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^Iransfar from Circ. Dept
JUL 1913

THE PRINCIPLES

INORGANIC CHEMISTRY

i^fij^

-| HE HEW YORK
PUBLIC LIBRARY

051276

AC 'OR. LFNOX AND

\ILO N F01INDATI0N8.

R 19'3 L

♦ . •

• • •
• • • ,

Mirat-BOUmi 1902.' Seamd Bdjii^l »«&.* •
'. .• . V...* •

••••!•

• • •

•■ • I .-.•V . ^

«. « 1 1

DEDICATED
TO UT DEAR WIFE

ft}elene

IN GRATITUDE FOR LOYAL HELP

TRANSLATOR'S PREFACE
TO SECOND EDITION

In the present English edition the translation has been ravised in
accordance with the second German edition published at the beginning
of the present year, and only a few alterations, necessitated by the
advance of investigation, have been introduced. Of these, the moat
important is the section on lu-anium rays and radio-activity, which
has been entirely rewritten by the author for this translation.

In revising the proof-sheets 1 have enjoyed the excellent co-
operation of Mr. D, F. Twiss, M.Sc., to whom I would here express
my sincere thanks.

A. F.

BiKMINUHAM, July 1904.

PREFACE TO THE SECOND EDITION

The fftct that, in the space of three years, the four thousand copies
(orming tfae first edition were entirely exhausted, baa given me the
iraoce that in spite of certain, in some cases pas«iontite, opposition
to the line of instrtiction set forth in this book, a large and increasing
cwmber of yoiuiger and older fellow-chemiats believe, with me, in the
auitability of these new methods. This impression was strengthened
by the fact that the translations into English and Hussian which have
q^ieared have also reached a cireulaliun which is to be numbered by
thooiSQds of copies. Tratighkliona into Japanese and French are also
about to appear, L^tly, I believe that the same interpretation may
bs placed on the fact that in several text-books, both in German and

^gft other languages, these new ideas have been adopted and iipplied by

^^Mer authors.

^^H I liATe, therefore, found no cause for making any essential changes
TO this book, although I have felt it to he my duty to subject the
maleiial to a careful re\'ision, and, where necessary, to correct or
unplify it. In the case of the inti'odiictory paragraphs I have again
felt the desirability of rewriting them, and of developing the funda-
meBtal conceptions in a clearer and rtiore concise manner.

In carrying out the revision I have enjoyod the excellent assistance
of Dr. Herbert Freundlich, to whom I would here express my sincere
Uonks for hia extensive and intelligent aid, In expressing my thanks
iro the numerous colleagues and fellow^^hemists who have assisted me
by the communication of printer's errors and of objections, I would
also make the i-equeat that they will lend their valuable cooperation
ia the case also of this new edition. For such assistance I am

X PRINCIPLES OF INORGANIC CHEMISTRY

indebted more especially •to my colleagues, Professors Abegg
Vater; as also to the translator of the English edition, Dr. j
Findlay. Perhaps, also, I may hope that as the book passes into 1
quarters which have hitherto held themselves more aloof from
newer chemistry, criticism from the point of view of the requiren
existing there, may let me know the additions which may be neces

W. OSTWAU

Leipzig, October 1903.

TRANSLATOR'S PREFACE

Ix pre-seiitiTig the accompanying translation of the Grundlinien der
anirr^niithfn Chenm to English -aiieaking etudents, the tmnalator
bopes to ije thereliy contrilniting somewhat to a more wide-spread
knowledge of the a[jpHcation of the more recent developments of
General Chemistry, and conseijuently to a more just appreciation of
their importAnce in the stndy of the other htaticbes of tde science.

In the present translation the niii^takes which had crept into the
German edition have been, as far as possible, corrected, fknd othermso
Tarious minor changes have been made. As, however, these have all
been made either at the author's suggestion or with hia approval,
special attention need not be drawn to them.

One change, howev*cr, relating to the nomencljitiuG of the ions,
calla for special mention. The terminology adopted in this translation,
«rith the approval of the author, is that proposed by Professor .Jamea
Walker, F.RS. (ClmniMl Nm\s, 1901, 84, 162). I would express
my thanks to Professor Walker for his kindness in placing this
nomenclature before me in time for its incorporation in the present
translation.

The proof-sheets have all passed through the hands of the author,
I would here express my indebtedness to him for suggestions
iDsde while the book was pa.ssing through the press. My best thanks
are also duo to Messrs, R, S, Hutton, M.Sc., and Sydney A. Kay,
RSc, for their invaluable assistance in reading the proof-sheets.

A. F.

. USrVKBSJTY COLLF.OK,

LoN'DON, Jamtaty 1902.

PEEFACE

Thk first sketch of the present work dates back double the time
deciignnted by Horace as n«c9Mary for the muturing of a literary work,
and some of the attempts to overcome the diffiniltiea which were then
met with have occupied me during the whole period uf my activity na
a teacher. The recognition that such a task is, by its nature, unlimited,
iiiid that it is possible to timnt! it ajf but not to Itrintf it to a ctnwlusimi,
finally brought the resotutioii to maturity to give publicity to the
accompanying attempt.

The task which hereby presented itself was to bo incorporate the
new notions and theories of scientific chemistry in the course of
instnicttou that the student would, from the beginnitig, be made
ncquaiiited with the improved viewa instead of having first to learn
the older, untenable notiona, only to find out later that thcae nuiBt
be abandoned. It was therefore necessary to consideralily alter the
funditmental form which is at present found, with slight modification,
in the present text-books, I have endeavoured to do this only to such
an extent as appeared to >« demanded by the object in view, antl have
r«tsined as much :ui was possible of the approved forms. If in thia
respect I have Ijeen too radical in my prcicedure for the feelings of
sfirne of my colleagues, it should be remembered that new cloth in old
garments will not suffice here. On the coutrary, a connected whole
««ti be produced only when it is formed irj its entirety by une mind
Mtl eieeuted according to one plan.

I have retained, in the first place, the naturohistorical arrange-
Kient of the subject-matter. One coidd, perhaps, oven now venturg^
tie experiment of constructing chemistry from the commencement
» rational science on the liasis of a few geneml principles, and int
"Incing the description of the various substances only in illustratinn
theie general laws I have been deterred from this by the r

XIV

PEINCIPLRS OF INOKGANIC CHEMISTRY

of the histoiical connection, and bj the recognition of the fact th
diversity of substfinces is too great and a knowJecige of each of
too important t<i allow of such a method of treatment Vjeing tnajj
of for inatruction at the present time. Tlie course I have pn
therefore, is to insert the general laws in the traditional frai
the niituro-histuricai arrangement according to elements and
compounds, at those points where cause arid opportunity for U
sented tliemselves. The ttisk to be accomplished here haa'^
resemblance to an artistic problem ; for the insertion of the g^
laws could not be left lu chance occasions, but these laws themi
b»iJ to follow a systematic ai-rangemeiit which would ensure
comprehenBion ami tlie recoguitioii of their mutual connei
. Accordingly, I cannot regard the solution atteropted by me a,
only possible one, and wti imagine immerous other ways of atta
the end. It appeared to me, however, to be worth while to endej
to prove that &ueh a course of instruction is possible at all.

A text-book which pursues reformatory plans of the above ni
appeak naturally to two kinds of readers — the teacher and the atU'
and has therefore a double task to perform, which increasts the la
not a little. In this connection I have always, in cases of doubt,
had regard to the requirements of the student, and have thereby
led to a certain fulness of treatment which would not have
necessar)' had I written exclusively for the t«acher. If the lattet
to take much that is " self-evident " along with the rest, he has
the other hand, the convenience of finding the subject-matter air*
formed into shape, and only requires to modify it according to
personal views, without himself having to carry out the remouldin
the material for his pupils.

With regard to the student, I have felt myself pledged to
carrying out of the chief thought, viz. — to offer him a re
systematically arranged subject, strictly developed in such a
that for a comprehension of the new facts only a knowledge of l
which has preceded is assumeil, not of that which follows. To rer
the hrst study more easy, the discussions which in a hrst reading i
be omitted, either because of their being more foreign to the sub
in hand or iiecause of especial diHiculties, are marked with an aster
In all cases I have made it a ndu to introduce general discussi
odIj' when some readily intelligible facts furnished an example
which these considerations were to be applied. 1 have therefore
leaitatcd to return repeatedly to the same question whenever

PREFACE

me that its complete discussion at the point where it was
im intrwiuce^i would lend too far afield. The be^iiuier, especially,
kope to b*ve more thiiri co!(i[)ensttted for the losa of systeiuatici
w which such a method makes iiecesssiry, by the assurance of a
fuuiUarity with the subject.
Por Ute carrjing out of the rational eoiistniction of the chemtcnl
tftUta, ft method has proved suitable which, iis baa meanwhilu
tfftaxtd, was always applied by tiie recently deceased great master
lical investigation and teaching, Robert Uunsen. It consists in i
I a short summary of the cliernical relations which are familiar
i«tety ckne from K is daily life, after the fundamental conceptions of
^miftrjr have been established, but Viefore the regular description of
(obitaiioes tind iheir tmnaforniations. This summary approfiriuteiy
ihwt on the introduction of the conception of chemkfi! ekmeyits :
: only does that conception thereby receive ample illustration, but
br further aH vantage is obtained that where, m no often occurs, the
ity Arises of njentioning substances which are treated only at a
iit«r point of the course, reference can be made tjr> what has there
aid.

I have exercised particular care in the development of the
of ifms- Sufficient attention ib perhaps not paid to the
ity, the neceAsitj- even, of introducing this conception ns a
purely chemical and not as an electrical one. Even although,
Uitofically, it arose as tiie latter, its importance in chemistry dt;peuds
|4M0tially on it« giving expression to the chemiral tact of the iniimt/nal
uf the a>Mpvttents of stUh; and it is in this sense that I have
veloped it. The f.icts of electrolysis atid Faraday's law serve then
ly to widen tiud to dee{ien tlie conception obtained by a chemical
nethod. 1 believe also that this is the way in which these views can
W inttodoced even at a very earlv stage of cheniicil instruction, without
tBtkiog too great deuiands on the pupil.

lu this connection I cannot refrain from expressing my conviction
com]iarr(l with formerh', the demands made on lite intellectual
uion of tUo student of chemistry tiuiBt be incre;ised. In pro-
M chemistry develops from the condition of a descriptive to
a rntional pcienee, it makes gi'eater claims on the powera of
tboQgbt Aud al>%traction of its disciples. In this rcs|iect it approaches
mm Aiwl more tu |)hysics. Since, indeed, it is chiefly the same
wuUalii who are at the same lime learning chemistry and physics, the
activity with which the student of piiysica is accredited

PRiyCIPLES

VMj »lao be claimetl fur tbe ^ttulent of cbenmuy. [ cannot cooi
tbs &«t that I bAve Always been gnaXif griered bj tbe emaaoas
doMcat to a lower intellectital stage wbieh is so often (cnxml in
eleneotary ehemical text-buoica as comp&reci with tbe text-books of
pbjnriet or ol nuitbeRiatics designed for tbe a^me period of siudjJ
Thi)* rircnmrtance is certainly to a great extent tbe e»Bse of the idi
which 30 readily arises among the yoanger phy9ki«t8 that chemistry
a tdence of a lower rank.

rf the preaent-<]iiy chetnistrT, therefore, iimke« greater demaods on
the power of rational thinking, it also renders the purely memory
work of mastering tbe eubject considerably more easy for the stndetit.
The growth of the scientific interpretation and elucidation of the
iepaTAte facts of chemistry facilitates in the highest degree tbe
impression of them on the mind and their application, and at the
same time a&brds an incomparably greater intellecttlal enjo^'ment than
the itddy of the older, essentially descriptive chemistry could offer.
From ibe experience gained from lahoraton' teaching during a number
of years, I lielieve I may assert that it is just for those students
who are endowerl with some tendency towards independent thinking
that the study of chemistry becomes both more easy and more living
tbroQgh ita |>resentatiott in the tnoclern spirit. ■

A few words ongbt also to lie saifl reganling the fact that the^
intention of the present book is to be a t^xt^book of pure chemistry,
Hegard has been paid to the related sciences and arts only in so far as
dumiml f|neittion.s play a |iart in thera. This holds in the first place
for chemical iec}inolog>% and also for meJidne, agriculture, political
economy, etc. The nee«l of rendering more palatable the "in itself
'Iry " material of rheniistry by the addition of such matter has not
been exfierienred by me, nor can I recognise its existence. Tbe
■object -matter of chemistry ta dry only when it is limited to an
emuDeration of properties and to a collection of preparative receipts.
80 «Oon aA it !ft treated in a truly fci>-nlijk. manner, each chemical
compound beconiea the centre of so much general and therefor*
intereatihg discn8»i"fi that embarrassment is felt not on actrount of the
lark but on af.'counl of the abundance of relationships. In proportion
fM any branch of study becomes more scientific, the necessity arises of ^
-«-• riding it to its own sphere. ■

cfujrxe we do not liere speak against the acquirement of a
•Kiwli'dgc of tbe related sciences by the future chemist.
'. But such knowledge will be all tbe more sound

it is acquired by special atudy directed to that object ; for
moHR, neuessariJy scanty and incomplete, to whicii a text-
Iwok of chemistry must limit itself rather give rise to the danger that
the stad«nt thinks he knows things of which he has on some occasion
heard sach indications, and considers a closer atudy of them to be
nnneccMarv,

Much Blight still lie said lo explain and justify the method of
ttwUmeiit wherein the pivsent hook differs from others written for
tbm tmtae purpose. The Bmlirig out and the ciiticism of these details,
bowerer, ought, 1 think, to be left lo the expert teacher of chemistry.
in th« interest of the stwknt^ I have in all cases avoided a polemical
dMctusioti of oppc^tng opiniona ; and although I atu prepared to grant
the pooibiJity and probatjiUty of niistfikea in the views which I have
hare given as appearing to me to be the most api)ropriate, I neverthe-
lan belierc that I may assert that these -views are the outcome of
earefnl oottsideration. The first three chapters, for example, were
rvwritten four and, in [lart, five limes before they assumed the form
viuefa they noiv have. I would therefore beg the reader to believe,
in caacs where doubt may exist, that there was some special reason
foe the particiilar position adopted. This does not exclude but rather
invoirea my readiiiese, in any given case, to honour any opposing \ne\vs.

May thi$ liook, then, which, in a certain seose, forms the coping-
■tooc of a long course of active work pm'sued with affection towards
tike geoentl introduction and extension of the new fonndatiotia of
trj* laid by Horstmann, Willard Gibbsj van't Hoff, and Arrhenius,
liere the good hoped for, and help to enlist and train new troops

tlie victorious march of our splenditS science.

I canuot conclude these introductory remarks without remembering
IB gntatode the excellent agsistancc afforded mc by Messrs. Bottger,
Bodenat«iji, Brauer, Luther, and Wagner^ in that they read the proof-
ikeats and gave me much good adWce both a» regards the form of
ueument and the subject-matter. My special thanks are further due
t» Mr. Braiwr for the preparation of the figures, — over one hundred in
Bdaber. — which were specially drawn for this book. It will be easily
nee that tbey are not diagrammatic, but sketched from apparatus actu-
Jhf pat t<^ther ; the}' thereby form a considerable part of the didactic
the book relating to the performance of experiments.

W. OSTWALD.

CONTENTS xxi

CHAPTER VII

PAGE

Wateb ........ 109

Gtattii, 109. Preparation of Ture Water, 109. Properties : Colour, 112.
Density, 112. The Law of Continuity, 113. Graphic Representation,
113. The CoeflScient of Expansion, 115. The Degrees of Freedom of
Liquid Water, 117. Ice, 118. Properties of Ice, 118. Supercooling,
119. Heat of Fusion and Solidification, 120. Unit of Heat, 120.
Application of Ice, 121. The Transition of Water into the Gaseous
Sute, 121. Boiling, 123. Density and Extensity of W^ater Vapour,
125. The Water Vapour in the Air, 125. The Heat of Evaporation
of Water, 128. Superheated Water and Overcooled Vapour, 130.
Phases and Degrees of Freedom, 131. Influence of Pressure on the
Mtlting Point of Ice, 132. States of Equilibrium : Law of Reaction,
133. The Triple Point, 134. Vapour ftessure of Ice, 135. Water as
Solvent, 136. Relations between the Changes of the Vapour Pressure
»nii of the Freezing Point, 13". Chemical Proiwrtiea of Water, 137.
The Quantitative Composition of Water, 138. The Ratio of Oxygen to
Hydrogen by Volume, 139. Decomposition of Water, 140. The Law
of Combination of Gases by Volume, 142. The Law of Combining
Weights, 142. Combining Weight of Hydrogen, 144. The Combining
Weights of the Elements, 144. The Accuracy of the Law of Combining
Weights, 147. Chemical Symbols and Formula, 147, Chemical Equa-
tions, 148. The Atomic Hypothesis, 149. The Molecular Hypothesis,
151. The Action of Sodium on Water, 153. Caustic Soda, 154. Deli-
quescent Substances, 155.

CHAPTER VIII

HiDBOGEN Peroxide .156

Hydrogen Peroxide, 156. Hydrogen Peroxide as Oxidising Agent, 157. The
Molar Weight of Hydrogen Peroxide, 158. Preparation of Pure Hydro-
gen Peroxide, 160. Occurrence, 160. Catalysis, 160. Explosive
Properties of the Peroxide, 162. Heat Elfects, 162. The Heat of
Formation of Water, 163. Thermochemical Equations, 165. Heat
Effects in the Decomjiosition of Hydrogen Peroxide, 166.

CHAPTER IX

Chiori>-e .168

Foraution from Hydrochloric Acid and Oxygen, 168. lAnother Prejiaration
of Chlorine, 169. Properties of Chlorine, 170. .Solubility in Water,
171. Decomposition of Chlorine Water in Light, 172. Chlorine
Hydrate : The Pha.se Law, 173. Chemical Propcrtie.s of Chlorine, 174.

PRINCIPLES OF INORGANIC CHEJUSTEY

ComJjiistion irithout Oxygen, 175, Siib-Chloriiies aud Cliliirides, 176.
Chlorint and Hjdrogeu, 17r>. luilirect Foiinntioii of Hydtxichlonc
Acid, 176. Coaii>uaition of Hyrjragen Cbloriile, 1"7. Formation of
Hydrogen Chloride from ita Elements, 178. ElucLroljtic lYcparatioa
of Chlorine Dctonatiti^Gas, 170, Photochtmic*! Aotioiis, 181. Hyi)ro-
cliloric Acid, ISl. Properties of Hydrogen Chloride, 182. AliEoTiition
of Hydrogen Chloride by Water, 1S3. Hydroj^ou Chloride aud ^Vater,
184. PropertiPB of Actds, 187. Adds and Bases, 187. Combining
Proportinna betwoeu AoidM and Bftso5, 188, Rcciiiroiail Eslimatioo of
Acids and UasBs, 189. Vulnmctric Analisis, 190 Ioub, 191. Saks art<
Electrolytes, 193. Amou.'i and Cfttiona, 194. Tlit' First I^aw of Faraday,
19r>. Elcctri*iil Utiit", 196, ThoSfcoJidLaworFarndny, 1B7. •Primary
and Secondary Products of Electrolysis, 19S. DisBooiatioii of Electro-
lytes, 1^9. Electrolytic Solutians, 240. Thcraiucbeiuical Rulatioas o(
Hydrogen Chloride, 20!^. Thermochemistiy of the Salts, 203.

CHAPTER X

OXTGBS (JOMPOOSDB OF ChLORIXE .

Oxygen Compounds of ChlorLoc, 20fl. Hyinxihloroua Aciil, 207, Propsira-
tion of Auids from tlieir Salts, 208. Projiertiea of Hyiwcldoroiia Acid,
20fl. Decompositions of the Hypochlorites, 200. Liiw of Succcssivt
Reactions, 210. Free Eiu-rgy, !211. Chlorine Monoxide, 212. Chlorates,
213. PrejiaratiQU of Chloric Acid, 215. Solubility of Salts, 21(J. In-
fluent'ii of Teniperaturt and Pressure on tins Solubility, 217. Relation
between Solubility and Heat of Solution, 219. Crystallisatioti, 219.
Behaviour of Mixed Salts, 220. Perchloric Acid 221, Properties of
Perchloric Acid, 222, Other Oxygen Compounds of Chlorine, 223.
• ThormochemicAl Relations of the Oxygen Compounds of Chlorine,
224. • The Combinitsg Weight of Chlorine, 22&.

CHAPTER XI

Jbomise, Iodikk, Flvobike

A. Brtitni'nc : Gctiorat, 227. Hydrogen Bromide, 228, The Solution of
Hydrogen Bromide, 22P. Oxy-acida of Bromine, 231. B. lodint :
Gkneral, 2.52. The Law of Distribution, 233. Iodine Vapour, 234.
Sturch ItMlidu, 235, Hydrogen Iodide, 23.'.. Hydrogen Iodide und
Water, '237. Oxygen Compounds of Iodine, 23S, Periodic Acid, 210.
Chlorides of Iodine, 240, C. Fluorine: General, '-'12. Prepurutiou,
2-ia. Propertits, 2t2. Hydrogen Fluoride, 243. The Stri'iigth of
Acids, 244. DitfereDcc in Electrolytic Disaociaiion, 245. Actual and
Fotentifll Ions, 'iiS. The Diwociotion of Salts, 24S». • Hydrolyais.
260. General Remark? on the Halogens, 2S1 . Theriuocheniistry of the
Halogens, 253.

CONTEN^TS

xxui

CHAPTEK XII

AXD n* COMPOCNDS ....

iitlfkttr: Geaeral. 25tJ, FonuH of SiiJpliiir, *i5tf. CrystaUisatinti from

tk* Fa«(d klasa, 2of{. CryBtaHisation froiii Solution, 257. The Rugitiuij

[dubflity, 26". InUuencii of Pressure on tho Point of TrBiwtioij,

Stwpvndcd Tnu^iafamTAtion, 25S. Eiuiutiott'oj>y aud ^[onotropy,

JS8. Other Fomi« of Stiijihur, 2yS. Limiid Sulfiliur, 2^9. Ariiorjihous

Saljilmr, 259. * ExirtrinuMits, 260. Sulpliur Vapour, 2B2. Purification

ofSaJiJiiir. 203. * B. Cri/Ha.!ii : Genera], 2tf3. TW CrysUUip*

forms.. 2*1. Tlir Symmetry of CryatAls, 26f). Thu Seven Systems of

OyrtiLn, 2«Jf». Periverl Forms, 267. The other I'roporties of Crystals,

3S7. (xeiierk!isati<i]i, 2(19. C. SulphKrelltd ffydrugi-n : TIjo Cmtipouttds

4 Sqljilitir. iWy, Suljiiittietted Hydrogen, 270. DihuBk Acids, 270.

Th* l(in» of Dibasic Acids, 271. The Salts of Sulphuretted Hydrngeii,

tfi Pffijiariitioii. 2/2. ProfiL^rties, 271. Thu Soliihilily of Casus.

Ji't. • Eilatiou tn thfl Lnw of Distributinii, 27^. The Strength of

SuijiUiir»rtefI Hydrogen, '276. TWory of tlie Evolntiotxof Stdpharotted

Hydrogen frf.iu Iron Sulphide, 276. Analrticnj Reactiotis of SiUphur-

rttod Hydrogpn, 277. Sulphuretted Hydrogen ua a Rutlui^ing Agent,

I7ij, Pnr{>-»r»tii>n of Hydntgun Iodide, -78, Ut'comiMsittou of Sid-

[iliurnttcd Uydrog«n by Hcst, 379. Coiubnation of Slllphurnttad

a79. Analysis oC Sulphuretted Hydrogen, 279. Poly-

279. Hydrogen Persulptudf, 2S0. * Tlierniocheniicn.! Data,

C t!lu(/ihur Dioxuit ami Huiphurutts Acid: Composition, 281.

Htjiiakl Prui>er>i4?s, 2S1. Hi'havioni towards Watci-, 282. Sulphurous

Acid, 282. DiasocJAtion of Sulphurous Autd, 2S2. Bleaching AotioQ,

9tt. Pbfiiologioiil Action, 28:t. Prvparatiou. 284. Redncin^ Actiaus,

SM. rTr»JKnl]>lmrf«i8 Aoid, 2S5, ' Tli#niioch>iini(.'»l RelatiouN, 286.

E. Sulphur TeiaxitU aiui Hatphunc Aeui : Sulpluir Trioxide, !iS6.

Ukbufkc cure. 2«0. Propertii'S, 288. Action of Water. 287. Sul-

gilinric Arid, 2.S7. Mamiiiu'turing Prori^as, 28S. Action of tlit> Oxides

orXU»oj{«n, 2*a. CVmccntralioii of the Atid, 2Se. tVude and pun-

Add. lew. Solid Sutphuric Acid. 260. Aqueous Sulphuriy Acid, 21)1,

Thif Idim of Stilplioric Aciil, 292. Applications of Sulphuric Acid, 2U2.

lirtical Tcit, 2'Xi. Decoiu position* ol Suljihuric Acid, 294. Pyro-

knric Acid, 294. * ThtirniocheniiGdl H«Ution.f. 2yri. F. W/to-

Aeidn u/ Siitphiir .- Persnlphurii' Aciil, 29<i. IIydiosulphurou»

, 2»7. Thioaulpluirio Atid, 29S. Poljihionicr Acids, 301. Ditlii-

^Ariti, 301, TrithiDnauiou, 3tJ2. Trtmthioiwiiiou, 303. Ptnta-

i>Dl<- Acid, 303. O, ifalixjen CuMiKnuul.i of Sulphur: Chlorides of

I8«llihnr. 804. Chlorides of Sulphuric Acid, 304. H. Comhiniit'j

\ Wtigkl 1^ Sulphur. 307.

25<

CHAPTER XIII

Seleniam, 'iW. lnomorphisin, 311, Scletiioua Acid, 312.
dd, S13. Ctdorine Comiiounds of Selcuituu, 3ia. Tellurium.

305^

PRINCIPLES OF INORGANIC CHEMISTRY

CHAPTER XIV

NiTRWEN .....

General, 316. Preiiaration and Proiieniei, 316. Thi' Air, 318. Oxygi
Compuunda uf Nitrogen, 320, The Clieiuieal Prt»iierties of Nitri
Acid, 322. The Salts of Nitric Acid, 324. Kitrogen Pentoxide, 325,
* ThLTmochemica], 325. Kitric Oxide, 325. Nitrogen Peroxide, 327.
Tho Law of Mass Action, 330. The Inftuouce uf Temperature 04
Chcmica! Efiuilibriuni, aSl. Nitrous Acid, 332. Hyiwnltrous Acid,
333. Nitro-comixiunds, 334. Nttrosulphomi! Acid, 335. Other Nitro-
oompouiids of Sulpburif Acid, 337. Aqua Regiit, 337. Catilytio
Aotions of the ©."sidos of NitroKen, 33S. The Kulc of the Oxides of
Nitnig«u in the Frepuratioii of Sulphuric Acid. Transfer Catalysia,
339. Comparison of the CvygeD Compininds of Nitrogea with thosK of
the Halogens, 340. Aniiiiotiia, 340. Amido-toinliolitid.s, 315. Other
Oxj'gen- Hydrogen Conipuuud.'* of Nitrojifen, 3'J8. Hydrazine, 319.
Hy(ira?oie Acid, 350. Organic Nitrogen, 351.

CHAPTER XV

Pmosphorcs

General, 352. The Allotrojiic ModiJieationa of Phoaphortia, 3n3. Reeipwca
Tra-nslormation of tha two Kind.s of Phosphoru.s, 354. The Osuintion
of PhosplioniB in Air, 355. Phosphorus Vapour, 357. Application of
Pbosphoru!*, a5S. Hj'drogcti Couiiwunds of Pliospliorua,, 35S. Halogen
Comjioilwis of Pho.iplionts, 361. The otKci' Hahvgeu Comiitiiiiuls of
Phosphorus, 383. Oxygen Compounds of PlioBiihorus, 363. Phosphorus
Pentoxide, 364. Thu Phosphoric Acids, 3(13, Fyrophoaplioric Acid,
3tl8. Mctrtphosphoric Acid, 369. Ohloridta of PliOBphoric Acid, 369.
PhoaphoroiisAi:id, 3"U. Hyj>o[)hoHphor9u» Acid, 373. Hypophosphoric
Acid, 374. Lower Oxides of Pho-^phorus, 874. Sulphur Coni|M.>aud» of
Phuttphorua, 37i. Valency, 376. Bxtenaion of tbt Conception of
Vftlency, 377.

CHAPTER XVT

Cahb^s

General, 381. Adsorptiou hy Chdrfojil, 384, Graphite, 389, Dinmond,
3«7. Compounda with Oxygen, 388. The Critical PheuouiBua, 389.
Liquid Oarlion Diosidf, 392. So)utlou in AVator, 392. Carljontc Acid,
3»3. Tlio " Circulation " of Carbon, 304, The Coiuliiuiiig Woigl»t of
Carbon, 3M. Detection ef Curltoujc Acid, 396. Durirn tires of Carbunic
Acid, 305. AmiJeB of Carbouic Acid, 307. C(vrbon Stouoxide, 3t*9.
Heater Gai, 401. Formic Anid, 402. Acetic Acid, 403. HydTogen
Compounds of C*vlion, 403. Derivativfja of Metham', iOi. Radicles,
408. Methyl Alcohol, 406. The Radicle Methyl (lud Homologous

CONTENTS XXV

PAoa
S«ri«s. 407. Ether, 409. Unsaturated Compounds, 410. Coal Gas,
111 Oxalic Acid, 415. Carbon Disulphide, 417. Carbon Oxysulphide,
US. Cyanogen, 419. Relation of the Cyanogen Compounds to the
Ammonia Derivatives of the Carbon Compounds, 421. Cyanic Acid,
(21. Thiocyanogen, 422.

CHAPTER XVII

Siucox ........ 424

•jiccnl. 424. Silicon Dioxide, 425. Silicic Acid, 426. Geological Reactions,
423. Halogen Compounds of Silicon, 429. Silicon Hydride, 430. Silicon
Finoride, 431. Carborundum, 433.

CHAPTER XVIII

BjEu.\ ....... 434

fewnL iU. Boric Acid, 435. Other Compounds of Boron, 436.

CHAPTER XIX

1«*jS, HzLirM, AND COSGENERS ..... 438

irpin, 433. Helium, Neon, Krypton, and Xenon, 440.

CHAPTER XX

?«4S..R1I . .441

Gtimi Remarks on the Chemistry of the MetaLi, 441. Potassium, 442.
PuMirion, 443. Solubility, 444. Behaviour of Salts, 445. Theory of
V'.ntion Equilibrium, 446. Other Reactions of Potassion, 448. Potes-
•iuju Hydroxide, 450. Chemical Properties of Potassium Hydroxide,
iiJ. Potassium Chloride, 455. Potassium Bromide, 455. Potassium
Iciide, 456. Pota.<dium Fluoride, 456. Potassium Chlorate, 457.
Pf-tassinm Perchlorate, 460. Potassium Bromate, 460. Potassium
I>l«e, 460'. PotL-isium Carbonate, 461. Potassium Bicarbonate, 463.
Potassium Sulphate, 465. Potassium Persulphate, 466. Potassiuui
.''ulphite, 4«6. Potassium Sulphide, 466. Potassium Nitrat<-, m7.
Poussium Nitrite, 470. Potassium Silicate, 470. Potassium .Siliio
'.noride, 471. Potassium Cyanide, 471. Potassium Oxalate, 472. <llhi:r
Compoojids of Potassium, 473.

XXVI

PEINCIPLES OF INORGANIC CHEMISTRY

CHAPTER XXI

SODtCM

Qenersl, 475. Mctallii! Sodium, 406. Sodion, 478. Spi>ctr&l Pbenomeus,^
47ft. * Indirect Analyais, 480. Sctdium Hydroxide, 482. Sodium
Perojcide, 483. Sodiitm Chloride, 484. SixJium Brauiide and Sodium
Iodide, 486, Sodium Bromnti?, 4S8. Sodium Cliloratc, 488. Sodium
Nitrato, 489. Sodium Kitrite, 490. Sodium Sulpliate, 490. Acid
Sodium SulphMe, 494, Sixliuni Bulphitt', 404. Sixiium Sulphide, 4fl5.
Sodium Thioau][iLatu, 4Ei.'J. Sudiuui Carlwnati.-, 497. Sodium Phos-
phuta, SOI, Soflium Silifate, 502. Sodiutn Borate, 503. Sodium
Acetate, 603, The Corrihiniiig ^Weight of Sodium, 504.

CHAPTER XXn

ErBiDicM, CwE.siuM, Lithium, ast> Amuonivm

Q«neral, B0&. Rubidium and Civsiuiu, 505, LitLiuiu, &07. Lithium
Hydroxide, 507. Lithituii Carbfiiiftte, 507. Normal Lithium Phnsph-ite,
50S, Amrnoiiiuiii, 508. Ammonion, 509. Amniouium Hydroxide, 509.
Amuionium CUlorido, 510. Ammgnimu Bromide and Amiuouiuni loflido,
511. AnmiuDiam N^itrn.t«, rrl2, AiiiiDouiuni Nitrite, £12. Amiuoniuiii
Su][))i*tc, &rj. Ammonium I'liospliates, 512. Amniotiium CurbonataL
fil.S, Ammonium SulpUtde, f«13.

CHAPTER XXm

CALOltrit .......

General R«m4rk$ on the Alktilinv EiiTth MetAls, SIS. Calcium, r>17. Colctou,
617. Csloium Hydroxide and Calcium Oxide, 51 S. Soda Lime, ."ilfi.
Calcium C'arbouate, 520. Calcium Bicarlionftto, 523. CaUiium Chloride,
f>24. Cdii^imn Hy|iocldorito and Bloaeliing t'owder, 626. Calcium
Bromide nad Caleium Iodide, ^t27. Cnlciuni Fluoride, 5i!S. Calcimii
Nitratii, ;"i28. Calcium Sulphate, 528. Calcium Sulphide, 530. Calcium
Phusjihdtti, .^i;jL Ap&tite, 5^2. Calcium Acetate, 5ii3. Cdlcium Oxalnte,
53a, Calcium Carbide, 534. Calciam Silicate aud Gl»s6, 536, Corns
bioiiig Weight ol' Calcium, f>SS.

CHAPTER XXIV

MAQST(8ItnH . , ,

;.Q«neraI, 539. Magnesion, 540. Magnesium Hydroxide and Magiiusium
Oxide, 540. Magnej^iiim Chloride, 641, MiigQBsiiim Sulphate, 542,
Double SalU, 642. Magiieiiiuiu Carbooate, 544, Magnesium Phos-
pliateH, 545. Magni'aiiuu Sulpkidt:, 546. Muguesium Silicates, 540,
Magbcaium Nitride, 547.

CONTENTS xxvii

CHAPTER XXV

|-A<iE

STROBrnm, Babixtm, and BeryIiLich .... 548

G«iieiml, 548. Strontium, 548. Stroutium Oxide, 548. Strontium Hj-
dioxide, 549. Strontimu Carbonate, 549. Strontium Sulphate, 549.
Strontium Nitrate, 549. Barium, 550. Barium Oxide, 550. Barium
Sulphate, 551. Barium Carbonate, 552. Barium Chloride, 552. Barium
Nitrate, 553. Barium Peroxide, 553. Beryllium, 654. Summary, 55.'f.

CHAPTER XXVI

ALrnsiuif and the other Earth Metals 556

Gtnenl, 556. Aluminium, 557. Aluminion, 558. Aluminium Hydroxide,
S59. AInminates, 560. Aluminium Chloride, 561. Aluminium Bromide
»nd Aluminium Iodide, 562. Aluminium Fluoride, 563. Aluminium
Sulphate, 563. Alum, 564. Aluminium Silicate, 565. Double Silicates
of Alominium, 566. Other Salts of Aluminium, 567. Ultramarine, 567.
* The other Earth MeUls, 568.

CHAPTER XXVII

Ixw . .571

Otsml, 571. Commercial Iron, 572. The Ions of Iron, 574. Ferrous
Hfdioxide, 577. Ferrous Sulphate, 678. Other Ferrous Salts, .WS.
Ferric Hydroxide, 580. Magnetic Iron Ore, 582. Ferric Salts, 582.
F«mc Bromide and Ferric Iodide, 583. Ferric Fluoride, 684. Ferric
Sulphate, 584. Ferric Thiocyanate, 585. Other Ferric Salts, 585.
Ferric Phosphate, 686. Sulphur Compounds of Iron, 586. Ferric Acid
lod Ferrates, 687. Cyanogen Compounds of Iron, 687. Ferricysnide
C<}aipounds, 590. Other Complex Compounds, 591. Oxalates of Iron,
WL Iron Carbonyls, 593. Catalytic Actions of Iron, 593. Thermo-
'■'bemistiy of Iron, 594. Metallurgy of Iron, 594.

CHAPTER XXVIII

lutliAXESE ......

GtBtral, 596. Metallic Manganese, 696. Diiiianganion, 597. Manganou-r
Hydroxide, 597. Manganous Sulphate, 597. Manganoos Carbonat<i.
Vii. Manganous Sulphide, 597. Manganous Borate, 596. Mang.irii<
Compounds, 598. Manganese Peroxide, 599. Mangsnaaion and I'-r-
mtsgananion, 601. General Remarks on Oxidising and Badneing k'i<^ux-.
tOl. Complex Compounds of Manganese, 609.

XXX PRINCIPLES OF INORGANIC CHEMISTRY

710. Antimony Tri-iodide, 710. Antimony Trifluoride, 710. Antimonj
Trisulphide, 710. Complex Antimony Compounds, 712. Antimonj
Pcntachloride, 712. Antimonic Acid, 712. Antimony Pentasulphidi
and the Thioantimonates, 713. Antimony Hydride, 714. Alloys ol
Antimony, 716.

CHAPTER XXXIX

Arsenic ........

General, 716. Arsenic Trioxide, 717. Arsenious Acid, 718. Arsenic Tri-
ohloride, 719. Arsenic Trisulphide, 720. Arsenic Hydride, 722. Com-
pounds of Pentavalent Arsenic, 723. Arsenic Pentasulphide, 724.
ComiMunds of the Divalent Type, 724.

CHAPTER XL

Vaxadicm, Niobium, Tastalom, Gallium, and Indium

Vanadium, 726. Niobium and Tantalum, 728. Gallium and Indium, 728.
Gallium, 729. Indium, 729.

CHAPTER XLI

Tin and its Conueners

General, 731. Distonniou, 732. The Stannic Series, 733. Stannic Sul-
phide, 735. Alloys of Tin, 735. Titanium, Germanium, Zirconium,
and Thorium, 736. Titanium, 736. Titanium Nitride, 738. Ger-
manium, 738. Zirconium, 739. Thorium, 740.

CHAPTER XLII

UUANIIM, TVNUSIKN, AND MoLYBDKNCM ....

Goneml, 743. Uranium, 743. Chlorides of Uranium, 745. Sulphur
Comi>ounds, 746. Uranium Rays and R«dio-.\ctive Substances, 746.
Tungsten, "49. Chlorides of Tungstou, 7.'>0. Sulphur Comi>ounds, 750.
Molybdenum. 751. Molylvlenum Trioxide, 751. Lower Oxygen Coni-
)MUttds, 7">2. Chlorine ComiHiunds of MolyUlenuni. 752. Sulphur
Comi>t>unds. 753.

CONTENTS xxxi

CHAPTER XLin

FAOE

Gold and the Platisuii Metals .... 764

General, 754. Gold, 754. Gold Compounds, 755. Aureus Chloride, 756.
Sulphur Compounds, 757. Complex Gold Compounds, 757. Metallurgy
of Gold, 759. Platinum, 760. Compounds of Platinum, 763. Pal-
ladium, 765. Iridium, 767. Rhodium, 767. Osmium and Ruthenium,
768. Ruthenium, 769.

CHAPTER XLIV

TffE Choice of Combisixg Weights amd the Periodic System . 771

Gcntral, 771. Isomorphism, 772. The Molar Weight, 772. The Atomic
Heat, 773. Result, 773. The Periodic System, 774.

ISDEX ........ 781

1 Bodies and Substances. — In the outer world objects can he easily
rtOigiii'-wi hiiving a detinilf spatial limit or fomi and cJistingiiished
hj tbi^ir pioptTliea from what suirouiuls them. Such objects are
(ilJwi K-iu-K, Every body is chfinictfirised by t'he projteriies by means
<il iliicti it can he distitiguisbed from what sHrroiinda'if."; ..

If wo iniivgine Ji large number cthodJei plpcRtT ai(rf>'b^' -side and
comfojired w-ith one another, we eari cwrrftlate thera in viWibiiB Hiriiys.
Ws (an eunsidfr their size and ftjri/'';'«li>:l arrange ihem accordinc to
tlKSf 6]iatijil properties, or we nay neglect these and coiieider only
tfce other proiieriies : more pailicularty those wliicJi arr tli» w(v«"«»
*•« pwiion r/ the ^iren Ixxli/. Such properties we shall «ill' i^<f£t{/ir
iit.i. ""'. •' ' '*" •

wt lenve size and form out. <jf Bdbouiit and armnge ihe-jwdicvs
manner that those which' agj-^shi, iheir spedfli'.jp^operties
A in the jiame gi'oup, then tfef; bodies art calfcd '«.;/«/««(:»■.«.
ila*, the knifo, the borer, «nd thb varijui objeePs oti 'the tool-
Uni, are so many rtiffeient boilifs. If, hn'vnver, wo leaVe the form
'rfxiMw out of acconnt and consider them with reference to tlioir utht'r
tie* which arr independent of the form, we shall call them the
for tbpy all consist of the same hard, beavy, and tough material
tl, which exhibits the sjinic properties whether it is in large
pieces. Steel is, therefore, the sitbskitiry of which the above-
fvJia eutmst,
(b tlie ttine way, svery one will call the ycUow, pulvcrisable lumps
i^di huro with a pale bliie Ibtme, sulphur, no matter %rhcther they
small, regular or irregular in form. Sulphur is the name

SCO.

-'M', that language possesses a fairly large immber of
I'ltt 5ubataiiL-e«, is the expresnion of a geneiul exi>eri-
iif nature. Just aa in the case of animals and plants,

'lit iminiitttite titxlies can lie srmnUcii iiUo df/irul/- ^^ spmes,"

fvt

PRISCIPLE8 OF INOKGANIU CHEMISTRY

«jicli of which embnices a large tumibor of individuals or
substances with concordant properties. As is known, the numli
species in the case of aninuUs antl plants, iilthuugh, eerUunly,!
large, is still incomparably smaller than the number of the indivia
Likewise, the number of substtincca which difler in their prope
although large, is incorapaiably smaller than that of the single lxj(
This fact cJin also be expressed liy saying that in the bodies t
do not occur all iniaginuble collocations of properties, liut only cei
dfjhiHe ones- Every such collocation of properties which does ri
occur, characturiBes a riffinile .Twis/uAKr, and the fact that the Ix
which occur in nature cati he arranged in such groups or "subsl-i
apeciea," is the statement of an importJint law of nature, (ht fumiam.
law itf eJici/mfi'if. It is the object of chemistry, as a science, to k
the properties of .wiffifiinrrs * and the relationa which exist bctv
(hem.

2. Chemical Phenomena, — Accordingly, since Chemistry <i
with the (tbjeets and processes which m:ike up the outer world, it fc
part of the yatunil Semuvs. Although, in reality, there is only
Natural SciejieeJ ^Jctenflkig over the whole range of phenomenfi,
the necessrtv.'t>f./acilit;iUnjj*the survey of the whole extent of
kiiowljslg*^ &rfii'1ejl„ (ivenj-act-iin* early period, to the fomiation of i
divistotr^i'.ii'l.fl'hich were -grxiiibach together phenomena more cloi
rolirted toobo another, i.tf. skniW* phenomena. Such a sulKliviaio
foiyned by Chemistry.

■ .T:h6 exact detinition of the subjtJct-raatter of chemistry and of
hpiyKl^yy between it and the other branches of science related tc
caKhOt' Y>B given at this ]>oint,.8hice for this pnrpose there is neeess
a kViirwIt^ifge of facts which havetir.st to be given in this work. S
it will- simplify raatteis for thti- liegiuner to give him a token by wl
most «I.fcr.e chemical phenqmeua can bo recognised, and which '
therefore aftord him guidance as to the direction in which he hai
give his attteul'on.

We have seen that numerous gulstani'es can be distinguished wl

we consider their specific properties. These substances, however,

not represent something that is unchangeable, for we often obse

L4hat a body consisting of some deKnite substance undergoes liiaui

e. its relations to the instruments of sense by means of which

erceive it, and to its environment, are altered. Such changes <

"^be divided into two large, although not sharply defined, grou

Either ihttj afffci nttip unir &r some ftw relaiioiis utid pro^wtiea of

' Ab the ri-Hiilt of an inJonuitonoiis in tho usii of lajiguiige wbici), it is ta be ri^gretl
in very wiJe-spreiui, one often llmla in t«Jtt-l»ooks ami (nuMi'iirji llmt the two concfpti
of lioily »ui) *n1-BtU))<!e nrr not kt(it rigjtUy setwimte, Imt are luixi^d up ia such a i
LbiLt tli« won! bod)' is oft^n lifed wh«K tnilNjitJincti is uitea<ii<<l. UtscrifilioDs aiivb
*'SiiI|'hur is » yellow, lirittle tiot/y," iiiste.-kd of mihs/nnfr, orctir very fri'qtifntly. In 1
book, we »hall *lw!vyji ilraw a »lmr[) institiutioii ln'twouii the two iiiaas, atiii it in desir*
I thiLt tlie general Hcieiititie iisagL* shouhl. in tliis reapi^et, a\io tL^siimi! a tnoiv ilctinilc fo|

GENERAL PUINCIPLKS

amtuirrrd, i/r thnj itrr of n nunr iiuiirnl. nadtrc, ifti-ch that titf- luxltj
etmiiifriitian lUiajfons, ami iff plncr r,< Inkm hij ofhrr bi>ilir& liannij
tAar ffvifit' f/it/jtrrties.

Ph«noiu6ua of tiie former kintl ijeloiig to I'hi/sirs , those of the

to Chfinisirtt.

Take, for exAtnplc. some definite Iwcly. auch as a piece of eiilphur,

we push it, it chrtn<;es its place ; it rolls over the tiiblii, Nune of

ochrr |ir<vperties, however, undergo change ; it retains it^* yellow

ita form, its weight, etc. Movenienl is therefore a pkysifiH

bentMnenon.

We tiAti ylacv the pii^ct of sulphur in hot water, .tJid it acquires

Bwlfj the property of protlticiiig the sensation of warmth when

uu the skin. No other chsmge can be perceived. If we lub it

Ji a cloth, il AC({uire.s the property of iittnicting light ohjcctj?, sucli

scmps of {w{»er ; it hus become electrified. Mere, again, no other

Bge in it* properties can be leeognisfJ. Tlie.sc phenomena are,

efore, also to lie assigned to /i/i//^ /(•.<.

We BOW bring the piece of sulphur iu contact vfith u. Hanu'. It
taktat fire and t>egius lo burn with n blue' dame. Ti^e smell of bum-
ing Bulpbiir, also, becomes noticeivbJcs.-Jitrd.if the biirrtine .lasts some
ttatb th« sulphur diaiippear* ; it bbiieuL-' In' tin's i'rri'.:e5s not only
do ptrticulur projjerlies of the . sulplltir utidergo change, 'But the
■olpliiir dr^^ippears altogether, sd that we can no longer Etc it at. all.
^mi the smell which arises at the satife lime, and which wa.s not tliere
we ctiu conclude that aoraethJuig else has been produced" irom it.
cnse, theiffore, tht* suipluir"h3s- undergone a ch^mictil procebs.
recognisse such chemical ^iiTfps8&| everywhere arountrUh. The
; of |K!lroleiun and stearin -itj-oifa'^famps and canJleg.ot coal in
the tran»(onuatioii of food-Slibstawcet in tbu fnun^al organism,
SOS connected with the gorfiriiia-noii and growl^ j( plants,
rtiaiing of iron, the turning sour of tt\'n\i, the pucrefaclion of dead
kl and vegetable matter, and innumerable other phenomena of a
kind, are identified us ihemiful through the disii(>pearance of exist-
iflifs and the afipcarance of new ones po.9sessing other properties,
out the laws of M these phenninena is the tusk of the science

TllhtlV.

Experience, — In describing the simple phenomena with which
Imre just been occupied, we have smployed various conceptiouB
ideu of which we daily make use, and which are therefore familiar
•o u. For sC'ientilic pui-poses, however, we dare not rest aatisfied with
ike Mmcwhiit indefinite and arbitrary notions which we attach to such
•ortla in ortiinary life ; their full purport must be examined and their
DMUiing established with detinitcneiss.

which enters directly into the eonsciousneaa of a particular

is the changing conditicme of his mind. We soon distin-

[b«twe«n the inner and the outei- e.xjKjrieiices ; the former arc

I'ltlNCII'LKS OK IXOKGANIC CHEMISTRY chap.

(IcportfliTit (jii wir will, the latter are not, or are bo only indirectl)'.
On iu:coniil of ihi* iiiiie]«?iidence, we aseume that such experiences
hnvt: thiiir rnum'. ill KurnettiJng that is different from our pN^i-son, and
th« Uthilhy It/ tln-iio t- xpicrifiiCTS we call the outer world.

All uur MXjK'rierices form a serios of diverse states or processes
■ flilT«'riit(i nmoii^ thorasolves. An event is never repeated in exactly
'the «jittK.' wtty *wi it HjwI ont'e occurred.

Our rtihaiori to lifi; wimld, therefore, he that of a wanderer in the
UlmrknoHn of iiri iniktiown und trackless rcgioi), if it were not that there
itn.i cvc.titJi which ri'^iieut tht'ttiftelves, not in their entirety, it h true,
Imt Ntill to n fargo i-xtent. When we have exjierieneed a number of
Midi occtirrcncea, we are in a position to forcste the probalile further
ciiurw of one of them when it rccnrs. If it is an event which influ-
enceii our condition in some pjirticukr way, we are able to act so lis tu
|{ain the ^v*'JiUm\, fidvantagB, or suffer the lejist harm, from it.

The nwigtMtiiit) f)f such events as in large niejisiire repeat them-
BCi|vf«, i»t calltid f,rju-rifnii\ It eonisJi^ta, therefore, on the one hand, in
the rero^nitioti of'tho ti(rcumst;inces under which definite events occur,
imd, f<n ihi'-n^lj/'r hand, in' out knowledge of the cmirse of the ovente
or of till' k!TsffUL"nKi of tltuittpiirtxi. .

1 "Oanteptidna and Lawtf of Nature.— Not science only, hut
alt incntai life v*hiUever, hogins with the collecting of such similarities
and' the (lihlinguiHliinjr of thcnr from others. Kven the brute does this
when it ^ocUh shelter in the thickei, from rain or from a pursuer,
h<!tMiiii|fl j*ueh action hail before ■jir.yved successful in similar circum-
RUifiCKititv The most genornl rukitions of this kind are contain»J in
hin^iW)?r . Kvi'ry noun, like ."dog.'',br "stone," signifies that we are
dealing hjti;'a huge series of. <5eiiccirdant exi>eHences which present
doiinitftliuti ftlway* weuurrjtt" similarities. For thi-i! reason the word
Kulphur hii,1iHii*.«* not, ka'u* Say,' some one definite impression which I .
hai'o once liiul ut sonm parlif'ular time, but it is the summing up of
r«|aiatL<d inrpn-Ksions in which can be recognised a group of different
eliaructerinticK which always occur togetlier. The sum total of the
I'lHH'oritartt chiirnflerifitics — th^sf ti'likJi tifi- <Ii^'nrda>it bfinc! tjcdudrd —
iit (lion galheriHj Ingcther in one snch name.

ThiiH in till" i:i^r i>l ill '.viinl sulphur, I think of a yellow, solid
«ul>Ntance, whivli i;iii I"- 'i "'i tire, which becomes lifjuid at a nut
v«ry high Umiperatnre, which sinks, without dissohing, in water, and
iKH'onifN olectrilicd tm Iwing rubU'd. 1 do not think of sul]»hur as
hiivMig ft deliniti" shape or size, but rsither I denote by the name a
[iuh'c I if any nire in which I recognise the properties mentioned. It»
111*' fniniatinn, thorefor«\ of the name sulphur, there hits by no means
liiuMi tjdten into acciMUit the sum tots! of all properties of some definite
•liigti-" |titice, existent or imaginary. On the contrary, no attention has
linnn fwdil lo I he «i*e, form, and origin of the single bodies to which 1
Itlvii thi» name of snljihur. but .account hzis bevii Uken only of the

specific [froperties, i.e. those which are found in all piecea, indej^mlent
of these differences.

Such an exclusion of Jiff'tTt-'Uces in phenomena wliieh in other
rc8i)ects are similar, is cftjj*'*! alinttarfin/j, and the result of the abstrac-
tion, whieh in the more simple cases is condensed into one name, is
^tei'med a cemypiic/rt.

As is evidc^iit, one and the enme phenomonon can be classed under
differerii conceptions, according to the similarities of which we take
account. The range of a crmception, or the niiral>er of single pheno-
mena which can he included under it, can be so much the greater, the
fewer the points of agreement which are considered. At the one ex-
treme nre the single natnes which mark individuals, i.e. objects which
l^i-e to be characterised us only of solitJiry occurrence. In this case
[we have very great variety, and generalisation consists only in the
object always preserving essentially the same properties for a certain
time — its period of e.^cistence.

At the other extreme are the general conceptions, such as " thing "
or "ohject," in which emphasis is laid on no other property than on
that, that it can be distinguished from other things.

Now, //if mosl imptjTliinf uvrk of the sckiirei eondsts in the formal itm if
ituitafJe ivncfjitmui. A tmiUtJih conception is, however, one under which
is embraced as large a number as jwssible of single phenomena in such
a manner as to contain the largest possible number of definite state-
ments regaitding each. The content of such statements is given by
the Ijiu's <f Xfi(nn:

5. Time and Space. — One of the iirat things wc experience, is
the change of day and night, and the unbroken repetition of t&ia
cbiinge of light and darkness in our surroimdings has therefore led
to a funthimental conception, that of iimr. Since thia change is quite
indejiendent of our will, we employ it as an objecHve measure of the
events of our life, ami refer these to the marks or signs which the
change of day and night affords ns.

For many occurrences this measure is too large. It Js therefore
divided into parts. The 5,\th |mrt of the day-and-night period, cal'"^
the hour, i» used aa the unit iti daily life. For scientific purposes,
yjj'jjTjlh part of an hour, or the urtlunth part of the whole pe
serves as the nnit, and is called the i'-amd.

Experience also teaches ns that intiumerable differeiice= '•
can exist side by side al Ihr sami- tinu-. This diversity is eoi
conception of s^rr, in which are .summed up all generalitii
ties by means of which vve can arrange and review co-exif

The diversity, which we call .-'ptKe, is a threefold c
itself in the three dimensions — length, breadth, and hei^
measurements are carried out either in one dimenairin
length), or Jn two dimensions (areas), or in three (space m- ;

The unit of length is the length of a platinum rod prfc

PRINCIPLES OF INOUGANIC CHEMISTin

ilepeiiiJuiit on our will, the lattet' are not, or are so only iim
On account of this nuleiiendenee, we .■issiime that such t\\!
havti their cjiuae in something that is diiTerent froiu our jit.i
the totality of these experiences we call the outer world.

All tmr expuriences form a series of diverse states or j'
diflerint,' amoiif; themselves. An event is never repeated in"'
the same wiiy as it had once occurred.

Our i-elation ti> life would, therefoie, be that of a wander*'
darltness of an unknown and tmcklesa region, tf it were not Oi
are events which repeat themselves, not in their entirety, it
but still to a large extent. \\'h6n we have experienced
[■BUch occurrences, ^ve are in a position to foresee the prot
course of one of them when it recurs. If it is an event
erices our condition in some piirticuliir way, wc are able to an
gain the greatest advantage, or sutler the teast harm, from iL

The rt-'crignititm of such events as in large measure rop».
selves, is called txperieitre. It consists, therefore, on the one
the reco^nitioiiof*the*oirei]matances under which dotinitfi eveir
and, on tlyi'gthfi hand, Jr(,-o"yr .knowledge of the course of ti;
or of tViiii^^iL'iiile of thaiif, parte! .

4,'p€ibipeptii6ns arid'Ija^.^.Jlf Nature. — Not science •
all nfentiil life ivhatever, bcf^pVft'itlr the collecting of such s.
ami* the dijitiTiguifihing of thenr from gthers. Even thf! bruif
vvhfn it *ieeka shelter in the '.thicket from nun or from n
Iwceua^'iSUch action hiul before ;[)t'>uvjjd successful in simila
stiifiGf;^'. Jhe most general rfeUiCi.onR of thi."? kind are con'"
laHgurtgf.,*JlCvery noun, like .flog .".or "stone," signiKes th^
dea!iTtg'.tvj<4j' % large sei-ies *yf.jeqjj_cordant oxi>tiriences which
doliiiit«^ti!)ltl*I(i^v"^J'» Beein^jn^ Nju Parities. Foi- this reason '
sulphur sij^i/Ii^s pot, Ict'u* Bay- some out! definite imprcs8ii>"
have once Bad. ai? some g^tiJiUar time, hut it is tb« smnjn"
rejieated imjiresBioils'ir! whicli can be recognised a group of
chanicteristii's which always occur together The sum toi ■
eoncordanl characteristics — 'ihvsf irlnck art' ifisMnhinf Itfinij ■
is then gathered together in one such name.

Thus in the case of the word sulphur, I think of a yd'
substance, which can 1m set on fire, which becomes liquid
very high temperature, which sinks, without dissolving, in n
becomes electrified on being rubbed. I do not think of e*-
having a definite shape or size, but rather I denote by th*:,
piece of any she in which I recognise the properties menl
the formation, therefore, of the name sul]»liur, there has
l>06n titken into account the .sum total of all properties of som
ainglo piece, existent or iniaginary. On the contrarj', no atti
been paid to the siste, form, and origin of the .single bodies t
give the ruime of snlphiir, but account has been taken on

iis, tt-niin'ratuiv.
jiccount. of this
I 'lit its ioii(/ili"ii.<.
ilial tlu'V can lit'
ul>stiiiK'e j)a-<siTi<i
vs pivsi'iit wln'ii

. ami the inaiiiK-r
:cot obsei'vatiini.
is refU'cteil Ida
(lice.

is groater tlian

ir in watn- and

'tter, I romlmli'

. howevt-r, it i-i

••x|>cniiio]it.

• : to «k-tiT)iiiiii'

V, w<! hriiig the

onliiiary, ami

:'« way mc Irani

•imch a cliar^fMl

'he j;oIil Ii-avi'-

■: fi'll villi an

"n we in>trt a

>i(;cc of »iil|)hiii-

lu'. Ii<|iii'l -lat'-

iiir, ri|iii".-< lit
.•irart4Ti.-'<l l.\
cjfiMrs i-li;iii-.'<-.

in Ili<: :.;;.
iriiii |.<.-..i:i ■
• ulii- rji.-i •. . •
nl'l. '>«i' : ■ '••
ill ?!i. ■ |. .■■
]>r>;- ■'.•
«h. r • ■ ...

•t ■:: •

Paris. This is approximiitelj equal to tins TTrrrnVrFTnTt'' P^ft of I
earth's meridian, and was originally intended to be exactly equal
this. Since, howei^er, two rods of this length can be compared m
each other with much greater accuracy than the ratia of one of tht
to the earth's ttifrtdiaii tan lie detertuiiied, that relation haa been, ve
wisely, discarded, and a considerable number of similar rods have be
made and compared exactly with tbe standard one,

These rods are kept at fliffcrent places, bo that Hhould one tir otl
of them by some miachance Ijc destroyed, the imit itself would s(
not be lo3t.

This unit is called a mrhr. It is e«pial to rather more than hi
the height of a man of average stature. For scientific purposes, t
metro is divided into 100 parts, cidled the ccuHmefre, which in writii
is abbreviated to cm. Other divisions into decimetre and inillimeti
of which 10 and 1000 respectively are contained in a metre, are bett
not to be used in science. When the magnitudes which have to I
expressed are much greater or much smaller than a centimetre, thi
are written in the form m x lU" cm. The indices most used are +
and - 4, The length 100,000 cm. or 10''" cm., h called a kilnmetn
a German mile is therefore nearlj* equal to 7 ■ 10'' cm.' The lengi
10 "' cm. is called a micron ; it is one-thousandth of a millimetre, ar
is at the limit of the raicroBcopically visible. It is also denoted I
the Greek letter fx.

The iHe.ksure9 of arm and volunu' are denved from the roea8^^
of length, liy tiiktng as the unit of area and volume a stpiare and a cul
respectively, the length of whose side or edge is 1 cm. Tiic form<
unit is called a S'piarr (ruiimiiff:, abbreviated sij. cm., the latter, a cult
ceiitimetrf, cc. Tiiese are the only unita emploj-ed for the purposes i
pure science. In daily life and also in science, the litre, abbreviate
lit., wliich contains 1000 cc, and which is equal to the cubic contei
of a culje whose edge is 10 cm., is often used as the nuJt of volnme."

(>. Properties. — -Thr nnits which have just been defined servi
along with other.", for the pntjioso of more accurately cliaracterJsing th
pro])crties of thi^ diH'erent boilics and siib.stances. Properties of aul
stances, or specific properties, are, for example, colour, density, powe
of refracting ligiit, electrical conductivity, and many others. Thes
pwjperties occur Jn a pirticnhir Rubstance always in a definite mannei
and to a definite e.Mttrjl, In future they shall be called shortly, prt
perties of the substance,

Be-sidcs these, there are other jjeeidiarities which can appear in

^ Au Englkti mile i« nearly 160,(433 em., or rstlier lens thu 1*01 x 10° cm.

" TlilH mctbod of (ImvlUg the luciuiures of nrea aliil vdIuiiic with tlte }irlp
piare ami tla* eitlte, is lij- no ineivii!! tictieswirj', !»or is it the only one, Kor i'lamplt
OBft eiiiilii iiw; as ntiiLs ii triangle niul n. telrnhpilroM of 1 (.lit. siilt, a cirde iiinl a Sfilion
of 1 i-jii. ra<Iiii»bly the iijqst !iiiita')l«, jssiic« it ullowii nf Xho wisiest calcnlttion ol' nreus
voliiiueii iKim mmusnnmnatt of \mt&r uiagiiitudes.

GENERAL PRINCIPLES

ig of the aubatiiiicc consiilereil, siieh as, temperature,
irge, piesBiire, iJiumination, etc, Oti account of this
nrii^ltity we shall call these, not its properties but its citmiHitms.
Tboee dillVrr from the specific properties in the fact tbiit thoy cau be
! imported to the body or altered at will, without the aubstfince pushing
lata another, whercfta the specific jfrnjifHif-s are always present when
Um BtthstJUice is present.

Tba optical properties of a substance, i.e, its ro/mtr, and the manner
ill wbieb it reflects light, or its lustrt, are open to diiec-t observation.
That a piece of anlphur is yellow, iuici that the light is reflected to a
fair extent from its suifaco, can lie seen at the first glance.

I can learn, however, that the density of sulphur is greater than

'tltat of water, only when I place the piece of sulpluu* in wetter and

note whether it rtoata or sinks ; since it does the latter, I conclude

that SDl{jbur is fJenser than wat«r. In whitt ratio, however, it i»

denser, can be learned only by making a quantitative experiment.

So it is also with the other properties of sulphur; to detorinine
Itlieiti, an experiment mnst be made. That is to »ny, we bring the
Ki(i8tance into relations which are difl'erent from the ordinary, and
note its hehiivioiir under these new conditions. In this way we learn
llMtsulpbur is a non-conductor of electricity, when we touch a charged
eliCtroaci'jfM' with a piece of sulphur, and find that ttie gold It-avea
do not I'all tttgciher, or when we connect ti gsilvauic cell with an
electric >>ell, and find that the bell does not ring when we insert a
piece of sulphur in the circuit. Furtlier, by heating a piece of sulphur
in a giaas tabe, we learn that it melts or j^asses into the liquid state
at a not very high temperature.

Tli« litst mentioned expenment, the melting of sulphur, represents
a transition lo a group of other properties which are characterised by
^ the fact that the nature of the substance itself undergoes change,
rbicb it did not do in the former experiments.

The Qtmbusliftiiitii, likewise, of sulphur when heated in the air, is
mch a profierty. Further, if we mix some sulphur with iron powder
and hoat the mivMiro in a test-tube, a thin walled glii.s8 tube closed at
one enil, it suddenljr becomes inc^uidescent, and when cold, l>Qth the
■tlpbor and the iron are seen to h.-jve dis,ippeated, and in their place
aubstante has been produced witii quite ditlerent properties.
in whicli certain substances disappear and other ones are
luced, have alrcarly been designated aa rhemiail, in contradistinction
the phmiaii or those in whicli the substances mnintain their exist-
|rnc«. A^«i shall, therefore, divide the propertie.'i of a given substance
niito physu-ai and i^liemicid ; the former being those we observe when
sulistiinre remains unchangetl, the latter being seen when the
ita.nc6B are converted into others, '

• The ijuestiou is often raised, whether processes such as fusion,.
wbcB the letaperature is raised, or solntion in a solvent, are to be

PRINCIPLES OF INORGANIC CHEMISTRY

regarded as chemical or as physical. Disagreement, Bowever, on this
quostifHi is -without point, since nothing of an easentijil nature depends
on the decision ; for thiss, evidently, is of conacijucnec only with regard
to the arbitrary phm of treatmonL If we retain the definition already
given, wo shall recognise that Rulphur with its specific properties
certainly disapj^ars when it is made to a*smne the liquid state, by
hcattnt; or by treatment with a solvent It therefore undergoes a
chemical change. Many, however, designate anch clianges as physical,
sinue it is easy lo recover the sulphur in the solid form with all its
properties, by lowering the tetnperatnre or by evaporating ofi' the
solvent. But a substance which has undergone chemical change can,
in general, also be again obtained from the new substances produced,
although more complicated methofis are often necessary. It will,
therefore, otj the whole, be better to class these changes along with
the chemiml.

7. Homogeneous Substances and Mixtures. ^Whereas iu
everyday life, for the purpose of charaeterising a aiibstauee, w^e make
use of those properties which appeal to our senses, and which allow only ■
of making rough distinctions, it is the task of chemistry to aRcertain with '
all possible exactness all the properties which can be employed for the
cliaTiicterisation of a substiiuce in the sense in which we have define*!

it. This is possible, however, nnh/ vlifii fvenj prrt of the sjilisfamr kiui
eradhj llt^ smitr pivperlirs as mrij other p<ui. If we consider, for ex-
iimple, a piece of granite, wo readily convince ourselves that this stone
is made up of parts having ditferent propertiefi. Beside the white,
very hard grains there are others which are less hard and of a reddish
colour, and l>etween these there are rather soft, lustrous laminie. In
determining the properties of such a body, various results would
therefore be obtained, according as the one or other small piece was
examined.

We cannot, therefore, designate granite as a substance in the
chemical sense, but rather as a mixture of differfnt SHhsUmict.g, As the
characteristic of a substance in the chemical sense, we must demand
that all portions into which it can be sejmrated, exhibit the siime
properties. Such substances are called umfm'm or hcmofjenatm.
According to this, vhcmhttij is the scit-nre if itnifin'm or homotfetifous
subdaiu^e.^. Simple a.s this conception appears, it required a long
time — a time to be reckoned by centuries — ibr it to be formed with _
sufficient clearness, atid the older history of chemistry as a science, fl
might !« called the history of the labours in the working out of this
conception, The difficulty lay essentially in the fact that a sufficient
distinction wns not made between miiiuiys and homogeneous sub-
stances, with the result that the reguiarities which arc peculiar to the
latter but not ti> the former, could not 1>p discovered.

8. The Exactness of the Law of Properties. — The statement

that aulphnr i? denser th.ui water, and that it melts at a modemte

u be m!nlc> in ii much iiiorp definite form by staiini; in
density of !>ulpbi)r is gre.'it«r than thfit of water, and iit
wLit ivnipcnature the fusion of sulphur occurs.

In a like manner, mimy other projjerties, and espcciiilly physical
properties, can be expressed in definite meiLSure, .ind the question
•riaea, how do different s^imples of the s;une subsUince behave when a
^Mfttitative detertiiiinatlori of their properties is made.

On« might imagine tkit siihstaiices behsive in a manner similar to
*p««ics of aniniiiis and of plant^i. The different specimens of one
t.ff. the common tnouse, resemble, it is true, but do not
etely agree with one another in size, growth of hair, colour,
etc On the contrary, within cert.iin limits, they show difier-
wilh reg;ird to their properties. In like manner one could
that the properties of difi'ercnt si)ecimens of the siime sub-
ftance ha^e closely appi-oximate values — that those values, however,

Knot *jiiit^ deftnite but vary within certain limits.
Tlie innumerable itiveatigaiions of this point which have Keen
ertaken, show that the law of projierties of substances hoKls not
r approximately but ejradh/, and, therefore, ihf iiimsttruble prfipfrlies
i0at»t apeanuiis of tlu same mbatunct a^ree )mt only appttmmakli/ fmJt

It must be at once oraph.isised that it is not intended here to

the ahsolute validity of the law. The absolute can never be the

Ifj«ct of experience, and, in fact, it is not admissible to employ the

lute with reference to any relationship based on experience,

Ing of the iissertion is rfither thia, that experience has, so

•iHnm MO de\'iatioTis which are beyond the limits of the possible

of observation. For, every measurement is exact only within a

MCtaiji limit, and all conclusiun.s wliieh am drawn from the^e measure

OMit* can be valid only to this limit. Thus, the density of sulphur

(U be •Ictermined otdy with a limited degree of accuracy, and if the

aoae vajae hits Iteen obtained with di^erent speeimeoH, the identity

<aa Le aascrted oidy to thi.s limit. The meaning of Die assertion that

ike pnipertieis of different ."jpeciraenfl of the same subataiice are the

Moe, ui only this, that within the limit* of error hitherto reached, no

tfcreaoM b*V(>i been found.

The accimuiy with which a magnitude is known must always he

in fractions of ti$ ndw, and not ivs a concrete number. If in

,'.nt of a length the possible error amounts to O'l em.,

i«s a large or a small degree of accuracy, according as

iinft. If we measure a distance of 20 metres to

' . inurement is very exacts, for the error amounts

K &t moet, iifiiisiiib of its value. On the other han<l, if a length of

S^eoL If koowtt with such a limit of error, the me;t.^ureiment is not

T«y exact, for the error cJvn amount to ^^tl) of the ruciiaurcd value.

9. Pare Sabstances and Solutions. — Tn the law which has just

PKLNCIPLES OF IN0KGA:SIC CHEMISTRY

of liquids, in so far as they arc not bouiwleil by rigid walls, iipj
the form of a horizontal plane.

Gases have neither a dofiiiitc form nor a ilotinite volume; th
completely every vessel into which they are broiigjit.

All these relations are further subject to special laws, whic
be discusaed m their appropriate place.

By riieans of the chanictoriatics we have just giveti, we shall
na a rule, no dirticulty in deterniiuing whether a body is soliil, 1
or gaseous. If a iKxly, when placed oti a. plane, retains its shape
solid ; if it spreads out whilv, at the same time, a l)onnding pli
sarftice, is formed on the top, it fa a li({Uid ; if it exhibits in no
tion ft hounding plane of its own, it is a gas. Between these
physical states there are, it is tnie, intermediate states which
times render the decision difficult ; still those arc not vpvy fret
and for the pi'eaent vvc need not discuss tlioni in greiJter detail.

A giveii liudy doffi not under all circiimstiuices remain ii
phystcal st«'ile in whreh it is at a given time ; the physical
depends especially on the Inupcrahire, In this case, the genera
holds that with risimj lnuifKrature, a solid subsfanee can become liqu
ffttseot/s, iiiiii II Ikiiiid ime t/asmits, hut nei'cr tlte mnverse. On the
hand, with lowering of tempenitni'e, gases become liquids or s
and liquids become solids.

Althongli the sense in which the change takes place caiim
departed from, the liquid state need not. liowever, appear as an i
mediate state between the gasooius and the solid. On the cont
casea not unfroqnently occur where with rise of temperature, s
pass directly into gases, and by eo<.^ling, gtises pass directly
solids.

The laws which these transformations obey, will be disci
later (Chap. VII.),

15. Sumniary. — The Loaception of suhMante has been develi,
By this name are designated the classes into which the inanimate b(
can be arranged according to their properties. Experience tei
that it is possible to arrange the naturally octuning or the artiflc
prepared bodies in classes so that the individual mcmbors of a
have the same specific properties, liy properties in this sense
understood only those which are essential, and which caiuiot be g
to or tjikon from the body at will. Expedence teaches further
different bodies which belong to the same class or which consis
the same subsUvnce, agree not only approximately but exiu'tli/ m I
pi-ojwrties, so that the value of any property determined on
specimen may cunhdontly be expected to b« fonnd in all specimen
the same substance.

Tltr lidv <ij nutufi' tliiit clii.'fiifs aiii be furtticd of liclieif whirh c
aitirAif veUh one miother in their essfiitutl properties, is the fundiiwenUti
of chemintrrf.

ili^atlcal in siil>8t.iiice only wben they show entire agreement in all

specific properties, the task of testing whether two substances

the SAme or not, ftp{>eais impi-aeticable. Aiifl utill, chemists are

identify subsfiinces with certainty after testing some few

Ae surnumiitinit of tliis rlifficulty is renrlcred possible by the
foodamcntAl law of chemistry aliejuly given (p. '2). Tliis law, iii its
^■piicttion to ihc prfscnt question, cun be stated thus : fVfieN iim
mptf f.ntirrJtf in »nii^ few prirpertie^ fhey agree nlso wif/t regard
■ yrpfxtriies.

hiw, likt.' all other laws of nature, is only a suninutry of
v«I facta. It does not jfrescrihc ibat something t/ifi// happen, but
Aii'it what relations exist. For this reason the term "law,"
nwed from juriaprwdenee. is not lery suitable for expressing
eh rc^ilttrities in natural phenomena, and it can bo used without
Btagc only when the rHstinction, to which we have juat drawn
[I, between a law of tinlure and a. civil Liw hiis, once for all,
' ijiiit'' L'iciir.
II, Indacti<m. — The toUd number of cases classed tinder a law of
WJtre can, evidently, be dii-ided into two groups; a small one, em-
ihe caaea which have been tested, Hnd a very largo one, to
I Iwlong the cases which have not been examined. For the task
.1 law in all cases in which it applies could not be under-
th<' Irtlvour involvetl would he too great,
Sm. indeed, the necessity for such an examination is not felt ; for,
ilh« fart that in all cases whicli have been observed tbe law hiiB
Wn founrl vjiliil, we niiiy ctmcliide with a high degree of prob,ibi!ity
i it will hold eijually iti those cajses which may in future he inveeti-
bI This probability becomes all the stronger as the number of
rrctigstcd increases, and the more the cases chosen for cx-

hTft independent of one another,
en the univcriid validity of the relationship has been cstab-
1>A«1 with a tlutinite measure of probability, we are accustomed to
npni it a« » hitr »f nature. However, the liistory we have jtisi given
itenis of such a law, implies that it cannot have the character of
y, and it is quite possible that, follmving on the many coii-
•omfl should be found which do not conform to the
irpfdeednre which we have to aiiupt in such cases will be
t'^r. For the piescnt, we accppt the statement that the
■uTo Jiic conclusions as to probabilities, Imsed on ex])ene(ice.
Icttions are calleil iiuineiivf, and the procedure liy which
nned h called imiii''ii«ii, The whole of natur.al science is
vftd such inductive conclusions.
I* So(aetiaie& the nce<l has been felt of pliicing the laws of nature
Mm certain foundation than ij furnished by conclusions by
hcwwl on experience, since these afford itn protection against

M OIlNMft of Wolght in Chemical Processes.— If we choose out

(am -i'/ut «'i»v(t»iigiUiiiii itimii* iif the ieiiiuiiicnib[« t.-henikvil phenomena
wiiV:it MixJM *)jil)>' Hnmiiil lis, AV*5 iirc struck with the changes in the
ffHHfiiif Ht Um ndlmluin'tiM tiikiilti pin in the chemical process. When
f^ #|ii#4)ii tit ti ttiiitlli' 111' the petroleum in a knip Imnis, the«e &ii1>-
W#/M^ wufji li> ijjuafi|iiwir oritirL^y : the wood nr ctmt burning in the
ttfu l«»viu ltuhnii\ only a'()th to ^^tti ^^ '*'^ weight of fwh. On the
t4k«f l»4«i(, th« iiiil|(hiiriii iieifl ■manufacturer obUiiiis about three
UiifHty'HHii >*f' m\\t\i\uir lu-M for every kilogram of sulphur convertwL
(11 i vn;ij<lii urn thorofori'i connected with chemical processes,

yii •• M<(w 111 lihk whether any generalisations vwn be made

I > liJivu just cited appear only to lead to the

i.'tMUiit*»um WmI til chtfiniral iiiocesses diminution as well ^ increase
if) wttjght tutty oi.ciir. Tht^Ne tire, however, not suitable examples
ffffr (|«>ciijirtg (lib <{ijii»lii)ri, for the proceeseii take place with the

HiibiitHncvH in free communication with their ^
aurroundings, especially with the air, and do fl

lit t hiMvfore allow of ji bahince being drawn
iiji. 'I'd uL'hieve this w« must conduct the
Dxpitrinients in a cloaed space.

1 7, Experiments. — At the bottom of a
lai|.;i', ihiii-Hl"**» tli*sk (Fig. 2), and resting on a
lijyuf of jiMbciitofl. is a small dish eontajning a little
phut)|jli(>j'ii>ii. Phtmphorns is ii substance which
i'ni|iiireH only a slight elevation of temperature
In fiuuac it tn take firo. The Hask, closed
by a gnnuid-in stopper, is accurately counter-
poitttid on the iKdarice, The part where the
jilitisplioruB rests is then warmed, and the latter
lire In ti uliort time thr phosphorus becnnieH cxtin-
Ibu Davit liiiii Imjcoiimj filled with dense, white fumes.

THE LAWS OF CONSKRVATIOX

sgsin placini; the flask, after it has become cold, on the Imlance,

tfkot^iif iM4/fit lit iJiKtimtL

' The flaak nniet be allowed to cool before being reweighed. So

it is wami it warms the air surrounding it, and this, tiBcending,

fth** flask slightly upwards, and makes it therefore appear too

• HecomdAry oircumstanoea of a similur nature, which more or less

the reeult, are always met with in carrying out quantitative

' nertts. If an csact result is desijed, they must be known atid

Of inHncnce either obviated or, if this is not [jossible, taken into

oimt. The real difficnlty of exact mcasnrcmeiit lies in these

utwlM7 iiiHtienccs, and ordy by a varied ex]>eiieiicc, obtained by

»ing :h(! expcrimenta under as many diflerftit conditions Jts

lan one succeed in so controlling those influences as to obtain

"fiments. Conipiired with this, the carrying out of the

emmit is generally an easy matter.

The fact jiiat deseriljod, that when conibusiion takes phice in a

^icc no change in the totiil weight is observed, althouj;h

initmtancea diaapjwiir and others are
yl, is a general one. No matter what
oImukis are burned under these conditioriB, a
(k»H|!B of weight never occurs. This law also
» Out restricted to combustions akiiu', but is
twiorall chemical processes. To iUiistrato this
( a»j perform the following exj»rinients.

Airi<i^ test-tnbe is placed in a conical flask

ilk wide mouth (an Erli-nmeyer flask) (Fig.

Two «ul»stimces which, on contact, react

th one another, are placed, one in the conical Hask, the
tost tube, so that they are kept separate. The Mask
having been carefully closed and its weight deter-
mined, the substances are bronght into contact by
tilting the whole app;iralus. Chemicjt! reaction then
takes place, generally acconipiinied by rise of
temperature. On placing the apimratus, after
cooling, again on the balance, its wriffht is wrw to he

* Another method of {performing this experiment
*. Thi^ nicthiffl is more convenient, but the two-

• tW MViviug «ii!i»l»iices whiirb i^ive ri-ii; to t-ln'inicttl reactions rncoglii!<»bIe by
chiuigtM, luiiy l« ii«tj4, luctstlf iu contentmtuil .■^olittiou ;— Pota^siu^l ciirbonale
MlcaUom iKluriilt (whitr pr«-ci|nt3.t«), nthcr biLrutc uiiil umistie pot4V4}i (brQun-hWk
(■nfOitoK anthiioTiy tTifH<>n<K' nmt schImiui sulpliitle (omiiKe-rol iircciiiiUl*), miv
ioha»! (I »nhitioii). silver niliate am! ferroii.i sulpluite (nepdrn-

^m ^ M !k' ai'iil aii<l iixlic )ii.-)i< (tcparutbii of iodiDc), chlonl

..-M ' ...iu.iitiuii of IV

IC. Oh.'

for (L'k)h'
which I.
atnouri!
the 8h .1
fiUncfs
rtre 1e;tv ■
other 1 1

kil(>;."~ •

COIU i

in IV
for '

CHAP.

Lttil this must be

teshi of one gram is

'•ndy there exists

:7iiis expression in

laJl eijujilly fast.

s il holds goo<l only

A litis condition can

■aaty which a definite

f proporticiKiI to the

>d the fi'ee fall, two

acquire tbe sauie

OTvi' tire jjiujiorfiomii

^■» MPt eqiutl, it follows

_«. The forces are, in

/ htufij kniifs, there-

«(ig. Let the two

J ilistomes, .<, they

The amounts of

-y. iuv u\s rind u'j.s,

- The wiiTosfionding

^^^I (u these. From the

^(B follov?, I'.V division,

jtJon we h;ne just

t." So little IB this

« cuinot see until noiv

^ with !tt)ythitig else,

two rjiiaiitities of

apthin,!; direi-tly to do

r of the kinetic energy

H'ity {p. -22). The

,:rrue of which hcKJies

iixpressioti in nnivcrsal

proportionality be-

tiieitns of the other.

■ ,a it is eqiud to tho

,,f the weight gives

. , the eiue -when we

tin 'IS the unit of

is Bmltiples ami its sub-

THE LAW« OF CONSERVATION

divisions. Of these, the ones most employed are the kilogram, which
is equal to 1000 or 10' gm,,ttn(l the lutlligmm or !0"*gTn. The other
magnitudes^ (decagram = IQ gm., hcctogmm =100 gm., decigram =
O'l gm., centigram = O'Ol gm.) are but sohlom used, and for scientific
purjjoses .should never 1)6 nsed at all.

For the chemist., now, tieilhcr the question, how nuiuh kiiietio
energy a bwiy acquires under a given velocity (the mass), nor the
question, what force it e.xercises on its support (the weight), is of
supreme interest. An exphmation is therefore necessary iis to why the
balance is, rightly, cfilfed the most important inatrunient in scientific
chemistry,

When wc buy substances fur churaica] purposes, for example, coal
or food, which is of course done by weight, the mas* and the weight

of these things have likewise no direct iiiterewt for us. Tbc determining
factor is iluti fkf chemuul ^fahies, the nutritive value or the heat that can
be obtained by combustion, arc also projwftvnial to the mmn awl the
weitjhl. These values are all energy magnitudes. In maiis and weight,
therefore, we have a measure of the chemical energy, or tbc work
which the bodies can do by chemical transformation; and we determine
the weight when we wish to meamtre the amount of chemical eflect.
How this is done in det.-»il will l>e discussefl later (C'hap. Vlll),

* The chemist's lialanee (Fig. 5) is a lever with two equal arma.
Weighing consists in allowing the body whose we' ^ " 'a to l>e ileter-
minwl, to act on one end of the lever, while ditl'er ts of Icnowa
value are made to act on the other end, until e<iui itablished,
i.e. until the lever turns neither in one direction 'er,

* The balatices used in ordinary life differ ily in
Kn«iiV«v.« from those used for scientific purposes nary
kilogram balance will still show ditTerciices of I gm i.,

PRINCIPLES OF INORGANIC CHEMISTRY

CHAl'.

the best scientific balances, when loaded vvith 1 kilognim, will show u
difference of one hundredth of a milligram, or 000001 gra. The fonnBr
has therefore a limit of error of 0001, the latter of 000000001.
The latter therefore allows «jf tho determiriation of weight and mass
ratios with proportionately greater exactness.

* This increase in the senaitivenej^s of the Wlance is effected by
rainimiiiing, us far as possible, the hiridraiicea to movement due to
friction. The axis of rotation of the bcjim of the balance is formed
by a knife-edge made of hard steet or agate, resting on a plane of hard
stone. In the same way, the axes from which the pans for the weights
and for the body to be weighed are suspended, are fornjed by knife-
edges resting on phines. The three knife-edges must be parallel to
one another and ici the same plane.

* To prevent the knife-dlges from wearing away too rapidly, they
nnist be allowed to rest on the planes only during tlie time the luilance
is being used. Every good balance is therefore furnished with an
arrangement for "arresting" it, This is so made that by turning a
knob or a handle, the scale pans are fii-at raised from the end knife-
edges, and then the beam from the plane on which it rests, The
weights, etc. are placed on the scale pans while the Imlance is " arrested."
On slowly " releasing " the balance, it can he seen in what direction
the balance tiiruB, and whether the weights have to lie increased or
diminished.

* Since it mcKlerately gowl balance detects amounts, even as small
as O'OOOl gm., uno would require weights of a convsponding value, in
order to finish th<^ weighings. These are very inconvenient to handle,
and chemical balances are therefore furnished with another arrange-
ment for determining the smallest weights. The Ktlance beam, from
the middle to the end knife-edges, ia divided into ten parts, and there
is a contrivance by means of which a weight of O'Ol gm., which from
its form is called a "rider." am be placed at any point on the beam.
According to the law of levers, the efl'ect of the weight is smaller, the
nearer it is placed to the axis of rotation. If, for example, the rider
is placed at a distjitice from the axis equal to ^^(jths of the length of the
I>eanv, it acta as a weight of 0*003 gm., and every tenth of the beam]
corresponds to one milligram,

* In weighing, therefore, it is necessary lo counterbalance a body!
only to within 001 gtn, with weights, ;uid then to move the rider till]
com[>lete etpiilibriuni is obtaine<l. The tenths ami hundredths of the)
beam length give the milligrams and tenths of a roilligram which have]
to be added to the weights,

* The ijroduction of erjuilibrium is shown by a pointer attached toj
the beam of the balance and moving in front of a scale. h>ince a goodj
balance does not remain at rest but contiiuics for a long time oscillatingJ
like a pendnhim, one obser\'es the extreme positions of the pointer,]
or the deflections, and Uikes the mean of tliese.

THE LAWS OF COXSEBVATIOX

^M * To complete tlte wiglbiiig it b not expedient to olitan th« fa»l

^H^jastmeot hy shiftily tte rider, as ire h^Te jtut tximmed for tlie aake

PVr clmmoB. ' Ratbov aw » made of Um bet that the diaage of thtt

powtion of rest » proportioaal tn U»0 exeen of weight. If tbe tiautgB

of aero CMued bjr a ^aage in tfae wc^t of 1 aiiU^nv bas bHS

detcnuiMd, h ia oolj neceasaiy to Mt the rider at tfc« maneat wkals

icnth to be able to calrolate, from tbe d«TMttoe of the point of rvt

»nr obtuoed from that wbea tbe babuioe is 'Bri?Trtr* or tbe xoro, tbe

turns of a iBiUigraiii vlueh voald make tbe eqnQtbriaB perfect.

26. Deni^ aad XxtOBlitf. — Tbe aids to tbe deinkxM

t of miiiirni and «rdgbu jost eooaadered, Ions tbe baH

of an MpeitMt ptopertj poaaMaed hj afl i

wUcb, bf f Willi at tbe great varialiaa of eta valoe &«■

wbataaee^ it ^vKbIj Bted' for dhliagiiiibiiii; tm

^^■B ■ tbe irfflwKy and the edmaitf (SawmifbiQ.

^B Whea dejning tb« ooaccptioii of

^^nittcd to take tbe maat into aeooont <p. I ), is also tbe ^hmo

]ml bjr a given pieee of tbe anbrtaace. Sinee, bowerer, tbeae two
mtgaitiidfa vaiy «■*— *******"**y and ta tbe mtn» degree, tbeir rmlm
s dfgtniW' yroi—ty of tbe ■abatancee, aad, aeeordiaig to tbe
bw. must always bave tbe aaine Talne for a ^tcq eabstanee

IDveo cooditioiM.
I If we demiCe tbe naaaof a gnren tprrinm of a anbrtaaee \ty mk,
pd tbe epnoe whicb H occnpiea, or the voIosk^ hj i; we eaa fnr^ tb^j
pa tjipneaiiaii m w and r m. Tbe former, tbe maas in unit
M oillad tbe 4t%aily or tbe ^ledfic ^tvdxy : tbe kttcr, tbe vohnae <
mtt mete, i* called tbe epedfic roliuae : we wUI call it tbe 4itum^.
The onita in arfaidi tbeae magaitndea are aieaawitad hate
the mte of warn is the gna, and thai of vofaat
Sinee tbe oiaaa is exprened by tbe waam
ve^ht, tbe denaiiy is eqqal to tbe we^fct of tbe body in
bf ita rolnaM in cobtc eentinetras ; beoee tbe
psritr. Tbe cxtcaatty has the ifrijaiinil rahie. If we csD
■tH^tantjr V and tbe ertenaity ', we hare tbe relatioa 4=\ t

^H Of tbeae two iiipttniinni. tbe denatty bat, as a ndc. the
^Bhe^ on t'vLM'm^ a body we fint estnute its roisae with tbe ere,
^^■i ebCaia en idea of ito weijj^t only wlwn w have takaa it
^^pd. Otoe rafcea, tbeieftae, inWiintanlf, the weight to tbe
^nf aet tbe vnioiBe to tbe we^^ For aeieratifie lairpnaia it ii <
' (» tmfkar fhm oppeaite rektioo. For the

■tiiifiii in • body, wbereai voloBe d^wodi on prea
I kaipenime, and it » wan tationel to refer tbe rariahle ^

thr iartfaUe dlan cjuuriely.

Ia aecae^nee witb tbe eoouaon eactMa. boverer. the

lUBIadaeftanfc *A*<> raeerre tbe faaeiBwist place.

TEINCIPLKS OF INORGANIC CHEMISTRY cmav.

Fio. i!.

•27. Measurement of Densitj and Extensity. — To deteraune
the ratio between volunif and mass, .a mLa.suii.'nieiit of both magni-
tudes for the given body is necessary. The innss is determined
by w«?ighing {p. 25) ; the determination of the vohime varies with
the physical state of the body. It is easiest in the coae of
li«]uid9.

The most direct method consifita jij filling a vessel of known
capacity wtth the Hquid, and determining its weight. Such vessels
can be raafle of various kinds according to the iiecuracy aimed at A
very ray>id nnd convenient method consists in the use of a vessel of j
the form shown in Fj,^. fi, called a pipede (small jiipe). It conaista,
essentially, of a narrow lu!ie, widcnucJ in the middle, and is filled hy
dipping one end in the liquid and snckiny at tfie other. On the upper
tube is a circular mark fonning the limit of a definite cubic content,
which usually amonnta to a round number of cubic centimetres. In
^^ filling, a slight excess of lifjuid is

sucked up, and then, closing the
upper end of the pipette with the
index linger, the excess is cautiously
allowed to run out till the liquid
stands at the mark- The filled
pipette is placed on the balatice in
a horizontal jwEition, resting on a bent wire carrier (Fig. 6). If the
empty pipette with the canier hjis been previou-sly counterpoised, the j
^increase in weight gives directly the weight of the liquid.

The deterniiruiiion is simplest when a [lipette of exactly 1 cc,
ipaeity is used, and a weight niatle which counterljidancesi tlie empty
pipette along with its carrier. In accordance with commercial use,
such a weight i^ called the fure. The extra weight is then directly
equjil to the density of the liquid, since, of course, the divisor, the
volume, h equal to 1. Such a determination can be carried out with
an error which is hsa than 000 1.

Another method h liased on the principle of Archimedes, according
to which a body sunk in a liquid espei iences uu upward pressure equal
to the weight of the liquid displaced. A glass sinker, closed on all
sides and hung liy a hair or fine platinum wire, is counterpoised on
the balance ; it is then sunk in the liquid tn be investigated, arul the
decrease in weight, or the upward pre.saiu'c, determined. The volume
of the sinker is determined by conducting the same experiment in
water: the upward pressure in grams is equal to the volume in cubic
cemimelres (p, 2-1). If this experimeiii is not performed at 4' C, one
finds from the tables of the exjiiu | i water the weight of 1 cc. at
the temperature of the experini' vides the upward ■ 're

found by this.

In this Ciise also it is m b to make a

volume is exactly — ""^ to " The loss r

THK LAWS OF COXSKRVATION

Bctly (in the case uf iU ve. jifu^r moving' the dcdmal point one
lie left), tbtf density of the liquid.
Finally, for rapid «leterminiitioiis of the density, the hiftlrtnnfUrf is
Tbts coRsisttj {Fig. 7) of » gUiss Hoat terminating at the lop in
twrrow' tube within which there is :i si-ule. Tlie instnunent is so
t it ^mxts. perpend icTilarly in tho liquid to
g»ied. Since a tloaiing body sinks to such
that the wei{;;ht of the liquid dispkced is
U% the wfiglit of the body, the poaition of rest
with the density of tlie Iiqin<l, and the scale is
the point whore the stem pajssos through the
of the liquid. The scale is generally g;radiiated
allow uf reading off the rlensitics flirectly.
otht^r si-iiles are in use which have dili'erent
ikccunling to their itiveiitorsv, and whose zero
numsponde to the lU-nsity of water. For scientific
j«ipo«« these have no imixiitJinct-.

2^ Densities of Solid Bodies are doterminod by
riaef nietho^Fs. Generally, they are weighed first

«f»J then in water or other liquid. The first - —
;luiig gives the m.'is.s, the secofid the loss of
w the upward pressure, and from that the volume.

yiu. r.

\\'^hen the
^ weighing is carried out in water, the upward pressure ia equal
volume (the influence of temperature being allowed for ; viiU
IfmV If another liquid must bo used, as in the cajse of substances
^oMe in irater. its density must first be determined by one of tlie
}n»t de'jcribetl, and the upward pressure must be liivided by
of this, For the volume of the liquid ia equal to its weight
by Its density (p. 11 y
Ifl earrjing out such eiperiments, regard must often be had to
'ie t»ci tkitt the liodies are not [present in large pieces, but in grains
or small pieces. In ibis case they are weighe<l under
water in an open vessel of glass or plattnuin, as in
Kig. 8. The weight of the vessel under similar conditions,
viz., immersed an the liquid, must, of course, be previously
determined.

Another method, employed especially with siuall
quanljtie*, cooabti in mixing together two liquids, one of
which 10 deiuwT, the other less dense than the solid to Ije
tUTe«dgat«d, ao w to give a liquid whose den-sity is equal
to that of the «olid body. Thi.s identity is shown by the
that the bo<ly neitber rises nor sinks, but remains BTisjMnded
1 14* liqtdd. Thr experiment is carried out by I^keing the
Ij flnt of all in a stuall i)uaulity of the lighter liquid, in wliich
to the bocton. There is then cautiously added eo much of
oiIms' liquiil till tJte tiupeiwion is produced!. I'enerally one will

PHIXCIPLEf^ OF IXOIJGANIC CHEMI8TRY

juld mtlier too much uf the sei^uiul liquid ; the errur taw, ho^vei
easily loctified by the addiiiuii of sumn nf the lighter liquid.

When suspension takes place, the density of the niixtufe i|
rained by one of the methods described on pp. 28 iind '2'J,

* As a heavy liiiiiid there ia used methylene iodide or
tBlrabroniido ; as a light one, benzene oi- toluene. These liqi
be obtained commercial ly.

The neceBSury informiition for the determimitioii of the Aei
gaaea wdl be given later (Chap, V,),

29. Influence of Pressure and Temperature on the Dei
— It hiis fih'eittly Ijeen mentioned that althou^li the muss ex per
no i'hiinge in any procesR, the volume is dcpemlcnt both oi
temperature and on the pressure. The density of a sul>stanct
therefore likewise vary with the.se tircumstances ; iind in ord
make a statement definite, the values of both of these must bdl
at the same time. II

The influence of pressure, now, ia generally very small. The v<
of iifjuid substances is diminished only by some hundred thousa
of ita value when the pressure ia increased by 1 atmosplicre, ai
the case of solid ItfMiiea this rnfluejicc is in moat cases still smallei
is therefore necessary to ha^■o I'cgard to this variability only ii
case of very exact investigations, J

The influence of kwprraiiirt ie, however, much greater.!!
volume of a given body is (with few exceptiuns) increased by a r
temperature. The amount of increase ia very difl'erent in the a.
different substances, and ia in {general greater for liquids thai
urjUds, As a rough estirautc one can assume that liquids ex])an
about one thousandth of their volume for every degree of rise,
is, however, only a very rough approximation, since the am
varies not only fi'om liquid to liquid, but also with the teinpen
iteeli. The higher the temperature, the greater ie the relative inc
of vohime with the temperature.

In the case of accurate statements of the density of liquids, ti
fore, a statement of the teraperatuie is necessary, Approxi:
statements, such as will often be marie in this tiook, refer to !
temperature — aiy 18" C.

30. The other Kinds of Energy. — In the discussion of perfect
imperfect machines (fi. 2 1 ), there still remains the question, What l»ec(
of the work which in imperfect machines disapjiejirs ? In order to
an answer tti thi.s, let us make a machine which is an im/HT/a
}M)ssil'!i.\ so as to mak«* the ofl'ect produced by this ipiaKty as ctea
possible. In other words, we increase the frictiun to such a de
that the machine cfjnsunics almtjst all the work that ia put into it
gives out only a amnU araoutil uf it in external work.

The result of such an increase of the friction is seen in the cas
badly kept axle-hetiring-i in driving-engines, vehicles, etc. Thuse p

iir PUEN'OMENA OF COMBUSTION AND OXYGEN 39

nor of oxygen. Since a substance is characterised only I'V
►prIJcs, such a auitement as the ahovn his no rctil meaning, ami
mdj" a short iiiacnirate method of expressing ilcfinite regiilaritii s
ifh trill he diseiusscd later (Chap. IV.).

Tills truithod of expression is, however, so generally used that wo
Duut retain it for the sake of iiitGlligibilit<p, thoitgh with the reserva-
tioo jost made.

58, Combinatioil. — The process of the conversion of oxide of

ooviiry into merc-Hry and oxygen can be reversed. By heating

mawry in rontJict with air, i.r- with the oxygen of the air, to almut

iti iuiling point, it is converted into oxide of mercury. The process,

totefer, re<]uires days in oiiler to yield an appreciaKlc amount of

rtniry.

single subauuice is hereliy produced from two different

the process is called a etr/nhimifioii : ihe reverse profess,

Morersnun nf one subst^mce into two — oxide of mercury into

meratrr and oxygen— is called a dcrofiipo^iUoH. In the same way,

awrvury and oxyjien are called the rm!!ifilii''nf.< of oxide of mercury.

•nii this, a etjjiijmtind of the two other siihatiitices. It is looked upon,

ecmfiosUf suhatance with regard to its constitncnls ; still

in reminded of the reservation we have just made.

39. Quantity Relations. ^Ketiirniiif( to our experiment, we can
noK the question a% to the quantity relations of the participating suh-
ttiiioe*. From the experiences of common life, one will be inclined
touramo that in the coniersion of a sulujtance A into a substunco B,
the amount of B oUtained will diminish and increnfle in the sjime ratio
M tlw amount of A used. However, from tlie sitme experiencesj one
w«wid conclude that although the "yield" would on the whole agree
with lhi» role, it would, in mdividual cases, show more or leas devia-
^jiui froffi it>

^^1 Lot us perform sniuble experiments by decomposing various
^^^■Btekr weighetl-out amounts of oxide of meroiry and measuring
^^^^^^^■11 evolved. (The necessary precautious ti> lie taken here ^vill
^■^mmtljr di.«cus.sed ; vuU Chap. V.) W'e find that the miw of iftit
tf OTulf of inm'uii/ iitiof in ilir nmuuid nf oxi/;jen ohtnined is
ihW xmltj apprurimatehj litit. v.^it/i nil the mvuraaj vMh whkli tw can
^^Mine the WKtisurrmmt.

^H The relation which wc here meet with is a ca&e of a general law
^Biatiire.

^B M^n our srulnitiinff ix rontfrrlfd into nmthrr, thfre ejdsfs n definitr,
vmtriidtU hrren thir im^ht if the SHhstan^f dmijipearinf^ <ind thut

*i Ikt suL^l • 'irai.

Wr cjiti at once extend this l.iw and say that when two substances
tanbine with one another to form a third substance, an invariable
nktion «lso exists between the two substances. For the weight of
lie lafastaace produced stands, in accordance with the law just stated.

FKINCirLES UF INORGANIC CHEMISTRY

[If

feasible to create wnik out of notiiing, and tliat msjchiiies at 1>9
give out only the iuuouut of work which is put into them, we^
the positive Iwiv of Ihf comtervatinti uf uwk tii [jerfi^ct tnfichtnes.,
further (juestion as to where the lost work remains in imp
maehiiiefi, has led to the I'ecognition that work can be converteo
other forms of an equivalent thing, which is called energy ; and i
final result of the impossibility of fierpetual motion therL^ is deve
the law of the conservation of energy — one of the most il^Jf
laws of nil luituj-al scietiee. ^

* Similar (ievelopmwita of fruitless labour into positive law
be recognised in other part.s of natural science, and we shall at a,
time have to occupy ourselves with such cii^es (cf. Chap. IV.). 1

31. Smnniary. — -The production and disappearance of subnl
during chemical processes raises the fjuostion, whether these chj
obey any iaw3 ; and it is found as a universal experience, wit
exception, that the toud uriffhf of the substances taking part in
chemical process remains uncliaiigod. The total weight of the
substances produced is equal bo the combinecJ weight of th«
stances disappearing.

There holds, therefore, for all chemical processes (and for all|
known processes likewise) the !"W of tin: t'^ui.^'rntfkm <.f Wfiijht.

The fHiiii.'. of a given btidy is proportional to its weight, the
of mass to weight beinj;, for all bodies, independent of their c
properties, constant at a given spot. Hence there also obtains fo
processus, the chemical ones included, the law uf the awsantiitmnf j

The two magnitudes, weight and mass, have no direct rela
to one another, an<i the law of their proportionality is a pii
empirical law.

An iruiirect relation between mass and weight is found by the
of the conception of work. Denoting )»y this name the protluct <
force and the distance over which it acts, the law cati be stated,
the simple "machines," that in the limiting, ideal cjise, the v
can be neither increiksed nor diminisbed by such machines. Tl
exists, thei'cfore, for tiiem a htu- of the rfjiistrt^iliou tf ntirk.

In special cases, work aiiparently disappears. In these case
can always bti shown that something else is produt-erl at the si
time wluch is proportional to the work which has disappeared, .
which can be reconverted into work. If we denote all such thi
as can arise from and be converted into work by the name riirifft/t i
if we ineaaiu'e the diflTerent kinds of energy in units based on
conversion of a detiuitt! amount of work taken as the unit, there be
g(X)d, "[uite universally, a fan; if the mmenmiioii if ai*ti\fi/.

There are various kinds of energy. Besides work in the se
just denoted, !d>ir:fir incy;r!/i Hedriral enerfftf, c/frmiotl riirrtji/, hrnt, w
characterised »■? various kinds of energy.

The unit of energy is called the frti. It was defined as twice

THK tjVWS OP CONSERVATION

gram

contained iii 1 grarn of any l>ody when it hae the velocity of
e iu 1 aecoiid.

Kxiy has the mass m and the velocity c, both measureil in

imrt* jiist given, its kinetic «;nergy is equal to imf-.
Wfen 1 gram fall* through I centimetre, under the influence of
'. acquires the velocity of 44'2C cm. /sec. Its kinetic energy
_. ..i=>re, tiiual to 9^0 ernzs. This has been produccJ from tht<
k ol gravity, which is eipial to the product of the force of givivity
ifiUiiic*!. Since the latter is equal to unity (1 cm.), the
X Vie o<iual to Sf^O, The force with which graWty acts on
». therefore, eqiud to !*S0 units.
'"xjy of n grams on falling ilirough 1 cm, acquires the same
-tnce, as e.xjwriment shows, jdl heavy 5jo<lies fall equally fast
., :ie energy, therefore, amounts to OfO tl Accordingly, the
loro} of gra%-itr acting on n gm., amounts to 980 ti units.

In thftnidr^^ weight and mass have a special importance, from

iKp Ivt that the chemical energy which can be obutined by the trans-

1 of any Biibstance, is [froportional to its weight and its mass.

value '«f substances use<l for chemical pui'itoses, f.g. articles

i or fuel, are measured according to the amount of chemical

vhich can be iibtained from them, the weight is also a measure

tk chemicii value of different quantities of the same substance.

In mnclnsion, we may grouji together the units we have selected

i"r \ht tneasuremcJit of the different magnitmies. These unit^ art;

aniwisally uaed in acience, and are called ahsoluit uniin.

Unit of Time
,, [..ength
„ Mftss
„ Energy

^uonii
Cejitiraetre
Gram
Erg

sec,
cm.
gm.
e.

TlieJ^st two units are not independent of one another since, when
'w of tljero i* given, the other can bo determined from it with the
Wpnf the first two.

Froiu thcs« funilamRntal units, compound units are derived by
•"irtftjt the proper nuignitudes. Thus, the unit of velocity is the
♦tlf«ity of I centimetre in 1 second, I cm./sec. The unit of force is
^ which acting over I cm. perfoims the work I e., and is therefore
''jnseBttd by 1 e., cm. It is ctdlefl a dtpie. The unite of area and
'■uae nxv given by cm.- and cm.* The unit of density is 1 gm./cm.' ;
•^ irf exlenaily 1 cm.'gm.

42 PRINCIPLES OF INORGANIC CHEMISTRY CHi

The formation of compounds from their constituents takes pla
definite proportions hy weight, which depend only on the nature ol
substances, and not on the circumstances under which the compo
are produced. This law of constant proportions hy vjeight Iwlds fc
kinds of chemical transformation whatever.

The exactitude of this law is of the same order as that of the
of conservation of weight in chemical processes, i.e. no deviations
it have as yet been proved.

nur.w PHEXOMEXA OF COMBUSTION AND OXYGEN 36

« Is Increase of Weight on Combustion Universal ?—

Sutce :hi" tirsl siippositicm, that cijiuhitstiuii and decrease of M*<?ight

i/Mav»gn hand in hHnii, does not. turn out to be tnie, one mny suppose

iitetlbe wpposite is the ease, i.e. that increase u( weight uKvaya occurs.

Fat k foUowa from the law of conservation of weight, that burning

^Mraieniu and burning alcohol do not disuppear into nothing. New

fflnUoces must, thereforej bo produced, and the following experiment

wiJJ readily convince one of this. Take a large, dry tumlijur and

J lli«}cj it over » tlatiid so that the dame bunia inside. The turabler is

fihta seen to become immediately covered with a film which has

cnetly tluf appearance of the film of moisture which forms on cold

nodow panes. Ont* closer investigation one can convince oneself that

til« film consists of water. .Since this phenomenon does not occur

•iwii th« tmiibler ia held over the mil it lamp, it follows that mitrr is

fbraied in the Hame.

Portbw, if a similar tumbler be rinsed out with limy-imter and
thai bdil in this condition over the flame, a white solid is formed in
iW lim^-VTAtcr which looks exactly like chalk. This phenomenon also
only when thti lamp is lit.
• Tbe liin«?-watt'r for this exfjeriiuent is prepared by shaking lime
wat«f, and then allowing thu milky liipiid to sbiiid in a closed
ttJo. In a few houi-t* (he lime siiiks to the bottom, and the clear,
ktaat liquid is then puured oft' into another bottle. As a rule,
thy again become!^ milky, .oid must stand some time to become

fxjierimcnts show that, .-dthough in the combustion of the
h'piids, th"? latter cerliiiidy disappuar, new substances are
»«•»!, which ejioape direct observation only from the fact that
(ker occur as vtf»rx

Pnieeases, by means of which the presence of certain substaucea
eu be detected, such as the formation of the film on the tumbler and
"i ' in the i>revioMsly clear liquid, are called readims,
■ - necessary fnr th<'m, iritt/rnts. The formation of the
I A rrvictiun for water vajtour, and lime-water is a reagent for
er substance which is also foriiietl iti the combustion of petroleum
aleuhu].
giTC, then, a projiei' answer to the question, whether in the
lion of petroleum or of stearin an increase or dimi tuition of
care must l>e taken that the gases formed do not escape
'•jt are hcM fast. This is effected by means of a white
nlBUiirc wliirh is sold under the name of caui>ttc soda, and is
fcvn«d jitto nuls or broken into irregiUar pieces. With this substance
ftht upper part of a lamp cylinder ia loosely filled, a piece of wire-
\ipxatc flxeH iiil/j the cylinder preventing the caustic soda from falling
i "*'•*. The cylinder is then placed oti the balance in such a way
All « fmalt Lamp or » candle can be placed underneath it (Fig. 9^

PRINCIPLES OF INORGANIC CHEMISTRY chap.

C^^.

Wbtn the whole has Iweri brought into eqiiipoisG the lamp ia lit. In
a »hort time that side of the bulance on which the lamp ia, sinks,

thus proving that the petroleutn and tUe
stearin on comVmstion iwe eotiverted into
stihstiincus which are heavier than the
|Nirt of the combust] iilo substance which
disappears.

From these experiments we con draw
the general conclusion that combustion
consists in the chemicfd action of the
combustible subsUinees cm some other
substance which combines with them to
form new substances. For, accunling
to the law of the conservtitiou of
weight, thti incrcrisB of weight can bo
produced only Ity the addition of another
ponderable substance to the substances
"Tl iindorgoing comhustiotr.

This substanco will ho sought for in
the air, since, in the ciiee of the processes
\vf arc considering, thwe is no j>ussiljility
of the access of any otlicr ponderable
f""'- " substance.

34. BehaTiour of the Air during Combustion.^ For the
purpose of fretting a more exact knowledge of the process of com-
bustioTi in this direction, we mnat shut it ot!" from the rc.^t of the
outside world in such a wnj that we can investigate all the clianges
which occur in the participating substances. We therefore cany ou^
the combustion in a closed space, in a c^lass Hask.

The first thing that we notice here is, that in a given vohtme of
air it is not possible to burn any qtiantity of oil, but that the iiroount
burned is gre;itcr, the greater the volume of the air. There is, therefore,
eotnething contained in the air which is neceeeary for combustion.

The air, however, doesi not consist entirely of this something,
Ko matter what subs{%<inccs are burned in a given tjuatility of air, one
never succeeds in using up the whole amount of air j on the contrary,
adout Jlhs of it remain behind. In this residue, coml.aistion can
tio longur bo produced, and closer investigation shows thut tlie ga«
remaining has other properties than the air. From this it may be
concludeil that the air ia not a simple substance, but a mixture (a
Bohition), consisting of a substance which is necessary for combustion,
and of another which docs not effect combustion.

35. Oxygen. — Tliat the power of the air to support combustiott
depends on the presence of a gaseous substance which does not con-
etitute the whole air, but only about |,th of it, was stated by the
chemist Schecle (born at Stralsund), towards the end of the eighteenth

I
I

hi PHENOAIEN'A OF COMBUSTION AND OXYGEN 37

(cntory. Scbeeic foiifirnietJ bis opinion, wlijeh was o(>posed to the
tiwi autiDg idea^ of thi> " tieiiieiitiiry " nature of the air, hy showntig
hm to prepare a 8iil»tiirtce wliicii htu] the power of supporting com-
f.i-tioii in H much higher degree tLan ordinary air, ami which left
"ui iiu residue iricap,iWc of 8vi|ipurting oombustioiu
Sf!iL*!« i>l»t;iinL'd hi.* gjis, wliioli he calted jire-tiii; hy stnmgly hp;it-
'iir; 'hf <uli<<l;iiu-e well known liy the name of ^tdfjKtre. He nfterwards
ill ihe lanie irifuiner from the minora! p^mbtdtn.
-i-iiJeiitly of Sohccle, th<j same substance was discovered

Trij. 10.

later l>y Priestley, who prepared it by strongly heating a
•rf-yeilow aubstHUce cjilled ujidc nf mtrmftj.

last exfwrimoiit is the most convenient for repetition. The
powiJcr (oxidt! of mercury) \a placed in a hunt tube of hard
(Fig. 10), The Lui>e is cl used by a |wrforated cork, carrying a
be with indiiiruhbei- tubing atUichtjd. On heating the tube
the oxide of mercury, thia subatanco first becomes darker,
in colour. After some time a film with a metallic lustre
on the tube near the heated jiarb. If the end of the ga»-
- p!ace<l under water, buhbleg of ga& are seen to rise.
Hot Di . ikcti for air, which is caused to expand by the heating,

tad pwwily jsw^ajies from the tube. We can resuiily convince our-
fciowKVer, that the g;»B is not ordinary air; for if a 8])lintcr of
Itch hu been III and then blown out, so that only the charred
Iwii feebly, l>e brought to the mouth of the tu!ve, it at once

PRINCIPLES OF INORGANIC CHEmSTRY

II. Metals

F. Alakali metals. j

G, AUcalinc *artti iiii'tulij. r
H. Earth lUBtals. J

I. Tliu iixiii gruup. I

,1. Tlie oopiwr gi-oQii.

K. Other meUls. I

Li^ht metals.

Heavy mtitaU.

The above grouping is by no means idenl, still it has the ac
tags of bringing together the most important natural groups of
element.

The two divisions of the metaU, the light and the heavy,
»o formed thiit the first division contJiins the metals whose dei
does not exceed 4, while to the second division belong the metals
higher density. With this apparently rather external and arbit
diBtiiiction, there lire bound np important <;herai«il differences, w
form the real justification uf the division.

We pass now to the characterisation of the individtial elemeAti

Non-Metals
A. Hydrohen anu the HALOGEire

llydr'Kjita is a tolonrless gsis which is more difficult \jO bring
the liquid and solid state than any otiier aubstivnce except heliuni.
is the lightest of all known aub-stancoa, for 1 cc. of it woiglis ur
" normal " conditiotis, i.e. at 0' C. and under a pressure of 76
mercury, only OOOOOSO grd. It does not occur in appreciable quan
in the I'ree state in nature, although there is proha.bly a very si
quantity of it present in the air.

la conijKjuuds, liyilrogen is met with very frequently. Wa
which covers Jtha of the earth's surface, is a compound of hydro
with oxygen. Moreover, hydrogen is present in almost all
substances of which the bodies of animals and plants are built up.

Fliroriiw is a faintly yellowish-green coloured gas ivhieh does
occur in uature, and which can be prepared oidy with difficidty, si
il at once interacts chemically with almost all substances.

Its naturally occurring compounds are not rare ; the best knowi
Jtuorspui:

Chloriw, likewise, does not occur free in nature, and must
L prepared from its compounds. It is a yellow -green coloured (.
'With a puweiful smell, and has a very b;jrmfn] action on life of
kinds. By moderate pressure, it can be condensed to a yellow-grt
coloured, ody liquid, which is prepared on a maimfaeturing scale a
sold in raetid bottles. Chlorine, also, has the power of readily formj
chemical compoundB.

THE CHEMICAL ELEMENTS

Is of chlorine occur widely in nature, Tho iimst important
jwti is fi/iniiion ■fdlt, the familiar white substance, ivhich is
liiUe in water and whit'h we are wont to add to almost all our food,
UfirKkhrif «i*W is a compound of chlorine and hydrogen.
Hrrjmtmf is m darlt l»rown-red lirjuid, transparent only in i|uite thin
|en,uid is om(> of the few elements which are liquid at ordinary
Even at room temperature, it passes very readily into
[pllow-red, heavj' vapour which has an exeeodingly disiigreeuble
ell, aad has a caustic action on all organisms. It shares with
buriite &nd chlorine the triilely extended eomhining power, but
IWOKS this to a less degree than thoi^e elements. Bromine does
not i«Cor fre« in nature.

The best kno»™ compound nf bromint^ is potassium liivmitff:,a white
■hiioidily soluble in wat«r, which finds application in medicijie and
in pitctognpHy. The bromine compounds occur, indeed, widely
Qtod ill" nature, but genendly in smidl ijuantities, so that
ninij belongs to the somewhat rarer elements.

Mint is a solid, cryi^talline substance of a blackish-violet colour,
Tilha lusU:* which apjiroaches that of the metals. It volatilises
at fi0(i'm tempeniiure ; aufficicut, however, for it to have a
land not pjea&atit smell. At higher temperatures ii melts and
pBW into a vapour of a fine violet colour.

Imlinc dissolves in various liquids, giving solutions which are

nioB coloured brown, sometimes violet. A solution of iodine in

ti» onaploycd in medicine under the name of tincture of iodine.

tiwn liquid having the snjcU of its two components.

Tiiiiine' diHcs not occur free in nature ; its com pounds are 8pai-s?ely

n^mtcil. P'tn.'<4iiitiu uiflith; a wiiito salt readily becuniiiig yellow

Wniru (vildured owiu;^ to the separation of iodine, finds frequent

B. The Oxygen Group

■ji is a jjas which forme a constituent of the atmospheric air
^^h), and Jis siich is exceedingly important for living nature.
f»ark or energy which the organisms require for the exercise of
hoctiotis is derived from the combination of the substances of
ihev consist with oxygen. Likewise, all phenomena of com-
Itie&ns of which we wami our houses and drive our

ad on the co-operation of oxygen.
gaa Is, in thin layers, colourless ; in very thick ones,
Ijr strong cooling it can be condensed to a bluish liquid which
i« -IRO' C.

Beddes the large quantities of oxygen which occur free in the

tliere are also enormous quantities of the element contaiued in

tponndi. Most of the compound substances which we find at

•

PIUNCIPLES OF INORGANIC CHEMISTIiY chap.

the earth's surface contain oxygen. Of these compounds, the moat
important is water {cf. p. 16). In weight, oxygen far surpasses all
other elements at the earth's anrffiee.

On account of the great importance of oxygen and of its cora-
pounda for all life, and on account of the very numerous compounds
which it forms, this element occupies a 5j>eciftll)' prominent place in
cheniistiy, and may be designated as the most important of all the
elements.

Sidjilnir is a well-known, yellow, solid substance which melts at
130 ' C. to a honey-coloured liquid and readily inflames in the air. It
bums with a bine flame, forniing a gaseous oxygen comiKiund which is
easily recognised by its pmigont odour..

Sulphur docs not conduct electricity, and readily Iwcomes negatively
elcictritied on Iwiiig rubbed.

.Sulphur is widely distributed in nature. It occurs in large
quantities, especially in volcanic regions, sometimes pure, sonietinies
impure through admi.\lure with earthy matter. Not inconsidei-able
quantities of sulphur are also found in places where a decomposition
of salts crintainini; sulphur is effocted by peat or brown coal.

Sulphur is met with in much lirger (juantity in chemical compounda
than in the free state, (fifpswn and iron pipiies may l.»e mentioned a»
the beat known of these substances.

Besides the oxygen compound of sulphur just mentioned, a
hydrogen compouud forces itself on the oliservation through its
conspicuous and nnploassiiit smell. This substance is produced in
the deconipo.sition of nnny animal siibstaneea, t.g. eggs, and the
"smell of rotten eggs" thereby produced is in reality the smell
of this compound, sntphurelted hydrogen.

SeltaiiiiH and Tdlumtm are two very rare elements whose com-
pounds are similar to those of sulphur, whereas the free elemen-
differ in their properties. Selenium is generally a black-red, solid
substance which does not conduct electricity. Besides this, however,
another form of selenium is known which has a half-metallic lustra,
and a slight electrical conductivity. In nature, selenium occurg:
almost entirely in the form of compounda j occasiomdly, it is found i
traces accotin>anyin,i^ sulphur,

Tellurhim ia a grey, solid substance with metallic lustre, and
conducts electricity like a metal. It, also, occurs in natvire genendlf
in compounds.

I
I

*il

tafl
=d^
r,

C. The Nitrugen Group

Niirngen is a gaseous element occurring, to a preponderating extent,'^
in the free state ; the amount of the nitrogen compounds in nature is
small compared with that of elementary nitrogen. It form:
chief cousttluec* "* atmospheric air, which is a mi.vture (r

THE CHEMICAL ELEMENTS

(fmiesl conipoundl of *ths nitrogen and !,tli oxygen by volume. As
I*' imdorsttKid fruiii thi? known properties of the !»ir, nitrogen is
ijttrlta«, (xlonrtcsi, jind taateless. By great colli it, also, can be
oiieii5«(l U} :i h'fjuif] ; with greater difficulty, hmvever, than oxygen,
bulling jKiint lies lower than that of oxygen, viz. - 194 C,
Although llit» liiti'ugeri fomjmnnds are, in amount, inferior to the
frw nitrogen, they are, nevertheless, of very gtent imf»urtauce, since
•niwl iTn{.)ortJtnt constituents of thi.' vegeta^ilo suid animal structures
niiT«wri compounds. Especially the siihsfaiec of the musu-tes mid
- of the cells, tlie so-called pmfopltjim, to which the rerd
in I j uitjichetl, are nitrogenous,

tii lie Ijetler known compounds of nitrogen in the nniieral

bgidom, utlt/fetrt- and Sff/ umm'iiti't'^ may be mentioned.

In comradistinetion to the elements wc have hitherto mentioned,

litrogen |x)sse8ses only in a very alight degree the power

.ig chetuically with other sribstances. It is, therefore,

Jdtitii-vjd i45 a chemically inert or indifferent clement. To obtain

KB compounds one mnnot, therefos'ej as ii rule, start from

1 itaelf, but the desired substance muet be prepared from other

com])Oiu)d«.

Fketphorv:^ ie an element which is cU«sed along with nitrogen, not

"f their similarity in the elementary state, but because of

:v of the eorreisponding compounds. The fiee elements

J are widely different.

Tluiplionis 19 known in two dift'orent fojniK, which possess quite
nl pn»{ierties, but represent chemically, both ol them, elementary
ilihttnis. Tbi.s is seen from the fact that both forms, in their
tiori with other suWstjinees, always give the same eompunniU iq
^nms piVipuMjons, and each can be converted into the other Milhont
The diffeicnce tietween them must he interpreted in somewhat
as the diltercncu between water :md ice, only that in the
lonis the transformation does not Uike place so e^isily.
lir*t fonn of phos|ihoiiuj is a semi-transparent, faintly yellowish
which has the property of ap]M?«ring luminous in moist air :
evulvijfi fumes and changes into an acid lir|uid, Tbii? i^duc
■ ["hosphorus. even at the ordinary tempenitnre, mm-
Hi _.ti ; it undergoes slow combustion. At a somewhat

lugW Knifioratiirr. the alow combustion paRsas into rapid combustion,
k the phosplmrus burns with a bright, yellowish-white flame,
(nmwtion of white fumes. *

>ud form of phosphorus appears as a black- red powder

itiier fumeii nor appe<irs ^nninous in the aii*, iior becomes

JdiaetL This r<d plinspk'/nis, also, Uikes firo much less easily

first mentioned u/nh- jihoaphiiriin ; having once taken fire,

r, it Iwims in the .vime way as the whitfs form,

varictj can be transformed into the other by the action of

»t^

50 PBIXCIPLES OF l^NORGANIC CHEMISTRY

beat. The lelatiuns which are hero met with will be discuss
(Chap. XV.).

Only coTiiiJoiiiids of phosphorus occur in naUire. These alst
«ti impurtant [KUt in living nature, The bones of the vertt
animals contain compoiinils of phosphonis, and serve aa the at
point for obtaining thu element.

Arseniti, in its cotnpoundB, is closely allied to pbospboni.*, and i
free state, also, lias a certain similarity to it, It ib a black subs
with !i feplile meuUic Instre, and eunducts I'lectricity like a r
< bi being hcnterl, it passes into a vapour without previously rael
the vapour, likevvise, osi cooling, |)«sst;s directly into solid arsenic.

Ill nature, arsenic occui*a Ijoth in the elementHry sUite an
compounds, especitilly with the heavy metals.

The most conspicuous property of arsenic is its great poisonous
All compjunda of this element aro more or less poisonous. Mt
tlie crises of arsenical poisoning occur with an oxygen eompoun
this element, wliich is commonly called whitr urscnic or simply arsi
it is a white, almost tasteloss jiowdcr, slightly soluble in water.

D, The Carbon Grouh

lite

Cmiion,- — The peculiarity which was found in the cuse of son
the preceding eleniefita, that tht-re e-vist different solid forms w
yield exactly the sjime transformation products, is present in a
marked degree in the ease of carbon, for this element is knowi
three ijuitc distinct forms. Ordinary black charcoal, the purest 1
«if which is soul : graph'tie, the material of lead pencils ; and, liu
ibe tlliimmid, the coloui'less, strongly rot'ractiiig .-ind exceedingly 1
precious stone,. — all con.ssst of c.arb(3n, and }'ield, in all chemical
foniiatinna, equal quatitities of tlfe Siime final prnduct.

Besides tliese forms of elcmenttiry carbon, which getiendly^
in nature mixed with impurities, there aro lumieroua componndi
derivatives of car1>on. It is present in enormous qusntities in
mineral world (in limestone), and forms a never sibsent eoustituon
all Di'ittiHlsnis. The diflercnt comjioundft of carijon occurring in
animid and vegetable kingdoms ijive rise, in chemical actions,
numerous other compounds. Al«ove ;i!l other elements, carbot
endowed with the greatest power of forming diilerent derivative*,
the number of sulwitancea which contain carbon so greatly exceeds
number of the compouuds of the other elements that the cliemistrj
the carbon compounds forms, under the name of unjtiim dwmistr,
special part, and, indeed, as regards the number of known substatv
the larger ])art of idl chemistry,

These nrgfivicmmimuiulAcfynnisi, in the simplest eases, of carbon \
hydrogen ; to tliem belongs petroleum, which is a mixture of varj

'MKNT.S

DntiwjwUnis" of similar composition ;in<l jiropoities, Oxygen, ii>
iiiition, is cotitaJMed in the substances which are classed together
BiJer itie name of the fnU, and also in the starch and aitgar-Ukc
rhicli occur to u specially larye extent in ]Jttnt8, The
I of which thtf muscles and the nerves arc huilt up, and
cheniicid jirot'csses uf life fur the greater part tjike place,
hesiiles the alre/wly-inentioned eleiuenta, nitrogen and gene-
ndlr »ls4i sulphur »nd phosj)hi>rus. That carljon is contained in sill
llieie siilffltiinces is ri.'a,di!y seen vvhcti they are strongly heated. The
"(birring ' which thereby takes place con^isU essentially in the other
*leiMUl« escaping as vulAtily com pun nd*-, Icavlniy; Miind the portion of
thvorban which does not disappeiu- with these conipomids, :is churcofd.
After oxygen, carlion must be designated &a the mOBt important
nt.

Uom n an eleuient which does not occuf in the free state oo the
In th« form of an oxygen conipouud, known as Mficif acid,
\ derivatives of this, silicon is, however, one of the moHt widely
'd elements,

like carbon, can be obtained in various forms, as a In own

iron-giey brittle mass with metallic lustre. This

ifts electricity.

An oxygen comjjoiuid of silicon, silicic acid, constitutes, as tjnart?.,

... ..... ,^j jjj^ g^jji j^„^j ^jip iiiountaina. Compounds of silicic acid

niftals, esjteciaily of the jtroup of light metals, compose

id titi; nwk?, Silicon is, therefore, essentially the element of

cruat of the earth.

tail element which doe.? not occur to a lar^-e extent in nature.

'fotuid free, but must be pi'e)iared from its compounds. The

tiw of cletnentary Imron are similar to tho.se of silicon.

m^tiit important comfjound of lioron is likewise that with
This ii c<jritained in htntj, a salt use*! in the arts for soldor-
ftir suior oth<T pur|K»ses. anil vvliit:h is the best known of all
nyin of lM>ron.

E. Thk AKr.oN (iKori'

atmiMplieric air there are found in very small quantitie-s a
which have only recently been discovered, and which are
by the peculiarity that none of them btLs ever been
<:h«mirsl combination. Tbey are known, there-
fci^ oel rutary state.

1W hm^f*- koowQ is itrgvn, which is present in the air to the
of rstlker more than , ^tfa part by weight, and remains Whind
the oUwr coapoaetita have been converted into stable chemical
It i* s coloqrleas gas, which, on account of its inability

52 PUIXCIPLEM or INORGAlsIC CHEMTBTRY

ii) form cheisiic'ii! couipouiicls, is also odourless and tasteless. Its deni
is greiiLef than that of air.

Beaidea argon, a few other yasea of similar chemical indiffere
liavo been discovereil. These, likewise, occur in the air, but in m
smaller ijujintity ; they are also contained in measurable qiiani
oiiclosed iti some minerals. They are called HcUuiit, Nmn, Kn/p
and Xfiwn.

The Light Metals
F. The Metalh of tkk Alkali Group

The metals of this group have many properties in common. Tl
have a low density, some of ihem lower than that of water. Ti
power of forming chemical compouiid.s is very highly developed,
that they never occur frea in nature, but must first be prepai-ed
onergetic means from their cr>nipDutid.s. By reason of their gr
combining power thoy liavc the property of roaeting cbemicaUy w
most other substances, and can, therefore, be preserved only by obse
ing special precantions.

P»fassi\tm. — Fresh surfaces of this light metal show a fine sib
lustre. It readily melts, and is, even at the ordinary tempemlu
soft like wax. ;U a red heat it passes into vaptjur.

In nature, only coniponnds of potassium occur. As the best kno"
of these, mltpdre and jwhis/ies; may be cited. The most important
rarniillilf, wliich is obtained in large <[uan titles in some parts
Germany, apparently as the residue left ou the evaporation of
pieviously existent sea. Plants require p<3ta8sium compounds 1
iheir growth, and where these are not present in suflicient ijuaiitity
the i5oil they are added as manure in the form of carmdlite, or of t
compound preparoil from it ant) tich<*r in potassium, /wltL^Mum rhhmi

Potassium compounds of all kinds play an important part
the arts and manufaeturee. Potassium is also of im|»orUince in t
or2;a!iisra of man and the animals ; it forms an essential component
tlie red Idood corpuscles.

The ek-ments rulmi'mm and at^i^liiui are allied to pntussiunr, Th«
properties ai-e almosi identical mth those of potassitmi, Ijoth-
elements and in compounds. In njiitriist with potiissium, howev*
they occur in veiy small amount in nature.

Sodium is, in its properties, a Hjiht metal very Bimilar to poUissiui
Its compounds are likewise found in enormous quantities in natui
The best know n and must important of tliese is comnnm .tttll (p. 41
which consists of sodium and chlorinr. It Hcrvea as startingpoinl f
the prt'jvaratiou of most of the other Hodium comijounds, ;is also of tl
chlorine eomponnds. Soda and 6Ui>ibft'.f jsalt are also compounds
sodium.

THE CHEMICAL ELEMENTS

IMhtttM is a rare element, which, in its pt'Operties and fompoundfl,
least vfith thr other elements of this group. It finds no grciit
JcUirtlt.

(h ThK Al,KALtNK EakTH MeTjU^

The Qtemcnte of this group share with the alkali ineUils the

of » low density and of a hit;hly developer! combining

rcr. Whereas these, however, cannot be exptjsed to the air with-

ftt once combining mtji the oxygen, the alkilinc earth metals in

dry state remain unchanged in the Jiin They nee also much more

and more diflicuk to melt and to voLitilise than the alkali

BMtals; ihey have, therefore, more the character of the ordinary

■MfUla.

X«g*rmum \s a white metal, somewhat of th» colour of tin, which
unchanged in the air as long ns t-he ttmjwratiiro is low. On
healed it takes fire and bnrns with a hriiliant light, forming an
trgeu compound.

CuiDpuiinds of magnesium oecnr very largely in nature. Almost

rocks which contain sJUdc acid also contain magnesimn in the

a com[M>und with silicic ncid. Thtre are also other mineralt-

icontaiir magnosium. In daily life several magnesium coinpoumU

fafiplication ; the most im])ortant are iiiaifiifsia, which ia an oxygen

iiond of the metal, and A'/'scwi HftUs.
Metallic mag;Qe«ium doet; not occtir in nature any more than nay
'. tin iitbrr light metals.
Cuicium is similar to magnesium, Imt oxidiaeH with much greater
Comjmunds of this eleniunl occur in nature in largo
and have an ei^eutial »haru in the hnilding np of the
oitli'f crast.

*>f Mich compounds there shoidd he mentioned limeti<m>- and
Mntiit , the latter contains magnesium as well as calcium.

Marhir, the use of which is known, is a sifccially imrt) form uf
fiaenancL Prom liiiiestfine mortar is piepired. fiypsum, also, and
«<nir ' ' h find a similar application to mortar, contain cjdcinm.

T^- impounds are largely applied in the manufactures.

Hxtnifwiii and iMrini/t are two «4enifnt,s which, in tlieir whole
Wkariour, are chjecly allied to calcium. Tlicir conijujunds, huwever,
■oif b much smaller quantity, although they cannot jictually Ik>
4aputrd as rare.

la»Uy, UrtiUtum iiiiist be mentioned as an element Kelonging to

«k««^ro«p. It has the same relation to the other menilw-rs as lithium

tuitathp fMhfr aikaii ni>?uds, *.r. it shows less ijinularity to the other

Bcmlnr-^ ' . tu one another. It is a rare clement, deriving its

.rrence in the mineral bervl.

PRINCIPLES OF INORCxANIC CHEMISTRY rn

H. The Eahth Metals

The elements of this group have the character of tho ordins
metals in h much more prnnoimced msinutn' tfiaii those of the ji
(.cdiiig groups. Of the large lUimljer of metals ivhirh could
mentioned hero, only one, ithimiininn, can c hiiiu orjr attetitiDU, since i
comjiounds of the others occur so rarely in nature that they play
important part, either ivith regard to the composition of the so
crust of the earth, or through application in the arts or in metlicina

Alittiiimnm, which does not occur free in nature, is, in its oxyg
compoiinil and del ivatives of it, widely distriiiuted, and is, af(
oxygen and silicon, the thin! must frequent clement in the earti
cnist. It is an almost unfailing constituent of the rocks whi
contain silicic acid. When these undergo mechanical and chemi<
disintegration under the action of moisture and other atmosphei
influences, ditn separates out, which is a compound conUtiniiig silici
and aluminium along with oxygen, and which, in different forms, ib
chief ctuiststuent of the aedimeutary or stratiiiied nx^ks. The teclmic
application of clay to the making of bricks, vessels, ami uitidelh
objects of all kinds is also lery llJiportiint.

in recent years the metal ahiminiuni has been prejiared in larj
quantities from ita compounds with the aid of the electric current.
is, a.s 13 known, a white, light metal which keeps well in dry air hut
readily attacked in water, especially in salt water.

The remaining very rare alkaline &irtli metals we shall m
describe here. The best known are smiulium, yiti'mm, Ifnithanm.
Kvium, iieodfjiiiium, pntxeodifmiHriif ifilerbiuw.

The Heavy Metals

Mkials <ir THK Iron Group

Iroti is an element the properties of which, on account of it
universal u.so, are well known. It is a tiard, difficultly fusible nietfl
which remains unchanged in perfectly dry air, but in moist air, am
under the Influence of various substances, very quickly iitslg, i.e. form
a coni]tound with the oxygen of the lur.

The somcwhut different proporlics which iron exhibits aw cast
iron, wrought-iron, and steel, arc due to the presence of small amount
of other suhstiinccs, more especially carbon. The properties of puri
iron agree most nearly with those of wrought and ingot iron, whicl
are the purest comraercial kinds of iron.

lu nature, the occurrence of iron in the elementary state ia ex
ceptional ; its compounds, however, arc universally distributed ami
occur in large quantities. On the whole, iron (occurs less frequently
than almniniura, but more frequently than c^ilcium ami niagnesuun.

Tire CHKMICAL KLENfEXTS

hmt^h imri eum|K)iiii(k ui*t] preiieiil only \» small amount in the
ve»ft?t(i}j|e orgatib«»i». ihi^y ajipoar, tievurlh^lpss, lo jiliiy n
tant f>ai't, since the n.ii lilotHl rijr|ni.siL-|es of the vorli'luiite
well as the grcoti ceils of assiniilatiiig nluuU, oontaiii troti.
AlUad U> iron are the Fiearly related ck-mejits mtihijtnirif, roUili,
Mid wnW. They all belong to the less freijiient, nlthough nut mre,

Miiui/itwf.n , ill the tneUiilic sUite, grciillj rcsomblea iron, only thiit

still more esisily tliaii ihn lattfi', therebj' herajning creiicd witli

A-Uxon'ii yxygen compoinjd. In th« luetaliiL' stiiti.' it is tiut riiiulii

QMd lu coni|ioiuiil with oxygen, pyrolusitc, liuwc'vor, which i»

Juyrd fur the |inKluctioii of a coluuf fof pottery, has a vaiiicd iiiirV

iportont Application in tht* avla.

It is, even in niuiat Jiir, much mure resistant than iron un«l
but fimls little appliration as a nietftl. Its must remurk-
properly is that its oxygen compound dissolves in glass with ;t
d>ri( l>lu« colour. It finds application, thctefore, for the prodtietioiv
i>l k blae colour, cobalt Hne or nmnli, and also for the colourinj^ of
I ani] pottery.

yirirJ is still Ifr^s cfaungeable in the air than coliaU and is, tliere-

, ased for making articles intended to resist hi<at and motsliirG.

■utie of other metals ani also, with lliP hel|) of the eluctrie

• ] w ith iiirke] ; these nickel-plated articles preserve ihi'

If of that metivl, ninca nickel is also fairly hard and

(•Its. In lhi'« fact iit^t* the importance of this clement as regartU

Sit]i;*-:itions. Nickel mmj'oiniilf arc of no great importance,

I mixnl with copper and zinc fonits fSmfutn silKt-r.

i-. a metal very similar to iron, i>nly harder and niori-
•tni remains ( I utte nnchangwl in the air, hot is cjiaily attacked

Hy 1 iiid>-. The purf mutid bts no applieation ; addition

Jcl ■ rl improves the steel.

h nature it occurs chietfy in the fonn of an oxygen com|>onn(l
•Wl al»> conirtins iron, anJ is called rfmme ironxtonr.

It fomu r»rioiu compounds, of which flm/mir add and poiamitm
dniKir have a varie<I application in the art*. The artistti' colours
*J«^ehrogM! yellow and chrome red, are derivatives of chromic swid,

iltied to chr^^mium in their chemical relati<«ns ai-e several metallic
dMnU of rare 'jccnrrencc and pon^essing no great importance ^ it
■fi ke soflkieDt at this point to give their names. They are molf/lh
■<*«ii. .'u.».n.«-Ti, mnaumm.

melab nw and auimium are, in many respects, relate*!
- i»' nn:-..u« %d Uic iron gntU}i, but show, on the other hand, a cert>uii
■iSifdty bi maetteaian.

ZfaK » a weU-knowii grey -white roeuL, rather more resistant t«
Ai air tkan iruo, but inferior to this in ditticnlt fusibility and
^KikiAJal tatactij^ Aa it ran he readily rolled to sheeta atxl

PETNCIPLES OF INOHGAKIC CHEMISTKY

soldered, it, is iLpplied for all purposes for wliich a not very t
n:*^t.iil, but one which is fairly rQsistant to water, can be used in I
form. I

In iifttiirti, ziiji.' uccurs only in the furm of com|R>iiiids, of w
that with sul[>huf*, called dm' hlemh', is the most imj)ort.'itit.

Ctufmiiun is a nictal which is very similar to ziric, only softer
more oasilj' fusible, and which occurs in snaidl amount along with
m its natundly occurring compfninds or ore&. The artists' co
cadniinni yellow or, shortly, cadmium, is the i*idphnr compound of
metal.

J, MkT.^L'S of THK ColM'EH (JUOIT ■

The metals hero grouped together are diatingiiiahBd from
preceding onefi by a greater reaistwnce to the ehemical inrtiiencei
air and water. This is, certainly, nu perfectly universal characteri
for while some of the raemViera of this jfrou]) belong to the X
metals which, under ordinary circumstances, do not chaiige at
others become more or less i[uiel<ly coated in moist air with layer
oxygen compounds which tlestroy their nioUdlic lustre. The actioi
however, uaimlly lestricted to the surface, so that, after all, a fa
great durability with respect to the destnictive ehemical influence
present.

Connected directly with this property is the fact that these me
can be niore readily obtained from their nRturally occurring compou
or i>rcs, than those pieviously mentioned, and also that they are of
found in the free stiite. In this and the next group, therefore,
meUils first met with in the history of the arts j>re found, and
metal mentioned in the oldest literary moniimcnt<s, and uaui
rendered in English by " bronze,'' is a mixture, the chief constitu
of which is LOjiper, the typical element of tins group.

Co^ifivr is a mct>,'d which bits lioen long known, and the rose-
colour of which is found in no other metal. The true colour of cop
is seen only on freali surfaces, .since it ^ptickly tarnishes in the i
and becomes covered with a coating of oxygen and sulphur comixtuji
which, however, is very thin and attains to no gi*eiit thicknesB ©i
after many years.

Co|jper is an excellent conductor of electricity and is, therefo
used for all kinds of electric conductors. Its chemical resistibili
combined with its toughness ami high melting point, give it a wii
technical applicability.

In nature, metallic copper is not of rare occuiTence ; of much mt
frequent oecnrronce, however, are its compounds with sulphur ai
oxygen.

Of t!ve better- known compounds of copper, (^wr irihitfl, a bU
crystalliuo salt, mr\y be mentioned.

THK CIIE>nCAL ELENrEXTS

Ltitd is a gr«y, soft metal o£ high density and low mcltitig-poiirt.
lt» btA sorfices exhibit a high metfiUic lustro : they tsiniish, htiwcvftr,
rtadilj through taking up uxygen from the air. Tlie coating
thin, »nd the \eiu\, therefore, resists further destriu'tion for u
long lime. It shows 4 similar lichaviour with resjwct to man)'
tt^MT aWawlw, BO that it is indispenwible in chemical manufactories in
L^jfaek oo«Toii«e snhstAnoes iu% prepared.

^H^ On •ceount of its great goftness, pure lead is not much used, By
^^■njm^ it with otb«r metals it can Iw mnde hiirder, without its lo^iug
^^^i cheaticft] mistihility. It is aIso used fnr coating other meiiib,
aptdaDy irrni.

In natuns lead occurs chiefly in the form of a sulphur compound,
»kich i« called ^<i«n, and is the most impoi-ta,nt leafl ore.

Load ooffipoonds are largely used in the arts, iMhiirgr is an
dxygen cwapound : tm^r of Uad a compound with .-icetic acid.

The loHj eompoiuids act on organisms as cumulative ftoiiwns, i.e.
1^ eAsels cl anal] amounts, which singly are not appreciable, are
Med and tUtiiQately produce ver^* serious symptoms.

noaeljr related to I<ad in many respecta in the rare metal IhnlUunt,
•kich, in gther vaptctA, is allied to the alkali metalx.

Mtrnay it a meiBl, liqtdd at ordinaiy tem^jieratares, which solidifiea^^l
C aad boQa at t 357^ C. It belongs to the noble meta]fv^^|

^^■M^fBUMiiW it* hri^itt surface in moist air, i.e. it dcres not com-
^^^Hntk the uJirgeu. At a higher temperature, however, combina-
' ^nuke* phee (p. 39)l

Being tb« f^Ir metal which is liquid at ordiuary temperatvred, it
>* videiy empI'iTcrl for pbyncal afifjaratos, meb a» thennometen and
lan^MCera, and far other porpoaea io teduiical acienee. Its utility b
|MUf wihwrwl hf ha MnrhanBeaMenew in air; ita high density,
«ha, Hoaiiai fur cone parpoaea.

la vmXMire, it oeeon ta the free states bat chiefly a» a uUphnr
w^iiiuimI Tkts ta ndled dtmaUrr ,• the ardata' eoloar ol the
^■e ' is flpcnany pore odphkle of merauy, which
•tiienJly prepmd. ^

The aoiohie menoif 1 iw^iiMiiili act as pnwefful poiaooa;
y*n a wide<p|iBeMioii m waticiiii

M«v- ia « vhita aatal wUdi ia aot affiDcttsd by oxygen,
■tnis which aOvcr ohfoeta wwerinwa exhibit ia due to
of * mifAmr eeafaand throiagh the actkm of air coetaianc
*.hiy .' ...- ,/ .*\..^ mtifkmnm •niataaeoL

4 eoaaparatiTely fare oecnrrenee, bItct hdkiogi U»
*^ m>Ye ^'rrr>4^ ■cttla ; oo thk aad oq ite

a*a BMMl for

aiMeaad partly m

PRINCIPLES OF INORGANIC CHEMISTRY

comparatively high tetnpemtures. This view would, however, n
quite a coneetr one. Ou making the appropriate iiivestigatio
temperature can be foiuid at which combustion just begins, and
that below this point no combustion takes place at all. On thi
traiT, we are dealing here with a gradual transition. ^

Combustible substfinces, therefore, combine with oxygen i
temperatures, but ivilh rrrt) dijfhvnt rfliH'itif,-<. The higher the teir
ture, the more rapid is the comltination ; on the other hand, a
temperature falls, the process becomes slower and soon dimint^
as to be inappreciable. I

* 54. Slow Combustion. — A body can, accordingly, bog
combine with oxygen tit certain niedinm temperatures, without t;
fire. Ignition occurs only when the heat developed in the combu
raises the atljaccnt portions of the body to such a high temjier
that these also burn with sufficient rapidity. The temperature ^
these adjacent parts attain, depcndi^, on the one hand, on the an
of heat convoyed to them by the combustion, and, on the other 1
on the amount of heat which they lose by conduction and radii
Not until the former exceeds the latter to such an extent tha
temperature of rapid combination ia attained, can tiiis rapid combu
^ike place. From this it follovis that ignition or the initiatic
an independent combustion, depends quite as much on the form
distribution of the substances as ois their natiuc, as onr evorj
expenenee with regard to the ignition of combustible subsU
teaches us.

55. iDfluence of Temperature on the Velocity. ^The
that the velocity of chemic;d processes, i.e. tlie ratio of the am
transformed to the time rcqtiirod, rapidly incrcises with rising tem
ture, ia quite universal, and is valid for chemical processes of all k
We have, further, no ground for supposing that any chemical pn
which takes place at a higher temperature, cannot take place at a It
If we (!o not note any transformation, it may be because it takes ]
too slowly for our observation.

The stock of coal in the cellar bums while it is stored in the C
just as when Jt is in the fire ; only, in the former case, witb so {
slowness that wc can detect no diB'orence even after several years.
large quantities of coid, however, are stored under such condr
that the dissipation of the heat developed in the slow eombustii
prevented, the tenipeivitnre rises, tlie process ia accelerated, and
become ao rapid thitt it passes into vigorous combustion,
phenomenon is called tlie sfimilona't)-'! hjHitioH of coid.

5R. Physical Properties of Oxygen— -Tu determine the df
of O-xygen, one must determine the weight of a given amount and
volume occupied by it (p. 27). The latter can be easily done
glass tube gni(lu;ited in cubic centimetres. The weight ia less eaa
determine, as oxygen i« very light, and the determination of its w«

OXYGEN

I vesstfls necessary causes didiciilties. We adopt, therefore,
mcthml.

Fouisiura €blt>ra.te, as we know, evolves oxygen on being heated.
I the ressel, a white aubstanee reiniiins beljind ; a further siilistaiice
mot pixKJuced. If, therefort-, the weight of the jHJtassiiim chlorate
km for the ex|>eiiiiicnt be deterniiued, and, afterwartis, the weight
Ihc rofti'lue, the ditfereiice is equal to the weight of the oxygen.
itmi. If tbis is coHecte*! in a siiitaljle measuring-vessel (Fig, 12),
I Tohune can be read oft' and its density calculated by the formula
= ««.R If the exjieriment is performed with 1 gm. of potassium
it is found that after complete decomposition, the oxygen
uQ cooling down to lootu temperature, occupies, in round

■ trfe

«^ffr

2yu cc. The loss uf WKighl of the potassium chlorate
OMutta to 0-392 gin,, and the density of oxygen is, therefore,

0*00135.

Normal Temperature and Normal Preaaure.— This re-

ili «, Luwyver, not yet defined witii sutiicieut exiiftness. The

oocupiod by a gas depends, in large measure, o\i the pressure

iperatiirr, and ^Tilues for ibe density, varying within wide

will, therefore, be obtained when the determination is per.

lumlrr tlifi'erent conditions. An agreement has, therefore, been

until regard to a iiofmul (em/iemhre and a twnititt jrre.-isure, at

'the (lenutiea of gases shall be determined. As jjoruml tem^Ata-

ture the melting point of ice ia taken ; on tho centigrade thermom
this point is marked 0 '.^ ■

As normal pressure there has been adoptetl the menu otmM
pirssare, which is taken equal to the pressure of a column of mei
76 cm. high.

Since, however, the density of mercury is idsa dependent oi
'temperature, we mii.<it add that the teniperatwe of the mercuiy
be 0'^ C. The density of mercury is then equal to 13'o95 ; 1 cc. we
therefore, 13*595 gm., and a column of 1 sij. cm. section and U
high weighs 7G x 13-595 = 1033"2 gm. I

The pressure of one atmosphere is, therefore, equal in efi'ecX
■weight of 1033 gm., or rather more than 1 kilogm., on an an
1 aq. cm."

58. Boyle's Law. — The volume occupied by oxygen gaa cann
1^ always determined at 0"* C. and «

f atmospheric pressure, and the d

mi nation made under other condi
must be appropriately reduced.
this purpoae, a knowledge of
behaviour of oxj'gen U> chang*
prcssitic and f<'mpeiahi)v is necessa
A knowledge of tho first it
tained by means of the appai
shown in Fig. 13. The oxyge
contained in a gradtiated tube,
lower end of which passes )nt<
indianibber tube ; to the other
of this a movable vessel is att^u
Part of the measuring tube,
indiaruhbor tube, and the v
arc filled with mercury, Tho p
ure umier which the oxygen et
CJin be altered \>y raising and luwc
the vessel, Tlie vohime occu
' '"- '^- by the oxygen can be read of

the graduated tube. The pressure in cm. of mercury h the

' III Groat UritAin, foT ihu imrpoius of 4Ally life, iliemmnieteni will] the Ka])n
' icftli! aw used. On this ncule the inetting point of ict is marked aS", Oue degi
the Falirtiihuit acala i« eqnal to {llis of it degrep ini the cculijirwle st-ale.^Tr.

* Siace the weight of a given mats varies soruewhut with the locality. tl»* m
piesaare flethiwl jiIxivl' is ti»u subject to the Mitiie, variation. In eBJ!fS of pt-eitfrr i
n««» it k lu^iuuvtl that the weijilit deterii)iimtioQ i$ tttadu nt !«a^ltvel and In the 1b(
of tW, at, that tht iktertutuation, when luode eltiewheri.'. ■« recolculnted tn tbene
ditions.

Tlie mJoplion of absdvtt! unit* is still better. Since the force with TiiiScb 1 gnwi
iu constqnfuce of gravitation, is, nt spn-luvel ami in Utitudi; 45°, (miu&I to B
xljttnliiLK iiuils (p. 2J}, it follow?- Ihot tlip prcssLrii of tfte fttuifSpliiTi' is equ
P80'53 X 1033'2^1,OlS,13t), «ir very neurly 10' ahtwlute uiiits. A coltitnn of iiiercu
(histeiul of 76) cm, high would give, almost extwtly, 11}* absolute i»iit» of pressora.

V?*

OXYGEN

EdtlMexterDal atmospheric pressiue (height of the barometer) and the
Idiffepeiipe of level of the two surfaces of mei'cury. This difference of
veJ is w he peckone*! with iiogiitive sign when the outer tnerciiry surface
ituAt lower than that which bounds the oxygen. A miraber of corre-
^coding values of volmne and pressure are in this way determined.
Br means of such measurements, which have been carrit-d out by
ittus |>hysicists with great care, it has been fouufl that a very simple
rdalicio exists between ])reBsure and vohune. Denoting nny two
by /', and y/j, and the coiTeaponding volumes of oxygen by

r^ lad fy the formuk holds, ji', i /»., = c, ; ij, or, ^'i'", =/'A- The
pBMUiM are^ therefore, inversely proportional to the volumes, or
(kifnimct$ of idl amrsfmndifui mlnrs of jtrrs.mrr ajui volitmc art' cijmil.

J\t Inc ftrund h*re Jor irr.ijgm '/as is noi jKnili'ir to (his siibftniicf, l>vt
at$ ^jmtllif ftnr nil uthrr giiscs. It was discovered in 1G60 by Boyle,
lod is called after him.

39. The Law of Gay-Lussac and. Dalton.— Pressure is not
lk« only circumstance which iiitlut'iifcs thf volumf^ of a gas. The
(«(ain« chnnge-s also with the ti:iiij»iiilnfr, increasing and diraitiistiing
in the suae sense as the (empernture rises and falls. To detormine
tbe UDoant of this change it is necessary to choose another fixed
taafctature bcfiiiiea that of melting ice. The tcmirerature of boilin.i:
w»Mr, and, since this thaiigea with the pressure, the temperature of
wKr boiling under a prepare of one atmosphere ( = 76 cm. mercury)
mrtt k-i iucb a teniperatuvo.

To utitaifi the amount of the change of volurao between these two
lOBpomtarce, we use the same apparatus as was employed in demon-
Mtatiag Boyle's law {Fig. 14). The graduated tube containing the
ozfi^ is nuTounded with a glass^ mantle in which aie placeil
valtf and pieces of ice. The oxygen soon assumes the
tflapetaUire of melting ice, and, after the outer vessel has
Van flu placed that the iwo mercury surfaces stand at an
afitti heighit, the volume occupied by the oxygen at 0 C. and
•adtr the iheu existing atmospheric pressure, mn be read ofl'.

Tbn ice ia then removed, and in its place steam is passed
tboa^ the mantle. The volume of the oxygen increases,
lad, hiring again brought the two mercury surfaces to the
■■wbdgbt, we can read oft' the vulume which the oxygen
TiifMH under thi> sjvmc pressure as before, and at the
(ai|ansan: of lioilirtg water. Exact measurements of the
■■Nat of change show that the volume has increased in
Ik* ftvfiimion 1 : r3t>7.

Tlin Ttlntiirn has nlsit pivvi^d to ht. a tiukeriujl iaiv iHihd Jor

ffuis. The numlrtir obtaiiio<l is, therefore, the exprcsaion

spectid properly of <j.v\"icn but of a it>iirci.s-itl fn"pertif

I nMtc. The law, that ;dl ga.sea expand by the same ""• '"■
Wtween con'es[»ondiug temperatures, was discovered eimultuiua

PRINCIPLES OF INORGANIC OHEMIRTKY cri

oiialy by Dal ton and Gay-Lussac in tlae year 1801 ; it is generally ca
after the latter. In symbols, the law can be formiilatecl thus :

(> = (l +«t)i;

where r, is the volume at the temperature /, r„ that at the meli
point of ice, and a the hundredth part of the expansion between
melting point of ice (0 €.) and the boiling point of water (100° '
In numbers, a = 0-00367 or 1/273.

This formula gives the expiinsion starting from the temperatur*
melting ice. To obtain the expansion between any two temperatn
t and t\ the above formula is applied to l>oth temperatures, and
eliminated from the two equations. There is obtained

l + at'

= tV

From thiis it i.s seen that the volume observed at temperature I
reduced to the volume at normal temperature, 0" C, by dividing it
the quantity 1 + <i^. m

* It must be specially emphasised that the quantity a q|
hundredth part of the expansion of unit volume between the melt
point of ice and the boiling point of water, and nut. let us a
between any one temperature and another 100 C. higher. As <
easily be seen, the value of a, the a'efficknt ff rjfausion of tjo$r$, woi
b€ dependent on the choice of the initial temperature,

fiO. The Temperature Scale. — Since the expansion by heat 1
the same value for ;ill gases, independently of their nature, the chai
of volume of gases is owed for temperature diviaiona. The tompe
ture of melting ice is called zero, and that of water boiling un<
atTnospheric pressure 100. This range of temperature is divided ii
a htjndred parts or de^ree-s which are assumed proportional to (
change of volume. To distinguiBb this graduation from others wh
are also used, it is called the centignule or the Celsius scale, and
denoted by C.

Let, then, the volume of a given quantitj' of oxygen or of anotl
gas contained in a tube, be denoted by 0 C. (Fig. 15), the volume
the boiling point of water will be defined by the spot marked 100"
and the volumes Off and w will be to one another as 1:1'367. 1
length rs is divided into one hundred parts, and each of these pa
denotes 1 ' C. Such a tube, in which the gas is enclosed by means of
easy-moving piston, and which is grailuated in the manner justdescrib
could, e\idently, be n.sed as a tfiernHmidtr or measurer of tcmperatTil

61. The Absolute Zero. — The tempei-aturos, however, which \
met with, are not confined to the range between the melting point
ice and the boiling point. Beyond the latter, we can, evident
extend our thermometers indefinitely, for there ia no evidence oj
h'mit for higher temperatures.

OXYGEN

Towards the other side, however, our thermometer is limited, for

jwtcan subtract only a elefinite Dumber of degrees before reaching the

[ifni point of %-<>lumt>. This number can be calculated as follows. If

the Tiflume w = 1, the volume fs = 0367 ; one degree is the

illi [wrt. of this; its vfjliime, therefore, amounts to 0003G7,

I we on stihtrfw-t, in the rlirection of o, only as many Llegioos as

inmnilK.T of time* this fraction is contained in the unit. Now,

lODOSCT ~ 273 ; if we eoujd lower the temperature 273' below the

point, the oxygen or any other gaa must occupy the volume

fwrt from the fact that all gases liquefy before this condition is
taditxl, sijch a low temperature hits, as a matter of fact^ never been
podneed ; the lowest jxiiiit which has been reached lies at 260
W«r the melting point of ice, and the incroneing ditKcullies of
<WeDd]ng lower make it quite improkiblc that the point - 273" will
wwlk ttjachcd. This point is called the uhsohitr zno,

•2. The Absolute Temperature. — The designation of the tem-

patniT tif meltinj^ ice by 0 C results iu the temperatures below

tb biving negative values. Ttiis is not only arbi- & f^

\Bgj, but, in a certain sense, inconsistent, since

temperatures never have the relation to one

of [Msitive and negative magnitudes iu the

sense. In science, therefore, another

konin^ the temperature has come into

»ero there is taken that unattainable tem-

fBUan 273 C. below the melting point of ice, and

tip tem^tcratnre is counted from that point upwards,

•Ttk the same degree divisions as in the centigrade

BentleB the gain of entirely avoiding negative

MBpnwmv uumWrs, there is the further advantage

All «itli this method of reckoning, the law of ex-

lUbon of gasm ossum&s an es{iocially simple form ;

rt* ^imnt hrf»m^ nimjtly jmi]»iiii>innl ti> flie trntpfmiiirr.

^^ik* tfotame <>t of our gas thermometer (Fig. 15) is

^^KUai into 273 parc^, and if this gnid nation is con-

^^■l^iipirards to any extent, the vulnnie measured

l^^^pi umtA gives directly the numerical value of

ItP Unpei^ture. The temperature measured in this

wtumt n called the ahfitlnlr temjitraturi; in contra-

■hoinrtion to the ffniUiindf temperature reckoned

the melting point of ice. The relation between

twit scales 19 very simple, for the absolute degrees

t lo 273 units more than the centigrade degrees.

..9

t7T

iccT

Fkj. l.i.

If the former

1(1 by T and the latter by I, we have the relation
T = 273*^

PRINCirLES OF INORGANIC CHEMISTRY chak

into contact with the gas. We repeat the experimetit wkb the gaa
obtaiiierl frum potassium chlot-ite and observe the same phenomenon.
A glowing woo<l-c]ii[) is a mtgienf for oxygen, and the rmHwn consists
in its iiifliiming.

49. Explanation of the Oxygen Reaction. — Since the com-
bustion of vviiful ill itii tJiki's phu'f ill tlic tost of the oxygen therein
eontnined, tlio ijitestion musi lie :i«kt'cl why the photiomennn has such
an essentiiilly diHortint sispect in pure oxygen from that in mt. The
unswer is :is foUows :—

Wltcn the wotjcl bnrns, u certiiin amoynt of lurat is produced,
which serves to hfai the givaeons products of combustion, ftncl the
higher the tenipemturo thertjby rises, the brighter will be the light
etnitted sind the more rapid will lie the comJmstion. When, now,
the conibn3tJon tfikes phiee in nir, n<Jt only must the protlucts of
combustion be raised in tcni[}er,vtnre by the beat produced, but also
the rit^m^'M which is coutatnecj alottgwith the oxygen, in four times its
(imonnt, in the air. On account of tbe much gi-eater amount of sub-
sturicB to be heated, the temperature does not rise so higli in the case
of eond>u&tioiis in air as in pure oxygen, and, therefore, the phenomena
of combustion are much (ess tnergetic.

This result of our considersuion, obuined deductively (p. 40), can
be tested liy mixing pure oxygen with other gases which neither
burn nor supj»ort combnstion ; as a matter of fact, the vigorousneaa.
of the combustion becomes less in such a mixture, and if the propor-
tion of oxygen in it is very sniail, no combustion at all can be brought
about in it.

ivu. Combustion of other Substances. — It follows from the ex-
[lUination Just given that other subslatiues also, which burn in air, will
exhibit the [ihenomena of tombustinn much more vigorously in o.\ygen,
And atili fiuther, one nnifit expect that substances can exist which
mnnot be made to burn vigorously in air, because the requisite
leinptTtttme ie not rpuched, but which can burn ligorously in oxygen.
Kxpcrience confirms both conclusions.

The first phenomenon is seen in tlie case of sulphur and phos-
phorus. Sitlpliur burns in air with a jMile bbie Hamc, scarcely visible
ut dayligbt. If, hovveviT, the burning sul|)!mr be introduced on a
long-stcmmerl iron spoon into a bottle of oxygen, it flares up vigor-
oiwly iiml ni|)i<lly burns with a bright blue flame.

'I'lu' liitTt'ience Is seen still more clearly wilh phosphorus. A piece

•i| i)li()r(j)bnni>< placed in a similar sption and ignited, burns in the air

wilh 11 yolluwish-white Hame, similar to that of a csuidle. If the

Hpwii be lowered into oxygen, the bottle forthwith liecomes filled

wilb n Min-brifrbt light.

'A. Ootabustion of Iron. — A substance which cannot be easily

>in<lt' V> burn in tiir, is iron. When a (iicce of iron, a watch-.spring for

1 >, uinib.-, in beaitiil in air, it certainly combines with the oxygen, and

OXYGEN

the compouniJ produced coata the iron as a grey, brittle mas*

khich bfCiika off on bending the iron. It dots not, however,

continue burning, and it is only wheji small panicles of iron are

•scattered in the Haine that they can be heated so as to bnrn eniiroly
(p. 34).
The combustion of iron in oxygen, however, takes place much
more readily. A thin steel wat^^h-spring, to the eud of which is
^Attached a piece of toucti-woad or tinder, cun be burned in oxygen
Htike wood. First, the glowing tinder bursts into a vigorous flume,
whereby the end of the watch-spring becomes whito-hot; then the

I iron begins to bum with scintillations, and the product of* combustion
lalla tlown from time to time in the form of a whitediot slag. To
prevent this craekiug the glass, it is well to fill tlie bottle oiie-thinl
full with water,
52. Oxides. — Almost all the chemical elements are capable of
entering into combination with oxygen, ami of forming new aubatances
with corresponding incresise of weight. From the Greek name for
oxygen, oxi/gtnkm, its compounds with other elements (and also with
£ome compound aubstarices) are called o/iides. Thus, oxide of mercury
is, as we have already learned, a compound of mercury with oxygen.
In nature, oxygen and its compounds have a very large distribution.

I From its oc^mrence in at]no8j)heric air, which surrounds the whole
Hirface of onr earth and penetrates into all its interstices, it foUowft
Ihat those subsUinces which can form comiiounds with oxygen at the
Oidinary temperature, must have done ao to a large eA't<itit in the
course of the centuries. This is one of the causes of the wide
distribution of oxygen com])ourids iti mituie.

53. The ExisteDce of Combustible Substances. — Combustible
jbetaiices, i.i: substances capable of eombining with oxygen, are, ntiver-
theless, present in large amount in nature in the unburnt condition,
ind the ijuestion arises, why these have not been burnt up long ago.
Thus a piece of charcoal or of sulphur can lie exposed to the air for
fears, or indeed for centutieH, without apparently undergoing com-
bustion. That this may tsike place, the sulphur must- be i</nikd, and
re have to ask what fresh circumstance is thereby introduced.

Igniting consists in heating one spot of the combiislihle body to a
>tnparatively high temperature (somewhere about ">00 to 600"). It
i^uite indifferent in what manner the heating is eWocted ; the tem-
perature and contact with oxygen are alone of importance. The
beated part then begins to bum. An amount of heat is thereby set
ree by which the adjacent parts of the combustible substance, in their
are heated. Combustion pisses over to these parts, and so the
goes on till all i» burned.
The only respect in which the burning portions are distinguished
from those which are not burning is in their temperoiurf. It seems as
rif most substances had the power of combining with o.tygen only at

PRINCIPLES OF INORGANIC CIIEMISTRV cum

the three Yariables are chosen as the magijitudes to he arhitrarilv
fixeil.

This relation is expressed by saying, the ifttsemt^ state kits two dtijrn'i
of freedam.

For iinderstundiiig the behaviour of diSerent systems, n knowledge
of their degrees of freedom Is -a matter of fundamental importance, and
this is true not only for the physical, hut also for the chemical be-
haviour. Much use will, therefore, be mtide later of the conception of
the (/fjiCfKt (if frwhm i>/ u ffyslttm.

* 66. Geometrical Representation of tte Gas Laws.^ — It will
be recalled that in ^lathenuitics the fact of the mutual dependence of
two variable magnitudes, of such a kind that, one of ihem being given
the other must assume a definite value, was expresaed by saying thai
the one is &funciion of the other. In Boyla'a law

i«-C,

wh«re p is the pressure, r the volume of a gas, and C a constiint, p is
a. function of r. Conversely, e is a function of p, for this relation is,
necessarily, always mutual.

As can be seen from this example, the content of a quantitative
law of nature can be expressed by saying that it represent* two (or
several) meaauniWc properties of a system as functions of one another.

When the function is given in the form of an algebraic equation
there can be calculated for each value of the one variable the corre-
sponding value of the other, and when snch calcuktions have to be
frequently performed, a table of the required e.Ktent can, once for all,
be drawn up. In many ca«es, however, especially in the investigation
of new relations, an algebraic expression for a really ejdsting depend-
ence is not known. In audi ca.'sea it is important to possess a method
which allow.s of showing clearly the connection between the magni-
tudes, BD that the general relations can bo judged. For this jmrpose
the reppoAtation by means of f^o-onlinatui is generally used in the
experin^' tii ecienccs.

^je*t i»fiiJMM«r found by racaaurement that to a definite value yTj

'.-, in !<■ corresponda a value v, of the other. On

• 'l':r, 16), starting from a point which has

T"j.i?t»*rtliKU. measm'ea off, towards

of thf

a hoi
been i
the righ .

JO Co

<^!»jiof X,, i.'\ a distance

which contains as many of the suitably chosen ts of length as the
amount of the numerical value of Tj. From the point a-j the value of
Vn also in suitable units, U meassured in a perpendicular direction.
The point Vj so obtiiined is then a representation of the quantitative
relations of the two values. This process is repeated for a second pair
of corresponding values x,jf.,, and a second point is thus obtnincil. By
continuing the process, a number of snch points ieobfciined, and if an
unbroken line be now drawn through all these, a clear picture of tb«

OXYGEN

relation between the two variable magnitudes of the phenomenon
under invoatigiition is obtained. The horizontal lengths are called
the abicimtf, and the \'ertical ones the ordimks of the points inserted ;
Ijoth together arc designated as the c^y-f'r'.limik:<.

The method of repicsontfl-tion employed permits also of the repre-
sentation of negative magnitudes, if the rule be laid down that these
shall be reckoned towards the left and downwards from zero, while the
j.iositiTe magnitudes are reckoned towards the right and upwards.

• 67. The Law of Expansion. — In illustration, let us apply the]
method, in the first place, to known laws of natnre ; the curve
thereby obtained will lie a ropresentjiliori of these functions. Ab
first exatnple we may take the law for the expaitsion «/ gitsfs h/ hmi.

Fli:. W.

temperatures being regarded as the abscissae, the yo' ^ -"a as the

orditiAtes. First of all one calculates the volumes r, corr
different vaJuea of i, according to the formula for co^'it"

» = %(! >a-ft&ii«r

UBoming any defin)':
obtains a table such

ding to
ure

iVoe

1'073
1-184

i-aer

i of / as abaciBsae, those of p as ordina*
iced (Fig. 17).

OXYGEN

doubtful nature of its resixlta in mind. In the present case the
suppoeitioti would be wrong, since all gases already change their
physical state in the kuowii ranges of tempciature a^>o^'e the absolute
sero, and become h'qnid or solid.

* 68. Representation of Boyle's Law. — The relation between
the voluiue and iJiessure of a gas at constant temperature is repre-
sented by the formula /n- = C, irheio C is a jnajTrntude which varies
with the amount of the giiA •.aid with the temperature, but for given
values of these remafns constant. The expression is, evidently, not
one of the firet degree with respect to p and t\ since it contains a

to'-

10 se

Fill. IS.

30 y

not

of the two, but is of the second degree. Accordingly, it will
be represented by a straight line. Assuming the constant C = 100,
one obtains the following table : —

1 lot)

5 -Hi

10 10

20 r.

100 1

The geometrical representation gives the cnrvt-tl Hue of Fig. 18,^
which ie called * reefanifulur hi/^miioht. The twu brunches appmac^
the axes more and more, without over touching or cutting them
Straight lines which possess this jiroperty with relation to a curve, are
called astfmptiifr.f ,- and the miinner of approach is called iwjmiilolictj
ice, simultaneously with the approach to the one axis, the cur\

PfilNCIPLES OF INORGANIC CHEMSTEY CI

becomes more tiiid more disUiiit from the other, this relation ia
exjiressioii of the fact that the volume of the gaa never becomes z
however gresit the pressure, and, likewise, the pressure never beco
Ztivo, however grciit the vohimc. However, the extension of
concUisiori indefinitely ivould again b» an extrapolation (p. 76),
which the eonesixHiding dubiety wtmld attach.

69. Density of Oxygen. — After these long but ueceaaary
limiriaries, we can calculate, from the observed volume v of
oxygen at the temperature ^ and under the pressure j>, its "redu
volume " /■„ <it' 0^ and under tlie pressure p„ (equal to the presaur*
one atmosphere or 76 cm. mercury), by means of the formula

pv _ pv

jai+aO 76(1+0-003670'

According to the very exact measurements of Morley, the weigh'
I ec. of oxygen under noruittl conditions, amounts to 0*0014290 gi
its density is, therefore. OOn 14290. Conversely, 1 gm. of oxy;
occupies, under normal conditions, (599-8 cc. ; its extensity is, thi
fore, 69^8. At any other pressure p and temperature t, these val
are —

Density: 00014290.^^^^ ^^^3^^^j.
Extensity:C99-8'^il-^2:«^^\

70. Liquid Oxygen. — For a long time oxygen waa known oi
in the gaseous state ; it was only in 1877 that.Pictet and Caillei
sinndtaneously and independently, converted it into a liquid. T
lias a bluish colour and boils, under atmospheric pressure, at — ISO"
On increasing the pressure, the boiling jtoint rises. In this way,
increasing the pressure to 50 atmospheres, tlie boiling point can be rai!
to - 118 . At a higher pressure, the phenomenon of boiling o
not be brought about at all ; on the other hand, above - 118 'Jxy|
cannot be liquefied by any pressure, however great. These extre
values at which g;i8 «iil liquid can exist side by side, are called 1
rritkil values ; 50 atmospheres is, therefore, the critical preaaure, a
- 118 C. or 15;V A. the eriticid temperature, of oxygon. More exj
information regarding the Ivehavionr of suljstances in the neigh bo
hood uf the criticid point will be given later (Chap, XVI,),

Whereas formerly, liquid oxygen could bo obtained only in sm
quantity after laborious preiiiiration, C. Liude perfected a method
1896, by means of which oxygen could be convertfd into the liqi
state by a continuous process. The method dcpmids on the fact tl
strongly compressed air undergoes cooling on expansion. The ex

OXYGEN

'ed is then omiiloyed to cooJ tlown a further quantity of
air, 3o that wlien tliis expands a consitierably lower
UBpmtiire is produced -, by repeatiog this cycle uninterruptedly,
the t«BJf»emfur« c«ri soon be lowered ao fur that the exfjanded air
becomfs li<|t]jd.

Fnjiu the mixture of oxygen and nitrogen thus obtained, nitrogen

ipontes off tirsl. sinee ita boiling point lies ul - 194 , niiicli lower,

lore, than that of oxygen • a mixture is liift liohinj which liecomes

dngly rich ill oxygen, and, «t last, is almost pnio liquid oxygen.

ic production of liquid oxygen has, on this account, liecome 60

lat attempts have been made to employ it, mixed with

itA ail ex])Iogive.

ri. Gommemal Oxygen.— Although oxy^'en, in unlimited

Douftt. is ;iL the disposal i.'f f\-ery one, the manufacture of oxygen for

Jc his, how*ever, already become a considerable industry. This depends

lactthat the oxyc^en in the air is diluted with nitrogen, and,

eforr, in the case of combustion does not produce such a high

as the pure gas. Where, tliereforc, it is of importance

very high temperatures, pure oxygen must be employed, and

3jicci:*Ily ])ropitreil.

Biaical methodi* eraployeil for this purfiosc cannot lie

crilicd here. Thti prcp>iratiori from potassium chlorate is too

ive for the manufacture on a large scale ; otlier substjinces are

sfl which, at certain temperatures, absorb oxygen from the air and,

tcmj^eraiiires, give it up again.

' the princi[>le of one method can be described here. It
on the easy preparation of liquid oxygen from the air (see
ilanl From the mixture of oxygen and nitrogen [jroduced, by this
SMtW, the nitrogen is removed by partial evaporation. By using
by produced for the liquefaction of fresh portions of air,
able to 86[)arate the oxygen and nitrogen of the air fttirly well
DC another, and this, too, at a price wiiich makes the com-
profluclion appear reiuiinerative.
lie iixygen prepired for sale is [mmped into steel cylinders (Kig.
104) under a pressure of 100 atmospheres, and can be withdrawn
them with any desired velocity by turning a screw-valve. For
a*e of continuously maintaining definite velocitiea in spit* of
I emptying of the ejdinder, there are pressure-reducing valves,
aiiig of which enlarges more and more as the pressure in the
btr becomes less, and which, in this way, eflect a discharge wliicb
lust independent of the pressure. As a rule, commercial oxygen
(untAttis 5 to 1 0 per cent of niirogtfii.

72. Other Properties. ^Ab is to be expecte^l from the great

»oc of thia elennrit, the mefisurement of many other properties

Ml carried out on oxygen. Their importance is, however, as a

noc so great that they should be sepai-ately discussed here. Obe

PRINCIPLES OF INORGANIC CHEMISTRY

nf thcin, however, ^fi^. the soltihilili/ in miki; will be given, since it (
comes under diacuesioD. It is small j 1 vuliime of wjiter lUssolve
0", 0049, and at 20^ 0031 volumes of oxygen. From atmospl
air, in whkh oxygen is present only to the extent of one-fifth, ot
fifth part will be dissolved. From this it follows that at 0 , 32
of oxygen reijuire 457 lit. of wsiler for solution, when the soluti*
saturated with pure oxygen. If it is' saturated with air, 32
oxygen would he contained only in eomothing like 2 '3 cubic metn
water.

Further, it is deserving of mention tbat oxygen is ptiraiinu/nelie
it is attiiicLed by a magnet, similarly to iron. On account oL

small density, this property ia
observable in the case of the gJw
the case of licjuid oxygtn, howeve'
can be cicai'ly observed.

73, Ozone. — -When oxygen is
posed to the inHuenceof electrical oet

„ tioiis, its volume changes ; the vol

Ortigtn contracts and the oxygen, at the s
time, assumes new properties,
exporimpnt is best carried out in
Bjjparatus consisting of two ti
placed one within the other, and fi
together. These tubes are coa
within and without, with an electi
conductor ; each coating is conne*
with a jjolo of an induction mach
and tixygcn ii? passed in a slow cim
through tlie space between the
tubes.'

74. Characteriaticfi. — That so
thing litfw lilts been formed
evidenced first of all, by the fact t
the issidiig gas has a strong sm
which is irritating to the muc
membrane and induces coughj
Further, a piece of bright ^il
whicli nndergooB no change, eitber
air or in pure oxygen, becomes bli

when held in the stream of gas. Lastly, a colourlOBs solution
potassium iodide (p. 47) becomes coloured dark blown when

OtQne

Y\a. Il>,

' J\ii A(Ivai]()^reisti!i tuoilitiuatioii of Uie nppAnitni coDJtiats iu fniiiiiug \\n\\\ rtjutiug
Uilute »iil|rhiirie ai'iil (wbicli in u fairly ^ocui uomluctnr of elettriclty), {Fig. It)).
nienilA at tlie liqilJil, tlie appnmltis, wliik- liring useiL, is kc^it con], H cotiditioii wliicl)
^ejtL iiillimtice tiii llif yield, niitce ojsone is dtstroyed >i>' wurmiiig. I'.f. it is convci
sgnhi Into ordiii(i)'y oxygun.

OXYGEN

oxTgen is conducted through it, whereas ordinary oxygen
, elTtKU Al! these propt>rtios are again lost wlieti the altered
Cts paased through a heated g!tLS!^ tube.

' hero stand face to faec with tlit^ tnct that a simple, or unde-
Dposible, substance zi&sumes otijer properties without pussin<; into u
' totBf>ound by iDteractiotj with another substance. For, the
! the elt'Ctriesd apparatus, with which the oxyg*ii is in contact
its alteration, remains entirely iinth.inged, as abo does the
tulteiri which the altered oxygen again paases into ordinary

igen, endowed by means of the electrical treatment with
ies, is produced also under many other conditions. Even
quantity, it is recognisjible by its remarkable smell, on
4cooant <if which it has? received the name of oriwir.

'5. Pure Ozone. — The oxygen in our apparatus is converted,

all, <>niy in small part into ozone, so that the issuing gas is :»

itsn of oxygen with a small percentage of ozone. Pure ozone tan

► (ikwncft by passing the rai.\ture through a tube cooled by liquid

igen ; the ozone condenses then to a lii^uid of a cornflower blue

wliiL-h ^tasse.'^ at -110 into a blue gas. Working with this

luj^rou."*, airif.e it readily explodes, passitig, with development

rfkett, into onlinary oxygen.

7f», Relation of Ozone to Oxygen. — This last fact gives ua the

IPJ" to the Muderstanding of thii phenomena. The fieat which the ozone

'felop* on pa«fiiiig into ordinary oxygen was contained in the ozone,

it 1* true, a» Iteat, but as oncrgj- of another form, whicb is called

I aerfff. We can, therefore, write the equation

o.vygen + energy = ozone.^

ling oxygon to the influent-e of electrical oseilhitiona, there
to it the energy wliich it rerjuires for its transformation

At b evident, osrone can be formed from oxygen only under sneh
Midukms that the necessary energy can be transferred to the latter.
tAuattfr of fact, this is the case in all circumstances (to he specified
f) wbith liikd to the fonnation of ozone (lidf' Chap. XV,).

itropy. — Elements which, by rt-a-son of different energy-
► difforent properties, are called alhlru/ii/:. Oxygen and ozone
fbrr, nllotwpic mini ifi cations of the shim elnrw^if. The fact of
t^fzutence of nllotropy follows, on the one hand, from the fact that
4» different forms are convertiljle into one another willwuf r^-suhr,
the other h:ind, from the fact that e(|ual weights of both forms
ilical product* with equal weights of other substancea. Thus,
nation of a combuBtible substance with oxygen or ozone,

Bri u tint t" Im« l.hoiiKlit fif tu* exjiTejisilit; that nrJiiiiu-j" oxygen coutxillB
I only tlikt osone coulaln.t morf energy tlmn onlinftry oijgeii,

82 PRINCIPLES OF INORGANIC CHEMISTRY oh

exactly the same compounds are obtained, and in these not
remains of the difference between the two kinds of oxygen.

Besides the difference in chemical behaviour and in energy-con
there also exist between oxygen and ozone differences in their phj
properties. More especially has there to be mentioned that the de
of ozone is to that of oxygen as 3 : 2. One cc. of ozone weighs, v
normal conditions, 0*002144 gm., and 1 gm. of ozone occupiet
volume 466*5 cc.

78. Technical Application. — Since ozone acts more quickly
more energetically on oxidisable substances than oxygen, it is prej
at the present day, on a large scale, by an electrical method, ai
employed in the arts for bleaching, purification of starch, resinifict
of oils, etc.

CHAPTER VI

HYDROGKN

T9. PreparatiOIl from Water. — Ifater is oue of the most important
and iridelj distributed compounds of oxygen. Besides oxygen, this
nbstance contains another element which is called hydrogen, and
*liicb can be obtained from water by the withdrawal of oxygen. This
<M be done, for example, by means of red-hot iron. Wo have con-
meed ourselves (p. 64) that, at a moderately high temperature,
iroo combines with oxygen. If iron, in the form of thin wire, or
tunings, or otherwise finely divided, be heated in a tube to redness

iMC ^^=s^

Kio. 20.

•ad steam be passed over it (Fig. 20), the latter is converted into a
pi »hich can, like oxygen, be collected over water.

*0. Identification of Hydrogen. — The gas which is collect€d
resembles oxygen in its outward appearance ; like it, it is colourless,
odoarle&s,' and tasteless, and is not dissolved by water to an appreciable

• Tin: ,"»- obtained from steam and ordinary iron exhibits au uniilea-saiit smell,
tanin-eot of petroleum. This, however, is due to the formation of other substances
fcoi tir carlau containe*! in ordinjirj- iron, and does not occur when pi(re iron is used.

PRINCIPLES OF INOKUANIC CHCMISTIIV

exttsnt. It can, however, l>e reiidily distitiguishcHl fi-om oxygon h
WGllknowii reautit/ii (tf that gnK A glowiiig spli titer of wood dot
iiiliiinuj, but is extinguished. If, however, a splinter hnrniug w
rtamo h& lirought into the gas, it also, it is true, is extinguished
the gas itself takes fire and burns with a piile flame. Hydr
therefore, cannot support the combustion of ^^■oo^l, hut is itseU
liustiUi' in ail". ^

81. Detection of Oxygen from Water. — If the iron be
wards cxaniined, it will be found to be cojityd with n l)lack-i;roy, fi
mass which has the same properties as the substjuice produced b
burning of iron in oxygen, and is, in faca, like it, an oxide o:
The following process, therefore, occurs ; —

water + iron - hydrogen + oxide of iron.

82. Other Methods of Preparation of Hydrogen. — Tb

periment just de.'jcril.ted is of great histuriciil importjince since it se
in its day, to prove the compound n.tture of water (which was forii
regarded as an element). It yiulds, however, little liydrogeii,
inconvenient to carry out

The experiment becomes much easier when, instead of in
metal is used which decomposes the water even at a low tempera
This ^lecomposition occurs with the light metals, f.y. mit<intsinin,
«ater be poured over magnesium powder, such as is, at present, t
used for the production of a bright, sudden light in photographinj
action, certainly, Uikea place at the ordinary tempt^rature ; on hea
however, till tli« water boils, a gas is slowly evolved which crtl
collected in the onlinary way, and can be shown to be hydrogen^
Imrning with a pale-blue flame. ^

The evolution of gas can be greatly accelerated by dissoh'in
the water a little magnesium chloride, a salt- like compoum
magnesium. This does not take any part in the reaction but
dissolves the oxklc of magnesium which is formecl, and thus frees
surface of the metidlic particles from the coating of this siibsW
by \^'hich the action of the water is retarded.

Liistly, there are light metak which decompose water with ene
even at the ordinary temperature. This is the cjise, for example, '
sodium {p. 52). On Vjringing a Httlo of tliis metal in contact '
water, an energetic action takes place whereby so much hea
develojMd that the metal melts. For the purpose of coHeciing
gaa hereby jiroduced, one can proceed as follows.

A little sodium is placed on the water in the trough and pre;
under the surface with an inverted spoon nwule of fine wire-gi
(Kig. 21). The evolved giis then ascends through the meshes of
gauze, while the metal is kept back. If the spoon be placed iindei
inverted tube, filled with water and standing in the tiough, the
can be collected anil be shown to be hvlrogen.

HYDROOEN

Flu. V'l.

Also, the sodium may be wi*appetl in blottfng-pjiper (or in wire-
fpneji,and quickly bronght under the mouth of the tube by means of
> tonga. The waU-r then
fCMknto* t»\]y aftui- some
tMBmU to the sodium, and
th* rises iirithin the tube,
it acts on the water
crolm gas. In this
»!«», the gjLs c«Ti \k
n, by iL<i combustibility,
tn he hjiirogeti.

it a nilo, the g;i8 so
•(kamd hums not with a
Ifac bat with A yellow
Imc This is due to the
pMHe of dmjie of liqiiid,
"^^ eontttin the ifxinim '"
irf which has been
to this the flame owes iu yellow colour. If one wishes to
the gas must be allowed to stand some time tili the drops
h*Te settletl and the gas has become free from fumes,
Cbemical " Forces." — If the metho<ls by which oxygen was
are comjjared with those employed for the prepanition of
kfd^ps, an t^sentjal difference is found, Dxide of mercury and
paiMm chlorate decompose at moderately high temperatures
i» OTgna «nd the other constituent, without the participation of
«»*W ntbetanee. Hydrogen, however, was obttined, not by the
•e <«>fititueot of water Iwing separated aa an rlinH'nt, but by its
MK^ nito another runi/tifuinl, and the formation of hydrogen from
•■r tfikm place all the more easily the more energetically the cora-
(feHi^ «f the oxygen with the substance added takes place, i.r. the
■• oMe the newly formed compound is.

vonditioas are also met with in many other cases. If we

oMBpound of the suljstances A ■'- B, and bring into contact with

■fwiiHce C, which can combine with A to form a very stable

then this compound A + C is formed along with the

9^» lodg time the following picture wa-; made of these relations —
• p>^r» which u etill much used, although there are important
vkcre it does Dot prove to be correct. The various substances
^■ciaed at bong endowed with forces, in virtue of which
mntuaUf hiad one another. If, now, the force betweeri
greater t&ui that between A and B, C must decompose
id A - B, when both come together ; A is bound or
, am! Ft i* displaced from ite compound with A and aet

PRINCIPLES OF INORGANIC CHEMISTRY

On opening the tap H the air in the apparalua fiist of all es<
the iicid flows from C into A, iind, whtii A is filled, comes into ci
vritii the zinc in B. Evolution of giis liegins forthwith, and the I
gen which is geneiateil escapes through the tap H. If more j
<le\'elope»l than can pass through the tfip, the au-id is forced Imc
of B into A and C ; it comes out of contnct with the zinc, an
t! volution of gas is interrupted or diminished. On the other ha
more gas is withdrawn the acid passes back to the zinc, an.
evolution of gas takes place more quickly.

Although this antotnatic regulation is an advantage, the appa
has the disadvantage that the fresh acid from C is mixed wit]
partially spent acjil in A, and its action thus interfered witli.
full effect of the acid can, therefore, never be obtained, as can bi
with the apparatus first described. '

85. Drying of Qasea.— The hydrogen, which can in this wi
obtained in any desired quantity, is not quite pure, since it tak<
watei* vapour from the aqueous liquids in the presence of which
produced. To free it from this, the gas is [mssed over subBt
which retain the water. There are many such desiccating aj
OTie f>f the most convenient ia mldum chloride, a white, very h
acopic salt which is formed as a waste secondary product in i
chemical manufactiu-es, and is, therefore, very cheap, A tube is
with this salt and placed in the path of the hydrogen, the sim
way being to attach the tube directly to the generating apparati
indicated in Figs, 23 and 24.

Concentrated sidphuric acid is another and much more efife
desiccating agent Hince this is a liquid it is either placed in a ip
bottle (Fig. 25), in which the gas is made to bubble through the U<
or spread out over some material which has a i
surface, and is not attacked by the acid, such as bp
gkiss or, better, pumice-stone. It can then bo pi
like a solid substance in tubes, and in this case
must only bear in mind that the volume of the
iiicieasBS through its attracting water and flows d
to the lowest parts of the ap|)aratu&. A ooUeci
chamlNsr fur this acid must, therefore, be provi
In Fig. 26 is shown a drijinff-kmrr which is inter
for large quantities of gas, and which fulfils t
requirements; it can also be used for calc
chloride.
— Besides the Jitjueous vapour, the hydrogen
quenlly contains also very fine drops of tho lt<
I from which it has been evolved (p, 85), These piaa through w
bottles, but are retained, with certainty, by a plug of cotton wool.
Other impurities which are usually contained in the hydrogen
uot occupy ns here, since they are njostly of tio account for

HYDROGEN

aoan

oS§8
QaQcy

JSspt'iJraente which are to be peri'ormetl. By these traces of foreign
sui»staiicea, only the fact that pure hydrogen ia completely odourless
is masked ; inipuce hydrogen htia a slight ottour, r^ — ■

which it Joses, however, by approfiririt* pm-ifim- _^

tioij.' ' jQ^

86. Physical Properties of Hydrogen. —
The moat conspicuous property of this element
is its small density ; of all known sttb^tiinceB
it h;is, tis haa alr^dy been iiaid, the Bmallest
density.

If a flaak of uboiit h litre capacity, closed
hy a stopper and good - fitting glass tap, he
weighed, first filled with air and then exhausted,
a difference rvf weight ni rather more than 1 gm.
is found. If the exhaust«l Hask be filled with
hydrogen under atmospheric pressure, the increase
of weight amounts to only about 01 gni. — if
anything, rather le&s. This shows thut hydrogen Fm. sa.

is at least ten times as light as air. By CJcact experiment the ratio
is found to be 1 : 14'4.

On comfHiring the weights of like volumes of oxygen aiifl hydrogen
at 0' and under a pressure ot 76 cm., the ratio ia found 15*88 : I or
16:1-008.

Since 1 cc. of oxygen under normal conditions weighs 0OO142S
gm., the weight of 1 cc. of hydrogen, or its ateolule density under
normal conditions, must be fl 0000900.

87. Molar Weight.— This ratio holds, in the first place, for the
two gases under norma! conditions. On account, however, of the
identity of the laws of pressure and temperature in the case of all
gases (pp. 68 and 69), it rem&ins unchanged w^hen the densities of
oxygen and hydrogen are compared nl auif pressure und Ifinperaiuu;
supposing only th;it both ga-^es are at the same temperature and
pressure. When, therefore, the weight of a gas »% any pressure and
temperature is compiiied with that of the same volume of .i tmrinal
(fits nnder the same conditions, a constant ratio-number is obtained
which is indejieitdeiit of the pressure and the temperature, and is
determiued only by the nature of the gas.

For such a normal gas (here is taken, not an actual substance, but
an inuigituinj ijiis vhidi is 32 times <w light as &rij<ien. The historical
development which has led to the choice of this partitnlar n
will be given later (Cliap, \\l.). For the present, it is siittidi
state the fact.

The ratio of the weight of a given gas to that of an c<(ual voJ
of the normal gas under the same conditions is called its mok<

' The purification can be effei'ttd Hy luentLR of potassilaiii pennsugsQat* coiitiiinv
• wuh-liottle throujj;)! whicli tlie ^as )nlsi««s.

PRINCIPLES OF INORGANIC CHEMISTRY ch.u".

'v;eiffkt. Since this nume has been derived from certain h}"|Ktthet.ical
notions roganling the constitutiun of the gases — notions wliich txre not
I essential to the actujil facts — we shall give preference to the shorter
luame vfUir nri<jUl, although, at present, the other is still the one
tmost used.

Since the norrtuil gas is taken as 32 times lighter than oxygen, its
absolute density under iiormal conditions, i.t: at a pressure of 76 cm.
and 0 , is equal to 0'0OOO4460 gm, and its extensity to 22,400 cc,
, Both numbers ate of great imi>orUttice and find manifold application.

^The ituihir wnijlif of a f]ti» is got, therefore, lij' dividing its weight
by the weight of an equal volume i' of the normal gas under the
pe pressure p and at the same tetnperature i. This weight ff is
md, according to the formula on p. 73, to be

y = 000004406

76(1 +0-003670'

The volume is here measured in cc. and the pressure in cm. mercury.
If ({ is the weight of the gas, the molar weight is, according tn
definition, Gfg, or introducing the value of g, the absolute tempeniture
T ^ 273 + f, and collecting all numerical factors,

molar weight = 6234 — •

° pv

Accoiiling to definition the molar weight of oyj'gen is 5 2 '00.
Prom the data given aliove for hydrogen, it follows that the molar
reighi of hydrogen is 2'016.

The mular weight of a gas can also, according to this, be regarded

^te the weight of that amoiint (\i gas which occupies the same volume

[«, under the same pressure ji, and at the same temperatiU'e /, as 1 gm.

rof the normal gas. From the equation pi' = fT or prjT = r, we see

llliat the constant r depeml.'i only on the presaure, volume, and

tporatnrc } it a«aumefi, therefore, the same value for difterent

when these magnitudes arc equal. F'rom the definition of

weight just given, it therefore follows that (Ik coni^Utiii v vutii

tor tiu snnif mliie for a vKiSar wiiijht »f imr/ <iiid firiy ;/«.•:, independent

oiita nature. The constant roforrcd to the molar weight ia called R.

