer,1  in  conjunction  with  a  large  number  of 
his  pupils  (E.  and  O.  Fischer,  v.  Pechmann,  Konigs,  Knorr, 
E.  Bamberger,  Paal,  etc.),  has  minutely  investigated  this 
subject  of  condensation  in  the  most  admirable  manner, 
as  have  also  Kekule",  Fittig,  Ladenburg,  Victor  Meyer, 
Hantzsch,  Claisen,  W.  H.  Perkin,  Graebe,  Liebermann, 
Collie,  and,  in  fact,  almost  all  chemists  who  have  occupied 
themselves  with  organic  chemistry  of  recent  years ;  indeed, 
this  study  seemed  for  a  time  to  be  the  chief  feature  of 
organic  chemistry.  The  ardour  for  carrying  out  such 
syntheses  increased  more  especially  after  it  was  seen  that 
the  chemical  processes  going  on  in  plant  organisms — i.e.  the 
formation  of  compounds  rich  in  carbon  from  carbonic  acid, 

1  Adolf  von  Baeyer,  born  at  Berlin  on  30th  November,  1835,  became  a 
pupil  of  Bunsen  and  of  Kekule,  and  applied  himself  under  the  stimulating 
influence  of  the  latter  to  organic  chemistry,  which  he  has  enriched  by  a 
wealth  of  admirable  and  important  work.  His  untiring  study  of  con- 
densation reactions  has  led  him  to  results  of  the  highest  value,  which  will 
frequently  be  referred  to  in  the  special  history  of  organic  chemistry.  From 
his  laboratory  there  has  come  forth  much  work  of  a  fundamental  nature ; 
we  need  only  recall  here  that  of  Graebe  and  Liebermann  on  alizarin,  and 
that  of  E.  and  0.  Fischer  on  rosaniline,  etc.  Since  1860,  in  which  year 
Baeyer  became  assistant  professor  in  Berlin,  he  has  continued  energetic  as 
a  teacher— first  at  the  Berlin  Technical  College,  then  from  1872-75  in 
Strasburg,  and  lastly,  from  1875,  in  Munich,  where,  as  head  of  the  Uni- 
versity laboratory,  which  was  built  after  his  own  plans,  he  has  found  a 
brilliant  sphere  of  action. 


364  THE  MODERN  CHEMICAL  PERIOD  CHAP, 

water,  and  ammonia — were  for  the  most  part  based  upon 
condensation.  The  history  of  organic  chemistry  can  tell 
of  many  results  of  efforts  to  imitate  such  natural  processes, 
or  at  least  to  prepare  products  which  occur  in  the  vegetable 
kingdom  (acids,  colouring  matters,  alkaloids,  carbohydrates, 
etc.)  from  substances  of  simpler  composition.  The  most 
important  of  those  vegetable  acids  which  had  long  been 
known  were  prepared  synthetically, — oxalic  acid  from 
carbonic,  succinic  acid  from  ethylene,  malic  and  tartaric 
acids  from  succinic,  and  citric  acid  from  acetone  (which, 
like  ethylene,  could  be  built  up  from  its  elements) ; 
further,  benzoic  acid  from  benzene,  cinnamic  acid  from 
benzaldehyde,  and  so  on.  By  those  observations,  the  list 
of  which  might  be  extended  by  numerous  others  on  the 
artificial  formation  of  acids  occurring  in  the  animal  and 
vegetable  kingdoms  (e.g.  the  syntheses  of  chelidonic,  vulpic, 
and  uric  acids),  the  chemical  constitution  of  these  sub- 
stances was  determined  with  greater  precision  than  had 
hitherto  been  possible. 

Similarly  from  the  synthesis  of  vegetable  colouring 
matters  and  other  bodies — e.g.  alizarin,  purpurin,  indigo 
blue,  cumarin  and  vanillin, — trustworthy  conclusions  have 
been  drawn  with  respect  to  their  rational  composition.  The 
important  problem  of  preparing  the  sugars  and  vegetable 
alkaloids  artificially  has  been  taken  in  hand  with  success, — 
witness  the  beautiful  researches  of  Emil  Fischer1  upon  car- 
bohydrates, which  have  lately  led  to  the  artificial  formation 
of  grape  sugar,  and  the  ingenious  synthesis  of  conine  by 
Ladenburg.2 

One  may  safely  express  the  opinion  that  a  clear  idea  of  the 
chemical  constitution  of  these  and  other  difficultly  accessible 
classes  of  compounds,  whose  proximate  composition  has  as 
yet  been  but  imperfectly  worked  out,  will  only  be  arrived 
at  after  they  have  been  synthetised  from  simpler  ones  of  known 
structure.  The  history  of  the  synthesis  of  organic  com- 
pounds has  already  proved  the  truth  of  this  axiom  in 
numerous  instances. 

1  Cf.  the  special  history  of  organic  chemistry.  2  Ibid. 


v       CHEMICAL  CONSTITUTION  OF  ORGANIC  COMPOUNDS    365 

The  chemical  behaviour  of  organic  compounds  is  in  every 
case  regarded  as  an  aid  of  the  first  importance  in  working 
out  their  constitution,  and  has  been  valued  accordingly 
ever  since  organic  chemistry  began  to  flourish.  A  short 
sketch  only  can  be  given  here  of  a  few  of  the  more  important 
methods  which  have  been  applied  during  these  last  decades, 
with  the  object  of  getting  at  the  chemical  constitution  of 
organic  compounds  from  their  reactions,  transformations  and 
decompositions. 

The  general  principle  of  such  methods  consists,  in  contra- 
distinction to  that  of  the  synthetic,  in  investigating  the 
products  obtained  by  the  chemical  alteration  of  the  com- 
pounds in  question,  and  in  deducing  the  constitution  of  the 
latter  from  these.  In  many  cases  of  transformation  the 
chemist  keeps  his  attention  fixed  upon  particular  elements 
or  atomic  groups  united  to  carbon,  the  carbon  framework 
itself  undergoing  no  change ;  in  many  others,  on  the 
contrary,  carbon  is  separated  as  carbonic  acid,  carbonic 
oxide,  or  even  in  a  more  complex  form.  For  those  classes 
of  substances  which  are  among  the  best  investigated,  special 
reactions  have  been  discovered  which  make  it  possible  to 
decide  whether  a  hitherto  unknown  compound  belongs  to 
this  or  that  group.  Of  recent  years  great  attention  has 
been  paid  to  the  refinement  of  such  reactions.  To  mention 
only  one  or  two  important  steps  in  this  direction: — 
Phosphorus  pentachloride,  acetic  anhydride  and  hydriodic 
acid  have  been  found  of  inestimable  value  for  determining 
whether  an  organic  compound  contains  hydroxyl,  and,  if  so, 
what  function  that  hydroxyl  performs.  Further,  the  trans- 
formation of  nitro-  into  amido-compounds  by  reduction, 
and  that  of  the  latter  into  oxy-derivatives  by  oxidation, 
the  conversion  of  cyanides  into  carboxylic  acids,  of  hydro- 
carbons into  acids,  and  of  amido-  into  diazo-compounds,  have 
all  become  typical  reactions,  which,  when  rightly  interpreted, 
lead  very  quickly  to  the  explanation  of  the  constitution  of 
such  bodies.  Lastly,  we  may  recall  here  the  beautiful  method 
of  V.  Meyer  and  E.  Fischer,  by  which  the  presence  of  the 
carbonyl  group  in  a  compound  can  be  proved  by  means  of 


366  THE  MODERN  CHEMICAL  PERIOD  CHAP 

hydroxylamine  or  phenyl-hydrazine.  All  the  above  and 
other  similar  reactions  have  for  their  aim  the  definite  recog- 
nition of  the  role  of  elementary  atoms  or  compound  radicals 
in  organic  molecules,  and  with  this  the  partial  solution  of 
the  constitution  of  these  latter;  in  numberless  instances 
this  aim  has  been  accomplished. 

The  decompositions  of  organic  substances  into  others 
poorer  in  carbon,  which  may  be  made  use  of  for  deciding 
the  same  point,  are  legion,  and  will  just  be  touched  upon 
here,  in  order  to  illustrate  the  principle  of  the  method. 
This  plan  is  the  direct  opposite  of  the  synthetic;  while  by 
the  latter  the  constitution  of  an  organic  compound  is  deduced 
from  that  of  its  components,  the  former  leads  to  the  same 
conclusion  through  a  study  of  the  resulting  decomposition - 
products.  To  give  only  one  or  two  examples : — Let  us  recall 
the  important  inferences  drawn  by  v.  Baeyer  from  the  decom- 
position of  derivatives  of  uric  acid  into  simpler  bodies  ;  the 
constitution  of  those  compounds  thus  deduced  by  him  was 
subsequently  confirmed  by  direct  synthesis.  The  researches  by 
Frankland,  Geuther,  Wislicenus  and  others  on  the  modes  of 
decomposition  of  aceto-acetic  ether  must  also  be  mentioned, 
researches  which,  conjointly  with  other  synthetic  ones, 
cleared  up  the  constitution  of  the  latter.  Further,  carbonic 
acid,  formic  acid,  etc.,  are  very  often  eliminated  from  organic 
compounds,  whose  decomposition-products  thus  furnish  a 
clue  to  their  rational  composition.  The  changes  produced 
by  oxidation  in  the  case  of  numerous  substances,  such  as  the 
ketones,  quinoline  bases,  naphthalene  derivatives  and  unsatur- 
ated  compounds,  furnish  excellent  proof  of  the  invaluable  aid 
given  by  researches  of  this  nature  towards  solving  the 
question  of  chemical  constitution.  For  further  details  on 
this  point,  the  reader  is  referred  to  the  special  history  of 
organic  chemistry. 

By  this  co-operation,  by  the  use  of  the  various  methods 
which  are  now  an  integral  part  of  organic  chemistry,  the 
problem  *of  the  rational  composition  of  carbon  compounds 
has  been  brought  distinctly  nearer  to  its  solution. 


INORGANIC  AND  GENERAL  CHEMISTRY  367 


The  Main  Currents  in  Inorganic  and  General  Chemistry 
during  the  last  Thirty-five  Years. 

The  doctrine  of  the  saturation-capacities  of  the  elements, 
which  has  proved  of  such  extraordinary  importance  for  the 
development  of  organic  chemistry,  has  not  by  any  means 
found  the  same  rapid  and  general  application  in  inorganic. 
After  Odling,  so  early  as  1854,  had  applied  Frankland's  idea 
of  valency  to  the  oxides  of  a  large  number  of  the  elements, 
remaining  however  at  the  same  time  enchained  by  the  type 
theory  (cf.  p.  325),  gradual  attempts  were  made  by  a  number 
of  chemists,  either  in  text-books  or  in  their  experi- 
mental researches,  to  engraft  on  inorganic  compounds  the 
ideas  which  had  so  quickly  found  acceptance  with  respect 
to  the  linking  of  carbon  atoms  among  themselves  or  with 
other  elements.  The  gain  which  arose  from  this  was  first 
apparent  in  the  systematising  of  these  compounds,  which 
became  classified  into  natural  families  according  to  the 
valencies  ascribed  to  the  individual  elements.  Similarity  in 
saturation-capacity  formed  the  common  link  which  held  the 
different  members  of  such  groups  together.  Thus  Frankland 
had  already  recognised  the  analogy  between  nitrogen,  phos- 
phorus, arsenic  and  antimony,  from  the  fact  that  they  were 
all  capable  of  acting  either  as  tri-  or  as  pentavalent.  Along- 
side of  carbon  were  ranged  silicon,  titanium  and  zirconium, 
as  being  in  the  main  tetravalent  elements,  whereas  boron, 
which  had  formerly  been  ranked  along  with  carbon,  was  seen 
to  be  trivalent,  and  was  relegated  to  another  group.  These 
and  similar  efforts  to  introduce  clearness  into  the  syste- 
matising of  the  elements,  by  classifying  them  according  to 
their  chemical  values,  soon  led  to  the  establishment  of  the 
important  Natural  System  of  the  Elements  (cf.  p.  370). 

The  problem  of  interpreting  the  constitution  of  inorganic 
compounds  similarly  to  that  of  organic,  by  getting  at  the 
relations  which  exist  between  their  component  dements, 
has  not  been  treated  with  the  same  care  as  in  the  case  of 
the  latter.  For  substances  of  simple  composition  the  diffi- 


368  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

culty  of  the  point  was  usually  under-estimated  ;  this  showed 
itself  more  particularly  in  the  arbitrary  attempts  at  ex- 
plaining the  constitution  of  inorganic  compounds  on  the 
supposition  that  the  valencies  of  the  elements  were  invariable. 
Thus  it  was  often  overlooked  that  the  chemical  behaviour  of 
a  substance  was  not  in  accordance  with  the  structural  formula 
assigned  to  it.  Sulphur  chloride,  for  example,  was  given 

S-C1 
the   formula,     |         ,  without  any  heed  being  paid  to  the  fact 

S-C1 

that  one  of  its  atoms  of  sulphur  behaved  quite  differently  from 
the  other.  And  the  constitution  of  phosphorus  oxychloride 
could  only  be  illustrated  by  the  adherents  of  constant 

/0-C1 
valency  by  the  formula,  P\~ Cl       ,  a    formula   which   in- 

xci. 

dicated  an  (unproven)  difference  between  one  chlorine  atom 
and  the  other  two. 

And  how  the  ordinary  rules  were  strained  in  order  to 
indicate  the  composition  of  more  complex  compounds ! 
According  to  Wurtz,1  the  constitution  of  bodies  rich  in 
oxygen  could  usually  be  explained  by  assuming  the  oxygen 
atoms  to  be  linked  to  one  another;  take,  for  example, 
periodic  anhydride,  in  which  seven  atoms  of  oxygen 
were  linked  together  in  a  chain,  with  the  two  supposed 
monovalent  iodine  atoms  at  either  end.  This  very  one- 
sided assumption  of  a  constant  valency  of  the  elements 
was  however  gradually  superseded,  a  sounder  view 
taking  the  place  of  such  artificial  explanations.  But  trust- 
worthy methods  of  arriving  at  the  constitution  of  complex 
compounds  are  scarcely  yet  developed  in  inorganic  chemistry, 
although  in  organic  much  has  already  been  done  in  this 
direction. 

The  researches  of  greatest  value  for  inorganic  chemistry 

which  have  been  made  during  the  last  few  decades  are  those 

upon  particular  elements,  more  especially  upon  such  as  had 

hitherto  been  imperfectly  or  even  not  at  all  investigated. 

1  Lemons  de  Philosophie  Chimique,  p.  157. 


v  RELATIONS  BETWEEN  THE  ATOMIC  WEIGHTS          369 

Thus  the  work  of  Roscoe l  on  vanadium,  of  Marignac 2  on 
niobium  and  tantalum,  and  of  Zimmermann,  Kruss,  von  der 
Pfordten,  Moissan  and  others  on  uranium,  gold,  titanium, 
fluorine,  etc.,  have  enabled  those  elements  to  be  put  in  their 
proper  place  among  the  others ;  this  of  course  only  became 
possible  after  their  chemical  character  had  been  thoroughly 
examined.  The  same  applies  to  the  more  recently  dis- 
covered elements — thallium,  indium,  gallium,  scandium  r 
germanium,  etc.,  which  have  likewise  been  investigated  by 
their  discoverers  in  a  masterly  manner. 

All  these  researches,  which  will  be  referred  to  again  in 
the  special  history  of  inorganic  chemistry,  have  had  the 
same  ends  in  view,  viz.  the  establishment  of  the  chemical 
character,  and,  in  particular,  of  the  combining  relations  of 
the  element  in  question,  and  the  most  careful  possible  deter- 
mination of  its  relative  atomic  weight.  In  addition  to  all 
this,  an  increasing  value  has  come  to  be  laid  upon  the  obser- 
vation of  its  physical  properties.  Such  investigations  upon 
individual  elements  became  more  systematised  after  it  was 
clearly  seen  that  a  close  connection  existed  between  their 
chemical  and  physical  properties  on  the  one  hand  and 
the  magnitudes  of  their  atomic  weights  on  the  other. 
Of  course,  when  it  came  to  a  question  of  proving  this 
intimate  relation,  the  first  thing  was  to  determine  the 

1  Sir  Henry  E.  Roscoe,  born  in  1833,  was  a  pupil  of  Bunsen's.     For 
nearly  thirty  years  he  held  the  chair  of  chemistry  at  Owens  College,  Man- 
chester, resigning  in  1885.     His  work  has  been  for  the  most  part  in  in- 
organic and  physical  chemistry,  the  Photochemical  Researches  by  Bunsen 
and  Roscoe  (London,  1858-1863)  deserving  mention  here.     He  is  also  well 
known  as  the  joint  author  of  Roscoe    and    Schlorlemmer's    Treatise   on 
Chemistry,    as  well  as  of   other  smaller  text-books  on  the  science.     His 
Lessons  in  Elementary  Chemistry  has  run  through  numerous  editions,  and 
has  been  translated  into  a  great  many  different  languages. 

2  J.  C.  Marignac,  born  at  Geneva  in  1817,  retired  several  years  ago> 
from  the  professorial  work  to  which  he  had  devoted  himself  in  his  native 
city  since  1842,  and  died  there  on  April  15th,  1894.     With  the  exception 
of  some  researches  on  the  naphthalene  derivatives,  his  most  important 
work  has  been  in  the  determination  of  the  atomic  weights  of  numerous 
elements,  and  in  other  subjects  of  inorganic  chemistry.    A  detailed  account 
of  his  life  and  his  services  to  the  science  has  been  given  by  E.  Ador  in  th# 
Archives  des  Sciences  Physiques  et  Naturelhs,  vol.  xxxii,  p.  5. 

B   B 


370  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

relative  atomic  weights  as   accurately   as   it   was   possible 
to  do. 

The  efforts  of  many  chemists  had  already  for  a  long 
time  been  directed  to  improving  as  far  as  practicable  the 
methods  of  determining  atomic  weights,  before  the  importance 
of  this  question  for  the  systematising  of  the  elements  had 
come  to  be  recognised.  The  memorable  labours  of  Berzelius 
were  followed  during  the  forties  by  those  of  Turner,  Dumas, 
Marignac,  Erdmann,  Marchand  and  Pelouze,  and  were 
crowned  by  the  classical  researches  of  Stas l  upon  the  atomic 
weights  of  oxygen,  chlorine,  bromine,  iodine,  nitrogen,  sul- 
phur, silver,  etc.  In  Stas's  case  the  extreme  limit  of 
accuracy  was  reached  which  was  possible  with  the  means  at 
command.  But  this  certainty  with  respect  to  the  magnitudes 
of  the  relative  atomic  weights  only  extended  to  some  of  the 
elements,  the  values  hitherto  assigned  to  many  (e.g.  molyb- 
denum, antimony,  platinum,  osmium,  iridium,  etc.)  being 
exceedingly  inaccurate.  Much  has,  however,  been  accom- 
plished in  this  direction  of  late  years.2 


The  Periodic  System  of  the  Elements. 

Prout's  hypothesis,  according  to  which  the  atomic  weights 
of  all  the  elements  stand  in  a  simple  relation  to  that  of 
hydrogen,  acted  for  a  long  period  like  a  ferment,  in  that  it 
gave  rise  to  continually  renewed  speculations  upon  the  con- 
nection which  existed  between  the  elements  and  their  atomic 
weights.  The  observed  fact  that  chemically  analogous  ele- 

1  Jean  Servais  Stas,  born  at  Lowen  in  Belgium  in  1813,  died  in  1891 
at  Brussels,  where  he  had  occupied  the  chair  of  chemistry  in  the  Military 
School  for  a  number  of  decades.     His  unique  services  in  the  determination 
of  the  atomic  weights  of  the  elements  are  universally  recognised.     The 
various  papers  on  this  subject  were  published  by  him  in  a  collected  form 
in  the  well-known  work,  Eecherches  sur  les  Bapports  rdciproques  des  Poids 
Atomiques,  and  in  the  Nouvelles  Recherches  sur  les  Lois  des  Proportions 
Chimiques,  etc.     Organic  chemistry  and  forensic  analysis  are  also  indebted 
to  him  for  most  important  investigations  (see  Special  History). 

2  Cf.  the  Special  History  of  Inorganic  Chemistry. 


v  THE  PERIODIC  SYSTEM  OF  THE  ELEMENTS  371 

ments  possessed  either  nearly  equal  atomic  weights,  or  atomic 
weights  separated  from  one  another  by  definite  numerical 
increments,  afforded  food  for  such  theorising.  For  almost 
seventy  years  attention  has  frequently  been  drawn,  with 
more  or  less  emphasis  and  ability,  to  regularities  of  this 
kind  ;  the  discussions  of  the  point  by  Dobereiner,  L.  Gmelin, 
Pettenkofer,  Dumas,  Kremers,  Odling  and  others  may  be 
recalled  here.1  But  it  is  only  of  comparatively  recent  years 
that  a  systematic  classification  has  followed  from  those  efforts 
to  discover  a  connection  between  the  atomic  weights  and  the 
nature  of  the  elements. 

In  the  year  1864  Newlands2  in  England  and  Lothar 
Meyer3  in  Germany — independently  of  one  another — 
arranged  a  number  of  the  elements  according  to  the 
magnitudes  of  their  atomic  weights,4  and  thereby  observed 
that  while,  at  a  superficial  glance,  the  elements  following 
one  another  showed  apparently  no  regularity  in  properties, 

1  Cf.  L.  Meyer's  Moderne  Theorien  (fifth  German  edition),  p.  133. 

2  Chem.  News,  vol.  xxxii.,  pp.  21  and  192;   also  Newlands'  pamphlet, 
The  Discovery  of  the  Periodic  Law  (London,   1884).      Mendelejeff,  in  his 
Grundlagen  der  Chemie,  p.  683,  calls  attention  to  the  fact  that,  so  early  as 
1862,  some  parts  of  the  periodic  law  were  enunciated  by  Chaucourtois. 

3  Lothar  Meyer,  born  19th  August,  1830,  filled  from  1876  until  his  death 
on  April  29th,   1895,  the  first  chair  of  chemistry  in  the  University  of 
Tiibingen,  after  having  previously  worked  as   an   academic  teacher  in 
Breslau,  Neustadt-Eberswalde   and   Karlsruhe.     His   first   experimental 
researches  dealt  with  questions  of  physiological  chemistry  ;  but  he  after- 
wards turned  his  attention  more  to  theoretical  and    physico-chemical 
problems.     The  outcome  of  this  was  his  valuable  work,  Die  Modemen 
Theorien  der  Chemie  (fifth  edition,  1884),  which  has  been  translated  into 
English  by  Professors  Bedson  and  Carleton    Williams   under  the   title, 
Modern  Theories  of  Chemistry  ;  compare  also  his  Grundziige  der  theoret- 
ischen  Chemie  (1890).     The  efforts  mentioned  above,  which  he  made  with 
the  object  of  firmly  establishing  the  periodic  system  of  the  elements,  led 
him  on  to  a  careful  review  of  all  that  had  been  written  on  their  atomic 
weights  (cf.  his  and  K.  Seubert's  meritorious  work,  Die  Atomgewichte  der 
Elementeausden  Originalzahlen  neu  berechnet,  1883)  ("  The  Atomic  Weights 
of  the  Elements  newly  Recalculated  from  the  Original  Numbers").      A 
detailed  account  of  Lothar  Meyer's  life  and  work,  from  the  pen  of  his 
pupil  Seubert,  is  to  be  found  in  the  Berichte,  vol.  xxviii,  Ref.  p.  1109  ;  and 
another  by  Bedson  in  the  Journal  of  the  Chemical  Society  for  1896,  p.   1403. 

4  Cf.  Moderne  Theorien  (first  German  edition,  1864). 

B  B   2 


372  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

after  the  lapse  of  a  certain  period  the  chemical  and  physical 
behaviour  of  the  elements  now  succeeding  each  other  strongly 
recalled  that  of  the  previous  group,  in  fact  repeated  it.  The 
elements  which  resembled  one  another  were  therefore  united 
into  groups  or  natural  families,  and  these  in  their  turn 
were  distinguished  from  the  periods,  which  comprised  the 
elements  whose  atomic  weights  lay  between  those  of  two  suc- 
cessive members  of  a  natural  family.  This  attempt  to  classify 
the  elements  according  to  the  magnitude  of  their  atomic 
weights,  and  to  deduce  from  this  an  important  connection 
between  the  latter  and  the  properties  of  the  former,  called 
forth  at  first  more  astonishment  than  recognition.  Indeed, 
Newlands  did  not  escape  banter  on  the  subject,  being  asked 
whether  he  would  not  try,  with  a  similar  result,  to  classify 
the  elements  according  to  the  initial  letters  of  their  names. 

After  the  year  1869  these  very  imperfect  beginnings 
were  soon  greatly  extended  and  improved  by  Mendel  ejeff1 
and  Lothar  Meyer,2  quite  independently  of  one  another,  the 
atomic  weights  of  various  elements  having  in  the  mean- 
time been  determined  with  greater  accuracy  than  before. 
Mendelejeff  made  what  was  for  that  time  the  bold  attempt 
to  classify  all  the  elements  according  to  the  magnitudes  of 
their  atomic  weights,  the  correctness  of  some  of  which  was 
extremely  doubtful.  He  was  thus  able  to  show  that  the 
elements  which  belonged  to  a  natural  family,  i.e.  those 
which  were  chemically  similar,  followed  one  another  in 
regular  periods.  In  this  way  the  elements  were  brought 
together  into  a  natural  system,  as  it  was  termed,  in  which 

1  Ztschr.  Chem.  for  1869,  p.  405;  and  more  fully,  Ann.  Chem.,  Supple- 
ment, vol.  viii.,  p.  133. — D.  J.  Mendelejeff,  born  at  Tobolsk  on  February 
7th,  1834,  has  devoted  himself  to  researches  on  physical  constants,  e.g. 
specific  volumes,  expansion  of  gases,  etc.     He  is  best  known  by  his  famous 
treatise,  Die  Periodische   Gesetzmassigkeit  der   chemischen   Elemente,  and 
also  by  his  very  original  text-book,  Grundlagen  der  Chemie.     Since  1866 
he  has  held  the  chair  of  chemistry  in  the  University  of  St.   Petersburg, 
having  previously  occupied  that  in  the  Technological  Institute  there. 

2  Ann.  Chem.,  Supplement,  vol.  vii.,  p.  354;    and  also  in  the  recent 
editions  of  his  Moderne  Theorien. 


v  CONSEQUENCES  OF  THE  PERIODIC  SYSTEM  373 

however,  there  was  much  that  was  arbitrary  because  of  the 
inaccuracy  of  many  of  the  atomic  weights.  But  the  funda- 
mental idea  developed  by  the  above  investigators,  viz.  that 
the  elements  arrange  themselves  on  the  one  hand  into 
periods,  and  on  the  other  into  natural  families,  and  that 
all  their  properties  are  periodic  functions  of  their  atomic 
weights,  has  been  strengthened  and  verified  in  every  direc- 
tion by  many  subsequent  investigations.  The  latter  applies 
more  especially  to  the  chemical  valency  of  the  elements, 
the  electro-chemical  character,  the  atomic  volume,  the 
thermo-chemical  behaviour  and  other  physical  properties, 
all  of  which  stand  in  periodic  dependence  to  the  magnitude 
of  the  atomic  weight. 

These  efforts,  so  invaluable  for  the  systematising  of  the 
elements,  have  led  to  many  important  deductions.  Thus, 
in  virtue  of  the  periodic  system,  definite  values  could  be 
assigned  to  the  hitherto  uncertain  atomic  weights  of  various 
elements ;  for  each  element  claims  a  place  of  its  own  in  this 
system  and  an  atomic  weight  corresponding  with  this  place, 
the  magnitude  of  the  latter  being  calculable  within  certain 
limits.  When,  for  example,  only  the  equivalent  of  an 
element  was  known,  the  atomic  weight  could  be  deduced 
from  its  behaviour  and  from  the  position  thus  accruing  to 
it  in  the  natural  system,  as  was  actually  done,  e.g.,  for 
beryllium  and  indium.  Further,  a  choice  could  be  made 
between  different  definite  values  for  one  and  the  same 
element,  and  the  more  suitable  one  taken,  to  be  afterwards 
verified,  of  course,  with  the  utmost  care.  In  this  way  the 
periodic  system  has  been  applied  in  the  happiest  manner  to 
correcting  the  atomic  weights  of  molybdenum,  antimony, 
caesium,  etc. 

Other  conclusions  of  a  speculative  nature  have  likewise 
been  drawn  with  the  best  results  from  this  classification  of 
the  elements  into  periods  and  natural  families.  The  gaps 
shown  by  the  system  at  the  time  it  was  brought  forward, 
and  in  a  lesser  number  to-day,  were  and  are  intended  to 
be  filled  up  by  new  and  hitherto  undiscovered  elements. 


374  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

Mendelejeff  sought  to  predict  from  the  positions  of  such 
blanks,  not  merely  the  existence  of  elements  and  their 
approximate  atomic  weights,  but  also  their  properties  and 
chemical  behaviour,  together  with  that  of  some  of  the  com- 
pounds which  they  would  form.  His  prognostigations  have 
been  fulfilled  in  the  most  striking  manner  by  the  discovery 
of  gallium,  scandium  and  germanium,  and  by  the  verification 
of  their  behaviour  as  foreseen  by  him.  On  the  other  hand, 
the  position  in  the  periodic  table  of  the  elements  argon  and 
helium,  recently  discovered  by  Rayleigh  and  Ramsay,  pre- 
sents great  difficulty,  as  these  elements  show  no  definite 
chemical  reactions.  (Cf.  the  Special  History  of  Inorganic 
Chemistry.} 

The  perception  of  the  fact  that  the  physical  and  chemical 
properties  of  all  the  elements  show  a  periodic  dependence 
upon  their  atomic  weights  is  therefore  a  result  of  this  natu- 
ral classification.  But  the  discovery  of  the  common  cause 
which  underlies  these  peculiar  relations,  and  its  formulation 
into  a  law,  still  remain  tasks  for  the  future.  Some  chemists 
have  thought  to  lift  this  veil  already  by  assuming  that  all  the 
various  elements,  or  at  least  those  belonging  to  a  natural 
family,  may  be  referred  back  to  still  simpler  ones.  We  per- 
ceive clearly  here  a  reapproach  to  Prout's  hypothesis,  which 
threatened  to  exercise  such  an  unfavourable  influence  on  the 
rational  development  of  the  atomic  doctrine,  had  not  the 
ablest  chemists  of  the  time  raised  a  protest  against  its 
admissibility.  During  the  last  few  years  Crookes  has  again 
brought  up  this  ticklish  question,  whether  the  so-called 
elements  are  to  be  regarded  as  simple,  and  not  rather  as 
compound.1  According  to  him,  all  the  elements  have  re- 
sulted by  gradual  condensation  from  a  primary  material 
which  he  terms  protyle,  this  view  having  been  arrived  at 
from  his  observations  on  the  phosphorescence  spectra  of  the 

1  Cf.  Chem.  News,  vol.  liv.  ;  also  Crookes'  Presidential  Addresses  to 
the  Chemical  Society  in  1888  and  1889,  published  in  the  Society's  Journal 
for  those  years.  Compare,  too,  W.  Preyer's  Das  genetische  System  der 
chemischen  Elemente  (1893). 


HERMANN  KOPP  375 


yttrium  earths.  The  peculiar  nature  of  these  yttrium  earths, 
which  consist  of  a  variety  of  substances,  has  conduced  greatly 
to  speculations  of  the  kind. 

But  until  the  transformation  of  one  element  into  another 
has  been  incontestably  proved  by  experiment,  chemists  can- 
not give  up  the  idea  of  indivisible  elementary  particles,  i.e. 
the  present  atomic  theory. 


The  General  Significance  of  Physico-chemical  Investigations. 

The  relations  thus  discovered  between  the  atomic  weights 
of  the  elements  and  their  physical  properties  have  materially 
contributed  to  enlarge  our  knowledge  of  the  boundary-land 
between  physics  and  chemistry.  Many  investigators  had 
previous  to  this  followed  the  example  of  H.  Kopp 1  (who 
began  his  stimulating  labours  in  the  forties),  in  assiduously 
tracing  out  the  connection  existing  between  the  chemical 
constitution  of  compounds  and  their  physical  behaviour. 

1  Hermann  Kopp,  born  30th  October,  1817,  at  Hanau  (at  which  place  his 
father  was  an  esteemed  physician),  after  studying  at  Heidelberg,  was 
drawn  through  Liebig's  attraction  to  Giessen,  where  he  became  assistant 
professor  of  chemistry  in  1841  and  professor  at  a  later  date.  At  Giessen  he 
remained  until  his  removal  to  the  University  of  Heidelberg  in  1864,  where 
he  continued  to  work  in  full  vigour  until  shortly  before  his  death,  which 
took  place  on  February  20th,  1892.  His  services  as  a  historian  of 
chemistry  have  already  been  frequently  referred  to.  All  his  historical 
works  [Geschichte  der  Chemie  ("  History  of  Chemistry  "),  4  vols.  1843-47  ; 
Die  Entwickelung  der  Chemie  in  der  neueren  Zeit,  1873  ("The Development 
of  Chemistry  in  Recent  Times");  Beitrdge  zur  Geschichte  der  Chemie 
("Contributions  to  the  History  of  Chemistry");  Die  Alchemie  in  dlterer 
und  neuerer  Zeit.  ("  Alchemy,  Old  and  New  ")]  are  distinguished  by  their 
comprehensiveness  and  thoroughness.  He  possessed  in  a  remarkable 
degree  the  gift  of  sympathetically  tracing  out  the  development  of  im- 
portant ideas  and  hypotheses.  The  stimulus  produced  by  his  physico- 
chemical  researches  was  a  highly  gratifying  one  (cf.  the  special  history  of 
physical  chemistry).  In  addition  to  all  this,  he  took  a  share  in  the  editing 
of  Liebig's  Jahresbericht  and  of  the  Anncden  der  Chemie  und  Pharmacie, 
besides  writing  his  Lehrbuch  der  theoretischen  Chemie  (1863)  for  the  Graham- 
Otto  series.  Immediately  after  Kopp's  death,  A.  W.  von  Hofmann  de- 
livered in  his  memory  one  of  those  biographical  addresses,  which  none 
could  do  so  well  as  he.  (See  Ber.,  1892,  Ref.  p.  505). 


376  THE  MODERN  CHEMICAL  PERIOD  CHAP. 

The  advances  made  in  this  direction  fall  to  be  treated  of  in 
the  special  history  of  physical  chemistry.  Here  it  need 
merely  be  said  that  it  has  come  to  be  more  and  more  recog- 
nised, especially  within  the  last  thirty  or  forty  years,  that 
chemical  investigation  runs  the  danger  of  becoming  one-sided 
without  a  free  use  of  physical  aids.  Chemists  have  perceived 
the  necessity  for  their  science  of  physico-chemical  methods. 

Thus,  what  a  wide  application  have  not  the  latter  found 
in  the  estimation  of  the  molecular  weights  of  elements  and 
compounds !  The  determination  of  vapour  density  has 
proved  its  value  for  the  attainment  of  this  end  in  an  infinite 
number  of  cases,  and  has  been  applied  to  the  solution  of  the 
most  important  theoretical  questions ;  thus,  of  recent  years 
the  saturation-capacities  of  numerous  elements,  e.g.  tungsten, 
vanadium,  beryllium,  thorium,  germanium,  aluminium,  etc., 
have  been  established  by  the  aid  of  this  process.  The  con- 
stant relations  between  the  molecular  weight  of  a  substance 
on  the  one  hand  and  its  point  of  solidification  and  the  vapour 
pressure  of  its  solutions  on  the  other,  first  definitely  formu- 
lated by  Kaoult  and  de  Coppet  (independently),  have  rapidly 
become  the  basis  of  easily-carried-out  methods  for  the  deter- 
mination of  molecular  weights.  In  fact,  the  investigations 
on  the  physical  behaviour  of  solutions — e.g.  their  electric  con- 
ductivity, osmotic  pressure,  vapour  pressure,  etc. — have 
during  the  last  few  years  enlarged  the  boundaries  of  general 
chemistry  to  an  extent  that  was  undreamt  of. 

We  need  only  refer  here  to  the  deduction  of  the  atomic 
weights  of  elements  from  their  specific  heats,  and  of  equiva- 
lents from  the  electrolysis  of  salts,  in  order  to  emphasise  the 
significance  of  physical  methods  for  establishing  the  most 
important  of  chemical  values.  Of  the  wealth  of  work  which 
has  been  accomplished  in  the  branches  of  spectrum  analysis, 
thermo-chemistry,  electro-chemistry,  upon  the  doctrine  of 
affinity  ( VerwandtschaftsleJire),  and  in  the  investigation  of 
the  connection  between  optical  properties  and  chemical  con- 
stitution, an  account  will  be  given  in  the  special  section. 
The  position  of  chemistry  to  physics  will  there  come  out 
more  clearly  than  is  possible  at  this  point.  Thanks  to  the 


v  OSTWALD  AND  VAN  'T  HOFF  377 

labours  of  Ostwald,1  van  't  Hoff2  and  others,  the  physical 
conceptions  of  the  transformation  and  conservation  of 
energy  have  now  come  into  general  application  in  chemistry 
also,  more  especially  in  the  explanation  of  affinity-pheno- 
mena. 

Similarly,  the  relation  of  chemistry  to  other  branches  of 
science  can  only  be  properly  represented  by  going  into  details. 
This  will  show  itself  in  the  case  of  mineralogy,  which  is 

1  Wilhelm  Ostwald,  born  at  Riga  on  September  2nd,  1853,  taught  first 
in  the  University  of  Dorpat,  then  at  the  Riga  Polytechnic  from  1880  to 
1887,  and  has  since  the  latter  year  held  the  chair  of  Physical  Chemistry  in 
the  University  of  Leipzig.     The  amount  of  work  which  he  has  already  done 
in  this  branch  of  the  science  has  been  very  great,  the  subject  having  been 
immensely  advanced  both  by  his  researches  and  his  writings.     Up  to  1887 
his  papers  were  published  in  the  Journal  fur  praktische  Chemie,  but  since 
that  date  in  the  Zeitschrift  fur  physikalische  Chemie,  which  he  himself 
and  van  't  Hoff  started,  and  continue  to  edit.     Some  papers  have  been 
brought  out  in  the  Ber.  der  Konigl.  Sachs  Gesellschaft  der  Wissenschaften. 
His  large  Lehrbuch  der  allgemeinen  Chemie  (2  vols.),  of  which  two  editions 
have  so  far  appeared,  and  also  his  Grundriss  der  allgemeinen  Chemie,  have 
found  universal  acceptance.     Part  of  the  former  has  been  translated  into 
English  by  M.  M.  P.  Muir,  while  the  English  edition  of  the  latter  is  by 
James  Walker.  His  Hand-  und  Hilfsbuch  zur  A  usfuhrung  physiko-chemischer 
Messungen  (1893),   also  translated  into  English  by  Walker,  is  of  great 
practical  value.     A  smaller  work,  Die  wissenschaftlichen  Grundlagen  der 
Analytischen  Chemie  (1894),  is  also  highly  original— in  fact,  the  only  book 
of  its  kind  ;  it  too  has  been  translated  (by  G.  McGowan).     Lastly,  his  large 
work,  Elektrochemie,  ihre  Geschichte  und  Lehre  (1896),  is  thoroughly  apposite 
at  the  present  time,  and  deserves  special  mention.     In  addition  to  these, 
Ostwald's  Klassiker  der  exakten  Wissenschaften,  being  reprints  of  classical 
scientific  papers,  have  made  these  accessible  to  any  reader  of  German  (the 
"Alembic "  series  is  their  analogue  in  this  country). 

2  J.  H.  van  't  Hoff  was  born  at  Rotterdam  on  the  8th  of  August,  1852. 
After  studying  at  Delft,  Leyden,  Bonn,  Paris  and  Utrecht,  he  became  a 
lecturer  in  the  Veterinary  College  of   the  last-named  city  in  1876,  and 
Professor  of  Chemistry  in  the  University  of  Amsterdam  in  1878  ;  in  1896 
he  was  made  an  honorary  professor  of  the  University  of  Berlin.     Van  't 
Hoff  has  shown  himself  to  be  a  man  of  singularly  original  mind,  and  his 
work  will  be  frequently  referred  to  in  the  special  sections  of  this  book.     In 
addition  to  his  numerous  papers  contributed  to  scientific  journals  and  his 
share  in  editing  the  Zeitschrift  fur  physikalische  Chemie  along  with  Ostwald, 
he  is  the  author  of  the  following  works  :— La  Chimie  dans  VEspace  (1875) ; 
Dix  Anne'es    dans    VHistoire  d'une   Theorie  (1887) ;   Ansichten  uber  die 
organische  Chemie  (1878-1881)  ("  Views  upon  Organic  Chemistry  ") ;  Etudes 
de  Dynamique   chimique   (1884);  and  Lois  de  V  fiquilibre  chimique  (1885). 


378  THE  MODERN  CHEMICAL  PERIOD  CHAP,  v 

united  to  inorganic  chemistry  by  a  firm  band.  The  con- 
nection with  physiology  is  proved  by  the  fact  that  organic 
chemistry  is  absolutely  necessary  to  the  latter.  In  fact,  to 
whatever  quarter  we  turn  in  the  extensive  range  of  the 
natural  sciences,  we  find  that  chemistry  is  to  most  of  them 
an  indispensable  aid,  and  to  the  remaining  ones  useful 
in  a  high  degree.  The  history  of  the  different  branches  of 
natural  science  shows  in  the  most  distinct  manner  this  con- 
stantly recurring  reciprocal  action. 


SPECIAL  HISTORY  OF  THE  VARIOUS  BRANCHES 

OF  CHEMISTRY  FROM  LAVOISIER  TO  THE 

PRESENT  DAY 


CHAPTER    VI 

SPECIAL    HISTORY    OF   THE   VARIOUS    BRANCHES 

OF  CHEMISTRY  FROM   LAVOISIER  TO  THE 

PRESENT  DAY 

Introduction. — In  the  general  history  of  this  period  the 
attempt  has  been  made  to  set  forth  the  more  important 
ideas  and  points  of  view  which  have  led  to  the  development 
of  particular  doctrines,  and  at  the  same  time  to  give  a 
description  of  the  latter.  In  conjunction  with  these 
objective  discussions,  short  sketches  have  been  appended  of 
the  lives  of  those  investigators  who  have  exercised  a 
permanent  effect  upon  the  development  of  chemistry,  and 
more  especially  upon  the  systematising  of  it. 

Up  to  the  fourth  or  fifth  decade  of  our  century,  the 
leading  chemists  were  able  to  cover  in  their  work  a  very 
large*  part  of  the  ground  which  was  either  occupied  by 
chemistry  itself,  or  in  which  it  was  an  indispensable  aid  ;  we 
have  but  to  think  of  Berzelius  and  Liebig,  and  of  their  labours, 
which  were  at  the  same  time  both  pioneering  and  funda- 
mental, in  analytical  and  pure  chemistry,  physiology  and 
mineralogy.  But  during  the  later  decades  the  tremendous 
growth  of  the  science  has  necessitated  a  large  subdivision  of 
work,  indeed  an  almost  one-sided  specialisation  in  research. 
This  may  even  give  rise  to  the  apprehension  that,  with 
increasing  specialisation,  a  danger  is  run  of  losing  sight  of 
general  guiding  principles.  Organic  chemistry  may  serve  as 
an  example  of  this  subdivision  of  labour,  particular  branches 
of  it  having  been  opened  up  which  in  themselves  alone  are 
sufficient  to  absorb  the  full  energies  of  large  numbers  of 


382  HISTORY  OF  THE  VARIOUS  BRANCHES  OF  CHEMISTRY  CHAP. 


capable  investigators  ;  take  for  instance  the  chemistry  of  the 
aromatic  compounds,  and  more  especially  that  portion  of  it 
comprising  the  pyridine  and  quinoline  bases  and  similar 
compounds  richer  in  nitrogen.  The  new  journals  unmistak- 
ably reflect  this  subdivision  of  labour.  While  formerly 
Poggendorffs  Annalen,  Liebig's  Annalen,  the  Journal  fur 
praktische  Chemie,  the  Journal  of  the  Chemical  Society,  &c., 
contained  papers  in  every  branch  of  the  science,  we  now  find 
journals  exclusively  devoted  to  inorganic,  physical,  physio- 
logical, agricultural,  pharmaceutical  and  applied  chemistry. 

In  the  following  special  section  of  this  book,  which  deals 
with  the  different  branches  of  chemistry  in  succession,  such 
facts  and  investigations  are  recorded  as  have  contributed  to 
the  true  advancement  of  the  various  parts  of  our  science. 

The  history  of  analytical  chemistry  is  placed  first  in 
order,  since  the  latter  is  an  indispensable  aid  to  all  chemical 
research,  and  therefore  to  all  the  other  branches  of  chemistry, 
pure  as  well  as  applied.  Following  it  comes  the  history  of 
pure  chemistry,  which  divides  itself  into  inorganic  and 
organic,  although  there  is  no  natural  partition  between  the 
two.  Next  to  pure  chemistry  stands  physical,  with  whose 
history  that  of  the  doctrine  of  affinity  (  Verwandtschaftslehre) 
is  intimately  bound  up.  It  was  the  endeavour  to  discover 
relations  between  chemical  and  physical  properties  which  led 
to  the  establishment  of  this  important  middle  kingdom 
between  chemistry  and  physics. 

That  chemistry  is  necessary  for  the  healthy  growth  of  other 
sciences  is  particularly  shown  in  the  history  of  mineralogical, 
physiological  and  pathological  chemistry,  which  are  also 
treated  here  according  to  their  historical  development.  The 
opening  up  and  cultivation  of  the  fields  of  mineralogy, 
geology,  and  vegetable  and  animal  physiology  are  indis- 
solubly  connected  with  the  names  of  such  distinguished 
chemists  as  Lavoisier,  Vauquelin,  Klaproth,  Berzelius  and 
Liebig. 

Last  in  order  comes  the  history  of  technical  chemistry, 
which  illustrates  in  the  most  brilliant  manner  the  influence 
of  chemical  research  upon  the  development  of  chemical 


vi    HISTORY  OF  THE  VARIOUS  BRANCHES  OF  CHEMISTRY    383 

industry.  To  give  a  historical  account  of  the  penetration 
of  the  scientific  spirit  and  of  chemical  methods  into  this 
branch,  a  branch  hitherto  worked  empirically,  is  a  task 
which  repays  itself  in  a  special  degree. 

As  an  appendix  to  the  whole,  an  attempt  has  been  made 
to  picture  within  short  space  the  growth  which  chemical 
instruction  has  undergone  in  the  course  of  the  present 
century. 


384  HISTORY  OF  ANALYTICAL  CHEMISTRY  CHAP. 


HISTORY  OF  ANALYTICAL  CHEMISTRY  IN  RECENT  TIMES. 

The  main  problem  of  chemistry,  the  investigation  of  the 
true  composition  of  compounds,  necessarily  carries  along  with 
itself  the  constant  endeavour  to  elaborate  and  perfect  the 
means  employed  for  arriving  at  this  end.  Thus,  since  the 
time  of  Lavoisier,  analytical  methods,  which  constitute  the 
tools  for  the  solution  of  this  problem,  have  been  and  are 
being  improved  in  a  continuously  increasing  degree. 


Qualitative  Analysis  of  Inorganic  Substances. 

Even  so  early  as  during  the  phlogistic  period,  men  like 
Boyle,  Hoffmann,  Marggraf,  and  especially  Scheele  and 
Bergman,  had  collected  together  a  large  number  of  valuable 
observations,  by  means  of  which  it  was  possible  to  test  with 
certainty  for  many  inorganic  compounds.  In  a  knowledge 
of  the  various  reagents  which  served  for  this  end  Bergman 
was  the  furthest  advanced ;  he  it  was  who  first  attempted  to 
publish  a  system  for  the  qualitative  analysis  of  substances  in 
the  wet  way  (cf.  p.  143).  From  the  analytical  course  of  pro- 
cedure which  he  proposed,  and  which  had  for  its  aim  the 
separation  of  different  substances  into  particular  groups  by 
converting  them  into  insoluble  compounds,  the  methods  in 
use  at  the  present  day  have  developed  themselves.  To  the 
perfecting  of  this  (previous  to  the  time  of  Berzelius,  who  also 
worked  with  the  greatest  effect  in  this  branch),  Lampadius 
and  Gottling  materially  contributed ;  the  former  published 
in  1801  his  Handbuchzw  chemischen  Analyse  der  Mineralien 
("  Text-Book  on  the  Chemical  Analysis  of  Minerals  "),  and 
the  latter  his  Practische  Anleitung  zur  prufenden  und  zer- 
legenden  CJiemie  ("  Practical  Introduction  to  the  Chemistry 
of  Testing  and  Decomposing"), — works  in  which  the  best 
analytical  methods  of  the  time  are  given. 


vi  DEVELOPMENT  OF  QUALITATIVE  ANALYSIS  385 

The  many  and  varied  observations  collected  by  Klaproth, 
Vauquelin,  Berzelius,  Stromeyer  and  others  in  their  analyses 
of  minerals  further  helped  to  strengthen  the  qualitative 
method.  The  text-books  of  analytical  chemistry  by  C.  H. 
Pfaff  and  Heinrich  Rose  enable  us  to  judge  of  the  rate  of  its 
continuous  development ;  alongside  of  the  latter  of  those 
works,  which  became  justly  celebrated  and  ran  through 
numerous  editions,  must  be  placed  the  well-known  and 
highly  prized  Anleitung  zur  qualitativen  chemischen  Analyse 
("  Introduction  to  Qualitative  Chemical  Analysis  ")  of  R. 
Fresenius,  which  covers  the  whole  ground  on  the  subject, 
and  is  a  marvel  of  thoroughness  and  accuracy.  The  pro- 
cedure in  qualitative  analysis  has  undergone  no  material 
alterations  since  Fresenius  first  published  his  book,  and  is 
treated  of  in  numerous  works,  most  of  which  are  intended  to 
instruct  the  beginner  in  its  principles.1 

Qualitative  analysis  in  the  dry  way  has  been  perfected 
by  the  more  general  and  improved  use  of  the  blowpipe, 
which  Berzelius2  and  Hausmann  were  in  a  high  degree 
instrumental  in  introducing  into  chemistry  and  mineralogy. 
This  valuable  little  instrument  has  been  employed  with  the 
greatest  success,  more  especially  for  the  detection  of  the  con- 
stituents of  minerals ;  Bunsen's  important  flame-reactions 3 
have,  however,  enabled  it  to  be  dispensed  with  in  a  number 
of  cases.  Among  the  most  noteworthy  of  dry  reactions  are 
the  spectroscopic,  which,  thanks  to  their  extraordinary 
delicacy  and  certainty,  serve  for  the  detection  of  the  most 
minute  quantities  of  many  metals,  and  have  rendered  pos- 
sible the  discovery  of  a  number  of  new  elements.  Spectrum 
analysis,  through  which  we  are  able  to  deduce  the  nature  of 
a  glowing  substance  by  examining  the  light  which  it  emits, 

1  Out  of  the  large  number  of   such   text-books,  those   of  Beilstein, 
Birnbaum,  Classen,  Drechsel,  Geuther,  Meclicus,  Rammelsberg,  Stadeler- 
Kolbe,Will,  Odling,  Harcourt  and  Madan,  Thorpe,  Clowes,  and  Jones  may 
be  mentioned. 

2  His  pamphlet,     Ueber    die    Anwendung    des    Ltithrohrs    ("On    the 
Application  of  the  Blowpipe  "),  was  first  published  in  1820;  cf.  also  p.  144. 

3  Ann.  Chem.,  vol.  cxxxviii.  p.  257  ;  also  in  a  much  extended  form  as 
a  separate  pamphlet. 

C    C 


386  HISTORY  OF  ANALYTICAL  CHEMISTRY  CHAP. 

was  founded  by  the  masterly  researches  of  Bunsen  and 
Kirch  off;1  Talbot,  Miller,  Swan  and  others  had  before  this 
investigated  the  spectra  of  coloured  flames,  without  however 
applying  their  results  with  a  definite  aim  to  the  analysis  of 
substances.  The  first  proposal  to  utilise  the  different  flame 
colourations  for  distinguishing  potash  from  soda  salts  was  made 
long  ago  by  Marggraf2 

Quantitative  Analysis  of  Inorganic  Substance*. 

The  accurate  investigation  of  the  behaviour  of  bases,  acids 
and  salts  towards  different  reagents,  especially  towards  such 
as  yield  with  them  either  sparingly  soluble  or  insoluble 
precipitates,  constituted  the  basis  of  the  gravimetric  estima- 
tion of  individual  substances.  Before  the  time  of  Lavoisier 
few  attempts  had  been  made  at  quantitative  analysis,  but 
the  path  which  it  was  bound  to  follow  had  been  already 
clearly  indicated  by  Bergman ;  for  he  was  the  first  to 
enunciate  the  principle  of  converting  the  substance  to  be 
analysed  into  a  convenient  form  of  known  composition,  and 
then  deducing  from  the  weight  of  the  compound  thus  pre- 
cipitated or  otherwise  obtained  that  of  the  substance  in 
question.  At  that  date  chemists  either  already  knew  or 
became  acquainted  with  the  precipitation  of  silver  solutions 
by  hydrochloric  acid,  of  solutions  of  lime  salts  by  oxalic  or 
sulphuric  acid,  of  lead  salts  by  liver  of  sulphur  or  sulphuric 
acid,  and  many  similar  reactions.  It  was  Klaproth  who 
taught  the  ignition  of  precipitates  before  weighing  them,  in 
those  cases  where  they  did  not  suffer  decomposition  through 
this  procedure,  and  he  also  co-operated  largely  with  Vauquelin 
in  developing  the  quantitative  analysis  of  minerals.  The 
observations  of  both  of  these  chemists,  especially  of  Klaproth 
(who  directed  his  efforts  to  ascertaining  correctly  the  com- 
position of  those  compounds  into  which  the  constituents  of 
the  substances  to  be  analysed  were  usually  transformed), 

1  Pof/g.  Ann.,  vol.  ex.  p.  161. 

2  Cf.  p.  143.   It  has  been  already  mentioned  that  Scheele  made  the  same 
observation. 


vi  DEVELOPMENT  OF  QUANTITATIVE  ANALYSIS  387 


attained  to  a  fairly  high  degree  of  accuracy ;  and  this  also 
applies  to  the  analyses  of  salts  carried  out  by  Wenzel  at  an 
earlier  date,  although  to  these  hardly  any  attention  had  been 
paid.  Richter's  endeavours  to  establish  the  quantitative 
composition  of  salts,  and  the  success  which  followed  them, 
have  been  sufficiently  described  in  the  general  history  of  this 
period  ;  in  spite  of  the  fact  that  his  analyses  were  not  par- 
ticularly accurate,  he  understood  how  to  draw  important 
and  correct  deductions  from  them. 

Lavoisier,  who  had  from  the  outset  of  his  scientific  career 
clearly  grasped  the  importance  of  proportions  by  weight,  and 
with  this  of  quantitative  analysis,  examined  more  par- 
ticularly the  composition  of  oxygen  compounds,  Thus  he 
established  with  tolerable  correctness  (for  example)  the 
relation  of  carbon  to  oxygen  in  carbonic  acid,  but  only 
approximated  to  that  of  hydrogen  to  oxygen  in  water,  and 
was  wide  of  the  mark  in  the  relation  of  phosphorus  to  oxygen 
in  phosphoric  acid.  He  also  sought  to  apply  the  values  which 
he  had  obtained  for  the  composition  of  water  and  carbonic 
acid  to  establishing  the  composition  of  organic  substances. 
Lavoisier,  however,  introduced  no  original  methods  for  the 
quantitative  analysis  of  inorganic  bodies  and  their  separation 
from  one  another. 

Proust  effected  infinitely  more  in  this  branch,  his 
analytical  work  leading,  as  has  already  been  stated,  to  a 
clear  grasp  of  the  law  of  constant  proportions,  and  of  the 
alteration  by  definite  increments  in  combining  proportions. 
Quantitative  analysis  was  also  strengthened  and  extended  by 
the  establishment  of  stochiometry  (which  found  its  perfect 
support  in  Dalton's  atomic  theory),  since  a  check  upon  the 
results  obtained  was  thereby  rendered  possible. 

Endeavours  were  at  that  time  mainly  directed  to  the 
determination  of  the  relative  atomic  or,  to  speak  more 
correctly,  combining  weights.  The  splendid  results  obtained 
by  Berzelius  from  his  pioneering  labours  in  this  direction 
have  already  been  detailed.  He  devised  a  large  number  of 
new  gravimetric  methods  of  estimation,  and  tested  those 
already  in  use  for  the  separation  of  substances,  working  out 

c  c  2 


HISTORY  OF  ANALYTICAL  CHEMISTRY  CHAP. 


better  modes  for  attaining  to  this  end.  His  researches  on 
the  composition  of  chemical  compounds  embraced  every 
element  which  was  at  all  well  known.  Berzelius,  far  more 
than  any  other  man,  developed  the  principles  by  which 
atomic  weights  could  be  established ;  and  the  degree  of 
accuracy  at  which  he  arrived  in  his  analyses  is  seen  from 
the  tables  of  atomic  weights  published  by  him  after  the 
year  1818  (cf.  pp.  218  and  224). 

The  great  task  of  determining  the  atomic  weights — the 
constants  of  the  atomic  theory — with  the  utmost  possible 
accuracy,  has  led  ever  since  the  time  of  Berzelius  to  the 
development  and  improvement  of  gravimetric  methods ;  for, 
what  is  required  here  is  to  establish  by  various  procedures  an 
unalterable  value  for  each  element,  a  value  which  shall  form 
the  basis  for  the  composition  of  all  the  compounds  of  that 
element.  The  efforts  and  speculations  to  round  off  these 
numerical  values  in  accordance  with  Prout's  hypothesis  were 
replaced  by  exact  quantitative  determinations.  Among  the 
latter  the  researches  of  Dumas,  Erdmann  and  Marchand, 
Marignac,  and  Stas  deserve  special  mention.1 

The  systematic  development  of  quantitative  analysis  was 
thus  mainly  promoted  by  the  investigation  of  mineral  sub- 
stances, since  the  chief  requirement  here  was  to  find  out 
modes  for  separating  their  constituents  from  one  another. 
After  the  valuable  preparatory  labours  of  Bergman  (with 
whom,  for  instance,  the  fusion  of  silicates  with  alkaline 
carbonates  originated),  and  the  researches  of  Klaproth, 
Vauquelin  and  Proust,  it  was  Berzelius  who  worked  out 
entirely  new  methods ;  we  need  only  recall  here  his  plan  of 
decomposing  silicates  by  hydrofluoric  acid,  and  that  of 
separating  metals  from  one  another  by  means  of  chlorine. 
He  it  was,  too,  who  first  employed  far  smaller  quantities 
of  substances  than  the  large  amounts  recommended  by 
Klaproth,  who  introduced  the  spirit-lamp  which  bears  his 
name,  thus  facilitating  the  ignition  of  precipitates,  and  who 
taught  how  to  incinerate  the  filter-paper  and  determine  its 

1  Cf.  Lothar  Meyer  and  K.  Seubert,  Die  Atomgeivichte  der  Elemente 
,(1883). 


vi          BERZELIUS,  H.  ROSE,  WOHLER,  FRESENIUS,  ETC.        389 

ash ;  in  fact,  to  speak  generally,  he  was  the  first  to  make  use 
of  a  large  number  of  practical  contrivances  and  apparatus 
for  the  carrying  out  of  analyses.  His  greater  analytical 
researches,  such  as  those  upon  platinum  ores  and  on  mineral 
waters,  show  Berzelius  as  a  master  in  devising  good  methods 
of  separation. 

His  pupils,  more  especially  H.  Rose1  and  Fr.  Wohler, 
worked  up  the  valuable  experiences  of  their  teacher,  extended 
them  largely  by  wide-reaching  observations  of  their  own, 
and  made  analytical  methods  public  property  by  their 
admirable  books  2  on  the  analysis  of  minerals  and  chemical 
bodies  generally.  R.  Fresenius,3  until  quite  lately  our  chief 
exponent  of  analytical  chemistry,  likewise  perfected  and 
strengthened  this  branch  of  the  science  in  all  its  various 
parts  by  collating  and  sifting  the  methods  formerly  in  use, 

1  The  brothers  Heinrich  and  Gustav  Rose  belonged  to  a  Berlin  family 
which  produced  distinguished  chemists   for   several    generations.     Their 
grandfather,  Valentin  Rose  the  elder,  a  pupil  of  Marggraf,  and  also  their 
father,    Valentin    Rose    the   younger,    were   energetic  pharmacists    and 
chemists.     Gustav  Rose,  who  was  born  in  1798  and  died  in  1873  as  Pro- 
fessor of  Mineralogy  at  Berlin,  was  only  connected  with  chemistry  in- 
directly.    But  Heinrich  Rose  (born  1795,  died  1864)  was  an  ardent  exponent 
of  the  science,  and  enriched  it  by  most  important  work,  especially  in 
analytical  and  inorganic  chemistry  (see    special   history  of  these).      He 
reciprocated  fully  and   truly  the  affection  of   his  master  Berzelius,  as   is 
vividly  shown  in  the  beautiful  memorial  address  which  he  gave  of  the 
latter  (cf.  p.  209).     In  his  two-volume  Handbuch  der  analytischen  Chemie, 
H.    Rose  collected  together  in  a  masterly  manner  the  best  of  the  then 
known  methods  in  qualitive  and  quantitative  analysis. 

2  H.  Rose,  AiLsfdhrliches  Handbuch  der  ancdytischen  Chemie  ("  Detailed 
Textbook  of  Analytical  Chemistry") ;  Fr.  Wohler,  Die  Mineralanalyse  in 
Beispielen  ("  The  Analysis  of  Minerals,  illustrated  by  Examples  "). 

3  C.  Remigius  Fresenius,  born  at  Frankfurt  on  the  Maine  in  1818,  became 
assistant  to  Liebig  in  Giessen  in  1841,  and  assistant  professor  there  in  1843  ; 
in  1848  he  opened  his  now  universally  known  laboratory  at  Wiesbaden,  which 
has  undergone  a  continuous  extension,  and  been  frequented  by  students 
from  all  parts.     His  text-books  of  chemical  analysis,  of  which  the  Qualitative 
appeared  for  the  first  time  in  1841,  and  the  Quantitative  in  1846,  have  had 
an  extraordinarily  wide  distribution,  as  their  numerous  editions  in  different 
languages  prove.     Every  one  who  has  used  them  systematically  cannot  fail 
to  have  been  struck  with  their  wonderful  accuracy  and  at  the  same  time 
great  breadth.     Fresenius  died  suddenly,  while  still  in  active  work,  on  June 
llth,  1897. 


390  HISTORY  OF  ANALYTICAL  CHEMISTRY  CHAP. 

and,  more  especially,  by  working  out  many  new  ones.  By 
founding  in  1862  the  Zeitschrift  fur  analytische  Chemie, 
Fresenius  supplied  a  centre-point  for  the  analytical  branch 
of  the  science.  It  is  impossible  to  enumerate  here  what 
other  workers  (among  whom  Liebig,  Thomson,  Stromeyer, 
Bunsen,  Turner,  Scheerer,  Rammelsberg,  Gibbs,  Blomstrand, 
R.  Schneider,  Pelouze,  and  Winkler  may  be  named)  have 
done  for  the  development  of  quantitative  analysis. 

We  may,  however,  mention  here  that  the  galvanic 
current  has  of  late  years  been  called  in  to  the  service  of 
analysis,  the  quantitative  determination  of  many  metals 
being  rendered  possible  by  its  aid.  After  Gibbs  (in  186  5) 
had  worked  out  the  electrolytic  determination  of  copper, 
and  other  chemists  had  subsequently  busied  themselves  with 
similar  investigations,  Alexander  Classen1  rendered  special 
service  in  the  development  of  the  method.  This  branch  of 
chemical  analysis  is  of  the  utmost  use  for  metallurgy,  in 
which  even  already  it  forms  an  important  part  of  docimacy. 
The  latter,  originally  confined  to  the  determination  of  the 
noble  metals  in  the  dry  way,  has  expanded  into  an  important 
branch  of  analytical  chemistry,  particularly  sine  e  C.  Fr. 
Plattner's  comprehensive  researches  and  the  publication  of 
his  classical  book,  Die  Probierkunst  mit  dem  Lothrohr  Leip- 
zig, 1835),  ("Docimacy  by  Means  of  the  Blowpipe").2 

Volumetric  Analysis. 

Besides  the  analytical  methods  which  have  been  touched 
upon  above,'  volumetric  ones  have  become  developed  within 
the  last  seventy  years  or  so;  these  are  of  great  use,  par- 
ticularly in  manufacturing  chemistry  and  pharmacy,  and 
have  therefore  the  widest  application.  Since  in  volumetric 

1  Cf.  his  work,  Handbuch  der  chemischen  Analyse  durch  Electrolyse 
("Text-Book  of  Chemical  Analysis  by  means  of  Electrolysis").  In  the 
Berichte,  vol.  xxvii.,  p.  2060,  there  is  a  further  paper  by  Classen,  in  which  he 
gives  very  useful  data,  regarding  particular  points  in  electrolytic  determina- 
tions. 

2  Cf.  Kerl's  Metallische  ProUerkunst  ("Metallic  Docimacy"),  (1886); 
Balling's  Probierkunde  ("Docimacy"),  (1879),  and  his  Fortschritte  im  Pro- 
bierwesen  ("Advances  in  Docimacy"),  (1877). 


vi  VOLUMETRIC  ANALYSIS  391 

methods  no  weighing  is  required  after  the  standard  solutions 
have  once  been  made  up,  and  the  wished-for  results  are  arrived 
at  simply  by  reading  off  the  amounts  of  the  solutions  used, 
much  time  is  saved  and  at  the  same  time  sufficient  accuracy 
attained,  the  requirements  of  technical  analysis  (more 
particularly)  being  thereby  met. 

Gay-Lussac  must  be  regarded  as  the  man  who  introduced 
volumetric  methods  into  the  science,  and  rendered  them 
available  for  chemical  industries;  before  him  various  in- 
vestigators— of  whom  Descroizille  and  Vauquelin  must  be 
specially  mentioned — had  attempted  to  apply  such  methods 
empirically  to  comparative  determinations  of  chemical 
products. 

Gay-Lussac  worked  out  with  the  greatest  care  his 
methods  of  chlwimetry  (1824),  of  alkalimetry  (1828),  and  of 
the  determination  of  chlorine  and  silver  (1832).1  Notwith- 
standing the  excellent  results  which  those  volumetric  pro- 
cesses yielded,  they  received  but  slowly  the  recognition  which 
was  their  due.  The  application  of  permanganate  of  potash 
to  the  estimation  of  iron  by  Margueritte  in  1846,  and,  more 
particularly,  Bunsen's  process  with  equivalent  solutions  of 
iodine  and  sulphurous  acid  (by  means  of  which  a  large 
number  of  different  substances  can  be  accurately  estimated 
by  one  and  the  same  reaction)  are  landmarks  in  the  history 
of  "  titrimetry,"  which  soon  after  this  began  to  rank  alongside 
of  gravimetric  analysis.  One  of  the  chief  promoters  of 
volumetric  methods  was  Friedrich  Mohr,  who  both  improved 
old  processes  and  introduced  many  new  ones ;  he  rendered 
great  service  by  the  publication  of  his  Lehrbuch  der  chemischen 
Titrirmethode  ("Text -book  of  Volumetric  Analysis").2 
Among  the  many  investigators  who  have  enriched  this 
branch  of  the  science  we  may  name  J.  Volhard,3  who  devised 
an  exact  method  (the  determination  of  silver  by  means  of 
ammonium  sulphocyanide)  capable  of  numerous  applications. 

1  Cf.  his  Instruction  sur  Ufissai  des  Matieres  par  la  Vote  Humide  (1833). 

2  The  latest  edition  of  this  is  edited  by  A.Classen.     Among  other  valu- 
able books  on  volumetric  analysis  are  those  of  Cl.  Winkler,  Medicus,  and 
Fleischer  in  Germany,  and  of  Sutton  in  England. 

3  Cf.  Ann.  Chem.  vol.  cxc.  p.  1,  et  seq. 


392  HISTORY  OF  ANALYTICAL  CHEMISTRY  CHAP. 

In  organic  chemistry  volumetric  analysis  has  not  been 
able  to  take  up  anything  like  the  same  position  that  it  has 
in  inorganic,  the  methods  as  yet  introduced  being  wanting 
in  precision.  Among  the  most  noteworthy  processes  here 
are  Fehling's  for  the  determination  of  grape  sugar,  Liebig's 
for  that  of  urea,  the  volumetric  estimation  of  phenol  by 
means  of  bromine,1  etc. 

Development  of  Methods  of  Gas  Analysis. 

The  history  of  the  volumetric  analysis  of  liquids 
naturally  leads  us  on  to  a  description  of  the  efforts  to 
analyse  gases  qualitatively  and  quantitatively.  It  is  worthy 
of  note  here  that  the  systematic  qualitative  analysis  of  these 
was  much  later  of  being  developed  than  their  quantitative 
determination.  The  first  attempts  in  this  direction  were 
made  by  Scheele,  Priestley,  Cavendish  and  Lavoisier,  to  be 
followed  by  those  of  Dalton,  Gay-Lussac,  Henry,  de  Saussure 
and  others  at  the  beginning  of  this  century.  But  it  has 
been  through  Bunsen's  fundamental  researches2  that  the 
quantitative  analysis  of  gases  has  been  brought  to  such 
perfection  that  those  methods  which  depend  upon  the 
absorption  or  combustion  of  the  gas  under  investigation  are 
among  the  most  exact  of  our  science,  having  required  but 
trifling  modifications  since  he  first  published  them. 

In  addition  to  Bunsen's  methods,  others  have  been 
worked  out  with  a  special  view  to  technical  gas  analysis; 
although  the  same  as  the  former  in  their  main  principle, 
these  allow  of  determining  the  composition  of  the  so-called 
industrial  gases  by  the  aid  of  simple  apparatus  within  a 
short  time,  and  with  sufficient  accuracy.  Cl.  Winkler  and 

1  Cf.   Degener,  Journ.  pr.   Chem.  (2),  vol.  xvii.   p.  390 ;  Koppeschaar, 
Ztschr.  Ann.  Chem.  for  1876,  p.  223. 

-  These  researches  of  Bunsen's  began  about  the  year  1838,  and  were 
Collected  together  under  the  title  of  Gasometrische  Methoden  (Brunswick, 
1857  ;  second  edition,  1877) ;  this  most  valuable  work  was  translated  into 
English  by  Roscoe.  Kolbe,  in  the  HandworterbucJi  (under  the  article 
"  Eudiometer  "),  had  already  brought  the  details  of  these  methods  before- 
public  notice  so  early  as  1843. 


vi  DEVELOPMENT  OF  ORGANIC  ANALYSIS  393 

W.  Hempel  have  rendered  great  service  here  by  materially 
simplifying  the  apparatus  required  and  by  generalising 
methods.1  Among  others  who  have  done  good  work  in  gas 
analysis  of  recent  years  may  be  mentioned  Frankland, 
Pettersson,  Orsat,  Coquillon  and  Bunte. 

The  qualitative  analysis  of  gases  has  only  quite  recently 
been  developed  scientifically,  and  here,  too,  Winkler  has 
laboured  with  success ;  by  the  systematised  use  of  absorptives 
he  has  divided  gases  into  different  groups,  thus  proceeding 
in  the  same  manner  as  is  done  in  the  analysis  of  substances 
in  the  wet  way.  The  recent  work  by  Ramsay  and  his  col- 
laborators in  connection  with  the  two  new  gases  argon  and 
helium  must  also  be  referred  to  here.  The  improvements  in 
methods  of  gas  analysis  have  drawn  the  attention  of  chemists 
to  gases  in  an  increasing  degree,  and  have  proved  of  the 
greatest  benefit  to  theoretical  as  well  as  to  practical  chemistry. 

The  Analysis  of  Organic  Substances. 

The  fact  that  animal  and  vegetable  products,  which 
came  to  be  comprised  under  the  term  "  organic,"  always 
contain  carbon,  usually  hydrogen  and  oxygen,  and  frequently 
also  nitrogen,  was — as  already  stated — a  long  time  of  being 
recognised.  Here  again  we  have  a  brilliant  proof  of 
Lavoisier's  far-seeing  glance,  and  of  his  power  of  drawing 
general  conclusions  from  detached  observations.  It  had 
indeed  struck  previous  experimenters,  e.g.  van  Helmont  and 
Boyle,  that  spirit  of  wine,  wax,  etc.,  form  water  when 
burned,  while  Priestley  perceived  that  carbonic  acid  was 
produced  at  the  same  time;  in  fact  Scheele  stated  in  1777 
that  both  of  these  compounds  were  products  of  the  com- 
bustion of  oils.  After  it  had  become  clear  to  Lavoisier  that 
carbonic  acid  consisted  of  carbon  and  oxygen,  and  water  of 

1  Cf.  Clemens  Winkler,  Anleitung  zur  chemischen  Untersuchung  der  In- 
dustriegase,  Freiberg,  1876-77  ("  Methods  for  the  Chemical  Examination  of 
Industrial  Gases  ") ;  the  same  author's  Lehrbuch  der  technischen  Gasanalyse 
second  edition,  1892),  ("Text-Book  of  Technical  Gas  Analysis") ;  and  W. 
Hempel's  Neue  Methode  zur  Analyse  der  Gase  (Brunswick,  1880),  and  Gas- 
anaJytische  Methoden(189Q). 


394  HISTORY  OF  ANALYTICAL  CHEMISTRY  CHAP. 

hydrogen  and  oxygen,  he  went  on  to  deduce  the  composition 
of  organic  substances.  Thus,  with  the  discovery  of  what 
were  the  most  important  elements  of  organic  compounds, 
the  first  step  in  qualitative  organic  analysis  was  reached. 
The  principle  of  arriving  at  the  constituents  of  organic 
bodies  by  transforming  them  into  compounds  of  known 
composition  has  ever  since  been  retained.  In  the  same  way 
nitrogen,  which  Lavoisier  himself  recognised  as  being 
peculiar  to  many  organic  substances,1  was  detected  by  con- 
version either  into  ammonia  (Berthollet)  or  sodium  cyanide 
(Lassaigne),  and  phosphorus  and  sulphur  by  conversion  into 
phosphoric  and  sulphuric  acids  respectively. 

While  the  elementary  constituents  of  organic  compounds 
are  thus  easily  arrived  at,  the  detection  of  the  compounds 
.alongside  of  one  another  is  a  much  harder  task ;  only  small 
beginnings  have  as  yet  been  made  at  a  systematic  course 
•of  qualitative  organic  analysis,  in  the  sense  in  which  we 
apply  the  term  to  inorganic.2  In  many  instances  one 
has  to  depend  upon  isolated  characteristic  reactions  of 
organic  substances,  e.g.  in  the  investigation  of  colouring 
matters,  alkaloids,  protein  substances,  carbohydrates,  etc. 

The  quantitative  analysis  of  organic  compounds  has 
developed  itself  from  the  observation  that  carbonic  acid  and 
water  are  products  of  their  combustion ;  the  method,  there- 
fore, which  served  for  the  detection  of  the  constituents 
carbon  and  hydrogen  was\applied  in  a  perfected  form  to 
their  exact  determination.  Lavoisier  was  again  the  first 
to  point  out  the  right  path  here ;  he  attempted  to  burn  the 
organic  compound  in  question  -completely,  and  to  estimate 
the  resulting  carbonic  acid  and  water — the  latter  indirectly. 
In  order  to  be  able  to  deduce  the  amounts  of  carbon  and 
hydrogen  themselves,  it  was  necessary  to  know  the  quanti- 
tative composition  both  of  carbonic  acid  and  of  water ;  but, 
since  the  values  obtained  by  him  for  these  were  not  very 

1  How  uncertain  the  tests  for  the  elements  of  organic  substances  were 
at  the  beginning  of  this  century  is  shown  by  the  fact  that  Proust  believed 
he  had  proved  nitrogen  to  be  an  integral  constituent  of  acetic  acid. 

-  Cf.  Barfoed's  Qualitative  Analyse  organischer  Ktirper  ;  also  Allen's 
Commercial  Organic  Analysis. 


vi  METHODS  OF  ORGANIC  ANALYSIS  395 

accurate,1  it  was  impossible  that  the  results  of  his  analysis 
of  an  organic  substance  could  turn  out  correct,  and  this  all 
the  more  from  the  method  of  the  combustion  being  such  as 
to  involve  errors  in  itself. 

Lavoisier's  process  for  easily  combustible  substances  was 
to  burn  a  weighed  quantity  in  a  known  volume  of  oxygen, 
contained  in  a  receiver  closed  by  mercury,  and  then  to  esti- 
mate the  resulting  carbonic  acid  together  with  the  residual 
oxygen;  from  these  data  the  amounts  of  carbon,  hydrogen 
and  oxygen  were  calculated.  For  difficultly  combustible 
bodies,  such  as  sugars  and  resins,  Lavoisier  (as  we  now  learn 
from  his  recently  published  journals) 2  used,  instead  of  the 
free  gas,  substances  which  yield  up  their  oxygen  upon  being 
heated,  e.g.  red  oxide  of  mercury  and  red  lead ;  he  thus 
adopted  the  plan  which  later  on  became  the  standard  one, 
while  at  the  same  time  he  estimated  the  weight  of  the 
carbonic  acid  produced  by  this  oxidation  by  means  of  a 
solution  of  caustic  potash. 

Had  those  researches  become  known  at  that  time,  organic 
analysis  would  doubtless  have  undergone  a  more  rapid 
development  than  it  actually  did.  The  efforts  of  Dalton 
(1803),  Saussure  (about  1800-1803),  and  Thenard  (1807)  to 
arrive  at  the  composition  of  organic  compounds  by  exploding 
their  vapours  with  oxygen  and  analysing  the  resulting  pro- 
ducts would  never  have  been  made.  Gay-Lussac  and 
Thenard3  endeavoured  to  solve  this  problem  in  a  more 
felicitous  manner  by  the  combustion  of  the  organic  substance 
with  chlorate  of  potash ;  from  the  amounts  of  resulting 
carbonic  acid  and  residual  oxygen  they  calculated  the  per- 
centage of  carbon,  hydrogen  and  oxygen  in  the  substance 
under  analysis,  and  attained  in  some  instances  at  any  rate  to 

1  The  following  are  Lavoisier's  figures  for  the  composition  of  carbonic 
acid  and  water  (the  correct  values  being  given  in  brackets) : — 

/-Carbon  28  percent.  (27 '2) 

Carbonic  Acid  .  .  .  |  Oxygen  72  „  (72'8) 
Water-  {  Hydrogen  13' 1  „  (11-1) 

I  Oxygen       86 '9      „         (88  -9) 

2  (Euvres  de  Lavoisier,  vol.  iii.  p.  773. 

3  Recherches  Physico-chimiques,  vol.  ii.  p.  265. 


396  HISTORY  OF  ANALYTICAL  CHEMISTRY  CHAP, 


serviceable  results.  Compared  with  this  method,  uncertain 
as  it  was  on  account  of  the  violence  of  the  combustion,  the 
one  followed  by  Berzelius  showed  a  marked  improvement ; l 
for  here  the  organic  substance,  mixed  with  chlorate  of  potash 
and  sodium  chloride,  was  gradually  decomposed,  and  then 
not  merely  the  resulting  carbonic  acid  but  also  the  water 
determined  directly — the  latter  by  means  of  chloride  of 
calcium.  A  further  advance  was  made  by  Gay-Lussac 2  in 
1815,  in  the  use  of  black  oxide  of  copper  as  the  oxidising 
agent.  But  the  rounding  off  of  the  whole  procedure  by  the 
introduction  of  a  convenient  bulb-shaped  apparatus,  and  the 
consequent  simplification  of  the  manipulation  required,  is  due 
to  Liebig.3  Since  his  time  elementary  organic  analysis  has  not 
altered  essentially,  the  modifications  introduced  having  had 
reference  to  the  combustion  furnaces  (now  heated  by  gas 
instead  of  charcoal),  and  to  the  mode  of  carrying  out  the 
combustion ;  with  respect  to  the  latter,  Koppfer's  method  4 
must  be  mentioned,  a  method  by  which  the  substance  is 
burnt  in  a  current  of  oxygen,  with  the  aid  of  platinum  black. 
Plans  for  the  combustion  of  organic  compounds  in  a  stream 
of  oxygen  had  before  this  been  proposed  by  Hess,  Erdmann 
and  Marchand,  Wohler,  and  others. 

Quite  recently  W.  Hempel5  has  succeeded  in  carrying 
out  the  combustion  of  organic  compounds  in  oxygen  under 
pressure  (i.e.  in  autoclaves),  and  has  perfected  the  method  so 
much  that  it  is  now  possible  to  make  accurate  determina- 
tions, not  merely  of  carbon  and  hydrogen,  but  also  of 
nitrogen  and  sulphur.  Messinger  6  has  also  been  successful 
lately  in  estimating  the  carbon  of  organic  compounds  in  the 
wet  way,  by  oxidation  with  permanganate  of  potash. 

The  exact  determination  of  nitrogen  in  organic  com- 
pounds first  became  possible  after  Dumas 7  (in  1830)  had 

1  Annals  of  Philosophy,  vol.  iv.  pp.  330,  401. 

2  Schweigger' 's  Journ.,  vol.  xvi.  p.  16  ;  vol.  xviii.  p.  369. 

3  Pogg.  Ann.,  vol.  xxi.  p.  1 ;  also  his  pamphlet,  Anleituny  zur  Analyse 
organischer  Korper  ("The  Analysis  of  Organic  Compounds"). 

4  Ber.,  vol.  ix.  p.  1377.  5  Ber.,  vol.  xxx.  p.  202. 

6  Ber.,  vol.  xxiii.  p.  2756. 

7  Ann.  Chim.  Phys.,  vol.  xliv.  pp.  133,  172;  vol.  xlvii.  p.  196. 


vi  FORENSIC  AND  HYGIENIC  CHEMISTRY  397 


devised  his  admirable  method.  For  many  nitrogenous 
organic  substances  the  process  worked  out  by  Will  and 
Varrentrapp1  at  a  later  date,  in  which  the  nitrogen  is 
estimated  as  ammonia,  has  proved  itself  thoroughly  appli- 
cable. In  addition  to  these,  the  recent  method  of  Kjeldahl2 
must  be  mentioned,  a  method  which  is  found  to  be  of  great 
use,  especially  in  agricultural-chemical  analyses  (for  the 
determination  of  protein).  Since  this  method  was  devised, 
it  has  been  materially  improved. 

Only  a  bare  reference  can  be  made  here  to  the  numerous 
methods  for  the  determination  of  the  halogens,  sulphur,  phos- 
phorus and  other  elements '  which  occur  less  often  in  organic 
substances.3 

Analytical  methods  have  found  the  most  extended  appli- 
cation in  judicial  cases,  in  questions  of  hygiene,  and  in  all 
the  branches  of  technical  chemistry;  a  short  historical 
account  of  them  must  therefore  be  given  here.  Forensic 
chemistry,  whose  task  consists  in  the  absolutely  certain 
detection  of  poisons,  could  only  reach  its  present  stage  of 
development  after  analytical  methods  in  general  had  been 
placed  upon  a  firm  basis.  Fresenius  admirably  depicted  in 
1844  the  position  and  duties  of  a  forensic  chemist  at  that 
date.4  The  great  progress  which  has  since  been  made  in 
the  precision  with  which  poisons  can  be  detected  is  dis- 
tinctly seen  by  an  examination  of  the  various  works  on 
legal-chemical  analysis  which  have  been  published  from  time 
to  time.5  In  addition  to  Fresenius — J.  and  R.  Otto,  Marsh, 
Graham,  Stas,  Mohr,  Husemann,  Dragendorff  and  others 
have  rendered  special  service  in  working  out  good  methods. 
The  Stas-Otto  process  for  the  detection  of  individual  alkaloids 

1  Ann.  Chem.,  vol.  xxxix.  p.  257. 

2  Ztsc.hr.  anal.  Chem.,  vol.  xxii.  p.  366  ;  vol.  xxiv.  p.  199. 

3  Cf.  Fresenius'  Quantitative  Analysis. 

4  Ann.  Chem.,  vol.  xlix.  p.  275. 

5  Reference  may  be  made  here  to  Otto's  Anleitung  zur  Ausmittehmg  der 
Gifte("  Methods  for  the  Detection  of  Poisons  "),  sixth  edition,  1884  ;  Christi- 
son's  Treatise  on  Poisons  in  relation  to  Medical  Jurisprudence,  Physiology, 
and  the  Practice  of  Physic,  which  was  first  published  in  1829  and  which  ran 
through  numerous  editions ;  and  to  Stevenson's  new  edition  of  Taylor 
on  Poisons. 


398  HISTORY  OF  ANALYTICAL  CHEMISTRY  CHAP. 

has  proved  of  great  importance  for  the  development  of  this 
branch ;  since  the  discovery  of  the  ptomaines,1  it  has  had  to 
undergo  some  modifications,  as  the  resemblance  between 
many  of  the  reactions  of  these  products  and  those  of  the 
vegetable  alkaloids  may  easily  give  rise  to  most  serious 
mistakes,  and  in  fact  has  already  done  so. 

A  special  branch  of  chemical  analysis  is  represented  by 
the  methods  of  testing  and  investigating  used  in  industrial 
chemistry.  Since  these  have  for  their  aim  the  attainment 
of  a  fair  degree  of  accuracy  within  the  shortest  possible  time,, 
volumetric  processes  are  the  ones  most  frequently  employed. 
The  rapidity  with  which  acids  and  alkalies,  chlorine,  many 
metals  in  their  compounds,  and  other  substances  can  be 
determined  quantitatively  by  volumetric  methods,  has 
rendered  it  possible  to  exercise  a  continuous  control  over 
manufacturing  processes, — with  what  benefit  need  not  be 
said. 

A  glance  into  the  most  recent  text-books  of  technico- 
chemical  methods  2  is  sufficient  to  convince  us  of  the  high 
degree  of  development  to  which  these  have  been  brought. 
A  large  number  of  processes  have  in  the  course  of  time 
been  devised,  more  especially  for  the  commercial  analysis  of 
organic  products ;  we  may  recall  here  the  estimation  of  sugar 
by  polarisation,  the  rapid  determination  of  the  heating  power 
of  combustibles,  the  valuation  of  coal-tar  dyes  by  test-coloura- 
tions and  by  specific  reactions,  and  the  estimation  of  alcohol, 
fat,  albumen  and  starch,  not  to  speak  of  numerous  other 
methods  which  have  become  standard  ones  in  chemical  tech- 
nology. 

For  technical  chemists,  and  in  an  equal  degree  for 
medical  officers  of  health,  the  development  of  the  analysis 
of  articles  of  food  and  drink  has  been  of  the  first  importance  ; 
the  pharmacist,  too,  frequently  finds  it  needful  to  apply  the 
methods  which  have  approved  themselves  in  such  cases.  By 
their  aid  the  analyst  is  able  to  decide  whether  the  products 

1  Cf.  the  special  history  of  physiological  chemistry. 

2  The  works  of  Post  (Brunswick,  1882),  of  Bockmann  (Berlin,  1888),  and 
of  Sutton  may  be  mentioned  here. 


vi  ANALYSIS  OF  FOODS  AND  DRINKS  399 

are  what  they  pretend  to  be,  or,  if  they  should  be  adulterated, 
the  nature  of  such  adulteration.  The  reader  has  but  to  recall 
to  mind  the  quickly  executed  methods  for  analysing  milk, 
butter,  meal,  feeding-stuffs,  wine,  beer,  coffee,  etc.,  in  order 
to  appreciate  the  true  blessing  of  these  applied  analyses. 
The  gradual  but  continuous  work  of  numerous  investigators 
has  rendered  possible  the  development,  within  a  comparatively 
short  period  of  time,  of  the  processes  which  have  become 
standard  ones  here.  We  cannot  now  refer  in  detail  to  the 
services  rendered  by  single  individuals  in  this  branch.  Full 
particulars  are  to  be  found  in  Konig's  admirable  work,  Die 
menschlichen  Nahrungs-  und  Genussmittel  (Berlin,  1883),  a  book 
which  furnishes  a  complete  review  of  the  subject,  and  at  the 
same  time  indicates  clearly  the  share  which  different  chemists 
have  taken  in  it.  The  Bibliothek  fur  Nahrungsmittel- 
chemiker,  edited  by  F.  Ephraim,  and  published  by  Barth  of 
Leipzig,  forms  an  excellent  summary  of  works  of  this  class ; 
and  in  C.  Fliigge's  Lehrl)uch  der  hygienisclien  Untersuchungs- 
methoden  ("Text-Book  of  Methods  of  Hygienic  Research") 
hygiene  possesses  a  splendid  guide  for  such  investigations. 
Among  English  books  on  the  subject,  A.  Wynter  Blyth's 
Foods,  their  Composition  and  Analysis  (4th  Edition,  1896) 
must  also  be  mentioned. 

As  the  importance  of  the  analysis  of  foods  and  drinks 
became  by  degrees  better  appreciated,  the  greater  refinement 
of  analytical  methods  increased  the  need  for  laboratories  in 
which  such  investigations  should  be  carried  on  continuously. 
The  long-cherished  wish  of  many  that  the  State1  should  con- 
trol these  laboratories  and  their  chemists  has  not  yet  been 
realised.  But  the  importance  which  is  now  attached  to  this 
branch  of  analysis  is  shown  in  the  increasing  provision  made 
by  universities  and  technical  colleges  for  instruction  in  it. 
Marked  advances  have  also  been  made  in  this  direction  in 
Great  Britain  of  late  years,  thanks  to  a  considerable  extent 
to  the  care  and  vigilance  exercised  by  the  Institute  of 
Chemistry. 

1  The  German  Government  is  referred  to  here. 


400  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP. 


THE  PROGRESS  IN  PURE  CHEMISTRY  FROM  LAVOISIER 
TO  THE  PRESENT  TIME 

While  only  the  main  currents  of  chemistry  have  been 
depicted  in  the  general  history  of  this  period,  we  have  now 
in  the  following  section  to  pick  out,  from  the  endless  number 
of  experimental  researches  made,  those  which  have  materially 
contributed  to  the  extension  of  our  chemical  knowledge. 
This  rich  material  is  divided  between  the  two  great  branches 
of  inorganic  and  organic  chemistry.  If  we  glance  back  over 
the  labours  of  the  last  fifty  years,  we  recognise  that  organic 
chemistry  has  gone  on  preponderating  more  and  more  over 
inorganic ;  the  former  has  outgrown  the  latter, — its  elder 
sister.  But  inorganic  remains  nevertheless  the  basis  upon 
which  organic  chemistry  rests,  although  on  the  other  hand 
we  must  not  forget  that  important  fundamental  principles 
and  doctrines  (e.g.  the  doctrine  of  valency  and  the  true 
conception  of  chemical  constitution)  were  first  fruitfully 
developed  in  the  domain  of  organic  chemistry. 