To Cklculate the value of this, we apply the equation pr^T - R to

tit aonBal gas at 0" and undei' atmospheric pressure. In this case,*

»=*i,400 cc^ |t= 1,013,130 in absolute units (p. 68), and T= 273.

tt = 8'3l * 10^ in absolute units.' The equation

pr = RT--8-31 X lO'T

-rti.we, tor R molar weight of any and every gaa,

■sm ' ■ umwdcowl in itmosjiliurea, jtt=l and R = 82'l. Up is reckoned
« 1 n m. »=l«n {p. 68) and R - 8-4S X W. It it b*»t to keep to absolute

(Tdrogen

' It ran>i|, however, be noted that tlie general gas-law, jis well as

ftlw pirvUwj (that of Boyle and of Gaj-Lussac), is uoi cutiiflti rjrad.

[Oil tke contrary, all gases deviate more or less from it, the deviation

raii|;»Il the smaller tbe more dilute the gases are. We arc dealing

|k«, therefore, with a '^ limit in^ law'' (p. 20), to which the actrial

Dces approximate, but which they never entirely fnlKL

' I'mier ordiniiry eondittuus of temperature and pressure, these

MfiMiioriP are. in the case of most gases, small, and amount to scarcely

-hiindrctlth of the theoretical value. A gas which woidd comjiletely

' the law pF - RT, is calletl an " ideal gas." The rtornial gas above

'tteHtJMted is assumed to be an ideal gits.

' Stiiet!, formerly, the densities of gases were, almost exclusively,
i^mtA to the density of (aV as the unit, it is necessary to cs.labHsh
ikntioof our molar weight to these numbei's. Now, a litre of air
•Ofb* 1*293 gni. ; it is, therefore, 28"9 times as heavy jis the normal
pL To cjjcttlate the molar weight from a density referred to air,
tkblUsr mtjst Ijc multiplier I by 28'1> : in the reverse case, the number
lii--! \h, liivided by 2iiU.

5 ExpeiiffietltS. — The small density of hydrogen win be de-

»t«i (u varions ways. A small balloon of coUoiliura, golti beater's

■ caoulehouc, is filled with hydro):?en and allowed to go free,

hydrogwD is, in round numbers, fourteen times as light as the

pkcod air, it cxpcrienccfl a corresponding upwnril force amounting

I gm. for every litre, arifl the iMilhmn. therefore, fpiiekly

tills. The 8;m\c thing can be shown liy lilowing soap-bubbles

1 livilrngen ami allowing them to ascend.

projierty is made use of on the large scale for making
llouns, which are, essentially, bags of silk rendered air*tight
with hydrogen. The total load which such a balloon can
isive of its own weight) is found, .tceording to what has
Ui I*, in rounfl numbers, 1 kilogm. for each cubic metre.
however, only in the neighbonrhnod of the earth's surfsiee ;
killer one a-wcTids, the less dense does the air become, and the
W (U haoynncy .

Thi |»roptrty of hydrogen can be demonstrated in another way.

TvMgiaM cylindera are filled with the gas over water and snppoi-tod

UMapright }*oeition — one with the month upwards, the other with

^anotii downwards <Fig. 27). If, after a few moments, a Hame be

Wo^^li; H cylinders, the inverted one ^vill be found to bo still

rSki * .;;en while the Other coiitfuius oidy nir

i*H. Aefaaviour of Hydrogen at Higher Pressures.— In its

tics as a gu^s. hydrogen, of all knowji GitbtiUiuces, approximates

■Mtl noarly lo the "idear" gaseous state. On closer inveBtigatioo,

^owttT, > deviation is found, aiich that with incrc4«ing pressure the

livne of hydrop2n diniinighes Ir'-nf than it ought to according

•■ Etojlr* I«w. This deviation increases as the pressure becomeia

part whidi w ifukpendful of ih>'
pi'esstirr, DeTiotiiig tbe toul
volume \>j V, and that pai't which
obeys Bnylo's law, and for which,
thcit'fore, iit constant temperaturej
the fiqimtion pv — V. holds good, by
(!, and denoting by h the other
pjirt whicb is imi«pendent of the
pressure, we have V = v + 6. Sub-
stituting for V in the equation
/rt' = C iti value V-6, we obtain
^V — b) — G iiH the expression for
the behaviour of hydrogen at all,
and espuciftUy ut high, pressures.

A clear picture of the substance

of this law can be got by imagining

the hydrogen to con&ist of small

piirticlcs of greater density, between

which is itn empty space. The

1 sitter would obey Boyle's law,

while the former would represent the itieumprassible part of hydrogen.

In the cose of hych-ogen at 0 ;md under atmospheric pressure, the

value of h amouuts to 0*00062 of the total Aoluine.

The equation p(y ^h)~G shows that the diminution in volume
is smaller the more the pressure increases, and that when the pressure
is very high, Y can be only slightly greater than /'. In this case,
hydrogen behaves almost like a liquitl, for a liquid also has the
property that its volume dimini^ih^s only slightly with great increase
of pressure.

* In the case of the other gases, the deviations from the law
}iv= KT are gonei-ally such that the ga^es are, at first, morf com-
presstble thaiv accoMing to Boyle's law, At very high pressureB,
however, they all behave similarly to hydrogen-

90. Liquid Hydrogen. — By the application of very effective
cooling arrangements, the principle of which has been pointe»l out on
p. 78, it hasi i-et'cntly become possible to observe hydrogen in the liquid
state. It appears ;is a colourless liquid, the density of which at its
boiling point is only 0 07, but which, nevertheless, forms a t[iute visible
surface and exhibits, in all respects, the behaviour of a liquid substance.
Hydrogen boils under atmospheric pressure at - 'iofJ'o', or only 20'5'
above the absolute zero ; by alloiving it to lioil under reduei'd pressure,
this temperature c^n only be slightly lowered. At this temperature,

I
I

nviti.'OfiEX

ii'J gRS€« ' (oxygon ;uid air as welt) are tmnsfortnecl into
rhe vapour jircaisiire of which is exceed iiigly small. ThiiB,
tifounpte, if the closeil cud of a bent tube, tilled with jiir., be placed
m a ttsjel of liquid hydrogen (Fig. 28), the vijjpor part at once
Ittumet free from air ami »ho\vB a vacuum sncli as can scareely be
i^Utogi with the rery best pumps.

SM Ajrf«w/cii was obtained by allowing liquid hydrogen to
*»f»jrate »n mctiu. It fomierl a transparent ice with frothy Burface.
inrctuif: fMitnt liea at about 257 .
! Diffusion, — If two cylinders with even-^tiund, broad rime are
{.tnJ iir tight on ont' another with the beIi)of a little gruase (Fig. 29),

\zJ

i^-

Kio. 28.

Fto. K'.

i Upper one hfis been filled with hydrogen, one would expoci
tBgfaler hydrogen would remain above and leave the lienvier
" neath. If. however, on the following day, the two cylinders
l<M*AiUj scparjited from one another and imniediaUjly closed
^giaa plat«*« which are held in readiness, hydrogen will bu found
9 kiL For if a Hanii- be brought near, the gaB contained in both
tjtaien takes fire, and the paie hydrogen tiame nishes with a whiatliiig
\toth cylinders, -
bit mutual Kpreading of the gases ijjto one another is called

eption of ticliani. — TV.

th« eiimliiistlou of lirdrogen here exhibit* othtr phenomen* th»ii
iarilniatur* witli i

PltlNClPLES OF INOUUANIC CHEMISTKY

neJH

difjuiion. \l is ;i unite universal pliBnomeHoii ; "U gu^a diy _^
fiiu- iituitlitr, and tilt diffu-mioit ijonn mi iinfil rarh ffti.^ it uniform/ itJieti§
ihnmijinnii tin- wh'iU' Afiurr,

92. Dalton's Law of Partial Pressures. — DUl'urent giwus, tl
fort?, Avhich are present in tlie same sjmce, helirive as if eacli were t
itlone, for eiich separately obeys the lnw (hiit in a givon space a g
not jit rest until it fills the space unifortnly. For iitixmus t<fuilibr
Iherefort; tU)t Ihr I'lltil pressure, hut fw rarh tjas mdij iia jmrtinl pieasun
Ihv jifrssHrr uiiirh it wrndd cr/rl if if nkmc oiTirftieil I fir sjnin; if of tireo

This is ii fact of grejit importance, since miiny other j)hcnon
exhibit<?d by gases are determined by thu partial pressures vi tl
Thus, for example, the partial pi-essnre is the determining factor
gaseoiia eqiiilibrinni in chemicd pnn-esses, wbieli wit) he cnnsidi
later.

Ill ortier to exjiross these relations fur the purpose of calculal
one has only to take into accuiint that the total pressure of a gasc
mixture is the sum of the jmrtial pressures, ami that caeh g;is pret
is uniformly distributed througlioui the spiteu, the total volume
therefore, enual to the volume of each gas. If, therefore, P'

total pressure
\] I the total vohune,

values for the single gi
being denoted by /»j,
/J,,, . . . and I',, ('„ t'jp .
we have the equal)

n^Pi^Ps'' - ■ . >

and i\ = f'^ - '"a = ■ - - ^
The law of pwri
pressures which has j
been stated was e^tublisl
by Dal ton, and is c*|!
after him. It is a spef
case of H more genei'aj l|
according to whieh, in i^
given gas mixture (1
components sf which
tint ciiemically intent^
each single gas beha^
with respect to all 1
properties, fia if it wi
alone present in the to
apace under a pressi
equal to its pjirtial pre
nre. ^Ve slmll have many opportunities later of becoming ai^ijuain^
with individual cases of this general law. i

93. Velocity of Effusion. — A cell of porous clay, such as IB m

Fl>.. »u,

lIYDKUdEN

Wv\ ;jlv,inir iMttrries, is closud hy a t-ork through which passes h glass

Piir 1 metre long iFig. 30). This tuVie dips into :t vessel containing

[oAiiitnil water, tiiici a beaker is iiivtrted over the clay cell. If, now,

.iful i-urrent of hjdrogets be jxissed into the beaker, a stream of

itiiila is ieeti to pasa out of the lower end of the tube, which shows

tkt pressure in the iiiterioi- of the cell has siiddeiily increiiseiL

diort time this cease? »ml equilibrium i:: established.

If ibe beaker W now removed, the water ascends just as ijuifkly

il»e ttibc, « sign of ilerrtnge of prtssiire in the Cfll. The water

A certain height and then sinks again, since the porous cell

nuintain a peramnent difference of pressure.

Tlew phenomena are due to the fact that hydrogen pafises touch

an mpidly thao the other gases, rjj. air, through small openings

■tk » the pores of the clay cell. When, therefore, the cell is

■nomded with hydrogen, && in the first part of the experiment, this

pBirtmtes rapitlly into the interior, since it« partial pressure there

l«ro. For the same reason, the air passes at tlie same time out of

ittD into the hydrogen outside. The movement of the hydrogen

jilu-e, however, much more quickly, and, therefore, an excess of

a produced in the interior of the cell, whirh drives the air

tb« tube in bubbles. Etjidlibrium occurs when the gases on

nie« of the cell-M.nll have tlie same eompossition.

now, the extemul lij'drogen is removed, the same processes are

in the reverse sense ; the hydrogen, on aceouTit of the diffcr-

the fiartial pressures, p{is.ses outwards, ami it does so moic

f than the air can i»enetrtite inwards ; henee the diminution ot

Rerencea of velocity, similar to those which are here found in

\ of effusion through the pores of the clay, are seen in the case

I diflhAJon of two gases into one anntltcr, without a separating

B«ith kinde of movement are, indeed, siuiilar, but we are

rilh ((uite the same phenomenon in the two cases. Wc

uirk, gunendly, that hydi-ogen difl'usea more rajudly than

~^fut^ and that the velocity of difl'usion is, in general, all the

T. the ]:^nsL\.*:t lh»- density of the gas,

* H ^e Law of Effusion of Graham and Bunsen. — ^The
apBriatiit on the diHi-ieriCfS of the veloi-ity of effusion of gases in
tki bra wo have just been considering, is not suitable for quantitative
4'tsmiimti«»D&. The fallowing, hovvever, is a suitable form.

Tke apparmttis in Fig 31 is a gaJ!-measurijig tube set in a liquid
•ikiriii^ two Biarks m^ and m^. At the upper end there is a tap^
*kfieb, iioweve'r, does not open free into the air, but into a space closed
l7>lkiii pUtuturn ]>late pierced with a fine hole. If the lube is fliled
••iBBwwb.*: WIow the mark j(i, with ga-s and the tap opened, the gas
■ fiftm: the fine opening, and the time can be noted which

till uj<: inuid iiasses from the lower to the higher mark.

PRINCIPLES OF INORGANIC CHEMISTRY chap.'

The ordinarj liglit of tho sun and of nmny stars uxhibite hlwki
lines at exactly tJie same points of the siJOf'tnim at wbicb the byilrogeu
lijU's ajipear hriijlit. Ikilh kiruls of lints rire Yury closcl}' reliiied. At]
a later stage ive ishall enlLT in detail into the relation between thein
we would only mention here that these black lines prove the presiaoce
of hydrogen with the same certainty as the bright ones, It is, indeed, ^
the same phenomenon appearing under diHei'ent conditions. ■

96. Hydrogen burns to Water.— As a test for hydrogen, its T
combustibility in air has been used. The question as to what thereby
becomes of the buniing hydrogen turn bo answered with the knowledge
we have already gained. We have aeon that iron and sodium, by

=5^

Pitl. 34.

acting on water, puss into oxygen compounds, whereby hydrogen is
formed. Accoi'ding to this, water is a comjiound of hydrogen and
oxygen, and since combuatioti consists in a combining with oxygen, we
should expect water to lie the product of the combustion of hydrogen.
As a matter of fact, wc can convince ourselves by direct experiment
thiit water is tho product of combisstion of hydrogen, J

If n large, dry beaker be held OA'er the Hiimc of burning hydrogen,"
a dew is quickly formed which looks exactly like the film of moisture
on a cold window-pane, and behaves like tt. Special arrange-
ments are necesrary if it is desired to collect the water in larger
quantities.

Iti Fig, 34 a liuruer is represented (cf. p, 103) in which, by meauftl
of pure oxj'gen conveyed to it, hydrogen can be burned. Since large
amounts of heat are hereby produced, the bm-ner is placed in a wide

HYDROGEN

giiiss Hask which can be cooled by surrounding it with water. If this
apparatus is put in actioii, a few cubic centimeties of a colomliias liquid
soon coltticl, which, in all its properties, ahrnvs itsulf to be pure water.

uT Combustion of Hydrogen by means of Oxygen Com-
pounds.— Fitr the foi'mation of water it is not necessary that tho
oxygen be presented as the
free element to the hj'drogerr,
oxygen compounds, or o.xidea,
can also J>e iised for the pur-
jKJse. If hydrogen be passed
over oxide of mercury placed
ill a bulb-tube {Fig. 35), no
action, ceiuinly, takes place
it ordinary temperatures ;
BO soon, however, as the
oxide of mercmy is mtr-
full}/ heated metallic mer-
cury tiiakcs its appearance,
and tcaitt^r is deposited on the
colder pstrts of the tube,
first as dew, and tijen in
small drops.

Quite similar phenomena
iire observed when the
orides of other metals are
used in place of oxide of
mercury. By heating oj-ulti of lend in ii cunent of hydrogen, metallic^
lead and water are obtained. Tiie oxide of !ead, under the name of
litharge, is obtained in large quantities by heating metallic lead in
air, the lead hereby combining with the oxygen contained in the air.
When f'(j[*/wf ojitk., obtained by strongly heating copper in air, is
heat«d in hyrlrogen, red metallic copper and water are produced.
Hydrogen may, therefore, be used for the purpose of obtaining the
metals from their oxides. This method finds no application on a
targe scale, because there are cheapei* means of effecting the same
reault : for scientific work, however, such methods are, not un-
f re*| uen tly , en i [tiny et 1 .

98- Rerersed Processes. — The processes we have just described
take place accrn'ding to a scheme which ia similar to that of the
di«placemcnt of hydrogen from water by iron, only that they represent
the reverse process, the displacement of a metal from its oxide by
hydrogen (p. 83).

It is therefore of interest to ask whether hydrogen will not alaOi
diiplacc the itofi from iron oxide. If the previous experiment is
I^teated, using, however, oxide of iron in place of oxide of mercury,
quite similar phenomena are, its a matter of fact, oliaerved. VVattfr

¥t<i. ss.

051^-; ft

100

PRINCIPLES OF INORGANIC CHEMISTTJY

again makes its appenmnce, anrl the oxide of iron passes into
This, it is true, does not look like ordinary iron, but has the ap;
ance of a black powder. Tbis, liowever, is due on5y to the fact
the molting point of iron is much highei* than tho tomperatxire j|
ia roachod in the bulb ; the ii-on jjarticles, therefore, cannot unitfl
coherent mass. If, however, after eooliny, the contents of the
are taken out an<l rubhed with a smooth, hard abject, the mel
lustre and the grey eulonr fif iron are seen.

Tht; interaction between iron and aqueoua vapour can, there
be reversed, and if we write a chemical equation in the form

Iron + water vapour = iron oxide + hydrog^in,

it can be read in eithei' direction, the substances on the left h
capable of being converted into those on the right, as wei
conversely. Indeed, more exact investigations have shown that i
of these opposed reactions can take place at the same temperature,

99. The Chemical "Forces." — Such a behaviour is contra^
to tho notions aliont '• displacement," indicated on p. 85. S

In the sense of this thccn-y, the force between iron and olj
must, acconling to the experiment described on p, 83, Ijc greater I
that between hydrogen and oxygen, }>eemise iron dectimiwses
water. C'onveraely, according to the experiment on p. 99, the f
between hydrogen and oxygen is greater than that between iron
oxygen, because hydrogen decomposes the oxide of iron.

Since it is irajwssible for both propositions to be correct at
Bame time, it follows that the tlwun/ which leads to these propoait
must be false.

100. Mass Action. — As a matter of fact, the investigation of
and of fiimilar raaes has shown tliat not only the nature an<l, say,
temperature are the determining factors for the occurrence of a thew
process, but also tfw ratio nf t/ic suhntnnces present to the tjireit mlum
the wnrenlnilwiif as well. In the present case, the water vapour \
on the iron till a certaiu amount of it has been converted i
hydrogen, and a definite ratio between the hj'drogen and the wi
vapour obtains. Conversely, iron oxjilu is decomjxMcd by hydro
till a definite ratio is established betiveen the hydrogen remaining
the newly Ibrnied water vapour, a ratio which is the mme us
proditr.ed by thr retvi'sc method.

A mixture of hj'drogen and water vapour corresponding to 1
ratio acts neither on iron nor on iron oxide. The ratio is, moreo'
also tlependent on the tmipenitmr.

The two apjmrently opfmsed experiments of p. 8.'^ and p. 99 j
ceed as follows; — If iron is heated in wat("r vapour a ^^t/ww of
latter is decomposed, and a eorroaponding amount of iron oxide fom
The gas mixture, on being cooled in the pneumatic trough, loses '

HYDROGEN

101

• njiour it coDtains, which aeparatos out in the liquid stiite, and
' hvdrogcij is collectetL This is ihe exijeriment of p. 83.
1 On ihp other hand, if hydrogen be conducted over hot iron oxide,
rtcou i>f it etitii bines with the oxyg<-:ti of the lattor to form water;
«ij*r jtortioii uf the hydrogen renifijiis unchanged, Oii passing the
anre tjiruui^h the colder [«irt of th« hnlb-tube the water sepamtes
> a liquid and Twcomes visible ; tlie remaiuing hydrogen escapes
uticcd In this way the notion Atisee that in both cases entirely
«ilr rcictions take place.
101. Chemical Equilibrium. — Where two opposite proceeaeB
ntally hmit one another the state is called one of cfmmmil fqnilihnnm.
Whnu formerly the ■view was held that such a tiling occurs only in
ilBppliona) cases, there is now^ roasniL to ^issume that all chemical
lead to an equilibrium. In many tases of chemical oqiult-
however, the concentrations of some of the reacting substances,
ling to equilibrium, are so smalt as to escape the ordinary
detection. The impression is then produced that the re-
I tekes place only in one direction.
A long historical development lies buried in the statement, that at
• p^en lemperaturo chemical equilibrium is determined by the
of the reacting substances. For, although the fact that
l^ontity relations of the re.-ictiiig substances exorcise an important
the chemical eijuilibrium had been already known for
years, it was a very long time before the correct form
for the law which obtains here. From the usual name,
m* tekm, one might conclude that the mass or amount of the
acto^ sub»uuices is the determining factor ; this, however, is not

^^H^t OB xxQVf suppose a state of equilibrium established under given

^H||ms between the substances ju.st considered — iron, iron oxide,

H^Hp, and aqueous vapour. Push, now, a partition into the

I *MBiin wluch the above substances arc contained, so that a p&i*t of

tkaixed g»se8 is shut off from contact with the solid substaitees j no

ffany in the equilibrium can I>e thereby produced. For the gases

VQV ia et|iiilibrium wiih one another and with the solid substances,

•d «qiutibrium in a uniformly filled space occurs <i( cti-rif jmnt, and

(■■B^ therefore, be dependent on the size of the space filled. By

tie Hfiuation here imagined, however, the ithsoiuie amount of the

fm m e({tulabrium with the solid substances is chunged. Th(> ahso-

tamoanls cannot, therefore, be determinative for the equilibrium.

tfae iteparaticn the gases present have been sepiratod in fhf

since tljcy were unifonaly distributed thiougli the

otherwise no equilibrium woidd have taken pliM;o. It

fT tuiumiii^, or the ratio of the amounts, nf the

th-. Ite erjuilibrium.

Tb» Jumpiest jitid taoHi appropriate expression for the t\uaut\U'

le non-e&sential, nbsohite
WM< nJitmr, or the n>H'-^»fmtuiiis
Th» is Uie expression which nai
'MR a«« from tins example of what]
na^TutaJefi is, hy which we exprcasj
owdopWfTit of the theory of chemical
•pmA Oft the fact that the concentra-
' «■« Bitroduccd fis the rletciTniniug
ictwapts bad been made to find the

Sabst&nces on Chemical Equi-
ps irell tho special la^- that 'Ac

I ■■■■y i'li fheniifnl I'quilihnum. For
- ^ e'^pressed hy their extcnsities,
-■^uri' and the temperature
\;iiit ihat it is of no account

-.,-_^.^ iwB, aijueous vjipour, hydrogen, and

V iiKliflerent ho^v much of the two

.*. liuu I'Aide, is present, and in what pro-

'.^tf* wmowhttt stratige, and was formerly,

abt One can convince OTieself, however,

>» hv {hn siimo course of reasoning as we

^' v<Jf the gaseous portion ; if equilibrium

iiim>t lie altered Uy » spatial sepiration

' ih is in equilibrium from the other.

' with more simple cimea of the same

uor !ind ice, or generally, between a

- An at the temperature of fusion, is

tMnoiiiit in which the two forms are

.' holds for the equilibrium between a.

UluMvise, also, in the soniewhat lEore

■ iitii between a solution and the solid

■ ■!! IS saturated.
1 1- \'HH piit forward the general expression,

•;ui fpiiions of the mmr Sf/fitcm the absolute
M thvottnl, bvt only ike ronrmirafmis urithin '

^^yt^ FIftine. — Tho large amount of beat set

»■ .■irrii canses the tcmperatme of the

unt. In the ciiso. of combustion in

Ml liigh, since the heat is distril)Ute«I

■ < til). Much higher temperatures

WATER

119

propertT** in ciystak which can vary at all with the direction are

ilcpewlent on this.

in contrarlistinction to the tTystalline substances which possess the

peealtarity jiist mrntioned, there are the nmorphyiis substatices in

rUch ihiit |iecuh;iiif_v is Hot preaent. Gliisa, for example, is an
laaqthooB substance. Two rods, cut in any directions out of ft
; kpr piece of ghisa, behave in all respects identically when they havo
thiwae shape. On the other hanf], two rods of ice, one of which is
«t, «•?, perallet, the other perpenrhcular to the face of a naturally
{onn«fl sheet, behave differently ; for example, one hieaks much more
■sly than the other.

The crystalline nature is seen most clearly in ice which has been
ikkbftucanie ite shape nndisturbed. Thus, the ice on the surface of
Intfling oiaaaes of water first forms in long needles, joined to one

Fli>, *».

[■mct at an angle of 60 , and the ice flowers on window-panes are
ftfviK an expression of the crystalline nature of ice.

j^ .^ .-I however, of which snuw consists can fonn in the
IcMt (li<-° latiner, for they form floating in the air. As a

nle, sertAwly, tiiese crystals are small and indistinct; under certain
flPoaaMtaocut, however, they grow so large that they can lie seen
vidi lb« iviktMl «ye. They then usually appear as flat star^^ developed
»*f«H!lH; to a threefold tvnimetry. Some snow crystals are shown
h Rg. 49.

Tbe pfwporty of occurring in crystalline shape i» a very wide-
tflmd peculiarity of solid stdistanees, and the formation of crystals
■aj geaenUy \ve denoted as a property of pure substances. The
■tat«, on the other hand, is confined almost entirely to
The crystalline form is an ini[iortant characteristic of solid
and we shall repeatwlly have an opportunity of discussing
»t later.
|'8vp€rcooUll{^. — The formation of ice in water which has
t«j 0 d'.es not necessarily oc^^Hr. On the contrary, with
water can be cooled to several degrees below sero without it

:>T / -'

(it
eh
ill.

•i iisu.i//.'*

-. :-.-r;il)le «/ » *

:;.iie.l. J/"

• •••■lit (jiiitiir 1 *,

■ •.' Itv alu-nif -'

■ ..■<, luiwovoi', r '

■ i'V alli>\\'iri_i4' ^*

■ ■ .-lit, (»r l>y iij;''*-'
•■:i one aridtliei".

-- •■■.• to reiulor it .'i'^

:.• i'viiii^ vei'v wiil<.'
. -s .-ifc due the di-^'

■ ;.ii'tvl with the pi'<

- ■ -I.T is sliowii ill Fit

■liei' open at the ho

"iie tiihe fmiiished v

• n' withdrawal of the

^•;i'iiiiir arraiigeiiient thi

. ■'. yaised liy the iiitrodi

■■. tlie gas can l.)e rediu

• ■ ise, Imt it (hx's imt n

.'.'. of the hell.

.' amoniit uf water whi

■ f\>r sinail o|)cratioiis ot'

HYDEOGEX

105

dor iti-tule the vessel of water in such a way as to leave

pewe tilled with waicr (Fig. 39). The inner cylinder

the top or remain opoii. Li the lutter case the

doubled, but the complete expidsion of the gas is

Ii is the form which is nwst largely employed, and it

iiu-iple, more particularly, that the enormoiia gasometere

tttilattories are built

•bolder without movable jiarts, %vbich is largely ustxl tn

i«, i» shown in Fig. 40. To use this, it ia first filled with

d the gJis is then intnxJucod either through the tube h ov

ig tiic delivery tube of the generator

idas .<• In either case the displaced
through the latter. When
been filletl, the Uibulus *s is
> screw cap and the tap h also closed,
then poured into the upper vessel,
ing the Up u; water Aovts into the
subjects the gas to a pressure
to the height of the column
Under this pressure the gas
rhen the tap h h opened. When
gw is required, the taps w and h

I _

«burt tube jr, which is fumished with
Ha be used for filling larger vessels.
Ih> placed mouth downwards in the

tel vl water over the open end of fi«. 4o.

<;. On opening w and ;), water
own through ir, and a correeponding amount of gas escapes

v»ter-level r served to indicate how mtich gas is present in the

iw, when tlie laiter is not made entirely of glass.

Detonating Gas. — The Daniell Imrner is so arranged that

i;i»(i.s (^an only mix immediately before they are bui lied. If

mjiieti Uj previoiisjy mix oxygen Jtnd hydrogen, so a& to be

burn them from a single tul>e, it ia found that the whole

mixed gases instsmlly takes fire and combines with a loud

le resRel usually being shattered. This explosion ia very

will) somewhat larger qiiiintities becomes dangerous. One

re, avoid inflaming mixtures of hydrogen ami oxygen

ing suitable precautions. Sucli mixtures, called dctmnling

lway« formed when a freshly charged hydrogen apparatus,

partuilly hlled with ajj-, is put in usa If the gas which ia

vod be collected in small lubes and brought into contact

tne, ibc first samples behave like air and exhibit no special

Soon M g^ is obtainetl which tidies fire with a whistling

106

PRINCIPLES OF INORGANIC CHEMISTRY

noise, the fame mshing into tlie tube. These piieiionienii first bt
more marked and then weaker, and, at It-ngth, wlien all the ai
been driven out of the apparatus, the gas burns quietly just at
hydrogen does. ■

On urruimt of thr damjer of an exiiliisiori, one mugt neivr f»»m
in the ahofc maiiwr the ht/drmffn taken frmn a genfifitnr or t/ns-i
which /his sIwhI s«jw' iivir, to ^e if it ej:filo<lfs. Shotikl it exphjdf
gas m\iat be allowed to stream for some time out of the gene
until a siiinple in a small tube is shown, by its combustion, to Iki
The contents of a gus-holder mnst, without fail, be rejoetwl if
have assumed explosive properties. ■

The characteristic prnportj of the explosive mixture is seA
clearly by preparing a mixture of two volumes of hydrogen ant
of oxygon, and passing it into sortp-water, so that a froth of bu
filled with the explosj^-^e mixture is formed. If this froth be s<
fire (after the rest of the mixture has been removed) it burns w
report like the shot of a gun.

105. Further Particulars concerning the Combustioi
Detonating Gas. — While at comparativt-l}^ Iiigh tcinperutures
conibinaliou of hydrogen and oxygen tftkcs place with great viol
the two gases can be left in coTitact with one another at the ordi
temperature for a very long time without chemical action Uiking |
between them.

This behaviour changes when certain metals are introduceii
the gas mixture, and in this respect phlmnm (p. 60) is the l
effective. If a piece of j'»/v' {ilntinum loil be allowed to project
a tube containing the explosive mixture standing over water,
volume of the gas quickly diminishes, ami in certain eircumatance!
platinum becomes so warm, owing to the heat of combination, th
glows and causes the exjilosion of the mixture.

Since the platinum foil, being a solid substance, can act only a<
surface, its effect increases as the siu'face is enlarged. Platinum
be obtained, l»y means of chemical reactions, in a finely divided, spc
state. Such s/k>ih}s/ philimim very quickly becomes incandescent in
explosive mixture and causes an explosion.

To nioderato the reaction, the sponsfy plaUnum, in the form (
powder, is mixed with clay anti formed into balls. The mass acte<
by the heat profhiced is thereby increased and the temperature 1
lower ; these balls, therefore, effect a faiily rapid foi'mation of w.
from the mixture of oxygen and hydrogen, but not ignition.
Apparatus in which this phenomenon can be well shown is represet
in Fig. 41.

Many other raetala act in the same way as platinnm, moal
them, however, only at a somewhat higher temperature.

TliB platinum, and no less the other metals, undergoe-s no cba
during this action. Also, a given small quantity of platinum

HYDROGEN

107

con%*ert unlimited amounta of the explosive mixture to water ; the
action of thfi platinum, therefore, doeR not, as in the case of a cliemicaL
combination, take place in defitiite proportions, but is imleptmleist of'
th.e relation between the amounts of the gas mixture and the
platinum.

ReactioHB of this kind occur very frequently in chemistry. Not
only can other gas mixtures be caiii^ed to entf r
into ehemitvil reaction by meaiis of platinum
and other metals, hut h'rjuid and gaseous sub-
stance also can exert »uch actions in Hqiiidii
and gases; by means of those, chemical re-
actions which do not or do not appi-eciably
take place without them proceed rapidly, and
the acting substances can cnuae unlimited
amounts of the other suliatances to react,

106. Catalysis. — For the sake of having
a short designatioii for these important pheno
mena, we shall call actions of this kind aifnliftie.
The sii1>stanee, through the presence of which
the action takes place without itself passing
into the producta of the reaction, is called the
eaial^ic subftanrc or ea/alif»T. The process
itself is called mfnh/m.

To gain an understanding of these pheno-
mena we recall the consitleration put foi-w-ard
on p. 65, according to which innnmeraiilo sub-
stances, lietween which chemical refictiona could
occur, can remain in contact with one another
without our being alile to detect smch actions.
At that time it was explained that the most appropriate interpretation
of these facta is that in all such cases the possible chemical reactions
do, as a matter of fact, take place, bnt to such a small extent or with
such slowness that they cannot be detected In a measurable time.

The following shows that this vie-w is ijuite compatible with the
universal experience. By time measurements of the progress of many
chemical reactions, the approximate nde has been obtained that the
velocity of chemical reactions is, on an average, rloubled by a rise of
10" in the temperature. That is to say, if a reaction at a given
temperatiu-e re<juires, aay, a tjUartcr of an hour to reach a certain
point, at a temperature 10' higher it would require only 7| minutes,
and at one 10 lower 30 minutes. If the temperature is lowej
100 a 2'* - 102t times longer period is necessary, or in our c\amj
about 1 1 days. On descending fartlier 50 or, on the whole, 'Uily '
moderate atnount of 150', it woiUd be a year before the re-iction h
proccefled so ftir as it had done in a quarter of an hour at the tighi
temperature.

Hir.. 41.

PRINCIPLES OF INORGANIC CHEMISTRY ch

It agt'ecs, therefore, very well with general experience to r
the liossiUe chemical reactions in the cases mentioned as ut
occurring, and escapiiig detection only through their very
velocity. So also the height of a. hill or the form of a coast ap
to UB as something definite atid unehanyeable, although we know
every hill is unccasiniily l)ecmning lower, by the gradual falling
of the rock of which it consists into the valley, and that ■
coast is changing its shape under the action of the waves.

Sul/slancfS liif whonf jtresence dttwhj occurrint) rmdions arc tiaxlt
are tleMt/ntrkd us positive attuJi/^ers. Since we are dealing here only
L'haiiges in tho velocity of reactions which would take place in
case, these catalytic actions lose to a great extent the quality o
expoctednoss which at first sight they appear to have.'

To obtain ii picture of the way in which a catalyser acta, imag
wheel-work in which the axles move with great friction, as a n
say, of the oil having become thick, and which therefoi'c runs i
only very slowly. If a little fresh oil be placed on the axlea
%4^heel-wo!k forthwith runs liowti nmch more quickly, although
available tension of the spring (which corresponds U) the work (
aVile from the chemical roaction) is in no way altered by the oil.
fiction of a catalyser may be compjired with that of the oil in
respect, and also with respect to the fact that the oil is not used t
acting.

We shall soon have an opportunity of studying other peculiai
of catalytic actions. ^

' B<;»i<if4( the jj(«irti¥ cativlyiers (ir ncMlerahtr^i, riei/atiee cotnlyserti or rttamir

CHAPTER VII

WATER

^- — ^The product of the interaction of oxjgeii mid
en. or the conifjound of tbese two elements, lias sLown itself, in
kCions of this point which have been made, to he identical
I waier which we tiud so very widely distributed in natui'e. In
with the law of the identity of the properties in all
oi a given substance, n-c may proceed to t\ scientific
arwtigalion of water with that which occurs ready fomied in nature,
vx luring first to prepare it for this purpose from its two elements.
Water i» one of the most widely distributed substunces in nature.
1 ody arc f ths of tlie earth's surface covered with liijuid water, bat
•tmosphcrc also t;oritaitis enormouB quantities of wraer in the
KtAte, antl in the jiolai- regions »nd mountain heights fiolid
fiUrtaJcrs »ii essential share in the structure of the earth's surface
hiddition to this the solid fmrtion of ihc< earth's surface is every-
vfaic pennejited with water; water is indispensable for the building-
^<<fllie vegetable and animal structures, and whore organic life is
I (ben &l8»j 15 water present.

I<t* Preparation of Pure Water. — Naturally occurring vvater

\teitt quite pure^ since it always comes into contact with other

w* and partially dissohes them, The preparation of

fly" pure water is an impossibility, for the very reason

CTinnot exclude vessels of some kind, some portions of

in always be dissolved. On the other hand, it is not a

vorj' great difficulty to prepare a water which, towards

behaves as pure.

mcthfid moj^t used for- obtainiuy such a water is to convert it

ly into ntfX'iir. The impurities present in natural water are,

ftie inri*t part, not nieaaurably volatile at the temperature of boiling

f, IIK) , and therefore remain l>ehind when the water is converted

' npour. Some occasional impurities, however (eapccially ammonia

fltfbonic scid^ are wiore volatile than water; they pass over,

almost entirely with the first purttons of the vapour.

]09

lae

PRINCIPLES OF INORGAI^^IC CHEMISTRY

Wftlcr Vlnxrtir

In gin.

4-11

S-4

127

17-1

22-8

tains, on an avei-age, only ttree-fonrths of thia amount. The
varies with the state of the weather, and one speaks, therefore,
or dry mt. Still, air which is called moist scarcely ever con
Biuch uater vapour as it could contain, and air which ia c^Ud
may contain as much as half the maximum amount.

The cauBo of this lies in the grejit vnrialileness of tlie vapouj
sure with the tcmpeniture, as is seen from the following tji1>le,
giv«s the amount of water in grama contained in I cc, of air
saturation point.

Temperature.
0"
6"
IC
16'
20'
26'

If, at one jpoiut, the aii' has taken up as much water vapo
corresponds to the vapour pressure, and it reaches a pluci; ivhc
becomes warmer, it becomes unsaturated, i.e. the coneuntratio
water vapour Jn it is smaller ilian corresponds to the ecjuilibrium.
the other hand, if the air falls to a lower temperature, part oi
water separates out in tlu- liquid or solid form, as dew, rain, or »
and on being heat*>d aguiii to ita former temjwrature the air ]» t
unsatni-ated. The diH'erences of tenipeniture, therefore, at the ea
surface continually act so that the air euntaina less w-ater vapour
corresponds to saturation, and for thia reason our atmosphere is n
completely saturated with water vapour.

The presence of aqueous vapour in the air i.^ so far of import
to the chemist that ull objects exposed to the air take up more or
water, Not only do substances which are soluble in water, sue]
salt and sugar, become moist in air containing water, but
insoluble substjmces, such iis ghss, stone-s, metaU, textiio fab
become covered with a thin film of water, which must, when neeew
be taken into account. The amount of watir taken up depends on
nature of the substance, and is, for the rest, proportional to the siiri
Bodies with a ];i.ij;e snrfaee, powders and cellular structures, aucl
are produced in plants, take uj> a specially large amount uf Wat
•responding to their large surface.

* This water does not have the properties of litpiid water.
only does the object not feel wet, but the nipour jfressure of this i
face-held water also is lower than that of liquid water at the 8)
temperature, anil it is all the Uiwor the smaller the amount of wj
on a given surface.

Ill many cases it ia necessaiy to remove this water. For examj^
to obtain the exact weight of a liody in powder, it must bo weigl
without its film of water. The most simple means of freeing the bc

WATER

127

=,&

liita ooosists in ii/uUintj it. for, as the temperature rises, the

pmsuro of the surface water also increases, and the hitter

ioU) ibe rehitively dry, hot air. If, however, it is not

o»»hle to raise the temperatiire of the body, it is drieil by being

in dry air. For this purpose ghtas apparatus, c^illeil df-siceatrtrs,

iw«J, Vi^. 53. They coritaiii ii substance which combines with

aiul withdravTs this from the iiir. Into this dry air there again

itcs wrater fmni the substance to be dried, and this procesft

too until the ^'afH>^I^ pressure

&t«r on the siib.st{ince has

Its axnuU ns that of the

In combiiicsd with the desiccat-

[fubitanoe.

M such desicuating sub-
liavelj«en pruriously men-
fp, S8) ; others will be

doMd a» occasion serves. ^

Stnoe th« drying process, as j^™. mi.

nr drscrilied, JejH-nds on the

nf tbe Witter vapour from the body to the drying substance, it

placi* ;ill the quicker the more rapid this movement ia. If,

e, wtf till the dosiecator with hydrogen instead of with Jiir, iho

will dry more tjuickly, because the diHiisioii of tlie lujneous

takes place more quickly throujrh the lighter hydrogen than

the heavier air. The drying, however, jiroceeds most quickly

I tkc tie^cc.itor is exhaiuited, because the movement of the aqueous

ir tbcn takes place without any hindrance. It would be a mistake

imfpmv ibat the substance could Vw brought to a hii/hfr deijree

[dljlMK ill an exhaui^ted demceatar thtin in one containing air; for

f tBpuar pressure \& the same whether air is present or not. The

viaie dtfrr«iice ia one of rapidity, and in a given hmiifd timr a

iK^KUoce wonld certainly become drier in an exhausted desicciitor than

ia«*r o^nt^ining air.

Wenitst alwj take intoconsitleratiim here, that aa the body becomes
: ita Txpatir pressure dimitiiahes. Since, now, the parage of the
to tic desiccating sultslance takes place all the more quickly
if^tttler ll»«3 concentration of the water %'apour, there lies a retard-
n^ factor ill the progress of the drying itself. This is a universal
pbagmeoon. When any state of equilibrium atrivea to establish itself
filkarertain velocity, this velocity diminishes in the same mejtsure
of c}iiilibiiijm is a|)proachod, for, in general, the velocity
process is projMirtional to its distance from the jtusitioii of

k.
_ other tilings it follows from this, that, strictly speaking,^
■te of equilibrium will be reached wdtf itj'Ur an injiintdif itm^l
Sioioe, however, our means of measurement are of limited

112

PRINCIPLES OF INORGANIC CHEMISTRY

has the form of it tiihe lient rotiml liki- a screw, and is mfuie of
tin, because this metal is practically not attacked hy water. It st
in a larger vessel tli rough which w.-itei* is, allowed to flow, in this
also from below upwards. The warm water which passes out at
top may be snitjibly used for feeding the atili, so as to recover a
of the heat. Such a.n apparatus is repreaented in Fig. 44.

To demohstra.to the effect of distillation, a quantity of watt
eolourod with ink and distilled from an apparatus, such as is ^how
Figs. 42 rtiid 4;l The water ftasses over colourless and tAstelese,

109. Properties — Colomr. — At ordinary temperatuiea w
is a transparent, colourless liquid. This absence of colour, howe
is only apparent ; in thick Inyers water exhibits a distinct, fine 1
coloration, which is peculiar to pure water and is not in any way
to admi.icturos. The blue coloration is produced owing to the
that water alisorbs yellow and red rays, i.e. converts them into h(
when these are withdrawn from white light the complementary co]<
blue, remains. This blue colour is seen in lakes and seas contair
very pure water ; in most cases df natiu'ally occurring water ii
masked by the presence of coloured admixtures.

110. Density. — -A.s hiis already been mentioned, the densityof wt
bas been made equal to unity, the unit of ma.ss, 1 gm., having b

fc.Aacribed to the unit volume 1 ce. of water." This numlwr, howet
holds only for the definite temperature 4", since the density of wai
like that of all other substances, changes with the tcmporatiu-e.

In the case of water this change occurs in a manner cssentis
dilferent from that in the case of other substances. On heating wa
from 0 upwards the density does not tieereasef as is usually the cs
but it imrfti.<iis. At V water atUiius it« maximum density, and thii
the reason why this temperature has been chosen for the definition
unit density. From 4 onwards the density of water, as of all otl
substances, decreases with rising temperature, and a.t 100' amounts
about ^^th less than at 0". The extensily, or the specitic volus
behaves in the revei*se manner ; it has its smallest value at 4'^, Mid
all other toiTiperatnres Its value is greater.

The following table gives a summary of the relation betweea t
temperature and the density and exienaity of water ;■ —

d f

0* 0-flOS)S74

4* 1 001)000

10° 0-»9ar;iB

20' o*ni»s2ri2

40* 0 1l»233

60* (>-»S8ia

60° 0-983ai

70' 0'97790

80° 0'»719l

90'' 0•l>6.^5f^

100' 0'»5863

roooi27

1-000000

1 oofiL'sri

l-OOlT.'il
] 001311

J -ooTTa

1 •01201

i-oiflur

1 -02260
102S1>0
1 03,^71
1 -OWIB

WATER

113

W 20*

W 40' SS*

Fto. *."i

SO* JO' 80' SO' je&

c «*tn<j relation rnii he represented by the geometiical method
^>tA on pi. 74, the temperatures being tiiken as abscissae, ii>ul the
(lUifiMty n^ ttnliiu>t«'3.
In this war we oht»in
Fig, J.T, uhich repre- ?2
ibf relation of
ftloiue Ui the tern- '"

dacreaae in the

between 0* 06

sn small that

ilie ri' presented

figurtf. it 02

ciu«e u lu>veriii^

•e by oj.ly ^^
To repre-
the scfile of t*m-

na well :t3 tliai nf volumes, mitst lie considerably increased.
14c dingraia would be itlttained by takiug the tempenitttrea ten
aad the volumes u. thousand times, na great. Our drawing would,
•, thetN:by ln'ctjmu much too large. If, however, we eximiino
!• with regard lo tiiiit pi>rtioti which interests hb juat now, we
tJlai (here ia & large enipty space between the ciu've ami the
line. We can leave this out, and instead of the base- line
UiiU|iuiuiin<; to the rolnnie zero, we ciiTi cho<»so another near the curve
For such a purpose it is well to choose a line corresponding to
IO*.H»<). Oti this line the temperatures are marked ott'
ten limes larger than before. Peq^endieular to it there
i\tA off, not the volumes themselves, but only their differences

value 1-OilOa
tkis way Fig. 46 is obtained. To render the measurement
t^ n'hole field is divided by a rectangular network. In a

manner which ia
readily intelligible,
the numerals pkcefl
at the edges allow
of the extenaity
corresponding to
each temperaliire,
and J'ifc irmi, being
rejid off. The figure
j(f* is repeated only up
to 10 .

1 1 L Tlie Law

.ty.^ — In the table on p. 113 only the densities and volumes

to certain definite temperatures are given. The c^ueation

M I I I I I I I I I

( —

9 I

Pl». 46.

ittling

PRINCIPLES OF INORGANIC CHEMISTRY chap.

now arises as to how the inbeTmediate values, for which thare are no
data, can be ascertained. For this puqxjise use is matle of a general
law, the appiicatiiJti of which is so familiar tu ws that it appears
axiomatic?, although, like all the other laws of natuce, it is a Bummary
of mariifold experience.

The law in tjueation is called the law of «»t/tn«i/y, and is to the
following effect : — When two magnitudes change simiUtJineously with
one another, so that for a definite value of the one theie is also always
a, definite value of the other, ilm: aimutfatitoux (himgr^i alicat/s leiiMUi
pfDpuitiuiuU, When, therefore, the one mi^itude isallowfd to jncreaee
continuously, the other alao increases eontinuousJy, and if the one
change is madu smaller and smaller till it liecomea zero, the change of
the other magnitude also becomes zero.

It follows frora this that when two (not too remote) values A| and
A.^ of the first magnitude are given, to which there correspond the
values B, and B.^ of the second, the values of B, corresponding to values

iiit«rni(HJiat43 between A, and A„

lie between B, and B.„

If tlio values A, and Aj are sufficiently close, one may even assume
a jfropurrlkmaiiUj between the two series of values. If Aj; is a value
intermediate betwoen Aj and A^ and Bj; the corresponding value of
the other magnitude, we may write the following equation : —

A^^A. . Vllr
Aj - A. B, - b;

from which we find B^ to be,
Bx-B,

li:ly\-^.)-

Thin foj'niula allows of the calculation of intermediate values which
have not been detcntiii)c<i, from the measured values on either side of
them. Jt i« all the mote exact the closer the measured values are to
one another. If in any given ciLse it is not exact enouf^li, it can be
n^jtlac!! il by a nwire complicated fonnula, which also depends on
prinri|>|«.' i>f continuity, which, however, will not be deduced here.

'l"hc proceesa which we have just described is called iiikrpohti.
The metiuid will be familiar to tlie reader from the use of logarithm
tables, where the values of the logarithms or nutnbeis not given in the
tablcB are <>btained from the adjacent ones by means of such a calcula-
tion by pruiioitiun.

It lies in the nature of what we have just been considering, that
the method can be ueed only for oblaining whriwdMU values, and may
by no means be extended beyond the region of measurement. Such
methwl^cjr^ra^w/o^fW— is a|iplieable., at most, only in closest proximi
to the last point measured, and readily leJids to errors if extendi

WATER

133

il«; pressure had been estublished automatically by the freeaing

ittle water. Since ice has a, volume -,\th greater than that of

tbf solidification of a. atnjill amount in the closed sjiiicG is

It to prodnco ft very considetalilc pressuro.

Thi* peculiarity of ice of melting und<?r pressure has a great

oil thp meteoroloj;ieal and geographical properties of solid

When two pieces of ice are pressed against one another they

lilt ih«i surface of pressure ; the issuing water which escapes from

forthwith solidifies again, and the two pieces of ice are

>gether to a whole. Thia is the cause that loose snow

It masses when it is pressed. As ovary one knows from

owballs, this cohering of the snow occui's all the more readily

its temperature is to the tnelting point; the reason of this

fmoi what goes before.

Thm same peculiarity brings it about that the snow on the tops

moantains gradually pi.sse3 into n^-^s. It also efTecta the

pfcenomenon of the fiowttig of i/litderg. As h known,

m-BUM€S move slowly d&wuwanls from the heights of the

to the valleys, as if they consisted of a semi-fluid mass.

^iidqe to the fact, that at all fuirt-s where the ice-mass rests on the

I a lti|iiefactioii lakes place at those points which are under the

pre&sure, and this causes a sliding. The ice behaves like a

*jr with aututuatic greasing, and so sct.s itself in motion under

ipreBuro-

* It b tau^y to ctmviriee oneself of this pi-ofjerty )>y pressing lumps
[*t toother if! suitahle moulds. Even when the temperature i&
By kept below zero the lumps unite to form clear masses of ice,
L^ HI] ^,1)1 the moulds like a metal cajit.

is do not Whave iike water ; in the ease of almost all the
meg p)im becomea huiher and not lower with innriiKt: of pn'SS}irf..
' fSktracf lies in the fact that water, .'is contraste<l with other
«?p.rti</.« on solidification. Sidjstances which have a smaller
ia Ui* solid state than in the liquid exhibit i /■«/' in the melting
pretfcAiire
States of Equilibrium — Law of Reaction. — The relation

1 th* cliarjge of volume on solidification and the shifting of
Ipaiunf solidification with the pressure is not a chance one, but
•itjr. ll ia a case of a universal law that holds for all statjes
iiun. It can l« expressed as follows : If a sij^ttin in cijui-
ii mbffdfd fcj « amstfiwit l>ij which fh<: i-tpnlihrinm »■< ihifftd., ft
Aii'i pUttf which npposfs the ronsfraint, Lt; dm b>/ which its effttct is
dairvffd.

Ijr tfaJK principle, now, to the presetit case, in which we have a

of ic« ami water at 0 in equilibrium. If we exorcise a

on the mixture hy diminishing its volume the etjuilibrium is

and a proceis must occur by which the pressure ia agam

PRINCIPLES OF INORGANIC CHEMLSTKY

rnAi*.

puirtially relieved, i.r. by which ii diminution in volume ia prodticeJ.
This consists in ke melting, for liijuiil water occupies a smaller space
than the ice from which it is producetl. The melting point of w
must, therefore, sink with pressure.

If, on the other hand, the volume diminishes on solidification, this
latter must Ug brought about by increase of pressure, Le. the melting
point rises i^-ith the preaaur<'.

The foundation of the above- stilted nniversid law, which has a
manifold ftpplicatinn in chemistry and physics, lies in the conception of
njtiUihriuiii. By wjiitlihrium we nnderstanr! ii statu which u^nds to
re-establish itself when it is disturbt'd, This tendency finds exfircs-
sion in the occurrence of phenomena which seek to reverse the
disturbance, and the getioral expression of this tendency is the l»w
enunciated above.

* The term equilibriuni is, as is known, derived from mechanics.
There it is usual to distingui.sh three kinds of e([ni]ibriura : stable,
unstjible, Jiud indifferent. In chemistry the conception of etjuilibriuoi,
jis is apparent from the definition just given, is applied only in the
form which correspnndii to staUe equilibrium in mechanics,

130. The Triple Point. — On applying to water the rule just
enounced, that increase of ttie phases runs parallel with the diminution
of the degrees of freedom, we come to the conclusion that it must cer-
tainly be possible (o have three phases of water side by side, but thai
such a sy.stcm htis no degrees of freeilom left. It can, therefore, exist
only at a definite temperature antl a tJetimte pressure.

Such a possibility does, as a matter of fact, exist when ice anil
water are introduced into an empty space. The space then l>ecome»
hllfd with aqiieous vajJour, aitd we have ice, water, and vaiiour side
by side.

The proSBtu'e is, in this case, equal to the pressure of water at 0'
viz. 0-4 cm. niercnry ; the tom|jerature is very nearly eijual to O',
It is not exactly equal to this, for 0" has been defined as the ruelti
jmint of ice under atmospheric pressiu"e ; under the pressure of 0
cm. prevailing here, which is almost cvactly one atmosphere less, tha
temperature is therefore - 0'0073 (p. 132). The pressure is, accord-
ingly, a little higher, but the difference doe^ not affect the h
decimal in the number stated.

JVfc.w rtrf the onh/ ru/TJ6!f of (cnij>m\ttirr. and pffssttre at itiiich tkt
three phasrs of lealir can f^i^t side hy side, and any change of ont
of these values causes the disappearance of the one or other phase.
H the pressure is raised, the vapour disappears ; if it is lo^vered, thej
water disappears. If the temperature is raised, the ice disappears;
it is lowered, the water di-sajipcars.

!>uch an [nvarialile point, in whicli three phases of a substance
exist side by side, is also called a Mpk point. Speaking generally
every substance will pos-sess a triple point situated in proximity lo

VII

AS'ATER

135

Vtn, M,

the melting point. Since, however, the melling points are scattered
rtver the whole range of the measurable temperatures, so also are the
triple (Kjiots, and ma,njr of tliese are accessible only with difficulty.

131. Vapour Pressure of Ice. — As ha« been experimenutlly
anti theoretically' |irt>ve<], water anrl ice'have the same vapour pressure
at 0". It iiniouuts, <ih ulreiuly stated, to 0'4 cm. mercury,

We may, however, iiak how the \'apour pressure of water roolett
lielow 0 is related to that of ice at the same tempemture. This is
explained in Fig. 66. The temywratnte is measured on the Kiseline ;
the vapour pressure curves of the water and of the ice are dejjoted by
'f and i. At 0 the two lines cut :
»t that, points therefore, the vapour
prcMore uf both forms of the sub
HUiiioe water is the .same. To thr
left of this IB shown the vapour
pressure ciu'vc of the supereooled
wAter OS an unbroken continuation
of th«t of the warmer water ; it
lies above the vapour pressure curve
of ice. At the same temperature,
therefore, supercooled water has a greater vapour pressure than ice.

This iu the reason why supercooled water citnnot exist in contact
with ice. Imagine a two-jimhe4 tube. Fig. 57, filled at v with water
and at i with ice. At 0 the whole will remain in rest, since the
vajiour pressure of ice is eqjial to that of water. At temperatures
below zero, however, the pressure above the water is greater than that
above the ice. Vapour must, therefore, be eonstoutly given off liy th«*
water and l>e taken up by the ice, and this can cease only when all
the water has become converted into ice.

VVc can now enounce, the general primiple : T/mt whifk is in cqni-
lAfiuiii in oiw way must Ijc in eiiuilibrium itt. tvenj way ; and Unit which
in <w<! ittty is not in etptiHd'nyw mv in ih> wrnj ht. in equilihrium. If,
therefore, tec and supercooled water are not in eqnilibiium as regards.
their vaijour,*, neither can tliey Vte in ef|uilibrinm v\hen they are
in immediate contact, and in both cases the transformation must
occur iji the same scjise.

The pi'inciple of which we have just made use is of the greatest
import&nce, and hua a very varied application. It ranks along with
the principle of the conseruition of energy, and,
like it, can be deduced from the impossibility of a
perpeluitm mohilf. Whereas the latter principle
denies the possibility of creating enerf
nothing, the former principle denies
bility of stitinij in moiiot), }&r ih<' pi'rfi
'iWriSr, fwiffT{ uhick is at rest. In this way, also, a /wr/v/ftt
would be possible, as can be re^idily seen from isolated t

134

partially r*
This consi
than the »■
tiiftsi, trhnrii' ■

If, tja Uje I.I
latter must l»»i '
|ioiiiL riaes with

The foil-.-
mauifoUl H}<, '
j'ljuiiihTiuw. ii
le-rsstnlilUh it*'
sion iij tbi! *i
!li«tiirlKiiic<:'. rf
i>nUUcLlttnl '

* Tht) ■
Thoro it i ■
tuist«blc, ;^iii'
ii« ia Apjittr'-ii
form wbic'li cm

1,10. Th©
enouncmJ, ttiAT

of tilt' 1 i ■ i ■

tain I y ■ ■
such H "tyi'i '
mily ai. a 'ii

Sucli -*
walor nrr i >
filk'4 Krilh
by sitie-

Tbo in
via. 0-4 ^

t^DQSTRY CHAP.

of the etiei^

kinetic onergjf

The Walter

beat. If it n'eie

. tt would ultim-itdy

ki not be iiecessjirj- tit

M f»/i/.i7r^. That this

dixi not, sfmianeoviif,

aw dfairtfd hf esqmiemi.

^firpefumt imhile of th^

■» ^ ^ntedi and a jvrpftHvm

^^P^ *1 rest wtHiM hare

^^Msibility of the forrocr

iM !*« itopi>sRiIiility ttf the

BMB wtiich fallim' from the

b fpito of its itppu>eni

«*5ic«*r, it allows of rmviiu

^Utonce* form Sf<lri(k'iii,

^ >•*. Tiiese still t?xhibit

-»«. I«i «l60 Oilier proijcrtied,

IV.' property of formiug

r -» djwnistiy, since cherai«J

i^ «tlMtance». The raii;^ of

* maeb. more limitod and

'Sfefittii of solnlions did not

-^et iitjd gasi's are rendprwd

■« fnK|uer(t prelimiiiariria t«

tfo jtarticipating siibstuncc^

VII

WATER

volatile does it take part in the vapour pressure, and then the toiling
point may fali throiigb the addition, altliough the pjirtial pressure of
ihe water vapour in the vapour raixture is always less than the pressure
of pure water at the same temperature.

For the rest this inHuetiije obeys definite and very reraarkabJe
Iaws, of which we shall presently apeak (Chap. VIIL).

The freezintf point of wakr m quite similarly affected by diasolved
aiilfitances, sinking jirofKirtionally to the amonnt of dissolved substance.
Tlii« law also, like tho foregoing one, holrls only for dihite solutions.

153, Relations between the Changes of the Vapour Pres-
sure and of the Freezing; Point.— The phenomena of the lower-
ing of the vapour pressure and of •
the freezing point, throuj^h disaolved
substances, are interdependent. As
wiis explained on p. 135, water
&nd ice at 0° are in equililjiiuii],
Iweauae at this temperature both
have the same vai>ou.r pressure.
If, now, the ia]>i>ur pi-essure of
mter is diminished through the
ihltion of a iott\g\\ aub8ta,nce, the

.utioD can no longer I»e in equilibrium with ice at O'', but only at a
perature at which both pressures arc again equal. If, in Fig. S8,
w represent the vapour pressure curve of liquid water and f tliat of
ice, the lajHJur pressure curve of a solution will, Recording to what
has been svid, have the position «, The identity^of the vapour
pressures of solution and ice occur."! at the jioint where the two curves
i and s cut, — in any case, therefore, below 0 ', — and this point will be
s<i much the lower tht; more the vapour pressure of the solution has
been ditninished, A consUnt relation, therefore, which is independent
of the Mature and amount of the di.sBolved substance cvists lietween
the lowering of the vapour pressure and of the freezing point.
SoUitinna which exhibit the mime diminution of the vafjour pressure
miiat also exhibit the same lowering of the freezing point. Stated in
mimliers, the relation is such that a solution whose vapour pressure is
I J nth less than that of pure water freez«>fl I'OS" lower than pure water.
The regularities which have been set forth here in the case of

H|M|aeoua eolntiooK are ni^t restricted to these, l»ti are,, on (/<*• mntrart/,

^^mdrerm/lif niHi.f for Ikpiiif lioltttion.-i nf t-rfrt; kiwi.

I 134. Chemical Properties of Water. — The reaction.s which

occur by the action of watei* on ctther substatices are, on tVie one

determined by the fact that it is a derivative of oxygen and hyt

to that it can give rise to other oxygen ami hydrogen comjHJiind

the other hand, water can combine with substances without the ei

tion of one of its components. Such compounds are called Ay*

from the Greek name for water.

1.16

PRINCIPLES OF INORGANIC CHEMISTRY chaiv

We }iave already become acquainted with some of the first reactions,
nfimely, those ivhich led to the production of hydrogen, whereby the
BUiratauces added combined with t}ie oxygen. Keactions whereliy,
conversely, the hydrogen is bound sijid the oxygen set free are also
known, and will be discussed !at*r (Chap. IX, }-

The compounds produced by 'the taking vip of kdh the eleruents
of water, which are called hi/dmlrs, are very various in kind. Many
of them am he agiiiii very readily resolved into their components ; by
ft rise of temperature, especially, water ia formed from them as vapour.
In the case of such hydrates it is usually assumed that they cojitaiii
the water "as such," in contradistinction to such compounds m do not
give off water. This method of expression, however, has no deh'nite
meaning (cf. p. 3D), and closer investigation shows that an unbroken
transition exists between the two classes, all the hydrates being
taipable of being arrsvoged in a connected series, according to tlie
ease vritb which they give ofl' water. The measure of this readiness
is the pressutv of the mpimr above these substances at a definite
temperature, We shall enter more fully into these relations at a
later point (Chap, XXI.).

^^'atc^, likewise, frequently exercises an influence on chetaieal
reactions through \ts two compotients, oxygen and hydrogen. Since,
for the reasons just given (p. 136), most chemical reactions are carritxi
out in aqueous solution, we have in all these cases the further possi
bility of the water also acting chemically.

This (-otisista, essentially, in tho fact that in cbejoical reactions
the elements of water can, at the same time, leave or enter a substance.
If hydrogen be conveyed to a substance contaiinng oxygen, tho latter
may cither tjvke up the hydrogen, or it can also lose oxygen, which is
then eliminated with the hydrogen as water. Likewise, a substance
containing hydrogen i^an, in contact with oxygen, become either richer
in oxygen or poorer in hydrogen, the oxygen in the first case
being simply taken up, in the second case forming water which is
eliminated.

The taking up of oxygen is called o.ndati(m : its withdrawn!,
redHCiion. In the sense of what has just Ixien said, however, tha
result of the oxidation can be a decrease of the hydrogen instead of
an increase of the oxygen ; in the same way, a reduction con result
in an increase of the hydrogen instead of a loss of oxygen. In
aqueous solution it is frequently not an easy matter to decide whicJi
of the two possibilities has occuri-ed. It is, therefore, generally agreed
to regard the hiking up of hydrogen also as a re<3uction in any given
case, and the loss of hydrogen as an oxidation. We shall also continue
to nse these expressions in the double .son.-ie,

135. The Quautitative Composition of Water. — The experi
ments describeti on pp. 9tt ft,, which demonstrate the composition
water from oxygen and hydrogen, ciy^Jji^^uitable elaboration, W,

WATER

141

I eoadactora of the first class. So gooq, howiiver, as tlie current

from a conductor of the secomi ctaas to one of the firstj in

wUrii H flows without the tmnsportsitioii of guhstaiK-o, an accumulation

I the lnuwp«>rtc<i substances muat occur at the junctions of the two

ion, Aiiil these substances &Q[mrate out.

TIba ilk u\itrr t/te fitfilnijen luoirs mlh iht jumiiir rlrrfrkift/, the

mth the nftintirr. At that point, therefore, where the poai-

« el«!rtricUy (msscs out, the mtlunle, hydrogen appeal's ; at the

Bl where the positive electricity

or where the negative

3ty passes out. the aiuxie,

fgm Kppcars.

In nnlcr to carry out the electri-

Jec«tn[)ositioii, or fUetrulf/m, of

therefore, the latter must

]tUocd between two niettiltic

whioh (rtcct the pjissage

llW current. Tlie ai>|>iirA{ias hiive

dtinvnt cnnstructioii, aeconiirig to

it parp»e in view. An apparatus,

{iQqiose of which is not U>

of the miMt advantageous

olysin f«»ssib!t', but of a con-

Bt demonsinuion of tlie \)V0- jlom- r

■61. in rejirfrtfUtL-d iti Fig. 5',l, £ ^P^ \

Tht water ' h contained in a U-

ub#, the liinl/« of which Jire fuirly

md cbMcil at thu top hy Uips.

iht lower p^irl of the tul)e

Uiiram wirrs are sealed in, and

iKmm" are attAclird two jiliiieM of

:u'jUk] by m^ans of which

I ciurent ia conducted

'lb*" liquid. At these jilates oxygen on the one side, and hydrogen

! other, are evolved, the gases asceniiing in the limlia and colleet-

emcftth the Uips. The displacetl lifjuid p,-issc3 throuj^h a tbinl

' for»t, and througli a rjbJjer tulve into a collecting vessel at

IV liirh can Ix- placed in any desired position. After the

I-*! gnnie time and a sufficient tjuantity of gaa ha^s been

iuwing fact* can be recognised: —

Ihr evolved fpises do not occupy the Asime volume. Do the coii-

^Bkt (me appcsir* in larger amount, and on making a nieasurenient it

"ifcomi that it^ volume i.s twice as great m that of the other.

' f*» OiM «t^icnra«it "lie tio«;s not usl- |j«re water, 'mt a "Ultilc wiltitinti of mtykarti
**i «r MitWt/ tmln. Tbr riinmlix Tnr lliin ami ii1si> tlu- nyvm i-inct illtcuuiioii of Die
WMM wltl W Kivcn »i I Ixtrr pniot ICIiap, IX.).

.:mistkv .hap.

» -i'.i- volume ratio «i

. '•.<\ty of wator vapour

.:;.ii gives the volumes

:■■■: in one j^ni. of wator,

• >. /;( ///(■ rtniiii'iiiin ri'tnli-

■ ■■•idl'OiJril irhidl li'i< //('/I

■j:to.s are as fuljows : —

:■■ • •■.\< vajxmr.

- .....'.. Keen canie<l out for thi-

. -.. . ■■e-s /.<-. for the pressure oi

Since, now, the ratio of the

- .-H^iys remains the same, how-

.•njieraturc are altered, tliese

^-. -.- .uid teni))eratiires ; therefore

• u^cr. — ^Ve can convinee oiu-selves

•..iition in a eleai- manner, by

» iiul measuring the volume of

:.:■ is most easily eHceted with

^..:- .1 current of suflicient potential

. \r. the two constituents of the

. ^I'liiurless gases, at those points

.^ :he li(iui(l. One of these gases

•. : kindles a glowing wood-s])linter.

-".on, hut can be ignited in contact

,- ..- :'ame ; it is tliei-efore hydrogen.

. > •.on of water by the electric evu-reut

<merja : — U'hile, arf is kjioii^ii. the

VII

WATER

of conductors of tbe first class. So aoon, however, ae the current
passes from a conductor of the second class to one of the first, in
which it flovvR w-tthoiit the transpoi'tiition of substance, an accumulation
of the transported substjincea must occur at the junctions of the two
conductors, and tbeee substaijces sepjirate out.

Tkm, in teater the hijdrogen moiv^ with the posiiitr fiedridlrf, tfie
aitffftn with the •ntffafiri;. At that point, therefore, where the posi-
tive electricity jiusaes out, the miinjde, hydrogen appears ; at the
point where the positive electricity
enters, or where the negative
electricity {wsses out, the atwde,
oxygen appears.

In order to carry out the electri-
cal decomposition, or rkclrolpis, of
water, therefore, the latter must
be plae«d between two metallic
conductors which eflect the passage
of the current. The apfjaratua have
different construction, according to
the purpose in view. An apparatus,
the purpose of which is not to
allow of the tnost afivantiigeou*
electrolysis possible, but of a con-
venient demonstration of the pro-
eaneco, is represented in Fig. 59.

The water ' is contiiiued iii a U-
tulw, the limbs of which are fairly
long and closed at the ttrp by tajjs.
At the lower |mrt of the tube
platinum wires are scidcd in, and
to these are attached two [ilates of
tbe same mcUil l»y means <)f which
the electric current ia contlucted
into the liquid. At those piatea oxygen on the oue side, and hydrogen
on the other, are evolved, the gases aacemiing in the limlis and collect-
ing underneath the taps, The displaced liquid passes through a third
tube at the foot, and through a rubber tube into a collecting vessel at
the side, which can be placed in any desired position. After thu
CTirrent has passed some time and a suificieMt i|uantity of gaa hiLs been
evolved, the following fact* can be recognised : —

The evolved gjises lio not occupy the siame voltlmc. On tho Con-
trary one appears in larger amount, and on making a measurement it
Is foun<l that its vohuue is twice as great as that of the other.

' For IliU «%penmeiit oue doe^i not um< pure wat«r, but a dilute soliitii^ti of sulphutk
ptid or attittii' tuela. The remoiis for this and a\x>.< thi' more uynct discussion of t)ie
dectrnlytk pmceisefi wil[ lie (pveii nt h lnt«r ]H>iiit (Cliaji. JX.).

Frit. iii.

1 1 1

I'fflNXlPLES OF IXOKGANIC CHEMISTKV chap.

'I'!.

tjon of weight, must also be equal to the ifitin u/
tij tht eiemrnix, or to a ratiotifil niulttple of tins,
tuhtning weights of the compouiid siihstaiiceB ai'o
hat ihey are never smaller than llie suin of the
wintKiiiiii^ wt>i(;hut oi the elements in order to avoid fractious of th«'
ot^luliilHitf,' wi-t^htH of the latter.

I io. Oouibinm^: Weigiit of Hydrogen— In order to choose u.
V.'' "!• i-^n s!inj>ly' a4sutiie tlie combiJiing weight to bit

|n. , ,.i^i>ims limsily, so that equal vulutues of the ga86l

nlav tinUiiui ilt« mHiH' niimlkjr of combining weights. According to
lilt* iMiio i)( lU'iiKitii'M^ then {\K dO), the cunibinijig weight of hydrogen
iituot 1)0 tn«lu Dtjuiil to I '0(>t$ if oxygtin is equal U^ 16.

\ ilithiuUy, how«ver, arises when the pi-oduct of combination,
¥ui0i. I* iMkoii into Hccoiiiit. Adopting the stand-point that the

1 i%tv ilin-etly proportional to the gas densities,

II I, fixmi the figures on p. 125, the value 9'U08.

Mil •vmilniiiiig weight oi WMter would, therefore, not be equal to
Liti* «itui i>i ihv ixuubiiiiiii; weights of it-s elements, but oolv to

hix\i I JO*,

' 'tioieforw, not possible to make the combining weights simp!}'

j^i tl to iho gas densities or to the molar weight* (p. 00)

«( I tutu ^'ontratJiotiuns. In the course of the doveiop-

iii . IV' riltt-'nipls have boeu made in various ways to remove

ill uUvtiwi* The following is the methoii now nniversallv

. rv- fiftfrniimd si> thai ihtrr is alimtfs a vkdr

„ ■i4hniiii/ tiritfhU nmhiinfii in f/if molar trriffhlt.

: weight of ojrtffiett, as iuvs already been done,

■■i liyihHigen to 2tH6, the molar weight of

■ut evpuil to 180 16, as can Ire aecn frum tbiJ

li\\ If, iin thi! ittlier hand, we put the ntmhining

iqu.d to lii, and that of hydrogen to I 008, we

lit which has just been stated. The molar

lu liktnviae of hydrogen, then crjnta.ins two com-

. i'U'Hioiit.><, wliile in the molar weight of ai|ueouA

.d two L'liinbiiiing weights of hydrogen and

• t vvlni'li is eqvul to the tombining weight of

thU Bubatance, therefore, molar weight and

'■ *- nhnwii itself to l>e sufficient also for &U

' vdrugen and oxygen are contained. Not

itu-es has exhibited a molar weight in

tuiuunt than 1 fi parts of oxygen or 1 -008

-VMS Weights of the Elements. — By deter
, .„ .•A**i t'ltunetil combines with oue combining

^^^W^jpUL 5i^>i

WATER

145

weight, or 16 parts, of oxygen, the combining weight of that element
18 obtained.

Now. to be sure, it is not necessary to iusume that only ot« com-
bining weight of the other elements always comhinea with one
combiniiig weight of oxygen, but, as in the case of water, there may
be rexLsiJiis for regarding other assumptions as better. In fact, there
are numerous instances where such is the case. (Since these, however,
follow oniy from a. more exact knowledge of the chemical relations of
|lb« elements, the digcii»sion of them must be postponed, and we shall
'immediately give the results here.

Further, the other elements are not all capable of giving compounds
with oj-t/ijrit, although the majority of them arc. Also, the oxygen
compounds of some elements ciinnot be exactly investigated with
j-egnrd to their composition, or analysed, so that the question arises
how, in these cases, the combining weights are determined.

On this point information is afforded by t!ie definition of combin-
ing weight given on p. 143. These numbers are valid not only for the
compounds witii o.xygcn, but also for all compounds of ihe elements
with otH' another. If, then, the fact has been established that an
element li combines with o-tygen so that for every 1 6 gm. of oxygen
there arc present b gm. of the element, and if there bo (ieteruiined the
atnount '• of a third element C which cjui unite with h gm. of B, then
Ithe number e is also t)je combining weight of the element C.
I /« girnefiii : Thf wfiijht of n/i f:h-iiie)it n'liirh atn contbine mtk the c<nn-
•hinin<f WfiijM nf <tmt/irr i-lfiiifiil, rrft-iri'ii to neitgen ^ 1%, is equal io thr
he^inhiff wrif/hl of Hint elcitmit.

^^By means of this principle, it is evident that the combining weight
ERhe and the same element can be determined in very different ways,
■*nd through the medium of entirely different, elements. This has, in
[fact, been done, and the combining weights, determined by such
pifferent methods, have always proved trj be idenlica! within the limit
pf the exjjerimental error. In the-ie investigations we have an oxceed-
Ijngly important confirmation of the law of combining weights,
\ The following t^tble gives a list of the combining weights of the
elements so far as known with some degree of accuracy ; the valuea
are given such that there may be an en'or in the last place of less than
half a unit.

Table op the Combininu Weighth or thb Elbments

Aluminiam

Aotimouy

Afjfon

Arsenic

Barium

Beryllium

Biaiuulh

Ek>ron

Al = 27 1
SI. = 1 20 "2
A = •^9-9
At- 7a*0
Bn = 137*1
Bp = 91
Bi =208 ■.'5

B = no

10.

11.

12.
13.
14.
1,^

Broiniiie

Cdiluiiitm

Cwsimii

Calcium

Carbon

Ct'riiim

Cliloiine

lU. Chromium

|tr= 79 '96
Cil = il'i-4
C8 = 133
Oft= Wl
C = 121
Co =140
CI = 35-

17, Cobalt

18. COTVI»T

19, Erbium
£0. FluorJiji-
21, (tndoliniiiut
2'i. Gnlliiin)

23. Gerniniiiiim

24. Quid
2S.' Helium

26, Hj'tJroffi;3i

27. iDiliiiiii

20. Iridium

30. Iron

31. Krypton
Si. Lanthanum

33. Lead

34, Litliiuiu
'iH. Magiie.'jMiin

36. MaiiH7»iieae

37. Merc-iiry

38. Molybaemiin

39. Kemljiuiurii

40. Neoi)

41. NioktO

42. Niobium

43. Nitri»geii

44. OsmiDTii
4.1, Oxygen
411. Pdlladiiiui
47. PlioHpborUK

A glance at the table shows that the combining weigl
wiLhiii very ivido limits ; in round numbers, from 1 to 240.
theac thej are distributed pretty unifonnly over the whole i
n urn bora.

It ia also remarkable that the combining weight of hydr
as can be seen from the tiihlc, so near unity, without being exact
to it. This hag the following historical reason : — The combining
were at tirst so determined that hydrogen was put equal t
Since, however, only very few elements are capable of forming h
compounds, tho indirect mtithod just described had to be apj
determining their combining weights, Thi.t was carried out I
taining the combining weight of oxygen with refcrenco to li
= 1, and then refemng the other elements, by means of their
compounds, to the tmmber for oxygen thus determined, wli
been found equal to 16 00. For such elements, in the eas6 c
oxygen compounds could not bo investigated, measaremer
carried out with the help of elements whose combining wei|
been determined with reference to oxygen and not to hj
Oxygen was, therefore, the practical basis of all the combinia

Co= 5i)'0

48.

Platinum

Pt^

c«^ oaa

4fl.

PotaBaium

K ^

Er=l(}9

Piaaeodyniiuni

Pr =1

F = 18

&1.

Rhmliimi

Kk = l

t;<! = ]5fl

52,

Huliidium

Kb =

Ga= TO

53.

Kutlieniura

Eu=l

Ge= T2-5

54.

Ssniariiim

Si, =]

Aii = l!>7'2

5S.

S<»bdiniii

He =

He= 4

56.

Selenium

Se =

H = 1-008

57.

Silver

As=l

III =114

S8.

Hiltcon

8i =

I =iy6'86

59.

Sodium

Nii =

Ir =3tt3-o

60.

Strontium

Sr =

F(?= 66'{»

61.

Sulphur

S =

Kr= 81-8

a-2.

TafitAllllll

Ta =1

La = 138-9

(13.

Tellurium

Tl- =1

PI. =20a-9

64.

Tfrbiiim

Tb=1

T-i = 7-03

65,

Thnilium

Tt =i5

Mg= 24-36

66.

Tlicritim

Tb=-.

Mn= b^'Q

07.

Thirliiini

Tu =1

Hi{=2000

68.

Tin

Sii. = 1

ilo= 08-0

89.

Tit&uiuni

Ti =

Nd^i43-a

70.

Tun|;stflii

W =]

N(i= 20

71.

Unuiiuiii

U =!

Ni = 58-7

72.

Vftnadiiitii

Vd =

Nb= 94

73.

Xfuon

X =

N - U-04

74.

Ytterbium

Yb = '

Ob ^191

75.

Vttriutu

Y =

0 = le-flo

76.

Zinc

Zn -

l\l=]0«-5

77.

ZirvouLUiii

Zr =

P = 81 0'

rATER

I4T

riln>gen was only choeeii formally as siich Iwcause its combining

t was tb« smAllest of all.

In Tvoeiit dines, bow, the diacoverj waa made ttat the ratio 1 : 1&

dpQgen : oxygen, had been rather inaccurately determined, and

it is reilly'l 000 : 1588, or 1008 : 1600. The cUoice bid,

to b« made n.«. to which of these two relations should be

, «nd the decision was given in favour of the second. The

catatial nesaon for this wjis that the nnmher 16 for oxygen had,

~ , iklwvys formed the real hash of all deterniinntions and calcula-

with tb*r combining weight*. If, therefore, the number 16 were

to 15*88, all numliers referred to it must <dso be changed.

Bg, however, the number 16 for oxyj^en, rtnci changing only

drogen from 1 to 1008, no such recatculiitioti uf the other

rpqiiirod, since only the value for hydrogen was affected.

Torlht' future, then, the number 16 has been aflopted as the basis of

U|M»iDltitiiug weights of the other elements,

^■12. The Accuracy of the Law of Combining' Weights.^

^■l the gi& law iti only i\ limiting Uw (p. Dl), and since we have
^Hn the Uw of combining weights on it, the ijuestion must arise as
"Itirtat degrtd of accuracy this law possesses, and whether it also is
tale regarded as a h'miting law.

Experience has shown that tfie law of Uie. comhinin^ weights is os cxttd
• Ifcf foe of the conservalvm of u-riiffit, i.e. the limit of its accuracy has,
t» tft, not Ijeen found.

Tin* it connected with the circumstance that the law of combining
•<i{hta reiB&ins valid whether we are dealing? with gases or with sub-
in *ny other physical state. The dednrtkm of the law from the
t«s of gases was miide for the sake of clearness ; itBfoumlulion
ever, is the result of (jtmrititative chemical analysis,
Gbemlcal Symbols and Formule.— Since all compound
can be represented as combinations of tlie elements, their
caa be stated by designating the elements from which
tkjraici prodaced. Tfaia designation takes a very simple form when,
wtetA of the names of the elements themselves, abbreviated, readily
■te%)Ue <yinbol3 are employed.

SkH a method has been in use almost as long as chemical writings
«»i^ inr crcn in lh« oldest alcheraiatic works the most impjrtant
d ikt vubstances occurring are represented by individual symlwls.
IWag of sQch a $ymlK>|!c lan|;uage also exist-s throughout the whole
^Vrispaent of scientific chemistry. These very manifolJ attfmpta,
*"•«», received a fJcrmaTient form only after the law of combining
'B^tt* WW discovered, and after iJerzelius had made an exceedingly
■■fk Jod fnittabie proposal for fixing the symbols.

WlnTeaid, namely, aU fomier syniboU had been more or lesa
"Wttirily cliosen and offered no hold to the memory, Berzeliiw
'virtdUiea Irom the names of the elements themselves, itittodudw^

148

FlilNCIPLES OF INORGANIC CHEmSTRY

the initial letter of these as symbol for the element. Ih orJtT to |
tliffereiices in langimgc out of rMJCount, he used the Latin or Gr
Qamea as the hasia of the abbreviations. In those frvqiifiit ta.
whfit^ several elements commence witb the s<vme letter, the aid of
additional characteristic letter is taken.

In this way the symbols given in the tahlc on pp. 145 and 1
were obtained.

Wliilc, in former times, 6uch symbols had <>\i\y a qualitative sig
fication, the law of ctmibining weights makes it posijible to attseh
them also a quantitative meaning. This conaiBts in also iindcratandi
by the symlrol of each element a amibimnrj nxigki of that elemei
The symbol O for oxygen, therefore, not ordy signilies that elemei
but also IG parts of it by weight.

Since the combinations between the eleinents take place only
the proportions of the combining weights and of whole midtiples
these, it ie only necessary, in order to state the qualitative ai
quantitative conijiosition of a compcruful, to write down the symbc
of the elements present and the factors by which the combintl
weights of each have to be inultiplied. For the sake of convenience
haa become customary to write the factors in the position of suffixes 1
the symbol of tlio element. The eonijKJsition of wuter of two cwmljii
ing weights of hydiogcri and one of oxygen is, therefore, wiiiten I
the form H.jO, the factor 1 being, as is usual, omitted.

This formula expresses the fact that water is produced Jna
2 X I'OOS parts of hydrogen and 1 < 1G"00 parte of oxygen by weigh
and that it contains the.se and no other elements.

In the case of substances whose gaseous density and molar weigl
can be determined, it is farther usual to write the formula' so ll
they ex]]iress a molar weight of the substance designated. Since tt
combining weights were chusen on the principle that a whalr numli
of combining weights is contained in a molar weight, this can alwajj
bo done without having to use fractions of a combining weight. Sm
formula), therefore, allow also of detJucing the gaseous density,
which, of conrBc, the molar weight is equal.

144. Chemical E<luatiolia.— By reason of the laws of the
servation of weight atnl the trmaervation of kind (p. 60), ebemic
processes can be written in the form of etjiiattons in which the sv
stances are represented by their symbols. As a result of the two hn
named, we have, first, that the icciijiih on both sides of a eliemio
equation must agree j and, second, that on each side of the equattc
the stfMie elfvii'nfii wilh the same niinila' of coml'ium/j ■ttei(}b(s jmijit nee
The way, however, in which the elements are corabitied with
another can be different.

Fur example, the formation of water from oxygen gaa and hydr
gen gas is expressod by the following equation :—

0 + 2H = HjO.

WATER

119

write the equations in such a manner that the
stand on the left hantl, and those formed in the
Oil the right. Since at a very high tenipcrnturo water
into ilA elements, this process would be written in the
Jar: —

HjO = 0 + 2H.

in >«? neeii, when more than one combining weight of the
nnder coiisi<lcr.»tion takes part in the reaction, tlie corre-
EMTturs lire written b^fmr the fornmta, whereas the factors of
Bta vhieh are proseiit in moru than one combining ivoight
(such jis Lvilrtigen in water) arc written as a snffix

is %'ery frequently the caae, it is desired to express, at
tiine, by means of the formula, the molar weight of the
, the equatioii hjis, genet-ally, to be written
weight of hydrogen and of oxygen each coii-
mmbining weights of the elements ; we must, accordingly,

aucb an equation we can, at the same time, fr&m the
a tnokr weight, tell the t'ohime ratios of the reacting
present example shows directly that one volume of
two voliuiies of hydrogen yield two volumes of water

[fonaiilie which signify molar weights are not as jet dis-
froiD llic^e intended only to denote combining weight*.
be ca]le<l an imperfection. In this hoaV molai- weights,
ch arc known, will j;*mii rally be written.
Ihe Atomic Hypothesis — For the representation of the
»iiiprehetisive laws to which the weight and volume ratios
jpounds lire subject, u hypothetical conception has been
bee lh« time these laws were first iiiBcovered, whieh affords a
retiiont picture of the actual relations, and possesses, there-
it value for the purposes of instruction and investigation.
jn the abf<ve h}'|>othesis has been made the basis of
and modes of representJition throughout the whole of
that the results of chemical invesiigation are almost
ittfDnmnieatetl in that hitiguage. For this reason alone
Ige of the hypothesis is necessary.

aera), an h^'pothesis is an aid h rqnrai-nlatuHt. Of the
of the outer world, some are bo familiar to us from
experienre, that we know the relations which esiat
Dm with great certainty. If now we finil a new and un-
claaa of phenomena, we unconsciously seek for similar oi\e&

among those that are known. If we succeed in discovering sw
similarity we gain two advant-iiges. In the first pUce, the fixing
ttie new facts in the mGmory id very greatly facilitated !>y the oat
the similarity, and in the second place, the similarity alfords u
means of tnnking pi-obahle jjresumptHiti^ concerning the bohtiviou]
the new pheiiomcnji. under conditions under which they have ii|^
been investigated. ^

* As compa-red with the less known, such a group of similar il
well-known phenomena form thu basis of the hypothesiB. Since
all phejiomena those of mcclmnics are uaaally the most familiar to
by fur the most hyjjotheses are mechanical analogies of non-niechani
phenomena.

* The same character is possessed also Ijy the present hypotha
The j)ecnliaHtic3 of the weight relations of chemical processes I
*' explained " by a definite assumption concerning the meehani
nature of the substances.

This assumption consists in regarding all substances as compo6
of very small particles or ahms. The atoras of each elementary r
stance arc alike among tliemselvee, and single, and arc different fn
the atoms of every other element. The atoms of a cbemicjil compoui
are alike among themselves, but are composed of the atoms of i.
elemontB by the ititeraction of which they are produced.

From these [issumptions the laws of chemical combination follo
directly. The assumed identity of the atoms or the atomic groui
which form a definite substance gives a picture of the theorem of t!
definitencsB of the properticB of every substance. The assumption i
the difference of the nature of the atoms of the different elemeo
explains the inconv^crtibility of the elements into one another, nil
the assumption that the atoms of ttie elements remain intact in tl
compoilnds, and are only ditterently grouped together to form, in ea<|
case, an atom of the compound, makes the law of the coonectid
between the derivatives of each element clear. |

On the same foundation aUo, the (iinintitaikyi laws of comhiDatid
are made intelligible. Since all the atoms of a definite element ai
assumed to be identical among ihemselve,'!, we must also assua
identity for the weight of each atom. When, therefore, two or mgl
different .itoras combine in a definite manner to form a compound, U
propox'tions by weiglit in which the compound ia formed are also ftffl
hy the number and kind of tlio elemontary atoms. Since, finally, I
comiiouiids are regarded as congeriea of the corresponding elemental
atoms, the proportions l>y weight of these must be represented luiivtt
sally by the numbers which are obtained by multiplying the weight <
each kind of atom by the number of them. In this picture, thcrofoH
tho combining weight of an element a.ssimies the signification of Ul
weight of an atom, and the designation atomic tvei^ht in place of cot
bining weight Uttfi a universal currency.

WATER

151

ibn limits hore given, llie atomic hypothesis has proved
exceedingly useful iiid to instructian and invc^tigatiutt, since
\y fiieilitAtes the interpretation and the use of the general hiws,
iiut not, however, ho led astray by thia agi-eement between
and realitj, and confound the two. So far as we have treated
processes oeciured in such a way aa if the
iposed of atoms in the souse explained. At l*eat
this the iKiiisihilitt/ that they are in resdity so ; not,
lift. For it is impossible to prove that the lawis of
l^rmWI combination lannot be deduced M'ith the same completeness
ns of quite a diHereiit assumpiioti.

One do«ss not require, therefore, to give up the advantage of the

hyjwlhesis if one bear-s in mind that it is an illustration of the

reladotu in the form of a suitable and easily manipulated

boi wfaieh may, nn no account, be substituted for the actual

One must alwa^vs l>c prepared for the fact that sooner or

reality will lic different from that which the picture leads

I expect

E«])ccijiUy, when any other well-founded speculation leads to a
the atomic hypothesis, one must not, on that account,
nilation ;is wrong. The blame can tjuite well attach to

ic hypothesis, in the sense developed here, was put for-
rI W J. Djdton in the year 1S03 ; the testing of its most im-

Pl consequence, tlie law of combining weights, was perfonned b}'
liB (p. 143). On account of its entii"o aHi'^ement with experi-
jte atomic hyp)jthesi.s attiiined to a position of great considera-
l^tniversal sipplicaiion, so that, even at the present day, it ndes
sxeltuivaly in chemistry .
tlub book ako we shall not deviate cssentiully from the general
M^ Still, it would cert4iinly be to the interest of the science if
pwtr <»re were exerciswi in thi.'s connection, and for that leason we
kit hav laid stress on uaing the forms of expression of the atomic
lyp^dkceis as sparingly as ever the present usage of language will

146- Kie Molecular Hypothesis.— Just as the laws of weight
tx^ooicdkl pr'jccB»c8, 3o ul*ii the laws of mlumf in the iTiteraction of
pKiu Mibstances have given riae to mechanical hypotheses, which
hit« played a similar though not so important a part in the develop-
; tj chemistry aa the utomic byiKjthesfs,

liac*^ gases combine in equal or in multiple volumes, the most

astumplion is that the same numlK-r of atoms is contained in

I Wumes of the diflcrcnt elementai-y gases. In fact, this assump-

|w» at first made.

fiih this assumption, however, the fact that iuk} volumes of

and one volume of oxygen yield two voltimes of aqueous

152

PRINCIPLES OF INOKGANIG CHEMISTRY

vapour catmot he brought into agreement, For, let the niimli
atoms in the unit of volume be K, and let us make the appropvi
assnraption that the same law holds also for the aqueous vapc
2N atotne of water must be produced from N atoms of oxygen and
atoms of hydrogen, i.^*. in each atom of water half an atom of oxj{
must be contained.

This is not the only difficulty of this kind ; on the contra
similar ones are eneounteiefl in nearly every case of combinati
Ijetwt^en gaseous substances.

To avoid this contradietion, therefore, it was necessary to i
tin^uish between the atojiUi and the umalkst imrtides of fhj; gast^.
we assume that the latter, which are called mnlemks, are compw
of st-^veral atoms, the volume ratios of the gjises can be satisfactop
represented.

The conaideKition of all known cases has shown that a very aiiiif
assumption suffices here. The contradiction can be avoided if, in t
case of tho eleraentjiry ga.ses, fjj. oxygen and hydrogen, the molectil
are regarded as being formed e^ch of tut' atoms. In the cAse of otb
elements other assumptions are in part necessary, and these will |
discussed when we come to them.

According to this assumption there arc contained in «/w«f i-eitiiit
of the different gases, not an equal number of atoms, but an tfH
numhf'r of Tuoh'diles. If, as mentioned, (he molecules of oxygen M
hydrogen each consist of two atoms, and if N is the nnmbex' of mot
cules (not of atoms) in the unit of volume, we have the foUad|
calculation : — ^M

One volume of oxygen contains N molecules, and therefoi^l
atoms. With two volumes of hydrogen ( = 4N atflms) it forma f*
volumes of aqueous vapour, in which, therefore, 2N moleculea {
water must be contained. If one as.sumes that each water molecu!
consists of one atom of oxygen and two atoms of hydrogen, exact]
2N molecules of water vapour can be formed from the atoms preset!
and the actual relations receive a correct representation.

Tho molecidar hypothesis stands to the conception of the molj
weight (pp. 90 and 144), previously introduced on the basis of the la
of Gay-Lussac, in the same relation as the atomic hypothesis stands '
the conception of the combining weight, and the molar weight appeal]
in the tight of tho hypothesis, as the relative weight of a molecule,
the tnoItYtdar tmijkl. For, if an equal number of molecules is assut
in equal volumes of the difTerent g,a8cs, the weights of the differ
molecules must be to one another as the weights of equal gas votum^
i.(. as the gaseous densities or the mol.ir weights.

The requirement that the molar weights shall be expressible
inlfi/ml valnes of the combining weights assumes the cleaHy
telligiblo form, that no fractions of atoms are to be assumed in
molecules.

\A^VTEK

name nioiectdar weight is in u;eneral use for the previously
! I'otii'epttun of the molar wei^'ht. It may also bo omployod
'l«itly of ihe hypothesis on which it is based, if olio bears in

^u^lM iliiii it expresses an actual relation, viz. the gaseous density,
• The bypolhcsia just dcvelopod was put forward by Avogadro
' \ rjn'fe aJmost sinmltaneously in the years ISU and 1812. The
':■.(! that in erjiial volumes of gases equal numbers of molecules
' i3 sometimes callerl the hw of Avogadro, This is mfa-
. a hypothesis can never Ihs a law. It may be callud the
of Avoga«lro. The law on which these considerations are
^iiK<i i! that of the rational volume ratiiDs in the reactions between
Hrs, discovered by Gay'Lussitc.

^U". The Action of Sodium on Water.^Of the <haiige8

uke place liy the inieiJictiou between water and sodium fp. Si),

■s yet, considered only the evolution of hydrogen from the

We sL'Jl now pass to the investigation of the other products.

the first place, the water which had been used for the reaction

ita outward appearance, unchanged ; the product which has been

irrnn the scnlium must therefore be sfAnbh. and yield a mlourkss

irtn. Thut something new is present, is shown, however, by the

vhich is unpleiisanlly soap-like, and by its power of exhibiting

not shovrn by water. One of the most conspicuous of these

is the alteration of certjun colounng substances. A piece of

coloured purple with litmus (a colouring substance extracted

lichens) immediately becomes blue when raoiatone<l with the

fortued. A piece of cokmrlesa paper containing the artificial

jtmvlphihuleiu, whicli is used by electricians as "pole reagent

" for determining the direction of the electrical current in a con-

", hecctneA coloured purple- red, and paper coloured with the

**rgetftblc dye turnu-rir, becomes red-brown.

t tmkea pWe in the case of these changes cannot bo explained

IjMBter ; th«y serve, in the first place, as an identification sign for

^pnhitance produced.

Tft obtain this substance in the pure condition, the water in which
i>bdiiBolv«d must be removed. This is done I>y heating the solution
dl ll boil* ; the water then passes into the form of vai»ur and
lp(i, while the dissolved substance, which is not volatile, remains
■und.

Tkiii ttietho<l which is generally used for obtaining the substances
t»mt in Nujlutions when they are not or are only slightly volatile,
rriUum. The apparatus used for the pitiposo vary accord-
tie on which the oijcration is carried out ; they all agree,
n. (i.iii- of such a shajM:^ that the aurfa.ce of the evaporating
kv!p( ;L-i large as possible. For the velocity of evaporation, or
unt of liquid evaporating in unit time, increases, cetetis }wrihii,
iMnally with the evaporating surface.

154

PRINCIPLES OF INORGANIC CHEMISTRY

148. Caustic Sod&. — On evaporating the solution produce
the action of ssoflium on water, a white suT>atance is obtained which
solid at ordinary temperatures, but which readily fuses and redissob
in n small quantity of water with development of heat. It is the sai
Bubstance as served in the combustion experiment described on p.
for retaining the gaseous and vaporous products of combustion. 1
little of the substance be diasolved in water the liquid exhibits all t
colour reactions of the solution produced by the action of sodium i
water.

That this siibsuiiee also contiiins oxygen as well as sotlium folioi
from the fact that it was foi'med, with evolution of hydrogen, fro
water and swlium ; in it there must be present the oxygen which w^
previously in combination with the hydrogen evolved. The prodw
however, need not consist of sodium and oxygen otily; it may all
contain hydrogen from the water.

That it does, in reality, still contain hydrogen is shown by ll
following experiment. If a little of the Bubstancw is mixed with fine!

powdered iron, and the niixtui-c heati

rJ^ in a amall tube of resistiint ylass, close

yi:^ by a uork through which a drawa-«i

/(^f glass tube passes (Fig. 60), there soo

y^/v^*v escat>e9 from the opening a gas which ca

^^^r >^ bs set on fire, and can be immediate^
|Hr identified as hydrogen by the film (

f~T moisture formed on a cold glass hel

yl over it.' Since the iron, being 8

" clement," contains no hydroge
must come from our substance.
— — £■ The result of more exact an«
~^^~>-V shows that the product consists (

c YiSi sodium, hydrogen, and oxygen in tl

p,a,,Mi. proportions 23 '05 : I'Ol : 16-00 Ij

weight It contains, therefore, an evqui
nimiher of combining weights of hydrogen and o.icygen. The con
bining weight of sodium has been found ecjual to 23-0.'J ; since tl
chemical symbol for sodium is Na, the formula NftOH is obtained f(
the compound. In chemical languay;e it is called sotliiim ht/dro.ride, \

Ienusfie mijit.
The name sodium hydroxide is intended to indicate that, beaidi
oxygen, hydrogen is also contained in the comjiound.
Compounds which are constituted in the same way aa sodiot
hydroxide, i.e. which, along with the njeud, contain an equal numbi
of combining weights of oxygon and hydrogen, occur in large nunibel
for aiiHoat every metal can form such comjwunds. In consequence t

emg a
anoipi

' Tliv A«nve at the Iij'itrogeu
ilnuse »s given oti p. 35,

geueraUy coloured yellow, unU this from the s«|

rfn

WATER

156

uiuiag tbe»e elements in commoti they possess certain con-

jiiTiportii?*. 80 that it has Ixteii foiinil convenient to give

I tlim « »p».Tial (Amily name, and iilso to ^ave i\ special *3esigj«ation to

•' - rp OH. The tuetallic compimnds arc called fewis, and the

'[f, hvdrtjjyi. lltint's are, ihcirforf, annpMmh of «w/rt/s mth

.\W the tnetitls combine with hydroxyl in such a way that tfl

i;^ weight of the metal also one hydroxyl is present. On

uj, , other reasoiis have often led to asauming comTiinitig

t nr the DietalB such that two, three, and even four hydroxyl

-' -utited with one comliining weight of the metal. The
, hydroxides or hasc-s then have the forniuls- M{0H)2.

JI(iOll)j, where M is the symboi of the nietiil. These metals,
bstses [(reduced from theMi, iire aceordiugly called di-, tri-,

in so far as they are soluble in water, all behave in the

w»y as caustic soda with respect to the colouring substances.

tioRs, then, belong, not to the different metals from which

have been prwluced, but to the common component,

iji_Deliqqe3ceDt Substances. — On evaporating solutions of
^ it is found tliiit the last portions of water are difficult to
ce the vapour pressure of the concentrated solutions is very
1 muller than that of pure water.

rereely, caustic soda, freed from water, has the property of

moist in air by condensing on itself the aqueous vapour

'"^■cnl bi the latter (p. 125), and it ultimately takes up so much

■fitr lliat it Ijfpieties lo a solution. Caustic ssoda, therefore, is called

iHtfuneati substance.

■dlj^roperty of deliqueBeing is not one belonging exclii'^ively to
^^^Hw^ but also belongs to many easily soluble 3alt«. The coti-
^^Rn* it is that a solution is produced which has a smaller vapour
^BZTD ihnn the mean vajwur pressure of (he water in the air. Such
'*v1iitanee continues to withdraw water from the moist air until the
pressure of the water \'apour becomes equal to tliat of the
produced. If the air is renewed, as in the case of substances
I in open vessels, the process comes to an end only when a solu-
bccti produced, the vapour pressure of which is equal to the
procure of the water in the air.

on an avcnige, ihe air is saturated with aquoons vapour to
lieui of 60 to 70 per cent, all substances will deliijuosce which
•olutions the vapour pressure of which is less than 0*6 of
Iti water at the same temperature.

fHAPTER VIII

HYDROGEN PEROXIDE

l"iO. Hydrogen Peroxide.— By means of reactions, the det
wliich cannot be understoiwl till later (Chap. XXV.), it is posrihJe
prepare a second compound of hydrogen and oxygen which hits
different composition and easeiitially different pro]jerties from wnU
This tompoimd is called hyiirofffii peroxide, a name which expresses llu
it contjiins more oxygen than water, which would have to be cal!<
hydrogen o.\ide.

The coniitosition of hydrogon peroxide is given hy the formu!
H.,0^, This states that for the same amonnt <if hydrogen doublet
much oxygen is contained in the new compnuid ais in water. I
numbers the formula shows that the compound is composed of 2 x I*O0
parts of hydrogen and 2 x 16 •00 juirt^ of oxygen, by weight; it
ifinlar or raulecuiar weight, therefore, amounts to 3-1 OIG. If th
weights of oxygen and hydrogen present are divided hy this nunihtl
and multiplied by 100, thtj percentage composition of hydrogen pe^
oxyde is obtained. The result is 94"1 per cent oxygen and b-9
cent hydrogen.

Hydrogen peroxide is a thickish liquid with & dettdty 1'5, andj
colourless. It is not easily prepared quite pure, and when it
obtained it very readily decomposes spontaneously, so that its oxistend
is always only » passing one. The decomposition takes place hc
ing to the ei^^uation

2HjOj = 2H30 + Oj,

i.e. ttas substance decomposes into wittor and oxygen gas.

Nevertheless, by cooling very concentrated solutions, bydrog
peioxide has recently been obtaineil in the form of clear eryst
melting at - 2^.

On account of its great rendineaa to decompose, hydrogen peroxi^
is usually prepared and used in the form of a tUluk solutiim^ in whi(j
it is much more stable. Since it dissolves in all pro[)ortione in wat
solutions of any desired strength can be prepared, and the strength

CHvr. VIII

HYDROGEN PEROXIDE

157

usually stated by the number of I'olumos of oxygen which can be
evolved from one volume of the solution on decomposition. Since
2 x 34 <^m. of peroxide evolve 3'J gm. of oxygen, which umlcr oniinary
conditions occupy a volume of 22-4 lit. (j>. 90), it follows that every
grnui of peroxide ovolvcs 303 cc. of oxygen. A one per cent Bolution,
containing, therefore, 1 gm. in 100 cc, accordingly evolves 3*53 times
its volume of oxygen, and the solution ordinarily uaed of strength
10 volumes of oxygen contains, therefore, rathtr k'ss than 3 per cent
of [leroxiJe.

This solution looks like wtiter, but has a peculiar astringent taete.
It has no definite smelL It siovirly evolves oxygen, so that it mtist not
be kept in perfectly close veasols, since these could thus be readily
burst. The decomposition is much lesa in the cold than in the hwit,
and is, moreover, very greatly influejiced by the presence of other
substancoa. The jtsroxide can be bent preserved in it solution con-
taining a small fiuantity of some acid or a little spirit of wine.

151. Hydrog:eii Peroxide as Oxidisinnf Agent. — ^The case with
which the peroxide decomixiaes into water and oxygen is also seen
in the presence of such substances as can chemically combine with
oxygen. Hydrogen penjxitle is therefore an ojndimitj uriaiL .Since
gaseous oxygen is spontaneously fomjed from the peroxide, m\d the
reierse reaction does not take place to a measurable extent, wo must
conclude that the peroxide is a stronger oxidising agent than gaseous
oxygen, i.r. the i>eroxide can still give up oxygen ttj such substances
as are not capable of forming compounds with oxygen jFfW. This
concluaion is ba.scd on the follow^ing reasons: —

It can be proved generally that the action of any oxidising agent
can, tJiooretically, be repbu'ed by the action of oxygen giw under an
appropriate pressure. Tht« highest jiressure of oxygen corresponds to
the strongest oxidising agent, and rirr rirm. Iiuagine this pressure
determineiJ for each oxidifiing agent (which is generally possible by
indirect means), we can then arrange these in a series of decreasing
pressures, and we can assert that with a higher oxidising ,igont we
can, indeed, prepare every lower one from oxygen antl the other
component, but not conversely, just ii.s the pressure of oxygen can,
spontaneously, only diminish, but not increase. Since oxygon gas can
be prepared from hydrogen jicroxide, but not hydrogen peroxide from
oxygen, the peroxide must be the higher oxidising agent.'

These oxidising properties are jM»rticularly conspicuous in the case
of the pure peroxide. In contact with it lead powder ignites spon-

' In Bj^ipljiug this rouioniag. It in atxennAry tn know that ia the cane of au oxidjiiing
■gvut txiiliijg ill tlie coiiditioD of a solution, Itii poidtiou iu the »erie!! Ls Tariable. It i
depenilctit on the coiia*utratioij iif tbe solutiou, and hi all llie lower tlie moTO tUlttfi
the MtlutioB u niiule. The miine part in pUycil by the pi-cssure 4ir gaaas, an, Lti>lee4'^
foUovs from what 1>il« boen s&iil. For solid xuhttiiiioes and uiitiiixed liijiiidii, huwevet
tlie position in lU* serJM in fixeil, ami iiiiilergi'*-* (in npurtoiiilile iilteralioii only tbrou "
cbjiuge of t«nipt!riiiiiTe, which vsriei^ from u«4e to uomu.

CHAI",

153. Preparation of Pure Hydrogen Peroxide. — Hydrogen

peroxide is much less volatile tlum wiiter. When, therefore, a soluiioii
of the siibataiicci is evaporated tho vv.itt'r passes ofl', and a solution,
riclier in pejoxicU", remains behind. Altliough the (Iecoia]rasa!>iIity of
the peroxide lupidly increases with increasing conceiitratiun, fairly
strong solutions can still be obtained if one st^irLs with ver) jmra
material, and carries out the evaporation at a moderate teinjwratiire.

Under reduced pressure the concentrated sohition can finally be
sepanited into water and almost pure peroxide. For this purpose
the jiarts of ti distilling apparatns (p. Ill) are connected air-tigfit
together, and after the licjuid to he distilletl has been introduced tlie
appiiiiitns is exhausted.

The purpose of thstillation under reduced pressure is to enable one
t-o accomplish the distillatiun at a lumr innpiratnre. Since the vapour
pressure of all subsUinces rises with the temperature, and boiling
occurs when the vapour pressure has become equal to the extertial
pressure, the substanre will boil at a temperature which is all the
lower the smaller the external pressure is made.

The lower the tempeniturc!, however, the less is, in general, the
aitioHnt of deamijwsilion, since the 'velocity of this, like that of all
chemical ]>roces8es, mpi^lly increases with rising tcmperatura Dis-
titlation under reduced pressure, therefore, is employed in ull . cases
where a subst<ance has to be tlistilled which is not stable at;i»tiie
temperatiiie of its ordin.iry boilinj; point.

\Vlien a solution rich in peroxide is treated in this manner, where-
by the temperature must be kejit Tinder 80", water with a little
peroxide first distils over and then almost pure jjeroxide. His
distillate is collected in a seiwirate vessel, and in this way the
substance is obtained in a very piu^ condition. Such a process,
depending on the differences of the vapour pressiu-es, is called
fs'iu:ti"tiid iiiHfiUati<m. In chemical pnictice this method finds very
widespreail applicatiion.

151. OccurriinCfi. — Hydrogen j)cruxide occurs in very small
quantitiea in nature, traces of this subetuiite being contained in rain
and snow. Likewise, small qutinLities of peroxide are produced in
many cases of combustion and also in other oxidation processes. There
are a number of very delicate rfcietions imed for the detection of such
small jiniounts, Tlie-'^e, however, cannot lie diacussfd here, since iher
presiippisc a knowledge of other substances. They w ill be discussed
at a suitalde fijijioi tunity later (Chaps. XXIX. and XLI.),

15a. Catalysis. — i^ince hydrogen peroxide can dtjcompose sptin-
taneously into water and oxygen, a question arises similar to that asked
on p. 05 with regard to the combustion of substances in the oxygen of
the air: AV'hy, then, does the hydrogen peroxide not decompose ? The
imswer is similar: It does decom[>ose, but with ver.v varying velocity.
To illustrate the existing relations by an analogy, one can imagine the

Vlll

H\rDROGEN PEEOXIDE

161

hydrogen peroxide replaced hy liquid oxygen contained iib a vessel
which is not completely clotsed. The oxy^oti in this vassel is also not
in a {tcrmanent condition of ccjuiUbriuni, but it e&uupfis; stillr although
it i& in communication with h sp.ice of lower pressure, its piesstire
does not fall to thu lower value iiiditittanimtslt/, but only slowly, and
this with a velocity which depends on the aisse of the opening and on
the amount of friction which takes placft in the opening. If the
optining ia very anuj.!!, it may be a long time before the e&wipe of the
oxygen becomes tioticeahle. Every circumstance which makes the
opeuing more accessible will hasten the lowering uf the pressure;
every circumstance which makes it lesB accessible will lengthen the
period of the existing condition.

In the case of hydrogen peroxide, now, there are, as a matter of
fact, very varioiiB circtinistatices known which ivct in the sense of an
etilarrfing or diminiabing of the opening, if. which change the velocity
with which thii^ spuritaiioouf; and continual decomposition takes place.
Thus, porous and pow(3erud substances greatly accelerate the evolution
of oxygen. The action is, however, hy no meivns a purely mechanical
one, for different powders of similar fineness have a very different
action according to their chi-niical nature. Pyrolusite, which in like
manner also accelerates the (lerfectly similar decomposition of potassium
chlorate when heitted (p. B3), is aspeciaOy effective. By shaking a
solutioD of hydrogen peroxide with pyrolusite in an apparatus which
allows of the evolved oxygen being c<tllected and measured, the
amount of hydrugcn peroxide in the solution can be easily and
quickly dt-'termiried.

On investigating the pyrolusite after the experiment it Ls found
to tie unchanged. Finely divided platinum, which likewise remains
unchanged, ;»ct,s in a similar manner. Other finely di\'ided niotiils, such
as copjjer and c^idmium, dr> not appreciablj' hasten the decomposition.

Such substances which iict tin jiyrolusite and platinum do here,
w 9U to alter the velocity ol' a chemical process without themselves
being chitnged by the process, have already been mentioned (p. I07)j
they are called mlali/xcff, and the action itself is called mtahjtic

• (.)f the calalysci"s it can be stated generally, that ikey cannot
briwi afnj\i{ Tmdions which uuitld /wt of tlifinsrlvrs tuku placf sjmntiuiemslif
if eifri ttiih) with a ivrti entail ivlocili). If it wei'c the case that a
reaction could be brought about by a catalyser in a direction opjiosite
to that which it tj«kcs by the action of the participjiting svihstances
idoM, one could allow the substances to internet alternately with
And without a catalyser, and thereby, time after time, obtain reversi
pTOccs-sea. Thejie processes cou!d bo useil to perform work, and
couJd thu.'i e.stablish a pffjiftuum nuibUe of the second kind (p. 1.3fi)
which is in opposition to experience. Thus it is not to lie expectei
that a eatalyser could be found through the action of which oxygen

160

PRINCIPLES OF INOKa.\:Sl

JIISTEY CHAP.

153. Preparation of Pure Hydrog

|>eroxide is much loss voljitile tliau wuwr
of the substance is cva|Joratetl the \x
riclier in peroxide, reniuins behiiuL .\
the peroxide rapidly incroases with
strong solutions can stilt be obtnir •
material, and carries out tlie evajn

Under roduced pressure thi' i um
sepiratcd into water and almost pui
the parts of a distilling apiriuui'
together, and after the iiipiid u< ■
.ippmatuB is exhtiiiated.

The purpose of distillation iiU'i
to iiccomplish the distilktion at. .<
preBsnre of all substances n--
occurs wheti tlie vajxjur prt
pressure, the sinbstanco will
lower the smaller the exlcriin I

The lower the temperati
avimint of decompmitinn, dntt- il ^

chemical proceases, rapidly incrc
tilhition under reduced pri'--i '
where a substance h;is ti> I-
tempeiaUire of its ordinary b

When a aohitiou rich i» i-
by the temj>erature must !>
peroxide first distils over ■

jri^'en peroxide.'
entical -ivitb the
iitv of a pt^i'j'ftiiitiii

distillate h collected in
substariee is obtained ir
depending on the ditf'
fnutmutf ih,^t>llafi'm. lii
widespread applicatiuu.

154, Occurrence.
quantities iu nature, tr;t'
and snow. LikcHnse-, ^i
many cases of comlm-
are a number of vci
ismalt amounts. Tl.
presuppose a knowtf

at a suitable oppoiiin

155. Catalysis

taneously into watet
on p. 65 with regai-i
the air: Why, tlien.
answer is similar: li
To illustrate the exi>^i

■-BBifc. — Approximately

^-'jT-K, since it readily

The cause of this

irat^r and oxygen

i;f action perha|)s of

ill!! jmrliotiLS (jeeom«

_ ,.iii(junts of heat a

advance one aiioth

o^oaion.

,«{ rMctions take place in

'a For example, whtia

iiid the vapour pressure^

in the reverse manner

^..t-cnt it st'ify of I'lptilifriiiim

^gtr^ state which can lie

Jo, the approach to the state

gffre iif slowness.

i i.f the pcro.xide the heiii

;>fiiitiiience of pyrolusite or

■3 A .1 thermometer, for the

Tif ardiuary solution, which

^^^ on sudden decoEoposition,

.'hwt were avoided.

XitAtx a knowledge of those

«ji*a,is an important tjtsk

-rr many general questions.

•j£ the amounts of heat given

^-r^ if rwfftjH cuunccted with

^^^*» diemieal processes are the

•^2 i<*i£ things, plants as well as

^ ^ fi life ; since, also, the ener^"

-,'t fixim chemical sources, — the

■radily seen. We shall here

>tigJitions.

1^ il<f 0 kirul of enrriit). It is
. jiiixliiced with especial ease
ill)' chemical reaction occurs
II generid, a different energy
of the two amounts appears

■ (qii«iit™t«t siiliiticms. In tlie c«>e o(
"i yit KhOUtmiiiciti.H fiimintion of sninlt

IIYDROOEN PEROXIDE

163

iilt, the prDdnclioD of oLiier forms of energy

V sloped if the energy of the products is smaller

•itiltsUinces ; the temppra-ture of the reacting

' -''ly, if the subfiUujces are converted into

I j;y than the ori^ual ones, the energy

II in the form of heat frrtm the reacting syetem,

■ I this falls. Both cases are possible, but the

ninn; frei[iiont.

M wliich the chemical reaction takes place is siir-

• nilk ijf uaUT, the heat which is generated passes

. in (hti converse case, is taken from it. If iho

is known, and if the change of toniperatiire be

proilnct of the two numhei's gives the i[UMiitity

For tlie itnit uf if-il, or the raiurk, has been

M20) iLB the quantity of heat which is necessary to change

Uro of I gm. of water 1 . If S gm. of water experience

ijte.ralnre of / , the corresponding quantity of heat is

^et]Ual Ui lis N/ joules.

iderit, liowevt-r, the quantity of heat developed varies with
'}/ ih: fiilist'uiwti, and is, indeed, proportional to this.
nUtain definite nntnbers, therefore, the quantity of heat
rrt'd to deiinite amounts of subataiice. For this purpose^
5 melliod of procedure is in general use :
ctiiMi is expressed by a chemical equation, and is itiiiigined
atiL-p bt'Lvvefn as many grains of the different reacting 6ul>
b<-" nuiutjflrs of the corresponding combining weights amount
v^uantiiy of any sulwtance whose weight in gram.>i is equal to
of the combining weights contained in the fonnula, we have
moU of the subsUinee (p. 159). In short, therefore, the quan-
hual in chemical reactions are calculated for moles of the
substances.

The Heat of Formation of Water. -To give an example
hiiit just bcfii said, let us consitlei' the development of heat
octuni in the combination of oxygen and hydrogen. Evidently
is very considerable, since it gives rise to such a great elevation of
t<»mppraMire as the evperimonts mentioned on p. 103 show.
be cx|)erirnenLs which have been performed in this connection
that in this proco.ss 68,400 calories are develuped, when one
li«=rlg'(j2 grn. of water is formed fr<.im its elements. An idea
of chis quantity is obtained on consiiiering that, according t(j this^ more
than a litre of water coulrl be heated from 0' to boiliua through
the combustion of 3 gni. of hydrogen.

• This number can be at once used for an intercstinj
If we imagine the heat which is developed used only fa
temperature of the aqueous vapour produccil l>y the comb'
clctOQUting gaa, the temperature of the Hame of the (.

PfimcIPLES OF INORCiANIC CHEMISTRY

0 is obtained hy dividing ttis quantity of heat, 68,400
the Htiiotmt (if liL'iit requiicd to raise 18*02 gm. of aqueous vajjotir
degree, or tlic thermal cifji/icilj/ of thii; amount of vapour. Since
round numbers, 9 calories are required to heat 18 gni. of water vap
1°, the result of the calculation is that the temperature ol" the o
hydfogon Hume must be 63,400/9 = 7GOo". This number proves, h
ever, t* bo much too high, since measurements have given values wh
do not much exceed 2500°.

* The cause of this disparity must be sought for in twodirectio
In the first place, the thermal ca{)jicity of atjueous vapour has \
gi\'eu value only at lower Icnipeiatiiri'S ; at higher temperature
becomes greater, and the temperature must therefore become low
But then — and this is the chief point — the combination of oxygen a
hydrogen to water is not at all compitste at higher temperatures, t
the higher the temperature is, the gi'cater is the portion whi
remains uncombincd. The combustion, therefore, raises the tempei
ture of the iiame only to the point where a further (^levjrtion wru
efl'ect a separation of the water produced into its elements. Furthi
combustion then takes place only in propoition as heat is withdra.*
by uonductioii and rJidtation, and must be replitced by fresh combuslio
This temperature is then the true temperature of the flame ; for tl
oxyhydrogen Hame this is, as already mentioned, about 2500 .

On the basis of the law of the conservation of energy, we can sUt
in the first place, that the same quantity of heat, G8,400 cal., as w
developed in the foimation of one mole of water from its eleniL'rtl
will be again d/ww/wi/ iu the (hvoiHitositioii of water into its element
For if this wore not the case, it would be possible, by the altenial
formation and decompoaition of a given amoiuit of water, to cause tl
proiluctimi or the di8a|)peumuce of any desired auioimt of energy.

The further conclusion can also be ilnjwn, that the same quanti^
of heat pro mole will always be developed, no matter in what w^
water is formed from it^ elements, whether by combustion with flaift
or by any other process. The correctness of this iissertion a
also he proved from the law of the conservation of energy. In tl
case we must only hold to the auppositiofi that no other forma '
energy appear or disappear.

On the other hand, the development of heat must be difTereiit,
water is produced not frnui the gaseous elements but from some oth
stibstances which can yield o.Yygen and hydrogen. And, indeed, t
difference must amount to exactly as much as the amount of h4
developed or absorbed in the conversion of the gaseous elements it
Uhe compounds in que-stton. This theorem, alao, is based on the U|
of the cunscivation of energy.

With reference to the problem before us, the principle of ^he c(
aervation of energy in its roost general application assumes
foUowhig form : —

165

can, in genural, 1* ascribed to every aubstance existing in
Snite state a definite content of energy, which le proportional to
f«B()imt of siiliatanco, and which for a mole has a definite vhUic.
»ti6oInt< Hinftiint of this energy is unknown to ua, since we cannot
WAV tthslnict from a stllistflnco tdl the energy whieh it contiuns.
howevLT, meiisiire the dijl'rren''''s of energy between two sub-
{■■^efore and ;ift«r tfte chemical process, for these are the amounts
ergy which are devt^ioped or iibsorhed as heat in the reaction,
lenergy relatiorm of suhsutuces cun he represented in the form of
Ktions in which the energies of the single substHnces are so ropre-
»t thi'ir iMHeit-ncfs ba^e licfinite values.
Thermochemical Equations. From this there follows a
of atiUsng the results of hm;ii niwisiirements in ii mariner
for odcidation. The cheniieal formula of a substance reeeives
significance that it represents not only the composition
etifrif^ (onietd of th*; Buhstance, The equation of a
mtA proceae, then, which, apart from this, contains on either side
L'lenipnt^ in e^jnal amounts {p. 148), must be supplemented
nt^mt'nt of the nmouut of energy which is necessary to miil<e
of thi* energy on both aides also cijual. This is the difFer-
he amount.s of energy of the anbstauce^ before and after the
nacficw, i.t the amount of lieat developed in the reaction.

Tor example, to express the change of energy in the formation of
^nurfroni iu elements, in the form of such an e<piation, we write

■m.^ + Oj = 2H,p + 2 X 68,400 cal.,

re read thus : The energy of two moles hydrogen and one

"■ "" i exceeds that of two moles of water by 2 x 68,400 cal. ;

AVgen and hydrogen unit* to form water, water is produced

Ijiio^n amount of energy etjual to GH,4uO cal. pro mole of water.

LTWuUithod of writing allows, iu the tirst [tlace, of tlie results of

litfiiig represent«d in an unambiguous tnanner. It has

fgreat advantage that it also makes it possible to calculate

^ kcate of reaction of processes which cannot be dii octly measured.

DpthfMi of doing this will be given immediately when we come to

ui actual aise.

irds the form of tlieae calculationSj it has to be fiuther
Ml that in future the iibsohite unit of energy, the mj {\\ 23),
•WW iia«d iu |)lace of the arbitrary luiit of heat, the calorie. Since
«■ tniit is uio liuiall for the accuracy of themiochtmiciil mejtsurements
^^ana jutained, the kilojoulo, /;y"=10"' erg, is iiaed in its place.
^' ' iloriea to kilojoules, we have the equation 1 cal. =

or 1 i(j-239'l cal. The ecpiatiou, thci-eforo, for the
M ivi'tT from its elements reiivds

PRINCIPLES OF INORGANIC CHEMISTRl
IGO. Heat Effects in the Decomposition of Hydroffi

Peroxide.— The developnienL of heat wiiii^h awomjiaiiics the deM
position of liydrogeii peroxide into water and oxygen gas (p. 162) a
be represented in el tiimilar manner. The reaiilt obtained by meAsitl
ments is that an amotint of heat is developed eiju;il to 97 Ig |l
mole of hydrogen peroxide. We must therefore writ«

2H2O5, = 2H„0 + 0„ + 2 ^ 97 kj.

From this there follows, by rearraDgement,

2H4O + Oj = SH^Oj - 2 - 97 kj.

Tins ecjuation differs strikingly frrjio tbe feirmer one.
the previous case the forinatinn of the coiiipouiid \v;is accompanied I
a development of heat, the compound containing, therefore, less enai)
than the ctimponentfi. the opptiaite is here the cuso. One must ra
therefore, assume that firrji process of comlii nation takes place wi
evolution of heat r the reverse is also possible, although lesfi frequen

If we write the two equations

2H5, + Oj=2H20 + 572i;;/-
and 2 H,0 + O J - 2 HjOg - 1 9 4 fr/

below one another and add, we obtain

2H5J + 20j = 2H.O2 +2x189 kj.

Expressed in words, this equation reade : In the combination
oxygen and hydrogen to form hydr-ogen peroxide, 189i; are develop
for every raolo.

In thiB way we obtain the heat of reaction of a procesa which ct
not lie curried out in such a way that it tain be tneasiired, and whil
therefore, cannot be directly investigated. The justification for tl
calculation lies in the fact that every formula in a Ihermochemii
equation represents a definite amount of energy, and in the fact tl
energy magnitudes can be added without limit. The calciilatii
therefore, presupposes nothing more than the validity of the law of I
conservation of energy.

On subtracting the upper equation from the lower we obtain

2H5,05, + 2H3=4H,0 + 2 X 383^'. ^

That is : on the conilnistion of hydrogen to water by means
hydrogen fj«roxide, 3S3 kj pro mole of peroxide are evolved. Ha
again, the heat effect of u reaction has been calculated which caai
be subjected to direct measurement.

As can be seen from these calculations, one can, on the basis ol
few measurements, calculate the beat effect of quite a number

vni HYDROGEN PEROXIDE l67

metioiu which take place or could take place between the reacting
nbstuicee. The number of calculations possible increases very rapidly
vitli the number of direct measurements. There is a whole branch of
toentific chemistry, known as thermochemistry, which has the study of
tbece relations for its object.

These calculations can be most readily reviewed, if for each com-
poand the (positive or negative) heat effect which accompanies or
would accompany its formation from Us elements is calculated. This is
ailed the h^nU of formation. The heat of formation of Avater is equal
»286i/; that of hydrogen peroxide, 189 Ij.

In the sequel we shall give the heats of formation of the most
impotant substances so far as thoy are known ; from them there can
tkoi be calculated the heat effects of the other reactions in which these
nbataoces take part.

CHAPTER IX

CHIX)RINE

161. Formation from Hydrochloric Acid and Oxygen.—

now turn to the study of hydrochloric acid, which was used (p. 86
the preparation of hydrogen. From those experiments it foUoi
that hydrogen is one of its constituents. It contains, besides, ano<

Fia 151.

element called chlariiie, which in that experiment did not bea
visible because it united with the zinc, for which very reason, ind<
hydrogen was formed.

To obtain this other clement we must proceed in the rev<
manner : to set free the chlorine, we must convert the hydrogen i
a compound which am be separated. This we am effect by acting
hydrochloric acid with oxygen. If this action took place in the desi
way, hydrochloric acid plus oxygen would pass into water plus chlori
and we should attain our object.

As a matter of fact this process is practicable. If a current of

168

CHLORINE

173

1* ■ ' (• chlorine atid water wero produced from hvtlrucbloric

jU3i. „ 11, a crtiitraJictiori set^nis to be tonuiined tti the foregoing

iot, loc in thiit cjise (jxiuMly ihe opposite reaction took place,
[cidoritie in contact with water formed it more hihIjIc system than
acid aud oxygen, The dift'ereFice liea in the fact that in
■ we were deiditig witli tjusrnns hydrogfii chloride, but
.'/• iz<ptt</u.< .-iflnliiDi of it. The atabilily of a compound
jocntt}- much greater in sotutioii than in tlie pure state, and
joii reactions cm, therefore, reiidily iiti(leri;o reveraul, iiecnrditig
t'ne or the other condition obtains.

166. Ghlorme Hydrate — The Phase Law.— When gaseous

is pa.ssc<i mVf ice-cold water — it is hest to have some pieces

Lin floating in the li(|iiid — a greeniiih crj.stalline suliatance soon

unl. This consists of ehk>ririe and water according to the

. i'L - tiHjO, and is caJletl e/ihi'tni' Iii/ilriitf'. Undur attju.isphoric

ihie suWuince is stJible only "p to + 9'6'' ; if liwiteil tin a

tempemture it deconipoaca into chlorine, which escapes as a gas,

wMer (Baliirated with chlorine), which remains behind. If the

be iocreased, chlorine hydrate can he kept at stJll higher tera»

i; if it l»e loweret], the temperature of stability of the hydrate

lower. There corresijonds to each leni|ieratiire, therefore, a

prvKure of the chlorine gsis, at which the hydrate can exisL

Thwe relations show the {greatest aiuiilarity to those existing in

U a volatile liquid (p. 122), where the possibility of litjiiid

f»^mr existing side by side is ako associated with a <iefinite

•rhrt-U incifases with rising tcm]icrattne hut is iiiflepcudent

f al>«)hue amounts of the two fomis. In this axsti

, til uce of chlorine hydnite in contact with gaseous chlorine

ioci is rejjnlated only by a relation between pressure and

r, and the ijnantity relations have no triHiience.

A difJerrnce exists here, however, in so far aa, in the condition of

ihtffe are present, not itcn phases (p. 131), but (hnf, viz.

byxiru(<.'. saturated arjueoiis solution of chlorine, and gaseous

. Thi* is due tti the fact that we are not now dealing with

! eqailibriiuit <>f a siuijli- substance, as in the ca^se of water, but with

"■*-*■ TTfr", water and chlorine. In the same meaKiu'e as the

of 8uf>stajicea increases, the number of phases which can exist

' tiilc aLh; increases.

vr*l*r along with vapour or along with ice, i.f. two phases

i^can exi*t bide by ai<le at lUffaeni temperatiu'es, but three

[tU. WHtor, vapour, and ice, only at om i^iinjle temperature, so in

CMC there can exist Ihrvc phases side by aide at diflereal

afid there must be a single p<jiut at which fvwr phaaca

! (Htawiit. Such a point is got when we assume ice as fourth

Ai It matter of fact^ ice, chlorine hydrate, chlorine water, and

I gu can exist side by side at the temperature - 0 24 . This

170

PRINCIPLES OF INORCIANIC CHEMISTRY chaj».1

ooncentraterl hydrocliluiic acid is plsiccrl. The evolution of gas takes
place jri proijortion as then m-M is allowefl to How U> tlie Itloaching
powder.

The theory of this procsss caiiiint be given till later (Chii
XXIII.) ; it must suffice here to intlicate that we are again dealii
with an oxidation of the hydrochloni: acid^ the hydrogen of this being'
converted into water.

1S3. Properties of CiloriBe. — Uy these methods a gaseous
substance is obtjiitud of ;i yellowish-green colour, whicli is distingniBhed
hy very Hti'iking pri>perties from all the gases hitherto dfscribed. It
jMisses&es in the highest degree the uupleaaant stnell we liave already

''4

Frri. rtS,

mentioned, hfis r corrosive action on the mucous membrane of the
mouth and nose, and ia therefore very harmful and poisonous. This
gas cannot, like oxygen or hydrogen, be collected over water, since it!
is fairly soluble in that licniiil. In other cashes mercury is used for suet 1
gases, but it cannot W employed here, since it inimeiHately eorahinea
with ehlcirine. In order tit iiolleet the gas, use k made of it-s great
ifrnsUij ; if the gas is conductcil to tJie bottom of a dry l>ottIe, it
remains at the bottom and gradually displaces the air. By holdinj,'*
piece of white {rnjier behind tlte l>nttle, it is easy to obser\-G the pro-j
greas of the tillirig, the green gas forming a distinct contrast to the
colourless air. When the bottle is filled, it is closed by a groundMH
stopper, rendered tight \iHth vaseline, jind the filling of a. fresh bottle
is proeoeded with.

Since .some chlorine always escapes into the air during this pro- 1
cess, the preparation must be carried out in a good-drawing fume]
<"' or else in tho open air. Also, while the Irottle is being filledij

CHLORINE

it nwiy be cloeeil by a doubly bored cork through which it supply and
a rlisL'hiirge tulie puss. I'y mfans of a iviish-bottle wiUi nuistio eoda,
it is thoti possible to reiulef the escaping gas itmociioua.

As is seen from this Iwhavioiir, tho density of chlorine ga* ia con-
siderably greater than th it of air ; its molar woight has been fomid
by ineasui-emeiit to he 71. Chlorine is, tbcrcfoni, alxmt 2-3 times as
Leavy as oxygen (M.W. = 33), and "in times as heavy as air.

Chlorine is diatinpiished from the gases hitherto considered by
the fact that tt c^beys the giis laws with much less exactnt^ss. Like all
gases of comparatively great density, it exhibits meaaurable deviations
even under oiTlinary conditions; for with increase of pressure or fall
of temperature it« density infteasee iiwre than it ought to, according to
the gas kws.

C'-onneeted with thi^ is the fact that chlorine on be fairly easily
condensed to a liijuid. At 0" a presaiire of 3'7 atmospheres is
Kiifficieni for this; at room temperature (18 ) the pressure amounts to
IG'5 atmospherea, and the critical temperature is reached oidy at 146*.
Above this temiiciature chlorine cannot be converted into a liqaid by
any pressure. 'J'he highest pretsaure just undemejith this temperature
by which chlorine can still \m lifjuefied, i.r. the crUiail prrssure, anjounta
to 94 atm.

These properties, then, make it possible to condense chlorine into
steel bottles which have been tested for a considerably higher pressure
than the criticiil preeeure, and in which the chlorine can be stored and
transportofl. Although chlorine under ordinary conditions, espcciallj*
when moist, eagerly combines with almost all riictalB, carefully drietl
cblnrine shows itself so inactive that there is nothing to prevent its
manipulal:ion in met,'dlic vesaels. By means of an a<ijn9tiihle cock the
p.s can be witbdratvn from such a holder (Ftj;. 37, p. 105), as desired,
and one is thereby sparetl the very troublesome preparation of the gas
when much of it ia required.

The peculiar action which water here exhibits is not limited to
chlorine ; there are very many reactions which take place only in the
presence of water with such velocity that the result can be observed
in a ineasurahle time. AH these must be numbered along with the
oiirthflic pfiemimfnu {[>. 107).

Liquid chlorine has the green-yellow colour of the gas in a much
higher degree. It is an oily liquid, of density 1-56.

At lower temperatures chlorine passes into a solid, crystalline sub-
stance which exhibits the .^ame green-yellow colour aa is shown by
chlorine in its other states,

164. Solubility in Water. — Chlorine dissolves in water in fairly
large amount ; under ordinary circumstances one litre of water absorbs
about three litres of chlorine. The solution, which has the smell and
taste, as well as the corrosive and bleaching properties, of chlorine gas,
is called diioriiu' imtfr, and is used for cliomieal and medical purposes.

€ BOKO ASIC c

,t»a'

ol ^«'-

\ie

ic^T:^!

e)i

,i\t

:d^..^\.^'K:^'

\,^^

^v\'*'-;\wv^^«..\;,. wn^

v^*-'

**.■ oU*^ Aeix^

w hm.„ ; only
. wbttiib gj-cfri, 'jM^
kw fijiftlly goes out

•colour ,

the eyy

*«d is ^

.'^ 'insod
''quid ^

^^^« IB

V''»nus r

,.,„ caa I,; ^^J-^*^ t
. ««>•• '^ ^''^ i^'-oduet'^J
,.npertie8 arp _.

,,,ibu*tirjrj of k '^^■•c

Hydrochloric >'

-•■'<■'<■ !•« .ij, ;;«

'-""•"ininKh'r;
■■"8"«ni„ ,1,/V'

"'^•'■f^' ■•"MfJ ,1

OVt'

CHLORINK

nn washing out tlm contents of the botfle witli water ; these
exactly the aamo pioperties jvs were shown by the product of
Unbtutiati of hydrogen in chlorine.

burning of a ifttj- ctijitHf in chlorino depends on the same
Wtkx also consists chieHy nf hydrogen and cjirlioji (along
Hidi tome i>xy^ti). If a burnijij: wax candle lie introduced into a
ItlUe of chlorine, it continues to brmi ; at the sjimo time, however,
|w ttmie becomes dusky rerl in colour smd emits large (juantitiea of
,or carbon, sinoe the chlorine cannot, under these conditions,
with the carbon. In this case, also, the fontiation of
en cbloride can be easily demonstrated.

of the iniportitnt technical applications of chlorine dejwnd

power of withdrawing hydrogen from sulistjinces eontuinrng

therefore destroying them, i.e. converting them iuto otlier

tjje one hand, chlorine is used for hhiKkin^. The vegetable
frum vhlcfa textile fabrics and paper arc made are generally not
as it is desirahle they shouM be for use or for being further
contain natural dyes wliich must be removed from them.
purpose they are treated with chlorine, which removes
n from the d>es and converts them int« other, ison-coloiu'eil
i«.
with this dehydrogenising action, urithfUtm- takes place by
of the chlorine. This depends on the co operation of water,
u we have already seen, is decompoiied l>y chlorine with
■/' tjsitf/rn. If this process takes placu in the presence of
■ihciAnces which can form oxygen compounds, these are formed
readiness, i.e. the substances are oxi<l!aed.
ibe other hand, chlorine is useil for didn/triititf anil derilixiwj.
•ctioo also depemU on the withdiawal of hydrogen from or' the
experieDced by malodorous and other harmful substances
the agency of chlorine. Especially is chlorine a vjoliMit
fpT tbe small living organisms by whose activity rotting,
ioai, luid auch like, are caused, and which play a part in the
of certain diseases. The apjiJicatio!! of chlorine for such
ia, tinfortnrtately, very greatly limited by the fact that it
■ An a rery harmful substance for the higher organisms, and on
■''•»e*lut more prolonged action can give rise to serious symptoms.
i^z. Composition of Hydrog-en CMoride. — The comliinatiou of

i«ith hydrogen is, likewi.sc, subjeit to the liiw of Gay-I.Hssuc
N^hig the vohmie ratios in the interaction between gaaes (p. 142)..
chlorine and hydrogen combine in i-quul \olunies, and the
ilorjc acid gas formed occupies the ssame vohinie !*.s waa
y occupied by the mi.xed gases. Whereas, therefore, there
the formation of water vapour, a diminution from three
to two, wc have in the present case a rombiunlim mthmil

178

PRINCIPLES OF INOHaANIC CHEMISTRY

ikangr of nitumr. The inohir weigJifc of hjdrochloric acid
therefore obtained as the half of the sum of tfie molai* weigh t£
t'hlorine uud hydrogen. This calculation is, in rnitnbers,

Clj+Hj = 2HCl
70'90- 2'02= 2 ^ 36'46.

One mti convince oiieself of these [t'laijons, both by Uie deco
position of hydrogen chloride, that is, hy amih/m, and by the fonq^
of hydrogen chloride from its elements, that is, by si/HMfjuV. ^

When an electric ciinent is conducted tbroug;h hydrothlorie a«
liy means of two iilatinum pliites, chlorine iijipears iit the one plal
and hydrog<Mi at the other. The energy which was set free on t]
foriDiitJon of the hydroj^eii chloride from chlorine and hydrogen, at
on the solution of th« hydrochloric ucid gas in water, is itgain giTK
hack by the electric current, which therefore makes it [jossiblc for t]
two elements to sepirato in the free state. The dt-tiiils of this proce
will later form the subject of exhaustive ctuisidenition ; at this ptwn
we rest satisfied with the result that the hydrochloric acid is de«0B
jiosed by the electric current, and that it« elements are evolH
separately.

Tina experiment is performed in the apparatus &howii in Fig. 5S
on p. 141. On st^arting the jirocess- by passing the electric cnrreni
jtfter the apparatus has been filled with strong hydrochloric acid, gl
is at first seen to be evolved only at one electrodp ; tliis g«* j
hydrogen. At the other electrode there is only ii yellow.greft
eolonition produced, because the chlorine evolved dissolves in tb
hydrochloric acid. Gradually tlii.? becomes saturated with chlorfnj
and gas is evolved regularly al both plates, or "electrodes."

After the fiiHt portions of gas have been allowed to escape, l\\
opeiiinu; the taps, it is easy to saiisfy oneself that the two limbs of tli<
apparatus become sinndtanoously filled with equal volumes of gas, and
that, as a matter of fact, therefore, equal volumes of the two ga
produced in the dQcomposition of hydrochloric acid.

That one of the gases is hydrogen is shown by the fact
burns with a blue flame in the air. The other gas can lie recog
as chlorine, even by its colour; the smell and the bJeuchiiig acli
H piece of litmus paper confirm this.

1 7'^. Formation of Hydrogen Chloride from its Elements.—
Ff, on the other liatid, a mixture of equal volunie.'* of chlorine lUid
hydrogen is prepared, it can be ignited by an electric spar-k in the
sjime way us detonating gas, and is completely converted, with
explosion, into hydrochloric acid. In this cjisc, however, there att
some remarkalile jjhenornetui to be obsorvei}.

It is not Muly by rise of temperature that a mixture of eq
volumes of chlorine and liydrogeti, which, on account of the similarity
mentioiicil, is cUled ehUwiue ddonalhig pus, passes into hvfiro]

is found an
extubit esaaly tie

the fO^wJM wi

relsttnos. Wax

ImtOe of Alnriar. il
the fb

Boot or esrii^ amet ike
combine vitk «br

8(NM «f tfe
on it» ppfweat «l
it, and
sul

On th»
fifattai tpon

dy«d, lot

For tUs iiiiiiMi tk(9^ 4

liy«ii ugui fnmk tke 4y^

cotapmuMii.

Along vrtfc tUs

wbidi, am ve

otlMr

nitb spedal i«MMM% u*.

On the oikr knd, cU«vr ii nnd fw
TbiB aelian abo depwJi «■ ikr »itUraval «C I
uxidatiao cxperioMed b|r ■aledavuBB and
tkrottgh tbe v^tnejeif
poiMO ftr tfce
patTclMtkMi, and

purpoaw ii^ aitetnaatdr, twt gntdv
is jJio a rt(7 NmW Mhrtanry for tW
aotnewhat WOfV fniMBBd aeUia an ^ve nae ta <

clitdrioe vitk Itydn^BV >^ Bwwi, miijut to tls knr of

re^urding tbe

In fact, rUofine

hrdrochlonc

previoofljr oocafiad br tk

VTM, in lie iiHWilwia «< *ater rapcnr, a

voJiiiBea U> tvvi^ nv baxe is tW frotiit

180

PRINCIPLES OF INORGANIC CHEMISTRY

acid is decomposed by the t-lectric current in the vesse! A (Fig.
ivliich 16 furnished with two electrodes of carbon (thin arc-lij
cirbonB), or of platinum. Under these conditions the gases pro<iu*
immediately mix and, ^ftei* the evolution has been going on for a h
or a whole hour, in the right proportions, In the bullis which I
blown on the delivery tube, there are a few drops of water, to free t
gases from the bydroehloric acid which they carry over. Atta^bprl
th& dtilivej-y tube is a scries of glass bulbs blown out of thin glass ai
connected by thin- walled capillaries ; they may be 4 to (> cm.
diameter. These are filled with the exi>losive mixture by displa*
nicnt. Since this is heavier than air, the low of bvdbs is placed in J
upright position and the gas passed in at the foot. All this must 1
done in a wifik light, with exclusion of daylight; for this pur|Kis(? ti

.'V

if:

Fm. ((i.

light is most conveniently supplied by a lamp with yellow cylinik
Kuch as is used for photographic purposes. After tlio gaa has hoi
prissing for at least half an h<mr, precautions being taken to cany off tb
excess, the two ends oi the row of bulbs are closed, for the time l*iiH
with wax ; one then proceeds Ui melt off the Indljs from one another.

Although the chlorine detonating gas can be caused to exitlode li(
beat, the capillujies can, without danger, be softened in a small g*
Hanie and closed by drawing out. The gas which is direcllj' lie*W
burns, certainly, to hydrochlotic acid, but the combustion does nd
pass into the bull is, because the heat which is develojiod is taken u
by the glass walls of the tiifie.

With tiie bulbs of chlorine detonating gaa prepai'ed in this *»!,
the experiments deaerilied can also be carrieil out : the exploaioB i
these is unattended witii risk, since the light glass splinters can seapw
do any damage. Instead of sunlight, burning magnesium can be ui
ti> bring about the explosion : either magnesium powder is placed it*

CHLORISE

18F

! tul>e 1 cm. wide ami blown into a flame, Of a lanip is employed such

kttsed in taking flust-light ])htJtOfi,'^rapl<fi. In both ca&m the Imlbe
witTi the e.\ji!()siv(i mixture ninst Iw placed very close to the flame.

17r». Fbotochemicail Actions. — It follows from the experiments
described, that the action of light on the chlorine detonating giis,
similarly to that on chlorine water (p. 172), consists in increasing the
velocity of combination of the two components. It has been repeatedly
explained that there is [-ejison to suppose that in every syatcm in wliieh
a chemical ])roce3s can take phice, thiit proi-esn really docs tjike jdtice,
although often only with an immeasurably snifdl velocity. In the case
of the chlorine deloniiting gas, also, we may make snch an asstimption,
and the action of light consists in increasing this immeasurably small
velocity to a measurable one.

In fact, it has been shown by appropriate investigations, that the
Telocity of tiTmsfonnatioti of the chlorine detonating gas into hydro-
chloric acid is proportional to the atrenyth of the light acting.

* The manner of this action is still somewhat obscure. Wc mast
by no means assume that the energy of the light ia expended in bring-
ing al>ont the reaction. No energy ia consumed in the combination of
the guises ; on the contraiy, a fairly large amount of energy is set free,
as follows from the phenomena of explosion, and the spontaneous
tranijmiiision of the combustion through a tube at the end of which
it is initiated. From the observation that completely dry chlorine
rJetonating g»s is scarcely sensitive to light, combined with some other
facts, it becomes probaI>le that we are dealing here with a rather
complicated process which takes jjlace with the co-operation of the
elements of water.

176. Hydrochloric Acid, — HudrtKhUme acid ia met with in com-
merce as a lirpiid like wat(»r, which, in the pure state, is colourless ;
the crude hydrochloric acid, however, is generally colotired yellow
through contaniination with iron. This is not the pure compound
hydrngeii chloride, Imt a .lolntion of it in water, Pru-e hydrogen
chloride is a gaa, and as such is difficult to employ and to transport.
A solution of it in water, containing rather more than a third of its
weight of hydi'Ogen chloride, is therefore used, Solutions containing
this amount or more of hydrogen chloride fiiim in the air, gas being
given off; solutions containing le.ss than 20 per cent of hydrogen
chloiide no longer furae at the room temperature.

In or«ler to obtain pure hydrogen chloride gas from its solution,
commercial hydrochloric acid, it w necessary to withdraw the water
from the latter. We have already learned that concentrated mljfftiiric
ttrid can be used for such purposes. Accordingly, our iippfiratus con-
sists of a liottte tlnriiigh the coi-k of which pass a dropping-funnel and
delivery tube, The tnlre of the di-fjpping-fnrmel, which is filled wii
fuming hydrochloric acid, is diiiwn out to a narrow point and reach<
to the bottom of the flask. If the tap be opened and the hydrwhlor

182

PRINCIPLES OF INORGANIC CHEMISTRY

acid .'illowetl to puss slowly into the 8ul]jhurk- acid, the water
up l>y tlif tfittbi- und the hydrogen t-hlondc uscapes as a gas.

The tipper part uf the gonorating fljisk does not become coloi
^^ hydrogen chloride is, therefore, colnurless. lb cannot be collected
^H water, nor can it he collated wt'tl liy displacement, since it is
^^ slightly heavier thari air. It can, however, be collected over mer
I since this is not attacked by hydrogen chloride when both siibsH
I are pure.

^^ * The use uf mercury for collecting such gaeea as are readil}
^^■;Bolved by water is due to Priestley (1780), and ivas, at the tiro
^■important invention, since it lod directly to the knovvledgt; of qu
number of gjiaes which are dissolved by water, and of which, there
one could previously know nothing. The mercury trough whi<
uacd in sucli operations is genei-ally made of porcelain, and of ml
form that the ijiiautity of this rather expensive metal required U
it is as small as possible,

177, Properties of Hydrogen Chloride. ^Hydrog«n chlorii
a colourless gas, the density of which amoiintB to M)-^), correspoii'
to the formula HCI. It is, therefore, ft little heavier than air.
pressure and cold, it can be converted into a liquid; at — llJ
aolidiHos. The liquid boils urnler atmospheric pressure at - ^0'
pressure at 0 amounts to 2 '8 atm.

Liquid hydrogen chloride h a colourless, rather iuditf'ercnt lie
exhibiting little of the chemical roactivily which can be observe
the case of its aqueous solution. The liquid neither acts on me
nor reddens litmus, nor, when water U carefully excluded, dot
show any of the other properties of acids. This reniarkahle eoni
to the behaviour of the aqueous solution has great significance
will be explained later {|k ]s4).

Of the other properties of hydrogen chloride the lao^t strikin

1^,^^ , its great solubility in water. At r

/ temperature, one volume of water abs
/ +50 volumes of the gas. By the ab
/ tiou, a large quantity of heat is develo
/ which point* to a rojiction between
ff water aiid the hydrogen chloride

^f This reaction is of a special kind,

/ / «'ill be discussed more foUy at a

^M I The great solubility of bydr

___^H_/^ chloride in water win be shown by blo'

^Z^^EZ^ a little water up through the mercur

^^^^^^^H the gas collected iti a cyliiuler, by ni

- ■ .^^^^^^^^ ,,f a pi(>ette bent at the lower end (Fig.

Vw.fA. I'he mercury immediately aseeiidii an

the gn* 18 pure, again fills the cylinder. There generjifly remains.

CHLORINE

183

>le ■)f air utiiibsortwci, since it h veiy (iitfioult to lumove
of foreign gases.

Ttus vjiter which was adikul has Ix'fii uunveited, by thu alworption
hydroiien chloride, into Injiirorblmic add. If :i piew of iiietiilHc
)«Kiuiu liti iitlnxiuced under the mercury and alluwed to piaa up
hvilix>chloric atid, it decomposes this, coiiihiuirig with the
atnl iJherating the hydrogen. 'When the ovohititm of gas has
it ia easy to convina* oneself that the p\A is hydrogen and that
linne in half that otTtipiiMl !iy tlu* hyLlrogfii ehioridf gus.'
[178. Absorption of Hydrogen Chloride by Water.— In pass-
^vJmirrri chknidf in comparatively large iju.uility into water for
• of preparing
iu» uvdnx;hloric ncid^
{■ceautions miis^t )>c
on atcoutit of the
of the altMM-ptiaii.
)ip|Mmtti8 used for thij;
is shoim in Fig
The bj-drogen chloride
is gfiienvlcd in A , //
mi ciMjity wash'ltottle,
'' a wash 'h<tt tie half
with water. The two
ies are curinect«il
toppOHid to one another, // ^^oo^
Itlttt in H the gas enters
the short and
through the long
'', in the reverse manner, receives the gas through the long
When the gns is evolved, it first fills the empty bottle />, and
pi WW over intfl r, where it is alisorhed hy the water; the
air cseajjes through the short tube. If, now, for any reason,
iution of giis should cease, the water would, if iho bottle H
Sot there, f>:w« hack into the generating flask A, on account
the alisoqition of tlie gaa ; by the action of the water
ibe concetitniled sulphuric acid, an explosion might result,
_in ,ir>\' <;i>*e, the esijeriraent would l>e spoiled. The hottle
•\ this contingency. If regurgitation .should occur,
i.<.tt get farthci' than B, and if the pressure in A is further

'^'

V\n. Vt,

.vs (if tliH eipcriiui'iil, tlie npparfttns niB«t (>rt?vioni'Iy be unrtfiiHy
'itlimr nf the hydrogen clilnriJfe, on Hccoulit nl Ith tfrefit "nlll-
• • sinnll. Also, otu) muft not omit to iiriii^ tha kos under the
iiteui'nn^'iit nf the eijHfrinieiit. Tlii» is iiKWt wmply mctiiuplixhfd
inJer mercury, iilaoinn it In h lurge veiiw-l <rf water, ami wnkiiig
<vater outride and in>'l(le i« the laiiic. It ix li^rv presupposed
Hlri>Kcji rtilorltk "Ver iiiemirj', llinl gn> also ^t'■^ liodcr alliiO-

184

PRINCIPLES OF INORGANIC CHEMISTRY

reduced, air pasacs from C through the liquid in Ji. \\ bei
presBvu-e in A again rises, the liquid is fii-st tarc&l over from i
(J again, and the altsoqitiou gcics oti regularly.

Besides the one described, there arc many other safety arnuigd
ments to prevent the liquid passing buck into the generator. One e
the simplest ot these consists in inserting an open funnel tuhe in Ux
cork of the generator itself (Fig, 67). It will be easy for tha readei
himself to work out the action of this in the ease of dinriniabdi
pressure. ;

When sfjmowliat larger quantities of hydrogen chloride are dial
solved in water, the temperature of the solution rises* to an viudesiral
hoiglit, owing to the heat developed in the process. The solution
therefore cooled by placing the bottle in cold water or surrounding il
with ice.

In iho commercial preparation of hydrocblonc acid, the hydroj
chloride is, of course, not prepared by the method employed by
It is obtained by the aetion of sulphuric acid on common salt, accord
iii^ to a chemical reaction, the theory of which cannot be developed til
later {Chap. XlLl.

179. Hydrogen Chloride and Water. — Most gases dissolve ii
water to a much less extent than hydrogen chloride, and the ut>sorp
tion followB a law discovered by Henry, which states that the araounl
dissolved is proportional to the pressure. In the case of hydroclilorii
acid, this law is not even approximately fulfilled ; on the contrary, tin
greater portion of the gas is absorbed independently of the pressure,
and an increase of pressure effects only a small increase in the amoUB
dissolved.

This behaviour points to the fact that in the case of the al«orp
tion of hydrogen chloride a sjiecial chemical process also takes part
Tliis process consists in the rtements i>f hi/ilrnrfcn diloridi' pa^siiiii, m tupi/ot
siilufitw, inhanothff o»iiJit<cn, It is very reitiarkable t!h-At itnhiidri»tf, jiqak
liydrogoii chloride docs not exhibit the pro^wrties of an acid (p. 1S2J
although it conUdns the elements of one. This is due to the fju't tlul
the characteristic properties of acids are not exhibited by the com
poncnts of hydrogen chloride until this is converted, through soluti
in water, into the other condition.

When, therefore, hydrogen chloride ia dissolved in water, two jiro
cesses occur. One portion of the acid, which ts ull the gi-eater tlH
more dilute the solution, jiassos into the new eoiulition ; anotbi
portion dissolves unchanged lus hydrogen chloride. The first iMirtiu
does not follow Hrnry'is law of the absorption of gases, but only tb
second. For this i-cjison, the amount absorbed increases more slow^
than the pressure.

There is a further remarkable phenomenon connected with thi
Hydrogen chloride, in the pure state, boils at - ^d" under atmospiiei
pressure J water boils at + 100 . One would suppose, therefore, th«

CHLOKINR

isri

inta of a<|ueoiis solutions of hydrochloric ftcid would lie
b«8e two temperAtiires. This, iiowever, is the case only for
»ntnite«1 solutions ; more tiihite solutions, on the other hand,
AiykfT temperature than water, so that by the ivdditfon of
poUule substance to water, the volatility is not increased but
t

|lation between composition and boiling point is represented
rv« (Fig- fiS), in which the percentage content of hydrogen
|_measurei) on

ikxis, and
under
iro on
c;in
the curve

ISO"

/eo'

ae"-

raaximitni at
bespnnding to
lutiiiii, and »U
b|tores boil
■the -20%

pet causes the
; bcliaviour on

(. We pre-
, on distilla-
Dinpnsition of
^e«t e^-i<lently
lly in such a
I tbe boiling
for the more
the lower
ion, must
firat, nnd the

|tut therefore, necessarily, boil higher thiin the oiiginal

If now the strength of the iicid solution is below 20^,

ttg. rfiffTf ililiife ncitl must difltil over, and a stronger, higher

1 remains iK'himL Thi» continues until the residue contnina

fdrogon chloride. Au acid of this strength cuniiot leave ii

iilig iHwidue, for it is itself the highest boiling mixture; it

Irforc, ilistil over unrjutngfd, smd this lias been shown by

It tn be the ciise.

rwlr, if one sttirts with au acid stronger than I'^f/., sv still
eid luust distil over, fur the weaker acid has the higher boil-
I Jind therefore remaina behind. But this sefviration, also,
lairricd on indefinitely, for when the strength of the solution
y/ no acid of higher boiling point ctm be fortned, because
th, and the liqui*! must distil over unchanged.

Fid. ffl.

loossa

.^ OF DJORGAXIC CHKMIHTRY chak

^UMii with aa acid uf 'irtr/ <.'unc'entratii)ri ; tku^
uaias at che last iiu acid of 20%, audi
V dtlnte or more concciitr»t<^ acid will bej
irtMi with an acid containing !efi« or morel

■;u heim tatuit of regarding this conslant boilti^|
■uMftl coiapocitid. It is not one, fur the com-
Aii 'loiling acid ia dependent on the pressure I
ii is carried out Under 2*3 jittn,. tW|
I i.t()t>tj atm., 23%, of acid.

■ he }nish of what has been said above, we I
■ in that n-fHf solution, the Iwiling point of

the neighbouring riohttions on eitber sid«

■ composition. By quite similar reasoning
j-5.ii that soliitiona, also, the Iwilitig point of I

of the neighbouring solutions on either sidetj
ii-«tiIhitioii. In this case, however, the solHtionj
tion appears not in the residue but in the]

. ^^ naluaon^ wliit-h iiiue l»cen described for hydrocMoriel

, >ci uf a jihtmortienon which appears in a striMjig

I' I di'tigen chloride ijaa, and which ia also noticeable

n i.ttcfl hydrochloric jidd, viz., the fuminif of tkia

known that hot water fiimeij or forms a mi«t

n result of its higher temperature, it gi?w

• HI tluiti can remain in the gaseous state at the

ajf. Wutcr, howevei-, of the temperature of the

h«rni a mist, for it cannot jKissihly give off mot*

^, .*i» Iw i-ontjiined in the vapour form in the air. Con

\vUt\K-hloric acid, however, fumes even without beinjr

'wMii»«t ^ this '3 t-tat the evaporating hydrogen chloriJo

«4U>r ^aponr in the air, ivith \vhich it foinis a liiiuui the

^m*.* ol' whii'li is much Rmaller than that of the toticen-

lliii Kohition will, therefore, be precipitated in the

|)ilutc acid does not fume, for the reason tljat iti

■ { form a less volatilt? solution with the water vapour in

Uny i:(iriuun more water than the difticiiltly volatile 30"^

i.tlier Imnd, the concentriited acid fumes only in ii>0]d

■ iwitver concentrated, Iw placeii in a bottle the interior

, h u>d with sulphuric aeiil, no trace of fumes or mist it

... , , , V .-Vtiu.

'Hniip considerations we may conclude that evcrjr-substanrt

HI with water a solution (or compouuJ) of ctw^idcrablj

|Hm |toint, nmst fume in moist air, whereas this cititi"t

«u>wltiiK'es which do not have that property. We shall

CllLOi;i\K

187

•eqoel liar« frcijiient upjxirtuuity of uppiying and conKrmiDg
iram.

, Properties of Acids, — Hydrochloric acid, or the aqneuiis

ut hydrogeii chloride, is a strong acid. In the name nt'id thore

up « *rhoJe series of properties poseessod in common by

of iliffereiit composition. Of these properties the longest

is the tu-iii ifi.tif, whicli, us we know, is jiossessed by very

■t niliscanees. A setonil property shown by all sulistances with

is the {lower of reildeninif the colouring-matter lilmus

IV A third common property is that of endnnij kt/dntffm when

Jo contact with certain metals, such as zinc or magnesium.

Rt ia, for ua, the most importaiJt property of all. One can

ber it is a property of all »cid giibstjinces b^'' hrini^iiig acid

vi all kinds, such as vinegar, acid fniit-juices, dilute hydro-

Eteki or ralphuric acid, a golution of citric iicid, etc., in contact

rium potrder In all cases, a more or less vigorous ev<jlu-

gM takes place, and on testing the gas, it is found to be

«c introduce the name aciii for the substances possessing these
wc can say that all afvh lon/nin lii/dii'/jm, trkkh Ihet/
itr Ike tirtwii nf iiiii{fti^jsiian. The objection might be raised,
hydrogen comesi from the water in which all the acids were
; with reganl to hydrochloric aeid, however, we alremly know
I oonkiiiii; hydrogen, and tlie sume has been proved by chemical
with regard to the others. On tlie other Jiand, water does

ibiy act on magnesium at room temjieratiire.

propnrties we have just descrilied arc not possessed by all

compounds ; they are wanting in thu ease of water, and also

\m of spirit of wino, petroleum, stearin, etc. It is ea.sy to

PoiMBell that these substancGS contain hydrogen, by setting them

kbd holding over the flame a cle^n, dry glass ; it ia immediabely

with a dew of watei' drops. The hydrogen of the acids, there-

also be in the special condition mentioned on p. 184, by

of which it acijnires properties bclojiging only to the acids.

relations we shall immediately explain.

ids and Bases.— The properties which we have employetl

ieHiiticatiun of acids disiippear when aiiistk soda (p. 15-t) is

1 Ui the acid liquids. This ts seen most clearly in the case of the

»ge with litmus. Dilute hydrochloric acid is coloured red

1 of litmus solution. If a soluiion of caustic soda is now

ftddci to this, the colour at first rem-iina unchanged, then

Bt, which disivppear on stirring, are seen in the liijidd where

nnln drops, wnd finally, the whole liiiuid smlck'nly Ivecomes

By working farefiiliy, it is easy to recognise that the blue

w prolucc<l by a single drop of the caustic soda solution. .

h Ihi MiM Umr, nil Ihr oifirr pvopfrilfs of Ifw acids have flisnjtjmared.

jmatajnJBi- or inorganic chemistky chap.

•• toMsv tMtos wad and does not evolve hydrogen witli
^•w«\tt«r. ^uulur exiwriments can be performed with all

j.'il M«k/Utio nuut therpfora have taken plAoe by the inter-

itoir afdti and nvustic soda, the product of which is
.ju4atiikt> Uw U<]iud. A rcBJdue is obtained which, in
u b« cmrnvn sail.
'At. ct^mmon salt consists of thtonne and fodium
•«iiia aiul hydrochloric acid jicid common salt, the
iiintHl iu tht'tn must have Iweu converlwl into
i hn*iic '»■'■»*' "Jther substances are bydroj;en from the

d »>.\yjivn plus hydrogen or hydcoxyl from the
tnokcs up, however, tlie composition of ttnter,
. \ thus second product formed by the Action of
-.vustic sodii.
-I'l-ti more clearly when the reaction is expressed

:U5»

rtw<

NaOH + HCl = NaCl + H,0.

../ vA.>«tttr can likowiao be proved by experiment. If dry

< - is pjiased over some pieces of caustic soda, water

h ^ixmt evolution of heat, and can be condenswl ;

■ jwtioti, common salt retnaiiis as the residue.

■!h><r substances which, like caustic soda, neutraliso

I-*, giving rise to new substances accompanied by

watt'r. So far as they arc soluble in wattr, they cwi

n.«d by the fact that they restore the blue colour to

«.» boon made red by acids, and withdraw from tli«

..f evolving hydrogen with inagneaium or other

the sjinie substances as we previously (p. 155)

vai^ conipounda of metals with hydroxyl, and whieb

■ -*■ (foundation) k due to the fact that these snh

yw** ilnj «oyt'iVi/(i/i7'' constituent of salts, whereas most of

t W more or less ea-sily expelled by heating. That portion

,>iv HlJible to heat Wfis formerly regarded as the more

I wrtN culled the foundation or base.

btnlng Proportions between Acids and Bases.—

mKicIi Inkcs place between bases and ucids, and which jgives

•vuintion of a salt along with water, presupposes a per-

I iitio between the amounts of each. It we add a bast

iw nuK'li of the hydrogen will disappear as is necessary fw

fn (if water with the hydroxyl, viz., !-01 gm. hydrngeu tn

l^vdruxyl. Wo long as Injilngcn \& in excess, the liijuid will

i'tiiK;tion, for this is not interfered with Ity the presenci!

mbiilJinces. By continued addition of the base, a poinl

L"HLOl;lNK

189

when all tlie liydrogeii has disapi>eared, iintl
the Vwisa Such a. liquid will therefore exhibit
fcher of acids nor of bases ; it will, for example, eolour
l»lu€ nor refl, but will leave its inirple colour unchanged.
id is called wnfral. This property is prtseessed by water
iolutiuns uf most of the salts. For example, rntumon salt

SotutKMIS.

t«n Im« nnade of tlicse phetioinemi for ninny purposes. If it
41 nf forming salts from acids and JMises, litmus is used, best
jiper, to determine if the components have been employed
proportions; so long as blue litmus paper is coloured
is too little base ; if rei) is coloui'ed blue, there is too little

II1U piiper can also be used Uj show whether a salt is free
imiruttion with at-id or base,

yUeciprocal Estimation of Acids and Bases. — Tlie
It application of theso phenomeuei, however, is to the
of ihe quantity or the concentration of acids and ijaaef.
Be solution of caustic soda he always used, the amount of It
noutralise dittereut solutions of an acid will be /tiOjU'idiDuil
titit* "f thr ticul.

aethod of iletermination liased on this is carried out as
L'hc solution )>f caustic
ined in a tube of
imeter, graduated
of etched lines into
limetreti ami fractionu
smtl closed at the
iy a. tap. For
a piece of
nlqtig can be iislh:!,
pressed together by
I pinch -cock; further,
|«ake of the lu-tter
uf the outflow, (V
tube, flruwn out
"^M inserted iri the
This apparatus ib
(Fig. 6a).
line the amount
any givi'ii sample,
dilute hydiochloric
^|t of IiiniU8 solution
the burette is tilJed

lyo PRINCIPLES OF INORGANIC CHEMISTRTfJ

outflow jet. The caustic soda ia. then allowed to flow
acid until the ret! colour of this BudileTiIy clianges to blu
ajiproaeh of this poiiit ciiu be seen, since, shortly before it is
blue pittches, which at first disappear on stirring, arc fomiec
the caustic si>ila Hows into the acid. The caustic sotla is the
drop ]iy drop, and the amount by which the blue coloration
duced can be obtained to within one drop. The amount
solution used can be read on the graduation of the burette,
that the amount of acid can bo cakutated.

For this pnifwise th«; stretigtli of the (.■;iust(c siwhi sohtlion'
known. As a rule, it is prejiared U) as to contain one co
weight, equal to 40"l)(; i,'ni. of cauatic soria, in ono litre of i
Kuch a solution is called normal. Exartly a litre of this roI
rer|uii-ed to neutralise as much acid as contains i'OI gni. hy
for example, 3<j'4(j gni. hydrogen chloride. If it cc. of t

. - , L ,1 >^ , " -^ 36 46

solution havf, been used, thi-^re must nave iM?en ~Ynf^n~

n > 0"03646 gra. hyilrogen chloride present.

As a rule, it is not a matter of determining the absolute ar
aeiiJ, but the rAuweiitmtiim of given fiohitions. To aacertaiii '
acid coutiiined in a deKjiitu amount of the solution has tn I
mined. This amount can Kw weighed out, htit it is. ni
veiiient to measure it xolumotrieally. For this
apparatus called jiipiitis arc used (Fig. 70). They ct
narrow glass Lubea, widened in the mirldle, and are
such a size as to contain, up to a mark on the neck,
number of cubic centimutres. To fill them, the lirjuid ii
/^ up past the mark ; tltey are then closed by the forefin
the Ii(|nid is allowed to run out exactly to tiie mark,
contents are then einjitiod into the vessel in which ihe
nation is to l>e made.

By the operation of neutraltsation from a bur
"titration," the amount of acid in the measured vc
iiacertained, and from that it is easy to calculate the
contained in unit volume, that is, the concentration,
example, we h:ive measured off .■>■ cc, of acid with the
atid havo used u te. of normal soda solution, the corice
"" ' ' ia equal to n;s combining weights in a litre, or
in a cubic centimetre. If il is the combining weight, M
is the amount of the substance in grams in a cubic centimetre.
184. Volumetric Analysis. — This method of chemical 1
tuent liy means of tii|iii<ls ol known conient, is called n
aiiiilj/xix, and the operiiLinti, titrtdion. The method is not lit
the reciprocal determiriiition of acid.s and Ijiises ; on the c
ihej-e are a nnmlier of other rcactiojis which take place in
solution accotiijMniefi by change of colour or other well

CHLORINE

191

Pio, 71,

^(nismeTi*. Q,, ^]| ^„j,jj peaetioiis methods of volumetric unnlyslB
m ^ biased.

SomUotis which in one litre contaitr one combining weight of the
i\6 smuaUince in grams, are called normti}.^ If thoy contain only a
teiitri of this amount, they are called deci-normal {«/in), and so on.
lo prejutve tiie aolutions. the requisite quantiiies of the
(itteUiicea ai'e weighed out and introduced into fliisks of
the ueaueil ca[iacity. This volume is exactly marked off
by 3 ring on the neck of the flask (Fig. "I)- Such
isare called mfaswimf flttsks.

Lastly, rtii-amring cyliiulers (Fig, 72) are used in volu-
leirie stmilysis where coniptratively large quantities of
i([ui(l bfive to he mestsured, the volume of which is not
^^^van ill round numljera. They consist of cylinders set
^^■la foot JinJ furnished with etchetl graduHtion marks.
™ l*<a. Ions.— It has already been several ttmcfi pointed
out tfint tin? htidroiffn of ncuh behaves in an essentially
JifTereiit manner from the hydrogen of other compounds,
it shvaya gives the same reactions, independently of what the other
cutupwedt* of the acida may be ; l<n' example, it is always displace-
ahic by luagnesiuiii and other metiila, and to it the common projierty
of acids, Ihiit of reddening litmus, is due.

In tlifi suTDG way, the liijilfti.ryl of haiin always shows concordant
properties. It is the cause of the reddened litmus being chii.nge<l to
lilue, anil on ii, depends the formation of new compounds, mIIs, witli
tht! .simultaneous productitui fif water, under the action of acids.
Tb<s«e propertii'a belong only to the hydroxyl of IwLses, and are not
shown by other hydroxyl ciitiipoiind*! which are ktiowti in
targe numljer.?.

A similar' imlcjajndence of the chemical properties of the
coiT»}H>unc]s [losweseing them i» shown in the case of the suits.
The following exampk will make this clear.

If a small rjiiantity of a soluble sHrer salt, t-.g. silver
nitrate or lunar caustic (]i. US), is added to a dilute solution
of hydrochloric acid, a wlute precipitjite is immediately pro-
duced which, on shaking, becomes flocculeut and looks like
cunlled milk, and which ha.** the property of becoming grey
when exjH)St?d Un li^ht.

If, now, ditferent aalcs are prewired from hydmchloric
acid, either by decomfKJsiii^' the acid witli metals or .saiurp
it with bases, itii these .-"iM* huiy the ,v/mr pni/i^rtt/ ; they all <
tlie precipiUvte with silver salts, artd the metal with which the hj
chloric acid has formed the sail is without influence on the prodm
km] nature of the precipitate.

' lu Urcnl BriUiiu iL L< cuRtottmri lo ilijlnie a uuruinl soluti-n h-j ■■hi.' wliicli oon
in I litre ihc hfdnfgen- fjjvinairni r>{ tha ael'we agent weisjJieii in gniuta.— Ti.

^VI,

PRINCIPLES OF INORGANIC CHEiMISTRY crav.

circuit in contact with the electrolytes are calletl tleclrmkf. Wo haA-c
seveml tiroes, previously, inade use of tho phenomena of clcctrolyeis
for the pui*[>03c of sepivrating and identifying the components of an
electrolyte in a simple mfinner (pp. HO and 178).

The exhaustive ini'es ligation of the anbstancea which possess the
property of oleetrolytes has shown that they are ionic com pounds or
salts, and only these. Sxlh nfe ilrdivlykx, i.c. the property of c«n.
ducting the electric current, with decomposition, is inseparable from
the presence of independently reacting components or tons.
^^ Thus water, for example, is not an electrolyte.' We can conTinc«

^H ourselves of this fact by means of the decomposition apparatus shown
1^^ in Fig. 73, This consists of a heaker filled with the liquid to be investi-
I gated, to which the current from an clectxic cell (an accumulator) ii

r led by two electrodes of platinum. This metal is chosen because it ii

not attacked by the substances which separate out at tho electrode;!
most of the other metals are not so resistant. To recognise ihe
passage of the current any current iudiciitor, c.j. an electric bull,
can be used. A measurement of tho current can at the same lime be
effected by using as indicator a current meter oi* ampere-meter, which
must indicate luuidredlhs of an ampfre.

If the vessel is filled with pure water and the circuit closed, the
instrument shows no deflection. On a<lding a little hydrochloric acid,
caustic soda, or common salt, to the liquid, a current forthwith passes,
the measuring insti*ument shows a deflection, and ^s is evolved at the
electrodes.

187. Anions and Gations.^The more exact inveati^tion of the I
processes whiclj tiike place in electrolytes imder the influence of Uw
current, has yielded the following results.

The ht/dm/e». of the acids always separates at the so-called ntgatixt I

' Siieakiiig strictly, water h certainly sd electrolyte, bat it poMeaaes lliU propoiyltj
an eic»«<1iug]y AiiKtll dcgTL>e. K cu'k) of water willj a ^^cction of 1 sq, cm. oaodtwdl
vor^e ttiaii a coliimii of nit)n<ur.v u initliori kilnniDtreii in leiigtli. having a aectiou of 1 q.
cm. At a later stn^e we shall Jistusa the projieitiea of water which dtipeuil oa ihii sin*U I
Conductivity ; wu leave tlietti nut of account here, in order not to complicate the I
(Ic^crii»tioa.

CHLORINE

195

».<. the electrode at which the posritive current leaves the
te u> i>jiss into the metallic conductor. At the same electrode,
metiiU (if the salts Ajuiear. This k reiMliiy seuii if a silver or copper
be de»-oin|M)sed in the apparatus described ; the foniier motiil forms
ii«!««lle-8hai>ed ervatals, the latter covers the electrwle with a. red
ang which exhibits the colour of pure copper.

I The ions which rvander to the negative electrode and separate
ibppc, lire called ni/wHx,' and the electrode is called the aithixh.
rogen is "the cation of iicick j ttie metala are the cations of the
[ and bases.

At the second electrode chlorine appears in the decomposition of

rrxbluric acid »iid of the salt-like nietaltic chlorides, and can lie

hy iia colour and its reactions. The ions which move in

nte direction to the cations are calle<l ttnUjiis. Chlorine ia

the anion of hydrochloric acid and of the metallic chlorides.

kIb at which the finions acjiarate is callwl the tmixk.

Fw the sake of shortness, we have here, in tlie first place, desig-

iJiat which separjites at the electrodes by the name of the ions.

>miiit, however, not be forgotten that the ions preserve their ionic

only iu the sointions. At the electrodes, the electric current

on through the rnctallic condoctore, while the ions are elimi-

1 »t these point-s. In tliis process the ions are converted at the

Jc« into the allntropic or isomeric forms (p. 193), and this goes

il in hand with a change in their electrical relations, which we shal]

1 if «ll ronsidcr.

!>'■ Tbe First Law of Faraday. — By a series of careful meaauie-

, Fanuiay, in 1S33, established the law that the amounts of the

which jseparftte at the electro<les are strictly proportional

^quantity of the electric current which was passed through the

From this the idea arises that tlie passage of the clectri-

i{h the electrolyte is united with the simultaneous movement

so that no current at all can p^iss if it is not airried by

laccordAiice with the relation which we have just stated to exist
the direction of the current and the chemical mitnre of the
which 90f»ar!ite out, the cations (hydrngfii und mctak in the
•&u«> are to be regarded as the carriera of quantities of iumtivi'
ity, whereas chlorine, a« ion, transports neguUre electricity. At
<feetrwlc3, the current leaves the ions, being propagated in tho
■tttffie conductor without the simultiineous movement of substance.
Ife can therefore malfe the distinction between ions and the
AtA or compjunds produced from them, clear to onrselves by
tJie ions as electrically charged aubstenccs, whereas the
in the onJinary slate are non-electrical. This view is a

' Hsmmb i* intendnl to cxprc&s that these loos wntulrr dowuwitnla iu tlie ii)re<:t]0&
> ilMlik cvnc&t.

196

PRINCIPLES OF INORGANIC CHEMISTRY chap.

good representation of the actual relations, and it may be emjiioyed
without eiitering more fidly into the way in which the electrical
charge on the ions is united with the subat^inces. This new concep-
tion is in harmony with the criterion mentioned above (p. 193), that
the ions differ from the noniona of like coraposition in their eju-r^i
mtifeiii, for an elet'tricaDy charged body has necessarily, i\i consequence
of its charge, ii ilitloieiit content of energy from an uncharged one.

189. Electrical UEitS. — To enahle the connection betvreen the
chemical and elcctrica! i)tieriomena to he clearly expressed, some of the
fundamental laws of electricity must be here recalled.

By various means, such as galvanic cells, dynamos, thermopiles, etc.,
a process can ho brought about in conductors of electricity which is
called an fMrie (uriml. By it, all kinds of work, l>oth mechanical
effects fis well sh choniical defonipoHitions, can be performed at any
point of the c((ndnct.or, and heat or other fnmis of energy jirodneed.
The electric current, therefore, represents a special form of ejierffif.

The current can be measured by applying the law of Faradfty
which has just been enunciated, aceorditig to which the itmtuiii f)f
tlfdrkihj piissitig through an electrolyte ia projmrttotml to the nmmnl
of mhsl'tna- which is at tlio same time decompos3ed. If, therefore, ati
electrolytic cell bo introduced in the circuit, the quantity of gii*
evolved, for e.xample, is a inca-siire of the amount of electricity which
has passed through. By slrrmjth t>f oirrr'nf there is luiderstood the
quantity of electricity which has passed, divided by the fintr required,
or, the amount which passes in unit time. Tire strength of the current
Ciiu therefore be measured by the amount of gas evolved in unit time.

The unit of quantity of electricity is called the (tmtomh ; it \m
been determined in a nirtnncr which cannot he cxphnned here. To
reihice the coulomb to a measm-c with which we are familiar, we make
IX8B of the fact that for the evolution of 101 gm. hydrogen, 96,540
coidombs must pass through the electrolyte.

A current which iji eaeli second conveys one coulomb through the
conductor, is called an (O/i/wvv. In order, therefore, that a current of
one ampere shall liberate 101 gm. hydrogen, it must flow for 96,540
Beeonds, or 2() hours and 49 minutes, throutih the electrolyte.

Very weak currents are measured in niillifimperes or thousandths
of an ampcie.

A current is not determined by the niimlier of amperes alone, for
cun'ents of the aaine nnmlier of amperes can produce very different
effects, according to the nature of the conductor. The relations here
are the same as in the case of a stream of water which can. with the
same amount of water, perfomi various amounts of work, acconling to
the pressure or the height of fall. The magnitude of the electric
current corresponding to the pressure is called poliiitiai, and its unit
is ctdled the rulL For the prcijent, however, we do not have to occupy
QUi'!ielvo.s with this magnitude.

CHLORINE

197

* Apparama are iimde wliich depend on the magtietiv mcuoii of the
current, and on which the strength of tlie current can be rei%d directly
ixi amiwres. For clicniieal piirposea an instrument on which niilli'
ampei-es can be read off, is the moat auilable. For the measurement
of stronger cvn-rents auxiliary apparatus (shunts) are given along with
giich instntnietits, which icduce the sensitiveneBs to a. definite fraction,
generally a tenth or a htiiidrethh.

190. The Second Law of Faraday. — FrojTi the law that the
iou9 of the clt'Ctrolytea ;ire united with definite amoinitB of electricity,
some tnip>rtajit conclusions can bo drawn, whicti aliow of ii con-
sidenible extensirtn nf the electrnchendtat rtdatiytis.

Hydrochloric acid solution is an flectiically ntntml body. If,
then, th(? hydrion in it has a positive charge of the above large
amount, there must also Imj negative electricity of exactly the same
amount present. This is united with tlje chlorine, which thereby
pasaea into chluridion. According to the law of combining vveighta,^
there are 35-45 gni. chlorine to 101 gm. hydrogen; coni^eqnmibi, oM*
//rum-ion or 35-45 ijnt. </ chl/rridiim, is united wilh 96,540 coidnmbs of
Mtfalire t:kiiricili/. ,

Similarly, the Boludons of all salts are electrically neutral. If
we consider, for example, such amounts of the different chlorides
contain 35"45 gm. chlorine, the amounts of the metals present along
wilh it must also be united with 90,040 conlombs of positive electricity, '
independent of their nature. Theae amoimts are equal to the com-
bining weights of the respective metals, which are each united with
one combining weight of chlorine ; consequently we can state the
universal conclusion : —

Tiu itMouith iif the liiffei'ad ions united teith fhe same quaniUies &f
tUitricihi, nre in tltf jrfufmriiim of the combining weif/hf.s of ilteti ions.

In this form, the theorem holds, certfunly, only when the combining
weights aje so chosen that they coriespund to I'Ol gni. hydrogen or to
(35'45 gm. chlorine. There are, however, metals which combine with
two, thi'ee, or raore combining weights of chlorine ; in their caae the
amount of electricity is a corresponding multiple, and they are willed
jiiitifcftlrtd ; Ukewise, there are pt/lijvalrnt aiiiimii. Wc shall discuss these
relations at a later stage.

The theorem just enunciated was also discovered by Faraday, and
is also called tfie law of Faraday. This law, therefore, contains two
biW3 which, indeed, arc corinect-ed ivith one another but have i-espect
to different tilings. Ifecapitulating all that has been said, we may
express it in the following form: — _ ____^

In tUcirijlfftes, the dfeii-iciti/ nm-es (nih/ tcithJi&mi<^^'i^^^i^^P^
of Iheir ami/Kvmiita, the i<ms. Thf tpmidihj nf/iltdridt)^ kan^^pi'i^^
jKtrtii/nal to ihc qnnntifi'if <>j the vm-a and atiu
iHuUtjih of fhi-f, fftT ertrtt t/iam-ioii of any sm

* The law of Faraday has a certain'ij

19S

PRINCIPLES OF INOKGANIC CHEMISTRY

Lussac with respect to the volumes of gases in chemical cr>ml*inatioiii
Just as the amouats of gases present in eqnal voiumes tire projjortionf
to the uunihining weights or to inuHii)]t!s of these, the amounts of lb
joiia united with equal qnaiititios of oloctricity are Jtlso profwrtional t
the combining weights or to fractions of these.

*■ Ifll. Primary and Secondary Products of Electrolysis.-
If very dilute hydmeliloric arid i^s aulijticted to cdectrolysis, hydruguui
nbtaiucd, na before, iit the cathode; uo chlorine, however, appears*
the anode, but, in its &tead, an eiiuivalent amount of oxygen is evolved

This is due ta the fact that the water ta decomposed by chlorine mH
formation of hydrogen chloride and oxygen, according to the cquatim
2H/) + 2Clj = 4HC1 + O^ {p. 172). This ]>rocess, it is trne, tnkes pliirt
with measurable velocity, only iu light ; we may, however, nsmta
here, as irt sitniUr cases, that the process takes place without ligblj
only very alovvly. It can, in fact, be Hccelci'ated by phitinuni awl
similar catalysera, even in the dark, to such an extent as to becon
measurable. The occxirrence of oxygen in the electi'olysis of dilti
hydrochloric acifl is, therefore, generally inteq>i-etod in such a wij
that it is assumed that chlorine is first formed, and that this then
on the water, nndcrgoing double decomposition with this to fo
oxygen and hydrochloric aeid ; the oxygon is accordingly callfld
secottdmy product of electrolysis.

Doubt, however, arises ae to this view, because of the fact that
assumes hydrochloric acid to be cientviposfd by the current and to
formed again under the same conditions with the co-oper-ation of
water present. Such an assTimption can be avoided liy means of
able considerations ; these, however, wo shall not put forward he
but we shall formally retain the view just given, which has, in
first instance, no disadvantage anil simplifies the discussion.

Such secondaiy prochicta are often formed when tbo ions, aft(
they are disc;harged, do not constitute substances which are
under the existing circumstances.

Thus, copper and silver, as has been mentioned, are oliminat«tl i
metols from their salts ; they are, therefore, primnry products, \%
however, sodium chloride is electrolysed, there is obtained (when con
centrated solutions are uwd), on the one side, chlorine, but at tJi<j
cathode there i.s obtained not sodium but hydroijai. This arises froo
the fact that sodium, which would be eliminated as "primary " produe
cannot exist in contact with the aqueous solution, hut must immediat
piisa into caustic soda with evolution of hydrogen (p. 84). Chie inafl
therefore, again assume that sodium is indeed eliminated, but that
the moment of its iMssiiig from the ionic into the metallic state H
reacts with the water with formation of the secondary products,
a matt*r of fact^ caustic soda is found at the cathotle, tor on addiof
red litmus solution to the liquid, it inimediately becomes blue.

If a solution of caustic soda or soilium hydroxide be subjected

gen, for the reasons just given, makea its appiiarance

C- At the anotle hy<li'oxidii:i!i, Oil', is tliecharged. Tliis

exist alone, hut the douliled comjiound, 0.,Hg ar hj'dTOgen

is known. This sTibstance, huivever, on account of its

r, is also not produced, nr at least is so only in traces ; on the

the reaction 4011 = 211^0 + 0„ occurs antl free oxj-gen is

Thia oxygeo, therefore, is also to l>e regjuded as a secondary

K-

^r til

whether the products of the
For in the second case, the

pr«diicc"l
^■rimairv'

c^ ^

law ia necessarily fulfilled

primary or secondary.
the secondary substances
« connected with those of the
by aiuiple chemical cfjiiations,
former must, therefore, ueces-
pr«diicc«l in amoimts which

nn<\ chemically e<iuiva- i>0=
innairj*.

iges in the conditions
M, OHO may sometimes

m priBftary or the secoiulary

at will. For example, if, in

ulysif of sodium hydroxide or

faloride, the platinum rathodn f f

nl by one of mercury (Fig. 74),

Sip ia evolved but the
plres in the mercury. If,
the TBiercury containing the sodium be placed in pure water,
iforuiation iNa - '2I1„0 = 2NaOH + 11., slowly takes place ;
ifl cvolvctl and the li<juid reacts alkaline.

IMssociation of Electrolytes.— An important fact, which

jrlher light u\i the difference between electrolytt-fl and iion-

^^ts the following. It has previously been explained that

^■Vght of substances soluble in vmter, can be determined by

^ which they produce in the freezing point of water, one

ny snlwtance dieaolved in a litre of water causing a depression

If the ipiantity of hydrochloric acid which causes such a

n bet determined, it is foeuKl that altout 1 9 gm. are sufficient.

sTDAtteat moliir weight which tan be assumed for hydrogen

the sum of the combining weights of chlorine and

iiiolar weight, also, is obtained from the gaseous density

jeo chloride (p. 178). New relations, therefore, are met with

aire a special interpretation.

itAtnvd when we take into account the facts which have

forth concerntng tlie hf/rpciulevl heharimtr of the umi.

of the other hydrogen com|munds, as, for example,

irit of wine, water, sugar, etc., no common property cau

20-2

PRINCIPLES OP INORGANIC CHEMISTRY chap.,

Further, we shall sometimes Eod it necCissiiry to distingHisb tbft
substances in the condition of ions from tbe others. For ihh purpo^
the cations will Im designated hy u point, the anions by » dash. H"
represents, thcreforo, hydrion ; CI', chluridion. On arcuiint of thr
necessity Ihul rMejitiraJlij nptmitfjtl amoimls of catiom and anumn must bt
pruseni in mlidiorts (p. 197), eirry wmpirk chtmiml etptalwn must, wirt
long ocrur in it^ cimtuin eriuirttknf amoujth of catimis and unions on ti*
sama nul^ of ihi' nhjn of equnliti).

Thus, far example, thv process tsf the formation of eodium chloride j
from hydrochloric acid and cjuistic sodft will have to be represontedj
by tbo following equation, if it is desired to rejiresent ihd processe*
by the ions : —

irCl' + Na'OH' = NaCr + lUO.

This cqtmtion shows that tho ions chloridinn and sodion remain
unchanged in the process, it^ their reactions, intleed, also ^versist in the
solutioti uf common sjdt jn'odnced. For this gives, on the one li«ml,
the precipitate with silver siilts which is chaificteiistic of cblon*Uon, and,
on tlio other htuul, when electrolysed with a mercury cathotle, it yield*
a solution of sodium in mercury, just as cjtustic soila .ilso does (p. 199).

The ions hydroxidion and hydrion, however, are used up, because
they have combined to form uudissocialed water {p. 194). For this
reason the reliction both of hydrion and of hydroxidion have dis-
appeared, for tho liquid no longer reacts acid, nor can tbe bsisic
properties of caustic soda be any longer detected.

19+. Tbermochemical Relations of Hydrogen Chloride.—
Since chlorine burns in hy<]rugen, the heat developed in the combuslion
can be directly measured ; the followinj» equation is thus obtained : —

CU + H. = 2HC1 + 2x92 kj.

This number applies to the fonnation of fjatKOHn hydrogen chloride.
If this is dissolved in water, a further very considerable quantity of
heat is developed. The necessity is here felt of distinguishing the
disaolved liydrogen chloride from the gaseotis, since these two forms
possess, in conformity with the diflorence of their properties, verr
differi>nt energy.

Where \va are dealing with aqueous solutions, it has become
customary to designate the condition of mbifMti of substances by ibe
addition of aq. (aqua). Now, certainly, the development of heat on
dissolving hydrogen chloride varies, according as the solution produced
is more or less concentrated. This is easiiy seen from the fact that on
dilutitig a concentrated solution of hydrochloiic acid, a fairly liirgB
quantity of heat is cJevcloped, If, however, the ddution is carriwl
further, this heat becomes less and less, and there is ultimately a fiinl
condition reached when a measurable fjuiuvtity of heat is no longer
developed. It is to this condition that tho symbol aq. refers.

CHLORI?iE

203

If hydrogen chloride is clisfiolvcd in a large quantitj of water, 72 kj
developed, and we have the equation

HCl + a<i. = HCl3q. + 72i>

Oil adding this equation {rDiiltiplied by 2) to tlie preceding one,
there follows

II5 + C\ + aq. - 2HCI aq. + 2*164 ^7,

which gives tbe heat '>( f'ormiition of the thssolird hydrochlorie acid
from its t'lcnients.

U»5. Thennochemiatry of the Salts. — If a strong atid, «.(?.
bydi-ochloric acid, is neutfalised with a. strong hase, f.ff, ctiustie soda,
a quantity of heat equal to .j7 IJ is doiclopcd. The quantity of heat
18 foiinil to W identtcfil, no matter what acid or baae is used, it being
assumed that both iiro *' stroTig," and that both ai"e in the condition of
dilute aqiieonii solution.

The reason of thia hiw becomes at once apparent if we recall the
fact that the formation of a salt from its acid and biwe in dilute
aqtieous solution, consists in the hydritm and the hydmxidion com-
bining to form water, while the two other ions remain unchanged side
ay side (p. 202). The heat development of 5" kj is nothing else than
th-c kral of /(trmation of water Jrinn Injilrirm and liijdivritlitin. Since in
the formation of any and all sattJi from strong (I'.t'. nefirly completely
dissociate<l) acids and bases, the same process of the formation of water
Iways take.s ptace, the corresponding heat development must also have
the same value.

At the same time it follows that deviations arc, in general, to Ire
expected, if any of the suppositions made arc not fulfilled, i.e. if acid,
base, or salt is slightly dissociated. To the heat of fommtion of water,
57 kf, there must then be added the quantity of heat whidi is developed
»hBo^^led in the decomposition of the acid or base into it-s ions or in

formation of the undissociated portion of the salt, and the obser\'ed
heat of neutralisation is the sum of the corresponding magnitudes.
Wc shall have an opportunity later of mentioning such caaes.

Further, it was mentioned on p. 193 that the elementary^ ions have
different (plan ti ties of energy from the free elements. It may be asked
if it is posjiible to measure this difleretice.

,\ method, which cannot be de.%cril>ed here, has, indeed, been found
for this purjiose ; but since no other method of attaining the same
object could be found, it has hitherto not been possible to test it)^
t. It led to the conclusion that the transformation of hydrog

XDto dissolved hydrion causes no appreciable change of encrg.
e have, therefore, the folJowing thermochomical equation : —

H, + aq. = 2H" aq. + 0 Ij.

204

PRINCIPLES OF INORGANIC CHEMISTKV

If this basis be assumed, the beats of form&tion of all ot]
can bo determined.

For example, it was found (p. 203) that n. dilute aqueous solul
of hydrochloric Jtcid is produced from its elements and water i
a heat development equal to 164 ^7. Siace this solution conti
chlorine and hydrogen in the form of ions, we should, tnking thi« i
account, write the equation : —

Clj + H, + aq. = 2C1'H- aq, + 2 x 1 64 ly

= 2Cr aq. + 2H* aq. + 2 > I C* i^.

Subtracting from this tlie e(|uation H^ + aq. = 2H' aq.,
follows

Clj + aq. = 2CI' aq, + 2 x 1 64 kf.

In other wonls, the heat of fomuition of dilute hydrochloric
equal to the heat of formation of chloridion, since the heivt of foi
of hydriofi is nought.

This conclusion can be at once gcueraliacd. Si»ce, M regai
hydrion, the same relations are found in the case of all acids so
they are electrolyticaliy dissociated, the rule obtains for all ai
the heat of formation of their dihite aqueous solutions is equal
heat of formation of their anion.

When sodium is dissolved in hydrochloric acid, the hydrogen
the add eecapoe and sodium chloride is produced. The developi
of heat which thereby occurs is very considerable. This has
determined, indirectly, and been found equal to 239 kj. This co
spouds, therefore, to the equation

■

2Na + 2H'C1' aq. = H, + aNaCl' aq. + 2 x 239 ly.

If we again subtract the equation H., + aq. = 2H' aq. from this and 1
on each side, the common member 2C1' aq., wo obtain

Na + aq. = Na" aq. + 239 kj.

That is to say, the conversion of metallic sodium into sodlQI
accompanied by a dovelopmeut of heat of 239 kj. This is the
amount of hei\t as was developed in the action of sodium on lijl
chloric acid, for the simultaneous convei-gion of hydrion into
hj'drogeu gives no heat effect.

This theorem, also, can be extended generally, It holds for 61
othei' dissociated acid and every other metal. ^\'e cau, tbdl^
enuneiatw the general law : —

If !/ wdai acts on an acid wilh the forvwtion nf a .mlf and fjfnern
of hf/dropeti, tfu ammtni if heal ^ehich is derelof>ed dejKhda only on
tiaiurg of the ntflal, ami is indepcfuU'id of ike acvl. This heat is equa
the heat of transformation of the met.'il iuto its catiott.

CHLORINE 205

The first part of this law is an experimental fact, and was known
pg before it was deduced on the basis of the theory of electrolytic
tion.

Should any of the substances with which we are dealing be iindis-

iated or only slightly dissociated, deviations from the simple law

ir ; the cause of these is the same as in the case of the deviations

B the constant heat of neutralisation, discussed on p. 203.

' The transformation, therefore, both of chlorine and of sodium, from

)b ordinary to the ionic condition, is accompanied by a very consider-

fto development of heat Although the difference of the total energy
tlie two conditions, of which the heat development is an expression,
Bot a direct measure of the tendency of the elements to pass into
ht ionic condition, still the one moves to some extent parallel to the
-, and from the large values of the heat development we can infer
value for the tendency to transformation. In fact, it has been
iy mentioned that both elements possess a very considerable
reactivity. On examining the nature of these reactions of
and sodium more closely, it is found that in the majority of
tails are formed, that is to say, we have before us a mani-
of the tendency of chlorine and sodium to exchange the
for the ionic condition.^

> Em in the ffiti saltn, which are not eleutrolyticnlly dissociated, the components
acarer to the condition of the ions than to that of the free elements. This is
the fact that the passage of the solid salts into the ionic condition, on lieing
in water, give« rise, in general, to only inconsiderable heat ell'ects, in most
indeed, to abmrption of heat.

CHAPTER X

(iXYfiKN COMPOUNEJS OF CHLORINE

196, Oxygen Cfunpounds of Chlorine. — ^VTiereas hydrogen

fTOmbiite with chlorine only in one proportion, this latter ele

fomiB several compounds vnth oxygen. There is a stil! larger no

of subfltences which contain hydrogen along with chlorine and oxj

All these compounds are distinguished from hydrogen cbioridel
a cireiimstJince of essential importance. They bear the same leli
to it as hydrogen peroxide does to water ; hydrogen chloride is
from its elements with loss of energy, and cannot, therefore, dec
spontaneously into them, Imt, for the pi-oduction of the oxygen
pomida of uhbrine, energy must be coinmunirated. Accor
these compounds exhibit the property of decomposing spontan
:i.f, without the comnmniciition of energy, and this instability
larked in the case of sonic of them that they decompose
explosion. The reason for this is in entire accortlance with
relations set forth in the case of hydrogen peroxide (p. 162).

The way in which the energy necessary fur the formation of
compounds must be communicated, may vary in different cases.
most frequent and, for general reasons, the most tmporttttrt way :
is the ciumkitl. If the posajble processes are conducted in such
that along with the desired substance, other substances are pr
whose formation is accompmiod by the liberation of large qu
of energy, this enerf;y can be ttsed for the purpose of product
comparatively unstaVjlo compound. For the successful communi
of this energy, however, it is not sufficient that any reaction whi
which will yield energy, be allowed to take place along wil
desired one ; such a reaction would act merely as a corresj

elevation of the temperature, and it worild have no efifect, or

harmful one. On ilu- mnlranj^ if Li an tvsfiniial antJUimt that tht
rmdmis it depemhni on one aiiofkei; or lie " muplal *' uitk one tiin>t}tef,\
that (he one (amiot Uiki pktcv vnlJiunt She other. It can be seen from
chemical equation whether this condition is satisfied, If this can 1
separated into two equations which are independent of one anot

204

OXYGEX COMPOUNDS OF CHLORINE

207

ebMBtcal |irocesses are not "cuupled " ; if such a separation cannot
le, the above condition is aitisfied.

lus. for example, it might bo expected that the large dovelop-
of energy which accomimnies the formntion of water from its
it«, could cause the siroultaneoiia fotmalton of hydrogen peroxide
ixygen and hydrogen, the energy nec^.^'3SElry for tliia latter reaction
; jielded by the former by some such reaction as ia expressed by
ITiatioti

3H,. + 20. = '>H,0 + HjO„.

ftXpectntioii Ls not confirmed by experience, a fact which h m
jy irith the rule jiiat giveo, for the eqiuition can be resolved into
tvu eqtiatiuiis

2H. + O, = 2HjO and II^ + Oj = Hp^.

processes are, therefore, not coupled or niiititally conditioned.

iBflUsrotts examples of coupled processes will be given by the

which lead to the formation of the oxygen coiupoiinds of

otwl which will be given immediately.

19*. HjrpOChlorous Acid- — It haa l>een alrejMly mentioned (p.

tbjit thJotitif is iibstjrliL'i 1 by caustic soda sohition. The product

euioot consist entirelj' of sodium chloride, for this is formed

auBtiG sods and hi/ilmi^t^ii cJiloriih. As a matter uf fact, sodium

ia icideed formed, accompjiiiiod, however, by u new substance.

aoliitioQ produced haa not the purely saline taste of commoo

; a caustic one. Like free chlorine, it has a hltnfkimj action

^•grtablo colours, e.ij. litmus ; it acts as a powerfid disinfectaut,

tbc a<l«lition of hydrochloric acid, it evolves chlorine, which can

ifiod by its colour and smell. Common salt, however, gives no

Ale resction with hydrochloric acid.

kbove process takes place, according to the equation

2NaOH + CU = NaCl + NaClO + H^O.

«rit lorme«J, therefore, sodium chloride and another compound
lOmt&ins oxygen.

i this cumpound, XaClO, bo prepared froo from sodium chloride,

(ImoiI that it4 aqueous solution is au electrolyte, but docs not give

Wictj-'UB of ehloridion, for no pi-ecipitatti is obtained with silver

• In solntion, which contains sodium chloride, of coiu-se

iitate, but only in half the amount that corresponds to

F«fcluruH: piesent.

I this it follows that this second substance is, indeed, a salt, but

aci cbluridion. The chlorine, must, therefore, be present in

combination, and the most obvions possibility^ and the one

with actual fact, is that it forms an ion CIO' with the

aodion Iwing the other ion of the salt.

208

PRINCIPLES OF INOEGAXIC CHEMISTRY

Tlierc must therefore bo an acid HCIO, formed by the combinatx
of hydrogen with tho ion CIO', -which on neutralisiitjon with caittt
BOtla again yi6ld3 the original salt, according to the equation HClOfi
NaOH = NaCIO + II^O. Such an acid am, indeed, be prepari|
This acit] has received the mime of hypttchhtrtnLs (tciil ; its sails
cfille<l hf/pochlrjrili-Ji and tbo iors CIO'' hi/fOchhrofioH. The sodium ,
alreadv mentioned is ctiHcd stdiuiu htquirhlirritc.

1 98. Preparation of Acids from their Salts.— For this pur
II general metliod i3 used, which can he described in the following wor
To ohkiin the acid coiresprnding to a ijiren salt, the. salt is ticcomj)Oft4l
unothtr aciii.

That such a preparation ia possible can be seen if we desijtiiiiite 1
desired acid by HA, whcro A is a simple or complex anion, and ji
salt by MA, where M represents some metal ion. Further, if HB^
anothei' acid, tho following reaction is possililo by the interaction
the two substances : —

MA + HB=HA + MB.

There would be obtjdned, therefore, if the reacuou took pii
desired acid ami the salt of the acid added. There remains ill
further t.iak of separating the two substances in order U> obta
acid in a pure state.

Applying this rule at once to the caae before us, we should hai
decomjiose the sodium salt NaClO with hydrochloric uciil. The d<
acid, niong with sodium chloride, would be obtained, according tol
reaction

NaClO + HCI - NaC! + HC!0,

and the two snbatfincas would then have to be separated.

It has lieen found, now, by exporience that the reaction
sented by the general scheme always occurs, but is vrrrr n m
one. In all cases only a portion of the substances present under^
reaction, and another portion remains unchanged. In other words,;
all ihcso cases chemical tquUih-'ia are established {p. 101). Fori
equilibria it is necessary that the concentrations of the reacting i
statites shall he in a definite rehitioti to one another, dependii]geramre, and on several
circuRistances.

If, now, one of the participating substances is removcti,
equilibrium can no longer e,Yist, but the reaction must take plitce
means of which the substance removed is again replaced. If the
tioo thns formed is also withdrawn, the same process goes on
and in this way the jeaction can be carried so far that the total poeafl]
amount of the product is ultimately formed,

On this fact is based the prepiration of hypochlorous arid by 1
reaction dcscrilred. If dilute hydrochloric acid is addeil to the sodill

OXYGEN COMPOUNDS OF CHLORINE

part of the salt is converted into eodium cliloride and

ftcid, while another pjirt remains undecoraposed On

the mixture, the hypoehbrous acid, which is the most vola-

foiar substances present, passes over, and the amount of it in

le is diminished. For thie reason fresh acid must be formed

due ; if this h also removed by distillation, all the acid which

Fonuetl from the ([uantities of the substances present, must

ultimaidly formed, and be found in the distillate. And this

tier of fact, the case.

out the experiment it is necessary to proceed with care

leas hydrochloric acid than corresponds to the eijiiation,

neoessary to employ dilute acid, and to so add it th;it there

len; exist an excess of hydrochloric acid. In the present

is necessary hecuuse of the fact that hydrochloric acid

hypochloious acid, as will be presently disciiseed. In

where simh action is not lo be feared, these precautions

I ftofjertiei of Hypochlorous Acid.— The aciueous solution

T*us acid, nfiLiiiDc'd in this mtinoer, ahowis not only the

ertiefi of acids but aUch some special proi>erties, which in

'nusk the former. The sulutioii is colourless but hae a

sell, einular to that of chlorine. It acts as a powerful bleaching

rards organic colouring matter, and its action && a disinfectant

for snmU organisms, is almost equal to that of chlorine.

It similarity showTi by the solution of hypochlorous acid to

' adution of chiorini?, is due to the fact that the latter under-

il trausformBlion into hypochlorous acid and hydrochloric

ling to the equation

Cl2 + H20 = H0Cl + HCl.

tion. also, does not take place completely, but only
LAud to an extent which ia dependent on the concentration
sture. In the reverse manner, hydrochloric acid and
acid act on one another with formatioQ of chlorine and
reaction, however, is also not a complete one, and, there-
|mle which has just been given, that the reaction can be made
ce completely in the one or the other direction, by removing
iing reaction prmlucts, will hold also for it.

Eipositions of the Hypochlorites. —The most im-
f»e «pe4;Jal pryperties of hypochlorous acid deiterid on the fact
Its oxygen with extreme readiness, thereby passing into

b« iCMoo wby the deeompoeition of scMlinui hv-pocbloriUs with hydTncbloric-
■nW nat carefully so a.-! to avoid bnviny: at any time nu Excess of the iiciil
' petet. If Ihi* ciro is not oliserved chlorine L» formed, mhjch oo diatill*-
> MW with the hypocliloTou* acid and renders It impure.

212

PRINCIPLES OF INORGANIC CHEMISTRY chap.

necessary energy is drawn, almost without exception, from the heat
contained in it. To this class belong, therefore, all processes which
take pla£« spontaneously mnth fall of temperature. Examples of tbU
are not rare. A volatile liquid evaporates spontaneously Avith fall of
teruperature into a space which is free from ite I'apours ; ealts di^.- '
3{jontanGously in water with fall of teropemtnre, and many chen
processes also take place epontaneoualy with fall of temporattu'e. All
these cases are exHmples of the fact that in spite of the decrease of
the free energy in processes which take place spontaneously, the total
energy can increase.

The question aa t<) bow the free energy is to be measured cannot
be discussed here. It is sufficient to know that the fact that a reaction
takes place sjxfntanoously is a sign that the free energy of the system
(3 thereby diminished.

If we apply what haa here been said to the case we were just con-
sidering, the Rystem chlorine plus caustic soda will be designated iu
the form with the greatest free energy. The system produced from
this, sodium chloride plus sodium hypochlorite, has less free energ),
and sodium chloride plus oxygen has the smallest amount of f«e
energy. The following figiu'e gives a picture of the relations, tie
values of the free energy being represented by the porpendicukr
heights ;—

Jo,

45faOH + 2Cl,

SNftCl + 2NsOCI + 2H,0

*•

4Naa+2HjO + 0,

From the appearance of the figure it will be seen why it is tliat,
starting from the highest step, the lowest is not immediately reached,
Init that a halt is first maile at the middle one. This furnishes an
answer to the question nsked above (p. 210).

20-5. Chloriiie Monoxide. — Hypochlorous acid is not known iji
the pure, i.e. the anhydrous, state. On attempting to prepare it, tht
elements of water leave the acid, and a compound of chlorine and
oxygen remain.s behind. This compound is no longer an acid, since it
coHtains no hydrogen.

This process takes place in accordance with the equation

2HC10 = HjO + CljO.

X OXYGEN COMPOUNDS OF CHLORINE 213

The new «ub«tance is called chlorine motioxide, since it eontaius mif
combining weight of oxygen. Since it is obtained from bypocWoroue
acid by loss of water, it is also called hyporhlor<»t£ anhi/drMe. Thie
nomenclature is employed fairly generally ; various substances which
are formed from other suhstances by the loss of the elements of water,
are called ajthi/tlrides of theae aubetatices.

* Thia name was introduced on the supposition that in the
original substances not merely the elements of water are eontainetl but
also " ready formed " water, and this conjecture arose because aome
eobstances gave off water with exceeding readiness and rapidity. But a
deeper knowledge of the facts has shown that there exists a continuous
transition from those which readily give off water to those from which
water can be obtained only by especially powerful rctctions. It is,
therefore, more scientific to in no case assume the presence of pre-
formed water, especially as uo definite meaning can be attached to such
a supposition.

Chlorine mono3dde is obtained most readily by carrying out the
reaction leading to the formation of a salt of hypochlorous acid
(p. 209), with an oxide from which the salt is not formed. For this
purpose mdtk of mercury ie the best. When a current of dry
chlorine is passed over mercuric oxide,^ the following reaction takes
place : —

HgO + 2Clj-HgClj + CUO.

In this equation Hg is the symbol for mercury ; its oxide is com-
poeed of equal combining weights of mercury and oxygen. The
chlorine compound of mercury, or mercuric chloride, remains behind as
a solid substance, and the cJiloriti'- mmu/Tide, which is gaseous at room
temperature, escapes and can be collected.

Chlorine monoxide is a yellow-brown gas with a strong, unpleasant
smell, which can be condensed to a liquid at 5'. It dissolves in water,
paasisg slowly into h}'pochlorou8 acid. In the gaseous and fitill more
in the liquid slate, it is very unstable and readily decomposes with
explosion, forming oxygen and chlorine. These explosive properties
find an explajiation in the fact that heat is liberated by the decom-
position (p, 16'3). Tlie gas also decomposes into its elements under the
influence of light, but generally withont explosion.

204, Chlorates,— The stops in the transformation of chlorine and
cAuatic soda described on p. 212 are not the only possible ones, for
there are still two others which lie between the middle and the
lowest. The solution o! NaCl + NaOCl, which is obtained by passing

1 In oTtlcr llittl the leftctinii mny take plact' Mtisfftotorily, the mcrcMrie oiide rwjaired
for Uiii! ejperiiDont must htt i>f a »p(?ojnl nature. If too fiuefy rliviilixi, the ie«i'tiou p>ea ,
too quickly and an explosion tiin^ txcnt ', if it is too cojirse, the reaclion wili be t
•low ariil the got will Tie contauiiiiHteil with cbloiiiie. A suitiiblv oxide is oljtaiiied 1
gently heating the oxide pTuixiretl by precipitating niLTcuric diloride with cau.-itic iodl J
sqaeous solntioi).

214

PRINCIPLES OF INORGANIC CHEMISTRY

chlorine into a si^lution of c»ivistic soda, undergoes a change in
properties on being kept some time. This change takes place BW
quickly in the heat find when a alight excess of chlorine is present |
the solution. Its bleaching power and its smell gnMiimllj disappei
and aftei' some time it contains no more hypochlorite, for it evollj
no chlorine on being treated with dilute hydrochloric acid in the col
If the solution is now evaiKjrated, two salts are obtained — sodia
chloride and another salt which, like sodium hypochlorite, also ca
Uiins oxygen. It is shown, however, by analysis, to have a compOi
tion which 13 expressed by the formula NaClO^, and is called stidi*
rhhrafe. It is, therefore, the sodium salt of a new anion, cA/omi
ClO'j. This ton is also not precipitated by silver sixlta; almost all I
salts which it forms are readily soluble. The reactions whicb
place are, therefore, represented by the eriiiations

2NaOH + Clj = NaCl + NaOCl + H^O,
.WaOCl = 2 NaCl + NaClO^,

or, omitting the intermediate stage,

6NaOH + 3Clj = 5NaCl + NaClOg + SH^O.

Since sodium chlorate is a very soluble salt, and can be ae
oidy with difficulty from the simultaneously formed sodium chl
it is better to prepare the corresponding jiotasiium salt by
chlorine into a solution of potassium hydroxide. Since potaasji
all its chemical relations exhibits an exceedingly great similai
sodium, the reactions which take place are of exactly the same
as those descn'beil, and need not be again explained. Pofassirttn
along \rith potassium chloride, is obtained as the protiuct of tha
action; and since the former salt is much less soluble than the
in the cold, it sepiirates out on allovring the solution, obtained by
action of chlorine on potassium hydroxide, to cool.

The salt thus obtained is already well knowii ; it is the ^ni< "
for the preparation of oxygen in the laboratory (p, ('
potassium chloride formed at the same time is a salt very smiiiiW'
sodium chloride.

From what was previously stated, it is known that p .ii^-i
chlorate, on l»eing heated, decomposes into oxygen and p. >t,t.--.i>i
chloride, the game behaviour being likewise shown by sodium chlonttt
The decomposition takes place according to the equation

'JKClOj = 2KC1 + 3O2,

where K is the symbol for potaasiuni.

As ciin bo seen, this is tha last step in the action of chlorine
hydroxides, and to the three steps given on p. 212 there must
added a fourth, between the hj-pochlorite and the lowest. We fll
soon aoe that even a fiflli step must be inserted.

OXYGEN COMPOUNDS OF CHLORl

215

rotifrirmiiy with the smaller full l>etwet;ti the chlorate and the

stejts, the Iasi tr.msfoniuitioii ilaes not proceed so loadily and

as that of chlorine into hyijochloiitet and of the latter into

At ortiinary temperatures, thu chlorates are practieally quite

aod only at ci iniparativelj' high temperatures does the feactinn

«o rapid that it can liu observe*!. That the reaction ^'ati I>e

tbrough the influence of catalytic agentSj has already been

(p. 6.'^) ; l»sides the subatance then mentioned, pyrolusite,

fof irtHi is a very effective accelerator of the decomposition.

15. Preparation of Chloric Acid. — Chloric acid cannot be

ly obtAin«<i from potaesium or sodium chlonite. The aijiieons

of the salt, it is true, undergoes partial deeonip<:>aition by

mddf, in accordance with the genera! rule (p. 208) ; but as the

•chI cannot h* distilled, tbt! sepaialion cannot be carried out

iune way as in the case of hypochlorous acid. Recourse has,

to be bad to another raethotl.

: we cou6td«r the equation

MA + HB = MB+HA

on p. 208, we see that the desired acid can be prepared not

|by removing it from the sphere of the reaction, but also by

«ly removing the salt MB, As a rale, certainly, the salts are

lUt. ao that the method of distillation uaed for removing ihti

[ cannot be employed. On the other hand, however, many salts

and by their precipitation the reaction is made as

OS by ihe removal of the acids.

CBTTT this idea into practice, the ions M and B have only to be

so thill they together give an insoluble salt ; that is to gay, a

: the desired acid has to be prejiiired which yields an insoluble salt

aeid, and with this acid the salt has to be ilecom|H>sed.

f-we already know a metal Mhich gives an insoluble salt with

acid, vjg. sih'er. Silver chloride is so very .>iparinglj

thmt even very dilute solutions of cldoridcs and silver salts

l« precipitate (p. 191). In the general equation, therefore, M

W Rpktced by silver and B by chlorine. If silver chlorate be

>ud lie decomposed with hydrochloric acid, silver chloride

»cid are formed acconling to ihe cijuation

AgCIO^ + HCi = IICIO, + AgCl.

symbol for silver,
HBtbt chlorate can be obtained in the same way as Bodium or
' ^••■^•OS chlorate, by the action of chlorine on silver hydroxide.

Th* ■»• principle can ]>e carrie<l out in various other ways, since
tfWf imalnhle salt gives a possible combination. Indeed, foc lb.e

216

PRINCIPLES OF INORGANIC CHEMISTRY chap.

actual preparation of chloric acid, other aubatances ;ire mostly employed,
especially ktrium chlomte and aulphuric ucid. With these the same
result is obtained, since liariam sulphate is aUo a very difficultly
soluble Bait.

In employ] nt; this method of preparation, tho amounta of the
reacting suhsfciuiocs muet be determined exactly, so that neither tbe
one nor the other shall bo in excess and contaminate the chloric acid
which remains behind. In the method itself, howoYcr, is contaiaed a
security against this, for the one substance must be added to the
solution of the other only so long as a precipitate is formed. The
clejir liquid is tested with a small quantity of the first substance to «ee
if an excess of the second has not been added, and one continues
testing with the two substances alternately until a sample of the
solution gives no precipitate either inth the one or with the other.

* It must not be thought that in thia way an " absolutely " pure
solution is obtained. Thia would be the case only if the precipitate
were absolutely insoluble, which, however, is never the case. \Vheu,
however, the solubility of the precipitate is known from other measure-
ments, the amount of impurity still present can be calculated.

The solution of chloric acid thus obtained, is a strongly acid, i
colourless liquid, which, although faii'ly stable in dilute solution,
elowly decomposes into oxygen and hydrochloric acid. The latter
Bubstance acts in turn on the remaining chloric acid ^th formation of
chlorine and water, so that oxygen and chlorine are finally obtained.
Expressed in equations, we have

and

or, combined together,

2HC103 = 2HCU30.,
5HC1 + HCIO3 = 3H,0 + 3CU

4HCIO3 = 2H5O + 2CI2 + 50^.

The decomiwsition tsikea place all the more rapidly the moro
concentrated the solution becomes and the higher the temperature
rtaes- By reason of the large quantities of oxygen which are evolved
in the decomposition, chloric acid is a strong oxidising agent.

Chloric acid as such finds no application, but the chlorates are
largely used. Fuller information with regard to this will be given
under the rei^pective metiils.

206. Solubility of Salts. — In order to suceessfoUy perform tbe
above-mentioned separation of two salts by crystallisation, on the
biiais of difference of solubility, a knowledge of the general laws to
which the solutions of solid substances aie siibjeet, is necessary. The
most important of these are the following.

When a solid substance dissolves in a liquid, there is for escb
tempei-ature a definite i^dnhtliti/f t.c. a definite ratio between the
""■i^imts of the dissolved substance and of the solvent This ratio

rlie expresBed in two ways: either by tal<ing the total amount of
Ift aolation or onlj the amonnt of the solvent, as unit, ur putting it
|oil to 100> The former method of cakulatioii is the one most
litKble for scientific purposeis, but the tatter is almost entirely used,
H we shall retain it here. The mlubiliti/ will, accordingly, i)e
■leaetited by the amount of solid subatance which can diseolvu in
IJN ports of the solvent

If leea of the solid substance is brought into contact with the liijuid

eorrespoDds to the solubility, it a.11 dissolves and the solution is

9HaatuntUd, because it can still take up further quantities of the

1 tqlwtaLBce. If more of the solid substance is added, an amount

cormponding to the solubility, and the excess remaina uiidie-

Th« solubility is quit« independent of the amount of this

and the isame concentration is therefore found, whether the

is in contact with much or mth little of the solid substance.

! solubility is therefore an expression of the equilibrium between

aad the liquid portion, just as, for example, the melting point

Bflo substance is an expression of the equilibrium between the

land the liquid form. In both cases, the equilibrium i;; independ*

the relative and absolute amounts of the participating phases.

' italrmfnl itpiiltfi quit'' uuiKr.Tsnlbj in III! equilif'Ha hdirscii diffarerif

When the solid substance is not present, one of the factors of
quilibrium i» wanting, and there is no eauiBe present to prescribe
eoncentmtion. From this it follows that a solution ahmf
InoC have a definite concentration. In the case of nuitnturalfd
tluB requires no further explanation ; us small quantities of
sibstance as we please can be dissolved in a given qjiantity
( liquid. The theorem, however, must also apply t^o more eoncen-
solotione, i.#. there can be solutions which contain more of the
batuice than corresponds to the condition of equilibriiuu in
of the solid form,
* Aa a matter of fact, such solutions can Iw prepared in various
[tvp, If tlie solid substance ie not present, they are, nithin eerbain
^aiu. iast as stable as the unsaturated solutions ; in contact with the
ni, however, they behave in the opposite way to these.
■j« the unsaturated solutions dissolve the solid form^ there
Kfuitu from the suj>frsntit rated solutions, as they are called, so
I d the solid substance that the condition of saturation Is again
" \^

lofloence of Temperature and Pressure on the

ilj. — If the tempo^raturc cbanges, the solubility in general
la the ease of most solid substances, the solubility
r (be temperature rises ; in the case of some, however, it
The change of solubility with the temperature is usually
i^nNDted by a curve, the temperatures being messui-ed tovrarda the

220

PRINCIPLES OF INORGANIC CHEMISTRY

procedure is known elb rea-ijslaUisniwn. Of the substances givwt'
Fig. 75, potaesium chlorate can he recrystalliseJ very well from i
solutions, since the difference of solubility at different temperatoi
is very great. The method is less suitable for potassium chJi^
and not at all suitable for sodium chloride, For the purpowi
recrystallising these substances other means mtist be employed
Itrhich the solid substance is «iused to separate out.

* These differences of behaviour can be made clear by an
^ment- If potassium chlorate be added to boiling vvat«r as long
dissolved, so much of the salt is deposited on cooling that the lii
forms a firm paste. From a solution of ]K)tassium chloride saturati
in the heat, a much smaller amount of crystals is deposited, and fn
the solution of sodium chloride, practically none.

Solutions may l*e made to crystallise not only by change
temperature but also hy diminishing the amount of solvent. In t
case of volatile liquids this is best effected by vr-a}x>nitk>n. Tbiu^ I
example, by evaporating the water of the naturally occurring eo
tiona of common salt, the mli sprimp, the sidt contained in then
obtained in the crystalline condition. This method of a'ljshlluati
by evaporntim is used almost more frequently than the method
cfyatallisation by cooling.

210, Behaviour of Mixed Salts. — Regularities similar
those just set forth obbiin in the cise where several salts, of, genenJI
several solid substances, are present at the same time. In this c
also there corresponds to each temperature a definite condition
saturation which is independent of the relation between the amotui
of the different phases. When several salts are present the solubiBi
of each single salt, certainly, is no longer the satne as when il
present atone, but they exercise a mutual influence on one anf
This, however, afi'ects only the numerical value's and not the
relations.

If, now, the point of saturation of a mixed solution is exc

this does not, in general, occur at the same time for both salts,

jtho solution which h supersaturated for the one is still unsati

rith respect to the other. For this reason only the onf.

substance separates out from the solution, and its Beparatiou f, im

other is thus effected. t

For exatiiple, on eiaporating a solution of any mi.xture oi«
only that salt ivill, in the first instance, separate out whose poiit
siituration is first reached. On withdrawing the crystals which
.deposited from thf solution, the substance is obtained in the pure bI
'Only when the point of saturation of the other substances is rej
do these sefKirato out along with the first, and mixtures are obtaim

In such ca-ses thy separation can generally be cirrieLl further
making use of the different variation of the sohibilities with
temperature. For example, if a solution of potassium chloride

OXYciiN (.(IMPOUNDS O? CHLORINE

to my, M'hen hjpo*litoiou.s acid dec-otu poses iiitu liydrfttlilorii-

ad oxygvu, VJ Ij are developed. When, therefore, hyjwchlorovis

as an oxidising agent, the hetit which is thereby developed

ewh comhiaing wt-ij^ht of oxygen, greater by 39 kj than if

ition tCMjk pbce with free oxygen. This wuiild suggest that

acid, quite a^Kirt from its gre^iter velocity of reaction,

« stronger oxitUaing agent than free oxygen, and thai it

Ell I* ciijjBiMc of oxidising substances not oxidised by this.

is lUAkes us return to the point meationed on p. :ilO. iSitice the

Qtion of byjKK'hlorou.s acid into oxygen and hydrochloric acid

I place witli ct^nsiderabic diminution of the froe energy, it can be

th« purpose of prepiiring oxides which roiild be formed from

ily with increiwe of the free energy, and which, therefoie,

ectly formed from it. Since the tanking up of oxygon fnmi

Iy|3oc1i](>roii5 acid by the substances in question necessarily takes

■1' -ifioously with the decomposition of the acid, we have here

J. " which has been characterised as a presupposed eondi-

in ij^iii^ tlic free energy of one process to reudtir anotlier process

(p. 207). Thus, for example, dilute hydrochloric acid can he

oxidi:»e<l to chlorine and water liy means of iiy|uichlorou8 aci<l

>), OL pnx'esa which is not possilile with free oxygen, Ifecaiise the

furnuition of tree oxvgeti from chlorine and water takes place

lie heat of foi-mation of cMork add is given by the following

H, -c CU - 30.^ + aq. = 2HCI0, aq. + 2 > i 00 Ij,
2CU - aO,. ^ aq. - 4H(."10!, aq. -4-4.'! kj.

tltifr we obtain the heat evolved irv oxidation by means of chloric

HCIO, ar], = HCl atj. + 30 + G4 kj.

u m. heat evolution, therefore, of 21 ^7 for each combining weight
fgao. Thifi numttor is considerably smaller than in the case of
acid, which is in agreement with the smaller oxidising
I chloric acid.
rJilori'- add, the corresponding equations are : —

H, - Clj ^ 4O5 + aq. = 2HflO^ n.i.[. -h 2 . 1 GUj
" 2C1, - 70j t &q. = 4HC10^ nq. + 4 > IS Icj
1 1 CIO, aq. = HCl aq. .40-3 kj.

all three equations the greater stability and feebler oxidising
of perchloric acid finds expression,

Jis The Combinmg Weight of Chlorine. — For the purpose
liaijig the combining weight of chlorine with sutticient exact-
lawmewhat indirect meibod has been found necessary. First,

22«

PRINCIPLES OF IXOKGANIU CHEMISTRY chai-.:

poUissium chlorate was converted, l.iy heuting, intu jHitassium cbloric
and oxygen. Calfulating, in accordance with the equHtitin

KClOa = KCl + 30,

hoiv much potaasmm chloride is combined with 3 » Ifi 4H part* I
weight of oxygen, the utirabcr obtmned represents the coiiibijiiiiy weig
of potassium chloride referred to oxygen eijiml to If). Since, now, en
gram of potassjntn chlorate on ignition leaves a residue of O-60f*5
losing, therefore, 03915 gm. oxygen, we have the proportion

KCl :48 = 0-6085; 0-3915.

which gives for the combining weight of potassium chloride, K(
= 74-59.

Next, it was determined how mncii silver chloride eoiild
obtained from a -^iven amonnt of potassivini fhloride. Since one
bining weight of chlorine is contained in each salt, the ratio of
weights in which the one is formed fnnn the otfier is also erjual toj
ratio of tlieir comliining weights. It was found thiit from eiicb gr
potassium chloride, 11*224 gm. silver chloride was obtained. Hen

AgCl;74r>9= l-fl224: i,-

hom which wb find, AgCi = I43*ay.

Lastly, a weighed quantity of silver was converted into saii.
chluride. Each gram of silver yielded thereby 1 3284 gm. aflt
t'hloride, tid%ing up, therefore, 0*3284 gm. cljlorine, Calcidatin^
the aid of this relation how much chlorine is contained in one
bining weight of silver cliloridc, the wimbining weight of chloiiiwj
found from the projiortitui

('I:l4;i-3H . 0:{2H4: 1'3284

to be, CI = 35*4,").

From these determinations, we can further obtain the eombinil
weights of silver and pot^isslum. Subtracting the combining weij
of chlorine from the combining weight of silver ohioride which
found eijual to 14^*39, there follows, Ag ^ 1 07*1)4. A similar calo
tion ill the case of potassium chloride yields K = KCl - CI = "iH
-35-45 311*14.

The re;»son that such an indirect method has been employiHl ia (ii*|
to the fact that the simple oxygen eomponnds of chloriin* cannot, «
account of their nniit/tble nature, be prejwired sufficiently pure
analysed with sufficient exactness. The transformations above des("ril)«<^,
however, can bs performed with very gre;it exactness, and thii" is th
determining reason for preferring tbo indirect to the direct method.

OXYOEN COilPOUNDS OF CHLORINE

soda, which was indicated od p. 212, must, la accordance with what
bag l>een saiil, f>e completed as follows : —

MS*»m - u'Cii

12N»OCl+l2S»CI

4NftC«:is+30!>&OI

istao4-4-2is«ci

wNici+nn,

For the sake of shortness, the 1 2H.,0, pnidticed in the paasiige to
th« second stage, have been omitted, since they take no farther part
in the irunsfnrmations.

213. Otiier Oxygen Compounds of OMorine. — The substances
hitherto descrilied do not exhaust the possible mittil»er of compounds
of chlorui*-' with hydrogen and ovygeii, although the substances still
r.U? iv treiited are of inferior importance to those slreatly mentioned.
^ftlf a chlorate is decomposed with a .strong acid, f.j. sidjihunc acid,
PHiric sR'id is first formed, in accordance with the general scheme.
This sulwtance is, however, not stable in (he anhydrous condition,
and immeJiately undergoes decomposition, in accorrlance with the

gition
4HCKlj = 2H,0 + 4C10.. -^ O^.
■ It uthor worda, water is formed from the components of the acid, this
I hjging necessary for the prodnction of the (more stable) ion of chloric

^^ The compound ClO^ formed at the same time, bears the name of
rki^rriM dut.niln or ddcriuf jientrifl'', and appears as a yellow-brown gas
which can Itc condensed to a similarly coloured liijuid at a tempera-
tui-c under 10'. Both gas and liquid are extremely explosive. This
can be «bo*vn by placing on the bottom of a wide-mouthed Ijottle of
2 to 3 litres capacity, a small d.ish conCainin<; some {wtassiam chlorate
I aitd allowing a few tlrops of concentrated sulfihuric acid to fal! on
ihii The yellow gas is evolved with a jiecnliar crackling sound due
to small explosions. If a ivarni metal rod, the temperature of which
be much l>elow that of the visible red-heat, )>e introiluced some
lents later into the ga-s, tbig decomposes with loud detonation into
'chlorine and ^txygen.

Chlorine peroxide is not the anhydride of atiy definite acid, but,
when brought in contact with cauatic soda,- yields sodium chlorate and

228

PRINCIPLES OF INORGANIC CHEAUSTRY

after 5 to 10 minutes. This appears remarkable, since the differe
of density as compared witli hvdrugen is much grcatt-r th;in
consjiaved with air, and, therefore, the work to Ik; performed
givtvity is iilso greater. That, nevertheless, brornjiie vapour
hydrogen mix more quickly is due to the fact that dijf'ushn pr
more rapidly in hydrogen because, in this case, the mutual frict
the gasys is less. The viilocity of diffusion obeys, to 8ome
thouyfa by lui means exactly, the same law as the velocity of efl
(p. 95), and is, in the case of hydrogen, about four limes as
as in air.

From determinations of the density of bromine vapour, its too
weight has been found to be IGO, or five times as great as that
o.xygen. Bromine vapour is, therefore, 5*5 times as heavy *»
Sijiee the combining weight has been found to be half as great
exact figure being 79 DC), the composition of bromine vajtour is
sented by the formula Br^. At very high temperatm'es, the
weight becomes somewhat less. Since similar relations are found i
have been more fully investigated in the case of iodine, we shAll
this phenomenon at that point.

Bromine dissolves in wjiter, forming a yellow to brown colU
liquid, which possesses the smell of bromine and can be used in
of pure bromine when oidy a small quantity of the subst
required. The solution, saturated at room temperature, cont
about 'A per cent of bromine. If the water contains saline
pounds of bromine in solution, more bromine is dissolved,
deeomposiible compound.^ of bromine being formed wlijcb, iti
of their relations, behave like free bromine. These relatione,
will be diacussed more fully under iodine,

From the aqueous aulutiou of bromine (bromine water)
separates out, on cooling, a solid hydrate whicli behaves quite sii
to chlorine hydrate (p. 173).

217. Hydrogen Bromide. — With hydrogen, bromine for
compound, lilSi-, which is \'ory similar to hydrogen chloride,
reaction lfctw<"cn the elements, however, is not ncai'ly so vigorouil
in the case of chlorine. If bromine vapour be mixed witli hydrog
[lo sudden rcartion takes place either on passing an electric sjKirk or(
'esLpositig the mixture to sunlight; only a partial combination of i
gtiaei occurs. The reaction can be accelerated by employing cattJjf
agents, and for this p«riK>,'ie, platiinim and the nieUiJs like it
been found tt> be specially active. If a suitable mixture of hydt
and bromine vajjour be pjissed through a gently heated tulve filled wifl
finely divided platinum, the issuing gases contain large quantities
hydrogen bromide, and, by suitable tuTaiigement, the reaction is
cally coraptete.

Hydrogen bromide is obtained more easily, and in a manzd
more suited for experimental pui-poses, by the simultaneous attil

F5R0M1SE,

nine »m\ phosphorus t>n water. The chemical reaction which

\kv» plskce ciinnot be completely explftined till we come to

»ru* ; siifliw it to indicate that n partition of the elements of

-ei^iiJts. The <)xy;y;<'n combines with the phosphorus ami the

eii with the bromine. Bromintj alone is not a.b!e to tlecomjiosc

u this would be associated with an jncreiiae of the free energy

). If thi* reaction, however, be joined with another in which a

nJile diminution of the free energy occurs, so that over the whole

Uiere is it diminution of the free energy, the reaction liecomes

ft. The .mxiliary process in this case is the corabinalion of

•h (ihosphorus, which, iis we know (p. G4), is accompanied

r.ttiori of large iiuantities of energy.

••\|»fnment i.s carried out aa follows. Red phosphova'5 along

in»i' water is placed in a small flask, through the cork of

piws >t dropping-furinel containing

le, and a delivery tube (Fig, 70).

IB is connected a U^tube filled

iUiene<l reil jihosphtjriiH spre-nl

pieces of glaft.«. The purpose

is to convert any Itromine

rbjch may escape from the

into hydrogen bromide. On

the bromine to drop slowly

flask, a violent reaction, ac-

I by Hashes of li^ht, takes

from the end of the U-tul^a a colon rless gas escapes which

fumes in the air and is absorbed with extreme readineas

It thus behaves very similarly to hydiogeii chloride.

gju cannot be c^tlectod satisfactorily over mercury, since it is

Xttvul by this metal, mercury br«»mitlc and hydrogen being

; still the reaction does not pi-oceetl rapidly. On account of

density it can Imj colIecte<l, like chlorine, by displacement of

In this case tlie appearance of a thick mist at the mouth is

) that the ve^isel is full.

molar weight of hydrogen bromide is 81, eorreapouding to
Biula HBr. The gaa shows noticeable deiiations from the
bwa.

pressure and cold, hy<lrojj;en hrotnide can be converted into it
•fbich boils at - 73°, and, like liquid hydrogen chloride, has
tomjwratively slight reaetivity.

l The Solution of Hydrogen Bromide. — An aipieous mUi
i hydrogen bromide can bo obUiined by connecting to the
litjg apparatus (Fig. 76) the arrangement described on p. 183
tinii of a gas. The solution, saturated at 0'', contains 80
hydrogpn brottiide ; it is very stnjngly acid, fumes in the
a density of 1 S. More dilute solutions do not fume iso

230

PRINCIPLES OF IXOKOANIC CHEMISTKY

CHi

much, atid the 4S per tent solution is in the eaoie condition as th«
per cent solution of hydrogen chloride ; it distils over wn'th iinchan,
composition. The relations described in the wise of hydrojijeri chloi
(p. 185) arc repeated rjuite similarly in the ciise of hydrogen bromi
l8o thiit they need not be again desc'riiwd.

The charaett^tstic reftctions of acids are displiiyed in thu &ime
by hydrogen bromide as by hydrngeti chloride, so that equivi
solutions of the two acids liohave almost identically, not only qa
tivlively Imt also quantitatively. Hydrobromic acid, therefore, beloi
to the strongest acids, aud even i« moderately dilute solutioM
largely dissociated into its ions.

Hydrobromic acid acts on the metals in the same way as hyd
chloric acid : hyth'tHifiii is evolved and the hroiniiifn of the metals
formed. These are ideritie;d with the compounds which arc nb
bv the action of the hydroxides of the same metals oji bvdrubm
acid, water being atmultaiieously formed, ami with those ubuiinow
the direct action of bromine nn the respective metals.

In the latter case the action is, in general, not so energeti
the case of chlorine, but the difference is not very great. An
this 13 obtained by intro«liiciiig a piece of thin rolled metal'
{tinfoil), such as is used for wrapping up chocolate unci such tln'i
intfl liijiud bromine contained in a test tube. The two elemei
immediately combine with the prmluutiuii of a dark red Harac
the evolution of thick \'apoiu^. On account of the poisonous
perties of those, the experiment must be c^uried out in a fti
chamber with good draught.

The aqueous solutions of hydrobiomic acid and of mnsl. of I
metallic bromidQ.s contain bromine sjij^ hitnuidum. In this fonu
exhibits the general property of ions of electrolytic touductivity, ol
the numerical values of this generally agree very closely with ihi
of the equivalent chlorides. A reaction with «7*vt eoliiiions is a
given, and the precipitate of silver bromide which is produceil by sili
salts in all solutions containing bromidion is very similar to sili
chloride in appearance, but i.i of a yellowish colour and is much I
fiolnbltf than silver chloride. The reactions by means of which the t
substtuices can he distinguished from one another will be given und
silver. For the rest, bromidion is not coloured.

When chlorine i<a passed into soluttonB containing bromidioiV
exchange of conditions tsvkes place ; the chlci-ine p.asscs into thlorWH
and bromidion into bromine. For this reason, all .such srilutioti&
addition of clihirine water becctme yellow in colour, and since
coloration is quite ^isible even with a verj* .small concentration
bromine, it serves as a test for bromidion. Since cliloridion cannot,
course, react with chlorine, chlorine water can also he used to
tingatab between bromidion and chlnridioti, and for the identifier
of^ the former in presence of the lallev.

BHOMiNE, lODINK, b'LUORINK

2-fl

ring a iIahIi U> indicate the ions, ns mentioned on p. lO'l,
>n in question wotiiil be written,

I'Br + (X = 2Cl' + Br.,.

Ho bromiilion, of coni-st, cau be ijresent in solution unless fui
snl amount of some catioti be also present ; the latter, hnu'ever,
no pai't ill ihe prcx'ess, which takes place in the same way what-
the ca(»on may Ih;.

reaction is used foi- the preparatiori of bromine fmni the

in irhich bromine com|>ounds occur itatnralljr, more especially

!tbe imithcr liipiorB obtained in the warlting up of the potsissiiini

Stassfurt (p. -"ri). All these sjdt solutions contain the broniino

todic form, .ind on passing in chlorine urid distilling the liiptid,

Hilly vohuite bromine pusses over with the atcnm. The chlorine

for this purpose can silso be prepared in the liijutd itself by

ft hyiKwhlorite {e.ii. blenching powder), for example, and then

klori« /icid. By means of h priliminary tleterniination of the

t<if bromine in the li([Uiirs, however, care must lie tnUeri ralher

little than too much chlorine, in order that the bromine

be not contjtniinated with chlorine.

. Ozy-acids of Bromine. — Urnmijie js remlily disstjlved by a

of cAti3ttr soda, the lifpiid remaining bright yellow in colour.

sodittm Itromifle, the liipiid then contains sixlium fii/jmhioitiHe.

tioo agrees entirely with the eorrcsporjding one in the case of

for it. tJike.'* place according to the oquatitm

2NaOH + Br, - Nallr ^ NaOBr f 11/).

be Milutjirti produced ia used in the hiboratory. It contaiiia
ii>m>/n, BrO', and by reason of the oxygjen of the latter it has as
an oxidising action as h^-pochlorite sohitjon.

he corresponding acid, hypobromons acid, HOHi', can also be prc-
iti diinte a<jUfous wrihition. It is very similar to hypochlorous

ttanding some tmie, es[)ecially when an excesjJJ of bromine is
jWMmt, the solution [la-ssefi into one containing l/timmnkiit, BrO^', along
bmmidiou. In this case alsn it is better to use a solution of
nmn iiydroxide. On iulding bromine to such a sohition without
. until it« colour is (Hjnnanent, the jwtaasium bromate separates
[jce in the fnrm of a crysUUine precipitate. Neglecting the
liate hyjmbi'nniite singe, the reaclion is

GlvOH - 3Brj - aKBr + KBri)., <■ Mip.

[Fmin this salt bromic acid, HHrO,, can Iw obUiined in a,t\v\ew\s
itiun in the s.uni^ irttr .m chloric aekl was tibtained fvotu tWovvvVc.

232

PRINCIPLES OF INORGANIC CHEMISTRY

It is very Bmiilii.r to cLloi'ic acid, only still more easily det'Omi
It 13 not known in the anhydrous condition.

PerbroniateB have not yet been prejiared. and no oxygen com[
o£ bromine is known corresponding to chlorine monoxide and chlfl
dioxide. In general, the compounds of bromine containing
decompose more easily than the corresponding chlorine compot

The aimhiiting tmijhi of brmidnc has been determined in a
similar to that iiaed for chlorine. It amoimts to 79&6, or
exactly iyO, The deviation from the ronnd number, however, is
due to experimental error, but hjva i>een proved beyond doubt.

IS. loilini

230. General- — Iodine is allied to chlorine and bromine, aiidj
it third similar element. Of the three, it has the highest eoml
weight, amimnting to 1l'G86, ainl its [iro|ierties show deviations:
those of bromine chiclly in the same direction iis those of br
deviate from chlorine.

At ordinary temperatures, iodine is a solid, crystalline siibsto
of a purple-black colour with an indication of metallic lustre.
density its .3. At 114 it melts to a deep brown lii[uitU Even
ordinary temperatiues it emits some vapour, which can easily
lecognisail by itJs reddish-purple colour when a little iudine is
tallied in a fairly large veaael. Iodine, however, does rrot
till 184".

Iodine vapour is of a fine violet colour. For the piirjiose
observing tbia colour and at the same time also the great ciensity
iodine vapour, a large, roimd-bott-omcd Hiiak is strongly beate<l ini
large flame, being kept diligently turneii the while, and a few crysti
of iodine are then thrown into the liut Hask. The iwline is at onci
converted into a vapour of a dark violet colour, which remains atl
bottom, and which, when the vessel is moved, shows itfieU in a
flegree subject to the force of gravity.

The density of iodine vapour is very considerable, Iwing ah
rune times as gi'oat as that of air. The molar weight is 2n4 and \
vapour has, therefore, the formula I.,. An account of its behaviouf (
high temperatures will be given |jreseiitly.

In water, iodine i.s only sjmringly soluble, but still snfticiently fol
the brown colour with which it |ias.sea into solution to be delocited l
fairly thick layers. If a salt-like iodide is present in the water, niue
larger quantities are dissolvetJ with a brown colour. This is duo to
formation of an ion I.,', iia will be immediately discussed.

In other liquids, iodine is generally more soluble. In spirit
wine it dissolves with a brown colour similar to that of the aqueoi
iodide solutions. This solution is used in medicine, and is ealU

BKOMINK. IODINE. FLUORINE

233

wdine. Oilier s«»lv'euU, such as carbon djaulphicle aticj

, dissolve il with ji fine violet colour similar lo that of

On what these differences of colour depend ia as yet

rn, but it appears tiiat in the brown solutions easily decom-

cnoipounds are formed between iodine und the siiilvent:,

ai(Ueous solution of iodine ig iilmken with carlion disnlphide/

of ihe iodine disiippears from the aqueous aolution, and the

I dualpbidc is euloured purple. The iodine, therefore, lejivos the

in order to dissolve in the carbon disidphide. This is an

lpl«" "f .-i generfii phfnomcnon which is sidijot't t-o definite liiws,

I - The Law of Distribution. — If to two liquids A and B, which

<or ralher, are only slightly) ndseibie with one another, a aub-

l»e ailded whioh is soluble in both, this aubstiince will, in general,

e tti both Htjutds and % stiite of equilibrium will be eatablislnid.

tote is determined by the law thut thf .■fnhstn fle^': is th^tribitifd

ihe /«rv* »)livn(.s iH .fwh a vai/ (hut the rutin of its e(»ii.Yiihvtum in

' nmfSant.

tats rotio ia inde)>eudent of the amounts of the two solvt.'nt.'i,
of the ali«olut« concentration, at least >rithiu delliiite limits,
di*|)».'i>ils only on the nature of the three suljstanees and on
emjHTJtiure.

For exaiuple, iodine its disti'ibnted between water and carl>on

iide in the ratio I : 600. If, then, any ijuantities whatever of

iodine, and carbon disulphide arc shaken together and the two

r>a« then investigated, there will be found in each cubic centi-

(•l the carbon ilisulphide solution TiOO times as much iodine as

cc. of thf aqueous solution.

is evident from these numbers, the concentration in carlion
lidc is very nincb greater than in water ; for this reason, also,
[greater part of the iodine passes, as the experiment shows, into
I former, when an aqaeoiis solution of iodine is shaken with
disnlphide.
law holds only for the iodine present in the elementary
not for any compounds of iodine that may be present,
djstilphide be render&l a deep violet colour with iodine
solution tiiorj shaken with a solution of caustic Btnhi, the
colour disappears and the iodine passes into the aqueous
Here, however, it no longer exists aa iodine, but has
Jt« with the cauatic soda.* If hycU'ochloric acid be added
Iiition, by which means free iodine is again fonned, and the
be shaken, the carbon dir^nlphido again becomes ir'iolet In

■

(Wttin iliralpliide m a cotujiauud of 'iulptmr and i^jirlion, aail Corrnh n llMvy.

linisi.l rill. Il i]ii«s tin) luijt with water,
Ti' ■ ' ich Ukc filmre litre ogree tutiroly with those given by chlorine or

^'■^0, «!)<{ the reader is, therefore, refen^Nl to the eiplAOStion of
P*w iiic\)uiul> {p. ^0/).

234

PRINCIPLES OF INORGANIC CHEMISTRY

222. Iodine Vapouir. — It haa already been mentioned that
Vapour of iodiiiu has the niohir weight 254. Tbta VJihie holds
temperatures above the boiling point up to about 500', If
tfluiportiture hn niiaed still higher, the ioiiiiie vapour expands moi
than a norrujil gas^ iidd its molar weight, therefore, liecomes gmAlk
The deviation becomes all tlic greater the higber the tomperaturo
idlowed t*j rise. At 1500", finally, the half value is reachetl, and
further elevation of the tempentture has no longer any effoet.

This atatcmeut is true ordy when the pressure V8 et|ual to
atnrospherc. If it is less, too small flensities are found even :tt let
tempeiatui'es, and the half value U sooner reached. At t«niperatun
above thie, however, the molar weight an<iai remains constant. Thi

relations ure made dear in Fig. 77. The molar weights are meaaii
dou (HV.irds. ami the temperatures to the right. The numlHsis filacsl
beside the curves give the presstires.

The idjovo facts ahovv that when iodine vapour ia heated, i
trausformntion of the vapour 1,^ into I takes place, according to tbi
equation I^ - 21. Such a decomposition of one substance into simp!*'
substances ia called ilhufH'Lilioii. From the fact that the decorajjositioa
increases with rise of tem]i.orature, it ia to ho concluded that heat i»
absorbed in the process, in accordance with the repeatedly exprcW
general principle of resisUiuce to ch.'Uige. Since the second forw
would, under the same pressure, occupy double the voltune of the 6iA,
and, therefore, if the volume is the same, would exert twice lb*
pressure, the transformation of 1^ into 21 would, at constant volume
c£insB an increase iif the pressure. From this fuct it can he concluded
on the ground of the Bunie general principle, that the decunipositi<v4
will lie promoted by diminution of [)ros9ure. since the decomiMsitio^
0|ipo(ies the latter. This conclusion is bnriio out by the experiindn
represented iii Fig. "7,

HKOMINK, lomxi:. KLUDKINK

235

'Coirtpnrwi with I.„ tbi; suWstaiire I most lie regarded us n. nf>w
ice with (Jifferetit (iroperiies. Uwiog to tho diHicnltv^ of investi-
al ftiich high IcrnfiemUu'es, it has hitherto heeo itn|K)ssible to
line these differeiiws quantitatively except in the case of the
ity. It has, howevci'. Wen stated iliat a cliange in iho colour of
riiir hx-i t»<>'ii oliHorvod.

Starcb Iodide. — Ett-meniary iodine in the piire stiile, whether

jr or in solution, ts, even of itself, distinguished by ixs strong

Still siriiillur i]«arititiea tlitui can be detected by the t-olour of

ioilin« can hv det-ectetJ liy the colour of a remarkable cotnpoiitid

ch iodine forniB with xdirrh.

StATch ii» an organic subet-mce {tliat is, a aiilistaiice t'oritiiirting
' -'-d of carl.Kjn. hydrogen, and oxygen, which occui-s very
;to<l ii) plants collected chictty in the scetls or the
DTalent jiortimis cvl' the vegetable* nrgiiriism. It is pre|>4red mostly
(ntatues and from wheat, and is obtained in the form of a white
rhkh is insoluble in coM wat-er, but in hot water swells up to
ktinous mass. If much water b<; taken, nay, a hundred times a&
I the weight of thf starch, a liquid is obtained which can be
hot from the undissolved cell-walls, and which then appears
' am! remains, liquid.

rim anliition of starch, naw, has the pnijierty of yielding a fino
edoor with free iwiini". This coloration is exceedingly strong.
very feebly brownish coloured solution obtained by shaking iodine
WkUir, becomes of a dark lilue colour with st^uch solution, and
somewhat richer in iodine are rendered ojianue. Tln.> compound
is bene fonued, cuntjiin.s tlie iixliiie only very feebly united ; it
in almost every respect like free iodine, and it is therefore
rod in many chemical icactions in which iiHline ia prt>duced
uknl up, as nil iudjcatiir fnr tbe tirst or for the last traces of
Nine.

a itolution of i>t-irch iodide, ns the blue auJ»atance is called, is

1. it l)ecouie9 coluurless at a temperature n \iulc below the

poinl. e-vhibitinj; imly the feebly brownish colour of iofline.

ing. the blue colour nfiuiit appears, showing that the compound

>lg>in formt'd from its cnuipmcnts.

" This experiment can bo rendered very clear if only the lower
pnjon <jf the colourless- solution, obtained by heating in a test tubu.j
Ukwded by partially immei^ing tlie tube in cobi water, 'hdy this
"ill then lieennie blue, and a.s the eixjlcd tifjuid is the 8|ioc]
it will remain undistuibed at the bottom and the
i iirly abrupt. In pro|Mirti<m iis the solutiim cools, the
[Ukutoor gradual ly moves upwards.

Tim olonr phenomenon serves for the <letectioii both of iwline and
^iUrrh, ;ind has, for \xtth purjioses, a great value,

JK- Hydrogen Iodide. —Iodine and hydro^iieti unite to form

336

PRINCIPLES OF INORGANIC CHEMISTRY

CHAP

bydriodic acid, which, in accordance with its formula HI, has
density 128. Like the other halogen hydnicids, it is, ;it nrditi
temperatures, a colourless gas. Its litjucfactiun, Uowever. vino
atmospheric pressure, t:ikes place even ut - 34',

The iiiiioii of tilt! two eleuieiit^ is still toss stable than in the
of hydrogen bromide. If ii mixture of hydrogen and iodjny \ ;n">nr •"
equ:d voIiuhks lie heated, only a portion of the mixture coin
form hydrogen iodide, the other pottion remaining uncorabinert, iiiu
proportion, also, is not altered by adding platinum sponge : the fir
invariable atati; will only be very much more quickly reached,
point varies some«"hiit with the tempenitnre ; at ,')20\ 76 per cent)
the mixture combines.

Conversely, already formed hydrogen iodide, when heated, imrtiallji
decomposes into iodine and hydrogen, the mixture finally having
indeed, exactly the same composition as before. In this cswe
presence of piatiimm sponge accelerates the decoliipositioii juist as i|
the former case it accelerated the combination, in conformity ivith i
genenii law of catalytic acceleration.

In accordance with the formula

H, + I, - 2HI,

two volumes of the com^iound are pioduced from two volumos of
mixed gjiaes ; the reaction, therefore, cakes place without change fli
volume. Now, we have just seen (p. '2'Si) that a diminution (if tb>
preasure promotes that reaction which, at consUmt volume, would b»
accompanied by increiise of pressure. On attempting to apply tkii
rule here, the tlifficulty arises that neither of the two possible reaction*
— neither the formation nor the decomposition of hydrogen i<Klidi
wttuld cause an increase of pressure. The conclusion to be drawn
from this is that in this case change of pressure has no infiuencp OB
the chemical equilibrium. This conclusion has been confirmed by
experiment.

This case can be generalised, and we can enunciate the rule: v
ilfJinHe slaffi tire ttof altered hi) f/itrH j»WfSiie.\ n clmniji' in tht^ sftiteskai,
roHremrlif, lut iafimiKe on Ike prix:e4;stts, AVith the help of this rule,
coiicliisionsi can sometimes be drawn which are as important »s tht
rule is simple.

Hydrogen iodide can be prepared, siniilnrly to hydrogen bromidB.
l>y means of phosphorus and water, as ivcll as by heating iodine aiKl
hydrogen in the presence of platinum. The reaction is in this ca«
much less violent. Red phoaphoniH, water, and iodine can be tnixwi
in the order given, in the profwrtions 1:4:15, without any considct^
able reaction taking place ; on heating, hydrogen iodide is then evolved
and can be collected by downward displacement, as it is four tim^
heavier than air.

Oti account of the readiness wit\\ %v\i\tti \t dewsiiv^acah, almost i

BROMINE, IODINE, FLUORINE

247

iioi iucr»;i;*t? indefimtelj, for it must reach iU maximum when
tioii i^ o>iii|tlt.'t-e.

• nisIT^^r of fact, meiisuremetits of the conductivity hiive shown
is » tiiaximuta for the strength of acids wliicb c;mnot he
Hydrochloric acid, oven in moderately dilute solutions,
to this loaximan], and must, therefore, he desi^dtod as
•tnmgest acids. To the sanu; ckss belong the other halogen
Fntb the exception of hydrofluoric acid, which is considerably less

I iKasociation nf hydrochloric, hydrobroniic, and hydriodic acids,

•8 tbai nf all other acids, inere;ises with the dilution. In the

tit\Av there is given the fractional dissociation nt the ordinary

lurr (20'), the dilution being expressed by the ituuiber of

ui which 1 "01 '^ni. of hydrotteri is cunttiined.

10 0 S>5

100 O-SS

IMA 0-99

tlF, fiiilphiini- Aciil.
irlO 0-57

o-aa or*

11 -Si* 0-92

Aci-'tio Aciil,
0-013
0-050

0'125

therefore, the first three acids change only slightly with
the othiTs do so to a large extent, and tend to asaum« the
1 — a value which is already almost reached by the former. Tin-

■fjuir ihf (10</,«-, t^ie limrf Itttllll/ do (kflj Upp'Mih 01U <W(f>/A(T ill

relatioMS ol>cy certain laws which we shall not coneider,
Qiitil a Inter point.
fMVbeti wc speak, therefore, of the ftrejitjth of an acid, we lueati its
tttvn, i.t. ihc fraction of the total amount which is in the form
The cctm-eption applies, naturally, only t« aqueous solutions.
1 ttren^i varies also with the leropeniture and the dilution, but
{h (h« absolute valued of the degree of dissociation are thereby

the i^<ifr of the difleront acids remains unchanged.

As approximate mesisnrc of the strength of an acid is afforded

Tube eompKrison of its conductivitj with that of an c<[Uivalent

I of hrdruchlorie acid. Since at fairly great dilution, Lho latter

01.1 nmt«-.ria!ly fall short, of complete dissociation, the conductivity

acid rcferrefl to hydrochloric acid ef^iial to unity, gives the

of ilM hydrogen which is in the ionic condition, or the degree

BCtation of the acid. We have here, it is true, neglected

IB ooqiilitions, still these cannot give rise to any considerable

I W tlie wxy -acids of the halogens, chloric, bromic, iodic and per-
adils are diwociated to approximately the same extent as
chloric aci<ll. Ilyptjchlorous acid, on the other hand, is very
btly dissociated ; the exact degree of diasociation, however, is

23 H

PRINCIPLES OF INOH(^ANIC CHKMI8TRY

dilute" hydrochloric acid, do uot dissolve it to a miicli greatei' ex
than water'.

The anawer to this question is thiit thu iodine can combine
the iodidioii of the hydriodic acid in accordance with the eqr
r + I^ - Ij' to form tniaduiitin I,^', which is colouied browu. The c»l
binatioa does not take place oonJidcLciy, ahout half of the iodidii
reniaining unconibined. Hence, about as much free iodino dissol
in the tJoUitiun of dilute hydriodic ucid as there is iodine already
sent in the fui m of iodidion. In more concentrated solutions, bowe'
the sornbility of the iodine is considerably greater.

From what luus been said, it follows that iodine must di
to the ^amu extent in the solutions of alt metiillic iodides caj
of forming iodidion. This has been found by expeiiiuent to
the cose.

These considerations can be generalised. When in dilute suludoi
the solubility of a siiVjstance is increased ly the addition of hiioiIii
aubatanco, this is to be explained by the conversion of the solute t
another comimnnd, to an e.xtenl corresponding to the incre4ise of I
soliibility, by the substance added. So much pa.s5cs into ssoUltion ^
the unconibined portion amounts to about as much as it would da
the pure solvent; the excess is in a. Btate of combination,

The fact that this rule has been expressed only for dihiti' sohitioi
is conditioiied by the circumstance that additions alter the uatUrt
the solvent and thereby influence the solnbtlity. An example of tl
is to be found just in the ease of iodine, which is dissolved more ecpft
ally by concentrated solutions of hydriodic acid and of iodides, in mn(
larger Cjuaniities than it ousiht to \}C from the above cause alone.

In the browTi Bolutions of iodine in iodides, therefore, only a snu
porLioii of the iodine can ho regarded as existing in the free stu
namely, an amount not greater than is ilissulved by water (p. Sr
Still, the solution« mostly behave as if all the iodine diasolvmi w«
free, This in due to the fact that in proportion as the free itxliiie i
reujoved by any reaction, fresh i(xline is fonned by a splitting upfl
the ion 1.,' into I' + 1... This process takes place so quickly that thef
is at no time a complete absence of free iodine so long ;« na
triiodidion, i/, is stilJ present.

It ran be seen that the iodine is indeed combined and not free, l]
shuking a i9.olut.ion of iodine in carbon disulphide with a large tpiantit
of hydriodic acid or pota.ssinm iiKiide sohition. Although no apprec
able amount of iodine can be removed from this solution by pun* wall
(p. 2.T.T)| the violet colour in this case for the greater part disappeart
and the iodine ]iasses into the aqueous solution with a bro'if
colour,

226, Oxygen Compounds of Iodine. On dissolving iodine
caustic soda si>lution, sodium hypoiodite or Ay/'"""'/'««'n, I*)', is fi
formed in accnniapce with tlio same scheme as iji the case of thu

BKOMINE, lODIXE. FLUOlilNE

249

a nature that ions are removed l>y it^ aitd that it continues
Ks iona of the particular kiml are present, il will depend on
ttnu^itat of all possible ions. By means of this rule each
kte ca«e oui he decided.

iu», the precipitJition of chloridion bv silver solution is,

itly, a pr..i-ess ■wliich gives the amount of the jiDtfitlial ion.

tJie silver ia present in sufficient amount, the procesi? docs not

il all the chloritlion, not only that jvrcsent at tho 1>eginning,

For the riilnridion is removed from the solution K.r the

pitAtion of the silver chloride in the solid st^ite, and the process

itinue so ton^ iis chloritlion can still he formed from the

iate<l rhlfiride presunt.

determiiuiliuii of the eluctrictd conductivity, howovor, gives
ion oidy as to the amount of the ioun miilij jncMvi or the
for by such a ineAsurement no ions, or only a vjinishingly
I UDonnt of ioTiB, are nged up.

this it is clear that in oi'der to measure the state of

jn «tr, genemlly, the concentration of jmy ions, only those

are directly appliciihlc by which the amount of the ions

or is onlv veiy s+iiijhth', altered,

i2i6. The Dissociation of Salts. — Whereas in the cuse of the

,and, w we .«hall Hnd later, to a c-ertiiin extent also in the ease

bases, great \'arioty exists in the degree of disaociation, — all

lie T&luea, in fael., oeeurring, — the behaviour of the neutral salts

more uiufomi. Almost all these are dissociated to a fairly

•Mftent, and only in quite exceptional cases are salts found which

lilitt dc\'iationii in this resjvect.

Eicej)l til these speeial cases, therefore, it will not be necessary
I the c»8e of L'Uemicnl rmetions between salt solutions to refer
]y tu the suite of ilissociation, The actual conditions will he
ated very closely if we assume that all the salt present is
into ite ions, and tluit the reactions take place exclusively
the ions.

An tniiM-trtant conclusion which can be drawn from this is that

iliflerent salt solutions are mixed with one .another, the liquid

pru«}i)ced will always he of the mine nature, i/ it ionUiin thf

ieiu HI the !uiii>t uiii'mttt, no matter what the arrangement of

ions was in tbe salts used for the preparation of the solution.

of equivalent amounts of sodium chloride and potassium

va in no resjjcct be distinguished from one prepared from the

[idin^ amounts of potiissium chloride and soilium iodide.

Ihcr, since the state of the snhstJinces present is not altered by

ig the two solutions — for the substances were pteseiit as ions to

with and are so also after the mixing — none of those processes

place hy which the occurrence of chemical change is characlJsnaeA.

occufs no change either nf the t.enjpH?rature or of tine vo\\ime OT

240

PRINCIPLED UF INURGAiMC CHKMISTKV

This oxide .ilao dissolves in wnter, but is thereby transfiinnM
once into the acid, combining again with the elemcnls of water.

If the oxide he still more strongly heated, it flepomposes ii
oxygen and iodine, uhich is recognised by its violet ciilour.

If iodic acid and hydriodic acid be brought together, they spei
act on one another, with formatioji of water and iodine —

H- 10.j' + 5H- r = 3H,0 + 31,.

This reliction doea not occur on bringing pot^issium iodide
iodate together, since the hydrion necessary for the formation
water is wanting. If this, however, be abided in the form of so)
acid, iodine immediately separates out. This reaction can be ubq4
a sensitive indicator for the presence of hydrion. In the case of atn
acids or high concentration of hydrion, the reacti<in proceeds aorapii
that the varitnis steps cannot be folloii'ed ; with very weak acids,
ever, it can be seen that the reaction is not complete in a m
but that it refpiires time.

•2-27. Periodic Acid. — If sodium iodate be subjected to the
of specially energetic oxidising agenta, it takes up a further combi;
weight nf oxygen 'ind pa.«Ms into the ssdt of ^wrinJii: nriii, livhich
solution forms jyf7"(«if(HWH, 10^'. The periodic acid corresponds
certiiin extent to perchloric ai'iil, but differs from it by the fact
in the pure state it is a solid substance, the composition of
is not roprcsontod by HlU^, but by the formida Il.tO^, cnntai:
two combining weights of water more. On careful heating, peril
acid also loses water and forms an anhydride LO, ; by cai
dehydration an intcrraeiUatc substance of the composition HIO,
be obtained.

The behaviour of periodic acid towards bases is different from
of the acids hitherto discussed. Besides the salts of the formula MIH
corresponding to the salts of perchloric acid, periodic acid forms isiill
with three and five combining weights of metal. The formul* of tl
are obtiiined by imagining ono or two molecules oi water added
the fonnula HIO^, and the hydrogen of the compound thus fo
replaced by metid. In other words, there exi.st Itesides the
HIO^ also the acids H.,IO. and H,,IO^,. Acids such as these
contain several combining weights of hydrogen replaceable by m
are called /w/y/xi.fi'; acids. They contain polybasic onions ; in the pi
oaae the trivalent ion 10^,'", and the pentavalent ion 10,."'". We shi
disGVias the rvlations of these acids later, with the help of a simpli
and better known exumple (Cliap. Xll.).

228, Chlorides of Iodine.— In the ex|ieriraenfc on the decoi
position of liydrogen iodide with chlorine described on p, 23T, it
observed th-^it if the chlorine is present in excess, the iodine does n<
separate out w the usual dark histvous. tv^*^**'^'*! bwt that, a rodd

miNE, IODINE, FLUOlilKE

241

liquid of ihe ivpfwaiiince of bromine, and also reddish-yellow
»ro proituced. Both these are new finlistJtnees formed by the
linn of chloriin! with iwline.

nwl-brtjwn liquid has the composition lUl, is called iodine

ilorkle, and is forrucd witli extreme rejwliness hy passing

over i»j«liue. Under the influRnce of the chlorine, the iodine

and by stJirting with weighed (|tiautitiea the ex|}erinient can

ipced when the iriL-rejise of weight corresponding to the

hu taken place.

substance can l>e solidified Ly eold, and ia obtained in two
one of which melts at 14 , the other at, 27". Of thesu two
Ui« one inth the higher melting point is stable; the other
biiwc%'er, is produced more readily by spontaneous aolidification
the lii)uid is ctJoJed down. If a little of the higher melting form
gbl into contact witli the furm of lo>v'er inciting point, the latter
1 uito the former ; the reverse transfornmtion oev^er takes place.
the liquid cooled below 14% in the neighbotirhood of which
the litpiid does not spontaneously solidify, the one or the
9e|wnites out, arconling as crvsttds of the one or other form

,IW rehilions describtHl here are found in the case of a largo num-

lb»tauce*i. Besides the liquid foi*m, only one kind of which

i prAMnt, there are often several solid forms possible, eaeh of

. Ina itfl Bpecisd melting jjoint. The form with the lower molting

. » always unstable with respect to the form of higher melting

M that it c;»n pass into the latt^er, wherciw the reverse tninsfor-

nevrr (tci-urs, ' This phenotnenon is called poli/morphisin, and

ErTttiil forms polymorphic forms.

BhhtIw the iodine monochloride, there is another comi>oiiml, itniiiu:

It'l,. It is easily obtained by passing an excess of chlorine

iodiiie; the brown liquid which is first produced soon solidi-

red-y«*Ilow crystals, which cannot Vie melted at ordinary

M they pre^nously decomiiose into chlorine and vapour

monochlnride- If the decompfjsition bo hindered by an

of pressure, a meltifi*;; point under 10 atm, can \te observed

iwr.

compounds art? decomposed by water with formation of

ic acid, iodic acid, and froo ioduie. Still the trichloride

dissolve partially in water without decomposition, and to be

on mixing coucoiitrated sohitiona of iodic ;iciii and hydrogen

Batidca these conijwnnds, there exist compound* of iodine and
nine uid of iodine and tluorine. These will not be discussed here.

iier»l, Diily for tlic Iwlinvkmr ii( the milwljiuii-e in Uib iid<;liIiour-
i^^iiTii. Af tviujHTatiuv/' iv)iiv)i /if at II greater distance \w\ci'>»i Vtve

il-ii:.

i'LV>me fvrcrtn-ii.

244

PRINCIPLES OF IXORGAXIC CHEMISTRY

Bf mcwRirementa of the electric condueti 1*117 of aqtattom 1
bplroflaoric acid, it h fotmd that it is much less
>na than the other halogen hyiJracid». A. normal nolotjoti,

mole in the litre, is rather more tba.n 3 per cent
^«b«teai the other halogen hydracids are dissociated to 80
Hydroflnorie acid is, therefore, a considerably weaker acid
otbera.

In its general tiehaviour also, Ruoridion diSiers easet
the other halogen iona. With silver aolutions it gives no
on the contrary, iilrer fluoride is rciwiily soluble in v
the other hand, mkium Huoride \& a diffii'tiltjy soJuUle
wheread the other halogens form extremely soluble comf
calcium.

233. The Strength of Acids.— The new adds which
become kmtwn to ub, tjive occasion to some further general
tionn in .-i-iniililicatioti of those niiide on p. 187. Acids
number of common pro{>ertie8 which clearly manifest thetn's
th« colour re<«;t)on8 witli litmus and aimilHr colouring stihstanci
which tAn «,\m>, by means of numeroua other reactions, be q[nantit
determined.

This fiimilarity in action is approfiriately attributed to the on
of the same Bu1>stance, bydiogen. In the first place, non, we
that the acid properties were by no means exhibited by all hrd
conijifrtuuls ; all hydrogen, therefore, is not of this nature. The
hydrogftn is chanicteriaed cbemic;illy by the fact that it tan be rep
by nietalw, as has already been explained on p. 187.

It woul<l, therefore, be expected that those quantities of diffia
acids which contain erjual amounts of hydrogen (hence called Hjfl
vitlent), woidii aUo exliibit equal acid actions. In certain resjieetfil
m the caae ; thus, duch aniouiit.s of diH'ercnt acids alwavs neutnli
jMjimI amounts of the aame Imse (p, 18S)}, and evolve with medals, tf-'
nift<j;iu«i«m, e(ju/il qiuuitities of hydrogen. On the other hand tiers
are other reactionH in which the diH'ereiit acids behave diffen-jitlj.
l''or example, on intrfxlucing piece§ of zinc of equal size into euni'*
lent nolutionn of hydrochloric acid, sulphuric acid, and acetic acid, li*
ini't.td actH, it. ik true, on all tlie acitls with evolution of liydioijeii, «'*'
iho amotuil. (jf hj'drogeii which is M//imrf/''/^ evolved is the sameiniH
WW08 ; l-he irlnnhj, however, with which the reaction takes place in i^
different Ofutea, is very diffeient. It is greatest in the case of hydl*
chloric acid, Ichs in tbo eiiae of sulphuric acid, and very smalt in tlw
c«Ki> cif acetic iieiil.

* ThcftiA diirci"oncc8 rmi be clearly shown by placing the acids vritb
thc< xinc in sroall Wtwka litted witli gas-delivery tubes, and collwtiiig
till! tiviilvctl hydroj;!.'!! in thice cylinders of equal section pJaced eideliy
ntdw and standing over water (Fig. 78). The diflerencBa are quite distiac*
afUsr 8 to 10 minntea if equivalent normal solutions, i.e. solutions W"'

mOMINE, todTn

^UORINE

'247}

01 KID- hydrogen in the litre, are used. In order to be
nt of itnpuritic« whicli may he present in the zinc, and whith
A «!iffcrcncc in the «nolutioTi of gas, equal ijimntities of ii
Intion of copper sulphate is ad.ded to em/h of the solutions.
utinti therein" Itofoniea r.ipid juid iinifiH-m, and the collection

19 in)t l»e^uti until si>nit!wh;it iatrr.
]cl with tht'sf, tJtece run other difl'ercneas which have refer-
t! vplocitj of chemicjil pr<K:e>i.si«s and the etiiiilihrium relations.
cb cases, seveml
will })e (lis-
ter, th« nt'ids are
in till- Aaine
that we must
that Uiere are
iiferenctfe aitach-
the acids them-
1 iiirlcpt'iidcnt
nUm of the rc-

> "vy

^^^tf4f

Bifference in
ic Dissocia-

has been al-

Via. Tn.

ntioned that the acids in af|iioi»us soUition aro electrolytes,
net the electric mirrcnt with d(.'tomp<isition. If, now, the
tt fij ft(inrifli-iit whitiiniA of tht- differtsnt :«ci(l9 lie w>ni[>iirL'd, it
that in this resjject also the acids fonn the same seqiieitce as
of their last mentioue<i properties. Hyflrochloric acid
liwt, aalphuric aeid less well, and acetic acid iniicb worae.
lut iH foniid in every detail, and \% present also in the ininierical
It followB from this tbiU we arr dfyding with the operation of
KUisft, ami any interjirfitation of the deserihfd rclatiuns must
nitnt of ail these properticii.

power of cJindncting the electric current was attributed (p. 200)
t»l condition of the partici{)atitig substances, the ionic condition.
(Otuiition iho components exist in a certain degree of indcfwnd-
ooe another, or of freedom, and this finds its expression just
iWsrof tranBjHirting opposite electricities in opposite direction.^.
name indejjen<Ioiice in proved 1)y the identity of the cbeniictd
nf an ion. iiutcpeuiiently of the prf sence of other ions (p, I f^9).
j^ri^it ditJ'ereiHe.s in electrical conductivity of equivalent sobi-
»cid«, .uid the corrcspr^ndlng dirterences in cliemicnl reactivity,
attributed bo the tact that md the wkalc antuuid inii out)/ n
the ttcui /ircjteiif is in n Mttle t/f free »*»«?. By this portion
trie conduction ts perfornTO<l. and on it dcjjend the velocity
iUHuin in the case of the n.-actions of the acids. (>f the
of an acid, then, a portion is present in the atiite

2.')4

PKINXIPLES OP INOROANIC CHEMISTRY

value. The equality of tliu immbets in the case of the forme:
u due t<> the fact that these are to a large extent diasociat
ions in the dilute aqueoua solutions used ; the heat of neutrali
is, therefore, equal to the heat uf formation of water from i
hydrion and hydruxidion, as wa< shown on \t. 203, The j^roater hr-at'
neutralisation in thu ease of hydiofliioric acid is connected with
alight dissociation in aqueous sohition (p. 203), and, indeetl, it t
concluded that the disfioeiation of hycIroHuoric acid into its iiMis
jilitce with erobdiiin of heat For wo can regard the neutralisjiticnj
this acid by caustic soila as if tho acid first dissociated into ions
the hydrion then corabineil with the hydroxidion of the sofla u.i f(
water, while the HuoridJon and the aodimn remsiin side l»y side in
solution, in accordance with the circumstance that smJium Auoi
being a neutral salt, is, in aciueous solution, dissociated to a
extent into ions {p. 249). Th& toUi\ heat evolution consists, th
of the heat of dissociation of the hydrofluoric acid and of tho
formation of water from hydnon and hydroxidion. The latter rei
gives a heat development of 57 kj ; the excess, 68 - 57 = 1 1 frj, is, tli(
fore, the hoat developed in the dissociation of hydrofluoric acid ii
iona.^

On comparing the heats of forniadon of the halogeii hydracida
the known chemical reactions which occur between these and tl
halogens, it is found that tliere take place between tliem those n
whicli are ;iccorapjinied by an evolution of heat. Thus, chlorine
places bromine and iodinr^ from their hydrogen compfmnds, and»
aqueous solution, an amount of heat equal tolC4-Il>< = 46i/«
164 - 55 = 109 Ij is set free. Very nearly the same evolution of
is found in the case of the salts of the halogens, becjuise the beat*
neutralisation of the three acids with mo.st bjLsee are eijiial, and the
intiuence is, therefore, eanuclled.

* Similar relations can be frequently observed, and have given
to tho idea that orn; can predict tho direction of the correspond
chemical reaction from the sign of the " heat effect," by which tei
there is undorstooil both the dcveloprjient ami the absorption of hi
Such a theorem would contain the assumption that only those chetnii
reactions can take place which develop heat.

* Now, allhrmgh, as a matter of fact, the majority of the kiMH
chemical rejictiona take pluue with development of heat, thfre arc
a few known iti which ihc opposite, the absorption of heat, occurs,
that the temperature of the reacting substances falls spontaneom
The attempts to attribute the absor|ition of heat in such c
Bocondary reactions or to changes of the physical state, have faili

' Sinci' the liydTofluorie rw'iil is Msnif vihnt iliitsiitiateii, iiixl iit.vi the sodhisi Buot.
cutitairi'^ wHiit; iiudi'uociiilt*'! Mill., thin iiiiiiitn.T (hw.i imt ^jv<i the i^liole aatamii foi
ihdIp, but ouJj- II pRrt- Tliii cii-outiitLiuice chiiiigcs BiHiii'Whdt tbo numerical valtie of I
reHuic, tint not iu geuvrai c!ijir:uler.

BKOMINK, IODINE, FLUOKLNE

255

ice lietxriva primary and secondjtry leactions is jusL as
that Ixntweeu physical and cbLnniVal eluiigos of state. On
itnuy. the conclusion was una voidable that such a iheoreni can-
cstalili^htMi. since it ia in contradiction to tho facta.
If vre n'cil) the atiitfaifnta inadt.' on p, 211, we see that it is the
ncv of the /rrf rnntfif that deUirmines a chfuircal teaction. The
aeca of the" heiits of formation, however, are a meuisurf not of the
oi the /rft but of the fftdl energy. For this reason, direct
ioiiB caiinot he drawn from the one set uf figures with ivgard to
ker set.

So far, howevflr, as determinations havo heen possible, the differ-

hetweon the free an<l the total energy art', in general, not greut.

(T eonclnde, therefore, with a certjiin degree of (jrobability, that

ises where the diff'Tenees of t!ie total energy are large, the

ing diflerent-es of the fri'e energj- will havf, if not the same

leiiat the same sign. With this reservation, it will certainly

tUe to draw conclusions as to the direction of the reaction from

of the heat of the reaction, In all cases, however, in which

of reaction is small, the conclusion becomes doubtful.

Ch»c i'*se in which a reaction takes phict' spontaneously with

joo of heat, can l»e at once (lisruased on the basis of the table

SS."?. On :uJ(}i!iL; :i solution of hyilrochloiic acid tu a solution of

fluoride an absorption of lieat of 10 ij occurs. Tins is due to

tiial in this case the ions of hydrofluorit acid, fluoridion, and

eoni« together. HydroHnoric acid, now, ia slij^htly diKsoeiiited

; il« ions, therefore, must combine whtmever they come

This comliination, however, is accompanied by an tibsrn-p-

heat, for the ilnMH-utlitm of hydrofluoric acid into its ions,

luive juat seen, flft-rhps heat. Since the other ions, viz.

ipci and sodiou, remain unchanged in the experiment, no otht^r

<if a heat efTect exist, and the reaction takes place, as observation

'», with absorption of heat.

Sincf- in tbi* reaction undissociated hydrochloric acid is chiefly

<-ns was formerly interpreted na if the "weaker hydro-

jilacwJ from iu compound with sodium by the stronger

le ac]d." A3 the above consideration shows, the impelling

lies not »o umch in the liydrochloric acid as in the hydroHuoric

the alight dissociation of which conditions the reaction. This

it i» true, take pLice only in the presence of a " strong " acid, for

I an acid is one that is to a large extent dissociated into its ions,

\y fiieb an one, therefore, can yield the reqiii.site amount of

I'KINCIPLES OF INORGANIC CHEMISTRY

235. Actual and Potential Ions. — since hydrion has jutt

bCMMi d««i{^t«*) n:» till; siibsUnue wtiicb manife8t<<i the typical viii
reiiotlon», mid it lias further been shown that in solutions of scetic
Hoid iif nuNlurHt« coiiceDtration only I to ^ per cent of th« hFclrogn <
i* iirtMii'Tit ill thfl itmie lorm. one might suppose that on titrntiii'
Miili c!vu»iif ttinlii iht" Ttnl colour of the litmu!? would disappear after
this hyUiiim lijwl betni convei-ied to water l>y the additiou of a feir
|HH' (H'lii (if t\\v iH|iiivalpnJ of alkiiH. This j^ uoi the case. On ihe
ciiiuinn, «t' havt' soen ibat the difltfrent adds rc»4iiir6 exactly u
much tUk;di ua v»nx«ii>mtU to their equivalent (|i. 189). Fol- tht

iutMH'w (J iioutrAhxatJiHi, thi-refnre, it is a question not merely of lie
ijkili'iuii I'ul of 'lit ihc jnul hyilnigeii. whether it is present as ion «r
liut

Thin it(i|Mit<til r»*niiadii'iioii is reniu\etl when we consider more
Wt^^iilly wimt \» thi» nmrst' of tlie process of neutralisation, tin
uildtium ol cMUHtio swdit, the ioiia H' and OH' in the first plime act
^tii AunlWr tiiiil ftM'iii water. Their exists, however, a chemical
iH|uUtl)ttuiii which ()e]iends on the proportions of the participating
•ulwlmiiH'*, KutwiHvu llifl jwrtion of (he iicid which Iwis p,'issed into ions
Hud Hu» MU<l(*HiH'iHt*H{ {Ktrtioii. If one of tlic auLsfciinces is rcmovptl.
Ihul it>Metitm iutt.it iniiiuHliittely take plficc by v\hich it it; n^.!'
ivplui'inl III |«x»jH»rtit>n, therttfore, as the liydrion is removptl ■
etMiiltliiiilU'ii with the hydiM.xvdiwi, -^ fi'fi^ amutint miwt be prodiaed
li,v \\w dii«<nH'»Htii"i '•* ''■•• *tili utj<lisS4}ciated portion, Tliis hen
ItiiiiinlivMt i^u ti»k<» t ui; as there is undissociated acid present,

hut wlu'U this k« u*i'vl lip the hydroxion will no longer }n'. Iwund,
mid tlu' lilue etvltiMr of linntfi must appe-ar.

Nt'W, nil pi II kms proceed, as experience ahowa, w

qiHcKly llint It > nex'er licen possible to measure their

vi)h>i,<ltv. Ill thtv CH««t t^ mir i«.\]Miriniont, therefuro, we see oidy tk
tlhid vt^ull, mud on tilr»ti«ui witli cHiistie eoiUi we do not obtain l\\t
iituimiit ot h\diiou ;i»r«rti/ lU thf furhfuitir moment, but the aiuotmt
lit ()// \\w hydruui thtii t\»jt U* foriutH.1 from the substances pre^nt;
Uol tlit> it/utt' iiiiiouni vif tlu' iousi, fiut tiii' jxitatliiil.

TIk* wuh(> huldit for (he a^-tion of the nu'tJvts, r.tf. zinc, on the siciJs.
wlit'io tho tuhd (iiiiouiit of the possible hydrion is ultimately evoHd
lu liydro^ui pw, Iti this ease, howevw, the velocity is lueJisnray*.
atid il in foinul to W all the jfrwater, the ^treater the conceiilnition d
th»* hydrion (u-tually pn'«t>nt. The sinne i« found in sdl processe*
» liii'h di'pond oil thv hydrion and whioh proceed with measurable
veliH'ily

T[u< qumiion ait lo the conditions under which only the actual
and under which the [Hitciitial ions !in> to W considered, cau U
auHWei-ed to the ^tlect that the former are all-important when lb
jimnunt itt tlie ion* prcnent ia unaltered, or is altered only in aa
iiiuornparably slight dcxit'c, by tlio process If, however, the pntcea

SULPHUR AND ITS COMPOUNDS

257

lime, the surface cnist of aolirl siilpliur be broken .iml
1- jturtiuu |xjiircd out, the crystals which have been formed
" ' a large number of them will be foiuid on breaking
(Knr.

a ahorl tinic after they have been forme*^!, those piyatals are
ber-yelliiw colour aiul can be bent slightly mthoiit broakiiig.
oiTiiig day, the aijpeariuiee of the crystsds has con3iderHl>ly
ly have assumed the lemon-yellow colour of the ordinary
juid have hecomu brittle.
CTystallisation from Solution. — If, on the other hand,
be di&Bulvod in a suitable sulvent, the best being carlton
do (p. 233), and the lit)uid be allowed to evaporate, crystJilIIne
»lso separates out. This, however, has the octahedral foiuis
rni aul|jhar and utulergoes no change on being kept at room
re.

werer, tiie octahedral sulphur (natural or artificiat) be heated
tures of over 100 , without being melted, it also becomes
knd brittle.
The Regions of Stability. — The above phenomena are due

* thAt to each of the two forms of sulphur there corresponrls
vi temperature in which the one form is stable, but in which

• form is unstable and is converted into the former. The
the uclahedml sulphur extends from low lemjieratttres up to
of the prismatic sulphur fi'om OG' to 120', its melting point-

6 , prlsmiitic sulphiir is unstable and passes into octahedral;
€\ octahedral sulphur is unstable and gtasses into prismatic.

relatioofi ahow a very great similarity to the rtciprocal trans-
ID of ice and water, or, generally, in fusion and solidification.
OMee so also lu the present, there is a temperature above
the one fonn, and below which only the other form, is staWe.
tills point, therefore, the one form passes into the other,
y ai thi^ one temiteratiirc can the two forms exist together.
Influence of Pressure on the Point of Transition. —

that we are dealing here with a airigle aubatance we shall

irdance with the pluise law (p. 173), that there will be

t6iaper»ture and one delinito pressure at which three phases

le by side. At 96 , these phases are oclJihedral sulphur,

ihur, and sulplmr vapour. If we exclude the vapour, the

vhich dbteniunes a definite, very small pressnre, the tern-

etjuilibrinm of liie two forms of sulphur ntries with the

The temperature of transition, indeed, ia raised by pressure,

prismatic sulphur oucupies a larger volume than the

However, as in the case of ice and water (]>. 132), a very

t« here necessary in onler to effect a slight shifting of

<ii equiUbriuni. For the rest, the two forms of aul\jhmr

hpeodent subatances. Sot ouW the cryataUvtie Corms,

the

253

FRIXCIPLES OF INORGANIC CHEMISTRY chat

bat also the Seusity, the power of refracting light, the melting |X)int
and alt other jtroperties, are diflerent. Tlie cleirBity of prisnwHc siiljihiir
is l*9fi, thill of octahednil, "i'O".

The prismatic ciystiils obtained from the fused sulphur, and vhxck
have become opuque, have the density 2*07, the density of the
octahedral form. This ia the simplest proof ibiU they have reiU)
become converted into octahedral sulphur. A\"e have the reverse
phenomenon in the case of the octahedral sulphur tmnsformcd bv-
heating.

240. Suspended Transformation. — Just as water tnu he eoold
beloiF 0 withutit suHilifying to ieo, the temperature of traiisformntiou
of the two forms of sulphur can Iw over.^tep()ed from bi.ith sides. If
octahedral sulphur Ije rapidly heated, it melts iit 115 , which is its trut
melting point It', however, it bo slowly heated, so that it has time to
undergo transformation, fusion is observed at 12IJ , the melting point
of prismatie sulphur.

247. Enantiotropy and Monotropy. — A compariBon of th*

behaviour nf the tvi^o forms of sulphur here desciil.ted mth thtj two
chlorides of iodine (|), 24U), reveals an easenti.'tl difTcrence. 'WlioreM
ill the casiG of the cUlorides of iodine, only the one fann is stable mi
tbe other is unstable, in the c:a8e of sulphur, both forTn:^ are atabk
each one being stable in its own range of temperature and unstable in
the range of temijerature of the other.

The difference lies in the fact that in the case of Bulpbur, tbe mell-
ing point of the more readily fusible fojra is abo\e the teniperat«i*e of
ttansitioii at which the stability of the two forms changes, whereas in
the case of the chloridejj of iodine, the leas stjible form melts befon
the temperature of transition ia rcacherl.

Substances like iodine monochloriflc, which can undergo transforffl-
ation only in one direction, are cuUi'd mfniohnpic, and those which, like
sulphur, can change m both directions, (•ncatiiulrttjnc.

248. Other Forms of Sulphur. — Other crystalline forras ot
aulphur, differing from the two already deacril>ed in form and ia
other properties, can be obtained by strongly heating small qtiantitiet
of aulphur and allowing it to cool rapidly. They are, however, Jl
imduhk with reference to the octahedral and prismatic sulphur, and,
according to the temperature, pas.s into the one or other of these. In
respect of these forma, therefore, sulphur is imnwhvpk.

We need not hero describe these forms in greater detail, as they
are only of rare occurrence.

Snfphiu* has also been known for a long time in the fonn oifiwat
uf suljihur and milk uf /:iilp/nn: These two kinds of sulphur are not
special foi-ma in the scientific sense, but represent only peculiar stalM
of division of sulphur and consist chieHy of octahedral sidphur, at leart
idxtr lieing kept some time.

Flowers of sulphur ia produeed in the distillation bo which eulpbur

SULPHUR AND ITS COMPOUNDS

T- ■ he purjKiM' of purification (p. 263). So lung as the

1 1 !'>er is cold, the vnjmiirs on fiiliiiig down solidify in

an crystals, *nd sfjlphiit' h »l>lained iti the furni of h yellow jiuwder
liich has bern known from the time of tlie akliemist^ a^ Howcrs of
ur. Tilts powder almost always coiitaiua, however, amaU quanti-
unorpbous sulphur.

Ui« name miik of sulpknr there is denoted a very finely divided

trf sniphiir which is precipitated from ai[iicoua aolutiona in

main rMctiono, These processes will Ije deacribed later. In this

•alpbur is obtained in such a fine powder that its yellow colour

almost iiitisiblo, and it emits almost eutirely white eiu'fiice

(p. 13). On account of it^ liner atiite of division and corre-

ly l*i"ge Burfjice, thia form of sulphur more readily utidergoes

change ; on tliis fact depends tiio application of milk of

in medicine. Milk of sulphur does not rliffer chemically from

sulphur.

249, Liquid Sulphur. — As already mentioned, prigmutic sulpliur

at 120 ; It tht-'reliy changes into a light yellow, mobile liijiiid

on cooling, solidiHes at once to prieimatic sulphur. In small

however, and by excluding particles of solid sulphur, liquid

or can be strongly supercooled. It then e,\hibits properties quite

to thoec of supercooled water.
If the melted sulphur be further heated, it exhibits very remark-
|U» phenomena. Whereas, in geneml with rise of tempeititure, the
ittvna) friction of liquid* decreases, we find the opposite behavioiu"
h Um c»ae of liquid suljihur. The higher the temperatnie rises,
\%t more viscid duea it become. At the same time it becomes
Auka ill colour, and at 250 it passes int-o a ilark red niase, which
HI to viitcoiis that the vessel may be turned upside down without
{It numifig out. On further heating, the ma»s aj^ain l^ecomes more
Ufiid, without, however, losing its dark colour. At 450' the
Im^qr is again ipiite liipiid and boils, passing into a red-broivn

I The beatcil sulphur, on bfiiig allowed to cool, again passes through
UlthAK conditions ii> the revenue ordor ; it fic^t becomes viscid, then
wpai tgaiu and light in colour, and soliditiofi, finally, in prismatic
ettAali.

Amorphous Sulphur. — Strongly heated sulphur behaves
pu- tiilferently on being rapidly cooled, as r.i/. by pouring it into
wstcr. It then assumes a viscid character like that of elastic
i»»-nibl»er, and is called luintrph'M.t sulphiu'.

designation ik'nott'S that the sulphur in this form is not
le, although it e.thibits, to a certain extent, the prnjMnrties of
body. On the other liand, it can be regarded as a liquid with
ptat internal fric«-ion. Thia view is aupjxjrted by the fact thai &tni^'C-
|inat, «olid tnhstances, on heating, exhibh a, irjittinuifus trivuBiUoiv \n\io

260

PRINCIPLES OF INORGANIC CHEMISTRY

the liquid state ; no definite melting point can be obsened, but
internal friction continuouslj- decreases. All the other properties ;
change coutinnouslj', until a state with the characteristic properties (
a liquid is produced.

The amorphouB, viscid eiilphur does not remain in this eondjtj
at ordinary temperatures. After some days, sometimes also only i
a fairly loTig time, it changes into an opiique, brittle mass which,
its density, proves to be octahedral sulphur.

We must conclude from this that at ordinary temperatxiree,
amorphous sulphur is a k%t sltihle form than the octahedral. Aei
matter of fact, the latter is the only form of sulphur which is stable (
room temperature ; all the other forms, of which there are sevj
besides those already mentioned, pass in course of time into uctabe
aidphur. This is, accordingly, the only form which is found in natil

The fact that the rapidly cooled sulphur does not immediately]
into that form which h stable at the cxistiuL; temperature, but thtti
first asaimies a less sudjle form, is a special case of the general lawt'
when changes of state, take place those forms are usually prodn
which are the least stixble of the forms possible under the existing (
ditions {p. 210). The forma first produced afterwards change into!
more stable ones, when this becomes possible. The velocity of
triiiisformatiou varies g^r'catly, and the transformation may take ph
in tlie fmction, of a second or may last for yeai*s or centuries.
changes in the properttcs of litjuid sulphur with the temperature ^
have been described, lead to the conclusion that sulphur, in the liqd|
as in the solid state, can assume dift'erent allotropic forms. It
hitherto not been ixissiblc to prepare these forms in the pure state i
to characterise them.

* if}]. Experiments. — On account of the variety of its for
suljihur is apeciidly wiA] adapted for a study of the reciprocal relationi
aud conditions of stability of ditt'erent forms of the same subst
These relations can be observed in a very iiiBtructive mamior
introducing a small piece of sulphur into a tube alxjut 2 cm. irh
exhausting the tube, and sealing it ofT.

On slightly heating the spot where the sulphur is sittiated, the :
gives ort' vajTOiu*, and or> tlie colder jiarts of the tube drops (not cryt
of sulphur are deposited, although the temperature is there much heltfi
the point of solidification of sulphur. The less stable, liquid fo
therefore, is first produced.

If the lube be allowed to remain in this state for some hours and I
deposit of drops Iw examined with a lens, the following apjiearance i
found. Many of the drops still remain liquid, .is can be seen from thtj
transparency ; nlhers have solidified to crystids, Whore a crystal ha
formed, it is quickly encircled liy a clear ring, the surrounding droj
disafipearing. This is due to the fact that the vapour pressure of
£rffstallisai sij/phiir is smaller than that ot the itquW at the same

•81JLPHUK AND ITS COMPOUNDS

161

kture. For the crystalline form is the more stable of the two, and
t, in accordance with the considerations put forward on p. 135, also
s the sjDAHor vapour jitessure, Snlpbur distils, therefore, from the
>s to the crystalis, antl the foriut?r tiisappear f roni the neigbbourhood.
Occasionally, also, othor regions are seen in the tube where no
ital has formed, but where, nevertheless, the forniatiou of a "halo"
mm\. On closer examination of such a spot, it is seen that the
-re of the clear space is occupied by a drop which is largrr than those
minding it. In ficconlance with the reasoning just applied, we
t conchide that larger diops of aiilpLur have a smaller vapour
{■ure than aniall oiicb. This also is the caMe, and follows from
iCtly similar considerations.

Thus, on bringing two drops into contact, they imit* with a cer-

force and form a single drop. This union lakes place in

tequence of the surface tension of the liquids, by virtue of which

}uid tends to assume that shape which has the smallest possible

surfsMje. In the case of largo masses of liquid, the surface tension
anftll compared with the influence of gravity ; in the case of
11 quantities of liquid, however, it is the determining factor and is
cause of the spheiical shaj)t of the drops,

Now, the surface of the sphere formed by the fusion of two drops
smaller thati the sum of the two spherical surfaces before the
m. Since the surface tension tends to diminish the surface, there
ts also tho tendency to form a large drop from several tsmall ones,
3 tendency exerts itself in all ways in which the object can be
ined. Since it can also lie attained by distillation, the cause of

distillation, viz. the dilTerence of the vapour pressure, must be

I that this tendency ia given eH'cct to. The vapour pressure of

II drops, therefore, must be greater than that of lai^e drops, as
sriment also shows.

If the tube with the deposits of liquid and solid sulphur at various
'A be allowed to remain undistiu-bcJ for a fairly long time, the
»it« all disappear, and there is only the large piece of sulphur
L in the tube, which has now become clear. All the sulphur has,
■cfore, distilled over to the large piece. The cause is the Srtme as
ire ; for solid substances also have a surface tension, and, therefore,
e exists tho tendency to make the surface as small as possible or
pieces as large i*a jjossible.

For the itilabiVdii, oxaetly the same considerations hold as for the
jni* pressure. If a glass plate, sitch as is used as an object
microscopic purposes, be held over heated sulphur until a de|
been formed on it, and if a drop of water (or of
d e\*aporation ) be placed on this and the whole
sr-glasR, exactly the sjime phenomena of "halo"
consiuuption of the less stJible forms by tho miX
srved. This experiment serves at tho same time tc

262

PRINCIPLES OF INORGANIC CHEMISTFtY rm

the .'^i)liil»iUty of sulplmi- in tliese liquids, a solubility that is
small that it has not been ]}ossil>le in any other way to meaisurc it.

Applying these considerations to the conditions of transformatio
ni the octahedral an<l piismalic sulphur, wcs can draw the followid
conclusions. The solubility of the former in any solvent mtist, l»oI<l
96 \ bo smaller, and, above 96 , be greater, than that of the prismali
Consequently, the solubility at 96', the point of transition, must be T
same for both furma. All this has been confirmed by experiment.

Since the considerations on which the concltisions t
are general, the law can be cntuiciated for all allotropic forms
the less stable forms must be more soluble than the more stable,
that at the point of transition the solubility of the two must be
Useful application of this law can be made in caeca where the
formations are difficult to observe for the purpose of distinguishing I
stal')le from tlio tmst:il>le forms,

252. Sulphur Vapour. — A similar variety of conditions is eha
by sulphur in the vaporous, as in the solid and Hi:]uid form. At temi
atures in the neighbourhood of the boiling point, the molar weight (|
sulphur vapour is 220 ; the higher the temperature ia t^iecd,
smaller does the molar weight become, luuil at 1000 it has falleitl
64, and at still higher temperatures it retnins this value,
numbers are for atmospheric pressure. If the vapour of siilpbnrl
investigated under smaller pressures, it is found that at a given
jjerature the motar weight is all the smaller the lower the pr
This variability also ceases when the molar weight reaches the
G4. Sidphur v.T.{)our, therefore, follows neither the law of Boyle
that of Gay Luaaac, and only when the moJar weight has
equal to 64 does it behave in accordance ^rith these laws.

A similar behaviour haa already been met with in the caaft '
iodine (p. 234), and the same interpretation of the phenomena can1
applioil in this case, i.f. the vapour of sulphur exists in several fo
with different molecular weights. Since the combining weight
sulphur is 32, the forinuta S., must l« ascribe<l to the vapcmr wli
is stable at the hii;h temperatm-e and low pressure. With rcj
the more dense form, the present case is more difficult than th
iodine, tn bo far as no region is known in which the density is
stant. Even at the boiling point of sulphur wc are in the regie
variable vapour density. f?ince the highest observed value of
density amounts to 230, we can only conclude that the deul
vapour contains more than six combining weights, or that iin
formula S„, n is at least greater than 6.

From determinations of the molar weijijht of f/wso/rcc? sulphur :
different solvents (cf, p. ir>8), the formula S, has lieen found for
It can therefore be assumed with some degree c»f probability that
denser aulphnr vapour also has the formula S^, and that the vapour
variahle density eonaists of a mixUira ni S , Awd "Ay Xaverthelesa, ;

SULPHUR AND ITS COMPOUNDS

263

^ probahle tlmt other kinds of sulphur vapour S,,, where n is a whole
lumber between 8 and 2, moro particularly S,^ are also present.

bVVith reference to the law set forth on p. l!34, it follows as a
cessity tluit on diminishing the pressure the less dense form of the
pour S^ should be formed at the expense of t!io more dense S^^.
Dm the fact also that thia tivinsfonniition is broiight about by eleva-
[)ii of temperatui-o, it citii lie concludeti thut the transformation from
I to H.J tiikes plni-fl with absorption of heat.

J53. Purification of Sulphur. — Use is made of the changes of
He which sulphur undergoes, for the purpose of purifying it. As found
In nature, it is usually mixed with other intnerala, clay, fktid sand. Iti
pieUy, the sulphur ore is piled up in a heap furnislied with air chan-
pels, like the wood pile for the burning of cliarcoal, and is set fire to.
The heat produced causes tlie sulplmr to ujeU, and this flows away In
(fairly pure condition, leaving the dirticultly fusible impuritiea behind.
By this methofi a loss of sulphur is incurred oiving to the combustion
>f a portion of it, hut this is by far the cheapest means of generating
^e beat necessary for the melting of the sulphtir.

To completely free the alr&idy fairly pure sulphur so obtained
ivm all rion-voliitile impurities, it is tli^itiUrd from iron retorts, and the
rapours are lerl into large chambers of mason work. At the com-
uencetnent of the distillation these chjimbei's are cold, and the sulphur
rapours condense to a tine powder of sulphur particles. These are, at
irst, amorphous (cf, p. 259), btit soon pass for the greater part into
he erj'stalline condition. The powder ta in ]>art collected and is
tlaced on the market under the name of fiowers of sulphur (p. 258).
)n continuing the distiil,'*tion the temperature of the chamljer rises
ibov'o 120 , and the sulphur then collects in it in the tiquii! atiite.

The liquid sulphur can he run oli' through an opening at the bottom
if the chamber. It is collected in wooden moulds, in which it solidifies
n rods of a slightly conical shape known as i'»lf xulphur.

* B. Crystals

254. General. — The two known forma of solid sulphur differ not
»nly in density and other properties, but also very materially in the
onn of their crystals, and the general ijuestion arises, therefore, as to
he laws of crystalline form. All the more importance attach e-s to this
[Xiestion from th« fact that the cryatilline form is a proitjerty of almost
11 solid substances, and constitutes a very important means of describ-
(ig and identifying these.

In the Bret place we draw the distinction between the two conili*
ions of solid sulMtances, the amttri>hoits or formless, and the CfiKfalNii''
r formed. Since, however, the outward shape can be charim.,i 9,1 wi^
ontie other more general chai-acteristic must be sought fov V. «!«&
£ which the two conditions can be distinguished. j

264

PRINCIPLES OF INORGANIC CHE4USTRY

Tke essential nature of crystalline bodies is found in the fact
their projwi'ties vary in a manner depending on the ditfduitt m
For example^ a liidl of glass and one of octahedral snlphiir, on
warmed, will bchavo differently. AVhereaa the gbiss bidl rei
sjihefi\ otily increasing somewhat in size, the ball of giilphur
}mng warmed, into an dNpsnidt the axes of which have a simpW
tion to the shape of the crystal from which the ball was cut.

Another example is furnished by the conduction of heat
glass plate be cyvt-red with a layer of wax am) the point of a
inet^l cone be placed on this, liie wax is melted in the form of]
circle, because the heat is distributed ecjUally quickly in alt dire
If the same experiment be carried out with plates eut from crv
the melting takes place not in circles but in pflipsKg whose axes 1
difl'orent relative lengths accowling to the position of tho plate in I

Kl(J. SO.

original crystal, and likewise atind in a definite relatiou to the sh
af the crystal.

255, The Crystalline Forms, — By the name criA</i(f, one
lecustomed to think, in the first iristjince, of the regular furms whi^
substances assume on passing into the solid state.-Hiid wliich
often be observed in such cxijuisite beauty in the ease of nat
fornted solid bodies. The examples discussed teach that those fo
are merely a definite expression of a much more comprchenihl
regularity. The forms are only an expression of the general fact
in crystals all proporlios which can be brought into relation with I
direction in spate undergo regular variation with this direction,
the properties which concern us here, the most important is cer
the external shaj)e, sineo it is, on the one hand, the one which
forces itself on the observation, and, on the other hand, exhibits tb
most tnaoifolJ varitfty to be met with in the ease of crystals,

CrystallihG forms have the general property that they are l>o«
only by plane surfaces. If one examine, however, a group of
taneoiisly formed crystal.'! of the aanie subatance, f.tj. a vhisk _
quartz crystals, it is soon seen that the appearance of the irulividtl
crystals is very vaiied, the outlines of the bounding planes being quili
difTerent. AJl the same, these various crystals (Fig. ftO) preservB
cenain /'eJat/onship of form, wl\\c\i at oiwe iotces Itauir on ono'« aode

SULPHUR AND ITS COMPOUNDS

ser investigation shows that although the outline and th$ size
which bound the crystals change, it is always iwsaible to
ee the different crystals that ki f wry /inY of ihr. oitf there sinmis
fact of Dm otlver jinrallel ti> it. From this it follows that tho an<jles

tFhich the various corresponding faces of two crystals nieet, nif
Wy* iiiJt ^uftie:. 0*ing to one or other of the faces being formed
itively near or relatively far from the middle point of the crystal,
I faces cut one another diflerently, but the angles between them
3Ain the same.

Furtlier, a cursory examination showa that the crystals are
ime/rtoil structures. By this there is understood that different faces
or in a crystal, which are similar to one another and are repeated
I regular manner. Thus, for example, the sno\v cryaUils figured on p.
} have the property that each may fw regarded as consisting of three
iSIar parts ;iii aimed round the ci'ntre at angular distances of 120^

256. The Symmetry of Orystfl'!*— -"^'I ^^^ regularities exhibited
ciystaU can be dediiccil on the baais of the conception of symmetry.

Three kinds of symmetry are to be distinguished. The first h
it which c.vists between an object and its mitTor-jmage ; the plane of
I mirror is cjdled the j/tunt of sifmiiiffiy of the structui-o.

A second kind of symmetry arises by rotating an object round a
tnite axis through an angle eijual to a simple fraction of the total
ation, and repeating the robitioji until the object again roachea its
ginal position. According as this angle is A, Jrd, ]th, or Jth of

total rotation, we speak of a liinary, ternary, quaternary, or senary
B of symtnctry. (Other grades, such as quinquenary, septenary, or
her, arc not possible in crystals.)

The third kind of Bymnictry ariacG from a combination of the
t just deacribetij by roluiioit nntl re/lection. If the object is brought
5 jt« next position by a rotation followed by a reHection, so
t by repeating this process a number of times it again comes into

original poeition, such a structure possesaea the third kind of
Mietry. For our studies, it is essentiidly the first two kinds of
imetry, reflection and rotation, that are of account.

By using tlie three kinds of symmetry, or two or one of them,
I by tonihiiiing them in every possible way, thirty-two different
SB are obtained.

AU the crystals which occur correspond to one of these cases,
that fiy the application of the principle of symmetry a complete
tern of all jKisaible crystalline forms is obtained.

257. The Seven Systems of Cry atals.— Into all theso cases-
rever, we cannot enter. Hut rau-st content ourselves with the ct
>riautiou of seven of the larger groups.'

Owing to ttie nocesaity f -^
kdkftteil ; ttiey cAnnot hr.

266

PRINCIPLES OF INORGANIC CHEMISTRY

CHJ

Crystals possessing the least symmetry (no element of symmel
or a binary symmetry of rotation and reflection) are called tritin
The simplest form of this is the oblique angled parallelopiped (Fig.

Crystals with one plane of symmetry are called monodinic.

Via. 81.

Via. S2.

Fio. 83.

simplest form is the parallelopiped with four rectangular and I
oblique angled faces (Fig. 82).

Crystals with two planes of symmetry perpendicular* to one anot

{Cl:?i

Fici. 84.

Fio. Ki>.

Fio. 87.

are called rhombic. Their simplest form is a rectangular {xirallelopipt
(Fig. 83).

Crystals with a quaternary axis of symmetry are called .quad^

' Wlicn two planes of .sytnnictry are not at right angles to one another, a thirf '
of symmetry i."i required by the reflection of the one in the other, and by th« t*^
of this thinl, a fourth, eto. If, therefore, more than two planes of symroetr* "
in a straight line, are to be excluded, t\iey m\is\.\^ xwtxv*\xdvittVat to ona •»

26;

impleat form ia a rectangular i>ara,lle]opit>ed witli quailnitic baae

wiUi a te-mury axis of symmetry are called tntfunal. The
form ia a tbre»f-si«Jerl v'v^hi prifun {Y\^. 85).

with a senary axis of totution uro ealkfl hexagmiaL The
form is the aix-sidcil right prism (Fig. f?G).
stals with three Innary axes of symDietry perpcndicuLir to one
nntl also nfnimlrtil are called ra/ular. By eijiiiviilent ia mwiiiL
be eryetal always presents the same shape wh^n it is turned so
Ut« »xea of symmetry assume positions previously occupied by
■ f «jttifrtetry. The simplest form of the regnlivr trystaU is
-'. >^''}-
►6. SeriYed Forms. — Besides? tliu simplest forms just mentioned,
|«rG mariy otiiprs rlerivable from thoai geometrically, which obey
of symmetry valid for the particidar kind of eiyatul.
prBsibiliiies which arise -ire, however, so numerous that
in«il be treated here. We shall, however, state a law which
Lb«ir njutiia! contieclioti clear.

iti6 a large number of small crystals of one of the simplest
I neotioaed above, and all of the same size, to bo given. By
Bg tb«se in a regular
othrr forms can be
op. From a nnm1i«r of
cubes, for example, the
•hown in Fig. 88, which
as an octithedrou,
built up. It is oidy
y to imagine new planes
broti^ii the comets of the
toudiiog these corners,
It amounts to the .^anie
one imagines the cubes tu
ill that the unevcnness
[ hy x!b« re-entrant corners
kmger be noticed.
It« lav in question states
ftxntrririf) in different
a xvlftmici, ran be built vp in iiu VMnne)' dfscrUted from small
"tf Ou ximplrM frtrrti^ the fondUiotis oj ifymmcttj being al Ihr sujint

iw stated here can bo eicprcssed mathematically in various
at we have aaid will be sufficient to show that the cryatal-
of a given substance can be characterised by the statement
jplf^ form.

The Other Properties of Crysta,ls. — As has already Weu
oa p, i'6'4, aII the properties of crystals which can iw ati^

Flu. S!i,

268

PRINCIPLES OF INORGA^'IC CHEMISTRY

kiWay become dependent on the direction in space, have a
pOrientation, The question arises, thei-efore, whether any com
exists between the externa.! shape of the urjstals and the orientatid
the other properties.

T!ie answer is that such a coimection certainly oxists. It ctm^
stated thus : The st/mnu-fii/ m ibr (trrangemnii of (hf other jrrop
(tliai-ita cmlamtd in the ^ynimrtnj rrUttious of Hk rxfmud fffnn.

Let us take, as tin example, a chemical phetioMeuoii which
occxirs in the case of hydrated crystals, viz. rffiorcsctucn. This con
in the water evaporating at ditferent pointa of the crystal, a comp
eoritaining less water, which can he distinguished Irom the main]
tioii by its different colour, remaining behind aa a powder. If '
efflorescence is allowed to tnko place with such precautions as tO I
the foi'tnatiou of detached spotSj it cjvn be esUiltUshed that the
of eiHorescenee assume forms which have the same properttetl
regards symmetiy as the crystal forms, and the position of Avhichi
corresponda to these forms.

If the crystal is mjuUr, the efHorescence figure is alwaj!
sphere, for in regular eryistale there are throe planes of sy
perpendicular to one another and eijuivalent. Of the shapaij
tinned as occurring, the sphere and the ellipsoid, the sphere
only one through which three etjuivalent perpeadi(;ulttr pi
symmetry can be laid.

The crystals of the triijonaJ, <puttlmtic, and hexarjonal syaten
one axis of symmetry in which three, four, or six planes of sya
lie. An ellipsoid which can be divided in this way must bo al
a,dal one, i.e. an ellipsoid produced by the rotation of an ellipse (
one of its axes. This axis of rotation must coincide with the
Bytnmetry of the crystal, since it is only in this way that the ollip
'can be divided by the corresponding planes of symmetry into
three to six identical portions.

It is not possible, however, to distiiiguish tn-, tetiu-, or he
crystals by the difference of the ellipsoids of efflorescence,
nionoaxial ellipsoid may contain any number whatever of pla
symmetry laid through its axis of rotation. It makes no dif
therefore, whether there are three, four, or six.

liesides the monoaxial ellipsoid, there is the triaxial. It is
duced by the rotation of an ellijise about one of its axes, the
axis being lengthened or shortened during the rotation, so
etida (and at tlio same time also all other poiuU of Uie
describe nut circles but eUipHes. Such a form has Witv plarii
symmetiy, which ai'o determined by the axes of the goneiating'eliip
and are pterjiendicular to one another.

The same symmetry relations are also met with iti the case of
rlwvihic crystals, It is to be expected, therefore, that the efflor
forms of the rhombic crystala w\W h^ vc^iveftfcWtfeA % i^v«s.\a.l elll(

317LPHUK AND ITS COI

269

qrmmetry of which coineitlo witli those of the ctystaUiiie

CODclusioti is confirmed in every case hy experience.

le eaae of monoclinic crystsils only r/7tf plaiio of symmetry

FOnly one of the three planes of aytiiniotry nf the ellipsoid,

csaii Iw determined by the crjatjillitie forin, mvi the two

ii)det«rmiiiate, i.e. they lie in a manner whith is dependent

of the eryslAl but not on its form,

K of triciinic cryelnla there is no plane of s^'mmetry.
>id of efflorescence is, therefore, entirely indepemJent of the

Generalisation, — What has just been statetJ for efflorescence,
aiao for nj:uiy othtr properties of crystals, viz., for ai) those
wgenwnt in the crystal cim, in the most general case, be
by a triaxial ellipsoid. Under this definition come the
Q «xf light, of hejit, of electricity, the changes of form by
all sides, Sdd atill other properties. The most important of
the tranamission of light;, for the optical propeittes of crystals
}cct«d to a thorough scientitic investigaiioii, and arc used
ificatioQ of the crj"sialline .system in those eases where the
le gives no information ur no t;Dmplete information. It
generally, that every opiicul phenomenon in a crystal is
the symmetry relations explained above, and that from the
of the nature of the symmetry of any optical phenomenon
b coDcIusioii can Ikj drawn as to the crystalline system,
stated.

C SulphurefUd Htflrogrn

be Compounds of Suphur. — Sulphur is enpsblo of fomiing
with alnjo^t all elements, in some cases in veiy difl'erent
Mc*re especially, all wftals fomi ■with sulphnr com-
Imvu generally a sJuiiSar eouipnsitinn to the coiTe-
lag oxygen cora|K)nnds, and which lurc called sulphides. Many
iwv occur uliiuHhoitly in nature and form sources for obtaining
juid also sulphur.

flulphur forms a number of acids with hydrogen and
chief of these being sulphuric acid. The salts nf thi&
Kt«8, al£o occur widely distributed in nature, and tind a
ktioD it) the art« aiid iti medicine.
ncc oneself of the power of sulphur to enter into com-
oo, the following exiJeriments may bo performed. Heated in
IT .1,1,,!.,,, liurna with a blue flame, forming an oxygen compound
- smell, sulphur dioxide, A mixture of sulphur and
Mioportion of 4 psuts to 7, becomes incandescent
ted, the »n)/»hitr eo/jjbi/ii'ng ivith the iron to lovm
'^ti^-hiiit uiuss of irofi sulp/iidc. If sulphur be heated to \>o\\\ug.

270

PRINCIPLES OF INORGANIC CHEMISTRY

ill a test tube aitii sirips of tliiii copper-foil ho inlnidiiced into ,
vapour, the copper bocoiues iiiaindesccnt and combines witi
Bulphur, also forming a black compound. Metallic mercury comll
with sulphur even at room t-emperatiire. If 1 part of siilphii
rubbed together with 6 parts of mercury iu a mortar, conibiu
tii-kes place irith formation of uicrcuiy sulphide of a deep blaekj
Likewise, silver combines with sulphur even at ordinary tempec
silver coins and other objects of silver rapidly become bla
pocket in which sulphtir matches have lain, the small (juant
sulphur present combining; with the silver.

2G2. Sulphuretted Hydrogen. — Similarly to chlorine, bT
and iodine, sulphtn- can cniubhie ivitb hydrogen to f<»rm an acifl,
is called hydrogen sulphide or sulphuretted hydroguti. At nnlin
temperatures it is gaseous, but can be condensed by pressure and i
to a liquid which boils, under atniospherie pressure, at - 6i .

The molar weight of sulphuretted hydrogen i& Si ; it cout
parts of sulphur to 2 parts of hydrogen, Since the combining
of sulphur is 3'J, the fornuda of sidphnrctted hydrogen 18 H„S. Cn
the halogen hydracids, sulphuretted hydrogen contains hm coml
weights of hydrogen replaceable by metiils, and in consequence >
there is an esacnlial difterence in the combining power of this

■2CS. Bibasic Acids. — If we consider whut compounds
formed when the hydrogen of the sulphuretted hydrogen is
by metals, e.tj. sodium, we find there are two different salts cone
according as only one combining weight or holh combining wei|
hydrogen are replaced by metal. Expressed in fonnulse, we
e.xpect the eompoutuls, NaHS and Na.jS. As a miitter of
compounds are known.

To distinguish it from the acids which contain only one cob
weight of rephiceable hydrogen, which can, therefore, react wit
one combining weight of a base to form a sjilt, and which an
monobasic aciili?, sulphuretted hydrogen is called a dilnLsiel
Generally, a dibjisie acid is one which contains in a mole. It
bJning woighls of replaceable hydrogen.

The salts of dibasic acids in which both hydrogens are
by meUds, are cJilled ncutmi or nwmul salta. Salts which contain i
one combining weight of metal along with one hydrogen, and
therefore, still contain the characterislie conqionent of nclds, hydt
are called acid sjilts.

The former are also called senmduiy and the hitter
Further, they are tlesignutcd by using the Greek numerals
and di-, which refer to the number of combining weights of
(not of hydrogen) present; monosodium sulphide is the salt Kl
disodium sulphide, Na,S. Finally, compounds conL-iining the
IIS are called /ii/ilrnsidpkules ; NaltS is sodium hydrosulphida
these terms are in use aide by side.

SULPHUR AND ITS COMPOUNDS

271

M. The Ions of Dibasic Acids. — Whereas monokisk acids

ttaikUi iiiUi ions iti only oire w.iy, two <lifferetit reactifjiis are

in the case of Ibe dibtisii: iicids, yicliliui; two cliHereut kinds

Tbe dissociation occurs, iti the first place, according to

lOQ

Hy4 = H' + HA'.

A i« the divdlctit atiion of ibe aciil. That is to say, a
il anion HA' is formed alonj; with Lydrion. This process
ids exactly to the oi\linary electrolytic dissociutioji of the
acidft.
' reaction, however, then occurs, via. :■ —

HA'=H' + A",

rxlcnt anion luiflergoing a further dissociation into hydrion
dimlcnt union A." The reaction

U.A = 2H + A ".

might be nj^nlcd &s that directly taking place, can be
of a« the residt of two processeia occurring one after

loeout solutions of such acids, therefore, always contain two
iioRt, aiid the different acida are dietinr^ished by the extent
one or ollser process takes plac^e.

eiatioQ of a dibasic acid into its ions always lw':;ins with

ion. If the acid is not very strong, this proccsa greatly

tto0, and the second stage of the dissociation takes place only

i^^ ' ■'■ .. r. In other words, such acids behave estactly like

ilissociating iitto hydrJon and a monovalent, anion.
the .jUitr hand, if the acid is very strong, the ion HA' furtlier
into If and A", and the solution will principally contain
(•diraleDl iun.

solution of an acid salt of a wfak dibasic acid, having the
Mil A, forms the ions M' and HA', and ;ia the latter possesaea
»wcr of dissociatifin only in a slight degree, only a small part of
HA' di&sociiite fnrther into A" and H'. The acid salt, there-
behaves a|)proxitiiately like a neutral salt and reacts fwbly acid,
or (iti cons6([uence of hydixjlysis, p. 250) alkaline in proportion
the arid decreaaes in strength.
li, bow«ver, we have a i>alt of a strong dibasic acid, the ions
and HA' arc, H is true, first formed, hut the latter undergoes
I'tn into the ions H' and A', The solution of such
the ions A", M*, and H. Hydrion, therefore, is
»t tti toiujuarativel}" large iimoimt, and the solutiuji hehavca
ipnily like the solutiozi of an acid.
An ejuuaple of the Snt case is sS'orded by sulphuretted hydrogiTv,

372 PRINCIPLES OF INORGANIC CHEMISTRY < iM

even the primary salt of vviiich undergoes byrlrolysis nn<t the«
reacta alkaline. Wo shall [jrcsently meet with Jiii example of
eecoml case in sulphtiric acid.

• On dissolving the neiitnil milt MjA, the ions 2M' and A'
directly formed, and in the case of strong acids the matter re^ts
In the case, however, of a dibasic acid in which the second dissocial
is only alight, a revtu-se action appears. Since the ion AH' is
more stabk* than the ioix A', there is a tendency for the former ta|
produced at the expense of the latter. The hydtioii which is pr
in small amount through the dissociation of the water, is draiTTi
to form this ton according to the er|nation A" + H* = HA'. Hyd
ia thereby used up, and the corresponding amount of hydroi
remains over. This is a process very similar to that of the hyt
of the salt of weak munobitsic acids {p. 250), the effect of wi
also that an excess of hydroxidion is finally present. The
therefore, ac*.|uires an alkaline reaction ; it turns red litmus
blue, and phenolplithalein red.

2G5. The Salts of Sulphuretted Hydrogen.— The ab
dift'ereiice can be very clearly observed in the case of aulpbi
hydi*ogen. The "acid" salts, I'.g. NallS, in aqueous solution,
almost neutral to litnuis ; the normal salts, e.g. Nji,^S, however, ,
strongly alkaline. Thia is liue to the fact thtit H8' behaves i
extremely weak acid. In the sohition of the sodium salt Nal
ion present,'' HS', is so slightly diaeociated that the reaction of
hydrion, the reddening of litmus, is not ^isiblo. In the saint
the normal salt, hydrolysis (rkie snpm) occurs to a Laryo
according to the equation

S" + HjO = HS' + OH'.

The hydioxidion formed is the catise of the tiwniiig blue of red !
or, in general, of the alkaline reaction.

* The relations described here are very frequently foundj and i
only with the relative strength of the dibasic acids with rcapwA I
their two hydi-ogen ions. More especially is hydrolysis of the nor
salts of very fi-equcnt occurrence in the case of dibasic acids of madS
strength. Hence arises the contradiction that the snlts, whio
account of both hydrogens present Iwing replaced by metals, are
fifidnd salts, do not react neutral but alkaline. It is preferably
fore, to use the term narmal salts, or one of the other names
o& p. i!TO.

266. Preparation. — Sulphuretted hydrogen is obtained
decomposition of its salts, the metallic sulphides, by slronger
Thus, it can bo obtained from the two sodiulii salts of sulphured
hydrogen tiy means of hydrochloric acid, according to thi^ oquatiuniij

NajS + 2HC1 = 2NaCl + H,S,
NaHS + HCV = 'KQC\ + fi^.

SULPHUR AND 1T« COMPOUNDS

273

>B can be seen from the second eqiiiition, the ticicJ smIi 13 the more
sonomical for tho preparation of sulphuretted hydrogen, since for the

Si amount of salt only half the amount of hydrochloric acid ts
iwd.

On account, however, of its cheapness, vvii sulphide in generally
sed instead of soclium snlphiile for the preparation of sulphuretted
ydrcigen. We have already gnt to know this Biibataiiee as the pro-
Uct of the interaction between sulpliur and iron (p. 26i}) ; it is also
repared on the lar^c scale in a similar mitniier. Under the iiiHuence
f hydrochloric acid the following reaction takes place :■ —

■ FeS + 2HC1 = FeCl., + H,S.

The iron sulphide consiatis of eqiiid combining weights of iron and
ilphlir; the symbol Fe denotes ii*on. On comimring the formula of
lis componnd with that of sulphuretted hydrogen, }i,,S, it is seen
at one combining weight of iron has taken tho plarc of twa com-
ining weights of hydrogen. Sia-h metals are called dimlrvt, whereas
letaJs which, tike sodium, cnn replace oirly one
irubining weight of hydrogen, are called mont^mUvt.
rivalent and pol}'v:ilent metals are also known.

Sulphuretted hydr'ogen is f)repared ar>d used
I large quantities in the laborattirj' on account of
i action on metallic salts, which ivill be presently
icntioned. For its pre]>;irHtion on a comjmra-
vely amall scale, the appir'uLua descnbed on p. 87
m be used, iron sidphide, ni targe pieces, being
ktfoduced into the lower part and decomjxised
ith hydi-ochloric or sulphuric acid. Where,
owever, larger (piantitJes of suljihuretted hydro-
BQ are regularly required, the apjMiratus shown in
ig 8ff will lie found serviceable.

This consists of three bottles with tubiUures at
i« bottom, placed one almve the other. From the
>p bottle a tube passes to the bottom of the
liddle one, and from the neck of this a tube,
Trying a pineh-uock, pisses to the lowest bottle,
liich is filled with iifln sulphide. The sul-
Duretied hyilrogen is led away through a short
"be, also fitted with a cock, which passes
iroii^h the doubly-bi>reri coik of the lowest lioitle.

If the top Iwttle be filled with dilute hydrochloric acid and
fo cocks opened, the acid tivsi Hows into the niiihlie bottle, and f'
is it passes in drops, by siiilahlc regidation of the cock, to tb""
Jphide in the lowest bottle. The sulphTrieited hydrogen it
ojved, and can be leil »if tbrtiugb the second tube lo be i

27*j

PRINCIPLES OK INORGANIC CHE

ably small, vapour- piessiiri', so that the law of d
regarded us valitl for all sulistatues. This is alsu '
to be the case (p. i'^'.i).

The ftssumption, boivever, must remain fulfill
which is distributed uiiderj^oes uo chemical chr
vents. In such a case tho law of distribution lU'
but the law of Henry also loses its vahdity (p,
closQ connection tietwcen tlie two laws is seen.

270 The Strengrth of Sulphuretted Hy
hydrogen is not a strong ticid. It ciin Iw i
fH[ueous solution by boiling or by means of i^
which cannot be done in the case of the soltui
acids, such as hydrochlonc acid. Its salts, aj
by other aeitlK, us is evident from tho descrij

The detei'miiiiition of the eleciriral coti
tiotia of sulphnrptted hydroijen yields ver .
it may be concluded thai only quite a snial'
(lassed into ions, the greater portion -bci
sulphuretted hydrogen. Wbeti, therefori
come together in solution, they at one-
of quite a small residue, to form undissu-
and if the concentration of this is gr«
solubility under atmosjjhcric pressure, t|.
of bubblca.

As a matter of faeti in the evolc
sulphide in solution and hydrodilorie ■•
be assumed : —

Na'^" + 2H'Cr - -J

or, since on both sides the sodion am

S" ^ L'H-

271, Theory of the E volutin
from Iron Sulphide. — How ar-

tlie gas from hydrofbloric acid arn
generally regarded as iu.stiliiblf. t "I
is li'tt insoluble, although it is
solubility, however, is sutKciont I
thp solution along with difcrrion.

takes place, more iron sulpl
repeated so long as iron buIj,.
Only when the concentration •
and that of the difeirioit ■,
eitablished, and tho evolutioti

1 II tha «
th)- sulphm

ualido, caiiBt

rifttf

A Hydrogren by Heat.

''•. Oil Ijeinf; hesited

lUr sind b>'(lroJ!;en.

ixl under the amne

•nling with a chcmi-

dttygeu. — Siilphunuted

' Milphur flumo. If the

HO walls of the cylinder

hnr. This is due to the

vdiogen unites rnuuh more

iJous. Therefore, if there

L-ylinder. oidy tlie hydrogen

.• ihie cixfic fdso, the Bu]i>lmr !»

!iiic division

Hydrogen, — That sulphuretted

valent by the exj>erimeiJt just

•iti be proved by converting this

ib, <?,</. mercury oxide, is heated in
"tgen. The following reaction then

fI^ + H..{).

• I nod "Water aru formed- The latter
•old receiver and identified hy its pro-

'tlphuretted hydrogen can be sat free by
V dinded copper is heated in a current
r following reaction takes place :

■ Cu = CiiS + U...

I hydrogen are produced.
■ uposifig anl]ihtirerted hydrogen with formu-
Widongs idso to the noble metals, especially to
K<ir this reason, silver objects become black in
H'.,ining sulphuretted hydrogen. To t
i.i nitig of eilver spoons which come in
( I I'gg-dishes,
hides. When a solution of .sotlium
1 >-idphur, the latter dissolves and the 1"
"ir. By evaponitioM of the snlutic
^j to Na^S, can be obtained in the cryst

278

PRINCIPLES OF INORGANIC CHEMISTRY

vrhvn difcrrion and liisiilphidion cumi" U>}^Hh^,r in sohition, that
(round being fot-nied according to the ('<|U.itiiJti

F<?" + S" = FeS.

This occurs, for example, when a sohitinn of anflium siilphitlc is
vnih one of ferrous chloride

Nii;S" + Ft!" Cr^ = FcS ^ 2Na"Cr.

l<'ui- this rt'asoji fi biivck pivcipitatc of iron sidjiludo is obtainod
thusc condiiion«.

Those diffirttUli/ s<iJ tilth mfUfUii' sulphides which nrr iwf jirecipUnlfd
acid ,^oliifioi> hj sHljiliurrf/rd hi/diog(^n, enu he jn-rri^nUikd fvnw a
mlufifni. hij sodium .mlpliide, (if siiiiihir midili/ mluhle stiiphides,
hehaviour is also made usl^ of in analytical chemistry.

273. Sulphuretted Hydroifen as a Reducing Agent-
exposed to the air, ;i solution of iupn'ous sulplmrelU'd hydrujjen
Itecoiufs tiicljid and depusits sv whitf precipitate. The ]ii|uid wli
remains is pure water. The procoss consists in the oxidation of
sulphuretted hydrogen by the oxygen of the air —

2H,S + 03 = 2HjO + 2S.

The ftulphur soptirates out in a state of very fine division, and
therefore, the white colour of milk of sulphur (p. 259).

Hy reason of this power of combining with oxygen, siilphuret
hydrogen acts as a reducing agent, and it is occasiorjally usetl for
purpose of removing oxygen. Similarly, hydrogen compunud-
prepared ivith the helji of sulphuretted hydi'ogen.

274. Preparation of Hydrogen Iodide. — If. for e\;uii|iw
fiulphiu-ett-eti hydrogen be passed into water in (H'esence of itxlitic,
follo^nng reaction takes place :

or, expressed as ions :

H^S + 21 = a + 2Hi,
S" + 21 - S + 31'.

That is, from sulphuretted hydrogen and iodine, hydrogen iodide <
sulphur are forraeil. In this way an nijuemtf. solution of hydr
iodide can be easily prepired.

On the other hand, ijitM'oit^ hydrogen iodide, on gently healing, i
oo sulphur with formation of iodine and sulphuretted hydrogen
The oiuse of tins difference lies in the fact that in the former easel
hydroE^en iodide dissolves in water and {jassoa into its ions. The ifli
of hydriotlic acid are much mwe stable than hydrogen iodide it
and are therefore fonne<l nnder the above eonditions. In the se
case, no water is present, and the greater stability of the aulphweti
hydrogen comimred with the undissociat«d hydrogeti iodide, c-ausffli
that case the reversal of the proceaa.

Hi + s:^H„s.

'"575. Decom|>o3itioii of Sulphuretted Hydrof en by Heat.
A|kurettoil hvdrugeii iuelf js a\so iioi very aUililu. (hi beiitj; heatt'd
^■Bil-but tube, it partially decomposes into sulphur niiil Uydrogeu.
^■te other haod, sulphTirett*d hydrogen is formed under tlic »«inp
^pMons from its elements, so that wa are hi'ic ile^diug v^ ith (% citctiii-
^quilitiriuin according to the eijuation

kC. Combustion of Sulphuretted Hydrogen. Sni|>iun<>ttc(l
^41 rertdily Imnis iri the air with ;i hluv suli'bui- Hftmc. If the
eontainefl in a cylinder be ignited, the walls of the cylimlor
covered with a white cojitiiig of aulithur. This is ihm to tlic
ibe hydrogen of the Bulphurutted hydrogen luiitos tutieh inor«
rjth the oxyyirti lluin the sulphur dooa. Tlieii'fore, if lhuri»
ily of air, aa in the interior of the cylinder, only the liydroj^en
d the itulphur scpurutes out. In thh ease sihn, the aiilphur is
white by rejvsou of itj? state of fine divisjiiii

Analysis of Sulphuretted Hydrogen. -That sulphuretted

rontaiuii suljiliur, is made e^'ident liy the experiment juMt

1; the pre.ierice of hydrogen can be proved by cunvwrting thin

iter.

tJii& puqK>8e » metallic oxide, ^.;/. mercury oxide, iu heated in

It erf dry sulpburelled hydrogen. The following reaction then

HgO ^ HJS = HgS + H.,0.

to s»y, mercory BolpUide !ind water an* formed. The latter
euily collected in a cold receiver Jind identified by ifc« pro-

Further, the hydrogen of sulphuretted hydrogen can }»■■ msI free l»y
ttala. For example, if fir>elr rUrided copper i« heated in a rurn-iiL
•alpbaretted hjdrojien. the following reaction takes phice:

H> ^ Co = CnS -^ H..

ooffper sulpinde and

■jiilTtt, For
is doe ths

^\io<l«r| <wgm or Wtfc

PoljralpU
gki togethcrvNk

: ytUoir in 'tjiJkmi
►lannirir.V- -

hydrogen an? prrxjuced,

ulpburetied hydrogen with forron-

atiO to the noble metaK cspt-ciully to

Mb oewon, silrer ohjecta liecome block in

■dphnretted hydrogen. To the aaoie

of mivtr qnuns which come into contsct

s aolation of ndiara mlplikt* i«

_, dtaaolvea and the liquid beeooMK

nat^mmtimi of the aolution, eompoqaA* oA
tm he ohtMUted in the cTx^iaSaatilUlfA. T^-

280 PRINCIPLES OF INORGANIC CHEMISTRY

solutions themselves behave quite simiUHy to those of sodium sulph
they cotidnct electrieity, and are, therefore, to be regarded as
solutions. The ions arc*, on the one hand, sodion Na , and, on
utfaer handj S.," to S.", or HS.,' to HS^'.

The relations are simitar to those in the ca$e of iodine, wh«
ion r can pass into tht> Iji-own ion 1/ by taking up two fiirthe
bining weights of iodine (p. 238).

Of the polysulphidiona only Sj " and H^, ' have been charact
with any degree of exactness ; the lower ones behave like mixt
S" and k;'.

279. Hydrogen Persillpbide. — The above solutions
differently when acted on by adds, according as the acid is
gradually to tlie solutioti, or the sohition poured into excels oi
In the first case, suJplnirettod hydrogen is evolvetJ and the exc
sulphur separates out as milk of sulphur; this is the usual
preparing milk of sulphur, sodium aulphi<lo, however, being
by calcium sulphide. The reaction takes place according to
equation

NajS, + 2HC1 = 2NaCI + H,S + 4S,

when the pentasiilphide is used, and in a corresponding manner'
the other sul[jhideB.

If, however, the concentrated solution of the sulphide be added]
excess of hydrochloric aciii, no sulphuretted hydrogen escapes,
oily drops separate out and iinite to i\ yellow liquid. This hia
composition H„S,„ where u, lies between 2 and 5. It is called hydr
persulphide, and may be regarded aa a mixtiiro of the acids H.,S, i
H.,S,,, in which I'ai'ying amounts of hydrogen sulphide are dissolved. ]

The lii)uid i.* \erj unstJible, readily undergoing s]Ktnt;ineMU6
composition into sulphur and sulphuretted hj'drogcn. It exhibit*,!
this respect, some resemblance to hydrogen peroxide, for ita
composition ia promoted by audi substances as mechanically fa
an evolution of gas. DilFerences are fotnid only in so far
hydrogen persulphide is Imt sparingly -soluble in water.

* 280. Thermochemical Data- — Sulphuretted hydrogen
formed iVom solid rhombie .sulphur with devLdopment of 11 kj;
solution in water further li) kj are developed, so that the heat
formation of dissolve*! sulpluiretted hydrogen is 30 k/.

In ilie forniiktion of hydrogen persulphicJe, an absorjrtion of
equal to 22 fcj accomjiiinies the taking up of the first atom of sulp
In this respect, therefore, there is a similarity to hydrogen |»emxS
The rest of the sulphur is (iissolved without Jippi-eciable heat effect

The heat of neutraiisuttou amoiuits, fur thi' first equivalent, tot
kjf for the second, tu /em. I'Voju this it likewise follows thai
reaction consists essentially in the formation of the salt NaHS, or I
the ions Na.' + HH', and that smUutw ftu\\Av\de \n d\\ute wi\uuon

Sitljiftiir Dittridf tiiid Sul^ilmmts Acid

ition. — In the combustion of sulphur in uii* oi
i* formed which causes the well-known puajfent smell of
njr, iuul is a cnmpninid of fiiilphiir

ibustioii is ciiiried out in an
ip._(/. in the ajipanitus, Fig. 90),
that the volume of the gas is not
rent from thiit of the oxygen.
p-gen is O^, the compound which ia
equal volume must ;ilso cont^un
liifjing weights of oxygen.
Iinolar weight of the gjia has been found
d4 or somewhat over this, according
and temperature. It contains,
along with -' ^ 16 - 32 pirta of
'32 parts or one combining weight of isulph

rtn. 5(1.

«r, .'lud its formula

Physical Properties. — Sulphur dioxide is a gas which,
\ sumll ]jreBsiues, t-xhibits deviations from Hoyle's law, in the
thai as the pressure ijicrenses the volume diminishes nmre than
ktnaUy t-o the pressure. Further, it can lie liquefied by
e pressure and cold. At atmospheric pressure, the temptniture
izing mixture of ice and salt i.^ sufficient ; if sulphur dioxide
d into a glass vessel surrounded by this mixture, it conileuaefi
Y mobile liquid as eloar as water. In the following luble i
le relntion i>etween pressure and temperature : —

rule, the votane U antiiewkat smaller, tx'cauiiB ulong witb tbe cotnpottStd
K) foiTueil .some 80, wlik'b, cqinbiiieii witli traces of itiotataTo prennt, fOfUnta
itile eomponnil.

2H2

PUIXCIPLES OF IXORGANIG CHEMISTEiY

Tcmj«rnt«rf.

I'nsisBiirB,

T*tn|jijTi>tiii'<>-

rn>».ur>-.

-30"

OaS* atiii.

■irS-

1 -n-r •till.

ae'

0-4fl „

10'

•2-2(4 . .

-ao'

a(>:j ,.

16*

5! -7 2 ..

-15°

ivm „

20'

3-il ,.

100 ,.

25"

3-84 ..

- ti'

i-ar. „

SO"

4-52 ..

i'.">:i ..

40-

Hi.'- ,,

As can bo scon, the boiling point at atmospheric pressure is - \{
Tlie criticjil magnitudes are: pressure 7!) atm., tem|>er.itiire 157 .

Liquid aiilplmc dioxide ia now placed on the market in
cylinders, similarly to liquid Lhlorine. In cases where large qt
ties af the substance are required, the use of such cylinders is
convenient.

•283. Behaviour towards Water. — Sulphur dioxide dia
fairly abundantly in water At higher teni pern tu res the solub
follows tt( some extent the law of Henry. At room temperature
volume of vrnmr dissolves about 50 volumes of sulphur dioxide.

The aqueous solution sinells strongly of the gas. which can
entirely oxpellfd by twilirig. Towards litmus, the solution til
the reaction of au acid ; it therefore contains hydrion. Since sii
dioxide does not contJiin any hydrogen, ihe acid must have
produced by the union of it witb water, and therefore have
formula SO, + 7iH,,0. The value of ii cannot be ascertained
iiualy.Hit^ of the liquid, since this contains excess of water. If,
over, the liquid be neutralis^'d with c«uatie sodw »nd the sodtuin'
of thft acid jiresent prepared by (evaporation, this is found to
the composition Xfi„SOj,.

From this it is to be concluded that the add luis the comj
tion H,SO,,.

284. SuIphuroilB Acid. — This acid, known nut in the pure
dition but only in solution, is called ftuiphuroux itciti. Sulfthur die
is Bomelimes designated by this name^ but that is incorrect. K&ti
it must 1>B called su!phuroU:i acid anhydride, beciinse it is for
from sulphurous acid by loss of water. As can Iw gne.ss«jd from
formula, and as is found by analysts of the salts, aiilptiurous jund
a diliasic acid, and can form normal Siilts of the formula M.,S03
acid salts MHSO^, where M represents a combining weight of I
monovalent metal.

2Hii. Dissociation of Sulphurous Acid. — In the sense of

considerations set forth on p. *J + 4, sul|thurous acid is a coiupanati*
weak acid, the second hydrof^eii of which shows very little tonda
to pass into the ionic stiite. This is evident from the fact that
acid cannot be titrated with caustic soda and litmus. Even Ijeforol
equivalent amount of base hsis been added, the colour changes si
;uitt condnntiualy from red, through violet, to blue, without it
possible to distinguish a sharp ttaivKitlQiU. \eciOY4\\\^'5, vVft a(\u

SL'LPHUR AND ITS COMPOUNDS

283

sulmioii of the normal sodium salt, which htis been purified by repeated
reciystallidation, also exhibits an alkaline reaction. This arisses through
be action of the water on the ions of the salt. According to the
jUation

Na,'SO/ + H,0 - Na'IISO; ^ NaOH',

thi ioD of the acid sulphites HSO^' is formed at the expense of the
water, hydroxidion being thereby also produceil, which cauaes the
characleristic blue coloration of litmus. This rejiction, however,
takej) place to a ]ess extent than in the case of sulphuretted hydrogen
(p. 27 \).

28fi, Bleaching' Action, — Sulphurous acid and its salts possesa
some |)r<ipertiesi which ;*re of iniportauce technicjilty. Sulphurous acid
bleaches vftrioua organic eoloiiritig Bubstanees, and is therefore used
for the decoloration of silk and wool. These substances cannot be
bWchcd with chlorine, because they thereb}' become hard and brittle.
To cai-iT out the process of lileaching, the snbstaneea are hung up
in a moist condition in chambers which oati be closed, and in these the
gtdphiir dioxide required is generated by the tombimtion of sulphur.
When after some time the ble-aching has taken place, the substances
Qiust lie carefully wiished in order to remove the transformation
productJi of the colouring substances and the excess of sulphurous
ncid.

* This property can be clearly demHinstrntcd by placing a nundjer
of coloured flowers near burning sulphur, and covering the whole with
a glass bell-jar. In a short time all the flowers l>ecoTne white.

• Tlie colour, however, is not completely destroyed, as in the case
of chlorine, l)ut can be restored. This Uikea place, to a certain extent,
Bfjontaneuusiy, on standing some time in the air ; more tjuickly by
moii^tcning the blejiched blossonis with dilute sulphuric acid. Under
tfaew conditions blue colours which are turned red by ncids do not, of
eoUTBe, appear again ; in their pLico red appears.

287. Physiological Action. — ^ Sulphurous acid has, further, a
powerful action on vegetable organisms, from the highest orders down
to the iQouhls luid similar forms of life. This shows itself in an
tindesirable manner in the neighbourhood of foundries and chemical
works in which sulphur dioxide is generated and in part diffused
through the air, in the fact that vegetable growth more or leas com-
pletely dies out. Even the sulphur contained in coal prtMluees similar
effects in towns. Tliis imjx^rtant jffoperty of sulphurotis acid finds
iLieful application in the "curing " of wine and beer for the purpose of
keeping away mould and other organisms, which would have a detri-
tnenU'd action on these lifjuids. This is the purjjoae of the process oL
sulphurin;j wine casks, i.e. of biu'ning auljihur in the interior of tb
which has been in vogue From remote times. For similar pur
IsLTge qtmntities of sulphurous acid siilts arc used in liiew^rios.

282 PRINCIPLES OF l.\( Mi' jfJC CHEMIST

['l>

itm|H^nitun>.

I'njsstiiif.

- 30'

l)-:t!> iitiii.

ar.

0-l!l ..

-20'

0 •(!:.! ..

'itt

ii-Sii ..

10 ■

1-(IU ..

- r,"

i"r> ..

1 ■.'.:•, .

As can bo seen, the lioilin-
The critical miignitiulcs aro : ;

Litjuid sulphur (lioxi(1<- '
cylinders, similarly t(i h'tpii'
ties of the Hubstiinco arc '••
convenient.

283. Behaviour tov
fairly abundantly in w.r-
follows to some extent •!.
volume of water dissu'v-

The aiiucons soliirj. ,^
entirely cxjielli'd by hi^
the reaction of an aciJ
dioxide does not ciit!-
produced by the ni'i
formula S()..-t «ll.ft
analysis of the lii|Mi<
over, the liquid In* <
of the acid prosi-'i
the composition N

From this ji •
tion 11, SO...

28i. Sulp;
dition but milv ;■
is som<.>tinie.-< «ii--
it must bi- iMii
frcmi sulphui'ipi- -^ "
formula, ami .. - '
a dibasic aciu. ■
acid salts i\\ '»■
monovaioni i"-'

.-cc ■>! sulphur d

_rr*. i* carried oi

■^is ■>! the ()xyg<

- r -.£:her employed

-:r- k2 aqueous sohi

...r i-7 10 per cent

■Hm:«?d solution o

r ^!llphu^ dioxic

^-sr.oilly, and is em

., :::' '". is also the ra

...r for kboratory j

j^ ■.ci.'entnited sulph

.e -:i delivery tube,

^ai ~^r dropping funnel

.^ j»; il the same time

.,e«B- zio water, which re

— .>i::;aurousacidre{idilya

..-J-. fiiii'h has the com])osit

... a:^'.'CS *C'd is a reducing a

^, >^-rssiry for this transi

.;rn <■'*" ^^^*^ ''® remove*]

-TT hydrogen of enterinj.

_^_„;.4 i-n acts not by withd

- rxample of thi.s hist prot

_. v.'i •"> iodine, which takes j

-. .; -H.o=i].,so,^2Hi.

.„,„• i-v. into hydriodic acid. Si
jf '< detected by me^uis of s
" "^ , iAfvl for the volumetric do
» ,.,:, T of sulphurous acid with
"■~ .BTi-'" riuch employed, has now bi
"^ ^.p(i.er.t meth«Hls. The inconvf
.^j -jat the composition of tht
/..rftaiB^'.*' "ixh'rgoing change, ow:
^ \jtjixc by the oxygon of the air.
ZJS.'i. Dlfef ' .^ «!ijvft act on io<1ine in the sam
consiilt!i'iition-~^ """■ '^^jaryty- but they have the second
weak ai:id, :** •'>-■■ ,^ .„^ oxygen of tlie air can, howc
to ]iass IIU..J*- •'■"^"^"^ ^ jiiing to tlic .suhuion a sma
ficid ciinnvb,^ '***fl^ ,iaHr. * siro'l'"' .xtibsfaiiccs. So sni
er|uiv:iloiil

and i-oai " ___-

possiblij '"^'jIiiBp****^ ** " catalytic one.

; -g^ wight of the solution is suf
^'■tfitr- "*'^ undorgoos no <hangc ;

AND ITS COMPOUNDS

285

jua Acid. Fruin the hot, con cent fated solu-

^tn-i" of the alkali raeuUs, salts crystallise out which

i[HiHitinii of iicid salts, because they contain no

mim salt, more especiallj', fornjs very reatlily,

»Ve ihe composition represented liy the formula

ring this formula with that of the ucid suIphiteH,

but the sidt hfV* been formed from this, with tho

ifein«nt« of water —

2KHS0,, = K._,S.p,. + Hjy.

Jent AiitoQ which is combined with potassium ii^ therefore
sllw wrresponding acid must, accordingly, have the formula
It cMi be Iwked upon as a comjiourid of sulphurous acid
• dioxide —

H.SC>, T SO, = H^S^O,.

tw, it be fktteniptcd to prepare this acid from the
in nit, only the ortUnaiy sulpIiuroiiB ucid is obtained. The
therefore, passes at tlie moment of its Ijlifratifm into
ucid. or, what is perhaps more ci>rrect, the sulpluuoiis
contains smalt amounts of the acid H„S„0. along with the
r aciil ; the different forms, however, p;tss so i(uickly into
►tier that they cannot be investigated individually.

is tailed jii/rfuftiljiliiiivHS acid, and its aid ts arc
pf rrwnlphites. The name is due to tho fact that h sinnlar
v.- r.f pJiojjilioric acid Ii;i.s been obtaiiicil by heating that acid.
'J I . Tbermochemical Relations. — The combustion of sulphur
us dioxide develop.s 'I'iil kj, the solution of the latter in
furtber yj, kj^ ko that the heat of formation of the ai(ueou8
S29 kj. When one equivalent of caustic soda is added to the
67 tj arc develo[>ed ; a second etjuivalent yields further
From this it follows that the formation of the ions H and
from the undissociatcd acid, 1T.,S( •,,, takes place with a
ncnt of beat of more than lU hj ■, since the acid is already'
di*'«Kiate<i, the whole amount of heat does uoi ."^how itself.
uivA dissociation, HS( ).,' = H + SO.,", .ippciirs to take place
«oy oonsitleraftle heat effect, since the beat of neutralisatiou
TefT near lo the normal 57 kj.

K. Suijihiir Trio-riilr itu<l Sulphxric Acid

Snlphur Trioxide. — Although sulphur dioxide is not the
onifK.nu"' oC oxygen with sulphur, it is essentiidly tho only one

l>n><l»L'*d in tho direct iiit<?raction, i.r. in ctmibustion, even
lygsn i« present in great abundance. A higher oxide of

>»^«!=JLSIC CHEMISTRY ciir

of sulphur (liowdc and ui
i» carried out by burning
■ of the oxygen in the ar,
dtber omployed as such or k
«a aqueous solution saturat**)
<miy 10 per cent of sulphurom
ted solution of acid wxlium
gf sulphur dioxide on sivliam
lly, and is emplojed for the
«ijlttiDii is aUo tbe nioi^t conveoieut
■ nJF for laboratory purposes. For
■r «incentrat«d sulphuric acid in *
ti. and delivery tube, and to alio*
B ibe dropping funnel. The sodium
•mI »t the same time the sulphurous
into water, which remains beliinil,

[»hurou8 acid re-adily absorbB ox Vfjen.

t vhich has the coniposition IL^yO^, ami

. acid is a rrdiu:i}ig agent, bfcaus* it

aeeessary for this iransformatioo from

can also be removed from wrater if

hydrogen of entorinj^ into another

.».Kaa then acte not by withdrawing oxygen

• - -vjimple of this last process is artbrdd

- i«i i«i iodine, whi<'h takes place atrordiiij

- A.v-fi««, into hydriodic -icid. Since very small

_,! - AD W detiu'ted by meatis of atarch <p. 2;}5l

^ ^B %e med for the volumetric dotecmination of

add. or of sulphurous acid with iodine. Thi«

-Jrninrh enipluyed. lias now been abandoned
..m^eiuent methods. The inconvenience of the

» ^tt tk«l the composition of the solutions of
^^^laally undergoing change, owing to
^^tioa by the oxygen of the air. Solutioi

■^ ^Heh act on iodine in the same way, do not

^M^^Oft. b"t they have the second. The spou-
< ■At oxygen of the air can, however, be al
_ adding to t'^*^ solution a small quantity

_mHt or similar substances. So small a ((uaiitity
. .j^ weight of the solution is suilieient for this

._^r>x it*<"'f undergoes no change ; the action iiM,
tjmt^ as a tatalytic one.

■Ffi SULPHUk AND ITS COMPOUNDS 285

i'JO. PyrosulphuroUS Acid. -From the hot, concenlrateJ aolu-
liuHsof the ."itid BLiIpliitLs of the alkuli metals, salts crystallise out which
du not have the composition uf iiuid salts, because they contain no
hyilni^en. The poUissinm salt, more esiieciitlly, farms very readily,
iiiifl )H found to have the composition roproscuted hy the formula
K.XO-. On comparing this fortnulB with thai of the acid sidpLites,
KHSd.p it is seen that the aiilt has been formed from this, with the
loi'i of the elements of water —

SKHSO^-K^-SA + Hp.

The divalent anion which is combined Tiith potjiasium i« therefore
SjO.', and the correspomling acid muat, accordingly, have the formula
H,-S.,0.. It can be looked npon aa a compound of aulphuroue acid
and sulphur dioxide^ —

H.,s(;)., + so, = H AO,.

If. however, it be attempted to prepare this acid from th<.'
potajfsium salt, only the ordinary sulphurous acid is ohtiiined. The
new acitl, therefore, piisscs at llie monietit of its liberation into
sulphurous acid, or, wliat is perliupa more correct, the sulphurous
acid also contains small amoiuits of the acid H.jS„0., along with the
ordinary acid ; the different fonna, however, pass 90 quickly into
one atiotlier i!i«t they cannot be investigated individually.

The itcid H^S.,Of, is i ailed pt/rmitlji/niiouji tuki, and its salts arc
callewl pjrosulphites. The name is due to the fact that a similar
derivative of phosphoric fitid has Iteen obti-tiricd hy heating that acid.

•291. TiiermocheiiLical RelatioDS. — The comhtistion of sulphur
to guseous dioxide develops L'!>7 Ij, the suhition of the latter in
water, further 3'.J /.y, so that the heat of formation of the aqueous
acid is 329 i'j. ^Vhell one equivalent of caustic soda is added to the
solution, 67 }^j are deveioi>ed ; a second equivalent yields further
55 it;;*. From this it follows that the fomvalion of the ions H' and
HSO^' from the undissociated acid, H.,SO;,, takes place with a
development of heat of more than H) }.j ; since the acid is already
slightly ilissociated, the whole amount of heat does not show itself.
The second dissociation, HS<J^' = H" + 80^", appears to take place
without any considerable heat eflTect, since the heat of neulrali&ation
55 kj is very near to the nomifd 57 !:J.

E. Sulpfiur Triaritie atul Sulpfmrk Acid

-J*^-2. Sulphur Trioxide. — Although sulphur dioxide is not the
Lighcflt comjtouiid of o-vygfii with sulphur, it is essentisilly the only one
whjcii is pro<luced in the direct interaction, i.e. in comlnistiori, even
when oxygen is present in great abundance. A hiuhcr oxida '

2efi

PUI.NCIPLES OF IXOUGANIC CHEMlSTIiV

indeed, ihaL it (.'aiiitcit lie made use uf for riianufactujin^ pit
For tliis reason, the sulphuric iicid was foriiferly prepared in
waj, viz., by strongly heating iron vitriol or suli^hfttu of ii-on.
process is, cbeniically, not very simple, atui the details uf it
given under iron. It has, at the present day, only an hii
import^incc, ainra it is no longer used.

The muthrxl still chJeHy employed iit the present time (cf.
tlepends on the oxidntion of suiphur ilioxicle or sulphurous acid
this is iiecflerated by a jmrticular expedient to such an extent
has Ijecome a productive manufacturing method

The method waa developed from experiments made to replii
oxygen of the air by more quickly acting oxidiaing agents. So
was burned with the addition of jiofaissium nitruti* or saltpetre.
Bubstance hiis the formula KXO., ; it contain.'!, therefore, a
itraount of oxygen, with which it readily parts. In these exp<'riii
it was found that much more sulphnric acid was produced than
have lieen formed from the oxygen of the saltpetre. The causvj
this Waa fotuid to be that the oxidation of the suiplinrnui; ncid
the oxygen of the air takes place much more quickly in the pre
of the gaseous oxygen compounds of nitrogen which are pi-odv
under the aljove conditions than when it is alone.

297, ManiLfa.Cturing Process. — The above-mentioned
then amounted to this ; Suiphur djoxiele was formed by the combu
of aulphiu', and the gas was mixed with air and water vapour in
amount net'easary for the formation of sulphuric acid, the prodii
of which was sufficiently accelerated by the miditJou of oiid
iiitrofien. The various stiiges through which the process liius.
cannot be described here ; it will be sufficient t-o give a descrip^
the arrangement of a present-day snliduiric add itianufaetory.
sulphur dioxide is, at present, generated only to a small extent
sulphur itself ; for its formation the sidpliur compounds of iron
chiefly used. These are burned in suitable fn maces, forming |[j
o.xide, which remains Ijehind, and sulphur dioxide, which ea
Liirgt^ (|uantitiGS of sulphuric acid are also formed from other
containing siriphur, which, for the puri^jse of obtaining the meljdaj
them, arc "roasted," i.e. heated with access nf air. The sulpb
passes into sulphur dioxide, and tlie metals form oxides.

The hot mixture of sulphur dioxide smd air is firat of aU l&l io
an empty chamber, whore the sniall, solid particles carried over
the gas, "flue-dust," are deposited.

Tlie gases then enter at the foot of a tower (the Glover tow«
filled with acid-resi.s.tiiig stones, and are met l>y a counter-stream
crude, dilute aulpliurie acid, such as is formed in this proeess.
this arrangement the hot gases are cooled by causing the evaporalid
of the water contained in the dilute flulpburic acid ; the acid is ihe
concontriUL'd. At the siin\i' tmio, tVic add x^ l\:<it;d from the osid

SULPHUE AND ITS COMPOUNDS

989

»gcn which it contains {tvie itt/nt), und these aro again brought
lie |irfjces«. In this way, not only is a loss of these coni-
rely valiiAble »iib&U[ice» liVoidDd, but the sulphuric acid is a,t
time (re<*fl fVrmi sin impurity which would 1>e very detri-
in itg furtlxM- trcituiunt and iipplicaiion,

the lower, the giises pass into sevciid hirge thanibera lined

with lead |)kt<^s. (Lead is attficked by sulphuric ncid to a

ively slight ex-tent.) luto these chambers, st^ani and oxides

>n are also introduced : oxidation to sulphuric acid occiifs,

falls as a Hnii rain to the bottom of the chaiubor.

the hist chamber there escajies not only the nitrogen of the

*ir, l»ut aUo tlie oxides nf nitrogt^n present, so fat as they

hboen alworbed Tiy the dilute iicid formed in the chambars,

iber acid," In order that theso oxides niny not be lost,

led through a 8«uoeid Uiwor (the Gay-Lussac tower) in which

sulphuric acid is tritkliiij,' in an opposite direction. The

rnoMlily Hissolvps iar^ic cjuantities of th« oxides of nitrogen, and

ins this v.ilitahle UMiterial. The atniosphene nitrogen jmaBes

. bu^v cbtmuey, whith iiiiiintairia the draught through the whole

oC app«r:itiis. The contcntnited snlphuno acid charged with

cid«s of nilrugfii is tntrofJucud into the tii^st tower, where thu

of nitrogen are given otT.

Actioti of the Oxides of Nitrogen. — As to the cause of the

ion of ihf ■iiilphuric aeid fui-matioii by the oxides of nitrogen,

ti in existence for a hundred years. According to

■ '•.-* in the alternate reduutiori of the oxides by ihtj

dtnxide ami their re-oxidation by the oxygen of the air.

iU of thia thcury cannot be discussed till the oxides of

ttre treated. Sijice the OKides of nitrogen are fotmd at the

»nd the end of the imjcesa in the same condition, and are

U|v w<? must at this point be satisfied with designating the

action Jis a citidytic one,
OOBCentratioa of the Acid. -The acid obtained by tfai»
onLkins abtnit Go per cent of acid and 35 per cent of water.
aount of wuter, in the form of steam, must Imj introduced into
ckaniWr iu order that the formation of mdphuric acid shall
quickly and regularly. For most of the applications of
*cid, bowovtT, this water must be i-emoved.
is rlfecte*! in the first place in flat lead [Kins which are
from ttlwivr. When the sulphuric acid attains a concentration
pr-r €3i*nt, it IwginB to attack the lead. It in then evaporated
m flmt platinum retorts. At first, almost pure water passes
It wheu the acid has reached a concentration, of 98 5 per cent,
■ •■i n»(arly the »ame composition fis the liiguid, and further
liccomes impossible. Bcfon' (he jjcjd has reached X\\\%
it w rati wtft mrbois, in which it in tmDsi»rted,

292

PRINCIPLES OF INORGANIC CHEMISTRY

303. The Ions of Sulphuric Acid. — Being a dilj^tsic
Bulpburic ficid tan ffirm twu kiiuis at' jinions, viz. thu numon
HSO^' and the divalent SO^". Concent rated solutions of the
chiefly contain the fui-mer ; the greater the dilution, tlje more i^
this disaociiile into tlit: divulenl ion and hydrion. Like almost dl
Lions hitherto montionefl, both these ions are colourless a.nd p088ea»(
bonapicuoiii? pr(j|.iertit'8.

3U4. Applications of Sulphuric Acid.^In the laKoratory, i
still more in tlu' arts, .suljilinrif acid is a sul isttincf of ii
importance and manifold applicAiion. Its importance for tbe cil
industry has been justly com))Hred with that of iron for the enjjii
industry. The manifuld applimlion of sulphuric acid depends i
fact thai it can he used in two ways for oht^aining other acids'
their salts. Since it is, as a rule, only tlie rmlls of the varioia ■
that ure got directly, ;u)d from ihf^se the free acids must then bo (
tallied, a.(i acid suitable for this object, finds a very varied applic

The use of sulphuric acid for this piirpo.se depends on the con
ation of several circumstances. Apart from its cheapness, the facti
it is a slroDii acid, i.' . one largely dissociated into ions, and has a i
fioilinfj /loijit, in the determining factoi*.

Certainly, on niukins^ a comparison, it is found thai in eq«
lent Bolutioiu'i. i.r. sijluiions containing eipud amounts of hy(
hydrochloric acid is a better conductor than sulphuric acid, and
Ithe former, therefore, is more dissociated, However, the eom«
anifiUev degree of dissociation of sulphuric acid (cf. p. 247) i«
than compensiitod for by its small \<ilatilit;v Thus, hydroct
acid is prepared from sodium chloride by means of sulphuric
JMJCOi'ding to the eipiation

2NaCl + H.,SO^

Na^SO, + 21IC1.

The possibility of generating the stronger acid from its aalu
means of the weaker, depends on the difference of the volatility of I
two acids. When sulphuric acid acts on sodium chloride, onljj
atn;dl riuantity of hydrochloric ucid is nt first formeil, and the re
would stop, i.f. a chemical equilibrium would be eslablistied, if all
suliscauces remained together. Even on gentle heating, however, i
hydrochloric acid jwisses off in the gaseous state. The ecpjtlil
ii thereby disturbed, frash hydrochloric acid must lie fornn-il,
therefore, fresh soflium chlmidf he discomposed. If this hydrochl
acid be also lemovcd, the process goes on until, finally, kII
awlium chloride is decomiiosecl or :dl the sulphuric acid is used
(cf. p, 20.S).

In the decomposition of sodium chloride by sulphuric acid,
aimilar processes, two sUtges can be clearly distinguished. The
half of the decomposition always takes plBC« much more easily, i.«.|
u lower temperature tliun the second. This depends on the dili

SULPHITE AND ITS COMPOUNDS

sulphuric acid. The pix>ces8 ts separable into two stages,
ite«l by the following ei|uations : —

UM\ + NaCl - NallSO, + HCl
N.1H.SO, + NaCl = NajSO^ + HCl.

in ihc caisr of all polyI>iisic acids, the one combining weight of
EQ 8|>lit8 oil' tirst unil most readily ; the aplitting off of the
I occurs with miith j.Teater difficulty. For this reaaon, even when
ihimng wctghte of sodium chloride are present, there is, at
ily the acid solium sulphate formed, according to the first
n, and fine i"ond>ining wciglit of sodium chloride remains. Not
reaction is essentially over, and a higher temperature is
1, does the second process, the decomposition of the s(Miinni
by tbe i»cid sodium sulphate, liiko place, with formation of the
Bulpbate.
Jpburic acid can lie used also m a aecoixd way for the prcpjira-
free acids, from their salts. With some metals, cspociinlly
(Ba> and l«*j*d (Ph), it can form vuiy diHicultlj' soluble Sidt.?.
if aiiueoiis solutions of the iMirium or lo;iil salt of the acid
ion lie railed with snlphuiic acid, barium or lead sulphate is
and separates out in the solid state, while the acid remains
In this way, for example, chloric acid, HClOj,, is obtained

Analytical Test. ^ This aame circum^stance, the ulialif

t(f fmrivm suijihtU, h employed for the detection anfl esti-

of sulphuric acid and its salts ; in general, of the ion SO^".

rvrr barifni, Bfv", comes together with the ion 80^", the pre-

of bwriiim sulphate (HaSOj) sefMirates out. Since eulphurje

I fnirly strong acid, the small solubility of barium sulphate is

tft any cojisjdenible extent by the jireaence of free

276). The reactioit, therefore, is also given in aaJ solutions.

tb«re any otbvt substance by means of which barium sulphate

lend appcciably whililc in at|Urous lirjuids. This roactiou,

i« n rery ffrlnin crit^n'ion for the presence of .SO^"-ion, and

can arise only from the fact that selenic acid {mif infra),

is TiTy similar to suljiliiirie acid, yields a similar, difficultly

fiiuU' with barium aalts. When we come to selenic add,

ihall shovr how such an error can W- excluded.

Hkrttion may be asked, if the two different ionSj HSO/ and

K'?, in conformity with tbe ditrerence of their eomixtsition,

■ projH'rticB and char.ictertatics. As to the former, there

irit the deti'clion of these differences is not easy, since

- a knowledge of the proportions of Iwth ions in a given

Irhnugh this problem is not insoluble, still it is so com-

. it cannot be discussed here.

On the other hand, for tbe detection and the estimation of Bul-

394

PRINCIPLES OP INOKGANIC CHEMISTRY

pburic acid by hariiim t'ompoiinds, it is a mutter of indifTerenosj
what propoi'tiotis tlie ions HSO/ and SO^" ale present in a solu
By pretijiitation aa barium sulphate, certaitdy, only f>C>,"-ion is Rt I
removed; so aoon, however, Jis this takes place, a. fresh amo
formed from HSO^'-ion, in (iceoitJaDce witli the erpiadou
- H' + SO, . This is also [nccipitated) ami so on untiJ practic
the sidphaiiion has been j>ii*ci[jitHt«l, Only when the concenirai
tlie hydricHi is very gieiit, that is, when the solution is very auid,
a measurable nuaiitity of H80^'-ion remain uiidissociatcJ, and
precipitated. Hence the rule that the precipitation of barium i
must not he carried out in a too acifl solution.

30ti. DecompositLon of Sulphuric Acid. — Sulphuric

fairly stable siibatiint'e. It undergoes oxidation to a higher
only under quite sjieeiid conditions by means of the electric ci
Reduction tiike.s place more readily, and use is sometimes maile of)
processes for the j>rep?iration of sulphur dioxide. Such re
occui'a, for example, on heating sulphuric jwid with copper.

Copper is a divalent metal, the sulphate of which has the (i
CuSO^. On heating copper with .sul]>huric acid, the usual displa
of hydrogen by metal would first tjike place —

Cu + H^>SO^ = CuSO, + H,.

The hydrogen, however, is not evolved, hut is oxidised at the oxf
the oxygon of a second mole of sulphuric acid ; this is reduc
sulphurous acid, which immediately decomposes into sulphur die
and water. In forroulfe,

The two e»[Uattons can be combined into one, and we obtain

Cu + 2H2SO, = CuSO, + 211^0 + ISOj.

Mercury and silver behave similarly to copjier. In the case of a
the reduction goes still further, sulphuretted hydrogen lieijig ion
under certain circimistancea —

oH,SO^ + 4Zn = iZnSO, + 4H2O + H,S.

This reduction occurs only when the solutions are fairly con
trated. Dilute sulphuric acid reacts vnlh ^inc, with formatiou
hydmgen —

Zn + H,SO, - ZnSO^ + U^.

307. Pyrosulphuric Acid. — The compound of sulphuric acid 1

trioxide, H^S„Oj, meutioned on p. 287, is a special acid, to which

name of pyi'osulpliuric acid \vaa beetv ijwftw. ^ov X.W tiOTa^und

SULPHUR AND ITS COMPOUNDS

itaelf, bm the corresiwnding salts t;in be prt.'pured, e.</. thei
It NsjSfO.. The siilts ivre iibtaijjeil liy hertttng tlie aciid ■

«.y.

SHNjuSO, = Na.S.O^ + H/).

tuore strongly, the salts lose snl|>hui- trbxide and pass into
;ulphatc«« t,</.

NajSjO^ = Na,80^ + SO,.

however, Ije specially noted that in aqueous solution the cor-
ng ioii, SnO,", is not known. On soliilir»n, the pyrosulphat*s
! water and \>s\,sh iiibo the acid suIp]i:iU!i»

XsjS^O-

H,0-2NbHSO'

pparently proceeds so qnickly that it haB not

iblo to (listiT)guisfi between the solution of a, pyro-

and an etpiaHy strong solution of tho con-csponiling acid

Fri.»m exjKjrienw gaimnl from other arjrts of n aimilur

iti'vri, hfiwfver, cases are known I'n whioh dUlerences can be

flf t^x-leil between the ioiia of the nornud and of the pyro-acids.

Jotj. Thermocbemical Relations. — The heat of formation of
lulphur uioxide from its etetnmits is 432 kj. Its hcHt of vaporisa-
\49 i^ ; its he;it of formation in the vapoiir form amonnts, there-
3S3 kj. Sintc> the heat of formiitton of the iltoxido aruounis
I'j, this would, by coniburtion to the trioxide, develop 86 f,y,
o( lhi» ^eat heat evolution, this process takes place only very
I and incompletely, and, in order to bo of use for manufactuiing
it must be accelerated by ciitnlysera, t\<j. platinum,
trioxide dissolves in water with great development of heat,
Dg In 164 dj. Bulphurie acid, H.,SO^, dissolves in water \rith
aent of 75 to 88 kj ; at great dilution the heat effect still
to & measunible extent. By the formation of sulphuric acid,
frotn trioxide and water, about 85 hj are developed.
Ilie bc»t of neulralisatton and sulphuric acid varies according na the
the normal salt is formetl. If a mole of caustic &ml& is added
of sulftbunc acid in dilute solution, ao that the acid salt is

llaO), (52 %■ are devcIo|i€d ; the
the considerably greater evolution

mjSO, r XaOH = NaHSO^
rnolv of cuustic sofla yields

v'iL 69 kj.
the large amfuuji of heat which is developed on dissolving
ric acid in water, one may conclude that the dissociation of the
it« ions is accom]vani<?rl by a greater development of heat. In

.-DormAJ sotutintis ii^ed in ihe exjieritnetits, the tirst citagc of the
Ition H^SOj = H' ' II.SO^' is fairly complete, and the second
ISO^' = IV * HO/, ii;is pmceeded aborrt half way. By t\vo acU<a\\
Bnt mole of tntigth soda, ihe normaJ heat of neutraWsatVoTv,

-'fc^ -»- • ><"^fei5lC CHEMISTRY

ar aalpfaor to siilphtihc acid—
5^», + 6HC1

■mtnioFe. ctui hte destroy vi!

It b Uierefore use<l ui rmniir
vxtite fabrics blfucheti by it

< AMBulphati^, and atir excvsi ni

Mid spun materffils hy tlir

In tbe case of the decUonn

■a excess of the salt gencr "■

of writing paper and jl

A knoirlodgc of this fact la i<t

JoBcl of oxidation by maui
>rrordi»g to the scheme

0. • 2Sai,

ih.iii..i!i. but a new divaknt ionl

I -^11 I'll Moiilimiic iKtd, ITliij

:> ! r .iliitiii with relatcid Ril)-|

i: tlif tnLnsfunnatiort uf tUl

nitkii&» :ind sfajArpness, UHl
. //f*- iinaJt/nis can be
iitcnnined by means
Further, the metho
>ill»tances which )ik>ei
.--iiim iodtde, e.ff. fliinnM*
il!iL> deternunatioti of
_ these to nt't on a knofil
.1)1(1 titrwtinj; the residiif |

I ( t» KT'v-

ily on the variety of '* I

(' fact that an aqiietfwj
^ L»rful reducing
iiscd by the free
-■ analyses just dtscriB
but., in this case, t\ittt\
Why of this soIuUdti «»]
lonvenient and theicfof'

mam

SULPHUR AXD ITS COMPOUNDS

I solution. !.*■. in the ahwncc of hydn&ri. whoroas jt immwlialdy
jtigiMu dpconoiKieition in tlu- jir«.'seiice of the latieir, Thu reason itf
I is a^MS U> be sought for in the fact that in the sccoml c&sv uioru
|lr cfiinpoand£ c«n hv fomoed, for whosf formation hyiiricm is

J. T€tr&thiOD3JliOtt- — The formation of the sodiiitri i^ali of this

th«* ill tinn of iiiiliiic on swiitini thruRul|ih.'tto hsiB alnvidy hi'i-ti

(|i. 3<>0). For the piirftos*; of jirepiiiing tiit- free aciil kitfi

aiK is u»ed. This is (Jrcumposod with liii- calculatfd qutuitity

■ accortling to the <?(mation

2Pl>S,03 + '21 = PbSp,, + Phlj.

ijr as in the coriespondiii}; reaction with tin? sodiDm sjilt, there

lead t«tr&thioniitf and k-ad iwlidc. The former pasMes into

lh«* latti-r separates out. Frorn the filtered solution, hiui ia

tod as «Urticiikiy solutile lead sulphate by the careful addition of

Icnlphtiric itcid, whilf lh<.' idrathionic ticid remain!! in solution.

solution }ias a strong add taste and reaction^ iind ie much lean

tlun that of ditiiionit add. .Sulphur soon separates from the

which aimnttancouely evolves «ulpirur dioxide and contains

iMnd. The decompo&ition eiisuca according to the equation

Ujifi^ + H„0 - H^j + HJSOj + 2S.

516. PentatMonic Acid. — This is obtaim-d by passing sulpburctt'j*!
J>ii|i;eii itilit ,>ii a*{iieiiti8 soJuiiou of sulphurous acid. WiiereaM onit
Ition uf the substances dimply undet^oea tratiflfoi-niation Co sulphur
inttx, according u* the e<(tiHtioti

•iHj5 + HjSO, = 3S T 3H^0,

Mli«r puctioii forma penlAthionie acid and wat^-r, recording to the
iBHH>n

1 0H.SO, ^ alljS = SH^^O^ -r 1 'iHjO.

* ikrstiiin, s portion of (be aolpliur caa be tepanted. The other
mkin, boweTcr, ie present io soch m Sat: ftate of diviirion. in wbut i*
feed aiUoidnl tolmtifm, that u {K:hsvc« «]iiio«t likfr a diwoh cs) »iib<rtanc4-,
it Dot rrtainril br a tih«r. By prepahng a salt o( prnuihioni«
ft^m this aoiution, recrrstallisitum, elc^ pur« aalu of jtenlathton-
be o^ttatned. We »liall, bovrrer, iwt rnt«r her« on a dencnjition
troubleBone method* bjr which thb object ia attataed.

add M aba oMtaUe, and mditj deeonpoM* iai**
urrfOB acid, sulphuric acid, and aohilnir.
Solabotw coniauiing ooe of the higher pofytkniaiitea aooa oodwy*
io« in •Qch a way that ocher tUooataa are prudaecd.
,g., the uHhkmmtK! fmmtm into ArtJatmrnUf and tctnthWiaate.

lHEMISTKV

i.-iw.

. i*N'a.,S..(), - \:is.(.i
-. :hi.Tefiiri', viTv '!iTK'.;;

:-' of thy i-}ili.iiiiii' l-
:. .1 ivd-lirowij li.,ui!'. ■•
•■■.■:v un])le:is:iiit md.
. :.:)«■ .sition is i^xjne-Ni!

I", fieezi's at - SO .
..:. ■'1 which it dissohv-
■- .'■ can lio .igiiiii M'lw
.n. The iinHiochldiiie

•v.iter : tin; chloriii'; i?
■.'.yh-.ir jiartly SL-i):ir.i:ij

■^-.-phurif arids. 1[\v

with the anmuiit >ii
-:■ '.vprifStMitiMl by .in

;irts tot- viilcaiiisiiij:
i.jt'er Iwconics inurr

::.■:. ■.h'l.iriili-. it is ahsoilied:
^ ■'.: lht> tompeiature ami
r.-. I'jmji'iiind 81 'I., was first
• : time, howo\>.'f, sit!j.ivJi
Ik • definite compound, afjJ J

Xli

SULPHUR AND ITS COAfPOUNDS

305

^ assumed to be united to oxygen to form hydroxyl. The suitability
of this assumption is seen from the fact that the actual reactions of
this 8ubstiini:e arc in agreement with it.

Thu*, in fact, derivatives of sulphuric acid are known which hare
tte sJime rolatitui to it as the metitl chlorides biive to the metal
ttjtlroxtdea, and which, therefore, support the assumption that in
s^ilpburic acid hydrogen and oxygen are united toijether to hydroxyl.

* A " proof " of thia aasumiTtiori is -mi given l>y those comiionnds.
The actual phononietion is that the elements 0 and H are elimiuHtcd
io the proportions OH, and CI simultaneously enters. It cannot J
Oowever, be asserted that these two elements, in oitler that they may 1
oe siinultaneoufily eliminated, tnud previously liiive i>een nnilcd, for]
^here are numerous cases in which such an assumption cannot i^e

Sustained, The sole purpose of this assumption, therefore, i^ to statt^

Lhst the reaction in questifm often and ea.sily occurs.

* On such relations all the so-called "constitutional fomiulre" of
substances are based. These are a short expression for the chemical
reactions actually observed. Since the latter, however, depend on
other conditions besides the chemical nature of tlie substances, — t'.tj.
on temperature, pressure, presence of other substances,- — it is to be
anticipated that a definite constitutional formula can represent the
behaviour of the given substance only within a «letinite range, and
vrill prove all the less satisfactory the more deeply and compre-
beneively the chemical behaviour of the substance is known.

* Such diversity can, if necessary, be expressed by the assumption
of several constitutional formula' ; but this i» ordy a makeshift. For
the complete representation of the chemical behaviour, a numerical
chftracterisation of the mutual relations of all the tmusformatioti
producbi of the substance would be neceswiry, From such a stand-
point, the chemistry of the present day is still very far removed.

If sulphui'ic acid be written as a hydro.vyl compoundj we obtain
the fuiTniilii SO^(OH).,- The atomic group S0._, i^ called auljilnui//,
and the two possible chlorine derivatives would have the following
formulaj and names : —

tS0^(OH)Cl, Sulphuryl hydroxychloride,
SO^CU, Sulphuryl chloride.

le first name is not used, a^ being too long; the first compound,

"^tich still contains one acid hydrogen, is called chlorosulphonic acid.'

Chlorosulphonic acid is olitained from sulphur trioxide and

hydrogen chloride, which comljine on being gently heated^

SOj + HCl = S0.(0H)C1.

forms 3 colourless liquid of density 1"7, and boils at 152 .

' ITie name i* due to the fact tlmt in organic cireiuistrr unmeroii!* coiitiiouDils
•iJpLBjic tcitl un kiiowij of the fortimln K.SO.OH (whtry R is a 4:onjpoiiuJ *Tailii.-lH '
*lUcL iiw called ^illphouic aciils.

306 PRINCIPLES OF INORGANIC CHEMISTRY

Chlorosulphonic acid fumes in moiat air, Itecxiiise it undel]
traiififortuatiuii with the atiuoous vapoiu- to difficultly volatile sul{
acid and hydrochloric acid —

S02(0H)C1 + H^O = HgSO, + HCL

Thia reaction, viz., the re-forraation of the oHginal acid from
chloride by the action of water, is a genentl rouiction of ib«
chlorides.

* In this respect the acid chlorides differ essentially fr
metal chlorides, with which they have a fiirnml Himilarity (p.
Whereas metallic hydroxides undergo transforniation with hydroct
acid to metallic chlorides and water, the acid chlorides, on the
hatid, undergo transformation with water to hydroxide and
chloric acid. The reaction, RGl + n.,0 - K . Oil + MCI, proce
the first case from right to left, in the second case from left to :

* If, now, we reiiiemher that, in principle, no chemical
can be cmtpkk, we can say that the two cases differ from one an
essontially irt the fact that the one or other side of the equatio
reaction predominates. Or, aa we can say with reference to
wag set forth on p. 250, the acid chlorides undergo almost
lii/i/riili/sb; with water.

* Whilo the previous remarks dealt with the reactions
particular substances with a small amotnit of ^vater, thtt\
cesses which take jilace on solution in much water must also
special consideration. Under these conditions, ion formation
occur, and, in general, tko^e rendionn take phce in irfiirh ^pfdail^
ioD.'i litr formed, Among these, chloridion must^ in the first place,]
reckoned.

On decomposing chlorosulphonic acid with much water, there^
the reaction

S0,(0H)C1 + 11,0 = 2HS0;' + HCl',

i,(?, the ions of sidphuric and hydrochloric acids are formed.
these two acids are largely dissociated tuto ions, i.e. form very
ions, this reaction is practically complete?.

The decoraposaltility of the chloride by water is therefore
crejised, owing to the corresponding acid being able to form sta
jna.

In accordance with these consideratione, it must be rcarded
possible that hydro.xides e.>:iat which stand Mtrre/i amis ami h<t.vi
such a way tliat the two sid^ of the equation of reaction to
extent counterbalance one another. They will, therefore,
certain conditions, act as umls : under other cornlitions, as biisfs,
shall soon have an opportunity of indicating such substances (CIu

xni.).

The second chloride of s\i\p\\ViT\c a.c\d, svL[|v(iuit|( chlm'tde^ SO,!

SULPHLR AND ITS COMPOUNDS

307

by the direct combination of sulphur dioxide and chloiino.

lion ili>e3 not take place very quickly, hut is grcr'itly accelerated,

iodly, hy the presence of camphor (un organic substance). It

a& a co1oui*Igss, very mobile liquid, having the density 1'6"

ig at 69 \ The fact that the boiling point of sulphnryl

BO much lower than tbnt of chlurosulphonic acid is an

oi the general rule that the boiling point of the chlorine

is always eonsiflcrably lower than that of the corresponding

f\ ooapounds. The same is seen on comparing chlorosnl phonic

>ilitig point 152) with sulphuric itcid (boiling point 340"),

Ipliur^"] chloride fumes only slightly in the air, because it reacts

jmora slowly with water than ehlorosiilphonic acid does. The

I'Ooiupound is formed hy the action of a small quantity of water

CI. -r HjO = SO.,(OH)L'l -r HCi ; with much water, sulphuric and

chloric acids are'fonned— SO,CL + 2H.,0 = H^SO^ -f 2HCL

[As the ikcomjK>sjtion of sulphiiryl chloride by much water takes

inch more slowly than that of chlQrD.<iuIphonic aeid, it looks as

former pstssed directly into sidpburic and hydrochloric acids

{MBsiog through the intermediate stage of chlorosulphonic acid.

chluroaulphonic acirl which is formetl undergoes decomposition

tly tli»t at no time during the reaction can any considerable

of it be (ietoctod.

Similar relnlioiis are often found. In all cases, therefore, where

iuteniie<liatc stages are apparently |>a;^ed over, it must be

minri ihjit they may escape observation owing to difl'erences

I Telocity of reaction, as in the above case,

the two chlurides of sulphuric acid, a chloride of pyroaul-
•ci<l — j'lftostilphnn/l chloride, fi,.0J3U — is also known. It is
hy withdrawing the elements of water (by means of phos-
petttoxido) from chlorosul|>horuc acid, 2S>0.i(OH)01 - H^O =
It is a liquid similar to chlorosuljihonic acid, only more
auc] having a greater density. Its density is 1*82, and its
paint 142 , Its vapour, on being heated, decomposes into
poxi«Ie, sulphur dioxide, an<i cbU^inno.

Her, pyrosulfihiiryl chloride reacts in a manner similar to
chlorides of aulphuric acitl. The reaction does not appear ao
1 in the case of chlorosulphonic acid, because it takes place
»wly.

H. Comfdiiiiig JFeighl nf Sulphur

I. Since sulphur form* a large number of compounds which can

with cjcactness, very varying methods ha^c been employed

rdctermination of this iiupfirtant combining weight. The most

il»er was obtained by Stas by determining the ratio in which

tiled with sulphur to form silver siiljjhide. On the other \va.T\t\,

inin^ f^^ aiaount of silver which can be oblaiaed Itotu i

308

PRINCIPLES OF INORGANIC CHEMISTRY chap.

weighed quantity of silver sulphate, he obtained the data ne
for the independent calculation of the desired number.

For example, by heating 59'4225 gm. silver in sulphur vap
68'2482 gm. of silver sulphide was obtained: the two weights;
the ratio 1:1-1485. Further, 81*023 gm. silver sulphate yie
56*071 gm. silver on being converted to this by heating in a cu
of hydrogen, in accordance with the equation AgaSO^ + Hg = H^SOJ
2Ag. Since in silver sulphide, AggS. the ratio of silver to sulpb
the same as in silver sulphate, there correspond to the amount of i
found, 64*3985 gm. silver plus sulphur, or 8*3275 gm. sulphur, and j
remainder, 16'6245 gm., is oxygen. Since in silver sulphate there j
four combining weights of oxygen to one of sulphur, we have the |
portion 4 x 16 : a; = 16*6245 : 8*3275, and a;= 3206. The mean
of all such determinations has given the same number, S = 32*06.

CHAPTER Xin

SELENIUM AND TELLURIUM

»20. General — Similarly to the triad chlorine, bromine, and
odine, the elements of the sulphur group also form a trinity of
imilar substances whose properties vary regularly with increasing
ombining weight. The analogy of the combining weights is seen, in
lie first place, from the following table : —

Chlorine

35-45

Sulphur

32-06

Bromine

79-96

Selenium .

79-2

Iodine

126-86

Tellurium .

127-6

As can be seen, the combining weights of the corresponding mem-
■^ra of the two groups are very nearly the same. Whereas, however,
ialphur and selenium have rather smaller values than chlorine and
Vomiue, the relation is reversed in the case of iodine and tellurium.

A similarity also exists between the two groups in the fact that the
*8t elements in each, chlorine and sulphur, occur very widely dis-
rtbuted in nature, while the other two pairs are relatively sparingly
^und. Further similarities will become apparent in describing
^lenium and tellurium.

321. Selenium was discovered in the year 1817 by Berzelius in
be deposit of a sulphuric acid manufactory at Gripsholm. It is an
Ument which, like sulphur, can exist in different allotropic forms,
^recipitatcd from aqueous solution, it is obtained as an amorphous red
abstance, and, with very dilute solutions, is got in the colloidal state,
e. it is apparently in solution and passes through a filter.

From comparatively concentrated solutions, selenium is obtained as
bright red precipitate which, even under the influence of the tempera-
L«e of boiling water, cakes together to a dense, black-red mass. At
17 selenium melts and forms a dark, viscous liquid which solidifies,
»i being quickly cooled, to an amorphous mass of a black-red colour,
""hich breaks >vith a conchoidal fracture. If this amorphous selenium
e kept some time at a temperature of 100' to 150', it becomes cryst-
He and grey, with a somewhat metallic lustre. At 650' it boils.

Whereas the amorphous selenium does not conduct the elect

309

PRESCIPLES OF EN'ORGAXIC CHESIISTRY

CHif

extent, the property of conducti^-itr it

fana.

the special peeoliarity is met with, that tit |

" ol gT»t»nine seleniam depeiirls on the illunrnr

it «xpefi(M«B. Its conductivity is all the greater tb

t^ U^» wtiA it rNeh-es. On altering ths strength oftW

in AQ exceedinglj' short time, aiiti hn, \
•ipplimtion to the electrical transmission <i
h. kMB mat jtM been determined on what this p«iu!iimt;
Im U appenn that traces of foreign substances, ntoff
ol tiM arieaimn eoupoonds of the heavy metals v^ki *
urn Mix«d vitk aeleniasi, pby a great part 'I

B amfmmdi, tdeniaiii gna,tly resembles sulphur, for hinirf
mtmimu miid, and tilenk aevi are not only nnalogoir^Iv ««■
to tk* corrMpoadii^ stilphur compounds, hut, in i ;
Iht* • «M0Kr bdnnonr. From the sjiecfnl description of tliu -"

ibcce simibuiiits and differences will become appnttiit
The tmnUmimf wiigid of teleniutn is Se ^ T9'2.

H^e, is » culourless gas itnth a veiy un[jl
, VMsaJKi^ tilAt of ^tearing radish. It is very }X)iBonotis, and oil*
lor Ipocial oare in vorfctng with it. It r&adily dissolves in waict*]
hnn anOBBtw The solution has n feebly acid reaction, and in contact
«iUk t)w air red adeoittm tinickly separates out, the hydrogen oi tk
hydrogtn oombining u-ith the oxygen of the air to (off
» ♦ O, = SR.0 + 2Se.
QwAnCMk aatNiMe is the hydrogen acid of selenium in the

^<iroyB snlphide !S the hydrogen acid of sulphur; il»
ttrtaliira enntnin;: the ions Se" and HSe', both of whirl) s"

._„^ lrt» nits of hydrogen ^elenide are the iiictnllif .vIrniM

rwivw 1,4 tb« t«o coiubming weights of hydrogen, seleniut^

lik,V%lK\W^ k' «Ub«^ mid i\s salts, therefore, contain either two

^' i^H^ <l4 a OMMio^ent metal or one combining weight o{*

^^Wt «tCL. S*l««iiiretted hydrogen can be obtained by '^

tr^Hyw acwia on metallic selenides. The method iisn^

• \\' yxuffDm fcrroiis seleniile, FeSe, by heating selenium fi'''

1 \ h> tK«kt this with hydrochloric acid. In a rafin"'',

(. -i^ma tiv the preparation of snlphuretted h3-di"ogeiJ (P

■ ^UvhI* «ml seleniuretted hydrogen are formed in

I'oSo ^ 2HC1 = HjjSe + FeCI^

Viy^m ifeo «»tntkitM of the tlifferent heavy metuls, sekniiirt** •*
li !■* th* «>rrespondiiig selenium compounds as it"

.«Kt?ss, The compounds of Belenium with sj*''"'
in\ however, readily soluble in water. In tlic *"'
V^VAHk ^ti^>uutJ*.»»i; sunilarly lo seleniuretted hydrogen, so thst «'*'

■I

SELENIUM AJSB TELLURIUM

311

time a red preciijilaio of selenium is ileixjsitetl from their solu-

This property is maile use of for the jmrpose of obtaining or

ifying $elenititn, Tho crude material is fused with Bodium

ide (or with sodium cailioimte, which ficts in n similar manner),

filtered solution of the melt is exposed in shiiUow vessels bo

poiaofious action of sekniuretted hydrogen mentioned above,
itially <in its ready d«?composaLility Uy oxygen. Selenium
»tes out in the tissues in n finely divided foini, iitid ucts
icnjiiviUy ;un! nieuhanicalty ns an irrit<iiit.

Isomorphism. — The seleniuui which separates out under
atluertce of the oxygen of the air on soluble metallic seieiiides is
line, and, un cltjser examination, it is found to exhibit the same
forms as monoelinie (prismatic) sulphur, whtuh sei^arates
the fused m:i88. Further, elemcntaiy selenium ottui's in some
'BstUTolly occurring kinds of sulphur ; it is mixed uniformly with
l\ed ill the sulphur, and imparts a rather dark, reddish colour
Lastly, a large niunber of corresponding cmiijimiuds of the two
ttin exist, himug the same rrifslallme form and capable of forming
sneoiu '^ iiiLrtil rn/sttils," i.f. crj'stals the composition of which is
led by the laws of stoichiometiy, but which, like that of
CAD exhibit every relation within flcfinito limits. This is.
(o the ordinary behaviour of substances which otherwise
rstallise out side by side, so that jmrf crystals of //«« one kind
side by side with pure cryativls of the oihirr kind.
facts are eml>raeed under the conception of ifotiunj/hifni
form). In the first place, two substances are called
when they have the same crystiilline shape and can fonn
reuils. Thus sulphur and selenium are ieomorphou.s in
th«ir monocljnic forms-, lor both elements not ordy erystal-
sly in like shapes, but when they together pass into the
they form mixed crystals of varying composition, which is
iiomI essentially by the relative amounts of the two elements in
»ther litjtLon

ono of the two iaomorphoiis stibstances has the property of

kliising in different forms, thi^ other substance has often the s-ime

and the different forms are alike in pairs. Thus it is to be

that there should bo a rhombic form of selenium correspond-

the rhombic form of sulphur, for such a relationship is found in

ncher ca»es. 8uch a form of selenium, it is true, is not known, .

kturally occurring rhombic crystals of sulphur are found which

Oioro or less selenium. Selenium ia, therefore, capable of

mixed crystals with thonibic suljthur, and from this it may bo

leaj as probable that a rhombic form of scleniunt e.Yigts, although

rtiApei «o little stable under the conditions hitherto etaploy^d

bos not yet been posaibie to observe it.