SPECIAL  HISTORY  OF -INORGANIC  CHEMISTRY 

The  great  revolution  in  ideas  with  regard  to  the  consti- 
tution of  many  substances,  which  was  brought  about  by 
Lavoisier's  system,  has  been  described  in  detail  in  the 
special  part  of  this  book.  A  large  number  of  bodies,  which 
had  formerly  been  looked  upon  as  compound,  belonged  from 
thenceforth  to  the  elements ;  while  many,  which  had  been 
considered  simple  substances,  were  either  proved  to  be  com- 
pounds, or  were  to  be  regarded  as  such  from  their  analogy 
to  others.  The  clarifying  process  which  Lavoisier  had  com- 
menced went  vigorously  forward,  thanks  to  the  efforts  of 
Klaproth,  Vauquelin,  Proust,  Davy,  Berzelius,  Gay-Lussac 
and  others.  But  we  are  still  far  from  having  attained  to  a 
clear  and  definite  knowledge  of  the  nature  of  all  the 


vi  THE  DISCOVERY  OF  PARTICULAR  ELEMENTS  401 

-elements  and  their  compounds,  new  elements  being  from 
time  to  time  added  to  the  long  series  already  known;  and 
the  relations  of  those  to  the  others  have  to  be  established 
by  an  accurate  study  of  their  chemical  behaviour.  Emphasis 
has  already  been  laid  upon  the  great  effect  which  the  so- 
called  periodic  system  has  had  on  the  classification  of  the 
elements. 

Historical  Notes  on   the  Discovery  of  Elements — The  Deter- 
mination of  their  Atomic  Weights. 

The  knowledge  of  the  elements  was  increased  to  a  very 
large  extent  soon  after  the  death  of  Lavoisier  (who  had  not 
himself  discovered  any),  and  this  exactly  in  proportion  as 
methods  of  chemical  analysis  became  more  perfect.  While 
Lavoisier  was  able  to  bring  forward  twenty-six  elements  in 
his  Traite1  de  Chimie,  the  number  of  those  whose  existence 
has  been  definitely  established  has  now  extended  to  at  least 
sixty-eight. 

To  the  aid  which  was  rendered  by  improved  methods  of 
analysis,  other  means  specially  effective  for  the  discovery 
of  new  elements  soon  came  to  be  added.  Among  these  was 
the  application  of  the  galvanic  current  to  the  decomposition 
of  chemical  substances,  the  production  of  higher  tempera- 
tures, and  the  breaking  up  of  haloid  compounds  by  means  of 
the  alkali  metals;  in  spectrum  analysis,  lastly,  chemistry 
now  possesses  an  invaluable  instrument,  which  has  already  led 
to  the  isolation  of  a  number  of  most  important  elements. 

After  the  establishment  of  the  atomic  theory,  the  original 
task  of  acquiring  a  qualitative  knowledge  of  a  new  element 
and  its  compounds  was  supplemented  by  the  further  and 
higher  one  of  determining  its  relative  atomic  weight,  and 
explaining,  on  the  basis  of  the  atomic  hypothesis,  the  con- 
stitution of  the  compounds  which  it  forms  with  other 
elements. 

For  oxygen,  which  Lavoisier  was  the  first  to  claim  as  a 
simple  substance,  the  elementary  nature  was  always  after- 
wards maintained.  Nitrogen,  on  the  other  hand,  was 

D   D 


402  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP, 

temporarily  regarded  by  Davy  (1808)  and  by  Berzelius l 
(1810)  as  a  compound  of  an  unknown  element,  nitricum 
with  oxygen,  because  only  in  this  way  could  they  find  an 
explanation  of  the  basic  properties  of  ammonia,  in  which 
they  likewise  assumed  the  presence  of  oxygen.  Davy  was 
the  first  of  the  two  to  give  up  this  hypothesis  in  favour  of 
the  simpler  one  of  nitrogen  being  an  element,  Berzelius  only 
doing  this  in  1820.  Pure  nitrogen  has  just  been  subjected 
to  a  searching  process  of  diffusion  by  Ramsay  and  Travers,2 
but  the  various  fractions  were  found  to  have  precisely  the 
same  density,  i.e.  the  gas  showed  perfect  homogeneity. 

Hydrogen,  too,  was  for  a  short  time  looked  upon  by 
Berzelius  as  being  compound,  i.e.  as  containing  oxygen,  and 
the  same  applied  to  sulphur  and  phosphorus,  in  which  the 
presence  of  hydrogen  and  oxygen,  besides  that  of  other 
unknown  elements,  was  conjectured.  That  many  dis* 
tinguished  chemists  were  inclined  to  regard  chlorine  as  the 
oxide  of  a  hypothetical  element  has  been  already  detailed, 
as  has  also  the  profound  influence  which  this  view  exercised 
upon  important  sections  of  chemistry.3  Before  this  idea  had 
been  abandoned  by  Berzelius,  iodine — discovered  by  Courtois 
in  1811  in  the  ashes  of  marine  plants — was  shown  to  be  an 
element  analogous  to  chlorine,  through  the  splendid  re- 
searches of  Davy,  and  still  more  those  of  Gay-Lussac.4 
Bromine,  isolated  by  Balard5  in  1826  from  the  mother 
liquor  of  sea-salt,  and  the  investigation  of  which  was  materially 
promoted  by  Lowig's6  labours  in  1829,  completed  for  a 

1  Cf.  Kopp,  Gesch.  der  Chemie,  vol.  iii.  p.  218. 

2  Proc.  E.  S.  for  1898.  3  Cf.  p.  239. 

4  Ann.  de  Chimie,  vol.  xci.  p.  5  (1813). 

5  Ann.  Chim.  Phys.  (2),  vol.  xxxii.  p.  337. 

6  K.  J.  Lowig  was  born  in  1803,  and  died  at  Breslau  in  1890.    After  study- 
ing under  L.  Gmelin  and  Mitscherlich,  he  taught  at  Zurich  from  1833  to  1853, 
in  which  year  he  became  Professor  of  Chemistry  at  Breslau,  continuing  in 
that  post  until  1889.      Among  his  publications  we  may  name  : — Das  Brom 
und  seine  chemischen  Verhdltnisse  (1829),  and  his  Lehrbuch  der  Chemie  (1832 ;. 
second  edition,  1849),  which  latter  was  long  in  use  as  a  text-book.     His  most 
important  experimental  work  is  referred  to  in  the  special  history  of  the  sub- 
ject, while  a  memorial  notice  by  Landolt  is  to  be  found  in  the  Berichte,  vol. 
xxiii.  Ref.  p.  905. 


vi  DETERMINATION  OF  ATOMIC  WEIGHTS  403 

long  time  the  group  of  Berzelius'  "  halogen "  elements. 
Fluorine,  the  acid  constituent  of  hydrofluoric  acid,  has  only 
quite  recently  been  isolated  for  the  first  time  by  Moissan  l 
(in  spite  of  a  great  many  previous  attempts 2),  by  the  electro- 
lysis of  hydrofluoric  acid  under  suitable  conditions,  and,  as 
was  to  be  expected,  has  been  found  to  be  a  substance  of  the 
most  violent  chemical  energy.  Those  researches  of  Moissan 
upon  fluorine  are  among  the  most  noteworthy  in  inorganic 
chemistry  in  modern  times. 

The  atomic  weights,  those  all-important  constants,  have 
been  determined  with  great  accuracy  for  the  non-metallic 
elements  already  spoken  of,  and  by  various  different  methods 
in  each  case.  For  oxygen,  nitrogen,  chlorine,  bromine  and 
iodine,  the  classical  researches  of  Marignac  3  and  Stas  4  have 
yielded  the  most  reliable  values ;  for  fluorine  the  determina- 
tion by  Christensen 5  may  be  regarded  as  the  most  exact. 
Of  late  years  the  ratio  between  the  atomic  weights  of 
hydrogen  and  oxygen  has  been  re-determined  by  a  number 
of  different  methods,  with  the  result  that  a  value  has  been 
arrived  at  which  is  slightly  different  from  that  hitherto 
accepted,6  viz.,  1*0032: 16.  It  is  hardly  necessary  to  say 
that  the  fixing  of  this  constant  deserves  all  the  attention 
which  has  been  paid  to  it;  among  the  recent  minute  ex- 
perimental researches  on  the  subject,  those  of  Cooke  and 
Richards,  Scott,  Rayleigh,  Morley,  Keiser  and  Noyes  may  be 
mentioned. 

Tellurium  (chemically  analogous  to  sulphur,  which  had 
been  known  for  so  long,  but  had  first  been  characterised  as 
an  element  by  Lavoisier)  was  discovered  by  Miiller  von 
Reichenstein  in  1782,  and  investigated  by  Klaproth 7  in 

1  Ibid.  (6),  vol.  xii.  p.  472  (1887) ;  Comptes  Rendus,  vol.  cut.  p.  861 ;  and 
Ann.  Chim.  Phys.  (6),  vol.  xxiv.  p.  224. 

2  Cf.  Gore,  Phil.  Trans,  for  1869,  p.  173. 

3  Cf.  Ann.  Chem.,  vol.  xliv.  p.  1 ;  vol.  lix.  p.  284 ;  vol.  Ix.  p.  180. 

4  Untersuchungen  ilber  die  Gesetze  der  chemischen  Proportionen  (Leipzig, 
1887)  ("  Researches  upon  the  Laws  of  Chemical  Proportions  "). 

5  Journ.  pr.  Chem.  (2),  vol.  xxxv.  p.  541. 

6  Cf.   Ostwald,  Lehrbuch  der  Allgemeinen  Chemie,  vol.  i.  p.  43  et  seq. 
(second  edition).     Ostwald  holds  that  the  atomic  weights  should  be  referred 
to  oxygen,  taken  as  16,  instead  of  to  hydrogen  taken  as  1. 

7  CreWsAnn.,  vol.  i.  p.  91. 

D  D   2 


404  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP. 

1798;  an  intimate  knowledge  of  it  was  however  first 
arrived  at  through  the  investigations  of  Berzelius.1  Selenium 
was  discovered  by  Berzelius 2  in  1817,  and,  along  with  its 
more  important  compounds,  examined  by  him  in  the  most 
thorough  manner.  The  atomic  weights  of  the  two  last 
elements  have  only  recently  been  settled,  after  great  fluc- 
tuations, that  of  selenium3  being  now  taken  as  79*07  and 
that  of  tellurium4  as  125,  previous  determinations  having, 
for  a  long  time  caused  the  wrong  value  127-128  to  be 
ascribed  to  the  latter.  This  higher  value  was,  no  doubt,  due 
to  the  difficulty  of  freeing  tellurium  from  other  elements  of 
higher  atomic  weight.  Since  the  work  of  Stas  on  the  sub- 
ject, the  number  31*98  for  sulphur  has  been  accepted  as 
firmly  established. 

The  discovery  of  the  analogues  of  nitrogen, — phosphorus, 
arsenic  and  antimony,  to  which  bismuth  may  be  added, 
took  place  a  long  time  ago ;  but  it  is  only  of  late  years 
that  they,  and  more  especially  their  compounds,  have  been 
accurately  investigated.5  For  phosphorus,  the  correct  atomic 
weight  arrived  at  by  Berzelius  was  confirmed  by  Dumas 
{who  found  the  value  31*02);  similarly  his  atomic  weight 
for  arsenic  (75)  was  corroborated  by  Pelouze  and  Dumas. 
But  on  the  other  hand  R.  Schneider  and  Cooke  have 
proved,  by  their  researches,  that  the  value  assumed  by 
Berzelius  for  antimony  was  much  too  high. 

Boron  was  discovered  simultaneously  and  independently 
by  Gay-Lussac6  and  Davy,7  both  of  whom  isolated  it 
from  boracic  acid,  which  already  Lavoisier  had  regarded  as 
the  oxide  of  an  unknown  element.  Guided  by  a  similar 
view,  Berzelius  succeeded  in  1 8 1 0  in  discovering  the  element 

1  Pogg.  Ann.,  vol.  xxxii.  p.  28. 

2  Schweigger's  Journ. ,  vol.  xxiii.  pp.  309,  430. 

3  Eckmann  u.  Petterson,  Ber.,  vol.  ix.  p.  1210. 

4  Brauner,  Ber. ,  vol.    xvi.  p.  3055 ;  Brauner  has  more  recently  found 
a  higher  value  than  this,  but  he  concludes  from  his  experiments  that,  in 
those  cases  where  the  value  obtained  is  greater  than  125,  this  is  due  to  the 
presence  of  some  foreign  substance  (which  has  not  yet  been  isolated)  in  the 
tellurium  (cf.  Ztschr.  Phys.  Chem.,vol.  iv.  p.  344). 

5  Cf .  Thorpe  and  Tutton,  Journ.  Chem.  Soc. ,  vol.  Ivii.  p.  545. 

6  Recherches  Phys.  Chim.,vol.  i.  p.  276. 

7  Phil.  Trans,  for  1809,  p.  75. 


vi  ALLOTROPIC  MODIFICATIONS  OF  ELEMENTS  405 

combined  with  oxygen  in  silica,  although  he  was  only  able 
to  prepare  silicium  pure  for  the  first  time  in  1823  by  the 
action  of  potassium  on  potassium  silico-fluoride ; 1  with  this 
he  devised  an  important  method  for  the  isolation  of  various 
elements. 

The  definite  knowledge  that  diamond  and  graphite  are 
modifications  of  the  element  carbon  belongs  to  the  beginning 
of  the  new  period ;  in  addition  to  the  researches  of  Lavoisier 
in  1773  and  those  of  Tennant  in  1796,  the  proof  furnished 
by  Mackenzie — that  equal  parts  by  weight  of  graphite, 
charcoal  and  diamond  yield  equal  amounts  of  carbonic  acid 
on  combustion — was  of  special  importance  for  the  recog- 
nition of  the  similar  chemical  nature  of  the  three  substances. 

The  phenomenon  of  allotropy,  the  term  applied  by 
Berzelius  to  the  existence  of  one  and  the  same  substance  in 
different  modifications,  has  been  observed  with  especial 
frequency  among  the  non-metals.  The  oldest  example  of 
it  was  that  offered  by  carbon,  whose  allotropic  forms  show 
the  greatest  conceivable  differences  among  each  other; 
experiments  are  still  being  made  on  these  different  modifica- 
tions, more  especially  on  the  conversion  of  amorphous  carbon 
into  diamond, — 2  a  feat  which  has  been  accomplished  by 
Moissan.  The  most  remarkable  case  of  it,  however,  is 
afforded  by  the  conversion  of  ordinary  oxygen  into  the 
chemically  active  ozone,  which  was  discovered  by  Schonbein,a 
although  van  Marum  had  a  long  time  previously  (in  178  5) 
called  attention  to  the  peculiar  change  produced  in  oxygen 
by  the  electric  spark.  The  beautiful  investigations  of 
Schonbein,  Marignac  and  de  la  Rive  established  the 
substantial  identity  of  ozone  and  oxygen,  while  those  of 
Andrews 4  and,  more  especially,  of  Soret 6  proved  that  the 

1  Pogg.  Ann.,  vol.  i.  p.  165. 

2  Cf.  Moissan,  Comptes  Rendus,  vol.  cxvi.  p.  218. 

3  Pogg.  Ann.  vol.  1.  p.  616  (1840). 

4  Phil.   Trans,  for  1856,  p.  1  ;  or  Ann.  Chem.,  vol.  xcvii.  p.  371.     An- 
drews and  Tait,  Phil.  Trans,  for  1861,  p.  113 ;  or  Pogg.  Ann.,  vol.  cxii.  p. 
241. 

5  Compt.  Rend.,  vol.  Ixiv.  p.  904;  or  Ann.  Chem.,  Suppl.,  vol.  v.  p. 
148. 


406  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP. 

molecule  of  ozone  was  made  up  of  three  atoms  of  oxygen. 
Quite  recently  Shenstone  has  succeeded  in  obtaining  a  very 
much  larger  yield  of  ozone  from  oxygen  than  was  formerly 
held  to  be  possible.  Reference  must  be  made  here,  in  passing, 
to  the  remarkable  observations  of  van  't  Hoff  and  Jorissen, 
Victor  Meyer,  Engler  and  others  on  the  "  rendering  active  " 
(Activirung)  of  oxygen  by  other  substances,  such  as  the 
phosphines,  aldehydes,  etc.  It  has  been  shown  that  the  slowly 
oxydised  substance  renders  exactly  the  same  amount  of 
oxygen  active  as  it  takes  up  itself.1 

The  allotropic  modifications  of  sulphur  were  investigated 
by  Mitscherlich,  and  those  of  selenium  by  Berzelius  and, 
later,  by  Hittorff.  The  transformation  of  ordinary  yellow 
phosphorus  into  red  was  also  observed  by  Berzelius,  but 
was  first  discovered  with  certainty  by  Schrotter 2  in  1845, 
and  its  conversion  into  the  metallic  modification  by  HittorfF. 
The  discovery  of  "  black  "  sulphur,  and  of  two  further  modi- 
fications of  that  element — one  of  which  is  soluble  in  water — 
belong  to  the  present  time;3  as  does  also  that  of  a  new 
form  of  phosphorus.4  The  proof  that  boron  and  silicon, 
already  long  known  in  the  amorphous  state,  also  exist 
in  the  crystalline  form,  is  due  to  Wohler.  That  allotropic 
forms  of  metals  can  also  exist  has  been  shown  by  the 
observations  of  Carey  Lea,  E.  A.  Schneider  and  others  upon 
silver ; 5  but  there  are  still  many  points  here  which  are 
obscure.  Nevertheless,  it  remains  an  undoubted  fact  that  a 
number  of  elements,  especially  among  the  non-metals,  are 
capable  of  existing  in  more  than  one  form.  Lastly,  reference 
may  be  made  here  to  the  discovery  of  allotropic  modifications 
of  chemical  compounds,  e.g.  mercuric  sulphide  and  iodide, 
arsenic  trioxide,  etc. 

To  the  metals  which  were  regarded  as  elements  by  La- 

1  Cf.  Ztschr.  Phys.  Chem.,  vol.  xxiUp.  34  ;  vol.  xxiii.  p.  668  ;  Ber.,  vol. 
xxx.  p.  1669.  2  Pogg.  Ann.,  vol.  Ixxxi.  p.  276. 

3  Knapp,  Journ.  pr.  Chem.,  vol.  xliii.  p.  305 ;  Engel,  Gompt.  Rend.,  vol. 
cxii.  p.  866. 

4  Vernon,  Phil.  Mag.,  vol.  xxxii.  p.  365. 

6  Cf.  E.  v.  Meyer,  Journ.  pr.  Chem.  (2)  vol.  Ivi,  p.  241,  for  the  literature 
on  the  subject. 


vi  THE  METALS  OF  THE  ALKALIES  407 

voisier  many  new  ones  were  subsequently  added,  so  a  short 
account  of  the  isolation  of  these  must  be  given  here.  The 
memorable  discovery  of  potassium  and  sodium,  together 
.with  the  conjoined  discussion  upon  the  nature  of  chlorine, 
had  such  a  deep  influence  on  the  development  of  important 
chemical  doctrines,  that  it  has  already  been  referred  to  in  detail 
in  the  general  section  of  this  book.  The  relative  atomic 
weights  of  these  two  alkali  metals  were  determined  by 
Berzelius  with  fair  accuracy,  allowing  for  the  fact  that 
he  assumed  their  values  to  be  four  times  greater  than  those 
now  assigned  to  them.  Marignac,  Dumas  and  Stas  after- 
wards arrived  at  much  the  same  figures  in  their  investiga- 
tions already  referred  to. 

Lithium  was  discovered  by  Arfvedson,1  a  pupil  of 
Berzelius,  in  1 8 1 7  ;  he  found  it  to  be  a  constituent  of 
various  minerals,  e.g.  petalite,  and  recognised  its  analogy  to 
potassium  and  sodium,  but  was  unable  to  isolate  the  metal 
itself.  The  latter  was  first  properly  investigated  in  1855 
by  Bunsen  and  Matthiessen,2  who  obtained  it  by  electrolysis. 
The  red  colouration  which  its  salts  impart  to  the  spirit-of- 
wine  flame  was  noticed  by  C.  G.  Gmelin  in  1818. 

The  discovery  of  rubidium  and  caesium  3  in  lepidolite  and 
in  the  Dlirkheimer  mineral  water  by  Bunsen  and  Kirchhoff, 
by  the  aid  of  spectrum  analysis,  was  the  first  great  gain 
which  accrued  to  chemistry  from  this  new  method.  Since 
the  chemical  reactions  of  the  salts  of  these  two  alkali  metals  are 
very  similar  to  those  of  the  salts  of  potassium,  their  presence 
would  undoubtedly  have  been  overlooked  but  for  the  spec- 
troscope. Indeed,  several  years  before  the  discovery  of  caesium , 
the  careful  analyst  Plattner4  had  examined  the  mineral  pollux, 
which  is  rich  in  that  element,  and  had  been  unable  to  explain 
the  deficiency  in  the  results  of  his  analyses,  this  being  really 
due  to  his  taking  the  caesium  sulphate  present  for  a  mixture  of 
the  sulphates  of  potassium  and  sodium.  The  atomic  weights 

1  Schweigger's  Journ.,  vol.  xxii.  p.  93. 

2  Ann.  Chem.>  vol.  xciv.  p.  1U7. 

3  Pogg.  Ann.,  vol.  ex.  p.  167 ;  vol.  cxiii.  p.  337 ;  vol.  cxviii.  p.  94. 

4  Ibid.,  vol.  Ixix.  p.  443. 


408  HI&T-QRJ^^INORGANIC  CHEMISTRY  CHAP. 

of  caesium  and  rubidium  were  correctly  estimated  by  Bunsen, 
although  too  low  a  value  was  at  first  assigned  to  the  former,, 
in  consequence  of  the  supply  of  material  at  disposal  being  in- 
sufficient. The  atomic  weight  of  lithium  was  definitely  de- 
termined by  Stas  as  7*01. 

The  metals  barium,  strontium,  calcium  and  magnesium 
were  isolated  by  Davy  from  their  amalgams,  which  Seebeck 
had  been  the  first  to  prepare ;  but  for  a  long  time  previous  to 
this  baryta  and  lime  had  been  regarded  as  the  oxides  of  un- 
known metals.  Strontia  had  been  discovered  by  Klaproth 
and  Hope,  independently  of  one  another,  and  had  been  char- 
acterised as  being  similar  to  lime.  Berzelius,  Marignac  and 
Dumas  determined  the  atomic  weights  of  these  four  metals. 
Magnesium,  which  has  of  late  years  increased  in  importance 
for  manufacturing  purposes,  has  been  found  by  Clemens 
Winkler l  to  be  an  excellent  reducing  agent  for  metallic  oxides. 
His  comprehensive  researches  were  carried  out  with  the  ob- 
ject of  learning  how  the  various  metallic  oxides  comported 
themselves  to  magnesium,  and  what  capacity  the  reduced 
metal  showed  for  combining  with  hydrogen.  Space  will  not 
allow  more  than  this  brief  reference  to  the  valuable  results 
from  the  above  piece  of  work,  which  has  at  the  same  time 
added  to  our  knowledge  of  many  of  the  elements.  Kamsay 
also  found  magnesium  to  be  the  best  agent  for  taking  up  the 
nitrogen  of  the  air  in  the  preparation  of  argon. 

Beryllium,  whose  oxide  Vauquelin  had  discovered  in  1 7  9  8 
in  the  mineral  beryl,  was  first  obtained  by  Wohler 2  in  1828, 
by  acting  upon  its  chloride  with  potassium.  The  atomic 
weight  gave  rise  to  important  discussions,  since  it  remained 
for  a  long  time  uncertain  whether  this  amounted  to  twice  or 
three  times  its  equivalent  number.  The  point  was  only  de- 
cided by  the  recent  researches  of  Nilson  and  Pettersson  3  on 
the  subject,  which  proved  that  beryllium,  as  a  diatomic  ele- 
ment, possesses  the  atomic  weight  91.  Later  work  by  Kriiss 
and  Moraht  would  make  it  appear,  however,  that  this  number 
is  still  a  little  too  high. 

1  Ber.,  vol.  xxiv.  pp.  873,  1969.  2  Ibid.,  vol.  xiii.  p.  577. 

3  Journ.  pr.  Chem.  (2)   vol.  xxxiii.  p.  15. 


CADMIUM  AND 


Cadmium  was  first  observed  by  Stromeyer  in  1817,  then 
subsequently  rediscovered  by  others,  and  recognised  as  being 
similar  to  zinc  in  character ;  its  atomic  weight  has  lately  been 
redetermined  with  great  accuracy  by  Partridge.  Thallium, 
isolated  by  Crookes 1  in  1 8  6 1  from  the  selenious  mud  of  the 
sulphuric  acid  manufacture,  owes  its  discovery  to  the  character- 
istic spectrum  given  by  its  salts.  The  chemical  nature  of 
this  metal,  which  approximates  on  the  one  hand  to  lead  and  on 
the  other  to  the  metals  of  the  alkalies,  was  mainly  established 
by  Lamy,  while  Crookes  determined  its  atomic  weight. 

Aluminium  was  isolated  for  the  first  time  by  Wohler  2  in 
1827,  by  the  action  of  potassium  upon  its  chloride,  and' 
thus  the  conjecture  which  had  long  been  entertained,  that 
alumina  was  the  oxide  of  a  metal,  was  confirmed.  The 
production  of  the  metal  on  a  large  scale  from  its  abundantly 
occurring  oxide,  by  means  of  the  electric  current,  is  a  feat  of 
modern  manufacture  (see  Special  History).  The  elements  in- 
dium and  gallium,  which  together  with  aluminium  constitute 
a  family,  were  only  discovered  comparatively  recently,  the 
first-named  in  1863  by  Reich  and  Richter,3  as  a  constituent 
of  the  Freiberg  zinc  blende,  and  the  second  in  1875,  also  in 
zinc  ores,  by  Lecoq  de  Boisbaudran.4  Here  again  it  was  the 
characteristic  spectra  of  the  two  metals  which  led  to  their  dis- 
covery. Their  atomic  weights  were  determined  by  the  dis- 
coverers, and  that  of  indium  with  especial  accuracy  also  by 
Cl.  Winkler  5  and  by  Bunsen  ; 6  while  the  atomic  weight  of 
aluminium  has  been  worked  out  with  the  utmost  care  by 
Mallet.7 

The  isolation  of  the  metals  which  constitute  the  cerium  and 
yttrium  groups  has  presented  unusual  difficulties.  Although 
the  discovery  of  yttria — impure,  it  is  true,  from  admixture 
with  other  earths — was  accomplished  by  Gadolin  nearly  a 
hundred  years  ago,  and  investigators  of  the  first  rank  have 

1  Chem.  News,  vol.  iii.  p.  193.  2  Pogg.  Ann.,  vol.  xi.  p.  146. 

3  Journ.  pr.   Chem.,  vol.  Ixxxix.  p.  444;  vol.  xc.  p.  172;  vol.  xcii.  p, 
480. 

4  Comptes  Rendus,  vol.  Ixxxi.  pp.  493,  1100. 

5  Journ.  pr.  Chem.,  vol.  cii.  p.  282. 

6  Pogg.  Ann.,  vol.  cxli.  p.  28.  7  Phil.  Trans,  for  1880,  p.  1003, 


410  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP. 

busied  themselves  with  the  question,  the  chemistry  of  the 
cerium  metals  is  not  even  yet  completely  cleared  up,  and  may 
possibly  remain  unsolved  for  a  considerable  time  to  come. 
After  Klaproth  and  Berzelius  had  simultaneously  prepared 
cerium  sesquioxide  from  cerite,  and  the  latter  had  recognised 
this  as  the  oxide  of  a  metal,  Mosander  discovered  two  new 
oxides  in  crude  yttria,  the  metals  of  which — lanthanum  and 
didymium — he  isolated.  A  few  years  later  (in  1 8  4  3)  he  added 
to  these  two  others,  erbium  and  terbium,  whose  existence 
and  nature  is  not  yet  however  definitely  settled,  in  spite  of 
the  admirable  work  which  has  been  done  on  the  subject. 
This  has  given  us  a  better  knowledge  of  yttrium,  while  yttria, 
which  was  formerly  held  to  be  a  homogeneous  substance,  has 
proved  itself  a  mixture  of  the  oxides  of  various  metals,  of 
which,  however,  only  one  or  two  have  as  yet  been  isolated  ; 
witness  the  discovery  of  scandium  by  Nilson,  and  of  ytterbium 
by  Marignac.  The  most  recent  additions  to  our  knowledge  of 
the  chemistry  of  this  group  of  elements  have  been  made  by 
Krtiss,  Cl.  Winkler,  Bettendorf,  Crookes,  Brauner  and  others. 

Cobalt  and  nickel,  whose  discovery  belongs  to  a  preceding 
era  (cf.  p.  149),  have  lately  been  the  subject  of  important 
researches,  more  particularly  because  of  the  remarkable 
compounds  which  they  are  capable  of  forming  (see  p.  428). 
Winkler1  has  proved  that  Kriiss'  and  Schmidt's  view2 — 
that  another  element,  hitherto  unknown,  was  present  in 
nickel  and  cobalt  prepared  in  the  ordinary  way — is  erroneous ; 
and  he  has  also  given  us  most  careful  re-determinations  of 
their  atomic  weights. 

The  elements  molybdenum,  tungsten  and  uranium, 
which  belong  to  the  same  group  as  chromium,  were  dis- 
covered like  the  latter  itself  in  the  first  decades  of  the 
modern  period ;  but  their  investigation  is  still  being  proceeded 
with,  thanks  to  the  extraordinary  diversity  of  the  compounds 
which  they  form  with  other  elements  (see  below).  Vau- 
quelin  discovered  chromium  in  1 7  9  7  as  a  constituent  of  red 
lead  spar,  and  he  also  contributed  materially  to  a  knowledge 
of  its  compounds;  Klaproth  pointed  out  independently  at 

1  Ber.,  vol.  xxii.  p.  890.  2  Ser.,  vol.  xxii.  pp.  11  and  2026. 


yi  MOLYBDENUM,  TUNGSTEN,  URANIUM,  ETC.  411 

the  same  time  that  there  was  probably  a  new  metal  con- 
tained in  that  mineral.  The  presence  of  molybdenum  and 
tungsten  in  their  oxygen  compounds  was  foreseen  by  Scheele 
and  Bergman,  the  former  being  isolated  in  1783  by  Hjelm, 
and  the  latter  by  d'Elhujar.  Uranium,  lastly,  or  rather  an 
oxide  of  it  which  was  looked  upon  as  the  element,  was 
detected  by  Klaproth  in  1 7  9  8  as  a  principal  constituent  of 
pitchblende ;  Peligot l  was  the  first  to  correct  this  error  by 
proving  that  the  supposed  element  contained  oxygen,  and 
also  by  preparing  metallic  uranium  itself.  The  atomic 
weights  of  chromium  and  uranium,  as  determined  by  Peligot, 
have  been  corroborated  by  the  recent  estimations  of  Cl. 
Zimmermann,  Berlin,  and  especially  Meineke.  For  molyb- 
denum, a  somewhat  higher  value  than  that  obtained  by 
Berzelius  has  been  arrived  at  from  the  work  of  Dumas, 
Rammelsberg  and  others.  The  atomic  weight  found  by 
Schneider,  Marchand  and  others  for  tungsten — viz.  183*5 — 
has  maintained  its  ground. 

The  elements  which  resemble  tin  in  character — viz. 
titanium,  zirconium  and  thorium  (to  which  germanium  has 
within  the  last  few  years  been  added) — belong  practically  to 
the  chemical  history  of  this  century ;  for,  although  the  oxides 
of  titanium  and  zirconium  were  discovered  at  the  end  of  last 
century,  the  isolation  of  the  elements  themselves  was  first 
accomplished  by  Berzelius,  by  means  of  the  method  already 
mentioned — viz.  the  decomposition  of  the  double  fluorides 
with  potassium.  Berzelius2  also  discovered  thoria  (ThO2) 
and  thorium  in  1828;  the  atomic  weight  of  this  element 
was,  however,  only  definitely  established  at  a  much  later  period 
by  Nilson,3  the  value  then  obtained  by  him  being  subse- 
quently corroborated  by  the  determination  of  the  vapour 
density  of  thorium  chloride.4  Germanium,  the  youngest  at 
present  of  the  metallic  elements,  was  discovered  some  years 
ago  by  Cl.  Winkler,5  and  led  in  his  hands  to  some  admirable 

1  Ann.  Chim.  Phys.  (3),  vol.  v.  p.  5. 

2  Pogg.  Ann.y  vol.  xvi.  p.  385.  8  Ber.t  vol.  xv.  p.  2527. 
4  Nilson  u  Kriiss,  Ber.,  vol.  xx.  p.  1671. 

Clemens  Winkler,  born  in  1838,  has  held  the  Chair  of  Chemistry  at 


412  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP. 

experimental  work,1  which  threw  the  clearest  light  upon 
its  nature  and  that  of  its  compounds.  The  impulse  to  look 
for  a  new  element  was  given  him  by  the  analysis  of  a 
Freiberg  silver  ore,  which  invariably  showed  a  deficit  of  about 
7  per  cent.  This  led  to  the  surmise  that  some  substance  was 
present  for  which  the  analytical  methods  in  use  were  in- 
adequate, just  as  in  the  case  of  caesium,  already  mentioned. 
The  atomic  weight  of  germanium,  as  determined  by  Winkler, 
agrees  with  the  position  which  naturally  falls  to  this  element 
in  the  periodic  system. 

Vanadium,  tantalum  and  niobium — elements  nearly 
related  to  antimony  and  bismuth — have  only  become  well 
known  through  comparatively  recent  researches.  Vanadium, 
recognised  as  a  constituent  of  certain  lead  ores  by  del  Rio 
so  early  as  1801,  but  more  definitely  by  Sefstrom  in  1830y 
was  isolated  in  the  metallic  state  by  Roscoe2  in  1867,  who 
proved  that  the  substance  hitherto  taken  for  an  element 
really  contained  oxygen  and  nitrogen.  The  chemical  relations 
of  this  element  and  its  compounds  were  admirably  worked  out 
by  him,  and  the  atomic  weight  determined  with  certainty. 

The  investigations  of  Hatchett,  Ekeberg,  Wollaston  and 
Berzelius  on  the  minerals  columbite  and  tantalite,  in  the  two 
first  decades  of  our  century,  had  already  pointed  to  the  pre- 
sence of  the  elements  which  afterwards  received  the  names  of 
tantalum  and  niobium,  although  the  elements  themselves  had 
not  been  obtained.  Nor  did  the  work  of  H.  Rose  3  lead  either 
to  their  isolation  or  to  a  correct  knowledge  of  their  compounds, 
for  in  this  case,  too,  niobium  dioxide  (Nb202)  was  regarded 
as  the  element  itself.  It  was  the  researches  of  Blomstrand  4 

the  School  of  Mines  in  Freiberg,  Saxony,  since  1873,  having  previous  to- 
that  been  engaged  in  practical  mining  work  for  fourteen  years.  Inorganic 
and  technical  chemistry  are  indebted  to  him  for  some  most  admirable  re- 
searches, which  have  frequently  included  new  methods,  valuable  either  in 
the  laboratory  or  the  manufactory.  His  most  important  papers  are 
referred  to  in  the  special  history  of  analytical  and  of  inorganic  chemistry. 

1  Journ.  pr.  Chem.  (2),  vol.  xxxiv*  p.  177 ;  vol.  xxxvi.  p.  177. 

2  Phil.  Trans,  for  1868,  p.  1 ;  or  Ann.  Chem.,  Suppl.,  vol.  vi.  p.  86. 

3  Pogg.  Ann.,  vol.  xcix.  p.  80;  vol.  civ.  p.  432. 

4  Journ.  pr.  Chem.,  vol.  xcvii.  p.  37. 


vi  THE  PLATINUM  GROUP  OF  METALS  413 

and  of  Marignac *  which  first  furnished  definite  standpoints 
for  a  review  of  the  chemical  behaviour  of  the  two  elements 
and  their  compounds,  and  for  the  fixing  of  their  atomic 
weights. 

The  metals  of  the  platinum  group,  with  the  exception 
of  platinum  itself,2  have  all  been  discovered  during  this 
century  as  constituents  of  platinum  ores.  Platinum  was 
only  obtained  perfectly  pure  after  suitable  methods  had 
been  worked  out  for  separating  it  from  the  accompany- 
ing metals.  Its  employment  for  making  certain  kinds  of 
apparatus,  so  important  for  the  development  both  of  scien- 
tific and  of  technical  chemistry,  also  belongs  to  the  present 
period. 

Palladium  came  in  1803  under  its  present  name  into 
commerce,  as  a  new  metal,  without  its  discoverer  being 
known;  it  was  only  at  a  later  date  that  it  was  learnt 
to  have  been  isolated  by  Wollaston  from  platinum  ore.3 
The  remarkable  property  which  it  possesses  of  combining 
with  hydrogen  was  first  observed  by  Graham.4  The  discovery 
of  palladium  led  Wollaston5  on  to  that  of  another  of  the 
platinum  metals,  rhodium,  which  he  thus  named  because  of 
the  rose-red  colour  of  its  solutions.  It  was  investigated 
carefully  by  Berzelius,6  who  made  a  minute  study  of  the 
platinum  metals  generally,  and  by  C.  E.  Glaus;7  the 
separation  of  rhodium  from  other  metals  is  due  primarily  to 
Bunsen,8  and  to  Deville  and  Debray.  Tennant 9  was  the  first 
to  direct  the  attention  of  chemists  to  indium  and  osmium,  as 
two  new  metals  which  were  contained  in  the  residues  left  from 
the  solution  of  platinum  ores  ;  while  to  Deville  and  Debray 10 
we  mainly  owe  the  method  of  preparing  both  elements  (the 
heaviest  substances  as  yet  known)  pure.  Ruthenium,  lastly, 

1  Ann.  Chim.  Phys.  (4),  vol.  viii.  p.  5.  2  Cf.  p.  149. 

3  Phil.  Trans,  for  1804,  p.  428.         4  Phil.  Mag.  (4),  vol^  xxxii.  p.  516. 

5  Phil.  Trans,  for  1804,  p.  419.         6  Pogg.  Ann.,  vol.  xiii.  p.  437. 

7  Beitrdge  zur  Chemie  der  Platinmetalle  (Dorpat,  1854),  ("  Contributions 
to  the  Chemistry  of  the  Platinum  Metals  "). 

8  Ann.  Chem.,  vol.  cxlvi.  p.  265. 

9  Phil.  Trans,  for  1804,  p.  411. 

10  Comptes  Rendus,  vol.  Ixxxi.  p.  839  ;  vol.  Ixxxii.  p.  1076. 


414  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP, 

was  likewise  discovered  in  platinum  ores,  as  well  as  in 
osmiridium,  by  Glaus,1  who  has  further  given  us  most  of  our 
knowledge  of  this  element  and  its  compounds,  together  with 
its  atomic  weight.  Debray  2  also  investigated  ruthenium  and 
its  oxygen  compounds  comparatively  recently. 

Up  to  a  short  time  ago  the  atomic  weights  of  the 
platinum  metals  had  only  in  part  been  determined  with  the 
requisite  definiteness.  For  platinum  itself  the  most  reliable 
value  was  supposed  to  be  that  obtained  by  Berzelius,  viz, 
1967,  until  Seubert3  showed  (in  1880)  that  this  figure  was 
too  high  by  at  least  two  units.  The  atomic  weights  of 
palladium,  rhodium  and  osmium  were  also  determined  by 
Berzelius,  but  required  further  corroboration ;  this  applied 
more  especially  to  that  of  osmium.  Of  late  years,  however, 
K.  Seubert 4  has  re-determined  the  atomic  weights  of  iridium,; 
osmium  and  rhodium,  Keyser  5  that  of  palladium,  and  von 
Joly  6  that  of  ruthenium,  with  the  result  that  those  important 
constants  have  been  brought  into  order  in  the  above  two 
groups.  At  the  same  time  the  periodic  system  of  the 
elements  has  celebrated  a  new  triumph,  for  it  is  only  now 
that  the  platinum  and  palladium  metals  accord  with  it, — 
i.e.  they  now  occupy  the  positions  which  they  ought  to  do 
according  to  theory. 

Within  the  last  four  years  the  number  of  the  elements 
has  been  increased  by  two  of  peculiar  interest — viz.  argon,7 
discovered  in  the  air  by  Lord  Rayleigh 8  and  William 

1  Ann.  Chem.,  vol.  Ivi.  p.  257  ;  vol.  lix.  p.  284. 

2  Comptes  Rendus,  vol.  cvi.  pp.  100,  328. 

3  Ann.  Chem.,  vol.  ccvii.  p.  29;  Ber.,  vol.  xxi.  p.  2179  ;  also  Dittmar 
and  Arthur,  ibid.,  vol.  xxi.  Ref.  p.  412. 

4  Ber. ,  vol.  xi.  p.  1770;  Ann.  Chem.,  vol.  cclxi.  p.   257;   vol.  cclx.  p. 
314. 

5  Amer.  Chem.  Journ.,  vol.  xi.  p.  398. 

6  Compt.  Rend.,  vol.  cviii.  p.  946. 

7  Chem.  News,  vol.  Ixx.  p.  87  (1894) ;  British  Association  Report  for 
1894 ;  Phil.  Trans,  for  1895,  vol.  A.  part  2,  p.  187. 

8  John  William  Strutt,  third  Lord  Rayleigh,  was  born  on  November  12th, 
1842.     After  a  brilliant  career  at  Cambridge,  where  he  was  senior  wrangler 
of  his  year  and  Smith's  prizeman,  he  succeeded  the  late  Clerk  Maxwell  as 
professor  of  physics  in  the  University  of  Cambridge  (1879 — 1884).     Since 
1887  he  has  held  the  chair  of  Natural  Philosophy  in  the  Royal  Institution. 


vi  ARGON  AND  HELIUM  415- 

Ramsay,1  and  helium  discovered  by  Ramsay  in  the  mineral 
cleveite.2  Helium  had  already  been  found  to  exist  in 
the  sun's  chromosphere  by  Janssen3  so  long  ago  as  1868, 
i.e.  he  observed  in  the  spectrum  a  new  bright  yellow 
line  which  he  designated  D3.  The  spectrum  was  further 
studied  that  year  by  Frankland  and  Lockyer,  who  also  gave 
to  the  new  hypothetical  element  the  name  Helium.4  The 
isolation  of  argon  arose  from  and  followed  upon  careful 
determinations  of  the  atomic  weight  of  nitrogen  by  Lord 
Rayleigh,  who  found  that  nitrogen  obtained  from  air  was 
always  specifically  heavier  by  a  distinct  amount  (about  J 
per  cent.)  than  nitrogen  prepared  from  chemical  compounds. 
The  original  paper  in  the  Philosophical  Transactions,  already 
quoted,  will  undoubtedly  rank  as  a  classic,  the  investigation 
having  been  a  particularly  brilliant  one.  It  is  interesting  to 
recall  that  a  hundred  years  ago,  Cavendish,  reasoning  from  the 
results  of  his  own  experiments,  had  with  marvellous  acuteness 
suggested  the  possibility  of  such  a  gas  in  the  air,  and  had 
surmised  its  approximate  amount.  Thanks  to  its  incapacity 
for  combining  with  other  elements,  argon  remains  behind 
after  all  the  other  gases  in  the  air  have  been  got  rid  of. 

Although  a  physicist  in  the  first  instance,  some  of  his  work  has  been  of  the 
highest  importance  for  chemistry,  notably  that  upon  the  density  of  nitrogen, 
which  led  him  and  Ramsay  on  to  the  discovery  of  argon  ;  and,  in  a  second- 
ary degree,  his  determination  of  the  ratio  of  the  atomic  weights  of  hydrogen 
and  oxygen. 

1  William  Ramsay,  born  at  Glasgow  on  October  2nd,  1852,  studied 
chemistry  under  the  late  Professor  Anderson  at  Glasgow  University,  and 
then  under  Fittig  at  Tubingen.     After  acting  for  some  years  as  chemical 
assistant  at  the  Andersonian  College  and  afterwards  at  the  University  of 
Glasgow,  he  was  appointed  in  1880  professor  of  chemistry  in  University- 
College,  Bristol,  and  also  principal  of  that  college  in  the  following  year. 
In  1887  he  succeeded  Williamson  in  the  chair  of  chemistry  at  University 
College,  London,  which  post  he  still  holds.      His  earlier  investigations 
were  in  organic  chemistry,  but  for  the  last  twenty  years  or  so  they  have 
been  mostly  in  physical  and  inorganic,  both  of  which  branches  he  has 
greatly  advanced  by  a  wealth  of  work.     In  addition  to  his  numerous  pub- 
lished papers,  he  is  the  author  of  the  well-known  and  original  text-book  : — 
A  System  of  Inorganic   Chemistry  (J.  and  A.   Churchill,   1891),  besides 
of  smaller  works,  his  last  published  volume  being  The  Gases  of  the  Atmos- 
phere (Macmillan  and  Co.,  1896). 

2  Chem.  News,  vol.  Ixxi.  p.  151 ;  Journ.  Chem.  Soc.,  vol.  Ixvii.  p.  1107, 

3  Compt.  Rend.  vol.  Ixvii.  p.  838.  4  Lockyer,  Proc.,  U.S.,  vol.  xvii.  p.  91. 


416  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP. 

Helium,  first  obtained  by  heating  cleveite  with  sulphuric 
.acid,  and  since  found  in  small  quantity — often  together 
with  argon — in  a  good  many  other  minerals,  as  well  as  in  the 
gases  from  some  mineral  water  springs,  is  equally  indifferent. 
Up  to  now,  in  spite  of  persistent  effort,  no  compound  of 
-either  argon  or  helium  has  been  prepared.  And  further, 
although  most  careful  and  laborious  diffusion  experiments 
with  both  gases  have  been  carried  out,1  with  the  object  of 
seeing  whether  they  were  really  elementary,  the  densities  of 
both  have  remained  unaltered,  i.e,  it  has  been  found  im- 
possible to  subdivide  them  by  diffusion  into  two  or  more 
components.  From  the  ratio  of  the  specific  heats  at  constant 
volume  and  constant  pressure,  it  follows  that  the  molecule 
.and  atom  are  identical  in  both  argon  and  helium,  i.e,  that  the 
.gases  are  monatomic.2 

The  above  short  survey  of  the  discovery  of  elements 
during  the  present  chemical  period  is  sufficient  to  allow  of  our 
properly  appreciating  the  extent  of  the  achievements  in  this 
branch  of  the  science.  Since  chemists  have  had  before 
their  eyes  the  task  of  assigning  a  definite  place  in  the 
periodic  system  to  each  element,  the  discovery  of  a  new  one 
has  possessed  quite  another  charm,  and  also  a  far  higher 
significance  than  was  formerly  the  case.  What  is  now 
aimed  at  is  to  determine  the  atomic  weight  of  each  with 
such  accuracy,  and  to  examine  its  chemical  behaviour  with 
such  completeness,  as  to  permit  of  its  being  classified  in 

1  Ramsay  and  Collie,  Proc.  R.S.,  vol.  Ix.  p.  206  (1896) ;  Ramsay  and 
Travers,  ibid.  vol.  Ixii.  p.  316  (1897). 

•  <  2  Ramsay  and  Travers  have  just  discovered  another  gas  of  characteristic 
spectrum,  which  is  present  in  the  air  in  very  small  quantity,  and  to  which 
they  have  given  the  name  krypton.  It  is  monatomic  and  has  a  higher 
density  than  argon  (the  discoverers  expect  that  its  atomic  weight  wfll  be 
found  to  be  81  or  82,  in  accordance  with  the  periodic  law).  They  found  it 
in  the  gas  from  the  last  10  c.c.  left  on  evaporating  about  a  litre  of  liquid 
air. — Further,  by  fractionating  about  20  c.c.  of  crude  liquid  argon,  they  have 
succeeded  in  subdividing  the  latter  into  the  following  three  elementary 
gases,  each  of  which  has  a  well-defined  spectrum : — argon,  metargon, 
and  neon.  The  atomic  weights  of  argon  and  metargon  will  probably  be 
about  40,  and  that  of  neon  about  20.  Argon  and  metargon  have  been 
proved  to  be  monatomic,  but  neon  has  not  yet  been  tested  for  this  ;  it  will 
no  doubt  be  found  monatomic  like  the  others.  (Proc.  £.8.  for  1898.) 


vi  DOUBTFUL  ASSUMPTIONS  OF  NEW  ELEMENTS          417 

this  system.  In  the  case  of  none  among  the  recently  dis- 
covered elements  have  those  efforts  been  followed  with  such 
signal  success  as  in  that  of  germanium.  On  the  other  hand, 
as  argon  and  helium  cannot  be  properly  fitted  into  the 
periodic  system,  a  suggestion  has  been  made  to  set  up  a 
separate  group  of"  inactive  elements  "  (Lecoq  de  Boisbaudran; 
J.  Thomsen.)1 

We  find  in  chemical  literature  many  accounts  of  sup- 
posed new  elements,  which  afterwards  turned  out  either  to 
have  been  prepared  before,  or  to  be  mixtures  of  substances 
partly  already  known  and  partly  unknown.  A  passing 
reference  may  be  made  here  to  the  fantastic  attempts  of 
Winterl  2  at  the  end  of  last  and  beginning  of  this  century, 
who  imagined  that  he  had  decomposed  several  metals 
into  different  elements.  But  even  investigators  of  eminence 
fell  into  errors  which  could  only  be  explained  by  defects 
in  the  analytical  methods  of  their  day ;  thus  Bergman 
(in  1781)  looked  upon  iron  phosphide,  prepared  from 
"  cold-short "  iron  by  means  of  hydrochloric  acid,  as  a 
new  metal,  to  which  he  gave  the  name  of  siderum,  and 
Richter  claimed  impure  nickel  as  an  element,  terming  it 
nickolanum.  Even  Berzelius  thought  that  he  had  dis- 
covered (in  1815)  a  hitherto  unknown  earth  in  some 
Swedish  minerals,  but  he  corrected  the  error  himself  by 
showing  that  the  supposed  new  body  was  phosphate  of 
yttria.  The  history  of  the  cerium  metals,  to  which  yttrium 
belongs,  and  also  of  tantalum  and  niobium,  shows  more 
especially  a  great  many  such  errors,  while  even  at  the  present 
day  a  number  of  new  elements  are  being  brought  forward 
whose  homogeneous  nature  is  in  the  highest  degree  doubtful, 
e.g.  decipium,  mosandrium,  and  philippium.3  Similarly,  so 
little  is  known  yet  ofmasrium*  discovered  in  1892,  and  of  the 
element  still  more  recently  obtained  from  bauxite,  that 
nothing  can  be  said  about  them;  and  the  same  remark 
applies  to  lucium  and  russium  (Barriere  ;  Chrustschoff  ). 

1  Ber  vol.  xxix.  Ref.  p.  830. 

2  Kopp,  Gesch.  d.  Chemie,  vol.  ii.  p.  282. 

3  Comptes  Rendus,  vol.  Ixxxvii.  pp.  148,  559,  632,  etc. 

4  Mon.  Scient.  for  1892.  p  .514. 

E   E 


418  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP, 

Extension  of  the  Knowledge  of  Inorganic  Compounds. 

The  general  standpoints  arrived  at  during  the  present 
chemical  period  for  the  comprehension  of  inorganic  chemical 
compounds,  more  especially  the  opinions  with  regard  to  the 
constitution  of  acids,  bases,  and  salts,  have  been  entered  into 
in  detail  in  the  first  section  of  this  book.  It  remains  now 
to  give  an  account  of  the  development  of  special  knowledge 
in  this  branch  of  the  science.  An  exhaustive  treatment  of 
the  subject  is  of  course  impossible  here ;  only  researches  of 
particular  moment,  which  have  materially  aided  in  extending 
the  knowledge  of  chemistry,  can  be  mentioned. 

Hydrogen  Compounds  of  the  Halogens. 

The  remarkable  behaviour  of  hydrogen  with  respect  to 
chlorine, — the  readiness  with  which  those  two  gases  com- 
bine, was  first  investigated  by  Davy  and  Gay-Lussac,  and 
afterwards  made  the  subject  of  important  physico-chemical 
work  by  Roscoe  and  Bunsen.1  The  researches  of  Davy  and 
Faraday  2  contributed  greatly  to  a  more  intimate  knowledge 
of  hydrochloric  acid,  showing  among  other  things  how  to 
condense  the  gas,  while  those  of  Roscoe  and  Dittmar3 
established  the  chemical  relations  existing  between 
hydrochloric  acid  and  water.  Gay-Lussac  and  Balard 
investigated  hydriodic  and  hydrobromic  acids,  while  the 
fundamental  researches  of  Gay-Lussac,  Thenard  and  Berzelius 
contributed  a  knowledge  of  hydrofluoric  acid  in  aqueous 
solution,  and  those  of  Gore  4  and  Fremy 5  of  this  acid  in  the 
gaseous  state,  these  latter  thus  establishing  its  composition. 
Nickles  fell  a  victim  to  the  frightful  action  of  anhydrous 
hydrofluoric  acid  in  1869.  Ampere  was  the  first  to  point  out 
the  analogy  between  fluorine  and  chlorine. 

Oxygen  Compounds  of  Hydrogen  and  of  the  Halogens. 
The   investigations  which   led   to   a  knowledge   of  the 
composition  of  water  have  been  already  described ;  the  first 

1  Poyg.  Ann.,  vol.  c.  p.  43  ;  or  Phil.  Trans,  for  1857,  p.  355 ;  Ann.  Chem., 
vol.  xcvi.  p.  357  ;  cf .  History  of  Physical  Chemistry. 

2  Phil.  Trans,  for  1823,  p.  164.  3  Ann.  Chem.,  vol.  cxii.  p.  337. 

4  Phil.  Trans,  for  1869,  p.  173.     5  Ann.  Chim.  Phys.  (3),  vol.  xlvii.  p.  5. 


vi  PEROXIDE  OF  HYDROGEN,  ETC.  419 

quantitative  determination  of  its  constituents,  to  which  but 
little  exception  could  be  taken,  was  made  by  Berzelius  and 
Dulong.1  The  discovery  of  peroxide  of  hydrogen  2  by  Thenard 
in  1 8 1 8  showed  that  water  was  not  the  only  oxide  of  that 
element,  while  the  chemical  behaviour  of  this  peroxide,  which 
was  examined  by  Thenard,  Schonbein,  etc.,  and  of  recent 
years  by  Scheme  3  and  Traube,4  stamps  it  as  one  of  the  most 
remarkable  of  inorganic  compounds.  It  also  appears  to  play 
an  important  part  in  many  of  the  processes  of  nature,  and 
the  interest  in  it  is  heightened  still  further  by  the  value 
which  it  promises  to  have  for  technical  chemistry.  Wolf- 
fenstein  has  lately  succeeded  in  preparing  pure  hydrogen  per- 
oxide without  difficulty  by  distilling  it  in  vacuo.5 

The  various  stages  of  oxidation  of  chlorine,  iodine  and 
bromine  have  been  the  cause  of  much  valuable  work  since 
the  beginning  of  our  century,  e.g.  that  of  Gay-Lussac  on 
chloric  acid,  of  Stadion  on  perchloric  acid,  of  Davy  and 
Stadion  on  chlorine  peroxide,  of  Millon6on  chlorous  acid, 
and  of  Balard 7  on  hypochlorous  acid.  The  knowledge  of 
some  of  these  compounds  was  much  enlarged  by  Pebal's 
latest  researches,8  which  established  the  nature  of  the  so- 
called  euchlorine  and  of  chlorine  peroxide.  The  oxygen 
compounds  of  iodine  became  known  through  the  investi- 
gations of  Davy  and  Magnus ;  periodic  acid  (discovered  by 
the  latter)9  and  iodic  acid  led  later  on  to  a  knowledge  of 
several  series  of  salts,  from  whose  composition  important 
conclusions  as  to  the  saturation-capacity  of  iodine,  and 
therefore  of  the  halogens  generally,  were  drawn.  Excepting 
argon  and  helium,  fluorine  is  the  only  element  which  does  not 
combine  with  oxygen. 

1  Ann.  Chim.  Phys.,  vol.  xv.  p.  386  ;   for  later  determinations  of  the 
ratio  H2 :  0,  see  p.  403.         2  Ann.  Chim.  Phys.,  vol.  viii.  p.  306  (1818). 

3  Ann.  Chem.,  vol.  cxcii.  p.  258  (Schone  gives  here  a  review  of  the 
previous  literature  on  the  subject). 

4  Cf.  Ber. ,  vol.  xx.  p.  3345  ;  vol.  xxii.  p.  1496  ;  vol.  xxvi.  p.  1471. 

5  Ber.,  vol.  xxvii.  p.  3307.         6  Ann.  Chim.  Phys.  (3),  vol.  vii.  p.  298. 

7  Ibid.,  vol.  Ivii.  p.  225. 

8  Ann.  Chem.,  vol.  clxxvii.  p.  1  ;  vol.  ccxiii.  p.  113. 

9  Pogg.  Ann.,  vol.  xxviii.  p.  514. 

E   E   2 


420  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP. 


Sulphur,  Selenium  and  Tellurium  Compounds. 

To  the  early  known  compounds  of  sulphur  and  oxygen, 
sulphurous  and  sulphuric  acids  (the  anhydride  of  the  latter 
having  been  discovered  by  Vogel  and  Dobereiner),  others 
came  to  be  added,  viz.  "  hyposulphurous  acid "  by  Gay- 
Lussac,1  and  dithionic  acid  by  Welter  and  Gay-Lussac  (in 
1819).  The  constitution  of  the  first  of  these,  which  is  really 
thiosulphuric  acid,  was  only  made  out  at  a  much  later  date.2 
The  thio-acids  containing  more  sulphur,  and  nearly  related 
to  sulphuric  acid,  were  discovered  at  the  beginning  of  the 
forties  by  Langlois,  Forces  and  Gelis,  and  Wackenroder; 
the  question  as  to  whether  the  pentathionic  acid  of  the  latter 
really  exists  has.  recently  been  vigorously  discussed.3 

To  the  above  sulphur  acids  there  has  of  late  years  been 
added  Schutzenberger's  hyposulphurous  acid  (H2S02)  the 
chemical  behaviour  of  which  is  of  great  interest.4  The  two 
well-known  oxides  of  sulphur  also  received  an  addition  in 
R  Weber's  sesquioxide,  S2O3.5  Lastly,  mention  may  be 
made  here  of  per-sulphuric  acid,  whose  existence  Berthelot 
showed  to  be  probable,  and  for  the  anhydride  of  which  he 
assumed  the  formula  S2O7 ;  recent  researches  by  Elbs  and 
others  have  solved  its  true  composition,  viz.  HS04,  which  thus 
corresponds  with  that  of  permanganic  acid.  Neither  of  these 
compounds,  however,  (i.e.  S2O7  and  HS04)  has  yet  been 
obtained  pure.  The  enormous  impetus  given  to  chemical 
industries  generally  by  the  development  of  the  sulphuric  acid 
manufacture  must  also  be  referred  to.  It  is  only  within  the 
last  few  years  that  such  simple  derivatives  of  sulphuric 
acid  as  the  amide  and  imide  have  become  known  ;  and 

1  Ann.  Chim.,  vol.  Ixxxv.  p.  199  ;   sodium  hyposulphite  (thiosulphate) 
was  first  prepared  by  Chaussier  in  1799,  and  afterwards  more  carefully 
examined  by  Vauquelin. 

2  Cf.  Schorlemmer,  Journ.  Chem.  Soc.  (2),  vol.  vii.  p.  256. 

3  Cf.  Curtius  u.  Henkel,  Journ.  pr.  Chem.  (2),  vol.  xxxvii.  p.  37  ;  Debus, 
Journ.  Chem.  Soc.,  vol.  liii.  p.  278 ;  or  Ann.  Chem.,  vol.  ccxliv.  p.  76. 

4  Comptes  Rendus,  vol.  Ixix.  p.  169. 

5  Pogg.  Ann.,  vol.  clvi.  p.  53. 


vi  COMPOUNDS  OF  NITROGEN,  PHOSPHORUS,  ETC.         421 

the   same  thing  applies    to  fluor-sulphuric  acid   and  other 
compounds.1 

The  compounds  of  selenium  with  hydrogen  and  oxygen 
were  investigated  by  Berzelius,  and  an  account  of  them  given 
in  his  memorable  treatise.  After  him  there  came  Mitscherlich, 
who  discovered  selenic  acid,  and  therewith  furnished  a  beauti- 
ful confirmation  of  the  analogy  between  selenium  and  sulphur 
more  especially  from  the  isomorphism  of  the  sulphates  and 
selenates.  This  chemical  similarity  has  not  however  been 
maintained  in  all  respects,  Michaelis  2  having  recently  shown 
that  the  salts  of  selenious  acid  probably  possess  a  constitution 
different  from  that  of  sulphites. 

The  chlorine  compounds  of  sulphur,  selenium  and  tel- 
lurium, the  study  of  which  has  helped  to  characterise  these 
elements,  have  been  examined  at  various  times  ;  by  his  in- 
vestigation of  tellurium  tetrachloride  Michaens  has  lately 
furnished  an  excellent  proof  of  tellurium  being  tetratomic. 

Even  if  we  desired  to  mention  only  the  more  important 
of  the  investigations  which  have  aided  in  the  discovery  and 
elucidation  of  the  hydrogen,  oxygen  and  halogen  compounds 
of  nitrogen,  phosphorus,  arsenic  and  antimony,  it  would  be 
necessary  to  record  a  long  series.  Among  them  were  the  re- 
searches of  Davy,  Berthollet  and  Henry,  which  made  clear 
the  composition  of  ammonia, — so  long  looked  upon  as  con- 
taining oxygen.  The  discovery  of  phosphuretted  hydrogen 
(PH3)  by  Gengembre  3  in  1783,  and  the  examination  of  it  by 
Pelletier  (who  was  the  first  to  prepare  it  pure),  only  became 
fruitful  after  Davy's  investigations  ;  the  last-named  eluci- 
dated the  composition  of  this  gas,  and  pointed  out  its  analogy 
to  ammonia,  this  being  emphasised  still  more  sharply  by  EL 
Rose  later  on.  Thenard  4  discovered  liquid  phosphuretted 
hydrogen,  and  recognised  in  it  the  cause  of  the  spontaneous  in- 
flammability of  the  not  completely  pure  gaseous  compound. 

1  Cf.  W.  Traube,  Ber.,  vol.  xxvi.  p.  607;  Thorpe  and  Kirwan,  Ztschr. 
anorgan.  Chem.,  vol.  iii.  p.  63;  or  Journ.  Chem.  Soc.  vol.  Ixi.  p.  921. 

2  Ann.  Chem.,  vol.  ccxli.  p.  150.  3  CrelVs  Ann.,  vol.  i.  p.  450. 
4  Ann.  Chim.  Phys.  (3),  vol.  xiv.  p.  5.     Compare  also  Gattermann  and 

Haussknecht,  JSer.,  vol.  xxiii.  p.  1174. 


422  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP. 

Arseniuretted  and  antimoniuretted  hydrogens,  which  are 
analogous  to  ammonia  in  composition,  were  first  obtained  in  the 
pure  state  by  Soubeiran l  and  Pfaff.2  The  former  compound 
cost  Gehlen  his  life  in  1815,  from  his  not  suspecting  its  ex- 
treme poisonousness ;  and  the  same  fate  has  recently  befallen 
H.  Schulze  (of  St.  Jago).  The  great  importance  of  the  forma- 
tion of  arseniuretted  hydrogen  for  the  detection  of  minute 
quantities  of  arsenic  in  judicial-chemical  analyses  (Marsh's 
process)  is  well  known. 

The  oxygen  compounds  of  nitrogen  played,  as  already 
described,  an  important  part  in  the  history  of  the  atomic  theory, 
even  although  the  true  composition  of  all  these  oxides  was 
not  at  that  time  made  out.  The  number  of  the  oxides  of 
nitrogen  known  in  Dalton's  time  was  supplemented  by  nitro- 
gen peroxide,  whose  relation  to  the  others  was  arrived  at 
through  the  researches  of  Berzelius,  Gay-Lussac  and  Dulong ; 
and  by  nitric  anhydride,  discovered  by  St.  Claire  Deville. 
The  various  obscure  points  with  respect  to  nitrous  acid  and 
nitrogen  peroxide  have  been  for  the  most  part  explained  by 
the  recent  investigations  of  Hasenbach 3  Lunge,4  Ramsay  5 
and  others.  The  discovery  of  hyponitrous  acid,6  the  acid  cor- 
responding to  nitrous  oxide,  enlarged  still  further  the  series  of 
the  oxy-acids  of  nitrogen.  W.  Wislicenus  and  Paal,  in- 
dependently of  one  another,  succeeded  in  preparing  hypo- 
nitrous  acid  by  the  interaction  of  hydroxylamine  and  nitrous 
acid,7  and  since  then  Hantzsch  and  Kaufmann  have  proved 
that  its  molecular  weight  corresponds  to  the  formula 
N202H,8 

Reference  must  also  be  made  here  to  the  important  dis- 
covery of  hydroxylamine,9  which,  from  its  value  as  a  reagent, 

1  Ann.  Chim.  Phys.  (2),  vol.  xxiii.  p.  307. 

2  Pogg.  Ann.,  vol.  xl.  p.  135. 

3  Journ.  pr.  Chem.  (2),  vol.  iv.  p.  1. 

4  Cf.  Ber.,  vol.  xviii.  p.  1376 ;    vol.  xxi.  p.   67. 

5  Journ.  Ghem^  Soc.,  vol.  xlvii,  pp.  187  and  672;  vol.  liii.   p.   621  ;  vol. 
Ivii.  p.  590  ;  Phil.  Mag.,  vol.  xxiii.  p.  129;  vol.  xxiv.  p.  196. 

6  Divers,  Proc.  R.  S.t  vol.  xix.  p.  425  ;  Zorn,  Ber.,  vol.  x.  p.  1306. 

7  Ber.,  vol.  xxvi.  pp.  771  and  1026.       8  Ann.  Chem.,  vol.  ccxcii.  p.  317. 
9  Lessen,  Ann.  Chem.,  Suppl.,  vol.  vi.  p.  220. 


vi  HYDROXYLAMINE  ;  OXIDES  OF  PHOSPHORUS  423 

has  led  to  a  knowledge  of  many  remarkable  compounds, 
especially  in  organic  chemistry.  For  a  long  time  known  only 
in  solution,  it  has  now  been  obtained  in  the  free  state.1  Fremy's 
acides  sulfazotts  have  only  of  late  years  been  recognised  as 
being  really  sulphoxyl-derivatives  of  ammonia  and  hydroxyl- 
amine  (e.g.  HO.N.  (SO2OH)2  and  HO.NH.SO2OH).2  The 
discovery  of  the  more  or  less  analogous  amido-amine  3  (diamid- 
ogen  or  hydrazine,  H2N.NH2),  filled  up  a  long-felt  gap.  By 
its  interaction  with  other  organic  substances,  a  large  series  of 
most  important  compounds  has  been  prepared.  From  one  such 
derivative  of  hydrazine  is  obtained  that  remarkable  compound 
hydrazoic  acid  (or  azo-imide),  N3H,  which,  in  spite  of  its  ex- 
cessively explosive  nature,  has  been  thoroughly  investigated 
by  its  discoverer,  Curtius.4  W.  Wislicenus,5  Noelting  6  and 
others  have  devised  further  methods  for  preparing  it. 

Of  the  oxygen  compounds  of  phosphorus,  phosphorous  and 
phosphoric  acids  were  known,  although  very  imperfectly,  in 
Lavoisier's  time  ;  the  former  was  first  prepared  pure  by 
Davy,  by  treating  phosphorus  trichloride  with  water,  but  its 
chemical  constitution  was  only  cleared  up  by  later  investiga- 
tions. The  recent  admirable  paper  of  Thorpe  and  Tutton  7 
upon  phosphorous  oxide,  P4O6,  shows  that  the  real  properties 
of  this  substance  are  very  different  from  those  formerly 
attributed  to  it.  The  labours  of  Clarke,  Gay-Lussac  and 
Stromeyer  prepared  the  way  for  the  recognition  of  the  mutual 
relations  existing  between  ortho-,  pyro-,  and  meta-phosphoric 
acids,  these  being  subsequently  worked  out  by  Graham  ; 8  and 
upon  them  Liebig  established  his  far-reaching  theory  of  poly- 
basic  acids.9  Hypophosphorous  acid,  whose  salts  were  discovered 
by  Dulong  in  1 8 1 6,  has  been  the  subject  of  important  investi- 

1  Lobry  de  Bruyn,  Rec.  Trav.  Chem.,  vol.  x.  p.  101. 

2  Cf.  Raschig's  admirable  paper  (which  also  gives   a   review   of   the 
previous  literature  on  the  subject),  Ann.  Chem.,  vol.  ccxli.  p.  161. 

3  Curtius  u.  Fay,  Journ.  pr.  Chem.  (2),  vol.  xxxix.  p.  27. 

4  Ber.,  vol.  xxiii.  p.  3023 ;  vol.  xxiv.  p.  3341  ;  Journ.  pr.  Chem.  (2),  vol. 
xliii.  p.  207. 

5  Ber.,  vol.  xxv.  p.  2084.  5  Ber.,  vol.  xxvi  p.  86. 

7  Journ.  Chem.  Soc.,  vol.  IviL  p.  545. 

8  Phil.  Trans,  for  1833,  vol.  ii.  p.  253.  9  Cf.  p.  244. 


424  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP, 

gations  and  discussions.1  Hypophosphoric  acid,2  H4P2O6r 
has  also  lately  been  added  to  the  above  oxygen  compounds. 

The  discovery  of  the  halogen  compounds  of  nitrogen  and 
phosphorus  has  proved  of  particular  interest,  the  latter 
being  largely  employed  for  the  preparation  of  many  other  sub- 
stances, because  of  the  readiness  with  which  they  enter  into 
reaction.  Chloride  of  nitrogen  was  discovered  by  Dulong,& 
who  suffered  serious  injury  in  consequence  of  some  of  it  ex- 
ploding unexpectedly ;  this  dangerous  substance,  whose  com- 
position was  hitherto  uncertain,  has  of  late  been  made  the 
subject  of  important  investigations  by  Gattermann,4  who  has 
succeeded  in  preparing  the  pure  chloride,  NC13.  The  analogously 
formed  iodide  of  nitrogen  was  first  prepared  by  Serullas,5 
while  Bunsen,  Stahlschmidt  and,  quite  recently,  Raschig  6 
have  contributed  towards  a  knowledge  of  its  composition. 
The  chlorine  compounds  of  phosphorus  were  prepared  in  the 
first  decade  of  our  century,  the  trichloride  by  Gay-Lussac  and 
The'nard,  and  the  pentachloride  by  Davy.  The  trifluoride  of 
phosphorus  has  only  recently  been  prepared  by  Moissan ;  the 
pentafluoride,  isolated  by  Thorpe,7  is  of  especial  interest  from 
its  not  decomposing  even  at  high  temperatures,  unlike  the 
other  penta-haloid  compounds  of  phosphorus.  Wurtz  dis- 
covered phosphorus  oxychloride,  which  is  of  great  value  as  a 
reagent  in  organic  work,  and  H.  Rose  antimony  pentachloride. 
The  oxybromide  of  phosphorus  has  been  known  for  some 
time,  but  it  is  only  lately  that  Moissan  has  obtained  the 
oxyfluoride. 

The  halogen  compounds  of  boron  and  silicon  were  mainly 
investigated  by  Berzelius  and,  later,  by  Wohler  and  Deville,8 
and  they  constituted  the  material  from  which  those  elements 
themselves  and  others  of  their  compounds  were  prepared ;  the 

1  Cf.  Wurtz,  Ann.  Chem.,  vol.  xliii.  p.  318 ;  vol.  Ixviii.  p.  41. 

2  Salzer,  Ann.  Chem.,  vol.  clxxxvii.  p.  322  ;  vol.  cxciv.  p.  28  ;  vol.  ccxL 
p.  1  ;  vol.  ccxxxii.  p.  114  ;  Sanger,  ibid.,  vol.  ccxxxii.  p.  1. 

3  Schweigger's  Journ.,  vol.  viii.  p.  302. 

4  Ber.,  vol.  xxi.  p.  751. 

5  Ann.  Chim.  Phys.,  vol.  xlii.  p.  200. 

6  Ann.  Chem.,  vol.  ccxxx.  p.  212. 

7  Ann.  Chem.,  vol.  clxxxii.  p.  201.  8  Ibid.,  vol.  cv.  p.  67  et  seq- 


vi  COMPOUNDS  OF  BORON,  SILICON  AND  CARBON          425 

above  researches,  in  fact,  greatly  extended  the  knowledge  of 
these  substances  generally.  Among  other  points,  the  discovery 
of  boron  nitride  and  silicon  hydride  may  be  mentioned  here.1 
To  the  careful  investigation  of  volatile  silicon  compounds  is 
due  the  definite  establishment  of  the  atomic  weight  of 
that  element,  and,  with  this,  of  the  composition  of  silica,  to 
which  another  formula  than  the  present  was  previously  given. 
In  recent  years  there  have  been  further  important  researches 
on  the  halogen  compounds  of  boron  and  silicon 2  by  Moissan,. 
Besson,  and  Sabatier. 

Of  the  simple  compounds  of  carbon,  which  from  long 
custom  are  assigned  to  inorganic  chemistry,  the  greater 
number  were  discovered  and  examined  at  the  beginning  of 
this  century.  Details  have  already  been  given  with  respect 
to  carbonic  acid  and  carbonic  oxide.  The  study  of  the 
phenomena  of  combustion,  and  particularly  of  the  processes 
which  go  on  in  the  flame  of  burning  carbon  compounds,  in 
which  the  two  gases  just  mentioned  play  a  prominent  part, 
was  first  taken  up  by  Davy,  who  advanced  the  subject 
immensely  by  his  beautiful  researches.  We  must  also  refer 
here  to  the  more  recent  investigations  of  Frankland,  Bloch- 
mann,  Heumann,  Smithells,  and  Lewes,  on  the  theory  of 
luminous  flames.  The  luminous  acetylene  flame  has  again 
within  the  last  few  years  been  the  subject  of  much  investiga- 
tion and  discussion  among  chemists,  the  object  being  to  get 
at  the  cause  of  the  luminosity.  The  results  have  proved 
that,  in  the  main,  Davy's  old  theory  of  luminous  flames  is 
correct. 

Carbon  oxychloride  or  phosgene,  which  has  proved  of 
exceptional  value  as  a  reagent  in  organic  chemistry,  was  first 
prepared  by  Davy  in  1811,  but  carbon  oxysulphide  only  com- 
paratively recently  by  von  Than.3  Carbon  disulphide,  on  the 
other  hand,  was  obtained  by  Lampadius  so  early  as  1796, 

1  Wohler  u.  Buff,  Ann.  Chem.,  vol.  cii.  p.  120. 

2  Compt.  Rend.,  vols.  cxii.  and  cxiii. 

3  Ann.  Chem.,  Suppl.,  vol.  v.  p.  236.     The  properties  of  the  pure  com- 
pound were  first  established  by  Klason  (Journ.  pr.  Chem.  (2),  vol.  xxxv.  p. 
64). 


426  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP. 

and  more  minutely  investigated  by  Clement  and  Desormes 
in  1802  ;  it  is  now  an  important  product  of  chemical  manu- 
facture. Its  composition  was  arrived  at  correctly  by 
Vauquelin  and  Berzelius,  after  the  most  confused  opinions 
had  previously  been  expressed  with  regard  to  its  containing 
hydrogen  and  nitrogen.  The  profound  influence  which  the 
classical  researches  of  Gay-Lussac  on  cyanogen  and  its  com- 
pounds exercised  upon  the  development  of  chemistry  has 
already  been  referred  to. 


Extension  of  the  Knowledge  of  Metallic  Compounds. 

From  the  endless  number  of  investigations  which  have 
contributed  towards  a  knowledge  of  the  metallic  compounds, 
and,  with  this,  of  the  metals  themselves,  the  most  important 
must  now  be  mentioned,  if  they  have  not  already  been 
touched  upon  in  the  general  section  of  this  book. 

The  discoverers  of  the  alkali  metals  also  aided  largely 
in  their  investigation ;  thus  to  Davy  is  due  our  knowledge 
of  the  oxides  of  potassium  and  sodium,  to  Gay-Lussac 
that  of  the  corresponding  peroxides,  and  to  Bunsen  that  of 
rubidium  and  caesium  compounds.  Sodium  peroxide  is 
now  manufactured  in  quantity.  The  enormous  influence 
which  these  researches  on  the  compounds  of  the  alkalies 
exercised  upon  the  development  of  chemical  industries  will 
IDC  detailed  under  the  history  of  technical  chemistry. 

The  peroxides  of  barium  and  calcium  were  discovered  by 
Gay-Lussac  and  Thenard.  The  knowledge  of  the  nature 
of  chloride  of  lime  was  advanced  by  the  researches  of  Balard, 
who  was  the  first  to  express  the  opinion — still  held  by 
many — that  this  substance  was  a  double  compound  of  cal- 
cium chloride  and  hypochlorite.  Since  that  time  numerous 
further  experiments  have  led  many  to  regard  it  as  an  oxy- 
chloride  of  calcium,  which  has  given  rise  to  a  large  amount 
of  discussion.1 

The  investigations  which  led  to  a  knowledge  of  the  com- 
1  Cf.  the  work  of  Gopner,  Wolters,  Kraut,  Lunge  and  others. 


vi  COMPOUNDS  OF  METALS  OF  THE  IRON  GROUP          427 

pounds  of  beryllium  and  thallium  have  been  cited  above.1 
New  oxygen  compounds  of  copper,  in  addition  to  the  oxides 
already  known,  were  obtained  by  Rose  2  and  Th^nard,  while 
Wb'hler  discovered  silver  suboxide  and  peroxide;  it  must 
however  be  mentioned  here  that  the  existence  of  the  former 
of  these  has  been  vigorously  contested.3  The  application  of 
silver  salts  for  the  fixation  of  light  impressions  (i.e.  in 
photography),  so  pregnant  in  its  results,  will  be  treated 
under  the  history  of  physical  chemistry.  Those  chemists 
who  shared  in  the  discovery  and  investigation  of  aluminium, 
indium  and  gallium,  also  contributed  at  the  same  time  to 
a  knowledge  of  their  compounds.  With  respect  to  the  com- 
pounds of  alumina,  pure  chemistry  has  frequently  been 
called  upon  to  elucidate  difficult  points  pertaining  to  the 
manufacture  of  ultramarine,  porcelain,  glass,  &c. 

The  compounds  of  the  metals  which  form  the  iron  group 
have  been  the  object  of  a  very  large  number  of  investigations, 
among  which  we  may  mention  those  on  the  different  stages  of 
oxidation  of  manganese  by  Liebig  and  Wohler,4  Mitscherlich  5 
and,  recently,  Franke.6  The  chlorine  and  fluorine  compounds 
of  manganese  were  studied  by  Christensen.  To  the  two 
oxides  of  iron  (FeO  and  Fe2O3),  a  knowledge  of  which  we 
owe  to  Proust  and  whose  composition  was  established  by 
Berzelius,  Fremy  added  ferric  acid,  which  he  also  carefully 
investigated;  the  existence  of  this  acid  was  surmised  by 
Scheele.  Light  was  thrown  upon  the  nature  of  the 
cyanogen  compounds  of  iron  by  the  beautiful  researches  of 
Gay-Lussac,  Berzelius,  Gmelin  (who  discovered  potassic  ferri- 
cyanide),  and  Liebig,  out  of  which  the  present  views  held  with 
regard  to  these  substances  have  developed  themselves.  The 

1  Cf.  pp.  408  and  409.  2  Pogg.  Ann.,  vol.  cxx.  p.  1. 

3  Wohler,  Ann.  Chem.,  vol.  xxx.  p.  1  ;     Fiiedheim,  Ber.,  vol.  xxi.  p. 
316.     On  the  other  hand,  von  der  Pfordten,  who  at  first  believed  that  he 
had  proved  the  existence  of  silver  suboxide,  has  subsequently  expressed 
himself  in  favour  of  a  "  hydrate  of  silver,"  the  most  probable  formula  being 
Ag4-H2O.     (Ber.,  vol.  xxi.  p.  2288.) 

4  Pogg.  Ann.,  vol.  xxi.  p.  584. 

5  Ibid.,  vol.  xxv.  p.  287. 

6  Journ.  pr.  Chem.  (2),  vol.  xxxvi.  pp.  31,  166,  451. 


428  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP, 

nitroprussides,  so  nearly  allied  to  the  ferrocyanides,  were  first 
obtained  by  Playfair,  but  their  constitution  has  yet  to  be 
satisfactorily  cleared  up. 

There  are  few  more  remarkable  metallic  compounds  than 
those  recently  discovered  ones  which  carbon  monoxide  forms 
with  iron  and  nickel,  when  the  gas  is  allowed  to  pass  over 
the  hot  and  finely-divided  metal.1  Nickel  tetra-carbonyl^ 
Ni  (CO)4,  is  especially  interesting  both  from  a  physical 
and  chemical  point  of  view,  and  it  is  to  be  hoped  that  by 
means  of  it  the  question  of  the  true  atomic  weight  of  nickel 
will  be  ultimately  solved.  Whether,  as  Mond  hopes,  the 
metallurgical  production  of  nickel  by  the  aid  of  this  carbonyl 
compound  will  be  possible,  remains  to  be  proved. 

The  metallic  carbides  and  several  compounds  of  carbon 
with  other  non-metallic  elements  are  likewise  very  striking 
substances.  Although  only  discovered  a  short  time  ago,  some 
of  them  have  already  acquired  great  technical  importance, 
especially  carbide  of  calcium,  which  is  used  at  present  for 
the  production  of  acetylene  gas,  and  which  will  assuredly 
play  an  even  greater  part  in  the  future  than  it  does  now. 
Silicon  carbide  or  "  carborundum  "  far  surpasses  corundum  as 
a  polishing  material  for  hard  substances.  Moissan's  splendid 
work  on  the  carbides — of  which  a  few  were  known  previously, 
but  had  only  been  superficially  examined — has  thrown  much 
light  on  these  compounds.2 

The  chemistry  of  the  cobalt  salts  was  enriched  by  the 
discovery  of  the  remarkable  and  highly  varied  ammonio- 
cobaltic  compounds,  which,  observed  by  Genth  for  the  first 
time  in  1851,  were  afterwards  investigated  by  Fr.  Rose, 
Gibbs,  Fremy,  and  especially  Jorgensen.3  The  last-named 
investigator  has  brought  the  extraordinarily  difficult  question 
of  the  chemical  constitution  of  these  bodies  materially  nearer 
to  its  solution,  by  systematically  examining  the  ammonia 

1  Mond,  Langer  and  Quincke,  Journ.  Chem.  Soc.,  vol.  Ivii.  p.  749  ;  Ber., 
vol.  xxiv.  p.  2248  ;  Berthelot,  Compt.  Rend.,  vol.  cxii.  p.  1343. 

2  Cf.  Compt.  Rend.,  vol.  cxvii.  p.  679  ;  also  vols.  cxv.   and  cxvi.  ;    but 
particularly  his  brochure,  Le  Four  Electrique  (Paris,  1897). 

3  Cf .  Journ.  pr.  Chem.  (2),  vol.  xxiii.  p.  227  ;  vol.  xxxi.  pp.  49,  262 ;  voL 
xxxix.  p.  1  ;  vol.  xli.  p.  429. 


vi          COMPOUNDS  OF  MOLYBDENUM  AND  TUNGSTEN         429 

compounds  of  those  other  metals  analogous  to  cobalt  in  this 
respect — chromium  and  rhodium.1 

The.  various  combining  relations  which  the  different 
members  of  the  group  of  elements  comprising  molybdenum, 
tungsten  and  uranium  show  towards  other  elements,  have 
only  been  fully  understood  of  recent  years.  The  admirable 
work  of  Berzelius  on  molybdenum  compounds  has  been 
supplemented  by  that  of  Kriiss 2  on  the  sulphides,  and  of 
Muthmann  3  on  the  oxides,  as  well  as  by  the  earlier  investi- 
gations of  Blomstrand,  Debray,  Liechti  and  Kempe  on  the 
halogen  compounds  of  molybdenum.  The  chlorides  of 
tungsten  were  examined  in  detail  by  Roscoe,  who  thereby 
advanced  the  knowledge  of  the  saturation-capacity  of  this 
element.  The  complicated  salts  of  tungstic  acid  were  first 
studied  by  Margueritte,  Scheibler,  Marignac  and  v.  Knorre, 
but  their  ultimate  constitution,  as  well  as  that  of  the 
phospho-molybdic  and  phospho-tungstic  acids,  has  still  to 
be  unravelled.  Tungsto-  and  molybdo-vanadic  acids  belong 
to  the  "  compound  acids  "  which  have  recently  been  investi- 
gated by  Friedheim.  The  chemical  nature  of  uranium  and  its 
compounds  has  been  worked  out  with  most  success  by  Cl. 
Zimmermann4  whose  able  researches  have  largely  supple- 
mented the  earlier  ones  of  Peligot,  Roscoe  and  others. 

Of  the  compounds  of  tin  and  its  chemical  analogues, 
the  isomorphous  double  fluorides  5  aroused  especial  interest 
from  their  proving  the  connection  which  exists  between 
silicon,  titanium,  zirconium  and  germanium.  The  peculiar 
nature  of  titanium  was  elucidated  in  a  striking  manner 
by  the  discovery  of  its  nitrogen  compounds,6  and  more 
recently  by  the  preparation  of  its  various  sulphides.7 

To  Roscoe's  admirable  work8  is  due  most  of  our  knowledge 

1  Joum.pr.  Chem.  (2),  vol.  xxv.  pp.  83,  321  ;  vol.  xxx.  p.  1 ;  vol.  xxxiv. 
p.  394. 

2  Ann.  Chem.,  vol.  ccxxv.  p.  1.  3  Ibid.,  vol.  ccxxxviii.  p.  109. 

4  Ann.  Chem.,  vol.  ccxiii.  p.  285  (contains  a  historical  review)  ;    vol. 
ccxxxii.  p.  274  ;  also  Alibegoff,  ibid.,  vol.  ccxxxiii.  p.  117. 

5  Marignac,  Ann.  des  Mines  (5),  vol.  xv.  p.  221. 

6  Wb'hler,  Ann.  Chem. ,  vol.  Ixxiii.  p.  43.  7  Ann.  Chem. ,  vol.  ccxxxiv.  p.  257. 
8  Phil.  Trans,  for  1869,  p.  679;  or  Ann.  Chem.,  Suppl.,  vol.  vii.  p.   70. 


430  HISTORY  OF  INORGANIC  CHEMISTRY  CHAP. 

of  vanadium,  as  he  worked  out  correctly  the  different  stages 
of  combination  of  this  element  with  oxygen,  chlorine,  &c., 
and  set  right  the  former  erroneous  assumptions  with  regard 
to  the  composition  of  these  compounds.  Gerland's  investiga- 
tions l  on  vanadyl  salts  and  vanadic  acids,  and  those  of  v.  Hauer 
on  the  salts  of  the  latter,  have  also  been  of  assistance  here. 

Similarly  niobium  and  tantalum,  whose  chemical  nature 
had  been  completely  misjudged,  were  given  their  proper 
position  among  the  other  elements  by  the  investigations 
already  cited,  more  particularly  by  the  determination  of  the 
true  composition  of  the  chlorides  of  both  and  of  niobium 
oxychloride,2  and  by  the  examination  of  niobium  fluoride  and 
hydride.3 

Valuable  work  has  also  been  done  lately  on  the 
compounds  of  gold,  by  Kriiss 4  more  especially,  which  has 
materially  amplified  the  earlier  researches  of  Proust, 
Berzelius,  Figuier,  &c.,  and  has  served  to  establish  the 
chemical  character  and  the  atomic  weight  of  this  element. 

The  literature  on  platinum  and  its  compounds  is  very 
voluminous,  and  gives  evidence  of  most  excellent  experimental 
work.  Reference  may  be  made  here  to  the  discovery  of  the 
peculiar  reactions  to  which  platinum  can  give  rise  in  virtue 
of  its  condensation  of  oxygen  (the  absorption  of  oxygen  by 
platinum  and  palladium  has  been  proved  to  be  true  oxidation, 
for  the  same  amount  of  heat  is  given  out  by  this  absorption 
as  in  the  formation  of  the  oxides  PtO  and  PdO)  5 ;  and  to  the 
numerous  investigations  on  the  platinum-ammonium  com- 
pounds, the  first  of  which  were  prepared  by  Magnus,  and  whose 
peculiarities  were  studied  by  Gros,  Reiset,  Cleve,  Thomsen  and 
Blomstrand/  The  recently  published  work  of  Jorgensen:6 

1  Ber.,  vol.  ix.  p.  874 ;  vol.  x.  p.  2109  ;  vol.  xi.  p.  98. 

2  Deville  and  Troost,  Gomptes  JRendus,  vol.  Ix.  p.  1221. 

3  Kriiss  and  Nilson,  Ber.,  vol.  xx.  p.  1676. 

4  Cf.  Kriiss,  Ann  Chem.,  vol.  ccxxxvii.  p.   274  (contains  a  historical 
review) ;  vol.  ccxxxviii.  pp.  30  and  241  ;  Ber.,  vol.  xxi.  p.   126;   Thorpe 
and  Laurie,  Journ.  Chem.  Soc. ,  vol.  li.  pp.  565  and  866. 

5  Mond,  Ramsay  and  Shields,  Phil.  Trans.,  vol.  clxxxvi.  p.   657  ;   vol. 
cxc.  p.  129. 

6  Journ.  <pr.  Chem.  (2),  vol.  xxxiii.  p.  489. 


vi  PLATINUM  COMPOUNDS,  ETC.  431 

Zur  Constitution  der  Platinbasen  ("  On  the  Constitution  of  the 
Platinum  Bases  "),  marks  an  important  step  in  the  recognition 
of  the  constitution  of  these  bodies.  The  compounds  which 
carbon  monoxide  forms  with  chloride  of  platinum,  discovered 
by  Schiitzenberger,  have  lately  been  carefully  investigated  by 
Mylius  and  Forster  and  by  Pullinger,  who  have  thereby 
contributed  greatly  to  solving  the  problem  of  their 
constitution.1 

The  researches  which  have  assisted  materially  towards 
a  knowledge  of  the  platinum  metals  have  already  been 
mentioned  under  the  history  of  the  individual  elements. 

If  we  throw  a  glance  over  the  wide  field  of  inorganic 
chemistry,  with  its  seventy  elements  approximately  and  their 
endless  compounds,  we  cannot  fail  to  recognise  the  fact  that 
the  atomic  theory  has  rendered  the  main  service  in  their 
classification.  The  endeavour,  too,  to  establish  periodic 
relations  between  the  properties  of  the  elements  and  their 
atomic  weights  has  introduced  order  among  the  motley 
array  of  the  elements  and  their  compounds.  The  question 
of  the  constitution  of  the  latter  allows  in  most  cases  of  a 
simple  and  satisfactory  answer ;  as  soon,  however,  as  the 
composition  of  inorganic  compounds  becomes  complicated, 
the  usual  aids  to  the  solution  of  such  points  no  longer  suffice. 
The  consequence  of  this  is  that  the  rational  composition 
of  a  large  number  of  compounds,  whose  empirical  composition 
has  long  been  known,  has  not  yet  been  cleared  up;  as 
examples  of  such  we  may  refer  to  the  metallo-ammonia 
compounds  (e.g.  those  of  cobalt  and  chromium),  the  poly- 
silicic  acids,  the  tungstic  acids,  and  the  host  of  compound 
acids.  Even  the  constitution  of  the  carbonyl  compounds  of 
nickel,  iron,  &c.  is  still  uncertain. 

1  Ber.,  vol.  xxiv.  pp.  2291,  2434  and  3751. 


432  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 


SPECIAL  HISTORY  OF  ORGANIC  CHEMISTRY 
IN  THE  NINETEENTH  CENTURY. 