312

PELNX^IPLES OF INORGANIC CHEmSTRY

Eiements which in the free state are isomorphous with
another, have the further peculiarity that their corresponding
pounds with other olenients are usually isomorphous. Thus,
example, aliuo6t nil the salts of sulphuric acid have the same crysi
forma as the con'esponding salts (j.f, containing the same metflls
having a similar formula.) of seletiie acid. Such relationships
often found, and they are also aometimea met with in cases where
isomorphism of the elements is known. Hence a wider conceptim
isomorphism lias been developeil, and the term if</morj'Jnjus in tht
sense ia applied to those elements which, whUr not fhemjiclt'/i
m/)rj.iln3iig, form munorphi/iis mmjutiimh of lil:c fonstUutirm. Of this
of isomorphism, also, several examples will be. cited later.

Since isomorphism and ijiniilanty of constitution go hand in
the fact of isomorphism can be used in doubtful cases to obtain a
to the formulation of the eorai>ounds of new elements, f.f. to the chi
of the most suitable combining weight from among the
midtiples (p. 144). In former times, os]>ecially, the rolationshipB
isomorphism were of great servico in this direction.

* In drawing sncli conchisions, however, it is necessary to cai
satisfy oneself that isomorphiia.m is really presenL Identity uf
oryatalline system and the possibility of ex^>ressing the forms of
two substances by the same cryatallographic constants within the
of exj>enment, are not sufKcient for the purpose, sinre chance a^
roent could not be excluded in this way. A sure criterion of
isomorphism is given if, along with the identity of shape, the pro;
of forming mixetl crysUils can be demonstrated.

323. Selenious Acid. — When selenium ia heated in the air or

pure oxygen, it takes lire and burns with a blue- white flame, fonnill

leniuro dioxide, HeO^,. At the ordinary temperature this eorapouui

nlike sulphur dioxide, ie not a gas, but a solid crystalline sul«taiU!

Oidy on being heated does it volatilise, without melting, and pass in

a vapour of the colour of chlorine.

Selenium dioxide, further, is formed by treating selenium with at
oxidising agent. As a rule, it is obtained by heating selenium
nitric acid, evaporating to <lryness, anrl subliming the residue.

Selenium dioxide dissolves in water and yields an acid liqi
which contains selenious acid, H.jyeOj,. By evaporation, this cOI
pound can be obtained in transjiarent crystals which, on h(!at)ng, la
water and pass into selenium dioxide.

Selenions acid is not a reducing agent like sulphurous acid. (
the contrary^ it readily gives up its oxygen, and elementfiry solcoJU
separates out. Thus, for example, it is reduced even by thu orgu
matter which is usually present in the dust of the atmosphere, aa
for this reason, the mouths of the vessels in which selenions acid is k$
are generally covered with a crust of red selerdum, and the prepM
tion Jtsoi/ assumes, iji course of time, a reddish coloration.

SELENIUiM AND TELLURIUM

313

redaction of aeleuioiis acid to sekuium takes place very eiisily

ly by tueaiis of auiphuious acid, in accordtitice with the

>n H ,S«0, -r 2 H./>03 = Se + IJ H.SO^ + H.p. The selenium first

out. iji the colloirlnl state, a red coloured, tra.iispareiit l)()uid

formed. On gtanding some time, quickly if heated, Helenium

out fls a brown -red precipitate. This phenomenon can be

identifying selenious acid and its salt*.

U- Seleilic Acid. — Powerful oxiJiainu agents are required in

to convert the anion of selenious acid to the highest sta^e of

m of fielenium, viz. the ion of selenic acid SeO^". The sodium

I abtaiced by fusing sodium selenite with sodium nitrate. The

[yieklB up one combining weight of oxj'gon, by which the former

.ed: Xa^SeO^ + O = Na^SeO^.

free acid is most easily obtained by treating silver selenite

dioiue. Silver l>romide and selenic acid (ire formed in accord-

ith the e<{Untion Ag^SeOg + B.JO + Br,, = H^,SeO^ + 2AgBr. In

jfto e»fTy out this reaction, the silver salt is covered with water,

line added, with shaking, so lotig as its colour disappears.

ai|uet>ii3 aiohiciori of selenic a.dd can lie concentrated by

lion, and a tbicki.sh liquid is finally obtained which has the

2'<; and thi* general appearance of concentrated sulphuric

Tbe pure acid solidifies to cj-yatals which melt at 58 ; the melt-

int is greatly lowered by quite small quantities of water. A

hydrai«, H^.SeO, + H^, melting at 25', is also known.

■ic »cid is distinguished from sulphuric acid by its powerful

1^ itriion ; it readily dissolves the noble metals and evolves

hydrochloric acid, thereby passiiig into sptenious acid —

<- i = ti,8t,-0a + CL ^ H.,0. The salts of selenic acid are

^bous ^{jl 311) with those of esulphuric acid, and also exhibit.

NCilubility relations. For example, its barium salt is just as

Jy iiolubic as barium sulphate, and the Siilte of the two acids

be readily confoimded, In order to identify selenic

Bocc of sidphuric acid, the liquid is previously treated with

»g agent. The former is thereby reduceiJ to selenious acid or

wUile the sulphuric acid remains unchanged, and can be

irnr«I as such,

.Chlorine Compounds of Selenium. — Of the remaining

of dfh'ijitim, t'Jruiiiiii h!niclihiritle has still to be mentioned.

kita^ crystalline sultstancc with the formula ScCl^, and is easily

by beating selenium in a current of chlorine. On being

is converted ioto vapniir without previous fusion. With

selenious and hydrochloric acids, in accordance with the

C1^ - 3H,0 = KpeO^ + 4HC1.

--' "^'h ni\\)hiit tetrachloride (p. 304), which is exceedingly
the corresponding selenium compound may be termed
ibJc 6utisunc€. Tbjg inavase in tfie stabih'ty of the cb\orwic

PRmCIPLES OF INOIiGANIC CHEMISTRY

compounds forms a mafketi contrast to the decrease of the stabilit]
the correspomliHg oxygen and hydrogen compounds.

Besides selenium tetrachloride there also exists a seleniutn
chloride, Sc^Cl.,, corresponding to sulphur monochloride. T
dark red-brown liquid from which, when heat^, aelenium tctnu!
escapes while aelenium remains behind — 2ScjC].^ = 3Se + SeCl^,
stability relations are, therefore, different here from what they
the case of sulphur, where the tetrachloride decomposes into
and monochloride.

326. Telluriuin. — While iodine is very similar to bromine,
in external a[jpijarancii, at least in the nature of iIk corres
compounds, the differences between selenium and tellunum are
pronounced, 30 that it has repeatedly been regarded as di
whether these two elements ought to be regarded as membera
same family.

Telliu-ium is a greyish white substance with a metallic 1
density is 6'4, and it conducts the ek-ctrtc current like a me
melts at 450 , and boils at 1400': The vapour \s oidy sliglitly
than coi'responds to the formula To^,

The annhininr) imrjht of tellurium, Te=127'6, is, as has
Ijcfn mentioned, greater than that of iodine, whereas the cci
weights of the other elements of this group aru smaller than thi
the corresponding halogens. Many investigations have therefore
carried out beeaiisc it wiis believed that tliis dcvtatitm was
incorrect determinations ; it has, however, been found with ci
that the numbers art^ as stnU-'d.

Bi^sides the metallic tellurium, there is also a black, apjiarcnl
amorphous form, in which tellurium is obtained by precipitation it{
its solutions. It has a considerably smaller density.

Telhuium coralnnes with the nietala to form tL-Uurides ; tb
correspond to the sulphides in composition, and have geiieralljr
metallic appearance. The telluridcs of the alkali metals nw sohihlft
water, ami form the ions Te" and HTo'. From theso tellui-iiini sepaiH
out under the inHuence of the oxygen of the air.

Tellurium hydride, H^Te, is obtained by tho action of the stM
acids on telltu-ides ; it is a gaa possessing an oH'ensive smell
poiKonoMa properties, behaves similarly to the hydmgen compoui
of sulphur and selenium, and in n<|ueous solution is, like these, read
decomposed by tho oxygen of the air.

Heated in the air, tellurium burns, forming the rftojn'J*, wh
is a wtite substance volatile at a red heat. Tdlnrmis aeXd, HjT«(^
obtained by o.vidising tellurium ivith nitric acid. It is a wliito
slightly soluble in water, and has only feebly acid properties. W
strong acids, the compound behaves as a base, hydrnxyl be
eliminated and a salt formed. Compounds arc hereby pro<liire(i wh
are derived from a tetracid biae, Tc(QH.^^= Ll^Te0.4+ II n T

SELENIUM AND TELLURIUM

aUoi very unstalile towards wa.t*i-, just as, in fact,
ich can act both as baee and as acid yield in both
i^only slightly stable compounds.

« acid CHti be converted into Mfitrv' acid, H,T«0^, liy

uli^iiig agents. This has no similarity to siilphiu'ip or

UteaA, for it forms a crvstalHnc mass, difficultly soluble in water,

Kflsin^ fct'bly acid propi'rties, The crystals which can be

from wator have the tompoaition n,.T«-'Oj + 2H^0 - Te(OH)(,,

beating;, pass first into the acid II.,TeO^, and then into ^the

de ToO,. The latter is a yellow mass, which is indifferent

•wnter.

c acid also exhibits liasic properties.

therefore, the oxygen eompoiindi^ of tcilurium agree in

uritb those of sutphiu- and selenium, their I'hfmiiuil Ufmamr

♦iifft'reut. It is, it is true, a general phcMomeiion that the

wiUi higher combining weight form more feebly acid or

Irongiy basic compounds compared with the relnted ch.uuents of

eombining weight, but it ia seldom that the phenomenon

tte Ap|>eiirance so abruptly as in the present case-

ly, it has to bo mentioned that tellurium combines with
iC to form the roiupftuiulB TeCI,, and TeCl,, and with bromine
TeUr, and TeBr^. These are crystalline substances, vola-
tbout decorapositiou at moderately high tempeiutures, and ro-
irag in i)!0[>erties the halogen compounds of the metaU, cj, of

CHAPTER XIV

NITROGEN

-327, General. — As was shown on p. 36, there is present in tl
besiiies oxygen, another substance which constitut.«s the gi-eat
both by weight ami by vohime. From the fact that the residue i
air after removal of tho oxygen can support neither combustion ne
it was called a:uk, but it is now call^ nilrof/tn. Its chemical sj
is N, from nitrogenium. This narae is due to the fact that nitr
an essential component of saltpetre (nitrum). Its combining wo^j
N- 14-04.

The properties of nitrogen are essentially those of the air
those due to oxygen. Thus, it is colourless, odourless, and only sl^
.soluble in watei". Its molar weight is 28 ; as gjia, therefore, it ha
formula N.,. It is distinguished from oxygen essentially by thai
tbiit it ia capabte only in u. very slight degree of reacting chei
with other Bubstancos. There are only very few substances whic
unite directly with nitrogen. If, however, the nitrogen haa
into combiiiiition, the subatfincea which are formed show a very i
siderable variety and power of transformation, so th;it the range
nitrogen compounds is a large and important one,

C6Mpoun{hof /lifrofjen arc of frequent jjecurrence both in the mii
and, more especially, in the organic kingdoms. Of the former
may be mentioned the irapoitant grou]>s of nitric tuM nnd nmin
ttese will presently be discussed in detail. In the organic king
nitrogen is in so far of egpeci»l importance as the substancM
which the phenomena of life are directly connected, and whose pt
appears to be necessary for the processes of life, vix., the a^/umin
all contain nitrogen.

328. Preparation and Properties. — In order to obuin nitr
it ia only necessary to free the ordinary ah" from the o.xygen it contJUB
For thi» purpose, metals arc most suitable which combine with oxyg
and yield solid, nnn-volatite oxides. The choice ia somewhat limite
from the fact that those nietiils which decompose water niu»t
excluded. These would form, ivydtogew ^tota t\v.ft tCMes of

avft

NITROGEN

3i:

prM6nt,aTi(l this would coiitamitiute the nitrogen, and could be

from

rogeii
niy with difficulty. The necessary

condi

ntions
iinited in capper.
current of air bo passed through a tube filled with copi>er in
form of turnings or of thin wire, and raised to a medium red heat,
np all iu oxygen t^j tbo copper and nitrogen escapes and cain
' eoQeeted over wnter (Fig, 02). A colourless gas 18 obtained, with
it 18 easy to tlemonatrnte the property that burning siibstancea,
f wood bat aleo sulphur and phosphorus, are extinguished in it,
densUt/ of the nitrogen so obtained is rather great-er than that
sn prepared from its compounds by chemical reactions. This,
, puzzling phenomenon has been explained by the fat;t that
r-i ' there is present in tho air a heavier gas which com-

iri. . f just as little as nitrogen does, and therefore remains

vnth this. This was separated in the pure state from

fio, K.

lerie nitrogen by Raylei^h and I^maay in 181)4, and has beau
to l>e an ulementjtry substance. It has been called artjon.

density of pure nitrogen btands to that of oxygen very nearly

nkUo 7 : 8. Nitrogen ia, therefore, the lighter component of the

tlicrefore, lighter than this itself.

— 19-1 , nitrogen can be conderisetl under atmospheric pressure

leotonrleos liquid, which at - 214' passes into a Boiid, ice-like eub-

tbe temi)erature is higher than - li6', gaseous nitrogen cannot
to aasujne tho liquid stat* by any pressure ; - He'' is, there-
I Um criiietii tfmperntiire of this substance. The criikitl jnesiuyc, or,
iro at wbifh, slightly below - 14G', condensation can stiU be
■iDDUnts Uj Ho atni.

lical criteria, by raejuis of which gaseous nitrogen can be con-
■ distinguished from other gases, scarcely exist. In general, one
ent to regard aa nitrogen, gases which are neither coiiiV>\i&l\\At
sujiport combustion, and which do not combine with TCifetsX*,

318

PRINCIPLES OF INOEGANIC CHESnSTEY chaf.

phosphorus, and the other reagents for gaaea which are in use. Sina
us has Ijcea mentioned, free nitrogen has little tendency to take pi:t
in chemiciil resictiona, it is generally of no great importance whellie:
nitrogen is present or not ; it acta only as an indifferent diluent (m
tho other gases with which it h associated.

If nitrogen, tinder a small preaaure, is rendercrl lunainous bv u
electric discharge in a tube arranged for that purpose (p, &71

^ctruin of numerous lines is observed which ia more ca^
■characterised by the appearance of bands shaded away on one
These consist of numerous fine lines which, on the one side, are cIokIj
crowded together, and on the other side are regidarly arranged furtha
a!id further apart. By means of this phenonieuon, the presence of
nitrogen in gases can be recognised with compmrative case.

329. The Air,— Although the air by which we are emroiinded is
a mixture, it has to he t^ikeii into account in so aiany phonomena thiU
a special discussion must be devoted to it here.

Air consists, in round numbers, of 0'21 parts of oxygen and OtS
p&rta of nitrogen, by \-ohime. If these volumes are midtiplied by th*
densities of the two gases and divided by the sum of the two numbers,
WQ obtjun as the proportions by weight 0'23 and 0"77 respectivelv.
The numbers are not perfectly constant, since proceaaes are continually
taking place in the air which tend to alter this ratio. Close investigi-
tion has, however, shown that the dift'erencea which nctually occur
move irithirv very narrow limits about the muan values, oxygen O"210,
nitrogen 0-7SI, argon 0'00& ijorts by volurat'.

The influences which tend to alter tht- composition of the air con-
sist, on the one hand, in the vnlkdrnwal of o-ri/ffcn by oxidations of sli
kinds, i.e. by rapid and slow owfjudidrus. On the other hand, ^t^
planis have the property of giving off oxygen to the surrounding m
and the almost constant composition of the air which is obiserved isM
expression of the fact that thesr. two opposed actions exactly colitite^
balance one another.

If one considers now, that the processes by which oxygen i*
removed are concentrated in the large towns, where, conversely, tbe
evolution of oxygen is very small, whereas, on the other hand, tk
evolution of oxygen by green plants occurs oidy in summer and during
the day, one might expect much gieater dilferenccs than actiwDy occur-
The cause of the ecpialisation is to be found in the great minvmaiH
which the ocean of air constantly undergoes. By reason of
the one-sided actions do not take jjJace on one and the same isol
portion of air, but are distributed over large and varying amountt
which stream pist over those different lucahties. These movement*
also produce an effective mixin-g of the different portions of the air, 11*5
the comparative constancy of the composition of the atmosphere is tin
result.

On account of the fact that the ratio of the volumes approximal^

NITROGEN

onnd uuin)»er 1 : 4, tho supposition has sometimes been
. that the air is a chemkai rxiui/».mnti oi thu two elonients.
' is iTTong, for the properties of the air are those which follow
proportiea of its components oti Uiking into account the pro-
of mixiiig. A chemical compoiiud, however, is characterised
let tliat its. ])ropetties are esaenLially different from the corre-
me»n valuus of the properties of its uoniponeiits.
«?xntDpIe, air alters in composition on being dissolved in
pcc oxygen dissolves to a larger extent than nitroycn. The
in wluch the two elements are present in water saturated
0-35 oxygen to 0*65 nitrogen. Further, the comjionents
can be se]mrated liy diffusion (p. 93), although not very
\y, since the two densities are fairly close to one another.
5S the tiro gases mentioned, the air also eoiitains as regular
its tvnifr ntfMiiry arijuii, and atrlxnt iluixidf. With regard to
the necessary data have already been given (p, 125); the
BtAOces will be discussed later.

W/k^ of the air can be performed in many ways. The
^^^nbed above ({>. 'il T) can be developed to a <piantitiitive one,
Bd in Fig. 92. This is done with grejitest accuracy by bringing
to a si»tee shut off by mercury, measuring the prcaaure, tern-
atid volume, and then removing tiie oxygen by means of a
bopper wire raised to a red heat by an electric current. Aft«r
he three magnitudes are again determined, and by this means
Dt- relation is obtained.
1>3 au apparatua coii-
for this purpose is

of glowing copper,

hu»D be used. This

^^■Uitagd tliat it re-

Ba oxygon very com-

rotn the air even at

mrj t«mp€ratur«j. The

m is introduced in the

thin rods into a gla.ss

I of the form .4 ( Fig, 94),

alM> completely filled

ter to the jHtint a,

r to be investigated is

4(Ute<) tube,

7>'i which is

1 with the iihsttrplion

hy Duuw of a narrow

xjumng the pressure

320

PKINXTPLES OF IXORGANIC CHEMISTRY CHjrJ

the phosplionu. Wlien the absorption of tb« oxygen is completed,]
the nitrogen is returned to the gas burette br the reverse prooen^ <

is there measared
the atmospheric pressoiftl
haa been re-establidbed lifl
bringing the water Icfs
ill Is and D to the fam$1
height

A third method, git-wj
more than a hiuidr
years ago by Volta (tk|
inventor of the Tolt
pile), depends on
oombination of oxjg«
with hydrogen. The
is placed over mercury^
in a graduated tube, iiiti
the upper end of wliidlJ
two platinum wires
fused ; the volume,

FBure, and temperatLire are measured, and hydmifii then added. B]
repeating the measurement, the total volume is ascertained.
allowing an electric apark to pass through the mixture, the oirgeu
combines with the hydrogen, and the former entirely disappoare
Bufflcient hydrogen has been added. If the gaseous residue is now
measured, ^rds of the voltimc which has disappeared consists
hydrogen, J^rd of oxygen. The amount of oxygen, by volume, in
air examined is, therefore, obtained by dividing the dttninutioii <il'
volume, after explosion, by ,3

Great importance was formerly attached to the determination ol
the amount of oxygen in the air, because it was believed that on il
B depended the good or iU health of man and beast. The fact, howev«r,

I that the variations which occur are very small, and that the volunwi

I concenti'ation of the oxygen in the air is altered much more than th»

^K amount of these variations by the comparatively small chiinges in tbs
^H presHure of the air and in the amount of vapour it c-ontains at different
^^m timeij and at ditlbrent heights, has led to the couviction that sucli
^™ inrtueitces arc not appreciable; the analysis of the air has therobj I
I much of its former interest.

I 330, Oxygen Compounds of Nitrogen.— The number of com-

I pounds which oxygen (partly along with hyclrogeu) is capable

f forming with nitrogen, is very great. Instead of treating thi

strictly systematically according to their comprtsition, it will be m
e'xpcidient to first cousidtT the most important and most wideU* distn-
buHad of them, from which the majority of the compounds are formed<
These are nihic acid and its salts, the nitriitr?.

NITROGEN

321

nit adtf u an aeiil of the conijiosition HNO.jj it contains the
tnonovAieiit itittanioii, NO,,'. Its occurreiice in the free
in nature is exccptioual, for the reason thitt it ie a strong acid,
, tlkerefi>re, at once forms salts. Atl the more freijiieut and widely
ited art* the salts of nitric acid, oi" the nitrates. Sitlljteiie, or
nilnkte. KNO^, has (teen known from ancient times, and
in th^ earth in places where nitrogonous aiiiniiil substances,
lly animal excremunta! niattt^r, is subjected to the action of the
licric oxygen. It can lie readily o}»tained by extracting the
itli water and evaporating the solution. Scdiaiu mtraie,
knavru as ChiH snltjtfiri; is found accninulated in the rainless
of Chili, and serves as the most imjiortant auuree of nitric nciil
its derivatives. Finally, it baa to be mentioned that the
oxygen, and water in the air can, under the influence of
processes combine to nitric acid, which is, therefore, not
lUy found in the form of its silta in rain-water, although in
11 jtmoimts.

nitric acid, HNO,, is obtained by diBtilling its salts with

ic acid. The con-esponding sulphate is formed, and the nitric

rhich is readily volatile, can be distilkd oH* from the non-vohttile

With sodium nitrate, the reaction takes plaeo according to th«

ZNaNO, + HjRO, = SHNO^ + Na,SO^.

ihia CAse, also, the process takes place in two stages ; acid
salphatc is first formed (p. 293), NaNO,, + M.^SO^ = NaHSO^ +
and the oth.-r reaction, NallSO, + NaN(.\ = Na^SOj - HNOj,,
'place only at higher tt'mperaturos. Since at the temperature
for thii I lie nitric acid ia unstable and decomposi's into other
«, it is usual to take the components in accordance with the
pATtial reaction, nilric acid being obtained along with acid
culphatc Likewise, it i* eustomaiy to add a little water to
tone acid, as aqneous nitric acid does nut decompose ncaiJy so
|eii U&'ited im the anhydrous acid.
uver, by carrying out the distillation in a rarefied atmosphere
temperature (p. 160), the above disadvantages c^n be
lo the maniifacturea, almost pure nitric acid is prepared
)arg/t scale at the }>resent day by lUatittatiori under reduced

nttnc add is a colourless liquid, with a density 156, and
H6\ It does not keep well, for even under the influence of
: decomposes into oxygen and lower (/.r. containing less oxygen)
bxukIa of nitrogen^ which dissolve with a yellow colour in the rest
laciil. Addition of water makes it much more stable. The cause
ia ihr same as that previously given in the caae of petcMoric
2S3); nitric acid has a great tendency to form ions, and, tWre-

322

PKINCIPLES OF INORGANIC CHEMI^TUY

foie, prcMiesses by whicli water js pr'«Jnced from the acirl, uke '
with especial readiness. This in what oceitra in the decomi>osit'
nitric acid under tin' iriHiumcc of light, for the hydrogen of
thereby passes into water.

On adding increasing tiniintitles of water to the acid, the

point of the latter rises not only to that of water but conaid

higher. The highest boiling point, 120" under atmospheric pf

is poBsessed by the 68 per cent acid. On further addition of

^'th© boiling point again sinks, and ultimately reiwhes tbut of wat

The relations which obtain here are therefore perfectly «ij
those in the case of hydrochlorie acid (p. 184). In thia c^ae
mixture of 0*58 nitrie acid and 0'32 water, which cor
approximately, to the formula 2HN0j; t 3HjO, niuat not be re|
as a ciiemical compound, for its composition changes witli the pr
In this case, indeed, the acid is all the more concentrated the
the pressure under which the flistillation proceeds.

331. The Chemical Properties of Nitric Acid.— The prop
which are possessed by nitric acid, tis an itiid, must be distingoB
from those which ptTtain to it iii respect of Mrr deeompositi
The former dej>end, as haa previously been expldned (p. 24.'i), i
ally on the degree of olectrolylic ijisaociation ; the otliers, htfcit
depend on the composition and the atability of the anion, and ff
imdissociated aijid.

With regard to tlie first point, nitric atid belongs to the stran
acids, and, in thia respi-et, ranks along with hydrochloric acid. Ac
Ingly, even at great dilution, it has an acid taste and reddens lit
Likewisi', it readily attaclcK and diasotves metals. In tins easi%
<!Vfr, hydrogen is freijucully not li^H'iated, but combines with,
oxygon of the nitric aciil to form water, corresponding rtnluctio
ducts b*'ing thereby formed.

Since the dissociaiiun increjisea with dilution, the geuer
properties of this substance will become moiit prominent in
solutions, whereas, on the other hand, the specific actions whict
jUBt been mentioned will be chiefly found in concentrat<i.l solut&

As can be gathered from the stjitenieiit made tt]>ove. thi
(litric acid d('eonipa.ies even uiuler the influence of light, this siil
belongs to the same type of uoisipouiida as ozone and hydf
peroxide, viz. compound!! which can give up oxygen and pass
more atablc subet'tnccs, and which, therefore, act as strong "jidii
itffmU. As a matter of fact, this is the most prominent propertfl
nitric ticid, and moat of its applications depend on it.

This property of nitric acid first became known in the ca»e of |
action on the nieuds. There are a number of metids, such as cot
mercury, and silver, which are not dis.solved by dilute acids. Onl
other hand, they are precipitiUed from their salts by hydrogen.
rjiiise of this Iie.s in the very diffeveia towdvUoTvR v\t\iicr which che

XTTROGEN

323

between llitr nu^tals, thi' hydrogen ami the ions, is estab-

Sinct* a substance acts rtll the more strongly, i.e. has a gi-eater

cy lo dieappear as such, the inort.- coiicenirjtLni it is, it can Ix'

that all metals will he precipitati'd frtrni their salts by hydrogi'Ji,

9 fnij.»!oyed in suiUible concentration. Such <* reaction as

>i - ZnSOj + H, could tiiea be reversiul, so th;it zinc and

ic aciil woiiiil be produced from zinc aiilphati- and hydrogrn,

diffeivut mctiils, now, are; distinguished by the diii'ereiit con-

of hydrogen retjuireil for such a n-action. Whereas, in the

xinc, it Would t(?4iiiri' to bf vt-ry ^eat, since, indt-ud, the

sition of the acids by this metal takes place so easily, it wouhl,

other hand, !h' VQvy small in the ease of silver, for hydrogen,

Jcr thf ordinary juessur^, anri therefore of the eortespondingly

mccntraliun, is ^^nilicicnt to precipitate silver in the metallic

Mil its salta. All the metah Ctiu, aecordin^ly, be arranged in a

be^tiinitig with the metal which reijulres the .greatest concen-

uf hj'drfigen for its piceipitation, and ending witb that which

iuni with the most dilute hydrogen. This series would be

lily divided into two (jjirts at that point at which the eon-

of the hydrogen eorre.-fponds exactly to one atmosphere,

it is tnie, an arbitrary choice, but it correspomis to by far the

numb«r of eases in which the beliiivioiir of tlio metala is tested

le» mto «iuestion.

_tho Hrst division, that of the metaU which evolve hydrogen,

the first place, all the light nietala, and, of the heavy metals,

»gin;4 to the iron groiift. The heavy metals of the other

belong chieHy to the second division, but tin is an exception.

sUuids on th"* border. These r«lations wilt be more fully

Uiitler the different metals,

metiils, now, which are not dissolved by dilute acids with

i»f hydif)j;eti, are, for the most part, readily dissolved Ity

This is due to the fact that the nitiic acid converts the

which i« first fornred in the fiction, although only in

irahly minute traces, into water by oxidation, and removes

pforr, frr*m the sphere of action. In other words, its action ie

itajn an exceedingly ^mall concentration of hydrogen, and

nwikti it (Missjlile for more of the metal lo piss into solution.

arc j*lao aotne tueuds, aiich as jiold ;mil iftatinum, which are

HiUed by nitric acid. This depends on the fact that even the

m>ntnition of hyilrogeu nbtaineil by mcjuis of nitric acid, is

to allow of a reiu'tioM tsiking place in the sense of a displace-

Jrogcn. In oixler to dissolve such mi?tids, stronger uxidis-

are re<|uire<l, hy which a still .snudlcr conei'iitration of

is achievMl.'

U »!•« oldalnw) with more ftelile ".xiiliaiag nui'iti. nrovi(ln\ \\\v. jt«»t>ict
]h /mrUimhrlr »utilr- We tball enter mto thU iit ti jHter time.

^^'••-'-^ e 3'»'e.A5'IC

NITROGEN

325

1, «inoe other oxidiaing agents (ajt. chloric acid) also decolorise

untuutAkalilp test consists iti the dark colomlion produced by
lt6 in li^iinck containing nitrates. Tlie theory and practical
of this reaclioti will be given aonjew-hnt later in connection
oompount! litre in i|ue5tion, viz, nitric oxide.
mtaxigen Pentoxide. — If pure nitric acid l>e treated with
»g agetil*, it loses the elements of wat*r and pusses intri
le <p. '2\'i), in ficcordanco with the cquatjon

2HN0.,-H,0 = NA-

effect this reoctiun it is not suflicient to use sulphuric iicid, Imt

p**w«rful desiccating ugenl known, viz, phosphorus pentoxide,

eiupluy«d This suhstance, which we shnll soon deatribe more

u a white, snow-like powder, obtjuned hy burning^ phosphorus

air. If this is added lo nitric acid contiiined in a retort, and

ttonc distilled after some time, the anhydride of nitric acid

orer as .1 rnoliilCf verj' volatile liquid, which soon solidiiies to

cJ-y»t--dlinc substjince, melting at 30 . This is exceedingly

and decMfnposes qiontaneoualy into oxygen and nitrogen

: 2NjO. = 4X0j + (X. The ilecnmpoaition, nlsu, is not pre-

by sealing up the substi^nce itj tubes and thus protecting it

aiCtion of the air ; such tubes usually explode after some

the preeeure of the gst&eous products of decomposition has

; great enough.

penujxide dissolves in water, with formation of nitric
expressed in the above equation taking place in the

334. Thermochemical. — The heatof formiidon uf solid nitrogen

linie Lt 5J kj, ihai of the gaseous, zero. On flissolvirig in water,

are developed, two moles of dilute nitric acid being thereby

We have, therefore, the equation 2N., + 5(\ + aq. =

!■<{. + :i X 1 25 ^7. If it h desired to refer the heat of formation

fUdd to the elements hydrogen, oxygen, and nitrogen, the

ilioD ui water, 2li, + 0„ = 2H,,0 + 2 x 280 kj, liaa to be

Aod there is obtained

H., + N, + 30j + aq. = 3HN0., at|. + 4 11 ^7.

teal m formation of one mole of dilute nitric add from hydrogen,

oxygen. And water, is, therefore, 203 Ig.
15, Nitric Oxide. — Lower oxides of nitrogen are formed by the
_g| totric iK'jil un copper or other metals. The nature of this
already been explained : it depends on the fact that the
of the nitric 4ieid which is replaced liy the metal combines
be oxygon of another {xirtion to foi-m water. Variovia products
lion Are here formed, acx-ording to the nietals, tho tempevaUxifc,

WVB

PRINCIPLES OF INORGANIC CHEMISTRY ciur

ift peculiarity of nitric acid of dissolving silver but of liMTri^
twttocked, is iised for the separation of mixtures or alio)* '
■o metals : on treatment witli nitri(3 aciii the silver [Jits-sps inltj
n, wUerens the gold remains uiidisaolvcd. On acfount of iU
I |K)wer, this acid wiis culled (ttiua Joitis bj' the abhemists,
liose metals which, like zinc iiiid miignesiutn, dissolve in lUuul
irith evolution of hydrogen, are also dissolved by nitric udi]
t« of the fact that they are diasolverl, the evolution of bydnige
se caAes api>eiirs greatly dindnisbed. This also is duo to
at the hydrogen combines with the oxygen of the nitric ttsU
fjiter ; in this cjise, however, the removal of oxygen goes furth
I pUce of the brown, gsiseous products of reduction, corapou
"ogen are formed which contain hydrogen. These have
ties, and remain, therefore, dissolved in the acid lirimtJ,
ion of salts. The last product of thia reaction is nmm
wilt be iliscnsaed firi'ther on,

2. The Salts of Nitric Acid. — Nitric acid is a niKnob
uid furni.'* otdy one class of salts, namtdy, monovalent null
lite of the funiiula MNO.[, divalent metals, salts of the formlj
I,),, etc. These salts can be formed in all the ways we liavtj
• in which salts aie formed ; for example, by the action of nitt
[UuBS or hydroxides,
nitrates all have the property of Iiein^ more or less
water, so that no precipitation reaction is known
j'By refwon of the large amount of oxygen they cojit^,
when thrown on incandescent charcoal, i.e. the
at the expense of the oxygen of the nitrate, rai
wmbincd with \'ivtd production of h'ght. The ox
iSfj the lie^t, for although the nitrates are much more i
_ »rid. they all cxhiliit the property of decomposing I
^^01 kJ^ t^nifMMiitrires with evolution of oxygen, the nrtW
^L^^i^ily remattting behind w oxide.
^^^^^ rannirtaiil iipplicaltiuis of the nitrates, also, depcit*
■^V^ :bey give up oxygen. These will he

Iff" .lis under the respective metals.

!-.. ijf nitric acid and of the nitrates de
.-a nitrat* is

id iJ

to ''
^ via. ^
able sut-

As A «)"
£id, and roo*
is yroperiy oi
on tlie metals,
ry, and stiver, v^
hand, they are pi
of thisUesin the v

I ia oxidised,
are evolved as tn

■Mantities of NO,'

vestigivted witl i

I be recognised

iP, and which is

i products. If,

a when heated, the

iL> teat is, however,

air. If tUa ii MUsd to aitne and flMiiciii is a ratart,
Xtore <^i)rfi!l«id ilter «cae tame, the aahjdridA of nitzic
tover as a mobile, ti0j Tokde bqndd, vUdl
^ etyttaUine whiifiiffr, aoila^ at 30 , Tkk k
«. aiid deeoatpont ■jwiiaiwMij iato a&j^ai
U: 2>.0^ = 4KO,^Of The iliiiiiiai|H«riM, dM^ in sot p«-
b^ ietKiig iq> the ariaNnrt in wtitii and
IB actaoD ol the air: Mid tahei ■■■Jly' iiipln4« after
riien tbe prciaiire fd the gMeoot prodneu of (kcoaqiontnii
great enou^.

atigen pentoxide (tiawliia ta water, with btmutioa ol nhzie
procew tspnmtA in the above en»at»on taku^ pbee iti

3:t4 Tbemuxhonial— TheheatofiorMatioBofaaiidi

kle is 5''i ^y. that at the j^niinm, aenk. Oa diwuliiug m
(uw derekiped, twu owies of dflate nitric add beiiig

We h*Tc iherelort, the eqfoatMCi SN, + 50, ■*■ af|. =

aq. -t 2 X 125 iy^ Ii it is deored to refer the beat of fonutioa
ie acid to the eleaMBtt hjdiogiBB, azyges, and nitrogen, the
: foniutioD of water, iU, + 0^= iHjO + 2 x Sg6 ^, has to be

and there i» obtaiiied

Hj + Nj + 30j -H aq. = 211X0, aq. + 41 1 i^.

formation of one aiole of dflate nitne add fran bjdmgen.
T^iren, ADfl water, i^ therefore, 305 Ij.
tic Oxide. — Lower oxides of nitrogeo are loraied bjr I
foitrjc M-i<J vn copper or other metals. The natim of/
bm atraadf been ejcplaineti : it depends on the fact ihaE
of the nitric acad which i» replaced by the metal cc/aA
oxjgen of another portion to fiorm water. Variotu prod
ion are here fortnefl. according to the metaia^ the temperati

328

PRINCIPLES OF INORGANIC CHEMISTRY

the vapour is black-red and almost opuqut even in thin layer
lowering tfie temperature and iricrwisiog the pressurej tbe fur
colour retuniii,

* Tlieso rc5atioTi8 ciin be easily made clear by filling two
tubes of ttbout 2 cm. diameter with the vapttiir of nitrogen {)(
under the same eonditions, sealing them off, and heating one at
Whereas tbe tnbe vshich is kc]5t at tht- onlinary temj>erature
pale brown in culonr, the heated one soon acrpiirea n prono!Uic
€olour. The comparability of the two tubes is assured by ib
that, mvdef these conditions, both tontaiu the same amount
stance independent of the temperature.

These phenomena are explained by the fact that there
different compounds of the stime composition, which are [wly
the one containing twice as many combining weights of the
com]«onent3 as the other. In accordance with the derssity, the in
has the formula NO^, the otlier N^O^. The former is dark coli
and is formed at a high tempeiitture and under a. small jiresaai
latter is almost colourleai?, and is formetl from the former unci
lopposite conditions. Under all circumstances, tbe vapour of nit
peroxide is a mixture of the two forms, and the relative aniouu
tiiese can be calculated from the density of the vapour.

* Thus, at TiO" and 4y'8 cm. pressure, the motar weight

been found etjiial to 62. If ar be the fractiun of the total

by volume formed by NO^, that formed by N^O^ is equal toj

and a mixture of the two has a molar weight I) = 4Gt4-(1

92 - D
Hence, x = — -- — , from which, substituting the value of

a; = 0'65, I'nder the above conditions, therefore, the vajvour
tained 0'65 volumes of the simi>le compound and 0'35 volui
the double comjHTund. Since the weight of the iatter te equ
070 volumes of the simple one, the fractional imionnt of the siin|

confound by weight is ^yTjT^--o.-o = 0-^»-

Theie exists, therefore, between the two forma NOj and
rhrmiml efpnlilirinm, in consequence of which the relative rpn
of the two forms are dcteimined by the temperature and pr
If two of these magnitudes are given, the third Is also fixed, i.e.
givfo temperature and a given pressure only one definite ratio
exist between the two component?, On the other hand, a yierfe
definito temperature is required if it is desirctl to obtain under a gii
pressure a given ratio between the components.

The law winch fhis eqitUihnnm o}iey» la expressed l)y the forrod

a- lb = k,
where a denotes th& concenlrat^ow ol "dwb tatuv ^O.^ -Mvd 'i thnt 'i'

NITROGEN

329

N,Oj ; !• i« a niagnittido which is depeudent on the temperature,
bicli, at constant t^mperamre, is constant. It is, therefore, idso
the fipulihrium ritnjttnni.

htm is understood the calculated amounts in moles of
CM present, divided by the volume measured in cc.

■ ^luition shows that when the codcentfstioii of the two

1* ii'd l»y increasing the total vohime, tho ratio of their

liueo uot reumin unchanged. For exiinipk*, if the volume is

incTBMed that '( diminishes to liaif its value, b must alao

not to hftlf but to a fourth, in ord<^r that the eqiiaticiii may

In other word*, on increasing the volume, ty. diminishing

a portion of the form N^O, must change into NO^, as

alwve &s the result of expi-ritiient.

we reflect that by the chan,ge just mentioned of the more dense

ihv le?*« detiMt; form, tht? jires^un? must liecome greater than it

lie if tin* chaiif^e did not occur, we see that the formula stated

is a restatement of the law wliich waa given in a qualitative

m Pi 2^(4 ; namely, fhrn a stf^fcm tiHdenjws clutngf, tht jrroctss

ioAkA opfioD^s i/iis fhange. If the pit^ssure is diminished, u

of the denser gas decotnjwses and again jiurtinlly cancels

iiiutiou of pri'ssiire. On the othi;r tian<l, if the volume is

ed, the pressure does not increase in the jsame proportion as

■ingle gaa. but a |>onion of the NO^ polymerises to N.,0^, and

ure caiuiut l)econie so great.

«T, it ha« been established that heat is developed in the

Ion of NOj t« N,0^. In accordance with the same principle,

if the tcmpcratiire bo raised, that process will occur which

tl»e rise of ternfifRxture, Kf. NX\ will decompos« into NO^

this process absorbs Iii>at. This crmclusion is also borne out

ta«ut.

Tkg fifrftantiioit of Htlrofien j>eroj-iile can be carried out by means of

thnd jilrcady mentioned (p. 326), by converting nitric oxide into

u by means of free oxygen. The brown vapours obtained by

on of nitric acid on metals, after having been drii'd, are passed

"tb oKjgt-n through a freezini; mixture, the current of oxygen

rogulalcd that it is prespnt in excess. The substance obttkined

ly punfidi by n>-diatilhition.

For th« preparation, also, use is mmie of the decomposition which

'■'' nitrates undergo when heated. Lead nitrate, for oxaniple,

II peroxide, according tu the following equation : —

2?bfN0,). - 4N0j + Oa + 2PbO.

A« htL» been alrearly mentioned, the peroxide dissolves in water.
»f»«« proCHS, however, it does not remain unducomjMised, but reacts
til th« elemeiilA of water to form nitric and nitrons acids —

I'm, ^ HM = HSO., + HNO.,.

330

PRINCIPLES OF INORGANIC CHEMISTRY

* Ttie heat ot formation of nitrogen peroxitle in its
foi'rn NO^ iiiiiouiits to - 32 kj ; it therefore absorlia energj'
forniatioti. In passing into the other form, N(,0^, heat is dereti
2 NO,, - N^O^ + 54 f.j.

337. The Law of Mass Action.^Thc relationships which
just been at-t forth form a special case of a genera! law which
all chemical states of equilibrium. It can l>e expressed iu the
ing form ; —

Let a chemical reaction between w^, w.„ . . . moles of the
stances A,, A,, . . . and «,, n.„ . . . mole.!; of fi,, B.,, . . . U
sen ted by an eijuation of the form

H'jA, + in^A^ + /":,A3

- «jBj + K,Bj + TijB^

then equilibriiirii will exist when the concentrations «,, n^ a^. .
lu, fi^ . . . of thft reacting substances have acquired eertain
Those values are given by the foilowiiig ecjuation : —

= k

f,"\ f,"- J -hi

' I • "-1 ' "i . • •

The conceiitriition!:. uf the substances standing on the one
the reaction eijuiition, therefore, appear in the numerator, and thd
the substances on the other side, in the denominator, of the fracti
and each concentration appears a;; a factor as many times ass
number of the niokvs with which the particular substance takoa
ill the reaction It is here presupposed that the reaction equation
written iu molar formul.e. Thi:' maicnitiide k is constant at a gi»
temperaturo, i.e. it is indt'itondeiit of the absokxtc value of the
centrations, but changes with ttie temperature.

Only ffitrnms and liissnilrai substances can have varying couce
tions. In the case of $i>Hf{ substances and homiitffiigoits tiifuidit,
concentration changes so little with the pressure tliat its inflnenai
scarcely appreciable. For this reason, in all cases where solid
stances and homogeneous liquids take part in an cquilibriuin,
corresponding members occurring in ttit^ fraction on the left of
eijuation become consLint, and can be brought over to the nght-
sifie, where they form all together a product which ia constant
constant temperature.

This siiiiiJc i-iiniition is ilte fimiulation of the lolmh fA«>ry of tJiemieatt
lihrium, and is iipplw^ in all mses wArre .rtich ijiit^lkmit Iwr^ to lit iitatfi-

* Aa an e.tample of its application, the mor*' exact discussion
the case mentioned on p. 100 may be given; this deals with lb*
chemical equilibrium between water vapour, iron, iron oxide, iUi4
hydrogen. The oxide of iron formed has the formula Fej,Oj, and
eqiiatioci, therefore, runs —

4Hj;U+3Fe = 'tH.^ + Fej,0^,

NITROUEN

331

the equation of efjuilibrium —

Here, howevef, n,^ und !>^ refer to solid substances (irun a,tid iron
oxide), and are, iherefore, conetant. On bringing them over to the
riglil, there follows, iti*ili^* = hj:la.^*, or, extracting the fourth root and

jmttiDg the exi>rfismon / f^b^/itj* equal to K, we obtain aJ!/^ = K.

That 18 to saj, the ratio of the concentration (or the imrlial pressure)
of the water vapour and the hytlrogcn must, at a given lomporature,
hare a constant valu«, or, the two conuenti-ations must be |>ro]rortionab
This is exactly what has bei-in givttii hy experjinent.

;^.18 The Influence of Temperature on Chemical Equili-
brium.— The view is often found vci'v wido-.-spread that at a very
high temperature all chemical comjioniids must deconipose into their
coniponentis, and that at places, tliert'fore, where such a temj>eratiire
previiiU, f.tf, on ibe sun, the chemical elemente can exist side by aide
only in the iincambined slate.

On questioning experiment and the theory wliich ims been devel-
oped on the basis of the general laws of energVt another answer is given
by l>oth. By applying tho general principle of movable equilibriuin,
which states that whenever an equilibritim is compelled uj chatige, pro-
cesses occur which oppose the compelling force, we runst say that at
higher tc^mperatiirea that reaction will occur which opposes tho rise of
lempenitnre, i.''. whiih ahAorbs kfuL If all chemictil defompositionB
took place with absorption of beat, the view cited above would be
torrecl. There are, however, numerous substances (and tu these the
oxygen compounds of nitrogen almost all belong) wliich are formed
from their elements with alworption of energy. It is just at higher
tompeniLures that such coniptiunds become more stable, and they can-
not^ therefore, be decomposed by heivt.

Numerous exainplca of this general law are known. Thus, the
vajiour prassure of every liquid increjisea with rise of temperature, i.e.
more liquid evaporates into the given space liecause tho evaporation
takes place with absoijjtion of heat. If a liquid should ever be found
which passed into vapour with 'hrr}»pmm1 of heat, it would also
nocossjirijy have the property that its vapour pressure would tlimnish
with rise of temjterature.

On considering the equatiioii of equilibrium on the precediog page,
from this point of view, it can bo said that, with a rise of tempera-
ture, those substances must increase which are formed with absorution
of lieat from the substances on the other side of the equatior
action. From this it cjin alwaja be seen in what seii^e a c]
equilibrium will be shifted with ri.se of temperature.

In the example cited above, heat is developed by the ac
•«v,ater vapour on iron ; cunversely, water vapour is forine<3 frot

332

PRINCIPLES OF INORGANIC CHEMISTRY

oxide and hydruywu with alisorpUon of hwiL Coiiseqiieiitly,
rise of temperature, the ratio of water vapour to liydrogen
increase, or, as the temperature rises, the decomposing action
iron on water \'apoiir becomes less and less. This resnlt, aU
given hy experiment before the theory was known.

This qufditativc principle has also been brought into a forai|
able for culeulatioii. We shall, however, refrain from the dedn
of this, as the fiualitative form is sufficient for the applications
will be mafJG of the [iiiueiple.

339. Nitrous Acid. — When nitrates, f.;/. potjissiuni nitrate,
treated wjtli rediieing siibstauces, they lose oxygen and ftass into I
Kilts of another acid, known aa nUivus mid. The new sak« are

For this reduction, heating with metallic lead is
employed. This acta a<?cording to the eijuation

geii

KNO,

Pb = KNOj + PhO.

By extracting with water, the readily soluble potassium nitrite (
be separated from the ditRcultly soluble lead oxide. Small qua
of lead which pass into solution by reason of a aide-reactie
precipitateil by fwiasing jn csu'bon dioxide.

On attempting to liberate the acid HNO,, fi'oni tlu^ sjdt, it is
hot to be stable in the free sUite. On pourlug sulpliurit; acid^
potossiuni nitrite, brovrn vapours are formed which, indeed, liarol
composition of an anhydride of nitrous acid, X/J^, but which proj
be a mixture of nitric oxide and nitrogen peroxide. If these
be passed into water, a feebly l)!ue coloured solution ia obt
which contains sonic nitrous acid, but which constantly evolves I
oxide and passes finally into nitric acid in accordance with the eqt
3HNO, = 2NO + HNO,, + li,0.

The same vapours are also obtjiined when nitric acid is decomf
with reducing agents under certain conditions. On heating nJtrioi
of density r:SO - 1-36 with arsenic trioxide (p. 50), the latter
up one combining weight of oxygen from the nitric acid, and
nitrous acifl formed breakis up into water and the browti vap
mentioned. Since the latter arc used in many important ch«
reactions, especially in orgfuric chemistry, this method of prej
is often u8od.

If the-se vapours arc cooled in a freezing mixture, a liquid of a
to green colour is obtained, and from this there can be separatedl
fractional distillation a portion of a dark blue colour, boiling at 3'f
which, especially at low temperatures, appeare pure blue. This
the composition of nitrogen trioxide or nitrous acid anhydride, and i
be regarded as the compound N„Oy

For the drtfriion of nUration NO.,' the general reaction for oxyg
compOMiuh of nitrogen by mew™ ol tervDwa saV-^Uivta (5. 3'261[, is, iti ih

NITROGEN

333

employed. It is distinguished from the ion NO.,' of nitric
lite fact that even on acidifying the salts of nitrous acid, or
it««, <rilh anv other stronger acidh-, the broivn vapours are
the nature of which lias just lieeii given. By niKinsof strong
Ig agents, NO,' can lie coiivert^^d itito NO,/. A volumetric
depending on this will l>e given later on, iiiidor potassium
namte.

ber, nitrosion unites with cobiilt (ji, S-'i) tn form "complex"
of which are readily recognised. This reliction, however,
e used for the detection of cobalt thiin of nitrous acid, and
l>e (jettcriHed under that metal.
beat of formation of nitrous acid in dilute afjuooua solution
©lenient^ is - 28 frj, in accordance with the equation H, + N„ +
= ^HNO. aq. - 2 >: 28 ^j.

Hyponib'OUS Acid, — liy suitably regulating the reduction

itnites, a further iimijunti>f oxygen can be removed from them,

hj/puftttnte", or the salts of hi/ptniitft/us acid, are obtained. Oi

nt metbo<ls of their preparation, the most easily understood,

,Uj, is that by means of sodium. This metal is di&solved in

, and a solution of sofliuni nitrate or nitrite is treated witji the

anuilgatn " so obtained. Moiliuni amalgam acts much more

dy on other sul>stanees than pure soiiium does, and is, there-

Rttur ftjJapted than the latter for many prepirations. The

can l>e formulated as follows : —

SN^Npa + SNa ^ 4H,0 = Na^N jO^ + SKaOH,

Ddinm nitnitt.' is used, and

•JXaNOj + 4N» + 2H,0 == Na^N^O^ + 4NaOH,

Kiium nitrite is emplo3'ed.

m the sodium salt, the difficultly soluble silver eixlt is preparwl
riPied by washing. On decomposing thiB salt witli hydrogen
! with e,xdu.?ion of water, by using ether (an organic com-
as solvent, byp*^'tiitroU9 acid, H^N^O,,, is obtained in the fomi
« crystalline lamina', which fire ^'ery unstable and explode
Thp aul>stance dissolves in water and yields a solution which
ktber longer, but which has also only a passing e.vistence. It
Ivee H giiS having the composition N^O, which is lUe anhydride
ilKMu acid.

e aubetanc*, N.iO, which licara the name vj(//oh,« ruu//; is

many cases in which hyponitrous acid ought really to be

It i» verr much more stable thiin the latter, and it has; not

found possible to convert it back into hyp>uitrous acid or

salu.

oxide is asimUy ptepureti by heating ammonmm mUaVA.

334

PRINCIPLES OF INORftANIC CHEMISTRY

With re^anl to this reMtion, the reader is lefetTfc! to ih* foil
section oil ihe atniniiiiiii ct»m pounds ; we shall here give the propyl
of the subtitancc.

AHfrmis lu-ii/e 13 a gas consisting of two combining weight* of
gen to one of oxygen, to which, in aeconl;ince with the ilensitjr
the formula N^U has to he ascrilird. It is colourless, has it
sweetish odour, and dissolves in water to a fairly large extent
room temperature water absorha about an equal volume of ihe
Likewise, the gas ia comparatively easily liquefied, since ita ci
teinporatiire lies ni + 39" ; the critical pressure amounts to 73
At 0 the vapour pressure umounts to 3fj atm., and the Vdpour pi
of one atmosphere is found at - UO , which is, therefore, the
boilinji point.

Nitrous oxide parts with its oxjgen still more reatlily than nil
oxide, so that not only phosphoms and brightly burning wood d
tiniic to liurn in it, but ;il»o charcoal and sulphur, if previou
sufficiently heiited, Sulplmr burning with a small flame, how$v<3;
extinguished when introduced into the jjas.

Nitrons oxide is taken up by the hlood and ciiuaea iinconsrfj
neas ; it is therefore employed for obtaining transient narcosis. 1

cftnnot be decomposed by the organism in sueli a way that
oxygen becomes avidliible ; if, theri^ore, nitrous oxiile hus tu be inJa
for a lengthened periud, it must be mixed with oxygen in the
proportions as the latter is present in the air.

In order to bo formed from its eleniejita, nitrous oxide wm
require to take up a large amount of energy, viz. 75 kj i 2N., + 0j
2N2O - 2 X 75 kj. In its decomposition, the same amount of *>n«
is given out in the form of heat.

341. Nitro-compounds. -The acid actiouH of nitric acifJ depend
the fact that hvdrion very readily splits oft" from the compound HXC
In view of the litct that other oxj-acids, r.g. ."julpiiuric acid, al;
reactions in whieii hyihortjl aets in the place of hydrogen, the q
■nmat 1)6 asked whether, in the case of nitric acid, oxygen and hydrogi
also act in common as hydroxy].

From the fact of the strong electrolytic diseoctation of nitric 3«Ji
it c»n, ill the first place, be presumed that if such reactions an*
occur, one will expect them to do so in the nhtencf of wnier {which,
coui'.se, causes the formation of hydrion). This is, in fact, found to b
the citse.

In organic chemistry, a large number of compounds are know
which are formed by the action of nitric acid on compounds contaii
ing hydrogen : the hydrogen from these, iilnng with the hydroxyl frwi
nitric acid, is eliminated as water, and the residual grtmp NO., of tb
nitric acid unites with the residue of the '.irganic substance, contjuiiin
one combining weight les."* of hydrogen. The group NO,, is cjillcd th
niir(hf}fnup, jukJ tlie compound R'i^Cl^tovmeA to aiitw;da.uee with th

NTTROtlE^N

335

«|uation KM + HSO.,= UNO. ^ H,0, is ualletl a nifyr,.

cxt«ntal ap|jearaiici; this process looks exactly like that of

cion of a salt, espedally if the byJroxyl is assumed to be

as such in the nitric Aci<l, and the equation, therefore, be

in the form NO.pH + HK = U. NO., + H,0. It would,

; lead to mistakes if one were to estimate the significsince of

nt agreemont so highly as to rogai-il l>ctth reactions as

\y ihi; Miui«>. For, tlie nitric acid would then have to be

aa the base, and the hydrogoii comjiound KH aa the acid, in

ion.

IS essential difference as compared with an onlinary salt forma-

ii4$t in the fact that we ures in thiis case not dealing with

ion iis in the formation of a aalt, for, neither is the com-

H an afid, nor tlie nitric aeid a liase, nor, Knally, the nitro-

d fonned a sidt, ALToniiity to what was said above, also,

reDCC }>econics usia^fially evident from the fact that the fonna-

nilro-compounds Uikes place all the more reiidily the more

\y w.vtcr is fxciwli't!, both the water originally present and

aeeri by the rcaetiori itself. The latter can Uo rendered

by adding desiccating ;igei)ts ; and, a* siicli, concentrated

nciii is. ordiiifirily empiuyed. Nitration, or the preparation

mpomid, is, therefore, usrialiy earriwi out in the presence

or smaller amoiintB of concenlraled aidpluuic acid.

tajwunds can be ftu-raed not only from nitric acid, with

on of hydroxyl, but also ['roni nilnmi' acisi, with elimination of

In order that such an eliminatidn may tiike place, there

nt in the substance which is to piss into the nitro-cnm

which will fonn a stable compound with the hydrogen.

t this will be hydroxyl, which will give water with the

We have then the equation

U.OH + IIN03 = R.N0^ + lljO.

Ilia tM|u»iion hai aim) only an apparent and no real reaembl&tice
fornirition. This is most clearly seen from the opposite ri'de
by the groups NO., and R,

ly. nilro-compounds csin be formed by the action of nitrogen
»>n nuch substances aa can directly form compoundfi by
1. The reaction corresponds to the fnnniitfoii of chlorides by
im of chlorine on substances of this clajjs, e.ff. nietals.
lereaa, in urgiinic chomistry, numerous nitri>con)pound8 are
tn, the niiml>er of iimigaiiic nitrocompounds is comparatively
Nevertheless, sonn- of them are of suHicieul importance to be
here.
WUrOsalpbonic Acid..^Tbe most important inorgamt Tv\wc>-

336

PRINCIPLES OF INORGANIC CHEMISTRY

conifKtuiid is nitrosul phonic or niiroaylsuiphuric acid, the oompoeiti

and reactions of which are expressed hy the formula ^jO^vrj » •

In order to obtain such a compound, one must act on the hyd
conjpoutid of the nidical 80.,(0H} with iritric acid, or nn the hydr
coniponnd of the same radical with nitrous acid. Both metbc
the desired result.

The hydrogen compoiiml of .SO.,(OH) is no other than sulpli
add (p. 282) ; nitrosulphonic aeid would, ther©fore,*be formed
sulphurous aeid and iiitric acid,

Aa a matter of fact, this comjiound is obtained when, in pluo<|
sulphurous acifl, its anhjdride, sulphur dioxide, HO^ is passed in
concentrated nitric aeid. This method has the esjiecial advnnli
that no water ia formed in the reaction, and the disturlMincea dos]
■it ar-e, therefore, not to be feared. The reaction takes place MB

according to the equation HNO., + S0., = 80„v.. . .

The object is also attained by the other method. If nitrou
{or its vapours, which have the same comyjosition as it, p.
introdnced into the hydroxyl compound of the radical SOj(Ol
into concentrated sulphuric acid, nitrosulplionic acid is formid
with water : tiie latter is tiiken up by the excess of sulphiiria

( ill

The equation of this reaction ia SO,(0H)j + HN03 = S0,,^|^

Besiiles these two typical methods, there are a number of
which can in principle be traced back to tbem. Some of these met
will be mentionwJ later.

Nitrosul phonic acid is a white, solid, crystalline substance, wfe
melts, with decompositicjn, at 7S'\ It is very sensitive to water, a.%
transformed l>y it into sulphuric acid and nitrous acid (winch, in
partially undergoes further decomijositiun, p. 332) — SO.,(OH)N(
H,0 = H.tSOj + HNO,^. It dissivlves, however, in concentrated sulpb
acid, and forms a very sUible solution, which stands being diluted I
some extent with water, corresponding equilibria being thereby
lished.

The compound also bears the name Imii'H'Chtvnher crffslnlf, fur ill
readily formed mtder the cotnlitions prevailing in the tttid chamll
in the prciKiration of sulphuric acid, when too little water is pr
By the addition of more steam, the leaden-chamber crystids, which I
not formed in the well-regulated process, can easily be mode tO(
appear.

Further, the retention of the valuable oxidea of nitrogen in
waste gases from the sulphuric acid manufacture, which i& effected'
treating them with concentrated snlphnrie acid in the "UayLii
tower" (p. 289), de]n'nds on the fonnation of nitrosulplionic noid niid
these comiitions. On mixing the aoUUion of nitroeulpbonic acidj

NITKOGEX

345

Further, beated platinum catalj'tically promotes the combusLion of

inntA. If ft hoaiecl gpiul of platinum wire is Imtig iu a tnixturo of

(or Mr) and atnrnonhi, it conUcueij to glow, nml fumes of

luniiim tiitrate »iu! nitritu are furnied. If a. mixture of ammonia

BXC«iB of air is rapidly imssed uvtr heated phitinura foil, covered

» Uiiii Inyer uf spongy piittiruini. the wiiole nf the timmoiiia

be ojcidistd to nitric add.

Of the mmmoniuru salts, that of nitric antl of nitrous acid aro of
iniportaiice here. The former yifkis largu crystals which very
lily dissolve in water, thereby producing a tonsiderahle lowering of
itur«. If placetl on glowing chftrcoal, it detonates, and wlien
illy heated decomposes smoothly into water and mtn>u,'i oridc —

[ This is the most convenient and usual methwl of preparing nitrons

(p. 333).
Ammoniam nitrite decoinpoBos in n similar way, only much more

NH,N02 = N,+ 2H./).

I That ts to say, water and nitrogen are formed. The react ion
place Tery readily ; it proceeds energetically even below the
ling point of water.

For tills purpose it is not necessary to first prepare pure
thxm nitrite, but it ia sufficient to briny the Eons NH^' and
ether, i.e. it is sufficient, in order to obtain a regtdar cuirent
1, to warm a soluble nitrite {fji. commercial sodium nitrite)
■n smmoniuni salt {r.g. ammonium suljthate) in :i(ineous solution,
It has been jv-sserted thai the reverse reaction, the combination
nitrogen with water to form ammonium nitrite, also occurs,
cally iiJ the evaporation of water in the air. It must, genemlly
lin^, it is true, be conceded that every chemical process which
K** pUcc ill a i1e6nitc direction also takes place in the reverse
; in all cases it is ordy a question of how murk is formed.
iboash exact determinations have not been made, it may be
that the formation of ammonium nitrite from nitrogen
water will most proljably ensue only to an exceedingly dujht
eo that it seems very doubtful whether it will be possible
dM«ct the amonnt formed, or indeed, whether the ammonium
tit« which may Ik' fmind baj* been formed in this way.
349. Ainido - compounds. — When potassium is warmed in
\n gM, it is converted into a white mass, which when fused
blue ; hydrogen is evolved in the process. This mass has the
ntion KXHj, and is formed in accordance with the reaction

346

PRINCIPLES OF INORGANIC CHEMISTRY

Just as in the cas^e of Iiydrogeii chloride, HCI, ami of wat-ir,
one cnnibiniiig vmght of hydrogen can he re[»!ftcpd by potassium ((
aiiotlier metal), so, iilso, it is posRible in the case of ninmonia, H
This replncement, however, bt'eoines gradually more difhciiH. Whei
most of the metals can displace hydrogen from hydrochloric *cid,
a, few can do so in the mse of water ; and in the case of ai
only the ulifjili luetiils have this [lower. The resulting product,
rather unstable ; on boing fairly strongly hcatied, it dncomposi
in conUiet with water it is converted into potassium hydi^oxii
ammonia, in a manner simdar to the conversion of a metallic hyd:
into a motaliic chloride mid water, in contact with hydrociiioric

The residue, NH,^, produced by the loss of one combining
of hydrogen from amnmuiii, has, in many compounds, a similar si,
cance to the residue of water, hydroxyl. It bears the name ffin»<A
so that the compound KNHo is called potassnmidf, and it is found
many compntmJ substances. Since it is formed from ammcinia by
loss of one liydrogen, it is infmovaknt and can take the pi;
Jiydrogen. chlorine, or hydroxyl, The amido -compounds are
readily obt;iineJ from (comparativvly unstablf?) chlorine compou'
actini; on these witli ammonia. The chlorine is then eliminated
with iiydrogen as hydnii^en cliloride, which nujstly eouiltines imm
ately with more amnioniii tu form aniraonitim chloride, and the ami
residue takes I he place of chlorine —

H. CI r2NH3 = It.NH.

NH^Cl.

Another method of obtaining amido-compounds consists in
action of ammoTu'a on hydroxyl compounds : R.OH + NH^ = li.NH,
ll.,0. As a rule, the action t^kcs place only at conapurativeiy hij
temperatures.

Thus, for example, snljihuriflamidf^ generally cjilled shortly sm/j
iimi'lf, is obtidnod l>y the fiction of ammonia on aulphuryl ehlorid
SO.Clj + 4NHy = SO.(NH2), + 2NH,( 'I. To ensure that the um[m
tine dues not rise too high, the sulphuryl chloride is dissolved in
suitable solvent, and the ammonia is [lasstxl slowly in,

Siilp/niiiiiilc is a colourless, crystalline compound, which readi
dissolves in water, and no longer exliibits the acid properties
sul[)hurie acid. Also, the solution docs not appreciabl}' iniuluct t
electric current, since the aribstance is not a salt.

On keeping the aqtseouM sobitioti, the conductivity slowly tncresiM
which shows that a salt is formed. This accui-s by the taking up
water; S02(NHj)j+ 2H.jO = (NHj2SO^. That is, ammonium sulplut
is formed.

This reaction is a general one. By the .action of water, the amiik
com|Kiunds pass into hydroxyl compounds jdus ammonia. Tlds is
reversal of the method of preparation of the amido-compoxinds gi
above ; the reversal lakes place on t,\\e >>asAs, cA v\vft Va.-w '^^i mass actiol

NITROGEN

339

ide. The latter substaiic*: 1ms already shown itself a \'ery
;vo and important accelerator in tlie iTiariulVu-ture of sulfihuric
».e. itt the oxidation of sulphurous iiciil by free oxygen (p.. 289),

number of other uuses are ;i1-io known in which it auts aa an
krator uf oxidation.

those aiBCB, therefore, where it is deaireii to increase the ifxidisiny
n as much ms possible, red, /umiiifj lutrir ucui, i.f. iin at-id which
ins lower oxides, especially nitrojjen peroxide, in solution, is used,
atid is obtained by distilling nitric ucid at a high temperature
t\), or, also, by jiddiiii; a. small quantity of a reducing substance
nic substance) during the dtBtiltation.

bnrereely, in those cases where we »re dealing with other actions
trie acid iti which oxidatiuti hue to be nmidril, acid ns free as
lie froiii lower oxides niu>it be used. This in recognised by its

colourless, and the lower oxiiles, which are more volatile than

itric acid, can be removed frnm the yellow acid by passing a
n of dry air through it. This is of importance, for example, in
reparation oi n:tro-compounds froin or^aiiic sidfstances {|i. 334V

4^, Tbe Hole of the Oxides of Nitrogen in the Preparation
ulphuric Acid. Transfer Catalysis. — Receiu researches
if US to fonu a sumewliiU nii»iT il..'fi!iitc T<lca refjurding the
BTation of the formation of sulphnric acid in the learlen clutnilicr
Igb the presence of oxides of nitrogen (p. 289). As the result of
Iment it has been found that whereas the ilired oxidation of
lUroiis acid by free oxygen takea place with great slowness, both
ormation of the iiitro-conipounds i>f sul[ihuric acid and of aimilar
inecs frotti the almve constituents in the presence of oxides of
;en, and the decomposition of these compotmds by excess of
', take place witli great rapiih'ty. The increase in tbe velocity of
ition of siUphuric acid by the oxides of nitrpgen can therefore be
ined by the assumjjtion of auch iutfimeilinif rtadifnii'. It has,
or, not been definitely detennineci what the interniediale
uicea are in the present cjtse, since there are quite a uuniber of
lets having a composition intermediate between sulphun>us acid
litrous acid, all of which have the property of rapid formation
ecomposilion. It is therefore proljable that there is not only
ingle intermediate substance produced, but that various inter-
.te compounds are formed and deconijiosed, the relative amounts
ea<s depending on the tcmjicratnre, tlie amount of water, and the
ntration of the substances involved.

ince these intermediate products undergo decomposition under
me conditions as those in which they are formed, we obtain
tiat criterion of the ciitalytic processes, viz., that the accelera*
nee does not appear in the end product, and does not, theref
in any stoichiometric relationship to the amount of the latter.
Biich unBtable intennediate forms can he produced at all depend*

348

PRINCIPLES OF INORGANIC CHEMISTRY OH4

in so many cases that it constitutes one of the most imjjortant
in the progiosa of sdeni.'o towards tho knowieflge nf new conifKMiai

The substances we have mentioned do not comjilete the list of
nitrogen derivatives of sulphuric iicid, hut we must here forego
discussion of further details.

* In tbo same way aa sulphuric acid, many other hytlroxyl
pounds can also yield iiraides and eimilur derivatives. Thus,
example, there ia im amide of nitric licid, NO^NH*, obtained
method whiuh cjiiijiot hyre ho dismissed ; it forms a white, crys'
mass, wliich ;it 70 lupidly decomposes into water and nitrons o:
On account of this decouiposabiliiy, it cantiot be- ohtained by hetl
ammimiiim nitrate, whereas, oiherwiaej heating iha ammonium
constitutes a fairly general method for obtaining the acid amides

3M). Other Oxygen-Hydrogen Compounds of Nitrogen.

Besides the componiids of rutrcfgen already descrihed, there
a number of others which contain both hydrogen and oxyi
The following Hat gives a review of the entire series of th
compounds.

The highest stage of oxidation of nitrogen, viz., nitric acid, can
(ormaliy regarded, by the addition of 2HjjO, as a compound of ni
wjiIj five h3'droxyl groups : HNO, + 2H.p = N(OII),. Doubting
fornuda in order to olitaiii an expressiitn for the nitrogen eompoum
with *iN, the following sei'ics is obtained by the gradua! replacemei
of the hydroxyl groups by hydrogen :—

Nj(0H)i,=4H,O + aHNO,: Nitrif acid.

= BH.jO ■*• NjOb ! Nitrogfii pentoKide-
N^fOIDjH^flH /) + >«' A: Nitroj*(Ma [icroxide,
NjlOH ),,Hs= 4H.p + 'JHNOs : Nitrons acid.
N3(0H)^H., = 5Hj( I 4 2N0 : Xitrir oxi.le.
K^OH )sH 4 = 4 H^Q + H^XjO, i Uyi«nitious »citl.

=fi'H^O+ N.4O ; ffilrous oxide.
Na(OH),Hj, = 5H5rj t-N.^; Nittogori.
Nj OH)iHs = 2H5<l + 2NHji«.iH) ; Hydroxy lauiiiio.
Nj<0Hy,Ilj = aH.,O + N..H„i:*)H) : DittUiide Uydr«t«.

= 3H.jO + NVl4: Dimnidf.
NjiOt! !„Hk- 2N H41 OH) : Ammoniiini liydroxidc
Aiiimunia.

X,(OH)H„

: I II known.
^N[(.: Uliktiowii.

According to this Uible, ammotiin appears n& the ]ast known tuem
ber of the series of reduction eorapoiinils of nitric acid, and between i
and nitro^'en, which stands in the middle, two stages are present wiiich
are known, and to which the names iti/dmxfflamine and dmmi*Sf {of
hjdmziiu) have been given.

H]}ih-()Tijhim\)ir, NH.,0, is formed under various conditions by ihs
reduction of nitric acid or other oxygen compounds of nitnigen. It it
obtained chiefly in the form of a hydrochloride, from which the pur*
compound cm he obtained hy (\ecoTaposi\.\QT\ Vv\>a ^ Vw&a, -wilVv «icVti

NITROGEN

341

the whole amount of gas can ultimately be made to combine.'

rurSt for example, when the gases are k«ipt in contact witb an

AmmonJA ia taken up by acids, and if sjiarks arc continued to

througli tlie gas mixturt wlule standing over an acid, all the

nltiinAtely disappcitr.
is ikp{mrent from tlie e^jiiution

ae diimiiUheg from 4 to 2, or to a half, uben tLc elements
ito combination. The reverse ciiange takes plact' wlieii the gas

change of energy occurring in the process is represented bj'
N. + 3H, = 2NH, + 2 > 50 kj.
is absorbed in large amount bj' water, viz., aliotit SOO
or O'fi part by weight, at room tempemtiire. It, however,
lows Henry's law to some extent, especially at higher tempera-
It can be completely removed from the solution by boiling.
this it is appart-nt that a31 solutions of ammonia must necessjirih'
-» •fi-.T.^r bttiling point than pure water. For if there were a
higher boiling jioint, this wcmld renmin behind during
....:. iti, and tinally pas£ over uiichati<:eil in composition.
aqueous solution of ammonia colours red litmus paper blue,
ore contains bydrnxiilion, OH'. It must be concluded,
thtkt in wat^r ammonia h[ts passed, at least jiartially, into
Mining hydroxyl. This can occur only by it taking
e 'f wat-er, and, therelorc, a compound of the general

I NUj t nU„0 is present. All known facts favour the vlow
= 1 , »ttd that the compound must, therefore, l>o wiitten
H^« or, giving prominence to hydroxyl, NH^OH.

B8 we recognised the cr»m[iound ion of nitric acid, NO3', to be

to the simple iou (.'l' of liydrochloric a«id, we also conclude

the solution of ammonia there is present along with hydroxyl

pounil cation NH^*, which corresponds to sodion, Na'. Hince

eoioMtied with only one hydroxyl, it ia monovalent, like

or sodion. In other respects, also, e.g. in the crystalline

rreeponding saline compountJs, the ion NH^', or nmmonion, is

mitar to potftssion.

onia must^ therefore, be regarded as the anhydride of

ium hytiroiinle, XH,OH. It has not as yet been possiijle to

anununium hydroxi<le itt the pure state, jiist as only the

lit! of sulphurous acid, SO,j, and not sulphurous acid itself,

ia ktiomi. As to its existence, however, or rather as to the

oe of the ion XH^' or amnionion, no more doubt exists than

ezifltence of tiie inn of sulphurous ucid, SO./'.

aaaotBOce is based chieHy on the fact that there are a large

&1>er of Milts wbich can lie prepared from ammonia and acids, and

350

PRINCIPLES OF INORGANIC CHEMISTRY

The substance has retoived the name lii/dni^ine (from as
nitt(>ij;en) ; it is alao called diamide, since the atojoit! groiij* NH^
long huen called amide.

Hydrazine is a colourless liquid which bods at 114° und sol^
at 1 . It coinliines witb witer in form a hydrate N.,H,jO, whjclp
volatile without lieuum position. Iji a further <niantity of water ii
solves, yielding a Ii<)Hid ivith an alkaliue reaction, from which the
of hydrazine can be obtaJnotl by neutralisation with acids.

Two aeries of such ailts are known, nionacid and diacid,
foniier have the (.imposition N^H,; , A, the latter, N^H,; . A,^
corresijonding hydroxides ai'o, therefore, N„H^(OH) and N,H^(OH)y]

The salts of the second scries are, however, very unstable
readily decomjiose into salts of the first series and free acicL
aqueous solution, the siime decomposition takes place almost
plutoly. The aqueous solution, therefore, even of the free
consists essentially of NmTIj(OH) and of the ions of tins monacifl
vis!. NjjH.^' and OH'. The iuijs fomjed frum this by accession
water, N^H„" antl 20H', are present to quite a small extent.

The sohitions of hydrazine havn a powerfully reducing action,
exceed in this respect even the liydroxylaniiue solutions.

352. Hydrazoic Acid. — The last eomfimmd of this series wl
we shall mention hero is hydrazoic acid, HNj,. It did not find a
in the general summary gi^en cm p. 348, since it contain-^ three
billing weights of nitrogen, and th;it list wa.s extended only to
comliitting weights of that element.

Hydrazoic acid was first obtained by the decomposition of orj^
compounds of complex composition ■, not until later w».s a method
covered for preparing it from simpler substances. One of ihe sitnpli
methods of prepaiiition is from hydrazine atid nitrous acid in m\
solution. There occurs the reaction N.,H^ + 11N0<, - HNj, + i
Further, the sodium salt of hydrazoic acid, iS'aNj,, is obtained 1>y'
ing nitrous oxide over heated smlamitlo (p. 346). The reaction
NH,,Na + N20 = NaN, T HjO. The acid can be obtained fW.m th
sodium salt by distillation of tho aqueous solution after the additiou
sulphuric acid.

On distilling the afjueous solution obtained hy one or other metbM
the acid first jiasses over and can in this way, finally also by* the
of dehytlr.iting agents, be obuiJncd in the pure state. liydrazoic aci
is thus olteined as a colour]«s.s liquid with a strong and very «:
pleasant smell, which boils at 37", and expkHies very readily with grea
violerjce. The same pro|)Ci'ty is also possessed by many of its salt
in the solid state. In solution, however, the acid ia fairly stfible

In the case of this compound, the acid properties are clear
although not very strongly developed : a I per cent iiqueouB soliiti
is dissociated to the extent O'tiOs into its ions. On account of tb
slight dissociation, it can Ik* jseparated fi-oni its aqueous solutions

XIV

NITROGEN

347

If tlie water is remwi^., tbt- jimiili' «iii l>e formed fi-om the lij-ilroxyl
euniymuml and Qminonia ; if, roiiversely, wews of water is present, it
convfiia the amitfo-compouiid into the hydroxy! compound.

The qiaestion may be naked if mi intermediate stage does not exist
between the sidpliHinide and thti iitutnoniuni sulphate, ju&t as cliloro-
sulphonic acid is an intermediate sta<;e between siilphuryl chloride and
Rulphuric Jicid. As a matter of fact, such ji coiu|>nmid exists. From
chlorosul phonic acid aud aiunioriia, there is formed stdphamink arid —

so„cion + 3NH,=so„JiS

2 - NH.Cl.

In harmony with tlie fact that acid hydrogen is still present,
gi/ljjutmiiiu' iTcid or nmuhindljilnirk odd is a monovalent acid. It is a
colourless subatancv which cTystallisca M'ell and readily dissolves in
wflt*jr witli an add reaction ; the solution is, however, a weajicr acid
than sulphuric acid. This is a general phenomenon ; the entrance of
an aroidn-prnup reduces the aeid properties,

Sulphaniinadion h produced in the form of its ammonium salt by ^
the gradual action of vvaUT on the diiisolved sulphamide —

By this reaction, aulphamitue acid shows itself still more clearly as
an intermediate compound biitwenn sulphamide and sulphuric acid.

Sulphamiiiic acid Ik aUu produced by a numlier of other reactiona,)
some of Mhich will be discujiised later'.

Sulpbarairde acid can also be regaided as a deiivative of nmmimia,
which has been formed by one hydrogen of the latter being elimiii.i ted
as wat«r with one liydroxyl of the sulphuric acid, the two residues
NHj »ntl HSO.j then uniting togethei'. Tlie question may be asked if
the same reaction may not occur more than oiiee with ammonia, so
that two or three of its hydrnf;ens expei-ience the same substitution.
Such is the caae, the following Bubatances beiny known : —

Amnioiiio,

DiAiiltifanminic mcid,

I"
N- H

llJ
I"

Sulphaniinic auid,

Trisnl|iliauiiuic leiil.

N H
I SO,pH

N SO,0H
I SOuOlI

Into the preparation and properties of these Biibstiiures we inhall
not enter here ; rather they imve been mentioned only for the pur-
pose of showing how conclusions by anahi^y may furnish a r.hic in
searching for new substjuiccH, the possilnlity oi' our definite re »p
giving rise to the presumption tliat similar reactions are po
Such conclusions do not always lead to a jiositiva reiiidt, since ci.-
stancea may exist which show that the analojiy in (jueetion dot
hold, or that it i» impracticable, Still the method has ^iroved.

CHAPTER XV

PHOSPHOKUS

354. GcQ^fS'l. — The n&me pkospkortis (light- bearer) was formerly i
to designate all substances whicb possess the profwrty of pmittitii; lig
without at ih»? same tirao having a correspoutlingly higii t-enip^raw
Tho name pho3phores(-ence, used iti physics fur the after himinfjice
shuwn by ceruiiti stjVistnnces after ti previous exposiu-e to light,
lelic of that usage. At the present day, the name phosphcmis ia
fined to 0116 element, whic-b also exhibits the above [jroporty of
liamineaconce, althouj,'h for a different reason.

Phosphorus was iliscovered ahoul the year 1670 by an alche
Brandt, who obtained it by the distiUation of the reBidiie left OD
u\'apot';itiun of luiman urine. He kept his incthoc! aocreL but it
soon found out by Ruukel in German)', and Boylfi" m blnglaiitj. Ga
and Scheelo also soon found that the bones of the vertebrate aaiu
were a much richer source of phoijphorus, and at the present day ill
still chirfiy prt!|)afcd from those.

The method of obtaining pluiaphorus depends on the fact i h*t
oxygen eonipouiid of phospborua, phospiioric (tcid, which i.s entitiuntj
in the bones, is leduced by chfircoal. The cbunoal combines %vith
iixygen, nnd the phospljortis is set free and distils over. The reactio
cannot bo ijiven here in detail, but will be more fully describBd Isti
(Chap. XXTII.)

In nature, phosphorus occurs only iJi the form of salts of the jii
nifintionecl [thosjdioric :K.)d, These compounds are veiy wide-spre
altbuugli they do nut occnr anywhere in krge qiuiiiiities. They are (
j^i'ea.t importtmee A>r organic life, since the ''protoplasm" of the
the suhsUiiiee to vrhich the actual vital activity is attached, nlwad
contains small amounts; of phosphorue compounds. The nerve
brain substances, nwre especially, arc comparatively rich iu phosphor
which is there present in the form of phosphoric acid dertvut.iv<«i

Salts of phosphoric acid or the phosphates arp also iudisp. ■
the growth of plants. As the soil docs not usually cDutain hm
this substaiico i% for the purpose of high cultivation, added to the mn

352

PH0SPH0KIJ3

35-

Itlikny other gases, especialiy the rapours of organic
B oil of turpentine or alcohol, Ijehave differontlj* ;
fpnmcnt llio luminescence, even when they arc present in very
1 awnnt. The reason is a great retanlation of the velocity of
between |>bof;{>horus and oxygen ; the phenomenon is, there-
k catalytic one. Thi^ behaviour is of importance for the above-
method of Jetecting phosphonis by means of tUo himin-
(ce it can make it appear as if phosphorus were absent when,
it ia preeeat.

(jk. 80) is formed in the slow combustion of phosphorus in

•ad can be rearlily recogtiised by its smell; that %vhieh i»

iA phosphorus smell h nothing but the amell of ozone.

of phosi>horus itself has a smell like garlic. One can

ooeseU of this by preventing the destruction of the vapour

ng trmces of a subaUnce which prevenU the slow oxidation.

stick ol phosphorus, half covered with water, is allowed to

I a large flask, whereby it is advantageoua to slightly raise

ipenU4ire, the air of the flask soon becomes full of ozone, and

Imiidons of this guhatance given on p. 80, especially the turning

I of potassium iodide and the bleaching of titniusH can be easily

*\.

[Bbwe osone is a substance which is formed from oxygen by the
f free energy, this energy must come from somewhere
iiily it 13 the oxidation of the phosphorus which yields
iviergy. In accordance with the principle stated on p. 206, such
out \to brought about only by a coupled reaction, and it must,
be concluded that the formation of ozone takes place in sitcfa
di»t the ratio of the amount of oxidised phosphorus to that of
I omie produced h definite and a whole number. This is, indeed,
the ex|>erit«ents made on this jK>int have shown that equal
Its of oxygen are used up for the oxidation of phosphorus and
funnaiion of ozone, ft has, however, not yet licen established
ihe rhemical reaction here ia.
>. Fhosphonis Vapour. — The combining weight of pbospborUft
«i, frotu its chemical relations, to be 31 ; the molur weight of
is, ca]c.ulated from its vapour density, has been found, how-
kl to 124, so that to this vapour the formula P^ must be
hi this respect, therefore, phosphorus differs essentitdly
fUtrogen, to which it exhibits many points of resemblance in
of it« compounds, and is related to sulphur,
very high temperatures, the density of phosphorus vapour
Exact measurements of the progress of this process,
priKUinably consists in the transformation into P^, are not

Ift Mcordance with the relations existing between white and red
as descriljcd on p. 354, the two forms have a very different

154

PRINCIPLES OF IXORGAN

onsists are found, on mieroscopic examinatioD, 61
ight, to be crystalline. The conversion of white
fis accorajtanied by an cTokition of heat efpial to 1!
35G. Reciprocal Transformation of the V
phoniS.—Thiit red jtliosphutiw is formed from
has already been mentioned. The velocity of I;
very greatly on tbe temperature ; at 300" it is
liowever, it is very great— so great, indeed, thl
takt<3 place. For, since a consideraMe amovint
in the transformation, the tcnipcratMre of thi
spont!inerm.sly, and the lelocit^' of traiisformatu
so increiiHed that a portion of the phosphorus i
the heat produced.

The velocity of transformation can be very]
means of catalytically acting substances, so that
formation even at a low temperature is consic
tically accelerating agent has been found in
even when present in very amall amoiuit.
dividecl product, which consequently has a brig
obtained from a solution of jellow phosphor
bromide (p. 3(>3) at 170".

Liyht exercises a simitar, accelerating inflc

lOephoniB which have been kept for some t

;las» bottle, becume covcic<l witli a red layer wh

of red phosphorus. In such a case, it can g<

that the outside parts, which have been most-.'

light, are eorrespondin^rly darker in colour.

Although such diflercnt conditions are kr
phosphorus pas.ses into red, thei-u is only one
reverse transfonnation. It consists in co\
phorus into vapour and ipiickly coaling th
condenses then to colourless liquiil or solid pi
If these facts are examined in the light o
we have seen to exL^t between polyinorjih
case of aidphur (p. 25^), we must regard tl
unsltilJe fomi compareil with the red. Thi»
various spoiTtaneons transfunuations which "
high' temperatures, and under the inliuenc.
although the huter circumstance is not ^
greater sobiltility of white phos(>bonis also
The formation uf white phosphorus i
case of the law tliat the lt;.i.t gluhh- form fir
In the case of ]>olymorphous sub-
possibilities. Either thi- two form*' ' "
either aide of which the relative ^ii:l'|
with sulphur (p. 258) ; or as in the

X\'

PHOSPHORUS

355

^^H (p. 2il}, tbe one can be the stable, the other the unstable form,
^^H tfaroughoiit tbe wliole aticessible rauge of Leiii|>erat.ure up to the
^^Bmelting point. Substancos of the first kind are called nmidifttr'q/ic,
^^Huiose of the second, nwrnlrupic. In the case of white and red phos-
^^Bpborus, is the relation-^bip one of emmtiotrupy or of monutidpy f
^^^ At faii'ly high temperatures, red phosphorus is certainly the more
•bkble, since it is produced spontaneously from the white. At lower
temperatures, the relationship is also the same, aa is pro^-ed by the
greater solubility of the white form. Consequently, phosphorus must
be regarded as monofroidc, and the red phosphorus is under all
circijn"istMj]ces the more stable form compared with the white. It is
also the more stable form with reference to H<iuiti phosphorus, since,
indeed, tbe conversion into red phosphorus at higher temperatures
takes place from the liquid, because white phospborua melts as
low a-& a",

OljjectioQ could be taken to thk view on the ground that white
pnospilionis can bo kept for a very long time, even in contact with the
red f OTiTi, without transformation taking place. Tliis, however, only
prov£?s that the velocity of tmnsfornjation at room temperature is
very small. This is not a mere assumption made to e.xplain tbe
present relations, but is seen to be in accordance with tbe rule when
the following facts are kept in view.

A^s has already been metitJoned several times, the velocity of
cheini^;^) reaction increases with a rise of temperature in such a way
tJiat ix rise of 10° or 15" corresponds to a doubling of the velocity,
and ttie reverse holds for & lowering of temperature. Now, the trans-
form£i.^i,-iij at 250' takes place in a few hours; assume it to occur in
one fciour, and assume, further, that a doubling of the velocity takes
place tjnly with every 15", then the reaction at lO" lasts 2'"' hours,
or ao^^yj, eight years. If we assuaie, however, that the velocity is
doul»l«>(i Jjy a rise of 10', then the lime of transifoiTnation at 20" is
foiiu^l to be 1000 years. This rough calcnlatiou shows that the
assuii^ption of ^ very small velocity of transformation at room tem-
p«rat.\i|-^; contains nnthiiij; contnidictory to the general laws.

^57. The Oxidation of Phosphorus in Air.^ — Not only does
tnere attach to the slow combustion of phosphorus in the air the
historical ititerest that it led, by reason of the peculiar emission of
^^g^t, to the discovery of this element, but there stiil exist at the
pfKSient day, questions of scientific interest with relation to this iong-
KOou'ii pljenomenou, which have not as yet received a satisfactory
aoswer.

Phosphorus is luminous in the air at ordinary t«mperata
*t the same time underffoos o.xidation. The higher the temj
nses, the more vigorous does this slow combustion become, pM
•bout 4o\ into rapid combustion.

If the concentration of the oxygen is diminished, c<j, by al

360

PRINCIPLES OF INORGANIC CHEMISTRY

phenomoiion, since the hydrogen pJjoaphidCj in consequence of
ready decompoaability, will always catitaiii traces of phrjspl
vapour.

If the apontaneoTisly inflammable gas is kept some titne, it
the property of spontaneous infiaminability, nltiuHigh analysis
detect any essential difference. It was, thei'efore, at first ih*
that two different kinds of hydrogen phosphide of the samo
position existed, until it was found that the property of spont*o<
intlammalnlity belonged not to the pure hydrogen phosphide PH,.
to atinther hj"<iridc of phosphoriia having the composition PjH^,
13 prodticed in small amount along with PH.„ and whose presoi
the canse of the spontaneous inflammability,

This C4\n be pi-oved by passing the spontfweonsly indanji
hydrogen phosjihide through a freezing mixtnro. The less vol
apontaneonsly inflamraablo hj'drogtm phosphido separates out, and
issning gas has now lost the property of igniting spontaneously

The cortipositiori of hydrogen phosphide recalls that of ammoi
and in view of the; manifold resemblanco between nitrogen and pi
phonis, biisic properties will also be looked for in the case of hydi
phosphide. .\s a matter of fact, these exiat, but in exceedingly
degree.

Hydrogen phosphide combines most readily M'itb the
hydraci<is, above all with hydriodic add. Both goses combine
on being brought together, forming a crystalline mass which hss
same cryst^illitie form a.s ammonium chloride. Its composition
represented by the formula PH^I, exactly corresponding to ammon
chloride, NH^Cl. On attempting, however, to ilissolve this whi
mass, which bears the namo j^hnsphuninm miiih (phosphomuni = PH.
in water, hydrogen phosphide is evolved, and we are left with
a solution of hydriodic acid,

* In order to obtain phosjjhonium io<lid<', it is not necesgary
prepare the two gases separately, but it am bo obtained I'n
operation by the action of phosphorus and water on iodine. For i.
purpose, white phosphorus (4 parts) is placet! in a retort along wi
iodine (10 pai'ts), and carefully heateil with water (3 parts). A twi
fold rt'Jictinn takes place, one portion of the phosphorus withdrawio)
oxygen from the w.ater, ao tltat the hydrogen can combine with th»
ioditio to hydrogon iodide. On the other hand, the hydrogen so pn*
dnced goes to form hydrogen phosphide. The totiil reaction caa 1|
expressed by the equation 51 + »P + 121120 = 4HP0g + 5PHJ.

The above mentioned hydrogen phosphidf^, which influmea spoB
tanoously in the air, has the composition P^H, : it is n colourlo*
Itquiti, which boils at 57\ It is sm unstable oubatance, and in hglii
as well as in contact with various catalytic substances it yields i
yellow, solitl siibstanco, P^H,, or mliil hijthvjrn p/wsjilmiey hydrogM
phosphide //(»y being formed at itve ttimt l^vcvc;.

PHO?

ito

mttik

3(;i. Halogen Compounds of Phosphorus. ^^Phosphorus com-

in 6f¥^r*l proportintis with all th,e halogens, so that we have

a l^Tge variety of different compounds. These are mostly very

Le. have a tendency to nntlergo decompositions with other

and are used as important reagents in many preparations.

chlorine is passed over phosphorus contained in a retort from

the air ha* been previously displacod by carbon rlio.vide, in

to prevent the phosphorus igniting spontaneously, direct com-

n of the two takes phice, Thts heat thereby clevelopeil is

nt lo vaporise the greater part of the compound formed, and

poudei»s«'s, therefore, in the receiver «s a colourless liquid.

The reaction proceeds in the above infinrier when u suffietent

it of phosphorus is pre.sent ; if, however, the chlorine is iu

another stibstance is formed, which will bo discussed later.

The aJioTe substance is obtained in the pure state by distillation,

phosphnrus Iteing added to retain any excess of chlorine which

ly lie present. It forms a colourless liquid which boils at 76\ and

a density IG. The molar weight of the vapour is 138. Accord-

thia. and in accoidauco with the results of analysis, it has thu

FC'lj ; it is called phvi^phonis Irkhhrhh^ or, iu view of the

ic* of a higher chloride of phosphorus, pfiospkorous clUoriiit.

osphorus trichloride reacts readily with water and other 8h1t-

oontojning hydrogen and oxygen. The reaction thereby pro-

J such n way that the chlorine combines partially or entirely

n to form hy<lrogen chloride, while the oxygen unites

-■iphoniis to form an acid, phosphorous acid, which will

ib»f later. In this way phosphorus trichloride acts aa a

itiug agent, and it is not necesssuy that the water should be

t aa such, but may be represented in the compounds mendy by

nl«. The reaction has nothing to do with the " predisposing

(p. 365), for as the hydrogen arifl the oxygen here ex|»erience

<i;tTerent fates, they need not have previously stood in any direct

to one another.

Tlw above mentione*! decomposition is aUo brought about by the

vapour of the air, and (or tliis reason phosphorus trichloride

when its vaponr comes in contact with moist air.

:h-? formation of the trichloride, 31(> i;/ are developed.

II rhlorinp is allowed to act on phosphorus or on the tii-

it is m.'uJily absorbeil, and there is formed a solid substance of

;> llowisht;reen colour, whicfi contains five combining weights of

loe lo on*i combining weight of ]ihi>Bpho!'us, and is therefore called

iJ.vri** peniiifhlin-iile or pho>iplu>ru' chhmk.

l»horu8 pentachloride, PCl^,, does not melt under the ordinary
■ c i(8 boiling point lies Wlovv its melting point. Since,
lioiling point of all ^ub.'itances rapidly rises as tXitj YTJe%s,\\v<i
tvhvreaa the meking point /a affected to 8carce\y ftxv sc^^^xeA-

362

PRINCIPLES OF INORGANIC CHEMIS

ifferr

able extent by jireasiire (p. 132), the boiling poiut cm
the pressure, be brought nearer and nearer to the mel
finally reach it. In the ease of phosphorus {letitaclilorid
tare is 148 , ami the pressure amounts to sever*
Umler these c-ircurasUmces, the pent-wliloride can aimul
in the solid, liquid, and vaporous sUUl's, just aa, e.g., i
(more exactly, at + 0*0073 , p. 134). Under a still gi
the peiitacliloride behaves like most other aubstances,
and afterwa,vds boils if the tempeniture is further raised

lu accordance with the formula PCI,, the vapour
pentachloride ahonld have the raolar weight 208. Th
of this, however, shows that this value is never reachr
sictual density of the vapour is less. The differr
density being so much the less the higher the td|
lower the pressure. In this respect, the vapour ofi
behaves in a perfectly similar manner to the
pero.Kide (p. 327).

Hero, also, it can be assumed that the vapour j
fitauce, but that the pentachlonde in the vapon
dissociates into [thosphorus trichloride and chlorine,
the eijuation PCI,. = PC1-, + CU. Such a mixture
chlorine mtist have half the density of the vapour ••
for, as the equation shows, one volume of the vri
the same ])resaui"e into two volumes of its dec'
The observed values of the molar weight tie b*
"208 and 104, and from the densities observed ii
the proportions of trichloride vapour and chloij
a mixture of that density can be calculated (p, ,

Confirmation of this ■view can bo obtaine
The vapour of the pentachloride has the yel
chlorine only in a slight degree. If, now, it
proportions chlorine must be mixed with any
to yield a ga-s of the same colour as the peui-a
be concluded that the same proportion of chlo>
The determination made in this way of the ■^'
vapour of the pentachloride agreed sufHciently
from determinations of the density, on th'
dissociation into ti'ichloride and chlorine.

Phosphorus pent^ichloridc fumes stron:
powerful irritant action on the mucous mf»
be exercised in working with it. With
decomposition, with formation of phosphi
{v'td^ infra). The pentachloride, also, act»
similarly to the trichloride. In this ca>
large amount of chlorine eontaineti in the
place comes into action, and the pentachi

367

"n it
'f the

'■e iitul
"' ""'b- salts

V'' :.''';;'■''

'It, ,;g , I ' 'S e.Y-

■^■W'.se of f . ; ^ <^"ii/iot
•lit « ^ *o»rerer

366

PKIXCIPLES OF INORGANIC CHEMIS

pboric acid. Whfn phosphoric acitl is spoken of witl
wttf^phosphoric acid is always meant.

Of the three acids, the tast is by fax the most
nature, compounds of it alone are found, and the i
spoataneously, in aqueous solution, into the ortiiopho
tta tho diHV'reut forms of sulphur at the ordinary toiv
iittiniately into rhombic sulphur as being the most ft

Orthitphosptioric acid is ohtaiaeti by dissolving;
oxide iti water and allowing the solution to stand /<•
preferably in Uio heat. The leuat stable form, vni-t
first formed, and this gradually pa.sseB into the sr,!
is obtained more conveniently by oxidising wli
dilute nitric acid. The ]ihos]jhonis dissolves witl
oxide ; the pliosplioric acid which \b formed citu L-
the exceeds of nitric a.cid and its reduction pr(idi!<
c*ntrating and heating.

Orthophosphoric acid is obtained iu this w >
which crystallises only slowly and with <lifficul'
of the piu'e acid is 4l2" ; the molting point i- '
of water, and likewise, also, hy the pre^em:*' ■
This is due to the general fact that the nul
stance is lowered by the presence of a fureijn

Impure phosphoric acid is ulitained fnini
the mamraala consist partly of the eakium *■;>
and jjartly of organic nitrogenoiift matter wJi
passes into gluo. If the bortea are heated i
black owing to the carbonisation of the ■•
tintiinj: the lieatitig, the charcoal burn- -
left in tlie form of white masses retairii',.
bones. This residue ia c;illed kmc-ask.

If powdered bone-aah is mixed with •
occurs a reaction of the kind describeil •
is a difficultly soluble sjdt, and for thi.>
sulphuric acid and calcium phosphiite, .
at the same time. On filtering tin ^
phoric acid witich is formed js sepai.i:.
sulphate.

Since, however, this salt is not O'
amount of it remains in the solution
pure calcium phosphate, and SiHn.
soluble compounds under the actini
ftcid obtained tn this way is uoi
many technical purposes.

As can be gathered from thi* di .
in water. Indeed, it is so soluble iL
been determined. Even small aiii'

':^ia, evftic
• .iiid phf

■ fhe c^^rrespoo
% however, urtj

^~«noos, b tbfl
out he ami
■urotber, »>. whi
~'^ under sii
-'■mfjs or ti
vheroaa son
■mber of mci
:-», Init that nf th«
-^ u'rt)ups Of Ij
' > can, in anj

'■ iti a list.
tMxd: —

adds and in tk

fied tlie In-,

tile middle ono

PHOSPHORUS

367

ioBjihoric ac'ui below room temperature, and thus eon vert it
soIuiioK which, certainly, contains only a small quantity of the

ue. of w&ter.

le aiitMouo solution reacts acid to litmus, and htis a jmro and

Illy *cid taste. Its electrical comiuctivity is comparatively

rmc mole of phosiihoric acid dissolved in 10 litres of water

only a tjiuirter tia much hydrion aa an equally dilute hydro-

tckl ^oltttioii.

Bphoric iioid is a tnhasie acid and can therefore form three

I of saJts ill which one, two, or three coml>iniiig weijihts of hydro-

peptaced by metals. Since there are two ditl'erent aci<l salts and

■mul sa]t> these are diatinguished by stating in Greek iinmerals

ly combming weights of hydrogeu are replaced. Tinis, mnnn-

im phvflphute \i the &alt KH^POj, r/^sodinm phosphate is

^^, and /r<-3ilver jihosphate is AgjPO^. In nature, only salts

last type, or normal salts, occur.

attempting to neutralise an ai[ueoug solution of phospiioric acid

lustic «oda with the aid of litmus, no sharp transition is obtained.

of the three combining weights of caustic soda which would bo

for the formation of the normal sidt according to the equation

\^- SNuOH = Sa.,P(>^ + 3H.iO, loss than two are required to pro-

tm alkaline reactiKU, and the 1>lue coloration of litmus appears

illy, so that no defirdte moment can be given at which the liquid

neuinil. Also, the amount of caustic soda ilepends on the

1 : the more dilute the solution, the sooner does the blue colour

cftuse of these phenomena is the difference in the dissociation

thrM hydrogens of phosphoric acid. The ilissociation H^PU, =

[H.l*<^,* <>cciu^ comfiararivelj' easily and in nieaaural>]e amount.

tirtht-r dissociation H^P<)j'=II" + HPO^' takes place only in very

. and the third die-sociatiori, llPO/'= H* + PO/", is ex-

tv^iy -light. When, therefore, a nonnal salt, c^. the solution

i*jPO^, Li dissolved in wattT, tlie corresponding ion V0^' cannot

but act* on the water of the solvent in the sense of the c<(uation

-»■ H.O = HPO^" ^ ( >H'. Hydroxidion is produced, and the liijuid

therefore, react alkaline. In other words, we have hero again

of hydixjlysia (p. 200).

dirafent ion, UPO^", also experiences in slijiht degree a
transformation in aqueous solution, HPO," + H,.0 = H.,Pf)^' +
so that the disodinm phosphate also undergoes slight hydrolysis,
tboreforo exhibits a feeble alkaline reaction. This is, however,

feebler than in the ease of the normal salt,
tince these diiferent equilibria exist side by side, and are also
It on the lempcralure ami the dilution, it is clear that on
ion the hydrion docs not suddenly disappear, as in the casyb
acidd^ htit its Aiiivunt dmiukhes gradually and cot\Ui«iwi^^.

368 PKINCIPLES OF INOEGANIC CHEMISTRY

For this reason, no sudden but only a continnoua change of col
occurs whiiii litmus ie present. |

The heiit of foraiatioii of the trivMliant phosplmnioii PO^". amo^
to 1246 kj ; that of the divalent hydrophosphanion, PO^H", 1277 j

3 or*. Pyrophosphoric Acid. — If oithophosphoHc acid is cartfl
heated to 2^>0', it loses water and is converted into pyrophoaph
acid, H^PjOj. This process takes place iii accordance with
cqiiation

A sure means of obtaining pure pyrophospboric acid is
such salts of oi'thophosphuric acid as contain just enough hydrog«ii
yield a residue of pyrophosphate. This happens in the case of .
salts in which two hydrogens are replaced by metal, r.p, ordinary
sodium phosphate. If this salt is heated, the following reaction
place —

2HNa2pO, = Na,PjO. + HjO.

The free pyrophosphoric acid can be obtained in awiueoiis
froro the pyrophosphate thus formed, by converting the Utt*r
tiithcultly soluble lead salt and decomposing this with sulphui'f
hydroget], I

Unlike pyrosul]fhui-ie and pyrosuJphuroua acids (pp- 294 and 2|
pyrophosphoric acid retains its state in aqueous solution for a tii
and change* ocdy slowly into orthophosphoric acid. The latter rw
sents the stable state to which the aqueous solution of the acid ml
all circiunaUinces approaches, The velocity with which this contlil
of eipiilibiiura is reached, depends on the temperature and the «
centratioii of the hydrion in the aohuion ; the latt-er accelerates '
transformation catalytically. For this reason, the transforaut
takes place much more quickly if nitric acid is added to the 8oIu^
and the concentration of the hydrion thereby increased.

Apart, from the composition of the salts, pyrophosphanion is (
titiguLshed by various reactions from orthophosphanion. Aa
apjjarcnt from the fomuda, it is tetrabasic, and forms, according
four series of saliva. The neutral or normal s^tlts eontjiin two d
bining weights of a monovalent metal or monovalent cation to (
combining weight of phosphorus, whereas normal stih^ of orthopi
phatiiou cotitaiii throe combining weights of a monovalent cation
one of phosi>horus.

To distinguish the two ions, silver nitrate is added to the bC
tion. If the ion PO^'", be presotit, a yellow silver .salt of the comp<
tion Ag.|PO^ is precipitiitod ; pyrophosphates, or the ion PjO."", yia
on the other haml, a white precipitate of the composition Ag^FJ
By means of this reaction also, one can obser^'e the slow tmnsfonDWrti
of a soiution of pyrophosphoric mtQ ortlio^hosphoric acid.

PHOSPHOKUS

SICtAphosplloric Acid. — On hualing orthophosphorie acid

Pstmn^lv. it frt*s(js into uiditphonphm'ir aciil, which aiiftlysis sLows to
the cotnfiosition HPO^. Its coiiifKjsitioM is, however, not repre-
itf! ^v- the simple fonnuJa but by a multiple formuJii (HPO.^)„, wljere
!»* number. There are various metapliosphoric acids which are
^ui> (JUlingutshed from one another by the difference in the vahic
■{ the chetnistrj of these compounds, however, hits as yet been
MwJ ap ouly to a rather fiinall extent.
Jbleta.j»ho6phonc ficid obtained in the aliove manner fortna a glass-

KBM which, at a moderately high tetiipeiiiUire, melts to u viscous
And, on cooling, forms an amorphons solid. The *' glacial "
B^ihorie acid of commerce is metaphosphoric acid. It dissolves in
Khyieldmg an acid liquid whose reactions are different from thosM;
^Viiiber phoaplioriu ai^ids. It givey, indeed, like pyrupho!;])horic'
1^^ white silver sidt, hut has the furtiier prot>erty of jmxipUalini/
■MUM, a property which is not pos-siessud by the other phospbotic
ik. A solution of motaphosplioric iicid is used, therefore, to detect
i freaencf «»f albumen, ejj. in urine. For this purpose, the solution
tte »ci«i uMsi be freshly prepared since, on keeping, it is slowly con-
into orthophospboric arid.

tills transformation, the same general remarks hold as were
for the corresponding transformation of pyrophoapliortc acid.
jihoric acid has, however, (lot l>een detected as an intermediate
idnct, although, on theoretical grounds, it ift probable that it is
had formed.

Also when phosphorus pentoxide is dissolved in w^ater, metaphos-
hHK teid IS formed as the first prorhict, anil not the form which is
|M stable under these circumstances, viz., orthuphusphuric acid, in
Rftrdjuice «rith the general law of the first appearance of the less
IM« fonu!>.

LJ68. Chlorides of Phosphoric Acid. — If otthophoaphoric acid
• capable ol further taking up one combining weight of water, a
■e acid would be prwluce<l : H^PO^ - HJ3 = H^PO. or P(OH)y
can imagine all the hydroxyls of this acid to V« replaced by
vtc obtain PClf,, the pbusphonis pentJichloride alrea^Jy de-
As a DUktter of fact, the chlorifle, when decomposed with
Wtr, jielfls pho.sphoric acid alont' with hydrochloric acid : Pt'b +
»H,0=H.,PO, rSHCL

xided this chloride, there is also known the chloride of ortho
loric acid, if the formtda of thi.s is written PO(OH),. This

Ic has the composition POClj, and i.s naually called phcvsphorus

fjxychhrule is a colourless liquid, which has the density
ti^ bkI which boil.3 at 107' and fumes in the air. It ia violently
MMDpoced bv water to hvdrochloric and orthophosphoric acids :
,♦ 3R.O'=W,PO, + .-iHCl

1-^

370

PRINCIPLES OF INORGANIC CHEMISTRY

Tbe coinpautid is prepared by the nctioii of small Jimou
water on the pentsvchlorido r PCl^ + H^^^POCl^ + 2HCL In
of wstcrj numerous other compounds can be used in which
and hydrogen arc present. If such a. compound is represent
the fotmula R . OH, the reaction tnkcs place according to ihfs eqo
K . OH + PCI. = R . CI + POCI,, + HCl. In the case of hydroxy) (
pounds, this reaction occurs so reudily and regulftriy that it is
deteriin'ne whether hydroxy] should be assumed in any giv(
{K»uiid or not. In organic chemistry, especially, phosphorus
chloride is used in this wuy as a reagent for hydroxyl.

As an example of this action, it may be cit«d that sulphur
on being treated witli phosphorus pcntachloride, yields chlorosu
acid or sulphuryl chloride (p. 305), according to the prop
used. The rc«ctions take place in accordance with the eqti
SO.,(OH}., + PCI.^HOSOjCl + HCl + POCl, and .SO,(OH), + 21
.SO^Cl, + 2POC];,+ 2HCl.

Similarly, nitryl chloride is formed by the action of the
chloride on nitric acid ; NO..OH + PC1,-N0X! + HCl + POCly .

Another prepanttioii of pliosphoiiis oxychloride is from phosp
pentachloride and pentoxide. It takes place accoiding to the
PjjOf^ + 3PCL, = 5P0C1^, if the two substances are mixed in the
proportions and heated in a sealed tube.

* The method of allowing subatanccfi to act un one aDolbefj
leeided glass tubes is employed when it is desired to use a fairly
'temperature abovo tlie boiJirsg point of one of the reacting suhst

untler atntosphcric preasure. The necessity for a higher temper
occurs when the reaction does not proceed qmrkhj etiough ul Ion
temperatures. Even in the case of substances sertled up in gliwfl lu
which must be made of strong glass and carefully scaled
volatile substance^ it is true, will partially vaporise ; tbe prea
the interior of the tnlie, however, thereby rises, and with it
boiling i>oint, so that the greater part of the substance does da
into vapour,

* The pressure hereby produced has, in general, only a
influence on the chemical reaction ; the essential point is the poaaili
of raising the temperature without the substance evaporating.

The heat of fonuation of jihosphorus oxychloride is 611 kj.

369. Phosphorous Acid.— \V lien phosphorus trichloride is
fionjpoeed with water, there is formed the compound POjjHg, which 1
acid properties and is called p/ioS^ilmrous acid.

The reaction which leads to the formation of phosphorous
represented by the equation PCl^ + 3H„0 = P{OH)j + 3HC1. It
place with great rise of terapHiraturo, and this can easily effect a fur
decomposition of the phosphorous acid. It is, therefore, expedient j
use concrntiidaf hiithochlork m'id in place of pure water. The by*
chloride formed will thou not be dissolved but will escape aa a {

PHOSPHORUS

.■^71

tb<* lioat of If actiiJti will therebj' bo diminished by the amount of
v.- 1! of solution of hydrogen chloride. The resulting acid liquid
iroin the exceaa of byJiochloric acid by evaporation on the
(1, and the jiure phosphorous ficid, melting at 74", crystalliees
rh<' liquid oti cooling,

■ ■roiis ncitl contains oiio combining weight less oxygen

LL-id, it can, Uy taking up oxygen, i>asa into the btter j

1 educing agent. On being heiited, it acts in this way

.i.ljy a ])ortion ia reduced lo hydrogen phosphide:

3H,PO

-icid

PH,.

We have here a.ssumed the formation of

as a matter of fact, this simultaiieotialy loses

into tueta phosphoric atid. The corresi)onding change

>ii uATi Y>e easily made. The hydrogen pho.'sphide which

:;es Kru at the teraperutHre of deconipOiJtlion, and burns

i-ili tlame.

I >u-* acid also Iteliaves as a reducing agent in aqueous

withdraws oxygen and halogen from many substances.

the silver and mercury salts, more especially, are reduced

meUils, which are precipitated from the solution. This

19 xiM.nl more especially for tho detection of disaolved

eompmnd^.

neuiralising phosphorous acid with the aid of litmus or any

tndicator, no Bharp tiuusiliuu is obtaiued. The liquid becomes

(before the sucoud equivalent of caustic soda or [wjlaah has been

tliat, at most, only two coiiihining weights of hydrogen of

can be replaced by metals in aqueous solution, and even in

■tate» QO salts of pho3|ihorous acid are known in which more

eombiDiiig weights of hydrogen are replaced. Phosphorous

th<!refof«, regarded as u dibasic acid, and normal phosplwsMti has

)rmula PO,H'.

This behaviour can be expressed by assuming that the two

hydrogens are joined to oxygen to form hydroxide,

the third is united directly to phospliorus. This would

<iH

th« fonnula UP Off, According to this, phosphorou!) acid

be a derivative of phosphoric acid, in which one hydroxy)

by hydrogen.

lie circumstance, however, that phosphnrouB acid is formed

UDootbly by the action of water on phosphorus trichloride,

Mffiast this, Tho formation of the acid by water is a

reaction of the acid chlorides ; these, on the othi^r baml,

mrutivea of the acids formed by the replacement of hydroxy!

inc. According to these reactions, phosphorus tricfiloride

tu be the chloride of phoaphorouB acid, and this ought, there-

'tn have the funuula P(OH)g,

two

372

PRINCIPLES OF INOKGANIC CHEMISTRY

* These contradictory views are not in-econcilable. It
necessary that all tlie hydrogen which is present in hycSroxyl
be replaceable by metala. Acctmliiig to wliat was said ou |'. 271,
gradual dissociation of a polybasic acid must take place with gi
difficulty with each successive step. We have here a case where
last stage is so difficult to attain that, uuder normal conditi
replacement of the tliird hydrogen by metals occurs, and the f(
P(OH),^ can be ijuite well rec(*ncilei! ^^^th the dibasic nature of
phorous acid. If it is desired to give expression to this, the ((
can also be written H2P0;(0H).

* The foregoing discussion furniabes an example of how ai
are made to express the so-called " constitution " of a compou
the way in which the formula is written. By this is meant t
formula is written in such a way as to give eiq>ression to Lhi
important Teactions of the substance in question, 8o thsit these
easily re^d out of the formula.

* Tlie means adopted for ibis consists in writing those el
which are often eliminated together in such a way that they
side by side in the formula ; they are sometimes still furtter
from the other elements by means of a bracket or a dot.

^ Huch a ae[>aration can, for example, be very well carried oat
the case of salts in ies[>eet of the two ions, and the forml
ammoniiira nitrate is, therefore, not written N^II^O^, which re
tlie total comjwsitiou, but in the form NH^ . NO^ to show that
Bait when dissolved in water dissociates into the ions NH/ and ""'

* In the case of the polybasic acids, which can form sevei
this eeparation causes some difficulty. In such cases it is cairii

* in sttch a way that all the hydrogen which could fonn hydrion if
dissociation were complete, is sepatated ; thus, phosphoric
written H.,POjj in this way all the three iiydrogens are
apjjear as ions, although, in a<|ueous solution, the third hydros;™
dissociated only to a very slight extent. In the case of pliospbow
acid, only two hydrogens are regarded »& ions, although we l
prohalily dealing only with a difference of degree, and not with
essential diii'erence.

'^ The demand for a universally valid formula can be still U'ss a
where we are dealing with oxy -acids which van, on the one hand, »i
off hydrion, and, on the other hand, when wat*r is excluded, acJ
hydroxy] compounds. This is the case, for example, witli siilpbt
acid. This difficulty is overcome by employing different (ormii
according to the reaction to which it i.% desired to give exp
Accordingly, sulphuric acid, as acid, is written H.,SOj, or H^-tJOi
hydroxyl compound, however, S0(,(0H)2. In other vr
" couatitution " of sulphuric acid camiot be represented by
formula, and use is therefore made of more than one, accordlni
they are required.

PHOSPHORUS

Juo Tuiglit, perhaps, also iintlt' the two fonniila* by using liiu

ttni staltti,i: tlie nile tliat the hydrogen attai^hed to the oxygen

»xyl is specially capable of being split off as hydrion. We wouhi

kowevcr, come back to the euntrndictloii of phosphorous acid,

mm tlie fact that no splitting off of hydrogen caii be detected in

of the biisic hydroxides.

be question must be asked, why it is that these relations give

mch changing forimdation, vihereaa many other relations could

kbllsboij with dfihiiileiioss and free from contradiction. The

is that it is here a question of re]>reaenting very varied

the laws of which depend on many more variables than are

in the chemical formula. The tsiak consists, indeed, of

a of a!l the transformations which one snljatancu can

i-s ; these tninsformations, also, so far as their result

>d, are not quite definite, but depend to a large e.\tent on

conditions, such sia temperature and pressure or conccntratinti,

diversities cannot, of coiii-se, be represented by the simple

of the relative arrangements of the elementary symbols, even

le aagistancc of iipiice, and a " constitutional formula " must

always remain one-sided and be limited to the representation

tte relations whii'h have a fipeeial importance from their fre([uent

aoe.

Uie very careful oxidation of phosphorus hi a slow ciurent of
white substance is obtained, which diffei-s from the phosphorus
le by its low melting p«>int (22;'i), and its \'olatility (iwiling
173°). Analysia shows it to contain three combining weights of
to two of phosphorus ; detenninations of the vapour density,
er, give the molar weight as 220, and leatl, therefore, to the
P^O^ It is the anhydride 0/ jtfienphwous acid, for

Pfin + ^HoO = 4H,P0,,.

ro. Hypophosphorous Acid. — ^The salt of this ucid is formed
[with hydrogen phosphide by the action of caustic soda or caustic

00 pb«sphonts (p. 359). The ro;u:tion takes place according

ei)tuiti)it>

*p4 .'^^-aOH + 3HJO

SNaPOjH, + PH.;

■alt produced is found in the solution. For the purpose of

ing the acid, barium hydroxide is used ; this acts in a quite

wa}', and gives rise to a solution of liariiim hfpiy>hoitp/i iir. The

obcaine^l pure by evajioriition and recryatailisatiou, and is ihen

ipuacd with the requisite amount of sulphuric add. From the

i»olution, the free acid is obtained by careful evaporation as a

line mass, which melt* at 17°, ancj is very sokible in water,

I\1)oph«j8phorous acid has the composition H ,P0., ; of the three

3T4

PKINCIPLES OF INORGANIC CHEMTSTRV c

ibinirig weights of hydrogen, however, only une lmii l« repL
letals, m that the acid is monoWsic. Hyjiuphospbosioti haa the
the formula PO^H.,'.

In its other reactiofia, hypophosphorou£ acid is very «ir
phosphorous acid. Like it, it is a reducing agent which preci^
noble metiJs from their solutions ; also, on being heattMJ, it
hydrogen phosphide, whicli immediately ignites.

The salts are almost all soluble in water, so that none of th«
he used for the identification of the imd.

An oxygen coinpourjd of plios]>horus, whi^'h would correspond 1
aniiydride. of this ticid and would hitvc the formula P.^f >( is not kn

371. Hypophosphoric Acid.— In the acid liquid which
phorus yields on heing left exiKtsed to moist air, there is coiit

tliesides phosphoric and phosphorous acids, a compound which is
mediate between those two ; this is called hipophmphuiif <triil, an
the composition MjP.,0,,. As can lie seen from the formula, it
tetrabasic itcid ; hypophosphiinion has the formula P.,0,. "".

The acid is obtained from the above mixture by pj»rtly nontr
it with caustic soda and allowing to stand ; the acid swlii
Nii.,ff„J:'.>OQ then slowly aeiJanites out, and this is converted in
spjiringly soluble lend salt which can be decomposed by mt
sulphnric acid or sulphuretted hydrogen.

nypophysphoric acid behiives, in general, aimilarlj' to phospho
acid, but im reducing properties arc less prnnounccd. On being h«
the free acid, like all the lower acids of pliosphorus, passes
phosphoric acid, with airaultivueous evolution of hydrogen pha
which jiartly burns and partly decomposes into hydrogen ami
jbosphorus.

372. Lower Oxides of Phosphorus. — Various invest
have re|)catodly jirepared .snlistanccs .sinular in appearance to
pho-sphorns, and have claimed them to be lower oxides of piiospli
Wince they have all been olttained aa insoluble .and non-volatile re
their puritieation and characterisation are diHicult, so that it if
doubtful whether one is dialing with pure substances.

373. Sulpliur Compounds of Phosphorus.— When white
phorus and sulphur are brought together, yellowish liquids are nbl
which fume in the air and .are readily infiammable. These were fo
long time regarded ns compounds of phosphorus with sulphur, hiili
has been found that they are only solnlii/us of the one element in i
other. Since the melting point of every solid stilistance is lowered

ithe solution of another substance in it, this must also l>e the case
phosphorus when sul{»hiir is dissolvecJ in it. The impreswon
cliemical combination ]ia<l tjiken place here was caused only by
fact, that the melting point of the phosphorus, which, for the jm
BubstiincOj is 44^, is hereby depressed to below room tompentturt!, i
that the solution* comparatively rich in sulphur remain liquid.

PHOSPHORUS

375

of the two elements, however, corresponding to Uie

apoiittds i>f phosphorus, are obuiined by ttUowing them to

another at a miideratcly high temperature. With white

ao much heat is thereby developer] that dangerous explo-

occur ; if red phosphorus, which contains much leaa energy,

>je*i, the heat development is correspjudiiigly lesis, and the

can be essity kept under control.

two siibetances are mixed in the proportions corresponding
formtslst Pj!>3 and P.>S._, the mixture plat-od in a glass flask,
ke Litter h«ited at one spot. Combiuiition then proceeds
, iHit witliout explosion, through the whole mass. The re-
oompound is, at Erst, Iit|uid, but soon solidifies to a yellow-
^sttllioe ni»S9. The two compounds P„Sj, and PuSj can
be digtiaguished by their appe^irance. The yellow-grey
M due to contamination with red phosphorus ; the pure coin-
are yellow, crystalline masses which look like sulphur, Imt
Jer in ciitour.

comfMunds do not take fire ejKintatieoualy in the air ; oji being

'lieate<I, they burn to sulphur dioxide and phosphonis pentoxide.

of sulphuretted hydiogen, because they are converted by

Tapour in the air into this gas and phosphoric or phosphoroua

P.^r •♦- 8H.,0 = 2H,P0j + 5H./>. They act similarly on cnni-

contajning hydroxyl, and convert these into the corresponding

emnpounds.

these compounds, there are still two other sulphides of

jrus, the composition of which is represented by the formuliK

PjS„, They can be obtained pure by melting the two

together in the proper projiortions and distilling under

pavasure.

I A eoane mixttu'e of various sulphides of phosphorus has recently
Bsn tued for the manufacture of matches, a» these suiistaDces do not

Ktbe poisonous action of white phosphorus (p. :i53).
1 view of the analogous composition of phosphorus pentiisulphide
the ctirn^sponrlin^: oxide, it may be asked if acids cannot be
krired from the sulphide, aij can be done in the case of the oxide. It
» wy probable that there o,x,ists a wholf series of acitls eorresfjontling
tike oxypen acids of phosj»horus. and Loutiiining sulphur in place of
They are, however, veiy slightly stable, since they are con-
by water into the corresponding oxygen compounds, with
!*a of sulphurrtted hydrogen. We shall, therefore, not enter
discussion of these compounds^ especially as similar compounds,
Itnore stable and bettei* characterised, are met with in thti case of
and will Iw then disfussed.
rr»t slal)ility, however, is possessed by phonpfuints srtlphorhknidfr
llphiir cnmpound roneNpon<litig to phosphonis oxycliloride. This
He comiMxition I'fclCI,,, and can be obtained by heatltlg phosphorus

.'{78

PRIXCI'E*T^E.S OF /\..i

•-^- ."'.■ »■

HE-MIS

fulfillwl. In the ca,$9c of tlic i,,ii.,
(lone :

II— H; CI— CI -, Br— iJr: I
II— F; I -01; 0=0: S
II— S— H ; H — Se — H ; I ■■
CI -0—0— II; (;l_(>_-.>

d— S— S-Cl; CI— S—CI •

0—0—0: H — S— 0- '
H— S— O— O — O— O- 1 1
H— 0— O— S — O— O- I!
of siilphiu-, selenium, and ■

P = 1' As .:

N = N;1 I ; |

P = 1» As .

Oil the other hiin.:
pounds

SCl^, s...<

and many otherss.

Various attempts !■
chiefly by assuniiii;,'
Thus, the above siili-;.
referred to a tetrju;:-
compounds, at least ! i

• '^- -o the sam
' :aoii- form,
10

-Ko.

CHAPTER XVI

CARBON

i>76. General.- — Carbon is one of the mo^t important elements in
respect both of the variety and wide distribution of its compounds and
of the importance which these have in nature as well as in the arts.
Although oxygen, hydrogen, and nitrogen are never failing conatitnenta
of living or organised atructurea, still carbon is frequently aiUed the
e>j*y<in»V rJimeid jhit exfeHrnef, b6caLtS6 it IS oti the combining relations
exhibited by tbia element that the diversity of the substances of the
organic kingdom most essentially depends.

But the pre-emiuent importjinee of carbon is due not only to its
Ijoing a coiistilnent of the substances of which the structures of living
things are built up, but much more to its being the expression of the
supply of energy which is exiiended in lital action. For a similar
reason, carbon is of iraportr-tnce in the arts, for by ftir the greatest (jart
of the chemical energy which ia set in motion for the accomplishment
of the most cliverse ends is derived fi-ora the chemical tnmsformations
of carbon.

ElemenhtTij earbon occurs in three dift'erent forms, ^vhich exhibit
relationships to one another similar to those found in the case of
sulphur or phosphorus. It exists in two crystalline forms and also in
an amorphous state. The different varieties of amorphous carbon
are usually, but probably incorrectly, classed together as one kind.
Indeed, there are important reasons for thinking that tbere are several
kinds of amorphous carbon, each possessing difl'erent properties, but
none of which are known in the pure state.

That which is called eharcMil is amorphous cai'bon in a more or
less pure state, On heating organic substitnces, e.tj. substances derived
from organisms, esjiecially plants, and containing carbon, a residue of
this element is generally obtained, whereas the other elcinents presen
especially oxygen and hydrogen, escape in the foriu of water and
lower carbon compounds of these elements. Moreover, the resii
contains any non-volatile substances which mny be present, as well
residual quantities of hydrogen and oxygen, which are larger
amount the lower the temperature of earboniaation.

381

382

PEINCU'LES OF INORGANIC CHEMISTRY

lu the chai'coiil prmluced, the structure of the material can in
cases, r.t), when obtained from "vvochJ, be recogniseil ; wootl cli
exhibits every cell of the wood well preserved. Tim is due U>
fact that At the temperatures which are reached under these coiiditi
•carbon is an hi/iifiible mbslancv. If tfie original material has ale
same property of itifusibilitj, as is the case with the substance for
the cell-wfdls of wood, the form is well retained on carboniMtt
In other cases, where the original material liquefies either before
during carbonisation, e.g. in the case of sugar, the charcoal whic
obtained has the appearance of a mass which has been fused;,
however, is due only to the fact that sugar, not carbon, is fusiblM

Sugar charcoal is tnucli purer than vvood charcoal, because in'
the presence cjtn easily be avoided of non-volatile impurities wltichi
present in the caae of wood charcoal, and which, on complete
bustiou, remain behind as a grey powder, the ask.

Soot is a atiJl purer form of carbon. This is obtained by
combustion, in h small supply of air, of volatile compounds of
and hydrogen, of which there are a large number. The hydij
then combines with the oxygen present, and the carbon is dcj
and can be collected in the form of a very fine and light p
Small fjuantiticH of hydrogen compouuds which it litill contain*
usually be got rid of by igniting it with excliiaiou of air.

The piopertioa of this form of carbon are tho well-kiiovm
colour, a small density, easy combustibility, small conductivity
heat and electricity, and a low degree of hardness.

All these properties, however, cannot be stated in definite iiuinben,]
but are found to vary to some extent, and tliat, indeed, in the folloi
iiig way. The higher the temjreraturo to whicli the amorphous carboul
was exposed, and the longer th.it temperature was allowed to act. wT
the cartion, the greater are the density, hardness, conductixity fofj
heat and esjjecially for electricity, and the less is its combustibility.
At the same time, the deep black colour passes into a grey one witln]
somewhat metallic lustre.

It has iu>t yet becTi settled whether the cause of these changes til
that the small particles of whicli the charcoal consists unite togetba;]
or "sinter," at the high tciniJcraturc to larger particles, or that there 1
are dilUrt^nt fot^tns of amorphous carbon which occur mixed together in i
charcoal, the harder, more dense, and better conducting of whicL formi
are increasingly produced at higher temperatures. The melting poinll
of charcoal is certainly aa bigli as 3000' or 3500", the temperature oJl
the electric arc, Imt it is quite possible that the general property olJ
amorphous substances, of having no duhnite melting point, is preMotj
also in this case, and that, therefore, oven at mtuih lower tcmjK'raturrvl
an incipient softening may occur which would !«m1 to the formation <
larger grains by tlie caking together of the smaller, lu this w»y,l
the above-mentioned changes can be pai-tially explained. It app€«r

CAEBON

383

ly in view of the increase of the hardness ami coii-

nn*re appropriate to iissmiie tbe existence of several

of amorphous carl>on, which (Hffer from one another iu the

ribed. and which in varying proportions make up ortUnary

retains the solid state with especial obsduacj. Only at

iperaiUTti of the ekctrie are, about STjOO , does softening and

lion occur. Further, lht«re h scarcely a solvent whitb dis-

e»rbon to any great extent. The only better-known one m

\ iroo, iu which carbon dissolves to the extent of a few per cent

ipsmtively high temperatures, and from which it separates out

the metel solitiifie^. Under these conditions, however, carbon

^not appear in amorphous form, but in the crystalline form of

itc, wiiich will Ite described later.

heaititl IU the air, carbon unites with oxygen, and is con-
C'lrUm diojdiie,
fossii charcml occurring in natiU'o, such as ai)thmc'de, axti,
/Tj fvai, consists, it is true, chiefly of carljoii, but it also
hydrogen and oxygen along with small quantities of nitrogen,
and very var^ving amounts of ash, i.e. mineral admixtuied of
The different sorts have all been formed in a similiir way
tjarcoal, viz. from the remains of previous vegetation by the
of the other elements and the formation of a residue of
This process has, however, taken place at a low temperature
paired very long periotls of time. This process of carln>nisation
ngressed furthest in the case of anthracite, which contains only
itQwll (juantities of hydrogen ; not so far in the case of ordinary
[■od Icoiit of all in the case of brown coal. The latter sub^tfinces
he regarded as carbon in the strict sense ; on the contrary,
fcomdatof derivatives, of complex composition and certJVinly very
kin carlwn, of the substances of which the original plant-structures
I built up, or of mixtures of such substances with amorphous carbon,
heating ordinary coal with exclusion of air, the hydrogen is
»wi in the form of carlxm compounds. This process is canierl
On a large sc;Je for two piirpoaea. On the one hand, coal rich
kydtvgen is subjected to heating or "drj"' distillation," and the
|u« eontaiidug carbon which are produced are collected in order to
f* uiwl, after purification, for illuminating or heating purposes. This
Buufaclurr of <vaJ gus plays a very important part, since gaseous fuel
LfioiMiMa irajjortant advantages over the solid or litpiid. Wo shall
into this tnnre fully lat*r.
)n the other hand, coal which is poor in hydrogen is also subjected
ilistdlation in order to obtain in the residues carbon which is
fre« from hydrogen, and which in many cases, especially for
llurgical purjwses, is to be preferred to coal containing hydrogen,
residues are called rokf, and are made on a very large scale.

384

PKINCIFLES OF INORGANIC CHEMISTRV

A jioiiit which is of essential iTOportitiice here is tlmt the
portion of the sulphui- pi-cseiit is removcrl in the carbonisation,
in this respect also n [mrificatiori is effected.

377. Adsorption by Charcoal. — The poroue and cello
fharatter which iimorphous churcoal fraquently assumes, wii«t>n
diiceJ ftom org*riic structures of a correspoiuling form, UfveloptJ
property which is possessed, indeed, hy all sulratances, but vrbt(ii,|
this case, appears with especial distinctness. This is the power
scssed by poroue charcoal of absorbing dissolved and gaseous sul»t
from mixturea, and so freeing theao giis mixtures or solutions
certiiin components.

If, for example, wine, litnms solution, or similar coloured solutio
are shuken with Knely porons charcoal {the moiit suitable bein^
cluirfMii, obtained by carbonising hones), and then fllt«red, ihe lu
passes through the filter either quite colourless, or, at Icjvst, consider
lighter in colour. Likewise, from turbid, impure, or e-vil-sn
water there is obtained, hy filtration through charcoal, clear
which lias lost its smell entirely or to a large extent. For
purposes of purification, charcoal is largely used botli in the art^
in the laboratory.

The processes with which wg are here dealing aro called fti
and depend on the fact that at the surface of contact botwcen a
body and a solution, a ilitlerent concentration of the dissolvwl
»8tance is produced from that in the interior of the solution. In
'Cases, the concentration of the dissolved substance at such bou
surfaces is greater than in the rest of the solution, but the op
can also occur.

The cause which produces this action is of the same kind u I
which etTecta HYlthiff. The bounding surfaces l)«tweeu different
are, generally, the scat of a pecnhar kind of energy which is
surfaci^. riurgi/. The phenomena of awrface tension or the pheiiomc
of capillarity represent only a small portion of the aciions of snr
energy ; indeed, this comes into operation in all cases where iliffcti
bodies come together, or where surfaces of stparwiuw jtre (ira^enl.

If, now, certain substances have the property of Incoming specia
concentrated at a bounding surface, they will be removed from a mIi
'tton in whicli they are present when such buundinj; Burfacw
formed in the ."lolntion. This is the wise with charcoal and the aUv
mentioned tojourifjg matters. A deJinite equilibrium is establish
between the portion in the solution and that absorbed on the char
the, greater part going to the charcoal.

This action depends, in tlie first place, on the nature of
jsBolved substiince, but to some extent also on the nature of
f-Bolid body. Substances of complex composition generally ptissess
a comparatively much greater extent, the pro[>erty of liecominjj
centrated at the bouutUng surfaces, whereas more simple nubeLtAna

CAKBON

385

*»par

III chiefly in the sotutioii. Since, now, most of tlie colouring

ters whii'h iip[jear as unweJconie conipsiiiion protlwcts in the

ration of organic substances huve a very cumplex nature, they

be fre<iuently removed from the stjliitions by this means. The

od is employed with very good results, for example, in the sugar

neries, in order to so far decolorise the dark brown beet juice thut

lite sugar can be obtiiineti from it.

The siirnt' holds also for the malodorouH produets of decompoaitiun
orgJinic bodies, animal excremental matter, etc., which, on account
their complex nature, are also, as a rule, abundantly aViSorbed by
rcoal.

Finally, what has just been ^id holds also for gas mixtures.
also condense to a more or less considerable extent on the
vorfaces of solid bodies, and again, the more complex and denser
es do so generally much more than the simple and light ones,
fliie former can, therefore, also be removed more or less completely
from mixtures with the other gases.

?5ince the action takes pla*e at the bounding surface between the
solid body and the liquid or the gas. it is proportional to the surface.
The amount which 1 sq. cm. of surfiicc can retain in this way is very
, small; in one special case (that of ammoina on glass) it has been
found equal to a .•.Tnnnrmjt'' E™- pi'O ^^l- cm. Even if in the case of
other substiincea the numl)er can become ten or a hundred tfraea as
great, still the amounts wHth which we are here de;ilirig are always
axceedingiy small. To olitiiin measnralde iimounts, therefore, very
|Mprg6 surfaces must be etnitloyt-d : for ti»e absorption of one gram of
■ammonia a sffuare surface of .50 metre aitle is necessary. Such large
surfaces are found only in the case of very fine powders, or of very
finely cellular stnietures.

This quality is posi^esiied by bone charcoal, because bones contain,
besides the organic rniittcr of a gluey nature, large fimounts of calcium
phosphate. On carhontHation, the celluiar structure is very completely
preserved by means of this embedded matter, and if the calcium
phosphate is removed by solution in hydrochloric aeid, a fairly ptu'e
charcoal is obtained which for a given amount of sub-stance possesses
an exceedingly large surface, and therefore exhibits the phenomena of
absorption with especial distitictnesa..

* If organic subatancea, i-.g. sugar, which do not themselves yield
on carbonisation a charcoal with largely developed surface, lie mixed
with calcitun phosphate or similar infusible and readily removable salts,
n strongly absorbing charcoal is obtained by the carbonisation nf such
mixtures, afTter removal of tlie admixed substance. In this ca^e |
large development of surface has been artificially caused, and ^rith
also, the corresponding action obtained.

Another action which is corusected with the one jti-'st describe<i ^
the mtaliftir ticfxlemtiim, especially of gas reactions, which is e5c©fttt/t

386

PRINCIPLES OF IKORUAXIC CHEMISTRY

by subelances with hirgely Jevelopeil surface. Thus, the oxida
many suUsUmces by free oxygen in gi'oatly ;i.ccelerateii when ct
is present. Likewise, gases which under given conditions
slowly on one iitiother, cuu l»e mntle to act more quickly wr
help of charcoal. In these cases, however, thi- ai-tioiis of chart-oal !
greatly surixussed by thu antilogous actions of s{tungy pktiniiiu.

378. Graphite. — (u-aphite is a crystufUnf iorm of tarlwn.
occura in nature as bluck-gi'ey masses with h feelily metallic luslr«,l
cryfitallisGS in forms Iwiongiii^ to the hexjigonal 5>3Stem ; it is fou
^various localities, especially in Bohemia, Cumberland, and Kiljeria.
density is 2"2f>, It is distinguished fi'ora amorphous carbon
greater density, its gootl tonductivity for electricity, and th«
difficulty with which it burns, It is possible to effect it" coint
OFily by heating it to a bright red heat in a current of oxygen.
Lthe denser and better conducting forms of amorphous carbon,
fdisliuijiiished by its very low degree of hardness. This circir
ItnakeB it probable that iimorpboua carbon which hus Iteen st
heated and has therehj- become a conductor, does not owe
property to the formation of a certain araoiml of grtiphite, for
carbon becomes at the same time very hard and does not giie a M
IBtreatt as graphite does.

Graphite can also lie obtaiired itrHfukiUit by allowing car^wo
crystallise out from fim'd iiifi<sls. It tins already been nientionfcl
this is best known in the case of iron, but there ai'e other
which dissolve small quantities of charcoal when heated, and
which the latter separates at lower temperatures in a crystalline I
as graphite. In the arte, graphite is preparetl by heating cli
rinixeil with lime to a high temperature for a long time in the ele
furnace. The lime cata5ytically accelerates the transformation id
graphite, probably by giving rise to an intermediate couijkjUI
(calcium carbide, p. ill). '

Graphite, also, must be divided into ditt'erent groups which exhilj
a somewhat different behaviour. It hag, however, not yet been leU
whether these differences may not jwrhaps be due only to mecha
differences, tin- one form consisting of innunu'ralile lamina; laid th
together, while the other forma more coherent niasees. We shall bw
thf refor»i, refrain from entering; on a discussion of those dilfert^uce*.
Graphite agrees with aimnphous carlioii in its resiatanco to fuai<
and volatilisation at comjiaratively high temperatures. It is
therefore, for making irunUta which have to withstiinii esptu
high temperature.^, and for this piu^pose it ts mixed with some clayJ
act ms liinding material and tbeii moulded. The sliyhl eonibnsllhil]
of graphit*^ allows of such crucibles being heated without special
cautions even in the air.

Some further u|iplications of graphite are due to its pioju-rtyj
being split into thin scales, LmH peneiU are made from graphite. '

CAIiBON

3d7

iKirm Hruly iniwiicred, ami, by admixture with clay or other

uiiticrial, fur:iR-d into thu well-kjiavvii ihin rods, to which

b imparted by sliglit tiring. According to the amount of

adde<l^ the pcDcil hjis varying hardness.

ther, graphite is used ns a lubriuid^ and this also de[)cuds on

dtsinte^niLJori into ^ujooth scules. These fill ii(j iiny uneven-

lh« rulilnn^' surfaces and quickly fiirm a saiouth ci*ating,

'^ on ft«sy gliding, \Vh«re it tan bft apiilied, graphite

intage over grease of Jjeiiig iiisfnsitive to ditferonces of

lure.

Diamond. — A second crystalline form of cyirbon is the

mi. In contradisticiction to the tvro other forms, diiimond is

It And colourleiis, but possesses the power of strung refnic-

disfiersion, so that, *vlien cut into regular forms, it exliibits a

Jentble tustri' iind pluy nf culuurs, to which its use as a gt-nt \»

That it L'OtiaiHU of pttrt* Liirbon is !>t'en IVoai the fart that it

oit cumbuBtiou carbun dioxidt-, and this also in eXActiy the

. proportions a« any other form of jiure carbon.

)uinond crystiiltises in tlie regular systom ehietly in octahedru,

often exhibit somewhat rounded odgt-s. Ita density is 3'5.

ropertr which is most itiiiMirUnt for its applications i% its great

Iq this resjtect it is .iu|i*-'riur to all other naturally occurring

Btul &bo t(( must uf tho.'rK^' thiit can be artificially prepared.

»1 for cutting glu-ss, f*ir drills for working in imrd rock^ for

used for turning very hard steel and emery Amcs^ etc. A

roiatiug disc of tinplate or of copjter into which diamond

have been pressed, cuts glass oiid othe^r hjtrd siibatances with

According a.s it. is desire! to use the duiiuoritl for wriiivij on or
gUss, differently formed pieces must Ik> used. For writing,
any point amy he used which when ]iroperly hetil will lierapc
iotftr* from the surface of the glass, and according to the sharp-
tit0 point and the pressiue employed, the finest lines can be
For tutting glass, the diamoTid must have a chisclshaped
rhifh will cleavf the gl!i--is ; such a diamond cuts, therefor*-', only
idclinitf position, and muiit be held accordttigly.

>on<U occur rather rarely in nature, so that their price is high.
iirtificuil preparation has recently been successful, but has as yet
only iiiiciohcopically small crystals. Diamonds are obtHined
iron which contfdns uarlMin and allowing this to fall in small
ittties ioto water, iso that it h suddenly cooled. If thi- iron h
dweolvod. a KTualt quantity of a cryiitalline dust is left whose
^luirdneivi, resistance to the action <if chemical agents, and
m on heating, tthow it to ije composed of dinmond. In
such artiiieial iliamurids are bUowh hn seen under the
ape.

PRINCIPLES OF INORGANIC CHEMISTKY

Although the pure diamond ii colourless, diamonda of all
colours, especially yellow, und from brown to black, occur iii
The latter, which have uo value as gems, are uaetl for technical pu
The colours are due to iinjmritieB, eapecially organic suljelAncesLJ
Ab regards the mutual stability-relations of these different fo

carbon, we ]>osgess se
exact knoMrlodge, ia
transitions take pi
with such excessive
that it is hardly
follow them cxpcninl
The following has
liflheil with some dej
certainty.

Amorphotis carbon
p,„. lui). be regai'ded as the

stable ; it coutainii the \
amoitnt of energy. Graphite must, very probably, In* regntdt
the most atable at comimrativeJy high temperatures. The Ffoson j
this ia, especially, that at very high temperatures diamond past
graphite. Accordingly, diamond would, with respect to »h
stand in the middle.

However, as 13 known, the relative stability of different formrl
the same substmce depends very miicli on the temperature, ladf
ia, therefore, not admissible to directly draw conclusions as t«
relations at ordinary temperatures from those existing at 3000'.

380. OompOUndS with Oxygen. ^Carbon forma two oKidet,!
combininiT weight uf carbon being Me to unite with one or with I
cumbiiiing weights of oxygen. The second of these compounds ii'
far the more important.

f'arhuH (iw.ride, CU.„ is a gas with the normal Meight Ai -. A
colourless, has a feeble but distinct taste and smell, and disioltll
fairly readily in water. At room temperature, water abeorbe
an equal volume nf the gas. With changes of pressure and tcntf
ture, carbun dioxide ebowa appreciable deviations from tlie simple
Uw8 ; by increase of pressure it can ha readily liquefied. In
following table the vapour pressures of carbon dioxide aie (d*
these are equal to the pressures which must just be cxcee«ied
order that the gas may paas into a liquid.

TejiijKMi,lurc.

rrtJtKBrfc

Tcniiientunv

l»n-*nji«.

-80°

I'OOBtm.

-10"

ai5-"*atlii.

^-o"

2-OS ,,

3.^M0 ,.

.m°

3-W „

+ 10"

4ft'05 „

-50'

a-ao „

*20'

.^8 84 ,.

-40"

lO-af. „

4 30*

73-84 „

-80*

If. -If. „

+ 31-

76-56 „

^20'

1S»'«3 „

*> CAi;&:»N" «<:

As can be seen from this tal>Je. the }ress.-.;rt ;: ".;.;.;f:*.-:\^v, »: .■*

eqnal to 35 atm. ; at - j^O the jikssktv ci I jk;r.-. :# *';*.v -.ov.:, -.n

tee to iiquvfr the gas. The critical wnijvnv.irv :* ;»". . ::::* •.# '.\\^

it up to which the coorersioii «.it' tiie isuj :\» a "iou-vi ^an 'v o'*o«:*\i

prusiire.

381. The Critical Phenomena. — Siiuv it wa# i» tUo *.i>o .<(

Aon dioxide that tlie critical phenomena won> liret disi-i<\ on'il in
me mutual connection, it will he upprojiriato to aisi-uss ihoM> nioio
By at this point. This will l)e best done with the help of a tliagiiiiu
■"resenting the relation oi prt-isun and lyiliiiii'.

In Fig. 101 the volumes are measured to the lijthl timl ilie
isures upwards. For every temperature then; will then he a line
iWch will represent the corresponding vahtcs of preMsiire and vulunio,
It therefore, any definite temperature is tuken, there will e<>rres|H)nd
^each pressure a definite volume, and wr mxii .■ all tlie rurrexpuml
ralues of thest; will be represented by a eonnertin)r line, wliirli i i
ed an isotherm, because it is a line of constant l«',ni)H-ratiire.
, For liquids, the isotherms have the followin/j form. If lli'-
[|n«ure weighing on a liquid be changed, the volume ehanKCM in tin-
'l^posite sense, but only to a very small amount, because iIh- iMwyv.-
'lAility of liquids is very small. If, thei-efore, in thi: above m. nii'in-d
digram, we measure the volume.-* to the rifilit and the \if. -nn-^
^wards, we obtain an almost perjiendieular line, sin',': almo-.t id'uf)' :il
tDlumes correspond to very difTerent iir«-i»siir»,'s, and i.h»; f'wjnci, ii:<:.'<-
lore, lie almost exactly under one another. ()ti a/xoiinf. >i\ rh': <'..v\ \
•■ewase of volume with dimini-hing pre^^ure, the \:','\i'-!iu i-,r ..<, ,.'.».
Bclines slightly to the right if w<r folio-* i*. :!'>:tt v^,;'-. <•,•.'.:.■'■>.:■.'
that is, in the dire«.-tion of smaller ,'»r^-.-. ;:•:» I;. }r .-j .';. ':<■
narked 13-1 shows on the left v.v:\. * '...■..': :•■■.'.:.-.:::.

At a definite minimal yvr^y-.T*:. '■■.■•...: :•:/.:.'. v. •-;
the liquid. If we now acEernp: •.•; :..-..-.*.■ .:''■■: v..'-. :•■■'-■■■■
inereasing the volum*. t* do n-.; v. x.-i*i-;. -. •. v..-. ■ff.-..' > y .''

•Dd the pressure reirjit.* ii,> v";.,.... ;.-.-; -,•- :>:•:.■ k' ■. .•- ■.-. • / •••
soMtant, A line r?i.>rie*Kiriri^ ■■.■■.■r..<*-i.'.'. •.■'-.-'.-. >• ■ '■■</'.

B a nOftZOhtni Irl^ iz. '.rir 'iia^riiT. P .'■ ■ ■ ■ >'x ■• • ■ . „■

ud vajiour. the i-'Xi-ina. i*. rr;>ii'^f.''"-t i ■.•-'' -■■•-■

ponion of th<- !iv '.i l' ir. i'.x. '. ■ ■ ■■' • "■■'

ToJume, aJi the ii:-J.i 3.Tafi7 •»■• i.;i.'-i • «-• • ''

present. So bo.^ w :u_-4 ;ccji;'^. 'aa ■'' ^ '• • '•'

volume increawfe. -i". Vt \ m:;«;'i .i^n:* • : •■■ -•■
The vajiour fonu*: i.Cj-.vri. ior.r-:..ii-' •- ■'■ -' ' '

:on£t., and the ir.r,ii.ra is Tiinr^'tmn;-": ■■ » .• ■' • ' <■
n Fig. l^. p. 77. ;r i iTiJwhoia. T'li- ■" ■■'

3-1= in Fig. IC

If now we ujm.^ -jie iMQe '.i\n(.t»u--r- ■ '
i^ier tSflSSnaxirt. T>> may. M lesin "^ ' • '•'"■

390

PRIXCTPLEH OF IKOKGANIC CHEMISTRY

CVk^l

word for word. The difference wbicli exists codsisLs in the fact
the volumes of the lirjuid, on account of the higher tempentvt,
mtber greater than preWoiisIy, under the same pressores - tbe li

isotbenn, dierefore.

the

leo

«r

yia. l«t.

to the right of the pti
•viouK one. Further, in
rapour^ on jMcoant of lk|
higher temperature,
pears at a ^eater [
the horizontAl partuo i
the isotherm, theefnl
starts higher up tii:!
previously. Fituillj. ,k\
iiqtiid entirely ev
at a stualler volnme. Fo;l
even if on accooot of tkl
higher t^mpemtuiv
vapour should have, at i|
given pressure. » «n»ll«r|
density, still the increw
of the vapour prwain
by which the volume i|
diminished, umonnt* t«l
much more, and the toU
result is a considienlihl
diminution of the voluml
of tho vapour. Thil
form for such an iaoth
at a. higher teniperatort]
is represented in Fig. 101 [
which the tihove nientioiuii
can be seen.

by the cune marked with 211, in
differences from the lower isotherm for 131

Tiie higher, now, the temfwrature i& taken, the nearer do thfl two
ends of the horizuntal straight lines come together, "(.f. the le«s do tit
volumes or the densities of the liquid and of the vaiJour differ tron
one another. On the isotherm 311" the two finally come together is
the point K.

The meaning of this is that in tho point K^ the densiiu.^ i,f liaai
and t'ujHiur futve hfamte ttqm^, and since, apart from thia, the compoa-
tion and thimical nature are the same, the two states become com
pletely idtniknl. At this pointy tlie aiUeal jtuint, therefore, tlw
distinction between Iif|nid and vajiour disappears.

At stil! higher ternperaturea the isotherms, of which there are still
some in the diagram, have nu UorizoutfLl middle poitiou hut are con
tinuous. Hcrt, aaoidmffh/, thr jikenumemi^f fiqihfadion und eivporatum
are no lont/ir jnt^ltle, omi all ckaitges of shiU take phtce cf/ntintwusljf. At

CARBON

jfirst the proximity of ihe critical point uiakeg itself stDl evident in the
flexures of the isothemis, aa is clearly shown in the isotherms SS'S"
■nd 3ii'5' ; nt 48-1 ", however, these have also disappeared, and the
Saothemia no longer differ easentially from those of a gas. The corre-
Bponding isotherms for air are inserted to the right at the top of the
diagram ; thestt show that carbon dioxide, under the high pressures
employed, (Ifviutes from the gas laws in such a way that the volumes
are considcrablv smaller than in tfie case of a perfect gas.

The region enclosed by the curved, dotted line, in which the hori-
zontals rejireaenting the stiites liquid plus vapour lie, can he called the
region of ttebTtigrumtis slates, since in it tu'i> phases are present.
Everywhere ahe, there is only out phase present: at the left edge,
liquid ; at the right, vapour. The diagram shows that ulmr thf fritiml
paint thfgf hw littler rrgkni-tf tire cmitinumish/ amitfcfcd nnlh finf. aiwthn.
In other words, it must bu possible to convert a liquid into a vapour
or a vapour into a livpiid without the one ever being observed to
separate from the other, or without liijuid ever visibly passing into
vafwnr, or mr.e ivrsn.

To perform this, carbon dioxide is, we shall suppose, first compressed
at a low temperature, so that it is completely converted into a lit}nid.
One thus conimeni;es with a point which lies to the left of the region
of heterogeneous states. If, now, the pressure is always maintained
high enough so as to remain in this region, and the temperature be
raised aliove 31 1", we always remain to the left of the central field
but reach a point higher than the [mint K. If tlic prcs.sure is now
diminished, while the temperature is maintained above the critical
value, we pass to the right along one of the isothecras. On this
i.sothertji the pressure can be diminished to any desired extent, and the
temperature also can be allowed to fall ; so long ae one avoids coming
into the htUroijrwom regim, the carbon dioxide ia undoubtedly in the
state, a fact of which one can convince oneself by retlncing the
to that of the atmosphere and opening the vessel.
Similarly, just as along a path above the point K, a Ivjiiid can be
converted continuously into a aqxmr or a ()>in without vapour ever
making its appearance along with it, so it is possible to convert a gas
continuously into a lifpiid leithmt n sciwniiii>ti of liquid n^tr l>r.o>ming
fisihir. For that purpose, it is only necessary to raise the temperature
above the critical value, and the gas can then be compressed without
its li<(uefying. Above the pres.sure corresponding to tht.' point K, or
the critical pressure, the temperature can be lowered below 31*1". If
the pressure be now diminislifd, Jt is found that tht> substance exists
in the licjuid st:ite.

The critical [joint K is characterised by three niagnitutj
miicid iemperaiarc, or the tem[ierature of the isotherm in whil
and i'a[>our become identical ; the r-ntintl /rresfftiiv correapot
this ; and the 'Ti/kni rttimii'-^ or the cviticnl dtiisiUj. The tv.

39S

PRINCIPLES OF INORGANIC CHEMISTRY

are the values of tie pressure and volume, or density, at the poi,
They are ohtained from the diagram by readijig oft' the eorres
distances on the axes of pressure and vohime. Thus, the cntic^
sure of carbon dioxide is found to be alioiit 7?i aliri. The
volume lias to ibe referred to some definite cjitiintity of substance;
one mole, or 44 gm, carbon dioxide, it amounts to 1 1 2 cc.

Three such critical constants belong to tvery pvire sn
Whereas the critical temperatures are to be foimd niuging fi
lowest to the highest temperatures, the critical pressures niuve
fairly narrow Irmit-s, between 20 and 100 atmospheres, vvhjch
exceed only in (juito exceptional cases. The critical voluuies of
mole are also not very different ; like the other critical eonstanis tl
increase with the molar weight of the respective substances, nnd
from 10 to some hundred ctilnc eentinietrea.

3iBi'. Liquid Carbon Dioxide. — On account of the modi
pressure by which carbon dioxide can be jiquchec!, even at the onlii
temperiiture, this sulwtance is now placed on the market in
quantities in t!ie h"«(uid form. For this purpose, the ;;as is pu:
into iron cylindoi-a (Fig. 37, p. 104), which are kept cool,
thereby eonvurted into the iit^uid state. The starting material,
dioxide gas, occurs abundantly in various localities. Especially
districts where volcainic activity, previous or existing, can Iw re-ogiii
copious streams of carbon dioxide are fret{iietit]y found escaping ira
fissures in the earth, and this gas is suitable fur being dire<'tly liqii«fa[
In Germany, such sources of carbon dioxide exist, especially in
Eifel district.

If liijuid carljon dioxide be allowed to streitm out into the air,
of it immediately evaporates. So nuicli heat is thereby withdw
from the remainder that its temperature sinks below the point
solidifioation of carbon dioxide, and the latter solidifies in the fona
a white snow. By allowing the liqtiid to stream into a bag of cli
woven cloth, the "carbonic acid snow" can be filtered oH', the
reniaininji; in the bag while the gaseous portion escapes through t
fabric.

The solid dioxide is used chiefly for producing low temperatur
For this purpose it is mixed with ether, which stilt remains lirpiid at I
temperature produced, and a paste is thus obtaineii whose tempfniti
u - HO . In a space pumped as vacuous as possible, llie temiieratUrt
this freezing mixtiu'o sinks, in conse<[ueiiee of the uccelerated evajxa
tion, to - 100\

383. Solution in Water. — In water, carbon dioxide dissolve*
accordance with the law of Henry {p. 274). Tim miuoous solution
an acidulous taste and caust;8 a prickling sensation. The rtdmhi
taste of spring water is produced essentially by the presern-c of cart
dioxide, which is presetit in abundance in most n;iinrai w.iters,
passes into these from the aoii, where it is being cuuhtanth drr

CARBON

393

alow combustion of the organic substances by tie oxygen of the ,
Sinc« ibe satumtiun wjtii tliii^ gas liaa Itiketi place nt a low tdtn-
BUch wawi-s are gennmlly sujiersatnratetl, and when they
varmer by Btanding in t.h«* uir, the gas slowly forms bubbles
I the walU of tbo vessels. This forraaiioii of bubbles in water con-
ing a*rl>on dioxide is regarded as a sign of a palatable drinking
It of course gi\es no security against the presence of other
of a borniful iiatnie.

in whicii larbon dioxide ia dissolved in somewhat larger

ita frt!i|ueiitly occurs in nature, and is used, as aerated or miuenil

for me<iicinal piir[xisca or as a Jjeverage. Large i|ttiuit)ties cjf

Br artificially saturated with carbon dioxide under the pressiii'e of

Iwft to three atmospheres are prepared, and are use<l, with adrli-

of various salts, for the same purposea

Liquids containing carbon dioxide are also produced in t\w teiiucu-
iff jiijiition-; containing sugar. In this prirecfs the sugar decora-
into itifohdi and enrlx/n du&lif, and in certain liipiids of this
ty. lieer and sfjaikiing wine, ihe fennentalion is conducted in
a wftT that the carbon dioxide does not escape, tint remains diB-

in larger or smaller amounts^ in thi- lir|uitt.
For the prepar.ition of aei-ai^jd liijuida, the gas was formerly chiefly
reared fnim natiiially occurring compoutids, the carliotuite*, by
tisof a^'ids. At ihe present time, Jiijuid carbon dioxide is chiefly
uyed, being mnnufactured in large quantilies and plained on the
ket at a very low price.
SSi, Carbonic Acid. — The snhition of carbon dioxide reacts feebly
litmus, the colouring substance beini; rendered not hii^lit rr<l
lljT ^/tine red. This, however, is essentially due to the small con-
tifin obtaioed in a^jueous solutions of the gas under oniinary
If the amount dissolved is increased by using higher pres-
a S4)1ution is obtained which also gives the ordinary bright red
with litmus.

Ill the aqueous solution, therefore, there is an aeiJ present, and
' ' xide is to W looked upon as the anhydride of this acid.
■ iris are the satne us in the case of sulphui-ous acid ; the
iikuf carlwinic acid is H.^COj,, and It decotupuses with extremftJ
into water and the atihydride CO^, carlion dioxide or carVmnto
uihydride.

CorhoDii: acid is a difnttir acid with very slightly developed acid
ties. Like the dibasic acids in general, it forms two ctirlmniom,
tot HCOj' and the (/Jvalent fO^". Since t-ven the procoas.,
,-H"-Hi'n^' takes place only to a very slight extent, the^
ilissociation, H('( >,,' = H' -t- C( *.,', is, for most ptu'posea
-mall. In aqueous solution, therefore, the monovalent'
U.XI,' isfunntMi by [ireference, and to this some of the characteristic
'»e carbonates are due.

394

PRINCIPLES OF INORGANIC CHEMISTRY

The salts of mrliQuk aciti, or the mdimiaifs, arc inostlj' very diffii
soluMo in water; (inly those of the alkali metals form an ox
atKl are easily soluble. Tlio lattur react fairly strongly alkaline,
from the tendeiicy of the ion L'Og" to ititflract with water and pa«J 11
HCO.; (tJO/ + H,0 = HCO; + OH'), a certain amount of hydroMdi
is priKinced, wherehy the alkaline reaction is effected. On adi
of acids, all carbonates evolve ctirbmi dioade, Carlwnic acid ti
formed, bat this can tjxisl in aqneoiis solution only to a small
ami mostly decomposes into the anliydride and water ; H^f 'O^ =
H.jO. Sint'e atrboiiic acid is, as has just biren mentioned, a very
acid, thiis reaction is brought aboni also by other weak acids,
the power of expelling citrbon dioxide from earbonatea am xlninrt
cousiiiered as a characteristic of the acids.

385. The " CirculatioD " of Carbon. — In nalnie, carbonic
and the carbonates occur in very large i^uantities. The air kl
contain.s carbon dioxide, the amount of which varies somewhat,
places where there is no special soun:e t>f the ga.s present, the ami
16 about ij-ifViT*'^ o^ '■''^ volume of the air. This atnouiit is in
by organic respiration and combustion processes of all kinds ; ad'
this, there are also considerable amounts of carbon dioride di
from volcanic action.

All organisms make \\p for the waste necessary For their vi
activity by the consumption of rhcmicul energy, which, for the gr
]>art, is the furt'/i/ uf ihr laiiiafiim of mrhon. Whereas auiniala;
those plants which do not contain chlorophyll can carry out the
tion only of already existing carlmn conipounds, and live from thi
the green plants can also carry out the opp<isitc process ; ^A^
deamiposc carhmi dwxbh- info fttriion {or campimtuis t>f airhm) uml
vyyijn. For this a i;on.siderab]e expenditure of energy is ucceisary,
and this tiie green plants deriva from the radiant energy of suidkU.
They thereby store up not only the supply of energy which thejr
roijuire for thoir own life, but they also yield the supply of energy
which is used by all the other organisms and which these tAkc up in
the form of food. By the oxidation of this carbonaceous food, tirst of
all the herbivorous and then indirectly through the niedinm of thetc
the carnivorous animals obUin thoir vital cnergj'.

By means of tb© oxidation In respiration, the carbon again reiujw
to the air as carbon dioxide, and a '* eircultitititt t/f tarhm" is produced
by which the mutual preservation of the vegetable and animal kingdonn
appears to be lastingly assured. However, for this end, it is not tlw
conservation of the mrhoit that is the real problem here ; the role d
carbon ia only to ettect the transport of the entfijy with which it i»
associated, which is the e-ssential thing. In fact, certain organiBmi
are known, e.g. the sulphur Imcttu'ui, which obtain their vital energy
not from the oxidation of Ciirbon compounds but by tpiiie differenl
chemical reactions. There are, therefore, organisms which do nol

CARBON

39&

my our^n for this purpose ; no organism, however, ia con-
which would not require to imve //*•'• ntryijif at iu disposal in
sr to exhibit any kind of vital activity.

So far, now, as our knowledge extends, ?!'/ stich ci/df exists inv
'fj. Here it is & caae of a current Bowing in one dirdctiun, which
the sun on to the earth, where it ih pai-tly xsfd «;< and
by the plants. The supplies stored ujj by the pliints
greatest p«rt further used u[> by the other orgstnisms, hiit a
piirt is prescned as fossil t'ornbustibiu material and serves in
times a* the tntie.1 impottjiut source of energy iti the itidustrial life
UL That the free energy which is derived from the sun find
in tttiB way is tiimlly used up, will by any process be again mafle
ible, wo have no Rijin ; on the conti"ar>', from the exi>erience
has been gained with the terrestrial pri>cesses, it is lo be
as probable thut siioh a reverse process, corresponding to the
ms rtoM* of a stream iiphifl, is not possible (p. 135). It ia,
of essential interest for the jiermanent maintenancy of life
large a portion ns possible of the mdiiint energy of the sun
l>roitj£bt into the storable form of chemical energy, and that,
its large a {tart as piissible of the earth's surface Iw covered
m pl;ii)t$. As ia well known, great impnivements in thi«
Still possible.

consider that, as already mentioned, the amounts of energy

the industries are also derived lor the most part from the

energy of carlton, namely, in so far as they are obtained by

stinn of coal or other fos--.it fuel, we see that this element is,

along with oxygen, the most important carrier of chemical

-tHde<Hi, of any energy whatever. It would be incorrect to

t3u-^x)n iituise as the currier. Tlie quantities of energy in

■n Itecouie free only by fmnhuMum, i.e. when the carbon com-

irith oxygen, and we must not assert that the energy was

lined solely in the one or other tdement. In other words, we are

with the energy eipiation

C + O, = COj + 406 kj,

.fwthia, e<wh niemlter is of i-'iual importance. Oidy, the carbon
lily apiwara to he tlie sole canier of the energy because tlie oxygen
srally acceesthle in the air and does ni>tj therefore, require to be
lly prepared and bought. If the ]ilttiits did not separate the
m in the gaseous form but as a solid compound rich in oxygen,
llatter would l«e just as necessary for the conservation of life and
fcwiung of eteatn t^ngines, a.« the solid carbon compoumls ; it, also,
W Ke consumed by anitnals, and would also be collected by man
lad plAf-ed on the market.

386. The Combining Weight of Carbon has been determined

396

PRINCIPLES OF LNOKGANIC CHEMISTRY

by combustion to carTion dioxide. The latter can be complel
retained by a concentrated solution of caustk potash or soda
weiglnid. If, thtrefore, the carbon is weiglied, and also the
appartitus before and after the expeiiinent, we c«n ascertaiti how oi
carbon dioxide has been foriaed by the combustion, and, by difiereni

• how much oxygen has combined with the carbon. In this way,
(imorphuus charcoal !is well aa graphite und diamond have
vostigatod ; with all three, exactly the same ratio bajs been oh
so that the dilTerent quiinlities of energy present In the dilfei^ent
of eai'bon exert no inHaeni-e on the combining weight. The
result of the (Jettemiinatioits wae that exactly 12'00 of carlwn
with two combining weights ( = 32) of oxygen, so tTint we have to
.C=1200.

J 387. Detection of CarboEic Acid. — Although carbon
on being dissolved \i\ water yields only very feebly acid solutii
readily fimns suits with dissolved bases ; it is, therefore, rapidly
completely ahsorbeil by aolntions of these. This behaviour is
use of for the detection and quatititati^'e detenni nation of
dioxide (^.(jf, in the air), and those brtses more especially are cm
which form insokible carbonates. Most frequently there is
solution of lime or calcium hydroxide, Ca(0H).2, whicli forms with tb

dibasic carbonic acid the sail CaCOg, or calcium carbonate.

Thi

precipitHted frum the solution in the form of a white powder, and
means of it small (jujintities of t-arlionic acid can he detected.

The formation of tliis white precipitate is snfficit^nt for the qual
tjitive proof of the presence of carbtmic acid. If a quantitatn
dctorminaljou has to be made, a measured volume of the lime solnttr
(lime w.-iter). the strength of whit-h has been determined by titntitc
with an acid (p. 190), is taken, and after the reaction h-t-s nccurri'd
precipitate is allowed t*> settle, and the amount of lime reniaimiig
determined in a meaeiired portion of the clear lifjuid ; the diflference
a measure of the carbon dioxide absorbed.

388. Derivatives of Carbonic Acid.— Although carbonic
itself !.■? not known, there exist not only a large number of salts wbii
contain carbanioti, Imt also compounds formed by the replacement
its kijiho.riih ; more especially, the chlorides and amides of carbonic act
are kiKuvn, sionie of which are of very great importance.

If carl»onie acid \\v written as a hydroxyl compound, there
possible, on account of the presence of two hydroxyls, tw6 chloriJi
and two amides, exactly as wo found in the ca^e of sulphuric »c*
(p. 305). Hcpresented schematically, we have the following coift
pounds : —

CARBON

CartMKiHT A(4>L

L-lilotiaeN.

Amiilv*.

/Ol

yliBi

^OH

yOB.

^oe

/^'

/NH,

■

\c.

"^NRj

;i9i

substances are kuown, some, hawever, only in tlie form of

caritNt vxtifhlvridt, C"0C1«, or tarhonyl chhndr (tlio i-esidue <.HJ

oartninvl), is produced directly from carboii jiKDioxide (p. 399)

dilorine, by mixing these two gases in e()iial jjropoitioris uttd

ing to sunlighL Here, as m many irther cases, the action of

IS very markedly accelerated by the tuHneiice of light To

It ftlao flue the name " phosgene gjia " for carboaiyl cliloride.

howex'er, the componnd is also formed without the aid of Ijglit,

not dealing here with the communication of a necessary tnerjry,

^e case of the redm-tion of carbon dioxide in the j^reen plants

S1>1;, but merely Ai'ith a case of iKcehniHun . the light acta

In defect <if sunlight, fkairml can also be used a» catalyser ; com-

:"' rr liketvise tfike^ place, especially on passing the gaaoous mixtnre

lijal charcoal.

lie reaction occurs in accordance with thy eipiation (.'O + L'l, =

1y That is to say, one volume of each of the two compouente

t>i ftinn one volume of the compound,
jtrkm oxychloride is a colourless gas with a suffocating odour,
GUI be readdy liquefied by means of a freezing mixture ; it boila^
ipbHric prcssurt', at + 8'.
flWcychloride behaves chetnieally as «. true acid chloride. It
poeed hy water, forming carbonic acid and hydrochlnric acid,
untnoina with formation of ammonium chloride and the amide
ic acid {riiit itifra),

chloride of carbonic acid, or chlon>carbonic acid, ClC'OUll,
lly oa,i]ed cbloroforaiic acid, since* the corresi)ondiug._ii^roKen
d, the mftuolifisic acid HCOOH, is callgoHofm^ouWliidj

Wjirti I

ii'D in the free state, but only as a
is ; these belong to organic cbei
Hied in detail here.
Amides of Carbonic Acid. — As;

Umide oJ carijoruc acid is fuitued hy ift

tnent of more compfi*
itiy, and will, th^e;^e£prfi, -^ '

alr««cly^b>'i?it Krtwftlri^l,^
Action f^ annavcfl\\!\ ovT

'-TlMfiV

PRCfCTPLES OF INORGANIC CHEMLSTRY ctu-

I'hiiw^afc SB lecardacce with the general reaction as i>:r
maa^ by th> ■friiin OXl 4 N H , ^ C0{ X H,), ^ 2 N H,C1. Th«|
»•«) st&«taiia» OB W aeparaieil by tivatmeal with aicohoJ, in wi
A, ,u£ aite tb« tauiHiiuuiQ chJoridr, is soluble, and the carhowl

mau amunr. oT iwAwudk, k obuioed M white erystals which »n|
aafeilb bi wmaa^aad hmra a eooliDgaiid sOBnewhat bi"it«r taete. Tbrjl
hava ■» aduw ftkacwter. and t]ieir aqueous solution does not cuniiiidl
ill ■iMiifcfi iBirial

Tfc* MM* aakiMMM is formed in the bodies of tbe maiumiAl
mfmkJfy tbr lointvaffm, ts tbe fiiuJ product of the meiaboJism of it«
•ilB«!|p» «^kk Bcoatained in the food and coneuitieil in vital actinti,]
■oil Imwh «^ mgimam diaolved in the watery excretion, the nnw- 1
fWtt ikm mim ti tk» eumTom, after being concentrated, it mostij I
; iftwU; ; hvm tLat of the omnivora., especially of xt»n, ill
W «klBM^ in tkis simple way, since its frystallisation a'
hiiiwillBWt by llto ptueaee of other substances. To the concenlratd
bi4«ii4 Hi Bit aitanc acid is added : a difticuUly soluble compound i^
iImi faawii wbick CfTvUQiMs out, tmd from whjeh the subistaiicu can
b» «Mli|y vbtelMik bf «iHlv«rtiiig the nitric Hcid into a salt by m\y bo^c
KmH itt MMfffWMW ia vain^t the compouna IS usually- called urro.

M» aMk df carbook maA, urea has the property of passing, fcy
«aaibi&»atKMi with wat«r, into the amntonitrm siitf uf f4xrhtmic arid.
O'' :fH.O = iXUjJ^COy At the ordinary temperatiire thif

•k*iyr » ^.vcaaiiiagiy slow; at 100 , however, appreciable amonnU
ul aMMMMMMl MKboiMte an formefi in an aqueous solution of ar»,
mm! tt »t«l » added, tbe transfonuaiicin pi-oceeds still more tjuickh.
ih* tatbiaw acid being evolved, and the conesponding ainnionium
mMi NHHHMW ia solitkioii. Stnmg bases have a similar action. In
yiMtwfvukv* iinae are present organic compounds ftoasessing tbe p<^«-cr
«ll .v^Ml•raUon, but of unknown composition, called fermmt-

itlt f»ij«»** Tbeee b»ve been formed by the schizomycet^s vvhirh
^l^lptUia ia tW uriae^ ami have the power of ucceleratitig this altsoq)-
IAm <rf waler kjr urea, even in neutral solutioti. Sometimes such
9mt>M» «M pwowtt iii the bladder of tbe li>ing orgaiiigm ; tii«
<ia>iTaiii»i caarboaaM tben formed has a corrasive action on tbe
g^p%iiUiiL <j»d «aB caaae very severe illneaft.

lut vi its occurrence in tbe animal organism^ iirea mi
*■ •lU »be ^ryiiiuc coiii|>ounds before its simple relation to

*c»d bad! been discovered. Since the organic conipituids were
.! »s being produced under the influence of a speciul
►rvt^ the notions of which, it was assumed, could nut
^ '4«Mide ibe organisti], u great ses^Kation wtis causes! when.

'" \VaWor discovered a method of preparing urea Jirtificiailv.

- iu tbv traiiiiiormation wliicii the amnionJutn salt of c^-an'ic
.< • i» a^iutixitis solution, and will he tlesciibed somewhat

CARBON

399

** synthesis " of itn oi-gjinie corajjound was followed later
!»le others, and although hy no means all tho compounds
in aoimala uml i>laiits have as yet been artilicially pre-
in the work which iias been directed towiinls this end, no
ic«f has been eiiebiiutercd which mjikes it impfoliable that, on
■tborou^h itave-stiy:ation, it will be possible to artificially prepare
oonaticuents of the organisms.

NH.
pXbe other amide of carbonic acid has the formula CO ; it is,

OH
an acid, and is called ntrbamic add.

lie »cid itself is not known. Its salts, the earbiimates, are

when ammonia and carbon dioxide coroe together in presence

Thus, the cakium salt is obtained by adding ammonia to

hydroxide and passing caibon dioxide into the mixture.

Iciuni carlwimate, Ca(OCOXH^)^ is soluble in water, while

rbonale is not, the formation uf a i^ohible calcium salt in

circumstances is a proof of the formation of the new salt.

ammemium salt of carbamic add is forme<l as a white crystal-

w on bringing ammonia and carbon dio.vido together. This

be carried out directly with tlio two gases, oi, more conveniently,

M are |.Mi*sed into anhydrous alcohol, in which the ammonium

*te s«x>n s<'parate-5 out.

irdance with the formida of the acid, the composition of the

Tgiven hy the formula NH^OCONH.,. If we write tho summed

aik we oI>tain C'0.,N.,H^ i.e. the sum of one mole carbon dio.icide

o moles ammonia. This \s. the explanaiiun why the mh an\ be

directly by the union of the two gases.

■ reives, the carhamates, even in aqueous solution, are fairly

i;dly when the solution has an alkaline reactioii. If, how-

r, ibe lii{uid t^ acidified, an ammortium salt is formed and carbon

is liberated. This reaction is represented by the etjmttion

J + H* ^ COj - NH^, which shows that carbamic acid can jtass

if into .imtnonia and carbon dioxide.

390. Carbon Monoxide. — When coal is burned in a restriiTted

ij of air, a gu* is formed which can burn in the air with a

eriftic blue flame, forming carbon dioxide. This phenomenon

f seen in a c<ial tire. When most of the hydrogen compounds

■ hare been burned, and the coal has become quite incandescent,

i lyir^ at the foot of the grate which comes into contact with

ing air, burns, it is true, to carbon dioxide, but this gas, on

>ugh the upper layer of glowing coal is, in accordance with

tior> rO., * V - 'H'i\ reduced to the compound CO, which

s the al»ove combust

gas.

ttiji

glowing

where abnnd.'iTice of air can again find access, the gas burns to
«dc with tho above-mentioned blue flame.

400 PRINCIPLES OF INORGANIC CHEMISTRY

This compoiuid, therefore, can he obtained by pji&siDg
dioxide over strongly heated charcoal. Since iii this procuss
energy is taken up, this must be communicated from without, i.e.
tube must be strongly heated. If the issuing gas is passed throu^l
sohitiijn of caustiu srida, the carbon dioxide which remains uiide
posed is absorbed, and the residue is pure carbon mono.vide.
order that this reaction may take place, the temperiituro must
above 700. At lower temperatures, carbon monoxide pivsses into I
dioxide with separation of carboa

Carbon monoxide is a colourless gsts with the molar weight
it must, therefore, have the formula CO. The density is equal to I
of nitrogen, and most of the physical properties of the two eqU
dense gases also show close agreement. Thus, the rritical magnic
are : —

( iirlwD monoxide. Vitragm.

t>itie».l temptratiire . , -140° -149"

Critical pressure! .... 36 Btni. 3& at

Critical moleiriilHr volurai- . . - 103 co.

The solubility of the two gases in water is also equally small.

Of the special properties of carbon monoxide, its fn/isin
should be mentioned, which, in certain circumstances, makes it ft
dangerous substance. This depends on the fact that the gaa can
bine to form a very stable compound with hiemoglobin, the col
matter of the red blood corpuscles. Now, hiemoglohin has the functli
of taking up the oxygen inspired into the lungs and of conveying il
through the blood canals to the parts of the body where, by iU oiidi
ing action on the different tisanes and their constituents, it mai
vital activity. But if the liamioglobin combine.? with carbon mo
it loses the power of taking up oxygen, and precisely the same
sui>ervene as on sufl'dcatioii.

Such cases of carbon monoxide poisoning ea.sily occnj- when ctisJ ii
burned in a stove which has an insufficient otitlet, or if this outlet U
closed. Every year such cases of poisoning occur through closing ibl
stove register too soon. Carbon monoxide poisoning may also
occa.-jioned by coal gas, which, on an average, contains O'l of its volu
of carbon mouoxide. Certain kinds of gas which are obtained by tin
action of steam on heated charcoal {water gas) contain much mon
carbon monoxide, and their use in daily life is, therefore, not withod
objection,

* The presence of curboa monoxide can be detected by the fi
that it is so readily absorbed by haemoglobin. If (he gas to
investigateil is paj^sed into a solution of the colouring matter of th
blood, the presence of carbon monoxide is shown by the appeai-anci'
two characteristic bands in the absorption spectrum of the colourin
matter. These, it is true, appear similar to those produced by oxygei
but they can be distinguished from the latter by tlje fact that <

:xvi

CARBON

401

ladiiition of reducing agents (cy. sodiiUH sulphide) they do not dis-
» appear, whereas the oxygen hands d<p.

With oxygen, caibon monoxide burns to dioxide in accordance
with t!ie equiitioii 200 + 02 = 2002- Two volumes, therefore, of the
monoxide unite with one volume of oxygen to yield two volumes of
carbon dioxide, and in this respect the relations correspond exactly to
tboije of detonating giis obtained from hydrogen and oxygen. With
oxygen or air, carbon tuonoxide also yields a " detonating gsis " or
explosive mixture, wliich, however, burns much leas violently than the
former.

This 18 not in any way due to u smaller development of heat, the
heat of combustion being in both cases almost exactly the same, for
it amounts to 28i (.j for one mole of carbon monoxide, and 286 kj
for one mttle hydrogen. The cause is that the relociU/ with which
the process of combustion is projiagtited in the explosive mixture,
is much smaller in the case of the carbon monoxide and oxygen than
of the hydrogen and oxygen mixture.

This velocity is greatly increased by the presence of a trace of
water vapour. In the case of the carbon monoxide mixture which
has been carefully dried with phosphorus pentoxide, the velocity is so
small that it is not possible to bring about ignition by means of an
electric spark ; a mixture of perfectly dry carbon mojioxido and
oxygen appears to be incombustible in such a way. If, however, the
mixture is heated from without, combination takes place.

* The same behaviour is evidenced by the fact that a jet of
carbon monoxide burns in moist air with the well-known blue tlame,
but is extinguished wlien it is brought into dry o.\ygen, whereas it
continues to burn in the nioist gas.

* All these ai'c caiali/ik actions. The assumption occaaionally
expressed that intermediate products are formed with the water, has
not been jiroved ; it may be right, but the mere assumption contri-
butes nothing to tlm explanation of the phenomenon itself.

391. Water Gas, — The great advantages possessed by gaseous
fuel with respect to cctmiitetencss of combustion and power of regulat-
ing the flame, ha\'e given rise to many experiments to prepare a
gaseous fuel, with as small a loss as possible, from the solid material,
ccwil or lignite. A very pranu.'jing reaction was found in the action of
water vapour on charcoal, correaponfling, according lo circumstances,
to one or other of the equations

C -^ H^O = CO + Hj

C + SH„0 = 2H, + COj.

In the former case, charcoal and water vapour are converted int
carbon monoxide and hydrogen, in the latter, into carbon dioxide and
hydrogen. Of the two reactions, the former predominates at bigb

2 D

402

PRINCIPLES OF INORGAAUC CHEMISTRY (sJ

t^mpemtures, while the second is favoured by a lowering <rf
tempeniture.

Neither of the two re;ictions can take place spontaneously, f i •
is accomiiaiiied hy an nbsorptiou of heat, amounting in the first l.i- ;
133 /cf, and in the second to 91 ij. The cotDinunicatiou d
necessary energy in some form must, therefore, be provided for.
method consists in raising the coal to a high temperature by comk
tion with the help of an air-blast^ and then passing in steam ; lAal
the temperature has again sunk bo low that the reaction would
air JA again injected, and the processes are repeated alternately. i>|
these operations, care roust lie taken, by roveraing the coDdudiie|
tubes, that the mixture of carbon dioxide aud nitrogen formeil in ti»|
heating process does not mix with the combustible gas formeii ^l
another period of tlie process.

The second method consists in mixing the steam with as much ii\
as is necessary to maintain the temperature. The pro<?e&$ is in ti»I
way a continuous one, and therefore much simpler, but the gas ptr\
<hlced has the disadvantage that it contains a fairly large amount li I
carbon dioxide and nitrogen mixed with it, and therefore does Bit
allow^ of such high temi»erature5 being iittidned as the pura "wnterl
gas- •

On account of the very poisonous nature of carbon monojddev ii I
will always be better to aim at producing a gas which contains »
little carbon monoxide as possible and a correspondingly larger aaionn!
of hydrogen. This is the same as saying that the operations ahouiil
be carried «iut at as low a temperature as possible.

39'J. Formic Acid. — Carbon monoxide can be regardo<l a* th.e\
anhydride of an aeid which is called /oj-mic add (CO + II.,0 = HC(X)Hl,
because it wa.'s tirst oViservfd in the ncid liquid which ants squirt OQsj
for defensive purposes. Still, no njiprcciable amount of formic taA]
is formed when carbon monoxide and water are brouglit togethrf
The sodium salt, or soilium fonmik, however, is obtained when carbon]
monoxide is passed over gently heat«d caustic soda. The reaction a\
CO + NaOH = HCOONa.

As is seen from the formula of the sodiiuu salt, formic acid is •!
nioitobii.tic acid in spite of th© fact that it contains two combiniugj
weights of hydrogen. One of these is not capable of being replaced ]
|jy metals, the other, however, can be so very well. Formic acid can-
not even be called an acid of medium strength, although it approacheif
very near to one.

Free formic acid can be easily obtained by the distillation of the
sodium, salt with aulphurie acid. It, is rather difficult to remove the
last tmces of water from it, since it readily decomposes again inlo
water and carbon monoxide. It is best effected by allowing the fairlj"
concentrated acid to partiaily solidify ; an anhydrous acid then
crystallises out and a more watery mother liquor remains. Puw

Ibs

W- x\

XVI CAEBON 40a

formic acid melts at 8*6 ; at the ordinary tempfirature it is a colour-
less licjuid with corrosive smell and action, whicli dissolves in water
in all proportions and reacts strongly acid. With bases or metals, it
forms Siilts which are mostly easily soluble in water and contain the
coloxiileas /urmtniioH HCO^'; by oxidisini; agents, it is readily oxidised
to carbon dioxide: HCOOH + O = CO, + H.O. It acta, therefore,
fl with respect to some substances, as a reducing agent, aeid it precipi-
tates, more ea[)ecially, the uoble metals such as gold and platinum,
but also Bilver unci mercury, from their salts.

Fornnic acid is usually classed with the organic fields l>ccause it is
the tirst member of a large series of similar acids which differ from it
in the fact that the non-ionisable hydrogen is replaced by the atomic
group C„Hj„.,.^ (ti being a whole number); in the simplest case, there-
fore, by CH^. The acid which is formed from formic acid by the
introduction o! CH^ in place of hydrogen, is called mefir ttnd ; it has
the composition CH^COOH - HC^O^H.^, and is monobasic like formic
«cid. Since acetic acid is readily formed from organic subatancea, it
is one of the longest known acids, and iti most languages it has given
the name to the group of the acids.

393, Acetic Acid has similar properties to formic acid ; it docs
not, however, exhibit the reducing actions of the latter, but is exceed-
ingly stable towards oxidising agents. It is a colourless liquid which
solidities (when supercooling is avoided) at 175 , and which, on
account of the ice-Hke appejirauce of the crystals, is called tflariid iif>:(ic
ami. It mixes with water in all proportions, yielding solutions of an
acid taste. A sohition containing about 3 per cent of acetic acid is
used for household purposes under the name vinegar. In the labora-
tory also, acetic acid is often used in cases whore it is necessary to
have an acid which is much weaker than the mineral acids, hydro-
chloric or sulphuric acid, but which has nevertheless a distinct acid
character and does not readily yield to other chemical attacks. Its
salts, the ucfltiti's, contain the colourless (iretankm, H.jCjOj'.

39i, Hydrogen Compounds of Carbon. — The number of com-
pounds which crubun forms with hydrogen is exceedingly great. The
treatment of these belongs tti organic chemistry, and only a few of the
most important of the compounds of this group will be mentioned here,
and their relations to the other simple carbon compounds discussed.

The simplest of all the substances of this grou[> is the compound
CHj, wiiich, from its occurrence, goes by the name of marsk-fjits or
fire-dariLjf , its systematic name is methtite. It is a component of the
gases which are evolved from decaying vegetation at the bottom of
stagnant waters. The gas is also frequently found in coal mines ; it
generally occurs shut up in cavities under some pressure, and escapes
when these are opened in the mining. The name methane is derived
from the relation which t!ie gas bears to mdhijl tdmhiJ (vida iufrr^
wood spirit.

408

PKINCIPLKS OF INORGANIC CHEMISTRY

and is called methyl. It does not exi&t alone any mow tban hydrox
does ; but as a constituent in organic comiioundB it plays a very n
portanfc part.

This follows from the fact, discovered empirically, that those ■
pounds in orj^anic chemistry which may be regarded as bein^ fcrmf
by the rejilacement of hydrogen by methyl, p.issess a very
resemhlawe to the parent compound. An example of this we
already mat vritix in tho cijse of formic and acetic acids. If
compare the two formula; HCOOH and CH.jC0OH. which rej
these two acitls, we sec that, as a matter of fact, acetic acid canl
derivcfl from formic acid by imagining the first hydrogen of its for
replaced by methyl.

Such a method of derivation can be employed in the case
organic .coropounde containing hydrogen. This can, in the
ioBtance, be done for methane itself, antl, in this way, the
obtained from methane CH^ the compound CH,, . CHj, wWe
called elhunr. In this compound, the same change can be

out, and we obtain pmpane, C'll^ . (.."H„ ,

CH,.

I'^Tidentlv, there

theoretical limit to thia substitution, and, indeed, hydrocarbons
this kind are known up to C^ and over. Pftrolcnm consists of hydr
carbons of this class.

On writing the summed formulae of these hydroi;arhons, we ob
the series CH^, C^H,;, C^H,, CjH,j,, and so on. Each successive hj
cfttlion differs from the previous one by CII.„ one hydrogen
eliminated each time and CH,, introduced instead. Such a aenes «
similar comiwunda which cau be derived from one another by
substitution of methyl for hydrogen, i.s Killed an humloffoits saies.

Besides the homologous series of the hydrocarbons, there is on« (
the ulmlwls, the aeida, the <Mim<Ie>s, etc.

Of the homologues of the above mentioned substancesj we
mention fthil nlvnJiol^ homologous to methyl alcohol, which is knfl
under the name of ^nrif of whu, nlntlwl, or sjmii. It has the com-
poaiLion C'H,('ll.,OH i>r C»H,.ll, and can he derived from methyl j
alcohol by imagining one comhiniiig weight of hydrogen replaced byl
methyl.

Eiht/l (ilrohul is prepared in very large quantities by the fenneti'
tation of stlgar and substances containing sugar. These have thAJ
composition C,)H,„0(„ and rlecompose, under the influence of a caialytie
agent, r?/mwsp, which is secreted by various organiama, especially \>f I
yeaat, into alcohol and carbon dioxide, according to the equntioii I
05H,.iO„ = 2C„n,|0 -t- 2(.'0j. The latter escapes, and from the aquconi
mixture tile ethyl alcohol is sefwrated in the pure state by distilliitioti. j
It boib at 78^

Ethyl alcohol is a colourless liquid with a feeble smell and burningi
taste. For the or^nism it is, when concentrated, an acute, when I
diluted, a slow poison. The phenomena of incipient poisoning bcccnn* j

atvi

CARBON

405

the process of salt formation, in ivhich hydrogen is also substituted.
Whereas in the case of the acids, by no meana all the hj'drogen can
be replacerl, in the case of organic compounds, all the hj'drogen can be
4ubstitvitt^d. Further, ivhereas the acid liydrogeii can be replaced only
by metals or metil-tike f;roups, the hydrogen of organic compounds
can be replaced by the most different elements or groups. Finally,
the compounds which are formed in the case of the organic eubstHinces
are not salts, but undissociable or indifferent compounds, It is, of
course, not excluded that organic substances may also yield acids,
bases, and sdts, but the formation and transformation of these follow
the same laws as in inorganic chemistry. With the organic com-
pounds, lioth kinds of processes, salt formation and substitution, may
occur, correspondingly different substances being produced.

Thus, for example, the following compounds are successively
obtained by the action of chlorine on methane (under the influence
of sunlight) : —

Miithyl iihloridfl CHaCl

Methjlpne clik.iride UH5OI,

Cblcirorovm CIICI3

Totrai-hlDrniethaiiQ UCij

All these substances are formed from methane, the hydrogen being
replaced step by step by chlorine. Further, all are indifferent or
non- saline aubstances. Their properties change gradually with the
increase in the amount of chlorine, as is shown in the following
table : —

DeiiBitSf. Boiling iiolnt.

Methyl eliloride . . . 0-9623 -aS-J'

Methylene chloride . . 1-3778 +41-6'

CJiloroform .... rfi'204 61-2^

Tetrachlumiethaiie . . 19320 76-7'

All these substances are only slightly soluble in water. The
Bolations do not exhibit any of the reactions of chloridion, i.e. on
addition of silver nitrate they remain clear. Also, neither the
solutions noi* the pure substances possess the property of conducting
the electric current.

The derivatives of methane containing bromine or iwline in place
of hydrogen, are perfectly similar ; their properties also undergo a
gradual change with increase in the amount of halngen. On the other
hand, if the corresponding chlorine, bromine, and iodine componnds
are arranged in a series, a similar gradation of properties is ohser\'cil.
This is shown, for the densities, in the following tabic : —

fiiimpli; (ubatitution
Double ,,
Triple ,,
Quadmple ,,

(Jlilnrinn.

nromlne.

\Mm.

0-952

1-064

2-199

i'37a

2 -OH 4

3-342

1'52B

2-900

4-008

1-632

>■»

l-S'2

406

PRINCIPLES OP INOEGANIC

With rtuoriiie also, corresprttiding compounds CF^, CF^H, CF,
are known. The general method of preparing these is by the in
action of the ch I oro-com pounds on silver fluoride. Varb<7n ieirafi\
is also obtained by passing fluorine over porous chai'coal at
temperature. I'he gas, the density of which corresponds to
formuU CF^, eojideueos to a liquid at - 15 under at
pressure. It is ditheultly soluble in water, but very readily solu
ether and in anhydrnua alcohol. It reacts with glass with fo
of CO., aud ii\V^. The above compoiinda are also readily form
the action of gaseous fluorine on carbon compounds.

39C. Radicles. — Considering the compounds juat described,
CH/;i, CHX'I,, CHCl^, and CCl^, we tun formally regard the
as clilorides of the groups CH^, CH^, CH, aiwl C. Of these, the
is combined with one, the second with two, the third with three,
the fourth with four comhiiniug weights of chlorine. .lust a«
called a metal which can combine with two combining weigbti
chlorine, divalent, so we may call the group CH., divalent, and
trivaleiit ; in this sense, carbon is tetravalent.

It is a reiiiarkafde fact thut hydrogen and the halogens do
form any other eompounds with carbon, containing only one comb
weight of this element, than the ones mentioned. In other woi
all these conipouiuls wirbon is feframlml, for the number of the
bining weights of hydrogen and the halogens together, is always
to four.

On the other hund, the group CH,, can be regarded as mono'
because it can combine with etill one combining weight of hydrogen oT
halogen J alone, it is incapable of existing. Likewise, the group CH|
is divalent, and so on.

The monovalent group CHg is called mrtliyl, the divalent CB;
iftfthtjlfw, the trivalcnt CH inHhrfit/l.

Of these groups or radicles, the first is the moat iuiportaiU, fur it
forma by far the most deriviitives. Such compounds iire fornwd not
only by the replacement of hydrogen by other elements, such as tli6
halogens, but, instead of elements, monovalent rndicli:t, such a& hydrojvl
or amidogen, may replace hydrogen an<l give rise to corres]M}nding
compounds. The nuuibor of such radicles is very great,, for everv
existing compound can, by the loss of one combining weight of
hydrogen or ininther clenient, pa.ss into a monovalent radicle.

31H. Methyl Alcohol. — Of these compounds, one of the moib
imjjortant is that with hydroxy!, CHjOH, which is called mrthtil olfM.
P'ormerly, the luime alcohol was used to designate only s]>irit of wind
the "volatile constituent of intoxicsiting beverages. It aflorwanla k-
came a class name, and the hydioxyl compounds of the hydrocarbon,
radicles ^^nerrdly are called by the name alcohol.

Methyl alcohol is formed, along with many other volatile siifc"
ataneea, by the t/zy distUiuilotif i.e. by the hoatitig, of wood.

CARBON

from the muxttire hy fractional distillalioti, and in the pure
L colourless liquid with a feeble odour and having the density
It is combustible and dissolves in water in all proportionB.
ig poiut is 66'.

lyl alcohol is a type of the tilrolwls. These are indifferont

rc&rting neither acid nor allcaline with vegetable colours, whose

solutions do not appreciably conduct the electric current, tmd

are therefore not dissociated into iona. The alcohols can be

with iictdfi without immediate eombiuation taking place. If

"two sul)6tances, however, remain mixed for n lengthened period,

dion alowly occurs, the course of which ia quite slnnlar to that

formation. Thus, from methyl ideohol and hydrochloric acid,

chloride (p. 105) and water are formed, and the corresponding

of reaction, CH3(0H) + HCt = CH^Cl + HjO, has an appear-

t© dniiUr to that of a salt formation, the methyl, 011^, playing

of a cntion.

Bver, the product of the action, the methyl chloride, is no salt
liuiry sense. As is seen from the statement of its properties

00 p. 4<J5, it ia, at the ordinary teDip«rature, a gas which is con-
into a colourless li<[uid only at - 23'7 . Its ai]ueous solution

not conduct the electric current at all, and on the addition of

latinn, no precipit-'ite of silver chloride is formed, ao that no

Me amount of ctiloridion is prcBctit.

towevcr, the silver solution is left very long in contjtct with

chloride, silver chloride begins to alowly separat* out. One is,

led to suppose that cbloridiou is indeed present irs the

aoIultUQ, but in exceedingly slight amount. By the long

led action of the silver solution the amount of chlondion 18

far iocre/ia^ that silver chloride can be precipitated,

et, the most appropriate view of this kind of compound is

let the oiitwani similarity between the alcohols and the

and betwt^en their acid compounds and the salts, there exii^ts an

rttemblance which is masked by the following circumstances.

, the dissociation of these substances into ions is so exceedingly

1 thit it cannot be detected by the ordinary means. Secondly,
iprocettes of dissociation into and recombination of the ious takeB

ijliiproportionatcly slower in the case of these substances (chiefly
fteoaon of the extraordinarily small concentration of their ions)
I the case of the typical bases and salts. It is suitable, there-
nol only to retain the name alcohol for the hydrosjl com[)ound8,
to call their acid derivatives not &alts, but to introduce a
Iname for them. They are called fgtns. Methyl chloride is,
, the liydrtH.-hluiii- at.-id cstor of methyl alcohol.
39'*. The Eadicle Methyl and Homologous Series. — From
*tWe, CH,, which is a " saturated" com])ound, there is formed, by
^ hydrogen, a monovjilent radicle which has the composition CHj,

41:

rRIXCIPLES OF INORGANIC CHEMISTRY CHI

so the hinhor tlu» prossiire. acetylene becr-E:-?* an explosive siib^taai
lUuliTijoini; deoom posit ion with gre.\: T:o'.rr.'>r -.rhen ilecomposition
started l>y atiy means at some ]v>ir.:. Thv *i\Tu^ pnjperty is exhiW
by .".■.■';'' aivtylene. Sinoe the cviiioal :e=:wrv.-.:re •"■!" ihisinuisS
aiul the iritii-al pressure >>> a:m.. :he iiriofi.::- r. vf tiie jpis cu
easily aiiom]>l:s::.-d. This •mv.-.v: :•:■:; :* w::bv;: ir.y irreat ilaiiger
A!'-.'.'- ■' (• ■■: ■•■ • .'. ■ '■■■!.• ;■ -N iv. ^'hi.h ■.•:i<c ■ :ilr slight pi
have to I>e ;ii»i>lie. s. -^.'.h. <v«!Tesp«jndiii(
greater pressuve*. i: Ivf^Tiw* :r. :h-- wb.'.e v;ry ■ Lit: jrennis and I
elainu'tl seveial viv.::ius.

i\i!;;uvttsi w;::: ;:;o j.~w: .»■••?.■:::::. .:" -rT.rTzy in :he fomati
oi a.e:yle;:e I'.vnu ;:s eliv.-.o'..:*. is :b-? :•...■: :h.i: :: :< f-.rmeti from
latter at very i:\jib. :e::::v-i::r-s - • :. o-'l. F:r example, if
elev;::: ■.■•:r:-. ri: ''■^.' a';"..'"--: :■;■ :»»>»'"•::•»"■;*.■:". :Tr.- ;ar'"'«"'r; r^.Ies in a
in whiiii i y.iiVjZWi :> riieser.: F:^. ". ll . "rfe- '.ar.t.;[- .;i>nil'ines with
ear''Oii wi:h f-.>::tM:i- :: •;: \.y:::'.-:~-i.

Th'.' v.:i :<'■.•::.•:•. ■.: a.e:y'-'-.r '..ii;:-.':* r. ••-■« p«;'\-v!r ■ t Tit?Ming
;'i:a:?s '-v-.th a si.".:::: :; ■;: i •..-•■,- i-.- ,' -...y, -. .jr .-.( a silrfri
i*:: e\;e>-* ■: au:rj'.":.i. :h-"S'.- vr-f';:: i:.i:es ■■•i'..^^; "ht; ■.■ar'V.'Q componl
or .•,'.:■■ i :rs •.: :'?.■: res-^»:i. ::••-; ~t-..il«. The *i\"-r ^r>;<-ir'iMte is wii
:he .■•.•ver •■ -e :-:'•. I". :'r.-' .'.r.- .• r.^ •::;■• n 'loth exTjit.lit' vi..Iend7:(
"v:: .; :••:..:<:•; •A::h a.:--i :"".y i^^:-. r:.i[tl ip zhn leKcylene.

t. '.. Coal Gas. — I":-e .■ z:' -.sii^ie rui silica :s ise*: f'-r h«ril
J..,: .■-....:.. ^.:.._. -■■-;,.<;.■<_ :-■[ -v2"';:. ■."."'liur ":!•' 'lame ^f •■•'.' -Wl

lUB -v:

".<■--,'. .■■; ■•■i>r''. in<i ".•: \~:r'ii

■ , •■ -., -i.i-M ■ .i-..:i. • ::.: .■•.■'.•»;

: : ■ V- ■■•.L ••i-!nat!; "-■: ; -i ■■::'•

.. ....... r .. ,.- ii,..,-^.. .-.;■.- .-.n^

■ -. • ..-i.'i •!!■ •■■'.at::- 'u!'- T:-' J^

- -. ■■: •: :i'.ir".''':- •■; ■:ir*'''nJ)i

- "^ v ■ ; ;i' '0 'Iir;.ii7i ,;i:".-. ■'■.■..• '

413

ft u mixture of hydrocarbons auti their derivatives. It
source for obtJiitiing laizau; naphtkahtit, ami anthnwene
Ijdrocarbons which are vt the greatest importance for the prepara-
I vi artificial dye stiiH's imd luedicameiUs ; from it there are also
pkePfA {rarijolic arid) and compounds related to it, which are
pnrposcs of disinfe^^tion Jind for the prepiratioii of smokeless
ier. Numerous ulher substances rtiL' prusent in gtis lar,
used OS crude mtvterial, so that it may be dissiguattd its the
■porlant starting suhstanca in the iiifhi^tnul fhrtiii-nfrfj of (he

working n|i of thf giis tar is also carried out essentially

liuiial Uititillittion, v;'\\h. the aid of lime and sulphuric acid,

of ibia heloug to the chemical technology of the organic

go*, which is evolved at the same time, ia freed by cooling and

from the t-ar ; and by passing it over a luixturG of lime and

irun, the euljibur compounds it contains, and which, Viy reason

ition of sulphur dioxide would have a baneful efl'eet when

»eU in inUabite<l rooms, are removed ; it \& then stored in

TfU-lioldeni for distributiot) through the network of tubes to the

NridiMl coRsumors.

Coal gas varies considerably in composition, according to the

Kmed for it« preparation. Its chief constituents are hydrogen,
, carbon monoxide, and some hydrocarlmns richer in carbon,
r cthrl<*ne, benzene, and naphthalene. The latter two com-
ikds artf re^]jectivcly liquid and solid at the ordinary temperature j
f can mix with the gas, thf re/ore, onlj' in amount corresponding to
r rapaur pressure, and again 6e|iara.te out when the gas experiences
CDoaiderable lowering of tempierature.

• To give au idea of the compositiou of ordinary coal gas, we give
I tiM remits of an analysis in wiiich the constituents are stated in
S ftf rolvme .- —

Hydrogen
M»thaii«

CmJ'*-

Url

dirt . I"

lfitrv|$vu .

ide

49>0

2-6
0-7

I ** bydrocarbons " consist chiefly of ethylene.
At first coal gas was chiefly propared for iliuminating [lui-poses,
chief attention vraa therefore directed to obtiiining a gas rich
rletic aud other "heavy hydrocarbons." Such can be obtained
in expensive kinds of coal, and the pnxluct, therefore,
correspondingly dearer. Meanwhile, the gjis has
very convenient for heating purposes and for diiv-

414

PStSCIPLES OF DtOBGANIC CHEMISTRY

piJl|Kwea» boweirer, • (

lue&iL Since in tb

of olwaining lerr ooot

gN {mcMoitBccnt light), h f

begin to cbieflr maBof

withovt coasiderAtion of tbe illoa

e»D be prepuwi mnch more cheaply t

be made BtroQgly luminous bi

\y befbre its coDsumption) a smaU ^

bjllrocarboiM (benzene or napht

it alraidjr mnch used. It is 00)7 »

in vbicb the above-oaa

tbe Tspour prenare of these being,

to effipct a suffieteiit earhuntti

metliod consists in tb

wbl^ ate nuMd to inciidUescetiee ii

A IMM* m fmmma. IW detnb of tbk mil be given h

bi tl» ^bwiatwjl cwdl gm k awd very extensively for
YW tfu mmd far Am {Hrpoee w iorented br R. Bunseo I

h omriBts (Fig. 103) of a jet fasteM

mm baae, from which the gms strea

a wider, upright tut>e, whicb is hi

witb ht«T;al diaaght holes beside t

In tbe tuhfi the coal gas is mizf

•ir, and the mixture biu-nfj at tbe

( mj^ e< tbe tube with a hot aiitl very

Vl luminoos flame, which de[)osits a

^^ oo a «Jd ohject when itttroduee

I f ' y^ it. This is due to the fact that b}

' I —■ — -of the druught-hotes the gas is mi*

VC — -^^ aa much air aa is necessary for tb(

^ — ^^^^*' tion of the hydrogen and the conve

•^ •* the carbon present into carbon mono]

XvWMtoiM olber fono^S of Imrncr, which have l)ecn >ubip

>«iisHM ywtpoaea, faaTt been mode on the principle of the

bvimwr. Im F%. 104 is shown the construction of a flat

Wlims iMjpiff veeaela.

Tbe uuxtwe of g»a and air which issues from the bt;
yKMi>'*« tbe vetueity iritb which it issues is, however, iisunll
^la tb« <ubU9tiuii U propagated )mek>v-ard^ more slowly than
>anl. If the flow of gas is reduced bdow a .
ute of matters is revt'rse*J, and the burner " strikee
IV *\*.i>«.t this, the access of air must, he rcfhieed at the eatne tii
MNMMk (miiw vi burner are so cor ts to do this autoi

tbe

Vki.

CARBON

415

ftaroe of a Bunseii burner consistH of two pjirts ; an iuiier,
hoUoiir coiic, and an outer, blue mantle. In tbe hollow cone
iboBtion of thfl hydrogen and of the carbon to cai'lioii

::^=^

rw. i(M.

asentially occurs ; its the outer mantle the combustion

b completed. For this reason, the inner cone has a

action on substances introduced into it, whereas in the outer

the JDJLDtle an excess of oxygen is present. Thcso difTerences

of for the purposes of chemical anal^-sis.

Uua purpose, besides the iune-r cone, 'r, «, mt (Fig, 105) and the

itte^ f'f "i '". ifunseii distjuguishcd the Inmviou.i fip^ aha, which

when the air-holes of the burner are partially elosccl. It

ent In the normal Bunscn flame. In these three portions

six reaction sjjaces, namely, the bum of the flame «, which is

j»rt of the flame ; the fiidnff s|)ace, /3, which is the hotteeb

u the Inner, and * the u^iprr &m!mnif Jfame ; while (5 is the

^ the npjxr rfihtrin'j flnmi: The former acts less vigorously,

ime«l air is still present, but it is hotter than the up|>er flame

conuiins an excei?^ of rc<lucing carbon.

IS. Oxslic Acid — By the oxidation of many carbon conifwunds

[ia formed an acid of the composition HjCjO^, which, by reason of

■ifold importance, we sshall also mention here. It ia cilled uxulk

eincH bulb ita hyflrogetU! are replaeealdc by metals, it is a

add.

lie acid ia a white crystalline substance, which readily dissolves

er, and gives an acid reaction ; it is found to l)e an acid of

strength. The ordinary crystallised oxalic acid contaiiiis

of cr^'stallisatioQ, and its composition is represented by the

lU H „C»0, + "JUjO. With bases it forms two series of salts, acid

irma'l, and most of thcBe are difticultly soluble in water. Of these

: ike must important are the acid potassium salt and the normal

■alt.

former, having the composition KHCjO^, occurs in many
; pOMOsing an acid taste, and can bo obtained crystalline by the
of the juice pressed out from these. For its preparation
formerly chiefly used t!ie wootl-sorrel {i>j-aiis), from which
!• Bane ux&lic acid is derived ; likewise, tbe pota^um salt is called

■

416

PRINCIPLES OF INORGANIC CHEMISTRY

The neuiiJil calcium salt CaC^O^ is vevy difficultlji
watei'. It CHicurg in almost all plarite, being found iu the <

very cLaTacieristic hj
cryatals which have (
pearancQ of envelopt
anfitjtical chemistry 1
importance from the it
it is the form in wbi
calcium ciniijKmiid^ a
t^MJted qualitatively «
termined quaiititHtivel
reagent for this purpt
ammonium salt nf oxa
is mostly used.

On being htiated,
ftcid first iJei;otn})OM
fonuic acid and car!
oxido, H^CyJ^^HO
COg, but this decom]
can be accomplishoc
with great care or vr
help of Muitttblc cat
On heiitiiig more at
the formic acid also
posea, and there are o
taibon dioxide, cai-bo
oxide, and water : Hj
CO^ + CO + HjO. Tl
of oxalic acid nn being
are converted, with ov
of CArbon monoxidi
carbonates, which u
cases decompose i
e.<!. CaCjO^^CaCOj
'^ CaO 4 COj + CO.

Further, oxalic «

composes into carbo

oxide and carbon

when treated with d<

iug agents, such as

— I trated sulphuric acid

— ' reaction is made us«

„ ,,, the convenient prei

of carbon monoxide

acid or a salt of this is warmed with conci^ntratod sulphuric ai

the escaping gases passed thi'ough a wMh-bottlo with cau£t

-XVI

CARBON

The carbon dioxide is absoi-bed by this, and pure cArbon monoxide is
obtJiinecl

Oxalic Hfid is fiiirly seiisitivu to nxidiaing agents, and is readily
idised by them to carbon dioxide : H.,U,0^ + O = 200^, ^ H.^0.
is reaction is also used in anniyticjil chetnistry, and we shall later
ave occasifih to rotijm to it (Chajj. XXVIIL),

403, Oarbon DlSUlphide. — When charcoal is heated in a current
of sulphur vapour, a compound of the two elements is formed. It has
the compoisition CtS^, for its vapour density i» 70, and analysis shows
it to contain C4 of snlphur to I :i of csr>ioii.

Carbon ilisniphide is a colourless lirjuid, whose density is about 1 '3,
ami whieh boils at 47". In the pure state it is almost colourless.
Oixlinary carbon disiUphidc, dwing to tho presence of other sidphnr
compounds, has generally lather a bad smell. It can be purified by
aking with metallic nicrcnry ;ind distilling.
Cai-bon diisiilplitde tefracbj and dispeiiiea light very strongly ; its
indices of refraction (at 1 7 '00 ), for the most important rays, are : —

Wftvc-lengtii
Index of refrtction

7U04

i-enae

fi887

1 'iaosB

SSBO X 10-»cm
] -63034

Wnve-Iengtli
Index of refnotion

52"0
rfl4320

4881

430d
1-67975

3968 x. lO-«ctn
1-70277

For this reason it hjs often been attemptt^fl to use it for optical
•jiparatns, ejj. for prisms in spectroscopes. Tliis, however, hjis not met
with success, since the great expjinsion by heat very reiidily causes dis-
turbances ; further, tarl>c)n disnlphide is somewhat sensitive to light,
and when exposed to light for a lengthened period it decomposes and
its properties change.

Carbon disulphide is a good solvent for many substances ; in this
role, we have aheady met with it in the case of sulphur and iodine.
It also readily dissolves fata and resiii.s, a fact on which many tecbnital
applications of it dejwnd.

Uy reason of Ijetng composed of two combustible elements, carbon
disulphide can bn ignited, and it bnin.|* in the air with a blue flame,
with formation of sulphur dioxide and carbon 'lioxido. Its (cmjpcmture
of iffnifif/ti is very low, so that the vapour of cai-I-K>n disulphide can be
ignited under circumstanca^ in which other combustible suhstanc
far from taking fire. Corrcspomling care must, therefore, be o'
in using this compound.

Mixed with nitrous oxide, carbon disulphide hurtis with t
which is especiitlly rich in ultr.aviolet and ■^nolet rays, and which,
fore, under certain circumstances, is used for phoLochemical pu
The sulphtu- dioxide thereby formed, however, is a hindrance
general uae.

2 E

418

PRINCIPLES OF INORGANIC CHEMISTRY m

Carbon tlisulpLido ia formetl from its elements with absMijuhnii
- 120 k)\ Its heat of combustion amourite to 1320 ky\ whereas th
the elements is only 1200 kj. In vory special circuni3tancc«(,
fore, it may be ciiised to ilecomposo oxploaively ; this, however, I
difficult, and, as & rule, it oxhibita no explnaivo propcrtiea.

From carbon diaulphide mi acid ia derived whieh bears the
relation to it its carbonic acid does t^ carlion dioxide. Only,
acid is not com posed of carbon disulphide and uxiirt, I ml of
disulphide pins .inlphirettfd hfjdrogcti, and bus, thereforfi, the;
poaition H„CW^.

From ibia example it will be seen that besides the oxyacids]
iirp others which ha^c a similar composition to these but
iulpUur in the jdatft of o.vygen. These are c;dled thii}-itfid.\ an
jibtne acid, ffimtrrhnuk. ndii, its such an acid, as can be seen by writi
the two formula; eide by side : — -

Aiihydride
Acid
Soiliam aa.lt

CO,
H,CO,

Nl^CO:,

CSa

HgCS,
NftnCSj.

The sodium salt of thiocarijaniim is obtwined by dissolving
diuiiiphide in a soliittoii of so<.lium sulphide, in accordance with
ef[ nation CS^ + Na^S = Na^CS^. From a solution of this salty
airbonic acid can l>e precipitated by aflditinn of an acid. Ub
ciirbonic acid, it oidy slowly decomposes, so that it separates o«l 1
an oily liquid, only slightly soluble in water. This is, however,
stable, bni slowly decomposes into carbon disulphide and sulphiirctK
hydrogen i H^CS,, = H.^S + CS.^.

The thiocarbonates have atUiined to a certain importi'ince fromi
fact that cai'bon diHulpliide has Iwen fovirid to be a means for destr
ing the phylloxera. Whereas carbon disulphide is so volatile as to I
inapplicable for thia pnrpose, the thiocarbonates are snitabie.

Under the iiiHncuce of the carlion dioxide in the air and m
soil, these are convertod into carbonates, carbon disulphide and »tt
phuretted hydrogen beinj^ split oH': Na.,CSj, + CO, + H^O = N(i„CO, ■
H*H f USj, The process Utkes place slowly, but still with snril
rapidity that the anioimt of carbon diaulphide present at each momctil
is aufticient to exorcise the desired action.

The existence also of a cumpoiind I'S has recently been rendoroJ
very i^robablc. It was obtained as a colourless gas, by heating cifP
ill the vapour of carbon disulphide (hluted with nitrogen, accorthri^
the oquation : CS., + C'li = ('S + Cutj.

404. Carbon Oxysulphide. — -In various ways, most easily bj tl
decomjjositio" of the thiocyanatea {ridf infra) with sulphuric acid,
compound, COS, ts formed which can be regarded as an interinedi*"
compound between ciirhon dioxide and carbon disulphide. It isiii!»'|
which is readily absorbed by water, with which it slowly intflracts, v\^^\

CARBON

+ 19

m nf carlxtitic acid and sulphuretted hydrogen : COS +■ 2H jO =
)» - HjS. This rcaclion is ^rcitly accelerated by the addition of

the salts of the two acids being formed.
krlion oxy«u]phJde smells eomewhiil like sulphuretted hydrugeri,
lily burns in the air with a blue Hamo, foiTaing carbon dioxide
shiir diitxidc.
Cyanogen. — When carbon and nitrogen are exposed to very
|it4:iii]>i.'r.tturcs, srich as exist, for example, in the ulectric arc (Fig.
p^ 412), these two eh-ments combine to form a giis which, in
xner: irilh its comiiositiyn and deusity, 52^ has the formul;i
Jij. Oil *«;t>uiit uf the blue couipounds which it yields with iron.
id which liave been known for loiiy, this subatance lias received thi
attv ■•.^tuo^en (producer (if Idue substfmee),

"•^en is It colourless gas with peculiar simell and poisonous
- .- -ti the organism. Its eritiwil temperature is 1;J4 , its ^iticixl
wnuv tia Mm. In its solubility in water it resembles carbon
mcidc, t^j which it also approximates with respect to its density
!2 »a cotn|va.red with 44).

F'l can be ignited in theair, anfl burns, with a charactoristie
; . inlet cobtiir. to carbon dioxide and nitio^oii. A consider.
amouni of hwit is thereby developed, amounting to more than
JHU h« given by the corresponding amount of charcoal. Oyaniiyen,
^■for«, *lsf.) belongs to those compounds which are formed with
Hrpliot) ttf ener;;y, and whose spontaneous foi'matioii occurs at lery
^P t»'.niperaturi;s. It is thus foiined on all occiisioits M-liere carbon
B nitrogrn cume together at a high tempeititui'e, c.i/. in the Wast
■mc« ill the prcpariition of iron. The heat of combustion of
Ifioogen (8 1087 lij, whereas that of two carljons aiuount-s Ui >^]2 kj \

It fonuation of the gas, tlierofore, 275 kj are absorlied,
D ita chemical relations, cyunogeu is analogous to the huiogfun,
bnnda whole series of cump^jumis in which the group CN behaves
chlorine or iodine. More especially, it forms with the niet^tls,
drj, which contjiin the colourless, hij^hty poisonous monn%alent
idiiin CN'.

In ihe firbt pl«»ce, there ahoulil be mentioned the hydrujfen com-
P"<ui(l Ht'N, hi/ihvci/tuik arid or prtissif ncuf. This conifwuiid is
"liTjiinrd by decomposing the met^dlic cyanides with an acid, just as
^turic acid is (ihtAincd from common sidt. The metallic cyauide»,
tre formed by allowing cju'Imih nitrogen, and the respccti\e
lUriila, or their carbonates, to act on otie another at a high tempci-a-
tarr. A tiHire exact deBcri|>tioii of what takes place here will ix"
ipien Utt-r mider the metals,
.J'nr the lil»eration of hydrocyanic acid from its salts, a strong aciti
«ie<imred. for hydrocyanic acid standi at the outemiost limit ot
|*wk Aciiia. The aipietfus solution scarcely exhibits an aciil
lioii, and dissolvwl nietjdiic cyanides can be decomposed oven by

nam

420 PRI^^CIPLES OF INORGANIC CHEMISTEV n

such weak acids us c&rbonic acid. In cousequenco of this the xwu
cyanides, when exposed tu the nir (contaiuiuj^ caiWiiic acid), smeil
hydrocyfinio .loid, and the aqueous solutions are ijartially djssodi
hydrolyii willy and react alkaline (p. 250).

In the pure stjit«, hydrocyaHii; acid is ji colourless |j<|iud irl
boils at 27 iuid solidifies at - 10 . It is u highly poisonota i
pound, which even in snmll amounts (|uiekly acts ktalJy. The a
of its ^Misunoua action is probfibl^* due to its being a retarding c&tjj]
for niitny phj'siologically impottant proceafios, especially the oxida
in the orgaiitsin.

Hydrocyiuiic acid tau Ijc delected even in sniall quAtititias bg
smell, which recalls that of liitter ahnonds. The reason of this i«
in liitter almonds a siiJistance, amygdalin, is pre.sent which decomp
under the inHuenee uf a. catalyser or enzyme, which i.s alsi> presci
other cellii, into hydrocyanic acid, augiir, and a volatile ml — oi
bitter almonds. Cnishcd bitter almonds, therefore, smell of hy
cyanic acid when, owing to the destruction of the cells, tb
substances, amygdalin and the enzyme, come tojtether.

Whereas the aqueous solution of hydrac3'anieiwid contaiua'
ingly few ions, the soluhle metallic compound.s, which, in a corrMp
ing manner to the chlorides, are obtaineil by the action of hydroxy
acid on the o.vide^ or hydroxides of the tnetals, are normally dissoci
into their ions. Thus, the solution of one of the best known met
cyanides, potassium cyanide, KCN, contains the ions K" and I
The ion CN' has a great resemtilancf to the ions of the halo^
ivith aigention, for example, it gives a ditRciiltly sohiltle cotnpoi
which is dejiositctl jis a white precipiuite, very similar to ai
chloride, whcu cyanidion and argcntion {f.ij. from jjotassiutn cjTi
and silver nitrate) are brought together in solution.

• For the purpose of detecting cyatiogeti comixjunds, use Li Q
of A'arioua very sensitive reactions, which may be shortly menti(
here, although their theory cannot be given till later (Chap. XXV
The liquid to he investigated, after being made alkaline by aitdititi
caustic soda or potash, is warmed with a niixture of ferrous and f(
salu, and hydrochloric acid then added. If cyanidion was preset
dark blue precipitate is obtained, or, in the case of very small <iui
ties, a blue or green -blue coloration. The blue iron compoun
hereby formed which baa given the mime to the whole groui>.

* Or, the liquid, with adtlition of yellow ummotiiura sulphid
evaponttcd to diyufss, the residnt; dissoht'd in a drop of wiiiwr,
feri'ic chloride added. If cyaniilion was pcesent, u bloorl-red oo
tion is ]jrridneed. Thi.s depend.^ on the formation of ibiwiinnanw
moans of the sulphur from the aiiuuoniuiu sulphide, and this gira
above reaction with ferric thloride. A knowledge of this test I
practical importance by reason of the t)ot infrequent cases of \)o\m
with pruBsie acid, or with cyanides.

CARBON

431

•*': Relation of the Cyanogen Compounds to the Ammonia
'atires of the Carbon Compounds. — When hytircuvHuic acid

[«m) ik-itl'. sttoiij,' liy<i,nwh)"rii; -.Kvi, a rpactitm h\ke» place, and
pi liile Jiml fiiriiiic iK'iil aiL' |trriclm'e<l. The t'eaction can

, ri ns fssfHtially a taking up of water: hy'lrocyaiiic acid
tffr vii'ld formic acid and amnionic, in acconlunce with the
I HCN - 2H,0 = HCOOH + NH,,

rctiction recalls the convoreioii of the atuides into the
urn salM of tln' con*es)wrnling arid* (p. 'M6), hut it differs
l»v the fact that tint mules of water are taken up instead of
I siiiljkltk' cases, therefore, there are two stiiges of dehydration
Mnmoniuni salts : the first yields the amiile, the hiecond a
nd for wfhifh the genemi tiatue mtriU has come iulo use. In
t caAe we have

Aintnootlun fonnate ..,.,. HtX>0 • NHj
Auiide of formic acid, or fornittiuid* . . HOO'NHj

Sitrilr of fonrne aeiii, or lij-ilrwyftnic »''i<l HCN

> toatter of fact, hydrocyanic acid can be obtain url from

formate by meana of strorigly flehytlrafing uycnt,s,
Btnilar series shows cyfttiogeii it<ielf to bt> the nitiile of uxalic

Animoiiittni cxaUt'' .

Ainiile nf oxaIu' ftcid, nr iimmidi.-

Xllritr DfuxRh')' aeiiJ, oi cviom^iiiii

[j^ Vic niay (nass through the scries not only by dehydra-
almvc rlnwHWardti, l>n( also Iiy absorption of water from
jiwards.
further extension <tf these indications li«long« to organic

Cyanic Aci(L — Of the oxyarids of eysmogen which woidd
>i»d lo llie acid* fnim liy(jochhti'nu.s dp to poi'chlone acid, only
nwiuVwr in known. By analogy, this should he called hypo-
acid, since its conjjvositioii is repieserited by the formula
iince. however, no other oxvgen conijiouiid is known, it is
acid,

Rcid is a very unstjthle coiiipouiid, It'VH tditaincd by

another (•oiiip4iuiid, ri/unnrif iKitl, which h.as the Mime couijMjsi-

three tiracjs (lie molar weight, H.,Ly,",,N.,. From the vapour

[ «tjti9lanvu there is dejmsite*!, in accordance with the law of the

tnee of the luistahle forms, not the stable cynnurie acid, but the

ftHiMr ariyJ, HtK'N. The eojidensHliou of this c(tmp<mnd,

bt« carried nut at as loiv a temperature ai* possible, for,

ng, eyanie acid is converted, with strong de\Hh)|iiu<'nl

»c)meiimts with explosive violeirce, into more stable fovrris, of

i there are aevend. If is a nilnurli-is !ii|i)ir9 with a «lrong smelly

bling that of acetic iicid.

4S2

PRINCIPtES OF INORGANIC CHEMISTRY ..iri

In arjueoiiH solutiort, tilso, cyatiic acid is not stable, hut is q
CQiiverted, by absorpttnii of water, iiiln aci(i aunnofiium airbonate.
process is represented by the follnwiiig eqiirttioii ; HOCX + 3
{NH^)HCOy. P'or this reiisoti, a solution of a cyaiiat* on
actdifierl effervesces ami evolves carburi ttioxitle jis if a carbonate
present. After the loaction. ati unimauiuiu ailt is present in
solution,

Although t-yanic acid is very nnst-atile, Ic. cyanaiiion, CNO',
exist, along with hydrion in eriuilibritiiH, the salts of cyftiutni
cyanates, are mostly veiy sUible compounds. They are formi
example, with great readincsB by ex{K>sing the cyanidos to iho
of oxidisintj agents, On this account, fused ijoUissium cjarn'i
pyworful reducing agoiit, which mthUraws the oxygfn from
meUdlie oxides and converts thera into metals. This reducti
bo shown with csjrecial ctise in the case of leeui oxide and bisiHUlh
under the litinid salt, the metala fuse together int<j drops which
bright like tnorcury. The same reaction is made use of for o'
ing cyanatos, especially potaasinm cyanate, from the etirresjxmdi
cyanides ; as oxide, iiyrolusite (p. S5), is mctstly employed.

A speuiiilly interesting reaction of eyaniu auid i." the transform;
which its ammonium salt undergoes, and ivhich led to the syntbeaii
urea (p. 398).

Amnionitun cyauate has tlie formula NII^OCN. and amtiiins
wne elements in the same proportions as urea, for l*oth have
total foiTuula CtT^N/). If, hou'*»ver, it is attempted to prej
anuiHjnium cyanate, urea is obUvined in its place. In thr mwvnti
however, it has been .shown that true ammonium cyanate jiossesa
the expected properties of this stibatimcf exista ; but it is ve)
unst^ible, and rapidlj' undergoes transformation into the isomei
compound nrea.

This reaction takea place so soon as the ions OCN' and NH', col

I together in aqueous aohition. On mixing any cyanate, f.7. potaawt

icyanate, and an iimmonium salt, f.ij. ammonium sulphate, in aqllM

aolufcion and evaporating the solution, n residue of putjissiutu siilphi

and urea is obtained, which can be readily sepaiated by nicAns

akuhoi.

* Converaelj , a small amoinit of ammonium cyanate i» fonned
an aqueous solution of urea, eajwcially on heating, so that a ebemi
e<iui]il)rium h cst^itilishod between the two isoiueric suiistances al
result of tlieir nuitual convertibility,

*08, Thiocyanogen.^If potassium cyanide or other cyanids
fused with uulphnr or a sulphur compound, or e\en if a solution
one of these salts is heateil with sulphur, the latter is taken up 1
a solution of a salt is obt,<iined of tlie composition MSCN, in the c
of [lotassiuia, therefore, KSCN, Tins cnmptiund. which gives a v
pronounced blo<xl-red or brown-retl coloration with ferric eaXta,

pvtassmm ihioafi nah , it is tlie ])<)ta«sium sail uf tbiocyananion.

oonipo&itiun of these compounds is i^imilar to that of the

»ci<l compounds, only that Bidphur is [jresont tn the place of

Thi,,rtniiik acid is flistin^iisht'd fnmi cvmiic ivtid l>v it« much

■!ily.

harntni suit, by precipitation with 8ali)huric acid (p. 2y3),

dilution of thiocyanie acid can be oVtUined ; this is a very

•i^iK. .» hose acid properties are not f^rwitly itifcrior to those of

cblorjc ftcid. In the free state, thiocyanic acid is uuknown ; on

ipting to pTe{«ti-e it, a r«ther complex deconijioaition occurs in

earhfm oxysulphide, COS, is formed (p. 418), The fomiation

Intier comfMUinil takes place directly by splitting ofi' ammonia

aid of water, a rcjiction which can be represented by the

ion HSCN ^ H.,0 = COS t NH...

The decomposition occurs on
medium strong solution of

puta^saium thiocyatuite v,\lh
acid.

ard t<h its similarity to the haUj^ens, thiocyananiou, SCN',

lalogous t« cjanaiiion ; il, also, gives with argentioii a white

itate> which^ in it<s external appearance, cannot ho distinguished

rcr chloride or siher cyanide,

rrespondiiig to the ifosi'ous cyanogen, however, no thiocyanogeu

11. There are suhst^tncos, it is trno, M'hich have the composi-

N, but these are certainly p<jlymeric eompovinds of the formula

, where n is a mimhcr pi-obably greater tbati '.i. They belong,

lore, Ut quite a different group of substatiLes, which are generally

lt«d in organic chfroistry.

CHAPTER XVII

SILIIXIN

409. General Silfcon stands to carbon in the same Relation as sni
to oxygen. The two eloments are similar in many respects, but '
more from one iincfther thuii, for example, chlorirR\ ftrominc
iodino do.

.Silicon, like carbon, occurs in tereral forms, of wliich an amor
and a fiptnlliiif form are accui-ately known. Amorphous silioMil
obtained by conducting its chlorine or fluorine coni|jound over he
potassium ; the metal unites with the halogen, and the silicon is
free. The soluljle potassium salt formed is remoi'ed by washing '
water, and the silicon is left behind ivs a greonish-brown powder
ia aranrpboua, and has the tendency to jiass into the colloidal slate ;
therefore, the washing is continued to a certain point, the silicon ,
into a ekidge ami begins to pass through the (liter.

Amorphous silicon is more easily obtained by beating its ox
(!onipouiid, finely jHtwdered quartz, with magtimiiin /Kunfer.
rnaj^nesiiini combiuea ivitli the o.xygeu of the silicon dio.\ide, forn
magnesium oxide, anil the fcilicon is liberuted. The latter caa
obtained pure liy extracting the product with dilute acid, in which l
magnejiiiitii oxide but not the silicon dissolves.

At a high temperature, silicon melts ; and on soh'difyiug, crystallil
silicon is formed as a grey mass with a raetnlHc lustre. The crys
tion is greatly facilitatcil by the adilition of a metal rhcIi as
the zinc can be removed by treating the product with dilute itcid&

.-iiti'H'fihntim silicon can be set on fire in the air, but its combustifl
ia very incomplete, Iwcauae the non- volatile silicon dioxide for
prevents further combustion. Cti/stnUiM sihmn does not noiic
change in tlie air even at a red lieat. Silicon is soluble in can
soda on heating, the silicon thereby taking up oxygen from the TmV
and passing into an acid, silicic acid, or rather into its sodium
The hydrogen of the water escapes as a gas.

The combining weight of silicon has been determined l»y
analysis of its halogen compounds, and .amounts to Si = 21* •4.

SILICON

425

L Silicon Dioxide, — By far the moal important corapoiiiid of

r; itlifou ithnilf or the ttfthifrlrit/e of silicic acicl. It has the
SiOj, or a multiiile of this, and occurs in enormouB iniiintitiea
re ixtth in ihe free state anti us salts. Tlie largest iiai t of the
surface is com[>o3ed of siiieon dioxide, or of its compouudB ;
Hjarter of the solid cnist of the earth is formed by silicon.
jn dioxide oociira in several %'arieties, two crystalline and one
It is most widely distrilmtedl in the crystalline form as
trock crystal, amethyst, amoky ijuiirtz. These and viirious
lerals are, chemiiyiUy, the same substance, and uppcjir to be
only by reason of the impurities to whith the difference in
due.

parest form is rod' tnjdat, which crystallises in aix- sided
id is colourless. The crystals possess the property of roUttivg
of polarised hght when this is passed throtiyh ptirallcl to the
'the piism. In some crystals the rota-
ibe right, it] olhei's to the left, and the
the rotation is closely related to a one-
tUogr&phic formation, by means of
and left crystals can also be dis-
The difference is seen in the hemi-
(Fig. 106); a right and a left
n ho nTr>re be superposed on one
an can u right and a left-hand glove.

rock crystal is clear as water, smoky topaz, or, better,
nrrfc, is brown to black, amtthyd violet, ordinary ifiHtrfs
and tnrbid. There are also yellow, rose- red, and other

3^ y

a constitneiit of many rocks, especially of granite,
By the action of water and earbotn'c acid, these riicka are
ted as well as ])artially changed chemically (rn/*" in/tn), and
irtz grains are left detaclsed, These are borne away and
■p by the rivers, and finally reach the sea in the form of
On the sea-bottom the sand masses frequently Irecome
l^un by means of a binding material (limestone or iron oxide)
fanilgffme, which forma extensive mmintjiiri ranges
vi quartz grains, lins been >iO formed.
has the dfosity 2'tifi, and a hardness 7, i>, it represents the
inlMt gnule after the diamond, C^uartz is used, therefore, for
: aietal (grindstunes and wfiet^tuiies) and glass.
Uhit crystalline form of silicon dioxide is called (riifpitiite. It
tfaoo^t solely in micrngcopic crystals as a constituent of rocks,
riense than (|tiartz (2'3 as comparetl with 3'(>fi).

silicon dioxide occurs as a mttieni! in %'ariou» rocks.

iride-spread and best known form is /"»', which forms

in chalk, and is coloitred by organic substances, yellow,

OHEMISTKY m

brown, or black. It is but slightly inferior to quartz in haiiltieis^
by reason of its conclioidal fracture sharp tidges cjin easily 1^ fori
on it. Ill prehistoric times, when tlie methods of obtaiuiiig and wi
,ing metals were imktiownj this mineral was used for making kai
^axes, and arrow heitds. It is the atone which was chieHy employ
in the " Stone Age."

Another form of amorphous silicon dioxide is opal. Chulcedli
jasper, etc., which were formerly regarded as amorphous, are "cryf
cryBt-alline," i.e. iire eoiu posed of very small ciystala Kifseigt
(diaU>m;iceon5 earth) is a fine powder consisting of the shells of
orgtini»m& (diatoms, etc.). In chemical ojwraljons. silicon dioxi^jfl
••liaually obtained nmoqjhous, and it is not very easy to cauee l^|
CTystalli.9c ; neverthele.ss, both crystalline forma have alreaily I
artificially prepared.

The amorphous varieties readily dissolve in boiling caustic «
with formation of salts, hut the ciystallitie forms are sc^ircely ulUcl

The molting point, of siHcou dioxide is so high thai the latter <lt
not melt in the ordinary fire, but does so in tlie oxy hydrogen fli
It then forms a vjbcohs li<jnid ^^■hich looks like fii.sed ghiss, aud
be blown. In lecent years vessels have been mjule of this amorij
"miartz gliias.'' On account of their small coeflicietit of cxpai
with heat, they can be subjected to sudden changes of temperaM
without crackinf^; thr-y are also very resistant to chemical action

411. Silicic Acid. — Silicon dioxide is the anhydride of an sud
silicic acid, or rather of a whole series of acids which can be
pounded of the elements of silicon ilioxide and water. The relati)
are similar to those obtaining in the case of the phosphoric acids,
more diverse.

As extreme member of the scries of the diftfereiit silicic t
there may be regarded the tetrabasic orthosilicic acid, Si(OH)j ; SiO,
2HjO = Si(OH)^. It is not known in the pure state, but in the f«
of its salts.

By lo-ss of water, it passes into the dibasic acid SiO((.)H).,
cotn|K)sitiot) of which currespon<Js to that of carbonic acid.

Other silicic acids are forraed by the union of several combiaii
weights of the oitho-acid with loss of water. From 2Si{0H)^ll
are formed Si.,O.H|„ SijO„H^, Si„O..II.„ In a similar mantier, coti
sponding " jiyro-acids " can be di^rivetl from several combining weigh
of silicic acid.

Unlike the phosphoric acids, the different Bilicic acida cannot
distinguished from one another by any reactions ■ that thew d\Krx«
types exist can be conclude<l only from the existence of the cotl
sponding salts which occur naturally in the crj'atidline form.

These salts of silicic acid or silicates are all practically insolut
in water, with the exception of thu silicates of tlio alkali met*
which can ))e dissolved, and whose solutions bear the name of mtl

ML These salts are readily obtained liv fusing «jiiariz with the

"••* (»r cariKinates of the alkali metals. Fnitn theso solutions,

iici J can he 8«t free by other acids,

Hb the mixing of an alkaline ailiait* svith add, '.;/. hydrochloric

IPl^e carriecj out in coiic^ntruted solution^ the silicic arid iic]Mirates

L in friftbie. gelatinous nifisses. If, howei'er, dilute soUitiona are

iployerl and an excesa of acid, no (jj-pcipitation is obtained, but the

laticin remains clear iind apparently unchanged. This looks as if

acid were difficultly soluble, so that it js partially prcci-

ifoui coneenLi-ated solutinns while it remains dissolved in

■cii waU'r. This is, however, not, the case ; the solution of silicic

id whieb is formed h no true solution, but the silicii- acid is present

\ iba cMeidal stat&

BCbis h seetr when the liipitil is subjected to dialysis, i.r. when
^Vplaced in a vessel whoKO walls are formed entirely or partially
F^urhroent paper or of bladder, and the vessel placed in pure
iMr. Tilt-* silt which is formed mid the excess of acid then pass by
^■ioD freely tbruiigh the meinbrune, while the silicic acid, Kke all
PRdal aubgtanc4?H, l» reuinud. If the experiment is continued for a
nnntier of days with frequent renewal of the water, all the salts, as
jbai can tie detected, will finally diffuse away, and the aolution in the
^B^r will eoatain only silicic acid.

^■bis %il»cic acid shows the chanict^ristic pfoperties of ''colloidal

IBBAns" or "pseudo-solutions." On evaporating to dryness no

OTirtaLi are formed, but there is left an amoriihous, glassy mass

•which only incompletely reMlissolves in water. Boiling and freezing

pmnt differ only exceedingly slightly from those of water ; .sfiecial

' ■ ■ - lions cannot bo d-^tccted, \iy adiUtiou of various sub-

(mIIv of sjilts, the liquid solidities to a jelly, especially if

ken somewhat concentnilcd by evaporation in the cold.

jiature silicic acid occurs very iiften in such a form. It gets

itural waters from the silicateB when these are decomposed

w add. Under suitable conditions, the silicic acid crystal-

liK* from such solutions ; smoky quartz, especially, has probably been

' 'in this wa}'. For, since it owes ita colonitiori to oiganic sub-

vltich arc destroyed bj' ignition, it must have been formed at

npeniture, and, duriiif; the period of iUs cxisteucc, can never

11 subjected to a red heat. The way in which it occurs, also,

"luitB its fomialion from solutions jirobable,

Silicic acid, or quartz, is e.Mtensively applie<l in the arts, Sand-
■noe if a gi-eally raluefl building material, because of its Ix^ing easil\'
tkwl ^ji'l resistant; quartz s;uid is used .is an addition to mortar
lior grinding. By fusinj^ quartz with the carbonates of the alkali
1 *llulitio earth metal.'', amorphous, transsparent masses are obtained,
, » ?fii.<M, find very manifold application. Colourless rock crystal
as m cheap ornamental stone, and also, on account of its i*otating

428

PRINCIPLES OF INOHGAIIIC CHEMISTRY cm

the plane of polarised Hght «nd of its transparency fnr light
wave-lengths, in the cojistruction of optical inBtniments, For sj*
glasses, also, ([iiarti! [s used, since, on account of its great h»r
it loses the polish less eiusily than glass lenses.

412. Geological Keactions. — Of all cheiniml processes ot-cutt^
on the «ai-Lh"s surface, the interaction of tiie naturally occurring sili
with water and c<irbonic acid is the one which, i[uaiititjitivcly, st
pre-eminent. The primitive rocks of the earth were essentially silic
the carbon, in all probability, was present as carbonic acid,
eorrespondi to the eciuilihrium at comjwratively high temperat
which ranst be assumed to have prevailed originally on the earth.

At lower temperatures the et|uilibrium changes in such a
that eai'bonic acid displaces silicic acid from its salts. In
words, a system consisting of im'honattji and frre silick a^id, or
dioxide, is, at lower tempeiutures, more stable than tkie system
diojidf and sUiaik. For this reason, the silicates of the
primitive rocks are subjected to uninterrupted chemical change,
which is added a mechanical disintegration by the action of wawr, i
changing tpnijjcratnre, and of the wind. The consequence of Uiiit
that the silicates which are decomposjible under iheae circumsb
are transformed, the noii-det'oniposable aie disintegrated, «!hI tarh
are formed from the ouTistituenta of the transformed rocks.

The silicates of the; alkjili metals, esjiecially, undergo this
position. Those, it is inic, do not occur in the free stale in
bnt only as double silicates combined Mnth the silicates of other mcUl
They liecome thereby mure stable., but atill not absolutely rcststani
and are therefore decomposed.

The ions of the alkali metals pjiss into the waters as sdlah
carbonates, and are partially retained in the soil by absorption.
retention is specially great in cultivated soil, where it is eonditionw
j;artially at least, by the presence of organic substances, AnoUifl
portion passes on into the sea. This is also the destination
alkaline earth metals, which are tlieie de|K>6ited ehicHy as carboD

Of the dis.iolvud silicic acid, a considerable pctrtion al.^o reacM
the sea, and is there utilised by various animals for building np
skeletons. Another portion forms hydi^ated iiia.gnesium silicaie will
the inagne-sium of the rocks. This ia a comptjund which, uo
certain circumstances, resists the action of water, and which ia
fore formed when iis constituents come together. The conversicm
the original rocks into serpentine or steatite, as the hytiratt'd iihciu
of magnesium is called in Jnineralogj', can constantly be rofogiused
various points.

Of the other metals which occur abundantly on the earth's sur
aluminium also is cajiable of remaining in combination with silifi^
acid, even under the e-visting conditions, ytlnmiminn silfulf is a v(
widely distributed constituent of the primitive rocks, hi the deooii

SILICON

429

and carHotiJc Jicid, or " woithering," alumiiiimn

discomposed, but remains as an amorphoiiji or crypto-

ine rrsidue when the other constituents have bfun dissolved.

ry finely tlivi<ied niHSs ie rairried by the rivers to the eea if it

pireriously l)een deposited at comparutively quiet sjwts as clut/,

eurih, or loam. On the sea bottom the tJeiiosited chiy slowly

ptt» into slate atid aimihir st'coiidiiry rocka'

means of tlieso vurions tmnsformutions, a one-sided change
pliM;e in the compositiou of the eitrths crust, the tendency of
(is tn more and more increase the amount of carbon in the torni
(iuni and magnesium carboniite, while the silicic acid which
hxtd formed salts with tlieee metals is separated in the free
By this process the amount of carbon dioxide in the air must
>wly become less, By the combustion of fossil fuel, it ialme, &
, Ainouut of the carboti which had been long removed fram the
Jn jjiveij biiek to it, and in isolated lociilitics where volcanic
uccim at a comjwirativcly small depth below the surface of
tk, tiie carbonates formed iti the wet way also appear t4i
decotnpodtioti as a consequence of the rise of temjierature,
wed by the streaming forth of carhoTiJc adil at the places
Still these amounts of carbon, which are again put into
ion, arc probably much less than the amounts which, in the
%iA ewlwnates, are withdrawn from circulation.

I wo consider, now, that all organisms must have recourse to

for the building up of their belies, we see that the slow

(ioD of the amount of floating carbon -capital which is taking

Da the surface of the earth must exercise a great influence on

vulding of life. It can be regarded as highly probable that

illy different state of affairs which, as may b*- concluded

[investigations of the geologists, prevailed in former periods,

!u€ to ilic influence of the larger amounts of carbon dioxide

fnt in the air, and ttiat in the future also, organic life will

variation in such a sense that the continued diminution will

in a ^nitalile manner,

|:j. Halogen Compounds of Silicon. — When a mixture of

dioxide and charcoal ia strongly heated in a current of dry

he, decomposition takes place, and there is obtained, besides

I tiionoxide, a volatile siibstJinee which analysis and vapour density

Ito have the composition SiC'lj. The reaction, therefore, takes

lin »ccorfhince with the equation SiO^ + 2C + 201, - SiCl^ + 3C0.

lirnras neither carbon nor chlorine alone can decompose silicon

the decomposition can be effected wiicn both substances act

The reason of this is that by the simultaneous action

r OMMlitiojio i-xinting in the tropica fl deooinpOisitioii of Ihv iiluniinimn siUefttfta
I piacf, •■> liiil tli« »ilku' aeiil is r<°iiioveil giu<l ahimiiiiiini hyJroxiiW ivrnftiQii

430

rRINCIPLES OF INORGANIC CHEMISTRY

of the tivo substances, pioducts uru formed which are miicL
stable, or twritain much less free energy, ihaji when the subst
act sepafati'ly. For chlorine iilcme would yiel<) free oxygen
witli silicon chloride ; ehajTOiil alonu, free silicon along with ci
motioxjdc ; whereas, when they .act together, the formation of
•Btauees with ;i lurye amount of energy, such as oxygen and
is avtiidixl Of the jirinciple which formfi the basis of this ii
use is frefjncntly mude.

Silicon chloride Ktn iilso be obtairied by the action i>f chl
on amorphniis silicon. It is a colourlesH liquid which fioils m
and has Uu* Junsity 1-5. In moist fdr it fumes strongly, since j
in very readily decoin[H)sed by water to hydrogen chU>ride and tilil
acid: SiCl^ + 4ri,,0 = Si(OH)^ - iUCl. This reaction show^ it lo I
the chloride of silicic add.

If silicon 1$ lieated not in a curi'ent of chlorine but in one
hydroi/cn fliUrriifi:, the latter is deccrmpi>Bed and :i cbtnnne con»iioiiiiwl(
silicon, which also contiiiiTS hydrogen and luis the ooniposiiittn SiHt
is formed. On hccoumL of the similarit,}- of this formula to thai
chloroform (i>. 40r)), the substance has been calli^tl .nliaM-hkiritftfrm.
is a colourteiis liiiuid which looks like silicon chloride, mnl, like tii
is also decomposed by water ; it boil.^, however, somewhat lower,
at 36 .

Corresponding to these chlorine compounds, there are also liromil
and iodine compounds which have an analogous comjMisitioii, and vriai
in accordance with the general rule, have hif^her boiling points,
the chlorine compomids, but which otherwise Ijehuvc ijuite sii
and are obtained in a .similar manner. Silicon iodide is a .solid
ordinary temperature, and pjusses into a liiiuid only at 150 .

414. SUiCOC Hydride.— A eomj)ound of the cotti|tosition Sillj
obt;ii[)ed, luixtjd with much hydrogen, wht'ii magnesium contJitHa]
silicon is dissolved in hydrochloric acid. Since it can be liqi
much more easily tb.*n hydrogen, it can be obtained pm-e by
auffiniently strongly. It possesses the property of igniting sjxint
ously in the air, and owing t^ the formation of smuke rings of
dioxide, it gives nac to phenomena which are quite similar to
which arc seen in the case of hydrogen phosphide. Its iK'havig
iko, with res{,H5ct to the dependence of the siK>ntaneous ignition
the density, appears to be similar to that uf hydrogen phosphide.

Whereas, therefore, in resjtect of the fornmhi, silicon hydride
motfaatie (p. 104) are to lie regarded m. similar compounds, they i
very great diHerences in theii' chemical properties. Similar differen
are also found in the case of many other compounds of carlxm
silicon of analogous compositioji.

A hydrogen compoiind of silicon, Si,H„, analogous to eth
(p. 408), is also known. It is a colourless iiquiil which boils at If{
and freezes at - 1'4 . It alao Uikea lire spontaaeou&Iy in the air.

SILICON

iflilicoii Fluoride. — With fluoriue also, silicon comlnnes,

a conipuund of aiiulogous com[ioaition, SiF^, which at the

ry teio|>eratme is a gas. This compound is very easily ob-

bjr aUowijig hytlrogeii tlnoride to act on silicon dinxide. Since

tImxiinpoAed by wat«r, dehydrating agents must be added to

the action of the water which is formed in the process. This

simply accomjiliHlied liy tre^iting ;v mixture of siliniii tliuxide

siUiiie Huorine conipmuid (f.tf. Huof-apar or calcium fluoride)

■n excess of concentrated sulphuric acid. In place of silicon

ie lUiv silicat* can he taken, since tiie hydrogon fluoride which is

mct& ill the same way on all silicates.
This reaction i» of great imiiortance analytically, since it gives
' nMAOS of i>rinf;ing into solution, and thcrolty making accesaible
■ia^ the natural and artificial silicates, which otherwise show
' resastjuice to clietnical acttous. P'or this purpose the silicates are
with strong hj'drotluoric acid and evaporated at a gentle heat.
process a platinum di-sh must be use«l, as vessels of other
w attacked. The silicon fluoride passes off' in (proportion
ta formed, and the metals present are obtained s,n fluorides.
these would give bother in the further aimlysiji, the evaponition
with the addition of -sulphuric aciil, the Hnorides thereby
into sulphates,

EUoon fluoride is a gaa at the ordinary t-emperaturc, and posses,
the inflnence of pressure and cold, into a Itijuid which boils at
- 100 .

eoDtact with wat«r, silicon fluoride also undergoes change ; this,
rer. follow* a somewhat different com-se from that in the case of
halogen compounds. In.stead of simply yielding h^ydragen
iU)d silicic acid, an intermediate jir<H:liict, h/ilroftuosiii^ic
fonaed according to the equation .'5SiF, + 111,0 = 2H„StFu +

itrta» the silicic acid separates out, the hydrofluosilicic acid
lv« in water and impart.^ to it an acid reaction. AVhere it is
to obtjun the latter, it is expedient to add so much hvdro-
ic «cid to the liijiiid that the .silicic acid which separates out
Jy passes into solution again —

Si(OH), r &HJ = H,SiF« + 4H,0.
wf jicid is tlicreliy increased and the troubleaonie filtr:ition

Ice the silicic acid whicli is formeil would soon atop tip the

'tube, it is neceasarv either to use an itivertwl furniel, through

IIm g*» 18 allowed to pass into the water, or the delivery lube

ie to open under the surface of n layer of^ mercury placed at the

of the resiH!l of water (Fig. 107).

[r<lrof1uosilicic acid is known only in a<pieouH solution. On

432

PRINCIPLES OF INORGANIC CHEMISTRY' out

evapumting such a solution, thii add pHSses otf enttr^y ; and if tiit
evaporation is canit'd out in a vessel of glass or of j>on'elttui. u
etched spot is produced. This m due to Lhtr fact- that tht» hyditiflu'^
silicic acid deci>mpo8c« into silicon Hufnide and hydt'ofliioric aci
proportion as the solution loses wntt^r ; the former escaped h» a. gsiK. . ;
the hydrotiiioric acid exerts its usual etching atition. While, tJierofonr.
a solution of hydrofluosilicic acid does not itself wttaek gloss, it doffivi
if it is evttpoi'ated.

* On these chemical pi-OL-ef*ses rlepends iho etchmif ttf rfhtsi^ wliiii
serves not only for the oruamcnfeuion of ohjectfl j)f daily tisc» but \>
Btill more important in the manufnctnre of scientific apparatus, hi
glass surface is coated with wiis, resin, or other substance capaMi' "i

withstanding the action of hydrofluoric acid for some timi*, and
coating is then reinoTCfl where neceftsjary, tiie atuface of the glass, on
sequent treatment with hydrofluoric acid, is attacked at all those
which are uncovered, while the jmitected parts retain their [lolish.

* For example, in order to graduate a burette (p. 1 89), a suita
tube, on which tfie desired volume has l>een measured off, is
with melted wax and the necessary strokes mafle in this coating
means of the dividing engine. After marking the figures also, com
tnited hydrofltioric acirl is brushed into the marks and again w;
off after a few minutes. If the wax ia then removed, the marks
found as hollowed lines in the glass, because the hytlrofiuoHc
dissolves a part of the glass wherever it comes into contact with it

* The etching can be performed more cheaply, but not »o
veniently, by first preparing hydrofluoric acid from a mixture
flnoraimr and sulphuric acid. The object is then pleiced over lii«|
mixture and the etching eflected by means of the vapoiars of the acid]
which are evolved. This reqinrea a considerably longer time,
length of which depends on the tempp.]

433

• The titcbitig prfHluce'l by the vapours is dull, while that effected

ill IS doir. This is fine to the fact that in the first

•■eiiiis .silicon rtunnde esfapeis, aiiit the other cnnatituoiiLB

left h' hind, vvhtio in tho aecoiul caai! i!)«< gkss is oom-

'] into sniuhli^ aiibstiuicea at tho jjarls attackad. If to

.tqiicous »cifl Biibstatices nre iwlded which produce a precipitate

■'- kI»®s, especially the nlkiili salts of hydroflvionc acid, a dull

^•siu also he obtjiiiied with the solution of the aciil.

1 nifluLksihcic :icid is ji JilMisic acid which forms many difficultly

-alts. Thus the salts of the alkali iiit«utis, more especially, nm

insoluble in wtttcr, and barium silicjiHunridu is so to such a

that it is Uijed for the separation of barium in analysis. The

is stable in acid solution ; by excess of alkati it is, however, decotu-

irith fonnatjon of a silicate and a fluoride. To this is due the

liiir l>efaaviour in the titration of thia acid with alkali, t'.if. with

ii 'I. If this base is added to a solution of hydrofluoeilicic

J t il with litmus, a blue coloration, certainly, in produced

amount of the alkali has li«.'en added coiTesponding to the

of the acid. After a few minutes, however, thiK colour again

into red. And twice as ranch soda can be still added before the

itui resmains pwinanctitly bhie. Thia is due to the occurrence of

following reaction .—

HjSiF^ t 6NaOH => 6NaF ^ Si(OH)^ + 2H.,0 ;
SiF/ + 40H' = Si(OH), + 6r.

Sodimn flaoride and silicic acid are formed. Since the latter doea not
act on litmus, the blue coloration occius when 6NaF are formed.

On ibis behaviour of the siilts of byiliofluosilicie acid an anajytical
SMtliod for ihe tleU-rmitiation of the alkali metals can he based, since
ibeae forui difficultly solulilo silicofluoridcs, which experience the above
^leootupotsitinn.

416. Oarborundum. — Of the other compounds of silicon we shall
ill fn«!ntioti, on account of its technical importance, iilicnn- earbidt or
rhon Mlicide. This is a greenish or black-coloured mas.'* obtained by
llo'wing carbon to act on Silicon dioxide at the very high temperature
of the electric f umac© : SiO, ^ ;^C = SiC + 2C0. The compound is
tinguished by its very conaidei-able hardness, and is therefore used
the artjt as a grinding material. In chemicitl respects it is very
It, since it is scarcely combuatible, the silicon rlioxide which is
covering the surface with a coating which is impermeable for
oxygtn. It is slowly attacked when fused with caustic soda with
»ccr»- of »ir, sodium carbonaio and siJicjite being formed.

Techtjjcaliy, the Huhatanuo is c^dkd nirlwitndum. (Hlier niLYtures
prepared in a similar manner, but containing more oubon, are used
Mtir tile manufacture of crucibles and for fire-resisting stones.

tl7. General. — Armmg thu riyii metallic element*, boron occupiw
T-ather isolate*] position, since the wleinents most nearly relntiHl u> i
must be sought for amorvg the muttils, namely, among the eaitli meuk
On account of the properties of the frco clement ami uf those of lb
tompoiinds, it is, however, not experlieiit to give boron a place among
tlie metals. It may best \>e classed along with silicon, from whii
it (JifFerB, however, in its typical compoundB having a didcrent cnra
position.

Boron is a solid substance which is cajmble of existing in eevenl
difierent forms, one ani&i'pl>xm.-s and at least one eri/stailhie. Amorplicrai
boron is obtained by pHssirig the vapours of tlit' chlorine cuni^witiJ
over heated sodium, or, quite similarly to silicon, by if^jnitinij tli«
oxygen compound with raagne9inm. After the removal of tlic d-
luixtiu'es, it forma a black powder of the density 2'6, which in niaaj'
respects behaves similarly to chaixoal, but is more easily oxiilisnd;
this occurs more especially by means of strongly oxidising subition*
even at the room tempera inre.

By the fusion nf iioroii trioxiile {ride infra) wiili aluminium, crjiul-
lised boron is obtained, which, on account of its hardness, has !>eW*
called " iLdanuinline Ijontn." It is not obtained ipiitc pure in this war,
but contains aliuniniimi derived fmui its prepaiiuioti. Since thit
metid is the element most nearlj' related to boron, the prndiift is no'
to be looked ujwin a,s a comyrouiul, but as a mixtui-c (possiVily \rilb *
diamond -like form of aluminium isomorplious ^^itb bt^ron. mid n"
known by itself).

BoroTi containinji; carbon, and tibtained from the two elements <*
a very high temperature, is of a siniiUr character, and also posaes5<3
an adamantine hardness. This also ought most probably to be regarded
as a solid sohition, and not a-s a chemica! compotuid.

The tvvo forms prolmbly sUmd to one another in the relation tki*
amorphous boron is unstattlo witli resfject to the crysudline, sis whica
phosphorus is with respect to red. In this case, however, the v

I tnuttlormatioQ at temperatiirefi below a red -heat Is apparently
Bneaauralily Rniall.

The coiniiinitig weight of Ijoroii is E = 11.

418. Boric Acid. — Of the compoumk of boron, the nioet im-

OrUint are fMiron Iriandc, B^Oj, and the corresponding him'- ndd, which

» lortnefl from the trioxide by talking uji tlie elements of water. The

Muting comjiomid which, on sunilogy with orthopliosjihoric acid, may

« call^ vrthobork acid, is represented hy the formula 6(011)^.

Uthougb it is known in the froe state, salts of the acid are not

ttkown wiUi certiiinty. On the eonirary, all known salts are derived

" coridetised " acids.

Id nature, lioric acid occurs as ^ti^solinc in lustrous, generally some-

yellowi*h coloured scales, which have a soft luid smooth feeling

foloble in water. Uot water dissolves a large quantity, cold

ccMpBrntiTely little. The crude boric acid can, therefore, be

ly purified by reerystallisntion. The purification m still more

:nlly efftt-ted by convfrtiTig the bone acid into its sodium salt,

and <Jeciiin[>rjsing this, after recrystallisiition, in concentrated

on with an acid, f.tf. hydrochloric acid. The boric acid then

.llises out sis, white scales.

liiric acid is a very weak acid, whose salts, on riissolution in water,

Vt hvdtxjiytically dissociated. The aqueouB solution of the acid has

• Kart«1y acid reaction, and conducts electricity only .slightly better

thic flure water. Further, it cannot be titrated with caustic soda,

■DC? (hi* alkaline reaction is gradually prfxiuced without a definite

i WtMeen acid and base being observed.

l>eing heated, buric acid loses water and passes into boroti

■ ; 2H^Bt)j = B/\+ sup. The anhydride formed melts to a

, ...-- .;ke inaRs. which is viscous and eiiti be dmwn into long threads.

I lie fuifrd sultstance dissolves various oxides of metals, ami can,

I tlnrefwe, l»e used in .soldering ; for this purpose, however, the more

L n;wlil> (iisibie alkali siiits uf buric Mcid arti employed.

^L liiric acid luis fairly strong untiseptic action, and is therefore used.

^■iniMiiciii*' and for pickling meat.

W A very remarkable property of Iwric acid is that it is fairly readily
I ^tile with steam, while its atihydiide is highly resistant to heat.

I A* » mmp;irison with the other anhydrides, e.p. that of sulphurio
■'■'' hows, this behaviour is iinnsu.il, for in by far the greater

I of cases the anhvdiides are much more readily volatile than

II 'lie liVfirtilee.

11 •>» this volatility of Imric acid with steam dej>ends the method of
'*^'Umijig it. In the volcanic districts of Tuscany, vajMjurs containing
wirif aeij igK^it; from the earth. By first passing these vapours into
■T'MjitiJ evaporating this water at a lower temperatiu'e, crystallised
"Jiraciil K obtained. It has lK)en foiuid that boric acid
tivtly less volatile the more concern rated its solutions

■

IS compare-

PRINCIPLES OF INORGANIC CHEMISTRY

able also that its relative volatility diminishes with falling tempdntq
On this ileijeiids the fact that boric acid dnm not, volatilise coniplcU
oti evaporating its solubimis.

With the vHjiour of alcohol, borie acid is still more readily vi
In this case it is the formation of !i compnuiid, an eetor (p. 407), whi
ettecta the volatilisation. If tlie alcithol is set on fire, the flam?
coloured tjiren liy the volatile oster of Iwric aciil. This phenoroem
can lie used for th« detection of borie add ; if this is in the form of
salt, it is only necessjiry to rub it ujj with sulphuric acid and to jM
alcohol over the mixture, in order to obbiiii the reaction.

As iu the case of phosphoric and silicic acids, there exist alao
the case of 1>oi-ic a-cid various " condensed " aciiia, which itre dt-ri
from orthoboE'ic acid, B(OH)^, by the loss of the elcmeuts of watt
From oi'tholioriti aciil only the monobasic " mctjiboric acid" caul
directly formed in this way; much greater diversitj', liowevrr,
jiroduced when seivfit combmitig weights of boric acid t.ogether li
the elements of water, Of the many such forms poasibk^ wu shi
mention otdv one, the dihiisic MnJioric acul H.,B.O-, the forawtii
of which is represented by the e<[Uation 4B{0n)^ - rdl.O = HjB,!)
Tliis h the acid of the Ijest known of all sohible borates, vi/.. '"«
Na^B^O;.

The boric aeida, like the silicic acids, form soluble sah« with tfc
alkali metals, wherejis all othei* metals yield difficultly soluble utti
When heated, the borates fuse to glas-s-like masse.? ; in thia state the
dissolve the oxides of the heavy metals, which then often eshiM
characteristic coloiu's. These phenomena serve for the detection o
such metals in analysis. Borates are also added to glass and eaunw
in order to im|wrt to these parti cuhu* properties, e.g. fusibility, smal
expansion with heat, and loiv power of refniction of light.

419. Other Oompounds of Boron. — On heating amorphnu
boron, or a mixture of boron irioxide and charcoal, in a current a
chlorine, there ia obtjiined, as in the case of silicon, a readil}' polntill
chlorine compound which condenses in the strongly cooled receiver 0
a liquid. In the pnre state this is colourless, boils at 17', and funi*
strongly in moist air, since it undergoes decomposition w-ith water <
boric and hydrochloric acids : BClj + SH^O = HjBOg + 3HC1, Frc«
the vapour flensity, the molar weight of this compound is found to 1
117, so that three combining weights of chlorine arc containetl in i
This is the reason whj' the coralvining weight of boron was not i
chosen that its corajioimds cnuld be formulated in accordance wi<
those of silicon, which they resemble also in other respectij. Simile
rwisons are furniflhetl t>y the otlitr halogen compounds of boron, whic
will presently 1x3 menlioneii.

Boron trichloride can be regarded as the chloride of orthoborl
acid, the three hydr-oxyls of which are replaced by chlorine. It maj
therefore, be presumed that it is formed by the general method <

fill BORON 437

pqwration of the acid chlorides, by the action of phosphorus penta-
Uoride on the acid. This is, as a matter of fact, the case, the reaction
l(OH)j + 3PCI5 = BCI3 + 3POCI3 + 3IIC1 being possible.

With bromine, boron forms a tribnnnide, which is quite similar to
ke chloride.

Bvnm trifluoride is obtained as a colourless gas, which fumes strongly

■ the air and is quite similar to silicon fluoride, by warming boron
rioxide with fluor-spar and concentrated sulphuric acid. In water it
iiHolTes with great rise of temperature and separation of boric acid ;

■ the solution there remains hydrofluoboric acid, HBF^. This, it is
Ine, has a different composition from hydrofluosilicic acid, but Ijchaves
|Bite similarly ; for exainple, it also forms difficultly soluble salts vnih
tte alkali metals.

The reaction takes place according to the equation 4BF3 + 3H,0 =
JHBF, + B03H3.

Hydrofluolwric acid is al.«o obtained by adding boric acid or
Vmm tnoxide to aqueous hydrofluoric acid ; these are quickly dis-
•Dlred with considerable rise of temperature.

Of the other compounds of boron, /www nitride should be

■rationed. It is formed by the direct combination of boron with

■trogen, and is generally formed in the preparation of boron if air

te Dot excluded. ' It c&u also be obtained by igniting boron trioxido

\ vitk-charcoal in a current of nitrogen. When pure, it forms a white

fnrder which phosphoresces in the flame, and when heated to a

F ■odente temperature with water vajjour is decomposed to boric acid

( ad ammonia : BN + 3HjO = BO3H3 + NH3.

CHAPTER XIX

ARGON, HKLrUM, AND CONGENERS

420, Argon. — It has already been raeiitioned {p. 317) thni t
nitrogen uliUuiied from the air differs from the " nrtificinl," r.c. oliUtin^
from chemifal compounds, in having n aomnwhat grtuiter deiisit
This iit first puzzling plieitonK^noii was finally explained (Kayleigh ai
Ranisiiy, 18114) liy the fact that in atmospheric nitrogen another gl
ia contained which resembles nitrogen in its disincliuatioti to foB
chemical compounds, and indeed, in this respect, is considerablj i
superior.

By convertijig the nitrogen of the air into non-gaseous compound
Ihv other coustitiient, which has been called ariioti, can be obtaina
pure. For this purpose there may be employed, for example, t6
[)ropcrty of tdtrogen of combining with oxygen under the infiufnce a
the eleutric disciiargo {p. 327). The nitrogen peroxide thus fonncdl
absorbed by caustic soda, and by adding the necessary antouiit d
oxygen the reaction can be continued till all the uitrogen is used up
The excess of oxygen citi then be ejusily removed by means of heatw
copper or phosphorus (p. 317). The same end ia atUiined by the iw»
of eertiiin raetala, e.//. magneeium or lithium, which readily *b»orb
nitrogen at a red-heat, A mixture of lime, magueaiuni, and soM
so<linm has been found verj' suitable.

The residual gas is colourless, otlourless, and tasteless, and Iim, «1
accoixlance with its density, the molar weight 40. It is, therdort
considerably more dense than nitrogen and oxygen. In the air *
forms the O'OOO pact by volume and the 0-012 part by weigln, Art
the ratio of it to the other constituents of tho air is not subjecl to soi
appreciable variations.

Since the gas docs not form any compounds with other elcmen*
no combining weight, properly speaking, can be assigned to it. C
the basis of the Uw of Gay-Ijusssic (p. H2), it may, however,
assumed that if it did form any compouuds, these must be form
with other gases in simple ratios by volume, and that, therefore, I
iiorraal weight 40, or some fraction of it, must be equal to

AUGON, HELIUM, AND CONGENERS

(MBbitiing wetghL What this fiuction is, however, wmnot « fniim
inax««L

deetaton can be here tirrived at by meJinis of the relation which

n foiuid to exist in the taise of other gases Uetween the com-

I and the aipitcify for heal. By capacity for hent there is

the ratio of the heat communicated to a bo<ly to the rise

f>eniUire prodiicefi. This ratio is cvifleiitly iill the greater, the

tbe amount of substance subjocted to the experiment. If it is

to one mole (p. 159) of the substance, this special capacity

is called the nwleadar heul or intilar Ittutt of the particular

tncc.

the amount of hejit be measured in Joules (p. 131), antl the

of tcmpei-nture, as uanal, in centigrade degrees, the following

be molectilAr heats of a nuiuber of gases : —

liufifecti

0.J

Cailwdi dirtxidi' CO^

N'il.riiiis oxide "S.fi

«n

VVatwr vajKiitr HjO

sxiilx

PttosX'l'^rt'iis cliliiride PCI,

DlWIinxirli'

Chlorol'uriu CIICI,

«9

wu chloridt^

HCl

3C «mallest values of the molecular heats are, accordingly, 20,

found in the cjuse of those gas«s ivhich contain two combining

bta in the molar weight : it is thereby a matter of indifforence

ihcT the comViined elements are like or different.

►ij »k'tcrmi»Hii.i; the molecular heat of argon, however, the value

obtained — a value., therefore, which is much smallor than that

ill dif i,'!ise» gi\cn. This leads to the jiresuniption that argon is

more 8im|»le in conijwsition than these gases, i.e. that it^s molar

I combining weights coincide, and that the formula of gt»soous argon

f^rn by the simple symbol A, and not A^.

presumption can Iw tested by analogy. From tbe chemical
of ixz-nwiy, the same conclusion has been drawn ; mercury
must al»t) have the formula Hg and not Hg^, since the com-
og weight an<l the molar weight have Itoth been found e<[ual to
A* a matter (»f f:ict, ibe determination of the molecuLar heat
[mercury has yiekle<l the value 1 3.
There in therefore snHicient reason for assunnng the identity of
( lioUr and combining weights of argon, and for ascribing to this
Dt the combining weight 40, whereby the formula of gaseous
I ^le«lme« A.

F«ir the rest, argon behaves similarly to the other gases. At - 1 86°,
vr onliTiary prenaure, it becomes liquid. At - 188", it solidifies.
II 'leftric discharges are passed through rarefied argon, a spectrum
Imanerong lines is obfeutied. According to the pressure Jtnd the
«mca! ciinditions, three different s|>ectra are obtained, the light in
cui« itji|>carii)g blue, red, or white.

440 PRINCIPLES or IXORGANIC CHEMISTRY chap.

421. Helium, Neon, Erypton, and Xenon. — A coTiside»fi
time ago the name lielium was given to »n unknown clomLnii,
fmaence of which in the sun's attnosi)here had been concluded fr
the occurrence of a strong and constant line m the yellow-green of i
spectnjm which conJ«l not be referi-ed to any known terrestrial elerae
Iti his investiyjitions on the occurrence of argon in minerals, the
jjjne was foiuid Ity Iiiitnsjii% one of the discoverers of argon, in

laea which are evolved on the ignition of certain minerals, r.</. cleT^
and he c«ta>:>li«hed the fact that it wjis duu to a gas similar to
and it accordingly received the natne hdium.

Helium is fotifid in some rare minerals which contjiiii the clei
ttramutn, and is obUiined from these Ijy heating, Fi-titn any niti
which may l>e preijent, it can In* free*! in the same way
given in the case of argon : from the argon wliieli is somet
also present, ii must be stftfirated \>y diffusion thronirh a ivn
clay partition ' (p. 94).

Helium is a very Ught gas, the molar weight of which is oiilj
it ia^ therefoi-e, only twice as heavy n« hyilrogen. Its critical
peratnre lies atcordingly very low. Foi the rest it shares
Ijro|icrties of arj^on, and has, more especially, the small niol<
heat 12, so that its cond>inin!; weight must he put e<|tia] tn it*
weight. With this value, He = 4, hcliiuii is, next to hydrogen,
element with the araaUeat combining weight, so far as one can
of such a thing in the case of an element which does not form
known compounds.

Furthei', in tlie residue from the evapomtion of liiiuid utniosph
air, still a nnmlicr of other gases have been discovcicd, which
chamcierised by their spectra and their density. They all like
msBess the small valne of the molecular heat, and in all cases,
fore, the molar weight has been put equal to the cond>iiiing weij
Their names are nevn (Ne = 20), hifpUm (Kr-8I*8), and
{X = 12^!). Krypton boils at - 151-7*, xenon at -109*1 .
molting points arc - 109° and ^ HO re8]^)ectively. Both «if
arc present in the air in e.xceedingly minute amounts ; there Wing i
fuvrt of krypton in seven million, and one part of xonon in
million parts of air by weight.

' llip !W]tamti<ii] i« ntaci elTeutMl \>y fntXiaMtX <li<ti]l«tion. On cooling lb* gi
mMiiH '>f 1i<]i>iJ nir, llie nr^n eixulcniies ninl the heliiun reiuiiins as a fUt
ppriimia, iu tlir liquirl argoii. f>i« jvllowiiig tlie tctiiperktltr« to liM, tH» hvUiuB t
i^T^t. By rvpcMtiug the Uqusfnotion uil gasifiuitioii, tlie giiM« e&u )•<• MrpwniUiL— 1

CHAPTKR XX

met

POTASSrifM

General Remarka on the Chemistry of the Metals. —
U tlic muiilmr of the metallic elcHKMits is much greiitor ilmn
the ri<ii]-nietiils, the rh<.>mistiy of them ia much iiiinpler and com-
\y Ima diverse This, is due to tht; fact that by fi»r the largest
Ukd ihe luiist iiu[K>rl.int of llie eompouiids of the nieljils are
character. Xuw, we htivo seen generally, that the tn'OjwrtieB
■kltx ill lufucouia aoiuiloit aie cniiditjuticc) ct^sentially liy the
ol their imtfi. If, thcroforo, a metal, ^.j?, silver, ftinns only
of cation, tbt^ Iwhaviour of hII its salts ill aqucoua solutiun is
if that of thu {uirticular cation is knuwii ; :t knowledges :>i the
which have mostly Iwcii trr«tc(jst.'d piv^ij.
fkr, thtjrt. .is tin- heliavjour in afiiieous »ohit.i(iii i,s c«<rn'eriied,
try f'f the metals is essentially j;iveu with the knowledge
tjil ioaa. Ill aimlytical chemistry we are concerned almost
r with aqueous solutions, and to what we there learn it is
ty ><uffici<?nt to adil a gtati/meiit of tlio solubility relations of
'I ' >5olubIe sidts., in onier to obtain the foundation of

:i-y. Fur genei-al cheniistrj, however, it is nocessary
& know If.dgt.- <jf the compoiuids in the solid statt; as well us of
iue or iitdirt'erent compounds which also exist in the taiae of
whereby grt'ater diversity is produced.
e variety ia, however, found among the ions themselves.
m«tal« form not only elementary ions with ditlercnt piopt'itics,
dtffcrenoea between which arc connected with dititrent valency,
t they «« also cajjaLle of forming with other elements dmiptfj: ions
fUb iprcijil properties. New groups of substances are thflreby
and in this direction inorganic chemistry is developing a very
r«»t dii eraity, which at the present time is by no meant exhausted —
\ Buuiy Gtaca, indeed, its outlines are scarcely known.

In general, every anion will 1h? able ut form a salt with every
itjcm. By virtue of a general nile, most of the salts in dilute a(\ueoviK

441

442

PKINCIPLES OF INORGANIC CHEMLSTRY

eolution are extensively disgociated into their ions, so that tha ^
of tiKse soliifwns differ hit little /mm. tin- mtn of the pmj'trtirA of i
Where, therefore, epocific properties, which do not ooirospond
rule, !ire raei with in salt aolutione, it can be conchidetl wTth cc
that the dis,sociatioii of the suit present is »nnilL From tJ
parativcly gr(jat rai'ity of such exceptions, there follows, coeiY
the great generality of the rule just stated.

Ill the following dt^scripiinns of the dilTerent metals, ther
stress will be kid nn the statement of the ions which cau be
from them, ;i.nd the propirtie,s esscnti;il for iheir characterisawd
be mentioued. In general, the methods employed for the dc
and determination of the niet^ils will be thereby given. To ihia^
is added the chemistry of those solid cnmpoiiiidB of the metals
are in any way importiint enough to find mention in this cletiie
work.

42;i. Potassium. — While the knnwkdge of some of the pot
coinpoiuitla L'lin "be follower] back almost to the most reniot*
ments of culture, the characterisjUion of the potassium compou
'derivatives of a sprckd vkm>'vt was first eH'ccted towards the
the eighteenth century by Marggraf. On account of the prcf
of pobkssium earVionate from creJim of tartar', which is deposit
the bariels in the termcntation of irine, that compound received
Dame of reijvtahle alkali, in contradistinction to miuenil alkali,
carbonate or soda. Althoujrh iiotassium hjdroxide or mustic
could not be decomposed, it was long felt that it was no sii
substance ; 1ml the actual proof that a niftnllk elemeiii formed
baris of the potassium compounds was first given in 1807 by H.
who decomposed potassium hydroxide by an electric current doril
from a voltaic battery, which had just then been in vented.

After it hacj been obtained in this way, the melhftd of [)i-cpariii
by pui'cly cliemical means was soon discovered, a inetbiHl which
fur long the only one employed. ITie most ini[)oi't,*tiit of
reactions is tlie heating of potassium carbonate with charcoid ;
monoxide and metallic potassium are formed, the latter of wB
volatilises and is condensed under rock oil : K.,CO., + 2C — 2K + 3C
Quite recently the electrical method of preparing it has Uton
adopted, since the necessary electrical energy can now be chc
generated in any desired amount.

I'otassJura is a silver-white metal which melts at fi2 , unA wl
even at the room lomporature, is so soft that it can W kauuied
easily cut with a knife. At 720' it volatilises ; the vapour is
green in colour. The colour can be rcndei;pd visible by heating
motat in a ghtsa tu^M' which h filled with a gas or vajiiiur free
oxygen ; the phenomenon, however, is visible only for a tnoml
since the potii.ssium vapoui" quickly attjicks the glass, which ther
becomes covered with a black coating of liberated silicon.

POTASSIUM

44;

^fniiinea with very great readiness with oxygen, sc

' » iilmiwit all subst/mccs which contain that element

''«r<!, uivJer the jfiitit action of tlie water vapour, v

''"c-9 tafnislie<l, owing to the formation of a layer o:

■ * «U nictallic" lustre can be observed only immefliatelj

"'•irfaco has In'fn niutle. If it is enclosed in a tul»e whicl

*>'■ filk'i! with hydrogen, and then fused, the metallit

iUs he rendered visible and permanently preservo<l.

'J"* of this properly, potassium must bo kept in such a waj

n:w iiQ neeess Ut it. In large i|Uantities it ih (ireservert ii

'Q ', sinaltiT ijiiaiititiea are kept nnder rock oil, sine« thii

"Htain oxygen. It, however, alisorlw gaseous oxygen

iiim kcfit under rocrk oil anon becomes eovrred witi

' »t cnmt which, however, only abwly becomes thicker am

'' ineUl fairly well.

i8 Very remaikable that in ilrtf oxygen potiissium is not (is

■•■v slowly) oxidised, wherejis the smallest amount of watei

•- produces a rapid reaction. We have already (p. 401

" L'.xaniples of such catalytic acceleration of oxic^^tion procesaei

• '111' presence of waU'r. Such behaviour, however, in spite 0

■ iicrality, must not be regarded as universal, for instance*

«i processes have been proved (f-.y, the comluiiation of nitrii

vrith Mjrygen, p. 3-20) where the reaction takes pl«ce with un

jjiiiijir»he(l velocity, even between the very carefully dried mibstitnces

('iiticerning the. determination of the cimibintng %veighl of p<>ta.ssium

' ntial [tointa have already been given under chlorine (p. 225)

mt^ (o K - 39-15.

♦ 24. Potassion.^Potiissium can form only one kind of ion, vig
I li.' uiotiovalent fKilassion, K'. With metallii: pota.«sinm the formatioi
takt^A place with very great ease and energy. The chemical jiropertioi
Iff the rui'tid are essentially characterised by this fact, for it reacts 01
i»ther subiitances in such a way that it passes int»j potassion, i.e. i
fonns n s;ilt. Since, 'further, the piissage of a iwlit/ salt into a liissolrei
<Mii» is in general accompanieri by only a slight change of eiieriry, it i
.,; no casQUtia! importance for these reactions of pot^tssium whether 1
4|tSj«olved or a solid salt is produced.

IsoJated examples of such reactions have already l>een uuMitioS
tlio method of o!)taining silicon and boron fioni their hiilogen
|K>und.s may be rcfalled. Since in these reactions the hi*loxen
pounds of potfissium, »'.«. salts of the metal, are formed, thuy
iin<ler the rule just stated.

The amount of heat which is libei-ated in the formation uf pot
from the metal ib very great ; it ts found, in accordance ' '
jiririciple)* explained on p. 204, to be 25y /y.

If this quantity of heat is added to the lieat of ionnt
jinion, the sum gives the heat of formation of the salt in c

442

PRINCIPLES OF INORGA>

solution are extensively dissociated into
(/ these solutions dijfer hut littlf. from the
Where, therefore, si)ecific properties, wl
rule, are mot with in salt sohitions, it i
that the dissociation of the salt pro-
parativcly great rarity of such excep
the grojvt generality of the rule just si

In the following descriptions of
stress will ho laid on the statement
from them, uiid the properties esscn'
be mentioned. In general, the nn"
and determination of the metals will
is added the chemistry of those sol
are in any way importiint enough ■
work.

42.3. Potassium. — \Vliilethc'
compounds can 'be followed bacN
ments of culture, the characteris:i
'dci'ivatives nf n sprciol clfinent v
the eighteenth century by Marg.
of potfissium carbonate from ci
the barrels in the fermentation
name of reijHatdf alkali, in com
carbonate or soda. AlthoujL'li
could not l»e decomposed, it
subsumce : but the actual j)r-
basis of tho pota.<.siuni compm.
who di>.comi)oscd potassium '
from a voltaic battery, whicl.

After it had been obtiiin-
by i)urely (.liemical means «
for lonu the only one em
reactions is the heating of i
monoxide and metallic ]m
volatilises and is condense
Quite recently the electrii.
ailoj)ted, since the nccess
generated in any desired

rotas.sium is a silver- >■
even at the room tempei . .
easily cut with a knife.
green in colour. The •;.-:
metal in a glass tube v .
o.wgen ; the phenoraeiij, •

■ •t

!-!Sl'.S

.^L-iicr

-■»h1 the :
III in a n
:rue, been

! i>i:lit, tho It

I insider

■ .PI ;
iii<ti<'

'uht together,^ a

ill- liquid. Tliii

mis a certain poi

> lias paaaed into i

•imted."

II saturation is define

i-inijn when (kis solid t

■■■ Mils of a given rafaBtai

'N'ciitrationa of satoratioi

I lit- general rule holds, i

always the smallest, and t

uluble in proportion as t

..<i of which is tmalier than that
,! ,ih.<iftui'ated ; those with a greal
THith kin<ls of solution are stable al
limit, the supersaturated within

iwtaiices in all tbtM idiyalctl atatM, and cai
i... ~« -oUd. liqnld, and gMe<ni MlutioiM of sol

,, , ■ J'THthHt. Iiowerer, the liquid aolaUoni of ■olid subs

.since the potiissmm vaJf »'«^ ^j_ in thaflnit inrtwce, confine the dU
b«'come8 covered with ¥*

"<»TUM +45

'stances and on the

I'll is bri)ii<(lit into

- into solution iinril

■st-fiblislu.'d. In the

■ibstiinw si'iKiratos in

. tiuit ii solutidii whii'li

jMilynioipliic siilistiuuo,

t'onn of till- sjwue sub-

.1 Avlu'ii l)oih ? 'ibstanws

:u- of e<|iiilibrium ciinnot

iicil and the unstal>li' be

■.lien the ntiiStiililc form Iwis

I I stable form. This 14 tin-

«-liich every solvent exorci."- s

iiicreasfd {r.ij. by cooling dowrj

■ility incrcaMCS with the teiniwra-

late in which it does not deiwsit

:iit in which de]>oaition occurs even

The fonmer state is called tiwia-

■lUndary between the two states is

; liuir pronounced ftsaturcs are Citsily

iinother substance arc added to a
: ium changes, in general, only slightly,
.• saturated.

i|ipear to be great deviations from this

•iri'u mentioned (p. 2:52) that the solubility

' ry small, but that large amoiuits of ioditie

ontaining io<lidion. At the same place this

! that in the solutions pro<luced the ioditie

. ))Ut was combined with iodidion Ui form the

turn, is partially dissociatMl into ordinary

iodine, !»; and the latter is present in such

^ to the solubility in ptu'C water.

-iniilar phenomena, therefore, which have the

■ isH of tbe solubilitj', the conclusion may always

.•!u).>stance which has passed into solution has

_-i-, whereby its actual hits become smaller than it.s

• ion.

cases of increased solubility, iliiiiin(ili"ii.< of the

;.;ri been observed. These are found espt'cially in ilie

<'i quite definite conditions, ami we shall now {kiss to

'if these.

.iivionr of Salts. — Salts also behave, in the first instance.

4T2

PRINCIPLES OF I\OK<iA\lC CHEMISTRY cH

Potassium cyaiiiJe is (i white, very soluble salt, whose
aoliiUon has an alkaline reaction ttiifl smells strongly of h?l
cyaniJe. This is tJiio to the fact that hydroiyjvnic acid is ;iiit*)!ir
weak add, whoau aalta aio jKU-tially diissuciiittHl hytlrolyttcalljj
aqueous sohitton ; the cnrbotiie acid of the air nho has a decomj!
uction on the salt. PoUissinni cyimidc is a powerful ikjtsoii ; in i
of this it is largely empluyi'd in the arts. It is used in phoi'.^
to dissolve silver salts, also in electropltttiiig with metiil*, espt-ci
gilding and silvering, and finally, in very large amotnits, for fxt
tlie tinely divided gold from the auriferous beds, espedully in
Africa. Since all these npplicationa depend oti the foriuatl
definite eonipounda with the heAvy metals naniad, they
oxplained in detail only under these metals.

In analytiail and preparutivc chemistry, potassium cyanide is i
as ft powerful reducing agent, which allows of many metjUs
separated from their oxides ami sulphides at it« temperature of fu
It is converted in the process into potassium cyanate and foV
thiocyanate respectively.

As to polajssium ajumde, the essential points have aire
given (p. 422). It is a ivliite salt readily soluble in water, whic
beiny ai-idified evolves carhon dioxide, while an anuiutniuni sajt
formed in the solution. Thi.^ reaction, which depends on the tr
mation of cyanic aeid, has also been already explained at the'
cited.

Potii!i.wim Uim:ijnim,t4', or sulphoeyanide, KSCN, ia the salt
Used in the applicattotia of thiocyananion, SON'. It is a colo
salt which readily dissolves in water, at the same timo produc
very considerable fall of temperature. It is easily obudiicd b_v b*
potassium cyanide with .^tulphur.

450. Potassium Oxalate. — Oxalic acid forms with poUissiutui
only the two salts which, according to the dibasic nature of the
are to ho expected, but also another salt which can l»e regarded
compound of oxalic acid with acid p4)tu.ssium oxalate. Of the salts!
oxalic acid, those with potassium arc the best known, b«causa
occur in the juices of various plants, from which they were early;
pared, and ha\c led to the knowledge of o.Yalic acid.

Normal potassium oxidate, KjC^O^ + H^O, is a white salt soluble t
water, and ia used in photography.

Acid potassium oxalate, KHC.jO^ + AH^O, is called miU hJ
rbecaiise it was first obtained by ev«])or(>tiou and crystallisation
the juice of the wood-sorrel. It is iess soluble than the norniid
and is used for removing iron and ink stains, since it converts ir
salts into soluble (complex) compounds.

I'olafisium tfiifj-irtfilf is the name gisen to the salt KH(."jO,j
HaCjOj + iHjO, whti h is easily obtiiinetl by mixing one uf the provio
salts with the necessary excess (or rather more) of oxalic acid in wiir

POTASSIUM

44:

^tet) the k>fls oF thf tiaU-s arc regankn] us independent coti-

^B ciiiwiiJor the sirujilesl case, thiit uf it siitt cotisfstirig of two
Pbt iijiii», aiul let the rnticKtiLi'iilu.in <if tli6 twu iotrs )i$ it niicl /i,
thr wndiRsctcintcd part r ; then, according to the law of mass
hk SMi), th« equation
■ ,t.l,^k.r

PB for «iK)'y solution of thu salt.
tliis ei|iiAt.iun /: is the " et|iulibrium constant," which also

- 'he temperature.

ituruiftl soIuUon. also, tfie same equation must hold. Let

>|j<imJuig values ho culled *(,„ f>t„ <"„ ; the eqnation then

«„. !>„ = k. c,_

the right side of this or^ nation nn values which are constant at
jpcniluiv. In thf case where a salt is aimplv dissolved in
two ioiiftHTO producoiJ in the same concentration,' and, thero-
Jf.. = v'jI''.. li'i^ '» definite v:dne. This vuUie varies with the
Atid Uiercfort" the soUiIiilit^' of pnre satts is in complete
with the genera! law* developed abovt'.
rover, the two inns are present in different concentnition, as
3is 4>f different salts ai'e mixed, it ia necessary for eqiiili-
tlie pfvtiuct of the two concentrations iij>„ shall assume a
■taut «'a1uc. The greater the one cnjicentratitm, therefore,
IBtUit the fttlier fje in order tliat cijiiililirium be estaliliahed.
aj>a which eon-esponds to uqnilibrinni is, therefore, called
prodncL In the C4ia« of diHicukly solulile salts this is small;

»' soluble sidts it is large. If the /nofiuH 0/ Uu- arnamtnttiims
br inns present in a solution is greater than the sohlbility
t»f the c.jiTesjKHiding salt, the snliit.ion is snpersiiturated in
> f)'. thi-i '^dt, and so ninch of it ninst separate out that in the
11 the value of tho solubility product is reached.
:it of concentrations iti a solution is snudlur tlian llie
1^ prwfuct of the corresponding sail, the solttticm exert* a
(action on the solid sail.

simple principles, the whole theory of precipitation anri

saline precipitates is contained. As simple also as it

itions, and there wilt b<

di>

app,

iquent

ly in th« sequel of making use of the light which is thrown
ila.

ntntkiti ti to Iw iiii^iwiirtil 1icr<.', an m nil L'i|RHtii>iiN ureijiiillliriurii, Lii iiiolt'Ji
Ung to our sv^t^ns, it wmiMi l>ti mort^ cnrrvct to reckoct iiioLes \)€t cc.
)ntmrr«r, \eiy siimll tiutiiK'rx wuiild tie there)))' oliininol, it i<> iiit>r«
aftmy the ikrivvil unit uiolcJltn:.

450

PRINCIPLES OF INORGANIC CHEMISTRY

qiutc emiill iju.intity ni this mixture is lulded to the h'iiuitl to be
for potiiHsioii and thv. whole well shjiken, all possibility of su
tifjii is done jnvay with, and a precipitate is iherofone stire to be fi
if the soluliility product ivas cxeeetled.

Another preciiiitant which is greatly used for |jotiis8ioii,
in qitfiTititativo determinations, is }ajdrof:M</rop!i(iimc ami,
but erroneously called platinic chloride. It is a compouod
compf>!iition Il^PtClr,, and is, therefore, so far us tUe fomitiJn ti
ccrncd, similar to hydroHnosilicic acid, H.,l^iF,j ((>, 4."U). A fui
aimihirity exists in the fact that l)oth j'ield ditficultly sohible s&ll*
potiti^sioii ; whereas, however^ liydroflnosiliciL' acid also vieldB a a\
aalt with sodion, and cannot, therefore, ho used for the scpanttioo
the two elements ; sodium platinochlonde, in contrast wilh po
platinochloride, is very readily goluhlo in water and alcohoL

If, therefore, hydrochloroplatinic acid is added to a solutiai
tainin^ potassion, the aohiliility proiluct ia exceeded even when
concentration of the former is very smiill, and the salt K
generally called potassium platinochloride, separates out ;i3 a
precipitate, which microscopic examination shows to consist of
transpfu'ent oetahedra. The reaction cnn be rendered much
sensitive by the addition of alcohol, since tho salt is much on
diffieidtly solulile in alcohol than in water.

Since hydwithloroplatjiiic acid is a strong!}' dissociated acid of
PHtno order Jis hydrochloric acid, the presence or ah«€nce of hydrifl
is of no account, although it haa an inttucnce in the ease of tju-un
acid.

■129. Potassium Hydroxide. — When iwtassinm is hnm^hi iu'
contact with wsder, violent actiun takes place ; hydrogen ia cvftlw
and usually takes tiro in consequence of the high tcnipontture prodncw
and tho potassium is lonvertM into potassium hydroxide ■JH.jU^:'
= iiKOH + H,.

Tiie fiitnie of the burning hydrogen haa a redilish-violct colour'
this is due to potassium, which imjutrts this colour i.u flanios in whie
It is prt?seiit The iiotnasium hydroxide which is fomied dtM>8 not,
a rule, dissolve inunediiilely in water, but forms a fustNl inwindesctl
IwiU which, on Hcc<nuit of its higli temperature, is not wetleti by ih
water; when all the potassium has l»ecn used up and the flame i«
tinj^uishcd, the hall still Hnats some time on the watci" until ita tcraper
ture has so far stink that wetting occura. It then dissolves with
great an evolution of heat that an explosive fommlioti of steani occtu
and small particles of the hot msiss are projected in all direcdoi
Since potasaiuni hydroxide has a strongly corrofiive action, tbc
particles can do coasiderahlo damage, and care must he Utketi hy
timely covering of tlie vessel th;U they do not hoconio scattered

The action >>f potassium on water is mtieh more moderate wll
the metal is dissolved in merciu-y. This solution is adled jio

-ii hiring the gtrien»l name for those raetallic altoji
t ; ■ iL-ury. In th« lalioratory it is prepnirerl by tiissolving

•Hie poUkssium in mercury ; considcriihte amounts of heat are set
in the process.

Om the Inrge sciile, polasaiiim hydroxide h prepared by the Action

{KtCasBtiitn ;inudgum on ivnt(>r, the nec<^&srvry ^ttiiHlgum bettig pre^xired

•a elrciru<tl tiictJuvl. If a sohition of potassiutii clilorirle is

Bftrolyseil, chloritliiin goes to the aiiotl*? anil potassion to the cathode.

taiter is foruie<l uf mercury, the potaasium, after losing its

charge, diseolvca in it and forroa potassium aitmlgam (p. 199).

in nnother part of the apparatus on water, and is converted

iunr hydroxide with evolution of hydrogen, in accordanco

he ei|iuitioii ffiveri alKive; the mercury, free from potttssiiim,

passes tiack to the cjithodic spacu.

•ultitirm of jMjtassium bydroxicle can also be obtained electitj-
ily by lising an aiioile uf some other metal, »■.(?, iron. In this
ni> potaaaiun) at all separates out, but only hydrogen is evolved,
tbe aimult-anoous formation of pottis!<ium hydroxide. It haa
y twen remarked (p. 11)8) that in thi.'S proees.s wo may look upon
itim as l>eing first formed, ami then n-acting secotidtirjly with
to give pota-sstuin hydroxide and hydrogcfi. Another, and per-
n»nre eorrect view, is to regard the hydrogen as primary by
i«g that the hydrion, which is present in small amount in the
Inter, \* discharged and forma hydrogen. The corresponding amount
ilrtixich'oii remains in solution, and fomis potassium hydroxide
the potiission. In proporiion as hydrion is thereby used up,
itity is formed from the water. Both ways of viewing
practically to the same result, and the consi*lcration3
caiuio tlie one or the other view to lie regarded as the better
be put foi^ward here, since at this point nothing of an essential
r depend* on them.
The methoil just given appears simpler than the previously
ibed nierctnv methotj. To it, however, there attaches the very
dtffictilty that the cathodic spfice, in which the c^u^tic potash is
hnoa), must be very carefully separated from the anodic space, id
•liith the chlorine is evolved, since, otherwise, the two substances
vwltl act on one another. At the same time it is required that the
ll«tric current shall pii.ss through unimpeded. The pirous si-pta of
pndnncnt jiajier, arjimal blackler, or clay which are usiudly employed,
ki not rcsi»i the simultjineous action of cldorine and caustic potash,
»i>d tlip tise of the method is dependent on the satisfactory aolulion of
tlic '"iliAphrsigin tjuestion."

Fimhcr, [lotassiiira hydroxide is obtained by a chemical method
% tlccctmpotting {wtasaium carbonate in dilute solution with calcium
liTdnjxidc, Since talciiim is a divalent metsil, the latter compound
'^ ' ' Ilia Ca(OH).,, and the reaction takes place in accordance

454

PRINCIPLES OF INORGANIC CHEMISTRY

aqueous solution it is very extensively disswiatecl into its iona,
tlie proportitB of hydroxidioii at*{j, tberefore, very stronjLiIy iJevelop
Even in very dilute soiutioM it colours litmus blue and phetiotphthali
red. Somewhat stixmger solutions have u soupy feeling. liecAUse
dissolve the skin of the fingei-s am! coiivfit it into « slimy
they exhibit a similar solvent action oa fats, htirn, hair, an<l
aninuLl substances, Acids of all kinds are nMitmlised, i.r. ctmver
into potassium salLs, and neutral ssdts cfHitaining other iiiL'tals
mostly decomposed in such a way tlitit potassium sjilLs are formed
the metals are deposited as hydroxides.

Since the last reaction is largely made use of in aiiulysls and
technitat piupoaes, a short discussion <»f it will bo given. If ii aoK

00 /f»t Witur

of caustic {Wt-asli is added to the solution of a scdt the metal ui ubici
forms u diflicidtly soluble hy<lroxide, this hyilrnxide will be precipe
tated, because so much hydroxidion is intrwlucod into the solution bj
lueaus of the potash that the solubility pro<Uict of the hydr'txidc in
qnestioii is greatly exceeded. Since, now, the hydroxides of almc
all the metals except the alkali metals are less wtluble than potn*sii:
hydroxide, their kvUs arc all decomposed in the above manner l»y
potash solution.

* Thus, solutions of sjitic salts give a white precipitate t.f xtud
hydroxide with caustic potash ; solutions of fiickol si\\i»-, a green ;
copper salts ii blue |irecipitntc of hydroxide. Aramoninni .salts on I>eu;
heated after the addition of caustic ixitash, evolve ammonia ijas, whic
can be dcteet-ed by its smell and by the fumes which il given
hydrochloric aciil (p. 342), iMJcause the anmiouium undergoes tranfl
fonnation with the hydroxy! to water and ammonia.

POTASSroM

All these reactions are due to hydioxidion uritl not to iKiUission,

: tbe Slime reactions are given M^licri tlie latter is repljiced by sitdion

|llie ion of anj other alkali motid. What has jns,l been said is,

(fore, not a descriptioti u( ajustic potiish In particiilftr, but of the

Iv dissiiciat^d hj-dTOKidos in general.
The special properties of potaasion have already l)cen given
4*3).

431. Potassium Chloride. — Tlie most widely distributed sidt of
ium, unci the out; which is most iuipoft*iiit techniejillV) is potiia-
ehloride, KCJ. It occurs naturally in rejjnlar crystals as ni/lmiie ;
iiiotitui, howovi'r, rti much hir^'cr quiintitios, niiited with m^gnesinm
as rarn"UUt'. The lattar mirnTid will bo descrilied under
lesitim, as will al80 the method of obtaining {Mtae&ittm chloride
it.

PutasBintn cliloride is a colourless salt which is rejidily soluble in
r, and which fuses only at a fairly high teniporature (730 ) to a
rlesa litpiid which, on eoiidifying, fonns the sanie regular crystals
obtained from the aquDmis solution. The soluliility of potassium
Ic ill water increaaes almost propnitionalty with the tenipera-
0 , lOti fiarta of water dissolve 28 parta of the salt ; at 100°,
»p. 21»).
le ffolutiutis exhibit the reactions of the ions of the ."salt.
Beitiq the cheiipeat potassium sjilt, potoissiutn chloride is used
|M-epi»rtng inimerous other potassium salts and as a fertUiseF.
is an (38fienlial cnnstilnent of plants ; the quantity of this
li ro^uired by the different plants is, however, different. More
Jy ill the case of the sugar beet is a large aniutint of putJis.'iinin
Now, the normal soil eotitaina rather conBiderabletpuuilities
sium, fhierty. it is true, in the form of compound silicates. On
int of the slight tendency to decomjwse, these silicates are, how-
availabte io such small amount that where there is a lojjg con-
occupation of the soil liy plants which take up large quantities
jtaanani, a conipens:itiou liy soluble potassium siilts is necessary.
pOfpofle is servcl by the manures containing p^:)tJlsai^m.
l^ose are obluined ivom. natnrrdty occurring tiiitiend beds which
widely tbroagh North and Middle Ctermany ; they have been
rltvd with most sucwsa at .Stna-sfni-t. There, arc found, lying on
eaornimiA Uyer of common sjdt {ao4lium chloride), extensive l»eds
[potash minerals (abrauin salts), from the nature of which it is prob-
that we ftte here <lealing with the residues of the evaporation of

432. Potassium Bromide, KBr, is a white salt which crystallises
rr^hu* fiimis, is reatlily solulde in water, and is generally employed
all pur]>08«« for M'hith bromidion is used. Large amounts of it
*ne ua<«l in photography for the prefwratiijri of silver bromide j it ie
sod in tQcdicine.

4T8

PRINCIPLES UF INOKCUNIC CHExMISTKV

MetfkUJc stidium is largely nsed in the arts ami in tlic ]at»or
Its former iiiifioitsiiice for ol)tainin<; other iJifficultly rLniticittlf
has heon lost, since tfie ohject can jijenerally lie attained more
by moiuia of magnesium or ahiiainium, or l>y the electro] vtic metl
It is used, however, as a jiowerful reducing ngetit in many reactid
organic chemistry, and for obtaining icactiie inLermediate prrxJc

For these purposes, the met*] is beat employed in a, conditiim
which it offers a large surface. Since, on acoount nf the softness nf 1
metal, it caiomt 1m3 rednced to small fiieeos by blows or by tiling, ill
M forced, liy nicjiris of an iron i

-^-^ ~y^ press (Fig. 110), ihroujih na

openings, and is thus obtoiiitJ
the form of wire or of riblwin, i
cording to the shape of the i
ing, Since in this sUite the me
very rapidly oxidises b the
the wire is allowed to fal) dir
into the liijiiid on which it ill
neb, or it is collected in a Uqu

which does not contain Qxy|

Petroleum, whieh is usually
ployed for this purpose, has
disadvantage that it is difficult 1
renuive ; for chemical pm-ji
therefore, it is better to use readily voiatilo hydrocarbon,s obtain
from the low -boiling portions of petroletitu (so-called petrol*
benzine or petrnJeum ether).

454. Sodion. — The description of the geuend charnct eristics wi
was given for potasaion can be applied almost word for word to noflio
This also is a monovalent ion, which is cotonrtess, and forms, alniu
exclusively, readily soluble salts, lu this respect it is even fcuperiori
potaBsiiiin, since thei-e ia .<icarcely a difficultly soluble salt of swliu
litiown by means of which this ion cotild bo readily anti oer
detected. Further, there is no compound of sodium known ttJiich I
formed in a<iueous solution, by the colour of which it is possible
detect sodion. This is due to the fact that in all atpieoiis soluliy
which contain sodinni, that element is preaent in thr form of sodiiK
or, in other words, nt» sodium compound can be disaolveii in wat«
without being converted for the must part into sodion.

The ddedion of sodium in anahjsis would, therefore, be a matter <
ditiiculty if it were not that there is anotJier property by means >
which it is rendered very easy. This is the yellow culoralion whid
is in(|iartcd to a Hanie liirougii the presence of sodium (p. %'^).
what foiin or com[)ound of sodium this yellow light has to Iw ascrilx
has not yet been determined with certainty, although it is very ]>roii«l>li
dill' to the incandeacegt vapour of elementary sodium ; for the purjMMS

V\u. 110,

POTASSIUM

457

t* oimI HF^' along with the ions 2F' and H', as the JisBocialion

tls of the Urn HF.,'.

. Potassium Chlorate, KCIO^, Jb a salt which cn'stfiUisfls in

>us monoclinic iHiuiruf. the aoluhility of which jti water is

tat low temperature^ but very coiiaiderahle at high. If the

Htr is rrprrsentefl as ordinatcs aii*l the temperature ^ts ahscissae

rs, \t. 218), n ciin'e is obUirried wfiich is convex on the under

the iucreaso of the soUihility is not ])roportioniil to the

ittire, but is more rupid.

foroialioH of f>otAS6iiim chloiute l»y piasing fhlorine iiitfl a

of caustic potash, does not differ from that of sfxlium chlorate

I. Since in this process only a sixth of tho potiissium is con-

into cblfir»t«, the potash is replacdl liy the cheaper cnlcium

ilc, which, in a perfectly similar manner, yields calcium chloride

loa cUoratu. To the solution is added potjissium chloride in

corresponding to the quantity of calcium chlorate ; on cooling

liquid, the product of the concentrations of jTOtassion and

ion is conaidorahly greater than the solubility prorluct of

chlorate, and this salt, therefore, ia deposited.

chlorine required for the reaction is now no longer pre[>ared

iiical nietho<], as formerly, hut elfcirtt/i/lmiUi/. As was shown

hydrogen and cuistic potash are formed at the cathode

ioe lit the anode, when a solution of potassium chloride is

«d. \rhile it is of essential importance to keep these two

M{iarat« where it is a question of ohtaiuing the caustic

they must be allowed to act on one another wlien the object

iBCOflAre potASsium chlorate, and, in contrast with the former

I* It oepecially advantageous to efi'cct the mixing of the two

ma quickly and !is completely as poasihle. In places, such

rland and Norway, where electrical energy can be obtitjncd

by means of water power, the whole amount of chlorates

i» HOW prepared in such a manner,

in thi» reaction all the potassium chloride can be finally

into chlorate and only hydrogen is formed as liy-pr(«lnct,

ical proces.*! can be siunmarised in the cfjiiation KCl + 3H.,0 =

* 3H.„ Such a process does not tJiko place spontaneously, since

tanccs on the right side of tho equation contain much more

<more both of total energj* and of free energy) than those on

fl, from which they are formed. To make such a jirocess possible,

B, free energy must he communicated, and this is done in the

le clertrtc current,

be action of tlte latter consists in converting the ions which

rfiflont into neutral substances (or, rice rer^i, neutral subatancea

g) at the electrodes. Sinct! clwinges of energy always accompany

ittformatiou, two ditleient cases may arise. In the first place,

of the transformations may ho accompanied by an cliniinaiton

480

PKINCIPLES OF INORGANIC CUKMISTRV

Of exiit'tly the Siime iiatuie is a. dark line in ilio yollovr of
solar speetnim, which is ohtoined l>y regttrtting sunUgtit which
passed through Ji narfovr slit, Uy mefttis of a jjrism. Wiierejts,
tliose contlitiona, the light given by incandcRiieut fiolid {or li(|U]*l)
_vield.s a ajiiiinnmis speftrum, i.e. a coloured band in vvliieh ihe
of the slit, (.'onsistiiig of colours of all freiiuencies, follow teit'h
witliout break fiom red to orange, yellow, gi'een, l>lue, and violtst,
light from th« sun is discontiimoiis. In this cjise, certain colon
light of certain frequeticits^ are missing from the coloured
that at these points dark iinagea of the alit appear, which foiin
tines across the spectrum parallel with the alit.

Similar dark lini-s can be produced artiticislly by ailnving
continitims Hglit of an incandescent body tn traverse a liol giis which
itself gives bright linea. These dark lines also appear at exactly
aime }K)ints as the bnght lines. Thus, a dark line in the yellow
obtained by bringing thv flame of a spiritrlomp, on the wick of whl
some sodium salt has been strewn, before the incandescent fibre of
electric lamp, and regarding this through the sodium Hame liy mi
of a prisra.

Tiie cause nf the production of these dark Hues is found in the 1»(
(establislicd by Kirchhoff in I860) that suhstances which emit defi
ray a especially strongly, also absorb these sume rays with w]
conipletenesB, the radiant energy being converted into heat or cbi
work. Or, to state it ditt'erently, emission and absorption dejiend
the aame way on the oscillation frequency or the wave length.

In tiie t'xpcriniont described above, the production of dark H
due to the fact that of the continuous strong light of tlie incandfj
carbon filament certain yellow rays are absorbed by the yellow jdcol
fianio and transformed into heat. At this point of the -r '•
thei'efore, only so much light is obtained as is emitted by tli
flame; and if tliis amount is less than the corresponding purtion ut
light from the carbon filament, the part appeara t/nd- in coiuftar
with tlie .surrounding portions. To eiistirc the succesri of tlie expert
riient, therefore, the continuous spectrum must be very bright, but
ai>sorbing gas ma«s only slightly luminous.

From these considerations, it 'w concluded that the sun consisu of
a highly luminous, and therefore \'ery hot core, which yields a eon
tinuoua apectnim. It is, therefore, prolmbly liquid or aolid. Tlii«
core is surrmnulcd by a gaseous mantle at a lower temperatiut* aiw
possessing feebler Inminosily ; in which the vapours of those gul«tann:<
are present the bright lines of which correspond to the dark line* d
the solar spectrum. In this way the presence of more than half Ui(
elements found on the earth has I>een recognised in the atmoqtbcr*
of the siui. The chief elements present are hydrogen, sodium, calcium
magnesium, inm,

* 456. Indirect Analysia. — If it is known that oidy thf i*

POTASSIUM

459

rule vvliich ia almost exclusively used for this

fact ibut it is, of all the chioniles, the one which

known iiinl ia the easiest ti* jirepire pure. In many

its slight flohibility at medium tt^mpenitures is a flis-

it is then n-placetl by the much more readily soluble

«»rnU? (whith see).

ailiitioti of oxygen from fuse^l jwtassiiim chlorate ia grtaitly

.bij" the [ireucace of foi-eigti substances which do not take

ixMuniou. lu this respect, ferric osidtj is ilie most

if finely ptuvderetl potassium tihluiute ia mixed with a fuurth

ht of ferric oxidt' and tlie mixture heated at one point, it

can(lcsc«M^t, and dccomjwsca with (dmost explosive violence.

ttiniigh feebler action is oxcrterl by manj^anese dioxide,

is therefurt" chieHy usefl to faciliUito the decomposiLion of

(p. «3).

n ia |Mirt|y t\n6 to the fact that the fine powder of the

od faciliUitea the evolution of gas owing to the presence

AS happonij in the ca^e of su]}crsutunited gius solutions.

Icoom pod lion of potaasium chloi-dt* into poUtwium chloride

not a process of disiiociution which leads to a measunible

lil>rium, but a process which takes pliioe only in one

'•tich as, «'.(/.. the combustion of charcoal h\ oxygen. The
, prmctically cannut be rev craed ; no racasur.^ble amount of
chlorate is fornieii by heating potiisaiuni chlondu in o.xygen.
uui chlorate has, therefore, to be regiuded us an luisuble
wbose existence depends on the fact that the decomposition
dergocs takes place ao slowly as lo be iuapjireciable by the
means of detection. Even at the temperature of fusion, the
f divcODiposition ia not (.-onsidei<ihte when the substance is
is mtalytieaily accelenitefi by the substjinces mentioned
Ia follows from the fact that powdera of approximately the
of finonostt and enclosing the same amount of air exert,
tcm|»eraturo, a verj' difierent action on the fused chlorate ;
only a modornte, the other a violent deconi position.
is all the more dangerous the larger the amount of salt
at one time. From the thennochemical measni-ements it
that in the decomjtosition of potassium chlorate into potassium
ide luiil oxygen, 34 kj are evolved. From this it follows thftt
th tuidiergoing decomposition must rise in ten]])erature : the
mcmtitm is, however, thereby accelemted. If, by using com-

r large «}uantitic.'(, the dissijMittoti of tho heat is made small,
ntnrr rises so high thai compicto decomposition occurs in a
These are, however, the phenomena of explosion.
' ytic iK'tiori of the stibjitJiiices named can be demonstrated
refulty foeing pure potassium chlorate and waiting till the evolution
r=ually occurs, has cea.?ed. If into the quietly flowing

482

PRINCIPLES OF INORGANIC CrHEMISTKY

made in the deterininstion of S, the error in the calculation of
be gretitor. In the first example, it amounts Xn 4 j>er cent,
second to moru than 20 per cent, of wiiieh one cnu wisily coi
oneself by performing the ciilculfition. This is dut- to the fact
the magnitude sought, ii", is proportional not to the uii5asure<j valat,
but to tlie difference tt - k, m the formid;* sliows. If, for ^Xitniple, k
half as great as S, an error of one hundi't'dth in S will lie cjiuiJ to
error of two hundredths in iy - k, and, accoi'dingly, the tlctermi
of X will be erroneous to the extent of two httndredths of itg
In gcnei^l, the relative error in the residt is to that in S as
S~ iv and it becomes all the greater the smaller the difterenoes

• The practical rules for the ehoiee of Inilireet nietlnxls, wb:
be deduced from the ahtjve, will out be given here ; on the
tit may bo left to the student to think these out.

457. Sodium Hydroxide,— Tlie proiwities of this im
compound have already iu'en described ; along with caustie po'
it foniia the type of a strong hise.

Towarils water, caustic soda behaves in the same wny as e
Jtash ; it disscjlves with gi'eat evolution of heat to form a very
'centr:ite<l solution, from which a hydmie 2NaOH, "HjO ae
OTit in the cold. On evapomtion by boiling, the solution pasftes. m
^the case of eaustic potash, into the fused, anhydrous rijtti|>ouin!; i
aon of this behaviour, which diH'etT5 from that which is usual
the ease of solvitiiins i»f solid substanees, in the same as in I
case of caustic potash. In moist air caustic soda tidies up water i:
deliquesces, but it resolidifies again by absorption of carbonic M
much more quickly than deliquesced eaustic jmiiish, bocaiifle I
nonnal sodium carbonate is not deliquescent ami is deptisiied in t
solid state.

For the preparation of caiistic soda, the methods ^vcn on ji. i.
can be T'cpeated almost word for word. It is now nbtainwl Ky fJi
trolysis from sodium chloiide or common salt, whereas, foniierlr,
was almost exclusively obtainetl by the decomposition of sodium o
bonate witli litne,

If it is a question of obtaining small quantities of sodium hjdroxi
for lalMiratory purposes, we may start wiih nn-tnHir soditiin and li
poae this with water. One of tiie sirajilest methods of prt-fmrinj; it i«
place rrujUillie siHlium (be-st in the form of wire or of ribJxm) in atii
of platinum or of silver standing in a desiccator eontiiining wal
The stKlinm decomposes the water vapour and is convertetl into caiisl
soda, while the hydrogen escapes. The desiccfitor must, therefore,
furnished with a tube which allows tlie hydrogen to [ias« out with(
allowing the atnios[ihe]'ic carbonic acid to enter. For thi.s purpfl
a tube filled with stala lime, i,'. a mixture of caustic sodii and liii
is used.

It can also be prepared by poiuing water over sodium amalL'

piiiiiii of

isalktn. Ttis is another example of the fact tlistt

yield acid siilte like <3ibasit* iioiils.

^siiim iiMkite is u siibstiiiii'O which e^n he used in miiny

ric analysis, since it crystallises anhydrous and cun be

On the one hand, by dissolving weighed quantities of

m definite 'KuI titre are obtained ; it CJin, therefore, be

■ the stju^in^ substance for the iletermitiation of acids and bases.

: hand, with exwss of potassium iodide and acid, it gives

I frc« iodine wliicb can be calciiluted from the oquation

- I OKI .- I IHl'l - 1 IKCI -r CH.O + 6L„ so that it cati also be

> liie basil* ft»r iodomelry (p. 300). However, it is not ijnitc cjiay

a. aait nf constant composition, for besides the salt just

there is a salt KHJI3O.J, whieh separates out from more

acid solutions.

Potassium Carbonate, K,,CO.,, was, before the discovery of

jH.:.L-.li bt?'l?, the ?»tlt of potassiiuu which was available in

abuiici.'tiH.-o. ;niil was therefore the most important. It is

tmJ.iAh because it wa-i obtained from the ash of wood and other

!itfi. Ill jiknts the |)Otassium salts of organic acids occur ;

I int- |ilMnt8 are burned, the Piirl>on of the acids passes into carbon

Hb and the potaaaiiim remaitts in the ash in the form of the

Ukte.

lib iibuiin it from this, the ash is extracted with water ; the soluble
||0f which the chief is pjtassitini carltonate, are dissolved, ami the
ytin conslituentc* remain behind. To obtain the salt itself, the
•OB must be eva{>orat'Cd. The expenditure necessary foi' this is
greater the greater the quantity of water, relative to the amount
rhich has to be reiiiove<i ; it is, therefore, of iinportJincf that
•hotdd be prepared which h eis concentrated as possibto. On
hand, it is just as importjint to extract the ealt as completely
from the ash, for which purjHJse repieated extraction with
I inter is oucessary.

fuliitiueut of these two apparently opposed demands becomes
lUe by means of the principle of munter cunmls, alrejiily mentioned.
ther« b« pveii a series of vessels with ashes, A, B, C, . . . If,
I A bi extracted with a certain quatitity of water, the solution, on
tea hand, is by no means saturatcil with potassium carl^onate, and,
hit ochcr b»ini, a large amouiit of the salt remains behind with the
h^ aace all the solution cannot be removed. For the extraction
|t there is u&ed, not pure water but the solution from A, and A is
ibeted vriiii a fresh portion of pure %vatet'. By this means a much
m eanuuitrated solution is obtiined from B and a much amaller
lu retoains in A. The solution from £ goes to C and dissolves
% talt ; the solution from A is used for the extraction of the
Ihaa in B, and by a tliird <|uantity of pure water the Bait still
in A can be almost completely removed. '

4I"-.

in .'III-
priM-. -
nrifliii'
has. 1.
liilii\ .

IK) ;. ■•
\

f I >]■(•!
il^ -

aii\
sal:
soil
uli

•• .■■•,|.,|
. ';' \n;
-••■I. i.'il

. r ■.■iiiiilii

rirassion.

POTASSIUM

463

leoua solution of potasaium earlrotiate has a fairlj' strong
in, slihI exhibits also the other chitractoristics of hydroxidion.
lo the fact that the ion CO.,", which is the immediate pro-
' ititin of the salt, reacts with the wjtter of the solution in
with the equaiion CO/ + H/J = HCO3' + OH'. Keactiona
tia\'o bocn discussed tit length iii connection \iith phoa-
(p. 3C7).

tsk c*rbormtc is n convenient st^irtiiig snlistance for the pre-

other polassium salts. Un the one hand, most free acids

jrrespoiuiing salts with (lOtaBsiiiin carbonate, ivith evolution

ioxide. Carbonic iicid is, :is hus alreath' been shown (p, 393),

'wes&k acid, and this reactiou therefore takeii place with great

jd completeness. On the other hand, carbonic acid forms

tlUy soluble salts with almost all inetfils except those of the

If. therefore* salts of thosu metals with any acids are

sth«r with pot;i.spiuni carbonate, the solubility product of

tciing metallic carbonate is <jxceeded, and the latter is

wliilo the ijotassiiini sail of the acid remains in solution,

it cau Ise obtained by evaporation after filtering off the

i»>. Fotassinm Bicarbonate. — In the aqueoua solutions of

i iiate, the iun CO,," is, as has already been mentioned,

... Ijy the action of the water into the ion HCO^' ; the

^KArsit^tdrtued, however, amounts to only a few per cent of the

P^Ktity. If, how*ever, carbon dioxide be passed into the solution,

lion t'O^" -f CO J - H»0 = 2HCO3' t^i,kes place almost completely,

tion of the acid or primar}' [wtassiiim carlwnate, KHCO,j, Jfj

yl( the aclution was concentrnted, the sohiltility product of this

and it is depusiteil in monoclinic crystals.

react* fsiirly neutral, but .still not so detinitely as that

t stroii^ at'td. ami dilute soliitioius e.xhibit even a distinctly

Twictiun. This ts due ti> the fact that the first ion of the

carbonic acid, although much stronger than the second, is,

C8S, the ion of a very weak acid. Hydrolysis therefore occurs,

from the solvent water uniting with HCO,,' to form nudissoci-

>tiic aci<l HmCOj, or its anhydride CO^. The presence of the

;d can lie easily denjonatrated l>y heatijig the solution ;

ihe boiling point hits been reached, hubbies of carbon

evolved. In proportion Jis carbon dioxide escapes, more

By reason, however, of the increasing concentration of

n, the equilibrium changes so as to become more and more

t! to carbon dioxi<le, and thi> evolution of the gas finally

ly to zero. The ratio nf the concentrations at which

epoiids on the degree of dilution, more carbon dioxide

«voIve<l the greater the dilution.

Jtbougb, therefore, acid potassium carbonate is partially decom-

486

PKINCIPLES OF INORGANIC CHEMISTKY

the secretion of sodmm is greatly promoted and a necessitv for
replaccmenl (.aiised. In the case of animal food, linwever, the
elcraonts are tsiketi iiji in the ]HOportions in-oper to tbc nan
orguniara.

In the case of the vertebrate iinimala, the sodiiun compyuiids
chicrtr ill the Wood plasma and in the fluids of tho trody.
pulassinin, as alreatly mentioned, colkt'ts in the 1i1o<mI forjui

From aqueons solutions of so<]ium chloride the \vell-kni«wii
crystals of the anhyrlrous aah sepnnile out at temperatures afni^e -j
Owing to the usually bad formation of these crystals, they en '
some mother liijuor, so that when heated they give off small amc
of water On heing heated, the enclosed water is converted ia
vapour, the prfssui'e of Avhich inereases as the temperature ris
it becomes so gre;it that the pieces of salt enclosing the liqi
shattered, ivhtroby n i-rackliiij^ noise is pioduced. Ha\'ing oiice tin
gone this treatment, the ssilt remains quiet on being again heated.

Frotn conccntraterl solutions of sodium chloride at lower tet
tiires, a hydrated salt of the formula JfaCI + 2H,.0 separales out ]
monoc-liriic crystals. Those are atjible ouly up to - 2 ' ; if be
above this temperature, they melt and form a liepiid fronj whirh
anhydrous salt immediately sepirates out in the form of small i.-u1k

*^ Even at the room temperature, these hydrated crystals
produced as an unstable form, when a sohition of conioion sjilt is S[
out in a thin layer on a glass plate and caused to evaporate rapidly |
blowing on it. Under these circumstances, the sepiimtioii of obliq
crystals can be observed with n low poAver of tlie microscopo ; inl
short time the ordinary cnbes of common salt appear here and ibe
and these aljsorb the for'nier crystals.

Common salt is used not oidy in food, but, being the most widfl
distributed sjdt of sodium, it is used sts the starting- [,k dm in
preparation of metallic sodium and of all other sodium componn
Some of its transformations have already been mentioned ; othei-s
be discussed presently.

400. Sodium Bromide and Sodium Iodide arc similar to sikIju

chloride, only more sohdtle than the latter. At lower tern)ionuur
Imth form hydrated crystals with iH.,0 of crystiillisation, isoniorpho
with those of the hydrated sixlium chloride. The temperatm-u, ho
ever, at which they melt and jmss into the anhydrous salt* and
saturated solution of theae, is higher. In the case of .sodium hron
the conversinn takes place at 50"', in the CAse of sodium ioiiide at ^71

On investigating the solubility of these salts in water, and
change with the temperature, the relations are fournl whicli jire rop
sented in Fig, HI, The cm*ve uiiirked NaBr+211,,0 refers to
hy<lratod swiiura bromide, that marked NaBr to the anhydrous i
Similarly for the two forms of sodium iodide. As can be siseti, i
of the two forma has its own solubility curve, which is indopiiiuleut <

SODIUM

4ST

TTif point where the r wo curves cut h the point where the
can coexist along with thu^ saturate*! solution. This is the
iperaturu at which the hydrated crystaJs commence to cnett,
» thiii it follow* that mich /arm of the mU has its mtm sohtbiliUj,
»t the two forms have the same solubility at the tonipuiaturc
iich tht.-y chaii|;e into one another. In this respect, therefore,
with different amoiuit.* of water of crystallisation behave like the
>t forms of allotropic siilretanccs (p. 262),
ihe (liiit^Diiii shows, the sohibility cnrves are both protliicod

A'**

KaBr

KCl

LVaei

the point of intersection. This .signifies that the transition

not jwrnxiniiiljt/ occur here any more than in the case of the

pition of sllolrojiic fortus;, l>ut that on Koth sides there niay he

ivmiiim. An exatuinatiou ot the diagram also teaches that

•table form hits ahvays a gi-catcr soluhility than the nioi'e

8f> that a isoliilion ajiturated io respect of the iinsiabh; form,

eing brought into contuci ^'ith " nuclei," i.e. already foraieil

«l the atal»le form, will deposit solid salt in this form ; the

on is, tlierefore, anpersatnrated with respect to this form.

for tatatnple, a «iturated solution of anhydrous sodium bromide

■fludeal 30 , and crystals of the hydrated salt are introduced into

488

PRINCIPLES OF INORGANIC CHEMISTRY .:ni

it, the latter will grow und the reaidiml solutiun \nll exhibit thcsn
eoncentration whioh bi-longs to this form. On the other hati<l, ft i
tiiin of the hyflnited salt, saturated at 50°, will he fniuiH to Wi
saturated with respect to the anhydrous salt, i.e, it will be able to ■
solve certain (luiwjtities of this salt. The presence of the hy<J
salt must, however, he Diost ciirofnlly avoided, for excessively
■inautittes of this are suHicient to cause the separation of tliat fa
If, however, the anhydrous suit is heated immediaiL«ly ]i(-for«r the(
perimeiit, all hydrated salt iis destroyed, and the aiiil can he dis
without fear.

The above discussion holdB universally. It shows tluit w$i
fpeak of the soluhilift/ of u stilt or, tfcneniUi/, of a utihtl fulmtunc
irhi'ii- wfi sltitg Ihf ftiriii u'hii^li in in e<ptUibrium wilh tJu stthtiion.'
general, every fonn hiis its own solubility, and the (joint at which
solubility of the two forma hecomes equal, is the tranailjon point of I
one form int^i the other.

Converaely, every etirve representing^ the change of solubility
the teraiienmire is, for each fonn, C0ntinuou.i, If u hrw/c in ihei
bility curve is observed, this is a certain pi'oof tfttif the solid
wliirh k m fi/tiUHirmm mih the soluiitm Iiitn jxt^ed i-itio atiotfier form i
(cmjHTiiture if the bmtk.

461. Sodium Bromate. — The pure compouud is of no sp
interest. Mixed with sodium bromifle, in which condition ihesaltl
obtained from bromine and caustic sotla (GNaOH + SBfj = XalM'j + l
5NaBr + SH/J), it constitutes a reagent which is used for lil>enitiu^|
a known quantity of bromine in solution. On aci'lifyiug the mixtarcf
the same amount of bromine is set free iis wiii5 used in the prepura-l
tion of the mixtui-e. The reaction can be exjjrcssed by the etpmtionl
HBrO^ T 5HBr=3H„0 T ;iBr^, or, writing the ions, BrO./ - 5Br'
6H' = SllgO ^ SBr^. The niixtuio is obtjiinej by adding broniiuf w|
caustic soda iintil the colour of the former is permanent, and tliiB |
evaporating the solution ; the excess of bromine is hereby driven off.

4G2. Sodium ChloTate. — In contradistinction to potjiswiiii I
chlorate, Kodium chloi'ate ia a salt which is very abundantly soluliif i"
water. A.t the present time, therefore, when the raethml of picpitrini;
it on a manufarturin;4 scale has beconiw known, this salt i.<i eni)tli})'«l
in many eases in which chluranion is used on account of lis oxidising I
action, and » here a more conccntratetl solution is desired than can t*j
attained with potnssium chlorate, It is obtained in a similar maiintr
to potassium chlorate. It forms finely crystallised cubes and nlbtf
forms of the I'cgidar syateni, and these have the property of rfitatiiij |
the plane of polarised light in a manner similar t« quartz. Wherctt |
however, tlie latter exhibits this phenomenon in u rcj^uliu- manner
otdy when the ligiit pisses through the crystal parallel to the fikiti
axis, sudiFim chlorate rotates the plane of polarised light by pqQU
•»»nonnts, no matter what the direction of the ray in the crystal * '

SODIUM

489

liicnt-e of tile ffict that these crystals Iwlong to the
while those of qtwrtK are ln?xagonaI.
Sodium Nitrate. — This salt, which crystalljafs anhydrous
rhoiiiboh«lm, melting iit 330^ is, at the present tky, the
xiportiint uf ihe eomEioiimb of iiitrii; uciil. It is found in large
in Chili. Since no min fsills in those districts, it has been
for this salt to l«e yHoservpd. How it has been formeil
5t, not be stated with ccrtiiinty or proljiihiltty ; the constant
in it of iodine compounds in the form of sodium iiKlate,
favour of its fonmition from the «ilts of sea-water. It is,
still a mystery what conditions existed to produce such a
]y oxidising effect that, along with the rdtiate, the iodine
kve pastteU into the itvdate. iind even a portion of the chlorine
;ljlor:tl« (which is also found in Chili saltpetre under certain
iDcce to the extent of several per cent), We may, [lerhaps,
I that at the litne of the formation of this salt some cause was
vrbicli mnisually large amounts of ozone were proiluced ; the
this would render the formation of these highly oxiiliswl
from any sotlium compounds present, intelligible.
crude Bodium nilmte is mixed with earth and clay, and is
hy a simple process of crystaUisation. The purifieation can
And successfully carried out by this method, since the moIu-
ihis salt changes very greatly with the temperature, as can
[from the following tables —

SotUBlUTY OF SODIIM NiiaATK

1(10 gm. wiit«T (ISsaoh'* —
*■ 68-8 gm. ofNttXO,

am nitrate is used in larj»e quantities for manuring purposes ;
the most important artiticiiil nitiflgeii uiHouro for cultivated
itul it« application is limiteil only by the juice. The nitrogen
easily avaiiiil'le for the plant in the form of nitranioti, and
therefore, the quickest action. Since, howe\er, the
ill this snltstanco, an it does jKitash^ phosphoric acid,
na, the mantiring with Chili sjdtpctre must be carried out
H«?ly liefore (he time ivhen the [ilant iei|uires the nitrogen.
tium nitriit*.' is further used in large i[Uiintities for the prepara.
I'liitric acid (p. 321) and for conversion into potassium nitrate
It ia idso used in the preparation of nitro-eompounds ; fur
B, the nitric acid is not first prepared from the salt, but a

490

PRINCIPLES OF INORGANIC CHEMIKTRY cm

mixture of sftdiiim nitmte Jiiul suliihuric acid, which on ilisfil
■H'ould give nitric acid, is directly eni|iloyed. I,iistly, a cunsid
portion of the salt i.s converted into smliuni Jiitrite, Hhich ie eiupkij
in uniirmous iiuaiitities in the preparation of artificial dyes>

Sodium nitrate cannot he used in jilace of potassium nitmw
the pi'c.paifitinn of giuipowder and blasting jKjwdcr, l>ecau««
powders made from it beciimc moist.

8iiie(3 tho Chili saltpetre defwaits are approaching exhaiistioii
some decades), the production of nitrates oi' of free nitric add
other wjurcus fs beginning to be a mutter of importance.

464. Sodium Nitrite, ^ — ^At the present day. Bodiuni nitrite
manufactured and nst<rl in largo quantities in place of pot^ariu
nitrite, from which it differs in the ease with which it can be
piired [Hire, It is a very soluble salt with a feebly alkalitio ren
when treated with acids, it evolves I'Cfl fumes of the oxides of
gen (p. Xi'2). It is obtiiinod, similarly tu potassium nitrite (p.
by huatiiiLr sodium nitrittc witii metjillic ioad.

465. Sodium Sulphate. — Tho normal sodium snlphat*, Nj
is well knoim in the fimn of hydratcd crystals of the comp
Na.,Sl)j, I0H^,O, by the name of (Jlniiber^a suit. It i-eceivtHl iti>
from tihiuber (liorii about the year 1640), a physician and ch«
who introduced it as a drug ; he ascribed to it gtisit hf.iling pof
and gave it the name "sal mirabile," Its action on the hn
organisra consists essentially in the fact, that when it gets into
intestines, it makes their contents more watei-y and thereby faciltt
the evacuation,

* This action arises fi'om the fact that the walls of the intfl
ofler considemble hintiram-e to' the diffusion of CJlauber's suit
enpt'ilisntion of rtmrenlmlwiis, the tctidericy towards which is rxerte
under ;dl eii'cumst.ances, cannot, in this case, be accttmplished
the dissolved substance mixing viith the Iwdy fluids, buU on
cotitraiy, water must pass from the latter into tlie int*stino.

* From this it follows thijt all other salts which have the
property of not passing through the intestinal walls, and which di» no)
exert any oilier actions on the (nganism, must also Itehfive in the WB
way. This is, indeed, the case ; miignesinni sulphate (Epsom salt
acts in exactly the same way as Glauber's St'dt,

The Bolubility relations of sodium sulphate are rather coinpliciil*
and arc represented in Fig. 112. Three different solubility uiirx
can bo distinguished, belonging to three different forms of tho
Of these form.si, one, stable at higher temperatures, is nnhydmrn;
mediutn temperatures, ordinary Glauber's salt with lOHjO of crysb
sation, is stable ; besides these, an unstaltlo sidt can ho obtaiW
lower temjjeratures containing 7HjO of erystidlisation.

On following the curves in Fig. 11 :J from right to left, wd h*"^!
in the first plate, the curve of the anhydrous salt, marked o, irhifh. i»|

SODIUM

491

8t witli ihe hfhijviom' of most s.'ilts, ascends as it passes in the
'f lower temperatures. The fact that the solubility of the
« irilh risiiiff tatijirniture^ jg connected with the other fact
r tli8si">lve3 in
I'lUiytcd sohi-

Viiih rtsAutioii of

or, abtjDi'plioii uf
I occur* when it sepa-

out from a super-
solution (p.

Fia. 11-2.

I The curve of the
rdrous $alt C4tn be
iiweti dowtiM'ai't-U to
a 20. From 32"
ivards, bow ever, the
9i» are mpfrtahir-
wilh rcsp<et of the ordinary Glauber's sail with 10H„0, and
can iht-rufore be obtoined only wlieii th« presetiee of this latter
ia itlrictly avaided. This requires some care; for, aa we shall see
mtly, thy salt is everywhere present in dust,

'At 32", the curve of the anhydrous salt is cut by the solubility

r« of (jh'u}>er'$ s^U (jnarkod with 10); at this point, therefore,

ults can exist along with the solution, since at tiiia |Kjint the

Kted soluttana contain the same amount of iudt. This state is

easily obtained by heating (Jlauber's salt to 32'. It appears

to undergo fusion. We are here dealing, however, with a more

lic«te<l pr<x't'SK, for the liquid does not h;ivo the same comjxjsitiou

|the solid GUuLer's sidt, but contains more water. This is due to

fwt that iinht/ifriiu.i salt separates out at the same time ; for thiB

the salt does not pass into a clear litpiid, no matter how long

\)» hcitcfK bat forms, after the Glauber'^ salt has disappeared, s

of anhydrous salt and sattirdted solution.

TkiB Lmnsition i<'nii>i?i"jiture of GJauber's sjdt is, when a pure

neo Lb employed, exceedingly constant, so that it can be used,

the melting point of ice, for readily obtaining an unvarying

Bptrature. The temperature is 32-3S3' on the international hydro-

i dicrraometcr scale,

lilt* wdubility curve of Glauber's salt with 10H,O, can Ite followed
Ownwoinls to somewhat below 0". Tlie solubility of the wdt di-
uiiiiliei very rapitlly as the temperature falls, so that at 0" the liquid
wtJuns only OOrt of sodium sidphate (cjilcuiated as anhydrous salt).

So far as we have yet considereil the relations, we are dealing
'rtii two indejicrident solubility curves, of which the one belongs to
Mibviirous salt, the other to the sail with lOH^O, The present
)(iistin>rui«he<l from that of sotlituu bromide and sodiutn iodide

492

PBINCIPLES OF INORGANIC CHEMISTRY

CBi

oril3' Ijy the fact that, otic of the curves slopes «]o\viiW!ir«ia, while
the case of the latter salts, hutb curves slope upwaiils.

It has to be specially noted that the hratik in the aolubility cii
at 32° is due solely Ui the fact that the w/iV/ pfiiise in the eiJol
equilibrium changes at this t^mpeniture. It wns formerly tfacM
that Bom&thing special t<:)ok f>lace iti the solution at this tBinperM
such as, saj', that helow 32° the suit was dissolved in a hydrat«d fa
above that temperature, in ari anhydrotis form ; even now, such
founded views are sometimes mot with. However, on in^e8tig«t^
the pro]}erticB of the solution at its ]>a;jsage through this point, no
o( break was found, and so far as the solution m concerned, l
temiwniture is in no way dislinginshed from other tenipemiu;
The only thing that changes at this temperature is the nature uf tl
Bolid salt, and this is the allsufficieiit reason for the occniTence of
new solubility cur\c.

The phenomena, now, become somewhat more compticatod fns
the fact that solutions can be fairlj' easily prepared which are >
sidcrnbly supersaturated with respect to the salt with lOHJ^. Imi
the phenomenon of siipei-siituration has in no case been studiei! m<i
fully than in the case of Glauber's salt.

Such supersaturated solutions are obtaintxl by beating Olaubn
salt with half its weight of water until all solid particles have f
appeared, closing the vessel and allowing it to cool tiown. The stopp
docs not require to be «ir-tight but only r/uH^V-tight ; a plug of wlUH
wool, for example, is therefore sufficient. If this is removed, after til
solution has cooled down, ctystjdiisation, as a rule, commences at ono
This is due to the fact that Rlauber'a sjilt is extremely widely d"
tribnted in the dust of towns, lieitig formed from the comptiutiti*
sodium everywhere present (p. 479), iind the anijihurons acid which
produced in the combustion of coal, and is derived from the siil|>hil
therein contivinod. If the experiment is carried out in the country fj
from such sources of dust containing Glauber's salt, the crystallisatii
can also be excliide^l. Since it was for lung not believed that this
the cause of the "spontaneous" crj'staOis;vtion of (ilaulier'a s:dt, th
eryBtallisatioti of the supersaturated solution appeared as aoraethiii
peculiar and mysterious. By working with other substances, howev(,«i
which do not, or oidy rarely, occur in the dust, one can con't-ince on*
self that in geneml supersaturated solutions possess a gteat stability;
and that it is only towanls nuclei of their own solid aubstauce thai lli»]
are unstable.

* The amountjii of solid sul>st<inco which give rise to ei'j'stallisatic
(ire small but not immeasuialdy so. The limit lies about one niilliotith
of a milligi'am.

On cooling down a supersaturated solution of fThiuber'a salt
about 5", other crystiUs make their appearance, which have the (.'OB*'
position Na,,SO^, 7H.,0, and whose solubility curve is also given "

SODIUM

493

1 1 1 2. Throughout it& whok- course, this curve lies above tlie

of the «alt with tOH.jU, fnnu which it follows that the scjlutions

H«<1 with the snlt 7, jiie always 8upei*SMtu rated with ies[wct to

lit in. If, therefore, sunie of the suit 10 is introthjeeri into a

cijmpose»i «>f salt 7 iiSorig with solution, the solutiou will, ia

9l pl»fe, ile|K»sit mlt ujiiil the point of siitumtioti with respect of

re:ich»xl, i.f. the coiiceutnition of the solution will rtmcli tlint

on the curve ICi whieh lies below the fonuer jioiiit ou curve 7,

a solutiou, however, is iiiiSriturateil with respect to 7 ; couse-

ly. ihrij 9«lt must dissolve. The solutiou thereby agtu'n becomes

iturattfJ with respect to 10, and this seijarutes out. This evi-

Ntlr g'')e» on until, finally, all the shU 7 has disappcai'ed a7icl is

" rnl by 10.

miy W: iiskeil, Why does the unstjible salt 7 separate out first at
i«5e, of course, the soIutioTi could give the stable S(i!t 10 directly 1
[■•ttsvrer is Ui be fouud in the uuiver-sal ru3e that the /csi siahh-
)nT-<t itpji^ar (p. 210).

Jty. if the solution be cooled down to about - 15", Glauber's

Bpontee out spontaneously from it and supei'saturation ec^kses,

khis too ivithiiut a oucleus of the Kolid salt bein^ necesKiry. The

in which the sejkiration does not occur without such a nucleus,

r distinguished aa the lu'fndnh/r jrijini), from that region, the

hTt^fivH, in which Kepiiration takes place without a nucleus.

i^ siipersaturation k'uib, in the Arst place, into the nieta-

and from this theo into the unstable. The limits of the

na are, however, difhcidt to fix, since the presence of dust

'great infltietice on the spontaneous formation of solid fonns from

Btftble titjuids.

be crystals of (Jlaiilier's salt fjflatesce in the air, !>. they lose
»nrl become cons'erted into a fine white powder of anhytln>us
The laiuse of this is that the vaftour pressure of Glauber's salt
nore exactly, of a mixture of Glauber's salt and iuihydrous salt) is
than the niewi vapour preaauro of the water in the air {p. 126),
Kl the fuilt must lose wat«r and pa^s into atihydi'oiis salt.
<>n the biiais of this remark, the objectioti may be made to
i: i'tI)knfttion of the crystallisation of anjieriuiturated .solutions of
aW.s salt by dust, that according to the above suiiement there
be no Glauber's salt present in the dttst, but only fffiorexal
bW* salt, i.e. ntKhijfltmiA salt. This ig so ; neveithelcss, e.i£peri-
ahows that even effloreaccd Glauber's salt can also eU'ect the
illisalioij of the supersaturated solutions, and loses this property
'when it has lieeji heated. In the elfloiesced salt at the nrdiiuiry
eratiire, then, there are iipp;irently sufticioiit traces of unchanged
nlwr's suilt pi-eseiit t£i bring id>out crystal ligation. Or, there is
on efflorescence, a form of the iwilt which in contact with
^whition inuaediatelv «nve« (ilaulx-r'a ,sdt, a behaviour which the

494

PRINCIPLES OF INORGANIC CHEMISTRY

anhydrous salt tertiu'nly does nut show, after it hiia Iwen iiean
Which of tJiew two iKjssihilities torrespontls tu the tnith, has t»otj
been ilet-ormitieil,

Intiict cryst;ils of Glauber's salt am he kept in tlry air
efflorescing ; if, hciweiur, etflorescencti has once begun at any |)u|
spreads out fniiu that poiut, and this it doca in accordance with i
which is detciniinud by the crystjdh'ne foi-m of the efUipresciiig
(p. i'64). We have here again a phenomenon of the nutnro <A
.mfHnUwu, which i%>iii be roinavetl only by the presence of a
phase. Applyinif the phase law t^1 this case, wo olitain the follnwinj-^
Since the given system consists of tii'o components, BiMlinm mif
and water, the stini of pluises a?ui degrees of freedoni is +.
hydrated sa\t and water \'apour are given as two phase*, the sj»t(
has still tuid doyrees of freedom, i.e. at a giv^en teinperntine, every v»
of the vapour pressure (vnthiri certain limits) can exist. If, bowe
another phase is added, only one decree of freedom remains, it,
every temperature there belongs a definite prossm-e. Such a sys
therefore, behaves as a [lUre liquid, for it has a definite vapour pr
which is independent f>f the amounts of the phases, I.e. irsdependi'itK
the relative quantities of Glauber's salt, anhydroiia salt, and
vapour. Observation shows that such a law does indeed hoM, I
this j»ressure is established mo to slowly than in the case of a licjiiiJ,

Since hutli solid pliasea are rerpiired for the definition of the syst«
just considered, it fiilliiws that one cannot sjieak simply of the v;tp
prej^sure of a hydrate ; on the contrary, il must be stated what oti
solid (or litpiiil) substance is also in equilibrhim with the vapott
Many salts form several hydrates ; every combination, theiffore,
two hydrates (or of a hydrate and the anhydride) nuist htver iu 01
vapoiu" pressure. This also has been eonfinncd by experiment.

Besides being used for medicinal purposes, sodium sulphate is aim]
employed as such in the manufacture of glass and in some olhffj
itidustries. It occurs as a by-product, and as an intermediate pri*ltiet|
in much larger tpmntities. As a by-product, it is obtained in tbl|
preparation of hydrochloric acid from common salt, and of nitric icil I
from sodium nitrate. The greater pan of the salt is convei-td inlfll
sodium tarlxtnate or ssoda. The methods by which this is acconi[iIi»WJ
will lie discussed imnn^diately.

Sodium sulphate also occius in nature. As a mineral, it is c»lW]
Hienuniile. It is a very fretinenl constituent of the natural wnteriij
waters which contain large quantities of this sjilt in solution, such "I
the Carlsbad waters, arc itsed as mineral waters for the reuiov*] rf]
disturbances of the rurtritinn.

406. Acid Sodium Sulphate.— The adt NaHSO, is [ire[iaicH>iti|
the same mannei- as thi- corresfionding potassiimi salt, is used forth*
same pu^po^ies, ;iud rxhibits the same chemical relations,

467. Sodium Sulphite. — The normal salt of the coiiip«i«iti""

SODIUM

4ii5

U^i}, occur* in commerce in large crystals; it is chictiy usetl
i<»t«>}rrin>hy for ftfUling lo the "tievulopers ' tn iircserve these
• uxj-gcii of the ttir. Tlie tleveluj^iers are alkiiliiie solutions

- cirgjiiiic t>um[ioijruis, the purpose of ivhick is to rt'duce ilie
r oiihijoiukIs of the exjioaed photographic plate to nietallif silver.
uiu &ulphjle, it is triK', scarcely jioasesst's the power to i^Hect iliis
ctiou, but it prevents to u cerUiin degree the oxidation of the
' • ill the air, ami so keeps this for a longer time iincolourod and

riie salt dissolved reatlily in water. On lieing heated, it ileconi-
i^ simiiitrly to sodium sulphate, into anliydroua salt utid a saiiuvited
tiun ; its sohitiilttj' exhibits corresponding changes.
Wben e.\po$ed to the air, the crystjds soon Ijecome covered with a
ing oi powdery sodium sulphate, which is formed by the oxidation
he salt. It can be seen, tln-refoi'e, from the nppearanee of the satt^

Kr it is still 6t to be used w not.
<i Sixiiam sulphite, NallSO.^, is, aUo known. It is dfliqnescentj
idi»e8 iti the air still nmte leadilj' than the normal salt. Itjs
x;ntnite»i soliiiiiiii is used in the artjs.

F. Sodium Sulphide.^With regard to the lieliaviour of tliu
volutici'f Iti sudinm sulidiide, Na„S, and of sodium hydroBul[»hide,
the rciiler inwy be referred to wUnt was stated in the c.we of
i«Kium sulphide (p. 4(5G). With regard, however, to the wlid .«i/is,
Wff he inent toned that from solutions of sodium snipldde. vfoH
Rd cf^'atftlft belonging to the rpmdratic fyetcm, ami eontJiinins
|0 of cryatallifation, can be obtained. Anhydrous sodium sulphide
>bliuiied <t« a flesh- coloui-ed mass by the reduction of sodium '
ibate with charcoal.

' " mixtures of viirious imlysulphides of sixlium, alonj; with

Iphate or sodium thiosul|thiite {according to the tempeniiure

jioyc*!), which are prepared under the name of lirer <>/ .oilphur ]>y

Bf tojicther aoda ami sulphur, are used in medicine and iti various

Itutries.

46'J. Sodium Thioaulphate is the best known salt of thio-

pbanioM (p. iy^K It h i»1jtained by warniiiij; solutions of normal

lijihile with sulphur ; the latter is dissolved, and the solution

utiu the i>alf. Na„S„U.p the ciimpf>sition of whicii ditler* frum

Hi m{ itie Ridpliitc only by one combinint^ weight of sidphnr. From

e solution it is obUiined by evaporation in the form ol large, trans*

ifent cryetala of the monoclinic system containing 5H„0 of cryslal-

atioD.

In tho manufactures, sodium thioaulphate la prei»ared from the

le of the "soda-wawte Vp. 49;>> ; by uxidati<Jii in the air.

I d into calcium thiosulphate, which is then transformed

ui salt )>y meaim of sodiuiti snlpliate.

is tjsetl iu farge fpuintities. To a certain extent it ia

496

PRINCIPLES OF INORGANIC CHEMISTRY

usod in photot;r.'ii)hy for " fixing." It has the property of dissoh
dilHcultly sultihlii s:tltsof silver, and pictures which have lieeii [irtxjiu
from these nre treated with this salt in orrjer to rcruo^'e the uncb*
silver salt, and to render the piclurea michangeable l»y light
theory of these processes will be given under silver.

Fiu'ther, thiosnlphate i.* used in large quantities as an "anticli
for the purpose of renioving the lust traces of free chlorine fnua 1
Lfibres of raateriid which has lieen bleached by its moans. Free chl
is converted by this salt into chluridioii, which is harndess; kL,
same time, snlpliuric acid is formeil. Tho reaction can be
]Sfa..S.03 f 4Cl., -^- r)H„0 = 2NaCl + 2H.S0^ + I3H01, or S^O.,"
5H;0=2SO/ + 8Cr; lOH.

Bromine acts similarly to chlorine. Iodine, on the other
converts the thiosulphate only into tetrathioiiate. Since the r
lias already been discussed on a former occaiiion {pp. 21)9 aiid 300),
shall only repeat the equaiiuii here : 2Na^S.,0j + L, - Na„S,0,
or, writing the ioni?, 2S.,0j," + l„~ !H,0„" -v 21'.

Sodium thiosulphate ia used, tlierefore, in volumetric annlvfl's
the determination of free iixline. For this purpose, it p<^'

very itiiportimt advantage that its solutions keep iierf«?ctl_v -.

atitl jire not oxidised. In this respect it is ^-eatly superior to sodil
sulphite, which was furmerly used for the same purpose. Care, caA
nmst be taken that the stdntioii of thiosulphate does imt beeome adi
in very dihite solutions, even the carbonic acid of the air i-ITects
decoHi position described on p. '29^, with deposition of sulphur. Sin
the iodine reaction ia very sensitive, it is just here that one prefenl
* uses dilute solntiona ; these must, therefore, be prepared shortly bef(
being used. This is best done by diluting a measured amount of
concentrated stock solution (e.ff. a normal solution) which remain*
changed for a long time. Such a normal solution contains, in accoil
atice with the above renetion equatirm, <jne tnole or 248"34 gm. of ti
crystallised salt N.^SjO^ + 5H^0 in a litre.

If a solution of sodium thiosulphate is added to a solution contK
in^' iodine, which may be neutral or acid, a corrosponding aniount
tlie free iodine disapiiears ; tho complete disappfinrance can be rewU
recognised by adding some dissolved starch and titrating till the Ml
colour of the starch iodide di.sappears.

This volumetric method is not Hmite^l to the determination u( fn
iodine, but can, evidently, be apjiliod to all sul.tstanccs which eitl
form itxiidion from iodine or, conversely, convert iodidion into fn
iodine. To the latter belong most of the oxidising agents ; to 1
former, many reducing agents. Thus, free chlorine or bromine asv
as chloric aci*l, liy])ochh>rou8 acid, iodic ficid, etc., can be titrated,
adding to them :in excess of potassium iiKiide and determining
amount of iodine liberiitcd \\y means of thiosulpbnte. As an exam
we shall describe the determination of potassium iodate. In ai

SODIUM

497

ijoii, :h)8 reacts with potaasium icKlide according to the equation
ilvl -^ 6HC1 = 6KC1 - 3L + SH^O, or, written in ionic form,
I - 51' -^ ttH' = SHjO + 3l.r For every mole of iodanion, six coin-
weights of free iodine nre formed, and, therefore, six moles of
tbiosiiipliate are used.
l^o/tmW suhstancea can he duteitniued by bringing them together
K measured excess of fr«e iodine (dissolved in potitssiuni iixlide),
■s tho amount of iodine remaining after the reaction, with

ror somu neat lions it is of importance to notice that in the inter-
in of imline and thiosulphate, the alkali titre of the solution does
laiige. Id other words, hydrion is neither used up nor formed
reaction.

tho crystallised sail is heated to 56", it melts without leaving a

i^jfliu' ; it behaves, therefore, differently from sodium sulphate

liiiiii suiphite. The fused salt may be allowed to cool without

ing ; if, however, a particle of the solid salt is introtluced,

ition commences at once. This fused substance is especially

showing that crystallisation is effected only by the presence

solid Bait, an(i does not consist, say, in a disturbance of " the

bic equilibrium of tin? atoms." Thus, if a glass rod whose end is

with a firmly adhering coating of tiie salt (all loose particles

' carefully rcmove<l) is introduced into a fairly large amount of

lojoltil fused thiosidphate, crystallisation proceeds solely from the

oaiwanl.^, auf] after a few seconds the glass rod with the bunch

Btals adhering tij it can l>e removed from the li<jlitd, without tfiia

ittifi/f (u C!i/.ttiiUiir.

'u. SodioiQ Carbonate. — Normal sodium carbonate, Na^iCOj, is
bite hiih wiiich readily dia-solves in water with alkaline reaction;
uihydrous it melts at 850'', and can unite with water i*i form

hyd rated compounds.
fsule* the anhydrona salt, at least four hydrates are known with
sty. By huiling down a hot satnrated solution, a salt of the
nla Na^CO,, + Wjii h deposited. If the sohitioii is allowed to cool
in the air. the ordinary crystallised sHtlt containing lOH^O ia
iiiiwl. On cooling dnwn the hot Katuratcd solution, with exclusion
it. two different salt* are obtaini'd, Wth of which contain THjO,
re a diflVrent crystalline form and also a different solubility.
ch of the two is formed, dejienda essentially on the concentratioTi
solution.

tides these salts, othi-'r hydrates with 3, 5, and 15 molecules of
cry*talli?ai!un have l»etin deaerilwd.
of thtsse hydrates has its own solubit
curves cut one another in a niann^sirtiil.ir iu that d

most.^'^t«iile l< iho.ne ,

1 4.0 ohc .i.(it-ij.n::-e'fei^niift]fV
n LA?;r ti'.;.>8!te''A''-

"^'W(, tile

aeiVj are

" £'-''nc J,
'.^o^Jf**; to
'** »<"H /or

'•"■'^^'^•d, into
• "'^e'- tJjat the

'i'Wre, I,

""';-.&^':!:'

500

PRINCIPLES OF INORGANIC CHEMISTRY ctiil

sulijljiir from them in aome form or otliei", and at tlip present Any thi
is succtisafully eanied out in those works where tlie l.v Blanc pnxta
is still in use. Since, however, the disappearance of this process is onlj
a question of time, it is not necessary for us Ws enter into a descriptan
of the methods of " sulphur regeneration."

The new method, which on the Continent has practiailly flntirrfy
replaced the older method, depends on the folUiwiui; reactioi*
Ammonia is absorljed by a aoUitititi of common salt, and cirbon dioxiiJl
then passed in. Sodium liicj!irl>oniite, which separates out in th^
Bolid state, and anmionium chloride, which remains in solulioti, irt
formed. Tiie latter is decomposed with lime into calcium chloridi* and
ammonia^ and the ammoida formed is used again in the prep!ir4tlua

The chemical process, then, amounta to this, that tho ions Nav
NH/, Cr, and HCO^' arc brought together in concentratc«l ^rihitim.
Under these conditions, there will be deposited, in aL-coni
principles already laid down (p. 4 4'>), that salt which has tb'
solubility ; in this rjtsc, aoiJium bicarbonate. It is true that iwithi
ammonia nor carbonic atid alone is dissociated to any jfreat eiiei
into ions, but the two immediatj^ly form ions when they come togi
in solution, since the ammonium bicarbonate is a salt which ii
is dissociated into ions in the same degree as any other neutt

The process woidil therefore I* eipially snccesaful if in jiUiv ui
ammonion some ottvor cation were employed, whose bicarVionuie i>
more soluble than sodium bicarbonate. In the ease of atnraoniom.
however, there is ihe special advantage that free ammonia can. <*.
account of its volatility, again l>e easily recovered from the n;si<l\iil
chloride by means of time.

The chemiciil reactions, therefore, can be summarised in the follet'
ing equations : —

NaCl - HNH,C0, = NH,C1 + xNaHCO,

2NH,C1 ^ CaO
NHg+HgO

CaCl, + 2NH3 - up

COj = HNH^COj.

Besides sodium chloride, calcium oxide and carbon dioxiiie ar#
used up. The latter are obtained from naturally occurring calciurt
carbonate or limestone, which decomposes into the two con.stttiientS'Ul
beating. Further, the sodium biwvrbonate is ]>lacud on the WHrkci
only in very small amount as such ; the greater |)art is «k'coin}Htfc<
by lieating into normal carbonate and carlwnic acid: 2NaHC0, =1
NajpCO^, + CO3 + H.p.i

' It is tint easy to see wliy the (K'tonijioiiitiriii of ihv ciilriinti cnrtioiintc wiil "' ^
ammonium plilariile is tiot nnitod hit-o ouc ojiejution, (or by hvntiii); th* two MonnislW
ctrhonnte would tn- olilaiTied, whii'li cimlit Iheu 1* iHssoJved m tln^ Milution <>t codib*'
Belt. The-cnTlum ilioxi<li> from tho ilectrmjMjiitioTi of the stMiimii liicailioiiiilt' wciuW IW
l>f exactly ^ultirittnt to ti|:»Lii precipitate Koiliuia bicnrlmautu froai the noliilioii. fmnc
nlily tBclmicB.1 di0]cnltj«s have liece^aitateii the intlirect process.

SODIUM

The soti.t obtained in this way (SoU'tiy process) Ss not only cheaper
itan by the Le Blanc method, but it is alao considerably purer.

For apncial purposes, pure soda ia obtained by precipitating the
..<»rbontitf5 from n com^untrated solution of the impure salt by means
: carbon dioxide, washing this with coid water and converting it by
► TOligly heating into the normal carboiiiitt*.

Iti analj'flis, sodium carbunate is employed for several purposes.
'» the one hand, it is used as a reagent for introducing carbanion,
Oj", into a given solution ; since many carbotiates are difficultly
3iluble ill water, the respective cations will bo precipitated by this
Edition. On the other hand, 8u<Hnin earlxmate is used for decom-
osing various salts at a red-heat, Kiore especially for decomposing
Jicate.-> anil rendering them suitable for analysis. For this pui-ptiae,
is tuixed with about an equal weight of potassium carbonate. Such
mixture moltjs much more readily than either "if the salts alone.
*Ilis in another example ol the mutual deprcissiou of the melting point
ride p. 477).

471. Sodium Phosphate.— Of the three sodium aaUs of ortho-
hosphoric acid, the Ijiist known is the disodium sidt Na.>HPO^ ; this
I tbe sdt meant when .iculium pkiis}<hnk- is spoken of without further
esigrmtion. It genemlly crystallines in large crystals containing
2H2O, which readily effloresce ; with moat of the other sodium salts,
owcver, it shares the property of formiiifj crystals containing different
mounts of water, according to the temperature of crystallisation.
Thus, more especially, a salt with TILO is known which is formed at
emp<5raiures above 35", and is also formid liy the efflorescence of the
liOrfi highly ityd rated salt.

At higher temperatures, the salt first loses ita water of crystallisa-
iion, and then the urireplaced acid hydrogen is given off as water, and
ihere is furmed the sudiiim mil of pyrophf>s}>h<iric arid: SNu^HPO^ =
S'a^P.jOj + HjO. This is the moat convenient method of preparing a
jjTophuaphate, and from this pyrophosphoric acid (p. 368),

* Tbe above reaction is of great historical interest. The change
3X the chemical reaction which accompanies tlic above transformation,
led, of a necessity, to the conclusion that the nature of the acid had
indergtine ati essential change hy the ignition, and after Clark and
Uraham had subjected the chemical processes which take place to an
jxact analytical investigation, aruJ had established the fact that theae
jorisist merely in a loss of water, it was possible for Liebig, on tbe
aasis of this residt, to put forward the thmrii of the jn'hjhtiMc xcids. For
jjnce at that time (1838) the metlio<ls for the ditt'iiuinatinn of
Bolar weights had not yet been- elalxirateil, all ncirls were forn*
'or the 8ake of simplicity, ag coutainiug only one combining '
'eplaceabla hydrogen. Liebig showed that the facta am
jonsistently and clearly represented by giving up this as
writing, where necessary (more especially in tlioge cast

602

PRINCIPLES OF INOEGANIC CHEMISTRY

aalbs can be prepared), the fornmlse of the arirls with two or
corabining weights of repkccalsle hydrogen. This method of for
tion received continuation through the cottceptiofi of molar «
which WHS aiibsequently developed.

The Jiqueous solution of disodiiirn phosphate reacts feebly all
Tho reason of this has tdready been given (p. 368) ; thu a
hydrogen of phosphoric acid iis only slightly dissocialfd. and a ce
amount of hydrolysis therefore occurs in the sotutione of the
sj lending salts.

In the laboratory, the solution of disodiiim phosphate is emf
to introduce phosphaniotv into reactions. By reasoTi of the natu
the dissociation of phosphoric acid, to which reference has Just
made, thtj Bohitiun of the salt cniitains, to a preponderating oxtcnt,l
ion HPOj". If, as is necessury for most of the precipitations, if
desired to liring tiic ion PO^'" into rmction, it is further neeesswyl
add :i base, the hydroxyl of which can form water wixh the hydr
of the ion HPO/', and thereby convert it into PO^'". This transfn
mation, it is true, tJikes pltice only to a small extent in the soloti
itself ; if, however, the ion PO^'" is continuously removed from
aolutiou by the deposition of a solid salt, a fresh quimtity
always be formed in order to establish chemicfil e(pu]il>iium iti
solution, and the object aimed at will be attained. Usually :inn«f>niil
is the alkali added, because an excess of it does no harm, which a\
sometimes not the case with an excess of caustic soda or potash.

If to a solution of the ordinary sodium phosphate the quantity of]
caustic soda required by the equation N:i,,HPO^ + NaOH = NiwPO, ■
H„0 is added and the solution evaporated, the trixoiiium plmsphiitil
is obUiined in hydrated octahedral crystals, which dissolve in waMirj
vrith a strongly alkaline reaction. By addition of phosphoric »cid
in accorflaiice with Na„HPO^ + H3PO, = SNaH^POj, and evaporaliot
mtmoforUum phmphHf. is obtained which crysUdliaes in two diticwnt
forms, each containing IH^O. On Wing heated this salt pjisse^ into
the .wiiium saU of mefiiphmphnnr add : NaH^PO^ = NaPO,, + H,().

The sodium salts of pyro- and metaphosphoric acids, which lav»l
just boen mentioned, arc the raoat im[iortant salts of these antontJ
While the pyrophosphate b,is only a limited application (in medicinflU
the metaphosfthate is largely used as a reagent iii qualitative analysitl
It is obtjiineil as a glassy mass by heating niouosodiuni phosphat*, jukJI
Joes not crystallise when it is dissolved in wator and the solutinn t»J
evaporated ; at a red-hefit it has the property of dissolving inwiyj
metaKic oxides, with production of a cliaracteristic colour. In using]
it, a small quantity is fused to a bead on a loop of platiniun wire, imij
to this is aflded a small quantity of the substance under invesitigii-
tion. The various heavy metals, more especially, give charjtcteristicj
colours in the " phosphate boftd."

472. Sodium Silicate behaves quite similarly tct pota«Hiu

SODIUM

503

icate, and is employed as soda vnkr-f/tn^s (p. -170), Together with
ther siliciite!;, it occurs both natuniSly {e.f/, as rdfrile) and us a matin-
ictured jiroduct ; thus, for example, ordbiaty ffhs."; ia a loixtiire of
otlium ;u)d calcium stlicati^>j,

^ 473. Sodium Borate. — Of all the suits of boric acid, a sodium
OTn]ioimd ia the best known and the most largely used. This salt ia
alle<l feed.'', and ha3 the comjrosition Na^B^I >j ; it is^ therefore, the
ndiuni salt of tetraboric acid, H^B^Uf, which may bo supposed formed
roui four combining \v<?ight* of ortholxiric acitl by the loss of SHjO ;
tHgBO.,- r.H20 = H,3^0..

■■ Borax is a tjult which is not verj' solultle in water ; at lower
■mperatures it crystallises with 1011,^0, above 5fii' with JiH^O. 'fh«
pfmer, or more hif^hly hydratetl fonn, is distingnishtd as prismnfic
prax from the less hydi'atcrl or ^icliihfiiral borax. The rulation exist-
ng bt'tween the twn sidts u nitnilar t^i that between Glauber's salt and
' anhydnivw Hmliuni sulphate (p. ti)!), only the octahedral IxH-ax is very
.oafiily fuinied, even in its region of instjibility below 56 , if nuclei of
'the prismatic form are excluded.

■ " \\Tjen be<at«d, borax loses its water, flrat swelling up to a spon^

'maas, and then, iis, the temperature is raised, forming a eolourlGss glass

"which, on cooling, solidities in the amorphouci condition.

' This hanij- gkina has, similarly tf" .scxlium nretafihosphate, the pro-

^ perty of dissolving moUiliic (ixideM with production cif ili-Htinctive

- colonitions, and is therefore used in qualitJitive analysis for the same

' piii'pttse as the lattei* salt. Ijj the case of borax, however, the melting

• point lies considerably liigher, and the colours are also to some extentj

ditlerent, so that the reactions in the ?jora.x and those in the phosphate

bead mii.st be ili.'jtingnishcd. To this -solvent power for metallic oxides,

tte application of bfirax in solihring is also due. Soldering consists

' in uniting two pieces of metal together by fitting them to one another

and filling up the .sjmce which is left with an ea.sily fnsiljlc niotiil in

the liquid form, In unler that such a junction may hold, the lt(}uid

mebd must wet iho surfaces to be united ; this is, howevtsr, hindered

l>y the layers of oxide with which most of the metals become covered

when heated. WheJi the l>orax melts, it covers the metal, and thus

prevents ihe access of atmospheric oxygen ; it also dissolves the oxide

which is present, and thus renders the wetting by the hquid metal

possible, 13orax i."* used in soldering with difficultly fusible, or hord

soldf!i (a mixture of copper, zinc, and silver) ; with ejisily fusible soft

solder {tin and lead) there are used zinc chloride, anmiouium chloride,

resin, or stearic acid, which have a similar action to Ijorax,

474. Sodium Acetate. — Sfdium m-rtatr, NaCjOjH.j, 5H.p, is a
salt which is rcJuUly soluble in water, and melts at 58" in its wate*"
crystallisation ; after the iublition of a small amount of «>»"
fused product can be cooled down without crystnllising.
liquid, which, if "nuclei" are excluded, will keep for yi

504

PRINCIPLES 0¥ INORGANIC CHEMISTRY cha^

perirnents on supercooling (p. llll) can he very cnnvenienllr
forraetl, since, as a rule, no miclei of the shU are pruseiit in th*i
and tho apparently spontatieons erystaJlisftlioti does not readily

In the laljoratorj, sodium acetate is often employed. It is
used in misdyticiil chi;miHtry for the purpose of prepiiring soU
which have nn meid reaction hut cotitaiu a vtri/ /vi'ill crmr^utrnf
h/dikm. Since several of the preeipitiitce employed for an;il3'tie
purposes aro dissulved by strongly acid li(|ind8, but arc siiflici*
inaolitble in weakly acid ones, an artifice like this is of great imj
a nee.

The above object is attained by adding sodium acetnt* to the I
tton which contains hydrion, «./;. kydrochlonc acid (or in which hyd
is formeri in the intended reaction). The ttcetanion thiis intn
into the solution combines with the f^reatei' portion of the hyd
prcsont to form uiidissouiated acetic acid, since acetic acid is a ral
wwik acid, a [id only a small amount of hydrion \a left. If
hydrion is formed in the reactiooj thiis undergoes the same
mation, always supposin;^ that there is acfiUmion stiU present-
sodium acctJite must, therefore, be added in sutficient excess.

470. The Combining Weight of Sodium has bii^n deter
in cntijunotion with that of silvi;r and chlorine (p, 221») by ;i*cer
how much silver is neiessary for the conversion of a definite an
of sotlium cidojiile into silver chloride, or how much silver chlo
Can bo obtained from a given amount of sodium chloride. In this'
it has been found, Ka- 2 3 0.*).

CHAPTER XXII

KUBinilSl, <;jES1US1, UTIIUM, and AMMOSIiai

ilieral. — To Ihe two idkali metals, [Kitafisiimj ami miilmni,

.%-ur wry ahuiulafilly in nature, there are ruljittHt three uthei'

wliicli nre firund much iwoii: s|mriiigly. One of these,

bats n snijiller combitiing weight ih.'wi the above mentioiiod

its, vijE. 7 03. The other two, ntliiilium niitl arsitim, hiive ji

cottiliiiiiiig weight, vix. 85*4 and 133. In their eheiiiical

ibe latter two ai-e «|uite analogoiis to potaasimn, while

i»Lituds alone iu the group, and its chemical analogues are

to V»© found in the elements of the next grouj>, ihiit of the

eartb metals.

n riew of this ciTctimstauce, it may be asked why lithium 18

preferably cli^sed along witli these other metals. The complete

«r to this can W given ntily after all thfi Jisstimptions necessary

a of.vnipn-hcusive systuintttisiitioti of the elements have been dis-

1. The deeifiive reason may be here givt^n, viz. that lithium

ii ttifnu'tiiltrit ioti, like the alkali nietalfi, whereas the ions formeil

the aJkiiliuo earth meljils are all <fi\'ii\out. The specitic heat and

relations arc tronhected with this, atid all favour the placing of

iom in the group of the alkali metals. It will also be found that

ona simdar to those founrl in the case of litbinm can be

ly and regidarly observed.

chapter itmiiiwiiutii {p. 508) also has been placed, becanse it
onovalttit cation Nil',, which is in many respects similar to
».
♦77." Rabidiom and Csesium. — After the foundations of sjitdium
m/|«u had been laid by Bunsen and Kircbhoff in 1860, the former
loeMded to apply the new method to several substances. And,
In the mother liquor from the salt wells at Diirkheini, he
new 8i»ectral lines which did not belong to any of the elements
itkoto known. In a masterly research '■ he separated the correspond-

alitatii«d V gm. i>f ruliidiiim chloride and 7 gm. ar cn.>9iain cbtoride Itota 'HO
. 9t mothvr lUjnoT, comspon>Uiig tr^ 44,'20l> kg^m. of inicpriil water.

PRINCIPLES OJ

jg suKstaiiees ;inii estaliltshed the fact tliitt two »ew alkuli Tu«tal&i

sent, which were especially similar to jMtsissiunu From the i
jf their moat pronounced spectral lines, he called them rtibidJuiD *
' and esesiiini (blue).

The two clcmstit* were suhaeqiietitly often observed^ biit aJi
verv small .'iniount. Hnbidiiira in found most ahnndnntly ill
muiher Hiniocs from th« Stassfnrt potfish t>aUs, from which it mj
rated in thu form of ius dilticuUly aoliibie double salt with Jilui
sulphate (alum), Ctesium comjmunds still remain very rare.

The chemistry of these two elements, so far as investigated,
perfeetly with that of tlie {wtassium compotunls. The rnrresT
salts are generally isomorphnuH, and exhibit similar solnbilit)' reli
lore especially do these metals form difficultly soluble salts wit
Hoi\& PtCl,;", SiF„", and B¥^ ; the acid gjdts of tart-irif ai-id ar^
difficultly soluble. For this rea.non there are no methods kno
which a tolerably sharp separation of these elements win l»e
and one has to Iw satisfiLMl with incomplete 8e]>aratiori8
slight dirt'erencea in aolubility, which must hv frequently
befoiij the object ts apprftxiiuately attained.

Thus from the previously concentrjitfd mixture of the
chlorides, by the addition of hydrochloroplatinie acid, Bunsen
rated a small precipitate which fonsisted of the It^ss soluble salt'* o{l
two new elements mi.Ked with the more soluble i>otassiuro platiji
ride, By ixiiling this precipitate with small (piantitieB of wat
adding the portion which passed into solution to the original Iw]
he olttained a less and less soluble platinum salt, which finally
almost free from potassium. Tlie sepamtion of rubiiliunj and 13
was effected by treating the carbonates, or the hydroxides, ,
alcohol.

Mdidlk ruhidmm, which can he obtained by dislilling
hydi'oxith? with magnesium, has the density In, melu at 38^ amlj
room temperature is very sitft. It readily volatilisea, &nd ignitai 1
taneously in moi.st air and also in dry oxygen. It disaolve^ in 016
forming ati amalgam, which behaves like potassium amalgam.

In oxygon, rubidium burns to a dark coloured dioxide, KhO_
dissolves in water, yielding the hydroxidu with fomiation of hyilr
peroxide and oxygen. The hydroxide is obtained from the sulf
by precipitating the sulphanion with kirium hydroxide.

Of the different salts of ruhidiutit, nothing s|>ecial has to heuudj

One peculiarity which is not found in an appreciable degree in
case of potaaaunu, is the pro{ierty possessed by mbidium and
of forming compounds with the halogens, in which tlirec or five (
bining weight.i of the latter to one comliining weight of the meul 1
present; comjjounds, therefore, in which the metal appears as lri-<
pontavaleiit. Such compounds with bromine or iodine are formed 1
eepecial ease. They are deposited as difficultly soluble crystalline ;

TTHIUM, AMMONIUM

HIT, on introducing the free

• Mir i(j4]ide. Through these

till' iieavy metfils thulliiiin

-linn, have also been ranked

imiiiifls are much more readily

'fi , attfl is still more readily

- (iij)mintls of the other alkali mt'Uls,

I Uy Arfvedson in 1817. Klenientiiry

i6[>ii Uy Htinseti uttd Matthiessen, hy the

-t of nil solid subsUmees; its density

•i ii (.ileum. It is a silver-white, somewhat

M-s not melt below 180', and does not

■ i. When htmtwl in the iiir, it iloes not

rv '200 , and it then burns with n white,

' l<.' [hsil of magnesium. It decomposes water

j,'(>n And formation of lithium hydroxide ; the

I Ifiss violent thim with the otlier alkali metfdB.

■imIi inetrtls, lithium forms a. monovalent, colour-

ftli ciui eoenbino to form salts with all anions. From

alkali tnetaU, lithion )k distinguished by its

- dilJimUhj .■idlidilf salts, whitrh will he mentioned

4thium is not capable of forming any bnt monovalent

lUuam Hydroxide is most easily obtained l»y decom-
hiiiai isid|ibate with Viarium hydroxide. On strongly con-
Hhe solution, lithium hydroxide, LiOH, se]>arate8 out as a
aa«s, whieh is readily soluble in water, although not so
ftc»u«tic potash or so<la, but does not deliquesce in air. The
h»«, howcvRr, essentially tlie same properties as those of caiistic
nnd <:inistif- .soda, for lithium hyrtro-xide is disHOci;ite«] into its
and OH', in idinost the same degre** na tbfr other alkalis,
con)|K)und3 of lithium with chlorine, brfmiine, and imline are
liu^ly readily soluble, and deliquesce in the air, since their 8<i.tu-
iolutions have a unialler vapour prcpsiire than the mean vajiour
ire of the water in the air. TIuiv dissolve in alcohol and in a
Inrf of ali-ohol and ether. Since the i-hlorides of the otluT alkali
jjUiU are almost insoluble in this mixture, use is made of thia 0"^^
ty fur the separation of lithium from these.
Ltthium Jffiirride, however, is very diffieuStly soluble in wat
Lithinm nitnUe and Kitlphnie are readily soluble in water

4SCi. Lithium Carbonate, Li.,CO,,, is difficultly aol

100 parts of water dis.'iolve only alxjut una part C
lier hand, lithium hiatirhmak is much more oasil

612

PRINCIPLES OF INORGANIC CHEMISTRY

acitl, however, which is split off is imraeiliAtely oxidised hy the at
spheric oxygen {p. ^37), free iodine is formed, and the same s«t»c»^
reactions octiit's over again. Tlio salt csiii he preserved hy cxcludfl
air aiui moisture.

187. Ammonium Nitrate. — This mh has already been metitto
on a former occjision ([j. 3-15), .since on aL-count of its decomj:
into rntrous oxide and writer on heuting, it is used for the pref
of rliiit gas. It }s obtained us a very aoluKile s;dt hy ntutrttlisiiigi
at-id with simmonia or animoiituTn carbonate, and evapntnting.
thrown on red-hot charcoal, it decora|K)se9 with production of
alone, or mixed with charcoaS, it can he made to e.vjilode, anil'
therefor*-' lifted in the prepiration of ^.tptmtvs. Th«36 are ignilj
with dirticulty, and can therefore be u-sed without danger. Since I
'substtince is converted completely' into gases and vapours, thf explo«l
effect is an adv!int:igeous rnie, esjiet-ially as the niti-oiis oxidi" (o
gives out a considurahle amount of heat on decomposinL; (p. 334-1.

488. Ammoniuin Nitrite, NH^NC^, is of interest on aceouti
its rnady cJecomposahility into water and niti"ogen (p. 345) ; in thai
state it ia known only as a deliquescent and decomposable cryst
mass.

489. Ammonium Sulphate, (NHjjSO,, is isomorphous
potassium sulphate, hut isj nmcli more readiiy soluble in water
the latter. Similarly to potassium sulphate, it forms various
salts, nnjre e.specially with the divalent sulphates of the
group and with tlic trivalent sulphates of the aluniinium
The solution is somewhat more strongly di380ciat*^d hydrolyt
than that of ammonium chloride. If the solid salt is heated, il
ammonia and piusses into the acid ammonium sulphate, NH,I
this ia a reaction which is peculiai" to the normal ammonium s»lUi
all pwlybasic acids.

490. Ammonium Phosphates. — Of the throe pusisible ann
phoapliates, only tlic first two are known, the mono- and the i
aiumottium phosphate, since the normal aalt decomposes so
into amnuoru'a ami diammoniiim pljo.sphate that it does not
The salts are of no special importance,

A salt which is lietter known is so*liiim ammonium ]>hosijli
NaNH^HPO^, 4H.,0, or miaviytsmic salt. It is usetl instead of sodiu
meta-phospbatc for blowpipe experiments, since it passes into the T
salt on^heatins- The deconijKisitioti takes place according io
eijuation NaNH^UPO^ = NaPU., + H./J + NH-j. Since this decon
tion is accompanied by a considerable swelling up of the «ill| i
more convenient not, as is usually done, to first prepare the "[iho
beitd " on the iihitinnni wire imuicdiately Iwfore thf! experiment.'
to directly employ sodium met.iphusphato. The name inu-mtiiMnif j
is due to the fact that the compound is formed in the evaporalion '
human urine (decomposed l>y putrefaction). This liquid exciietion

RUBIDIUM, CESIUM, LITHIUM, AMMOOTUM 513

•ageless constituents of the organism was regarded by the alchemistB
fi extract of the human miorocrtsm.

491. Ammonium Carbonate. — Normal amtnonram carbonate is

' unBtaltle, since it undergaus with great readiness the general

imposition of the iiramoniuni salts of polybaaic acids. On the

>r hand, the acid salt NH^HCOg is very stable, and scarcely smolla

untnonia. It crystallises from solutions of ammonia which have

o saturated with carbon dioxide. The two snltA cuml)ine ^Hth

unother to form a double salt, the so-called animoiiiuni sesqui-

boniito {XlIj).,UOjj + 2XH,IIC0j, which forms the chief constituent

coram<;rcici.l ammonium wirbonate. The latter usually also cou-

■*is uiHuiiiiiitim ciirhiimnftf or the wmmonium salt of airlxtmic acid

399), which is produced from the normal carbonate by loss of

.ter : (NH,)XO, = NH^OCONH. + H,0.

4yi!. Ammollium Sulphide. — The two comjjounds which aulphu-
ited hydrogen c.iti form witti ;immouiuui are largely employed in the
^Mjratoi'y. They are jvrepfJi'ed by passing sulphuretted hy*drogen gas
trough a strong aolutioo of ammonia. With excess of sulphuretted
^drogen, ammonium !iydroBulphiile, XH^HS, is formed in the solution j
to this is added as much ammonia as was orit,dna]ly takeii, a solution
f animouium sulphide, (XH,).,.S, is obtained. The latter solution does
«jt contain solely ammonium sulphide and its ions, any moro than the
Diresiwndtng compound is alone contained in the solution of the
Ikali sulphides (p. 4ti6) ; on the contrary, hydrolysis proceeds further
"IJ this case than in that of the latter, for we are here dealing with the
J^alt of a weak ba-sts vWth a w§ak acid. For those reactions, however,
~ Jj which sulphidion H" is consumed, the actual condition of the solution
a of comiKiratively little importance, since the sulphidion which is iised
"up in the reaction can be produced afresh m proportion as it passes
'out of the solution.

Both the above salts can be obtained in the solid state by mixing
Bulphuretted hydrogen and ammonia gas in the necessary propor-
tions: NH3 + H.j8 = XH^HS and 3XH;, + H^S = (NHJiS. In this
way, crystidline massea are obtained the vapour density of which
ahowB that, on vapurisatiou, they again <lecompose into their com-
ponents. The sulphide is exceedingly re;wlily volatile, the hydro-
flulphide less so,

* In the case of ammonium hydrosulphide, thorough investigations
have been made concerning the equilibrium between the solid sidt and
its vapour. If we denote the concentrations of the aiumorfc and of
the sulphuretted hydrogen by a and l> reapectivtly, and by c the con-
centration of iimmonium hydrosulphide in the vapom* (this is, indeed,
very small but not zero), then, in accordance with the general eipiatioi-
of equilibrium (p. 330), we have the relation oli/r.^k. The couce"
tion of the undissociatod ammonium hydrosulphide ia dependf
on the temperature, since, according to Dalton's law, the v

PEINCIPLES OF INORGANIC CHEMISTRY ca

sure of a gi%'eu substance remains the same whether other mibsUl
dJ"e present in the gas space or not. For eavh iemjtcratiir";, tlierd
the product ab must also be constant. It is a case of an eiiiiilibri
therefore, which is jwrfectly similar to that betweert a solid mlt i
it;; [jartiiilly ionised solution (p. 447). As a matter of buit, aiao,
following ]:M}culiarities were found :^

(a) If there is no excess of one of the components in the gM <■
(a — i), }i definite dissociation pressure is estiihtishcd which is dcpendl
only oil the temiwrature, und not on the reliitive amounts of sulid ^
stance and vapour. J

This follows from the efjuation, for if a = b, the equation aisstn
the form a- = kc, antl k as well as r depends only on the teinpemtiiill

{h) Lees of the solid substance evaporates into a space in irlj
ammonia or sulphuretted hydrogen is already present j the efTea
equal excesses of tho two gases is oijual. This also cf)rTe8pond^
the equation, foT the exjjression ahjc is symmclrical in iesp«ct'
a atnl h.

* The equilibrium of ammonium sulphide would necessariM
represented by an equation of the form a-bje^k, because two aj
of ammonia. rciCt with one mole of sutphurettetl hydrogcD. |
decomposition of ammonium aidphjde, however, does not take p
in such a way that the two gaseous components are formed, I
in such a way that anunotuuui hydrosulphide is produced along t
free ammonia. The conditions i»f equilibrium become thereby cusfi
cated, and will tiftt be discusseil here. i|

The aciueous solution of amniotiiuia $ulphide rapidly becd
coloured yellow in tho aJr, because the sulphuretted hydrogen wi
is split off by hydrolysis is oxidised by the atmospheric oxygen (
p. 278); the sulphur which is formed dissolves in the excess
ammonium sulphide to form polysnlphides, corresponding to the al
polysulphidcs (p, ^(^7). A tetra- and a hoptasulphide of ammunj
(NH4)„Sj arid (NH^).j,S;, have been prepared in ttie stilid state.

In the laboratory, ammonium .sulphide is used for the precipilatio
those metallic sulphides which are dissolved by free acids. The tU
of these precipitaiious has already been given (p. '277). I'otaa^
and sodium sulphide liuve the same action, but ammonium snlphid
preferred, liceause an excess of it can be more easily removed from
solution.

Vdlow aramonium sulphide is used for dissolving those me*
sulphide! whose higher sulphur- compounds can pass into thio-lj
and form soluble ammonium salts. Tin sulphide is an tx»i
of this. Further infurraatitin on this point will he given uiide^
respective metals.

Besides being used for obtaining sulphur com{X)nnda, ammoo
sulphide is also used as a reducing agent, espcLially
chemistry. The action depends on the corresponding pi

xn RUBIDIUM, CAESIUM, LITHIUM, AMMONIUM 515

dphuretted hydrogen (p. 278); ammonium sulphide has the advan-
igb that the reagent can be used in a much more concentrated form
IMi the slightly soluble sidphuretted hydrogen. Hydrogen is used

Lin the reaction, the sulphur is precipitated, and ammonia is
Ated. Fresh sulphuretted hydrogen can then be passed into the
lintion, if it is necessary to continue the reduction.

CHAPTER XXIII

CALCIUM

493. General Remarks on the Alkali&e Earth Metals.-^

nietiils nf this in;w group are distinguished from tlie alkali
easeritially hy their jiower of exchisively forming iltmltnf nthirn*.
is seen from the fact that, e.ci., the amount of ealrion which caJif
bine with a given amount of chloridioii, does not depress the fr
point of the aijiieous solution by the samo amount :ig tin* chloriJ
but only by half as tnllch. One tiiol«r weijjht of cideioti, tiiorefo
combines not with mic but with hvo moLii' weights of chloridioii,
for this roiison it must be regarded as diviileiit.

* Since the different ions cannot be handled separately, the ab
result was obtained iiidiredlff. If very dilute aohuioiis of pot
chloride and of calciiim chloride are prepared, iti which tlie
trations of the cliloridton are the same, and the freezing pointal
determined, tlie depressious of the latter are not eqnal butartinl
ratio of 4 : 3. Since, in the case of potassium chloride, an etjtial
of the depression ia due to each of the ions,' the share of tUo ch!c
in the solution of calcium chloride must also be put equal to two, i
the cakiou has only the effect one, i.e. attsj fialf ui strongly a*
jwtassion. From this the above conclusion follows.

Other differences, although not so decisive, are found in
solul'iUtt/ i-vl<i lions of the salts. Tims, for example, the no
curlwnates and phosphates of" the alkaline earth metals are
difHcultly soluble in water ; indeed it ia only the alkali metalf
can form readily soluble salts with the ions carbanion and phospli
(and with a series of similar iona). It haa, however, just
specially mentioned that in this respect lithium forms a ti-ansition.

The metals , of this group are less sensitive to free oxygen and I
oxygen compounds than the alkali metals; they are also mucli h
readily fusible and volatile than the latter. Here also the fl»0l9

^ Tliis i^ seBU from tli* fuct tJint one mok f = 74'fl giiu) of jiotAKijiun chWitb' gi»
(HpnvioQ of thu hevting |i(iuit whic)i i^ tU'ici> ha great an tlmt kIvcu by oue ino)* oi
UOiliuocUttsd substance!.

:xii RUBIDIUM, CESIUM, LITHIUM, AMMONIUM 515

Uphuretted hydrogen (p. 278) ; ammonium sulphide has the advan-
ige that the reagent can be used in a much more concentrated form
lan the slightly soluble sulphuretted hydrogen. Hydrogen is used
p in the reaction, the sulphur is precipitated, and ammonia is
berated. Fresh sidphuretted hydrogen can then be passed into the
)lution, if it is necessary to continue the reduction.

DS4

PRINCIPLES OF INOEGANIC CHEMISTRY

The reason of this is that oxalic acid is an acid the >^trcitgtli
electrolytic diasocidtion of wliich lies l>etween that of hydrvHbJi
acid and of ucotic ticid. If calcimn oxidate is brought into
with water, a very small (juantity of the precipitate dissolve!.
acetic acid is added to the liquid, it contains sadi a small amounti
free hydrioii that only an extremely slight change takes place is
chemical efjuiiilirium, in snch a svnm that qnite a small q
the oxalanion unites with hydrion to form iindiesociat.cd oxalic
thL' niotif>v;il:ent hydro-oxalariioii, C„O^H'; the consequence is a
amall intrease in the amouTit of salt passing into solqiioti. Si
it is, the solulnltty of calcium oxalate is very slight, this IncreaM
no account analytically.

The case is different when a strongly dissociated acid, like h
chhiHc acid, is addeij, A large amount of hydrion is ilipii introdi
into the solution, and, accordingly, a comparatively large amount
oxalanion, C.,Oj", disappears, owing to the fonniition of HL\,0,'
HX'.jOj, and must hv replaced by more calcium oxalate passing il
eolution, Accordingly, much more of the procipit-ite will bedissol'
and with sufficient amount of hydrochloric acid the whole preci|iil
passes into solution.

For this reiison, in precipitating calcion with oxalanion, one
not use a solution of firf. iixalir arid, whereby the iletriniental hy
would be introduced into the solution, but miniiovniin nmlale is
ployed. If the solution it-self is strongly iicid, the excess of byi
can be removed hy jwhlition of sw/j«m acttutt , acetaiiioii, b«iog
ion of a weak acid, unites with the greater part of the hydrioii
form nndissociated acetic acid, and only a harmless amount of hj
is left behind.

According to the temperature employed, the precipiUite of
oxalate contains various amounts of watei' of crystallisation, and
not^ therefore, be weighed as such in the quantitative detemiinatii
of calcium. It is, therefore, heated either gently to convert it
calcium carbonate (CaCjO^ = CaCOj + CO), or, since *ome
oxide can thereby be nmdily formed, it is better to heat it t*
bright red heat, whereby it i.s comiiletely converted into ralnum

Calcium oxalate ijs also found as a constituent of certain aril
calculi and very widely ilistrjbuted in almost all plants ; in the
of the latter the comparatively large, transparent oct-ihedra of hydi
calcium oxalate, which have the appeamnce of an envoloije, can
readily recognised under the microecope.