The  development  of  organic  chemistry  during  the  first  few 
years  of  this  century  has  been  already  described  under  the 
general  history  of  the  period  (cf.  p.  246)  ;  there,  also,  much  of 
the  pioneering  work  accomplished  in  this  branch  of  the  subject 
has  been  discussed,  in  so  far,  that  is,  as  it  had  a  determining 
influence  on  the  origin  and  growth  of  important  theoretical 
investigations.  In  this  section  the  attempt  will  be  made  to 
pick  out  from  the  superabundance  of  work  done  in  organic 
chemistry  that  which  has  proved  of  greatest  significance, 
and  to  arrange  it  according  to  its  nature  (not  according  to 
its  sequence  in  point  of  time) — more  especially  such  in- 
vestigations as  have  contributed  to  solving  the  question  of 
the  chemical  constitution  of  whole  classes  of  bodies.  The 
general  points  of  view  by  which  individual  experimenters 
have  been  guided  in  those  researches  have  already  been 
examined  at  various  times  in  the  first  section  of  this  book. 

Before  organic  chemistry  could  be  in  a  position  to 
develop  itself  independently,  the  following  two  conditions 
had  to  be  fulfilled : — In  the  first  place,  the  determination  of 
the  empirical  composition  of  organic  substances  was  necessary 
(how  this  question  was  solved  is  described  under  the 
history  of  analytical  chemistry)  ; l  in  the  second,  it  had  to  be 
proved  that  organic  compounds  were  subject  to  the  same 
atomic  laws  as  inorganic,  and  that  they  were  not,  as  many 
formerly  assumed,  to  be  classed  as  totally  distinct  from 
the  latter.  To  Berzelius,  more  than  to  any  other  man,  is 
due  the  removal  of  this  dividing  barrier  between  the  two. 

The  most  important  methods,  which  have  ever  since 
remained  standard  ones  in  organic  chemistry,  were  created 
by  the  fundamental  researches  of  Gay-Lussac  on  cyanogen  and 
its  compounds,  of  Liebig  and  Wohler  on  benzoyl  and 

1  Cf.  p.  393. 


vi  THE  HYDROCARBONS  433 

uric  acid,  ef  Bunsen  on  the  compounds  of  cacodyl,  of  Dumas 
and  Peligot  on  wood-spirit,  and  by  the  investigations  of 
Kolbe,  Frankland,  A.  W.  Hofmann,  Williamson,  Gerhardt, 
Wurtz,  Kekul4  and  others  during  -the  fifties  and  sixties. 
Many  of  these  researches  have  already  been  referred  to  in 
the  general  section,  because  of  the  influence  which  they 
exercised  on  the  development  of  views  regarding  the 
chemical  constitution  of  organic  compounds ;  but  it  will  not 
be  altogether  possible  to  avoid  recurring  to  some  of  them  in 
this  portion  of  the  book. 

The  recognition  of  the  totally  different  behaviour  of  the 
so-called  saturated,  unsaturated,  and  aromatic  substances 
was  of  the  first  importance  for  the  systematising  of  organic 
compounds.  A  precise  distinction  between  and  definition  of 
the  above  three  classes,  more  especially  of  the  two  latter,  has 
been  gradually  brought  about  in  the  course  of  the  last  few 
decades,  as  the  knowledge  of  them  has  been  extended.  In 
the  study  of  organic  compounds,  the  investigation  of 
physical  properties  has  of  late  years  acquired  very  great 
prominence ;  and  this  is  easily  intelligible  when  it  is  stated 
that  such  investigation  has  greatly  advanced  the  solution  of 
the  question  of  chemical  constitution. 


Hydrocarbons  and  their  Derivatives. 

The  hydrocarbons,  from  which  as  the  simplest  organic 
compounds  all  the  others  are  derivable,  have  been,  as  befits 
their  "  typical  "  importance,  the  object  of  numberless  investi- 
gations, which  have  led  to  the  development  of  doctrines 
of  the  utmost  weight.  We  have  only  to  think  of  the 
determination  of  the  composition  of  marsh  gas  and  of  ethylene, 
which  led  to  the  recognition  of  multiple  proportions,  and 
with  this  to  the  setting  up  of  the  atomic  theory ;  of  the  im- 
portance of  Faraday's  researches  on  butylene  for  the 
evolution  of  what  became  known  as  polymerism;  of  the 
labours  of  Regnault  and  others  on  ethylene  and  its  haloid 
compounds,  which  afforded  such  rich  food  for  the  theories  of 

F   F 


434  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP, 

substitution ;  and  lastly,  of  the  work  of  Kekule  and  his  pupils 
on  benzene  and  its  derivatives — investigations  on  which  most 
of  the  work  in  organic  chemistry  for  the  last  thirty  years  has 
been  based. 

Mitscherlich's  researches  on  benzene  (which  he  then 
termed  Benziri)  sixty  years  ago,  taught  new  methods  of  pre- 
paring hydrocarbons ;  the  formation  of  this  substance  from 
benzoic  acid,  in  consequence  of  the  separation  of  carbon 
dioxide,  became  typical  for  a  large  number  of  similar 
reactions,  e.g.  the  production  of  cumene  from  cumic  acid,  of 
methane  from  acetic  acid,  of  chloroform  from  trichloracetic 
acid,  &c.  Of  great  theoretical  importance,  too,  was  Kolbe's 
mode  of  formation  of  hydrocarbons  by  the  electrolysis  of  the 
alkaline  salts  of  the  fatty  acids,  and  also  that  of  Frankland 
by  the  action  of  zinc  upon  alkyl  iodides ;  the  latter  investi- 
gations led  to  the  discovery  of  the  zinc  alkyls,  and  opened  up 
this  especially  fruitful  field  in  the  synthesis  of  organic  com- 
pounds.1 The  researches  of  Wurtz,2  which  showed  how  the 
combination  of  different  alkyl  radicals  from  hydrocarbons 
might  be  effected  by  the  action  of  sodium  upon  two  alkyl 
iodides,  bore  much  fruit  subsequently  among  the  aromatic 
compounds  ;  for,  with  this  reaction  as  a  model,  the  homologues 
of  benzene  were  prepared  synthetically,  while  at  the  same 
time  the  simple  mode  of  formation  allowed  of  their  chemical 
constitution  being  deduced.3 

Another  synthesis  4  of  homologues  of  benzene,  depending 
upon  the  peculiar  interaction  of  aluminic  chloride  with 
mixtures  of  benzene  and  chlorine  compounds  (such  as  methyl 
chloride),  has  also  proved  itself  of  general  application,  as  well 
as  serviceable  for  the  artificial  production  of  other  bodies,  e.g. 
ketones,  acids,  &c.  Notwithstanding  the  care  with  which 
these  reactions  have  been  studied,  a  conclusive  explanation 
of  the  mode  of  action  of  the  aluminium  chloride  has  still  to 
be  given;  this  much,  however,  may  be  taken  as  proved — 
that  their  cause  is  to  be  sought  for  in  the  formation  of 

1  Cf.  p.  362.     2  Ann.  Chim.  Phys.  (3),  vol.  xliv.  p.  275. 

:!  Cf.  Fittig,  A  nn.  Chem.,  vol.  cxxxi.  p.  301. 

4  Friedel  and  Crafts,  Comptes  fiendus,  vols.  Ixxxiv.,  Ixxxv.,  &c. 


vi  THE  AROMATIC  HYDROCARBONS  435 


peculiar    intermediate    compounds    of    the    chloride    with 
aromatic  hydrocarbons  (Gustavson).1 

Berthelot's  method 2  of  forming  hydrocarbons  out  of 
different  organic  compounds  by  the  action  of  hydriodic  acid 
upon  them  at  rather  high  temperatures,  must  also  be  men- 
tioned here,  since  it  has  led  to  important  results  in  many 
cases.  And  reference  must  be  made  to  the  method,  so  fre- 
quently employed,  of  reducing  oxygen  compounds  to 
hydrocarbons  by  heating  them  with  zinc  dust.3  The  work  of 
Berthelot  on  acetylene,  of  Butlerow  and  others  on  the  buty- 
lenes  and  amylenes,  of  Freund  on  trimethylene,  of  W.  H. 
Perkin,  jun.,  on  the  derivatives  of  tri-  and  tetra-methylene,  of 
Liebermann  on  allylene,  &c.,  has  materially  enlarged  our 
knowledge  of  the  unsaturated  hydrocarbons.  The  remark- 
able processes  of  the  isomerisation  of  such  compounds  have 
recently  been  cleared  up  by  the  valuable  researches  of 
Faworsky.4 

Out  of  the  extraordinarily  large  number  of  investigations 
on  aromatic  hydrocarbons,  whose  constitution  has  given  rise 
to  important  discussions,  there  may  be  mentioned  here  (in 
addition  to  the  above)  those  of  Fittig5  and  Baeyer6  on 
mesitylene,  which  was  found  to  be  "  symmetrical "  trimethyl- 
benzene,  and  also  those  of  Graebe 7  upon  naphthalene,  and  of 
Graebe  and  Liebermann  8  upon  anthracene.  Important  con- 
clusions were  drawn  from  the  two  last  with  respect  to  the 
chemical  constitution  of  these  already  long-known  hydro- 
carbons, which  from  thenceforth  were  regarded  as  standing 
in  a  simple  relation  to  benzene. 

Other  coal-tar  hydrocarbons  of  complex  composition  have 
likewise  been  satisfactorily  investigated ;  thus  phenanthrene, 
the  isomer  of  anthracene,  has  been  shown  by  Fittig  and 

Ber.,  vol.  xi.  p.  2751. 

Ann.  Chim.  Phys.  (4),  vol.  xx.  p.  392. 

Baeyer,  Ann.  Chem.,  vol.  cxl.  p.  295. 

Journ.  pr.  Chem.  (2),  vol.  xxxvii.  pp.  382,  417,  532. 

Ztschr.  Chem.  for  1866,  p.  518. 

Ann.  Chem.,  vol.  cxl.  p.  306. 

Ann.  Chem.,  vol.  cxlix.  p.  22. 

Ibid.,  Suppl,  vol.  vii.  p.  257. 

F   F   2 


436  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 

Graebe l  to  be  a  diphenylene  derivative  of  ethylene,  fluorene 
by  Fittig2  to  be  diphenylene-methane,  and  chrysene  by 
Oraebe3  to  be  phenylene-naphthalene-ethylene.  To  Bam- 
berger4  is  due  the  elucidation  of  the  chemical  nature  of 
retene  and  pyrene.  Lastly,  the  important  researches  of 
Kraemer  and  Spilker  5  throw  light  on  the  question — how  the 
individual  compounds  occurring  in  coal-tar  may  be  formed 
during  the  distillation  of  the  coal. 

A  wide  field  has  been  opened  up  within  the  last 
ten  years  by  the  discovery  of  the  hydrides  of  aromatic 
hydrocarbons — compounds  of  remarkable  character.  It  will 
be  sufficient  to  refer  here  to  the  comprehensive  work  of 
Bamberger,6  Baeyer 7  and  Markownikoff  8  on  the  subj  ect.  The 
last-mentioned  has  proved  that  a  long  series  of  the  constitu- 
ents of  petroleum, — the  so-called  naphthenes — belong  to 
this  class  of  hydro-compounds.  Again,  many  of  the  latter 
show  close  relations  to  the  terpenes,  substances  about  which 
until  recently  very  little  was  known,  but  which  have  been  made 
more  and  more  accessible  by  the  admirable  systematic  work 
of  Wallach. 9  By  means  of  definite  reactions  it  has  been 
found  possible  to  introduce  order  among  the  dire  confusion 
of  these  "  ethereal  oils  ";  and  some  quite  recent  researches  of 
A.  von  Baeyer10  have  thrown  much  light  upon  the  constitu- 
tion of  the  terpenes. 

We  must  further  refer  to  the  admirable  work  of  E.  and  O. 
Fischer,  Zincke  and  others  on  the  phenyl  derivatives  of 
methane,  more  especially  triphenyl-methane ;  this  last  was 

1  Ann.  Chem.,  vol.  clxvi.  p.  361 ;  vol.  clxvii.  p.  131. 

2  Ibid.,  vol.  cxciii.  p.  134. 

3  Ber.,  vol.  xii.  p.  1078. 

4  Ann.  Chem.,  vol.  ccxxix.p.  102;  Ber.,  vol.  xx.  p.  365. 

5  Ber.,  vol.  xxiii,  pp.  78  and  3266. 

6  Cf.  especially  Ber.,  vol.  xxii.  p.  767;  vol.  xxiv.  p.  2463. 

7  Ber.,  vol.  xxv.  p.  2122;  vol.  xxvi.  pp.  229,  820. 

8  Journ.  pr.  Chem.  (2),  vol.  xlv.  p.  561 ;  vol.  xlvi.  p.  86  (this  last  gives 
the  literature  on  the  subject). 

9  Ann.  Chem.,  vol.  ccxxv.,  ccxxvii.,  ccxxx.,  ccxxxviii.,  ccxxxix.,  ccxli., 
•cclviii.,  cclxix.,  cclxxv.  andcclxxvii.  ;  also  his  lecture  on  the  Terpenes,  Ber., 
vol.  xxiv.  p.  1525. 

1  Ber.,  vol.  xxvi.  pp.  820,  2267,  2558  and  2861. 


vi  THE  ALCOHOLS  AND  ETHERS  437 

proved  by  E.  and  O.  Fischer  to  be  the  mother-substance 
of  exceptionally  valuable  aniline  dyes,  whose  constitution 
was  thus  explained. 

The  continuous  and  increasing  effort  to  express  organic 
compounds  as  derivatives  of  the  hydrocarbons  is  further 
shown  by  the  nomenclature.  With  the  object  of  systema- 
tizing this  on  a  uniform  plan,  an  International  Commission l 
of  chemists  met  a  few  years  ago  at  Geneva.  The  system 
adopted  by  this  Commission  makes  the  hydrocarbons  the 
basis  of  the  nomenclature  proposed.  But  whether  all  the 
branches  of  organic  chemistry  are  at  present  sufficiently 
advanced  to  allow  of  a  satisfactory  solution  of  the  question 
is  highly  problematical. 


The  Alcohols  and  Analogous  Compounds. 

The  close  connection  existing  between  the  alcohols  and 
the  hydrocarbons  was  clearly  recognised  when  methyl  alcohol 
(the  first  member  of  a  long  series  of  compounds  of  this 
nature)  had  been  successfully  prepared  from  methane,  by 
converting  the  latter  into  methyl  chloride,  and  then  trans- 
forming this  into  the  alcohol.  Formerly  regarded  as  the 
hydrated  oxides  of  hypothetical  radicals,  the  alcohols  were 
after  this  characterised  as  hydroxyl  derivatives  of  the 
hydrocarbons.  What  an  influence  Williamson's  researches 
on  the  formation  of  ether  and  Kolbe's  views  on  the  con- 
stitution  of  the  alcohols  had  upon  the  development  of  the 
opinions  now  held  with  regard  to  this  point,  has  been 
already  described. 

Among  the  most  important  of  the  investigations  which 
helped  to  establish  our  knowledge  of  the  alcohols  were  those 
of  Dumas  and  Peligot2  on  wood-spirit,  whose  analogy  to 

1  Compare  the  Rapport  de  la  Sous- Commission  nomme'e  par  le  Congres 
Chimique  de  1889,  &c.   (Paris,  1892) ;  the  report  by  Pictet  in  the  Archives 
des  Sciences  Physiques  et  Naturelles,  May  1892;  Tiemann's  report  in  the 
Berichte,  vol.  xxvi.  p.  1595 ;  and  Armstrong's  report  in  Nature  for  1892, 
vol.  xlvi.  p.  56. 

2  Ann.  Chim.  Phys.,  vol.  Iviii.  p.  5;  vol.  Ixi.  p.  93. 


438  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 

ethyl  alcohol  they  clearly  recognised.  The  true  composition 
of  the  latter  was  worked  out  by  Saussure,  who  thus  did 
away  with  the  fundamentally  erroneous  ideas  regarding  it 
which  had  prevailed  since  the  time  of  Lavoisier ;  the  latter 
had  indeed  arrived  at  a  correct  knowledge  of  its  constituents, 
but  not  of  the  proportions  in  which  these  were  present. 
Equally  important  were  the  fact  that  aethal  (C16H33OH),  dis- 
covered by  Chevreul,  was  characterised  as  an  analogue  of 
alcohol  by  Dumas  and  Peligot  in  spite  of  its  unlikeness  to  the 
latter,  and  the  corresponding  proof  by  Cahours l  for  the  amyl 
alcohol  obtained  from  fusel  oil,  to  which  isobutyl  alcohol2 
was  afterwards  added.  The  discovery  of  the  secondary  and 
tertiary  alcohols,  so  memorable  for  the  history  of  this  class 
of  compounds,  was,  as  already  stated,  prognosticated  by 
Kolbe.  The  series  of  the  secondary  carbinols  was  begun 
with  isopropyl  alcohol,  isolated  by  Friedel,  and  that  of  the 
tertiary  with  Butlerow's  trimethyl-carbinol.  The  modes  of 
formation  of  these  substances  (that  of  isopropyl  alcohol 
from  acetone  by  the  addition  of  hydrogen,  and  that  of 
trimethyl-carbinol  from  acetyl  chloride  and  zinc  methyl) 
have  since  been  extensively  made  use  of  for  the  preparation 
of  analogous  compounds. 

Carbinols  of  other  series  were  investigated  by  Cannizzaro, 
who  discovered  benzyl  alcohol,3  the  simplest  carbinol  of  the 
aromatic  series,  and  by  Cahours  and  Hofmann,  who  isolated 
allyl  alcohol ; 4  while  an  accurate  acquaintance  with  various 
new  primary  carbinols  of  the  fatty  series  was  arrived  at  by 
the  systematic  researches  of  Lieben  and  Rossi.5  The 
above-mentioned  investigations  were  also  of  great  importance 
for  the  development  of  the  views  upon  chemical  constitution, 
and  more  especially  upon  the  isomerism  of  organic 
compounds, 

The  knowledge  of  the  polyatomic  alcohols  had  its  be- 
ginning in  the  already-mentioned  important  researches  of 

1  Ann.  Chim.  Phys.,  vol.  Ixx.  p.  81 ;  vol.  Ixxv.  p.  193. 

2  Wurtz,  Ann.  Chem.,  vol.  xciii.  p.  107. 

3  Ibid.,  vol.  cxxiv.  p.  324. 

4  Ibid.,  vol.  c.  p.  356.        5  Cf.  Ibid.,  vol.  clviii.  p.  137. 


vi  THE  ALCOHOLS  AND  ETHERS  439 

Berthelot  on  glycerine,  as  representing  the  triatomic 
carbinols,  and  especially  in  those  of  Wurtz  on  the  diatomic 
glycols.  In  connection  with  these  we  would  call  attention 
here  to  the  notable  discovery  of  the  poly-ethylene  alcohols, 
and  of  ethylene  oxide  (distinguished  by  the  readiness  with 
which  it  enters  into  reaction). 

The  discovery  of  the  fact  that  certain  sugars  lare 
polyatomic  alcohols  is  of  quite  recent  date ;  mannite,  for 
instance,  is  a  hexoxy-hexane  and  arabite,  rhamnite  and  pentite 
are  pentoxy-hexanes.  The  "  carbohydrates,"  being  aldehydes 
or  ketones,  are  closely  related  to  these. 

The  derivatives  of  the  alcohols  known  as  the  simple 
ethers,  with  common  ethyl  ether  at  their  head,  have 
frequently  been  the  subject  of  important  investigations.. 
The  discussions  upon  the  constitution  of  ether  and  its  mode 
of  formation — discussions  which  lasted  for  many  years — were 
brought  to  an  end  by  the  work  of  Williamson  and  Chancel, 
which  led  to  the  discovery  of  mixed  ethers.2 

The  knowledge  of  the  compound  ethers,  frequently 
now  also  called  Esters,  has  been  greatly  extended  within 
the  last  sixty  years.  The  recent  observations  of  the  late 
Victor  Meyer  and  his  pupils  on  the  formation  of  esters  of 
aromatic  acids  are  of  great  interest  here,  the  constitution  of 
these  acids  determining  the  path  which  the  synthesis  follows.. 
To  the  neutral  ethers  of  the  acids,  the  number  of  which  has 
gone  on  continuously  increasing  (but  regarding  which  it  is 
impossible  to  mention  here  even  the  more  important 
researches),  there  have  been  added  the  so-called  ether-acids, 
whose  chemical  nature  has  been  cleared  up  by  the  work  of 
Hennel,  Serullas,  Magnus  and  Regnault  on  ethyl-sulphuric 
.and  ethionic  acids,  of  Pelouze  on  the  ethyl-phosphoric 
acids,  of  Mitscherlich  on  ethyl-oxalic  acid,  and  other  more 
recent  labours,  e.g.  that  upon  phenyl-ethyl-sulphuric  acid  by 
Baumann,  and  upon  ethyl-oxalic  acid  by  Anschiitz. 

Certain  of  the  compounds  prepared  from  ethyl  alcohol 

1  Comptes  Rendus,  vol.  xlviii.  p.  101 ;  vol.  xlix.  p.  813. 

2  Cf.  p.  298. 

3  Ber.,  vol.  xxvii.  pp.  1580,  3146;  vol.  xxviii.  p.  2773. 


440  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 

and  other  carbinols  have  played  an  important  part  in  the 
synthesis  of  organic  substances,  thanks  to  their  capability  of 
reaction ;  we  have  but  to  recall  here  the  discovery  of  sodium 
ethylate  by  Liebig,  that  of  chloro-carbonic  ether  by  Dumas, 
and  Debus'  investigations  of  the  products  which  result  from 
the  oxidation  of  ethyl  alcohol  by  nitric  acid. 

The  first  step  towards  a  knowledge  of  those  compounds 
so  nearly  allied  to  the  alcohols,  which  have  received  the 
generic  name  of  phenols,  was  Laurent's  investigation  of 
carbolic  acid  and  its  derivatives.1  Gerhardt  was  the  first  to 
point  out  the  analogy  between  alcohol  and  phenol.  Of 
great  importance  for  the  development  of  this  class  of  com- 
pounds, and  more  especially  for  their  technical  production, 
was  that  mode  of  formation  of  phenol  itself  which  was  first 
observed  by  Kekule*2  and  Wurtz,3  viz.  by  fusing  benzene- 
sulphonic  acid  with  potash.  This  reaction  soon  led  to  the- 
discovery  of  a  large  number  of  mono-  and  poly-atomic  phenols ; 
the  naphthols  and  other  oxy-derivatives  of  naphthalene,  the  di- 
and  trioxy-benzenes,  etc.  were  isolated.  The  reactions  of 
these  compounds  turned  out  to  be  of  remarkable  interest 
not  merely  from  a  technical,  but  also  from  a  purely 
scientific  point  of  view;  one  need  but  refer  to  the 
conversion  of  many  phenols  into  quinones,  and  to  the  various 
transformations  of  these  latter  by  chlorine  and  bromine.  The 
comprehensive  researches  of  Zincke 4  and  his  pupils  on  this 
subject  are  worthy  of  special  mention  here ;  the  nature  of 
the  peculiar  decomposition-products  of  the  phenols  allowed 
of  conclusions  being  drawn  as  to  the  constitution  of  the 
original  compounds. 

1  Ann.  Chim.  PJiys.  (3),  vol.  iii.  p.  195.     Runge  was  the  discoverer  of 
carbolic  acid  itself. 

2  Lehrb.  der.  organ.  Chemie,  vol.  iii.  p.  13. 

3  Ann.  Chem.,  vol.  cxliv.  p.  121. 

4  Ber.,  vol.  xxi.  p.  3540;  vol.  xxii.  pp.  1024,  1467  ;  vol.  xxiii.  pp.  230,, 
1706,  2200,  &c.  ;  Ann.  Chem.,  vol.  cclxi.  p.  208. 


vi  EARLY  WORK  ON  THE  CARBOXYLIC  ACIDS  44F 


Carboxylic  Acids. 

A  field  of  immense  extent  and  fertility  became  open 
to  chemical  research  with  the  systematic  investigation  of 
the  acids  contained  in  animal  and  vegetable  fats,  as  well  as 
in  other  natural  products.  The  important  work  on  the  fatty 
acids,  suggested  in  the  first  instance  by  Liebig,  and  which  was- 
accomplished  by  his  pupils  Varrentrapp,  Rochleder,  Bromeis, 
Fehling,  Redtenbacher  and  others,  and  that  of  Heintz1  upon 
palmitic  and  stearic  acids,  not  only  materially  supplemented  ' 
the  earlier  investigations  of  Chevreul  on  the  fats,  but  led 
to  the  discovery  of  new  and  wider  domains.  Important 
methods  for  the  separation  of  the  fatty  acids  resulted  from 
these  labours.  The  common  link  which  unites  the  com- 
pounds of  this  class  was  only  discovered  when  their  chemical 
constitution  came  to  be  understood.  The  successful  efforts 
of  Kolbe,  who  was  the  first  to  recognise  acetic  as  methyl- 
carboxylic  acid,  and  who  established  this  view  by  direct 
experiment,  have  been  already  described  in  the  general 
section.  It  has  indeed  been  from  acetic,  as  the  most  fully 
investigated  of  all  the  carboxylic  acids,  that  our  present 
ideas  upon  the  constitution  of  the  whole  class  of  compounds 
have  developed  themselves.  The  recognition  of  the  correct 
atomic  composition  of  acetic  acid  by  Berzelius  in  1814,  and 
of  its  relation  to  alcohol  by  Dobereiner  in  1821,  was  of 
great  importance  for  the  solution  of  this  problem. 

After  the  constitution  of  the  carboxylic  acids  had  once 
been  grasped,  it  became  possible  for  Kolbe  to  predict  the 
existence  of  other  members  of  this  class,  as  he  had  done  in 
the  case  of  the  alcohols,  and  thus  existing  blanks  could  be 
filled  up.  Of  special  importance  here  was  the  discovery  of 
isobutyric  acid,2  of  the  isomers  of  valeric  acid — itself 
already  long  known,  and  of  other  acids  richer  in  carbon, 
in  the  systematic  investigation  of  which  Lieben  and 

1  Ann.  Chem.,  vol.  Ixxxiv.  p.  297;  vol.  Ixxxviii.  p.  297;  Journ.  pr.  Chem. 
vol.  Ixvi.  p.  1. 

2  Erlenmeyer,  Ztschr.  Chem.  for  1865,  p.  651. 


442  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP.. 

Rossi1    and    Krafft,    among    others,    have    rendered    great 
service. 

The  knowledge  of  the  polybasic  saturated  carboxylic 
acids,  whose  chemical  constitution  was  likewise  only 
thoroughly  established  by  Kolbe's  speculations,  was  greatly 
advanced  by  the  work  of  Berzelius,  Fehling  and  others  on 
succinic  acid  (synthetised  from  ethylene  cyanide  by  Maxwell 
Simpson 2),  by  that  of  Arppe  on  adipic  acid  and  homologous 
compounds,3  and  by  the  discovery  and  investigation  of 
malonic  acid,4  &c.  The  ethers  of  this  last  acid  have 
served  for  the  synthesis  of  homologues  of  malonic  and  other 
polycarboxylic  acids,5  thanks  to  the  facility  with  which 
they  exchange  hydrogen  for  sodium ;  while  from  aceto-acetic 
ether,  which  so  closely  resembles  malonic,  there  have  been 
prepared  numerous  compounds  belonging  to  this  class,  to 
be  afterwards  systematically  investigated.  Drechsel's  memor- 
able synthesis  of  the  simplest  dibasic  acid,  oxalic,  from 
carbon  dioxide  and  sodium,6  also  deserves  mention  here. 
The  synthesis  of  the  mono-  and  polybasic  acids  has  proved 
in  most  cases  the  best  guide  to  their  constitution. 

The  wide  field  of  unsaturated  carboxylic  acids,  some  of 
which  (e.g.  acrylic,  angelic,  fumaric  and  maleic)  were  dis- 
covered at  an  early  date,  first  became  cultivated  with 
success  after  a  clear  idea  of  the  constitution  of  these  com- 
pounds had  been  arrived  at  through  Kekule's  admirable 
investigations7  on  the  two  last-named  and  on  the  pyro- 
citric  acids,  which  explained  the  behaviour  of  these  bodies 
to  nascent  hydrogen ;  and  after  Frankland  and  Duppa 8  had 
made  their  beautiful  syntheses,  which  resulted  in  the 

1  Cf.  Ann.  Ghent. ,  vol.  clix.  p.  75;  vol.  clxv.  p.  116. 

2  Proc.  JR.  S.,  vol.  x.  p.  574 ;  or  Ann.  Ghent.,  vol.  cxviii.  p.  373. 

3  Ann.  Chem.,  vol.  cxv.  p.  143;  vol.  cxx.  p.  288. 

4  Ibid.,  vol.  cxxxi.  p.  348. 

5  Cf.  Conrad,  Bischoff,  and  Guthzeit,  Ann.  Chem.,  vol.  cciv.  p.   121 ; 
vol.  ccix.  p.  211 ;  vol.  ccxiv.  p.  31. 

6  Ztschr.  Chem.  for  1868,  p.  120. 

i  Ann.  Chem.,  vol.cxxx.  p.  21 ;  vol.  cxxxi.  p.  81 ;  Suppl.,  vol.  i.  p.  129  ; 
vol.  ii.  p.  198. 

8  Journ.  Chem.  Soc.,  vol.  xviii.  p.  133;  or  Ann.  Chem.,  vol.  cxxvi.  p.  1. 


iv  UNSATURATED  CARBOXYLIC  ACIDS  443 


conversion  of  oxalic  ether  into  unsaturated  carboxylic 
acids.  In  fact  this  last  investigation  led  Frankland  to 
express  the  view  that  acrylic  acid  and  its  homologues  were 
derivatives  of  acetic  acid,  and  a  simple  explanation  was 
given  of  their  transformation  into  the  latter  (by  means  of 
potash).  The  more  recent  systematic  researches  of  Fittig  l 
and  his  pupils  on  the  unsaturated  carboxylic  acids  have 
contributed  in  great  degree  to  round  off  and  deepen  our 
knowledge  of  this  class  of  compounds.  The  latest  observa- 
tions on  the  molecular  transformations  of  the  so-called  a-/3- 
unsaturated  acids2  into  the  isomeric  /9-y-acids,  and  vice 
versa,  calls  for  particular  mention.  Remarkable  results,  too, 
have  been  obtained  by  A.  Saytzeff  and  others  on  the 
oxidation  of  such  acids  by  permanganate  of  potash.  The 
discovery  of  tetrolic  and  propiolic  acids  3  prepared  the  way 
for  an  acquaintance  with  the  carboxylic  acids  derived  from 
acetylene. 

The  discovery  and  careful  investigation  of  peculiar 
isomers  among  the  unsaturated  acids  has  been  carried  out 
more  particularly  during  the  last  ten  years.  The  observa- 
tions made  on  fumaric  and  maleic,  crotonic  and  isocrotonic, 
angelic  and  tiglic  acids  led  to  the  successful  attempt  — 
already  spoken  of  on  p.  356  —  to  explain  the  constitution  of 
these  and  similar  isomers  on  stereo-chemical  principles. 
Facts  bearing  on  this  subject  are  gradually  accumulating, 
t.g.  the  discovery  of  the  isomeric  cinnamic  acids  by  Lieber- 
mann,4  the  investigation  of  the  relations  existing  between 
erucic  and  brassidic  5  acids  by  Holt,6  Fileti  and  Saytzeff,  &c  ; 
but  we  are  not  yet  in  possession  of  a  theory  which  satisfac- 
torily explains  all  the  phenomena  of  this  kind. 

The  class  of  the  aromatic  carboxylic  acids,  with  benzoic 

1  Ann.  Chem.,  vol.  clxxxviii.  p.  87  ;  vol.  cxcv.  p.  50  ;  vol.  cc.  p.  21  ;  vol. 
ccvi.  p.  1  ;  vol.  ccviii.  p.  37. 

2  Fittig,  Ann.   Chem.,  vol.  cclxxxiii.  pp.  47  and  269. 

3  Geuther,  Journ.  pr.  Chem.  (2),  vol.  iii.  p.  448  ;  Bandrowski,  Ber.,  vol. 
xiii.  p.  2340. 

4  Ber.,  vol.  xxiii.  pp.  141,  512,  2510  ;  vol.  xxv.  pp.  90,  950. 


6  Ber.,  vol.  xxiv.  p.  4128;  vol.  xxv.  p.  1961. 


444  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP, 

acid  at  their  head,  has  been  the  subject  of  innumerable  and 
fruitful  researches.  We  have  but  to  recall  here  the  dis- 
covery of  the  peculiar  mode  of  formation  of  these  com- 
pounds from  hydrocarbons  by  oxidation,  as  well  as  by  the 
direct  introduction  of  the  elements  of  carbonic  acid  by  means- 
of  aluminic  chloride;1  and  the  splendid  investigations  on 
the  di-,  tri-,  and  poly-carboxylic  acids  of  benzene,2  to  the 
last  class  of  which  the  already  long-known  mellitic  acid  was 
found  to  belong.  The  aromatic  carboxylic  acids  of  unsaturated 
character,  like  cinnamic  acid,  etc.,  proved  particularly  easy 
of  examination  after  Perkin3  had  worked  out  the  reaction 
now  known  by  his  name — a  reaction  which  can  be  generally 
applied  to  their  formation.  Lastly,  the  isolation  of  phenyl- 
propiolic  acid 4  and  its  derivatives  has  led  to  results  of 
importance. 

The  esters  have  in  many  cases  proved  serviceable  for 
obtaining  other  important  derivatives  of  the  carboxylic 
acids;  thus,  by  means  of  the  reactions  which  have  been 
investigated  by  L.  Claisen  and  W.  Wislicenus,  ketones 
and  ketonic  acids,  etc.,  have  been  prepared  (see  those 
compounds). 

The  discovery  of  the  chlorides,  anhydrides  and  amides 
of  the  carboxylic  acids  deserves  particular  mention  herey 
since  these  classes  of  compounds  fill  an  important  place  in. 
the  history  of  organic  chemistry.  The  first  organic  acid 
chloride  was  benzoyl  chloride,  obtained  by  Liebig  and 
Wohler  by  the  action  of  chlorine  on  oil  of  bitter  almonds, 
in  their  classical  research  already  so  frequently  referred  to. 
The  general  method  for  the  preparation  of  such  compounds,  i.e.,, 
by  acting  upon  organic  acids  with  phosphorus  pentachlorider 
is  due  to  Cahours ; 5  since  then  this  reagent  has  been  a 

1  Friedel  and  Crafts,  Comptes  Rendus,  vol.  Ixxxvi.  p.  1368. 

2  Baeyer,  Ann.  Chem.,  Suppl.,  vol.  vii.  p.  1 ;  vol.  clxvi.  p.  325;  Fittigy 
ibid.,  vol.  cxlviii.  p.  11 ;  Graebe,  ibid.,  vol.  cxlix.  p.  18,  etc. 

3  Journ.  Chem.  Soc.,  vol.  xxi.  p.  53 ;  or  Ann.  Chem.,  vol.  cxlvii.  p.  229. 

4  Glaser,  Ann.  Chem.,  vol.  cliv.  p.  140;  Baeyer,  JBer.,vol.  xiii.  p.  2258. 

5  Ann.  Chem.,vol  Ix.  p.  254.  A.  Cahours  (1813-1891)  filled  the  chairs  of 
chemistry  at  the  Ecole  Centrale  and  the  Ecole  Polytechnique  of  Paris,  and 
was  at  the  same   time  Master  of  the  Mint  there.     In  addition  to  his 


vi  THE  ACID  CHLORIDES  AND  ANHYDRIDES  445 

standard  one  in  organic  chemistry,  and  has  proved  its  value 
in  the  most  varied  circumstances,  but  more  especially  for 
the  replacement  of  oxygen  or  hydroxyl  by  chlorine.  Phos- 
phorus oxychloride  was  applied  by  Gerhardt,1  and  phosphorus 
trichloride  by  Bechamp2  for  the  same  purpose;  these  are 
however  used  but  seldom  in  comparison  with  the  penta- 
chloride. 

The  great  capability  of  reaction  which  the  acid  chlorides 
possess  had  already  been  shown  by  Liebig  and  Wohler  in 
the  case  of  benzoyl  chloride,  from  which  they  prepared 
the  amide  of  benzoic  acid  with  ammonia,  the  ether  with 
alcohol,  and  the  sulphide  with  sulphide  of  lead,  thus 
introducing  at  the  same  time  general  modes  of  formation 
for  these  classes  of  compounds.  The  acid  chlorides  after- 
wards led  Gerhardt3  on  to  the  important  discovery  of  the 
acid  anhydrides,  which  have  likewise  proved  of  great  value 
for  the  synthesis  of  organic  compounds ;  take,  for  instance, 
acetic  anhydride,  so  often  used  for  obtaining  other  acetyl 
compounds  and  condensation-products,  and  phthalic  anhy- 
dride, an  extremely  reactive  substance.  Brodie4  then 
prepared  from  some  of  those  anhydrides  the  peroxides  of 
the  acid  radicals,  so  remarkable  in  their  behaviour,  which 
have  since  been  ranked  alongside  of  peroxide  of  hydrogen. 
To  the  acid  amides,  a  class  which  had  been  opened  up  by 
Dumas'  discovery  of  oxamide,  Gerhardt  added  the  anilides, 
and  thus  gave  the  impulse  to  the  sub-division  of  the  former 
into  primary,  secondary  and  tertiary  amides.  The  discovery 
of  the  aminic  acids  and  the  imides  of  polybasic  acids  must 

Ldcons  de  Chimie  generate  fiUmentaire — a  work  greatly  valued  in  France 
— he  published  numerous  researches  which  helped  materially  to  advance 
certain  branches  of  organic  chemistry;  e.g.,  papers  upon  amyl  alcohol, 
cuminol,  anisol,  oil  of  winter  green,  the  sulphines,  arsines,  stannines,  and — 
conjointly  with  A.  W.  Hofmann— upon  allyl  alcohol.  But  the  claim  put 
forward  by  Etard  in  his  obituary  of  Cahours  (Bull.  Soc.  Chim.  vol.  vii.  p.  1), 
that  the  latter  was  the  discoverer  of  sulphines,  is  mistaken  ;  the  priority  in 
this  belongs  to  von  Oefele. 

1  Ann.  Chim.  Phys.  (3),  vol.  xxxvii.  p.  285. 

2  Comptes  Rendus,  vol.  xl.  p.  944. 

8  Ann.  Chem.,  vol.  Ixxxii.  p.  131 ;  vol.  Ixxxvii.  p.  151. 

4  Proc.  R.  S.,  vol.  xii.  p.  655  ;  or  Ann.  Chem.,  vol.  cxxix.  p.  282. 


446  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP, 

also  be  mentioned  here, — compounds  which  are  closely 
related  to  the  amides ;  oxamic  acid  was  isolated  by  Balard, 
and  succinimide  by  Fehling.  And  reference  must  be  made, 
too,  to  the  connection  between  the  acid  nitriles  and  the 
primary  amides  of  the  acids,  the  latter  being  converted  into- 
the  former  by  the  abstraction  of  the  elements  of  water. 

The  investigation  of  certain  derivatives  of  the  carboxylic 
acids  has  led  to  results  of  very  great  moment,  in  that 
a  thorough  grasp  has  been  gained  of  the  relations  existing 
between  them  and  two  other  great  classes  of  compounds — 
the  oxy-  and  amido-aeids.  The  distinct  idea  which  is  now 
associated  with  the  terms  "  oxy-carboxylic  acid  "  and  "  amido- 
carboxylic  acid"  has  developed  itself  from  lactic  acid  and 
alanin  as  oxy-  and  amido-propionic  acids,  and  from  those 
other  compounds  already  known  for  such  a  long  time  before 
their  constitution  had  been  deciphered, — glycollic  acid  and 
glycocoll.  The  work  of  Wurtz,1  and  of  R.  Hofmann  and 
Kekule,2  among  others,  upon  those  substances,  and  especially 
the  decisive  investigations  of  Kolbe,  which  furnished  the  key 
to  a  thorough  explanation  of  the  facts,  laid  the  foundation  of 
our  present  knowledge  of  these  classes  of  compounds.3 

Of  great  importance  for  the  true  recognition  of  the 
relations  of  the  substances  just  named  to  one  another,  and 
to  the  carboxylic  acids  from  which  they  are  derived,  was 
the  transformation  of  the  amido-  into  oxy-acids  by  means 
of  nitrous  acid  (Piria,  Strecker,  etc.),  andjihe  conversion  of 
the  latter  into  the  corresponding  carboxylic  acids  by  means 
of  hydriodic  acid.  In  this  way  the  constitution  of  malic, 
tartaric,  aspartic,  lactic,  and  many  other  acids  was  definitely 
arrived  at,4  so  that  the  method  may  be  considered  as  a 
peculiarly  valuable  aid  in  elucidating  the  rational  composition 
of  many  organic  compounds.  Wislicenus5  has  contributed 
in  a  very  marked  degree  to  a  knowledge  of  the  various 

1  Ann.  Chim.  Phys.  (3),  vol.  lix.  p.  171. 

2  Ann.  Chem.,  vol.  cii.  p.  11 ;  vol.  cv.  p.  288.  3  Cf.  p.  319. 

4  Cf.  Schmitt,  Ann.  Chem.,  vol.  cxiv.  p.  106 ;  Kolbe,  ibid.,  vol.  cxxi.  p, 
232  ;  Lautemann,  ibid. ,  vol.  cix.  p.  268. 

5  Ann.  Chem.,  vol.  cxxviii.  p.  11  ;  vol.  clxvi.  p.  3;  vol.  clxvii.  p.  302. 


vi  THE  OXY-  AND  AMIDO-ACIDS  447 

lactic  acids,  his  work  on  the  subject  having  helped  greatly 
to  extend  the  doctrine  of  isomerism.  The  idea  of  "  physical 
isomerism,"  which  originated  in  the  different  behaviour 
of  substances  of  the  same  composition  towards  polarised 
light,  has  since  developed  itself  more  and  more,  Pasteur's 
memorable  researches1  on  Isevo-  and  dextro-tartaric  acids, 
and  on  the  inactive  racernic  acid  produced  by  their  com- 
bination, having  previous  to  this  thrown  much  light  upon 
the  subject.  It  has  been  already  explained  how  the  theory 
of  the  asymmetric  carbon  atom  arose.  The  few  isolated 
observations  which  led  to  its  establishment  have  since  been 
materially  increased,  and  prediction  has  been  verified  by  the 
discovery,  after  patient  search,  of  two  lactic,  mandelic  and 
malic  acids,  besides  other  compounds. 

Once  the  constitution  of  many  of  the  naturally  occurring 
oxy-  and  amido-acids  became  known,  the  synthetic  prepara- 
tion of  such  compounds  was  merely  a  question  of  time ;. 
thus,  lactic  acid  was  prepared  artificially  from  propionic  acid 
as  well  as  from  aldehyde,2  inactive  tartaric  acid  from 
dibromo-succinic,3  citric  acid  from  acetone,4  hippuric  acid 
(first  recognised  as  a  definite  compound  by  Liebig)  from 
glycocoll,5  and  salicylic  acid  from  phenol. 

This  last  leads  us  to  the  aromatic  oxy-acids,  and  to  the 
important  method  of  their  formation  from  phenates  and 
carbonic  acid,  discovered  by  Kolbe.6  A  complete  explanation 
of  this  general  reaction  has  only  of  late  been  given  by 
Schmitt,7  who  has  proved  that  the  production  of  an  isomer 
(sodium  phenyl-carbonate,  C6H5O.O.CO2Na)  precedes  that 
of  the  sodium  salicylate.  The  observation  that  the  phenates 
behave  very  differently  according  to  the  nature  of  their 

1  Ann.  Chim.  Phys.  (3),  vol.  xxiv.  p.  442;  vol.  xxviii.  p.  56;  vol.  xxxviii. 
p.  437. 

2  Wislicenus,  Ann.  Chem.,  vol.  cxxviii.  p.  11. 

3  Kekule,  ibid.,  vol.  cxvii,  p.  124. 

4  Grimaux  and  Adam,  Comptes  Rendus,  vol.  xc.  p.  1252. 

5  Dessaigne,  Jahresber.  d.  Chem.  for  1857,  p.  367. 

6  Cf.  Ann.  Chem.,  voL  cxiii.  p.  125  ;  vol.  cxv.  p.  201 ;  Journ.  pr.  Chern^ 
2),  vol,  x.  p.  95. 

7  Journ.  pr.  Chem.  (2),  vol.  xxxi.  p.  397. 


448  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 

^alkali, — that,  for  instance,  phenol-potassium  and  carbonic 
.acid  yield  the  isomeric  para-oxy-benzoic  acid  instead  of 
salicylic, — deserves  to  be  noted  here  as  especially  important. 
Ost's  discovery  of  the  phenol-di-  and  tri-carboxylic  acids, 
which  result  from  the  same  reaction  at  a  higher  temperature, 
must  also  be  recalled. 

Of  late  years  a  special  group  has  been  formed  of  a 
peculiar  class  of  oxy-acids  which  readily  change  into  the  so- 
called  lactones  or  intra-molecular  anhydrides,  with  separation 
-of  water.  Fittig,2  in  conjunction  with  his  pupils,  has  investi- 
gated this  remarkable  class  of  compounds  systematically,  and 
.has  largely  contributed  towards  a  knowledge  of  the  relations 
between  the  lactones  and  the  corresponding  acids,  and  also 
of  their  constitution,  which  formerly  received  a  different 
interpretation;  thus,  the  simplest  member  of  the  series, 
butyro-lactone,  was  previously  held  to  be  the  aldehyde  of 
succinic  acid.  The  relation  of  many  lactones  to  •  unsaturated 
acids  is  particularly  interesting.  Numerous  lactonic  acids  have 
also  been  examined,  and  found  to  be  carboxylic  derivatives 
-of  the  lactones. 

Aldehydes. 

The  knowledge  of  the  aldehydes,  so  important  from  many 
different  points  of  view,  has  gone  on  steadily  increasing  ever 
since  bitter  almond  oil  or  benzoic  aldehyde  was  first  investi- 
gated by  Liebig  and  Wohler,  and  ordinary  aldehyde  also  by 
the  former ;  the  latter  compound,  first  obtained  by  Fourcroy 
and  Dobereiner,  was  carefully  examined  by  Liebig.  The 
chemical  constitution  of  the  aldehydes  and  of  the  nearly  allied 
ketones  was  first  definitely  grasped  and  given  expression  to 
by  Kolbe.  Both  classes  of  compounds  acquired  special  im- 
portance after  their  capacity  for  combining  with  other  organic 
bodies  became  known;  they  were  thenceforward  largely 
utilised  for  the  synthesis  of  compounds  richer  in  carbon. 

1  Ibid. ,  (2),  vol.  xiv.  p.  95. 

2  Cf.  Ann.  Chem.,  vol.  ccviii.  p.  111.  ;  vol.  ccxvi.  p.  27;  vol.  ccxxvi. 
p.  322  ;  vol.   ccxxvii.   p.    1  ;  vol.  cclv.  pp.  1,  257 ;  vol.  cclvi.  p.  50 ;  vol. 
^clxviii.  p.  1. 


THE  ALDEHYDES  449 


Liebig  1  was  the  first  to  explain  the  relation  of  the  aldehyde 
of  acetic  acid  to  alcohol  on  the  one  hand,  and  to  acetic 
acid  on  the  other,  whereupon  Berzelius  pointed  out  clearly 
the  analogy  existing  between  aldehyde  and  acetic  acid 
and  bitter  almond  oil  and  benzoic  acid  respectively.  The 
mode  of  formation  of  the  aldehydes,  by  oxidation  of  the 
alcohols,  has  since  then  remained  the  general  one.  It  was 
only  discovered  at  a  much  later  date  that  members  of  this 
class  of  compounds  could  be  prepared  from  the  salts  of  the 
acids,  by  heating  these  with  sodium  formate.2  Still  more 
recent  is  the  discovery  of  the  method  of  preparing  aromatic 
aldehydes  from  phenols,  chloroform  and  alkali  (i.e.  nascent 
formic  acid),  a  reaction  which  has  led  to  the  isolation  of 
some  curious  compounds.3  And  quite  lately  Gattermann* 
has  made  the  remarkable  observation  that  aldehydes  are 
formed  by  the  union  of  a  hydrocarbon  with  carbon  monoxide 
in  presence  of  a  mixture  of  hydrochloric  acid,  cuprous  chloride 
and  chloride  of  aluminium.  The  aldehyde  of  formic  acid,  the 
first  member  of  its  series,  was  prepared  by  A.  W.  Hofmann,6 
the  simplest  representative  of  the  di-aldehydes,  glyoxal,  having 
already  been  obtained  long  before  by  Debus  (1856)  as  one 
of  the  products  of  the  oxidation  of  alcohol.  With  regard  to 
aldehydes  of  complex  composition,  many  of  these  were  long 
ago  isolated  from  various  ethereal  oils,  e.g.  oil  of  cinnamon,  oil  of 
cumin,  etc.,  and  recognised  as  analogues  of  ordinary  aldehyde. 
The  agreeable  odour  which  many  aldehydes  possess  rendered 
their  artificial  production  desirable,  and  so  in  this  way  van- 
illin, heliotropin  and  others  were  synthetised,  and  their  con- 
stitution established. 

Ordinary  aldehyde  has  been  ever  and  anew  the  subject  of 
important  investigations,  more  especially  since  Liebig  and 
Fehling  observed  its  tendency  to  polymerise  (into  para-  and 
meta-aldehydes).6  Liebig's  observation  that  benzoic  aldehyde 

1  Ann.  Chem.,  vol.  xiv.  p.  133  ;  vol.  xxii.  p.  273. 

2  Piria,  Ann.  Chem.,  vol.  c.  p.  114  ;  Limpricht,  ibid.,  vol.  ci.  p.  291. 

3  Reimer,  Ber.,  vol.  ix.  p.  423;  Tiemann,  ibid.,  vol.  ix.  p.  824  ;  vol.  x. 
p.  63. 

4  Ber.,  vol.  xxx.  p.  1620.  5  Proc.  7?.  £.,  vol.  xvi.  p.  156. 
6  Ann.  Chem.,  vol.  xxv.  p.  17  ;  vol.  xxvii.  p.  319. 

G  G 


450  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP, 

changed  into  the  polymeric  benzoin  in  presence  of  cyanide  of 
potassium  must  also  be  mentioned  here ;  it  was  the  origin 
of  further  work  which  led  to  the  discovery  of  such  interesting 
compounds  as  benzile,  benzilic  acid,  etc.  And  those  researches 
gained  an  increased  interest  through  the  discovery  of  aldol l  (a 
condensation  product  of  aldehyde,  of  the  same  percentage 
composition  with  it),  and  of  its  nearly  allied  compound,  cro- 
tonic  aldehyde ; 2  the  perception  of  the  constitution  of  the 
last-named  substance  was  of  importance  in  that  it  led  to  an 
explanation  of  this  "  condensation,"  and  therefore  also  of  other 
similar  processes. 

It  was  thus  from  aldehydes  that  a  knowledge  was  gained 
of  the  peculiar  chemical  reactions  now  known  generally  under 
the  above  name  of  condensations.  The  aldehydes  possess  in  a 
superlative  degree  the  capacity  for  combining  with  other  com- 
pounds of  similar  or  dissimilar  nature — e.g.  acids,  ketones, 
amines,  etc. — water  being  eliminated  (cf.  p.  363).  They  are 
thus  of  exceptional  value  for  the  synthesis  of  organic  com- 
pounds. A.  v.  Baeyer  was  the  first  to  point  out  that  formic 
aldehyde — the  simplest  member  of  the  series — played  a 
prominent  part  in  the  building  up  of  carbohydrates,  acids, 
and  other  compounds  in  plants. 

The  numerous  investigations  which  have  been  made  with 
the  object  of  explaining  such  reactions  of  aldehydes  with 
other  compounds,  under  elimination  of  water,  cannot  be  given 
in  detail  here.  Reference  can  only  be  made  to  those  of  W. 
H.  Perkin,  sen.,  who  showed  how  the  condensation  of  aromatic 
aldehydes  with  fatty  acids  might  be  effected, — a  reaction 
which,  developed  as  it  has  been,  still  continues  to  yield  rich 
fruit ; 3  and  to  the  researches  of  L.  Claisen,  who  has  systema- 
tically examined  the  manifold  condensation  processes  of  which 
the  aldehydes  and  ketones  are  capable.4 

While  an  extraordinary  number  of  new  and  important 

J  Wurtz,  Comptes  Rendus,  vol.  Ixxiv.  p.  1361. 

2  Kekute,  Ann.  Chem.,  vol.  clxii.  pp.  92,  309. 

3  Cf.  Ann.  Chem.,  vol.  ccxvi.  p.  115;  vol.  ccxxvii.  p.  48,  etc. 

4  Cf.  Ibid.,  vol.  clxxx.  p.  1 ;  vol.  ccxviii.  p.  121 ;  vol.  ccxxiii.  p.   137  ; 
vol.  ccxxxvii.  p.  261 ;  Ber.,  vol.  xxi.  p.  1135. 


vi  KETONES  AND  KETONIC  ACIDS  451 

compounds  has  been  obtained  in  this  way,  the  energies  of  many 
workers  have  also  been  devoted  for  a  long  time  to  the  pre- 
paration of  others  resulting  from  the  action  of  ammonia  upon 
the  aldehydes  (especially  benzoic  aldehyde),  and,  more  recently, 
to  the  compounds  similarly  obtained  with  hydroxylamine  and 
phenyl-hydrazine,  i.e.  the  aldoximes  and  hydrazones. 

The  thio-aldehydes  were  first  observed  a  long  time  ago,  but 
have  only  been  investigated  minutely  of  late  years,  more  es- 
pecially by  Baumann ;  remarkable  cases  of  isomerism  have 
been  discovered  among  them,  to  explain  which  recourse  is 
being  had  to  stereo-chemistry. — Mention  must  also  be  made 
of  the  discovery  and  gradual  examination  of  the  aldehyde- 
alcohols,  aldehyde-acids,  oxy-  and  amido-aldehydes,  and  the 
acetals, — these  last  being  closely  related  to  the  aldehydes. 
Like  aldehyde  itself,  these  various  substances  have  proved 
of  much  service  for  the  synthesis  of  many  important  com- 
pounds. 

Ketones  and  Ketonic  Acids. 

The  work  done  upon  the  ketones,  compounds  so  closely 
allied  to  the  aldehydes,  has  also  been  most  fruitful.  The 
simplest  member  of  this  class  of  bodies,  acetone,  had  already 
been  known  for  a  long  time  and  had  been  the  subject  of  fre- 
quent investigation  when  Liebig l  definitely  established  its 
composition.  Important  points  in  the  further  history  of  the 
ketones  were  (1)  the  discovery  of  their  mode  of  formation 
from  acid  chlorides  and  zinc  alkyls,2  and  (2)  the  preparation 
of  mixed  ketones  by  distilling  the  lime  salts  of  the  two 
carboxylic  acids  together.3  The  formation  of  those  peculiar 
compounds,  mesityl  oxide,  phorone  and  mesitylene,  from 
acetone  was  observed  a  long  time  ago,  but  it  was  only  com- 
pletely explained  after  similar  processes  depending  upon  the 
condensation  of  aldehyde  had  been  correctly  interpreted. 

1  Ann.  Chem.,  vol.  i.  p.  223. 

2  Freund,  Ann.  Chem.,  vol.  cxviii.  p.  1. 

3  Williamson,  Journ.  Chem.  Soc.,  vol.  iv.  p.  238  ;  or  Ann.  Chem.,  voL 
Ixxxi.  p.  86. 

G  G  2 


452  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 

The  remarkable  method,  discovered  by  Friedel  and  Crafts,  of 
synthetising  ketones  from  aromatic  hydrocarbons  and  acid 
chlorides  in  presence  of  chloride  of  aluminium,1  threw  open 
the  wide  field  of  fatty-aromatic  ketones.  The  behaviour  of 
these  last  towards  oxidising  agents,  especially  permanganate 
of  potash,  has  been  largely  investigated  and  has  led  to  very 
curious  results.2 

The  transformation  of  ketones  into  secondary  carbinols 
by  the  addition  of  hydrogen  has  been  already  spoken  of.3 
Equally  worthy  of  notice  was  the  conversion  of  acetone  into 
pinacone,4  a  diatomic  alcohol,  and  that  of  the  latter  into 
pinacoline ;  those  reactions,  extended  to  other — especially 
to  aromatic — ketones,  have  led  to  important  results.5 

The  analogy  of  the  ketones  to  the  aldehydes  is  very  clearly 
shown  by  the  fact  that  the  former  also  react  with  hydroxyl- 
amine  and  phenyl-hydrazine  to  produce  oximes  and  hydra- 
jzones,  the  investigation  of  which  has  likewise  proved  of  great 
value.  (See  below.) 

Entirely  new  fields  have  been  opened  up  by  the  investi- 
gation of  the  di-ketones,  to  which  acetyl-  and  benzoyl- 
acetones,  acetonyl-acetone,  naphthoquinone,  anthraquinone, 
and,  as  recent  researches  have  shown,  benzoquinone  and 
similar  compounds  belong, — substances  whose  nature  has 
been  elucidated  by  the  labours  of  Graebe,  Liebermann,  Fittig, 
Zincke,  Claisen,  Paal,  Combes  and  others. 

The  beautiful  condensation  of  esters  with  ketones,  discov- 
ered by  Claisen,6  has  made  known  to  us  the  so-called 
/3-diketones,  these  being  totally  distinct  from  the  correspond- 
ing a-  and  ^-compounds.  The  quinones  are  now  regarded 
with  special  interest,  on  account  of  a  quinonic  constitution 
being  assumed  for  many  dyes.  Indeed  Armstrong,  Nietzki 

1  Ann.  Chim.  Phys.  (6),  vol.  i.  p.  449  ;  or  Ber.,  vol.  xvii.,  Ref.  p.  376. 

2  Cf.  Popoff,  Ann.  Chem.,  vol.  clxi.  p.  289;  Glaus,  Journ.pr.  Chem.  (2) 
vol.  xli.  p.  396 ;  and  especially  Wagner,  ibid.,  vol.  xliv.  p.  257  (this  last 
gives  the  literature  on  the  subject). 

3  Cf.  p.  438. 

4  Fittig,  Ann.  Chem.  vol.  ex.  p.  25 ;  vol.  cxiv.  p.  54. 

5  Cf.  Zincke,  £er.,  vols.  x.  and  xi. 

6  £er.,\ol.  xxii.  pp.  1009,  3273,  etc. 


vi  THE  KETONIC  ACIDS  453 

and  others  suppose  that  this  actually  determines  the  dye- 
character  of  the  compounds  in  question. 

The  acids  known  as  croconic  acid,  carboxylic  acid 
(C10H4O10),  etc.,  prepared  from  potassium  carboxide,  were 
obtained  a  long  time  ago  by  Will  and  Lerch ;  the  beautiful 
researches  of  Nietzki1  have  shown  that  some  of  them  are 
related  to  benzoquinone,  while  others  are  derived  from  a 
compound  (not  yet  isolated)  containing  a  ring-shaped  mole- 
cule of  five  carbon  atoms.  The  obscurity  hitherto  surround- 
ing the  constitution  of  these  remarkable  bodies  has  thus 
been  dispersed.  They  are  now  known  as  poly-quinones. 

The  so-called  ketonic  acids,  certain  of  which  (e.g.  pyro- 
racemic)  have  been  known  for  a  long  time,  have  of  late  years 
awakened  the  interest  of  a  large  number  of  investigators, 
and  rightly  so ;  we  have  but  to  think  of  the  splendid  results, 
more  especially  from  the  synthetic  point  of  view,  which 
have  been  achieved  with  aceto-acetic  ether,2  levulinic  acid,s 
acetone-dicarboxylic  acid,4  benzoyl-carboxylic  acid 5  (which 
has  become  of  importance  through  its  relation  to  isatin),  and 
other  similar  compounds.  These  ketonic  acids  acquire  a 
still  greater  theoretical  interest  from  the  circumstance  that 
they  show  a  double  chemical  behaviour,  their  constitution,  as 
judged  from  certain  reactions,  being  that  of  hydroxyl  com- 
pounds, and  as  judged  from  certain  others,  that  of  carbonyl 
ones.6  Thanks  to  the  reaction  discovered  by  Claisen  and 
W.  Wislicenus,  of  which  mention  has  already  been  frequently 
made,  the  synthesis  of  the  ketonic  acids  has  been  carried  out 
most  thoroughly.  These  compounds  have  proved  of  the 
greatest  interest  in  many  respects ;  to  mention  only  a  few, — 
take  the  production  of  oxalo-acetic  and  formyl-acetic  esters  7 

1  Ber.,  vol.  xviii.  pp.  499  and  1833 ;  vol.  xix.  pp.  293  and  772. 

2  Of.  Wislicenus,  Ann.  Chem.,  vol.  clxxxvi.  p.  161  (contains  a  historical 
review). 

3  Conrad's  investigations  showed  this  to  be  j8-aceto-propionic  acid  (Ann. 
Chem.,  vol.  clxxxviii.  p.  223). 

4  v.  Pechmann,  Ber.,  vol.  xvii.  p.   2542;  Ann.   Chem.,  vol.  cclxi.  p. 
151.  6  Claisen,  Ber.,  vol.  x.  p,  430. 

6  See  General  Section,  p.  354. 

7  Ber.,  vol.  xx.  pp.  2931,  3392.     Claisen  and  v.   Pechmann  have  lately 


454  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 


and  the  remarkable  transformations  which  these  are  capable 
of  undergoing,  the  synthesis  of  chelidonic  acid 1  from  oxalic 
ether  and  acetone,  and  that  of  hydro-chelidonic  acid  and 
others.  And  if,  in  addition  to  these  points,  we  recollect  that 
a  large  number  of  interesting  compounds  like  camphor, 
menthone,  dehydracetic  acid,  pyrone  derivatives,  etc.,  belong  to 
the  family  of  ketones,  we  can  form  some  idea  of  the  extent  of 
the  field,  and  of  the  variety  of  results  to  be  obtained  from  it. 
Camphor,  especially,  with  its  almost  endless  allied  compounds 
and  derivatives,  has  for  some  years  past  been  investigated 
minutely  and  also  with  good  results,  but  the  views  of  different 
experimenters  as  to  its  constitution  are  still  far  from 
concordant.  Among  those  who  have  done  most  here, 
A.  v.  Baeyer  Beckmann,  Bredt,  Bourcault,  Friedel,  Tiemann 
and  Wallach  must  be  named. 


Carbohydrates  and  Glucosidcs. 

The  sugar  varieties,  which  are  so  widely  distributed  in 
nature,  and  many  of  which  have  been  known  from  an  early 
age,  belong  partly  to  the  alcohols  and  partly  to  the  aldehydes 
and  ketones.  Just  as  the  practical  importance  of  many  of 
these  bodies  has  increased  in  an  extraordinary  degree,  so  has 
also  their  purely  scientific  interest  augmented  with  an 
advancing  knowledge  of  the  close  relations  which  exist 
between  the  sugar  varieties  and  compounds  whose  constitu- 
tion has  been  already  worked  out.  Thus,  many  of  the  hexoses 
have  been  transformed  into  mannite,  which  is  now  known  to 
be  primary  hexyl  alcohol  containing  six  hydroxyl  groups  in 
place  of  five  hydrogen  atoms ;  the  rational  composition  of 
saccharic,  mucic  and  levulinic  acids,  which  are  more  or  less 
intimately  related  to  the  sugars,  has  been  arrived  at ;  and  the 
acid  ethers  of  the  latter  have  been  obtained,  &c.  Such 
observations  as  these  give  support  to  the  assumption  that 
those  carbohydrates  which  are  comprised  under  the  term 

proved  that  this  so-called  formyl-acetic  ester  is  really  oxy-acrylic  (Ber., 
vol.  xxv.  p.  1040).  1  jBer.,  vol.  xxiv.  p.  111. 


vi  THE  CARBOHYDRATES  455 

glucoses,  or — better — hexoses,  are  to  be  regarded  as  derived 
from  hexatomic  alcohols,  from  which  two  atoms  of  hydrogen 
have  been  withdrawn  in  such  a  manner  that  they  contain  the 
formyl  of  the  aldehydes  or  the  carbonyl  of  the  ketones 
{Baeyer,  Fittig,  V.  Meyer). 

The  investigation  of  the  individual  sugars — of  their 
-chemical  behaviour  and  the  products  of  their  decomposition- 
has  been  participated  in  by  a  great  number  of  chemists ; 
-among  those  who  have  actively  busied  themselves  with  the 
subject  we  may  mention  Brouchardat,  Brown  and  Heron, 
Kiliani,  v.  Lippmann,  O'Sullivan,  Salomon,  Scheibler,  Soxhlet, 
Tollens 1  and,  especially,  Emil  Fischer.2  Fischer's  beautiful 
investigations,  published  in  the  Berichte  3  during  the  last  ten 
years  or  so,  have  given  us  a  deep  insight  into  the  constitution 
of  the  sugars.  They  have  not  only  corroborated  the  assump- 
tion that  the  latter  are  partly  aldehyde-alcohols  (aldoses), 
and  partly  ketone-alcohols  (ketoses),  but  have  also  paved  the 
way  for  the  stereo-chemical  elucidation  of  the  numberless 
isomers  which  exist  among  them. 

Phenyl-hydrazine  (p.  365)  has  proved  itsel£  of  the  greatest 
value  for  characterising  individual  sugars  ;  and,  by  means  of 
the  osazones  produced  by  this  interaction,  the  conversion  of  one 
carbohydrate  into  another  can  be  effected.  The  aldehydic  or 
ketonic  nature  of  these  compounds  was  established  by  this 
reaction,  by  the  formation  of  addition-compounds  with  hydro- 
cyanic acid,4  and  by  other  means.  To  crown  all,  various 

1  Cf.  Tollens'  Handbuch  der  Kohlerihydrate  ("Text-Book  of  the  Carbo- 
hydrates," second  edition). 

2  Emil  Fischer,  born  on  the  9th  of  October,}! 852,  at  Enskirchen  in  Rhenish 
Prussia,  was  a  pupil  of  A.  von  Baeyer.   He  has  done  an  immense  amount  of 
brilliant  work  in  organic  chemistry,  much  of  which  will  be  referred  to  in 
the  special  section.     After  filling  successively  the  chairs  of  Chemistry  at 
Erlangen  and  (after  1885)  at  Wurzburg,  he  was  called  in  1892  to  Berlin  as 
successor  to  the  late  A.  W.  von  Hofmann.      His  Anleitung  zur  Darstellung 
organischer  Prdparate  has  established  itself  as  a  laboratory  manual, 

8  Victor  Meyer  and  Jacobsen's  Lehrbuch  der  organischen  Chemie,  p.  876 
et  seq. ,  contains  a  very  clear  account  of  the  chemistry  of  the  sugars,  besides 
giving  the  literature  on  the  subject.  E.  Fischer's  lecture  on  the  Sugar 
Group  (Ber.,  vol.  xxiii.  p.  2114)  and  his  rdsumd  of  sugar  syntheses  (Ber.y 
vol.  xxvii.  p.  3189)  should  also  be  read.  4  Kiliani ;  E.  Fischer. 


456  HISTORY  OF  ORGANIC  CHEMISTRY  CHAR 

sugars  (partly  new  ones,  partly  sugars  occurring  in  nature) 
have  been  built  up  artificially  from  such  simple  compounds  as 
formic  and  glyceric  aldehydes ;  in  this  way  E.  Fischer  has 
succeeded  in  synthetising  fruit  and  grape  sugars. 

That  the  systematic  arrangement  of  the  carbohydrates 
has  become  infinitely  clearer  from  these  researches  requires 
no  demonstration.  The  mono-saccharides  are  now  dis- 
tinguished from  the  poly-saccharides  (cane  sugar,  starch,  cel- 
lulose, etc.),  the  former  including  not  only  the  (6  -carbon) 
glucoses  or  hexoses,  but  also  compounds  of  similar  chemical 
character  containing  no  more  than  3,  4  and  5  atoms  of 
carbon  in  the  molecule. 

A  great  deal  of  work  has  also  been  done  upon  starch,, 
dextrine,  etc.,  among  others  by  Brown  and  Heron,1  Brown 
and  Morris,2  and  O'Sullivan.  But,  notwithstanding  this,  our 
knowledge  of  the  poly-saccharides,  which  are  regarded  as 
ethereal  anhydrides  of  the  glucoses,  is  very  imperfect  indeed 
in  comparison  with  that  of  the  mono-saccharides. 

The  glucosides,3  which  stand  in  the  most  intimate  rela- 
tion to  the  glucoses,  and  whose  occurrence  in  the  vegetable 
and  animal  kingdoms  awakened  the  interest  of  chemists  of 
the  highest  eminence  at  a  very  early  date,  have  been  the  sub- 
jects of  important  work  ever  since  the  memorable  investiga- 
tion of  Liebig  and  Wohler  on  amygdalin,  and  that  of  Piria  on 
salicin.  Among  other  researches  we  would  refer  here  to 
those  of  Will 4  on  myronic  acid,  of  Tiemann  and  Haarmaiirt 
on  coniferin,  of  Will  on  sesculin,  and  lastly  of  Tiemann  and  de 

1  Journ.  Chem.  Soc.,  vol.  xxxv.  p.  596;  or  Ann.  Chem.,  vol.  cxcix. 

2  Journ.  Chem.  Soc.  vol.  Iv.  p.  473. 

3  Cf.  the  article  Glycoside,  by  0.  Jacobsen,  in  Ladenburg's  Handwo'rter- 
buck  der  Chemie. 

4  Heinrich  Will  (1812 — 1890),  after  working  for  some  time  with  a  phar- 
macist, studied  chemistry  under  L.   Gmelin.     Coming  subsequently  into 
contact  with  Liebig,  he  became  Docent  at  Giessen,  succeeding  to  Liebig's 
chair  there  when  the  latter  was  called  to  Munich,  and  soon  making  hia 
mark   as  a   teacher.     Besides  producing  a  great  quantity  of  admirable 
experimental  work,  mostly  in  organic  chemistry,  but  partly  in  analytical, 
the  results  of  which  were  published  in  the  Anncden  der  Chemie,  his  literary 
labours  were  of  very  high  value,  notably  his  collaboration  in  editing  Liebig's- 
Jahresbericht  and  the  Anncden. 


vi  ORGANIC  HALOGEN  COMPOUNDS  457 

Laire  on  iridin,  the  glucoside  of  the  Florentine  iris  root — re- 
searches which  resulted  in  the  elucidation  of  the  decomposi- 
tion-products of  the  glucosides  named,  and  which  laid  the 
foundation  for  a  knowledge  of  the  constitution  of  these  and 
other  compounds  of  the  same  class,  so  widely  distributed  in 
nature.  The  expectation  that  those  natural  products  will 
ultimately  be  obtained  artificially  has  been  brought  within 
measurable  distance  by  E.  Fischer's  recent  discovery  of  a 
simple  method  for  preparing  the  glucosides  of  the  alcohols.1 


Haloid  Derivatives  of  the  Hydrocarbons  and  other 
Compounds. 

As  an  appendix  to  the  results  of  the  investigations  referred 
to  above, investigations  which  have  largely  increased  our  know- 
ledge of  the  hydrocarbons,  alcohols,  carboxylic  acids,  aldehydes 
and  ketones,  some  others  must  be  mentioned  here  which 
bear  upon  the  haloid  and  other  similar  derivatives  of  those 
compounds. 

Hand  in  hand  with  the  examination  of  the  hydrocarbons 
went  that  of  their  haloid-  and  nitre-derivatives,  for  in  some 
cases  these  were  easily  obtained  from  the  hydrocarbons,  while 
in  others  they  often  served  for  the  preparation  of  the  latter. 
The  formation  of  chlorine  and  bromine  compounds  from 
hydrocarbons  was  the  subject  of  highly  important  discussions, 
arising  from  the  experiments  upon  substitution-reactions- 
made  and  suggested  by  Dumas  and  Laurent,  and  for  the  ex- 
planation of  which  special  theories  were  advanced;  take,  for 
example,  the  first  investigations  made  in  this  direction — 
those  upon  the  action  of  chlorine  on  naphthalene,  ethylene 
and  ethylene  chloride. 

Other  views  began  to  prevail  when,  with  the  setting  up 
of  a  new  theory  of  the  aromatic  compounds,  the  difference 
between  the  hydrogen  atoms  of  the  benzene  molecule  and 
those  belonging  to  the  substituting  radicals  which  had  entered 
it  came  to  be  recognised.  This  difference  was  markedly  ap- 
1  Ber.,  vol.  xxvi.  p.  2400;  vol.  xxvii.  p.  1145. 


458  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 

parent  in  the  case  of  the  halogens,  and  was  clearly  demon- 
strated by  the  work  of  Kekule,  Fittig,  Beilstein  and  others.1 
Further,  the  study  of  the  remarkable  isomeric  relations,  pre- 
dicted on  theoretical  grounds  by  Kekule*  for  the  derivatives 
of  benzene,  led  to  the  thorough  examination  of  the  haloid 
substitution-products  of  the  aromatic  hydrocarbons. 

After  substitution  by  chlorine  has  been  more  or  less  in- 
vestigated, attention  was  directed  to  the  action  of  bromine 
.and  iodine  upon  organic  compounds.  And  here  it  was  soon 
recognised  that  the  presence  of  certain  reagents  such  as 
phosphorus,  iodic  acid  and  mercuric  oxide  had  a  wonderful 
effect  in  facilitating  the  replacement  of  hydrogen  by  these 
elements. 

Closely  connected  with  this  were  the  researches  on 
the  so-called  "halogen  carriers,"  which  include  a  large 
number  of  the  elements — those,  namely,  whose  compounds 
with  the  halogens  are  capable  of  partially  yielding  up  the 
latter  again ;  this  explains  their  action  as  halogen  conveyers. 
The  above  action  has  been  examined  more  especially  in  the 
case  of  the  aromatic  hydrocarbons;  without  entering  into 
details,  we  would  refer  here  to  the  investigations2  on  the 
.subject  carried  out  at  L.  Meyer's  suggestion  by  Aronheim, 
Page,  Scheufelen,  Schwalb  and  others,  and  to  those  of  Will- 
gerodt.3  The  earliest  observations  on  this  point  were  made 
by  H.  Mtiller  in  1862,  when  he  noticed  how  chlorine  was 
conveyed  by  iodine  in  the  action  of  the  former  upon 
benzene  and  its  homologues. 

Two  classes  of  peculiar  iodine-oxygen  compounds  have 
.lately  been  added  to  the  aromatic  group  by  Willgerodt 4  and 
Victor  Meyer5  respectively.  Corresponding  in  composition 
with  the  nitroso-  and  nitro-compounds,  they  have  been 

1  Cf.  Ann.  Chem.,  vol.  cxxxvi.  p.  301 ;  vol.  cxxxvii.  p.  192  ;  vol.  cxxxix. 
p.  331. 

2  Cf.  Ann.  Chem.,  vol.  ccxxxi.  p.  152  (contains  a  historical  review). 

3  Journ.  pr.  Chem.  (2),  vol.  xxxiv.  p.  264 ;  cf.  also  Neumann,  Ann.  Chem., 
vol.  ccxli.  p.  33  ("Sulphuric  Acid  as  a  Carrier  of  Iodine"). 

4  Eer.,  vol.  xxv.  p.  3494;  vol.  xxvi.  pp.  357,  1307,  1532. 

5  Ber.,  vol.  xxv.  p.  2632 ;  vol.  xxvi.  p.  1354  ;  vol.  xxvii.  pp.  1592,  2326  ; 
-vol.  xxviii.  p.  83. 


vi  ORGANIC  HALOGEN  COMPOUNDS  459 

named  accordingly  (e.g.  iodoso-benzene,  C6H5IO,  and  iodo- 
benzene,  C6H5I02).  The  interesting  iodonium  bases  must 
also  be  included  here. 

Attempts,  which  have  been  to  some  extent  followed  with 
success,  have  also  been  made  to  determine  the  laws  govern- 
ing the  substitution  of  definite  hydrogen  atoms  by  halogens ; 
in  connection  with  this  the  recent  systematic  experiments  of 
Victor  Meyer  and  his  pupils  deserve  mention.1  An  infinity 
of  work  has  been  done  in  this  direction  with  aromatic  com- 
pounds, the  object  being  to  determine  the  order  in  which 
the  hydrogen  atoms  of  benzene  and  its  homologues  and  of 
their  derivatives  are  thus  replaced. 

The  numerous  researches  on  the  combination  of  halogens 
with  unsaturated  hydrocarbons  were  of  very  great  moment, 
the  first  example  of  such  an  addition  being  afforded  by 
ethylene.  It  would  be  out  of  place  here  even  to  mention 
only  the  more  important  investigations  bearing  upon  reactions 
of  this  nature;  but  it  may  be  stated  generally  that  our 
present  views  with  respect  to  the  constitution  of  unsaturated 
compounds  have  resulted  in  great  degree  from  the  behaviour 
of  such  hydrocarbons  to  the  halogens  and  halogen  hydrides. 
These  addition-reactions  have,  besides,  proved  of  unexpected 
value  in  the  explanation  of  cases  of  stereo-isomerism  (cf.  p. 
358). 

The  modes  of  formation  of  haloid  derivatives  of  the 
hydrocarbons  are  typical,  i.e.  are  also  applicable  to  other 
classes  of  compounds,  e.g.  acids,  ketones,  etc.  And  the  same 
holds  good  for  the  chemical  behaviour  of  such  compounds, 
this  having  been  in  most  cases  first  established  for  the  haloid 
derivatives.  To  mention  only  one  or  two  of  the  researches 
which  have  advanced  our  knowledge  of  the  subject — take 
the  discovery  and  investigation  of  trichloracetic  acid  by 
Dumas,2  that  of  chloral  by  Liebig  and  Dumas,3  and  that  of 
monochlor-acetic  and  monochloro-propionic  acids,  from  whose 
chemical  behaviour  the  constitution  of  the  corresponding  oxy- 

1  Cf.  V.  Meyer  and  Fr.  Miiller,  Journ.  pr.  Chem.  (2),  vol.  xlvi.  p.  161. 

2  Ann.  Chem.,  vol.  xxxii.  p.  101. 

3  Ibid.,  vol.  i.  p.  189;  Ann.  Chim.  Phys.,vol.  Ivi.  p.  123. 


460  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP, 

and  amido-acids  was  established  by  Kolbe.  It  is  impossible 
to  record  here  even  the  most  important  work  of  recent  years 
in  this  direction,  but  a  passing  reference  must  be  made  to 
the  production  in  theoretical  quantity  of  aromatic  halogen 
derivatives  from  the  corresponding  diazo-  or  amido-com- 
pounds.1 

Mention  must  lastly  be  made  of  the  important  part 
which  the  halogen  compounds  have  played  in  organic 
syntheses;  take,  for  example,  their  interactions  with  sodio- 
aceto-acetic  ether,  sodio-malonic  ether,  and  the  zinc  alkyls,, 
besides  many  other  synthetic  reactions. 

Organic  compounds  of  fluorine  have  repeatedly  been  the 
object  of  research,  notwithstanding  which  our  knowledge  of 
them  is  still  limited.  Although  six  decades  have  passed 
since  methyl  fluoride  was  described  by  Dumas  and  Peligot,, 
it  is  only  within  the  last  few  years  that  the  systematic  study 
of  these  fluorine  compounds  has  been  taken  in  hand  by 
Moissan,  Meslans  and  others. 


Nitro-  and  Nitroso-compounds. 

Mitscherlich's  discovery  and  investigation  of  nitro- 
benzene2 paved  the  way  for  a  knowledge  of  the  nitro- 
compounds;  the  formation  of  this  substance  from  benzene 
and  its  relation  to  the  latter  were,  however,  only  clearly 
understood  after  the  adoption  of  Dumas  and  Gerhardt's  view 
that  nitro-benzene  was  a  substitution-product  of  benzene. 
Since  then  the  group  nitroxyl  (NO2)  has  been  ranked  as  a 
substituent  alongside  of  the  halogens.  There  is  scarcely  any 
reaction  which  has  been  more  frequently  applied  among  the 
aromatic  compounds  than  the  action  of  nitric  acid  upon 
them ;  take,  for  instance,  the  discovery  of  mtro-naphthalene, 
of  di-  and  tri-nitrobenzenes,  and  of  the  nitro-derivatives 
of  benzoic  acid,  benzoic  aldehyde,  phenol,  etc.  Picric  acid, 
which  was  so  much  earlier  known  than  nitro-benzene,  was 
first  characterised  as  trinitro-phenol  by  Gerhardt.  It  may  be 

1  P.  Griess  and  also  0.  Sandmeyer,  Ber.t  vol.  xvii.  pp.  1633,  2651 ;  vol. 
xxiii.  p.  1880.  -  Ann.  Chem.,  vol.  xii.  p.  305. 


vi  NITRO-  AND  NITROSO-COMPOUNDS  461 

taken  for  granted  that  nitro-derivatives  of  every  aromatic 
compound  are  known,  or  at  any  rate  can  be  prepared. 
Attention  will  be  called  later  on  to  the  history  of  some  of  the 
classes  of  compounds  proceeding  from  these  nitro-derivatives, 
e.g.  the  amines  and  azo-compounds,  which  have  been  destined 
to  play  such  a  prominent  part  in  industrial  chemistry. 

The  first  nitro-derivatives  of  saturated  compounds  date 
from  the  year  1872,  when  Kolbe  discovered  nitro-methane l 
and  Victor  Meyer  nitro-ethane.2  The  modes  of  formation  of 
these  substances  were  particularly  calculated  to  arouse  the 
reflection  of  chemists,  since  it  was  to  have  been  expected 
here  that  compounds  of  quite  other  constitution — ethers  of 
nitrous  acid — would  have  been  obtained  instead.  The 
thorough  investigation  and  explanation  of  the  chemical 
nature  of  nitro-ethane  is  due  to  V.  Meyer.  Those  splendid 
researches3  of  his  resulted  further  in  the  discovery  (by 
himself)  of  other  remarkable  compounds,  which  include  the 
nitrolic  acids  and  nitrols.  It  must  however  be  mentioned 
that  the  constitution  of  the  nitro-paraffins  hitherto  assumed, 
viz.  R(NO2),  has  of  late  been  called  in  question  more  than 
once,  on  the  ground  of  the  chemical  behaviour  of  these 
compounds.4 

The  nitrolic  acids  and  nitrols  have  been  proved  to  be 
representatives  of  the  two  classes  of  isonitroso-  and  nitroso- 
<jompounds,  which  have  repeatedly,  and  more  especially  of 
late  years,  awakened  the  interest  of  chemists.  It  was  those 
investigations  of  Victor  Meyer  and  his  pupils  which  estab- 
lished the  constitution  of  the  isonitroso-compounds,  and 
showed  how  they  were  formed  by  the  action  of  hydroxyl- 
amine  upon  substances  containing  the  radical  carbonyl. 
Thanks  to  this  perfect  reaction,  so  universally  applicable, 
many  substances  which  were  formerly  numbered  among  the 
nitroso-compounds  have  since  been  recognised  as  really 
belonging  to  the  class  of  their  isomers.  On  the  other  hand, 

1  Journ.  pr.  Chem.  (2),  vol.  v.  p.  427. 

2  Ber.,  vol.  v.  pp.  399,  514. 

3  Ann.  Chem.,  vol.  clxxi.  p.  1 ;  vol.  clxxv.  p.  88;  vol.  clxxx.  p.  111. 

4  Nef,  Ann.  Chem.,  vol.  cclxxx.  p.  263. 


462  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP, 

the  above  reaction  has  proved  itself  a  convenient  means  of 
testing  whether  or  not  compounds  contain  the  radical 
carbonyl.1  From  those  simple  researches  there  have  thus 
been  drawn  valuable  conclusions  with  respect  to  the  consti- 
tution of  whole  classes  of  compounds,  e.g.  of  the  quinones.2 

The  compounds  obtained  by  the  action  of  hydroxylamine 
on  the  aldehydes  and  ketones — the  aldoximes  and  Jcetoximes 
— have  for  a  number  of  years  back  been  much  studied  by 
the  late  Victor  Meyer,  Beckmann,  Behrend,  Hantzsch,  Auwers 
and  others,  on  account  of  the  remarkable  cases  of  isomerism 
that  they  show.  In  fact,  the  investigation  of  isomeric 
oximes  and  the  peculiar  chemical  behaviour  of  these  sub- 
stances, form  the  basis  of  the  stereo-chemistry  of  nitrogen 
(cf.  p.  359).  Only  a  few  chemists  (Glaus,  Minunni  and  Nef) 
have  brought  forward  arguments  against  this  view,  seeking 
to  explain  these  isomers  on  structural  grounds. 

Organic  compounds  containing  the  group  phosphyl  (POg) 
were  also  prepared  a  few  years  ago;3  the  constitution  of 
these  is  analogous  to  that  of  the  nitro-  and  of  the  iodo- 
compounds  (p.  459 — 460). 


Development  of  the  Knowledge  of  Sulphur  Compounds. 

The  examination  of  organic  sulphur  compounds  has 
proved  of  great  value  for  the  development  of  our  views 
upon  the  constitution  of  organic  compounds  generally,  and 
more  especially  upon  the  saturation-capacity  of  the  sulphur 
group  of  elements.  Their  investigation  has  led  to  the 
abandonment  of  the  one-sided  opinion  that  sulphur,  selenium 
and  tellurium  can  only  act  as  divalent  elements,  by  furnishing 
proofs  that  they  may  also  be  tetra-  or  hexa-valent. 

The  earliest  known  of  those  compounds,  which  contain 
sulphur  combined  in  the  same  manner  as  the  alcohols,  carb- 

1  In  phenyl-hydrazine  E.  Fischer  discovered  an  analogous  and  equally 
serviceable  reagent  for  carbonyl  compounds,  which  has  proved  of  the  utmost 
value  in  establishing  the  constitution  of  a  very  large  number  of  substances 
— the  sugars,  for  instance  (cf.  p.  455).  2  Cf.  p.  452. 

3  Michaelis  and  Rothe,  Ber.,  vol.  xxv.  p.  1747. 


vi  SULPHONIC  ACIDS  AND  SULPHONES  46$ 

oxylic  acids,  ethers,  etc.,  contain  oxygen,  was  mercaptan,  dis- 
covered by  Zeise ;  its  true  constitution,  as  a  hydrosulphide 
corresponding  to  alcohol,  was  recognised  by  Liebig.1  To  this- 
there  were  soon  added  ethyl  sulphide  and  its  polysulphides, 
whose  analogy  to  the  sulphides  of  the  metals  was  obvious. 
The  similarly  constituted  selenium  and  tellurium  compounds 
were  to  a  great  extent  worked  out  by  Lowig 2  and  Wohler.3 

Of  organic  acids  which  contain  sulphur  in  place  of 
oxygen,  thiacetic  acid,4  discovered  by  Kekule',  was  the  first 
known,  although  benzoyl  sulphide  had  previous  to  this  been 
regarded  as  the  "  thio-anhydride "  of  such  an  acid.  Since 
then  the  number  of  these  acids  and  their  corresponding 
aldehydes  has  been  greatly  extended  (cf.  p.  450).  Thio- 
glycollic  acid  (analogous  to  glycollic)  and  its  analogues  have 
been  investigated  mainly  by  Klason.5 

By  the  action  of  powerful  reagents  on  many  of  the 
compounds  containing  divalent  sulphur,  which  have  just 
been  spoken  of,  it  has  been  found  possible  to  prepare  others 
in  which  the  sulphur  present  possesses  a  higher  valency — 
compounds  which  are  comparable  with  sulphurous  and 
sulphuric  acids,  and  which  can  be  derived  and  in  part 
prepared  from  the  latter.  The  earliest  known  of  these 
were  the  sulphonic  acids  and  sulphones,  whose  first  repre^ 
sentatives — phenyl-sulphonic  acid  and  diphenyl-sulphone 
(Sulphobenzid) — were  obtained  by  Mitscherlich,6  by  acting 
upon  benzene  with  sulphuric  acid.  These  compounds,  how- 
ever, only  came  to  be  fully  understood  after  Kolbe  had 
shown  them  to  be  derivatives  of  sulphuric  acid  and  its 
anhydride.  Previous  to  this  (in  1844)  he  had  enlarged 
the  then  existing  knowledge  of  the  sulphonic  acids  by  hi& 
work  upon  methyl-sulphonic  acid  and  its  chlorine  derivatives. 
The  important  discovery  7  of  the  transformation  of  hydrosul- 

1  Ann.  Chem.,  vol.  xi.  pp.  2,  11.  2  Pogg.  Ann.  vol.  xxxvii.  p.  552., 

3  -47171.  Chem.,  vol.  xxxv.  p.  Ill  ;  vol.  Ixxxiv.  p.  69. 

4  Ibid.,  vol.  xc.  p.  311. 

5  Cf.  Ibid.,  vol.  clxxxvii.  p.  113. 

6  Pogg.  Ann.,  vol.  xxix.  p.  231 ;  vol.  xxxi.  p.  628. 

7  Lowig,  Pogg.  Ann.,  vol.  xlvii.  p.  153;  Muspratt,  Ann.  Chem.,  vol, 
Ixv.  p.  251. 


464  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 

phides,  disulphides  and  sulphocyanides  into  sulphonic  acids 
furnished  a  general  method  for  the  preparation  of  the  latter. 

In  a  similar  manner  the  conversion  of  the  alkyl  sulphides 
into  sulphones,  which  contain  two  atoms  of  oxygen  more  in 
the  molecule,  was  effected.1  Kolbe  was  again  the  first  here 
to  point  out  definitely  the  analogy  between  sulphones  and 
ketones,  and  sulphonic  and  carboxylic  acids.  There  have 
been  added  lately  to  the  di-ketones  the  di-sulphones  and  the 
.sulphone-ketones  (products  intermediate  between  the  two), 
in  whose  investigation  R.  Otto  2  has  done  more  than  any 
one  else.  The  di-  and  tri-sulphonic  acids,  which  correspond 
to  the  poly-carboxylic,  have  been  known  for  a  long  time, 
Hofmann  and  Buckton  3  having  been  the  first  to  investigate 
them. 

The  mercaptals,  sulphur  analogues  of  the  acetals,  were 
prepared  by  Baumann4  by  the  action  of  aldehydes  upon 
mercaptans ;  and  the  mercaptols  were  got  in  the  same  way, 
ketones  being  substituted  for  aldehydes.  Among  the  di- 
sulphones  produced  by  the  oxidation  of  the  mercaptols  is 
the  well-known  soporific  sulphonal. 

Von  Oefele's  discovery  of  the  sulphines 5  was  particularly 
pregnant  in  its  results,  because  the  existence  of  these  com- 
pounds stood  in  contradiction  to  the  assumption  that  the 
sulphur  atom  was  invariably  divalent.  And  the  same 
applies  to  the  investigation  of  the  sulph-oxides  by  Saytzeff,6 
and  to  that  of  the  sulphinic  acids,  whose  formation  and 
chemical  behaviour  was  cleared  up  by  the  work  of  Kalle, 
Otto,  Klason  and  others.  Mention  must  also  be  made  here 
of  the  remarkable  conversion  of  sulphinates  into  sulphones,7 
and  of  sulphites  into  sulphonic  acids 8  by  means  of  alkyl 
iodides,  those  reactions  having  led  to  conclusions  respecting 

1  Von  Oefele,  Ann.  Chem.,  vol.  cxxxii.  p.  80. 

2  Journ.  pr.  Chem.  (2),  vol.  xxx.  pp.  171,  321 ;  vol.  xxxvi.  p.  401. 

3  Ann.  Chem.,  vol.  c,  p.  133. 

4  Ann.  Chem.,  vol.  cclxxiv.  p.  173;  Ber.,  vol.  xxvi.  p.  2155. 

5  Ann.  Chem.,  vol.  cxxvii.  p.  370;  vol.  cxxxii.  p.  82. 

6  Ibid.,  vol.  cxliv.  p.  148. 

7  Otto,  Ber.,  vol.  xiii.  p.  1274. 

8  Strecker,  Ann.  Chem.,  vol.  cxlviii.  p.  90. 


vi  ORGANIC  AMMONIAS,  ETC.  465 

the  constitution  both  of  the  sulphinic  acids  and  the  sulphites. 
By  the  discovery  and  careful  investigation  of  the  thionyl- 
amines,  Michaelis  has  added  another  class  to  the  list  of 
sulphur  compounds. — Organic  compounds  of  selenium  and 
tellurium  corresponding  to  the  above-mentioned  sulphur 
ones  are  as  yet  but  sparingly  known. 