512, G&lcilim Carbide — If carlmn acts on lime at a very hi|
temperature, there occiiis the reaction CaO + 3C = CaC, + < "O. T!
compound CaC,_, which is formed is called fuldum rurinik, and h
been manufactured for some vearR in very large quantities for
version into acetylene {]j. 410),

The reaction is carried out in the electric furnace, but the proa

CALCIUM

635

:>thing to do uith electrolysis, the cuiTcnt serving only to pro-
j the requisite high tempei'atiii-B, and to yield the large amounts

rgy which the

rui^iiiies. In

113 Hti experi- ^

electric furnace

BUled, formed

of refractory

calcititQ car-
forms altnrtst
irless crystiils,
cammereiul pro-

Kkj. I IX

appears as :i black grey mass of irregular lumps, having the
.eristic smell of phosphoretted hydrogen, which, however, is
\y to impurities. Its density is 3-22, ittid jt doys not melt
a white hfi.it.

he nmst itu|wirt«trit reaction of the carbide is that it is decom-
by water with formation of calcium liychfjxjde and awtijlfm' .•
•¥ 2H.0 = Ca(0H)2 + CjHj, In this reaction a considerable
it 4>f heat IB developed, so that if water is allowed to come into
t with a compniratively largo quantity of carbide, the tempera-
can rise to a r«l-heat. The acetylene is, however, decomposed
siich conditions, nnd a poorly luminous gjis is ohudned. Those
ene ^cueratJU's, thi.'reforc, are the best in which the carbide falls
• comiMit^tively large quantity of water, or in which the rise of
rature is otherwise avoided.

The problem of making an automatic acetylene generator, which

rs capable of simple solution on the principle of the appariitiis

Iwil o!i p. 87, h^s in reality turned out to l>e very difficult. This

le, on the one hand, to the f^ict just mentioned, and on the other

1, to the fact that calcium cjubirte reacts powerfully even with water

; «o that the so-called a/tfr-^^nditiion of gas, i.e. a constant evolution

even when the appsiratus should be at rest, is difficult to avoid.

Tlie detrimental effect of moderate heat on acetylene can be

It shovru l)y allowing the gas to pass thrniigh a horizontal tube

enterifig the burner. So long as the tube is cold, the flame

very brightly, but srj soon as it is heated even to a dark red

the flame l>eeomca almost non liuniuous, and charcoal is depimited

ttibe.

during the interaction between lime and carbon, nitrogen
air) is allowed access, a compound, ailriiim i-t/anamitJe, CaCNj,
When this is treated with hot water the nitrogen is split
ftaiBtonia : CaCN, 4 3H/) = CaCO, + SNH^. The same reaction
plac« slowly in the cold, so that the substance can be used aa a
litrogeD manure. (Cf. p. 489.)

536

PRINCIPLES OF INORGANIC CHEMSTRY

513. Calcium Silicate and Glass.— Silicates of caldutn occur i

the pure sUite in natitro, fortniny mnmporteiit TiiitierMls which b«
Imt a slight disLribiitton (wolhisfouiti-). (.'nni1>itif'd vt*ith other siJic
liowev'er, ivilcium silicfitu is a very frequent coiistitiii'iii of th»* unUti
CKCurring minerals.

As H cluittiicul lirodutt, also, calcium -silictte it«eif is of no i(j
portance, but is of great importance when mixed with the aitic
of the alkali rnotals. The.'^e mixtures c<infititut« (?/ffAf, the wcll-kno
resistant and transparent m.iteml which finds an applicAtioii
all di^parttnctits of diiily life, in the matinfiirUire^ in art, suwi
science.

Ghisa is iL mixture of p<itJis5inm ur sodium silicate ami cal
silicate. This is the L-onifMjsitioti of ortlinury vvimlow-glaaa tir
glassware. For special piir]w)SC3. still other metal oxides are
and fllsu phosphoHe ;iiid boric acids in place of silicic acid.

The chemical composition of good glass agrees jipproximately
the formula A^CaSi,jOj^j| where A signifies potassium or soilium or 1
Ordinary glass, however, genei^ally contains lees silicic acid, sific«v
then more easily fusihle.

Glass is amorphous, <is is showji by its isotiopic nature and
absence of a definite melting point. In certain glasses there itij
tendency for some portions to separate out in the crj'atalliiic
this is known as dnitrijindifnt, and it is endeav^fmrctl to avoiii
condition by a suitable change in the prfiportioiis of the mixln
All the same, devitrification occurs in the case of almost all gL
when they are muintfiined for a long time at a temporatiu-e neiir
point of aoftuning, but with good glass the process Uikoa plare
extreme slowness.

Whilst alkali silicate is fairly readily dissolved by water, glaail
very resistant to this. It iis attacked least of all liy acid Rolatw)
pure water attacks it more strongly, and alkaline aidutions
strongly (;f all. By exposure for some time to the action of sb
the surface of glass vessels becomes leas easily attacked. Moreove
the resistance of the glass dojienda very largely od it* eomp)8iticinJ
it is all the less the poorer the glass is in silicic acid and the richer
is in alkalis. Further, the remarkable behaviour has l>een discnver
that glas-s which contains [lotash or soda itlinie, is much more rcsista
than glass which contains both alkalis together.

* By reason of the inclination towards economy of fuel, it
formerly become a custom in glass-works to manufacture a re&thljj
fusible glass, rich in alkali, so that the liad and small resistant
actor of such ghisses became a source of distress. The sci
investigationa which were, in consequence carried out, .sinnie of Wfi
have been mentioned above, at OTioe led to a suitable udjiistment
the factors which must be taken into account for maiiufuctiir
inu-poaes, and at the present time there is produced at many

CALUIUM

537

iiilly At JeoH, a glass for Jipiiaratus which ia considerahly

qiialitv to the hest sorts of ^Hass jirevioualy made.

action of watur on giAsa cou^Ists in free alkftli and iUkali

potstung into soliilfoii, a hydratcd silicjitt; contaiiiiug less alkuli

left. This action increases very mpidly with rising temperatiiro,

)ve 20f> HO glasa withstands thi? action of water.

manufiiciure of ijlasa, one starts ivith silicon dioxide (quartz

Msium or scxliuin cJirbooatf, ntid talciiitn cnrkmate. Tlio

Its, mixed in the profwr proportion -i, me tir.^t maintained for

tau! at a modei'ate red heat ; the silicates are theit'by formed,

fusion, only sintering, occurs. This is done in order that tho

dioxide may estape without the mass being thrown out of the

by the evolution of gas. The "frit" is then fused at a higher

tore, «nd is maintained at such a temperature for a sufliciently

[Ume to allow the gas bubbles to escape, anil the undissohW

of the mass to sink to the bottom.
If thf glass is to be worked up by [jonrin^ into nionhb, it may be
ia the above condition of a thin liquid. Generally, however, the
ig ''blown," and for that fturpose it must be rendered more
by lowering the temperature. The blowing of glass is a
ling of it with the help of mrfitre femkm. A certain amount of
iquid glass la taken ttp with an iron tnlie, the "blow-pipe," and
up like a soap-hnbble. The fundamental form which is
is tbcrpfore a holhtw syihere ; under the action of gravity, of
il force, and especially by suitably heating and cooling
piirts of the object, rery various forma can Ik) prmluced.
^or many pieces of apparatus, especially when small and compli-
the glass is worked bf/arr (fii- hhu-^piju; after it has been brought
hr form of tnln-s of varioiiti thirkness sind %vidtli in the glass-
Th(«e lubes are obtained by fii-st blowing a built, then (using
>n ro*l to a point diametrically op|)OHite to the blow-pipe and
ly separating the two points of attachment from one another. A
h'RgatiKl ellipsoid is formed, the middle portion of which does
Seviate materially from a cylinder. In working before the blow-
the lame aids are etnploj'ed as in the works, viz. surface tension
qiitable heating.
Moulder! objects must be "annealed," and this must be all the
carefrdly done the thicker and larger these objects are. The
fcling consi.its in allowing the temperature of the glass to sink
very slowly, Quickly cooled gbis-s contains internal strains,
the following manner. In rapid cooling, a low tcra-
>n established at the surface, and the outermost layer
the interior ia still very hot. The external voluraif of
lump corresponds, therefore, to the volume [w^ssessed by the
lit4*n<>r jKirtion at the high temperature ; when the mass has become
,CuUi, the interior tends to contract, nnd thereby exerts on the

■

522

PRINCIPLES OF INORGANIC CHEMISTRY

partictil»r, it is in*lepeix<iertt of the jiroportifnis in which the two
substiinces, cakiuui c-arljunate ami lime, aro presfiit ; it is also
pendent of the relative amounts of the solid ami gaBOfiiis phiisea.

* This follows as a necessary conseqtienet; from the pbaM
There are two components, lime and tarlKHi dioxide, frcmi whidi
the phasus present can be ooniiMjnnded. Since there are three pf
present, viz. carbon dioxide, lime, and calcium carlwnate, there i«
nnr ilcfjnf of ftrfiiom, i,i?. to each tempemture there corres]
perfectly definite pressure, and the amounts of the phases ha
JnHiienco.

* The same follows from the law of mass attitjn. If we call
eoiu-entnition of carbonate, oxide, and wirboji <lioxitle v, I,
resjjt^ctively, we obtain the equation l.d = k.r, in which f:, the equilil
constant, is a fnnction of the toraperature. In this equation, ho'
the concentrations of the solid mibstances, «' and /, are consUuit,''
consequently il must be a function only of the temperature.

As an examination of the table shows, the "burning" of lime
mere heating cannot be carried out under a teni{>erature of 812",
it is not till this temperature that the pressure of the atrboii dj
reaches one atmosphere and the escape of gas ia assured. Since,
ever, this equilibrium depends not on the absohite preasuro but
on the jjai-tial presmire of the carlwn dioxide, the dpfompositioa
lie carried out at a niui-h lon-er temperature by keeping the
pressure of the carbon dioxide sutlicienLly low. This can bo doM
allownng atjother gas, most simply air, to stream over the healed
boniile ; at each moment, then, there escapes (at most) so much
dioxide that the partial pressiu'o corresponding to the particular
jierature is estjihlished.

The great similarity which this phenomenon beare to that of fh
boiling and e;a]ioration of volatile liquids, is easily seen. The U»i
peraturc of 81 2 is, so to say, the boiling jwiini of calcium carbonate.

The use of Hme for iimrlar, which has ali'widy been mcntioncil scvenl
times, depends on the converse change into calcium cjirbonatc. Morttf
is a mixture of lime, sand, and water j in using Jt, the stone* which
have to be cemented together are moistened with water, a layer of
mortar is introduced between them, and the whcde is left to ll*
influence of the atniosphei'e. By means of the carljon dioxide whidl
the latter contains, the ciUcium hydroxide ia slowly converted inlocM"
bonate, water being thereby set free : Ca(OII)^ + CO^ = CaCO,, + H.O.
The crystids of carbonate, which are slowly fonne*!, unite with «t
another and pasa partly into the pores of the fitonea, the solubility i
the lime enabling a certain, although small, amount of it to get in ther«
In this way the well-known fimi cementing together is gradually pro
duced, and liecomes firmer as time goes on, since even in very oil
mortar there is usually a cerUiin amount of hydroxide present.

The fact that miter is set free in the hartlening of mortar under th

CHAPTER XXIV

HAfiKBSttTM

15- GeneraL — Magneaium bears the same relation to calcium aa
dues to potassium. This relation tiiuls t'xpression iiol otily
ic values of the tomhining weights, but jvlso in ihe similan'ties
le otbtjr meiuljera of the group. This is particularly w«tl seen in
tb;»t raagiiesium is of nntre fre<|uent occurrence tha» calciura,
I, in its properties, it dlffeis fmni OAlcium more than lh<? latter
fr<»ra the corresponding elements of higher combining weight,
tiiini anil birium.
at an elementary metal is present in the nuv^gnesiiim siilt, was
Lil by D«vy aa indubitable from the time that the corresponding
lima recognised in the casie of potassium and sodium. Bnnsen,
cr, was the first to prepare the met;d iti^elf. He obtained it by
iWtrolysia of the fused chloride.
The «k«ctrulysis can be performed in the lecture I>y employ-
earufdlite as electi-olytt; and using the _ ,

represented in Fig. 1 1 4. The partition
prolongation of the crucible nro of
mill-biMtn], the cathode is. a, piece of
wire, an<l the anode a thin arc-carbon. The
h of the cunent is about 3-10 amperes.
agnesium is now inanufacture^l in very
amoiiui by electrolysia, and is used foi*
purposes. It is a white., rather tough
■etal, which keeps fairly well in the air : it is
•fiurely Ntinclced by cold watijr, but in boiling
*Wer it slowly evolves hydrogen. In dilute
•6d9 it very rapidly dissolves, with energetic evohition of hydrogen,
^t melts at about 7^0". and volatilises at a bright white-heat.

Oeat«d in the air, niagne^^ium burns with a very bright, white
flttBc, which is largely marlft im: of. For example, instantaneous
pfas can be easily taken by magnesium light. For this
magnesiuni ie used in powder form, and is either blown
fi.JO

Km. IH.

528

PRINCIPLES OF INORGANIC CHEMISTRY

carljoiiiitc which is fnriued has, hy reasiiti of its aliglit aoltibilitr, i
action on free iodine, wiiercjis ]M>t<'isBium carbonate would partly cuiif
free iodine into iodide (tnd iodcite, i.e. would to a. certain extent
the fortnation of free iodine,

503. Calcium. Fluoride.— Unlike the other halogen coiuf
of calcium, eitldimi jlwiridt', CaF^ is very difficultly soluble in
The salt forma a widely distributed mineral which is known by
name of fimr-sjutr - it crysttUUses in cubes and in other fbrma of
regular system, is colourless atid transjMJ'ent iu the pure aUiie, 1
lAving to the presenL-e of impurities, is generally coloiu'od in vt
bright tints.

The name fliior-spiii' is denved from its application in metidlur
work for rendering the slags which are theru formed, readily fiuih
This action depends on the general fact that the freeiin^ fwini oTj
liquid is depressed hy the solution in it of fnreign subetances ; itj
course, of no im]Kirtance for this action whether the freezing
at 0 or at 1000 . The clement flnorine, also, haa received its
on accoinit of its preparsttion from Huor-spar.

* Another niime which is coiniected with this l&jimresfenct, i
is used to designate the property possessed by certain Buhstancci^
changing incident light into light of (generally) greator wave-le
This property was first investigated with some degree of thoroilgll
in the case of certain kinds of Hnor-spar, but the property is »
freijuent one, and is more stronHly developed in some other «a\stb
than Duor-spar

Fluor-sjmr is the most important starting substance for olM
hydrofluoric acid and the other fluorine compounds. Even
present time large quantities of it are used dii-ectly for the puqioaei
etching glass ; the salt is mixed with concentrated siilphiunc
the articles to be etched are exposed to the action of the \a\
hydiolluoric acid which sire evolvetl.

504. Calcium Nitrate, Ca(NO.,)„, is being luiceasingly for
through the activity of the nitrifying bacteria (p. 467) in the soil,)
calcium is the most widely distributed of the sait-forming ele
which have here to be taken into account. In locnlitiee where
formation of nitrate is aliUndant, such aa in the neighbourhood of i
housos, the anhydrous suit sometimes crystallises out during
weiUhcr un the istotiG walla in the form of thin needles which hAlj
alnioHt the appearance of mould. As a rule, iin great accunudation i
the salt occurs in the soil, since the nitititea formed are at oocc
up l.*y plants.

The pure salt is %'ery soluble in water, and, at mc^liiuti tcmj:
tnres, crystidlises with 4H2O. Iij also, is capable of forming a
largo ntmdjcr of diflcrent hydmtcs.

505. Calcium Sulphate, t'aWt^, is difficultly soluble in water ;^
occurs very vvidoly distributed in nature, and, after calcium uirlHin

CALCIUM

529

"e most abundant salt of cak-ium. It occurs in two forms. It
.-8 must frequently as <fi/pmm, in moiioclinic, sometimes very large

~|f'anspai-ent crystals with two moles of watet of cryat^ilUsatioti ;
lore raralj" as anhjjnk, in imhy (Irons, rhomUic ci'yatjiLs. The

"3jlity of these two forma is different, gypsum being more ditiicultly

Kthau anhyilrite. In tlie presence of water, therefore, the latter
less stable form ami changes into gypsum ; in thia case, also,
sence of a " nucleus '' of the more stable form hajs an ©ssential
^«nce on the process.
S'he .solnbility of gypsum amounts to about i gm, per litre ; aa the

iraturc rises, the solubility first increases, reaches a maximum at
Kd then di'treasi'.^. On being heated to 120", gypsum loses fths
water of cryisUlliHation,' »nd the transpt»rent crystals art thereby
' «rtcd into a ehalk-white powder, which has a manifold application
Sr ths name of jilitnter oj Paris. Thia depends on the fact that the
c3er again tidtes up its water of crystalli-^tion in contact with water ;
long needles of the crystallised gypsum are thereby again formed,
these, intergrovcing with one another, form a compact mass. This
serial is miMle use of for moulding objects for uats and works of art,
Jjlastering walls, for bandages in snrgery, etc. The hardening of,
&er of Paris which hitw been alaketl with water tjikes place in abouM
UBTter of an hour, and is accompanied by a feeble but appreciable
cif tetiiperattirc.

■* Phiiskr of Paris is a chemical compound, a hemilii/tlriite, 2t,!a80^,
>, which can be obt^iined in ci'yatals by allowing ordinary gypsum to
Ki with concentrated nitric acid and then evaporating off the htter.

* If gypsum is heated above 300°, it loses all its water, and no
^er sets with water. It is then said to be " dead Immf." In thia
tlition it is prn1»ably the siimc .is the natural anhydrite, which also
IS not combine with \^'ater in mefisurable time. If, however, gypsum
lehydrated at a low tempcraLirre over sulphuric acid, it can part with

jta Mater of crystallisation without losing its power of setting.
» peculiar difference in behaviour is probably due to the presence,
gypsiun dehydrated at low temperatures, of "nuclei," or traces of
lecomposcil hyilrale, which in the case of deiwl Inirnt gypsum have
n destroy I'd l)y the high temperature employed.

* The fiillowiiig experiment illustrates this view. If effloresced
iilwr's salt, in which " nuclei " are still present (p. 493), is mixed
h a little water, the mixture at once hardens to a solid mass of
aber'a salt ; but if the powder is previously heated, bo thjit the
lei are destroyed, and is then mixed with water, avoiding the
oduction of nuclei from without, no solidification occurs, but a past'
>rmed consisting of a saturated solution of the anhydrous salt al
ii undissolved substance.

The vBjjour presiure ot the vrster of (.Tyttallisatioii HmomiU to ouu at^'
, b«t llic teiii|jfiaturc iim-rt lie rai.wd to l-Q" to obtoiti a rapid <rB™in|)OH\^

542

PEINCIPLES OF INOBGANIC CHEMISTRY

by heating without undergoing decomposition, for it loses hy
chlonde, and magnesium oxido or a liftsic chloride is formed ; Algtlj
H.,0 = MgO+ 2HCI. This refvction is made usi; of on the Wge
far obtaining hydrochloric acid ; in receni times this h&^ become
greater importance from the fact that the formerly very ahum
source of hydrochloric acid constituted by the Le Blanc method
matmfacturing stxla is beginuiiig to fail. For tbia reason ma^flrfii
used even iu those alkali v^'orks which use the ammonia jirocfsi
the decomposition of the ainmoinum chloride which is forrued (i>.
because raagneaiuni chloride can be much more easily decom
uteiuii th»Ji Ciileiiuu chloride.

Magnesium chloride forms double salts with potasjsium or ammonv
chloride, of M-hich that with potsiasium chloride, MgCl„.KCI.C
called cartudlik, is the most important natuiuUy occurring pol
salt. It is found in large quantities at Sta^sfm't and in other |mi1>
Middle and North (.lerniany, and is separated into its c"om])onenl»
crystalUsiHion in the heat. The rather complic^ibed eqiiilibriuin
tions which exist in «ueh solutions, show that in geneml it is
expedient to work at high temperatiu-cs. For example, if earn;
heated without the addition of water, it Hfjuefies at 176 , and di
the greater part of the potassium chloride in the solid state ; on
down, almost all the rest of the potassium chloride erystalljsea
carnallite, and the magnCBium chlorirle remains in the mother li(

The greater part of the magnesium chloride produced in the
fricture of the potash salt finds no application at present, but is ti
into the river channels. It is to be deaired that somtf techi
practicable means may bo discovered to put an end Ut this,
various j^wints of view, detiimental waste.

5 1 9. Magneaium Sulphate, MgSO^, is a suliatance well kno'
under the name of Ejimmi ^itHft ; it has a bitter Uiste, due to magncsiun
It usually crysUdlisce in rhombic crystals with 7H„0. It can, bow
ever, occur in a number of other forms containing finin li'IfOU
iHjO, according to the temperature. Mono-hydrated n
phate occtira in the Stassfurt salts &% Idejseriie. Disaolvi'i
sulphate is a constituent of many mineral waters,* to which ii imjurti
a bitter taate, and which are known us magnesia waters. The anion
of Epsom salts in the intestine is quite similar to that of Glauber's sillt
but a specific action is also exerted.

Magnesium sulphate unitet^ with potasaium or ammonium ^ul^ibH
to foi-m double salts of the formula MgSO^ - K,SO, . 6HjO. The fxjt*
aiitm compound has the mineralogical name srhoenUf, and is lued «
potash manure.

520, By double salt there is understood a crystalline comjwWW
of several norm.il satt,'} with one ani^tiier. This combination en»J»

' Th« Dunic Kpsoru saiu i» dtrived from the uucumnM of this salt id tlii; miwi''
waters at EpBoni. — Tr.

MAGNESIUM

543

[y in the solid sitite, for the aqueous solmions of these
lt« exhibit exactly the =;inie relictions an hehnig tit tlir ions
ingle Siilt*, ami no reat'tioiia which could btlorig to any new
•.ict«nuiiiation of the mula.r weij^hts uf these iiqueoiis solu-
showiEi thai uo comhinaticm between thb single salts exists
procinble o.vlciit ; for the depression of the fiecdng point, for
is e«|ua.l t^* t\u' amii of the dt'prcssions whit-h mo eunsed by
le isnlls iiitder the sanit- eouditions.
holi]» in the tic^t in>itanct! for diJute aolution&. In coiicen-
lutions cerUtin pheuonteiia point ),o cunibiiiutioii existing in
« certain, although not hirgu, extent.
rule, diiuble wilts are Ima soluble in water than tht> com-
If the <lifii.Ti.inco is gieat, these double salts rKidily crystal-
Eron «»Iiitions in which the coniputietits are brtmgbt together. If,
Bver, th« solubilities are of the juiine order, it <le[HMMls on the teni-
lure aiid the relative amounts whether cryiibils of the doidile snll
I aue of the component* are ubiuiiied on concentnition. Iii some
a&lts can be obtain<?(l only front solutioutj which cuntuin a
of one uf the comfKinonU. This holds, for example, for
isadon of carnallite, which is formed only from solutions

large excess of magnesium chloride.

sails are genei'ally so constituted tba,t the gin<jle salts have

eitlier the cation or the anion, in common. Double salts with

It oitiontt and anions do indeed occur, but they fire more seldom.

lit of this nature is Itainite, KCl . MgSO^ . 3H^0, which occurs

Se <:'imf>l<x miis must ]>e distinguished from the double salts,
s the double salts, they can be formifl by the union of two simple

rm their reactions in aolutinti difl'er from those of the latter,
ebows that new substances (ions) are formed. Further iiifor-
Uun couctirutng this interesting class of compounds will be given
- -V M we conie to descHbe some complex salts [r. Chap, XXVIl.).
I and alkaline eiul.h ruetalis do not form any etmiplex cations.
jilii.ns mi/Zuffs, also, must bo distinguished from the
. - They arise by the crystal lisiit ion of isouiurphous snlis
nj a common solution ; thus, for example, a ntixtsi scdutiMii of
liidiuin and pjlaseinm sulphates, or of sodium i>u]ph»te and sodium
riute, dt>pottita crystals whose composition also appears as the sum of
e two components. These mixtures differ from the ilouble salts in
t Ucl tliat their corajwncnts are not, or are osdy accidentally, present
I «m»btning proportions, and in thf fact that t/ieir anHf>i>:*itk<n ctinVji
4ifi if'th the rompiiSilitm of ihr ^ilnikm from which they are
Their composition, therefore, cannot he represented by an
chemical formula, but only by one with itidetinite or con-
Bily varying coefficients. They are usually written in the form
^>jSO,, and Na^(S,Se)0,. 10H«U. the dements which replace one

54-i

PRINCIPLES OF INORGANIC CHEMISTRY

another in indefinite proportions being placed iji hrackets and sep

Tlie ilonhlc sjilts, however, arc rihiays foinpournlt'il in conibii
pro[>ortions, iind tuiti, therefoiti, be represented by a chemical forn
with definite, inti'gi-;»l coetlicieiit^.

521. Magnesium Carbonate, MgCO^, ia a salt veiy chifictiW

soluble in water, which oceurs in rsatnre in large masses. As ;i mine
it is calhai ituf;fiu'.4tt, and crystallises ifi rhornbohudra wliich are is
phoius with thiisu of calo-spar.

When atjiiuoiLs sfdutioiis tontainiEJg magnesion and curbatiion ;
mixed, a white, j^elatitioua precipiUite is deposited, and carbon dio
is evolved at the same time. This prt'cipitjite is not pure magnfl
ttiihoriat*.', but a varying mixture of ciirboiiatc and hydroxide.
higher the teni])uratur« and the j^eater the dilution, ilie greater it I
aiiiuiint of hydroxide and the less that of the carbonate contained
thu precipiCatJi', Washed with Avat^ir and dried at a fow teinperniii
this hiisic niagnesinm carbonate ia placed on the market in the form I
a light and loose pusrder, and is used iti medicine as a mild alkali.
is called nuiiiHfisia alba.

* The cause of this reaction is found in the hi/ihvl_i/j:i.< which
carbonates undergo, and in the small sohibility of magnesium hydroxiJa
In the aqueous solutions of calcium carbfnuite, also, hyilmlysis occur
and the ions HC'O.,' and OH' are formed from carbanioji, CO/,
the action of the water, Since, however, calcium hydroxide is
more soluble than tlie carbonate, the solubility product of the fo
is never reached, in spite of the presence of hydroxy! ; and altlio
the aobitioti reacts alltalirie, it deposits no hydroxide. In the
way, when the ions Ca", CO.,", HCO^', and OH' come together,
happens in the precipitation of a calcium salt with a soluble carln
the sohihiliiy product of the calcium i:arbon:it€ is much sooner re
than that of the hydro.vide ; the precipitate, therefore, in spite ofi
hydrolysis which occurs, consista of normal carbonate. On tlie olh
hand, in the caae of magnesium, the solubility product of the hydroiidd
iii, under such conditions, reached about the same time as that of I
cai'l lonato.

The normal carbonate can be prepared from the basic salt by :
peiidinj; the latter in water and passing in carbon dio.vide. AiU
some time crystjUline crusts of the hydrate, MgCO^ + 3H.,(.), w*!
formed. On being treated with much water, especially in the biutj
it again passes into the basic hydrate.

Magnesium carbonate forms various double salts with the ilkalfl
carbo[iates. One of those, MgCO,. KHCO., . 4H„0, ia deposited Triffl]
carbon dioxide, under pre^isure, is passed into a solution of potassiuBil
chloride containing magnesium carbonate in suspension ; magne
c)doride is formed at the same time and remains in solution,
this double sJilt is treated with steam under presaurei, it dw;orop

av MAGNESIUM 547

d, except olivine, contain more silicon dioxide than corresponds to
e compoeition of an orthosilicate. They are distinguished l)y 1)eing
a peculiarly soft and easily worked nature, accompanied by a great
sstance to high temperature, and on this depend their applications.
hey are mostly fairly readily decomposed by sulphuric acid.

525. Blaj^eBiom Nitride. — Magnesium nitride, Mg^^X^, is ob-
jned as a yellowish, porous mass by heating metallic magnesium
> incandescence in nitrogen or ammonia gas. It is decomposed
ith energy by water, with formation of ammonia and ma<.'-
Miom hydroxide : MgjNj + GHjO = 3Mg(0H)., + 2NH3. In this way
unonia can be obtained from free nitrogen (p. 351); for practical
irposes, however, the method is still too expensive.

CHAPTER XXV

STRONTIUM, BARIUM, AND fiEKYLLlUlt

52G, Ceneral. — Allied ti* ealcium are two motalsof higher combiiui
weigiU whitbiire very simil^ir to calcium in many respecta, and whi
bear the same reliition to it. as ruliidiiim and csesium i\^^ to p»)ift«sir
Tli!^ relation finds fxpressioii not only in similar diffcrenceis of
combining weighis, but also in iaomorphiam, in the relative fi
of occurrciitti on thf earth's surface, and in many other respects.
general summary of theso points of agreement will he given at li
end of the book.

Thejje two metala are called Stronthim and Barium. They ant^
is true, much rarer than calcium, but cannot Itu di-signate*] m
elcmetit^ in the sam« senso as nibidium and cjssiuiti vait. On
contrary, they are of sufficiently frvqiiont occurrence lo allow of bd
being characterised as elements aa early as the eightennth cMitui:
(strontium in 1793 by Hope, barium in 1774 by Scheele), and
their com]iounds being applied for various purposes.

327. Strontium Ima the combining weight 87*6, and occnrt
nature tliiefly as i^Hljilmh' and cuifHjnak. Metallic strontium can
fairly readily obtained ]iy tlio electrolysis of the fuaed chloride; it«
alao bo obtained by preparing strontium amalgam by the action
sodium amalgam on a concentrated solution of strontium chloriiic,
xlifitilling oft' the mercnry. It is a yellownah, rather tough mot»l vhk
energetically rciicts with water even at raom teinjvetature,

Strontiimv forms oidy the diridehl ion Sr", whose s<j]ulioii«
eolourli'ss, and whoso heat of fomiatioii is 501 kj.

528. Strontium Oxide, SrO, is obtaim-d by heating thecarboiut
or, more easily, tbe nitrate. The dissociation of strontium carboiul
tjikcs place with much greater difficulty than in the case of ralcii
carbonate, i.e. at the same ti3m[icratui'e ita diaaoeiation pressure
considerably sm:dler (p. 621). ytrontiiun oxide unites witii wntw
form itrotdhim hijthvxide with great evohition of heat. Tin" l«U
can also he obtainod directly from the tarboriaie by heating this m
current of steam; the decomposition then occurs nutri' (M'""

XXV

STRONTIUM, BARIUM, AND BERYLLIUM 54?

; this aid. This is duo, on the one hand, to the fact that the

|ire*surP of the carbon dioxiile ia tliminishcd hy the steam

>22), ami, on the other hand, to the fact that in place of the oxide

is formed the hydroxide, which stflnds on a lower level.
>29, Strontium Hydroxide is more readily 8<jluble in water
Iciiiin hydroxide. Fi-om the hot sfittuated Bolution there are
i, on cooling, hydrated ctTsUils of the composition Sr(OH), •<-
The solution exhibits the properties of a strong txise, and the
linatifin of the electrical conductivity shows that there is a large
ree of dissociation into the ions Sr" and 20H'.
}30. Strontium Carbonate occurs as a mincrsil under the name
tittnile. This crystalUaea in forma of tho rhoanbjc syatem, which
f'isomorphous with thuso of aragonite (p. 520) ; a form correspond-
to calc-spar is nut knoi^i. When the ions Sr" and CO.," come
ber in af|ueoua solution, strontium earbonate is dejiosited as a
very difficidtly sohible precipitate, which soon pjissea into the
ftUine state.
|Rtrontianite is used \\» the initial substance in the preparation of
Br strontium com|Jounds, Other salts can be readily obtained from
(.carbonic acid can bo expelled hy almost all acids. In onier
tttrontianite into strontium hydroxide (an operation which
of importance on account of the use of the latter in the augar
industry), it can be heated in steam. It is also convertwl into
Itrontium oxide when heatetl with charcoal : SrCO., + C = SrO + 2C0.
This reaction is facilitated by water vapour : SrCO^ + C + H»0 =
JrtOH)j + 2C0 {vide mpra),

531. Strontium Sulphate, SrSO^, is a white salt which is very
Icultly soluble in wati.r ; it occurs naturally as f^ltdine (so-called
il^ frequently being of a blue colour, due to impurities),
mincnd crystallises in rhombic forma, and is isomorphons with
bjdrite. From aqueoiis solution it is obtained as a white pre-
ate when the ions Sr" and SO^" come tJ>gether. Its solubility
it at the litiiit uf what can be used in analysis ; when necessary,
tefore. the sohihility is reduced by the addition of alcohol,
la order to convert strontium .sulphate into other salts, it is
'rwiuotxl to strontium sulphide with charcoal: SrSO^ + 4C = S^S-s-
L'0; this can lie easily decomposed with acids. To prepare the
oxi<le from it, the sulphide is heated in a current of steam :
i^ 2HjO = Sr((OH),) + H.,S. By systematic crystallisation from
ous solution, also, the atJphiile can be decomposed, as in the case
[falcium (p. ."i-IO), into hydroxide, which crystallises out, and hydro-
liiidc, which remains in solution ; by boiling the solution sulpbur-
hy<lrogen can be expelled and the sejiaration can thus be
fttinueil.
?i52. Strontitim Nitrate, Sr(NOs)j, crystalUses anhydrous, and
lily 8oluble in water; it is used in p^Totechnics for making red

550

PRINCIPLES OF INORGANIC CHEMSTRY chaI

fire. For this purpose it is mixed with potHsdmn chlomu-
combustible siibstance, aulphur or charcoiil. Strontium hj*."; tin
perty of imparting a I'eii colour to flames, and bv this means it
Ijo roadily detected, aa the coloration also appears in the non-hr
^HB flame. The spectroBcopic decomposition of thU dazzling U^ht shi
it to be fairly coinplex ; a sharp blue line is the most chantcteristic.

533. Barium, Ba, has the cotnbining weight 137'4, and occi
naturally as sulphate and carl>onatc.

Mclallir liarium is of a whit« colour, melts at a red heat, Kiid
more energetically with water than strontium or cak-iiiin. We
here, therefore, a repetition of the same state of affaire as in thfl
of alkali metals, viz. the action with oxygen and oxygen compoiii
is more enorgetif the higher the combining weight of tbo motal.

Metallic barium is prepared by the same metho<ls as were gi'
for strontium. It has as yet not found any appHmtion whatever.

Biirium forma only the divalent ion IJa", which is coloiirlesa J
has a poisonon.s action on the organism. It can be rejMlily tK'terte
by means of the excoedingly difhcultly soluble precipitat<j which
yields with sulphaniuo, 80^".

534- Barium Oxide, BaO, is obtained most readily as a wlul
heavy, crysLiUino mass, by the decomposition of the nttn»te by hit
nitrogen peroxide and oxygen being evolved and barium oxide rcniaif^
iiig behind: 2Ba(NOy}2 = 2BaO + 4N0o + Oj. The tempeniturc
which baritxm caibonate loses its carbon dioxide in so high that it
not suitable for the preparation of the oxide.

The oxide unites with water, with the evolution of much heat,
form bitrium bt/ilroHih or kuyta, lJa(OH)„. This is still more readi
soluble in water than strontium hydroxide and, like the iatUr,
crystallises from it.s hot saturated solutions in large crystals wit
SH„0. A solution saturated at room temperature conUiins 37
cent hydroxide ; it is therefore about ^th normal (p. [91) with re«p«
to hydroxyl.

Baryta is used for vaHona piu-posea. It» dilute solution is tw
for the volumetric estiniation of acids (p, 189); for thia purpose il
specially .suitable fnmi the fact that it attacks glass much leas thia
corresponding solution of caustic poUish or stida, and because It o
never contain carbonate, from the tact that Ijarium carbonate is a vcr
difficultly soluble salt, and is therefore precipitated as soon asilfonni
Thia last circumstance is of importance, becjuise the presence of
bonic acid renders the reactions of alkalimetric indicaUirs indiftiaci
and therefore impairs the exactness of the determination. To preffi
the atmospheric carbon dioxide changing the titre of the solution, iJ
bottle rind burette used for baryta arc furnished with gnard-tui*
filled with soda lime, and are always kept connected with oncaiiotbeii
as is shown in Fig. 115. The burette is filled by sucking at the inJi«
rubber tube g and opening the clip b,

>NTIL'iM, BARIUM, AND BEUVLLIUM

551

is also used in ftiialytjcfi! chcniistry in cases whore it is

employ a strong busc, the est'css of which cah he siibse-

rcwJily removed. Thus ina^nesiuni is separated from potaa-

8«)dituii by preparing the

d adding excess of Iwiryta

'ation of these. All three

to are therijby convertetl into

ddea; that of Tiia<^iiesium is

tated, while those of the other

iilrmg with tlie excess of

renuiins in solution. If earbon

i la now jjasaed into tho boIu-

ium is pjiecipitateil as

after filtration, tliere

solution of the alkali

The precipitate consiats

m sulphate, barium carbonate,

gneaium bydroxiilo ', it is

with <liiute aulplniric jieid,

>j the magneeium hydroxide

into solution ae sulphate, and

it b»rimn is converted into

ie. Tlio two cat! be easily

UmI by filtration.

r maniifu'ituring purpoBes also,

GUI be simikrly employed. It hjis already been mentioned that

c polaab or uaustic sothi can be pi'cpared from the sulphates

baryta (p. 483).

e pre]iaratioii of baryta, barium sulj)hate is chieHy employed.

reduced U> sulphide by means of charcoal, and converted into

with steam (cf. the correspiondiiij; processes in the tuise of

from the solution of the sulphifle, also, the sulphur can

loved by boiling with a metJiUic oxide, f.ij. co]>per oxide : BaS +

a,0 ='lia(OH)^ -r CuS.

15. Barium Sulphate, baSO^, occurs fairly widely distributed
Bre m the mineral kfamj .y^rfr or htri/fe,^. Both these names are
iBion to tlie great density wiiich this compound, like all Ijaiiura
Unds, exhibits ; it amoiuits to 4 5, while that of most of the non-
ic minenUs u about -'i>,

lium sulphate crystallises in rhombic forme, and is isomorphous
nhydrite and celestine. It is formed in all eases where the ions
id .S(>/' come togethei-, and, as it is very difficultly soluble, it is
liately dejmsite*! aa a ivhite, heavy piecipitiitc. The use of
biu'ium >alt3, i.e. of barioii, for the detection and determination
ibanion, wlticli fallows from the above reaction, has already been
times mentioned.

552

PRINCIPLES OF INORGANIC CHEMISTRY en

Since sulphmic (aiii is a strong acid, other acids do not have i
gresit solvent, action on barium smlphate. Further, since bariiun
in no \v;iy p;Lss into other more complex ions, there is no soli
whereby Itariuni sulphate ciiii be rendered soluble in aflueciua Uqil
It can be dissolved only in eome unbstan^es which d& not have
ionising action, c.j?. concentrated fiuliJhuric ncid. So soon, however,
the ions are causetl to be formed by flilnttori with water, the barii
sulphiite is ftgjiin precipitated.

On iiccount of this resistance to chemical attack, the nstun
occurrinjtj heavy spiir, when cut in plates, is used in the manufaictllli
for lining iippai-atiis in which Btrong jicilIs are woi'ked with.
artificially prepared bai-iura sulphate is use<l m a pigment^ under
name pcrmunfrit whiie. It is prepared liy dissolving the natimi
occurring barium carlronate in hydrochluric acid, ftUfl precipitating t
clarified liquid with sulphuric acid. Hydrochloric iicid is rege
and cjin be useil for dissolving further ciuantitiea of wirhonate.

In onler to convert biii'ium aidphate into other barium com
it is reduced with charcoal to bariian suiphidi, which cttn he real
decomposed by acida with evolution of sulphuretted hydrogen. '.
fusion with excess of alkali carbonate it is converted into ffin
carliomUe ; the alkali sidphatfl which is formed can be removed 1*
washing.

536. Barium Carbonate, lJaCO.y occurs naturally, as frithrritf^
rhombic crystals which are isi>inorphous with aragonite and «ilnmi
anite. It is used us a convenient starting material for the ra&ni
factiu'e of other barium snlta, for which purpose the 8ul>st*ince
decomposed by acids. Its conversion into oxide by heating is no
practicalile, because the tetuperature of measurable dissociation
too high.

On bringing the ions Bn" and CO," together, barium carlwnal*
obtained as a whit* precipitate, readily aolulilo in almost all iwidi

In preparative chemistry, pure bnritini carlKiimte is very largel
vised for the prejjaration of the barium suits of the most varies! acidi
Thcsei mostly crj'stallise well, and can therefore bo easily freal in
impurities. Their mo.st importjint property is, however, that they »
suited for the preparation of (he free acid in aqueous solutinn, Utaus
they are all decomjwaed by Kutphuric acid, barium sulphate Iwia
thereby precipitiited, and the acid in question remaining free in sohl
tion. Examples of this have alrwidy been given (<t.ff. p. 215),

B37. Barium Chloride, BiCU, isobtaiiied by dissolving witbcrit
or biirium sulphide (from sulphate and charcoal) in hydrochloric acit
on concentrating the solutions, barium chlorido crystallises out
lustrous, heavy crystals with iH.^O, which become anhydrr.ug milj
a fairly high temperature. Unlike the chlorine compounds of tii
other metals of this group, barium chloride floes not losts bydrochlofll
ikcid on dehydration, but maintains its neutral reaction.

STRONTIUM, BAltlUM, AND BERYLLIUIVI 553

irium chloride is used in the lahoratory as a. reagent for the
ion and eettiontinn of stilpli.itiion,
^8. Barium Nitrate, Ba(N03).^ is a 8«lt which isnotabtimlantly
Id in wattT, and whtcli is employetl in analytical chemistry in
! trf bariimi chloriHo, when it is not dfsircd to introilnee rhloridion
• the solution. If froe nitric acid is added to a satnnited solution
ftbo ea\u a crystalline precipitate of Iwuiiun nitrate is soon deposited.
«une occurs when nitric acid is added to the solution of any other
salt.
m reaction is not especially peculiar to barium nitrate, Ijut de-
. on the increase of the nitranion by means of nitric acid and the
mdlng overstepping of the solubility product (p. 447) ; in the
of ViariuTii nitrate, however, the phenomenon ia specially well
kcd, l^ei-Atise this salt stfinds at the limit of those which are
xted as soluble (100 parts of water dissolve alniut 9 pwits of
'nit at 18'), and Ite solubility product in therefoi'e easily exceeded.
Iteginner is sometimes deceived by this precipitate, mistjiking it
fcr btiriiim sulphate ; the distinctly crystalline nature and the solu-
lity ifi pure water, after pouring oft" the mother liquor, are, howe\er,
pent to distinguish them,
irium nitrate is used in pyrotechnics for the preparation of green
The green flatnc-coloration ia prorhieed also in a non-himinous
p» flame, especially when the specimen conUuning lairiuin is moietened
tiih hydrochloric acid. On spectroscopic examination it yields a
' ■ ' 1 spectrum, which is charaeterised by a sharp yetlow-

tp, although le«s bright, green- blue line, along with

5r.it Barium Peroxide, BaO,„ is obtained as a white powder by
ting harium oxide to a temperature between 450" and 550° in a
etit of oxygen. At a higher temperature it again loses oxygen,
ilh« eipiilihrium between the si)lJ<l oxide and peroxide and the
:i'r(, 13 governed by exactly the same laws as the dissocia-
■ iiu car!>onate (p. 521).
Bwiuni peroxide ia important as being the most convenient starting
■Jwtance for the prcjiaration of hydrogen peroxide (p. 156). For
Ail purpcwe it is treated with dilute acid, whereby the reaction occurs :
B«OjT 2H" = Bji" + H,jOjj. The anion of the acid forms the corre-
ipomliTig barium salt, c/7" BaOj + 2HC! = RtCl^ + H.p^.

It would ap[jareMtly !« moat suitid»le to caiTy out this reaction

sulphuric ui'id, because the barium sulphate, being practically

iable, would be deposited and leave a pure Bolutinn of hydrogen

ie. This, however, cannot Iw done, since sulphuric acid scarcely

SUckd the anhydrous haritim peroxide. The reaction, however,

"""''■ occurs with hydrochloric acid, and the operation is carried out

■»a. A certain amount of hydrochloric acid is saturated with

> the barion is precipiuvted with sulphuric acid, and the aolu-

554

PRINCIPLES OF INORGANIC CHEMISTRY

tioti, which now contains liyilrochloric ticirl, is allowc*i W act on
portions of puroxide. Tlu'ae alternate oix^nit irms are continii«l
sufficient hydrogen [wroxide has accumulated in tbe solution,
chloi'iilioti is then precipitated by the addition of silver sulphate,
the snlphanjon thereby introduced is removed with Itaryta.

* Another methoii is to first iidd a small quantity of baryta
to tbe hydrochloric acid solution of peroxide in order to remove
metallic oxides ])rc3cnt as impurities, and then to preripiUte
filtered liiiuid with luiryfai. Barium peroxide agiiin seimral'es out ;
however, in the form of a crystalline hydrate, which can l>c
deroniiKtsed with sulphuric acid. The hydi-ate is freed from
banum chloride present by washing, and is preserved for use in
moist state, since on 1>eing dried it agfiin becomes more difficu
decomposable. The composition of the hydrate is BaO^. SH^U.

ri4rO. BeryUiuin, — Beryllium occupies the same position
the alkaline earth metjvls as lithium does among the alkali metiik
combining weight is tbe smallest, and its siniilanty to the otli^
elements of the group is least. Its properties exhibit a JlA
tendency towartis the next group, that of the eaitb nietiiU, The (
bining weight of berylfiom amounts to 9'1.

Mtinllic biri/llittui rati be prepared by electrolysis, by the reddo
of the oxide with magncsinni, of the chloride with swliuni, and ii<
ways. It is a white metal, which is still more stable to moist airl
magnesium, and decompoJica water only slowly even when heated,
ia readily dissolved by dilute acids, with evolution of hydrogen,!
passes thereby into the ionic state.

Besides the tyiJical divalent ion Be", beryllium also forms otherio
contiiining oxygen ; these will l>e discussed later. Of the metals hithr:
considered, it is the first thai is cajwble of forming diflcrcnl ions.

BcrijUmi, Be", ia colourless and is distinguished by a cons]iicu"iu^j]
sweet taste. This fact procurwl for the element the passing naiae
'//kcimwot {still occasionally used in France and England); tlie im
beryllium is derived from that of its most important naturally oc<W"l
riJig compound, Ix't-yl, which is a silicate containing aluminium.

BeiylHon forms various salts, of which the chlonde, BeCl,„ajjd
sulfdiatc, BcSO^, arc the best known. They ai'c both soluble iii^
and the solutions react acid. This is due to incipient hydrolysis,!
beryllium hydroxide is u weak base,

Ben/Ilium hidroxide^ Be(0H)2, ia obtained as a white, gelatine
precipitiite on bringing beryllion and hj'droxidion together; il is nol
measurably soluble in water, and has )io l>asic reaction. It dis.solve«i
acids, with formation of beryllium salts, and on being heiited is con
verted into a white powder of ber^dlium Cfxidc.

Beryllium hydroxide dissolves in caustic potash or caustic stx
Since these bases, by reason of their containing liydroxyl, should, :
accordance with well-known principles, diminish the solubility of her

STKONTIUM, BAEIUM, AND BERYLLIUM 555

Iiroxide, this contnuliction ro<jiiiros ait oxplftimtion. This is
by tho fact tliat the comiwund BcO^Hj can ajilit oft" liydrioii
1 bebave like a very weak acid. Acconiiiigly, it gives the two ions
eOj' and BeO^" (jiiat its carbonic aciti gives the ions HCO^' and
,'^ aiid it is these and not Iwryllion, Be", that are present in the
■ioD ill iniestioa. The wjmpound is also obtained by fusing beryl-
^ydroxidc with caustic main, and dissolving the melt in water.
Kthis aikuline Hohition is allowed to stand a long time, or if it is
■ to boiling, nlm^wt all the beryllium hydroxide is precipitated.
i qttc^itioii now arises why the chemiail equilil>rium, which hail pre-
Baly existed, is now disturbed, aiucc no new substance has been
led The answer is to the effect that the beryllium hydroxide
idl is preeipitaltitl is a different, and indeed a more attvble and
i iolnble, form uf the hydroxidu thiiu the freshly precipitated form
tdt is Boluhlii in alkalis. In other woids, the newly prepared sohi-
I is suf>rr»nhtntUii with reajwct to the wru'f stafilc fimii of the
Iroxide, and therefore cannot continue to exist when the latter form
IMent. Since this form is not present in the newly prej>ai'ed
^B, the precipitation can commence only after the fii-st tracea of
tm been formed. At the ordinary temperature this cwcurs slowly,
({aickiy when heated.

541. SllDimary. — The properties of the corresponding compounds

be elements of the second group change in the same order a.s the

.btoitig weights, so that the relations which here prevail c«n be

IjF impressed on the memory by making the sense clear in which

ehjinge tsikcs place. In the following t.ible the properties which

liecn considered are given, and the arrows which are added indi-

whether the Aaluea of these increase (-?-} or decrease {-«f-) with

BMiitg combining weight.

or THE AlKALIXK EaiITH KktALS and of TUEIIl C0MlKJ17!irDS

Cowbtning weight ...,.,,, -^
KaactiTily of the metal ,......->-

Deiurity of tbe elements anil of the corresiponJing i:i}iii[iouiiila ->
IWMtc iicorwrties oT tlie liytlrosiJeft ..... -^

Sill ability of the hyiIro.\iiiee -^^

Solabililj of the halogen compouuds, iiitrates, nud s^ilitliatei ^

CHAPTER XXVI

ALUMINIUM AND THE OTUER KARTlt METAlS

542. Greneral. — The group of the e^irth metals, to which we now t^
ig characterised by the fact that the elements contained in it f
trimkiit ailvjiis. The pirallelism which exists between th<3 eleme
of the first and second groups in respect of combining weight*
general character, is also found here, with, however, an
diflorence. Of the elements of the thii-d grouj), there is
which occurs frequently in the earth's crust ; but this one is
in great abundance. All the other elements are exceedingly
and their properties and compounds are therefore comjiaratively lib
known.

The dindnution of the reivctivity of the metal with oxygen
water, which was met with in some of the members of the
[group, is found here in a still higher degree, so that ahrmnivm,
[inost important element of the third group, is a metid which is at
Ipreseni day applied in the arts, and as such plays a not iiieoiisidersh
Irdle. At the sJimo time, the Imsic properties of tlio hydroxides,
weakening of which wan also indicated in the secoarl group, hti
become so small that there is no strong base in this grouii. As iMUl
it is in the cjiae of the elements with small combining weight thattl
effect is moat conspicuous ; in the case of the first element which rai
be iudiided in this group, viz. bitrtm, the complete revei'sal has aJ|^fl
taken place, for this element has entirely lost its rtieUillic clu^^|
and foiTOs an acid hydroxifle, boric acid (p. 435).

The elements belonging to this group, together with their combi
ing weights, are : —

Boron (ll'O), aluminium (27'1), scandium (441), yttrium (89
lanthaniuu {138-9), etc, ytterbium (ITS). With regard to these*
woukl make the following remarks.

AVhile the combining weights from toron to lanthaniun correspon
to thoae of the metals lithium to cH-sinm nnd horyllinm to liariui
we have here a higher member, ytterl»ium. with a combining weigl
173, which is not represented in the Hret two groups. It may

&5S

jt^^u^ai

Ixxn ALUMINIUM AND OTHER EARTH METALS 557

thai sucli repreaentotivGs do exist, but have not yet been

'Fiirther, ail etc, has been inserted after Imithanum. This signifies

there exist at this point not ^tue element but a number of elements

rh are all very close to on© another, and have therefore an almost

claim to this position. This occurrence of several element* with

differences recalls the occurrence of numerous small pknetary

]itm ai a fwin of the solar system where, by analogy, one would

fe exjiected a large planet.

543. Almninium, — Of all the light metals, aluminium U the

widely diotributed on the earth'a surface. It forms a eonstitueut

(ftlmost all mfdijllint silknte rocks; and of the secondary formations,

•A«y* and shtU formatiuns are fomied from fihimiiiium siltwite. A

Bwltxlge of the compounds uf this metal, iheiofore, extends back as

[MS chemical knowledj^e at all can be traced.

From the time of the discovery of the alkali metala, it was regarded

lubitable that a mrtal must he cont-uitied in clay. Wiihler, how-

VA8 the first to obtain metallic aluminium by the action of

on the chloride. The method of separating the element from

|r<)m|M3nnd!? by Aftirvh/m was given bv liunaen (1854).

The tiiune aluminium is derived from tdum [<ilumen), liecause

liiiium is conciined in this long-known salt.

At the present day, aluminium ia pi o]>ated on a very large scale

ihe electrolysis of its oxide. The oxide is fused by the heat

l«toped by the passage of the electric cunent, the iduminium goes

[the cathode, and the oxygon which separates at the atiodc combineB

Vh the charcoal, of which the anode consists, to form carbon mon-

To facilitate the fusion, the electrolytic vessel also contains

er compoiincU of altmiiuium, cc/, ciyolite (riik in/id) ; since oxygen

more readily separulod than fluorine (which la the corresponding

W coiisiitiient of cryolite), this addition does not alter the chemical

cUon, ami only aluminium oxide requires to be thrown in to replace

I wed up material.

}Idti}!if tthtmiaium is a white, somewhat bluish metal which

kinii tolerabiy unchanged in the air. This is due to the fact that

tly becomes covered with an invisible, thin, and firmly adhering

rof aliuniniimi oxide, which protects the metal underneath like a

tiish. It mells at TOO , and can hv Iioth cast and mechanically

ought into the shape desired, as it is not hard and iss very ductile.

liiu, thm wire and very thin foil, like gold-leaf and silver-leaf, can

le ; the Litter is greatly used for " silvering,*' atnce sidphiu-oiis

I do not bi;icken it. Aluminium is a good conductor for heat and

city.

Oh account of it« lightne-ss (density = 27), ita silver-like lustre, and

(lurabilily in the air, aluminium, especially since the electrolytic

tlhod baa rendered it cheap, has become greatly used for ordinary

558

PRINCIPLES OF INOKGANIC CHEMISTKY

utensils, )jnt it does not seem hitherto to huve Iwen received (
entire favour. This is perhaps to be accounted for hy the fact I
although it resists the action of pure water, it ia rather t.lm
attacked by siilt solutions of all kinds. Further, the oxidation of
metal generally occurs in spot«, so that holes are there formed w
can be repiiired only with difficulty. Its resistance to mechan
action also is small.

* When Hluminium is alloyed with mfrcimj, it app'ars to usi
quite different properties. It ia amalgamated by rubbiug its sjir
with a mercury salt, e.'j. mercuric chloride, with some press-ure, '
parts which were at tii'st bright o» account of the mercury, iratn
ately become dull, and a moss-tike growth of aluminium hydro]
arises from them. This phenomenon is explained by the ttct t
although the protecting layer of oxifle is formed at the amalgaim
parts, the coating does not adhci"e, on account of tlie liiiuid natrnn
these, and the oxidation, therefore, pursues its course. It 1;; antt
the mercury produces an increased resietivity of the aluminitun
thing which is theoretically imposaiblo), but the rod ehemiad actti
of the aluminium is allowed free Hcoi>e to exert itself.

* The amalgamated aluminium is employed as a leduciiiga^
On account of this behaviour, objects made of aluminium nnwt
carefully proteetetl from contact with mercury.

While, oven at corafwratively hiyh temperatures, massive alumini
is only superfiuially and inappreciably attacked by oxygen, the /i
dicidfil nietid burns with a Iirilliant light at a red heat. This caii
shown by holding aluminium foil in the flamti, or by blowing fin
divided metal, aneh as is used in the form of aluminium broj
through the flame. It takes fire, however, with greater ditKcislty tJ
magnesiiuu.

Aluminium dissolves in dilut<3 hydrochloric and sulphuric M
with energetic evolution of hydrogen. In nitric acid it nmt
becomes passive, Le. becomes coated with a Inyei- which is not attacl
by the aeid, and then remains unchanged. Further, aiumitu'tim rea«
dissolves ill a solution of c<m.stic potash or soda, with evolution
hydrogen. Thia is due to the formation from the aluminium of
anion containing oxj'gen ■ we shall return t<i this later Ui'it '"/
Sidt solutions, also, especially solutions of ammonium salts, diiwfl
the metal fairly readily.

Alumliiiuni forais alloys with various metals, and some of these
technically valuable. Tiiey will be mentioned under the i-espod
metjd.5. ^Ve would oidy mention here that an alloy (magiuiliuni)
lieen prepared from aiuiuiniuni and magnesium, which is stated;
have technically valuublo properties, and to be stable in the air. I

544. AltuniniOD. — Aluminium foiTira a single, elementary. liivaJl
ion, Al'" ; it can further act as a constituent of complex ions. '

Alumiuion ia colourless, and its salt« are for the most part solul

AL.UM1N1UJI AND OTHER EARTH METALS

559

ive an astringeitt taste, but have othei'wise no gi'Cat physio-

action. Since uliirniniuni hydroxide is h weiik liase, nil the

ahimiiiiutii are hijihvhjtifalhj tUssocmlnl to »n uppreciiihle

aqueoiiH sohuioii, and diowforc react acid. In the case of

of tho strong acids, this hydruIyBis is alight ; in tho ease of

of trcak acids, howt-i er, it Ix'comes cotisidenible, especially

EC the ions of the other more frequently occurring light

altiniinion does not occur in me.isuralile amount in uatiual

It is -ittiKiiiited ant from the rock,s in ihe form of niuwiiiiam

(or alu/ttmiiint lii/rlyri'h; an exceedingly difficultly solubk' tom-
I which. thtTtfnre. dmis mtt juiss into solution.
&. Aluminiiim Hydroxide. — Jbimiulum /it/drmitk, Al{0H)5y
pecipitatetl ;vs a gelatinoiis, uncoloured precipitate from solutions
la^tiium Ktitt-, by the addition of a soluble base ; in the air it
> water, and when he.itod to r(?dnesa is converted into aluniinium
e, accofling to the eqiialion 2A](0H), = Al.,0., - 3H/),
41uiniixiuni hydi-oxide is practically insoluble in water, and is a
' we^k base. Since it contains tliree hydro-xyls, it can form three
alts, in which one, two, or three hydroxyls are replaced by
Salts in which unreplaced hydroxyl is still present ara called
//j!, coiTespondtug to the acid sjiUh which contain uni'cphiced
|ydri»gen. In geneiul, however, the kisic salts are nnicli less
ply chanictfrised than the acid ones; whereas the latter mostly
lis*,* vrdi, and can therefore bo easily prepared in the pure state,
■nioqjhoviB form predominates in the ease of the basic salts, whose
ition in the pure state is therefore difficult. For this rejison
rill, in the secjuel, generally not receive special description.
account of the slight development of bjisic properties in the
aluminium hydroxide, and ita exceedingly srnall solubility, it
jpitAtad even by very weak soluble bases, e.g. by ammouia,
prMtiuce of animoniimi salts. In this way it differs fi'om
rtlroxidea of the alkaline earth mctids, and can, thcrcfoic, be
'for tho se|>aration of aluminium from these, especially from
^esium.

CAUfltic pobtsh or soda of coniso also proeipitato aluminium hydrox-
iro the solntions of its ssilts. The hydroxide, however, readily
Irrs in an rj-cesf- of these substances, and forms clear solntions
jngly alkaline reaction. This is due to the fact that alununium
title can also act as an acid by splitting off hydrion from iU
cyl groups (»'Wf irt/rn).
This property of aluniinium hydroxide of acting as an acid, is the
B tfi»t metallic aluminium readily dissolves itt caustic {aitash or
-with evobuion of hydrogGU (|), 558). If such a solution and
le of aluminium in hydrochloric acid are prejiiu'eil, nnil the
lutioMS are mixed, aluminium hydroxide is precipitated, and

5()0

PRINCrPLES OF INORGANIC CHEMISTIiY

sodiunt cblortde remains in solution. The reaction is represent
the e<ju(Uioii NajAlOg -, AICI3 + 3H,0 = aNaCl + SA^OH),.
the reacting ions into account, we should write, AlOg'" + Al" + Sl
= 2Al(0H)y.

By loss of water, alurainiiim hydroxido can give rise to
anhydridea, which bear the same relation to one iinother as the 1
cJritles of phosphoric acid. According as one, two, or three con
ing weights of water are eliminated from two combining wwg
the hydroxide, there arc obtained, bcsiides Al(UH)^ the cocap
AljOf.H^, A10,H, and ALO.,.

All these compomida occur in natui'c : the normal hy<t
Al(OH)^ is hijdfonjiUite ; Al^Ojll^ (generally greatly conUuuin
with other substances) is Uiuxile ; AlOjH is dumpare ; and AUO, 1
carmulum,

Bauxik is of im|H)rtance as being the starting substaDce in
inanuf;ieturc of mctaJtic aluminium (p. 557). Ct/ntmhim is, on ace
of its hanlness, which ia nearly eqmil to that of diamond, an imp
mineral technically. It crystallises in rhoml>obodra, In it«
grained varieties, called tmntf, it is employed as a gi*intling niat*
for glass, steel, and other hard substances. TranajMrent coruiidu
coloured -blue by adiidxtnres, is valued as a geiu unilt^r the nM
supjthird : a red form, whose colour is due to a small amount
chromium, is called Ji('»y, and is also a vahuvble gem. Small and I
finely coloured rubios are used iis axle-bearings in watches and
metiauring instruments, where movement with as little friction
possible is reipured. Corundum, in all its forms, is very bttle m
ceptible to chemical influences, and it ia only ^rith dilticulty ihilitj
can be converted into soluble compounds by fusion with Cinistic 1
or acid sulphates.

5-iO. Aluminatea. — The compounds in which aluminium bydnt'J
ide oecuis as an acid, are c.Tilled alumiiuiffs. Since aluminium hj
ido contains three combining weights of hydrogen, it must be reg
as a tribasic aci(i ; atiice, however, it ia a very weiik acid, the uoroalj
comiionnds, in which all three hydrogens are replaced, are not aatjl
prejjare, and in anueous solution thoy decompose to a greater or Itfl
extent owing to hydrolysis,

* A aubslarice which ia capable of acting at the syimt* time '
acid and as base, can be only a uml- acid and base. Fur tiie
acti(m necessitates tlie presence of hydrion ; the biiaic action, llinti
hydro.xiilion. Tbe two kinds of ion, however, cannot bo [jTC*e<it^
iiKjftlKfr in any great concentration, since they would utnte to font I
water, which ia only very slightly dissociat^id. If, therefore^ an acid|
is strong, i.K. splits off much bydrion, it certainly carinftt split flff]
more than an exceedingly small amount of hj'dro.vidion, tlie amoiinM
of which is liraiteJ by the chemical equilibrium of the two ioui IB
water. The same holds for wesik bases.

ALUMIXIl'M AND OTHEK EARTH llETAUS

in ihe case of phosphoric acid, the aqueous soUitions of the
|lBniinat4?% c-onlain lliret- tliflereiit unions, viz. the monovalent H^AIO,',
llbd «iival.Tjt H^VIOj", arul the trivalent AlO,,'". Since we are dealing
»ith a wejik .-vcid, the iiionovulent ion will preilntninate.

Of the nliiniinntf's, the stuliinii comptmuds, more especially, lire
liBiiwn : they enrrc-ii'timl to the three possible typea, NaHjAlO^,
Sak,IIAli)^ and Na-^AtO^. These substances are soluble in water, and
do I itltse well ; their solutions react stroivgly alkaline, and are

Wi • ' For if such solutions, vspMially of the first nnd second

^pev, Ijc kejit sntiif time, iht-y lose a great part of the alumina they
pBlttiun, this being deposited as a cryst<itline precipitate on the bottom
wf the vcsJM'L 'Hiia is due ti> the same phenomenon as in the case of
ben'Uiuni hydroxide (p. 554); the aluminium hydroxide which is
d«pu6ii«d is a nn/rtt ghihh foi'm than the nitmrphous and gelatinous
■^ aiid solutions, therefore, which are saturated with respect of the
^MT are Biif^K-tsatunited with respect of the former. Accordin|;!y, so
^B as the first crystals ol" the more stable form are prtxluced, it
MBuiucs to separate out, and does not atop until the new equilibrium
b rt«rhc<!.

Attiminium hydroxide is not appreciably soluble in amvumm,
becau&e the bxsic properties of the latter are too we^ik. That is to
l»y, if ainmonion and abimtnain'on are brought together, they pass
btto the urtdissociate<l coinpounds, aumionia and aluminium hj'droxide,
M h «k>wn by the eijuati.Mi H.,A10.; + NH'^ = A1{(»H),, + NH.,. This
Vhaviour is made use of in analysis. ^VheIl it is reqm'red to
prwipitrtte abiminium hydroxide from an abimiuate, an acid may be
Used for the purjMise ; an excess of the acid, however, ag:iin dissolves
Ihe aluTuina, and it is theiufnre diffitulr to efiect a complete separation.
If, however, an aiiimontuni siilt bo aibied t<i the solution of an

iiinate. the above reaction takes ]tlace and the ahuuina is deposited,

an excess of amnioiunm salt exerts no solvent action.
The other light metals also form alumiuates. Of the.'iie, the
Ily occurring spinfJ is of interest ; this rjin be regarded as the
tlride of mononiagneaiuni aluminate, MgH^Al^O^, for it has the
^fotuiKr^itiou M-AIJ),. and Mj^H,.M,0,. - 2H/J = MgALO^.

^ptnfi crystallises in the regul.ir system, generally in rhombic
ahedRi, and is the type of a fairly large series of ccirresiwuding

Doq>houfi nompountU which are composed of equal combining

IEhtB of the oxides of a divalent and a trivatenb metal, for the
Btla of spinel can also be written MgO, Al^O^,
Knee the place of magnesium can be t%kcn by iron, manganese,
E etc., and that of .iltiminium by chromium, iron, manganese,
, there are a hirge uumlter of lompounds of the type of sjnnel,
Vmie of which will be mentioned later. They all crystallise in the
ICgQlar system.

U". Aluminium Chloride. — The conqMuun! Alt'l^ is formed

' -2 o

562

PRINCIPLES OF INORGANIC CHEMISTKY niifJ

when metallic alumniilim is henteil in n curreul of liy<li'<>jieii chli
Hydrogen is lilieratw), ami ahimininm thlorirk' readily mMi
fnrmiiig a white tr^sUilline nifisa in the colder ]>arts of the a|i[ULi
Formerly, when ahimiriiuui was not a clieap subatjiiicc, (he rlik
was prepai'e*! by beating a mixturo of alumitdum oxitle and clui
in It cuiTejrt of chlorine. The proceBs ia represented hv tins e<)Uftli
A]./>, ^ 3C:i, - 3C = 2A1C1, . 3C0,

Aluiiiiiiiitni chloiiilf bulls ;it iilKim 183 . Tho inoltiiije [Hjiiit ■
somewhat higher — liKi' ; oi> being hfiiterl, thurefnri", urifliT finliMTj
pressure, it, jwisacs flirectly from the soh'd into tlu^ v)ip«r<nis «fj»tA
By huiiting it in n closftl vessel, so thai the boiling poitit is misrtLJ
ciin be fuaed.

* Alumiiiinni chloride is used in organic chemistry in numer
preparations, which depend on the fact that in prwciiee of almtiinii
chloride, mixtures of a chlorine and ic hydro^ieii comiwuiid -iiflit 4
hydrogen chloride, the residnt's then eumltiuing t.o form thi' in
conipoiiiid. In organic chennstry such a jinx-esi* is caflcd sytdm
(in tlie narrower sense), and for siith piu'poses aliiiniiiiiiiu chloride
of Gspaciiil iniporUiiiL'e.

Aluminium chloride fumes in the air ami leacts v>-ith wulvr with
very considerahle evolution of hmt. An hydrous alimiinium diloridl
rannot be again obtained from the aqueous eolution ; from the Ktmnglf
eonaentratefl solntion a sjdt crystallises ont with :iH.,U, which, <ii
lieing lieated, conijiletely decomposes irtt-o hyflrogen chloride uhiek.
escapes, and aluminium oxide which remains behind : 2AI(-'l,^ - ;'HI>
AljU.,-.6IlCl.

Aluminium cblorido readily iinitoe with other chlorides to l<
double salts, ami more esijeciatly ho with jwUt^fium and «
ckturiiii's. These compounds' crystatlise well, and in tiii'm ttlntniTiiilBl"
chloride hiij* lost ita volatility. The sodium compound nmlu witk
exceeding eaa^^, and was formerly used a& the starting BUhBiaiicc for
the preparation of metallic tduininium.

On account of its ready volatility, the molar weight of aluminiooi
chlonde was early determined, and was found, in agitcnieiil witi
certain theoretical aBsumplions, to cun*espond to the fornnihi M,i\-
Siibsequeriitly, these theoreticHl views brcsime doubtfid, ami a thoroHjtIl
iuvcMtig-ation showed that in the neighlmnrhood of the boiling \>om\
certainly, vapour densities were observed which corresponded tt|>pr<)ii-
matoly to this fornmU (although they were always too low), hut lli«»
the values rapidly diminished as the temj)eraturc rose, and at t^roiHfW
tures between 4nO and 760" remained constant nml corres|)ond«l W
the fornmlii AlL'l.^.

548. Aluminium Bromide and Aluminium Iodide -.irv virf

airoiliir to the chloride, but less vohitile. They sut> rc;idily furmw
from the elements, and in organic phtunistry have a use similar lotW
of the chloride.

ALUMINIUM AND OTHER EARTH ilETALS

56.'?

'M Alaituniom Fluoride, AlF.,, is olitahied at a red-heat from

(Aiaiiiiuin Htiil hyfh'ii^'i'ii tliioride) nml al.su frntn alutniruiini oxiilo

Vd ivilrofien Huoride, itnd is vcrv Tiiiich less volatdii than the other

■Ic^'ti cMJitipDund.^ [>f a.)iiiiiiniiim. tt fnmii) small, luslruiu cryeUls

liicli l>L'hHvo iriilitfurently tuwiinls w-Uur. and starcely disaolve in it.

' i;t is trwiiwi whh aqueous hy*1ri.ifluoiic lUi'ul, it dissolves in

iiy. The ^(iliitinn, luiwever. is .strongly aiipei-tMitii rated with

ijM^jt to (he A\mvv diHicuUly sohiKIc fonii of aluniiniiim Hnoridu,

ikh IS ^^Inwly ile[K)sit<'d !^|Niiitaii<-(iiiHly.

AJuminium tlittiridi' is ^nlidile iti Ity^lroliuoric aeid, and forms

h >Lh kt/tlroHwHtlrimuiu- itrid, II^All'"g, thb xoiliam milt of which

wry difficultly sttltible in water. It occurs in large quantities

Grevnlaud. and iti* a iiitu«ral this compound, Na.;,Alt\^ ia called

■fo ia used for the preparation of .Wj» tilung with pure

' hi/'irtmi/r. For this iHirjMwe it ia hefiied with iiiiik of

B or fiiBed with time, whereby calcium fluoridu and sodiiun

{ninutc .tre formed ; the Intter p£iss<es into isolation ur can ]h<

r»«.lwi with Witter: Nii,AlF„ + 3CftO = 3CaFj + Nit^AlO,. The

-iihuiou is dectHiipiisfd hy ])a*sing iti a curivni of eailHJU

iu'feliy siKiiuni cjiilmnate is formed and alnniintuiu hydiox-

i» |.irci(iiut<"d : :JXa.,AI< \ • :tL"0, + HHJ) = 3NaJJ0,j + 2AI(UH).,.

EAlomiTiiTim Sulphate. — Of all the s:dta of alumitiiimi, the
is the one which hits the largest a|>plieiitioti, and it is
? Tnuiiiifaciiired on a larpe scale. It is nbuiined l>y heating
tmnititu hyilri>xi«le with sidplmric acid ; the solntiori pi'^Mluet'd
ilifi«s> at H euitalrle coucejitratiuii, t-o an- imlislitictSy erystallino
• of the lormuU Al^(SO^)^, IHH^U. The siilpluite can also Im
pvod by healing iilumuiiiun hilicatt; with aulphuric acid, silicic acid
Bg thereby act free. A pure salt can be obuiined from the com>
rml prixiiu^t by precipitating the coticentrated solution with
(•kol. An oily liquid is; then depoi^ited, which is a su]H;r6i)tni'ated
Bliun of aluiDinium 4ulph»tt> in water <witii a very little alcohol) ;

ron Bolirlifies U) lustnjus scales of a salt with l8HjO.
It i» no rare thin^ for aqueouii Holutiotifi i*f salts which aru
itvltly milnble in alcohol, to l>e fir^i precipitated, by the addition
Uwt Utter, as a conccntiatod !<olutioii which is immiscililc with the
*!>( ifap alcohnlic solutirtn. The fortnation of the aiipersntumtetl
iaUon fif/ore that of the solid cry suds ia only uunther case of the
W oeaarrno' nf tltn irsfs Jtlti/ilr j'unns.

Oq accinint of liydj-olvHts. the aqueous solution of alutiiiliiunt eiU-
Ue reacts acid. It c.iu dis^^olve fairly con»idenil<le quantities of
Utinimn hydi'oxide, with foruiatiou of basic salta ; diffictdtly soluble
It* are nllimately dejuiHiiod.

ttc aluminium sulphutn in which only cme of the three
fU is rHplttccd by sulphanion, AL(OH)jSOj + THjO, occurs

564

PRINCIPLES OF INORGANIC CHEMISTRY

naturally ;i9 olnminitt; and is iiswl in the piejwfatioii of the noil
jilnminiuni sulp!i;U<.', and of its. ilonltle salt, (rlmn.

.')51. Aluin w;i3 the name fjiven originally t*. a doiihle sjtlt
aluminium and iHJiriisaium sulphate, AIK(SO^),, . 1211^0, whidi cry«
lUfsg in fine octahedra belonging to tte regular system, on mixing
sciUuitins of the single salts. In the cold it i.? much less soIoMe ij
the single salts, and Ji snhitinn prepared from the BJitinuted i^Iiitit
of tliese is strongly supursatnrat^fl in respect of ithini. The sup
saturation {Iocs not, it is triio, disappear spontaneonsly, as the soluti
is in the metastjihlo condition ■ in onr surroundings, however, so
alimi ia so largely distrilmted that acjircply no object whicli luis U
iu the air is free from it. As a rule, therefore, the nucleus which
necasHiiry for tho foi-mation of crystals is immediately preswnt
this i» excluded by heating thu Jiijuids and vt=^s>a«ls to ! 00° (where
the alum melts in its water of crystidlisation) and tin? entnince of du
avoided, f-rystallisAtion remains suspcndi'd for any l<*ngth of tinic

Alum WHS formerly the most important soil of itlttmiuhim.
bliungh the potaasium sulphate contained in it had either no effect
had a disturbing oflect in its applications, alum was nererthelei
employed, because none of the simple salts iif atuminiuni crvsiallil
well, and thus amnot be easily frw<d from impurities. Sine* t|
method was discovered of preparing pure ahiniiinuin bydroxiik lli
way of siKliura aluminatc), and so of preparing pure alnnnnium m
phate from this, alum has lost its importance, and is now hieing Bi'U
aiid more replaced by the .simple sulphate-

* With this also, the former methoifH of preparing alura tt
beginning to disappear. It used to be prepared from a liasie potassiui
almniuium tin!]ihate, which occurs natinvdly as iilaiii-sloiii; liy lieHtin
this and extnicting with water ; alum thereby passed into solutiii
and alnmiidum hydroxide retuaincd behind. Further, ii was obuin*
from fd%m shak, a silicate of aluminium pornieatorl with sulphirl*
imn. This was roasted, and then allowed to undergo oxidation in ill
air From the sulphur of the iron sulphide, snl]ihuric acid is Innned
this converts the alumiinum silicate into sulphate, which is thi-ii c:
tmcted with wattT and made to crystollise by the addition of potasniit
sulphate.

On l>eing heated, alum melts in its water of crystallisation ; o
raising the tempetature, it loses its water and fonns a spongy, wM
mass cHlled hiirnt uium. The latter is used in medtcino.

The most impirtant use of altiminium sidphate, or of alum, i»
lii/iinij. Many dyes are itiaipabte of combining directly Mrith llie fibi
of the cloth in such a way that the colour is not withfirawn bv Vi'sK
and soap. If, h"Wfvei-, the doth is previously treated with ^duiniriiiil
aalts it can be permanently dyed. This is due to the fact itiat
fibre absorbg and unitc.H with the aluminium hydroxide, which
always present in the sufution, as the aluminium salta are uliri

ALUMINIUM AND OTHER EARTH METALS

ifiai'wbai hytlnilysefl Further, the dyes have the iK>wer of uniting
rilh ;ituiiiiiiiui]i hyilmxide to form the prjuiticaily irisolnblej fiiiely-
nlourtfil '■ lakes," arxl in this way tlie union between the dye and the
' f>\ by tht- aUimiiiinni hydroxifle.

II filiunijitnni sulphjite is the typf. of a large series of

ar sait«. M'bifh Jiiive it similur fuiiiimsiiioM, atul ciysiiillifie in the

fi.»mis of ihe rcgiilur system. The pliicc of potaesium can be

by rubiilium, fscfium, itmmo»mm, and a largp number of m'^ank

iirrx (if annutiiiiiim, as Well Jvs by the b<vivv metsd ihafliHw, hut

, bv solium ur liihinni. TIr' jjIiicli uf ahiniininni can be tiiken by

• K'tals, which fnnn Innilnif ions, such as irwi, ihiinniiiw,

-', infihtm, etc. Finally, in phit'c of the sulphfiiiiuti we win

|ki»-e selenftiiion, SeOj". Heiiue, we bsive :i jiiwit lUvei'S^ity heie ■ for

illl ihcsi- double salt-* the name ahim lias been Jidopted, the names of

tie metals presoiii being prefixed. These fdums sire isoraorplions irith

•her, and the t-ii()ei"sjiturate<] solution of one of tbeni is niiide to

<• by A nucleus of any other.

Ri'>.t. Aluminium SUicate. — It has a!re;uJy been several times
dont«i that the rn^ks of which the earth's erust was primarily
wl nsiHt essentially of silicates, ilie metals uf which, Itesidoa the
freijUiLTjt alkali and alkaline eurth metals, forniorl^' mcutionecl, aie
aliimininni and iron. On tmdergoing (leconip<.isitioii by water and
mrboii dio.vidt! (" weathering "), the first mentioned pass into carbon-
while magnesium pjirtially, and alnnniiiiuii entirely, remain
d as sim])le silicates.'

inioni silicate is called dai/, and is formed in the umoiphous
in very finely divided form, in the weathering of (he rocks.
»k, it is readily carried jiway by fltiwing water, and is deposited
wly when the movement of the water becomes very sIom*. Acconling
" ' ' .;ree of purity, it possesses various projvertieSj and is cjilled by

Plii; purest form is called hwHii, or chimt rhn/, and is generally found
abtics where roeks, piKjr in magnesium, are decompoBed by Hater
•nu airlKin dioxide, but are not trana]Mjrted mechanically. The water
»** thin carried away the other constituents m solution, ami the
»kniiiiimij wlicjite, with more or less quartz, has remained behind,

I**^'' pure f<>rni.«, which jire freijuently contamtnatc^'f, nittre especially
*itlitulritnii t-arljonatc, (piartz, and iron oxide, are called chi>/, ot potlrr's
«f'A. Mm I contains a large quantity of calcium carbonate, and hum
woiaiit* t^f.^aI•t^ KUid as well.
|Th« use of aluminium ■iilicHte is very old, and widely extended. It
Sniji tm the fact that it yields a tenacious mass itnih wakr, capable
sing iaou!do<:l ; on drying, this luidergoes regular contraction, and

[ tliuJa oiTtalu fondiLiotts (tucnrriiig itj the tropich, which, howevnr, csanot as yet Ite
^" »1 I" ileUil. (tltitniniiirn silkate Is bUo d«cgnipoJ)«il, iu such a way that sUicic
t'away whilt ftlujiuuiuin hydroxide (ns hatixite) is left behind,

•

lumii

• ' II;. 1 .. ; :
r, f ->.-■;-,.

• I. :>■;■:<- -..^

!i- Iii;.s.. -i -■-;

- "•-*t iiia:ori:.i
■ ;:!i <ilrVatf. wfr

•'■•••'■ :•' .« d..i:'
-;■ > Tn..i:!,i,si .,„,^^ ^

"•" " ''■■'• "i: Ware ■■
■>]«i- .i:;o water -
■•■■' ^'-^rb a thin, r^

ALUMINIUM AND OTHEH EARTH METALS

567

in thom. Ordinary folspiir, or oiihodiWii'. is [jotjLssium Hluniinium

AlKSi.,0^. ll occurs widely tlistribuied in iiiouoclinic crystals,

niiist lie regnnlod aa one of the most imjMirtitni snunjiis of [xitash

ibu soil. Tlip f'Mln ffbjiar, or nlltif/-, li.ta a eorrespoiiding Lompctsi-

«, contntnitijg s'kIiuim in plai;c of potassium ; it is IrnUnk. Ainorthilr

a culciuai fi?lsp;ir, which is isomorphous with alliite, and can unite

ith ir in all prDpuriifjns Uv form niixetJ crystula ; it has the composi-

' )^. hMinif of these ndxtiires have received special names,

■■■I.*' ami In!iiviloi'i/f.

Another groMp of «lkuli ulnminium siliaUes ih that of mifu, whic-h

I (lii3linjL;uished hy its povvur of cleJl^ itig, its elasticity, and resiBtancc

p hij;h tempenitiirp. Some kinds of mica coiitjiiii miignesium in pk'ue

the aikiili metiils. Thi' foiniul;i is donhtful.

554. Other Salts of Aluminium. — Since in using aluminium

ftfl a M'ftdiitiJ in dyt'ing, the alumina is deposited on the fibre,

corresponding amount of acid remains in the solution, and «s it

r« it begins u> hinder the deposition. By using a weak and

»tile aciil, the f>roc<jsa can he ciirried on to luxich greater ad ran tagi; ;

such purposes, therefore, iiluminium nredile is used. This salt is

iiM-*] fmni Jihuntriitin) sulphate hy /lecomposing it with liarium or

i!*!Uii(L', whereby the correspunding Hulphate, being insohihle, is

ibedL The same obje^"t is attained more simply hy the addition

iy soluble aceUite, f.^. sotliura acetate, since this has the same

in diminishing the concentration of hydrion.

iminium acetate is a very deconip*isable salt; even ou boiling

lUeous sobitioii it iiS decnm^Kised intu atumina (or a very Imaic

ite), which is precipitated, and acetic acid, which remains in solution.

>i*due to the increase of hydrolysis with risiiTg temperatuiu For,

I thr hydrolysis deiwuda on tlio ainoutit of hydrion aod hydroxidfon

ined in the water, and since this increases with rising temiMjra-

Ijecause the dissociation of water into its ions is accotnpanied by

jtiofi of heat, the degree of hydrolysis must also increase as the

sraiure rises. Moreover, the reaction is thereby accelerated, and

■III snpersaturation therefore exciufleil.

,111 I%i.-si>lt(itf occurs as a mineral in various forms. It

it knox^n us tniipmixi', which is used us a gem, and is coloured

owing lu the presence of copper.

5. Ultramarine h the. name given to & siihstance of a fine blue

which WAB first obtained from the ta/t^L- lazuli, in which it occurs

wiih a colourless miitrix, and has l>ec?i nseil as a valuable

!>rit. FVom analysis, rilnrainiura, silicon, sodium, ami suiphtu' are

tfl be the chief constituents, and in 1^28 Gmelin succeeded in

iring a blue dye-stuff of the nature of ultramarine by treating

aa with fllauber's salt, silicic acifl, and charcoiil. Since then, the

1 pre]>aration of this colour, which is distinguished by its

ageablenefis in light anr| by its 1>eauty, has grown to a large in

■

568

PRINCIPLES OF INORGANIC CHEMISTKY

tiustiy, Kiiolin is hejitwl with GlHuber's sail, w mxla, charTual, i
sulphur, at first with t?xt;hision of air, and the »iu!l-green culoiu
product is then nasied with sulphur, with acce.as of air, whereiip<jn I
blue (;ij!(iur develops. A aeries of diH'erenL coloura, from red-videt
Muu-green, \a obuiiiied by varying the relative nmoiinte of the origh
substauces and the methud of treatment. Tht; ultnuuarine is nuul
really for use by washing with water and levigjition.;

Whilu ultranijirine is stable to light and air, even in the present
of lime, it is decomposed eieti by aval ur'nh, thereby b««omii
colourless and evolving milphureikd hinlrogcn.

In spite of its having long been known, And of the t«chnicil
preparation of idtramariiie having been practised for many yeais, tfai
chemical nature of this substance is not yet clear. The sodium in il
can be replaced by si!vt<i' find pot^issium ; so far it behuves like a alt
Its formida, hmveviT, is not known, since wc hdVf as yet no meiiiwol
separating the finro subslanLa from «ny impurities it contains.

* 556. The other Earth Metala. — The elements already iiwd-
tioned which are alUud ti:i alnminiuni, viz. scanditim, yttrium, lio
tlnumm, cerium, pniseociynilumj neodymium, samarium, an*l yticriiiiim,
along with a number of still less certain compaiittms, are all otlhi-u
very rare, and occur only in isolated jHirts of the eiirth's cni<tt, in
Scandinavia, and in North and South Ainerica. Their properlifs art
similar to those of aluminium, subject to the aanie deviations its
fourid iti the other groups, with increase of the combining wei,
that is, the free metals are all the more readily oxidisitble tb*! gi
their comliining weighty and, in the aame sense, the bases Injmim
stronger.

The lit/droxidrs are whitCj amoiphoua precipitates, which, howow,
no longer dissolve in alkali hydroxides ; the higher nicmbci^ are even
able to form carbonates. With potassium sulphate they form doubk
salts, which are slightly soluble in water, and almost insoluble in
excess of jiotjissium .sulphate soUition. The latter behaviour is diiolM
the diniiiRitiun of the solnlulity by the presence of the sidphaniofl
(p, 447), and is by no means a pjcouliar property of these douliic s*lt»
The fomposition of the double salts, however, does not corrcsjKiml Ifi
that of alum, but ia expressed by the formula 5IK.,(K0^),,. Fiiriher.
in the higher members the property of forming more highly oxidised
com [rounds or peroxides is found.

By reason of this close agreement in the properties, it is no co»T
mutter to separate these elements, which generally occur mixed is
nature, from one another. Nor are there any methods of 8e^>.initi(»
applicable to them such as are employed for other arudytical purifos*
but one has to be content with iiurtial separation on the }>asis of slijjM
differences in solubility, of chemical equilibrium, and of decomposiiliilitj.
by repeated |ierfonnanee of which the object is more or less attainw-
In fact, almost every investigation which has been rarrietl out irit"

ALUMINIUM AKD OTHEK EAIJTH METALS

569

live thoroughiie.<8 liaa shown thnt one <jf athur of the aii1>-

hilheito regarded an simple is a mixture, iiiid the whole hisloiy

d«\ elojmif nl uf thiis pan of chcniiMiry may l>e designated iis the

iaulatiijci of tit<w indJvidiiais from the total fiinonnt. It is by

» jiroliiible that these sepju-ations have alrtady reai'hed a

c conclusion.

chanicteristic of the various elements of this group, there is,
*11, the romhiiiiiiif ttfiifht. By some niethoil or other, m jMtrtial
lion of the mixture of Biiljstances is otfected, f,g, by purtial
i^iit;tt)Oii of the Biilt solution wjlii ijisnttic-Jent ammonia, and this
ihij«i I* repeattid until the coriibiniiig weight of the fractions obtained
loiigt.T changes tm further sepaialiun. Another very important
on ia afiVinled by the npfunl properties. Alany of these elements
ery complicated speclium on allowing the electri*-- sjjark to pass
I CArlioti points muij^tt-i) with tsolutiona of their aalta. Siitee,
given conditions, each element fHissesses a perfectly definite
tn, it can lie seen whether the ap«etrum chatiges by partial
.tioQS. Where this is the ease., we are certsiinly dealing with a
The higher members also exhibit ahforptioH siKCirn, some
rw jilsu '■mission .^/irfti'ti. The former are obtained by allowing
ght to puss through solutions of the .salt in question, and then
ng it with the spectroscope. l>ark bands are then 3een in
positions, which are also chaiueteristic for the diflerent elements.
•, the oxides of the higher memliers, when heated to inwindes-
lo not emit ainliiiwm^-i light, as sulid substances usually do,
le emitted light is fonnd by tlie spcctroseoiJc to consist of isolated
siniilar to the light of incandescent jt^ases. In this ease, however,
arc much hrosider than in the latter ease.

tiother kind of optical phenomeiiou, the importance of which for
terisiition of the elements ha.'s not yet been fully demon-
nsists in the pluis^thwescaicr jtroilueeil by the lufhiMh' ntys.
electrical discharges of high potential are allowed to paaa
lltQQgh a highly *':icuuus space, niys of a special kind are emitted from
the i-athfxle, which are propagated in straight luies, and which render
hniinrtiui many substances with which they come into contact. The
%ht ifaua prorlucerl ditt'ei^ also in diH'erent substances ; still, difTerencee
<*oir in cA.«es where chemical differences ate unknown, so that it
'!*» But iippear safe to draw conclusions from the one as to the

Sioatidiutti, ifttrivm, and tanlJuinui/i yield colourless salts, and form
"olj OTIC oxide, of the composition M^O^. Besides the tnvalent
oydrojriile Cc(OH)^, whcoe salts are colourless, rfrttim yields a t^tra-
''ItTit hydroxide, CelOH)^ (and a corresponding oxide, C^O^), which
*'*jfiirm9 sjdte, whose solutions are brovm. We have here, therefore,
^*'> kiuds of ions whose chemical composition is not difl'erent, but
have different properties, depending on the different valency.

Qeaeral.— MetJiUic iran was not obtained from it* imturally

ling eompoiindij at so early a, tlnle aa same of tlie other metab,

Ily csopper and fin. This is due to its high point of fusion, find

much ^eiitPi' difficulty in obtjiining it in the metfOtic aUite from

i]K>utuls. I'has, in prehistoric ttmea iron does not apjTe;ir until

'broiuHi. ty. mixtures cont4iifiiiig copper as essential constituent,

WHB apparently at first a gresit rarity.

Sotwithstnnding the wirle distribution of iron, it scarcely ever occurs

D till-' tneiallic state on account of its tendency to form compounds

with o\ygen arid aitlphnr. The chief occurrence of metalhc iron,

fxc^yit in somi" rather accidental cases through the iiction of chemical

■ coiioectod ivith volcanic activity, in in certain lui-tfm-ilgs.

ire masses which do not originally belong to the enrth. hut

irhidi. in the course of their flight througli spac-e, tipproiich so closely to

I earih that. (HV'ini^ to atmospheric friction, they lose their kinetic

y, which is thereby {-onvertcd intjj heat, and fall to the enlth,

ny of these nwisses conaiat of iron.

Massses of native iron also occur, although rarely {e.p. at Ofvivak in
firp»nliuid), whose meteoric origin is donl>tfuJ, although no explanation
1 ^.n given of any other possible origin.

ironiaa grey, wnacious metal, which fuses with great difficulty,

•bout ItiOO" ; it combines with free oxj'gen quickly at high tempera-

ilowly at low ones. In the heat essentially conipiMinds i»f the

Dii!» Fe,(>j to Fe^O, are formed; in the cold, iron hydroxide

j(OH)p is formed. The hydrogen necessary for this is taken up in llie

lit water ; in fact, iron " rusts " or oxidises at a low temjteraUire

'b moist, not, or not measurably, in dry air. Since the rust does

•><* Cohere, it doM not protect the iron against further oxi<lation

* . 5381.

Al fell temperatures water is decomjjosed by iron. The decomposi-

lof «-4tcr by red-hot iron is a cbissical experiment (p. M3). Even

tdw unlinarj' temperature decomposition takes place with evolution

571

5TJ.

PKINCIFLES OF INORGANIC CHEMISTRY

nf liydroged, Imt cxceodingly slowlv, su that the (■volution of hyc
call l»e oljserved only iiy ueiiij^ Uirge surfaces (iiou powder),
dissolved aven by l\iv wejikcst ;ii:ids, thereliy pasauig into dn
difuniwi w'ith evolution of hydj'ogeu.

The L^ombiiiitig weight of iron has been foimd to be Fc = 55"9.

6r>8, Commercial Iron. — Commercial iron is not pure, hut i
taina up to jw lumh as 5 [X'l- ei^tut of carbon, wiiich h;is a very j
influence on its piopcrties, and :ilso smaller riii.inlitie* of
impu rides. While pure iron, although very tenacious, is ciimiMnttiv
soft, its hai'driesB increuses witli the amount nf carhon it t'ontsiina^i
its hehaviom* i\\. raodeiatety high tempt-mtures heuomes essent
difTLTCnt.

There are three thief kinds of cummorctrt.1 iron, \-\e.. ifnuujhi-in
deel, tmd rmt-intn ; the first (;onttuns the snaallest, the last the hiji
amount of earboiL Wrought- iron appioxi unites most nearly hoih'i
conipusitiiiu and in properties to jituf irorr ; it is Uiugh, not very
and on beitig Injated (itst becomejs soft like wax or siofliiim
melting. This property i* of the grciitesL importunce for the tech
working of iron, as it renders it possible to shape the tnctiil and
unite iliftereat pieces without it being necessary to niise the lemf
tiare to the nioltitig point of iha metal. Oti the contmry, it is suflick
to heat to the tcmperiitiu-e of softening (about IJOO'). aoas to attaial
object by pressing, rolling, and forging. The uniting of the twopw
of iron by pressure (hammering) ia called wrldimj. The wniperitb
necessjiry for this is bright red-heat.

The properties of wrongbtiron do not uadergo ossontial chji
when it is healed and suddenly cooled. The character of s/'-'A 1"*^
ever, depend.s in the highest degree on such treatinetit.

8teel is iron which eonUiins from OX u> '2 "3 per cent of cu
hut h otherwise as pure as possilile, The earlHm is cheniically
binecl with the iron, and this carburetted iron or iron carbide FfljCj
fttloyed with the rest of the iron. The result of the prosenco of
foreign substance is, in the lii'at place, an appreciable sinking of
melting [>oint ; at 1400" steel in liquid and can be cast, Ca^t-sict-I
a metal couaisting of fine crystalliTie grains, which, like wroughl-ipH
softens before melting, and can therefore be forj^ed. By such
ment steel acquires a fibrous or sinewy chjii-nctor, similar ui wroti
iron. 11 the stool h made red-hot and then suddenly cooled, it bwon
brittle, and at the same time acquires its highest degree of hardn
It is then so hard that it scratches glass, and is hence called y^Jii/
If this steel is ugain carefully heate<l, all degrees of hardness l'-iij
imparted to it, for it increases in softness the longer oi the higbtr !
is heated. This process ia called the ffiiijif-niuf nf steel.

k& an index of the degree of tempering to be attained, use
been made from olden limes of the colours which a bright steel sur
acquires on ineiug heated. At about 220", the mctjvt begins to oxidi*

ith a measiiraHe velocity, and the oxide produced forma a
ting on the metal. If the thickness uf this coating is nf the
a wave length of light, the corresponding interferenco culonrs,
ciilours tif thin plates," begin to apjiear. Since the shortest
iaihle waves, the vitdet, is first extinguished, the first tarnisjj-
lo Ap[ie4r is the iompU"ment«n- eoionr, pale straw -yellow,
iws through the colours orange, purple, violet, blue, nnd fiTmlly
1 gTCV. To each of these coloiu's there ewrespomls a iletinite
>f hrtrdnesa of the steel. Steel for tools to work iron is allowed
I the yolloM- stage, for brass the purplc>-i'e<l stage, while tools
d are allowed to become blue. Although cohmr iitnl hardness
ucactly eorrespttnd, still the eorresinindcnce is suffiinent for an

t workman.
t titility of steel in the arts is due to the diversity in the
inlnesfi which it tan acquire. In the soft state it can lie
to any desired form, and the nhaped.objcets can then be brought
Jegrec of hanlness.

t is only in recent years that the theory of itmjterinfr h.t\s been
lear. Iron carbide, Fe.(t\ mentioned above, is not only itself
Wxi, but it forms with pure iron a homogeneous tnixture, a
lohition," which is also hard ; so much the less hard, the less
it contains, if, now*, such a solid j^nlution. cnnsiBtina; at higher
(tares of carbide and iron, is slowlt/ eooled, it breaks up at about
to pare iron and iron carbide, which exist aa a conglomerftte
side. Since pnre iron is soft, it itn|jart* this property also to
tUire.

f, however, the cooling is performed rispuUfi, the breaking up of
d solution does not occur, and the latter therefore preserves ita
Is. The solid solution hei-eby becomes metastable or to a certain
Bupcrsatui'ated

rbiii explains, in the first place, why i|iicncbed ateel is hani,
lowly cooled st«ol is soft. The temjierinfi of hard steel, now,
I in the separation of the solid solution Into its two eonstittieuts
I elevation of the temperature, the sei^iiratlon occurring all the
ftpidly the higher the temperatnre. By sudden cooling, the
] the mixture attained at any point is preserved, since, at the
y temperature, the velocity of change is immejisurably small,
fresponding degree of hardness is tlien o'tUlned.
rhese eonsiilerations also make clear tiie fact, learned by cvpori-
liat the lemi>er depends not only on the temperature but also
timfy in such a way that a lowci' tenipeniture foi- a long fieriotl
I same effect ;ib a hijslier temperature for a shorter time.
t lemperijig can be carried out in one operalicm by app>opriati'ly
5 Ui alK.\e fiTiJ until the desired mixture of iron and solid snlu-
he e((uilibrium between which alters with the tenipi>ratnre) is pro-
fisting this state by suddenly cooling. The It-mpemture

57'J

PKINCIl'LES OF INORG.

«f hyilroffsit, hut <!xcee«liii;ily slowly, %
fjui In; oliMirviMl only by UKiri;^ birgc »i
(liiMMJvwl itvttii liy the wtuikest ;ici(I.s,
tlif/TiioH with «!volution of hydrogen.
Thi! (xjinbiriing weight of iron has h

r».*iK. Commercial Iron. — Comme:

tiiinri u|> U) iiH much )ih 5 i>cr cent of (
infliKiriLM! on its i)ro|H'rtio.s, and alst
linpui'ilicH. Whili! pure iron, although
wtft, iu hanlnt'HH incrwi-scs with thi> am
itH hohaviour at nioderat^^ly high tei
dilToront,

'!'h«r« aro throe chief kinds of coi
slrrl, and rusf-iniii ,- the fiixt contains tl
Hinouut of carhon. Wrought-iron apjj
tHmi|H>siti(Ui and in properties to piiir ii
Hud on being heatwl first Iweomes si
molting. This property is oi the great
working of in>n, as it renders it possib
unite tUlVorent pieces withoiit it In'ing i
tuiv to the tJielting jHunt of the metal,
to iieat to the teniper.iture of softening
t>bjtvt by pivssing. rolling. an<l forging
of i»"o« by pivssure \hatiuneringi is ca
n«>i>t»a!»j>ry t\>r this is bright ivd-heat.

The pivjvrties of wro'.tght iron do
when it is heat«>1 and suddenly cimUvt
ever. dejHMids in liie highest dej;;vo on

5T4

PRINCIPLES OF INORGANIC CHEMISTRY

^necessAry for obtaining a definite degree of hardness depends on
»mount of fcirboii prest-nt. If this irs known, the icmpemturf rc<imr
to prmliicc ii> given degree of hatMiness can he deciried heforehand.

If lh« lunomit of ciiflwn increiises to from 4 to 5 per cfnt,
ojeitiisg point of t!ie iron heconicii still lowor, and the nicjUil lose*
toughness and the power of assuming the fibious Londitioii, i>ui it
retains the power of being tempered to a certain degree. Sucb'iroo
called i'ns/-ivim.

Two kinds of caat-iron are distinguished, wftilr and irr*y- '
former ia obtained by quickly cooling ; it is very hard ami crvstalBi
and contains th« greater part of its carbon chemically etwiibineii
carbide. Wlien tlio caHUiion is slowly cooled, part of the
Beparalea out in fine himinae as trra-phiie, which iraparts a grey
to the iron. At the mmw- time the metal bei-ome« loss hard and
and the grain liner. In this condition wistiron is used for innumeW
purjxjseji where etwe in the .shaping of the object by casting' has to
taknn into jiccouut, and where the smaller reftistunce of the inecal
pulling strain and landing is no essential drawliack.

55y. The Ions of Iron. — Iron forms iLci> kinds of elementary
well i*s a large riniiilnir of toniplex ions contiuntiig (jther elements aloJ
with the iron. We shall in the fii'st place treat of the former.

The elementary ions of iron arc di- and ti'ivylcnl ; the former
ilted diferriim, the latter Irifenidii, and all the cotnpo«ind& which
derived from the former are designated fernuis cnmpoundu, in c
distinction to those derived from the lattei-, whJch are designated fi
cotn|)oundii. The ferrous compounds possess a simlUu'ity U> tlioH
magnesium, the fen'ic to those of aluminium.

ihfrrriim in the pure state is almost colourless. Most of the ni
which contain diferrion exhibit a greenish coloration, which is uiuii
regarded us that of the diferiion. It apjwiars, huwever, tu hv du
the greatest pait to the presence of a tnice of triferrion, since 4
coloured compounds of the two exist winch even in very email amtt
produce the green coloration.

• Although liifermm does not absorb the visible rays to any grd
Wtent, it absorl>8 those of //rwii wavti length, the ultra-red or ihelm
t'at/!f, in a very pronnunecd degree. A vessel with parallel watb, fill
with the aululiiHi of a ferrous salt, is the most ertective imvins
freeing light rays (c.f/, in projection apyxinitus) from the dark h
rays which are proaeut, and thus uf avoiding the harmiul heating
the objects. The same property ia possossed by glass contaiuiB^
ferrous silicat*.

Diferrion has an "inky " tiiste, t.«. the taste of ink is due to ik*
presence of iron, which i.-^ chieHy in the form of tlifernon,

The salts of diferritm are, as already metitiuned, very simibif**
those of miit)iic^-t'i!i, and are in many cases iaomorphous with iliw
like the aolntions, they have a greenish colour. The general rmitwi

&7^

fact that this salt

lotjillu! iron or iron sul-

lit li(|iii(t till it crystal-

Iber \va.y. Iron sulphide

tlic moist state this is

into ferrous suljihatc,

,^. The rock containing

Ui the air and moiistened;

large quantities of ferrous

method al pre|jaratioii h

to use the iron vitriol for

or "oil of vitriol" from iron
>tbe air or "roasted," whereby it
[•ulpliate : 4Fe80^ -^ 0, + SH^O =
latter salt iletojnposeB into
ferric oxide, in accordance with
^.-f HgSOj + SO^. The resulting
])hiir trioxide, on account of the
Bioist air {p. 2W6) ; it therefore con-
in contradistinction to the non-
Jen chambers, which does not contain
sill was prepared in fairly large quan-
irz, it was also called Xordhnuj<fii

. method is no longer used, as the nianu-
i by the contact method has completely

ibatc, ftirrous siilphute uiiitea with potassium

igomorphous with this, to form monocJinic

type K.jFe{HO^)^ . 61],.0. The aviiiummta

jO, which ciyst.tJlises well and docs not o-vidise

lysis (cf, Manganese).

13 Salts. — Fari'iw chkni/fe, FeCl.,, is a Kilt

lohiblc in water, and which in solution rapidly

ill the lalxinitory it is obtained in large quantities

jf sulphuretted hydrogen from iron sulphide and

On concentrating the solutions it is obtained in

sh crystals cot}tiuning 6H„0, which very readily

he air with browrj cmst« of basic ferric salt.

ia obtained in the anhydrous state by heating
'of hydrogen chloride. The latter is decomposed
of hytlrogen, and the ferrous chloride sublimes at.
^t in white -grey, lustrous scales, which feel like
salt dissolves in water with great evolution of he*

58i

PRINCIPLES OF IKORGANIC CHEMISTRY CHi

from it. The reaction SFel^ ■+- 1^ = 2FcI,,, therefore, doe* not
placo completely, but the reverse reaction tan also occur to a
extent. If the ioflinn. ta remove J from the eqtiilibrinm, the
reaction mast take place more find more, and ferrous icKlide
ultimately remain. The reaction, however, becomes increasingly i
cult the more totline is removed from the solution.

Writing the ions which are present, the equation runs 2Fe'"
31' = 2Fe" -^ I.,, and the reader may he referred to the considenit
set forth on p. 570.

* This reaction is used for linalytieal purposes for the sej:
of iodine from chlorine and bromine. For this purpose excew
ferric salt is added to a solution containing the halogens as ion«,i
the liquid is distilled. The ioilinc then passes off with the 5t«
while the Lromidion and chloHdioii remain behind. The volatili*
iodine is absorbed in a solution of potaaaium iodide, and titrate*!
thiosulphate.

* A mixture of ferrous and ferric iodides is obtainetl as an itiwr
mediate product in the piepiimtion of potassium iodide. Iodine i
iron, in the proportions .^Fe:8l, are mixed with water, wlier^byj
is dissolved, and the solution is precipitated with caustic itlknli
potassium carbonate. Potas-siuni iodide is foraied in the solution, i
the iron is deposited as tlic black ferrosoferric oxidn (p. f>8'2), wbic
can be more easily filtered and \va-slie<l than the other oxides of iron.

567. Ferric Flnoride, FoFj, is distinguished by the fact tb»t
is extrcmel3' slightly dissociated into its iorisi, and does not, therefor
exhibit the reactions of triferrion Jind fliioridion. It is a difficoltll
soluble, white compound, which forms with ihe alkali fluorides
pounds of the tyjw of cryolite (j>. 563), constituting the alkali ealt» i
a trivalent Unofen-jiniuti, FePy'".

568. Ferric Sulphate, Fc5,(S0^),„ is obtained by adding ta
solution of ferrous sulphate half as much sulphuric acid as is ther
contained, and evaporating the solution with addition of nitric
(to oxidise the diferrion to triferrion). After heating the residue the
is finally olitained a yellowish-white powder, which apparently d"
not dissolve in water. If left for some time under water, howe«r,|
it dissolves in aljundance, and fairly concentrated .solutions can
prepared. It is a sjilt, therefore, which has a very small solu

The solutions appear ^^ow^^-red, but the colour is all the paler tl»
more free ficid is added. This is due to hydrolysis, which is diminia
by free acid. Tlia hydpolysis again increases when the solution i^
greatly diluted.

Ferric sulphate crystallises along with potassium or ammoniural
sulphate to form Jilums, which are culled iron irhtms. The mI*
crystallises in oetahedni, which generally appear ^-iolot (probably owinj
to the presence of a trace of manganese). When pure the salt »

KON

585

colourless, tinged with yellow. Iron alum is generally used
it is necessary to employ a. ionic salt in cases where ferric
for siame reason, cannot I>e used.

Ferric Thiocyanate, Fe(SCN).j, is exceed ingly solnblo in

antl in the undissofiatecl state is of a deep red-lirown colour.

lest )iffloimt of triferi-ionj therefore, CAfi be deU-cterl by adding

I of thiocyiinaiiiofi (c.<7. potassium thiocyanate) to the solation.

the reaction is duo to the undissociated ferric thiocyanate (for

h thiocyananion iind triferrion are colourle.s8, or only slightly

Hired), it will, ceteris .paribu«, he all the more difitiuct the greater

oimt of the undigaociated coniponnd present,

object is, in the first instance, attained by a large excess of
on. If to SI sohttion eontuiniiig only a very little triferrion,
equivalent amount of thificy;ina,nion is added, the coloration
uce*i is very feeble ; it beoonics more pronoimcetl the more the
Qlraiion of the thiocyananion is increased. Furthefj the reaction
more distinct if the liquid is shaken with ether. Ferric
natfi in the imdissociated state is soluble in ether; the imdis-
etl portion, therefore, passes for the greater part into the ether,
fre«h amount of the comjxjund is formed in the aqueous sohition, and
also goes into the ether. When equilibriuni is finally established
is much mora undissociatejcl ferric thiocyanate in the ether than
was previously in the aqueous solution. As a conaequence, the
itiveness of the reaction is correspondingly enhanced.

* If a concentrated solution of sodium or ammonium sulphate is
led to a liquid coloured red \rith ferric thiocyanatc, the red colour

weaker, and finally disiippears. This is due to the fact that

the presence of a large amount of sulphanion, the triferrion

up for the formation of un<lissociated ferric aidphate, which is

coloured. The salts of monobasic acids do not act so strongly,

the ferric salts of the polyWsic acids are generally much less

than those of the moTjobasie acida. Fluorides act very

ly (cf. p, .534).

0. Other Ferric Salts. — frryir nn-tnie is an unstable salt, thu
iour of which is, for iinalytical pur|»oses, of interest. If sodium
IftUle (or acetanion in any other form) is added to the solution of a
ferric salt, the liquid becomes dark red in colour, owing to the forma-
tiati of vnduaonakd ferric acetate. This reiiction is used as a reagetit
far kc^tic a«id, but similar colorations aro produced by a number of
otber anions, so that the reaction is not unequivocal. If the red solu-
tion is heated it hecomea turbid, snd a precipitate of Iwisic acetate is
fttmed, which contain.s all the iron. In this way iron (in the ferric
4Ut«} am be precipitated from acid solutions, which is of importance
for many separations.

• If the liquid is agjiin allowed to become cold in contact .with the
precipitate, it slowly regains its red colour, and the iron begins to pass

586

PRINCIPLES OF INORGANIC CHEMISTEY

into solution, ^^■^len, therefore, an exact separation ia required, l
precipitate must be filtcretl hot.

''' The explanation of this reaction is the same aa in the case
alumiiiinm iieetiite {p. 567). Since acetic acid is a weak acid (||
hydrion of which ia still further diminished by the excess of acet
from the sodium acetate added), hydrolysis largely occurs, and In \
heat this goes so far that ferric hydroxide, or basic ucetatei, h
pitiited. The reverse process tiikea place at a lower teniporatnre
account of dirain>:tion of hydrolysis.

571. Ferric Phosphate, FePO,. is precipitated from a
of a ferric siUt, aeiditied with ac^3tic acid, by the addition of
phosphate, as a white, slimy precipitate which, unlike most of
other phosphates^ ia not appreciably soluble in acetic aciiL
property is also made use of in analysis.

573. Sulphur Compounds of Iron. — If iron mid sulphur
heated together a hlack mass of the comjx).sition FeS is formed,
we have wlready got to know as the starting substance in tho pp
tion of sulphuretted hydiogen. The compound am be prepared I
iiny deairod amount by raising the end of an iron bar to a rcd-l
lowering this into a large crucible, itnd adding sulphur in lumps.
two elements combine with so great a rise of tenipeiriture thiil
iron sulphide is moiled, and the preparation can I*f i^ontiniied
simultaneously fidding more aulphiu" and pushing the iron
farther in.

* A liydrated sulpliide of iron of a black colour is formed wb«
sulphur and iron filings are mixed in the projjortions 32 : 56, moi£i«a
with water, and allnwed to stand. The reaction cominenees slo
but is accclej'iitcd by the heat produced, and in the cjisc of
quantities St may be su violent that the nuiss becomes ineande
Such experiments were formerly often made in imitation of voI<
phenomena. Since, however, the lava of the natural volcanoes
not consist of iron sulphide, it is only a cjiso of oxtornaJ resemblancftl

Iron sulphide is readily decomposed by acida, with formation
ferrous salt and ^^dphurdied In/divfjiii (p. 273), anrl it is therefore
formed when snlphnrettcd hydrogen is passed into solutions of ferrtHi
Sidts, By mefinrf of unnitoniitm ttulphiali; however, a black precipit
of hydratod iron sulphide is formed in ferrous solutions; when finely
divided it appe;*rs greon-black, and forms a vorj' sensitive reaction fo
iron. Iron sulphide rapidly oxidises in the air, ferrous sulplmte
first formed (p, 578), ao that it cannot be washed on the filter will
beginning to dissolve.

Iron sulphide occurs native as maffnetic pifrifes in yollow-lrtD*
masses, with a metidlic lustre. These liave very nwirly the comiwisitio
of the simple iron sulphide, but always contain a slight excess of aulpbuRj
How this deviation from the law of constant pi"oportions is to
interpreted has not yet been explaitied.

moN

679^

' belongs to the next grxiup : this is due to the fact that thU saU
partially isomorphous with the other vitriols,
>n vitriol can be pi^epiired by dissolviivg metallic ii-on oi" iron sui-
te in dilute euiphuric acid and evapuniting the liquid till it erystud-
It is, however, \»«u«lly obtained in another way. li-oii sulphide
very widely distributed in naturo. In the nioiat gtnto this is
d 0!i contact with oxygen and passes into ferrous aiilphato,
Jig to the equation FeS + 20^ = FeSOj. The rwk containing
Bolpfaide is therefore spread out exposed to the air and moistened ;
a shaft time, by extracting with water, large ijuaiititied of forrous
can be obtained from it. This method of prepanitinn is
lieap that it was formerly the custom to use the iron vitriol for
?paration of sulphuric acid.

la order to obtain sulphuric acid or " oil of vitriol '* from iron

the salt was first hciited in tlie air or " roasted," ivhorcby it

convcn<xl into Imsic ferric sulphate : 4FeS0j + 0„ + 2H„0 =

)^(0H). On being heated, this latter salt ducom])oaea into

Imric acid, sulphur trioxide, Mud ferric oxide, in aeoordance with

equation i*FeSO^(OH) ^ Fe^Oj, + H,SOj + SO3. The resulting

of sulphuric acid and sulphur trioxide, on account of thu

ce of the latter, fumes in moist tiir (p. 2H6) ; it therefore con-

" fuming sulphuric acid," in cnntmdistiiK'tion to the tion-

icid prefwrefl in the Iciiden chambers, which does not coiiUiin

Since this fuming acid was prepared in falrli' largo quan-

Nonlhfiusen in tlie Harz, it was also called Nwdfiitn:irn

»rid.

At the present lime tliis method is no longor used, aa tho mariu-

of sulphur trioxide by the contact metho<l has completely

I all the others.

magnesium sulphate, ferrous sulphate iinitea with potasHJum
lie and the sidls^ isomorphous with this, to form nionocjinic
iilphtiles of the type Kjre(yO^)^ . 6 H.jO. Tho inmmmium
^)JP^:{SO^}„ . Gll.,0, which ciystaUises well and does not oxidiito
r, is used in analysis (ef. Manganese).
Other Ferrous Salts. — Firrtnis chloride, FoCl^, iH a mdt
is very readily soluble in water, ami which in solution rai)iilly
in the air ; in the lalxtratory it is obtjiinud in large qiumtiticH
preparation of sulphurcttcil hydrogen from iron sulpliido and
chloric acid. On concentratsiig tho solutions it is obtained in
rni of greenish cryeUds containing GH^O, which very nwlily
Diated ill the air with brown cruAts of liasic ferric unh.
lus chloride i& obtained in the anhydrous state by heating
a cun'ont of hydrogen chloride. The hitter is decomposed
Uboration of hydrogen, and the ferrous chloride subliraos at a
hi red-heat in white grey, lustrous scales, which feci like talc.
I anhydrous salt di^soivee in water with great evolution of heat.

580

PRINCIPLES OF INOEGANIC CHEMISTKY

Concerning fenvus hromidi: and fenms ioditir, there i& iioUiingi
to noto. The aqueous solutions of these suits are readily ohtainedj
bringing the free h.ilogens together with exeess of metallic iron;
aalta are very reiulily aohible.

Ferrous carhortufe, FeUOj,, occurs naturally as a. valuable iron
sptithk iron ore. It crystallises iti rhorabohedra which are
phonB with those of calc-apiir and of magneaite ; in the pure stab
is almost colourless, but is generally coloured yellow-brown
incipient oxidation. From aiiueons solutions of ferrous siUta
carbonates precipitate it as a greeiiish-white snbstiince, which
disaolves in acids, with eU'ervescenee, and which also Ijecomes r»tl
rapidly brown owing to oxidation.

563. Ferric Hydroxide.—By the addition of bases to solutio
of ferric sjilts, feri'it; byili'oxido, Fe(OH).„ is obtaineii as a lirof
flocculont precipitate, which is very slimy when prceipiiated in
cold. If the liquid is heated along witli the precipitate, the
acquires a firmer character, and can be readUy filtered.

Ferric hydroxide is a very weak biise, and is practically insoluli
in water. In acids it is soluble when frt^shly precipitated, niidiiit]
has not been heated ; it passes, however, into less soluble forms i
on standing for some time in the heat, pjirtial anbydriiJe fori
presumably occurring. On being heated to a red-heat it lQ«e» '
and is converted into ferric oxide, Fe^O.^ according to the eqt
2Fe(0H)j = Fe^O^ + 3H^0, This ignited iron oxide is almost ine
in acids, and passes into sohition only on being warmed for days
concentrated hydrochloric iieid ; it dissolves more quickly when it i«
at the same time reduced to ferrous salt.

Ferric hyilryxitle possesses the property to a very high degree rf
forming ct>U<)ii!<d sfiluHims. These are obtained by dissolving Lt!«hly
preeipitatofl ferric hydroxide in a concentrated aoiutioit of ferric
chloride, whereby soluble basic salts are formed, and dialyaing tliit
through a partition of parchment paper into pure water. The aquDoUl
solutions of ferric chloride, like those of atl other ferric aalta, •(•
partially hydrolysed into free acid and colloidal ferric hydroxid*
Since hydrochloric acid diffuses very i|uit-kly, while ferric hvdroxid*
and basic ferric chloriJc cjin hardly pcnctrat'O the parclmicnt jiaper,
the hydrochloric acid present first of all p/isscs out. The chemiol
e<(uiUbrium of hydrolysis is thereby disturbefl, more hydrochloric a/oi
must be split off', atni this is in turn removed I)}' diHusion. Th«
reactions continue until finally only or almost only colloidal fonr
hydroxide is left in the dialyser.

The solution so obtained is of a dark blood-red colour, and exhibit
the characteristic properties of colloidal solutions in the most distini
mannar. It does not possess electrical conductivity to any c«»nsitle
able extent ; its boiling point and freezing point, abo, differ only ii
appreciably from those of pure water. Addition of electrolytes ;>»»

IRON

581

it, the ferric hydroxide separating out as a flocculont niAsa

lical nvictionado not take place with it, or do so only very slowly j

esj»ecially, it exhibits none of the analytical cbai<ict«n sties of the

kits, which will bo montionetl hiter, since it does not contain

ion. On standing with hydrochloric acid it gradually passes

a liquid possessing the properties of the solution of ordinary ferric

aride.

alutions of colloidal ferric hydroxide fire pi-eparod in the above

for medicinal purposes, und are soi<l under the mime ftnitm

turn ftinitfAtfum (dialysed iron).

ifith hydroxide and oxide of iron occur in nature ; both are ini-

iron ores, and are callefl brown iron ore and hiematite respec-

elr. The former occurs in brown-black lustrous masses, which, on

iig ground, yitild a ff>'!lou-<-fiiow)t jKtu-^er. Iron oxide cry-staltises

rhomlMjhydra whith are iaomorphous with those of corundum

i6*>), and have a black metallic appearance ; in this form it is

iron 'flmiK. The concretionary iron oxide (kidney ore) has a

3U3 hlnck apjiearance similar to brown iron ore ; on being ground,

r, it gives a red powder.

Iron oxi<ie and hydroxide are extreinely widely distributed in

In the primitive rocks, iron regnlarly occurs in the foiiii

licate ; in the weathering, the silicic acid i& removed and the

ide remains. This mixes with all sedimentary rock?, and im-

thcm a yoUow-bi-oi^-n to red colour. When reducing actions

ar, fw, for example, through adnnxture with organic substances, the

ie hydroxide is reduced to the dark-coloured coniifound mentioned

wi p. 577, and this gives a grey blue or greenish-blue colour to the

rticular substances. This colour is frequently seen in the case of

containing iron; when these are "fired" the organic siihsUtnce

destroyed, and the iron passes int^j ferric oxide, whereby the pre-

a«ly blue clay become of a rod coloitr.

Ferric hydroxide re^scmbles aluminium hydroxide in many respects,

wpecially in the fact that the salts of both have a similar composition,

I and are also mostly isomorphous. Like nhirainium hydroxide, ferric

I hydroxide is completely precipitated by ammonia from Boluiions of

I ferric salts. It differs, however, fiom ahiminium hydroxide in the fact

that it ia not dissolved by strong Itasos ; in fact a method of separating

tile two h^rdroxides can lie based on this dilTerence. The method,

however, is not very exact, for the diHerence, or the inability of ferric

Ihydroridc to form ainons containing oxygen (p. 5(50), is oni}' one of

degree; in very concentrated .solutions of the alkali hydroxides, ferric

bjrdrojdde dissolves (juitc apprecialjly, and for this re^ison raustic alkalia

in iron l^^iler's almosit always contain iron. On <iiluting the

, the compound decomposes and the ferric hydroxide is gradu-

i depoeited as a broi.vn precipitate on the bottom of the veasel.

Id tbe presence of many organic substances, such as tartaric ftcid.

582

PRINCIPLES OF INORGANIC CliEMISTRY

sugar, glycerine, etc,, nil of which contain several hydroxyl
feme hydi-oxide is not precipitiited by aJkalia from sohitions of i»
salts ; ou the contrai-Vj elear brnDwii liquids are formed which
the reactions of iron only imperfectly. The description of the
pounds hereby produced belongs to organic chemistry ; they are
likti compounds in which the iron ia present not as cation but as
of a complex anion. Tliey have received mention here from the 1
that they are extremely readily formed, and when formed they
the analytical detection and the precipitiition of the iron more ilif
In such cases the organic substiincG must be destroyed, which is no
easily done by strongly heating.

564. Magnetic Iron Ore. — Ferric oxide unites with ferr(iQf|
oxide to form a compound which occurs abundantly in nature, and
a very vahialjlc iron ore ; FojO,, '- FeO = Fe,,0^. It is called wj
iron tire, its it frc<iuently exliibits a strong natural luagfietism;
chemicaJ name is ferrosot'erric oxide.

Magnetic iron ore crystallises in regular octahcdra, and is iw-l
morphuus with .fpind (p. 5fil), which consists of aluminium oxideaadl
magnesium oxide, AUO^ + MgO. M can be seen, the two c«»o)jH>nnd»
arc constituted after the same type, since Vioth contain one coiuhinin^j
weight of a monoxide, MO, to one of a eesiiiuoxido, M^Oj. In the jnt-j
sent case, however, iron is the only metal present, its divalent form
taking the place of magnesium, and its trivalent form that of aluminium.
Ifi magnetic iron ore, therefure, both the isomorphic relations com*]
simultaneously into force.

If ferrous salt and ferric sjilt bo mixed in such proportions thtl 1
there is twice ;is much iron in the case of the latter silt as ici the!
former, atwl the mixture Ite poured into excosis of caustic soda, a hlack
grantdar precipitate is tiltbuoed, whicli may Itc looked n{>on as k
hydroxide of the above compound, A salt-forming K'l.se, also. appoM*
to exist; this is a C(im]>ound of ferrous and ferric hyrfroxide, and
to it is duo the greenish colour of the ferrous salts. This conipnuud,
however, if it exists, is very luistable, its salt* decomposing ulrafirt
coraploiely into niixtuics of ferrous ami ferrie salts.

065. Perric Salts. — Fem<: cJthiriile, FeL\ is obtairje<i by heatin|]
iron in a current of chloiiiui. It then sidjlimos as dark-green crystiU
with a meUdlic lustre, and is much more easily volatile than ferroa»|
chloride.

These crystals dissolve in water with grcjvt rise of tertiiKratun.
and yield a yellow-brown solution from which the anhydrous salt
cannot be again obtained hy evaponitiun and heating. Four difierent
hydfates contaiiung from (iH.,0 to i'H.,0 crystallise out, accord iiig W-\
the temperature, and on attempting to drive oH' the last tract's nf wat«
by iie.'iting, hydrogen chloride is eliminated at the sjime time, and iron |
oxide remains Viehind.

Hydrated ferric chloride can be obtained by dissolving ferric oxidfll

IKON

591

Since an increase in the positive charge h equivalent to
of the negative, the following ions correspond to one
aer: —

Diferrion Fe ' and FcTrocyanidion Fe(C>r),"".
Triferrion Fe*" &iid Ferricyanidian Fb(CN),"'.

pspondeiice is aUo given expression to in the Datnes.
Ee getieral properties of the ferricyanides are sitpiliir to those of
Iferrocyanides. In these compounds, hIso, neither the reactions of
ion nor those of cyanidioii can be detected. A diiforeoce, how-
is shown in the reactions with iron siilts.
If iliferrion and ferricyanidion come together, h blue precipitate is
aed which is veiy similar to Prussian blue, but has ;i somewhat
eot composition. For the salt which is formed, ftrrous frrri-
!f, has the comjiosition Fe,,[Fe{CN)J.rt or in sum Fej(CN),j. It
ktaiiiF. therefore, 240 combining weights of cyanogen to one of
while Prussian blue contains 2*53 combining weights of cjanogou
ione of iron.
Xo precipitate is produced with ferric salts, but the liquid only
jmes somewhat darker in colour. Ferric ferricyanidc is soluble iii
er, and in the undissociated state is dark coloured.
By means of coticentmted hydrochloric acid, bydroferricyanic
H,Fe(CN}^p can he blterated from the solution of its salts, and
be obiaine^J in brown needles which are readily decomposable and
readily soluble in water.
The ferriius compound is decomposed by alkalis in the same way
ifni^ian blue, for potassium ferrocyanide ami ferric hydroxide are
ie»1, iuid not potae&ium ferricyanide and ferrous hyflroxitle, as one
aid expect. This is due to the fact that the potiissium ferricyanide
niarily formed is retluced by the ferrous hydixixide, which is a very
ong reducing agent, to the ferrous compound, the fen*oiis hydroxide
ng coti V Rrt^ed into ferric hydroxide.

S7G. Other Complex Compounds. — With many other sub-

nces Iteside* cyanfjgeii, iron is ciipable of forming coraj)!e.\ eom-

tids which contain compound ions in which iron is present, and

erefore do not yive the reactions of iron, or do so oiily very in-

apletely. The description of most of these substances must be

littcd here ; only a few of them, which, for some six;cial re&son,

licfly analytical, arc of iniportiuiee, can be mentioned here.

In the first place, there must )« mentioned the cura|hiuTids which

formed when nitne adih or higher oxygeti comijounds of nitrogen

brought together with ferroufl &alt£. The latter compounds are

tri reduced to nitric oxide, and this unites with the diferrion to

the compound ion FeNO". This is, however, rather tinstable,

it undergoes decomposition even on lioiling tlie solution, nitric

ie escaping and diferrion being again formed. This behaviour 14

592

PBINCIPLES OF INORGANIC CHEMISTRY

made use of for tbe preparation of pure nitric oxide from mixed ^
On it also analytical rnetliock of detecting nitric oxide and the hij
oxj-compouriils of nitrogen dejiend (p. 327).

Further, tlie complex iron anions can be formed by the com
f>f ferric hydroxide \»-ith organic {and also with some inoi
substances containing hydroxy], which were mentioned on p,
They are recognised by the fact that their aolutitms are uot pi
tated by alkalis.

577. Oxalates of Iron. — The oxalates of iron, which hai
from all time been regarded as a chemical puzzle on account
the differences of their colour from the onlinaiy colaurs of the f(
and ferric compounds, must also be reckoned among the
comtMWnds.

\\'hen free oxalic acid is added to a ferrous salt^ a cr;
line procipifcitc of ferrous oxalate, difficultly soluble in water,
deposited. Unlike the other ferrous salts, this is not greenish
orange coloured, tike a ferric salt. It dissolves with a strong
red colour in an excess of potassium oxalate, and from this
the salt K,,Fe(CoO^)., can be obtained iti crystals. In the aolnl
therefore, a salt of the complex ferro-oxalanion, Fe(CjO^).,", is fona

* The solution of potassium fen-o-oxalate, which is |>rcpiired
the moment it is to be used by mixing solutions of forruus i
phato and normal potasaiura oxalate, is, on account of its powerful
ducing properties, used in photography for developing silver bronud
plates,

Moist ferric hydro.vido readily dissolves in oxalic acid to yield
liquid which, unlike the other ferric salts, is coloured ^reen. "Tk
colour is, however, emerald green and not [lale green, like that of tl
ferrouij salts. From the solution, badly crystallising ferric oxaltl
can be obtained, which reailily decomixtsoa. If, however, auothi
oxalate is added, tine crystalline, green coloured salt^ of the cotnpki
forro-oxalMnioii, Fe(C20^)a"', are obtained, e.ff. Kj,Fe(CX\),j,

The Holnlious (also coloured green) of these sjdts {wsseas in
high degree the property of surimtieeiifss to liffhi. In sunlight,, a sold
tion of ferric oxalate almost insttvntaneously deposits a yellow jirocipi
tate of ferrous oxalate, and carbon dioxide is evolved : ^^ealCjO^),
3Fe(CgOj) + 2C0,. Tlie salt^ of ferrioxalic acid behave in a suiultf
manner, being converted into the corresponding salts of ferm-oulit
acid : 2K.,Fe(C,0,)., = 2K.Fe(C.,0,)2 + K.fJ\ + 2CO,. These pb*
iionieria are made niic of for the production of photographs, esiwcinlljP
of platinum pictures, a graded reduction being allowed to take pU»
by exposure under a " negative," and the potassium forro-oxalat* thw
produced being used for the reduction of platinum from a comi»uni
present. The solution has also Won used as a cheiaical photouie«r,
iy. an apparatus for measuring the strength of the cbemicaily sftiKe
light Apart from other objections, the results aro of little vaiiu,

IRON

593

the fatl that every sensitive substance has its particular range oi

waves whicli it absorbs untl makes use of for chemical reactions.

is, therefiire, no siuh tiling as a, " cheniieat intensity of light"

.ih&olute sense, and every chemical photometer intlicates the

of only A flefifiite range of rays of the light subjecte<l tt>

%lion, this range bt'ing dependent on the nature of the

)m«ter.

>*, Iron CarbOQyls. — Carbon monoxide combines with ir<iu to

very reraurkable (.■timpijiinds, 'whicli are slowly formed when the

components come into conttict at the orduiury or at a slightly

teiuperatiire. Various snljsl^incea are hereby formed, conUiiji-

>m 4 to 7C0 to iFe, which on cooling condeiiso to brownish

red liquids ; tbey are reivdily volatile, so that they mix iti the

lUs- Bl-at« witli the excess of carbon monoxide. Theii' Velocity of

.lion in HI) small that even by using finely divided iron with a

giirfftce, ordy very small amounts are formed, which are dithcult

lUte and to prepare pure.

Appreciable amounts of these ctimpoiuids are formed in iron

which convey gas rich in carton mniioxide, especially when the

iuitfi are long iirid the carlmn niotioxide has, therefore, time to

with the iron, \\hile for ordinary purposes these traces of iron

ic g:i« are of no impoiliiuce, they have proved very inconvenient

ic Hpplicatioti of such gaa for iiwdiHlesri'nt light, as th« iron oxide

(h is pro«3ticed in the conibuetion U deposited on the incandeseeot

itle», and im^ktirs their iJiuniinating power.

Uj^ttcr known example of such comijonndfi will be deecrilied
!r nirkel.

''>'■ Catalytic Actions of Iron-— Both in the ionie state and
tiiaenais coTnj)<)nnd;i, iron frequently e.verciaes a very considerable
lytic influence, especially on oxidation proceaaes. To obseni'e this
only necessary to mix dilute soJutiojis of hydrogen peroxide
hydrogen io<lidc, or better, potassium iodide plus acetic iu;id.
;ion slowly occurs in which iodine is liberated and can be
viaible by nu'anss of stivrch. If quite a small amount of
Ilia ssalt is added, the blue eolorjitton occurs incomparably
utckly. A similar accelerating action has been proved in the
many other reactiotis.
t the pre^ui time, no regularities of a more general nature are
reapccting these relationa. It is of imporisince, however, to be
of them, since the physiological importance of iron probably
inilg on iheta. The presence of iron has been detected both in
red blood corpuscles and in the green colouring matter of the
••"imilaM'ng ]>knt cells (i.e. those which reduce carbon dioxide in
%k). and altlinugh at the present time the laws of these relations
pitjDot be stated, nevui-theless the fact above mentioned indicates an
direction for investigation.

594

PRINCIPLES OF INORGANIC CHEMISTRY

580. Thermochemistry of Iron.— The heats of formaua

the moat iKiportant coinponrttls nf iron aiT : —

Diferrion Fe " 93 ky

THferrion Fe ' -39 ,.

FerrBus liyJrrtxiilti Fc(On).. f>71 ,,

Ferric hydroxide Fe{OH)a ' %'2'^ .,

Ferrosofurrit uxide FujO^ 310" ,,

Ft'frous chloridt! FcClj 313 ,.

Ferric, ohlnride FeC]-, 402 „
Ferrous siiliihide (hydi-at^d) FeS + HjO 100 kj.

581. MetaUurgy of Iron. — -As meUiUic iron does not a
native to any grtait extent, the very lurge i|iiantities of this in
which are used in the iiidustrios must be lajunifactiiie*.! fmut
coiiapoauda For this purpose the oxygen compounds, irhioh
reduced ivith charccud, are alraoat exclusively used.

This reduction is t-arried out chieHy in the blasts furnace, whio
an upright, eloiigtited, egg-shapt'd a{«ice enclosed by m«soriry . i
this alternate byers of iron ore and coal, alimg with the iuldicJ
neceBsary for the production uf a readily fusible slag, are itiLrodn
from the top. In the low er pari of the furnace there is ii nan
cylindrical t^paee into which heated air ia blown, and in vbieh
fused iron colle<;ts.

The thfiiiges which the ore midergoea in such a furnace are ml
varied. In the u|)pei* jmrts it ia only healed, whereby w«t«l|
eliminated from hydraterl ores, Cijrlxtn dioxide fconi iron OArbonj
and the ores arc converted into ferric oxide or feirosofemc nd
In the lower, hotter parts of the furnace, thie ia reduced to mei
iron by the carbon monoxide which is present in abundance.
the tBm[>erature is not nearly high enough to melt the iron,
reduced, spongy metal sinks down along with t!ic excess of cha;
to the lowest piirl of the furnace, where the highest temperatui
reached through the coniliuation of the charcoal in the injucle<J j
The iron here combines with carbon and fuses together, fortning 4
iron or crude iron, and collects at the bottom of the furnace. I

The iron ie run off from time to time and formofl into loi^
blockB, or used for making castings. The slag which is fonnt;^
the same time, and which is essentially a mixture of various |
cates, floats on the fused iron, and can continually run off tbroi
an nverfiow.

The crude iron obtained in this way contiiins, besides about 4
cent of carbon, silicon, phosphorus, sulphur, ami also manganeal
vaiying amounlB. For the conversion of this into wT-ongbt-iron I
steel, not only must the amount of carbon l>e reduced, but the c\
admixtures, which diminish the \ulue of these other kinds of i]
must be removed as far as possiltle. |

For this puriwse, aeveml methods are employed, wb

•Dutber, however, tmly in the technical deteila, hut which nil

Biniint to the ejimn thing cliemi<:nlly, viz, the removiil of the foreign

.•:3 b_v o-fitfiition. Tht fhemical refictions are most rew-Hly

_."le in the HfH.'ti'mefprtkYs^, whtL-h is at jireseiit uhieHv used

I The iron is iiunxlticed in the fused state into u largo pcar-shapetl

Jtteei, ainl berited air is blown through the molten muss. The

■ipurities then burn more rapidly thiui the iron, and the products of

Oxidation pjtss 01!" in the giiseoiis state, or pass into the alag which is

fciinnfMnt'uiisIy (oi-tned. While, in this injinner, carbon, silicon, und

>o\phur cair Ite rcjidily removed, the removal of the phonphorus was

sun.'cssful tvs long iis thyie Wiis used for thn vessel h lining which

isisted esseiitiully of cl.ty. Xot until this wns repLtced by a /»i[^

ig conaisting of limo or niagnesia., whereby the phosphorus pjisses

thf siLig iis the corresponding /'//ftAyiArt^r, did it liecome itossible to

^<mm1 wronght-iron or atcel from crude iron rich in [ihosphorus.

, rich )i! phosphoric acid which is thereby formed, is used as

yi^ niii'urUint fertiliser in agricultui-o (p, 532), and is tailed 'J'fumias

WVt *ft«r the inventor of the method.

K The eoiirse of decarbonisation by the Bessemer process, which
WM plncv in a very short time, cjin be controlled by spectroacopic
tWrvation of the flame produced, and can be internijited at the
dwirwi moment. If '2 per cent of carbon is still left in the iron,
rteel is formed ; if the amount of airbon ia reduced lo 1 p«r cent, and
IcB. a kiml of wrought-iron is obtained which is called ingot iron.

CHAPTEE XXVni

MiNGANSSB

582. General. — Tbe element maiiganeae ts very cicwoly related
ifoii, It iliHl'i-s from it in being more re^Mlily oxiiHsed, mid in i
higher coiiijjoiinris Inning more residily forniud than \n the ca?ie of ii
Fur tho rust, ih« corrospomiidg (.'umpomuls of iniiiigitjiese tunf in»ii a
very similfir to one anothi^r, iind in niiMiy caaes are isnmurphous.

In nature, manganese uccurrf very widfily <listriljutt^i], but i» itiUr
less alnindaitt than iron. It is found chiefly as munyune^ fYiurK
MnOj, the mnuy applimtiuns of whicb we have repeatedly iiottil.

In its chemical relations, manganeao is chatticteriBed hy thu vi
grtMit diversity of its compounds. It forms not leiss than five oxi<Ii
tjon stages, the lower mombers of wincli fomi bases, ihe highor, actil
There is, accordingly, a corr«?Mp(tiKJiugly large niimlter fif <)ifler«B
dts coritjiining manganese. By reiison of this it exhibits very divcn
r relations of affinity and isoiuoqihisin ; whoroas tliu lowest sfrie* (
eompijuiide ia allied to magiieaiiira, the following ones exliibil i*
niorfihic relations with aluminium, titanium, sulphur, arid rhlorine.

The combining weight of manganese is Mil = SS'O.

583. Metallic Manganese. — Pure mangstnt'se waa formerly litt!
known. The uu-tal fuses with still *iroater ditfitulty ihan irttn. aiH
like the latter, it unitet* at a liigh tempeniturc with furlioii, st> th
the clement obtained by the reduction of the oxygen comjiouiifls wi
charcoal always contains a fair qiwutity of carbcin. Manganese
from rarbon ctm now be reaHih' nhtainetl by reduction with aluininiui
according to the method of (Mildsehniidt, and manganese is thus feui
to be a reildish-gryy, lustrous metal which is harder than in»n
keeps very well in the air, wheieas the e^ubonised metal which *
fomierly known oxitlised very ia]jidly. It is very leatlily disailvi
by acids, and in this respect prolmbly takes the first place among ti
heavy metals ; even in dilute acetic acid it evolves hydrogen wit
great vigour. By the dissolution, the corresponding manganoiiM ail
is formed.

Mauganeae is not used in the free state, but is employed in keg

S9«

itHies as an afldition tn ircin. White cnido iron (p. 574) generally
bntains larger or smaller amoiuita of it. Such aii iron is especiiJly
kutahle fur being traated by the Bessemer process, as the great hcMit
LMCvlulioTi iif manganese facilitates the maintonunce of the rttquisitc
Wk tempeniture.

^584. Dimanganion.— The fii'si series of compounds which maii-
pu>p«e ('.tnn». is deri\ yd from the divaleiil ion Mn ", which, in mmiy
BqwctB, has a great similaritj' to magnesion. Diraangiinion hfts a pale
Bddi«h colour, no !ip$dHl physiologist) act>>i)i, aiid it^ heat of fortna-
ioa is 210 frj. All 3olnble mangadons ssalts are distinguished from
he ferrous salts by the fact that t-hey do not oxidise in the air in acid

|^>i5. Hani^anottS Hydroxide, MnCOIDj, is obt«ined asa reddish
^Be precipitik^ wht'ti i\ sohuinm of a manganons salt ia precipitated
witli alkalis. In the (air, this precipitate rapidly becomes brown,
tbereby passing into tnariganic hydro-vide, Mti{0n)3. It is not dis-
vAvfui hy excess of alkalis, but is so by ammonium salts. The reason
i»erfully the same as in the case of mngiiesiitm hydroxide (p. 541) ;
lie degree of solubility, also, ie altont the same. The ammoniacal
•cJution. however, behaves dift'erently in ao far as it rapidly become.^
brfiwT) and turljid in the air. This is due to the absorption of oxygen,
"wiiercby manganic hydroxide is fonned, which is much too weak a
to lie anltible in ammonium salts.

X heating the carbonate or by precipitating hot, the anhydride,
noTjs oxide, MnO, is obtained in the form of a greenish powder.
i the nianganous salts, the chlori'h; MnCI^, may in the first place
'ntioned. It is obtained in the impure state as a residue in the
imtion of chlorine from manganese peroxide or pyrolusito (p. 1 69).
a pale ri'ddi.ih, easily solublf salt, which crystaltisea with 411^0.
686. maD^anotls Sulphate, .MnSO,, crystallises genendly iu
iwd, redilish crystals \^^itll 4ll.,0; besides this, it can crystallise with
THjO it) the forms of fcrrou." sulphate, with 5fl^0 in the forms of
a^jp-T sulpliate, etc. With the alkali sulphates, also, it forma mono-
iloiiblo sah.s ..f l!iL> type K.fi>(\ . .MnSO^ . 6H.A
!$s7. Mang^anous Carbonate, MnOO,,, can l« iiiitained as a
rwiiJiith preripiuto, by precipit;»ting nianganous salts with carl>onatea ;
ULudiliscj in the air, but much les^ mpidly than the hydroxide. In
^Birei the carbonate is found as mmif/ttnesi^ spar ; this occurs in
^■ifioleili-a, which are isomorphous with those of caU-fipar.
PP^i^i^ Manganous Sulphide, MnS, is the mo.st soluble of the
' Wlphur compounds of the heavy metals which are formed iu..A||iu^Up
^yimioo. It is decomposed even by acetic acid, &ncL^^ff^int!tiVOiji
Ifet W precipitated from aolutions of nianganous salte j^KlTsulphitrjttCTl
P^'Hgen, hut only with alkali sulphides. If thlr'^rocQijtetjon irf

■

698

PRINCIPLES OF INOEaANIC CHEMISTRY

caji,

centrated solutions in the heat, anliydroua maiiganoiia siil|)iiide
Bometimes precipitated, under conditions which are not yet esac:
known, as a grey-green powder. In the air the sulphur curapnil
oxidises very riipidly, so that it must be washed witli a solution
ammonium sulphide" when use is uitide of it for the precipitation
mangaiiesi.' in (tnalysi.s,

589. Manganous Borate is obtained by the precipitation of
manganous salt with borax, and i« placed on the market in the form
a brown powdet. It is used in large quantities for the preparation
varaiab. This is due to its catalytic properties. There are ccrtal
vegetable oils, e.(f. linseed oil, which oxidise iti the air to rosim
masses. With the crude oils, this o-tidatioii tak«s plae* only s\nw\f
if, howovor, the oil is hoated atid a small quantity (less than 1 pi
cent) of m:ingnnoU3 borate is a<lde<S, the absorption of oxygerj is great!
accelerated eatalytically, and a rapidly drying oil or a varnish
obtained. Further, dimanganioii has the property of very gix»1
increasing the action of certain organic cafcalysers which accele
oxidation, the "oxidases."

590. Macganic Compounds. — -The compounds of trivalent
ganese or the manganic compounds, ai'B formed from the roarigano!
compounds by oxidation. Even in the ease of iron a coiiai<icnihl
diminution of the kvsic properties accompanied ihe corrcspondii
tiausforraation, a fact which found expression in the incipient hydi
lysis of the salts ; in ihe case of manganese, however, the ditferonc« i
much greater. The hydrolysis of the manganic comptiundiS in lu^aeoi
solution is so great that such compounds are quiii; unstable, ao
rapidly decompose with separation of mangaiuc h\'dioxi*!e, AIn(OH)j

For this reason, very little is known regarding the jn-opTtiM
the ion Mn"*. Its colour appears to be violet-red, and the du
brown colour of some solutions of manganic salta ia the result
liydrolysis, since the manganic hydi'oxide is dark-brown in colour.

The normal hydroxitle does not occur in tialure, but \-xr'm
anhydrides of it do. The partial anhydride MnO(OH) ia caIU>d /mn
panila ; mauganoae suaqnioxide, or the complete anhytlride, MujO^
called braunik, and Mnj,0_, ImmmimnHt.

In the solid state, some of the manganic salts are known as ve
defined compounds, The sulphate is obtained by warming maiigao<
jieroxide with concentrated sulphuric acid until it has dissolved t9
dark-coloured liquid, and then washing the |)aate of sulphate, which
formed even in the heat, free from sulphuric acid by means of aittl
acid. It is a dark-green powder, which Jisaulves in wst*r
violet-red colour, which very speedily clianges to brown, m
hydroxide being deposited. Manganic chloride, MnCig, is also formi
temporarily, when manyanic hydroxide is dissolved in cold c«>»
trated hydrochloric acid, and on dihition with water beliaves like *i
sulphate.

^CVlIt

MANGANESE

599

Those miittgariic salts, howevei', which are not ionL^ed to any great
Xbetit, iimlerKo only a s)it;lit hy^lrolysis, ivs was to be fores'^L'n uucord*
Pg to the ihuury <tf liyJi'olysis. To these thL^ie belongs, in iho iirst
■slarii-e, the tluttruK-, MnF,, wbiL'h am he prepttred by dissolving

luaiik- hydroxide in aquoous hydrntliiorie acid, and whieh can be
! in (iark-rwl crystals. This fonns double siilta wiib the alkali
.if the tyjje K,F,,. MnF,^ , i>H..(>.

lujjUy, the phosphdte, MnP<J^, appears to be a slightly dissociated
mlt h di?snlvt's in excess of pfimphoi-ic acid to a rt"d-viulet hquid,
wkieb ia stable even at the tcmiMiratini' of boiling.

S!i|. M&C^aneae Peroxide. — Teti-aYaloDt manganese forms the

Erojcide Mti(OH),, the anhydride of which ia the oft-mentioned
gsoese pecDxide, MnOj. Since even in the ease of trivaJent
gUKsse the basic jtropi^rties had practically di«ap[warcd, Jt is
BMural that tetravajent inaiiganeac is no longer capable c*f fonuing
lalu likf a Ikis<». On tUt* utber hand, the acid properties which are
jnsent in a pronounceil manner in the higher stages of the manganese
junds, bi'ijin to be indicated here.

anganaso peroxide occura fairly abundantly in nature as />vr"/M.<fVf,
the muBt im])ortant of all the naturally occurting compounds of
nese. It occurs in grey-black crystals, the powder of which is
(not brown).

he hiidniJide, Mti(OH)j, is obtained by suijjccting nianganoua
lo strung o-vidisiiig action.^ in nexitral or alkaline Hijuids. As
lin^ agbtjt there can be U8e<l chlorine, bromine, or a hypochlorite.
hydroxide is <lark-ljif>wii in colour, and amisrphous, and |>asses
"If into the colloidal st-atc. By moderatfi dehydration, the inter-
itc anhydrido, MnO(OH),, which has the same apjjcarance, is
ncxl.
the hydroxide is treated with cold, concentrated hydrochloric
«id, it diA»oh'e.« with a dark brown-green colour ; if the aolutiori is
^uedialeiy diluted with a hirge quantity of water, the hydroxide is
^^b depouittid. This h due to the formation of a tetrachloride,
^Kl^, which is hydroly-sed by much water. If the solution is
Hpne<l, it becomes colourless and evolves chlorine ; manganous
' fHorid<' remain:; in the roaiduo. The reartion for the pie].iaratioii
chliiriiie given on p. 169 Uikes place, therefore, in two stiges,
hloride Iwing first formed and tlien decomposing into chlorine
dichloride. The oqualions are MnO, 4- 4HC1 - MnCl^ + S^HjO,
MnC\ = MiiClj + Clj.
w m.'»iignnese perhvdroxide prepjircd as above given, generally
lo<j little oxygen on analysis. This is due U* the fact that the
rmnd, MnO(<>H).. or iLMnQj, can act like an i\nd, corresponding
fcrWnic su'i<l <H' sijjjthujuns acid, and form s;dt-s. If the manganeBe
ide IM formed in pre-'sence of a Viaso, all the manganese piisses
comp«^jinid ; in the absence, however, of another base, part of

600

PRINCIPLES OF INOEGAiJIC CHEMISTKV ai

the manganese in the divalent state is incorporated in the jireripiu
the iimnganous salt of the above acid, nmtiffnnims rwid, the formula
which is Mil , MnO^, cqiial to Mn.iC),,, being formed. If, boweru
base is present, ctj. lime, ailriiun manffunile is formeil, and ill t
manganese passes into the t^^truvalent state.

* This redaction is made use oi for the rttjeitmrfiim of the nu
ganese liquoi-g in the miunifactiue of chlorine from hydrochloric u
and pjToliiaite. The renitisito amount of lime is mided to the lifjuc
in ordei' to convert the inHii^anous chloride into tunngaTiuns h)*droxi(l
and still one eomhining weight of lime more. If air is Klovvn thniti
this nitxtnre, uxiilatiori tiikes place mpidly and readily, Jintl lailctt
nuingaMite. CfuMtiOj, is deposited as u black prfei|jitat«-". known
Weldon mud. This again yields chlorine with hydrochloric ;icid, b
half as much hydrochloric sicid more is required, as can be seen frc
the equation CaMnO^ + CHCl = CaCl^ ^ MnCl^ + CI,.

* At the prefient day this method is Vieing more and more giv
up, as the electrolysis of the alkali chlorides yields more chlorine thi
vnw be made use of in the arts.

Besiik's being used for the prepanition of chlorine, mangan
peroxide is, employed in pottery works for the prorhiction of bniwn a
violet colours. Melts to which manganeic peroxide ha« been addi
are coloured violet ; if iron is present at the same time, a dark-brtm
colour is produced.

Manganeae peroxide is also employed in the rnarnifacturo of gl
It is there tised in order to remove the greeiusli ctjloratioti which
glass aaatimes owing tr* the presence of ferrous comfjounds (p. 5S8
The action is probably due to an oxidation of the ferrous to the f«
compound, the yellow colour of which is much feebler. Besides tku
the yellow coloiu' of the ferric glass ie counteracted by the vitili
colour of the manganese salt, and iin impcrccplible neutral tinl
|)]'oduccd.

* Glass which has been decolorised with inanganosc oxhiliit« ttM
remarkalile property that it slowly becomes red-viulet in colour whei
exposed to light. This colour passes through the whole mass of tin
glasH, but is absent from those parts where the light was naik^ned, U^
for example, behind letter.'^ fixed on sho]) windows. This phcnoiuenn*
ts a proof that in spite of tiie apparently solid nature of the ^'la*^
choiiiicsil processes can occur in the interior of the maRs, as in a liqui<
which is not in equilibriura.

* Manganese pertjxide is ako used for making galvardc colls, »iiic#
it conducts the electric current, and aa a catho<Je gives a fairly higb
potential with zinc as anode, The pl"OCe8Ses taking phtce ui galvanic
cells will be discussed in lietail at a later jioint in connection witlii
simpler case ^Cliap. XXXII.) ; at this point it will he sufficient t0 5l«t«
that such cell.s are generally formed of an oxidising agent ami *
reducing agent, separated from one another by an intermcdialc con-

MANGANESE

601

-5-i>-

generally a salt solution, svml where necessary, a porous
On making the proper connection, tin olectric current is
3 whereby the reducing agent is oxidisetl at the expense of
ising agent ; the chemical energy which tliereby liecomes free
work necessary for the electric current. In the above ctjil
d of n)»ngancse ]^}ercixide and zinc, the manganese peroxide is
ising and xinc the reducing agent. Both these jire inunei'sed
ition of sal ammoniac, and when the circuit is closed the zinc
p *nd the manganese peroxide is rediiccd to manganous oxide.
Jnch » cell can be c^isily made as follows. A mixture of
and coke (for the sake of the condnctionj is pkced at
in of a tumbler, a rod of
ting charcoal is introduced
j!''*ml the glass filled with a
of ammonium chloride ; a xinc G

spcndwl in the u((pcr psirt
liquid in 8uch a way that it
n touch the manganese per-
d the charcoal (Fig- 1 16). On
lite sine and the charcoal by
a conductor, an electric current
irongh the latter. Such a cell
ih^ cell) lasts for a long time
Hnall, intermittent cnrrent.a are
rom it, as, €.g., for electric
pr strong, continuous currents
dess, l»ecause the necessary chemical reactionB do not occur
lly rapidly, and the cell therefore quickly loses its ele^tro-
tftCK wbeu much used. It recovers its electromotive force on

ignitiou, manganese peroxide loses oxygen, and is converted
■ganoso-maiiganic oxide, Mn^O^, corresponding to ferrasoferric
The reaction is 3MnO„ ^ .Mn.,0^ + O^. This wbs formerly the
hy which oxygen wjis preparcil in the pure statt,-. and ft has
f a certain historical iniptjrtiinre. '

e rannganoBO niangaruc oxide, although not of exactly con-
lion, is formed when any of the other oxides of manganese
w»e carbonate is ignited in the air, and this form is therefore
"weighing manganese in analytical separations. As has been
1. however, the composition i* not quite constant ; this dettends
wciftlly on the teniiperatnre, the amount of oxygen decreasing
AS the temperature rises.

Sfangan&aion and Permangananion. — Although com-

»of A jicntjivalent nianganeae arc not known, mangivnic acid,
can be regarded as a partial anhydride of the hydroxide of
M niangan"ese. for Mn(OH)„ - 2HjO = MnOjlOH)^ ^ HJInO^.

Fm. 11«.

602

PRINCIPLES OF INORGANIC CHEMISTRY

x^rv^lI

Tliis iiiteq>retAtioiD;, faowerer, is in tke fint instance nn!
for neitlter is tlie liexahj^dtxxtidft itadf nor cotuponiK^
sponding to it known. It will be found, bowevi^r, rhat -.ka
tiktioii is a oonrenient on« in diacoaBiBg the (>xid.itiitii iit\<]
procenn of the manganeae compoandK.

Fr«e DKui^mr arid is uoi ktxiwa ; it is nti more possilile to
it pure tltto it it to pnptiR thiosnlpfanric ««iii. for i(« anioo (C
exist idoug with hTdrton in solution witfaoat at onoe iiniicr^oinj
{omuttion. h is koowu only in its sahs, which are liable io
soltittons, )Mit in neutral or acid Mlntioaa are imnieiliatelj ivcir
into pemuuigananioti. The analriia «l the suits, atid, mvn <inc
the pronounced iaomorphisiD of those with the sulphntts, Xwl •>
fonnula MnOi' for the anioD, and H^linO, for the actri.

The salts of omngaDte acid, or the mampanfiirsi, are tmt
formed by heating any manganese eompoand with strong ba£«t«
carbonates. If potassium or aodium earbooftte («>r better, a
of these) Lb heated to foaioQ and « trace of Btttig;tiie$e iu ant
added to it, the latter dieHolTes with abanrprtiovi of oxy^n ^<^«
air, and imparts a tine dark-green colour to the molt. On >•
mass appears almost black when a fair amount nf nuingf)in»<
sent, and greeisjsh-blue when only very little is taken. Thi .
is ao sensitive that it can be used for the detection of niaii^nfi' •
cntde potashes, patches of a blue-green colour are frei^iK'ntii i
due to accidental tmces of manganese, which uii heating hit-e
converted into nuuig^mate.

* In order to prepare potassium manganate, a mixture i
lusite »nd caustic pot«sb is heated in the air ; oxygen t8
absorbed, and a black mass of potassium mang&nate is formed,
this is dissolved in water a dark green, almost oiMtque solution t£
eren with very small amounts.

• The istimorphism of manganese with sulphur is seen whc;. ;•
sium sulphate is added to the above solution, and this .illn-At-
crystallisc. The crystals of potassium sulphate sre obuiiiied, culdB*]
in ail tints of bright and ditrlc greeju

The sohiLiori of the enitie i>oui^ium manganate ramsiins undii
when it contains a large amount of potash. On iiddiii" ;mr aci'
sohitioii acquires a fine red colour, and then conLiitis; jinntlipr i;iimi'
which is derived from Itrjifirmknt mangimcse. The same colour-rl^
occurs on alU>wing the dilute solution to stand in the air : tbr
change is then effected by the carbon dioxide of the air. In i>
from green to red, the solution jwisses thrott^h a numlicr ni
metljjite dolet «nd blue coluiirs, iiiid this change of colour lias in
for the sulwtance the name " mineral chameleon,"

On adding a fairlj- large excess of onlinary Caustic potash
solution after it has become red, the colour again changes fairlr
to green.

Ht/ff

:^i

MANGANESE

603

rtbe

\»aA

till* red-t'oloured liquid is evaporated, a salt crvsUlMses out

bliick crystals with a nieUUic lustre, tho cojiii»ositi(jii of whieh

nied by the formula KMiiO^. Apparently, therefore, it coti-

same ions as potji-ssium nuinganatej onlj' m diiferetil profior-

there being, in the present atse, only one comJ>ining weiglit of

m to one of the ion MnO^', instead of two tis in the case of

iganfttes. This, however, furnishes the essentijil tlistiiution

11 the two compouiidB, a distinction which ia similar to that

n ferrocyanide :ind ferricyiinide. The ions of potitasiunj man-

are 2K' and MnO," ; those of the refl salt, which is called

um prrmiin;j(inittf, K" and MnO^'. ^''herefis, therefore, the former

MtiO^", is similar to that of divalent .'nilphaniim, the comim^ition of

latter, Mn( )^', is sncli as to make it more compirable with that of

mouovalent yeirhhnniwii ClO^'. As a mutter of fact, the two are

otift, !ind if jMitassinm perchlonite is alkiww! to crvstalHse in

of some potassium permanganate, mixed crystals are obtained

from bright to dark red in colour ; this can be seen with especial

Hiatinctriess under the microscope.

'ertnauganic acid can lie regarded as a partial unbydride of kej)ta-

njarigjKiese, for, MnfOH). - 3n.,0 = HMriOj. In agrpoment with

af WHS set forth on p. 348, pennaiigjnde acid has, aeeonlingly, to

■i"d a« a higher stage of ojcidation of manganese than mangiinic

. i must therefore be forme«l from the latter by moanss of oxidis-

nt0. As a matter of fact, the transformation takes place most

hly when chlorine is passed into the solution of the maugatiate, for

following reaction then takes place : i*KjMnO^ + Cl^ = 5KMnO| +

^ The equation of the ions is, aMnO/' + Cl^ - 2MiiO; + 2Cr.

reaction therefore consists in the transfer of one negative charge

1mm MnO," to the chlorine.

bi the tj-ansfomiation of the manganates into permanganates in
ioil M)lution, a portion of the mnngaitanion acts as an oxidising agent,
the manganic acid being reduced to manganese peroxide.

The reaition may, for example, be written: SK^MnOj^ 4HN0j,=
iKMtiOj + +KNO.{ + MnOfl ■«- 2H.,(). It is, liowever, more instructive
to write it so as to show oidv the reacting ions. We then have
SMnO/ r 4H" = 2MnO^' ^ MnO", + 2H,0, This shows that hydrion is
up in the process, and this explains why it takes place in acid
Hon.

.1 the reverse tranfiformation from permangananion to maugaii-

takes place in aJkab'ne solution h to be attributed, on the one

lo the coTisumption of hydro.xidton, which, of course, takes place

w^^ easily in solution containing a large quantity of liydruxyl. The

- action which is at tbf .<«ime time iiecess<iry is probably

- (1 by organic suliatances, which arc generally present dissolved

m the caustic poUish. Whether, in accordance with the equation

iCJ.' + MnO, + 40H' - .SMrtO^" + -iHiO, permangananion along with

604

PRINCIPLES OF INORGANIC CHEillSTRY

manganese peroxide can change into njiiDganariion with consiimpticm
hydroxy 1, has not yet lieeii sufficiently iiivestio;;ite>l.

Ill contradistinction to manganic acid, permanganic ncUl is ri
staljle in acjrl solution. An aqueous solution of ijernianj^iinie
Ciin lie olitained by decomposing the Ixirium salt in dilute solution wil
sulphuric acid. A reU solution is thus obtiiined which looks like
of any permsinganate whittever, and which condnet*) electricity like
e4iuivale.nt solution of hydnx^hloric acid. Permanganic acid i»
fore a strong acid, whosse a(|ueiius solutions are Ijii'i^ely dissociat
at a moderate fliliitinn.

Of the salts of pcrmtinganic acid, the most importunt is I
polasaium salt already mentioned, ns it ib not very readily solnhle i
crystalliaes well, and cjin therefore easily be prepjirod pure. It
manufactured on the large scale, and in recent times to a large eit«
by otectrolytic o.vidation.

I'uii pormangnnic arid, HMnO^, is not known, but it« nnJiyii:
MiigO,, is. It is oht»iiricd as a brown-green, oil}' lirpiid, whi
separates out in drops liy nirefnlly adding conccntnited siilphiinc
to dry pot^kssinm pcrnmtiganat-e ; it is very volatile. Even at
Oiflinary temperature it is converted into a red-violot, readily d*
posable vapour which, on alight provocation, decomposes with exploei
into oxygen and manganese peroxide, the latter floating aromid
brown, cobwob-liko flakes.

The permanganates are very powerful oxkiisifii/ in/tnJ--', and arr a
as such. Fairly large quantities are used in the chemical indiwU
especially for the oxidation of organic substances. To the same |;i
perty is due its application for purposes of disinfection, treatment
wounds, etc.

The mode of aclioTi of pennangananion in oxidation varies accoi
ing as it is employed in acid or in alkidine solution. In the fore
case !i miiTig.tiJouB salt is formetl, in the latter manganese peroxii
Since the latter is a higher stage of oxidation than dinianganinn, t
oxidation action is more fully taken advtuitage of in the forroero
than in the latter.

The oxidising action is so powerful that almost all organic u
stances are attiicked by permanganate. The hydrated niangaw
perovide which is thereby formed separates nut on the substance* a
colours them dark bimvii. (hi accouni, therefore, of the resulting (
com(K)sition, solutions of permanganates must not be filtered thrmi:
paper nor kept in contact with indiarnbbor, cork, or such subatancia.

* The brown coloration can be readily removed by m^ns of i
phurous acid ; soluble manganous sidphale is thoi'eby formeil : MnO,

* The same reaction also takes place even in the absence of wnt

' In part, also, luaisfciJiGM ilitliioiinte Us fonnfd : Mii0j + 2S0j = MnS,0, (cf. pv Ml
the Intter it formeii cMetLy wlien cry<*talliiii> penixiile is used, and at & low tcmptrtti;

iMANGANESE

605

ttlieretore mode use of in order to remove sulphur dioxide from gas

iTlie solutions of the permaugiirtutes can all be reiidily idendfied by

fine red-v'io!el cukmr. On exiiminiiig the transmitted light by

of the prism, five fairly shiirp absorption hands are seen lying

en the yellow and ihc greeii. With cquivaleirt snliitions, these

have exactly the i^lne position und chiifacter for all perman-

Il4» ; they ure shown also in exattly tlit! same way l»y free per-

»ni(" acid. This proves that wc are deuliiig here with a definite

LTiy of permangiuiatiioii, MnOj', which reniains independent of the

ion present at the same time in thesulntiou. Sint'iJ the&e bands

I be mea&urt'd with great essietness, it hss beon [wesible in this casu

JVC the idcrnity with great strirtness.
[PolAssiuni ixntnarigHnate is employed in analytical chemistry. For
its solutions are so strongly coloured that even very small
Ijlities can be recognised, a method for the vohuuelric determina-
mi rflticttuj iiitCHlK hus, been liiised on the fact that, on oxidising
Ijemiungiinate, the re*l colour' disuppeara bo long am reducing 3u1>
ib still preseni. So soon us ihii has been used up, even a very
lit excess of permanganate can lie recognised by the permanence of
trcd coiorHliOfi,

This nn'thod is chiefly ustjd for the dotermiiiatioii of iron, sijiee in

solution this is immediately converted, even in the cold, from

rion to Iriferrion. Since the manganese in passing from permaii-

uon tu dimanganion sinks from the hcptavalent to the divalent

five o:xtdatio!) units are av^iUbU-. With these, five combining

ghla tjf tliferrion can be oxidised to trifcrrion, sinee for ea<?h com-

ug tt eight only one unit is neceasary. If the liquid is imagined

with sidphuric acid, the equation, when written in the usual

nins : lOFeSOj -r 2K.MnU^ ■.■ ell^SQ^ = SFeslSa^)^ -c K.SO^ +

1^50^ + 8HjO. Omittittg the uon-u:*seiitial ions, we obtain the much

iimple equation : oFe" ^ .MnO/ + 8H' = 5Fe"" + Mn* + 4Hj,0.

The determination is performed by placing the solution of per-

ite in a htircttc furuiBhod with a glass stop-cock and allowing

■ to run into the soktion of the ferrous salt. Since the method

on the nxidatiori >*f diferrion to trfferrion, all the iron which

Pi desired to determine must be present as di/miim. lei order to

un this, or, us the ease may be, to make sure of this, the acid

is treat«4l with metallic kIik', whereby any trifcrrion which may

not is converted iiiio diferrion, a eorres|wnilinf; amount of linc

into Holutiftn ; 2Fe"" + Zn — 2Fe" - Zn". The permanganate

hen allowed to flow intfl the s*jluiiou until the last drop gives a

uli colonition to the liquid. The liquid must be maiiiUtined fairly

nii^ly acifl, us a large amount of hydrioii is used up in the reaction,

J«lrochltiric acid, however, must not be used, since this is partially

lo ehlorine, and too much permanganate is therefore required.

N PRIXCIPLES OF INORGANIC CHEXOSTRV <u

• It is only in the present* of iriferrion that this o.\
chloric aciil takes place in sufficient amount to cause aii
luialjsis. If no iron is present, tl is possible even to h«
iolutions of the two eub6t«nc6ft without appreciahle actioa oenr-.
We are therefore here dealing with a case of catulytie iailiMBOt ''-
presence of rliiuftngaiiiun greatly retards the oxidAtion td |ij<dn«t.r
acid hy peraiangaTiate ; if, therefore, for other reasons, iron miM
titmled with pemiuiifpuiiitc in hydrochloric acid solution, it is Drag*:
tn previotuly a<ld an abundance of nianganaus sulphate.

Besides )>eiiig used for the determination of iron, ptsnnaagMBft
chiell}' enipluyerl for the titration of oxalic acUi aitd ttiltaiw
The former tbereby passes into earbou dioicide, uod ▼• bn
equation 5C\,0;' +'2MnO/ + I6H = lOCOj * 2Mii ' + 8H/). In
o«(iiati<)n, '-"2O4 ' is the ion of oxalic acid. If it is desired to wnV
emuition with respect to mvdissociated oxalic ackl, it is onlv m
to unite the corresponding I OH' with the 5CjO ", and wt
5CjO^Hj + -iMnO; -. nK = lOCO^ r 2Mn " + SH^O. In the
state of atfairs, this other method of writing the reaction malw '
diffefiince.

This method is used not so much for the determination of
acid (which can (« more conveniently detcrniine<l by me'^ns of bni
as for the estimation of oxalates, tr.^. calcium oxalate. On
of the great 8ensit!vene3$ of the reaction, much smaller nuaiititiB«
calcium oxalate can be determined with permanganate than hv »«>
ing ; and the method ia, therefore, employed where its accuns'
determination iis possible of very small quantities has to be m*it

The volumetric determination of nitrous acid is also carried («ii
acid solution, and fcikes place in accordance with the equation '2}AtA\
oNO^' + 6H" = 2Mn ' + SNO/ + 3Hp. The reaction does m 1^
place instantaneously, and, of course, occtu^ all the more slowlri
concentration of the nitrous acid decreases ilm-ing the reliction.

Finally, the use of pemiangiinate for the detcrniitiaiioti d
ganest itmlf in the form of dimunganion, must be mentioned. Vili
the two ions meet in feebly acid solution, they tuidergo douhled«»l
position to man^atieae peroxide, which is deposited as a brown iirKip
tate. If the precipitation is carried out in the hent, the precipe
settles HuflBcientiy quickly, so that the supernatant liquid tt ■
becomes clear, and it can be seen whether it is coloui-ed pi»k'
excess of permanganate. We obtain the (xjuation of the reacti*
we consitler that all the manganese is converted into the t4)tn^
form. Each combining weight of dimanganion must therefore ub
two units, while the huptavtdent manganese of pt^iTuaticanamonaifi^
up three units. Two molecules of pcrmangananion, therefore, :
with three molecules of dimanganion, and wo have 3Mn " + '*M(it
40H'=5MnO., + L>H.p.

Hydroxyl is therefore usett up in the reaction, and the lit

le acid if we starteil w-ith a neuhJil solution. In stroogly acid
pillion tlie icactiotr itnes not ncLiir. Fuith<;r, pun- manganese peroxide
I formed only whom a Iwise is present which cun coniUine with il to
|ni< a mariKunite (p, 600). Al\ these poiiditions jire fulfitlL'd if the

^ipitAtinn is t'lurit'Ll nut in jiruseiR-e of an t'xerss of :iiii- luHlr.

, 5'J3. General Remarks on Oxidising and Reducing Agents.

kAU oxitfising agents can (in the prt'serice of wjiter) hi.- fonvially
■Md«'<l Jts hydruxyl mmpuiinds, and all rwlucing ajfonts a,s hyilrugt-u
^■IhiikIj i)f the piirtit'iihir ekMiietits. Th<^ fornuiln' itf the.w
fwroxides and hyfk'ides arc chosen snt-h tbiit th<!y are obtained by
le a^ldition of the elemonta of water lo tho various sulistutices. In
le «-a»e i>f manganese, for exampk, we have : —

I VI iiiiifatii'c Afrit's
Ma.ugaiiale »n)e.<i
of

Mii((iH), divalent
MiiiOH), triTalcnt
MiiO.. + -2H.p=Mii(Oir*^ ti-trHVfllimt
H„MiiiOi + -2H„<*= Mn(OH),j licxavalent
HMiiO^ + 3(1^0= Mu(OH >j lie[»tav8lent.

an example of » st'ries of reducing agents, we choose the

ids of sulphur Taking sulphiirit acid, the hydrogen coni-

of S0|, as the initial aubstatice, we liii\e the following formulte; —

Siil|(tiilrii) mnd
Siit|iIinrMiiK »ci<l
Sulphur
Sulphuretted hydrogeti

H.,803+H.jO-WO,, H,

In order, ihcrefore, t« oxidise sulphuretted hydrogen, for example,
"pharic iieid, 10-2 = 8 oxidation nnita must he taken up, ]f
dulion is to he carried nut in ucid 8oluti<m with perniiinganate,
iby dinvtnganion is formed, thert' ar«, for eiich molecule of
gftQiite, 7 - '2 = '} oxidation units available, and since 8 and 5
no common factor, 5 parta of sulphuretted hydrogen muat he used
l> 8 partA of permanganate.

In orrfer to complete the equation, we must consider that the
Uinns pRKluced, viz. jS molecules potassion and 8 molecules dimiiti-
Itnioii, re<]uire together 24 equivalents of anion, of which .5 S yiold
nly 10 as SO^". Other 14 equivalents of .some acid must thert'foT«
B added, e.tt. "H^SO^- We therefore obtain the etpiiition 511^8 +
iKMnO, - 7H,S0,''= 8MnS0^ + 4K.,S04 + 12HjO, or, leaving out' the
iuch remaiti unchanged,

6HjS + SMnO; + HH' = 5S0," + 8Mn' -. 1 2tip.

^Ki imiMrliint point is with regard to the alteration of the acid or
I^Pcondition of the reaction mixture in the process, for in general
brh a change takes place in o.\idations, and we ha\ e to ask how this
} calculate*!. The answer is practically contained in the above

608

PRINCIPLES OF INORGANIC CHEMISTRY cm

oxamples, still it may be useful to describe the methcxi in detail.
18 as fiiUuws ; Making use only of the elements of water fiesideii
reacting substances, one examines whether after writing the eq
obtained from the ccmsitlemtion rjf the oxi<iaiiori values, excess of
or excess of liydroxide api>«ara on the right-hand side. If
point of view we write the equation for the oxidiitioii of sulph
hydrogen witli permanganate, we obtain —

5H,S + 8KMuO^ + '2H/y = 4K.S0, + MnSO^ + 7Mn(OH)j

Besides the neuird saltfl, tlit^refore, 7Mn(0H).j are formed, i.e. I
equivalents of hydroxyl lemain uiiaaturaled, and as man)' ei|iiiviJ<ail
of an acid must tliereforc be added in order that the same acid or
condition may be prmlueed as before the reaction.

Thi' (.■alculation becomes still more simple in the following w»y
From the practically neutral siulphuretted hydrogen the dilwiaic snl|ibi
acid is formed ; since flH.iS are oxidised, this correspotids to iiii inert
of the acid by 10 ci:jujva)entfi. On the other hand, 3 e<i«)Virf(
of l)ji30 ai-i! fomwd fiom the neutral perroangaiuite, vijt, one monoTil
potaali and one divalent manganous hyilroxide. The SKiMiiO^, than
fore, make the reaction mixture more basic to the extent 3 *8 = 2
equivfdenta. Subti-acting the 10 equivalents of acid from this, llwi
remains a basic excess of H etjiiivalents, and for tht-s«? a corrispiinii
iiig amonnt of acid is necessary in order to maintain the condilii
unchanged,

in oxidation and reduction processes, therefore, a change in til
neutrality, or, more getieraliy. In the add or basic condition, general
occurs. If hydrion is used up in the reaction, this will, in sttortlani
with the law of mass action, tsikc place all the more resuiily the itKi
hyiirion is present, or tlie more acid the solution is. The satnt* huld
good when hydrion is not used np, but hydroxidion is formed. I'K
since the latter tuiites with hydrion to form nentral water, the I'
pmcesses are equivalent in the. presence of water. If, on the coatrat
hydrion is formed in the process, the latter «il] take phice Iwtu^r
the presence of hydro.xidion, and will \\e retarded or rendered practicaH
impossible by the presence of hydrion, In both cjises, indeed, chctnti
lequilibria ate est;ibli.<ihed. Very frequently, however, these equiiiln
'are so much towards the one side of the rejietioti eqnatiofii that il
not possible to detect the presence of the substiinees oji the titlier sid*
An example of this is afforded by the transfnrmatinu of rauujiaa
anion into perroangananion, and ii>-f- tvrm (p. 602). Since in the ca*
of the direct change hydrion is used u]\ corresponding to the eqimti
3Mu()/' + 4H' = 2MnO,' + MnOj + 2H.A the tratisfurmation will
promoted by the presence of hytlrion, and the solution wil! eontiuil
permanganate. If the hydrion is decreased by the presence of a Isrja
amount of hydroxidion, the mangananion is stable. Another ex.iiitpl
is afforded by the behaviour of io<:line in presence Mid absence

:xvin

MANGANESE

^ydroxiftion. Frpe ioiline reacts with hydroxidioii to form iodatiion
faud iodidiuu. in iiccaiilance with the C"f[iiatioii 31.^ + 60H' = 51' + 10^' +
'SHjO. In this retiction nnieh hydrfixidion disappeurs, atifl the
timi must therefori? tJike plact' more cji.sily when it is present ;

_ I inatti'i" (if fiitt. it taki^s pliite id jilkulinc solution, e.ij, in a solution
^of ciiustic ,sot!a. If, liowevtr, hydrioii is added, tho leuctioti is reversed,

•and elementary iodine is ,'tgain iset fruc : Til' t 10^' + 6H' - Slj + SH^O.
594. Complex Compounds of Maaganeae. — Manganese can
1 with eviiuogei), LOiii[iiinnds which urc quite similar to those
hieh wc have already discussed in detail in the wise of iron. In thia
ksose also we have the two series of compounds derived from a tetra-

Ivalerit mao^iioocyanidioti, M(i(CN)g,"", aivd a trivaleiit manganicyani-
Idion, Mn(CN)y'", and both are ohtained in a manner simihir to the

corros[jontling iron compounds. Tbey are both, however, less stable,
■and the raanganicyanidea, moi-e especially, through their readiness to
^Undergo decomposition, roenU the suits of tnvalent manganese.
W Potassium mjiugjinocyanidci, K^Mn(CN),| + 3HjO, is isomorphous
I with |iotAS3ium forrucyanide and erystjillises in dark blue ciystals,
fc which, however, yield an almost colourless solution. Potassium
I naangaidcyanide, K.,Mn<CN)|,, is red, antl is isomorphoua with potassium
Ifcrricyanide. Its aqueous solutions decompose oa being boiled, the
jkinanganese being deposited aa manganic hydroxide.

CHAPTER XXLX:

CHROMIUM

59S. General. — In many of its chemical jK'culiarities chrtiiuium
closely iillied to the metnls of the iron grutip, espedally to iron
raiingunese. On the othur hand, it is t'«1iited to the eleiucnU molyb
denuna, tungsten, and uranium, which must \ui placed in the I^st group
of metals, au that thromium coiild Iw gi'OU^jed jiiat as well with thim
It ifl soniewhiit; aiintrary, therefore, in which group it is placed ; that it
is here classed iu the iron i^roup is floiie for didiictic reasona

Chromium is closely related to manganese in the m]|i)l>cr of tie
aeries of compounds which it foctua. Where^is, however, in th* L-a»
of manganese, the acids coi'respouding to the higher stages of oxidation
were somewhat unstabie, those belong in the case of chrnmiiiiu to lii
moat imjKirtitut iind best- known oomponiids.

Chromium fonns the following serios of compounds : —

Salts of the divnlent dichromion, Cr".

Salts of the trivalent trichrumiuu, Cr"", arid complex cnni.

pounds derived from it,
Chrojiiium trioxide, CrOj,, and acids derived from it
Chromium peroxide, whose composition is not yet known wrtli

certainty,

The condiiiiing weight of chromium is Cr = 52'1.

506. Metallic Chroinium. was for long knowrt only in the form
of au impure jHiMluct cotitaiiiiiig carlxjri, since the fusion of pun
chromium could not be effected on account of its high melting-poinL
By the reduction of ehroiuium oxide with aluminiunt, in acconlmn
with a general raethwl given V>y II. Uohl.schmidt, very pure tnet&Ilif
chromium is now manufactured in huge quantities. It is used in the
iron inilustry to aild to steel (chromium steel).

• This preparation is (.'.trciKl out by mixing chromium oxide witll
aluminium powder, both caiefiilly driwl, and initiating the reaction
with a small quantity of the mixture. For this a verv high temper*-
ture is necessary ; this is producetl by mixing alwaiinium [)owder iritli

eio

CHROMIUM

Gil

xide, forming a pill of this, aaij sticking a piece of

if'lw.'U into it. If th«* miLgnesiiiin rililxjn is t^nitt'cl, which

ue tt'ith a tuatL-h, tht- comtmstion of thti ahiniijiium with the

f ihe Ijariiim peroxirlp bt'gins; the mass thereby liecoraes ivhite-

aiid initiatos the reaction in the nuighlwiiring pnctiotis of the

mittm nitxtiire In pmjwrtion as this undtrgoi^s tniriafomuitiun,

of the mixture is ad(!eil ; the tenipei-ntiire therehy aooii riaos bo

that the chroinium fuses.

• The mtiihixl h;is the advantage that it does not require a specially

I furn»<re, hut can be cai-ried out in an ordinary enicihk\ prcfer-

oae <ff magnesia ; tho oiitside of the crucible Ijecomes ordy slowly

On account of the high L^mpcralurp uf fu^ioti of chrntiiiiiin,

iparation of the fused metjil ia aiiccessfuJ oidy when fairly largo

Ititics Are emplaytxl, but then with case.

A similar method is used fur preiwriHg other metfils, and also
ihr production i»f vijry high teni[wraturefl. In tho latter case cheap
.■•perally iioii oxitltf, are umJ. With such niixtin*es fusions,
etc,, can be c^irried nut on the fijHtt with gn-at ease and
III}'. BO tliat the methwl is of great technical im|Kirtaiicc.
rominm ia a lustrous ivbite, very hard metid, the melting- point
ich is alsout 2000°. Its density is 6*H. It renjuins utichangwi
lur ; fven at a red-heat it becomes only sltiwly ctmtcd with a
yer <if oxide, which exhibits the eoloura of thin plates. It is
cd hy dihit« hylrochlorie and snlfihuj'ic ai ids. with I'voliititm of
Nitric acid ilocs nut attack it, .since it be(:omi!S "passive"
■cid.
* Cfhromium passes into this passive state, i.e. ccjisea to be attacked
Msdt, even Vjy lying in the air. The metal when in this state is
attacked at the urdinary temperature by dilute acids. Treatment
tbe metal with strong oxidising agents hiis the sime effect. If the
e metal is allowed lit He for a fairly long time under acid, or if
ed, dissolution with evolution of hydr«tgen suddenly com-
the metal is used as an anorle (p. 195) in dilute acid, it is
by weak cuiTcnts into its lowest compound, a chromons sidt.
however, the strength of the current ia increased, ths metal suddenly
I- y :,, di)iftn|vf in the form of its highest sUigc of combination aa
: • icid. The ptisaive metal likewise becomes active, i.e. becomes

|»>b«ble in ucitls when it i» touched with a piece of zinc or similar metal
acid.

n explanation of these remarkable phenomena, snfticif-nt in all
iilar*. ha** not yet been found.

Cbromoas Compounds — IMefircmiion, Cr", is coloured blue,

a very prononiiced tendency to pass into the trivalent tri-

It is a very slronj: rerlucinjj agent, and can e^en rleconipose

with evolution rif hydio};en. The '^hromoiis sidts cAn, therefore,

taioed pure only with ditticulty, and in aqueous solution cannot

612

PRINCIPLES OF INORGANIC CHEMISTRY

be long kept uitbout pjissing into ctnoniic salts. Tii»*T
easily ohLiined hy dissolving meUiJlic fljiouiiiiiii in diluu* acids;!
can also be prej«ued by the induction of chromic conipnuKiii
metallic /.UK. From the solutions Iwisos precipitate cliromous hyd
i<le, Cr(()H),i, as it yi-Uow precipitate, whicli in thu mnjst st^itc {M
into chronuc oxide with evolution of hydrugeii, iiiid is uxidisetl n|^
immediately in the fiir. Through the spoiit«iit'OU8 oxidrttion nf chmi^
ittu.algjim in the air. lilaek rhramiMs tijuh is formed, which passeij
th<' ^reeii chromic oxide on being |K>wdercd. I

From the nnhitions of the chromons salts excess of sodium aci
pieeipitjites diffitnltly solnidi.' (•hTiniunin mrtitt,', n rlark-ri-d, iTj'stjJ
salt, which can be wjished and dried if /»ir is excliitied : it is ul|
the only fiiirly stivlile chronioiis compound. The afjn&ous £<»liii
prepared \vith the help of hydrochloric Jicid, is used for the absorfi
of fiee oxygen.

By igniting chromic chloride (iHdf infm) in a ciirreril of hydr
white, difficultly volatile clinmunis chloride, CrL'U which dieeolT^
water with a blue colour, is obtained.

ofts. Chromic Compounds. — Tiifhrrnnion is violet colounyl,
in its pi'opertiea is mosl nearly relati'd to ahimtnion and irifnrj
with which it is iaoTOorphnua, It has also a highly developeil teiulf
to form complex com]iuiin(Is of all kinds, some of which ar« vil
8ome green. ;

Chrmiiir hjjdiit.ridf is obtJiincd a3 a lihic-green precipit^ue byi
action of ammonia on solutions of the chromic salts, whereby ai
amount of the .salt readily passes into complex ammonia eomjxnl
Chromic hj'droxidc precipitateti with alkali hydroxide diseolve
excess of the precipitant to n fine green-co loured liquid, in which
corres|-H>ntling tdkali chmmiU', i.e. a salt of the anion Cr(OH),0!
contsiined. The solution, however, is very nnsialile ; a les.^ hy*lj!
hydroxidf" of a grnen colour, which is les.s sohible than the one ditl
precipitated, separates out(piick!y when heated, and slowly Ju the<
Such pbenometia have already been diacuflsed in the case of Iwrvl
and alutuitiium.

By partial dehydration various jwrtial anhyd rifles are ohl^
from chromic hydro-vide. One of these, of the composition Cr/MQ
is used !*fi a ]>igmoni on account nf its fine green colour. On ignl
ilniitnk iwidi', Cr^Oj, is formed ; this tan also Ito obtained in rrj
line form by the decomposition of volatile chromium conipouniJ9L
then cryatttllises in the fonu of conindiim (p, 560) and fumis IiJ
green, lusti-ous rhombohedra.

Chroraiiim o.xide unites with oxides of divalent metals to I
substances of the type of .'^piitcl^ which are found in regular crj)
iaomor])hous with this .substance. Of such compounds by fur
most important is chrome ironstune, a mmpound of chromitmi i|
with ferrous oxide, FeCr„0., which crystallises in l<litck oeta

CHEOMIUM

613

the compound of chromium most found. Chrome irotistone, tbere-
^ re, forms the stiirtiiig substance for the preparatioTi of other chromium
mnapuunih.

Of the suits of the chromic scries, we nnist first mt'tition the
KJori'lt', ivhich is olitained in the aiihydrons state by beating chromium
padde and charcoal in a cun*ent of chtorino. It sublimes in the form
C a fine violet-red (peach-blossom red) substiince, consisting of small
•Btrous scales, which appear to lie insoluble in water. On very loirg
^imtacl, however, some passes into solution. The dissolution takes
IBace very tjuickly, with appreciable rise rif temjjerature, when some
,jroioious chloride is added to the water. Other strotij^ reducing
jj^nts have a similar action. A sufficient theory of this acceleration
■■as not yet been given.

From the aqueous sohttioTi a green wilt with 611.^0 is obtained,

hich cannot lie directly converted into the anhydrous chhiride, since,

Jce the chlorides of all weak bases, it loses hydrochloric at-irl on being

.sated. The green solution ia nut to be regfuxled as the (pitrtially

, jdrolysed) normal chloride with the ions CV ' and 3Vl', for on

Iding silver nitrate only |rds of the chlorine present is precipi-

•ted. The last third is therefore not present as ion ; the eoUition

flo contains free acids. The chloride of a complex divalent edition

mtaining chromium and chlorine, e-i/. ClCr", is therefore present.

n standing for a lengthened period in dilute solution, the green

Jour of the sttlution changes to violet, and at the same time almost

1 the chloiine can he pretipitatt'd by stiver nitrate. This corresponds

1 the formation of the normal chloride, which is accompanied by the

--"oduction of the violet colour belonging to tricliromion. On con-

mtrating and heating the solntiun the green ioji is again chiefly

•tmed. None of these reactions are cojnplete, and to each tempera-

tre and concentnition there corresponds a definite equilibrium

jtween the t\v*o foinia. A solution contJiining almost solely the

armal sjilt is ftbtained by dissolving the freshly precipitated chromic

vdroxidc in hydrochloric acid.

Tk* two chlorides can be pr-epared in the solid state — the normal

le by the trysiallisation of the solntion saturated with hydrogen

'lloride ill the cokl, the nther in the heat. Both salts contain 6H^0 ;

le normal salt is grey -blue, the other is greerv.
^ 59y. Chromic Sulphate, Cr.,(.SO^),,, exhibits a similar variety of
•^haviour, and has been still more thoroughly investigated. From
• (ueous solution.*! the salt with OH^O ts obtained, and its solutionB
thibit the \ioIet colour of the normal trichromion. If the solid sidt
b heiited til! it lias lost alxtnt ^H.,0, it becomes green, •
■»lution, immediately after being prepared, exhibits a v
utncincti'vity, and conttins therefore scarcely any ions'
ticti^'ity increases very rapidly ; but birium chloride
■-ecipitJVte, which shows that no sulphanion is pret

PRINCIPLES OF INORGANIC CHEMSTSY^

contrary, various chrotHBulphiiric acids, or their chromic »atu
formed.

If mixtures of chromic sulphate and sulphuric acid iii v&rioui
jiortions are wanned, BuHstanccs are obtained, the aqtieoiLs solutifl
which give no retictioti with iiarion, and therefore coiitflin no I
Neither do they exhibit the reJictioiLS of trichromion. Tlipy nt
omifilex fkrot/ufitijtiiiirir iiads. The amount of hydriuii which
contain corresponds to the hydrion of the Bulpliurjc acid added..
this way as much as SH^SO^ am be combined with Cr„(SO,}j. '
Bohitions are not stable, but soon detoniposc into their coiiipona
the presence of the ions Cr" and SO^" can then be dot**cted. I

C?bt'oijiio sulphate forms a regular alum, (immf 'tlum, with potJtH
and ammoniiini sulphate ; this crv'stanises in very lar^e i«"tJthc(!r
a dark purple colour. If a crystal of chrome alum is suspL'ndtd
saturated solution of ordinary alum and cryBtalliBittion alUiwwl to J
place, the dark octahedron ia obtained regulaily enoloswl in a coloiu
one. Such rogulafly zoned crystals* art! also a sign of iwiuiurpli
between the substances which can form ihcm. ,

Chrome alum ia generally prepared by the reduction of jMitsin
bichromate {vide, infra) ; it is used in dyeing and for many nl
purposes. With animal glue the chromic hydroxide, which is split
hydrolytically, forms a compound which is insoluble in hot wsi
it has a " tanning " action on the glue. Use fa frequently maiJfl
this property. ',

GOO. Sulphur Compounds of chromium cannot be prcfwircd
the wet way. Sulphiucltcd hydrogen is without action on chfitni
salts, an<l with ammoniiin> sulphide rhroinhau kijdnu-idf is prrcipitti
while sulphuretted hydrogen escapes. That is to say, the hvdrcl
of chromiimi sulphide is bo considei-ahle that the compouail can
exist, but decomposes into the Rubatances which arc formed froa
by the action rrf \vater.

At a red -heat anhydrous rhnniiiutn .iitlj'/iid^ is formed from
elements in the form of nietjil-grey, vei-y stable crystals.

601. Cliroinic Acids. — When any chromium corajjound is Im(
with strung bfvses or their carbonates, they absorb oxygen from
air and form salts of the divalent anion CrO^". The simiUril]
this fortnula to that of aul^dianion ie not onlj- an exl<?raal a
the two anions are isomorphoua, i.e. their salts with the sjinie eal
have the same form ;ind crystallise with one annther in vm;
proportions.

Chromanion, CrO^", jb of a pure and strongly yellow colour,
ail the Bolutions of the chromates, therefore, exhibit this coloiu".
solubility relations of the chromates agree closely with thow rf
Bulphates. Thus, the alkali meuds fonn soluble sitltjs ; of the alh
earth metals, Imiitim forma an extremely difficultly soluble s»|t.!
the others form increasingly more soluble salts. Of the chrtiimU

CHHOxMIUM

615

, th.1t of lead must be called flifficiiltly soluble ; this
D agrees vnih wKai we Ii;ive in the case of lend sulphate.

602. Potassium Chromate, K^CrO^, is a salt which ci ystallises
Aobyilruiui rhoiiibit crystals. It is prejiarert commercially by fiiBing
I iiiittirally wcurring chrome iranatone with pnhi-^hcs with access of
. From the aqueous anlutioii it is usual to first prejwie the hotter
mtAilisjjig potassium rlichroiuate (riil€ iiifru) ; from this tht normal
ronuite can Ik ohtuimi) by aildiiig the reqiiisite quantity of potassium
draxide ur |)Ot,Lssium eiirbonate.

Potaasiuin chromate is, at the ordinary ttmiperatures, a sulphur-
How salt ; on being heated it bocomes of a bright red colour, but on
»Iing again iis-stimes its yollow colour. We are here dealing with
? shifting of the rt^gion in which the fuUt ahsorba the raya of white
;ht with tht' tenipeniture, — tho region of the absorption shifting, ■with
fttti teiiipemture, from the violet (which givt-s the coraplemeiitary
Mryeliuw, cf. p, I'J) towards the green — thiit i??, Unrards the region
longer wavelengths.

TTiQ aqueous sohniou of potassium ehromate oxhibits an alkaliue
ictioii. This is not clue to the chromic auirl being a weak acid in
e inie sense, but U tlu* to the grwit tendencv of thi* chromatca lo
into saltij of the i:otiden,*ed dichromic acid, whereby a process
to hydrolysis is cH'ected. For if any acid, even a weak one, is
the solution of pouissium chromate, a change of colour from
I orange occurs, and from the solution another potrtssium salt
the com|H>sition of which is represented fiy the fommla
jGrjO-. U is therefore the potassium salt of the etitvlmsfd anion,
r,0.', uf. an anion formed from ehromaniori by the taking up of
imtnium trioxidc. AV'e have alreaih- met with such compounds in
e CU3C of sidfihurous and sulphuric aeitls, which were distinguished

■'pyri»-acifls'" from the normal ones. The corresponding chi-omic
id, however, is not called pyrochromic acid but dichrmftk atid.

The tranefrjmiation of chromanion into dichromauinn takes place
cording to the equation iJCrO/' + •2H" = Cr/_)." + HjO. For it,
erefore:, hydrion is necessary, and the reaction accordingly occurs on
idifylag the chromates, which contain the ion CrO^", In the
Intions of the normal chromates iho hydrioii of the water is used
r tbis purpose ; for this reiison hydroxidion remains over and the
lution reacts alkaline. The hydr**lyais which ^iccurs here differs
M onlinary hydrolvjtia (p. 290) in the fact that in this case a con-
^■d ion is formed and not a neutral compound.