Organic  Nitrogen  Compounds, 

An  exceptionally  wide  field  in  organic  chemistry  was 
opened  up  by  the  discovery  of  the  nitrogenous  bases  corre- 
sponding to  ammonia.  When  their  connection  with  the 
latter  was  found  out,  the  question  of  their  chemical  con- 
stitution in  general  was  solved,  A.  W.  Hofmann's  classical 
researches1  on  the  substituted  ammonias  and  ammonium 
bases,  whose  salts  result  from  the  action  of  alkyl  iodides  upon 
ammonia,  deserve  the  first  mention  here,  since  they  led  to 
the  true  perception  of  the  constitution  of  these  bodies,  and 
established  a  basis  upon  which  they  might  be  system atised. 
His  splendid  work  upon  aniline  and  its  numerous  substitu- 
tion-derivatives (e.g.  cyan-aniline),  begun  in  1 843,2  and  on  the 
addition  products  of  this  base,  immensely  enriched  organic 
chemistry.  These  investigations  resulted  in  the  discovery  of 
a  wealth  of  new  and  striking  facts,  e.g.  the  observation  of  the 
influence  exerted  by  halogens  entering  the  aniline  molecule 
upon  the  chemical  character  of  the  resulting  compounds.3 
Upon  the  basis  of  those  labours,  which  prepared  the  way  for 
a  knowledge  of  the  aromatic  bases,  the  aniline  colour  industry 
has  since  developed  itself  in  the  most  brilliant  manner. 
From  a  theoretical  point  of  view,  also,  these  researches  on  the 
di-  and  tri-amines  and  on  the  corresponding  ammonium  bases 
(obtained  from  ethylene  bromide  and  ammonia)  were  of 
special  importance ;  Hofmann,  in  fact,  worked  out  and  ex- 
plained organic  nitrogen  compounds  generally  as  no  other 

1  Ann.  Chem.,  vol.  Ixxiv.  p.  117;  vol.  Ixxv.  p.  356;  cf .  also  p.   296  of 
this  book. 

2  Ibid.,  vol.  xlvii.  p.  37,  and  numerous  later  papers. 

3  Ibid.,  vol.  liii.  p.  1 ;  cf.  also  p.  284  of  this  book. 

H  H 


466  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP, 

man  has  done.  His  investigations  on  the  formation  of 
substitution-products  of  ammonia  contributed  more  than 
anything  else  to  the  establishment  of  the  "  typical "  theory 
towards  the  end  of  the  forties  (cf.  p.  295  et  seq.). 

The  observation  that  the  organic  ammonias  result  from 
the  nitro-compounds  by  reduction1  was  a  point  of  special 
significance  in  their  history,  this  step  having  been  first 
effected  by  Zinin  2  in  the  conversion  of  nitro-  into  amido- 
benzene.  The  above  reaction  has  proved  itself  of  the  greatest 
use  as  a  general  method,  has  served  for  the  preparation  of 
di-  and  tri-amines,  and  has  since  been  applied  with  success  in 
innumerable  instances,  besides  having  been  extended  to  the 
later  discovered  nitro-compounds  of  the  fatty  series.  The 
mode  of  formation  of  the  primary  amines  from  the  cyanic 
•ethers,  discovered  by  Wurtz,3  must  also  be  referred  to  here 
as  of  historical  importance,  since  the  simplest  organic 
.ammonia,  methylamine,  was  first  prepared  in  this  way. 

From  the  vast  number  of  observations  on  the  chemical 
behaviour  of  the  classes  of  compounds  in  question,  we  can  but 
pick  out  a  very  few,  such,  namely,  as  have  led  to  the  elucida- 
tion of  their  constitution  and  to  the  discovery  of  new  and 
important  groups.  To  what  an  unlooked-for  significance 
the  action  of  nitrous  acid  upon  amines  and  similar  bodies 
(a  reaction  which  had  already  been  studied  by  Hofmann 
.and  others)  attained  in  the  hands  of  P.  Griess,  who  demon- 
strated the  conditions  under  which  diazo-compounds  were 
formed,  and  examined  these  with  the  utmost  success !  To 
the  latter  there  were  afterwards  added  the  azo-compounds 
.and  hydrazines,  classes  which  are  of  such  importance  as  also 
to  merit  a  detailed  description  (see  below).  The  transforma- 
tion of  aromatic  amines  into  valuable  dyes  by  oxidation, 
observed  by  W.  H.  Perkin,  sen.,  A.  W.  Hofmann,  and  others, 
marked  the  commencement  of  a  new  era  in  chemical  industry. 

1  Bamberger  and  Wohl  have  found  that  the  first  product  of  a  moderated 
reduction  (in  neutral  solution  with  zinc  dust)  is  phenyl-hydroxylamine — a 
compound  of  great  reactive  power  (Ber. ,  vol.  xxvii.  pp.  1348,  1432). 

2  Journ.  pr.  Chem.,  vol.  xxvii.  p.  149. 

3  Ann.  Chim.  Phys.  (3),  vol.  xxx.  p.  443. 


vi  ORGANIC  AMMONIAS,  ETC.  467 

Only  a  passing  reference  need  be  made  here  to  the 
-conversion  of  the  organic  ammonias  into  quinoline,  acridine, 
-quinoxaline  and  other  basic  substances  by  similar  processes 
of  condensation,  since  these  reactions  will  be  considered 
further  on,  especially  in  their  connection  with  the  pyridine 
and  quinoline  bases,  and  the  relations  of  the  latter  to  the 
.alkaloids. 

Great  advances  have  been  made  in  the  artificial  produc- 
tion of  naturally-occurring  nitrogenous  substances,  by  suit- 
able transformations  of  ammonia  or  amines.  The  important 
work  effected  by  Hofmann  on  the  mustard  oils  brought  out 
clearly  the  relation  existing  between  this  class  of  compounds 
and  the  amines,  and  furnished  a  firm  basis  for  arriving  at 
their  constitution. 

Oil  of  mustard  itself  (allyl  iso-thiocyanate),  which  is 
obtained  from  the  seeds  of  the  black  mustard,  was  prepared 
from  allylamine,  and  also  by  converting  allyl  iodide  into  the 
thiocyanate,  which  changes  on  heating  into  the  isomeric  iso- 
compound.  Hofmann's  investigation1  of  the  chemical  be- 
haviour of  the  mustard  oils  and  their  isomers  the  thiocyanates 
left  no  doubt  as  to  the  constitution  of  these  two  classes. 

After  the  base  which  was  isolated  from  herring  brine 
had  been  recognised  as  identical  with  the  artificially  pre- 
pared trimethylamine,  further  researches  led  to  the  synthesis 
of  the  physiologically  important  compounds  choline  and 
neurine  from  trimethylamine  and  ethylene-chlorhydrin,2  and 
also  to  that  of  betaine,  a  substance  found  in  the  juice  of 
beet.  And  just  as  trimethylamine  served  for  the  formation 
of  the  latter,  so  from  methylamine  and  monochloro-acetic 
acid  sarcosine  (found  naturally  in  the  juice  of  flesh)  was 
obtained  ;  further,  by  assimilating  the  elements  of  cyanamide, 
sarcosine  was  converted  into  creatine.  These  reactions  left 
the  constitution  of  the  compounds  perfectly  plain.3  Refer- 
ence must  also  be  made  here  to  the  synthesis  of  many  com- 

1  Ber.,  vol.  i.  p.  176. 

2  Wurtz,  Ann.  Chem.,  Suppl.,  vol.  vi.  pp.  116  and  197. 

3  Volhard,  Ann.  Chem.,  voL  cxxiii.  p.   261  ;  Jahresber.  d.   Chemie  for 
1868,  p.  685. 

H  H   2 


468  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP, 

pounds  nearly  related  to  urea,  e.g.  guanidine,1  and  parabanic, 
oxaluric  and  barbituric  acids,2  which  were  known  as  deriva- 
tives of  uric  acid  long  before  they  were  prepared  of  set  pur- 
pose from  urea.  Uric  acid  itself  was  synthetised  a  few  years 
ago,3  after  many  unsuccessful  attempts.  Indeed  urea  and 
guanidine — compounds  of  such  great  physiological  impor- 
tance— have  proved  themselves  singularly  suited  for  building 
up  complex  "  condensed  "  compounds,  for  instance,  with  the 
ketonic  esters  and  di-ketones.  The  constitution  of  the  guana- 
mines,  substances  obtained  by  the  action  of  organic  acids  upon 
guanidine,  has  lately  been  worked  out  by  Bamberger,4  The 
remarkable  and  highly  nitrogenous  compounds  prepared  from 
amido-guanidine  5  must  also  be  mentioned. 

The  study  of  the  amides,  which  include  urea  and  several 
others  of  the  compounds  just  mentioned,  has  gone  on  simul- 
taneously with  that  of  the  amines.  Here  we  can  only  refer 
to  the  important  conversion  of  these  substances  into  cyanides 
(by  means  of  phosphorus  pentoxide),  and  their  re-formation 
from  the  latter;  and  to  the  interesting  behaviour  of  the 
substituted  amides  with  phosphorus  pentachloride,  a  reaction 
which  has  been  studied  more  especially  by  Wallach,6  and 
which  has  led  to  a  knowledge  of  certain  peculiar  bases,  the 
oxalines.  Hofmann  7  worked  out  the  curious  transformation 
of  amides  into  amines  containing  an  atom  of  carbon  less  in 
the  molecule  by  subjecting  them  to  the  action  of  bromine  in 
alkaline  solution.  The  corresponding  thiamides,  investigated 
by  Cahours,  Hofmann,  and  many  others,  have  on  their  part 
been  converted  into  other  nitrogenous  compounds,  e.g.  the 
amidines,8  the  study  of  which  has  likewise  yielded  many 

1  Ann.  Chem.,  vol.  cxlvi.  p.  259. 

2  Ponomareff,  Bull.  Soc.  Chim. ,  vol.  xviii.  p.  97 ;  Grimaux,  ibid.,  vol. 
xxxi.  p.  146. 

3  Behrend  and  Roosen,  Ann.  Chem.,  vol.  ccli.  p.  235. 

4  Nencki,  Ber.,  vol.  vii.  p.  776  and  1584;  Bamberger,  Ber.,  vol.  xxv. 
p.  534. 

6  Thiele,  Ann.  Chem.,  vol.  cclxxiii.  p.  133. 

6  Ann.  Chem.,  vol.  clxxxiv.  p.  1 ;  vol.  ccxiv.  p.  193. 

7  Ber.,  vol.  xv.  p.  765. 

8  Wallach,  Ann.   Chem.,  vol.  clxxxiv.   pp.  5  and  91 ;  Bernthsen,  ibid., 
vol.  clxxxiv.  p.  321 ;  vol.  cxcii.  p.  1. 


vi  PHOSPHINES  AND  PHOSPHONIUM  BASES  469 

useful  results.  The  exhaustive  researches  by  Pinner1  are 
worthy  of  special  notice  here  ;  he  has  prepared  the  amidines 
from  the  highly  reactive  imido-ethers,  and  has  thoroughly 
studied  their  chemical  behaviour. 

Through  the  discovery  and  investigation  of  the  organic 
compounds  of  phosphorus,  antimony  and  arsenic,  the  con- 
nection existing  between  those  three  elements  themselves 
and  also  their  relation  to  nitrogen  were  proved  in  the  clearest 
manner,  so  that  here,  as  well  as  in  other  cases,  the  study 
of  organic  compounds  has  thrown  a  brilliant  light  upon 
particular  branches  of  inorganic  chemistry.  The  phosphines 
and  phosphonium  bases  first  became  known  through  the 
classical  and  comprehensive  researches  of  A.  W.  Hofmann,2 
and  the  corresponding  compounds  of  the  aromatic  series 
through  those  of  Michaelis.3  The  organic  compounds  of 
phosphorus  were  thenceforth  recognised  as  derivatives  of  the 
well-known  inorganic  ones, — phosphuretted  hydrogen  (PH3) 
and  phosphonium  iodide,  and  phosphorus  tri-  and  penta- 
chlorides.  The  study  of  the  organic  compounds  of  arsenic 
and  antimony,  the  former  of  which  were  admirably  investi- 
gated by  Bunsen,  and  at  a  later  date  by  Cahours,  Baeyer  and 
Michaelis,4  and  the  latter  by  Lowig,  Landolt,  Michaelis5 
and  others,  likewise  led  to  the  conclusion  that  those  sub- 
.stances  were  derivable  from  the  inorganic  compounds  of 
the  elements.  The  influence  exercised  by  some  of  these 
researches  upon  the  development  of  the  doctrine  of  valency 
has  been  already  sufficiently  referred  to  in  the  general 
.section. 

The  field  comprising  the  organic  compounds  of  nitrogen 
is  by  no  means  exhausted  with  the  description  of  the  classes 
which  have  been  shortly^  alluded  to  above.  A  number  of 

1  Compare  his  monograph,   Die  Imidodther  und  ihre  Derivate  ;  or, 
failing  that,  Ber.,  vol.  xvi.  p.  1654;  vol.  xvii.  p.  2520  ;  vol.  xviii.  p.  759. 

2  Ber.,  vol.  iv.  p.  605 ;  vol.  v.  p.  104  ;  vol.  vi.  p.  306. 

3  Cf.  Ann.  Chem.,  vol.  clxxxviii.  p.  275. 

4  For  the  literature  on  the  subject,  cf.  Ann.  Chem.,  vol.  cci.  p.  184, 

5  Cf.  ibid.,  vol.  ccxxxiii.  p.  39 ;  Ber.,  vol.  xxvii.  p.  244. 


470  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 

others  must  be  referred  to  here,  with  regard  to  the  chemical 
constitution  of  which  much  has  also  been  accomplished; 
many  of  these  are  now  of  great  technical  importance. 

Of  the  azo-compounds,  azo-benzene  was  the  first  to  be 
discovered  (by  Mitscherlich),1  while  much  later  there  came 
azoxy-benzene  by  Zinin 2  and  hydrazo-benzene  by  A.  W. 
Hofmann.3  The  now  universally  accepted  views  held  with 
regard  to  these  three  kinds  of  azo-compounds  are  due  to- 
Erlenmeyer,4  and  still  more  to  Kekule,5  who  assumed  in  azo- 
benzene  two  doubly-linked  nitrogen  atoms,  and  in  oxyazo-  and 
hydrazo-benzene  two  singly-linked  ones.  The  ready  produc- 
tion of  these  and  similar  substances  from  diazo-compounds 
has  greatly  tended  to  advance  our  knowledge  of  them.  The 
investigations  of  Griess,  Kekule,  Victor  Meyer,  H.  Caro,  Witt 
and  others,  which  showed  how  diazo-  could  be  converted 
into  azo-compounds,  have  led  to  the  establishment  of  a 
flourishing  industry — the  manufacture  of  azo-dyes.  The 
doctrine  of  isomerism  has  also  been  enriched  by  a  wealth  of 
observations  arising  out  of  these  labours.  The  remarkable 
molecular  transformations  of  hydrazo-compounds  into  the 
isomeric  diamido-derivatives  of  diphenyl  and  its  homologues,. 
and  of  diazo-amido-  into  amido-azo-compounds,  also  fall  to 
be  mentioned  here.  In  this  class  it  was  the  amido-  and  oxy- 
derivatives  of  azo-benzene  and  its  homologues  which  first 
found  employment  as  dyes.  The  view  held  by  many, — that 
the  above  substances  are  to  be  looked  upon  as  derivatives  of 
quinone  or  quinone-imide  respectively,6  is  of  importance  for 
understanding  the  connection  between  chemical  constitution 
and  dye-character. 

The  diazo-compounds,  so  remarkable  for  their  reaction- 
capacity,  were  discovered  by  Griess  7  and  investigated  by  him 

1  Pogg.  Ann.,  vol.  xxxii.  p.  324.          2  Ann.  Chem.,  vol.  Ixxxv.  p.  328. 

3  Jahresber.  d.  Ghemie  for  1863,  p.  424. 

4  Ztschr.  Chem.  for  1863,  p.  678. 

5  Lehrb.  d.  Chem.,  vol.  ii.  p.  703. 

6  Cf.  Goldschmidt,  Ber.,  vol.  xxv.  p.  1324. 

7  Peter  Griess  (1829—1888),  a  pupil  of  Kolbe's,  became  assistant  to  A. 
W.  Hofmann  in  London,  but  relinquished  that  post  after  a  short  time,  on 
receiving  in  1862  the  appointment  of  chemist  to  Messrs.  Allsopp  and  Sons> 


vi  DIAZO-COMPOUNDS ;  GRIESS  471 

in  a  long  series  of  admirable  researches,  which  disclosed 
their  most  important  characteristics.  Griess  showed  how 
they  were  formed  by  the  action  of  nitrous  acid  on  aromatic 
amido-compounds, — a  reaction  which  had  previously  been 
studied  under  other  conditions,  and  had  not  led  then  to  the 
discovery  of  those  bodies.  In  a  number  of  papers 1  dating 
from  the  year  1859,  which  followed  one  another  with  great 
rapidity,  the  above-named  investigator  made  the  chemical 
world  acquainted  with  the  diazo-derivatives  of  phenol, 
aniline  and  benzoic  acid,  and  with  their  remarkable  pro- 
perties. The  view  accepted  by  most  chemists  with  respect 
to  the  constitution  of  these  bodies,  according  to  which  two 
atoms  of  nitrogen  are  linked  together  as  in  the  azo-com- 
pounds,  originated  with  Kekule.2  Another  view,  in  which 
one  of  the  nitrogen  atoms  is  assumed  to  be  pentavalent  and 
the  other  trivalent,  was  expressed  by  Blomstrand,3  who 
brought  forward  arguments  in  its  favour. 

The  existence  of  diazo-compounds  in  the  fatty  series  has 
only  been  proved  comparatively  recently  by  the  exhaustive 
researches  of  Curtius4  on  diazo-acetic  and  diazo-succinic 
ethers.  The  first  of  these,  obtained  by  the  action  of  nitrous 
acid  on  amido-acetic  ether,  shows  certain  points  of  resem- 
blance to  the  aromatic  diazo-compounds,  but  also  many  differ- 
ences ;  its  power  of  combining  with  other  substances,  nitrogen 
being  eliminated,  is  more  strongly  marked  than  in  its  aromatic 

at  their  well-known  brewery  at  Burton-on-Trent.  Although  continuing 
there  engaged  in  this  branch  of  technical  chemistry  until  his  death,  he  at 
the  same  time  carried  out  a  number  of  most  valuable  scientific  researches. 
His  brilliant  discovery  and  investigation  of  the  diazo-compounds  led  him 
on  to  the  azo-dyes  ;  he  was  thus  the  father  of  this  now  enormous  industry. 
Griess's  work  generally  was  marked  by  great  refinement  of  execution,  as 
well  as  great  power  of  observation.  A.  W.  von  Hofmann  has  left  us  a  full  and 
sympathetic  account  of  his  life,  while  E.  Fischer  and  H.  Caro  have  told  of 
his  services  to  science  (Ber.,  vol.  xxiv.  Ref.  pp.  1007,  1058). 

1  Ann.  Chem.  y  vol.  cxiii.  p.  201 ;  vol.  cxvii.  p.  1 ;  vol.  cxxi.  p.  257  ;  voL 
cxxxvii.  p.  39. 

2  Ztschr.  Chem.  for  1866,  p.  689. 

3  In  his  Ohemie  der  Jetztzeit,  p.  272;  cf.  also  Ber.,  vol.  viii.  p.  51 ;  and 
Strecker,  ibid.,  vol.  v.  p.  786. 

4  Journ.  pr.  Chem.  (2),  vol.  xxxviii.  p.  401. 


472  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 

congeners.  Diazo-acetic  ether  is  therefore  of  very  great 
value  for  the  synthesis  of  other  compounds.  Diazo-methane 
(the  simplest  of  the  diazo-compounds),  discovered  by  v. 
Pechmann,1  is  also  of  the  greatest  interest, 

Another  class  of  bodies,  the  hydrazines,  which  stand  in  a 
near  relation  to  the  diazo-compounds,  was  discovered  in 
1875  by  E.  Fischer2  and  carefully  investigated  by  him.3 
Phenyl-hydrazine— the  first  of  the  series  to  be  discovered — 
has  proved  of  the  greatest  value  both  as  a  specific  reagent 
and  as  an  aid  in  the  synthesis  of  complex  compounds.  Its 
relation  to  diazo-compounds  was  definitely  proved  by  Fischer, 
through  its  formation  from  diazo-amido-benzene  or  diazo- 
benzene  chloride  and  its  conversion  into  diazo-benzene  imide. 
The  importance  of  phenyl-hydrazine  and  similar  bases  for 
the  preparation  of  hydrazones  and  osazones  has  already  been 
referred  to ;  they  have  also  been  of  material  aid  to  the  theory 
of  stereo-isomerism. 

The  production  of  derivatives  of  pyrazolone  and  indole 
(besides  other  condensed  compounds)  by  the  aid  of  phenyl- 
hydrazine  must  be  mentioned  here.  The  latter  substance  is 
also  now  used  in  large  quantity  for  the  manufacture  of  the 
well-known  febrifuge  antipyrine.  The  simplest  member  of 
this  series— hydrazine  itself — whose  discovery  is  noticed  in 
the  history  of  inorganic  chemistry,  likewise  reacts  with 
the  greatest  readiness  with  aldehydes,  ketones,  and  similar 
substances,  and  hence  has  also  proved  of  signal  service  in 
extending  the  domain  of  nitrogen  compounds  (cf.  the 
papers  by  Curtius  and  his  pupils  on  hydrazides  and  azides 
of  organic  acids,  Journ,  pr.  Chem.  (2)  vol.  1.  and  succeeding 
volumes). 

Within  the  last  few  years  some  remarkable  reactions  have 
been  carried  out  with  diazo-compounds,  which  have  led 
either  to  hydrazones  or  to  so-called  formazyl  derivatives ;  the 
reader  is  referred  to  the  latest  papers  on  the  subject,  which 

1  Ber.t   vol.    xxviii.    pp.    855  and  1624;  cf.  also  Bamberger,    ibid.    p. 
1682. 

2  Ber.,  vol.  viii.  p.  589. 

3  Ann.  Chem.,  vol.  cxc.  p.  67  j  vol.  cxcix.  p.  281 ;  vol.  ccxii.  p.  316. 


^i  CYANOGEN  AND  HYDROCYANIC  ACID  473 

•explain  these  reactions.1  Von  Pechmann's  researches  on  the 
oxidation  of  diazo-compounds  and  on  their  constitution  are 
also  worthy  of  note. 

After  the  discovery  of  the  iso-diazo-compounds  by  Schraube 
.and  Bamberger,  the  constitution  of  the  diazo-compounds 
became  a  burning  question.  The  addition  of  new  facts  has 
greatly  enlarged  the  chemistry  of  the  subject.  Blomstrand's 
view  (p.  471)  has  again  come  into  favour;  Hantzsch,  on  the 
other  hand,  adheres  strongly  to  the  opinion  that  certain  series 
of  isomeric  diazo-compounds  are  stereo-isomeric ;  while 
Bamberger  can  find  in  the  experimental  results  no  proof  for 
Hantzsch's  idea,  but  contends  that  a  structural  isomerism  is 
probable.  This  controversy  has  now  gone  on  for  some  years 
without  any  definite  result  being  arrived  at,  although 
Blomstrand,  not  long  before  his  death,  expressed  himself  in 
favour  of  Bamberger's  theory.2 

Since  Scheele's  discovery  of  hydrocyanic  acid,  the 
cyanogen  compounds  have  been  the  subject  of  frequent 
investigation  by  the  most  able  chemists,  so  that  the  know- 
ledge of  them  has  been  immensely  increased.  The  develop- 
ment of  this  branch  of  organic  chemistry  is  in  a  great 
degree  due  to  the  marked  property  possessed  by  most  of 
these  compounds  of  changing  into  isomers,  and  also  of  com- 
bining with  other  substances  to  yield  new  compounds. 

The  composition  of  prussic  acid  and  of  many  of  the 
cyanides  was  worked  out  by  Berthollet  and  Ittner,  and 
especially  by  Gay-Lussac  in  his  classical  researches,  in 
which  he  discovered  cyanogen  and  recognised  its  analogy 
to  the  halogens.  He  it  was,  too,  who  assumed  in  yellow 
prussiate  of  potash  (a  substance  already  known  for  a  long 
time)  the  presence  of  the  radical  ferrocyanogen,  while 
Berzelius,  adhering  strictly  to  the  dualistic  theory,  explained 
it  as  being  a  double  salt  of  iron  protocyanide  and  cyanide  of 

1  V.  Pechmann,  Her.,  vol.  xxv.  p.  3175  ;  Vol.  xxvii.  p.  219.     Bamberger, 
Ber.t  vol.  xxv.  pp.  3201,  3539 ;  vol.  xxvi.  p.  2978.      W.  Wislicenus,  Ber., 
vol.  xxv.  p.  3459. 

2  Cf.  Ber.,  for  the  years  1894 — 1897  ;  also  Blomstrand,  Journ.  pr.  Ghent. 
2),  vol.  liii.  p.  169 ;  vol.  liv.  p.  305 ;  vol.  Iv.  p.  481. 


474  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP, 

potash.  The  discovery  of  potassium  ferricyanide  by  L. 
Gmelin  in  1822,  and  that  of  the  so-called  nitro-prussides  by 
Playfair 1  extended  the  knowledge  of  cyanogen  compounds  of 
complex  composition,  in  which,  at  Graham's  suggestion,  the 
radical  tri-cyanogen  was  assumed. 

Sulphocyanic  acid,  together  with  its  salts,  was  discovered 
by  Porret,  and  subsequently  investigated  by  Berzelius,  who 
established  its  composition;  Liebig  succeeded  in  isolating 
cyanogen  sulphide  in  1829,  and  he  also  showed  what 
remarkable  products  were  obtained  from  the  decomposition  of 
ammonium  sulphocyanide,  viz.  mellone,  melame,  melamine, 
etc.2  Of  recent  years  Reynolds,  Volhard,  Delitzsch  and  more 
especially  Klason,3  among  others,  have  advanced  our  know- 
ledge of  this  class  of  compounds. 

Cyanic  acid,  whose  chemical  behaviour  and  relation  to  its- 
own  isomers  gave  rise  to  important  discussions  respecting  the 
constitution  of  all  of  them,  was  first  isolated  by  Wohler,4 
who  was  led  during  the  investigation  of  its  salts  to  his 
memorable  discovery  of  the  artificial  formation  of  urea.5 
Cyanuric  acid,  obtained  by  Serullas  from  the  solid  cyanogen 
chloride  which  he  discovered,  was  recognised  by  Liebig  and 
Wohler  as  being  of  the  same  percentage  composition  as- 
cyanic  acid.  The  influence  which  this  observation,  taken  in 
conjunction  with  that  of  the  isomerism  of  both  of  these 
compounds  with  fulminic  acid,  had  upon  the  doctrine  of 
isomeric  substances,  has  already  been  discussed  in  the 
general  section  of  this  book.  The  haloid  compounds  of 
cyanogen  have  been  known  for  a  long  time,  cyanogen 
chloride  having  been  obtained  by  Berthollet,  and  the  iodide 
by  Davy ;  but  cyanamide,  which  was  destined  to  become  of 
so  much  importance  for  the  synthesis  of  organic  compounds,6 
was  first  prepared  in  1851  by  Cloez  and  Cannizzaro.7 

1  Phil.  Trans,  for  1849,  vol.  ii.  p.  477.         2  Ann.  Chem.,  vol.  x.  p.  11. 

3  Cf.  more  particularly  Journ.  pr.  Chem.  (2),  vol.  xxxvi.  p.  57 ;  vol. 

xxviii.  p.  366.  4  Pogg.  Ann.,  vol.  xv.  p.  619;  vol.  xx.  p.  369. 

5  Cf.  p.  252. 

6  Cf.  Volhard's,  Strecker's,  and  Drechsel's  researches,  more  especially 
Journ.  pr.  Chem.  (2),  vol.  xi.  p.  284. 

7  Comptes  Rendus,  vol.  xxxi.  p.  62. 


vi  NITRILES  AND  CARBAMINES  475 

Owing  to  the  readiness  with  which  they  unite  with  other 
substances,  the  cyanogen  compounds  as  a  whole  have  been 
of  great  service  for  opening  up  new  branches  of  the  sciencer 
and  for  advancing  our  knowledge  of  these ;  take,  for  exampler 
the  formation  of  guanidine  and  its  derivatives  from  cyana- 
mide  or  cyanogen  chloride  and  ammonia,  and  also  the 
formation  of  derivatives  of  the  last-named  compound.1  The 
tendency  shown  by  hydrocyanic  acid  to  combine  with  alde- 
hydes and  ketones  has  already  been  mentioned ;  this  property 
has  rendered  it  possible  to  synthetise  a  large  number  of  oxy- 
carboxylic  acids. 

The  compounds  of  cyanogen  as  well  as  of  thiocyanogen 
with  organic  radicals  have,  thanks  to  their  diversity  and 
capacity  for  transformation,  yielded  an  almost  inexhaustible 
material  for  investigation.  The  alkyl  cyanides  or  nitriles, 
with  methyl  cyanide  at  their  head,  were  first  prepared  by 
Dumas2  from  the  ammonium  salts  of  the  fatty  acids,  by 
acting  upon  these  with  phosphoric  anhydride;  the  amides 
afterwards  replaced  the  ammonium  salts  of  the  acids  for  this 
purpose.  The  exceptionally  important  connection  which 
exists  between  the  nitriles  and  the  fatty  acids  was  demon- 
strated by  Frankland  and  Kolbe  3  when  they  converted  the 
former  into  the  latter  by  treatment  with  caustic  potash. 
Another  passing  reference  may  be  made  here  to  the  general- 
isation of  this  reaction,  and  the  consequent  production  of  an 
immense  number  of  carboxylic  acids  and  their  derivatives 
from  simpler  compounds,  even  although  it  was  spoken  of 
when  those  compounds  themselves  were  being  described. 
The  investigation  of  mandelic  acid,4  resulting  from  oil  of 
bitter  almonds  and  hydrocyanic  acid  in  presence  of  hydro- 
chloric, gave  the  first  impetus  to  the  study  of  the  compounds 
obtained  under  similar  conditions  from  other  aldehydes  and 
ketones.  The  simplest  nitrile  of  the  aromatic  series,  phenyl 

1  Cf.  Erlenmeyer,  Ann.  Chem.,  voL  cxlvi.  p.  253  ;  A.  W.  Hofmann,  ibid.r 
vol.  cxxxix.  p.  Ill ;  Ber.,  vol.  i.  p.  145,  etc. 

2  Comptes  Rendus,  vol.  xxv.  pp.  383  and  442. 

3  Ann.  Chem.,  vol.  Ixv.  p.  269. 

4  Liebig,  Ann.  Chem.,  vol.  xviii.  p.  319. 


476  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 

cyanide  or  benzo-nitrile,  was  first  observed  by  Fehling.1 
Since  then  the  number  of  these  nitriles  has  been  enormously 
extended,  all-  those  which  correspond  to  the  important 
carboxylic  acids  being  known.  The  amidoximes — derivatives 
of  the  nitriles — which  were  discovered  by  Tiemann,2  are  of 
particular  interest.  The  imido-ethers,  which  result  from  the 
nitriles  by  the  addition  of  one  molecule  of  an  alcohol,  are 
also  worthy  of  note,  because  of  the  ease  with  which  they 
yield  the  amidines,3  compounds  of  great  reactive  power* 
The  cyanogen  compounds  corresponding  to  the  halogen  fatty 
acids  are  also  nearly  related  to  the  nitriles;  the  simplest 
members  of  this  series,  viz.,  cyano-carbonic  and  cyan-acetic 
acids,  have  led  on  to  important  transformation-products, 
thanks  to  the  ease  with  which  they  enter  into  reaction. 

The  isocyanides,  isonitriles,  or  carbamines,  which  are 
isomeric  with  the  nitriles,  were  discovered  simultaneously 
by  A.  W.  Hofmann 4  and  Gautier,5  by  different  procedures, 
their  existence  having  previously  been  foreseen  by  Kolbe. 
The  perception  of  the  cause  of  the  isomerism  existing  between 
these  two  classes  of  compounds  marked  an  important 
advance  in  theoretical  chemistry.  The  conclusive  explana- 
tion of  the  similar  isomerism  between  the  alkyl  thiocyanates 
and  the  mustard  oils,  of  which  mustard  oil  proper  (allyl 
iso-thiocyanate)  was  the  earliest  known,  is  due  to  Hofmann ; 
the  latter  succeeded  both  in  preparing  the  iso-thiocyanates 
.artificially,  and  in  proving  at  the  same  time  their  chemical 
constitution  from  their  various  decompositions.6  The  dif- 
ference in  constitution  between  the  thiocyanates  arid  the 
mustard  oils  was  especially  seen  in  their  transformations. 
Hand  in  hand  with  the  acquirement  of  the  above  knowledge 
went  the  gradual  establishment  of  the  views  upon  the 
-analogously  constituted  cyanic  and  isocyanic  ethers;  and 

1  Ann.  Chem.,  vol.  xlix.  p.  91. 

2  Ber.,  vol.  xvii.  pp.  126,  1685,  etc. 

3  Cf.  Pinner,  JBer.,  vols.  xvi.  and  xvii.,  and  especially  his  monograph  : — 
J)ie  Imidodther  und  ihre  Derivate  (Berlin,  1892). 

4  Ann.  Chem.,  vol.  cxliv.  p.  144 ;  vol.  cxlvi.  p.  107. 

5  Comptes  Rendus,  vol.  Ixv.  pp.  468  and  862. 

6  Ber. ,  vol.  i.  pp.  26  and  169 ;  vol.  ii.  pp.  116  and  452. 


VI  POLYMERIC  CYANOGEN  COMPOUNDS  477 

here  again  Hofmann  acted  as  the  pioneer  with  his  researches, 
after  the  simplest  compounds  of  this  nature  had  been  ob- 
tained by  Wurtz  and  Cloez.  The  ease  with  which  the  isocyanic 
ethers  and  the  corresponding  mustard  oils  assimilate  the 
elements  of  ammonia  and  the  amines  led  to  the  discovery  of 
the  extensive  class  of  the  substituted  ureas  j1  the  simplicity 
of  the  reaction,  upon  which  the  formation  of  these  substances 
was  based,  allowed  of  the  explanation  of  the  numerous  cases 
of  isomerism  which  occur  here. 

The  question  of  the  chemical  constitution  of  the  polymeric 
cyanogen  compounds  presented  far  greater  difficulties,  the 
number  of  these  having  increased  to  an  extraordinary  extent 
after  it  was  proved  that  cyanuric,  fulminic  and  cyanic  acids 
had  all  the  same  percentage  composition.  It  is  only  com- 
paratively recently  (i.e.,  since  1884)  that  a  certain  degree 
of  clearness  has  been  arrived  at  with  regard  to  the  constitu- 
tion of  the  cyanuric  and  isocyanuric  compounds,  and  this  has 
been  due  more  particularly  to  the  admirable  investigations 
of  A.  W.  Hofmann  and  of  Klason,  and  also  to  those  of  Rathke, 
Weddige,  Bamberger  and  others,  These  researches  have 
proved  that  isocyanuric  acid  and  isomelamine  are  not  in 
themselves  capable  of  existence,  although  derivatives  of  both 
are,  The  doctrine  of  stable  and  unstable  modifications, 
already  referred  to,2  was  developed  and  strengthened  mainly 
from  observations  made  upon  these  polymeric  compounds. 
The  obscurity  surrounding  the  compounds  of  this  nature,  as 
well  as  those  decomposition-products  of  ammonium  sulpho- 
cyanide  known  under  the  names  of  mellone,  melame  and 
meleme,  and  the  bases  resulting  from  the  nitriles  by  poly- 
merisation (cyan-ethine,  etc.),  is  now  beginning  to  vanish, 
and  a  knowledge  of  their  constitution  is  being  gradually 
acquired.  The  recent  work  of  Otto  and  Voigt,  Weddige  and 
Krafft  has  introduced  us  to  the  true  alkyl  cyanurates,  the 
isomeric  cyan-alkines  (which  are  obtained  directly  from  the 
nitriles  by  the  action  of  sodium  or  sodium  ethylate) 
possessing  a  totally  different  constitution.  E.  v.  Meyer's 

1  Cf.  Wurtz,  Ann.   Chem.,  vol.  Ixxx.  p.  346;  A.  W.  Hofmann,  ibid., 
vol.  xxxiii.  p.  57.  2  Cf.  p.  354  et  seq. 


478  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 

investigations l  on  this  subject  have  proved  that  the  cyan- 
alkines  are  to  be  regarded  as  amido-miazines  or  amido- 
pyrimidines ;  the  mode  in  which  they  are  formed  is  an 
instructive  case  of  polymerisation,  this  being  brought  about 
by  the  migration  of  hydrogen  atoms.  The  formation  of  the 
di-molecular  nitriles,2  which  from  their  behaviour  are  to  be 
•classified  as  imido-nitriles,  depends  upon  a  similar  reaction, 
but  one  which  does  not  go  so  far. 

The  rational  composition  of  fulminic  acid  and  allied  com- 
pounds, e.g.,  fulminuric  acid  and  other  isomers,  is  now 
becoming  much  better  understood,  thanks  to  the  pioneering 
researches  of  Liebig,3  and  the  investigations  of  Kekule,4 
Schischkoff,5  and,  more  recently,  of  Steiner,  Carstanjen, 
JChrenberg,6  and  especially  Nef,7  the  last-named  chemist 
assuming  a  divalent  carbon  atom ;  the  point,  however,  has 
not  yet  been  made  absolutely  clear. 

Historical  Notes  on  Pyridine  and  Quinoline.8 

An  extensive  group  of  nitrogen  compounds — the  pyridine 
and  quinoline  bases — has  only  been  worked  at  with  success 
of  quite  recent  years,  although  these  substances  were  in  part 
discovered  during  the  earliest  decades  of  the  century ;  their 
investigation  has  been  carried  on  with  the  utmost  zeal  ever 
since  it  came  to  be  recognised  that  the  vegetable  alkaloids 
were  among  their  derivatives.  The  researches  of  Anderson  9 
on  the  volatile  bases  of  bone  oil,  those  of  Williams  10  on  the 

1  Journ.  pr.  Chem.  (2),  vol.  xxxix.  p.  262,  besides  preceding  numbers. 

2  E.  v.  Meyer,  ibid.,  vol.  xxxviii.  p.  336  ;  vol.  xxxix.  p.  188. 

3  Ann.  Chem.,  vol.  xxvi.  p.  146. 

4  Ibid.,  vol.  cv.  p.  279.  5  Ibid.,  vol.  ci.  p.  213. 

6  Journ.  pr.  Chem.  (2),  vol.  xxv.  p.  232 ;  vol.  xxx.  p.  38. 

7  Ann.  Chem.,  vol.  cclxxxvii.  p.  265. 

8  With  regard  to  the  sources  of  the  following  notes,  cf.  the  pamphlets 
of  Metzger,  Hesekiel  and  A.  Pictet  on  these  bases,  and  Calm-Buchka's 
work,  Die  Chemie  des  Pyridins  und  seiner  Derivate. 

9  Phil.  Trans.  E.,  vol.  xvi.  p.  4,  and  vol.  xx.  (2),  p.  247  ;  Phil.  Mag.  (4), 
vol.  ii.  p.  257 ;  Ann.  Chem.,  vols.  lx.,  Ixx.,  Ixxv.,  Ixxx.  and  Ixxxiv. 

10  Phil.  Mag.  (4),  vol.  viii.  p.  24 ;  Phil.  Trans.  23.,  vol.  xxi.  (2),  p.  315, 
etc. 


vi  PYRIDINE  AND  QUINOLINE  479 

similar  bodies  contained  in  coal  tar,  and  Gerhardt's  observa- 
tion on  the  production  of  quinoline  from  quinine l  were  the 
first  beginnings  in  the  cultivation  of  this  field,  which  has 
.since  been  worked  with  such  wonderful  success.  The  in- 
vestigation of  these  substances  received  a  special  impetus 
from  the  recognition  of  the  similarity  between  the  pyridine 
bases  and  quinoline,  and  of  the  distinct  analogy  between 
these  substances  and  the  aromatic  compounds.  The  earliest 
attempt  to  explain  the  constitution  of  pyridine  and  quinoline 
was  due  to  Korner,2  and  it  bore  the  richest  fruit ;  he  assumed 
these  bodies  to  be  benzene  and  naphthalene  respectively,  in 
which  a  methine  group  (CH)'"  was  replaced  by  the  trivalent 
nitrogen  atom.  This  hypothesis  was  applied  to  the  facts 
already  known,  to  which  a  large  number  of  new  ones  were 
being  continually  added,  with  the  result  that  they  were  with- 
out difficulty  made  to  accord  with  it.  The  theory  of  the 
aromatic  compounds,  which  had  by  this  time  become  strongly 
developed,  gave  those  endeavours  a  more  or  less  secure  basis 
to  go  upon,  especially  when  it  came  to  criticising  and  sifting 
the  rapidly  augmenting  number  of  isomers  among  the  pyridine 
and  quinoline  derivatives. 

The  connection  of  pyridine  and  quinoline  with  benzene 
and  naphthalene,  assumed  in  the  above  hypothesis,  was 
clearly  proved  by  a  succession  of  beautiful  researches.  We 
may  refer  here  to  the  analogous  behaviour  with  regard  to  ox- 
idising agents  shown  by  the  alkylated  pyridines  and  the 
alkyl  derivatives  of  benzene.  The  investigation  of  these 
relations,  more  especially  those  of  the  isomeric  methyl-  and 
ethyl-pyridines  and  the  pyridine  mono-carboxylic  acids,  we 
owe  to  the  admirable  work  of  Weidel,  Skraup,  Ladenburg 
and  Wischnegradsky.  Just  as  the  admissibility  of  the  hy- 
pothesis respecting  the  constitution  of  benzene  was  arrived  at 
from  the  number  of  its  substitution-products  which  could 
actually  be  prepared,  so  in  like  manner  a  similar  deduction 
was  drawn  for  pyridine,  viz.  that  only  the  theoretically  pos- 
sible methyl-pyridines  and  pyridine-carboxylic  acids  were 
capable  of  preparation,  and  no  more. 

1  Ann.  Chem.,  vol.  xlii.  p.  310.  2  Cf.  p.  350. 


480  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP, 


Among  the  experimental  researches  which  have  furnished 
further  support  for  the  above  view  must  be  mentioned  those 
of  Konigs,  Ladenburg  and  A.  W,  Hofmann,  which  distinctly 
proved  the  connection  between  pyridine  and  piperidine  (the- 
latter  containing  six  atoms  of  hydrogen  more  in  the  molecule 
than  the  former).  The  analogy  between  this  compound  and 
pyridine  on  the  one  hand,  and  hexahydro-benzene  and 
benzene  on  the  other,  thus  became  at  once  apparent. 
Ladenburg  found  that  sodium,  acting  on  an  alcoholic  solu- 
tion of  the  particular  substance  in  question,  was  a  most  ex- 
cellent reducing  agent  for  pyridine  bases,  and  since  then  it 
has  been  used  with  good  effect  in  numberless  instances. 
We  have  but  to  think  of  the  conversion  of  trimethylene 
cyanide  into  piperidine  and  pentamethylene-diamine  ;  thi& 
last  compound, produced  from  the  above-mentioned  cyanide  by 
the  addition  of  eight  atoms  of  hydrogen  in  the  molecule,  was 
proved  to  be  identical  with  the  ptomaine,  cadaverine, 

The  different  modes  of  formation  of  pyridine  bases  from 
substances  of  simpler  composition  likewise  assisted  towards  a 
knowledge  of  their  constitution,  We  may  refer  here  to  the 
synthesis  of  one  of  the  collidines  from  aldehyde-ammonia,  as 
well  as  from  ethylidene  chloride  and  ammonia :  to  that  of  a 
chloro-pyridine  from  pyrrol-potassium  and  chloroform  ;  to 
the  researches  of  Hantzsch,  which  resulted  in  the  artificial 
production  of  lutidine  ;  and  to  the  production  of  /3-methyl- 
pyridine  from  glycerine  (Stoehr). 

The  synthetic  investigations  of  quinoline  and  its  deriva^ 
tives  have  proved  themselves  extraordinarily  fruitful ;  they 
have  served  more  particularly  to  confirm  the  constitution  as- 
cribed to  those  compounds,  this  being  also  deducible  from  the 
products  of  decomposition  of  the  latter.  Out  of  the  great 
amount  of  work  done  in  this  branch,  only  one  or  two  re- 
searches can  be  mentioned  here,  viz.  those  of  Skraup,  who 
(doubtless  stimulated  by  the  previous  investigations  of 
Konigs  and  Graebe)  discovered  the  general  method  of  pre- 
paring quinoline  and  its  derivatives,  by  the  action  of  glycerine 
on  the  aromatic  amines  ;  Baeyer's  beautiful  investigations  on 
the  formation  of  quinoline,  oxy-quinoline,  etc.,  by  the  con- 


TI  PYRIDINE  AND  QUINOLINE  DERIVATIVES  481 

densation  of  o-amido-phenyl  compounds;  the  synthesis  of 
quinoline  and  its  homologues  from  a  mixture  of  o-amido- 
benzaldehyde  and  other  aldehydes  by  Friedlander ;  and  that 
from  aniline  and  aldehyde  by  v.  Miller  and  Dobner.  The 
syntheses  of  homologues  of  quinoline  and  of  quinoline- 
carboxylic  acids  effected  by  C.  Beyer  and  W.  Pfitzinger  are 
also  closely  connected  with  the  above  modes  of  formation. 

While  these  syntheses  have  made  clear  the  constitution 
of  quinoline,  other  investigations  have  established  its  con- 
nection with  pyridine ;  thus  it  was  seen  that  the  quinolinic 
acid  obtained  by  oxidising  quinoline  was  a  pyridine-dicar- 
boxylic  acid,  the  formation  of  which  was  in  every  respect 
analogous  to  that  of  benzene-dicarboxylic  acid  from 
naphthalene. 

The  minute  study  of  the  derivatives  of  quinoline  has  led 
to  a  systematic  investigation  of  the  whole  field,  the  researches 
of  Ad.  Glaus l  and  his  pupils  on  the  halogen  derivatives  and 
sulphonic  acids  of  quinoline  deserving  special  mention.  In 
this  way  other  compounds  of  analogous  constitution  have  been 
isolated,  e.g.,  the  naphtho-quinolines  and  anthra-quinoline. 
The  discovery  of  iso-quinoline  and  its  preparation  from 
derivatives  of  naphthalene  (Gabriel,  Bamberger,  and  Zincke) 
also  calls  for  notice. 

The  bases  known  as  the  di-  and  tri-azinesj  which  have  been 
investigated  with  much  care  during  the  last  few  years,  stand 
in  the  closest  relation  to  pyridine  and  quinoline,  just  as  these 
do  to  benzene  and  naphthalene.  In  this  connection  the 
work  of  Stoehr  and  of  L.  Wolff  on  pyrazine  and  piperazine 
derivatives,  and  that  of  Pinner  on  pyrimidine  must  be 
mentioned.  The  latest  researches  on  cyanuric  compounds 
have  shown  these  to  be  derivatives  of  triazine.  Among  the 
highly  nitrogenous  compounds  which  proceed  from  quinoline, 
the  quinoxalines  (Huisberg  and  others),  which  are  analogous 
to  the  pyrazines,  and  the  quinazolines  (Weddige,  Paal,  Wid- 
mann  and  others),  analogous  to  the  pyrimidines,  must  be 
named. — Specialization  in  organic  chemistry  has  of  late  years 
increased  to  such  an  extent  that  we  have  now  detailed  works 

1  Journ.  pr.  Chem.  from  1888  onwards. 

I   I 


482  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 

dealing  with  branches  of  it  that  were  either  unknown  or  dis- 
regarded only  a  short  time  ago.1 

A  still  greater  interest  than  that  aroused  by  the  discovery 
of  the  compounds  just  named  was  awakened  by  the  proof 
(gradually  arrived  at  from  a  long  series  of  admirable 
researches)  of  the  intimate  connection  existing  between 
pyridine,  quinoline  and  iso-quinoline  and  various  vegetable 
alkaloids,  whose  constitution  was  thereby  explained.  Wisch- 
negradsky  and  then  Konigs  were  the  first  to  express  the 
opinion  that  the  alkaloids  were  derivatives  of  pyridine  or 
quinoline.  They  grounded  this  view  upon  the  conversion 
of  pyridine  into  piperidine,  which  is  a  decomposition-product 
of  the  alkaloid  piperine  contained  in  pepper,  and  on  the 
retransformation  of  piperidine  into  pyridine ;  to  this  was 
added  later  on  the  precisely  analogous  conversion  of  conine 
into  conyrine,  a  propyl-pyridine.2  Quickly  following  the 
recognition  of  this  last  important  fact  came  the  further  one  3 
that  this  alkaloid  of  hemlock  was  the  dextro-rotatory 
modification  of  a-propyl-piperidine. 

Ladenburg's  ingenious  synthesis  of  conine  4  consisted  in 
the  preparation  of  a-allyl-pyridine,  the  conversion  of  this  (by 
means  of  sodium)  into  a-propyl-piperidine,  and  the  sub- 
division of  the  latter  optically  inactive  substance  into  its 
active  components. 

The  complete  synthesis  of  other  vegetable  alkaloids  is 
without  doubt  merely  a  question  of  time  ;  some  of  them  have 
already  been  partially  built  up  from  their  decomposition- 
products,  e.g.,  atropine  from  tropine  and  tropic  acid  (Laden- 
burg),  5  and  cocaine  from  ecgonine,  benzoic  acid  and  methyl 
iodide  (Merck).6  In  the  case  of  most  of  the  alkaloids, — 
nicotine,  piperine,  the  alkaloids  of  opium,  hydrastine,  quinine, 
strychnine,  etc.,  the  nature  of  their  products  of  decomposition 

1  Cf.  0.  Kiihling's  admirable  Handbuch  der  stickstojfhaltigen  Orthokon- 
densationsprodukte  ("  Text-book  of  the  Nitrogenous   Ortho-condensation 
Products."  Berlin,  1893). 

2  A.  W.  Hofmann,  Ber.,vol.  xvii.  p.  825. 

3  Cf.  Ladenburg,  Ann.  Chem.,  vol.  ccxlvii.  p.  80  (1888). 

4  Ber.,  vol.  xxii.  p.  1403. 

3  Ann.  Chem.,  vol.  ccxvii.  p.  74.  6  Ber.,  vol.  xviii.  p.  2952. 


vi      RELATION  OF  PYRIDINE,  ETC.,  TO  THE  ALKALOIDS     483 

affords  a  basis  for  conclusions  with  respect  to  their  con- 
stitution. The  subject  is  too  wide  to  be  entered  upon  in 
detail  here.  But  it  may  just  be  stated  that  in  most  cases 
the  degradation-products  show  that  a  close  connection  exists 
between  the  alkaloids  and  pyridine,  quinoline,  or  iso-quinoline 
as  their  nitrogenous  nucleus.1  In  addition  to  conine,  the 
constitution  of  the  following  important  members  of  this  class 
has  now  been  fairly  well  established: — nicotine  (Pinner, 
Blau) ;  pitocarpine  (Hardy  and  Calmels) ;  cocaine  (Einhorr^, 
Merling) ;  and  papaverine  (Goldschmidt). 

The  above  very  short  summary  of  but  a  few  of  the  many 
investigations  which  have  been  carried  out  in  this  branch 
is  of  itself  sufficient  to  show  how  necessary  is  a  knowledge 
of  the  chemical  nature  and  constitution  of  the  pyridine  and 
quinoline  bases  for  the  proper  understanding  of  the  alkaloids, 
and  what  a  rich  harvest  may  still  be  expected  here. 

Certain  non-nitrogenous  compounds  also,  which  are 
naturally  related  to  the  alkaloids,  viz.  meconic,  comenic, 
pyromeconic  and  chelidonic  acids,  whose  constitution  re- 
mained quite  obscure  although  the  substances  themselves 
had  long  been  known,  have  been  shown,  more  particularly  by 
the  recent  researches  2  of  Ost  and  of  Lieben  and  Haitinger, 
to  be  naturally  connected  with  pyridine.  Light  was  thrown 
upon  their  constitution,  as  also  upon  that  of  the  similarly 
constituted  compounds  obtained  from  citric  and  malic  acids,3 
by  the  important  observation  that  they  are  converted  by 
ammonia  into  oxypyridine-carboxylic  acid.  And  Lieben 
and  Claisen's  successful  synthesis  of  chelidonic  acid  4  has 
finally  solved  the  problem. 

1  The  literature  on  this  branch  of  the  science  is  already  voluminous  ; 
the  reader  is  specially  referred  to  Pictet's  admirable  monograph : — Die 
Pflanzenalkaloide,  etc.  (Berlin,  1891). 

2  Journ.  pr.  Chem.  (2),  vol.  xxvii.  p.  257 ;  vol.  xxix.  p.  57 ;  Ber^  vol. 
xvi.  p.  1259. 

3  A.  W.  Hofmann,  Ber.,  vol.  xvii.  p.  2687  ;  v.  Pechmann,  ibid.,  vol. 
xvii.  p.  936 ;  vol.  xix.  p.  2694. 

4  Wiener  Mwwttshefte,  vols.  iv.,  v.,and  vi.  ;  Ber.,  vol.  xxiv.  p.  111.    ^ 


I  I  2 


484  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 


Pyrrol  and  Analogous  Compounds. 

Another  group  of  compounds,  of  which  pyrrol,  furfurane 
and  thiophene  are  the  representatives,  has  been  the  subject 
of  the  most  ardent  investigation  during  recent  years,  with 
the  result  that  the  constitution  of  these  substances  and  also 
that  of  many  of  their  derivatives  has  been  cleared  up.  The 
analogy  existing  between  those  compounds  gradually  came 
to  be  recognised ;  they  all  contain  the  same  nucleus,  consist- 
ing of  four  atoms  of  carbon  and  four  of  hydrogen,  this  being 
combined  in  pyrrol  with  the  imido-group  (NH),  in  furfurane 
with  one  atom  of  oxygen,  and  in  thiophene  with  one  atom  of 
sulphur.  Their  similarity  to  benzene  became  more  apparent 
the  better  they  came  to  be  known,  and  was  shown  in  a 
particularly  striking  manner  in  the  investigation  of  thiophene 
(discovered  by  Victor  Meyer)  and  its  derivatives.  The  work 
which  has  been  done  upon  this  class  of  bodies  is  amongst 
the  most  brilliant  of  our  time.1 

The  artificial  formation  of  thiophene  from  succinic  acid 
and  phosphorus  trisulphide,  2  that  of  pyrrol  from  succinimide 
by  means  of  zinc  dust,  and  the  conversion  of  pyrrol  into 
the  compounds  richer  in  hydrogen — pyrroline  and  pyrrolidine 
(Ciamician) — are  reactions  of  special  importance,  which  helped 
greatly  to  elucidate  the  constitution  of  these  bodies.  Pyrrol, 
which  was  observed  by  Runge  in  coal  tar  and  named  by  him, 
and  first  isolated  by  Anderson,  has  with  its  rapidly-augmenting 
host  of  derivatives  been  closely  and  comprehensively  ex- 
amined by  Ciamician,  Dennstedt,  Paal  and  others  of  late 
years,  Schwanert 3  a  long  time  ago  having  made  the  funda- 
mental observation  that  pyrrol  could  be  produced  from 
ammonium  mucate. 

The  work  done  upon  furfurane  (which  was  discovered  by 
Limpricht  4)  is  to  be  taken  in  conjunction  with  that  upon 
pyromucic  acid  (first  observed  by  Scheele,  and  recognised  as 
a  distinct  compound  by  Labillardiere)  and  its  aldehyde  fur- 
furol  (discovered  by  Dobereiner  and  examined  by  Stenhouse, 

1  Cf.  pp.  350—351.  2  Ber.,  vol.  xviii  p.  454. 

3  Ann.  Chem.,  vol.  cxvi.  p.  278.  4  Ibid.,  voL  clxv.  p.  281. 


vi         FURFURANE,  PYRROL,  AND  INDOLE        485 

Fownes  and  others).  The  analogy  in  behaviour  of  the 
latter  to  benzoic  aldehyde  was  proved  more  especially  by 
Baeyer  and  E.  Fischer,1  and  the  close  connection  between 
pyromucic  and  maleic  acids  by  Hill.2  Paal's  beautiful 
investigations  have  shown  that  derivatives  of  furfurane, 
thiophene  and  pyrrol  are  produced  from  7-diketones  and 
7-diketonic  acids,3  and  have  thus  contributed  in  a  marked 
degree  to  solve  the  constitution  of  these  compounds  (i.e.,  of 
pyrrol,  etc.). 

Among  the  aromatic  compounds  proper,  to  which  the  sub- 
stances just  named  show  a  great  similarity  in  chemical  be- 
haviour, indole  (discovered  by  Baeyer)  was  recognised  by 
him  as  being  an  analogue  of  pyrrol,  and  was  made  the  basis 
of  important  researches  which  resulted  in  showing  its  relation 
to  the  compounds  of  the  indigo  group,  more  particularly  to 
isatin,  oxindole  and  dioxindole.  Various  derivatives  of 
indole  have  lately  been  prepared  by  a  method  discovered  by 
E.  Fischer, — i.e,  from  the  condensation  of  phenyl-hydrazine 
with  aldehydes  and  ketones.4  Cumarone,  obtained  by  Fittig 
and  Ebert  from  cumarine,  has  been  designated  by  Hantzsch  5 
the  "  furfurane  of  the  naphthalene  series,"  and  he  has  con- 
firmed this  view  by  some  ingenious  syntheses  of  its  deriv- 
atives. The  analogy  existing  between  the  three  compounds 
furfurane,  thiophene  and  pyrrol,  and  diphenylene  oxide, 
sulphide  and  imide  (carbazole)  respectively,  was  perceived 
about  the  year  1885. 

For  some  years  past  the  attention  of  a  large  number  of 
investigators  has  been  given  to  the  study  of  compounds 
which  are  related  to  pyrrol  and  its  analogues  as  pyrazine  and 
pyrimidine  are  to  pyridine,  or  quinazoline  to  quinoline 
(cf.  p.  481).  Those  remarkable  compounds  the  azoles 
(pyrazole,  glyoxaline,  triazole,  etc.)  are  pyrrol  derivatives  of 
this  kind,  which  have  been  made  known  to  us  by  the 
researches  of  Marckwald,  v.  Pechmann,  Bladin  and  others. 

1  Ber.,  vol.  x.  p.  13. 

2  Hid.,  vol.  xiii.  p.  734  ;  Journ.  Chem.  Soc.,  vol.  xl.  p.  36. 
a  Cf.  Paal's  monograph  on  the  subject  (Wurzburg,  1890). 

4  Ann.  Chem.,  vol.  ccxxxvi.  p.  116. 

5  Ber.,  vol.  xix.  p.  1290;  also  vol.  xx. 


486  HISTORY  OF  ORGANIC  CHEMISTRY  CHAP. 

Pyrazolone,  iso-pyrazolone  and  their  derivatives  have  proved 
of  special  interest  in  the  hands  of  Knorr  and  his  pupils, 
Curtius  and  von  Rothenburg,  etc.  The  thiazoles  and 
oxazoles,  derived  from  thiophene  and  furfurane  respectively, 
have  been  studied  by  Hantzsch,  Claisen  and  others. 

Organic-metallic  Compounds. 

After  it  had  come  to  be  seen  that  not  only  hydrogen, 
oxygen,  nitrogen,  sulphur  and  the  halogens  could  combine 
directly  with  carbon,  but  also  arsenic  as  well — a  point  which 
Kolbe  was  the  first  to  indicate  in  his  interpretation  of 
cacodyl,1 — new  fields  in  organic  chemistry  became  opened  up 
in  rapid  succession.  Frankland's  discovery  2  of  the  action  of 
zinc  on  methyl  and  ethyl  iodides,  in  which  the  metal  breaks 
up  the  iodide  in  order  to  combine  with  the  alkyl  radical,  led 
to  a  knowledge  of  the  organo-metallic  compounds.  Thanks  to 
the  readiness  with  which  these  enter  into  reaction,  they  have 
been  destined  to  aid  in  the  development  of  organic  chemistry 
to  an  unlooked-for  extent,  more  especially  as  regards  syn- 
thetic methods.  With  the  aid  of  the  zinc-alkyls  many  other 
organo-metallic  compounds  were  prepared  and  minutely  in- 
vestigated in  due  course,  e.g.  the  ethyl  compounds  of  tin, 
mercury,  lead,  sodium,  aluminium  and  other  elements.  3 
Among  the  last  were  those  non-metals  of  which  organic 
compounds  had  not  previously  been  known ;  boric  methide 
and  other  similar  substances  were  prepared  by  Frankland,4 
and  the  important  alkyl  compounds  of  silicon  by  Friedel 
and  Krafts,  the  composition  of  these  latter  proving  the 
complete  analogy  between  that  element  and  carbon.  To  the 

1  Cf.  p.  324. 

2  Journ.  Chem.  Soc.,  vol.  ii.  p.  263;  ov  Ann.  Chem.,  vol.  Ixxi.  p.  171 
(1849). 

3  Cf.  the  papers  of  Buckton,  Odling,  Frankland,  Cahours,  Ladenburg, 
etc. ,  in  the  Philosophical  Transactions,  Journal  of  the  Chemical  Society,  and 
Annalen  der  Chemie. 

4  Proc.  JR.  8.,  vol.  xii.  p.  123 ;  or  A nn.  Chem.,  vol.  cxxiv.  p.  129.     For 
aromatic  compounds  of  Boron,  see  Michaelis  and  others,  Ber.,  vol.  xxvii.  p. 
244. 


vi  ORGANO-METALLIC  COMPOUNDS  487 

organo-metallic  compounds  of  the  fatty  series,  various  others 
belonging  to  the  aromatic  have  since  been  added,  the  first  of 
these  having  been  mercury  di-phenyl.1  Magnesium,  bismuth 
and  thallium  alkyls  have  also  been  prepared  within  the  last 
few  years.  The  peculiar  compounds  of  nickel,  iron  and 
platinum  with  carbonic  oxide,  which  find  a  place  alongside 
of  the  organo-metals,  have  already  been  spoken  of  under  the 
metals  themselves. 

The  short  description  which  has  just  been  given  of  the 
development  of  organic  chemistry  is  sufficient,  notwith- 
standing its  incompleteness,  to  allow  of  our  recognising  the 
main  currents  which  have  prevailed,  and  which  still  do  so,  in 
this  branch  of  the  science.  The  review  of  the  numberless 
organic  substances,  which  have  been  investigated  during  the 
last  fifty  or  sixty  years,  is  materially  facilitated  by  the  general 
points  of  view  which  have  become  gradually  established 
from  the  classification  of  those  compounds  and  from  the 
deduction  of  their  chemical  constitution.  A  prominent  place  in 
this  respect  is  to  be  given  to  the  gradually  growing  perception 
that  organic  compounds  might  be  looked  upon  as  derivatives 
of  inorganic,  and  to  the  increasing  certainty  with  which 
their  constitution  could  be  defined  on  the  basis  of  the 
saturation-capacities  peculiar  ^to  the  atoms  of  the  various 
elements. 

1  R.  Otto,  Ann.  Chem.,  vol.  cliv.  p.  93.     Cf.  more  especially  Michaelis' 
work  on  the  phosphenyl  compounds,  etc. 


488  "•"HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP. 


HISTORY  OF  PHYSICAL  CHEMISTRY  IN  RECENT  TIMES1 

The  influence  which  certain  branches  of  physics  have  ex- 
ercised on  the  development  of  chemical  doctrines  cannot  be 
estimated  too  highly.  It  was  through  the  introduction  of 
physical  methods,  more  particularly  through  the  application 
of  weighing,  measuring  and  calculating  to  chemical  problems, 
that  chemistry  first  became  an  exact  science.  The  import- 
ance of  those  methods,  in  so  far  as  they  have  had  a  deter- 
mining influence  on  the  chemical  tendency  of  the  present 
period,  has  already  been  entered  into  in  the  general  section 
of  this  book.  From  the  time  of  Lavoisier  onwards,  it  came 
to  be  more  and  more  clearly  seen  that  an  intimate  connection 
existed  between  the  chemical  and  physical  properties  of  sub- 
stances. Definite  relations  were  found  to  hold  good  both  be- 
tween the  proportions  by  weight  of  substances  which  enter 
into  chemical  combination  and  between  the  volumes  of  com- 
bining gases  (Avogadro,  Gay-Lussac).  Investigators  sought 
to  determine  the  more  important  physical  constants  of  com- 
pounds in  their  various  states  of  aggregation,  e.g.  the  specific 
gravity,  specific  heat,  etc.,  as  well  as  the  changes  in  physical 
properties  which  were  brought  about  by  chemical  reactions, 
and  thus  to  arrive  at  general  relations  from  which  the 
chemical  constitution  and  physical  behaviour  of  different  sub- 
stances could  be  elucidated.  To  the  efforts  at  solving  such 
problems  as  these,  physical  chemistry  owes  its  origin  and 
gradual  development. 

Although  Lavoisier,  in  conjunction  with  certain  eminent 
physicists  (Laplace,  in  particular),  took  up  some  of  the  above 

1  With  regard  to  the  sources  of  information  on  which  this  and  the  follow- 
ing sections  are  based,  the  reader  is  referred  to  W.  Ostwald's  admirable 
Lehrbuch  der  allgemeinen  Chemie,  1st.  edition  in  two  volumes,  1885 — 7 ; 
2nd.  completely  revised  edition,  of  which  two  volumes  have  so  far  been 
published,  1890—1897  (cf.  note  1,  p.  377).  W.  Nernst's  Theoretische  Chemie 
(1893),  which  has  been  translated  into  English  by  C.  S.  Palmer  of  Colorado, 
is  also  a  book  of  originality  ;  and  this  remark  likewise  applies  to  the  earlier 
work  with  the  same  title  by  Horstmann. 


vi    HISTORY  OF  PHYSICAL  CHEMISTRY  IN  RECEmiES   489 


problems,  and  Gay-Lussac  at  a  later  period  established  the 
relations  which  exist  between  the  volumes  of  different  gases 
and  their  chemical  composition,  while  Dulong  and  Petit 
pointed  out  the  connection  between  the  specific  heat  and 
atomic  weight  of  the  elements,  the  boundary  land  between 
physics  and  chemistry  was  first  systematically  explored  by 
Hermann  Kopp  ;  with  the  investigations  of  the  last-named 
chemist  on  the  relations  between  atomic  weight  and  specific 
gravity,  on  the  laws  which  regulate  the  boiling  temperatures 
of  liquids,  and  so  on,  the  history  of  physical  chemistry  is  in- 
timately bound  up.  The  attention  paid  to  physico-chemical 
questions  has  gone  on  steadily  increasing  during  the  last 
three  or  four  decades,  and  this  applies  in  a  special  degree  to 
such  as  bear  upon  the  relations  between  the  thermo-chemical, 
optical,  and  electro-chemical  behaviour  of  substances  and 
their  chemical  constitution.  All  this  work  in  physical 
chemistry  has  found  a  rallying  point  in  the  Zeitschrift  fur 
physikalische  Chemie,  which  was  projected  by  Ostwald  in  1  88  7, 
and  which  has  throughout  been  edited  by  himself  and  van  't 
Hoff. 

But  there  is  another  allied  branch  also,  viz.  that  of 
chemical  affinity  (Verwandtschafi),  which  has  been  greatly 
benefited  by  the  investigations  just  referred  to.  With  the 
aid  of  physico-chemical  methods,  and  the  calculations  re- 
quisite for  these,  a  beginning  is  being  made  towards  the 
solution  of  the  old  problem  respecting  the  cause  and  nature 
of  chemical  affinity.  It  will  therefore  be  appropriate  to 
speak  of  the  history  of  the  doctrine  of  affinity  while  describing 
the  development  of  physico-chemical  researches.  Through 
both  of  these  branches  there  runs  the  continuous  endeavour 
to  make  chemical  reactions  capable  of  mathematical  treatment. 

The  behaviour  of  gases  and  vapours  has  been,  almost  more 
than  anything  else,  the  subject  of  fruitful  physico-chemical 
investigations,  doubtless  because  the  physical  properties  of  a 
substance  in  the  gaseous  state  are  observable  with  fewer 
complications  than  in  any  other,  and  hence  definite  relations 
between  these  properties  and  the  chemical  constitution  of 
the  compound  are  more  readily  apparent. 


490  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP. 

Determination  of  Vapour  Density. 

The  laws  of  Boyle  and  Mariotte  and  of  Gay-Lussac, 
which  expressed  the  connection  between  the  volume  of  a  gas 
and  its  temperature  and  pressure,  prepared  the  ground  for  a 
knowledge  of  other  relations.  Gay-Lussac's  law  of  volumes, 
which  has  already  been  treated  of,1  was  the  first  result  in 
this  branch  which  benefited  chemistry  in  an  exceptional 
degree.  The  recognition  of  the  intimate  connection  between 
the  specific  gravity  of  a  gas  and  its  molecular  weight  we  owe 
to  Avogadro,2  although  it  was  a  long  time  of  taking  root  in 
the  science;  this  "law  of  Avogadro,"  which  expresses  the 
above  relation,  still  governs  chemical  research,  and  is  an 
indispensable  aid  in  the  determination  of  the  molecular 
weights  of  many  chemical  compounds. 

The  due  appreciation  of  its  value  has  led  to  continuous 
endeavours  towards  simplifying  and  refining  the  methods  for 
determining  the  specific  gravity  of  gases  and  vapours. 
Dumas,  as  already  mentioned,  was  the  first  to  devise  a 
generally  applicable  method  for  vapour  density  determina- 
tions,3 and  by  this  he  achieved  great  results.  Another  plan, 
according  to  which  the  volume  of  vapour  produced  from  a 
given  weight  of  substance  is  accurately  estimated,  was  worked 
out  by  Gay-Lussac  and  afterwards  modified  by  Hofmann.4 
And  to  the  above  methods  there  was  added  in  1878  that  of 
Victor  Meyer,5  which  depends  upon  the  measurement  of  the 
air  (or  any  other  indifferent  gas)  which  is  expelled  from  the 
apparatus  by  the  vapour  resulting  from  a  given  weight  of 
the  substance  in  question.  The  improvements  which  those 
methods  have  undergone  since  their  introduction  cannot  be 
entered  into  here,  but  emphasis  must  be  laid  upon  the  point 
that  through  their  means  the  all-important  knowledge  of  the 
relative  weights  of  the  atoms  and  molecules  of  elements 
and  compounds  has  been  immensely  advanced. 

The  determination  of  the  specific  gravity  of  vapours  has 
proved  in  certain  cases  the  most  reliable  means  of  decid- 

1  Cf.  p.  214.  2  Cf.  pp.  215  and  294. 

3  Ann.  Chim.  Phys.,  vol.  xxxiii.  p.  341. 

4  Ber.,  vol.  i.  p.  198.  5  Ibid.,  vol.  xi.  pp.  1867  and  2253. 


vi  DETERMINATION  OF  VAPOUR  DENSITY  491 

ing  between  the  values  arrived  at  by  different  methods, 
stochiometric  or  otherwise,  and  so  getting  at  the  correct 
atomic  weights  of  the  elements.  To  give  only  some  more 
or  less  recent  instances  of  this,  we  would  refer  to  the  de- 
duction of  the  atomic  weights  of  silicon,  beryllium,  thorium 
and  germanium  from  the  vapour  densities  of  their  chlorides. 
Starting  with  Avogadro's  hypothesis — that  the  vapour  density 
is  proportional  to  the  molecular  weight — chemists  have  been 
able  to  deduce  from  the  specific  gravities  of  gasified  elements 
most  striking  conclusions  with  respect  to  the  number  of 
atoms  in  their  molecules  at  different  temperatures.  One 
has  but  to  think  of  the  results  of  Dumas'  and  Mitscherlich's 
investigations  x  on  the  vapour  densities  of  sulphur,  arsenic, 
phosphorus  and  mercury,  the  molecules  of  which  contain 
different  numbers  of  atoms,  as  was  deduced  at  a  later  date 
from  the  specific  gravity  of  their  vapours  after  the  revivifica- 
tion of  Avogadro's  law.  The  reader  is  further  referred  to  the 
important  work  of  V.  Meyer  and  of  Nilson  and  Pettersson 
on  the  vapour  densities  of  compounds,  more  especially  of  such 
as  show  a  varying  composition  with  changing  temperature. 
Aluminium  chloride,  for  instance,  has  the  simplest  molecular 
weight  which  is  possible  (that  expressed  by  the  formula 
A1C13)  at  a  temperature  sufficiently  high,  but  one  double  as 
great  (A12C16)  at  lower  temperatures  ;  and  the  same  applies 
to  stannous  chloride  (SnCl2  or  Sn2Cl4),  etc.  The  latest  ef- 
forts of  workers  in  this  field  are  being  directed  to  the  de- 
composition of  molecules  into  their  elementary  atoms,  by 
making  use  of  exceedingly  high  temperatures  (V.  Meyer). 

These  few  examples  are  sufficient  to  illustrate  what  has 
just  been  said  above.  The  significance  which  is  attached 
to  the  results  of  vapour  density  determinations  is  most 
strikingly  shown  in  the  fact  that  such  estimations  are  held 
to  be  the  most  reliable  means  of  getting  at  the  valency  of 
an  element,  The  amount  of  care,  however,  which  is  requisite 
here,  is  proved  by  the  different  results  obtained  by  different 
experimenters,  and  is  particularly  apparent  in  the  be- 
haviour of  aluminic  chloride,  from  whose  vapour  density  the 

1  Cf.  p.  225. 


492  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP. 

conclusion  was  drawn  (and  held  to  until  quite  recently)  that 
aluminium  was  tetravalent,  although  the  whole  behaviour  of 
the  element  pointed  to  its  tri-valency ;  this  has  now  been 
confirmed  by  the  determination  of  the  normal  density  of 
vapour  of  the  chloride. 

Dissociation. 

From  the  observations  made  upon  what  are  known  as 
anomalous  vapour  densities,  the  cause  of  which  has  been 
recognised  in  a  gradually  increasing  decomposition  of  the 
compound  with  rise  of  temperature,  the  doctrine  of  dissocia- 
tion— so  important  for  physical  chemistry — has  developed 
itself ;  the  name  "  dissociation  "  was  first  made  use  of  by 
H.  de  St.  Claire  Deville  to  express  decompositions  of  this 
nature.  He  was  the  earliest  (from  the  year  1857)1to 
work  systematically  at  this  branch  of  the  science,  which  has 
also  been  made  the  subject  of  important  investigations  by 
others  since,  e.g.  Debray,  Cahours,  Wurtz,  Horstmann,  Isam- 
bert  and  A.  Naumann.  Most  of  these  experimenters  did  not 
confine  themselves  to  cases  of  so-called  abnormal  vapour 
density  alone,  but  studied  generally  the  gradual  increase  in 
decomposition  of  chemical  compounds  under  an  increasing 
temperature.  Of  late  years  the  assumption  that  every 
electrolyte  is  dissociated  in  solution  has  come  prominently 
forward  (see  below). 

The  Liquefaction  of  Gases. 

The  investigation  of  the  transition  of  gases  and  vapours 
into  the  liquid  and  solid  states  has  given  rise  to  work  of 
exceeding  importance.  We  have  but  to  recall  the  com- 
prehensive researches  of  Faraday  2  on  the  liquefaction  of 
gases  which  were  at  that  date  held  to  be  uncondensable, 
and  especially  the  remarkable  investigations  of  R.  Pictet,3 
Cailletet,4  Wroblevsky  and  Olzevsky,5  which  proved  that 

1  Cf.  Comptes  Rendus,  vol.  xlv.  p.  857. 

2  Phil.  Trans,  for  1823,  p.  160 ;  and  for  1845,  p.  1. 

3  Comptes  Rendus,  vol.  Ixxxv.  p.  1214 ;  also  in  subsequent  volumes  of 
the  Archives  des  Sciences  Naturelles. 

4  Comptes  Rendus,  vol.  Ixxxv.  p.  1213  (1877). 

5  Ann.  Phys.,  N.  F.,  vol.  xx.  p.  243,  etc. 


vi  LIQUEFACTION  OF  GASES  493 

there  was  no  known  gas  that  could  withstand  the  combined 
effect  of  sufficiently  high  pressure  and  low  temperature.  Nitro- 
gen, oxygen,  hydrogen  and  argon  were  thus  all  reduced  by 
these  experimenters  to  the  liquid,  and  nitrogen  and  argon  to 
the  solid  states,  and  their  boiling  temperatures  determined, 
— observations  of  very  great  moment.  The  recent  work  of 
Linde  and  Hampson  has  greatly  simplified  the  process  for 
the  liquefaction  of  air,  which  will  probably  in  the  future 
prove  of  importance  from  a  technical  point  of  view,  e.g.  may 
cheapen  the  production  of  oxygen.  Dewar  has  just  suc- 
ceeded in  obtaining  a  measurable  amount  of  liquid  hydrogen 
(about  50  c.c.  at  one  time).  Liquid  hydrogen  is  clear  and 
colourless,  it  shows  no  absorption  spectrum,  and  the  meniscus 
is  as  well  defined  as  in  the  case  of  liquid  air.  The  boiling 
point,  determined  by  Dewar  with  a  platinum  resistance 
thermometer,  is  —  238°C.,  and  the  density  of  liquid  hydrogen 
at  its  boiling  temperature  is  0'07  approximately ;  it  is  thus 
by  far  the  lightest  liquid  known.  Hydrogen  does  not  possess 
in  the  liquid  state  the  characters  of  a  metal.1 

Thirty  years  ago  Andrews  2  had  made  a  thorough  study 
of  the  conditions  under  which  a  gas  can  be  liquefied,  and 
had  established  the  important  conceptions  of  "  critical  tem- 
perature "  and  "  critical  pressure,"  Mendelejeff 3  having  some 
time  before  this  made  certain  fundamental  observations  on 
the  subject. 

Light  was  thrown  upon  the  behaviour  of  gases  to  liquids 
in  the  first  decade  of  the  century  by  the  investigations  of 
Henry  and  Dalton,  which  established  the  fact  that  the 
amount  of  absorption  of  a  gas  or  of  a  mixture  of  gases  by  a 
liquid  is  dependent  upon  the  pressure,  and  this  law  was  after- 
wards confirmed  by  Bunsen's  classical  researches.  4 

The  Kinetic  Theory  of  Gases. 

The  thorough  investigation  of  gases,  of  their  physical 
behaviour  in  particular,  led  to  the  setting  up  of  a  theory  by 

1  Journ.  Chem.  Soc.  for  1898,  p.  528. 

2  Pkil.  Trans,  for  1869,  p.  575;  or  Pogg.  Ann.,  Suppl.,  vol.  v.  p.  64 
(1871). 

3  Ann.  Chem.,  vol.  cxix.  p.  11.  4  Ibid.,  vol.  xciii.  p.  1  (1855). 


494  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP. 

means  of  which  the  various  phenomena  exhibited  by  them— 
specific  heat,  diffusion  and  friction — have  been  brought 
together  under  one  common  standpoint  and  explained  in  a 
satisfactory  manner.  The  fundamental  idea  that  a  gas  was 
an  assemblage  of  moving  particles  had  previously  been  put 
forward  by  D.  Bernoulli  in  1 7  3  8  and  by  Herapath,  and  Joule 
had  in  1851  made  a  great  step  in  advance  by  calculating  the 
mean  translational  velocity  of  these  particles.  This  idea,  in 
the  hands  of  Kronig  and  more  especially  Clausius  (in  1857), 
gave  birth  to  the  modern  kinetic  theory  of  gases,  which  has 
been  so  splendidly  worked  out  by  Clausius  and  Maxwell,  and 
since  then  perfected  in  detail  by  Boltzmann,  O.  E.  Meyer, 
van  der  Waals  and  many  others.  It  may  be  regarded  as 
springing  from  the  mechanical  theory  of  heat.1 

Spectrum  Analysis. 

The  examination  of  the  optical  behaviour  of  glowing 
gases  and  vapours  has  exercised  a  most  profound  influence 
upon  physical  chemistry.  Spectrum  analysis  has  grown  out 
of  some  apparently  insignificant  and  disconnected  observa- 
tions made  by  Marggraf,  Scheele,  Herschel  and  others  upon 
the  light  emitted  by  flames  coloured  by  certain  salts. 
The  spectra  of  such  flames  were  investigated  by  various 
physicists,  among  whom  Talbot,  Miller  and  Swan  deserve 
first  mention  ;  but  it  was  only  after  Kirchhoff2  (in  1860) 
had  made  and  proved  the  definite  statement — that  every 
glowing  vapour  emits  rays  of  the  same  degree  of  refrangi- 
bility  that  it  absorbs, — that  spectrum  analysis  became  de- 
veloped by  Bunsen  and  himself  into  one  of  the  great  branches 
of  our  science.  Its  importance  for  analytical  chemistry  has 
already  been  touched  upon. 

The  application  of  the  spectroscope  to  the  determination 
of  the  composition  of  the  heavenly  bodies,  and  with  this  the 
firm  establishment  of  stellar-physics,  must  be  mentioned 

1  For  an  account  of  the  development  of  the  above  theory,  see  0.  E. 
Meyer's  work,  Die  Kinetische  Theorie  der  Gase  (Breslau,  1877) ;  also  Watson's 
Kinetic  Theory  of  Gases. 

2  Pogg.  Ann.,  vol.  cix.  p.  275. 


vi  SPECTRUM  ANALYSIS :  ATOMIC  VOLUMES  495 

here.  With  respect  to  general  chemistry,  the  efforts  to  ar- 
rive at  harmonic  relations  between  the  lines  of  the  spectrum 
themselves,  and  at  a  connection  between  those  lines  and  the 
atomic  weights  of  the  elements  which  give  rise  to  them,  ap- 
pear to  be  well  founded,  as  is  seen  from  the  work  of  Maxwell, 
Balmer,  Stoney,  Soret  and  Lecoq  de  Boisbaudran.1  A  com- 
plete theory  of  the  spectral  phenomena  peculiar  to  gases  re- 
mains still  a  problem  for  the  future,  although  much  admir- 
able preparatory  work  has  been  done  on  the  subject. 

Atomic  Volumes  of  Solids  and  Liquids. 

The  endeavour  to  establish  relations  between  the 
physical  properties  of  solid  and  liquid  bodies  and  their 
chemical  composition  has  given  rise  to  a  large  amount  of 
investigation,  of  which  the  most  important  must  be  men- 
tioned here.  H.  Kopp  was  the  first  to  work  out  in  a 
through  manner  the  connection  between  the  specific  gravity 
of  elements  and  compounds  and  their  atomic  composition, 
Dumas,  Herapath,  Karsten,  Boullay  and  Ammermuller  having 
previously  given  some  attention  to  the  subject.  After 
establishing  the  atomic  or  specific  volumes  of  these  latter, 
Kopp  succeeded  in  discovering  a  number  of  relations,  and, 
more  particularly,  in  working  out  the  specific  volumes  of  the 
elementary  atoms  in  compounds  ;  it  thus  became  possible  to 
calculate  the  atomic  volumes  of  complex  compounds.2 

The  work  done  of  recent  years  in  this  branch,  among 
which  that  of  Thorpe,  Lessen,  Staedel  and  R.  Schiff  may  be 
mentioned,  has  for  the  most  part  been  carried  out  upon  the 
principles  laid  down  by  Kopp  ;  it  has  resulted  in  bringing 
out  many  new  points  of  view,  and  has  led  to  a  number  of 
modifications  in  the  values  arrived  at  by  him.  The  formerly 
accepted  opinion — that  the  atomic  volumes  of  the  elements 
in  their  compounds  are  mostly  invariable — has  been  greatly 
shaken  by  this  later  work.  Among  the  numerous  researches 

1  Cf.  Ostwald's  Lehrbuch,  2nd.  edition,  vol.  i.  p.  260  et  seq. 

2  Cf.  Kopp's  pioneering  researches,  Ann.  Chem.,  vol.  xli.  p.  76 ;  vol. 
xcvi.  pp.  153  and  303.     The  last  piece  of  work  which  he  carried  out  dealt 
with  the  Molecular  Volumes  of  Liquids  (Ann.  Chem.,  vol.  ccl.  p.  1). 


496  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP, 

(in  addition  to  H.  Kopp's)  which  have  been  made  with  the 
object  of  discovering  a  connection  between  the  volumes  of 
solid  compounds  and  their  atomic  composition,  those  of 
Schroeder  are  especially  worthy  of  note.  He  assumes  volume 
units  *  of  chemically  analogous  elements,  and  believes  that 
he  has  in  this  found  the  key  to  the  solution  of  the  above 
problem  (the  doctrine  of  "  Parallelosterism ").  But  here 
again  we  are  still  far  from  a  knowledge  of  any  law  governing 
the  atomic  volumes  of  solid  or  liquid  compounds,  whereas,  in 
the  case  of  gases,  the  simple  relations  existing  between 
specific  gravity  and  composition  were  worked  out  a  long 
time  ago.2 

Laws  regulating  the  Boiling  Temperature? 

Kopp  was  likewise  the  first,  in  his  classical  researches,4 
to  point  out  a  connection  between  the  boiling  temperature 
and  the  composition  of  compounds  (more  especially  of  organic 
ones),  in  so  far  that  he  drew  from  his  results  the  deduction 
that  approximately  equal  differences  in  boiling-point  corre- 
spond to  equal  differences  in  the  composition  of  organic 
substances.  And  even  although  this  supposed  regularity 
turned  out  to  be  only  applicable  to  certain  compounds,  and 
could  not  be  relied  upon  for  other  series,  still  Kopp's  work 
gave  a  powerful  impetus  to  the  search  after  actual  relations 
— expressible  by  figures — between  boiling-point  and  chemi- 
cal composition. 

The  question  arose, — in  what  manner  does  the  different 
chemical  constitution  of  isomeric  and  chemically  analogous 
compounds  exercise  an  influence  on  their  boiling  tempera- 
tures— to  be  subjected  to  examination  by  Kopp.5  Other 
more  recent  and  more  extended  investigations,  e.g.  those  6  of 

1  These  mnits  he  terms  Steren.  2  Cf.  pp.  214  and  490. 

3  For  the  literature  on  this  subject,  cf .  the  article  Siedepunkt  in  Fehling's 
Handworterbuch  by  Nernst  and  Hesse. 

4  Ann.  Chem.,  vol.  xli.  pp.  86  and  169;  vol.  Iv.  p.  166,  etc. 
6  Ann.  Chem.,  vol.  1.  p.  142  ;  vol.  xcvi.  p.  1. 

6  Cf.  A.  Naumann,  Allgemeine  und  Physikalische  Chemie("  General  and 
Physical  Chemistry"),  (1877),  p.  553  et  seq ;  Ostwald,  Lehrbuch  der  aMge- 
meinen  Chemie,  2nd.  edition,  vol.  i.,  p.  330  et  seq. 


vi  LAWS  REGULATING  BOILING  TEMPERATURE  497 

Linnemann,  Schorlemmer,  Zincke,  Naumann  and  others,  have 
resulted  in  showing  that  there  are  a  number  of  definite  rela- 
tions here  also,  without,  however,  having  rendered  it  possible 
to  formulate  a  precise  law  setting  forth  the  dependence  of 
boiling-point  upon  chemical  constitution ;  but  it  has  been 
clearly  established  that  there  is  a  distinct  connection  between 
them.  It  is  possible  that  a  closer  knowledge  of  the  intimate 
relation  sought  for  may  be  arrived  at  rather  from  the 
occasionally  observed  anomalies  (e.g.  the  lowering  of  boiling 
temperature  with  increasing  molecular  weight,  as  in  the  case 
of  the  glycols  and  certain  chlorine  compounds,  etc.)  than  from 
regularities.  The  efforts  to  establish  definite  formulae  for 
the  relationship  of  the  vapour  pressure  of  liquids  to  the 
temperature  have  been  followed  with  great  success ;  they  have 
resulted  in  the  laws  worked  out  by  Duhring,  Winkelmann, 
and  Ramsay  and  Young. 

There  have  not  been  wanting  zealous  endeavours  also  to 
discover  regular  relations  between  the  temperatures  at  which 
solid  substances  become  liquid  and  their  composition,  but  no 
definite  results  have  been  arrived  at  in  this  way.  Of  more 
importance,  however,  have  been  the  researches  made  with  the 
object  of  determining  melting-point  and  heat  of  solidification, 
e.g.  those  of  Pettersson  and  Nilson,  and  those  on  the 
influence  of  pressure  upon  melting-point  (James  Thomson, 
Bunsen).  KrafFt  and  Weilandt1  have  recently  made  some  very 
remarkable  observations  on  the  great  reduction  of  the  boiling- 
point  in  a  very  high  vacuum. 


Specific  Heat  of  Solid  Bodies. 

The  work  which  has  been  done  upon  the  specific  heat  of 
elements  and  compounds  is  among  the  most  important  in 
the  whole  field  of  physical  chemistry,  the  dependence  of  this 
property  on  the  atomic  composition  having  been  definitely 
established.  We  would  recall  here  the  Dulong-Petit  law  of 
the  approximate  equality  in  the  specific  heats  of  solid 

1  Ber.,  vol.  xxix.  p.  1316. 

K  K 


498  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP, 

elements,  the  significance  of  which  for  the  development  of  the 
atomic  theory  has  already  been  detailed  in  the  general 
section  ;x  the  extension  of  this  law  by  Neumann ;  and  its  en- 
largement by  Regnault's  classical  researches,  as  well  as  by 
those  of  H.  Kopp,  Weber  and  others,  which  proved  that  the 
specific  heat  varies  with  the  temperature  at  which  it  is 
determined.  And  even  if  the  confidence  felt  in  the  applic- 
ability of  the  Dulong-Petit  law  was  shaken  by  the  marked 
deviation  from  it  shown  by  certain  elements,  still  its  useful- 
ness in  a  very  large  number  of  cases  and  the  great  value  of 
its  principle  remained ;  as  Berzelius  had  predicted,  it  formed 
"the  foundation  of  one  of  the  most  beautiful  pages  in 
chemical  theory."  The  investigation  of  the  specific  heat  of 
liquids  has  not  led  to  conclusions  of  such  a  general  nature 
as  have  resulted  in  the  case  of  solids. 


Optical  Behaviour  of  Solids  and  Liquids. 

A  long  series  of  excellent  experimental  researches  has 
been  induced  by  the  endeavour  to  discover  definite  relations 
between  the  optical  behaviour  of  solid  and  liquid  substances 
and  their  chemical  composition.  The  earlier  labours  of 
Becquerel,  Cahours  and  Deville,  and  the  later  ones  of 
Gladstone  and  Dale,  Landolt,  Briihl,  Kanonikoff  and  others 
have  led  to  conclusions  of  importance  respecting  the  con- 
nection between  the  constitution  of  a  substance  and  its 
power  of  refracting  a  ray  of  light.2 

The  working  out  of  the  refraction-equivalents  pertaining 
to  the  individual  elementary  atoms  within  their  compounds 
has  led  to  the  discovery  of  stochiometric  regularities  with 
respect  to  refraction.  Of  special  interest  is  the  proof  that 
the  varying  function  or  mode  of  combination  of  the  elements, 
carbon  in  particular,  has  a  determining  influence  on  the 
molecular  refraction.  If  the  latter  is  accurately  known, 

1  Cf .  p.  220. 

2  For  the  literature  on  this  subject,  cf.  Landolt  and  Bernstein's  Physi- 
Jcalische-Chemische  Tabellen,  p.  220 ;  and  Ostwald's  Lehrbuch,  2nd.  edition, 
vol.  i.  p.  415  et  seq. 


vi  CIRCULAR  POLARIZATION  499 

then  conclusions  may  be  drawn  from  the  refractive  power  as 
to  the  constitution.  Deductions  of  this  kind  have  been 
applied  more  especially  to  solving  the  question  of  the  consti- 
tution of  benzene.  The  great  class  of  keto-compounds  has 
also  been  investigated  optically,  with  the  view  of  making 
certain  of  the  constitution.1 

Only  a  passing  reference  can  be  made  here  to  the 
importance  to  crystallography  of  the  observed  relations 
between  light  refraction  and  crystalline  form,  and  to  the 
pioneering  work  of  Brewster  and  Fresnelon  the  subject. 

Another  optical  property  of  many  substances,  more  especi- 
ally organic,  has  greatly  excited  the  interest  of  chemists 
in  quite  recent  years,  viz.  circular  polarisation,  which  it  has 
been  attempted,  and  with  success,  to  connect  closely  with  the 
chemical  constitution  of  the  compounds  in  question.  After 
the  first  memorable  investigations  of  Arago,  Biot  and 
Seebeck  had  been  made,  the  observation — that  certain  sub- 
stances, whether  in  the  solid  or  liquid  state,  are  capable  of 
turning  the  plane  of  polarisation  of  light — was  held  to  be 
of  importance  for  physics  alone.  It  has  only  been  since 
Pasteur's  beautiful  researches2  on  the  optically  active 
tartaric  acids,  and  the  inactive  racemic  acid  produced  by 
their  combination,  that  relations  between  optical  activity 
and  crystalline  form  have  been  discovered,  and  deductions 
drawn  from  these  as  to  chemical  constitution. 

The  desire  to  gain  light  upon  this  point  produced  in 
1 8  7  4  a  theory,  which  was  given  out  at  the  same  time  and 
independently  by  Lebel 3  and  van 't  Hoff,4  and  which  is 
based  upon  the  hypothesis  that  the  cause  of  this  optical 
activity  is  to  be  sought  for  in  the  presence  of  one  or  more 
asymmetric  carbon  atoms,  i.e.  a  carbon  atom  which  is  linked 
to  four  other  different  atoms  or  radicals.  Should  this 

1  Cf.  particularly  the  latest  investigations  by  Briihl,  Journ.  pr.  Ghent. 
(2),  vols.  xlix  and  1 ;  and  the  most  recent  volumes  of  the  Berichte,  especially 
vol.  xxix.  p.  2902. 

2  Comptes  Rendus,  vol.  xxiii.  p.  535  (1848)  ;  vol.  xxix.  p.  297  ;  vol.  xxxi. 
p.  480. 

3  Bull.  Soc.  Chim.  (2),  vol.  xxii.  p.  337. 

4  Ibid.  (2),  vol.  xxiii.  p.  295. 

K  K   2 


500  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP. 

assumption  become  fully  demonstrated  (and  it  has  this  in  its 
favour, — that  an  asymmetric  carbon  atom  has  been  found  in 
every  optically  active  substance  whose  constitution  has  been 
determined  with  the  necessary  accuracy),  then  it  may  with 
confidence  be  stated  that  there  is  an  intimate  connection 
between  this  physical  property  and  chemical  constitution. 

We  may  again  refer  shortly  here  to  van 't  Hoif  s  spacial 
conception  of  the  distribution  of  the  four  valencies  of  the 
carbon  atom  (represented  as  in  the  middle  of  a  tetrahedron, 
with  its  four  affinities  at  the  four  corners),  and  to  the 
extension  of  this  hypothesis  by  Wislicenus,  who  has  ex- 
plained by  its  means  the  constitution  and  formation  of 
geometrical  isomers,  e.g.,  fumaric  and  maleic  acids,  and  the 
crotonic  acids,  with  their  derivatives,1  and  also  the  chemical 
behaviour  of  these  compounds.  Such  speculations  have  very 
quickly  proved  themselves  fruitful,  in  that  they  have  led 
to  the  perception  of  relations  which  had  been  hitherto 
overlooked. 

In  addition  to  what  has  just  been  said  with  regard  to  circular 
polarisation,  mention  must  be  made  here  of  the  work  done 
upon  the  rotation  of  the  plane  of  polarisation  by  a  magnet, 
since  stochiometric  regularities,  i.e.,  relations  between  mag- 
netic polarisation  and  chemical  constitution,  have  been 
brought  to  light  in  this  case  also  by  the  careful  investigations 
of  W.  H.  Perkin  sen.2 

Diffusion,  etc. 

The  properties  of  liquids  which  are  comprised  under 
the  designation  "  capillarity,"  together  with  the  friction  3  and 
diffusion  of  liquids  and  of  solutions  of  solids  in  liquids, 
have  given  rise  to  numerous  and  valuable  researches. 
Ramsay  and  Shields  4  have  proved  that  by  the  measurement 

1  Cf.  p.  356. 

2  Journ.  pr.  Chem.  (2),  vol.  xxxi.  p.  481 ;  or  Journ.  Chem.  Soc.  vol. 
xlv. ,  p.  421 ;  also  Journ.  pr.  Chem.  vol.  xxxii.  p.  523. 

3  Internal  friction  is  treated  historically  in  Ostwald's  Lehrluch,  2nd. 
edition.,  vol.  i.  p.  550,  where  one  also  finds  an  elegant  method  for  its  quan- 
titative determination. 

4  Journ.  Chem.  Soc.  for  1894,  p.  1089. 


vi  DIFFUSION  ;  THEORY  OF  SOLUTION  501 

of  the  molecular  surface  energy  of  liquids,  the  latter  can  be 
divided  into  two  classes,  viz.,  those  of  which  the  molecules 
are  as  simple  in  the  liquid  as  in  the  gaseous  state  (and  this 
applies  to  the  generality  of  liquids),  and  those — such  as 
water  and  the  alcohols — in  which  the  molecules  form  com- 
plices. This  complexity  of  liquid  molecules  has  been  con- 
firmed by  Guye.1 

Graham's  memorable  researches2  gave  a  powerful  im- 
pulse to  the  investigation  of  fluid  friction  and  diffusion ; 
here,  too,  relations  have  been  found  between  these  pheno- 
mena and  chemical  composition.  Mention  must  be  made, 
in  conjunction  with  this,  of  his  division  of  substances  into 
crystalloids  and  colloids,  according  to  their  behaviour  on 
diffusion.  The  reader  is  also  referred  to  the  work  upon 
osmose  (so  nearly  connected  with  diffusion,  and  of  such 
great  importance  for  physiology)  by  Jolly,  C.  Ludwig,  Pfeffer 
and  Briicke.  Pfeffer's  observations  on  osmotic  pressure 
have  proved  of  the  first  importance  for  the  dissociation  theory 
of  solution  (see  below). 

Theory  of  Solution  ;  Electrolytic  Dissociation?1 

For  about  a  dozen  years  past  a  number  of  eminent 
investigators,  who  have  devoted  themselves  to  physical 
chemistry,  have  been  occupied  with  the  question  of  solution  ; 
among  those  who  have  done  most  to  extend  this  subject, 
van  't  Hoff,  Arrhenius,  Ostwald,  Fr.  Kohlrausch  and  Planck 
must  be  named.  The  fundamental  idea  underlying  this 
work  was  that  substances  in  highly  dilute  solution  are  in  a 
state  which  is  comparable  with  that  of  gases.  While  this 
idea  was  not  a  new  one,  van  't  Hoff  was  the  first  to  make  the 
following  definite  statement,  and  to  bring  forward  strong 
arguments  in  its  support,  viz.  that  the  osmotic  pressure  of  a 

1  Ann.  Chim.  vol.  xxxi.  (6),  p.  206. 

2  Phil.  Trans,  for  1850,  1851,  and  1861 ;  or  Ann.  Chem.,  vols.  Ixxvii., 
Ixxx.,  and  cxxiii. 

3  For  the  historical  development  of  these  speculations,  see  Ostwald's 
Lehrbuch ;  Nernst's  Theoretische  Chemie ;  van't  Hoff,  Ber.,  vol.  xxvii.  p.  6  ; 
Horstmann,  Naturwissenchaftliche  Rundschau  for  1892,  p.  465. 


502  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP. 

solution  (e.g.  a  solution  of  sugar  in  water)  is  equal  to  the 
pressure  which  the  same  quantity  of  dissolved  substance 
would  exert  if  it  were  in  the  state  of  gas  and  filled  the  space 
at  present  occupied  by  the  solution. 

Similar  relations  to  those  observed  in  the  determination 
of  osmotic  pressure  had  been  found  by  various  experimenters 
(Blagden,  Rudorff,  de  Coppet,  and  Raoult)  when  they  estab- 
lished the  facts  that  the  freezing  point  of  a  solution  is 
dependent  on  the  concentration  and  the  nature  of  the 
dissolved  substance,  and  that  the  lowering  of  the  vapour 
presure  of  a  solution  or  the  raising  of  its  boiling  point  also 
depends  on  the  amount  of  substance  dissolved. 

Raoult  was  the  first  to  point  out  the  great  significance  of 
these  laws — laws  which  are  theoretically  deducible  from 
van  't  HofFs  axiom — for  the  determination  of  the  molecular 
weight  of  a  dissolved  compound.1  From  those  laws,  therefore, 
the  deduction  was  immediately  drawn  that  equi-molecular 
solutions  (i.e.  solutions  which  contain,  in  equal  volumes  of  the 
solvent,  quantities  of  different  substances  proportional  to 
their  molecular  weights)  show  the  same  osmotic  pressure, 
freezing  point,  vapour  pressure  and  boiling  point.  And, 
thanks  to  the  facility  with  which  freezing  and  boiling  tem- 
peratures can  be  determined,  methods  were  quickly  devised 
by  which  the  molecular  weights  of  substances  in  solution 
could  in  this  way  be  arrived  at.  E.  Beckmann  has  rendered 
signal  service  in  the  practical  elaboration  and  the  scientific 
testing  of  such  methods,  while  Raoult,  Auwers,  Eykman  and 
others  have  striven  to  make  this  procedure  for  molecular 
weight  determination  applicable  as  far  as  possible  to  every 
case. 

Of  quite  exceptional  importance  were  the  deductions 
drawn  when  the  osmotic  pressure,  freezing  point  and  boiling 
point  of  solutions  of  salts,  acids  and  bases  were  viewed  in  the 
light  of  the  above-mentioned  theory.  The  marked  devia- 
tions which  were  observed  in  this  case  found  a  simple  explana- 
tion in  the  assumption  that  these  compounds  un3erwent 
dissociation  when  the  solution  became  very  dilute, — an 
1  Ann.  Chim.  Phys.  (6),  vol.  ii.  p.  92. 


vi  ELECTROLYTIC  DISSOCIATION ;  ELECTROLYSIS         503 

assumption  which  is  in  accordance  with  the  numerous 
observations  on  the  electric  conductivity  of  such  -solutions. 
Arrhenius  was  the  first  to  attempt  an  explanation  of  this 
behaviour  of  the  dissolved  electrolyte  by  assuming  an 
electrolytic  dissociation,  according  to  which  every  electrolyte 
in  aqueous  solution  undergoes  dissociation  into  its  ions,  the 
degree  of  dissociation  depending  on  the  dilution  and  on  the 
nature  of  the  electrolyte  itself.  Although  this  hypothesis 
has  met  with  great  opposition  in  many  quarters,  and  although 
it  may  seem  at  first  sight  to  be  far-fetched,  there  is  no 
denying  its  exceeding  usefulness  for  the  explanation  of 
numberless  chemical  processes  ;  it  has  proved  itself  of  special 
importance  for  electro-chemistry,  analytical  chemistry,  and  the 
doctrine  of  affinity.1 

Electrolysis  of  liquid  or  of  dissolved  Substances. 

The  importance  of  the  first  work  which  was  done  upon 
this  subject  for  the  development  of  the  electro-chemical 
theory  has  already  been  shortly  touched  upon  in  the 
general  section.2  The  connection,  so  early  assumed  between 
electricity  and  chemical  action,  received  the  most  brilliant 
confirmation  from  Faraday's  electrolytic  law,  according  to 
which  equal  amounts  of  electricity,  when  passed  through 
different  electrolytes,  set  free  equivalent  quantities  of 
analogous  substances  at  the  two  poles.3  This  law  was 
vigorously  contested  by  Berzelius,  because  it  appeared  to  him 
to  imply  that  all  the  components  of  the  substances  decom- 
posed by  the  current  were  held  together  in  these  by  equal 
affinities.  Later  experimental  researches  have  corroborated 
the  validity  of  this  law  in  its  full  extent,  and  permit  of  our 
hoping  for  a  definite  solution  of  the  important  problem  of 
chemical  equivalents,  and,  with  this,  of  the  true  saturation- 

1  Cf.  Kiisser's  very  able  paper  in  the  Zeitschrift  fur  Elektrochemie,  vol. 
iv.  p.  105,  entitled  Ueber  lonenreaktionen  und  ihre  Bedeutung  fur  die  Elektro- 
chemie ;  Nernst's  Die  Elektrolytische  Zersetzung  wdssriger  Ldsungen  (Ber., 
vol.  xxx. p.  1547);  Dampier  Whetham's  "Solution  and  Electrolysis "(1895); 
and  Ostwald's  recent  work  "The  Scientific  Foundations  of  Analytical 
-Chemistry." 

2  Cf .  p.  229  et  seq.  3  Cf>  p>  228> 


504  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP, 

capacities  of  the  elements ;  the  reader  is  here  reminded  of 
Renault's  investigations l  on  the  various  "  electrolytic 
equivalents  "  of  one  and  the  same  element,  according  to  the 
nature  of  the  compounds  in  which  it  is  contained. 

These  and  other  observations,  together  with  the  above- 
mentioned  conceptions  regarding  the  nature  of  solution,  have 
helped  to  make  clearer  the  process  of  electrolysis  itself,  in  so 
far  that  they  have  shown  the  intimate  mutual  relations 
existing  between  chemical  and  electrical  energy.  In  the 
light  of  this  Faraday's  law  appears  as  the  expression  of  the 
fact  that  equal  quantities  of  electricity  require  equivalent 
amounts  of  ions  in  their  passage  through  different  electrolytes. 
Electric  conductivity  and  its  relations  both  to  physical  pro- 
perties and  chemical  composition  have  frequently  been  made 
the  subject  of  investigation,  among  others  byG.  Wiedemann, 
Lenz,  Long,  and  W.  Ostwald.  The  recent  work  of  the  last- 
named  chemist,  and  of  Walden  and  others  of  Ostwald's  pupils, 
more  especially,  has  proved  that  a  close  connection  exists 
between  the  conductivity  of  acids  and  their  affinity  for  bases. 
Electro-chemistry  has  been  advanced  in  an  extraordinary 
degree  by  the  attempts  to  solve  the  problem  of  electrolytic 
dissociation;  and  there  can  be  no  question  that  both 
theoretical  chemistry  and  electrical  manufactures  have  been 
and  will  continue  to  be  greatly  benefited  by  such  researches. 
Organic  chemistry,  too,  has  of  recent  years  come  into  much 
closer  contact  with  electro-chemistry,  as  may  be  seen  in  the 
important  experimental  work  of  Gattermann,  Elbs  and  others, 
and  in  the  comprehensive  reports  of  Lob,  Neumann  and 
Elbs.2 

It  has  been  attempted,  too,  to  connect  magnetism  with 
chemical  properties.  The  researches  of  Plticker,  and  especially 
those  of  G.  Weidemann,3  have,  in  fact,  resulted  in  showing 
that  there  are  certain  definite  relations  between  the  intensity- 
of  the  magnetism  of  compounds  and  their  chemical  nature. 

1  Ann.  Chim.  Phys.  (4),  vol.  xi.  p.  137. 

2  Cf.  Ztschr.  fur  Mektrochemie,  vol.  iv.  p.  81. 

3  Pogg.  Ann.,  vol.  cxxvii.  p.  1 ;  vol.  cxxxv.  p.  177. 


vi  ISOMORPHISM  AND  CHEMICAL  CONSTITUTION          505- 


Isomorphism,  etc. 

The  investigation  of  the  connection  between  the  forms- 
of  solid  bodies  and  their  composition  has  been  of  great 
importance  for  the  development  of  chemical  doctrines.  The 
growth  of  crystallography  benefited  mineralogy  in  the  first 
instance,  but  it  also  led  to  the  discovery  of  isomorphismr 
which — as  already  stated  in  the  general  section1 — exercised 
great  influence  upon  the  atomic  theory.  The  services 
rendered  here  by  E.  Mitscherlich,  to  whom  even  his  friend  G. 
Rose  owed  much,  may  again  be  recalled  at  this  point. 
Mitscherlich  did  away  with  the  erroneous  conceptions  which 
ascribed  the  crystalline  form  of  a  substance  to  the  presence  of 
minute  quantities  of  other  bodies,  and  proved  irrefutably  the 
connection  existing  between  crystalline  form  and  chemical 
composition.  The  deduction  drawn  both  by  himself  and  by 
Berzelius,  viz.  that  in  true  cases  of  isomorphism  of  several 
substances,  the  chemical  constitution  of  all  became  known 
as  soon  as  that  of  any  one  of  them  was  made  out,  because 
similarity  of  crystalline  form  is  "  a  mechanical  consequence 
of  similarity  in  atomic  constitution," — this  deduction  was 
soon  overthrown  by  observations  of  a  contrary  nature.  It 
was  found  that  dissimilarly  constituted  substances  might  be 
isomorphous,  and  analogously  constituted  ones  heteromor- 
phous ;  Mitscherlich  himself  added  to  his  brilliant  discovery 
of  isomorphism  that  of  dimorphism  and  polymorphism,  while 
Scherer  pointed  out  cases  of  the  so-called  polymeric  isomor- 
phism, which  proved  that  elementary  atoms  might  be 
replaced  by  atomic  groups  without  change  of  crystalline 
form. 

These  and  other  similar  observations  have  resulted  in  the 
view  that  isomorphism  is  only  to  be  applied  with  great 
caution  as  a  means  for  determining  chemical  constitution,, 
otherwise  false  conclusions  are  unavoidable.  A  passing 
reference  may  be  made  here  to  the  later  researches  of  H. 
Kopp  upon  the  relations  between  isomorphism  and  atomic 
volume,  and  to  those  of  Schrauf,  Pasteur  and  others  upon  the 

1  Cf.  p.  221. 


.306  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP. 

phenomena  of  isogonism.  The  problem — what  changes  of 
crystalline  form  are  produced  through  the  substitution  of 
particular  atoms  by  other  atoms  or  radicals — has  been 
systematically  attacked  by  P.  Groth1  in  the  case  of  certain 
groups  of  organic  compounds  ;  the  phenomenon  of  the  partial 
alteration  of  crystalline  form,  in  consequence  of  such  substi- 
tution, he  terms  morphotropism.  But  much  study  is  still 
required  for  the  investigation  of  this  newly  opened  out  branch 
of  the  science.  Among  recent  researches  in  this  field,  those 
of  Retgers,  published  in  the  Zeitschrift  fur  pJiysikalische 
Chemie  must  be  mentioned ;  apart  from  his  most  admirable 
work,  he  has  critically  examined  that  of  other  investigators 
like  Dufet,  Bodlander  and  Wyrouboff. 

The  so-called  allotropism  of  elements  and  compounds  is 
probably  closely  connected  with  polymorphism,  i.e.  with  the 
fact  that  the  same  chemical  substance  can  exist  in  different 
forms.  A  most  important  distinction  between  the  two  kinds 
of  phenomena  consists,  however,  in  this, — that  we  have  in 
the  former  case  chemical  as  well  as  physical  differences. 
Reference  has  been  already  made,  under  the  history  of  the 
elements,  to  the  discovery  of  certain  of  the  more  striking 
"  allotropic  modifications"  of  these.2  But  it  may  be  men- 
tioned at  this  point  that  material  progress  has  recently  been 
attained  in  this  branch  through  the  investigation  of  the 
physical  constants  of  such  allotropic  bodies,  e.g.  their  specific 
heat,  heat  of  combustion,  atomic  volume,  etc.3 

Speaking  generally,  chemists  lean  to  the  idea  that  the 
same  cause  underlies  both  allotropism  and  polymerism,  and 
that  therefore  the  former  is  to  be  explained  by  assuming  that 
different  numbers  of  atoms  (of  one  and  the  same  element) 
.are  grouped  together  into  dissimilar  molecules  ;  as  has  been 
stated  already,  the  molecular  weights  of  oxygen  and  ozone 
have  been  established,  and  thus  the  difference  between  them 
explained. 

1  Pogg.  Ann,,  vol.  cxli.  p.  31. 

2  Cf.  pp.  405-406. 

3  Cf.  the  work  of  Hittorff,  Lemoine,  and  others. 


EARLY  WORK  IN  THERMO-CHEMISTRY  507 


Thermo-  Chemistry. 

It  is  now  a  long  time  since  the  first  attempts  were  made 
to  determine  the  amounts  of  heat  liberated  during  and  in 
consequence  of  chemical  reactions,  with  the  object  of  there- 
by arriving  at  a  measure  of  the  affinities  active  in  those  pro- 
cesses. But  the  efforts  of  Laplace  and  Lavoisier,  Davy^ 
Rumford  and  others  in  this  direction  remained  incomplete, 
their  methods  for  the  estimation  of  heat  quantities  being  too 
inexact. 

Thermo-chemistry  only  became  firmly  established  with 
the  exact  measurement  of  the  thermal  changes  accompanying 
chemical  reactions.  Of  the  earlier  investigations,  those  of 
Favre  and  Silbermann  on  heat  of  combustion  deserve  special 
mention,  because  the  calorimeter  was  materially  improved  by 
these  chemists.  Emphasis  must  also  be  laid  here  upon  the 
almost  forgotten  labours  of  G.  H.  Hess,1  who  deduced  from 
his  own  observations  the  all-important  principle  of  the  Gon- 
stanz  der  Warmesummen  (i.e.  that  the  heat  evolved  in  the 
formation  of  a  given  compound  is  always  the  same),  and  thus 
taught  in  1840  the  application  of  the  first  law  of  the  me- 
chanical equivalent  of  heat  to  chemical  reactions,  before  the 
law  itself  had  been  brought  forward. 

From  this  principle  Hess  2  established  the  point  that  the 
.amount  of  heat  evolved  in  any  chemical  reaction  was  always 
the  same,  whether  the  reaction  was  consummated  at  once  or 
by  degrees  in  separate  instalments.  This  law,  taken  in  con- 

1  To  Ostwald  belongs  the  merit  of  having  referred  with  emphasis,  in  his 
Lehrbuch  der  allgemeinen  Chemie,  to  the  services  of  the  St.  Petersburg 
chemist,  Hess,  as  the  founder  of  thermo-chemistry.     On  p.  12  of  vol.  ii.  in 
the  1st  edition  of  his  book  (among  other  passages)  Ostwald  expresses  himself 
as  follows  :     "In  his  fate  we  find  a  repetition  of  that  which  befel  Richter, 
the  importance  of  whose  work  for  stb'chiometry  was  for  so  long  overlooked. 
Hess  himself  (Journ.  pr.  Chem. ,  vol.  xxiv.  p.  420)  assigned  to  the  latter  his 
proper  position  by  correcting  the  mistake  of  confounding  Richter  with 
Wenzel,  which  was  due  to  Berzelius.     It  is  now  again  needful  that  the  same 
loving  service  should  be  rendered  to  him,  who  on  his  own  part  did  justice 
to  an  investigator  wrongly  criticised  and  too  little  esteemed  in  his  own 
day." 

2  Pogg.  Ann.,  vol.  1.  p.  385  (1840). 


508  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP, 

junction  with  the  principle  at  which  Lavoisier  and  Laplace 
had  arrived  fifty  years  before — viz.  that  the  decomposition  of 
a  compound  into  its  constituents  requires  exactly  the  same 
amount  of  heat  as  is  evolved  during  its  formation!  from  the 
latter — constitutes  the  basis  of  thermo-chemistry. 

Since  the  conception  of  heat  as  energy  of  motion  found 
perfect  expression  in  the  mechanical  theory,  and  especially 
since  the  development  of  the  term  energy,  the  above  prin- 
ciples appear  as  self-evident  deductions  from  that  theory. 
The  earliest  application  of  the  mechanical  theory  of  heat  to 
thermo-chemical  processes  was  made  by  Julius  Thomsen,1  who 
has  devoted  himself  to  investigating  thermo-chemically  the 
more  important  chemical  reactions,  e.g.,  the  formation  of  salts, 
oxidation  and  reduction,  and  the  combustion  of  organic  com- 
pounds. This  branch  of  the  science  has  been  enriched  by 
him  in  an  extraordinary  degree,  both  by  the  working  out  of 
new  methods  and  by  the  systematic  investigation  of  numer- 
ous chemical  processes.  In  addition  to  Thomsen,  Berthelot 2 
and  especially  (since  1 8  7  9)  F.  Stohmann  3  have  contributed 

1  Julius  Thomsen,  born  at  Copenhagen  in  1826,  where  he  continues  to- 
work  as  Professor  at  the  University,  has  since  1852  applied  himself  with  the 
utmost  ardour  to  building  up  and  developing  thermo-chemistry.     The  large 
number  of  scattered  papers,  which  contain  the  records  of  his  comprehensive 
researches,  were  some  years  ago  collected  together  and  published  by  him 
in  four  volumes  under  the  title  Thermochemische  Untersuchungen  ( "  Thermo- 
chemical  Researches"). 

2  M.  P.  E.  Berthelot,  born  in  Paris  in  1827,  became  professor  in  the 
College  de  France  there,  and  recently  held  for  short  periods  the  posts  of 
Minister  of  Education  and  Foreign  Minister  ;  he  first  made  himself  known 
by  the  beautiful  researches,  already  spoken  of,  entitled,  Sur  les   Com- 
binaisons  de  la  Glycerine  avec  les  Acides.     He  soon  directed  his  attention 
to  the  synthesis  of  organic  compounds,  which  at  that  time  had  been  but 
little  studied,  and  in  his  comprehensive  work,  Chimie  Organique  fondde  sur 
la  Synthese  (1860),  gave  a  detailed  account  of  the  observations  and  discus- 
sions in  this  branch  of  the  science.     Later  on  he  turned  with  all  his  energy 
to  the  experimental  solution  of  thermo-chemical  problems,  which  he  col- 
lected together  in  the  two- volume  book,  Mdcanique  Chimique  fondde  sur  la 
Thermochimie  (1879) ;  while  last  year  (1897)  he  published  a  large  work  in 
two  volumes  entitled  Thermochimie.     To  him  we  also  owe  a  number  of 
valuable  historical  works,  dealing  more  particularly  with  the  development 
of  alchemy  and  with  the  oldest  chemical  writings  of  the  Middle  Age    (CL 
p.  23,  Note  2). 

3  Cf.   his  papers,   published  in  the  Journ.    pr.    Chemie  since    1879, 


VI  THERMO-CHEMISTRY  509 

In  conjunction  with  their  pupils  a  large  number  of  important 
observations  in  thermo-chemistry,  and  have  materially  as- 
sisted in  the  refinement  of  calorimetric  methods. 

The  efforts  of  these  investigators  were  mainly  directed  to 
the  discovery  of  relations  between  the  thermo-chemical  values 
(which,  calculated  upon  the  molecular  weights  of  the  reacting 
substances,  were  termed  molecular  heats)  and  the  chemical 
constitution  of  compounds.  The  heats  of  combustion,  in 
particular,  furnished  much  food  for  speculations  of  this  nature. 
But  although  regularities  of  various  kinds  became  apparent, 
e.g.  with  respect  to  the  heats  of  combustion  and  heats  of 
formation  in  homologous  and  other  series,  very  great  caution 
requires  to  be  exercised  in  forming  deductions  as  to  constitu- 
tion from  calorific  values ;  this  has  lately  been  clearly  shown 
by  Bruhl,1  in  a  critique  upon  such  attempts.  A  salutary 
limit  has  thus  been  placed  upon  the  too  great  extension  and 
over- valuation  of  the  conclusions  drawn  from  thermo-chemical 
work,  a  temperate  criticism  (on  the  part  of  Lothar  Meyer  and 
others)  having  previously  done  away  with  the  erroneous  view 
that  an  absolute  measure  of  affinity  was  furnished  by  the 
heat  evolved  or  absorbed  in  the  formation  or  decomposition 
of  chemical  compounds.  In  spite,  however,  of  this  failure, 
thermo-chemical  investigations  will  certainly  prove  to  be  in- 
dispensable for  the  perfected  doctrine  of  affinity  of  the  future. 
It  should  be  added  that  the  results  of  Stohmann's  researches, 
e.g.  those  on  the  heat  of  formation  of  the  various  hydrides  of 
benzene,  promise  to  throw  light  upon  the  constitution  of  these 
compounds. 

Photo-chemistry. 

This  short  account  of  the  growth  of  physical  chemistry 
would  be  incomplete  if  nothing  were  said  respecting  the 

Friedrich  Stohmann,  born  in  1832,  is  Professor  of  Agricultural  Chemistry 
in  the  University  of  Leipzig,  having  previously  filled  a  similar  post  at 
Halle,  while  before  that  he  was  Director  of  the  Agricultural  Experimental 
Station  at  Brunswick.  He  is  well  known  by  his  numerous  and  fundamental 
works,  e.g.  Handbuch  der  Zuckerfabrikation,  Handbuch  der  Stdrkefabrika- 
tion,  etc.  ;  and  by  his  editorship  of  the  Encyklopedisches  Handbuch  der 
technischen  Chemie. 

1  Journ.  pr.  Chemie  (2),  vol.  xxxv.  pp.  181,  209. 


510  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP. 

chemical  action  of  light.  The  latter,  a  particular  form  of 
radiant  energy,  gives  rise  to  various  chemical  reactions,  of 
which  the  great  process  of  assimilation  in  plants  was  the 
earliest  to  attract  the  attention  of  chemists.  The  detailed 
treatment  of  this  process,  first  observed  towards  the  end  of 
the  last  century,  belongs  to  the  recently  developed  science  of 
vegetable  physiology. 

The  earliest  superficial  observations  on  the  action  of  light 
upon  compounds  of  silver  were  made  by  Schultze  so  long  ago 
as  at  the  beginning  of  the  eighteenth  century ;  indeed,  Boyle 
had  noticed  the  blackening  of  chloride  of  silver,  but  had  as- 
cribed it  to  the  influence  of  the  air.  The  fundamental  ex- 
periment which  called  photo-chemistry  into  life  was  made  by 
Scheele,  who  thus  proved  himself  a  pioneer  in  this  as  in 
other  branches  of  the  science  ;  he  studied  the  action  of  the 
solar  spectrum  upon  paper  covered  with  silver  chloride,  and 
established  the  point  that  the  effect  begins  first  and  is 
strongest  in  the  violet  portion.  We  must  recall  here  too  the 
experiments  of  Ritter,  who  observed  the  action  of  the  ultra- 
violet rays  ;  and,  especially,  the  epoch-making  discoveries  of 
Daguerre  and  Talbot,  who  succeeded,  after  many  attempts,  in 
permanently  fixing  light-pictures.1  This  gave  birth  about 
1839  to  the  art  of  photography,  so  enormously  developed  of 
recent  years. 

1  The  following  notes  may  be  added  here  upon  the  history  of  photo- 
graphy (cf .  Schiendl's  Geschichte  der  Photographic,  published  by  Hartleben, 
Vienna) :  Niepce  had  associated  himself  with  Daguerre  in  his  work,  but 
did  not  live  to  see  the  perfecting  of  the  Daguerreotype  process.  Talbot 
replaced  Daguerre's  silver  plates  by  paper  rendered  sensitive  to  light. 
Among  the  further  advances  made  in  photography  may  be  mentioned  the 
production  of  negatives  upon  glass  and  the  application  of  substances  for 
attaching  the  chloride  of  silver,  e.g.  albumen  and  collodion  (Niepce  de  St. 
Victor — the  nephew  of  the  Niepce  mentioned  above — and  Legray,  1847) ; 
the  multiplication  of  photographic  pictures  through  pressure  by  means  of 
the  so-called  photo-lithography,  heliography,  and  the  phototype  method, 
which  in  time  became  superseded  by  the  splendid  autotype  process 
(Meisenbach)  and  the  heliotype  one  (Obernetter) ;  and,  lastly,  the  pre- 
paration of  plates  particularly  sensitive  to  light  (bromo-gelatine,  etc. ),  or,  to 
speak  generally,  the  introduction  of  the  so-called  dry-plate  process.  Much 
interest  has  been  aroused  within  the  last  few  years  by  the  discovery  of 
colour-photography  by  Lippmann  and  others,  but  the  subject  is  as  yet  in 
its  infancy. 


vi  PHOTO-CHEMISTRY;  ACTINOMETRY  511 

The  foundation  of  comparative  photo-chemistry,  which 
is  termed  actinometry,  was  laid  by  the  memorable  researches 
of  Bunsen  and  Roscoe,1  Draper2  having  previously  made 
important  experiments  in  a  similar  direction.  These  in- 
vestigators, along  with  others,  e.g.  B.  H.  W.  Vogel,  made 
clear  the  laws  to  which  the  actinic  rays  are  subject. 
Especially  remarkable  were  the  results  of  the  observations 
on  the  absorption  of  chemically  active  rays,  and  upon  photo- 
chemical induction,  a  term  employed  by  Bunsen  and  Roscoe 
to  designate  the  process  by  means  of  which  the  substance 
sensitive  to  light  was  brought  into  such  a  condition  that  it 
underwent  decomposition  proportional  in  amount  to  the 
intensity  of  the  light.  In  addition  to  the  above,  mention 
must  be  made  here  of  the  remarkable  researches  of  Tyndall 
upon  vapours  and  gases  sensitive  to  light,  in  whose  decom- 
position the  action  of  the  light  is  shown ;  thus  /he  proved 
that  the  vapour  of  amyl  nitrite  (to  give  an  instance)  was 
decomposed  by  the  actinic  rays. 

The  phenomena,  whose  investigation  has  just  been  dis- 
cussed, come  properly  speaking  under  the  doctrine  of 
affinity,  whose  task  it  is  to  show  that  chemical  reactions,  i.e. 
the  formation  and  decomposition  of  chemical  compounds, 
are  the  results  of  definite  measurable  forces.  True,  this 
important  branch  of  the  science  is  still  far  from  attaining  to 
such  a  goal ;  but  the  development  of  the  doctrine  of  affinity,3 
a  short  sketch  of  which  now  falls  to  be  given,  shows  that 
much  zealous  work  is  being  done  with  the  view  of  solving 
the  difficult  problems  involved  here. 

1  Phil.  Trans,  for  1857,  p.  355,  and  for  1863,  p.  139  ;  or  Pogg.  Ann.r 
vol.  c.  p.  43  (1857) ;  vol.  cxvii.  p.  531. 

2  Phil.  Mag.  for  1843. 

3  Compare  the  admirably  clear  rtsumd  given  by  Ostwald  in  his  Lehrbuch 
der  allgemeinen  Chemie,  2nd  edition,  vol.  ii.  p.  1. 


.312  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP. 


Development  of  the  Doctrine  of  Affinity  since  the 
Time  of  Bergman. 

In  a  previous  section  of  this  book  an  account  has  been 
given  of  the  earlier  efforts  to  arrive  at  a  knowledge  of  the 
phenomena  of  affinity.  Through  most  of  the  speculations 
•upon  this  question,  ever  since  the  time  of  Boyle,  there  runs 
the  assumption  that  the  so-called  force  of  chemical  affinity 
is  in  the  main  identical  with  that  of  gravity ;  only  in  that 
the  former  is  exerted  within  very  small  distances,  whereby 
the  form  of  the  material  particles  has  to  be  taken  into 
account,  are  differences  between  the  two  forces  apparent. 
The  attempts  to  estimate  the  affinity  of  substances  for  one 
another  remained  at  that  time  (i.e.  previous  to  Berthollet) 
very  imperfect,  because  it  was  sought  to  determine  qualita- 
tirely  the  relative  intensities  of  the  affinities  under  arbitrary 
conditions,  without  taking  physical  considerations  into 
account.  This  period,  from  about  the  time  of  Geoffrey 
(1718)  to  that  of  Berthollet  (18  00),  is  characterised  by  the 
bringing  out  of  "  Tables  of  Affinity  "  (  Verwandtschaftstafeln).1 

Bergman's  doctrine  of  chemical  affinity  and  his  de- 
terminations of  the  latter  belong  in  part  to  this  evolutionary 
stage,  although  he  paid  more  attention  to  the  influence  of 
temperature  upon  the  phenomena  investigated  by  him  than 
his  predecessors  had  done.  The  reaction  proper  against  the 
merely  empirical  conception  of  these  latter  is,  however,  to  be 
found  in  Berthollet,  whose  Essai  de  Statique  Chimique  was  a 
protest  against  the  neglect  of  physical  conditions  during 
chemical  processes. 

Bergmans  Doctrine  of  Affinity.21 

Although  the  work  of  this  investigator  belongs  to  the 
phlogistic  period,  his  doctrine  of  affinity  can  only  be 
conveniently  treated  of  here,  in  order  that  it  may  be 
compared  or  rather  contrasted  with  that  of  Berthollet. 

*  Cf.  p.  138. 

2  Cf.  Bergman's  Opuscula  phys.  et  chem.,  vol.  iii.  p.  291  (1783). 


vi  BERTHOLLET'S  DOCTRINE  OF  AFFINITY  513 

Bergman's  conception  of  the  phenomena  of  affinity,  or  perhaps 
it  would  be  more  correct  to  say  his  method  of  designating 
these  phenomena,  came  into  such  general  adoption  that  it  is 
to  be  found  even  now,  at  least  portions  of  it  are,  in  many 
text-books. 

The  chief  law  of  his  doctrine  states  that  the  value  of 
the  affinity  between  two  substances  which  act  chemically  upon 
one  another  is  constant  under  similar  conditions,  and  there- 
fore that  it  is  independent  of  the  masses  of  those  substances. 
Bergman  assumed  the  universal  force  of  gravity  as  the  cause 
of  affinity,  this  being,  however,  greatly  modified  by  the  form 
and  position  of  the  small  particles  of  the  reacting  bodies. 
Partly  from  his  own  speculations  with  regard  to  affinity, 
and  partly  from  the  incorrectly  determined  composition  of 
neutral  salts,  he  drew  erroneous  conclusions  with  respect  to 
the  magnitudes  of  the  affinities  of  bases  to  acids,  and  vice 
versa ;  he  thus  set  up  the  tenet  that  an  acid  has  .  the 
strongest  affinity  for  that  base  of  which  it  saturates  the 
largest  quantity,  in  order  to  form  a  neutral  salt.  Berthollet, 
as  will  presently  be  shown,  deduced  precisely  the  opposite 
from  his  own  assumption, — that  mass-action  comes  into 
play  in  chemical  processes.  It  is  noteworthy  that  Bergman' 
recognised  the  impossibility  of  carrying  out  absolute  affinity- 
determinations,  and  that  he  devoted  his  entire  energies  to 
making  relative  ones  (by  decomposing  one  compound  by 
another),  and  then  collating  these  in  "  affinity  tables." 


Berthollet 's  Doctrine  of  Affinity. 

Against  Bergman's  ideas,  and  especially  against  the 
assumption  that  affinity  is  independent  of  the  masses  of  the 
interacting  substances,  Berthollet  raised  a  lively  opposition. 
Setting  out,  like  Bergman,  with  the  hypothesis  that  affinity 
is  identical  with  gravity,  he  went  on  to  emphasise  the 
undeniable  conclusion  that  the  forces  of  chemical  affinity, 
like  those  of  general  attraction,  must  be  proportional  to  the 

L  L 


514  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP. 

masses  of  the  acting  substances.  The  further  deductions 
from  this  principle  he  worked  out  with  masterly  clearness  in 
his  Essai  de  Statique  Chimique. 

These  views  of  Berthollet  did  not  at  the  time  receive 
the  recognition  which  they  merited,  mainly,  no  doubt, 
because  their  author  came  into  collision  with  the  established 
facts  of  chemistry  by  carrying  his  deductions  too  far.  His 
fundamental  law  of  the  dependence  of  chemical  action  upon 
the  masses  of  the  substances  concerned  in  it  led  him  to 
regard  the  "  chemical  effect "  of  any  body  as  the  product  of  its 
affinity  and  mass.  From  this  he  drew  the  further  conclusion 
that  the  formation  and  composition  of  a  chemical  compound 
depended  substantially  upon  the  masses  of  the  acting 
constituents  which  went  to  produce  it.  According  to  this 
view,  any  two  substances  must  combine  with  one  another  in 
constantly  varying  proportions ;  with  this  deduction,  how- 
ever, Berthollet  found  himself  in  a  serious  dilemma. 

But,  if  he  went  too  far  here,  he  so  immensely  advanced 
the  doctrine  of  affinity  and  followed  up  its  true  aims  by  a 
more  discreet  application  of  his  fundamental  principle,  that 
the  errors  into  which  he  fell  may  well  be  forgotten.  He 
pointed  out  with  perfect  clearness  that  it  was  impossible  to 
determine  the  absolute  values  of  chemical  affinities,  seeing 
that  these  were  necessarily  dependent  to  a  great  extent  upon 
the  physical  properties  of  the  substances  which  were  formed  or 
decomposed  by  the  chemical  reactions  in  question.  Ac- 
cording to  him,  such  determining  (and  opposite)  properties 
were  cohesion,  i.e.  the  mutual  attraction  of  the  small  particles 
of  any  substance  for  one  another,  and  elasticity,  i.e.  the 
tendency  of  those  particles  to  occupy  the  greatest  possible 
space.  He  saw  in  the  greater  or  lesser  insolubility  of 
substances  a  measure  of  cohesion,  and  in  their  volatility  a 
measure  of  elasticity,  and  by  means  of  such  conceptions 
conclusively  explained  chemical  changes  in  which  the  separa- 
tion of  a  precipitate  or  the  escape  of  a  gas  or  vapour  had  a 
•determining  influence  on  the  course  of  the  reaction.  In 
fact,  he  stated  distinctly  that  a  complete  rearrangement 


vi  BERTHOLLET'S  DOCTRINES  SUPPLANTED  515 

(  Umsetzung)  of  substances  can  only  take  place  if  cohesion  or 
elasticity  comes  into  play,  and  never  by  the  mere  action  of 
affinity  alone.  He  thus  brought  forward  entirely  new 
points  of  view,  which  have  borne  much  rich  fruit. 


The  Supplanting  of  Berthollet 's  Opinions  by 
other  Doctrines. 

The  first  good  which  resulted  from  Berthollet's  concep- 
tion consisted  in  the  recognition  of  the  uselessness  of  tables 
of  affinity,  in  so  far  as  these  were  supposed  to  give  the 
relative  affinities  of  different  substances.  The  important 
fundamental  idea  of  his  doctrine  of  affinity,  viz.  that  the 
chemical  action  of  a  body  is  proportional  to  its  mass,  and  is 
therefore  to  be  expressed  by  the  product  of  this  into  the 
affinity  (i.e.  by  a  factor  still  to  be  determined),  led  Berthollet 
to  conclusions  which  were  directly  opposed  to  many  known 
facts,  and  to  numerous  other  data  worked  out  at  that  time 
by  Proust.  The  controversy  between  these  two  men,  which 
turned  upon  the  question  whether  chemical  compounds  are 
built  up  of  elements  in  proportions  which  only  alter  in 
amount  by  certain  definite  increments,  or  in  proportions 
which  continually  vary,  has  already  been  discussed  in  the 
general  section  (cf.  p.  185  et  seq.). 

In  bringing  forward  his  theory  Berthollet  either  neglected 
to  pay  sufficient  heed  to  the  stochiometric  relations  known 
at  that  time,  or  else  his  knowledge  of  these  was  incomplete. 
It  is  precisely  to  the  circumstance  that  he  carried  his  theory 
of  mass-action  too  far,  and  made  it  the  starting-point  for 
the  most  far-reaching  deductions,  that  we  have  to  ascribe 
the  miscredit  into  which  his  principles — notwithstanding 
their  clearness — fell,  in  fact  they  were  held  to  be  totally 
erroneous.  It  was  thus  that  Bergman's  doctrine,  although 
based  upon  wrong  assumptions  and  therefore  leading  its 
author  to  false  conclusions,  kept  for  so  long  a  time  the 
upper  hand,  and  this  all  the  more  readily  since  it  could  be 
better  made  to  accord  with  the  atomic  theory.  The  re- 

L  L  2 


516  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP. 

vival  of  Berthollet's  principles  was  reserved  for  quite  recent 
times,  after  various  isolated  experimental  researches  had 
furnished  proof  of  their  admissibility. 

After  Berthollet's  temporary  overthrow,  the  .rapidly 
developing  atomic  theory  formed  the  main  subject  of  in- 
terest for  chemists ;  and  hand  in  hand  with  its  development 
went  that  of  the  electro-chemical  doctrines,  whose  object  it 
was  to  show  that  the  closest  connection  existed  between 
electricity  and  the  force  termed  affinity. 

The  doctrine  of  affinity  now  sought  to  perfect  itself 
through  the  development  of  electro-chemistry ;  Berzelius' 
theory  caused  Berthollet's  to  be  neglected.  The  successful 
work  which  has  since  been  accomplished,  with  the  object 
of  getting  at  the  actual  relation  between  electrolysis  and 
affinity,  enables  us  to  perceive  now  that  in  those  efforts  the 
investigators  of  that  time  were  carried  too  far. 

These  endeavours  could  only  result  in  showing  the 
qualitative  differences  in  the  affinities  of  different  sub- 
stances ;  in  fact,  the  electro-chemical  theories  reached 
their  culminating  point  in  the  proof  of  an  analogy  between 
the  electrical  and  chemical  properties  of  substances.  Fara- 
day's electrolytic  law,  which  threw  light  upon  the  quanti- 
tative side  of  electrolytic  processes,  did  not  give  any  informa- 
tion as  to  the  relative  magnitudes  of  the  affinities  of  the 
substances  in  question. 

The  fortunes  of  the  most  important  of  the  electro- 
chemical theories,  that  of  Berzelius,  have  already  been 
described.  Blomstrand's  ingenious  attempt l  to  bring  it  back 
to  life  again  has  indeed  shown  how  valuable  it  is  for  the 
explanation  both  of  chemical  processes  and  of  the  constitu- 
tion of  compounds ;  but  it  was  unable  at  that  time  to  aid 
materially  in  penetrating  the  obscure  domain  of  the  phenom- 
ena of  affinity. 

New  prospects   were   opened    out   for   the  doctrine   of 

chemical   affinity  by  the  thorough  investigation  of  thermo- 

chemical  processes,  whose  importance  for  physical  chemistry 

has   already  been  referred  to.       But  in  this  case  also,  as 

1  Cf.  his  work,  Die  Chemie  der  Jetztzeit  (1869). 


vi  REVIVAL  OF  BERTHOLLET'S  DOCTRINES  517 

in  the  application  of  electro-chemical  conceptions  to  the 
problems  of  affinity,  the  worth  of  thermo-chemical  deter- 
minations very  soon  became  greatly  over-estimated.  Thus, 
even  Julius  Thomsen,  who  was  for  a  long  period  the  most 
eminent  worker  in  this  field,  regarded  the  heat  evolved 
or  absorbed  in  chemical  reactions  (more  especially  in  the  for- 
mation and  decomposition  of  compounds)  as  an  absolute 
measure  of  the  affinity ;  in  his  view  the  work  of  affinity  was 
transformed  into  measurable  heat. 

But  although  the  inadequacy  of  thermo-chemistry  for  the 
solution  of  the  problems  of  affinity  has  now  been  made 
manifest,  its  present  and  future  significance  must  not  be 
depreciated.  On  the  contrary,  by  the  careful  application  of 
thermo-dynamic  principles  to  the  interpretation  of  chemical 
processes,  great  benefits  have  already  accrued  to  the  doctrine 
of  affinity. 

The  Revival  of  Berthollet's  Doctrines. 

The  most  powerful  impulse  to  a  further  healthy  develop- 
ment was  given  to  the  doctrine  of  affinity  by  the  revivifica- 
tion of  Berthollet's  theory.  This  was  accomplished  in  its 
fullest  extent  by  the  publication  in  1867  of  the  work  of  two 
Scandinavian  investigators,  Guldburg  and  Waage. 

Several  years  previous  to  this  H.  Rose  had  proved  with 
absolute  clearness  the  mass-action  of  water  in  many  reactions, 
e.g.  in  the  decomposition  of  alkaline  sulphides  and  of 
potassium  bisulphate,  and  in  the  formation  of  basic  salts. 
The  attention  of  such  distinguished  workers  as  Rose, 
Malaguti,  Gladstone  and  others  had  further  been  directed  to 
the  study  of  the  mutual  decomposition  of  two  salts,  whether 
those  were  soluble  or  one  of  them  was  insoluble.  In  fact, 
attempts  were  made  to  work  out  in  various  ways  the 
relative  affinities  of  particular  substances,  and  thus  to  solve 
a  problem  which  Berthollet  had  sketched  out  theoretically. 

The    ideas     of     the    latter    received,    lastly,    valuable 
experimental   confirmation   from   the   extremely   important 
researches  of   Berthelot   and  Pe'an   de  St.  Gilles1   on   the 
1  Ann.  Chim.  Phys.  (3),  vols.  Ixv.  Ixvi.  and  Ixviii. 


518  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP, 

formation  of  compound  ethers  and  ether-acids  from  an 
alcohol  and  an  acid.  In  subsequent  theoretical  discussions, 
these  and  the  more  recent  valuable  experiments  of  Mensch- 
kutkin1  (which  furnished  information  with  regard  to  the 
chemical  equilibrium  existing  between  different  substances 
and  to  the  time-rate  of  reaction)  were  applied  with  success  to 
proving  and  confirming  the  correctness  of  Berthollet's  axioms. 

The  observations  on  chemical  equilibrium  in  reciprocal 
processes  especially  contributed  to  the  general  adoption  of 
those  doctrines  of  Berthollet ;  it  was  thought  then  (and  still 
is)  that  the  values  thus  obtained  offered  the  surest  data  for 
arriving  at  the  relative  affinities  of  substances  taking  part  in 
a  reaction.  With  regard  to  the  ideas  held  respecting  such 
states  of  equilibrium,  the  opinion  prevailed  for  a  long  time  that 
a  statical  equilibrium  must  be  assumed.  A  reversal  of  this 
was  prepared  for  by  the  view  originated  and  propounded  by 
Williamson2  in  1850,  which  was  also  worked  out  in- 
dependently by  Clausius  several  years  afterwards,  viz.  that 
the  atoms  of  substances  are  in  a  state  of  continual  motion,  not 
merely  during  chemical  reactions  but  also  when  the  sub- 
stances are  apparently  at  rest.  A  dynamical  equilibrium 
thus  took  the  place  of  a  statical,  i.e.  an  equilibrium  of  the 
opposing  reactions.  Pfaundler  has  of  late  ingeniously  applied 
such  speculations  to  the  explanation  of  the  phenomena  of 
dissociation  and  of  reciprocal  reactions  generally. 

But  although  Williamson  emphasised  the  point  that  his 
speculations  were  in  accord  with  Berthollet's  principles,  a 
sufficiently  secure  and  broad  basis  was  still  wanting,  upon 
which  they  could  at  that  time  be  further  developed.  Such 
a  foundation  for  the  building  up  of  the  doctrine  of  affinity 
was  furnished  by  the  above-mentioned  work  of  Guldberg  and 
Waage,3  who  took  Berthollet's  axioms  as  their  immediate 


1  Cf.  Ann.  Chem.,  vol.  cxcv.  ;  Journ.  pr.  Chemie  (2),  vols.  xxv.  xxvi. 
and  xxix. 

2  In  a  paper  read  before  the  British  Association  at  Edinburgh ;   Ann. 
Chem.,  vol.  Ixxvii.  p.  37, 

8  Etudes  sur  Us  Affinitds  Chimiques  (1867) ;  this  was  published  in  German 
in  the  Journ.  pr.  Chem.  (2),  vol.  xix.  p.  69. 


vi  THE  GULDBERG-WAAGE  THEORY  519 

starting-point,  reanimated    these    anew,  and    proved    their 
agreement  with  facts. 

'  Like  Berthollet,  the  investigators  just  named  stated  the 
chemical  action  of  a  substance  as  being  proportional  to  its 
active  amount,1  the  latter  being  given  by  the  quantity  con- 
tained in  unit  of  space.  The  intensity  of  the  interaction  of 
two  substances  is  expressed,  according  to  them,  by  the  pro- 
duct of  the  active  amounts  ;  but  a  coefficient 2  still  remains  to 
be  determined  which  shall  express  the  dependence  of  the 
reaction  upon  the  nature  of  the  substances  taking  part  in  it, 
the  temperature,  and  other  factors.  By  the  aid  of  such 
hypotheses  the  relations  existing  between  the  amounts  of 
the  reacting  substances  and  their  actions  3  can  be  deduced 
mathematically.  Important  conclusions  have  also  been  drawn 
from  them  with  respect  to  time-rate  of  reaction  and  chemical 
equilibrium,  and  these  have  been  found  to  agree  sufficiently 
well  with  the  results  of  actual  experiment. 


The  latest  Development  of  the  Doctrine  of  Affinity. 

Guldberg  and  Waage's  theory,  based  as  it  was  upon 
Berthollet 's  principles,  has  had  an  extraordinarily  stimulating 
effect.  It  has  led  in  particular  to  the  successful  determina- 
tion of  the  specific  affinity-coefficients  of  different  substances, 
especially  of  bases  and  acids ;  and  these  experimentally- 
determined  constants  have  been  made  use  of  to  test  the 
correctness  of  the  theory  itself.  Among  the  work  done  with 
this  aim  in  view,  that  of  Ostwald  4  deserves  special  mention  ; 
he  has  determined  by  different  methods,  volumetric  and 
optical,  the  manner  in  which  a  base  is  distributed  among 
different  acids  present  in  excess,  and  has  deduced  from 
this  the  specific  affinity-coefficients  of  the  latter.  Julius 

1  "  ....  seiner  wirksamen  Menge  proportioned" 

2  Such  affinity-coefficients  have  hitherto  only  been  determined  in  par- 
ticular cases,  and  then  only  approximately. 

3  Wirkungen. 

4  Published  in  the  Journ.  pr.  Chem.  since  the  year  1877. 


520  HISTORY  OF  PHYSICAL  CHEMISTRY  CHAP. 

Thomsen 1   had    previously  attempted   to   solve   the    same 
problem  by  thermo-chemical  methods. 

Ostwald 2  further  sought,  some  years  ago,  to  deduce  the 
affinity-coefficients  of  acids  from  reactions  which  go  on  with 
a  measurable  velocity  under  the  influence  of  those  acids,  e.g. 
the  decomposition  of  acetamide  and  of  methyl  acetate,  and 
the  inversion  of  cane  sugar ;  in  this  case  too,  the  results 
obtained  have  shown  a  sufficiently  near  agreement  with 
calculation.  The  reader  is  referred,  lastly,  to  the  remarkable 
relations — already  spoken  of  — which  have  been  discovered 
by  Arrhenius,  and  also  by  Ostwald,  between  the  affinity- 
coefficients  and  the  capacity  for  (chemical)  reaction  of  acids 
and  bases  on  the  one  hand,  and  their  electrical  conductivity 
in  dilute  solution  on  the  other.  Ostwald's  researches  3  have 
thrown  a  surprisingly  new  light  upon  the  chemical  relations 
— especially  upon  the  constitution — of  the  compounds  investi- 
gated, showing  as  they  do  that  the  affinity-coefficients  of 
substances  alter  definitely  according  to  the  constitution  of 
the  latter.  At  the  same  time  it  has  turned  out  that  the 
position  or  function  of  the  atoms  has  a  determining  influence 
upon  these  coefficients,  this  important  fact  being  most 
apparent  in  the  case  of  isomeric  compounds,  e.g.  the  oxy- 
benzoic  and  chloro-propionic  acids,  etc.4  The  general 
conclusion  to  be  drawn  from  these  and  other  allied  researches 
is  that  the  specific  chemical  actions  of  acids  depend  upon 
their  hydrogen  ions  and  those  of  bases  upon  their 
hydroxyl  ions. 

The  limits,  within  which  this  short  account  of  the  de- 
velopment of  the  doctrine  of  affinity  is  necessarily  con- 
fined, would  be  widely  overstepped  were  the  results  of  other 
investigations — even  taking  only  those  of  importance — to  be 
described.  Merely  a  passing  reference  can  be  made  to  the 
work  of  Wilhelmy,  which  has  led  to  a  better  knowledge 

1  Pogg.  Ann.,  vol.  cxxxviii.  p.  575. 

2  Cf.  Journ.  pr.  Chem.  for  1884  and  1885. 

8  Cf.  Journ.  pr.  Chem.  (2),  vol.  xxxii.  p.  300 ;  and  especially  Ztschr. 
phys.  Chem.,  vol.  iii.  pp.  170,  241,  and  369. 

4  Cf .  also  Raoult's  work  bearing  on  affinity-coefficients,  as  developed  by 
Planck  and  others. 


vi  AIMS  OF  THE  DOCTRINE  OF  AFFINITY  521 

regarding  time-rate  of  reaction,  and  to  that  of  Menschutkin, 
van  't  Hoff,  Horstmann  and  others,  which  has  resulted  in 
making  clear  the  conditions  of  chemical  equilibrium  in 
various  reactions. 

The  hypothesis  that  the  small  particles  of  substances  are 
in  continual  motion,  not  merely  during  chemical  reactions, 
but  also  when  the  whole  system  is  in  a  state  of  equilibrium, 
is  now  held  to  be  indispensable  for  the  new  doctrine  of 
affinity.  The  clear  comprehension  of  the  various  kinds  of 
energy,  and  especially  of  the  relation  of  chemical  energy  to 
the  other  forms,  such  as  electric  and  thermic  energies,  etc., 
has  resulted  in  greatly  developing  this  branch  of  the  science.1 
The  chief  aim  of  the  doctrine  of  affinity  is  to  convert  chemistry 
into  a  branch  of  applied  mechanics — an  aim  which  Berthollet 
and  Laplace,  notwithstanding  the  imperfection  of  the  appli- 
ances at  command  in  their  day,  had  the  prescience  to 
designate  as  the  highest  possible. 

1  Compare  the  able  treatment  of  energetics  in  Ostwald's  Lehrbuch  der 
allgemeinen  Chemie,  2nd  edition,  vol.  ii. 


522  HISTORY  OF  MINERALOGICAL  CHEMISTRY          CHAP. 


A     SKETCH     OF     THE     HISTORY  OF    MINERALOGICAL 
CHEMISTRY  DURING  THE  LAST  HUNDRED  YEARS.  * 

Mineralogy  only  attained  to  the  rank  of  a  science  after  it 
had  recognised  the  fact  that  chemistry  was  indispensable  to 
it  for  ascertaining  the  composition  of  minerals.  It  is  true 
that  even  in  this  century  Mohs,2  who  did  so  much  for 
minerals  physics,  almost  denied  that  the  chemical  characters 
of  minerals  had  any  signification ;  but  the  system  which  he 
set  up  was  only  temporarily  adopted  by  a  few  scientists. 
The  benefits  which  accrued  to  mineralogy  from  the  applica- 
tion of  chemical  aids  were  so  obvious  that  the  latter  could 
never  again  be  dispensed  with.  Mineralogy  has  been  brought 
to  its  present  high  position  by  the  joint  assiduous  work 
of  mineralogists  and  chemists  together.  The  beautiful  aim 
— of  making  clear  the  connection  which  exists  between  the 
physical  and  chemical  properties  of  individual  minerals — 
has  firmly  retained  its  place  for  the  mineral  chemist  ever 
since  the  labours  of  Berzelius,  Mitscherlich,  G.  and  H.  Rose, 
and  others  were  consummated. 

The  first  modest  attempts  to  gain  a  knowledge  of  the 
chemical  composition  of  minerals  were  made  in  the  seven- 
teenth and  first  half  of  the  eighteenth  centuries,  but  these 
did  not  extend  beyond  mere  superficial  observations  of  a 
few  qualitative  reactions.  In  the  second  half  of  last  century, 
however,  there  was  much  important  preparatory  work  done, 

1  Cf.  Kopp,  Oeschichte  der  Chemie,  vol.   ii.  p.  84  et  seq.  ;   v.  Kobell, 
Geschichte  der  Mineralogie  (1650-1860),  more  especially  p.  303  et  seq. 

2  Mohs  set  up  the  axiom  that  a  mineralogist  had  merely  to  consider 
the  natural-history  properties  of  minerals,  i.e.  crystalline  form,  specific 
gravity,  hardness,  and  so  on.     If  their  chemical  behaviour  is  taken  inta 
account,  then,  he  expressly  states,  mineralogy  oversteps  its  legitimate 
bounds  and  entangles  itself  in  difficulties.     This  renunciation  of  the  most 
important    aid    to    mineralogical    research    is     certainly    characteristic. 
Berzelius  was  fully  justified  in  comparing  such  a  mineralogist  to  a  man  who 
objects  to  use  a  light  in  the  dark,  on  the  ground  that  he  would  thereby  see 
more  than  he  actually  requires  to  do. 


vi  THE  EARLIER  HISTORY  OF  THIS  BRANCH  523 

which  helped  materially  to  found  the  science  of  mineralogy. 
Mineral  chemistry  had  its  distinguished  exponents  in 
Bergman,  and,  a  little  later,  in  Klaproth  and  Vauquelin, 
whose  services  in  devising  methods  for  the  analysis  of 
inorganic  substances  have  already  been  referred  to.1  The 
chemical  investigation  of  minerals  was  carried  on  at  that 
time,  upon  the  principles  which  they  laid  down,  by  numerous 
other  workers,  among  whom  we  may  name  Lampadius, 
Bucholz,  Wiegleb,  Westrumb,  Valentin  Rose  the  younger, 
Kirwan,  Gadolin  and  Ekeberg. 

The  extraordinary  benefit  which  accrued  to  mineralogy 
from  the  introduction  of  the  blowpipe  by  Cronstedt,  and  its 
subsequent  use  by  Gahn,  Bergman,  Rinman,  and  particularly 
Berzelius,  may  again  be  emphasised  at  this  point.2 

Even  before  the  gradual  development  of  a  mineral 
chemistry,  and  also  simultaneously  with  it,  Rome"  de  1'Isle, 
Werner,  Haliy  and  Bergman  had  recognised  crystallography 
as  being  essential  to  the  study  of  mineralogy,  and  had 
applied  themselves  to  it.  Haiiy,  in  particular,  achieved 
wonderful  results  in  this  branch ;  he  referred  back  the 
various  crystalline  forms  to  a  few  primary  ones,  and  took 
account  of  chemical  as  well  as  of  physical  properties  in 
classifying  minerals.  That  he  carried  his  deductions  too 
far  here  is  seen  from  his  well-known  axiom  that  difference 
in  crystalline  form  signifies  also  difference  in  chemical  com- 
position. 

The  endeavours  made  to  classify  minerals  during  that 
period  are  for  the  most  part  characterised  by  the  desire  to 
recognise  their  chemical  as  well  as  physical  properties.  If 
this  had  only  a  subordinate  signification  in  Cronstedt's, 
Hauy's  and  especially  Werner's  systems,  it  was  on  the 
other  hand  put  prominently  forward  by  Bergman3  as  an 
essential  aid  to  the  classification  of  minerals,  so  far  as  this 
was  possible  with  the  then  existing  chemical  knowledge. 
But  few  of  the  mineralogists  of  that  day,  however,  subscribed 
to  Bergman's  principles,  most  of  them  giving  in  their 

1  Cf.  p.  384  et  seq.  2  Cf.  p.  385. 

3  In  his  Sciagraphia  Eegni  Mineralis,  etc.  (1782). 


524  HISTORY  OF  MINERALOGICAL  CHEMISTRY          CHAP. 

adhesion  to  Werner's  system,  in  which  only  a  very  modest 
place  was  assigned  to  mineral  chemistry. 

A  new  life  began  for  mineralogical  chemistry  when  Ber- 
zelius  turned  himself  to  its  study.  Basing  his  arguments  upon 
his  own  comprehensive  labours,  which  had  for  their  aim  the 
exact  determination  of  the  composition  of  minerals  and 
artificial  inorganic  compounds,  he  was  enabled  to  show  that 
the  doctrine  of  chemical  proportions  (and  therefore  the 
atomic  theory)  was  applicable  in  its  fullest  extent  to  minerals 
also.1  He  was  the  first  to  characterise  these  latter  as 
being  in  every  respect  "chemical  compounds."  At  the 
same  time  this  gave  him  occasion  to  classify  them  simi- 
larly to  substances  prepared  artificially,  and  thus  arose  his 
Chemical  System,2  in  which  he  gave  definite  expression  to 
the  view  that  mineralogy  should  only  form  a  part  of,  or  an 
appendage  to,  chemistry.  The  order  of  the  minerals  in  his 
system  was  determined  by  the  position  of  their  electro-positive 
constituents  in  the  so-called  "  tension  series."  Ten  years 
later  3  Berzelius  altered  his  principle  of  classification,  in  so 
far  that  he  came  to  look  upon  the  electro-negative  con- 
stituents as  primarily  determining  this,  and  he  arranged  the 
minerals  accordingly.  For  his  two  main  classes  he  took 
non-oxidised  and  oxidised  substances,  and  between  these 
he  divided  minerals  with  a  marvellous  perspicacity.  All 
previous  attempts  at  classifying  minerals  according  to 
chemical  principles  were  thrown  into  oblivion  by  Berzelius' 
system. 

The  development  of  this  system,  whose  main  features 
were  subsequently  reproduced  in  later  classifications,  was 
influenced  in  the  highest  degree  by  an  observation  made  by 
N.  Fuchs,  viz.  that  certain  substances  can  replace  each  other 
in  minerals,  and  still  more  by  the  extension  of  this  doc- 
trine through  Mitscherlich's  discovery  of  isomorphism.4  The 
results  of  the  analyses  of  minerals  hitherto  obtained  were 
henceforth  regarded  from  entirely  new  points  of  view  and 
were  in  many  cases  simplified  to  an  unexpected  extent.  A 

1  Of.  p.  205.  2  Schweigger's  Journ.,  vols.  xi.  and  xii.  (1814), 

3  Leonhard's  Zeitschrift  fur  Mineralogie,  vol.  i.  4  Cf.  p.  221. 


vi         LATER  DEVELOPMENTS  OF  MINERAL  CHEMISTRY       525 

high,  perhaps  too  high,  significance  was  now  attributed  to 
crystalline  form  in  its  connection  with  chemical  composition. 
This  over-estimate  quickly  became  manifest  after  Mitscherlich 
discovered  the  first  cases  of  dimorphism, — to  be  extended 
later  on  to  tri-  and  polymorphism.  Haiiy's  principle — that  a 
difference  in  crystalline  form  also  means  a  difference  in 
chemical  composition — was  thereby  overthrown;  and,  in  spite 
of  the  opposition  of  this  distinguished  investigator,  the 
doctrine  of  isomorphism  took  its  place  triumphantly  in 
mineralogy. 

The  various  mineralogical  systems  which  were  brought 
forward  after  that  of  Berzelius,  i.e.  after  the  year  1824, 
are  almost  all  characterised  by  the  endeavour  to  classify 
minerals  according  to  their  chemical  composition,  a  greater 
or  lesser  signification  being  at  the  same  time  attached  to 
their  physical  properties.  In  addition  to  G.  Rose's  classifi- 
cation of  mineral  bodies,  which  rested  upon  a  purely  chemical 
basis,  the  mixed  systems  of  Beudant,  C.  F.  Naumann, 
and  Hausmann  may  be  named  here  as  having  become  best 
known. 

The  nomenclature  of  minerals  has  by  no  means  kept 
equal  pace  with  their  strictly  scientific  investigation.  The 
empirical  principle  still  prevails  here,  this  being  apparent 
from  the  way  in  which  minerals  are  named  after  their 
discoverers,  or  after  localities  in  which  they  are  found,  or 
according  to  their  physical  properties,  etc.,  instead  of  the 
name  expressing  or  at  least  indicating  their  chemical  com- 
position. 

Mineralogy  owes  its  present  flourishing  condition  to  the 
immense  development  of  mineral  chemistry.  Berzelius  and 
his  pupils,  among  whom  Chr.  Gmelin,  E.  Mitscherlich, 
Wb'hler,  H.  and  G.  Rose,  Svanberg  and  Mosander  may  be 
mentioned,  were  the  first  to  really  open  up  the  ground 
which  Bergman,  Klaproth,  Vauquelin  and  others  had  pre- 
pared. It  is  impossible  to  give  a  detailed  account  here 
of  the  wealth  of  new  methods  which  have  been  devised  for 
the  analysis  of  minerals,  and  for  the  separation  of  their 
individual  constituents.  The  almost  inexhaustible  field  of 


526  HISTORY  OF  MINERALOGICAL  CHEMISTRY          CHAP. 

minerals  has  ever  since  then  been  investigated  chemically 
by  numberless  workers.  To  the  problem  which  naturally 
comes  first,  viz.  the  establishment  of  their  empirical  composi- 
tion, the  further  and  higher  one  was  added  of  getting  at 
their  chemical  constitution.  The  silicates  in  particular,  on 
account  of  their  extraordinary  variety,  have  given  rise  to 
continually  renewed  investigations.1 

The  limits  of  this  short  account  of  the  development  of 
mineralogical  chemistry  do  not  permit  of  citing  even  a  few 
examples  of  the  services  rendered  to  this  branch  of  the  science 
by  such  men  as  Stromeyer,  Th.  Scheerer,  Rammelsberg,2 
Bunsen  and  others.  Among  other  chemists  who  have  done 
good  work  for  mineralogical  chemistry  the  following  may  be 
named  : — v.  Bonsdorff,  O.  L.  Erdmann,  Marignac,  Th.  Thom- 
son, Blomstrand,  Deville,  v.  Hauer,  Hermann,  Th.  Richter, 
Sandberger,  Smith  and  Brush,  Streng,  Cl.  Winkler,  P. 
Jannasch,  Th.  Petersen ;  to  these  many  more  names  might 
be  added. 

1  Efforts  have  not  been  wanting  to  apply  specially  to  minerals  the  more 
recent  chemical  views  which  have  been  arrived  at  with  respect  to  the  con- 
stitution of  organic  compounds.     Wurtz  was  the  first  to  do  this,  by  com- 
paring the  poly-ethylene  alcohols  (discovered  by  himself)  with  the  poly- 
silicic  acids.     That  such  attempts  to  explain  the  structure  of  the  most 
complex  silicates  have  often  overshot  the  mark,  and  have  therefore  re- 
mained unfruitful,  is  due  to  the  circumstance  that  the  methods  employed  for 
gaining  an  insight  into  the  constitution  of  organic  compounds  cannot  as  a 
rule  be  applied  to  inorganic. 

2  C.  Rammelsberg,  born  in  Berlin  in  1813,  worked  from  the  year  1840 
partly  at  the  Technical  College  (Gewerbeakademie)  and  partly  at  the  Uni- 
versity there,  and  was  from  1874  until  a  few  years  ago  head  of  the  second 
chemical  laboratory  of  the  latter ;  he  is  since  dead.    His  researches,  which 
greatly  enriched  inorganic  and  especially  mineralogical  chemistry,  appeared 
for  the  most  part  in  Poggendorfs  Annalen.    He  rendered  very  great  service 
by  the  publication  of  his  Handbuch  der  Mineralchemie  (second  edition, 
1875),  and  of  his  Krystallographisch-physikalische  Chemie  (1881-82). 


vi  ARTIFICIAL  PRODUCTION  OF  MINERALS  527 


The  Artificial  Production  of  Minerals  * — Beginnings  of 
Geological  Chemistry. 

To  the  older  analytical  method,  which  was  the  one 
naturally  first  followed  in  the  investigation  of  minerals,  the 
synthetic  method  has  in  recent  times  been  added,  with  the 
result  that  mineralogical  chemistry  has  been  enriched  by  an 
extraordinary  number  of  new  facts  and  has  led  to  the  de- 
velopment of  geological  chemistry.  The  endeavour  to  imitate 
and  to  explain  the  natural  production  of  minerals,  by  pre- 
paring them  artificially  under  various  conditions,  has  been 
the  cause  of  many  memorable  researches,  of  which  a  short 
account  must  be  given  here. 

After  Berzelius  had  defined  minerals  as  chemical  com- 
pounds whose  composition  was  dependent  upon  the  same 
laws  as  that  of  compounds  artificially  produced,  the  problem 
at  once  arose  of  preparing  mineral  substances  from  their 
components.  But  several  decades  passed  by,  during  which 
mineral  chemistry  was  developed  by  improved  analytical 
methods,  before  the  synthesis  of  minerals  was  definitely 
taken  in  hand  with  this  conscious  aim  in  view.  Only 
isolated  observations  on  the  artificial  formation  of  such  sub- 
stances, e.g.  of  calc-spar  and  arragonite  by  G.  Rose,  and  some 
experiments  made  by  Gay-Lussac,  Berthier  and  Mitscherlich, 
fall  to  be  recorded  during  the  first  half  of  this  century ; 2  the 
brilliant  development  of  this  branch  of  mineralogical  or 
geological  chemistry  only  began  in  1851  with  the  memor- 
able labours  of  Ebelmen,  Durocher,  Daubr^e  and  Se"narmont. 
These  investigators  elaborated  a  series  of  methods  which  led 
to  the  production  of  minerals  under  conditions  similar  in 
part  to  those  found  in  nature.  It  was  justifiable  to  draw 
careful  deductions  with  respect  to  naturally  occurring  pro- 

1  Cf.  Die  Kunstlich  dargestellten  Mineralien,  etc.  ("Artificially-prepared 
Minerals"),  by  C.  W.   C.  Fuchs  (Haarlem,   1872);   and  the  Synthese  des 
Mine'raux  et  des  Roches,  by  Fouque  and  Michel  Levy  (Paris,  1882). 

2  The  earliest  observation  of  this  nature  was  doubtless  that  made  by 
James  Hall  upon  the  transformation  of  chalk  into  marble  in  1801. 


528  HISTORY  OF  MINERALOGICAL  CHEMISTRY          CHAP, 

cesses  from  these  methods  of  formation ;  at  any  rate, 
hypotheses  which  were  brought  forward  to  explain  the 
formation  of  minerals  and  rocks  could  be  put  to  the  test  in 
this  way.  Geology  thus  gained  a  firmer  foothold,  and  found 
in  chemistry  an  indispensable  helpmeet.1 

Reference  may  be  made  here  to  Bunsen's  beautiful  in- 
vestigations 2  upon  the  geological  conditions  of  Iceland,  and 
especially  upon  the  geysers,  and  to  those  on  the  formation  of 
volcanic  rocks,  all  of  which  were  productive  of  new  views ; 
and  also  to  the  labours  of  G.  Bischof,3  who  was  indefatigable 
in  advancing  chemical  geology. 

Among  the  distinguished  array  of  investigators  who  made 
further  advances  in  this  direction,  and,  in  particular,  who 
discovered  new  modes  of  formation  of  minerals,  H.  St.  Claire 
Deville  and  Troost,  Becquerel,  Debray,  Hautefeuille,  Wohler, 
Rammelsberg,  R.  Schneider,  and  especially  Fouque*  and 
Michel  Levy,  stand  out  pre-eminent.  Of  recent  years  Friedel,. 
Sarasin  and  Moissan  have  carried  out  important  syntheses  of 
minerals. 

The  chief  founders  of  the  synthetic  method  in  mineral- 
ogical-geological  investigations  have  been  Frenchmen,  and  so 
reference  is  with  perfect  justice  made  to  a  French  school  in 
this  branch,  the  five  gentlemen  last  named  being  its  principal 
exponents  of  recent  years.4 

The  modes  of  formation  of  minerals  observed  by  them 

1  Senarmont  expressed  himself  in  the  following  significant  words  with 
regard  to  the  necessity  of  chemistry  for  geology  :  "  (Test  a  la  chimie  minera- 
logique,  que  la  gdologie  doit  I'utile  contrdle  experimental  de  ces  conceptions 
rationelles.     Les  mindraux  cristallisds  ont,  en  ejffet,  une  origine  toute  chimique, 
et  c'est  I' 'experience  chimique  qui  doit  servir  d'appui  a  la  geologie,  si  elle  veut 
faire  unpas  de  plus  dans  Pe'tude  des  roches,  qui  en  sont  composes." 

2  Ann.  Chem.,  vol.  Ixii.  p.  1 ;  vol.  Ixv.  p.  70. 

3  Cf.  his  Lehrbuch  der  chemischen  Geologie. 

4  Fouque"  and  Michel  LeVy  consider  that  the  cause  of  this  pre-eminence 
in  the  above  field  is  to  be  found  in  the  "  nature  of  the  French  national 
character."     The  argument  with  which  they  support  this  assumption  (see 
p.  5  of  the  work,  Synthese  des  Mindraux,  etc. )  is  so  characteristic,  that  it 
may  find  a  place  here  :  "  Notre  gdnie  national  rdpugne  &  Vidde  d'accumuler 
un  trop  grand  nombre  de  fails  scientifiques,  sans  les  coordonner,  et  si  cette 
tendance  nous  entraine  quelquefois  cl  des  hypotheses  hasarddes,  elle  a,  d'autre 
part,  le  mdrite,  de  nous  induire  aux  experiences  synthdtiques." 


vi  SYNTHESES  OF  MINERAL  SUBSTANCES  529 

vary  greatly,  the  processes  being  partly  wet  and  partly  fusion 
ones.  To  mention  only  one  or  two  of  the  more  important, 
take  the  production  of  many  natural  minerals  by  the  slow 
mutual  decomposition  of  two  salts  in  solution,  e.g.  the  form- 
ation of  quartz  and  calc-spar  from  gypsum  and  silicate  of 
potash  in  presence  of  carbonic  acid ;  the  deposition  of  arti- 
ficial minerals  from  solution  (formation  of  gypsum) ;  the  pro- 
duction of  calc-spar  or  arragonite  according  to  the  conditions 
prevailing ;  the  decomposition  of  various  substances  by  water 
under  increased  pressure  (formation  of  quartz,  wollastonite, 
apophyllite,  etc.);  and,  lastly,  the  production  of  numerous 
minerals  by  processes  requiring  fusion  and  a  white  heat — pro- 
cesses similar  to  those  which  go  on  in  volcanoes  (formation  of 
tridymite,  olivine,  and  other  silicates). 

The  synthesis  of  the  numerous  sulphides  of  copper,  iron, 
zinc  and  cadmium,  partly  in  the  dry  and  partly  in  the  wet 
way,  also  deserves  mention,  and  this  applies  too  to  the  arti- 
ficial production  of  gems,  e.g.  of  the  ruby  by  Fre'my  and  of  the 
diamond,  the  latter  having  been  obtained  by  Moissan  in 
minute  crystals,  by  suitably  cooling  a  carboniferous  iron  from 
an  excessively  high  temperature. 

Since  nature  but  seldom  allows  her  workshops  to  be  spied 
into,  the  numerous  experiments  on  the  production  of  minerals, 
made  in  imitation  of  natural  processes,  and  which  have  been 
carried  to  a  successful  issue,  possess  the  highest  significance 
for  the  explanation  of  those  processes.  The  repeated  proofs 
that  one  and  the  same  mineral  can  be  artificially  prepared  in 
the  most  diverse  ways,  by  wet  as  well  as  by  fusion  methods, 
has  rendered  the  former  one-sided  conception  of  geological 
processes  (i.e.  the  view  that  rock-masses  have  been  produced 
either  in  the  wet  way  or  by  igneous  action)  almost  impossible 
now.  The  synthesis  of  minerals  has  riveted  still  more  firmly 
than  before  the  already  long-established  link  between 
mineralogy  and  chemistry. 


M  M 


530  HISTORY  OF  AGRICULTURAL  CHEMISTRY          CHAP. 


DEVELOPMENT  OF  AGRICULTURAL  AND  OF 
PHYSIOLOGICAL  CHEMISTRY 

The  history  of  these  branches  of  chemistry  is  primarily 
associated  with  the  work  done  by  Liebig,  of  which  a  short 
description  has  already  been  given  in  the  General  Section. 
It  is  true  that  this  gifted  investigator  had  many  predecessors, 
who  found  out  various  isolated  chemical  facts  of  great  import- 
ance for  vegetable  and  animal  physiology ;  but  it  was  he  who 
first  with  far-seeing  glance  collected  such  facts  together  under 
general  points  of  view,  and  conjoined  them  with  still  more 
important  observations  of  his  own.  The  ideas  of  a  Palissy 
upon  the  necessity  of  mineral  substances  for  plant  life ; l  the 
investigations  which  towards  the  end  of  the  seventeenth 
oentury  led  Malpighi  and  Mariotte  to  definite  conclusions  with 
respect  to  the  nutrition  of  plants  through  their  leaves  and 
roots ;  the  bold  and  comprehensive  speculations  of  Lavoisier  2 
regarding  metabolism  in  plants  and  animals, — his  conviction 
that  the  life  processes  are  made  up  of  a  series  of  chemical 
reactions  ;  lastly,  the  work  of  Fourcroy,  Vauquelin,  Proust, 
Berzelius  and  Chevreul  upon  products  of  the  animal  body  ; 
— all  these,  together  with  other  labours,  served  to  prepare 
the  ground  upon  which  Liebig  afterwards  raised  the  edifice 
of  chemistry  in  its  relation  to  agriculture,  physiology,  and 
pathology. 

Those  branches  of  chemistry  are  most  closely  interlaced 
with  organic,  for  one  of  their  main  problems  consists  in  iso- 
lating compounds  of  an  organic  nature  and  establishing  the 
composition  of  these.  To  this  is  added  the  further  task  of 
elucidating  the  role  which  such  substances  fill  in  the  organism. 
Vegetable  and  animal  physiology  are  especially  indebted  to 
chemistry  in  questions  of  nutrition. 

1  Cf.  p.  90. 

2  These  are  set  forth  in  a  paper  written  in  1792,  but  only  published  in 
1860  (in  vol.  iv.  of  the  (Euvres  de  Lavoisier}. 


vi  THE  HUMUS  THEORY  531 


Agricultural  Chemistry  and  Vegetable  Physiology.1 

The  work  done  in  physiological  chemistry  towards  the 
end  of  last  century  and  the  beginning  of  this  by  Priestley, 
Ingen-Houss,  Senebier  and  Th.  de  Saussure  had  led  to  many 
important  results  with  respect  to  the  nutriment  of  plants. 
One  might  now  suppose  that,  from  the  analysis  of  the  ashes 
of  plants,  a  distinct  connection  between  the  plants  and  the 
soil  would  have  been  apparent.  The  decomposition  of  car- 
bonic acid  by  the  leaves,  which  was  observed  by  those  workers, 
ought,  one  might  further  suppose,  to  have  pointed  to  car- 
bonic acid  as  the  main  source  of  the  organic  matter  of  plants. 
In  like  manner  the  early  made  observation  that  salts  of  am- 
monia were  highly  conducive  to  the  growth  of  vegetables,2 
might  have  found  an  explanation  in  the  recognition  of  am- 
monia as  the  source  of  their  nitrogenous  constituents. 

These  deductions,  however,  which  now  appear  to  us  self- 
evident,  were  not  drawn,  and  it  was  sought  to  credit  humus 
as  being  the  universal  nutrient  of  plants,  without  paying  any 
heed  to  those  older  fundamental  observations  which  have 
just  been  mentioned.  The  processes  of  nutrition  of  plants 
were  thus  entirely  misunderstood,  for,  according  to  this 
doctrine,  they  fed  like  animals  upon  organic  matter. 

This  assumption,  which  dominated  agricultural  chemistry 
for  many  decades,  found  its  chief  advocates  in  Germany  and 
France  in  Albrecht  Thaer  3  and  Mathieu  de  Dombasle  re- 
spectively. In  their  opinion  inorganic  salts,  the  importance 

1  For  the  literature  consulted  on  this  subject  (in  addition  to  the  books 
and  papers  cited  below),  see  the  Geschichte  der  Botanik,  by  J.  Sachs  ;  Lehr- 
buch  der  Pflanzenphysiologie,  by  Pfeffer ;  Lehrbuchder  AgrihUturchemie,  by 
W.  Knop  ;  Chimie  et  Physiologie  appliquees  a  V Agriculture,  etc.,  by  L. 
Grandeau  ;  Neues  Handworterbuch  der  Chemie,  vol.  ij.  pp.  119  and  1012  ; 

and  Ville's  Artificial  Manures etc.  (English  Edition  by  Crookes). 

See  also  Storer's  Agriculture,  in  some  of  its  relations  to  Chemistry  (2  vols.). 

2  Nicolas  Leblanc  pointed  out  the  importance  of  salts  of  ammonia  in 
this  respect  so  long  ago  as  at  the  end  of  last  century. 

3  Cf.  his  work,  Grundsdtze  der  rationellen  Landunrthschaft  ("Principles 
of  Rational  Husbandry").     Even  Saussure,  the  originator  of  the  doctrine 
of  plant  nutrition,  fell  into  the  humus  theory  error. 

M   M   2 


532  HISTORY  OF  AGRICULTURAL  CHEMISTRY          CHAP. 

of  which  could  not  be  absolutely  denied,  acted  merely  as 
stimulants,  and  not  as  if  they  were  essential  to  the  growth 
of  the  plant.1  Indeed,  Thaer  held  that  the  formation  (i.e. 
creation)  of  earths  in  plants  through  their  vital  forces  was 
possible.  In  this  assumption  he  followed  the  opinion  of 
Schrader,  who  so  early  as  the  year  1800  imagined  that  he 
had  proved  by  actual  experiments  the  generation  of  the 
ash-constituents  of  plants  by  the  vital  forces.2 

Liebig  put  an  abrupt  end  to  this  period  of  unscientific 
attempts  at  explaining  the  process  of  plant  nutrition  by  his 
critical  demolition  of  the  humus  doctrine.  Taking  his  stand 
upon  a  large  number  of  investigations  carried  through  by 
himself  and  his  pupils,  in  conjunction  with  earlier  work  done 
by  others,  he  brought  out  in  1840  his  book,  Die  Chemie  in 
ihrer  Anwendung  auf  Agrikultur  und  Pkysiologie5 ("Chemistry 
in  its  Application  to  Agriculture  and  Physiology ")  ;  in  this 
he  did  battle  with  the  arbitrary  axioms  of  the  humus  theory, 
and  completely  undermined  the  foundations  of  the  latter, 
hitherto  looked  upon  as  secure.  The  following  sentences  by 
Liebig  constitute  the  quintessence  of  his  doctrine ;  they 
already  contain  the  complete  programme  of  the  agricultural 
chemistry  which  has  been  created  since  that  time.  "  The  nutri- 
tive materials  of  all  green  plants  are  inorganic  substances." . . . 
"  Plants  live  upon  carbonic  acid,  ammonia  (nitric  acid),  water, 
phosphoric  acid,  sulphuric  acid,  silicic  acid,  lime,  magnesia, 
potash  and  iron ;  many  of  them  also  require  common  salt." 
..."  Dung,  the  excrementa  of  the  lower  animals  and  of  man, 
does  not  act  upon  plant  life  through  (the  direct  assimilation 
of)  its  organic  elements,  but  indirectly  through  the  products 
of  its  decomposition-  and  putrefaction-processes,  i.e.  by  the 
transformation  of  its  carbon  into  carbonic  acid,  and  of  its 
nitrogen  into  ammonia  or  nitric  acid.  Organic  manure,  which 

1  Several  writers  have  ascribed  to  Sprengel,  who  achieved  so  much  for 
botany,   the  merit  of  having   proved  the   indispensability  of   the    ash- 
constituents  for  plants,  but  this  is  incorrect. 

2  This  erroneous  view  was  first  combated  upon  good  grounds  by  Saussure,, 
and  then  by  Davy. 

3  The  incitement  to  this  work  came  from  the  British  Association  for 
the  Advancement  of  Science. 


vi  LIEBIG'S  GREAT  SERVICES  533 

consists  of  portions  or  debris  of  plants  and  animals,  may  be 
replaced  by  the  inorganic  compounds  into  which  it  breaks 
up  in  the  ground."  1  From  these  axioms  Liebig  drew  the 
all-important  conclusion  that  the  soil  must  be  replenished 
with  whatever  constituents  have  been  withdrawn  from  it 
by  the  culture  of  plants,  if  its  exhaustion  is  to  be  provided 
against. 

In  the  further  development  of  this  pregnant  doctrine, 
whose  victory  over  the  old  system  was  soon  complete,  dis- 
tinguished pupils  of  Liebig  took  part  as  well  as  himself. 
Indeed  nearly  every  agricultural  chemist  since  that  time  has 
come  either  directly  or  indirectly  from  Liebig's  school. 
Boussingault  2  strove  independently  after  similar  goals,  and 
the  services  which  he  rendered  in  earring  out  researches  on 
the  nutrition  of  plants  by  new  methods  must  be  emphasised 
here.  The  now  world-famous  field  experiments  of  Lawes  and 
Gilbert  at  Woburn  in  Bedfordshire,  begun  more  than  half  a 
century  ago,  and  which  are  being  continued  with  unabated 
vigour,  will  always  hold  a  distinguished  place  in  the  history  of 
agricultural  chemistry.  And  the  service  which  the  late 
Georges  Ville  rendered  to  this  branch  of  the  science  by  his 
work  in  France  should  also  be  borne  in  mind. 

Definite  researches  were  first  made  in  order  to  explain 
the  chemical  conditions  existing  in  the  soil,  from  which 
plants  are  supplied  with  their  purely  mineral  constituents. 
These  included  the  investigation  of  the  processes  involved  in 
the  weathering  of  rocks,  through  which  soil  is  produced. 
Liebig,  Boussingault,  Deherain,  Dietrich  and  others  showed 
by  their  investigations  what  were  the  parts  played  by  the 

1  Liebig  himself  carried  out  practical  experiments  in  manuring,  and 
succeeded  in  changing  a  sandy  piece  of  ground  in  the  neighbourhood  of 
Giessen  into  a  productive  garden  by  the  aid  of  mineral  manures  alone. 

2  J.  B.  Boussingault,  who  was  born  in  1802  and  who  died  in  1886,  first 
became  known  through  his  adventurous  journeys  in  South  America,  where 
he  turned  his  catholic  knowledge  to  brilliant  account.     After  returning  to 
France  he  devoted    himself    more    and   more    to    agricultural-chemical 
questions,  which  he  treated  partly  in  experimental  researches,  and  partly 
in  his  detailed  works,  ticonomie  Rurale  ;   Agronomie  ;   Chimie  Agricole  et 
Physiologic  (1864). 


534  HISTORY  OF  AGRICULTURAL  CHEMISTRY  CHAP. 

active  agents  here, — water,  carbonic  acid  and  oxygen; 
they  also  came  to  the  conclusion  that  free  nitrogen  as  such 
was  not  directly  assimilated  by  plants,  but  this  view  has 
been  overthrown  by  the  work  of  Ville,  Hellriegel  and  others 
(Of.  below).  It  is  only  after  rocks  have  been  "weathered"  that 
the  inorganic  substances  necessary  for  the  nutrition  of  plants 
are  brought  into  such  a  condition  that  they  can  be  as- 
similated by  these.  The  valuable  experimental  work  done 
by  E.  Wolff,  Henneberg,  W.  Knop,  F.  Stohmann,  Zoller, 
Lehmann  and  Nobbe,  among  others,  upon  the  composition 
of  different  soils  must  be  mentioned  here,  and  also  the  closely 
allied  experiments  by  them  on  the  nutrition  of  plants  in 
sterile  soils  and  in  solutions  of  salts, — dry  culture  &&&  water 
culture.  These  methods  have -served  to  solve  the  most  im- 
portant questions  regarding  plant  nutrition. 