For this reason, also, a solution of chromic acid, H^CrO^, cannot
121, since, indeed, the hydi'ion necessary for the transformation is
Bicnt. When a concentrated solution of pota.nsium dicbromate is
■ted with excess of sulphuric acid, chromuuu (rui.ritie, CrOj, the
hydride of chromic and dicliromic acid, se}mrate8 out in long,
i, aeedle-fihaped crystals, which are readily soluble in water and

616

PEINCIPLES OF INORGANIC CHEMISTKY oh»I

exhibit [Mwerful oxidising actions. The acjiitjtiiis solution of eli
irioxide does not hui e the i>right yellow eoloiu- of chromaitioa
the orange colour of dichj-omanioii, and its behaviour also with
to the ilcpresisioii of the freezing point and electricjU cniulticti^
allows only of the view that it contains lh<? ions Ci'J}-" aiid
If potassium tliehnimate is mixeil with ]iot.iissiniii hyflroxide,
solution IfeL-omi'i^ liright yellow and contains pot^ssjura chrei
The follo^ving reaction occurs : Cr„0/' + 20H' = 2CrO,' - HjO.
is tbe rei erae of the reaction jtist given, and occurs under the irifl
of hydroxidioii. Dichroraanion, therefore, cannot exist in meaaiiral
quantity in preaence of hydroxidion, any more tli.an chrotnanion
in presence of hydrion.

At the present day chromium trioxide is placeil at a chcjiii jnH
on the nmrket, Mnce it is gieatl}' used for galvanic cells and i» i
oxidising agent in the cheraiail industry, and since its ready soluMlii
nilows nf more concentrated solutions of it being prepared than
jwtassiuni dichromatc, which was fonuerly employed. Kvea on beii
healed it loses a part of its oxygen and passes into chromium "xidl
The t;h!Lng<j takes place more easily in presence of acids, Ci^poriiiC
sulphuric acid, which form a con-esponding chromic salt. This; buH
good also for the application of chioniium trioxide as an oxiiiisii
ag«ut. HydrochloriL- acid ovolvee not oxygen but chlorinf, beifl
itself oxidised,

603. Potassium Dichromate is a rod-colourod salt which re»<i
ftltnost neutral ; in itii solution, therefore, the presence of mi «»
chromato is not to be aaaumed, It readily fuses to a dark liqiik
which on cooling undergoes crystjillisation and falls to a i»».mrlcr, I
is moderately soluble in water (1 ; U), at room leniiH'nitnre) ; i
crystallises anhydrous.

When potassium dichromate and aulphuric acid are used fi
oxidation purposes, chiotue alum is formed : KjCr^O- + 4TLStV=
2KCr(S0jj + 4H.,0 + 30.

Thti corresponding sodium salts, miiuw chrmimk and *»fni«
dtfhnmuili', replace the potassiuni sidts at the present time in itw
applications, since they can be niauiifacturad more cheaply thnn lli<
latter, by the fusion of chrome ironstone with soda (and lime, W
facilitate the reaction). The no!-mal chmmate crystallises with XilWfi
in the form.* and possosaitig the general solubility relations of GUnWi
salt (p. 490) ; the dielirmmitc cryst^illises with '2H„0.

Of the other chromatcs, Imriiim rlirmiinlr may fie mentioncw
This is obtaine*! as a bn"<;ht yellow prec-ipitate when the iotift Ba " in
CrO^" come together in solution. The salt is very stable, withsUUiiJl
» red-heat without decomposition, and is therefore usetl as a yrfW
pi^ent tor painting porcelain.

Bafiiiin dichromate is not known in the pure form, but it* eatW
(•nc* in solution can l»e gathered from the known facts, if th« k*

CHUUMIUM

617

id CtjOj" are bmnght together in soliitiiui, 1>;irinm fbiimiate'

the cntrespcjiidiiig aalt is fomied, ami the sciiuli<)ri hct'onu's

Tlif [irecipitation is not complete, since, for example, if equivalent

e» of lariuni chloride and poUissitim diehrniimt.e are used, about

i)( the ImriliiH rcituiins iti solution, and the latter hjis the

colour uf difhroiiianion. The cause of this is that in the

ijf dicliromate, chromanioii is also present, being formed in

DUill amount hy the transformation of liichroinsnion into

Uiion through the interaction with nater : Ci.,0-" + HjO =

+ 2H". This reaction is the reversal of that given on p. 615 ;

! is A ease of cheinical eqiiilihrinm, none of the |xissihle reactions

Bomplcte, but at the fnd all the substaucea concerned in the

rium must be present. By precipitation as liariuin chromate

liianioti is removed for t!ie solution, a fresh anTount is, formed

alstj preeipittited, and so on. That all the diehromatiion does

into L"hi"omanion is due to the faet that hydrinn is produced

line time, as the above equation shows. The amount of this

t as the reaction proceeds, the stability of the chronianion is

t diminished, that of the dichromaTnon is iriureased, and tiiially

fiura must Ikj established. In the solution dichromanion atid

exist side by side withciut Iwini; iire<^ipitated, which proves

nam dichromatA is a rojulily soluble compound. The cause of

iTersion of dichromanion into chromanion is, therefore, in the

case, the ditticult solubility of barium cbromate. Since these

rations evidently holfl good universally, every cation that forms

fultly soluble chromate wil! precipitate this frttm solutions of

Hiromates. This is, jw a matter of fact, the case, e.g. lead.

IB oxidising action of chronuc acid can lie made use c»f for its

wive {tetenni nation by employing it to liberate iodine from

in iodide, or, in other words, to convert iwlidion into iodine.

tiaoji is

Cr/V + HH* + 61' = 2CY" -t TH/J r 3\„

b 6 equivalents of some anion must be added to l>otb sides in
9 make the equatjun complete. From this it can be se«n that
•mount of hydrion is used up in this reaction, which is possible,
It, only in presence of much acid. For one combining weight
nium three combining weights of iwline are set free ; by meatis
Ittlpbatc {p. 496) the amount of the latter can caf^ily be
y det>;nnined.

Sensitire Chromate Mixtures. — Although the chromates

not to any great extent sensitive to light, they Iwcome

Ttiry high degree when they aro in contact with reducing

e.g, organic matter like paper, indiariibl:»er, glue, etc. And

B is, strange to say, greater in the case of the dry

, tlian when these are moist. On this property a large numbei'

PRINCIPLES OF DIOKGAXIC CHEMISTRY JtH

of pbotiogrspliic sod pltote-mediaiiical ci«tbods ttepend, name d tb^i
qAjr be mentianed bere.

A mixtare of ^oe mod a solntile chrotnate on exposiirt* w
aeqtttra the propertT tbu the gtne beeoimBB iwuoiuht*, I'his is d
tlw fact ihtt the duuniic mad is rednceti to ehroniium nxidi-. «^ii|
forott an iznolehle ooRipoiiod vith U)« glue (p. 6 1 -J ). If »um» cuW
it)g nalter u added to the Abore mixture, ^tid pii{>er is «wkil «ii
this *nd expOied to light anJer a tiHrmpArent ]>ieture, the aw^\
becomM inBoloble at thoee paru on which ihe lij^hi has WnabV'
act^ while it reinaiiia soiaUe at the parte where the u|i:i.
the pictare were. If the prepated [Mpcr is treated, aft >
with warm water, the coating is dissolved at tho^ie [)«rti« when- it »
prtiCected from the action of light, while the colour remAim at a
exposed parts. In order to obtain a picture, therefore, in it»
pelabVins, a "negative" must l»e used. i.*-. a transparent pirtuft
whii'h the dark parts are tmnsparetiC abd the bright parts upKjO
Such pictures are obtained by the ordtnar)* photo^^]-^phic methoii
silver silte (Chap XXX V',^.

Another methrtd depends on the fact that a mixture of glar
chromatid acnuires at the exposed part* thu property of takiw »
the "i/y priiilin^ ti^nr, while the non-expos«d portions (after i\*
meiii with water) are not coloured Ity this. If, therefore, the prinsii
colour n rolled over such a picture and a white paper pLoced on i-
print is obtained in which the exposed parts are again dark and ^
iinexpoficfl bright.

If !i metal plat-e is coated with the chrcunate-glue mixture, and il*
pftrt remaining soluble after exposure removed with warm water,
ex|io9ed metal can be deeply etched by pouring acid on it. la
way blocks for printing arc obtained.

Theiiie examples do not exhaust the whole of the poeaibHilies,
we mu8t refniiii fruni further detjiils.

60.^. Ohromyl Chloride and Ohlorochromic Add.— 1^
similarity of chromic acid to 5ul[>huric acid is further exhibil*!
the fact that it ran form the two chlorides which can Iw d«Tl
from the acid by the replacement of hydrosyl by chlorine.

Hp distilling a mixture of pjtassiiim dichromate and sodium cUifli
with sulphuric acid, chromifl ckhniJ'; ("rfJJ.'lj, in foi-njed (is a red liqO
similar to bromine, which ImuIs at 118 , and has an appreciable nfit
pressure even at the ivrdinary temperature. As the suhslanco l* ^.
sensitive to water, the water foinied in the reaction must be houiuiy
using add containing aiihytidde, or fuming acid

Chromyl chloride flecomposos, after the manner of the acid chlorii"
into chromic acid and hydrogen chloride :

CrO.a, + -»HjO = HjCrO, + 2HC1.
The process is, however, half reversible, since, in concenWA

CHROMIUM

619

Million, throraic acid and hyclruchlnric i\ch] luidergn partial cuiiihiria-
yjtin with formatiori of the corrfspaiiditig first chloride of chmmic add.
Hn k tiut kuown in the free state, but siiits of chlorochrnmiLmon me
|BwfL The state of affairi? is therefore exactly the reverse of that
oliUining in the cjtsts of suliihurif acid, where the free acid is known
but not the stilts. Potassium chlorochroniiite, KCi'O^Cl, is obtained
it iiii ofniige, anhydrous salt by crystallising jMitassiiim dichromate
turn a sinmg solution of hydrochloric acid : K„(t,^0. + !.*HC1 =
2KCrO„Cl + H^O. f)u recrysUiUising from jmre vrater, it again de-
wmjxjstB into hydrochloric acid antl potaaaiiitn diehromate. On being
he»t«d it evolves chlorine.

• The formatiim of chrumyl L-h lurid e is used for the detection of
liiI«jridion in presence of bromidiun and iiKlidion. On distilling the
ttlu in question with poUissiiini dichromate and fuming sulphuric
«iil. (.■tiloriiie passes over as thromyl chloride, while bi-omine and
ioditie distil over in the free state. The distdlate is treated %vith
*(D]noni&, whereby chromyl chloride yield-s a yellow aohition of
uniDomuni chmnjate, while bromine and iodine di.s.sah e to a eolourleBs
dilution.
.A rhrftiiiiyl fiwsule. CrOoF.,, a red, very volatile liquid, is also
71 ; similarly to the chloride, it is obtained by the distillation of
hrumate with fluor-sjMir and fuming sulphuric acid. It \s very
ilv decomiiosed by water.
KOfi. PerChromiC Acid. — By this name a higher stage of oxida-
of chruiniura in deRigiiuted, which is formed by the action of
pci'oiiiU on an acid solution of dichromic acid. The solution
once beeomes hlutr . the coloration, however, is not sudile, for in a
•bort time oxygen is evol^cil Jind a chromic sidt is loft in the solution.
The jjhenometioD can be made to la-st longer by .shaking out the liUie
iiiil with ether ; the blue substance then putties into the ether, in
eh it keepa much longer.

[The funifRisiiion of this blue compound has, it is true, been
Snniiied. but the relatiouH which art' met with ia this reaction

not been sufficiently explairied in order to be treated here.
I'iiince the bine coluration Itecitnies visible with oven very small
of hydrtigen [veroxide, an acidiiied solution of a chromate
ftiKjd as a rejigent for hydrogen peroxide.

607. CobSilt ami nickel are two metals allied tii iron, and similar
it as far as the coiiiptmnfls of the fermits aeries are concerned, l>i)t ti
compounds corrosporifling to the fcrrif series are unstabk^ or iinknowTU
These metals, further, share with iron the property of being in»rkiKlI||
mii^iirtkj and thcv hIso jicconipany iron in metoorites. Their <ic
renc(3 m nalnre is not exitt;tly rare, tmt they iii-e much moi-c sjwn'iigljr
distributed than iron. Thej' ouenr chii'fly as constituents of i.'oiiifjier
sulphur and arsenic compounds, and from these they are obtaincil ly
first of all lieitig freed from the auljihur and arsenic l>y roasting,!.',
ex^josure to the oxidising action of the air at a high temjtfiTitUM,
whereby they [Mias into the respective oxides. These oxides are
separatud from one another in the wet way by the fractional p»-
cipitatioa of the ssdts prepared from them.

The two elementa are grey or yellywish-whit« uieuds, ttu joeUkji
point nf which is very high, although lower than that of pure iroa
They are hard and tenacious metals, which tjike on a verv fine jwlisli;
they rem;iin almost niicbanged in thf aii', and have a fairly considM-
able technical vahio.

Tho two elements* form divalent, eltimentary ions ; further, tbw
have a jjreat tendency to form complex ions of M kinds. In the I'fi*"
of cobalt, more espofi.'illy, an extraoi-diiijii-y wealth t>f tliflerent eiiin-
poundn (Exists, these being ehielly compoimd,'* with nittogcn in it« varimi*
forms of eombination, cyanogen, ammonia, and tbe oxygen eomiKtund*-

The combining weights of these elements hav<' been determinwt hy
the analysis of their halogen compounds, and have been found to 1»*
Co = 69-0, Xi = S8-:.

60S, Metallic Cobalt wkn be easily obtained as a powder b^
heating the oxi(Je in a cun-ent of hydrogen, In fused masses it ■
most easily obtained by voduction with aUnninium, according to tM
method of Goldsthmidt. It is a tenacious metjil, which can Iw rewlilj
polished, and which exhibits a high lustre. In the metallic atat«
has as yet found no uppliealinri in the art*.

Q20

U'. XXX

COBALT AND NICKEL

621

most ficifU h dissolves only very slowly, with evolution of

n, hut dissolves readily in nitric acid. The solutions which

'armeii are <:oir)urt><l red, irrespective of the miture of the iicid ; it

1m? coiioli(rU'!i] irom this that thii ro<l colour is due to folMJtion.

> cohattioii, Co", contained in the snlts is divalent, and in its geneiul

mour is similar to difenion.

[With alkftlis, it^ sjilts yield a Itlue- violet precipitate of eobidi
Ox'OH),, which is converted into its anhydride, green
ooMtt, CoO, on fieing hciitwt out of coiitiiet with oxygen,
a red-Lciit it takes up oxygen from the n'\r, iind -tn o.ruie, C'o.jO^,
correspotiding t<j iiiitguctit iron uiv, i^ furnn-Ll, wliieh is agdn converted
into the uiorioxidf at u white-heiU.

< olwlt hydroxide dooa not dis.si>lvc in cxcefis of idkalis {except in
r^ when the solutions are very concentpated), but rciitlily does so
snltitiouit of Ainnjorunm s^dt^;, Tlie reliction Ja, in the tirt^t instance,
•amiLir to that in the case of raagneaiimi hydroxide : hut if .-i large
atxm of jininionia is added, the red colour changes t-o a yellow-brown,
u*!kieli ghtiws that a new, complex compound Ikis Iwen formod. If the
piid is diluti'd with much water, h!ue cobalt hydroxide sepujatos tmt
fli»cculcnt precipitate. As in the case of manganese, the am-
tiiiicjii solution atwnrha oxygen frona the air, whereby complex salta
'funned which will be mentioned later.

Of ihi* »altfi of cobalt, cotmit nitrate, {CONOj|)j, is the best known ;

is ;i reiulily soluble sidt crystallising with 6I1.,0, anrl is used in

niyiicjil chendstry,

60t*. Cobalt Chloride, CoCl^ . SH/), is also rejuHly sohihle. It

w a laige niiuibor of lower hydrates, of which the leas hytlmted

> are of a blue colour. The concentrated iuineoiis aohition^t, .'d^o,

fib arc red in the cold, exhibit .1 hlue colour when heated. This

<xam still niore readily when the solnti-in contaiiis a large amount

chloridion in the form of sodium chloride or hydrochloric, aciil.

hf Crtuse of this is that under these circumstances complex anions are

•rtuetl, proljid)ly by the taking up of chloridion by cobalt chloride,

jrhkh are blue in colour.

• This phenomenon ivaa fonnerly regarded as a great curiosity,

rr>\nh chloride was useil as a "aymfifithetie ink," For, on

Titirog on [Ktpcr with a solution of this salt, the pale-red tracinga are

»fwly reciigiiisable in the ordinary state. On heating the paper,

if-itT, and thereby converting the Siilt into the less hydraled form,

lii'Wae colour appeai-s very distinctly.

Textile m-iterial moistened with a concentnit-od solution of the 8jdt>,

sillies various coloiu^a when exposed to the air, according to the amount

'^BKnatDfe in the latter. In dry air it is blue ; in moiat, pale red ; in

tbr intennediate slates, violet colours appear. Suth material is uaod

hygi'OBcope, because, from its culoiir, an idea can be obtained

luouiiL of moisture in the air and the probability of rain.

f.L'L' n.i

■ Til.- ■

ruli;i|l . ;li ' .
mU<. T .

liirm-, ■•
liuM. .

.'Illll .1!: '

I. '■ ■

|Hllll,.

n.l.,-
imi' '

I.I ;
\ . i

li'.
I'l ■

• CHEMISTRY

;. :i«'al i-nni posit ion n:
■ins thive to »i\- •-
r>miul;*?. theivfoiv-.
VMiiKI 1.., <.-..Cl,.. ..NM
. -. iiowi'vt-r, «I«» Hot '»•:..•
-. vm- st.tliK.' and ti • :. '
■ '.^ial ro.u-ti«:>ii.s which •!..■:-
.r»'. tliuri'finc, sjilt.s «•! '-
■••' of iiiuiiioiiia. Tliev

, . •[ .IS <-<)in]>OUIu1s iif r-

■S-'\}i 11. .)„'". Ill tn>]H.ii:: •
'. also, which are ior.".,i. -
■■•M»-tioiis of these ir'T>. ?

■ »•■ :hat tht> ok-nieiits "i ■':,■
■ "•.i>".t'\ cation.

■.- .i -urvt'V of the v.n: ■..■;.

!;■ these eoiii]>oun<Ls :« ::j
» .viloiit. The coiiii>i".:j.i- . .
••^•."'".0 anions are ti!i::<-l

■ ■■•.s.ii'le aiiion-i ajij o.a

"'. .;'.:im"iiia. Tv> t]-. :» :•■.. -, :..
>rv -.-^ I ;■ T'.H'ie th;'.:; '.h'-c -

COBALT AND NICKEL

62n

i«Te, especially aa many probleraa regarding their natiiro still

im&olved. We shall merely state generally that thu complex

of the^e salts are almost all more or less brightly coloured :

desigtiattou of these salts, indeed, is dorived from their

orations. The " luUocolMilfk " salt^ are the compoiinda of the first

the pttrimrfo-sa]ia belong to the second, the jjruseo-^ fiiwro- and

ll€ tu the third type. The complex cations mostly form strong

with hydroxyl, which arta solulile in viator and exhibit the re-

jia of hydrojridion in a most pronounceil manner. Their salts ate

ientlr very difficultly soluble in water.

15. NickeL— Unlike cobalt, which is not employed in the
lie stiite, metallic niclcel is a nukterial which is greatly used. It
formerly used only for alloys ; thus Grrnutn silrrr i& an alloy of
nickel wtlh zinc and copper. Some decades ago, however, the
difficulties eaaeed by the high t<;mperature of fusion of nickel have
horn overcomo (especially since it was found that it could be rendere<l
MKire easily fusible hy the addition of metallie magne,siuui or aluminium),
■1x1 at the present day nickel is extensively employed in ciiscs where
ii it required to use a tenacious and hard metal, and one which keeps
wtU in the air and is difficultly fusible. It finds increasing use, there-
e, for ajjparatua in the laboratory and for household utousiJs.
urlher, large quantities of nickel are dfjxisitetl on other metals
the help of the electric eiin-ent. It coats these with a resistjint,
t silver-white layer, which keeps well in moist air, so that the
iiuf of various objects made of iron and brass has Ix'come an
,Te industry.

The electrical de[>ositioti of a nietiil ijepends oii the fact thai at
tip catliixle of a circuit, the cations pa-ss from the slate of iuns into
l-be neutral state. In the case of nickclion, this passes into metallic
nickel, which is ileposited at all points where the current leaves the
)><)iuii. In this process various circumstances, such as strength of the
*WTetit, nature of the solntion, etc., have a considerable influence on
*!ieiher the metal is deposited in a coherent, lustrous layer or as an
Incoherent jjowder. The practice of cfedro-piaHnff, as this process is
oiled, depends on the knowledge and application of the conditions
which etusurc the formatjun of a gooil deposit. This subject, ivhich is
important iti the arts, has been only very little investigated
itifically, BO that no general rules «in lie given.
In order that the nickel-plating bath, which constantly gives up
to the object to be plalod, may nut become exhausted, the anode
le of meUdlic nickel. By this means the anion is not discharged.
the contrary, as much neutral or metallic nickel passes into the
&laic as is separated at the catliixlo. and the whole proi'ess con-
in luotal passing into ions at the anode, and being transported by
current to the cathode, where it again passes from the ionic stat^
the nietillic- In this process the current would, themeticully,

2 s

ll'

tke I

62&

PRINCIPLES OF INORGANIC CHEMISTRY cmjJ

have practically no work to psiform ; Jis ft matter of fact, howeTB^
larj/cr or smiitler nniount of wurk ratist be j>erformefl by the ei
on account of the cliH'ereucea in the couceiitmtion and otbcr cimvi
stances, a fact which hods expression in the so-called pilari^tliun of A
bath or the " hath potential."

Nickel forms a divalent elem$ntar}' ion, mchlmt, Ni", which a
a fine green colour ; this colour is present in all solnlioiis of niti
salts which contJiin this ion. Nickel, it is true, ca^n also form a higlu
stage of oxitLition, hut this is extremely luistable, nmi does not Wha'
as a salt-forming oxide. Nickel can form complex ione, but theneai
neither ho varied nor so stable iis in the c;ise of cobalt ; this forms t
most essential difference betweett the otherwise very similar elenicBtil
Nickel salts are obtained by the solution of mctsiUic nickel in iiitr
acid ; in the case of nickel, the decomposition of atijueotis sfi
solutions with evolution of hydrogen takes place only very feebly*!
slowly. If iiqmi regm U employed, the chloride is obtained ; byerapl
rating the nitrate with Bulphoric acid^ the former is converted intoti
sulphate.

From the green solntions of the nickel salts, soluble Ijjises give

pale green precipitate of nkkd hydroxide, Ni(OH).„ which loses v»M

when heatcdj and ia converted into grey nkkel oxiih, NiO, Kicb

hydroxide is not soluble in alkalis, but dissolve* in anunouia. As ti

liquid thereby l>ecomes of an azvu'e blue colour, it must be conclmifl

that a new ion is formed. The investigation of the M»Ud salU bl

shown that wo are possibly dealing with two different ion*, nne (

which contains INH^, the other 6NIIj, to one Ni ; the ions, therfion

have the fonnula? Ni(NlI^)/' and Ni(NH^),.". They are both bluf.

* The complex ions of nickel containing ammonia diflTor frwiu t!ifl<

of culjalt, not only in being derived fi-orn divalent nickel, but also i

being ranch less stable. Whereas most of the cobalt-ammonia !■<*

ponnd-s can be brought together with bases, and even in some rjia

boiled with them, without ammonia being cliniinateil to any ap|in«

able extent, the salts of the nicket-ammoiua ions in the sohd txA

slowly lose their ammonia even in the aii', and njinckly on hc*un

The dissociation pressure of those compounds therefore in respect i

the ammonia has an apprccitable value even at the ortlinary tempei-atiiM

while in the case of the colwdt compountb it is immeasurably small.

The nickel salts are similar to those of cobalt and generally i"

niorphotis with them. Of these salts aonie importance is posscsswl \

nickel sulphute, which ia generally obtained in ijiiadratic crystals*"

6H^0, a form which is seldom found in the case of the other lilrinll

it can, however, also crystallise in the forms of magnesium siilplj*

and ferrous sulphate. With potassium and ammonium Butphatts

forms double salts of the oft-raentioriei! type. Nickel sulphate anoi

double salt with amtnnninm sulphate are used in large quantities 1

the preparation of baths for nickel-plating.

COBALT AND NICKEL

627

\'kh potassrimi cyanide, the nickel salts nt first deposit a green
pitAttf of ittckrtttus cifiniiiii', whioli dissolves in excess of potasaiimi
' and 3-ieId8 a yeliirK liquid. From this change of colour it can
• Men that a new ion ia prmJuced ; on evaprorating the aoliuion a
oir salt of the composition K.,Ni{CN)^. H„0 cr^'stalliaes out. The
^ atnnuimt which forms the basis of this salt does not have an
Ji^us composition to the complex ions of iron, manganese, and
Ub, for it is only divalent. With regard to its stability, also, it
Hi greatly from these compotinda. On acidifying the solution one
■ not obtain free hytlronickelcyanic acid, but a greenish predpitnttj
PpekelouB cyanide is produced and hydrocyanic acid escapes. The
ad, therefore, immediately decomposes according to the equation
.SiiCS), = Xi{CN)„ + 2 HON. A separation of cobalt and nickel
n be ba.sed on this reaction.

U(l^>- Nickel CarbonyL — If carbon monoxide is kept in contact
B finely divided nickel at a temperature of about 30', the two
iDBiancea combine to form a colourless liquid which boits at as low as
t , and has an unpleaaant smell and poisonous action. The coni-
Mtiou and vapour density are represented by the formula ?ii(CO)j.

The liquid is not appreciably soluble in water, but it readily dis-
ilvM in organic liquids, such as benzene and turpentine. In the air

tjiscs to snbatancea of complex composition.
I a somewhat higher temperature, nickel carbonyl again decom-
into its constituents ; for each temperature there exists a relation
til tlie fiirbon monoxide and the vaporous nickel carbonyl at
binH equilibrium exist^s vnth metalUc nickel : w^ith rising temperature
le «i{ailibrium *hifts in favour of the carbon monoxide.

By reason of this, nickel can be separated in the pure state from
» ores after it has been reduced to spongj' metal at a low temperature.
■rbon taonoxide is passed over it, and the resulting gas mixture is
RUcd : metallic nickel is thereby defiosited and the liberated carbon
MDozide can be iiseil for tlie conversion of fresh quantities of nickel,
br t«cbnicnl purposes, however, this process cannot be employed,
wanse, under the above conditions, the carbon monoxide also under-
M decomposition into carbon and carbon dioxide, 2C0 - C + COj,
'bich disturlts the cycle of processes.

^he change of equilibriuin with rise of temperatiu-e brings it
metallic nickel cjin ')e dt-LiiJed from a lower to a higher
Carbon moUox'ilc is enclosed in a glass tube, atone end
bich there is niekd spoi'^-*, :iru the end at which the nickel h not
is heated to lOU or -.oTm'wUal over this. After a short time
kftboiend 1>ecomea covered with a fine mirror of metallic nickel

CHAPTES TTVT

xac jlSb

417.

>FnM tW

«t tk«

rbt^

for tW mtt p««»i

^eartjooaCe aad cQiemte), and

ifoai bodi
430* ad 1

> « vkite, fadrij' aoft

aft »5(r. la Umt

IweUf. Siaee, bcnrever, Um xtne h^dioriJe

KMBWI

oxidsKiaii

ike aaderljfTDg

for the BOtt put ■hnvfy, and ofafecSs aiili^
one nmtt 'tht udhuntta <d air and water fmijr weJL

Caat stK k eoanely crjvtalliae aad brittle. I^
flMftol ii iMMed to wflUwbM OT«r 100*, it hnromea aoft .
and ean b« luuBinend aad rolled. Hmriag ones
nMat, H imiahu tenadooa eren at the ordinaty
bcated to about SOU , it again beeomea extreBdy faitele, and at i
tcmpecaUire tan be ground to a powder ; on bein^ yM^I^H^ it :
MHnewbAt brittle character.

Zinc i« etoplojed not only in the pore state, but alao to a
txtetA in alioya. lu moat important ajloj is tfaat with copfi«r;lt1
called brau, and will be tre:it«<l under copper. With copper '
nickel it fomu Gennan miver (p, 025).

Zinc ia also oied for coating iron in order to protect it {tob
thin is then Itnown as "^U-anised" iron. Iron objects which
constantly expjoed to the air, Buch aa railings, agricuhural imoti
etc., are in this way renderefi durable. It is true that zinc in
with iron oxidiecH more quickly than when alone, but tfao oxidatiial
limited U) the surface.

At 420 zinc f" "ml this temperature is low eoougfa to aOo*^

62S

UP. XXXI

ZINC ANT) CADMIUM

629

n mUblil being largely used for castings. At 950' zinc is converted
Ho s Tapoiir, which burns la the air with a brilliant blue Hame, forming
be oiide. The ilensity of this vapour yields the rnttiar weight fi54 ;
a this number also represcnta the combining weight, the foi inula of zinc
n the vaporous state is 2n. It contains, therefore, only one combining
reight, whereas most of the elements in the gaseous or vaporous form
hift the double formula. The other metale, howevefj so far as they
IR knuvn in the vaporous state, exhibit the same peculiarity as zinc.

It is on the ^'olatility of zinc that its manufacture depends. The
diygcn ores are heated directly with charcoal ; the sulphide, after
licitig convrrted into zinc oxide by roasting in the air. The metal formed
sj" the reduction of the oxide with charcoal voiatiliaes and is collected
n suiuble roceivera with exclusion of air, while the impuritie-s remain
wLirid in the retort

In this process a portion of the metat is obtained in a form in
rhicli it is often used in the Ial>orat4jrv, viz. as zitic litwt So long as
ie temperature of the receiver remains below the melting-point of
■L the metal is deposited in the fMrm of a fine grey powder. (The
Bb'ons are exactly the s;ime as in tlie formation of flowers of
idphiu-.) This powdery fonn of zinc is more suitable for many
ittemical purposes than the fused ; in using it, however, it must be
■aneiobered that it generally contains a considerable amount of zinc
Hide in consequence of an incipient oxidation.

Recently many attcrapt.s have been made to obtain Kiiic from its^
aw by first convening it into a suit and then deuompositig this by
■KUis of the electric current. The diHiculty of obtainijig a coherent
BUal (tm from oxide in this way does not appwr as yet to have been
fnnome.

61S. ZiBCion. — Metallic zinc readily dissolves in acids with
tTolution of hydrogen {p. 187)^ and is convcrtetl into the cotresponding
one lalt, zindvit, Zn", being formed from the met,it.

Ziiicion ta divalent, itnd resemblea inagnesion in many respoctj^.
like the latter it is colourless, and with the ditt'erent anions it forms
lilti which have similar solubilities and the same crystalline forma as
kk* miLgnesium salta. Zincion is a poison for the higher organisms ;
mrerthcWs, it has been found us a constituent of some plants M-hich
paw in soil containing zinc.

The h«at of formation of zincion from the metal iii 147 l;J. This
K iWefore, also the amount of heat developed by the solution, of
vat in acids (p. 204).

* During the dissolution some remarkable peculiarities are observed.
1^'iw line appears as almoat insoluble iu dilute acids. So soon^ how-
•Kr, »8 there is added a small quantity of a salt of copper, silver, lead,
"f Jnrae other met;d, which is eliminated from its solutions by zinc, a
'*pM evolution of hydrogen at once occurs. The cause of this is at
t>>«g»en 00 touching a piece of zinc immersed in an acid with a piece

€30

PRINCIPLES OF INOBGAN

5inSTRY

of another metal. Hydrogen is abundantly evolved, but only >t
exirfatc of the othur metal, while the zinc passes quietly ttito mhilfi
If diH'ereiit metals are used as cathtxlcs for sin electrical current
dilute acid, it is seen that for the evolution of hydrogen at a sudi
of zinc El much higher potential is required than in the case c»f t
i<other metal.

* The process may therefore be pictured as if the zinc withdn
the charge from the hydrion, passing thereby into zincioii, while
hydrogen assumes the gaseous form. This passage into the gusw
state takes place (for reasons which are not yet known, but which ai
detected by the potential) with much greater difficulty at a aurfate
zinc than at the snrfaci> of another metal, and for this reason the d*
composition is slight so long as only zinc surfaces are available for tb
evolution of gas. If, however, the zinc is connected by a eoiiducta
■with anoth^" metal at the surface of which the hy<lrogeu can be moM

.*fe

Zn.

Flo, 117.

readily evolved, the formation of the Kincion and the eliminalion of tin
hydrogen take place at different points, an electric current passini;
the Slime time through the metals and the acid. In Fig. 1 1 T a dttf
picture of these relations is given. I'^rom the zinc, denoted by Zn, tb*
metal dissolves as ion ; the requisite amounts of positive clettricit*
arc withdrawn from the hydrion present in the solution, thcst chap*
passing in the direction of the arrows through the metallic conduct
to the zinc. The simultaneous production of an electric ciirrenl i^
therefore, the necessary condition for the disaolution of zinc and tbi
evolution of hydrogen occurring at two tlifferent points.

* The above arrangement affords at the aime time an insiglit inw
the production of electric currents in the old voltaic cell, consistinl "
zinc, copper, atid dilute acid. Fuller information On this point willl''
given at a later point (Chap. XXXII.),

619. Zinc Hydroxide, Zn^OH)^, is dejMsited as a white, floccul«n
precipitate on the addition of dissolved bases to a solution containiol
zincion. It is soluble in an excess Iwth of alkali and of amroani«<
although for different reasons in the two cases. The solubilitj i"

ZINC AND CADMIUM

alkali depends on its property of splitting oil'hyddon from its hydroxy),
•mi iLercfore of acting as an licici. Tliese sulutioiii^ contain an alkali
aivrt/^, f,;f, KjZnO.,, and the new ions Zn(J.,' and HZnO,'. The reason
vt tile Bolubiliiy is therefore the same as in the (.-ase of jilunjina (p. jGO).
The solubilitj? of zinc hydroxide in ammonia, however, depends oti
ether causes. We might regard it as being due to an influence exerted
on the solubility by the presence of ammonion, such as occurs in the
cue rjf the othenviae very simihir magnesia (p. r»41). This appears,
licwever, to be excluded from tlie fiict that zinc hydroxide m.nst be a
tittch weaker Ijase, as is evident from ita solubility in alkalis (p. 5IjO).
(k the contrary, we ha^'e here to Jisaiime the formation of new
laeuiiinoiiium iotis, Zn(NHg)„"', where n has presumably Bcveral
iVdnas. The behaviour of zinc hydroxide is therefore comparable
with th&t of nickel hydroxide, in which eaae the formation of new
{out WM rendered visible by the change of colour.

* This aseiuuption is supported by the fact that the zinc salta,
esptciaily the halogen compounds, even when dry, readily combine
witii iimraonia without undergoing decomposition.

kOn being heat«d, zinc hydroxide loses water, and is converted into
te ::iM &tidf, ZnO. The same compound is obtained by heating
metallic einc in the air ; in this way it is prepai'cd on the large scale
for use aa a pigment under the name zim^ ukile.

Over white lead, which is employed for similar purposes, zinc white

fclhe advantiige of beitig less [kusohous, and of remaining white even
1 atmosphere containing sulphuretted hydrogen, whereas the formei'
l»«oine« d*rk in colour. White-lead, however, has a better covering
power, since it has a considerably higliL'r coefficient of refraction than
sine white, and for this leason it is still often preferred.
^» • Tfie use of colourless substances, as white paints, depends on the
H^ that in the small jiarticles of which the paint consists the light
"^oergoes repciated refraction, and is nltimately totally reflected. This
tobJ reflection eflecta the "covering" power, i.e. the op.Hcity of the
Wer. Of the variously directed rays in an op;M|UC botly, the number
rf those which are totally retlect«d is all the greater, the greater the
indei of refraction, because the angle at which the light rays can still
pii} through dec reaaeis in the swrno proportion. Hence proportionately
flayers suffice in ortler to refioct all the incident light.

Zinc oxide is white in the cold, but appears yellow when hot ; on
woling it ags-iu acijuires a whit« colour. This colour change must not
I* regarded as a sign of the conversion of the zinc oxide into another,
pwliaps allotropic, condition, for it does not take place suddenly, as in
well a caae it would do, but gradually. It is solely due to the fact
tiUit the region in which zinc oxide absorbs fay.? moves, on healing,
from the ultra-violet [jortion of the spectnim, in which it is situated at
^ otdinary temperature, towards the visible violet portion. This is
'JfT general phenomenon, viz. that the region of absorption of rays

G32

PRINCIPLES OF INORGANIC CHEMISTKY cHxtJ

changes in the above sense ■mih ibe temperature. White subst
bet'ome yellow on Ueing lieutefl, yellow ones red (p. G] 5), and red *
brown ; blue and green suliatanccs, on the other hand, geneiuny i
no marked change of colour on heating. Conversely, yellow and :
sutetances (with the exception of organic dyes) l>ecoiiie more pale, i
even colourh'ss, on being cooled, say in litpiid air.

620. Zinc Ohloride, ZnCl,, is a white, readily soluble salt, wiS
boils as low as 730, and can be easily obtained in the flry or wnt
by the action of hydrochloric; acid on zinc or zinc o.?ide. On beiiigJ
evaporated to dryneBS, the afjueous sohition loses liydroihloriL' ackJ.
The product can be agciin freeil from oxygen by distiJlatiun in a ourrenfc
of hydrogen chloride or by the electrolysis of the fused aalt, the »p
zinc which separate out acting as a purif3ring agent. Zinc chlo
melts very readily to a clear, strongly refracting liquid.

Zinc chloride is used as a preventive of the destruction of wood I
micro-organisms and fungi, f.g. in the case of railway sleepers. Fur
it ia used as a Hux for soft solder. In tliis case its action is due to iti
power of dissolving mettdlic oxides (p. 4.'i5).

A concentrated sohition of zinc chloride diasolvos large quantitittl

OH I

of zinc oxide. From the eolution an oxychloride, Zttp, , ciyetaUtH*!

out. If the solution ia very concenti-ated, the whole solidifies to aj
hard mass of oxychloride. This phenomenon is made use of for ttej
praparation of a cement, a solution of zinc chloride of syrupy consist- 1
ency being rubbed together with zinc oxide shortly before it is requirrfl
for use.

On diluting the solution containing the oxychloride with waMrj
that substance (or, in the case of very dilute solutions, zinc hydroxiiJeH
is precipitated. Since almost all coinraerdal zinc chloride containtj
oJtycbloride, i.e. has lost hydrogen chloride on evaporation to dryneai,!
the sjimc phenomenon ia there met with, the salt yielding a turbid|
solution, or, oti dilution, dejjositing a white precipitiite.

The formation of a basic precipitati? U also promoted by the hydro I
lytic decomposition of the zinc chloride in the solution. On accounlj
of the feebly basic properties of Iho hydroxide, this decomposition il
rather considerable, and manifests itself in the acid reaction exhibit
by the solutions of all zinc sidts.

621. Zinc Sulphate, or zinc vitriol, ZnSO^, generally crystalli*
with 7H/) in the rhombic fonns of magnesium sulphate. According
to the temperature, however, it can crystallise with other amounts
water, ami in other forms. It ia a colourless aalt, very reatiily solub
in water, and can be obtained by the action of sulphuric acid on an
oxide or metallic zinc ; it is employed in the arts find in medicine,
forms, with the sidphates of potiissium and ammonium, double
containing GH,,0.

622. iZinc Carbonate, ZnCO^, occurs naturally a& calamin

ZINC iVND CADMIUM

633

led

Fcase

lued zinc ore. It crystollisea in rhombohedni, which aro

irphous with those of C3ilc-s|mr. As in the cuse o( magnesia, hviir

/«, varying with the tempecature and the dilution, arc mostlj

hy prt'fipitttting aqueous solutions of zinc sfilts with alkali

■l»nate5. They are converted into zinc oxido by ignition, Pre-

lon as carbonate, and weighing as oxide, are nseri fot- the

ic&l deteimi nation of zinc^

'^. Zinc SUicS.te also occurs naturally as giliceoits fahiminf. It
usifd ill the manufacture of zinc.

t. Zinc Sulphide, ZnS, is obtained a-s a white, hydrated pre-
.te by the addition of ammonium sulphide to zmc s*dta. Of the
r known heavy metals zinc is the only one which forms a white
this serves as a convenient cliatucteristic in analysis. Zitic
de is soluble in dilute aci<ls with liberation of sulphuretted
:eo. The reaction t-ikes place in a manner similar to that in
of iron sulphide (p. 5H6), but with the difference that zinc
olpbide is considerably leas soluble. This is the re^ison that a neulral
station of zinc sidphate or zinc chloride is precipitated by svdphurette^l
fdrogen -, not until a pretty con.siderable portion of the salt has
ladargone double decomposition does the concentration of the hydrion
Irodaeed reach such a value a.s to hinder further precipitiition. If the
fionoentration of the hydrion is raised to this value to start with, by
Uw aildition of hydrochloric or sulphuric acid, no precipitation is pro-
^ued by sulphuretted hydrogen. For equilibrium depends only on
relative concentnitionK existing in the solution, and not on the

t of the solid substances.

ti, however, by suitable means the concentration of the hydrion is

8o low that the state of Cffuilibrlum is not reached, the zinc can

i03t completely precipitjited from acid solutions. As has been

iooed several times, this is broTight about by the addition of an

The acetanion present then withdraws the hydrion prwlnced

er to form undiasociiited acetic acid, and only a verj' smitll

ion of till* hydrion escapes this combination.

* If ill ihi.s manner zinc is precipitiitcd from acetic acid solution in
inweDce of cobalt and nickel, white zinc sulphide is first deposited,
black colwdt sulphide and nickel sidphide do not make their
feppe»mnce till later. In this way the presence of zinc along with
poie other metals «ui be detected in analysis.

In nature, zinc sidphide occurs in brown to black masses, and ia

zinr t/iftnle, or simply hlfiide. It is an Important zinc ore. The

lU" is removed by roasting, and the oxide formed is reduced with

I The process which occurs in the roasting is represented by

le equation '2ZuS + SO^ = 2ZiiO + 2S0^ The sulphm- dio.vide thereby

irodaced is used for the preparation of sulphuric acid. This is done

ouly for the sake of utilising it, but also in order that it may not

into the air and exert its destnictive action on plant growth-

prodao

634

PRINCIPLES OF INORGANIC CHEMISTRY en

625. Cadmium. — This elenient, %vliicli is very aimilai* to a
occurs in com]tiiriitively small amount in nature, aissiX-mttHl wiihll
metal. As it is more remlily volutilc than zincj it LoUecta in ihie I
portio[is of the distiibite in the prcpaiution of the latter. It is a Win
white metal, almost as soft as leiid ; it melts at 320" and boils at 77
Its vapour denaitj points to a mokr weight, which is of|iml to i
combining weight., Cd=n2"4; the formula of the element in 1
vaporona .state is therefore Cd, similarly to zinc

Catlniium fonns only one element«ry ion, divalent i^nlmion, G
The metiil diaaolves, althcuigh very slowly, in twpieous aeitls with Utn
tion of this ion. Cadinioiv is colourless, and acta as a rather nral(
poison on the lower and higher organisms. Its beat of formation fri
the metiil is 77 kj.

The cadmium salts in acjueous solution are diatinguislied hy
fact that many of them are considerably less dissociated ittto ions i
fche corresponding salts of the other divalent cations. This is esjjem
noticeable in the case of the halogen comfKjunda.

From the aqueous solutions of the cadmium salts alkali liy(lraxi(
precipitiite white aiilmimn fitfdraf.kle, which is insoluble in an cxmw
the |irecijiit<*nt. This is in agreement with the germnd incre^isc ni
brtsic properties with increaain*; coinlnriin^ weight in the case ol simi
elements. Cadmium hydro.icide is soluMe in excess of ammonia. T
solution contains complex caiiminm-ammoma ions, (.Vl(NH.|>„'.

By heating the hydroxide, and by the cnmbastion of the tnett*!
the air, cadmium oxide is obtained as a Iirowri powder, which raad
diasolvfes in acids to form ca<lmitim salt-i.

Of the salts the miphaic should be mentioned. This still cxhib
some similanty to the sulphates of the magneaium series, bnt
considerable divergence. Thus, it crystallises ^X the ordinary tempa
ture in accordance with the formula 3(CdS0^) . 8H,<J, for whiflh tin
is no analogy known in the case of the true " vitriols." The foniwti
also of the typieal double salt with potassium or ammonium sulpL
does not take place quite readily.

The sulphate is readily soluV>lc in wat«r; in the case of the
with yjrds molecules of water of crystallisiition the t«jTiperaliiro
very little influence on the solubility. It ja used in medicine., an
also employed for the conatmction of electricsd "at^inibird i-clls.'

The hiiiogrii comjioitwh of cadmium exhibit especially clearly
above-mentioned slight dissociation in a<jt»eous solution. Of the tJl
compounds, Mdmium (Idoridi; is most, farhnium ioffide least, dissocial
The latter salt forms crystjdline lamina> of a peaj'ly lustre, which
solul.tle in alcohol. On account of this property it is employed
photograi»hy as an iodising sidt.

* Apart from the small comiuerfvity, the following exporiia
demonatrates very clearly the slight degree of dissociation of ca^lm
ioilide. If cadmiuin hydroxide is brought together with water

3CXI

ZINC AND CADMIUM

635

riolphthalein, no itlkaline reaction can he detected, becaiia?
it' is too slightly soluble. The same thing is oliserved on
>luiion of potassium nitrate or sulphate instearl of water. If
a neutral solution of jjotiiAsinm ioriuhx, however, a strong
' faction is obtained on shukiiig up. The reason of this is that
,L»tn which passes into solution from the hydroxide is con\orted
iisssctciated cadmium iodide. A fresh quantity of hydroxide
niisi therefore piiss into solution, and this must go on till cijuilihrium
attJiiiKMl In this proeesa the hydroxiflion of tha hydroxide remains
w*r (along with jHitassiura from the potassium iodide), and the solution
Biut exhibit the reaction of hvdroxidlon, i.e. must react alkaline. In
IwmuliP wc have tM{OH)j + 21' ^ Cdl^ 4 20H'.

fil'fi. Cadmium Sulphide, CdS, i'a obtained aa a fine yellow pre-
fipitate on p;ii^sin^ sutjiimretted hytirogen into a neutral solution of a
s:\lt. If the sohition is acidified, precipitiition occurs never-
ind a very considerable amount of acid must be added before
nlphureited hydrogen ceases to produce a precipitjit*. Similar
diemical equilibria are obtained to those described in the case of zinc
mlphide (p. 6.'13), with this difference, howt-ver, that the concentration
fA hydrion necessary for equilibrium must be very much greater than
in the case of zinc.

If we have a solution in which cjidmium sulphide has just been
formed, and we add pot«issiiim iodide (or any salt containing iodidion),
Uie cadmium sulphide imntediately passes into solution. The reason
it tMfe is again that owing to the fonnation of undissociat«d cadmium
lide, cadraion disappears from the solution, and must be replacefl by
dissolution of a fresh portion of the precipitate.
On account of its pure yellow colour, cadmium sulphide is used in
ntiny under the simple name " ciidminm," since other cadmium
nn<ls are not employed fis pigments.

,\ii amalgam of cadmium and mercury is employed by dentists

filling foi' teeth, because it possesses the pr-opcrty of being soft

■aaily moulded for a short time after being prepared, but of very

solidifying to a coherent, hard mass, This dt-peiida on the fact

t the comjfound of the two metals is a crystallino snbstiince,

(irhich i« hard at the ordinary temperature, but which can Iw easily

Supercooled In the soft nifuis, therefore, we have a superfuaed

.IgAm. When crystallisation has commenced it proceeds slowly

rotlg^ the whole mass, which thereby l>ecQmes h&rd.

CHAPTER XXXII

COPPER

627, GreneraL — Between tbe metals of the new group, which
called after copper, and those of the former gionps, many point*
relationship existv The circumstance that most of the heavy meta
can form several series of compounds, i.e. ions of different valenc;
causee a ci'os&iug and interweaving of these mutual relationships irhii
render it impossible to draw up a simple list of the elements in sui
a wity that tljo most nearly related always stand together. F<
indeed, on following out one of the existing series, other ones nnist I
interrupted ; for the sum of these mutual relationships caijiiot i
represented hy means of a straight line, but only aa a m^iich bi-aiichi
river system, or still better perhaps, aa an arterial system exliibitin
manifold anastomosis.

Thus in copper we have, on the one hand, a metal which in certu
compounds shows itself to bo related to the elements of the raagiiesit
and iron series, while other componnde exhibit close relationships
silver and tneri;ury. We have already frequently met with sut
ambiguity of behaviour, e.(f. in the case of iron, and especially
manganese ; it points to the fact that a systematisation of the chemi
elements according to a single scheme is iinpfjssible, for a
exhaustive system must necessarily conUiin all the exiatiug
ships, and must, therefore, be of such a form that these div'
receive adequate expression. The satisfactory solution of this proWa
has not jis yet been attained, and wo must at the present time get o7(
the tlifficulty by pointing out, when necessary, the various relationahi]
existing.

628. Copper, — -Of the heavy metala alreafly discuasedl, copp«r
the first that is found in any conaiderablo qmmtity in iho metallic
ou the earth, and it belong.'?, therefore, together with Bilv4^i' and go\
to the metallic elements wbteh have been longest known. It is di
tinguished from all other motala by its bright -red colour, whic
however, is seen only on fresh aurfacea. Even in a very short tii
these become covered with a dark coating of oxygen or sulphur coi

630

COPPER

rhich, although it does not destroy the metallic histre, chutigeB
red colour of the pure raetal into the hrown-red, which is
ftUed copper-red,

er melts at 1050°, has the density 8*9, and ia, at the ordinary
are, a tenacious metal which can be mechanically uioiilded,
l^iesiets well the influerices of the atmosphere and of nioisturo.
g exposed for a lengthened period to moist air, it ia true, it
covered with a layer of oxygen compounds ; this, however,
msj thin, and effectually protects the metal underneath. At
f eopper combines fiiirly ja[)idly with oxygen to form a black,
dde, which readily breaks off in scales and oxpoees the uiider-
tal to fresh attack.

bMNint of hs chemical reaistibilityj its good mechanical proper-
^itB melting point, copper ia largely employed for utensils ol
|. Another very extended sphere of applicjition of copper
oti its great cnndadmiij fvr the fkxlnc CHirent. In this
It is superior to all other accessible metals (siher is alone
to it), and very large quantities pf it are therefore employed
&-tecbnicB. For this purpose it mast be very pure, since the
Hty is greatly lowered even by very small amounts of foreign

ies being used in the pure state, copper is also extensively
1 for alloys. Brass has already been mentioned ; others will
later.

combining weight of copper is Cu = 63"6.
The Ions of Cfopper. — Copper forms two kinds of elemen*
, the monovalent monocuprion, Cu', and the divalent dicuprion,
he latter is allied to the divalent ions previously described,
er belongs t-o a new type. Of the two, the divalent one is by
aost frequent and better known, and, for that reason, Bhall be
iribed.

formation of dicuprion from metallic copper does not Uike
arly so readily as that of the ions of the metjils hitherto
1. Without the co-operation of the atmospheric oxygen,
sids have no appreciable action on metallic copper, and only
id or hot concentrated sulphuric acid Lave a solvent action,
not hydrogen but a reduction product of the paiticidar acid
sd. On the other hand, hydrogen gas acts on fioUitions of
klts^ eliminating copper from them with the simultaneous for-
(f free acid.

ader ordiuaiy tondiiions, this reaction occurs ao slowly tliat it
te detected. If, however, the action of the hydrogen is acceler-
the presence of a catalyaer, e.^, metallic platinum, the action
elected.

!le dissolution of metals in nitric acid is accompanied
H of a portion of the acid. The process citn lie rcf

688 PKINCIPLES OF LVOKGANIC CHEMISTRY m

the scheme given on p. 607, if i^o write nitric acJd as a liydroxrl (.■o
poiunl of peiitavalenl nitrogen. The series ia : —

Nitrif «oid. IINO,^ + 2H,jO = N lOH )»

Nitrog«u |H!ro)tide. T^O^+iRfi^yiiOlD^
Kitroua Btid, HNO^ + HvO =K(OH)a
Nitric oxide, NO + H,0 ^ N"(OH \^

Hypouitroiis iiciJ, 4UjN,0a =N(OU)|

In the oxiiliBing «i"t!un of nitric acid, from one to four oxirfftl
tmite can take part, dependiiiy uii which of the lower members thoi
is eouverHed into, and tbe ccjiuitton has to he written ttccoKltngly.
for example, it is desired to express tho oxidatiou of copper to die
rion with formation of nitric oxide (which 13 the predominant reneli
on treating copper with nitric ncid), we liave the following, Ki
mole of copper requires two miiL^* in order to pa^a iuto dicnprion ;
mole of nitric acid, however, yields three units. Consequently,
must allow two moles of nitric acic3 to react, with three of copf
The three raoles of copper, however, require further six moles of nit
acid in order to pass into normal nitrate ; altogether then, eight md
of nitric acid act on three of copper :

3Cu + 8HN0, = 3Cii(N03)2 + 2N0 ^ 4HjO.

* Similarly, it is found that sulphuric acid on passing into
phurous acid, yields two oxidation imits, ami these arc exactly ra
cient to convert one molo of coppej' into dicnprion. One moie mon
sulphuric acid serves for the formation of the salt, so that we fini
have

Cu + 2H2SO^ = CuSOj + SO2 -¥ 2HjO.

In its solutions, dicuprion is greeciishblue in colour. If any olh
colour is shown liy a cwpric salt, we must t^onclude that tht« undS
sociated portion of the salt is also coloured. Thia is, as a matttr
fact, often the case.

For the higher organisms, dicuprion is a rather powerf<U poi**
while moukle, for example, can flourish ici presence of cnpjwr sajta

The heat of formation of dicuitrion from the metal amount*
-66 kj \ it is therefore negative, while that of the metallic catiol
liitherto considered was ])03itivG>, The difficulty of the frinnati<>D
the ion from the metul, and the ease of the i-cvcrso traTisfonuaUo
which we meet with in the case of copper, are connected with this fa

630. Copper Hydroxide. — From the solutions of cupric ml
strong bases precipitate ciqnk hfj<Iroi'iJt, Cu(UH).j as a bright V
snbatiince, which on being kept fur some time under ibc soluUoti, mi
quickly on heating, becomes dark brown, at the same time losing WJU
and piissiiig into ctiprk o-iidi; CuO. It may be asked how it is possi
for a BUbstance to lose water while lying under water, of which it I

or* *8 uitich at its disposjil as it re(|iures, The answer is that
ipric hjclroxide is not at all a sUiWe toinpoiiiul at ihw ordinary And
^higher temperatures, and the fact that it is prorluced before the form
* Ich is most stalile under the conditions, viz. eojijier oxide and water,
A case of the law of the prior formiitioii of the nnstal>Ie fomis.
Copper hydroxide is not soluble in alkalis except in very small
11, when the solvent is very concentrated. In the presence of
may organic sulistiinces it disBolves with fonnation of complex com-
ouods of dark hluc colour. Ammonia also jwecijjitatefl t^uftric salts
ith formiitioii of hydroxide ; an excess, however, a^ain eft'octs dissolu-
on. The litiuid thereby becomes of a dark corn-tiower liiue. This
I • sign that a new ion has Ijeen produced ; as a matter of fact, from
B dark-blue solutions salts can be obtained in the .solid state contain-
igtbe cation Cu(NH.5)/'.

Copper hydroxide is not a strong ba.se ; it ia one of the weakest of
te hydroxides of the divalent ions. This is shown in the distinct
lydrolysis of its salts, in consefjiieiice of which the solutions of the
•ItB of strong acids all react acid. Cupric salts of weak acida exhibit
jienomena of decomposition ; some, f.17. the carbonate, cannot be
pbuined at all in the normal condition, but only salts containing
pydn.xyl, or basic salt*, are known.

Besides being formed by the decomjxjsition of cupnc salts, copper

ide IB also obtained by the direct oxidation of copper in the air at a

r«d-b«at. Cuprous oxide, the anhydride of cuprous hydroxide

*n//«jl, is first formed, but this also pa-sses into cupric oxide under

ive conditions.
upper oxide is very readily reduced to the metal by means of
hTdrogen with production of water. 1 1 haa already been mentioned
ttat this reaction was used in order to detemiino the ratio of combina-
tion hctween hydrogen and oxygen, This same property of rciidy
reducibility conditions the use of copper oxide in urtfimie itli'maitari!
mi. The substance to be investigated is mixed with uxcffss uf
r oxide, the mixture placed in a tube and the whole heated, after
tioii apparatus for water (calcium chloride) ami for carbon
Ic <cau*tic [X»tash or soda lime) have lieen iittached. By mean*
the oxygen of the copper o.xide the carbon of the organic compound
biirnefJ to carbon dioxide, the hydrogen to water. Tliese products
Jected and weighed, and from this the amount of the above
Is contained in the organic compound (also weighed) can he
itied.
An}' nitrogen which is present is evolved in the free state, and the
Imount can also be detcrmitied by collecting and measuring the gas.
1 631. Cupric CMoiide. — Anhydrous cujirk ■rkloiiik, CuClj, is
prmed by the combustion of f ojjper in a current of chlorine, as a
fcllow.V>rowii powder which dissolves in anhydrous solvents with a
yellow colour, whereas its aijueous solution is blue or green

640

PRmClPLES OF IS ORGANIC CHEMISTRY Ctti

according to the concentration. From the solution the salt nil
2H^0 cryatallises out ; on account of adhering mother liquor, ti
jeneraliy appe^irs greeuj but in tho pure state it is bright btue. T
rhydrated salt on being bested loses bydrogeti chloride along with I
water, like many of the other chlorides of this group, and is convefl
into an oxychloride. The anhydrous siilt experieucea the same tni
formation on bciTig h&ited in oxygen ; chlorine is evolved at the m
time : 4CuCU + 0^ = 2Cu20Cl„ + 2CI3. By means of hydrogen chlorii
the oxycblorkle is again converted into the chloride : Cu.OCL i- 2H'
= 2CuCl„ + HjO. This reaction is made use of for the munnfaLture
[ehlorine ; the catalytic acceleration of the oxida-tion of hj'drogl
[chloride with free oxygen (p. 169), alao, is attributed tg tho ahern*

ccurrence of these two processes in the mixture of oxygen

Ihydrogen chloride, bnt this view still lacks experimental fuutidjaiion.

Concentrated aqueous solutions of copper chlon'de appear gna

If fuming hydrochloric acid is added, a yellow-brown li<|uid is obUiini

Tho latter coloiu* is the individual colour of the undissuciat*d coppi

chloride, the dissociation of which is i-educed almost to zero by

large excess of chloridion. So long as considerable amounts of and

aociated salt are present in the fairly concentrated solutions, t

mixed colour formed by the yellow of the chloride and the blue of t

dicuprion is produced. Very dilute solutions in which tho dicuprii

predominates, exhibit the blue colour of that ion. On being beate

r dissociation is diminishe*! ; the yellow colour of the undissociated

Lappears also to becoaie more intense (p. 631), so that for this re

J, the solutions change colour towards the green. If we write wi
a solution of copper chloride nn paper, the characters become yellfi
on being heated at those paits where the strongly coloured, anhydroi
salt is formed, and on cooling disjippear again where the
coloured hydrated salt is formed through the attmction of
fi'ora the air. This solution can therefore also be used ob
pathetic ink" (p. 6-!l), but must not be applied with a i
because iron acts on solutions of copper with precipitation of
metal.

As has just been mentioned, cupria chloride readily forms 01
chlorides with loss of chlorine. These compounds vary in ioni]>ositii
according to the cunditions of formation. Tho one best chjiract«ri»
is the compound ('u^W^Oll).,, which occurs in nature as tiUimtniU^ ti
is also readily formed whore chlorine compoutida, water and oxyga
act on copper. It is a briglit green substance which forms rhomll
I crystals, and is scarcely soluble in water. It dissolves rejidily in ai
^nd in ammonia, aa indeed could be expected from its composition.

632. Copper Sulphate.— Cupric sulphate or mppn vitriol. <.\iS(
is obttiined 011 tlie large si-ale by^ the oxidation of naturally occurrii
sulphur compounds of copper. It is a salt which cryatalliaes iu bh
triclinic crystals with 5H,_,0, and which is similar to the otb

COPPER

64t

lols^in it« profiertJes. Accoiiding to the temperature, the salt

lip other <iiijitittties of water and exhibits forms which occur in

of the iul[thate8 of other divalent ixr^tals (cf- p, T}7ii). It »lso

ilises aton^ with potassium and ummonitim sulphate in double

th (jH^O. The water of cryBtallisalion passes off fairly readily,

Willi 1 iljO !ii fii-st remaining behind, which is more difficult to

!rat«. The unhydroii* sulphate is dirty white in colour; iti the

n Hbwjrbs water and again becomes blue. The dehydrated copper

hate IS sometrmes nsetl as a desiccating agent, especially for liquids,

'<)iint of the eonvenience of being atile to tell when the desiccation

[•lete, from the non-appeariincc of the blue colour in freshly

siilphjite.

an fli-fti-if rurrti't is jwissed through a solution of cojiper sulphat*,
Boetallic cop[jer is deposited as? a coherent coating on the cathode. As
IH is jMrticnlarly cjisy to obtain a good precipitate with copper (p.
•2f>>. the process is made use of not nniy for coating other objects
irith copp<T, but also for shiiping objects in copper, and thus of pro*
g ;t sort of cold metallic casting. The dejiosit fills out very
y the form of the cathode, and when it has acquired a certain
ues8 it can lie retno\ ed as ii coherent mass. For this reagoii it is
for talking casts of printing blocks. These are Hrst cut in wood
then CAst in warm gutt.H-]jercha oi' in very readily fiisildc metal
smuth), and the cast ia then made the ciithode of an electric
t in a solution of copper snlphate. The anwle consists of cufnicr
er that the amount of copjwr contjuned in the solution shall
a unchanged (p. 620). Non-conducting casts, such as those of
pt'fcha or evfisura, are first covered with a conducting layer, e.t/.
ibbing with gi-dphite.

'he same process is made use of for the purpose of purifynuj ini-
copper. The impiu-e copj>er is then made the anode, and a thin
of pure copper is used for the cathode. On this, very pure
r. "electmlytk copper," is deposited if a current of very small
I«lenlial is employed, for the impurities either are not dissolveii, but
Hnk in the bfitt^m fis "atiofje mud," or they are not separated out at
the cathode <«.;;. iron), and must be removed from the solution when
tiity have accmiiulated too much. The copper, for example, which i&
for electrical purprises, and w^hich must bo \'ery pure, is treated

way.

ic can spare one's self the special genemtioii of an electric current

hy niiikiiig the separation of copper a part of the reactions in a voltaic

«»1!. As a matter of fact, the process of electrical copper casting,

itiictrvttrpififj, was discovereti through copper sulphate lieing used as an

sint; agent in a voltaic cell, whereby the deposited copper took

shape of the cathode.

ch a cell is represented in Fig. 118. A' ii the cathode of copper,

porous cell of Hred clay which allows the current to pass, but

2 T

642

PRINCIPLES OF INOKGANIC CHEMISTKV

ckj

checks the mixing of the liquid:^ and Z is nn aiioiie of meUiiic m
K is surrouiuJed l>y a solution of copper sulpimtc, Z by a sohiliuu
zinc sulphate. When, then, A' iind Z are cnrinectwt l*y ;i mclallk
ductor L, the Jeposition of cupper on A' occurs, while an e<nii\"al«
atrtount of zinc is at the same time di)^solved from Z. During I
process an electric current passes thivugh t!ie conductor in. the <ilii

tioii of tb<; aiTow, an<i can Ik? ««i
dotecti'd and measured hy instrting
inrreiit indicator in the circiriL

The chemical process, ther«fo
consists in metallic coj.iper Wiug i
posited from the ct>pper sulphatt c
zinc dissolving to zinc sul|)hui«,
,.,___ >vt' write the wjuation of the lutit, '
f (rr-| huve first of all: Cu"TS(V+i;B
I Uu + Zn" + SOj" ; uiiiitting <jii eith
aide the ion SO,", which renai
unchiiriged, we nittain Cii" -r i!n
Cii + Zn". The proct^sa. therefa
simply consists in the topper i
zinc exchiingtng their nJe as joiu,
since the ionic state is detennined
the positive electrical charge, in
cnprioii yielding up '\U charge to
zinc, which thereby |)as8es into nnQa
wKile the copper is deposited in 1
Tiisudlic state.
This proceae immediately ciccni-s ivhen metallic zinc jb introdat
into a solution of copper sulphate ; copper is. deposited and line
disaolved. An electrical current cannot, however, be obtained in tl
way. The resuson of this is that the transference of the charge* ul
place everywhere within the liquid, ao that it is not possilJe t« 1
hold of and conduct the electrical movement. In the arranfjem*
shown in Fig. 1 18, which is called after its diBCOvcroi', the Ikniirilc«
the solution of the zinc and tiie deposition of the copper take pljwf
gepiirate points, imd this becomes jrossible only wheTi the riece«i
eijualisation of electricity occurs through the medium of the lii|uiil
the one hand, and of the condnetor on (he other.

63v3. Voltaic Cells. — In urder that the above process, wherehy
electric current is gincrated in the Danicll cell, may CK-ciu-, it is evidi
that the reaction.? on which the cell is based should occur even wi
out this sp'cifil (irrungenient, since there would otherwise be no
to make the process take place. Now, howe\er, only those procM
occur in which free energy is available ; » voltaic cell is therefore
apparatus by means of wliich free chemical energy is converted i
free electrical energy.

«^" '- '-■■^'•■"

i "

Fio. llf.

COPPEK

643

It will lliert^foit-' 1*6 possilile to constnict other cells after Llie
aJl«ni of the Daiiiell, liy rephtcinn; the zirie and the copper bj other
itetals placed in eolations of their sjilts and connectetl with one
mother. This is, as i\ matter of fiu^t, the ciise ; with every aiich
nmbination a evil ia oht-ained in which one of the meUils is redivceii
Inim Its sjilt and dejwsjted in tlie metallic state, while thu other ia
wiilised, i.r. is dissolved as ion. Which of the two connected raetaU
will sssiinie one or the other rfile, is found hy introducing each metal

Ktht" solution of tiie other ; onu uf the metals will then precipitate
Kher from its solution, while the other metal will lejive the
ton of the first unchanged. The precipitating metal is then
llnys the anode, which aUo riissolves in the ceil the .'same as in the
ditM-f experiment, and the precipitated metal is the cathode, for it is
il«|jo9ited in the cell in the sunie way us in the direct iictinn. From
tkeie experimentJi it is found that a given metal can both precipitate
uvd be precipitated ; cadndum i-lindnateg copper from solutions of
»tpper salts, but is deposited from its solutiona in the metallic state
Irr zinc.

Tiic law which olttains here can be expressed as fidlows : II is

• iirrnngr nli tlir mfioL* in n xint/lr $eriei ia stti'h ft v'<nf that rurh

< tfll the niftiil^i lollowiiig from their tiqueuvs .■ioiviunis, hvl »s

• f fit/ ftic.h of [he prtrMiiiif iiiirK On account of the electrical

.; :.; of this serii's, to be prosently mentioned, it is called the

ffUtal ffrifn of the metala.

34. Electrical Potential. — The work which an electric current

rform depend:* not only on the strength of the eiirrenl or the

mint of cbctricity which in unit of time piiesoa throii^^h a section

the rontiuctor, but on another magnitude fin well, which is called

fentitil, the unit of which, fixed once for all, is called the ivli,

^ electric irica^u descent lamp, which is supplied by a current

ipffe {p. 196) at a potential of 50 volts, gives the same light

whiclt uses a current of 5 amperes at 10 volts, while at n

ial of 200 volts :i current of 0"2.i ampere ia sufficient to produce

tne effect

'rom this example it is at once seen that the electrical work of a
iirent is measured Ity the fnn!ni{ of sirriit)ih of cmraU <nni pi)ienliiif.
k b^a great einiilarity to the perfornmuco of work by a falling mass
r ; in this case hIso the work depends on the tpiantity of the
, And on the height of fall, and the amoimt of work which can
Cained with the ^nme quantity of water is all the greater, the
r the bright ihrough which the water falls. To the tjuanlihi of
there rorresjxmds the uiairrdtude, which has been called qunntiin
tUrinriitf, and which can be measured, in accoi-dancc with Faraday's
ly"), by the amount of suhatjince sejKtrated electrolytically on
hg an electrolytic cell in the cijicuit. Tu the heitjlii of full there
i^tooda the property of electrical euergj^ which has just been

648

PRINCIPLES OF INOBGANIC CHEMISTBV

is filled with jiure water, it behaves eaaentially like any ordinarr ell
cell, fur imrlor slight pressure the water flows througli, only m
elowly than when the precipitate is absent. If, liowcver, instea*!
the pure wjiter an a<(ueous solution, e.g. of ordinary sugar, i» [iU<
in the cell, this does not, in the first itietiince, filter through. U ti
pressure is iucreased, percolation cumniences at a deflnitc pressure, bl
it is not the augar solution that filters through, but pure water.

If the experiment is performed with diflerent solutions of evys
it is found that a definite pressure is necessary in each case in onli
that the water may pass through, and this preseure is proportional
the concentration of the solution.

If, after being cloi^ed and a tuanometcr attache<j, the cell \s jiUe.
in pure water, the latter eontiuiies to pass through the eell-waU uc
the same pressure is produced as that luirier which the water ooit
be forced through the cell- wall.

Various other siibataitces behave in a manner siniilar to migu
they arc kept back by the cell wall and generate a pressure. There
substances, however, which are not kept hack by the cell-wall , thi
also, do not generate a pressure (or only a comparatively small i
when they are partially rotaiued).

We must conclude, therefore, that the pressure is duo to dl
dissolved substance ; tlie water cannot give rise to it becatuc it fl
pass through the cell-wall.

On comparing solutions of diH'erent .substances which do not pa
through the cell- wall, with respect to the pressure whicli they protliK
it is found that the same pressure is prtniuc-fd by Mu>y sdntufin th >«
centratwns of whkh <tre in the ratio of th^ molar weitjfik of the. liiiMr
substnnce.^. These pressures, therefore, which are called o.<motii: ftt
siires, could be used for the deteiToination of the molar weight
dissolved substanct^s, in the same maun«r as the deprcssioit uf til
freezing point and the lowering of the vapour pressure (p, 15*1
The experimental difhculties in the carrying out of such njeasurt
menta, however, are very great.

The teraiterature exercises an influence on the osmotic firessui*
imder ordinary conditions, the latter increases ab^.int Jrd pet rent ft
BTery degree.

On the whole, therefore, the osmotic pressure follows similar Ui
to the gas pressure ■ the latter is also proportional to the coiicentratif
or density of the gas (Boyle's law, p. 68), and for every dtgrfl
increases by 1/273, i.e. about Ji-d per cent (Gay Lnssac's law, p, 691,

The resemblance, however, e.ictends still further If, for cxainpl
the osmotic pi'esaure la determined which is exerted by a detini
solution of carbon dioxide, it is found to T>e just as gixat a* thi
exerted by the same junount of carl>on dioxide when it oconpit'S
the gaseons sute tlie Siime volnme .-is the solution, Thus
therefore, u dissolved subatsvnce behaves as n gas, and its osmo

COPPEE

643

ttrii.'iil jKitentia] is nt the present time tbe most fruitful method of
Brmiiiing this iniporUint ntid not eaaily accessible magnitude.
Un constructing cells containing the iihove thrve me!tu.U iiiid ulso the
er possil»le cells, the following values of the potentials ure olitainedi —

SilTer-copper
Silver-cadmium ,
CoptnT-oudmiuin

047 volt
075 ,.

On compnring these v«lue8 with the former, it is fonnd that the
ential of the comhinution silver-zinc is equal to the gum of the
entials silver - copper plus copper-ziuc or silver - cadiuium plus
nium-iinc, etc. Writing the values

Silwr =1-57 VI lit
CoiiptT =1'1(1 ,,

Catiiiiitiiii ^oari ,,

Zino

= Q-M

tbftt the potential of any combination of these metals is equal

Uhe difference of the corresponding numbers. These numliers may

etcfure be ejijled the poiifniiah of the smjU tiiftah, in -which case,

inly, the zeru, Zri ~ 0, has been arbitriirily choaeu. This,

fever, has no influence on the result, for if any other metal is put

Uj iQTO, and the corresponding values of the potot>tial ure

li'ulatod with due regard to the sign, another aeries is obtained which

hibitfl the same differences between the separate members, and hits

same meaning, therefore, wa the former aeries.

Thia series is the numerical expression of the potential series

.643} ; it is tlie expression of a fundamental property of the metals.

Tlja numbers depend on the tempei utnres, but their relative {xjaitions

I not greatly change within the range of temperatures investigated;

fregnrds this [unut, however, our kuowle<lge is as yet rather scanty.

Ilifi foUomng table gives a more complete list of jHitetitiuls. In

i^fBtic has not been taken as the zero, but another zero has

which gives expression to the actual change of the free

in the passage fmm the metftllic to the ionic sUite. We cannot

plain liere tiow this zero haa been derived, and this is of no

rrrtance, in the tirst instance, since we ure concerned only with the

erefices, and these are intlepetideut of the zero.

Ctfsinm

Till

—

Rubidium

—

Li><ai!

-O-ll) vnlL

rutnflsitim

—

Ilydrogeu ■

0-/S ,,

Sixlitiiii

—

Antimony

—

MftgJiesiiint 4 1-24 volt

Risninth

Aluiiiiiiiuni

1-03 ,,

AjTMuic

—

Miiti^alit:se

O'S- ,.

Cr>[i|ior

-0-59 ,.

'Aim

0-61 „

Mm-iiry -

1-03 ,,

f'mliniurii

0-je ,,

Silver

-106 ,,

Tliiillium

iril ..

PnUudiiim -

1'07 ,.

Iron

o-M ,.

Pbtiimm

Cobalt

|J'02 ,,

riftld

—^

Niekol

0'02 ,,

650

PRINCIPLES OF INORrTANIC CHEMISTRY

udl

cupratta oxide. On tjeing further heateJ in the air,^ it is converwi"!
black etipric oxide ; on removing this btuck coating, however. Fx
piece of oxidisi^d copper, it is foim>i to i>e generally red oilniT";
the side next the metal, i.e. to consist uf c-iiprous oxide,

Th« corre9|)otidinj!; ruprims hijitniXMif. t'ii^(OHl>.r, or '
obtatriM] as a luipk-retl powder by thn decunajxisition '.
chloride, to lie presently mentioned, with caustic potash or aod^

In riHture cuprous oKiHe ot-eurs !ia riv/ copper ore, aud ii
highly valued ore on iircount of its richness in coppe^r ; it can i
be cxjnvarted into rMtftAlItc copper by rednrtion with charcoal.

(/uprotis oxidt? i^ alsir formed an iho product of redoetkt^
FehHnp;'s sthliition witli grapif-iiugar and similar suUstAnces (p. 6&S}.
can hf. prepared in this way. In moist air it is oxidised tocnpnt4
or to basic carbonate.

On treating cupric oxide or liyriroxide with acids, not tliei
aponding cnprons, but the cupric stilts, are generalh' formed, .
of the coppt'r is def.HJsitfd in the niet;iUiL' state its a blackish-red |
With snIphiiHt: add, for example, the reaction Utkc^ place
to the equation Cu.,tj -^ H.,SOj = Cu -• CiiSO, -*- WjO, On con
the ions the process can Ije interpretc<l as inking place in 8iirb»<
that cuprous sulphate is firat formed, the moiiocnprion of *rt|
however. imme<liatcly undergoes traiisfornuitton into dirTiprim •^l
metallic copper r 2Cii = Cii" + Cu. The wiUitioii contains diiup'l
to a preponderating extent, liut It is in accordance with the [^
relations to a-ssiiuic that it ia a ease of chcTuical ciiuilibrium h«m>il
the two ione and the metallic copper, in which .1 Lir^e concenm**!
of dicuprion is opposed by a very slight comcntration of ruooonipn*!

If inst«Ad of sid[vhiiric acid a hiilngen hydmcid, thiocvanic »«i'l
some other acid wluch Ciin form a very ditticultly solu^ite n
is t:iken, the above dccnmpositinn does not take place, anr)
tive cnprous compounds arc formed. Thi* is exphiijje<l bv the;
that mouocuprion is present only in a negligibly small amount in
solution protlnced, since, of course, the salts are dit^cuhlv soluble
decom|X)sition of nionocuprion into dicuprion and metal can the
take place only to an inappreciably slight extent.

642. Ouprons Chloride is a vrhito .salt, onl}"^ Very .slightlv»M
in water : it can be obtained by boiling a solution of cnpHc cWfli
in strong hydrochloric acid with copper |>owder. The colour at
darkens, but a yellowisii Itipiid is firndly obtained, which on
poured into much water deposits a snow-white precipitate of cttp
chloride. This niu*t be wa.shed as far »a possible with exclusion nifi
as it otherwise rapidly passed into cupric oxy-chloride (p. 64l».

This reaction is the reverse of the one given before ; wherau in '
previous ease monocuprion decom|x>aca into dicuprion and me
copper, we have in this ca.se the reverse transformation of cupric
■wiih metallic copper into cuprous salt. The reasoti U 'bs"' i"

COPPER

351

chloric ricid solution raonocuprion is present only in very slight
uii , unci fiirtlier, the fattt that cupious chloride, which is almost
ihlc in wtit«r, dissohes iti hytlrochlonu actd, proves that iti this
the chloride is either dissolved as such (withoni dissocijititjn), or
|bkt a coiopoiind of the tvrit constituents, a hydrochlurocupric rtcJd, has
bead f<«itied. No ini. estimation h(»s us yet been carried out a;* U< how
thf oiu* iiT the oiher jiossihility piedonii nates,

anirnotiia ulsfj t-uprnus chloridt' dissolves tr> a colourless li(|uid,
rhich ciiproammoniim, L'u(NH.j), is contained. The chloride of
ion. CiiNHjCl, can be obtained in colourleBs, regular crystals by
njling a sohition of amruoninm chloHd*? with cojiipei' powder and
ttflrin^ the litjuid pro<luc«l to cool slowly, The aijiioous solution
nea alntoHt iuniiediatfly bine in the air, oxygon bcirip absorlwrl.
Hb sohvtious of fuprons chloride, tliu acid as well as the aramoni-
il. aUorb a considerable amcmtil of i'irt»m itimujxuh: This appe^irs
1^^ ruber firmly bound, b«t can be removed from the lif|Utd by
^■nnrd pumping. We are dealing in this ca»o with the formation
I^Ftumplcx cation, similar to the cntnplex ion produced from diferrion
loi aitric oxide (j). oOlJ, which, liktj this, is not very stable, and
an ajiprefiable dissociation pressure. The reaction is used
he derermination of carbon monoxitle in gasemis mixtures, but
for the refi=;ons just iiicutioned, be employed with some care.
U.I. Cuprous Bromide, CuBr, is very similar to ciipmua
I chloride.

|b^44. Cuprous Iodide is formed along with free iodine, when
^P^ion and iodidion come toj^ether in solution, according to iho
'•^ti<>n 12('u*' ¥ 41' = 2CuI + I.,, In this process we can regard the
'iicuftijtm as losing a [jositivc charge, and thereby neutralising the
negative charge of one iodidion. The monocuprioii prmhtced at once
wjlid cuprous iodide, with a second <|uanlity of iodidion, and
X«s out. If a reducing agent is added at the eommencement,
the dicuprion ciui he converted to monocuprion, euprous
b itJone without free iodine is deposited. This is effected, for
iple, by sulphurous acid or an acid solution of ferrous sulphate,
"ince the cuprous ioilide is sobible ordy to an exceedingly slight
*ro*m, even very small qtiatititi^js of iodine can in this wfiy be sepa-
i»t«i from a solution, and the method is employed wmunercialiy for
"ihtaining iodine from the mother liquon? containing iodirlion along

K comparatively Urge ipiantities of other halogen.*,
iiprou* iotlido is a reddish white, hea\'y powder which yields
-,-.»■ oxide and iudine by diaiilliitiou with pyrolusite, and potassium
J^iv and cuprous oxide by JHiiliiig with caustic potjjsh. It di.'jHolves
Bmonia similarly to cuprous chloride.

The interaction between io lidion and dicuprion, described alx>vo,

^not oc-ciu- instant/ineoiuly, but with a measurable velocity which

nee very ainaU with increasing dilutioti. Thus very dilute solutions

ia eretndf aad cmiw ejmaait m
SCu" ♦ 4CX'= SfoCN -.. <CX)j. Tl» m a
eTaoofpen gMw In onfer to hsre a
it t« onlj ntdtmmrj Uf htut ta^?edier eqmraleiit mlnriiw ai
■tlpiiate mad potAasnim ertnadt.

«47. Complex Copper OoBpounds. — We have alna^f q
of tbe fonustiuu t4 j^ complex compounii of dacupoott aad
vlucll m dkaracferited bf ibe [frodttctioti ot a dark bine
tbe mixed ufAntiott. In this tbe cev ion Cn(NH^," »
«Alt« ffl which are obtained bf adding excess of anunooia to tit
tTon* of ihf mpeetive co|>per aalts.

(H theitc salu the bent knoim is tbe sulpliate, Ca(NH,>,SO,*
b ewrily olitained bj adding ammonia to a cuncentmt«d euJi
copfMir )ii)]phat« until tb« «<j!ittioQ has again ><«eonie qnit« dar,'
th^^n fK)uriri^ a layer of alcohol on the top. Thi? salt is oolj
■lightly Bfjliib]*? in alcohol, and is depositfid in Wfli-fonued, dark'
ciyttals a« the alcohol slowly diffitses into the Ui)derlviii|« \'mwA.
the wrnifl way various other salts of the same ion can he ohtii
Solutions of th«se salts are used in comhating certaia panuitcs (mil
on vineii.* "» •

Copper forms other complex comiwunds of a similar coiMl

CXXII

COPPER

653

t'xcess of alkfili lo cupiic salts in prestTHie of certiiiii organic

■ id!?, e,(f, sugar or tiirfcirii* fioM. In lliis cusc also r tliirk lilue

- jiriniuc't'*! fi'oin wlncli ii s;ih (if the bshhu colour ciin Itc olttiiiiieil.

— .-. sal U acids cMtvlainiiig copper are present, the coni|)«<*ition of

KirlLich depends on thnt of the Kiibatance rniployed, and CAunot be

V-"- id here. In {^'eneral the |iro[M'rty of fonnitig such cninpounds

J in the samo organic liyfli'oxyl corapoimds as hitMl^r the

jjiii:)jiit.ktii»n of ferric nxide liy btises (p. 592).

I d .-lucli coTiipuiinds the W^t known is t'thlin/fit unlufit/n, which is
0>>ui(if«l hy jiddin^ {urUiric und and excess of cjiustii.- putnHli tct a solu-
tion of copper iiul(ih;ite. It is a dark liltie liijiiid, whieh is changed by
us reducing dgents in such a manner that it deposits a precipitate
rrf ri"*! cuprous (>xi<io (p. rt50). It can serve, lherofi)re, for' the detection
I.I -wh siittstantes, an«i it is used for this piii*p«sie in analysis, f..ff. Jiir
llir lirtcction of grapt'sngar in urine.

In the iHiprous series siwh- complex copper comiwimda have be«n
llnody meiiitionod. It has still to be remarked that cuprous cyanide
Ivea in potaissiuin cyanide \o form a eolonrlcsa liipud, from which
eomplex salt KCiUCN)^, the potassium sidt of cuprocyanidion, is
nod. Thi.s jiohition is very stabitij and contains excoe<lingly little
on, so thai ail si>lid copper com|>ounds, even copjxjr sulphide,
live in potassium cyanide with fonuaiiiin of tliis complex salt.
'&iit:ige i.s idsty tiikiHi of this behaviour in analy^ig,
CopjKT also forms a number of eonipkx com])ounda in wlueh sulphur
part, and wlitch are derived fiom sulphurous and tliioaulphnric
This reference lo their existence must suffice here,
IS. Metallurgy of Copper.^ On accoimt of the large con-
Bpiion of eopper in the art^, its manufacture from the naturally
imng ores is an )niport,icit industry. So long as we are dealing
oxygen ttres, red copper ore, or the I>»sic carbonates, reduction
charcoal, vt'hicli takes place very readily, is all that is necessary.
caae of the .snlplmrous oi'ea, the most importjint of which are
■ pyritfs and itirieyntrd copper we, the task is more eoniplicuted.
tiiroe ores arc compounds of copper anlphidc with iron s.ulphide,
iho pr^panitioti of pure copper requires at the same, time the
itnnlion of sulphur and iron. This is rendered! more ditheult by
fact that the siilphiu* combines much more firmly with copjwr
liiin with iron, so that it can be removed only with ililficidty. On
ig 8ubject4.Hl to an oxidising itroceaa of roasting, ferroaoferrtc oxid«
chiefly formed along with cuprous sulphide, and by fusing this
tiire with the addition of ailireoua 8ul)3t<'inccs, a slag consisting
ntialJ}' of iron silieaie and a mixture or an alloy of ropjwr and
itw sulphide is obtained by repeating the ojwmtion. When the
'Uiit of sulphur has become sufficiently small, the crude copper
f^il'ick copper) is cast into plates and subjected to elecu-wtyisis in an
*^(l8otmion of copper sulphate, with a piece of copper foil ;w cathode.

654 PRINCIPLES OF INORGANIC CHEMISTRY CH. xxxa

In this way pure copper is obtained, and the copper sulphide, vrhiA
along with the other impurities forms the anode mud, is again fused
along with other portions of the ore.

The development of the method of electrolytic deposition hu
further led to the extraction of the copper ores in the wet way, tii*
metal being separated electrolytically from the solutions of copper nit
obtained. For this purpose ferric salts are mostly used, which d).<«olr«
the cuprous sul{»hide with formation of cuprous salt, themselves being
reduced to ferrous salts, and sulphur being deposited.

On re-fusing the copper cuprous oxide is formed, which dissolve!
in the liquid metal, but on cooling again separates out and renders it
brittle. For this reason the copper directly before being cast must be
subjected to a reducing treatment (stirring with a pole of wet vrood).
If the reduction is carried too far the tenacity of the copper is impaired,
])resumably through the conversion of traces of other metallic o.xidei
into the metallic state. This last operation must, therefore be pe^
formed with care and frequent sampling.

CHAPTER XXXIII

LEAl>

VJ. GeneraL^ — Lwil is alliwl to strontium and barium in like manner
* .iiic iuiil liulniiuui tire allied to inay;nHsiiiui. ffdviimi, vvhii-b exlultits
f1nl)«n» ii\ i-sotnorphisni in liuth diivctioiit^, .stands in th<* middli-. (Jn
ic "thiT hnnil, lead is decidedly « heavy nu^tat, and forms an in>!oluK]e,
W coloured sulphur conipouiid.

In nature lead is fairly widely tlisitriljiit^'d. lie ni<»*it iniportiint
attimlly occurring ore is /««/ aulphkif, from which by far the largest
inioiuit of xhv in^'tal is nhtaiiied. The carbonate and the sulfjhatc.
thii'h ar<? istjinorphotts with the corresponding gaits of strontium ami
uium, are itUo futuid.

Stftailie Ifiiil has been known from olden times, as it cjiri l« re^ulily
litained from its ores. Its many a]>] plications depend, on the one
uuul, oa it* low melting point, 330 , and its great density, 1 1 4, and,
m the olhwr hand, on its softnijss and (.■nnseqiient plasticity, Thy last
»ro|i«riy renders it possible, especially at u somewhat higher tempeia-
tire, to form lead hy pre-Baure like a plastic maas, and in this way to
•nxiurp wire, tubinfj;, and such like.

In nifjist air lead oxidises very rapidly, liut only superficially, jfo
Aat on the whole it is fairly resistant. It should be metitiotied herf
:l»t it resists the action of perfectly pure watei- much less than that
>f ordinjiry spring or rivei- water. Thia is due to the fiwt that in the
■Inner case, under the joint action of water and atmosjiherie oxygen,
W hydro.\iJo is produced, which is slightly soluble in water, and

feftlrc does not protect the lead. In impure water, which contains
■nion iind carbanion, the eorresponding lead salts are formed,
*liicli have an extreniely amaU solubility, and form a firmly adhering
*Vcr on the tea*!. Thus leml pipes can be quite well used for the
'"Hilary water supply, but not for distilled water.

The combining weight of lead has been determined by the eonver-
'•*ri of the meuil into the oxide, and nrf r^/.vr. It has lieen found to
e I'b = 20r. «.».

Plumbion. — Lead forms only one divalent elementary ion,
les this several containing oxygen, and also complex ions,

666

PRINCIPLES OF INORGANIC CHEMISTEY

CMJ

Pliimhiori, Pb ", is colourless, and in its i-ompoiiiids reserables hui
in nuuiy respects. It is n jwwurfnl jjoist»i for higher organisuw. a
thmugh accuraulatiun is vety harmful when repfat4jjly taken ijil-:- I
system t-ven in sin.'ill doses. For this reason woikmi^n who have
work with lead ;iro constantly exposed to iho poisonous action, ai
great attention and cleanliness itre leijuired in order to resist t
danger.

The heat of formation of plurabion from the metel is + 2 kj,

Correajionding to its positiun in the potential seriea, lead hits
special tendency to pass into tht* ionic state. Free acitls aiv n
approcinljly duconiposcd l>v lead, so that oxidising a>ieiils miimt
employed in order to dissolve it. The liest solvent for met,'»llic le
is nitric jicid, which forms one of the few readily sniuhle Jcad sal
most of the lead salts (wing ditficnltly sohxble.

From the solutions of the salts, tia.ius give a whites flot'culeni jn
ci|)itato of li'd4l h/ilni^ide, Ph(OH)j, which iloos tiol dissolve in ejnc**
amnuMiia, hut iif; sohihle in excess of alluili. The i-eason is thi* s*i
HA ill the case of alumina, which liohavea in a simitar manner. I
splitting off hy<lri<jn. lead hydnjxide can form anion.s of the coiupoaitii
PhOg" and HPbO„', the alkali sidt« of which are suhible in water.

Lead hydroxide is aiightly soluble in wat^r. It u reatlily forrw
when lead, water, and atmoHplierie oxygen come together, Sttnu^
to say, in this oxidation, as in many others which occur with fi
oxygen in preijenco of water, hytlrogen peroxide ia formed at the aji
time. Meaaurementa have shown that the amount of peroxide cor
eponds to thai of the lead hydroxide, so that the reaction \im to
wiitteij as follows : —

Pb + 2HjO + Oj = Pb(0H)3j + HjOj.

* It is probable that the first product of the reaction is a singl
substsuice, pnrha[i.s ii conipouni! Ph(OH),, which decoiiiposci iut
Pl((nll),„ and UJK- This reaction wiudd then be another cxatppl
of the fact that the unstable eoiiiponnds tire iwualty fomiod befon^ il
stable. This view, however, ie rendoT'cd somewhat doubtful by ih
properties of the atdiydrido of the assinned compound Pb(OIl),, «■
lead peroxide F'bO.,, which is a well known stiible stdistunce.

* The formation of hydrogen peroxide, or of uther eompound
belonging to the peroxide tv|>e, has been proved in the case of miirt
oxidations by free oxygen, so that it appeara to he the rule. Th
peroxide, certaitdy, genei'ally decomposes so rapidly with evolution
free oxygen that ha whole amount can never be dot«rminetl, and onl
very slight traces aie found if special prttcautions are not olwcrvw
The rational iriter|iret.iti<>ri of tho.se long tieglected hut very geiien
phenoiiiona is given by the law above-mentioned of the occurreitou
the unstiibic fnrms together with "coupling" (p. 206).

Le^wi hydnixide loses water very readily and passes iulo the pol

XXIII

LEAD

655

1 loured lead oxide, PbO. The same compound h olitained fn

"d rimount hy heating ]eatl lo above its melting point in the

temperature is raised above its nieltin^ [Kjint, it forms

■A, lustrouB scales, and in ordinary life is i-allcd Uikvyje.

■ 1 for many jmrposes in the aita, e,g, in the manufacture of

i»^-o, ; -t the prepAKition of varnish, in dyeing, etc,

fiSl. Le&d Chloride, PbCl.„is slightly soluble in cold water, more
i^uble in hot, and crystullisea in .inhyilrous needles. It unites with
Md uxide to form basic s<dt«, which are obtainod by heating ammonium
lUoride MHth Hthurgc ; they are of a pale yellow colour, and are Used
II a pigment under the tiame Ntiplci ydlmo.

L' :! hrvmide is similar to the chloride, only still leas soluble.

uxiide, Pbl^ is still more ditticultly soluble. It crystalliaes

eaturnted solutions in lamina; of a gold histre ; precipitated

a disM.ilved lead sjdt in the cold by means of an iodide, it ia

«f^airip<l as a yellow powder. It undergoes slight decomposition in

thai a mixture of Iea4l lo^lide and starch when ox[Kjeed to

lupidly becomes dark through formation of starch iodide. It

ith potassium iodide to form a double salt, which is stable

i) J II ijij^ntACt with solutions which contain a large excess of potassium

Me ; it is decomposeil by pure water with separation of lead iodid&

2. Lead Nitrate, Ph(NOa)^ crystallises anhydrous in forms of

gjjlar sysU-'m, and is isomorphous with bjirium nitrate. It is

:ly obtained by dissolving leatl or lead oxide in dilute nitric acid ;

iDcenti^tefl acid it is precipitated from its solutions, owing to the

of the eoncentration of nitranion. Strong nitric acid is there-

almost witliiont action on the metal, because the nitrate produced

■3 a protecting layer.

On being heated, lead nitrate decomposes into lead oxide, oxygen,
d nitrogen peroxide: SPbjXOj), = 2PbO + 4N0j + Oj. Tiiia bc-
rioiir is made use of for the preparation of nitrogen peroxide
329).

653. Lead Sulptiate, PbSO,, is a white ealt extremely difficultly
water, and is always formed wben plumbion and sulphanion
her in solution. It is very similar to barium sulphate, but
of its greater density it is deposited more rapidly than it
•ototions. It is readily soluble in a soluUon of ammoniuiu
>te eonuuning exceu of ammonia, and is thereby easily dis-
ngqisbed from barium aulphate. Tbis solubility depends or the
iormation of a complex salt, the lead uniting with the anion of LaxtArie
to form a complex compound. This, again, is another case of the
lon of organic hydroxyl compoundrt containing metals, which bas
eereral times mentioned {pp. oSl and G53). Since plnmbion U
itiidrawn from tht solution throngh the formation of this complex,
sulphate must psiss into solution in order to cover the loss^ aari
Its eo6» on either until all the lead sulphate i» diflsolved, or ttn^

nSTRy

i'^i^rwLEs or isomga^c chzm

'^'"^jSfiSJ^^ «-.W-fced between tie dife

dnet in workiog up te«l «ilpbi.le for netellie lendT ^™'*"

To the diffioih liability of le«i «lpfc«. fe j„„ ^,^ ^
for Iininfi the reactron chambers «ad cottewtoating rmm tuti
nmiufacUire of mdphunc und fp, 2«9X Uwler t£ artion oT
the metal rery rapfdlj becomes cftrered wftfa » fi,„ j^^^^ ^j ,
which protects the under! ring met^L

Lead sulphate k appreciably kAiMb in cooeentaited n
acid, and erode sulphunc add alniaat alwaja eonUdna a b«»
ot lead. Wbetlier this is dqe to tbe fornMftioa of aci^
PbHj(SO»)y or whether solphurie aekl ia a solrent for lead
such, has not yet been decided. Oti dUndnK with
sulphate is again precipitateil, since, oirtng uj the nraa^H
pbaiiion, it is still leas soluble in dilute snJpfatuic addlth^
water.

• This behaviour, yv~ that the $olubitity of a salt in water
4imini<«h«d and then increased by the Atidiiioti of its acid, k
goiieraL The diminution is a regolar plkenoiiiei>i>ii - jt jg ,|„^
just been aaid, to the present of the anion hr reaaun of wl
solubility product is reached even at a tntich siuAller conceotnli
the cation (by which the solubility of the salt i$ here measondi
frequently occurring increase of the solubility iq Terrc^Mll
acid has generally its cause in the formation of a new solaUc
pound between acid and salt^

On account of its difficidt soliibiiity, lejtd sulnluite is ijs<d
gepamtion of phimbion from it« solutions in qtiatitatire aimI
tive analysis. In order that nothing may be lost in the wai
sulphate is first washed with ditut*? sulphuric acid and this'
displaced by alcohol, in which the sulphate is much less solubk-
water.

654. Lead Chromate.— On roixing solutions containiiw <
manion and plumliioii, a vellow precipitate of Uad rArmnate is
which is very difficultly soluble in water, and which, on rt
strong colour, is used aa a pigment under the name
When mixed with Pmesian blue, chrome yellow sjives a hue a
colour called ** yw*^* «nTuiAuj." Basic lead chromute h^l3 * rdk*
red to carmine-rod colour, and is also used as a pi<iQeut nnd«
name ckromf oramje a.iid chronu retl.

The same precipitiite of normal lead chromate is also ohtaimi
iising a solution of a dkhrmiate- aa the prwipitant ; hvdri<m \t tkl
prfuhiced, and the sohition reacts acid, The details of this ocoeV
©.xacily the same as in the case of the precipitation of ha^m

659

dichrontAU's (|n 617). If the atiiou of the lead salt is that of a

•cifl. the precipitation under these conditions rensnins iMtmi-

sincu the hydrion foiined reduces the conceiitnitiou of the

rniuitiion a^nd increases that of diclirom<itiio[t to $uch an extent that

solubilit)- product of lend chroniate is no longer rt-ached. If,

rever, the lead sj^lt of a weak acid is employed, f.'j. lead acetate,

L-ipitation is practically complete, because the hydrion produced is

the most part converted into UUtHssociattx.1 acetic acid.

Lciui chromate dissolves in strong liases with fortnation of a yellow

HHJd. Since cliromanion is criiitained in this, the plumHon must

rr also disappeared, iia othiiuise solution i\"ould be imfxjssible. As

of fact, the cation, Pb", is converted into the anion PbO„"

under the influence of the large amount of bydroiridion

int : Pb * + 40H' = PhO/ + 2H,0.

• This Iwha^iour is evidently a genei-al one ; all hydroxides which,
lead hydroxide, possess l>oth basic and acid prai>erties, miist
X the same reaction, ie. the dittieidtly soluble salts which they
with nnj acids aie dissolved by alkalis. This is, as a matter ol
the case ; thus, the difficultly soluble salts of alumina, such as the
ihate, dissolve readily in a solution of caustic jwt;ish.
Besides Iwing used its a dye, lead chromato is also employed in the
itory, similarly to copj>er oxide, us an oxidising agent in the
tary analysis of organic substances-
fiaS. Lead Acetate, r'li((;'o(3^H3) SH^O, or sm/ar of lead (so called
ild sweet ta;^te), is, nf all the l&id salts, the one most used in the
•ince it is reailily soluble, and therefore allows of the employ-
it of plumbiou where iiecessary. It is obUiincd by the action
cride acetic acid ou lead oxide, the siilt lieing purified by

llisation,

l.cifl acetate is very i'ea<iily soluble in water ; its solutions are

slightly uu'bid oiviug U\ the presence of a ivhite precipitate.

[ consists I'f Iciul carbonate, which is formed by the action of

bonic acid in the air on the salt ; this action is facilitated by

latility of acetic acid.

If carlion dioxide is passed into a solution of lead acetate, lead

.te is immwliiitely dt'])osited as a while, cryst^dline jirecipitate.

riMCtioii is, however, not cuniplcte, and an equiiibrium is Hnally

vA in the solution t>elM-ecu the remaining plumbitm, acetiini<»n,

ion, hydrion, and the undisaotiated substances produced from

ioua. No carbonate is precipiuted by carbon dioxide from the

aaltfi of strong acids, e.g. lead nitrate, nor from the acetate if

tnt acetic acid has Iteen added at the commencement.

The relations obtaiidng here are fairly similar to those found in

iptution of \\u'. zinc salts liy sulphuretted hydrogen (p. fiS.'i),

in this case a much smaller concentration of hydiion is

for e«(uilibrinin.

860

PRINCIPLES OF INORGANIC CHEMISTRY

Lead oxJ<i<i dissolves atbundantly in aolutious of nonn*l
^acetate, iind forms basic salts, several of which, ''.fj. Pb(C.^Ojnj)(l
have boen prepared in the solid state. The solutions are
vinegar of ktid, and aie eniployod in medicine and as a reageot ia
Llftboratoiy. They contain appreciable amounts of hydroxidioa,
'they react alkaline to vegetable colours,

656. Lead Carbonate, I'bCO^ can be obtained as a
precipitiite from solutions in which the ions Pb" and CO,
together. Like njagnesium, lead has, although in u leaa prunoi
degieo, the tendency to form basic carbonates, In natui-e tbi; noi
CArl>0!iate is fonnd in the rhombic forms of aragonito, with wh'u-h h
isomorphous, and is called vliile Imii or eenwite.

H'hiU: lead, the ivhite pigment most largely employed, i>
of various basic carbonates. It is obtained by allowing carlwn diend
to act on lead oxide ; to facilitate the reaction, acetic acid is genen
used as an auxiliafy subfitance. Acconling to the older Dutch pruo
spirally rolled lead plates were placed in pots in which there wu
little vinegar, and ivere covered with dung or spent tanner's ba
■which yields the carbon dio.vide by its slow oxidation in the air
these circuuistance.ecoiii,e covered with a layer
basic carbonate which is shaken oil" from time to time. At present
is usual to triturate litharge with some lead acetate and water, and
pass carbon dioxide (obtained by himting limestone) over the miilal
Further, a solution of basic acetate can be pi-eparetl from le;ul aceU
and litharge, and this be decomposed with carbon dioxide. In
iray normal carbonate is precipitated, while acetic acid, along wi
aome lead acetate, ia left in solution. Tlie liquid is again used lo
solve lead oxide, and so on. As can be seen, the same react ions irlii
here occur sejmmtely took place also in the first process side by si(I<
Lead acetate here plays the role of a catidyser by accelerating 1
combination of caHion dioxide and lead oxide, a combination «h:
would take place without its presence, only too slowly for maiiuii
taring purposes. In the present case the cause of the accelerai
be recognised to some extent, since by means of the acetic
lead oxide ia converted into the dissolved condition in vrbich it
more readily unite with the carbon dioxide.

In other vvoihJb, tho velocity of the actifiii of acetic acid on 1*
oxide, and the precipitjition of tho carlionat^} by carlion <lioxide, j
together much ^cater than the velociti,' of direct combination of If
oxide with carlion dioxide. It is probable that it will be pissiMc
attribute many cases of catalytic action to such causes.

* The chai-actcriatie of this explanation is that in place of t
dii'cct rcjietion, a serjes of intermediate reactions occur, which !<
to the same final result iis the direct reaction. If thtsr intmiwii
reueiions mTiir inore mpidly than the direct reaction, tho cxplanntioii
the catalytic accelerating action of the intermediate substance is gii

LEAD

661

jh overlooking tlve most essential part of this explftnatioii, how-
one htw become acctistoioed to see an "explanation" of catalytic
plenitions in ihe mere possiHlit;/ of such intermediate reactions, with-
thinkitig of the necessity of proving that these intermediate! re-
iiiiis must pro€i!ed more rapKlly than the direct reiiction, if the
pnKcss is tu be accelerated.
657, Lead Sulphide, — From solntions containing plumbion, sub
ettctl hydrogen, e^en in the jircsence of hydrion (if this is not
concentrated), precipitoites brown-black lead sulphide. Conceu-
Ited acid prevents the precipitation, or re -dissolves the precipi-
sulphide. We arc again dealing here with one of the equilibria
ch have been repeatedly discussed, and which in this case is char-
by a vi'ty slight solubility of the sulphide, and therefore a
hie lack of sensitiveness to hydrion.
is solubility is so small that even the small ajpount of plumbion
killed in the complex salts is sufticieni t-o exceed the sohdnlity
«luct oQ passing in sulphuretted hydrogen. For this reason all
saltfi, even the complex ones, are preeipitateil by sulphuretted

itric acid oxidises leafl sulphide to sulphate,
nature, lead sidphiJe occiu-a in the fomi of regular cubes vrith
r metallic lustre. It ie a eoft mineral of great denaity {7-5),
is widely distributed and is willed galaia. Thi.s is the most im-
t lead ore.

8. Compounds of Tetravalent Lead.— As in the case of

; where the aaka of the nHjriuvalcnt type were krjowti only in

ilid state, since monoeuprion immerliatcly underwent iransfor-

in ill solution, so, similarly, there is a series of lead compouitds

csaii be referred to tetravalent plnmbfoit, Pb"", although this ion

not occur to any considemltle extent in solution. The reason of

tabitity of such salt* is, however, to be found in another direc-

it Ims to be sought for in the fact that the aiihydritie of the

eot hydroxide (I'bO,, = Ph(0H)4 - SH^O) is a particularly stable

icidtly soluble compound which, with the co-operation of water,

ys formed in cases where the tetravalent ion Pb"" might he

The hydrolytic reaction, Pb"" -i- 2H„0 = PbOj 4- 4H', there-

.kes place, I.e. le^id peroxide and free acid are formed.

pmtriile, PbO^, is a brown substance which has, in the crystal-
conditiiin, an almost metallic lustre ; it is practicsilly insoluble in
Iter, and is alwayii formed when Iciid comjwunda are subjected to
erful oxidising actions. It is generally prepared by the actiOQ of
hijig powiler on lead chloride in alkaline solution ; it is vitod in
Jerablc quantities »s an oxidising agent in the chemical indiistriea.
'n being carefully heated in the air lead oxide also undergoea
ion, not, however, to the peroxide, but to a corajwund of that
oxide ; 2PbO + PbO., - t'b.^0^. The pi'oduct is a powder of

662

PEINCIPLES OF INORGANIC CHEMISTRY

a bright red (.■oloiir, wliich has been known for a long time,
employed as a pigment ; it ia Ciillod niiuuun or red lend.

* From this name is derived the deaignution ndniahtre for
ornamentn.1 tlosigns on manuscripts, because of the use of this pigi
(or of eimtiiliac. which \v;ia fi>rmeily cbiifusod with it) for that piira
At the present day the word has niiothor aigiiificatioti, which hif,
a slight connection with the original one.

On treatitig niiniiira with dihite acids which fomi soltible
salts, e.rf. nitric acid, lead iiitnite passes into solution, Jind lead
oxide remains behind as a brawn powder : PbyO^ + 4 HNO, = Pb(
2Pb(N0g),. In this way lead peroxide was formorlv chiefly ohtai

Another snd v^ry important method of preparing Icul pcrovi<
by the eonvci'sion of leanl salts, e.ff. of lead sulphate in ililutc siilphl
acid, by mwins of the electric current at the !mo<ie. Ih* inenns of
CiUTcnt, siilphanion, SO/', is brought to the an(»de and dischnrp-*!, i
there occnrs tlie reaction PbSO;, + SO/' + 211^,0 = PliU, - ^ll./id,.
accordance with what was stated above, it esm be assuniwl
tbere first occurs the reaction PbSO^ + SO/ = Pb(SO,)j^ the sulpi
of tetrnvjilont loid being formed ; this \& hydrolyticully dissociat^^l
the water and passes into leiul totrahydroxidc and sulphunV .viil,
lead peroxide and sidphuric acid, according Ui the etjuatirtn Pl*(t^llJ
2H,jO = PbOg -I- 2H.-,S0^. These reactions are of grofit impiirU
for the construction of electrical Mcumuiultmi, and will preetiutly
considered more in detail.

If lead peroxide is treated with anhydrous or only rfijiJ
hydrated acids, icith which therefore hydrolysis is exchided,
coiTesponding saline derivatives am lie obtained. Thus, lead
oxide dtssohes in fuming hydrochloric acid in the cold to a ti
coloured liquid finm which, by the addition of ammonium cblor
a yellow ammonium salt of hydtoplumlncWoric acid, (NU|)jPlit.'^
obtained; on decomposing this with concentratetl snlphuric acid
acid HjPbCIf, is formed which immediately decom|Kmes into hydi
chloride and lead tetrachloride, PliCI^. The tcliuchloride is foil
be a yellow li^piiil which duos not solidify till - 15", and w|
readily decomposes into load chioriile and chlorino. AVhcn dii
in much water it undergoes the above mentioned hydrolytic dii
tion into hydrochloric acid and lead peroxide : PdClj n
PbOj + 4HCl

The sulphate and acetate of tetravalent Ifeul cjin also be jire'
under suitable conditions ; they are yellow salts which are cul<
broivn by iviitei- owing to the separation of peroxide.

The hypithettcal lead tetrahydroxidp t^an also act as an <»<
hydrogen of the hydroxyl being split oH" as ion. As can be seen
the fortnula HjPliOj atirl that of its fti-st anhydride, lI,J'bO„ n
valent as well as a divalent acid can be derived from t
hydroxide. Minium can be regartled as the leatl salt of the tetrelj

LEAD

66S

for if ■we replace the 4H by 2Pb we obtain Pb^PbO^ = Fh./}^, the

mht ttt miiniuH. The decomposition of the latter also by mesins

dilute acitU spyjiks in fiivuiir of this view ; acids first effect the

itjon of the free phimbic acid which decomposes into water and

I anhydride, load peroxide.

, Aiirttber t*mpoand of the tetraljasie imd is that with lime, which

unned by hejiting » mixHire of learl" oxide and lime in the air,

eby oxTi'geii is taken up. On being heated in carbon dioxide,

is decomposed into calciuni carlionatc, leatl oxide, and iij-i/ffai ;

being hwited in the air the carbon dioxide again escapes, oxygen

in absorbixi, and adaum jilumhak is foi-med. A commorcial

of obtaining pure oxygen has been Imsed on tbes^ transfor-

jns.

alkali met^iU, on the other hand, yield salts of the dibasic acid.
peroxide dissolves in a strong solution of canstic potash, and
Um (jolutiyn the salt K,PbO,, + 3H.,0 can be obtained in the
vtAlUne condition, In the solution \vbith contains excess of caustic
poush, the presence of the tetravalent ion PbOj"" may also he assumed.
659, The Lead Accumulator. — If two lead jilates, one of which
vere<1 with Jeiid peroxide, are placed in dilute sulphuric acid, an
tire voltaic cell ie obtained the potentiMl of which is 2'0 volte, and
h can yield a strong current. The chemical process taking place
this cell consists, on the one hand, of nietallic lead being converted
intii lead sulphate, just as the zinc of the Danioll celt is converted into
xiiac sulphate, only that in this ease the lead Biilphate, un account of
Hi difficult soluliiiity, forms a firm layer on the electrode. On the
other hand, the lead peroxide is reduced from the tetravalent stage to
the divalent, and also forms lead sulphate, with the sulphuric acid
fireaeiit. The reaction which yields the energy for the cuiTent is
IJ^affcfore represented by the expiation

Pb + PbO. + 2HjS0, = 2PbS0^

3H,0.

^^The remarkable thing about thie cell is that it can be easily
Irevenr^. That is to say, if a current is passed through the cell in
j Vhe opfiositt' direction, the sulphate is at the one pole reduced to
imctiUic lead, and at the other oxidised to lead peroxide (p. 602).
]The cell, therefore, again passes into its former condition, and can

K'u yield a current.
At fij-st sight this appears a fact of very small importance. For
•rding to the law of the conservation of energy there can be
obtaintnl from the charged cell only as much electrical energy aa was
I'QSod up in the charging ; in all eircumsunces, therefore, there is no
[gain, and indeed, in consideration of the unavoirlable hisses, there is
ercn a profitless consumption of etcctricul energy. This is certainly
cane : the advantage, however, which lies in the possibility of

PRINCIPLES OF INORG^\A'IC CHEMISTRY

storing coinpftratively large tjuantities of electrical energy in a
weight, and of rendering any portion of it available for use whei
desired, is so gteiit that the above-mentioned loss is willingly ac-
Considfir, for example, a factory in wbieb large amounts of eli
energy are required from time to timCj while in tlio int-erv'ab littll
necessary ; the dynamo would then have to he large enough to n
the powerful currents withoftt being damaged, while in the intemli
would liHve to run empty. If, however, an eU^clrical accumulator
connected with the plant, the dynamo would hare to be consi
only for the average consumption, and not for the maiimalj
during the time of large consumpttim the accumulator would
energy, while in the intervals of small consumption the accumi
would take up the energy of the dynamo and retain it for use w
required.

This result would be obtained by inserting a voltaic cell which ud
act in the doulile nianncr, i.e. which can on the one hand yield t
current, and, on the other, can atore, by rae^ns of the reverse ehi
reaction, the current of opposite direction, Tlusi property is
by mjtny cells, f.</. the Daniell, in which, by the reverse current, an*
is (leposited and copper diasolved, copper sulphate therefore beinj
formed.

Hitherto, however, the kati acacmHlator which ha« just been,
described is the only one which hiis proved to possess vitality, rin*
it has the advantage of contaifiing onh/ om' metal. This is rendered
jwssible by the circumstance that the metallically conducting 1<*1
peroxide is a very strong ojcidising agent, while the metallic lead i«l»
as a (moderate) reducing agent, In the cells of the tyjx; of tb»
Daniell, which contain two metals, one cannot, in the long ruB,
prevent the solution of the one metal (cop(»er) passing into that «
the other (zinc), whereby instead of the indirect chemical proce*^
which yields the current, the direct prf»cess occurs, which only yiei<li
heat, and the cell therefore no longer acts.

A U:ttd accuitmhktT, therefore, consists of two lead plates placed ill
dilute sulphuric acid. In onler that as large an amount of electricd
energy as possible may be absoi'bed for a given weight of tlia accuma*
lator, the plates are made porous, so that the acid has as far as pussilw
access to every part. To eombiue this retiuirement with the greatart
possible durability of the jilates is the re^l problem of llie tilcctric«l
accuranlator. The problem isi generally solved by filling up 8 lew
grating with spongy lead, obtained by the electrical reduction of varioa*
lead coinjxmnits. Such a jilate of spongy load is then connecte<l wiik-
a second plate, in which the spongy lead has been converte<l into lew
peroxide liy electrical oxidation- Such plates are prepared, fur cx-j
ample, by filling in the load grid with a mixture of lead oxide
sulphuric acid in the form of a thick iiaste, susjjondnig two such pin
after the paste has solidified,, in dilute sulphuric acitl, and jiaAaLUj

LEAB

665

3ugh it. On the one side the lead sulphate present is then
metallic lead, and on tlie other oxidieed to peroxide. The
the transfonnation can bo recognised in the evolution of hydro-
the formor plate and of oxjgen at the latter ; at the same time,
potential of the current necessary for charging rises. The accumu-
ir is then ehartjud. When, after the charge has been withdrawn,
accumulator has to bo recharged, care haa to Ije taken that the
ner peroxide plate is again used for the same transforoiatioD, as
erwiae the plates will be destroyed.

As can be seen from the equation of the reaction given on p. 663,
jhuric acid passes inio conibimttion while the accumulator is in
tm, and is again set free when the cell is charged. In the amount
iiilphun'e iicitl in the accmiiiiktor, therefore, we have a measure of
condition of charging, and iia the density also changes with the
aunt of acid, a hydrometer floating in the ]i4|uid allows of the
ditioii as to charge being easily determined. This is of importance,
» experience has shown that an accumulator deteriorates on stand-
for a lengthened period in the uncharged condition, lieeauae the
i «ulph.ite in the plates partially loses its chemical reactivity.
660. Metallurgy of Lead. ^For the manufacture of lead, galena
ibe only ore which has to be considered in practice. This is first
tteJ, whereby a part of the sulphur escapes as sulphur dioxide,
lie another portion remains fiehind in the roasted mass, the lead
phide l>eing converted into lead siUphate. The mixture of lead
de, lead salphat«, and unchanged lead sulphide is then fused with
sbliioo of air, whereby the following reactions occur : —

PbS + 2PbO - 3Pb + SOj
PbS + Pb80, = 2Pb + 2S0g.

Tn this particular case, therefore, the unchanged lead sulphide acta
4 replacing ag<"iit oti the oxygetiated pnxlucta formed, and the result
metallic lead along with sulphur dioxide.

The " work le<id " thus obtained generally contains silver, to
Uin which it is further trejited ; the processes for this will be
cussed under silver.

CHAPTEIl XXXIV

MERCURY

661. General. — In its chemical reladonB niercury is most n
allied to copper, since it forms, Hko it, two elementary ions, a iufi
valent and ;* divrtlent, which in tnany respects also ivre similar to tii'
of copper. With cadmium it shfires the tendency to form sJightl
disaoeiated halogen compounds of the divalent series.

MdaUk mr.ratrif occurs free in nature, and In' reason nf ii* bcii
liquid at mcilium temperatures it has attracted attention from remcA
'times. In tlio older history of chemistry, while the experimwit*
conception of a chemical element was not yet developed, mercury «»*
regarded as the 1)1)6 of the nieUdlu- clmracter ; this found expression
in the fact that mercury was regarded as a constituent of all mewlt
The endeavours to prepare gold and silver from liaae metals, whici
f»re connected with this view, had genendly for the first purpt^se, tin
** fixing " of the mercury, i.e. making it ii on- volatile. For this reaMHi)
and through the discovery made about the fifteenth century of ilw
powerful medicinal actions of the mercury prepiirations, the ctieniiitr/
of mei'cury became kno\^^ii at an earlier period than that of most d
the other metals.

Duiing the development of the newer period of chemistry »t ibt
end of the eighteenth century mercury again played a considciablf Ti>\t.
This was due, in the first place, to the chemical properties of inercutT'
oxido. The possibility of converting the metal into its oiidf bf
heating in the air, and of efTectitig the seijaration of this into nn'till
and oxygen by more sti'ongly hcjiting, was of the greatest imjKirtniit*
for the correct interpretation of the phenomena of o.itidation (p. 37)i
On the other hand, the introduction of the mtreiny putujimtk (n>iijA
for the investigation of gases at once led to the discoveiy of a sot
of hitherto unknown substances (p. 1^2).

■ Up to the present day mercury has not lost iU iroporUUK-t l<
acieutific investigation. Its liquid nature, fairly great chemical resist
bility, considerable density, etc,, assure its unceasing use for phvfi
chemical apparatus, of which the (heniwmeier and barvrmter

see

'er nvti

MERCURY

only he mentioned as the most important. Since, being a lie[iii(]
metal, it is not subj^t to the vuriatiims which are exhibite*! by the
K>lid metnts in consequence of being wrollgliC^ it is employed as A
tundard metal for electro-cheraical apparatus, and many other scientific
Implications could also be mentioned.

Metallic mercury has the density 1 3 "59a at 0". Its expansion by
tieat is, up to the boiling point of water, so nearly propoitionfil to that
of t!ie gascB that the mercury thermometer agrees well with the gas
liermometer over this range. At - 39'4°, mercury solidifies to a
Iver-like solid metal ; it therDby readily oxhibita in a considerable
egroe the phenomena of supercooling (p. 120). At 358" mercury
oils under the pressure of the atmos]ihere. Since, in many meaaure-
'mi^nti, the vapour pressure of mercury at comparatively low tempera-
tores also comes into acconnt, we give the following table of vapour

res:-

0°

0 00002 i:iu.

1SS°

0'29rtii

20*

0-00013 „

200'

1-S2 „

40*

0-0007 ,,

250^

?-5S „

to* .

0-0028 „

800'

24-2 „

SO'

0'W93 ,,

350*

668 „

00°

0-0280 „

toes

From this It ia seen that up to 100' the vapour pressure is small,
viz, lees than 1 mm.

In the air mercury behaves in general as a "noble" metal, ».<r. it
not oxidise spontaneously. This ta not, however, in all strictness
he ca«e, for if it is maintained for a lengthened period at about 300°,
]y becomes covered with red crystals of mercury oxide. Water,
tiding in contact with mercury, as&umea poisonous properties,
bethor this is due to the solution of a trace of o-\ide formed, or to
solution of metal in water, has not yet been doterminod.'
Tht? (rmibimjtg teevjht of mercury lias been found by analysis of
jtbe oxide and sulphide to be Ug- 300*0. The vajMjur density shows
lie molar weight to be 200 ; the two are therefore equal. On account
its low boiling point mercury was the first metal in the case of
which this remarkable relation was established (p. 477),

Pure mercury does not wet glass ; if, however, it contAiiss foreign
metals dissolved in it, it becomes covered with a film of oxide, the
effect of which is that the metal no longer flows over glass and other
rarfaces in round drops, but "leaves a tail." This is a very sensitive
tett of the purity of the metal.

In order to purify mercury, a task which is constantly occurring

' Tlmt taetAllic tiieKUry CAP diiiaolve ia water mnfit bt' rcrganlcil M inchibitJiVle.
r, «n gaaa diraolre iu WBter ; ainee mercury has nu appreciable although aniAll, vapour
I even al rwim temperature, its vapour must ulno he soluble in wnter. There id,
liowevw, no iliffcrence l>ctween a solution of lii^uiJ bu4 one of vaporous mercurj-, since in
tlie cue of ■ Boltition oaly tli« existing aiate h of iioportance a&il not thti fanuer states
[ it* eoropooenU.

P8I2K3PLES OF ESORGANIC CHEMISTRY

p, it is dic^kea wilh dilute i^ititphunc acid, to whicb J
■• tirapBof potasstun dichrotnate are added ; it is then
waailMi irith a \aTgB quantity of water and dried bf
gmAf beadag it In this way considerable impuri^H
oMt be 44iakkljr removed. The fairly pure metal ii
■ttatwiil. to Bow in small drops through the appamtoi
aiMim in Fig. 120, ^vhich is filled with a. dilute i&i
aolntBKi o£ mercuroiis nitrate (vide infra). ThsU
mttibjods depend on the fact that the oxidising agenti
onptored oxidise the contuminating metiila nihM
tfaan the mercury ; in order that the object inaj b(
uLt;un«d, tine division is nQcessary.

6i'2. Mercury Ions. — Mercury forms two element
ary ions : oioriomercurion, Hg', and dimoreurion, Hg .
In itB properties the former is allied • to monocnpriiwi
•ad KTgeation ; the latter does not exhibit any verj
^■'-^tjjy' l\ doM relations to other tuetfilij. In cnrnpamtivcly coii'
V" I dsolrated solutions monomercQrion, perhaps, oMiJniM
Lbe divalent double ion of the formula Hgj" ; in vorj
ililute solutions, as monovalent Hg'. For the salwcl
cIoMlless, and until the corresjwtiding relations bftVt
h9«a explained in the case of the other mono^enl
. •if tiw haKrr met&ls, we sSmll use the simple method of wriUSj
1 1 ' tl»v «6pecially as it does not conflict with any experlmenul

tiK,- -V .Urn tliacuned here.

.HiDiiMNBKMnm is Conned when salts of mercury are prepared t'
>f an tsxcess of metallic mercurj'. The moat eonreiueni
•Hcrcury is dilute nitric acid ; if Uio great a conceiitratJor
' litid 100 high a temperature are avoided, nierctiroui
ii'xl with evolution of nitric oxide (p. 32G). If, owing f
ni»o» jlist mentioned, mercuric nitrate hai; l>een fonucd, it n
xl u> aUow the solution to stand for some time over meuJli
irv ill ortJer to again convert it into mercurous salt Tin
'.; ~ 2Hg' then takes place almost completely.
i^' of metidlic mercur}', however, monomercuriiMJ •
■ il tu tliinercurion.
-ULiotis of the two ions cannot be distinguished by the)
^'tkUcOk aifi<>« ihey are both colourless. Their compotuids, h&*
"h tha same anion have frequently very rlilTereut 8oluk|||
:iui bo distinguished by this means. ^|

lih^ two ions are violent jmsmis both for the higher atiil the ToU
Ifii^iUUMiM. Sinw, however, raonomercHrion forms a very diificulll
^Ivjilfi couifwunJ with the chloridion occurring everywhere in tJi
wbert'bv its concentration and therefore its action
tw tfXciMHiingiy small values, mercury poisoning occti
lit ftwt, almost exclusively by means of dimercurion.

MERCURY

6G9

663. Mercnrous Compounds. — From the solutions of mercurous
Jte, Wack wnuivas "xuk', Hg,/*, is preuipitJited l>y Imses, The
mnirous hydroxide, the formation of which might lie expected, is go
ixtable that it hits not Wen poasible to detficl it with certainty; on
i formation it :ipjKirent!y passes tmmediutely into ita anhydride.

rrouis oxido is a black, unstable powder which on lieing kept for
time is converted into mercuric oxide and metallic mercury :
^0 = HgO + Hg; iu sunlight the conversion is rapid.

Ttie lasie properties of this oxide are only feel*ly developed, for
<t merciirons salts, so far as they are soluble in water, undergo
piirolysiB with formation of preeipitnte of ditticultly soluble basic
lis. In order to obtain clear solutions excess of free acid must be
kkd.

This hold.?, for example, in the case of merairoiis nitrate, HgNOj,
liicSi is readily obtainqil by dissolving mercury in dilute nitric acid.
I the cold the salt crystallises from the solution containing excess of
id ; on attempting, however, to I'e-dissolve it in water, a white pre-
pitdte of basic nitrate is deposited, the amount of which is all the
later the gi-eat^r the amount of water compareil with that of the
It. The solution can be agjiin m-ide clear by the juidition of nitric
id, and there is a definite concentration of free acid, varying with
le t«Biperature, at which no decomposition of the salt occurs.

664. Mercoroua Sulphate, Hg„St>^, is a salt, very difiietiltly
fliilile in \i;»ter, which is formed by warming mercury with con-
ntrated sulphuric acid. Half of tbe sidphuric acid then acts m an
titiising agent, and passes into sulphur dioxide and water ; the other
>If of the acid yields merciu-otis sulphate, which is deposited as a
kite, coarsely crystalline pijwder. If the oxccbh of sulphuric acid is
SBOved by washing with water, hydrolysia commences after the main
)rtion of the acid bas l.K5cn removed, and the sjdt becomes dark in
ilour,

Mercuroua sulphate Is used as the initial substance in the prepara-
on of other mercui'y compounds, and for the

riction of electrical Btandaixl cells.
Such standard cells serve the purpose of
fttiishing at all times a definite value of electiical
otcntial for the purposes of measurement. The
Km largely' employed of these cells ia repre-
SBled in Fig. 121. In the one limb there is
■mtjuned mercury covered with mercurous sul-
'^te, and in the other there is a If! per cent
Jixtunsof cadmium and mercury; the remaiuing
P*M IB occupied with a sjilurated solution of
•*liiiimn sulphate, to which some crystallised
•dmiiim sulphate has been added. Tlie potential of such a

b=?^

Via, m.

tc to r0l86 volt; by using fairly pure substances, the same

HDNCIPLES OF INORGANIC CHEMSTRY tm.

m ilmtft obtaiaad to within a ten-tbousaiidtb of iu value,
kfM^ liij^dy with the tempcmtuie.

Qlloride, HgCl, is a white salt^ sohiUic v'\\k
m wabcr, aiid has long been employed in luediciM
cmlammL By reason of its small Roluhtljtv it yussei,
■ liamiy iato tk» sjstem, and therefore exhibits eorreg|A>mliiiglfi
[ actwwi Its tappjication iii medicine de[>ends on this.
CaiiiHMii » vhtamad on bringing together a soluble niercuroii; «al(^
(boft mercurous salts are precipitated not oiilv hji
*)i Domal chlorides, but also just as completely by hvtiro-
eaL This behaviour could be foreseen, for the solubility of
liaMe saits in acid? depends, indeed, on the fact that tbdl^
fJDCiB tindiiisociated compounds with the hydrion of tW
to that the omcentration of the anion is diminisiied, aiid]
iiililhliiji pmlnet thereby not attained. In the present case
i|Mni, bieMise the anion of calomel, viz. chloiidion, is that
kofr tha stnmgcet ^cid^ and is therefore not converted to any vuR*
■lanJitd aitteiae iixto the undissuciated condition even by thu ndiiitiom
lu Fur tys reason the concentration product of a cidooulJ
1, utMj rwmaitia essenttidly nnchanged on the addition of a MtroBg"
liti Qo more posses into solution. I

ttmkEiti^ <.-jl<»mel with a concmiirakd sohition of sodium chiori(l*(
ir»)cW»»nf :m:kI, howcvei', a quite appreciable amount of it [wmm
»t the same time some mercury is r]i-nosited. Tliii.
. . >ti expiained in the citse of the iodine cutupuuiid, in wbidij

lut'lt iui>re dititiitct.

sulphate also is converted into calomel on being treated

ici of soiliuni chloride or hydrochloric acid, becauae tin

rift.fiur aore ditUcuItly solulile. As a rule, however, it is obtained

the ^plukte by subliming it with conunon aidt, whereby tl*

■f.tinetl in semi-transparent crj'atalHne ni.HNW8 with »

-ic toti accomit of ita high index of refrtWJtion). Sinctii

itty» morv or less mercuric chloritle ia mixed with it, calomd,

iii tu btf XE«1 for medicinal purposes, must l»e previously c«*-

.Mnwttid with water in oi-der to remove the yery poiuoiiuiis,

hUiridc.

• lily volatilises, and its vapour density was thertfon»

This yields the molar weight 235, comjsponding

iitila UgCl. Since mercury was regarded as bciojj

i> result stood in conflict with a fonuer, specially'

. MCiicding to M-hich the different elements posseaj

■ !.■ I .dcucy ; the double formula HgXU however.i

.1 agrneiiietit with the div^alency of mercuri'i

i.ition < 'llJg - UgCI. A lively discussion tlicre-

I ilier the va|iour of ealoiael is unifonn uf lu*

^r... ..^^ ^iKUfic chloride and mercury, according

XXXIV MEKCURY 671

DquAtioii Hg2Cl2 = HgClj + Hg. An unequivocal decision of this point,
supported by numerical data, has not yet lieen effected.

Mercurotis bromide and iodide are similar to calomel. The iodide
is a greeuisli powder, vi'bich is most easily obtained l)y rubbing io<line
luid mercury together in the proportiona of their combining iveight«,
and which decomposes with extreme readiness into niercnric iodide
and free merctiry.

66(5. Mercuric Salts arc obtained from the merciu-ous compounds
hy Biibjecting those to oxidising actions. Thus, wcrcmic nitrate,
Hg(NC>^).„ is formed on dissolvirig mercury in coticeiitrated and \*'arm
giitric acid, and can l>e obtained in colourless crystals on evaporating
the solution. In the same way mercurous sulphate, on being heated
|"with an excess of 8nlj)hiu'ic acid, passes into mercuric sulphate witli
;renewed evolution of sulphur dioxide : Hg„SO^ + HaS0^ = 2tIgS0^ +
SO, + H,0.

The mercuric salts exhibit the property of hydrolysis in a niucb
higher degree than those of the mejxurotis series. Since in this case
the liasic saltK are characterised by a. yellow colour, the occutTcnco of
the decomposition can be readily recognised. Nevertheless, a number
of sidts of the mercuric type are known, which can be dissolved in
water without sign of decomposition ; this is due to special properties,
which will be discussed immediately.

Maettrk oxide, Hg^*, i^ obtaineil from the mercuric salts by means
of soluble bases. The hydi'oxide is nut known ; it may thci-efore be
again assumed that it is iridee<l first formed, but that it immediatety
passes into its anhydride.

Mercuric o.vide is a yellow to red powder, the colour of which
^depends on the fineness of its division. If it {b precipitated from
cold solutions it apfiears yellow ; when precipitated hot an orange-
coloured ])recipitate is formed. It is obtained as a red crystalline
poivder by heating racrcui-ous or mercuric nitrate to a nioderate
tempei-atiu-e ; nitrogen peroxide and oxygen escape (cf. p. 657), and
mercuric oxide remains behind. The decomiKisition can easily be
made complete without the temperature being reached at which the
oxide decomposes into the metal and oxygen.

As has been repeatedly mentioned, mercuric oxide is also produced
directly from mercury and oxygon by allowing the iwu to act on one
^nuther at about SOO . The reaction is, however, very slow. In this
ease a condition of equilibriumj depending on the temperature, is
established between mercury, oxygen, and met'curic fi.xide. According
to the temperature and pi-easure of the oxygeu the reaction «in be
(lliade to tjiko place iji one or other direction.

I The prcpjiration of mtTcarif. niinile hiis been ateady given. The
baijic nitrate which is preeipitiited from the ailta by water has the
composition Hg,/N0.j)„(0II)4. It readily dissolves in hj'drochlc
Acid, forming a clear solution.

672

PRINCIPLES OF INORGAJSIC CHEMISTRY m

The same holds for mercmic sidjiJmte, HgSO,. The basic
which is obtained as a yellow cryatalliiie precipitate on ti
the normal salt with water, has a corresponding com]
HgaSOJOH)^, find under the name "htijieih minrrnl" is a\
medicine. Recently, raercurie sulphiite has become of imiKirtiun c a»
catalyser for the oxidation of organic substances by hot snlj>hnri<' m-ii
both for anfilytic'^1 itnd techmcal purposes (oxidation of niiphilmlw
to phthalic sicid for the preparation of artificial indigo).

The bt'havioiu" of the hAilogeu cinnpminds is in marked contrast
that of the mercuric salts of the oxyacids. So far as they are aoluU
they dissolve in water without appreciable hydrolysis, and eihili
nothing of the ready decomposiibility of the above salts.

The explanation is found on determining the electrical conductivil
of t!ie solutions of these substances. This is found to be very sli^bi
and it follows from this that we are here dealing with salts which, uii
like the preponderating majority of such substances, are not gifatlj
dissociated into ifms ; they am exhibit the reactiong of the ions^ tbcr*
fore, oidy in a Yery limited degree.

The salt which is most dissociated is mercuric chloride, Hgt'lj
This chlorine compound of mercury has also been known for a tw]
long time. On account of its poisonous pro[>erties and its methixi a
preparation (by the aublimation of mercuric saltB, ospceiallj llM
sulphatej with sodium chloride) it is called corrosive sublimate.

Mercuric chloride i& a colovirlcss, erystailine salt, which is raodil*
ately soluble in water; it has a considerable density (7 "2), and ill
Bolutions have been found to l>e a very liolont poison for higher
well as lower organisms. It is therefore extensively used in medicint
as a disinfectant, t,('. for the purpose of killing tlie apores of Uannlut
schi^omycetes, and aucb like, and its use is limited only by the fact
that it is also a powerful poison for the human organism. Snwll
quantities of it exercise a specific, medicinal action.

At 205^ mercuric chloride melts, and Iwils at 307', so that itoia
be readily volatilised, and thereby purified. Its vapour density yielA
the molar weight 271, corresponding to the formula HgC]„.

* The solutions of mercuric chloride are fairly easily reduced w
realorael. Of these reductions, that irith oxalic acid (p. 415) t« of
'particular interest, as it takes place with measurable velocity <mlj' to
li^ht, while in the darkness it remains practic:dly at a atiiiul-*tilL
This reaction has therefore been used as a means of measuring tli*
chemical action of light or as a chemical photometer. It is represenwd
by the equation 2HgCL + C.O^H, = 2HgCl + 200, + 2HC1. Carboo
dioxiile and hydrochloric acid are therefore formed in the reaction ; U
counteract the action of the latter one of the salts of oxalic scid, «.#
ammonium oxalate, is used instead of the free acid. The indicati(ti
of this photometer are also only individual (p. 592).

From its solutions mtrcunc oxide is precipitated by soluble, strong

■tftf, Kill on quantitative iavestigation it is found that the amount of
ride precqtilatet.l never corresponds to the amount of base tiikcn, but
/ttft*. Conversely mereuiiL' oxide dissolves in solutions nl" other
llorides. and liquids are produced ^^ ith a strongly alkaline reaction.
hii ih dill? to the fact that the solution of inercuiic chloride contitina
lljr very little dimerciirion. On adding a base, i.e. liydroiidion, there
ut be a certain, finite concentration of t!ie latter before the fiolu-
lity jifoduct of the meretiric oxide is ronched and that substance
fcipitated. On the other hand, when chloridion is atlded to aa
[ueoKs solution of mercnric oxide (in wjiidi the presence of Jimer-
tcktii and liydroxidion must be assumed), the greater jiart of the

»[CU!ion present is converted into tnidissociatod mercuric chloride,
more mercuric oxitle must pass into solution in order that the
iltibility pniduct may be again established. This process is repeated,
id when equilibrium is finally reached there is an appreciable amount
I bydroxidion, from the mercuric oxide, ])reseut in the solution.

Mercuric cidoride is extremely stable to concentrated sulphuric
nd, and even on heating no evolution of hydrogen chloride occurs,
'or is it acted ou by concentrateil nitric acid, which attacks all other
iKne chlorides with evolution of chlorine or nitrosyl chloride (p. 338).
I* behaviour in Ixtth cases is due to the very alight electrolytic
JMMiation of mercuric chloride.

Jpercuric chloride crystallises along with the alkali chlorides, form-
ic eotnpouiids which appear to occupy a position intermediate between
lie ordinary double salU, the cotnponents of which exist side by side
n Ktlulion, and the complex salts, the ions of which are formed by the
tnion of Uie one salt with the ion of the other ; that is to say, the
felti partly oxist.side by side in solution, and are paitly combined in
>lw above complex compounds, and the relative quantities of the two
Upend im the temperature and the concentration.

* Strictly speaking, such a view holds fur all ilonlile salts and
complex salts, and the two are distinguished frum one another only by
the fact that the one or the other greatly predominates. In the case
»f the aliove. merctiry compounds we have ai>pareutly the case, which
i»thi.Twise does not frequeutlj' occur, that the two portions are present
ill »,]»Mi equal amounts.

riie complex salts whose presence can here be assumed, are the
»lbli sahs of the mercurichloride ions HgCI..' and HgCl^". From the
wliitioiia of the mixed single salts corapoundH of the one or other type.
*t KHgCl., antl K,HgCl^, .ire obtained, according to the concentration
aail the temperature, and we must therefore regard both as beitisj present
togctiier in isolntion. If for any reason one or other of these compounds
Mtaaies out, the fqiulibrtum in the solution is disturbed ; the com-
Jted is again forniei] at the expense of the substance present, and
•**!>. A more thontuyli investigation of the conditions of equilibrium
tMttiil to be carried out.

«T4

PRINCIPLES OF INORGANIC CHEMISTKY mJ

* The above relations me of importance for the appiicaiion
corrosive subHtnate for purposes of disinfectioti. It has Ijeen fo"
that, the poisonous action of the mercury salts is propDrtiot);i) tot
coiK'untration of the dimfrniritm present. By the jiddition of
chlorides, now, the concentration of the dimercurioit is cer
UiiuitiisheiJ, either l>y the formatinn of the abovi? menttoneti coun
ions or by the diminniion of the dissociation in consetjuence of
mass action of the tiiloridion. The addition, therefore, of
chlnridw to corrosive suliliiimte, which ia fretptently matie, all
cn.iisesH dimituition of tiie jjoiaonous iiction as compared with a sol
of purt' sultlinuit^ conttiining an equal aniounl of mercury, ainl wll
Ut'cessary one must be- aware of this iijflui?ncc in ordi^r not lo tual
tuistakes in estimating the disinfecting power of a given solution.

The formation of, the coriespoiidinj; /i^/dminerruriekltme ofiti
he recoirnised on treating mori-uric chloride with concentrated hjt
vhloric acid. ConM(iend.>k' -imounts of that salt then ]nis» into solitti
with a remarkable rise nf temperature, and the solution no longd
fiinies; it therefore contains much less free hydrochloric jiciil. I)b
cooling the muss solidilie.s to crystals of the composition ilH|,^'l.,.

Mfi-curic chloride unites with mercuric oxide lo form ruiripniiK
iiri/rliliit-uie.", which have tlie general formula jHHgCl« • «HgO, in whiel
the lutio tft : ii can vary frcnii 6:1 to 1 : 2. The viirious com{wutiil<]
.nre obtained by ireatinj^ varying amounts of oxide with more or 1«J
concentrated solutionis of the chloride at diflerent temperatures. The
compounds coniparutively rich in o.icide are red, brown, or bliick, scniel
oven violet ; those rich in chloritle !)re lighter tti colour, vnt-yiii;.; wl
jwle yellow. While tlic latter give nji cliioridu to water, the furaerj
do so oidy Jji a very slight degree, so tliat an aqueous scilutioti of]
mercuric chloride loses almost all its chloride on being shaken wftli.1
merctuic cxide. This rwietion is made use of in tho pre[iar>ition ufi
hypochlorou* arid from i hlorfiu' water by means of mercuric oxide.

C67. Mercuric Bromide, HgBr.^, is a white, very filiglttly soluWeJ
Kalt, which is^ very similar to the chlmide, nnd can Ik- reii<lily (ihlaiiic^ [
trom its elements. In all its chemical relationships aUo it is so cliwly
analogous to the chloride that the preceding deecHptioti could 1»
repCJited almost word for woi-d. Its electrolytic disj-ociatioii is itill '
less thnn that of the chloride, its tendency to form com])lex coni|iou«il»
greater.

668. Merctiric Iodide, Hglo is a red substance which is only
silightly si'liible in water (1 : 120), but readily dissolves in alcohol,
from which it sejw.rates out on evaporation in red tpiadratic crysuk
It is most cHBily obtained by rubbing mercury and iodine together i"
tiiB projKjrtions 4 : 5 by weight.

If tlie substance is heated it becomes yellow above 126", pasaingit
the mulie lime into another crystalline form ; on Iwing kept in ^^
cold ii aguin cbangea into the red variety. It ia therefore an eiwntio-

StXiv MERCUUY 6T5

'•>]ut* suhdtaoce, and IHG"^ is the iransition U'lnpertiture which sepamtefi
ke ti*xi regions of stjibility from one anoihtr (]>. 257).

• H iii any way, however, soIiJ nwrcmic iodide is caused to foiiii
I a lower tenijwrature, it is always the yellow form that firal appcwrs.
his is ou« of the most striking examples of the rule which has often
Md mentioned that the unatalile forms appear first. This can be
ladily observed by precipiUiting nierLuric chloridt' with a solution of
rrtjusitim io<iide, A bright yellow precipitiitc h first formed, wliith in

lew moments ehanges into the red one. The yellow form iiuiiiitaitis
* existence longer when formed by the precipitation of an alcoholic
aintion of the sjdt with water. In consecpienco of its very fine stnte
t division it is very light yellow, almost white, in colour. The
tnvcrsioD into the stable red form is greatly accelerated by light.
n»en exjHjsed to sunlight the vessel with the light yellow pre-
i{iitat4! becomes r^jd in a few mirmtes on the side turned towards the
ight.

* Further, when the red salt is volatilised, the vajwur always
ondeuses on the colder portions in the yellow form. This Oi'cura, no
lutter whether the vapour has been generated from the red or the
^Jlow salt, which shows that the distinction between the solid forms
lots not exist in the vjiponr.

Mcrcnric iixlido is a very stalfle comjHjund, which is scarcely attacked
^ dilute solutions of the oniinary reagents. This in due to the fact
^ftit is even luss dissociated into it*, ions than mercuric chloride
P^ On the other hand, it ia formed with extreme ease from its
BntMitueiits.

Mercuric iorlide forms very stable complex coraponnds with the
^idine conipounds of the other metals. Tht-ise will he tlcscribed

^pThe behaviour of mrrcurie Jtmritle is iu striking contrast with the
ptal slability of mercuric chloride, bsomide, and iodide. Mercuric
<ixide, it is true, dissolves iti excess of hydrofluoric acid, but on diluting
the mhitioii with water a basic salt of a yellow colour is deposited, and
Uthin is treuted with further quantities of water pure mcrctiric oxide
raauiis behind free from HmH'ine compounds. This is a beliaviour
jwculiar to the oxy-salts of mercury, and shows the considerable
i*i(ivuition of Ibiorine from the other lialugenB <p. 242).
^Bc^- Mercuric Sulphide. — While a sidphur cumijound corre-
|iPHing to iiieicuroufi uxidi; is not kn<)wn, the eom[>onnd HgS, cor-
twpouiling to mercuric oxide, ia a verv stable substance which is readily

RieJ, occui-s naturally, and has long been known.
' If the *iolution of a rtnixuroas salt is precipitated with aidphur-
lliydrogen, a black precipitate is indeed formed ; but on investiga-
tion lliis is found to be a mixture of mercuric sulphide and metallic
wtrrury. It can be assumed ihiit the mercuroiis sulphide first formed
''wumpoBcs into tliese two substances : Hg^S = HgS + Hg.

676

PKINCIPLES OF INOKOANIC CHEMISTRY

CUi

Mercuric snlpliklo is obtaiiioi! as a Itlack powder by triturating I
two components tngetlier. It is ;ilso olitjiiueil by the pjeoipitalioti
njerciuic couipoiinds witli sulphiireLted liydrogcn. In this case it
imliffcrent wh^tber the snliitiori icat'ts injUl or neutral, aincc mcnia
sulphide is extremely diHit'idtly solulile, and its precipitation i» th«
fuic not appreciably affet'tod Ijy a<jids. From the other tneuj
sidphides it is distinguishi^d by the fact that it does not have I
least tendency to uxidisie iu the air. It is a uiuth more stat
compound than mercuric sulphate, which could h^ prodiue<l !>y i
oxidation.

In naiture mercuric sulphide occurs in comparatively ]ai'goquanliti«
It constitutes the most important ore of mercury, and is called nun
hiir. Pure citniabiir crystal) ise.'i in refi-grey, hexagonal mwsse* with
metallic lustre, and on being ground yields a powder of ;» Hne re(i foliaj
It is another form of mercuric sulphide; the black product nmj Ij
regarded ns amorphous.

From the fact that the black form was first produced in tiie form
tion of mercuric sulphi<ic, it van bo concluded that it is the less *ub
and the red crystalline form the more stable variety. This foilm
from the spontaneous tmnsformntion of the former into the latter,
a solution of alkali siUphide (iu which mercuric sulphide is soinewld
soluble) is ]«oured over the black mercuric sulphide, red f.pf*t# al
formcil after some time iu the black mass, and these continue to f.TO
until the whole mas.s has become red, if. has become converted iai
the cry.stalliiie form.

The more stable red form can also bo obtained by the alow id
limatiim of the black sulphide.

■* Being the less stable fonn, the black mercuric sulphide mu*l I
more soluble in rdl solvents than the red. If, therefore, the liijiiiJ
saturated in respect of the black fi>rni, it is suporsaturated in re»p«(
of the less aoltible red form, and if any of the red form is present, <
is produced, a further cjuautity of the red sulphide mit&t there fepaml
out- The solution thereby Incomes tinsatui-ated in respect of tlie hl«
form, and a further portion of this is dissolved. In this way pre? i|iitl
tion and solution are repeated until the unstable form has coniplfl*)
disappeared. Transformations of this kind are therefore genenlj
accelerated by solvents, since these act as iMtermediuries, whwai
otherwise only those portions of the two forms which are in dvet
contact can influence one another.

On account of its fine colour cinnabar is used as a pigment. H'
however, not very stable to light. The two forms of mercuric gulplii<l
are nut appreciably soluble in dilute acids, and nitric acid also i* oi'l*
out action on them. They tlissolve, however, in aqua rcgia or otli<
reagents, which evolve free chlorine. Tins behaviour is due Ui tM
slight stability of the oxygen salts of nu^rcury anti the great stfthiliff
of the halogen compounds. This is made uao of for the annlytiw

substance, whi'ch is not inetalUc silver, as it does nut dissolve
iiit.ric acij. It has recently been shown thiit silver sub-
i-hlnrirle, Ag,,Cl or Ag_,Cl„ is here formed, whieli can be again con-
rwted into silver chloride by nieans of chlnrine. Under the infliieiica
of Uie light, a decomposition of the silver chloride into sub-chloride
•nil frt'r fhlorine occurs; equilibnnn is establislied when the conceii
[ tratiod of the ehhirine in contact with these two substinces hits reached
a definite value. This viduc is a,l] the greater tlie stronger the light,
•ikI becomes vanishitigly snjali in darknL>,ss. In the case of this eqiiili-
•riuni, therefore, the strength of the ligtit plavs a rule simibir to that

Krnjietatiire in the decomposition of calcium carbonate by heat,,
t the deeoin|joBition is cjkrried out under such conditions that the
ino can pass into other compounds, it is unlimited, and occurs in
pojwrtion to the strength ot" the light and to the time. The use of
«Iver chloride for making copies of pb()to.,u'ni|jhii.- negatives depends on
this. The binding of the liheratcd chlorine is effected by the organic
ftimiMiurids wliicli (*re aUvays present.

• The action of light on silver chloride take-s place more slowly
liiaii in the case of the other halogen compounds of silver. It is there-
fere not nsed for taking photographs directly, as it is not sufficiently
•cnsitive fur this piirposp.

• In the case of silver chloride, it is the blue and the violet raj-s
tlut exliiliit the graitest chfuucal activity. The region of active rays,
!»n«ever. can \m shifted to a considerable extent by the presence of
otkcr subetiinces.

Silver chloride is the form in which chloridion is identifier! and
esiiimited ; the estimation is effected by adding excess of silver nitrate
to die isotntion in question, and filtering off and weighing the .silver
diluridf prf>duccd.

Conversely, silver c*n be efitimated in the form of silver chloride.
iThi« meihrxi has been elaborated chiefly for the estimation of thiB
metal in kir-sihcr in governmental mints^ The method is carried
out Viy diasniving a weighed amount of the metal, and adding a sola-

tof sodium chloride of known strength nntil a ]>rccipttate just
I lo be protluced. The property of silver chloride of coheriog
- f.ci.her renders this niethwl possible ; for a solution which uill con-
UiiH an excess of silver chloride can Ije made ijiiite dear by shaking,
lieeauic tlic silver chloride forms into tlakee, which in a few moments
link down and leave a clear liiititd. It is easy to see if a turbidity i<
pruhue'l in this on the addition of sorlium chloride. This i» histort>
calir the first case in which the method of volumetric analysis (p. Id0)i
*iw elalxjrate*!.

Silver chloride accumulates from many chemical analysed : further,
it iia a form of compound into which other silver compounds can be
^fadily converted, and in which silver can Im? separated from other sub-
is. The need often arises, therefore, of again preparing metallic

678

PRINCIPLES OF INORGANIC CHEMISTRY ch

of obtaining eyanogerk gfis {p, 418). In this procoaa a portion of
cyanogen jilwiiys Bi'panites out iu the polymerised condition asaW
brown powder ai ]iaraeyanogeii.

If the solution of mercuric cynriide is mixed with that of an alka
cyanide, a considerable evoliitioi] of heat occurs, which indifatw t
formation of a new coniponnd. This can also be obtained in the mI
f state ; the potassium compound has the composition K.^Hg(CN}j, «
is the potaastum salt of u nierciirieyanidion Hg(CN)j'", which is simill
ill composition to the nickelcyanidion (p. SST),

The t!oiTfsponding acid II.jHg(t'N)^ is not very staVjIe, l«U tiecoi
poses rea<iily into nieiTuric cyanide anfl hydrocyanic Jicid.

671. Complex Oompounds of Mercury. — As might b* oxpecti
from the alight dissociation of tlie halogen f'OiMix>unils of mercury, tW
metal has a great tendenry to form complex fompoiinds, T.ho aijwfi
solutions of" which contain dimercurioti only in extremely small aiimiiii
and in which mercury foi'ins a component of more comidex ion*- or sail
Such complex compounds are met with, on the one hand, in tht* ci,
of the halogen derivatives; on the other hand, stiljdnsr and riitrogt
also have the power of foiining many such compounds with raercurjB
Un account of the large number of such substances these cannO
be treated exhaustively here, and tt»e characterisation of the mo
ihiportant types must suflice.

In the first place, tho three heavier halogens form such compli
compounds, the stability of which inereusea with the combining wfi;,'lrt
of the halogens. The most important type rejjreBente4l here is tl
of the halogenmercuric ion HgA^", where A denotes the hatngen.
will be sufficient if we describe the relations in the case of thi
iodine compound, which is the most stable, and which, on ai'couiU
the difficult soliibih'ty of mercuric iodide, gives rise to tho most rewlilj
understood phcuuniena, {cf. p. 671).

Mercuric iodide reudily dissolves in aijneons solutions containiBi
iodidion, and it does so nl! the more abundantly the more concentraW
the solutions. On dilution, mercuric iodide is prrcipitafcii, tnU tbi
always remains in the solution rather more of it than corresjHimh M
the relation Hgl„:2r. Tho sulutioiis are pale yellow tn rol""ri
exhibit none of the reactions of mei-cury, and partly yield tho m
sponding salts in the solid state on evaporation, /■..'/. the potassium ^
K^Hgl^ ; they contain the complex anion Hgl^ "■

No mercuric oxide is precipitated from their solutions by 1^*
adilition of strong bases ; oil the other hand, mercuric oxide dtMui'i
abundantly, for cx!ini[ile. in a solution of potassium iodrdi* yieliling
solution with a strongly alkaline reaction. In ihts case iho reacttOB
4KI + HgO + up = KoHgl, 4 2K0H, or writing the ions. Il
HgO + H/>= Hgl/' + 20ir, takes place to a large extent. Siitb *"
alkaline solution of ptitutAmurn im^rftinc k»lilf is used under the tia""
of " Nessler's reagent" for the detection of .small traces of aiunioi"^

SILVER

689

ture is therefore produced on the plate in which the bright pjirtfl

jkUin n. dense, the tiark parts a slight or no precipitate. If, after

^ci«iit development, the remaining silver bromide is removed by

jiving ill smliuiii thiosulphiite, a "negative" is obUiined, i.e. a

lure with opiiipn* high-liglits and transparent shadows.

Ill what ihf [nopecty »jf tlie ilhiminattid silver bromiJe of deing

quickly redito'd dept-nds, is still somewhat a matter of dispute,

ir the ninst. prnlndiJo view is that under the action of tlie light an

^lieot reduction occurs, and therefor*! a picture of silver sub-bruniide

Vtt^n in the nudevelopeil pktc, and is invisible only on account

I'ilBlill density. Tiiia is contirrned l>y t!iu fact that by treatment

free bromint) or any other oxidising agent, the "Intent'' picture

to disappear, Le. its power of being dovidopod is destroyed,

I The development, now, depends on the fact that a sapei-saturated

of silver is pruibiced by the reducing liqittH, from which metal

ejKisited at those parts where there are already nuclei of silver

ent (p. 492). The-se are fircsumably formed by the developer

the readily reducible suh-broniidt;.

iS'2. Silver Iodide, Agl, is ;dso inunediately formed when its

come togeihor, and of the three lialogen compounds of silver it is

the most diffieidtly soluble. It is a yellow powder which is

ulvwl only in traces, even in amraorda, and reipiires comparatively

amounts of sodium thiosulphat-e for its solution. It readily

s, however, in potaasium cyanide. This proves that the con-

tion of argenlioQ is relatively greatest itt its eoniplex ammonia

id, is smaller in the thiosulp>hate compound, and is Bmatlcst in

] cyanogen compound.

I* Silver iodide was formerly chiefly used as photographic siib-
ce, and this bi.th for the method uf Daguerre (the hrst real photo-
lic method) and for the later rolladhi in prwess svhich is still in
tr particular purposes.

Tbe method of Daguerre depends on the fact that the " develop-
it" of an exposed silver iodide plate is jicconiplishe<I by exposing
f illuminated pl»t« to the vaiiom-s of mercury.^ A plate of silver

' The tiii.tory of the dt*»if«r>' of this metlioil is instnicttve ; it is rvlateit aa follows.

I>vaemr tixl tintl «tUiu|iteil to ntilitie (lirwitlj tha bliu:keni»K "f lUver imliilt^ in lit;hC,

■ Hit iiiul ilirvctetl bi« tftfiirts to prcp.triiif; th« luyer ill sncli * WAy tlittl Hin blackeiiiug

I^Ud occur u» quickly ax possible. Ou oue occuiiou hn hsd jnxt biigua to take a

^^■iv, tta( liail lii interrupt Ilia work, aiiil <<iiic« no blackening hoi! ak yet raade iti

^^Kmnce on thi- platf, hv iuteuilei) to u«e it for a Fnrtber experiment, and plsced it

^^BIdn in a iliik {>rir». Next day he found tbc piclurt! on the pliite. He was !KK>n

Plnft KMarn himself that a. picture wim nlwayt proi.liiL't^xl wlipii h^ placed a plate, aftei-

i diort eipusurc, in the pzv^, bat waa unuwira o^ to w]iic;h of the olijects prenent ia tlie

fiS('bi)Tr.! pr<i.hiiCTl this effect. He therefore renioviid these objects one nfteT the i>th*fr,

Umyn olitsLDed pictiire.<< even wtieu th« cupboard wa£ qisiie empty. In other

under th*-* same uoDilitions, no picture waa proiluctvl. Fiually, he discoovred

ry wlitch Itiid hittu fijiiU in th« Jnliit-'s of th^ wood, and ou niakiug thi^ itppto-

aeut. hi! foutid thnt the picture w«>i devttlop»l by h(>iug (sft ovvt metallic

2 Y

€80

PKINCIPLES OF INOKGANIC CHEMISTRY cm,

aramonium is replated hy merinry, only that in this case one coiubitlil
weigfil of mereurj, cm account of its dh'ukncy, replaces two combiu
weights of hydrogen. From these con si derations we obtain, in tb
first instance, the following cations : —

DimeTcuraminoQion

Merciiramnioaion

Merpiinfliamnionion

Hg..N
HkH„X,

In the case of dimercurammonion, all the by*lrogeii of lb
ammonium is replaced Ijy roeixury ; in morciirjimmonion, only tb
half ; and mercurdiammouion, finally, coneajjonds Uj tivo comUnm
weights of ammonium, which have together lost two hyrlrogt'iis, xh
having been replaced hy t)ne combining' weight of mercury.

The hydroxide corresfionding to iliiiiercuraiuinotiioM is ubUiittMi
ullowing finely divided mercuric o.\ide to stand under concetitruM
jinimonia sotutiin, Without apparontly any great eha.iige taking pUo
— the coiour only becomes somewhat liifhter — thei>e occurs the reacticl
2HgO + NH^ = Hg.,N(OH} + H,,0. The hydroxide produced is ahaiM
insoluble in water, explodea on Iwiing heated, and forms with most I
the acids yellow to brown colmired salts, which are also almost iusolilttl)
Of these, the ifkiii/f is the heat known, iia it is formed ns a bro*
precipitJite when ammonia is iidded to an alkaline sobition of jxitiiisini
mercuric iodide {p. (J78). Even extremely small aniuunts of jimmoni
can in this way be detected by the yellow-brown coloratiim of ib
liqtiid, and this reaction, called by the name of its discoverer, li
Nfsxlef rftidtcti, is used both for the detection and the appr<)xinj«l
estimation of very small amounts of ammonia, such as occur, fa
example, in the ordinary wutt-r-supiily. For <piantilative jiurjMjsia til
coloration which is produced by the water to be iiuestigatod, is cmb^
pared with a .seiies of colours j>roduced by known, gradntcd ajiioiiiil
of ammonia (in the form of very dilute eolntlon of ammonium ehloriilt
under the same conditions.

Of the two other types, the chlorine compounds are the ^
known ; they aic forme<l by precipitating solutions of mercuric clil"Tiu
under diflerent coiuiitions with anjmonia. If a solution of the tnercni;
salt is a<lded iti the cold to excejis of dilute ammonia, mririinti)mii>M«t
fhloiHflf: IlgH.jNCl is precipitated as a white substance which, on bcii^
heated, sublimes with decomposition without previous melting. Ti
sublimate consists chiefly of calomel, while a mixture of nitrogen sa
ammoniu. escapes; the latter generally blackens the sublimaw (J
calomel: GHgHoNCl^ oHgCl + 4NH,j + N* This compoiim!
formerly used as a medicament, and was called innisihle prrfipMr.

If the ammonia is allowed to act on the mercuric cidoride in In
solution in tho presence of much amnionium chloride, a Wqmi
obtained which h clear when hot, anil which on cooling deposit* snii
crystals of a white salt ; this is the chloride of mnmrdvniiiuoniitiu,'!''

MEKCUllY

681

il, therefore, the fornmla HgH,,Nj,CL. This formula vnu be resolved
Ito mercuric chloride plus ammoaiii. IlyCl., + UNll., ; the conipleic
itOKi of the salt is, however, seen from the iact that it does not
ttAve any ammonia with a solution of caustic potash, and is only
)i!omjH)*etl liy this reagent on heing strongly heateJ. Siiiice on being
sitfii the salt melts to a eleiu* yellowish liquid, it was called fimble
m^iilf to distinguish it from nierciirammoniuni chloride or infusible
l^tate,

besides the al)ove compounds, there are othoi-s belonging to the
imonia series which, however, uill not be mentioned here, as they
MfcBot been investigated in sufficient detail
^3. Other Complex Nitrogen Compounds. — Another complex
Tcnry »aU containing nitrogen which nnist be mentioned is poiaasium
.Tcurinitrite, K.,Hg(JsO^)^, which is obtained by iliBsolvitig mercuric
ide in a solution of pot-asBium nitrite (whereby tliere is an evolution
heat), and destroying the bsisic reaction with acetic acid. From
s solution a fijiciy crystalline, bright yellow salt is obtained, which
t the above composition, and is readily solrd^le in water. The
lution is neutral, and can be boiled without decomposition ; it does
t exhibit, thereforei, any of the hycb'olysis of the norma! mercuric
U.

Further, mercury enters extremely readily into organic com {rounds
citaioin^' tiie imUie group, NH. The substances produced do not
hibit the reactions of mercury, and therefore contain this element in
x)njplex. Since they belong to organic chemistry, however, the
lU-raerit that they are characteristic of merciuy must stiHice here.

Compounds, further, containing the amide group, XH.„ show these
operties, but in a less degree than the iinido compounds.

To this class also belong the cyanogen compounds, concerning
ta^the necesBftry infomiatitjn has already been given (p. (578).
H4. Complex Sulphur Compounds. — The tendency of the two
Hnt», .sulphur and mercury, tu lomliiiie, which is disclosed in the
■■stability nf mercuric sulphide, .asserts itself also In the formation
TOtuplex compounds on allowing the lower oxyacids of sulphur and
Kretiry comjxmnds to come together. Thus, mercuric oxide dissolves

the normiil alkali salts of sidphurous acid and thlosulphnric acid,
ith great rise of temperature and protluction of an ulkaUue reaction ;
I thtBC two salts most of the other difficultly .<iDhd>le salts of mercury
* »lso reaflily soluble. The cause in both cases is to be found in
w disappearance of dimercurion, owing to the formation of a complex
nupound-

By dissolving mercuric oxide in polai^iuin sulphite and crystallis-
% ihere is obtained the salt K2Hg(S0^).,, which is the potassium salt
iiiercuriaulphoston, Ug(SOg)/; potassium hydruxiile is also formed
t the same time, and reiimins in the mother liijuor. The cxist-
JWof this salt in the strongly alkaline liquid is sufficient to ahow

PRISClPLEi) OF INOBG.V^^IC CHEMISTKY can-

liition of the complex aalt, howevei', the cutn-enttnlioii (
clw la !^ smoJl tbat this dirfit^t reaction ducd not occur lo

eztmat, and the i^panition of .^ilvrr takes place onl r a
FlMMmiZ Um tiJeetrit! current.

tiuoeaiiieriDg the forjniila of potaj^siuin arg^ntirynnidi
VVj, it is »e«n that the product of eloctiolysis shiiiiW li
n- hand, piiuissiuin, and, on the other, the rlistliarjrwi anim
> Instouil of this silver appears at the cath«xli\ and tin- !i(i(*i
^(coiuuan^ of silver) dissolves. We are liealing in twith caset. witjj
"Ht-OiUmL jmumdary reactions.

• Tha sepuratiun uf potjissian at the eathode would reijutix!
di higgler potential than thtit uf »rgeutton, in ^pitc of the cnial
ri?tWr»ri*>i> of the latter. Thua the conduction of the curreni ii
I iliiiUulyte, it is true, is etlected as far as the cathoile by pota&iun

mro of electrieity at the eathode, hovrevcr, occurs not !i;
i»f poUission, but by th;»t of the argeiition. FornallTi
»r can also Iw exjiressecl by saying that [lotassiuiii i« m
fifrtneil, but at once undergoes double doconijjosjtion with ih*
-.■tit with sepaiiition of silver, acconiing to the eqimiui
I k.i^.v. .\r^ - K = Ag + 2KCN. Silver and poUissinm cyanide art
Itlwntiikre funned.

* At the aiioilo the ion .-\g{CN)/ is dischargetl, and uvU on ill
•TM'tnllv' -tilvur, silver cyanide beiiig formed according to the equation

' ■Nl.' = 'iAjt,^'N. This is at once dissolved to potasntui
.tiide by the excess of pntas-sium cyanide present^ and On
lou of the latter is again made gootl by the iwtassiuni cyaniA
III. ij i> tormed at the eathode. It is necessary, however, to kecfihi
uh iu trtiiiyrm^nl, as otherwise the prttasaium cyanide would atitttuB
Mtliotle, and would hindtT the separation of die silvei;
LfuKle a deposition of ailivor cyanide would imniediatdj
Lur wii jitc<"Uit of ,1 ];*«k of potJissium cyanide,

tii>7 Complex Salts in the Voltaic Cell— When voltaic cftlli

«n c«^'n»truetej with silver in solutions of ordinary silver salts, it
; . ! .1, ., ui)yer j)j almost at the end of the potential aeries, which
v( the formation of the ion t^akes place* with greater ditficiillj
!i. lis.- t>f most of the other metjds, and conversely, the ti
■ i.i\ ui [lass into the metal. Thus with zinc there is obtJiiii
.:(i;*l rr»7 volt, and even with copper there is a potential
.L {\\ 645), If, however, the solution at the silver electrod
Itliutxi by a solution of potassium cyanide, then according to tl
r ■ (itou of this the potential of silver sinks much below copp««

' very concentrated solutions can even sink below nnc.
iiiiunoH of {KJtassium cyanide the silver loses its character ■*
|lliv>bl« uwt*U. and acquires that of a readily oxidieahle one. This i
f«JiM> *j^|«w««l chemically, for if nilver powder is shaken with
^^iuiK-o oi potaasium cyanide it is fairly rapidly diseolved. and

IBCcr

SILVER

693

liein* acidified a white precipitate of silver cyanide is deposited from
die liquid.

Similar pheiiomi.'iia are often found in tlie case of su1>stfiiiees wliich
fomj lomplex compounds with silver (and other metals Ivehave ijuite
Mmiliirly). To find tLe cxplan;itiun we sli:dl firdt miike ourselves
injUKinted with another, generally smaller, deviation from the potential
tmoL

Cells can be t-onetructed in which one of the metals, instead of
kdiig surrounded by a solulion of its salt, is in contact with its solid
bIl Thia is the case, Uir example, in the lead accumulator, one
etortHle of which ia (brmeit of lead in solid lead sulphate (|i. 663). If
thf |wiieutial of such cells is iii\ cstigtitcd, it is found that the jmrtictdar
tetal h»5 always shifted its position in the potential acriea, and always,
iriihuui exemption, foimrds the tinr md. Thus in a cell of ainc and
diver there is found, when the ainc electrode is left unchanged : —

Zint: o^iuat silver in silvvr iiitrnti'

,, ,, ailv«r uJiloride .

„ ,, silver bromide .

,, ,, silver ioiliile

1 'i>t volt

O-flS ,,

0-66 ,,

In the ca^e of the iodide, tlierefore, the jiotential decreases by 0'91
roll, and is considerably different for the throe "insoluble" salts.

The explanation ia found on more closely studying the process
rliicb ixciini on the passage of the current through such a cell. On
lie silver »ide the silver is tra.nsformetl ti(jrii the ionised state into the
metallic. Arpention, however, can exist only in mhdimi. We must
lb*Tefore coin'lmie that, in spite of their apparent insolubility, all the
ibove salu are really dissolved. This has also been proved in other

fi, for if as pure water as po.^ible is shaken with silver ciiloride the
irical conductivity perceptibly increases, i.f. conducting ions pass
the licjuid, and these can only be silver and chloride ions, since
ftone other 'm-v. pfjssiltle.

Now, the work which is necessary for the separation of an ion from
iu w.!ut.ion depends not ottly on the miture of the ion, but also on its
(SKfviraivtn in the solutioo, and it becomes all the greater the smaller
tlie coitceninition. Conversely, a metal passes all the more readily
into its ion the smaller the concentration of this in the sohition in
which it jt^ to Ije formed. If this is correct the position of every metal
nmf >je shifted toward.? the zinc cud, when it is [ilaced in a solution
which i* Ic*? concQutnited in respect of this ion, and eirr ivrsti. It must

tfforc 1)6 pnssilile to fonstruct cells which will exhibit an electro-
re force, simply by placing the same metal in two solutions of
of its salt* of different concentration. This ia indeed the cHse,
tnd the currents which are thereby produced act always in such a
wtise that the melul in rht* dilute solution is dissolved ; conversely,
in the concentrated solution mi'tiil is <lt'[n)sit<Kl. In other words, the
nirmita tend to riptnlw thr difimm'j'if r>f ffmcentrtttiffn.

684

PRINCIPLES OF INORGANIC CHEMISTRY aur

state from solutions by means t>f rednciftg agiints, it vnn assiuue a gitit
variety of coloura aecanling to fircumstiincus. It ajifiears tliat tbt
j^eDow and brown forms of silver, more ospedally, whicli sejiarste out
under the action of ligiit on mixtures of silver salts and organic
substances (which h;ive n reducing fictiati), are amorphous ; ibey in
more i|uick]y attacked thati iha grey and black forms of silver, and
(d.so change into these luidtT the inlliiento of catalysera.

Metallic silver also has the property of passing into ihc roIMM
comlition, This coUoidid silver 18 obtained by rodncin'; silver in
idkiiliiie liquids, and iilso when an electric arc is produced bel«<Tn
silver electrodes under ivater ; bj the latter means, the silver is firsl
volatilised and thou suddenly precipitated in the siiiTonnding wattr,
whereby it passes int-o the less stable form of colloidal silver. TLtae
solutions are of u hrowti or red colour ; the forms of colloidal sib er
obtained by choiidcal means dry up to masses with a metallic )iistr«,
the colour of which lan he altered by slight influences, so th;it it (iaas«
through all shades of yellow, red, violet, and greeh. Notwithstanding
their metallic lustre, these masses do not behave like metallic ailTcr,
since they do not conduct the electric current. Thoy are unstulk
and are converted by many catalytic inHuencea into oitfinary whiu'or
grey silver.*

Silver ia not attiicked by dilute acids except nUrir uriii, irhich
readily dissolves ii- with evolutioti of nitric oxide and fominiion ui
silver nitrate. It dissolves to the sulphate, also, in conct'nti"ate<l hoillDj!
Kuli)hiirtc acid, whereby euljdiur dioxide escapee. It is very resistftiii
to basic sidistiijices ; crucibles and ilishes of silver are used in the laboni'
tory in working with caustic potash and soda, as that metal is nol
attacked to any considerable extent even on fusing these siiViBianoesi.

Irt the pure state silver is a white tenacious metal, which nut he
readily drawn into wire, and made into very thin sheets hy rallitig uf
hammering. For use it is alIoye<l with 1 0 per cent of copper in ordw
to make it harder. It conducts heat and electricity very well, mkI
occu[iic8, in this respect, the first phiee among the metals.

The lombiidtig iciitjhf of silver is an important inagnituric, since on
account of the oxeellent properties of its halogen corapounJ* fnf
analysis, many other combining weights have beeJi dcterminwl !>)'
mean,-* of those. The following method has been used in order to
establish the combining weight of stiver with respect to oxygen.

Weighed rpiantities of silver chlorate were ve^Jnced to sii'*"'
chloride ; since three condtining weights of oxygen are contained in
•one combining weight of cidorate, we have the proportion : —

loss of weight of chlorate 3 x combining weight of oxyge^
weight of siU'er chloride combining weight of sdver chlorida

Thlis, in one experiment, 1 03-980 guv. of silver chloride h«*

XXXV

SILVER

685

obtained from 138(HU gm. of silver chlorate. Since the thrL*e(oUl
coiiibtiiing weight of oxygen is, in accordance with our assHmptinn
(p. lU), 48*UO(.i, the combining weight of silver chloride is 143':i.sl,

Silver was now converted into silver chloride. U the i:on)l>iiiing
Teight of silver chloride is divided in the same ratio iis thtit in
which analysis has shown these elements to be combined in silvnr
thloridc, the two separate combining weights are obtained.

Thus, 144-207 gm. of silver chloride were obtained from lOS'.'VTy

of alive r. \\'e have therefore tlie proportion :- —

%re CI

a : Ag = (144-2(J7 - 10S%5ry) : 108-579,

CI denotes the combining weight of chlorine, and Ajj; tliut of
iilifcr. Hence : —
K Ag = 10"-93 and CI = 35 '45.

677. ArgeDtiOD. — Silver forms oidy one kind of eletnontary
ioti, vit niociovalent argention, Ag'. Besides this, it can enter into
Mny comjilex ions, especially such as contain nitrogen and Bul[>bHr.

Argention is colourless, und with respect to the ]*ro[)ortiea of ito
(iHajimmds, it is allied to the monovalent ions of coppiir and mercury.
On the other hand, there e.xist relations of isomorphism with Hndinm.
It is the ion of a strong base, for the solnble silver salts react ijnit*
ueuinLi and exhibit no hydrolysis, allhougb atmoet all the aalta of tbo
tieary metals do.

Tins is not in conflict with the fact that ar^^ention posAcw rnadily
into the metal am! is formed from this with difliculty, for we are
tUiiliog in the two case^ with essentially dtfTerenl chemical relatiomt
H^ transformations. The heat of formation oi argention frurn the
Hml has a targe negative value; 106 vf^ must bo absorbed in order
tb«t silver may peas into its ion. Metallic silver i» also readily pre-
{ur«d from its salts; as a rule, contact with any organic nidwlance.
<»p«eiiJly in light, is sufficient for ihi-s, these Mibstanrex tb»-n becoming
tinnrii or black in colour owing to the finely divided stiver which
•epifBtes ont-

Argention is a strong poison for all ov^nninmt*. lu actiona, how
'Vftr, are restricted by the chloridion, which is everwhere prevent, and
^th which it forms a ditficnltly soluble rf<roponnd.

67*;. Silver Oxide. — From the »oliition« ol the filvfr «iltit
'otuble liases do not preeipitiit** the hydroxide aa one would exfject,
•^'it it^ anhydride, julrrr 'atdf, Ag,0. Tlii* ta a brown powder,
*bich is sulficiently s<r>|iible in water to impart to it on alkaline rc-
*':tion to vegetable dye«, and whirb crmibinea very rwlily with add*
'^ furtii silver "iaiti.. In the falioratnry it t« aa«<i t/i renwe h<^F ■"-'■
'fOBi (lisaolve*! b^log'rn rf7vn[i']nMlii, ami lo RpUce tt lir "xyv

' oxyl. For tbii purpoce it n lfe»Wy prafar' ' '

693

PRINCIPLES OF INORGANIC CIIEMISTKY ciur.

the two combiuing weights of the hydrogen of the thiosulphnric mid
is replaced. Since it is aHsumefl that one of these is present iji tlis
thiosulphuric add as hydroxyl, the other as sidpiihydrvl, ihi- further
afisuniption is proliable that the silver rcpliices the hydrojit'ii of tin
sulphhjdryl, hceaitse its powei of coniVjiiiiug with sidphur is cerUittly
morn highly develfipt-rl ihitn its jKtwerof coniliiniiig with oxyi^'ii. Tli»
argentitiiiosidphaiiiiMi whifh is here formed would therufore have Lht
formula, AgS . S(J^'.

From the solutions obtained by the satui-atiuu of sodium thioral-
phiitt? with silv'LT .'Jalts two difiticiit salts crystallise out, (Jive uf lhe««
is dithinikly Rolnhie, and its conjposilion corrcspftrnU to the alifn»
formulii, the hydiogen beiiiy rt^place*! by sodium ; thi- other is n;fliiilj
soluble, <-otiluin8 twice as much sodium, but its n»tur« has rutl yrt
been cleiirt'd up. The forrauh« of these aalts are Nu(SUj. SAsUiid'
2Nii(S(J,,SAg) + Nh._,S,0,,,.

Thu complex chiiractcr of the coraponndi* is proved not oijly bytht
solubility relations, but also l>y the fact that they both have a rcmarl;
ably sweet U»ste, due to the ion AgS.St),,', whereas otherwisfi the
silver compounds have an luipleaaiini, metallic, astriri^ent taste.

The formation of thtjse compounds occuis when sodium thiosiilplww
is emjihiybd to diBSolve difficultly solidde silver suits. This ap|»Iic.ttion
is very witk'Jy extended in phutogi-aphy. If it is desired to separaK
the silver from them, an a!knli sulphide, which prt'cipit;ttes silvrr
sulphide from the solution, is the roost suitjdjle for thf pMr)iorje. The
solubititi' of silver sulphide is bo small that it is pmctically eoTii|)k't«Ij'
proeipitated even from the complex enmpound.

Smiium su-ifltife behaves siniiUu*ly lo sodunn thiosidpliate. A s«lt,
Na(y03)Ag, which ia difHeultly soluble in water, and which eon iw
regarded as the sofJium salt of argentisulfihosion, is also known.

690. MetaUurg-y of Silver. — Most of the silver is obtainnl ill! »a
adniixtiin? in lead in the pi'cjiaration of the latter nielal from i;.iK"ti»
(p. 6t».'j). For the purpose of .sc]j;irating the two meluls Ufcc is ukmI'*
of the dirtcrenec in their Whaviour to oxygen. The lead containing
silver is fusefl snd exposed to the action of the atmospheric oxygfn
tht- lead is thereby oxidised, its oxide flomng off a.*. Iithnri\f, ami tte
silver reroains behind. The completioiT of the separation is rocogiii**'!
by the disupjiearance of thd coating of leiid oxiiJ*- anil the appe»n<n<»
of the lustT'oos surface of the silver (the pdijwitlinti nj .<ili',-t ).

If the argentiferous lead, or u-nrk^inid, is very jjoor in j^ilvcr, it
is more advantageous to separate it by means of a i)roces8 of cryslallitt*
tion into pure lead and an alloy richer in silver. This is doiir lijt
allowing the fused w<jrk-lead to slowly cool. I'nrf lead then crystal"
Uses out ami a mother Iknior, comparatively rick in sihft, reni»Ji
behind, just as from a salt solution ])ure water crystailiseii out a* loJ
and a motiior litjuor richer in salt is formed, fly eontinuiiif; tit
se]iaratioii, a condition is finally reached in which silver also begini i

dd8

PRINCIPLES or INORGANIC CHEMISTkY ch. xjq

If a small quantity of B is added to pure A, the melting point
the latter fttlls, in accordance with the general rule ([i. 1-1). it
depression being all the grenter the larger the amount of B aJdd
The change is Jilmost proportional to the amount added, so tb»t tl
corresponding temperatures lU'e represented by an almost atraij
line ((/-. !

The same csonsiderations can be applied to B ; from the point i
straight line miiat idso f^Jtik towards the left representing the tcmpei
tiii'es at which Llie liquid mixliu*e ia in e«.(uiiibrimii with stolid B, i
the melting points of B in presence of the mixed liquid. The W
lines will cut in a point k.

Now, along ak the liipiid is in equilibrium with solid A, along i
with solid R In the point k, therefore, the Iic}uid is in ecjuililiriu
with both solid substances, and tm the two lines cut only in one piin
there is only twi' litjiiid mixture which is in equilibnnm at one and 111
same time with the two solid substances. i

This folIowB also from the phase law. We have two coiuponcflK
and in ttie point k four phases are present, vIk. the liquid, the l*
solid substances, and vapour.^ There is therefore no tiegree of freedtl
remaining, and all the varra>>fo9, viz. preasure, temperature, and coj
positit.m, have definite vahie.s.

If, tlierefore, any liqiiid mixture whatever is cotiled, that on* i
the two substances will sepiirate out which is in excess wjtli respect
the composition represented by the point k. This continues with
of temperature until the poiut k is reached. At this point ibft
substances sej)arate out tit (Ik sarin- fimi' and in audi proijortionft t
the melting^ puintam! the coniptjsition of the liquid remain uncbaai
A nii.xtuie corrfspoading to k behaves, therefore, like a Kimpl^
sffincr, fur it exliiiiits a constant melting point although it is » nuxttii
The relations are very similar to those in the case of acids of coiiil
boiling point (p. 185),

Such a mixture of constant melting point is called a euttHk ml
and the point k the titltcUr. jmiU, The melting (Wiint of a eu
mixture ia, necessarily, always umhr thai of its compoiiont*, and isi
the more so the nearer the melting point.s of the two pure substanoi
are to one another. Fig. lliii, in which various [jossiblo case* *l
represented, allows of these relations being readily seen,

' Utile vapour i« eidiided one degree of freedom i» cbtftineii, I'.c, the [xymiit
(very alightly) wiUi tlie itrtHisure.

CHAPTER XXXVI

THALLIUM

General. — Thallium occupies a remarkable intermediate jxiaition

tweeti vurious other elementg. By reason of the pliyaical properties

khe free element it is allied to lead, for, like this, it is soft, ductile,

has a high density. Its hj-droxide, which is reiidily sohilile in

"•"•t^r, piix>urL'i5 it a jioaition along with thi; tdkali hw/w/n, with which

it is isvuiiorptious in various compounds ; its ditficiiltJy soluble halogen

ii|ioiind3 hring it near to sihvt; atpper, and mvirtify, and in another

rJL-g of compounds it exhibits relations to the trivalent elements

tninium and iron.

Tlialliiim waa discovered by means of the spectroseope ; all its
lilH)u»dfl on being beated it) the. Btinsen flame, in which ihey quickly
atUifte, give a green tolomtioji which on hein^ exaraini-cl with the
ctroscopii appears as a single bright green line.
ThaUiiim ocenrs only in small quantity in nature, but, like all the
demciiiB which can be detected in small amounts, it has been found to
U fairly widely distributed. It is obtained as a by-product from the
fltiMiust in sidphuric acid worka in which pyrites containing thallium
is employed, ami also, in ssisociation witli zinc, from zinc ores. In the
latlar way it eoukl be ubtaiued in fairly large amount* if there were
*n.v detaand (or it.

•^ ba« already been mentioned, metiillic thallium is very similar to
lead but is still softer. Its density is lltf, its melting point 290'.
h makes n grey mark on paper, but this soon di3ap{>ears owing to
wiUtion. Fresh s-urfsvces of the metal, which have an almost silver
*!iile q>[H;arance, quickly tami.sh in the air through oxidation. In
ihc poti^iitial series it stands between cadrainni and iron, and is tbere-
itif ii metal which readily replaces hydrogen from dilute acid.s. As a
»tter of fact, it dissolves in dilute acids which do not form difficultly
•la salts, e.ff. aulphiu-ic acid and nitric acid, and is precipitated in
I ti>«taUic state from its solutions by zinc and ctidmium.
Thttlliuin forma two kinds of elementary ions, monovalent mono-
llion, Tl*, and trivalent trilhallion, Tl"". The former conditions

690

700

PKIXCTPLES OF INOKGANIC CliEMlSTKY

le similarity uf thallium to the alkali metala, the latter tliat I
luminiiini.

693, Thallous salts iira formed with evolution of hyclnigen b
dissohiiig the metiil in dilute acids. Solution in nitric acid, wliic
takes place with reduction of the ktter (very dilute acid yielt
hydrogen), also le.idsj only to thallous nitnit*. By means of in
chWine, however, thallous eompoMnds can lit converted into tlioll)
comjiouiids.

6!>4. Monothallion is colmirlesa; has, like luad, a fMisunuDi
action ; and can he recognised 1>y tiie formation of various Hilficultl]
sohible salts, especially the yellow iexlide. It is not precifiiiaii'H It
alkali hydroxides and i;,irbonaU?s, and is thereby tlistinguishwl inifl
the ions of all other heavy metals. Its heat of formation is almuri
zero, being only 7 kj.

695, Thallous Hydroxide, TIOII, ia obtained by the iieeonl
position of thalluus sulphate with baryta, as a liquid with a stroiij;!
alkaline reaction which is dissociated into its ions, monothallion tn
hydroxidion, quite as extensively as the alkali hvdroxidps, m
exhibits, therelore, the same Iwisic prcjperties. It turns rod litma
paper blu«i, renders turmeric brown, imd makes the skin of the fiusefl
slippery when Tnoisteiicd with it. On evaporatijig the solutfon
the yellowish eolcnned hydroxitlc cryBtallising wirh lU^O ■
obtained ; in contrast with the hydroxides of the albdi metals, (hi
very readily hmes the elements of water and pusses into thallous «xi<4
or TljO, which is black-brown in colour. The dehydration lakes yiM
even at the teniperattire of the boiling water, so that on evaporating I
solution of the hydroxide on the watcjr-bath, black-browni line* ««
formed at the edges, but these inuiiediiitely disapiwar when the hqiil
is passed over them.

606. Thallous Sulphate, Tl^SO^, crystalliBcs !udiydrou.s in M
rhombic forms of pi>ta.?aiuni snlphiiti*, with wiiich it is isomorplioui
It is fairly soluijle in water. AVith the sulphates of the triviilenl
metals, also, it fornis' doulile salts which crystallise in regular fnna^
and are perfectly analogous to the altims ol' the alkali metals. It (Ml
also form tlie corresponding inonoclinic dnnble sjilta with the divalcM
sulphates of the vitriol series.

697. Thallous Nitrate, TING.,, also eiyatallises anliyiirous; i
18 soluble in about ten times its weight of water at room temperatnrti
and melts at 205 . By mixing it with other nitrates, masses ojin hi
obtained which molt at a comparatively low teniperaiure ; these fini
application sis heavy liijiiids (jiolid thaliou.s nitrate has the density S''(

(J98. Thallium Carbonate, TI.,CO.,, is an anhydrous 6i»li wind

dissolves in twenty times its weight of water, yielding a lif|nid wis

an alkaline reaction. The &alt tiissolvea more readily in water cob

i tainiug excess of carbonic acid, but the acid carbonatti is not knu»1

with certainty in the solid state.

THALUUM

TOI

i« photpkatet mad haniet at monotkillioo »n abo aohible in
; so that in Uw respect also tluUium is aUi«d to tbe alkati
letals.

6'J9. Thallons Salpbida 1\S, is a browThblack predpitiite vhkb
lsf(irtut«(i liy irulphuretted hvcJro»«ii lu lU'UtnU, but not in acid si>liitioas
fit th.-illotis suits. Tbe soiuhility and therefore sdso tbe oimlitiiHK ol
]X(<cipitation &ro most nearly akiii to those of tine sitlphkie, attltoi^gk
(lulloiis sulphide iippears to be somewhat more soluble. A«CQniil>glT',
thfl precipitjvtefl sulphide redisisoh es in dilute acids.

700. Thallons CMoride. — In it^ halogim compounds thalUum ia
mmt closcl>' allie«l to silver, for these substiinccs are white i*r y^low
diliit'iiitly soluble powders which are sensitive to light ; their sulubtHtJ
-)J* iliiniiiisJics with increasing combining weight of the hidngeu.

Thrillous chioridt*, TICI, is obtained as a white preeipitJite whii-h
►Inwiy darkens in the light, when the ions of the sail ctmie logetlier

in solution. AlK>tn three btmdred times its weight of water is
mjiiired to dissolve it.

It lA iui;ohible in ammonia, but dissolves in sixliiim tbiosulphate

with fomiiition of a comfdex tonipuund. It exhibits no tendemy lo

funn toniple.v compounds with soluble ehioritles ; the salt is therefore

|ioM>ipii;tied from atpieous solutions on the addition of hydroehturie

ttiil or chlrirides, owing to the increase of chloridion. It is converte<l

illfl soluble thallic chloride by treatment with chlorine under watvr.

I Till. ThalloQS Bromide is a yellow-white prwipit^ite. the solu-

iWlity of which is considerably less than that of the chloride, to which,

Hfcrer, m it* either pdiportics it is simitar.

^h02. TballotlS Iodide is depositeil lis a yellow precipitate even
i fcoo very dilute solutions, when its ions come together. It retpiii-es
la.OfK) part« of water for its sohition. and. for known r^isona, it is
«ill less soluble in n Wution «f pottis-siuni ioflidc This salt is
'employed for the detection and sepiu-iiiicvn of thallium. In dilut* acids
Itiinot appreciiibly more soluble than in [inre water, as it is tht' salt
•>! Ibtf strong hydriwlic iicid (p. 41I'!').

(•.>.3. Thalious Fluoride is, in eoutrast with the other iiiilugoii
«m()ounds, a readily soluble salt.

The irivaleru, frithnUkm is of a somewhat yellowish colour, anni niortothailion only by fairly strong oxidising agents, such
»• clitnriiie m iierniangjinate. Cfinversely, it very rejMiily pia-scs a^iiii
'iit<Jiaonothallian.

*"4. ThftUiC Hydroxide is obtained as a liinwn precipitntv Hiniilar
•n apjHsirutiee to ferric uxide, o(j aflding suluble bases Ui n ihallic salt.
On being dried it assumes the conifKisitton TIO(OH); the fri'shly
pwcipitated substance is pmbably Tl(UH)j,. On being healcid, t!io
Mroxide loses water and readily also oxygen, so that it {MinMes iiiUi
'Mloiw oxi(b\ Thallic oxide, Tl^O.,, is also (ibtained when mibtlions
subjected to electi'olysis ; it sepHrati» <tt't i ,1ie

702 PRINCIPLES OF INORGANIC CHEMISTRY CH. xxx;i

anode as a black coating, but it is difficult to obtain it of a, definite
composition.

Thallic hydroxide is a very weak base ; its salts are greatly
hydrolysed in aqueous solution, and when the dilution is fairly
great almost all the hydroxide is precipitated from it, the acid
remaining in solution. The most stable is the chloride, which can
be obtained from the sub-chloride by means of chlorine. The bromide
is less stable, and on attempting to prepare the iodide a mixture of
thallous iodide and free iodine is obtained.

705. Thallic Sulphate, Tl2(S04)3, can form alums with the alkali
sulphates. The double salt from thallous sulphate and thallic sul-
phate, which should also yield an alum, has, however, another form
and a different amount of water of crystallisation ; its composition is
Tl . T1(S0^)2 . 6H2O, in which the one Tl is monovalent and the other
trivalent.

The combining weight of thallium is Tl = 204"1.

'•"" General. — For thi^ purposes of analysis, bismuth is cIhsijcH along
nth rbc metals of the copper group, boeauso it forms a sulphMle which
I in&olttlile in iHhite acids »4 well us in alkali sulpliidcs. Atcnnting to
te chemiciil ■■iffijiitv% howcv^jr, it is sy closely connectol with antimoriy
Ind »rB«mic, whifh l>eloiig to the last group, that it must he treated
|on^ with those, and ia therefore suitably placed at the |)oint of
^musicioii from the otie group to the other. Of these elenionta it
las the highest comhining weight ; for this reason, in accordance
Hth tKp giTieral mle, the basic properties are mwe atrnrif^ly naarkcd
D it than iet the (>ase of its congeners. As the cnnibiiiing weight
iBcresBes, the latter rapidly ]o.% their metalHi- ohanicter and tbe
mrer of f<jmiin<,' basic oxides, and finally lead to the iion-nietjitlic
llcnients phospliorus and nitrogen, in which the acid forming pro-

Ciee ttre completely develu])ed.
Mtialik bi-imttth is a white, somewhat reddish metal of & well-
ked crystalline chiU-aLter : it is brittle, is not ductile, and falla
Id a powiler when struuk H'ith a hammer. It melts aa low as 270',

£Hl a bright white heat passes into a v.ipour, the density of which
to the molar weight 'JO'S, which coincides with the combitmig
_ht. It remains unchanged in the air, aitd is also very resisUint
^ water. It is not attacked by dilute acids ; iU position in the
^cenlial series is between copper and silver, and it therefore inclines
inwards the noble metals. It therefore occurs in nature in many caaea
Met! in the unromhin'''i utate ; it al^i occurs crimbtned with sulphur
tjnuth rthtnrt. Bismuth is readily dissolved by nitric acid with
Uion of bismuth nitrate and nitrous oxide.

{ismuth readily forma alloys with other metals whereby, in

jiee with th« general law, the melting point flinka. By

adidilion of tear], tin. and cadmium, alloys are obtained

3ch liquefy even tinder 1(J0 ; they fuse therefore in boiling

prater.

The combining weight of bismuth has been determined by weighing

703

704

PRINCIPLES OF INORGANIC CHEMISTRY

fUJ

the TOetal and the oxide obtained from it. It is not known wil
perfect cerUiirrtv, and we shall t»ike it as Bi = 208'5.

"07. Bismutllioil, — Bismuth forms one kind of elemt'titary in
viz. the trivah'iit liisiniiLliioti, Bi". This is almost the only inn deriv(
from hisniuth, for the teiulency of this? ttiotd.! ti> form <"ompi«xe.i ,
oxtremelj slight, and with the exception of sotHe orgatjie ions ic
taining bismuth, othera are searcety known.

Bi-smuthioii is coloiirlcBs and forms an extremely weak '«r*' vr\
hydroxyl. As a consequence, th« phennmenuii of fn/ilntltin^ a
nifirked in the wise of thu bismuth snlt« that it citn In; regiirded
a characteristic in Jiniilynia. Si net- the basic corapoimdi* wbirt n
hert'by furmod are dithcnltly solnble in water, the- bifiinuth siilr* iif
jirmfihifnt Ity mere dilution with wattT ; the prt>ci[i]i,iitc is agai
disstjlvetl on tlie addition of acids.

The host known bismuth salt ii? the nHroU, whifh is obtAiiiffl fl
hydnited crystals, Bi(NO.,)., . 5H(,(), by cryslalli.siition from th*' soliin
of bismuth in nitrjf acid. On pouring water over these crysuli
a snow-wliite, crystalline, powder of a basic nitrate?, Bi(OH},N(L
deposited, which i,^ a[)plicd in medicine under thw luiine of l/urm
}tttJiuih-tfti\ The nitric acid which is split off passes into ibe solutii
ami enables another portion of the bismuth salt to remain diagolvfid
There exist*!, therefore, in the solution in respect of the precipiui
of the basic salt, an eijuilibrium which is characterised by I he fact tlul
the concentration of the hydroxyl from th<.' wal<T is reii'ierod snfficK'tiiij!
small by means of the hydrion of the free acid to allow the soiulnlitj
product of the basic SJilt to be rejiclied.