These  researches  all  went  to  prove  that  the  same  substances 
as  are  found  in  the  ashes  of  plants  are  the  true  nutrients  of 
the  latter,  and  are  absolutely  indispensable  to  them.  But 
they  did  more  than  this,  in  showing  the  significance — indeed, 
the  determining  influence — as  regards  nutrition,  not  merely 
of  the  nature  of  the  nutritive  materials  contained  in  the 
soil,  but  also  of  the  form  in  which  these  are  present,  and 
of  their  action  upon  the  other  constituents. 

The  earliest  series  of  experiments  on  the  absorption  by 
different  soils  of  the  mineral  constituents  which  serve  as 
food  for  plants  was  due  to  Liebig,  while  similar  work  by 
Henneberg  and  Stohmann,  Peters,  Knop,  Zoller,  etc.,  must 
also  be  recorded ;  these  observations  were  likewise  of  great 
importance  for  the  explanation  of  the  action  of  manures. 

A  few  words  must  be  added  here  about  nitrification  in 
soils  and  the  assimilation  of  free  nitrogen  by  plants, — 
the  most  important  discoveries  in  agricultural  chemistry  of 
recent  years.  So  long  ago  as  1849  the  late  Georges  Ville,  then 
director  of  the  Agricultural  Experiment  Station  at  Vincennes, 
proved  by  actual  experiment  that  certain  plants  could  and 
did  assimilate  free  atmospheric  nitrogen ;  but  at  the  time 
his  conclusions  were  strongly  disputed,  being  directly  opposed 
to  those  of  Boussingault  and  Liebig,  and  also  to  subsequent 


vi  NITRIFICATION ;   ASSIMILATION  OF  NITROGEN         535 

investigations  by  Lawes,  Gilbert  and  Pugh  in  1857.  An 
important  experiment  bearing  on  the  point  and  extending 
over  many  years  was  begun  in  1 8  5  5  by  Herr  Schultz  of 
Lupitz  in  Altmark,  Germany.  He  grew  lupines  on  very 
poor  soil  with  the  addition  of  non-nitrogeneous  manures  only, 
and  found  that  notwithstanding  this,  the  soil  became  richer 
in  nitrogen  year  by  year.  The  next  step  towards  the  solu- 
tion of  the  question  was  the  discovery  in  1877  of  the  now 
well-known  process  of  nitrification  in  soils  by  MM.  Schloesing 
and  Miintz,  this  nitrification  being  the  work  of  definite 
microbes,  some  of  which  have  been  isolated  by  Winogradsky, 
Warington,  and  P.  Frankland ;  while  the  recent  work  of 
Hellriegel  and  Wilfarth  (in  1888),  Frank,  Schloesing,  Ber- 
thelot  and  others  has  proved  that  the  direct  assimilation  of 
atmospheric  nitrogen  by  leguminous  plants  is  brought  about 
by  the  agency  of  certain  micro-organisms  originally  present 
in  the  soil,  which  enter  the  root  at  a  very  early  period  of  the 
plant's  growth.  At  the  place  where  the  micro-organism 
enters,  a  disturbance  is  set  up  and  a  nodule  or  tubercle 
formed,  in  which  the  micro-organism  multiplies  rapidly. 
These  nodules  are  highly  nitrogenous  substances,  and  through 
their  agency  the  plant  is  somehow  enabled  to  assimilate  the 
free  nitrogen  of  the  air  and  to  convert  it  into  albuminous 
compounds ;  but  how  this  is  actually  brought  about  has  still 
to  be  explained.  Cultures  of  these  specific  bacteria  are  now 
prepared  on  a  manufacturing  scale,  under  the  name  of 
nitragins,  for  application  to  soils  naturally  deficient  in  them ; 
but  whether  they  will  actually  be  of  value  on  ordinary  arable 
land  remains  to  be  proved.1 

Notwithstanding,  however,  that  an  immense  number 
of  new  facts  have  been  brought  to  light  through  these 
and  other  labours,  the  fundamental  principles  of  Liebig's 
doctrine  have  undergone  no  alteration  since  he  first  gave 
them  to  the  world  in  his  pioneering  work  of  1840.  He 
clearly  recognised  in  all  its  broad  features  how  plants  draw 
their  nutriment  from  the  constituents  of  the  air  and  the  soil. 
1  Cf.  A.  P.  Aitken,  Transactions  of  the  Highland  and  Agricultural 
Society  for  1898,  p.  299. 


536  HISTORY  OF  AGRICULTURAL  CHEMISTRY          CHAP. 

Upon  this  he  based  his  doctrines  of  rational  husbandry, 
which  have  already  borne  the  richest  fruit,  and  in  the 
elaboration  of  which  scientific  and  practical  men  are  still 
engaged. 

Development  of  Phyto-Chemistry. 

After  the  importance  of  various  inorganic  substances  for 
the  life  of  plants  had  come  to  be  recognised,  the  pressing 
question  arose  for  physiologico-chemical  investigation — How 
and  in  what  phases  is  the  formation  of  organic  substances 
from  carbonic  acid,  ammonia  and  water  consummated  ? 
The  problem  to  be  solved  here  consists  in  isolating  the 
chemical  compounds  present  in  the  various  organs  of  plants, 
and  in  establishing  their  physiologico-chemical  relations  to 
one  another, — a  magnificent  task,  and  one  which  has  already 
occupied  many  able  investigators. 

The  conversion  of  carbonic  acid  into  organic  com- 
pounds under  the  influence  of  water  and  light,  the  process 
of  the  assimilation  of  carbon,  which  was  already  correctly 
apprehended  in  its  main  outlines  by  Saussure,1  has 
naturally  formed  the  subject  of  numerous  investigations. 
Thus  recent  researches  by  Lommel,  Pfeffer,  N.  J.  C.  Muller, 
Engelmann,  and  others  have  elucidated  the  nature  of  the 
light  rays  which  are  active  here.  Much  valuable  work  too 
has  been  done  upon  chlorophyll,  although  the  opinions  of 
men  like  Sachs,  Pringsheim,  etc.,  differ  as  to  the  part  which 

1  Cf.  his  Recherches  Chimiques  sur  la  Vegetation  (1804).  Previous  to 
this  Ingen-Houss  had  observed  the  assimilation  of  carbonic  acid  and  water 
by  the  leaves  of  plants,  but,  being  enchained  by  the  phlogistic  theory,  had 
not  perceived  that  the  oxygen  thereby  liberated  came  from  this  carbonic 
acid.  The  above  relation  was  first  made  clear  by  Senebier,  and  became  a 
certainty  after  Saussure's  masterly  researches,  through  which  the  balance 
between  the  substances  absorbed  and  eliminated  was  approximately  ascer- 
tained. Ingen-Houss,  too,  and  Saussure  still  more  definitely,  recognised 
that  the  converse  of  this  assimilation  process  (i.e.  a  breathing  in  of  oxygen 
and  giving  out  of  carbonic  acid)  goes  on  in  various  parts  of  plants. 
Saussure  and,  after  him,  Dutrochet  and  others  further  observed  the  evo- 
lution of  heat  which  accompanies  respiration  in  plants,  and  thus  established 
a  noteworthy  analogy  between  the  processes  in  the  vegetable  and  animal 
organisms. 


vi  PHYTO-CHEMICAL  RESEARCHES  537 

this  substance  plays  in  the  assimilation  of  carbon.  Specula- 
tion has  still,  however,  pretty  free  play  in  the  answering  of  the 
questions — What  is  the  organic  compound  which  is  in  the 
first  instance  produced  from  the  carbonic  acid,  and  what  are 
the  intermediate  products  in  the  formation  of  starch, 
•cellulose,  albumen,  etc.? 

A.  v.  Baeyer's  view — that  formic  acid  is  produced  in  plants 
by  the  reduction  of  carbon  dioxide,  and  is  then  converted 
into  carbohydrates  by  numerous  condensations, — has  been 
corroborated  to  some  extent  by  the  laboratory  experiments 
of  O.  Loew,  Bockorny,  E.  Fischer  and  others.  This  assumption 
is  at  any  rate  the  simplest  that  could  be  brought  forward  to 
explain  the  nutrient  action  of  carbonic  acid. 

The  multifarious  substances  produced  by  plants  have  been 
the  objects  of  ardent  investigation,  more  especially  since  the 
stimulus  which  was  given  to  the  subject  by  Liebig's  work  ; 
the  chemistry  of  plant  life  has  been  developed  alongside 
of  that  of  animal  life,  particularly  since  the  close  of  the 
forties.  Reference  must  be  made  here,  in  passing,  to 
Rochleder's  researches  in  this  field  (so  important  from 
the  chemical  point  of  view),  upon  caffeine,  various  glucosides, 
tannic  acids,1  and  other  vegetable  products.  The  attention  of 
phyto-chemists  has  been  directed  in  a  special  degree  to  the 
nitrogenous  compounds  which  are  formed  in  plants,  i.e.  to  the 
albumens  in  the  first  instance,  and  then  to  the  compounds 
produced  by  the  breaking  up  of  these.  After  Mulder  had 
pointed  out  the  similarity  of  the  former  to  animal  albumen, 
they  were  investigated  by  Liebig  and  his  pupils,  and  they 
have  formed  the  subject  of  excellent  work  by  Ritthausen 
during  recent  years.  The  hope  that  conclusions  might  be 
arrived  at  with  regard  to  the  constitution  of  the  albumens 
from  the  nature  of  their  decomposition-products,  more 
especially  from  the  amido-acids  like  leucine,  asparagine, 
glutamic  acid,  etc.,  has  not  indeed  been  realised ;  but,  from 
the  point  of  view  of  vegetable  physiology,  the  researches  on 
the  nitrogenous  compounds  which  are  formed  during  the 

1  Kraus's  monograph  : — Grundlinien  zu  einer  Physiologic  des  Oerbestoffes 
(1889)  shows  the  importance  of  the  tannic  acids  in  vegetable  physiology. 


538  HISTORY  OF  AGRICULTURAL  CHEMISTRY          CHAP. 

germination  of  seeds  and  other  processes  have  furnished 
much  valuable  preparatory  work  for  the  future  development 
of  that  branch  of  the  science.1 

There  are,  besides,  many  other  vegetable  products 
containing  nitrogen  which  have  occupied  the  attention  of 
chemists  as  well  as  of  physiologists,  e.g.  various  glucosides 
such  as  myronic  acid  and  amygdalin,  and,  in  particular,  the 
great  class  of  the  alkaloids, — compounds  whose  importance 
for  chemistry  has  already  been  discussed. 

The  carbohydrates  in  their  signification  for  the  life  of 
plants  have  likewise  been  much  investigated,  with  regard 
both  to  the  conversion  of  some  of  them  into  others  by 
chemical  means,  and  to  their  physiological  modes  of  forma- 
tion; but  here  again  the  necessary  link  is  often  wanting 
between  particular  products.  The  reader  is  referred  to 
the  pioneering  investigations  of  Briicke,  Nageli,  Sachs  and 
others  upon  starch  and  the  substances  formed  before  it,  e.g. 
dextrose,  and  upon  the  connection  which  exists  between 
the  formation  of  starch  and  the  activity  of  chlorophyll ;  to 
the  excellent  work  of  Cross  and  Be  van  and  others  on  cellu- 
lose; to  the  numberless  researches  on  the  sugar  varieties, 
especially  dextrose  and  cane  sugar,  the  occurrence  of  the 
latter  in  beetroot  and  its  technical  production  from  the  same 
having  created  a  chemistry  of  its  own ;  and  to  the  laborious 
work  which  has  been  and  still  is  being  done  with  the  object 
of  elucidating  the  chemical  nature  of  the  glucosides  and 
their  peculiar  behaviour  to  ferments.  The  most  important 
of  the  investigations  upon  vegetable  fats,  ethereal  oils,  and 
various  other  (vegetable)  compounds  belong  in  the  main  to 
organic  chemistry  proper,  and  have  been  referred  to  under 
the  history  of  this. 

1  Cf.  the  investigations  of  E.  Sehulze  and  others. 


vi  RESEARCHES  IN  PHYSIOLOGICAL  CHEMISTRY         539 


Development  of  Zoo-Chemistry }• 

The  physiological  chemistry  of  the  animal  body,  zoo- 
chemistry,  has  made  extraordinary  progress  since  the  early 
investigations  of  Fourcroy  and  Vauquelin,  Chevreul,  Berzelius 
and  others  were  made.  From  the  examination  of  the 
chemical  constituents  of  animal  organs,  secretions,  etc.,  an 
advance  was  made  to  the  infinitely  more  difficult  problem — 
Under  what  conditions  are  those  substances  formed  in  the 
organism,  and  what  are  their  relations  to  one  another? 
From  the  chemical  investigations  which  arose  from  this, 
animal  physiology  was  first  constituted  into  the  science  as 
we  now  know  it.  And  this  applies  in  a  special  degree  to 
the  important  question  of  nutrition,  and,  speaking  generally, 
to  the  modern  views  of  the  metabolic  processes  of  the  animal 
body.  Chemical  investigation  has  thus  been  the  means  of 
dispelling  the  obscurity  in  which  so  many  erroneous  views 
grew  and  flourished. 

Since  the  publication  of  the  above-mentioned  researches, 
the  most  distinguished  physiologists  and  chemists  have  co- 
operated in  the  development  of  zoo-chemistry,  in  so  far 
as  this  has  aimed  at  a  knowledge  of  the  substances  of  which 
the  animal  body  is  composed.  From  the  large  number  of 
excellent  investigations  of  this  kind,  only  one  or  two  can 
be  touched  upon  here.  Reference  must  first  be  made  to 
the  work  of  v.  Bibra,  Mulder,  Fre'my  and  Heintz  upon  the 
constituents  of  bones,  through  which  the  true  composition  of 
these  was  established.  Schmiedeberg's  investigations,  made 
in  1891,  have  been  the  first  to  throw  light  upon  the  nature 
of  the  substances  present  in  bone  cartilage. 

The  question  as  to  the  nature  of  the  albumens  has  given 
rise  to  many  important  researches,  especially  since  Mulder 
first  proved  the  presence  of  compounds  of  this  kind  in  plants, 
and  Liebig  and  his  pupils  strove  to  arrive  at  their  composition ; 

1  The  numerous  sources  of  physiologico-chemical  investigations  are  to  be 
found  in  Hoppe-Seyler's  Lehrbuch  der  physiologischen  Chemie.  Cf.  also 
Bunge's  Lehrbuch  der  physiologischen  und  pathologischen  Chemie.  Only  in 
a  few  instances  have  direct  references  been  given  here. 


540  HISTORY  OF  PHYSIOLOGICAL  CHEMISTRY          CHAP. 

but  they  have  not  as  yet  led  to  a  knowledge  of  the  true  con- 
stitution of  these  bodies.  Among  those  who  have  worked 
at  this  subject  may  be  mentioned  A.  Schmidt,  Graham, 
Brucke,  Johnson,  Hoppe-Seyler,  Kiihne,  Hammarsten,  Leh- 
mann,  Schiitzenberger,  Nencki,  Drechsel  and  Harnack.  To 
the  physiologist  the  question  of  the  behaviour  of  albumen 
in  the  animal  body  (in  particular,  the  changes  which  it 
undergoes  during  digestion,  etc.)  is  of  more  importance  than 
its  rational  composition.  Some  investigations  will  be 
referred  to  later  on,  in  which  an  answer  to  such  physiological 
questions  is  attempted. 

The  most  important  of  the  researches  which  led  gradually 
but  ultimately  to  a  true  explanation  of  the  composition  of 
fats  have  already  been  spoken  of.1  The  part  played  by  fats 
in  metabolism  has  only  been  satisfactorily  worked  out  of 
recent  years,  and  the  same  remark  applies  to  the  carbohy- 
drates.2 The  pathological  occurrence  of  those  substances  has 
also  given  much  occupation  to  chemists,  who,  by  furnishing 
definite  tests  for  sugar,  albumen,  etc.,  have  in  many  cases 
lightened,  and  even  rendered  possible,  the  diagnosis  of  a 
disease  by  the  physician. 

As  in  all  the  other  branches  of  chemistry,  so  too  in 
physiological  and  pathological,  have  special  methods  of  a 
zoo-chemical  analysis  gradually  developed  themselves  and 
become  indispensable. 

The  investigations  that  have  been  made  with  the 
object  of  elucidating  the  chemical  processes  which  go  on 
in  the  animal  organism,  and  with  this  the  processes  which 
condition  or  accompany  life,  are  almost  innumerable.  Our 
present  knowledge  of  the  various  animal  fluids  which  take 
part  in  such  processes  has  only  been  attained  by  the  most 
arduous  labours.  To  mention  but  one  or  two  of  these,  refer- 
ence may  be  made  in  the  first  instance  to  the  more  important 
of  the  researches  on  the  secretions  which  promote  digestion. 
The  classical  investigations  of  C.  Ludwig,  Brucke  and  Cl. 

1  Cf.  p.  441. 

2  With  regard  to  the  chemical  importance  of  the  carbohydrates,   see 
p.  454  et  seq. 


vi  GASTRIC  JUICE,  BILE,  BLOOD,  ETC.  541 

Bernard  proved  that  the  secretions  from  the  glands  were  to 
be  looked  upon  as  resulting  from  essentially  chemical  pro- 
cesses. The  importance  of  the  saliva  for  digestion  was  also 
shown  by  its  chemical  investigation ;  Leuchs,  in  1831,  dis- 
covered the  ferment  ptycdin  which  saliva  contains,  and  which 
has  the  power  of  transforming  starch  into  sugar,  and  the 
chemistry  of  the  saliva  has  since  been  materially  advanced 
by  the  later  work  of  O.  Nasse,  C.  Ludwig,  Briicke,  Herter 
and  others. 

Many  scientists  of  repute  have  occupied  themselves  with 
the  investigation  of  the  gastric  juice  ;  thus  the  work  of  C. 
Schmidt,  Bidder,  Beaumont,  Frerichs,  Lehmann,  v.  Wittich 
and  others  has  resulted  in  establishing  the  composition  of 
this  secretion,  and  also  the  peculiar  nature  of  pepsin,  the 
ferment  which  it  contains.  The  excessively  important  part 
played  by  the  latter  in  the  digestion  of  the  albumens,  which 
are  thereby  converted  into  peptones,  has  been  mainly  arrived 
at  through  the  labours  of  Lehmann,  Hofmeister,  Henninger, 
and  more  recently  Neumeister,  Kuhne  and  Chittenden. 

Our  knowledge  of  the  pancreatic  fluid  and  of  its  power- 
ful influence  on  the  digestive  process,  which  is  due  to  the 
presence  in  it  of  particular  ferments,  we  owe  to  W.  Kuhne, 
Htimer  and  others. 

The  chemistry  of  the  bile,  lastly,  which  originated  with 
Strecker's  memorable  work1  on  the  bile-acids  and  their 
decomposition-products,  has  been  subsequently  extended  by 
Stadeler,  Frerichs,  Gorup-Besanez,  Maly,  etc. 

The  present  knowledge  of  the  chemical  composition  of  the 
blood  and  of  its  various  constituents  (so  difficult  to  separate 
from  one  another),  together  with  the  chemical  behaviour 
of  these,  is  the  outcome  of  an  infinite  number  of  laborious 
investigations ;  and  it  is  still  very  far  from  being  complete. 
Reference  must  be  made  here  to  the  pioneering  work  of  Al. 
Schmidt  upon  the  causes  of  the  coagulation  of  blood ;  to  that 
of  C.  Schmidt,  Hoppe-Seyler,  Htifner,  Preyer  and  others  on 
haemoglobin  and  oxy-hsemoglobin,  and  the  behaviour  of  these 
to  gases,  and  also  to  the  successful  application  of  the 
1  Ann.  CJiem.,  vols.  Ixi.  Ixv.  Ixvii.  and  Ixx. 


542  HISTORY  OF  PHYSIOLOGICAL  CHEMISTRY  CHAP. 

spectroscope  here;  further,  to  the  memorable  researches 
which  finally  established  the  composition  of  the  blood-gases 
and  especially  the  difference*  existing  between  arterial  and 
venous  blood  in  this  respect.  The  services  rendered  by  C. 
Ludwig  deserve  to  be  particularly  emphasised,  the  investiga- 
tions which  he  carried  out  along  with  his  pupils  from  the  year 
1858  far  surpassing  the  earlier  ones  of  Magnus  and  of  L. 
Meyer  in  accuracy. 

The  numerous  researches,  by  means  of  which  the  quantita- 
tive relations  between  the  air  inhaled  and  exhaled  by  animals 
were  exactly  determined,  have  been  of  the  utmost  value  for 
a  knowledge  of  the  metabolic  processes  of  the  animal  body. 
We  have  only  to  recall  here  the  experiments  carried  out  on 
a  large  scale  by  Pettenkofer  and  by  Regnault  and  Reiset  since 
the  year  1862,  and  the  important  observations  by  C.  Ludwig, 
and  by  Pettenkofer  and  Voit,  on  the  effect  of  muscular  exer- 
tion upon  the  consumption  of  oxygen  and  the  production  of 
carbonic  acid. 

The  exceedingly  numerous  researches  on  the  substances 
which  occur  in  blood  serum,  on  the  inorganic  constituents  of 
blood,  and  on  the  pathological  changes  which  the  latter 
undergoes,  cannot  be  entered  upon  here. 

Milk  has  been  the  subject  of  frequent  investigation  ever 
since  Chevreul,  Lerch,  Heintz  and  others  established  its 
principal  constituents.  Much  attention  has  been  paid  in 
more  recent  work  to  the  process  of  coagulation,  to  the  changes 
which  milk  undergoes  in  the  organism,  to  the  nature  of  the 
albuminous  compounds  which  it  contains,  and  so  on  ;  witness 
the  important  researches  on  the  subject  by  Soxhlet,  Ham- 
marsten,  Hoppe-Seyler,  and  especially  Lehmann. 

Much  excellent  chemical  and  physiological  work  has  been 
done  upon  urine — the  secretion  of  the  kidneys.  Take,  for 
instance,  the  observations  on  the  artificial  production  of  urea, 
of  such  moment  from  a  chemical  point  of  view,  and  those 
upon  uric  acid  and  its  manifold  transformation-products,  the 
synthesis  of  which  has  already  been  achieved.1  Then  there 
are,  too,  the  important  physiological  and  pathological  investi- 
1  Cf .  The  History  of  Organic  Chemistry,  pp.  467-468. 


vi  CHEMICAL  COMPOSITION  OF  FLESH,  ETC.  543 

gations  by  Liebig,  Voit,  Bischoff,  Fick  and  Wislicenus  on  the 
separation  of  urea  in  its  bearing  upon  metabolism ;  the  re- 
searches on  the  formation  of  hippuric  acid,  by  Wohler,  Liebig, 
Dessaignes  and  Meissner;  on  that  of  the  phenol-sulphuric 
acids  by  Baumann ;  on  the  formation  of  sugar,  albumen,  gly- 
curonic  acid,  cynurenic  acid  (an  oxyquinoline-carboxylic  acid) 
and  indole ;  and  on  the  separation  of  all  of  those  substances 
just  named  in  the  urine. 

The  explanation  of  the  manner  of  origin  of  these  and  other 
substances,  which  are  partly  found  under  normal  conditions 
and  partly  under  pathological,  has  long  been  recognised  as 
constituting  an  important  problem  of  physiological  chemistry. 
From  the  results  of  a  large  number  of  observations,  a 
systematic  method  of  analysing  urine  has  gradually  been 
developed,1  and  this  daily  stands  the  practising  physician  in 
good  stead;  for,  from  the  occurrence  or  accumulation  of 
certain  substances  in  the  urine,  the  latter  can  recognise 
particular  diseases  with  greater  precision  than  by  any  other 
sign. 

The  work  which  has  been  done  upon  the  chemical  composi- 
sition  of  flesh,2  a  subject  to  which  peculiar  difficulties  are 
attached,  can  only  be  briefly  referred  to.  Liebig's  classical 
researches  on  "  the  constituents  of  the  fluids  of  flesh,"  3  and 
the  nearly  allied  ones  of  his  pupils  Schlossberger,  Scherer, 
Strecker  and  Stadeler,  prepared  the  way  for  later  and  even 
more  ambitious  labours ;  we  would  refer  here  to  the  observa- 
tions of  Helmholtz,  Ranke,  Briicke  and  others  on  the  effect  of 
muscular  action  upon  the  chemical  processes  which  go  on  in 
muscle-substance, — observations  to  which  the  first  incitement 
may  have  been  given  by  Liebig's  ingenious  and  far-reaching 
speculations.  The  important  part  which  glycogen  plays  in 
these,  as  well  as  in  other  processes  (e.g.  the  processes  of  the 
liver),  was  arrived  at  through  the  admirable  work  of  Briicke, 
Cl.  Bernard,  Klilz,  v.  Mering,  Voit,  etc. 

1  Compare  Neubauer  and  Vogel's  book  -.—Anleitung  zur  Analyse  des 
Harns. 

2  Cf.  (e.g.]  Falk's  book,  Das  Fleisch  (1880). 

3  Ann.  Chem.,  vol.  Ixii.  p.  257. 


544  HISTORY  OF  PHYSIOLOGICAL  CHEMISTRY          CHAP. 

From  the  rich  material  of  facts  relating  to  the  chemical 
composition  and  physiological  importance  of  particular  parts 
of  the  animal  organism,  which  have  thus  been  accumulated, 
the  views  regarding  the  metabolic  processes  of  the  animal 
body  have  been  developed,  and  indeed  completed,  in  certain 
of  their  details.  The  establishing  of  the  laws  which  govern  the 
nutrition  of  animals  was  long  ago  felt  to  be  of  the  first  import- 
ance. And  here  again  Liebig  gave  the  powerful  impulse  to 
the  first,  even  if  incomplete,  solution  of  this  question  from  the 
chemical  standpoint. 

The  service  which  he  rendered  with  regard  to  the  develop- 
ment of  the  doctrine  of  metabolism  appears  especially  great 
when  one  recalls  to  mind  how  erroneous  were  the  opinions  of 
physiologists  respecting  the  chemical  processes  going  on  in 
the  animal  body,  before  he  set  forth  his  views  on  nutrition  and 
other  physiological  processes  in  his  standard  work,  Die  Thier- 
ckemie  oder  die  Organisclie  Chemie  in  Hirer  Anwendung  auf 
Physiologic  und  PatJiologie  (1842),  ("  Animal  Chemistry,  or 
Organic  Chemistry  in  its  Application  to  Physiology  and 
Pathology").  The  most  eminent  physiologists  of  that  time, 
Tiedemann,  Burdach  and  others,  were  by  no  means  fully  con- 
vinced of  the  necessity  of  chemistry  for  their  science ;  to  ex- 
plain the  processes  in  the  organism  they  had  recourse  to  "  vital 
forces,"  many  of  them  indeed  flatly  refusing  the  aid  of 
chemistry.  It  was  left  to  Liebig  to  form  a  truer  estimate  of 
the  problems  of  physiology  and  of  the  means  to  be  used  in 
solving  these ;  the  opinion  which  he  expressed — that  it  must 
adopt  the  methods  of  physics  and  chemistry — coming  as  this 
did  with  the  full  weight  of  his  authority,  was  quickly  taken 
to  heart.  And  what  a  change  came  over  physiology  in  con- 
sequence ! 

The  powerful  influence  exercised  by  Liebig  on  the  de- 
velopment of  the  doctrine  of  metabolism  has  already  been 
frequently  referred  to.  But  a  short  resume  may  be  given 
here  of  the  main  conclusions  of  his  comprehensive  work  and 
ingenious  speculations.  He  endeavoured  to  establish  the 
various  importance  of  different  nutritives  for  the  animal  body,, 
in  so  far  that  he  defined  the  albumenoids  as  plastic  compounds 


vi  METABOLISM  545 

which  served  mainly  for  building  up  the  tissues  and  as  the 
source  of  muscular  power,  and  the  fats  and  carbohydrates  as 
respiratory  compounds,  which  went  for  the  most  part  to  pro- 
duce the  animal  heat.  It  was  he  in  fact  who  first  drew  sharp 
distinctions  between  nutritive  substances  among  themselves, 
and  between  these  and  other  substances  which,  while  not 
directly  nutrient,  bring  about  metabolic  changes  in  the 
organism.1  And  he  also  successfully  determined  the  relative 
values  of  the  former  by  direct  experiment. 

The  potent  effect  of  Liebig's  ideas  respecting  nutrition 
and  metabolism  showed  itself  during  the  succeeding  years  in 
the  splendid  work  which  was  done  by  Bidder  and  Schmidt, 
Bischoff,  Voit,  Pettenkofer,  Frerichs  and  others,  as  the  result 
of  his  stimulus.  By  the  aid  of  improved  methods  and, 
especially,  by  the  use  of  larger  respiration  apparatus,  Liebig's 
views  were  subjected  to  a  sharper  scrutiny,  and  thus  under- 
went many  corrections,  more  particularly  with  respect  to  the 
role  of  albumen  and  to  the  formation  of  fat.  But  in  all 
essential  points  he  was  right.  To  the  elucidation  of  the 
functions  and  actions  of  particular  nutritives  in  the  animal 
body,  the  classical  researches 2  of  Voit  and  Pettenkofer, 
together  with  those  of  their  pupils  (among  whom  were  Ranke, 
Forster,  Rubner,  Falck,  Fr.  Hofmann  and  Renk)  upon 
nutrition,  and  therefore  upon  metabolism,  have  contributed 
in  an  especial  degree.  An  important  deduction  drawn  from 
these  researches,  viz.  that  fat  is  produced  from  albuminous 
matter,  has  lately  been  disputed  by  Pfliiger 3  as  having  no 
sufficient  basis.  This  eminent  physiologist  is  further  of 
opinion  that  it  is  not  the  carbohydrates  and  fats  but  the  albu- 
mens which  are  the  sources  of  muscular  power. 

The  aims  of  the  above  branch  of  physiological  chemistry 
are  so  intimately  connected  with  those  of  hygiene  that  the 
two  overlap  at  this  point.  Hygiene  may  indeed  be  looked 
upon  as  a  branch  of  chemistry,  having  found  in  the  latter 
science  the  most  powerful  of  all  aids  to  her  development. 

1  Genussmittel. 

2  Most  of  these  were  published  in  the  Zeitschrift  fur  Biologic. 

3  Pfluger's  Archivfiir  Physiologic,  etc.,  vol.  xli.  p.  229. 

N   N 


546  HISTORY  OF  PHYSIOLOGICAL  CHEMISTRY          CHAP. 

Reference  has  already  been  made  in  the  history  of  analytical 
chemistry1  to  the  continuous  improvement  in  the  methods  of 
analysis  of  foods  and  drinks,  a  point  of  such  immense  import- 
ance to  the  community  in  general. 


Fermentation ;  Putrefaction? 

The  various  processes  by  which  ferments  are  set  in 
action,  and  by  which  their  action  is  conditioned,  have  now 
attained  to  such  a  supreme  importance  for  hygiene  and 
for  physiology  as  a  whole,  that  a  few  words  must  be  said 
here  with  regard  to  the  development  of  our  knowledge  of 
the  processes  of  fermentation  and  putrefaction  during  recent 
years. 

It  is  a  long  time  since  the  vinous  fermentation  first 
attracted  the  attention  of  chemists,  but  Lavoisier  was  the 
earliest  to  recognize  that  the  two  main  products  re- 
sulting from  it — alcohol  and  carbonic  acid — came  from  the 
sugar  present ;  at  the  same  time  he  attempted  to  work  out 
the  quantitative  relations  between  the  latter  and  the  two 
former  compounds.  As  to  the  reason  for  the  breaking  up  of 
sugar  in  the  presence  of  yeast,  no  views  were  expressed  at 
that  time  which  were  at  all  tenable.  Before  it  was  known 
that  yeast  consisted  of  living  cells,  Liebig's  mechanical- 
chemical  theory  of  fermentation 3  gained  many  adherents. 
This  theory,  which  was  propounded  in  the  year  1839, 
attempted  to  explain  alcoholic  fermentation  and  other 
similar  processes  from  one  common  point  of  view.  Liebig 
here  regarded  ferments  in  general  as  easily  decomposable 
bodies,  from  which  the  stimulus  to  the  decomposition  of 
fermentable  substances  proceeded.  This  view  recalls  that 
which  Stahl  and  Willis  had  brought  forward  long  before,  for 
they  also  assumed  a  transference  of  the  motion  of  fermenting 

1  Of.  p.  398. 

2  For  the  literature  consulted  here,  see  the  articles  "Fermente"  and 
"Garung"  in  the  Handworterbuch  der  Chemie;   A.  Mayer,  Lehrbuch  der 
Gahrungschemie  ;  and  Schiitzenberger,  Gdhrungserscheinungen. 

3  Cf.  Aim.  Chem.,  vol.  xxx.  pp.  250  and  363. 


vi  RESEARCHES  IN  FERMENTATION  ;  PASTEUR  547 

particles  to  a  large  number  of  others.  Some  investigators 
had  contented  themselves  with  attributing  to  yeast  a 
"  catalytic "  action,  but  this  simply  meant  the  employment 
of  a  word  to  cover  their  ignorance  of  the  subject. 

In  1 8  3  6,  i.e.  shortly  before  Liebig  had  brought  out  his 
theory,  Cagniard  de  Latour,  Schwann,  and  Ktitzing  made 
simultaneously  and  independently  of  one  another  the  impor- 
tant discovery  that  yeast  consists  of  low  organisms  which 
are  self-propagating.  The  subsequent  comprehensive  re- 
searches of  Pasteur l  entirely  confirmed  the  correctness  of 
these  observations.  From  all  this  the  vitalistic  theory  of 
fermentation  followed  as  a  necessary  consequence,  although 
its  recognition  was  retarded  by  the  force  of  Liebig's  great 
authority  ;  according  to  this  theory  the  decomposition  of  the 
sugar  is  dependent  upon  the  vitality  and  consequent  activity 
of  the  yeast  fungus. 

Other  processes  of  fermentation  were  now  investigated 
from  the  standpoint  thus  obtained,  with  the  result  that  low 
organisms  were  found  to  be  the  cause  of  the  action  in  their 
case  also.  We  would  refer  here  to  the  splendid  researches 
of  Pasteur  upon  the  acetic  and  lactic  fermentations,  of  equal 
importance  physiologically  and  chemically  ;  to  the  discovery 
of  the  particular  fission  fungi  which  gave  rise  to  various 
fermentations ;  and  to  the  work  of  Rees,  de  Bary,  Brefeld, 
A.  Mayer,  Fitz  and  others,  the  object  of  which  was  to 
elucidate  the  conditions  of  the  life  and  especially  of  the 
nutrition  of  organised  ferments  (more  particularly  yeast  and 
its  connection  with  fermentation),  and  also  the  products  of 
these  latter.2  E.  Chr.  Hansen's  wide-reaching  investigations 
in  this  branch  have  been  of  the  utmost  value,  more  especially 
to  the  technical  side  of  the  brewing  industry.3 

1  Cf.  his  large  works,  fitudes  sur  la  Btere,—sur  le  Vin,—surle  Vinaigre. 

2  C.  Schmidt  found  succinic  acid,  and  Pasteur  glycerine,  among  the 
products  of  the  vinous  fermentation.     It  is  only  of  comparatively  recent 
years  that  sufficient  attention  has  been  paid  to  the  various  alcohols  con- 
tained in  fusel  oil,  which  are  now  recognised  as  products  of  secondary  fer- 
mentations. 

3  Hansen,    Untersuchungen    aus    der    Praxis    der    Gdhrungsindiistrie 
(Munich,  1890). 

N   N    2 


548  HISTORY  OF  PHYSIOLOGICAL  CHEMISTRY          CHAP. 

Much  vigorous  discussion  has  ultimately  led  to  agree- 
ment upon  the  most  important  of  the  disputed  points,  with 
regard  to  which  the  views  of  different  workers  were  formerly 
far  apart.  A  twofold  growth  of  the  yeast  cells  is  now  estab- 
lished, viz.  (1)  a  growth  in  presence  of  oxygen,  which  is  not 
followed  by  fermentation,  and  (2)  one  in  absence  of  oxygen, 
through  which  fermentation  is  produced.1 

The  difference  between  organised  and  unorganised  fer- 
ments, the  latter  of  which  are  termed  enzymes,  came  to  be 
clearly  recognised,  this  being  mainly  due  to  Pasteur's  work. 
The  extraordinarily  important  functions  of  these  unorganised 
ferments  in  the  animal  and  vegetable  organisms  has  led 
physiologists  and  chemists  of  the  highest  eminence  to  devote 
their  close  attention  to  the  subject,  but  as  yet  no  satisfactory 
theory  of  the  action  of  such  ferments  has  been  brought  forward; 
in  conjunction  with  this,  reference  must  be  made  here  to  the 
work  of  Nasse,  Htifner,  Traube,  Hoppe-Seyler,  Nencki,  Al. 
Schmidt  and  Wurtz.  Quite  recently  Btichner 2  has  isolated 
an  enzyme  which  is  capable  of  inducing  the  alcoholic  fer- 
mentation in  the  absence  of  yeast  cells. 

The  phenomena  of  putrefaction,  which  were  placed  by 
Liebig  in  the  same  category  with  the  processes  of  fermenta- 
tion (both  being  brought  about,  in  his  view,  by  similar 
mechanical-chemical  causes),  acquired  a  heightened  physio- 
logical interest  after  it  was  perceived  that  they  were 
connected  with  the  presence  of  certain  peculiar  organisms. 
Here  again  the  researches  of  Pasteur  and  also  of  Nencki, 
Hoppe-Seyler,  etc.,  stand  out  pre-eminent.  The  chemical 
examination  of  the  products  of  putrefaction  has  led  to 

1  Liebig  maintained  an  antagonistic  attitude  to  the  vitalistic  theory  of 
fermentation  ;  he  did  not  indeed  contest  the  organised  nature  of  yeast,  but 
would  not  acknowledge  that  the  latter  itself  gave  rise  to  fermentation 
through  its  life  processes.     Instead  of  this  he  assumed  in  yeast  the  presence 
of  an  albuminous  ferment,  which,  on  the  death  of  the  former,  he  imagined 
to  bring  about  the  decomposition  of  the  sugar  into  alcohol  and  carbonic 
acid.     Nageli's  attempt  to  explain  the  phenomena  of  fermentation  may  be 
looked  upon  as  an  effort  to  reconcile  the  vitalistic  and  mechanical  theories 
(cf.  his  Theorie  der  Gdhrung,  1879). 

2  Ber.,  vol.  xxxi.  p.  568. 


vi       THE  PHENOMENA  OF  PUTREFACTION ;  PTOMAINES      549 

remarkable  results,  which  have  also  a  high  importance 
for  the  chemist.  Most  interest  has  been  centred  in  the 
nitrogenous  compounds  which  originate  from  the  decomposi- 
tion of  animal  albuminous  substances  by  putrefaction ;  thus 
we  would  recall  here  the  discovery  of  various  amido-acids, 
of  indole  and  its  homologues,  and,  particularly,  of  the  so- 
called  ptomaines}-  The  formation  of  these  powerful  poisons, 
which  have  also  been  called  corpse  alkaloids,  because  of  their 
likeness  to  the  alkaloids  from  plants,  is  of  the  first  im- 
portance to  the  forensic  chemist,2  seeing  that  cases  have 
occurred  in  which  the  ptomaines  have  been  confounded  with 
the  true  alkaloids,  on  account  of  similarity  in  reaction.  The 
Italian  toxicologist  Selmi  was  the  first  to  clearly  recognise 
the  important  role,  from  a  forsenic  point  of  view,  of  these 
putrefaction  bases,  and  he  it  was  who  gave  them  the  generic 
name  by  which  they  are  now  known, — the  ptomaines. 

In  addition  to  Selmi — Otto,  Husemann,  Dragendorff, 
Robert,  Brieger  and  others  have  rendered  good  service  in 
extending  our  knowledge  of  these  substances.  Brieger,  in 
especial,  and  also  Nencki,  Stard,  Gautier,  Guareschi  and 
Mosso  have  succeeded  in  characterising  certain  ptomaines 
chemically.  The  constitution  of  some  of  them  has  been 
recently  established,  witness  the  beautiful  syntheses  of  cada- 
verine3  and  of  putrescine,4  which  have  been  respectively 
shown  to  be  penta-  and  tetra-methylene  diamines. 


The  Relation  of  Chemistry  to  Pathology  and  Therapeutics. 

The  phenomena  of  putrefaction  possess  the  highest 
interest  for  pathologists,  because  such  processes  lie  at  the 
root  of  many  diseases.  An  increasing  knowledge  of  the 
causes  of  these  proceeses  has  thus  resulted  in  the  establish- 

1  For  a  historical  notice  of  these  peculiar  compounds,  cf.  Beckurts' 
Ausmittelung  giftiger  alkaloide  ("Detection  of  Poisonous  Alkaloids"), 
(Archiv  Pharm.  for  1886,  p.  1041);  also  Armstrong,  Journ.  Chem.  Ind., 
vol.  vi.  p.  482.  2  Cf.  pp.  397-398.  s  Cf.  p.  480. 

4  Ber.,  vol.  xx.  p.  2216  ;  vol.  xxi.  p.  2938. 


550  HISTORY  OF  PHYSIOLOGICAL  CHEMISTRY          CHAP. 

ment  of  a  close  connection  between  chemistry  and  pathology, 
the  former  having  now  become  indispensable  to  the  latter. 
And  this  necessity  for  chemistry  has  shown  itself  not  merely 
in  the  investigation  of  the  products  of  putrefaction ;  through 
its  means  the  more  delicate  tests  for  the  recognition  and 
distinction  of  disease-producing  bacteria  have  been  elaborated, 
and  it  has  thus  been  instrumental  in  helping  to  found  the 
new  science  of  bacteriology.  This  subject  cannot,  however, 
be  entered  into  here. 

Above  all,  it  has  been  reserved  for  chemistry  to  direct 
the  attention  of  physicians  to  remedies  for  counteracting  the 
pathological  processes  induced  by  micro-organisms.  Only  a 
passing  reference  can  be  made  here  to  the  wonderful  results 
which  have  been  achieved  in  medicine  and  surgery,  and  also 
on  the  large  scale  in  the  preservation  of  food  and  drink,  by 
the  use  of  antiseptics.  One  is  probably  not  wrong  in 
assuming  that  the  old  practices  of  smoking  flesh  and  of 
dipping  wood  into  tar  drew  attention  to  the  carbolic  acid 
which  the  latter  contains,  and  the  antiseptic  action  of  which 
has  now  found  such  world-wide  application  in  Lister's 
method  of  treating  wounds.  The  discovery  of  the  anti- 
fermentation  and  anti-putrefaction  powers  of  salicylic  acid 
by  Kolbe  originated  in  the  idea  that  this  compound 
tended  to  break  up  into  carbolic  and  carbonic  acids  in  its 
passage  through  the  organism.  The  last  decade  has 
introduced  us  to  a  large  number  of  new  antiseptics,  which 
are  now  used  more  or  less  in  medical  and  hygienic  practice ; 
these  are  mostly  substances  which  stand  in  a  near  chemical 
relation  to  phenol,  e.g.,  the  homologous  cresols  and  thymol, 
the  sulphonic  and  carloxylic  acids  of  these,  the  iodo-deriva- 
tives  of  phenol-  and  oxy-quinoline-sulphonic  acids,  etc.  The 
assumption  made  by  various  investigators — that  axitifer- 
ments  and  antiseptics  act  by  precipitating  or  chemically 
altering  the  readily  decomposable  albuminous  substances 
— explains  the  role  of  these  in  a  sufficiently  satisfactory 
manner ;  for,  when  those  bodies  are  got  rid  of,  the  ferments 
are  deprived  of  their  necessary  nutriment. 

The  nearly  allied  question  of   the  great  benefit  which 


vi  ANAESTHETICS,  FEBRIFUGES,  ETC.  551 

chemistry  has  conferred  upon  medicine 1  by  enlarging  its 
stock  of  remedies  can  only  be  touched  upon  very  briefly,  as 
any  detailed  treatment  of  the  subject  here  would  overstep 
the  limits  of  this  work.  With  the  history  of  medicine  in  the 
earlier  ages  the  conditions  were  quite  otherwise  ;  for,  in  the 
iatro-chemical  as  well  as  in  the  phlogistic  periods  the  latter 
was  in  the  main  conjoined  with  the  history  of  chemistry, 
whereas  now  chemical  investigation  pursues  totally  distinct 
aims. 

To  mention  only  one  or  two  of  the  specially  important  services 
which  chemistry  has  rendered  to  medical  science,  take  the 
introduction  of  narcotics  and  anaesthetics — chloroform,  ether, 
nitrous  oxide,  chloral,  bromide  of  potassium,  sulphonal,  etc. 
A  number  of  other  chemical  compounds  have  been  proposed 
as  anaesthetics  during  the  last  few  years,  but  none  of  them 
have  entered  into  serious  competition  with  chloroform,  ether 
and  nitrous  oxide.  And  the  same  remark  applies  to  the  sub- 
stances newly  recommended  as  soporifics,  e.g.  urethane,  para- 
aldehyde,  aceto-phenone,  etc ;  compared  with  sulphonal  and 
chloral,  these  have  but  little  importance. 

Reference  must  also  be  made  to  the  success  with  which 
naturally  occurring  sedatives  and  febrifuges  have  been  re- 
placed by  others  artificially  prepared,  e.g.  quinine  by  antipy- 
retic remedies  like  salicylic  acid,  acetanilide,  antipyrine, 
phenacetine,  etc.  It  has  already  been  shown 2  how,  with  the 
acquisition  of  the  knowledge  that  the  alkaloids  are  derivatives 
of  pyridine  or  quinoline,  a  firmer  foothold  was  gained  for  the 
artificial  formation  of  these  natural  products — an  object  which 
has  been  striven  after  for  so  long. 

1  H.  Thorns'  work  :—Die  Arzneimittel  der  organischen  Ghemie  gives  an 
excellent  summary  of  the  rapidly  extending  list  of  artificially  prepared 
medicines  ;  compare  also  Beckurts'  reports  on  Pharmaceutical  Chemistry 
in  the  Jahrbuch  der  Chemie,  vols.  i — v. 

2  Cf.  pp.  482-483. 


552  HISTORY  OF  PHYSIOLOGICAL  CHEMISTRY          CHAP. 


The  Eelation  of  Chemistry  to  Pharmacy. 

With  the  rapid  enlargement  of  the  medical  treasury, 
the  problems  which  confront  the  pharmacist  have  likewise 
grown  in  a  very  high  degree.  If  the  latter  is  to  do  justice  to 
the  demands  which  are  made  upon  him,  he  must  be  equipped 
with  a  catholic  and  thorough  knowledge  of  chemistry.  The 
development  of  pharmaceutical  chemistry  in  recent  years  is 
for  the  most  part  concurrent  with  that  of  particular  branches 
of  the  pure  and  applied  science.  The  discoveries  of  inorganic 
and  organic  compounds  which  have  proved  of  importance  for 
pharmacy  have  likewise  been  of  great  value  for  chemistry 
itself.1 

In  the  domain  of  analytical  chemistry  we  see  the  assid- 
uous and  scientifically  educated  pharmacist  striving  after 
similar  aims  with  the  chemist.  The  former  ought  to  have  a 
thorough  knowledge  and  be  master  of  the  approved  analytical 
methods  which  are  required  for  the  testing  and  examining  of 
officinal  drugs  as  well  as  of  food  and  drink,  and  should  also 
be  prepared  for  legal  cases  where  chemistry  comes  into  play.2 

Pharmaceutical  chemistry  is  in  fact  connected  in  the 
most  intimate  manner  with  pure  chemistry,  for  both  have  the 
same  foundations.  If  we  would  convince  ourselves  of  this,  we 
have  but  to  look  through  the  numerous  recent  text-books  of 
the  former  branch,  to  perceive  that  in  contents  and  arrange- 
ment they  are  much  the  same  as  those  of  the  pure  science. 
So  long  ago  as  1844  H.  Kopp3  expressed  himself  pertinently 
on  the  subject  as  follows  :  "  Since  the  end  of  last  century 
pharmaceutical  chemistry  has  deviated  more  and  more  from 
the  direction  which  it  still  followed  during  the  earlier  decades 
of  the  latter,  when  it  merely  borrowed  from  the  investigations 
of  scientific  chemistry  those  results  which  had  a  bearing  upon 
the  preparation  of  medicines.  It  became  more  and  more 
nearly  allied  to  purely  scientific  chemistry  ;  pharmaceutical 

1  Cf.  The  History  of  Pure  Chemistry,  p.  400  et  seq. 

2  Cf.  pp.  397-399. 

3  Geschichte  der  Chemie,  vol.  ii.  p.  119. 


vi  RELATION  OF  CHEMISTRY  TO  PHARMACY  553 

text-books,  which  formerly  were  mere  collections  of  empirical 
recipes,  came  to  have  a  genuine  scientific  character,  while  the 
journals  originally  brought  out  for  pharmacy  became  import- 
ant miscellanies  for  pure  chemistry." 

At  the  close  of  last  century  and  beginning  of  this  one  the 
relation  of  chemistry  to  pharmacy  was,  however,  different 
from  what  it  is  now.  Then  the  latter  was  an  Alma  Mater 
for  the  former,  whereas  now  these  positions  are  exactly  re- 
versed ;  pharmacy  enjoys  to-day  the  fruits  of  a  highly  de- 
veloped chemistry.  In  earlier  times  the  study  of  pharmacy 
was  in  truth  the  only  road  to  that  of  pure  chemistry,  and 
this  is  why  the  most  eminent  chemists  from  the  end  of  last 
century  until  well  on  in  this  one  came  from  the  pharma- 
ceutical school.  We  have  but  to  recall  here  the  names  of 
Scheele,  Rouelle,  Klaproth,  Vauquelin,  Liebig,  H.  Rose  and 
many  others. 

The  pharmaceutical  institutes  which  began  to  spring  into 
life  at  the  close  of  last  century  were  of  great  value  for  the 
education  of  chemists  who  wished  at  the  same  time  to 
become  pharmacists,  for  in  these  any  young  man  who  was 
anxious  to  learn  received  a  course  of  systematic  instruction. 
The  Trommsdorff  Institute  in  Erfurt,  founded  in  1795,  de- 
serves special  mention  in  this  connection.  And  good  text- 
books of  pharmacy  were  not  wanting  then  either,  e.g.  Hagen's 
ApothekerJcunst  ("The  Art  of  Pharmacy  "  1 7  7  8),  Gottling's 
Handbuch  der  Pharmazie  (1 80  0),Hermbstadt's,TrommsdorfFs, 
Westrumb's,  and  Buchholz's  text-books,  etc.  The  Pharma- 
ceutical Society  of  London  dates  from  1841. 

A  historical  account  of  how  pharmacy  proper  has  de- 
veloped along  with  chemistry  during  the  present  century  is 
unnecessary  here,  for  the  reasons  already  given. 


554  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP, 


HISTORY  OF  TECHNICAL  CHEMISTRY  DURING  THE 
LAST  HUNDRED  YEARS.1 

The  immense  development  of  large  chemical  industries 
and,  in  fact,  of  all  the  branches  of  chemical  technology  during 
the  present  century  is  the  natural  consequence  of  the  great 
advances  in  chemical  knowledge,  and  the  rational  application 
of  these  to  technical  processes.  The  light  of  scientific  re- 
search has  thus  been  shed  upon  the  latter,  and  new  branches 
of  industry  have  been  grounded  upon  exact  investigations^ 
The  history  of  technical  chemistry  offers  a  continuous  series  V 
of  examples  of  this  beneficial  action  of  theory  upon  practice. 
On  the  other  hand,  numerous  questions  have  arisen  in  the 
course  of  technical  working  which  have  given  rise  to  investi- 
gations of  the  highest  value  for  pure  chemistry. 

The  great  advances  which  have  been  made  in  chemical 
technology  only  became  possible  with  the  development  of 
analytical  chemistry,  which  allowed  of  a  olear  insight  into  the 
composition  of  the  original,  intermediate,  and  final  products 
of  technical  processes.  Since  the  beginning  of  this  century 
methods  of  research  have  gradually  become  more  perfect,  , 
methods  which  more  and  more  meet  the  requirements  of  the 
technical  chemist,  and  which  have  constituted  andf  still  * 
constitute  the  most  important  aids  to  the  development  of 
chemical  industry.  Many  of  these  methods  have  already 
been  referred  to  in  the  history  of  analytical  cjjemistry,2  but 
the  reader  may  also  be  reminded  at  this  point  of  their  use 
with  respect  to  the  wants  of  everyday  life.  The  testing  and 
examination  of  articles  of  food  and  drink  are  now  carried  on 

1  For  the  literature  on  the  subject,  see  Wagner's  Jahresberichte  and  hi& 
Lehrbuchder  Technologic  ("Annual  Reports"  and  "  Text-Book  of  Tech- 
nology") ;  A.  W.  Hofmann's  JBericht  ilber  die  Entwickelung  der  Chemischen 
Industrie  ("  Report  on  the  Development  of  Chemical  Industries,"  etc., 
1875-77) ;  Karmarsch,  Geschichte  der  Technologic,  etc.  ("History  of  Tech- 
nology," etc. ) ;  and  the  text-books  referred  to  in  the  succeeding  pages. 

2  Cf.  pp.  390,  392  and  398. 


vi  GROWTH  OF  CHEMICAL  INDUSTRIES  555 

in  a  very  large  number  of  laboratories,  the  methods  employed 
here  having  been  elaborated  from  purely  chemical  investiga- 
tions. This  applies  in  a  special  degree  to  the  analysis  of 
water,  which  is  of  such  enormous  importance  alike  from  a 
hygienic  and  an  industrial  point  of  view.  We  have  only  to 
think  how  necessary  it  is  to  establish  the  chemical  composi- 
tion of  a  water  before  employing  it  for  any  manufacture ; 
and  the  various  processes  of  purification,  too,  to  which  it  has 
to  be  subjected,  before  it  can  be  used  for  many  purposes,  are 
based  upon  rational  chemical  researches  and  observations. 
Another  benefit  which  water  analysis  has  conferred  upon  the 
community  at  large  consists  in  its  having  rendered  possible 
the  artificial  production  of  mineral  waters,  and  thus  called  a 
flourishing  industry  into  life ;  the  great  services  rendered  in 
respect  to  this  by  F.  A.  Struve  (1820)  deserve  to  be  recalled 
here. 

In  the  following  pages  mention  will  be  chiefly  made  of 
such  work  as  has  either  led  to  the  introduction  of  important 
novelties  into  chemical  technology  or  to  the  opening  up  of 
new  branches  of  the  latter. 

It  is  hardly  possible  to  estimate  the  benefit  to  the  national 
well-being  which  has  accrued,  more  especially  in  Germany, 
England,  France,  Switzerland  and  Belgium,  from  the  growth 
of  chemical  industries.  Take,  for  example,  the  coal-tar  colour 
manufacture  in  Germany,  which  has  arisen  upon  foundations 
of  purely  scientific  work,  and  the  alkali  and  sulphuric  acid 
manufactures  in  Great  Britain.  The  former  illustrates  in  the 
most  perfect  manner  the  principle  of  the  refinement  of  matter, 
a  troublesome  and  almost  worthless  waste  product — tar — being 
now  worked  up  by  chemical  processes  into  a  vast  number  of 
valuable  substances.  And  the  same  applies  in  greater  or 
less  degree  to  the  chief  chemical  industries  of  all  the  coun- 
tries mentioned  above ;  in  every  case  men  are  striving  to 
bring  individual  chemical  processes  to  the  highest  state  of 
perfection  by  utilising  all  the  waste  products.  The  soda 
industry  of  to-day  offers  a  specially  good  instance  of  this,  for 
in  it  we  find  competing  processes  successfully  carried  on, 
simply  because  they  have  called  to  their  aid  every  means  of 


556  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 

rational  chemical  investigation.  There  is  indeed  hardly  any 
branch  of  chemical  manufacture  of  which  the  same  may  not 
more  or  less  be  said. 

Reference  may  also  be  made  here  to  the  development  of 
technical  instruction,1  which  has  of  course  contributed  im- 
mensely to  the  advancement  of  chemical  industries.  Tech- 
nical schools  and  colleges  belong  for  the  most  part  to  the 
present  century.  The  earliest  of  those  on  the  continent  of 
Europe  were  the  ficole  Polytechnigue  of  France,  founded  in 
1794,  and  called  at  first  the  jfrcole  Centrale  des  Travaux  Publics, 
the  Vienna  Polytechnic  Institute  (1815),  and  the  Berlin  Tech- 
nical College  (1821).  The  chemical  laboratories  of  the  above 
and  other  similar  institutions  in  Dresden,  Darmstadt,  Hanover, 
Stuttgart,  Munich,  Zurich,  etc.  have  continued  to  increase  in 
importance  as  aids  to  the  furtherance  of  chemical  manu- 
factures. As  every  one  knows,  Great  Britain  is  by  no  means 
so  well  equipped  with  technical  schools  and  colleges  as  many 
of  its  neighbours  on  the  Continent,  but  public  opinion  is  now 
becoming  awakened  on  the  subject,  and  the  want  is  being 
gradually  supplied. 

The  literature  on  technical  chemistry  has  sprung  from 
insignificant  beginnings.  Hermbstadt's  works  on  Dyeing, 
Bleaching,  Distilling,  etc.,  which  were  published  in  and  after 
the  year  1820,  deserve  mention  on  account  of  their  value  at 
that  time.  During  the  last  fifty  years  immense  strides 
have  been  made  in  this  respect,  as  is  witnessed  (e.g.)  by  the 
excellent  encyclopedias  of  Prechtl  and  Karmarsch,  Muspratt- 
Stohmann-Kerl,  Bolley,  Ure,  Watts  and  Thorpe,  and  also  by 
the  text-books  upon  chemical  technology,  among  others  those  of 
Dumas,  Payen,  Knapp,  Wagner  and  Ost,  in  which  the  results 
of  theory  and  practice  are  given  together.  In  addition  to 
these,  the  weekly  and  monthly  journals,  among  which  Dingier 's 
Polytechnisches  Journal,  Wagner's  Jahreslerichte  (now  edited 
by  F.  Fischer)  and  the  Journal  of  the,  Society  of  Chemical 
Industry  may  be  named,  supply  us  with  information 
upon  the  results  of  current  chemico-technical  investigation. 

1  Cf.  the  excellent  historical,  critical  and  statistical  work  of  Egon 
Zoller  : — Die  Universitdten  und  technischen  Hochschulen  (Berlin,  1891). 


vi  METALLURGY  OF  IRON  AND  STEEL  557 

By  such   means   the  closest   connection   between  chemical 
industry  and  the  pure  science  is  permanently  maintained. 

The  Progress  of  Metallurgy.1 

Although  the  production  of  iron  and  steel,  as  carried  on 
in  the  phlogistic  period,  gave  rise  to  chemical  work  through 
which  the  mutual  relations  of  cast-iron,  wrought-iron  and 
steel  were  in  some  measure  explained,  there  still  remained 
a  variety  of  problems  in  connection  with  these  to  be  solved 
at  a  later  date.  The  improvement  of  analytical  methods 
rendered  it  possible  to  detect  and  estimate  the  various  im- 
purities in  iron, — silicon,  phosphorus,  sulphur,  arsenic,  etc., 
— and  at  the  same  time  to  recognise  their  influence  in 
modifying  the  properties  of  the  metal.  The  blast  furnace 
process  was  explained  by  the  excellent  investigations  of 
Gruner,  Tunner,  L.  Binman,  and  others,  the  analyses  of  the 
furnace  gases  by  Bunsen 2  and  Playfair  3  aiding  in  a  special 
degree  towards  the  elucidation  of  the  reactions  which  go  on 
in  it.  The  determination  of  the  composition  of  pig-iron — the 
proof  that  a  chemical  compound  of  iron  and  carbon  exists — 
was  also  conducive  to  the  establishment  of  a  theory  of  the 
blast  furnace  process.  The  Bessemer  process  for  the  pro- 
duction of  steel  (1856)  was  the  result  of  the  clear  perception 
of  the  connection  existing  between  iron  and  steel,  while  the 
chemical  investigation  of  the  products  which  are  formed 
during  its  various  stages  greatly  assisted  its  development. 

The  Thomas-Gilchrist  process  for  dephosphorising  iron, 
introduced  about  the  year  1878,  has  been  a  wonderful  success. 
Light  was  shed  upon  the  theory  of  it  by  various  analytical 
researches,  e.g.  those  of  Finkener ; 4  while,  on  the  other  hand 
scientific  experiments  by  A.  Frank,  P.  Wagner,  and  others 
have  led  to  the  utilisation  of  the  phosphoric  acid  which 

1  Compare  the  works  on  metallurgy  by  B.  Kerl,  Stolzel,  Balling  and 
others. 

2  Cf.  Pogg.  Ann.,  vol.  xlvi.  p.  193. 

3  Brit.  Assoc.  Reports  for  1845,  etc. 

4  Cf.  Wagner's  Jahresber.  for  1883,  p.  136. 


558  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 

accumulates  in  the  slag  produced  in  the  process — the  Thomas 
slag, — so  that  this  latter  has  now  become  an  artificial  manure 
of  the  first  importance,  being  sold  in  a  fine  state  of  division 
under  the  name  of  "  basic  slag."  The  ingenious  application 
of  the  spectroscope  to  the  examination  of  the  Bessemer  flame, 
whereby  the  end  point  of  the  reaction  can  be  clearly  distin- 
guished,1 and  the  introduction  of  the  Martin  process  must 
also  be  referred  to. 

As  another  example  of  the  utilisation  of  by-products,  we 
may  take  the  successful  working  up  into  iron  of  iron  pyrites 
from  which  all  the  sulphur  possible  has  been  driven  off.2  The 
desire  to  waste  no  material  of  any  value  is  also  shown  in  the 
process  of  manufacturing  copper  from  pyrites  whose  sulphur 
has  been  already  utilised, — a  process  elaborated  from  chemical 
researches. 

The  metallurgy  of  nickel  has  developed  rapidly  since 
German  silver  began  to  be  prepared  upon  a  rational  system, 
and  especially  since  its  employment  as  an  ingredient  of 
coins ;  the  German  nickel  coinage  dates  from  1873.  Nickel 
has,  however,  been  long  known  to  the  Chinese,  and  used  by 
them  for  making  a  variety  of  articles.  An  alloy  of  nickel  and 
iron  is  now  employed  for  armour-plating  ships  of  war.  A 
passing  reference  may  also  be  made  to  the  remarkable  at- 
tempts to  separate  nickel  from  its  ores  in  the  form  of  the 
volatile  compound  with  carbon  monoxide,3  and  to  regenerate 
the  monoxide  from  this. 

Numerous  improvements  have  been  made  in  respect  to 
the  production  of  silver,  among  others  the  Augustin  and 
Ziervogel  extraction  processes,  and  the  Pattison  and  Parkes 
processes  for  the  desilverisation  of  lead  ;  while  the  metallurgy 
of  gold  has  also  been  facilitated  by  the  introduction  of  good 
methods  for  separating  the  latter  from  other  metals,  e.g.  by 
that  of  d'Arcet  (1802),  that  of  Plattner,  and  especially  the 
now  well-known  cyanide  process.  The  most  important  addi- 
tions to  the  technology  of  platinum  were  made  by  Deville  and 

1  Roscoe,  Chem.  Neius  for  1871. 

2  Gossage,  Chem.  Centr.  for  1860,  p.  783. 

3  Mond,  Mon.  Sclent,  for  1892,  p.  785  ;  or  Nature  of  July  7th,  1892. 


vi  ELECTRO-METALLURGY  559 

Debray  after  the  year  1852,  in  the  fusion  of  large  quantities  of 
the  metal  and  the  introduction  of  methods  which  gave  a 
larger  yield. 

The  galvano-plastic  process,  i.e.  the  precipitation  upon  one 
metal  of  a  thin  layer  of  another  one  by  means  of  electricity, 
has  proved  itself  of  great  importance.  The  original  observa- 
tion in  this  direction  was  made  by  de  la  Rive  in  1836,  and 
this  was  followed  by  the  publication  in  1839  by  Jacobi,and  a 
little  later  by  Spencer,  of  the  process  from  which  the  more 
perfect  electro-metallurgy  of  to-day  has  developed  itself.  The 
share  taken  by  the  late  Werner  Siemens  in  this  development 
should  not  be  forgotten. 

Among  the  metals  which  have  been  isolated  during  the 
present  century,  aluminium  was  first  made  available  for 
technical  purposes  by  the  assiduous  and  successful  labours 
of  H.  St.  Claire  Deville,1  while  the  Stassfurt  mineral 
carnallite  has  proved  itself  a  convenient  source  from  which 
to  prepare  magnesium.  The  methods  by  which  those  metals 
are  actually  produced  have  grown  out  of  the  work  of  their 
discoverers.2 

The  application  of  electricity  3  for  the  extraction  of  metals 
from  their  compounds,  i.e.  Electro-metallurgy,  has  made  very 
great  progress  during  recent  years,  e.g.  for  the  production 
of  copper,  zinc,  gold,  and  especially  aluminium.  Sodium, 
which  was  before  this  used  in  such  large  quantity  for  the 
manufacture  both  of  aluminium  and  magnesium,  is  now  con- 
sequently of  much  less  technical  importance ;  but  as  sodium 
peroxide  is  coming  into  vogue  for  bleaching  wool,  silk  and 
feathers,  there  is  probably  a  fresh  field  of  usefulness  in  store 
for  this  metal.  The  production  of  carbide  of  calcium, 
already  referred  to,  must  also  be  mentioned  in  connection 
with  electro-metallurgical  processes. 

1  Comptes  RenduSj  vols.  xxxviii.  xxxix.  and  xl. 

2  Cf.  The  History  of  Pure  Chemistry. 

3  Compare  E.  Ger land's  report  in  the  Chemiker  Zeitung  for  1893,  No. 
30  ;  Cl.  Winkler,  ibid.   1892,  No.   22  ;   and  especially  Borcher's  Elelctro- 
metallurgie,  1891.     See  also  a  short  paper  by  Thos.  Ewan  on  The  Industrial 
Applications  of  Electro- Chemistry  (Nature  for  June  2nd,  1898). 


560  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 

Numerous  improvements  have  also  been  made  in  the 
course  of  the  century  in  the  manufacture  of  alloys  of  every 
kind.  Thus,  from  zinc  and  copper  there  have  been  pre- 
pared malleable  brass,  similor,  etc.,  and  from  aluminium 
and  copper,  aluminium  bronze,  besides  a  great  many  alloys 
and  amalgams  of  tin,  including  type  metal ;  this  last  used  to 
be  made  from  antimony  and  lead  only,  but  to  these  tin  is 
now  added. 

This  century  has  also  witnessed  the  production  of  all 
sorts  of  metallic  compounds,  among  which  mineral  pigments 
take  a  prominent  place.  The  most  important  improvement 
in  the  manufacture  of  white  lead  was  due  to  Thenard(lSOl), 
Scheele  having  before  this  made  some  fundamental  observations 
on  the  subject  (p.  147).  Zinc  white,  which  was  made  on  an 
experimental  scale  by  Courtois  so  long  ago  as  at  the  end  of 
last  century,  was  first  brought  into  general  repute  by  Leclaire 
in  1840,  after  which  it  came  to  be  produced  on  the  large 
scale.  The  introduction  of  chrome  colours,  especially  of  chrome 
green  and  chrome  red,  both  of  which  are  so  highly  valued  for 
enamelling,  belongs  to  the  present  century.  Schweinfurt 
green,  a  double  compound  of  cupric  arsenite  and  acetate,  was 
discovered  by  Sattler  in  1814;  it  was  greatly  in  vogue  for 
a  long  time,  but  is  now  superseded  by  other  colours  on  account 
of  its  poisonous  nature.  The  extended  application  of  many 
metallic  salts,  formerly  prepared  in  small  quantities  only,  to 
new  purposes  (e.g.  of  nitrate  of  silver  in  photography,  and  of 
the  yellow  and  red  prussiates  of  potash  in  dyeing)  has  led  to 
the  rise  of  entirely  new  branches  of  manufacture.  There  are 
now  but  few  salts  of  any  of  the  more  plentifully  occurring 
metals  which  have  not  some  use  on  the  large  scale ;  for 
instance,  stannous  and  stannic  chlorides  and  various  salts  of 
aluminium,  iron  and  manganese  in  dyeing,  and  compounds  of 
mercury,  bismuth,  antimony,  zinc,  etc.,  chiefly  in  pharmacy. 


vi  MANUFACTURE  OF  SULPHURIC  ACID  561 


Development  of  the  Great  Chemical  Industries. 

The  great  chemical  industries  are  a  product  of  our  own  time, 
their  growth  having  gone  hand  in  hand  with  the  growth  of 
pure  chemistry.  The  manufactures  of  sulphuric  acid  and 
soda,  which  may  be  looked  upon  as  the  basis  of  all  the  others, 
and  which  are  naturally  followed  by  those  of  hydrochloric 
acid,  bleaching  powder,  chlorate  of  potash  and  other  salts  of 
potassium,  nitric  acid,  etc.,  only  attained  to  their  full  vigour 
after  the  various  processes  involved  had  been  explained  by 
chemical  investigation,  and  after  the  most  favourable  conditions 
for  those  processes  had  been  worked  out.  The  introduction 
of  easy  methods  of  analysis  into  technical  industries  has  also 
been  of  the  utmost  service  to  them. 

Important  practical  improvements  were  made  in  the 
manufacture  of  sulphuric  acid1  so  early  as  the  beginning 
of  the  present  century,  e.g.  the  amount  of  steam  required 
was  regulated,  and  the  process  was  made  continuous  (the 
latter  by  Holker).  The  first  attempt  to  explain  this 
remarkable  chemical  process  of  the  formation  of  sulphuric 
acid  from  sulphurous  acid,  air,  water  and  nitrous  gas 
was  made  by  Clement  and  Desormes,2  who  recognised 
the  important  part  played  by  the  nitric  oxide.  Later 
researches  by  Peligot,  and  more  especially  by  Cl.  Winkler,3 
R.  Weber,4  Lunge,  Schertel  and  others,  have  served  to  eluci- 
date the  reactions  which  go  on  between  the  above-mentioned 
substances,  and  have  therefore  been  of  the  utmost  value  in 
respect  to  the  manufacture  of  the  acid ;  they  have  led,  for 
example,  to  an  exact  knowledge  of  disturbing  conditions, 
which  can  therefore  now  be  provided  against.  To  Reich  is 
due  the  merit  of  having  brought  the  technical  process  under 
due  control,  by  his  analysis  of  the  chamber  gases ;  and.  ever 
since  Cl.  Winkler  called  technical  gas  analysis  into  life,  this 

1  Cf.  Lunge's  Manufacture  of  Sulphuric  Acid  and  Alkali. 

2  Ann.  de  Chimie,  vol.  lix.  p.  329. 

3  Cf.  Hofmann's  Bericht,  etc. ,  vol.  i.  p.  382. 

4  Journ.  pr.    Ghem.,  vol.  Ixxxv.  p.    423 ;     Pogg.   Ann.,   vol.   cxxvii. 
p.  543. 

O  O 


562  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 


has  been  a  regular  part  of  the  operation.  How  essential  for 
the  manufacture  the  observations  on  the  chemical  behaviour 
of  nitrous  acid  to  sulphurous  and  sulphuric  have  been,  is 
sufficiently  evidenced  by  the  introduction  of  the  Gay-Lussac 
and  Glover  towers  to  which  they  gave  rise,  and  which  have 
made  the  process  into  one  complete  whole. 

But  if  scientific  chemistry  has  thus  proved  itself  so  neces- 
sary for  technical,  the  latter  has  likewise  done  much  to 
advance  the  former ;  for  many  important  discoveries,  e.g. 
those  of  selenium  and  thallium,  have  been  rendered  possible 
by  its  aid,  and  researches  of  high  value,  such  as  those  of 
Lunge  upon  the  various  stages  of  the  oxidation  of  nitrogen, 
have  arisen  from  technical  questions. 

The  preparation  of  sulphuric  anhydride  from  sulphur 
dioxide  and  oxygen,  which  was  formerly  merely  a  lecture- 
room  experiment,  has  been  converted  into  a  technical  process 
through  the  admirable  researches  of  Cl.  Winkler,1  and  thus 
an  important  reagent  has  been  made  available  for  many 
branches  of  chemical  industry.  Sulphurous  acid,  whose  sole 
technical  application  (practically  speaking)  for  a  long  time 
was  in  the  manufacture  of  sulphuric  acid,  is  now  condensed 
on  the  large  scale  and  used  for  the  bleaching  of  wool  and 
silk,  and  as  a  refrigerant,  and  it  has  also  recently  found  an 
extensive  employment  in  the  production  of  the  so-called 
sulphite-cellulose  and  in  the  precipitation  of  lime  from  sugar 
juice.  The  utilisation  of  sulphurous  acid  for  these  purposes 
is  all  the  more  striking  when  we  remember  that  in  the 
roasting  of  sulphides  it  used  often  to  be  allowed  to  escape 
into  the  air,  to  the  great  detriment  both  of  human  beings 
and  of  vegetation. 

The  Soda  Industry. — The  transformation  of  common 
salt,  which  occurs  so  abundantly  in  nature,  forms  the  founda- 
tion of  this  immense  industry,  whose  history  commences 
with  the  beginning  of  the  present  chemical  period.  Nicolas 
Leblanc  2  was  the  first  to  succeed  in  converting  salt  into  soda, 

1  Wagner's  Jahresber.  for  1879  and  1884. 

2  This  remarkable  man,  who  was  born  at  Issoudun  (Indre)  in  1742  (and 
not,  as  usually  stated,  in  1753),  derived  no  pecuniary  benefit  from  his 


vi  THE  SODA  INDUSTRY  563 

with  sodic  sulphate  as  an  intermediate  product,  Malherbe 
and  De  la  Metherie  having  some  time  previously  attempted 
to  utilise  the  latter  substance  in  the  same  way,  but  without 
material  success.  It  was  in  1791  that  Leblanc  commenced 
the  actual  manufacture  of  soda,  but  political  conditions  and 
other  circumstances  hindered  its  growth  for  a  long  time,  the 
chief  difficulty  being  the  high  duty  on  salt.  In  the  year  1823 
Muspratt  began  the  erection  of  his  alkali  works  at  Liverpool ; 
his  name  deserves  a  foremost  place  in  connection  with  the 
development  of  the  soda  industry.  The  advantages  which 
have  accrued  to  the  manufacture  of  soda  from  chemical  inves- 
tigation are  incalculable,  but  space  will  not  allow  of  entering 
minutely  into  them  here.  The  simple  analytical  methods 
which  supplied  the  necessary  information  as  to  the  composi- 
tion of  the  raw,  intermediate,  and  final  products  were  and 
are  still  of  the  first  importance  for  the  regulation  of  the  tech- 
nical process.  The  formation  of  soda  from  the  sulphate,  by 
fusing  the  latter  with  coal  and  limestone,  was  ultimately  so 
far  explained  by  exact  chemical  experiments l  (after  various 
unsuccessful  speculations  on  the  subject  by  Dumas  and  others), 
as  to  allow  of  a  tenable  theory  of  this  fusion  process  being 
brought  forward. 

Scientific  researches  have  also  given  rise  to  numerous  im- 
portant improvements  in  the  soda  manufacture,  e.g.  to  the 
beautiful  process  of  Hargreaves  and  Robinson  (by  which  sul- 
phate of  soda  is  prepared  directly  without  the  previous  pro- 
duction of  sulphuric  acid),  to  the  introduction  of  revolving 
soda  furnaces,  and  to  many  processes  for  utilising  and 
rendering  harmless  the  unpleasant  alkali  waste.  With  re- 
spect to  the  last,  we  would  refer  here  to  the  work  of  Guckel- 
berger,  Mond,  and  Schaffner  and  Helbig,  who  succeeded  in 
making  various  laboratory  reactions  practicable  on  the  large 
scale.  But  the  greatest  advance  of  all  in  this  direction  is 

great  labours.  He  died  in  the  utmost  poverty  in  1806,  his  death  being  due 
to  despair.  A  monument  has  recently  been  erected  at  his  birthplace  to 
his  memory. 

1  Cf.  Dubrunfaut  in   Wagner's  Jahresber.  for  1864,  p.  177 ;   Scheurer- 
Kestner,  ibid.  1864,  p.  173  ;  and,  especially,  Kolb,  ibid.  1866,  p.  136. 

O   O   2 


564  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 

the  recent  and  exceedingly  simple  process  of  Chance,1  by 
which  nearly  all  the  sulphur  in  alkali  waste  can  be  recovered 
at  a  very  cheap  rate ;  the  result  of  this  has  been  to  enable 
the  Leblanc  process  to  compete  on  more  equal  terms  with  the 
younger  ammonia-soda  and  electrolytic  processes  (see  below). 

Purely  chemical  observations  have  also  led  to  what 
was,  until  quite  recently,  unquestionably  the  most  important 
of  all  the  innovations  in  the  soda  industry,  viz.  the  conver- 
sion of  common  salt  into  carbonate  of  soda,  without  the 
intermediate  formation  of  sulphate  at  all,  by  the  ammonia- 
soda  process.2  Although  the  reaction  upon  which  this 
method  is  based  is  extremely  simple,  it  took  a  very  long  time 
before  the  most  favourable  conditions  for  it  were  established, 
and  before  it  was  made  into  a  practical  success ;  but  this  was 
ultimately  achieved  by  E.  Solvay.  The  manufacture  of 
"  ammonia  soda "  and  of  artificial  manures  has  grown  so 
enormously  of  late  years  that  the  demand  for  salts  of  ammonia 
has  increased  proportionately ;  but  this  requirement  has  in  its 
turn  been  met  by  the  introduction  of  improved  apparatus  for 
the  working  up  of  gas  liquor,  and  by  the  attempts  to  extract  the 
nitrogen  of  fuel  in  the  form  of  ammonia,3  at  the  same  time  that 
the  heat  from  the  fuel  is  itself  being  utilised.  Here  again  the 
mutual  influence  of  one  branch  of  manufacture  upon  another 
is  apparent,  and  also  the  benefits  accruing  to  these  from 
scientific  investigations. 

The  production  of  "  ammonia  soda  "  has  now  attained  to 
such  a  height  that  the  manufacture  of  "  Leblanc  soda " 
has  been  greatly  prejudiced.  For  many  years  back  chemists 
have  been  striving  to  solve  the  problem — how  to  obtain 
hydrochloric  acid  or  chlorine  from  the  waste  products  of  the 
ammonia  soda  process ;  should  this  be  ultimately  accomplished 
on  the  practical  scale,  then  it  is  hardly  conceivable  that  the 
Leblanc  process  can  continue  to  exist.  The  numerous  patents 
referring  to  the  processes  carried  out  on  the  large  scale  by 

1  Journ.  Ghent.  Ind.,  vol.  vii.  p.  162. 

2  For  the  history  of  this,  cf.  Hofmann's  Bericht,  vol.  i.  p.  445. 

3  Cf.  Mond,  Chemiker  Zeitung  for  1889,  Nos.  81  and  82  :  or  Journ.  Chem. 
Ind.,  vol.  viii.  p.  505. 


vi  HYDROCHLORIC  ACID  ;   BLEACHING  POWDER  565 

Weldon  and  Pechiney,  Solvay  and  others  show  that  no  efforts 
are  being  spared  to  overcome  this  difficulty. 

Chemical  labours  have  exercised  a  less  profound  influence 
upon  the  manufacture  of  hydrochloric  acid,  which  is  neces- 
sarily produced  in  such  quantity  in  the  Leblanc  process, 
although  laboratory  researches  have  led  to  important  im- 
provements with  regard  to  its  condensation  by  water,  and 
to  its  purification  from  admixed  substances.  It  may  be 
mentioned  here,  as  a  curious  point  in  chemical  history,  that 
this  acid,  which  is  at  present  so  cheap  and  which  has  at 
times  been  almost  worthless,  was  in  Glauber's  time  the  most 
costly  of  the  mineral  acids. 

The  manufacture  of  chloride  of  lime,  which  uses  up  large 
quantities  of  hydrochloric  acid,  has  also  derived  great  benefit 
from  chemical  research,  in  fact  it  may  be  said  to  have  arisen 
from  the  latter.  Berthollet's  experiments  upon  the  bleaching 
action  of  chlorine  and  the  chlorides  (i.e.  hypochlorites)  of 
the  alkalies  led  to  the  manufacture  of  the  bleach  liquor 
known  under  the  name  of  Eau  de  Javelle.  Chloride  of  lime 
was  first  produced  by  Messrs.  Tennant  and  Co.  in  Glasgow 
in  the  year  1779.  Weldon's  beautiful  process1  for  the 
recovery  of  the  manganese  dioxide,  required  in  the  pre- 
paration of  chlorine,  from  the  otherwise  worthless  chlorine 
waste — a  process  which  has  been  in  practical  working  since 
1867 — grew  out  of  exact  laboratory  experiments;  at  the 
same  time  its  development  gave  rise  to  a  rich  harvest  of  scien- 
tific results.  Deacon's  method  of  producing  chlorine'2  directly 
from  hydrochloric  acid  likewise  originated  in  apparently 
trivial  observations ;  a  strictly  scientific  explanation  of  the 
action  of  the  copper  salt  on  the  mixture  of  hydrochloric  acid 
and  air  in  this  process  has,  however,  still  to  be  given. 

The  recent  rapid  development  of  electro-chemistry  is 
strikingly  shown  in  the  electrolytic  production  of  chlorine, 
caustic  alkali,  hypochlorites  and  chlorates  from  the  chlorides 
of  the  alkalies.  This  method  has  already  entered  into  serious 

1  Chem.  News  for  September,  1870. 

2  Journ.  Chem.  Soc.  for  1872,  p.  725. 


566  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 

competition  with  the  older  processes  for  obtaining  these 
substances.1 

Bleaching  powder  itself  has  been  the  subject  of  numberless 
investigations,  made  with  the  object  of  arriving  at  its  consti- 
tution. It  may,  in  fact,  be  said  that  there  is  no  other  substance 
of  equally  simple  composition  regarding  the  nature  of  which 
so  much  doubt  still  prevails,  notwithstanding  all  the  efforts 
which  have  been  made  to  clear  this  up.2 

The  two  other  halogens,  bromine  and  iodine,  also  became 
in  due  course  important  from  a  technical  point  of  view, 
although  their  much  lesser  abundance  in  nature,  and  con- 
sequent less  extended  practical  application,  cause  them  to  be 
produced  in  small  quantities  as  compared  with  chlorine. 
The  manufacture  of  these  is  based  upon  the  original  work 
of  Gay-Lussac  and  Balard.  Laboratory  experiments  have 
also  led  to  the  production  of  iodine  from  mother  liquors 
which  were  formerly  looked  upon  as  valueless,  e.g.  those  from 
Chili  saltpetre  and  from  phosphorite  after  its  treatment  with 
acid.  To  A.  Frank  3  is  due  the  merit  of  having  made  bromine 
available  for  technical  purposes,  by  preparing  it  from  the 
Stassfurt  waste  salts.  Large  quantities  of  both  of  these 
halogens,  especially  bromine,  (in  combination  with  silver)  are 
now  employed  in  photography. 

Nitric  acid  also  plays  an  important  part  in  chemical  in- 
dustries, especially  since  the  development  of  the  manufacture 
of  explosives  on  a  large  scale.  Potassium  nitrate,  which  has 
been  known  and  valued  for  so  .long,  is  still  an  indispensable 
ingredient  of  black  gunpowder.  Since  the  introduction  of 
the  nitrate  of  soda  from  the  Chili  deposits,  nitric  acid  has 
been  prepared  from  it  (instead  of  from  the  more  expensive 
nitrate  of  potash)  by  the  old  process  of  distillation  with  sul- 
phuric acid,  the  latest  step  in  advance  here  being  the  distilla- 
tion of  the  nitric  acid  in  a  vacuum  (Valentiner).  At  the 
same  time  nitrate  of  soda  is  now  largely  converted  into  the 

1  Cf.  Oettel's  Entwickelung  der  elektrochemischen  Industrie  (Stuttgart, 
1896). 

2  Cf.  The  History  of  Inorganic  Chemistry,  p.  426. 
.3  Hofmanris  Bericht,  etc.,  vol.  i.  p.  127. 


vi  NITRIC  ACID  ;   EXPLOSIVES  567 

potash  salt  by  double  decomposition  with  chloride  of  potassium. 
This  process,  so  simple  from  a  chemical  point  of  view,  could 
however  only  be  carried  out  on  an  extensive  scale  after  the 
rich  deposits  of  potash  salts  at  Stassfurt  had  been  discovered ; 
and  it  required  careful  chemical  investigation  to  make  those 
salts  available,1  for  their  composition  had  to  be  worked  out, 
and  proper  methods  for  separating  them  from  one  another 
had  to  be  devised.  The  large  quantities  of  potassium  chloride 
which  occur  in  the  Stassfurt  mines  have  led  in  certain  instances 
to  the  carrying  out  of  the  Leblanc  process  with  it  instead  of 
with  common  salt,  and  to  the  consequent  production  of  car- 
bonate of  potash,  or  mineral  potash,  as  it  was  called  (H. 
Griineberg,  1861).  The  extensive  use  of  the  Stassfurt  potash 
(and  other)  salts  in  the  manufacture  of  artificial  manures  may 
also  be  referred  to  here ;  an  immense  new  industry  has  thus 
been  developed  concurrently  with  the  increased  produc- 
tion of  nitrate  of  soda,  superphosphate  of  lime  and  salts  of 
ammonia. 

A  reference  to  the  history  of  gunpowder,  and  of  explosives 
generally,2  must  not  be  omitted  here,  and  this  all  the  more 
because  the  discovery  and  use  of  the  latter  are  connected  in 
the  most  intimate  manner  with  the  development  of  the 
chemistry  of  the  time.  It  is  known  that  the  Chinese  and 
Saracens  made  use  long  ago  of  mixtures  similar  to  gunpowder 
for  fireworks,  while  in  Europe  it  has  been  employed  for  the 
propulsion  of  projectiles  since  the  beginning  of  the  fourteenth 
century.  But  five  hundred  years  passed  before  the  chemical 
reactions,  which  go  on  during  the  combustion  of  powder,  were 
in  some  degree  understood.  That  its  effect  was  due  to  the 
production  of  gas  was  stated  by  van  Helmont ;  but  it  was  only 
through  the  exact  experiments  of  Bunsen  and  SchischkofF3 
upon  the  composition  of  powder  gases  and  residues  that  the 
foundation  was  laid  for  a  theory  of  its  combustion,  this  being 

1  Cf.  A.  Frank,  Hofmanris  Bericht,  etc.,  vol.  i.  p.  351  ;  also  Pfeiffer's 
Kaliindiistrie  ("The  Potash  Industry,"  1887). 

2  Cf.  the  lecture  given  by  Lepsius  before  the  Gesellschaft  Deutscher 
Naturforscher  at  Halle  in  1891,  entitled,  Das  alte  und  das  neue  Pidver, 
p.  17.  3  Pogg.  Ann.,  vol.  cii.  p.  53. 


568  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 

further  developed  by  the  later  work  of  Linck,  Karolyi,  Abel 
and  Noble,  Debus  and  others. 

The  explosives  (with  the  exception  of  gunpowder),  whose 
preparation  now  forms  such  a  great  industry,  have  all  been 
made  available  for  practical  use  by  chemical  investigations.  The 
epoch-making  discovery  of  gun-cotton  by  Schonbein,  Bottger, 
and  J.  Otto  (independently)  in  1846  must  be  recalled  here ; 
its  chemical  nature  and  reaction  upon  ignition  were  cleared 
up  by  the  laborious  work  of  Lenk,  Karolyi,  Heeren,  Abel  and 
others.  Nitro-glycerine  had  been  known  as  a  chemical  pre- 
paration, discovered  by  Sobrero,  for  fifteen  years  before  it 
began  to  find  extended  application  in  1862,  as  the  result  of 
Nobel's  researches.  The  careful  investigations  of  Abel,  E. 
Kopp  and  Champion  upon  its  modes  of  formation  and 
chemical  behaviour  immensely  facilitated  both  its  own  manu- 
facture and  that  of  its  various  preparations, — dynamite,  etc. 
Since  1888  an  important  forward  step  has  been  made  here,  in 
that  nitro-glycerine  and  gun-cotton — up  to  then  only  applicable 
as  explosives — were  brought  by  the  process  of  "  gelatinis- 
ing "  into  a  condition  in  which  they  might  be  used  with 
safety  in  guns.  The  "  smokeless  powder,"  which  is  now  so 
much  employed,  but  which  varies  widely  in  composition  from 
the  various  methods  used  in  its  preparation,  is  also  to  be 
placed  in  the  same  category  as  the  explosives  just  mentioned, 
since  it  contains  nitro-cellulose.  Systematic  chemical  inves- 
tigation has  now  rendered  it  possible  to  prepare  this  powder 
with  a  definite  ballistic  value.  Reference  must  also  be  made 
again  at  this  point  to  the  famous  researches  of  Liebig  and  other 
chemists  upon  the  fulminates,  which  rendered  the  manufacture 
of  fulminate  of  mercury  and  its  use  in  the  preparation  of 
fuses  possible. 

The  whole  match  industry  likewise  owes  its  enormous 
development  to  the  increased  knowledge  of  chemical  pre- 
parations and  processes.  What  a  contrast  there  is  between 
the  "  chemical  tinder "  of  1807 — i.e.  matches  containing  a 
mixture  of  chlorate  of  potash  and  sulphur,  which  were  ignited 
by  dipping  them  into  sulphuric  acid — and  our  present  friction 
matches !  Those  prepared  with  phosphorus  were  introduced 


vi  MATCHES;  SOAP  569 

in  1833  by  Irinyi  of  Pesth,  Homer  of  Vienna  and  Moldenhauer 
of  Darmstadt;  they  have  since  then  undergone  many  im- 
provements, the  most  important  of  these  being  subsequent  to 
the  discovery  of  amorphous  (non-poisonous)  phosphorus,  which 
has  been  used  since  the  year  1848,  although  for  a  long  time 
only  in  small  quantity,  either  in  the  match  itself  or  in  the 
material  of  the  surface  upon  which  the  match  is  rubbed. 
Phosphorus,  which  last  century  was  still  a  chemical  curiosity, 
has  been  manufactured  on  the  large  scale  for  about  fifty  years. 
Scheele's  process  for  its  preparation  was  improved  upon  by 
Nicolas  so  far  back  as  1778,  and  has  been  materially  modified 
in  recent  years,  e.g.  by  Fleck. 

Hand  in  hand  with  the  development  of  the  soda  industry 
went  the  expansion  of  other  branches  of  chemical  manu- 
facture, prominent  among  which  was  that  of  soap.  In  order 
to  appreciate  the  influence  of  chemical  investigation  upon 
this,  we  have  to  recall  to  mind  the  pioneering  labours  of 
Chevreul1  on  the  subject.  The  knowledge  of  the  chemical 
nature  of  fats  to  which  they  led  was  perfected  by  later  work, 
particularly  by  that  of  Heintz  and  of  Berthelot,  which  finally 
proved  that  the  fats  were  neutral  glycerine  ethers  of  various 
fatty  acids.2  The  manufacture  of  stearine  candles  and  of 
glycerine,  which  are  important  both  as  commercial  and 
household  products,  may  be  regarded  as  the  fruits  of  the 
labours  just  spoken  of,  in  addition  to  which  those  of  A.  de  Milly 
(the  originator  of  the  stearine  industry),  Melsens,  and  Fremy 
deserve  special  mention.  Further  valuable  improvements 
in  these  manufactures  have  been  effected  by  chemical  inves- 
tigation within  the  last  few  years  (cf.  Deite's  book  upon  the 
manufacture  of  soap,  the  article  on  Soap  in  Thorpe's  Dictionary, 
by  the  late  Alder  Wright,  Schadler's  book  on  the  technology 
of  Fats  and  Oils,  and  W.  Lant  Carpenter's  volume  on  The 

1  M.  E.  Chevreul,  born  in  1786,  lived  until  1889.     He  occupied  in  his 
time  a  number  of  responsible  posts  in  Paris,  the  last  being  that  of  Director 
of  the  Dyeing  Department  and  Professor  of  Chemistry  as  applied  to  dyeing 
in  the  world-renouned  Gobelins  tapestry  works.     His  classical  Recherches 
sur  les  corps  gras  aborigine  animate  gave  rise  to  a  great  amount  of  work  of 
a  physiologico-chemical  nature  upon  dyes,  adipocere  and  other  substances. 