From solutions, bismuth hydroxide, Bi{OH)^, is prccipilau'd h)
excess of soluble bases. It is a. white preeipiiate which is wiliibh
neither in ammonia nor m caustic pota-sh. The fornier b(;liavi«iiii
due to the extremely slight development of its basic pi-oportiiJi; tin
latter shows that it cannot, as many other weak bases do, split n
hydrion and yield an anion containing oxygen.

On beiu!? heated, the hydroxide loses water and is converted \M
bismuth oxide, Bi,0,(, a yellow powder which, at a higher ttiroporatuMi
becomes reddi.sh->irown, melts, and Incomes crystalline on cixiling.

Jiij^i/iulh >-uf}>hiilr, BijiSO^),,, is obtained in the impure stat* If
heating bismuth with conceritratJjd .sidphurk jicid ; treatment with ffsLtf
converts it into the difficultly soluble baaic sulphate Hi„(OH)j(S0^Jt
With potassium snlph.^te it forms a well characterised double taili
KBi{SO^).j.

When >»iffiniii thiiixiilpholf is addetl to bisnnith salts, a clear liqni*

18 formed from which, owing to docom[M>sition, bismuth sulphide i»

slowly de]>osited. The anliition proliably contains the siKlium salt '»

a bismuth tbinsulphanion, for on the addition of potiissium salta aJiJ

Icohul a ditticultly soluble precipitate of KjBi(S„njj)jj - H,,CI i^

rdeposited, which is the potassitmi salt of the above ion. It has t**"

BISMUTH

705

oetnl to employ the pi-etipitatc, which is of a yellow colour, for
leleelioii ami Bcpur.itiorj of potassium.

E>8. Bismuth Chloride, BiClj, is very readily formed from
th and free cbloritie, tho combination taking place with con-
ab!e evoltition of heat. It is a white, soft, fmt cryitalliiie subslancal
h Ijcconiea very dark in colour throngh excess of bismuth ; thia
;« to the formation of a lower chloiiiio compound, perhaps BiCJ,
BgEi no such Bubatance hws been prepared in the pure atjite, With
t, tlie chloride at otice deposits a snow-white precipitate of basic
ide, or riitlier, the anhydi'ide of this, bisimdh myrld^irid*^, BtOCl.

ribatanee has a certain similarity to the monovalent chlorides of
and mercury, not only as regarrls if^ external a]Fpcarai:ice and
ifficult solubility, but also in its property of becoming grey in light.
linence can be girtn gnipliieally to this similarity by aastiming in
d iti the similar compoumls of bismuth, the mutio\'iilent ion
'hicb has beon called, bistttidhjl, Thia is, howuvor, so far, ouly
d aasuuiption, since there ia as yet no proof of the existence of
ID ion in th« solution.
rmuih luijchhridt', BiOCl, is bo dilHcultly soluble in water that it
employed for the precipitation of bismuth. J^or that purpose
Only necesairy to iutroduce chloridion in some form into the
)ii and thou to <lihtte tljis. The dilution must bo ao much the
r the moie highly acid the ]i(jmd was at the commencement; it
lisable, tlierefure, when employing this method, to remove the
of acid by means of a base.

le bromiilt' of bismuth is very similar to the chloride, and forma
very difficultly soluble lUijhroiiiuk of a white coloui-.
tmuih wii'ic is obtained from the elements or by the preeipita-
l bieniuth uilta with a largt^: excess of potassium iodide, and is a
red crystalline substance which in decomposed by water much
idowly than the other halogen compounds. With mucli wat«r
bill oxyiijdide is formed as a fine red powder,
tisuuiih iodide dissoivea in hydriodic acid and forms hydi*obi8-

liodic acid, HBiL

411^0.

W'ith the iodides of the alkali metals

lalts of this acid are obtained ; of these the potassium salt, KBil^,
lowTi in the form of ruby-red laminre. The complex hydrobia-']
ItodidioD, Bil^', is, however, only slightly stable, and with much
I decomposes into bismuth oxyiodide and free hydriodic acid.
*0&. Bismuth Sulphide, Bi„8,, in obtained as a black -brown
sitate on piuisijig svdphii retted hydrogen into bismuth solutiona.
IkObtained crystallitie by fusing mcUdlic bismuth with sulphur;
suth sulphide which is formed dissoivea in the metal and, on
separates out in clusters. It occui's in nature as bismuth
and 13 naed for the preparation of bismuth, which is obtained
lie glance by roasting and rednttion of the oxide formed with

1-L

706 PRINCIPLES OF INORGANIC CJ-TR^nSTRY ca. x

Bismuth sulphide is insoluljle in dilute acjds, but dissolves with
evolution of sulphuretted hydrogen on Ijeing heated with concetitniu^l
hycliochlorif acid. It is not appreciably soluble in alkali sulpliiiki, a
beiiiiviour which is opposed to that of the aulplxur compounds <if iit
nearest congeners, antimony and arsenic. By fusing tuj^etlitT liismutb
sulphide and alkali sulphides, however, fine crystwlline coniiiouiids
KBiS, and NaBiS.,, having a metallic lustre, can be obtainorj ; tiicisf,
however, j'apidly oxidise in the air.

710. Other Compounds. — It was mentioued above that a lowtr
chloride of bismuth probably exists, although it is' not known as a pu«
substance. The existence oF a corresponding oxygen compound, BiO,
has also been asserted. It is obtained as a dark hrovin powder W lb*
careful treatment of bismuth hydroxide with reducing substances or
by heating basic bismuth oxalate.

A higher oxide of bismuth, hwavth pniimuk, Bij(!)., ie obtiiiiiifd'
by heating the hydroxide with istroug oxidising agents. Further, i
mixture of bismuth oxide and caustic potash or soda when fused in
the air is oxidised to a brown mass winch, «n being treated ititli
water, deposits bismuth pentoxide contaminateii inth ulkjdi. In tli#
brown melt there possibly exists the alkali salt of a bisniuthic »ci<l
in JKj^ueuus solution, however, such salts cannot be obtained, as tliff
are immedijitely hydrolyaed. Bismuth pentoxide la obt;iinn] iis a
heavy, brown powder or as a hydrate of a red colour ; it is iiisolublt
in acids and liiises, and is converted by hydrochloric acid into tit
tricWoride, with evolution of chlorine.

ClIAPTEK XXXVIII

ANTIMONY

'11. General. — With anlimony we commence the consider.itiou of
be mcLals of the tin groU]>, in which a iiiimber of oleuients ure classed
Ogetber belonging to different natural families and forming corre-
ponding sul>groups. Their coramon characteriatie is the predom^inat.
Bg tendency to form nctW compounds in place of the biisit; ones yielded
iy liio other metals. Tbeit* oxides, espctiially those comparatively
tch in oxygen, l)ehave as the anhydridt-a o!' acids, and tlieir sulphur
ompotinds dissolve in the solutions of the alkali sulphides with
Drmation of th\o-sa(U {ride in/m). The 3ast characteristic which is
i importance in analytical chemistry has given rise to the fonisation
I the whole group, and the relations which are here met with will be
ireBently discussed in gi-eater dotjiil.

On account of the manifold and widely extending affinity relations
OEUiing Iwtween the elements, we shall repeatedly iind resemblances
to otber groups, and it would be possible to class several of the
lloaents considered here along with othei^s previously discussed. By
Msoo, however, of the variety of the relationships, a system of the
^lemeuts, sufficient in all respects, cannot be framed, and the arrange-
B«nfr which has here been retained has therefore been dotenained
iiefly by didactic considerations.

712. Antimooy. — Antimony is allied on the one band to bhinuth,
tad on the other, to arsfjik and pfio.fphorus. It therefore forms a
itutsition eletoent between the metals and the non-metals, but is atill
i^entially on the aide of the metale. Its combining weight is
a>= 120-2.

AtUimwif is A groy-white, lustrous metal, having the density 6-? ;
Wn the fused mass it solidifies in a distinctly crystalline form, and is
tt &11 temperatures so brittle that it can be easily gi-ound or pounded
^ ft powder. It melts at a redheat, and voktihses at a high tempera-
Ltire. The va]K>ur exhibits a variable molar weight in the neighbour-
jtoodcif 290, This number corresponds to no simple formula, but ties

leea Sb^ and Sb^ ; proltably, therefore, we are dealing with a
djfferent kinds of vapour, perhaps Sb^ and Sb.

PRINCIPLES OF INORGAmC CHEMISTRY d

Iti the iKjU'ivtial series antimony stonds beside bismuth ; it (
not, therefore, doconiposo diluto ;teids, and it also remains unchai
in the air. On being heated it readily oxidises ; a piece of antim
fused on charcoal before the blowpipe, continues to glow eren i
the flame has been removed, the antimony bnrning to antimony oi
If a small globe of strongly heated antimony is. thrown on a |
of paper witli npturned edges, it skips alwiit on this, burnitij
ihe while, and leaves very regularly marked, bvperbolic I
(Fig. V23}.

Besides the ordinary antimony, an aUotmpic fnrm of Icsa stabili

known, which is obtained as a silver-white metal, of densitj' 5'78
slowly decomposing a coiicetitrated solniion of antimony chlorid
hydrochloric acid with the electric current. The meud whia
deposited falls to a powder with alight explosion on being scrati
by a Bharp body, ordinary grey antimony being formed with
siderablo evolution of heat. This allotropic metal is not pure^
contains antimony chloride, the amount of which varies wilbj
conditions of the experiment. 1

713. Ions of Antimony.— Aiitimony can form coinpaumlj:
the trivalent and of the pentavaleiit typo ; only the former of tlj
however, yields a ha.<u- hidtojide, while the hydroxiiU- of the
tj'pe is an niyacid. They each show the basic and acid chs

A]!?TIMONT

709

tiTely only in a alight degTee^ and the number of well-ch&racterised
of antimony ia therefore not large.

~\e compounds of the tri'valent type are the better known and the

stable ; they are the only ones occurring in natiire. The

ounds of the pentavalent type are produced from the former by

ction of strong oridiging agents, and can be readily reduced

it exlstonce of a trivalent antimonlou is probable, since there are
Nations of antimony salts which Itohavc in general like salts. These
Jts, derived from the base antimony liydnrxidr, Sb(OH)j, are, how-
r, greatly hydrolysed in water, and clear solutions can be obtained
ily with a largo excess of acid. Consequently, tht- properties of the
BDt aDtimonion are not known with great exactness, and it can
said with regard to it, that it is colourless and has a yery
iioua action on the organism of the higher animals. In small
itiea it acts as an emetic.

[4. Antimony Hydroxide, SMOH),, is obtained as a white

itttte V>y the hydrolysis of the salts of antimony ; it readily loses

and is converted into the anhydride, antimony oxide Sb,Ojj. It

converted into salt« by treatment with concentrated acids ;

t^da undergo decomposition on dilution with water. It dissolves

jtllralja ; it has therefore the power of splitting off hydrioo

ing AS an acid in a similar manner to alumina. The corre-

g ialt8 arc rertncing agents, and, for example, precipitate silver

metallic stat« from its salts.

timony oxide, Sb,-,Ojp crystallises readily and proves to bo
ihous, crystallising either in regular or in rhombic form. Thd
has the density 5-3, the second, 5-6. It has not yet been
ilJabcd which of the two forms is the more stable : it appears,
kovever, to be the rhombic, since this occura much more abundantly in
Hturc. They aro both, at all events, more stable than the hydroxide,
!inct the latter, even under water, passes into the crystalline oxide,

715. Antimonioas Chloride, or antimony trichloride, SbClj, is
okained from metallic antimoiij' and chlorine by using excess of the
former ; pow<lered antimony takes fire spontaneously on being allowed
lo &11 into chlorine. It is obtained more cheaply by heating antimony
mlphide with concentrated hydrochloric acid, whereby sulphuretted
bydrogen escapes. The aijueous solution is evaporated and distilled,
»!iereu|>oa atdiydrous antimony trichloride passes over. The reraark-
«ble fact that the chloride does not hereby decompose into hydrochloric
wd and antimony oxide, as f.ff. aluminium cbjoride does, although
'ilumina. is a stronger base, is probably due to the fact that in concen-
trated solution antimony trichloride is very slightly dissociated into
jits ions, and therefore undergoes hydrolysis in a correspondingly slight
flegrce.

itimony trichloride is obtained as a white, crystalline, semi-soUd

710

PRINCIPLES OP INORGANIC CHEMISTRY CTUP,

mass [hittier of antimony), which melts readily and boils at 220". U
decomposed by water, difficultly soluble oxychloiides betDg depoalf
the composition of these depends on the »mouiit of water, the m
of chlorine whith they contain being all the lesa the larger the qiuafl
of water

Of these, the compound Sb^CjClo. being a cryatallioc substance,
best characterised, but even it decomjioaes into antimony oxide ti
hydrochloric acid on being treated with more water.

Antimony trichloride combines with hydrochloric acid to hm
complex hjdrcmitiwtmirMiirk and, the salts of which are obtained I
allowing soluble chloriiles and antimony trichloride to ervstalliae t
gether. The composition of these sivlts corresponds to various IJl*
and it has not yet been established whether we are dealing with van
ous complex acids or, partly, with double salts. The most frequci
type is M^SbCl,,, conUiiniiig {irolmbly the trivalent anion SbClf,'".

71G. Antimony Tribromide, SbBr^, is foi-med with great ri
of temperatufc on brJTijjinjj the elements together. In its projKrtii
it is very similar to the trichloride and, like it, dcconif^tses with wni
into basic bromide and free hyilrobromie acid. The boiling point
270^ the melting point 95 .

717, Antimony Tri-iodide, Sbig, is obtained from the elesneai
by warming, and crystidlises in three different forms whose relati
degrees of stability have not yet been determined. Accordinj; to ti
form, the colour of the crystiils is dark red or grecn-yclIow : tJU
melting point of the form, stable at higher temperatures, is lf>7', lb
boiling point, 400' ; the vapour of the tri-iodide is of a fine scarl
colour. With water it decomposes in the same manner as ihe othi
halogen compounds ; the solution containing antimony, which is iherch]!
pi-odiiced, is coloured yellow, from which the ]ireaence of undi8*wii»t«
iodide in the aqueous solution can be concluded. The jTccipitate
oxyiodide is rod to yellow in colour, ftnil the colour is so mttcli til
brighter the smaller the amount of iodine.

Antimony tri-iodide unites with the soluble iodides to fori
complex sidts, which belong chiefly to the typo MSbl^, with the anii

sbi;.

718, Antimony Trifluoride, SVd<^.„ is a wbito mass sitntlur b
the trichloridCf which can be dissolved in water wilho^it the seiorttlicH
of precipitates. This is probably due to very slight electrnlylic dii
sociation of the Huonde. Complex siUta are known with tlie ilkii
fluorides,

719, Antimony Trisulphide.— The compound Rb,K^ occurs il
nature as the most wirlcsjiread ore of antimony, and is called an/iwfilj
glance (or stibriite). It is a grey substance crystallising in long needl
of a metallic lustre ; it readily melts, and on being heated in the aii(
passes into antimony oxide, the stil|ihur being burned.

From solutions of trivalent antimony, the tristdphide is pr»

BISMUTH

705

pLXXVll

^rppoded to employ the precipitate, whJcli is of a yellow colour, for
^e detection iitnl scp^rattoti of potassium.

708. Bismuth Chloride, BiClj, ia vory readily formed from
bismuth and free chlorine, tlie comW nation taking place vnth con-
fciderable evolution of heat. It is a white, soft, but crj'stollJne substance
^'hich bec-omes very dark in colour througk excess of bismuth ; this

Eoints to the formation of a lower chlorine Gomiwund, perhaps BiCI,
Ithough no such substance has been prepared in tlie pure sfene. With
water, the chloride at once deposits a Bnnvv-vvhite precipitate of basic
phloride, or rather, tlio anhydride of this, bismuth ox^chlviid^:, BiOCl.
Fhis substance has a certain simila-nty to the monovalent chlorides of
lilver and mercury, not only as rej^ards its external appiianmee and
ts difficult solubility, but also in its }>roperty of hwotniiig grey in light.
pPromitience can be given graphically to this similarity by assuming in
ihis and in the similar compounds of bismuth, tlie monovalent ion
JiO', which has been called hknmlhijl. This is, however, so fiir, only
H formal aSiSum^ition, since there is as yet no proof of the existence of
luch an ion in the solution.

Bismuth ivitchluridt, lUOCl, is so diflicultly soluble in water that it
iati hfl employed for the precipitation of bismuth. For that purpose
% is only necessary to introduce chloridion in some form into the
lolution and then to dilute this. The dilution must l>e so much the
plater the more hi<;hly acid the liquid was at the commencement; it
8 advtsa!>le, therefore, when emi>loyiug this method, to remove the
(xccsa of acid by means of a base.

The hrmnith of bismuth is very similar to the chloride, and forms
ilso a, very difficultly soluble oxijbromkk of a white coloui*.

Piisinvih imiide is obtained from the elements or by the precipita-
aon of bismuth salts with a large excess of potassium iodide, and is a
>lack-i'cil cryst..illine substiince which is decomposed by water much
nore slowly than the other halogen compounds. With much water
riamuth oxy iodide ia formed as a fine red powder.

Bismuth iodide dissolves in hydriodic acid and forras bydi'obis-
Inuthiodic acid, Hljil^ . 4H.,0. With the iodides of the alkali metals
^e salts of this acid are obtained ; of these the potassium salt, KBil^,
|s known in the form of ruby-red laminae. The complex hydrobia-
(nuthiodidion, BiT/, is, however, only .slightly stable, and with much
ter decomposes into bismuth oxyiodide and free hydriodic acid,

709. Bismuth Sulphide, Uj.JS,^, is obtained as a black-brown
irecipitato on p:issing sulphuretted hydrogen into bifimuth solutions,
t is obtained crystjdline by fusing metallic bismuth with sulphur ;
ihe bismuth sulphide which is formed dissolves in the metal and, on

oling, separates out in chiaters. It occurs in nature as bismuth
nrf, and is used for the preparation of bismuth, which is obtained

El the glance by roasting and reduction of the oxide fori
coal,
,

712 PRINCIPLES OF INORGANIC CHEMISTRY CHAP.

The natural!}' occurring antimony glance is employed for the pn^
jmration uf metallic antimony. The red, amorphous form is used ts a
dye under the name antimony vermilion ; red, vulcanised indiaraWw
IB colonroii with antimony sulphide.

720. Complex Antimony Compounds, — ^Trivalent antimony
has, in a very marked degree, the jiropcrty, already mentioned in ibe
caee of other hydroxides, of forming complex componnds with organic
substances containing several hydroxyl groups. The most important
of these is the compound with titrkirk nriti, which yields an aniimtmffi
hirtaric arid ; U% cotitrast with the ordinary antimony compouuds tbts
compound is not dissociated hj'<lrolytical]y by water, so that it can 1«9
disaoived, and the solution diluted without the separation of bade
aubstancefs. Tlie exact discussion of these compounds nmst bo
reserved for organic ciiemistry ; they have been mentioned here
because tartaric acid is employed in analytical chemistry for the pur-
pose of preparing clear, dilute sohitions of antimony salts. For thia
purpose the ad<lition of a solution of tartaric acid to the h'qtiid »
sufficient. The formation of the complex compound takes place «o
quickly that the desired result is attained in a few moment*. From
Buch solutions antimony sulphide is precipitated by sulphureitcil
hydrogen, showing that the complex yields Bufficicnt antimonion for
the solubility product of antimony triaulphido to be exceeded.

721. Antimony Pentachloride.^By means of oxtdisiag ageiin*
it is possihle to pass from compounds of trivalent to those of pea!»-
valent antimony. If chlorine is passed over antimony trichlorida,
a heax'y liquid which fume.'? in the air ia produced ; this is alw
obtained from antimony and chlorine by using excess of the Isttfr
At 1 40" it commences to boil, and the determination of the vapcnir
density shows that it exists in the vaporous condition for the greBter
part nndecumposed. Chlorine is, however, verj' readily split off, aii<i
even when the boiling is continued, so much of it escapes that ttei*
remains a cmisiderable residue of trichloride. On the whole, therefore,
the compound behaves similarly to phosphorus pentachloride (p. 3CU
but is somewhat more stable.

Antimony pentachloride uiates with water and forms variou*
hydrates which, however, are formed only when a smalt quantity of
water is used, clear solutions being then produced ; when dissolved in
much water, it nndergoe.<j complete hydrolysis, anrl flithcnltly soluUe
antimonic acid is deposited. It combines with liydtochhiric acid to
form a fairly stable, crystallitie substance, which dissolves witlioul
decomposition in a small quantity of water, and has th«) compt>8ition
HjSbCl^^ . lOH.O.

An antimony jwntabromide is not known ; the existence of th»
pentaiodide is also doubtfrd.

722. Antimonic Acid. ^Antimonic acid, Sb(Olf),., or its uuhy-
drides, is obtained by the decomposition of antimony pentacldoriJt

ANTIMONY

L ipitatecl by sulpiiiu'etted hydrogen as a yollow-rec!, non-erjstalline
H^^^etance which, on being gently heated, pisses into grey, crystalline
|Bl^xiiony sulphide. Conversely, when fused atihnite is <]uickiy cooled,
^Sn amorphous mass is obtained which is translucent, and of a dark-red

tolour, and becomes yellow-red on being powdered. The relation
l^hich here exists is therefore similar to that between amorphous and
rsryetalline sulphur, the amoriihous form Iteing the less stiblo : the

velocity of transformation, however, at the ordinary temperature is so
L small that it cannot be observed.
I. Antiinony sulphide is not appreciably soluble in dilute acids ; it

dissolvea in strong hj'drochloric acid with evolution of sulphuretted

hydrogen. For this reason antimony is precipitated by Bulphtiretted

f hydrogen from add sohitSon, provided that the solution is dilute with

Srespect to the acid. When antimony sulphide has been brought into

'solution with concentrated hydrochloric acid, and if the li«juid which

'contains sulphuretted hydrogen is diluted, a precipitate of yellow-red

I antimony sidphide is obtained. The remarkable phenomenon that a

• precipitate (not due to hydrolysis) is prodiiced by dilution with water,

"is e.xplavned by the fact that the antimony trichloride present in con-

|ceiitrated solution contains the antimony almost entirely in the form

of an undissociated compound (p. 709) ; the antimonion necessary

for the reaction with the sulphuretted hydrogen is formed only on

dilution.

Antimony sulphide readily dissolves in the alkali sulphides, especially
the polysulphides. A compound of the penfciivalcnt series is thereby
formed, when excess of sulphur is present, atul the reaction will he
discussed later in greater detail.

Antimony sulphide also dissolves in concentrated and hot solutions

of the alkali hydro-^ides and carbonates; on cooling and diluting, it is

again precipitated as a brown poivder. This precipitate was formerly

applied in medicine under the name kerrrns ; since, however, it is a

variable mixture of amorphous antimony sulphide and antimony

I oxide, its medicinal action varies according to the method of its pre-

I paration. The reaction which here occurs has not yet been sufficiently

I explained ; we are dealing essentially with the formation of the alkali

I salts of antimony oxide (p. 709), and of the corresponding compounds

1 of antimony sulphide, which are stable in hot, concentrated solution,

whereas on cooling and on dilution, the equilibrium is again shifted in

the opposite sense, Le. antimony sulphide is again formed.

Use is made of the precipitation of the antimony compounds
by sulphuretted hydrogen for the detection and estimation of
antimony. Since the amorphous precipitate, even after being dried
at 100°, still contains appreciable quantities of water, it is, in quanti-
tative estimations, converted by careful heating in an atmospbert
free from oxygen {in a current of carbon dioxide), into the grey,
crystalline form which is of constant composition.

714

PRINCIPLES OF INOEGANTC CHEMISTKY ciur.

acid, but contains sulphur in place of oxygen. We bare ulrasdv
(p. 418) met with such a compound in the case of thiocarboiiic aciii
and the relationships ivhich are found were explained there.

In the case of the metals grouped together in the present clu,
the formations of such thio-ions is a general phenomenon, aad tie
BoluhiHty of their sulphides in alkali sulphides is due to the formation
of 8ohible alkali salts of svich thio-ions.

As ill the case of the oxj^acids, the higher compounds, i.t. thow
richei" in sulphur, have the more strongly acid character. For ihi*
reason, antimony trisnlphide is only very slightly snlulile in iho dilal*
solutions of the alkali wc/idsnljiliidos, but is readily eoluble in the
yellow solutions which contain ^Wysulphidea. In the former eaus a
salt of thioantimonosion, ShS^'", would be formed ; such an ion, how-
ever, does not enat, and the saline compounds con'es[joiiding to it
which are formed to a eertiiin extent in concentrated soIntiooB, it*
decomposed by water. The salt^ of thioantimoiiic acid, however, *«
very sUible, and theas are immediately formed when the neoMSMj
sulphur Ciin lie obtained from the polysulphide present

Free thioantimonic acid, HjSbS^, is not known. If hjdrion ii
introduced into the solution of one of its salts, sulphuretted hydrogen
and antimony pentasulphide are formed: 2H.,Sb}^^ = BlvS^ + 3H^
The ])roce$a corfesponds exactly to the formation of an aiihydride witb
separation of water, the place of water being taken liy sulphuretted
hyilroj^en in the case of the thio-ricid.

The nntimmy pentasulpkuh which eati be obtained in this w»y ii
very similar to the amorphous trisulphido as far as external appeannc*
is concerned. It readily decomposes into trisulphide and sulphttr, w
that amounts of sulphur varying with the previous treatment can b«
extracted from the product with carlMii disulphide. It is soluble no*
only in the monosulplndes of the alkaji metals, but also in tht
hydroxides ; in the latter case, antiraonato is formed iJi the solution
along with thioantimonate, or, the salts of an antimouje acid in whiek
only a part of the oxygen is replaced by sulphur are formed. It
dissolves even in the alkah' carbonates, although with sotue«b»t
gresiter difficulty. The pentasulphide obt-ained by precipit«ition froi
Schlippe's salt is employed in medicine under the name "jWJa
sxdphur of anfimii-nif."

The solutions of the thioaiilimonates mostly give precipitates witll
the salts of the hea\y metals which are practically insoluble in wawt
and are coloured yellow, red, or black. These compounds are liiki
Schlippe's salt — salt-like coinpouods of trivalent thiotmtiraonanion.

724. Antimony Hydride. ^ — The relationship of antimony M
nitrogen and phosphorua is seen with especial clearness in its poff*
of forming a gaseous compound with hydrogen, SbH^, whicii,
regards its composition, belongs to the same type as ammonia i
phosphoretted hydrogen. This compound, certainly, has uo bi

ANTIMOHY

^properties, but this constitutes no essential difl'erence, since these are
Ifpraetically ^ya^tillg even in the case of phosphorctted hydrogen,
b j^lnliiimir/ hjdrUk, SbH.„ is obtained hy the action of acids on.
ki&Uoys of antimony \rith other inetals which decompose acids, especially
httinc. In this way the antimony hydride is always obtained mixed
iiwith much hydrogen. It can ba separated from t!)c mixture by
strongly cooUng, but on volatilising the separated mass, it very
^readily decomposes and can Ijc preserved for some hovirs only l>y
feniployiiig special precautions, Its smell recalls that of hydrogen
Isulpliide.

I If. the mixture is passed through a glass tube heated at one pert,
the antimony hydride docoinposea at thiit spot, and metallic antimony
is deposited as a grey-black coating, which, on being heated, runs
together into drops, but cannot be rejuJily volatilised. It differs in
this respect from the "araeinc mirror," which is formed uiidor similar
conditions, and with which it could be confused. Further differences
will be given tinder arsenic.

; Antimony hydride bums with a white flame ; if a piece of
porcelain is held in this, unburnt antimony is deposited on it as a
bUck soot, which is converted at the edges into white, floury-looking
'antimony oxide. The antimony stains can be teiulily dietingnished
from the arsenic stains formed under similar conditioisa, by their grey
'(not brown) colour.

i In a solution of silver nitrate antimony hydride produces a black
[precipitate which oonUiins silver and all the antimony, so that the
Bolution contains only nitric acid and undecomposed silver nitrate.

725. Alloys of Antimony. -Of the various metallic mixtures
'for which antimony is employed, the most important is that with haif.
lEven fairly small quantitie^s of antimony considerably increase the
halxlrjess of lead, and in chemical manufactures, where the chemical
resistibility of lead is required along with moderately great mechaiucal
resistibility, such alloys, called kard lead, are employed. Tt/pe-m^tal,
also, which, along with a comparatively easy fusibility, must possess a
sufficient hardness and the power of exactly filling out the mould,
insists essentially of lead and antimony. Alloyed with tin, jxntimony
Ids BrUantda metal, which is used for domeatic utensils.

CHAPTER XXXIX

AKSENIC

726. G-eneral. — In accordance with its smaller combining weight,
arsenic deviates still more than antimony from the type of the meuli,
and exhibits greater similarity to the non-metal phosplioius ; at the
same time the tendency to form acid compounds iucrcasos. Id fiwt,
the resemlilaiice of arsenic to phoaphorns is so great that it might also
hare been treated along witb that element among the non-metals.

Kiementary arsenic occurs in various forms, which partly refill
those of phosphorus. The most stable form is a grey, (rysUiilim)
mass with a metidlic lustre. On being heated arsenic dots not fust
but passes, before reaching its melting point, into a brown-yelli**'
vapour. It can lie fused bj' heating under pressure ; it tlien aolitlili**
to a stocl-groy, lustroua mass with a crystalline fracture.

From the vapour density of arsenic the molar weight is found to
be 300; since the combining weight may be taken as 75, arsenic vapour
has the formula As^. In this respect, also, there ts a similarity ^
phos])tiorus (p. ^-57) and a dissJniilarity to the nietjd.s, in the cjise "f
which the molar weight coincides with the combining weight.

If the vapour of arsenic is ipiickly cooled aiiun-piamn imenif is
produced, various kinds of which are known. The most interesting
of these is obtained by very rapid and powerful cooling ; it is yeIlo»,
non-metallic, and is soluble in csirbon diaidphide ; it nupidly undergoc*
oxidation in the air with faint luminescence, and emits a smel! "f
garlic; in short, it is very similar to white phosphorus. To a certain
extent it differs from it in the great velocity of its 8[Kjntaneous tmns-
formation into the more stable form, which is greatly accelerated '>J
ligbt.

At the same time, other kinds of amorphotis arsenic are fonn*di
more especially a velvot-blaclf and a grey variety. All these forms
aie luistable, ami are rapidly converted, especially when warmed, intu
stable, crystalline arsenic, Their formation aflbrds fresh examples of
the principle that the unstable forms are produced before the stable.

That as a rule, only the crystalline form appeon to be formed

7ia

ARSENIC

717

the vapour, is due to the fact that the phosphoras-like arsenic

pr(.>duced changes almost instiintaneousiy into the more stable

Only whfcti the velocity of this change is diminidicd to a

VB.iue by rapid cooling ut a low temperature can the uustabte

first prmluL'cd be observed.

27. Arsenic Trioxide. — ^\'heii arsenic is hented with (icccss of
5n it luniis with a biiilkiiit uUite tliimc, forming an oxygeJi com-
Ito which, in accordance with its conitH>sition iirid ■iiipour density,
ormida As^O^ miist be assi^Tied. For it eontidns 2i piirts of
(II to 75 ijarts of rirsenic, and its vapour density yields thu molar
It 396. Strictly speaking, therefore, this compoinid would have
called arsenic hexo.x:idc, but one hits become aicustotnud to wriie
ominlii As,.O.j, iind to call the substance arsenic trioxtdc. In

Klfe, in which this compound ])lays a certain role, it is called
ic or simply aiyfmc.
c trioxide occurs in various forms. When mannfaclnrcd on
irgc scale it appears in the first instance as a transijarent glass.
I 13 gRuerally coloured alightl}* yellow by traces of impurities,
gliisa is aiiiorplimis arsenic trioxide. On being ke[it some time
■lass Ijccomes milk-white and looks like porcelain ; since this
:e is acceleiated by the moisture in the air, it proceeds from tbe
Ic towards the interior. On breaking a moderately large piece,
fore, which has on all sides assumed a porcelain-like ajipearance,
nel of unchanged glassy substance is frequently found in the
or. The porcelain-like mass is rfr/stnliiii>: arsenic trioxide. Since
a produced spontaneously from the amorphous form, it is the
Hritle of the two, and in accordance with a |;eneral laiv (p. 261)
K&U solvents less soluble than the amorphous fonn. When,
'ore, wat«r is in contact with the two forms the solution which
.lrat«d in respect of the amnrphoiis form will be BUpera;iturated
ipect of the cryatTiUiue form. The amount of the latter will
ore increase from the solution ; this liecome.'s un&ituratal in
(t of the aranr[>hous form, dissolves fresh c|uantitio3 of it, and
Its it fis crystals. This process is continued until all the
ihpas substance is converted into crystalline. This furnishes
i||ktiation of the accelerating influence of inoiatui-e on the
miation (cf, p. 676).

wger crystals of arsenic trioxide are obtained by dissolving the
mce in warm hydrochloric acid. 0[i cooling, it sejiaratcs out
ilowly and forms regidar octahetb'a with a diamond-like lustre.
[onned crj^t-ak can also be obtained by ssubliniation. Arsenic
ie, like metiillic arsenic, also pi.naes in'thout fiision into vapour.

Besides the regidar form of arsenic trio-\ide, a monoclinic, paeudo-
jjc form also exists. Tt occurs (rarely) in nature, and as a mineral
called rhiitiletite. The stability relations of the two crystalline

have not yet been determined.

PRINCIPLES OF INORGANIC CHEMISTRY cmr.

In the manufsicturos, wraenic trioxide is ohtaineil hy roastuij
arsenical oros. The trioxide is coUectod hy Icadinjj; the vapoiin
produced through chambors and paasagea of mjisonrj', in whicb the
trioxide is deposited i\s a powder known as "jmsim-jfifur." Thia it
pin-ififd hy resublinjjitioii from iron pots having cylinders placed over
them, and is thereby obtiiined ii» the glassy form-
Arsenic trioxide is only spjiringly soluble in wat^r. On placinj
the powder in water it is not wetted, and owing to the surface tension,
it remiiins floatitig on the water although ita density is 'il. Thi- lirat
of formation of tho trioxide AsjO^ is 647 i-j.

Arsenic trioxide rcmiily loses oxygen. In ordt-r ttj shuw ifii», ii'
small glass tube is dniwn out to a point, and fused off; a iwirticle of
arsenic trioxide is tlieJi placed in the point, ami alwve it a small piwc
of freshly ignited wood-charcoal. If the tu'>e is so healed tlrat tbo
chai'coal is tii'st caused to glow anil then the ai-senic trioxide ^olaliliNil,
the Jattei' loses its oxygen in conuiut witli the eharcoal, and the lificraled
arsenic is de|)08ited as a black coating on the coUler portions vi the
tube, This " arsenic mir/w " can be easily rocognist'd by it^J feebly
metidlic lustre and the brown colour which it shows in thin layers liy
transmitted lij;ht. By meana of this experiment very small (t»aiitili»
of the trioxide can he detected mth certainty.

■tt^en grcnitly diluted, arsenic trioxide is naod as a medicameaL
lb is remarkable, also, that the organism of man and the onimaU c&n
gradually become accustomed to large quantities of arsenic. By meaa*
of it horses acquire n healthy and spirited appearance, and arsenic
eaters also assert that they can undergo much more iKxJiJy t-xertion
under the influence of this substance. The organism accustomed to
arsenic, however, rapidly decays %*'hen the use of this suljsianoc i*
interrupted, and it tan be kept in an active condition only by reg«l«
or increased doses of the poison.

728. Arseaious Acid. — The aqueous solution of arsenic Irioxid*
has a feebly Jicid reiiction, anil eontains an acid which is formed from
the trioxide by the atldition of the elements of water. A decomposi-
tion takes place in the process, so that the acid cont^iins only one
combining weight of arsenic. , \\'hich of the two hydrates HjA^O, and
HAsO^ prcdaiDinales in the solution (for we must assume that both are
present, although in very varying amount) is unkno'v^Ti ; at all eventa,
the acid present in the solution behaves as a feeble monobasic ucid,
and the formula HAsO^, with the ions H' and AsOg', mil therefore I*
the most appropriate representation of the facts.

The electrolytic dissociation of arscnious acid is extremely sin*ll'.
its soluble salts are therefore dissociated hydrolytically to an appreci-
able extent, and the alkali salts, more especially, have an alkalin*
reaction. The salts of the other metals correspond to the ortho»ci<l
HgASjO^ and are mostly very slightly soluble in water. This is tru«
more esjwcially for the ferric salt, so that freshly precipitated ferric

ARSENIC

T19

rdroxlde by combining with the arsenious acirl can be iiscd as an
fective antidote in cases of poi§oiiiiig with this substonce. The
►pper salt ia green, and is omployetl as a colouring matt(T (^Sflwele'n
een). With copper acetate, co[)per araenite forma it double salt of a
illiaat green colour, which is applied under the name Schnrinjurttr
ten. On account of their coritaitdng arsenic, both siilistancee are
Uigerous, and their use for articles of daily use, and more especially
K> in WHll-paf.»ers, must by all means be excluded.

729. Arseaic Trichloride. — In a current of chlonne, arsenic
iims without external application of heat and forms a colourless,
E»vy liquid (density 2'2), which boits at lZi% and whose vapour
ields the molar weight IS'2. The latter rmmber forms the chief
iuon for assigning to arsenic the coral>ining weight 75. and to its
blonde the formula AsClj, for 7.'i is the smallest weight of arsenic
Rorring in a mole of any volatile arsenic compound.

Arsetiic trichloride can also be obtained by pouring sulphuric acid
Ter arsenic trioiide and ;idding pieces of rock salt. By the action of
be sulphuric acifl on the sodium chloride, hydrochloric acid is formed,
™1 lbi.s acts on the arsenic trioxide according to the eijuation
bjO, -!- 12HC1 = -iAsCl, + 6H/). Since, on the other band, arsenic
riehloridc is partially converted by water into trioxido and hydrochloric
.rid, the methofi ia successful only when a large excess of concentrated
rtjlphurie acid is employed whereby the water produced is bound.

A chemical etiiiilibrium, which depends on the concentration of
:liefour substances, exists between water, arsenic trichloride, hydrogen
sliloride, and arsenic trioxtde. An increase of the water promotes the

felllpoaicion of the trichloride ; an increase of hydrogen chloride, its
tniaiion. That ordinaiy aijueous hydrochloric acid also converts
pvt of the trioxide into chlnride, is seen from the increased solubility
of the trioxide in concentrated hydrochloric acid as cotnpared with
that in water ; the excess is dissohcd us chloride.

The presence of the chloj'ide in the hydrochloric acid solution ia
•fe) mule evident from the fact that on distillation an arsenical
distillate is obtained. Since arsenic trioxide or arsenious acid ia not
voktile under these conditions, the arsenic can jiass into the distillate
only in the form of volatile trichloride. This behaviour is of iniport-
•He for the treatment of araenical substances in analysis. Solutions
Pttnining arsenious acid and hydrochloric acid cannot be evaporated
Without a danger of loss of araanic.

* In order to avoid this we may either make the liquid alkaline
Mlore evaporating it, or the ar.scnious acid may be converted by an
oxidising .tgent into arsenic acid. A solution of the latter can be
t'Tipofated without lo&s even when strongly acidified with hydro-
fbloric acid. For arsenic does not form any pentachloride corre-
'{•onding to arsenic acid, nor any other volatile chlorine compound
''cilcnigiog to this atage of oxidation.

720

PEINCIPLES OF INORGANIC CHEMISTRl"

* The above gives a means of purifying sulphuric acid cont
sirseiiic. The arsenic is reduced to arsenious acid (if it ia not air
in this condition), and hydrogen chloride is passed through the be
acid; the arsenic is thDii volaliliaed as the trichloridtj.

* Conversely, hydrochloric acid can be freed from arseuic byj
oxidising the latter to iirsenic add and distilling the acid. Th»|
arsenic remains in th« residues.

Arstniic forms eimilar compounds with bromine and iixjinnj
AsBr^ and Aal^ j these have a higher boiliTig [toint and meltinjj pojiiu
At room temperature they are both solid ; the bromide me]ts at 'iJ'j
and boils at 220" ; the melting point and boiling point of the todid
are not defiiiitoly known, but they arc both higher than in the cas*o|l
the bromide.

The compounds are obtained by bringing together the
elements ; this is beat done under carbon disuli)hide, which aa
then be removed by eviiporatioii. The bromide is colourles*, tha
iodide red. Like the fhUttUh, both componnds are decomposed Ifl
water; the relative amount of the portion dissolving without dKOjn-l
position is not known. Tlic heats of formation are: AsCl^ ■i29ij;|
,\sBr.j. 18S lj\ Asl;j, 53 //.

730. Arsenic Trisulphide. — Arsenic trisulphide, Aa^S,, cor
s^ionding to the trioxide, occunj in nature. It forms yellow crysulll
with a slight raetiiUic histre ; on being gronnd it yields a brigktl
lustrous powder, which was formerly used as a pigment. To thi«i
name w/f/wn', the Tuineralogical name for arsenic trisulphide, is da*!
In older writings it is also <jftc.n calKnl fittidarui: Areenic iri»ul|>hii3»
is obtained as a sulphur-yollow powder, practically insoluble in walerj
Ijy precipitating acid solutions of arsenious acid with sulphnrettf
hydrogen. Since this is the way in which argenic is ordinarilfj
sopirated in analytical operations, it is important to know the
properties of arsenic trisulphide.

(Jn treating a dilute solution of arsenious acid in pure water will
sulphuretted hydrogen, the smell of the gas dis^tppoars ; no pretipitaa
is formed, but the solution botomcs yellow. If a cone of converg
light rays is allowed to fall on the liquid, the path of the ligSi^
becomes bright, owing to difi'nsion. This fact (and the polari*
condition of the ditrused light) shows that the arsenic trisulphide ill
the liquid is not really in solution, but is in suspension in a state <
very fine division. The particles are, however, so amaJl that they i
neither visible under the microscope nor are retained by filter pap
Their size is of the order of a wave-length of light.

If some hydrochloric acid is added to the liquid it becomes lurWd
and in a few moments arsenic trisulphide separates out in vftUo
flakes. Other substances, acids and neutral salts, act in the
manner as hydrochloric acid, and in a way that is fairly independtui
of their chemical nature. Great diflcrences are, however, fo

ARSENIC

ording to the vnlency ; precipitation is caused by a small cou-
eutration of divalent ami by it still Kinaller concentration of trivalent
dons. If the precipitate ia placed as quickly as possible after its
paration on a filter and the acid washed a\vay with pure water, it
Lgaiti pK.rtly piisses into n. liquid as before ; another portion reiiiains
insoluljle. If tlie precipitate is allowed to remain Bome time in the
loltition in which it was formed, it becomes completely insoluble. We
.gain recognise here tite properties of rolhidal soltdimi.^ (p. 427). The
brmation of such colloidal solutions ttikes place Tnoat easily in pure
'»ter. Addition of foreign substances, especially of a saline character
to which free acids and tiasea also belong) cjnises the separation of
he eolloidti! aubstaneea in the form of amorphous flakes. For this
eason the colloidal solution of arsenic tiisiilphide can be obtained
th sulphuretted hydrogen only from a pure solution of arseni-
us aciii. If the solution contaiij. for example, hydrochloric acid
long with the jirsenjous acitl, the arsenic trisulphide is at once formed
a Hoccuient precipitjite on lieing treated with sulphuretted hydrogen.
If the yellow colloidal sohition is kept some time it becomes more
nd more turbid, titu] gradually deposits more and more of the arsenic
irisulphinle as a precipitate. Tbis is also a general property of colloidal
lutiotis ; the ilisiiolvcd substance paaaea in time Bpontaneously into an
iisotuhle form.

The characteristic difference between colloidal solutions and the
,rue solutions, viz. that the former do not exhibit any elevation of
)h6 boiling point nor depresisioti of the freezing point as compared
th pure water {p. 427), is also found in the case of colloidal arsenic
srisulphida

Arsenic trisulphide, not in the colloidal condition, is practically
nsolnble in water and acids ; more especially, it is not attacked by
irly concentrated hydrochloric acid, and thereby differs essentially
rom antimony trisvilphide. It is rearlily oxidised by nitric acid
arsenic acid and sulphuric add. On standing in a moist con-
dition in contact with the oxygen of the air, it is also readily
xidisod.

Arsenic trisulphide is resulily soluble iti alkaline liquids of all
ind.5, caustic alkalis, alkali carbonates, amnionic, and also ammonium
jNrtranate ; it also dissolves in soluble sul])hides and hydrosulphides.
?"arious salts are contained in the solutions according to the solvents
sed ; these may i.»e regarded m arsenites in which some or all of the
omViining weights of oxygen are replaced by sulphur. We are there-
ore dejiHng with tba salts of ihioarsenosion, and the merabera inter-
jaediate hetween tho.se and the salts of arsenioua acid. In the latter
^ase we are dealing with mixtures the njiture of which has not yet
*eea explained. Arsenic trisulphide is again precipitated from ail
hese solutions by the addition of acids.

By means of its snlubility in ammonium carbonate arsenic

3 a

734

PRINCIPLES OF INORGANIC CHEMIRTEY

ClUf.

120". It fiimes strotigly in the air aa it undergoes decompiwiuim
witli water ; it dissolves in water with coijBi<Jeraljle evalittioa of hat,
formiiiy a clear li(|ujd. This atill contains, esj»epially wh<*u tonwu
trated, a ptirtion of the L-ldoride dissolved unt-hangMl, for on doiliui
this jijsses over witli thu steam. 'lliu grefttcflt jwrt is, howovtr.
hj'Jrolytically dissociated, and thu dilute solution contains csicntuilv
hydrochloric acid along with colloidully dissutvod stnnnic bjdroxidt
This is |jroved liy the fact that the solution exhtbita id I the jurojieniw
of a rcirre.-iporidiiigly dilute solution of hydrochloric acid, andalsuliy
tilt' f.act that in coui-ae of time the gieater portion of the tin scpanu*
out KB a wiiite, gelatinous prcci|)iui,te of atinmic hydroxide.

Wiien small quantities of water are allowed U> comltim' willi
Btannic ciiloride, rise of temperature being avoided, various hydrau*
are formed ivith from three to nine moles of watei* of erj-stalliB-
tion, the first of whith is the most stable. They are tr^vstaltifH!
substances which dissolve in water, and jicld solutioue wiiicli esbifnt
the 5nme properties as the solution of the totrachloiide wlit-n jirt^piunl
direetly.

The tetrachloride combinee with hydj'ochloric acid to rum »
hydrfiStannichloric ucid, H^SnClg, which can alwj be obtainc<i in tin
solid state with 6H.,0, The crystals melt as low tis 2B'^'. Tbe acid
forms good crystalline alkali salts, which are also foroie^l froiD tin
tetrachloride and the respective alkali chlorides, The auuuoniuu
salt, (NH^)„ynCljj, crystalliaes anhydrous, and is used iv* a luotdantiu
dyeing tinder tlie name of pinfc salt.

Stiititnc hydroxide, which slowly separates out from the aquwus
solution of atiinrdc chloride, isi immediately obtained by satiiralinw lit
solution with a basa A gelatinous precipitate of Sn(OH)j is formed,
which dissolves in dilute acids ; from these solutiona it sigain 66{»riti«
Bpontarieouslv alter some time. We are probably dealing here with*
colloidal solution wiiich undergoes decomposition, for the reasutt tii»l
the stannic hydroxide is slowly converted into another le*a m\u\ie
form. The same transformation also occurs iu the orij;i_nai lijdro-
chloric acid solution, for the hydroxide precipitated frooi solutions'^''
diifeient ages has different properties.

The precipitate redtssolves in exceaa of caustic jKJtash or soda, *
stiinidc salt or tttaniiitk being formed. The solution has a f-ininj^l.T
alkaline reaction, showing that the salt is hydrolylically disswint^l
From the solution in caustic ^wtash a salt, K,,tSnOj, can be obtaJnwl u"
crystals ; in this case, therefore, the stannic acid fortns a drvilen'
stannanion Snt ).,'", which is comparable with carbanion CO^". A num'*'
of other salts are also known containing several combining weigh''
of till to two of potassium, and are therefore salts of *'conckn»i"d
stitruiie acid ; they are, however, as a rule not well characterised, a«il
are uiistiible.

Differing from this stannic acid there is another compound uf il^*

inc id ihe arMenicali hjrilan||Hii n

Wd in it a farown^tifauk fitn at

m |irsdi]t«d itt a •Qv«r aolnEioa.

mctk>ft» ftro veij fflnlar to tbc«» «f aMnHmj hjdride
>i uml it ia (heselora of isportwiee to diiliagiiirit between
Mnt Fur iJiii porpoae s Milatii» of m #)■■ kgftMtrUg mar be
ijr eiied. In this tke aemauc Burrtr ipwdiiy doBslTts. vliil^
ir mirmr rvtiuiitis for m iatg bom imcfciiagfH Farthrr.
mumir U rviidity folaiilft, tkm untimtmj aurror U noc
bydrogen or smBMnrimk aalphfie wpoor converts the
^ito brif^t yelluw ■nctrie nlplmlr^ naufaible in hTdrtjehh.-ric
tW Utter iiiXJO yelktwred Aatinony sulphide^ nliible in faviirt^-
ACuL 11i« prvci{jlt&te prudaeed tn jiifcr aohitkMU by ar>«nic
Hrkle m ntper, tbe anpiiic juiMii^ into tafcatioa as arvenioos aci<J.
tmeuv hydride forms mUttt iitfiiwiilLi. and there is no antimony
■farina Th*^ last reartjon aiffmb a nouu of analyring mixturr<

Ml Compounds of Pentaraleat Anenie. — ^The com|-^unds

\mtn diKuta^il t^iti all h« nfdtrted ui tb*! trivalent type. Btr:>ide.s
i hiJtrr, af«enic forms tin> other <erie» erf «jaipoand«, one of which
Ifeipoads to thtf pcntaralcnt type!, wliilr there are also other coni-
Ittli which jw>iiit U) tbo «xM<oee td a di^-mlent type. The latter
:«uBiptuutivi*ly Dire and nninpnrlabt.

Wb«tt arwtiic trioskle is treated with r>x:di8iDg agents, ^.j. iiitrio
% a Botation is ofctainM frooi whkb. ou greatly concentrating.
MK and, UjAsO^, crystaltiaei oat.

In it< whole bdtariotir arsenic Mid tf very simiLir to orthophos-
One acid. I*tk« tht4 it it tri^ia^ic hat ju aoluble, normal salts are
rtialij hydrolyaed o« Iwing tJi«>oiri!ti tii uMter, and therefore react
kifiae All the aalt* of aneriic acvl sktt tHomorphous with the curre-
•allB of pbOHfilwrie aciJ ; in iart, it was in the case of the
atid pbttfphatet that «iiDiUhty of form along with cori-e-
no^ag composition wm finn ohiierved.

I Tlie «olttl7t}tty rclAtiofl* of the aalt» of arsenic acid have also a verv
^Muilarity to those of tht: ailu of the pbijisphoric acids.
(■ Tlw f<dIowiiii; (lilTer«[ic«ii, however, exist in the behaviour of
p tvn «nbstiu).cf8, itj ilm firHt pbce, one has not succeedtHl in
(Wfanng jiartial sinhyilridcs of arsenic acid, corresponding to i)yri>-
J^wplitjiic njid m«tapho0pboric acids. On the contrary, only ortho-
ttwic add, H,,A»0^ dong wiih its salts, aud arsenic pentoxido are
Down,

Furtlver, even on being guntly wnmitvd, arsenic acid loses water

mi g,^^,^ i^f^ li^ *iduh>*iiiii**, «4/ac!/.«; j^niaaUe, AsjOj ; while phos-

* ""i* (P- 869) an be dehydrated, by heating, only to mota-

■PwrieapkL

^MBte pBntozide is obtained as a white powder by heating

arsenic

VUlNOiri.ES OF INORGANIC CHEMISTBy

fcdd to a imwlt'iuU" «i)iiij>t'rjtturc. On being more strongly hcftle^ ii
loAM oxvgiMi, nml ]niM»i* into arsenic tnoxicle. When mixed niik
Wilier il liii«l forms h jwiaty nm«8, which is slowly converted inUi t
clour Hultilioti uf araotiiv firid.

Arsi^itie (irirl i^ luwl in Urn urte arxl inaniifacturee tA ft
oxidising iigvnl in l)it> [•rojuiraliou uf cot'Uiiii tires (fuL-b&iii).

Ttio ■<tiJ/> o( iii-stMiii- at'tt] urn of Hlighl im|iortaiice. While ihi
t>f th<' alkati inflJilx are rowtily Buluhle in water, the other met*!
iutv«ily imm dilliitnillly Muiublo s:tlts. The Tiiagne^iiini amaioniutu <ul
Mh^NH,>AhO,, which i» fornvi'ii uiulcr siwikr cotulitions to the roni
sitoMtljii^ |ih<«!vph)ito (p. 54 Ti), jtiKJ, «innl)irly to it, is used for the del
)iUtuMt»>it 4<t AnioDtc Aci<l, ikiul therefore iils.o uf arsenic, d«serTei' to
nientiimoti I'luier thn iu'tion of reiineiitg sul>st&nces (filter
untnuiu ov*l jpi*) !»m1 mi wjinniiiii, reducliun very reatlily
M^lntttijwUon »»t arsenie, ami Jitumiioii iiuisi b« paid W tl»

lit n>si|.^M.<t ivf iu t^lertrviiytic dissociation, araenic acid m
to {t)iiv<|>ht\ric Moitl. Even it{) to a grcmt dihuioa tW
tMM)lniitft ehit'rty the ions H" and HjAsO,', and thr
dt»«\«c>wiioii «!•« ijuito s«l»sidi;*ry. At the same

is ItM disiooifttvd ihait |tho6phono add, bot Uw iBflaiMea »

An anoMr ftmktMmide tmrmpomdutg to aiaMK add
iiM^l hv pMsi^g cblorine orar auiMtio tricMocHe aft - SO*.
in>lK>w crjnstaU which m«li at - 40' aod can W
«Ui«r. At a hi^biat ttmjptnMm* H d«co«BpoMa ■•»
cHkirinck ft ta, xhMtktn, nindh Ian suUe thm
MOi^ pentaeklnridf.

'iX Ax«aaicF«ita3mlliliid6.~ABDlKtMm<tf
7A^\.tiSy mhtn wariMd wHli exjtfkut, irtad^
i4 t)K< Utt<r, and forms a new
-» {> = X»,AsS,. \Xt an htr*
tlw Uivakmt cUaancnaBmii, AaS^'.
On aHwyring lo lilMRite tke rtiiinif iic «nf %
pwapHata it prodwrf, mtndb
bq> %M dw aiiniimitiia Aij^
»tas«)pUdie> In
It tkeacad is WA atalde, and
bid* aaid tadpfcorattad hjdiogwi.

t»4

iftit

«V^«S,

TS4.

wiA wdwo to foiiB the
; %• a krmr trpe than the

- Iijia|wiiii1 oecnra uttarmBjr in
«»» Wfmfand friM IW twa ninaniila bf faon^

*Iia ARSENIC 725

to arsenic trioxide and sulphur dioxide ; it dissolves in the solvents for
^nenic trisulphide leaving behind a residue of arsenic.

Arsenious iodide, Asis, is also obtained as a dark-red mass by
leating its constituents in a closed tube, and crystallises frum carbon
lisulphide in long needles. In chemical reactions it behaves similarly
) the sulphur compound, metallic arsenic being dejxtsited and the
>rresponding trivalent compoimds formed.

738

PRIX'CIPLES OF INORGANIC CHEMISTRY

BeeideB the tetraviilent sta^e of titatiuim, there also ettrt
divalent, u trivalent, and a hexavalent stnge, but ibe^f m-o "( ml
ordinate imjiortance. Rv hearing the vapour <>i the teirarhluridl
with hydi'oguii, the tricliloiide if^ nbtJiinetl in the farm of vittkt, stala
which dissolve in water, yii-hliiig ft violet liqiiiil which readily oxidisi
in the air and dopoaits titanic add. Tljese violet solutions can ai§o)|
obtained from the acid solutions of titanic acid hy reduction with m
or aodiiim amalgam. They citntain, presiimatily, a vtolet-cotonTwl
trivalent titaiiion, Ti ". With hydroUuoric acirl and soluhlc lluuntirf
salts of a trivalent titanifiiioridion, llFu", iiro formed, which are alwo
violet colour.

If tiuiiiium trichloride is heattid alone, it deconnntse« inl^i unn
chloridB, which escapes, and difiicultly volatile dichloridr, whid
collects in the colder p;irt.s of the apftaiacusasa hlack crystalline raiui^
volatile at a rccl-iieat. The tomjMmnd reacts violently with waKij
and yieltJs a yellow-lirotvn solution which oxidises in the air. Vm
poiinda of this series are also obtained by the very energetic rwiiictiol
oT the acid titiuiic aolutions %rith sodium amalgam. ;

Finally, there is a still hirjher stage of o.xidalion of titaniuui «hict
is obtained when hj'drogen peroxide is added to a solution of tilAiiil
acid in concentrated .sulphuric acid. The liquid immediately l»cconi«|
deep yellow in colour, and the reaction is visible with siidi itrui
quantities that it is employed ns inie of the best niethoii? of detectitij
hydr<»ge(f jiernxide. By rteutrulisinj^ the sulphuric acid, a yclluli
solid sulistant'i' of ihw compoKition TiO., can be separated.

"4". Titanium Nitride. — TitaniTim cxhibit.8 a s|HH-ial tetukncf
to combine with nitrogen. It unites so readily with the latter «l
moderately high teiiiperatures that most of the preparations wlid
were formerly regarded as miit;dlic titatiituii txmsisted chiefly i
titaniuirt nitride. A substance with a tnotidlic lustre, which is f]»
quently futmd in blast furnaco.'! and was formerly regarded as raoulHi
titjxniuni, Una t>een recognised as tihimiuii <yiinvif, Tij^C.^'j^ II
potassium tita.nifiuoride i.s reduced with swlium or jjot^issiuiu, lis
titanium formed at once combines with the nitrogen of the air. Ol
these nitrogen compounds, which are most easily olitaiued by h««tii^
titanic chloride with ammonia in a red-hot tube, two arc lttn>"H
correajKinding to the fornmlffi' Ti.|N^ and TiN,. These are cryatalliiifl
suhatancea with a metallic Justrc, which evolve ammonia lopioiul/
on being fused with caustic potash or soflii, pji.ssiiig thereby iiitft
titanatea.

The comliining weight of litaniiitu is Ti = 48" 1. ]

748. Germaniuni is an element of extremely rare occnrreJUA;
It can be rcdmcd from it.*! oxygen compounds by ignition *vitli cti*'*
coal, and js thu.s olitainefl a*? a very brittle metal which I'lisiis iiL .iIx'h'
900" and has the density of 6 -5 ; it ia insoluble in dilute ncirfs. '*,
dissolved by aqua regia, and is converted into the dicvide by "i^"''

3HAP. XL VANADIUM, NIOBIUM, TANTALUM, ETC.

aydrogen. Such compountls, more eapeciaUy with aulpburic acid, are
^owii even in the solid at^te.

By reducing the pentoxide with hydrogen, or with charcoal at a
high temperature, VfimiiHum IrinxUf, V.,Oj, is obtained as a grey-hlack
powder with metallic lustre. This was formerly regarded as metallic
vanadium, siuce, besides having a metallic lustre, it is also a good
conductor of electricity. It dissolves in acids to form dark-green Halta,
containing the trivaient, green trivanjuiion V "*, and which are also
olitaiued by reducing acid solutions of the [lentitxide with zinc.

Besides these two oxi+iea, the compounds V._,0, V^O,,, V^O^, and
(•Borae intermediate conqtoiinds have also been prepared. The}' have
'all a metallic appearance. The dumcif dissolves in dilute acids to
tform blue liiiuids, which evolve hydrogen, and have strong reducing
properties. They contain, presumably, a divalent, violet blue divan-
adion V".

The compounds with tha halogens, espciially with chlorine, exliibit
m greut variety as the oxygen com[K)und8. Htrtinge to say. a penta-
chloride, wliich would be expected, corresponding tn the pentoxide,
does not exi,=;t ; the highest chloride stage is the Iflmrhluriih, VCl^.
lAn oxychloride, however, viz. mnrnh/l chimkif, VOCt,j(VO = ntiiitd;il),
belonging to the pentavalent type, is known. It is obtfiined by firat
passing hydrogen and then chlorine over a heated mixture of vanadium
peiituxide and charcoal. It is a bright yellow liquid, boiling at 127',
which reacts witli water with groat rise of temperature, and fumes in
the air. From this VOCl, and Vt)Cl are obtained by reduction with
hydrogen ; they are both solid, crystalline substances, the former being
green, the latter broivn.

If :i mixture of vanadyl trichloride vajwur and chlorine ie paused
over red-hitt charcoal, the tftrachloriik, VClj, is obtained as a brown
liquid, bfjihng at 154'. On l>eing more strongly heated it decomposes
into cliloriiie and randiUHm frirhJmidi; VCI.,, whicli forms lustrous,
' violet-reil crystals, which recall chromic chloride. They attract moisture
from the air and deliquesce to a brown liquid. On heating ifie vapoiu"
with hydrogen the tetrachloride is converted into vunaiHnm (UfMoride-t
VCI2. This forms apple-green, difficultly %'oktile crystsils with a mica-
ceous lustre, which deliquesce in the air to a violet-lvhie liquid.

Finally, on strongly heating the dichloride in a current of hydrogen,
fnettdJif tnmuUum is obtaineil as an immelted, grey m-iss, which
acquires a metallic lustre on being rubbed, and does not dissolve in
dilute acid. It burns readily in a current of nitrogen, fonning'(V(n"f/ium
nitri^^, VN, a yellow-brown powder witli a metallic histre. On fuaion
with caustic potash the nitride is converted into vanadic acid with
evolution of ammonifi.

On [jassing siulfjimretlcd hydrogen into a solution of ammonium
vanadate in ammonia a preci)>itate is produced which, on continuing
tto pass the gas, dissolves, forming a fine, violet-red coloured liqu'

I maM

-•Mfihling [lotasHii
■^\\t has the coin
ithij series. On
I'i ,-» hnjwn prcfijiil
I* pure vjujutliuni ■
ink [Mjwdei' by fiisii!^
.<i(.\ ill its Lurii, ia obutiiitKi bj
■upliiirettwJ hyilrogen, or. I" ''•
in colour, and dissolves in
■ excess of sulphur, forming*

a cataly tiwdly accoleratiiig n i
oi fitiilirie to jvnitiiie lilatk. «
taaployed for that purpoBo in tbi
■ very small qMiiiitities of the acii! ure
cradon.

.lUMiuim has Ih^qii found e<[nal to all

"StaiSni nre two extremely rare cl«tn«Jit«,

-pectively lU und 183. Free iiioliiiia

i* the reduction of it-s ddoriiic witi

-^sta tho action of dilute acirls, Uu

^■OTB. Both clenicnte can be obtAinod in tit

-^ «K*i metals whkh mplt above IWU, stud

.aai s^rtoB, on thi^ side of tho base nivUl&

■u* A jipithxkir, Nbj,(J„ which is the Arihy

. -he alkidi wdts uf which are decompofitl

■r^Nnpitalino uf the hydroxide. Ot\ k»ing

^' n the peittoxide poises into u hEwlt,i

• ■ irmeily t*iken for the metal.

\mi a fie II lark! in' ute which can Imj obtajuw

> id) cliarcoal in a current of chlorine. I^

. .; melt Hi \iH anil boil at '_'U> . If in D*

■■Br i.!^ watcn- ia not avoided, Tintfiium osi/fhliHvli,

— .-•' !is a white maas, which docs not fuse, 1'H^

!<fnde ib also known, which is deposited i>>

II- of tlic pciitaehlciride.

.\ toiiipuuiids with tkiorinc, which exhibil*'

■v«i»inii, uiid which have not yet boon arrangMi

: tantalum are very similar to thu§e '*

*' srjtcleriiilic is jtutiimum tittUahJluoruii, ib^
Ltitalotiuoridioii, TaF/' ; the correapomiinj
I,- loiiued by dissolving the pentoxida in hyclT*

Md Indium. — The elements innjat nearly nJjtiw
Omenta arc to be found among the alkitliiu *<u^

properties developwl to a liighcr de^Tee thfin in the aise of the allied
jubstancea of lower conibitiini; weight. It is | precipitated fnim its salts
by iiiniDonirt m- alkalis, and is not soluble in excess of the precipitant.
Similitrl y to the other dioxides of this group it occiii-s in sevonil forms
piiRiscssing diffarent degrees of stability ; while the freshly prepared,
■ttiuie, ^'eliitinoiis hydroxidt! readily disaolveis in adds, a dittii-iiltly
Potulik' mwiiitication is formed on heating. On ignition, the hydroxide
puu«£ iuto the ilioxide, ThO.., wluth is a white, light powder. This
oxiiie is not aolublt in acid* excejit in hoi, tortfentrated sulyjhmic acid,
Tlie uN'iile obtained by heating the oxiilato, on being evitpoi-iitcrl with
mtriu acid or liydrochlon'c acid, gives fi residue which does not dissolve
io dilute acid but is aohihle iti vmter ; the solution is of a colloidal

tiutttT. This behavioiu" recalls tlmt of sUinnic acid {p. 734).
Of the stills, the sulphate and the nitrate are the best known.
iviiii tiidjihulf, Tiif.SO,)^, crystidliBea acconling to the temperAture
will) varying ftnumnts of water. These different fonns change com-
iBnitively slowly into one another, so that it is easy to prepare solu-
tions of one of these forms which are greatly aiipersjittirated for the
fitber forms. To this is due a peculiar beha^^ollr of the sulphatOj
"•hifh is uitufo use of for the purification of the thorium compounds.
Tiic aiibydruus sulpliate, prepared liy healing, is dissolved in ice-cold
Water. A solution is tlms produced which is sattirattMl in rcsptct of
lie anhydrous salt, but greatly sujiersaturated in resjiect of a liydrated
fith 4H..0. Since, also, tlic solubility of this latter salt decreases

^611!

Httun
ppar

tly with rising temperature, a solution prepared in the cold with
il» .'uihy<lroua sidt will become, on heatini;, more and more super-
united in respect of the «alt with 4H.,0, and the spontaneous
arsttion of this hydrate therefore soon occurs. On heating the
««lt whicli is deposited until it has lost it«s water of crystidlisjition, it
*gain bi'comes readily soluble, in coki water, and behaves as above
<ieiicrilK.id.

TltHrium nifntte, T'h{'SO^)^, &E„0, is a very readily soluble salt,
frhith is obtained by dissolving frealdy precipitated thoria in nitric
Kvi It is used for the preparation of incandescent mantles, a cotton
web V«3iiig riKiistoned with this srdt, dried, and heated. The. texture
bums and the thoria remains as a wldie, coherent frame-work. By
Ignition in a Hansen flame produced under prossme, whereby the
tnalerial appreciably contracts, the mantles are marie ready for use.
^m The iiiantles are retirleied himinoiis by being strongly heaterl in a
Bpc tally coni^tructed liunscn fl»mc. It is a remarkable fact that pure
Hioria gives only a piifn'ly hmiitious marillo ; in onler that it may
Womu powcrfidly luminous small quantities of certain other substances
■"iikI 1*0 added. For tid.s [uirposc the alrlition of 1 per cent of cerium
oxldv (p. 501)) lins lieen found to bo best. The cause of this influence
W fn,t yet been est^ddishefi quite free from doubt, but the most
view is that the atldition effects a catalvtic accelenition of the

742 PRINCIPLES OF INOEGANIC CHEMISTRY ch. xi

combustion of the mixture of coal-gas and air in direct contact wii
the skeleton of thoria. Besides this, the optical properties of thor
appear to be of importance.

The tendency to the formation of complex fluorine salts (cf. p. 7.1
is greatly diminished in the case of thorium ; thorium fluoride is
precipitate which does not dissolve in excess of hydrofluoric acid, ai
does not therefore exhibit the formation of a hydrothoriofluoric neu
A potassium thoriofluoride, KjThFg . 4H.,0, however, is known as a
almost insoluble crystalline powder.

A very remarkable property of the thorium compoiuids is, thai
influences are emitted by them which penetrate through solid suF>
stances and are characterised by their action on the photographic
plate as well as by the change in the electrical properties of the
air. We shall enter into these points in greater detail when we
come to discuss uranium, which exhibits these actions in a much
higher degree.

CHAPTER XLII

URANIUM, TUNGSTKN, AND MOLYBDENl^M

''<M. General. — These three eteoient* rosemblo chromium in many of
tioir firopetties, so that they niif^ht have Ijecn treated in coimectiou
Ttiih it. On acfouiit^ liowever, of tlieir forming thio-acida they so
DDiloiibtodly belong to the present €]ass of metale {chromiuni fonns no
*tit|ii)iir compound at uU in a<:[ueous solution), that it appears npprn-
prittle to aeiKirale them from dirominni.

The elements antniiiin, liiimaU-n, and molyljdetuitn are chiii'acleristd
by the /act ihiit their most sUible oxygen compounds have the coni-
poaiiori MO., and iire tho anhydrides of aciiJs. In accordance with
til* general rule, the acid properties are If a-st pronounced in the <aise
M the element with iha bigtiost combining weight, and become more
pronounced as the combining w^'ighl decreases.

All three belong to the less frequent elements, although they
Cuinot be characterised ^ rare. They are difficultly fusible metals,
wbich keep well in the air, hut which have found no application in the
pQre state.

Of all the known elenienta, uranium has the highest combining
weight, viz. U = 3."i8-5.

»752. Uranium. — ^Uramum was discovered by Klaproth. In the
of iufhiilk >iiifni.iim the same thing hap|iene(l as in the case of
Wnwlinm. viz, the copf>er-brown coloured dioxide, which is readily
lormwl by the reduction of the higher oxy^^en com|Kmnda, was mis-
Uken for the metal. The true uranium was 8uhs6()Uently obtained by
j|e action of sodium on the clilorine compound : it is a white, ditlicultly
■ble meul, which dissolves fairly reiadily in dilute acids, and in the
Builial series stand.4 near cadmium.

Bl'ntnitim fornus a winkle snrie.'^ of stagus of eomhinalion in which
ttw trivalcm to octavalent. Tlie bettur known and more iiufxtrtant
MDpounds are tbosie of the hexavalent ami those of llic tetnivalent

5y oxidation of tho luitunUly oeciirriiig comijoimila of uranium,
; of iiranyl, Le. of the divalent cation UO/, are obtained, The

744

PlllNCIPLES OF INORGANIC CHEMISTJtY

nortnal hydroxide of hexiivaleiit urariiiini, r(OH)„, Inia botli acid m
kisic pnnwrLiGS. The hitter are not Rufficieatly strongly (Jev«?Jofw
for all the isix hidiiixyls to b« lepliiceiible by acid resiilues ; two, hm
ever, can be replaced. In the salu, Uierefyrc, there exists thcitivulwi
cation U(OH)^", or its aiiiiydritle UO,"", uranyJ, wUicli forms aalt* h'ki
any other divalent cation.

* This occurrence of an " fixygenated metal" has been regardw
BOiuethiug remjirkable and extruordiimry, but it is readily inK"!]!*!!)!^
^wben regarded from th« point of view that in polyvalent .'wids *nJ
bases, the rcpkcemont of hydrion nr hydroxidiou becoint's more difficult
the fiu'th«?r the replacement proeoeds. Just as in a«[Ueoiis Ki)hitwB;
phosphoric acid behaves cbie% tis a dihiwic acid and forme sfdta uf di
anion PO^H", since those of the anion PO,'" sutler loo great hydroloii
to be present in any considerable i[Uarjtity, so the hydrulystt) of liio
uranium salts corresponding to the higher cations r(OII).,"', l'{011)j
etc., is too great for these salts to be present in appretjjable ani()iiut
For wveti the second cation, ir(OH)^", is so greatly hydrolyse*! thiUiU
salts have a distinctly acid readion,

Dinranylion, U0„", is of a bright yellow colour ivith ^een fluor
escence, and in the spectroscope exhibits n niindier of definiU! absorp-
tion bands. Of the salts, the iiHruh- UO.tXO^l^. 611,0 is the M
known; it forma yellow crystals with ji;reen fluoresceiiPe, which ftru
readily soluble in water and serve as the sUirung jxjint iii the prc]»ra
tion of other uranimn coniponncls.

From the nitmtc, soluble bases precipitate a yellow 8i]h«t*u«
which consists essejiiially of nranyl hydroxide, 110,(011), or UtOll),
but also always contains a quantity of the bivse in ihn form of »
Ul^anate or salt of uranic ai'id (litie in/ni), By evai>ora.tirig a sMdutmn
of nranyl nitrate in abtihol (in wluch the alcohol serves to desimv ili«
nitranion) a yellow powder of ihe conifMisition UO,,(OM),^, free tmis
alkali, ia obtained. AVith other methods of prefKiration tJie o<>iu
[wsition Is U^UH),,. This imim/l /if/ilnm'le dissolves in acids Ui^
forms the correBponding, often complex, uranyl Siilts,

Uranyl lias a (jrononnced tendeJicy Ui form complex compouiuJi
these are formed witfi almost all organic ai'ids. Of tliese the <^Ml')it,
which is very sensitive to light, and in .suiilighl evolves gas copioiuif,
is of interest. In this process we do not liave an uxidatiun of thfl
oxalic acid with reduction of tlie uranyl, but the eaeaping gaa i» »
mixture of carbon monoxide and carbon dioxiile, and a precipitate m
uranyl hydroxide is formed at the same time. The oxalic acifl thtf^
fore undergoes the same decomposition as by hiating with climiiiHtimi
of water (p. -1 IC)), and the iiraninni acts catalytic^vily. The nntiiy
salts of other organic adds exhiltit similar «lecoinpo«ition in the i'l^^U-
With phosphoric acid uranyl forms a plios/iluilr, L'O„HP0,. in-
soluble in acetic aciid, or, in the presence of ftmnioriium enlts, the wffl'
poimd U02(NH^)P0j. This precipitjition is tiscd for lUe vohuoctao

TIN AXI» ITS CONCKNKI.'S

_.■....-:.: ;iiiil tftiavaU-nt -••lii- 'i ".;

-aV . .-

'•■ ■'■ . '••■";. i^ fiiiniiil l.y li"-..*.' .

Li- . --'-..:^ -.. -.;- .-; uhii-li. wiili water, t!--- : .•

II ; — -. ;• - --..i';!;-'!!. It 'iisMihf- ;■ ...,
"lu..: ; ;-. . 1. ..:. ; :» ;»i-i« ."iiliililc ill .ii-i"i-

(ii-:. ;- Tr.r>-.- -.tit-likr i-<iiii|»iiiii<i- .

\\ ;:i L. :::.-. _'rrii.iiiiinii t'lrm- .1 ■ •
•jir.->- .". . .••: : ■.tii.'ul: iti iii<»i»t nii . •
^"».- ::: -'T .-.v! '.vi: ii riai- of ti-inji.: s-

-lr>i;j-:- • r.I'Oi'l'? uii iiK'tiiUir 1'. ::.. .■
«•;^^.•i.]' •! i' iv. .ir.il l»<>iN at 7l' .

A •/■..•■■.•.>■ <'(f< ,'<'/■//■/</>. (it'll . ,- .
-»rM.':i;i. hydriiU'. In a iu;:it-: ■ ■ ,

(;>:ii;aiir.iin {liMii*l«> i- :. ' ■

• it-F,. h'>w.-vt-r, (;.\i.-.t-. wl.!:.
e-jsil;';i>- !n.i<l. ami tHiiii- '•'
Kcultly ^oliibl*- in -wa:'-:.

Ill I:l:i>lii'tli4 anljllliili . I I-"*

*i5i'« iiitu «-iilIiii'lal ■■•:.;■
Ly l»y a larjii- vxci.'— • :
.iiaiiioii, (li.-S^., ]"r<'<:'..
t.Ui'i!is ifintaiiiiri_- ::-::.
Ss siiiiii;\vliat >iihi;-i- .'

• Titliii- ^'alts. 'J'h..- r:.:. • ■•

1 in it germaniu:.. ■ - •

Of tho OMiiijf ;■. - • . .
^fhi'l< i.T- the \»—'. .-:
"•inanif; siil|i:ii.-. . . '
"Jill aqiKM'ti:- -' -■;".. ■•
iiMe in rxcv-- :
nnous siilph:<;". ." •

74 V. Zirconiuni

CJitt' i.'f zir<''.'.' t ' ■ ■■
apifith in 17-
UL-fsiiim :\'--

IIP'I-. U!!'i-' -

iMe i-sy-.'.
'. lat?:4.-!'. •
■ses hi'>> ■■■ .
y n:-;-;^.-.:.* "
h tf'njf.'.-: :■
Zn.y r....- ■
■av.i'.::.' " -

746

PRINCIPLES OF INORGANIC CHEMISTRY

ciiAr

chlorlfte an.l irtvi^chhride. Tlie latter forais dafk^green crystftia, whick
dissolve in water to form a dark-grecii sojutinii ; regarding tlie latter,
it has lieoii staled that it is not of itself oxidised by tlie almos[»heric
oxygyn, but is so in presence of iron sidts. This is fipparently ;i!J0tlier
case 'if cat.'ilyiic araeleratioii.

From the totrachloride, a frirkloridr, UCI3, can Ih« ubtaincd bf
reduction with hydrogen ; this is a brown red mass which readily dik
solves in water, but with the latter forthwith evolves h>-tln>j;eii unei
passes into a basic chloride of tetravalent uranium. The Srvnh solution
gives with cjiiistic potash a brown precipitate of unmiuw tnhiiilwiMt,
which also vory'qnickly oxidises witli cvohitiuii of hydrogen.

7r)4. Sulphur OompoUUdS,— .A-mmoniuui Ridphide de|Mwit* •
brown precijritate from iiranyl salts; the precipiUite is nmntil sh/jiAw/',
UO.,S, which is, however, jMirtially decotnfiosed. For from the »iil-
phur compoinid even water splits off' stilpluiretted hydrogen, whirJi
jKirtially reduces the uranic oxide formed, and is eonverled mf»
Bnl)ihnr.

755. Uranium Rays and Radio-active Substances. — In iW
case ot" uranium a property was first observed which, however. h»»
since been found in varying degree in other elements also, and in
their compounds ; it consists in the following. If any uranium am
|)onnd is placed on a photographic plate covered with black jwpor, tba
jilate ijiirlergoes a change a-s if light had acted on it, i-f. it can W <le-
\clu]icd (i». (J5>0). This action takes place tdso through tivin plate's nf
iniea or of glass, but is dlniini^hnd by plates of greater thicknt**
proportionately with their density and thickness.

A further influence eniittcd by these aubstance.Si is that they iiwlc*
the air and other gases ole-etricnlly coitflMclire, so that an flleciric currntit
cim be passed through them. This property servea best for the mai-
aiu'omcnt of the influeMce. e.vercise4.

Finally, certain |)hosphorescent substances, more ©specially liimiun
platinocyanide (p. 7't"i), are rendered luminous by this action ; hut thit
effect becomes visible only with fairly high degrees of activity.

It has been found that these processes are due to certain mal*riiil
changes in the particular substances, in which large amounts ui energy
are developed. This energy assumes, in the first instjuice, the forri
of "radiations." i.f. it is profwgateil thi'ough s[iace with verv grw*
velocity, and essenti.illy in straight lines. Its propagation is inflnonicft
by the presence of boilies only in so far a» these absorb a delitiiif
(lortion of the energy which is finally changed into heat. This trani
formatiofi is, in the tirst degree, proportional to the niaas (density «
thickness) of the substances through which the radiation passes, wni
is independetit of their chemiwd nature. For the Tmt, the nwiiatiM
themselves are made up of ditl'ereut parts, which are distinguish!!
from each oiher by, amongst other things, their power of hem
absorbed. Whereas some are retained even by thin ftaper. otlwi

(041 UKAMLM, TUN(}?>TEN, AND MOLYBDENUM 747

kli [lenetnate through thick steel plates. Fladiationa having u> a
Btain extern ii siniihir ln^hiivioiir jire knnwii as " c.ithode riiys,"
'"lii<rh are jirwjuctiil frum the ctithodo when eleetrical diacharges oeciir
in very dilute giises ; from the anode also, similar rajs procet'd. The
«ln>ttiioAl ratliatiotis of the Hiibstances aljovo ineiiiioned, which are
dllod raclio-ficlive substaiieeB, <:aii be chaijicterised as foliows ; —

A portion, and that thu greiitest (when nn*!isured hy the imiount
€)i eticrgty invnlviHi), jtossesses in only n very slight tlcgree the (lower
«f penetrating ponderable Huhst.inres ; :md in a. magnetic ticld it is
4denat«il frotn its struijrht rourae in the same direction as a current
«f (K«itive electricity. Tliese rays aiUi designated us a-rays. Besides
these there are ^irays, whit h are more penetrating, are deviated by
• magnet in the Evinie ilirection a& a current of negritivc ekvtridty,
■nd are piiotn^rajjhically nctivt Finally, there are also y-rays, which
Iwtuive like the X-rays discovered by Kcintgen, are very iveiietrating,
and exiieripinee no deviation in the magnetic field. The investigations.
fc far tarried out, refer chiefl)' to the a-raya, the strength of whi<!h is
tteasnretl by tlie conductivity which thoy impart to the air.

This proiierty of irajjarting cunduettvity to the air by means of
lieir u-i-ays, is |»ssesse(l, in the firj^l jilace, bi' all uranium eompoiinds,
tna measure nearly proportional to the amount of uranium present,
«d nearly independent of the tcnipeniturc and other drcumstancea.
ft ta also met with in the case of tiie thorium compounds. The
proj)crty can, it is true, bp temporarily altered, but again appears
*iifT *omc time in its former strength ; and is, in the end, quite
iodrjieniJerkt of the treatment which the preparation has meanwhile
crgone.

In the rase of various minei-ala containing uranium and thorium,

radiation was found considerably more intense tlian in llie pure

lurtus of these elements. This led to the search for other sub-

icea |>oaaeBiaing a correspondingly greater radiation ; and various

les, such as polonium, actimiim, radio- tellurium, have been pro-

1 for thpfip powerfallj' radiating sul»stances. Altlioiigh it is

oulit^d that seieial such elements do really exist, only one of these

been isolated in any flegree of purity, and charaet«rised, namely,

rum, discovered lij M. anil Mme. (.'urie.

Jitulium ia au element of the alkaline earth group. In its pro|jterties
b io closely related to Ijarium, tliat it cati be sejiaratetl fi-om it only
hj" apprfjximat« methods (fractional crystiillisation of the bromides).
It differs from Ijarinni, firstly, in its exceedingly intense radiation ;

K secondly, in its apeetnun. It imjiarts a red ei>loration to the
e of the Bnnscn burner, whereas barium gives a green cotour. It
'» not yet known in the ractAlHf state, since it occurs in the minerals
e mentioned only in exceedingly minute amounts. Its cumbining
ht is U)v= 225.
pThe moBt remarkable proi}erty of radium, which it pOB«eB6es in all

748

PRINCIPLEH OF INORGANIC GIIEMISTRV m

its connwujuJs. is iliat of wiiitimiuualj' develofiirig energy, vrhkh laah
its ajjponraiHt?, iu the first place, in the fwin of radiations almtd]
dostrihcd ; but when thcso are retained by thick ciisings of meul,
IS traiisformee] iattt heat. One gt'nm of radium develops in nn lici
alioul 100 rftl, or 418 joules; or in a flecoiid, somctLin^ over w
million erga. Sinte an external source of this enuigy coiiM nut I
demonstrated, it ajipeai-ed as if the law of th« coiiservution of timq
WHS diaolioyed, until it was di8^*overed l>y lianisay and .S«:>ddy th
hrlium is lucRluced from the radium salt in amoujit jjiu[H>rt iorial d
the tiiiorgy devoloiwii. It may be assumed, thereforo, ibat wr bav
ht^re a case of true transmutation, such as the alf.benijsts, in vui;
attempted to bring about ; that is to say, we have hcru s case i
the transmutation of one element into another. Ther«^ is nn cotiUi
diction in the fai;t that this hitherto unknown reaction is asaociat
with a greater ilevelopmcnt of energy than usual, araountinf; to iMti
Qjilliou times more than that which is develo^ied in thu fomiaticm
water from an amount of detonating gas ei|uivalent to the hAm
ptwiui-'cd. A diminution in the weight of radium has so far not l»i
obaerved. From probable assumptions, it can be wthadaiwl that il
"average life," i.e, the reciprowil of thu fractional amount changtHl
a second, amounts, in tho case of aidium, to about 1 aOO years, &o du
a measurable diminution in Tivcight lould Ijo observed only by t«tii
fairly large auuiuuts of radium over a i>eriod i>r several years.

Helium is not tlie immediate protlnet of the sjnuitaneoiw trwii
mnUition of radium, but iutermediate subslances of greatly itif<?ni
stability are fornwd. These VKihave, in general, like elementjiry pM
of the type of argon and htdium. They are called em/inations, Th
emauatiejn from radium hsis a molar weight of about ICO <judgfd In
ditfiisiiHi experiments) ; can be eondensed at the t«m|»"ratuire of liqui
air ; p<)sse9seis ita own spectrum, having the tharatU-r of the heliiii
spectrum; but liiis an average life of only 128 houra. In its trai
formation it gives rise to other similar subBUinrcs of still lehs stabililj
BO that, on the whole, about five diflerent stages are pjisaed througl
wliieb differ iu their life. Uranium and thorium behave ainiilarly.

These fails lead to the assuniptiiui that the wrll-known flemei
uranium :ut(1 thoriuui have only a liarisilorj* tixisteute, and are uinl
going sp(miaiK'oii.B trnnsmutation with evolution of energy. 'Hie fii
product of their triuisformation appeal's to be helium, for this is alira;
found ill the minerals in which these two elements occur. On col
paring tho intensity of their radiation with that of radium and of tl
omanatiou, the conclusion is reached that their average life murt '
very great; in round munbers, a thousand million years,' This ti:

' JJfit infrp<)U«ntly tUe reiiuirk ia tieunl, lliat if t.lira priM-r.^* hml tlwiii
eternity, it rim.'it ultvtKly liavt) cimiplcU'ly nin its uoiiraB. Tliur*; Ims I.m 1*
to this, timt tlip lonccptioii of <?li<niity liiix no i>xart (ihysiral nicaiiing. Iii u tune «»<
llie liiitifs t»f wliicli ftvu' icnowii aeitliur lu one nor in the otlier <liroction, tl>B prt^fut
Iw lit smv (iiiiiit.

I ITRANIUM, TUNGSTEN, AND MOLYBDENUM 74 9

kfett than that assiimt«d by geologifits for the developtnent of the

16. Tungsten. — This element, was discovered in 1781 by
(e. MetiiUic tungsten can be obtained by the reduction of its
in a curcent of liydfogeu or ■with chiircoal ; it is a grey, very
Itly fiisii)le, hard metal, the density of which is 1 6. On account
,e two [ji'tiporiies it would \m very GMitablc for cannou balls if its
ibility ilid not act as u liiiidraiu'L' to its niaiiipiilatioti. It
ical application as an addition to steel (tunystsn steel).
le combining weight is VV =184,

ngsten forms mimy compounds in which it appears as divalent
Talent. Tho lower stages have basic properlitis ; the highest
compound ia a pronounced acid anhydride. Of all tht; stages,
e most stable.

ptipiiit hiiiriiif, W0|, the anhydride of tnngsttc acid, is obtained
■ellow powder by the action of acids on ita stdts, some of which
naturally ; it ia very slightly soluble in water, hut reiulily dis-
in alkalis. According to the temperature of [irecipitation, there
kined the anhydride (in the heat) or the hyilroxides W<t(UH)j
OjOU)..

dissolving the osdde or hydroxide in the calculated amount of
ih or canstic soda solution, and evaporating to the point
lisation, the normal tiuigsUites K^WO^ and Na„WO^ are
1 in hydrated crystals. These pass, however, ivith extreme
ito sjilts of more complex composition, the timgstic acid forming
Bsed acifs, which p;irtly crystallise out with the normal tung-
JLS double »;i.tt^s.

prmal tuiigsU-ites occur in nature, and constitute the ores of
leii. The ferrous compound, FeWO^ {which getiemlh- contains
mese), ia willed ivolfidM ; the calciiun compound, CaWO^, ichtudih. ,-
id aalt. schffUHnf:

i iKtiling a solution of an alkali tuiigstate with excess of trioxide,
'<]aantities of the latter are dissolvetl, and the iiirluhnnjduks,
Ojj,, are formed in which a very stable contleused tungstsmion,
', is present, the rejiciioiis of which differ entirely from thost^
nnal tungstauiou, WO,'. For example, the tlii^solveti s<dts are
sci^it.at«d by acid«. By the action of sulphuric acid on tiie
Itly soluble barium salt, a solution of metattuigstic acid can tw
ed, from which tiie latter can be obtained in yellow, extremely
H crystals, by evaporation.

•ent from meta.tungaltc acid, there is the scj-crilled colloidal
acid, which i* olttairied by dialysing a soluliou of a normal
slightly acidified with hyrirochloric acid. The liquid ilries
gummy mass, ^vhii:h re-dissolvoti in water, forming a sticky
I docs not taste a<cid, and is not precipitated from aohition by
other substances, as happens in the Cftse of colloids. The -sohi-

760

PRINCIPLES OF INOriGANIC CHEMISTRV cm

tion also exliibits an approciiiblo tlrpicssioii of the freezing point vth
lends to the (doubtful) fonnuhi ll.,Wj(Jjp.

Besides the above, other diversities have also beeii observed in tl
case of tiingstic add, depending on the very r«siid>' iind oft^tJ occiirri;
formiitiun of complex acids with other acids. The coi]ip«>uruU wi
silicic acid have been most ilionmghly tnvesf.i^ulcd ; similar eompcmii
wiih phosphoric, arsenic, vaundic, iodic, Iwiic. and other acids
exist. Tht* composition is thut of ihu above acids plus a lieliuil
generally a larj^er minibci* of combining weights of WOj ; in
process, the basicity of the otlicr jicids gencraliv* reniains uric:
but the complex JMiids prfidiiued rue mostly considerably strnn
the mother substances. A descriptioti of the diOeretit cumpHiro
would tJike us too fai-.

On treating tungstat*s with zinc in acid eoliition, th«" liijui
becomes dark blue, and on funher i-erluction lirown. It thru innuti
the tetravalcnt ion \\"". From this, tungstaiiion i& s«^ain rcAflil
formed by means of oxidising agents.

Very varied contpoiinds of the general foitmila Na„(WOjf, *i
obtained by weak reduction of Budiiim tinigstate (by fiisiun with tin
these have all a fini" mi'lalliy lustre, Iiave ditfercnt colour accarditiiL;'
the aTiiount of tungsten they contain, conduct electricity like u mcM
and are extremely resistsuil to the action of waiter, acids, and i
They find an application as "tungsten bronw,"

757. Chlorides of Tungsten. — On heating metallic tnugaten in
current of i hlorinc, with caiefid exciuaion of oxygen, the hej-addnrvi
WCl^, is obtidned in l>lnck-^nolet crystals, which melt at 2~b' ainl bo
at ."547 . The vapour ctiuLains a little free chlorine, au that on rHjual
di.stilhitiori chlorine escapt*, and the lower sU'jge, lunr/dru ^**
chloride, Wt-lf,, ifi formed in black green crystalSine newlfos, villi
melt at '2iH and boil at 27 (j. This substance also readily gplit* <
chlorine, and on distillation in a current of an inilifToreut ga« leave*
residue of tungsten tetrachloride, W( '!,, as a non-volatile, greyl'ro'
maas. By the action of rediicinE; agents, e.i). of hy<lrogcn, thi» w
pound finally passes into the dichkiride, WCL, which has a tiniilj
appearance.

Bcsidea th^se com[wunds, the oxychloiides, vix. \V0C1, *
\\'0.,CI^ are very reiwlily foinied in the presence of oxygen or wat«
The first comiKiiind foj-ms kmg. dark red needles, melting at 210
boiling at 22K ; rhe second, which is comparable with chroia
chloride, appear-s in bright yellow laminae, the melting point of whi
lies above the temperature of eidiiimation (aWut 2(50 ), On distill
tion it readily decom[ioseB into the preceding conij>ound and a resitl'
of tungsten trioxidc. Both undergo violent dectmi|HJsitioii with waU
forming tungstic aciil and hyilrogeti chloride.

758. Sulphur Compounds. — The add-fornung prupurtics
tungsten are exhiltiled also l.iy its sulphur compounds, for it ion

hiotnngstiites in which the oxygen of the tim^'states is gmdually
f|)Iftt-ftl by dii!|thui'.

Ky |j.'i.ising stilphnretled hydrogen into & aolation of an oJkali
;«ngsiate, the eoiTespoiidiiig thioLungstate, M^.WS^, is obUiiied oidy
•hen there is excesss of tdkali hydro!*idijhide. If no excess is jir»?sent,
ou diliuioji vdth watiT tho sulphur in the thiu-iicid is gradually re-
plai*d liy oxjg^n, sulphiiit-ttt^d hydrugen being evulvi.-cJ. Thiotungst-
miuti is _vcllaw in cipkitir ; by replieing the sulphur with oxygen, the
coiour tn'coniea utirres|>oiiding!y ]i;iler.

On adding acids to the tliiotnn^statcs, tungsten sulphide is pre-
et))ititle<l, and siiljdnirettfd hydiogon is evolved, thiotuugstic ncid,
which iti primardy formed, *lefl<nnposiiig iis usual int« these com-
fwm;nls. 'I'uMgstun tiisnlpbide is thusoblainwl ,'isa brown, ainoj'phous
pKcipilato which passes inlo colhjithd solution in water.

Fioiii luii^sttfn and sulphur at n high temptnatnru, a lower siil-
phiiic, WS.j, is obtJiined in grey, graphite like laminie, which are very
iUhle.

759. MolybdsmUU. — ^The chemical individuality of molybdciuiiu,
like ihjil <jf tuiigstcn, wjw cstabltsheil by Scheele> although the metal
ns nut obuined till later,

Moiybdennui rcsumbles ihu related elements in resfwft of the
Vtfioly of its coi)i(HJTuids, for ita viilency varies from two to six. In
j^ uase also, the compounds of the he.xavalent type are the most

HBTb^ combining weight of molybdenum is 96 0.
^Mjlfci'iJli'- Miolfjinltntim i.s obtained as a white, very difficultly fusible
TKtui whicli, like iron, Itecomes more readily fusible and very hai\l
tiiroiigli abfiuqition of carlion. It iti not attacked by dilute actilii and
tf oxidised by niiric iR-td. In the ]xitential series, it appears to s^taiid
J^u neigh lionrhood of lead.

H76O. Molybdenum TriOKide, the atdiyilride of uiolybdic acid, is
l^wined in the crude slate l>y roasting the iiaturallj' occurring molyl»-
•leimin sidphide, and is purifie<l by dissolnng in ammonia and repeated
TOttsting. It is a white substance which becomes yellow on heating:
M u red heat it melts and volatilises. It is readily reduced to the
ihet&l by means of hydrogen and charcoal.

Moly Wenum trioxide is the anhydride of a series of acids which
•ft- formed from it and the elements of water in varying proportions.
WhercAs in the ta»e of tungstic acid the racrjitungBtif acid at least was
fiMind to be well characterise*! and stable, no similar ci>in]Kmnd is
known in the present cuae, but the different polyniolylxlic acids apjHJar
to (lass f^uickly and readily into one another. L'omjjounds of tii*
iQoJyIxlic aoid, H^,.Mo,,0,j„ »re ihi- most frequent.

The jwwer of fonning compiex acids is here developed to a |iiU'-
ieularly high dcgi'ee, and molybdenum trioxide appears to unite with

752

PRINCIPLES OF IXORGANIC CHEMISTRY cm

molybilenum tnoxidi», or ite hydriite, is only sparingly soluble
vvaterj il. (jjisscs abiindaiitlj' into solution in free acids ; swit*
molybdic iicitl therefore give no precipitate of molybdie acid on addi
excess of another acid.

Of these complex compounds the phosphomolybtiic k
H.,POj . lOMoO., is tho best known. Besides the compound \ni
lOMoO., thero arc hIso compounds with perfectly similar projhcrti
containing Il.MoO, and l^MoOj.

The very difficultly soluble iimmoniura salt of these iwUh
obtained by warming an acid solutioa of ammoniutn molybdaLt wit
a tiquifl containing phosphoric acid. The liquid first hecf>iiies yelL'
and then deposits a yellow powder, which is the above amaioniiii
Bait. As is frequently the caae in the fonn;itioti of complex con
pounds, tho reaction does not tiike place instantaneously, but rei|uire
a moderately lon<^ time for its completion.

* Since the reaction occurs iti acid solution, and since a voryliirp
quantity of precipitate is obtained for a email quantity of pliosiilim
acid, the reaction is employed for the detection of phosphoric acid is
analysis. Care mtist be taken that the molyl>dic acid is present m
excess ;i3, otheiwiae, soluble compoutids can be formed.

From the ammonium salt the free pkonpIiotiMh/fMitf. ariti c»n he
obtained by wanning with at^ua regia, whereby the ainnioiuji is
destroyed with evolution uf nitrogen. The solution on coricentrHiiun
yields fine crj'sUila of the free acid. It can also be obtainwl W
warming phoBpboHc acid find molylKlic acid in tiie rftfjuisit* pw-
portions. Pyro- and meta-phosphoric acids do not give iba** eon-
pouuda. This free acid is yellow, very rcaflily soluble in ' ■
yields jjrecipitates with "alkaloids" (organic compounds, b.i-
tivcs of ammonia which occur in pianUi and have mostly ii ]mH'I'
physiological action) ; it serves therefore us a reagent for theac

7fii. Lower Oxygen Compounds.— If zinc is iiitro<Iiieed into the

acid solution of niolylKiic acJd, the Hqnid fii-st becomes blue, ami m
further redurtiou passes through various colours inUt bnjwu. THt
solntion then contains a salt of the trivalcnl molylKienit«i Mo". Bj
very powcrfid reduction one am descend still lower; tlie re«ultia|
solution, however, oxidises with extreme reatliness.

From tnolylxlenum trioxide, the eorreapoiidiiij; .■ir.fquii>jide, Mo.O,
is obtained as n black powder by reduction with hydrogen at » rrf
heat. If the temperature is only moderately high, the dioxide Moft,
is formed as a crystalline, violet, or co[*p..<r-rolour('d mass. Hetwcen
this ajid the trioxide are the readily formed blue ctunjioinidN th*
composition of which varies ami cannoL be (characterised with 8utiii"i«ii
sharpness.

762. Chlorine Compounds of Molybdenum — A chloridfi ror
responding!; to rimlybdeniun trio.xide is not known ; the highest clilurii
stage is u j)<'nlitrhli'nih\ MoCl,. This is obtained by gcntJy warrainl

URANIUM, TUNGSTEN, AND MOLYBDENUM 753

tc molyl>denuni in a current of chlorine ; it is a dark red vapour,
condenses to a liquid, boilijig Ht 268° and solidifyint^ at 194' to
green crystals. The chloride reacts violently with water and.
a bhie liquid which deposits a broivn precipitate of molybdenum '
ydroxido on addition of alkalis, while a molybdate retnaius in
)n.

hen the pentachlorido is carefully healed in » current of hydrogen,
ses into mnlyhiUnum tricMoriih; which is very similar in aiiiwiir-
lo red phosphorus. On l>eing more strongly heated, this de-
(ses into difficultly volatile dirhlnri'l/', which remains behiTid, and
k'rkh, which loJutilisea. The former is a yellow, uon-crj'st^iUine
the latter a brown powder. All tho chlorides react energeticnlly
ndergo double decomposition with watei*.

jsides the chlorides, there are also a number of oxyehloritlettf
of which arc very readily formetl. The compound WoOjCIm is
r white in colour, and is obtained by boating a mixture of molyb-
trioxide and charcoal in a current of chlorine. Besides it
are also formed the violet compound MojO^Cl^ and the green
B^ which become more volatile as the amount of chlorine
pea ; the compound hist mentioned volatilises even under l<iO\ _

biybdenum trioxide volatilises very readily at ISC-iOO' in a ■
it of chlorine ; this is due to ibe formation of a 'compound :
)jCI., = MoO., + 2HC1. Sjdts of molybdic acid are also de-
led, the molyljdic acid escaping and a chloride of the particular
remaining behind.

S. Sulphur Compounds. — In nature the compound MoS^
ae moh/h(kiium rilaito'. It is a grey-black subatance, similar to
, and is the source from which the other molybdenum com-
Bre obtained.

Jiteaing sulphuretted hydrogen into the solutions of the alkali

atea, the liipiid Iwcornes intense red- brown in coloiur and

bs a corresponding tfiwmoli/hilatF. A similar variety to that

\ by the salts of molybdic acifl is found also in the case nf the

f thiomoIyMic acid, with respect to the relation between acitl

me, 80 that the description of the different compounds would

>o far. On adding an acid to the solutions, a precipitate of

fHtim Irisuljikidi' ia formed with evolution of sujphui-ctted

fen ; it is a red-brown substance, which gives a colloidal solution

nre water.

a C

CHAPTER XLIII

fJOUl ANIt THE PLATINCH METALS

764. General — The meuls which have to be treated in this chapter
cnristitiite, along w-ith silvtjr, the group of the noble tntUiii, Bf
this designation there is uiiilci'stood metais which do not nnite wfti
the oxygen of the air either at high or low tempei-aturea, and whieh
ctiri 1)8 converted only with difficulty into com[xmMds l»y means ol
chemical reactions. In otlier words, they are metallic eletiieRt« which
in the elementary state contain much less free energy than di«r
compounds.

Such a stiitement cannot of course be made quite general, sin« it
depends on the nalnre of the compounds wluit diftererice nf eiii:r;>7
exists between their free energy and that of their coni]K>nents. Tlins,
in fact, we see that towarfla certiiih roagvnts the nohle metals kibvf
as base, i.f. pfiss spontaneously into componnds. The reagent* wtich
Lave this action tin the noble metals are chiefly those l>y wliiehtiw
metals are converted into complest compounds.

Of the elements grouped together in this chapter, pi>lii occujjitt *
rather solitjiry position, while the six phtiiitum ftiftah form » veil
arranged group of three pairs. This is seen from the followin;^ uA>\t,
in whicii the neighbouring elements are especially similar to chcIi
another. The chemical similarity followa the values of the combininj;
weights : —

PalliKliimi ,

106'ii

PInlitmm

l$H-8

RtiodiuTii t ,

103-0

Iridium .

193-0

Ruthi-iiiuiii

101-7

Owaium.

ISl

765. GrOld. — The element gold occurs in nature almost ertiwlj
in the metallic state ; in spite of its rarity it may, hy rea.son ol it»
remarkable projjerties, he regarded as that element which hna Wn
longest known and which was earliest used.

(jold is a lustrous, yellow metal, whoso density is 19 '3, au«l wliicb
melts at 1035°. In the air, it remains imchanged tit all tempertttutv;
moisture also has no influence on its lustre. By reason of it& ^

754

iAP.XUir GOLD AND THE PLATINUM METALS 755

«rabiUtj it has lieen usjed from oUlen times a* a ataudard of value
d for eiiabliiig this staiidaid to }>e iireaervod. At the present day it
s been adopted by most countries us the >msis of their coinage.
Gold is not atfcackcrl by dihite or concentrated at'ids, so that it

K"n$ as a residue (as a brown {>owd«jr) wli^n auriferous metal is
d wntb tiitric acid or with concentrated sulphurio acid, which has
timiiar action. On the other hand, it dissolves fairly readily in
Jorine water and in other liquids which give off free chlorine. A
kture of nitric and hydrochloric acids has the latter property
iw 337), and is used under the name of " aqua regia " (since it disaolves
le king of the metals) for the prejwiratiou of gold compounds.

Of the niechanicitl projwrtiea of ^o!d its malleability is the chief ;
lis allows of the inet^il being rolled or beaten out to extremely thin
aves. These leaves transmit green light. Still thinner films of gold
» obtaintHJ by chemical i^recipiUitton from solution. Finely divided
)ld, aucU as is oblaineil by reduction on the skin when thia is
loisteaed with gold solution, appears red-violet. This property is
•de use of in photogra])hy for the purpose of imparting the well-
tiown brown-violet "photographic tint" to the browti positives,
Miasting of finely divided silver (p, (i87). For this purpose the
ictures are treated with a very dilute, neutral or alkaline solution
■gold, whereby the gold is precipitated by the metallic silver of the
iciure, while the silver j>aases into the corresponding compound. ,

fJold which is precipitated from soUition in a very finely divided
edition, generally appears blue by transmitted light, wliile the
ddent light is dispersed with a brown colour. If, however, pre-
pitation takes place in a veiy diluteil condition, purple-red solutions

colloidal gold are obtained ; these are precipitated by salts and
hibit the genenil properties of colloidal solutions.

* The simplest means of obtaining such solutions consists in
owing an electric arc to pass between electrodes of gold under
Iter to which a trace of alkali luis been addod.

In fused glass also, gold dissolves in a colloidal condition and yields
i fine red-coloured ^vhl-mhtj fjlinut. Finally, a solid solution of colloidal
Id in stannic acid, obtained by the precipitation of gold solutions
bh stannous chloride, has long been known by the name of pui'ple of
aius, and is employed in porcelain jrainting.

The combining weight of gold is Au = 197"2.

766. Gold CompoUDds. — Itogarding the ions formed by gold
ire is a£ yet nti sufficient knowledge. It is known that gold acts
th as a mono- and a.s a tri-valent element; in the solutions also of
I irivident compounds, trtvalent triaurion, Au" , can be assumed (the
inovident gold compounds are not appreciably soluble in water) ; it
however, unknown m what proportion these solutions contain the
I Au" along with other cumjilex iona, such ae gold forms with ease
i ill considerable niuubers.

756

PBINCIPLES OF INORGANIC CHEMISTRY CHir

The beet known gold compound is gold (Jiloride, whicli ia formed «o
dissohnnjj; gold in nquti regia. A yellow solution is produced frpai
which hjdroatirkhktri^ add, HAuOl^, cao be obtained in j'ellow, rtnulil/
eolublo crystals, by careful evapoiiition. On beating somewhat inw*
strongly, hydrogen chloride escapes and gold trifJiloridc, AuCI^ reraaini
behind as a brown, crystalline mass which is bIso readily soluble, III
aqueous sohitiun has an acifi reaction and contains the gufd in llie forii!
of a. complex anion of the composition AuOCl^", for the trichloriitp
unites with the solvent water to form the compound H,Au(>Clj. which
partially dissociates into its ions. By no means all the gold chlnnilt
however, apiwai's to undergo this traiisfoi-mation.

The hydioaurichlork vciJ^ HAnCl,, ia much better charackris*'!
A large number of weU-cryatalHsed salts of the anion AnCl^' are known.
which, however, are generally destgiiated as '*gokl chloride donW*
salts." They arc obtained by the action of the solution of hydn>clilori'
auric acid on any salts of the particulai" base, best on the chloridw.
they are often used for the cbaract(?risation of organic bases.

Of the salts of anrichloririion, AuCl,', the pof^Ufiitvi ^df hits lo W
mentioned which, according to ihc condition.? of crystal! isatinn, cnriUl-
lises with varying amounts of water {over sulphuric acid in anhyiircHM
crystals); also the sodium salt NaAuCJ^. i'HoO, wliich is wuploywi »
"gold salt" in photograpliy (p. 755).

Strong bases decompose both the trichloride and the hyilmnuri-
chloric aeid, and a yellow-brown precipitate of (impure) auric hydroxide,
An(OH),„ is formed ; this is sohible in excess of the base, since ibf
hydroxide lias weak acid properties. The pnfu.^iuw >tur>'t<, KAnO.
which is formed under these condition.? has also been obtained in ik
solid state as a bright coloured salt, from which metallic gold is vrrj'
readily precipitated (ejj. l»y dust).

By precipitating gold chloride with Ijaryta, difficultly soluble ^iw""
aurate is obtiiined which leaves a residue of fairly pure gold hyrlroridc
on being treated with dilute nitric acid. This hydroxide drtes nnJ
dissolve in dilute acids but does so in conceiui'ated nitric acid, with
which it forms an aurinitric acid similar to hydroauricldoric »ciJ-
Gold trihydroxide must therefore be regarded as an essentially «**
hydroxide.

From solutions of gold, reducing agents of all kinda, e.g. fommt
salts, sulphurous acid, oxalic acid, etc., precipitate metallic gold, which,
acconling to the contlitions of expeiimcnt, appears as a yellow (t^^
cipiUte of metallic )n.stre or as a brown powder. The commeiiremcm
of the separation is always signalised l>y the solutions assuming a Wut
coloratio]! by transmitted light.

7G7. Aurous Chloride. — By carefuily heating gold tlibrut*
to 180°, the compound AuCl is obtaiited according lo the c*|i»
tion : AuClji = AuCl + do. It is a yellow-white powder, which <Ii
not dissolve in water but decomposes accor<iiug to the ctiiiaUoi

GOLD AND THE PLATINUM ilETALS

lAuCl = AuClj, + 2Ai], into gold tricliloride, whiuh dissolves, ami
neullie gold, which remains behind. Aurous chloride forms with the
ilMi chlorideji complex salts, wliich can he derived from an auro-
iLluridion, AiiCl^'- They are obtained bj tarefiilly heating the corre-
(potiding auric compounds ; on solution in water, howei'er, these salts
undergo the same decumpusitioji us aurous chloride,

7fi8. Sulphur Compounds.^On account of the reducing action of
Hlmrcltcd hydro°:eK, the ssulphur compounils of the aurous seriefi are
■B stable and more easily prepared tiian those of the auric series,
iuroua sulphide, Au^S, is obtjiiiiod {mixed with sulphur) by passing
lulphurettetl hydrogen into a boiling solution of gold chloride. It ie
I diirk precipitate which yields a brown colloidal solution with pure
■tor. The solutioti doe$ not exhibit th@ reactions of a sulphide, and
fitfore contains only a uegligible amount of iroTi.

Aurous sulphide unites mth alkali sulphides to fonn thio-Balts
f the fonnula SIAuS, whieh are sulublo in water but are quickly
ecomposed la the air oiving to oxidation. By fusion with alkali
iilphides, therefore, gold is rendered aoluHlc owing to the foiiuation
i the above compounds. They are immediately decomposed by
ei(l&

On treating a solution of gold chloride in the cold with stdphur*
Lt*l hydrogien, a more highly aulphuretted compound of gold, liaviiig

Koxiiiiatelj' the composition AuS or Au.jSg, is precipitated. It is
liCk amorphous mass which decomposes into gold and sulphur on
g heated, is insoluble in acida, and can be brought into colloidal
»lntion by treating with potaaaium cyanide and then i^ith pui-e water,
"his precipitate dissolves in j'ellow but not in colourless ammonium
ilpluMe, *v'ilh formation of ummonium tkio<iuriile, NHjAuS,.

769. Complex Gold Compounds.— As is evident from the
escriptioii oi the more simple guld compounds, the saline derivatives
E gold are chietty of a complex character, i.e. the gold is not present
1 them as an elementary ion. Besides these there also exist a large
umber of other complex gold compounds ; such com|K3Uuds are
irmed with especial readiness with cy^anogen and aul]>h\u'.

The gold compounds are for the most part readil}' soluble in potafr
iim cyanide, and give rise chiefly to two ecries of salts, the aurous
id the auric cyanides. The former are derived from tmroctfaaiditut,
u(CN),'t which coiTcsponds to argenticyanidion, and are formed by
iBsohing aurous compounds in alkali cyanides. The compounds of
le second eeriea are the salts of uurici/anulwn, Au(CS)^', and are
iraed from auiic comjiounds and cyanides ; they are the better
lown and the more important of the two classes.

In neither c:ise have the free acids been prepared, but a number
: salta are known. Those ar« colourless ; they do not exhibit the
'dinary reactions of gold, and are, for example, not nearly so readily
iduccd as these.

■

f58

PRINCIPLES OF INORGANIC CHEfflSTRY chat.

The potassium salt, KAn(CN)^, crystallises with liHJJ in colmir
less, readily Bolnhlo plates, and has a technical iniportjinctj in tww
(Afferent directions. On the one hamJ, it is used for the electro-elding
of other metals. For this purpose it has the same adrantages u
are possessed by potassium argenticyanide for silvering (p. COl), JU
a rule, it is not first prepared fipecially, but potassium cyanide is
electrolysed between gold electrodes until a sufficient amount of the
BubsUmce has been formed in the liath. Us formation Uko* pliwi
at the an'xle where cyanogen is liberated from the potassinm cvaiiitiii;
the former immediately yields gold cyanide with the gold, which
thon dissolves in the excess of pota-ssiiim eyanide with formationof
potassium auricyanide. At the same time, hydrogen is liberated and
caustic potash is formed at the cathode ; the latter must be remored
by addition of acid.

Another application depends on the fact that metal lie gold dis-
solves in a dilute solution of potassium cyanide, with crwipenition of th«
atmospheric oxygen, to form potassium auiicvanide, according to the
equation : 2Au + 8KCN + 20™ + 4HjO = 2KAu(CK)j + 6K0H + H,.0..
Ab can be seen from the equation, Cfttjetic potash and hydri>p;n
peroxide are formed 1>esides the gold salt. It has ulrcady Iwen
mentioned that the formation of the peroxide in oxidatione by mean*
of free oxygen is a frequent phenomenon (\>. 160). The ainive re-
action is made use of ou the large scale for the extraction of gold
in thoM cases where it occurs so finely divided that tevigation or
amatgamation cannot be aucceasfiilly employed {vii/r. infra). South
African gold, more especially, is obtained in this way. The gold t»
again separated by electrolysis from the solutions (for which very
dilute poUussiura cyanide must be employed).

Gold therefore behaves as a base metul towards tlje aolutinii nf
potassium cyanide, for it dissolves in it under the joint action of th*
almosphfric oxygen, in mueh t!ie same way aa copper rljssolret in
hyrlrochlorie acid under the influence of the air. . This is dtie M
its passing into a complex compound in which the concentrtttion «f
elementary anrion is extremely sniiill. It has idready het^n jwintrtl
out that the smaller the concentration of the uietal ifm in the resuitini;
solution, the more does the metjil liehave as a base niotal t-owards th»t
reagent (p. 695). This refers not only to the electrical behaviour,
for this is only an expression of the chemical properties, but t« »ll
chemical processes.

These relations can be interpreted in the following general manner.
As has already been frei(uently emphasised, every pos-sible suh«taiM«
has a tendency to fornjation, and this is all the greater the smaller it»'
coticentratiou at that point where it could be foi-med. Of a iteccsFitr,
therefore, under given conditions, traces of every possible 9nlj*Uinoi
must bo formed. Tlie noble metals, now, are those for which im*
measurably small concentrations of their ions suffice to countsrM''

xra GOLD AND THE PLATIKUM METALS 759

hi tendency to further ion-formation. For this reason gold appears
tisoltihle in the ortlinary acidt;. If, however, the conditions are such
hu. even theae minute amounts of iona tiisiippear by being used up
n the formttiion of complex compounds, more gold must puss into
olutioii, aiid this must continue until the concentration of uurion
leceasary for ctjuilibrium lias been established in the solution. A
loble metal, therefore, will iippear aa base only in those sohitiona with
be components of which it forms complexes, and it will appear all
ibe more liase the more stable these complexes are in respect of the

rion, or the leas the amount of meUd ion split ofl' by the comi»lex
given, absolute concentmtioti. This view has been universally
loniirmecl by <jxperience.

We find here the explanation of the solubility of gold in aqua
*gia, although gold is not (or rather, is only slightly) soluble in nitric
tcid. The hydroaurichloric acid which is formed is a comparatively
ftftble complex compound in whose solution the concentration of
kurion is only very smalt, while the solution in nitric acid contains
Dore gohl and is less sUible. Aqua regiji, therefore, dissolves gold not
teostuee it is a stronger oxirlising agent than nitric acid, but because
^Id is a less noble metal with respect to aqua regta than with respect
U> nitric acid. It is still less noJde towards potassium cyanide solution

free oxygen, which are in themselves no very effective oxidising

I n-vi.

Gold also forms complex com[xiund8 with substances containing
tulphnr. The simple thio-acids of j;old have already Iteen mentioned ;
re have still to mention the complex compound which gold forms
vith the thiosulphates. By the action of a solution of sodium thio-
lulphate on neutral gold chloride, a salt of the composition
KayAa(Sj05)3 is obtained ; it can be precipitated from the solution
by the addition of jikohol, has a sweet tji^t*, and does not exhibit the
reactions of the ordinary solutions of gold salts. The corresironding

E'thiosidphuric acid, Hj|Au(S^,03).„ can also be prepared by derom-
fkg the barium salt (obbiiued in a similar manner to the potassium
'.

These compounds plity a r6le in the " toning " of positive silver
pictures in photogmphy, tis they are contained in the combined toning
Uid fixing aolutioiis.

770. Metallurgy of Gold, — Since by far the largest amount of
gold occurs ill the metallic st.Ue, the metallurgy of gold was for long
K iMfhunittd nud Dot a chemical operation. The auriferous sand \«^&
treated -vdih. running water which carried away the light sand but
left the heavy grains of gold behind. If the gold was not containeil
ill sand but in the solid rock {e.fi. in quartz), this operation had
to be preceded hy a mechanical disintegration of the rock, unless
f% was prcfi-rrod to fuse the whole stone, with suitable a<lditions,
the gold, being the densest component, sank to the bottom.

760

PRINCIPLES OF INORGANIC CHEMISTRY ciur.

Gold, howe^'er, frequently occurs in such a fine stJite of divisian
thflt it is carried away in tho prucesa of levigation. Iii these caees it cmi
be extrncted witb mercury, in which it is readily soluble ; the mercury
is recovered by diatillation.

Still more finely divided gold fa extract«<l with a very dilnt*
solution of potassium cyanide (p. 758).

Metidlic gold is not employed in the pure state for coinage and
articles of jewellery, as it is boo soft, but at most is used in th«
laboratory for cauetic alkali fusions, l>ecause it ia mors resistant to
caustic potash and soda in the heat than is platinum or silver. For
ordinary usage, gold is alioyed with other nietjils, generally cupfwr.
The amount of gold contained in the alloy for coiaage is reguLil*d bv
(tovernnient : English gold coinage contains 91 '66 per cent of gold

771. Platinum. — Of the iix motala of the platinum group
raeutioned above (p. 754) platinum itself is the mosl frequent and the
most imimrtimfc. Like gold it occurs native and is obtained by
levig.ation. Crnde "platinum ore" contains all six metals in varying
amounts, and must he subjected to a rather complicated process of aejiBra-
tion in orcier that the components may be obtJuned in the piu-e slate.

Platinum is a grey-white metal having a density 21*4, and meitixig
at 1770^ It can be welded at a bright red heat, can be dniwn t«»
tine wire, and possesses great resistibility to chemical influences. U
is, more eapeciallyj not appreciably dissolved liy pure acids ; in
durability under tho action of boiling sulphuric acid has already l«en
mentioned (p. 28tt), It is dissolved by iujua rogia, but also rather
slowly. It is also fairly stable to electiolytically liberated chlorine.
It is attacked, however, in cases where it can combine nt a red heat
with phosphorus ; many a platinum crucible has been eaten through
by igniting phosjihates along with cjirbon. Platinum iB also attacked
by melting caustic potjish or soda, while the alkali carbouutea can hn
fused without danger in platinum vessels. On lieing bealod for a loeiK
time in contact with carlton, the platinum absorba eomo of it, anrf
becomes brittle. It mi.Kes witb rciidily reducible metskls, and ffirni*
easily fusible alloys ; such metuls, therefore, must not come inlocojilac
with hot platinum vessels. It is indifferent towards hydrofluoric acnl

These properties render phitimim of great value boili in thu
laboratory and in the ai'ts ; indeed, so much of the ntetal is used in
the liiitor, tliat its jtrico has risen to several times its former value.

In the labonitory ulatirinm is lined for the most varied purpos**,
in the form of ciiiciVjies, dishes, wire, and foil, esjK'ciail}' for exact
analysis. In the arts it was formeriy chietly used for concentrntion
retorts in the sulphuric acid manufacture. On account of the eliiuigo
to the anhydride process now taking place in the sulphuric acid raaiiU'
lacture (p, 28C), the platiniira does not become fix*, for the dC
process also rctjuires platinum, alihough for other purposes. In
commercial electrolysis also, electroiles of platinum are often used.

GOLD AND THE PLATINUM METALS

A widely extended application of platinum is due to the fact that
ts coefficient of expansion is almost the same as thuit of glass.
^'latiiium wires fire, therefore, employed for leading electric conductors
tir-tight through glass. Whereas, formerly, use was matle of this only
In 9de»tiJic apparatus, large quantilies of pktituiro are now used for
the conducting junctions in electrical incandescent lamps, the interior
Bf which must be exhausted. Further, much platinum is used in
Slectrotechnics for coating electrical contacts, since the platinum sur-
hce» are not oxidised by the sptirks wliicli are there formed, aud thore-
bre retain their conductivity.

On account of its high melting point, platinum doea not fuse in
Dniinary flames, not even in the hottest part of the Bunsen flame. It
Ban be readily fused, however, in the oxyhydrogon flame (p. 102), and
this is used in the art-s on a large scale for the purpose of fudtlg
platinum to a mass ; the crucible material is made of Imnifc lime.

Since most of the platinum compoumlH decompose at a red heat,
leaving a residue of metallic platinum, the latter is in this way obtained
IMQ imfused, finely divided mass, known as phtinxtm sponijtr. In this
Hk platinum exhibits very pronounce»i catalytic properties, chiefly in
(Be acceleration of niunerous gas reactions. Several examples of this
have already been given ; the most impoitunt, technically, is the pre-
paration of sulphvir trioxide by means of spongy platinum. It must,
however, be emphasised that such catalysers show by no means a
Uniform behaviour in accelerating all slowly occurring reactions. On
tti contrary, so far as yet known, the relationship between reaction
^■catalyser is an inJindnal one.

* Spongy platinum was used by Diibereiner, the discoverer of the
above property, for the construction of the lamp named after him,
Irhich was greatly used at the time of
its discovery (1S23), when matches did
aot exist. It depends on the fact that

Eent of hj'drogen gas, when caused
ke on a piece of spongy platinum,
under its influence so quickly ivith
the atmospheric oxygen that the iiK^tal
becomes red-hot and ignites the hydro-
gen. The Dobereincr lamp, therefore,
tonsists of an automatic hydrogen gene-
rator (the amingement of which ia seen .^

from Fig. 12ri), filied with zine aud sul-
E>hurie acid, and of a piece of platinum
spofjge placed in a small box opposite
the e.xit tap. In recent times, the same
l»rinciple has been employed for the ignition of gas flames by the mere
l»|)eDing of the tap, eajiecially in the case of incandescent burners.
Since the catalytic actions of platinum take place at its surface, they

Km. ls^

762

PRINCIPLES OF INORGANIC CHEMISTRY cai?.

are, for a given amount of metal, all the more comifleralite the greaKr
the surface. This is seen in the very finely divided platimira which it
obtained on rednciug alkaline jilalinum solutions with organic sib-
stances, e.;!. formic acid (p. 402). The metal 13 then depositeil in the
foitn of a very fine powder which, on aecomit uf its black coloiff, ii
called plitthiiim Had; and which exhibits the above-mentioned catalrlic
propertius in a high degree. On being heated to rwlness, it cakes
together, and forms grey spongy platinum.

Besides the catalytic actions, platiiuim black also exhibits abwiq*'
tion phenoniena which, by reason of its fine division and correspotifliftgly
large surface, are ajs dearly seen as in the case of charctwJ (p- ^fi).
On account of this property it is somewhat difficult to prepsire platintan
black pure.

Finally, platinum is obtainwl in the most finely divided atato by
disintegration by mean* of ;ui electric arc under water (Bredjg). A
black -brown coloured colloidal solution is then produced, whicli
exhibits perfectly similar catal3'^tic actions to the other forms, ctuji
when present in extremely small amounts. By addition of salt*, lt»
pliitiimm is readily precipitated from these solutioiiB, and thereby k*M
a gi'cat part of its catalytic activity.

* Apparently connected with these catalytic actions h the proju-nv
of platinum of dissolving large quantities of difTorent gases, espt'cullj"
hydrogen. Hydrogen diffuses through red-hot platiruim with tli<
greatest ease ; but, even at the oitlinary temperature, platuiitiu,
especially in the form of platinum black or spongy pUtiinim, an
absorb fairly largo quantities of the gas. The hydrogen therelir
increjvses enormouBly in re-activity, and acta in accordance with iti
position in the potential series (in the neighbourhorol of lead), rdm"
ijig, for example, more noble metals from their salts, and forming fh«
corresponiling compounds, i.e. the acid. It must not be supposed that
the chemical affinity or the chemical potential of the hydrogen il
changed ; such an assumption, which is certainly very often mMlt,
would bo a contradiction of the fundamental laws c)f the theory oJ
energy. For, if it were the ease, one might gsnerate hydrogen
without the presence of platinum, and then in the presence irf pbtiuiira
allow it to pass again into the same combination, and would use wfi
loss work for the first process than is gjiined in the second ; in olInT
words, any amount of work whatever would bo obtained wttboirt
expenditure, or from nothing. This, however, is shown ity expen*
ence to lie iinjiossible.

* The cjiuse of the changed action of the platinum lies ratlier to
the ticcflernlvtii of the reactions of hydrogen, and ia, tlinrefar*",
cakilytic action. Gaseon.s hy<lrogcn reacts so slowly at the ontinaJT
temporattire that it appears like an indifferent substance, and fruB
the fa;ct that in the presence of platinum the reaction boconiea vinTiH
in a short time, while otherwise it would require houi-s or pcrh*i*

772. Compounds of Platinum occur in two aeries, in which the
tal a^-ts as tlivaleiit or tetravalent. The latter are the better known
nd the tttore stable.

Elementary plalttiion is formed neither in the one tior the other
cries in any considerable amount ; on the contrary, all the more stable
ompounds of this metal are of a complex character. The variety of
bese complexes la exceedingly gieat ; only a very few of them can be
rented here.

On dissolving platinum in aqua regia, a yellow -rod solution is
ormed which, on evaportition, yields crystals of hi/'/ropl<iiiniMimr
fid, H.jPtClg. This compound (s a strong dibasic acid, which does
lot contain any considerable aniounL of chloridiori, for it does not
live a preci];>itate of silver chloiido with silver salts, but one of silver
ilatinichloride, Ag^PtCl,,. Further, on electrolysing a solution of the
cid or one of its salts, it is found that the platinum moves towards
he anode and not to tho cathode, for the liquid during electrolysis in
be neighbourhoo<l of the catho<ie becomes poorer, and in the neigb-
lourhood of the anode richer in platinutn,' which shows that the

ttinnm is not present as a edition.
Of tlie salts of hydroplatinichloric acid, we have already met with fl
dilficiiltlj soluble jiittasmum mli {p. 450), since it Is used for H
be Mparatioo and andyticiil estitnation of potosdnm. It is a salt H
rbtch crystallises in anhydrous, regular octahedra, and is much more
eadily soluble in hot than in cold water. By addition of alcohol it is
Imost entirely precipitated from its aqueous solution.

Sodium plaiinkhhrride ib readily soluble in water, and crystaUisea
ritb 6H,0. Ammonimn pla!i$niikhwide resembles the potassium com,-
toiuid in being difficultly soluble ; it is used for the separation of
ilatinum from the solutions of the crude platinum ores. On Iieing
leated it readily deconijm,ses into ammonium chloride and chlorine,
rhich escape, and metallic platinum, which remains behind in the form

pongy platinum (p. 761).

By carefully heating hydro[>latinichloric acid in a current of chlorine,

iii«f» tetritchlt/rule, PtCl^, is obtained as a crystalline mass similar to
Ijoroptatinichloric acid, but not deliquescent. It readily dissolves in h
rater ; the solution contains, liku that of gold chloride, an oxy-add, H
IjPtCl|0, which is formed by the absorption of the elements of
rater. The very dilute solutions have the remarkable property that
beir conductivity very rapidly increases when they are illuminated,

tAt lli« eloctrodot themselTes tile Te&otioii is ujiporeiitly thA aitpcnlte. meunic ^^H
mm iiepsrfttitig out on the vathode. This ii, bowover, a scconilary reaction ^^
Be to the fact that the hyrlroRen, which is conducted by tho current to the cathode,
M (UBcharged there, but redncei tho pUtinam soluticm pruicut. ami tbe metal is

764:

PRINCIPLES OF INORGANIC CHEMISTRY cau.

— a behaviour which is pi'obably conDected with a hydrolysis and
sjilittitig off o£ hydrochloric acid.

Oti adding excess of soditim carbonate to & solutioa of Uydroplatini-
chloric iicid, concentratirig and extracting the residue with acetic acid,
platinic liydmxidt, Pt(OH)^, is obtained as a red-browti jiowder, which
is soliiblo in strong auide (but not in weak acids like ucetic acid) and
in alkalis, "the solutions in acids contu-in plutinic salts, which at
greatly dissociated hydrolytically, l>ut presuraabJy also contain a little
tetnipMinkni (Pt"") ; they are of a yellow-brown colour. The alkiliiie
solutions contain pkilmtks^ ie. salts of the acid H^PtOj^ soma tt
which ha'V'e been prepared in the solid state.

IVom tlia solutions of the platiiiuin compoimda, sulphuretted
hydrogen slowly precipitates black plittinitm .fiiljihide, which dis«olvei
in excess of alkuli sulphides to a ilark-brown solution, vt-ith formation
of a thioplatiuic acid.

From the compounds of platinichloridion, compounds of pkiiiUf
chhridion PtCl^" are formed by means of reducitif^ agents. Thii«, on
warming an aqueous paste of potassium platinichloride with cupMUi
chloridf, a dark solution is obtained from which dark-red crystals of
the soluble salt KoPtC!^ separate out. The free acid is knowa only
ill solution ; the anion PtCl^" is niby-red in colour. The potassinm
salt is employed in photo^riipiiy for the [>roduction of platiaotypes.
which consist of metallic platinum. For this purpose it is spread on
paper, along with ferric oxalate, and exposed to light ■ in the light tii«
ferric salt ts reduced to ferrous salt (p. 592). If the paper is tlien
passed tliroiigh ;i solution of potikssium oxalate, a reduction of the
platinum occurs at those parts at which the action of light hid
occurred, and a positive is obtained in a grey-black colour which, la
accordance with the stability of metallic platiimm, is very resistuttto
air and light. With a very weak acid solution of potassium pUtinO'
chloride, also, silver prints can be converted into platinum onc«, i-t, oni
can " tone " with platinum.

From the solutions of the platinochlorides, alkalis pi-ecipitat^ UadC
pliilinous hijdroxide, which has no acid projierties.

Flutirmts chk^ide, PtCl^, is obtained by heating hydropl
chloric acid to aSO'^-^OO'', or by heatiuj^ spongy platinum to llw
same tempemture in a current of chlorine. It is a green -browB
powder, which does not dissolve in water, but is readily soluble in
lu'iirochloric acid ; with the latter it forms a hydroplatinochloric
acid.

On passing carlion monoxide over platinoua chloride, very remark-
able compounds are formed which contitin the components in thf
proportions 1:1, 1 r 2, and 1 ; 3. The first volatilise* without decoo
position at about 250^, and thus stands in conspicuous contrast to »U
other platinum comjjounds, which are not volatile, but decompose it
the heat. Thoy are yellow or yellowred crystalline substances.

GOLD AND THE PLATINUM METALS

765

allowing a solution of potassium platiiiochloride to stand with
ium nitrite in a warm place, piihissium jdntinoiiiirite, K.,Pt(Nn.,}j^,
tt crystallises out in colourless, ciiffieultly fluluble t'rystala. The free
I, H._,r't(N0j,)4, has also been jirepare<j. Tlie salts lentlilj' take up
I combining weights of halogen.

Of the numerous other series of complex compounds which platinum
118, we may still mention the ammonia and the cyimogon com-
LiMi& The iimtruMui fomfmumls bulong to two series, eorresjxinding
ibe platjnoiis and pUtinic compounds, Thtjir empirical composition
hat of divalent or bolRivalent salts of platinum combined with one
:our combining weights of ammonia, NH^, often along with water.
peover, they exhibit sfwcific properties, showing that they are salta
new ciitioiis in which neither the ammonia nor the platinum gives
QSTUi) reactions These compounds are very similar U) the corre-
udiiig compounds of cobalt (p. 623), more especially also in the
; that the halogens anil acid residues present are only partially
uraled as ions, and in jwirt form constituents of thu cations. The
^xidcs of several of these have been prepared, and are soluble
■tDces with a strongly alkuline reaction. For the theory of these
jpotindg cf. p. 6 '24.

The complex compounds with ri/anoffen are derived from the
B.1eiit jdiitiiuz-ct/iiniiihii, Pt(CN)^". The potassium salt is formed
dissolving plaiinous chloride in a solution of poUissium cyanide,
I also by melting potassium cyanide with spongy platinmu ; it is
iright yellow salt exhibiting a blue iridescence. The barium com-
ijld is formed by mixing platinoiia chloride and l>arium carbonate
b water, and passing hydrocyanic acid into the hot liquid. It is a
;ht yellow salt exhibiting violet-blue iridescence. The laagneEiuin
, which can be prepared in the same way, is crimson red with
en metallic lustre, the property of surface iridescence, dependent
the crystalline form, being p^tssessed by all the salts of this series,
s barium compound .dso exhibits in a very marked nuinner tha
inoiaenon of fluor&seencej and it converts, not only the oi-di-
y tiltni- violet, but alsio the Rontgen and uranium rays (p, 746)
J visible light, and its application is in accoiYjance with this
perty.

From the solution of the barium salt, the free hjilmplaHmxifanir
f is obtained by means of dilute sulphuric acid ; it is colourless in
ition, but in the solid state it exldbit* a variety of lustrous colours,
ording to the amount of water it contains.

The salts of this series readily t«ke up two combining weights of
agen, but these are only feebly united ; the corre-sixtndiiig com-
Lods likewise generally crystallise well.

773. Palladium. — Palladium was discovered by WoUaston in 1803
platinum ore. It is the least noble of the platinum metals, as it
dily dissolves in nitric acid, It resemblea platinum in its combining

766

PRmCIPLES OF IXOEGAXIC CHEMISTRY csht.

relations, for it foi-ms divulent and tetra^-alent tompoiinda ; in thi
ciiSG, however, the diviileiit compounds iire the more stalde.

Metallic palladium has a dutisity of 11 8, atut melts ut l.'iOO . [{
is a metal aimilar to pUitinum, and has th^ special property of nriitin(
with large amounts of hydrogen to form a compound of met*lli»
Appearance, the nature of which baa not yet hecn sufliciently oxpUinei
The combination of the two substances takes placo most rapidly *l
100 , and is all the more rapid the more finely the metal is divided
With finely divided metal, 800 volumes of hydrogen are ab&»>rl«d Ij
one volume of the metal. Still more hydrogen is absorbed oj
emplojing the metal as cathode in dilute sulphuric acid ; the amoiinl
of gas then absorbed increases with the strength of the current;
portion of the hydrogen so absorherl, however, eacajxis immediately
the current is stopped, while another portion is in stalile combinatioa
If the temperature is raised, the jjalladium hydride again decomjKwel
into its components j it does not, however, follow the ordinary In*
of diasoeiation, according to which the pressure ia independent of ih*
degree of decomposition ; in this aise there is a dependence.

The hydrogen absorl'ed by {jiiUadiuro hits a strongly redndni
action, and it has therefore often been regarded as oxistitig in a speciil
condition. In this ctise, however, as in the sasc of platinum, we *«
dealing only with a catalytic acceleration of the reaction.

* If galvanic cells are constructed containing hydrogen along wilii
viirious metals, such as gold, platinum, or palladium, no electrotni>tJv«
force 19 observed if the hydrogen ia always present in excess. Tliii ii
a proof that the chemical potential of the hydrogen is not increased by
the palladium.

Of the chemical compounds of palladium, puliadutfu tdtnU,
Pd(NO.,).,, may bo mentioned, which is formed by dissolving dt4
metal in nitric acid. It is a very delirpiescent salt^ the solution flf
which is dark brown in colour ; this colour may be ascribed to dipl-
hidion, Pd". On adding alkali carbonates to these solutions, mrboA
dioxide is evolved, and a dark bro^*^^ precipitate of palladions hydroxid«r
which on ignition decomposes only with difficulty into metal and OIT-
gen, is deposited. Dipalladiou unites with jodidioti to form a dark-
brown compound, which is soluble with extreme difficulty in watrc
Since bromidion and chloridiou do not give such a precipitate, p«t-
ladions nitrate can be used as a reagent for iodidion.

If tmlladiura is dissolved in a large excess of acjua regia, a sulutioit
of hijdm}niUmlkhioric aail, H..PdCl,., is formetl from which the poti*
sium salt can be obtained as a difficultly soluble crystalline jrowdef
consisting of scarlet octahedra. lHvi.'U on heating the acid solutioii W
boiling, chlorine escapes and hfdioiHilMufhlimc iwhi, H.,PdCI^, is furintJi
the potassium salt of which is very similar to the corresjMXiding |ii*'
tiiious compound (p. 764).

On evaporating a solution of palladium in aqua regia to dryiMi^

GOLD AND THE PLATINUM METALS

T6T1

I
I

irogen chloride and chlorine escajje, and jxilhilious chhrrdf, PdClj,]
jbtained, which dissolves Jn water with a red-brown colour.
The ci>iiihiiiitt<i w^eight of [Kilhttiium is Pd = I06-o.
774. Iridium. — On troutinj; plutiimm ore with aqua regia, part
I the iridium 13 dissolved along with the jjlatinuni, rtiid jiai'l remaina
Djed with osniiitm as osmiridiuin, which is not attacked by aqua
ITie dtaaolveJ jiortion is jiretiin'tiited along with the plntiniun
^ m&ans of ammouiucti chloride, and its presence h recognised eveu
comparatively small amounts by the fact that the comjiouud of
Utitium chloride and iimtnonium chloride h;iH a y<illow-red or red- 1
»wu colour instead of brij^ht vbIIow. This purtion of iridium is uftea
in the platinum used in the arts, since the metal thereliy becomes |
ler an<l more resistant to chemical influences.
f^Fure iridium scarcely melts even iti the oxyhydrogcn flame, and'
an be worked only with difficulty. It has the density 22, the hard-
nen of slightly tempered steel, and is only slowly attacked even by
tqus regia ; it is more readily attacked when it Is iu a state of fine I
ion. On gently heating a mixtni'c of the metal and common {
in a cuiTent of moist chlorine, the former can be converted into
sodium salt of divalent iridichloridioo, IrCl,".
Iridium forms three series of compounds in which itisdi-, tri-, and
letravalent. The divalent compounds are the leiist stable and are
little known ; the other two series pass very readily on*' into the
Dther, so that it is hardly possible to say which i^ the more stable. Iii^|
hath series the typical compounds are the complex iridiuuichloride ions ^^
Kihe trivalent ij'idochloridiou, IrCl,,"', and the divalent iridichlorid-
tan, IrClg". The foi-mcr anion is green-brown, the latter dark-red.
Xhe change of colour accompanying the ready conversion of the twe

Eies into one another gave rise to the name of the element (frota^|
^ a rainbow). ^1

Potassium hidicMoridf, Iv^IrCl,,, resembles potassium platinichloride
itB solubility relations ; it crystallises in small dark-red octahedi'a,
I 18 obtained by heating a mixture of finely divided iridium and
potassium chloride in a current of moist chlorine to a gentle red heat
The corresponding sodium salt crystallises like the platinum com-
pound with 6H.,0, and is readily soluble. By reduction with
totphui'uua iicitl in acid (or with alcohol in basic) solution, chlorine and
■iiimn chloride are split off, and sodium iridochloride, NaglrCl,,. 1 2H„0,
j^eh is a very soluble 8:dt, is obtained. The potassium salt obtained
in a similur manner from the iriihchlonde^ is also readily soluble.
Both are readily reconverted by oxidising agents into the higher
leries.

With ammonia iridium forma numerous complex ha86«, whicli are
ilar u> those of platinum, ^_

The combining weight of iridium is Ir= 193*0. ^M

a relation similar

(68

PRINCIPLES OF INOEGANIC CHEMISTEY chap.

to that of yjalladium to platinum. Like iridium il fotms tlirec ferin
of t;ompoiincls ; in contrast with iridium, however, the highosi series it
here the least stable. This depression of the region of siaUIiiy
towaiflis the lower type is present also in the case of pallaiiiiini
compared with platinum, and occurs in both cases in the element of
lower combining weight.

Rhodinni occurs in convparatively small quantity iii platiiiUTn or**
It was discovered in 1803 by Wollaeton, and has obtained its njim
from the rose-red coloiu- of its salts.

Metallic rhodium is less refractory than iridiiiiu, but more so than
platinutii. In the pure sUtte it k ductile and bus the density 11
The finely divided metal has very pronounced catAlytic prtjpertiM
for example, it rieeompoaea formic acid in aqueous solution into
bydi'Og<?Ji and ciirlwn dioxide : HoCO„ = H„ + COj, i.e. it so greatly
accelerates this reaction, which takes place of itself in very siuiU
amount, that the giiaes escape with efferveBcence, Other urganic
compounds are also chungecl in a similar niRnner ; this is s, proof that
very many of these substances are unstable comiwiinds, and gaitt .in
rippearanco of stability only from the slowness of their spontjinooitf
decomposition.

Tht? best known compounds of rhodium are those of the tri*-*!*;!!!
type ; from these, apparently, two different rhodiumchkiride iotiS;, ni.
RhCl^"" and IthCl,,'", appear to be derived ; suits, at least, of thew
two types are known. The aUcaH salts are soluble with a red culour
in wator.

A fiiirly large number of complex ammonia compounds are «)»
known in the case of rhodium.

The combining weight is lih = 103'0.

770. Osmium und Ruthenitim are ilistinguishe<l in a very
characteristic iii:iiitier fnim the other four plalimini inetjds by their
propcity of forming Tauii/i/ volatile iKrygrn cotn^mituiit - these are Jiro-
duced, although slowly, by heating the metals in the air, and volatiliw
with the steam in the treatment of the crude platinum om with aqu»
regia. These compounds contain four combining weights of oxvj
one of the metal, and behave as almost indilTorent sidsstaiicM ;
events, the acid properties of iho hydroxides (unknown in the tttt
state) are only feebly developed.

Osmhtm has the density 22*5 in the crystiilline state and is th«
densest of all known substances. It is almost infu.sibli^, is very b«r<lt
is insoluble in afpia regia, bur. passes slowly into the volatile tetioii'l*
on heating in oxygen. Jiy fusion with zinc and treatment of tlie
.^.lloy with hydrocldoric acid, it is obtained in a finely divided stiiW
as a black powder, which, on being heated in the air, smoulders iUiil
forma the tetroxide ; from tin, however, it is obtained in cryst^ils with
a metallic lustre.

Omiiridivm, which remains after treating the platinum ore, forro*

XUll GOLD AND THE PLATINUM >tETALS 76&

banl, silver-white laminse, and is used for tipping gold pen-nibs, wliica"
do not wear down with use. On being heated with tiomnioti salt in a
eurreiit of wet chlorine [mde saprn) the c^mium volatilises in the form
of the tetroxide.

Oituittm Mrorul« is a white, reiulily fusible cryftUilJine mass which
hIowIj dissohes in water and readily volatilises with Btoam. It has a
•troQg, veiy iinpleaaant ^mell, recalling that of chlorine, and a highly
{Ntisonous action, because it ia reduced hy the tissnea to metallic
Oimjutti, which is deposited and exercises a continual irritation ; the
eyes, more especially, are powerfully attacked. The solntions exhibit
oxidising actions but no acid reaction ; if an alksdi '\& added, the
greater portion of the teiroxide can then be distilled off, showing that
the corresponding salt mideigoes hydrolysis lo a large extent, and ia
therefore formed only in very small amount.

Aqueous solutions of osmium tetroxide are used in histology fi
hardening animal tissues.

On careful reduction, the alkaline solutions of osmium tetroxide
are converted into the salts of osmtinion, OsO^,', the acid not being
own either in the free state or as the anhydi'ide. That a new anion
been formwl ia evidenced by the faet that the liqiud, which was
viously colourless, becomes red-violet; on addition of acids, bow-
er, the osmic acid decomposes into tetroxide, which volatilises, and
e hydroxide of tetr&valent osinium, which is deposited aa a black
precipitate, if any oxyaeid has been used ; in hydrochloric acid, how-
ever, (.he latter is soluble.

LWith chlorine, oamium forms two oamiumchloride ions, OsClj'"
d OsCl^". The former anion is cherry red, the latter golden yellow.
The salu of the secotvd series are foifmed by treating osmium and
alkali chlorides with tnoist chlorine, those of the first are obtained by

ttlie reduction of the latter, and are unstable.
Finally, osmium compounds of a divalent \,j\m havu been obtained
the reduction of the hij^hor compounds. The corresponding salts,
in which the osminni is present as a divalent cation, are dark-blue in

(iloiir ; they oxidise very reiidily to a higher stage.
The combjniuf,' weight is 08 = 191.
777. EutheniuiQ was discovered by Clans in 1845. It ia a grey
etal of density 1 1, which fuses only with diffietilty but more rctdily
an osmium. It is fairly resistant to aqua regia ; on fusion with
ustic potash and 3alt[>etre it is attacked with formation of imtassium
nithenate.

distilling the solution produced white a current of chlorine is

s&me time jiassed through it, ruthenium teiroxide passes over aa

low crystalline mass, which melte as low as 26°, and boils about

at this temperature, however, explosions readily occur. It

ims to be formed also in minute traces on heating ttie metal in the

The vapour h yellow, and the molar weight corresponda to the

3 D

770 PRINCIPLES OF INORGANIC CHEMISTRY chap, xliii

formula RuG^. It dissolves in water, forming a yellow liquid, which
is unstable.

From the oxide, two series of salts are formed with bases, nith
loss of oxygen, viz. the dark green perrvihenates, MRuO^, and the
orange-red ruthenatss, MgRuG^ ; between these two, therefore, the same
relation exists as between the permanganates and the manganates,
and their reciprocal transformation also takes place under perfectly
similar conditions, the latter being more stable in alkaline liquids, the
former in acid or neutral.

With chlorine, ruthenium forms compounds of the di-, tri-, and
tetravalent type ; the last two form rutheniumchloride ions, RuClj'
and RuCl/ ; the former are yellow, the latter red.

The combining weight of ruthenium is Ru= 101*7.

Ja the

'78, Gen&ral. — In tlie preceding chapters the question as to which
of the possible multiples of the L'ombuiing weight of each elemetit U
the most suitable has not been discussed, and we now pi-oceed to
ex&muie whether a. general ati&wer can be given to the question at all.
As the roost obvious rules for the choice of the coml>iniag weights,
lie two foilowinj,' will evidently be kid down, viz. the funnulae shaU,
the first p!ac*, be as iiwpU -ah possible, and, in the sueoud phic*'.
ftympfMiuis sludl Imre .nmitnr formula;. These two rules lead, in
cases, to concordant results — in other cases, however, to contru-
dictory ones.

Thus, according to the piiiiciple of siiiqilidfj/, the conibiiung weight
of those elements which form only one compound with oxygen will l>e
thoeen, so that the compound contains one combining weight of each
element. This is, for instance, the case with zinc and cadmium, whose
oxides are written ZuO and CdO. In the second place, in accordauire
»ith the principle nf dmitmili/, of the two oxygen compounds of copper,
«iij>ric oxide must \>f< formulated in agreeinent with zinc oxide, because
ties*' two exhiliit vaiious points of similarity in thfir compounds.
Hence, it follows, that cuprous oxide must be written Cu^O-

If now, we are dealing with stiver oxide, we should, in accordance
with the principle of simplicity, write the formula AgO, and uiake
Ag=215"8. This, however, would be in conflict with the second
principle, for the silver compounds are very similar to the cuprous
com|>ouiids. We have the choieu, therofore, of violating the one or
other principle ; they cannot both Iw followed at the sjime time.

Similar holds in the case of iron nnd ajumiiiiimi. On account of
its Btmilarity to zinc oxide and cupric oxide, ferrous oxide must be
mitten FeO ; from this, the formula FejO., would follow for ferric
Dxide. Alurotuium forms only one oxygen eompttund, and would,
liherefore, in accordance with the principle of simplicity, have to be
irritten AlO, Al being made eijual to 40*5. In this ivay, however,
Ittentloti is not paid to the undoubtedly very great similarity to feixic

771

772

PRINCIPLES OF INORGANIC CHEMISTRY chai'.

osdde, and in order to give expression to thia we must write ALO^
and thus violate the principle of Biniplicity.

To give effect to both of the ahove prinL'ipIea at otie iind tho lamo
time is not possible withont producing contradictions, and one W
often to decide which of the two principtus one will violate. In
general, the [irinci|ile of siniiUirity has the preference.

779. Isomorphism. — It is, liowever, not easy in any given csmw
decide as to the degree of similarity to be taken into account. Silver
oxide and lead oxide also show a considerable amount of tiinilarity itt
their geneml rektious, more especially in respuct of the solubility nf
their trnltA, und yet the two are difTerently formulated, viz. Ag.,t> wid
I'bO. lu order to arrive at definite mles, wo must give up the general
" similarity " and chooae some demonstrable property as b/isis. In
isofrwfj'hisvi (p. 311) yrQ obtain such a pro|»erty. We ahnll therefore
lay down the principle : The combining wdghts shall be chosen sarh
that isomorphons suhstances h^ve similar formula?. As a matter of
fact, this priiiciplt' can l>e followed without obtaining eontratiiction*,
and all isomorphous pairs and groups* mentioned in this book bB»»
roceived concordant fonuuld.',

A complete system of combining weights, however, caituoi be
obtained in this way, since the isomorphous groups are mostly re-
stricted to a small number of compounds, and the relations eitsting
between elements belonging to different groups (e.y. mangJuicBej we
not sufficient to unite rU the groups. Further aids muat therefure
be looked for.

780. The Molar Weight. — ^Such an aid ia afforded by t lie con
ception of molar or molecular weight, if we lay down the condition
that aUforrnulm comqmnd'mfj tn a molar weight sltull confuin unJji a tehek
7uintbfr of amLUmng weights of the elements (p. 90). The molar weigW
is a number which can be deduced from the gaseous density or from
the dftnx'S.sii>n nf the freezing point or elevation of the Imiliiig i«iinl
(p. 159), ami which C4ui be determined independently of doubtful sup
positions, and purely by experiment. The question whether the al»ov»
condition is fulfilled can therefore Ije tested in the case of all sub-
stances which cun be observed in the gaseous state or of whidi
solutions can be prepared. As a matter of fact, various doubtful cmM
have been decided by this means. Thus, for example, beryllium w*i
regarded by many investigators aa an earth metal, and ita chlorid*
was, in analogy to that of aluminium, written BeCljp i.e. there imi
taken aa the combining weight of beryllium that weight which '
combined with 3 x 35-46 {Mirta of chlorine, vii!. 13o. When, liowimilj
one succeeded in determining the vapour density of beryllium chlorjdi
its molar weight was found to be 80. Prom this it follows that only
tim combining weights of chlorine can be contained in berytlitini
chloride. The combining weight of the element must therefore W
taken as 9, and the chloride be written BeCly

THE CHOICE OF COMBINING WEIGHTS

rT3

latae consideriitions, of course, lead much further than those of
M^phism alone, but even they are not perfectly decisive. It is,
id, concetvable. although generally not very probable, that besides
lompoimds whose molar weights are known, other eompoutids of
■ticiilar element exist, the molar weight of which contains only al
ton of the combining weight deduced from the former compound.
would not necessitate a contradiction bo the other compounds, but
d merely lead to the aasuniption of several combining weights in
ormer compounds. In other words, from the molar weights there
)e deduced only the limit above which the combining weight does
Lie, but it cannot be proved that the combining weight is not
ction of that hitherto chosen.

'81. The Atomic Heat. — A law discovered in 1818 by Didong
Petit, and which has since then been confirmed in many other
fc admits of no such doubt. This states that the thenma! cajjacity
M elements refen-ed to one combining weight, or the atomic hraty
Qfitaot and equal to about 6 calories or 25 ij for each degree.
Jy the term thermal capacity of a body there is understood the

h>etwecTi the amount of heat communicated to the body and the
ition of temperature wliicli the latter exjierienccs. If, therefore,
heat Q is introduced into the body, the temperature of which
iby rises f , the thermal cap;tcity of the body is k - Q/i, This
^ty k is evidently proportional to tiie weight of the body investi-
K for the elevation of temperf»ture will be smaller in the same
OTtion as the amount of subetance increases to which the same
tity of heat is communicated. It has, however, also Vieen found

equal weights of dift'ercnt s\ibstai3ce3 experience very different
itiou of temperature with the same amount of heat ; that is,
ther words, the specilic heat of dilTerent aubiitJinceB is different,
ihe term specijk heal has been applied to the thermal capacity
red to the unit of weight. If, however, we refer the thermal
sity not to equal weights, but weights which are in the ratio
lie combining weights, these qviiiitilirs of mfistuwr have Ihc mine

I\l mfxii'iti/ when we are dealing with the einntKts in the solid
I Calling the thermal capacity refeiTed to the combining or
p weight, by the name atomic heat, the law states that the utomie
\j lilt stditl elewriiU arf eipwL
rhis law is not universally valid. In the first place, as above-
ioned, it {.<; valid only for the solid state - liquid, and especially
>U6 elements, are not subject to it. Further, it is valid not for all

Klements, but only for those whose combining weight is not loss
0. The elements which are below this limit have, in the sense
e law, too small an atomic heat.

'82. Result, — If we now ask how these different principles for
;hoice of the combining weight can be united, in sn far as thoy
Ltbe same elements, we flnd that they agree well with one another.

PEINCIPLES OF INORGANIC CHEMISTRY OHUf,

A system of combiiiiiif; weights can be tlniwn up which allows of A
expression of all iBomorphism relations by toncoitlant fonuulte, and
all molar weights by integriil values of the combining weights, i
whereby also the atomic heats of the solid elements (with combinim
weight above 30) tire expressed by approximately the same numlieit
.These are the combining weight-s of which use has continually 1««
'made in this book, and which ure at the present day ^Ili^ er»allj
accepted by the chemists of all countries. Nrwhere in this work hs
it been necessary to write formulrei representing actually determiii'
molar weights with fractions ' of the combining weight*. Further, ii
all cases of isoraor|>hism, the formuhe of iaoraorjihif compounds
similar, and that the rule of Dulong and Petit is fulfilled is seen frua

loiiowing t

auie : —

'LitSiium

JtoIvMeuum

Beryllium

Uiltlfii- Ilium

Ui>rcm .

. 18 to 17

Khodium ,

Carbon .

. 3 to 23

Pailailium .

Sodiitm

Silver

iMa^teNJuiii

2<J

Cadmium .

Alnmininm

Juillnui

Silicon .

. IS to 24

Tin .

Phosphoms
Sul|jliur

Antimouy

•u

TBlliiriuni

I'otaflstuTn

Iodine

Cnkiuni

IjillthnUlllti

Chroniiiitti

2«

Tungsten .

Mahgaiiuse .

Iridiuiti

Iron

rJAtinuni .

Cobnlt .

r.oid .

Mekel .

Osmium

(Jl ![)[>«■ .

Mercury

Zin«

•2(1

Tlinllimn

fiiiHiitm

'23

I.<:,id .

Arsoiiic

Hiiiniiitli

Si'lt'tiiiim

•25

Thoiium

ilircuninm

ITrfHiium

:i<S

783. The Periodic System. — Attention has been n'|waledl]f
drawn to the existence of regularities between the combining wt-ij^hH
of similar elements, whicii generally assumed the form that tiic aiJ«
fereiicea in the numerical values of correspfnuiJug elements in difforent
groups are approximately equal. The i|uost)on here arises whctbd
we are dealing with any fairly general regularity, and if so how lliisi
to be expressed.

The iinawer has been sought for in very different ways. As tisuiJ,
the simplest has been arrived at last. If the elements are arrange*!
a series simply according to the numerical values of the cotnbinial

1 In sam« few eiWeJ fractions hava lieen niiltcn in tbe iitiil*nirnt of lUv wnler
cryrtallitutioij of suits. Siin't;, nl presciiU nioliir weigM« ctn 1* ilelrTttjiiiwl onlj *
gnats or vajiours mid lor ilisttolveil unfistunce^, liut not for Millil nulistuiK-*!*, iia c
tradictiou «xist.9.

THE PERIODIC 8YSTEM

without regard to any other circumstatice, the following is the

eaulu

In this series aimilar elements always occur at regular intervala. If
ken th« geries ii^ divided into a, number of soctions, »o thut each section
KMnraences with a member of a definite fftinily, it is found that the
econd, third, and following positions of the sections are ajao filled by
llements eorrespoudiug to one another.

The tiible on p. 776 has arisDii by dividing the series of the elements,
IB determined by the values of tlse comliitdng weights, into such
leetions ; these eectioiis have then been plaoed one below the other.
^^« way perpend iculai' columns ai'c obUiined in which Biinilar or
^■led elements inland under one another.

"The ditt'erent roivs havo also been altenmtely shifted somewhat
relatively to one another. As can be seen, the mutual relation between
those olemcnts which aro moat closely allied to one another thereby
deceives better exjireasion.

Thus, in the column headed 0, we find all the elements of the
Irtnm Itfpf, which are distinguished by their inability to fonn cheTiiiciil
»iQpound8. Under 1. there n,re, on the one hand, the monovalent
llkal) metals, on the other hand the numomleni heavy metata, copper,
iSlver, gold.

Under II. there stand the dimknl alkaline earth metala, and along
(ritb them the diiatent heavy metals of the Kinc group.

Under III. are the /rimkiit earth metals {dong with the correspond-
ing heavy metals, gallium and indium.

Under IV. the te(mtvkiii elements are found. The first repre-
leutatives of these -have no longer a metallic character, just as the
Irst non-metal appeared in the precetling group in the case of boron ;
ihe metals of the titanium group on the one hand, and of the tin
^oup on the other, then follow.

Column V. also conta.ina, to begin with, non-metals which can a«t
Is trimhni or as peiilmuleat ; in the lower portion there are the
torresiwnding tri- ami pentavalcnt raet4i]s.

In column VI, are di- and h4'£imileni elements ; the non-metallic
jharacter can be followed further down the column.

Column VII. contivins the typical non-metals, the halogens, which can
let, on the one hand, as 7rto»(?valent — on the other band, as //pp/flvalent.

Finally, the last column contains the two families of the iron metals
ind tiie platinum metals, which do not quite fall into line with the
lest of the sy&teni.

Iti all these columns the general rule can be observed that the basic
jn^perties (i.e. the tendency t'O form cations) increases with increasing
jombitting weight ; the ]iovver of forming anions, however, decreaaes.

As can be seen, the table is not complete, but contains many

itionB unfilled. It cannot be otherwise, for there is no justification

je assumption that all existing elements have already been dis-

776

PRINCIPLES OF INORGANIC CHEMISTRY chap.

<»

1 "^

Co,

o
l-t

c«

' «^

*•«.

1 . . •«

f-H

- a • •

l-^

f-t

;

E-

O
H

I-"

•A

l-t

9»

•<

;zi

.- H

Cd
PL,

«" § o" S "

•^

t-H

o»

'^ r^ O

to r-i

•X

sojv

THE PERIODIC SYSTEM

covered and investigated. It is, Iiowever, wortby of notice that up to
the combining weight 140, scarcely aii element is wanting. At this
)[ioint there is a large blank, and only between 170 and 240 is there
;ain some degree of completeness. At the time, about 1860, when

K regularities above described were discovered by Newlimds, L.
yer, and Mendelcef, many more of the elements were wanting, and
t was possible, according to the law of similarity, to predict with very
air approximiition the jiropertiea of those elements whose iilaces were
^impty. In this way Mendole^ef, especially, predicted the properties of
leveral elements unknown at that time, and the discoveries wiiich were
BUbsetinentiy made amply confirmed most of these predictions.

Besides the general relatioHs of cliemieal combination, the arrange-
nent of the elements according to the mngnitnde of their combining
■MBghbs aflbrds a fairly complete si/gtemniimlmi nf Hit. pht/mal pro-
^^tiea, both of the free elements and of their correapotiding com-
K>unds. ThuB, on passing continuously along the horizoutid rows, we
>as8 through a regular transition from the region of the metals to that
>f the nnn-mctala, to again commence with metiile at the beginning of
% new row.

The whole series, then, falk into a ntlmber of periods, and the
(Fhole system has therefore received the name perwdic [nv\ The
aeriodic character ia seen most clearly by graphically representing
iefinite properties of the elements. Such a representation is given
n Fig. 126 of two properties, the atomic volume^ and the melting
>oint.

Most of the properties of the elements, so far as they can lie
measiu-ed, yield similar figures, so that it has been stated generally :
7%<! properties of Ike elemenln are periodic /uncii&ns of iheir rtmtUninij
weights.

The same relations are seen also in the cose of comparable
Bompounds, e.g. the oxides, chlorides, sulphides, etc., in respect of
fclieir (iiflerent properties. Compare, for example, the solubility
Fclfttions of the chlorides of the elements and their behaviour gene-
rally with water, in the light of the table.

The form of the above regularities, finally, leads to the view that
the vahjes of the combining weights themselves must stand in a
regular relation to one another. The first idea is that the members
lire characterised by constant differences of their combining weights.
We can at once satisfy ourselves, however, that only a very rough
Sipproximation to such a relation exists. Thus, for example, the
iifferences butween the corresponding element* of the first and second
horizontal series amount to — 16, 16, 15*3, 16'1, 16"4, 17"0, 16'1, 16'5,
Und is therefore fairly consta.nt although the deviations are far above

' By atomic volume i« meaiit the prorluct of the extensity und the conilnliiinj; ii
In iccorilance witb tlitj iletinition of extenitty (p. 27), it rtpreseuto the Tolumo
icciipieil hy the coinUiniog wuight in grams of the (lartictilar elecnciit.

^^^^^pSciple^^norgani^hemistr^^B

KtmiM, #11

Linear fiinctlouE, 76 ^^M

KiEselpihr, 426

Liquid bodies, 13 ^^M

Kieserit*. 542

IJquiiK neutral, ISd ^^U

Kiln^nui, 23

Lithar^ 67, 6&7 ^^H

Kilojmilft, 185

Litliion, a07 ^^^M

Kiloini'tre, 8

Lithiinn, r>a, 507 ^^^M

Kilowrttt, mi

carlvoiiate, 507 ^^^^^^

Kinetic energy, 21, 22 :

coriibiiiin^ wdg-lit, 146, 505

Kipp's npjiaratuB, 87

fluoride, o07 , ■

KJrdilioff, 50S

hydroxide, 507 ^M

Klaiirnth, 739, 743

nitrate, 507 ^^^^|

Krypton, 440

pho'iplmte, f>OS ^^^^M

combining weiglit, 144, 440

sulyihAte, 507 ^^^^^|

Knnkel, 362

litmus ^^^M

^^^H

Lniitndarite, 5G7

Lcmin, 565 ^^^H

^^^ft Lrtming'a miidnre, £80

Lumineeceuce of phosplMMiu, S55

^^^P Lantlmnum, 54, S6S, fiC9

Lunar ortustic, 58, €86 ,

cottibiniiig wBight, 14S

Lustre, 7, 13 ^^m

Lnpis lazuli, 567

Lnteo-eobalt isrUts, S25 ^H

U\v. n

^^^^^1

fiint1a,nicnta], of ciemlatry, 2

Mocliitieti, ideal, 20 ^^^^|

I.i^*J, 57, 656

MagneKin, 53, 541 ^^^^^|

.i<x-tati', (if.9

utbA, ^^H

liri'tiiidt^ 657

^^^^H

oarlioliiito, S60

nitJitiitA, 546 ^^^^^1

diloridc, «357

Magai>»iuti, 5i0 ^^^^^M

cliromntc, S58

MapiiMitB, 544 ^^^^^B

cQriiiiining wdRht, !■;■■ i«,.ii

Magnesium, ri3, 84. !>'.iV ^^M

hvitroxt'le, 65ft

iodide, fl57 *%

Ktumaniwn phn^qdinte, 540, &^^|

cnrliouste, 544 ^^|

metAllnrgy of, Mi

chloride, 541 ^^|

nitrate, «67

coniliining wpiglit, 144 ^^H

oxide, 656. 657

electrolytic prcparfttton ot, iX^^M

l)ent!ils, am

itydt'asid]>liiiili>, 540 ^^|

iwroxiik, 661

laydioxi'lu, 5tO ^H

ml, 662

light, 53S ^^^H

sugar of, 659

^^^^^H

snlplmte, aS7

^^^^^^

milliliide, 661

phogphntes, 545 ^^^|

letTQcliloritlc, 662

platiuooyaiiido, 766 ^^H

linegar of, fiSO

f,ilic?llt^!S, r'46 ^^^^^H

vitriol, 658

542 ^^^^1

white, CflO

sulphtdf, 1)46 ^^^^H

LewloQ-chamber crystals, 3Sf)

Magnetic iron nre, G82 ^^^|

U Blanc, 493

pj-ritcfi, 588 ^^^^B

Ln^laticli^ cell, 601

Mtlocliilu. •14 il ^^^H

Lecoq rte BoisWldratl, 7^0

Manjimiintiioii, 601 ^^^^H

> Liglit, ultemical strength of, fifl'J

Mangiumtes, ((02 ^^^^U

dctroniimsitiori of dilorine water in, 172

Mauganest-, 55, 506 .S^^l

Light-seTiiiitive chromate mixtiireB, 017

cciniliinLiig vrejjjlit, 146, Ss^^^H

Lin>c, Imraiim of, 521

complex comjMmmts, 009 ^^M

light, 103 "

l^lass, 600 ^H

milk of, 518

heptoxide, 604 ^H

pnstLV rAS

metallic, 506 ^^H

H ahked, r>]S

lierosifdi!, 696, &0fi ^^^^M

^^B sIokinK of, 519

spar, 597 ^^^^|

^^^^

tetrachlririJo. 699 ^^^M

^^^^ LimestniiL', 5^, 621

Manganit rtcid, 602 ^^^H

^^^^r Ijiniitiii^ Inw, 20

chloride, 693 ^^^^H

V Lindf, rs

compoands, liS6 ^^^^H

^^^B

791

MetALitimotiii! acid, 713

„i

Metophoapborif acid, 385, 3<)ft

^^^H

MetastAble liiijit, &S0

^^^^^H

r«giou, 120) 493

^^^H

Mctastatmic aciii, T3.'i

^^^

Mfltiitnijgstio acidf 749

Metav:uii«lJc acid, 7'i6

MeteoriU-B, 571

Methaiu', 403, D33

Metheny), 40<i

^^^H

^^^^BBf^M

Methyl, 40e, 407
idcohol. 406
cliloridt!, 407

Methylttit, 406
chloride, 405

■

^^^^h1"

Metre, 6

Mica, mr

Microciisroic salt, 512
Micron, 6

■

^^^^^Kiiiif, 11)

Mildew, 052
Milk ^iak&. .133
MiUwiniwre. 196

^^^^%fli».

MUliiiietre, Q
Miueml waters, 30S

^^^^■pi dSO

Minifttuw, 662

^^^^^M

^^^^^Bm, KOO

Minium, 662

^^^^^

^^HP^*'^

Mist, 131

Miied crystids, 311

Mixtnrei' £

constant Ixjiling, 1815

iBuinorphennsgMS
Molar Avaigbt, SB, 153, 77a

^^^^^1

Mole, 159

Muleuultir heat, 439
hypothesis, 151
weight 89, 152

^^^H[[ti~s

Molecale, 152

^^H

^^^^^Bklv,

Molybt!ettum, 55, 743, 751

^^MHtiSS

chlorine eoiiipinmd* of, 752
colnliiiiiiig weight, 14H, 7i»l

^^^§ni;'j

osychloride.*, 753

^^K. -..nn

trioside, 7S1

^^^^HCItlU]Mil)<gitH, t}7i'

trinnlphide, 7113

^^^Ew«l«ftt. lid, ilriT

MoiiocolciiiMi phosphate, 532

^^^H

^^^^^^nails.

MoiioLlinic syeti-ni, 2fii3

^^^^^t

^^^^^^^fc;n co3]ipi>iiuiU, tli9, &81

Monocu prion, 6S7

^^^H

^IBffranuponiKls, <!81

Monoiu*ri:nnoii. ti68

^^^^^1'

■ noT

Muuotlmllioii, 700

^^^^^1

^M^ limt «(, 439

Monotropy, 253

^^^^^

^^^■llt'i,

Mordant. 5<J7

^^^^^^

^^B»m(»lrr of, 082

Morley, 139

^^^^H

^^■cid.

Mort«r, 622
Mosaic gold, 73ri

^^1

^^^B ilcpmitinu of, 6'2{i

Mother lifiuor, 4tJ8

^^^^^^^^H

^^^^Biuiiark.^ on th« (:h«iiiti;ti','i o(.

Naplithnlenei, 41$, 41i ^^^^M
Niipleii vellow, 6Ti7 ^^^^^|

I^H

^^Kt. 'Hi

Niitnrnl Hcieiioe, 2 ^^^^^H

^^^^^^^H

^^^■*tri«« of, 645

N&ture, Idws of, 4, 5 ^^^^^M

^^^^^^H

^^^Bo nltrk acid, t]St

Kegative, ^^^^M

■

792 PRINCIPLES OF INORGANIC CHEMISTRY ^

Keoclyuiiurn, 5-4, 5ti8, sro

Normal salts, 270 ^^^^|

combiuitiff wetghl, 116

^^^^H

Henti, 1,2, no

tctuperatUTc, ^^^^H

ootnbining weight, 14S

Nuvletu, 130 ^^^^1

Sei^lcr'd reagent, 680

^^M

Neutral Bstts, 270

Ofi-iTok, 571 ^^^^B

Nickel, 55, aao, 625

Oli^oclojte, £67 ^^^H

atiimotiin lous, 62(i

Otivini'. ^^^H

cnrbonyl, 627

Ojml, 426 ^^^^1

coitibiaing wnight, H€, 620

Ortlin&tt^s, ^^^^^|

cynnidjon, 627

Or^uic ciiemi-stry, .^0 ^^^^^|

byiJroride. 626

nitrogen, 3f^l ^^^^H

oxide, 626

Orpiment, 720 ^H

pl&tiQf;, 62&

Orthoautimnnic acid, 713 ^H

^■^ atilplinte, €26

Ortlioljortc: ncid, 43& ^H

^^^DTiclieiion, ijjie

Ortlioclnfi«, 5t!7 ^H

^■KiekeUms cvatiidc, 627

OrtliophoH|iliuriu acid, 366 ^^^^H

Niobiniii, ,'>9, 726, 728

Orth<isiliciu acid, 426 ^^^^|

combining weight, 146, 7^8

Oaiiiii.- acid, 769 ^^^^H

oxyehloride, 72S

OsiuiriiJiiini, 7tt8 ^^^^H

pentachlorida, 728

OsiatiiUD, 60, 763 ^M

pentoxide, 728

tnnnbiiiittg %\tighu 146, 76ii ^H

trichloride, 72S

hydroiciitf, 769 ^H

Nitrate*, 320, 324

tiitroxidu, 7tJil ^H

Nitric itcid, 320

Osmotic pi'ciisuTe, 647 ^H

Buhyilride, 325

law* of, 648 ^^^M

cboiuical jiroperties of. 322

Outer world, 4 ^^^^H

he«t of farnmtion, 325

Uxalates of iron, 592 ^^^^H

idtintiAciitioii of, ^2i

Omilc ncid. 415 ^^^M

H>lts of, 321

OxiAanea, 5B8 ^^^^H

Bolntton of inetala in, 637

Oiiditinu, 138 ^^^^^

Nitric oxiile, 325

of phciBpli(»rtia in m, 35'> '

eoinpouniia with iron salts, 326, 591

Nilrile, 421

in, <i5S ^M

Nitrites, 332

Oxidest, 65 ^H

Nitro-compoundii, 334, 337

Uxidising at'«Dt«> ^"*- '^^-< ^i^' ^^^^H

urgnnic, 334

llauie of thu Buusi'U turucr, IK^H

^^^Nltrogen, 4S, 316

Oxygen, 36, 47, 62 ^M

^^^B 'baKtena. a'll

nud umne, €1 ^^M

^^^V corotiiotiiig weight, 146, 316

comliining weight, 1i6 ^^^^|

^f d«teetlon of the oxy-ooiinpoatidis of, 826

commercial, 79 ^^^^H

■ orgnnic, 351

deniiity, ^^^H

^M aity-compouadi nf, 320

^^^^H

^H catalytic octioua of, 33S

pliyslcivL pri.i|NfrliB8, 66 ^^^^H

^^^_^ oxjgeu-tiydrogen oompoands 348

rBatlion of, 64 ^^^^^H

^^^B pentuxLde, 32.'i

Oiy-h}'drr}t;eu flniiie, 102 ^^M

^^^r peioJcido, 327

Otuue, aO, 357 ^^^M

^ heat of formation, 330

oxygea, 81 ^^^^H

^1 preparation, 329

^^^^^1

^H trioxidc^ 332

Pallndium, CO, 765 ^^M

^m Kltrosiilijhontc ncid, 33Jj

chloride, 767 ^1

^1 Nitrosyi chloride, 33 S

corubiniiig weight, 146, 767 ^H

^1 Nitrous acid, 332

hydridt!, 766 ^H

■ air, ;;26

uitmte, 766 ^H

H Anhydride, 332

Psrtial presaurcs, Dnlttm's Uw nf, 94 1

^1 nxiilii, 334

Pttssire st«t« of chromium, till J

^1 Nitryl chloride 333

Pentathioulc ocid, 301, 803 ^m

^H Non-coiidiii'toni, 193

Perc1dornte.4, 221 ^H

^1 Ncut-HiKtds, 4&

Porchlaric acid, 221 ^^^^1

■ 17ormsl gM, S&

Piircliromic ncid, 618 ^^^^^M

^^^^ prasttre, 67

r«riod»t^, 240 ^^^H

INDEX

793

Item, 771, 774

Pinch-cock, 87

white, 652

Pink salt, 734

luioD, 601

Pipettes, 190

c acid, 603

Pitchblende, 745

Plaster of Paris, 529

e, 604

Platinates, 764

mobile, 81, 135

Platinic hydroxide, 764

it kind, 136

Platinochloridion, 764

;ond kind, 136

Platinocyanidiou, 765

es, 770

Platinotype, 764

c acid, 296

Platinous chloride, 764

hydroxide, 764

408

Platinum, 60, 760

647

black, 762

173, 174

catalytic actions of, 761

combining weight, 146, 754

coaiplex compounds, 763

ilein, 153

metals, 754

Ls, 397

sponge, 106, 761

n. 367, 368

tetrachloride, 768

, 367

Plnmbiou, 655

lyUIic acid, 752

Poison-flour, 718

III, 360

Poisonous action of mercury salts 672

Polarisation, 626

■ence, 531

Polonium, 747

?ent paint, 531

Polymolybdic acids, 761

acid, 364, 365

Polymorphism, 241, 520

ic determination of, 744

Polysulphides, 279

, 531

Polythionic acids, 301

s acid, 370

Porcelain, 566

, 49, 352

Potash caustic, 453

forms of, 353

Potashes. 52, 461

i weight, 146, 357

Potassamide, 474

)a of, 64

Potassion. 443

363

reactions o^ 444, 448

359

Potassium, 62, 442

360

amalgam, 451

160

argeuticyanide, 691

de, 369

aurate, 756

Hide, 363

auricyanide. 768

iriile, 361

bicarbonate, 463

ride. 363

bisulphate, 465

;, 364

bromate, 460

ou, 352, 533

bromide, 455

carbonate, 461

, 363

chlorate, 457

oride, 375

chloride, 455

:omi)ound.s of, 374

chroinate, 55, 616

e, 361

combining weight, 146, 443

e, 363

cyanate, 472

363

cyanide, 471

;57

dichromate, 616

ferrate, 587

oal actions. 181

ferrocyanide, 588

stry, 172

ferri-oxalate, 692

ic prints 687

ferro-oialate, 592

of, 759

fluoride, 456

y, 683, 688

fluorothorate, 742

, chemical, 592, 672

fluotantalate, 728

enomena, 3

hydride, 473

hydrosulphide, 466

■ 794 PRINCIPLES OF INORGANIC CHEMISTRY ■

H Potassium tydrojlde, 4r.O

PurjiUTbo-salta, '326 ^^^^^|

H lilietnkal properties i>f, JiiS

Pyriti-s, ^^^^H

^B iolate, 160

PyToantimoa»t«s, 713 ^^^^H

^^B ioilicle, 4^t>

Pvrolt]slt«, 599 ^B

^H iri<loc1i1oride, 767

P>Ti>pltos|jhoric acid, 36&, 3S8 ^H

^B maugamcyuuidi!, 099

Pyrosulpburic uiid, :!04 ^H

Prrosalpliuroua acid, 285 ^H

PyHMwlphuTv] chloride, 307 ^H

^H )iitrit«, 470

pjiotechiiici, 540, 553 ^^1

^H oxaliite. 473

^M percliloratc. iCd

^H p^iiiiaugnwate, iiiml>ticttl nlhplication of,

Qundriitk system, 266 ^^^^H
Quartz. 51 ^^^^1

QaicklimE!, S19 ^^^^H

^1 per!iUl|>Imte, 4(i(S

H (gas constant), 90 ^^^^H

■ j.ldt.lninMoride, 763

RadiclBa, 400 ^^^^|

^M platinooUlnridCi T<S4

RiMlio-Rctivitr, 746 ^^^M

^1 plntuioi'yivniftei Ttvri

Kadiuitt. 747 ^^M

^m platinoiiitritc, 7fl')

comMuing weight, 747 ^^^^M

^1 polvsiilfjWdes of, -Iti?

Ramsay, 43S, 74S ^^^M

^U pyriwil pliftU<, 465

Rayiei^^. 438 ^^^M

^1 pyrOBiilpliite, 4 (56

Reaction, hi»at of, lfl6 ^^^^^|

^1 silicate, 470

^^^H

^H silii!otluorii]e, 471

Beactiotu, 35 ^^^^H

^m sulphate, 4()&

geological, 42S ^^^H

^H Ea1]>hiiltf, ^€S

intermediate, 660 ^^^M

^H siilpliite. 4K6

qncwASirfi, law of, 210 ^^B

^1 tetrnxaluti;, 4*2

lle:tge])ts, 35 ^^^^H

^1 tliincyAuate, 472

B«alga). ^^^M

^M titmmte, 737

RccrMAili^tiou. S20 ^^^^B

■ PoUutinl. 19«

Red Uro, ^^^H

^1 inrifi, *24S

Reducing ageuts, 607 ^^^^H

■ ofci'lh, 044

llnme. ^^^M

^1 aorii!« lit the lucttils, 045

Heiluctiou, 13&, 576 ^H

^^^ Potter's «?artl], 5l!5

R«frigiirftting lunehines, 343 ^^^^B

^^^Kl^jueodyiuiuiii. 54, &6S, £70

Regular syitetn, 267 ^^^^1

^^^f coi:i billing wtiight, Hi

Reich, ^^^M

^^^^ Pi-aaBO-snlts, 625

Retarded, 108 ^^^^1

■ PreelpStnte, fu»i1)le, 681

lletort, 110 ^^^H

■ inruKihit:, msi

Reversed procesaes, 99 ^^^^B

H PrccipiUtiuu, theory of, 447

RhCMlinm, 60, 767 , ^H

^m Preasute, I'riticftL, 361

chJoriue colnlionndi of, 7^i ^^M

^B iofluuuce of, on iletisity, 30

conihining woight, 146, IrtH ^H

^^^ on melting point of ice. 132

Uhombic iiysteju, 266 ^^M

^^^^ ou flolubSlity, 217

Richter. 729 ^M

^^^H osmotic 647

Rock crystal, 42n ^H

^^H Inw9 of, 646

»aU. 434 ^M

^^m Pri«stk-y, »7

HubiiMnm, u'i, 505 ^H

^^V Prunnry salts, 270

couiliining w«ight, 146, JOB ^^M

^F Prints, photogia[ihii,, 687

Ruby, &tiO ^M

^B ProceBsea, cliumical, 7

Rupert's drops, 53S ^M

^1 »l)ontaneciiisly iweurriug, 211

RqjitiDS, &71 ^M

■ Pr<jpunu. 408

Rnthenates, 770 ^H

^M Propurtie-v 6

Rutlifuio-chlwidion, 7"0 ^H

■ (•XRctnest.'i of law of, 8

KntheniUBi, 60, 769 __ ^M

^1 prutnptAsm, Htj'Z

comli'illiiig weight, 146, 770 ^H

^M Pru!i,iiiiii l)liii'i ''iSl'

tbtroiidc, 769 ^H

^H PmsisiBtc ol' ]>utn.<i1i, yellow, 5S8

Rutile, 737 ^H

H PrusAic acid, 419
H PseuiloiHorphs 26(>
^H pseuilo^^ltHictis, 427

Sal aminoulnc, 49, Sll ^^H
mirnbile, 490 ^^^M

INDEX

795

el, 416, 472

Silver iodide, 689

17, 49, 52

metallurgy, 696

., 485

nitrate, 686

193, 200

oxide, 685

r of mixed, 220

sub-chloride, 687

543

sulphate, 690

ou of, 249

sulphide, 691

270

thiocyanate, 694

i70

Simple substaaces, 10

270

Sintering, 103, 382

V, 270

Slaking of lime, 519

' of, 445

Smalt, 55, 622

icmistry of, 203

Smoky quartz, 425

568

topaz, 425

g weight, 1 46

Snow cr}'8tal8, 119

?20

Soapstone, 546

425

Soda, 52, 498

ash, 499

caustic, 35, 154, 482

ompounds, 407

crystals, 499

54, 568, 569

felspar, 567

g weight, 146, 556

lime, 519

, 352, 548, 749, 751

water-glass, 503

eeii, 719

Soddy, 748

749

Sodion, 478

Sodium, 52, 84, 475 .

alt, 713

acetate, 503

)42

action on water, 84, 153

;er greeu, 719

ammonium phosphate, 512

484

bicarbonate, 498

bLsulphate, 494

alts, 270

borate, 503

, 313

bromate, 488

:id, 312

bromide, 486

314

carbonate, 497

8, 309

chlorate, 214, 488

? weight, 146, 309, 310

chloride, 484

less to light, 310

chloroiridite, 767

•ide, 313

chroraate, 616

i\ hydrogen. 310

combining weight, 146, 504

IS of the )>alaDee, 25

dichromate, 616

546

flame coloration, 478

hydroxide, 482

426

hypobromite, 231

424

iotlide, 486

429

metallic, 476

m, 430

metaphosphate, 502

g weight, 146, 424'*

nitrate, 489

125

nitrite, 490

lous, 425

peroxide, 483

131

phosphate, 501

130

platinichloride, 763

583

polysulphides, 495

688

press. 478

f plates, 688

})yrophosphate, 502

■, 690

silicate, 502

686

sulphate, 490

? weight, 146, 684

solubility relations of, 490

U, complex, 695

sulphide, 495

391

sulphite, 494

HI of, 696

thiosulphate, 495

796

PRINCIPLES OF INORGANIC CHEMISTRY

Solar spectram, 98, 480
Solder, 503

soft, 603, 735
Soldering, 503
Solid bodies, 13

substances, inflaence on chemical equil-
ibrium, 102
Solubilities, measurement of small, 620
Solubility, 444

and heat of solution, 219

curve, 486

intluence of temperature and pressure
on, 217

of a salt in presence of its acid, 658

of different forms of a substance, 261

of gases, 274

of salts, 216, 445

apparent increase of, 445

diminution of, 445

proiluct, 447
Solution equilibrium, theory of, 446

heat of, and solubility, 219

law of, and law of distribution, 275

saturated, 444

supersaturated, 217, 444
Solutions, 9

electrolytic, 200

colloidal, 427
Solution, pure, 10
Solvay, 501
Soot, 382
Space, 5

Spathic iron ore, 580
SpeciKc gravity, 27

heat, 773
Spectrum analysis, 61

of hydrogen, 97
Spectrum phenomena, 479
Sjiecular metal, 736
Spinel, 661
Spirit, 408

of hartshorn, 343

of wine, 408
Spot test, 527
Square centimetre. 6
Stability, regions of, 257
standard cells 634
Stannates. 734
Stannic acid, 734

chloride, 733

hydroxide, 733, 734

sulphide. 735
Stannous bnimide, 733

chloride, 732, 733

hydroxido, 732

ivxlide, 733

sulphide, 7-33
Starch io.iide. 235
Staissfurt salt-beds, 455, 542
Steel, 572

chromium, 010

Stone age, 426
Stoneware, 566
Strength of acids, 244

of current, 196
Strontianite, 649
Strontion, 549
Strontium, 53, 548

carbonate, 549

combining weight, 146, 548

hydroxide, 549

nitrate, 549

oxide, 548

sulphate, 549
Struvite, 545
Sub-chlorides, 175
Sublimate, 672
Substances, 1

pure, 9

undecomposable, 43
Substitution, 404
Sulphamide, 346
Sulphaminic acid, 347
Sulphur, 48, 256

amorphous, 259

bromide, 304

chlorides of, 304

combining weight, 143, 307

compounds, complex, 681
of phosphorus, 374

dioxide, 281

flowers of, 259, 263

fluoride, 304

milk of, 258, 280, 531

mouochloride, 304

regeneration, 500, 531

roll, 263

trioxiile. 285

vapour, 262
Sulphuretted hydrogen, 269, 2S0. !>>'>

analytical reactions. 277

evolution, theory of. 276

salts of. 272

strength of. 276

therinocheniiitxy of. 2?0
Sulphuric aciii 2^7

apj'lications of. 292

!»que<'>u?, 291

cldorides of. 3'.'4

dccomiMsition of, 294

dihvdrate. 291

ious ot. 292

prep-iration ft^ni fen-v^as fsljhi'.e,

soli.i. 2?-'

test for. ia analysis. :^.'"

thermochemiitry -f. i.-o
Sulpttinvjs acij. i;«.2

bleacbiEC stftioa ■-•i. C'*-

dis^viition of. 2>i;
Saii'hun-Iaiuide. o4^
Sclphuryi cllc-nde, $•:'

INDEX

797

ydrozycliloride, 305

Thermochemistry of the halogens, 253

vapour, 130

of hydrogen chloride, 202

r. 119

of hydrogen sulphide, 280

water, 130

of mercury, 682

led solutions, 217, 444

of nitric acid, 325

lion, 217

of oxygen compounds of chlorine, 224

of salts, 203

emical, 147

of sulphuric acid, 295

f crystals, 265

of sulphurous acid, 285

ink, 621

Thio-acids, 418

Thioantimonates, 713

linium chloride, 562

Thioarsenates, 724

Thioarsenites, 721

Thiocarbonates, 418

9, 726, 728

Thiocarbonic acid, 418

! weight, 146, 728

Tbiocyananion, 422

Thiocyanic acid, 422

ic, 58

Thiocyanogen, 422

1,448

Thiogermanates, 739

1, 315

Thiomolybdates, 763

8, 309, 314

Thioplatinio acid, 764

315

Thiostannates, 735

! weight, 146, 309, 314

Thiosulphates, solubility of silver com-

pounds in, 695

(14

Thiosulphnric acid, 298

ide, 315

Thiotungstates, 761

J15

Thiovanadates, 728

id, 314

Thomas' slag, 532, 595

J, absolute, 71

Thoria, 740, 741

Thorite, 740

on density, 30

Thorion, 740

on solubility, 217

Thorium, 59, 740

on velocity of chemical re-

combining weight, 146, 740

66, 107

nitrate, 741

rays, 742

f steel, 672

sulphate, 741

cid, 436

Thulium, combining weight, 146

ethane, 405

Time, 5

•n, 733

Tin, 59, 731

acid, 301, 303

alloys, 735

on, 750

combining weight 146, 732

a, 745

foU, 781

roxide, 701

salt, 733

702

tetrachloride, 733

9, 700, 701

Tinned iron, -4^36

7, 699

Tinstone, 59

; weight, 146, 702

Titanfluoridion, 737

)niide, 701

Titanium, 69, 736

, 700

combining weight, 146, 788

701

cyanide, 738

(01

dioxide, 737

■; 700

nitride, 738

tetrachloride, 737

Titration, 190

Toluene, 30 ,

700

Toning and fixing bath, 759

701

Toning in photography, 759

494

lacity, 164, 439, 773

Transition point, a(ff<7 o '' '-^ ^^ '^^T/^s^^n.

iiical equations, 165

if^ CH/,- n,. '^'-^A

nistry, 162

K ,3 '''^"H. 'fi

H 798 PRINCIPLES OF IS0RGA>1C CHE^nSTKY ]

^H Triclinic aystciTi. 266

Vftii»aitui». 726 1

^M Tricol«ttion. 023

comJiiniug HreJRiJ, Ufl, 72$ 1

^H Triilj-niite, 425

tlkhloniJe, 727 ^^m

^H Trifurrion. ri74

diojcldr, ^^|

^H Trigalliou. 7:31)

in«t9llic, 7^7 ^^1

^H Trigonnl 5)'st«in, 207

^H Tn-inilion, 730

Tide, 727 ^H

^^ Tri-ioUdtou, '^iiS

-->'-?r. 7-2S ^H

^H TViiualigutiicu, !r96

^^^^ Tripln poiiil, 131

^^^^ft Trutxliiun phosphate, S02

tricblonde, 7ir7 ^H

^^^^P Trigul[ituiuitiic aciil, 347

tiioiide, 7*i7 ^^M

^^^^ Trithiouic acid, 301, 302

Vatiadyt trichloride. 727 ^^

^H Trititnuion, T3«

Vfrpour den^ilieti, Tar}'ing, 327 I

^H 'rrivAQfidioa, 727

Vbpour pM^snni, 122 ^^M

^H Trouo. 498

of toe, 185 ^M

^H Tatf, themuil, 523

of soudl drops, S<1 ^^|

^H Tangsteii, 55, 743, 749

Yarnisb, 5&S ^^H

^H bronze, 7£iO

Velocity of chemical re*ct!oaUk ^^H

^B chlonileH, 750

temperature on, 6Q, 107 ^^H

^H conttiiniDg wvii^ht, 1J€, 749

Verdigris, 046 ^H

^H oxychlcrrides, 7&0

TinegM, 403 ^"

^H Eteel, 749

Vitriol, 678

^^H snlpliidu, tf'l

oil ot, prepMstlQa from femoB ■)]

^1 trioxjtie, 74<.l

579

^H Tungiitic lu^i'l, 7 19

Volt. 18«, 643

^H cALloirlnl, 749

Voltaic eell 680, 642

^H Turiueric. U>i

complex lalto In, A0&

^H TQTjwtb iiiinLTiil. U7'i

Volume, critical, 891

^H TimjiioUt!, 5'i7

nUo of oxygon aad hjrdrogem, 1S9

^H 'I'ype-iLieUl, 71&

«p«cittc, 27

Volnnuo, taw of, ta gaaooua oouliiiu

^H nittttm«rine, 567

14S

^H UniK otiaolute, 9^

Vnlcantsing of cuoiitcbonc, S04

^M dt-etrlcaU 19ti

^H UuBiiturntecI i;oiiipoiiiulfi, 410

Water, 46, 98, lOU

^^M AolutLous, 217

actioti of ^iuiu on, 153

^H ITaiitutilu rugi'iu, 120

as solvent, 136

^H Umaitini, ^.~i, 749

bath, 129

^H chlorltks, 74S

cbemicnl propertiuK oL 1S7

^H tonibintiig whisht, 14U, 7*3

coefficient of compressiliility ot 11

^^H ^liuu, 745

<%lour of, 11^

^H ra)-!<> 7-1 a

composition of, 138

^H Iritij-flroiidt, 74fi

decomitositjon, 140

^H yellow, 74ri

density, 112

^H 1 rmnoiiE Lyilruxiile, 745

depeujiiuce of it» vapatir prpMV

^H M.IU. 745

tenipersturi!, I2S

^H (Jtniiy), 74 U

g»,4oi ^m

^H lUumoiiKuii pliosiiliate, 741

glaaa, .470 ^M

^H liyitroxiJr, 744

hanlnest of, 524 ^"

^H 744

heat of farmnliou of, 189

^H nitrulK, 7-14

heot of vsporiution of, 12S

^H oxaktu, 744

liqwid, degre«!i of freedom ul, 117

^H plicwphiite, 744

pnru, 109

^H HulphAte, 745

vapour, density and e«t«n«itT »f. |

H * Unw,498

in tl)e lUT, 125

H Urea, 39S

Watt. 644
Weigljt, 23

^1 ijmtiiuto or, 422

^^1

cbiiuiKe of, la chemical prooaMM, 1

^H Vnleucy, 376, 377

cmiserv'fttioji of, 16

^^^^ Validity of laws abBolute, 9

increase of, in couibusUou, 34

INDEX

7?9

Welding, 572
Weldon mud, 600
White lead, 660
Witherite, 552
Wohler, 398, 557
WoUaston, 765, 768
Wollastonite, 536
Work, 19

conservation of, 20

lead, 665, 696

unit of, 23

Xenon, 52, 440
combining weight, 146, 440

Ytterbium, 54, 568

combining weight, 146
Yttrium, 54, 568, 669

Zero, absolute, 70
Zinc, 55, 86, 628

blende, 633

carbonate, 632
I chloride, 632

Zinc, combining weight, 146

commercial preparation, 629

dost, 629

hydroxide, 630

oxide, 631

oxychloride, 632

silicate, 633

solution in acids, 629

sulphate, 632

sulphide, 633

vitriol, 632

white, 631
Zincates, 631
Zincion, 629
Zircon, 739
Zirconia, 739
Zirconion, 740
Zirconium, 59, 739

combining weight, 146, 739

hydroxide, 739

salts, 740

silicate, 739

sulphate, 740

tetrachloride, 740

THE END

«3 EAST .RO,-D¥.'AV.

Printed *>- R. & R. Clakk, Limited, Edinburgh.

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