2  Cf.  p.  441. 


570  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 

Manufacture  of  Soaps  and  Candles,  etc.,  1895).  From  a 
commercial  point  of  view,  the  working  out  of  methods  for 
determining  the  value  of  any  oil  or  fat  and  for  detecting 
adulterations  has  been  of  the  first  importance  (see  Benedict's 
admirable  work,  Analyse  der  Fette,  Berlin,  1897 ;  English 
edition,  revised  and  enlarged  by  Dr.  J.  Lewkowitsch,  1895). 

Closely  connected  also  with  the  soda  industry  stand  the 
manufactures  of  ultramarine  and  of  glass.  The  former 
substance,  which  is  in  a  special  degree  a  product  of  chemical 
research,  was  discovered  in  1828  by  Chr.  Gmelin,  and 
also  at  about  the  same  time  by  Guimet.  It  has  given  rise 
to  a  large  amount  of  scientific  investigation,1  which  has  led 
to  material  improvements  in  the  manufacture  of  the  various 
kinds  of  ultramarine,  and  has  also  explained  particular 
parts  of  the  firing  process,  but  from  which  no  final  opinion 
has  yet  been  formed  as  to  the  chemical  nature  of  this 
curious  product.  The  two  hypotheses  still  oppose  one 
another — viz.  (1)  that  ultramarine  is  a  definite  chemical 
compound,  and  (2)  that  it  is  a  mixture  similar  to  glass. 
The  recent  work  of  F.  Knapp 2  has,  however,  begun  to 
throw  some  light  upon  the  cause  of  the  colour  of  ultra- 
marine. 

Although  the  production  of  glass  reached  a  high  state  of 
development  in  olden  times  through  pure  empiricism,  it  too 
has  greatly  benefited  by  chemical  research.  The  manufacture 
of  glass  with  sulphate  of  soda  and  the  -improvements  in 
flint  and  crystal  glasses  belong  to  the  present  century,  while 
progress  has  also  been  made  in  silvering  (by  Liebig),  and  in 
glass  painting,  through  the  discovery  of  new  mineral  colours. 
The  investigations  of  Wohler,  Knapp,  Ebell,  M.  Muller  and 
others  resulted  in  elucidating  the  chemical  reasons  for  the 
different  colours  of  different  glasses.  Lastly,  laboratory  work 
has  greatly  advanced  the  art  of  imitating  the  precious  stones, 
and,  generally,  of  producing  new  varieties  of  glass.  The 
chemical  reactions  which  go  on  during  the  formation  of  glass 

1  The    work    of     Leykauf,    Biichner,     R.     Hoffmann,     Knapp    and 
Guckelberger  may  be  referred  to  here. 

2  Journ.  pr.  Chem.  (2),  vol.  xxxviii.  p.  48. 


vi  EARTHENWARE  AND  POTTERY  ;   MORTAR  571 

have  given  rise  to  much  experimental  -work,1  but  the  conclu- 
sions drawn  from  this — as  to  whether  glass  is  a  true  chemical 
compound  or  not — have  been  very  various.  Chemical  analysis 
has  of  late  years  produced  results  not  merely  of  scientific 
interest,  but  of  very  great  practical  importance  with  regard 
to  the  manufacture  of  glass.2 

Water  glass,  which  was  known  to  Agricola,  Glauber,  etc., 
was  made  available  for  technical  purposes  by  Fuchs  in  1818, 
and  has  since  then  been  used  for  a  great  number  of  different 
purposes — e.g.  for  impregnating  wood,  preparing  cements, 
protecting  frescoes,  etc. 

Earthenware  and  Pottery. — Important  practical  im- 
provements in  this  old  field  of  industry  are  associated  with  the 
names  of  Wedgwood,  Littler,  Sadler  and  others.  C.  Bischof,3 
Richters,4  and,  more  recently,  Seger5  have  rendered  good 
service  in  their  chemical  investigations  upon  the  nature  of 
fireclay,  and  on  the  connection  between  its  composition  and 
its  behaviour  at  high  temperatures.  The  labours  just  cited 
have  also  done  much  to  improve  the  manufacture  of  pottery, 
by  enabling  the  proper  mixtures  of  the  ingredients  to  be 
made.  The  ceramic  art  is  further  greatly  indebted  to 
chemistry  as  regards  glazing  and  the  burning-in  of  colours. 

The  preparation  and  application  of  mortar,  especially  of 
hydraulic  cement,  have  likewise  been  greatly  advanced  by 
purely  chemical  work,  whereby  a  nearer  approach  has  been 
made  to  the  solution  of  the  much-discussed  problem, — how 
the  hardening  is  to  be  explained  from  a  chemical  point  of 
view.  Many  investigations  have  been  made  with  a  view  of 
arriving  at  the  explanation  of  this,  the  chief  property  of 
cements,  among  others  by  Winkler,  Feichtinger,  Michaelis,6 

1  Pelouze,  Ann.  Chim.  Phys.  (4),  vol.  x.  p.  184 ;   R.  Weber,   Wagner's 
Jahresbericht  for  1863,  p.  391  ;  Benrath,  ibid.,  1871,  p.  398  ;  also  Benrath's 
book,  Die  Glasfabrikation  ("  The  Manufacture  of  Glass,"  1875). 

2  See  the  investigations  of  Schott,  Mylius,  R.  WTeber,  Forster,  Gray 
and  Dobbie,  and  others. 

3  Dingl.  Journ.,  vols.  clix.  cxciv.  cxcviii.  and  cc. 

4  Ibid.,  vol.  cxci.  p.  150. 

5  Ibid.,  vol.  ccxxv  ii.  p.  70. 

6  Cf.  his  pamphlet,  Die  hydraidischen  Mortel,  etc.  (Leipzig,  1869). 


572  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 

F.  Schott,1  Fr.  Knapp  2  and  Michel.3  The  old  view  of  the 
hardening  process,  viz.  that  it  consists  entirely  in  the  gradual 
formation  of  a  calcium  silicate,  had  to  be  abandoned  as  in- 
sufficient ;  but  a  complete  theory  of  it  still  remains  to  be  given. 

The  advances  made  in  the  manufacture  of  paper  can  be 
but  partially  touched  upon  here,  the  more  especially  since 
they  belong  chiefly  to  the  domain  of  mechanics.  The 
attempts  to  utilise  raw  vegetable  products,  particularly  wood 
and  straw,  for  the  production  of  paper,  were  first  successfully 
carried  out  in  the  year  1846.  In  caustic  soda  a  reagent 
was  found  by  means  of  which  cellulose  could  be  prepared 
from  these  materials ;  while  of  late  years  a  solution  of  calcium 
sulphite  in  sulphurous  acid  has  shown  itself  especially  well 
adapted  for  this  purpose.  The  above  process  for  the  produc- 
tion of  sulphite  cellulose  resulted  from  the  chemical  investiga* 
tions  of  Tilghman  and  especially  Al.  Mitscherlich.  The 
conversion  of  cellulose  into  cane-sugar  or  alcohol  is  another 
problem  which  has  been  often  attacked,  and  from  many 
different  sides,  but  it  still  remains  to  be  solved.  Should 
this  ultimately  be  successfully  carried  out  on  the  large  scale, 
a  complete  revolution  would  be  effected  in  agriculture  and 
husbandry  generally.4 

The  manufacture  of  starch  and  of  the  products  obtained 
from  it  has  also  derived  great  advantage  from  chemical 
investigations.  The  transformation  which  starch  undergoes 
upon  treatment  with  acids  has  only  recently  been  cleared 
up  in  some  degree  by  the  work  of  Marcker,  Musculus, 
O'Sullivan,  Payen,  Brown  and  Heron,  Salomon,  Allihn,  etc. 
The  earliest  observation  on  the  production  of  starch-sugar 
was  made  by  Kirchhoff  in  1811,  and  from  this  an  important 
branch  of  industry  has  now  arisen ;  dextrine,  which  has  for 
long  been  used  as  a  substitute  for  natural  gum,  is  obtained 
as  the  intermediate  product  here. 

1  Dingl.  Journ.,  vol.  ccii.  p.  434;  vol.  ccix.  p.  130. 

2  Ibid.,  vol.  ccii.  p.  513. 

3  Journ.  pr.  Chem.  (2),  vol.  xxxiii.  p.  548. 

4  For  details  regarding  cellulose  and  its  applications,  vide  Cross,  Bevan 
and  Beadle's  excellent  book  on  Cellulose,  etc.,  (1895). 


vi  THE  MANUFACTURE  OF  SUGAR  573 

The  beet-sugar  industry  has  developed  into  something 
enormous  from  experiments  instituted  by  chemists  on  a 
small  scale.1  Marggrafs  discovery,  in  1747,  that  sugar  was 
present  in  the  juice  of  beet,  was  not  at  that  time  capable  of 
being  applied  commercially.  Achard,  a  pupil  of  Marggraf, 
and,  in  a  lesser  degree,  Hermbstadt,  Lampadius  and  others, 
again  took  up  at  the  end  of  last  century  the  problem  of 
obtaining  sugar  from  beet  on  the  large  scale,  and  they  did 
succeed  in  devising  a  process  which  was  carried  out  in 
numerous  factories  during  the  years  of  the  Napoleonic  wars, 
when  the  trade  of  the  Continent  was  driven  in  upon  itself. 
But  this  process  was  unable  to  live  long,  being  a  very 
imperfect  one,  and  giving  but  a  small  yield  of  sugar.  It 
is  from  the  year  1825  that  the  real  rise  of  the  beet-sugar 
industry  dates,  various  factors  entering  into  its  growth,  not 
the  least  of  which  was  the  practical  application  of  chemical 
knowledge.  We  have  but  to  think,  for  example,  of  the 
development  of  saccharimetric  methods,  whose  aim  was  the 
determination — either  by  chemical  or  by  physical  means — of 
the  percentage  of  sugar  in  beet  juice  ;  of  the  improvements 
in  the  refining  process ; 2  of  the  recovery  of  the  crystallisable 
sugar  in  molasses,  and  so  on.  The  filtration  of  the  refined 
juice  through  bone  charcoal  was  first  recommended  by  Figuier 
in  1811,  and  then  by  Derosne  in  1812,  and  has  since  become 
an  essential  part  of  the  process.  The  use  of  vacuum  pans 
for  evaporating  the  syrup  was  introduced  by  Howard  in  1813, 
since  which  time  many  improvements  have  been  made  in 
them.  The  extremely  convenient  diffusion  process,  for 
obtaining  the  juice  of  the  beet,  was  discovered  by  Roberts 
(of  Seelowitz,  Mahren)  in  1866,  and  soon  came  into  general 
use,  at  first  in  Austria.  Osmosis,  which  was  first  applied  on 
the  large  scale  by  Dubrunfaut  in  1863  for  extracting  the 
crystallisable  sugar  from  molasses,  has  been  developed  by 

1  Cf.    Stohmann's  Zuckerfabrikation    (1893);     E.    0.    v     Lippmann's 
Geschichte  des  Zuckers  ;  and  the  article  on  sugar  in  Thorpe's  Dictionary  of 
Applied  Chemistry  by  Newlands  Brothers. 

2  The  decomposition  of  saccharate  of  lime  by  carbonic  acid  was  intro- 
duced by  Barruel  and  Kuhlmann. 


574  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 

researches  in  physical  chemistry, — another  instance  of  the 
practical  utility  of  scientific  investigation. 

A  passing  reference  may  be  made  here  to  the  good  done 
to  this  branch  of  industry  by  agricultural  chemistry,  in  the 
determination  of  the  most  favourable  conditions  for  the 
growth  of  beet,  and  the  investigation  of  the  composition  of 
the  soils  and  manures  employed,  etc.  Indeed,  there  is  hardly 
any  other  branch  of  technical  chemistry  so  intimately  con- 
nected with  agriculture  as  the  beet-sugar  manufacture.  The 
production  of  artificial  manures  has  received  a  powerful  im- 
pulse from  the  immense  quantity  of  beet  now  under  cultiva- 
tion. Lastly,  pure  chemistry  itself  has  benefited  in  many 
respects  from  the  careful  investigation  of  beet  juice.1 

The  so-called  saccharine,  a  compound  containing  sulphur 
which  is  now  manufactured  from  the  toluene  of  coal-tar,  and 
which  is  used  to  a  certain  extent  in  lieu  of  sugar,  offers  an 
example  of  the  assiduity  with  which  every  branch  of  chemical 
industry  is  being  exploited  with  the  object  of  imitating 
natural  products  by  artificial  ones,  and  even  of  replacing 
the  former  by  other  more  active  substances. 


Fermentation  Processes? 

The  development  of  the  various  manufactures  involving 
fermentation  has  been  immensely  advanced  by  chemical 
investigation,  while  at  the  same  time  the  nature  of  the  pro- 
cesses themselves  has  been  brought  into  clear  relief.  In 
place  of  the  contact  theory  of  Berzelius  and  Mitscherlich, 
which  was  merely  a  re-statement  of  the  facts  in  other  words 
and  no  explanation,  we  now  have  Pasteur's  vital  theory  of 
fermentation.  To  this  also  the  "mechanical"  theory  of  Liebig 
had  to  give  way,  while  Pasteur's  opinion  with  respect  to  the 
physiological  functions  of  yeast  became  in  its  turn  subsequently 

1  E.  0.  v.  Lippmann,  loc.  cit. 

-  For  the  recent  literature  on  the  subject,  see  Hansen's  Praxis  der 
Garungsindustrie  ;  Jorgensen's  Mikroorqanismen  der  Gdhrung  Industrie  ; 
Marcker's  Spiritusindustrie  ;  and  Thorpe's  Dictionary. 


vi  FERMENTED  LIQUORS  ;   ACETIC  ACID  575 

modified  to  a  material  extent  through  the  researches  of 
others.1 

The  labours  undertaken  with  the  object  of  testing  or 
establishing  theoretical  views  have  also  had  a  determining 
influence  upon  the  practical  working  of  fermentation  pro- 
cesses, since  the  knowledge  thus  gained  has  rendered  it 
possible  to  subject  these  processes  to  a  better  control  than 
was  formerly  the  case.  Among  the  more  important  obser- 
vations in  this  branch  during  the  last  few  years  is  that  of 
Effront  upon  the  favourable  effect  of  a  minute  quantity  of 
hydrofluoric  acid  on  the  fermentation  process. 

The  good  which  has  been  done  by  the  application  of 
analysis  to  fermented  liquors  is  evident  at  a  glance,  since  any 
defects  in  their  mode  of  preparation  thus  become  apparent. 
A  knowledge  of  the  normal  composition  of  wine  and  beer  has 
led  to  rational  suggestions  for  the  improvement  of  those 
drinks.  It  would  be  out  of  place  here  to  attempt  even  a  bare 
enumeration  of  the  more  important  innovations  in  this  branch, 
many  of  which  are  due  to  Pasteur.2 

The  manufacture  of  spirits  may  be  cited  as  one  of  the  great 
branches  of  industry  which  has  been  helped  to  its  present 
high  state  of  development  by  chemical  work.  We  have 
also  the  enormous  production  of  alcoholic  preparations 3 
from  spirit  itself,  as  well  as  from  the  first  and  last  runnings  of 
the  still ;  the  manufacture  of  ordinary  and  of  compound 
ethers,  the  latter  of  which  are  so  largely  used  in  perfumery 
and  for  making  artificial  liqueurs ;  and  that  of  chloroform, 
iodoform  and  chloral,  whose  importance  in  a  medicinal  sense 
is  sufficiently  well  known. 

The  knowledge  that  the  formation  of  acetic  acid  from 
alcohol  depended  upon  the  oxidation  of  the  latter,  formed  the 
basis  of  the  Quick  Vinegar  Process*  the  development  of  which 

1  Cf .  The  History  of  Physiological  Chemistry,  p.  546  et  seq. 

2  Cf.  especially  the  works  of  Pasteur,  Hansen  and  Jorgensen. 

3  E.g.  Ethyl  iodide,  bromide  and  nitrite  ;   propyl  and  isobutyl  com- 
pounds, etc. 

4  This  process  was  first  carried  out  by  Schiizenbach  in  Freiburg  in  1823, 
and  then  by  Wagenmann  in  Berlin  in  1824. 


576  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 

was  the  direct  consequence  of  Dobereiner's  work ;  while,  on 
the  other  hand,  the  technical  production  of  pyroligneous  acid, 
methyl  alcohol,  acetone,  etc.,  arose  from  the  chemical  investi- 
gation of  the  products  of  the  distillation  of  wood. 


The  Aniline  Colours  and  other  similar  Dyes.1 

There  is  no  industry  which  better  illustrates  the  practical 
good  that  accrues  from  scientific  chemical  researches  than  that 
of  coal-tar,  the  working  up  of  this  substance  and  perfecting  of 
the  numerous  methods  involved  in  so  doing  having  set  in 
motion  and  continued  to  permanently  occupy  the  energies  of  a 
large  army  of  chemists.  It  was  clearly  proved  here  that  pure 
chemical  work  was  the  necessary  preliminary  to  the  develop- 
ment of  each  and  every  branch  of  the  whole  coal-tar  industry. 
In  no  other  section  of  technical  chemistry  have  there  been  so 
many  discoveries  made  by  systematic  investigation  as  in  that 
of  artificial  dyes. 

Out  of  the  large  number  of  important  investigations  by 
which  the  industry  has  been  advanced,  only  the  most  striking 
can  be  mentioned  here,2 — those  which  have  had  an  undoubted 
influence  in  shaping  this  branch  of  chemical  manufacture. 
This  applies  to  A.  W.  Hofmann's  classical  researches  upon 
aniline  and  its  derivatives,  and  upon  rosaniline,  the  base  of 
fuchsine  (magenta),  and  its  derivatives;  and  also  to  the  notable 
work  done  by  E.  and  O.  Fischer  upon  para-rosaniline  and 

1  Cf.  especially  Nietzki's   Chemie   der   Organischen  Farbstoffe   ("The 
Chemistry  of  the  Organic  Colouring  Matters,"  1889) ;  G.  Schultz's  Chemie 
des  Steinkohlentheers,  etc.  ("The  Chemistry  of  Coal-Tar,"  etc.,  1886-90). 
R.  Mohlau's  Organische  Farbstoffe  welche  in  der  Textilindustrie  Verwendung 
finden  ("Organic  Dyes  used  in  the  Textile  Industry,"  1890) ;  and  the  very 
valuable  report  on  the  Progress  of  the  Colour  Industry,  etc.,  published 
half-yearly  by  H.  Erdmann  in  the  journal,  Chemische  Industrie.     The 
utility  of  such  a  report  may  be  gauged  from  the  extraordinary  amount  of 
literature  continually  appearing  in  this  branch  of  the  science. 

2  For  the  references  to  special  papers,   see   The  History  of  Organic 
Chemistry,  the  works  cited  in  note  1,  and  Caro's  lecture  on  the  Develop- 
ment of  the  Coal-Tar  Colour  Industry  (Ber.,  vol.   xxv.   Ref.  p.  955). 


-vi  THE  COAL  TAR  COLOURS  577 

rosaniline,  which  established  the  constitution  of  these  com- 
pounds. The  deep  significance  for  technical  industry  which 
the  investigations  of  Coupier  and  Rosenstiehl  on  the  toluidines 
possessed  is  sufficiently  well-known,  while  important  results 
also  accrued  from  these  to  the  pure  science.  The  beautiful 
discovery  of  green  dyes  from  oil  of  bitter  almonds  and  benzo- 
trichloride  by  0.  Fischer  and  Db'bner  (working  separately)  in 
1877  may  likewise  be  recalled,  as  also  the  proof  that  these 
substances  were,  like  rosaniline  and  aurine,  derivatives  of 
triphenyl-methane.  It  must  not  be  forgotten  that  Mansfield's 
work  of  fifty  years  ago  laid  the  necessary  foundation  for  the 
development  of  the  aniline  industry,1  for  it  rendered  possible 
the  production  of  benzene  and  its  homologues  from  coal-tar 
on  the  large  scale,  and  also  of  nitro-benzene. 

The  first  aniline  dye  which  was  produced  upon  a 
technical  scale  was  the  violet  prepared  by  Perkin  in  1856, 
by  acting  upon  aniline  with  bichromate  of  potash  and 
sulphuric  acid.  A.  W.  Hofmann  observed  in  1858  the 
formation  of  aniline  red  (magenta),  which  was  shortly  after- 
wards manufactured  by  another  method  by  Verguin  of  Lyons, 
and  introduced  into  commerce  under  the  name  of  fuchsine. 
This  was  quickly  followed  by  Hofmann's  discovery  of  aniline 
blue,  aniline  violet  and  aniline  green,  which  were  further 
proved  by  that  chemist  to  be  derivatives  of  fuchsine.  The 
discovery  of  methyl  violet  by  Lauth  in  1861  2  and  that  of 
aniline  black  by  Lightfoot  in  1863  were  of  great  practical 
importance.  While  the  constitution  of  this  last  compound  is 
still  enveloped  in  mystery,  that  of  the  other  aniline  dyes  is 
now  for  the  most  part  known,  thanks  especially  to  the  investi- 
gations of  E.  and  O.  Fischer,  mentioned  above.  In  addition 
to  this,  new  and  important  methods  for  the  production  of 
rosaniline  dyes  have  been  discovered  and  developed,  e.g., 
formic  aldehyde  and  carbonyl  chloride  are  now  used  for  the 
synthesis  of  magenta,  methyl  violet,  and  allied  compounds. 

1  Journ.  Chem.  Soc.,  vol.  i.  p.  244,  vol.  viii.  p.   110.     Mansfield  fell  a 
victim  to  his  work,  dying  of  the  severe  burns  which  he  received  as  the 
result  of  an  explosion. 

2  This  dye  was  not,  however,  prepared  on  the  large  scale  until  1867. 

P    P 


578  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 

Chemical  research  has  also  borne  rich  fruit  in  respect  to  the 
alizarine  industry.  This  valuable  dye  was  formerly  prepared 
entirely  from  the  madder  root,  but  is  now,  practically  speaking, 
obtained  only  from  coal-tar,  this  revolution  having  been 
brought  about  by  Graebe  and  Liebermann's  successful 
synthesis  (in  1869)  of  alizarine  from  anthracene,  a  constituent 
of  coal-tar.  In  fact,  the  madder  plantations  of  Alsace,  the 
south  of  France  and  Algiers,  which  were  in  a  flourishing  con- 
dition twenty-five  or  thirty  years  ago,  have  now  almost  ceased 
to  exist.  In  addition  to  this  great  practical  triumph,  the 
purely  scientific  results,  which  consisted  in  the  determination 
of  the  chemical  constitution  of  alizarine  and  similar  com- 
pounds, must  also  be  borne  in  mind. 

A.  Baeyer's  successful  conversion  of  phthalic  acid  into 
colouring  matters  (the  phthaleins)  was  of  practical  import- 
ance, since  it  led  to  Caro's  discovery  of  the  beautiful  eosin 
dyes,  while  it  also  proved  itself  fruitful  from  a  purely 
scientific  point  of  view,  as  the  elucidation  of  the  constitution 
of  these  phthaleins  threw  light  upon  other  branches  of  the 
subject. 

From  the  memorable  researches  of  P.  Griess  upon  the 
diazo-compounds,  supplemented  by  those  of  Caro,  Nietzki, 
Witt  and  others,  the  manufacture  of  azo-dyes  has  arisen ;  the 
modes  of  formation  and  constitution  of  these  were  so  clearly 
made  out  by  the  above  investigators  that  an  endless  series  of 
valuable  colouring  matters  can  now  be  produced  by  certain 
typical  reactions.  The  first  azo-dye  was  brought  into  com- 
merce under  the  name  of  aniline  yellow  so  long  ago  as  1864, 
without,  however,  its  true  constitution  being  known.  It  is 
only  since  1876  that  the  enormous  development  of  this 
industry  dates ;  quickly  following  upon  one  another  came 
chrysoidin,  the  tropseolines  (most  of  which  are  yellow  and 
orange  dyes),  the  Ponceaux  and  "  Fast  Red  "  of  commerce 
(red  dyes  distinguished  by  their  purity),  together  with 
Biebrich  scarlet  and  crocein  scarlet.  The  most  important 
discovery  of  recent  years  in  this  direction  was  that  of  the 
"  substantive  cotton  dyes,"  obtained  from  benzidine  and 
similar  compounds  by  Botticher  and  others  in  1884,  as 


vi  INDIGO  BLUE  AND  OTHER  DYES  579 

examples  of  which  we  may  cite  Congo  red  and  chrysamine. 
The  fact  that  there  are  more  than  150  azo-colours  in  the 
market  is  sufficient  evidence  of  the  immense  number  of  such 
compounds. 

The  chemical  investigation  of  methylene  blue  and  the 
safranines,  new  dyes  of  great  value,  has  been  of  much  import- 
ance both  practically  and  theoretically,  the  rational  composition 
of  the  former  having  been  arrived  at  by  Bernthsen,  and  that  of 
the  latter  by  Nietzki  and  Witt.  The  great  aim  of  so  many 
of  the  researches  upon  the  organic  colouring  matters,  viz., 
the  elucidation  of  their  relations  to  other  compounds  from 
which  they  are  readily  derivable,  has  in  the  above  cases  been 
attained ;  methylene  blue  is  derived  from  thio-diphenyl- 
amine,and  the  safranines  from  phenazine.  Similarly  rosaniline,. 
aurine  and  numerous  allied  substances  have  been  proved  to 
be  derivatives  of  triphenyl-methane ;  the  azo-dyes  to  be 
derivatives  of  azo-benzene  and  azo-naphthalene ;  and  alizarine, 
purpurine,  etc.,  to  be  derivatives  of  anthraquinone.  It  is  also 
now  known  that  the  indophenols  and  indamines,  the  eurho- 
dols  and  eurhodines,  the  rhodamines,  etc.,  are  derivatives  of 
definite  chemical  compounds  not  in  themselves  dyes,  but 
which  become  so  by  the  entrance  of  certain  atomic  groups 
into  the  molecule.  Various  attempts  have  lately  been  made 
by  Witt,  Nietzki  and  Armstrong  among  others,  to  discover 
definite  relations  between  the  chemical  constitution  of  dyes 
and  their  colouring  properties,  but  these  speculations  have  as 
yet  no  claim  to  be  looked  upon  as  constituting  a  theory ;  they 
are  more  or  less  only  a  re-statement  of  facts. 

The  chemical  investigation  of  indigo  blue,  the  most 
valuable  of  all  blue  dyes,  has  also  been  ardently  prosecuted, 
with  a  view  of  arriving  at  its  constitution,  which,  however,  is 
not  yet  definitely  settled.  Most  of  our  knowledge  on  the 
subject  is  due  to  v.  Baeyer.  He  succeeded  several  years  ago 
in  preparing  indigo  artificially  from  simpler  compounds  con- 
tained in  coal-tar,  but  until  quite  recently  no  one  was  able  to 
convert  any  one  of  the  known  syntheses  into  a  practical 
commercial  process.  The  new  Heumann-Lederer  method, 
however,  by  which  indigo  blue  is  prepared  from  phenyl-amido- 

p  p  2 


580  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 

acetic  acid,  is  carried  out  in  a  modified  form  by  the  well- 
known  Badische  Aniline  and  Soda  Manufactory,  so  that 
"  artificial "  indigo  is  now  in  the  market. 


Dyeing  and  Tanning. 

The  processes  by  which  colours  are  fixed  upon  vegetable  or 
animal  fibres  have  been  greatly  improved  since  the  chemical 
nature  of  dyes  came  to  be  known,  although  there  are  some 
cases  in  which  a  true  explanation  is  still  required  of  the  mode 
in  which  the  fibres  themselves  and  certain  mordants  act. 
The  earliest  attempt,  even  if  it  was  an  imperfect  one,  to  get 
clear  ideas  upon  this  subject  was  made  by  Macquer  in  1795. 
The  empiricism  which  prevailed  for  so  long  in  the  dyeing 
industry  has  gradually  been  done  away  with,  thanks  to  the 
efforts  of  chemists  to  obtain  a  truer  insight  into  the  reac- 
tions which  dyeing  involves.  Attention  must  be  called  here 
to  the  investigations  of  Knecht  on  the  subject,  according  to 
which  the  fixation  of  dyes  by  wool  fibre  is  dependent  on  the 
chemical  nature  of  the  latter. 

With  respect  to  the  application  of  the  more  important  dyes, 
previous  to  the  discovery  of  the  coal-tar  colours,  it  may  be 
mentioned  that  indigo  was  used  in  Europe  from  the  first  half 
of  last  century,  and  madder  red  from  the  second  half,  while 
picric  acid  came  into  vogue  at  the  beginning  of  the  present 
one.  The  use  of  extract  of  campechy-wood  (which  is  still 
very  considerable)  dates  from  about  the  year  1840,  and  that 
of  the  dye  from  the  yellow  berries  of  the  Chinese  plant, 
Sophora  japonica,  from  about  1848.  Reference  must  also  be 
made  to  the  improvements  in  the  application  of  metallic 
colours  in  dyeing,  e.g.,  Prussian  blue,  chrome  yellow,  chrome 
orange,  etc. 

Tanning,  whose  processes  up  to  1860  or  so  were  almost 
purely  empirical,  has  been  made  susceptible  of  scientific 
treatment  through  the  investigations  of  Knapp,  Eittner, 
Bottinger  and  others.  This  subject  ought  to  have  a  great 
interest  for  chemists,  seeing  that,  according  to  Knapp,  it  con- 


vi  CHEMICAL  PREPARATIONS  581 

stitutes  a  special  case  of  dyeing,  many  analogies  being  apparent 
between  the  two.  The  researches  on  the  various  tannic  acids 
have  been  of  value  from  a  theoretical  point  of  view,  both  to 
chemistry  and  to  vegetable  physiology.  Among  the  important 
practical  innovations,  for  which  this  branch  of  manufacture 
has  to  thank  chemistry,  the  mineral  tanning  introduced  by 
Knapp,  Heinzerling  and  others  deserves  notice.  But  there  is 
as  yet  no  general  theory  of  the  various  tanning  processes. 

Various  Chemical  Preparations. 

An  immense  industry — that  of  so-called  chemical  prepar- 
ations— has  gradually  been  developed  on  scientific  lines  from 
apparently  insignificant  beginnings,  which  had  their  origin  in 
the  work  of  the  apothecary;  such  ''preparations"  belong 
partly  to  inorganic,  and  partly  to  organic  chemistry.1  As 
instances  of  this  we  may  take  the  great  increase  in  the  pro- 
duction of  silver  salts,  bromine  and  iodine  for  photographic 
and  other  purposes,  and  the  manufacture  of  numberless  other 
metallic  salts,  not  to  speak  of  newly  introduced  compounds 
like  the  peroxides  of  hydrogen  and  sodium.  The  already 
imposing  list  of  inorganic  preparations  is  being  continually 
added  to.  Here  again  it  is  scientific  investigation  which  has 
led  to  the  use  of  such  substances  in  manufactures  generally. 

The  manufacture  of  organic  preparations  is  still  more 
extensive.  What  a  multiplicity  of  compounds,  for  instance, 
is  comprised  under  the  term  alcoholic  preparations !  The 
various  alcohols  themselves,  their  ethers  and  esters,  chloro- 
form, chloral,  iodoform,  aldehyde,  etc.,  are  now  all  essential  to 
chemical  manufactures  and  to  medicine;  while  among  the 
phenols,  carbolic  acid  and  the  cresols,  hydroquinone,  pyro- 
catechin,  resorcin,  pyrogallol  and  others,  together  with  many 
of  their  derivatives,  have  found  extended  application  in 
medicine,  photography,  and  for  disinfecting  and  other  pur- 
poses. 

1  For  the  scientific  importance  of  this  branch  of  industry,  and  indeed 
of  technical  chemistry  generally,  compare  H.  Wichelhaus's  Wissenschaftliche 
Bedeutung  chemischer  Arbeiten  (1893). 


582  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 

The  manufacture  of  organic  acids,  of  which  acetic  acid  has 
already  been  referred  to,  also  shows  a  continuous  develop- 
ment ;  many  of  these  compounds  which  occur  in  nature  are 
now  prepared  artificially  on  a  large  scale,  the  methods  fol- 
lowed being  based  upon  scientific  investigation.  Thus,  sali- 
cylic acid  is  produced  from  carbolic  (Kolbe  and  R  Schmitt), 
benzoic  acid  from  toluene,  phthalic  acid  from  naphthalene, 
cinnamic  acid  from  benzoic  aldehyde,  and  oxalic  acid  from 
wood  by  treating  the  latter  with  alkali,  etc.  This  last  pro- 
cess was  discovered  by  Gay-Lussac  in  1829,  and  its  practical 
application  now  constitutes  an  important  industry. 

The  manufacture  of  aldehydes  is  likewise  the  result  of 
scientific  work.  Some  of  these,  such  as  benzoic  aldehyde,  are 
of  importance  for  the  colour  industry,  while  others,  like 
vanillin  and  piperonal,  are  flavouring  essences  or  scents.  The 
so-called  ethereal  oils  belong  to  this  last  category ;  and  much 
has  been  done  by  the  researches  of  Wallach,  Semmler, 
Tiemann,  Bertram  and  others  to  place  their  manufacture  on  a 
sound  basis.  Systematic  investigation  has  also  brought  about 
great  advances  with  regard  to  the  vegetable  alkaloids,  as  is  evi- 
dent in  the  strenuous  endeavours  to  prepare  artificial  com- 
pounds which  shall  have  the  same  physiological  actions  as 
quinine,  morphine,  atropine,  etc. 


Various  other  Products  from  Coal-tar  ;  Illuminants. 

Coal-tar  is  the  raw  material  from  which  many  other 
organic  preparations  are  obtained, — it  is,  in  fact,  a  rich  mine 
for  numberless  useful  substances.  Formerly  a  troublesome 
waste  material,  it  is  now  of  at  least  equal  value  with  the  other 
products  from  the  distillation  of  coal.  The  manufacture  of 
ammonia  and  salts  of  ammonia  from  gas  liquor  is  now  a 
thoroughly  rational  one,  thanks  to  the  careful  chemical  ex- 
amination of  the  latter,  and  it  forms  a  large  and  important 
branch  of  industry.  In  consequence  of  the  rapidly  increasing 
consumption  of  ammonia  salts,  more  and  more  attention  is 
being  paid  to  the  problem  of  utilising  the  ammonia  which 


vi  OTHER  COAL-TAR  PRODUCTS ;    ILLUMINANTS  583 

escapes  into  the  air  when  coal  is  either  converted  into  coke  l 
or  is  completely  burnt.  L.  Mond  2  has  lately  set  up  an  in- 
geniously constructed  apparatus  on  a  large  scale  at  North wich 
in  Cheshire,  which  serves  not  merely  for  heating  purposes, 
but  at  the  same  time  allows  of  the  condensation  of  the  am- 
monia produced.  The  manufacture  of  coal-gas  has  developed 
in  a  more  empirical  manner,  and  has  thus  been  less  influenced 
by  recent  chemical  researches  bearing  upon  the  subject  than 
many  other  branches  of  industry  ;  but  here,  too,  much  good 
has  been  done  by  the  application  of  the  methods  of  gas 
analysis,  and  chemical  experiments  have  also  borne  fruit  in 
the  introduction  of  improved  modes  of  purifying  gas.  It  is 
interesting  to  note  here  that  acetylene,  which  is  itself  an 
electro-technical  product,  appears  destined  to  enter  into 
serious  competition  as  an  illuminant  with  the  electric  light. 

The  great  influence  which  chemical  investigations  have 
exercised  upon  the  production  of  other  illuminants  has  already 
been  touched  upon,  and  is  shown  in  the  manufacture  of  stearic 
acid  from  animal  fats.3  Attempts  have  been  made  upon  the 
large  scale  to  employ  (the  liquid)  oleic  acid,  which  occurs  so 
plentifully  in  nature,  for  the  production  of  candles,  by  making 
use  of  the  well-known  reaction  with  caustic  potash,  which 
converts  it  into  (solid)  palmitic  acid.  The  flourishing  paraffin 
manufacture  4  of  Scotland  and  Germany,  with  its  various 
valuable  by-products,  also  owes  much  to  chemistry.  '  But  the 
latter  has  still  many  problems  to  solve  both  in  this  field  and 
in  that  of  the  petroleum  industry,  as  is  evident  from  the 
recent  work  of  Markownikoff,  Beilstein  and  Engler  upon  the 
chemical  nature  of  petroleum  ;  these  researches  are  bringing 
us  nearer  to  a  solution  of  the  origin  of  this  useful  substance. 
A  short  reference  has  already  been  made  (p.  425)  to  the 
theoretical  points  which  bear  upon  illumination,  and  to  the 
causes  of  the  luminosity  or  non-luminosity  of  different  flames.5 

1  Tar  is  now  an  important  by-product  in  coking. 

2  Journ.  Chem.  Ind.  for  1889,  p.  505.  3  Cf.  p.  569. 

4  Paraffin,  which  was  discovered  in  wood-tar  by  Reichenbach  in  the 
year  1830,  is  obtained  practically  from  lignite  or  bituminous  shale. 

5  Cf.  also  Hans  Bunte  on  "Recent  Developments  in  Gas -Lighting,"  Her., 
vol.  xxxi.  p.  5. 


584  HISTORY  OF  TECHNICAL  CHEMISTRY  CHAP. 


Heating  Materials. 

That  the  knowledge  gained  through  chemical  analysis  of 
the  composition  of  different  kinds  of  fuel,  of  their  products  of 
combustion,  and  of  their  chemical  behaviour  generally,  is  of 
the  first  consequence,  requires  no  demonstration.  It  is  of 
course  impossible  to  refer  here  to  the  large  number  of  im- 
portant investigations  in  this  field,  but  reference  must  be  made 
to  the  fundamental  work  of  E.  Richters  and  F.  Muck  ; l  to  the 
improvements  in  the  methods  of  analysis  of  furnace  gases,2 
which  permit  of  conclusions  being  drawn  with  regard  to  the 
course  of  any  particular  combustion  ;  and  to  the  improvements 
in  heating  apparatus  which  have  been  brought  about  by 
chemical  work, — the  construction  of  generators  and  regener- 
ators, whose  history  is  inseparably  connected  with  the  names 
of  Aubertot,  Thomas,  Laurens  and,  above  all  others,  Siemens. 
"  Water  gas,"  prepared  by  passing  steam  over  red-hot  coal,  is 
now  much  used  for  heating  and  illuminating  purposes,  and  it 
will  undoubtedly  become  even  more  employed  in  time  ;  this 
is  notably  a  case  in  which  a  great  manufacture  has  arisen 
from  experiments  on  a  very  small  scale. 

Speculations  regarding  the  origin  of  coal  deposits,  and  the 
metamorphoses  which  these  undergo,  have  received  much 
support  from  the  work  which  has  been  done  upon  the  com- 
position of  coal  and  of  the  gases  which  are  found  enclosed  in 
it.  And  it  is  mainly  to  chemical  research  that  we  owe  the 
means  of  averting  or  at  least  diminishing  the  great  dangers 
to  which  coal  miners  are  exposed  from  explosions  of  fire-damp, 
— witness  the  Davy  safety  lamp.  The  subject  is  still  being 
assiduously  worked  at  from  time  to  time  both  by  chemists 
and  by  practical  engineers.  The  zeal  which  the  various 
recent  "  Fire-Damp  Commissions "  of  different  countries 
showed  in  their  investigations  is  still  fresh  in  the  public 
memory. 

1  Cf.  Muck,  Grundzuge  und  Ziele  der  Steink&hlenchemie  ("  The  Outlines 
and  Aims  of  the  Chemistry  of  Coal,"  2nd  edition,  1891). 

2  Cf.  Winkler's  Anleitung  zur  technischen  Gasanalyse   ("Methods    of 
Technical  Gas  Analysis") ;  also  p.  392  of  this  book. 


vi  VALUE  OF  CHEMICAL  RESEARCH  585- 

The  above  short  sketch  is  sufficient  to  indicate  how 
enormous  have  been  the  benefits  which  laboratory  research 
has  conferred  upon  every  branch  of  technical  chemistry,  and 
how  the  latter  has  been  raised  to  a  higher  level  by  a  con- 
tinuous infusion  of  the  scientific  spirit.  Nowhere  can  we  find 
a  better  illustration  of  Bacon's  maxim  :  Scientia  estpotentia. 


586        CHEMICAL  INSTRUCTION  IN  THE  19TH  CENTURY    CHAP. 


THE  GROWTH  OF  CHEMICAL  INSTRUCTION  IN  THE  NINE- 
TEENTH CENTURY,  MORE  ESPECIALLY  IN  GERMANY,  t 

At  the  beginning  of  this  century  there  was  a  marked  want 
of  those  facilities  which,  during  the  last  few  decades,  have 
been  at  the  command  of  any  one  desirous  of  devoting  himself 
to  the  study  of  chemistry.  At  that  time  there  were  practi- 
cally no  laboratories  for  general  instruction.  In  lectures  upon 
physics,  mineralogy  and  anatomy,  chemistry  was  relegated  to 
a  very  subordinate  place.  It  is  true  that  there  were  chairs  of 
chemistry  in  various  universities  and  colleges,  but  the  lectures 
on  this  subject  were  usually  conjoined  with  those  upon  one  of 
the  others,  just  named,  in  such  a  manner  that  chemistry  was 
forced  into  the  background.  Chemical  literature,  lastly,  was 
still  poor  in  works  which  either  gave  a  review  of  the  state  of 
the  science  at  the  time,  or  furnished  regular  reports  of  the 
latest  discoveries  in  it. 

In  France,  where  towards  the  end  of  the  eighteenth 
century  it  began  to  be  perceived  that  instruction  in  natural 
science  must  be  fostered  by  every  means  at  command,  a  start 
was  made  far  before  any  other  countries  in  respect  to  the  devel- 
opment of  chemical  study.  Up  till  then  apothecaries'  shops 
were  the  only  places  where  work  in  practical  chemistry  could 
be  carried  on,  and  there  merely  after  certain  prescriptions  and 
not  according  to  scientific  methods.  Yauquelin  was  the  first 
to  organise  a  course  of  instruction  in  his  small  laboratory  for 
students  anxious  to  learn,  while  after  the  first  decade  of  the 
century  Gay-Lussac  and  Thenard  also  taught  in  their  labor- 
atories, which  however  were  exceedingly  cramped.  Fourcroy 
had  already  done  an  immense  deal  to  raise  the  standard  of 
scientific  instruction,  and  he  contributed  greatly  by  his  bril- 

1  In  addition  to  the  books  referred  to  in  the  succeeding  pages,  compare 
E.  Zoller's  book,  mentioned  on  p.  556,  and  also  Wallach's  essay  in  Lexis' 
Die  deutschen  Universitdten,  vol.  ii.  p.  35  (1893). 


vi  DEVELOPMENT  OF  CHEMICAL  INSTRUCTION  587 

liant  lectures l  to  ensure  to  chemistry  a  worthy  position  as  a 
course  of  study.  But  it  was  only  after  Liebig  had  taken  up 
the  subject  with  his  accustomed  energy,  that  chemistry  came 
to  be  taught  in  the  higher  schools  in  essentially  the  same 
manner  as  that  to  which  we  are  now  accustomed.2 

The  importance  of  lectures  on  chemistry,  illustrated  by 
experiments,  for  the  proper  understanding  of  chemical  re- 
actions, was  recognised  a  long  time  ago,  more  especially  in 
France.3  But  during  the  early  decades  of  the  present 
century  this  aid  to  study  hardly  existed  in  the  higher 
teaching  institutions  of  Germany,  and  the  so-called  natural 
philosophy  of  that  day  was  such  that  it  sorely  handicapped 
the  development  of  exact  scientific  research.  Chemistry,  in 
particular,  was  looked  upon  by  the  natural  philosophers 
as  being  no  science  at  all,  and  was  degraded  by  them  into  a 
mere  experimental  art. 

The  efforts  made  by  Davy,  however,  backed  as  these  were 
by  an  exceptional  talent  for  devising  and  carrying  out  experi- 
ments, and  also  by  Gay-Lussac  and  Thenard's  admirable 
lectures,  resulted  from  the  beginning  of  this  century  in  an 
increasing  demand  for  lectures  with  appropriate  experimental 
illustrations.  Liebig  has  left  to  us  a  graphic  description  of 
the  effect  which  Gay-Lussac  and  Thenard's  discourses  had  upon 
himself,  at  that  time  a  youth  of  eighteen.  From  this  account 
it  is  evident  that  these  lectures  gained  an  indescribable 
charm  from  the  "  mathematical  method,  which  transformed 
each  problem — wherever  possible — into  an  equation,"  and  by 
a  lucidity  of  expression  which  was  "  conjoined  with  a  wonder- 
ful experimental  skill." 

We  know  tha,t  it  was  the  lectures  given  by  Marcet  in 
London  which  induced  Berzelius  in  1 8 1 2  to  abandon  the  old 

1  Compare  Pariset's  vivacious   £loge  de  Fourcroy,    cited  in    Hofer's 
Histoire,  vol.  ii.  p.  557. 

2  Cf.  below ;  also  0.  L.  Erdmann's  valuable  and  too  little  known  pam- 
phlet, Ueber  das  Studium  der  Chemie.     Liebig  willingly  acknowledged  the 
great  debt  which  he  owed  to  Gay-Lussac,  with  whom  he  had  worked  as  a 
student  (cf.  Ber.,  vol.  xxiii.  Ref.  p.  824). 

3  Cf.  The  work  of  Rouelle,  p.  118,  note. 


588        CHEMICAL  INSTRUCTION  IN  THE  19TH  CENTURY    CHAP, 

method  of  instruction  and  to  make  use  of  experiments  in 
introducing  students  to  chemical  science  ;  and  the  result  of 
this  was  conclusive.  The  subsequent  good  achieved  by 
Faraday,  Liebig,  Wohler,  Bunsen,  Wurtz,  Kolbe  and  especially 
A.  W.  Hofmann,  through  the  new  lecture  experiments  which 
they  devised,  requires  but  to  be  mentioned.  Those  experi- 
ments and  many  others  have  since  taken  a  permanent  place 
in  the  teaching  of  chemistry. 

Practical  instruction  in  chemical  laboratories,  as  com- 
monly carried  out  at  the  present  day,  was  developed  by 
Liebig.  The  gradual  introduction  into  laboratories,  through 
his  example,  of  teaching  methods  based  upon  a  strictly 
scientific  foundation,  created  a  wholesome  reaction  against 
the  still  prevailing  tendency  of  the  natural  philosophy  'of 
the  day,  which  was  combated  by  Liebig  all  the  more 
energetically  from  his  having  himself  suffered  under  its 
pernicious  influence.1  He  first  emphasised  with  all  the  force 
at  his  command  that  the  true  centre-point  of  chemical  study 
lay  not  in  lectures  but  in  practical  work.  With  what  energy 
and  under  what  sacrifices  he  gave  personal  proof  of  this  is 
well  known.2  True,  Berzelius  had  already  given  instruction 
in  his  laboratory  to  a  limited  number  of  pupils,  mostly  elder 
ones,  who  in  their  turn  propagated  their  master's  doctrines, 
but  the  real  development  of  chemical  teaching  is  due  to 
Liebig.  He  it  was  who  laid  down  the  order,  now  classical, 
in  which  the  various  branches  of  the  subject  should  succeed 
one  another,  viz.  (1)  the  systematic  study  of  qualitative 
and  then  of  quantitative  analysis,3  (2)  exercises  in  the  making 
of  preparations,  and  (3)  attempts  at  independent  research. 

Liebig's  laboratory  was  the  centre  from  which,  after 
about  the  end  of  the  twenties,  the  brightest  light  radiated. 
He  was  the  first  to  enunciate  and  apply  the  principle  that 

1  Cf.  pp.  263-264. 

2  Cf.  the  Memoir  of  him  by  Kolbe  in  the  Journ.  pr.   Chem.   (2),  vol. 
viii.  p.  435 ;  also  Weihrich's  essay  (already  quoted),  p.  264,  note  2. 

3  The  co-operation  here  of  R.  Fresenius,  who  was  at  one  time  assistant 
to  Liebig,  and  the  stimulus  given  by  him  towards  the  creation  of  a  system- 
atic course  of  analytical  work,  will  remain  in  lasting  remembrance  (cf.  p. 
389) ;  the  great  service  rendered  by  Will  must  also  be  emphasised. 


vi  m    ERECTION  OF  GENERAL  LABORATORIES  589 

his  pupils,  be  they  students  of  pharmacy,  technical  chemistry, 
mineralogy  or  physiology,  should  learn  to  treat  chemical 
questions  practically.  Thanks  to  the  wonderful  stimulus 
which  he  was  able  to  exert,  there  was  founded  in  his  modest 
laboratory  a  school  which  left  its  stamp  upon  the  chemistry 
of  the  succeeding  decades,  and  whose  beneficial  influence 
is  still  felt  all  over  the  world  at  the  present  day.  The 
peculiarity  of  Liebig  as  a  great  teacher  consisted,  according 
to  Kolbe,1  in  his  "  being  able  to  stimulate  his  pupils  to  original 
thought,  and  to  inoculate  them  with  the  scientific  spirit 
while  they  were  working  out  his  own  ideas." 

The  most  eminent  among  the  teachers  of  chemistry  on  the 
Continent  since  the  time  of  Liebig,  of  whom  Wohler,  Bunsen, 
Erdmann,  Kolbe,  Kekule,  Wurtz  and  A.  W.  Hofmann  may  be 
named  here,  made  the  essential  principles  of  his  method  of 
teaching  their  own,  while  each  added  of  course  much  that 
was  new,  with  the  most  beneficial  results.  The  principles  on 
which  chemistry  is  taught  are  the  same  both  in  the  German 
Universities  and  the  Technical  High  Schools. 

Numerous  teaching  laboratories  were  in  due  course 
founded  in  the  other  German  universities  and  colleges  on 
the  model  of  the  Giessen  one,  and  about  these  a  few  notes 
may  fitly  find  a  place  here.  How  badly  off  Austria  and 
Prussia  were  in  this  respect,  even  so  recently  as  the  year 
1840,  was  vividly  depicted  by  Liebig  in  his  two  pamphlets 
entitled  Ueber  den  Zustand  der  Chemie  in  Qsterreich? — und 
in  Preussen  3  ("  On  the  State  of  Chemistry  in  Austria,  and  in 
Prussia  ").  Even  in  Berlin  there  were  up  to  that  time  no 
facilities  for  the  study  of  practical  chemistry.  H.  Rose  and 
Mitscherlich  were  hardly  in  a  position  to  give  regular 
laboratory  instruction,  the  space  and  means  generally  at 
their  disposal  being  very  insufficient ; 4  and  the  same  thing 
applied  to  the  other  "  high  schools  "  of  Prussia. 

1  In  his  work,  Das  chemische  Laboratorium  der  Universitdt  Marburg, 
etc.,  p.  26.     In  this  the  principles  of  Liebig's  method  of  instruction  are 
described  with  exceptional  clearness. 

2  Ann.  Chem.,  vol.  xxv.  p.  339.        3  Ibid.,  vol.  xxxiv.  pp.  97  and  355. 
4  Cf .  A.  W.  v.  Hofmann' s  Chemische  Erinnerungen  aus  der  Berliner  Ver- 

ffangenheit  (1882V 


590        CHEMICAL  INSTRUCTION  IN  THE  19TH  CENTURY     CHAP. 

In  the  meantime  laboratories  began  to  be  established 
elsewhere  in  Germany,  e.g.  at  Gottingen,  where  Wohler  set 
up  one  in  the  course  of  the  thirties,  to  be  rebuilt  and  enlarged 
in  1888;  and  at  Marburg,  where  Bunsen  began  a  regular 
practical  course  in  1840.  The  chemical  laboratory  which 
'Erdmann1  instituted  at  Leipzig  in  1843  remained  for  a 
long  time  the  pattern  of  what  a  well-organised  place  of  the 
kind  should  be.  It  was  only  in  the  course  of  the  fifties  that 
Heidelberg,  Karlsruhe,  Breslau,  Greifswald  and  Konigsberg 
followed  suit  with  laboratories  properly  equipped  for  the 
purposes  in  view. 

A  new  era  in  the  history  of  chemical  institutions  began 
about  the  middle  of  the  sixties,  the  famous  laboratories  at 
Bonn  and  Berlin,2  both  built  according  to  A.  W.  Hofmann's 
plans,  being  completed  in  1867,  while  the  equally  well- 
known  Leipzig  laboratory,  designed  by  Kolbe,  was  finished 
in  1868.  The  experience  gained,  both  during  the  erection 
of  these  and  by  their  subsequent  use,  has  been  applied  with 
good  results  in  the  planning  of  later  and  even  in  some 
respects  finer  institutes.  Of  the  other  new  German  labora- 
tories, those  of  Aachen3  (18 70),  Dresden  (1875),  Munich 
(1877),  the  Berlin  Technical  College  (1879),  Kiel  1880), 
Strassburg  (1885),  Gottingen  (1888),  Heidelberg  (1892) 
and  Halle  (1894),  may  be  specially  named.  In  Austria, 
too,  various  excellent  laboratories,  have  been  built  during  the 
last  two  decades,  among  which  those  of  Graz  and  Vienna 
stand  out  prominent. 

1  Otto  Linne  Erdmann  was  born  at  Dresden  in  1804,  and  died  in  1867 
while  holding  the  post  of  Professor  of  Chemistry  at  Leipzig,  where,  since 
1827,  and  especially  after  the  organisation  of  the  laboratory  which  he  had 
himself  founded,  he  laboured  with  wonderful  energy  and  with  great  suc- 
cess.    His  rich  experiences,  and  the  views  to  which  they  gave  rise,  were 
set  forth  in  the  weighty,  if  short,  pamphlet  entitled,  Ueber  das  Studium 
der  Chemie  (1861).     That  he  was  also  active  in  a  literary  sense,  his  Lehr- 
buch  der  Chemie  and  Orundriss  der  Waarenkunde  ("  Outlines  of  a  Knowledge 
of  Technical  Products  "),  etc.,  prove.     In  1828  he  started  the  Journal  fur 
technische  und  okonomische  Chemie,  which   developed   in    1834    into   the 
Journal  fiir  praktische  Chemie.      His  numerous  experimental   researches 
have  helped  to  enrich  mineral  chemistry,  the  chemistry  of  the  carbon  com- 
pounds, and  also  chemical  technology. 

2  Up  to  that  date  Berlin  was  without  any  large  laboratory  for  general 
instruction.  3  ^  ^ix  la  Chapelle. 


vi  TEACHING  IN  FRANCE  AND  GREAT  BRITAIN  591 

Among  the  many  German  University  teachers  who  have 
exercised  a  marked  influence  during  the  last  forty  years, 
and  who  have  not  been  already  mentioned,  von  Baeyer 
takes  a  foremost  place,  while  in  addition  there  are  Glaus, 
Erlenmeyer,  E.  Fischer,  Fittig,  Ladenburg,  Lothar  Meyer, 
Victor  Meyer,  Strecker  and  Wislicenus. 

The  other  countries  of  Europe  have  not  kept  pace  with 
Germany  in  the  establishment  of  institutes  for  the  teaching 
of  chemistry.  There  were,  it  is  true,  laboratories  in  France 
at  the  beginning  of  the  century  in  which  such  men  as  Gay- 
Lussac,  The"nard,  Dulong,  Chevreul  and  others  carried  out 
their  work,  but  the  opportunities  for  general  chemical 
instruction  were  extremely  few,  the  above  institutes 
receiving  but  trifling  support  from  the  State.  And  the 
fees  which  a  laboratory  student  had  to  pay  were  ex- 
orbitant, being  1500  francs  for  an  eight-months'  course. 
Even  the  efforts  made  to  establish  teaching  laboratories 
during  the  thirties  by  Dumas  and  Pelouze,  and  later  on 
by  Wurtz,  Gerhardt  and  others,  were  followed  with  but  scant 
success,  because  these  chemists  were  thrown  entirely  on  their 
own  resources. 

Those  conditions  were  only  improved  after  Wurtz  in 
1869  presented  his  report x  upon  the  German  laboratories 
to  the  French  Minister  of  Education,  in  which  he  insisted 
upon  the  necessity  for  establishing  properly  equipped 
laboratories  for  practical  instruction  in  chemistry.  He 
stated  that  at  that  date  there  was  in  France  only  one 
chemical  institute  with  the  necessary  means  at  command 
— that  of  the  ficole  Normale  Supfrieure,  under  the  direction 
of  H.  St.  Claire  Deville.  E.  Fremy,  well  known  by  his  work 
in  inorganic  and  technical  chemistry,  had  set  up  a 
laboratory  in  1864;  and  in  the  introduction  to  his 
Encyclopedia  of  Chemistry  he  gives  a  detailed  account  of 
the  principles  upon  which  chemistry  was  taught  in  it. 
Fremy  died  in  Paris  in  1 8  9  4,  at  the  age  of  eighty. 

In  Great  Britain,  too,  it  is  only  within  the  last  twenty-five 
or  thirty  years  that  the  lack  of  roomy  and  well-equipped 

1  Les  halites  Etudes  pratiques  dans  les  Universite's  allemandes  (1870). 


592         CHEMICAL  INSTRUCTION  IN  THE  19TH  CENTURY    CHAP. 


laboratories  has  been  remedied;  and  to  this,  especially  of 
late  years,  the  recognition  of  the  fact  that  the  industries  of 
the  country  would  be  enormously  benefited  thereby  has 
greatly  contributed.  The  first  laboratory  in  Britain,  small 
though  it  was,  in  which  a  young  man  had  the  opportunity 
of  working  practically  at  the  subject,  was  that  of  Thomas 
Thomson1  in  Glasgow, established  in  1 8 1 7.  This  was  therefore 
the  first  chemical  laboratory  for  general  instruction.  After  the 
founding  of  the  College  of  Chemistry 2  in  London  in  1845 
(which  quickly  rose  into  a  flourishing  condition  under  the 
leadership  of  A.  W.  Hofmann),  the  country  became  by 
degrees  well  supplied  with  suitably  equipped  laboratories, 
in  which  instruction  substantially  upon  the  lines  of  the 
German  school  was  given.  In  addition  to  the  Universities 
and  a  few  of  the  older  institutions  for  higher  education  in 
London,  etc.,  each  of  the  University  Colleges  now  scattered 
over  the  country  possesses  its  own  chemical  laboratory,  and 
the  same  thing  applies  in  greater  or  less  degree  to  the 
colleges  and  schools  for  technical  instruction  which  continue 
to  be  founded  with  considerable  rapidity.  In  fact,  the  mind 
of  the  country  is  now  becoming  to  some  extent  awakened  to 
the  importance  of  the  subject.  Among  the  chemical  labor- 
atories, more  or  less  recently  erected,  those  at  Manchester, 
Leeds,  Edinburgh,  the  City  and  Guilds  Institute  (South 
Kensington,  London),  and  Cambridge  may  be  specially 
named. 

In  Switzerland,  Holland,  Belgium,  Italy,  Russia,  Scandi- 
navia and  America  are  now  to  be  found  numerous  chemical 
teaching  institutes,  arranged  and  fitted  up  in  accordance  with 
the  requirements  of  the  age. 

The  increasing  necessity  for  specialisation  in  chemistry, 

1  Cf.  p.  194. 

2  The  College  of  Chemistry  was  taken  over  by  Government  in  1853,  and 
was  made  a  part  of  the  Royal  School  of  Mines,  while  at  the  same  time 
retaining  a  quasi-separate  existence  under  its  own  name.     In  1872  it  was 
moved  from  its  old  premises  in  Oxford  Street  to  South  Kensington.     The 
name  College  of  Chemistry  was  finally  merged  into  that  of  the  Normal 
School  of  Science  and  Royal  School  of  Mines  in  1881.     In  1890  the  N.  S.  S. 
and  R.  S.  M.  were  rechristened  the  Royal  College  of  Science. 


vi     IMPROVEMENTS  IN  LABORATORY  APPARATUS    593 

and  the  consequent  resulting  division  of  labour,  has  made 
itself  evident  in  the  establishment  of  laboratories  for  certain 
definite  purposes  only.  Thus  we  now  find  institutions 
existing  solely  for  researches  in  chemical  physics,  agri- 
cultural chemistry,  technological  chemistry,  physiological 
chemistry,  pharmaceutical  chemistry  and  hygiene.  What 
a  contrast  between  the  present  facilities  for  chemical  study 
and  the  opportunities  of  only  a  few  decades  back ! 

Among  the  more  important  improvements  which  have 
been  aimed  at  and  achieved  in  the  construction  of  labora- 
tories during  these  last  decades,  are  those  which  have 
reference  to  arrangements  for  supplying  plentiful  ventilation 
and  good  light.  Then  the  means  for  carrying  out  chemical 
operations  have  also  been  both  greatly  increased  and  im- 
proved, e.g.  coal  and  charcoal  fires  have  been  superseded 
by  gas,  the  Bunsen  burner  having  played  an  important  part 
here.  The  apparatus,  too,  employed  by  chemists  has  under- 
gone many  refinements,  as  is  readily  seen  in  the  delicate 
balances  and  the  appliances  for  filtering,  distilling,  heating 
under  ordinary  and  increased  pressure,  etc.,  which  are  now  in 
common  use.1  The  making  of  preparations  is  at  present  an 
easy  matter  compared  with  what  it  used  to  be,  this  being  in 
part  due  to  better  methods  of  procedure ;  by  far  the  greater 
number  of  these  substances  can  now  in  fact  be  bought  pure. 
Chemists  are  thus  freed  from  the  difficulty  which 

1  The  following  points  may  be  referred  to  with  advantage  here  : — Water 
suction  pumps  were  introduced  by  Bunsen  in  1868,  and  injector  pumps  a 
little  later  by  Arzberger,  Zulkowsky,  etc. ,  to  be  used  for  filtering  and  pro- 
ducing a  vacuum.  Simple  distillation  was  immensely  facilitated  by  the 
introduction  of  the  Liebig  condenser,  while  a  reflux  condenser  appears  to 
have  been  first  made  use  of  by  Kolbe  and  Frankland  in  1847.  Dittmar 
and  Anschiitz  (independently  of  one  another)  were  the  first  to  distil  under 
diminished  pressure.  The  water-bath,  for  which  Berzelius  devised  a  con- 
venient form,  has  since  been  improved  by  arrangements,  elaborated  by 
Fresenius,  Bunsen,  Kekule  and  others,  for  keeping  the  water  in  it  at  a 
constant  level.  The  use  of  gas  regulators  for  the  maintenance  of  a  uniform 
temperature  may  also  be  mentioned,  and  this  again  in  conjunction  with 
Bunsen's  name.  Caoutchouc  tubing  appears  to  have  been  first  brought 
into  general  employment  by  Berzelius.  And  the  first  mention  of  the  use  of 
sealed  tubes  for  carrying  out  chemical  reactions  under  pressure  is  to  be 
found  in  Wohler  and  Liebig's  research  on  uric  acid  derivatives. 

Q  Q 


594       CHEMICAL  INSTRUCTION  IN  THE  19-TH  CENTURY    CHAP. 

was  ever  present  with  them  sixty  or  seventy  years 
ago, — of  having  laboriously  to  prepare  even  their  most 
simple  reagents.  Berzelius  had  to  make  his  own  yellow 
prussiate  of  potash,  the  pure  mineral  acids,  spirits  of  wine 
for  burning,  etc.  And  how  simple  were  the  arrangements 
generally  in  his  laboratory  ! l  Many  of  the  aids  to  practical 
work  which  are  now  accepted  as  a  matter  of  course  had 
in  his  day  no  existence. 


Chemical  Literature. 

The  manuals  and  text-books  of  chemistry  and  also  the 
journals  have  increased  to  a  very  large  extent  of  late  years, 
thus  greatly  facilitating  the  study  of  the  science.  For  a  long 
time  Lavoisier's  Traite"  de  Chimie  remained  the  pattern  of 
what  such  a  book  should  be,  and  upon  it  numerous  others 
were  modelled,  e.g.  those  of  Girtanner,  Gren,  and  Thomson. 
Berzelius'  large  book  on  chemistry  exercised  an  extraordinary 
influence,  especially  after  it  had  been  translated  into  other 
languages,  and  contributed  in  an  exceptional  degree  to  the 
spread  of  chemical  knowledge. 

This  great  work,  great  both  in  its  conception  and  in  the 
manner  in  which  it  was  carried  out,  was  afterwards  taken  in 
many  cases  as  the  standard  for  the  arrangement  of  chemical 
matter  in  text-books  which  appeared  later.  Of  these  a  few 
may  be  mentioned  here  : — Thenard's  TraiU  de,  Chimie  $Umen- 
taire ;  Mitscherlich's^eAr&wcA  der  Chemie ;  Liebig's  Organische 
Chemie  ;  Wohler's  Grundriss  der  Chemie  ("  Outlines  of 
Chemistry  "),  from  which  sprang  the  well-known  and  widely- 
read  work  of  the  same  title  by  Fittig  ;  Regnault's  Cours 
Mtmentaire  de  Chimie,  which  formed  the  basis  of  Strecker's 
Kurzes  Lehrbuch  der  Chemie ;  Graham's  Elements  of  Chemistry, 
from  which  arose  Otto's  large  work,  the  organic  portion  of 
which  was  written  by  Kolbe,  while  H.  Kopp  wrote  the 
general  theoretical  part  (inorganic  and  organic),  and 
Buff  and  Zamminer  the  physico-chemical.  Gerhardt's 

1  Cf.  Wohler's  description,  Ber.,  vol.  xv.  p.  3139. 


vi         TEXT-BOOKS  AND  DICTIONARIES  OF  CHEMISTRY        595 

Traite  de  Chimie  Organique  (1853  to  1856),  known  as 
the  text-book  of  the  type  theory,  greatly  contributed 
to  the  propagation  of  the  latter,  while  Kekul^'s  book, 
which  began  to  appear  shortly  after  the  last  volume  of 
Gerhardt's  Traitt  had  been  published,  served  to  develop  the 
"  typical "  view,  and  (in  its  second  volume)  strengthened  his 
own  assumption  as  to  the  mode  in  which  atoms  are  combined 
with  one  another,  i.e.  the  structure  theory.  It  is  unnecessary 
to  mention  here  even  a  few  of  the  numerous  text-books  of 
chemistry  which  have  been  written  since  then,  for,  belonging 
as  they  do  to  the  present  era,  they  are  already  sufficiently 
well  known.  A  palpable  want  has  recently  been  supplied 
by  the  publication  of  W.  Ostwald's,  Nernst's  and  Horstmann's 
admirable  text-books  of  general  theoretical  and  physical 
chemistry,  while  Lothar  Meyer's  Moderne  Theorien  has 
greatly  helped  to  extend  the  interest  felt  in  questions  of 
theoretical  chemistry.  Some  of  the  best  known  text-books 
on  technical  and  physiological  chemistry  have  been  already 
referred  to. 

There  has  likewise  been  no  lack  of  chemical  encyclo- 
paedias since  the  great  success  of  Liebig,  in  conjunction  with 
Wohler  and  Poggendorff,  in  the  Handworterluch  der  reinen 
und  angewandten  Chemie,  which  began  to  appear  in  183*7. 
Wurtz's  Dictionnaire  de  Chimie  pure  et  applique'e,  Watts' 
Dictionary  of  Chemistry,  and  Ladenburg's  Handworterbuch 
der  Chemie  have  been  written  upon  a  similar  plan.  The 
publication  of  Fremy's  Encyclope'die  de  Chimie  must  also  be 
recalled. 

Among  the  larger  treatises  of  chemistry,  which  are 
intermediate  between  the  text- books  proper  and  the 
dictionaries,  that  of  L.  Gmelin  justly  excited  the  admiration 
of  his  contemporaries  by  its  consistent  thoroughness.  In 
Beilstein's  Handlmch  der  Organischen  Chemie,  already  in 
its  third  edition,  the  present  huge  mass  of  material 
on  the  subject  has  been  sifted  and  arranged  in  a  masterly 
manner.  Dammer's  Handbuch  aims  at  doing  for  inorganic 
chemistry  what  Beilstein's  does  for  organic. 

The   periodical  journals,  whose  number    has   gone    on 

Q  Q  2 


596       CHEMICAL  INSTRUCTION  IN  THE  19TH  CENTURY    CHAP. 

steadily  increasing,  have  exercised  the  greatest  influence 
upon  the  enlargement  and  spread  of  chemical  knowledge, 
more  especially  since  the  beginning  of  this  century.  A 
short  account  has  already  been  given 1  of  the  condition  of 
this  class  of  literature  towards  the  end  of  last  century.  In 
Germany,  after  the  third  decade  of  the  present  one,  all  the 
more  important  chemical  researches  were  for  long  published 
either  in  Poggendorff  s  Annalen  der  Physik  und  Chemie  or 
in  the  Annalen  der  Chemie  und  Pharmazie,  which  was 
at  first  edited  by  Liebig  alone,  but  afterwards  in  con- 
junction with  Wohler.  The  latter  journal,  more  particularly t 
soon  became  the  medium  in  which  were  discussed  the  experi- 
mental and  speculative  chemical  questions  of  the  day.  And 
no  one  was  better  qualified  to  deal  with  those  exhaustively 
than  Liebig  himself. 

In  France  the  Annales  de  Chimie,  founded  in  1789 
(the  year  of  the  Revolution)  by  Lavoisier,  Fourcroy  and 
Berthollet,  has  always  been  appreciated  and  loyally  supported. 
Since  1816  it  has  appeared  as  the  Annales  de  Chimie  et 
de  Physique,  its  first  editors  under  this"  new  title  having  been 
Gay-Lussac  and  Arago,  and  it  has  all  along  contained  the 
records  of  pretty  nearly  all  the  more  important  French 
chemical  researches.  The  Comptes  Rendus,  which  has  been 
published  weekly  by  the  Acade'mie  Frangaise  since  the  year 
1835,  includes  among  its  numerous  papers  only  comparatively 
few  and  short  accounts  of  chemical  investigations. 

In  Great  Britain,  up  to  the  year  1841,  papers  on  chemical 
subjects  were  published  either  in  the  Philosophical  Transac- 
tions, the  Transactions  of  the  Royal  Society  of  Edinburgh, 
etc.,  or  in  other  more  recent  journals  which  have  since  been 
superseded,  such  as  Nicholson's  Philosophical  Journal,  and 
Thomson's  (later  Phillips')  Annals  of  Philosophy.  Since  1841 9 
or  at  least  since  1848,  the  Journal  of  the  Chemical  Society 
has  been  the  main  organ  of  scientific  chemistry  in  this  country. 
Apart  from  the  original  memoirs  which  it  contains,  this 

1  Cf.  pp.  175  and  179. 

2  Until  the  year  1839  this  journal  bore  the  simpler  title,  Annalen  der 
Pharmazie. 


vi  CHEMICAL  JOURNALS  597 

journal  has  since  1871  greatly  extended  its  usefulness  by 
giving  copious  abstracts  of  papers  which  have  appeared  in  the 
chemical  journals  of  other  countries. 

And  the  other  European  countries  have  not  been  behind- 
hand in  the  publication  of  chemical  journals ;  according  to 
the  degree  in  which  chemistry  has  found  in  them  a 
permanent  home,  so  have  journals  of  every  shade  and 
variety  sprung  up.  Most  of  these  were  and  are  still  con- 
nected with  learned  corporations — academies  and  chemical 
societies — in  Austria,  Italy,  Holland,  Belgium,  Switzerland. 
Russia,  Roumania  and  Scandinavia,  and  the  same  remark 
-applies  to  the  United  States  and  Canada. 

In  Germany  more  particularly,  which  has  now  for  long 
been  the  chief  centre  for  scientific  chemical  interests,  thanks 
to  the  favourable  conditions  for  scientific  instruction  there, 
.a  number  of  new  journals  for  the  publication  of  papers 
on  purely  chemical  subjects  have  been  added  to  those 
older  ones  just  mentioned.  Among  these  are  the  Journal 
fur  Praktische  Chemie,  begun  by  Erdmann  in  1834, 
continued  by  Kolbe  from  1870  to  1885,  and  since 
the  latter  date  edited  by  E.  von  Meyer;  and,  especially, 
the  Berichte  der  Deutschen  Chemischen  Gesellschaft,  which 
was  brought  into  life  with  the  founding  of  the  German 
Chemical  Society  at  Berlin  in  1 8  6  8,  and  in  which  one  finds 
a  record  of  pretty  nearly  all  that  is  being  done  in  scientific 
chemistry,  either  in  the  form  of  original  papers  or  of  abstracts l 
from  other  journals.  Mention  must  also  be  made  here  of 
the  Kritische  Zeitschrift,  known  later  on  as  the  Zeitschrift 
/ur  Chemie,  which  was  supported  by  such  men  as  Kekule', 
Erlenmeyer,  Fittig  and  others,  and  the  critical  utterances 
in  which  have  often  helped  to  throw  light  upon  disputed 
points  in  chemistry.  The  Chemische  Centralblatt  is  also  a 
valuable  journal  of  reference  for  every  branch  of  the  science. 

Mention  still  remains  to  be  made  of  the  Jahresberichte 
{"  Yearly  Reports  ")  on  the  progress  of  chemistry  and  allied 
branches  of  science.  The  reports  which  were  edited  by 
Berzelius  (from  1821  to  1847)  are  unique,  and  are  abso- 

1  These  abstracts  are  no  longer  printed  in  the   Berichte,   but  in  the 
•Chemische  Centralblatt. 


598       CHEMICAL  INSTRUCTION  IN  THE  19TH  CENTURY    CH.  vi 

lutely  indispensable  to  any  one  who  desires  to  make  a  de- 
tailed study  of  the  progress  of  chemistry  during  those 
years.  The  continuation  of  them,  which  was  undertaken  by 
Liebig  in  conjunction  with  other  chemists,  cannot  be  com- 
pared with  these  earlier  volumes,  the  new  Jahresberichte 
having  been  restricted  into  mere  epitomes  of  reference  with 
regard  to  current  chemical  work.  The  Jahrbuch  der  Chemie,. 
begun  in  1891,  and  edited  by  R.  Meyer  in  conjunction  with 
various  collaborators,  aims  at  giving  a  concise  statement  of 
the  more  important  advances  in  pure  and  applied  chemistry. 

The  critic,  whose  use  as  a  fermentive  and  corrective 
agent  will  be  denied  by  no  one,  seems,  with  but  few 
exceptions,  either  to  have  disappeared  from  the  chemical 
literature  of  recent  years,  or  at  all  events  to  be  at  present 
dormant.  It  is  well  to  remember  that  the  critical  acumen 
which  was  brought  to  bear  upon  the  occasional  errors  of 
chemical  investigation  by  Berzelius  and  Liebig,  and  at  a 
later  date  by  Kolbe,  had  a  consolidating  and  not  a  disinte- 
grating effect,  even  in  those  cases  where  the  critic's  argument 
had  a  strongly  polemical,  and — to  the  subject  of  the  attack 
— a  personal  flavour. 

The  value  of  a  minute  study  of  good  original  papers  has 
time  and  again  been  insisted  upon  by  the  great  teachers  of 
chemistry.  The  records  of  such  experimental  labours  offer 
to  the  student  the  best  means  of  following  out  the  author's 
train  of  thought ;  they  thus  strengthen  the  historical  sense, 
and  at  the  same  time  strongly  incite  to  criticism  and  to 
emulation.  They  are  therefore  to  be  looked  upon  as  among 
the  best  literary  aids  to  the  study  of  chemistry.  At  the 
same  time  they  possess  a  high  educational  value  from  their 
style  and  form  alone.  As  Erdmann  well  says  in  his  short 
treatise,  already  cited,  p.  60 :  "  By  making  use  of  such 
sources  of  information  the  student  learns  at  one  and  the  same 
time  from  a  master  of  the  science  how  and  in  what  form 
scientific  results  should  be  stated,  how  to  distinguish  between 
what  is  and  what  is  not  essential,  and  how  to  condense  the 
subject-matter,  while  at  the  same  time  omitting  from  it 
nothing  of  importance,  so  that  no  necessary  element  shall  be 
wanting  for  its  critical  examination." 


INDEX  OF  AUTHOKS  AND  SUBJECTS 


INDEX    OF    AUTHOKS'    NAMES 

The  figures  in  thick  type  refer  for  the  most  part  to  those  pages  upon  which 
biographical  notices  occur,  although  they  are  also  employed  in  some 
cases  for  others  on  which  points  of  special  importance  are  recorded. 


ABEL,  568 

Abukases,  30 

Achard,  573 

Afzelius,  192 

Agatharchides,  12 

Agricola,  3,  47,  59,  83,  84,  88,  93, 

95 

Aitken,  A.  P.,  535 
Albertus   Magnus,   30,  31,    34,  56, 

137 

Algarotus,  94 
Allihn,  572 
Ampere,  257,  418 
Ammermiiller,  495 
Anaximenes,  6 
Anderson,  478,  484 
Andrews,  405,  493 
Anschiitz,  439,  593 
Arago,  499,  596 
d'Arcet,  558 
Archimedes,  12 
Arfvedson,  407 

Aristotle,  2,  5,  6  et  seq.,  15,  20,  38 
Armstrong,  452,  579 
Arnaldus  Villanovanus,  32,  43 
Aronheim,  458 
Arppe,  442 

Arrhenius,  501,  503,  520 
Arzberger,  593 
Aubertot,  584 
Augustin,  558, 
Auwers,  462,  502 
Avenzoar,  30 
Averrhoes,  30 
Avicenna,  30 
Avogadro,  215,  290,  294,  490 

BACON,  Francis,  101,  585 
Bacon,  Roger,  30-31,  43 


Baeyer,  A.  v.,  349,  354,  358,  363, 

366,  435,  436,  450,  454,  469,  480, 

485,  537,  578,  579,  591 
Bahrens,  62 

Balard,  402,  418,  419,  426,  446,  566 
Balling,  557 
Balmer,  495 
Bamberger,  363,  436,  466,  468,  472, 

473,  477,  481 
Bancroft,  147 
de  Bary,  547 
Barriere,  417 
Barruel,  573 
Basilius  Valentinus,  36,  37,  41,  46, 

47,  48,  51,  52,  53etseq.,  94 
Baudrimont,  62 
Baumann,  439,  451,  464,  543 
Baume,  139,  154 
Bayen,  131,  177 
Beadle,  572 
Beaumont,  451 
Bechamp,  445 
Becher,  109,  110,  134 
Beckmann,  E.,  341,  359,454, 462,502 
Beckurts,  551 
Becquerel,  498,  528 
Behrend,  341,  462 
Beilstein,  458,  583,  595 
Bence  Jones,  228 
Benedict,  570 
Bergman,  124,  137,  138  et  seq.,  247, 

384,  386,  417,  512,  523 
Berlin,  411 

Bernard,  Claude,  541,  543 
Bernoulli,  494 
Bernthsen,  579 
Berthelot,  23,  26,  28,  29,  39,  45,  46, 

57,  153,  167,   168,  328,  420,  435, 

508,  517,  569 


602 


INDEX  OF  AUTHORS'  NAMES 


Berthier,  527 

Berthollet,  172, 173-174,  185  et  seq., 
421,  473,  474,  513-519,  565,  596 

Bertram,  582 

Berzelius,  203-210,  210-213,  216 
et  seq.,  223  et  seq.,  229-237,  240, 
241  et  seq.,  248  etseq.,  251-253, 
255  et  seq.,  279,  281  et  seq.,  292, 
313,  388  et  seq.,  396,  402,  404, 
405,  408,  410,  411,  419,  421,  422, 
424,  426,  429,  430,  441,  449,  474, 
503,  516,  522,  523,  525,  587,  588, 
593,  294,  597,  598 

Besson,  425 

Bettendorf,  410 

Beudant,  221,  525 

Bevan,  538,  572 

Beyer,  C.,  481 

v.  Bibra,  539 

Bidder,  541,  545 

Biot,  499 

Biringuiccio,  85 

Bischof,  C.,  571 

Bischof,  G.,  528 

Bischoff,  543,  545 

Bisehoff,  C.  A.,  359 

Black,  119-121,  128,  144,  180 

Bladin,  485 

Blagden,  166,  502 

Blaise  de  Vigenere,  97 

Blochmann,  425 

Blomstrand,  237,  329,  340,  390,  412, 
429,  430,  471,  473,  516,  526 

Blyth,  A.  Wynter,  399 

Bockorny,  537 

Bodlander,  506 

Boerhave,  60,  113,  114-115,  133, 
135,  137 

Bolley,  556 

Boltzmann,  494 

v.  Bonsdorff,  526 

Borcher,  559 

Bottger,  63 

Bottger,  Rud.,  568 

Botticher,  578 

Bottinger,  580 

Boullay,  253,  495 

Bourcault,  454 

Bourdelin,  118 

Boussingault,  274,  533,  535 

Boyle,  Robert,  3,  59,  92,  100, 
103-107,  128,  133-136,  140  et  seq., 
510 

Brand,  149 

Brandt,  149 

Brauner,  410 

Bredt,  454 

Brefeld,  547 


Brewster,  499 

Brieger,  549 

Brisson,  152 

Brodie,  445 

Bromeis,  441 

Brown,  455,  572,  456 

Brucke,  501,  538,  540,  543 

Briihl,  349,  498,  499,  509 

Brush,  526 

Buchholz,  523,  553 

Biichner,  548,  570 

Buckton,  464 

Buff,  328 

Buffon,  140 

Bunge,  539 

Bunsen,  260-261,311,  385-386,  391, 

392,  407,  413,  418,  424,  426,  433, 

469,  493,  494,  497,  511,  526,  528, 

557,  567,  589,  593 
Bunte,  583 
Butlerow,  332,  334,  336,  344,  435, 

438 

C^SALPIN,  88 

Caetano,  62 

Cagliostro,  62 

Cagniard  de  la  Tour,  547 

Cahours,  259,   438,   444,  445,   468, 

469,  492 
Cailletet,  492 
Calmels,  483 
Cannizzaro,  335,  399,  438 
Carlisle,  229 
Caro,  470,  576,  578 
Carpenter,  569 
Carstanjen,  478 
Cavendish,    121-122,   128-130,  145, 

150,  169,  415 
Champion,  568 
Chance,  564 
Chancel,  299,  439 
Chaucourtois,  371 
Chevreul,  438,  441,  530,  542,  569, 

591 

Chittenden,  541 
Christensen,  403,  427 
Christison,  397 
Chrustschoff,  417 
Ciamician,  484 
Claisen,  L.,  355,  363,  444,  450,  452, 

453,  483,  486 
Clarke,  423 
Classen,  390 
Glaus,  Ad.,  345,  348,  349,  351,  360, 

462,  481,  591 
Claus,  C.  E.,  413 
Clausius,  494,  518 
Clement,  426,  561 


INDEX  OF  AUTHORS'  NAMES 


603 


Cleve,  430 

Cloez,  474,  477 

Collie,  363,  349,  416 

Combes,  452 

Conrad,  453 

Cooke,  403 

de  Coppet,  376,  502 

Couper,  329,  333-334,  337,  345 

Coupler,  577 

Courtois,  402,  560 

Cousin,  168 

Crafts,  434,  452 

Crell,  180 

Croll,  74,  97 

Cronstedt,  144,  149,  523 

Crookes,  374,  409,  410 

Cross,  538,  572 

Curtius,  423,  471,  472,  486 

DAGUEBBE,  510 

Dale,  498 

Dalton,  181,  188-195,  199,  493 

Dammer,  595 

Daniell,  242 

Daubree,  527 

Davy,  Humphry,  195-199,  229  et 
seq.,  238,  239,  241  et  seq.,  290, 
402,  404,  408,  418,  419,  421,  423, 
424,  425,  426,  507,  584,  587 

Davy,  J.,  198 

Deacon,  565 

Debray,  413,  429,  492,  528,  559 

Debus,  189,  440,  449,  568 

Deherain,  533 

Deite,  569 

Delitzsch,  474 

Democritus,  7,  9 

Dennstedt,  484 

Derosne,  573 

Descroizille,  391 

Desormes,  426,  561 

Dessaignes,  543 

Deville,  H.  St.  Claire,  413,  422,  424, 
492,  498,  528,  559,  591 

Dewar,  350,  493 

Diesbach,  147 

Dietrich,  533 

Diodorus  Siculus,  12 

Dioscorides,  5,  11,  15,  16,  18,  50 

Dittmar,  418,  593 

Dobbie,  571 

Dobereiner,  249,  371,  420,  441,  448, 
484,  576 

Dobner,  481,  577 

Dombasle,  531 

Dragendorff,  397,  549 

Draper,  511 

Drebbel,  95 


Drechsel,  442,  540 

Dschabir,  29 

Dschafar  or  Geber,  29,  30 

Dubrunfaut,  573 

Dufet,  506 

Duhamel  de  Monceau,  118,  136, 146, 
147,  149 

Diihring,  497 

Dulong,  219,  220,  242, 419, 423, 424, 
591 

Dulong  and  Petit,  220,  497 

Dumas,  224,  225-227,  253,  258, 
272-275,  276-277,  280  et  seq.,  323, 
370,  371,  396,  404,  407,  433,  437, 
438,  460,  475,  490-491,  495,  556, 
563,  591 

Duppa,  442 

Durocher,  527 

Dutrochet,  536 

EBELL,  570 

Ebelmen,  527 

Ebert,  485 

Effront,  575 

Ehrenberg,  478 

Eiloart,  357 

Einhorn,  483 

Eittner,  580 

Ekeberg,  181,  204,  412,  523 

Elbs,  362,  504 

d'Elhujar,  411 

Eller,  115 

Empedocles,  6,  8 

Engelmann,  536 

Engestrom,  144 

Engler,  583,  406 

Epicurus,  7 

Erasmus  of  Rotterdam,  62 

Erastus,  72 

Erdmann,  203,  370,   388,  396,  526, 

587,  589,  590,  597,  598 
Erlenmever.  334,  336,  338,  470, 591, 
,  597 

Etard,  549 
Ewan,  559 
Eykmann,  502 

FAGGOT,  155 

Falck,  545 

Faraday,   227-228,   251,   418,    433, 

492,  503,  516 
Favre,  507 
Faworsky,  435 
Fehling,   392,   441,   446,   449,  476, 

496 

Feichtinger,  571 
Fick,  543 
Figuier,  430,  573 


604 


INDEX  OF  AUTHORS'  NAMES 


Fileti,  443 

Finkener,  501 

Fischer,  Emil,  358,  363,  364,  437, 

455,  457,  462,  472,  485,  537,  576, 

577,  591 
Fischer,  F.,  556 
Fischer,  G.  E.,  184 
Fischer,  0.,  363,  437,  576,  577 
Fittig,  345,  435,  443,  448,  452,  455, 

458,  485,  591,  594,  597 
Fitz,  547 

Flamel,  Nicolas,  35 
Fleck,  569 
Fliigge,  399 
Fordos,  420 
Forster,  545 
Forster,  431,  571 
Fouque,  528 
Fourcroy,  163,    168,    171,   172,  174 

et  seq.,  586,  596 
Fownes,  485 
Frank,  A.,  557,  566 
Franke,  427 
Frankland,  E.,  285,  310,  316  et  seq., 

322  et  seq.,  329,  330,  331,  336,  361, 

366,  367,  415,  425,  434,  442 
Frankland,  P. ,  535 
Fremy,  418,  423,  427,  529,  539,  569, 

591,  595 

Frerichs,  541,  545 
Fresenius,  R,  385,  389,  397,  588, 

593,  529 
Fresnel,  499 
Freund,  435 

Friedel,  434,  452,  454,  528 
Friedheim,  429 
Friedlander,  481 
Frobenius,  152 
Fuchs,  571    • 
Fuchs,  N.,  524 

GABRIEL,  481 

Gadolin,  409,  523 

Gahn,  144,  146,  149,  181,  523 

Galen,  48 

Gattermann,  424,  449 

Gautier,  476,  549 

Gay-Lussac,  195,  199-201,  210,  214 
et  seq.,  239-241,  249,  290,  391, 
395-396,  402,  404,  418-420,  422- 
424,  426,  427,  473,  489,  490,  527, 
562,  566,  582,  587 

Geber  (Dschafar),  29,  30 

Gehlen,  422 

Gelis,  420 

Gengembre,  177,  421 

Genth,  428 

Geoffrey  the  elder,  62,  117,  138, 154 


Geoffroy  the  younger,  117. 
Gerhardt,    283,   286-295,    300-307, 

327,  337,  440,  445,  460,  479,  591, 

594 

Gerland,  430,  559 
Geuther,  366 
Gibbs,  390,  428 
Gilbert,  533,  535 
Gilchrist,  557 
Girtanner,  594 
Gladstone,  498,  517 
Glaser,  108, 155 
Glauber,  86,  90,  92-97,  137 
Glover,  562 
Gmelin,  C.  G.,  407 
Gmelin,  Chr.,  192,  525 
Gmelin,  L.,  227,  243,  278,  290,  295, 

371,  474,  495 
Goldschmidt,  483 
Gomperz,  7 
Gore,  418 

Gorup-Besanez,  541 
Gottling,  553 
Goulard,  155 

Graebe,  353,  363,  435,  452,  480,  578 
Graham,  244,  413,  423,  501,  594 
Gray,  571 
Gren,  180,  594 
Grew,  155 

Griess,  320,  460,  466,  470-471,  578 
Grimaux,  157,  161,  163,  166,  468 
Gros,  430 
Groth,  506 
Griineberg,  567 
Gruner,  557 
Guareschi,  549 
Guckelberger,  563,  570 
Guimet,  570 
Guldberg,  517  et  seq. 
Gustavson,  435 
Guye,  501 
Guyton  de  Morveau,  133,  163,  168, 

171,  173,  175 

HAARMANN,  456. 

Hagen,  154,  553 

Haitinger,  483 

Hales,  128,  129,  131 

Hall,  527 

Hammarsten,  540,  542 

Hampson,  493 

Hansen,  E.  Chr.,  547,  574,  575 

Hantzsch,  359,  360,  363,  422,  462, 

473,  480,  485,  486 
Harden,  189 
Hardy,  483 
Hargreaves,  563 
Harnack,  540 


INDEX  OF  AUTHORS'  NAMES 


605 


Hasenbach,  422 

Hatchett,  180,  412 

v.  Hauer,  430,  526 

Hausmann,  385,  525 

Hautefeuille,  528 

Hatty,  523,  525 

Hawksbee,  107 

Heeren,  568 

Heintz,  441,  539,  542,  569 

Heinzerling,  581 

Helbig,  563 

Hellot,  147 

Hellriegel,  535 

Helmholtz,  v.,  543 

van  Helmont,  59,  61,  75-79,  128 

Helvetius,  61 

Hempel,  393,  396 

Henneberg,  534 

Hennel,  439 

Henninger,  541 

Henry,  180,  341,  421,  493 

Henry,  W.  C.,  188 

Heraclitus,  6 

Herapath,  494,  495 

Hermann,  526 

Hermbstadt,  553,  556,  573 

Hermes  Trismegistos,  24,  25 

Heron,  455,  456,  572 

Herschel,  494 

Herter,  541 

Hess,  396 

Hess,  G.  H.,  507 

Hesse,  496 

Heumann,  425,  579 

Hiarne,  146 

Higgins,  196 

Hill,  485 

Hinsberg,  481 

Hisinger,  204,  229 

Hittorff,  406,  506 

Hjelm,  411 

van  't  Hoff,  357,  377,  406,  489,  499- 
502,  521 

Hoffmann,  Friedrich,  113,  142,  152 

Hoffmann,  R,  446,  570 

Hofmann,  A.  W.  von,  72,  179,  209, 
284,  295,  296,  297  et  seq.,  439, 
449,  465  et  seq.,  468,  469,  470, 
476,  477,  480,  490,  576,  577,  589, 
592 

Hofmann,  Frz.,  545 

Hofmann,  K.  B.,  11,  14,  15,  17,  18, 
19 

Hofmeister,  541 

Holt,  443 

Homberg,  107-108,  144 

Hooke,  107,  132 

Hope,  408 


Hoppe-Seyler,  539-542,  548 

Horstmann,  488,  492,  501,  521,  595 

Howard,  573 

Hiifner,  541,  548 

Humboldt,  A.  von,  214,  264,  273 

Hunt,  Sterry,  301 

Husemann,  397,  549 

INGEN-HOUSS,  531,  536 
Irinyi,  569 

Isaac  Hollandus,  35,  41 
Isambert,  492 
Ittner,  473 

JACOBI,  559 

Jacobsen,  455 

Jannasch,  526 

Janssen,  415 

Japp,  309 

Jolly,  501 

Joly,  v.,  414 

Jorgensen,  428,  430,  574,  575 

Jorissen,  406 

Joule,  494 

Julius  Firmicus,  26 

Juncker,  133 

KALLE,  464 

Kane,  257 

Kanonikoff,  498 

Karmarsch,  556 

Karolyi,  568 

Karsten,  495 

Kaufmann.  422 

Kay,  328 

Keiser,  403 

Kekule,  307,  308  et  seq.,  328-330, 
332,  336,  338,  339,  344  et  seq., 
347  et  seq.,  352,  353,  433,  440,  442, 
446,  458,  463,  470,  471,  589,  593, 
597 

Kempe,  429 

Kerl,  556,  557 

Keyser,  414 

Kiliani,  455 

Kircher,  62 

Kirchhoff,  G.  S.  C.,  572 

Kirchhoff,  Gust. ,  386,  494 

Kirwan,  130,  180,  523 

Kjeldahl,  397 

Klaproth,  178-179,  385,  386,  388, 
403,  410,  411,  523 

Klason,  463,  464,  474,  477 

Knapp,  406,  556,  570,  572,  580,  581 

Knecht,  580 

Knop,  W.,  534 

Knorr,  363,  486 

v.  Knorre,  429 


606 


INDEX  OF  AUTHORS'  NAMES 


Robert,  549 

Kohlrausch,  501 

Kolb,  563 

Kolbe,  285,  306,  310,  311-322,  329, 
330,  338,  345,  361,  437,  438,  441, 
446,  447,  448,  461,  463,  475,  486, 
582,  588,  589,  593,  594,  597,  598 

Konig,  399 

Kdnigs,  363,  480,  482 

Kopp,  E.,  568 

Kopp,  H.,  4,  375,  489,  495,  496, 
498,  505,  594 

Koppfer,  396 

Korner,  350,  353,  479 

Kortum,  62 

Kraemer,  436 

Krafft,  442,  477,  497 

Kraus,  537 

Kremers,  371 

Kronig,  494 

Kriiger,  341 

Kriiss,  369,  408,  410,  411,  429,  430 

Kuhling,  482 

Kuhlmann,  573 

Kiihne,  540,  541 

Kiilz,  543 

Kunkel,  109,  147,  153 

Kiisser,  503 

Kiitzing,  547 

LAAR,  355 

Labillardiere,  484 

Ladenburg,  348,  349,  353,  363,  479, 

480,  482,  591,  595 
de  Laire,  456 
Lampadius,  425,  523,  573 
Lamy,  409 
Landauer,  144 
Landolt,  469,  498 
Langer,  428 
Langlois,  420 
Laplace,  168,  488,  508 
Lassaigne,  394 
Lauraguais,  153 
Laurens,  584 
Laurent,  278  et  seq.,  286-292,  293- 

295,  301,  440,  457 
Lauth,  577 
Lavoisier,  4, 129,  158,  159,  160-172, 

247,  386,  392-395,  401,  403,  405, 

530,  546,  594,  596 
Lawes,  533,  535 
Lea,  C.,  406 
Le  Bel,  357,  499 
Leblanc,  149,  531,  562 
Leclaire,  560 
Le  Cor,  35 
Lecoq  de  Boisbaudran,  409,  495 


Lederer,  579 

Lefevre,  108 

Lehmann,  534,  540,  541,  542 

Leibniz,  102 

Lemery,  107-108,  134,  154 

Lenk,  568 

Lenz,  504 

Lepsius,  567 

Lerch,  453,  542 

Leuchs,  541 

LeVy,  528 

Lewes,  425 

Lewkowitsch,  570 

Leykauf,  570 

Libavius,  57,  59,  74,  88,  91,  93,  95, 
97 

Lieben,  438,  441,  483 

Liebermann,  351,  363,  435, 443,  452, 
578 

Liebig,  243,  246, 251, 253,  254  et  seq. , 
258-260,  262-270,  274,  284,  306, 
396,  423,  427,  432,  440,  441,  444, 
445,  447-449,  451,  456,  459,  463, 
474,  478,  530,  532-533,  535,  536  et 
seq.,  543,  544,  546,  568,  570,  574, 
587,  588  et  seq.,  594,  596,  598 

Liechti,  429 

Lightfoot,  577 

Limpricht,  484 

Linck,  568 

Linde,  493 

Linnemann,  497 

v.  Lippmann,  455,  573,  574-576 

Lippmann,  510 

Lister,  550 

Littler,  571 

Lob,  504 

Lockyer,  415 

Loew,  537 

Lommel,  536 

Long,  504 

Lessen,  341,  495 

Lowig,  402,  463,  469 

Loysel,  163 

Lubbock,  180 

Lucretius,  7 

Ludwig,  C.,  501,  540,  541,  542 

Lunge,  422,  561 

MACKENZIE,  405 

Macquer,  117,  119,  146,  147,  580 

Magnus,  270,  419,  430,  439,  542 

Malaguti,  517 

Malherbe,  563 

Mallet,  409 

Malpighi,  530 

Maly,  541 

Mansfield,  577 


INDEX  OF  AUTHORS'  NAMES 


607 


Marcet,  587 

Marchand,  370,  388,  396,  411 

Marcker,  572 

Marckwald,  485 

Marggraf,   115,  116-117,   143,   146, 

150,  153,  157,  386,  573 
Margueritte,  391,  429 
Marignac,  369,  370,  388,  403,  405  et 

seq.,  410,  413,  429,  526 
Mariotte,  106,  530 
Markownikoff,  436,  583 
Marsh,  357 
Marsh,  422 
Martin,  558 
van  Marum,  405 
Maslema,  30 
Mathiessen,  407 
Maxwell,  Clerk,  494 
Mayer,  A.,  547 

Mayow,  107,  129,  130,  135,  164, 165 
McGowan,  377 
Meineke,  411 
Meissner,  543 
Melsens,  283,  569 
Mendelejen^Smtf  seq.,  493 
Menschutkin/518,  521 
Merck,  482 
Mercurius,  25 
v.  Mering,  543 
Merling,  483 
Mersenne,  102 
Meslans,  460 
Meusnier,  168 

Meyer,  E.  von,  406,  477,  597 
Meyer,  Lothar,  371,  372,  458,  591, 

595 

Meyer,  O.  E. ,  494 
Meyer,  Richd.,  598 
Meyer,  Victor,  350-351,  355,  359, 

363,  406,  439,  455,  458,  459,  461, 

462,  470,  484,  490,  491,  591 
Michael,  356,  358 
Michaelis,  A.,  421,  462,  465,  469, 

486,  487 

Michaelis,  W.,  571 
Michel,  572 
Miller,  386,  494 
v.  Miller,  481 
Millon,  419 
Milly,  A.  de,  569 
Minderer,  93 
Minunni,  462 
Mitscherlich,  AL,  572 
Mitscherlich,  E.,  221-222,  225,  406, 

421,  427,  434,  439,  460,  463,  505- 

506,  522,  524,  525,  527,  589,  594 
Mohlau,  576 
Mohr,  391,  397 


Mohs,  522 

Moissan,  369,  403,  424,   425,   428, 

460,  528,,  529 
Moitrel  d' Element,  129 
Moldenhauer,  569 
Mond,  428,  430,  563,  564,  583 
Monge,  163,  168 
Moraht,  408 
Morley,  403 
Morris,  456 

Morveau.     See  Guyton  de  Morveau 
Mosander,  204,  410,  525 
Mosso,  549 
Muck,  584 
Mulder,  537,  539 
Miiller,  Fr.,  459 
Miiller,  H.,  458 
Miiller,  M.,  570 
Miiller,  N.  J.  C.,  536 
Miiller  v.  Richenstein,  403 
Miintz,  535 
Musculus,  572 
Muspratt,  556,  563 
Muthmann,  429 
Mylius,  431,  571 
van  Mynsicht,  73,  97 

NAGELI,  538,  548 

Naquet,  338,  344 

Nasse,  O.,  541,  548 

Naumann,  A.,  492,  497 

Naumann,  C.  F.,  525 

Nef,  461,  462,  478 

Nencki,  540,  548,  549 

Neri,  89 

Nernst,  488,  496,  503 

Neubauer,  543 

Neumann,  F.  C.,  498,  504 

Neumann,  Kaspar,  115 

Neumeister,  541 

Newlands,  371 

Newlands  Brothers,  573 

Newton,  140 

Nicholson,  229,  596 

Nickles,  418 

Nicolas,  569 

Niepce,  510 

Niepce  de  St.  Victor,  510 

Nietzki,  452,  453,  578,  579 

Nilson,  408,  410,  411,  491,  497 

Nobbe,  534 

Nobel,  568 

Noble,  568 

Noelting,  423 

Nordenskiold,  125,  173 

Noyes,  403 

ODLING,  307,  326,  327,  371 
v.  Oefele,  320,  374,  445,  464 


608 


INDEX  OF  AUTHORS'  NAMES 


Oettel,  566 

Olympiodor,  25,  26,  27 

Olzevsky,  492 

Ortholph  von  Baierland,  49 

Ost,  448,  483,  556 

Ostwald,  377,  488,  489, 501,  503, 504, 

519,  520,  595 
O'Sullivan,  455,  456,  572 
Otto,  J.,  397,  568,  594 
Otto,  R.,  464,  477,  487,  549 
Overton,  360 

PAAL,  363,  422,  452,  481,  484,  485 

Page,  458 

Palissy,  62,  83,  85-86,  89,  90,  530 

Palmer,  488 

Paracelsus,  3,  59,  67-72,  94 

Pariset,  587 

Parkes,  558 

Parmentier,  177 

Partridge,  409 

Pasteur,  358,  447,  499,  505, 547, 548, 

574,  575 
Pattinson,  558 
Payen,  556,  572 
Pean  de  St.  Gilles,  517 
Pebal,  419 
Pechiney,  565 

v.  Pechmann,  363,  453  472,  473,  485 
Peligot,  275,  411,  429,  438,  460,  561 
Pelletier,  177,  421 
Pelouze,  370,  404,  439,  591 
Perkin,  W.  H.,  jun.,  435 
Perkin,  W.  H.,  sen.,  363,  444,  450, 

466,  500,  577 
Peters,  534 
Petersen,  526 
Petit,  210,  219,  220,  221 
Pettenkofer,  371,  542,  545 
Pettersson,  408,  491,  497 
Pfaff,  385,  422 
Pfaundler,  518 
Pfeffer,  501,  536 
Pfitzinger,  481 
Pfliiger,  545 
v.  d.  Pfordteii,  369,  427 
Phillips,  569 
Pictet,  483,  492 
Pinner,  469,  476  481,  483 
Piria,  446,  456 
Planck,  501 
Plato,  9,  38 
Plattner,  390,  407,  558 
Playfair,  311,  428,  474,  557 
Pliny,  5,  6,  11-20 
Pliicker,  504 
Poggendorff,  596 
Ponomareff,  468 


Popoff,  341,  452 

Porret,  474 

Porta,  90 

Pott,  116 

Prechtl,  556 

Preyer,  541 

Priestley,  122-124,  130,  131  et  seq.,, 

162,  392,  531 
Pringsheim,  536 
Proust,  183,  185-188,  387,  388,  400, 

430,  515 

Prout,  201-203,  374 
Psellus,  Michael,  30 
Pseudo-Aristotle,  26 
Pseudo-Democritus,  26 
Pseudo-Geber,  34,  39-40,  41,  42,  46, 

47,  50-51,  52-56,  59 
Pugh,  535 
Pullinger,  431 
Pythagoras,  9 

QUINCKE,  428 

RAMMELSBERG,  390,  411,  526,  528 
Ramsay,    130,    374,  393,  402,   408, 

415,  416,  422,  430,  497,  500 
Ranke,  543,  545 
Raoult,  376,  502 
Raschig,  423,  424 
Rathke,  477 

Rayleigh,  374,  403,  414-415 
Raymund  Lully,  32,  33-34,  43,  52, 

57 

Reaumur,  147, 152 
Redtenbachei?,  441 
Rees,  547 
Regnault,  258,  281,  433,  439,  542, 

594 

Reich,  409,  561 
Reichenbach,  583 
Reiset,  430,  542 
Renault,  504 
Renk,  545 
Retgers,  506 
Rey,  132 
Reynolds,  474 
Rhazes,  30 
Richards,  403 
Richter,  J.  B.,  181-184,  185,  387. 

417 

Richter,  Th.,  409,  526 
Richters,  571,  584 
Riecke,  359 
Rinman,  146,  523,  557 
del  Rio,  412 
Ripley,  35 
Ritter,  510 
Ritthausen,  537 


INDEX  OF  AUTHORS'  NAMES 


de  la  Rive,  405,  559 

Roberts,  573 

Robinson,  563 

Robiquet,  249 

Rochleder,  441,  537 

Rome  de  1'Isle,  221,  523 

Romer,  569 

Roscoe,  189,  369,  412,  418,  429,  511 

Ruse,  341 

Rose,  Fr.,  428 

Rose,  G.,  389,  505,  522,  525,  527 

Rose,  H.,  209,  385,  389,  412,  421, 

424,  427,  517,  522,  525,  589 
Rose,  Valentin,  the  elder,  389 
Rose,  Valentin,  the  younger,  152, 

389,  523 

Rosenstiehl,  577 
Rosetti,  90 
Rossi,  438,  442 
Rothe,  462 
von  Rothenburg,  486 
Rouelle,  117, 118-119,  136,  137,  154, 

161 

Rubner,  545 
Riidorff,  502 
Rumford,  507 
Runge,  484 
Rutherford,  130 

SACHS,  536,  538 

Sabatier,  425 

Sadler,  571 

Sala,  Angelus,  59,  80,  95 

Salomon,  455,  572 

Sandberger,  526 

Sandmeyer,  460 

Sarasin,  528 

Sattler,  560 

Saussure,  Th.  de,  392,  395,  531,  536 

Saytzeff,  443,  464 

Schadler,  569 

Schaffner,  563 

Scheele,  124,  125-127,  129,  130  et 
seq.,  143  etseq.,  147,  149,  150-155, 
162,  183,  238,  386,  392,  427,  494, 
510,  560 

Scheerer,  390,  505,  526,  543 

Scheibler,  429,  455 

Scherer,  180 

Schertel,  561 

Scheufelen,  458 

Schiel,  302 

Schiendl,  510 

Schiff,  R.,  495 

Schischkoff,  478,  567 

Schloesing,  535 

Schlossberger,  543 

Schmidt,  A.,  540,  541,  548 


Schmidt,  C.,  541,  545 
Schmidt,  F.  W.,  410 
Schmiedeberg,  539 
Schmieder,  62 
Schmitt,  K,  319,  447,  582 
Schneider,  E.  A.,  406 
Schneider,  R.,  390,  404,  411 
Schonbein,  405,  419,  568 
Schone,  419 
Schorlemmer,  341,  497 
Schott,  571,  572 
Schrader,  532 
I   Schraube,  473 
Schrauf,  505 
Schroeder,  496 
Schrotter,  406 
Schiirer,  90 

Schiitzenberger,  420,  431,  540 
Schiitzenbach,  575 
Schultz,  535 
Schulze,  H.,  422 
Schulze,  E.,  538 
Schultze,  510 
Schwalb,  458 
Schwanert,  484 
Schwanhardt,  148 
Schwann,  547 
Scott,  403 
Seebeck,  408,  499 
Sefstrom,  412 
Seger,  571 
Seignette,  97 
Selmi,  549 
Semmler,  582 
Senarmont,  527 
Sendivogius,  62 
Senebier,  531  536 
Sennert,  59,  80 
Serullas,  424,  439,  474 
Seubert,  414 
Shaw,  114 
Shenstone,  263,  406 
Shields,  430,   500 
Siemens,  W.,  559,  584 
Silbermann,  507 
Simpson,  Maxwell,  442 
Skraup,  353,  479,  480 
Smith,  526 
Smithells,  425 
Sobrero,  568 
Solon,  9 
Solvay,  565 
Soret,  405,  495 
Soubeiran,  422 . 
Soxhlet,  455,  542 
Spencer,  559 
Spilker,  436 
Sprengel,  532 

R  R 


610 


INDEX  OF  AUTHORS'  NAMES 


Stadion,  419 

Stadeler,  541,  543 

Staedel,  495 

Stahl,  4,  59,  110-113,  133 

Stahlschmidt,  424 

Stas,  275,  370,  388,  397,  403,  404, 

407 

Steiner,  478 
Stenhouse,  484 
•Sterry  Hunt,  301 
Stevenson,  397 
Stoehr,  480,  481 

Stohmann,  508,  509,  534,  556,  573 
Stolzel,  557 
Stoney,  495 
Storer,  531 

Strecker,  466,  541,  543,  591,  594 
Streng,  526 

Stromeyer,  385,  390,  409,  423,  526 
Struve,  F.  A.,  555 
Suidas,  2 
Svanberg,  525 
Swab,  144 
Swan,  386,  494 
Sylvius  de  le  Boe,  59,  80-81,  82, 92, 

93 
Synesios,  26,  27 

TACHENIUS,  59,  80,  81-82,  92,  93,  96 

Talbot,  386,  510 

Taylor,  397 

Tennant,  405,  565 

Tertullian,  24 

Thaer,  531,  532 

Thales,  6 

v.  Than,  425 

Thenard,  L.  J.,  200,  239,  395,  418, 

419,  424,  426,  427,  587,  594 
Thenard,  P.,  421 
Theophilus  Presbyter,  46 
Theophrastus,  5,  15 
Thorn,  H.,  551 
Thomas,  557,  584. 
Thomas  and  Gilchrist,  557 
Thomas  Aquinas,  31 
Thomsen,  J.,  417,  430,  508,  517 
Thomson,  James,  497 
Thomson,  Th.,  189,  194,  202,  390, 

526,  592,  594 
Thorpe,  104,  123,  167, 198,  228,  244, 

423,  424,  430,  495 
Thot,  25 

Thurneysser,  62,  72 
Tiemann,  454,  456,  476,  582 
Tilghman,  572 
Tillet,  133 
Tollens,  455 
Traube,  F.,  355 


Traube,  M.,  419,  548 
Travers,  402,  416 
Trommsdorff,  177,  553 
Troost,  528 
Tunner,  557 
Turner,  203,  390 
Turquet  de  Mayerne,  73,  97 
Tutton,  423 
Tyndall,  511 

VALENTINEB,  566 
Valerius  Cordus,  98 
Varrentrapp,  397,  441 
Vauquelin,  176-177,  385,  386,  391, 

408,  410,  426,  523,  586. 
Verguin,  577 
Ville,  531,  533,  534,  535 
Vinzenz  of  Beauvais,  30 
Voigt,  477 
Voit,  542,  545 
Vogel,  543 

Vogel,  B.  H.  W.,  420,  511 
Volhard,  320,  391,  467,  474 
Volta,  145 

WAAGE,  517  et  seq. 

van  der  Waals,  494 

Wackenroder,  420 

Wagenmann,  575 

Wagner,  452 

Wagner,  P.,  557 

Wagner,  R.,  556 

Walden,  504 

Walker,  Jas.,  377 

Wallach,  436,  454,  468,  582,  586 

Ward,  148 

Warington,  535 

Watson,  494 

Watson,  W.,  149 

Watt,  167 

Watts,  H.,  595 

Weber,  498 

Weber,  R.,  420,  561,  571 

Weddige,  477,  481 

Wedgwood,  571 

Weidel,  353,  479 

Weihrich,  264,  588 

Weilandt,  497 

Weldon,  565 

Welter,  420 

Wenzel,  186,  387 

Werner,  A.,  341,  359 

Werner,  A.  G.,  523,  524 

Westrumb,  177,  523,  553 

Whetham,  503 

Wichelhaus,  581 

Widmann,  481 

Wiedemann,  G.,  504 


INDEX  OF  AUTHORS'  NAMES 


611 


Wiegleb,  62,  177,  523 

Wilcke,  120 

Wilfarth,  535 

Wilhelmy,  520 

Will,  397,  453,  456,  588 

Willgerodt,  458 

Williams,  478 

Williamson,  295,  298  et  seq.,  326, 

337,  439,  518 
Willis,  107,  134 
Winkelmann,  497 
Winkler,    01.,    392,    393,    408-410, 

411-412,  526,  559,  561,  571 
Winogradsky,  535 
Winterl,  417 

Wischnegradsky,  479,  482 
Wislicenus,  J.,  356,  357,  358,  366, 

446,  453,  500,  543,  591 
Wislicenus,  W.,  355,  422,  423,  444, 

453,  473 

Witt,  470,  578,  579 
v.  Wittich,  541 
Wohl,  466 
Wohler,  252,  254,  262, 270-272,  389, 

396,  406,  408,  424,  427,  432,  444, 

456,  463,  474,  525,  528,  543,  570, 

589,  594,  596 


Wolff,  E.,  534 

Wolff,  L.,  481 

Wolffenstein,  419 

Wollaston,  195    199,  412,  413 

Wray,  153 

Wren,  107 

Wroblevsky,  492 

Wurtz,  295-296,  298  et  seq.,  307, 
310,  327,  328,  337,  368,  424,  434, 
439,  440,  446,  450,  466,  467,  477, 
492,  526,  548,  591,  595 

Wyrouboff,  506 


YOUNG,  JAS.,  244 
Young,  Sidney,  497 


ZEISE,  463 

Zamminer,  594 

Ziervogel,  558 

Zimmermann,  Cl.,  369,  411,  429 

Zincke,  436,  439,  440,  452,  481,  497 

Zinin,  466,  470 

Zdller,  534,  556,  586 

Zosimos  of  Panopolis,  24,  27 

Zulkowsky,  593 


R  R   2 


INDEX    OF    SUBJECTS 

The  figures  in  thick  type  refer  to  those  pages  upon  which  subjects   are 
treated  in  detail  or  points  of  special  importance  are  recorded. 


ABSORPTION  of  gases  by  water,  129 
Academia  Caesar ea  Leopoldina,  102 

del  Cimento,  102 
Acaddmie  Franqaise,  176 

Royale,  102 
Academies  and  Learned   Societies, 

formation  of,  101-102 
Academies,  Spanish,  28 
Acetaldehyde,  449 
Acetic  acid,   19,  96,  153,  441,  575- 
576 

acid,  constitution  of,  282-283,  316, 
et  seq.,  441 

acid  (glacial),  153 

acid,  synthesis  of,  361 

aldehyde,  polymers  of,  449 
Aceto-acetic  ether,  354,  442,  453 

tautomerism  of,  354 
Acetone,  451 

-dicarboxylic  acid,  453 
Acetyl,  315 

theory  (Liebig),  258 
Acetylene,  435 

as  an  illuminant,  583 
Acid  amides,  444,  468 

anhydrides  (Gerhardt),  300,  444, 
445 

chlorides,  organic,  444,  445 

nitriles,  314,  475 

theory  of  (Lavoisier),  167 
Acides,  172 
Acids,  51,  91 

constitution  of  (Berzelius),  233  et 
seq. 

constitution  of  (Davy),  241 

constitution  of  (Liebig),  243-246 

nomenclature  of  (Lavoisier),  172 

organic,  153 


Acids  from  plant  juices  (Scheele),  153 

manufacture  of  organic,  582 

always  contain  oxygen  (Lavoisier), 
167  et  seq. ;  contro version  of  this 
view,  197,  238  et  seq. 
Acrylic  acid,  442 
Actinometry,  511 
Adipic  acid,  442 
Adjective  dyes,  147 
Aer  vitriolicus,  131 
yEsculin,  456 
^thal,  275,  438 
jEthereum  (Kane),  257 
dZtherin,  253 

theory,  the,  253-254 
Affinitas,  137 
Affinity-coefficients,  specific,  519  et 

seq. 
Affinity,  degrees  of,  334 

determinations  of,  512-521 

doctrine  of,  512-521 

doctrine  of  (Bergman),  512-513 

doctrine  of  (Berthollet),  174,  185, 
513  et  seq. 

doctrine  of,  its  latest  development, 
519 

simple  elective,  138 

tables  of  (Geoffrey),  117,  138,  512 

units  of,  341 

views  as  to  its  causes,  137-140 
Affinity,  chemical  (Boyle),  105 

chemical,  views  of  the  Phlogiston- 
ists,  137  et  seq. 

doctrine  of  (Guldberg  and  Waage), 

517,  519 

Affinivalenten  (Erlenmeyer),  338 
Agricultural- chemical    experiments 

at  Woburn,  533 


614 


INDEX  OF  SUBJECTS 


Agricultural  chemistry,  530  et  seq. 
Liebig's  great  services,  269,  530 

et  seq. 
Air,  composition  of  atmospheric,  122, 

130-131,  145 
Albumens,  vegetable,  537 

animal,  539 

Alchemistic  period,  the,  21-64 
Alchemistic  speculations  of  the  13th 

and  14th  centuries,  41 
Alchemists,      practical-chemical 
knowledge  of  the,  45  et  seq. 
Alchemy  among  the  Arabians,  28  et 

seq. 

at  the  European  courts,  35,  61,  62 
books  on,  23 
decay  of,  58  et  seq. 
during  the  last  four  centuries,  58- 

64 

general  notes  upon,  2-3 
in  Egypt,  23,  37 
in  the  Christian  countries  of  the 

West,  30  et  seq. 

its  relation  to  the  Platonist  philo- 
sophy, 22 

origin  of,  21,  23  et  seq. 
position  of  chemists  of  repute  in 
the  16th  and  17th  centuries  with 
regard  to  it,  59  et  seq. 
problems  of,  32  et  seq. 
relations  of,  to  astrology,  25 
special  history  of,  37  et  seq. 
theories  of,  37  et  seq. 
Alcohol,  57,  98 

constitution  of  (Berzelius),  256 
meaning  of  the  word,  98 
preparations  from,  575,  581 
Alcoholometry,  beginnings  of,  152 
Alcohols,  437,  440 

constitution  of  (Kolbe),  318 

polyatomic,  438 

secondary  and  tertiary  (Kolbe), 

318 
Aldehydes,  448-451 

constitution  of  (Kolbe),  318 
formation  of,  449 
Aldol,  450 
Aldoses,  455 
Aldoximes,  462 
Alembic  Club  Reprints,  214 
Alexandrian  Academy,  the,  21,  26, 

37,38 

Algaroth,  powder  of,  94 
Alizarine,  578 
Alkahest,  52,  96 
Alkali,  50 

Alkali  metals,  discovery  of  by  Davy, 
197,  238 


Alkali    metals     (Gay    Lussac    and 
Thenard),  200,  239 

atomic  weights  of,  407 

compounds  of,  426 

earlier  views  on  their  nature,  239 
Alkali  waste,  563-564 
Alkalies,  decomposition  of,  238 
Alkalimetry,  391 

Alkaloids,   derivatives  of  pyridine, 
etc.,  482-483 

synthesis  of,  482 

tests  for,  397-398 
Alkarsin,  261 
Alkyl  cyanurates,  477 

cyanides,  475 
Alkyl-pyridines,  479 
Alkyls,  metallic,  487 
Allo-isomerism  (Michael),  356 
Allotropy,  405,  406,  506 
Alloys,  560 
Allyl  alcohol,  438 
Allylamine,  467 
Alum,  17,  52,  90,  93 

earth,  confounding   of  this  with 

lime,  93 
Aluminium,  409,  559 

bronze,  560 

chloride,  syntheses  with,  434 
Amalgamation  processes  for  obtain- 
ing silver,  47,  88 
Amalgams,  560 
Amides,  444-445 
Amidines,  468,  476 
Amido-acids,  organic,  446 

constitution  of  (Kolbe),  319 
Amido-miazines,  478 

-pyrimidines,  478 
Amidoximes,  476 
Amine  bases  ( Wurtz,  Hofmann),  295 

et  seq. 

Amines,  465  et  seq. 
Ammonia  as  a  type,  296,  300 

gas,  discovery  of,  129 

manufacture  of,  582-583 

salts  as  medicines,  93 
Ammonia  soda,  564 
Amygdalin,  268,  456 
Amyl  alcohol,  438 
Anaesthetics,  551 
Analysis,  introduction  of  the  word 

by  Boyle,  106,  141 
Analysis,  development  of,  384  et  seq. 

legal-chemical,  397-398 

of  articles  of  food  and  drink,  398 

of  gases,  128,  145,  392 

of    inorganic    substances,  384  et 
seq. 

of  organic  substances,  393  et  seq. 


INDEX  OF  SUBJECTS 


615 


Analysis,   qualitative,  82,    96,    140 

et  seq.,  384  et  seq. 

quantitative,  144,  178,  386,  et  seq. 

technical,  398 

volumetric,  390 

Ancients,  practical-chemical  know- 
ledge of  the,  9  et  seq. 
Anhydrides  of  organic  acids,  444 
Aniline,  465,  576 

black,  577 

blue,  577 

colours,  576  et  seq. 

green,  577 

red,  576 

violet,  577 

yellow,  578 
Annalen  Chemische  (Crell),  180 

der  Chemie  undPharmazie  (Liebig), 
266,  596 

der  Physik,  180 

der  Physik  und  Chemie  (Poggen- 

dorff),  180,  596 
Annales  de  Chimie,  175,  596 

de  Chimie  et  de  Physique,  596 
Anthracene,  435 
Antimoniuretted  hydrogen,  422 
Antimony((BasilValentine),36, 47,54 

compounds,  organic,  469 

pentachloride,  424 

pills,  94 

preparations,  37,  49,  54,  94 
Antiphlogistic  system,  the,  158,  168 
et  seq. 

in  Germany,  177 

in  other  countries,  180 
Antipyrine,  472 
Antiseptics,  155,  550 
Apothecaries'  shops,  49,  91 
Apparatus  for  collecting  gases,  129 

of  the  alchemistic  age,  34 
Aquafortis,  51 

regia,  51-52 

vita,  57,  98 
Arcana,  70 

Arabian  academies,  28 
Arabians,  chemistry  among  the,  28 

et  seq. 

Arabite,  439 
Archeiis,  70,  78 
Argon,  122,  393,  414,  416,  419,  493 

helium,    and    other     monatomic 
gases,  their  position  in  the  Per- 
iodic System,  374,  416-417 
Aromatic   compounds,    meaning   of 
the  term,  349-351 

theory    of  (Kekule"),  346 

(Ladenburg,  Claus,  and  Baeyer), 
348-349 


Arsenic  and  its  compounds,  55,  94, 

404,  422 

Arsenic  acid,  151 
Arsenious  acid,  55,  151 
Arseniuretted  hydrogen,  422 
Arsines,  etc.,  469 
Ashes  of  plants  as  manure,  17 
Asparagine,  constitution  of,  319 
Assimilation  in  plants,  510,  534,  536 

et  seq. 

Asymmetric  carbon  atom,  355 
theory  of  (van    't   Hoff  and   Le 

Bel),  SSGetseq.,  447 
Atom  (Laurent),  294 
Atomic    compounds    (Kekule"), 

339-340 

heat,  220,  497-498 
hypothesis,  the,  181,  188   - 
theory,  (Dalton's),  188,  194 
theory,  further  development  of, 

194  et  seq. 
theory,  further  development  of, 

by  Berzelius,  210  et  seq. 
preparatory  work   for  (Richter), 

181,  (Proust),  185 
volume,  495 

weight  determinations,  203,  388 
weight  (Laurent),  293-295 
weight  system  of  Berzelius  and  the 

opposition  to  it,  205,  223-225, 

227 

weight  tables  (Berzelius),  218,  224 
weight  tables  (Dalton),  193 
weights  (Berzelius),  211   et   seq., 

217  et  seq.,  223  et  seq. 
weights,  correction  of,  373 
weights,       deduction       of,       by 

Cannizzaro,  335 
weights  (Dumas),  225 
weights,    Dumas'    opposition    to 

those  of  Berzelius,  225 
weights       (Erdmann     and 

Marchand),  370 
weights  (Gerhardt),  290  et  seq. 
weights,  improvements   in  their 

determination,  370,  387,  403 
weights  (Marignac),  370,  388,  403 
weights  of  the  metals,  406  et  seq. 
weights  of  the  non-metals,   401 

et  seq. 
weights,  periodic  arrangement  of, 

370  et  seq. 
weights,  ratio  of  those  of  hydrogen 

and  oxygen,  403 
weights,  relative  (Berzelius),  210 

et  seq.,  218,  223 
weights,   relative    (Dalton),    191 

et  seq. 


616 


INDEX  OF  SUBJECTS 


Atomic  weights, relative  (Thomson), 

195 

weights  (Stas),  370,  388,  403 
weights,  uncertainty  as  to  them 

generally,  227 
weights,  uncertainty  as  to  those 

of  the  metals,  218,  221 
Atomicity  of  the  elements,  334,  338 
Atoms,  conception  of,  181 

of  various  orders  (Dalton),  191 
spacial  arrangement  of,  252,  344, 

356  et  seq. 
Atropine,  482 
Aurum potabile,  44 
Azo-compounds,  470 
Azo-dyes,  470,  578 
Azo-imide,  423 
Azoles,  485 

BACKWARD  substitution,  283-284 
Bacteriology,  550 
Balance,  importance  of  the 

(Lavoisier),  161,  169 
Barium,  408,  426 
Bases,  designation  of,  by  Lavoisier, 

172 

Basic  slag,  557-558 
Basicity,  law  of  (Gerhardt),  289 

of  acids,  243  et  seq. 

of  acids,  criterion  of,  245 
Beet  sugar  industry,  275,  573 
Beetroot  sugar,  116,  149,  573 
Benzene,  constitution  of,  as  deduced 
from  molecular  refraction,  499 

constitution  of  (Baeyer),  349 

constitution  of  (Glaus),  348 

constitution  of  (Kekule),  346 

constitution  of  (Ladenburg),  348 

derivatives,    isomerism    of,    347, 
351  et  seq. 

hexagon  formula  of,  347 
Benzin,  434 

Benzoic  acid,  97,  256,  443,  582 
Benzoic  aldehyde,  448 
Benzoyl-carboxylic  acid,  453 
Benzoyl  the  radical  of  benzoic  acid, 

254 

Benzyl  alcohol,  438 
Berichte  der  Deutschen   chemischen 

Gesellschaft,  597 
Berlin  Academy,  the,  102 

blue,  147 
Beryllia,  176 
Beryllium,  408,  427 
Berzelius-Liebig    Letters,  the,    209, 

246,  259,  266,  272,  274,  284 
Bessemer  process,  the,  557 
Betaine,  467 


Biblical  characters  as  alchemists,  24 

Bile,  acids  of  the,  541 

Bile,  chemistry  of  the,  541 

Bismuth,  47 
preparations,  93,  94 

Bitter  almond  oil,  254,  577 

Bitter  salt,  155 

Black  oxide  of  manganese  (investiga- 
tion of  by  Scheele),  127 

Blast-furnace  process,  the,  557 

Blood,  chemistry  of  the,  541-542 
gases,  542 

Blowpipe,  144,  385,  390,  523 

Boiling  point  of  solutions,  502 

Boiling  point,  laws  regulating  the, 
496-497 

Bonds,  central,  351 
double,  351 

Bone  charcoal  for  sugar  refining,  573 

Bones,  constituents  of,  539 

Boracic  acid,  116 

Boron,  404,  424 
methide,  486 

Brandy,  distillation  of,  90 

Brass,  15,  147 

Bromine,  402,  566 

Bronze,  13,  14 

Bunsen  burner,  the,  593 

Butylene,  433,  435 

CACODYL  compounds  (Bunsen),  261 

compounds,   constitution   of, 

315-317 

Cadaverine,  549,  480,  483 
Cadmia,  15 
Cadmium,  409 
Csesium,  407 
Caffeine,  537 

Calcination  of  the  metals,  132 
Calcination  of  the  metals  (Lavoisier), 

164  et  seq. 
Calcium,  408,  426 
Calomel,  95 
Calorimetry,  508-509 
Campechy  wood,  extract  of,  580 
Capillarity,  500 
Carbamines,  476 
Carbides,  metallic,  428 
Carbinols,  secondary  and  tertiary,  438 
Carbohydrates,  454-456 

their  significance  for  plant  life,  538 
Carbolic  acid,  550 
Carbon,  405,  425 

as  a  constituent  of  organic  com- 
pounds, 247 

bisulphide,  425 

compounds,  saturated  and  unsatu- 
rated,  344  et  seq. 


INDEX  OF  SUBJECTS 


617 


Carbon,  determination  of,  395-396 
assimilation  of,    by  plants,   536 

et  seq. 

double  linkage  of,  358 
oxysulphide,  425 
Carbonate  of  ammonia,  53 
Carbonic     oxide,     composition     of 

(Dalton),  190 
acid,  79 

acid,  composition  of,  387,  394 
acid,     composition     of     (Black), 

119-120,  128 
acid,    composition    of    (Dalton), 

190 

Carborundum,  428 
"  Carboxylic  acid,"  453 
Carboxylic  acids,  441-448 

acids,    constitution    of     (Kolbe), 

317-318 

acids,  saturated,  441  et  seq. 
acids,  aromatic,  443-444 
acids,  unsaturated,  442 
acids,  chlorides,  anhydrides  and 

amides  of,  444  et  seq. 
Carbures,  172 
Cavendish's    researches    on    gases, 

122 

Cellulose,  572 
Cement,  571 
copper,  47 

Ceramic  art,  the,  17,  147,  571 
Cerium,  179 

metals,  the,  409-410 
Chelidonic  acid,  454,  483 
Chemia,  first  use  of  the  word,  26 
Chemical  compound,  different  from 

a  mixture,  136 
art,  the,  9 
combination,    according    to    the 

ancients,  8 
combination,    according    to    the 

Phlogistonists,  135 
composition,  distinction  between 
empirical          and  rational 

(Berzelius),  233 
compound,  meaning  of,  8,  41-42, 

134  et  seq. 
compound,  old  ideas  regarding,  8, 

41 

constitution    of     organic     com- 
pounds, methods  for  investiga- 
ting this,  361  et  seq. 
equilibrium,  statical  and  dynam- 
ical, 518 

equivalents  (Lavoisier),  169 
"tinder,"  568 
industries,  the  great,  561 
journals,  382,  595  et  seq. 


Chemical  nomenclature  (Lavoisier), 
171 

nomenclature  (Berzelius),  234 

nomenclature    of    organic    com- 
pounds (recent),  437 

notation  (Dalton),  194 

periods,  the  various,  1  et  seq. 
Chemistry,  agricultural  and  physio- 
logical, 90,  530  et  seq. 

analytical,  in  the  modern  period, 
384399 

analytical,  106,  124,  136,  141 

analytical,    its    development    by 
Boyle,  106 

antiphlogistic,  168  et  seq. 

applied,  83  et  seq.,  146  et  seq.,  554 
et  seq. 

geological,  527  et  seq. 

in  ancient  Egypt,  9,  12,   13,   16 
et  seq.,  23  et  seq. 

in  olden  times,  5-20 

inorganic,  367  et  seq. ,  400-431 

its  meaning  at  different  periods, 
2  et^  seq. 

meaning  and  origin  of  the  word, 
2,  23 

mineralogical,  522-529 

organic,  246  et  seq.,  432-487 

pharmaceutical,  48  etseq.,  91,  154, 
552 

physical,  488-521 

pneumatic,      founded     by      van 
Helmont,  78 

pneumatic,   its  further   develop- 
ment, 128  et  seq.,  145 

tasks  of,  in  the  various  ages,  1 

technical,  in  recent  times,  554-585 

technical,   in  the  iatro-chemical 
age,  87 

technical,  in  the  phlogistic  period, 
146 

the  aims  of,  1  et  seq. 
Chili  saltpetre,  566 
Chloral,  459,  551 
Chloraldehyde,  258 
Chloride  of  lime,  426,  565-566 
Chlorimetry,  391 
Chlorine,  148,  402 

discovery  of,  127 

its  action  upon  organic  substances, 
457  et  seq. 

recognised  as  an    element,    197, 
239-240 

supposed  composition  of,  240 

the  name,  239 
Chlorophyll,  536 
Choline,,  synthesis  of,  467 
Chrome  colours,  560 


618 


INDEX  OF  SUBJECTS 


Chromium,  410 

discovery  of,  by  Vauquelin,  176 
Chrysamine,  579 
Chrysene,  436 
Chryso'idine,  578 
Cinnabar,  95 

Cinnamic  acids,  isomeric,  443 
Circular  polarisation,  499 

polarisation,  magnetic,  500 
Citric  acid,  153 
Classification  of  organic  compounds, 

278-280,  289,  302 
Coal  gas,  583 

Coal-tar  colour  industry,  576  et  seq. 
Coal-tar,  products  from,  582 
Cobalt,  149,  410,  428 

-ammonia  compounds,  428 
blue,  90 
Cocaine,  483 
Cohesion,  514 

Coins  of  alchemistic  gold,  61 
Colcothar,  55 
Collidines,  480 
Colloids,  501 
Colour  photography,  510 
Combining  proportions,  proof  that 

these  are  constant,  185  et  seq. 
weights    (Gmelin),    227,    291, 

295 
Combustion    according    to    Stahl, 

110-113 

according  to  Hoffmann,  114 
according  to  Mayow,  107 
correct    explanation    of,    by 

Lavoisier,  164  et  seq. 
-ladder  (Gerhardt),  289 
phenomena  of,  425 
theory  of  (Lavoisier),  158  et  seq., 

166-167 
Composition  of  substances  according 

to  Becher,  109-110 
Compounds,  atomic,  339 

classification  of,  at  the  beginning 

of  the  Modern  Period,  172 
molecular,  339 
Comptes  Rendus,  596 
Condensations,  450 
meaning  of,  362 
of  aldehydes,  452 
Congo  red,  579 
Coniferin,  456 
Conine,  482 

synthesis  of,  364 
Conservation  of  matter  (Lavoisier), 

169 
Constitution,    chemical  (Berzelius), 

231,  252 
chemical  (Gerhardt),  304-307 


Constitutional     formulae      (Kolbe), 

318-319 
Copper,  13,  47,  88,  560 

oxide  for  organic  analysis,  396 

vitriol,  18 

Copulee,  283,  284,  313  et  seq. 
Copulated  or  conjugated  compounds, 

283,288,  313e«6-eg.,  324 
Copulation,  a  consequence  of  satura- 
tion capacity  (Frankland),  325 

meaning  of,  283,  322  et  seq. 
Corpse  alkaloids,  549 
Corpuscular      theory      (Berzelius), 
216-217 

theory  (Boyle),  106,  139 
Cosmetic,  old  Egyptian,  18 
Creatine,  467 
Cresols,  550 
Criticism,   importance   of    (Kolbe), 

598 

Croconic  acid,  453 
Crotonic  acids,  443 
Crotonic  aldehyde,  450 
Crystalline  form,  its  connection  with 

composition,  221-223 
Crystallography,  523 
Crystalloids,  501 
Cultures,  dry  and  water,  534 
Cumarone,  485 
Cyan-alkines,  477 
Cyanic  acid,  251,  474 
Cyanamide,  474 
Cyanogen,  200,  473 

compounds  of,  473-478 

iron  compounds  of,  427-428 

polymers  of,  477 
Cyanuric  acid,  474 

Daltonism,  188 

Decipium,  417 

Decomposition  of  molecules  into 
atoms,  491 

Decomposition    of   organic   com- 
pounds.. 366 

Deduction,  significance  of  (Aris- 
totle), 5,  10 

Dephlogisticated  air  (oxygen),  131 

Dephosphorisation  of  iron,  557 

Desmotropism,  355 

Destillatio  per  decensum,  19 

Dextrine,  572 

Diagonal  formula  of  benzene,  349 

Di-aldehydes,  449 

Di-amines,  465 

Diamond,  artificial  production    of, 
529 

Di-azines,  481 

Diazo-acetic  ether,  471-472 


INDEX  OF  SUBJECTS 


619 


Diazo-compouncls,  466,  470  et  seq. 

oxidation  of,  472 
Didymium,  410 
Diffusion,  500 

-process  for  sugar,  573 
Digestion,  540 
Di-ketones,  452 
Dimorphism,  505 
Dissociation,  492 

electrolytic,  501  et  seq. 
Distillation,  19,  49,  57,  90,  593 
Distilleries,  90 
Di-sulphones,  464 
Docimacy,  beginnings  of,  47 
Docimacy  of  the  noble  metals,  88, 

390 

Double  atoms  (Berzelius),  236 
Drinks,  analysis  of,  399 
Dualism  (Berzelius),  233,  243  et  seq. 

fight    against,    237   et    seq.,   275 
et  seq 

overthrow  by  Unitarism,282  et  seq. 
Duplication  of  the  metals,  26 
Dye   character   and   chemical   con- 
stitution,    supposed     connection 

between,  470 

Dyeing,  17,  48,  90,  147,  580 
Dyes,  147,  576 

Dyes,  distinction  between  adjective 
and  substantive,  147 

synthesis  of,  364 
Dynamic  hypothesis,  the,  359 
Dynamite,  568 

EARTHENWARE,   17,  47-48,    85,  89, 

571 

Earths  (Becher's),  110 
Eau  de  Javelle,  565 
Ecgonine,  482 

tichelle  de  combustion  (Gerhardt),  289 
Effect,  chemical,  514 
Elasticity,  514 
Electric  conductivity,  503 
Electro-chemistry,  504,  516,  565 

-chemical  equivalents  (Faraday), 
228 

-chemical  theory  (Berzelius),  230 
et  seq.,  516 

-chemical  theory  (Davy),  229 

-metallurgy,  559 
Electrolysis,  228  et  seq.,  242,  503 

Faraday's  law  of,  228,  503,  516 

of  salts  of  fatty  acids,  314 
Electrolytic  determination  of  metals, 

390 

Electrolytic  law  (Faraday),  228 
Element,  meaning  of  the  term 

(Boyle),  105,  134 


Element,  meaning  of  (Lavoisier),  170 
Elements,  Aristotle's  four,  7 

classification  of,  161 

discovery  of  in  recent  times,  401 
et  seq. 

discovery    of    in    the    phlogistic 
period,  150  et  seq. 

discovery  of  supposed  new,  417 

natural  families  of,  372 

of    the    alchemistic     period,    37 
et  seq. 

of  the  Phlogistonists,  134-135 

old  views  regarding,  6  et  seq. 
Elixir,  for  transmuting  metals,  41 
Encyclopedias  of  chemistry,  595 
Energy,  508  et  seq.,  521 
Enzymes,  548 
Eosin  dyes,  578 
Equilibrium,  dynamical,  518 

statical,  518 

Equivalents,  electro-chemical,  228, 
503 

of  the   elements  (Gerhardt),  290 
et  seq. 

of  the  elements  (Gmelin),  290 

of  the  elements  (Laurent),  294 

first  table   of    (Richter-Fischer), 
184 

of  the  elements  (Wollaston),  199 
Equivalents     instead     of      atomic 

weights,  199,  227 
Erbium,  410 
Erucic  acid,  443 
Esters,  439 
Ether  as  a  fifth  element,  8 

-acids,  439 

constitution  of,  256 

from  alcohol,  98,  152 
Ethereal  oils,  20,  436 
Etherin  theory,  the,  253-254 
Ethers,  compound,  439 

mixed,  298,  439 

simple,  439 

varieties  of,  152 

(Williamson),  298 
Ethionic  acid,  439 
Ethyl,  256 
Ethyl  ether,  439 

ether,  formation  of  (Williamson), 
298 

sulphide,  463 

-sulphuric  acid,  439 

theory,  the,  256 

Ethylene,  composition  of  (Dalton), 
189-190 

oxide,  439 
Eurhodines,  579 
Eurhodols,  579 


620 


INDEX  OF  SUBJECTS 


Experimental  lectures,  265,  586 

et  seq. 
methods,  development  of,  by 

Boyle,  103-104 
Explosives,  567-568 

FATS,  19,  98,  153-154,  540 

Fatty  acid  series,  structure  of  com- 
pounds of  the,  344-346 

Fatty  acids,  441 

acids,  constitution  of  (Kolbe),  314 
et  seq. 

Fatty  oils,  &c.,  19 

Fermentation,  79,  546  et  seq. 
former  views  regarding,  152 
processes,  546  et  seq. ,  574 
significance  of  (v.  Helmont))  77-78 
theories,  546  et  seq. 

Ferments,  organised  and  unorgan- 
ised, 547-548 

Ferric  acid,  427 

Ferricyanogen,  474 

Ferrocyanogen,  473 

Ferrocyanogen    compounds   (Berze- 
lius),  206 

Filter  papers,  incineration  of,  388 

Filtering  appliances,  593 

"Fire  air"  (oxygen),  131 

"  Fire-damp  Commissions,"  584 

Fixation  of  carbonic  acid  by  alkalies 

(Black),  119-120,  128 
of  mercury,  27 

"  Fixed  air"  (Black),  120 

Flame  colourations  (Marggraf, 

Scheele),  143 
reactions  (Bunsen),  385 

Flesh,  chemistry  of,  543 

Fluorene,  436 

Fluorine,  403 

its  analogy  to  chlorine,  418 
compounds,  206,  418,  424 
compounds,  organic,  460 
oxygen  compounds  of,  460 

Foods,  analysis  of,  399 

Formazyl  compounds,  472 

Formic  acid,  153 
aldehyde,  449,  450,  537 
production  of,  in  plants,  537 

Formulae  (Gerhardt's),  304-305 
graphical  (Kekule),  343 
rational  (Kolbe),  321 

Formyl-acetic  ester,  453 

Four- volume  formulae,  293 

Freezing  point  of  solutions,  502 

Friction,  fluid,  501 

Fuchsine,  576 

Fulminate  of  mercury  (Kekule),  308 

Fulminic  acid,  478 


Fulminic    acid,  isomerism   with 

cyanic  acid,  251 
Fulminuric  acid,  478 
Fumaric  acid,  443 
Furfurane,  350,  484 
Furfurol,  484 
Furnace  gases,  557 

GALL  apples,  juice  of,  98 

Gallium,  374,  409 

Galmei,  15 

Galvanic  current  used  in  analysis, 

390 

Galvano-plastic  process,  the,  559 
Gas  analysis,  392 

analysis,  beginnings  of,  145 

analysis,  technical,  392 
Gas  regulators,  593 
Gas  sylvestre,  79 
"  Gas,"  the  generic  term,  79 
Gases,  absorption  of,  493 

critical  pressure  of,  493 

critical  temperature  of,  493 

discovery  of  many  by  Priestley 
and  Scheele,  123-124,  127,  128 
et  seq. 

kinetic  theory  of,  493 

liquefaction  of,  492-493 

their  first  collection  over  mercury, 
129 

the  chemistry  of  gases  in  the 
phlogistic  period,  128  et  seq. 

van     Helmont's     researches    on, 

78-79 

Gastric  juice,  541 
Geber's  writings  and  doctrines,  29 
Geometrical    isomerism   (J.    Wisli- 

cenus),  356  et  seq. 
Generators,  584 
Germanium,  374,  411 
German  silver,  558 
Glass,  history  and  manufacture   of, 

16,  47-48,  89,  147,  570 
Glauber's  salt,  92 
Glucoses,  454-455 

constitution  and  synthesis  of,  454 

et  seq. 

Glucosides,  456 
Glycerine,  154,  328,  438-439 
Glyceryl,  328 
Glycocoll,  319 
Glycollic  acid,  319 
Glycogen,  543 
Glycol,  328 
Glycols,  439 
Glyoxal,  449 
Glyoxaline,  485 
Gold,  11-12,  46-47,  88,  558 


INDEX  OF  SUBJECTS 


621 


Gold,  amalgamation  of,  12 

compounds  of,  430 

determination  of  its  atomic  weight. 
430 

separation  from  silver,  12,  88 
Goulard's  lotion,  155 
Gradverwandtschaft,  333 
Great  chemical  industries,  the,  561 
Groups  of  elements,  367,  370  et  seq. 
Guanidine,  468 
Guanamines,  468 
Gun-cotton,  568 
Gunpowder,  567 
Gypsum,  93 

HALOGEN  carriers,  458 
derivatives  of  hydrocarbons,  457 

et  seq. 

Halogens,  the,  239-240,  402,  403 
compounds  of  the,  239,  418,  424 
hydrides  of,  418 
their  action  on  the  unsaturated 

hydrocarbons,  459 
Handworterbuch  de  Chemie,  267,  595 
Heat,  latent  (Black),  120 

latent  (Lavoisier   and    Laplace), 

162 

nature  of  (Lavoisier),  162,  170 
of  combustion,  507  et  seq. 
of  formation,  constancy  of  (G.  H. 

Hess),  507 

specific,   its    relation    to    atomic 
weight  (Dulong  and  Petit),  220 
Heat-capacity  of  atoms,  220 
Heating  materials,  584 
Helium,  393,  415,  416,  419 
Hermetic  Society,  62 
Hermetic,  24-25 

art,  24-25 

Heterologous  compounds,  303 
Hexagon  formula  of  benzene,  347 
Hexoses,  454 

Historia  naturalis  of  Pliny,  5 
History  of    chemistry,  alchemistic 

period,  21  -64 
of   chemistry,  from  Lavoisier  till 

now,  158-598 
of      chemistry,      iatro  -  chemical 

period,  65-99 

of  chemistry  in  early  times,  5-20 
of  chemistry,   phlogistic  period, 

100-157 

Hoffmann's  drops,  98 
Homologous  compounds,  303 
Humus  theory,  the,  531  et  seq. 
Hydracides,  241 

Hydrates  of    the    metallic  oxides, 
discovery  of,  187 


Hydrazine,  423 
Hydrazines,  472 
Hydrazoic  acid,  i23 
Hydrazones,  451,  455,  472 
Hydrides  of  aromatic  hydrocarbons,. 

436 
Hydrocarbons,  433-437 

synthesis  of,  361,  434 

aromatic,  435 

researches  on,  433  et  seq. 

unsaturated,  433  et  seq. 
Hydrochloric  acid,  51,  91 

acid  gas,  129 

acid,  manufacture  of,  565 

acid  as  a  type,  302 
Hydrocyanic  acid,  153,  474 
Hydrofluoric  acid,  418 

its  first  use  for  etching  glass,  148 
Hydrogen,  78,  121,  402 

acids,  241  et  seq. 

a    constituent    of   organic    com- 
pounds, 247 

as  a  type,  302  et  seq. 

as  the  primary  material  (Prout), 
202 

as  the  unit  in  the  determination 
of  atomic  weights  (Dal ton),  192 

compounds  of  the  halogens,  418 

determination  of,  395-396 

properties  of  liquid  (Dewar),  493 

replacement  of   in    organic  com- 
pounds, 458-459 
Hydrogen    acids,     theory    of    the 

(Davy;     Dulong),    241     et    seq.. 

245 

Hydro-phthalic  acids,  349,  358 
Hydroxylamine,  422 

as    a    specific   reagent,    365-366, 

451,  462 
Hygiene,  relations  of,  to  chemistry, 

397-399,  545-546 
Hyponitrous  acid,  422 

IATRO-CHEMICAL  doctrines  of  Para 
celsus,  69  et  seq. 

doctrines  of  Sylvius,  81 

doctrines  of  van  Helmont,  76-78 

period,  the,  65-99 
latro-chemistry,  general  notes  upon 
3 

problems  of,  66 
latro-chemists,     practical-chemical 

knowledge  of  the,  87  et  seq. 
Illuminants,  583 
Indamines,  579 
Indigo  blue  (Baeyer),  579 

blue,  artificial  production  of,  579 
Indium,  409 


622 


INDEX  OF  SUBJECTS 


Indole,  485 

derivatives  of ,  472 
Indo-phenols,  579 
Induction,  photo-chemical,  511 
Inductive  methods,  the  gradual  ap- 
preciation of,  32,  65,  101 
Industrial  gases,  393 
Industries,  the  great  chemical,  561 
Inflammable  air,  121 
Inorganic  compounds,  structure  of, 

343,  367  et  seq. 
Inorganic  compounds,  systematising 

of,  367,  371,  et  seq. 
Institut  National,  176 
Instruction,    growth    of    chemical, 
586-598 

systematic    chemical,    207,    265, 
271,  312,  586  et  seq. 

technico-chemical,  556 

chemical,  in  laboratories,  176, 194, 

204,  207,  265,  588  et  seq. 
International  Commission  on  chemi- 
cal nomenclature  of  organic  com- 
pounds, 437 
Iodine,  402,  566 

recognised  as  an  element,  240 
Iodine  (Gay-Lussac),  200 
"  lodo-benzene,"  459 
lodo-   and  iodoso-compounds,    351, 

458-459 

lodonium  bases,  459 
lodoso-benzene,  459 
Ions,  503 
Iridin,  457 
Iridium,  413 
Iron,  13-14,  47,  89,  147,  557-558 

industry,  the,  557 

ores  used  in  olden  times,  13-14 
Iron-carbonyl,  428,  487 
Iron,  chloride  of,  95 

compounds  of,  427 
Isatoic  acid,  320 
Iso-butyric  acid,  441 
Iso-cyanides,  the,  476 
Iso-cyanuric  acid,  477 
Iso-diazo-compounds,  473 
Isogonism,  506 
Isologous  compounds,  303 
Isomerisation  of  hydrocarbons,  435 
Isomerism,  250-253 

geometrical,  356  et  seq.,  500 

of  position,  352-353 

physical,  447 

in  spite  of  identity  in  structure, 

356 
Isomers,  250-253 

structural- chemical,  interpreta- 
tion of,  351  et  seq. 


Isomers    among     the    unsaturated 

acids,  443 

Isomorphism  (Mitscherlich),  221  et 
seq.,  505  et  seq.,  524 

appreciation  of  its  value  by  Ber- 
zelius,  222-223 

polymeric,  505 
Iso-nitroso  compounds,  461 
Iso-propyl  alcohol,  438 
Iso-pyrazolone,  484 

Jahrbuch  der  Chemie,  598 
Jahresberichte  der  Chemie  (Berzelius), 
208,  597 

der  Chemie  (Liebig),  267,  598 
Journal,  Allgemeines  J.  der  Chemie, 
180 

de  Physique,  175 

fiir  praktische  Chemie,  312,  597 
Journal  of  the  Chemical  Society,  596 

of  the  Society  of  Chemical  Indus- 
try, 556 

Journals,  chemical,  595-598 
Journals,  old  German  chemical,  179 
Juices,  the  animal,  van  Helmont's 

views  upon,  77-78 

Kermes  mineral,  the,  94,  155 
Ketones,  451-454 

constitution  of  (Kolbe),  318 
Ketones,  fatty  aromatic,  452 
Ketonic  acids,  451-454 
Ketoses,  455 
Ketoximes,  462 
Krypton,  416 

LABORATORIES,     establishment    of, 

556,  586  et  seq. 
for  students,  207,  265,   312,  586 

et  seq. 

improvement  of,  590 
instruction  in,  586  et  seq. 
recent,  590  et  seq. 
technical,  593 

Laboratories,  Egyptian,  9 

Libavius'  effort  to  establish 
chemical  laboratories  three  cen- 
turies ago,  75 

Laboratory  fittings  and  apparatus, 
593 

Lactic  acid,  153 

acid,  constitution  of,  319 
acids,  the,  319,  446 

Lactones,  448 

Lactonic  acids,  448 

Lana  philosophica,  55 

Lanthanum,  410 

Lapis  infernalis,  95 


INDEX  OF  SUBJECTS 


623 


Latent  heat  (Black),  120 

Law  of  Boyle  and  Mariotte,  106 

Lead,  14 

acetates  of,  57,  96 

sugar  of,  57,  96 
Leblanc  soda,  562  et  seq. 
Lecture  experiments,  587 
Lehrbuch    der    Chemie   (Berzelius), 

207 

Levulinic  acid,  453 
Leyden  papyrus,  the,  23,  24,  26 
Liebig-  Wohler  Letters,  the,  254,  262, 

263,  268,  272 

Liebig's  Autobiography,  263 
"  Life  air"  (oxygen),  131 
Light,  chemical  action  of,  509-511, 
536 

refraction  of,  499 
Lime  used  in  ancient  times,  19 
Linkage,  interchange  of,  351,  355 
Linking  bars  (Couper),  334 

of  atoms,  332  et  seq.,  343 
Literature,  the  more  recent  chemi- 
cal, 594  et  seq. 

technico-chemical,  556 
Lithium,  407 
Lucium,  417 
Lutidine,  480 

MADDER  red,  578 

Magenta,  576 

Magisterium,  41 

Magnesia  alba,  155 

Magnesium,  408,  559 

Magnetism  of  chemical  compounds, 

504 

Maleic  acid,  443 
Malic  acid,  153 
Malonic  acid,  442 
Manganese,  149 

black  oxide  of  (Scheele),  127 

compounds,  427 
Mannite,  439 
Manuals  of  chemistry,  74,  108,  114, 

119,  154,  266,  271, -273-274,  295, 

312,  594  et  seq. 
Manures,  artificial,  567,  574 
Marcasitae,  56 
Marsh  gas,  79 

gas  as  a  type,  309 
Martin  process,  the,  558 
Masrium,  417 

Mass-action,  513,  514,  517  et  seq. 
Matches,  568 
Materia  Medica  (Dioscorides],  5 

prima,  42,  63 

Matiere  de  chaleur  (Lavoisier),  170 
Meconic  acid,  etc. ,  483 


Medicines  of  various  orders  for  the 
transmutation  of  metals,  40 

of  ancient  times,  18  et  seq. 

of  Paracelsus,  70-71 

of    the    iatro-chemists,   73  et  seq. 

of  the  phlogistic  period,  154-155 

recent,  550-551 
Melame,  474,  477 
Melamine,  474 
Meleme,  477 
Mellitic  acid,  444 
Mellone,  474,  477 
Melting  points,  497 
Mercaptals,  464 
Mercaptans,  462-463 
Mercaptols,  464 
Mercurius   philosophorum,    27,    30 

et  seq.,  40  et  seq. 
Mercury,  15,  47 

as  a  constituent   of    metals,    39 
et  seq. 

salts  of,  53,  95 
Mesdem,  the  old  Egyptian  cosmetic, 

18 

Mesitylene,  353,  435 
Metabolism,  animal,  542,  545 

vegetable,  530  et  seq. 
Metalepsy,  277 
Metallic  calces,  59,  164,  165,  112 

chlorides,  91-92 

compounds,    recent    work    with, 
426  et  seq. 

oxides,  55 

salts  in  the  alchemistic  age,  52-53 
Metallo-orgaiiic  compounds,  322  et 

seq.,  486-487 

Metallurgy,     furtherance     of,     by 
Agricola,  84,  88 

in  the  alchemistic  period,  46 

in  the  phlogistic  period,  146 

of  the  ancients,  11 

of  recent  times,  557-560 
Metals,  colouring  of,  38 

derivation  and   meaning  of    the 
word,  11 

duplication  of,  26 

ennobling  of,  21,  25  et  seq.,   37 
et  seq. 

increase  in  weight  on  calcination, 
132,  164. 

nature  of  (Boyle),  134 

nature  of  (Stahl),  134 

old  chemical  theory  of  the,   38 
et  seq. 

oldest   knowledge   of   the,   11    et 
seq. 

supposed  composition  of,  in  the 
alchemistic  age,  39,  41 


624 


INDEX  OF  SUBJECTS 


Metals,  transmutation  of,  2,  8,  21    | 

et  seq.,  37  et  seq. 
Metamerism,  252 
Methane,  composition  of  (Dalton), 

190 

Metargon,  416 
Methods,  analytical,  386  et  seq. 

technico-chemical,  398 

synthetic,      in     organic 
chemistry,  361  et  seq. 
Methyl  violet,  577 
Methylene  blue,  579 
Microscope,  its  application  to  chemi- 
cal research  (Marggraff),    117, 
143 

Milk,  chemistry  of,  542 
Mineral  potash,  567 
Mineral  system,  the  chemical  (Ber- 
zelius),  205 

pigments,  560 

pigments  of  ancient  times,  18 

tanning,  581 

waters,  artificial,  555 

waters,  analysis  of,  in  the 

Phlogistic  period,  142 
Mineralogical  chemistry,  522-529 

systems  (Berzelius  and  others),  525 
Minerals,  analysis  of,  176,  178,  205, 
384  et  seq.,  389,  525 

artificial  production  of,  527-529 

classification  of,  523  et  seq. 

classification  of  (Bergman),  124 

Klaproth's  researches  on,  178 

nomenclature  of,  525 
Mixture-weights  of  the  elements  (L. 

Gmelin),  203 
Modern  chemical  period,  the  (from 

Lavoisier),  158-598 
Molasses,  crystallizable  sugar  from, 

573 
Molecular  compounds  (Kekule),  339 

weight,     determination     of,     by 
vapour  density,  376,  490 

weight,      determination     of,     in 
solutions,  376,  502 

heat,  509 

weight  (Laurent),  294 
Molecule,  definition  of  the  term,  by 

Laurent,  294 
Molecules,   liquid,    complexity    of, 

500-501 

Molybdenum,  410,  429 
Molybdic  acid  (Scheele),  151 
Monochlor-acetic  acid,  459 
Mono-saccharides,  456 
Mordants,  17,  47,  90,  147,  580 
Morphotropism,  506 
Mortar,  571 


Mosaic  gold,  147 

Mosandrium,  417 

Mucic  acid,  153 

Multiple  types,  302 

Muscular  power,  sources  of,  545 

Mustard  oils,  the,  467,  476 

Myronic  acid,  456 

NAPHTHALENE,  435 

Naphthenes,  436 

Narcotics,  551 

Natural  Philosophy    of  the    early 

part  of  this  century,  263 
Neon,  416 
Nestorians,  the,  28 
Neurine,  synthesis  of,  467 
Neutralisation,  law  of  (Richter),  183 
Nickel,  149,  410,  558 
Nickel-carbonyl,  428,  487 
Nickolanum,  417 
Nicotine,  483 

Niobium  (Marignac),  369,  410,  430 
Nitragins,  535 
Nitric  acid,  51-52,  148,  566 

acid,  composition  of,  122,  150 
Nitric  oxide,  130 
Nitrification,  534 
Nitriles,  475 

dimolecular,  478 
Nitro-benzene,  460 

reduction  of,  466 
Nitro-ethane,  461 

-glycerine,  568 

-methane,  461 

-prussides,  428 
Nitro-compounds,    organic,    460    et 

seq. 
Nitrogen  chloride,  424 

compounds,  inorganic,  422  et  seq. 

compounds,  organic,  465  et  seq. 

discovery  of,  130 

estimation  of,  275,  396-397 

diffusion  of  (Ramsay  andTravers), 
402 

direct  assimilation  of,  by  plants, 
535 

density  of,  415 

group  of  elements,  atomic  weights 
of,  404 

group  of  elements,  compounds  of, 
422  et  seq. 

oxides  of,  422 

iodide  of,  424 
Nitrolic  acids,  461 
Nitrols,  461 

Nitroso-compounds,  461 
Nitrous  acid,  150 
Nitrous  oxide  (Davy),  K6 


INDEX  OF  SUBJECTS 


625 


Nitrum,  16,  52 

Nomenclature,  chemical  (Lavoisier, 
etc.),  171-172 

chemical  (Berzelius),  234 
Nordenskiold's  Life  and  Journals  of 

Scheele,  125,  173 
Notation,  chemical  (Dalton),  194 

chemical  (Berzelius),  235-237 
Nuclei,       original       and       derived 

(Laurent),  278 

Nucleus  theory  (Laurent),  278-280 
Nutrients,  544-545 
Nutrition  of  animals,  544  et  seq. 

of  plants,  531  et  seq.,  536  et  seq. 

Oelsiiss,  154 

Oils,  ethereal,  20,  582 

Oils  (fatty)  known  in  ancient  times, 

19 
Optical  activity,  its  connection  with 

chemical  constitution,  357 
Organic  chemistry,  development  of, 

up  to  1811,  246  et  seq. 
special  history  of,  432-487 
compounds,  chemical  behaviour  of , 

365 

compounds,  constitution  of,  317, 
251  et  seq. ,  303  et  seq. ,  332  et  seq. , 
344  et  seq. 

compounds,  modes  of  decompos- 
ing, 366 

compounds,  structure  of,  336,  344 
substances,    qualitative   composi- 
tion of,  248,  393 

substances,  quantitative  composi- 
tion of,  248,  393  et  seq. 
Organic  compounds,  knowledge  of, 

in  the  phlogistic  age.  151 
classification  of,  278-279,  289,  302 
compounds,    distinction  from  in- 
organic, 246-247 

Organo-metallic  compounds  (Frank- 
land),  322  e*  *eq.,  486-487 
Orthrin,  255 
Osazones,  455,  472 
Osmium,  414 
Osmose,  501 

Osmosis  of  sugar  solutions,  573 
Osmotic  pressure,  501-502 
Ostwald's  Kla**ikert  214 
Oxalic  acid,  153,  582 

acid,  synthesis  of  (Drechsel).  442 
Oxalines,  468 
Oxalo-acetic  ester,  453 
Oxaluric  acid,  468 
Oxazoles,  486 

Oxidation  theory   (Lavoisier),   166- 
167 


Oxy-acids,  constitution  of  (Kolbe), 
319 

organic,  446 
Oxydes,  172 
Oxygen,  absorption  of,  by  palladium 

and  platinum,  430 

"  rendering  active  "  of,  406 

atomic  weight  of,  403 

acids,    theory   of   the,    167,    197, 
237-238 

law,  the  (Berzelius),  212 

as    the    unit    in    atomic    weight 
determinations  (Berzelius),  217 

importance  of,  for  the  antiphlo- 
gistic system,  171 

importance    of,    for    the    atomic 
theory,  210  et  seq. 

discovery  of,  124,  127,  131  et  seq., 
165 

compounds  of  the  metals,  426  et 
seq. 

compounds     of    nitrogen,     phos- 
phorus, etc.,  422-423 

compounds  of  the  halogens,  418 

compounds  of  sulphur,  420 
•  Oxy-muriatic  acid,  239 
Ozone,  405-406 

PALLADIUM,  413 

"  Panacea"  of  the  ancients,  27,  44 

Paper  manufacture,  572 

Parabanic  acid,  468 

Paraffin  industry,  the,  583 

"  Parallelosterism,"  496 

Para-oxybenzoic  acid,  448 

Para-rosaniline,  576 

Pathology,  its  relations  to  chemistry, 
549  et  seq. 

Pattinson  process,  the,  558 

Penta-methylene-diamine,  480 

Pentite,  439 

Pepsine,  541 

Peptones,  541 

Periodic  system  of  the  elements,  370 
et  seq. 

Periods  of  the  elements,  371-372 

Periods,  the  various  chemical,  1  et 

seq. 

the  various  chemical,  their  charac- 
teristics, 1-4 

Perkin's  violet,  577 

Peroxides  of  organic  acid  radicals, 
445 

Per-sulphuric  acid,  420 

Petroleum  industry,  the,  583 

Pharmaceutical  preparations  of  an- 
cient times,  18 

Pharmacy,  development  of,  71 

S   S 


626 


INDEX  OF  SUBJECTS 


Pharmacy  in  the  iatro-chemical  age, 
91  et  seq. 

its  relations  to  chemistry,  552 
Pharmacy,  text  books  of,  553 

instruction  in,  553 
Phenacetine,  551 
Phenanthrene,  435 
Phenols,  440 

manufacture  of,  581 
Phenyl-hydrazine,  472 

as    a    specific   reagent,    365-366, 

451,  455,  462 

Phenyl-propiolic  acid,  444 
Philippium,  417 
Philosopher's  stone,  the,  30  et  seq., 

40  et  seq. 
Philosophical  Transactions,  the,  102, 

596 

Phlogistic  period,  general  history  of 
the,  100-128 

period,  merits  of  the,  155-157 

period,  special  history  of  the,  128- 
155 

period,  the,  100-157 

system,  fall  of  the,  168 
Phlogisticated  air  (nitrogen),  131 
Phlogiston  an  element,  135 

assumption  of  the   hypothetical, 

110  et  seq. 

its  identification  with  hydrogen, 

122,  130,  159 

theory,  beginnings  of  (Becher),  110 
theory,    development   of   (Stahl), 

111  et  seq. 

theory,     its     development    after 
Stahl's  time,  115  et  seq. 

theory,  general  notes  on  the,  4 

theory,  its  value,  113 
Phlogistonists,  practical  -  chemical 

knowledge  of  the,  140  et  seq. 
Phloroglucin,  tautomerism  of,  354 
Phosgene,  425 
Phosphines,  etc.,  469 
Phosphonium  bases,  469 
Phosphoric  acid,  117,  150 

acids,  basicity  of,  244 
Phosphorous  oxide,  423 
Phosphorus,  149,  404 

manufacture  of,  569 

pentafluoride,  340 

allotropic  modifications  of,  406 

hydrides  of,  421 

oxygen  compounds  of,  423-424 
Phosphyl  compounds,  462 
Photo-chemistry,  509-511 
Photography,    historical   notes   on, 

510 
Phthaleins,  578 


Phthalic  acid,  578 

Physical  chemistry,  special  history 

of,  488-521 
chemistry,  its  general  significance, 

375  et  seq. 

methods,  application  of,  to  chem- 
istry, 156,  376 

Physics,  influence  upon  chemistry  at 
the  beginning  of  the  phlogistic 
period,  101 

Phyto-chemistry,  536  et  seq. 
Picric  acid,  460,  580 
Pigments  of  antiquity,  the,  17-18 
Piperidine,  408 
Pitocarpine,  483 
Planets,  their  relation  to  the  metals, 

25 
Plant  juices  first  used  as  indicators 

by  Boyle,  131 
Plant-nutrients,  532  et  seq. 
Plastic  compounds  (nutritive),  544 
Platinum,  149,  413,  558-559 
bases,  430 

chloride,  compounds  of  with  car- 
bon monoxide,  431 
compounds,  430 
metals,  the,  413-414 
their  atomic  weights,  414 
Poisons,  methods  for  detecting,  397- 

398 

Polarity,  electric,  of  atoms,  230-231 
Poly-azines,  350,  353 
Poly-azoles,  353 
Polybasic  acids,  doctrine  of  the,  243 

et  seq. 
Poly-carboxylic  acids,  442 

-sulphonic  acids,  464 
Polymerism,  252 
Polymorphism,  505,  525 
Poly-saccharides,  456 
Porcelain,  17,  63,  147,  571 
Position,  determination  of  chemical, 

352-353 

Position-isomers,  353 
Position  of  elements  in  the  periodic 

system,  373 

Potash,   distinction  of,   from  soda, 
92,  118 

industry,  the,  567 
salts,  deposits  of,  567 
salts  as  medicines,  92 
Potashes,  16,  17 
Potassium,  238,  407,  426 

carboxide,  acids  from,  453 
Potter's  art,  the,  17,  47,  89,  571 
Pottery,  17,  47,  89,  571 
Powder,  smokeless,  568 
Precious  stones,  artificial,  16,  570 


INDEX  OF  SUBJECTS 


627 


Precious  stones,  old  imitations  of, 

16 

Precipitates,  96 
Prediction  of  alcohols  (Kolbe),  318 

of    new   elements    ( Mendel ejeff), 

373-374 

Preparations,  chemical,  their  manu- 
facture, 581-582 

old  chemical,  18 

old  medicinal,  18,  19 

officinal,  in  the  phlogistic  age,  154 

technico-chemical,    in    the    phlo- 
gistic age,  147 
Pressure,  critical,  493 
Priestley's     researches     on     gases, 

123-124 
Primary  material,  assumption  of  a, 

374 

Princes  as  patrons  of  alchemy,  61 
Principe  oxyyine,  167 
Prism-formula  of  benzene,  348-349 
Progression,  law  of  (Richter),  183- 

184 

Prom,  255 
Propiolic  acid,  443 
Proportion-numbers  of  the  elements 

(Davy),  199 

Proportions,   doctrine   of   chemical 
(Richter),  182  et  seq. 

law    of    constant    (Proust),    181, 
185-188 

law  of  multiple  (Dalton),  189  et 
seq. 

law  of  multiple,  further  developed 

by  Berzelius,  etc. ,  210  et  seq. 
Protyle  (Crookes),  374 
Prout's  hypothesis,  201  et  seq.,  370 
Prussian  blue,  147 
Prussic  acid,  153,  473 
Pseudo-forms  of  compounds,  354 
Ptomaines,  398,  549 
Ptyalin,  541 
Putrefaction,  548  et  seq. 

bases,  398,  549 
Putrescine,  549 
Pyra/ine,  485 
Pyrazines,  481 
Pyrazole,  483 
Pyrazolone,  484 

derivatives  of,  472 
Pyrene,  436 
Pyridine,  constitution  of,  350,  479 

bases,  478  et  seq. 
Pyrimidine,  481,  485 
Pyrimidines,  481 
Pyroligneous  acid,  153 
Pyromucic  acid,  484 
Pyrrol,  350,  484 


Pyrrolidine,  484 
Pyrroline,  484 

QUALITATIVE  tests  for  substances, 

141-144 
Quantitative  researches,  period  of, 

158  et  seq. 

Quick  vinegar  process,  the,  575 
Quinazoline,  485 
Quinazolines,  481 
Quinoline,  350,  480,  485 

derivatives  of,  481 
Quinoline,  synthesis  of,  479  et  seq. 
Quinones,  452 
Quinoxalines,  481 
Quinta  essentia,  8 
Quintessence,  96 

RACEMIC  acid  (discovery  of),  206 

acid,  isomeric  with  tartaric,  252 
Radical  theory,  first  steps  towards 
the,  246,  249 

theory,  the  newer,  313-320 

the  older,  253-262 

theory,  supersession  of  the  older, 
285 

theory,  fusion  of  the  older  radical 
theory  with  the  type  theory  by 
Laurent  and  Gerhardt,  286 
Radical  vinegar,  96 
Radicals,  oxygenated,  255,  257 

chemistry  of  compound,  259 

compound,  247,  249 

polyatomic,  302 

the  clearer  definition  of,  260 

variability  of,  257,  279 
Reaction,  time-rate  of,  518-519 
Reactions,  specific,  of  organic  com- 
pounds, 365 
Reagents,  introduction  into  analysis, 

141  et  seq. 

Reciprocal  reactions,  518 
Reform  of  chemistry  by  Lavoisier, 

166,  170 

Refraction-equivalents,  498 
Regenerators,  584 
Replaceable  value  of  elements,  323, 

326-327 

Residues,  theory  of  (Gerhardt),  287 
Respiratory  compounds  (nutritive), 

545 

Retene,  436 
Rhamnite,  439 
Rhodamines,  579 
Rhodium,  414 
Rosaniline,  576 
Royal  Society,  the,  102 
Rubidium,  407,  426 


628 


INDEX  OF  SUBJECTS 


Ruby,  artificial  production  of,  529 

glass,  89,  147 
Russium,  417 
Ruthenium,  413 

SACCHARIDES,  456 

Saccharimetry,  573 

Saccharine,  574 

Safety  lamp,  the  Davy,  197,  584 

Safranines,  579 

Sal,  50 

ammoniacum,  53 

mirabile,  92 
Salicin,  456 

Salicylic  acid,  319,  447,  550,  582 
Saliva,  chemistry  of  the,  541 
Salmiac,  53,  93,  149 
Sal  nitri,  52 
Salpetrce,  52 

Sal  polychrestum  (Glaser's),  155 
Salt  as  a  constituent  of  the  metals, 
41 

its  meaning  in  the  alchemistic 
and  iatro-chemical  periods,  50, 
82-83 

Rouelle's  definition  of  a,  119,  136 
Salts,  constitution  of  (Berzelius),  233 

constitution  of  (Liebig),  245 

nomenclature  of  (Lavoisier),  172 
Saltpetre,  52,  92 

as  a  manure,  17 
Sarcosine,  467 

Saturation-capacity,  assumption  of 
a  constant  (Kekule),  338  et  seq. 

-capacity  of  the  elements  (Frank- 
land),  322  et  seq. ,  325,  337 

of  carbon,  327  et  seq. 
Scandium,  369,  410 
Scheele's  Letters  and  Journals,  125 

researches  on  gases,  129 
Schweinfurt  green,  560 
Secretions,  animal,  541 
Seignette  salt,  97 
Selenium  (Berzelius),  404 

compounds,  inorganic,  421 

compounds,  organic,  463 
Sheep's-wool  grease,  20 
Siderum,  417 

Silicates,  fusion  with  alkaline  car- 
bonates (Bergman),  388 
Silicon,  406 

alkyl  compounds  of,  486 

compounds  of,  424 

carbide,  428 
Silver,  12,  46,  88,  558 

mirrors  (Liebig),  269 

nitrate  of,  53,  95,  560 

allotropio  modifications  of,  406 


Silver,  oxides  of,  427 

extraction  of,  from  ores,  558 
Smalt,  90 
Soap,  17,  148 

manufacture,  569 
Societies,  learned,  101-102 
Soda,  17,  18 

artificial  preparation  of,  118,  148, 
149,  569 

industry,  the,  562-564,  565 

salts  as  medicines   in  the   iatro- 
chemical  age,  92 
Soda-waste,    working    up  of,    563- 

564 

Sodium,  238,  407,  426,  559 
Sodium  peroxide,  426,  559 
Soils  from  a  chemical-agricultural 

point  of  view,  531  et  seq. 
Solar  spectrum,  chemical  action  of 

the,  510 
Solder,  14 

Solidification,  Raoult's  law  of,  502 
Solution,  theory  of,  376,  501  et  seq. 
Soporifics,  551 
Spagiric  art,  the,  25 
Special  history  of  modern  chemistry, 

381  et  seq. 
Specific  gravity  of  gases,  129 

heat  (Lavoisier  ;  Laplace),  162 

heat  of  solids,  497 

heats  of  the  metals,  relation  to 
their  atomic  weights  (Dulong 
and  Petit),  220 

volume,  495 

Spectrum  analysis,  385-386,  494 
Spirit-lamp  (Berzelius),  388 
Spirit  of  wine,  49,  57,  98,  152 

sweetening  of,  57 
Spirits,  manufacture  of,  575 
Spiritus,  50 

fumans  Libavii,  95 

igno-aereus  (Mayow),  130 

Mindereri,  93 

salis,  50-51 

tartari,  97 
Starch,  19,  149,  456,  538,  572 

sugar,  572 
Stassfurt  salts,  567 
Statique  Chimique  (Berthollet),  174, 

185,  514 

Stearine  candles,  569 
Steel,  89,  146,  557 
Steren,  496 
Stereo-chemistry,  355  et  seq. 

of  nitrogen,  359  et  seq,  462 
Stereo-isomerism,    355  et  seq,   443, 

459,  473 
Stibines,  &c.,  469 


INDEX  OF  SUBJECTS 


629 


Stochiometry,  387 

founding  of  (Richter),  185 
Strontium,  197,  408 
Structural  formulae  (Couper),  334 
Structure,  chemical,  332,  336  et  seq. 

theory,    beginnings    of   the,    332 
et  seq. 

theory,  development  of  the,  342 

et  seq. 

Sublimate,  53 
"  Substantive  cotton  dyes,"  578 

dyes,  147 

Substitution,  first  observations  upon, 
276 

-form  (Gerhardt),  288 

laws  of  (Dumas),  276 

theory  (Laurent),  278 

partial    admission    of,    by    Ber- 
zelius, 284 

Succinic  acid,  97,  442 
Sugar  from  beet  juice,  116,  149,  573 

estimation  of,  392 

refining  of,  573 
Sugar,  known  by  the  ancients,  19 

from  sugar  cane,  99 
Sugars,    synthesis  and  constitution 

of,  455-456 
Sulphines,  464 
Sulphinic  acids,  465 
Sulphite  cellulose,  562,  572 
Sulphone-ketones,  464 
Sulphones,  464 
Sulphonic  acids,  463-464 
Sulphonal,  464 
Sulphoxides,  464 

Sulphur,  allotropic  modifications  of, 
406 

atomic  weight  of,  404 

balsam,  56 

as   a  constituent  of    the  metals, 

39,  55-56 

Sulphur  auratum,  94 
Sulphur,  compounds  of,  420 

compounds    of    the    alchemistic 
period,  55-56 

compounds,  organic,  460,  465 
Sulphur  >  .'//'/•,  152 
Sulphur,  milk  of,  56 
Sulphur  philosophorum,  52 
Sulphur,  recovery  of,    from  alkali 

waste,  563-564 
Sulphures,  172 
Sulphuretted  hydrogen,    discovery 

of,  129 
Sulphuric  acid,  51,  91 

acid,  anhydrous,  562 

acid,  fuming,  148 

acid,  manufacture  of,  148,  561 


Sulphurous  acid  gas,  19,  129 

acid,  practical  utilisation  of,  562 
Symbols,  chemical  (Berzelius),  235 

(Dalton),  194 
with  bar  across  them  (Berzelius), 

236,  283 
Synthesis  by  condensations,  362 

of  organic  compounds,  361  et  seq. 
Syrians,  culture  among  the,  28 
System,   chemical,   of  the  minerals 

(Berzelius),  524 
natural,    of    the     elements,    370 


periodic,  370  et  seq. 
Systematization   of  inorganic 
compounds,  367 

of  organic  compounds,  433 
Systeme  unitaire  (Gerhardt),  303-304 

Tables  des  Rapports  (Geoffrey),  117 

Tables  of  affinity  (Geoffrey),  117 

Tannic  acids,  537 

Tanning,  580 

Tantalum  (Marignac),  369,  412-413, 
430. 

Tar,  products  from,  582 

Tartar,  96-97 
emetic,  73,  97 

Tartaric  acid,  153 

acids  (optically  isomeric),  447 

Tartarus,  70,  97  . 

Taurine,  constitution  of,  319 

Tautomerism,  354-355 

Technical  Schools  and  Colleges,  556 

Tellurium,  403-404 

compounds,  inorganic,  420-421 
compounds,  organic,  462-463 

Temperature,  critical,  493 

Tension-series  of  the  elements  (Ber- 
zelius), 231-232 

Terbium,  410 

Terpenes,  436 

Terra  pinguis  (Becher),  110 

Tetrolic  acid,  443 

Text-books      of     chemistry.        See 
Manuals 

Thallium,  409,  427 

Therapeutics,  relation  of,  to  chemis- 
try, 494-495 

Thermo-chemistry,  507-509,  517 

Thiacetic  acid,  463 

Thiamides,  468 

Thiazoles,  486 

Thio-aldehydes,  451 

Thiocyanogen,  475 

Thionylamines,  465 

Thiophene,  350,  484 

Thomas-Gilchrist  process,  the,  557 


INDEX  OF  SUBJECTS 


Thorium,  411 
Thymol,  550 
Tin,  14,  89 

compounds  of,  429 

dioxides,  isomeric,  251 

perchloride  of,  95 
Tinctures,  38 
Tincture  for   changing    silver  into 

gold,  27 

Tinder,  chemical,  568 
Titanium,  179,  411 
Titrimetry,  201,  390 
Toluidines,  577 
Traite"  fiUmentaire  de  Chimie  (La- 

vosier),  164 

Tri-    and  Tetra-methylene    deriva- 
tives, 435 
Tri-amines,  465 
Tri-azines,  481 

Triazole,  485  ,--"  .    •     '  ' 

Tri-methylamine,  467 
Trichloracetic  acid,  275, -.280,  283, 

459  .    . 

Trimethyl-carbinol,  438  <•'«!/*"'' 

Trimethylene,  435 
Triphenyl- methane,  436 

-phosphine  oxides,  isomeric,  340 
Tropseolines,  the,  578 
Tungsten,  410,  429 
Tungstic  acid  (Scheele),  151 
Turpentine,  oil  of  (known  to   the 

ancients),  19 
Turpeth  mineral,  95 
Tutty,  15 

Two-volume  formulae,  293 
Type  metal,  560 

Type  theory,  the  newer  (Gerhardt), 
300  et  seq. 

theory,   the  newer  (Kekule),  307 
et  seq. 

theory,  the  newer  (Sterry  Hunt), 
301 

the  newer  (Williamson),  298  et  seq. 

the  newer,  preparatory  work  for, 
295  et  seq. 

theory,  the  older  (Dumas),   280- 

281 
Types,  chemical,  281 

condensed,  302,  307 

duplicated,  302,  307 

(Gerhardtfs),  300  et  seq. 

mechanical,  281 

mixed,  308-309 

real,  as  opposed  to  formal,  307,  321 

auxiliary,  303 

ULTRAMARINE,  570 

Unitarism,  beginnings  of,  237  et  seq. 


Unitarism,  development  of,  275,  281 

et  seq. 

Universal  medicine,  44 
Universities,  establishment  of,  65 
Unsaturated  compounds,  345 
Uranium,  179,  410,  429 
Urea,  estimation  of,  392 

synthesis  of,  252,  361 
Ureas,  substituted,  477 
Uric  acid,  153,  268 

derivatives  of,  468 

synthesis  of,  468 
Urine,  542 

analysis  of,  543 

chemistry  of  the,  542-543 

VALENCY    of    the    elements.       See 
Saturation-capacity 
tant  or  varying,  337-342 
*ine  of,   its  influence  on  the 
••••(  •  &&&$pment  of  chemistry,  331 

maximum,  338 

,  326-328 

oFcarbon,  327-330 
definite,  331 
varying,  325,  336 
its  application  to  inorganic  com- 
pounds, 367 

Vanadium  (Roscoe),  369,  412,  429 
Vanillin,  449 

Vapour       density      determination, 
methods  of,  &c.   (Dumas,  Gay- 
Lussac    and    Hofmann,   Victor 
Meyer),  225,  376,  490  et  seq. 
densities,  abnormal,  492 
pressure  of  liquids,  497 
pressure  of  solutions,  502 
Vegetable  physiology,  530  et  seq. 
Versuch  iiber  die  Theone  der  chemis- 
chen    Proportionen   (Berzelius), 
213,  235 
Vitriols,  52 

"Volume-atoms"  (Berzelius),  216 
Volume    theory     (Berzelius),     216, 

229 
Volumes,    law     of,     extension    by 

Avogadro,  215 
law  of  (Gay-Lussac),  200,  214  et 

seq.,  490 

law  of,  its   appreciation  by  Ber- 
zelius, 216  et  seq. 
specific,  495 

Volumetric  analysis,  390 
analysis,  beginnings  of,  201 

Wahlverwandtschaft,  138,  333 
Water  as  a  type,  298  et  seq. 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

LOAN  DEPT. 

This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 
Renewed  books  are  subject  to  immediate  recall. 


LOAN 

jUN  11  1973 


REC'D  LD     NV  1  2  1974  o  1 


LD  21A-50m-ll,'62 
(D3279slO)476B 


General  Library 

University  of  California 

Berkeley 


YC    10742